Grey Iron Casting

Grey cast iron also known as flake graphite cast iron, is a type of casting iron in which most of the carbon is present as flake graphite corresponding to form I of IS7754.The propertises of grey cast iron depends on the distribution, sizs and amount of graphite flakes, and the matrix structure. These factorys are in turn, influenced mainly by the manufacturing conditions, chemical composition, solidification time and rate of cooling in he mould. Grey cast iron exhibit low to moderate strength, low modulus of elasticity,low notch sensitiviy, high thermal conductivity, moderate resistance of thermal stock , and outstanding castability.

Grey cast iron is the most widely used of all cast irons and engineers often simply refer to grey cast iron as cast iron. Grey cast iron contains 2,5%-4% carbon and > 2% silicon. The silicon encourages formation of graphite from the unstable cementite. The graphite is in the form of irregular flakes which show up when the metal is fractured as the identifiable grey matrix. Because of the presence of graphite cast iron is brittle unless it is specially treated.

Grey cast iron is highly dependent on the rate of cooling of the casting and of the section thickness. Thin sections can have reasonable tensile strength which is not maintained as the section thickness is increased. The properties of the grey cast iron is very dependent on the proportions of graphite in the matrix. If all of the carbon has separated from the molten metal (full graphitisation) then the grey cast iron resulting will have graphite flakes in a ferritic matrix

Sulfur is present in cast iron and generally is is kept low . Manganese is often present and combines with the sulfur as a precipitate. Both elements on their own restrict the formation of graphite.

The mechanical properties of grey cast iron result from the effects of chemical composition and the cooling history.In general as the combined equivalent of carbon and silicon is reduced the strength of the cast iron is increased.When tensile strengths above 350MPa are required, for thicker sections, alloying additions of chromium, nickel or molybdenum are required.