Study on the mechanical behavior of twinning-induced plasticity steel processed by warm forging and annealing

Abstract

The microstructures and mechanical properties of a 30Mn–3Al–3Si twinning-induced plasticity (TWIP) steel in the warmly forged and annealed states were investigated in the present study. It is shown that the as-forged and low-temperature annealed steels have similar grain morphologies and defect configurations, i.e., predominantly deformed grains together with recrystallized fine equiaxed grains as well as highly dense and complex dislocations. However, the high-temperature annealed steel showed completely different microstructures characterized by fully recrystallized grains and very few dislocations. The initially high density of dislocations in the forged and low-temperature annealed steels greatly promoted the multiplication of dislocations in the subsequently tensile deformation, leading to not only pronouncedly enhanced tensile strength but an apparent yield-point phenomenon. Compared with as-forged and low-temperature annealed steels, the high-temperature annealed steel exhibited relatively fewer increments of dislocations after tensile deformation but much more twins. These changes in the microstructures were responsible for relatively low strength and high plasticity of the steel.