US2025084515A1PendingUtilityA1
High-strength steel sheet and method for producing same
Est. expiryJan 14, 2042(~15.5 yrs left)· nominal 20-yr term from priority
C21D 8/02C23C 2/06C22C 38/14C22C 38/12C22C 38/06C22C 38/02C21D 2211/008C21D 2211/002C21D 2211/001C21D 9/46C21D 8/0273C21D 8/0236C21D 8/0226C21D 6/005C22C 18/00C22C 38/60C22C 38/34C22C 38/26C22C 38/005C22C 38/008C22C 38/10C22C 38/002C22C 38/16C22C 38/32C22C 38/38C22C 38/50C22C 38/58C22C 38/04C23C 2/29C23C 2/40C23C 2/024C23C 2/02C23C 2/0224C23C 2/28C21D 8/0263C21D 8/0205
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Claims
Abstract
A high-strength steel sheet having a tensile strength of 1320 MPa or more is disclosed. The above-described high-strength steel sheet includes a specific component composition including Ti and the like, wherein a diffusible hydrogen amount in steel is 0.50 ppm by mass or less, tempered martensite and bainite are 70.0 to 95.0%, fresh martensite is 15.0% or less, retained austenite is 5.0 to 15.0%, an average grain size of a precipitate A, which is a carbide, nitride, or carbonitride containing at least one selected from the group consisting of Ti, Nb, and V is 0.001 to 0.050 μm, a number density NS of the precipitate A having a major axis of 0.050 μm or less is 10/μm2 or more, and a ratio of the number density NS and a number density NL of the precipitate A having a major axis of more than 0.050 μm is 10.0 or more.
Claims
exact text as granted — not AI-modified1 . A high-strength steel sheet comprising:
a component composition including, by mass %: C: 0.130 to 0.350%, Si: 0.50 to 2.50%, Mn: 2.00 to 4.00%, P: 0.100% or less, S: 0.0500% or less, Al: 0.010 to 2.000%, N: 0.0100% or less, and at least one element selected from the group consisting of Ti: 0.001 to 0.100%, Nb: 0.001 to 0.100%, and V: 0.001 to 0.500%, and a balance consisting of Fe and inevitable impurities; and a microstructure, wherein a diffusible hydrogen amount in steel is 0.50 ppm by mass or less, a total area fraction of tempered martensite and bainite in the microstructure is 70.0 to 95.0%, an area fraction of fresh martensite is 15.0% or less, an area fraction of retained austenite is 5.0 to 15.0%, an average grain size of a precipitate A, which is a carbide, nitride, or carbonitride containing at least one selected from the group consisting of Ti, Nb, and V is 0.001 to 0.050 μm, a number density N S of a precipitate A S , which is the precipitate A having a major axis of 0.050 μm or less, is 10/μm 2 or more, and a ratio N S /N L of the number density N S of the precipitate A S and a number density N L of a precipitate A L , which is the precipitate A having a major axis of more than 0.050 μm, is 10.0 or more.
2 . The high-strength steel sheet according to claim 1 , wherein
the component composition further includes, by mass %, at least one element selected from the group consisting of: W: 0.500% or less, B: 0.0100% or less, Ni: 2.000% or less, Co: 2.000% or less, Cr: 1.000% or less, Mo: 1.000% or less, Cu: 1.000% or less, Sn: 0.500% or less, Sb: 0.500% or less, Ta: 0.100% or less, Zr: 0.200% or less, Hf: 0.020% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, and REM: 0.0100% or less.
3 . The high-strength steel sheet according to claim 1 , comprising a plating layer on a surface.
4 . The high-strength steel sheet according to claim 3 , wherein the plating layer is an alloyed plating layer.
