Effect of pH on Condensate Corrosion of Type 409 Stainless Steel for Automotive Mufflers

The corrosion behavior of type 409 stainless steel in simulated muffler condensates with different pH values was studied by polarization curves and electrochemical impedance spectroscopy (EIS).The composition of passive films formed on 409 SS surfaces was analyzed by XPS.The results showed that 409 SS was in active corrosion state as pH was equal to 2,while it changed to passive state as pH increased to 3.The passive films formed under acidic conditions enriched in Cr-compounds with many defects while they enriched in Fe-compounds under neutral and alkaline conditions with less defects.As a result,409 SS showed much higher corrosion resistance in the neutral and alkaline condensate solutions than in the acidic ones.