High-alloy ferritic cast irons with different graphite microstructures for exhaust manifolds and turbocharger housings

Abstract

Abstract It is well known that ferritic cast irons with 4 to 5 wt.% Si provide good service and low cost in many elevated-temperature applications. In terms of cast iron microstructures, both spheroidal graphite and compacted graphite cast irons are currently used to produce engine exhaust manifolds and turbocharger housings. Between the two graphite morphologies, the mixed graphite microstructure has been proposed and evaluated in the aspects of molten metal treatment, solidification characteristic, microstructural stability, standard tensile testing, long-term hot oxidation and thermal cycling testing. The effects of graphite morphologies on the material properties are presented. The samples with mixed graphite structure showed an improved ductility at medium temperatures and thermal fatigue resistance.