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WO2023181640A1 - Feuille d'acier à haute résistance et son procédé de fabrication - Google Patents

Feuille d'acier à haute résistance et son procédé de fabrication Download PDF

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Publication number
WO2023181640A1
WO2023181640A1 PCT/JP2023/002913 JP2023002913W WO2023181640A1 WO 2023181640 A1 WO2023181640 A1 WO 2023181640A1 JP 2023002913 W JP2023002913 W JP 2023002913W WO 2023181640 A1 WO2023181640 A1 WO 2023181640A1
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WIPO (PCT)
Prior art keywords
less
strength steel
steel plate
content
steel sheet
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PCT/JP2023/002913
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English (en)
Japanese (ja)
Inventor
潤也 戸畑
勇樹 田路
秀和 南
Original Assignee
Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to MX2024011508A priority Critical patent/MX2024011508A/es
Priority to KR1020247030587A priority patent/KR20240152342A/ko
Priority to CN202380027218.3A priority patent/CN118804993A/zh
Priority to JP2023528940A priority patent/JP7323093B1/ja
Publication of WO2023181640A1 publication Critical patent/WO2023181640A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention relates to a high-strength steel plate that is excellent in tensile strength, flatness in the width direction, and resistance to work embrittlement, and a method for manufacturing the same.
  • the high-strength steel sheet of the present invention can be suitably used as a structural member for automobile parts and the like.
  • High-strength steel sheets used in automobiles are required to have excellent work embrittlement resistance and yield ratio from the viewpoint of component performance.
  • high-strength steel plates are used, which have excellent resistance to mechanical embrittlement that does not cause embrittlement due to press forming, and have excellent impact absorption properties in the event of a collision, which is correlated with YR. It is preferable to do so.
  • Patent Document 1 describes that warpage of a steel plate adversely affects operational troubles in a forming line and dimensional accuracy of products.
  • the present inventors found that the dimensional accuracy of a product is affected not only by the warpage of the steel plate but also by the flatness in the width direction of the plate, which is evaluated using steepness.
  • the steepness in the width direction is preferably 0.02 or less.
  • Patent Document 2 provides a high-strength steel plate having a tensile strength of 1100 MPa or more and excellent YR, surface texture, and weldability, and a method for manufacturing the same.
  • the technique described in Patent Document 2 does not take into account flatness in the width direction of the plate and resistance to work embrittlement.
  • Patent Document 3 provides a hot-dip galvanized steel sheet with excellent press formability and low-temperature toughness and a tensile strength of 980 MPa or more, and a method for manufacturing the same.
  • the technique described in Patent Document 3 can improve the embrittlement of the steel plate due to a temperature drop, it does not take into account the embrittlement of the steel plate due to processing. Flatness in the width direction of the plate is also not considered.
  • the present invention was developed in view of the above circumstances, and provides a high-strength steel plate having a TS of 1180 MPa or more, a YR of 85% or more, and excellent flatness in the width direction and resistance to work embrittlement, and a method for manufacturing the same.
  • the purpose is to
  • the present invention has been made based on the above findings. That is, the gist of the present invention is as follows. [1] In mass%, C: 0.030% or more and 0.500% or less, Si: 0.01% or more and 2.50% or less, Mn: 0.10% or more and 5.00% or less, P: 0. Contains 100% or less, S: 0.0200% or less, Al: 1.000% or less, N: 0.0100% or less, and O: 0.0100% or less, with the remainder consisting of Fe and inevitable impurities.
  • the amount of tempered martensite is 90% or more in area fraction
  • the amount of retained austenite is less than 3% in volume fraction
  • the total amount of ferrite and bainitic ferrite. is less than 10% in terms of area fraction
  • the average crystal grain size of prior austenite is 20 ⁇ m or less
  • the average value of the occupancy of the packets having the maximum occupancy in the prior austenite grains is 70% or less in area fraction.
  • high strength steel plate is
  • the present invention it is possible to obtain a high-strength steel plate having a TS of 1180 MPa or more, a YR of 85% or more, and excellent flatness in the width direction and resistance to work embrittlement. Furthermore, by applying the high-strength steel plate of the present invention to, for example, automobile structural members, it is possible to improve fuel efficiency by reducing the weight of the vehicle body. Therefore, the industrial value is extremely large.
  • FIG. 1 is a diagram showing the structure of a packet having the maximum occupancy in prior austenite grains and a method for calculating the same according to the present invention.
  • FIG. 2 is a diagram showing the concept of steepness ⁇ of a steel plate according to the present invention and its calculation method.
