Study On Microstructure And Properties Of High Carbon Medium Manganese Fe-Cr-B Alloy/42CrMo Composite Roll

The composite roll integrates the advantages of mechanical properties of two kinds of metal materials.It can not only meet the requirements in wear resistance,thermal fatigue resistance and oxidation resistance of the working layer of the roll body,but also ensure the requirements in the toughness of the roll core.So,it is the main development trend of the roll.This paper involves basic research work of the composite roll.The high carbon and medium manganese Fe-Cr-B alloy/42CrMo low alloy steel composite roll was prepared by combining the solid-liquid composite casting method of fast cooling Fe-Cr-B alloy melt in electro-slag mold with electromagnetic induction heating 42CrMo alloy steel roll core.The microstructure and mechanical properties of the clading layer and composite interface of the composite roll were investigated.Optical microscope?OM?,scanning electron microscope?SEM?,energy dispersive spectrometer?EDS?and X-ray diffraction?XRD?were used to analyze the microstructure,alloy element distribution and phase composition of the clading layer and composite interface.Rockwell hardness tester was used to test the macro hardness of the clading layer and area of the composite interface.Pendulum impact tester was used to test the impact toughness of the samples with composite interface.On this basis,the mechanism of the variation of microstructure and mechanical properties of the composite interface and cladding layer are analyzed.The results are obtained as follows:The as-cast interface structure of the composite roll can be divided into three sub-region,i.e.,composite interface area,cladding sub-region and roll core sub-region.The microstructure of cladding sub-region is mainly consisted of pro-eutectic dendrite matrix,reticular eutectic and fine honeycomb peritectic.The microstructure of the composite interface zone is consisted of fine lamellar pearlite perpendicular to the interface,and the microstructure of roll core sub-region is consisted of lamellar pearlite,massive ferrite and a small amount of reticular carbide.The alloy elements contained in the high carbon and medium manganese Fe-Cr-B alloy and 42CrMo low alloy steel composite roll mixed and diffused with each other during melting as well as in the formation of the composite interface.The alloy elements C,Mn,Cr,Mo and B diffused from the cladding layer to the core,while element Fe from the core to the cladding layer.With the increase of Cr content in the cladding layer,the size of eutectics decreased and the honeycombs increased.There was no obvious changes in the structure and morphology of the composite interface and the roll core sub-region.After austeniting at 1050?followed by air-cooling,partial eutectic network on the cladding sub-region was broken.The composite interface region transformed into high-carbon martensite,while the roll core sub-region into a mixed medium and low carbon lath martensite and needle martensite,which resulted in the slight improvement of impact toughness.The as-cast phases within the cladding layer were mainly consisted of?-Fe,M₂B,M₃?C,B?,M₂₃?C,B?₆ or M₆?C,B?and a small amount of retained austenite.Due to the difference of cooling rate,the microstructure and mechanical properties in the as-cast cladding layer are quite different from the outer layer to the inner layer.The elongated pro-eutectic structure gradually coarsed,the continuity of network boride enhanced and the amount of M₃?C,B?carbon-boride gradually increased and the precipitatedM₂₃?C,B?₆ or M₆?C,B?carbon-boride particles gradually reduced.With the increase of Cr content,the amount of pro-eutectic borides in the cladding layer gradually increased and the size gradually became larger,the number of precipitated particles of M₃?C,B?,M₂₃?C,B?₆ or M₆?C,B?carbon-boride gradually increased,the content of martensite in the matrix structure increased,and the hardness of the coating layer gradually increased.