Effect of Pre-Corrosion on the Fatigue Behavior of 347H Austenitic Stainless Steel at Elevated Temperature

Abstract

The combined damage induced by the nitrate molten salt corrosion and cyclic loading at elevated temperatures is an important damage issue for the reliable operation of concentrated solar power (CSP) plants. In previous works, the effect of the molten salt pre-corrosion on the fatigue behavior of 347H stainless steel remains insufficiently understood. Based on this, the present work investigated the corrosion behavior of 347H stainless steel in nitrate molten salts at 565 °C, with particular attention to chloride impurities. The effects of pre-corrosion on cyclic deformation characteristics, fatigue life, and failure mechanisms were discussed. The results indicated that the oxide-scale growth follows approximately parabolic kinetics in chloride-free salt, whereas chloride-containing salt exhibits sub-parabolic growth with a lower kinetic exponent. Chloride addition produces a thicker and less stable oxide scale characterized by cracking, spallation, and chromium depletion. The pre-corrosion does not alter the cyclic hardening characteristic of 347H stainless steel but significantly reduces its fatigue life. The corrosion-induced damage morphology also changes the subsequent fatigue crack initiation behavior. The relatively uniform oxidation promotes crack initiation at the oxide layer-substrate interface, whereas chloride-induced scale degradation introduces more severe local damage and accelerates crack initiation and propagation.