Study On The Burning Behavior Of Tungsten Carbide In High Chromium Cast Iron By High Frequency Induction Surfacing Technology

In the high frequency induction surfacing layer based on high chromium cast iron,the addition of WC particles can effectively improve the microstructure and the overall wear resistance of the surfacing layer.But burning of the WC particles will seriously affect its strengthening effect on the surfacing layer.Therefore,the study on the behavior of WC particle's burning in the surfacing layer has very important meaning.In this paper,28 sets of surfacing layer based with WC and high chromium cast iron were prepared on the surface of Q235 steel by using different process parameters in air and vacuum environment.The metallographic organization and properties of the samples were studied by OM,SEM,EDS,XRD,hardness test,wear test and other test methods.The burning behavior of WC particles in the surfacing layer was analyzed in detail.The effect ofprocess parameters on the burning loss of WC particles was studied.Based on these researches,the influence of WC particles burning on the performance of high frequency induction surfacing layer was studied.The morphology of the surfacing layer was analyzed.The results show that the bottom of the surfacing layer is sub-eutectic structure due to the dilution of the base metal.WC particles are deposited at the bottom of the surfacing layer,and a diffusion layer with a certain thickness is formed around the particles.There are W-containing carbides in the form of massive and fishbone:Fe6W6C,Fe3W3C,Fe4W2C.Thermodynamic analysis shows that during the surfacing process,WC particles are dissolved by the high-temperature metal liquid,and the W2C phase decomposes:W2C?2W+C;WC phase decomposes:2WC?W2C+C and W2C?2W+C,and the W and C atoms generated by the decomposition form carbides during the cooling process.The morphology of WC particles was analyzed.The results show that the burning of WC particles includes oxidative burning and high temperature burning.When the amount of flux added to the air is insufficient,the WC particles are severely oxidized and burnt.Therefore,the proper amount of flux added is important for preventing the burning of WC particles.The vacuum environment can reduce the degree of oxidative burning of WC particles.In the air and vacuum environment,the WC particles in the high-frequency surfacing layer are burned in high temperature,and the surface of the WC particles dissolves and diffuses,forming a diffusion layer around the particles.The results showed that the decomposition and diffusion of the surface elements of WC particles strengthen the connection strength with the matrix,which is of great significance to prevent the particles from falling off.However,excessive decomposition and burning will seriously affect the strengthening effect on the surfacing layer.Therefore,the thickness of the diffusion layer produced by the burning of the WC particles and the effective volume fraction of the WC particles in the surfacing layer are used to evaluate the degree of burning of the WC particles in the surfacing layer.The effects of surfacing time,surfacing current and flux addition amount are separatively used as the single independent variables to study the degree of WC particle burning loss.In the air,as the surfacing time is prolonged or the surfacing current increases,the degree of dissolution of the WC particles gradually increases,this causes the thickness of the diffusion layer to increase,and the effective volume fraction first increases and then decreases.When the thickness of the diffusion layer is too small,the WC particles are poorly bonded to the matrix,and the WC particles are easily detached,resulting in a small effective volume fraction of the WC particles.When the thickness of the diffusion layer is too large,the WC particles are severely burned,and the effective volume fraction of the WC particles is also small.As the amount of flux added increases,the degree of dissolution of the WC particles is increased,but the degree of oxidative burning is reduced,and thus the thickness of the diffusion layer and the effective volume fraction are increased.In vacuum,the effects of surfacing time and surfacing current on the thickness of the diffusion layer and the effective volume fraction are the same as those in the air.Because the vacuum environment can reduce the degree of oxidation loss of WC particles,the dissolution of the WC particles is intensified as the flux addition amount increases.The thickness of the diffusion layer increases,and the effective volume fraction first increases and then decreases.The burning loss of WC particles in prepared samples were comprehensively analyzed.Using the thickness of the diffusion layer and the effective volume fraction as independent variables,the effect of WC particle burning on the performance of the surfacing layer was studied.The results show that with the increase of the thickness of the diffusion layer,the Rockwell hardness and microhardness increase first and then decrease,and the wear resistance of the surfacing layer increases first and then weakens.With the increase of the effective volume fraction,Rockwell hardness and microhardness gradually increase,and the wear resistance of the surfacing layer is gradually enhanced.When the thickness of the diffusion layer is 3.35?m and 5.56?m,which is the optimum diffusion layer thickness,the effective volume fraction reaches the maximum of 15.37%and 19.36%.WC particles have the best strengthening effect on the surfacing layer.The surfacing layer has the highest Rockwell hardness and microhardness,and the wear resistance is the best.