The Study On Microstructure And The Wear Resistance And Fatigue Performance Of High Nitrogen Martensite Stainless Bearing Steel

40Cr₁₅Mo₂VN as a new type of high nitrogen martensitic stainless bearings steel, its microstructure, sliding wear, rotating bending fatigue and contact fatigue were studied. The main conclusions are as follows.The microstructure of tested steel after final heat treatment consists of fine cryptocrystalline martensite, retained austenite and carbonitrides. The width of martensite lath ranges from 50 to 200nm. The volume fraction of retained austenite is 4.66%, and the thickness of the thin film of retained austenite ranges from 50 to 100nm. The types of precipitated phases are M₂₃C₆（≥250nm） and Cr₂（CN）（≈50nm）. Chain and dispersed state inclusion is in tested steel, and the probability of chain inclusion in view is about 10%. In addition, the components of inclusion are Al₂O₃ and CaO.In sliding wear tests, the friction coefficient decreases with the increasing of load and frequency, and the wear rate increases with the increasing of load and frequency. The PV value （PV=stress×linear velocity）, indicates the severity of the bearing condition. When the PV=1.27MPa-m/s, the wear mechanism is adhesive wear; 1.27<PF<1.65MPa-m/s, the wear rate increases obviously, and the wear mechanism is adhesive wear; 1.65≤PF<3.53MPa-m/s, with the increasing of the abrasive dust, wear rate increases slowly because the alleviated effect of abrasive dust layer. PF≥3.53MPa·m/s, the accelerated wear stage presents because of abrasive wear and plastic extrusion.In rotating bending test, the rotating bending fatigue strength of tested steel is 957MPa. Specimen fracture were mainly caused by the machining defect on the surface and subsurface inclusion. The crack initiation probability caused by inclusion is 82.4%, and the crack initiation probability caused by the machining defect on the surface is 17.6%. The diameter values of inclusion range from 14.3 to 36.3μm, and the distance values between inclusion and surface range from 12.2 to 224.6μm.In contact fatigue test, the rated contact fatigue life and the mid-value life are as follows:L10=0.97×107 times and L50=1.14×107 times. The failure modes of contact fatigue are the inclusion crack initiation and bigger carbide crack initiation, and the inclusion crack initiation is the main mode. In addition, the fatigue crack growth is usually along with carbides in the subsurface, which are about 2μm in diameter, and the distance of adjacent carbide is less than 5μm.