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    • 专利摘要:
    Patent specification: "High strength hot rolled steel plate containing bainite with excellent isotropic working capacity and method of production". The present invention relates to a high strength hot rolled steel plate containing bainite. This bainite high strength hot rolled steel plate contains, by weight percentage, 0.07 to 0.2%, excluding 0.07%, c, 0.001-2.5% si, 0.01- 4% mn, up to 0.15% p (excluding 0%), up to 0.03% s (excluding 0%), up to 0.01% n (excluding 0%), and 0.001-2% al, with the remainder comprising faith and incidental purity. in the middle towards the thickness ranging from 5/8 to 3/8 the plate thickness in terms of the steel plate surface depth, the average pole density values of the orientations {100} <011> to { 223} <110> is 4.0 or less and the crystal orientation pole density {332} <113> is 4.8 or less. The steel plate has an average grain crystal diameter of 10 µm or less and the apparent transition temperature of charpy fracture (vtrs) of -20 ° c or below. The steel plate has a microstructure comprising 35% or less of proeutectoid ferrite and a phase generated by low temperature transformation like the rest.
    公开号:BR112013024166B1
    申请号:R112013024166-7
    申请日:2012-03-29
    公开日:2019-05-28
    发明作者:Tatsuo Yokoi；Hiroshi Shuto；Riki Okamoto；Nobuhiro Fujita；Kazuaki Nakano；Takeshi Yamamoto
    申请人:Nippon Steel & Sumitomo Metal Corporation；
    IPC主号:
    专利说明:

    Invention Patent Descriptive Report for HIGH-RESISTANCE HOT-LAMINATED STEEL SHEET CONTAINING BAINITE HAVING ISOTROPIC WORKING CAPACITY AND THE SAME PRODUCTION METHOD.
    Technical Field [001] The present invention relates to a high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic work capacity and its production method.
    [002] This application is based on, and claims the benefit of, priority over Japanese Patent Application No. 2011-079658, filed on March 31, 2011, the full content of which is incorporated herein by reference.
    Background of the Technique [003] In recent years, to reduce the weight of various elements in order to improve the fuel efficiency of a car, a reduction in thickness has been promoted by obtaining high strength of an iron alloy steel plate or similar and application of light metal such as aluminum alloy. However, compared to heavy metal such as steel, light metal such as aluminum alloy has the advantage that the specific strength is high, but has the disadvantage of being significantly expensive. Therefore, the application of light metal such as Al alloy has been limited to special uses. Thus, in order to promote weight reduction in several members more cheaply and more widely, the reduction in thickness to achieve the high strength of the steel sheet has been necessary.
    [004] The reach of the high resistance of a steel plate causes the deterioration of the properties of the material such as forming capacity (working capacity) in general. Therefore, how to achieve high strength without deteriorating material properties is important in the development of a high strength steel plate
    Petition 870190008815, of 01/28/2019, p. 12/93
    2/72 co. In particular, a steel plate used as an automobile member such as an internal plate member, a structural member or a lower member must have bending capacity, flange stretching workability, deburring workability, ductility, fatigue life , impact resistance, corrosion resistance, etc., depending on their use. It is important how these material properties should be presented in a highly dimensional and well-balanced manner.
    [005] Particularly, among auto parts, a part obtained by working with a plate material as raw material and presenting a function as a rotor, such as a drum or a bearing constituting an automatic transmission, for example, is an important part that serves as a mediator or transmission motor output to a wheel axle shaft. Such a part presenting a function as a rotor must have a circular shape and homogeneity of the plate thickness in a circumferential direction to decrease friction, etc. In addition, to form such a part, forming methods such as deburring, stamping, ironing and grouting are used, and great emphasis is also placed on the final ductility by local elongation.
    [006] Furthermore, in relation to a steel plate used for such a member, it is necessary to improve a property that the steel plate is shaped and then attached to an automobile as a part and then the member is not easily broken even when being subjected to impact caused by collision or similar. In addition, to ensure resistance to impact in a cold region, it is also necessary to improve toughness at low temperature. This low temperature toughness is defined by vTrs (Charpy fracture appearance transition temperature), or similar. For this reason, it is also necessary to consider the impact resistance itself of the member of
    Petition 870190008815, of 01/28/2019, p. 13/93
    3/72 steel described above.
    [007] That is, a thin steel sheet for a part that needs to have uniform thickness of the sheet such as the one described above needs to have, in addition to the excellent workability, plastic isotropy, and low temperature toughness as very properties important.
    [008] To achieve the high strength property and the various properties of the material such as, in particular, forming capacity as above, in Patent Document 1, for example, a method of producing a steel sheet in which was described a steel structure is made of 90% or more of ferrite and the balance being bainite, in order to achieve high ductility resistance, and bore expansion capacity. However, in relation to the steel sheet produced by applying the technique described in Patent Document 1, plastic isotropy is not mentioned. In the condition that the steel sheet produced in Patent Document 1 is applied to a part that needs to have circularity and homogeneity in the thickness of the sheet in a circumferential direction, a decrease in production is considered due to false vibration and / or loss by friction caused by an eccentricity of the piece.
    [009] In addition, in Patent Documents 2 and 3, a technique of a high-strength hot-rolled steel sheet has been described to which a high strength and excellent forming ability in the flange stretch are provided by the addition of Mo and making the precipitates thin. However, a steel sheet to which the techniques described in Patent Documents 2 and 3 are applied must have 0.07% or more Mo, which is an expensive bonding element, added to it, and thus has a problem that the production cost is high. In addition, also in the techniques described in Patent Documents 2 and 3, plastic isotropy is not mentioned. In the condition
    Petition 870190008815, of 01/28/2019, p. 14/93
    4/72 that the techniques in Patent Documents 2 and 3 are also applied to a part that needs to have circularity and homogeneity in the thickness of the plate in a circumferential direction, it is considered a decrease in production due to false vibration and / or loss by friction caused by an eccentricity of the part.
    [0010] On the other hand, in relation to the plastic isotropy of the steel sheet, that is, a decrease in the plastic isotropy, in Patent Document 4, for example, a technique has been described in which an endless lamination and a lubricated lamination are combined. And with that, an austenite texture in a crude laminated layer of a surface layer is regulated and the anisotropy in the plane of an r value (Lankford value) is decreased. However, in order to perform lubrication lamination with a small coefficient of friction over the entire length of a coil, endless lamination is necessary to avoid bite failure caused by slipping between the biting cylinder and the laminated plate material during lamination. . However, to apply this technique, investment in equipment such as raw bar joining equipment, high-speed scissors, etc., is necessary, and thus the load is large.
    [0011] In addition, in Patent Document 5, for example, a technique has been described in which Zr, Ti, and Mo are added together and the finishing laminate is finished at a high temperature of 950 ° C or more and therefore , the strength of the class of 780 MPa or more is obtained, the anisotropy of an r value is small, and the forming capacity in the flange drawing and the deep drawing capacity are achieved. However, 0.1% or more of Mo being an expensive bonding element needs to be added, and so there is a problem that its cost of production is high.
    [0012] In addition, a study to improve the low temperature toughness of a steel sheet has been proposed so far, but a
    Petition 870190008815, of 01/28/2019, p. 15/93
    5/72 high strength hot rolled steel sheet of the type containing bainite having excellent isotropic working capacity which has high strength, has plastic isotropy, improves the bore expansion capacity, and also achieves low temperature toughness described in Patent Documents 1 to 5.
    Prior Art Documents
    Patent Documents [0013] Document for Open to Public Inspection [0014] Document for
    Open to Public Inspection [0015] Document of
    Open to Public Inspection [0016] Document of
    Open to Public Inspection [0017] Document of
    Open to Public Inspection Description of the Invention
    Patent 1: Application for
    I o H6-293910
    Patent 2: Application for
    I o 2002-322540
    Patent 3: Application for
    I o 2002-322541
    Patent 4: Application for
    I o H10-183255
    Patent 5: Application for
    I o 2006-124789
    Japanese Patent
    Japanese Patent
    Japanese Patent
    Japanese Patent
    Japanese Patent
    Problems to Be Solved by the Invention [0018] The present invention was invented in consideration of the problems described above, and has the objective of providing a high-strength hot-rolled steel sheet containing bainite having excellent isotropic work capacity, which has high strength, it is applicable to a member needed to have working capacity, bore expansion capacity, strict uniformity of sheet thickness and circularity after work and low temperature toughness, and has a steel plate grade of 540 MPa and a production method able to produce the steel sheet cheaper and more stable.
    Means to Solve Problems
    Petition 870190008815, of 01/28/2019, p. 16/93
    6/72 [0019] To solve the problems as described above, the present inventors propose a high-strength hot-rolled sheet containing bainite having excellent isotropic working capacity and a production method described below.
    [0020] The high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic working capacity, contains in% by mass,
    C: greater than 0.07 to 0.2%;
    Si: 0.001 to 2.5%;
    Mn: 0.01 to 4%;
    P: 0.15% or less (not including 0%);
    S: 0.03% or less (not including 0%);
    N: 0.01% or less (not including 0%);
    Al: 0.001 to 2%; and a balance consisting of Fe and the inevitable impurities, in which the average pole density value of the {100} <011> to {223} <110> orientation group represented by the respective {100} <011> crystal orientations , {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> to a central portion of the thickness of the plate being a range of 5/8 to 3/8 in the thickness of the plate from the surface of the steel plate is 4.0 or less, and the pole density of the crystal orientation {332} <113> is 4.8 or less, the average diameter of the crystal grain is 10 μίτι or less and the transition temperature of fracture appearance Charpy vTrs is -20 ° C or less, and the microstructure is composed of 355 or less in a structural fraction of ferrite eutectoid and the balance of a phase that generates the transformation at low temperature.
    Petition 870190008815, of 01/28/2019, p. 17/93
    7/72 [0021] The high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic working capacity according to item 1, also contains:
    one type or two or more types of elements between% by mass,
    Ti: 0.015 to 0.18%,
    Nb: 0.005 to 0.06%,
    Cu: 0.02 to 1.2%,
    Ni: 0.01 to 0.6%,
    Mo: 0.01 to 1%,
    V: 0.01 to 0.2%, and
    Cr: 0.01 to 2%.
    [0022] The high-strength hot-rolled steel plate of the type containing bainite having excellent isotropic working capacity according to item 1, also contains:
    one type or two or more types of elements between
    In mass%,
    Mg: 0.0005 to 0.01%,
    Ca: 0.0005 to 0.01%, and
    REM: 0.0005 to 0.1%.
    [0023] The high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic working capacity as per item 1, also contains:
    in mass%,
    B: 0.0002 to 0.002%.
    [0024] A method of producing a cold rolled steel sheet
    Petition 870190008815, of 01/28/2019, p. 18/93
    8/72 hot high strength of the type containing bainite having excellent isotropic working capacity includes:
    on a steel bar containing:
    in mass%,
    C: greater than 0.07 to 0.2%;
    Si: 0.001 to 2.5%;
    Mn: 0.01 to 4%;
    P: 0.15% or less (not including 0%);
    S: 0.03% or less (not including 0%);
    N: 0.01% or less (not including 0%);
    Al: 0.001 to 2%; and the balance being composed of Fe and the inevitable impurities, initially performing a hot rolling in which rolling at a reduction rate of 40% or more is performed once or more in a temperature range of not less than 1000 ° C nor greater than 1200 ° C;
    executing the second hot lamination in which the lamination at 30% or more is performed in a pass at least once in a temperature region of not less than T1 + 30 ° C nor more than T1 + 200 ° C determined by the Expression 1 above; and adjusting the total reduction ratios on the second hot rolling to 50% or more;
    performing the final reduction at a reduction rate of 30% or more on the second hot rolling and then starting primary cooling in a way that the waiting time period t seconds satisfies Expression (2) below;
    adjust the average cooling rate in the primary cooling to 50 ° C / s or more and perform the primary cooling so that the temperature change is in a range of not less than 40 ° C nor greater than 140 ° C;
    Petition 870190008815, of 01/28/2019, p. 19/93
    9/72 within three seconds after the end of the primary cooling, perform the secondary cooling in which the cooling is performed at an average cooling rate of 15 ° C / s or more, and after the end of the secondary cooling, perform the cooling air for 1 to 20 seconds in a region of temperatures less than the temperature of the transformation point Ar3 and at a temperature of the transformation point Ar1 or higher and then perform winding at 450 ° C or more and less than 550 ° C .
    T1 (° C) = 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr + 100 x Mo + 100 x V ··· (1) [0025] Here, C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the element content (% by mass).
    t 2.5 x t1 ··· (2) [0026] Here, t1 is obtained by Expression (3) below.
    t1 = 0.001 x ((Tf - T1) x P1 / 100) 2 - 0.109 x ((Tf - T1) x P1 / 100) + 3.1 ··· (3) [0027] Here, in Expression (3) above, Tf represents the temperature of the steel bar obtained after the final reduction at a reduction ratio of 30% or more and P1 represents the ratio of the final reduction at 30% or more.
    [0028] The production method of the high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic working capacity according to item 5, in which the total reduction ratios in a temperature range of less than T1 + 30 ° C is 30% or less.
    [0029] The production method of the high-strength hot-rolled steel sheet containing bainite having excellent isotropic work capacity according to item 5, in which
    Petition 870190008815, of 01/28/2019, p. 20/93
    10/72 the heat generation by work between the respective passes in the temperature region of not less than T1 + 30 ° C nor greater than T1 + 200 ° C in the second hot rolling is 18 ° C or less.
    [0030] The production method of high-strength hot-rolled steel sheet containing bainite having excellent isotropic working capacity according to item 5 in which the waiting time period t seconds also satisfies Expression (4) below.
    t <t1 ... (4) [0031] The production method of the high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic working capacity according to item 5 in which the waiting period t seconds also satisfies the expression [5] below.
    t1 t t1 x 2.5 ... (5) [0032] The production method of the high-strength hot-rolled steel sheet of the type containing bainite having excellent isotropic working capacity as per item [5], in which , primary cooling is started between the rolling chairs.
    Effect of the Invention [0033] In accordance with the present invention, a steel plate applicable to a member that needs to have working capacity, bore expansion capacity, bending capacity, strict uniformity of plate thickness, and circularity after it is provided work and toughness at low temperature (an inner plate member, a structural member, a lower member, an automobile member as
    Petition 870190008815, of 01/28/2019, p. 21/93
    11/72 as a transmission, and members for shipbuilding, constructions, bridges, marine structures, pressure vessels, pipes and machine parts, etc.). In addition, according to the present invention, a high-strength steel sheet having excellent toughness at low temperature and grade of 540 MPa or more is produced in a cheap and stable manner.
