Pig Iron is the intermediate iron product between smelting iron ore and usable cast iron products. Grey Cast iron (CI) is made when pig iron is re-melted in small cupola furnaces (similar to the blast furnace in design and operation) and poured into molds to make castings. Cast Iron is considered as an alloy of iron with greater than 2% carbon, and usually with more than 0.1% silicon and there are are 3 other important types of cast iron (CI products) apart from grey cast iron.
The presence of flake graphite in the silicon-iron matrix make grey iron castings a unique material. The presence of graphite, the distribution pattern and the length of the flakes determine the strength and quality of cast iron.
Primarily there are 4 types of cast iron –
- Grey Cast Iron
- Ductile Iron
- Malleable Iron
- White Cast Iron
We will discuss more about Grey Cast Iron here –
In gray iron, slower solidification produces a larger graphite flake size. A slower cooling of the casting will produce a lower hardness in the metallic matrix.
- Fatigue properties
- Damping properties
The properties of grey iron can be determined by the amount of additional elements in the grey iron :
Cast iron contains small percentages of silicon, sulphur, manganese and phosphorus. The effect of these additional elements on the cast iron are as follows:
- Silicon: About 3% of silicon can be present in cast iron. It provides the formation of free graphite which makes the iron soft and easily machinable.
- Manganese: It makes the cast iron white and hard. It is often kept below 0.75%. It helps to exert a controlling influence over the harmful effect of sulphur.
- Phosphorus: It aids fusibility and fluidity in cast iron, but induces brittleness. It is rarely allowed to exceed 1%. Phosphoric irons are useful for casting of intricate design and for many light engineering castings when cheapness is essential.