Method of manufacturing a cold-rolled steel sheet and plated steel and cold-rolled steel sheet having excellent strength increased ability of heat treatment after molding

摘要

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet easy to be processed before a heat treatment, because of its low strength and capable of effectively increasing the deformation strength and rigidity of members or parts thereof by the heat treatment at a relatively low temperature in a short time after the forming.;SOLUTION: The steel sheet has a composition containing, by mass, ≤0.15% C, 0.005 to 1.0% Si, 0.01 to 3.0% Mn, 0.005 to 0.02% Al, 0.006 to 0.020% N and 0.002 to 0.10% P also in a range satisfying N(%)/Al(%)≥0.3, and the balance Fe with inevitable impurities. In the steel, the product of the precipitated Mn% and the precipitated Si% is ≤0.00010, and solid solution N is contained in ≥0.0015%. The steel sheet further has a steel structure consisting of ferrite or essentially consisting of ferrite.;COPYRIGHT: (C)2002,JPO