    Brief Description of the Drawings [0034] FIG. 1 is a view showing the relationship between an average pole density value of the {100} <011> to {223} <110> orientation group and isotropy (1 / | Ar |);
    [0035] FIG. 2 is a view showing the relationship between the pole density of the {332} <113> crystal orientation and an isotropic index (1 / | Ar |);
    [0036] FIG. 3 is a view showing the relationship between the average diameter of the crystal grain (pm) and vTrs (° C); and [0037] FIG. 4 is an explanatory view of a continuous hot rolling line.
    Mode for Carrying Out the Invention [0038] As a configuration to implement the present invention, a high-strength, hot-rolled steel sheet of the type containing bainite having excellent isotropic workability will be explained in detail (hereinafter referred to simply as hot rolled steel plate). Incidentally, the mass% relative to the chemical composition is described simply as%.
    [0039] The present inventors have seriously studied the high-strength hot-rolled steel sheet of the type containing bainite suitable for application to a member that needs work capacity, bore expansion capacity, bending capacity, strict thickness uniformity plate and roundness
    Petition 870190008815, of 01/28/2019, p. 22/93
    12/72 after work, and low temperature toughness, in terms of working capacity and also the reach of isotropy and low temperature toughness. As a result, the following new knowledge was obtained.
    [0040] Initially, to obtain isotropy (decreasing anisotropy), the formation of a texture transformation from non-recrystallized austenite, which is the cause of anisotropy, is avoided. To achieve this, it is necessary to promote the recrystallization of austenite after finishing lamination. As an environment, an optimal laminating pass program in the finishing laminate and achieving a high laminating temperature are effective.
    [0041] Next, to improve the toughness at low temperature, make the grains fine in each fracture of a fragile fracture, that is, the refining of the grain in each microstructure is effective. For this, it is effective to increase the nucleation sites for α at the time of transformation from γ to α, and it becomes necessary to increase the edges of the austenite crystal grains, which can be sites of nucleation and displacement density.
    [0042] As its medium, it becomes necessary to perform lamination at a temperature of the transformation point from γ to α or higher and at a temperature as low as possible, that is, to make austenite remain unrecrystallized and in a state of a fraction of non-recrystallization being high, cause the transformation from γ to α. This is because austenite grains after recrystallization grow rapidly at a recrystallization temperature, become crude for an extremely short time, and become crude even in an α phase after transformation γ to α to thereby cause a significant deterioration in toughness .
    [0043] The present inventors have invented an entirely new hot rolling method capable of, at a higher level, equi
    Petition 870190008815, of 01/28/2019, p. 23/93
    13/72 to release isotropy and tenacity at low temperature, which was considered difficult to achieve because they resulted in conditions opposite to each other by means of normal hot rolling.
    [0044] Initially, regarding isotropy, the present inventors obtained the following knowledge regarding the relationship between isotropy and texture.
    [0045] To obtain the uniformity of the plate thickness and the circularity that satisfy the property of the piece in a state in which the steel plate remains worked without being subjected to trimming and cutting processes, at least the isotropic index (= 1 / | Air |) must be 3.5 or more.
    [0046] Here, the isotropic index is obtained in such a way that the steel sheet worked on a specimen No. 5 described in JIS Z 2201 and the specimen are subjected to a test by the method described in JIS Z 2241. 1 / | Air | the isotropic index being defined as Ar = (rL - 2 x r45 + rC) / 2, where the plastic stress ratios (r values, Lankford values) in the rolling direction, in a 45 ° direction in relation to the direction of lamination, and in a 90 ° direction in relation to the lamination direction (sheet width direction) are defined as rL, r45, and rC respectively.
    Crystal Orientation [0047] As shown in FIG. 1, the isotropic index (= 1 / | Ar |) satisfies 3.5 or more since the mean pole densities of the orientations group {100} <011> to {223} <110> represented by the respective crystal orientations of {100} <011>, {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> at a central position the thickness of the plate being in a range of 5/8 to 3/8 in the thickness of the plate from the surface of the steel plate is 4.0 or less. Provided the isotropic index is 6.0 or more desirably the uniformity of thickness and circularity that
    Petition 870190008815, of 01/28/2019, p. 24/93
    14/72 sufficiently satisfy the property of the part in a state in which the steel sheet remains worked can be obtained even if variations in the coil are considered. Therefore, the average value of pole densities in the {100} <011> to {223} <110> guidance group is desirably 2.0 or less.
    [0048] The pole density of a random X-ray intensity ratio. The pole density (random X-ray intensity ratio) is a numerical value obtained by measuring the X-ray intensity of a standard sample with no concentration in an orientation and a test sample under the same condition by X-ray diffractometry or similar and dividing the X-ray intensity obtained from the test sample by the X-ray intensity of the standard sample. This pole density can be measured by an X-ray diffractometry, an EBSP (Electron Back Scattering Pattern) method, and an ECP (Electron Channeling Pattern) method.
    [0049] Regarding the pole density of the {100} <011> to {223} <110> orientation group, for example, the pole densities of the respective orientations of {100} <011>, {116} <110>, { 114} <110>, {112} <110>, and {223} <110> are obtained from the three-dimensional texture (ODF) calculated by a series expansion method using a plurality (preferably three or more) of pole figures outside the pole figures of {110}, {100}, {211}, and {310} measured by the method, and the arithmetic mean of these pole densities is calculated and thus the pole density of the group of orientations described above is obtained, Incidentally, when it is impossible to obtain the intensities of all orientations described above, the arithmetic mean of the pole densities of the respective orientations of {100} <011>, {116} <110>, {114} <110>, {112} < 110>, and {223} <110> can also be used as substitutes.
    [0050] For example, for the pole density of each of the ori
    Petition 870190008815, of 01/28/2019, p. 25/93
    15/72 crystal entations described above, each of the intensities of (001) [1-10], (116) [1-10], (114) [1-10], (113) [1-10], (112) [1-10], (335) [1-
    10], and (223) [1-10] to a cross section φ2 = 45 ° in the three-dimensional texture can be used as is.
    [0051] Similarly, as shown in FIG. 2, since the pole density of the crystal orientation {332} <113> in the central portion of the plate thickness being the range from 5/8 to 3/8 in the plate thickness from the surface of the steel plate is 4, 8 or less, the isotropic index satisfies 3.5 or more. As long as the isotropic index is 6.0 or more desirably, the uniformity of the sheet thickness and the circularity that sufficiently satisfy the property of the part in a state in which the steel sheet remains worked, can be obtained even if variations in a coil considered. Therefore, the pole density of the {332} <113> crystal orientation is desirably 3.0 or less.
    [0052] Regarding a sample to be submitted to X-ray diffraction, the EBSP method, or the ECP method, the steel sheet is reduced in thickness until a sheet thickness is determined from the surface by mechanical polishing or similar . Then, the stress removed by chemical polishing, electronic polishing, or similar, and the sample is produced in such a way that in the range of 5/8 s 3/8 in the thickness of the sheet, and a suitable plane becomes the measurement plane . For example, on a steel piece with a size of 30 mmφ cut from the position of 1/4 W or 3/4 W of the width of the plate W, polishing with a fine finish is performed (medium toughness in the center line Ra: 0 , 4a to 1,6a). Then, by chemical polishing or electronic polishing, the tension is removed, w the sample to be submitted to X-ray diffractometry is produced. In relation to the width direction of the plate, the steel part is desirably removed from the steel plate from the position of 1/4 or% from a final position.
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    16/72 [0053] As usual, the pole density satisfies the limited pole density range described above not only in the central portion of the plate thickness, the range being 5/8 to 3/8 in the plate thickness from the surface of the steel sheet, but also in as many thickness positions as possible, and with this the local ductile performance (local elongation) is also improved. However, the range from 5/8 to 3/8 from the surface of the steel sheet is measured, so as to generally make it possible to represent the material property of the entire steel sheet. Thus, 5/8 s 3/8 of the plate thickness is defined as the measuring range.
    [0054] Incidentally, the crystal orientation represented by {hkl} <uvw> means that the normal direction of the steel plate plane is parallel to <hkl> and the rolling direction is parallel to <uvw>. Regarding the crystal orientation, the vertical orientation to the plate plane is usually represented by [hkl] or {hkl} and the orientation parallel to the lamination direction is represented by (uvw) or <uvw>. {hkl}, <uvw>, etc., are generic terms for equivalent planes, and [hkl], (uvw) each indicate an individual crystal plane. That is, in the present invention, a body-centered cubic structure is desired, and so, for example, the planes (111), (-111), (1-11), (11-1), (-1-11 ), (11-1), (1-1-1), and (-1-1-1) are equivalent to make it impossible to ornament them differently. In such a case, these guidelines are generically referred to as {111}. In an ODF representation, [hkl] (uvw) is also used to represent orientations of other low-symmetry crystal structures, and so it is common to represent each representation as [hkl] (uvw), but in the present invention, [hkl] ( uvw) and {hkl} <uvw> are synonymous with each other. The measurement of crystal orientation by an X-ray is performed according to the method described, for example, in Cullity, Elements of X-ray Diffraction, new edition (published in 1986, translated by MATSUMURA, Gentaro, published by AGNE Inc. ) in
    Petition 870190008815, of 01/28/2019, p. 27/93
    17/72 pages 274 to 296.
    Average Diameter of the Crystal Grain [0055] Next, the present inventors examined the toughness at low temperature.
    [0056] FIG. 3 shows the relationship between the average diameter of the crystal grain and vTrs (transition temperature of the appearance of Charpy fracture). As the crystal grain diameter is smaller, vTrs become low in temperature, and low temperature toughness is improved. As the average crystal grain diameter is 10 μίτι or less, vTrs becomes -20 ° C or less as a target, and so the present invention is durable enough to be used in a cold place.
    [0057] Incidentally, low temperature toughness was assessed by vTrs (transition temperature of the appearance of Charpy fracture) obtained by a V-notch Charpy impact test. In the V-notch Charpy impact test, a specimen it was done based on JISZ2202 and the test was performed according to the levels defined in JISZ2242, and vTrs were measured.
    [0058] In addition, the low temperature toughness is greatly affected by the average diameter of the crystal grain of the structure, and thus the measurement of the average diameter of the crystal grain in the central portion of the plate thickness was also performed. A microsample was cut to have a crystal grain diameter and microstructure measured using an EBSP-OIM® (Electron Back Scatter Diffraction Pattern-Orientation Image Microscopy). The micro-sample was polished using an abrasive colloidal silica for 30 to 60 minutes to be made and was subjected to an EBSP measurement under 400 magnification measurement conditions, area of 160 μm x 256 μm, and the measurement step of 0, 5 μm.
    [0059] The EBSP-OIM® method consists of equipment and
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    18/72 a software in which a highly tilted sample in a scanning electron microscope (SEM) is irradiated with electron rays, a Kikuchi pattern formed by electrodispersion is photographed by a highly sensitive camera and undergoes image processing by a computer, and so a crystal orientation at an irradiation point is measured for a short period of time.
    [0060] In the EBSP method, it is possible to quantitatively analyze a microstructure and a crystal orientation of a sample surface. The area of analysis of the EBSP method is an area capable of being observed by SEM. It is possible to analyze the area with a minimum resolution of 20 nm using the EBSP method, depending on the SEM resolution. The analysis is performed by mapping the area to be analyzed to tens of thousands of network points. It is possible to see the distributions of the crystal orientations and the sizes of the crystal grains within the sample in a polycrystalline material.
    [0061] In the present invention, from a mapped image that the difference in orientation between crystal grains is defined as 15 ° being a lower limit value of a large angle of inclination of the grain edge commonly recognized as grain edge crystal, the crystal grains were visualized and the average diameter of the crystal grains was obtained. Here, the average diameter of the crystal grains is a value obtained by EBSP-OIM®.
    [0062] As described above, the present inventors have revealed the respective requirements required for the steel sheet to obtain isotropy and toughness at low temperature.
    [0063] The average diameter of the crystal grain directly related to low temperature toughness becomes small as the temperature of the finishing laminate is lower, and the low temperature toughness is improved. However, the average value of pole densities in the {100} <011> to {223} <110> orientation group in
    Petition 870190008815, of 01/28/2019, p. 29/93
    19/72 central portion of the plate thickness corresponding to 5/8 to 3/8 from the surface of the steel plate and the pole density of the crystal orientation {332} <113>, which is one of the isotropy control factors , are inversely correlated to the average diameter of the crystal grain. That is, it is the relation in which when the average diameter of the crystal grain is decreased to improve the tenacity at low temperature, the average value of the pole densities of the group of orientations {100} <011> to {223} <110> and the pole density of the {332} <113> crystal orientation is increased and thus the isotropy deteriorates. A technique that achieves isotropy and low temperature toughness has not been described so far.
    [0064] The present inventors have seriously examined the high-strength hot-rolled steel sheet of the type containing bainite suitable for application on a member that needs to have workability, hole expansion capacity, strict uniformity of sheet thickness and circularity after work, and low temperature toughness is achieved and its production method. As a result, the present inventors thought of a hot-rolled steel sheet made under the following conditions and method of production.
    Chemical Composition [0065] Initially, the reasons for limiting the chemical composition of the high-strength hot-rolled steel sheet of the type containing bainite of the present invention will be explained (which will hereinafter be sometimes referred to as the hot-rolled steel sheet of the present invention). invention)
    C: more than 0.07 to 0.2% [0066] C is an element that contributes to increase the strength of steel, but it is also an element that generates iron-based carbides such as cementite (Fe3C) to be starting points of fr
    Petition 870190008815, of 01/28/2019, p. 30/93
    20/72 tures at the time of bore expansion. When C is 0.07% or less, it is possible to obtain an effect of improvement of the resistance by a phase of generation of transformation at low temperature. On the other hand, when C exceeds 0.2%, the central segregation becomes remarkable and the generation of iron-based carbides such as cementite (Fe 3 C) to be the starting points for fractures in a secondary chip surface at the moment of drilling is increased, resulting in the fact that the drilling property deteriorates. Therefore, C is adjusted to more than 0.07% to 0.2%. When the balance between resistance and ductility is considered, C is desirably 0.15% or less.
