Stainless steel

from Wikipedia, the free encyclopedia
A Bialetti espresso pot made of stainless steel
Sculpture sewer peg made of stainless steel in Berkenthin by Tim Adam
Fretting corrosion ( fretting corrosion ) on a stainless steel shaft

Stainless steel , rust-proof steel or stainless steel ( NiRoSta for short ) stands for a group of corrosion and acid-resistant types of steel .

history

In 1821, Pierre Berthier recognized that the addition of chromium leads to stainless steel. At that time, however, metallurgy was not yet ready to implement this technologically.

In the German Reich, Eduard Maurer and Benno Strauss from the Krupp company registered two patents on stainless steel in autumn 1912; these were granted in 1918. In Austria, Max Mauermann developed the first rust-resistant steel in 1912. In the Anglo-Saxon world, Harry Brearley on the British side and Elwood Haynes in the USA are considered the inventors of stainless steel. He applied for his patent in 1913; it was only issued in 1919.

The Germania shipyard had built the Germania yacht for Krupp in 1908, also using stainless steel . It took a few more years before the material could also be produced inexpensively on a large technical scale. The global production of stainless steel was 41.6 million tons in 2015 and 50.7 million tons in 2018. Around 8.4 million tons of stainless steel were produced in Germany in 2014.

Synonyms

Synonyms for stainless ("rustproof") steel are

  • Stainless steel , generally also called stainless steel ; In technical terms, the term stainless steel is only used for types of steel with a particularly high degree of purity, which do not necessarily have to be high-alloyed and rust-free
  • Inox (formed from the French inox ydable, which means something like "non-oxidizable" or "rustproof")
  • Cromargan , trade name of WMF
  • Nirosta , the brand name of Outokumpu Nirosta (formerly ThyssenKrupp Nirosta) is seldom written Nieroster or Niroster, or Niro for short. The name is derived from Ni cht ro stender Sta hl from.
  • Remanit , brand name of Edelstahl Witten-Krefeld . Remanit is also used as a material for works of art in public spaces, for example by Friedrich Becker for his Remanit fountain for the exhibition halls of the city of Hanover . Remanit has been registered as a trademark with the DPMA since 1926 under the number 360467.
  • VA steel

In Germany, special terms are used for the following two groups of types of stainless steel, but these are not synonyms for stainless steel, but rather designate a specific type of steel:

  • V2A (testmelt2 austenite , created in 1912 for alloy type X12CrNi18-8 or also called 1.4300) is no longer produced today. The successors to 1.4300, 1.4301 (X5CrNi18-10) and the classic steel for automatic machining 1.4305 (X8CrNiS18-9) are among the most common representatives of the V2A group.
  • V4A (similar to V2A, but alsoalloyedwith 2% molybdenum (Mo), which makes this steel more resistant to corrosion by media containing chloride - salt water, swimming pools, chemical industry, etc.) A frequently used representative of the V4A group is 1.4401 (X5 Cr Ni Mo 17-12-2).

Also VA steel derives from these numbers. The steel grades V1A, V3A and V5A are used less.

The word / figurative mark "Edelstahl Rostfrei" is registered as a collective mark with the Office of the European Union for Intellectual Property in all member states of the European Union and in Switzerland with the Federal Institute for Intellectual Property. The trademark is owned by the trademark association Edelstahl Rostfrei e. V. in Düsseldorf. As a material seal, the trademark “stainless steel” indicates the quality of the material used. The trademark users undertake to select the appropriate material as well as the appropriate processing and processing of stainless steel. The association monitors the use and strengthens the reputation and importance of the quality seal in the public with effective advertising measures.

description

Stainless steel is characterized by a proportion of more than 10.5% chromium , which must be dissolved in the austenitic or ferritic mixed crystal . Due to this high chromium content, a protective and dense passive layer of chromium oxide forms on the material surface. After special treatment, this passive layer can also be used to color the steel surface. Other alloy components such as nickel, molybdenum, manganese and niobium lead to even better corrosion resistance or more favorable mechanical properties. Since chromium is cheaper than nickel as an alloying element, a higher proportion of chromium is preferred with a smaller proportion of nickel (assuming the same corrosion resistance).

properties

Stainless steels are mainly characterized by the following common properties:

Steels without added nickel form ferritic crystals and have the following properties:

Steels with a higher nickel content (approx. 70% of production) form an austenitic structure and have the following properties:

