Influence of Cr and Ni on High-Temperature Corrosion Behavior of Ferritic Ductile Cast Iron in Air and Exhaust Gases
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Influence of Cr and Ni on High-Temperature Corrosion Behavior of Ferritic Ductile Cast Iron in Air and Exhaust Gases M. Ekstro¨m • P. Szakalos • S. Jonsson
Received: 25 May 2012 Ó Springer Science+Business Media New York 2013
Abstract Due to an expected temperature increase of the exhaust gases in heavyduty engines in order to meet future emission regulations, there is a need to develop materials that can operate at higher temperatures. The exhaust manifold in the hot end of the exhaust system is specifically affected since the most common material today, SiMo51, is already operating close to its limits. Accordingly, the effects of Cr and Ni-additions on the high-temperature corrosion resistance of this material in air and exhaust gases were examined. It was found that the addition of 0.5 and 1 wt% Cr improved the oxidation resistance in air at 700 and 800 °C by the formation of an SiO2 barrier layer as well as a Cr-oxide at the oxide/metal interface. However, no Cr-oxide was detected after exposure to exhaust gases, probably due to a water vapor-assisted evaporation of Cr from the oxide. The addition of 1 wt% Ni resulted in a deteriorated SiO2 barrier layer and reduced oxidation resistance. Keywords Ferritic ductile cast iron Water-assisted evaporation Exhaust manifold
M. Ekstro¨m (&) S. Jonsson Division of Mechanical Metallurgy, Materials Science and Engineering, Royal Institute of Technology, 100 44 Stockholm, Sweden e-mail: [email protected] S. Jonsson e-mail: [email protected] P. Szakalos Division of Surface and Corrosion Science, Chemical Science and Engineering, Royal Institute of Technology, 100 44 Stockholm, Sweden e-mail: [email protected]
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Introduction In the present work, the effects of Cr and Ni additions on the high-temperature corrosion behavior of a ferritic ductile cast iron, intended for use in exhaust manifolds, have been investigated. Due to more stringent exhaust emission legislations, the exhaust gas temperatures in heavy-duty engines are expected to increase. In the near future, this requires materials that can operate at higher temperatures, especially in the hot-end of the exhaust system. Today, a Si-alloyed ferritic ductile cast iron, called SiMo51, is used in the turbo manifold. This material is already operating close to its limits and higher exhaust temperatures will therefore push the material beyond the required strength and oxidation resistance for the application. A candidate material for replacement of SiMo51 is an expensive high-Ni ductile cast iron, called Ni-resist D5S. Thus, the aim of an ongoing project is to find cheaper replacements that can operate in temperatures up to 800 °C. The high-temperature corrosion behavior of SiMo51 and Ni-resist in air and exhaust gases has been studied thoroughly by Tholence and Norell [1–4]. When pure iron oxidizes in air at high temperature, it grows a multi-layered scale of FeO, Fe3O4 and Fe2O3. The oxide scale that is formed on ductile cast iron is characterized by a sub-layer that grows into the material and a top layer tha
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