The aim of the production of steel is steel , so iron alloys with low carbon content and the desired properties for the casting or forging such as elongation at break , hardness , corrosion resistance or formability to manufacture. The branch of steel production is called the steel industry .
A steel plant is a plant in the metal industry , mostly by means of blast furnace pig iron and then from the pig iron steel produced. The employees of a steelworks are called steelworkers or steel cookers .
In modern times, steel is increasingly being produced in integrated steelworks that integrate pig iron and crude steel production (primary metallurgy) , steel production (secondary metallurgy) and semi-finished products in one plant in order to save transport , energy and thus costs . In steel production, carbon dioxide and slag are always produced as by-products.
Unalloyed steel is produced in primary metallurgy. The two most important routes are the blast furnace converter route (72% of world production) and the electric steel route (27.5% of world production).
Route blast furnace converter
The blast furnace converter route consists of the reduction of iron ore to pig iron in the blast furnace and the downstream processing of the pig iron in the converter to produce crude steel.
In the blast furnace process, pig iron is first produced from iron ore with the help of coke . Then the steel is produced from the pig iron using further processes, and scrap is usually also used for this purpose.
Steel production from iron ore is currently usually carried out by means of a blast furnace . The iron ore is mixed as lump ore, pellets or sinter together with the reducing agent (coke) and other components ( limestone , slag- forming agent , etc.) to form the so-called Möller and then charged . The blast furnace is a metallurgical reactor , in which the counterflow the burden column with hot air, the so-called wind responding. Burning the carbon from the coke creates the heat and carbon monoxide required for the reaction , which flows through the Möll column and reduces the iron ore. The result is pig iron and slag that are tapped periodically . The slag is processed into high-quality slag . The top gas produced is used in power plants to generate electricity.
Since the pig iron still contains a great deal of carbon and usually too much sulfur, it has to go through further process steps. Desulphurization usually takes place while the liquid steel is being transported to the steelworks. This is done by adding calcium oxide, which reacts with the iron sulfide contained in the pig iron to form calcium sulfide ( called desulfurization of lime ). In a further process step, the so-called freshening , the carbon is oxidized by blowing oxygen and liquid steel is produced. After the desired elements have been alloyed in, it is cast into a semi-finished product in a strand or in the mold . Potting requires special techniques; a distinction is made between calmed and non-calmed steel. Calming is understood as the binding of the dissolved oxygen in the melt by adding aluminum or silicon to the alloy . This has an influence on segregations (material segregation , e.g. sulfur deposits) or cavities ( cavities caused by the shrinkage of the material) in the cooling steel . Both are associated with a loss of quality.
An alternative pig iron production process is currently being tested with a pilot plant based on the so-called Hisarna process.
Production of steel from pig iron
A distinction can be made between so-called blowing processes and stove-freshening processes.
In the blow molding process , the pig iron is refined with oxygen or air. The oxidation process , which lowers the carbon content ( freshening ), provides enough heat in these processes to keep the steel liquid, so an external heat supply is not necessary in the converters. The blowing processes can also be divided into inflation processes and bottom blowing processes. The bottom blowing processes include the Bessemer process and the Thomas process , but these are no longer relevant today. The most widely used inflation process is the Linz-Donawitz (LD) or oxygen inflation process. Liquid pig iron and up to 30% (on average around 20%) steel scrap are poured into the LD converter and slag -forming agents are added. A lance is oxygen blown onto the melt. In the process, unwanted accompanying elements such as sulfur , phosphorus , carbon , etc. burn in the steel and pass into the flue gas or slag. The completeness of the removal can be determined with the Baumann print . The added scrap is melted due to the enormous heat development associated with the combustion. A variant of the LD process is the oxygen blow-through process or a combination of blow-through and blow-through processes (LWS process according to Loire-Wendel-Sprunch or TBM process according to Thyssen-Blas-Metallurgie), in which oxygen is injected through nozzles in the floor Converter, optionally in addition to the oxygen lance, is blown in.
In the hot metal process , the oxygen required for oxidation is removed from the scrap and ore added to the pig iron. In addition, heat must be supplied externally to the fresh oven converters. The best known stove-freshening process is the Siemens-Martin process . The freshness and heating effect are based on an oxidizing mixture of fuel gas and air, which is passed over the flat melting hearth. The Siemens-Martin process is no longer used due to its insufficient productivity and has now been replaced by the oxygen blowing process.
The disadvantages of the blast furnace are the demands on the input materials and the high emissions of carbon dioxide. The iron girders and the coke used must be lumpy and hard, so that sufficient cavities remain in the Möll column to ensure that the blown wind can flow through it. The CO 2 emissions represent a heavy burden of greenhouse gases. That is why there are efforts to replace the blast furnace route. So far, however, no process has been able to establish itself against the blast furnace. These include, the sponge iron - and pellet production in rotary kilns and Corex - Midrex - and Finex process.
The most widespread so far are the Midrex or HYL direct reduction processes, which produce sponge iron or HBI ( Hot Briquetted Iron ) as solid feedstock. This is still loaded with a certain amount of gangue from the parent ore, but the carbon content is usually not higher than 1%.
