Cold-rolled steel sheet and method for manufacturing same

A method for manufacturing a cold-rolled steel sheet, comprising:

• a hot rolling process of directly or once cooling and then heating a cast slab containing, as a chemical composition, by mass %, C:
• more than 0.140% and less than 0.400%, Si:
• 1.00% or less, Mn:
• more than 1.30% and less than 4.00%, P:
• 0.100% or less, S:
• 0.010% or less, Al:
• 0.100% or less, N:
• 0.0100% or less, Ti:
• 0% or more and less than 0.050%, Nb:
• 0% or more and less than 0.050%, V:
• 0% or more and 0.50% or less, Cu:
• 0% or more and 1.00% or less, Ni:
• 0% or more and 1.00% or less, Cr:
• 0% or more and 1.00% or less, Mo:
• 0% or more and 0.50% or less, B:
• 0% or more and 0.0100% or less, Ca:
• 0% or more and 0.0100% or less, Mg:
• 0% or more and 0.0100% or less, REM:
• 0% or more and 0.0500% or less, Bi:
• 0% or more and 0.050% or less, and a remainder:
• Fe and impurities, to 1,100° C. or higher, and performing hot rolling on the heated cast slab to obtain a hot-rolled steel sheet;
• a coiling process of coiling the hot-rolled steel sheet at a temperature of 550° C. or lower;
• a cold rolling process of descaling the hot-rolled steel sheet after the coiling process and then performing cold rolling on the hot-rolled steel sheet to obtain a cold-rolled steel sheet;
• an annealing process of heating the cold-rolled steel sheet after the cold rolling process to a soaking temperature of 820° C. or higher and 880° C. or lower so that an average heating rate from 700° C. to the soaking temperature is slower than 10.0° C./sec, and annealing by soaking the cold-rolled steel sheet at the soaking temperature for 30 to 200 seconds;
• a post-annealing cooling process of subjecting the cold-rolled steel sheet after the annealing process to bending-bending-back deformation one or more times with a bending angle of 90 degrees or more in a temperature range of 800° C. or lower and 700° C. or higher using a roll having a radius of 850 mm or less while applying a tension of 3.0 kN or more, to cooling so that both an average cooling rate from 700° C. to 600° C. and an average cooling rate from 450° C. to 350° C. are 5.0° C./sec or faster, to bending-bending-back deformation one or more times with a bending angle of 90 degrees or more in a temperature range of 350° C. or lower and 50° C. or higher using a roll having a radius of 850 mm or less while applying a tension of 3.0 kN or more, and then to cooling to a cooling stop temperature of 50° C. or higher and 250° C. or lower;
• and
• a tempering process of tempering the cold-rolled steel sheet after the post-annealing cooling process at a temperature of 200° C. or higher and 350° C. or lower for 1 second or longer.