Comparison of Austempering and Quench-and-Tempering Processes for Carburized Automotive Steels

Austempering was examined as a replacement for the current quench-and-tempering process as a method of heat treating carburized low alloy steel automotive components. Three carburizing grade steels, SAE 8620, 4320, and 8822, were carburized and heat treated by both processes. Twelve austempering and three quench-and-tempering parameters were used. The effect of heat treatment on the case and core microstructures was examined. Distortion was characterized using Navy C-ring samples, which were measured before and after the carburizing and heat treatment process. X-ray diffraction was used to measure residual stress and retained austenite. Charpy impact and Rockwell C hardness testing were performed. Austempering produced improved distortion and residual stress characteristics over quench-and-tempering, while maintaining similar or improved mechanical properties. Full data sets for distortion and mechanical properties were developed. Wear and fatigue testing are identified as necessary next steps to fully examine the viability replacing the quench-and-tempering process with austempering