A history of steelmaking

If you look at some of the world’s most iconic structures, there was a key point in history when wrought iron was all but replaced by mild steel as the structural material of choice. Designers and builders suddenly switched to steel when constructing anything from buildings and bridges to railways and warships.

So what happened? Let’s take a quick lesson in steel history and learn how the steelmaking process has evolved since ancient times into the hard and durable steel products we know and use today.

The origins of steel

Steel has been produced on a relatively small scale for thousands of years. The earliest known steel was discovered 4000 years ago in Turkey. Archaeologists and historians also report steel being used for weaponry in the pre-Roman Iberian Peninsula (now modern Spain and Portugal), and later by the Roman Military and the Chinese. At this stage, steel production was incredibly slow and variable.

Across the world, several distinct steelmaking processes had been developed, including wind furnaces and crucibles. These processes produced a range of steels, such as quench-hardened steel in ancient China and the legendary Damascus steel in India around 500BC. Damascus steel was known at this time to be the finest steel in the world as it could bend under pressure without breaking and hold its edge.

Later, specially-designed blast furnaces were introduced for the smelting of iron ore into pig iron, which could then be worked into steel.

Modern steelmaking and the Bessemer Process

Up until the 17^th century AD, the production of steel was time consuming and costly. However, with the expansion of railways across both Europe and America at this time, metallurgists were striving to come up with a more efficient production method.

In 1856, the creation of the Bessemer Process revolutionised steel production. British metallurgist, Sir Henry Bessemer, pioneered the process of blasting oxygen through molten metal. As oxygen passed through the molten metal, it would react with the carbon, releasing carbon dioxide and removing impurities like silicon, thus producing a more pure iron.

At first, however, the process removed too much carbon. Further experimentation led to the introduction of a compound of iron, carbon and manganese (known as spiegeleisen) that helped to remove the excess oxygen and stabilise the carbon content.

The remaining hurdle was to find a way to remove phosphorus, an impurity that makes steel brittle. In 1876, twenty years since Bessemer’s initial work, it was discovered that limestone could be added to the Bessemer Process that would draw phosphorus from the pig iron into the slag.

It was this final innovation that meant iron ore from anywhere in the world could be used to make steel. The Bessemer Process saw steel production costs massively reduced and wrought iron all but replaced with mild steel.

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