On the Tensile Behavior of Heat-treated Hydrogen Charged 316L Stainless Steel

Abstract

It is well established in the literature that the precipitation of different carbide types and intermetallic phases in stainless steels can lead to drastic consequences in their mechanical and corrosion behavior. Chromium carbide particles precipitate at grain boundaries, creating chromium depletion zones that expose the stainless steel to high corrosion penetration in harmful working atmospheres. The aim of this work is to evaluate the effect of electrolytically charged hydrogen on the mechanical behavior of heat treated AISI 316L austenitic stainless steel samples. To achieve a homogeneous distribution of carbides, specific heat treatments were conducted before tensile tests. Subsequently, a group of heat-treated samples were hydrogen-charged. After tensile tests carried out at high (0.003 s⁻¹) and low (0.000003 s⁻¹) strain rates, the resulting fracture surfaces exhibited mixed behavior in hydrogen-charged samples, i.e., ductile-brittle, in comparison with the ductile morphology obtained in uncharged ones. Additionally, in hydrogenated samples, cracks were associated with fine chromium carbides. Coincidentally, there was a ductility loss in hydrogen-charged samples, which was not observed in uncharged ones. In order to identify hydrogen-carbide interactions, combined studies of Differential Scanning Calorimetry (DSC) and a selective metallographic technique made it possible to identify grain boundaries and carbides/matrix interfaces as the main hydrogen traps. Finally, regarding strain rate effects on mechanical properties, it could be stated that when the strain rate decreases, the embrittlement effect of hydrogen is more explicitly manifested in conjunction with a microstructure sensitized by heat treatments and revealed by the mixed mode of fracture in hydrogen-charged samples.