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Automotive exhaust gas condensate causes severe corrosion inside mufflers. Corrosive condensate became a problem following the introduction of three-way catalytic converters in exhaust systems. The authors previously established a new laboratory test method that simulates condensate corrosion. This test method contributed to the development of new stainless steels for automotive mufflers. The addition of molybdenum (Mo) and copper (Cu) to ferritic stainless steels was found to be effective in improving condensate corrosion resistance, and the effect was arranged using the index [%chromium (Cr)+3×%Mo+1.5×%Cu]. A field test was carried out to investigate the corrosion behavior of mufflers under actual conditions. Aluminized steels showed severe damage by general corrosion. On the other hand, 19%Cr-Cu ferritic stainless steel exhibited excellent corrosion resistance. The corrosion behavior in the field test showed good agreement with the results of the laboratory test.

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.