Stainless steel (according to EN 10020) is a designation for alloyed or unalloyed steels with a special degree of purity , for example steels whose sulfur and phosphorus content (so-called iron components ) does not exceed 0.025% ( mass fraction ).
Differentiation between stainless steel and stainless steel
A stainless steel does not necessarily have to meet the requirements of a stainless steel . Nevertheless, in everyday life, only stainless steels are incorrectly referred to as stainless steels.
The corrosion resistance of stainless steel is determined by the chromium content, which causes so-called natural passivation to a sufficient extent .
In order to achieve a particularly uniform surface, some manufacturers carry out chemical pickling and passivation after components have been completed.
If stainless steel comes into contact with particles of ordinary iron, rust quickly forms, which can also lead to the formation of initially superficial flash rust and ultimately to deeper corrosion ( pitting ) on the actually stainless steel. Many stainless steels are also sensitive to substances containing chlorine such as road salt , hydrochloric acid , halides , chlorine cleaners and bleaching liquor containing chlorine , and to a lesser extent to hydrochloric acid, sulfur dioxide or silver cleaning agents .
Steel groups (EN 10027-2)
The stainless steels include, for example, high-purity steels in which components such as aluminum and silicon are separated from the melt through a special manufacturing process, or, for example, high-alloy tool steels that are intended for later heat treatment.
The steel group numbers for stainless steels according to EN 10027-2 know the following designations:
- 10 to 18 - unalloyed stainless steels
- 20 to 89 - alloyed stainless steels
Alloyed stainless steels
By far the most common alloying elements are:
- Chromium (Cr) for chromium steel
- Chrome and nickel (Ni) for chrome-nickel steel
- Molybdenum (Mo) for molybdenum steel , with Cr chromium-molybdenum steel , also with Ni
- Titanium (Ti), with Cr and Ni for titanium steel , with niobium (Nb) and aluminum (Al) for the production of high-temperature resistant stainless steel .
- Niobium (Nb)
- Tungsten (W) for heat-resistant steels, mostly in connection with molybdenum (Mo), vanadium (V) and cobalt (Co) e.g. B. HSS
- Vanadium (V) mostly in connection with chromium and molybdenum e.g. B. X 22 Cr Mo V 12 1 (turbine blade steel)
- Cobalt (Co) for the production of high-strength cobalt steel with hardnesses> 60 HRC .
There are also a number of special steels with other components.
Example: X5CrNi18-10, material no. 1.4301. According to the standard, the number 43 stands for “rustproof”, with> 2.5% Ni, without Mo, Nb and Ti. Contrary to the old German DIN spelling, this steel designation according to EN is without spaces.
A steel is considered to be high-alloyed if the mass fraction of one of its alloying elements is more than 5%.
Special precautionary measures are necessary for processing high-alloy steels, as both inhaled grinding dust and welding fumes can cause cancer . The dust generated during the grinding process can irritate the respiratory organs.
V2A and V4A
The designations V2A and V4A were chosen at the beginning of the 20th century in Germany for the first corrosion-resistant types of steel with useful technical properties. V stood for trial and A for austenite .
The names are not clear. In metal construction and sheet metal trading, V2A usually refers to the CrNi steels 1.4301, 1.4541 and 1.4307, while V4A stands for the CrNiMo steels 1.4401, 1.4571 and 1.4404.
DIN EN ISO 3506-1 defines the marking of CrNiMo steels for connecting elements and includes 1.4401 in group A4, 1.4404 in group A4L and 1.4571 in group A5.
Some stainless steels by material number and purpose
Note: In some cases, American AISI material names are also given below, which are still in use internationally. The tolerances of the AISI material designations are i. d. Usually larger, so that z. B. a 1.4435 is always a 316L, a 316L but u. a. can also be a 1.4404.
