12x18n10t characteristics steel magnetic properties. Food grade stainless steel: GOST
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 glass containers, since the popular today's polypropylene foam does not meet all necessary requirements. In addition, its service life is much shorter than that of products made of steel.
Many are interested in how to distinguish food grade stainless steel from a material unsuitable for food storage? To answer this question, it is worth considering the pros, features and classification of this metal.
Advantages of food grade stainless steel
If we talk about the advantages of food 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 regulations for the dissolution of heavy metals.
In addition, it has long been proven that instead of pans with non-stick coating it is much more useful to use dishes made of food grade stainless steel. The best cooktops and refrigerator surfaces are made from the same material.
What stainless steel is considered food
Suitable for storage and food preparation, it is a highly alloyed metal, which includes 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, 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.
Is it really true that the regulations do not say anything about food grade stainless steel? GOST 5632-72 is perhaps the closest normative document, which can be used when choosing the best alloy for domestic applications. In that state standard we talk about grades and corrosion-resistant and Let's take a closer look at this classification.
08X18H10
Under this brand, austenitic corrosion-resistant stainless steel is produced. 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 does not come into contact with caustic soda or sulfa solutions.
12X18H10T
The European analogue of this grade 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 manufacture of kitchen utensils and cutlery. Such food stainless steel is most often found in stores. The material gained such popularity due to the high degree of adhesion and the ability to adapt to different operating conditions.
This dish can be safely heated or stored in it products in the freezer.
20X13-40X13
Steel of this type belongs to the category composite materials, therefore 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 one of these markings is on the dishes, then you can safely buy it for household use. This stainless steel does not rust, tolerates a sharp change in temperature well, and is also a fairly ductile and wear-resistant material.
12X13
In Europe, this material is produced with the marking AISI 410. Steel of this type is more often used in the manufacture of equipment for winemaking, food processing and the manufacture of alcohol. In addition, this material is characterized by increased heat resistance in a slightly aggressive environment.
08X17
In Europe, this steel is produced under the brand name. Such stainless steel is indispensable if the food in the dishes is subjected to thermal this type is characterized by the highest strength. However, this material is rapidly deformed in a sulfur environment. At the same time, stainless steel does not rust and can withstand mechanical stress. It is recommended to buy 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 food storage. In order not to delve into the difference between food stainless steel and 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 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 a marking is on the dishes, then it is suitable for cooking and storing food.
But sometimes it happens that a 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% acetic 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 invariance of color suggests that 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 completely inactive, since stainless steel is 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 for supporting documents. Any utensils must be produced 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 poor-quality and dangerous utensils for human health.
Depending on the purpose, working conditions, aggressiveness of the environment, the products are subjected to: a) hardening (austenization); b) stabilizing annealing; c) stress relief annealing; d) step processing. Products are hardened in order to: a) prevent the tendency to intergranular corrosion (products operate at temperatures up to 350 ° C); b) improve resistance to general corrosion; c) eliminate the revealed tendency to intergranular corrosion; d) prevent the tendency to knife corrosion (welded products work in nitric acid solutions); e) eliminate residual stresses (products of a simple configuration); e) increase the plasticity of the material. Hardening of products must be carried out according to the regime: heating up to 1050-1100 ° C, parts with a material thickness of up to 10 mm should be cooled in air, over 10 mm - in water. Welded products of complex configuration in order to avoid the leash should be cooled in air. Holding time during heating for hardening for products with a wall thickness of up to 10 mm - 30 min, over 10 mm - 20 min + 1 min per 1 mm of maximum thickness. When quenching products intended for operation in nitric acid, the heating temperature for quenching must be kept at the upper limit (while the exposure of welded products must be at least 1 hour). Stabilizing annealing is used to: a) prevent susceptibility to intergranular corrosion (products operate at temperatures above 350 °C); b) removal of internal stresses; c) elimination of the detected tendency to intergranular corrosion, if for some reason hardening is not advisable. Stabilization annealing is acceptable for products and welded joints made of steels in which the ratio of titanium to