Resistance of Automotive Exhaust Flexible Coupling Alloys to Hot Salt Attack, Stress Corrosion Cracking and High Temperature Embrittlement

Automotive exhaust system flexible couplings must resist fatigue and a variety of corrosion mechanisms resulting from exposure to road salts. Increasing operating temperatures and extended warranties are creating ever higher demands on flexible coupling materials. In addition to corrosion and fatigue resistance, materials must have good metallurgical stability. This translates to retention of initial mechanical properties after extended operation at high temperature.

Comparative time-temperature hot salt attack profiles were determined for several austenitic stainless steels and nickel base alloys over the temperature range of 430-870°C (800-1600°F) for times of 0 to 1,333 hours. Temperature and alloy composition regimes where stress corrosion cracking (SCC) can occur are also outlined. In addition, the effect on mechanical properties of 300 to 2,000 hour exposures at the above temperatures is determined. Results of these tests are related to alloy composition and calculated equilibrium phase constitutions.