Effect Of Cryogenic Treatment On Mechanic Properties And Friction And Wear Mechanism On High Speed Steel

The mech&iic characteristics and tribological behaviors of treated and untreated W6Mo5Cr4V2(M2) high speed steel at room temperature and high temperature is investigated. The result shows that the room temperature hardness of M2 high speed steel increases by l.l-l.5HRC and red hardness by 1.3-2.OHRC. Suited cryogenic treatment can抰 reduce impact toughness. The impact toughness maximum belongs to cryogenic treating at long time. In wearing, the exfoliation is big masses for untreated samples and little pieces for treated, the exfoliated speed of untreated samples is more quick than treated. The antiwear ability of treated samples is good, particularly at pressure of 1.5 Mpa~ speed of 0.5 mIs~ room temperature. But when friction couple is 6OSi2Mn or 9SiCr, the wear-resistance of treated samples is less than untreated. FeC phase is discovered on the wear surface of treated samples at high temperature wearing by XRD, while not discovered under other conditions. It is concluded that FeC is precipitated at high temperature wearing. It is worked out that the c/a ratio of martensite and carbon content of retained austenite of treated M2 d is smaller than untreated, it is shown that a small amount of carbon comes from retained austenite. It is observed that the twin size of untreated martensite is 20-7Onm and of treated martensite is 1 0-2Onm using TEM. The fore is transformation twins while the behind is deformated twins. The tiny carbide participate in treated martensite twins, size 6-1 Onm, form in graininess or short-stick. Cryogenic treatment can increase hardness because cryogenic treatment make a part of retained austenite become martensite and carbide participating strength. The martensite c/a ratio decreasing and retained austenite state changing counteract toughness loss of retained austenite transformation. Scattered tiny carbide can improve antiwear ability. Hardness and plasticity . toughness are better, the wear-resistance of the material is better. So cryogenic treatment can improve wear-resistance.