In order to reduce the toxic emission in the exhaust gas and to improve the fuel efficency of automobile gasoline engines, the maximum gas temperature has been raised from 1173 K to 1273 K, further to 1323 K in the future. As the castings for exhaust gas components, ferritic heat resistant or ferritic stainless steels have the adequate performance under 1173 K, but they lose the strength over 1173 K. Austenitic cast steels are serviceable up to 1253 K, but none was able to endure the severe thermal fatigue over 1273 K. The thermal fatigue resistance generally gets better with higher strength and lower thermal expansion. In this study, authors extracted the effects of alloying elements on both properties for the experimental austenitic 12 cast heats. They found that W, C and Nb increase high temperature strength, and W Ni, C, Cr and Nb decrease mean coefficients of thermal expansion. Based on the above they designed new austenitic cast alloys, 0.25/0.30 C, 0.8/1.0 Si, 20/25 Cr 13/40 Ni, 0/6 W 0.7/1.5 Nb, Bal. Fe. Their thermal fatigue resistance was proven by the fluidized bed test truly excellent and unrivaled as predicted by finite element method analysis. (VDEh)
Development of austenitic cast steels for high temperature automobile engine exhaust gas systems
Entwicklung von austenitischem Stahlguß für Hochtemperaturabgassysteme von Fahrzeugmotoren
Titel japanisch
Electric Furnace Steel (Denki-Seiko) ; 73 , 2 ; 93-100
2002
8 Seiten, 13 Bilder, 3 Tabellen, 15 Quellen
Article (Journal)
Japanese
SAE Technical Papers | 2003
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