    Si: 0.001 to 2.5% [0067] Si is an element that contributes to increase the strength of the steel and also has a role of deoxidizing material of the molten steel, and thus it is added according to the need. When Si is 0.001% or more, the effect described above is presented, but when Si exceeds 2.5%, the effect of increasing resistance is saturated. Therefore, Si is adjusted to 0.001 to 2.5%.
    [0068] In addition, when its content is greater than 0.1%, Si, with an increase in the content, suppresses the precipitation of iron-based carbides such as cementite and contributes to improving the resistance and improving the expansion capacity of hole. However, when Si exceeds 1.0%, the effect of suppressing the precipitation of iron-based carbides is saturated. Therefore, Si is preferably greater than 0.1 to 1.0%.
    Mn: 0.01 to 4% [0069] Mn is an element that contributes to improve the resistance by reinforcing the solid solution and reinforcing the quick cooling and is added according to the need. When Mn is less than 0.01% the effect of its addition cannot be obtained and, on the other hand, when Mn exceeds 4%, the effect of the addition is saturated, and thus Mn is adjusted to 0.01 to 4%.
    Petition 870190008815, of 01/28/2019, p. 31/93
    21/72 [0070] To suppress the occurrence of hot fracture by S, when elements other than Mn are not sufficiently added, an amount of Mn that allows the content of Mn (% by mass) ([Mn]) and the S content (% by mass) ([S]) to satisfy [Mn] / [S] □ 20 is desirably added. In addition, Mn is an element that, with an increase in its content, expands the austenite temperature region to a low temperature side, improves the hardening capacity, and facilitates the formation of a continuous cooling transformation structure having excellent deburring. When the Mn content is less than 1%, this effect is not easily seen, and thus Mn is desirably 1% or more.
    P: 0.15% or less [0071] P is an impurity contained in cast iron, and is an element that is segregated at the grain edges and decreases toughness. For this reason, it is desirable that the content of P is as low as possible, and when it exceeds 0.15%, P adversely affects the workability and the welding capacity, and so P is adjusted to 0.15% or less. Particularly, when the hole expansion capacity and the welding capacity are considered, P is desirably 0.02% or less. Incidentally, it is difficult to adjust P to 0% in terms of operation, so 0% is not included.
    S: 0.03% or less [0072] S is an impurity contained in cast iron, and is an element that not only causes fracture at the time of hot rolling but also generates an A-based inclusion deteriorating the expansion capacity of hole. For this reason, S should be decreased as much as possible, as long as S is 0.03% or less, it is within a tolerable range, and so S is adjusted to 0.03% or less. However, when the capacity for bore expansion to such an extent is required, S is preferably 0.01% or less, and is more preferred.
    Petition 870190008815, of 01/28/2019, p. 32/93
    22/72 0.005% or less. Incidentally, it is difficult to adjust S to 0% in terms of operation, so 0% is not included.
    Al: 0.001 to 2% [0073] For the deoxidation of molten steel in a steel refining process, 0.001% or more of Al is added, but the upper limit is adjusted to 2% because an increase in cost is caused. When Al is added in large quantities, the content of non-metallic inclusions is increased and the ductility and toughness deteriorate, and thus the content of Al is desirably 0.06% or less. The content is also desirably 0.04% or less.
    [0074] Al is an element that has a function of suppressing the precipitation of iron-based carbides such as cementite in the structure, similarly to Si. To obtain this effect, Al is desirably 0.016% or more. It is also desirably 0.016 to 0.04%.
    N: 0.01% or less [0075] N is an element that should be decreased as much as possible, but as long as N is 0.01% or less, but as long as N is 0.01% or less, it falls within tolerable range. In terms of resistance to aging, however, N is desirably 0.005% or less. Incidentally, it is difficult to adjust N to 0% in terms of operation, so 0% is not included.
    [0076] The hot-rolled steel sheet of the present invention can also contain one or two or more types between Ti, Nb, Cu, Ni, Mo, V, and Cr as needed. The hot-rolled steel sheet of the present invention can also contain one type or two or more types between Mg, Ca, and REM.
    [0077] Hereafter, the reasons for limiting the chemical compositions of the elements described above will be explained.
    [0078] Ti, Nb, Cu, Ni, Mo, V, and Cr are each an element that improves resistance by reinforcing precipitation or reinforcing solution
    Petition 870190008815, of 01/28/2019, p. 33/93
    23/72 solid type, and one type or two or more types between these elements can also be added.
    [0079] However, when the Ti content is less than 0.015%, the Nb content is less than 0.005%, the Cu content is less than 0.02%, the Ni content is less than 0.01%. The Mo content is less than 0.01%, the V content is less than 0.01%, and the Cr content is less than 0.01%, its addition effects cannot be sufficiently obtained.
    [0080] On the other hand, when the Ti content is greater than 0.18%, the Nb content is greater than 0.06%, the Cu content is greater than 1.2%, the Ni content is greater than 0.6%, the Mo content is greater than 1%, the V content is greater than 0.2%, and the Cr content is greater than 2%, the effects of the addition are saturated and the economic efficiency decreases . Therefore, it is desirable that the Ti content is 0.015 s 0.18%, the Nb content is 0.005 to 0.6%, the Cu content is 0.02 to 1.2%, the Ni content is 0, 01 to 0.6%, the Mo content is 0.01 to 1%, the V content is 0.01 to 0.2%, and the Cr content is 0.01 to 2%.
    [0081] Mg, Ca, and REM (rare earth element) are each elements that control the shape of non-metallic inclusions to be the starting point of the fracture to cause the deterioration of the work capacity and improve the ability to work, and a type or two or more types of these elements can also be added. When Mg, Ca, and REM are each less than 0.0005%, their addition effects are not shown.
    [0082] On the other hand, when the Mg content is greater than 0.01%, the Ca content is greater than 0.01%, and the REM content is greater than 0.1%, the effects of the addition are saturated and economic efficiency decreases. Therefore, it is desirable that the Mg content is 0.0005 to 0.01%, the Ca content is 0.0005 to 0.01%, and the REM content is 0.0005 to 0.1%.
    [0083] Incidentally, the hot rolled steel sheet of the present invention may also contain 1% or less in total of one type
    Petition 870190008815, of 01/28/2019, p. 34/93
    24/72 or two or more types between Zr, Sn, Co, Zn, and W within a range that does not impair the characteristics of the hot rolled steel sheet of the present invention. However, the Sn content is desirably 0.05% or less to suppress the occurrence of a failure when hot rolling.
    B: 0.0002 to 0.002% [0084] B is an element that increases the hardening capacity and increases the structural fraction of the low temperature transformation generation phase, being a hard phase and thus is added as needed. When the B content is less than 0.0002%, the effect of its addition cannot be obtained, and when it exceeds 0.002%, on the other hand, the effect of the addition is saturated, and there is also a risk that the recrystallization of austenite in hot rolling is suppressed and the texture of the transformation from γ to α from non-recrystallized austenite is reinforced to deteriorate the isotropy. Therefore, B is adjusted to 0.0002 to 0.002%.
    [0085] Furthermore, B is also an element that causes the plate to fracture in a cooling process after continuous casting and, from this point of view, it is desirably 0.0015% or less. It is desirably 0.001 to 0.0015%.
    Microstructure [0086] In the following, metallurgical factors such as the microstructure of the hot rolled steel sheet of the present invention will be explained in detail.
    [0087] The microstructure of the hot-rolled steel sheet of the present invention is composed of 35% or less in a structural fraction of pro-eutectoid ferrite and the balance of the low-temperature transformation generation phase. The low temperature transformation generation phase means a transformation structure in continuous cooling and is a structure generally recognized as baini
    Petition 870190008815, of 01/28/2019, p. 35/93
    25/72 ta.
    [0088] Generally, steel sheets having the same tensile strength are compared, and then where the structure is a uniform structure occupied by a structure such as the transformation structure in continuous cooling, the microstructure has a tendency to be excellent in elongation. location as typified by the hole expansion value, for example. Where the microstructure is a composite structure, composed of pro-eutectoid ferrite being a soft phase and a transformation phase at low hard temperature (transformation structure in continuous cooling, including martensite in MA), the microstructure has a tendency to be excellent in uniform elongation which is typified by a n hardening coefficient of work value.
    [0089] In the hot-rolled steel plate of the present invention, the microstructure is designed to be a composite structure, composed of 35% or less in a fraction of proteutectoid ferrite structure and the low temperature transformation phase balance to finally balance the local stretch as it is typified by the ability to bend and the uniform stretch.
    [0090] When the pro-eutectoid ferrite is greater than 35%, the bending capacity which is an index of local elongation decreases significantly, but uniform elongation is not improved, and thus the balance between local elongation and uniform elongation deteriorates . The lower limit of the structural fraction of pro-eutectoid ferrite is not particularly limited, but when the structural fraction is 5% or less, the decrease in uniform elongation becomes significant, and thus the structural fraction of the pro-eutectoid ferrite is preferably greater than 5%.
    [0091] The transformation structure in continuous cooling (Zw) (low temperature transformation generation phase) of the
    Petition 870190008815, of 01/28/2019, p. 36/93
    26/72 hot-rolled steel of the present invention is a microstructure defined as a transformation structure positioned in the middle of a microstructure containing polygonal and pearlite ferrite to be generated by a diffusive mechanism and a martensite to be generated by a non-diffusive cutting mechanism as described in The Iron and Steel Institute of Japan, Society of basic research, Bainite Research Committee / Edition; Recent Research on Bainitic Microstructures and Transformation Behavior of Low Carbon Steels - Final Report of Bainite Research Committee (in 1994, The Iron and Steel Institute of Japan) (reference literature).
    [0092] That is, the transformation structure in continuous cooling (Zw) (low temperature transformation generation phase) is defined as a microstructure composed mainly of bainitic ferrite (a ° B), granular Bainitic ferrite (ub), and quasi-polygonal ferrite (aq), and also containing a small amount of retained austenite (yr) and martensite-austenite (MA) as described in the reference literature mentioned above on pages 125 to 127 as an optical microscope observation structure [0093 ] Incidentally, similar to polygonal ferrite (PF), the internal structure of aq does not appear by caustication, but the form of aq is acicular, and is definitely distinct from PF. Here, of a desired crystal grain, the peripheral length is set to lq and the equivalent circle diameter is set to dq, and then a grain having a ratio (lq / dq) that satisfies lq / dq □ 3.5 is aq .
    [0094] The continuous cooling (Zw) transformation structure (low temperature transformation generation phase) of the hot-rolled steel sheet The present invention is a microstructure containing one type or two or more types between ° B, aB , and aq. In addition, the transformation structure in continuous cooling (Zw) (low temperature transformation generation phase) of the steel sheet
    Petition 870190008815, of 01/28/2019, p. 37/93
    27/72 of the hot melt of the present invention can also a small amount of yr and MA, or both, in addition to one type or two or more types between a ° B, aB, and aq. Incidentally, the total yr and MA content is adjusted to 3% or less in a structural fraction.
    [0095] There is sometimes the case where the transformation structure in continuous cooling (Zw) (transformation phase at low temperature) is not easily discerned by observation under an optical microscope in caustication using a nital reagent. In such a case, it is discerned using EBSP-OIM®. The EBSP-OIM® (Electron Back Scatter Diffraction Pattern-Orientation Image Microscopy) method consists of equipment and software in which a highly tilted sample in a scanning electron microscope (SEM) is irradiated with electron rays, a Kikuchi pattern formed by electrodispersion is photographed by a highly sensitive camera and the image is processed on a computer and thus the crystal orientation at an irradiation point is measured for a short period of time.
    [0096] In the EBSP method, it is possible to quantitatively analyze the microstructure and crystal orientation of a crude sample surface. As long as the area to be analyzed by the EBSP method is within an area capable of being observed by the SEM, it is possible to analyze the area with a minimum resolution of 20 nm, depending on the resolution of the SEM.
    [0097] The analysis of the EBSP-OIM® method is performed by mapping the area to be analyzed to tens of thousands of equally spaced grid points. It is possible to see the distributions of the crystal orientations and the sizes of the crystal grains within the sample in a polycrystalline material. In the hot-rolled steel sheet of the present invention, for convenience one can be understood from a mapped image with a difference in orientation en
    Petition 870190008815, of 01/28/2019, p. 38/93
    28/72 three packages defined as 15 ° can also be defined as the grain diameter of the transformation structure in continuous cooling (Zw) (low temperature transformation generation phase). In this case, a wide angle of inclination of the grain edge having a crystal orientation difference of 15 ° or more is defined as the grain edge.
    [0098] In addition, the structural fraction of the pro-eutectoid ferrite was obtained by a Kernel Average Misorientation (KAM) method being equipped with EBSP-OIM®. The KAM method is that of a calculation, in which the differences in orientation between pixels of the first approximations being adjacent six pixels of a certain regular data measurement hexagon, or the second approximations being positioned 12 pixels out of the six pixels, or third approximations when 18 pixels are positioned outside the 12 pixels, they are measured on average and the value obtained is adjusted to the value of the central pixel, it is executed in relation to each pixel.
    [0099] This circulation is performed so as not to exceed the grain edge, This calculation is performed so as not to exceed the grain edge, thus making it possible to create a map representing a change of orientation within a grain. That is, this map represents the stress distribution based on a change in local operation within a grain. Note that in the analysis, the condition that in the EBSP-OIM® method, the difference in orientation between adjacent pixels is calculated is adjusted to the third approximation and one showing this difference in orientation being 5 ° or less.
    [00100] In the examples of the present invention, the condition that in the EBSP-OIM (trademark) method, the difference in orientation between adjacent pixels is calculated is set to 5 ° or less, and the third approximation of the difference in orientation described above is greater than 1 °, which is defined as the cooling transformation structure
    Petition 870190008815, of 01/28/2019, p. 39/93
    29/72 continuous (Zw) (low temperature transformation generation phase), and it is 1 ° or less, which is defined as ferrite. This is because the high temperature polygonal transformed pro-eutectoid ferrite is generated in a diffusion transformation, so the displacement density is small and the tension within the grain is small, and so the difference within the grain in the crystal orientation is small, and according to the results of several examinations that have been performed so far by the present inventors, the volume fraction of polygonal ferrite obtained by observing an optical microscope and the fraction of area of an area obtained by 1 ° or less from the third approach of the difference in orientation measured by a KAM method substantially agree.
    Production Method [00101] In the following, the conditions of a production method for the hot rolled steel sheet of the present invention (which will hereinafter be called the production method of the present invention) will be explained.
