During the mid-70's, there was an industry-wide tendency away from castings and towards forgings and fabrications, due, in part, to the attrition of iron foundries because of safety and pollution legislation. But recent years have shown a marked return to castings for their machinability and flexibility in design. Iron castings allow for :
Castings with complex internal and external geometries are possible often reducing the need for other manufacturing operations such as machining, forging, and welding.
Iron castings provide superior dampening of mechanical noise and vibration.
A single casting can replace mult-part assemblies and fabrications.
A National Center for Manufacturing Sciences study has shown that in certain machine tool applications, replacing fabricated structures with ductile iron castings resulted in a 39-50% cost savings.
The term "cast iron" designates an entire family of metals with a wide variety of properties. Steels and cast irons are primarily iron that is alloyed with carbon. Steel always contains less than 2% carbon, which all cast irons contain more than 2% carbon. Cast irons must also contain appreciable silicon.
The high carbon content and the silicon in cast irons make the excellent casting alloys. They are easily melted, and very fluid in the liquid state. Irons also solidify with little shrinkage and contraction problems.
There are four basic type of cast iron which are best differentiated by their microstructure. The four basic metallurgical types are gray iron, ductile iron, white iron, and malleable iron.