Steel material for mechanical structure, extremely suitable for lamination, quenching-crack resistance and torsional property and motor shaft.

摘要

A product of machine structural steel having a formability of the as spun, quenching-crack resistance, and torsional properties superior, comprising, on the basis of mass percent: C: 0.35% to 0 ,fifty%; Si: 0.05% to 0.15%; Mn: 0.20% to 1.1%; P: 0.02% or less; S: 0.005% to 0.035%; Cr: more than 0.1% to 0.2%, Mo: 0.05 to 0.5%; Ti: 0.01% to 0.05%; Al: 0.01% to 0.05%; N: 0.01% or less; B: 0.0005% to 0.0050%; Cu: 0.06% to 0.25%; Ni: 0.05% to 0.2%, optionally V: 0.01% to 0.30%, and optionally Nb: 0.005% to 0.05%, wherein an LD value represented by the equation is satisfied following (1) of 120 or less, and including the rest of the composition Fe and unavoidable impurities. (See formula) wherein C, Mn, P, S, Si, Cr, Ni, Mo, and Cu in the equation each indicate the content (mass percent) of the respective elements.