Temperature Effect on Twin Initiation during Equal-Channel Angular Pressing and Mechanical Properties of Twinning-Induced Plasticity Steel

Abstract

To examine the effect of temperature on twinning initiation and strain accumulation, a twinning-induced plasticity (TWIP) steel with chemical composition of Fe-25Mn-1.66Si-1.23Al was successfully prepared and subjected to severe plastic deformation (SPD) with equal-channel angular pressing (ECAP) at room temperature and warm temperature (300 °C), respectively. The microstructure was analyzed using different techniques, while its mechanical properties were measured by performing micro-tensile tests before and after the ECAP procedure. With such analyzed microstructure after ECAP procedure, the grains of the investigated TWIP steel are found to be elongated and the grain size decreases sharply especially at room temperature, compared to that before the ECAP procedure. The transmission electronic microscope (TEM) micrographs confirmed the existence of twins in all ECAP extruded conditions; however, at room temperature and after multiple passes of ECAP process at a higher temperature, it is easier to initiate secondary twins with a complex morphology. One pass of ECAP at room temperature can cause a strain effect of two passes at 300 °C. Strain hardening behavior was analyzed through ln(dσ/de) − lnσ plot; the results show that the annealing samples present a relatively high strain hardening capability while the strain hardening capability of ECAP-ed samples reduces gradually with the amount of total strain applied by the ECAP.