    [00102] The present inventors explored the conditions of hot lamination by having austenite recrystallize sufficiently after finishing lamination or during finishing lamination to guarantee isotropy, but suppressing the grain growth of the recrystallized grains as much as possible and achieving isotropy and low temperature toughness.
    [00103] Initially, in the production method of the present invention, the method of producing a steel bar to be carried out before the hot rolling process is not particularly limited. That is, the production method of the steel bar, subsequent to a casting process by a vat oven, a steel converter, an electric oven, or the like, in various secondary refining processes, an adjustment of components is performed in order to achieve a composition
    Petition 870190008815, of 01/28/2019, p. 40/93
    30/72 desired chemistry. Then, a casting process can also be performed by normal continuous casting, or conventional casting, or another method such as thin plate casting.
    [00104] Incidentally, a scrap can also be used as a raw material. In addition, when a slab is obtained by continuous casting, the slab can be transferred directly to a hot strip mill as it is in the state of a slab at high temperature, or it can also be cooled to room temperature and then reheated in a heating oven, and then hot rolled.
    [00105] The plate obtained by the production method described above is heated in a plate heating process before the hot rolling process, but in the production method of the present invention, the heating temperature is not determined in particular. However, when the heating temperature is greater than 1260 ° C, the yield decreases due to flaking, and thus the heating temperature is preferably 1260 ° C or less. On the other hand, on the other hand, when the heating temperature is less than 1150 ° C, the operational efficiency deteriorates significantly in terms of programming, and thus the heating temperature is desirably 1150 ° C or more.
    [00106] In addition, the heating time period in the plate heating process is not determined in particular, but in terms of avoiding central segregation, etc., after the temperature reaches a predetermined heating temperature, the heating temperature it is desirably maintained for 30 minutes or more. However, when the cast plate after being cast, is transferred directly to a hot strip mill as it is in a high temperature cast plate state to be laminated, the heating time period is not limited to this.
    Petition 870190008815, of 01/28/2019, p. 41/93
    31/72 only.
    (First Hot Rolling) [00107] After the plate heating process, the plate extracted from the heating oven is subjected to a rough rolling process initially by a hot rolling process to undergo rough rolling without waiting, and so it is a roughed bar is obtained. [00108] The roughing lamination process (first hot rolling) is carried out at a temperature of not less than 1000 ° C nor greater than 1200 ° C for reasons to be explained below. When the rough rolling finish temperature is less than 1000 ° C, the reduction is carried out in a state in which the vicinity of the roughened bar surface layer is in a non-recrystallization temperature region, the texture developed, and the isotropy deteriorates. In addition, the resistance to hot deformation in the roughing lamination decreases, thereby creating a risk that an impediment will be caused to the roughing rolling operation.
    [00109] On the other hand, when the finishing temperature of the roughing lamination is greater than 1200 ° C, the average diameter of the crystal grain is increased to decrease the toughness. In addition, the secondary scale to be generated during the roughing lamination grows a lot, thus making it difficult to remove the scaling scaling or finishing lamination to be carried out later. When the finishing temperature of the roughing lamination is greater than 1150 ° C, there is sometimes a case where inclusions are removed and the hole expansion capacity deteriorates, so it is desirably 1150 ° C or less.
    [00110] Furthermore, in the roughing lamination process (first hot rolling) in a temperature range of not less than 1000 ° C or greater than 1200 ° C, lamination at a reduction rate of 40% or more is performed once or more. When the reason
    Petition 870190008815, of 01/28/2019, p. 42/93
    32/72 reduction in the roughing lamination process is less than 40%, the average diameter of the crystal grain is increased and the toughness decreases. When the reduction ratio is 40% or more, the diameter of the crystal grain becomes uniform and small. On the other hand, when the reduction ratio is greater than 65%, there is sometimes the case where inclusions are removed and the hole expansion capacity deteriorates, and thus it is desirably 65% or less. Incidentally, in roughing rolling, when the reduction ratio in one final stage and the reduction ratio in the stage before the final stage are desirably 20% or more.
    [00111] Incidentally, in terms of decreasing the average diameter of the crystal grain of the final product, the diameter of the austenite grain after roughing lamination, that is, before the finishing lamination, is important and the grain diameter of the austenite before the finishing lamination is desirably small.
    [00112] As long as the diameter of the austenite grain before the finishing lamination is 200 μm or less, it is possible to greatly promote grain refining and homogenization. To efficiently obtain this promotion effect, the diameter of the austenite grain is desirably adjusted to 100 μm or less. To achieve this, lamination at a reduction rate of 40% or more is desirably performed two or more times in the roughing lamination process. However, when in the roughing lamination process the lamination is performed more than 10 times, there is a concern that the temperature will decrease or the scale will be excessively generated.
    [00113] In this way, the austenite grain diameter before the finishing lamination is reduced, which is effective to promote the recrystallization of the austenite in the finishing lamination later. This is supposed to be because the austenite grain edge after roughing lamination (ie, before finishing lamination)
    Petition 870190008815, of 01/28/2019, p. 43/93
    33/72 functions as one of the recrystallization cores during the finishing lamination.
    [00114] The diameter of the austenite grain after roughing rolling is measured as follows. That is, the steel bar (roughed bar) after roughing lamination (before being subjected to finish lamination) is cooled as much as possible, and is desirably cooled to a cooling rate of 10 ° C / s or more. The structure of a cross section of the cooled steel bar is etched to make the edges of the austenite grains appear, and the edges of the austenite grains are measured by an optical microscope. 'On that occasion, magnifications of 50 times or more, 20 visual fields or more are measured by image analysis or by a method of counting points.
    [00115] The roughed bar obtained after finishing the roughing rolling process can also be joined between the roughing rolling process and the finishing rolling process to then have endless rolling so that the finishing rolling process run continuously. On that occasion, the roughed bars can also be wound in the form of a coil once, stored in a cover having a heat insulation function according to the need, and unwound again to be joined.
    [00116] During the hot rolling process, the temperature changes of the roughed bar in the direction of rolling, in the direction of the width of the plate, and in the direction of the thickness of the plate are desirably controlled to be small. In this case, according to the need, a heating equipment capable of controlling the temperature variations of the roughed bar in the direction of the rolling, in the direction of the width of the plate, and in the direction of the thickness of the plate, can be arranged between the thinning in
    Petition 870190008815, of 01/28/2019, p. 44/93
    34/72 roughing lamination process and the finishing laminator in the finishing lamination, or between the respective chairs in the finishing lamination process, and thus the roughed bar can be heated.
    [00117] As a heating equipment system, several heating systems such as gas heating, electric heating, and induction heating are conceivable, but as the heating system makes it possible to control the temperature changes of the roughed bar in the direction of lamination, in the direction of the width of the sheet, and in the direction of the thickness of the sheet to be small, any of the known systems can also be used.
    [00118] Incidentally, as a heating equipment system, an induction heating system having an industrially good response to temperature control is preferred. If among several induction heating systems, a plurality of induction heating equipment of the transverse type capable of being exchanged in the direction of the plate width is installed, the temperature distribution in the direction of the plate width can be controlled arbitrarily according to the width of the sheet, and thus the transverse type induction heating equipment is more preferred. In addition, as a heating equipment system, a heating equipment consisting of a combination of induction heating equipment of the transverse type and induction heating equipment of the solenoid type that stands out in heating over the entire width of the plate is the most preferred.
    [00119] When the temperature is controlled using these heating equipment, it is sometimes necessary to control the amount of heating by the heating equipment.
    Petition 870190008815, of 01/28/2019, p. 45/93
    35/72
    In this case, the temperature of the trimmed bar internal cannot actually be measured, and thus actual previously measured data such as temperature of the loaded plate, time period of the plate oven's existence, the atmospheric temperature of the heating oven, the extraction temperature of the heating furnace, and also the transfer time period on the rolling table are used to estimate temperature distributions in the rolling direction, in the direction of the plate width, and in the direction of the plate thickness when the roughed bar reaches the heating equipment, and then the amount of heating by the heating equipment is desirably controlled.
    [00120] Incidentally, the control of the amount of heating by induction heating is controlled as follows, for example. A characteristic of induction heating equipment (transverse induction heating equipment) is that when an alternating current is applied to a coil, a magnetic field is generated inside it. In an electric conductor positioned in the magnetic field, a eddy current has an opposite direction to the current in the coil in a circumferential direction perpendicular to the magnetic flux by an electromagnetic induction effect, and by Joule heating of the eddy current, the electric conductor is heated.
    [00121] Eddy current occurs more strongly on the inner surface of the coil and decreases exponentially towards the inside (this effect is called the skin effect). Thus, as the frequency is lower, the current penetration depth is increased and a uniform heating pattern is obtained in the direction of the thickness, and conversely, as the frequency is higher, the current penetration depth is decreased and a heating pattern that peaks at a surface layer and
    Petition 870190008815, of 01/28/2019, p. 46/93
    36/72 has a little overheating and is obtained in the thickness direction. [00122] Therefore, by the induction heating equipment of the transversal type, the heating of the roughed bar in the direction of rolling and in the direction of the width of the plate can be carried out in a conventional manner, and also in terms of heating in the direction of the thickness of the plate, changing the frequency of the induction heating equipment of the transversal type, the penetration depth is varied and the heating temperature pattern in the direction of the plate thickness is controlled, thus making it possible to achieve uniformity of temperature distributions . Incidentally, induction heating equipment of the changeable type is preferably used in this case, but the frequency can also be changed by adjusting a capacitor.
    [00123] Regarding the control of the heating amount by the induction heating equipment, a plurality of inductors having different frequencies can be arranged and in a distribution of a heating amount for each of the inductors can be given in order to obtain the heating pattern required in the thickness direction. In relation to the control of the amount of heating by the induction heating equipment, an air gap for a material to be heated is changed and thus changing the air gap, the desired frequency and the heating pattern can also be obtained.
    [00124] The maximum height Ry of the steel sheet surface (roughened bar surface) after the finishing lamination is desirably 15 pm (15 pm Ry, l2.5 mm, ln 12.5 mm) or less. This is expensive because the fatigue strength in hot rolled or pickled alo sheet is correlated to the maximum Ry weight of the steel sheet surface as also described in Metal Material Fatigue Design Handbook, edited by The Society of Materials Science, Japan,
    Petition 870190008815, of 01/28/2019, p. 47/93
    37/72 on page 84, for example.
    [00125] To obtain this surface toughness, the condition of an impact pressure P x flow rate L □ 0.003 of a water at high pressure on the surface of the steel sheet is desirably satisfied in the flaking. In addition, the subsequent finishing lamination is desirably carried out in up to five seconds to prevent a scale from being generated again after flaking.
    Second Hot Rolling Mill [00126] After the roughing laminating process (first hot rolling mill) is completed, the finishing laminating process is started as the second hot rolling mill. The time between the end of the roughing lamination process and the beginning of the finishing lamination is desirably set to 150 seconds or less. When the time between the end of the roughing lamination process and the beginning of the finishing lamination process is greater than 150 seconds, the average diameter of the crystal grain is increased to cause a decrease in the vTrs.
    [00127] In the finishing lamination process (second hot lamination), the start temperature of the finishing lamination is adjusted to 1000 ° C or more. When the start temperature of the finishing lamination is less than 1000 ° C, in each pass of the finishing lamination, the temperature of the lamination to be applied to the roughed bar to be laminated is reduced, the reduction is performed at a temperature of non- recrystallization, the texture develops, and so the isotropy deteriorates.
    [00128] Incidentally, the upper limit of the start temperature of the finishing laminate is not particularly limited. However, when it is 1150 ° C or higher, a bubble to be the starting point for a spool-shaped scale defect is likely to occur between the iron base of the steel plate and the carpal surface before it
    Petition 870190008815, of 01/28/2019, p. 48/93
    38/72 finish mines and between passes, and thus the start temperature of the finish laminate is desirably below 1150 ° C.
    [00129] In finishing lamination, the temperature determined by the chemical composition of the steel sheet is set to T1, and in a temperature region of not less than T1 + 30 ° C nor more than T1 + 200 ° C, the lamination at 30% or more is performed on an appeal pass at least once. In addition, in finishing lamination, the total reduction ratios are adjusted to 50% or more.
    [00130] Here, T1 is the temperature calculated by Expression (1) below.
    T1 (° C) = 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr + 100 x Mo + 100 x V ··· (1)
    C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the content of the element (% by mass).
    [00131] T1 itself is obtained empirically. The present inventors learned empirically from experiences that recrystallization in an austenite region of each steel is promoted on the basis of T1.
    [00132] When the ratio of total reduction in the temperature region of not less than T1 + 30 ° C nor greater than T1 + 200 ° C is less than 50%, the rolling tension to be accumulated during hot rolling is not enough and the recrystallization of austenite does not proceed sufficiently. Therefore, the texture develops and the isotropy deteriorates. When the total reduction ratio is 70% or more, sufficient isotropy can be obtained even when variations attributable to the variation in temperature or the like are considered. On the other hand, when the total reduction ratio exceeds 90%, it becomes difficult to obtain the temperature range of T1 + 200 ° C or less due to the generation of heat by the work, and also the lamination load increases to cause the risk that lamination becomes difficult to perform.
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    39/72 [00133] In finishing lamination, to promote uniform recrystallization caused by the release of accumulated tension, lamination at 30% or more is performed in a pass at least once at not less than T1 + 30 ° C or more than T1 + 200 ° C.
    [00134] Incidentally, to promote uniform recrystallization, it is necessary to suppress the amount of work in a region of temperatures from less than T1 + 30 ° C to as small as possible. To achieve this, the reduction ratio less than T1 + 30 ° C is desirably 30% or less. In terms of plate thickness accuracy and plate shape, 10% or less of the reduction ratio is desirable. When isotropy is also obtained, the rate of reduction in the region of temperatures below T1 + 30 ° C is desirable.
    [00135] The finishing lamination is desirably finished at T1 + 30 ° C or more. In hot rolling at less than T1 + 30 ° C, the granulated austenite grains that are recrystallized once are elongated, thereby causing the risk that the isotropy will deteriorate.
