Understanding Heat Treat Distortion

Preliminary results have been obtained to determine the influence of manufacturing operations prior to heat treat on gear distortion. Gears for aircraft engines and other applications are carburized to produce a hardened case to a specified thickness. The carburized case has different properties than the parent material and behaves differently during heating and quenching. The different properties are primarily responsible for gear distortion but are typically accounted for in the post heat treat operations. Unpredicted distortion, however, still occurs and accounts for a significant amount of scrap and rework. Data on material processing and properties of 9310 gears correlated to distortion are discussed. Preliminary modeling results of carburizing and quenching processes are provided in conjunction with this data. Additional areas where material property and other process data are needed are discussed in this paper.