two-phase steel sheet and method of manufacturing it

专利摘要:
summary patent of invention: "steel sheet with composite structure and manufacturing process". the present invention relates to a steel sheet of composite structure containing:% by mass, 0.01 to 0.1% of c; 0.2 to 3% of mn; 0.04 to 1.5% al; 0.015 to 0.2% of it; up to 0.01% p; up to 0.005% of s; up to 0.01% of n, which satisfies [ti] - 48/14? [n] - 48/32? [s] ? 0%, and satisfies 0.001? ex.c (%) / fsd (%)? 0.01, where ex.c (%) = [c] - 12/48? {[ti] + 48/93? [nb] - 48/14? [n] - 48/32? [s]}, and the remainder being composed of faith and impurities, in which in this steel sheet of composite structure, the microstructure at a depth of 1/4 of the thickness of the sheet is a composite structure in which the main phase comprises polygonal ferrite that it was hardened by precipitation with thi carbide and the second phase comprises a plurality of low temperature transformation product grains present in an area proportion (fsd (%)) of 1 to 10%, with the transformation product grains low temperature have an average crystal diameter of 3 to 15 µm and have a distance between the grains of low temperature transformation product closest to 10 to 20 µm on average.
公开号:BR112015006077B1
申请号:R112015006077
申请日:2013-09-26
公开日:2020-01-28
发明作者:Sakurada Eisaku；Shuto Hiroshi；Okada Hiroyuki；Yokoi Tatsuo
申请人:Nippon Steel & Sumitomo Metal Corp；Nippon Steel Corp；
IPC主号:

专利说明:

Descriptive Report of the Invention Patent for BIPhasic STEEL SHEET AND METHOD OF MANUFACTURING THE SAME.
FIELD OF TECHNIQUE [0001] The present invention relates to a biphasic steel sheet composed of ferrite and low temperature transformation products and a method of manufacturing it. This application is based on and claims the priority benefit of earlier Patent Application No. JP 2012-212783, filed on September 26, 2012, the content of which is incorporated herein by in its entirety by reference.
BACKGROUND OF THE TECHNIQUE [0002] In recent years, the weight reduction of various parts that make up a car has been promoted in order to improve the fuel consumption of a car. Weight reduction means differ depending on each performance required of the parts and, for example, for a structural part, the thickness thinning achieved by increasing the strength of a steel sheet is carried out, and for a panel part, the application of a light metal such as an Al alloy to a steel sheet and the like are carried out. However, when compared to steel, light metal such as an Al alloy is expensive, so it is mainly applied to luxury cars in the real world.
[0003] On the other hand, demand for automobiles is being shifted to emerging countries from developed countries, and from now on, both weight reduction and price reduction are expected to be achieved. For any parts, it is necessary to achieve the increased strength and weight reduction of steel, achieved by thinning the thickness.
[0004] Aluminum forgings and smelting have been advantageous
Petition 870170008192, of 02/07/2017, p. 7/14
2/73 sos for wheels for passenger cars in terms of design. However, although pressed steel products have recently been used as wheels for passenger cars, materials and methods are being devised, products that have the design equivalent to that of an aluminum wheel are emerging.
[0005] In particular, in addition to the excellent fatigue strength and corrosion resistance that have been required so far on a wheel disc seen by an end user, the design and beauty equivalent to that of an aluminum wheel are also required on a wheel. steel. Similarly, also on a steel sheet for wheel disc, the improvement of viability to improve the project as an improvement of surface and part property to guarantee beauty is required, in addition to the increase of resistance that reaches the thinning of thickness, and the fatigue strength and corrosion resistance that have been required so far.
[0006] As properties that have been demanded until now in the steel sheet for wheel disc, the bulging viability, stamping and fatigue resistance have been considered as important in particular. This is because the work of a hat portion is challenging between the wheel disk formatting steps and the fatigue resistance is managed by the stricter standard among the wheel member properties.
[0007] Currently, in order to emphasize the fatigue strength of a limb like a high-strength hot-rolled steel sheet for wheel disc, excellent 590 MPa graded ferrite / martensite steel sheets have been used in fatigue property (what is called biphasic steel). However, the level of resistance required in these steel sheets is increased from the 590 MPa grade to the 780 MPa grade and the strength tends to increase further.
3/73 [0008] In Non-Patent Document 1, a method of ensuring uniform elongation even with the same strength was described by transforming a microstructure of a steel sheet into a composite structure such as a biphasic steel composed of ferrite and martensite (to be described as DP steel, hereinafter).
[0009] On the other hand, DP steel has been known for the local deformability, typified by the formation of bending, hole expansion and deburring being low. This is due to the difference in strength between ferrite and martensite being large, so that a high concentration of stress and deformation occurs in the ferrite next to the formed martensite and cracking occurs.
[0010] Based on this finding, a sheet of high-strength steel whose orifice expansion ratio is increased by reducing the difference in strength between the structures has been developed. In Patent Document 1, a sheet of steel was proposed in which the resistance is guaranteed by applying bainite or bainitic ferrite as its main phase to considerably improve the orifice expandability. The steel is designed to be composed of a single structure and, thus, the deformation and stress concentration described above are prevented from occurring and a high orifice expansion ratio can be obtained.
[0011] However, steel is designed to be composed of a unique structure of bainite or bainitic ferrite and, thus, the elongation deteriorates considerably and the achievement of elongation and orifice expansion cannot be achieved.
[0012] In addition, in recent years, high strength steel sheets have been proposed in which excellent elongation ferrite is used as a single structure steel structure and an increase in strength is achieved using Ti, Mo carbide , or the like (for example, Patent Documents 2 to 4).
4/73 [0013] However, the steel sheet proposed in Patent Document 2 contains a large amount of Mo. The steel sheet proposed in Patent Document 3 contains a large amount of V. Additionally, the steel sheet proposed in Patent Document 4 needs to be cooled in the middle of the lamination to produce fine crystal grains. Therefore, there is a problem that the cost of the alloy and the cost of manufacture increase. In addition, even in this steel sheet, the strength of the ferrite itself is considerably increased and, thus, the elongation deteriorates. The elongation of single-structure steel composed of bainite or bainitic ferrite is excellent, but the hole elongation-expandability balance is not necessarily sufficient.
[0014] Additionally, in Patent Document 5, a biphasic steel sheet was proposed in which in DP steel, bainite is used instead of martensite and a difference in strength between the ferrite and bainite structures is reduced, to increase, thus, the orifice expandability.
[0015] However, as a result that an area ratio of the bainite structure was increased in order to guarantee strength, the elongation deteriorated and the balance of orifice expansion and elongation was not sufficient.
[0016] In addition, in Patent Documents 7 to 9, steel sheets have also been proposed in which the ferrite in a DP steel is strengthened by precipitation and, thus, a difference in strength between the ferrite and the hard structure is reduced.
[0017] However, in this technique, Mo is an essential element to cause a problem in which the manufacturing cost increases. Additionally, despite the fact that ferrite is strengthened by precipitation, the difference in strength between ferrite and martensite, which is a hard structure, is large, resulting in the fact that an improvement effect of
5/73 high orifice expandability is not achieved.
[0018] On the other hand, in order to transform a microstructure into a double phase of ferrite and martensite, Si is often added to these DP steels in order to promote the transformation of ferrite. However, when Si is contained, a tiger-list inlay pattern called red inlay (Si inlay) is generated on the surface of the steel sheet, so that it is difficult to apply DP steel to various steel sheets used for very well designed wheel discs required for beauty.
[0019] In Patent Document 10, a technique related to a sheet of steel with the ability to obtain an excellent balance between elongation and orifice expansion was described by controlling a fraction of martensite in a DP steel to 3 to 10% in a grade steel sheet of 780 MPa or greater. However, 0.5% or more of Si is added in this way, making it difficult to avoid the Si fouling pattern, so it is difficult to apply the technique to various steel sheets used for very well designed wheel discs required to have beauty.
[0020] In relation to this problem, a technique of a hot-rolled steel sheet of high tensile strength with the ability to suppress the occurrence of red scale has been described by suppressing the amount of Si added to 0.3% or less and additionally obtaining high strength and excellent flangeability by adding Mo and creating fine precipitates (for example, Patent Documents 11 and 12).
[0021] However, in steel sheets that have the technique described above described in Patent Documents 11 and 12 applied to them, the amount of Si added is about 0.3% or less, but it is difficult to suppress the occurrence sufficiently red inlays, and additionally add 0.07% or more of Mo which is a
6/73 expensive alloying element is essential, so there is a problem that the manufacturing cost is high.
[0022] Additionally, in Patent Document 13, a technique to prevent the occurrence of red scale has been described by defining the upper limit of the Si content. However, there is no description of the technique on fatigue chamfer property.
[0023] Additionally, in Patent Document 14, a technique was described to enhance a low cycle fatigue property by adding Al. However, there is no description of the technique on the fatigue chamfer property which is a fatigue property under concentration of tension.
PREVIOUS TECHNICAL DOCUMENTS
PATENT DOCUMENTS [0024] Patent Document 1: Patent Publication Open to Public Inspection n ² JP 2003-193190 [0025] Patent Document 2: Patent Publication Open to Public Inspection No. JP 2003-089848 [0026] Document Patent 3: Open Patent Publication for Public Inspection No. JP 2007-063668 [0027] Patent Document 4: US Patent Publication Open to public inspection No. JP 2004-143518 [0028] Patent Document 5: Patent Publication Open to Public Inspection No. JP 2004-204326 [0029] Patent Document 6: US Patent Publication Open to public inspection No. JP 2007-302918 [0030] Patent Document 7: US Patent Publication Open to public inspection No JP 2003-321737 [0031] Patent Document 8: Open Patent Publication for Public Inspection No. JP 2003-321738 [0032] Patent Document 9: US Patent Publication Open to
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Public Inspection n ² JP 2003-321739 [0033] Patent Document 10: U.S. Patent Publication Open to Public Inspection No. JP 2011-184788 [0034] Patent Document 11: U.S. Patent Publication Open to Public Inspection No. JP 2002-322540 [0035] Patent Document 12: U.S. Patent Publication Open to Public Inspection No. JP 2002-322541 [0036] Patent Document 13: U.S. Patent Publication No. JP 2007-082567 [0037] Patent Document 14: Open Patent Publication to Public Inspection No. JP 2010-150581
NON-PATENT DOCUMENT [0038] Non-Patent Document 1: O. Matsumura et al., Trans. ISIJ (1987) vol. 27, p. 570
DESCRIPTION OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION [0039] The present invention aims to provide a high strength biphasic steel sheet with high deburring viability that has a tensile strength of 540 MPa or greater and that has excellent surface and property properties fatigue chamfer and a method of manufacturing it.
MEANS TO SOLVE THE PROBLEMS [0040] The present inventors repeated careful examinations on the relationship between a structural constitution of a biphasic steel that has a high ductility as well as a high strength and uniform elongation, deburring viability, and a chamfer property. fatigue based on the premise of a steel component that does not contain Si for the purpose of preventing a pattern of Si fouling. As a result, they found a method
8/73 to balance uniform elongation, deburring feasibility, and fatigue chamfer property at a high level by controlling a steel component, a state of dispersion, shape, size and nano-hardness of a temperature transformation product low which is a second phase. That is, as a substitute for Si, Al was added appropriately to avoid a Si fouling pattern, and to create a composite structure in which polygonal ferrite is determined as a main phase and a low temperature transformation product is determined as a second level. Additionally, they learned optimal ranges of a fraction, size, and the like of the low temperature transformation product that could achieve elongation, deburring viability, and fatigue chamfer property. In addition, they clarified that by conceiving not only the steel component, but also a method of hot rolling, these optimum ranges can be obtained with repeatability. The present invention was made based on these findings, and the essence of it is as follows.
[0041] [1] A two-phase steel sheet contains:
[0042] in% by mass, [0043] C: 0.01 to 0.1%;
[0044] Mn: 0.2 to 3%;
[0045] Al: 0.04 to 1.5%;
[0046] Ti: 0.015 to 0.2%;
[0047] Si: 0 to 0.5%;
[0048] Nb: 0 to 0.06%;
[0049] Cu: 0 to 1.2%;
[0050] Ni: 0 to 0.6%;
[0051] Mo: 0 to 1%;
[0052] V: 0 to 0.2%;
[0053] Cr: 0 to 2%;
9/73 [0054] W: 0 to 0.5%;
[0055] Mg: 0 to 0.01%;
[0056] Ca: 0 to 0.01%;
[0057] REM: 0 to 0.1%;
[0058] B: 0 to 0.002%;
[0059] P: 0.01% or less;
[0060] S: 0.005% or less;
[0061] N: 0.01% or less, [0062] where [Ti] - 48/14 x [N] - 48/32 x [S] 0% is satisfied and when Ex.C (%) = [ C] - 12/48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] 48/32 x [S]} is determined, 0.001 2 Ex.C (%) / fsd (% ) 2 0.01 is satisfied, and a balance that is composed of Fe and impurities, in which at the position of 1/4 of the thickness of a sheet thickness, a microstructure is biphasic with the main phase of the same compound of strengthened polygonal ferrite by precipitation by Ti carbide and its second phase composed of 1 to 10% in fraction of area (fsd (%)) of transformation products at low temperature dispersed plurally, and an average crystal diameter of the transformation product at low temperature is from 3 to 15 pm and an average value of a closer distance between the transformation products at low temperature is 10 to 20 qm.
[0063] [2] The two-phase steel sheet, according to claim [1], contains:
[0064] in mass%, [0065] Si: 0.02% to 0.5%.
[0066] [3] The two-phase steel sheet according to [1] or [2], contains:
[0067] one or two or more among, in mass%, [0068] Nb: 0.005 to 0.06%;
[0069] Cu: 0.02 to 1.2%;
[0070] Ni: 0.01 to 0.6%;
10/73 [0071] Mo: 0.01 to 1%;
[0072] V: 0.01 to 0.2%;
[0073] Cr: 0.01 to 2%; and [0074] W: 0.01 to 0.5%.
[0075] [4] The two-phase steel sheet according to any one of [1] to [3], contains:
[0076] one or two or more from mass%, [0077] Mg: 0.0005 to 0.01%;
[0078] Ca: 0.0005 to 0.01%; and [0079] REM: 0.0005 to 0.1%.
[0080] [5] The biphasic steel sheet, according to any of claims [1] to [4], contains:
[0081] in mass%, [0082] B: 0.0002 to 0.002%.
[0083] [6] The biphasic steel sheet, according to any one of [1] to [5], where galvanization is carried out on the surface of the same.
