Patent ID: 8992697
Filing Date: 2015-03-31
Classification: C21D,C22C

Abstract:
1. A high strength press-formed member obtainable by hot press-forming comprising a steel sheet constituting the member, the steel sheet comprising a composition including by mass %, C: 0.281% to 0.69%, Si: 3.0% or less, Mn: 0.5% to 3.0%, P: 0.1% or less, S: 0.07% or less, Al: 3.0% or less, N: 0.010% or less, Si+Al: at least 0.7%, and remainder as Fe and incidental impurities, wherein a microstructure of the steel sheet comprises martensite, retained austenite; bainite containing bainitic ferrite, an area ratio of said martensite with respect to the entire microstructure of the steel sheet is 10% to 85%, at least 25% of said martensite is tempered martensite, content of retained austenite is 6% to 40%, area ratio of said bainitic ferrite in said bainite with respect to the entire microstructure of the steel sheet is at least 5%, total of area ratios of said martensite, said retained austenite, and said bainitic ferrite in said bainite with respect to the entire microstructure of the steel sheet is at least 65%, and average carbon concentration in the retained austenite is at least 0.65 mass %.