carbon is more than 5 or niobium to carbon is more than 8. more than 0.08% carbon. Stabilizing annealing should be carried out according to the regime: heating to 870-900 °C, holding for 2-3 hours, cooling - in air. During heat treatment of large-sized welded products, it is allowed to carry out local stabilizing annealing of the closing welds according to the same regime, while all welded elements must be subjected to stabilizing annealing before welding. When carrying out local stabilizing annealing, it is necessary to ensure simultaneous uniform heating and cooling along the entire length weld and adjacent zones of the base metal to a width equal to two or three joint widths, but not more than 200 mm. Manual heating is not allowed. For a more complete removal of residual stresses, annealing of products from stabilized chromium-nickel steels is carried out according to the following regime: heating to 870-900 ° C; holding for 2-3 hours, cooling with an oven to 300 °C (cooling rate 50-100 °C/h), then in air. Annealing is carried out for products and welded joints made of steel, in which the ratio of titanium to carbon is more than 5 or niobium to carbon is more than 8. Step processing is carried out to: a) relieve residual stresses and prevent a tendency to intergranular corrosion; b) to prevent the tendency to intergranular corrosion of welded joints of complex configuration with sharp transitions in thickness; c) products with a tendency to intergranular corrosion, which cannot be eliminated by another method (hardening or stabilizing annealing). Step processing must be carried out according to the mode: heating up to 1050-1100 ° C; holding time during heating for hardening for products with wall thickness up to 10 mm - 30 min, over 10 mm - 20 min + 1 min per 1 mm of maximum thickness; cooling with the maximum possible speed up to 870-900°C; exposure at 870-900 °C for 2-3 hours; cooling with a furnace up to 300 °C (speed - 50-100 °C/h), then in air. To speed up the process, stepwise processing is recommended to be carried out in two-chamber or two furnaces heated to different temperatures. When transferring from one furnace to another, the temperature of the products should not be lower than 900 °C. Step processing is allowed for products and welded joints made of steel, in which the ratio of titanium to carbon is more than 5 or niobium to carbon is more than 8.
Many private consumers are concerned about the question of whether stainless steel is magnetized or not. The fact is that it is impossible to visually distinguish ordinary steel from stainless steel, and therefore the method of checking the material with a magnet is widespread. It is believed that stainless steel should not be magnetized, but in practice this diagnostic method does not always allow you to get a reliable result. As a result, often materials that do not magnetize perfectly tolerate contact with water. On the other hand, products that have passed the "test" become rusty. As a result, the question of whether or not stainless steel is magnetized becomes more and more confusing. What determines the magnetic properties of stainless steel?
The term "stainless steel" refers to various materials, the composition of which may contain ferrite, martensite or austenite in its structure, as well as their various combinations. The characteristics of stainless steel depend on the phase components and their ratio. So which stainless steel is magnetic and which is not?
Stainless steels that are not magnetic
Most often for the production of stainless steel is used chromium-nickel or chromium-manganese-nickel alloy. These materials are non-magnetic. They are extremely widespread, which is why many consumers, based on their practical experience give a negative answer to the question of whether stainless steel is magnetized. Non-magnetic steels are divided into the following groups:
· Austenitic. Austenitic class materials (for example, AISI 304 steel) are used to produce equipment for the food industry, containers for food liquids, kitchen utensils, as well as a variety of refrigeration, marine and sanitary equipment. High resistance to aggressive environments provides a wide distribution of this type of steel.
· Austenitic-ferritic. These materials are based on chromium and nickel. Titanium, molybdenum, copper and niobium can be used as additional alloying elements. The main advantages of austenitic-ferritic steels include improved strength and greater resistance of the structure to stress corrosion cracking.
Stainless steels that are magnetic
· Martensitic. Thanks to quenching and tempering, the material is characterized by high strength, which is not inferior to the corresponding parameter of standard carbon steels. Martensitic grades find their application in the manufacture of abrasives and in the engineering industry. Cutlery is also made of them, and in this case, you can safely give a positive answer to the question of whether food grade stainless steel is magnetized. Materials of classes 20X13, 30X13, 40X13 are widely used in a ground or polished state, and class 20X17H2 is highly valued for its unsurpassed resistance to corrosion, surpassing even 13% chromium steels in this indicator. Due to its high processability, this material is well suited for all types of processing, including stamping, cutting and welding.
· ferritic. This group of materials is lighter than martensitic steels due to the lower carbon content. One of the most sought-after alloys is AISI 430 magnetic steel, which finds its application in the production of equipment for food production plants.
Practical value magnetic properties of stainless steel
Magnetic properties of high quality austenitic stainless steels.
