Study On Microstructure And Wear Resistance Of M2 High Speed Steel By Selective Electron Beam Melting

As a critical component of industrial machine tools,cutting tools play a vital role in determining the core competitiveness of the manufacturing industry.As such,they require high precision,efficiency,and reliability.M2,a type of high-speed steel,is a valuable material in the production of cutting tools due to its exceptional hardness,impressive red hardness,and robust wear resistance.Additive manufacturing technology based on the concept of“discrete+stacking”offers many advantages such as rapid design and formation of complex parts.Its rapid solidification characteristics promote the formation of fine tissues,including submicron cell structures and carbides,making it one of the most competitive preparation technologies for precision cutting tools.The Selective Electron Beam Melting（SEBM）technology uses a unique powder bed insulation process that effectively reduces residual stress caused by rapid cooling.The implementation of this process mitigates the possibility of defects,such as cracks,and facilitates the stable formation of steels containing medium to high levels of carbon.The defect density（such as pores and unmelted powder）and microstructure of materials formed through SEBM are influenced by the melting and solidification process,as well as the thermal history determined by preheating temperature and scanning parameters.These factors ultimately determine the service performance of the material.Therefore,this paper presents a systematic investigation of the effect of different scanning parameters（electron beam current and scanning speed）and two powder bed preheating temperatures on the density,microstructure,hardness,compressibility,and friction and wear properties of formed M2 high speed steel.Investigated the impact of scanning parameters and powder bed preheating temperature on the quality of M2 high-speed steel produced via SEBM.Results showed that the density of the formed parts initially increased with the volume energy density（VED）,then stabilized,and eventually decreased gradually.if the energy density VED is too small,defects like unmelted powder and poorly melted areas may occur,while if it is too large,keyhole defects may occur.Moreover,increasing the powder bed preheating temperature from 750℃to 820℃significantly enhances the relative density of M2 high speed steel parts.Increasing the preheating temperature of the powder bed in the M2 high-speed steel formation process has a positive impact on the uniformity and density of the structure of the formed parts.This is due to the reduction of temperature gradient,elimination of thermal stress,and decrease in the formation of defects such as cracks.Optimal process parameters for achieving high surface finish,low internal defects,and high density of 99.7%in M2 high speed steel are an energy density of 43.6 J/mm³ and a powder bed preheating temperature of 820℃.Investigated the impact of process parameters on the microstructure and carbide structure of M2 high speed steel formed by SEBM.The findings indicate that SEBM-formed M2 high speed steel consists ofα-Fe phase,carbide precipitate phase,and a small amount of retained austenite phase.The microstructure of M2 high speed steel parts is characterized by cellular grains,with an average grain size of approximately 2⁵μm.The crystal texture of the M2 high speed steel formed through in-situ heat treatment process and high alloy content is not easily noticeable.The carbide types present are feathery M2C,fishbone M6C,and irregular massive MC,which are relatively small in size.The size of carbides,as observed through TEM,is approximately 20⁶0 nm and dispersed throughout the matrix.Investigated the impact of process parameters on the hardness,compressive properties,and frictional wear properties of M2 high speed steel formed through SEBM.The fine grain structure and martensitic phase of M2 high speed steel contribute to its high hardness.The results showed that the M2 high speed steel formed parts had a hardness of 70.11 HRC and a compressive strength of 2731 MPa when the energy density was 43.6 J/mm³ and the powder bed preheating temperature was 820°C.As the powder bed preheating temperature increases,the fracture type of M2 high speed steel changes,resulting in improved brittleness.The optimal process parameters were found to be an energy density of 43.6 J/mm³ and a powder bed preheating temperature of 820°C.Under these conditions,the M2 high speed steel formed part exhibited the best wear resistance,with an average friction coefficient of 0.4749 at room temperature and a wear rate of3.58±0.36×10^-5mm³N^-1m^-1.When M2 high speed steel formed parts experience frictional wear,the frictional vice causes grinding chips to form,as well as plough grooves and a significant amount of continuous flat black oxide film.This film plays a lubricating role,which weakens abrasive particles and ultimately improves the wear resistance of M2 high speed steel.