Research On The Microstructure And Abrasion Resistance Of High-boron Submerged Arc Hardfacing Alloys With Composite Powder Particles And Solid Wire

High boron hardfacing alloys with beautiful weld beads are suitable for wear-resisting ones.However,they are very fragile in nature.In order to develop some wear-resisting welding consumables with economic and prepmium properties based on the results of our research team as well as improve their toughness,a new scheme which includes such parts as B₄C powders were selected as the main boron-containing components,alloying treatment on chief wear-resisting phases of Fe₂B and carbon-fixation technology,were carred out in advance and many composite powder particles were prepared.They were heated into a puddle in the submerged arc welding conditions with solid wire as arc carriers,and so a series of high boron alloys were deposited on Q235A base metals.The effects of alloying elements such as Cr,V,Ti,and Nb on M₂B phases,and their abrasion resistance were investigated by optical microscopy（OM）,X-ray diffractometer（XRD）,scanning electron microscopy（SEM）as well as energy dispersive spectrometer（EDS）.Firstly,the effects of chromium content on the morphology of M₂B phases and abrasion resistance of FeCrB2CMn Si system alloys were investigated.The results indicate that,the matrix is made up of martensite and ferrite,and the hard phases consist of M₂B,M₃（C,B）,M₃B₄,etc.,in which M represents such element as Fe,Cr.With the increasing of chromium content,the primary M₂B phases in hardfacing alloys change from（Fe,Cr）₂B,whose characteristic index of diffraction peaks is equal to the ones of Fe₂B,to（Cr,Fe）₂B whose characteristic index of diffraction peaks is identical to the ones of Cr Fe B.Their micro-hardness average value rises up from 1026HV to 1622HV.For their abrasion resistance,the results of wear test show that the marked improvement at first attributes to the significant advancement of the micro-hardness of primary M₂B phases and the subsequent decrease in a narrow range is related to the reduction size of secondary M₂B phases.The analysis on worn morphology of hardfacing alloys shows that the dominating wear mechanism mode changes from micro-spalling to micro-cutting with the increasing of chromium content.Secondly,the effects of vanadium content on the morphology of the microstructure and abrasion resistance of FeCr8B4VCSi system alloys were investigated.The results indicate that,the matrix is made up of ferrite and martensite,and the hard phases consist of M₂B,M₃（B,C）or M₂₃（C,B）₆or M₂₃C₆,（Cr,Fe）₂B,VC,etc.For their abrasion resistance,the results of wear test show that wear mass loss are decreased markedly at first and then rises up with a narrow range.The analysis on worn morphology of hardfacing alloys shows that the dominating wear mechanism mode changes from fracture wetting induced by heavy plastic deformation into micro-cutting caused by minute plastic deformation.With the increasing of vanadium content,the explicit characteristics are the appearance of the structure in spider net or Chinese stamp shape and the precipitation of V₃B₂ phases.Then,the effects of titanium and boron content on the morphology of the microstructure and abrasion resistance of Fe V8Cr2B4Ti Si C system alloys were investigated.The results indicate that,with the increasing of titanium content,the eutectic of（α-Fe+（Fe,V,Cr）₂B）in square and spider shape appeare and the complex phases of（V,Ti）C are precipitated.With the increasing of boron content,the volume fraction of primary（Fe,Cr）₂B phases is adavanced up to at least 60%.The microhardness of bulky phases rises up from 1382HV to 1844HV and it is attributed to the appearance of V₃B₂phases.Finally,the effects of niobium content on the morphology of the microstructure and abrasion resistance of Fe V8Cr2B4Nb Si CMn system alloys were investigated.The results indicate that,the matrix is made up of ferrite,and the hard phases consist of（Fe,Cr）₂B,M₃B,Nb C,VC,etc.,in which M represents such element as Fe,Cr.With the increasing of niobium content,the crystal lattice detortion of（Fe,V,Cr）₂B phase get larger.VC phases nucleate at the cores of Nb C phases with the precipitation in adavance,and then grow up into a radiate shape surrounding Nb C phase with dot shape.