Effect of particle hardness on mild–severe wear transition of hard second phase materials

This study analyzes the effect of particle hardness on the transition from mild to severe abrasive wear. White cast iron with 1.9 wt% Cr with austenitic and martensitic matrices, white cast iron with 13.8 wt% Cr and 24.4 wt% Cr and mottled cast iron, and four types of abrasive with different hardness were used in pin-on-abrasive paper tests at 4.6 N of load. The microstructure of the alloys was characterized by optical microscopy and the micromechanisms of abrasive wear were characterized using scanning electron microscopy. The hardnesses of both the abrasive and the alloys were selected to obtain a HA/H range ratio (in which HA is the hardness of the abrasive and H is the alloys' hardness) much wider than the one reported in the literature until now. The relationship between wear rate and friction coefficient versus HA/H ratio was analyzed. The results show that when the HA/H ratio is less than 1.9, an increase in abrasive hardness produces significant increase in wear rate. However, when the ratio HA/H is more than 1.9, increasing the abrasive hardness has little effect on the wear rate. Comparing these results with the ones from the literature for homogeneous materials and hard second phase materials, the regions found in this study correspond to the severe wear region, the mild–severe wear transition, and a small mild wear region. A correlation between the friction coefficient and the HA/H ratio was found: the friction coefficient increases proportionally with the increase of HA/H to achieve a HA/H ratio of about 3.3. For HA/H values above 3.3 the friction coefficient is relatively constant.