Corrosion behaviour of nitroxy-QPQ additively manufactured 17-4 PH steel on marine and nuclear reactor components

The study investigates the corrosion behavior of untreated and nitroxy QPQ treated 17-4 PH stainless steel under NaCl environments. Potentiodynamic polarization tests reveal that the nitroxy layer forms an oxide coating, leading to a passivation phase with gradually increasing current density. Oxidation at different temperatures shows variation in corrosion potential, with the lowest current density observed at 450 °C, indicating enhanced corrosion resistance. SEM images of untreated steel show severe crevice and pitting corrosion, whereas nitroxy QPQ treated surfaces exhibit reduced corrosion, with minimal disturbance at 450 °C. Elemental analysis confirms the formation of oxides and nitrides, with increased oxygen content in oxide layers and decreased nitrogen content due to the formation of chromium nitrides. The oxide layer, enriched with oxygen, nitrogen, and chromium, acts as a passive film, protecting against corrosion even in NaCl environments. Elemental mapping further illustrates the correlation between oxidation temperature and corrosion resistance, with higher temperatures resulting in reduced corrosion rates. The combined nitriding and oxidation process enhances corrosion resistance by forming a dense and adherent oxide layer, serving as a barrier against corrosive agents.