Prevention of High-Temperature Surface Degradation in SiMo Cast Irons by Cr and Al Alloying
Abstract
High silicon molybdenum-alloyed cast irons (SiMo) with spherical graphite are widely used for cast thin-wall exhaust manifolds, worked in high-temperature oxidation environment; therefore, prevention of surface degradation during service is important for such common application. The base SiMo and two alloyed by 1 pct Cr and 3 pct Al cast irons were tested at high temperatures in air and a combustion atmosphere to study the microstructural processes of surface degradation. It was shown that surface degradation of SiMo cast irons involves several microstructural processes, including the formation of multilayered oxide scale and development of internal porosity, resulting in decarburization of graphite nodules. Monitoring weight change of the specimens and Leco C analysis were used for decoupling the rates of surface oxidation and metal matrix decarburization. SEM/EDX analysis was used to study the phase composition of scale and high-resolution TEM analysis was performed to determine the detailed information about the atomic structure of protection layers formed on scale/metal matrix interface. The results were used to qualify and link different surface degradation mechanisms. In the base SiMo cast iron, the protection efficiency of formed amorphous silica layers is limited by intensive decarburization at temperatures above 700 °C. It was shown that Cr and Al alloying prevents surface degradation and suppresses decarburization by developing thermally stable oxide films on metal-scale interface, thus allowed to increase a safe working temperature up to 800 °C in air and the combustion atmosphere.
Recommended Citation
S. N. Lekakh et al., "Prevention of High-Temperature Surface Degradation in SiMo Cast Irons by Cr and Al Alloying," Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, vol. 51, no. 6, pp. 2542 - 2554, Springer, Dec 2020.
The definitive version is available at https://doi.org/10.1007/s11663-020-01975-w
Department(s)
Materials Science and Engineering
International Standard Serial Number (ISSN)
1073-5615; 1543-1916
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2020 Springer, All rights reserved.
Publication Date
01 Dec 2020
