A broad range of alloys are available under the name ‘iron’; these alloys are classified according to the percentage of carbon content. Malleable iron and cast iron (also called grey cast iron) are two popular alloys. Major differences between Malleable Iron and Cast Iron lies in their formation, carbon content, applications, advantages and disadvantages.

Carbon Content:
Malleable iron comprises 0.08% to 0.2% carbon. However, Cast iron, comparatively, has increased carbon content than malleable iron. Its composition of carbon varies from 2% to 4.5%.

Formation Differences:
The process of producing malleable iron involves making white cast iron first and cooling the cast iron quickly, preventing graphite flakes from forming inside. The white cast iron is subjected to heating for a considerable period of time with certain materials.  These periods are characterised by the decomposition of carbon content of iron that is knocked out of the metal, whilst some of it converts into graphite particles.  The reduction in the volume is made up by the addition of liquid metals to prevent breaks. The resultant output is malleable iron.

Cast iron can be produced in a bloomery furnace. A bloomery furnace employs direct reduction to smelt iron and this means that the iron never passes into a liquid state. For other iron casting types, when the furnace turns out too hot, the iron absorbs sufficient carbon to form grey cast iron. On cooling, it forms graphite flakes.

Advantages & Disadvantages:
Grey cast iron is corrosion resistant and possesses high dampening capacity. However, it is highly brittle; as it is hard, it is tough to create a smooth surface and can drastically lower tool life too.

Malleable iron, on the other hand, is quite machinable and ductile. The main disadvantage is that it shrinks when cooled. This is because it loses volume while it cools.

Applications:
Grey cast iron goes into making shrink-free cast pieces such as motor blocks. Malleable iron is used in the manufacture of the compressor, compressor hubs, universal joints, compressor hubs, crankshafts, connecting rods, flanges and components for heavy-duty equipment including railroad and marine equipment.