The Corex process is more recent and produces a liquid, raw iron-like raw material with a carbon content of around 3.5 to 4%. The Corex process is a two-stage smelting reduction process in which pig iron can be produced from non-coked coal and iron ores. The aim of the smelting reduction process is to combine the smelting process, coal gasification and direct reduction to produce liquid iron, the quality of which corresponds to that of blast furnace pig iron. Smelting reduction combines the process of direct reduction (pre-reduction of iron to sponge iron) with a smelting process (main reduction). The process therefore runs in two stages in separate units. First the ores are reduced to sponge iron, in the second step the final reduction and melting to pig iron takes place. The energy required for the melting process is provided by burning coal (not coked). Large amounts of carbon monoxide are produced as exhaust gas, which is used as a reducing gas.
Sponge iron is used for cast iron or in the electric arc furnace .
Direct reduction with hydrogen
There is also the option of using hydrogen as a reducing agent instead of coke . In this case, the process would only produce water vapor instead of carbon dioxide. However, this process requires electrical heating of the ore, and the hydrogen would also have to be extracted first. SSAB , LKAB and Vattenfall are working together on the "HYBRIT" project, which aims to produce steel using this hydrogen process. If the project is operational on a commercial-industrial scale as planned in 2030, it should be able to reduce CO 2 emissions from Sweden by 10% and CO 2 from Finland by 7%, according to the company . In 2018, the construction of a pilot plant began.
Electric steel route
In electric steel processes , the heat required for melting is generated by an electric arc . The electric arc furnace is charged with scrap, sponge iron and / or pig iron. In addition, lime to form slag and reducing agents are added. The arc running from the graphite electrodes to the melting material generates temperatures of up to 3500 ° C. For this reason, alloy elements that are difficult to melt, such as tungsten and molybdenum, can also be melted down as ferro alloys . All types of steel can be produced with electric arc furnaces, but they are mainly used for the production of quality and stainless steels due to their high costs. In it, scrap is heated using three ( AC ) or two ( DC ) electrodes until the steel is liquid. A melting process takes about 30 minutes. The capacity of the tiltable electric ovens is 100 to 200 t . With an electric furnace, around 1.5 million t of steel can be melted per year. The raw steel is poured into a steel ladle. Melting by induction is reserved for smaller units for high-alloy steels due to the specific higher system costs.
Secondary metallurgy and casting
In the secondary metallurgy , the raw steel is treated ready for casting (deep decarburization in a vacuum system , alloying in a ladle furnace ). For alloy steels, metals such as B. chromium , nickel , cobalt , molybdenum , tungsten or manganese are added.
The liquid steel is then poured into the so-called mold , where it solidifies:
- In ingot casting , a simple geometry is used for the mold and the resulting ingot is usually processed further.
- If the mold designed so that the steel almost the final contour for an application achieved is casting .
- In continuous casting , the mold is designed in such a way that a hot, already solidified strand emerges from the bottom. The strand is then divided into sections of any length.
Remelting processes can be used to produce special steels, e.g. B. the electroslag remelting process (ESR).
It follows i. d. R. Forming or rolling .
- Meteor trips
- Originally the iron was processed by iron meteorites . Enormous temperatures could be reached in clay ovens, which were charged with charcoal and air through bellows. 1300 to 1600 ° C are necessary to melt out the iron-nickel alloy that is contained in the meteors (80 to 95% iron).
- Racing fire
- The first racing ovens were made around 1500 BC. Built. These are clay stoves into which charcoal and iron ore were placed in layers. Temperatures between 1200 and 1300 ° C arise in the racing furnace, which melt the dead rock and allow it to run off as slag. This is where the name comes from: Race of Rinnen. The iron is reduced by the charcoal. The result is a shell interspersed with slag particles , which can be further processed by forging .
- Piece or wolf oven
- From around the 12th century onwards, the furnaces were no longer built in the ground, but above ground (forerunners of the blast furnaces) and additionally supplied with air by water-driven bellows. The steel was also worked with water-powered hammer mills.
- Cast steel
- The pig iron is melted together with scrap in the cast steel process that has been used since 1742 . The oxygen content in the scrap freshens the pig iron and thus improves the quality of the steel.
- Puddling process
- The puddling process was invented in England in 1784 by Henry Cort (1740-1800). The already tough pig iron mass is turned with bars so that as much of the surface as possible can come into contact with the ambient air. Through this oxygen contact, the pig iron is refined and processed into steel (see also Eiffel Tower , Griethausen Railway Bridge ).
- Crucible steel
- The steel was manufactured in a crucible furnace with a precise chemical composition, see also Wootz . Now generally replaced by electric steel .
- Thomas, Bessemer and DSN processes
- These are converter processes in which gases are forced into the pig iron melt through the bottom nozzles of the converter. The Thomas and Bessemer processes use air, in the DSN process (Steam-Oxygen-Neunkirchen) oxygen is used together with water vapor instead of air. The Bessemer process, also known as the "acidic wind-freshening process", was developed in 1855 by Henry Bessemer . The Thomas process (also known as the “basic wind freshening process” and known for its converter shape: the Thomas pear ) was invented in 1878 by Percy Gilchrist and Sidney Thomas . They differ in the brick lining of the furnace, which has either an acidic or a basic effect and thus has different properties (in the Thomas process, a dolomite - tar mixture).
