Evaluation of the Effect of Dynamic Sodium on the Low Cycle Fatigue Properties of 316L(N) Stainless Steel Base and Weld Joints

Abstract

Low cycle fatigue (LCF) tests on 316L(N) austenitic stainless steel base and weld joints were at 823 K and 873 K at a constant strain rate of 3 x 10 (-3) s (-1) with strain ranges varying from +/- 0.4% to +/- 1.0% in a servo-hydraulic fatigue test system under flowing sodium environment. The cyclic stress response exhibited a similar trend as that in air comprising of an initial rapid hardening, followed by a slight softening stage before saturation. The fatigue lives are significantly improved in sodium environment when compared to identical testing conditions in air environment. The lack of oxidation in sodium environment is attributed to the delayed crack initiation, reduced crack propagation rate and consequent increase in fatigue life. Comparison of the data evaluated in sodium with RCC-MR design code, derived on the basis of data obtained from air shows that the design based on air tests is conservative.