BEST fasteners made of AISI 304 and AISI 316 stainless steels allow you to create a reliable fastening that is resistant to corrosion. They are assigned increased responsibility in the construction and industrial industries, in the food and chemical production- wherever exposure to various aggressive environments is expected. Therefore, it is important to know: what steel the fasteners are made of. In everyday life, an opinion was 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, the definition of steel, based on the magnetic properties of the product, is unprofessional and often misleading. When we talk about the “magnetism” of an alloy, we are actually considering the question: what is its magnetic permeability (or magnetic susceptibility).
Nickel-chromium 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 are distinguished by a low carbon content against the background of an increased content of chromium and nickel. Alloys of grades A4 are additionally alloyed with molybdenum to increase corrosion resistance in aggressive environments:
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Steel grade according to GOST R ISO 3506 |
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A2 |
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≤ 4 |
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Nickel-chromium alloys after quenching for austenite have high ductility due primarily to the high nickel content (8-14%), coupled with a low carbon content (not 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 obtained alloys. For example, some A2 steels have μ r=1,8.
In addition, thermomechanical production processes significantly change the magnetic and phase structure of products made of chromium-nickel alloys. For cold deformations of workpieces, mandatory during production processes there is an increase in magnetic permeability finished products due to the structural transformation of austenite. Changes in the 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 a magnetic susceptibility meter can give an unexpected result for an alloy that is considered to be non-magnetic. Hardware subjected to mechanical stress during production, such as drawing, bending, work hardening, etc., can cause a magnet to be attracted to itself, even if they are made of A2 steel grades 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 of regulated alloys will ensure the durability of fastening operation even under the influence of various aggressive environments.
The BEST-Krepezh company has been specializing in the supply of fasteners and anchor elements made of corrosion-resistant austenitic steel grades A2 and A4 in accordance with GOST R 3506-2009 since 2003. The hardware manufacturers selected by us during this time have proven themselves to be invariable high quality of its products, which undergo mandatory certification in Europe. In addition, each batch of BEST Fasteners is subjected 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 complies with the requirements of GOST. In especially difficult questions or disputable cases, we apply for expertise to the researchers of the Moscow Institute of Steels and Alloys (NUST MISiS). However, you have the right to confirm your results yourself in any other independent laboratory.
BEST-Fastening specialists have accumulated great experience in the field of stainless fasteners and anchor products for industrial and construction direction. If necessary, we confirm the composition of the alloying elements with an Analysis Report indicating the corresponding steel grade. In addition, the company's specialists provide assistance in the selection and calculation of fasteners.
Contact technical department BEST Fasteners for advice at any stage of the project.
Good day, dear distillers! We recently encountered a surprising phenomenon for us. Some details of equipment made of stainless steel AISI brands 304 magnetize and rust. Which surprised us a lot. Accordingly, we decided to look into this issue in more detail and this is what we found out.
AISI 304 stainless steel is chromium-nickel and belongs to the austenitic group of steels, that is, it is not magnetic. As well as its analogues steel 08X18H10, 08X18H10T, 12X18H10T, etc.
However, under certain physical influences, metal products of this group can exhibit magnetic properties. So, for example, when welding any type, under the influence of high temperature, the alloying elements burn out and the structure of the metal changes at the site of the weld. Accordingly, in this place the metal begins to exhibit magnetic properties. A change in the structure of the crystal lattice of a metal also occurs under mechanical action, such as metal forging, thread rolling, pressing, metal bending, etc. Which also leads to the manifestation of magnetic properties. At the same time, the general chemical and physical properties of steel do not change.
Now for the rust. First of all, rust can appear on the weld. What might cause this to happen. In the process of welding, a film is formed on the surface of the seam, which has low resistance to an aggressive environment, so it can become covered with corrosion, that is, rust. Also, rust can appear in small spots on the metal itself. This is due to the way the metal is processed, so to speak, beauty guidance. After welding, the structure is cleaned with a steel brush, so-called risks are induced. Microparticles from this brush get stuck in a softer stainless steel, they then appear as rusty spots when interacting with moisture contained, including in the air. Both of these types of corrosion are simply removed with a polishing sponge and no longer appear.
In general, in the process of studying these issues, we realized one thing, physics is an interesting and fascinating science that will surprise us more than once!
Sincerely, NOVATRA store team!
Information taken from scientific sources.