US 11,939,640 B2
Method for producing hot-rolled steel sheet, method for producing cold-rolled full-hard steel sheet, and method for producing heat-treated sheet
Katsutoshi Takashima, Tokyo (JP); and Yoshimasa Funakawa, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Filed by JFE Steel Corporation, Tokyo (JP)
Filed on Feb. 18, 2021, as Appl. No. 17/178,518.
Application 17/178,518 is a division of application No. 16/086,426, granted, now 10,961,600, previously published as PCT/JP2017/011076, filed on Mar. 21, 2017.
Claims priority of application No. 2016-070740 (JP), filed on Mar. 31, 2016; and application No. 2016-231185 (JP), filed on Nov. 29, 2016.
Prior Publication US 2021/0180151 A1, Jun. 17, 2021
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); B32B 15/04 (2006.01); B32B 15/18 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/08 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/16 (2006.01); C22C 38/18 (2006.01); C22C 38/20 (2006.01); C22C 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C22C 38/38 (2006.01); C22C 38/40 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/58 (2006.01); C23C 2/02 (2006.01); C23C 2/04 (2006.01); C23C 2/06 (2006.01); C23C 2/12 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01); C23C 28/02 (2006.01); C23C 30/00 (2006.01); C23G 1/00 (2006.01); C23G 1/08 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/01 (2013.01); B32B 15/012 (2013.01); B32B 15/013 (2013.01); B32B 15/04 (2013.01); B32B 15/043 (2013.01); B32B 15/18 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0247 (2013.01); C21D 8/0263 (2013.01); C21D 8/0268 (2013.01); C21D 8/0273 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C22C 38/18 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C22C 38/38 (2013.01); C22C 38/40 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/58 (2013.01); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/024 (2022.08); C23C 2/04 (2013.01); C23C 2/06 (2013.01); C23C 2/12 (2013.01); C23C 2/28 (2013.01); C23C 2/40 (2013.01); C23C 28/021 (2013.01); C23C 28/023 (2013.01); C23C 28/025 (2013.01); C23C 30/00 (2013.01); C23C 30/005 (2013.01); C21D 8/0236 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C21D 2211/009 (2013.01); C23G 1/00 (2013.01); C23G 1/08 (2013.01); Y10T 428/12757 (2015.01); Y10T 428/12799 (2015.01); Y10T 428/12951 (2015.01); Y10T 428/12958 (2015.01); Y10T 428/12972 (2015.01)] 10 Claims
 
1. A method for producing a hot-rolled steel sheet, the method comprising:
hot rolling a steel material, of a composition comprising, in mass %, C: 0.05 to 0.12%, Si: 0.80% or less, Mn: 1.30 to 2.10%, P: 0.001 to 0.050%, S: 0.005% or less, Al: 0.01 to 0.10%, N: 0.010% or less, one or more selected from Cr in an amount of 0.05 to 0.50%, and Mo in an amount of 0.05 to 0.50%, one or more selected from Ti in an amount of 0.01 to 0.10%, Nb in an amount of 0.01 to 0.10%, and V in an amount of 0.01 to 0.10%, and the balance Fe and unavoidable impurities, under the conditions where a rolling reduction of a final pass of finish rolling is 12% or more, a rolling reduction of a preceding pass of the final pass is 15% or more, and a finisher delivery temperature is 850 to 950° C.;
subjecting the steel after the hot rolling to first cooling in which the steel is cooled to a cooling stop temperature at a first average cooling rate of 50° C./s or more, the cooling stop temperature being 750° C. or less;
subjecting the steel after the first cooling to second cooling in which the steel is cooled to a coiling temperature at a second average cooling rate of 5° C./s or more and less than 50° C./s; and
coiling the steel after the second cooling at a coiling temperature of 650° C. or less.