Micro-Structural Characteristics of Cast Irons

Whenever a cast metal is selected for specific appl-ication, first choice always goes to cast-irons in view
of cost consideration. Cast irons are the least expensive to cast into shapes. Alternative is chosen only when the mechanical or physical properties of cast irons are found inadequate. Cast irons are essentially pig iron, remelted with addition of cast iron scrap, steel scrap and ferro-alloys to modify the composition to the final speci-fication. The major consituents of cast irons are thus, carbon, silicon, manganese, phosphorus and sulphur. In cast iron, the carbon content is usually in excess of the maximum solubility limit of carbon in iron. The carbon ranges from 2 to 4%. In cast irons, carbon is present in two forms. A stable form shows presence of carbon as free
graphite and an unstable form indicates presence of carbon in a combined form. The family of cast irons are classi-fied depending on the form of carbon present.