Recrystallisation driving forces against pinning forces in hot rolling of Ti-microalloyed steels

In this work the pinning forces exerted by TiN particles in the austenitic phase in four Ti-microalloyed steels have been determined and compared with the driving forces for recrystallisation determined in each rolling pass. The thermomechanical simulation has been carried out in the laboratory by means of torsion tests in a sequence of 20 passes with the final passes in a mixed austenitic/ferritic phase. The driving forces were found to be approximately two orders of magnitude higher than the pinning forces, which explains why the austenite in these steels barely experiences hardening during rolling and why the accumulated stress prior to the austenite → ferrite transformation is insufficient to refine the ferritic grain.