US 12,421,567 B2
High-strength hot-rolled steel sheet
Yukiko Kobayashi, Tokyo (JP); Jun Takahashi, Tokyo (JP); Tatsuo Yokoi, Tokyo (JP); Riki Okamoto, Tokyo (JP); and Takeshi Toyoda, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/918,903
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Apr. 15, 2021, PCT No. PCT/JP2021/015587
§ 371(c)(1), (2) Date Oct. 14, 2022,
PCT Pub. No. WO2021/210644, PCT Pub. Date Oct. 21, 2021.
Claims priority of application No. 2020-074180 (JP), filed on Apr. 17, 2020.
Prior Publication US 2023/0287530 A1, Sep. 14, 2023
Int. Cl. C21D 8/02 (2006.01); C21D 9/46 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/14 (2006.01)
CPC C21D 8/0226 (2013.01) [C21D 9/46 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/14 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A high-strength hot-rolled steel sheet having a chemical composition comprising, by mass:
C: from 0.030 to 0.250%;
Si: from 0.01 to 1.50%;
Mn: from 0.1 to 3.0%;
Ti: from 0.040 to 0.200%;
P: 0.100% or less;
S: 0.005% or less;
Al: 0.500% or less;
N: 0.0090% or less;
B: from 0 to 0.0030%;
a total of one or more of Nb, Mo and V: from 0 to 0.040%;
a total of one or more of Ca and REM: from 0 to 0.010%; and
a balance of Fe and impurities, a mass ratio [Ti]/[C] of a Ti amount to a C amount being from 0.16 to 3.00, and a product [Ti]×[C] of the Ti amount and the C amount being from 0.0015 to 0.0160,
the high-strength hot-rolled steel sheet:
having a mean dislocation density of from 1×1014 to 1×1016 m−2; and
comprising at least bainitic ferrite,
wherein a total area ratio of the bainitic ferrite and ferrite is 70% or more and less than 85% [90%],
wherein a total area ratio of martensite and retained austenite is 5% or more and 30% or less,
wherein, in ferrite crystal grains and in bainitic ferrite crystal grains, a mean number density of TiC precipitates is from 1×1017 to 5×1018 precipitates cm3,
wherein an amount of Ti present as a TiC precipitate precipitated in a matrix not on dislocations is 30 mass % or more of a total amount of Ti in the steel sheet,
wherein a tensile strength is 850 MPa or more, and
wherein [Ti] and [C] represent the Ti amount and the C amount in mass %, respectively.