Fatigue Crack Initiation in 403 Stainless Steel in Simulated Steam Cycle Environments: Hydroxide and Silicate Solutions

Abstract

The fatigue crack initiation behaviour of a 12%Cr turbine blade alloy (403 stainless steel) was studied at a single alternating stress level of 448 MN m⁻² in deaerated solutions of NaOH at pH 10,12, and 14 and in 1M Na₄SiO₄ solution (pH 10) at 100°C. Fatigue life in the hydroxide solution increased with increasing pH and was also good in the silicate solution. Long cracks of similar appearance were found to be initiated on the surface of the steel in all the solutions except NaO H at pH 14, in which short incipient microcracks of a transgranular nature initiated on the specimen surface, regardless of the selective attack that occurred at grain and phase boundaries. It was found that increasing the pH of the hydroxide solution and the presence of the silicate anion both cause the initiated cracks to propagate into the bulk of the material in a transgranular mode, thereby resulting in a longer fatigue life.