A Research On The Nitriding Layer’s Microstructure And The Performance Of Fatigue With Friction And Wearing Of High Performance Nitrided Bearing Steel

In this paper, vacuum induction melting of 0.30-C-Cr-W novel nitriding bearing steel with high-performance as experimental material to study each phase transition temperature and the the effect of temperature on quenching and tempering treatment. To study the physical properties of after quenching and tempering treatment and its effect on the use and to study the mechanical properties that are strengthening and toughening mechanism of the steel when it change from the tempered to nitriding. To study the structure and properties of nitrided layer after nitriding and to study the rotating bending fatigue and fracture mechanism after nitriding. To study the friction and wear properties and antifriction and wear resistance mechanism after nitriding.The Ac3, Ac1, Ms, Mf temperatures were 860 ℃, 810 ℃, 415 ℃, 220 ℃ of experiments steel and after quenching of 870 ℃ will get martensite completely. The dates of the elastic modulus and the thermal expansion coefficient after quenching and tempering show that the experimental steel has a good performance of maintainning dimensional stability. Magnetic properties of quenching and tempering state show that the steel with high saturation magnetization and low coercivity. Experiments steel is soft magnetic and easy to demagnetization.The contribution of the grain, the dislocation,the solid solution of alloying elements,the second phase, which belog to the experiments steel nitrogen after nitride, for the strength were 221 MPa, 147 MPa, 251 MPa, 424 MPa. The main effect of second phase for strength is by the fine dispersed M3 C. From quenching to nitriding, the ferrites become broaden and the decreased of dislocation density and the solution of alloying elements of the experimental steel core part are main reasons for the increase of plasticity and toughness. The decreased of dislocation density and solid solution of alloying elements are main reasons for the fall of hardness. The compound layer after nitriding is the nanoparticles VN reinforced γ`-Fe4 N phase. The compound layer and the diffusion layers are inlaid, which with a good combining.The rotating bending fatigue strength of the experiment steel after nitriding is 850 MPa. The fracture modes are internal inclusion crack and surface defects crack. We can improve the fatigue life by 2 to 3 magnitude order on the basis of 104 to 106 if we improve the uniformity of stress and surface microstructure. We can improve the fatigue life by one magnitude order at the least on the basis of 106 to 107 if we control the internal inclusions reach to below 20.75μm.The nitrided layer after nitriding can effectively reduce the friction coefficient. The experiments of double crusher frictional wear show that: whether or not exists a lubrication condition, nitrided layer can reduce the friction coefficient by 28% to 54%. Nitrided layer is conducive to keep the oil and dispersing sliding friction between the nitrided layer and reducing effect of the seize occlusion.