COLD ROLLED STEEL SHEET HAVING EXCELLENT FATIGUE PROPERTY OR THE LIKE, AND PRODUCTION METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet which is useful as a material for automobile automatic transmission or the like, and to provide a production method therefor.;SOLUTION: The cold rolled steel sheet is produced by subjecting a hot rolled steel sheet having a composition comprising, by weight, 0.17 to 0.25% C, ≤0.05% Si, 0.5 to 0.9% Mn, ≤0.03% P, ≤0.015% S, 0.02 to 0.08% Al, ≤0.008% N, 0.02 to 0.07% Ti and 0.003 to 0.006% B, and the balance substantially Fe, subjected to hot rolling and coiling at 480 to 560°C, and having a pearlite+cementite fraction of ≥30% and a ferrite grain size of 5 to 15 μm to cold rolling at a draft of ≥50% without performing annealing treatment. As the steel structure control effect in the hot rolled sheet by the prescription of the C and Si contents and the composite addition of Ti and B, the cold rolled sheet provided with wear resistance equal to that of the conventional material (S35C cold rolled sheet), press blanking properties and improved fatigue properties can be obtained in the process of hot rolling-pickling-cold rolling where annealing before the cold rolling is obviated. The cold rolled sheet can be used as being a hard drawn material with refining heat treatment obviated after blanking.;COPYRIGHT: (C)2004,JPO