Throughout history, man has used different types of metal, such as gold, silver, copper, bronze and tin, but it was with the discovery of iron and the beginning of the third prehistoric period, “the iron age”, that humanity started moving towards what is known as “civilisation”. From the analysis of the most ancient archaeological finds, the first iron used by men was of meteoritic origin, which is an alloyed form with a high nickel content. Initially, this metal alloy was processed by heating it to incandescence with small coal-fired furnaces and then beating it with an anvil: this technique characterises the Bronze Age and was used by various civilisations, both in Central Asia and in the Mediterranean region. It was precisely the metal-working knowledge developed during the Bronze Age that allowed the transition to production by direct reduction from iron ore, which was treated in the presence of coal, initially in bloomeries with air entering by natural draft and, later, forced with bellows. Given the relatively low temperatures that could be reached in these furnaces, the metallic iron was collected in the form of a spongy mass containing slag, which was eliminated by reheating and hot hammering.

To take a (very big) step forward, it will be necessary to leave prehistory and enter history. It was only towards the end of the 14th century that the first blast furnaces were developed, i.e. furnaces that could reach the melting temperature of iron, so that the product obtained was no longer sponge iron, but a metal product with a high carbon content, i.e. cast iron. This could subsequently be “refined” into steel, reducing its content of carbon, silicon and other elements, by burning in excess of air. Almost 400 years passed before steel of a more homogeneous quality could be produced in consistent quantities. In around 1740, Benjamin Huntsman, a watchmaker from Sheffield engaged in experiments to find a more resistant material to build springs and knives, discovered that it was possible to reduce the carbon content of cast iron, and therefore produce steel, by melting it in crucibles mixed with pure iron. The process developed by Huntsman, which was long and not particularly efficient, remained the only possibility for producing moderate quantities for several decades. It was only between the late 18th and early 19th century that more efficient methods were developed to achieve high temperatures in blast furnaces. The first method, which was based on blowing hot air, was then superseded by an even more technologically advanced method, known as “puddling” (to “puddle” means to stir and mix). The puddling process stems from the invention of the reverberatory furnace, attributed to Henry Cort and patented in 1784. This type of furnace had great advantages: blowing systems (bellows) were no longer needed and, more importantly, high levels of production could be achieved.

However, a persisting issue was the large quantities of energy needed to make the furnaces work. A partial solution was found in 1855 by Henry Bessemer, who invented the “converter”, a thermally autogenous reactor, in which energy is produced by exploiting exothermic chemical reactions involving the elements that compose cast iron (carbon, silicon, etc.), thus reducing the use of external energy sources. This method made it possible to produce greater quantities of steel at the expense, however, of quality, as it did not allow the elimination of the sulphur and phosphorus present in the cast iron. The solution to this came from the Londoner Sidney Gilchrist Thomas, another central character in the history of the iron and steel industry, who patented a new converter in May 1878, in which the acid quartz-containing Bessemer coating was replaced with a basic cover containing dolomite. The Thomas converters were adjusted and improved various times and remained in operation until the mid-1900s, when the modern oxygen converters (the so-called Basic Oxygen Furnace or BOF) were introduced.

Starting from the late 19th century, steel became a crucially important material for the economy of the western world. The discovery of new industrial production processes represented a real revolution for the time. Suffice it to say that, in a little over twenty years, world production rose from less than 1 million tons in 1879 to almost 30 million tons in 1900. Steel began to be used in the transport sector, replacing iron in the construction of railway networks, with steel rails proving more durable and resistant than iron ones. Its use was also extended to sea transport, in particular for the construction of locomotive boilers and of the ships themselves, including large vessels such as ocean liners. Great works of the time in which steel was used include the Eads Bridge (1874), the first bridge to have a steel and iron load-bearing structure, built over the Mississippi, and the Eiffel Tower in Paris, completed in 1889. A symbol of the industrial age, the latter was made of puddled iron, an alloy obtained from cast iron and similar to steel, with a total mass of more than 10,000 tons and a height of 324 metres.

Further progress was made over the next few years, and producing different types of steel become possible. In 1904, chromium was discovered to strongly inhibit corrosion and, in the same year, the Frenchman Léon Guillet produced a stainless steel alloy with a low carbon content. In 1912, Eduard Maurer discovered austenitic stainless steel, and Krupp patented an alloy called 18/8, containing 18% chromium and 8% nickel. In 1913, the Englishman Harry Brearley developed a martensitic stainless steel alloy intended for the cutlery sector. The techniques and production processes were further refined in the period between the two world wars, and steel was increasingly used for the construction of civil structures, such as, for example, skyscrapers: the Empire State Building, inaugurated in 1931 and standing 381 meters tall, was built using 57,000 tons of stainless steel. Today, steel is among the most used materials in many sectors, while production technologies are becoming increasingly advanced and increasingly oriented towards recycling. But that is another story.