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

摘要

During quench hardening processes for steel components, both the thermal gradient and phase transformations in the part contribute to distortion and residual stresses in the final part. Most transmission gears have unbalanced geometry, which will cause a temperature difference from one region to another during quenching, aside from the temperature gradient from surface to core. The unbalanced temperature distribution 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 to different phases at different temperatures. By modifying a quenching process, such as quenchant type, agitation, immersion direction 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 by using a boost/diffuse process, followed by an immersion oil quench process. The predicted carbon distribution and distortion are compared against the experimental measurements. The correlations between temperature, carbon distribution, phase transformation, and stress changes are described using the modeling results. The causes of distortion and residual stresses are discussed.