Strain rate dependence of ferrite dynamic restoration mechanism in a duplex low-density steel

The ferrite major dynamic softening mechanisms, particularly in duplex microstructures, have long been a matter of debate among steel scientists. It has been shown in the present work that a marked increase in the strain rate at a high temperature leads to a transition in the ferrite softening mechanism in low density steels. In contrast to the current widespread view, ferrite was found to soften through continuous dynamic recrystallization at a low strain rate and via discontinuous dynamic recrystallization at a high strain rate. The latter mechanism is largely associated with the interphase mantle regions, rather than the scarce original ferrite-ferrite boundaries. In these regions, the new grains were observed to develop through the growth of highly-misoriented subgrains.