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    • 专利摘要:
    HIGH RESISTANCE STEEL SHEET AND METHOD FOR PRODUCTION OF THE SAME.The present invention relates to a sheet of high strength steel that includes,% by mass, C: 0.03% to 0.30%, Si: 0.08% to 2.1%, Mn: 0.5 °% to 4.0 °%, P: 0.05% or less, S: 0.0001% to 0.1%, N: 0.01% or less, Al soluble in acid: more than 0.004% and less than or equal to 2.0%, Ti soluble in acid: 0.0001% to 0.20%, at least one selected from Ce and La: 0.001% to 0.04% in total, and an iron balance and unavoidable impurities, where [Ce], [La], [Al soluble in acid], and [S] satisfy 0.02 (Minor equal) ([Ce] + [La]) / [Al soluble in acid] < 0.25, and 0.4 (Minor equal) ([Ce] + [La]) / [S] (Minor equal) 50 in a case where the mass percentages of Ce, La, Al soluble in acid, and S are defined to be [Ce], [La], [Al soluble in acid], and [S], respectively, and a microstructure includes 1% to 50% of martensite in terms of an area ratio.
    公开号:BR112012028661A2
    申请号:R112012028661-7
    申请日:2011-05-10
    公开日:2020-08-25
    发明作者:Yoshihiro Suwa；Kenichi Yamamoto；Daisuke Maeda；Satoshi Hirose；Genichi Shigesato；Naoki Yoshinaga
    申请人:Nippon Steel & Sumitomo Metal Corporation；
    IPC主号:
    专利说明:

    Descriptive Report of the Invention Patent for "SHEET OF: STEEL OF HIGH RESISTANCE AND METHOD FOR PRODUCTION OF MES- 'MA". - Field of the Invention The present invention relates to a sheet of high-strength steel that can preferably be mainly pressed and used in the undersides of automobiles and more and structural materials, and is excellent in terms of hole expansion and ductility, and a method of producing it. z 10 Priority is claimed in Japanese Patent Application No. 2010-108431, filed on May 10, 2010, and Ja- '- - Ponesa Patent No. 2010-133709, filed on June 11, 2010, the contents that are incorporated here by reference.
    Description of Related Art A sheet of steel used for the structure of a car body needs to have favorable formability and strength. Like a sheet of high strength steel having both formability and high strength, a sheet of steel composed of ferrite and martensite, a sheet of steel composed of ferrite and bainite, a sheet of steel including austenite retained in the microstructure, and more are known.
    The complex microstructure steel sheets above are described in, for example, Patent Citations 1 to 3. However, there is a demand for a complex microstructure steel sheet having a more favorable hole expansion than in conventional technique in order to satisfy demands for an additional decrease in the weight of modern automobiles and the ability of the parts to have more complicated shapes.
    A sheet of complex microstructure steel including martenite dispersed in a ferrite matrix has a low yield ratio, a high tensile strength, and excellent elongation. However, in the complex microstructure steel sheet, stress is concentrated at the interfaces between ferrite and martensite, cracks easily occur at the interfaces, and thus the complex microstructure steel sheet has the
    | 2/68 disadvantage of weak hole expansion.
    : In contrast to the above, Patent Citation 4 describes' a high-strength hot-rolled steel sheet having excellent - hole expansion which is required for recent wheel member and lower materials. In Patent Citation 4, the amount of C in the steel sheet is decreased as much as possible so that a solution-hardened or solid-precipitated ferrite is included in the steel sheet that includes bainite as a major part of the microstructure in a fraction of appropriate volume, the difference in hardness between ferrite and dim bainite, and generation of unrefined carbides is prevented. In addition, Patent Citations 5 and 6 describe methods, in which unrefined inclusions based on MnS present in plates are dispersed and precipitated on a steel sheet as thin spherical inclusions that include MnS in order to provide a steel sheet of high strength which is excellent in terms of hole expansion without fatigue deterioration characteristics. In Patent Citation 5, deoxidation is performed by adding Ce and La without substantially adding Al, and fine MnS is precipitated in thin and hard Ce oxides, La oxides, cerium oxidesulfides, and lanthanum oxysulfides, the totality of those generated by deoxidation. In this technique, MnS does not elongate during lamination, which is why MnS does not easily serve as a starting point for cracking or crack propagation track, and hole expansion can be improved. Patent Citation [Patent Citation 1] Unexamined Japanese Patent Application, First Publication No. H6-128688 [Patent Citation 2] Unexamined Japanese Patent Application, First Publication No. 2000-319756 [Citation Patent 3] Japanese Unexamined Patent Application, First Publication No. 2005-120436 [Patent Citation 4] Japanese Unexamined Patent Application, First Publication No. 2001-200331 [Patent Citation 5) Application for Unexamined patent Ja-
    | 3/68 ponesa, First Publication No. 2007-146280. [Patent Citation 6] Japanese Unexamined Patent Application, First Publication No. 2008-274336 - SUMMARY OF THE INVENTION Problems to be solved by the invention The high-strength hot-rolled steel sheet as described in the Patent Citation 4, in which a major part of the microstructure is bainite, and the generation of unrefined carbides is suppressed, exhibits excellent hole expansion, but the ductility is weak compared to a - 10 steel sheet mainly including ferrite and martensite . In addition, while the generation of unrefined carbides is suppressed, it is still difficult to prevent cracking in a case where a strict hole expansion is performed.
    According to studies by the inventors, it has been found that the above disadvantages result from elongated sulfide-based inclusions mainly including MnS in the steel sheet. When the steel sheet is deformed, internal defects are caused in the vicinity of inclusions based on elongated unrefined MnS that are present in and in the vicinity of the surface layer of the steel sheet, internal defects propagate as cracks , and fatigue characteristics deteriorate. In addition, elongated unrefined MnS-based inclusions are prone to serve as starting points for cracking during a hole expansion.
    For this reason, it is desirable to make MnS-based inclusions in a thin spherical shape while preventing MnS-based inclusions from being stretched as much as possible.
    However, since Mn is an element that increases the resistance of materials together with C or Si, in a sheet of high-strength steel, it is common to adjust the Mn concentration to a high percentage in order to ensure the resistance. In addition, when a heavy treatment for desulfurization is not carried out in a secondary refinement, 50 Ppm or more of S is included in steel. For this reason, MnS is usually present in 4/68 plates.
    - In addition, when the concentration of soluble Ti is increased to. in order to improve flangeability by stretching, the partially soluble Ti SÍ binds with unrefined TiS and MnS in order to precipitate (Mn, Ti) S.
    Since MnS-based inclusions (hereinafter, three inclusions of MnS, TiS, and (Mn, Ti) S will be referred to as "MnS-based inclusions" for convenience) are prone to deform when steel is rolled hot or cold rolled, MnS based inclusions are elongated, which causes hole expansion degradation.
    . 10 In contrast to Patent Citation 4, in Patent Citations 5 and 6, since thin MnS-based inclusions are precipitated into plates, and MnS-based inclusions are dispersed on the sheet. steel as thin spherical inclusions that do not easily serve as starting points for cracking while not deforming during rolling, it is possible to produce a hot-rolled steel sheet that is excellent in terms of hole expansion.
    However, in Patent Citation 5, since the steel sheet has a microstructure mainly including bainite, sufficient ductility cannot be expected compared to a steel sheet having - microstructures mainly including ferrite and martensite. In addition, on a sheet of steel having microstructures mainly including ferrite and martensite, which are significantly different in hardness, the hole expansion is not significantly improved until when MnS-based inclusions are finely precipitated using the Patents Quote techniques5e6 .
    The present invention was produced to solve the problems of conventional techniques, and provides a complex microstructure like a sheet of high strength steel that is excellent in terms of hole expansion and ductility, and a method of producing it.
    Problem Resolution Methods Hole expansion is a characteristic that is dependent on the uniformity of the microstructure, and in a main multiphase steel sheet
    l 5/68 mainly including ferrite and martensite having a great difference in - hardness in the microstructure, stress is concentrated at the interfaces between fer-, rita and martensite, and cracks are prone to occur at the interfaces. 7 Additionally, the hole expansion is significantly impaired by sulphide-based inclusions in which MnS and others are elongated.
    As a result of thorough studies, the inventors found that when chemical components and production conditions are adjusted in order to prevent the hardness of a martensite (martensite) phase in a multiphase steel sheet mainly including ferrite and marten- - 10 to increase excessively, and inclusions based on MnS are finely precipitated through deoxidation by adding Ce and La, the, - hole expansion can be significantly improved even in a sheet of steel having a microstructure in which ferrite and martensite are mainly included, and the present invention is completed.
    However, an example in which TiN is precipitated in thin and hard Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides together with MnS-based inclusions has also been observed, but it has been confirmed that such an example has small influence on hole expansion and ductility.
    For this reason, in the present invention, TiN will not be considered as an MnS-based inclusion partner.
    The purposes of the present invention are as follows: (1) A sheet of high-strength steel according to an aspect of the present invention includes,% by mass, C; 0.03% to 0.30%, Si: 0.08% to 2.1%, Mn: 0.5% to 4.0%, P: 0.05% or less, S: 0.0001% to 0 , 1%, N: 0.01% or less, Al soluble in acid: more than 0.004% and less than or equal to 2.0%, Ti soluble in acid: 0.0001% to 0.20%, at least one selected from Ce and La: 0.001% to 0.04% in total, and a balance of iron and unavoidable impurities, where [Ce], [La], [Al soluble in acid], and [S] satisfy - zem0.02 <([Ce] + [Lal) / [acid-soluble AI] <0.25, and 0.4 <([Ce] + [La]) / [S] <50 in a case where the mass percentages of Ce, La, Al soluble in acid, and S are defined to be [Cel], [La], [Al soluble in acid], and [S),
    respectively, and the microstructure of the high-strength steel sheet includes - 1% to 50% of martensite in terms of an area ratio. 7 (2) The high strength steel sheet according to the above O) / may also include,% by mass, at least one selected from a group consisting of Mo: 0.001% to 1.0%, Cr: 0.001% 2.0%, Ni: 0.001% to 2.0%, Cu: 0.001% to 2.0%, B: 0.0001% to 0.005%, Nb: 0.001% to 0.2%, V: 0.001% 1.0%, W: 0.001% to 1.0%, Ca: 0.0001% to 0.01%, Mg: 0.0001% to 0.01%, Zr: 0.0001% to 0.2 %, at least one selected from Sc and lantanoids from Pr to Lu: 0.0001% to 0.1%, As: 0.0001% to 0.5%, Co: 0.0001% to 1.0%, Sn : - 10 0.0001% to 0.2%, Pb: 0.0001% to 0.2%, Y: 0.0001% to 0.2%, and Hf: 0.0001% to 0.2%. "(3) In the high-strength steel sheet according to the above (1) or (2), the amount of the acid-soluble Ti can be more than or equal to 0.0001% and less than 0.008 %. (4) In the high strength steel sheet according to the above (1) or (2), the amount of the acid-soluble Ti can be from 0.008% to 0.20%. (5) In the steel sheet of high strength according to the above (1) or (2), [Ce], [La], [Al soluble in acid), and [IS] can satisfy 0.02 <(1Ce] + [La]) / [ Acid-soluble AI] <0.15. (6) On high-strength steel sheet according to the above (1) or (2), [Ce], [La], [acid-soluble Al], and [ S] can satisfy 0.02 <([Ce] + [La]) / [Al soluble in acid] <0.10. (7) On high-strength steel sheet according to the above (1) or (2 ), the amount of acid-soluble Al can be more than 0.01% and less than or equal to 2.0%. (8) On high strength steel sheet according to the above (1) or (2) , the density in number of inclusions having an equivalent circle diameter 0.5 to 2 um in the microstructure can be 15 inclusions / mm or more. (9) In the sheet of high-strength steel according to the above (1) or (2), of inclusions having an equivalent circle diameter of 1.0 µm or more in the microstructure, the percentage in number of inclusions a-
    lengths having an aspect ratio of 5 or more obtained by division: the long diameter by the short diameter can be 20% or less. "(10) In the sheet of high-strength steel according to the above - (1) or (2), of inclusions having an equivalent circle diameter of 1.0 um or more in the microstructure, the percentage in number of inclusions possessing at least minus one of MnS, TiS, and (Mn, TI) S precipitated to an oxide or oxysulfide composed of at least one of Ce and La, and at least one of e and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at least one of e and S can be 10% or more. - 10 (11) In the sheet of high strength steel according to the above (1) or (2), the density in volume number of elongated inclusions pos-, - assuming an equivalent circle diameter of 1 µm or more, and an aspect ratio of 5 or more obtained by dividing the long diameter by the short diameter can be 1.0 x 10º inclusions / mm or less in the steel structure. (12) In the high-strength steel sheet according to the above (1) or (2), in the microstructure, the density in volume number of inclusions can ssessing at least one of MnS, TiS, and (Mn, Ti) S precipitated to an oxide or oxysulfide composed of at least one of Ce and La, and at least one of e and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at least one of e and S can be 1.0 x 10º inclusions / mmº or more. (13) In the sheet of high-strength steel according to the above (1) or (2), elongated inclusions having a circle diameter equivalent to 1 µm or more, and an aspect ratio of 5 or more obtained by | division of the long diameter by the short diameter can be present in the microstructure, and the average equivalent circle diameter of the elongated inclusions can be 10 µm or less. (14) In the sheet of high-strength steel according to the above (1) or (2), inclusions having at least one of MnS, TiS, and (Mn, Ti) S pre-precipitated to a compound oxide or oxysulfide of at least one of Ce and La, and at least one of e and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at least one of e and S can
    | 8/68 be present in the microstructure, and inclusions may include a total of - 0.5% by mass to 95% by mass of at least one of Ce and La in terms of an average composition. Á (15) In the high-strength steel sheet according to the above (1) or (2), the average grain size in the microstructure can be 10 µm or less. (16) In the sheet of high-strength steel according to the above (1) or (2), the maximum hardness of martensite included in the microstructure can be 600 Hv or less.
    - 10 (17) In the high-strength steel sheet according to the above (1) or (2), the sheet thickness can be 0.5 mm to 20 mm.
    (18) The high-strength steel sheet according to the above (1) or (2) may also have a galvanized layer or a galvanized layer on at least one surface.
    (19) A method of producing a high-strength steel sheet according to the aspect of the present invention includes a first process in which molten steel having the chemical components according to the above (1) or (2 ) is subjected to continuous casting in order to be processed in a plate; a second process in which hot rolling is carried out on the plate at a finishing temperature of 850ºC to 970ºC, and a steel sheet is produced; and a third process in which the steel sheet is cooled to a cooling control temperature of 650 ° C or lower at an average cooling rate of 10 ° C / second to 100 ° C / second, and then rolled at a rolling temperature. —Mentof more than and equal to 300ºC and less than 650ºC.
    (20) In the production method of the high strength steel sheet according to the above (19), in the third process, the cooling control temperature can be 450ºC or lower, the winding temperature can be 300ºC to 450ºC, and a hot-rolled steel sheet can be produced.
