High Silicon Cast Iron with Mixed Graphite (MG) Shapes for Elevated Temperature Applications

Both spheroidal graphite (SG) iron and compacted graphite (CG) iron are currently used to produce engine exhaust manifolds and turbocharger housings. The graphite morphology nodularity is typically specified lower than 30 or 50% for CG and higher than 80% for SG. The so-called mixed graphite (MG) high-Si cast iron has been proposed and developed in this work, in which the nodularity was defined from 30 to 80%. It was also referred to as hybrid graphite (HG) iron. A series of material and casting evaluations were conducted for MG high-Si cast iron, including melt treatment, solidification curves, microstructures, tensile properties, hot oxidation, thermophysical properties, and engine exhaust simulator (EES) testing. Middle temperature brittleness (MTB) from 400 to 500 C of MG was improved over CG and SG specimens. The EES testing showed that the cycles to failure for MG parts were equal or longer than those of CG and SG cast iron parts for three different manifold applications.