HEAT TREATMENT RESPONSE OF STEEL FATIGUE SAMPLE DURING VACUUM CARBURIZATION AND HIGH PRESSURE GAS QUENCHING PROCESS

A hollow R.R. Moore rotation fatigue sample made of AISI 9310 is processed using vacuum carburization and high pressure gas quenching. The vacuum carburization schedule is designed to through carburize the thin wall section of the fatigue sample to 0.7% wt.% carbon, followed by 10 bar nitrogen quench. Some samples showed significant bow distortion after quench hardening, and further investigations indicated that the unbalanced wall thickness from machining is the main cause of the bow distortion. In this paper, DANTE, a commercial heat treatment software is used to study the cooling, phase transformation, and stress evolution during quenching. The effect of unbalance wall thickness on distortion is also investigated. Residual stress state in the quench hardened sample is critical to the fatigue performance during rotational bending fatigue tests. In this study, the unbalanced geometry has insignificant effect on the residual stresses after quench hardening. However, the unbalanced geometry will affect the applied stress significantly during a rotation fatigue test.