High Temperature Oxidation/Corrosion Performance of Various Materials for Exhaust System Applications 2006-01-0605
Durability requirements for exhaust materials have resulted in the increased use of stainless steels throughout the exhaust system. The conversion of carbon steel exhaust flanges to stainless steel has occurred on many vehicles. Ferritic stainless steels are commonly used for exhaust flanges. Flange construction methods include stamped sheet steel, thick plate flanges and powder metal designs.
Flange material selection criteria may include strength, oxidation resistance, weldability and cold temperature impact resistance. Flange geometry considerations include desired stiffness criteria, flange rotation, gasket/sealing technique and vehicle packaging. Both the material selection and flange geometry are considered in terms of meeting the desired durability and cost.
The cyclic oxidation performance of the material is a key consideration when selecting flange materials. This study evaluates the high temperature oxidation/corrosion performance of various exhaust flanges, based upon a high temperature oxidation/corrosion test procedure. Components tested were production flanges made from carbon steel and stainless steel, utilizing both wrought (stamping) and powder metallurgy (PM) materials. The in-depth analysis provides a direct comparison between the different alloys and flange designs in terms of rate of oxide formation, and the changes in mass, thickness, microhardness and microstructure.