WNr. 1.4003 (X2CrNi12)
A ferritic, corrosion-resistant steel with 10.5–12.5% chromium and a nickel addition. It is far more resistant than general structural steels , but more cost-effective than the higher alloyed rust and acid-resistant steels. WNr. 1.4003 is characterized by a combination of good corrosion resistance and abrasion resistance with high static and dynamic strength values, good weldability and problem-free deformability. Welding by all known methods is possible without difficulty. The properties of the steel are only negligibly affected by structural changes in the heat affected zone. Its application is WNr. 1.4003 is best where previously unalloyed or low-alloy steels had to be surface treated by painting or coating to achieve better corrosion properties, but where the use of rust-resistant stainless steel was ruled out for price reasons.
- Use: rail vehicle construction - passenger and freight wagons etc .; Commercial vehicle construction - truck bodies, conveyor technology - belt conveyor systems, tipping bodies etc .; Machine and apparatus construction - water technology, air conditioning, sugar industry, agricultural technology - silos, stable equipment, viticulture piles etc .; other - profiles, construction area, cable ducts etc.
WNr. 1.4006 (X12Cr13), AISI 410
A martensitic chromium steel with a chromium content of 11.5 to 13.5%. It combines good mechanical properties with good corrosion resistance in moderately aggressive, chloride-free media. The material is resistant to hydrogen and hydrogen sulfide. A smooth (industrially polished) and residue-free surface is required to achieve optimum corrosion resistance. Good resistance in an oxidizing atmosphere up to 600 ° C is given. The material is available both annealed and tempered. The corrosion resistance is higher in the quenched and tempered condition than in the annealed condition. The steel is easy to weld using manual arc and TIG welding processes. Resistance welding , on the other hand, is only possible to a limited extent. Preheating is required. The machining is practically no different from the unalloyed carbon steels of the same strength level.
- Use: mechanical engineering, plant engineering, apparatus engineering, pumps, hydraulic engineering, kitchen equipment
WNr. 1.4016 (X6Cr17), AISI 430
A ferritic, 17 percent chromium steel with good corrosion resistance, whose share in the production of stainless steels is approx. 16-18%. The polishing ability is very good, as is the deep drawing ability and the flexibility . Stretch drawing is only possible to a limited extent. When forming , it should be noted that the steel tends to become brittle at temperatures below 20 degrees Celsius . Cold formability is improved if the material and tool are heated to 100 to 300 degrees Celsius, which is particularly recommended for sheet metal thicknesses over 3 mm. Sharp folds parallel to the rolling direction are to be avoided. Welding is possible with electrical methods, but embrittlement and a reduction in corrosion resistance occur in the welding area. The machinability is comparable to that of alloyed case-hardening steels. As with all soft qualities, the formation of built- up edges and an obstructed chip flow must be expected.
- Use: The high chromium content gives the steel good resistance to water, water vapor, humidity and weak acids and alkalis. The possible applications are very diverse, e.g. B. for household and kitchen appliances, in the hospitality industry, in food and beverage production, in the furniture industry, interior design, medical technology and in certain branches of the chemical industry, in plumbing, heating and air conditioning systems and in many other areas.
WNr. 1.4021 (X20Cr13), AISI 420
A chromium alloyed stainless tempering steel with a medium carbon content. It is always used in the remunerated state. Good corrosion resistance is only guaranteed if the surface is finely sanded . The polishing ability is very good. Welding is only possible if certain precautionary measures are taken and is generally not recommended. The machinability is comparable to alloyed heat treatable steels and does not cause any particular difficulties.
- Use: The steel can be used wherever components, devices and instruments that should have a medium strength are exposed to the effects of water, steam or humidity. It is widely used in mechanical engineering, turbine construction, pump construction, for fittings, knives, household appliances, sporting goods, medical and surgical instruments, etc.
WNr. 1.4104 (X14CrMoS17, formerly X12CrMoS17), AISI 430F
A heat treatable, rustproof free- cutting steel with 17% chromium and molybdenum additive , which is alloyed with sulfur to improve machinability. The higher sulfur content reduces corrosion resistance and toughness . This quality is not suitable for cold forming , nor for joint welding.
