Steel material

A steel material having a chemical composition of, by mass%,

• C:
• greater than 0.05% to 0.2%,
• Mn:
• 1% to 3%,
• Si:
• greater than 0.5% to 1.8%,
• Al:
• 0.01% to 0.5%,
• N:
• 0.001% to 0.015%,
• a sum of V and Ti:
• greater than 0.1% to 0.25%,
• Ti:
• 0.001% or more,
• V:
• 0.1% or more,
• Cr:
• 0% to 0.25%,
• Mo:
• 0% to 0.35%, and
• a balance:
• Fe and impurities, the steel material comprising
• a steel structure being a multi-phase structure having a main phase made of ferrite of 50area% or more, and a second phase containing one or two or more selected from a group consisting of bainite, martensite and austenite, wherein:
• an average nanohardness of the second phase is less than 6.0 GPa;
• and
• when a boundary where a misorientation of crystals becomes 2° or more is defined as a grain boundary, and a region surrounded with the grain boundary is defined as a crystal grain, an average grain diameter of all crystal grains in the main phase and the second phase is 3 μm or less, and a proportion of a length of small-angle grain boundaries where the misorientation is 2° to less than 15° in a length of all grain boundaries is 15% or more;
• an average grain diameter of VC and TiC is 10 nm or more;
• and
• an average intergranular distance of VC and TiC is 2 μm or less.