Electrochemical behaviors of ultra high strength steels with corrosion products

The electrochemical behaviors of ultra high strength steels, 300M and AerMet 100, with corrosion products which were formed during salt spray test were studied using potentiodynamic polarization curve, EIS, SEM, scan Kelvin probe (SKP) and Raman spectroscopy. The results show that the corrosion products on the steel 300M are γ-FeOOH and Fe(OH)₃, and those on the steel AerMet 100 are β-FeOOH, Fe₃O₄ and γ-Fe₂O₃ after salt spray test. Because of the compact characterization, Fe₃O₄ and γ-Fe₂O₃ have a better protection property for substrate by hindering the permeation of O₂ and Cl^-. The corrosion potentials shift negatively and corrosion current densities become larger with increasing salt spray time, meaning a faster rate of anodic dissolution for these two steels. After salt spray test, the values of Kelvin potential for the two steels are 0.5-0.6 V positive than those before tests, and more uneven. For 300M, the corrosion resistance of rust layer becomes larger/smaller with the corrosion productions gathering/drapping on/from the samples. The electrochemical reaction for AerMet 100 is diffusion-controlled process and the value of Warburg impedence which expresses the diffusion-hindering effect becomes larger. The corrosion resistance and protection ability of corrosion products for steel AerMet 100 are better than those of steel 300M.