Study On The Preparation Of Mo-Fe-B Hardfacing Materials And The Microstructure And Properties Of Cladding

Mo₂Fe B₂ based cermet is suitable for coating materials due to its excellent mechanical performance,low preparation costand similar thermal expansion coefficient,thermal conductivity and density to steel.Based on this background,using welding methods for in situ synthesis of Mo₂FeB₂ based cermet coating material on steel surface to improve the wear resistance and the service life of materials.Mo-Fe-B series handmade flux cored wires for welding were welded on the surface of45 steel by oxygen acetylene and argon arc,which used Mo,reduced Fe,Fe B and WC powders as raw materials.Based on the principles of welding metallurgy,Gibbs free energy criterion and Mo-Fe-B phase diagram,the metallurgical process and the phase composition of the surfacing layer were deduced.The hardness and wear resistance of the surfacing layer and welding interface hardness gradient were taken as the performance index.The influence of WC on the microstructure and properties of hardfacing layer with different welding methods and the influence of Mo/B and welding current on the microstructure and properties of hardfacing layer under argon arc welding conditions were characterized by optical microscopy,scanning electron microscopy and XRD.The microstructure and properties of the surfacing layer and interface between Mo-Fe-B and marketed cast tungsten carbide tubular wire were investigated under the condition of oxygen acetylene flame surfacing.The results show that the welding preparation of Mo₂Fe B₂ based cermet coating is feasible.The microstructure of cladding layer was uniform,which had high density and good combination with substrate interface.And the hard phase in tissue mainly includes Mo₂FeB₂,MoB,Fe₂B,CrB,?Fe,Cr?₇C₃ and so on.It's indicated that Mo₂FeB₂ in the surfacing layer could significantly improve the hardness and wear resistance of the steel surface.Less WC burning under oxy acetylene welding conditions had greater effect on the microstructure of cladding layer,which could restrain the precipitation of dendrite during solidification of molten pool and was good to the formation of Mo₂FeB₂ phase.As the addition of WC was 25%,the microstructure was composed of uniform Mo₂FeB₂ particles,eutectic boride hard phase,massive WC and Fe based solid solution.The surfacing layer obtained the highest hardness and the best wear resistance..When argon arc welding current was 110A,Mo/B atom ratio and WC addition had little influence on the properties and microstructure of cladding layer.The microstructure was mainly composed of the cellular dendrite and eutectic Fe based solid solution and eutectic boride,carbide or boron carbide.When the welding current is 80A,granular Mo₂FeB₂ and bulk Mo₂Fe B₂ were observed in the surfacing layer,but no Mo₂FeB₂ appeared in the surfacing layer interface.The surface hardness and wear resistance of surfacing layer increased significantly.There was a metallurgical bonding transition zone with a width less than 100?m and without crack defect at the interface of oxygen acetylene flame and argon arc sample of Mo-Fe-B.The structure of the surfacing layer of the oxy acetylene flame formed by casting tungsten carbide was composed of round spherical,granular WC and Fe matrix.Crack defects were found in both the surfacing layer and the interface of oxy acetylene flame.