公开(公告)号：US11332804B2

公开(公告)日：2022-05-17

申请号：US16966762

申请日：2019-01-21

Applicant: JFE STEEL CORPORATION

Inventor： Seigo Tsuchihashi ,  Shinsuke Komine ,  Tatsuya Nakagaito ,  Hidekazu Minami

IPC: C21D9/46 ,  C21D8/02 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/10 ,  C22C38/12 ,  C22C38/14 ,  C22C38/20 ,  C22C38/32 ,  C22C38/60 ,  C23C2/06

Abstract: A high-strength cold-rolled steel sheet or high-strength coated steel sheet that has a tensile strength (TS) of 780 MPa or more and has high ductility, stretch-flangeability, and in-plane stability of stretch-flangeability and methods for producing the same. The high-strength cold-rolled steel sheet has a specified chemical composition and a microstructure comprising, by area fraction, in a range of 50% to 80% of ferrite, 8% or less of martensite with an average grain size of 2.5 μm or less, in a range of 6% to 15% of retained austenite, and in a range of 3% to 40% of tempered martensite. A ratio fM/fM+TM being 50% or less, where fM denotes the area fraction of martensite and fM+TM denotes the total area fraction of martensite and tempered martensite, and a standard deviation of the grain size of martensite at certain portions being 0.7 μm or less.