- Use: For turned parts in automatic work, if no great requirements are placed on corrosion resistance.
WNr. 1.4301 (X5CrNi18-10), AISI 304, (V2A), SUS304
1.4301 is the first commercial stainless steel grade and the most frequently used with a production share of 33%. It is an austenitic , acid-resistant 18/10 Cr-Ni steel which, due to its low carbon content, is intercrystalline resistant after welding with sheet thicknesses of up to 5 mm even without subsequent heat treatment. It is approved for a temperature load of up to 600 ° C. At higher working temperatures, the titanium-stabilized steel according to WNr. 1.4541 can be used. The electrical conductivity is 1.4 · 10 6 A / (V · m). Steel is one of the few materials that is suitable for very low temperature applications down to near absolute zero . The weldability is good after all electrical methods; gas fusion welding should not be used. The steel has a very good polishability and a particularly good deformability through deep drawing, folding, roll forming, etc. During machining, tools made of high-alloy high- speed steel or hard metal must be used because of the tendency to work hardening . The steel is not resistant to chloride ions .
- Use: The steel is resistant to water, steam, humidity, food acids and weak organic and inorganic acids and has a wide range of uses, for example in the food industry, in mechanical engineering, in beverage production, in the pharmaceutical and cosmetics industry, in chemical apparatus engineering Architecture , in vehicle construction, for household objects, cutlery and appliances, for surgical instruments, in cabinet and kitchen construction, in sanitary facilities, for jewelry and works of art. The corrosion resistance is significantly increased by electropolishing . This is particularly required in pharmaceutical, food, medical and facade technology. This Cr-Ni steel is unsuitable for use in swimming pools and in seawater (see also stress corrosion cracking ).
WNr. 1.4305 (X8CrNiS18-9, formerly X10CrNiS18 9), AISI 303
An austenitic 18/10 Cr-Ni steel, which is alloyed with sulfur to improve the machinability, so that machining on automatic machines is possible ( machine steel ). The higher sulfur content reduces the corrosion resistance. It is better than material 1.4104 and roughly corresponds to that of material 1.4016. This quality is not suitable for cold forming, nor for joint welding. Due to the sulfur content, machined surfaces are roughened during electropolishing .
- Use: For turned parts in automatic work, if better corrosion resistance than material 1.4104 is required.
WNr. 1.4306 (X2CrNi19-11), AISI 304L
An austenitic, acid-resistant Cr-Ni steel with an extremely low carbon content, which provides increased resistance to intergranular corrosion . Sheets over 6 mm do not have to be post-treated either, even if they were welded under less favorable conditions. The weldability is good by all electrical methods, but gas fusion welding should not be used. The steel can be polished very well. As a reference value for the highest application temperature, 500 degrees Celsius is given. Because of the extremely low carbon content, the hardness, strength and yield point in the quenched state are particularly low, lower than with all other austenitic Cr-Ni steels. This results in particularly good cold formability. Because of the tendency to strain hardening, sharpened tools made of high-alloy high- speed steel (HSS) or hard metal (sintered metal material) must always be used when machining .
- Use: The chemical resistance is comparable to that of 1.4301, so that there are also similar possible uses. However, the cold formability is even better.
WNr. 1.4307 (X2CrNi18-9), AISI 304L, (V2A)
An austenitic, acid-resistant Cr-Ni steel with similar properties to 1.4306, but with a lower corrosion resistance and a lower Ni content. Minimum tensile strength : 520 N / mm². It accounts for 20% of the production of stainless steels.
- Use: The chemical resistance is comparable to that of 1.4301, so that there are also similar possible uses. The costs for 1.4307 are lower than for 1.4301 with the same corrosion resistance.