  • C is one of the important basic components of steel, and in particular, in the present invention, it is an important element that affects the fraction of tempered martensite and the resistance to work embrittlement. If the C content is less than 0.030%, the fraction of tempered martensite decreases, making it difficult to achieve a TS of 1180 MPa or more. On the other hand, when the C content exceeds 0.500%, the tempered martensite becomes brittle and the work embrittlement resistance deteriorates. Therefore, the content of C is 0.030% or more and 0.500% or less. Preferably it is 0.050% or more. Preferably it is 0.400% or less. More preferably, it is 0.100% or more. More preferably, it is 0.350% or less.
  • Si is one of the important basic components of steel, and in particular in the present invention, it suppresses the formation of carbides during continuous annealing and promotes the formation of retained austenite, so it is an important element that affects TS and the amount of retained austenite. It is an element. If the Si content is less than 0.01%, it becomes difficult to achieve a TS of 1180 MPa or more. On the other hand, when the Si content exceeds 2.50%, retained austenite increases excessively, making it difficult to achieve YR of 85% or more. Therefore, the Si content is set to 0.01% or more and 2.50% or less. Preferably it is 0.05% or more. Preferably it is 2.00% or less. More preferably, it is 0.10% or more. More preferably, it is 1.20% or less.
  • Mn is one of the important basic components of steel, and in particular, in the present invention, it is an important element that affects the fraction of tempered martensite and the resistance to work embrittlement. If the Mn content is less than 0.10%, the fraction of tempered martensite decreases, making it difficult to achieve a TS of 1180 MPa or more. On the other hand, when the Mn content exceeds 5.00%, the tempered martensite becomes brittle and the work embrittlement resistance deteriorates. Therefore, the Mn content is set to 0.10% or more and 5.00% or less. Preferably it is 0.50% or more. Preferably it is 4.50% or less. More preferably, it is 0.80% or more. More preferably, it is 4.00% or less.
  • P 0.100% or less Since P segregates at prior austenite grain boundaries and embrittles the grain boundaries, it lowers the ultimate deformability of the steel sheet, resulting in a decrease in work embrittlement resistance. Therefore, the content of P needs to be 0.100% or less. Although the lower limit of the P content is not particularly defined, it is preferably 0.001% or more since P is a solid solution strengthening element and can increase the strength of the steel sheet. Therefore, the content of P is 0.100% or less. Preferably it is 0.001% or more. Preferably it is 0.070% or less.
  • S 0.0200% or less
  • S exists as a sulfide and reduces the ultimate deformability of the steel sheet, thereby reducing the work embrittlement resistance. Therefore, the S content needs to be 0.0200% or less.
  • the lower limit of the S content is not particularly specified, it is preferably 0.0001% or more due to production technology constraints. Therefore, the S content is set to 0.0200% or less. Preferably it is 0.0001% or more. Preferably it is 0.0050% or less.
  • Al 1.000% or less
  • the Al content is set to 1.000% or less.
  • it is 0.001% or more.
  • it is 0.500% or less.
  • N 0.0100% or less
  • N exists as a nitride and reduces the ultimate deformability of the steel sheet, thereby reducing the work embrittlement resistance. Therefore, the N content needs to be 0.0100% or less.
  • the lower limit of the N content is not particularly specified, it is preferable that the N content is 0.0001% or more due to constraints on production technology. Therefore, the N content is set to 0.0100% or less. Preferably it is 0.0001% or more. Preferably it is 0.0050% or less.
  • O exists as an oxide and reduces the ultimate deformability of the steel sheet, thereby reducing the work embrittlement resistance. Therefore, the content of O needs to be 0.0100% or less.
  • the lower limit of the O content is not particularly defined, it is preferable that the O content is 0.0001% or more due to production technology constraints. Therefore, the O content is set to 0.0100% or less. Preferably it is 0.0001% or more. Preferably it is 0.0050% or less.
  • a high-strength steel plate according to an embodiment of the present invention has a composition containing the above-mentioned components, with the remainder containing Fe and inevitable impurities.
  • unavoidable impurities include Zn, Pb, As, Ge, Sr, and Cs. A total content of these impurities of 0.100% or less is allowed.
  • the high-strength steel plate of the present invention further includes, in mass%, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.200% or less, Ta: 0.10% or less, W: 0.10% or less, B: 0.0100% or less, Cr: 1.00% or less, Mo: 1.00% or less, Ni: 1.00% or less, Co: 0.010% or less, Cu: 1.00% or less, Sn: 0.200% or less, Sb: 0.
  • At least one element selected from the following and Bi: 0.200% or less may be contained alone or in combination.
  • the contents of Ti, Nb, and V are each 0.200% or less.