    (21) The method of production of the high-strength steel sheet according to the above (19) may also include, after the third
    so, a fourth process in which the steel sheet is preserved, and cold rolling is carried out on the steel sheet in a thickness reduction of 40% or more; a fifth process in which the steel sheet is annealed at a maximum temperature of 750ºC to 900ºC; a sixth process in which the steel sheet is cooled to 450ºC or less at an average cooling rate of 0.1 ºC / second to 200 º * C / second; and a seventh process in which the steel sheet is kept in a temperature range of 300ºC to 450ºC for 1 second to 1,000 seconds in order to produce a cold rolled steel sheet. (22) In the production method of the high strength steel sheet - 10 according to the above (20) or (21), galvanizing or galvanizing can be carried out on at least one surface of the hot-rolled or hot-rolled steel sheet. cold rolled steel sheet. (23) In the production method of the high-strength steel sheet according to the above (19), the plate can be reheated to 1,100ºC or higher after the first process and before the second process.
    Effects of the Invention According to the present invention, it is possible to stably adjust the chemical composition of molten steel, suppress the generation of unrefined alumina inclusions, and precipitate sulfides in a plate through thin MnS based inclusions by control of Al deoxidation and deoxidation by adding Ce and La.
    Since thin MnS based inclusions are dispersed in the steel sheet as thin spherical inclusions, do not deform during rolling, and do not easily serve as cracking starting points, it is possible to obtain a high-strength steel sheet that is excellent in terms of hole expansion and ductility.
    Since the high strength steel sheet according to the above (1) is a multiphase steel sheet mainly including ferrite and martensite, the ductility is excellent.
    In addition, on the high steel sheet | resistance according to the above (16), once the hardness of the martensite phase is controlled, it is also possible to highlight the effect of improving hole expansion by controlling the inclusion morphology.
    In addition, in the production method of the high strength steel sheet according to the above (19), it is possible to produce a multiphase steel sheet mainly. including ferrite and martensite, in which thin MnS-based inclusions are 'dispersed, that is, a sheet of high-strength steel that is excellent in terms of hole expansion and ductility.
    BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view showing a relationship between the maximum hardness and the hole expansion of a martensite phase. Figure 2 is a flowchart showing a method of producing a sheet of high-strength steel according to an embodiment of the present invention.
    DETAILED DESCRIPTION OF THE INVENTION: Hereinafter, the high strength steel sheet of the present invention will be described in detail. Hereinafter, mass% in chemical components (chemical compositions) will be simply denoted by%. First, experiments that have been done until the completion of the present invention will be described. Deoxidation in various quantities (chemical components in molten steel) of Ce and La was carried out together with deoxidation of Al in order to produce plates. The plates were hot rolled to produce 3 mm hot rolled steel sheets. In addition, hot-rolled steel sheets were preserved, then cold-rolled in a 50% reduction in thickness, and annealed under a variety of tapering conditions to produce cold-rolled steel sheets. The inventors provided cold rolled steel sheets for hole expansion tests and stress tests, and investigated the densities in number, morphologies, and average chemical compositions of inclusions in the steel sheets. As a result of the tests above, it was found that in molten steel obtained by adding Si, then adding Al, then adding one or both of Ce and La, and thus deoxidizing, in one case where ([Ce] + [La]) / [Al soluble in acid] and ([Ce] + [La]) / [S] are in predetermined ranges, the oxygen potential in molten steel
    | 11/68 the concentration of ALO abruptly decreases; being generated decreases, and a - steel sheet which is excellent in terms of hole expansion can be obtained. Here, [Ce], [La], [Al soluble in acid], and [S] represent% by mass "of Ce, La, Al soluble in acid, and S which are included in steel, respectively (hereinafter , the same expression as this description will be used).
    The amount of increase in the hole expansion ratio of a cold-rolled steel sheet to which one or both of Ce and La were added with respect to the hole expansion ratio of a cold-rolled steel sheet to which neither Ce nor La were added was varied by the - 10 hardness of a martensite phase in the steel sheet, and the amount of increase increased when the hardness decreased.
    : —— It can be confirmed that, when the maximum hardness of the martensite phase was 600 Hv or less, the hole expansion would be improved more clearly by adding one or both of Ce and La. Maximum hardness 15 — martensite phase refers to the maximum micro Vickers hardness value obtained by randomly compressing an indenter with a gf load in a hard phase (other than a ferrite phase) 50 times.
    The cold-rolled steel sheet to which neither Ce nor La was added (the steel sheet used to compare the expansion ratio of - hole) was annealed under the same conditions in order to have the same tensile strength such as the cold rolled steel sheet to which one or both of Ce and La have been added. In this case, it was confirmed that uniform elongation of the cold-rolled steel sheet only that neither Ce nor La were added and uniform elongation of the cold-rolled steel sheet to which one or both of Ce and La were added were equal, and Ductability deterioration due to the addition of Ce and La was not observed.
    However, in a microstructure that is substantially composed of bainite, the hole expansion was significantly improved by the addition of Ce and La, but the ductility was small compared to the steel sheet mainly including ferrite and martensite.
    Reasons why the hole expansion has been improved by adding Ce and La are considered to be as follows:
    It is considered that when Si is added to molten steel in. plate production, SiO inclusions, are formed, but SiO inclusions are reduced to Si by later addition of Al.
    Al reduces inclusions of - SiO>, and deoxides oxygen dissolved in the molten steel in order to form inclusions based on ALbO. Some of the inclusions based on AIlZO3; they are removed by flotation, and the rest of the inclusions based on ALO; remain in molten steel.
    After that, when Ce and La are added to the molten steel, a small amount of Al; O; remains, but the 10-based AbOs inclusions in molten steel are reduced and decomposed, and thin and hard Ce oxides, La oxides, cerium oxides, and lanthanum oxides are: -— formed by deoxidation using Ce and La .
    When deoxidation of Al is appropriately performed based on the above deoxidation, similarly to a case in which deoxidation of Al is rarely performed, it is possible to precipitate MnS in the thin and hard Ce oxides, La oxides, and cerium oxidesulfides formed by deoxidation by the addition of Ce and La.
    As a result, it is possible to suppress deformation of the precipitated MnS during rolling, and for that reason elongated unrefined MnS in the steel sheet can be significantly reduced, and the hole expansion can be improved.
    Additionally, since it is also possible to decrease the oxygen potential of molten steel | by deoxidation of Al, fluctuation in the chemical composition can be reduced.
    Reasons why the degree of improved hole expansion is varied by the hardness of the martensite phase in steel sheets having the same tensile strength and uniform elongation are considered to be as follows.
    Hole expansion is significantly affected by the local ductility of a steel, and the most dominant factor in relation to hole expansion is considered to be the difference in hardness between microstructures (here, between the martensite phase and the ferrite phase) . Other powerful dominant factors in relation to hole expansion include the presence of
    non-metallic versions, such as MnS, and many Publications report that they will. which are formed from the inclusions when the starting points develop, and connect together so that the steel breaks. - For this reason, if the hardness of the martensite phase is excessively high, there are cases in which, even when the inclusion morphology is controlled by the addition of Ce and La, and voids due to the inclusions are suppressed , stress is concentrated at the interfaces between ferrite and martensite, voids are formed due to the difference in strength between the microstructures, and thus the steel can break. : 10 The inventors recently found that if the cooling conditions after hot rolling in the case of a sheet of steel: hot rolled and the ringing conditions in the case of a cold rolled steel sheet are properly controlled, and the The hardness of the martensite phase is reduced, it is also possible to highlight the effect of suppressing the occurrence of voids by controlling the morphology of the inclusions.
    In addition, the inventors have found that a sheet of steel that is excellent in terms of ductility and hole expansion can be obtained by guaranteeing a predetermined amount or more of martensite in a microstructure mainly including ferrite and martensite, and controlling the morphology of ins - clusionsporaditionofCeela.
    However, it is possible to add Ti to the molten steel after Al is added and before Ce and La are added.
    At this point in time, since oxygen in the molten steel is already deoxidized by Al, the amount of oxygen to be deoxidized by Ti is small.
    After that, due to Ce and Laquetem, inclusions based on ALO were added to the molten steel; they are reduced and decomposed, and fine Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides are formed.
    As described above, it is considered that when complex deoxidation is carried out by adding Al, Si, Ti, Ce, and La, a small amount of AIZO; it remains, but thin and hard Ce oxides, La oxides, cerium oxidesulfides, lanthanum oxysulides, and Ti oxides are mainly formed.
    | 14/68 | During complex deoxidation by adding Al, Si, Ti, Ce, and - La, if deoxidation of Al is properly carried out on the basis of deoxidation as described above, similarly to a case where deoxidation of " Al is rarely performed, it is possible to precipitate MnS, TiS, or (Mn, Ti) S in hard oxidesfinose, such as Ce oxides, La oxides, and Ti oxides, or thin and hard oxysulfides, such as cerium and oxysulfides lanthanum oxysulphides. As a result, in a case where a predetermined amount or more of Ti is added to molten steel, the types of chemical elements included in inclusions slightly vary, but a mechanism that suppresses elongation of inclusions based on MnS was the same as in a case where Ti is rarely added.
    'Based on the discovery obtained from experimental studies, the inventors studied the chemical compositions, microstructures, and conditions of steel sheet production as described below. First, a sheet of high-strength steel according to an embodiment of the present invention will be described.
    Hereinafter, reasons why the chemical compositions are bound in the high strength steel sheet according to the embodiment of the present invention will be described.
    C is the most fundamental element that controls the hardness and strength of steel, which increases the hardness and thickness of an extinguished hardened layer in order to improve the fatigue strength. That is, C is an essential element to guarantee the strength of a steel sheet. In order to form low temperature and retained austenite transformation phases that are necessary to obtain a desired high strength steel sheet, the C concentration needs to be 0.03% or more. When the C concentration exceeds 0.30%, formability and fusibility deteriorate. For this reason, in order to obtain the necessary strength and ensure formability and fusibility, the C concentration needs to be 0.30% or less.
    When the balance between strength and formability is taken into account, the C concentration is preferably 0.05% to 0.20%, and more preferably 0.10% to 0.15%.
    | 15/68 Si is a major deoxidizing element. In addition, Si increases - the number of austenite nucleation sites during heating for extinguishing, and suppresses the development of austenite grain in order to refine the grain size in a quench-hardened layer. In addition, Si suppresses carbide formation, and suppresses degradation of grain boundary resistance due to carbides. In addition, Si is also effective for forming bainite, and plays a critical role in terms of ensuring total strength. In order to develop the above effects, it is necessary to add - 10 0.08% or more of Si to the steel. When the Si concentration is very high, even in a case in which the deoxidation of Al is sufficiently performed, the: SiO concentration, in inclusions increases, and unrefined inclusions are prone to be formed. In addition, in this case, stiffness, ductility, and fusibility deteriorate, and decarburization and surface flaws increase in order to deteriorate fatigue characteristics. For this reason, the upper limit of the Si concentration needs to be 2.1%. When the balance between strength and other mechanical properties is taken into account, the Si concentration is preferably 0.10% to 1.5%, and more preferably 0.12% to 1.0%.
    Mn is a useful element for deoxidation in a steel production step, and an effective element for increasing the strength of the steel sheet together with C and Si. In order to obtain the above effect, the Mn concentration needs to be 0 , 5% or more. When more than 4.0% of Mn are included in steel, the ductility degrades due to Mn segregation and enhancement of solid solution strengthening. In addition, since the base metal's meltdown and stiffness deteriorates, the upper limit of the Mn concentration is 4.0%. When the balance between strength and other mechanical properties is taken into account, the concentration of Mn is preferably 1.0% to 3.0%, and more preferably 1.2% to 2.5%.
    P is useful in a case where P is used as an element for strengthening a solid substituting solution that is less than an atom of Fe. When the concentration of P in steel exceeds 0.05%, there are cases where P secretes if at austenite grain boundaries, the boundary strength of - grain degrades, and formability may deteriorate. For this reason, the upper limit of the P concentration is 0.05%. When solution / solid strengthening is not required, it is not necessary to add P to the steel, and for this reason the lower concentration of P includes 0%. However, for example, the lower limit of the concentration of P can be 0.0001% taking into account the concentration of P included as an impurity. N is an element that is inevitably incorporated into steel since nitrogen in the air is captured in molten steel during molten steel treatment. N has a nitrite-forming action with chemical elements, such as Al and Ti, in order to promote refinement of the microstructure in the base metal. However, when the N concentration exceeds 0.01%, N forms unrefined precipitates with chemical elements, such as Al and Ti, and hole expansion deteriorates. For this reason, the upper limit of the N concentration is 0.01%. On the other hand, when the N concentration is reduced to less than 0.0005%, the cost increases, and for that reason the lower limit of the N concentration can be 0.0005% from the point of view of industrial viability , S is included in the steel sheet as an impurity, and prone to segregate into steel. Since S forms elongated unrefined MnS based inclusions in order to deteriorate hole expansion, the concentration is preferably extremely low. In conventional techniques, it was necessary to significantly decrease the concentration of S in order to ensure hole expansion.
    However, when an attempt is made to decrease the S concentration to less than 0.0001%, the desulphurisation load during secondary refinement increases, and the desulphurisation cost increases excessively. In a case where desulphurization during secondary refinement is assumed, when the cost of desulphurisation according to the quality of the steel sheet is taken into account, the lower limit of the S concentration is 0.0001%. However, in a case where costs for secondary refinement are also suppressed, and the addition effect of Ce and La are more effectively used, the concentration of S is preferably more than 0.0004%, more preferably 0.0005% or more, and more, preferably 0.0010% or more. - Furthermore, in the present modality, inclusions based on MnS are precipitated into thin and hard inclusions, such as Ce oxides, La oxides, cerium oxidesulfides, and lanthanum oxysulfides, in order to control the inclusions morphology based on MnS.
    For this reason, inclusions do not easily deform the lamination, and elongation of inclusions is prevented.
    For this reason, the upper limit of the concentration of S is specified by the relationship between the concentration of S and the total amount of one or both of Ce and La as described below.
    For example, the upper limit of the S concentration is 0.1%. In the modality, since the MnS-based inclusion morphology is controlled by inclusions, such as Ce oxides, La oxides, cerium oxidesulfides, and lanthanum oxysulfides, even when the S concentration is high, it is it is possible to prevent S from adversely affecting the qualities of the steel sheet by adding one or both of Ce and La in an amount that corresponds to the concentration of S.
    That is, even when the concentration of S increases to a certain level, a substantial desulphurization effect can be obtained by adding one or both of Ce and La to the steel in an amount that corresponds to the concentration of S, and steel having the same qualities as extremely low sulfur steel can be obtained.
    In other words, since the concentration of S is appropriately adjusted according to the total amount of Ce and La, the flexibility is great for the upper limit of the concentration of S.
    As a result, in the modality, it is not necessary to perform desulfurization of the molten steel during the secondary refinement in order to obtain extremely low sulfur steel, and it is possible to skip the secondary refinement.
