Research On Effect Of Processing Parameters On Interfacial Microstructure Of The Fe-Cr-B Alloy/45# Steel Composite Roll

The bonding quality of composite interface was the critical for making a successful composite roll.In this paper,Fe-Cr-B alloy was chosen as a cladding layer and carbon steel containing 0.45%C as roll core for making a composite roll.The roll was prepared by a liquid-solid composite casting method combining the rapid cooling and solidification of the Fe-Cr-B alloy melt with an electromagnetic induction heating the carbon steel core.Research focused on how the process parameters,such as compound ratio(the ratio of the thickness of the Fe-Cr-B alloy coating to the diameter of the 45#steel roll core),the temperature of carbon steel roll,the pouring temperature of Fe-CrB alloy and the heating time of electromagnetic induction,influence the bonding quality and interface microstructure of the composite roll.Optical microscope(OM),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)were used to analyze the microstructure of the composite interface.X-ray diffraction(XRD)were employed to analyze the phase composition of composite interface,and Vickers microhardness tester to analyze the hardness of the area of composite interface.Based on research results,the microstructural transformation mechanisms of the composite roll and interface were investigated.The results were obtained as follows:The as-cast microstructure of the composite interface was consisted of three areas,i.e.,cladding sub-region,composite interface region and roll core sub-region.The microstructure of the cladding sub-region was mainly consisted of the eutectic dendrite matrix and reticular eutectic,composite interface region of the pearlite,and the roll core sub-region of the granular ferrite and grain boundary carbides or carbborides.Due to the difference of alloy element species and content between Fe-Cr-B alloy cladding layer and steel roll core layer,the alloy elements on both side of the composite interface interdiffused during the cooling and solidification process.Element Cr,Mn,Ni,Mo and B diffused from the side of cladding layer to the core layer through the composite interface area,but element Fe diffused from the side of core layer to the cladding layer through the composite interface area.However,element C from both sides all diffused toward the composite interface area.The compound ratio of the Fe-Cr-B alloy cladding layer to the carbon steel core roll was selected as 0.67,1 and 1.5 respectively.With increasing of compound ratio,the area of the cladding sub-region increased,dendritic matrix grain coarsened,the reticular eutectic reduced,and continuous network broken in the cladding sub-region.The composite interface area changed from the straight fine line to the curved thick line,and finally transformed into the winding band.The grain size and area in the roll core sub-region also increased.So,the bonding quality of the composite interface improved with increasing the compound ratio.The temperature of carbon steel roll core was selected as 850??900? and 950?respectively.With increasing temperature of the carbon steel roll core,the area of the cladding sub-region increased,the dendritic matrix grain coarsened,the reticular continuous eutectic network gradually broken,and the quantity of reticular eutectic decreased in the cladding sub-region.The composite interface zone changed from mechanical to metallurgical bonding at first,and then its quantity and scope increased,and eventually turned into a thick continuous curved line.Moreover,the grain size and the area in the roll core sub-region increased constantly.So,the bonding quality of the composite interface was improved with increasing the roll core temperature.The pouring temperature of Fe-Cr-B alloy was selected as 1545??1575?and1605?respectively.With increasing Fe-Cr-B alloy pouring temperature,the area of dendritic matrix grain in the cladding sub-region increased,the continuous network of eutectic decreased and finally broken up,and its quantity decreased in the cladding subregion.The composite interface also changed from mechanical to metallurgical bonding,and its region changed from the discontinuous fine line to the continuous thick curved line.The grain size and area in the roll core sub-region increased continuously.So,the bonding quality of the composite interface was improved with increasing the Fe-Cr-B alloy pouring temperature.The electromagnetic induction heating time was selected as 8min,15 min and30min respectively.With increasing electromagnetic induction heating time,the region of the cladding sub-region significantly increased,the size of dendritic matrix grain in the cladding sub-region increased,but the reticular eutectic decreased.The composite interface area changed from mechanical to metallurgical bonding,and transformed from the incomplete,discontinuous and straight line to the winding line.The region of roll core sub-region significantly increased,and the grain size in the region also increased.So,the bonding quality of the composite interface was improved with increasing the electromagnetic induction heating time.