  • the lower limits of the contents of Ti, Nb, and V are not particularly defined, the strength of the steel sheet is increased by forming fine carbides, nitrides, or carbonitrides during hot rolling or continuous annealing. Therefore, it is more preferable that the contents of Ti, Nb, and V are each 0.001% or more. Therefore, when Ti, Nb, and V are contained, their contents are each 0.200% or less. More preferably, it is 0.001% or more. More preferably, it is 0.100% or less.
  • Ta and W are each 0.10% or less, large amounts of coarse precipitates and inclusions will not be generated and the ultimate deformability of the steel sheet will not be reduced, so the work embrittlement resistance will not deteriorate. Therefore, it is preferable that the contents of Ta and W are each 0.10% or less. Note that there is no particular lower limit to the content of Ta and W, but the strength of the steel sheet is increased by forming fine carbides, nitrides, or carbonitrides during hot rolling or continuous annealing. It is more preferable that the contents of Ta and W are each 0.01% or more. Therefore, when Ta and W are contained, their contents are each 0.10% or less. More preferably, it is 0.01% or more. More preferably, it is 0.08% or less.
  • the content of B is preferably 0.0100% or less.
  • the lower limit of the B content is not particularly specified, but since it is an element that segregates at austenite grain boundaries during annealing and improves hardenability, it is preferable that the B content is 0.0003% or more. preferable. Therefore, when B is contained, its content should be 0.0100% or less. More preferably, it is 0.0003% or more. More preferably, it is 0.0080% or less.
  • each of Cr, Mo, and Ni is 1.00% or less, coarse precipitates and inclusions do not increase and the ultimate deformability of the steel sheet does not decrease, so the work embrittlement resistance does not deteriorate. Therefore, it is preferable that the contents of Cr, Mo, and Ni are each 1.00% or less.
  • the lower limit of the content of Cr, Mo, and Ni is not particularly specified, but since they are elements that improve hardenability, it is more preferable that the content of Cr, Mo, and Ni is each 0.01% or more. . Therefore, when Cr, Mo, and Ni are contained, their contents are each 1.00% or less. More preferably, it is 0.01% or more. More preferably, it is 0.80% or less.
  • the Co content is preferably 0.010% or less.
  • the lower limit of the Co content is not particularly specified, since it is an element that improves hardenability, the Co content is more preferably 0.001% or more. Therefore, when Co is contained, the content should be 0.010% or less. More preferably, it is 0.001% or more. More preferably, it is 0.008% or less.
  • the Cu content is preferably 1.00% or less.
  • the lower limit of the Cu content is not particularly specified, since it is an element that improves hardenability, the Cu content is preferably 0.01% or more. Therefore, if Cu is contained, the content should be 1.00% or less. More preferably, it is 0.01% or more. More preferably, it is 0.80% or less.
  • the content of Sn is preferably 0.200% or less.
  • the lower limit of the Sn content is not particularly specified, but since Sn is an element that improves hardenability (generally an element that improves corrosion resistance), the Sn content should be 0.001% or more. It is more preferable. Therefore, if Sn is contained, the content should be 0.200% or less. More preferably, it is 0.001% or more. More preferably, it is 0.100% or less.
  • the content of Sb is preferably 0.200% or less.
  • the lower limit of the Sb content is not particularly defined, it is more preferable that the Sb content is 0.001% or more since it is an element that controls the softening thickness of the surface layer and enables strength adjustment. Therefore, if Sb is contained, the content should be 0.200% or less. More preferably, it is 0.001% or more. More preferably, it is 0.100% or less.
  • the content of Ca, Mg and REM is preferably 0.0100% or less.
  • the lower limits of the contents of Ca, Mg, and REM are not particularly stipulated, but since they are elements that spheroidize the shape of nitrides and sulfides and improve the ultimate deformability of steel sheets, the contents of Ca, Mg, and REM are More preferably, each amount is 0.0005% or more. Therefore, when Ca, Mg and REM are contained, their contents are each 0.0100% or less. More preferably, it is 0.0005% or more. More preferably, it is 0.0050% or less.
  • the contents of Zr and Te are preferably 0.100% or less.
  • the lower limits of the contents of Zr and Te are not particularly specified, but since they are elements that spheroidize the shape of nitrides and sulfides and improve the ultimate deformability of the steel sheet, the contents of Zr and Te are respectively 0. More preferably, the content is .001% or more. Therefore, when Zr and Te are contained, their contents are each 0.100% or less. More preferably, it is 0.001% or more. More preferably, it is 0.080% or less.
