Fatigue crack propagation estimation of SUS 630 shaft based on fracture surface analysis under pitting corrosion condition

For the purpose of reducing the diameter and the weight of the propulsion shaft of a high-speed craft, the high strength alloy is normally used. In general, the stainless SUS 630 is selected as the shafting material. While pitting corrosion existed in such kind material can be a problem to considerably reduce the fatigue life of the shaft. In this paper, the prediction model of the fatigue crack propagation behavior of SUS 630 in accordance with the Paris law has been established. Together with the rotating bending fatigue tests with various loads on shaft specimens in various extent of pitting corrosion conditions and the fatigue fracture surface analyses through the scanning electron microscope (SEM), the material the coefficient n is 2.71 and C is 1.63E−14 for 450 N/mm2, n is 3.25 and C is 8.96E−16 for 400 N/mm2, and n is 3.04 and C is 3.60E−15 for 350 N/mm2 based on the range of ΔK is from 26 to 46 (MPa √m). In addition, the fatigue lifetime of SUS 630 shaft under various extent of pitting corrosion condition is found to be in a range of only 2.5–27% of that of the uncorroded condition.