Ferrous High-Temperature Alloys for Exhaust Component Applications 2010-01-0654

There is a wide spectrum of cast ferrous heat resistant alloys available for exhaust component applications such as exhaust manifolds and turbocharger housings. Generally speaking, the ferrous alloys can be divided into four groups including: ferritic cast irons, austenitic cast irons, ferritic stainless steels, and austenitic stainless steels. Selection of a suitable alloy usually depends on a number of material properties meeting the requirements of a specific application. Ferritic cast irons continue to be an important alloy for exhaust manifolds and turbocharger housings due to their relatively low cost. A better understanding of the alloying effects and graphite morphologies of ferritic cast irons are discussed and their effect on material behavior such as the brittleness at medium temperatures is provided. The nickel-alloyed austenitic cast irons, also known as Ni-resist, exhibit stable structure and improved high-temperature strength compared to the ferritic cast irons. Austenitic cast irons with varying nickel contents were evaluated in terms of microstructure stability, heat treatment, oxidation and thermal fatigue resistance. For the most demanding applications requiring even higher elevated-temperature strength, creep, and fatigue resistance, ferritic or austenitic stainless steels may be selected. The chemical composition, microstructures, and properties of cast stainless steels are reviewed. Synthesizing this information on material behavior provides a guide to aid in the selection of ferrous alloys for high temperature applications.