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High-temperature mechanical- and fatigue properties of cast alloys intended for use in exhaust manifolds
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.ORCID iD: 0000-0001-5212-2227
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
2014 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, Vol. 616, 78-87 p.Article in journal (Refereed) Published
Abstract [en]

In the present work materials for use in exhaust manifolds of heavy-duty diesel engines were tested in air from 20 to 1000 degrees C with respect to mechanical properties. Two cast irons, SiMo51 and Ni-resist D5S, four austenitic cast steels, HF, A3N, HK30 and HK-Nb, and one ferritic cast steel, 1.4509 were studied. The experimental work included thermal conductivity, thermal expansion, uniaxial stress-strain testing, low-cycle fatigue testing up to 30,000 cycles and fractography. Below 500 degrees C, SiMo51 is superior. At higher temperatures, a transition from elastic to plastic strain dominance was observed for the cast irons, reducing their performance. Carbide-forming elements increase heat conductivity and result in a dendrite-like fracture surfaces during fatigue testing. The austenitic steels are superior only at higher temperatures.

Place, publisher, year, edition, pages
2014. Vol. 616, 78-87 p.
Keyword [en]
Low-cycle fatigue, High-temperature mechanical properties, Ductile cast iron, Cast stainless steel, Exhaust manifolds, Physical properties
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-156112DOI: 10.1016/j.msea.2014.08.014ISI: 000343352400010ScopusID: 2-s2.0-84906506637OAI: diva2:777933
Vinnova, 2009-01433

QC 20150109

Available from: 2015-01-09 Created: 2014-11-21 Last updated: 2015-05-07Bibliographically approved
In thesis
1. Oxidation and corrosion fatigue aspects of cast exhaust manifolds
Open this publication in new window or tab >>Oxidation and corrosion fatigue aspects of cast exhaust manifolds
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis.

The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated.

The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life.

These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 87 p.
cast exhaust manifolds, high-temperature corrosion, high-temperature low-cycle fatigue, high-temperature corrosion fatigue, ductile cast irons, cast stainless steel
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-166274 (URN)
Public defence
2015-05-29, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20150507

Available from: 2015-05-07 Created: 2015-05-06 Last updated: 2015-05-07Bibliographically approved

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