Microstructure And Mechanical Properties Control Of Surfacing Deposits For Roller Based On Cold Metal Transfer Technology

Some problems,such as wear,peeling off,crack,fracture often occur during its service for rolls,which ultimately lead to the failure.Repair of rolls can extend its life and reduce production costs.In order to make the repaired back-up roll meet the requirements of high strength,hardness,wear resistance and good toughness in production,alloy system with high hardness and high wear resistance was designed in this paper,and the corresponding flux cored wire were prepared.A new type of cold metal transfer technology was used to carry out the surface overlaying test.The shape,microstructure and properties of the hardfacing layer under different welding processes and different alloy composition systems were analyzed.And then cold metal transfer process and alloy system were optimized.Orthogonal experiment was designed considering the three factor of wire feeding speed,welding speed and torch angle in cold metal transfer process.The effects of welding technology on weld quality,hardness and wear resistance was analyzed and the process parameters were optimized.The results showed that when the wire feeding speed is4.8m/min,the welding speed is 6mm/s and the welding gun angle is 70°,the hardfacing layer possess good weld formability,high hardness and the best wear resistance.For hardfacing alloys design,the purpose of this study is to obtain the microstructure of uniformly dispersed MC-type carbide and martensite with excellent toughness.Combined with JmatPro thermodynamics calculation,hardfacing alloys were designed with different niobium and nickel content.The results showed that the increase of niobium content inhibits M₂₃C₆ carbides and promotes the formation of MC-type carbide NbC.However,when the content of niobium is too high,the hardness of deposited metal will be reduced.The addition of nickel will make the Ms point decrease,which is conducive to the formation of martensite and retained austenite,but the harden ability tendency of hardfacing increase for the case of higher nickel content.The prepared flux cored wire was used to overlay using the optimized CMT welding process.Microstructure and properties of hardfacing layers were studied.The results show that the microstructure of the hardfacing layer is mainly composed of?Nb,Ti?C,martensite and retained austenite.With the increase of niobium content,the carbide content increases and the grain size decreases.When the niobium content exceed 1.5%,the grain size increases.With the increase of nickel content,the content of martensite and retained austenite increases.When the niobium content is 1.5%and the nickel content is 1.0%,the grain size is the smallest,the hardness of the deposited layer is 55.9 HRC,and the wear resistance is the best.The hardfacing layers were subjected to tempering treatment.Test results show that fine carbides uniformly distribute in martensite matrix after 2 hours tempering at 550?.In addition,the hardness of hardfacing layers increase for the secondary hardening effect.