What is steel framework




steel refers to all metallic alloys whose main component is iron and whose carbon content does not usually exceed 2.06%.

definition

According to the classic definition, steel is an iron-carbon alloy that contains less than 2.06% (mass) carbon (exception: cold work steels). This definition is also followed by DIN EN 10020, according to which steels Materials with a mass fraction of iron greater than that of any other element, the carbon content of which is generally less than 2% by weight C are. From a chemical point of view, steel is an alloy of iron and iron carbide.

With higher proportions of carbon one speaks of cast iron, here the carbon is in the form of graphite.

properties

Steels are the most commonly used metallic materials. By alloying with carbon and other alloying elements in combination with heat and thermomechanical treatment (simultaneous thermal treatment with plastic deformation), its properties can be adapted for a wide range of applications.

The steel, for example, can be made very soft and therefore extremely malleable, like the tinplate of tins. In contrast, it can be made very hard and therefore brittle, such as martensitic steels for knives (knife steel). Modern developments aim to produce steel that is strong and ductile (deformable) at the same time, as a contribution to the lightweight construction of machines.

The most important alloying element in steel is carbon. It lies as a compound (cementite, Fe3C) before. The importance of carbon in steel results from its influence on the steel properties and phase changes.

In general, steel with a higher carbon content becomes stronger, but also more brittle. Alloying with carbon creates different phases depending on the concentration and the ambient temperature: austenite, ferrite, primary, secondary, tertiary cementite and phase mixtures: pearlite, ledeburite. Accelerated cooling of austenite, in which carbon is dissolved, can result in further phase mixtures such as fine (ex sorbite) and finely striated pearlite (ex troostite) as well as acicular / granular bainite ("intermediate stage") and massive / acicular martensite or hardenite ( see also hardening (steel)).

The phase composition of steel is described for the equilibrium state with the iron-carbon diagram.

The density of steel or iron is around 7850 kg / m³, the modulus of elasticity around 210 kN / mm².

The melting point of steel can be up to 1530 ° C, depending on the alloy content.

Change in steel properties

Steel can adopt desired properties (hardness, ductility, notched impact strength ...). The three basic methods that can of course be used in combination to change the steel properties are:

Types of steels

According to DIN EN 10020, a distinction is made between two main quality classes:

The short names of the steels are specified in DIN EN 10027. Today around 2500 different types of steel are produced.

The steel materials are divided into groups according to the alloying elements, the structural components and the mechanical properties.

Depending on the alloy content, it is divided into:

Unalloyed steels

Unalloyed steels are divided into steel materials for subsequent heat treatment and those that are not intended for heat treatment.

Low alloy steels

Low-alloy steel is when the sum of the alloying elements is greater than or equal to 1% but does not exceed the 5% limit.

Low-alloy steels have fundamentally different properties than unalloyed steels. Technically important is their significantly better suitability for influencing the mechanical properties through heat treatment and, with special alloy combinations, also the increased heat resistance.

High alloy steels

High-alloy steel is when at least one alloy element exceeds the 5% limit

High-alloy steels are required for special properties. Scale resistance, maximum heat resistance, rust resistance or special physical properties can only be achieved with high-alloy steels.

Classification according to areas of application

Other important properties for the user are the areas of application and possible uses of the steels. It is therefore useful to have a label from which this can be seen:

Manufacturing

please refer:Steelmaking

Economic and historical importance

The smelting of iron is already for the 2nd millennium BC. In the then Hittite Empire. The first production of a simple steel is on the beginning of the 1st millennium BC. Dated (see article Eisen).

In the 12th century AD, the charcoal blast furnace was developed in Europe, the process temperature of which made it possible to melt iron ores. At first, this iron was not malleable because of its high carbon content; it first had to be “cleaned” by burning out the carbon and other accompanying elements.

Cast steel was first produced in 1740 by the Englishman Benjamin Huntsman using the crucible steel process. Alfred Krupp founded the first German cast steel factory in Essen in 1811. The impetus for the sudden increase in steel production came about 150 years ago through the simultaneous application of several technical inventions: the steam engine provided the iron industry with a powerful and flexible workforce, coal mining produced the coke necessary for steel production, and the development of the railroad and steam shipping created new, large sales markets for steel.

The steel industry was of enormous political importance in all countries, regardless of economic considerations, as it was also a question of national prestige. The importance of steel for that time is symbolized by the Eiffel Tower, which was built from steel as a monument to technical progress on the occasion of the Paris World Exhibition in 1889.

