Research On Microstructures And Properties Of Tungsten Carbide Particle Reinforced Iron-based Composite Surfacing Layers

Iron-based alloys have been widely used due to their good comprehensive performances and competitive price.The addition of ceramic reinforced particles can make the iron-based surfacing alloys possess the strength and toughness of metals as well as the good wear resistance and corrosion and high corrosion resistance.The WC ceramic particle has such characteristics as the high hardness,good wear resistance and good wettability with iron matrix.It is an effective way to solve the wear failure in the mining,nuclear and metallurgy fields that the WC particle is added into the flux-cored wire to prepare the WC particle reinforced iron-based composite surfacing materials.In this thesis,the influence of shielding gas species,WC particle shape and content,as well as the welding current on the microstructures and properties of WC particle reinforced iron-based composite hardfacing layers were studied by the means of optical microscope,scanning electron microscope with energy disperse spectroscopy,X-ray diffractometer,vickers hardness tester,rockwell hardness tester and abrasive wear testing machine,in order to provide some theoretical reference for the practical application and anti-wear design of the surfacing materials.The microstructure observations indicate that the hardfacing layers are mainly consisted of dendrite matrix,interdendritic carbides and WC particles.The deposition and solution-diffusion phenomena appear for the WC particle.The W and C elements react with the Fe and Cr elements in the iron matrix,and thus the complex carbides with the streamline,block,chrysanthemum and fishbone morphologies form in the surfacing layers.In addition,the honeycomb diffusion layer can be seen at the edge of WC particle.The type of shielding gases was optimized.When the pure CO₂ gas is used as the shielding gas,the thickness of diffusion layer at the edge of WC particle is about 5μm,and the wear volume is 63%lower than that where the pure Ar gas is used.It means that the wear resistance is the best when the shielding gas is CO₂ gas.The results of hardness tests show that with increasing the content of WC particles or increasing the welding current,the forming quantity of carbides in the surfacing layers and the hardness of surfacing layers increase.The results of wear tests reveal that the wear mechanism is mainly the micro-cutting,plastic deformation and hard phase peeling for the WC particle reinforced iron-based composite surfacing layers.When the addition content of spherical and non-spherical WC particles are respectively 10%and 15%,the microstructures of surfacing layers are uniform,the wear loss is the smallest and the wear resistance is the best.When the welding current for the spherical and non-spherical WC particle reinforced iron-based composite surfacing layers is respectively 240A and 270A,the wear resistance of the surfacing layers is the best.