[0084] [7] A method of making a two-phase steel sheet includes:
[0085] on a plate that contains:
[0086] in mass%, [0087] C: 0.01 to 0.1%;
[0088] Mn: 0.2 to 3%;
[0089] Al: 0.04 to 1.5%;
[0090] Ti: 0.015 to 0.2% or less;
[0091] Si: 0 to 0.5%;
[0092] Nb: 0 to 0.06%;
[0093] Cu: 0 to 1.2%;
[0094] Ni: 0 to 0.6%;
[0095] Mo: 0 to 1%;
11/73 [0096] V: 0 to 0.2%;
[0097] Cr: 0 to 2%;
[0098] W: 0 to 0.5%;
[0099] Mg: 0 to 0.01%;
[00100] Ca: 0 to 0.01%;
[00101] REM: 0 to 0.1%;
[00102] B: 0 to 0.002%;
[00103] P: 0.01% or less;
[00104] S: 0.005% or less;
[00105] N: 0.01% or less, [00106] where [Ti] - 48/14 x [N] - 48/32 x [S] 0% is satisfied and when Ex.C (%) = [ C] - 12/48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] 48/32 x [S]} is determined, 0.001 <Ex.C (%) / fsd (% ) 2 0.01 is satisfied, and a balance that is composed of Fe and impurities, perform the heating to a temperature SRT _min (° C) or higher, which is defined by Expression (1) below, and then in hot rolling , perform crude lamination at a reduction rate of 20% or more in a temperature zone of at least 1,050 ° C and at most 1,150 ° C for at least one pass, and then begin finishing lamination within 150 seconds in a temperature zone of 1,000 ° C or higher and lower than 1,080 ° C, and complete the finishing laminate with the total reduction ratio for plural passages of at least 75% and at most 95% in a temperature zone at least one Ar3 + 50 ° C transformation point temperature and at most 1.00 0 ° C; and within 3 seconds, cool to a lower temperature than the Ar3 transformation point at an average cooling rate of 15 ° C / sec or more, and then cool to a temperature zone greater than 600 ° C at an average cooling rate of 10 ° C / sec or less for a period of time of 1 second or longer and shorter than
12/73
100 seconds, and then cool to a temperature zone of 350 ° C or lower at a cooling rate of 15 ° C / sec or more, and wind up.
SRT _min = 10780 / {5.13 - log ([Ti] x [C])} - 273 Expression (1) [00107] [8] The method of fabricating the two-phase steel sheet according to [7], additionally includes:
[00108] in hot lamination, perform the gross lamination at a reduction rate of 20% or more in a temperature zone of at least 1,050 ° C and at most 1,150 ° C for plural passages, where the total reduction ratio of the gross lamination is not less than 60% and a maximum of 90%.
[00109] [9] The method of manufacturing the two-phase steel sheet according to [7] or [8], additionally includes:
[00110] perform the cooling to a temperature zone of 100 ° C or lower and perform the winding.
[00111] [10] The method of manufacturing the biphasic steel sheet according to any one of [7] to [9], in which when cooling to the temperature zone above 600 ° C at a cooling rate average 10 ° C / sec or less over a period of 1 second or longer and shorter than 100 seconds, when a total cumulative diffusion dimension L _total Ti in the ferrite is expressed by Expression (3) below adding If a dimension L of Ti diffusion in the ferrite expressed by the expression (2) below for a very short time aT / sec from a cooling completion temperature for winding, 0.15 L _to 0.5 and t = _al satisfied.
L = ^ D (T + 273) t Expression (2) L _to t _al = Z ^ (D (T + 273) At) Expression (3) [00112] Here, D (T + 273) is a diffusion coefficient volume in T ° C. t is a diffusion time period.
[00113] D (T) is expressed by Expression (4) below with the use of
13/73 a diffusion coefficient D0 of Ti, an activation energy Q, and a gas constant R.
D (T) = D0 x Exp (-Q / R- (T + 273)) Expression (4) [00114] [11] The method of making the two-phase steel sheet according to any of [7] to [ 10], in which when cooling to a temperature zone above 600 ° C at an average cooling rate of 10 ° C / sec or less for a period of time of 1 second or longer and shorter than 100 seconds, a sheet of steel is immersed in a galvanizing bath to galvanize its surface.
[00115] [12] The method of making the two-phase steel sheet according to [11] additionally includes:
[00116] on a galvanized biphasic steel sheet, perform an alloy treatment in a temperature range of 450 to 600 ° C.
EFFECT OF THE INVENTION [00117] According to the present invention, it is possible to obtain a sheet of biphasic steel of high strength excellent in uniform elongation, deburring viability, and fatigue chamfer property, and additionally also excellent in surface property as well as having a tensile strength of 540 MPa or greater, and the industrial contribution is extremely significant.
BRIEF DESCRIPTION OF THE DRAWINGS [00118] Figure 1 is a view showing a fatigue test bevel.
MODE FOR CARRYING OUT THE INVENTION [00119] A biphasic steel sheet is a sheet of steel in which hard products of transformation at low temperature typified by martensite are dispersed in soft ferrite, which achieves high uniform elongation as well as being of high strength. However, in the time of deformation, the stress concentration and deformation occur
14/73 each due to a difference in strength between ferrite and martensite, and voids that cause ductile fracture are likely to be generated and grow, so it is common for local deformability related to deburring viability to be quite low.
[00120] On the other hand, in relation to a fatigue chamfer property to evaluate a fatigue property under stress concentration, it is known that most of a fracture life is derived from the propagation of a fatigue crack. In biphasic steel in which hard transformation products at low temperature typified by martensite are dispersed in soft ferrite, it is conceivable that when a fatigue crack propagates through soft ferrite, the hard transformation product at low temperature becomes an obstacle to propagation of the fatigue crack, propagation speed decreases, and the fatigue chamfer property improves.
[00121] However, detailed examinations are not carried out on a fraction, size, and the like of the transformation product at low temperature in the biphasic steel sheet, generation behavior and void growth that cause ductile fracture, and the propagation speed of a crack of fatigue. The optimal microstructure with the capacity to achieve improvement in local deformability related to the deburring viability of the biphasic steel sheet and decrease in the propagation speed of a fatigue crack is not necessarily defined.
[00122] Additionally, components and a method of fabricating a steel sheet with the capacity to satisfy all avoidance of a Si fouling pattern related to a surface property of a steel sheet for the purpose of achieving design and beauty equivalent to those of an aluminum wheel with a steel wheel, security of post-coating corrosion resistance, deburring feasibility, and fatigue chamfer property are not neccessarily defined.
[00123] In this way, the present inventors repeated careful examinations on the relationship between a structural constitution of a biphasic steel that has a high ductility as well as a high strength and uniform elongation, deburring viability, and a fatigue chamfer property with based on the premise that a steel component does not contain Si for the purpose of preventing a Si fouling pattern. As a result, they found a method to balance uniform elongation, deburring feasibility, and fatigue chamfer property at a high level by controlling the steel component, the state of dispersion, shape, size and nano-hardness of the transformation product at low temperature, which is a second phase.
[00124] Concretely, the Si content was controlled to 0.5% or less, thereby avoiding the Si fouling pattern. Additionally, in order to bring the fraction of area (fsd (%)), size and the like of the transformation product at low temperature for appropriate ranges, the amount of Ex.C was controlled in a range that satisfies 0.001 2 Ex.C (%) / fsd (%) <0.01 (where Ex.C (%) = [C] - 12/48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] - 48/32 x [S]}, here). Additionally, in the position of 1/4 of the thickness of a sheet thickness, a biphasic microstructure was determined with its main phase composed of polygonal ferrite strengthened by precipitation by Ti carbide and its second phase composed of 1 to 10% in fraction of area (fsd (%)) of low temperature transformation products dispersed plurally. Then, an average crystal diameter of the low temperature transformation product mentioned above was set at 3 to 15 qm, and an average value of a closer distance between the low temperature transformation products was set at 10 to 20 qm. As a result, they made it clear that it is possible
16/73 balance uniform elongation, deburring feasibility, and fatigue chamfer property at a high level.
[00125] As a test method by which the difference in deburring viability appears clearly, an orifice expansion test is proposed. An orifice expansion value obtained by this test is widely used as an index to assess local deformability related to deburring viability. The occurrence and progress of a crack in an expanding hole is caused by a ductile fracture with generation, growth, and connection of voids determined as elementary steps. In a structure that has a large difference in strength, such as the two-phase steel sheet, there is a high concentration of stress and deformation due to hard transformation products at low temperature, so that the voids grow easily and the expansion value of orifice is low.
[00126] However, when the relationship between the structure and the behavior of generation and growth of voids and the relationship between them and the orifice expandability were examined in detail, it became clear that depending on the dispersion state of transformation product at temperature low to be a hard second phase, the generation, growth, and connection of voids are sometimes delayed, to make it possible to obtain an excellent orifice expansion value in this way.
[00127] Specifically, when low temperature transformation products are dispersed in an island format, the area fraction fsd is 10% or less, the average crystal diameter is 15 μm or less, and the average value of the distance of closer approximation between the transformation products at low temperature is 20 μm or less, the generation, growth, and connection of voids are delayed, to make it possible to obtain, in this way, an excellent orifice expansion value.
17/73 [00128] This is due to the fact that when low temperature transformation products are made small and the quantity per volume unit is reduced, low temperature transformation products that have void locations in them themselves or in the vicinity of boundaries between ferrite and low temperature transformation products are reduced and the respective intervals between low temperature transformation products are increased, thus the voids are not easily connected and void growth is suppressed. In addition, the hardness of the transformation product at low temperature is limited to a certain range, and thus the occurrence of void locations that are an initial stage of deformation can be avoided and non-uniform void growth is suppressed.
[00129] On the other hand, the fatigue chamfer property can be improved by dispersing the hard transformation product at low temperature and reducing the propagation speed of a fatigue crack. In the case of biphasic steel, it is known that the speed of propagation of a fatigue crack changes depending on the dispersion state of the transformation product at low temperature being a second hard phase, and if the dispersion state is optimized, the effect is displayed.
[00130] Concretely, since the low temperature transformation products dispersed in an island format, the area fraction fsd is 1% or more, the average crystal diameter is 3 pm or more, and the average value of closest approach distance between transformation products at low temperature is 10 pm or more, a fatigue crack to pass through soft ferrite remains on or avoids the transformation product at low temperature which is a hard second phase, and thus the speed of propagation of the fatigue crack decreases and the resistance to chamfer fatigue improves.
18/73 [00131] Additionally, since the products of transformation at low temperature, which is a second phase, have the average crystal diameter of 3 to 15 qm and have the average value of the closest distance between them, from 10 to 20 qm, and are in a state of being dispersed in an island shape over an area fraction of 1 to 10%, excellent uniform elongation that biphasic steel exhibits can be obtained.
[00132] In the above, the characteristics of the present invention were explained in principle, and the requirements that define the present invention and preferential requirements will be explained, sequentially. First, the components of the present invention will be explained in detail. By the way, in relation to the component,% means% by mass.
[00133] C: 0.01 to 0.1% [00134] C is one among the important elements in the present invention. C not only forms transformation products at low temperature to contribute to resistance by strengthening the structure, but also forms precipitates with Ti to contribute to resistance by strengthening by precipitation. However, when C is less than 0.01%, these effects to ensure resistance of 540 MPa or greater cannot be achieved. When more than 0.1% C is contained, an area ratio of the transformation product is increased at low temperature which is a second hard phase and the orifice expandability decreases. In this way, the C content is determined to be 0.01% to 0.1%.
[00135] Additionally, as long as 0.001 Ex.C (%) / FSD (%) 0.01 (Ex.C (%) = [C] - 12/48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] - 48/32 x [S]}) is satisfied on the condition that the fraction of area of the second phase is determined for fsd (%), the dispersion state, hardness, and the like of the product low temperature transformation process which is a
19/73 second hard phase are optimized, the generation, growth, and connection of voids are delayed, an excellent orifice expansion value can be obtained, and the end of a fatigue crack remains or deflects, and thus the propagation speed of the fatigue crack decreases and excellent resistance to chamfer fatigue can be obtained. By the way, in the expression that expresses Ex.C (%), [C] is the content of C (% by mass), [Ti] is the content of Ti (% by mass), [Nb] is the content of Nb (% by mass), [N] is the content of N (% by mass), and [S] is the content of S (% by mass).
[00136] Mn: 0.2 to 3% [00137] Mn is not only an element involved in the strengthening of ferrite, but also an element that expands a temperature from the austenite region to a low temperature side to expand a temperature zone of a two-phase region of ferrite and austenite with an increase in its content. In order to obtain the biphasic steel of the present invention, it is necessary to promote separation of two phases of ferrite and austenite during cooling after finishing lamination. In order to achieve the effect, 0.2% or more of Mn must be contained. On the other hand, when they are contained above 3% of Mn, the plate cracking significantly occurs during casting, so that the content is determined to be 3% or less.
[00138] Additionally, when more than 2.5% Mn is contained, the hardenability increases too much, which results in the fact that a desired microstructure cannot be obtained by a common method. In order to obtain the desired microstructure, it is required to cool and maintain the air for a long time to precipitate the ferrite during cooling after finishing lamination, and productivity decreases, so that the content is desirably 2.5% or less. 2.2% or less is additionally desirable. Additionally, when elements other than Mn are not added sufficiently
20/73 with the purpose of suppressing the occurrence of hot cracks caused by S, it is desirably contained the amount of Mn that makes the content of Mn ([Mn]) and the content of S ([S]) satisfy [Mn ] / [S] 1 20 in mass%.
[00139] Al: 0.04 to 1.5% [00140] Al is involved in the generation of ferrite in a similar way to Si because it is one of the important elements in the present invention as well as being a deoxidizing element. Al is also an element that, with an increase in its content, expands a temperature from the ferrite region to a high temperature side to expand a temperature zone from a two-phase region of ferrite and austenite, so that it is contained actively as a substitute for Si in the present invention. In order to achieve the effect, 0.04% or more of Al needs to be contained, but when they are contained above 1.5%, the temperature of the ferrite region is expanded to the too high temperature side and thus , makes it difficult to complete the finishing lamination in an austenite region, and the worked ferrite remains on a product sheet and the ductility deteriorates. In this way, the Al content is determined to be not less than 0.04% and a maximum of 1.5%. In addition, when more than 1% Al is contained, there is a risk that inclusions of non-metals such as alumina will be increased and deteriorate local ductility, so that the content of the same is desirably 1% or less.
[00141] Ti: 0.015 to 0.2% [00142] Ti is one of the most important elements in the present invention. Simultaneously with the transformation of the ferrite that progresses during cooling after the completion of the hot rolling, the rest of Ti after being precipitated as TiN in a region of austenite during the hot rolling precipitates finely as carbide such as TiC to strengthen by precipitation ferrite grains
21/73 of the biphasic steel of the present invention and, thus, the strength is improved. In order to achieve this effect, Ti that is 0.015% or more and satisfies [Ti] - 48/14 x [N] - 48/32 x [S] 1 0% needs to be contained.
[00143] On the other hand, even when more than 0.2% Ti is contained, these effects are saturated. Additionally, 0.001 Ex.C (%) / FSD (%) <0.01 (Ex.C (%) = [C] - 12/48 x {[Ti] + 48/93 x [Nb] 48/14 x [N] - 48/32 x [S]}) is determined on the condition that the fraction of area of the second phase is determined for fsd (%) and, therefore, the dispersion state, hardness, and similar of the product of low temperature transformation which is a second hard phase are optimized, generation, growth, and void connection are delayed, and an excellent orifice expansion value can be obtained. In addition, the tip of a fatigue crack remains in the transformation product at low temperature or avoids the transformation product at low temperature and, thus, the propagation speed of the fatigue crack decreases and an excellent fatigue strength can be obtained. chamfer. Additionally, when more than 0.15% Ti is contained, there is a risk that a funnel tip is likely to be clogged in the casting time, so that the content of the hopper is desirably 0.15% or any less.
[00144] The steel used for the steel sheet of the present invention contains the above elements as essential components, and additionally can also contain Si, Nb, Cu, Ni, Mo, V, Cr, W, Mg, Ca, REM, and B according to need. These respective elements will be described below.
