Effect of SO_2 on oxidation of type 409 stainless steel and its implication on condensate corrosion in automotive mufflers

摘要

The influence of trace SO_2 in simulated automotive exhaust gases at 400 ℃ on the oxidation and subsequent condensate corrosion of 409 stainless steel was investigated by means of mass gain, SEM, Raman spectroscopy, GDOES, Mott-Schottky and polarisation curves. SO_2 suppresses the growth of oxide films, especially nodular oxides rich in magnetite and maghemite, due to forming sulphates on the oxide surfaces. The oxidised specimens show passive corrosion in simulated condensate solutions. The passive current density decreases noticeably with adding SO_2 into the oxidation environments, indicating that SO_2 may inhibit the condensate corrosion of mufflers through the thermal oxidation process.