Refining of heat treatment process parameters on large cup-type SAE4140 alloy

This study used the cup-type forgings of SAE4140 Cr-Mo alloy with a diameter of 420mm, a length of 700mm, and a thickness difference of 10mm at two ends as the object. It adopted the Taguchi method to conduct the optimization of thermal refining for experiment and analysis. The workpiece was compared with the current conditions so that the quality of workpiece after quenching could obtain the optimum parameters for thermal refining of this type of workpiece. Based on the experimental result, after quenching and tempering of the cup-type forging Cr-Mo alloy, the hardness test showed that, the most significant factor was the placement and tempering temperature. When the cup opening faced upward, the hardness difference of the two ends was HRC 2~2.5, otherwise the difference was HRC 4 ~ 5. The verification experiment shows when the hardness of the workpiece after quenching and tempering reached HRC 52 and HRC 36 or above, respectively, these results can be used as the standard for on-site test of heat treatment.