Patent ID: 7776161

Claim:
A high strength cold-rolled steel sheet having good r-values consisting essentially of: in mass, 0.11 to 0.25% C, 0.001 to 3.0% Si, 0.01 to 3.0% Mn, 0.001 to 0.011% P, at most 0.05% S, 0.0005 to 0.030% N, 0.005 to 0.3% Al, and a balance of Fe and unavoidable impurities; wherein the cold-rolled steel sheet is produced from a hot-rolled steel sheet having 97% or more in volume percentage of bainite, wherein the cold-rolled steel sheet has an average r-value of 1.2 or more and a metallographic microstructure composed of ferrite and precipitates, and wherein 30% or more in volume percentage of the carbides composed mainly of Fe and C in the precipitate exist inside the ferrite grains.