  • higher corrosion resistance than low-nickel chromium steels (especially resistance to stress corrosion cracking )
  • high toughness and thus poor machinability (for example when drilling, turning) and increased tendency to "seize" in threads (the latter especially when these are heated, for example in containers in the chemical and pharmaceutical industries)
  • Largely non-magnetic when de-energized
  • comparatively low yield point (200–300 N / mm²) with relatively high tensile strength (700–1300 N / mm²)
  • high coefficient of thermal expansion (for example a value of 16.0 × 10 −6  K −1 for the material 1.4301 compared to a value of 10.5 × 10 −6  K −1 for carbon steel)
  • Density 1.4301 (V2A): 7.9 g / cm 3 , 1.4401 (V4A): 8.0 g / cm 3
  • not hardenable by annealing and subsequent quenching
  • Surface hardening is only possible through plasma nitriding , Kolsterising or cold forming
  • easy to connect by welding
  • Thermal conductivity : 15 W m −1 K −1
  • Electrical conductivity : approx. 1.4 10 6 S / m ( Siemens per meter)

Machinability

The machinability of stainless steels presents greater problems because of their lower thermal conductivity compared to other steels.

Nickel discharge

Nickel can dissolve from the alloys and migrate into the skin or food, which can lead to health problems . The European Directive 94/27 / EC (12) stipulates a limit value of 0.5 μg / cm² per week in order to avoid problems with permanent skin contact over a longer period of time. Both the low-nickel alloy 1.4016 and 1.4301 and 1.4404 clearly fall below this limit value with <0.03 μg / cm² per week in acidified artificial sweat.

Due to the good passivation with a high chromium and nickel content, alloys with a high nickel content (e.g. 1.4301 ~ 10% nickel) do not have a higher nickel output than alloys with a very low nickel content (e.g. 1.4016 <0.5% nickel). Only sulfur as an alloy component of free-cutting steels allows nickel to be discharged e.g. B. increase in 1.4305 to ~ 1.5 μg / cm² per week.

use

The roof of the Fisher Center for the Performing Arts at Bard College is made of stainless steel.

Because of the good formability of sheets made of stainless steel, parts made of this material are becoming more and more popular in industry, in the home or in medical devices. Although most stainless steels are very difficult to machine, their use mostly offers advantages. In addition to hygienic aspects (in brewing, the food industry and pharmacy, sterilization with steam), the durability of the parts produced and advantages in environmental protection should also be mentioned here. However, the disadvantage compared to other steels is the mostly low tensile strength and often the lack of hardenability (see further text). Also noteworthy is the lower antibacterial effect compared to copper and its alloys, also known as the oligodynamic effect .

Many cryostats would not be possible without stainless steel . The poor thermal conductivity and thin walls (for example pipes with a wall thickness of less than 0.3 mm) enable good insulation between the cryofluid and room temperature . Other advantages are UHV -Dichtheit of welding connections and low magnetism .

Heat-resistant stainless steels are marketed as heat-resistant steels . They can be used at temperatures up to 900 ° C.

Materials used and composition

The generic term stainless steel includes a large number of alloys that differ in their alloy components, properties and possible uses. Material numbers are assigned to the individual alloys so that they can be clearly differentiated .

Austenitic steels

Steels with more than 8% nickel have an austenitic crystal structure at room temperature and have a particularly favorable combination of processability, mechanical properties and corrosion resistance.

Material number 1.4301 - X5CrNi18-10

The most common type of stainless steel alloy that we encounter in everyday life is the alloy X5CrNi18-10 ( material number 1.4301, label 18/10, also known as V2A). This type of alloy accounts for 33% of the production of stainless steels, a further 20% for the similar steel 1.4307 (X2CrNi18-9). 1.4301 is a relatively soft, nickel-containing, non- ferromagnetic austenite steel for, for example, pots , cutlery (with the exception of knife blades ) and sinks . The designation 18/10 refers to the proportion of chromium / nickel.

The material is not resistant in the presence of chlorine-containing media such as salt water or the chlorine-containing atmosphere in indoor swimming pools. The alloy is very tough and tends to harden when it is cold worked. This makes processing by drilling, punching or machining more difficult.

