Corrosion Performance of Austenitic and Ferritic Alloys in Automobile Exhaust Train Environments

The performance of several commercial austenitic and ferritic alloys has been evaluated from 1300-2000°F in cyclic air + 10% water vapor and a gasoline engine exhaust gas from 1300-1800°F. The engine exhaust environment was found to be the most aggressive. This was attributed to the gas having passed over the specimens at a relatively high velocity (20-30 ft/s). The significance of undescaled and descaled weight losses, metal loss, depth of internal attack, and total depth of damage is discussed, along with visual inspection and microstructure. It was concluded that several corrosion parameters must be considered in evaluating an alloy's performance. For the austenitic alloys, a general trend of increasing performance with increasing nickel content was observed. As a class, the austenitic alloys exhibited better behavior than the ferritic alloys, with the exception of 18 SR. This latter alloy was equivalent to alloy 601 in oxidation resistance, but suffered significant edge attack at higher temperatures.