Steel Production: How it all started and where we are now

The steel industry of the 21st century has come a long way since the 1855’s Bessemer process that led to mass production of steel post the Industrial Revolution. It was this process that replaced the wrought iron that was prevalent for centuries. This led to the cheaper production of steel, with a huge reduction in labour costs and efficiency was boosted enough for industrial level manufacturing of steel. But steel had its own share of unsung glory and was developed and used by many civilizations long before the Bessemer Converter. Here is a brief account of the history of steelmaking and its progress over the years:

According to the data obtained from studying the artefacts of 900 BC, it can be said that the Egyptians had developed a way to produce steel, ahead of its time. They had learned the exquisite properties of steel and had incorporated reheating of quenched steel at around 350° to 500° C, through a process called tempering. Today’s TMT technology of steel production which is extensively used by all the leading manufacturers owes its roots to this process. The Chinese were able to produce heat-treated steel during the early Han dynasty (206 BC-AD 25).The crucible steel production process of the 6th century BC, at production sites of Kodumanal in Tamil Nadu, Golconda in Telangana, Karnataka and Sri Lanka and the Tamils of the Chera Dynasty produced what was termed as “the finest steel in the world”, i.e. Seric Iron. It was exported to the Romans, Egyptians, Chinese and Arabs by 500 BC.The steel was exported as cakes of steely iron that came to be known as "Wootz".

Wootz steel in India had a high amount of carbon in it.The Romans had helped to spread the technology for steelmaking, but with the fall of their empire, the steel production continued in Europe to some extent. By the beginning of the 15th century, water power was used to blow air into bloomery furnaces; as a consequence of which it was possible to increase the temperature in the furnace to above 1,200° C. In 1751, Benjamin Huntsman of Sheffield, Englandre-melted the European Blister Steel in clay crucibles at around 1600°C, giving rise to ‘crucible steel’. Later, it spread to the rest of Europe, only to be replaced by the Bessemer Converter.

Bulk production of steel was possible after Henry Bessemer had obtained the British patents in 1855 for a pneumatic steelmaking process and his own creation: The Bessemer Converter. He had used a pear-shaped vessel lined with ganister (a refractory material containing silica) into which air was blown from the bottom through a charge of molten pig iron. He soon realized that the subsequent oxidation of the silicon and carbon in the iron would release heat. If a large enough vessel was to be used, the heat thus formed would be more than offset the heat loss. The temperature of 1,650° C was thus obtained in a surprising time of 15 minutes with a charge weight of about half a ton in this converter. This led to the mass production of steel throughout the world that flourished in the post-modern era.

Then came the open-hearth process which was developed in the 1860s by William and Friedrich Siemens in Sheffield. The furnace was fired with air and fuel gas that was preheated by combustion gases to 800° C. A flame temperature of about 2,000° C was easily possible that was sufficient to melt the charge. The great advantage of the open hearth was its flexibility: the charge could be made from only the molten pig iron, or all cold scrap, or any combination of the two of them. Thus, it was possible to produce steel from a source of liquid iron that could be shaped based on any set of requirements.

In the Post World War 2 era, the abundance of industrial grade oxygen fostered the steel manufacturing process by directly blowing oxygen into the charge. The Linz-Donawitz (LD) process, developed in Austria in 1949, blew oxygen through a lance into the top of a vessel that was similar to the Bessemer Converter. This oxygenated Steelmaking improved the combustion capacity of the furnace that reduced the defects thus formed, casting a steel that was uniform in composition.
Towards the end of the 20th Century, due to humongous technological development in the steel sector, the manufacturers had moved from the age-old processes to a new technique by pouring molten steel in stationary moulds to cast ingots. These ingots were re-heated to form mild steel rods, which were used for reinforcement in cement-concrete mixes to easily build constructions upto 5 stories. This cold-rolling process replaced the age-old brick and mortar style of constructions, making the use of steel in infrastructure prevalent.

Further, the mild steel was perfected by the Thermo Mechanical Treatment process of steel manufacturing. The steel thus formed has much better properties than mild steel, due to its austenitic, martensitic, pearlite, bainite, and spherodite properties in its microstructures. TMT steel rods are produced by processing steel billets, using Tempcore technology, where hot rolled billets are cooled rapidly with jet sprays on its periphery to obtain hardness. They are reheated to form tempered martensite on its outer layer to ensure great strength. The heated bars are then compressed in heavy presses to expand and harden them at the same time. The heated, elongated bars are cooled at an atmospheric temperature to form a core of ferrite-pearlite, which helps the bar maintain its characteristic ductility.

TMT Steel is one of the most sought-after building material in modern constructions as it offers exceptional strength and ductility while being affordable and long-lasting. Their exceptional properties are a result of centuries of innovation and technological developments in metallurgy. Agni Steels is a proud manufacturer of high-quality TMT steel rods in India, and hopes for the advancement in the process using their expertise of over 2 decades of steel manufacturing. 

1 comment:

  1. Thanks for sharing this useful article. while thinking of construction TMT Bars play a important role.


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