The Steel Age 1800s-present

_Elsa_

‘The development of steel can be traced back 4000 years to the beginning of the Iron Age. Proving to be harder and stronger than bronze, which had previously been the most widely used metal, iron began to displace bronze in weaponry and tools.

For the following few thousand years, however, the quality of iron produced would depend as much on the ore available as on the production methods.

By the 17th century, iron's properties were well understood, but increasing urbanization in Europe demanded a more versatile structural metal. And by the 19th century, the amount of iron being consumed by expanding railroads provided metallurgists with the financial incentive to find a solution to iron's brittleness and inefficient production processes.

Undoubtedly, though, the most breakthrough in steel history came in 1856 when Henry Bessemer developed an effective way to use oxygen to reduce the carbon content in iron: The modern steel industry was born.'

The Bessemer Process and Modern Steelmaking

The growth of railroads during the 19th century in both Europe and America put enormous pressure on the iron industry, which still struggled with inefficient production processes. Steel was still unproven as a structural metal and production of the product was slow and costly. That was until 1856 when Henry Bessemer came up with a more effective way to introduce oxygen into molten iron to reduce the carbon content.

Now known as the Bessemer Process, Bessemer designed a pear-shaped receptacle, referred to as a 'converter' in which iron could be heated while oxygen could be blown through the molten metal. As oxygen passed through the molten metal, it would react with the carbon, releasing carbon dioxide and producing a more pure iron.

The process was fast and inexpensive, removing carbon and silicon from iron in a matter of minutes but suffered from being too successful. Too much carbon was removed, and too much oxygen remained in the final product. Bessemer ultimately had to repay his investors until he could find a method to increase the carbon content and remove the unwanted oxygen.

At about the same time, British metallurgist Robert Mushet acquired and began testing a compound of iron, carbon, and manganese, known as spiegeleisen. Manganese was known to remove oxygen from molten iron and the carbon content in the spiegeleisen, if added in the right quantities, would provide the solution to Bessemer's problems. Bessemer began adding it to his conversion process with great success.

One problem remained. Bessemer had failed to find a way to remove phosphorus, a deleterious impurity that makes steel brittle, from his end product. Consequently, only phosphorus-free ore from Sweden and Wales could be used.

In 1876 Welshman Sidney Gilchrist Thomas came up with the solution by adding a chemically basic flux, limestone, to the Bessemer process. The limestone drew phosphorus from the pig iron into the slag, allowing the unwanted element to be removed.

This innovation meant that, finally, iron ore from anywhere in the world could be used to make steel. Not surprisingly, steel production costs began decreasing significantly. Prices for steel rail dropped more than 80% between 1867 and 1884, as a result of the new steel producing techniques, initiating the growth of the world steel industry.' (Source)

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