    For this reason, it is possible to simplify the production of steel sheet processes and therefore reduce costs for desulphurisation. | Generally, since Al oxides are prone to form
    | 18/68 bunches in order to be unrefined and deteriorate hole expansion, it is - ”preferable to suppress acid-soluble Al in molten steel as much as possible.
    : However, the inventors recently found areas where oxides Í based on alumina are prevented from forming clusters in order to be unrefined by controlling the concentrations of Ce and La in molten steel according to the concentration of the Al soluble in acid while deoxidation of Al is carried out. In the areas, of inclusions based on AO; formed by the deoxidation of Al, some of the inclusions based on AlO; they are removed by flotation, and the rest of the inclusions based on AbhO; s - 10 in the molten steel are reduced and decomposed by Ce and La which must be added later, thereby forming thin inclusions.
    For this reason, in the modality, it is substantially unnecessary to add Al to the steel, and, in particular, the flexibility is great for the concentration of the acid-soluble Al. For example, the concentration of Al - soluble in acid may be more than 0.004% considering the relationship between the concentration of Al soluble in acid and the total amount of one or both of Ce and La, which will be described below.
    In addition, in order to jointly use Al deoxidation and deoxidation by the addition of Ce and La, the concentration of the acid-soluble Al can be more than 0.010%. In this case, unlike conventional techniques, it is unnecessary to increase the amounts of Ce and La in order to ensure the total amount of deoxidizing elements, the oxygen potential in steel can also be decreased, and variation in the amount of each chemical element in the chemical composition can be suppressed. However, in a case where the effect of using Al deoxidation and deoxidation by adding Ce and La together is also enhanced, the concentration of the acid-soluble Al is preferably more than 0.020%, and more preferably more than 0.040%.
    The upper limit of the concentration of the acid-soluble Al is specified by the relationship between the acid-soluble Al and the total amount of one or both of Ce and La as described below. For example, the concentration of acid-soluble Al can be 2.0% or less considering the above ratio. Here, the concentration of the acid-soluble Al is determined by 'measuring the concentration of Al which dissolves in an acid. For analysis: from acid-soluble Al, the fact that Al dissolved (or Al solute in a solid solution) dissolves in an acid, but AI2O; 3 does not dissolve in an acid is used. Here, examples of the acid include a mixed acid in which chloric acid, nitric acid, and water are mixed in a ratio (mass ratio) of 1: 1: 2. Using such an acid, Al which is soluble in acid and ALO; which is insoluble in the acid are separated, and the concentration of the acid-soluble Al can be measured. However, acid insoluble Al (AlzO; z which is insoluble in acid) is determined to be an unavoidable impurity.
    B Ti is a major deoxidizing element, and the number of austenite nucleation sites increases when carbides, nitrites, and carbonitrites are formed, and the plates are sufficiently heated before hot lamination. As a result, once austenite grain development is suppressed, Ti contributes to the refinement of crystal grains and an increase in the strength of the steel sheet, promotes dynamic recrystallization during hot rolling, and significantly improves expansion of hole.
    For this reason, in a case where the above effect is sufficiently enhanced, 0.008% or more of the acid-soluble Ti can be added to steel. In a case where the above effect does not need to be sufficiently ensured, and in a case where the plates cannot be sufficiently heated, the concentration of acid-soluble Ti may be less than 0.008%. Examples of imaginable situations in which the plates cannot be heated sufficiently include a case in which the hot rolling operation rate is high and a case in which sufficient heating capacity is not provided in hot rolling. However, the lower limit of the concentration of acid-soluble Ti in steel is not particularly limited, but it can be, for example, 0.0001% since Ti is inevitably included in the steel.
    In addition, when the concentration of Ti soluble in acid
    yields 0.2%, the deoxidation effect of Ti is saturated, unrefined carbides, - nitrites, and carbonitrites are formed by heating the plates before: hot rolling, and the qualities of the steel sheet deteriorate. In this case, an effect according to the addition of Ti cannot be obtained. For this reason, in the modality, the upper limit of the concentration of the acid-soluble Ti is 0.2%.
    For this reason, the concentration of acid-soluble Ti needs to be 0.0001% to 0.2%. In addition, in a case where the effect of Ti carbides, nitrites, and carbonitrites is sufficiently assured, the concentration of the acid-soluble Ti is preferably 0.008% to 0.2%. In this case, in order to more reliably prevent unrefined Ti carbides, nitrites, and carbonitrites, the acid-soluble Ti concentration can be 0.15% or less. On the other hand, in a case where the effect of Ti carbides, nitrites, and carbornitrites and the Ti deoxidation effect is not sufficiently ensured, the acid-soluble Ti concentration is preferably more than or equal to 0.0001% and less than 0.008%.
    When the plate is heated to a sufficient heating temperature before hot rolling, carbides, nitrites, and carbonitrites formed during casting can be produced to temporarily dissolve in order to form solid solutions. For this reason, in order to obtain an effect according to the addition of Ti, the heating temperature before hot rolling is preferably higher than 1,200ºC. In this case, since carbides, nitrites, and fine carbonitrites precipitate again from Ti solute, it is possible to refine the crystal grains of the steel sheet and increase the strength of the steel sheet. On the other hand, the heating temperature before hot rolling exceeding 1,250ºC is not preferred from the point of view of costs and scale formation. For this reason, the heating temperature before hot rolling is preferably 1,250ºC or less.
    The concentration of acid-soluble Ti is determined by measuring the concentration of Ti dissolved in an acid. For analysis of acid-soluble Ti, the fact that Ti dissolved (or Ti solute in a solid solution) | it dissolves in an acid, but Ti oxides do not dissolve in an acid is used. Here, examples of the acid include a mixed acid in which chloric acid, nitric acid, and water are mixed in a J (mass ratio) ratio of 1: 1: 2. Using such an acid, Ti that is soluble in the acid and Ti oxides that are insoluble in the acid are separated, and the concentration of the acid-soluble Ti can be measured. However, acid insoluble Ti (Ti oxides that are insoluble in acid) is determined to be an unavoidable impurity. Ce and La are likely to reduce AO; formed by deoxidation of Al and SiO, z formed by deoxidation of Si, and serve as sites of precipitation of inclusions based on MnS. In addition, Ce and La form inclusions (hard inclusions) including Ce oxides (for example, Ce20; e: CeO;), cerium oxidesulfides (for example, Cez02S), La oxides (for example, LazOs and LaO ;), lanthanum oxysulfides (eg, LazO, S), La Ce-oxide oxide, or cerium oxide-lanthanum oxysulfide which are hard and thin, and do not deform easily during lamination, as a compound main (for example, the total amount of the compounds is 50% or more).
    There are cases where hard inclusions include MnO, SiO ;, TiO ,, TizOz, or AbO; due to deoxidation conditions. However, when the main compound is Ce oxide, cerium oxide, La oxide, lanthanum oxide sulphide, Ce-oxide La oxide, or cerium oxide sulphide lanthanum, the inclusions hard enough they serve as the MnS-based inclusion precipitation sites while maintaining its size and hardness.
    The inventors have experimentally found that the total concentration of one or both of Ce and La needs to be 0.001% to 0.04% in order to obtain the above inclusions.
    When the total concentration of one or both of Ce and La is less than 0.001%, inclusions of AlO; and SiO> inclusions cannot be reduced. In addition, when the total concentration of one or both of Ce and La exceeds 0.04%, large quantities of cerium oxysulfides and lanthanum oxysulfides are formed, and the oxysulfides are not further refined.
    | 22/68 so that the hole expansion deteriorates. For this reason, the total of at least one selected from Ce and La is preferably 0.001% to 0.04%. In order to reduce AlO inclusions more reliably; and SiO inclusions, the - total concentration of one or both of Ce and La is more preferably 0.015% or more.
    In addition, the inventors paid attention to the fact that the amount of MnS reformed by oxides or oxisulfides which are composed of one or both of Ce and La (hereinafter sometimes also referred to as "hard compounds") is expressed using the concentrations de Ce, La, - 10 eS, and obtained an idea that the concentration of Sea total concentration of Ce and La in steel are controlled using ([Ce] + [Lal) / [S].
    'Specifically, when ([Ce] + [La]) / [S] is small, the amount of the hard compounds is small, and a large amount of MnS alone precipitates. When ([Ce] + [La]) / [S] increases, the amount of the hard compounds becomes greater than that of MnS, and inclusions having a morphology in which MnS precipitates in the hard compounds increase . That is, MnS is reformed by the hard compounds. As a result, hole expansion is improved, and MnS is prevented from stretching.
    That is, it is possible to use ([Ce] + [La]) / [S] as a parameter that controls the inclusion morphology based on MnS. For this reason, the inventors varied ([Ce] + [La]) / [S] of the steel sheet, and evaluated the morphology of inclusions and hole expansion in order to clarify the composition relationship that is effective for suppression. elongation of inclusions based on MnS. As a result, it was found that when ([Ce] + [La]) / [S] is 04a50, the hole expansion is drastically improved.
    When ([Ce] + [La]) / [S] is less than 0.4, the percentage in number of inclusions having a morphology in which MnS precipitates into the hard compounds significantly decreases, and the percentage in number of elongated inclusions based on MnS that are likely to serve as starting points for cracking increases so that expansion of hole degrades.
    When ([Ce] + [La]) / [S] exceeds 50, large amounts of cerium oxides and lanthanum oxysulfides form inclusions - unrefined, and therefore hole expansion deteriorates. For example, when ([Ce] + [La]) / [S] exceeds 70, cerium oxidesulfides and lanthanum sulphides form unrefined inclusions having a diameter of cir- —circle equivalent to 50 µm or more.
    In addition, when ([Ce] + [La]) / [S] exceeds 50, the MnS-based inclusion morphology control effect is saturated, and so the effect that is appropriate for costs cannot be be obtained. From the results above, ([Ce] + [La]) / [S] needs to be 0.4 to 50. When the degree of - 10 control of the inclusion morphology based on MnS and the costs are raised in account, ([Ce] + [La]) / [S] is preferably 0.7 to 30, and more preferably, 1.0 to 10. Furthermore, in a case where the inclusion morphology based in MnS they are more efficiently controlled while the chemical components in cast steel are adjusted, ([Ce] + [La]) / [S] is more preferably 1.1 or more.
    In addition, the inventors paid attention to the total concentration of one or both of Ce and La with respect to the concentration of acid-soluble Al in the steel sheet of the modality, which is obtained from molten steel that has undergone deoxidation by Si, deoxidation by Al, and deoxidation by one or both of CeeLa, and obtained an idea of using ([Ce] + [La]) / [acid-soluble AI] as a parameter that appropriately controls the oxygen potential in molten steel.
    The inventors have experimentally found that, in a case where ([Ce] + [La]) / [acid-soluble AI] is 0.02 or more in molten steel that has undergone deoxidation by Si, deoxidation by Al, and then deoxidation for at least one of Ce and La, it is possible to obtain a sheet of steel that is excellent in terms of hole expansion. In this case, the oxygen potential in the molten steel abruptly decreases, and, consequently, the AlO concentration; formed decreases. For this reason, even in a case where Alox deoxidation is actively performed, similar to a case where Al deoxidation is rarely performed, a sheet of steel that is excellent in terms of hole expansion can be obtained. In addition, in a case where (ICe] + |
    [Lal) / [acid-soluble AI] is less than 0.25, costs for Ce or La - decreases, and oxygen transfer between chemical elements in molten steel 'can also be efficiently controlled based on the affinity of each 7 chemical element to oxygen.
    However, in the modality, it is not necessary to actively perform deoxidation by Al, and it is simply necessary to control the total concentration of at least one Ca Ca and the concentration of Al soluble in acid so that ([Ce] + [La]) / [Acid soluble AI] satisfies more than or equal to 0.02 and less than 0.25. It was confirmed that, in a case where ([Ce] + [La]) / [acid-soluble AI] is less than 0.02, the amount of Al added to at least one of Ca and La it becomes very large even when one or both of 'Ce and La are added to steel, and for that reason bunches of unrefined alumina that deteriorate hole expansion are formed.
    In addition, in a case where ([Ce] + [La]) / [acid-soluble AI] is 0.25 or more, there is a case that the inclusion morphology is not sufficiently controlled.
    For example, cerium oxysulfides and lanthanum oxysulfides form unrefined inclusions, and sufficient deoxidation is not performed on molten steel.
    For that reason, ([Ce] + [La]) / [Al soluble in acid] needs to be more than or equal to 0.02 and less than 0.25. In addition, in order to also reduce the cost, and appropriately control the transfer of oxygen between chemical elements in the molten steel, ([Ce] + [La]) / [acid-soluble AI] is preferably less than 0 , 15, and more preferably less than 0.10. As such, even when desulfurization through secondary refinement is not carried out, a sheet of steel that is excellent in terms of ductility and hole expansion can be obtained by controlling (ICe] + [La]) / [S] and ([ Ce] + [La]) / [Al soluble in acid]. Here below, in the modality, reasons why the quantity of each optional element in the chemical composition is limited will be described.
    Chemical elements are optional elements, and can be arbitrarily (optionally) added to steel.
    For this reason, chemical elements may not be added to steel, and at least one selected from a group consisting of chemical elements may be added to steel.
    However, since there are cases where chemical elements are unavoidable. Typically included in steel, the lower limit of the concentration of the chemical elements is a threshold value that determines unavoidable impurities. - Nb, W, and V form carbides, nitrites, and carbonitrites with C or N, promote refinement of the microstructure in a base metal, and improve rigidity.
    In order to obtain complex carbides, complex nitrites, and more, 0.01% or more of Nb can be added to steel. However, even when a large amount of Nb is added so that the concentration of Nb exceeds 0.20%, the refinement effect of the microstructure on the base metal is saturated, and the cost production increases. For this reason,: the upper limit of the Nb concentration is 0.20%. In a case where the cost of Nb is reduced, the concentration of Nb can be controlled to 0.10% or less. However, the lower limit of the Nb concentration is 0.001%.
    In order to obtain complex carbides, complex nitrites, and more, W can be added to steel. However, even when a large amount of W is added so that the W concentration exceeds 1.0%, the microstructure refinement effect on the base metal is saturated, € the production cost increases. For this reason, the upper limit of the W concentration is 1.0%. However, the lower limit of the W concentration is 0.001%.
    In order to obtain complex carbides, complex nitrites, and more, 0.01% or more of V can be added to steel. However, even when a large amount of V is added so that the V concentration exceeds 1.0%, the refinement effect of the microstructure on the base metal is saturated, and the cost production increases. For this reason, the upper limit of the V concentration is 1.0%. In a case where the cost of V is reduced, the concentration of V can be controlled to be 0.05% or less. However, the lower limit of the V concentration is 0.001%.
    Cr, Mo, and B are chemical elements that improve the hardness of steel.
    Cr can be included in steel according to need in order | to also ensure the strength of the steel sheet. For example, in order to. To achieve the effect, 0.01% or more of Cr can be added to steel. When a large amount of Cr is included in steel, the balance between strength and ductility deteriorates. For this reason, the upper limit of the concentration of Cré20%. In a case where the cost of Cr is reduced, the concentration of Cr can be controlled to be 0.58% or less. In addition, the lower limit of the Cr concentration is 0.001%.