[00145] Si: 0 to 0.5% [00146] In the present invention, Si is not essential. Si is involved in the generation of ferrite as well as being a deoxidizing element, and it is an element that with an increase in its content, expands a temperature from the ferrite region to a high temperature side to
22/73 expand a two-phase region temperature zone of ferrite and austenite. In order to obtain the biphasic steel of the present invention, Si is desirably originally contained. However, the Si notably generates a tiger streak pattern of Si inlay on the surface of the steel sheet and significantly deteriorates the surface property. Additionally, there is sometimes a case that it greatly decreases the productivity of a scale removal step (pickling and the like) in a precision adjustment line.
[00147] When more than 0.07% Si is contained, the Si fouling pattern begins to be found here and there on the surface of the steel sheet. When its content is greater than 0.5%, the surface property deteriorates significantly and the productivity of a pickling step deteriorates greatly. Even if any scale removal method is performed, a conversion treatment property deteriorates and the post-coating corrosion resistance decreases. Thus, the Si content is determined to be 0.5% or less.
[00148] On the other hand, Si is an element that has the effect of suppressing the occurrence of defects based on fouling such as fouling and fouling fouling, and when 0.02% or more is contained, the effect can be obtained. However, although Si is contained above 0.1%, the effect is saturated, and in addition, the conversion treatment property deteriorates and the resistance to post-coating corrosion decreases. Thus, when Si is contained, the Si content is determined to be not less than 0.02% and a maximum of 0.5%, and is desirably 0.1% or less. Additionally, in order to make the Si fouling patterns zero, the Si content is desirably 0.07% or less. However, fouling-based defects such as fouling and fouling
23/73 depending on the need, and the Si can also be less than 0.02%. A steel component that does not contain Si is also within the scope of the present invention.
One or two or more of Nb, Cu, Ni, Mo, V, Cr, and W.
[00149] In the present invention, Nb, Cu, Ni, Mo, V, Cr, and W are not essential. Nb, Cu, Ni, Mo, V, Cr, and W are effective elements to improve the strength of the steel sheet by strengthening by precipitation or strengthening by solid solution. Therefore, one or two or more of Nb, Cu, Ni, Mo, V, Cr, and W are contained as needed. When 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%, the Cr content is less than 0.01%, and the W content is less than 0.01%, the effect described above cannot be obtained sufficiently. Additionally, even when more than 0.06% of the Nb content, more than 1.2% of the Cu content, more than 0.6% of the Ni content, more than 1% of the Mo content, more than 0.2% of the V content, more than 2% of the Cr content, and more than 0.5% of the W content are each added, the effect described above is saturated and the economic efficiency decreases.
[00150] Thus, when these are contained according to need, the Nb content desirably is at least 0.005% and at most 0.06%, the Cu content is desirably at least 0.02% and at maximum 1.2%, the Ni content desirably is at least 0.01% and at most 0.6%, the Mo content desirably is at least 0.01% and at most 1%, the V content desirably it is at least 0.01% and at most 0.2%, the Cr content desirably is at least 0.01% and at most 2%, and the W content desirably is at least 0.01% and at most 0.5%.
[00151] One or two or more of Mg, Ca, and REM
24/73 [00152] In the present invention, Mg, Ca, and REM are not essential. Mg, Ca, and REM (rare earth element) are elements that control the shape of a non-metal inclusion to be a starting point for fracture and to cause deterioration of viability and improve viability. Therefore, one or two or more of Mg, Ca, and REM are contained as needed. Even when less than 0.0005% of each of Ca, REM, and Mg is contained, the effect described above is not exhibited. Additionally, even when the Mg content is determined to be more than 0.01%, the Ca content is determined to be more than 0.01%, and the REM content is determined to be more than 0.1%, the effect described above is saturated and economic efficiency decreases.
[00153] Thus, when these are contained according to need, the Mg content desirably is at least 0.0005% and at most 0.01%, the Ca content desirably is at least 0.0005% and at most 0.01%, and the REM content desirably is at least 0.0005% and at most 0.1%. By the way, in the present invention, REM refers to an element of La and the series of latanids, is often added in mischmetal, and contains elements of the series such as La and Ce in a complex form. The metals La and Ce may also be contained.
[00154] B: 0.0002 to 0.002% [00155] In the present invention, B is not essential. B has an effect of increasing the hardenability to increase a structural fraction of a low temperature transformation generation phase which is a hard phase, to thereby be contained as needed. However, when the B content is less than 0.0002%, the effect cannot be obtained, and although B is contained above 0.002%, the effect is saturated. Therefore, the B content is desirably at least 0.0002% and at most 0.002%. On the other hand, B is an he
25/73 that causes the question of plate cracking in a cooling step after continuous casting, and from this point of view, desirably the content is 0.0015% or less. That is, it is desirably at least 0.001% and at most 0.0015%.
[00156] Regarding the steel component of a hot-rolled steel sheet of the present invention, the remainder except the elements described above are Fe and impurities. As impurities, one contained in a raw ore material, scrap, and the like and one contained in a manufacturing step can be exemplified. The respective impurity elements are allowed to be contained when necessary in a range where the operation and effect of the present invention are not inhibited.
[00157] P: 0.01% or less [00158] P is an impurity element, and when it exceeds 0.01%, segregation for crystal grain boundaries becomes noticeable, the grain boundary fragility is promoted , and local ductility deteriorates. In addition, the embrittlement of a welded portion also becomes noticeable, so that the upper limit is set to 0.01% or less. The lower limit value of P is not defined in particular, but setting it to less than 0.0001% is economically disadvantageous.
[00159] S: 0.005% or less [00160] S is an impurity element, and negatively affects weldability and fabricability during casting and fabrication capacity during hot rolling, so the upper limit is set to 0.005 % or less. Additionally, when S is contained in excess, thick MnS is formed which decreases the orifice expandability, so that for improvement in orifice expandability, the content is preferably reduced. The lower limit value of S is not defined in particular, but to determine
26/73 the same for less than 0.0001% is economically disadvantageous, so this value is determined preferentially for the lower limit value.
[00161] N: 0.01% or less [00162] N is an impurity element that is inevitably mixed in the steel's refining time, and is an element to form nitride combined with Ti, Nb, or the like. When the N content is more than 0.01%, this nitride precipitates at a relatively high temperature, so the crystal grains are likely to become coarse, and the coarse crystal grain can become a starting point of a deburring crack. In addition, this nitride content is preferably lower in order to use Nb and Ti effectively as will be described later. In this way, the upper limit of the N content is determined to be 0.01%.
[00163] By the way, when the N content is more than 0.006% in the application of the present invention to a member in which aging deterioration becomes a problem, aging deterioration becomes severe, so that it desirably is 0.006% or less. In addition, when the present invention is applied to a member based on the premise that it is allowed to remain at room temperature for two weeks or more after manufacture, to then be subjected to work, the N content is desirably 0.005% or less in view of aging deterioration measures. Additionally, when it is considered that a member is allowed to remain under a high summer temperature environment or it is used under an environment exported to regions located on the equator by boats, ships, and the like, the N content is desirably less than 0.004%.
[00164] Like the other impurities, 1% or less in the total of Zr, Sn, Co, and Zn can also be contained. However, Sn is desirable
27/73 is 0.05% or less due to imperfection in the hot rolling time.
[00165] Subsequently, the microstructure of the biphasic steel sheet of the present invention will be explained in detail. The microstructure of the two-phase steel sheet of the present invention is limited as follows. [00166] In the position of 1/4 of the thickness of a sheet thickness, the microstructure is biphasic with its main phase composed of polygonal ferrite strengthened by precipitation by Ti carbide and its second phase composed by 1 to 10% in fraction of area (fsd (%)) of low temperature transformation products dispersed plurally. The average crystal diameter of the low temperature transformation product mentioned above is 3 to 15 μm. An average value of a closer distance between the transformation products at low temperature is 10 to 20 μm. By the way, the microstructure is specified in the position of 1/4 of the thickness of the thickness of the sheet where average characteristics appear.
[00167] Ferrite is the most important structure to guarantee uniform elongation. In order to obtain the graduation strength of 540 MPa or greater even when the fraction of area of the low temperature transformation product which is a second hard phase is 10% or less, the ferrite structure needs to be strengthened by strengthening by precipitation. In addition, in order to ensure elongation, it is important that the main phase of the microstructure is not bainitic ferrite which has a high displacement density, but polygonal ferrite which has a low displacement density and which has sufficient ductility. Thus, the main phase of the steel of the present invention is determined for polygonal ferrite strengthened by precipitation by Ti carbide. By the way, the Ti carbide referred to here is a compound that has Ti and C that contribute to strengthening by precipitation of the structure of Ti ferrite as its main with
28/73 component, and it is also acceptable to contain, for example, N, V, Mo, and the like in addition to Ti and C.
[00168] As long as the component is fixed, the average grain diameter and density (pieces / cm3) of precipitates containing TiC are substantially inversely correlated. In order for an improved margin of precipitation strength to become 100 MPa or greater in terms of tensile strength, of precipitates containing TiC, the average grain diameter needs to be 3 mm or less and the density accurate to be 1 x 10 ¹⁶ pieces / cm ³ or more.
[00169] In the present invention, the low temperature transformation product which is a second hard phase is mainly martensite or bainite (aB) which does not contain coarse carbide between sheets. However, it is permissible to contain less than 3% in total due to the area of retained austenite (yr) and constituent of Martensite-Austenite (MA). In addition, the martensite referred to in the present invention is fresh martensite (M) when the winding is carried out in a temperature zone of 100 ° C or lower where a carbon diffusion speed is sufficiently slow. It is tempered martensite (tM) when a winding temperature is higher than 100 ° C and a point of Ms (a point of remnant austenite obtained after the transformation of the ferrite progresses during cooling after finishing lamination ) or lower. The low temperature transformation product in the previous case is a structure mixed with tempered martensite and bainite.
[00170] The tempered martensite and bainite ratio of this mixed structure (low temperature transformation product in the previous case) is affected by the winding temperature and the relative relationship between the winding temperature and the Ms point temperature described above. By the way, when the Ms point is lower
29/73 than 350 ° C, most of the low temperature transformation product is bainite which does not contain coarse carbide between blades which is made higher than the Ms point and 350 ° C or lower. However, it is difficult to distinguish metallographically tempered martensite and bainite referred to here, and in the present invention, these are termed as tempered martensite (tM).
[00171] The transformation product at low temperature needs to be dispersed in an island shape in a corner, an edge, and a grain boundary of a ferrite grain. This is due to the fact that, in relation to the ductile fracture that is thought to be involved in the deburring viability, in a mechanism in which voids occur and then grow to connect, the shape of the transformation product itself at low temperature that is thought to be a place of occurrence of a void is an island shape and, thus, the stress concentration is relaxed and the occurrence of voids that cause fracture of the transformation product at low temperature to be suppressed.
[00172] By the way, the shape of the island indicates a state where the products of transformation at low temperature are not continuously arranged in an aligned manner, and additionally the individual shape of them is desirably a shape close to a sphere with little concentration of locations of tension. As long as the average crystal diameter of the low temperature transformation product is 3 to 15 pm and the average closest distance between the low temperature transformation products is 10 to 20 gm, the temperature transformation products each have an appropriate size and are dispersed appropriately to be in an "island shape".
[00173] Additionally, the low temperature transformation product which is a second hard phase is an important structure in terms of ensuring uniform elongation. When the fraction of area
30/73 (fsd (%)) of low temperature transformation products dispersed in an island shape becomes less than 1%, it is difficult to guarantee 15% or more of uniform elongation at 540 MPa graduation, for example. In addition, an effect of delaying the spread of a fatigue crack is lost. On the other hand, when it becomes larger than 10%, the intervals between the low temperature transformation products that are imagined to be void locations become small, the voids are likely to be connected, it is likely to be ductile fracture is caused, and deburring viability deteriorates. Therefore, the fraction of area (fsd (%)) of the transformation product at low temperature in the microstructure is limited to 1 to 10%.
[00174] The average crystal diameter of the low temperature transformation product needs to be limited to 3 to 15 μm in terms of equivalent circle diameter. This is due to the fact that when the average crystal diameter of the low temperature transformation product is less than 3 μm, the effect that the low temperature transformation product becomes an obstacle to the propagation of a crack fatigue to delay the speed of propagation is lost, and when it is more than 15 μm, the shape naturally becomes complex, stress concentration portions are generated, fracture of a thick transformation product at low temperature is caused early , and local ductile fracture caused by voids negatively affects the deburring viability. The same is desirably 12 μm or less.
[00175] Additionally, the average value of the closest approximation distance between the transformation products at low temperature needs to be limited to 10 to 20 μm. When the average value of the closest approximation distance between transformation products at low temperature is less than 10 μm, the intervals between the products
31/73 of transformation at low temperature become small, voids are likely to be connected, ductile fracture is likely to be caused, and deburring viability deteriorates. On the other hand, when the average value of the closest approximation distance between the transformation products at low temperature is greater than 20 qm, a fatigue crack propagates selectively through polygonal soft ferrite, and the effect of delaying the propagation of a fatigue crack is lost.
[00176] The average nano-hardness of the transformation product at low temperature is desirably 7 to 18 GPa. This is due to the fact that when the average nano-hardness is less than 7 GPa, a difference in hardness between the transformation product at low temperature and a soft ferrite phase are reduced and excellent uniform elongation, which is characteristic of biphasic steel, is not exhibited. On the other hand, when it is more than 18 GPa, the difference in hardness between the transformation product at low temperature and a soft ferrite phase is increased by contraries, and voids occur locally in the initial deformation stage, and from there ductile fracture is likely to develop and local deformability to decrease. Additionally, a range of nano-hardness becomes 1.2 GPa or less in terms of standard deviation, and thus the occurrence of void locations in the initial deformation stage is suppressed.
[00177] Next, a method of manufacturing a steel sheet of the present invention will be explained.
[00178] In the present invention, a method of manufacturing a steel billet (sheet) that has the components described above to be carried out before a hot rolling step is not particularly limited. That is, as a method of manufacturing a billet steel (sheet) that has the components described above, it can also be determined that subsequent to a melting step by
32/73 a vat oven, a converter, an electric oven, or the like, the component adjustment is performed differently to obtain desired component contents in a secondary refinement step, and then a casting step is performed by normal continuous casting, ingot casting, or a thin sheet casting method or the like. By the way, refuse can also be used as a raw material. In addition, when a plate is obtained by continuous casting, an intact high temperature cast plate can be transformed directly into hot rolling, or the plate can also be hot rolled after being cooled to room temperature and then reheated in a furnace. heating.
[00179] The sheet obtained by the manufacturing method described above is heated in a heating oven at a minimum sheet reheat temperature (= SRTmin) or higher, which is calculated based on Expression (1), in a heating step sheet metal before hot rolling.
SRT _min = 10780 / {5.13 - log ([Ti] x [C])} - 273 Expression (1) [00180] When it is lower than this temperature, the Ti carbonitride is not sufficiently melted in a material base. In this case, it is not possible to obtain an effect in which the strength is improved by using precipitation strengthening obtained by fine precipitation of Ti as carbide during cooling after finishing finishing lamination or after winding. In this way, the heating temperature in the plate heating step is determined for the minimum plate reheating temperature (= SRT _min ) or higher, which is calculated in Expression (1). Incidentally, when the heating temperature is lower than 1,100 ° C, operating efficiency is significantly impaired in terms of a schedule, so that desirably the heating temperature is 1,100 ° C or higher.
[00181] Additionally, a heating time in the plate heating step is not defined in particular, but in order to sufficiently promote the fusion of Ti carbonitride, after the temperature reaches the heating temperature described above, the plate is desirably maintained for 30 minutes or more. In addition, when the plate is sufficiently and evenly heated in a direction of thickness of the plate, it is desirably maintained for 60 minutes or more. On the other hand, in terms of a decrease in performance caused by peeling, it is 240 minutes or less. However, when the molten sheet obtained after casting is transferred directly to be laminated in a high temperature state, the above is not applied.
