A Comparison of Strengthening Mechanisms of Austenitic Fe-13Mn-1.3C Steel in Warm and Cold High-Pressure Torsion

Abstract

A study on the role of deformation temperature on a twin-assisted refinement of austenitic structure and phase transformations in high-pressure torsion of high-Mn Hadfield steel single crystals (Fe-13Mn-1.3C, in mass. %) has been carried out. In high pressure-torsion, twinning has been experimentally confirmed as a high-temperature deformation mechanism and has been observed at the temperature 400 °C. An increase in deformation temperature of up to 400 °C decreases the activity of mechanical twinning but does not fully suppress it. A dense net of twin boundaries, which has been produced in cold deformation by high-pressure torsion at room temperature, possesses high thermal stability and stays untransformed after post-deformation annealing at a temperature of 400 °C. In high-pressure torsion at a temperature of 400 °C, the complex effect of high temperature and severe plastic deformation on the strengthening of high-carbon Fe-13Mn-1.3C steel has been observed. A synergetic effect of severe plastic deformation and elevated temperature stimulates a nucleation of nanoscale precipitates (carbides and ferrite) along with deformation-induced defects in austenitic structure. These fine precipitates are homogeneously distributed in the bulk of the material and assist high values of microhardness in high-pressure torsion-processed specimens, which is similar to twin-assisted microstructure.