Converting Pig Iron to Wrought Iron and Steel.
The pig iron can be further refined to produce steel or wrought iron. Both these methods reduce the carbon content of the pig iron, which in turn reduces the brittleness property of the metals.
Wrought Iron Process
Wrought iron is produced by pummeling the pig iron using mechanically driven hammers in a wrought iron works. This process prepares it for the next stage which is the heating and forging to the desired wrought iron designs and shapes.
This used to be an art of the blacksmith, but is now normally carried out by machines.
This process is used to remove impurities from the pig iron produced in a blast furnace. It has developed from the early methods used such as an open hearth, or a Bessemer furnace. Today we normally use an Electric Arc Furnace (EAF) or a Basic Oxygen Furnace. (EAF)
Both methods remove a high percentage of the carbon content from the pig iron, along with the impurities of aluminum, calcium (produced during tapping), sulphur, silicon, manganese, and phosphorus.
- Electric Arc Furnace (EAF)
The vertical circular steel furnace is brick-lined and has a roof which contains graphite electrodes. The electrodes are withdrawn and the roof is lifted to facilitate the loading of the pig iron to the bottom of the furnace. This is followed by a known quantity by scrap steel, which is dependent on the final grade of steel required.
Once the roof is replaced, the electrodes are lowered and an initial voltage is applied to them, and when the scrap steel has started to melt, the main voltage is applied.
When the metal is molten, oxygen is injected into it, with the impurities being converted to oxides and forming a slag. The oxygen also reacts with the carbon forming CO which is combusted adding heat to the process. Oxygen injection also reduces the carbon, nitrogen and hydrogen content on completion of the process, samples are taken and analyzed, and if acceptable, steel with content of up to 1% of carbon is poured into ingots.
- Basic Oxygen Furnace (BOF)
If the furnace has been designed to be linked to the blast furnace process, molten iron is carried in crucibles and poured into the BOF. This is a much more efficient method of removing the bulk of carbon and impurities rather than using solid pig iron
The crucible of molten iron can undergo pretreatment by the injection of magnesium, iron oxide to remove the sulphur, phosphorus, and silicon, or these impurities can be removed during the BOF process.
The BOF furnace is filled up to 20% scrap steel, and then the molten iron is poured into the furnace from the crucible.
Oxygen is injected through a water cooled steel lance into the molten metal promoting the same effects as in the EAF steel processing system.