Development of a Method for Corrosion Fatigue Life Prediction of Structurally Loaded Bearing Steels

Abstract

In this study a simplified method to predict corrosion fatigue properties for the Cr-alloyed bearing steel 100CrMnMo8 is proposed. With this method corrosion pits are assumed to act as defects, which could initiate fatigue cracks. A linear elastic fracture mechanics (LEFM) model was used to evaluate the critical corrosion pit size when mechanical fatigue crack propagation occurred. The unknown parameters in the prediction model were corrosion pit growth rate and the threshold stress intensity factor (ΔKth) for fatigue crack growth. In this study corrosion pit growth rate was determined for 100CrMnMo8 in a chloride-containing water solution by aid of a statistical method. Corrosion pit growth rate was found to be approximately proportional to the square root of time. The time dependence of corrosion pit growth led also to the conclusion that characterization of corrosion fatigue strength must be made with respect to both exposure time in a corrosive environment and the number of cycles to a runout level. ΔKth for fatigue crack growth was estimated from interrupted rotating bending fatigue tests in the corrosive environment in question. Since only the corrosion pit growth rate and ΔKth are needed as input in the proposed corrosion fatigue prediction model, much effort can be saved since this can reduce the amount of fatigue testing. Corrosion pit growth rate can be determined on unloaded test coupons in the desired environment. Hence, for materials selection, exposure tests followed by a corrosion pit size analysis can indicate the corrosion fatigue performance in a given environment.