History

The exact date when people developed the technique of smelting iron and produced usable metal is unknown. The oldest iron objects where discovered by archaeologists in Egypt and date from around 4000BC. Iron ornaments were used even earlier.

This relatively advanced technique of hardening weapons was known by 1000BC. The first iron alloys (wrought iron) were made by heating iron ore and charcoal in a forge.

Since the 14^th century metallurgists have been able to decarbonise iron by blowing air into the glowing mixture inside a furnace. During this process the iron ore is reduced to a brittle mass of metallic iron which contains a slag of metallic impurities and charcoal ash. The final mass was taken out of the furnace and then processed with heavy hammers, while it was still glowing, to remove the slag and strengthen the iron. The oxidation of the tailings contained in iron ore is called refining.

The produced iron usually contained about three percent slag and a small percentage of other impurities.

In 1784 the iron producer Henry Cort developed a new method called puddling. He processed the iron ore to steel in a reverbaratory furnace. The product of the puddling method is similar to wrought iron.

In 1855 The versatile inventor Henry Bessemer received a patent for his process to convert pig-iron which is rich in silicon and low in phosphorous to steel.

A year later the brothers Friedrich and Wilhelm Siemens solved the problem of generating high temperatures in a furnace. The brothers Emile and Pierre Martin took advantage of the regenerative furnace developed by the Siemens brothers and used it to produce steel the first time in 1864. This method is called open hearth or Siemens-Martin-Method.

In 1877 Sidney Gilchrist Thomas introduced a new method to improve the dephosphorization during the Bessemer process. His method is very suitable for the production of steel from phosphorous rich pig-iron.