Effect of hydrogen charging on the tribocorrosion performance of C45CE steel

Tribocorrosion of hydrogen-embrittled steel is a critical concern for materials, particularly used in applications involving high mechanical stress and corrosive conditions. Hydrogen uptake by steel structures, induced by an electrochemical process, can cause degradation of mechanical properties and induce cracks. It is widely known as hydrogen embrittlement. This study investigates the combined effects of mechanical wear and electrochemical corrosion on hydrogen-charged C45CE carbon steel, in the presence and absence of surface film. The tribocorrosion behavior of hydrogen-charged steel is evaluated through tests in corrosive solutions, accompanied by microstructural analysis. The method of hydrogen charging in carbon steel was carried out electrochemically under galvanostatic conditions in a 0.5M Na2S solution for 24 h. The tribocorrosion tests were done in a reciprocating tribometer in a borate solution under well-controlled mechanical and electrochemical conditions, allowing for imposing a specific surface chemistry. Dry wear tests were also carried out in the same tribological configuration. Results show that hydrogen reduces the fracture energy of the hydrogen-charged steel by 50 % despite no differences in hardness were observed. Hydrogen charging neither modifies the grain structure of the steel. The tribocorrosion results show that the hydrogen uptake has an impact on the steel degradation (hydrogen blocks deformation, increases the strain accumulation, and higher subsurface recrystallization was observed) when no passive film is formed on the steel (cathodic conditions). The main effect of hydrogen is grain refinement. In the presence of surface films (passive conditions), no difference was observed between the tribocorrosion behaviour of the charged and non-charged samples. When imposing passive conditions, hydrogen intake into the material can be oxidized, thus its effect on the tribocorrosion response is minimized. The surface of the material was embrittled by the presence of the passive film, regardless of the hydrogen charging.