| With gradually exhausting of W and Co resources, it is significant to study on a new VC carbide to reinforce iron matix composites because the abundant vanadium-titanium resources in Sichuan Panxi area.In the recent years, many papers of VC particles reinforced Fe matrix composites produced by casting technique have been reported. In this paper, a new in situ powder metallurgy technique was developed to produce Fe-VC composites. In order to improve the microstructure and properties of the Fe-VC composites, Ni,Cr,Mo alloy elements were added into this system. The effect of RE and Ni contents on the microstructure and mechanical properties of Fe-VC composite were investigated with different components. According to the experimental results and welding process, the Fe-VC composite was prepared as a welding material. The Fe-VC composite and 45 steel were welded by tungsten inert gas welding (TIG) with an austenitic stainless welding wire (ER309L) as filler metal. Fe-VC composite and 45 steel were vaccum brazed with pure copper as filler metal, the preferable brazing technology is ascertained with orthogonal test. Microstructures of the composites and the welding joint are analyzed in the means of scanning electronic microscope (SEM), electronic probe microanalysis (EPMA) and X-ray diffraction (XRD), and the mechanical properties of Fe-VC composites and the welding joint was tested. The results of microstructures and properties of Fe-VC composites were indicated: (1) The wettability of Fe /VC particles interface was enhanced by RE addition due to RE being able to purify the surface of crystal and contribute to sinter. However, the excessive content of RE can increase porosity in the microstructures and coarsen the VC particles, which is unfavorable for sintering densification. (2) The wettability of Fe /VC particles interface is increased with Ni addition, Fe-VC composites become more densification because Ni can induce liquid phase at the sintering temperature. (3) The matrix of Fe-VC composite is transformed from pearlite into martensite and remained austenite gradually with the increasing of the content of alloy elements.The results of Fe-VC composite and 45 steel TIG welding were indicated: (1) Fe-VC composite and 45 steel displayed excellent metallurgy bonding. The cracking zones of tensile samples were located at the composite side and its tensile strength is about 180MPa, which indicated that the applied welding method is reliable. (2)The alloy elements in the weld took on gradient distribution and the micro-hardness in weld changed with the amount of VC particles. Fourthermore, the structures of frature tensile exhibited brittleness quasi-cleavage frature. (3) The sizes of VC particles in heat affected zone were similar to those of Fe-VC composite substrate.The results of vaccum brazing Fe-VC composite and 45 steel were indicated:(1)The primary and secondary sequence affecting shear strength is thickness of filler metal, brazing temperature, hermostatic time and lap joint lenth. (2) The frige of Cu is shaped serration at the interface between Fe-VC composite and 45 steel. (3) Cu-Fe solid solution is formed by inter diffusion Cu and Fe during sintering, the shear strength of brazing joint is about 170MPa, the cracking zones of tensile samples were located at the composite side. The results of tests show: (1) Fe-VC composite containing 1-3μm VC particulates dispersed throughout martensite and austenite matrix, and excellent densificition and high hardness were obtained by liquid sintering at 1200℃. The addition of 0. 21% RE and 3% Ni are the optimal contents to greatly improve the microstructure and properties of the Fe-VC composite. (2) The test of TIG welding showed that the applied welding method, filler metal and weld process can satisfied the welding techniques of these two different materials. In addition, the quality of weld is reliable and there are no large cracks and coarse VC particles in the Fe-VC composite. (3) The preferable brazing technology are as follows: fillr metal thickness of 0.4mm, brazing temperature of 1100℃, thermostatic time of 10min and lap joint length of 13mm.
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