Comparative studies on resistance to pitting corrosion of manganese steels with different deoxidization degrees

Four manganese steels with different deoxidization degrees were selected. Their susceptibility to pit initiation was compared by means of potentiodynamic polarization tests in a 3% NaCl solution with pH 10. The pitting propagation rate was evaluated by indoor interval hanging plate tests in a 3% sea salt solution. The composition of inclusions and the corrosive feature were studied by scanning electro microscopy (SEM) and electron probe micro-analyzer (EPMA). The results indicate that the shape of sulphide inclusions change from a short spindle shape to a long strip shape with increasing deoxidization degree. Under the same condition, the lower the deoxidization degree, the stronger the thermodynamic stability becomes, and the weaker the susceptibility to pit initiation. Additionally, the results of interval hanging plate tests indicate that the manganese steel with a stronger deoxidization degree exhibit a stronger pit propagation rate.