HIGH-CARBON COLD-ROLLED STEEL SHEET AND PRODUCTION METHOD THEREFOR, AND MECHANICAL PARTS MADE OF HIGH-CARBON STEEL

摘要

Provided is a high-carbon cold-rolled steel sheet that can have good impact characteristics and hardness characteristics, and excellent abrasion resistance, after a quenching (hardening) treatment and a low-temperature tempering treatment (hardening and tempering treatment) performed after a quick solution treatment, that has a small reduction in secondary workability before the hardening and tempering treatment, and that has a thickness of less than 1.0 mm.　This high-carbon cold-rolled steel sheet has a steel sheet chemical composition containing, in mass%, 0.85-1.10% of C, less than 0.60% of Mn, 0.10-0.35% of Si, 0.030% or less of P, 0.030% or less of S, less than 0.60% of Cr, where Mn + Cr is less than 1.0%, and further contains 0.005-0.020 mass% of Nb, the balance being Fe and incidental impurities. As a result, the reduction in secondary workability before hardening and tempering is low compared to conventional steel materials. In addition, by forming a steel sheet structure in which carbides have an average particle size of 0.2-0.7 (μm) and a spheroidization rate of 90% or more, a quick 3-15 minute hardening and tempering treatment can allow production of mechanical parts having excellent wear resistance, sufficient hardness characteristics in the range of 600-750 HV, and excellent impact characteristics, i.e., an impact value of 9 J/cm2 or more.