    Primary Cooling [00136] In the finishing lamination, after the final reduction to a reduction ratio of 30% or more is performed, the primary cooling is started in such a way that the waiting time period of t seconds satisfies the Expression (2 ) below t 2.5 x t1 ... (2)
    Here, t1 can be obtained by Expression (3) below.
    t1 = 0.001 x ((Tf - T1) x P1 / 100) 2 - 0.109 x ((Tf - T1) x P1 / 100) + 3.1 ... (3) [00137] Here, in Expression (3) above, Tf represents the temperature of the steel bar obtained after the final reduction at a reduction ratio of 30% or more, and P1 represents the reduction ratio of the final reduction to 30% or more.
    [00138] Incidentally, the final reduction to a reduction ratio of
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    40/72
    30% or more indicates the lamination finally performed between the laminations whose reduction ratio becomes 30% or more outside the laminations in a plurality of passes performed on the finishing lamination. For example, when between laminations in a plurality of passes performed on the finishing laminate, the reduction ratio of the lamination performed in the final stage is 30% or more, the lamination performed in the final stage is the final reduction to a reduction ratio of 30% or more. In addition, when between laminations in a plurality of passes performed on the finishing lamination, the reduction ratio of the lamination performed before the final stage is 30% or more and after the lamination performed before the final stage (lamination at a reduction ratio 30% or more), the lamination whose reduction ratio becomes 30% or more is not performed, the lamination performed before the final step (lamination at a reduction ratio of 30% or more) is the final reduction of 30% or more. [00139] In finishing lamination, the waiting period of t seconds until the primary cooling is started after the final reduction at a reduction ratio of 30% or more to be performed greatly affects the austenite grain diameter. That is, it greatly affects an equiaxial grain fraction and the gross grain area ratio of the steel plate.
    [00140] When the waiting time period t seconds exceeds t1 x 2.5, recrystallization is almost complete, but the crystal grains grow significantly and the hardening of the grain advances, and thus the r value and elongation are decreased.
    [00141] The waiting period of t seconds also satisfies Expression (4) below, thus making it possible to suppress preferentially the growth of the crystal grains. Consequently, although recrystallization does not proceed sufficiently, it is possible to sufficiently improve the elongation of the steel sheet and improve and
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    41/72 fatigue property simultaneously.
    t <t1 ... (4) [00142] At the same time, the waiting time period t seconds also satisfies Expression (5) below, so the recrystallization proceeds sufficiently and the crystal orientations are random. Therefore, it is possible to sufficiently improve the elongation of the steel sheet and greatly improve the isotropy simultaneously.
    t1 t t1 x 2.5 ... (5) [00143] The waiting time period t seconds satisfies Expression (5) above, and therefore the mean value of the pole densities of the guidance group {100} <011> a {223} <110> shown in FIG. 1 becomes 2.0 or less and the pole density of the crystal orientation {332} <113> shown in FIG. 2 becomes 3.0 or less. Consequently, the isotropic index becomes 6.0 or more and the uniformity of the sheet thickness and circularity that sufficiently satisfy the property of the part in a state in which the steel sheet remains worked are achieved.
    [00144] Here, as shown in FIG. 4., in a continuous hot rolling line 1, the steel bar (plate) heated to a predetermined temperature in the heating furnace is laminated in a roughing mill 2 and in a finishing mill 3 sequentially to be a hot-rolled steel 4 having a predetermined thickness, and the hot-rolled steel sheet 4 is transported on an exit table 5. In the present invention, the production method in the roughing lamination process (first hot rolling) performed in the roughing mill 2, rolling at a reduction rate of 40% or more is carried out on the steel bar (plate) a time or more in the temperature range of not less than 1000 ° C or greater than 1200 ° C.
    [00145] The roughed bar rolled until a thickness predeter
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    42/72 mined in the roughing mill 2 in this way then undergoes the finishing lamination (it is subjected to the second hot rolling) through a plurality of lamination chairs 6 of the finishing laminator 3 to be the hot rolled steel sheet 4. Then, in finishing laminator 3, lamination at 30% or more is carried out in a pass at least once in the temperature region of not less than the temperature T1 + 30 ° C nor more than T1 + 200 ° C. In addition, in finishing laminator 3; the total reduction ratio becomes 50% or more.
    [00146] In addition, in the finishing lamination process after the final reduction to a reduction ratio of 30% or more is performed, the primary cooling is started in such a way that the waiting time period t seconds satisfies the Expression ( 2) above or one of the expressions (4) or (5) above. The initiation of this primary cooling is carried out by cooling nozzles between the chairs 10 arranged between the respective laminating chairs 6 of the finishing laminator 3, or cooling nozzles 11 arranged on the exit table 5.
    [00147] For example, when the final reduction to a reduction ratio of 30% or more is performed only in a rolling chair 6 arranged in the front stage of the finishing laminator 3 (on the left side of FIG. 4, on the front side lamination) and the lamination whose reduction ratio becomes 30% or more is not performed on the lamination chair 6 arranged in the rear stage of the finishing laminator 3 (on the right side of FIG. 4, on the rear side of the laminator), the start of the primary cooling is performed by the cooling nozzles 11 arranged on the output table 5, and thus a case in which the waiting time period t seconds does not satisfy Expression (2) above or Expressions (4) and (5) above is sometimes triggered. In such a case, the primary cooling is initiated by the
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    43/72 cooling nozzles between the chairs 10 arranged between the respective laminating chairs 6 of the finishing laminator 3.
    [00148] In addition, for example, when the final reduction to a reduction ratio of 30% or more is performed on the laminating chair 6 arranged in the rear stage of the finishing laminator 3 (on the right side of FIG. 4, on the lamination), even when the start of the primary cooling is performed by the cooling nozzles 11 arranged on the output table 5, there is sometimes the case that the waiting time period of t seconds can satisfy Expression (2) above or Expressions (4) and (5) above. In such a case, the primary cooling can also be initiated by the cooling nozzles 11 arranged on the output table 5. It goes without saying that as the performance of the final reduction at a reduction rate of 30% or more is completed, the cooling The primer can also be started by the cooling nozzles between the chairs 10 arranged between the respective laminating chairs 6 of the finishing laminator 3.
    [00149] Then, in this primary cooling, cooling is performed in which at an average cooling rate of 50 ° C / s or more, the temperature change (temperature drop) becomes not less than 40 ° C nor greater than 140 ° C.
    [00150] When the temperature change is less than 40 ° C, the recrystallized austenite grains grow and the low temperature toughness deteriorates. The temperature change is adjusted to 40 ° C or more, thus making it possible to suppress the hardening of the austenite grains. When the temperature change is less than 40 ° C, the effect cannot be achieved. On the other hand, when the temperature change exceeds 140 ° C, recrystallization becomes insufficient to make it difficult to obtain a desired random texture. In addition, the effective ferrite phase for stretching is also not easily obtained
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    44/72 and the hardness of the ferrite phase becomes high, and thus the elongation and local ductility also deteriorate. In addition, when the temperature change is greater than 140 ° C, an error up to / beyond the temperature of the Ar 3 transformation point is likely to be caused. In this case, even through the transformation of recrystallized austenite, as a result of the selection of the edging variant, the texture is formed and consequently the isotropy decreases.
    [00151] When the average cooling rate in the kidney cooling is less than 50 ° C / s, as expected, the recrystallized austenite grains grow and the low temperature toughness deteriorates. The upper limit of the average cooling rate is not determined in particular, but in terms of the shape of the steel sheet, 200 ° C / s or less is considered to be adequate.
    [00152] In addition, to suppress grain growth and obtain more excellent low temperature toughness, a cooling device between passes or the like is desirably used to bring heat generation through the work between the respective finishing laminator chairs to 18 ° C or less.
    [00153] The lamination ratio (reduction ratio) can be obtained by actual performance or by calculating from the lamination load, measuring the thickness of the sheet, or / and the like. The temperature of the steel bar during rolling can be obtained by the actual measurement by a thermometer placed between the chairs, or it can be obtained by simulation considering the heat generation by the work from the line speed, the reduction ratio or / and the like, or can be obtained by both methods.
    [00154] Furthermore, as explained previously, to promote uniform recrystallization, the amount of work in the region of temperatures below T1 + 30 ° C is desirably as small as possible and the rate of reduction in the region of temperatures of
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    45/72 less than T1 + 30 ° C is desirably 30% or less. For example, in case the finishing laminator 3 on the hot rolling line continues 1 shown in FIG. 4, passing through one or two or more of the rolling chairs 6 arranged on the side of the front stage (on the left side of FIG. 4, on the rear side of the lamination), the steel sheet is in the region of temperatures of not less than T1 + 30 ° C nor greater than T1 + 200 ° C, and passing through one or two or more of the lamination chairs 6 arranged on the side of the subsequent rear stage (on the right side of FIG. 4, on the anterior side of the lamination) , the steel sheet is in the region of temperatures of less than T1 + 30 ° C, when the steel sheet passes through one or two or more of the lamination chairs 6 arranged on the side of the subsequent rear stage (on the right side in FIG 4, on the front side of the lamination), even if the reduction is not performed or is performed, the reduction ratio below T1 + 30 ° C is desirably 30% or less in total. When isotropy is also obtained, the reduction ratio in the region of temperatures below T1 + 30 ° C is desirably 0%.
    [00155] In the production method of the present invention, the lamination speed is not limited in particular. However, when the lamination speed on the side of the final chair of the finishing lamination is less than 400 mpm, γ grains grow to be crude, regions where the ferrite can precipitate to obtain ductility are reduced, and thus the ductllity is liable to deteriorate. Although the upper lamination speed limit is not particularly limited, the effect of the present invention can be obtained, but it is real that the lamination speed is 1800 mpm or less due to the restriction of the facilities. Therefore, in the finishing lamination process, the lamination speed is desirably not less than 400 mpm or more than 1800 mpm.
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    46/72 [00156] In addition, within three seconds after the end of the primary cooling, the secondary cooling is performed in which the cooling is performed at an average cooling rate of 15 ° C / s or more. When the time period for the start of the secondary cooling exceeds three seconds, the perlite transformation occurs and the desired microstructure cannot be obtained.
    [00157] When the average cooling rate of the secondary cooling is less than 15 ° C / s, as expected, the perlite transformation occurs and the desired microstructure cannot be obtained. Although the upper limit of the average cooling rate of secondary cooling is not particularly limited, the effect of the present invention can be obtained, but when steel plate distortion due to thermal stress is considered, the average cooling rate is desirably 300 ° C / s or less.
    [00158] The average cooling rate is not less than 15 ° C / s nor more than 50 ° C / s, which is the region that allows stable production. In addition, as will be shown in the examples, the region of 30 ° C / s or less is a region that allows for more stable production.
    [00159] Next, air cooling is performed for 1 to 20 seconds in a temperature region of less than the transformation point Ar3 and the temperature of the transformation point Ar1 or higher. This air cooling is carried out in the region of temperature less than the transformation point Ar3 and the temperature of the transformation point Ar1 or higher (a region of two-phase ferrite-austenite temperatures) to promote the transformation of ferrite. When air cooling is performed for less than a second, the transformation of ferrite in the two-phase region is not sufficient and thus sufficient uniform elongation cannot be achieved, and when air cooling is performed for less than a second, the transformation of ferrite in the two-phase region is not enough and the
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    47/72 yes, sufficient uniform elongation cannot be obtained, and when air cooling is performed for more than 20 seconds, on the other hand, the transformation of the perlite occurs and the desired microstructure cannot be obtained.
    [00160] The temperature region where the air cooling is carried out for 1 to 20 seconds is desirably not less than the temperature of the transformation point Ar1 nor greater than 360 ° C to easily promote the transformation of the ferrite. A retention time period (air cooling time period) for 1 to 20 seconds is desirably for 1 to 10 seconds so as not to greatly decrease productivity.
    [00161] The temperature of the transformation point Ar3 can be easily calculated by the following Calculation expression (a relational expression with the chemical composition), for example. When the Si content (% by mass) is adjusted to [Si], the Cr content (% by mass) is adjusted to [Cr], the Cu content (% by mass) is adjusted to [Cu], the Mo content (% by mass) is set to [Mo], and Ni content (% by mass) is set to [Ni], the temperature of the Ar3 transformation point can be defined by the expression (6) below.
    Ar3 = 910 - 310 x [C] + 25 x [Si] - 80 x [Mneq] ··· (6) [00162] When B is not added, [Mneq] is defined by Expression (7) below.
    [Mneq] = [Mn] + [Cr] + [Cu] + [Mo] + ([Ni] / 2) + 10 ([Nb] 0.02) ··· (7) [00163] When B is added , [Mneq] is defined by Expression (8) below.
    [Mneq] = [Mn] + [Cr] + [Cu] + [Mo] + ([Ni] / 2) + 10 ([Nb] 0.02) + 1 ··· (8) [00164] Subsequently, in a winding process, the winding temperature is set to not less than 450 ° C
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    48/72 nor more than 550 ° C. When the winding temperature is greater than 550 ° C, after winding, hardening in a hard phase occurs and the resistance decreases. On the other hand, when the winding temperature is less than 450 ° C, during cooling after winding, the untransformed austenite is stabilized, and a steel plate product, the retained austenite is contained and martensite is generated, and thus hole expansion capacity is decreased.
    [00165] Incidentally, in order to achieve an improvement in ductility by correcting the shape of the steel sheet and / or introducing the mobile displacement, the skin pass lamination at a rate of reduction of not less than 0.1% or more that 2% is desirably executed after all processes are finished.
    [00166] In addition, after the end of all processes, pickling can also be carried out in order to remove the scale that adheres to the surface of the hot-rolled steel sheet obtained. After stripping, on hot-rolled steel plate, skin pass lamination or cold lamination at a reduction rate of 10% or less can also be performed on-line or off-line. [00167] In the hot-rolled steel sheet of the present invention, a heat treatment can also be carried out in a hot-dip line after casting, after hot rolling, or after cooling, and also in the rolled steel sheet heat treated, surface treatment can also be carried out separately. In the hot-dip line, the coating is performed, and thus the corrosion resistance of the hot-rolled steel sheet is improved.
    [00168] When galvanizing is carried out on the pickled hot-rolled steel plate, after the hot-rolled steel plate is immersed in a galvanizing bath to then be pulled up, a bonding treatment can also be carried out on the plate
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    49/72 hot-rolled steel as needed. By performing the bonding treatment, in addition to improving corrosion resistance, resistance to welding against various welds such as spot welding is improved.
    Example [00169] In the following, examples of the present invention will be explained, but the conditions of the examples are examples of conditions employed to confirm the applicability and effects of the present invention, and the present invention is not limited to those examples of conditions. The present invention can employ several conditions as long as the objective of the present invention is achieved without departing from the spirit of the invention.
