High-strength cold-rolled steel sheet excellent in bending workability

Abstract

A cold-rolled steel sheet has a chemical composition of C: 0.12% to 0.3%, Si: 0.5% or less, Mn: less than 1.5%, Al: 0.15% or less, N: 0.01% or less, P: 0.02% or less, and S: 0.01% or less, with the remainder including iron and inevitable impurities and has a martensite single-phase structure as its steel microstructure. In a surface region of the steel sheet from the surface to a depth one-tenth the gauge, the number density of n-ary groups of inclusions determined by specific n-th determinations is 120 or less per 100 cmof a rolling plane, where the distance in steel sheet rolling direction between outermost surfaces of two outermost particles of the group of inclusions is 100 μm or more. The steel sheet is a high-strength cold-rolled steel sheet which has a sufficiently minimized rate of bending fracture starting from inclusions and thereby has excellent bending workability.