Grey Cast Iron is made by remelting pig iron. It is an alloy of Carbon and Iron. Small amounts of Silicon, Phosphorus, Manganese and Sulphur are also present in it. The reasons behind its popularity are: ability to make complex structures and low cost. In addition, the excellent properties of Grey Cast Iron have made it one of the most widely used alloys.
- Relatively inexpensive.
- Easier to cast due to expansion.
- Grey iron also has unique properties which are useful for applications with sliding surfaces like hydraulic pistons.
- Free graphite within the structure acts as a lubricant and aids machining.
- Excellent damping and wear characteristics.
- Used where tensile strength and ductility are non-critical.
- Engine blocks.
- Valve bodies.
Ductile Iron is also known as SG Iron, Nodular Cast Iron and Spheroidal Graphite Iron. The main characteristics of this
material is the structure of the graphite. In Ductile Iron, the graphite is in the form of spherical nodules (hence the
name Spheroidal Graphite) rather than flakes as in Grey Iron. This nodular graphite structure inhibits the creation of
linear cracks hence the ability to withstand distortion.
- High tensile strength and ductility compared to grey iron.
- Tensile strength and ductility can vary across the range of grades allowing for irons to be suitable for a wide range of applications
- Load bearing applications.
- Replaces steel for many applications and achieves a significant cost saving.
- Easy to machine.
- Corrosion resistant compared to other ferrous metals.
The physical properties of different types of steel and steel alloys depend primarily on the amount of carbon and its distribution within the iron. Iron alloy containing carbon from as low as 0.03 percent (as in ingot steel) to 2.08 percent by weight (as in cast iron), and varying amounts of other
elements (mainly chromium, manganese, molybdenum, nickel, and silicon) depending on its end use. Higher amounts of carbon make the steel more fluid and castable, and lower amounts make it purer for specialized purposes such as electrical steel and stainless steel.
Stainless steel is an alloy of Iron with a minimum of 10.5% Chromium. Chromium produces a thin layer of oxide on the surface of the steel known as the ‘passive layer’. This prevents any further corrosion of the surface. Increasing the amount of Chromium gives an increased resistance to corrosion.
Stainless steel also contains varying amounts of Carbon, Silicon and Manganese. Other elements such as Nickel and Molybdenum may be added to impart other useful properties such as enhanced formability and increased corrosion resistance.