Effects Of V/Mo/W Alloying Elements On Microstructure And Abrasion Resistance Of Fe-B System Hardfacing Alloys

As a new type of wear-resistant alloy system,high-boron alloy that exhibit relatively good self-deoxidation and formability,is widely researched and applied.Compared to high-chromium alloy,more hard phases such as borides are appeared in such a system alloy,but it is much more brittle in nature and is unfavorable for improving their abrasion resistance.In order to improve the toughness of the hardfacing alloy,the main wear-resistant of Fe₂B phase in those high boron alloys are subjected to complex alloying treatment to enhance their toughness.At the same time,an appropriate amount of carbon-controlling components,such as strong carbide formation element V,were added to obtain in-situ precipitation of MC-type carbides for reducing the number of M₃（C,B）-type eutectic phases.Therefore,the toughness of high-boron alloys can be improved.High boron alloy was prepared by submerged arc welding（SAW）method of composite powder particles（CPP）and H08A solid welding wire.The main wear-resistant phase of Fe₂B is treated with complex alloying elements,such as Cr,Mo,W,V,etc.The microstructure and properties of this series of high boron alloys were analyzed and characterized by using metallographic microscopy（OM）,X-ray diffractometer（XRD）,scanning electron microscopy（SEM）and energy spectrometer（EDS）,microhardness and macrohardness testing as well as abrasion resistance testing.The microstructure of Fe-Cr-B-V high boron alloys is composed ofα-Fe,M₂B,M₃（B,C）,VC and V₃B₂,in which M represents Fe,Cr and other alloying elements.With the increaseof vanadium content,the main wear-resistant phase of Fe₂B transforms from（Fe,Cr）₂B to（Fe,Cr,V）₂B,and a new type boride of V₃B₂is precipitated from them.The average micro-hardness of hardfacing alloys are more than 1000HV_0.2.The average micro-hardness of V₃B₂can reach 1716.19HV_0.2,which is much higher than about 1100-1300HV_0.2of M₂B phase.The abrasion resistance of high boron alloys firstly increases up due to the successive primary precipitation of（Fe,Cr,V）₂B and VC,and then decreases down due to the crack of the main wear resistant phases and the exfoliation of the eutectic.The microstructure of Fe-B-Mo high boron alloys is composed ofα-Fe,Fe₂B,Fe Mo₂B₂and M₃（B,C）.With the increase of molybdenum content,white dot-like phases are precipitated,and their number gradually increases.Then they gradually appear in white block-like shape.Under backscattering conditions,it is white,which is obviously different from the gray image of the M₂B phase.XRD,EDS and microhardness tests,combining with the added components,confirm that the white phase is Fe Mo₂B₂.With the increase of molybdenum content,the microhardness and macrohardness of high boron alloys increase simultaneously.At 8.91%Mo,the macrohardness of high boron alloy is the highest mainly due to the precipitation of Fe Mo₂B₂phase,which advances the microhardness and Rockwell hardness of high boron hardfacing alloy.With the increase of molybdenum content,the wear mass loss of high boron alloys firstly decreases and then increases slightly.At 8.91%Mo,the wear mass loss is 6.2 mg,and its abrasion resistance is the best.The wear mechanism is firstly microcutting,and followed by a combination of microcutting and micro exfoliation,and then followed by the dominant micro exfoliation.The microstructure of Fe-B-Cr-V-W high boron alloys is mainly composed ofα-Fe,M₂B,Fe W₂B₂and M₃（B,C）.With the addition of WC,the main wear resistance of（Fe,Cr,V）₂B phase transforms into（Fe,Cr,V,W）₂B,in which a certain amount of W is dissolved.The microhardness of those bulk hard phases increases at first,then decreases and the highest microhardness is 1398.39HV_0.2.At 10.28%W,the average microhardness of irregular block-like phase is 1716.38HV_0.2,which is much higher than that of actual M₂B phase.The results of backscattered scanning electron microscope,EDS energy spectrum and XRD phase composition characterization,showe that a new white bulk-like phase is precipitated when the content is 10.28%W.The backscattered electron microscope image shows its morphology and image characteristics are similar to Fe Mo₂B₂and can be confirmed as Fe W₂B₂combined with energy spectrum composition analysis.The Rockwell hardness of high boron hardfacing alloys gradually increases at first,then decreases slightly and finally increases sharply.The overall wear mass loss shows a trend of first increasing,then decreasing and then increasing.When 5.14%W is added,the wear mass loss is the lowest with 30.24 mg,and its abrasion resistance is the best.The wear mechanism is mainly microcutting firstly,then mainly micro exfoliation,and finally microcutting with a small amount of exfoliation,which indicates that the toughness of high boron alloys is improved with the addition of suitable W content.