Material number 1.4571 - X6CrNiMoTi17-12-2 (historical) or 1.4404 - X2CrNiMo17-12-2

For use in the presence of chloride-containing media, the material 1.4571 or 1.4404 (colloquially V4A) is often used. In contrast to 1.4301, it has an increased resistance to chlorides due to its 2% molybdenum content. Applications include all areas that constantly come into contact with salt water, such as fittings in shipbuilding. In addition, it is used for the renovation of chimneys , in indoor swimming pools (for safety-relevant components that cannot be cleaned regularly or are wetted by water, higher-molybdenum qualities must be used,  e.g. 1.4529 ) and the chemical industry.

Other types of steel

For tools and knives are curable martensitic - ferritic used steels, in addition to chromium often vanadium contained and molybdenum and can be magnetized. Typical types of steel for this are X30Cr13 and the higher-quality alloy X50CrMoV15 (see knife steel ).

In the offshore region is also duplex steel , eg. B. 1.4462 (X2CrNiMoN22-5-3) application. For austenitic steels, the cheaper manganese can be used as an alloying element instead of nickel , but the general quality of these steels is lower.

Intergranular corrosion

The resistance to corrosion decreases with increasing carbon content, since chromium has a high affinity for carbon and hard, brittle chromium carbide forms mainly at the grain boundaries at the expense of protective chromium oxide. In addition, the steels then tend to intergranular corrosion. To counteract this effect and thus improve weldability , the carbon content is kept low and the corresponding types of steel are stabilized by adding niobium or titanium , which have a higher affinity for carbon than chromium. Purely ferritic steels stabilized in this way with a chromium content of 12 to 18%, such as X2CrTi12 (1.4512), X2CrTiNb18 (1.4509) and X3CrTi17 (1.4510), are the most important materials for the construction of exhausts in the automotive industry today. Almost 10% of the global production of stainless steels do not apply to this application. The cost-saving elimination of nickel and the lower coefficient of thermal expansion of the ferritic crystal lattice are the specific advantages of these steels. The additional alloy with molybdenum improves the corrosion resistance.

Meaning of the material numbers

Material number starting with Cr content Content of Mo, Nb, Ti
1.40 Cr steels with <2.5% Ni without Mo, Nb and Ti
1.41 Cr steels with <2.5% Ni with Mo, without Nb and Ti
1.43 Cr steels with ≥ 2.5% Ni without Mo, Nb and Ti
1.44 Cr steels with ≥ 2.5% Ni with Mo, without Nb and Ti
1.45 Cr, CrNi or CrNiMo steels with special additives (Cu, Nb, Ti, ...)
1.46 Cr, CrNi or CrNiMo steels with special additives (Cu, Nb, Ti, ...)

Abbreviations:

Overview of the material designations

European Standard

Material number.

European Standard

Short name

ASTM / AISI

designation

US number
1.4016 X6Cr17 430 S43000
1.4509 X2CrTiNb18 441 S44100
1.4510 X3CrTi17 439
1.4512 X2CrTi12 (old X6 CrTi 12) 409 S40900
1.4526 X6CrMoNb17-1 436 S43600
1.4310 X10CrNi18-8 (old X12 CrNi17 7) 301 S30100
1.4318 X2CrNiN18-7 301LN
1.4307 X2CrNi18-9 304L S30403
1.4306 X2CrNi19-11 304L S30403
1.4311 X2CrNiN18-10 304LN S30453
1.4301 X5CrNi18-10 304 S30400
1.4948 X6CrNi18-11 304H S30409
1.4303 X4CrNi18-12 (old X5 CrNi18 12) 305 S30500
1.4541 X6CrNiTi18-10 321 S32100
1.4878 X10CrNiTi18-10 (old X12 CrNiTi18 9) 321H S32109
1.4404 X2CrNiMo17-12-2 316L S31603
1.4401 X5CrNiMo17-12-2 316 S31600
1.4406 X2CrNiMoN17-11-2 316LN S31653
1.4432 X2CrNiMo17-12-3 316L S31603
1.4435 X2CrNiMo18-14-3 316L S31603
1.4436 X3CrNiMo17-13-3 316 S31600
1.4571 X6CrNiMoTi17-12-2 316Ti S31635
1.4429 X2CrNiMoN17-13-3 316LN S31653
1.4438 X2CrNiMo18-15-4 317L S31703
1.4539 X1NiCrMoCu25-20-5 904L N08904
1.4547 X1CrNiMoCuN20-18-7 F 44 S31254
1.4462 X2CrNiMoN22-5-3 F 51 S31803

The table lists the general stainless and acid-resistant steels.