For the National Socialists, who started an extensive armaments program in 1935, steel was an important material for the war effort. Among other things, the Norwegian campaign was aimed at securing supplies of Swedish iron ore, which was an indispensable raw material for steel production at the time. The Allies bombed the Ruhr area, the largest steel-producing region in Europe. At the end of the war, the air raids had destroyed around 20 percent of production capacity. It was not until 1957 that the pre-war level was reached again with crude steel production of 16 million tons.

The demilitarization of the German Reich decided at the Potsdam Conference also included a dismantling of the steel industry. Some of the dismantled factories went to the Soviet Union, which needed them to rebuild the country destroyed by the war. Resistance to dismantling soon arose in the western occupation zones, and so the Allies stopped dismantling as early as 1949. Another measure taken by the allied control authority was the so-called "unbundling" of the steel industry. This was intended to prevent the renewed emergence of dominant company mergers, such as the "United Steelworks".

In order to ensure joint control of coal and steel production, the coal and steel union was founded in 1952 on a French initiative. The European Union then gradually developed from the coal and steel union. As a result, the steel industry in the Federal Republic of Germany experienced a great boom. In 1961, 420,568 employees produced 33 million tons of crude steel, which was a peak in the number of employees. The West German steel industry set a production record in 1974 when it produced over 53 million tons of steel. Today the steel industry in reunified Germany needs around 92,000 employees to produce around 45 million tons of steel. This enormous increase in productivity was only possible through significant technical innovations, which often first took place in Germany.

Raw material situation

Although the earth's crust consists of five percent iron, the most important raw material for steel, the raw material requirements of industry are currently not being met. Beginning in the second half of 2003, there was a dramatic change in the raw material situation, which was primarily caused by the rapidly increasing demand for steel in the economies of the People's Republic of China, India and Brazil. For some years now, steel production in China alone has been growing annually by more than the current total production in Germany. Suddenly the production of the ore mines was no longer sufficient, the transshipment capacities of the ore ports were exhausted, and there weren't enough ships to transport ore. Similar developments occurred for coke, which is required for the production of pig iron, and for scrap as a secondary raw material for steel production.

The consequences of this development were underestimated by the large steel manufacturers in industrialized countries, so that the current demand for raw materials cannot be met. As a result, the prices of raw materials and steel products have multiplied. Steel is currently scarce and expensive.

There is no trend reversal in sight, steel production and the demand for raw materials will continue to rise, although the rate of growth is currently falling due to government intervention. The need for iron ore can be met by opening up new mining areas.

In addition to the steel industry, concrete and aluminum are also affected by this phenomenon. Another reason for the high oil price is the rising demand for raw materials in the emerging countries.

Alternative materials

In the automotive industry in particular, steel is in direct competition with materials with a lower density, such as aluminum, magnesium, plastics and fiber composites. Since the other metallic materials are consistently less strong than steel, the weight advantage can be compensated for by the targeted use of high-strength steels and structural measures (e.g. thinner sheet metal with recesses, but instead beads). Fiber composite materials have significantly higher strengths (tensile strength, modulus of elasticity) in the direction of the fibers, but the construction and processing is completely different than with metallic materials.

ecology

From an ecological point of view, steel is an excellent material because it can be recycled indefinitely with almost no loss of quality by melting the scrap back into steel.

The production of crude steel is energy-intensive, as the metallurgical process steps require temperatures of 1,500 to 1,800 ° C. From an ecological point of view, CO2 emitted because the blast furnace cannot be operated without a certain amount of coke and carbon due to the process. In Germany and Austria, however, blast furnaces have meanwhile reached values ​​that are at the procedural minimum. A further reduction is not possible for technical, physical and chemical reasons. For years there has been research into new processes for making pig iron. However, the processes implemented in practice are also based on carbon, one of the starting materials for carbon monoxide, which acts as a reducing agent for the iron ore, and so these new processes do not help to reduce CO either2Emissions.

See also

  • - Further data sheets on stainless steel and their processing.
  • Steel side: Photographs of almost all processes in steel production and steel processing
  • Transport Information Service: Specialized information on the transport of steel
  • http://stahl.profzone.ch/ - Information on the influence of alloying elements
  • http://www.lpm.uni-sb.de/chemie/begleitmaterial/Metallkunde.pdf - Comprehensive document on metal science, especially iron extraction and steel production. In Adobe PDF format.
  • http://www.stahldat.de Information on standard data etc. from steel
  • Hüttenwerke Krupp Mannesmann Flash animation "Paths of steel production"
  • KI-SMILE steel tests
  • http://www.iehk.rwth-aachen.de Steel Institute at the RWTH Aachen
  • http://www.expeditionvoestalpine.com Shows the exciting world of steel production

Categories: Alloy | steel