Critical Heat Transfer Coefficient Test Method for Gas Quenching Steel Hardenability

Gas quench, with advantages such as reducing distortion and residual stress, is developing rapidly with the intent to replace liquid quench. Medium and high hardenability steels are needed for gas quench, since the quenching power is lower compared to liquid quench. The traditional Jominy end quench test and Grossmann test, designed for liquid quench steel hardenability, didn’t properly determine the hardenability of high alloyed steels. In order to determine gas quench steel hardenability, a new test is required. In this paper, a critical heat transfer coefficient (HTC) test based on the Grossmann test is proposed. Critical HTC, a concept like critical diameter, was successfully proved to describe the gas quench hardenability of steel. The critical HTC of AISI 4140 steel is 430 W/m^2C and the critical HTC of AISI 52100 steel is 820 W/m^2C, which reveals that the gas quench hardenability of 4140 is better than 52100. In the paper, the critical HTC test requirements are presented and discussed.