Effect of hardness, microstructure, normal load and abrasive size on friction and on wear behaviour of 35NCD16 steel

Wear and friction properties depend on many parameters such as normal load and material hardness. However, coupled contributions of microstructure and abrasive particle size are less investigated. A contribution in this field is proposed with wear tests performed between a 35NCD16 steel and abrasive silicon carbide grains ranging from 35 µm to 200 µm under different normal loads (50-110 N). To vary hardness and microstructure, samples are subjected to water quenching and tempering at various temperatures (200-600 °C). These heat treatments result in a martensitic microstructure with various levels of carbon contents and carbide precipitations. For a given microstructure and hardness, the friction coefficient decreases with increasing the normal load and/or decreasing the abrasive particle size. However, the wear rate increases with increasing the normal load and/or the abrasive particle size. For high normal loads, the results also reveal that the friction coefficient decreases when the hardness and the martensite volume fraction increase. Nonetheless, for low normal loads, a transitional microstructure from martensite laths to carbides and equiaxed grains, for a tempering around 400 °C, impacts the friction coefficient. Whatever the normal load, this transitional microstructure also influences the wear rate.