Mechanical Behavior and Microstructure Evolution during Tensile Deformation of Twinning Induced Plasticity Steel Processed by Warm Forgings

The mechanical behavior and microstructural evolution of an Fe-30Mn-3Al-3Si twinninginduced plasticity(TWIP) steel processed using warm forging was investigated. It is found that steel processed via warm forging improves comprehensive mechanical properties compared to the TWIP steel processed via cold rolling, with a high tensile strength(Rm) of 793 MPa, a yield strength(RP) of 682 MPa, an extremely large RP/Rmratio as high as 0.86 as well as an excellent elongation rate of 46.8%. The microstructure observation demonstrates that steel processed by warm forging consists of large and elongated grains together with fine,equiaxed grains. Complicated micro-defect configurations were also observed within the steel, including dense dislocation networks and a few coarse deformation twins. As the plastic deformation proceeds, the densities of dislocations and deformation twins significantly increase. Moreover, a great number of slip lines could be observed in the elongated grains. These findings reveal that a much more dramatic interaction between microstructural defect and dislocations glide takes place in the forging sample, wherein the fine and equiaxed grains propagated dislocations more rapidly, together with initial defect configurations, are responsible for enhanced strength properties. Meanwhile, larger, elongated grains with more prevalently activated deformation twins result in high plasticity.