WNr. 1.4310 (X10CrNi18-8, formerly X12 CrNi17 7), AISI 301
The chrome-nickel alloy X10CrNi18-8 according to EN 10088-1 is often used for corrosion-resistant parts. The strength for standard parts such as disc springs is achieved with the X10CrNi18-8 by cold rolling. The maximum material thickness for disc springs is therefore limited to 2.0 mm. The work hardening leads to a more or less pronounced magnetizability. Areas of application: food industry and chemical industry, as well as spring steel in all branches. (E-module at 20 ° C approx. 190,000 N / mm², flexible from −150 ° C to 210 ° C).
WNr. 1.4316 (X1CrNi19-9)
Welding additive with a particularly low carbon content.
WNr. 1.4401 (X5CrNiMo17-12-2), AISI 316, (V4A)
Austenitic stainless steel with excellent corrosion resistance. Application: According to DVGW worksheet W541 (basis for the requirements for stainless steel pipes for domestic drinking water installations), the steel material 1.4401 (along with 1.4404, 1.4521 and 1.4571) is used most frequently. It is a chrome-nickel steel with added molybdenum. This steel is easy to cold-form (bend, punch, deep-draw), but it is not easy to machine. Because of its strong consolidation, appropriate tools are required. A strong deformation can slightly magnetize the steel. If the steel is kept at temperatures between 500 ° C and 900 ° C, chromium carbides can precipitate in the grain boundaries, which can catastrophically deteriorate the resistance to intergranular corrosion. A solution heat treatment is then required to dissolve the carbides, followed by a quick quench to prevent any re-precipitation. Quenching after thermal treatment is always recommended. This steel can be easily welded with all common methods, with the exception of the oxygen-acetylene flame. After welding, a solution heat treatment with subsequent quenching should be carried out in order to rule out the risk of intergranular corrosion.
WNr. 1.4404 (X2CrNiMo17-12-2), AISI 316L, (V4A, A4L)
Austenitic stainless steel.
- Use: Mechanical components with increased requirements for corrosion resistance, especially in media containing chloride and for hydrogen. AISI 316L is used in a wide variety of areas, in the pharmaceutical industry (manufacture of RDTs = cleaning, disinfection and drying machines), in medical and dental technology , as well as in swimming pool construction, as a ring earth in construction technology.
WNr. 1.4429 (X2CrNiMoN17-13-3), AISI 316LN
Austenitic stainless steel with excellent corrosion resistance. The addition of nitrogen in the alloy represents the main difference to Wnr. 1.4404. Has a very low magnetic permeability ( ). Further designations: 1.4429-ESU, 316LN-ESR, 316LNS.
- Use: Mechanical components with the highest requirements for corrosion resistance and low magnetizability. Frequent use in vacuum technology.
WNr. 1.4430 (X2CrNiMo19-12-3), AISI 316LSi
Austenitic stainless steel with a low carbon content.
- Use: Additive for welding similar CrNi and CrNiMo steels.
WNr. 1.4440 (X2CrNiMo19-12), AISI 316L
This material is used as a filler material when welding low-temperature steels (1.4016, 1.4301). The molybdenum content must be below 2.5% so that it can fulfill its task of welding 1.4016.
WNr. 1.4435 (X2CrNiMo18-14-3), AISI 316L
In terms of its composition, this material is very similar to 1.4404 and essentially differs in terms of its increased molybdenum and nickel content. The increased addition of austenite formers such as nickel reduces or completely prevents the formation of δ-ferrite in the structure. This has the advantage that this steel cannot be magnetized. Due to the higher molybdenum content, the resistance to pitting is greater than that of 1.4404.
WNr. 1.4452 (X13CrMnMoN18-14-3), P2000
Rust- and acid-resistant steel: Medical devices and instruments, spring wire, watch straps. Solution heat treatment: 1050 to 1100 ° C (water).
WNr. 1.4462 (X2CrNiMoN22-5-3)
This material is classified in the class of duplex steels because it consists of a mixture of austenitic and ferritic crystal grains. The optimal structure is achieved through heat treatment (solution annealing) with an austenite / ferrite ratio of around 50:50. This steel is primarily characterized by its high level of corrosion resistance, especially against pitting and stress corrosion cracking. Its yield strength is approx. 450–550 N / mm² and thus significantly higher than that of the usual stainless austenitic steels such as 1.4301 or 1.4404.
