Research On Microstructure And Wear Resistance Of Multi-elements Alloy Strengthened High Chromium Alloy Hardfacing Layer

Nowadays the carbides are mostly used as hard phase of wear-resistant materials,the higher the carbon content in the wear-resistant materials, the better resistance towear, but the high carbon content will cause weld defects and poor weldability. Basedon the very little difference between nitrogen and carbon atom radius,92pm and91.4pm respectively, nitrogen atom can be used as gap-atom elements as carbon atom.Besides, nitrogen atom become active under high temperature and can formcarbonitrides with carbon atom while combining with other alloy elements such aschromium, vanadium, titanium, zirconium, and molybdenum. Many properties ofsteels are improved by precipitated carbonitride and carbides through the metallurgicalreaction, including hardness, toughness, creep resistance, wear resistance andcorrosion. Therefore, hardfacing layer can be modified by nitrogen alloyingmodification in the process of overlaying welding. Precipitated size smaller carbidesand carbonitrides promote the microstructure refinement and precipitationstrengthening effect in the hardfacing layer. Nitrogen alloying hardfacing can becomea new way to improve the comprehensive performance of surfacing welding alloy.The paper addresses two methods of overlaying welding: welding wire-alloypowder surfacing and welding wire-alloy power block surfacing. Alloy powder wasdeposited on the surface of Q235steel by the methods respectively. Themicrostructures and wear resistance of two kinds of surfacing layers werecharacterized by optical microscope, scanning electron microscope, and wear tester.The results show that the microstructure of welding wire-alloy power block surfacinglayers mainly consists of austenite and carbide. With this technology, not only goodwelding technological properties, stable arc, less spatter, good slag, forming a goodweld were gained; but also good hardness and wear resistance. The Rockwell hardness and wear resistance of the surface using welding wire-alloy power block were1.25times and1.52times higher than those of wire-alloy power respectively.The hardfacing alloys with different single element alloy powder blocks weredeposited on Q235carbon steel substrate using gas metal arc welding （GMAW） underdirect current with a reverse polarity. The microstructures, wear resistance andnormalizing technique of hardfacing alloy layer were discussesed and analysed. Thegrain of hardfacing alloy layer was refined with the single microalloying elementscontent, such as Ti, V, Zr. The hardness and wear resistance of hardfacing layer wereincreased with the increaseing of alloy elements hardfacing layer. The microstructureof Fe-Cr-C-Ti surfacing alloy layers mainly consist of （Cr,Fe）7C3, TiC carbides,Ti_x（C,N）_y carbonitrides and α-Fe （C0.14Fe1.86and C0.12Fe1.88martensite）（BCT） besideslittle amount of retained CFe15.1austenite （Fe-C）（FCC） eutectics matrix. The hardnessincreases rapidly with titanium content increasing, hardfacing layer hardness valuereached60HRC when it is less than3%（wt%, similarly hereafter）, on the contrary,wear loss of the hardfacing layers decrease with increasing of titanium in thehardfacing layer.The microstructure, hardness and wear resistance of high chromium alloyhardfacing layer with single element, such as zirconium, vanadium, titanium andaluminum, were analyzed after960℃normalizing heat treatment. The results showthat lath and acicular martensite content of all alloys surfacing layer were increasedsignificantly with increasing alloy element content. The second phase particles weredispersed in the martensite matrix, which strengthening the strength of hardfacingalloy layer. So the hardness of hardfacing alloy layer can be improved by10%¹00%,the wear loss decreased obviously.Fe-Cr-C-Ti-Zr-V multi-alloy hardfacing layer with different vanadium contentwere obtained using gas metal arc welding （GMAW） under direct current with areverse polarity. The microstructure, hardness and wear resistance of high chromiumalloy hardfacing layer with alloy element, such as zirconium, vanadium, titanium andaluminum, were characterized by optical microscope（OM）, x-ray diffraction（XRD）,scanning electron microscope（SEM）, energy dispersive X-ray analysis（EDS）,Macroscopic hardness meter, and spectrometer. It is distinct that the high qualitymetallurgical bonding of substrate and deposited layer was obtained by metallurgicalreaction during gas metal arc welding （GMAW） process. The results show that themicrostructure of Fe-Cr-C-Ti-Zr-V multi-alloy hardfacing layers mainly consist of acicular martensite, lath martensite, retained austenite and M₇C₃carbides, and a largenumber of titanium-vanadium-zirconium carbonitride composite particles evenlydistributed between the martensite structures. The Rockwell hardness of Fe-Cr-C-Ti-Zr-V multi-alloy surfacing layer changes between53HRC and56HRC with theincreaseing the vanadium content. Though the Rockwell hardness value of Fe-Cr-C-Ti-Zr-V multi-alloy hardfacing layers when Vanadium content changes between1.0%and1.5%lower than the standard sample DH621, its relative wear resistance is1.34timesthe standard sample DH621. The carbide and carbonitride hard particles, which evenlydistributed in the Fe-Cr-CV-Ti-Zr multi-alloy hardfacing layers, can play the role ofthe wear-resistant skeleton in the wear process. The hard particles and matrix goodmatching effectively block grinding grain to hardfacing layer of micro cutting wear, soas to improve the wear resistance of hardfacing layer.