Effect of annealing treatment on the microstructure and mechanical properties of Fe-18Mn-0.8C-0.2 V TWIP steel

Abstract

The microstructure and mechanical properties of TWIP steels under different annealing treatments were investigated by static tensile tests, OM, TEM, and EBSD. Results show that the TWIP steel was dominated by full austenitic grains before and after tensile deformation. The TWIP steel exhibited optimal mechanical performance under the annealing treatment at 1000 °C, with the highest initial strain hardening rate (dσ/dε). The grain size increased with the increasing annealing temperature, and the relationship between strain hardening and true strain turns into three stages from two stages. The strain hardening index (n) has the same transition trend under different annealing temperatures when ε < 0.07. With the increase of true strain, the n reached a maximum value of 0.53, 0.62, 0.70 at the annealing temperatures of 800 °C, 900 °C, 1000 °C, respectively. With the increase of the annealing temperature, the elements of V or Ti compounds exhibited a decrease in content but an increase in size. The fracture of the TWIP steel exhibited typical equiaxed dimples. Deformation twins with different orientations were generated within the austenitic grains after the deformation process. With the increase of annealing temperature, the decreased space between twins results in the strengthening of the TWIP effect.