Microstructural evolution of AISI 304 austenitic stainless steel during straining at room and cryogenic temperatures: in-situ X-ray diffraction of synchrotron light

Full text: Austenitic stainless steels are among the most used in industry for structural purposes because of their good mechanical performance and corrosion resistance. Microstructural changes occurs during processing due to austenite instability. In addition, the transformation of austenite into another phase may occur through a compact hexagonal intermediate structure (HCP), called epsilon martensite, or directly to a body-centered cubic phase (BCC), called strain induced martensite (α'). These phenomena can lead to good features in the mechanical behavior of the austenite phase. The straining can be followed by transformation-induced plasticity (TRIP effect), or even Twinning Induced Plasticity (TWIP effect). Moreover, there are reports that at cryogenic temperatures, dynamic recovery / recrystallization can be suppressed, changing the mobility of dislocations. In these cases, the mechanisms of the TRIP effect and the TWIP effect are more evident. In-situ measurements of X-ray diffraction through synchrotron light were performed systematically during tensile tests at room temperature, -100 ° C and -180 ° C using the XTMS thermomechanical control system of the Gleeble machine, following so the microstructural changes of AISI 304 austenitic steel in each temperature condition. The experiments were performed at the National Synchrotron Light Laboratory - LNLS - Campinas / SP - Brazil. The strain-induced martensite quantification during the tensile test was performed by integrating the obtained X-ray peaks. The results show that the amount of martensite formed is directly proportional to the straining levels and inversely proportional to the straining temperature. (author)