Ring Gear Microstructure and Heat Treat Response

Abstract:

Ring gear distortion during atmosphere gas carburizing often results in non-uniform heat treat (HT) growth, taper and circularity error and may cause assembly issues, significant rework and scrap to gear manufacturer. Common industrial approach to this problem has focused on optimizing post-HT controls, such as quench apparatus, quench severity and hard grinding. However, impact of the initial forging conditions on HT response has not been fully understood.

In this study, ring gears with different initial microstructures and their HT response were studied in conjunction with statistical data analysis collected over 2-year period of time. It was observed that HT growth and circularity error strongly correlate to the initial microstructure and anisotropy within ring gear forging. This paper discusses several case studies with metallurgical data analysis and provides some recommendations on how to improve HT response uniformity.