| 摘要 |
A method of case hardening surfaces of steel parts insures the presence of a relatively high percentage of untempered martensite within a case hardened depth of at least ten thousandths of an inch. The untempered martensite provides for a Rockwell C surface hardness in the range of 59 to 68, and promotes greater resistance to abrasion and deformation. The method also creates compressive stresses in the surface case hardened depth, and thus measurably enhances the fatigue life of the latter surface as a contact bearing member. The method includes the completion of all conventional metal removal operations on the part including finish machining steps prior to heat treatment thereof. In one preferred form, the method includes the steps of (1) completing all machining operations on the part, (2) carburizing the part to achieve a high surface carbon concentration, (3) direct quenching the part in oil by means resulting in retension of 10 to 30 percent austenite in the case hardened depth, (4) time tempering the part and (5) work hardening the part to transform a substantial portion of the retained austenite into untempered martensite, resulting in a case depth having a composition including at least 5 to 20 percent untempered martensite. |
