Is the "stainless steel" magnetic or not? Food stainless steel: gost. how to define food grade stainless steel? What is the difference between food grade stainless steel and technical grade? Magnetic properties of steel 12x18n10t

It is the most popular material from which containers and utensils in contact with food are made. Stainless steel has good anti-corrosion properties, durability and low weight. However, it should be borne in mind 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 glassware, since the popular today polypropylene does not meet all 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 stainless steel from material unsuitable for storing food? To answer this question, it is worth considering the pros, features and classification of this metal.

Benefits of food grade stainless steel

If we talk about the advantages of food grade stainless steel, then it is worth highlighting:

• environmental safety of the material;
• ease of maintenance;
• material resistance to most chemicals;
• wear resistance;
• compliance with the 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 more useful to use dishes made of food-grade stainless steel. The very best hobs and refrigerator surfaces are made from the same material.

What stainless steel is considered food

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 properties. In case of contact with an aggressive medium, a special protective film forms 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 stainless steel, which additionally increase the anti-corrosion properties of the material.

GOST and stainless steel grades

If we talk about state standards, then they do not spell out the rules related to stainless steel. That is why experts find it difficult to answer which material is recommended to be used in Food Industry... In turn, the manufacturers of this stainless metal answer that regardless of its brand, it is suitable for food products.

Does the regulations 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 home use. In that State standard talking about brands and corrosion-resistant and Let us consider this classification in more detail.

08X18H10

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 is of low price and good quality. It is often used in the food industry, but only on condition that the metal will not come into contact with caustic soda or sulfamic solutions.

12Х18Н10Т

The European counterpart of this brand is AISI 321. This heat-resistant steel is also non-magnetic. This brand of stainless steel 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.

08X13

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 the ability to adapt to different operating conditions.

This dish can be safely heated or stored in it in the freezer.

20X13-40X13

Steel of this type belongs to the category of composite materials, therefore it is often used in the manufacture of domestic and industrial sinks, as well as for the manufacture of dishes for hygienic or thermal processing of food. The European counterpart of this brand is AISI 420. If the dishes have one of these markings, then you can safely buy it for use in everyday life. This stainless steel does not rust, tolerates sudden changes in temperature well, and is also a fairly plastic and wear-resistant material.

12X13

In Europe, this material is produced with the AISI 410 mark. Steel of this type is more often used in the production of equipment for winemaking, food processing and the manufacture of alcohol. In addition, this material is characterized by increased heat resistance in a mildly aggressive environment.

08X17

In Europe, this steel is produced under the brand name This stainless steel is irreplaceable if the food in the dishes is subjected to thermal, this type has the highest strength. However, this material quickly deforms in a sulfuric environment. At the same time, stainless steel does not rust and can withstand mechanical stress. It is recommended to buy frying pans from this material, since 08X17 is characterized by a high coefficient of thermal conductivity.

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 stainless steel differs from technical, it is much easier to read a few useful recommendations... They will allow you to quickly determine if a given material is suitable for food. This is useful for every consumer concerned about their health.

How to distinguish food stainless steel from technical?

To determine the composition of the anti-corrosion alloy, as well as the possibility of its use in everyday life, you can write out the brands that were listed above. If such markings are on the dishes, then they are suitable for cooking and storing food.

But sometimes it happens that the material of an unknown brand is in front of your eyes, and the seller insists that this alloy is absolutely environmentally friendly and cannot harm a person. 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. Consistency of color suggests that stainless steel is really 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 should be understood that this method is completely ineffective, since stainless steel can be magnetic and non-magnetic. Accordingly, the use of a magnet will not help in any way to determine whether the material can be used for food.

To choose the best metal, you should study the product information and ask the seller accompanying documents... Any utensil must be manufactured in accordance with certain norms and requirements. If there is no marking on the product, then it is better to refuse such a product. Otherwise, you can purchase utensils of poor quality and hazardous to human health.

