Fatigue property of ultra-long life of high strength 42CrMo zero-inclusion steel

The ultra-long fatigue properties of four high strength 42CrMo steels, two of commercial and two of zero-inclusion, produced by different heat treatment procedures are studied. The experimental results illustrate that in the regime of 10(6)-10(9) cyc, two commercial steels have no horizontal asymptote in fatigue S-N curves, so the conventional fatigue limit eliminates, but the fatigue limit of two zero-inclusion steels exists. SEM analysis shows the fatigue crack initiates from nonmetallic inclusion for commercial 42CrMo steels, and from surface of the matrix for two zero-inclusion steels. In the regime of 2 x 10(6)-10(9) cyc, it is very difficult to fracture for zero-inclusion steels, and the reliability of fatigue life is substantially improved.