Failure analysis and prevention of quench crack of eccentric holed disk by experimental study and computer simulation

Quench crack was visually detected then verified by visible-dye penetrant inspection on eccentric holed disk quenched into still-water quenchant. Metallography and fractography were carried out by optical and scanning electron microscope indicating the structure of band martensite and intergranular cleavage fracture. Although the quench crack criterion is still underway to be established by many researchers considering metallurgical characteristics and residuals stress formation, this study is solely based on predicting the susceptibility to quench-cracking by comparing the time change of tension residual stress to yield strength. The radial crack site observed on both sides of the disk was used as a nodal tracking. To study the crack propensity, simulation was also used to predict the formation of residual stress in the stir-water quenched and still-polymer quenched disk. The employed zone-based heat transfer coefficient (HTC) was derived from iterative modification method using LUMPPROB and DEFORM-HT package. Predicted cooling curve and cooling rate curve agree well with the measured ones. Still-water quenching produces residual stress surpassing the yield strength and less uniformity of cooling compared with the results from both still-polymer and stir-water quenching.