Evolution of cold-rolling work roll materials based on the elucidation of the cracking mechanism of thermal shock

Thermal shocks during cold rolling significantly reduce the service lives of work rolls. This study clarified the metallurgical changes that govern thermal crack initiation under rapid heating and cooling. Thermal shock studies were conducted using 1.0 wt% C steel with tempered martensite to replicate the physical phenomena and examine the associated phase transformations and stress evolution. Additionally, thermomechanical simulations using a fast Fourier transform were performed, enabling the stress contributions of different metallurgical phenomena to be decoupled and incorporating phase transformations to predict the stress evolution during thermal shock. The surface‑tempered martensite underwent reverse transformation to austenite during heating due to frictional heat and then transformed into fresh martensite during cooling. Residual stress analysis indicated that the maximum tensile stress occurred close to the interface between the tempered and fresh martensite, and numerical predictions of the stress evolution during martensitic transformation were consistent with the experimental measurements, validating the model. The dominant tensile stress was due to volume expansion during austenite‑to‑martensite transformation rather than tempering shrinkage, explaining thermal crack initiation. These findings provide insights into the formation of thermal cracks and offer guidelines for use in improving the durabilities of work rolls in cold‑rolling operations.