Simulation of the Kinetics of Microstructure Evolution during Destabilization and Tempering of a High-Chromium White Cast Iron

This study investigates the kinetics of microstructure development during the solidification and heat treatment processes of a white iron with 19 wt.% Cr. For this purpose, the as-cast microstructure with large eutectic carbides in austenite quantified by Scheil–Gulliver simulation and experimental studies was used as input for the precipitation kinetics simulations of destabilization and tempering heat treatments. Simulations showed that during the heating stage of destabilization, M₇C₃ and M₂₃C₆ secondary carbides nucleated and grew together. With increased temperature, it was observed that M₂₃C₆ dissolved completely and M₇C₃ reached a self-similar size distribution. During isothermal holding, secondary M₇C₃ carbides coarsened. Further, carbide precipitation in austenite was observed at the first 3 min of air quenching, and the total carbide volume fraction was found to increase by 26.4% at the end of destabilization. Subsequent tempering of the alloy at 450 °C led to precipitation of M₇C₃ and M₂₃C₆ tempered carbides in martensite and increased the total carbide volume fraction further by 5.3%. Similar to destabilization, it was observed that nucleation of these carbides took place during the heating stage of tempering. Although it requires further validation on a range of commercial high Cr white cast iron compositions and developments in regards to industrial heat treatment practice, agreement with the validation studies carried out in this work suggests that the presented modeling approach is useful for designing white cast iron alloys for better performance by optimizing the microstructure through heat treatment processing.