  • the Hf content is preferably 0.10% or less. Note that there is no particular lower limit to the Hf content, but since it is an element that spheroidizes the shape of nitrides and sulfides and improves the ultimate deformability of steel sheets, the Hf content should be 0.01% or more. It is more preferable to do so. Therefore, if Hf is contained, the content should be 0.10% or less. More preferably, it is 0.01% or more. More preferably, it is 0.08% or less.
  • the Bi content is preferably 0.200% or less.
  • the lower limit of the Bi content is not particularly defined, since it is an element that reduces segregation, the Bi content is more preferably 0.001% or more. Therefore, when Bi is contained, the content should be 0.200% or less. More preferably, it is 0.001% or more. More preferably, it is 0.100% or less.
  • each content of Ti, Nb, V, Ta, W, B, Cr, Mo, Ni, Co, Cu, Sn, Sb, Ca, Mg, REM, Zr, Te, Hf and Bi is preferable. If it is less than the lower limit, the effect of the present invention will not be impaired, and therefore it is included as an unavoidable impurity.
  • Tempeered martensite 90% or more in area fraction
  • the area fraction of tempered martensite is 90% or more.
  • it is 94% or more. More preferably, it is 96% or more.
  • the method for measuring tempered martensite is as follows. After polishing the L cross section of the steel plate, 3vol. % nital, and 1/4 part of the plate thickness (a position corresponding to 1/4 of the plate thickness in the depth direction from the steel plate surface) is observed in 10 fields at a magnification of 2000 times using an SEM. Note that in the above structure image, the tempered martensite is a structure that has fine irregularities inside and has carbides inside. Tempered martensite can be determined from the average value of those values.
  • the retained austenite amount is less than 3%] This is an extremely important feature of the invention.
  • the volume fraction of retained austenite is 3% or more, it becomes difficult to achieve YR of 85% or more.
  • the reason for the decrease in YR is that an increase in retained austenite causes a decrease in YS due to deformation-induced transformation of the retained austenite. Therefore, the retained austenite content should be less than 3%. Preferably it is 1% or less.
  • the lower limit of retained austenite is not particularly limited. It may be 0%.
  • the method for measuring retained austenite is as follows. Retained austenite was determined by polishing the steel plate from 1/4 part of the plate thickness to a surface of 0.1 mm, and then chemically polishing the surface to a further 0.1 mm using an X-ray diffractometer using CoK ⁇ rays. ⁇ , ⁇ 220 ⁇ , ⁇ 311 ⁇ planes and the diffraction peaks of ⁇ 200 ⁇ , ⁇ 211 ⁇ , ⁇ 220 ⁇ planes of BCC iron were measured, and the nine integrated intensity ratios obtained were averaged. Convert and seek.
  • Total of ferrite and bainitic ferrite less than 10% in area fraction
  • the total amount of ferrite and bainitic ferrite is less than 10%. Preferably it is 8% or less. More preferably, it is 5% or less.
  • the lower limit of the total of ferrite and bainitic ferrite is not particularly limited. It may be 0%.
  • the method for measuring the total amount of ferrite and bainitic ferrite is as follows. After polishing the L cross section of the steel plate, 3vol. % nital, and 1/4 part of the plate thickness (a position corresponding to 1/4 of the plate thickness in the depth direction from the steel plate surface) is observed in 10 fields at a magnification of 2000 times using an SEM.
  • ferrite and bainitic ferrite have concave portions and a flat structure inside, and have no carbide inside. The sum of ferrite and bainitic ferrite can be determined from the average value of those values.
  • Possible structures other than all the above structures include pearlite, fresh martensite, and acicular ferrite. These structures may be included because they do not affect the properties as long as they are in a range of 5% or less.
  • Prior austenite average grain size is 20 ⁇ m or less
  • the lower limit of the average prior austenite grain size is not particularly defined, but if the prior austenite average grain size is less than 2 ⁇ m, residual austenite may increase, so it is preferably 2 ⁇ m or more. Therefore, the average crystal grain size of prior austenite is set to 20 ⁇ m or less. Preferably it is 2 ⁇ m or more. Preferably it is 15 ⁇ m or less. More preferably, the thickness is 3 ⁇ m or more. More preferably, the thickness is 10 ⁇ m or less.
  • the method for measuring the average grain size of prior austenite is as follows. After polishing the L cross section of the steel plate, etching it with a mixed solution of picric acid and ferric chloride to expose the prior austenite grain boundaries, 3 to 10 fields of view are photographed using an optical microscope at a magnification of 400x. A total of 20 straight lines (10 vertically x 10 horizontally) are drawn at equal intervals on the obtained image data and determined by a cutting method.
  • the average value of the occupancy of the packets with the maximum occupancy in the prior austenite grains is 70% or less in terms of area fraction] This is an extremely important feature of the invention.
