Optimizing Automobile Flexible Exhaust Coupling Performance with Inconel Alloy 625LCF

Operating requirements for automotive flexible couplings are rapidly becoming increasingly severe. Higher temperatures, tighter emission requirements along with extended warranties and governmental demands for increased gas mileage are rendering present stainless steel coupling alloys marginally acceptable or, more often, unacceptable for a growing number of engine platforms. Requirements for longer life are demanding improvements in fatigue and corrosion resistant properties over those of currently employed alloys. This paper characterizes the strength, fatigue and corrosion resistance of INCONEL^® alloy 625LCF^® and relates these properties to the ever increasing requirements of automotive flexible couplings. Tight control of property variation is demonstrated for the fatigue properties by presenting data on a range of heats with differing gauges. The effect of aging during service on room temperature tensile properties is examined. Simulated road salt exposure tests have been performed over a broad range of temperatures and the results are presented. Alloy 625LCF is shown to meet the performance requirements of this critical exhaust system component.