Development of heat-resistant cast steel for exhaust manifolds

This paper presents a new heat–resistant cast steel developed for exhaust manifolds. Increased exhaust–gas temperatures accompanying recent trends towards leaner combustion and higher engine output have placed a severe thermal load on the exhaust manifold and turbocharger housing. The new cast steel displays better resistance to thermal fatigue than conventional ductile cast irons (DCI) and better cost performance than Ni–Resist (ASTM A439 austenitic ductile cast irons). In the material–design process, the properties required of the material were determined on the basis of statistical analyses. An experiment was then conducted using a test specimen that partially modelled an actual exhaust manifold and a heating simulation was carried out separately from the engine using an exhaust–system simulator. Finally, an endurance test was conducted on an actual exhaust manifold made of the new cast steel using a production system.