| 摘要 |
The present invention provides a steel sheet which has a chemical composition that comprises, in mass%, 0.18%-0.35% of C, 1.0%-3.0% of Mn, 0.01%-1.0% of Si, 0.001%-0.02% of P, 0.0005%-0.01% of S, 0.001%-0.01% of N, 0.01%-1.0% of Al, 0.005%-0.2% of Ti, 0.0002%-0.005% of B, 0.002%-2.0% of Cr and a remainder made up by iron and unavoidable impurities, a ferrite fraction of 50% by volume or more, an un-recrystallized ferrite fraction of 30% by volume or less, and a value of the ratio of the concentration (Cr?) of Cr that is dissolved in a solid form in an iron-containing carbide to the concentration (CrM) of Cr that is dissolved in a solid form in a matrix (i.e., Cr?/CrM) of 2 or less or a value of the ratio of the concentration (Mn?) of Mn that is dissolved in a solid form in the iron-containing carbide to the concentration (MnM) of Mn that is dissolved in a solid form in the matrix (i.e., Mn?/MnM) of 10 or less. |
