Effect of SO2 on oxidation of type 409 stainless steel and its implication on condensate corrosion in automotive mufflers

• Low temperature oxidation of 409 stainless steel in the synthetic exhaust gases.
• Trace SO2 suppresses the growth of oxide nodules rich in magnetite and maghemite.
• SO2 may reduce the defects such as Fe2+ ions in the thermal iron oxide layers.
• SO2 inhibits condensate corrosion through thermal oxidation effect of exhaust gas.

The influence of trace SO2 in simulated automotive exhaust gases at 400 °C 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. SO2 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 SO2 into the oxidation environments, indicating that SO2 may inhibit the condensate corrosion of mufflers through the thermal oxidation process.