[00182] After the plate heating step, in the plate extracted from the heating furnace, a hot rolling crude lamination step is started without any particular waiting time, and a coarse bar is obtained. In this stage of rough rolling, rough rolling must be performed at a rolling rate of at least 20% or more for at least one passage in a temperature zone of at least 1,050 ° C and at most 1,150 ° C.
[00183] When a rough rolling finish temperature is lower than 1,050 ° C, the resistance to hot deformation during rough rolling increases, which results in the rough rolling operation being damaged. When it is higher than 1,150 ° C, secondary scale that is generated during rough lamination grows too much, resulting in the fact that the flaking to be carried out later and the removal of scale in the finishing lamination can be difficult to be carried out.
[00184] Additionally, unless lamination at a lamination ratio of 20% or greater is performed on the raw lamination on
34/73 temperature zone, the refinement of crystal grains with the use of work and subsequent recrystallization from austenite, and anisotropy resolution caused by a solidified structure cannot be expected. In this way, the transformation behavior after the finishing lamination is affected, the shape of the transformation product at low temperature, which is a second phase in the microstructure of the biphasic steel sheet, changes from an island shape to a film shape, and the deburring viability deteriorates. In addition, when the cast plate obtained after casting is transferred directly to be laminated in a high temperature state, a casting structure remains, and the shape change of the transformation product at low temperature which is a second phase to the shape of film may be noticeable.
[00185] The number of lamination passes in the rough lamination is preferably plural passages, that is, it is two passes or more. When plural passages are applied, austenite work and recrystallization are performed repeatedly and the average austenite grains before finishing lamination are refined to 100 pm or less, resulting in the average grain diameter of the transformation product at temperature low which is a second hard stage is produced with 12 pm or less stably.
[00186] Additionally, the ratio of total reduction in gross rolling is preferably 60% or more. When the total reduction ratio is less than 60%, the effect of refining austenite grains described above cannot be achieved sufficiently. However, even when the ratio of total reduction in gross rolling is more than 90%, the effect is saturated and in addition the number of passes is increased to hinder productivity, and a decrease in temperature can be caused. Additionally, due to the reason
35/73 similarly, desirably the number of tickets is 11 or less. [00187] The finishing lamination is performed after the completion of the gross lamination. The period of time until the start of the finishing lamination after the completion of the rough lamination is within 150 seconds.
[00188] When this period of time is longer than 150 seconds, in the coarse bar, Ti in austenite precipitates as thick TiC carbide. As a result, the amount of TiC to precipitate finely in the ferrite at the time of austenite / ferrite transformation during cooling to be carried out later or at the time of completion of the transformation of the ferrite after winding and to contribute to strength by strengthening by precipitation decreases and the resistance decreases. In addition, austenite grain growth progresses and thus the average austenite grains before the finishing lamination become coarse, getting larger than 100 qm, resulting in the average grain diameter of the transformation product at low temperature which is a hard second phase is sometimes completed with more than 15 qm.
[00189] On the other hand, the lower limit value of the time period until the start of the finishing lamination after the completion of the rough lamination does not have to be limited in particular. However, when it is shorter than 30 seconds, a finish laminating start temperature does not drop below 1.080 ° C unless a special cooling device is used, and bubbles that are a starting point of fouling and fusiform fouling defects occur between the surface of a steel sheet base iron and fouling before finishing lamination and during passes, so that fouling defects are likely to be generated. Thus, it is desirably 30 seconds or more.
36/73 [00190] A lamination start temperature of the finishing lamination is determined to be 1000 ° C or higher and lower than 1,080 ° C.
[00191] When this temperature is lower than 1,000 ° C, Ti precipitates in austenite as coarse TiC carbide by pressure-induced precipitation during finishing lamination. As a result, the amount of TiC to precipitate finely in the ferrite at the time of austenite / ferrite transformation during cooling to be carried out later or at the time of completion of the transformation of the ferrite after winding and to contribute to strength by precipitation strength decreases and the resistance decreases.
[00192] On the other hand, when this temperature is higher than 1,080 ° C, bubbles that are a starting point for inlays and fusiform inlay defects occur between the surface of an iron base of the steel sheet and inlays before finishing lamination and during passes, so it is likely that these fouling defects will be generated.
[00193] A finishing lamination completion temperature is determined to be no lower than an Ar3 + 50 ° C transformation point temperature and a maximum of 1,000 ° C.
[00194] The transformation point temperature Ar3 is expressed simply, for example, by the following calculation expression in relation to the steel components. That is, it is described by Expression (5) below.
Ar3 = 910 - 310 x [C] + 25 x {[Si] + 2 x [Al]} - 80 x [Mn _eq ] Expression (5) [00195] Here, when B is not added, [Mn _eq ] is expressed by Expression (6) below.
[Mn _eq ] = [Mn] + [Cr] + [Cu] + [Mo] + [Ni] / 2 + 10 ([Nb] - 0.02) Expression (6) [00196] Additionally, when B is added , [Mneq] is expressed
37/73 by Expression (7) below.
[Mn _eq ] = [Mn] + [Cr] + [Cu] + [Mo] + [Ni] / 2 + 10 ([Nb] - 0.02) + 1 Expression (7) [00197] By the way, [ C] is the content of C (% by mass), [Si] is the content of Si (% by mass), [Al] is the content of Al (% by mass), [Cr] is the content of Cr ( % by mass), [Cu] is the content of Cu (% by mass), [Mo] is the content of Mo (% by mass), [Ni] is the content of Ni (% by mass), and [Nb ] is the Nb content (% by mass).
[00198] When the finishing temperature of finishing lamination is lower than the transformation point temperature Ar3 + 50 ° C, the transformation products at low temperature in the microstructure of the biphasic steel sheet are brought to a dispersion state where they are continuously arranged in an aligned manner. In addition, the average value of the closest approximation distance between transformation products at low temperature becomes less than 10 gm, voids are likely to be connected, ductile fracture is likely to be caused, and deburring viability deteriorates .
[00199] On the other hand, when it is higher than 1,000 ° C, even when a cooling pattern after lamination is controlled in any way, the transformation of the ferrite becomes insufficient and the fraction of area of the transformation product the low temperature in the microstructure of a product sheet becomes greater than 10%, and the deburring viability deteriorates after all.
[00200] Additionally, the finishing lamination is lamination with plural passages through a strip laminator, and the total reduction ratio is not less than 75% and at most 95%.
[00201] As long as the finishing lamination is carried out in a strip laminator that allows lamination with plural passages, the reduction is carried out through plural passages in the lamination, and
38/73 thus the non-recrystallization by lamination and recrystallization for a period of time interpassing until the next passage are repeated plural times. As a result, austenite grains are refined and the average grain diameter of the transformation product at low temperature in the microstructure of the biphasic steel sheet can be completed with 15 pm or less. However, when the total reduction ratio is less than 75%, the austenite grains cannot be refined sufficiently and the average grain diameter of the transformation product at low temperature in the microstructure of the biphasic steel sheet cannot be completed with 15 pm or less.
[00202] On the other hand, when it is more than 95%, the effect is saturated, and in addition an excessive load is applied to the laminator, so that it is not operationally preferred.
[00203] Additionally, a reduction ratio in each pass is desirably 10% or more. When the reduction ratio in each pass is less than 10% for three passes in the back support of a particular finisher and an average rolling ratio for three passes is less than 10%, grain growth progresses significantly during the three passes and after finishing the finishing lamination, and there is a risk that the average grain diameter of the low temperature transformation product in the microstructure of the biphasic steel sheet will no longer be able to be completed by 12 pm or less.
[00204] By the way, in the present invention, a lamination speed is not limited in particular. However, when the lamination speed on a final finishing support is less than 643.74 kmpm (400 mpm), the time period for each finishing lamination pass is extended. As a result, austenite grains grow to be thick, and there is a risk that the diameter
39/73 average grain of the transformation product at low temperature in the microstructure of a product sheet is no longer able to be stably finished with 15 μm or less. Therefore, the lamination speed is desirably 643.74 kmpm (400 mpm) or more. Additionally, when it is 1,046.07 kmpm (650 mpm), the average grain diameter of the low temperature transformation product can be completed with 12 μm or less stably, so that 1,046.07 kmpm (650 mpm) is additionally desirable. Additionally, even if the upper limit is not particularly limited, the effect of the present invention is achieved, but it is realistically 2,896.82 kmpm (1,800 mpm) or less due to the installation restriction.
[00205] After finishing the finishing lamination, in order to elaborate the microstructure of a product, optimized cooling is carried out by controlling an execution table.
[00206] First, the period of time until the start of cooling after the completion of the finishing lamination is within three seconds. When this period of time until the start of cooling is longer than three seconds, in the austenite before being transformed, the precipitation of coarse and misaligned Ti carbonitride progresses, the amount of fine and aligned Ti carbide precipitation to precipitate in the ferrite during cooling to be carried out later decreases, and the resistance can be reduced. In addition, austenite grains grow to be thick, and there is a risk that the average grain diameter of the low temperature transformation product in the microstructure of the product sheet will no longer be able to be finished with 15 μm or less.
[00207] The lower limit value of the period of time until the start of that cooling does not have to be limited in particular in the present invention, but when it is shorter than 0.4 seconds.
40/73 dos, the cooling is carried out in a state where a worked lamellar structure obtained by lamination remains, even in a product sheet, the low temperature transformation products are obtained, continuously arranged in an aligned manner, and the viability of deburring can deteriorate.
[00208] As for the rate of a first stage cooling step to be performed first after lamination is complete, an average cooling rate of 15 ° C / sec or more is required. When this cooling rate is less than 15 ° C / sec, perlite is formed during cooling, and a desired microstructure may not be obtained. By the way, even if the upper limit of the cooling rate in the first stage cooling step is not limited in particular, the effect of the present invention can be obtained. However, when the cooling rate is more than 150 ° C / sec, it is extremely difficult to control a cooling completion temperature to make it difficult to design the microstructure, so that it is desirably set to 150 ° C / sec or less.
[00209] A cooling stop temperature in the first stage cooling step is lower than the transformation point temperature Ar3. When the cooling stop temperature is the transformation point temperature Ar3 or higher, it is not possible to perform TiC precipitation control to precipitate finely in the ferrite during the austenite / ferrite transformation time during cooling in the second stage cooling step. and contribute to resistance. On the other hand, the lower limit of the cooling stop temperature of the first stage cooling step is not particularly limited. However, a cooling temperature of the subsequent second stage cooling step to be performed to exhibit strengthened
41/73 ferrite precipitation is higher than 600 ° C as a condition to exhibit strengthening by ferrite precipitation. Thus, if the cooling stop temperature of the first stage cooling step is 600 ° C or lower, precipitation strengthening cannot be achieved. In addition, when it becomes an Ar1 point or lower, ferrite cannot be obtained and, therefore, it becomes impossible to obtain a desired microstructure.
[00210] In the second stage cooling step to be performed next, an average cooling rate is 10 ° C / sec or less and, in the present invention, air cooling (stopped to cool) is kept in mind. During cooling in this temperature zone, the transformation from austenite to ferrite is promoted, and simultaneously with the transformation, fine Ti carbide precipitates in the ferrite, and a desired strength of the steel sheet is obtained. When this cooling rate is greater than 10 ° C / sec, a movement speed of an interface between these two phases in the transformation from austenite to ferrite becomes too fast, so that the precipitation of Ti carbide at the interface between the phases cannot accompany it and strengthening by sufficient precipitation cannot be achieved.
[00211] Additionally, when it is greater than 10 ° C / sec, the transformation from austenite to ferrite is delayed and a desired microstructure cannot be obtained. On the other hand, the lower limit of the cooling rate in the second stage cooling step does not have to be limited in particular in the present invention. However, unless heat is input externally by a heating device, or the like, the cooling rate in air cooling is approximately 3 ° C / sec despite the sheet thickness being 1.25 cm (half inch)
42/73 maximally, which is an upper sheet thickness limit assumed in the present invention.
[00212] Additionally, a cooling time period in the second stage cooling step is 1 second or longer and shorter than 100 seconds. This step is an extremely important step not only to promote the separation of two phases of ferrite and austenite obtaining a desired fraction of the second phase, but also to promote the strengthening by precipitation of fine Ti carbide in the ferrite obtained after the transformation is completed. When that period of time is shorter than 1 second, the transformation of the ferrite does not progress and a desired microstructure cannot be obtained, and in addition, the precipitation of Ti carbide in the ferrite obtained after the transformation does not progress, so that the desired strength and deburring viability of the steel sheet cannot be achieved. When it is shorter than 3 seconds, the transformation of ferrite and carbide precipitation does not progress sufficiently, so it is desirably 3 seconds or longer due to the risk that low temperature transformation products and ferrite resistance can no longer be obtained sufficiently.
[00213] On the other hand, even when it is 100 seconds or longer, the effect described above is saturated and additionally the productivity decreases significantly. When it is 15 seconds or longer, the average crystal diameter of the transformation product at low temperature of the biphasic steel sheet becomes thick, and additionally there is a question that the pearlite is mixed in the microstructure, so that the even desirably it is shorter than 15 seconds.
[00214] The cooling stop temperature in the second stage cooling step is higher than 600 ° C. When this
43/73 temperature is 600 ° C or lower, the precipitation of Ti carbide in the ferrite obtained after the transformation does not progress, so that the resistance decreases.
[00215] On the other hand, the upper limit of the cooling stop temperature in the second stage cooling step is not defined in particular, but when it is higher than 700 ° C, the separation of two phases of ferrite and austenite is not sufficient and a desired fraction of the transformation product cannot be obtained at low temperature, and in addition, the precipitation of Ti carbide in the ferrite is late and the resistance decreases.
[00216] In a third stage cooling step to be carried out subsequently, cooling is carried out at a cooling rate of 15 ° C / sec or greater. When that cooling rate is less than 15 ° C / sec, the pearlite is mixed in the microstructure, and thus a desired microstructure may not be obtained. By the way, a completion temperature for the third stage cooling step is a winding temperature. Although the upper limit of the cooling rate in the third stage cooling step is not particularly limited, the effect of the present invention can be obtained, but when a leaf split caused by thermal deformation is considered, it is desirably determined to be 300 ° C / sec or less.
[00217] In the third stage cooling step, the steel sheet is cooled to a temperature zone of 350 ° C or lower to be rolled. When that temperature is higher than 350 ° C, the desired products of the low temperature transformation cannot be obtained. Concretely, thick carbide is formed between the blades of bainite that constitute the transformation product at low temperature, which will be a starting point for the occurrence of a crack in the deburring time, and the deburring viability has been determined.
[00218] On the other hand, the lower limit value of the winding temperature does not have to be limited in particular, but when a roller is in a state of being exposed to water for a long time, appearance flaws caused by oxidation are considered, so that it is desirably 50 ° C or higher. In addition, when that temperature is 100 ° C or lower, most of the transformation product at low temperature turns into fresh martensite and uniform elongation improves so as to be advantageous to form with a n-dominant value such as bulging.
[00219] In order to exhibit strengthening by Ti carbide precipitation more efficiently in the cooling step after finishing lamination, it is necessary to control a cooling pattern up to the winding itself. Concretely, a total cumulative diffusion dimension Ltot _al of Ti in the ferrite expressed by Expression (2) below is controlled in the range of at least 0.15 and at most 0.5.
