Production Aspects of Spheroidal Graphite Iron

Abstract

Spheroidal graphite cast iron, also referred to as ductile iron, nodular cast iron, spherulitic iron, is essentially cast iron in which graphite is present in the form of tiny balls of spherulites, rather than flakes as in normal grey iron or compacted aggregates (nodules) as in malleable iron. The elements present in the normal cast iron are carbon and silicon, together with manganese, sulphur & phosphorus. Moreover alloying elements such as copper, nickel, chromium, vanadium and molybdenum may be present in varying quantities. In addition, some unwanted elements like lead, titanium, tellurium, bismuth, antimony and arsenic may be present in cast iron in minute quantities which seriously interfere with graphite crystallisation. Finally certain gases, such as hydrogen, oxygen and nit-rogen are also present in the normal cast iron. Such cast iron containing the above elements and gases will always precipitate their carbon as flake graphite. If such cont aminated graphite is purified, a spheroidal cast iron will result in which the free carbon is present in a more or less spheroidal or nodular form in the metallic, steel like matrix. This purifying treatment of cast iron is accomplished primarily by desulphurising so that the sulphur content is reduced to 0.01-0.008% and at the same time degassing the starting melt.