Microstructure And Wear Resistance Of Hypereutectic Fe-Cr-C Alloy With Nano-Y₂O₃

With excellent wear resistance, the hypereutectic Fe-Cr-C hardfacing alloys havebeen widely applied to repair and remanufacture the work-pieces used at low stressabrasion conditions especially because its microstructure contains a large number ofprimary M7C3. The primary carbide (M7C3) can peel off from the surface of Fe-Cr-Chardfacing alloys when its size is large, which results in lowering wear resistance.Therefore, it is significant to improve the wear resistance of the hypereutectic Fe-Cr-Chardfacing alloys with large primary M7C3.The Fe-Cr-C flux-cored wires with different additions of nano-Y2O3were developedin this work and the Fe-Cr-C hardfacing and smelting alloy were made. Themicrostructure of nano-Y2O3on the hypereutectic Fe-Cr-C hardfacing alloys wasinvestigated. At the same time, the effectiveness of Y2O3as heterogeneous nuclei of theprimary M7C3was calculated with the misfit theory and the first principle calculation.Finally, the effect of different carbide’s size and different matrix structure onhypereutectic Fe-Cr-C hardfacing alloys was studied.The microstructures of the hardfacing alloy consist of the primary M(M=Cr, Fe)7C3carbide and eutectic structure (eutectic M7C3carbide+retained austenite and its product).With the increase of nano-Y2O3additives, the size of the primary M7C3is decreased. Theaverage size of primary M7C3carbide reaches the minimum (16μm) when the addition ofnano-Y2O3is2.54wt.%. At the same time, the two-dimensional lattice misfit betweenthe face (001) of Y2O3and face (001) of orthorhombic M7C3is6.76%. The interfacialenergy between Y2O3and M7C3is0.198J/m2. The effectiveness of Y2O3as heterogeneousnuclei of the primary M7C3is middle effective to refine the primary M7C3. The primaryand eutectic M7C3are both orthorhombic structures and they exist some defects such asdislocation and twin crystal.With the decrease of the average size of the primary M7C3(the increase ofnano-Y2O3additives), the hardness, compressive strength and wear resistance ofhypereutectic Fe-Cr-C hardfacing alloy can be improved. When the average size of primary M7C3carbide is16μm, the hardness is HRC58, the compressive strength is1980MPa and the18h mass loss is0.59mg/mm2. The predominant wear mechanism ofhardfacing alloys/bearing steel is adhesive wear+oxidation wear, and that of hardfacingalloys/WC is abrasive wear+oxidation wear.Ferrite, martensite and tempered martensite are obtained by annealing, quenchingand tempering. When the matrix microstructure of the hypereutectic Fe-Cr-C hardfacingalloy is ferrite, martensite and tempered martensite, the hardness is HRC43, HRC73andHRC58. the microhardness of eutectic structure is452HV,939HV and697HV，the18hmass loss is1.15mg/mm2,0.38mg/mm2,0.61mg/mm2. The predominant wear mechanismis micro-ploughing+micro-fracture, micro-cutting+micro-ploughing+micro-fractureand micro-ploughing+micro-cutting.