Deformation-induced ferrite transformation in a low carbon Nb–Ti microalloyed steel

Laboratory thermomechanical processing (TMP) using single pass hot compression experiments on a low carbon Nb–Ti microalloyed steel have been carried out to study the effects of strain and strain rate on deformation-induced ferrite production through strain-induced transformation (SIT) at a temperature just above Ar3. The results show that the occurrence of SIT during deformation at 845 °C causes a dynamic softening behaviour in hot flow curves. With increasing strain from 0.25 to 0.8, higher volume fractions of strain-induced ferrite grains are obtained. The amount of strain rate plays an important role in the occurrence of SIT. Increasing the strain rate from 0.001 to 0.1 s−1 leads to an increase in the amount of minimum strain required for the initiation of SIT. Moreover, deformation to a strain of 0.8 with a strain rate of 0.1 s−1 produces equiaxed and homogeneous ultrafine ferrite grains of about 2 μm.