| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet for automotive automatic transmission members and its manufacturing method. SOLUTION: The cold rolled steel sheet is obtained by cold rolling, without annealing, a hot rolled steel plate of a slab which has a composition consisting of, by mass, 0.15 to 0.25% C,≤0.25% Si, 0.3 to 0.9% Mn,≤0.03% P,≤0.015% S, 0.01 to 0.08% Al,≤0.008% N, 0.05 to 0.5% Cr, 0.01 to 0.05% Ti, 0.002 to 0.005% B and the balance Fe with inevitable impurities. If necessary, after cold rolling, residual stress is regulated using a leveller in such a way that one side of the steel sheet has compressive stress and the other side has tensile stress. Owing to the incorporation of C, excellent hardenability and resin adhesiveness can be provided. Required hardness (Hv≥230) can be obtained at a relatively low cold rolling rate (≥30%) and, by the decrease in the cold rolling rate, the residual stress of the steel sheet can be reduced and the flatness of a blanked article can be improved. A remarkable flatness improving effect with respect to the large-diameter size and narrow-width size of a bridge part, where flatness can be hardly secured, can be produced. COPYRIGHT: (C)2007,JPO&INPIT
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