Influence of Intermetallic Precipitates on Pitting Corrosion of High Mo Superaustenitic Stainless Steel

Influence of intermetallic phases on the pitting corrosion of aged high Mo superaustenitic stainless steel is studied. To form the intermetallic phases the alloy was aged for 1 and 10 h at different temperatures in the range of 500–1000 °C. Chi forms at temperatures up to 800 °C. Sigma forms above 900 or 1000 °C depending upon the ageing time. Corrosion was estimated by electro-chemical polarization method in 3.5 % NaCl solution. The pitting potential decreases with increasing ageing temperature and/or ageing time. Sigma is more susceptible to cause pitting than chi. Depletion of Mo near the zones of sigma in the matrix is attributed to the pitting phenomenon.