Severe plastic deformation of a TWIP steel

The severe plastic deformation of a Twinning Induced Plasticity (TWIP), 0.61C-22.3Mn-0.19Si-0.14Ni-0.27Cr (wt%) steel by Equal Channel Angular Pressing (ECAP) at elevated temperatures was used to study the deformation mechanism as a function of accumulated strain and processing parameters. The relationship between the microstructures after different deformation schedules of ECAP at the temperatures of 200, 300 and 400 °C, strain hardening behavior and mechanical properties was studied. The best balance between strength and ductility (1702 MPa and 24%) was found after two passes at 400 °C and 300 °C of ECAP. It was due to the formation of deformation microbands and twins in the microstructure. The twinning was observed after all deformation schedules except after one pass at 400 °C. The important finding was the formation of twins in the ultrafine grains. Moreover, the stacking faults were observed in the subgrains with the size of 50 nm. It is also worth mentioning the formation of nano-twins within the micro-twins at the same time. It was found that the deformation schedule affects the dislocation substructure with formation of deformation bands, cells, subgrains, two variants of twins that, in turn, influence the strain-hardening behavior and mechanical properties.