Sources of Distortion Study during Quench Hardening using Computer Modeling

Quench hardening is a transient thermal stress process with phase transformations. It is inevitable for the component to go through plastic deformation filed due to phase transformations, which leads to distortion in the hardened part. Understanding the sources of distortion is necessary in designing the heat treat process and component configuration with more controllable and consistent distortion. It is worth to mention that a consistent distortion can be compensated by adjusting the part dimension prior to hardening. The possible sources of distortion include residual stresses prior to hardening, heating rate, furnace temperature, soaking time, cooling rate, cooling uniformity, and possible tooling constraints, etc. The significance of these effects varies according to the part geometry and heat treatment process. Characterization of material properties and computer modeling make it possible to understand the material and component responses during quench hardening, which is necessary for process improvement and part configuration optimization. In this paper, the hardening process of a spur gear with tapered thin wall made of AISI 9310 is analyzed, and the effects of several critical process variables on distortion is investigated. Suggestions on process improvements for reduced and consistent distortion are given based on the modeling results.