Limitations of Standard Probes for the Measurement of Spray Quenching

Spray quenching is an important technique used to quench parts after induction hardening. It has the advantages of rapid cooling of workpieces, and a repeatable process through the control of spray pattern, quenchant velocity, and pressure. There have been numerous efforts to characterize the heat transfer coefficient as a function of surface temperature in the literature. One method has been to use standard probes used to produce cooling curves for immersion quenchants. However, due to the high surface heat transfer, steep gradients can occur, resulting in thermal lag and an underestimation of the heat transfer coefficient. This improper estimation of heat transfer coefficient can have a significant impact on the prediction of the resultant microstructure, component physical dimensions and residual stress distribution. An examination of these thermal gradients as a function of probe diameter and material was accomplished, to determine the proper probe geometry to measure and calculate the resultant heat transfer coefficient was determined.