[00220] That is, when the total cumulative diffusion dimension L _total Ti in the ferrite is expressed by Expression (3) below by adding a dimension of diffusion L Ti in the ferrite expressed by Expression (2) below for a period of very short time Át / sec. of a cooling completion temperature for winding, 0.15 L _total = 0.5 is satisfied.
L = ^ D (T + 273) t Expression (2) L _to t _al = Z ^ (D (T + 273) At) Expression (3) [00221] Here, D (T + 273) is a diffusion coefficient of volume in T ° C and t is a diffusion time period, and D (T) is expressed by Expression (4) below using a diffusion coefficient D0 of Ti, an activation energy Q, and a constant of gas R.
45/73
D (T) = DO x Exp (-Q / R (T + 273)) Expression (4) [00222] When that _total L value is less than 0.15 gm, Ti carbide precipitation does not progress during cooling to result in anticipation, which results in the ability to strengthen by precipitation cannot be obtained efficiently. On the other hand, when it is greater than 0.5 gm, the precipitation of Ti carbide progresses too much during cooling and results in delay, which results in the fact that after all, the capacity for strengthening by precipitation cannot be obtained efficiently.
[00223] By the way, in order to achieve improvement in ductility by correcting the shape of the steel sheet and introducing mobile displacement, hardening lamination at a reduction rate of at least 0.1% and at most 2% it is desirably carried out after all steps have been completed. In addition, in order to remove encrustations fixed to the surface of a obtained hot-rolled steel sheet, decaling can also be carried out on the hot-rolled steel sheet obtained according to the need after all steps are completed. Additionally, after pickling, on the obtained hot-rolled steel sheet, hardening at a reduction rate of 10% or less can also be carried out on-line or off-line, or cold rolling can also be carried out at a rate of reduction of approximately 40%.
[00224] Additionally, before or after, or before and after the hardening lamination, the incrustations on the surface are removed. The step of removing fouling is not defined in particular. For example, pickling in general with the use of hydrochloric acid or sulfuric acid, or a device according to a line such as surface sanding by a sander or the like or surface removal using plasma, a gas burner, or the like can be
46/73 applied.
[00225] Additionally, after casting, after hot rolling, or after cooling, a hot treatment can be carried out on a hot rolled steel sheet with the present invention applied to it in an immersion deposition line at hot, and additionally on the hot-rolled steel sheet, an additional surface treatment can also be carried out. Deposition is carried out on the hot-dip deposition line, thereby improving the corrosion resistance of the hot-rolled steel sheet.
[00226] By the way, when galvanizing is carried out on the hot-rolled steel sheet obtained after pickling, the obtained steel sheet can also be immersed in a galvanizing bath to be subjected to an alloy treatment according to the need. When carrying out the alloy treatment, the hot-rolled steel sheet improves resistance to welding against various bores such as spot welding in addition to the improvement in resistance to corrosion.
EXAMPLE [00227] A to Z eaad steels that have the chemical components shown in Table 1 were melted in a refinement converter and secondary refinement step, steel billets (sheets) manufactured by continuous casting were reheated and reduced, each, to one sheet thickness from 2.3 to 3.4 mm by finishing lamination after rough lamination, and each was cooled on an execution table to then be rolled, and hot-rolled steel sheets were prepared. More specifically, according to the manufacturing conditions shown in Tables 2 and 3, hot-rolled steel sheets were prepared. By the way, all of the chemical compositions in Table 1 mean% by mass.
[00228] In Table 1, Ti * represents [Ti] - 48/14 [N] - 48/32 [S], in Tables 1 and 2, Ex.C represents [C] - 12/48 x ([Ti] + 48/93 [Nb]
47/73
48/14 [N] - 48/32 [S]), and in Table 1, Mn / S represents [Mn] / [S]. In addition, the rest of the components in Table 1 are Fe and impurities, each underlined in Tables 1 and 2 indicates that a numerical value is outside the scope of the present invention. Each of the K and R steels does not contain Si intentionally. In Table 1, “-” indicates that there is no intentional content.
[00229] In Table 2, “STEEL” indicates a steel that has the components that correspond to each symbol shown in Table 1. “SOLUTION TEMPERATURE” indicates the minimum plate reheat temperature (= SRTmin) calculated by Expression (1) . “TRANSFORMATION POINT TEMPERATURE Ar3” indicates a temperature calculated by Expression (5), (6), or (7). “Ex.C” indicates a value calculated by [C] - 12/48 x ([Ti] + 48/93 [Nb] - 48/14 [N] - 48/32 [S]).
[00230] In the manufacturing conditions in Tables 2 and 3, in the heating step, “HEATING TEMPERATURE” indicates a maximum final temperature in the reheating of the plate and “MAINTENANCE TIME PERIOD” indicates a period of maintenance time at a temperature predetermined heating In the crude lamination, “TOTAL AMOUNT OF TICKETS” indicates a total value of the amount of lamination passes in crude lamination, “TOTAL REDUCTION REASON” indicates a ratio of reduction in the crude lamination from the beginning to the conclusion of crude lamination, “QUANTITY OF PASSAGES at 1,050 to 1,150 ° C and at 20% or more ”indicates the number of passes of which lamination at a lamination ratio of 20% or more was performed in a temperature zone of 1,050 to 1,150 ° C,“ TIME PERIOD UNTIL THE START OF FINISHING LAMINATION "indicates a period of time until the start of the finishing lamination after the completion of rough lamination, and" AVERAGE AUSTENITE GRAIN DIAMETER IMMEDIATELY BEFORE THE FINISHING LAMINATION "indicates an average diameter
48/73 austenite grain grain just before a coarse bar is attached to the first finishing laminating support. The recognition of this austenite grain diameter can be obtained in such a way that a cut piece obtained by cutting a coarse bar before being subjected to the finishing lamination by cut scissors or the like is tempered as much as possible to be cooled down to the room temperature approximately, and a cross-sectional section parallel to a rolling direction is corroded to make the austenite grain boundaries appear to measure the diameter of austenite grains through an optical microscope. On that occasion, 20 visual fields or more at the position of 1/4 of a sheet thickness are measured at 50 or more magnifications by image analysis, a point counting method, or the like.
[00231] In finishing lamination, the “LAMINATION START TEMPERATURE” indicates a temperature just before a coarse bar is attached to the first finishing lamination support, the “TOTAL REDUCTION RATIO” indicates a reduction ratio during lamination of finish from start to finish of finishing laminate, the “AVERAGE REDUCTION RATIO FOR 3 PASSAGES ON THE REAR SUPPORT” indicates an average value of reduction ratios of the final pass that includes the final pass to the third pass in the finish laminate in which lamination continuous with plural passages is normally performed, “FINISHING LAMINATION OUTPUT SIDE SPEED” indicates a passing speed on the leaf exit side of the lamination support after a final finishing lamination reduction pass is completed, and “TEMPERATURE OF FINISHING ”indicates a temperature immediately after a l support outlet side amination of a final finishing lamination pass. By the way, the reduction ratio can be a performance value
49/73 actual performance calculated from a thickness of the sheet, or it can also be an installation value of a lamination support. Additionally, the temperature is desirably measured in the stop position with a radiation thermometer or a contact thermometer, but it can also be an estimated value obtained by a temperature model or similar.
[00232] The cooling step performed on an execution table is divided into first to third stages of the cooling step in terms of precipitation control and structure control. First, in the “FIRST STAGE COOLING STEP”, the “TIME PERIOD UNTIL THE STARTING OF THE COOLING” indicates a period of time until the start of cooling on an execution table after passing through a lamination support of a passage end of finishing lamination, “COOLING RATE” indicates an average cooling rate per water cooling, and “COOLING STOP TEMPERATURE” indicates a temperature at which the water cooling in the first stage cooling step is stopped. In the “SECOND STAGE COOLING STEP”, the “COOLING RATE” indicates an average cooling rate for cooling air without spilling water particularly, “MAINTENANCE TIME PERIOD” indicates an air cooling maintenance time period without spill water, and “COOLING STOP TEMPERATURE” indicates a temperature at which the air cooling maintenance without spilling water is complete. In the "THIRD STAGE COOLING STEP", the "COOLING RATE" indicates an average cooling rate until the water and winding cooling restart after air cooling and maintenance, and "WINDING TEMPERATURE" indicates a temperature just before a sheet of steel to be rolled into a shape
50/73 roll by a winder after stopping water cooling. By the way, “TOTAL CUMULATIVE DIFFUSION DIMENSION” indicates the total cumulative diffusion dimension Ltotal of Ti in the ferrite and is obtained by Expression (3) by adding the dimension of diffusion L of Ti in the ferrite expressed by Expression (2) for the period very short time Át / sec. from a cooling completion temperature to winding.
[00233] The microstructures of steel sheets obtained by manufacturing methods described in Tables 2 and 3 are shown in Table 4, and mechanical property, surface property, and corrosion resistance are shown in Table 5.
[00234] First, a sample was taken from position 1 / 4W or position 3 / 4W of a sheet width of each of the steel sheets obtained, and using an optical microscope, each microstructure in 1/4 thickness was observed of a sheet thickness. As a sample fit, a sheet thickness cross section in the lamination direction was polished as an observation surface to be subjected to corrosion with a nital reagent and a LePera reagent. From each optical micrograph in 500 magnifications of the cross-sectional sections of the sheet thickness corroded with a nital reagent and a LePera reagent, the “MICROSTRUCTURE” was classified.
[00235] Additionally, from each of the optical micrographs in 500 enlargements of the cross-sectional sections of the sheet thickness corroded with a LePera reagent, the “SECOND CHARACTERISTIC PHASE” which is a state of distribution of the transformation product at low temperature which is a second phase has been recognized by an image analysis. Here, the dispersion state of the low temperature transformation product is classified into one in which the low temperature transformation products are dispersed in
51/73 an island shape in a corner, an edge, and a grain boundary surface of a ferrite grain like “ISLAND FORMAT,” one in which they are island-shaped, but are continuously distributed parallel to the lamination direction as “ALIGNED STATUS”, and one in which they are dispersed to wrap a grain boundary surface of a ferrite grain mainly as “FILM FORMAT”.
[00236] Additionally, by the image analysis, the “SECOND PHRASE PHASE” which is the fraction of area of the transformation product at low temperature which is a second phase and “MEDIUM GRAIN DIAMETER IN THE SECOND PHASE” which is the average diameter of the grain of the transformation product at low temperature were obtained. “Ex.C (%) / fsd (%)” is a value of “Ex.C (%)” in Table 2 divided by “SECOND PHASE FRACTION.” By the way, the average crystal diameter of the transformation product at low temperature is one in which the equivalent circle diameters are weighted. In addition, low temperature plural transformation products were selected arbitrarily, the respective closest distances were obtained, and an average value of 20 points was determined for “AVERAGE DISTANCE VALUE OF HIGHEST APPROXIMATION BETWEEN SECOND PHASES”.
[00237] Hn nanohardness was measured using TriboScope / TriboIndenter manufactured by Hysitron. As the measurement condition, the hardness of the transformation product at low temperature was measured at 20 points or more with 1 mN of load, and an arithmetic mean and standard deviation were calculated.
[00238] The measurement of "FERRITE TiC DENSITY" which is a density of TiC precipitate was performed by a three-dimensional atomic probe measurement method. First, an acicular sample is prepared from a sample to be measured by cutting and it
52/73 tropolishing, and using focused ion beam milling together with electropolishing as needed. In three-dimensional atomic probe measurement, integrated data can be reconstructed to obtain a real image of the distribution of atoms in a real space. A numerical density of TiC precipitates is obtained from the volume of a three-dimensional distribution image of TiC precipitates and the amount of TiC precipitates. By the way, the measurement was performed in a way that ferrite grains are specified and five or more of the ferrite grains are used for each sample. In addition, as for the size of the TiC precipitates described above, a diameter calculated from the amount of atoms that constitute the observed TiC precipitates and a TiC network constant assuming that the precipitates are spherical is determined as the size. Arbitrarily, the diameters of 30 or more of the TiC precipitates were measured. Their average value was approximately 2 to 30 nm.
[00239] The mechanical properties, tensile properties (YP, TS, and El) were measured based on JIS Z 2241 to 1998 using a test piece No. 5 of JIS Z 2201-1998 taken from position 1 / 4W or position 3 / 4W of the width of the sheet in a vertical direction to the lamination direction. As an index of deburring viability, an orifice expansion test was employed. In relation to the orifice expansion test, a test piece was taken from the same position as the one where a tensile test piece was taken, and the deburring feasibility was assessed based on a test method described in the Federation specification. Japanese Iron and Steel JFS T 1001-1996.
[00240] Next, in order to examine the chamfer fatigue strength, a fatigue test piece that has a shape shown in Figure 1 was taken from the same position as the one where the en
53/73 pull-out was taken so that the side in the lamination direction could be a long side and was subjected to a fatigue test. Here, the fatigue test piece described in Figure 1 is a chamfered test piece prepared to obtain chamfer fatigue strength. Corner portions of the side surface (portions surrounded each by a dotted line in Figure 1) of this chamfered test piece are chamfered each with 1R to be polished in the longitudinal direction with # 600.
[00241] In order to address the fatigue property assessment in real use of an auto part, the chamfer was made by drilling with a cylindrical drill in the same way as that of the orifice expansion test part. By the way, a drilling clearance has been determined to be 12.5%. However, in the fatigue test piece, fine finishing sanding was carried out to a depth of approximately 0.05 mm from the topmost surface layer. A Schenck fatigue test machine was used for the fatigue test, and a test method was based on JIS Z 2273-1978 and JIS Z 2275-1978. “Owk / TS” which is the definition of the fatigue chamfer property in Table 3 is a value of a fatigue strength of 2 million cycles obtained by this test divided by a tensile strength.
[00242] The surface property was evaluated by "SURFACE DEFECT" and "HARDNESS" before blasting. When this assessment is equal to or less than the reference, there is sometimes a case in which the surface quality is assessed according to a pattern and unevenness of the surface caused by an inlay defect by subordinates and customers even after stripping. Here, "SURFACE DEFECT" indicates a result obtained by visual recognition of the PRESENCE / ABSENCE of fouling defects such as Si fouling, fouling, and fusiform, and the case of defects
54/73 fouling is present is shown as “x” and the case of no fouling defect is shown as “O ·” By the way, one where these defects are partial or the reference or minor is considered to be “LIGHT” and is shown as “δ”. “ASPEREZA” is evaluated by Rz and indicates a value obtained by a measurement method described in JIS B 0601-2001. By the way, as long as Rz is 20 pm or less, the surface quality is a problem-free level.
[00243] Corrosion resistance was assessed by "CONVERSION TREATMENT PROPERTY" and "POST-COATING CORROSION RESISTANCE." First, the fabricated steel sheets were stripped, and then subjected to a conversion treatment in which a 2.5 g / m ² zinc phosphate coating film is fixed. At this stage, measurements of presence / absence of absence of coverage and a P ratio as “CONVERSION TREATMENT PROPERTY” were performed.
[00244] The conversion treatment with phosphoric acid is a treatment using a chemical solution that has phosphoric acid and Zn as its main components, and is a chemical reaction to generate a crystal called phosphophilite: FeZn2 (PO4) 3- 4H2O between Fe ions to liquefy from the steel sheet. The technical points of the conversion treatment with phosphoric acid are (1) making Fe ions liquefy to promote the reaction and (2) densely forming phosphophilite crystals on the surface of the steel sheet. Particularly in relation to (1), when oxides attributable to the formation of Si incrustations remain on the surface of the steel sheet, Fe liquefaction is prevented and a portion to which a non-fixed conversion coating film, which is called from the absence of coverage, an abnormal conversion coating film treatment that is not normally formed on the surface of an iron, called hopeite, appears, due to no Fe liquefaction: Zn3 (PO4) 3-4H2O, is formed, and
Thus, performance after coating sometimes deteriorates. Thus, it becomes important to make the surface normal so that by liquefying Fe on the surface of the steel sheet with phosphoric acid, the Fe ions can be supplied sufficiently.
