Iron in Construction- Pig Iron, Wrought Iron & Cast Iron

Iron, represented as Fe in the periodic table is the chemical element that is found on the earth's mass on its inner and outer core. Pure iron, also referred to as ferrite is a relatively soft material. This naturally formed element is extracted and processed to form various materials.

Iron in its purest state is available in the form of iron ore or ilmenite. This natural form undergoes different stages of extraction and production processes that result, in: Pig iron, wrought iron, and cast-iron types.

1. Iron metal is extracted from iron ore by the process called smelting. This process gives the product called Pig iron or crude iron.
2. The pig iron is remelted in the puddling furnace to obtain wrought iron. 
3. Cast iron is manufactured by remelting pig iron with substantial quantities of iron, limestone, and carbon (coke), along with processes to remove undesirable contaminants. This remelting is done in a furnace known as a cupola furnace, which is more or less the same as a blast furnace.

1. Pig Iron

Pig iron is the product of smelting iron ore. It has a very high carbon content from 3.5 to 4.5 percent and hence are highly brittle and hard.

Pig Iron

Pig iron is not pure iron. It also consists of various impurities like sulfur, silica, and phosphorous.

Pig iron is not a saleable product. It is an intermediate product formed during the production of wrought iron, steel, and cast iron from iron ore.

2. Wrought Iron

Wrought iron is produced by remelting the pig iron in the puddling furnace. It is made by repeatedly heating and working it with tools to deform it to the required shape. It is hence also called worked iron.

It is rich in iron (98%) and possesses very less carbon content i.e. less than 0.08%. Hence it is more soft and ductile. It is highly resistant to fatigue and undergoes a large amount of deformation before failing.

Wrought iron is corrosion resistant. They have been used extensively by blacksmiths for traditional "wrought iron" products.

They are used to make chains, crane hooks, fences, gates, and carpenter tools.

3. Cast Iron

Cast iron is formed by melting and remelting the iron and mixing it with scrap metals and other alloys. The liquid mixture is then poured into molds, cooled, and then solidified. Hence, compared to wrought iron, instead of deforming the iron into the required shape, the shape is easily molded using cast iron.

Cast iron has high carbon content from 2 to 4%, along with other iron constituents. Due to the high carbon content and the way it is cast, they are very brittle, hard, and non-malleable. 

Cast iron cannot be bent, stretched, or hammered into the required shape. It has weak tensile strength, therefore it undergoes fracture before it deforms or fractures. 

Cast iron is used in pipes, machinery, and automotive parts such as cylinder heads, cylinder blocks, and gearboxes. It is resistant to oxidation damage but difficult to weld.

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