Research Of Preparation And Performance Of High Chromium Cast Iron Surface Composites

Abstract:To improve the wear resistance of high chromium cast iron’s work surface, a high chromium cast iron surface composites was prepared using the optimized cast-sintering technique. The preparation process of surface compound layer perform was developed and the microstructure and mechanical properties of the surface composites was also explored, in addition to these, this study compared the wear resistance of surface composites and high chromium cast iron.Through the optimization of powder metallurgy process of the surface compound layer perform, the composition of elements is defined as22%V、6%Cr、5.6%C、3%Ni、Fe (Bal.); the ball-milling process parameters are300rpm,24hour with the mass ratio7:1of the grinding ball and metal powder; the metal powder suppress process parameters are cold isostatic pressing,180MP with30S; the sintering process is vacuum sintering,1200℃with1hour; the theoretical calculation and experiment results showed that the carbonization reaction of V and Cr is feasible.The high chromium cast iron surface composites was prepared by cast-sintering with the casting temperature defined as1500℃. Metallurgical combination can be obtained between the surface compound layer and the matrix with element diffusion mutually. The density of the surface compound layer is7.08g/cm3. The microstructure of the surface compound layer was constituted by γ-Fe and evenly distributed V8C7and Cr7C3. Thermal expansion experiment showed that the thermal expansion coefficient difference is small between20℃and600℃, which ensures the good adhesion in the interface.The composites’tensile properties testing showed that the tensile strength is159MPa with brittle fracture style. Because of the low density the fracture which has the ductile fracture feature apeared at the side of the surface compound layer, far away from the interface.The comparison of wear resistance between high chromium cast iron and surface composites indicated that the friction wear resistance of the composites is18.3times higher than that of high chromium cast iron matrix while three body abrasive wear ability is nearly. The failure form of the composites is cutting furrows and fatigue spalling. By adding the size about100um ZTA ceramic particles in the surface compound layer, the three body abrasive wear resistance of the composites which has a better performance is1.5times higher than that of high chromium cast iron. The combination between ZTA and surface compound layer matrix is good. The composites ’enhancement mechanism is "shadow effect" of the reinforce particle and "support effect" from the reinforce particle to the matrix including the protection from ZTA to surface compound layer matrix in the surface compound layer and the protection from VC-CrC to y-Fe in the surface compound layer matrix, as well as the support from y-Fe to VC-CrC and the support from VC-CrC、γ-Fe to ZTA.