Gas quenching process optimization to minimize distortion of a thin-wall ring gear by simulation∗

Abstract

Abstract Of the differences between gas quenching and immersion quenching processes, the major difference is the presence of boiling during the early stages of quenching in oil or water. The formation of a vapor phase has a dramatic effect on both the overall and local rates of heat removal from the parts being quenched, and on part distortion. With the absence of a quenchant phase change, gas quenching is touted to result in uniform heat extraction, thus lessening part distortion. Gas quenching is not without inherent problems. Nonuniform gas flow around a part contributes to distortion, and nonuniform cooling at different locations contributes to the variance of distortion. This paper discusses difficulties associated with gas quenching a thin walled ring gear that is prone to distortion. Heat treat process simulation was used to model the low pressure carburization and high pressure gas quenching of a carburized 5130 steel ring gear. Process variables investigated include fan speed and cooling durations of different quenching stages. The intent is to reduce distortion by controlling the overall gas velocity through adjustment of the fan speed, whereby the local cooling rates can be controlled to better accommodate the dimensional change associated with steel phase transformations during quenching.