Structural and Wear Characterization of Heat Treated En24 Steel

Ni–Cr–Mo steels such as En24 steel are widely used in machine part members, gears and shafts. En24 steel is generally used in the hardened and tempered condition to achieve an optimum combination of hardness and ductility. In the present study, heat treatment response of En24 steel was investigated by variation of hardening and tempering temperature in relation to microstructure and hardness. The microstructures were studied through a combination of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hardness decreased with the increase in hardening temperature from 1123 to 1273 K, whereas it increased slightly with the increase in hardening temperature after tempering at 823 K. The martensitic microstructure (laths) became coarser with increase in hardening temperature. The hardness results were well supplemented by XRD results (Williamson-Hall (WH) & modified WH plots and qualitatively by dislocation density). The specimens tempered at different temperatures (in the range 473–823 K) exhibited decreasing hardness with increase in tempering temperature. The abrasive wear tests were carried out on hardened and tempered specimens. The abrasive wear volume loss decreased with increase in tempering temperature, which was attributed to coarsening of martensite. The worn out specimens were observed under SEM, which revealed micro ploughing and cutting as important mechanisms of material removal during abrasive wear.