    Mo can be included in steel according to need in order to also ensure the strength of the steel sheet. For example, in order to. 10 obtain the effect, 0.01% or more of Mo can be added to steel. When a large amount of Mo is included in steel, it becomes difficult to suppress: formation of pro-eutectic ferrite, and for this reason the balance between resistance and ductility deteriorates. For this reason, the upper limit of the Mo concentration is 1.0%. In a case where the costs of Mo are reduced, the Mo concentration can be controlled to be 0.4% or less. In addition, the lower limit of the Mo concentration is 0.001%.
    B can be included in steel as needed in order to also strengthen grain boundaries and improve formability. For example, in order to achieve the effect, 0.0003% or more of B can be added to steel.
    - Even when a large amount of B is included in steel, the effect is saturated, the cleanliness of steel is impaired, and the ductility deteriorates. For this reason, the upper limit of the concentration of B is 0.005%. In a case where the cost of B is reduced, the concentration of B can be controlled to be 0.003% or less. In addition, the lower limit of the B concentration is 0.0001%.
    In order to strengthen grain limits and improve formability by controlling the morphology of sulfides, Ca, Mg, Zr, Sc, lantanoids from Pr to Lu (Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er , Tm, and Yb) can be included in steel as needed.
    Ca controls the sulphide morphology by the spheroidization of sulphides or others, in order to strengthen grain boundaries and improve the formability of the steel sheet. For example, in order to obtain the effect, the Ca concentration can be 0.0001% or more.
    Even when a large amount of Ca - is included in steel, the effect is saturated, the cleaning of steel is impaired, and the ductility deteriorates.
    For this reason, the upper limit of the concentration - of Ca is 0.01%. In a case where the cost of Ca is reduced, the Ca concentration can be controlled to be 0.004% or less.
    In addition, the lower limit of the Ca concentration is 0.0001%. Similarly, since Mg has almost the same effects as Ca, the Mg concentration is 0.0001% to 0.01%. In order to spheroidize sulfides in order to improve the rigidity of the base metalloid, 0.001% or more of Zr can be added to steel.
    When a large amount of Zr is included in steel, the cleaning of steel is impaired, and the ductility deteriorates.
    For this reason, the upper limit of the Zr concentration is 0.2%. In a case where the cost of Zr is reduced, the concentration of Zr can be controlled to be 0.01% or less.
    In addition, the lower limit of the Zr concentration is 0.0001%. Similarly, in a case where the sulphide morphology (forms) is controlled, the total concentration of at least one selected from Sc, and lantanoids from Pr to Lu can be from 0.0001% to 0.1%. In the modality, 0.001% to 2.0% Cu and 0.001% to 2.0% Ni can be included in steel according to the need.
    The chemical elements improve the hardness in order to enhance the steel strength.
    However, in a case where the extinction is efficiently performed using chemical elements, the Cu concentration can be 0.04% to 2.0%, and the Ni concentration can be 0.02% to 1.0 %. Furthermore, in a case where scraps or others are used as some of the starting materials, there are cases where As, Co, Sn, Pb, Y, and Hf are inevitably incorporated.
    In order to prevent the chemical elements from adversely affecting the mechanical properties (eg, hole expansion) of the steel sheet, the concentration of each chemical element is limited as below.
    The upper limit of the As concentration is 0.5%. The upper limit of the Co concentration is 1.0%. In addition, the upper limits of the concentrations of Sn, Pb, Y, and Hf are all 0.2%. However,
    | 28/68 the lower limits of the chemical elements are all 0.0001% ,. . In the modality, the optional elements as described above can optionally be included in steel. - Then, the microstructure of the high-strength steel sheet - according to the modality will be described.
    Hole expansion is significantly affected by the local ductility of a steel, and the most dominant factor in relation to hole expansion is the difference in hardness between microstructures. Another powerful dominant factor regarding hole expansion is the presence of non - metallic inclusions, such as MnS. Generally, vacuums are caused by inclusions as the starting point, develop and bond together so that the steel breaks.
    That is, when the hardness of the martensite phase is very large compared to the hardness of other microstructures (for example, the ferret phase), there are cases where, even when the inclusion morphology is controlled by the addition of Ce and La , and occurrence of voids due to inclusions is suppressed, stress is concentrated at the interfaces between ferrite and martensite, voids are caused due to the difference in strength between the microstructures, and the steel can break.
    When the cooling conditions after hot rolling in the case of a hot rolled steel sheet, and the ringing conditions in the case of a cold rolled steel sheet are appropriately controlled, and the hardness of the martensite phase is reduced, the effect of suppressing the occurrence of voids by controlling the morphology of inclusions - may also be highlighted. In this case, the effect of controlling the inclusion morphology by Ce and La that are included in steel sheet is significantly exhibited as described above. Figure 1 schematically shows a relationship between the maximum hardness (Vickers hardness) of martensite and hole expansion ratios (hole expansion) 2. As shown in the figure, in a case where the hardness of the martensite phase is suppressed to a certain value so that the inclusion morphology is controlled using at least one of Ce and La, hole expansion can be significantly less
    compared to a case in which the inclusion morphology is not con- controlled.
    In addition, in a microstructure substantially composed of 'bainite, the degree of hole expansion improved by the addition of Ce and La is / great, but the ductility is weak compared to a steel sheet mainly including ferrite and martensite.
    In the modality, a sheet of steel that is excellent in terms of both hole expansion and ductility is provided.
    For this reason, the main microstructure is ferrite and martensite, and the microstructure includes 1% to 50% of the martensite phase in terms of the area ratio, optionally includes bainite and retained austenite, and has a residue composed of a ferrite phase.
    In this case, in order to obtain uniform deformability, for example, 'retained bainite and austenite are controlled at 10% or less each.
    When the area ratio of the martensite phase is less than 1%, the work hardness is weak.
    In order to also enhance the work hardenability, the area ratio of the martensite phase is preferably 3% or more, and more preferably 5% or more.
    On the other hand, when the area ratio of the martensite phase exceeds 50%, the uniform deformability of the steel sheet decreases significantly.
    In order to obtain a large uniform deformability, the area ratio of the martensite phase is preferably 30% or less, and more preferably 20% or less.
    However, some or all of the martensite phase can be tempered martensite.
    The ratio of the martensite phase is determined by the area ratio of the martensite phase in a microstructure photograph obtained using an optical microscope.
    Here, inclusions as described below are included in the microstructures (fasedemartensite, ferrite phase, bainite, and retained austenite). Since the hardness of the ferrite phase and the martensite phase included in steel varies with the chemical composition and production conditions (for example, the amount of stresses caused during the rolling or cooling rate) of steel, the hardness it is not particularly limited. - When taking into account that the hardness of the martensite phase is high compared to those of other microstructures, the maximum hardness of the martensite phase included in steel is preferably 600 Hv or less.
    The maximum hardness
    The maximum martensite phase is the maximum micro-Vickers hardness value obtained by randomly compressing an indenter with a load of] 10 gf in a hard phase (different from the ferrite phase) 50 times. - Then, the conditions for the presence of inclusions in the high strength steel sheet of the modality will be described. Here, the steel sheet refers to a laminated sheet obtained after hot rolling or cold rolling. In the modality, the conditions for the presence of inclusions in the steel sheet can be optionally specified from a variety of points - 10 healthy. In the first aspect in relation to inclusions, the density in 'number of inclusions that are present in the steel sheet and have an equivalent circle diameter of 0.5 µm to 2 µm is 15 inclusions / mm or more.
    In order to obtain a sheet of steel that is excellent in terms of ductility and hole expansion, it is important to reduce as much as possible inclusions based on elongated unrefined MnS that easily act as cracking starting points or propagation trails of fissure.
    As described above, the inventors found that in a case where ([Ce] + [La]) / [acid-soluble AI] and ([Ce] + [La]) / [S] are in the above ranges, since the oxygen potential in the molten steel abruptly diminishes due to complex deoxidations, and the AbO concentration; in inclusions decreases, a sheet of steel that is deoxidized by Si, then deoxidized by Al, and then deoxidized by at least one of Ce and La is excellent in terms of ductibility and hole expansion, similar to a steel sheet produced with little deoxidation by Al.
    In addition, the inventor also found that, since MnS precipitated into thin and hard Ce oxides, La oxides, cerium oxysulfides, and lanthanum oxysulfides that are formed due to deoxidation by the addition of Ce and La , and the precipitated MnS does not easily deform during lamination, the elongated unrefined MnS is significantly reduced
    made in the steel sheet. 'That is, it was found that in a case where ([Ce] + [La]) / [AI: acid-soluble] and ([Ce] + [La]) / [S] are in the above ranges, the density. the number of thin inclusions having an equivalent circle diameter of 2um or less abruptly increases, and the thin inclusions are dispersed in steel.
    Since thin inclusions do not easily aggregate, Most inclusions have a spherical or spindle shape. Furthermore, since inclusions having MnS precipitated in Ce oxides, oxides - 10 of it, cerium oxysulfides, and lanthanum oxysulfides have a high melting point and are not easily deformed, the inclusions maintain an almost spherical shape even during hot rolling. As a result, the long diameter / short diameter (hereinafter sometimes referred to as the "elongation ratio") of most inclusions is generally 3 or less.
    Since the probability of inclusions to serve as a starting point for fractures varies significantly with the shapes of the inclusions, the lengthening ratio of the inclusions is preferably 2 or less.
    Experimentally, attention was paid to the density in number of inclusions having an equivalent circle diameter of 0.5 µm to 2 µm so that inclusions can be easily identified through observation using a scanning electron microscope (SEM) or others more. With respect to the lower limit of the equivalent circle diameter, inclusions that are large enough to be sufficiently counted are used. That is, the number of inclusions was counted with respect to inclusions of 0.5 µm or more. The equivalent circle diameter is obtained by measuring the long diameter and the short diameter of an inclusion observed in a cross-section, and computation (long diameter x short diameter).
    While the detailed mechanism is not clear, is it considered that thin inclusions of 2 µm or less are dispersed in the microstructure at 15 inclusions / mm or more due to a synergistic effect of decreased oxygen potential in molten steel by deoxidation of Al and the refinement of inclusions based on MnS. It is assumed that, due to the above, the 'concentration of stress caused during the formation of hole expansion IS or others is alleviated, and an effect of abrupt improvement of hole expansion is exhibited. As a result, it is considered that, during repetitive deformation or hole expansion, inclusions based on MnS are thin, and therefore inclusions based on MnS do not easily act as starting points for cracking or crack propagation trails. , relieve stress concentration, and improve formability, such as hole expansion. As such, with regard to the morphology of the inclusions, is the density in number of inclusions that are present in the steel sheet and have an equivalent circle diameter of 0.5 µm to 2 µm preferably 15 inclusions / mm or more.
    In the second aspect in relation to inclusions, of inclusions that are present in the steel sheet and have an equivalent circle diameter of 1 µm or more, the percentage in number of elongated inclusions having an aspect ratio (elongation ratio) of 5 or more obtained by dividing the long diameter by the short diameter is 20% or less.
    The inventors investigated whether or not inclusions based on elongated unrefined MnS that easily act as cracking starting points or crack propagation trails are reduced.
    The inventor experimentally found that when the equivalent circular diameters of the inclusions are less than 1 µm, even in a case where MnS is elongated, the inclusions do not act as cracking partitions, and hole ductibility and expansion are not. deteriorated. In addition, since inclusions having an equivalent circle diameter of 1 µm or more can be easily observed using a scanning electron microscope (SEM) or more, the morphology and chemical compositions of inclusions having a circle diameter and - —quivalent of 1 µm or more in the steel sheet were investigated, and the distribution of the elongated MnS was assessed. The upper limit of the equivalent MnS circle diameter is not particularly specified; however, for example, there are cases where MnS of approximately 1 mm is observed in the steel sheet. ] The percentage in number of elongated inclusions is obtained as follows: Here, the elongated inclusion refers to an inclusion having — a long diameter / short diameter (elongation ratio) of 5 or more.
    Chemical compositions of a plurality (for example, a predetermined number of 50 or more) of inclusions having an equivalent circle diameter of 1 µm or more that are randomly selected using a SEM are analyzed, and the long and short diameter of the inclusions are measured from a SEM image (secondary electronic image). The percentage in number of elongated inclusions can be obtained by dividing the number of elongated inclusions detected by the number of all investigated inclusions (in the above example, a predetermined number of 50 or more).
    One reason that elongated inclusions are defined as inclusions having an elongation ratio of 5 or more is that most inclusions having an elongation ratio of 5 or more in the steel sheet to which Ce and La are not added are MnS . The upper limit of the MnS elongation ratio is not particularly specified; however, for example, there are cases where MnS having an elongation ratio of approximately 50 is observed on the steel sheet.
    As a result of the evaluation by the inventors, it was found that, in steel sheets, the percentage in number of elongated inclusions having an elongation ratio of 5 or more with respect to inclusions having an equivalent circle diameter of 1 um or plus it is controlled to be 20% or less, the hole expansion is improved. When the percentage in number of elongated inclusions exceeds 20%, since a number of elongated inclusions based on MnS that easily act as starting points for cracking are present, the hole expansion degrades. In addition, as the grain sizes of the elongated inclusions increase, that is, as the equivalent circle diameters increase, the stress concentration occurs more easily during formation and deformation, and therefore the elongated inclusions: easily act as points crack start or crack propagation trails, and the hole expansion abruptly deteriorates.
    For this reason, in the modality, the percentage in number of elongated inclusions is preferably 20% or less. As the hole expansion becomes better as the elongated inclusions based on MnS become smaller, the lower limit of the percentage in number of the elongated inclusions includes 0%.
    - 10 In a case where inclusions having an equivalent circle diameter of 1 µm or more are included, and elongated inclusions having] an elongation ratio of 5 or more are not present in the inclusions, or in a case where the Equivalent circle diameters of inclusions are all less than 1 µm, the percentage in number of elongated inclusions having an elongation ratio of 5 or more in inclusions having an equivalent circle diameter of 1 µm or more is determined to be 0%. It is confirmed that the maximum equivalent circle diameters of elongated inclusions are also small compared to the average grain size of crystals (metallic crystals) in the microstructure, and the reduction of the maximum equivalent circle diameters of the elongated inclusions are also considered to be a factor that can drastically improve hole expansion. In the third aspect in relation to inclusions, of inclusions having an equivalent circle diameter of 1.0 µm or more in the steel sheet, the percentage in number of inclusions having at least one of MnS, TIS, and (Mn, Ti ) Are precipitated in an oxide or oxysulfide composed of at least one of Ce and La, and at least one of e and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at leastdoesS is 10% or more. For example, on a steel sheet having ([Ce] + [La]) / [S] from 0.4 to 50, inclusions based on MnS precipitated in an oxide or oxis-
    sulfide including one or both of Ce and La, or an oxide or oxysulfide included. going one or both of Ce and La, and one or both of Si and Ti (the two compounds above). However, on a sheet of steel in which the acid-soluble Ti is less than 0.008%, there are many cases in which oxides or oxysulfides, including one or both of Si and Ti, are not formed.
