Investigating quench crack susceptibility in disc springs: a microstructural analysis of martensitic evolution and its implications

The current investigation delves into the influence of varying cooling rates, encompassing water, rapid quenching oil, and air, on the quench crack susceptibility (QCS) of disc springs. The assessment reveals that the average martensite lath width under water, oil, and air cooling conditions measures 0.61 μm, 0.66 μm, and 1.12 μm, respectively. Correspondingly, the residual austenite content amounts to 6.9%, 8.7%, and 12.3%. Notably, cracks are observed at the disc spring's perimeter during water cooling, whereas oil and air cooling effectively preclude such occurrences. Simulations demonstrate that residual stresses of up to 1011 MPa can arise at the disc spring cross-section corners under water cooling, significantly surpassing the stresses encountered under oil and air cooling, at 440 MPa and 73 MPa respectively. As the microstructure evolves, these residual stresses critically impact the grain boundaries of the original austenite, compromising the buffering capabilities of the martensite phase and residual austenite, thereby enhancing susceptibility to quench cracking.