Abstract
This work studied the corrosion behaviors of 15Ni, 23Ni, 31Ni and 40Ni steels in aerated 3.5% NaCl solutions with various pH levels (2, 7 and 10) at 25 degrees C. The observed microstructures of 15 and 23 wt.% Ni steels were consisted partially of martensite, while those of 31 and 40 wt.% Ni steels were fully austenitic. Polarization curves of the nickel-containing steels were determined using a potentiodynamic polarization technique. The corrosion potential (Ecorr), corrosion current density (Icorr), corrosion rate (Rmpy), pitting potential (Ep), primary passive potential (Epp) and passive current density (Ip) were evaluated from the polarization curves. The results indicated that an increase in nickel content resulted in an increased corrosion potential, but also a decreased corrosion current density or corrosion rate. Only the solution pH of 10, the passive characteristics of the 23Ni, 31Ni and 40Ni steels were remarkable. As the nickel content of those three nickel-containing steels increased, the primary passive potentials and pitting potentials were increased, but the passive current densities were decreased. Nickel additions improved general corrosion and pitting corrosion resistances of the nickel-containing steels when tested in basic, neutral and acidic 3.5% NaCl solutions. The effects of various nickel contents and solution pHs on general corrosion resistances of nickel-containing steels were also discussed.
