US 12,378,625 B2
Steel sheet, member, and production methods therefor
Shimpei Yoshioka, Tokyo (JP); Shinjiro Kaneko, Tokyo (JP); and Yuma Honda, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/794,418
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Jan. 21, 2021, PCT No. PCT/JP2021/001935
§ 371(c)(1), (2) Date Jul. 21, 2022,
PCT Pub. No. WO2021/153392, PCT Pub. Date Aug. 5, 2021.
Claims priority of application No. 2020-014442 (JP), filed on Jan. 31, 2020.
Prior Publication US 2023/0069838 A1, Mar. 9, 2023
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (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 38/12 (2006.01); C22C 38/14 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C21D 8/0273 (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 38/12 (2013.01); C22C 38/14 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 16 Claims
OG exemplary drawing
 
1. A steel sheet having a tensile strength of 1310 MPa or higher, the steel sheet comprising:
a chemical composition containing, in terms of mass %,
C: 0.12% or more and 0.40% or less,
Si: 0.01% or more and 1.5% or less,
Mn: 0.2% or more and 1.7% or less,
P: 0.05% or less,
S: 0.010% or less,
sol. Al: 1.00% or less,
N: 0.010% or less,
B: 0.0002% or more and 0.0050% or less,
at least one selected from Nb and Ti: 0.010% or more and 0.080% or less in total, and the balance being Fe and incidental impurities; and
a steel microstructure containing martensite at an area ratio of 70% or more, bainite at an area ratio of 30% or less, and ferrite and retained austenite at a total area ratio of 5% or less,
wherein:
at a 1/4 thickness position of the steel sheet, a number density of carbides having long axes of 0.5 μm or more is 60000 carbides/mm2 or less, in a ¼-to-¾ thickness region of the steel sheet, a number density of inclusion grains having equivalent circle diameters of 4.0 μm or more is 10 grains/mm2 or more and 30 grains/mm2 or less, and in a surface-to-¼ thickness region of the steel sheet, a number density of inclusion grains having equivalent circle diameters of 4.0 μm or more is 27 grains/mm2 or less.