A discussion of the formation of ultra-fine grains in low-carbon steels based on FE analysis

A FE analysis was performed to study the formation of ultra-fine grains in a new hot rolling process. It was verified in this paper that ultra-fine grains were caused by high level undercooling and high level strain. The level of undercooling and the level of strain of the strip during this new rolling process were studied quantitatively with FE analysis. It was found that the critical undercooling to achieve ultra-fine grain was about 190 K. Compression experiments were done with a schedule involving rapid cooling before deformation to achieve high level undercooling. Ultra-fine grains were achieved in compressed experiments and the critical undercooling to obtain ultra-fine grains was about 200 K, similar to that calculated by FE analysis.