| 摘要 |
PROBLEM TO BE SOLVED: To determine the chemical composition of a steel stock for gear, minimal in strain. SOLUTION: A steel stock, having a composition which consists of, by weight, 0.10-0.35% C, 0.50-2.5% Si, 0.20-2.50% Mn, 0.01-0.70% Mo, and the balance iron with inevitable impurities and in which Ac3 , represented by equation, Ac3 =920-203√C+44.7Si+31.5Mo-30Mn+40Al+13.1W+104V+40Ti, is regulated to 850-960 deg.C and also DI, represented by equation, DI=7.95√C(1+0.70Si)(1+3.3 Mn)(1+3.0Mo)(1+5.0V), is regulated to 30-250mm, is used. This steel stock is carburized at 850-1,000 deg.C, hardened at 800-950 deg.C, and tempered, by which the noncarburized zone of the steel stock is provided with dual-phase structure consisting of martensite containing 10-70area% ferrite. Further, one or more kinds selected from the group consisting of 0.01-0.70% W and 0.01-1.0% V and/or the group consisting of 0.005-2.0% Al, 0.005-1.0% Ti, 0.005-0.50% Nb, and 0.005-0.50% Zr are added. It is desirable to regulate DI to 30-150mm.
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