Statistical analysis of the effect of lead-bismuth eutectic on fatigue resistance of 316L

Abstract

Environments like liquid lead-bismuth eutectic (LBE) or air can have an effect on the fatigue resistance of nuclear materials such as ferritic-martensitic and austenitic stainless steels if compared to vacuum. This paper provides a quantitative assessment, supported by statistical tools, of the effects of LBE and air on the fatigue life. Low cycle fatigue tests were performed on cylindrical samples of 316L in three environments: air, vacuum, and LBE (oxygen concentration <10–5 wt% and temperature 350 °C), and the experimental data was fitted to obtain life prediction models. The independent modelling of three separate environment datasets via the Langer equation showed that the slope of the fatigue curve is comparable among the three environments. In all models the sample standard deviation was found to be of the same order, suggesting that variations in microstructure and composition of 316L among samples have a similar impact in all three environments. A simplified model was then proposed considering vacuum as the reference condition, and assessing the effect of air and LBE as a quotient of lifetime in vacuum and air or lead-bismuth eutectic respectively. Analysis of the fracture surfaces indicated the existence of an LBE-steel interaction which seemed independent from oxygen content. For both air and LBE environments, fatigue life was found to be reduced by a factor of around 3 when compared to vacuum. Statistical analysis revealed that the difference in life reduction due to air and LBE is not significant.