How is stainless steel made?

Stainless steel for knives: pros and cons, types and properties

The choice of brand and metal alloy is key in the production of knives. The quality of the product, its resistance to wear and mechanical damage, maintaining the sharpness of the blade, etc. depend on it.

Stainless steel for knives is increasingly being chosen as the main material and the reason for this is its special operational and technical characteristics.

To understand the relevance of such a choice, it is necessary to analyze all the pros and cons of choosing a material, first find out their varieties and key properties.

History of the creation of stainless steel

The first mention of stainless steel dates back to 1915. A British company from Sheffield announced the creation of a unique alloy that is resistant to corrosion, has an excellent appearance and is resistant to abrasion. According to the creators, it was an excellent material for cutlery, including cutting ones.

Naturally, the controversy regarding the stainless steel patent attracted a lot of attention because, in fact, the ancestor of the alloy was the classic high-carbon steel used throughout the world.

Despite this, the metal, in fact, has improved technical characteristics and has nothing in common with the production of a high-carbon alloy.

More than a hundred years have passed since the creation of the material and it is no longer considered an invention for cutlery, and stainless steel for knives is used to create piercing and cutting objects not only in the kitchen.

Advantages, disadvantages and main competitors of stainless steel

Stainless steel has been used in the production of cutting tools for over a hundred years. During this time, no direct analogues of the product were invented that would differ in similar technical parameters or price, so knives still have three main competitors:

1. Knives made of ferrous metal alloys. They are susceptible to corrosion, even taking into account external coating, the durability of such products is questionable, while a stainless steel knife oxidizes tens of times slower.
2. Ceramic. They have a couple of critical disadvantages: difficulty in maintenance and the inability to chop and cut dense or hard materials. Stainless steel does not have such disadvantages.
3. Cutting tools made of high carbon materials. The key to the production of such metals remains the addition of certain components. It is worth noting that there is now a wide range of stainless steel materials on the market, with the addition of high-carbon components, so comparison with analogues is not required here.

Classic 3 mm stainless steel used in production (cutting, forging or peening) has a number of physical properties that are significantly superior to analogues. The advantages of stainless steel products include:

• ease of maintenance;
• low cost of production;
• possibility of using various alloys and steel grades;
• elasticity of the material;
• lifetime;
• resistance to natural and chemical oxidizing agents.

It is these parameters that remain key in choosing a knife based on stainless steel. Despite the very impressive technical indicators, various alloys of stainless metals also have disadvantages:

• lack of usual shine,
• insufficient elasticity
• immunity to sudden temperature changes.

In fact, a lot depends on the type of stainless steel chosen in the product.

Types of stainless steel

Depending on the production method and the proportion of material used, stainless steel differs in a number of characteristics. Almost all known and popular stainless steel alloys are used to create knives, but the key here remains the method of operation, size and load level. It is foolish to say that a kitchen knife and a hunting cleaver have an identical load. That is why alloys of different characteristics and grain sizes are used in their production.

In most cases, it is the grain size that indicates the type of metal. Steelworkers, blacksmiths and cutting tool professionals can identify the type of stainless steel by its appearance, but for the average user, the production method and type of stainless steel remain a mystery.

In total, we can distinguish several main types of steel, which differ in the method of creation and processing, performance characteristics and appearance:

Ferritic

One of the cheapest types of alloy, which includes chromium (up to 30% content) and low-carbon (no more than 0.1% content) compositions. Ease of processing and good performance properties make it an excellent choice for the production of static elements.

Among the advantages: average metal strength, ductility and average density. For such a material, the destructive indicator is a temperature difference, which eliminates the possibility of hardening.

Ferritic alloy is rarely used to make knives, but can be found in inexpensive kitchen sets.

Austenitic or chromium-nickel

The complexity of the composition determines a special approach to production. Excellent resistance to corrosion and minor damage due to the content of nickel (from 6 to 12% of the composition), carbon, chromium (from 16 to 26% of the composition) and molybdenum.

