Effects of prestrain on fatigue behaviour in type 316 stainless steel

Abstract

The fatigue behaviour ot prestrained type 316 austenitic stainless steel has been studied. Two types of fatigue tests, conventional S-N tests in laboratory air and in 3%NaCl solution and stressincremental tests, were performed. Tensile prestrains evaluated are 5%, 15%, 25% and 58%. In laboratory air, fatigue strength increased with increasing prestrain, which was attributed to both work hardening and strain-induced martensitic transformation. In 3%NaCl solution, the fatigue strengths for all specimens decreased compared with those in laboratory air and fatigue strength increased with increasing prestrain up to 15%, but above that prestrain, it decreased significantly, Corrosion pit generation and growth in transformed martensite phase were believed to be primarily responsible for the observed behaviour. Based on stress-incremental test results, the coaxing effect became less pronounced with increasing prestrain, disappeared at 15% and then again appeared at the larger prestrains of 25% and 58%. The observed prestrain dependence in corrosion fatigue behaviour and coaxing effect clearly indicated that different mechanisms had operated below and above the prestrain of approximately 15%. Possible mechanisms such as work hardening and straininduced martensitic transformation were discussed.