Passivity and passivity breakdown of 13%Cr, 15%Cr and 13Cr5Ni2MoN stainless steels in chloride-containing solutions

The corrosion and passivation behaviour of three martensitic stainless steels was examined in chloride-containing solutions using Electrochemical Impedance Spectroscopy (EIS), Electrochemical Noise (EN) and potentiodynamic measurements. The characteristics of polarisation curves show that corrosion resistance of the examined steels falls in the following order 13Cr5Ni2MoN, 15%Cr and 13%Cr. The 13Cr5Ni2MoN steel showed a pitting corrosion resistance higher than the conventional 15%Cr and 13%Cr stainless steels. EIS results showed that 13Cr5Ni2MoN steel remained passive and free of pitting corrosion after 504 h immersion in the NaCl solution. The 13%Cr and 15%Cr conventional martensitic steels showed a decay in the film protection after about 864 h of immersion in the chloride-containing solution. In the same electrochemical conditions the 13%Cr steel was more noisy than the 15%Cr and 13Cr5Ni2MoN steels. The noise resistance was found to increase with increasing molybdenum content in the steels.