  • the occupancy of the packets having the maximum occupancy within the prior austenite grains influences the flatness in the width direction and the resistance to work embrittlement.
  • the packet with the maximum occupancy rate in the prior austenite grains means that, as shown in Figure 1, there are up to four regions in the prior austenite grains, called packets, that have the same crystal habit plane during transformation. indicates the packet with the largest occupancy rate.
  • the occupancy of one packet within a prior austenite grain is determined by dividing the area of a specified packet by the total area within the prior austenite grain.
  • the present inventors found that by reducing the occupancy of the packets with the maximum occupancy within the prior austenite grains, the strain between the packets was alleviated and the flatness in the sheet width direction was improved. I discovered that. They also found that by reducing the occupancy of packets, which have the highest occupancy within prior austenite grains, the structure becomes finer and crack propagation can be suppressed, thereby improving the work embrittlement resistance of the steel sheet. . Therefore, the average value of the occupancy of the packets having the maximum occupancy in the prior austenite grains is set to be 70% or less. Preferably it is 60% or less. Note that the lower limit of the average value of the occupancy of packets having the maximum occupancy in prior austenite grains is not particularly limited.
  • the occupancy rate of the packet having the maximum occupancy rate in the prior austenite grains is 25%. Therefore, the lower limit of the average value of the occupancy of packets having the maximum occupancy in prior austenite grains is set to 25% or more, but there is no need to limit it to this.
  • the method for measuring the average value of the occupancy of the packets having the maximum occupancy in the prior austenite grains is as follows. First, a test piece for microstructural observation is taken from a cold-rolled steel sheet. Next, the sampled test piece is polished by colloidal silica vibration polishing so that the cross section in the rolling direction (L cross section) becomes the observation surface. The observation surface is a mirror surface. Next, electron beam backscatter diffraction (EBSD) measurement is performed on a 1/4 part of the plate thickness (a position corresponding to 1/4 of the plate thickness in the depth direction from the steel plate surface) to obtain local crystal orientation data.
  • EBSD electron beam backscatter diffraction
  • the SEM magnification is 1000 times, the step size is 0.2 ⁇ m, the measurement area is 80 ⁇ m square, and the WD is 15 mm.
  • the obtained local orientation data is analyzed using OIM Analysis 7 (OIM), and a color-coded diagram (CP map) for each Close-packed Plane group (CP group) is created using the method described in Non-Patent Document 1.
  • packets are defined as areas to which the same CP group belongs. The area of the packet with the largest occupancy is determined from the obtained CP map and divided by the total area within the prior austenite grains, thereby obtaining the occupancy of the packet with the maximum occupancy within the prior austenite grains. This analysis is performed on ten or more adjacent prior austenite grains, and the average value is taken as the average value of the occupancy of the packets having the maximum occupancy within the prior austenite grain.
  • the method of melting the steel material is not particularly limited, and any known melting method such as a converter or an electric furnace is suitable.
  • the steel slab (slab) is preferably manufactured by a continuous casting method in order to prevent macro segregation.
  • the slab heating temperature, slab soaking time and coiling temperature in hot rolling are not particularly limited.
  • Methods for hot rolling steel slabs include rolling the slab after heating, directly rolling the slab after continuous casting without heating it, and rolling after subjecting the slab after continuous casting to a short heat treatment. Examples include.
  • the slab heating temperature, slab soaking time, finish rolling temperature, and coiling temperature in hot rolling are not particularly limited, the lower limit of the slab heating temperature is preferably 1100° C. or higher.
  • the upper limit of the slab heating temperature is preferably 1300°C or less.
  • the lower limit of the slab soaking time is preferably 30 min or more.
  • the upper limit of the slab soaking time is preferably 250 min or less.
  • the lower limit of the finish rolling temperature is preferably equal to or higher than the Ar 3 transformation point.
  • the lower limit of the winding temperature is preferably 350°C or higher.
  • the upper limit of the winding temperature is preferably 650° C. or less.
  • the hot-rolled steel sheet produced in this way is pickled. Since pickling can remove oxides on the surface of the steel sheet, it is important for ensuring good chemical conversion treatability and plating quality in the final high-strength steel sheet. Further, the pickling may be carried out once or may be carried out in multiple steps. Moreover, cold rolling may be performed on the pickled plate after hot rolling, or cold rolling may be performed after heat treatment.
  • the rolling reduction in cold rolling and the plate thickness after rolling are not particularly limited, but the lower limit of the rolling reduction is preferably 30% or more. Further, the upper limit of the rolling reduction ratio is preferably 80% or less. Note that the effects of the present invention can be obtained without any particular limitations on the number of rolling passes and the rolling reduction rate of each pass.
