Pitting mechanism of cemented carbide tool in the early stage of rock drilling

Surface pitting affects the working life of cemented carbide tools. The pitting mechanism of the cemented carbide tool in the early stage of rock drilling is investigated. Experimental results showed that the surface pitting appears in the cemented carbide tool as soon as the rock drilling begins, and the high concentration of heat on the tool surface in the early stage of rock drilling induces flash temperature. The models of flash temperature and thermal stress of the cemented carbide tool in rock drilling are established. Mechanical analysis indicates that the pits on the surface of the cemented carbide tool in the early stage of rock drilling are not formed by the scratching, fatigue, and crushing of the rock material. And thermal analysis shows that thermal stress is the major cause of the pitting on the surface of the cemented carbide tool in the early stage of rock drilling, for the thermal stress induced by flash temperature on the tool surface is much higher than its mechanical stress. Experimental results also show that most of the surface pits occur at the junction of the WC phase and the Co phase due to the thermal stress.