A2, A4 - Characteristics of stainless steel fasteners

Stainless steels A2, A4: structure, mechanical properties, chemical composition. Fasteners made of steel A2, A4 (stainless bolts, screws, nuts, washers, pins, 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 practically non-magnetic.

It is the 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 that indicates the chemical composition and applicability within this group:

Austenitic structure

Steel A2 (AISI 304 = 1.4301 = 08Х18Н10)- non-toxic, non-magnetic, non-hardened, corrosion-resistant steel. Easily weldable and does not become brittle. May exhibit magnetic properties as a result mechanical processing(washers and some types of screws). This is the most common group of stainless steels. The closest analogues are 08X18H10 GOST 5632, AISI 304 and AISI 304L (with a reduced carbon content).

Fasteners and products made of 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, instrumentation from stainless steel. steel for oil and gas production, food, chemical industry, in shipbuilding. Retains strength properties when heated up to 425oС, and at low temperatures up to -200oС.

Steel A4 (AISI 316 = 1.4401 = 10Х17Н13М2)- differs from steel A2 by the addition of 2-3% molybdenum. This greatly increases its ability to resist corrosion and acid attack. A4 steel has higher anti-magnetic characteristics and is absolutely non-magnetic. The closest analogues are 10Х17Н13М12 GOST 5632, AISI 316 and AISI 316L (with low carbon content).

Fasteners and rigging made of A4 steel are recommended for use in shipbuilding. Fasteners and products made of A4 steel are suitable for use in acids and chlorine-containing environments (such as swimming pools and salt water). It 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 quenching, 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:

Basic mechanical properties of bolts made of steel A2, A4different strength classes:

Chemical composition of stainless steel:

1) Maximum values ​​unless otherwise 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 the copper mass fraction if the nickel mass fraction is more than 8%.
5) Molybdenum is allowed at the discretion of the manufacturer. If for certain applications it is necessary to limit the molybdenum content, this should be indicated by the customer.
6) Molybdenum is also permitted 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 steels with a maximum carbon mass fraction of 0.03%, the nitrogen must be a maximum of 0.22%.
9) For stabilization, titanium must be ≤ 5xC up to a maximum of 0.8% and be labeled according to this table or niobium and / or tantalum ≤ 10xC up to a maximum of 1% and be labeled according to this table.

Austenitic chromium-nickel steels exhibit a particularly good combination of machinability, mechanical properties and corrosion resistance. Therefore, they are recommended for many 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 an increase in the content of alloying, especially chromium and molybdenum.

Magnetic properties of high quality austenitic stainless steels.

Hardware BEST-Fasteners made of stainless steels AISI 304 and AISI 316 allow to form a reliable fastener, resistant to corrosion. They are entrusted with increased responsibility in the construction and industrial industries, in the food and chemical industries - wherever the impact of various aggressive environments is expected. For this reason, it is important to know: what steel the fasteners are made of. In everyday life, the opinion was formed that corrosion-resistant alloys are non-magnetic. Therefore on construction sites It is customary to determine the composition of the alloy using a household magnet. The essence of the dough is simple, if a metal product attracts it, it means: “. .this fasteners are 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 "magnetism" of this or that alloy, in fact we are considering the question: what is its magnetic permeability (or magnetic susceptibility).

Chrome-nickel steels A2 and A4 in accordance with 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 content of chromium and nickel. A4 alloys are additionally alloyed with molybdenum to increase corrosion resistance in aggressive environments:

Chromium-nickel alloys after quenching for austenite have high ductility due primarily to their high nickel content (8-14%), coupled with a low carbon content (no more than 0.08%). Due to their 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 markedly change the magnetic properties of the resulting alloys. For example, some steels of grade A2 have μ r=1,8.

In addition, thermomechanical production processes significantly change the magnetic and phase structure of products from chromium-nickel alloys. With cold deformations of blanks, which are mandatory 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 due to the formation of ferromagnetic phases in the structure of these steels. As a result, checking austenitic steel products with a magnet or magnetic susceptibility tester can give unexpected results for an alloy that is considered non-magnetic. Hardware subjected to mechanical stress during production, such as drawing, bending, cold working, etc., can cause a magnet to be attracted to itself, even when made of steel grades A2 according to GOST R ISO 506.

