Density | 7630 kg/m3 |
Purpose | parts operating up to 600 °C. Welding apparatus and vessels operating in dilute solutions of nitric, acetic, phosphoric acids, solutions of alkalis and salts and other parts operating under pressure at temperatures from -196 to +600 °C, and in the presence of aggressive media up to +350 °C; austenitic steel |
Elastic modulus | |
Shear modulus | |
Weldability | Weldable without restrictions |
Forging temperature | Start 1200, end 850. Sections up to 350 mm are cooled in air. |
Chemical composition | Silicon:0.8, Manganese:2.0, Copper:0.30, Nickel:9.0-11.0, Sulfur:0.020, Carbon:0.12, Phosphorus:0.035, Chromium:17.0-19.0, Titanium:0.6-0.8, |
A2, A4 - Characteristics of fasteners made of stainless steels
Stainless steels A2, A4: structure, mechanical properties, chemical composition. Fasteners made of steel A2, A4 (stainless bolts, screws, nuts, washers, studs, etc.): mechanical properties, values of tightening torques and pre-tightening forces.
Austenitic steels contain 15-26% chromium and 5-25% nickel, which increase corrosion resistance and are virtually non-magnetic.
It is austenitic chromium-nickel steels that exhibit a particularly good combination of machinability, mechanical properties and corrosion resistance. This group of steels is most widely used in industry and in the production of fasteners.
Steels of the austenitic group are designated by the initial letter “A” with an additional number, which indicates the chemical composition and applicability within this group:
Austenitic structure
Steel group | Material number | Short designation | AISI number |
X 5 CrNi 18-10 / X 4 CrNi 18-12 | AISI 304 / AISI 305 |
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X 6 CrNiTi 18-10 | |||
X 5 CrNiMo 18-10 / X 2 CrNiMo 18-10 | AISI 316 / AISI 316 L |
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X 6 CrNiMoTi 17-12-2 |
Steel A2 (AISI 304 = 1.4301 = 08Х18Н10)— non-toxic, non-magnetic, non-hardening, corrosion-resistant steel. It is easy to weld and does not become brittle. May exhibit magnetic properties as a result of mechanical processing (washers and some types of screws). This is the most common group of stainless steels. The closest analogues are 08Х18Н10 GOST 5632, AISI 304 and AISI 304L (with reduced carbon content).
Fasteners and products made from A2 steel are suitable for use in general construction work (for example, when installing ventilated facades, stained glass structures made of aluminum), in the manufacture of fences, pumping equipment, instrument making from stainless steel. steel for oil and gas production, food, chemical industries, and shipbuilding. Retains strength properties when heated to 425oC, and at low temperatures to -200oC.
Steel A4 (AISI 316 = 1.4401 = 10Х17Н13М2)- differs from A2 steel by adding 2-3% molybdenum. This significantly increases its ability to resist corrosion and acids. A4 steel has higher antimagnetic characteristics and is absolutely non-magnetic. The closest analogues are 10Х17Н13М12 GOST 5632, AISI 316 and AISI 316L (low carbon content).
Fasteners and rigging made from A4 steel are recommended for use in shipbuilding. Fasteners and products made from A4 steel are suitable for use in acidic and chlorine-containing environments (for example, swimming pools and salt water). Can be used at temperatures from -60 to 450°C.
Strength classes
All austenitic steels (from “A1” to “A5”) are divided into three strength classes, regardless of grade. Steels in the annealed state have the lowest strength (strength class 50).
Since austenitic steels are not hardened by hardening, they have the greatest strength in the cold-worked state (strength classes 70 and 80). The most widely used fasteners are A2-70 and A4-80 steels.
Basic mechanical properties of austenitic steels:
ASTM (AISI) type | |||||
Specific gravity (g/cm) | |||||
Mechanical properties at room temperature (20°C) |
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Brinell hardness - HB | In annealed state | ||||
Rockwell hardness - HRB/HRC | |||||
Tensile strength, N/mm 2 | |||||
Tensile strength, N/mm2 | |||||
Relative extension | |||||
Impact strength | KCUL (J/cm2) | ||||
KVL (J/cm2) | |||||
Mechanical properties when heated |
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Tensile yield strength, N/mm2 | |||||
Basic mechanical properties of bolts made of steels A2, A4different strength classes:
Chemical composition of stainless steel:
Steel grade | Group | Chemical composition (wt.%) 1) Excerpt from DIN EN ISO 3506 |
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Note |
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Austenitic | 0,15 | 1,75 | |||||||||
16 | 10,5 | ||||||||||
16 | 10,5 | ||||||||||
1) Maximum values, unless other values have been specified.
2) Sulfur can be replaced with selenium.
3) If the mass fraction of nickel is below 8%, then the mass fraction of manganese must be at least 5%.
