Effect of cyclic oxidation on electrochemical corrosion of type 409 stainless steel in the simulated muffler condensates

The electrochemical corrosion behavior of 409 stainless steel after cyclic oxidation below 400 A degrees C was investigated in the simulated muffler condensates by using surface analysis and electrochemical measurement techniques. In the cyclic processes of condensate-dipping and oxidation, specimens may form defective oxide films and weak Cr depletion underlying the oxide films. Sulfate from the condensate-dipping will give rise to sulfidation during the cyclic oxidation, being detrimental to both the oxidation and corrosion properties of stainless steel. The oxidation above 300 A degrees C deteriorates the corrosion resistance, even leading to active corrosion in the acidic condensate solutions. Comparatively, specimens oxidized cyclically without condensate-dipping show much higher condensate corrosion resistance. It is suggested that the acidic condensate corrosion is accelerated by the synergetic effect of oxidation and condensation in the mufflers, and then may result in perforation through the defects such as cracks and nodules in oxide films on the stainless steel surface.