Influence of Hydrogen Content in Steel on Atmospheric Oxidation Behavior of Low Carbon Austenitic Stainless Steel

The influence of hydrogen content in steel on atmospheric oxidation behavior of low carbon austenitic stainless steel SUSF316L was investigated for clarifying the mechanism of SCC initiation in a boiling water reactor environment, which is closely associated with the localized oxidation and its acceleration. The stainless steel was charged with hydrogen by the means of cathodic electrolysis followed by subjecting the hydrogen-charged steels to the atmospheric oxidation test at 300°C for 10 h. The oxide films that formed on the non-charged and hydrogen-charged specimens were analyzed by optical microscopy, scanning electron microscopy, laser Raman spectroscopy and glow discharge optical emission spectroscopy. Experimental results revealed that relatively thick oxide films were formed on the hydrogen-charged specimen resulting in the hydrogen accelerated oxidation (HAO), when the hydrogen content was 35 mass ppm. However, there was almost no difference between the non-charged and the hydrogen-charged from the viewpoint of oxidation behavior when the hydrogen content was 24 mass ppm. The spinel-type oxides such as Fe3O4 and FeCr2O4 were identified by laser Raman spectroscopy only on the specimen surface where the HAO occurred. In addition, the Cr concentration in the inner oxide layer of the oxidation-accelerated specimen was around 20% and was lower than that of the non-charged (30-35%). The HAO seemed to be closely associated with this decrease in Cr concentration in the inner oxide layer.