4) There is no minimum limit for copper mass fraction if nickel mass fraction is more than 8%.
5) Molybdenum is allowed at the discretion of the manufacturer. If a limitation of molybdenum content is necessary for certain applications, this must be specified by the customer.
6) Molybdenum is also allowed at the discretion of the manufacturer.
7) If the mass fraction of chromium is below 17%, then the mass fraction of nickel must be at least 12%.
8) In austenitic steel with a maximum carbon mass fraction of 0.03% nitrogen should be a maximum of 0.22%
9) For stabilization, it must contain titanium ≤ 5xC up to a maximum of 0.8% and be designated in accordance with this table or niobium and/or tantalum ≤ 10xC up to a maximum of 1% and be designated in accordance with this table.
Austenitic chromium-nickel steels exhibit a particularly good combination of machinability, mechanical properties and corrosion resistance. They are therefore recommended for a variety of applications and are the most significant group of stainless steels. The most important property of this group of steels is high corrosion resistance, which increases with increasing alloying content, especially chromium and molybdenum.
It is the most popular material from which containers and utensils that come into contact with food are made. Stainless steel has good anti-corrosion properties, durability and low weight. However, it is worth considering that this material is not always resistant to aggressive environments; in this case, special food-grade formulations are used.
Of course, it is best to store food in steel or glass containers, since the foam propylene that is popular today does not meet all the necessary requirements. In addition, its service life is much shorter than that of products made of steel.
Many people are interested in how to distinguish food-grade stainless steel from material that is unsuitable for storing food? To answer this question, it is worth considering the advantages, features and classification of this metal.
Advantages of food grade stainless steel
If we talk about the advantages of food-grade stainless steel, it is worth highlighting:
- environmental safety of the material;
- ease of maintenance;
- resistance of the material to most chemicals;
- wear resistance;
- compliance with standards for the dissolution of heavy metals.
In addition, it has long been proven that instead of frying pans with a non-stick coating, it is much healthier to use utensils made from food-grade stainless steel. The best ones are made from the same material hobs and surfaces of refrigerators.
Which stainless steel is considered food grade?
Suitable for storing and preparing food - it is a highly alloyed metal containing 25% chromium. It is thanks to this chemical element that alloys are famous for their anti-corrosion characteristics. In case of contact with an aggressive environment, a special protective film is formed on the metal surface. Thanks to this surface layer, the metal does not rust.
In addition, titanium, molybdenum, nickel and other chemical components are added to food-grade stainless steel, which further increase the anti-corrosion properties of the material.
GOST and stainless steel grades
If we talk about state standards, they do not stipulate the rules related to stainless steel. This is why experts find it difficult to answer which material is recommended for use in the food industry. In turn, the manufacturers of this stainless metal respond that regardless of its brand, it is suitable for food products.
Do the standards really say nothing about food grade stainless steel? GOST 5632-72 is perhaps the closest normative document, which can be used when choosing the best alloy for household use. This State Standard talks about grades and corrosion-resistant and Let's take a closer look at this classification.
08Х18Н10
Austenitic, corrosion-resistant stainless steel is produced under this brand. European equivalent - This material is not magnetic. It is used in all industrial and commercial sectors.
This material has a low price and good quality. It is often used in the food industry, but only on the condition that the metal does not come into contact with caustic soda or sulfamine solutions.
12Х18Н10Т
The European analogue of this brand is AISI 321. This heat-resistant steel is also not magnetic. Stainless steel of this brand is often used in the manufacture of elements of furnace fittings, heat exchangers and exhaust manifolds. The thing is that this steel is suitable for use at high temperatures from 600 to 800 degrees.
08Х13
The European analogue of this material is AISI 409. This steel is widely used in the production of kitchen utensils and cutlery. This food grade stainless steel is most often found in stores. The material gained such popularity due to its high degree of adhesion and ability to adapt to different operating conditions.
This dish can be safely heated or stored in the freezer.
20Х13-40Х13
Steel of this type belongs to the category of composite materials, so it is often used in the manufacture of household and industrial sinks, as well as for the production of utensils for hygienic or thermal processing of food. The European analogue of this brand is AISI 420. If the cookware bears one of these markings, then you can safely buy it for household use. This stainless steel does not rust, tolerates sudden changes in temperature, and is also a fairly plastic and wear-resistant material.
12Х13
In Europe, this material is produced with the AISI 410 marking. Steel of this type is more often used in the production of equipment for winemaking, food processing and alcohol production. In addition, this material is characterized by increased heat resistance in mildly aggressive environments.
08Х17
In Europe, this steel is produced under the brand name This stainless steel is indispensable if the food in the cookware is subjected to heat. This type has the highest strength. However, this material quickly deforms in a sulfur environment. At the same time, stainless steel does not rust and can withstand mechanical loads. It is recommended to buy frying pans from this material, since 08X17 is characterized by a high thermal conductivity coefficient.
