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Tribocorrosion of hydrogen-embrittled steel is a critical concern for materials used mostly in harsh environments, particularly 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, focusing on the degradation mechanisms. The tribocorrosion behavior of hydrogen-charged steel is evaluated through the tests in corrosive solutions, accompanied by microstructural analysis and hydrogen diffusion studies. The method of hydrogen charging in carbon steel was carried out electrochemically under galvanostatic conditions in a 1M Na2S solution for 24 hours. The tribocorrosion tests were done in a reciprocating tribometer with a ball on a flat configuration using a 6 mm Al2O3 ball as a counterpart and an applied load of 2.6 N. The selected electrochemical conditions for the tribocorrosion tests were two applied potentials in the cathodic -1.5 V (MSE) and passive -0.5 V (MSE) domain of the steel in a borate solution. The duration of all the tests was 30 minutes with a wear track length of 4 mm. Surface and subsurface characterization of the worn surfaces was carried out after the tests to elucidate the degradation mechanisms.
Results show that there is no effect of hydrogen on the hardness of the hydrogen-charged samples. However, there was a decrease in the fracture energy when the same charging method was applied to Charpy samples. Hydrogen charging does neither modify the grain structure of the steel. The tribocorrosion results show that the hydrogen intake has an impact when no passive layer is formed on the steel (cathodic conditions). In that case more smearing on the charged sample surface was observed with higher subsurface recrystallization. On the other hand, under passive conditions, no difference was observed in the worn area of the steel, indicating that the passivation conditions govern the tribocorrosion response of the steel.