[00245] This absence of coverage can be recognized by observation by an electron scanning microscope, 20 visual fields are observed in approximately 1000 magnifications, and the case where the conversion coating film is fixed uniformly to the entire surface and no absence of coverage can be recognized is considered as no absence of coverage to be shown as "O". Additionally, the case where the visual field with recognition of no coverage is 5% or less is considered to be light to be shown as "δ." In addition, the case where there is more than 5% is considered as the absence of coverage to be assessed as “x”.
[00246] On the other hand, the P ratio can be measured using an X-ray diffraction device, a ratio of an X-ray diffraction intensity of the phosphophilite plane (100) and a diffraction intensity is taken of the X-rays of H from the hopeite plane (020), and the ratio of P is evaluated by reason of P = P / (P + H). That is, the ratio of P represents the ratio of hopeite and phosphophilite in the coating film obtained by carrying out the conversion treatment, and it means that when the ratio of P is higher, more phosphophyllite and phosphophilite crystals are formed thick on the surface of the steel sheet. Generally, P 1 0.80 ratio is required in order to satisfy anti-corrosion performance and coating performance, and under severe corrosive environment such as in a defrosting salt dispersion region, P 1 0.85 ratio is required.
[00247] Next, in relation to corrosion resistance, electrodeposition coating was carried out to have a thickness of 25 pm
56/73 after the conversion treatment and a coating and cooking treatment was carried out at 170 ° C x for 20 minutes, and then an incision that has a dimension of 130 mm was made in an electroplating coating film to reach the iron base with a knife that has a sharp end, and under a salt spray condition described in JIS Z 2371, 5% salt spray was performed at a temperature of 35 ° C for 700 hours continuously and then a tape (Nichiban Co., Ltd. 405A-24 JIS Z 1552) which has a width of 24 mm and which has a dimension of 130 mm was applied over the incision portion parallel to the incision portion, and the maximum peeled width of coating film obtained after the tape was peeled it was measured. With that maximum stripped coating film width of more than 4 mm, it has been defined that the corrosion resistance is lower.
[00248] Next, the results will be explained. By the way, in relation to Steel Numbers 32, 36, and 46, the sheet was passed through a hot dip galvanizing line of the alloy after pickling, and at a Zn bath temperature of 430 to 460 ° C, immersion was carried out in a deposition bath, and in Steel 32 and 46 among them, an alloy treatment was carried out at an alloy temperature of 500 to 600 ° C.
[00249] Steel numbers 1, 4, 9, 10, 11, 20, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38 , and 39 are in accordance with the present invention.
[00250] These steel sheets are steel sheets of grades that are 540 MPa and larger grades that contain predetermined amounts of steel components and where in the position of 1/4 thickness of the sheet thickness, a microstructure is biphasic with its main phase composed of polygonal ferrite strengthened by precipitation by Ti carbide and its second phase composed by 1 to 10%
57/73 in fraction of area (fsd (%)) of low temperature transformation products dispersed in an island format, 0.001 Ex.C (%) / fsd (%) <0.01 (Ex.C (%) = [C] - 12/48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] 48/32 x [S]}) is satisfied, an average crystal diameter of the transformation product the low temperature is 3 to 15 gm, and an average value of a closer distance between the transformation products, the low temperature is 10 to 20 gm, and high strength steel sheets can be obtained that have a value of orifice expansion λ 1 70%, which has a fatigue chamfer property of oWK / TS 0.35, and which has slight surface defects or no surface defects.
[00251] The steel numbers 32 and 39 contain Steel K and R which do not intentionally contain any Si, respectively, and their Si content is 0 or an impurity level. However, steel numbers 32 and 39 also satisfy the mechanical property of the present invention.
[00252] Steels other than those mentioned above are outside the scope of the present invention due to the following reasons.
[00253] That is, in relation to the number of Steel 2, the heating temperature is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength is low.
[00254] In relation to the number of Steel 3, the ratio of total reduction of the crude rolling is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the orifice expansion value is low.
[00255] Regarding the number of Steel 5, the number of passes at 1,050 to 1,150 ° C and 20% or more is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot obtained and the value of expan58 / 73 is orifice is low.
[00256] Regarding the number of Steel 6, the period of time until the start of the finishing lamination is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the resistance to traction and orifice expansion value are low.
[00257] Regarding the number of Steel 7, the temperature of the start of finishing rolling is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength is low .
[00258] Regarding the number of Steel 8, the total reduction ratio of the finishing lamination is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the expansion value of orifice is low.
[00259] Regarding the number of Steel 12, the finishing temperature of finishing lamination is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the orifice expansion value is low.
[00260] Regarding the number of Steel 13, the finishing temperature of finishing lamination is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the orifice expansion value is low.
[00261] Regarding the number of Steel 14, the period of time until cooling is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength and value orifice expansion are low.
59/73 [00262] Regarding the number of Steel 15, the cooling rate of the cooling (a) is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the value Orifice expansion and fatigue chamfer property are low.
[00263] Regarding the number of Steel 16, the cooling stop temperature of the cooling (a) is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the resistance to traction and the fatigue chamfer property are low.
[00264] Regarding the number of Steel 17, the cooling stop temperature of the cooling (a) is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the resistance to traction and the fatigue chamfer property are low.
[00265] Regarding the number of Steel 18, the cooling rate of the cooling (b) is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength and the orifice expansion value is low.
[00266] Regarding the number of Steel 19, the cooling maintenance time period (b) is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the resistance to traction and the fatigue chamfer property are low.
[00267] Regarding the number of Steel 21, the cooling rate of the cooling (c) is outside the range of the steel fabrication method of the present invention, so that the predetermined microstructure cannot be obtained and the expansion value of orifice and fatigue chamfer property are low.
60/73 [00268] Regarding the Steel number 22, the winding temperature is outside the range of the steel fabrication method of the present invention, so the predetermined microstructure cannot be obtained and the orifice expansion value is low.
[00269] In relation to Steel number 40, the C content is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the orifice expansion value is low.
[00270] Regarding the number of Steel 41, the C content is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength is low.
[00271] Regarding the number of Steel 42, the Si content is outside the scope of the steel of the present invention, so that the surface property is poor.
[00272] Regarding the number of Steel 43, the Mn content is outside the scope of the steel of the present invention, so that cracking of the plate occurs which makes lamination impossible.
[00273] Regarding the number of Steel 44, the Mn content is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength is low.
[00274] In relation to the number of Steel 45, the P content is outside the scope of the steel of the present invention, so that the elongation and fatigue chamfer property are low due to embrittlement.
[00275] In relation to Steel number 46, the S content is outside the scope of the steel of the present invention, so that MnS becomes a starting point for cracking and the orifice expansion value is low.
[00276] Regarding the number of Steel 47, the N content is outside the scope of the steel of the present invention, so that the thick TiN becomes a starting point of a crack and the expansion value of ori61 / 73 ficio is low.
[00277] Regarding the Steel number 48, the Ti content is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the fatigue chamfer property is low.
[00278] In relation to the number of Steel 49, the Ti content is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the tensile strength is low.
[00279] Regarding the Steel number 50, the Ti * value is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the orifice expansion value and the fatigue chamfer property are low.
[00280] In relation to the number of Steel 51, the Al content is outside the scope of the steel of the present invention, so that the predetermined microstructure cannot be obtained and the orifice expansion value is low.
TABLE 1
STEEL Ç Si Mn P s Al N You Nb Ass Ni Mo V Cr W B Mg Here Rem OTHERS You* Ex, C Mn / S NOTE THE 0.051 0.04 1.48 0.001 0.002 0.490 0.0031 0.116 0.014 - - - - - - - - - 0.00070.1024 0.0236 740 PRESENT INVENTION B 0.042 0.02 1.36 0.001 0.003 0.290 0.0035 0.073 0.009 - - - - - - - 0.0016 - -0.0565 0.0267 453 PRESENT INVENTION Ç 0.037 0.48 0.34 0.001 0.003 0.060 0.0031 0.063 - - - - - - - - - 0.0008 -0.0479 0.0250 113 PRESENT INVENTION D 0.012 0.02 1.54 0.001 0.002 0.525 0.0039 0.022 - 0.04 - - - - - - - - -0.0060 0.0105 906 PRESENT INVENTION AND 0.089 0.02 1.51 0.001 0.001 0.523 0.0036 0.122 - - 0.05 - - - - - - - -0.1081 0.0620 1514 PRESENT INVENTION F 0.052 0.45 1.55 0.001 0.002 0.577 0.0038 0.121 - - - 0.20 - - - - - - -0.1051 0.0260 775 PRESENT INVENTION G 0.057 0.09 1.54 0.001 0.002 0.506 0.0039 0.123 - - - - 0.08 - - - - - -0.1071 0.0299 963 PRESENT INVENTION H 0.052 0.02 0.24 0.001 0.001 0.574 0.0044 0.119 - - - - - 0.11 - 0.0014 - - -0.1015 0.0268 200 PRESENT INVENTION I 0.055 0.02 2.10 0.001 0.002 0.534 0.0037 0.121 - - - - - - 0.02 - - - -0.1062 0.0286 1313 PRESENT INVENTION J 0.051 0.01 2.44 0.001 0.001 0.522 0.0040 0.116 - - - - - - - - - - -0.1003 0.0254 2218 PRESENT INVENTION K 0.057 - 2.88 0.001 0.001 0.568 0.0038 0.122 - - - - - - - - 0.0006 - -0.1070 0.0303 2400 PRESENT INVENTION L 0.051 0.01 1.59 0.001 0.001 1,440 0.0038 0.119 - - - - - - - - - 0.0008 -0.1041 0.0254 1134 PRESENT INVENTION M 0.057 0.02 1.56 0.001 0.002 0.950 0.0036 0.122 - - - - - - - - - - 0.00070.1073 0.0299 823 PRESENT INVENTION N 0.051 0.02 1.50 0.001 0.001 0.080 0.0042 0.123 - - - - - - - - - - - Zr: 0.02% 0.1068 0.0242 1157 PRESENT INVENTION O 0.054 0.02 1.59 0.001 0.001 0.508 0.0075 0.119 - - - - - - - - - - - Sn: 0.01% 0.0915 0.0311 1324 PRESENT INVENTION P 0.052 0.02 1.51 0.001 0.002 0.520 0.0054 0.115 - - - - - - - - - - - Co: 0.002% 0.0944 0.0285 1003 PRESENT INVENTION Q 0.055 0.11 1.54 0.001 0.002 0.515 0.0037 0.184 - - - - - - - - - - - Zn: 0.004% 0.1682 0.0129 770 PRESENT INVENTION R 0.054 - 1.53 0.001 0.001 0.589 0.0037 0.050 - - - - - - - - - - -0.0354 0.0451 1272 PRESENT INVENTION s 0.120 0.01 1.60 0.001 0.001 0.560 0.0040 0.122 - - - - - - - - - - -0.1061 0.0935 1454 COMPARATIVE STEEL T 0.004 0.02 1.58 0.001 0.001 0.507 0.0035 0.124 - - - - - - - - - - -0.1100 -, 0235 1315 COMPARATIVE STEEL
