Kinetics of corrosion reactions on press hardened steel in atmospheric conditions under thin electrolyte films

Steels with high mechanical performance are prone to hydrogen embrittlement and environmental assisted cracking. Under atmospheric corrosion conditions, the source of hydrogen can be the steel corrosion process itself or galvanic coupling with a metallic coating. Electrochemical behaviour of Press Hardened Steel (PHS) under electrolyte films of different thicknesses using local electrochemical techniques was studied on a fundamental level. Scanning Vibrated Electrode Technique (SVET) was applied to study the evolution and localization of the corrosion process during PHS immersion in NaCl electrolyte. Kelvin Probe (KP) was used as a reference electrode to obtain cathodic and anodic polarization curves on PHS surfaces which were covered by thin electrolyte films (60 to 500 µm) of 0.1 M NaOH and 0.6 M NaCl. For both electrolytes, a strong increase in the oxygen reduction rate due to the decreasing of electrolyte thickness has been clearly demonstrated. Data are correlated well with a theoretical plot determined by Nernst-Fick equation. The influence of the rust layers on the kinetics of corrosion reactions under thin electrolyte films was investigated using KP.