Fatigue Properties of Nb-Bearing Stainless Steels for High Temperature Applications in Automobile Exhaust Gas System

Exhaust manifolds have been fabricated from stainless steels such as type 409 in place of cast iron in order to reduce the weight and to increase performance of the engine. In this paper, thermal fatigue and high temperature fatigue resistances of Nb-bearing ferritic stainless steels and type 409 have been investigated. The results obtained are as follows: Nb-bearing steels were superior to type 409 in high temperature fatigue resistance. Thermal fatigue resistance depended on a restraint ratio. The fatigue life of Nb-bearing steels was longer than that of type 409 in the condition of a low restraint ratio which might be near to the actual automobile exhaust system.