All other materials are used in special conditions, their cost is much higher. However, not all stainless steel can be safely used for cooking and storing food. In order not to delve into how food-grade stainless steel differs from technical stainless steel, it is much easier to read a few useful recommendations. They will allow you to quickly determine whether a given material is suitable for food. This is useful to know for every consumer concerned about their health.
How to distinguish food grade stainless steel from technical grade?
To determine the composition of the anti-corrosion alloy, as well as the possibility of its use in everyday life, you can write down the brands that were listed above. If such markings are on the utensils, then they are suitable for preparing and storing food.
But sometimes it happens that in front of your eyes is a material of an unknown brand, and the seller insists that this alloy is absolutely environmentally friendly and cannot harm humans. In this case, it is enough to place the metal in a 2% vinegar solution and wait for the reaction. If the shade of the material has changed, it has become dark, then it is better not to use it. The constancy of color indicates that the stainless steel is indeed food grade. It can be used.
There is another method that consumers often use after reading information on how to identify food-grade stainless steel. They use a magnet for this. But it is worth understanding that this method is completely ineffective, since stainless steel can be magnetic or non-magnetic. Accordingly, using a magnet will not help in any way determine whether the material can be used for food.
To choose the best metal, you should study the information about the product and ask the seller for accompanying documents. Any utensils must be manufactured in accordance with certain standards and requirements. If there is no marking on the product, then it is better to refuse such a product. Otherwise, you can purchase low-quality utensils that are dangerous to human health.
Magnetic properties of high quality austenitic stainless steels.
BEST-Fasten hardware made of AISI 304 and AISI 316 stainless steels allows you to create a reliable fastening that is resistant to corrosion. They are entrusted with increased responsibility in the construction and industrial industries, food and chemical production - wherever exposure to various aggressive environments is expected. Because of this, it is important to know what steel the fasteners are made of. In everyday life, the opinion has formed that corrosion-resistant alloys are non-magnetic. Therefore, on construction sites, the composition of the alloy is usually determined using a household magnet. The essence of the test is simple: if a metal product attracts it, it means: “. .this fastener is not made of stainless steel, but of ordinary steel..».
In fact, defining steel based on the magnetic properties of a product is unprofessional and often misleading. When we talk about the “magneticity” of an alloy, we are actually considering the question: what is its magnetic permeability (or magnetic susceptibility).
Chromium-nickel steels A2 and A4 according to GOST R ISO 3506-1 (according to AISI they correspond to alloys 304 and 316) are classified as austenitic corrosion-resistant steels. Among others, they stand out for their low carbon content against the background of a high chromium and nickel content. Alloys of A4 grades are additionally alloyed with molybdenum to increase corrosion resistance in aggressive environments:
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Steel grade according to GOST R ISO 3506 |
Chemical composition, % |
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Mn |
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A2 |
≤ 4 |
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≤ 4 |
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Chromium-nickel alloys after hardening to austenite have high ductility due primarily to the high nickel content (8-14%) coupled with a low carbon content (no more than 0.08%). Due to the austenitic structure, their magnetic permeability is close to the value of non-magnetic materials: 1.002 and higher. Despite this, steel grades A2 and A4 cannot be called non-magnetic, because their magnetic permeability is higher μ r=1. Various alloying elements noticeably change the magnetic properties of the resulting alloys. For example, some A2 grade steels have μ r=1,8.
In addition, thermomechanical production processes significantly change the magnetic and phase structure of products made from chromium-nickel alloys. During cold deformation of workpieces required during production processes, an increase in the magnetic permeability of the finished product occurs due to the structural transformation of austenite. Changes in magnetic properties are caused by the formation of ferromagnetic phases in the structure of these steels. As a result, testing austenitic steel products using a magnet or magnetic susceptibility meter may give an unexpected result for an alloy that is considered non-magnetic. Hardware subjected to mechanical stress during production, such as drawing, bending, cold hardening, etc., can attract a magnet, even when made from A2 steel grades according to GOST R ISO 506.
The only reliable indicator of the quality of hardware made from austenitic steel is the determination of its composition. Only fasteners made from regulated alloys will ensure durability of the fastener even under the influence of various aggressive environments.
The BEST-Fixture company has been specializing in the supply of fastening and anchoring elements made of corrosion-resistant austenitic steels of grades A2 and A4 in accordance with GOST R 3506-2009 since 2003. The hardware manufacturers we have selected over this time have proven themselves to be consistent high quality its products, which undergo mandatory certification in Europe. In addition, each batch of BEST-Fixture products is subject to mandatory incoming control to determine the alloy using a spectrometer. These preventive measures give us complete confidence that the composition of the alloying elements of steel meets the requirements of GOST. In particularly complex issues or controversial cases, we turn to the research staff of the Moscow Institute of Steels and Alloys (NUST MISIS) for expertise. However, you have the right to confirm the results yourself in any other independent laboratory.
