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The influence of Cr and Ni on the high-temperature low-cycle fatigue behavior of a ferritic cast ductile iron
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.ORCID iD: 0000-0001-5212-2227
2012 (English)In: Conference proceeding for 7th International Conference on Low Cycle Fatigue, 2012Conference paper, Published paper (Refereed)
Abstract [en]

 The current material in exhaust manifolds for heavy-duty diesel engines: a Si- and Mo-alloyed, ferritic ductile cast iron, named SiMo51, is operating close to its limits and improvements are needed. Thus, in the present study, the effects on mechanical properties of adding Cr and Ni to SiMo51 has been investigated with focus on low-cycle fatigue behavior in air, at temperatures up to 700°C. Both additions improve fatigue life but reduce elongation. Adding 1wt% Ni improves fatigue life up to 250°C whereas adding 0.5wt% Cr improves fatigue life at room temperature, only.

Place, publisher, year, edition, pages
2012.
Keywords [en]
High-temperature LCF, ductile cast iron, SiMo51, exhaust manifolds, fatigue life, Cr, Ni
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-122015OAI: oai:DiVA.org:kth-122015DiVA, id: diva2:620297
Conference
7th International Conference on Low Cycle Fatigue, Aachen Sep 2012
Note

QC 20130508

Available from: 2013-05-08 Created: 2013-05-08 Last updated: 2013-11-15Bibliographically approved
In thesis
1. Development of a ferritic ductile cast iron for improved life in exhaust applications
Open this publication in new window or tab >>Development of a ferritic ductile cast iron for improved life in exhaust applications
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. p. 51
Keywords
Material development, SiMo51, HK30, exhaust manifolds, high-temperature corrosion, high-temperature low-cycle fatigue
National Category
Metallurgy and Metallic Materials Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-122006 (URN)978-91-7501-711-2 (ISBN)
Presentation
2013-05-24, Marcus Wallenberghallen, Scania, Nyköpingsvägen 33, Södertälje, 13:00 (English)
Opponent
Supervisors
Funder
Vinnova, 2009-01433
Note

QC 20130508

Available from: 2013-05-08 Created: 2013-05-07 Last updated: 2013-11-15Bibliographically approved

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