Effect Of Heat Treatment Process On Microstructure And Tribological Properties Of M50 Steel

Bearing is a typical mechanical component friction pair,and wear is a typical failure form in its operation.Bearing steel is an important factor affecting the stability,reliability and service life of bearings.Heat treatment process is to improve the bearing steel microstructure,mechanical and abrasion resistance of an important means,is an important process in bearing production,including tempering treatment can reduce internal stress,change the content of residual austenite,carbide morphology and dimension,the dimension stability of bearing and service performance has an important impact,Among them,tempering temperature and number of tempering are two important parameters in tempering treatment.Meanwhile,cryogenic treatment is also of great significance for energy saving and emission reduction.Therefore,this paper takes the state M50 bearing steel as the research object and conducts tempering and cryogenic treatment processes at different temperatures and times to study the influence of different heat treatment processes on the friction and wear properties of M50 bearing steel.By means of scanning electron microscopy(SEM),transmission electron microscopy(TEM),XRD and Rockwell hardness tester,the microstructure,phase and hardness of M50 steel samples after different heat treatment were characterized,and the optimal heat treatment process of M50 steel was determined.The results are as follows:Grain boundaries,undissolved carbides and acicular and lard martensite are obvious in quenched microstructure.When M50 steel is tempered at 550℃,the acicular carbide in martensite and its boundary increases with the increase of tempering times.The martensite peak increases with the number of tempering,while the residual austenite peak decreases and disappears with the number of tempering.The content of retained austenite decreases gradually,but it is not completely transformed into martensite.The hardness increased with the increase of tempering times,but the hardness decreased slightly after the fourth tempering.Friction and wear tests show that there are slender scratches on the friction surface of the sample after tempering for four times,and the accumulation of abrasive debris increases obviously.That is,three times tempering makes the wear resistance of M50 steel reach the best.Therefore,the optimal tempering times of M50 steel is three times.As the temperature of the tempering temperature is 150 ～ 650℃,the thickness of the plate is increased by the increase of the width of the horse’s body,and the amount of the residual austenic body is reduced,and the hardness value of the residual austenic body decreases,increases and decreases.At the time of the 550℃ return,the hardness is higher,mainly because of the precipitation of the small alloy carbide,which has the ability to improve the hardness of the hard horse,and the residual austenitic elements can be turned into the hard horse phase.Friction and wear tests show that the wear resistance of M50 steel increases first and then decreases with the increase of tempering temperature between 350℃ and650℃,and the wear resistance of M50 steel reaches the best when the tempering temperature is 550℃.The wear resistance of M50 steel is mainly caused by slight abrasive grain and slight oxidation wear mechanism,and the surface is smooth and the wear is light.The dispersed carbide carbide in the matrix can resist wear,and the high hardness also improves the wear resistance to a certain extent,that is,the best quenching and tempering heat treatment process is austenitizing at 1090℃ for 20 min+three times tempering at 550℃.The carbide particles with alloying composition precipitated on the sample matrix after quenching are uniformly dispersed and fine,and the wear resistance of the sample is improved compared with that of the sample after quenching +550℃ three times tempering.The optimal process sequence of quenching tempering and cryogenic combination is immediately cryogenic quenching after quenching and then tempering twice,which improves the hardness and wear resistance of samples again.The specific process is austenitizing at 1090℃ for 20 min+(-196℃ cryogenic 1 h)+ tempering at550℃ for 2 h×2.