    Example 1 [00170] Ingot bars A to P having the chemical compositions shown in Table 1 were each melted in a steel converter in a secondary refining process to be subjected to continuous casting and then were transferred directly or reheated to be subjected to roughing lamination. In the subsequent finishing lamination, they were each reduced to a plate thickness of 2.0 to 3.6 mm and were subjected to cooling by cooling between chairs of a finishing laminator or on an exit table and then were coiled, and hot rolled steel sheets were produced. Production conditions are shown in Table 2.
    [00171] Incidentally, the balance of the chemical composition shown in table 1 is composed of Fe and the inevitable impurities, and each value underlined in Table 1 and Table 2 indicates that the value is outside the preferable range of the present invention.
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    Table 1
    Steel Chemical composition (% by mass)Ç Si Mn P s Al N You Nb Ass Ni Mo V Cr B Mg Here Rem Others Grades THE 0.070 1.20 2.51 0.016 0.003 0.023 0.0026 0.144 0.020 0.00 0.00 0.00 0.00 0.00 0.0014 0.0022 0.0000 0.0000 0.0000 Steel Inv. B 0.071 1.17 2.46 0.011 0.002 0.029 0.0040 0.179 0.017 0.00 0.00 0.00 0.00 0.00 0.0000 0.0000 0.0024 0.0000 0.0000 Steel Inv. Ç 0.067 0.14 1.98 0.007 0.001 0.011 0.0046 0.091 0.038 0.00 0.00 0.00 0.00 0.00 0.0000 0.0019 0.0000 0.0000 0.0000 Steel comp. D 0.036 0.94 1.34 0.008 0.001 0.020 0.0028 0.126 0.041 0.00 0.00 0.00 0.00 0.00 0.0000 0.0000 0.0000 0.0000 0.0000 Steel comp. AND 0.043 0.98 0.98 0.010 0.001 0.036 0.0034 0.099 0.000 0.00 0.00 0.00 0.00 0.00 0.0009 0.0000 0.0021 0.0000 0.0000 Steel comp. F 0.042 0.73 1.04 0.011 0.001 0.024 0.0041 0.035 0.019 0.00 0.00 0.00 0.00 0.00 0.0000 0.0000 0.0000 0.0018 0.0000 Steel comp. G 0.089 0.91 1.20 0.008 0.001 0.033 0.0038 0.000 0.000 0.00 0.00 0.00 0.00 0.00 0.0000 0.0000 0.0022 0.0000 0.0000 Steel Inv. H 0.180 0.03 0.72 0.017 0.004 0.011 0.0035 0.025 0.000 0.00 0.00 0.00 0.00 0.00 0.0000 0.0000 0.0000 0.0000 0.0000 Steel Inv. I 0.022 0.05 1.12 0.009 0.004 0.025 0.0047 0.102 0.000 0.00 0.00 0.00 0.00 0.00 0.0011 0.0000 0.0000 0.0020 0.0000 Steel comp. J 0.004 0.12 1.61 0.080 0.002 0.041 0.0027 0.025 0.025 0.00 0.00 0.00 0.00 0.00 0.0011 0.0000 0.0000 0.0020 0.0000 Steel comp. K 0.230 0.18 0.74 0.017 0.002 0.005 0.0051 0.000 0.000 0.00 0.00 0.00 0.00 0.00 0.0000 0.0000 0.0000 0.0020 0.0000 Steel comp. L 0.091 0.02 1.50 0.007 0.001 0.011 0.0046 0.026 0.000 0.06 0.03 0.00 0.00 0.00 0.0000 0.0000 0.0000 0.0000 0.0000 Steel Inv. M 0.100 0.03 1.45 0.008 0.001 0.020 0.0028 0.020 0.000 0.00 0.03 0.00 0.00 0.00 0.0000 0.0000 0.0000 0.0000 0.0000 Steel Inv. N 0.081 0.01 1.51 0.010 0.001 0.036 0.0034 0.022 0.000 0.00 0.00 0.48 0.00 0.00 0.0010 0.0000 0.0000 0.0000 0.0000 Steel Inv. O 0.090 0.02 1.55 0.011 0.001 0.024 0.0041 0.024 0.011 0.00 0.00 0.00 0.10 0.00 0.0000 0.0000 0.0000 0.0000 0.0000 Steel Inv. P 0.087 0.02 1.52 0.008 0.001 0.033 0.0038 0.023 0.000 0.00 0.00 0.00 0.00 0.91 0.0000 0.0000 0.0000 0.0000 0.0000 Steel Inv. Q 0.084 0.02 1.49 0.007 0.001 0.031 0.0039 0.000 0.000 0.00 0.00 0.00 0.00 0.00 0.0015 0.0000 0.0000 0.0000 0.0000 Steel Inv.
    50/72
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    Table 2
    Steel No. Metallurgical factors Production conditions Cond. of temp. heating Cond. rough rolling mill Finishing lamination conditions Component Temp. the point. transf. Ar3(° C) T1 (° C) Temp. heating(° C) Retention period(min) Number of times of reduction to 1000 ° C ormore than 40% or more Reduction ratio at 1000 ° C or more Period oftime forlam start. Termination(s) Total reduction ratio (%) Tf(° C) P1(%) Temp. maximum working heat generation(° C) Ex. Inv. 1 THE 859 895 1260 45 2 45/45 60 90 990 40 15 Ex. Inv. 2 B 723 903 1260 45 2 45/45 60 90 990 40 12 Ex. Comp. 3 Ç 720 887 1230 45 3 40/40/40 60 93 980 35 15 Ex. Comp. 4 D 798 896 1200 60 3 40/40/40 90 89 990 32 12 Ex. Comp. 5 AND 779 875 1200 60 3 40/40/40 90 89 970 32 12 Ex. Comp. 6 F 833 866 1200 60 3 40/40/40 90 89 960 32 12 Ex. Inv. 7 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 8 G 825 851 1200 60 0 25/25/25 90 89 950 32 12 Ex. Inv. 9 G 825 851 1200 60 3 40/40/40 180 89 950 32 12 Ex. Comp. 10 G 825 851 1200 60 3 40/40/40 90 45 950 32 12
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    Continuation...
    Steel No. Cooling condition t1(s) t 1x2.5 Period of time to start primary cooling (s) t / t1 Primary cooling rate(° C / s) Temperature change in the cooler. primary(° C) Secondary cooling time period (s) Secondary cooling rate (° C / s) Temp. Region air cooling(° C) Temp. in the cooler, air(s) Temp. coiling(° C) Ex. Inv. 1 0.40 1.00 1.0 2.5 135 90 1.5 30 660 2 470 Ex. Inv. 2 0.51 1.28 1.0 2.0 60 90 2.5 30 660 8 470 Ex. Comp. 3 0.62 1.55 0.8 1.3 65 110 1.0 40 680 5 470 Ex. Comp. 4 0.73 1.83 0.9 1.2 60 70 1.6 25 680 5 470 Ex. Comp. 5 0.71 1.79 0.9 1.3 60 70 1.6 25 670 2 470 Ex. Comp. 6 0.72 1.81 0.9 1.2 60 70 1.6 25 690 2 470 Ex. Inv. 7 0.65 1.63 0.9 1.4 45 70 1.6 25 700 4 500 Ex. Comp. 8 0.65 1.63 0.9 1.4 60 70 1.6 25 700 4 500 Ex. Inv. 9 0.65 1.63 0.9 1.4 60 70 1.6 25 700 4 500 Ex. Comp. 10 0.65 1.63 0.9 1.4 60 70 1.6 25 700 4 500
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    Continuation...
    Steel No. Metallurgical factors Production conditions Cond. of temp. heating Cond. rough rolling mill Finishing lamination conditions Component Temp. the point. transf.Ara (° C) T1(° C) Temp. heating (° C) Periodretention time(min) Number of times of reduction to 1000 ° C ormore than 40% or more Reduction ratio at 1000 ° C or more Time period To start lam. Finishing (s) Total reduction ratio (%) Tf(° C) P1(%) Temp. maximum working heat generation(° C) Ex. Comp. 11 G 825 851 1200 60 3 40/40/40 90 89 850 32 12 Ex. Comp. 12 G 825 851 1200 60 3 40/40/40 90 89 1050 32 12 Ex. Comp. 13 G 825 851 1200 60 3 40/40/40 90 89 950 29 12 Ex. Comp. 14 G 825 851 1200 60 3 40/40/40 90 89 950 32 25 Ex. Comp. 15 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 16 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 17 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 18 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 19 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 20 G 825 851 1200 60 3 40/40/40 90 89 950 32 12
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    Continuation...
    Steel No. Cooling condition t1(s) t 1x2.5 Period of time to start primary cooling (s) t / t1 Primary cooling rate(° C / s) Temperature change in the cooler. primary(° C) Secondary cooling time period (s) Secondary cooling rate (° C / s) Temp. Region air cooling(° C) Temp. in the cooler, air(s) Temp. coiling(° C) Ex. Comp. 11 3.14 7.85 0.9 0.3 60 70 1.6 25 700 4 500 Ex. Comp. 12 0.21 0.53 0.9 4.2 60 70 1.6 25 700 4 500 Ex. Comp. 13 - - 0.9 - 60 70 1.6 25 700 4 500 Ex. Comp. 14 0.65 1.63 0.9 1.4 60 70 1.6 25 700 4 500 Ex. Comp. 15 0.65 1.63 2.0 31 60 70 1.6 25 700 4 500 Ex. Comp. 16 0.65 1.63 0.9 1.4 5 70 1.6 25 700 4 500 Ex. Comp. 17 0.65 1.63 0.9 1.4 60 20 1.6 25 700 4 500 Ex. Comp. 18 0.65 1.63 0.9 1.4 60 200 1.6 25 700 4 500 Ex. Comp. 19 0.65 1.63 0.9 1.4 60 70 10.0 25 700 4 500 Ex. Comp. 20 0.65 1.63 0.9 1.4 60 70 1.6 5 700 4 500
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    Continuation...
    Steel No. Metallurgical factors Production conditions Cond. of temp. heating Cond. rough rolling mill Finishing lamination conditions Component Temp. the point. transf.Ara (° C) T1(° C) Temp. heating(° C) Periodretention time(min) Number of times of reduction to 1000 ° C ormore than 40% or more Reduction ratio at 1000 ° C or more Period oftime forlam start. Termination(s) Total reduction ratio (%) Tf(° C) P1(%) Temp. maximum working heat generation(° C) Ex. Comp. 21 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 22 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 23 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 24 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 25 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 26 G 825 851 1200 60 3 40/40/40 90 89 950 32 12 Ex. Inv. 27 H 813 858 1200 60 1 50 90 89 980 35 15 Ex. Comp. 28 I 751 876 1200 60 3 40/40/40 90 89 960 32 12 Ex. Comp. 29 J 699 865 1200 60 3 40/40/40 90 89 950 32 12 Ex. Comp. 30 K 800 852 1200 60 3 40/40/40 90 89 940 32 12
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    Continuation...
    Steel No. Cooling condition t1(s) t 1x2.5 Period of time to start primary cooling (s) t / t1 Primary cooling rate(° C / s) Temperature change in the cooler. primary(° C) Secondary cooling time period (s) Secondary cooling rate (° C / s) Temp. Region air cooling(° C) Temp. in the cooler, air(s) Temp. coiling(° C) Ex. Comp. 21 0.65 1.63 0.9 1.4 60 70 1.6 25 840 4 500 Ex. Comp. 22 0.65 1.63 0.9 1.4 60 70 1.6 25 580 4 500 Ex. Comp. 23 0.65 1.63 0.9 1.4 60 70 1.6 25 500 Ex. Comp. 24 0.65 1.63 0.9 1.4 60 70 1.6 25 700 28 500 Ex. Comp. 25 0.65 1.63 0.9 1.4 60 70 1.6 25 700 4 100 Ex. Comp. 26 0.65 1.63 0.9 1.4 60 70 1.6 25 700 4 650 Ex. Inv. 27 0.27 0.66 0.6 2.3 65 110 1.0 20 670 2 530 Ex. Comp. 28 0.89 2.22 0.9 1.0 60 70 1.0 20 670 2 530 Ex. Comp. 29 0.88 2.19 0.9 1.0 60 70 1.0 20 670 2 530 Ex. Comp. 30 0.82 2.05 0.9 1.1 60 70 1.0 20 670 2 530
    56/72
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    Continuation...
    Steel No. Metallurgical factors Production conditions Cond. of temp. heating Cond. rough rolling mill Finishing lamination conditions Component Temp. the point. transf. Ar3(° C) T1(° C) Temp. heating(° C) Periodretention time(min) Number of times of reduction to 1000 ° C ormore than 40% or more Reduction ratio at 1000 ° C or more Period oftime forlam start. Termination(s) Total reduction ratio (%) Tf(° C) P1(%) Temp. maximum working heat generation(° C) Ex. Inv. 31 L 772 858 1180 90 3 40/40/40 90 89 960 32 12 Ex. Inv. 32 M 779 856 1180 90 3 40/40/40 90 89 950 32 12 Ex. Inv. 33 N 662 905 1180 90 3 40/40/40 90 89 940 32 12 Ex. Inv. 34 O 766 871 1180 90 3 40/40/40 90 89 950 32 12 Ex. Inv. 35 P 705 866 1180 90 3 40/40/40 90 89 940 32 12 Ex. Inv. 36 Q 701 851 1180 90 3 40/40/40 90 89 940 32 12
    57/72
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    Continuation...
    Steel No. Cooling condition t1(s) t 1x2.5 Period of time to start primary cooling (s) t / t1 Primary cooling rate(° C / s) Temperature change in the cooler. primary(° C) Secondary cooling time period (s) Secondary cooling rate (° C / s) Temp. Region air cooling(° C) Temp. in the cooler, air(s) Temp. coiling(° C) Ex. Inv. 31 0.61 1.52 0.9 1.5 60 70 1.0 20 670 10 470 Ex. Inv. 32 0.73 1.83 0.9 1.2 60 70 1.0 20 670 10 470 Ex. Inv. 33 2.00 5.00 0.9 0.5 60 70 1.0 20 670 10 470 Ex. Inv. 34 0.99 2.47 0.9 0.9 60 70 1.0 20 670 10 470 Ex. Inv. 35 1.08 2.71 0.9 0.8 60 70 1.0 20 670 10 470 Ex. Inv. 36 0.81 2.03 0.7 0.9 60 70 1.0 20 670 10 470
    58/72
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    59/72 [00172] In Table 2, COMPONENT means the steel symbol shown in Table 1. TRANSFORMATION POINT TEMPERATURE Ar3 is the temperature calculated by Expressions (6), (7) and (8) above. T1 indicates the temperature calculated by Expression (1) above. t1 indicates the temperature calculated by Expression (2) above.