- OBM procedure
- In the OBM process (Oxygen- Bottom- Maxhütte or Oxygen-Bottom Blowing Metallurgy Process) oxygen and methane or propane are blown through the bottom of the converter. The process was developed in the mid-1970s by Maxhütte in collaboration with what was then Vöest-Alpine ("Division" Industrial Plant Construction). It is a method of steel production in which oxygen is blown into the melt through gas-cooled annular gap nozzles in the ground and the elements silicon , manganese , carbon and phosphorus are burned. The sulfur is bound with calcium and the oxides formed in the slag . The starting materials are pig iron , refrigerated scrap , aggregates, propane and methane. The reaction products are crude steel and slag (steel production). With the closure of the Neue Maxhütte in Sulzbach-Rosenberg in 2002, the last German OBM converter went out of service. In Charleroi (Belgium) there were OBM converters in the Duferco Carsid steelworks. The bottom injection technology is successfully used in converters for stainless steels (CLU = Creusot-Loire Uddeholm process and AOD ).
- Siemens-Martin process
- The Siemens-Martin process was the preferred steelmaking method from its invention in 1864 by Friedrich Siemens and Wilhelm Siemens and its implementation together with Pierre-Émile Martin until the first half of the 20th century. The SM furnace consists of the upper furnace with the melting chamber spanned by the vault and the lower furnace. Liquid pig iron, pig iron ingots or scrap are charged in the upper furnace . The regeneration chambers for air and gas preheating are housed in the lower furnace. In the upper furnace, the melting chamber is heated with oil or gas operated burners. The reduction of carbon (freshening) takes place through the excess of oxygen in the burner flame or through the addition of iron ore. The process has now been replaced by oxygen blowing processes. In 1993, the last German SM furnace was shut down in Brandenburg an der Havel . Today it is preserved as a technical monument.
The largest steel producers
The most important producer country for steel is China, followed by India and Japan. China alone is responsible for a little more than half of world production - India and Japan for 5.9% and 5.7% of world production volume, respectively. In Europe, Russia, Germany and Italy are the three most important producers. As a single location, Duisburg was for a long time in the first place in steel production. The most modern and productive blast furnaces are located there. Meanwhile, Shanghai has advanced to the first place in steel production (production volume). However, Duisburg remains the most important steel location in Europe.
A list of the largest steel companies is given here in a separate article. With Tata Steel and ArcelorMittal , two large steel groups are controlled by Indian entrepreneurial families.
One of the largest steelworks in Germany is the ThyssenKrupp steelworks Schwelgern .
In 2018, steel with a total volume of around 458 million tons was traded across borders worldwide. China was the most important international export country in terms of export volume, ahead of Japan and Russia. This makes China by far the world's largest producer and exporter of steel.
|#||country||Export volume (in million t)|
|1||People's Republic of China||68.8|
- ↑ http://www.stahl-online.de/index.php/stahlproduktion-sauerstoff-konverter-vor-elektroofen/
- ↑ tec-science: From pig iron to crude steel. In: tec-science. June 21, 2018, accessed on November 2, 2019 (German).
- ↑ http://www.stahl-online.de/wp-content/uploads/2013/09/131128-Jan-van-der-Stel-Ulcos-TGRBF-HIsarna-VDEH-Stahl-2013-final.pdf
- ↑ Steel scrap balance 2014: The steel recycling industry had to cope with a decline in total shipments of 1.7 percent. ( Memento of the original from April 2, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. At: bdsv.org. Press release, March 23, 2015.
- ^ Blast furnaces without coke . In: Technology Review , August 23, 2016. Retrieved August 24, 2016.
- ↑ H2Future project .
- ↑ Hybrit toward fossil-free steel. Retrieved November 18, 2018 .
- ↑ HYBRIT: Start of construction for the world's first pilot plant for fossil-free steel production. Retrieved May 9, 2020 .
- ↑ http://www.midrex.com/wp-content/uploads/Hadeed_Mod_E_2_million_milestone.pdf
- ↑ Reference: R. Sonnemann, S. Richter, H. Wolffgramm, G. Buchheim, H. Eschwege: General history of technology from the beginnings to 1870 . VEB Fachbuchverlag, 1981.
- ↑ worldsteel | Steel Statistical Yearbook. Retrieved February 7, 2020 .
- ↑ Duisburg location. thyssenkrupp steel AG, accessed on January 27, 2020 .
- ^ Trade Map - List of exporters for the selected product (iron and steel). Retrieved February 7, 2020 .
- Dieter Janke: Modern steel production. In: Chemie in our Zeit 15, No. 1, 1981, pp. 10-20 ( doi: 10.1002 / ciuz.19810150104 ).
- Photographs of almost all processes in steel production and steel processing , Stahlseite.de, accessed on November 2, 2012
- The Quarks Steel Mill , accessed November 2, 2012
- Viktor Macha: Photographs of almost all methods of steel production and steel processing (Czech photography)