Dynamic softening of ferrite during large strain warm deformation of a plain-carbon steel

The evolution of dynamic ferrite softening in a plain-carbon steel was investigated by torsion tests during warm deformation at 810 °C, in the two-phase (ferrite + austenite) region, and strain rate of 0.1 s−1 with different strains up to 50. The warm flow behaviour and ferrite microstructural parameters, such as grain size, misorientation angle across ferrite/ferrite boundaries, and the fraction of high-angle and low-angle grain/subgrain boundaries were quantified using electron back scatter diffraction. The results show that with increasing strain up to ∼2, the ferrite grain size and fraction of high-angle boundaries rapidly decrease and the fraction of low-angle boundaries increases. However, these parameters remain approximately unchanged with increasing strain from ∼2 to 50. The dynamic softening mechanism observed during large strain ferritic deformation is explained by dynamic recovery and continuous dynamic recrystallization.