The Research Of Deep Cryogenic Treatment Of Anvil-use YL20.3 Cemented Carbide

YL20.3 cemented carbide, a kind of tungsten carbide-cobalt hard metal, is utilized in the manufacture of cemented carbide anvil that plays an important role in synthesis of artificial diamond. Deep cryogenic treatment (DCT) as a kind of cryogenic treatment helps to change the structure and improve the properties of the material in order to improve the quality and life span of anvil. Therefore, it is a valuable subject to do research on DCT in the field of anvil-use cemented carbide.In the present work, the cemented carbide samples are subjected to different time of DCT namely 0～72h at -150℃. The response of mechanical properties of YL20.3 alloy to such various hours of treatment is evaluated in terms of microhardness, compressing strength, bending strength and impact toughness. According to the result, after DCT microhardness and compressing strength enhanced and reached maximun after 2h of DCT while bending strength falls a little, and impact toughness fluctuates within a small extend compared to the value before DCT. There is also an attempt to do circular DCT at the base of 2h DCT. However, the compressing strength decreases with the increasing times.X-ray diffraction is used here to analyze the phase structure and the surface residual macrostress of the material before and after DCT. The experimental result indicates that martensite transformation occurs in the Co phase, that is, Co phase has a tendency of transformation from a-Co toε-Co, and the residual compressive stress on the surface obviously goes up. These changes give rise to the increasing of hardness and compressing strength. Phase transformation leads to the decline of magnetic saturation and the increase of coercive force.Apart from this, the study of fracture and fatigue of YL20.3 cemented carbide is involved in this paper. Sample after 2h of DCT shows higher fatigue strength of the alloy in cyclic compressing test. Macrostructure of bending test sample is obtained from vertical binocular microscope to analyze the fracture behavior. Scanning electronic microscope (SEM) is used to observe the fracture mode. The pictures show that as for the samples of bending test, impact toughness test and low-cycle cyclic compressing test, the brittle fracture of WC/WC boundaries and interfacial fracture of WC/Co boundaries are the main mode, and ductile tearing of Co binder phase also exists. But on the fracture of high-cycle cyclic compression sample, much cleavage fracture of WC particles can be found. The fracture behavior of cyclic compressing test is that, under a cyclic force phase interface divorces, then gap forms, and crack generates, expands, gathers until fatigue ribbon forms, and at the end the material fails.