5 . A method for producing the high-strength steel sheet according to claim 1 , the method comprising:
heating a steel slab having the component composition according to claim 1 to 1100° C. or higher and hot rolling the steel slab at a finish rolling finishing temperature of 850 to 950° C. to obtain a hot-rolled steel sheet; coiling the hot-rolled steel sheet at a coiling temperature T of 400 to 700° C., retaining the coiled hot-rolled steel sheet, and then cold rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet; and subjecting the cold-rolled steel sheet to a heat treatment, wherein in the retention, when a total time during which a temperature of the coiled hot-rolled steel sheet is the coiling temperature T−50° C. or more is taken as t as a unit s, the following Formula 1 is satisfied, and in the heat treatment, the cold-rolled steel sheet is held in a temperature region T1 of 800 to 950° C. for 30 seconds or more, then cooled to a cooling stop temperature T2 of 150 to 250° C., and then held in a temperature region T3 of 250 to 400° C. for 30 seconds or more.
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6 . The method for producing the high-strength steel sheet according to claim 5 , wherein
the steel slab is casted and then cooled before the hot rolling, and in the cooling of the steel slab, an average cooling rate v1 at 700 to 600° C. is 5.0° C./h or more, and an average cooling rate v2 at 600 to 500° C. is 2.5° C./h or more.
7 . The method for producing the high-strength steel sheet according to claim 5 , wherein the cold-rolled steel sheet is subjected to a plating treatment for forming a plating layer after the heat treatment.
8 . The method for producing the high-strength steel sheet according to claim 7 , wherein the plating treatment includes an alloying plating treatment for alloying the plating layer.
9 . The high-strength steel sheet according to claim 2 , comprising a plating layer on a surface.
10 . The high-strength steel sheet according to claim 9 , wherein the plating layer is an alloyed plating layer.
11 . A method for producing the high-strength steel sheet according to claim 2 , the method comprising:
heating a steel slab having the component composition according to claim 2 to 1100° C. or higher and hot rolling the steel slab at a finish rolling finishing temperature of 850 to 950° C. to obtain a hot-rolled steel sheet; coiling the hot-rolled steel sheet at a coiling temperature T of 400 to 700° C., retaining the coiled hot-rolled steel sheet, and then cold rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet; and subjecting the cold-rolled steel sheet to a heat treatment, wherein in the retention, when a total time during which a temperature of the coiled hot-rolled steel sheet is the coiling temperature T−50° C. or more is taken as t as a unit s, the following Formula 1 is satisfied, and in the heat treatment, the cold-rolled steel sheet is held in a temperature region T1 of 800 to 950° C. for 30 seconds or more, then cooled to a cooling stop temperature T2 of 150 to 250° C., and then held in a temperature region T3 of 250 to 400° C. for 30 seconds or more.
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12 . The method for producing the high-strength steel sheet according to claim 11 , wherein
the steel slab is casted and then cooled before the hot rolling, and in the cooling of the steel slab, an average cooling rate v1 at 700 to 600° C. is 5.0° C./h or more, and an average cooling rate v2 at 600 to 500° C. is 2.5° C./h or more.
13 . The method for producing the high-strength steel sheet according to claim 6 , wherein the cold-rolled steel sheet is subjected to a plating treatment for forming a plating layer after the heat treatment.
14 . The method for producing the high-strength steel sheet according to claim 11 , wherein the cold-rolled steel sheet is subjected to a plating treatment for forming a plating layer after the heat treatment.
15 . The method for producing the high-strength steel sheet according to claim 12 , wherein the cold-rolled steel sheet is subjected to a plating treatment for forming a plating layer after the heat treatment.
16 . The method for producing the high-strength steel sheet according to claim 13 , wherein the plating treatment includes an alloying plating treatment for alloying the plating layer.
17 . The method for producing the high-strength steel sheet according to claim 14 , wherein the plating treatment includes an alloying plating treatment for alloying the plating layer.
18 . The method for producing the high-strength steel sheet according to claim 15 , wherein the plating treatment includes an alloying plating treatment for alloying the plating layer.Join the waitlist — get patent alerts
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