Study On Cast-weld Process And Composite Interface Of Bimetal Composite Roll Sleeve

The composite process of dissimilar metals is often limited by the physical properties of materials,such as melting point,linear shrinkage and casting size or shape.In the manufacturing of composite roll,when the cast iron is selected as working layer and the cast steel is selected as roll core,the roll maybe compound unevenly or even fail due to stress,segregation and inclusion in bonding zone.Aiming at the forming process of cast steel/cast iron composite roll,a low melting point transition layer was proposed.Combined with surfacing,electromagnetic induction heating and bimetal solid-liquid composite technology,the bimetal cast-weld composite technology was developed.The surfacing process parameters,electromagnetic induction heating process parameters and casting process parameters were optimized,and the low alloy steel/the high chromium cast iron(LAS/HCCI)composite roll was prepared by the optimized process.The cast-weld process of LAS/HCCI composite roll is mainly to prepare a certain thickness of material(low melting point transition layer)with melting point similar to that of HCCI on the pre-prepared LAS roll core by surfacing,preheating the roll core by electromagnetic induction coil and keep heating when pouring high chromium cast iron,so as to realize the metallurgical combination of LAS and HCCI.The experimental roll is designed,which is composed of roll core,inner sleeve and working layer.In the bimetal solid-liquid composite experiment,it can effectively reduce the volume of molten metal by using the low melting point transition layer,and solve the technical problem of bimetallic solid-liquid composite that is difficult to achieve large-area metallurgical bonding.It is calculated that the temperature field of bimetal cast-weld composite process is a logarithmic function of radius.The effect of process parameters on temperature field,stress and deformation of inner sleeve was studied by numerical simulation.The results show that when the current is 200 A?240 A,the voltage is 20 V?22 V,the surfacing speed is 1.5 mm/min,the swing amplitude is 40mm and the swing speed is 1.5 m/min,the metallurgical surfacing layer with the surface melting point of 1249?can be obtained.Two zones are formed in the surfacing layer,one is near eutectic structure of Fe₃(B,C)+Fe near low alloy steel,the other is eutectic carbide of(Fe,Cr)₂B+(Fe,Cr)₇C₃ far away from low alloy steel.The melting point of surfacing layer increases from1249?to 1463?between the surface of surfacing layer and LAS.Using medium frequency electromagnetic induction heating equipment to preheat,the temperature field distribution of the inner sleeve during the process of induction heating was obtained by simulation.The results show that when the power supply is 100 k W,the frequency is 1000 Hz,the current is 200 A,the coil is 7,and the distance between the coil and the workpiece is 50 mm,heating for 100 s can make the thickness of 18.27 mm inward along the surfacing layer rise to 900?,and the surface temperature of the surfacing layer is evenly distributed.With the increase of the thickness of the surfacing layer,the stress is concentrated on the inner wall and the stress value increases,but it has no effect on the deformation of the casting.The model of temperature field and flow field in the casting process was established,and the variation of the maximum temperature and high temperature duration of the surfacing layer under single factor and multi factor conditions was studied.The orthogonal experiment results show that the order of the factors affecting the maximum temperature of surfacing layer is casting temperature>preheating temperature>casting time>sand mold temperature,and the order of influencing the high temperature duration of surfacing layer is casting temperature>preheating temperature>sand mold temperature>casting time.Combined with the liquidus of surfacing layer,the optimal level combination was selected from orthogonal experiment,and the electromagnetic induction heating time was obtained by heat balance calculation,then the influence of electromagnetic induction heating time on the quality of composite interface was explored.The results show that when the casting temperature is 1420?,preheating the roll core to 900?,pouring for 10 s and keeping the roll heated for 60 s,the metallurgical bonded composite roll can be obtained.It is found that a pearlite metallurgical composite layer with a width of about 20?m is formed between LAS and HCCI,and the interface is clean without pores,inclusions and other defects.C.Cr,Mn and other elements diffuse in the composite layer,and the pearlite in the composite layer grows at a certain angle towards to LAS.The mechanical properties test show that the hardness of composite layer is between LAS and HCCI,which are 398 HV,546 HV and 882 HV respectively.The impact fracture is located at HCCI,about 6.4 mm away from the composite layer.It shows that the hardness increases gradually from LAS to HCCI,which improves the mechanical properties of the composite roll.