Abstract
Ultrasonic fatigue tests were carried out for a low alloy steel, SFVQ1A, under stress ratios R = -1, -0.5 and 0 at a frequency of 20 kHz in order to investigate the effect of R on giga-cycle fatigue properties. The results showed that fatigue properties depended on the cyclic frequencies. Fatigue limits obtained by each R well corresponded to Gerber diagram. Peened specimens showed interior fracture over N = 10^6. However, no reduction in the fatigue strength was found due to the interior fracture. The fracture origins were complex type inclusions, which consists of Al_2O_3, MgO, MnS and CaS with the sizes ranging from 9.7 to 66.3 μm. Effect of inclusions were discussed in conjunction with the influence of cyclic frequency on the S-N curves.
