Study On Super Solid Solution Precipitation Behavior And Red Hardness Of Plasma Cladding Layer Of M2 High Speed Steel

M2 high-speed steel(W6Mo5Cr4V2)also has excellent hardness and wear resistance at high temperatures,and is widely used in cutting tools and other applications.With the rapid development of manufacturing,the red hardness and wear resistance of M2 high-speed steel have been improved.High requirements,the industry often uses surface modification,alloying,heat treatment and forging to improve the performance of M2 high speed steel.In this paper,plasma beam cladding technology is used to prepare NiCrCu and W6Mo5Cr4V2 coatings on the surface of M2 high-speed steel.The longitudinal section of the cladding layer of different processes has been tested for hardness gradient,structure analysis,XRD phase analysis,and the surface element distribution has been carried out by EDS composition.Analyze and compare the wear resistance and corrosion resistance of the cladding layer.The results show that: the cladding layer is metallurgically bonded to the base material,the interface is well bonded,and there are no obvious defects such as pores and scum.The main structure is equiaxed crystals and dendrites,and the alloy element content of the cladding layer is significantly higher than that of the base material.The elements are dissolved in the substrate under the action of plasma,and under rapid cooling,a super-solid solution layer with a much higher content of alloying elements than the substrate is formed,and in the subsequent heat treatment,it is precipitated in the form of a large amount of dispersed carbides.The cladding layer of NiCrCu coating mainly contains Fe-Ni,Cr3C2,W2 C,Mo2C,WC,VC,Cu and(Cr,Fe)7C3 phases.W2 C,Mo2C,WC,VC and Cr3C2 carbides tend to be The grain boundary region precipitates.In the cladding layer of W6Mo5Cr4V2 coating,carbides are mainly M2C-type carbides formed by elements such as W,Mo,Cr and V and C.The area where the cladding layer is in contact with the substrate is easy to form fibrous eutectic M2 C carbide due to its faster cooling rate.In the area close to the surface,the cooling rate of the M2 C type carbide is reduced.Precipitation.Because the cladding layer is rich in a large number of alloy elements added to the coating,after the cladding is completed,there will be a large amount of retained austenite in addition to the martensite.After tempering at 600°C,the martensite and retained austenite will precipitate A large number of dispersed alloy carbides can obtain a good secondary hardening effect,so that the cladding layer maintains high hardness,wear resistance and red hardness.After tempering at 600°C,the average hardness of the surface of the NiCrCu cladding layer is 935.57 HV.After holding at600°C for 4h,the average hardness of the surface layer remains 941.33 HV,and the red hardness is excellent.The NiCrCu cladding layer has a high hardnessstrengthening layer depth of 0.9mm,far exceeding other surface strengthening treatments.The wear test under 50 N load and the corrosion resistance test of 3.5%NaCl solution show that the NiCrCu cladding layer has excellent wear resistance and corrosion resistance.The average hardness of the surface layer of the W6Mo5Cr4V2 cladding layer is 936.47 HV.After heat preservation at 600°C for 4h and 600°C for4 h,the average hardness of the surface layer is still about 890 HV,and the depth of the high-hardness strengthening layer is 0.32 mm.When the mass ratio of SiC powder added to the W6Mo5Cr4V2 coating is 6:1,the depth of the cladding layer’s high-hardness strengthening layer is 0.32 mm,and the surface hardness of the cladding layer can be increased to 1200 HV.After heat preservation at 600°C for 4h,the cladding layer surface The average hardness is still around 920 HV,and the hardness and red hardness are excellent.The cladding layer with this ratio has a lower friction coefficient and better wear resistance.When the weight ratio of Al2O3 powder added to the W6Mo5Cr4V2 coating is 1:6,the depth of the cladding layer’s high-hardness strengthening layer is 0.29 mm,and the average hardness of the cladding layer surface is 930.59 HV.After heat preservation at 600℃for 4h,the cladding layer surface is average The hardness is 870.48 HV.After the NiCrCu cladding layer is tempered at 600℃,the content of alloying elements of Ni,Cr and Cu gradually decreases with the distance.The rapid solidification after the end of the ion arc causes the non-equilibrium solidification of the cladding layer and the resistance and electromagnetic force of the cathode jet There will be deviations in the alloying element content between the cladding layer regions,especially the carbide-forming elements W,Mo,V and C are unevenly distributed in the longitudinal direction of the cladding layer.Different from the NiCrCu cladding layer,the W6Mo5Cr4V2 cladding layer adds a large amount of W,Mo,Cr and V alloy elements.The alloy elements are melted into the base material under the action of plasma beam and electromagnetic force.After rapid cooling,they are formed.Under equilibrium cooling conditions,the alloying elements are too late to diffuse,and a large amount of solid dissolves in the surface of the cladding layer,causing the content of surface alloying elements to increase.When the mass ratio of SiC powder added to the W6Mo5Cr4V2 coating is 6:1,the surface of the cladding layer contains a lot of Si elements.When the weight ratio of Al2O3 powder added to the W6Mo5Cr4V2 coating is 1:6,the surface of the cladding layer contains a lot of Al and O elements.