The only reliable indicator of the quality of austenitic steel hardware is the determination of its composition. Only fasteners made from regulated alloys will ensure the durability of the fastener, even under the influence of various corrosive environments.

BEST-Fastener has been specializing in the supply of fasteners and anchoring elements made of corrosion-resistant austenitic steels A2 and A4 in accordance with GOST R 3506-2009 since 2003. The manufacturers of hardware selected by us during this time have established themselves as unchanged high quality its products, which are subject to mandatory certification in Europe. In addition, each batch of BEST-Fasteners is subject to mandatory incoming control to determine the alloy using a spectrometer. These preventive measures give us full confidence that the composition of the alloying elements of steel meets the requirements of GOST. In especially difficult issues or controversial cases, we turn to the research staff of the Moscow Institute of Steel and Alloys (NUST MISiS) for expertise. However, you have the right to confirm the results obtained yourself in any other independent laboratory.

BEST-Fasteners specialists have accumulated extensive experience in the field of stainless fasteners and anchor products for industrial and construction directions. 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 technical department BEST-Fixture for consultation at any stage of the project.

ABOUT STAINLESS STEEL

In our country, there is an opinion that "stainless steel" does not magnetise steel and, accordingly, the main test for "stainless steel" is the application of a magnet to it. However, this is actually not the case, as there are so many magnetic grades of stainless steel. Therefore, if a magnet sticks to your stainless steel, do not rush to return the goods to the supplier, perhaps you have a ferritic grade of stainless steel. Below we will look at the properties, classifications and applications of stainless steel alloys.

Chemical composition and properties of stainless steel

Stainless steel or "stainless steel" is a complex alloy steel that is resistant to corrosion in corrosive environments. The main alloying element is chromium (the proportion in the alloy is 12-20%). To enhance corrosion resistance, nickel (Ni), titanium (Ti), molybdenum (Mo), niobium (Nb) are also added to the alloy; in various quantities depending on the required properties of the alloy. The degree of corrosion resistance of an alloy can be determined by the content of the main elements of the alloy - chromium and nickel. If the chromium content in the alloy is more than 12%, it is already a stainless metal under normal conditions and in slightly aggressive environments. With a chromium content of more than 17% in the alloy, it is a corrosion-resistant alloy in corrosive environments (for example, in 50% concentrated nitric acid). In the zone of contact of the chromium-containing alloy with an aggressive medium, a protective oxide film is formed, which protects the alloy from impact environment... Corrosion resistance of stainless steel is manifested precisely because of the presence of a protective film. In addition, the following characteristics are of great importance: metal homogeneity, surface condition, lack of tendency to intercrystalline corrosion.

Types and classification of stainless steel

Stainless steel is either magnetic (ferritic) or non-magnetic (austenitic). Magnetic properties do not affect the performance of stainless steel, in particular corrosion resistance. The difference in magnetic properties is a consequence of the difference in the internal structure of steels, which directly depends on chemical composition stainless steel. Checking steel for "stainlessness" with a magnet is like checking leather for naturalness with a lighter (it's useless because modern leatherette keeps the temperature much higher than leather).

All produced stainless steel is divided into three types:

Chromiums with subgroups:

Semi-ferritic (maratene-ferritic) Ferritic Martensitic

Chrome-nickel with subgroups:

Chrome-manganese-nickel with subgroups:

Austenitic Austenitic-martensitic Austenitic-carbide Austenitic-ferritic

Moreover, the first group is magnetic, the second and third are non-magnetic.

