Effect Of Tungsten Carbide And Carbon Equivalent On Structures And Properties Of Hypereutectic High Chromium Cast Iron Welding Layers Prepared By High Frequency Induction Cladding

High frequency induction heating process is simple and easy to operate.But since the thickness of the welding layer is thin?usually less than 2 mm?,and the dilution effect of the parent metal decreases the hardness and wear resistance of surfacing welding layer,the actual service life of the welding layer is shorter.Changing the degree of carbon equivalent of surfacing welding layer and adding tungsten carbide particles in the surfacing layer can increase the hardness and wear resistance of surfacing layer.But till present time no thorough and systematic study was carried out on the these aspects.This project first optimized the high-frequency induction surfacing process for hypereutectic high-chromium cast iron with different tungsten carbide contents and different carbon equivalents.The orthogonal test concludes heating time,welding current,welding flux as process parameters,the optimal value is as follow:current56 A,heating time 42 s,flux amount 14 g.Using the above process parameters,excellent surfacing welding layer with free of pores and inclusions was obtained.The tungsten carbide additions were 0%,10%,15%,20%,25%,30%,and carbon equivalents were 6.19%,6.76%,7.32%,7.88%,8.45%,9.01%respectively.High frequency induction welding samples prepared by using the process parameters mentioned above,were detected through test equipments to study the sample microstructure and properties.,to increase the wear resistance of the surfacing layer.Through metallographic electron microscope and XRD analysis,the surfacing layer microstructure mainly contains eutectic microstructure,primary carbide?M₇C₃?,tungsten carbide particles?WC,W₂C?and so on.According to the structure characteristics of surfacing welding layer,it can be divided into three parts:the top,the middle and the bottom.The top is a non-diluted layer,the middle part is a little dilution layer and the bottom is that the parent material dissolves a large number.The influence of the tungsten carbide and carbon equivalent of surfacing welding layer was studied and the results showed that:on the top of surfacing welding layer,with the increasing of carbon equivalent,the number of primary carbides and marten sites are also increased,but the eutectic carbides and the matrix microstructures are decreased gradually,With the increase of the content of tungsten carbide,the top part microstructure is unchanged.In the middle part,with the increasing of carbon equivalent,the primary carbides are increased,but eutectic microstructures of surfacing layer are decreased.At the same time,a small amount of tungsten carbide particles appeared in the tissue.In the bottom part,eutectic carbides increase along with the increase of carbon equivalent.But compared with the intermediate layer,the proportion of primary carbide carbon is small,and the amount of marten site in the matrix are increasing.As the increase of tungsten carbide content.The number of primary carbides and eutectic carbides increases slightly and the type of matrix remains basically unchanged.However,there are a certain amount of tungsten carbide particles in the middle of the structure.The number of particles increases substantially with the increasing tungsten carbide content.The properties of surfacing layer microstructure was analyzed and the results showed as:when the tungsten carbide content is certain,with the increase of carbon equivalent,the wear resistance is increased.But when carbon equivalent is reached at 9.01%,it decreases.As the increase of carbon equivalent,the middle and bottom's hardness and wear resistance gradually increase,but compared to the bottom,there is small increase in the middle.Thus,the carbon equivalent can increase hardness and wear resistance of surfacing layer,but over high carbon equivalent may not conducive to improve the wear resistance.At the top of the weld overlay,the wear resistance at the carbon equivalent of 8.45%is the best,which is 1.89 times higher than that of 6.19%.When the carbon equivalent is certain,with the increase of tungsten carbide content,the hardness and wear resistance of the top surfacing layer are nearly unchanged.The reason is that at the top there is no tungsten carbide particle.The hardness and wear resistance of the middle layer are slightly increased,because the tungsten carbide particles are very few.At the bottom of the weld overlay the fracture toughness gradually decreases,and the hardness and wear resistance increased rapidly with the increase of content of tungsten carbide.But when the content is more than 20%,the hardness and wear resistance increase slowly.Therefore,20%of the tungsten carbide particles have achieved the ideal effect.The wear resistance is four to five times higher than that of the non-carbonized tungsten particles.Above all,using the carbon equivalent of 8.45%,adding 20%of the 200tungsten carbide particles to hypereutectic high chromium cast iron,can ensure that the three parts of surfacing layer have ideal hardness and wear resistance.The overall wear resistance is greatly improved compared with the surfacing layer with6.19%carbon equivalent and 0%component of tungsten carbide.