    The morphology of inclusions is not particularly specified since MnS-based inclusions precipitate into hard compounds, and there are many cases where MnS-based inclusions precipitate around hard compounds like nuclei.
    Also, there are cases where TiN precipitates along with MnS-based inclusions in the thin and hard Ce oxides, La oxides, cerium oxidesulfides, and lanthanum oxysulfides. However, since TiN has little influence on ductility and hole expansion as described above, TiN itself is not included in MnS based inclusions.
    Since inclusions having MnS-based inclusions precipitated into the hard compounds in the steel sheet that do not easily deform during rolling, the inclusions have a shape that is not elongated, that is, a spherical or spindle shape.
    Here, inclusions that are determined to be non-stretched (spherical inclusions) are not particularly specified; however, for example, inclusions are an inclusion having an elongation ratio of 3 or less, and preferably an inclusion having an elongation ratio of 2 or less. This is because the elongation ratio of an inclusion having inclusions based on MnS precipitated on the hard compounds on a plate before lamination is 3 or less. In addition, when the spherical inclusion is a perfectly spherical body, the elongation ratio is 1, and for this reason the lower limit of the elongation ratio is 1.
    The inventors investigated the percentage in number of inclusions (spherical inclusions) by the same method as the method of measuring the percentage in number of elongated inclusions. That is, the
    chemical positions of a plurality (for example, a predetermined number of 50 or more) of inclusions having an equivalent circle diameter of 1.0 µm or more which are randomly selected using one - SEM are analyzed, and the long diameter and short diameter of the inclusions are measured from a SEM image (secondary electronic image). The percentage in number of spherical inclusions can be obtained by dividing the number of spherical inclusions having a detected elongation ratio of 3 or less by the number of all investigated inclusions (in the example above, a predetermined number of 50 or more ). As a re-. 10 result, in the steel sheet so that the percentage in number of inclusions having inclusions based on MnS precipitated in hard compounds Ú (spherical inclusions) is controlled to be 10% or more, the hole expansion is improved.
    When the percentage in number of inclusions having MnS-based inclusions precipitated in the hard compounds is less than 10%, the percentage in number of elongated inclusions based on MnS increases, and the hole expansion degrades.
    For this reason, in the modality, of inclusions having an equivalent circle diameter of 1.0 µm or more, the percentage in number of inclusions having inclusions based on precipitated MnS in the hard compounds is 10% or more.
    Since hole expansion is improved by precipitating an MnS-based inclusion number in hard compounds, the upper limit value of the percentage in number of inclusions having precipitated MnS-based inclusions in hard compounds includes 100% . However, since inclusions having MnS-based inclusions precipitated in hard compounds do not easily deform during lamination, the equivalent circle diameter is not particularly specified, and hole expansion is not adversely affected even when the equivalent circle diameter is 1 µm or more.
    However, when the equivalent circle diameter is very large, there is a possibility for inclusions to act as cracking starting points, and for this reason the upper limit of the equivalent circle diameter is preferable.
    approximately 50 µm. - Additionally, in a case where the circle diameters: inclusions equivalents are less than 1 µm, since the inclusions do not easily act as starting points for cracking, the lower limit of the equivalent circle diameter does not is specified.
    In the fourth aspect in relation to inclusions, of inclusions that are present in the steel sheet and have an equivalent circle diameter of 1 µm or more, the density in volume number of elongated inclusions having an aspect ratio of 5 or more obtained by dividing the - 10 - long diameter by the short diameter (elongation ratio) is 1.0 x 10º inclusions / mm or less.
    'The grain size distribution of inclusions is obtained through, for example, SEM observation of electrolyzed surfaces according to the SPEED method (Selective Potentiostatic Recording by Electrolytic Dissolution method). In SEM observation of a surface electrolyzed by the SPEED method, a test specimen surface obtained from a steel sheet is polished, then electrolyzed by the SPEED method, and the sample surface is directly observed using a SEM, whereby the sizes and density in number of inclusions are evaluated.
    The SPEED method is a method in which a metal matrix on the sample surface is electrolyzed using a solution of 10% acetyl acetone, 1% tetramethyl ammonium chloride, and methanol, and inclusions are shown. Electrolysis is performed, for example, in 1 cell for a 1 cm Sample surface area. An SEM image on the electrolyzed sample surface is processed by image processing, and the equivalent circle diameter and frequency distribution (number) of inclusions are obtained. The frequency distribution is divided by the intensity of the electrolysis in order to compute the density in number of inclusions per volume.
    The inventors evaluated the volume density of elongated inclusions having an equivalent circle diameter of 1 µm or more and an elongation ratio of 5 or more as inclusions that 7] act as starting points for cracking and deteriorate hole expansion. As a result, it was found that when the density in "volume number of the elongated inclusion is 1.0 x 10º inclusions / mm Or less, hole expansion improves.
    When the density in number of elongated inclusions exceeds 1.0 x 10º inclusions / mmº, the density in number of elongated inclusions based on MnS that easily act as cracking starting points increases, and hole expansion degrades. For this reason, the density in volume number of elongated inclusions having an equivalent circle diameter of 1 µm or more and an "elongation ratio of 5 or more is limited to 1.0 x 10º inclusions / mmº or less. Since the hole expansion improves as the elongated inclusions based on MnS decrease, the lower limit value of density in volume number of the elongated inclusions includes 0%.
    However, similarly to the second aspect in relation to inclusions, it is found that, in a case where inclusions having an equivalent circle diameter of 1 um or more and an elongation ratio of 5 or more are not present, or a case where the equivalent circle diameters of inclusions are all less than 1 µm, of inclusions having an equivalent circle diameter of 1 µm or more, the density in number of elongated inclusion volume having a ratio of elongation of 5 or more is 0%.
    In the fifth aspect in relation to inclusions, of inclusions having an equivalent circle diameter of 1 µm or more in the steel sheet, the density in number of inclusions volume having at least one of MnS, TiS, and (Mn, TS precipitated in an oxide or oxysulfide (hard compound) composed of at least one of Ce and La, and at least one of e and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Sie Ti, and at least one of the e S is 1.0 x 10º inclusions / mmº Or more.
    Research by the inventors showed that inclusions did not
    Long-based MnS had precipitated MnS-based inclusions 7 in the hard compounds and had an almost spherical or spindle shape. 'The morphology of inclusions is not particularly specified, - since MnS-based inclusions are precipitated in hard compounds, but there are many cases where MnS-based inclusions precipitate around hard compounds like nuclei.
    Spherical inclusion is defined in the same way as in the third aspect in relation to inclusions, and the density in volume number of spherical inclusions is measured using the same SPEED method as: 10 —the fourth aspect in relation to inclusions. As a result of research by the inventor on density: in volume number of spherical inclusions, it was found that in steel sheets for density in volume number of inclusions having inclusions based on MnS precipitated around the hard compounds like nuclei (spherical inclusions) is controlled to be 1.0 x 10º inclusions / mm or more, hole expansion improves.
    When the density in number of inclusions volume having inclusions based on precipitated MnS in the hard compounds becomes less than 1.0 x 10º inclusions / mmº, the percentage in number of elongated inclusions based on MnS increases , and expansion of degraded hole. For this reason, the density in number of inclusion volume having inclusion based on MnS precipitated in the hard compounds is 1.0 x 10º inclusions / mmº or more. Since hole expansion is improved by precipitation of a number of inclusions based on MnS using hard compounds as cores, the upper limit of density in volume number is not specified.
    Equivalent circle diameters of inclusions having MnS-based inclusions precipitated in hard compounds are not particularly specified. However, when the equivalent circle diameter is very large, there is a possibility for inclusions to act as cracking starting points, and for this reason the upper limit of the equivalent circle diameter is preferably approximately 50 µm.
    In addition, in a case where the equivalent circle diameters of 7 inclusions are less than 1 µm, no problem occurs, and therefore the lower limit of the equivalent circle diameter is not: specified.
    In the sixth aspect in relation to inclusions, of inclusions that are present in the steel sheet and have an equivalent circle diameter of 1 µm or more, the average equivalent circle diameter of inclusions having an aspect ratio of 5 or most obtained by dividing the long diameter by the short diameter (elongation ratio) is 10 µm or less.
    , 10 The inventors evaluated the average equivalent circle diameter of elongated inclusions having an equivalent circle diameter of 1 'one or more and an elongation ratio of 5 or more as inclusions that act as cracking starting points and deteriorate hole expansion. . As a result, it was found that when the average equivalent circle diameter of the elongated inclusions is 10 æm or less, hole expansion improves. This is assumed to be because, as the amount of Mn or S in the molten steel increases, the number of MnS-based inclusions being formed increases, and the sizes of MnS-based inclusions being formed also increase.
    As a result, attention was paid to a phenomenon in which the average equivalent circle diameter of the elongated inclusions increases as the percentage in number of the elongated inclusions increases, and the average equivalent circle diameter of the elongated inclusions has been specified as a parameter.
    When the average equivalent circle diameter of the elongated inclusions exceeds 10 µm, the percentage in number of inclusions based on unrefined MnS that easily act as a starting point for piercing increases. As a result, hole expansion degrades, and therefore the inclusion morphology is controlled so that the average equivalent circle diameter of the elongated inclusions having an equivalent circle diameter of 1 μm or more and a ratio of elongation of 5 or more becomes 10 µm or less.
    Since the average equivalent circle diameter of the elongated inclusions is obtained by measuring the equivalent circle diameters: of inclusions that are present in the steel sheet and have an equivalent - circle diameter of 1 µm or more using a SEM , and dividing the total equivalent circle diameters of a plurality (for example, a predetermined number of 50 or more) of inclusions by the number of the plurality of inclusions, the lower limit of the average equivalent circle diameter is 1 µm. In the seventh aspect in relation to inclusion, inclusions having at least one of MnS, TiS, and (Mn, Ti) S precipitated in an oxide or oxis- sulfide composed of at least one of Ce and La, and at least one do and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at least one of e and S are present in the steel sheet, and inclusions include a total of 0, 5% by weight to 95% by weight of at least one of Ce and La in terms of an average chemical composition. As described above, in order to improve hole expansion, it is important to precipitate MnS-based inclusions in the hard compounds and prevent elongation of MnS-based inclusions. Regarding the morphology of inclusions, inclusions based on MnS can be precipitated into hard inclusions, and, generally, inclusions based on MnS precipitated around hard inclusions like nuclei.
    The inventors analyzed the chemical compositions of inclusions having inclusions based on MnS precipitated in hard inclusions through SEM and energy dispersive X-ray spectroscopy (EDX) in order to clarify the chemical compositions of inclusions, which are effective for suppressing elongation of inclusions based on MnS. When the equivalent circle diameters of the inclusions are 1 µm or more, since inclusions are easily observed, the composition analysis was performed on inclusions having an equivalent circle diameter of 1 µm or more. In addition, since inclusions having inclusions based on MNs precipitated in hard inclusions are not stretched as described above, the stretching ratios are all 3 or less. For this reason, the composition analysis was performed on spherical inclusions
    with an equivalent circle diameter of 1 µm or more and an elongation ratio of 3 or less, which are defined in the third aspect in terms of inclusions. - As a result, it was found that when the spherical inclusions include a total of 0.5% to 95% of one or both of Ce and La in terms of an average chemical composition, hole expansion improves.
    When the average amount of the sum of one or both of Ce and La in spherical inclusions is less than 0.5% by mass, the percentage in number of inclusions having inclusions based on MnS precipitates - 10 of the hard compounds significantly decrease , and for this reason the percentage in number of elongated inclusions based on MnS that easily act as starting points for cracking increases, and hole expansion and degraded fatigue characteristics.
    However, the greater the average amount of the sum of one or both of Ce and La, the more preferable. For example, the upper limit of the average amount can be 95% or 50% according to the number of inclusions based on MnS.
    When the average amount of the sum of one or both of Ce and La in the spherical inclusions exceeds 95%, large quantities of cerium oxysulphides and lanthanum oxysulfides form unrefined inclusions having an equivalent circle diameter of 50 µm or more, hole expansion and fatigue characteristics deteriorate.
    However, the high-strength steel sheet of the modality can be a cold-rolled steel sheet or a hot-rolled steel sheet.
    In addition, the high strength steel sheet of the modality can be a coated steel sheet having a coating, such as a galvanized layer or a galvanized layer, on at least one surface thereof. high-strength steel sheet according to an embodiment of the present invention will be described.
    However, the chemical composition of molten steel is the same as the chemical composition of the high-strength steel sheet of the above modality. |
    In the present invention, an alloy of C, Si, Mn, and others is added to molten steel that has been blown and decarburized in a converter, and agitated in order to carry out deoxidization and adjust the chemical components. : However, according to need, deoxidization can be performed using a vacuum degassing apparatus.
    However, with respect to S, since the de-urifurization does not need to be carried out in the refinement process as described above, a de-sulfurization process can be skipped. However, in a case where desulphurisation of molten steel is required in secondary refinement in order to melt extremely low sulfur steel having an S concentration of 20 ppm or less, the amount of chemical components can be controlled. by performing desulfurization.
    Deoxidation and composition control are carried out as follows.
    After Si (for example, Si or a compound including Si) is added to the molten steel, and approximately three minutes pass, Al (for example, Al or a compound including AI) is added to the molten steel, and deoxidization is carried out. A float time of approximately 3 minutes is preferably ensured in order to produce oxygen and combined Al-joint in order to float ALOs. After that, in a case where addition of Ti (for example, Ti or a compound including Ti) is required, Ti is added to the molten steel. In this case, a float time of approximately 2 to 3 minutes is preferably ensured in order to produce oxygen and Ti to combine together in order to float TIO, and TizOs.
    After that, the chemical composition is controlled by adding one or both of Ce and La to the molten steel in order to satisfy 0.02 <([Ce] + [La]) / [Acid soluble AI] <0.25, and 0.4 <([Ce] + [La]) / [S] <50.
    In a case where optional elements are added, addition of the optional elements is completed before one or both of Ce and La are added to the molten steel. In this case, the molten steel is sufficiently agitated to adjust the quantities of the optional elements, and then one or both of Ce and La are added to the molten steel. The molten steel produced in the above manner is subjected to continuous casting in order to produce slabs. 'With regard to continuous casting, the modality can be sufficiently applied not only to the continuous casting of usual plate in which approximately 250 mm thick plates are produced but also, for example, continuous thin plate casting in which plates 150 mm or less thickness are produced. In this mode, the high-strength hot-rolled steel sheet can be produced as follows. - 10 The obtained plate is reheated to 1,100ºC or higher, and preferably 1,150ºC or higher according to the need. Particularly, Ú in a case where it is necessary to sufficiently control the morphology (for example, fine precipitation) of carbides and nitrites, it is necessary to temporarily form solid solutions by dissolving carbides and nitrites in steel, and therefore the temperature of heating of the plate before hot washing preferably exceeds 1,200ºC. A ferrite phase whose ductility is improved in a cooling process after lamination can be achieved by forming solid solutions by dissolving carbides and nitrites in steel.
