SAG usage wear-resistant steel with rare retained austenite achieve trade-off between impact toughness and strength

The impact toughness is the key to determine the service life of high strength wear-resistant steel for the lining boards of large-scale semi-autogenous grinding mill (SAG). It is difficult to predict the impact fracture failure of lining boards when SAG is running, which can cause damage to equipment once it occurs. Therefore, novel high strength wear-resistant steel was designed to improve impact toughness in this study. It is interestingly found that the microstructure contained finer bainite/martensite, and rare retained austenite (around 2 vol.%), which achieved trade-off between impact toughness and strength after the optimal heat treatment scheme (900 °C normalizing → 900 °C quenching → 300 °C tempering). The element segregation of Al and Si was improved and the start temperature of martensitic transformation during quenching was reduced, resulting in the refinement of martensite laths. Thus, the higher density of high-angle grain boundary (HAGB) and dislocation were obtained, which contributed to excellent impact toughness. Based on the instrumented impact curve, the total impact energy can be divided into four parts: elastic deformation energy (Ee), plastic deformation energy (Ed), crack stable propagation energy (Ep1) and crack unstable propagation energy (Ep2). Traditional toughening mechanisms focus on Ep1, which was based on the tortuous crack propagation path. Our experimental results show that Ed was another effective control unit to ensure the toughness. The difference between Ed and Ep1 in improving absorption energy was discussed in detail by combining HAGB density and dislocation density.