Patent ID: 8192565

Claim:
A steel comprising, by mass %, 0.05 to 1.2% of C, 0.03 to 2% of Si, 0.2 to 1.8% of Mn, at most 0.03% and greater than 0% of P, at most 0.03% and greater than 0% of S, 0.1 to 3% of Cr, 0.3 to 0.5% of Al, 0.004 to 0.025% of N, at most 0.003% and greater than 0% of O, at least one of 0.0005 to 0.02% of Ca and 0.0001 to 0.005% of Mg, and 0.002% or more of solute N in the steel, with a remainder being iron and inevitable impurities, wherein the steel satisfies a relationship of expression (1): (0.1 ×[Cr]+[Al])/[O]≧150 (1), wherein [Cr], [Al], and [O] represent a Cr content (mass %), an Al content (mass %), and an O content (mass %), respectively.