MORE DETAILS

Classification of materials by their magnetic properties Bodies placed in a magnetic field are magnetized. The intensity of the magnetization (J) is directly proportional to the increase in the field strength (H): J = ϰH, where ϰ is the coefficient of proportionality, called the magnetic susceptibility. If ϰ> 0, then such materials are called paramagnets, and if ϰ Some metals - Fe, Co, Ni, Cd - have an extremely high positive susceptibility (about 105), they are called ferromagnets. Ferromagnets are intensely magnetized even in weak magnetic fields. Industrial stainless steels can contain ferrite, martensite, austenite, or combinations of these structures in different proportions in their structure. It is the phase components and their ratio that determines whether the stainless steel magnet or not. Magnetic stainless steel: structural composition and grades

There are two phase constituents of steels with strong magnetic characteristics:

Martensite, from the point of view of magnetic properties, is a pure ferromagnet. Ferrite comes in two versions. At temperatures below the Curie point, it, like martensite, is a ferromagnet. High temperature delta ferrite is a paramagnetic.

Thus, corrosion-resistant steels, the structure of which consists of martensite, are magnetic stainless steel. These alloys react to a magnet like normal carbon steel. And ferritic or ferrite-martensitic steels can have different properties depending on the ratio of the phase components, but, most often, they are also ferromagnetic.

Martensitic steels are hard, hardened by quenching and tempering like conventional carbon steels. They are mainly used for the production of cutlery, cutting tools and in general mechanical engineering. Steels 20X13, 30X13, 40X13 of the martensitic class are produced mainly in a heat-treated ground or polished state. Chromium-nickel steel of the martensitic class 20X17H2 has a higher corrosion resistance than 13% chromium steels. This steel is distinguished by its high manufacturability - it lends itself well to stamping, hot and cold, processed by cutting, and can be welded by all types of welding. Ferritic steels of type 08X13 are softer than martensitic ones due to the lower carbon content. One of the most consumed ferritic steels is the magnetic corrosion-resistant alloy AISI 430, which is an improved analogue of the 08X17 grade. This steel is used to make technological equipment food production used for washing and sorting food raw materials, crushing, separating, sorting, packaging, transporting products. Ferritic-martensitic steels (12X13) have martensite and structurally free ferrite in their structure.

Non-magnetic stainless steel

Non-magnetic alloys include chromium-nickel and chromium-manganese-nickel steels of the following groups:

Austenitic steels take the leading place in terms of production volume. Non-magnetic austenitic stainless steel is widespread - steel AISI 304 (analogue - 08X18H10). This material is used in the production of equipment for the food industry, the manufacture of containers for kvass and beer, evaporators, cutlery - pots, pans, bowls, kitchen sinks, in medicine - for needles, ship and refrigeration equipment, plumbing equipment, tanks for various liquids. composition and purpose and dry substances. Steel 08X18H10, 08X18H10T, 12X18H10T, 10X17H13M2T have excellent manufacturability and high corrosion resistance in many corrosive environments. Austenitic-ferritic steels are characterized by a high chromium content and a low nickel content. Additional alloying elements are molybdenum, copper, titanium or niobium. These steels (08Х22Н6Т, 12Х21Н5Т, 08Х21Н6М2Т) have some advantages over austenitic steels- higher strength while maintaining the required plasticity, greater resistance to intergranular corrosion and corrosion cracking.

The group of non-magnetic materials also includes corrosion-resistant austenitic-martensitic and austenitic-carbide steels. A method for determining whether a non-magnetic steel is corrosion-resistant As the above information shows, there is no definite answer to the question - whether a stainless steel is magnetised or not. If steel is magnetised, can you tell if it is corrosion resistant? To answer this question, it is necessary to clean a small area of ​​the part (wire, pipes, plates) to shine. Two or three drops of a concentrated solution are applied and rubbed onto the cleaned surface. copper sulfate... If the steel is covered with a layer of red copper, the alloy is not corrosion-resistant. If no changes have occurred on the surface of the material, then stainless steel is in front of you. It is impossible to check at home whether steel belongs to the group of food alloys. The magnetic properties of stainless steel do not in any way affect the performance, in particular the corrosion resistance of the material

Types of stainless steel stainless steel