Patent ID: 9738956
Date: 2017-08-22
CPC Classifications: C21D,C22C

Claim:
1. An ultrahigh-strength steel sheet, comprising, based on a total mass of the steel sheet: from 0.05% to 0.25% of carbon (C); from 0.5% to 2.5% of silicon (Si); from 2.0% to 4% of manganese (Mn); 0.1% or less, excluding 0%, of phosphorus (P); 0.05% or less, excluding 0%, of sulfur (S); from 0.01% to 0.1% of aluminum (Al); 0.01% or less, excluding 0%, of nitrogen (N); and iron (Fe), wherein the steel sheet comprises martensite; and a soft phase comprising bainitic ferrite and if any, polygonal ferrite, the steel sheet does not comprise retained austenite, the steel sheet comprises, by area percent relative to the entire steel sheet: the steel sheet has a coefficient of variation [(standard deviation)/(arithmetic mean)] in equivalent circle diameters of grains of the soft phase of 1.0 or less, and the steel sheet has a tensile strength of 1100 MPa or more.