Unraveling the significant role of retained austenite on the dry sliding wear behavior of medium manganese steel

Abstract

For wear resistant steels, there is generally a linear relationship between the initial hardness and wear resistance, yet a high initial hardness limits the formability of components. The intrinsic ductility of austenite and strain hardening produced from the transformation-induced plasticity (TRIP) effect during service opens a new window for this contradiction. Herein, the wear resistance and the corresponding failure mechanisms of 5Mn steels after different heat treatment processes were evaluated using a ball-on-disk sliding test under dry conditions. The wear behaviors of the counterbodies were also studied to elucidate the wear mechanism of the tribo-system. The results show that the microstructures of the hot-rolled and air-cooled steel were mainly martensite. When the intercritical annealing temperature was relatively low (<695 °C), the microstructure primarily consisted of reversed austenite and ferrite. The samples annealed at 630 °C, 645 °C, 660 °C, and 675 °C had a similar initial hardness, while the sample annealed at 675 °C possessed a wear resistance that was 3.25 times that of the steel annealed at 630 °C. The large difference in the wear resistance was predominately due to the gradient of strain hardening provided by the varied amount and mechanical stability of the retained austenite. The transformation from austenite to martensite, which has an increased hardness, improves the work hardening. A strengthening layer formed with a certain thickness that provided stress support during the wear process and enhanced the wear resistance. When the annealing temperature reached 695 °C, a large amount of secondary martensite was generated from austenite that had a low thermal stability, which improved the initial hardness and wear resistance. The steels with a large amount of martensite had an enhanced wear resistance, but the elongation severely deteriorated, leading to unsatisfactory formability. The present work provides guidance for designing novel steels with an excellent balance of good formability and decent wear resistance by precisely adjusting the characteristics of the retained austenite.