Influence des mécanismes de déformation plastique et de leurs interactions avec l'hydrogène sur les processus de corrosion dans les aciers inoxydables AISI 316L alliés à l'azote

Hydrogen embrittlement is a process where absorbed hydrogen in metals leads to the degradation of mechanical properties. The FCC structure of 316L austenitic stainless steel offers high hydrogen solubility and low diffusion, making it a promising candidate for hydrogen applications. However, it can still be susceptible under certain conditions. Specially when other degradation processes, such as corrosion, are involved. This work aims to understand the interaction between hydrogen embrittlement, corrosion, deformation phenomena and the microstructure of 316L austenitic stainless steel. Additionally, it investigates the effect of alloying composition on hydrogen embrittlement, with a specific focus on nitrogen as an alloying element. This thesis aims to evaluate these different aspects through an experimental study. First, the characterization of hydrogen in the material was conducted, focusing on hydrogen solubility, diffusion, and microstructural evaluation, along with its interaction with nitrogen. Initially, the total hydrogen concentration after hydrogen charging was determined. Subsequently, the hydrogen profile through the thickness of the material was characterized using Glow Discharge Optical Emission Spectroscopy (GDOES) and Fick's law, providing key parameters such as solubility and diffusion. Then, the effect of hydrogen on the mechanical properties of the material was evaluated to better understand the plasticity-hydrogen-interstitial element interaction. An electrochemical hydrogen pre-charging was conducted on specimens, which were subsequently subjected to mechanical tensile testing until fracture. The results were analyzed using Kocks-Mecking representation to enhance the understanding of hydrogen-dislocation interactions. The tested specimens were characterized using various techniques (SEM, EBSD, and TEM) for further insights. In the final part, electrochemical characterization techniques were used to assess the impact of hydrogen and deformed microstructure-hydrogen interactions on the anodic reactions of the materials. First, the anodic process was studied using potentiostatic and potentiodynamic polarization techniques in an acidified NaCl medium. The effect of pre-deformation was then evaluated: specimens were deformed up to 5% strain and subsequently subjected to the same dissolution studies using both techniques. Similarly, this pre-deformation process was applied to hydrogen-precharged specimens to study the interaction between hydrogen, plasticity, and corrosion. The influence of nitrogen was characterized in all these studies. Overall, this study aims to provide insights into the effects of plasticity, and the synergy between nitrogen and hydrogen, on the corrosion behavior of 316L austenitic stainless steels.