Patent ID: 9121087
Filing Date: 2015-09-01
Classification: C21D,C22C,C23C

Abstract:
1. A high-strength steel sheet comprising, on a mass percent basis: 0.17%-0.73% C; 3.0% or less Si; 0.5%-3.0% Mn; 0.1% or less P; 0.07% or less S; 3.0% or less Al; 0.010% or less N; and the balance being Fe and incidental impurities, wherein Si+Al satisfies 0.7% or more, and wherein with respect to microstructures of the steel sheet, a proportion of an area of martensite is 10% to 90% with respect to all microstructures of the steel sheet, retained austenite content is 6% to 50%, a proportion of an area of bainitic ferrite in upper bainite is 5% or more with respect to all microstructures of the steel sheet, 25% or more of the martensite is tempered martensite, the sum of the proportion of the area of martensite with respect to all microstructures of the steel sheet, the retained austenite content, and the proportion of the area of bainitic ferrite in upper bainite with respect to all microstructures of the steel sheet satisfies 65% or more, a proportion of an area of polygonal ferrite with respect to all microstructures of the steel sheet satisfies 10% or less (including 0%), average C content of retained austenite is 0.70% or more, tensile strength is 980 MPa to 1862 MPa, and ductility TS×T. EL of 20,000 MPa % to 32,494 MPa %.