  • the cold rolled steel sheet obtained as described above is annealed.
  • the annealing conditions are as follows.
  • the annealing temperature T1 750°C or higher and 950°C or lower.
  • the annealing temperature T1 is set to 750°C or more and 950°C or less.
  • it is 800°C or higher.
  • it is 900°C or less.
  • the holding time t1 at annealing temperature T1 is 10 seconds or more and 1000 seconds or less. If the holding time t1 at the annealing temperature T1 is less than 10 seconds, austenitization will be insufficient, and the total area fraction of ferrite and bainitic ferrite will be 10% or more, making it difficult to achieve a TS of 1180 MPa or more. , and it becomes difficult to achieve a YR of 85% or more. On the other hand, when the holding time at the annealing temperature T1 exceeds 1000 seconds, the prior austenite grain size increases excessively, and the resistance to work embrittlement deteriorates. Therefore, the holding time t1 at the annealing temperature T1 is 10 seconds or more and 1000 seconds or less. Preferably it is 50 seconds or more. Preferably it is 500 seconds or less.
  • Average cooling rate from 750°C to 600°C is 20°C/s or more
  • the average cooling rate from 750°C to 600°C is set to 20°C/s or more.
  • the average cooling rate from 750°C to 600°C is set to 20°C/s or more.
  • the upper limit does not need to be particularly limited, but is preferably 2000° C./s or less.
  • the average cooling rate from (Ms + 50° C.) to the quenching start temperature T2 affects the average value of the total area fraction of ferrite and bainitic ferrite and the occupancy of the packet with the maximum occupancy in the prior austenite grains. (Ms + 50°C) - If the average cooling rate of the rapid cooling start temperature T2 is less than 5°C/s, the total area fraction of ferrite and bainitic ferrite becomes 10% or more, making it difficult to achieve a TS of 1180 MPa or more.
  • the average cooling rate from (Ms+50°C) to quenching start temperature T2 exceeds 30°C/s, the average value of the occupancy of the packets with the maximum occupancy in the prior austenite grains exceeds 70%, and The flatness of the plate deteriorates, and the resistance to work embrittlement decreases. Therefore, the average cooling rate from (Ms+50°C) to the rapid cooling start temperature T2 is set to be 5°C/s or more and 30°C/s or less. Preferably it is 10°C/s or more. Preferably it is 20°C/s or less.
  • Rapid cooling start temperature T2 is (Ms-80°C) or more and less than Ms] This is an extremely important feature of the invention.
  • the quenching start temperature T2 is set to (Ms-80°C) or more and less than Ms, and the quenching is performed in a state where the martensitic transformation rate before the start of quenching is 1% or more and 80% or less.
  • the average value of the occupancy of packets having the maximum occupancy in prior austenite grains is 70% or less, and the volume fraction of retained austenite is less than 3%.
  • the quenching start temperature T2 is set to be at least (Ms-80°C) and less than Ms.
  • Ms (Ms-50°C) or higher.
  • Ms (Ms-5°C)
  • Ms 519-474 ⁇ [%C]-30.4 ⁇ [%Mn]-12.1 ⁇ [%Cr]-7.5 ⁇ [%Mo]-17.7 ⁇ [%Ni]...
  • [%C], [%Mn], [%Cr], [%Mo], and [%Ni] represent the respective contents (mass%) of C, Mn, Cr, Mo, and Ni, and do not include In that case, it is set to 0.
  • the average cooling rate from the rapid cooling start temperature T2 to 80°C is set to 300°C/s or more. Preferably it is 800°C/s or more.
  • the upper limit does not need to be particularly limited, but is preferably 2000° C./s or less.
  • tempered martensite refers to a structure in which martensite at 80° C. or lower is heat-treated at a tempering temperature of 100° C. or higher and for a holding time of 10 seconds or longer. Therefore, when the tempering temperature T3 is less than 100° C., martensite is not sufficiently tempered, resulting in a structure consisting mainly of as-quenched martensite, and the as-quenched martensite deteriorates the work embrittlement resistance.
  • the tempering temperature T3 exceeds 400°C, the tempered martensite decomposes and becomes ferrite, making the area fraction of the tempered martensite less than 90%, making it difficult to achieve a TS of 1180 MPa or more. Become. Therefore, the tempering temperature T3 is set at 100°C or more and 400°C or less. Preferably the temperature is 150°C or higher. Preferably the temperature is 350°C or less.
