Fatigue behavior of 42CrMo steel and 40Cr in the very high cycle regime

摘要

The S-N curves of 42CrMo steel and 40Cr steel between 104 and 1010 cycles were obtained by ultrasonic fatigue testing at a frequency of 20kHz.The results show that the S-N curve of 42CrMo steel displays the characteristic of "the multi -stage type" and the S-N curve of 40Cr steel displays the characteristic of "continually decreasing type" up to 1010 cycles.Both steels exhibit no "fatigue limit" of conventional fatigue curve.The S-N curve under ultrasonic fatigue loading can be described with the equation of Basquin.The fatigue strength in 109 cycles has dropped by nearly 40% than that in 107 cycles.Compared to the S-N curve of 42CrMo and 40Cr steel,the results illustrate that the fatigue life of 42CrMo steel is much higher than that of 40Cr steel in ultra-high regime,the S-N curves of both steels are basically a coincidence in high-cycle stage,the S-N curve of 42CrMo steel is significantly delayed in ultra-high-cycle stage,Mo alloy element has no effect on the high-cycle fatigue property of steel,but Mo alloy element has an impact on the ultra-high cycle fatigue property of steel.As this result,the ultra-high cycle fatigue property of steels can be improved by adding Mo alloy element in the steel.The effect of Mo on the ultra-high cycle fatigue property of steels can be explained with the micro mechanism called "enrichment of interstitial atom".