Heat treatment significantly reduces the strength of the alloy, but cold hardening allows it to be increased. The complexity of metal processing makes it a rare basis for creating cutting tools.

In most cases, it is used in the production of high-quality and expensive knives that are designed for a long service life.

Ferritic-austenitic or two-phase

Like any two-phase alloys, ferritic-austenitic stainless steel has average indicators of the metals displayed in its name, so there is no point in analyzing them in detail. Cutting tools cannot be made on its basis, so you should beware of knives with such an alloy.

Martensitic

One of the very popular alloys in the world, containing chromium steel (no more than 17% in the composition) and carbon (no more than 1% in the composition).

Martensitic stainless steel is highly susceptible to forging, hardening and tempering, making it the best possible choice for knife production, particularly due to its price-quality ratio.

Thanks to hardening, the metal is quite dense and hard, which is considered a critical technical indicator, but the low chromium content in it negatively affects its resistance to corrosion.

In general, this is general information that may be important when choosing an alloy, but the question of what is the best stainless steel for a knife remains open. If you delve deeper, you should not touch on the alloy as such, but specifically on the grade of stainless steel, so that the answer to the question is not so vague. There are hundreds of grades of stainless steel, each of which has certain technical characteristics, which makes it almost impossible for the average user to study the issue in detail.

Choosing a stainless steel brand

As already mentioned, a large number of steel grades does not make it possible to fully consider the advantages and disadvantages of each. As an example, let's look at several options for stainless steel, which is common in use.

Stainless steel AISI 304

The “premium” segment includes AISI 304 stainless steel, which is widely used in chemical and food production. This grade of steel has improved corrosion resistance, which allows it to be used in the production of cutting, pocket and kitchen knives without fear of oxidation.

Austenitic alloy with a high content of chromium and nickel and unique resistance to short-term temperature changes, the ability to withstand temperatures up to 900 C0.

AISI stainless steel holds hardening well, but in terms of resistance to mechanical damage (cutting bones, wood, frozen foods) it is significantly inferior to the next contender for the title of best brand.

Stainless steel 12x18n10t

Austenitic stainless steel alloy 12x18n10t, which is used mainly in areas of increased environmental exposure.

More often, this steel is used in the production of building materials placed outdoors, but the presence of carbide-forming titanium in the composition has also found application in the chemical, food and oil industries.

Vague GOST indicators play a cruel joke on the consumer, which makes it possible to create second-rate metal by slightly varying the volume of components. Stainless steel of this brand is very expensive, so products based on it will not cost the buyer cheap, although its service life is, without exaggeration, long.

Stainless steel 1.4034 (X46 Cr13)

A knife made of stainless steel grade 1.4034 (X46 Cr13) is an excellent indicator of the high quality and strength represented by a martensitic alloy. An excellent indicator of strength, wear resistance and anti-corrosion effect, but the elasticity of the metal is relatively low, which makes this brand of stainless steel a good option only for kitchen or cutlery cutting utensils.

Summarize

When choosing a knife (regardless of its size, shape or purpose), the key indicator of quality remains the material of the spine and blade.

In fact, when choosing stainless steel as a base, the consumer receives an excellent and durable tool that is easy to use and has a number of unique technical parameters.

Stainless steel for knives is an excellent choice and you can understand this if you evaluate all the advantages and disadvantages of the material, as well as analyze in detail the key types and properties of alloys.

You might be interested in

Source: https://kavkazsuvenir.ru/blog/nerzhaveyuschaya-stal-dlya-nozhej

Stainless steel production + technology as they do it for 2019 – Business Hub

Steel production today is carried out mainly from waste steel products and pig iron. Steel is an alloy of iron and carbon, the latter containing from 0.1 to 2.14%.

Exceeding the carbon content of the alloy will cause it to become too brittle.

