Stainless steel is largely used in the car exhaust market and will be applied now for truck and off-road vehicles. In that field of application, designs are more and more complex with the integration of a catalytic converter and particle filter, consequence of more and more severe diesel depollution regulations. In particular, due to the necessity of reducing NOx emission established by Euro 5 standard (2009), Euro 6 (2014) and American Tier 4 (2014), new equipment were developed for diesel vehicles (truck as well as car). The most promising technology is called Selective Catalytic Reduction (SCR) and takes advantage of the reduction feature of ammonia (NH 3 ) on NOx. As NH 3 cannot be stored directly within the vehicle for safety reasons (toxicity & flammability of ammonia) urea in water solution was selected to initiate the reaction by means of a spraying nozzle. To get a better understanding of the involved hot corrosion mechanisms and afterward to improve material selection, a dedicated laboratory test was developed at Isbergues Research Center. The simulated test consists of spraying urea solution on cyclic heated stainless steel in a range from 200°C to 600°C. We evidenced a nitriding mechanism due to the urea decomposition on the surface of stainless steel at high temperature, and also the very different behaviours between austenitic and ferritic grades. The last one, in particular K41X (1.4509-441) and K33X (1.4513-molybdenum stabilized ferritic) grades show the best performance in particular when compared to the standard 304 austenitic grade. The paper will review the test set-up, the result obtained and will discuss the stainless steel grade selection for the SCR application.

Abstract. The use of stainless steel in automotive is not really new and began with the decorative trims because of its unique brightness and anticorrosion properties. Today, most of the stainless steel parts in vehicle are situated in the exhaust and powertrain systems. In fact, the exhaust line is subjected to a continuous evolution due to the more and more severe emissions regulations. Consequences are more acidic condensates, higher temperatures, and new high temperature corrosionfatigue mechanisms that lead to the requirement of more and more resistant stainless steels to guaranty longer component's lifetime. The stainless steels could also exhibit interesting and very high mechanical properties at the level of AHSS carbon steels but preserving their excellent elongation and structural applications could be also prospected. Therefore research efforts are currently attempted to introduce stainless steel in body-in-white or chassis parts, but also in bio-fuel tank components, battery and for the future, in fuel cells propulsion. This paper is the summary of a talk at INSA Lyon in December 2012 to celebrate the century of the stainless steel. Its objective is to deal with the research progress made to adapt the stainless steel family to the transformation of the automotive for 20 years. L'utilisation de l'acier inoxydable n'est pas récente et est souvent illustrée par la décoration automobile, une fonction esthétique exigeante où l'inox reste le matériau de référence. Aujourd'hui, l'essentiel de l'inox utilisé dans le véhicule se trouve dans l'échappement et l'environnement moteur. La ligne d'échappement s'est transformée et l'acier inoxydable s'est adapté aux contraintes des normes de dépollution et d'allègement, se traduisant par des condensats d'échappement de plus en plus acides, des températures plus hautes. En parallèle une augmentation des garanties fonctionnelles de la ligne d'échappement est régulièrement demandée. Les aciers inoxydables présentent aussi des propriétés mécaniques qui les placent aux niveaux des aciers THR tout en conservant un allongement supérieur. Actuellement un effort de recherche est entrepris pour incorporer de l'inox dans d'autres parties du véhicule en particulier la structure (caisse en blanc et pièce de châssis), le réservoir et la pileà combustible (notamment les plaques d'interconnexion du coeur de pile).

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