Influence of deformation temperature on the ferrite grain refinement in a low carbon Nb–Ti microalloyed steel

Grain refinement is one of the effective methods to develop new generation low carbon microalloyed steels possessing excellent combination of mechanical properties. In the present work, the microstructural evolution and ferrite grain refinement at various deformation temperatures were investigated using single pass isothermal hot compression experiments for a low carbon Nb–Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the stress–strain responses. The results show that there is a close relation between the microstructural evolution and true stress–true strain responses during the deformation. Microstructural observation indicates that very fine ferrite grains of about 1.8–3 μm are obtained by deformation at 830–845 °C, about Ar3 ± 10 °C. The obtained stress–strain curves suggest the occurrence of strain-induced dynamic transformation (SIDT) of γ to α at this deformation temperature range.