Difference Between Cast Iron and Wrought Iron

Main Difference – Cast Iron vs Wrought Iron

‘Casting’ is a form of a manufacturing process where liquidized material is poured into a mould and then allowed to cool down. To be specific, the process of solidification is called ‘casting’. The solidified material is broken out of the material upon completion. Metals commonly undergo casting in order to be put into various desired shapes. Cast iron and wrought iron are two such metals which have undergone this process. The main component of both cast iron and wrought iron is the Iron element itself. The main difference between cast iron and wrought iron is the amount of  carbon present in both forms. Cast iron has a carbon content higher than 2% whereas wrought iron has a very low carbon content compared to cast iron, which is less than 0.08%.

What is Cast Iron

As mentioned above, the Carbon content in cast Iron is higher than 2%, which differentiates it from other forms of cast irons. It can be further separated into two types called ‘white cast iron’ and ‘grey cast Iron’. The white cast irons contain carbide as an impurity and accommodates deeper cracks. In contrast, the grey cast irons contain graphite as an impurity and handle cracks at the surface level, initiating many new cracks.

‘Pig iron‘, the molten iron in a blast furnace, is another related term to cast iron. Usually cast Iron is produced by re-melting pig iron with a large quantity of iron and steel strips along with limestone and coke (for Carbon). Undesired products such as Sulphur and Phosphorous gets heated/burnt in the process, and a significant amount of carbon is lost here as well. However, carbon is re-introduced into the melted metal to meet the desired content. Cast iron has very good casting properties and is well known for its wear resistivity. It also absorbs vibrations well and has a good machinability. But its response to tension is very low. Some of the most common instances where cast iron is used are; oil pan, hammer, pitons, valves, motor blocks, cylinder blocks, knives, etc.

What is Wrought Iron

Wrought Iron is not necessarily melted, it is actually heated and then the desired shaped is obtained using various tools. Wrought Iron is made by mixing pig iron with ‘slag’, which is a glass-like mixture of metal oxides and silicon oxides. It is then being hammered in order to gain it shape; this process eliminates a lot of Carbon present initially. Wrought Iron is seldom used nowadays for manufacturing as its use has been largely replaced by the advent of mild Steel.

Unlike cast Iron, wrought Iron has a high melting point allowing it to be handled easily when hammered into shapes. Wrought Iron was used in the early days for railways, swords, cutlery, etc. A classic example is the Eiffel tower, which is made of a form of wrought Iron.

Difference Between Cast Iron and Wrought Iron

Definition

Cast Iron is a form of cast Iron with a Carbon content exceeding 2%.

Wrought Iron is a form of heated Iron with a very low Carbon content which is less than 0.08%.

Properties

Cast Iron is more resistant to wearing and has good machinability.

Wrought Iron is not brittle and has a moderate level of strength.

Melting Point

Cast Iron has a low melting point which makes it easier to be melted and poured into a mould.

Wrought Iron has a high melting point which allows it to be handled while hammering.

Usage

Cast Iron is still widely used for various applications.

Wrought Iron is seldom used as many of its applications were replaced by mild steel.

Image Courtesy:

“[Explored] Eiffel Tower” by Jeroen Bennink (CC BY 2.0) via Flickr

“Cast-Iron-Pan” by Evan-Amos – Own work. (Public Domain) via Commons

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