    [00173] HEATING TEMPERATURE is the heating temperature in the heating process. RETENTION TIME PERIOD is the period of retention time at a predetermined heating temperature in the heating process.
    [00174] NUMBER OF REDUCTION TIMES AT 1000 ° C OR MORE 40% OR MORE is the number of times reduction at a reduction rate of 40% or more in the temperature range of not less than 1000 ° C or more than 1200 ° C for roughing rolling. REDUCTION EASY AT 1000 ° C OR MORE is each reduction ratio (reduction pass program) in the temperature range of not less than 1000 ° C or more than 1200 ° C in the roughing lamination. It is indicated that in the Example of the present invention (steel no. 1), for example, the reduction to a reduction ratio of 45% was performed twice. In addition, it is indicated that in a Comparative Example (steel # 3, for example, the reduction to a reduction ratio of 40% was performed three times. TIME PERIOD FOR START OF FINISHING LAMINATION is the period of time since the finish of the roughing lamination until the start of the finishing lamination process TOTAL REDUCTION REASON is the reduction ratio in the finishing lamination process.
    [00175] Tf indicates the temperature after the final reduction to 30% or more in the finishing lamination. P1 indicates the reduction ratio of the final reduction to 30% or more in the finishing lamination. However, in the Comparative Example (steel n ° 13), the highest value among the reduction ratios of the respective lamination chairs in the steel lamination
    Petition 870190008815, of 01/28/2019, p. 70/93
    60/72 was 29%. In the Comparative Example (steel n ° 13), the temperature after reduction to that reduction ratio of 29% was adjusted to Tf. MAXIMUM WORK HEAT GENERATION is the maximum temperature increased by the heat generated by the work between the respective finishing passes (between the respective laminating chairs 6).
    [00176] TIME PERIOD TO START PRIMARY COOLING is the period of time from after the end of the final reduction to 30% or more in the finishing lamination until the start of the primary cooling. PRIMARY COOLING RATE is the average cooling rate at which the cooling corresponding to the amount of temperature change in the primary cooling is completed. TEMPERATURE CHANGE IN PRIMARY COOLING is the difference between the start temperature and the end temperature of the primary cooling.
    [00177] TIME PERIOD FOR STARTING SECONDARY COOLING is the period of time from the end of the primary cooling to the start of the secondary cooling. SECONDARY COOLING RATE is the average cooling rate from the start of the secondary cooling to winding, after which the retention time period (air cooling time period) is removed. COOLING TEMPERATURE REGION AIR is the temperature region where retention (air cooling) is performed from the end of the secondary cooling to winding. RETENTION TIME PERIOD ON AIR COOLING is the period of retention time when retention (air cooling) is performed. COILING TEMPERATURE is the temperature at which the steel sheet is wound by a winder in the winding process.
    [00178] Furthermore, in relation to the Example of the present invention
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    61/72 No 7 and No Comparative Examples 13 and 10, the relationship between the reduction ratio for each rolling chair F1 F7 of finish rolling and the temperature region is shown in Table 3.
    Table 3
    F1 F2 F3 F4 F5 F6 F7 Total reduction ratio at T1 +30 ° C or more Ex. Inv. 38.9 37.8 37.4 34.7 31.9 0.0 0.0 89 Ex. Comp. 29.0 28.8 28.8 27.5 26.6 25.9 25.6 89 Ex. Comp. 0.0 19.1 32.4 32.3 32.1 34.2 36.0 45
    [00179] In the Example of the present invention of steel No. 7, the steel plate was in the region of temperatures of not less than T1 + 30 ° C nor more than T1 + 200 ° C in the lamination chairs F1 to F5, and it was in the region of temperatures of less than T1 + 30 ° C in chair F6 and after it. In the Example of the present invention No. 7, in lamination chairs F1 to F5, the reduction to a reduction ratio of 30% or more was performed five times in the temperature region of not less than T1 + 30 ° C nor more than T1 + 200 ° C, and after the F6 lamination chair, no reduction was carried out practically in the region of temperatures below T1 + 30 ° C. The steel sheet was only passed through the F6 and F7 rolling chairs. As also shown in Table 2, in the Example of the present invention of steel No. 7, the total reduction ratio in the temperature region of not less than T1 + 30 ° C nor more than T1 + 200 ° C is 89%.
    [00180] Incidentally, the reduction ratio in each of the F1 to F7 lamination chairs is obtained by the change in the thickness of the plate between the entrance and the exit side of each of the F1 to F7 lamination chairs. In contrast, the ratio of total reduction in the temperature region of not less than T1 + 30 ° C or more than T1 + 200 ° C is obtained by changing the thickness of the sheet before and after the lamination passes carried out in the region of finishing lamination temperatures. As shown in
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    62/72
    Example of the present invention No. 7, for example, the ratio of total reduction in the temperature region obtained by the change in the thickness of the sheet before and after all the lamination passes carried out in the lamination chairs F1 to F5. That is, it is obtained by changing between the thickness of the plate on the entrance side of the lamination chair F1 and the thickness of the plate on the exit side of the lamination chair F5.
    [00181] On the other hand, in the Comparative Example of steel n ° 13, the steel sheet was in the region of temperatures of not less than T1 + 30 ° C nor more than T1 + 200 ° C in all rolling chairs F1 a F7 in finishing lamination. As also shown in Table 2, in the Comparative Example of steel No. 13, the total reduction ratio in the temperature region of not less than T1 + 30 ° C or more than T1 + 200 ° C is 89%. However, in the Comparative Example of steel No. 13, in each of the rolling chairs F1 to F7, the reduction to a reduction ratio of 30% or more is not performed.
    [00182] In addition, in the Comparative Example of steel n ° 10, the steel sheet was in the temperature region of not less than T1 + 30 ° C nor more than T1 + 200 ° C in rolling chairs F1 to F3, and the steel plate was in the region of temperatures of less than T1 + 30 ° C in the rolling chair F4 and after it. In the Comparative Example of steel No. 10, in rolling chairs F1 to F3 the reduction to a reduction ratio of 30% or more was performed three times in the temperature region of not less than T1 + 30 ° C or more than T1 + 200 ° C, and in addition, also in the region of temperatures of less than T1 + 30 ° C in the lamination chair F4 and after it, the reduction to a reduction ratio of 30% or more Fo performed four times. As also shown in Table 2, in the Comparative Example for steel No. 10, the total reduction ratio in the temperature region of not less than T1 + 30 ° C or more than T1 + 200 ° C is 45%.
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    63/72 [00183] The methods for evaluating the hot rolled steel sheet obtained are the same methods previously described. The results of the assessment are shown in Table 3.
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    Table 4
    Steeln ° Microstructure Mechanical properties Traction test Isotro-sink Hole expansion Folding capacity Tenaci-dade Structural fraction Average diameter of the crystal grain(pm) Average value of pole densities of the {100} guidance group<011> ~ {223} <110> Pole density of the orientation ofcrystal{332} <113> YP(MPa) TS(MPa) El(%) 1 / | Dr | λ(%) Minimum bending radius vTrs(° C) Ex. Inv. 1 Zw + 8% F 7.5 1.7 2.5 906 998 15 12.5 71 0.6 -58 Ex. Inv. 2 Zw + 6% F 8.0 1.7 2.5 857 1015 14 12.5 75 0.5 -48 Ex. Comp. 3 Zw 8.0 1.8 2.6 677 744 11 9.2 71 0.6 -48 Ex. Comp. 4 Zw 7.0 1.7 2.5 700 761 10 12.5 70 0.8 -68 Ex. Comp. 5 Zw 9.0 2.0 2.9 716 770 9 6.5 70 0.8 -31 Ex. Comp. 6 Zw + 36% F 8.0 2.0 2.9 412 588 28 6.5 68 11 -48 Ex. Inv. 7 Zw + 32% F 9.5 2.0 2.9 475 577 30 6.5 131 0.2 -25 Ex. Comp. 8 Zw + 28% F 10.5 1.7 2.5 484 580 28 12.5 125 0.1 -11 Ex. Inv. 9 Zw + 30% F 10.0 3.1 4.2 490 588 27 3.8 123 0.1 -20 Ex. Comp. 10 Zw + 34% F 7.0 42 5.0 482 581 28 3.2 88 0.2 -68 Ex. Comp. 11 Zw + 33% F 4.5 5.1 5.5 475 575 28 3.1 87 0.2 -125 Ex. Comp. 12 Zw + 26% F 11.0 1.7 2.5 458 560 29 12.5 132 0.1 -5 Ex. Comp. 13 Zw + 31% F 6.5 5.3 56 477 577 28 3.0 85 0.1 -80
    64/72
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    Continuation...
    Steeln ° Microstructure Mechanical properties Traction test Isotro-sink Hole expansion Folding capacity Tenaci-dade Structural fraction Average diameter of the crystal grain(pm) Average value of pole densities in the guidance group{100} <011> ~ {223} <110> Pole density of the orientation ofcrystal{332} <113> YP(MPa) TS(MPa) El(%) 1 / | Dr | λ(%) Minimum bending radius vTrs(° C) Ex. Comp. 14 Zw + 35% F 10.5 1.7 2.5 480 571 28 12.5 136 0.2 -17 Ex. Comp. 15 Zw + 34% F 12.0 1.7 2.5 478 585 26 12.5 135 0.2 6 Ex. Comp. 16 Zw + 33% F 11.5 1.8 2.6 481 579 27 9.2 130 0.1 0 Ex. Comp. 17 Zw + 34% F 10.5 1.8 2.6 471 577 27 9.2 133 0.2 -17 Ex. Comp. 18 Zw + 33% F 6.5 54 57 468 566 28 3.0 89 0.2 -80 Ex. Comp. 19 P + 44% F 8.5 1.9 2.8 420 521 24 7.5 67 14 -40 Ex. Comp. 20 P + 38% F 8.0 2.0 2.9 418 520 25 6.5 65 17 -48 Ex. Comp. 21 P + 45% F 8.5 2.0 2.9 409 510 26 6.5 66 18 -40 Ex. Comp. 22 Zw 8.0 2.0 2.9 581 644 15 6.5 76 0.9 -48 Ex. Comp. 23 Zw 8.5 2.0 2.9 601 650 14 6.5 75 0.8 -40 Ex. Comp. 24 P + 47% F 8.5 2.0 2.9 390 495 27 6.5 69 16 -40 Ex. Comp. 25 56% F + M 8.5 2.0 2.9 370 622 28 6.5 41 21 -40 Ex. Comp. 26 P + 37% F 8.5 2.0 2.9 400 503 26 6.5 69 18 -40
    65/72
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    Continuation...
    Steeln ° Microstructure Mechanical properties Traction test Isotropy Hole expansion Folding capacityment Tenacity Structural fraction Average diameter of the crystal grain(pm) Average value of pole densities in the guidance group{100} <011> ~ {223}<110> Pole density of crystal orientation {332} <113> YP(MPa) TS(MPa) El(%) 1 / | Dr | λ(%) Minimum bending radiusment vTrs(° C) Ex. Inv. 27 Zw + 15% F 8.0 1.8 2.6 548 655 26 9.2 141 0.1 -48 Ex. Comp. 28 67% F + Zw 8.5 2.0 2.9 396 522 30 6.5 122 11 -40 Ex. Comp. 29 F 11.0 2.0 2.9 355 462 35 6.5 140 0.1 -5 Ex. Comp. 30 Zw 9.5 2.6 3.7 986 1126 5 4.3 22 0.8 -24 Ex. Inv. 31 Zw + 8% F 6.5 2.0 2.9 588 711 24 6.5 105 0.1 -80 Ex. Inv. 32 Zw + 11% F 7.5 1.9 2.8 570 702 25 7.5 97 0.08 -58 Ex. Inv. 33 Zw + 9% F 6.0 3.9 2.8 592 720 24 4.8 101 0.1 -93 Ex. Inv. 34 Zw + 17% F 4.0 3.6 2.6 585 700 25 4.6 96 0.07 -127 Ex. Inv. 35 Zw + 14% F 6.5 3.7 2.6 578 695 25 4.7 93 0.1 -80 Ex. Inv. 36 Zw + 14% F 6.5 3.3 2.8 603 732 23 4.3 91 0.1 -80
    66/72
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    67/72 [00184] STRUCTURAL FRACTION is the area fraction of each structure measured by a method of counting points from an optical microscope structure. AVERAGE DIAMETER OF CRYSTAL GRAIN is the average diameter of the crystal grain measured by EBSPOIM®.
    [00185] AVERAGE VALUE OF X-RAY RANDOM DENSITIES OF THE ORIENTATION GROUP {100} <011> The {223} <110> is the pole density of the {100} <011> to {223} <110> orientation group to the laminated plane. POLE DENSITY OF THE CRYSTAL ORIENTATION {332} <113> is the pole density of the crystal orientation {332} <113> parallel to the laminated plane.
    [00186] TENSION TEST indicates the result obtained after the tensile test performed in the C direction on a JIS specimen No. 5. YP indicates the yield strength, TS indicates the yield strength limit, and EL indicates the elongation .
    [00187] ISOTROPY indicates the inverse humerus of | Ar | as an index. HOLE EXPANSION λ indicates the result obtained by the hole expansion test method described in JFS T 1001-1996. FOLDING CAPACITY (MINIMUM FOLDING RADIUS) indicates the result obtained by performing a test using a No. 1 specimen (tx 40 mm W x 80 mm L), at a press template speed of 0.1 m / s, according to the press folding method (cylinder folding method) described in JIS Z 2248. YP □ 320 MPa, Ts □ 540 MPa, E1 □ 18%, λ □ 70%, and bending radius minimum 1 mm were accepted.
    [00188] Incidentally, the length L between support points is L = 2r + 3t, where the thickness of the plate is adjusted to t (mm) and the internal radius of one end of the pressing template is adjusted to r (mm).
    [00189] In this method, the folding angle was adjusted to
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    68/72
    170 °, and subsequently an interposed object having a thickness twice the radius of the pressing template was used, the specimen was pressed against the interposed object to be wrapped around it, and with a 180 ° bending angle , a fracture on the outer side of the folded portion was observed visually.
