COLD-ROLLED STEEL SHEET AND PROCESS FOR PRODUCTION THEREOF

摘要

A cold-rolled steel sheet which has high hardness and exhibits excellent edge properties in blanking and excellent flatness even at enhanced temperatures and which is suitable for use in a clutch plate or ring, a clutch disc, or the like. A cold-rolled steel sheet which has both a composition containing by mass C: 0.01 to 0.15%, Si: 0.03% or less, Mn: 0.10 to 0.70%, P: 0.025% or less, S: 0.025% or less, Al: 0.01 to 0.05% and N: 0.008% or less and satisfying the relationship: (C%) + 0.15×(Mn%) + 0.85×(P%) > 0.21 with the balance consisting of Fe and unavoidable impurities, and a partially recrystallized structure having a mean ferrite grain diameter of 2 to 10µm and a degree of unrecrystallization of 25 to 90% and which exhibits Rockwell hardness (HRB) of 83 or above by virtue of the composition and the structure.