FEM prediction of retained austenite evolution in cold work die steel during deep cryogenic treatment

A multi-physical field coupling numerical model is built to reproduce the deep cryogenic treatment (DCT) of a cold work die steel Cr8Mo2SiV (SDC99) Navy C-ring specimen immersed in liquid nitrogen and to investigate the retained austenite evolution. In addition, the predicted results are validated via X-ray diffraction (XRD) analysis. The results indicate that, after QT, a large amount of unstable retained austenite (about 15.5%) remains in specimen, especially in the edge and corner of specimen. Subjected to DCT, the unstable retained austenite will continue to transform to martensite until its volume fraction is reduced to 2.3%. However, this austenite transformation is still incomplete, which principally congregates at the gap region of specimen. The predicted results agree well with the experimental data obtained from the XRD analysis.