  • tempered martensite refers to a structure in which martensite at 80° C. or lower is heat-treated at a tempering temperature of 100° C. or higher and for a holding time of 10 seconds or longer. Therefore, when the holding time t3 at the tempering temperature T3 is less than 10 seconds, martensite is not sufficiently tempered, resulting in a structure consisting mainly of as-quenched martensite, and the as-quenched martensite deteriorates the work embrittlement resistance.
  • the holding time t3 at the tempering temperature T3 is set to 10 seconds or more and 10,000 seconds or less. Preferably it is 50 seconds or more. Preferably it is 5000 seconds or less.
  • Cooling after tempering does not need to be particularly specified, and may be cooled to a desired temperature by any method.
  • the desired temperature is preferably about room temperature.
  • the above-mentioned high-strength steel plate may be processed under conditions that result in an equivalent plastic strain amount of 0.10% or more and 5.00% or less. Further, after processing, reheating may be performed again under the conditions of 100° C. or more and 400° C. or less.
  • the high-strength steel plate may be subjected to plating treatment during or after annealing.
  • Examples of the plating treatment during annealing include hot-dip galvanizing during or after cooling at 750° C. to 600° C. at an average cooling rate of 20° C./s or more, and alloying after hot-dip galvanizing.
  • the plating treatment after annealing for example, Zn-Ni electroplating treatment or pure Zn electroplating treatment can be exemplified after tempering.
  • the plating layer may be formed by electroplating, or hot-dip zinc-aluminum-magnesium alloy plating may be applied.
  • the type of plating metal such as Zn plating and Al plating is not particularly limited.
  • Conditions for other manufacturing methods are not particularly limited, but from the viewpoint of productivity, a series of treatments such as annealing, hot-dip galvanizing, and galvanizing alloying are performed on a continuous galvanizing line (CGL), which is a hot-dip galvanizing line. It is preferable to carry out the process using Line). After hot-dip galvanizing, wiping can be performed to adjust the coating weight. Note that conditions for plating and the like other than the conditions described above can be based on a conventional method for hot-dip galvanizing.
  • processing may be performed again under conditions that result in an equivalent plastic strain amount of 0.10% or more and 5.00 or less. Further, after processing, reheating may be performed again under the conditions of 100° C. or more and 400° C. or less.
  • tensile test For the tensile test, a JIS No. 5 test piece (gauge length 50 mm, parallel part width 25 mm) was taken so that the longitudinal direction of the test piece was perpendicular to the rolling direction, and tested in accordance with JIS Z 2241. A tensile test was conducted at a crosshead speed of 1.67 ⁇ 10 ⁇ 1 mm/sec, and YS and TS were measured. In addition, in the present invention, a TS of 1180 MPa or more was determined to be acceptable. A yield ratio (YR) of 85% or more was judged to be acceptable. Note that YR is determined by the following equation (2).
  • YR 100 ⁇ YS/TS...(2) (Flatness in the board width direction)
  • the flatness of the various cold-rolled steel sheets obtained as described above in the sheet width direction was measured by the method shown in FIG. 2. Specifically, a plate with a length of 500 mm in the rolling direction (coil width x 500 mm L x plate thickness) is cut out from the coil, placed on a surface plate so that the warp of the end face faces upward, and the stylus moves over the object to be measured. The height of the steel plate was continuously measured over the entire width direction using a moving contact displacement meter. Based on the results, the steepness ⁇ , which is an index indicating the flatness of the steel plate shape, was measured according to the method shown in FIG.
  • the resistance to work brittleness was evaluated by Charpy test.
  • Charpy test piece a plurality of steel plates were stacked together and fastened together with bolts, and after confirming that there were no gaps between the steel plates, a test piece with a V-notch having a depth of 2 mm was prepared.
  • the number of steel plates to be stacked was set so that the thickness of the test piece after stacking was closest to 10 mm. For example, if the plate thickness is 1.2 mm, 8 plates are laminated, resulting in a test piece thickness of 9.6 mm.
  • the laminated Charpy test piece was taken with the width direction of the plate as the longitudinal direction.
  • the ratio vE 0% /vE 10% of the impact absorption energy at room temperature between the as-manufactured (unprocessed) steel plate and the 10% rolled steel plate was measured.
  • "x” indicates that vE 0% /vE 10% is less than 0.6
  • " ⁇ ” indicates that vE 0% /vE 10 % is 0.6 or more and less than 0.7;
  • Those with vE 0% /vE 10% of 0.6 or more were evaluated as "excellent in resistance to work brittleness". Note that conditions other than the above were in accordance with JIS Z 2242:2018.
  • Tables 7 to 10 The results are shown in Tables 7 to 10. As shown in these tables, the examples of the present invention have a TS of 1180 MPa or more, a YR of 85% or more, and are excellent in flatness in the sheet width direction and resistance to work embrittlement. On the other hand, in the comparative example, any one or more of TS, YR, flatness in the plate width direction, or work embrittlement resistance is inferior.

