Modeling Application to Reduce Distortion of a Carburized and Quenched Steel Gear

During the quench hardening process for steel components, thermal gradients in the part, as well as phase transformation timing, contribute to the final part distortion and residual stresses. Most transmission gears have unbalanced geometry, which will cause temperature differences from one to another region, aside from the temperature gradient of surface to core during quenching. The unbalanced temperature in the part will lead to different phase transformation timing and final phase composition in the quenched part. The material volume expands with different ratios when austenite transforms at different temperatures to different phases. By varying quenching processes, such as quench rate, immersion orientation and speed, the distortions of the final part are expected to be different. In this paper, the commercial heat treatment software, DANTE is used to model the quenching process of a transmission gear. This transmission gear is gas carburized using a boost/diffuse process. The predicted case depth and distortion are compared against the experiments. The causes of distortion and residual stresses are discussed in detail. The effect of immersion orientation on distortion is studied, and an improved quenching process is suggested.