Patent ID: 9194030
Filing Date: 2015-11-24
Classification: C21D,C22C,C23C

Abstract:
1. A high strength thin steel sheet for superior press formability, comprising, by weight percent, 0.06 to 0.4% C, 1.0 to 5.0% Mn, 0.05 to 2.5% Si, 0.01 to 2.0% Ni, 0.02 to 2% Cu, 0.01 to 0.04% Ti, 0.05 to 2.5% Al, 0.005 to 0.1% Sb, 0.0005 to 0.004% B, 0.007% or less N, and balance Fe and inevitable impurities, and meeting relation of Ni+0.5×Mn+0.3×Cu≧0.9, which is defined as Ni*, and Al/Ni*≦1.3 at a same time, and relation of Ti≧0.028×Al, wherein the steel sheet is composed of polygonal ferrite as a matrix structure, austenite having a volume fraction of at least 33%, and the remainder of bainite, the austenite having a lath, a short side of which is less than 350 nm, wherein the Sb is enriched into a surface and grain boundaries of the steel sheet and inhibits the formation of an oxide on the surface of the steel sheet during annealing a cold-rolled steel sheet, wherein the steel sheet has TiN precipitates, the TiN precipitates being precipitated prior to MN precipitates being precipitated, and wherein the steel sheet has an elongation of 24% or more and a reduction of area of 40% or more, the reduction of area being a measurement of ductility.