    When the heating temperature of the plate before hot rolling exceeds 1,250ºC, there are cases where the surfaces of the plate are significantly oxidized. In particular, there are cases where wedge-shaped surface defects caused by selective oxidation of grain boundaries are likely to remain after downgrading, and the qualities of the surfaces after lamination are impaired. For this reason, the upper limit of the heating temperature is preferably 1,250ºC. However, the heating temperature is preferably as low as possible in terms of costs.
    Then, hot rolling is carried out in a finishing temperature of 850ºC to 970ºC on the plate in order to produce a steel sheet. When the finishing temperature is lower than 850ºC, the lamination is carried out in a region of two phases, and for this reason the
    tibility is degraded.
    When the finishing temperature exceeds 970ºC, 'austenite grain sizes become unrefined, the ferrite phase ratio decreases, and ductility degrades. - After hot rolling, the steel sheet is cooled to a temperature range of 450ºC or lower (cooling control temperature) at an average cooling rate of 10 ºC / second to 100 ºC / second, the steel is wound at a temperature of 300ºC to 450ºC (winding temperature). A hot-rolled steel sheet is produced as a final product in the above manner.
    In a case where the - 10 cooling control temperature after hot rolling is higher than 450ºC, a desired martensite phase relationship cannot be achieved, and for this reason the upper limit of the winding temperature regret is 450ºC.
    However, in a case where the martensite phase is ensured more flexibly, the upper limits of the cooling control temperature and the winding temperature are preferably 440ºC.
    When the winding temperature is 300ºC or less, the hardness of the martensite phase increases excessively, and for this reason the lower limit of the winding temperature is 300ºC.
    In addition, when the cooling rate is less than 10 ° C / second, pearlite is prone to be formed, and when the cooling rate exceeds 100 ° C / second, it is difficult to control the winding temperature.
    When a hot rolled steel sheet is produced by controlling the hot rolling conditions and the resir conditions - after the hot rolling in the above manner, a high strength steel sheet that is excellent in terms of hole expansion and ductibility, and mainly includes ferrite and martensite can be produced.
    In addition, in the modality, the high-strength cold-rolled steel sheet can be produced as follows.
    After casting, the plate having the chemical composition above is reheated to 1,100ºC or higher according to the need.
    However, reasons why the temperature of the plate before hot rolling is controlled are the same as in a case where the above high-strength hot-rolled steel sheet is produced. 'Then, hot lamination is carried out at a finishing temperature of 850ºC to 970ºC on the plate in order to produce a sheet —dry. In addition, the steel sheet is cooled to a temperature range of 300ºC to 650ºC (cooling control temperature) at an average cooling rate of 10 ºC / second to 100 º * C / second. After that, the steel sheet is rolled at a temperature of 300ºC to 650ºC (winding temperature) in order to produce a hot-rolled steel sheet as - 10 um intermediate material. When the cooling control temperature and the winding temperature are higher than 650ºC, lamellar pearlite is likely to be formed, and lamellar pearlite cannot be sufficiently fused through annealing, and therefore reason the hole expansion degrades. In addition, when the winding temperature is less than 300ºC, the hardness of the martensite phase increases excessively, which is why it is difficult to wind the steel sheet efficiently. However, reasons why the cooling rate and finishing temperature of the hot rolling mill are limited are the same as in a case where the above high-strength hot rolled sheet is produced.
    The hot-rolled steel sheet (steel sheet) produced in the above manner is preserved, then subjected to cold rolling in a thickness reduction of 40% or more, and annealed at a maximum temperature of 750ºC to 900ºC . After that, the steel sheet is cooled to 450ºC or less at an average cooling rate of 0.1 ºC / second to 200 * C / second, and subsequently maintained for 1 second to 1,000 seconds in a temperature range of 300ºC to 450ºC. A high-strength, cold-rolled steel sheet that is excellent in terms of elongation and hole expansion can be produced as a final product the way above.
    In the production of cold rolled steel sheet, when the reduction in thickness is less than 40%, it is not possible to sufficiently refine crystal grains after annealing. 7 In a case where the maximum annealing temperature is] less than 750ºC, the amount of austenite obtained through annealing is small, and for this reason it is not possible to form a desired amount of martensite on the steel sheet. When the annealing temperature increases, the austenite grain sizes become unrefined, the ductility degrades, and cost production increases, and for this reason the upper limit of the maximum annealing temperature is 900ºC.
    Cooling after annealing is important to promote - 10 see transformation from austenite to ferrite and martensite. When the cooling rate is less than 0.1 ºC / second, since pearlite is formed Ú so that the hole and resistance expansion degrades, the lower limit of the cooling rate is 0, 1 ºC / second. In a case where the cooling rate exceeds 200 ºC / second, it is not possible to sufficiently proceed with ferrite transformation, and ductibility degrades, and for this reason the upper limit of the cooling rate is 200 ºC / second.
    The cooling temperature during cooling after annealing is 450ºC or less. When the cooling temperature exceeds 450ºC, it is difficult to form martensite. Then, the cooled steel sheet is kept in a temperature range of 300ºC to 450ºC for 1 second to 1,000 seconds.
    One reason why the lower limit of the cooling temperature cannot be provided is that the transformation of martensite can be promoted by cooling the steel sheet once to a temperature - less than the maintenance temperature. However, even when the cooling temperature is 300ºC or less, since the steel sheet is kept at a higher temperature than the cooling temperature, the martensite is tempered, and it is possible to reduce the difference in hardness between martensite and ferrite.
    When the maintenance temperature is less than 300ºC, the hardness of the martensite phase increases excessively. In addition, when the maintenance time is less than 1 second, residual voltages induced
    thermal contraction remain, and stretching degrades. 'When the maintenance time exceeds 1,000 seconds, more bainite and other: more are formed than is necessary, and a desired amount of N martensite cannot be formed.
    As described above, when a hot rolled steel sheet is produced by controlling hot rolling conditions and cooling conditions after hot rolling, and a cold rolled steel sheet is produced from the hot rolled steel sheet. By controlling the cold rolling conditions, the gelling conditions, the - 10 cooling conditions, and the maintenance conditions, it is possible to produce a high-strength cold-rolled steel sheet that is excellent Ú in terms of hole expansion and ductility, and mainly includes ferrite and martensite.
    For this reason, in the modality, molten steel is processed on a plate, hot rolling is carried out on the plate at a finishing temperature of 850ºC to 970ºC in order to produce a steel sheet. After that, the steel sheet is cooled to a cooling control temperature of 650ºC or lower at an average cooling rate of 10 º * C / second to 100 ºC / second, and then rolled at a winding temperature from 300ºC to 650ºC. Here, in a case where a hot-rolled steel sheet is produced, the cooling control temperature is 450ºC or less, and the winding temperature is 300ºC to 450ºC.
    In addition, when a cold rolled steel sheet is produced, the rolled steel sheet is preserved, cold rolling is carried out on the steel sheet in a thickness reduction of 40% or more, the cold rolled steel sheet is annealed at a maximum temperature of 750ºC to 900ºC, cooled to 450ºC or less at an average cooling rate of 0.1 ºC / second to 200 ºC / second, and maintained in a temperature range of 300ºC to 450ºC for 1 second at 1,000 seconds.
    However, a flow chart of the production method of the high strength steel sheet of the modality is shown in figure 2 for ease of understanding. However, the broken lines in the flowchart indicate production processes or conditions that are selected according to the need. In addition, coating can be properly carried out - on at least one surface of the hot-rolled steel sheet and the cold-rolled steel sheet. For example, zinc based coating such as coating using galvanizing and galvanizing can be formed as a coating. The zinc-based coating can also be formed by electroplating or hot dipping. Galvanizing coating can be achieved by, for example, amalgamating a zinc coating (galvanizing coating) which is formed by electroplating or hot dipping at a predetermined temperature (for example, a temperature of 450ºC to 600ºC, and a time of 10 seconds to 90 seconds). A galvanizing steel sheet and a galvanized steel sheet can be produced as end products in the above manner.
    In addition, a variety of organic films and coatings can be formed on the hot-rolled steel sheet, the cold-rolled steel sheet, the galvanized steel sheet, and the galvanized steel sheet.
    Examples Hereinafter, examples of the present invention will be described.
    Steels that were prepared and cast in a converter and had the chemical components as shown in Tables 1 to 3 were cast in order to produce plates. The steels having each chemical component were heated to a temperature of 1,150ºC or higher in a heating furnace, submitted to hot rolling at a finishing temperature of 850ºC to 920ºC, cooled at an average cooling rate of 30 ºC / second, and rolled at a winding temperature of 100ºC to 600ºC, thereby producing hot-rolled steel sheets from 2.8 mm to 3.2 mm thick. The production conditions and mechanical properties of hot-rolled steel sheets are shown in Tables 4 to 6, and the microstructures of hot-rolled steel sheets are shown in Tables 7 to 9.
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    E 8 Ee EL LILI: &. 8 ê 8 - 8
    FENRSESINNNENENENNNNNDE Z = El ll Leal) Ss 8 ê ee Lo 1 ie: s 8
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    FENSFERPESNNPENENREENERS É 2 Ss 38 * gs 23: 8 8 88 | S) | sg E = 5 3 Ss Ss Ss Ss sS1sS | s | E ss IN 2 ses se | 8 | a ses sa 3: = S) S / S 3) Ss | S | S [ss sl = sas
    É Ss 8 88 s sl ess 2 É = 13 3 2 Ss 3 | 8 3 2338 E 3 gls als s es sl if ss 3 3 à, read: | 8 |: Given & 3 3 3 Ss EBNENENEBBEENTD :) 2a [38S33 8/3 | 3S 3835583 33: the feeds | Je those | s | and asda 5; & z Ff & 8 | s Rg | É & E Ss = | 8 = | = FS = & s E g18o | SS ss 3 | s | ê | 3SS SS 235 = E à ssseesas | s 5 s lslsldela: Yes
    Table4 7 Sheet. (from Açol - | Temperature | Temperature | Elongation Temperature 7 Traction No. - TS Ide hole 1 | TSXE1XA No. Heating ºC | Finishing ºC | Winding “C E1% MPa% lo Jo ugly oo fe fo uses] PE ES Pr Pr bem la leo o bs bo o oa
    PEA PE PA PM PA PP oo Jendeo oooo fe] o feel ooo and ho res ra Ja fo do fo foes fo o ough] motto fis fo fo fo fe de e Joss] PLA Pr PP in li fo fo fm fe de ea era las las fête fo fo fas fr o faces] Jam Ja fo fo ho E Je in le fio fo fo fm le lo foros lar fan fo do fo fa and o those [ae Je fio fo bo and the bro of Jess Jesm Jos fimo fa do fe fe de bos Jasm fas o fe 6 bra lar Jaz lo dao fo f a ds een] * The underlines in the Table indicate that the corresponding cell does not satisfy the manufacturing conditions according to the present invention.
    Table 5 with Tess Fe
    ] Tation number —TS | go hole A | TSXEIXA
    'Nº [Heating ºC | Finishing * C | Winding * C Ma E1% Mm letter ft get fo fo ds so bs ires] read er feso fo fo Ts bo = hos] leam dee fo fo fo To so = = | leesa Smooth jar fo do fas = do phases in foes wire fo 6 = 6 = bone] Bei en ee bo bo bo bo fue) o do bo bo ao e fes] east fes wire - fo fo fas fr and lose leem fes fra fo do ba fo ares] east wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire]] wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire wire fo e e fores] read Teo frio fo fo fe o ”Íreeos | lesse Teo wire fo fo fes oe res) canvas fot wire fo fo fo oo Óises leeat Joe fo fo ho o = bes leeat Joa wire fo fo bro so Jess leem Jos wire fomo fo fo fo fo deseo losat Jos fo fo fo boo fo = fes leem Jo ugly fo fo fas o James lr foz fe fo o da to dr fe slug Jos fso fo fo o ho o bes leem fog fo fo mo oo Bose lero photo wire fo 6 fes = e bre lota onnieso fo fo las oo Jesse * The underlines in the Table indicate that the corresponding cell does not satisfy the manufacturing conditions according to the present invention.
    Table 6
    “| dede ve e
    , Temperature | Temperature | [Elongation Temperature
    7 Steel No. | Traction No. - TS ide hole 2 | TSXE1XA
    Heating * C | “C | Winding * C E1% MPa 1% rm yarn o fo and bo dao "area hurts for fo o ds and de fes] foo f o f fo fo fo be fixed lara Je o o fo fe ds and asthma oo en af o fo mo eo fue]
    ease fes fo do o fas a bo ea in Je faso fo do fe de o fue] esa Jos fio fo ho fe rs bo faso fest fm f fa fa do ”PP Pr PP PT los fes fo do fo ln fe a fe lose fo wire oo fm oo spindle] read fer wire oo sf o fixed lee read lia eo o ls oe foz ln fes o de es wire + good canvas Jon fi do o f a des le do les fo do fm fe ba he seo lose on the wire of the bo to the knife] letom lerolizo do o do o fa] lerose lool oo fas and sa ta Ja foro fo fo fr o o pao lem Ja fo do o do o and sao lim la o do ds o knife] * The underlines in the Table indicate that the corresponding cell does not satisfy the manufacturing conditions according to the present invention.