WNr. 1.4541 (X6CrNiTi18-10), AISI 321, (V2A)
This material has excellent resistance to a wide variety of aggressive media including hot petroleum products, steam and combustion gases. In continuous operation in air, good oxidation resistance up to approx. 900 ° C, with temperature changes up to approx. 800 ° C. Resistant up to 650 ° C when operated in carbon dioxide .
Well weldable by all known welding processes. It is alloyed with titanium as a carbide former and is therefore resistant to grain decay in accordance with EN ISO 3651, so that, regardless of the cross-section, thermal treatment after welding is not necessary. The material is characterized by good ductility. Only well-ground tools are to be used for machining, otherwise the surface will harden, which makes further processing difficult.
- Use: nuclear power (also in liquid sodium), instrumentation in reactor construction, chem. Apparatus construction (very good corrosion resistance), e.g. B. Production of acetic and nitric acid, heat exchangers, annealing furnaces, paper and textile industry, petroleum processing and petrochemicals, fat and soap industry, food industry, cutlery , dairy and fermentation plants.
WNr. 1.4562 (X1NiCrMoCu32-28-7)
This material is an iron-nickel-chromium-molybdenum alloy with added nitrogen, which is also known under the name Alloy 31 ( UNS number N08031). The material developed by VDM Metals (formerly ThyssenKrupp VDM) closes the gap between high-alloy austenitic special stainless steels and classic nickel alloys . The material is characterized by excellent corrosion resistance in basic and also acidic halide-containing media, excellent resistance to sulfuric acid (even in highly concentrated form), excellent resistance to corrosion and erosion in phosphoric acid media, excellent resistance to general and local corrosion in chlorine dioxide -Bleaching plants in papermaking, excellent resistance in reducing and oxidizing media as well as in boiling 67% nitric acid .
- Use: The alloy is used in the chemical and petrochemical industries, in ore exploration plants, in environmental and marine technology as well as in oil and gas extraction.
WNr. 1.4571 (X6CrNiMoTi17-12-2), AISI 316Ti, (V4A, A5)
Well weldable by all known welding processes. Post-welding heat treatment is generally not required. In special cases, when the reduction of welding stresses seems appropriate for reasons of corrosion chemistry, a heat treatment should be carried out (e.g. ½ hour at 900 ° C). Good ductility . As with 1.4541, only well-ground tools should be used for machining. The steels can be polished. Due to the inclusion of very hard titanium carbides , however, grooves can be produced in the surface during mechanical grinding by pulling out the titanium carbide grains. However, due to the clogging with grinding dust, these become visible only after electropolishing. In many cases, this surface structure is unsuitable for use in pharmaceutical plant construction.
As a result of advances in the manufacture of stainless steels, variants with a low carbon content (1.4404) have replaced the titanium-stabilized grades. The use of 1.4571 compared to 1.4404 is only justified if strengths at high temperatures are required.
- Use: The increased resistance to corrosion and pitting predestines these steels for use especially in the broad field of chem. Apparatus construction. Other areas of application: nuclear power, vacuum technology, instrumentation in reactor construction, submarine construction, furnace construction, pulp, textile, paint, fatty acid, photochemical and pharmaceutical industries, as ring earth electrodes in construction technology. This material is also increasingly used in exhaust technology and wastewater treatment .
WNr. 1.4581 (GX5CrNiMoNb19-11-2)
Rust- and acid-resistant austenitic cast steel, is often executed as an investment casting. The material properties are finally set by means of a heat treatment in the form of solution annealing and subsequent quenching. It is resistant to mineral acids, tensile strength 440 N / mm², yield point Rp 0.2 185 N / mm², elongation at break A5 25%, impact work AV (ISO-V) 40 J, hardness HB 130–200. The niobium content (Nb) is eight times the carbon content (C ≤ 0.07%).
