Study On Microstructure And Properties Of Cladding Layer On Inner Wall Of Hydraulic Support Cylinder

With the increasing intelligence of coal mining and the increasing depth of mining,the service environment of coal mining equipment is becoming more and more harsh.The corrosion and wear failure of the inner wall of hydraulic support cylinders are widely concerned,and the strengthening,protection and repair of the inner wall of the cylinder have become the research focus in this field.In this paper,copper alloy cladding layer,austenitic stainless steel cladding layer and TiC-reinforced austenitic stain less steel cladding layer were prepared on the surface of 27SiMn steel for hydraulic cylinder by arc cladding and laser cladding technology respectively to strengthen the inner wall of hydraulic cylinder.The microstructure and corrosion wear properties of the arc cladding layer of three copper alloys were compared and analyzed;the effects of scanning speed and TiC particle addition on the microstructure and corrosion wear behavior of laser cladding layer of austenitic stainless steel were studied;the effects of 200℃ preheating and 420℃ post heat treatment on the microstructure and mechanical properties of laser cladding layer and substrate heat affected zone were discussed.The main conclusions of this paper are as follows:(1)The three copper alloy arc cladding layers mainly consist of α-Cu matrix phase,dendritic κ-AIFe3 and a small amount of spherical y-Fe phase.The microstructure of the Ni-rich X2 cladding layer is more uniformly distributed and has the best corrosion resistance;the κ-phase in the Al and Zn-rich X3 cladding layer increases and the grains become coarser,which has the worst corrosion resistance but the best wear resistance.The Al and Fe in the three cladding layers corrode before the Cu elements,and the wear mechanism under the emulsion lubrication is abrasive wear.(2)The phase composition of laser cladding stainless steel cladding layer is austenite,and the austenite grain morphology from the fusion zone to the surface of cladding layer is in the order of planar crystals-cytosolic crystals-columnar dendrites and equiaxed dendrites.Increasing the scanning speed and preheating or post heat treatment can significantly improve the corrosion and wear resistance of the cladding layer.After electrochemical corrosion in 3.5%NaCl solution,uniformly distributed pitting pits appear in the cladding layer,and its microstructure is honeycomb.The cladding layer exhibits adhesive wear and abrasive wear under dry friction conditions,and abrasive wear under emulsion lubrication conditions.The corrosion and wear performance of the laser cladding layer of austenitic stainless steel is significantly better than that of the arc cladding copper layer.(3)The microstructure of heat affected zone of laser cladding 27SiMn substrate is composed of martensite,bainite,ferrite and pearlite,with more martensite content near the fusion zone and more ferrite and pearlite content near the base material.As the scanning speed increases,the heat affected zone width becomes narrower,the martensite content increases and the hardness increases.When the scanning speed is 7 mm/s,the tensile strength and elongation of the cladding sample are the largest,and the impact toughness is 60.28%lower than that of 27SiMn substrate.(4)The martensite content in the heat affected zone of the substrate preheated at 200℃ is significantly reduced,the hardness is significantly reduced,and the tensile strength is improved.After the cladding specimens were annealed at 420℃,the heat affected zone is tempered brittleness,the hardness decreased obviously,and the tensile strength and impact toughness increased by 6.07%and 42.92%,respectively.(5)The microstructure of TiC-reinforced austenitic stainless steel composite cladding layer is mainly composed of austenite,TiC and a small amount of eutectic.With the increase of TiC content,the crystal shape of TiC changes from petal-like to massive and sphere-like;the corrosion resistance of the cladding layer decreases first and then increases,which is controlled by the amount of TiC melting and the degree of intergranular corrosion caused by it.The addition of TiC improves the hardness and wear resistance of the cladding layer,and the wear rates of 20-TiC cladding layer under dry friction and emulsion lubrication are reduced by 76.34%and 89.49%respectively.60-TiC cladding layer under dry friction is subjected to adhesive wear,and under emulsion lubrication is subjected to abrasive wear,and the wear resistance is significantly improved compared with that under dry friction.