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U 0.057 0.75 1.51 0.001 0.002 0.573 0.0043 0.116 - - - -0.0990 0.0319 1005 COMPARATIVE STEEL V 0.054 0.01 3.20 0.001 0.001 0.593 0.0043 0.122 - - - -0.1048 0.0277 2286 COMPARATIVE STEEL W 0.051 0.02 0.11 0.001 0.002 0.577 0.0039 0.116 - - - -0.0993 0.0259 58 COMPARATIVE STEEL X 0.059 0.02 1.55 0.080 0.001 0.567 0.0043 0.119 - - - -0.1028 0.0333 1405 COMPARATIVE STEEL Y 0.055 0.01 1.51 0.001 0.010 0.522 0.0044 0.116 - - - -0.0859 0.0337 151 COMPARATIVE STEEL Z 0.059 0.01 1.55 0.001 0.002 0.520 0.0200 0.122 - - - -0.0502 0.0467 777 COMPARATIVE STEEL The 0.055 0.01 1.60 0.001 0.002 0.547 0.0039 0.220 - - - -0.2039 0.0041 842 COMPARATIVE STEEL B 0.055 0.02 1.54 0.001 0.002 0.523 0.0039 0.002 - - - --0.0142 0.0580 811 COMPARATIVE STEEL ç 0.060 0.02 1.52 0.001 0.001 0.549 0.0088 0.020 - - - --0.0123 0.0626 1087 COMPARATIVE STEEL d 0.057 0.01 1.55 0.001 0.002 2,100 0.0035 0.115 - - - -0.1003 0.0316 861 COMPARATIVE STEEL
TABLE 2
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STEEL NUMBER METALLURGICAL FACTOR MANUFACTURING CONDITION HEATING GROSS LAMINATION O TEMPERATURESOLUTION (° C) TRANSFORMATION POINT TEMPERATURE Ar3 (° C) Ex, C (%) HEATING TEMPERATURE (° C) Maintenance time period (MINU-TO) TOTAL AMOUNTPASSASA-GENS TOTAL REDUCTION REASON (%) PASSAGE AMOUNT 1050 ° C TO 1150 ° C AND 20% OR MORE TIME PERIOD UNTIL THE BEGINNING OF LAMI-FINISHING NATION(SECOND) AVERAGE AUSTENITE GRAIN DIAMETER IMMEDIATELY BEFORE FINISHING LAMINATION (mm) PRESENT INVENTION 1 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 2 THE 1,192 806 0.0236 1,150 90 7 87 3 30 75 COMPARATIVE STEEL 3 THE 1,192 806 0.0236 1,230 90 5 54 3 60 125
PRESENT INVENTION 4 THE 1,192 806 0.0236 1,230 90 3 75 1 60 90 COMPARATIVE STEEL 5 THE 1,192 806 0.0236 1,230 90 7 87 0 60 100 COMPARATIVE STEEL 6 THE 1,192 806 0.0236 1,230 90 7 87 3 210 160 COMPARATIVE STEEL 7 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 8 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 PRESENT INVENTION 9 THE 1,192 806 0.0236 1,230 45 7 87 5 45 75 PRESENT INVENTION 10 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 PRESENT INVENTION 11 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 12 THE 1,192 806 0.0236 1,230 90 7 87 3 150 100 COMPARATIVE STEEL 13 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 14 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 15 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 16 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 17 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 18 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 19 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 PRESENT INVENTION 20 THE 1,192 806 0.0236 1,230 90 7 87 7 45 70 COMPARATIVE STEEL 21 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 COMPARATIVE STEEL 22 THE 1,192 806 0.0236 1,230 90 7 87 3 60 85 PRESENT INVENTION 23 B 1,137 812 0.0279 1,200 120 5 81 2 120 95 PRESENT INVENTION 24 Ç 1,116 902 0.0250 1,200 120 5 81 2 120 95 PRESENT INVENTION 25 D 965 823 0.0105 1,200 120 5 81 2 120 95 PRESENT INVENTION 26 AND 1,247 802 0.0620 1,250 30 9 86 7 90 90 PRESENT INVENTION 27 F 1,198 810 0.0260 1,230 60 9 86 7 90 90 PRESENT INVENTION 28 G 1,206 813 0.0299 1,230 60 9 86 7 90 90 PRESENT INVENTION 29 H 1,196 831 0.0268 1,230 60 9 86 7 90 90 PRESENT INVENTION 30 I 1,203 768 0.0286 1,230 60 9 86 7 90 90
PRESENT INVENTION 31 J 1,191 742 0.0254 1,230 60 9 86 7 90 90 PRESENT INVENTION 32 K 1,206 707 0.0303 1,230 60 9 86 7 90 90 PRESENT INVENTION 33 L 1,195 855 0.0254 1,230 60 9 86 7 90 90 PRESENT INVENTION 34 M 1,206 831 0.0299 1,230 60 9 86 7 90 90 PRESENT INVENTION 35 N 1,197 794 0.0242 1,210 100 5 81 2 120 95 PRESENT INVENTION 36 O 1,199 808 0.0311 1,210 100 5 81 2 120 95 PRESENT INVENTION 37 P 1,193 816 0.0285 1,210 100 5 81 2 120 95 PRESENT INVENTION 38 Q 1,240 814 0.0129 1,250 45 9 86 7 90 90 PRESENT INVENTION 39 R 1,127 817 0.0451 1,180 150 5 81 2 120 95 COMPARATIVE STEEL 40 s 1,274 789 0.0935 1,280 40 9 86 7 90 90 COMPARATIVE STEEL 41 T 1,005 824 ###### 1,150 180 3 77 1 150 100 COMPARATIVE STEEL 42 U 1,201 835 0.0319 1,230 45 9 86 7 90 90 COMPARATIVE STEEL 43 V 1,201 683 0.0277 PLATE CRACK COMPARATIVE STEEL 44 W 1,191 931 0.0259 1,220 70 5 81 2 120 95 COMPARATIVE STEEL 45 X 1,207 813 0.0333 1,220 70 5 81 2 120 95 COMPARATIVE STEEL 46 Y 1,199 815 0.0337 1,220 70 5 81 2 120 95 COMPARATIVE STEEL 47 Z 1,210 810 0.0467 1,230 70 5 81 2 120 95 COMPARATIVE STEEL 48 The 1,257 809 0.0041 1,260 30 9 86 7 90 90 COMPARATIVE STEEL 49 B 913 812 0.0580 1,150 180 5 81 2 120 95 COMPARATIVE STEEL 50 ç 1,065 814 0.0626 1,150 180 5 81 2 120 95 COMPARATIVE STEEL 51 d 1,201 890 0.0316 1,220 70 5 81 2 120 95
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NUMBER-RO DESTEEL MANUFACTURING CONDITION FINISHING LAMINATION COOLING FIRST STAGE COOLING SECOND STAGE COOLING THIRD STAGE COOLING COOLINGALL LAMINATION START TEMPERATURE(° C) REASON FORTOTAL REDUCTION (%) REASON FOR AVERAGE LAMINATION FOR3 REAR SUPPORT TICKETS(%) VELOCITYOUTPUT SIDELAMINATIONFROM FINISHEDMENTO (kmpm)TEMPERATURETERMINATION(° C) TIME PERIOD UNTIL THE BEGINNING OFCOOLING (SECOND) COOLING RATE (° C / SEC UNDO) COOLING STOP TEMPERATURE(° C) RATE OFRES-COOLING (° C / SEC UNDO) PERIOD OFMAINTENANCE TIME (MON UNDO) TEMPE-RATURE OFSTOPCOOLING (° C) COOLING RATE (° C / SECONOF) TEMPE-WINDOW RATURELAMEN-TO (° C) DIFFUSION DIMENSION CUMU-TOTAL LATIVA (mm) PRESENT INVENTION 1 1,040 90 18 1,158,696 806 920 1.1 50 680 5 4 660 70 100 0.16 COMPARATIVE STEEL 2 1,000 90 18 1,255,254 806 900 1.0 50 680 5 4 660 70 100 0.19 COMPARATIVE STEEL 3 1,050 94 21 1,126.51 806 910 1.1 50 680 5 4 660 70 100 0.19 PRESENT INVENTION 4 1,020 90 18 1,158,696 806 920 1.1 50 680 5 4 660 70 100 0.19 COMPARATIVE STEEL 5 1,040 90 18 1,158,696 806 920 1.1 50 680 5 4 660 70 100 0.19 COMPARATIVE STEEL 6 1,010 90 18 1,190,882 806 910 1.1 50 680 5 4 660 70 100 0.19 COMPARATIVE STEEL 7 985 90 18 1,448.37 806 900 0.9 40 680 5 4 660 60 100 0.20 COMPARATIVE STEEL 8 1,040 74 12 1,158,696 806 900 1.1 40 680 5 4 660 70 100 0.20 PRESENT INVENTION 9 1,060 90 18 1046,045 806 940 1.2 40 675 5 4 655 60 300 0.19 PRESENT INVENTION 10 1,040 84 7.6 1,126.51 806 890 1.1 50 680 5 4 660 60 50 0.19 PRESENT INVENTION 11 1,040 90 18 579,348 806 860 2.2 55 670 5 5 645 75 50 0.17 COMPARATIVE STEEL 12 1,020 90 18 643.72 806 760 2.0 55 670 5 5 645 75 50 - COMPARATIVE STEEL 13 1,040 90 18 1,367,905 806 1020 0.9 35 680 5 3 665 55 50 0.20 COMPARATIVE STEEL 14 1,040 90 18 643.72 806 870 3.6 55 670 5 5 645 75 50 0.17 COMPARATIVE STEEL 15 1,040 90 18 1,158,696 806 920 1.1 5 710 5 4 690 60 50 0.50 COMPARATIVE STEEL 16 1,040 90 18 1,158,696 806 920 1.1 30 800 5 4 780 60 50 0.58 COMPARATIVE STEEL 17 1,040 90 18 1,158,696 806 920 1.1 65 520 5 4 500 60 50 0.06 COMPARATIVE STEEL 18 1,040 90 18 1,158,696 806 920 1.1 50 670 15 2 640 60 50 0.15 COMPARATIVE STEEL 19 1,040 90 18 1,158,696 806 920 1.1 50 670 5 0 670 60 50 0.12
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PRESENT INVENTION 20 1,000 90 18 1,206,975 806 930 1.1 50 670 5 4 650 55 200 0.17 COMPARATIVE STEEL 21 1,040 90 18 1,158,696 806 920 1.1 50 670 5 4 650 5 50 0.19 COMPARATIVE STEEL 22 1,040 90 18 1,158,696 806 920 1.1 50 670 5 4 650 60 450 0.18 PRESENT INVENTION 23 1,020 91 20 1,158,696 812 900 1.1 40 685 6 4 660 65 150 0.21 PRESENT INVENTION 24 1,080 91 20 1,158,696 902 960 1.1 70 700 6 4 675 70 150 0.40 PRESENT INVENTION 25 1,050 91 20 1,158,696 823 930 1.1 50 690 6 4 665 65 150 0.23 PRESENT INVENTION 26 1,000 89 16 997,766 802 860 1.3 35 680 5 5 655 65 150 0.21 PRESENT INVENTION 27 1,000 89 16 1,046,045 810 870 1.2 40 685 5 4 665 65 150 0.21 PRESENT INVENTION 28 1,000 91 20 1,158,696 813 880 1.1 40 685 6 4 660 50 250 0.22 PRESENT INVENTION 29 1,080 93 22 1,206,975 831 965 1.1 75 710 7 4 680 55 250 0.25 PRESENT INVENTION 30 1,010 89 16 997,766 768 870 1.3 25 680 5 5 655 50 250 0.18 PRESENT INVENTION 31 1,000 88 15 933,394 742 850 1.4 15 665 4 10 635 45 250 0.16 PRESENT INVENTION 32 1,000 88 15 933,394 707 850 1.4 15 690 4 15 630 45 250 0.15 PRESENT INVENTION 33 1,040 91 20 1,158,696 855 920 1.1 40 710 6 4 685 40 350 0.37 PRESENT INVENTION 34 1.0.20 91 20 1,158,696 831 900 1.1 40 695 6 4 670 40 350 0.28 PRESENT INVENTION 35 1,010 88 15 933,394 794 860 1.4 35 680 4 5 660 40 350 0.21 PRESENT INVENTION 36 1,000 91 20 1,158,696 808 880 1.1 40 680 6 4 655 40 350 0.21 PRESENT INVENTION 37 1,010 91 20 1,158,696 816 890 1.1 40 685 6 4 660 40 350 0.23 PRESENT INVENTION 38 1,000 91 20 1,158,696 814 880 1.1 40 685 6 4 660 75 50 0.21 PRESENT INVENTION 39 1,010 91 20 1,158,696 817 890 1.1 45 670 6 4 645 75 50 0.19 COMPARATIVE STEEL 40 1,020 91 20 1,158,696 789 900 1.1 45 675 6 4 650 75 50 0.16 COMPARATIVE STEEL 41 1,010 91 20 1,158,696 824 890 1.1 40 690 6 4 665 75 50 0.24 COMPARATIVE STEEL 42 1,010 91 20 1,158,696 835 890 1.1 40 700 6 4 675 80 50 0.29 COMPARATIVE STEEL 43 SHEET TRACK COMPARATIVE STEEL 44 1,105 91 20 1,158,696 931 985 1.1 50 725 6 4 700 80 50 0.65 COMPARATIVE STEEL 45 1,010 91 20 1,158,696 813 890 1.1 40 685 6 4 660 75 50 0.21 COMPARATIVE STEEL 46 1,000 91 20 1,158,696 815 880 1.1 40 690 6 4 665 75 50 0.23 COMPARATIVE STEEL 47 1,000 89 16 1,062,138 810 870 1.2 40 685 5 4 665 75 50 0.21 COMPARATIVE STEEL 48 1,000 91 20 1,158,696 809 880 1.1 40 685 6 4 660 75 50 0.21 COMPARATIVE STEEL 49 1,015 88 15 965.58 812 870 1.3 35 685 4 5 665 75 50 0.23 COMPARATIVE STEEL 50 1,010 89 16 997,766 814 870 1.3 35 685 5 5 660 75 50 0.23 COMPARATIVE STEEL 51 1,020 91 20 1,158,696 890 900 1.1 35 725 6 4 700 80 50 0.54
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TABLE 4
STEEL NUMBER MICROSTRUCTURE MICRO STRUCTURE FERRITE DENSITY TiC (PIECE / cm ³ ) CHARACTERISTICS OFSECOND LEVEL FRACTIONSECOND PHASE fsd(%) Ex.C (%) /fsd (%) NANODURE OF SECOND PHASE Hn (GPa) STANDARD DEVIATIONTHE NANODURE OF THE SECONDPHASE sHn (GPa) SECOND STAGE AVERAGE GRAIN DIAMETER (mm) AVERAGE DISTANCE VALUE OF LARGEST APPROXIMATION BETWEEN SECOND PHASES (mm) 1 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 4.0 0.0059 11.9 1.0 8.0 18.8 2 PF + M 5x10 ¹³ ISLAND FORMAT 5.0 0.0047 10.2 0.9 12.0 10.0 3 STRENGTHENED BY PRECIPITATION PF + M 2x10 ¹⁶ ISLAND FORMAT 9.0 0.0026 7.0 0.6 18.0 3.7 4 STRENGTHENED BY PRECIPITATION PF + M 6x10 ¹⁶ ISLAND FORMAT 4.0 0.0059 11.9 1.0 15.0 10.0 5 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ FILM FORMAT 3.5 0.0067 13.2 1.1 14.0 12.2 6 PF + M 2x10 ¹³ ISLAND FORMAT 3.0 0.0079 14.9 13 17.0 11.8 7 PF + M 3x10 ¹³ ISLAND FORMAT 5.0 0.0047 10.2 0.9 7.0 17.1 8 STRENGTHENED BY PRECIPITATION PF + M 2x10 ¹⁶ ISLAND FORMAT 9.0 0.0026 7.0 0.6 16.0 4.2 9 STRENGTHENED BY PRECIPITATION PF + tM 2x10 ¹⁶ ISLAND FORMAT 5.0 0.0047 10.2 0.9 11.0 10.9 10 STRENGTHENED BY PRECIPITATION PF + M 3x10 ¹⁶ ISLAND FORMAT 5.5 0.0043 9.5 0.8 15.0 11.0 11 STRENGTHENED BY PRECIPITATION PF + M 2x10 ¹⁶ ISLAND FORMAT 4.5 0.0052 11.0 0.9 15.0 12.0 12 WORKED F + M 2x10 ⁹ ALIGNED STATE 3.0 0.0079 14.9 13 20.0 4.0 13 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 31.0 0.0008 41 0.4 18.0 6.0 14 PF + M 5x1011 ISLAND FORMAT 5.0 0.0047 10.2 0.9 21.0 5.7 15 PF + P 2x1011 _ _ _ _ _ _ _16 B NOT OBSERVED 17 B NOT OBSERVED _ _ _ _ _ _ _
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18 PF + M 2x1011 ISLAND FORMAT 10.0 0.0024 6.6 0.6 12.0 5.0 19 B NOT OBSERVED 20 STRENGTHENED BY PRECIPITATION PF + tM 2x10 ¹⁶ ISLAND FORMAT 3.0 0.0079 14.9 13 12.0 16.7 21 PF + P 2x10 ¹³ _ _ _ _ _ _ _ 22 PF + B + THICK q 5x10 ⁹ 23 STRENGTHENED BY PRECIPITATION PF + M 3x10 ¹⁶ ISLAND FORMAT 3.0 0.0093 17.1 15 11.0 18.2 24 STRENGTHENED BY PRECIPITATION PF + M 2x10 ¹⁶ ISLAND FORMAT 3.0 0.0083 15.7 13 12.0 16.7 25 STRENGTHENED BY PRECIPITATION PF + M 1x10 ¹⁶ ISLAND FORMAT 2.0 0.0053 11.0 0.9 15.0 20.0 26 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 8.0 0.0077 14.8 13 6.0 12.5 27 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 5.0 0.0052 10.9 0.9 7.0 17.1 28 STRENGTHENED BY PRECIPITATION PF + tM 6x10 ¹⁶ ISLAND FORMAT 5.0 0.0060 12.1 1.0 10.0 12.0 29 STRENGTHENED BY PRECIPITATION PF + tM 4x10 ¹⁶ ISLAND FORMAT 4.0 0.0067 13.2 1.1 9.0 16.7 30 STRENGTHENED BY PRECIPITATION PF + tM 5x10 ¹⁶ ISLAND FORMAT 6.0 0.0048 10.2 0.9 7.0 14.3 31 STRENGTHENED BY PRECIPITATION PF + tM 3x10 ¹⁶ ISLAND FORMAT 5.0 0.0051 10.7 0.9 9.0 13.3 32 STRENGTHENED BY PRECIPITATION PF + tM 7x10 ¹⁶ ISLAND FORMAT 10.0 0.0030 7.6 0.6 6.0 10.0 33 STRENGTHENED BY PRECIPITATION PF + tM 3x10 ¹⁶ ISLAND FORMAT 5.0 0.0051 10.7 0.9 7.0 17.1 34 STRENGTHENED BY PRECIPITATION PF + tM 4x10 ¹⁶ ISLAND FORMAT 4.0 0.0075 14.3 1.2 9.0 16.7 35 STRENGTHENED BY PRECIPITATION PF + tM 4x10 ¹⁶ ISLAND FORMAT 3.0 0.0081 15.2 13 12.0 16.7 36 STRENGTHENED BY PRECIPITATION PF + tM 3x10 ¹⁶ ISLAND FORMAT 5.0 0.0062 12.4 1.1 10.0 12.0 37 STRENGTHENED BY PRECIPITATION PF + tM 5x10 ¹⁶ ISLAND FORMAT 6.0 0.0047 10.2 0.9 6.0 16.7 38 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 5.0 0.0026 6.9 0.6 8.0 15.0 39 STRENGTHENED BY PRECIPITATION PF + M 3x10 ¹⁶ ISLAND FORMAT 5.0 0.0090 16.7 14 7.0 17.1 40 STRENGTHENED BY PRECIPITATION PF + M 3x10 ¹⁶ ALIGNED STATE 31.0 0.0030 7.6 0.6 21.0 0.9 41 Federal Police 2x10 ⁹ _ _ _ _ _ _ _ 42 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 4.0 0.0080 15.1 1.3 9.0 16.7 43 PLATE CRACK 44 B NOT OBSERVED _ _ _ _ _ _ _
