A new numerical simulation method that can be used to predict microstructure changes in ultrafine-grain generation in super short interval multi-pass rolling (SSMR) process is proposed. The SSMR process has been developed for manufacturing ultrafine-grained hot strips of about 1 μm grain size at ordinary rolling load. A new ferrite nucleation mechanism has been discussed in this process. Because multi-pass rolling and inter-pass and after-pass cooling are performed within a short time in a stable austenite temperature region, deformation strain is accumulated in the austenite. Then dislocation cells are formed inside a severely deformed and unrecrystallized austenite grain, and become the nucleation site of ferrite transformation. In this new simulation method, nucleation inside a deformed austenite grain was formulated in addition to nucleation at the austenite grain boundary.
