High cycle fatigue of metastable austenitic stainless steels

Metastable austenitic stainless steels are currently used in applications where severe forming operations are required, such as automotive bodies, due to its excellent ductility. They are also gaining interest for its combination of high strength and formability after forming. The biggest disadvantage is the difficulty to predict the mechanical response, which depends heavily on the amount of martensite formed. The martensitic transformation in metastable stainless steels can be induced by plastic deformation at room temperature. In this research, the martensitic transformation was provoked by means of torsion testing. Several torsion angles were selected to achieve different percentages of martensite at the surface of the specimens. The next step was to evaluate their effect on the fatigue life of the steel. Fatigue testing in the high cycle regime was done at different levels of mean stress. As a conclusion, the presence of martensite in the surface of the specimen led to an increase of the fatigue life when high mean stress was imposed. By contrast, at lower values of mean stress, martensitic transformation has no positive effect on the fatigue life.