| 摘要 |
<p>PURPOSE:To obtain a high strength gear steel excellent in softening property, minimal in quenching distortion, and having superior cold forgeability by forming a structure consisting of ferrite and pearlite under the prescribed working conditions at the time of rolling a billet of a steel having a specific composition and specific ideal critical diameter into a bar steel. CONSTITUTION:A steel having a composition consisting of, by weight, 0.13-0.25% C, <=0.05% Si, 0.3-1.0% Mn, Mn, 0.1-1.0% Cr, 0.2-1.0% Mo, <=0.020% P, 0.005-0.030% S, 0.01-0.10% Nb, <=0.005% Ti, 0.01-0.10% sol.Al, 0.005-0.020% N, <=0.0015% O, and the balance iron with inevitable elements is prepared. Further, a billet of the steel, in which carbon equivalent Ceq represented by equation A is regulated to 0.50-0.75% and ideal critical diameter D1 represented by equation B is regulated to 60-100mm, is heated to 850-950 deg.C and rolled into a bar steel by exerting water cooling between mills and regulating the final finishing temp. to 650-850 deg.C. Successively, this bar steel is cooled slowly at <=1 deg.C/sec cooling rate, by which a structure consisting of ferrite and pearlite can be formed.</p> |
