Effects of Environmental Factors on Pitting Behaviors of Two Stainless Steels in Simulated Seawater

The effects of environmental factors on the pitting behaviors of Z2CND18-12N austenitic stainless steel and S32760 duplex stainless steel in simulated seawater environment were investigated by means of potentiodynamic polarization, critical pitting temperature (CPT) measurement and corrosion morphology observation. The results showed that the polarization behaviors of each materials in artificial seawater and 3.5% NaCl solution at 30℃ were similar. The pitting potential E_b of S32760 was about + 1 100 mV (relative to saturated calomel electrode SCE, the same below). Z2CND18-12N in the two solutions showed apparent metastable fluctuation before the pitting breakdown, with E_b around +500 mV. S32760 showed excellent pitting resistance, but apparent metastable fluctuation occurred at 60℃. Pitting resistance of Z2CND18-12N was close to that of S32760 at low temperature of 3℃, but decreased significantly when the temperature increased to 30℃ and 60℃. The pitting corrosion resistance of Z2CND18-12N was weaker than that of S32760 duplex stainless steel. CPT of S32760 in the 3.5% NaCl and 10% NaCl were 86℃ and 79℃, with the corresponding values of 23℃ and 20℃ for Z2CND18-12N.