Study On Microstructure And Fracture Toughness Of WC Reinforced Steel Matrix Composite By Electroslagmelting And Casting Technique

Steel matrix composites with different WC contents and size in GCr15 matrix have been produced by electroslag melting and casting technique, where the contents of WC was respectively 20,30, 40 and 50 wt%.Evolution of the microstructure and various carbides in the WC/steel matrix composites was investigated. The microstructure of the material was characterized using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Energy dispersive spectroscopy (EDS) and transmission electron microscopy were performed to investigate the interfacial composition between WC particle and steel matrix and phase analysis. The fracture toughness and fractural mechanism were analyzed emphatically. The effects of the content and size of WC particles as well as heat treatments processing on the fracture toughness were studied systematically.In the composites with lower content WC particles, the higher solution of most WC particles makes cemented carbide compound in net along the grain boundary and small in-situ carbide particles are found in the matrix due to fast cooling. The microstructure in the composites with contents of 40% WC particles are characterized by two kinds of eutectics with different shape i.e. γ-Fe+ Fe₃W₃C (in anchor) and y+ WC (in branch), additionally, a few irregular block structure are found. The interface between the large WC particles and steel matrix forms the reaction layer with several mms which enhances the toughness of interface highly.As for the composites with 50% WC particles, the microstructure of different heat treatments have respective properties by virtue of the dissolution and precipitation of carbides caused by high temperature of electroslag melting and casting technique and following heat treatments. This alloy has three types of carbides, the properties and physical conditions differ distinctly from the first class carbide to the second class.The Single Edge Notch Beam method is suitable for the measurement of fracture toughness of the composites in the fracture experiment, with stable experimental data. The materials have higher fracture toughness and the main fractographic features are WC cleavage, quasi-cleavage of matrix, dispersed dimples and dimpled bands. The fracture toughness of experimental materials have been significantly improved by various heating treatments, reaching a peak value of 23 MPa·m^1/2 as-annealed. The higher the weight fraction of WC particles, the lower the fracture toughness of the composites while the largerthe size of WC particles, the lower the fracture of the composites. The hardness phases play a dominant role in fracture toughness and fracture behavior and the composites have a compound micro-fracture mechanism. Fracture surface analysis confirms that the fracture belongs to ductile and brittle complex fracture, for which some hard phase display partially cleavage fracture.