Steelmaking Process

The borderline between iron and steel was defined during the Industrial Revolution, with the development of furnaces which allowed not only the correction of impurities in iron, but also the addition of properties such as resistance to weariness, impact, corrosion, etc. Because of these properties and its low cost steel came to represent around 90% of all metals consumed by the industrial civilization.

Introduction



When men could produce enough heat to melt iron ore, the Bronze Age gave way to Iron Age. The cost factor played a key role in this change.

The borderline between iron and steel was defined during the Industrial Revolution, with the development of furnaces which allowed not only the correction of impurities in iron, but also the addition of properties such as resistance to weariness, impact, corrosion, etc. Because of these properties and its low cost steel came to represent around 90% of all metals consumed by the industrial civilization.

Basically, steel is a carbon and iron alloy. Iron is found throughout the surface of the planet, strongly associated to oxygen and silica. Iron ore is an iron oxide, mixed with thin sand.

Carbon is also relatively abundant in nature and may be found under various different forms. In the steel industry, mineral coal and, sometimes, vegetable coal are used.

Coal plays a double role in the production of steel. As fuel, it allows reaching high temperatures (around 1,500ºC) necessary to melt the ore. As a reducer, it combines with the oxygen from the material at high temperatures, freeing the iron from it. The process of removing oxygen from iron to combine it with carbon is called reduction and takes place inside a piece of equipment called a blast furnace.

Before being put in the blast furnace, the ore and coal are previously prepared so as to improve the performance and cost-efficiency of the process. The ore is transformed into pellets and the ore is distilled to obtain coke, obtaining also carbochemical byproducts.

During the reduction process, iron becomes liquid and is called pig iron or first-melting iron. Impurities such as limestone, silica, etc. form slag, the raw material for the production of cement.

The next stage is refining. The pig iron is taken to the steel shop, still liquid, to be turned into steel, by burning impurities and additions. The refining of steel is made in oxygen or electrical furnaces.

Finally, the third classic stage in the process of producing steel is lamination. Steel, during the process of solidification, is mechanically conformed and transformed into steel products used by the transformation industry, such as heavy and thin plates, coils, rods, wire, drawn products, bars, etc.

As technology evolved, the stages of reduction, refining and lamination are being shortened, ensuring higher production speeds.

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