More often than not, when it comes to selecting an iron alloy for casting, it is important to consider the required mechanical properties, budget, and post-casting methods including heat treatment and machining. These factors and some more decide the type of alloy to be used. Nowadays, the biggest challenge is choosing between ductile iron and cast iron.

Technically, ‘cast iron’ is nothing but iron alloys that are cast or produced in a foundry. An example of one such alloy is Ductile iron. Although a comparative newcomer on the foundry scene, ductile iron has some unique mechanical properties and characteristics that make it different from the rest of the iron alloys. The difference lies in the fact that “cast iron” is usually divided into gray or white iron alloys that have been around in the area of metal smithing for several centuries.

Types of cast iron in the foundry

SG Iron Castings or Ductile Cast Iron: First developed in 1948, it has become a major alloy for ferrous industries, and is less brittle compared to other cast irons.

Malleable Cast Iron: Before ductile iron was discovered, Malleable Cast Iron alloy was very popular. It’s a white cast iron that is subjected to heat for a very long time. Whatever conditions present in the heat treater should be duly controlled. When the malleable iron is done with, the resultant alloy is a lot less brittle. Malleable Cast Iron is still employed for very small, thin casting where the success ratio of ductile is relatively less.

White Cast Iron:  Compared to other cast irons, this alloy exhibits more cooling characteristics leading to a molecule called ‘cementite’ in its lattice. Brittle, as it is an alloy, it exhibits excellent abrasion resistance and hardness. White Cast Iron finds extensive use in the area of bearings and several other high-friction applications.          

Grey Iron Castings: Regular cast iron products are made out of grey iron, therefore when people call it such, this is probably the alloy that is referred to. Unlike its counterpart white cast iron, grey iron consists of a graphitic microstructure. It comes with a good damping capacity and excellent machinability. Both grey iron castings and white cast iron produce strikingly similar-looking casting. Only when they fracture, does their coloring become evident.