Cast Iron

Cast iron is also called as gray iron and it solidify with the eutectic, and is identifies the wide group of ferrous alloys. The alloy is identified by the color of the fractured surface. Due to the carbide impurities, the fractured surface is white and it is referred as white cast iron, and this carbide impurity allows the crack to pass straight through. Due to graphitic flakes, the fractured surface will be grey and as referred as grey cast iron and these graphitic flakes deflect a passing crack and will start the countless new cracks as the material breaks. The compositions of cast irons are around the eutectic point of the iron carbon system, the melting temperature usually ranging from 1,150 to 1,200°C, which is about 300°C, comparatively lower than the melting point of pure iron. Cast iron is tends to be more brittle, except for malleable cast iron. It is capable of resisting against damage and weakened by corrosion and rust.

How Cast iron is made?

Usually pig iron is re melted to make cast iron, along with the considerable amount of scrap iron and scrap steel and various steps are used to eliminate the contaminants such as phosphorus and sulphur. The carbon and silicon content are reduced from 2 to 3.5% and 1 to 3%, and before the final form produced by casting other elements are added for melting. The blast furnace by name cupola is sometimes used to melt the Iron, but more often it is melted in electric induction furnace. Soon after completing the melting process, the molten iron is poured into the ladle or holding furnaces.

Types of Cast iron

There are four types of cast iron; they are grey cast iron, White cast iron, malleable cast iron and ductile cast iron.

Usage of Cast iron

Due to its good fluidity, castability, low melting point, good machinability, deformation resistance and wear resistance, it has become wide spread application in engineering material and are used in pipes, machines, and automotive industry parts such as cylinder heads, cylinder blocks, and gear box cases.

The cast iron is used in constructing a tall building without using the thick walls for constructing the masonry buildings. The slim cast iron columns could able to support otherwise thick masonry columns can support the weight.

The air in the textile mills contained flammable fibres from the cotton, wool being spun. The mills should be constructed with non combustible materials and it is convenient to provide the textile building with an iron frame largely of cast iron by replacing flammable wood.

Questions:

• How cast iron is prepared?
• Mention types of cast iron?