| 摘要 |
PROBLEM TO BE SOLVED: To produce steel excellent in cold workability after spheroidizing annealing and induction hardenability having graded grains without grain coarsening even if induction hardening is executed under the conditions of high temp. and long time, to provide parts for machine structure using it as a base material and to provide a method for producing the same. SOLUTION: The parts for machine structure contain (1) 0.40 to 0.6% C, >1.0 to 0.30% Si, 0.10 to 0.60% Mn, 0.0005 to 0.005% B, 0.005 to 0.05% Nb, 0.005 to 0.05% Ti, >0.050 to 0.10% Al, and the balance Fe with impurities, and, in the impurities, <=0.015% P, <=0.015% S, <=0.10% Cu, <=0.10% Ni, <=0.15% Cr, <=0.10% Mo, <=0.005% N and <=0.005% O are controlled. (2) The base material has the chemical compsn. of (1) and provided with a quench-hardening layer of spheroidized carbides and graded grains of >=5 JIS grain size number. (3) The steel is heated to >=1200 deg.C, and thereafter subjected to hot working and then subjected to spheroidizing annealing and cold working to be formed into a prescribed shape, and, after that, induction hardening is executed finally to produce the parts.
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