Screws

The designation A2-70 is often found on screws made of stainless steel. A2 stands for the steel grade ( A  for austenitic, 2  for the grade), 70 for the tensile strength in kp / mm² (out of date) corresponding to 1/10 of the tensile strength 700 MPa. Components made of the special material X2CrNiMoN17-13-5 (material number 1.4439 / Alloy 317 LN) are to be preferred for the offshore sector and for seawater desalination systems . Screw materials made of stainless steels and their designations are standardized in the EN ISO 3506 standard. When replacing screws with conventional material with stainless steel screws, it should be noted that the material parameters (tensile strength, elongation at break, yield strength, etc.) of these stainless steel screws are usually below those of conventional screws with a strength class greater than or equal to 5.6. A simple replacement according to the 1: 1 principle must be carefully checked, especially for safety-relevant connections. In addition, additional corrosion can occur when there is contact between stainless steel and normal steels for electrochemical reasons.

The technical delivery conditions for stainless steels are generally regulated in the three-part European standard EN 10088.

The effective sum (also known as the PRE value ) can be used to estimate the corrosion resistance of a stainless steel . The higher this is, the more resistant the alloy is to pitting or crevice corrosion . Alloys with an active sum greater than 33 are considered seawater-resistant.

Other corrosion resistant alloys

Cr-Ni alloys that contain less than 50% iron and have even better properties with regard to corrosion and heat resistance are no longer counted as steels. These so-called superalloys are among the high-temperature alloys and are based on an alloy type NiCr8020 that was first described around 1906. With the addition of aluminum and titanium, these can be hardened and their strength is greatly increased at high temperatures. Modern trade names are e.g. B. Inconel , Incoloy, Hastelloy , Cronifer, Nicrofer. The latter is a highly corrosion-resistant nickel-chromium-molybdenum alloy that is divided into different alloys, depending on the additive (Nicrofer 3127, Nicrofer 5923, H-C4 or H-C22).

Such alloys are mainly used in jet engines , the power plant industry (gas turbines), the oil and gas industry , environmental technology ( FGD ) and chemical process engineering , i.e. wherever high strength at very high temperatures or under highly corrosive conditions must be guaranteed over the long term.

See also

literature

  • Hans-Jürgen Bargel, Günter Schulze (ed.): Material science (Springer textbook), 11th edition, Springer-Vieweg, Heidelberg / Berlin [u. a.] 2013, ISBN 978-3-642-17716-3 , p. 266 ff.
  • Manfred Rasch (ed.): 100 years of stainless steel. Historical and current issues. Clear text, Essen 2012

Web links

Commons : Stainless Steel  - Collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b Derek Lowe, Das Chemiebuch, Librero 2017, p. 250
  2. ↑ The patent: 100 years of stainless steel. ThyssenKrupp, archived from the original on July 31, 2012 ; Retrieved April 26, 2012 .
  3. ^ German Patent and Trademark Office: German Reich Patent No. 304126, granted on October 18, 1912
  4. ↑ German Reich Patent No. 304159. German Patent and Trademark Office, December 21, 1912, accessed on June 4, 2018 .
  5. ^ Hans Jörg Köstler: Mauermann, Max . In: New German Biography . tape 16 . Duncker & Humblot, 1990, pp. 427 f .
  6. ↑ Production of stainless steel decreased slightly , on stahl-online.de
  7. ↑ http://www.worldstainless.org/crude_steel_production/crude_2018
  8. ↑ ThyssenKrupp Nirosta: History 1687–1957 ( Memento from August 12, 2012 in the Internet Archive )
  9. ↑ Trademark Association Stainless Steel Rostfrei eV: Trademark statutes. Retrieved October 21, 2017 .
  10. ↑ a b EN 10088-1: 2005
  11. ↑ Colored stainless steel (Material and Applications Series, Volume 16), on euro-inox.org
  12. ↑ Ulrich Heubner: Stainless steel - when health counts . Euro Inox, Brussels 2009, ISBN 978-2-87997-309-8 ( PDF ).
  13. ↑ ThyssenKrupp Nirosta: Heat-resistant steels THERMAX® according to DIN EN 10095. (PDF; 335 kB) Accessed May 15, 2013 .
  14. ↑ M. Faller, P. Richner: Safety-relevant components in indoor swimming pools. Switzerland. Ing. Arch. 2000 (16), pp. 364-370 ( online (3.7 MB) ).