Study On The Effect Of Carbon And Boron Contents On Microstructures Of Fe-Cr-B/42CrMo Composite Grinding Roller

Grinding roller is an key component for medium speed pulverizes of coal-fired power station,so it has great significances to improve their service life.An experimental composite grinding roller that combined Fe-Cr-B alloy as cladding layer with 42 CrMo low alloy steel as core is fabricated using the solid-liquid composite casting method in this thesis.The microstructure is observed by optical microscope and scanning electron microscope and the alloy elements distribution in composite interface tested by energy dispersive spectroscopy.The phases within cladding layer are measured by X-ray diffraction and analyzed by the MDI Jade6 software.The hardness of the samples is tested by Rockwell hardness tester and micro hardness testers.On the basis of these observation and analysis,the microstructures and hardness of cladding layer as well as composite interface are studied.The effect of carbon and boron contents in cladding layer on the microstructures of cladding layer and composite interface are explored.In general,the main results obtained in this thesis are as follows.The hypoeutectic microstructures of Fe-Cr-B alloy layer are consisted of a dendritic matrix distributed a small number of irregular precipitated particles and interdendritic eutectic.The hypereutectic microstructures of Fe-Cr-B alloy layer are comprised by coarse stick-like primary M2 B borides,eutectic,peritectic and boro-carbides that supersaturated from austenite.The microstructures of Fe-Cr-B alloy cladding layer can be divided into three regions,i.e.,surface layer,intermediate layer and interior layer.Compared with surface and interior layer,matrix grains are much bigger and the continuity and integrity of net borides within intermediate layer are stronger.Besides,the borides in this layer are larger in size and more in number.The composite interface can be also divided into three areas,i.e.,sub-cladding layer,interface and sub-42 CrMo core layer.The interface that looks like a black band in microstructures is consisted of directional fine pearlite and a great number of irregular hard phases.The microstructure of sub-cladding layer is comprised of a dendritic matrix and a plentiful number of net eutectic borides.But compared with cladding layer,the volume percentage of net borides in sub-cladding layer is lower.The microstructure of sub-42 Cr Mo core layer is consisted of ferrite and fine pearlite.,The number of pearlite in this layer gradually increases and ferrite decreases from the interface to core.The volume percentage of eutectic and hypereutectic is greatly increased with increasing boron and carbon contents of Fe-Cr-B alloy.The volume percentage of primary borides,eutectic and wheat-like peritectic is also increased with increasing boron and carbon contents of Fe-Cr-B alloy.The continuity and integrity of banded interface is stronger with increasing carbon and boron content of Fe-Cr-B alloy.Besides,the number of hard phases in sub-cladding layer and pearlite in sub-42 CrMo core layer are increased and the microstructures of sub-cladding and sub-core layers fined with increasing boron content of Fe-Cr-B alloy.