Rotating bending fatigue behavior of medium carbon Cr and W nitriding bearing steel

Abstract

Aiming at the problem that the failure mode of bearing steels is mainly fatigue failure, RBF (rotating bending fatigue) test of medium carbon Cr and W nitriding bearing steel and analysis are conducted for the medium carbon Cr and W nitriding bearing steel. The microstructure of the bearing steel after hardening and tempering (880 °C+540 °C), the fatigue fracture after the RBF test and the effect of nitriding are analyzed. The ultimate strength influencing model of non-metallic inclusions and size on medium carbon Cr and W nitriding bearing steel RBF is established. The results of experiments show that the microstructure of the test steel after hardening and tempering is tempered sorbite, the main precipitations are M6C and M23C6 carbides, the mechanical properties are excellent and its fatigue limit is 729 MPa. Fatigue source are divided into surface defect cracking and the internal non-metallic inclusions cracking. Surface defects include the pits after the falling of non-metallic inclusions and the machining marks. Non-metallic inclusions are mainly magnesium aluminates. The bearing steel is kept at a constant temperature of 560 °C for 25 hours in NH3 nitrogen atmosphere, and the nitriding layer thickness is more than 360 μm, showing the nitriding process is suitable. The research has some reference value for the development of the medium carbon Cr and W nitriding bearing steel and the improvement of fatigue performance.

Keywords

• black metal and its alloys seepage
• nitrided bearing steel
• rotating bending fatigue
• surface defects
• non-metallic inclusions