| 主权项 |
1. A steel sheet comprising, by mass %,
C: 0.04% or more and 0.15% or less, Si: 0.3% or more and 0.7% or less, Mn: 1.0% or more and 3.0% or less, Al: 0.005% or more and 0.10% or less, P: limited to 0.03% or less, S: limited to 0.01% or less, N: limited to 0.01% or less, and a remainder consisting of Fe and unavoidable impurities, wherein the steel sheet has a steel structure obtained by performing a soaking for a soaking time of 15 seconds or longer and 35 seconds or shorter at a dual phase region temperature of Ac1 temperature or higher and lower than Ac3 temperature, next, performing a primary cooling to a temperature range of 250° C. or higher and 380° C. or less at a cooling rate of 0.5° C./s or more and 30° C./s or less within 3 seconds, and performing a retention in a temperature range of 260° C. or higher and 370° C. or lower for 180 seconds or longer and 540 seconds or shorter after the primary cooling, a yield ratio is 65% or less and tensile strength is 590 MPa or more, and the Ac1 temperature is a temperature expressed by a following Expression (1) in units of ° C., and the Ac3 temperature is a temperature expressed by a following Expression (2) in units of ° C.,
Ac1=732−26.6×[C]+17.6×[Si]−11.6×[Mn] (1),Ac3=924+56.1×[Si]−19.7×[Mn]−436.5×[C] (2), here, [C], [Si], and [Mn] represent a C content, an Si content, and an Mn content respectively, and a unit thereof is mass %. |
