Influence of elevated temperature on the very high cycle fatigue properties of bearing steels

The influence of temperature on the very high cycle fatigue properties of three high carbon chromium bearing steels (52100, 52100-VIM/VAR and M50-VIM/VAR) is investigated. Ultrasonic fatigue tests up to more than 1010 cycles are performed at 22 °C, 200 °C and 300 °C. At all temperatures, the dominant failure mechanism is interior defect-initiated cracking. Nonmetallic inclusions are the origin of fracture for 52100 and carbides for 52100-VIM/VAR and M50-VIM/VAR. The fatigue strength (fracture probability of 50% at 2×109 cycles) at 300°C decreases by 56-57% compared with 22 °C for both 52100 steels and by 41% for M50. 52100 steels soften at elevated temperature due to low tempering temperature, but M50 is thermally stable. The hardness decrease at elevated temperature is more pronounced for 52100 steels than for M50. The results are evaluated applying fracture mechanics principles. Based on the area-parameter model, an equation to predict the fatigue strength in the VHCF regime at different temperatures is proposed.