| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a cold-rolled steel sheet excellent in shape-freezing property and to provide a production method thereof. <P>SOLUTION: The cold-rolled steel sheet excellent in shape-freezing property is produced from a steel raw material having a composition containing, by mass%, 0.0010-0.0030% C, 0.05% or less Si, 0.1-0.5% Mn, 0.021-0.060% Ti, and 0.0005-0.0050% B, and B and C satisfying a B/C of 0.5 or more. The cold-rolled steel sheet is manufactured by subjecting a hot-rolling step, in which the steel raw material is finish-rolled at a finish rolling temperature of 870-950°C and winding is performed at a winding temperature of 450-630°C; a cold-rolling step, in which a cold-rolling reduction ratio is 90% or less; and thereafter an annealing step, in which heating to a soaking temperature in the range of 700-850°C is performed at an average heating rate of 1-30°C/s over a temperature range of 600°C or more, this temperature is kept for 30-200 sec, and cooling is performed at a cooling rate of, on the average, 3°C/s or more over a temperature range up to 600°C. Thus-obtained steel sheet has a structure composed of mainly ferrite with an average grain diameter of 10-30 μm, and has a proportional limit of 100 MPa or less. <P>COPYRIGHT: (C)2013,JPO&INPIT |
