Residual Stress Distribution, Distortion, and Crack Initiation in Conventional and Intensive Quench Practices

This study evaluates the effect of two different quench practices on distortion, sensitivity to quench cracking, development and distribution of residual stress, microstructural uniformity, and hardenability of standardized test castings. Navy C-rings made of AISI 4340 were quenched in this experiment. Some rings were quenched in a conventional draft tube immersion quench bath, and others were quenched in an intensive quench spray system to compare with the results from the conventional immersion quench bath. The rings were measured with a coordinate measuring machine, for distortion and flatness, before and after quenching. Hardness profiles of the quenched rings showed through hardness of 57.0-59.0 HRC, and the microstructures were largely martensitic. DANTE modeling software was used to predict the quenched properties of the rings, simulating microstructural transformation and residual stresses for each quench practice. XRD was used to measure surface residual stress distribution of the quenched rings, and results were compared to the predicted values by the modeling software. The surface residual stress was tensile for the conventional immersion quench and compressive for the intensive spray quench. Crack initiation correlated to areas of large tensile stress concentration and microstructural heterogeneity.