Engineering Facts On Cast Iron

Cast iron is a eutectic alloy of iron and carbon. The percentage of carbon present in the cast iron family is always greater than 2.0 % as per the iron carbon phase diagram. It is called as hypoeutectic if the percentage of carbon lies between 2.0% to 4.3% and hypereutectic if the percentage of carbon lies between 4.3% and 6.67%. Eutectic cast iron has an exact carbon content of 4.3% carbon.

It has several other constituents like silicon, manganese, sulphur and phosphorus. Cast iron is of various types and it is classified as grey cast iron, white cast iron, malleable cast iron, compacted graphite cast iron, spheroidal graphite cast iron and so on.

The shape of the carbon in cast iron influences the mechanical properties of cast irons. It has got higher compressive strength, hardness and wear resistance. It is formed accordingly and entirely depends on the inoculation treatment and solidification rate during processing.

Normally, any alloy or metal shrinks during its phase transformation from liquid to solid. But, cast iron expands on cooling due to the presence of graphite flakes.

In grey cast iron, carbon is present in free form as graphite flakes due to the iron-silicon inoculation. The presence of flake graphitic carbon in grey cast iron increases the vibration damping capacity. Depending on cooling rate, different types of flake shapes are observed in grey cast iron. They are classified as Type A Uniform distribution structure, Type B Rosette groupings, Type C Superimposed flakes, Type D Interdendritic segregation random orientation and Type E Interdendrtitic segregation Preferred orientation. Type A is the most desirable structure in cast irons. Type B is difficult to machine and the most undesirable is Type E. Sometimes, combinations of two or three type of flake shapes are observed and it entirely depends on the solidification rate during processing in the molds.

White cast iron is formed due to chilling. It is otherwise known as chilled cast iron used for fabricating the machine rollers. Combined carbon, Cementite, otherwise called as iron carbide is present in white iron. It is applied where extreme hardness is required.

Malleable cast iron is made by heat treatment called as malleabilizing and the carbon shape is approximately round. They are classified as white heart malleable iron and black heart malleable iron. Nodular iron or ductile iron or spheroidal graphite cast iron is formed due to the inoculation of iron-silicon-magnesium in grey cast iron. The mechanism behind the transformation of flake graphite to spheroidal graphite carbon in cast iron is not yet defined clearly and this is a challenging one. The properties of ductile iron are equivalent to steel and comparable. The strength of the nodular iron depends on the spheroidal graphite carbon count present in a particular area at a certain magnification. Compacted graphite is produced due to under treatment of ferro silicon magnesium, in which the structure of the graphite is nearly spherical.

Alloy cast iron is utilized for critical engineering applications where corrosion resistance, wear resistance and resistance to temperature is considered. Specific cast irons like high silicon cast iron, Ni-Resist and Ni-Hard cast iron exist. High silicon irons are used in transformers and Nickel-resistant and Nickel-hard cast iron are used where corrosion resistance is required.

Cast iron is cheaper and less costlier when compared to other engineering materials. It is a basic, easily available material and applied for various engineering applications.

About The Author
Dr.Thoguluva Raghavan Vijayaram hails from India and he has completed his PhD Research Degree in Mechanical Engineering (Metal Matrix Composites: Materials Engineering) from the Faculty of engineering, Universiti Putra Malaysia. He has published quality research papers in reputed International journals, National journals, International conference proceedings and in the Malaysian broadsheet. He has a wide range of work experience, both in academics and as well as in industry, consultancy, and teaching and especially in research and development work. His areas of expertise include: Metallurgical Engineering, Mechanical Engineering and Manufacturing Engineering and his special areas of research interests are in the field of advanced casting technology and techniques, composite materials and processing, powder metallurgy, Ferrous and Non-Ferrous foundry metallurgy, solidification science and technology, solidification processing of metals, alloys and composites, microgravity solidification, squeeze casting, die casting die design, heat treatment, Metallography, microstructure-property correlation ship, new materials and process development, aerospace engineering materials, computer simulation of casting solidification, FEM analysis and advanced engineering mathematics. Besides, he is a prominent writer and possesses wider experience in editing technical papers, theses and dissertations.

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