Strain Rate Sensitivity of 31Mn-3Al-3Si TWIP Steel with Partially Recrystallized Fine Grained Structure

Abstract

Strain rate sensitivity of the strength of TWIP (Twinning Induced Plasticity) steel with the mixture of recrystallized fine grains and rolling-deformation microstructures was studied. The 31mass%Mn-3%Al-3%Si TWIP steel sheet was severely cold-rolled to a reduction of 92% and subsequently annealed at various temperatures ranging from 600oC to 700oC in order to obtain the partial recrystallized microstructure with various fraction of recrystallized microstructure. The 600oC annealed specimen keeps similar morphologies as observed in the as-rolled structure consisting of both the fine lamellar dislocation cell structure and the twin/matrix lamellar structure; whereas, in the specimen annealed at 625oC or 675oC , the partially recrystallized fine grains (d~1µm) with a few dislocations evolve. The volume fraction of recrystallized fine grains increases with increasing of the annealing temperature while the mean diameter of the recrystallized grains is not changed largely. The tensile deformation behaviors were measured at various strain rates ranging from 10-3sec-1 to 102sec-1. The strength and elongation become smaller and larger, respectively, with increasing the fraction of the recrystallized microstructure. The activation volume of dislocations becomes larger with increasing the fraction of recrystallized microstructure.