S.G. Casting

Foundry is the most basic input industry and stringent demands of quality and quantity are being placed on it. With rapid industrialization and growth in other fields of production, up-to-date knowledge of materials and processes for casting is necessary in order to be able to produce sound castings economically.

In another article, we have talked about different types of cast irons. In this article, we will speak in detail about S.G. cast iron.

S.G. Cast Iron – Introduction
Also called as nodular cast iron or ductile cast iron, spheroidal graphite (S.G.) cast iron is a high strength cast iron. S.G. cast iron is produced by adding magnesium and / or cerium to the molten cast iron while it is being produced in foundry. Nodular / S.G. iron is a carbon-rich iron alloy. As S.G. iron contains high carbon content, the graphite is found as particles on the microstructure level embedded into metallic matrix. The term ‘nodular’ refers to the shape of the graphite particles which is achieved by adding magnesium / cerium. This is unlike the flakes like graphite structure of white or gray iron, and influences the properties of S.G. iron. Due to its mechanical properties nodular cast iron is also known as ductile cast iron. Compared to gray cast iron, the nodular particle shape increases strength and toughness becoming comparable to many grades of steel. Indeed, where cost is a concern and applications are not very critical, ductile cast iron is used instead of steel. A process called as inoculation further strengthens the S.G. castings. S.G. cast iron also undergoes heat treatment many times, and this makes a difference on the size, shape and distribution of graphite particles and the microstructure of the metallic matrix. The spheroidal graphite nodules distributed in the ferrite and/or pearlite matrix of S.G. iron is obtained through Magnesium inoculation; other alloying elements such as Molybdenum, Copper, Chromium, Vanadium and Nickel are also commonly added to the melt in order to obtain specific properties. The mechanical properties of ductile cast iron can therefore differ considerably especially in thick-walled casted components. This is because the local temperature evolutions at the surface and in the centre can differ considerably resulting in locally different microstructures. In general it is possible to produce different grades of S.G. cast iron, both in cast condition without heat treatment, and with heat treatment.