To enhance the pitching resistant strength of a gear by using steel which remarkably enhances the resistance to softening by low-temperature tempering at 300 to 350°C and by hardening tooth faces by means of carburization hardening, bright hardening and induction hardening methods.
The steel products regulated to satisfy the relations of the equation 5≤4.3xSi(wt%)+7.3xAl(wt%)+3.1xV(wt%)+1.5xMo(wet%)+1.2xCr(wet%)x(0.45÷C(wt%)) are subjected to carburization treatment so as to be regulated in the carbon concentration on their carburized surface layers to 0.6 to 0.9wt% and are subjected to hardening and tempering treatment at ≤300°C following to the carburization treatment or are once cooled after the carburization treatment and are then subjected to reheating hardening and tempering treatment at ≤300°C so that the hardness of ≥58 in HRC can be assured even by the tempering treatment at 300°C.
HAMASAKA NAOHARU
MORIOKA NORIKO
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