Some Factors Affecting Wear on Cemented Carbide Tools

Evidence has been obtained that, in extremely severe conditions of friction, fusion occurs at the surface of friction between cemented carbides and steel. It is shown that steel will fuse with tungsten carbide at a temperature between 1,300 and 1,325 deg. C. (2,372 and 2,417 deg. F.). A theory is put forward to account for the “cratering” wear on cemented carbide tools containing free tungsten carbide. According to this theory, a fused layer of an alloy between tungsten carbide and steel is formed at the friction surface and is carried away by the chip. Titanium-tungsten carbide does not fuse with steel so readily, and hence is worn away much less rapidly than tungsten carbide in steel-cutting at high speeds. Micro-examination of worn tool surfaces shows that the type of wear is consistent with this theory. The conditions existing at the tool-work surface are discussed and the type of temperature distribution in the tool near the cutting edge is estimated. It is shown that the temperature distribution near the cutting edge can control the extent of cratering, the “built-up” edge, and deformation of the tool. In the light of the theory, some of the basic properties required in a tool material are discussed.