The special corrosion conditions in the rear section of automotive exhaust systems make high demands on the stainless steels used for these components. Condensates bearing appreciable chloride ion concentrations and often low pH-values together with particles of electrochemical active soot can lead to pronounced pitting and crevice corrosion on the inner surfaces. Various steel grades are used, ferrites with different contents of chromium and molybdenum as well as austenitic types. For selection of an appropriate material enabling cost-effective constructions the corrosion resistance of different candidate grades has to be rated. To gain more insight into the mechanism of corrosion occurring in exhaust systems and the effect of the different alloying elements investigations simulating these special corrosion conditions were carried out. They comprised the impact of acidic chloride bearing media and the influence of electrochemical active carbon as well as the effect of alternating wet-dry cycles. Electrochemical investigations dealt with initiation, growth and repassivation of pitting and crevice corrosion. The effect of geometrical effects on crevice corrosion was investigated. Electrochemical active carbon showed a pronounced effect on the corrosion behavior by raising the free corrosion potential. Beside the step of pitting and crevice corrosion initiation also growth and repassivation influenced materials performance. Thus the alloying elements chromium and molybdenum showed a beneficial effect by increasing resistance to initiation of localized corrosion whereas nickel improved corrosion behavior by retarding growth of corrosion sites. So the PRE-concept (pitting resistance equivalent) is not sufficient to rate the corrosion resistance of stainless steels to wet condensates in exhaust gas systems. By giving a better understanding of the different alloying element effects on corrosion resistance the investigations provide valuable information for material development. In addition the study points out factors which are relevant for tests simulating the specific corrosion conditions in automotive exhaust systems.
Corrosion resistance of stainless steels to wet condensates in automotive exhaust systems
Korrosionsbeständigkeit nichtrostender Stähle gegen Kondensatfeuchtigkeit im Fahrzeugabgassystem
2008
7 Seiten, 5 Bilder, 3 Tabellen, 9 Quellen
Conference paper
Storage medium
English
nichtrostender Stahl , Fahrzeugbau , Abgasanlage , Kondenswasser , Korrosionsprüfung , chemische Zusammensetzung , Lochfraßkorrosion , Spaltkorrosion , elektrochemisches Untersuchungsverfahren , Korrosionsbeständigkeit , Kosteneffizienz , technologische Materialeigenschaft , Chromstahl , Chrom-Molybdän-Stahl , Chrom-Nickel-Stahl , Chrom-Nickel-Molybdän-Stahl , Chrom-Nickel-Mangan-Stahl
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