    [00190] MINIMUM BENDING RADIUS is the one that the test is performed by decreasing the internal radius r (mm) until fracture occurs and the internal radius r (mm) that does not cause fracture is divided by the thickness of the plate t (mm) to be made dimensionless by r / t. MINIMUM FOLDING RADIUS becomes the smallest in the case of close contact bending that is performed without the interposed object, and in this case, the MINIMUM FOLDING RADIUS is zero. Incidentally, the folding direction was set to 45 ° from the rolling direction. TENACITY is indicated by the transition temperature obtained by a Charpy test with V sub-size notch.
    [00191] The examples of the invention correspond to the nine examples of steels 1, 2, 7, 27, and 31 to 35. In these examples of steels of the invention, the high strength steel plate in which the texture of the steel plate that has the required chemical composition is obtained, the mean value of the pole densities of the orientation group {100} <011> to {223} <110> of the plate plane at a plate thickness of 5/8 to 3/8 from the steel sheet surface is at least 4.0 or less, the pole density of the {332} <113> crystal orientation is 4.8 or less, and the average diameter of the crystal grain at the center of the sheet thickness is 9 mm or less. The microstructure is composed of proeutectoid ferrite in a structural fraction of 35% or less in the center of the sheet thickness and the transformation phase at low temperature, and a tensile strength of the class of 540 MPa or more is obtained.
    [00192] Comparative examples of a different steel sheet
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    69/72 of the examples described above fall outside the range of the present invention for the following reasons.
    [00193] Regarding Steels numbers 3 to 5, the C content is outside the range of the present invention, and so the microstructure is outside the range of the present invention and the elongation is poor. In relation to steel No. 6, the C content is outside the range of the present invention and thus the microstructure is outside the present invention and the folding capacity is poor.
    [00194] In relation to steel No. 8, the number of times the reduction at 1000 ° C or more by 35% or more in the roughing lamination is outside the range of the present invention and thus the average diameter of the crystal grain is outside of the range of the present invention and the toughness is poor. With regard to steel No. 9, the period of time until the start of the finishing lamination is long, the average diameter of the crystal grain is outside the range of the present invention and the toughness is poor.
    [00195] Regarding steel no. 10, the mean value of the pole densities of the {100} <011> to {223} <110> orientation group and the polar density of the {332} <113> crystal orientation are both outside the range of the present invention and the isotropy is low.
    [00196] In relation to steel n ° 11, the value of Tf is outside the range of the present invention, and thus the average value of the pole densities of the {100} <011> to {223} <110> and a pole density of the {332} <113> crystal orientation are both outside the range of the present invention and the isotropy is low.
    [00197] Regarding steel No. 12, the Tf value is outside the range of the present invention, and so the average diameter of the crystal grain is outside the range of the present invention and the toughness is poor. In relation to steel No. 13, the value of P1 is outside the range of the present invention and in each lamination chair F1 to F7 in the finishing lamination, the reduction to a reduction ratio of 30% or more has not been performed,
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    70/72 and thus the mean value of the pole densities of the {100} <011> to {223} <110> orientation group and the polar density of the {332} <113> crystal orientation are both outside the range of the present invention and isotropy is low.
    [00198] Regarding steel No. 14, the maximum working heat generation temperature is outside the range of the present invention, and thus the average diameter of the crystal grain is outside the range of the present invention and the toughness is poor. With regard to steel No. 15, the time period for primary cooling is outside the range of the present invention, and so the average diameter of the crystal grain is outside the range of the present invention and the toughness is poor. With regard to steel No. 16, the primary cooling rate is outside the range of the present invention, and thus the average crystal grain diameter is outside the range of the present invention and the toughness is poor.
    [00199] In relation to steel n ° 17, the temperature change of the primary cooling is outside the range of the present invention, and thus the average diameter of the crystal grain is outside the range of the present invention and the tenacity is poor. to steel n ° 18, the temperature change in the primary cooling is outside the range of the present invention and thus the mean pole density value of the {100} <011> to {223} <110> orientation group and the pole density of the crystal orientation {332} <113> are both outside the range of the present invention and the isotropy is low.
    [00200] In relation to steel n ° 19, the period of time until secondary cooling is outside the range of the present invention, and so the microstructure is outside the range of the present invention, the resistance is low, and the bending capacity is poor. In relation to steel No. 20, the secondary cooling rate is outside the range of the present invention, and so the microstructure is outside the range of the present invention, the resistance is low, and the bending capacity is poor.
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    71/72 [00201] In relation to steel No. 21, the temperature region of the air cooling is outside the range of the present invention and thus the microstructure is outside the range of the present invention, the resistance is low and the bending capacity is poor.
    [00202] Regarding steel No. 22, the air-cooling temperature region is outside the range of the hot-rolled steel sheet production method of the present invention, and so the microstructure is outside the range of the present invention, and the stretch is poor. In relation to steel No. 23, the retention time period in the air cooling temperature is outside the range of the present invention, and so the microstructure is outside the range of the present invention and the elongation is poor. In relation to steel No. 24, the retention time period at the air-cooling temperature is outside the range of the present invention, and so the microstructure is outside the range of the present invention, the resistance is low and the bending capacity is poor.
    [00203] In relation to paragraph 25, the winding temperature is outside the range of the present invention, and thus the microstructure is outside the range of the present invention and the folding capacity is poor. With respect to No. 26, the winding temperature is outside the range of the present invention, and so the microstructure is outside the range of the present invention, the resistance is low and the bending capacity is poor.
    [00204] Regarding steel No. 28, the C content is outside the range of the present invention, and so the microstructure is outside the range of the present invention, the resistance is low and the bending capacity is poor. In relation to steel No. 29, the C content is outside the range of the present invention, and so the microstructure is outside the range of the present invention, the resistance is low and the bending capacity is poor. In relation to steel No. 30, the C content is outside the range of the present invention, and so the microstructure is outside the range of the present
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    72/72 te invention and stretching is poor.
    Industrial Applicability [00205] As previously described, according to the present invention, it is possible to easily provide a steel sheet applicable to a member that needs work capacity, hole expansion capacity, folding capacity, strict thickness uniformity plate and circularity after work, and low temperature toughness (an internal plate element, a structural element, a lower element, a car element such as a transmission, and elements for shipbuilding, bridge construction, marine structures, pressure vessels, pipes, and machine parts, etc.). In addition, according to the present invention, it is possible to produce a high-strength steel sheet having excellent toughness at low temperature and a grade of 540 MPa or more in a cheap and stable manner. Thus, the present invention is an invention that has a high industrial value.
    Explanation of the Codes continuous hot rolling line roughing laminator finishing laminator hot rolled steel plate exit table lamination chair cooling nozzle between chairs cooling nozzle 11
    权利要求:
    Claims (7)
    [1]
    1. High-strength hot-rolled steel sheet containing bainite having an isotropic working capacity, characterized by the fact that it consists of:
    in mass%,
    C: more than 0.07 to 0.2%;
    Si: 0.001 to 2.5%;
    Mn: 0.01 to 4%;
    P: 0.15% or less (not including 0%);
    S: 0.03% or less (not including 0%);
    N: 0.01% or less (not including 0%);
    Al: 0.001 to 2%; and optionally one type or two or more types of, in mass%,
    Ti: 0.015 to 0.18%,
    Nb: 0.005 to 0.06%,
    Cu: 0.02 to 1.2%,
    Ni: 0.01 to 0.6%,
    Mo: 0.01 to 1%,
    V: 0.01 to 0.2%, and
    Cr: 0.01 to 2%.
    Mg: 0.0005 to 0.01%,
    Ca: 0.0005 to 0.01%,
    REM: 0.0005 to 0.1%,
    B: 0.0002 to 0.002%; and the balance being composed of Fe and the inevitable impurities, in which the average value of the pole densities of the guidance group {100} <011> to {223} <110> represented by the respective crystal orientations of {100} <011> , {116} <110>, {114} <110>, {113} <110>,
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    [2]
    2/5 {112} <110>, {335} <110>, and {223} <110> to a portion of the center of the plate thickness with a range of 5/8 to 3/8 in the plate thickness from of the steel plate surface is 4.0 or less, and the pole density of the {332} <113> crystal orientation is 4.8 or less, the average diameter of the crystal grain is 10 pm or less and the temperature of appearance transition of a Charpy vTrs fracture is 20 ° C or less, and the microstructure is made up of 35% or less in a structural fraction of pro-eutectoid ferrite and the balance of a low temperature transformation-generating phase.
    2. Production method of a high-strength hot-rolled steel sheet containing bainite having an isotropic working capacity, as defined in claim 1, characterized by the fact that it consists of:
    on a steel bar containing:
    in mass%,
    C: greater than 0.07 to 0.2%;
    Si: 0.001 to 2.5%;
    Mn: 0.01 to 4%;
    P: 0.15% or less (not including 0%),
    S: 0.03% or less (not including 0%);
    N: 0.01% or less (not including 0%);
    Al: 0.001 to 2%;
    optionally one type or two or more types of, in% in mass,
    Ti: 0.015 to 0.18%,
    Nb: 0.005 to 0.06%,
    Cu: 0.02 to 1.2%,
    Ni: 0.01 to 0.6%,
    Mo: 0.01 to 1%,
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    [3]
    3/5
    V: 0.01 to 0.2%, and
    Cr: 0.01 to 2%.
    Mg: 0.0005 to 0.01%,
    Ca: 0.0005 to 0.01%,
    REM: 0.0005 to 0.1%, and
    B: 0.0002 to 0.002%;
    a balance being made up of Fe and the inevitable impurities, perform the first hot rolling in which rolling at a reduction rate of 40% or more is performed once or more in a temperature range of not less than 1000 ° C nor greater than 1200 ° C, perform the second hot lamination in which the lamination at 30% or more is performed in a pass at least once in a temperature region of not less than T1 + 30 ° C nor more than T1 + 200 ° C determined by Expression (1) below, and adjust the total reduction ratios in the second hot rolling to 50% or more, perform the final reduction to a reduction ratio of 30% or more in the second hot rolling and then initiate primary cooling in such a way that the waiting time period t seconds satisfies Expression (2) below;
    perform the final reduction at a reduction rate of 30% or more on the second hot rolling and then start the primary cooling so that the waiting period t seconds;
    satisfy the final reduction at a rate of reduction of 30% or more in the second hot rolling and then initiate primary cooling so that the waiting time period t seconds satisfies Expression (2) below;
    adjust the average cooling rate in primary cooling
    Petition 870190008815, of 01/28/2019, p. 86/93
    [4]
    4/5 flow to 50 ° C / s or more and perform primary cooling so that the temperature change is in a range of not less than 40 ° C or more than 140 ° C;
    within three seconds after the end of the primary cooling, perform the secondary cooling in which the cooling is performed at an average cooling rate of 15 ° C / s or more; and after the end of the secondary cooling, perform the air cooling for 1 to 20 seconds in a temperature region of less than the temperature of the transformation point Ar3 and the temperature of the transformation point Ar1 or more and then executing the cooling to 450 ° C or more and less than 550 ° C.
    T1 (° C) = 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr + 100 x Mo + 100 x V ··· (1)
    Here, C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the element content (% by mass).
    t 2.5 x t1 ··· (2)
    Here, t1 is obtained by Expression (3) below.
    t1 = 0.001 x ((Tf - T1) x P1 / 100) 2 - 0.109 x ((Tf - T1) x P1 / 100) + 3.1 ··· (3)
    Here, in Expression (3) above, Tf represents the temperature of the steel bar obtained after the final reduction at a reduction ratio of 30% or more, and P1 represents the reduction ratio of the final reduction to 30% or more.
    3. Production method of high-strength hot-rolled steel sheet containing bainite having an isotropic working capacity, according to claim 2, characterized by the fact that the total reduction ratios in a temperature range of less than T1 + 30C is 30% or less.
    4. Production method of high-strength hot-rolled steel sheet containing bainite having iso-working capacity
    Petition 870190008815, of 01/28/2019, p. 87/93
    [5]
    5/5 tropic, according to claim 2, characterized by the fact that the heat generation by working between the respective passes in the region of temperatures of not less than T1 + 30 ° C nor greater than T1 + 200 ° C in the second hot rolling is 18 ° C or less.
    5. Production method of high-strength hot-rolled steel sheet containing bainite having an isotropic working capacity, according to claim 2, characterized by the fact that the waiting time period t seconds also satisfies Expression (4) below.
    t <t1 ... (4)
    [6]
    6. Production method of high-strength hot-rolled steel sheet containing bainite having isotropic working capacity, according to claim 2, characterized by the fact that the waiting time period t seconds also satisfies Expression (5) below.
    t1 t t1 x 2.5 ... (5)
    [7]
    7. Production method of high-strength hot-rolled steel sheet containing bainite having an isotropic working capacity, according to claim 2, characterized by the fact that primary cooling is initiated between the rolling chairs.
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    同族专利:
    公开号 | 公开日
    EP2692894A4|2015-11-11|
    JP5376089B2|2013-12-25|
    EP2692894A1|2014-02-05|
    US20130319582A1|2013-12-05|
    TWI460289B|2014-11-11|
    BR112013024166A2|2016-12-06|
    CN103443320A|2013-12-11|
    WO2012133636A1|2012-10-04|
    KR101539162B1|2015-07-23|
    JPWO2012133636A1|2014-07-28|
    KR20130125824A|2013-11-19|
    CA2827844A1|2012-10-04|
    MX2013009507A|2013-09-26|
    US10364478B2|2019-07-30|
    US20170130294A1|2017-05-11|
    US9587287B2|2017-03-07|
    MX353192B|2018-01-05|
    TW201247894A|2012-12-01|
    PL2692894T3|2018-08-31|
    CA2827844C|2016-05-17|
    ES2678918T3|2018-08-20|
    CN103443320B|2015-09-23|
    EP2692894B1|2018-03-21|
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    法律状态:
    2018-10-30| B07A| Application suspended after technical examination (opinion) [chapter 7.1 patent gazette]|
    2019-05-07| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2019-05-28| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 29/03/2012, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 29/03/2012, OBSERVADAS AS CONDICOES LEGAIS |
    2019-11-19| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2011-079658|2011-03-31|
    JP2011079658|2011-03-31|
    PCT/JP2012/058337|WO2012133636A1|2011-03-31|2012-03-29|Bainite-containing high-strength hot-rolled steel plate with excellent isotropic workability and process for producing same|
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