Influência da temperatura de deformação no comportamento mecânico e microestrutural do aço inoxidável austenítico AISI 304

Abstract

The predominantly austenitic microstructure of austenitic stainless steels can be transformed into martensite by plastic deformation due to its metastability. Parameters related to straining conditions, such as the straining mode and temperature, influence this transformation. The present work aimed to verify the mechanical behavior of AISI 304 austenitic stainless steel submitted to tensile tests at ambient and cryogenic temperatures. The evolution of strain-induced martensitic transformation was studied by straining several specimens at different strain levels, followed by microstructural analyses using optical microscopy, hardness measurements, and ferritoscopy, in each sample. The mechanical tests with in situ X-ray diffraction were carried out on the XRD1 line of the National Synchrotron Light Laboratory, called “X-ray Scattering and Thermo-Mechanical Simulation Station” – station on the XRD1 line of the LNLS (XTMS), consisting of a simulator thermomechanical Gleeble 3S50® and an acquisition and instrumentation system developed by teams from the National Nanotechnology Laboratory (LNNano), National Synchrotron Light Laboratory (LNLS) and Dynamic System Inc (DSI). Several diffraction profiles were collected during the mechanical test with Synchrotron light, evaluating its crystallographic behavior and phase transformation phenomena during the straining. It was found that the deformation of austenitic stainless steel in a cryogenic environment causes a more significant increase in yield strength, tensile strength, and toughness when compared with deformation at room temperature, which is probably due to the activation of other deformation mechanisms when strain occurs in a cryogenic environment, partial suppression of dynamic recovery due to low temperature and phase transformation of austenite to straining-induced martensite 𝜖 and straining-induced martensite 𝛼’.