Hardening mechanism of high manganese steel during impact abrasive wear

To investigate the hardening mechanism of high manganese steel (HMS) during impact-abrasive wear (IAW), the microstructures and hardness evolution behaviours of the worn sub-surfaces of Mn13 (13.32% Mn and 0.22% Cr), Mn13-2 (13.23% Mn and 2.13% Cr), and Mn18-2 (18.35% Mn and 2.04% Cr) were investigated. The matrix hardness values of Mn13, Mn13-2, and Mn18-2 were 240.2, 256.6, and 266.5 HV, while their worn sub-surface hardness values were 670.1, 638.2, and 713.1 HV, respectively. The increase in the hardness values was attributed to the formation of epsilon-martensite and nano-sized mechanical twins in the worn sub-surfaces. The epsilon-martensite observed in the worn sub-surface of each of the three materials was similar. Therefore, the dif-ferences between the degrees of increase in the hardness values of the materials were attributed to the presence of the mechanical twins. The formation of the mechanical twins was affected by the stacking-fault energy (SFE), which increases with Mn content but decreases with Cr content. The degree of increase in the hardness increased in the following order: Mn13-2 (381.6 HV), Mn13 (429.9 HV), and Mn18-2 (446.6 HV). In summary, the degree of increase in the hardness of HMS during IAW can be improved by engineering a higher SFE for a higher number of mechanical twins.