Study On Microstructure And Wear Resistance Of H13 Steel By Laser Surface Strengthening And Cladding

H13(4Cr5Mo Si V1)has high thermal strength and hardness,good abrasion resistance and toughnessunder medium temperature,good cold and hot fatigue resistance,which can be widely suitable for manufacturing precision forging die,hot extrusion die,mandrel die and casting mold.The failure of mould starts from the surface.The service life can be extended effectively by improving the surface microstructure and mechanical properties.In this paper,laser melting solidification and Co-based power,Ni-based power laser cladding repairing were applied to the surface of H13 die steel with a 5 k Wpower carbon dioxide flow transverse flow transverse laser system.Stellite-6,St6+5%WC,St6+5%WC+1%RE,St6+2.5%WC+1%RE,St6+7.5%WC+1%RE,St6+10%WC+1%REcobalt based self-fluxingpowders were employed to enhance the H13 steel surface.The laser cladding nickel-based cladding layer includes Ni45,Ni45 + 5% WC,Ni45 + 5% WC +1% RE and Ni60 AA,Ni60AA + 5% WC,Ni60 AA + 5% WC + 1% RE.The microstructure,distribution of elements and phases etc.of composite coatings were studied by optical microscope(OM),scanning electron microscope(SEM)and X-ray diffraction(XRD).The micro-hardness and the wear-resisting property of coatings were studied by micro-hardness tester and friction wear testing machine.The following conclusions can be deserved:(1)The microstructure of H13 steel after laser melting solidification from the surface to the center can be divided into three areas: dendrite,the cellular crystal and martensite.The microstructure of high temperature tempering zone is mainly composed of coarse martensite and little of retained austenite.There is no new phase in addition to the phase in the matrix after laser quenching.The depth of the hardening layer is about 1.1mmand the maximum hardness of the hardening layer is 746HV0.2 after laser quenching.The relative wear resistance also has a larger increase.(2)The analysis shows that a metallurgical combination has been formed between the laser cladding layer and substrate.The phases of all cladding coatings are composed of ?-Co solid solutions as matrix phase and(Mn,Cr)7C3,Cr23C6,Co CX as strengthening phase.The phases composition of St6+5%WC and St6+5%WC+1%RE also containing Co6W6 C,WCandWC1-X.The micro-hardness of St6-based cladding is between 560 HV0.2and 710 HV0.2.The wear-resisting performance of the four cladding layers from high to low in turn is St6+7.5%WC+1%RE,St6+5%WC+1%RE,St6+2.5%WC+1%RE,St6,St6+10%WC+1%RE,H13 steel under the same testing conditions.(3)The phases in Ni45-based cladding layer are mainly consisted of ?-Ni dendrite and Fe Ni3,C6(Cr,Co,Ni)23,Mn23C6 as reinforced phase.The hardness of Ni45-based cladding layer is between 525 HV0.2 and 550HV0.2.The wear resistance of Ni45 based cladding layer is also higher than H13 steel.The wear mechanism is given priority to abrasive wear and peeling wear rather than serious wear.Abrasion resistance increased significantly after the WC added.(4)The microstructure of Ni60AA-based cladding layer is ultra-fine network eutectic in ?-Nisolid solution.The cladding layer is more sensitive to the crack.The cracks and pores are reduced after adding rare earth elements.The hardness and wear resistance of Ni60AA-based cladding layer have greatly improved than the matrix.The microhardness of Ni60 AA cladding(750HV0.2~800HV0.2)is about 1.78 times as much as the matrix.The microhardness of Ni60 AA + 5% WC + 1% RE cladding layer(800 HV0.2~900 HV0.2)is about twice as much as the matrix.