Iron-carbon alloys are called cast iron when the carbon is present in a proportion over 1.7% together with other elements in varying proportions. In addition to iron and carbon, other elements generally constitute the alloy including: silicon, manganese, phosphorus, sulphur and sometimes nickel, chrome and molybdenum.

Grey irons:
The name comes from the grey appearance of the fracture. They have structures with ferritic-pearlitic matrices in which irregular graphite flakes are dispersed, interrupting the continuity of the matrix.

The mechanical properties of grey irons depend on the chemical composition of the alloy as well as the average thickness of the castings.

Spheroidal graphite cast iron:
This is the fruit of studies researching melting and treatment methods that make it possible to modify graphite, transforming its lamellar shape into a nodular or spheroidal shape to avoid interrupting the continuity of the cast iron matrix. This eliminates the primary cause of fragility in the iron.
Another feature of spheroidal cast iron is its superior ability to be processed by machine tools, and its hardness is superior to steel and regular cast iron.
The castability of this cast iron is distinctly superior to that of malleable cast iron or steel. This makes it possible to pour very complicated castings.
Its resistance to atmospheric corrosion is 5 times greater than that of carbon steel.
Its resistance to oxidisation is considerably better than that of lamellar graphite cast iron.

This cast iron's areas of application include:

The mechanical properties of spheroidal cast iron are:

Spheroidal graphite cast iron alloyed with silicon-molybdenum (SiMo):
SiMo cast iron is suggested for high temperature applications (<760°C) in which resistance is required against thermal shock, oxidisation and flaking in heat. One of the problems of this material is its relative fragility. It is generally used in the annealed state.
A typical example of application: exhaust pipes for engines with turbocompressors.

SiMo cast iron's mechanical properties are:

Ni-Hard cast iron

Ni-Hard is a white cast iron alloyed with nickel and chrome, which possesses superior hardness and high resistance to abrasions. Its structure consists of carbons in an austenitic-martensitic matrix.
It is used when optimal hardness is required.

Ni-Hard's cast iron's mechanical properties are: 

Spheroidal Ni-Resist cast iron:

Ni-Resist is the commercial name given to a group of cast irons with high nickel content, with austenitic structures that are characterised by the following properties: resistance to corrosion, resistance to oxidisation and high temperatures, resistance to wear and erosion, superior strength, non-magnetism and superior electric resistance.