| 摘要 |
This steel has a prescribed component composition, and moreover has a steel structure that includes, in area percentage, 15-55% of polygonal ferrite and 15-30% of martensite and, in volume percentage, 12% or more of residual austenite, the average crystal grain diameters of the polygonal ferrite, martensite, and residual austenite, respectively, being 4 μm or less, 2 μm or less, and 2 μm or less, and the average aspect ratios of the crystal grains of the polygonal ferrite, martensite, and residual austenite, respectively, being 2.0 or less. Further, the value obtained by dividing the amount of Mn (in mass%) in the residual austenite by the amount of Mn (in mass%) in the polygonal ferrite is 2.0 or greater. |