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45 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 4.0 0.0083 15.6 13 9.0 16.7 46 STRENGTHENED BY PRECIPITATION PF + M 5x10 ¹⁶ ISLAND FORMAT 5.0 0.0067 13.2 1.1 10.0 12.0 47 PF + M 5X10 ¹¹ ISLAND FORMAT 7.0 0.0067 13.1 1.1 11.0 7.8 48 STRENGTHENED BY PRECIPITATION PF 5x10 ¹⁶ 49 PF + M 5x10 ⁸ ISLAND FORMAT 5.0 0.0116 20.6 18 15.0 80 50 PF + M NOT OBSERVED ISLAND FORMAT 11.0 0.0057 11.6 1.0 6.0 9 51 WORKED F + M 2x10 ⁸ ALIGNED STATE 4.0 0.0079 15.0 13 21.0 7.1
TABLE 5
STEEL NUMBER MECHANICAL PROPERTY SURFACE PROPERTY CORROSION RESISTANCE TRACTION TEST HOLE EXPANSION CANDLE OFFATIGUE SURFACE DEFECT ROUGHNESS CONVERSION TREATMENT PROPERTY RESISTANCE TO POST-COATING CORROSION YP (MPa) TS (MPa) El (%) λ (%) aWK / aW0 o: NONE Δ: LIGHT x: PRESENCE Rz (pm) PRESENCE / ABSENCE of Absence of coverage o: NONE △: LEVEx: PRESENCE P REASON PEELED WIDTHMAXIMUM (mm) 1 593 790 24.2 118 0.41 O 18.3 O 0.95 2.2 2 402 538 34.7 125 0.34 O 19.7 O 0.90 0.5 3 591 782 23.6 38 0.34 O 14.7 O 0.93 3.1 4 606 798 23.5 79 0.36 O 13.0 O 0.85 2.6 5 612 806 22.8 44 0.35 O 10.9 O 0.90 0.3 6 377 532 34.8 58 0.34 O 14.3 O 0.85 0.4 7 376 522 36.0 126 0.33 O 13.4 O 0.89 1.9 8 633 816 23.0 46 0.34 O 16.6 O 0.88 0.1 9 599 781 24.3 136 0.36 O 19.5 O 0.89 1.1 10 610 793 24.0 74 0.35 O 17.9 O 0.86 0.9 11 603 787 24.1 81 0.37 O 16.4 O 0.89 2.7 12 588 784 23.2 54 0.35 O 11.3 O 0.87 0.9
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13 623 822 19.1 41 0.33 Ο 12.5 ο 0.89 2.5 14 393 508 35.0 50 0.34 ο 16.3 ο 0.89 2.0 15 568 741 24.3 42 0.22 ο 12.3 ο 0.92 1.1 16 461 533 31.0 116 0.23 ο 14.7 ο 0.89 0.9 17 470 539 30.0 108 0.23 ο 11.9 ο 0.91 0.8 18 390 521 35.1 61 0.35 ο 15.7 ο 0.88 1.0 19 461 526 30.8 111 0.24 ο 17.1 ο 0.91 3.0 20 584 780 24.5 127 0.37 ο 13.4 ο 0.93 0.7 21 588 722 25.3 51 0.22 ο 16.3 ο 0.93 0.7 22 620 784 20.0 39 0.33 ο 10.6 ο 0.95 1.6 23 459 612 31.0 152 0.40 ο 16.6 ο 0.92 0.3 24 408 544 34.9 171 0.36 △ IF INCRUST 27.4 X 0.71 4.1 25 413 551 34.5 169 0.38 ο 15.5 ο 0.93 2.9 26 659 878 21.6 106 0.39 ο 20.3 ο 0.87 2.7 27 618 824 23.1 113 0.36 △ IF INCRUST 25.3 X 0.68 4.3 28 605 806 23.6 115 0.36 △ IF INCRUST 12.1 ο 0.87 3.8 29 406 541 35.1 172 0.39 ο 14.3 ο 0.91 1.8 30 702 936 20.3 99 0.38 ο 19.5 ο 0.91 2.5 31 744 992 19.2 94 0.37 △ INCRUSTATION 20.0 ο 0.92 3.2 32 848 1131 16.8 82 0.37 △ INCRUSTATION 19.2 ο 0.95 0.3 33 631 841 22.6 111 0.37 △ INCRUSTATION 16.9 ο 0.94 0.7 34 591 788 24.1 118 0.40 ο 16.3 ο 0.93 3.0 35 486 648 29.3 144 0.38 ο 12.0 ο 0.92 0.8 36 611 815 23.3 114 0.39 ο 11.3 ο 0.90 0.3 37 615 820 23.2 113 0.39 ο 11.7 ο 0.86 3.4 38 602 802 23.7 116 0.38 ο 17.9 △ 0.80 42 39 506 675 28.1 138 0.37 △ INCRUSTATION 13.3 ο 0.88 0.8
71/73
40 698 948 13.1 34 0.36 △ INCRUSTATION ' 11.6 O 0.93 0.2 41 366 455 37.0 128 0.35 O 14.4 O 0.92 3.0 42 636 871 21.0 96 0.37 △ IF INCRUST 31.1 X 0.61 7.9 43 PLATE CRACK 44 373 496 36.5 144 0.36 O 18.7 O 0.92 0.8 45 655 860 14.0 71 0.24 O 17.5 O 0.91 1.7 46 610 800 22.0 29 0.33 △ INCRUSTATION 13.7 O 0.94 0.1 47 518 690 24.0 51 0.34 △ INCRUSTATION 13.7 O 0.90 1.3 48 616 821 18.0 86 0.22 △ INCRUSTATION 13.7 O 0.93 0.9 49 342 520 34.0 66 0.38 O 11.5 O 0.87 0.1 50 605 738 19.0 68 0.25 O 13.7 O 0.94 1.4 51 695 766 11.0 33 0.34 △ INCRUSTATION 12.9 O 0.87 1.1
72/73
73/73
INDUSTRIAL APPLICABILITY [00281] The two-phase steel sheet of the present invention can be used for various uses such as shipbuilding, construction, bridges, offshore structures, pressure tanks, pipes, and machine parts, in addition to automobile members that are required to have viability, orifice expandability, and foldability as well as high strength such as inner sheet members, structure members and lower body members.

权利要求:
Claims (12)
[1]
1. Biphasic steel sheet, characterized by the fact that it consists of:
in mass%,
C: 0.01 to 0.1%;
Mn: 0.2 to 3%;
Al: 0.04 to 1.5%;
Ti: 0.015 to 0.2%;
Si: 0 to 0.5%;
Nb: 0 to 0.06%;
Cu: 0 to 1.2%;
Ni: 0 to 0.6%;
Mo: 0 to 1%;
V: 0 to 0.2%;
Cr: 0 to 2%;
W: 0 to 0.5%;
Mg: 0 to 0.01%;
Ca: 0 to 0.01%;
REM: 0 to 0.1%;
B: 0 to 0.002%;
P: 0.01% or less;
S: 0.005% or less;
N: 0.01% or less, where [Ti] - 48/14 x [N] - 48/32 x [S] £ 0% is satisfied and when Ex.C (%) = [C] - 12 / 48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] 48/32 x [S]} is determined, 0.001 í Ex.C (%) / fsd (%) í 0.01 is satisfied, and since a balance is made up of Fe and impurities, in the position of 1/4 thickness of a thickness of
Petition 870190072397, of 7/29/2019, p. 5/13
[2]
2/6 sheet, a microstructure is biphasic with its main phase composed of polygonal ferrite strengthened by precipitation by Ti carbide and its second phase consisting of 1 to 10% in fraction of area (fsd (%)) of temperature transformation products low dispersed plurally, and an average crystal diameter of the transformation product at low temperature is 3 to 15 pm and an average value of a closer distance between the transformation products at low temperature is 10 to 20 pm.
2. Biphasic steel sheet, according to claim 1, characterized by the fact that it comprises:
in mass%,
Si: 0.02% to 0.5%.
[3]
3. Biphasic steel sheet, according to claim 1 or 2, characterized by the fact that it comprises:
one or two or more in mass%,
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%;
Cr: 0.01 to 2%; and
W: 0.01 to 0.5%.
[4]
4. Biphasic steel sheet according to any one of claims 1 to 3, characterized by the fact that it comprises:
one or two or more in mass%,
Mg: 0.0005 to 0.01%;
Ca: 0.0005 to 0.01%; and
Petition 870190072397, of 7/29/2019, p. 6/13
3/6
REM: 0.0005 to 0.1%.
[5]
5. Two-phase steel sheet according to any one of claims 1 to 4, characterized by the fact that it comprises:
in mass%,
B: 0.0002 to 0.002%.
[6]
6. Biphasic steel sheet according to any one of claims 1 to 5, characterized by the fact that:
galvanizing is carried out on the surface.
[7]
7. Method of manufacturing a biphasic steel sheet characterized by the fact that it comprises:
on a plate consisting of:
in mass%,
C: 0.01 to 0.1%;
Mn: 0.2 to 3%;
Al: 0.04 to 1.5%;
Ti: 0.015 to 0.2%;
Si: 0 to 0.5%;
Nb: 0 to 0.06%;
Cu: 0 to 1.2%;
Ni: 0 to 0.6%;
Mo: 0 to 1%;
V: 0 to 0.2%;
Cr: 0 to 2%;
W: 0 to 0.5%;
Mg: 0 to 0.01%;
Ca: 0 to 0.01%;
REM: 0 to 0.1%;
B: 0 to 0.002%;
P: 0.01% or less;
S: 0.005% or less;
Petition 870190072397, of 7/29/2019, p. 7/13
4/6
N: 0.01% or less, where [Ti] - 48/14 x [N] - 48/32 x [S] £ 0% is satisfied and when Ex.C (%) = [C] - 12 / 48 x {[Ti] + 48/93 x [Nb] - 48/14 x [N] 48/32 x [S]} is determined, 0.001 í Ex.C (%) / fsd (%) í 0.01 is satisfied, and since a balance is made up of Fe and impurities, perform the heating to an SRTmin temperature (° C) or higher, which is defined by Expression (1) below, and then in the hot rolling, perform the gross rolling at a rate of reduction of 20% or more in a temperature zone of at least 1,050 ° C and at most 1,150 ° C for at least one pass, and then begin finishing lamination within 150 seconds in a temperature zone of 1,000 ° C or higher and lower than 1,080 ° C, and complete the finishing lamination with the total reduction ratio for plural passages of at least 75% and at most 95% in a temperature zone of at least one temperature transformation point Ar3 + 50 ° C and maximum 1,000 ° C ; and within 3 seconds, cool to a temperature lower than the Ar3 transformation point temperature at an average cooling rate of 15 ° C / sec or more and then cool to a temperature zone higher than 600 ° C at an average cooling rate of 10 ° C / sec or less for a period of time of 1 second or longer and shorter than 100 seconds and then cool to a temperature zone 350 ° C or lower at a cooling rate of 15 ° C / sec or more, and perform the winding;
SRTmin = 10780 / {5.13 - log ([Ti] x [C])} - 273 Expression (1)
[8]
8. Biphasic steel sheet manufacturing method, according to claim 7, characterized by the fact that it comprises
Petition 870190072397, of 7/29/2019, p. 8/13
5/6 additionally:
in hot rolling, carry out the gross lamination at a reduction rate of 20% or more in a temperature zone of at least 1,050 ° C and at most 1,150 ° C for plural passages, where the ratio of total reduction of the gross lamination is at least 60% and at most 90%.
[9]
9. Biphasic steel sheet manufacturing method, according to claim 7 or 8, characterized by the fact that it additionally comprises:
cool down to a temperature zone of 100 ° C or lower and wind up.
[10]
10. Biphasic steel sheet manufacturing method according to any of claims 7 to 9, characterized by the fact that:
when cooling to a temperature zone above 600 ° C at an average cooling rate of 10 ° C / sec or less for a period of time of 1 second or longer and shorter than 100 seconds, when a dimension of total cumulative diffusion Ltotal of Ti in the ferrite is expressed by Expression (3) below by adding a diffusion dimension L of Ti in the ferrite expressed by Expression (2) below for a very short time At / sec of a completion temperature of cooling for winding, 0.15 i Ltotal i 0.5 is satisfied;
L = ^ D (T + 273) t Expression (2)
Ltotal = Z ^ (D (T + 273) At) Expression (3) here, D (T + 273) is a volume diffusion coefficient at T ° C, t is a diffusion time period;
D (T) is expressed by Expression (4) below using a diffusion coefficient D0 of Ti, an activation energy Q, and a
Petition 870190072397, of 7/29/2019, p. 9/13
6/6 gas constant R;
D (T) = D0 x Exp (-Q / R- (T + 273)) Expression (4)
[11]
11. Biphasic steel sheet manufacturing method according to any one of claims 7 to 10, characterized by the fact that:
when cooling to a temperature zone above 600 ° C at an average cooling rate of 10 ° C / sec or less for a period of time of 1 second or longer and shorter than 100 seconds, a sheet of steel is immersed in a galvanizing bath to galvanize its surface.
[12]
12. Biphasic steel sheet manufacturing method, according to claim 11, characterized by the fact that it also comprises:
on a sheet of galvanized biphasic steel, perform an alloy treatment in a temperature range of 450 to 600 ° C.

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法律状态:
2018-11-21| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2019-04-30| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|

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2019-08-13| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |

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2019-12-10| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2020-01-28| 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 26/09/2013, OBSERVADAS AS CONDICOES LEGAIS. |

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2021-08-10| B21F| Lapse acc. art. 78, item iv - on non-payment of the annual fees in time|Free format text: REFERENTE A 8A ANUIDADE. |

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2021-11-30| B24J| Lapse because of non-payment of annual fees (definitively: art 78 iv lpi, resolution 113/2013 art. 12)|Free format text: EM VIRTUDE DA EXTINCAO PUBLICADA NA RPI 2640 DE 10-08-2021 E CONSIDERANDO AUSENCIA DE MANIFESTACAO DENTRO DOS PRAZOS LEGAIS, INFORMO QUE CABE SER MANTIDA A EXTINCAO DA PATENTE E SEUS CERTIFICADOS, CONFORME O DISPOSTO NO ARTIGO 12, DA RESOLUCAO 113/2013. |

优先权:

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申请号 | 申请日 | 专利标题

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JP2012212783|2012-09-26|

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PCT/JP2013/076149|WO2014051005A1|2012-09-26|2013-09-26|Composite-structure steel sheet and process for producing same|

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