Stainless steel is largely used in the automotive market, essentially for exhaust system. In that field of application, designs are more and more complex and the guarantee durations continuously increase. Thus laboratory tests were developed in order to simulate automotive environments and estimate their impact on stainless steel durability. Corrosion mechanisms greatly depend on the temperature and so the exhaust system could be divided in two parts which are: the hot part near the manifold (400<900) and the cold part near the muffler (20<400). For the hot part, the main corrosion mechanism is oxidation, also called dry corrosion. Laboratory test used for that high temperature application is the cyclic oxidation. The behaviour of each grade is evaluated through mass variation measurement on specimens exposed to a specific thermal cycle during x-hours. In the cold part, near the muffler, exhaust gas could condensate on the internal surface of the exhaust system to form complex acids. Consequently corrosion mechanism is more complex and is a combination of wet and dry corrosion. On that idea, a 'dip & dry' apparatus was developed in order to simulate that kind of corrosion on stainless steel grades, by cyclic dipping in an artificial condensate, drying and oxidized specimens in oven. After test, grades are compared through maximum corrosion depth measures. In addition, the external cold part of the exhaust system is visible and so, guarantee could also include cosmetic requirements. An experiment test based on climatic standard test with periodic heat treatment at 300 deg C was developed to mimic the external corrosion of exhaust system. Thus treated specimens are evaluated thanks to a cosmetic observation based on comparison with reference samples. All these corrosion simulation tests permit to develop a complete ferritic stainless steel offer dedicated to the exhaust market.
Corrosion simulation tests on stainless for automotive applications
Korrosionssimulationsprüfung der nichtrostenden Stähle für den Automobilbau
2008
5 Seiten, 8 Bilder, 4 Quellen
Conference paper
Storage medium
English
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