    Table 7
    TE E thin elongated inclusions Inclusions including sita sffetos | : TE GEETE de JAçolem naked in - naked-diameter in - naked) Percentage | Percentage Concentration Hardness iAço | Number of mere dejde circle of mere Relationship in number in average number - of maximum Area number In volume - equivalent volume%%% [Cel + [La]% EV (Inclusions dusions | average / one Inclusions mm Month mm o ledde bo bh bh lo pol hor le | o bh kb by Bond Jos bo | leslele bo bp bb a pe do her le |
    PPP O Lema o ho ho bp do baile fa o | hello bb do bo emo ls bes om | I pack the bb lo silly boi lo | read bh fe amo fo - bs los | I remember good fr fr good if | ee ho dh bo de fem bs - bas fomo | hembe ls o bh bh and bros fes bo | ease ho bh bb lo bora Jus be | ll he Ba o bo hunger bo for las | helm bo and bon le bo bh bb fes bo | I pack bon ls ho bh b bos be | edade bo bh bh kk bote for le | emas ho bh kb by hos bos bo | they bh bh de bois fas dos | the beautiful bo des des bo |
    Table8
    TE AND ES 1 thin Elongated inclusions Inclusions including sutites. sita í Lace sheet Density Density | diameter. Density in / Concenta- (of Steel jem number- | Percent Jem number | of circle | Porcen-- | ”Hardness No” ro of area tage in | of volumejequiva- - | tage in) number - average deposition Maxi relation Inclusions | number% [Inclusions [lens number% | to bedding ima HV 2 s 1mm mm%
    E lee far fa hd ho o ba bs as Joss | read fee and bo ho ls bar from Toa lo | . lee lee fr the db of be la foz les | read les fr do o o bs ba se se | 'les fes o do do fo fo o | read fee fo o do ho a Bee by Toa Tso | lee le and the 6 bseo ls les | read fes fr o o ds o beso bs fas Jow | lesse fes fe o do 6 and ba Ter Joss | Ee a da mo le | Bb db E Jo ba e br lr | lezm der fo o o ds o beso do Tao li | lee far do do o fo bow o fes Jow | read fes fe do do a bao de Tao faso | lee fee oh ho bb Jo be de bra fam | lee fee o o do ds ds bas lo fog ls | read fee and fra do bao ds | li fr ds fo bra e do Bow É Tr hos | in fe of beso ra ln Jia oa faro faso oo | read le fo fo ba bs do bow bh bos sa | lsm for fe fee fame fa og Tso | read fas fa Tao [ano faso a aa | la doe ds o de fo faso a fo Ts | read fe fis o o ds a Too and rs ses | read fo fe o fa fa o fas fam | lero ro fr fo doa and bom de Poa fame | motto ds o do ba ba hos ls |
    Table9
    TE E E | thin Elongated inclusions Inclusions including suffetos sita - Leaf Density Density | Steel Density | the number- | Nut in damero number Porcenta- Jem number | Concentration | Hardness Number of circles (Relation) In area ro | Ide - equal volume —em maximum volume in equivalent number% Inclusions Inclusions number% Inclusions | [Cels [La]% Hv mo mere% on average / pm im eder and Rb bh je bee be bs le | oo eds bob kb o bebo E ba | bob E's address do be leo bs ls | they Rb ko so bro so be de | sms le bh bh fo Boo le o as |
    PP eee is Rb ko fo bos bo je | esa bh bo bo do bow fr be | snes and Rb bo Bow la ks do | Bed of bb bo bo o bel ko be | lesm ls o bd fame fe de fo | ese los e bbb o bre be le = | eder bob ko Jo bao bs de | he and bb ko and bao bo bo e | in fes li bb do fe fucks bo ls | if fo and bb 6 so ha and bh be | edi e bo o do ham bs le le | ee and bb E ho Boo bo da dos | lenle fo hungry for fo aa be la fo | erale la fo was by Jos sa bs fa bes | am lr os the focus And Jos fame e de | ente e bo bow bo bo fe bo bs fe | lemla be ho how Bo de fe lo be dm
    Regarding cold-rolled steel sheets, first, 7 steels having the chemical compositions above were cast, heated] to 1,150ºC or higher, subjected to hot rolling at a finishing temperature of 850ºC to 910ºC, cooled at an average cooling rate of 30 ° C / second, and rolled at a winding temperature of 450 ° C to 610 ° C, thereby producing hot-rolled steel sheets from 2.8 mm to 3.2 mm thick.
    After that, the hot-rolled steel sheets were preserved, and then subjected to cold rolling, annealing, and maintenance under conditions such as showing in 10 to 12 Tables, thereby producing laminated steel sheets. - cold.
    The production conditions and mechanical properties of the cold rolled steel sheets are shown in Tables 10 to 12 and the microstructures of the cold rolled steel sheets are shown in Tables 13 to 15. The sheet thicknesses of the steel sheets cold rolled were 0.5 mm at
    24mm.
    z = | AND IS
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    S E 81 É es sls | s | e Je E É Fr mH ZSp É FS à E Fi s | o Ee and ES SIS | 8 8 Ss 5 ss 3 and o 22 2 = z E / º if ES / S / 88 S8SSS SS 8/8/8/8 5 28: Z 81529 $ ses ee | 8/2/2 / e / s 3 Llaslalaleels sl5 / sls | s | be $ 3 lslsslol8 8a to 8 | s | 8 / s 5 5 / sls | l8 / 8 / S / S without aiel E =, ze 3 to £ 3 lEdsassNRssDsseEeksE EEE! is | 5th SssSSSSEFSSSSESSSSSSSSESES al E ass. e leao als - sã E EE E HEREEMS: ã
    HESEREEFRERPESESPENSER 'E E = T / e in Ss 8 ss SI = 5) and g) s
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    Ê eg É 85 2: É EM: nel e Ss 8
    E 2 g E à: he) e & 2 8 E) = $ | à: SS Ses ss: £ E | 8 = E 8 5 P = = - e Ex & 3 85 FES: 3 2 2 s 8 8 8 = s E - e ss
    EPNERNPERPEFPERFERFEPERR 28 Ss> à ss ds ada: |
    & AND
    SET - It is El eee ee slelalales als ss / e ea = + / S / s: 2 & Es F 8 E 5/58 2/8/8/3/8/3 / S Ss S / 85 / SS / s Ss: SE [ale slelelela se sslelealels) lelslslels) lslelals - éE js se se ss 8 8 8/2/8 ss If ls 8 8 / Sls / S / 5/8 / o 3 AND FF
    E 88 Ss 8 / g s / 8/8 ss E = Rs s / sS) 8 Sa
    TE, e 8 ss 2 É 'di dh eERESEEEEESERS EEE] 3/8 a ss Ss ls Ss ss 5 ses = essss | | = ES] [8/8 SE An Si ai hi hi si hi Su ci] ce ci ese nei ei ec o | ST STSS]
    BEE 2 ss
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    E S Seal o io o nn SS IR SB ho Je o s e "
    EE es s & É Ss esteL a E 5 SEEEES = SS) [3 [é SS) 2/8 2 SS and SS s ist
    FE 2) is 2 5 = that ee Sa 8 2nd 8/5 ls 3 8 E
    ERA 3/5 É [É | 8 g / 8/8 / S | s ss ss and els ss / e / sn / a oo s el = E = EElalaess EsESEESERSSESE EESC EEE if E laleelelals slelslaslalsatseeelekeeee = E / S BE SI FSRSSESSSSESSESSs E 8/5 S / SS / 8/2 THESE ESSES SEE SES EEA:
    Í Í h: FE "=” HERTEES BI8 / S / 3 | 8 S BSISS 8/8 - FE. É E & lal8s R PEREIRA eis Tt elsle. =
    It's s2E Ea
    EZX 88 $ He BIS) if they) SISIR 8 8 8 so
    EE: + gl8 E 2/3 IE E / 2/2 / e 2/2 2 he eee eee ee ee ee. 3/8 Ss And Ss 8 = Y / A) à | ss | A A | a Ss a as Sã S / s SS SS a Si ei es em e ai ei e Si e e e ee Se Ze Es s / 8/5 s / 8 | s & Ejº - ê & Sê
    E 2 SC 8 Ss | ENS Ss o 8 se
    BE Fe fe Bs Sã SÉ 5/88 2 si 2 8 285 - "- ale. E nl E 8 815 E EF 8 E 212 8 E a £ | 8 $ | = if 5 see ns R = ss SR ess Es | & = | 5/5 / els | s / 2 | als | s / s / s / s / 5 | 5/3 / s / e / s / 8/8 / sla / o | e 8 Bls = edasasasE 25 aaa els | a S | EE TS FE se 2 | S / S | 8/8/3/8/3/3/8/8/8/8/5/5 8/8/8/8 / 8/8) E / 8/3 |
    Regarding the elongated inclusions in the steel sheets, the presence of unrefined inclusions was confirmed using an optical microscope, and the area density in number of inclusions having a diameter of - equivalent circle of 2 um or less with respect inclusions having an equivalent circle diameter of 0.5 µm or more were investigated by observation using a SEM. Even for inclusions having an elongation ratio of 5 or more, the percentage in number, the density in number of volume, and the average equivalent circle diameter were investigated.
    In addition, with respect to non-elongated inclusions in the steel sheet, the percentage in number and density in volume number of inclusions having MnS precipitated in oxides or oxisulfides (hard compounds) including at least one of Ce and La with respect the inclusions having an equivalent circle diameter of 1 µm or more, and the average value of - total amount of one or both of Ce and La that are included in the inclusions were investigated.
    The results of investigating inclusions in hot-rolled steel sheets are shown in Tables 7 to 9, and the results of investigating inclusions in cold-rolled steel sheets are shown in Tables 13 to 15, However, in Tables 7 to 9 and Tables 13 to 15, thin inclusions refer to inclusions having an equivalent circle diameter of 0.5 um to 2 µm, elongated inclusions refer to inclusions having an equivalent circle diameter of 1 one or more and an elongation ratio of 5 or more, and inclusions including sulfides refer to inclusions that have inclusions based on MnS precipitated in oxides or oxisulfides including at least one of Ce and La and have a diameter of equivalent circle of 1 one or more.
    First, the results of the hot rolled steel sheet production test will be described with reference to Tables 1 to 9.
    In sheet steel Nos. b9-h1 and c3-h1 in which Steel Nos. b9 and c3 is used, the C concentration exceeds 0.3%. In Sheet steel No. c1-h1 where Steel No. c1 is used, the Mn concentration exceeds 4.0%. In sheet steel Nos. a6-h1 and b10-h1, in which Steel Nos. a6 and b10 is used, the concentration of acid-soluble Ti exceeds 0.20%. As a result, in steel sheet Nos. b9-h1, c3-h1, c1-h1, a6-h1, and b10-h1, elongation and hole expansion were significantly small.
    In addition, in Sheet steel No. c2-h1, where Steel No. c2 was used, the Si concentration exceeded 2.1%, and ([Ce] + [La]) / [Al soluble in acid] was less than 0.02, and for that reason hole expansion was small.
    In sheet steel Nos. a7-h1 and b11-h1, in which Steel Nos. a7 e - 10 b11fused, the Cr concentration exceeded 2.0%, and for that reason the elongation was significantly small.
    : In sheet steel Nos. a1-h1 to a5-h1 and bi-h1 to b8-h1, where 7 Steel Nos. a1 to a5 and b1 to b8 was used, ([Ce] + [La]) / [S] was less than 0.4, or exceeded 50. For this reason, in steel sheets, the morphologies of in- - clusions were not sufficiently controlled, and degraded hole elongation and expansion compared to steel sheets having the same chemical composition except for Ce and La.
    In sheet steel Nos. A1-h2 to A6-h2, B1-h2 to B9-h2, and C1-h2 to C10-h2, in which steel sheet Nos. A1 to A6, B1 to B9, and C1 to C10 was used, —wind temperature was less than 300ºC. For this reason, Nos. of steel sheet above, the difference in hardness between martensite and decreased ferrite, and degraded hole expansion compared to Steel sheet Nos. A1-h1 to A6-h1, B1-h1 to B9-h1, and C1-h1 to C10-h1 having the same chemical composition.
    In sheet steel Nos. A1-h1 to A6-h1, B1-h1 to B9-h1, and C1-h1 to C10-h1, in which steel sheet Nos. A1 to A6, B1 to B9, and C1 to C10 were used, the inclusion morphologies were sufficiently controlled, and for this reason, stretching and hole expansion were sufficient.
    Next, the results of the cold rolled steel sheet production test will be described with reference to Tables 1a 3 and 10a
    15.
    Similar to the test results of hot rolled steel sheet production, in Steel Sheet Nos. a6-c1, a7-c1, b9-c1 to b11-c1, 1 c1-01 to c3-c1, where Steel Nos. a6, a7, ba to b11, and c1 to c3 was used, elongation or hole expansion was significantly small. : In addition, in Steel sheet Nos. a1-c1 to a5-c1 and b1-c1 to b8-c1, —inqueAteN ailaa5eb1a bs was used, ([Ce] + [La]) / [S] was less than 0.4 or exceeded 50. For this reason , in steel sheets, the inclusion morphologies were not sufficiently controlled, and degraded hole elongation and expansion compared to steel sheets having the same chemical composition except for Ce and La. - 10 In steel sheet Nos.
    A1-c2 to A6-c2, B1-c2 to B9-c2, and Ci-c2 to C10-c2, in which steel sheet Nos.
    A1 to A6, B1 to B9, and C1 to C10 was used, '- the winding temperature was less than 300ºC.
    For this reason, in Nos of steel sheet above, the difference in hardness between martensite and ferrite decreased, and degraded hole expansion compared to Sheet steel Nos.
    Al-ciaA6-c1, B1-c1 to B9-c1, and C1-c1 to C10-c1 having the same chemical composition.
    In sheet steel Nos.
    A1-c1 to A6-c1, B1-c1 to B9-c1, and C1-c1 to C10-01, in which steel sheet Nos.
    A1 to A6, B1 to B9, and C1 to 010 were used, the inclusion morphologies were sufficiently controlled, and for this reason, elongation and hole expansion were sufficient.
    Industrial Applicability According to the present invention, since it is possible to obtain a sheet of high-strength steel that can preferably be mainly pressed and used for lower parts of automobiles and other more and structural materials, and is excellent in terms of expansion of holes and ductility, the present invention significantly contributes to the steel industry, and has great industrial availability.
    权利要求:
    Claims (23)
    [1]
    CLAIMS x 1. High strength steel sheet comprising,% in mass: - C: 0.03% to 0.30%; Si: 0.08% to 2.1%; Mn: 0.5% to 4.0%; P: 0.05% or less; S: 0.0001% to 0.1%; N: 0.01% or less; * 10 Al soluble in acid: more than 0.004% and less than or equal to 2.0%; Ú Acid-soluble Ti: 0.0001% to 0.20%; at least one selected from Ce and La: 0.001% to 0.04% in total a balance of iron and unavoidable impurities, where [Cel], [La], [Al soluble in acid], and [S] satisfy 0.02 <(ICe] + [La]) / [acid-soluble AI] <0.25, and 0.4 <([Ce] + ILal) / [S] <50 in a case where mass percentages of Ce, La, Al soluble in acid, and S are defined to be [Ce], [La], [Al soluble in acid], and [S], respectively, and a microstructure of the same includes 1% to 50% of martensite in terms of an area relationship.
    [2]
    2. High-strength steel sheet according to claim 1, also comprising,% by mass, at least one selected from a group consisting of Mo: 0.001% to 1.0%, Cr: 0.001% to 2.0 %, Ni: 0.001% to 2.0%, Cu: 0.001% to 2.0%, 8: 0.0001% to 0.005% Nb: 0.001% to 0.2% V: 0.001% to 1.0%,
    W: 0.001% to 1.0%, x Ca: 0.0001% to 0.01%, Mg: 0.0001% to 0.01%,: Zr: 0.0001% to 0.2%, at least one selected from Sc and lantanoids from Pr to Lu: 0.0001% to 0.1% in total, Like: 0.0001% to 0.5%, Co: 0.0001% to 1.0%, Sn: 0 .0001% to 0.2%, * 10 Pb: 0.0001% to 0.2%, Y: 0.0001% to 0.2%, and - Hf: 0.0001% to 0.2%.
    [3]
    3. High strength steel sheet according to claim 1 or 2, wherein an amount of the acid-soluble Ti is more than or equal to 0.0001% and less than 0.008%.
    [4]
    4. High-strength steel sheet according to claim 1 or 2, wherein an amount of the acid-soluble Ti is 0.008% to 0.20%.
    [5]
    5. High-strength steel sheet according to claim 1 or 2, where [Cel], [La], [Al soluble in acid], and [S] satisfy 0.02 <(ICe] + [La]) / [Acid-soluble al] <0.15.
