Effect Of Preparation Technology On Microstructure And Properties Of M2 High Speed Steel Heat Treatment

M2 high speed steel is a high carbon,high alloy and high wear resistant steel that has been widely used as a material for the preparation of hot roll surfaces and various hard tools.For M2 high-speed steel,it is generally necessary to optimize heat treatment process to control the morphology and distribution of martensite and hard carbide in the structure to achieve a good hardness and toughness.In this paper,combined with the main production technology of M2 high-speed steel available in the market,the heat treatment microstructure and hardness of M2 high-speed steel prepared by three different methods of hot rolling,spray forming and laser remelting are compared and the microstructure of M2high speed steel is prepared by different methods.The mechanism and distinguishing characteristics of phase structure formation provide experimental basis for enterprises to choose the supply or processing mode of M2 high-speed steel on the market.The solidified structure of the M2 high speed steel prepared by the conventional smelting method has coarse mesh eutectic carbides M₂C and M₆C.High-temperature hot rolling can promote the melting,fracture and transformation of the meshed M₂C into MC and M₆C.High-temperature hot rolling can cause the lamellar M2C to dissolve,break,and transform into finely dispersed MC and M6C.Hot-rolled annealing M2 high-speed steel optimal quenching and tempering heat treatment process is 1170°C quenching and three times tempering at 530°C,each tempering time is one hour,the structure is tempered martensite,M₆C and MC,the maximum hardness of tempering is about 825 HV_0.5,after tempering,the carbide size is 2.92-3.40μm,and the size distribution is uneven.The solidification structure of the spray-deposited M2 high speed steel is a fine martensite matrix and a network carbide.However,since the formation process of the deposited blank is a layered accumulation of the liquid phase,the inert jet stream cannot escape in time,which may cause certain pores and loose defects to form in the liquid layer between the layer and the layer in the deposited billet.The high temperature hot forging annealing treatment can completely eliminate the deposition.The above solidification defects in the billet.The best quenching and tempering process of spray-deposited samples after hot forging annealing is 1170°C quenching and three times tempering at 530°C,each tempering time is one hour,the maximum tempering hardness is about 841 HV_0.5,and the microstructure is tempered martensite,M₆C and MC.The finely distributed fine M₆C and MC carbides have a carbide grain size of about 1.21-1.73μm.Compared to hot rolling techniques,spray deposited M2 high speed steel has a higher hardness,finer and more dispersed carbide morphology and size.Spray-deposited M2 high-speed steel surface for laser remelting can obtain finer microstructure and carbide size.The remelted layer can be quenched directly after tempering at 560°C for maximum hardness of about 850 HV_0.5,slightly higher than spray deposition and Hot rolled M2 high speed steel has the highest hardness.However,since the remelted layer is not quenched,the main carbide type of the tempered structure is M₂C,which is different from the main types of hot rolled and spray deposited M2 high speed steel tempered carbides M₆C and MC.In this study,the phase structure and microstructure of the remelted layer prepared by four laser process parameters are basically the same,and the tempering hardness is not much different,indicating that the laser remelting of M2 high speed steel surface has a wide range of laser process selection.