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Abstract

Le but de la présente invention est de fournir une feuille d'acier à haute résistance et son procédé de fabrication, la feuille d'acier à haute résistance ayant un TS supérieur ou égal à 1 180 MPa et un YR supérieur ou égal à 85 %, et ayant une excellente planéité dans le sens de la largeur et une excellente propriété de fragilisation anti-travail.　La présente feuille d'acier à haute résistance comprend une composition de composant prédéterminée, à une position d'épaisseur de plaque de 1/4, la quantité de martensite résiduelle est supérieure ou égale à 90 % en fraction de surface, la quantité d'austénite résiduelle est inférieure à 3 % en fraction volumique, le total de la quantité de ferrite et de la quantité de ferrite bainitique est inférieur à 10 % en fraction surfacique, la granulométrie cristalline moyenne de l'austénite antérieure est inférieure ou égale à 20 µm, et la valeur moyenne des occupations de paquets ayant une occupation maximale dans les grains d'austénite antérieure est inférieure ou égale à 70 % en fraction surfacique.
PCT/JP2023/002913 2022-03-25 2023-01-30 Feuille d'acier à haute résistance et son procédé de fabrication WO2023181640A1 (fr)

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MX2024011508A MX2024011508A (es) 2022-03-25 2023-01-30 Lamina de acero de alta resistencia y metodo de fabricacion de la misma.
KR1020247030587A KR20240152342A (ko) 2022-03-25 2023-01-30 고강도 강판 및 그 제조 방법
CN202380027218.3A CN118804993A (zh) 2022-03-25 2023-01-30 高强度钢板及其制造方法
JP2023528940A JP7323093B1 (ja) 2022-03-25 2023-01-30 高強度鋼板およびその製造方法

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4947176B2 (ja) 2010-03-24 2012-06-06 Ｊｆｅスチール株式会社 超高強度冷延鋼板の製造方法
JP2013104081A (ja) * 2011-11-11 2013-05-30 Kobe Steel Ltd 耐遅れ破壊性に優れた高強度鋼板およびその製造方法
WO2014129379A1 (fr) * 2013-02-19 2014-08-28 株式会社神戸製鋼所 Feuille d'acier laminée à froid à résistance élevée ayant une excellente aptitude à la flexion
JP2017503072A (ja) * 2013-12-11 2017-01-26 アルセロールミタル 耐遅れ破壊特性を有するマルテンサイト鋼および製造方法
JP6525114B1 (ja) 2017-11-29 2019-06-05 Ｊｆｅスチール株式会社 高強度亜鉛めっき鋼板およびその製造方法
JP6777272B1 (ja) 2019-02-06 2020-10-28 日本製鉄株式会社 溶融亜鉛めっき鋼板およびその製造方法
JP2021105197A (ja) * 2019-12-26 2021-07-26 日本製鉄株式会社 鋼材
WO2022209519A1 (fr) * 2021-03-31 2022-10-06 Ｊｆｅスチール株式会社 Feuille d'acier, élément, procédé de production d'une feuille d'acier et procédé de production d'un élément

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4947176B2 (ja) 2010-03-24 2012-06-06 Ｊｆｅスチール株式会社 超高強度冷延鋼板の製造方法
JP2013104081A (ja) * 2011-11-11 2013-05-30 Kobe Steel Ltd 耐遅れ破壊性に優れた高強度鋼板およびその製造方法
WO2014129379A1 (fr) * 2013-02-19 2014-08-28 株式会社神戸製鋼所 Feuille d'acier laminée à froid à résistance élevée ayant une excellente aptitude à la flexion
JP2017503072A (ja) * 2013-12-11 2017-01-26 アルセロールミタル 耐遅れ破壊特性を有するマルテンサイト鋼および製造方法
JP6525114B1 (ja) 2017-11-29 2019-06-05 Ｊｆｅスチール株式会社 高強度亜鉛めっき鋼板およびその製造方法
JP6777272B1 (ja) 2019-02-06 2020-10-28 日本製鉄株式会社 溶融亜鉛めっき鋼板およびその製造方法
JP2021105197A (ja) * 2019-12-26 2021-07-26 日本製鉄株式会社 鋼材
WO2022209519A1 (fr) * 2021-03-31 2022-10-06 Ｊｆｅスチール株式会社 Feuille d'acier, élément, procédé de production d'une feuille d'acier et procédé de production d'un élément

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JOURNAL OF SMART PROCESSING, vol. 2, 2013, pages 110 - 118

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