Iron and steel industry

A worker in high iron and steel furnaces

steel plant in Luxembourg.

The iron industry (from the Greek σίδερος, síderos, "iron") or siderometallurgy is the technique of treating iron ore to obtain different types of it or its alloys such as steel. The iron ore transformation process begins from its extraction in the mines. Iron is present in nature in the form of oxides, hydroxides, carbonates, silicates and sulfides. The most used by the steel industry are oxides, hydroxides and carbonates. The basic transformation processes are the following:

Óxidos - agraria hematita (February₂O₃) and the magnetite (Feder₃O₄)

Hidroxide - voluntary Limonita

Carbonates - organic Siderite or iron carbonate (FeCO₃)

These minerals are found combined in rocks, which contain unwanted elements called gangues. Part of the gangue can be separated from the iron ore before it is sent to the steel industry, there are mainly two separation methods:

• Imantation: It is to pass the rocks through an imanted cylinder so that those containing iron ore adhere to the cylinder and fall apart from the other rocks, which precipitate in a separate sector. The inconvenience of this process lies in the fact that most iron mineral reserves are in the form of hematite, which is not magnetic.

• Separation by density: All rocks are immersed in water, which has an intermediate density between the gang and the iron ore. The inconvenience of this method is that the mineral is humbled as this harmful in the steel process.

Once the separation is done, the iron ore is taken to the steel plant where it will be processed to convert it firstly into pig iron and later into steel.

Integrated iron and steel mills

An industrial plant dedicated to the complete process of producing steel from iron ore is called a steel industry or integral steel industry, while an industrial plant dedicated exclusively to the production and processing of steel starting from another steel or steel is called a steel mill. of iron.

Production process

The "steel" It is an alloy of iron and carbon. It is produced in a two-phase process. First the iron ore is reduced or smelted with coke and pumice, producing molten iron that is cast as pig iron or conducted to the next stage as molten iron. The second phase, that of steeling, aims to reduce the high carbon content introduced when melting the mineral and eliminate impurities such as sulfur and phosphorus, while some elements such as manganese, chromium, nickel, iron or vanadium are added. in the form of ferro-alloys to produce the type of steel demanded.

In the casting and lamination facilities, the raw molten steel is converted into ingots or into square slabs (slabs) or flats (flog) and later into hot-rolled profiles or sheets.

Processes in integral plants

A comprehensive plant has all the necessary facilities for the production of steel in different formats.

• Coke furnaces: get from coke and gas.
• High furnaces: turning the mineral into cast iron
• Acrylic: Conversion of cast iron or spider into steel
• Mold: produce large ingots (large steel casting parts)
• Debasting lamination trains: reduce the size of the ingots
• Finishing lamination trains: structures and hot sheets
• Cold lamination trains: plates and strips

Raw materials for a comprehensive plant are iron ore, limestone and coke. These materials are loaded in successive and continuous layers in a blast furnace where the combustion of coal aided by air blowing and the presence of limestone melts the iron contained in the ore, which is transformed into liquid iron with a high carbon content.

Photo of the SOMISA steel complex in Argentina.

At intervals, the liquid iron accumulated in the blast furnace is transformed into pig iron ingots or taken liquid directly in refractory containers to the steelworks. Historically the process developed by Henry Bessemer has been the star in the economical production of steel, but today it has been surpassed in efficiency by the processes with oxygen blowing, especially the processes known as LD Steelworks.

Molten steel can follow two paths: continuous casting or classical casting. In continuous casting, molten steel is cast into large blocks of steel known as billets. During the continuous casting process, the quality of the steel can be improved by additions such as aluminium, so that the impurities "float" out at the end of the casting and the end of the last ingot containing the impurities can be cut off. Classic casting goes through an intermediate phase that pours the liquid steel into square or rectangular molds (flasks) depending on whether the steel is intended to produce profiles or sheets. These ingots must be reheated in furnaces before being rolled in roughing mills to obtain square blocks (bloms) to roll profiles or rectangular planes (slabs) to roll flat or shaped plates. heavy coils.

Due to the cost of energy and structural stresses associated with heating and pouring a blast furnace, these primary facilities must operate in continuous multi-year production runs. Even during periods of falling demand for steel it is not possible to let a blast furnace cool down, even though certain production adjustments are possible.

Integrated steel plants are profitable with a production capacity of more than 2,000,000 tons per year and their end products are generally large structural sections, heavy sheet metal, heavy round bars, railway rails and, in some cases, billets and heavy tubing.

A serious environmental drawback associated with integrated steel plants is the pollution produced by their coke ovens, an essential product for the reduction of iron ore in the blast furnace.

On the other hand, in order to reduce production costs, integrated plants can have complementary facilities characteristic of specialized steelworks: electric furnaces, continuous casting, commercial rolling mills or cold rolling.

The world's capacity to produce steel in integrated plants is close to global demand, so competition between producers makes only the most efficient ones viable. However, due to the high level of employment at these facilities, governments often help them financially rather than risk facing mass unemployment. These measures lead, internationally, to accusations of improper trade practices (dumping) and conflicts between countries.

Processes in specialized steelworks

Photo of a hot laminator.

These plants are secondary producers of commercial steel or special steel production plants. They generally obtain their iron from the steel scrap process, especially from automobiles, and from by-products such as sinter or iron pellets (DRI). The latter are more costly and less profitable than steel scrap, so it is always a question of reducing their use to when it is strictly necessary to achieve the type of product to be achieved for technical reasons. A specialized steel mill should have an electric furnace and “scoops” or vacuum furnaces (converters) to control the chemical composition of the steel. The liquid steel goes into light molds or continuous casting to give the molten steel a solid shape. Furnaces are also necessary to reheat the ingots and to be able to laminate them.

Originally these steelworks were adopted for the production of large castings (cranks, large shafts, cylinders of nautical engines, etc.) that are later machined, and for light structural rolled products, such as round cast iron, beams, angles, pipe, light rails, etc. Since the 1980s, the success in direct casting of bars in continuous casting has made this modality productive. Currently these plants tend to reduce their size and specialize. Frequently, in order to have advantages in lower labor costs, specialized steel mills begin to be built in areas that do not have other steel processing plants, focusing on the manufacture of parts for transport, construction, metal structures, machinery, etc..

The capacities of these plants can reach around a million tons per year, with the most common dimensions in commercial steel or low alloys ranging from 200,000 to 400,000 tons per year. The older plants and those producing steel with special alloys for tools and the like may have capacities of the order of 50,000 tons per year or less.

Given their technical characteristics, electric ovens can be started or stopped with some ease, which allows them to work 24 hours a day with high demand or cut production when demand falls.

Laminators

The rolling mills are the machines in charge of laminating, that is, of flattening the steel that arises from the metallurgy and foundry process to create steel raw material in the form of plates or sheets, which can be stamped, stamped and/or plated for obtain secondary products of steel such as automobiles or auto parts, hardware and others.

These only include the following classes of machines for the process: rolling mills, wire rod mills, commercial profiles or cold sheet. To meet the needs of the process, this class of steel used in this process contains a low percentage of carbon, to give it greater malleability.