Steelmaking

The aim of the production of steel is steel, so iron alloys having a low carbon content and the desired properties such as hardness, corrosion resistance or ductility to manufacture.

A steel mill is a factory in the metal industry, which usually then produces steel using blast furnaces and cast iron from the pig iron. The employees of a steel plant called steelworkers or steelworkers.

Method

Blast furnace route

In the blast furnace process pig iron from iron ore using coke is first prepared. Thereafter, produced by other methods from the hot metal of the steel, to be additionally used is usually scrap.

Making steel from iron ore takes place is currently usually performed by means of a blast furnace. The iron ore is used as a lump, pellets or sinter, and other components (limestone, slag, etc.) mixed together with the reductant (coke ) on the so-called Möller, and then charged. The blast furnace is a metallurgical reactor, in which the burden column of hot air, the so-called wind reacts countercurrently. By burning the carbon from the coke to the required result, the reaction heat and carbon monoxide, which passes through the column and reduces the iron ore burden. The result consists of pig iron and slag are tapped periodically.

Since the pig iron still contains a lot of carbon, it must go through an additional process step. By blowing oxygen, the so-called refining, the carbon is oxidized and there is molten steel. After alloying the desired elements he is cast strand or in the mold to semis. The casting requires special techniques, a distinction is made between pacified and effervescent cast steel. Under Calm is meant to bind the dissolved oxygen in the melt by alloying with aluminum or silicon. This will affect resulting in growing cold steel segregations ( Materialentmischungen, such as sulfur deposits ) or cavities ( by the shrinkage of the material conditional cavities ). Both are associated with quality losses.

Direct reduction

The disadvantages of the blast furnace, the requirements for the starting materials and the high output of carbon dioxide. The iron carrier used and the coke must be lumpy and hard, so that sufficient voids remain in the burden column, ensure the passage through the blown wind. The CO2 emissions provides a strong environmental impact dar. reason efforts are to replace the blast furnace route. But so far no method compared to the blast furnace has been able to establish. These are, the sponge iron and pellet production in rotary kilns and the Corex, Midrex and Finex process.

The most widespread the Midrex or HYL direct reduction method, the sponge iron and HBI (English Hot Briquetted Iron ) have so far produce as solid feedstock. This is still burdened with a certain amount of gangue of the ore output, but the carbon content is usually not higher than 1%.

The Corex process is recent and produces a liquid, cast iron like starting material, the carbon content of about 3.5 to 4%. The Corex process is a two stage smelting reduction process (English: smelting - reduction), in the pig iron based on non- coked coal and iron ore can be produced. The aim of the smelting reduction process is to be generated by the combination of the melting process, coal gasification and direct reduction of molten iron, having the quality of the blast furnace pig iron. The smelting reduction process of combining the direct reduction ( pre-reduction of iron to iron sponge ) having a melting process (main reduction). So the process is in two stages into separate units. First, the ores are reduced to sponge iron, in the second step, the final reduction and melting into pig iron. The necessary energy for the melting process provides the combustion of coal (not carbonized ). In this case large amounts of carbon monoxide as a result the exhaust gas, which is used as a reducing gas.

Steel-making process

One can distinguish between so-called blow-molding process and open-hearth process.

In the blowing process, the pig iron is refined with oxygen or air. The oxidation process, which reduces the carbon content ( refining ), provides enough heat in these methods, to maintain the liquid steel, an external heat supply in the converters is therefore not necessary. The blowing process can be additionally divided into inflation process and Bodenblasverfahren. The Bodenblasverfahren include the Bessemer process and the Thomas process, but now have no meaning. The most widely used is the inflation method Linz Donawitz process (LD) - or oxygen process. In the LD converter, liquid pig iron and steel scrap are charged and added slag. A lance oxygen is blown onto the melt. Here in the steel burn impurities such as sulfur, phosphorus, carbon, etc. and become the flue gas or the slag. The completeness of the removal can be determined with the Baumann impression. By associated with the combustion enormous heat development of the beige passed scrap is melted. A variant of the LD- process is the oxygen Durchblasverfahren or a combination of inflation and Durchblasverfahren (LWS process according Loire spiral Sprunch or TBM method according Thyssen blow metallurgy), wherein the oxygen through nozzles in the bottom of the converter, if appropriate in addition to oxygen lance is blown.

In the open-hearth process, the necessary oxygen for the oxidation is removed from the pig iron added scrap and ore. In addition, the open-hearth converters must be externally supplied heat. The best-known open-hearth process are the open-hearth furnace. Fresh effect heating action, and are based on an oxidizing combustion gas-air mixture which is passed through the shallow melt pool. The Siemens - Martin process is no longer used because of its insufficient productivity and is now replaced by the basic oxygen.

In the electric steel method, the heat required for melting is produced by an arc or by induction. The arc furnace is charged with scrap, sponge iron and pig iron. Moreover, even lime for slag formation and reducing agents are added. The running to the melting of the graphite electrode arc generated temperatures up to 3500 ° C. Therefore, refractory alloying elements such as tungsten and molybdenum can be melted down than ferro-alloys. With arc furnaces all types of steel can be produced, but they are used mainly due to the high costs for the production of carbon and stainless steels. This scrap is heated above three electrodes until the steel is liquid. A melting process takes about 30 minutes. The capacity of the tiltable electric furnaces is 100 to 200 t. The crude steel is poured into a steel ladle.

In the secondary metallurgy, the melt is ready for casting treated ( ladle furnace, vacuum system ). The steel is then poured into the so-called mold. This mold may also consist of elements, which constitute a small-scale channel ( = the mold ) for continuous casting method. This then enables the use of the heat of the casting process, as much as possible for the subsequent shaping or rolling. To generate high-grade steels remelted be used, eg the electroslag remelting (ESR ). Alloy steels for metals such as chromium, nickel, cobalt, molybdenum, tungsten or manganese are added.

In the steelmaking slag is always formed as a byproduct.

In modern times steel is increasingly being produced in integrated steel works that integrate the production of pig iron, steel production and semi - fabrication in a factory in order to save transport, energy and costs.

Historical method

The largest steel producer

The most important steel manufacturing country is China, followed by Japan and the United States. In Europe, Russia, Germany and Italy are the three main producers. As a single location in Duisburg was from steelmaking long time in the first place. There you will find the most modern and productive blast furnaces. Meanwhile, Shanghai has moved to the first position in steel production (production quantity).

A list of the largest steel company is listed here in a separate article.

The largest steel plant in Germany is the ThyssenKrupp steel plant Schwelgern.