Due to the direct similarity to 1.4571, this cast steel is used in the same areas as, for example, as a pump housing with product contact.
WNr. 1.4841 (X15CrNiSi25-21, formerly X15 CrNiSi25 20)
Excellent corrosion resistance. Can be used in an atmosphere containing carbon dioxide up to 900 ° C. Resistant to smoking nitric acid at 20 ° C and molten nitrates up to 420 ° C, in continuous operation in air up to approx. 1150 ° C, can be used with temperature changes up to approx. 1000 ° C. The use of the material in the range from 550 to 850 ° C cannot be recommended for continuous operation, as it tends to precipitate σ-phases and therefore becomes brittle after cooling to RT .
The steel is suitable for fusion welding according to the various arc processes . Preheating and heat treatment after welding are not required. Flawlessly processable hot and cold. Heat treatment is recommended after hot and cold forming (1050 to 1100 ° C, water or air cooling). Machining can easily be carried out with the use of high-quality tools and the right choice of cutting conditions. The use of hard metal tools is recommended.
The steel is used where the excellent scaling resistance combined with high heat resistance is an advantage. Due to the high Ni content, however, it is sensitive to furnace gases containing sulfur, especially in a reducing atmosphere. Specifically: power plants, petroleum and petrochemicals, furnace construction, heat exchangers, air preheaters, cement kilns, brick kilns, glass production.
WNr. 1.4876 (X10NiCrAITi32-20)
This stainless steel is an austenitic iron-nickel-chromium alloy with additions of carbon, aluminum and titanium (UNS number N08800). The alloy is corrosion and heat resistant under oxidizing, reducing and nitrogenizing conditions. A grain size ≥ 90 μm can be set using a special solution heat treatment , which significantly increases the creep strength above 600 ° C. The alloy is used in industrial furnace construction, in the chemical industry, in environmental protection systems, in the automotive industry and in power plants. Typical applications are furnace muffles, containers, baskets, holders as well as steam / hydrocarbon reformers, ethylene pyrolysis and plants for acetic anhydride and ketone production.
WNr. 1.4916 (X45CrMoVN15)
Martensitic stainless steel with a high nitrogen content. The quality was developed by the German steel producer Buderus Edelstahl and is protected by trademark under the name "Nitro-B".
The steel has a fine microstructure and, due to its increased hardness of 60-62 HRC, its corrosion resistance and edge retention, is the ideal steel for the production of high-quality knives.
WNr. 1.6582 (34CrNiMo6)
This chrome-nickel-molybdenum steel is a heat treatable steel according to EN 10083-3 and 10263-4.
This high-strength and tough steel is used in vehicle and mechanical engineering. The tensile strength is 800 N / mm² but the steel does not have good welding properties.
WNr. 1.7218 (25CrMo4, previously Mo 25)
This chrome-molybdenum steel is a quenched and tempered steel according to EN 10083, construction number 72 - construction, mechanical engineering, container steel. The steel is low-alloyed ; it contains 0.25 percent by mass of carbon and 1 percent by mass of chromium. According to a standard analysis, it also contains 0.25 percent by mass of silicon and molybdenum and 0.7 percent by mass of manganese.
The international designations are 817M40 (BS), 25CD4 (AFNOR) and 4130 (SAE).
It has a tensile strength of over 700 N / mm² and good welding properties. For parts in automotive and aircraft construction that require high toughness, such as B. axles, steering knuckles, turbine parts, turbine rotors, it is mainly used. Bicycle frames are another well known application.
- Quality steel (sulfur and phosphorus content between 0.025% and 0.045%)
- Steel grade
- List of alloying elements
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DIN EN ISO 8044 defines corrosion protection as follows: "Modifying a corrosion system in such a way that corrosion damage is avoided (understood as the sum of all measures that contribute to this)."
and corrosion resistance as: "Ability of a metal to perform its functions in a given corrosion system without being impaired by corrosion."
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