BEST-Fixture specialists have accumulated extensive experience in the field of stainless steel fasteners and anchor products for industrial and construction purposes. If necessary, we confirm the composition of alloying elements with an Analysis Protocol indicating the corresponding steel grade. In addition, the company’s specialists provide assistance in the selection and calculation of fasteners.
Contact the technical department of BEST-Fixtures for advice at any stage of the project.
Considering the fact that stainless steel today is produced in a wide variety of brands, it is impossible to unequivocally answer the question of whether it is magnetic or not. Magnetic properties depend on the chemical composition and, accordingly, on the internal structure of the alloys.
A portable metal analyzer allows you to quickly determine the content of chemical elements and make a conclusion about the quality of stainless steel
What determine the magnetic properties of materials?
A magnetic field with a certain level of its intensity (H) acts on bodies placed in it in such a way that it magnetizes them. In this case, the intensity of such magnetization, which is designated by the letter J, is directly proportional to the field strength. The formula by which the intensity of magnetization of a certain substance is calculated (J = ϞH) also takes into account the coefficient of proportionality Ϟ - the magnetic susceptibility of the substance.
Depending on the value of this coefficient, all materials can be included in one of three categories:
- paramagnetic materials – coefficient Ϟ is greater than zero;
- diamagnetic materials – Ϟ is equal to zero;
- ferromagnets are substances whose magnetic susceptibility is significant (substances, which, in particular, include iron, cobalt, nickel and cadmium, are capable of actively magnetizing, even when placed in weak magnetic fields).
The magnetic properties that stainless steel has are also associated with its internal structure, which can include austenite, ferrite and martensite, as well as combinations thereof. At the same time, the magnetic properties of stainless steel are influenced both by the phase components themselves and by the ratio in which they are found in the internal structure.
Stainless steels with good magnetic properties
Stainless steel, in which the following phase components predominate, has good magnetic properties:
- Martensite is a ferromagnet in its pure form.
- Ferrite - this phase component of the internal structure of stainless steel, depending on the heating temperature, can take two forms. This structural form becomes ferromagnetic if the steel is heated to a temperature below the Curie point. If the heating temperature of the stainless steel is above this point, then high-temperature delta ferrite, which is a pronounced paramagnet, begins to predominate in the alloy.
From all of the above, we can conclude that the stainless steel that is magnetic is one in which martensite predominates in its internal structure. Just like regular ones carbon steels, such alloys react to magnets. By this feature they can be distinguished from non-magnetic ones.
Steel grade 30Х13 is less ductile than alloy 20Х13, despite its similar composition (click to enlarge)
This category also includes the 20Х17Н2 alloy, which is characterized by a high chromium content in its chemical composition, which significantly enhances its corrosion resistance. Why is this stainless steel popular? The fact is that, in addition to high resistance to corrosion, it is characterized by excellent workability using cold and hot stamping and cutting methods. In addition, products made from such material are well welded.
FerriticA common ferritic-type magnetic steel, which, due to the low carbon content in its chemical composition, is softer than martensitic alloys, is 08Х13, which is actively used in food production. Such stainless steel is used to make products and equipment intended for washing, sorting, grinding, sorting, and transporting food raw materials.
Martensitic-ferritic
A popular brand of magnetic stainless steel, the internal structure of which consists of martensite and free ferrite, is 12X13.
Corrosion resistance of steel grade 12Х13 (other name 1Х13)
Non-magnetic stainless steels
Stainless steels that are not magnetic include chromium-nickel and chromium-manganese-nickel. They are usually divided into several groups.
AusteniticThe most popular brand of such stainless steels, which occupy a leading place among non-magnetic steel alloys, is 08Х18Н10 (international analogue according to AISI 304 classification). Steels of this type, which also include 08Х18Н10, 08Х18Н10Т, 12Х18Н10Т, 10Х17Н13М2Т, are actively used in the production of equipment for the food industry; kitchenware and cutlery; plumbing equipment; containers for food liquids; refrigeration equipment elements; containers for food products; medical supplies, etc.
The great advantages of such stainless steel, which does not have magnetic properties, are its high corrosion resistance, demonstrated in many aggressive environments, and manufacturability.
Austenitic-ferriticSteels of this group, the most popular grades of which are 08Х22Н6Т, 08Х21Н6М2Т and 12Х21Н5Т, are distinguished by a high chromium content and a low nickel content. To give such a stainless steel the required characteristics (an optimal combination of high strength and good ductility, resistance to intergranular corrosion and stress-corrosion cracking), elements such as copper, molybdenum, titanium or niobium are introduced into its chemical composition.
