Seeing as we at Latham’s Security Steel Doorsets sell products which are made from, predominantly, steel (not a huge surprise there!), we thought it was about time to go back to basics at look more closely at this material. After all, we bang the steel drum all the time, talking about its superior strength and longevity over other door materials, but what is it that gives steel these properties in the first place?
Steel is made up of two elements – iron and carbon (referred to as an iron-carbon alloy), but a mixture of other elements will often be present too. So, before the steel can be made, both these elements must be sourced and properly prepared for the steelmaking process.
Because iron occurs naturally as iron oxide, a compound of iron and oxygen, the oxygen needs to be first removed, or ‘reduced’. The material you need to do this is carbon – and this carbon originates from coking coal. But first, the coking coal needs to have its impurities removed to be turned into coke – almost pure carbon.
The coking process involves heating the coking coal to an incredibly high temperature – between 1000-1100 oC – in the presence of oxygen, which works to remove impurities and volatile compounds. This results in the coke needed for steel making, which is first cooled down using water or air, ready to be transported.
As mentioned previously, the coke is needed to reduce iron oxide to remove the oxygen (and other impurities). This involves feeding the iron oxide and coke (as well as certain minerals used to collect impurities, known as fluxes) into a blast furnace where heated air (to about 1200 oC) is blown into. This hot air causes the coke to combust, producing carbon monoxide that (due to its high reactivity) reacts with the iron ore, as well as starting to melt it. There is an opening in the bottom of the furnace that is able to filter off the molten iron (iron that has been extracted from iron ore is known as pig or cast iron) and slag (a name given to the impurities).
This pig iron isn’t ready to go yet! It must be further refined to remove some of the carbon content and other impurities not previously extracted. Now, the carbon content in the steel is important – it is carbon that gives steel its renowned strength. But the carbon content after the reducing process is too high (around 4%), causing the pig iron to be too brittle. So the refining process must remove the excess carbon, but must be careful to keep just enough.
The resulting material is your iron-carbon alloy – the wonderful steel used in our steel security doors which we (and our customers) love so much!