    [6]
    6. High strength steel sheet according to claim 1 or 2, where [Ce], [La], [Al soluble in acid], and [S] satisfy 0.02 <([Ce] + [La]) / [Acid-soluble AI] <0.10
    [7]
    7. High strength steel sheet according to claim 1 or 2, wherein an amount of the acid-soluble Al is more than 0.01% and less than or equal to 2.0%.
    [8]
    8. High-strength steel sheet according to claim 1 or 2, wherein a density in number of inclusions having an equivalent circle diameter of 0.5 um to 2 um in the microstructure is 15 inclusions / mm or more.
    [9]
    9. High-strength steel sheet according to claim
    tion 1 or 2, in which, of inclusions having an equivalent circle diameter: 1.0 µm or more in the microstructure, a percentage in number of elongated inclusions having an aspect ratio of 5 or more obtained - by division of a long diameter by a short diameter is 20% or less.
    [10]
    10. High-strength steel sheet according to claim 1 or 2, wherein, of inclusions having an equivalent circle diameter of 1.0 µm or more in the microstructure, a percentage in number of inclusions having at least minus one of MnS, TiS, and (Mn, Ti) S precipitated to an oxide or oxysulfide composed of at least one of Ce and La, and hair. 10 minus one of O and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at least one of O and S 10% or more.
    [11]
    High-strength steel sheet according to claim 1 or 2, wherein a density in volume number of long inclusions having an equivalent circle diameter of 1 µm or more, and an aspect ratio of 5 or more obtained by dividing a long diameter by a short diameter is 1.0 x 10º inclusions / mmº or less in the microstructure.
    [12]
    12. High-strength steel sheet according to claim 1 or 2, in which, in the microstructure, a density in number of inclusions volume having at least one of MnS, TiS, and (Mn, TS precipitated in an oxide or oxysulfide composed of at least one of Ce and La, and at least one of O and S, or an oxide or oxysulfide composed of at least one of Ce and La, at least one of Si and Ti, and at least — less than 0 is 1 , 0x 10º inclusions / mmº or more.
    [13]
    13. High-strength steel sheet according to claim 1 or 2, wherein elongated inclusions having an equivalent circle diameter of 1 µm or more, and an aspect ratio of 5 or more obtained by dividing a diameter long by a short diameter are present in the microstructure, and an average equivalent circle diameter of the elongated inclusions is 10 µm or less.
    [14]
    14. High-strength steel sheet according to claim
    2 is "í é" 415 tion 1 or 2, where inclusions having at least one of MnS, TiS, and ; (Mn, Ti) S precipitated to an oxide or oxysulfide composed of at least: one between Ce and La , and at least one among O and S, or an oxide or oxysul-: fetus composed of at least one among Ce and La, at least one among Si and Ti, epelomenosum between O and S are present in the microstructure, and inclusions include a total of 0.5 wt% to 95 wt% of at least one of Ce and La in terms of an average composition.
    [15]
    15. High-strength steel sheet according to claim 1 or 2, wherein an average grain size in the microstructure is 10 um * 10 or less.
    [16]
    16. High-strength steel sheet according to claim 1 or 2, wherein a maximum martensite hardness included in the microstructure is 600 Hv or less.
    [17]
    17. High-strength steel sheet according to claim 1 or 2, wherein the sheet thickness is 0.5 mm to 20 mm.
    [18]
    18. High-strength steel sheet according to claim 1 or 2, also comprising a galvanized layer or a galvanized layer on at least one surface.
    [19]
    19. Method of producing a high strength steel sheet, the method comprising: a first process in which a molten steel having the chemical components as defined in claim 1 or 2, is subjected to continuous casting in order to be processed in a board; a second process in which a hot rolling is carried out on the plate at a finishing temperature of 850ºC to 970ºC, and a steel sheet is produced; and a third process in which the steel sheet is cooled to a cooling control temperature of 850 ° C or lower at an average cooling rate of 10 to 100 ° C / second, and then rolled at a winding temperature of 300 ° C to 650 ° C .
    [20]
    20. High-strength steel sheet production method according to claim 19,
    [21]
    o »———— Ô ——— 5/5 where, in the third process, the cooling control temperature is 450ºC or less, the winding temperature is 300ºC to 450ºC, and a sheet of steel laminated to hot is produced. : 21. Production method of the high-strength steel sheet according to claim 19, the method also further comprising the third process: a fourth process in which the steel sheet is preserved, and cold rolling is carried out on the sheet steel in a reduction in thickness of 40% or more; . 10 a fifth process in which the steel sheet is annealed at a maximum temperature of 750ºC to 900ºC; a sixth process in which the steel sheet is cooled to 450ºC or less at an average cooling rate of 0.1 ºC / second to 200 ºC / second; and a seventh process in which the steel sheet is kept in a temperature range of 300ºC to 450ºC for 1 second to 1,000 seconds in order to produce a cold rolled steel sheet.
    [22]
    22. Production method of the high-strength steel sheet according to claim 20 or 21, wherein galvanizing or galvanizing is carried out on at least one surface of the hot-rolled steel sheet or the cold-rolled steel sheet .
    [23]
    23. Production method of the high-strength steel sheet according to claim 19, wherein the slab is reheated to 1,100ºC or higher after the first process and before the second process.
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    同族专利:
    公开号 | 公开日
    KR20140041921A|2014-04-04|
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    KR101528441B1|2015-06-12|
    WO2011142356A1|2011-11-17|
    KR101458683B1|2014-11-05|
    CN102892910A|2013-01-23|
    US9238848B2|2016-01-19|
    MX2012012954A|2013-02-07|
    CN102892910B|2016-11-16|
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    JPS604248B2|1979-03-01|1985-02-02|Kobe Steel Ltd|
    JPH0118967B2|1982-11-24|1989-04-10|Sumitomo Metal Ind|
    JPH06128688A|1992-10-20|1994-05-10|Sumitomo Metal Ind Ltd|Hot rolled steel plate excellent in fatigue characteristic and it production|
    JP3769143B2|1999-05-06|2006-04-19|新日本製鐵株式会社|Hot-rolled steel sheet for machining excellent in fatigue characteristics and method for producing the same|
    JP4258934B2|2000-01-17|2009-04-30|Ｊｆｅスチール株式会社|High-strength hot-rolled steel sheet excellent in workability and fatigue characteristics and method for producing the same|
    JP4151479B2|2003-05-19|2008-09-17|Ｊｆｅスチール株式会社|Hot-dip galvanized steel sheet and manufacturing method thereof|
    KR101094594B1|2003-09-30|2011-12-15|신닛뽄세이테쯔 카부시키카이샤|High-yield-ratio high-strength cold rolled steel sheet excelling in weldability and ductility|
    JP4317418B2|2003-10-17|2009-08-19|新日本製鐵株式会社|High strength thin steel sheet with excellent hole expandability and ductility|
    JP4299716B2|2004-04-12|2009-07-22|新日本製鐵株式会社|Hot rolled steel sheet with low yield ratio and excellent ductility|
    JP4268559B2|2004-04-23|2009-05-27|新日本製鐵株式会社|High strength steel plate with excellent stretch flangeability|
    JP4901346B2|2005-11-07|2012-03-21|新日本製鐵株式会社|High-strength steel sheet with excellent stretch flangeability and fatigue characteristics|
    EP2048254B1|2006-07-14|2020-08-19|Nippon Steel Corporation|High strength steel plate superior in stretch flange formability and fatigue characteristics|
    JP4542515B2|2006-03-01|2010-09-15|新日本製鐵株式会社|High strength cold-rolled steel sheet excellent in formability and weldability, high-strength hot-dip galvanized steel sheet, high-strength galvannealed steel sheet, manufacturing method of high-strength cold-rolled steel sheet, and manufacturing method of high-strength hot-dip galvanized steel sheet , Manufacturing method of high strength galvannealed steel sheet|
    JP5194811B2|2007-03-30|2013-05-08|Ｊｆｅスチール株式会社|High strength hot dip galvanized steel sheet|
    JP5205795B2|2007-04-26|2013-06-05|新日鐵住金株式会社|High-strength steel sheet with excellent stretch flangeability and fatigue characteristics and method for producing the molten steel|
    JP4431185B2|2008-06-13|2010-03-10|新日本製鐵株式会社|High-strength steel sheet with excellent stretch flangeability and fatigue characteristics and method for producing the molten steel|JP4431185B2|2008-06-13|2010-03-10|新日本製鐵株式会社|High-strength steel sheet with excellent stretch flangeability and fatigue characteristics and method for producing the molten steel|
    US9617626B2|2011-02-24|2017-04-11|Nippon Steel & Sumitomo Metal Corporation|High-strength steel sheet exhibiting excellent stretch-flange formability and bending workability, and method of producing molten steel for the high-strength steel sheet|
    WO2013105631A1|2012-01-13|2013-07-18|新日鐵住金株式会社|Hot stamp molded article and method for producing same|
    EP2803744B1|2012-01-13|2018-05-02|Nippon Steel & Sumitomo Metal Corporation|Cold-rolled steel sheet and method for producing same|
    CN103074549B|2012-12-01|2015-02-25|滁州恒昌机械制造有限公司|Low-carbon multi-component alloy steel for excavator bucket tooth, and its production technology|
    CN103060713B|2013-01-22|2015-07-08|中国石油天然气集团公司|High-steel-grade anti-sulfur drill pipe material and preparation method thereof|
    JP5821861B2|2013-01-23|2015-11-24|新日鐵住金株式会社|High-strength hot-rolled steel sheet with excellent appearance and excellent balance between elongation and hole expansibility and method for producing the same|
    BR112015026643A2|2013-04-25|2017-07-25|Nippon Steel & Sumitomo Metal Corp|steel plate|
    CN103614664A|2013-10-22|2014-03-05|芜湖市鸿坤汽车零部件有限公司|A martensite alloy steel material used for an air valve of an internal combustion engine and a preparation method of the alloy steel material|
    CN103614658A|2013-10-22|2014-03-05|芜湖市鸿坤汽车零部件有限公司|High-strength wear-resistant low-carbon steel material and preparation method thereof|
    CN103614647A|2013-10-24|2014-03-05|铜陵市经纬流体科技有限公司|Rare earth alloy steel material used for valves and preparation method of the material|
    CN103667939B|2013-11-07|2016-02-10|安徽省智汇电气技术有限公司|A kind of spot contact bearing manganese steel material and preparation method thereof|
    CN103667890B|2013-11-08|2016-07-06|张超|A kind of alloy steel material for pump shaft and preparation method thereof|
    CN103643166A|2013-11-12|2014-03-19|铜陵市肆得科技有限责任公司|High temperature-resistant pump case alloy steel material and preparation method thereof|
    CN103643174A|2013-11-12|2014-03-19|铜陵市肆得科技有限责任公司|Antimony scandium-containing high-hardness alloy steel material for bearings and preparation method thereof|
    CN103643173A|2013-11-12|2014-03-19|铜陵市肆得科技有限责任公司|High temperature corrosion-resistant pump valve alloy steel material and preparation method thereof|
    CN103614666A|2013-11-12|2014-03-05|铜陵市肆得科技有限责任公司|High-hardness and low-carbon steel material for pump valve and preparation method of high-hardness and low-carbon steel material|
    CN103667943B|2013-11-14|2016-03-09|安徽荣达阀门有限公司|A kind of pump impeller is with containing scandium wear-resisting low-carbon steel and preparation method thereof|
    CN103667946B|2013-11-20|2016-01-13|马鞍山市益丰实业集团有限公司|A kind of tungstenic Heat-resistant alloy steel liner plate material and preparation method thereof|
    CN103667990B|2013-11-20|2016-01-13|马鞍山市益丰实业集团有限公司|A kind of heat-resistance abrasion-resistance alloy steel liner plate material and preparation method thereof|
    CN103667989B|2013-11-20|2016-01-13|马鞍山市益丰实业集团有限公司|A kind of rare earth abrasion-proof stainless steel lining material and preparation method thereof|
    CN103741063B|2013-12-23|2016-01-20|马鞍山市盈天钢业有限公司|A kind of Seamless Steel Pipes For Geological Drilling material and preparation method thereof|
    CN103741064B|2013-12-23|2016-01-20|马鞍山市盈天钢业有限公司|A kind of seamless steel tubes for liquid service material and preparation method thereof|
    CN103789630B|2014-01-24|2016-01-20|李露青|A kind of carbon steel work-piece production method for speed skate blade|
    CN103789616B|2014-01-24|2015-12-09|李露青|A kind of carbon steel work-piece for speed skate blade|
    DE102014101159B4|2014-01-30|2016-12-01|Thyssenkrupp Steel Europe Ag|Process for the surface treatment of workpieces|
    CN104911505A|2014-03-15|2015-09-16|紫旭盛业（昆山）金属科技有限公司|High temperature-resistance die steel|
    CN106460109B|2014-05-28|2019-01-29|新日铁住金株式会社|Hot rolled steel plate and its manufacturing method|
    CN104073735A|2014-06-30|2014-10-01|张家港市华尊宝特种材料科技有限公司|Low temperature-resistant specially-shaped steel tube and preparation method thereof|
    CN104493504A|2014-11-28|2015-04-08|周正英|Sliding seat|
    CN104480367A|2014-11-28|2015-04-01|周正英|Multifunctional submersible pump|
    CN104492553A|2014-11-28|2015-04-08|周正英|Closed sand mill|
    CN104495211A|2014-11-28|2015-04-08|周正英|Multifunctional belt conveyor|
    KR101657801B1|2014-12-18|2016-09-20|주식회사 포스코|Steel sheet having excellent strength and ductility and manufacturing method for the same|
    CN104862589B|2015-06-10|2017-03-08|武汉钢铁公司|A kind of wind-power tower steel of low-temperature welding function admirable and production method|
    CN105624553B|2015-12-31|2017-05-03|江西理工大学|High-strength steel plate with improved low-temperature impact toughness and manufacturing method thereof|
    WO2017213252A1|2016-06-10|2017-12-14|Sumitomo Chemical Company, Limited|Oxadiazole compound and use as pesticide|
    CN105937012A|2016-07-11|2016-09-14|吴用镜|Anti-corrosion alloy steel for drilling drill pipe|
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    CN109082598A|2018-09-06|2018-12-25|包头钢铁（集团）有限责任公司|The production method of hot forming steel plate and hot forming steel plate|
    CN111394654B|2020-04-23|2021-08-03|辽宁科技学院|La microalloy-added hot-press forming steel plate and preparation method thereof|
    法律状态:
    2020-09-08| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2020-10-13| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-11-10| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |
    2021-01-26| B11B| Dismissal acc. art. 36, par 1 of ipl - no reply within 90 days to fullfil the necessary requirements|
    2021-11-23| B350| Update of information on the portal [chapter 15.35 patent gazette]|
    优先权:
    申请号 | 申请日 | 专利标题
    JP2010108431|2010-05-10|
    JP2010-108431|2010-05-10|
    JP2010133709|2010-06-11|
    JP2010-133709|2010-06-11|
    PCT/JP2011/060760|WO2011142356A1|2010-05-10|2011-05-10|High-strength steel sheet and method for producing same|
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