Stainless steel materials have found a wide range of applications due to interesting properties such as high ductility, good corrosion resistance, low cost, easy for machining and plenty availability. However, their mechanical properties are significantly affected by the deformation-induced martensitic transformation. The martensitic transformation can occur upon monotonous mechanical loading as well as cyclic loading by imposing considerable magnitude of strain amplitudes (i.e., low cycle fatigue). However, enough knowledge about the effect of martensitic transformation on high cycle fatigue of metastable stainless steel is still missing in the literature. Consequently, further efforts are needed in order to determine the nature of this phenomena and its effect on high cycle fatigue properties of this material.

The traditional methods for fatigue characterization are extremely time consuming. The self-heating method is based on measuring of the temperature rising at the surface of the specimen as result of the micro-plasticity phenomenon. The self-heating method allows a rapid determination of the high cycle fatigue limit, but the prediction of the fatigue curve should be considered for such special materials like metastable stainless steels. Moreover, the self-heating measurements can help to better understand the mechanisms of simultaneous micro-plasticity and martensitic transformation during cyclic loading.

In this study, the metastable austenitic steel 304L is considered and a special attention is paid to explain the material's thermal response during cyclic loading (i.e. self-heating tests). The aim of this research is to study the self-heating behavior of a metastable austenitic stainless steel at different initial states. More precisely, the effect of a pre-hardening by applying a tensile plastic pre-strain is studied at room and low temperatures. In addition, microstructural evolution after cyclic loading is investigated using FERITSCOPE, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD).

The obtained results from samples without pre-strain show that by decreasing the test temperature, the mechanical properties of the material are changed; for instance, the yield stress increases and the sample needs more stress amplitude for getting the same value of the stabilized mean temperature. Therefore, the self-heating curves shift to the right side (i.e., higher stress levels). It means that the fatigue limit of this material is improved by decreasing the test temperature. On the other hand, the results of self-heating tests on pre-strained samples have enabled us to investigate the effect of an initial volume fraction of martensite on the cyclic behavior of this material. As for temperature, the self-heating curves shift to the right side showing the improvement of the fatigue limit by increasing the pre-strain ratio.

Consequently, this study confirms that fatigue criteria have to consider microstructural changes (both micro-plasticity and martensitic transformation) in order to improve fatigue life prediction of stainless steel structures.