Distortion Minimization During Gas Quenching Process

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During gas quenching, independent process parameters include the preheat temperature of the component and the temperature of the circulated gas. One of the most important dependent process parameters is the heat transfer coefficient between the component and the circulated gas. The heat transfer coefficient has significant influence on the quenching results, such as distortion, residual stresses, and hardness distribution. Large distortions after quenching will increase the cost due to the post-quenching processes, such as the grinding and hot rectification. The objective in this research is to minimize the distortion caused by quenching. In this paper, the surface of a component is divided into several regions, and different values of the heat transfer coefficient are imposed on each region. Constraints on the residual stresses and surface hardness distribution are imposed to improve the service properties. The heat transfer coefficients are ideal design variables to optimize the gas quenching process. The commercial finite element software, DEFORM-HT, is used to predict the material response during the quenching process. The response surface method is used to obtain the analytical models of the objective function and constraints in terms of the design variables. Once the closed-form response surface models are obtained, a commercially available design optimization tool, design optimization tool (DOT), is used to search for the optimum design point. This paper summarizes the methodology used to optimize the gas quenching process together with an application of a steel disk example.