| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a cold-rolled steel sheet superior in deep drawability, with high productivity and with an industrially easy process.SOLUTION: A steel ingot or a steel slab has a chemical composition including, by mass%, less than 0.010% C, 1.5% or less Si, 2.0% or less Mn, 0.10% or less P, 0.010% or less S, 0.0005-0.10% Al, 0.0060% or less N, 0.001-0.10% Ti, 0.001-0.10% Nb, and satisfying the relation: (C/12+N/14+S/32)/(Ti/48+Nb/93)≤1.4. The manufacturing method includes: subjecting the steel ingot or the steel slab to a multi-pass hot rolling process in which the total rolling reduction of two passes of each one and two preceding pass to the last pass is controlled to less than 45%, the rolling reduction of the last pass is controlled to more than 25%, and the last pass is finished at (Arpoint -30°C) or higher and 880°C or higher; cooling the plate to 820°C at an average cooling rate of 400°C/second or more within a period of 0.5 seconds after the completion of the hot rolling process; winding the plate in a temperature range of 400°C or higher but lower than 700°C to produce a hot-rolled steel plate; pickling the hot-rolled steel plate; cold-rolling the resultant plate with a rolling reduction of 60-95%; and annealing the obtained cold-rolled steel sheet in a temperature range of 700-910°C. |