The essence of the process of producing steel, which contains a much smaller amount of carbon and impurities compared to cast iron, is to convert these impurities into slag and gases during the smelting process and subject them to forced oxidation.

Steel production process

Process Features

Steel production, carried out in steel furnaces, involves the interaction of iron with oxygen, during which the metal is oxidized.

Carbon, phosphorus, silicon and manganese contained in pig iron are also subject to oxidation.

Oxidation of these impurities occurs due to the fact that iron oxide, formed in a molten metal bath, gives oxygen to more active impurities, thereby oxidizing them.

Steel production involves three stages, each of which has its own significance. Let's take a closer look at them.

Melting rock

At this stage, the charge is melted and a bath of molten metal is formed, in which iron, oxidizing, oxidizes the impurities contained in the cast iron (phosphorus, silicon, manganese).

During this production stage, phosphorus must be removed from the alloy, which is achieved by containing molten calcium oxide in the slag.

Under such production conditions, phosphorus anhydride (P2O5) creates an unstable compound with iron oxide (FeO), which, when interacting with a stronger base - calcium oxide (CaO), decomposes, and phosphoric anhydride turns into slag.

In order for steel production to be accompanied by the removal of phosphorus from the molten metal bath, it is necessary that the temperature is not too high and that the content of iron oxide in the slag is not too high.

To satisfy these requirements, scale and iron ore are added to the melt, which form ferrous slag in the molten metal bath.

The slag containing a high amount of phosphorus that forms on the surface of the molten metal bath is removed, and in its place new portions of calcium oxide are added to the melt.

Boiling bath of molten metal

The further process of steel production is accompanied by boiling of a bath of molten metal. This process is activated with increasing temperature. It is accompanied by intense oxidation of carbon that occurs when heat is absorbed.

Steel production process in electric furnaces

Steel production is impossible without the oxidation of excess carbon; this process is started by adding scale to the molten metal bath or injecting pure oxygen into it.

Carbon, interacting with iron oxide, releases bubbles of carbon oxide, which creates the effect of boiling the bath, during which the amount of carbon in it decreases and the temperature stabilizes.

In addition, non-metallic impurities adhere to the floating bubbles of carbon monoxide, which helps reduce their amount in the molten metal and leads to a significant improvement in its quality.

At this stage of production, sulfur, present in the form of iron sulfide (FeS), is also removed from the alloy. As the temperature of the slag increases, iron sulfide dissolves in it and reacts with calcium oxide (CaO). As a result of this interaction, a CaS compound is formed, which dissolves in the slag, but cannot dissolve in iron.

Metal deoxidation

Diffusion deoxidation involves the introduction of ferrosilicon, ferromanganese and aluminum into the molten metal slag. Such additives, by reducing iron oxide, reduce its amount in the slag. As a result, the iron oxide dissolved in the alloy passes into the slag, disintegrates in it, releasing iron, which returns to the melt, and the released oxides remain in the slag.

The production of steel with precipitation deoxidation is carried out by introducing ferrosilicon, ferromanganese and aluminum into the melt. Due to the presence in their composition of substances that have a greater affinity for oxygen than iron, such elements form compounds with oxygen, which, having a low density, is discharged into the slag.

Steel production in open hearth furnaces

By adjusting the level of deoxidation, it is possible to obtain boiling steel that is not completely deoxidized during the melting process.

The final deoxidation of such steel occurs when the ingot solidifies in a mold, where the interaction of carbon and iron oxide continues in the crystallizing metal.

The carbon monoxide that is formed as a result of this interaction is removed from the steel in the form of bubbles also containing nitrogen and hydrogen. The boiling steel obtained in this way contains a small amount of metal inclusions, which gives it high ductility.

Steel production can be aimed at producing the following types of materials:

• calm, which are obtained if the deoxidation process in the ladle and furnace is completely completed;
• semi-quiet, which in terms of the degree of deoxidation are between calm and boiling steels; It is precisely these steels that are deoxidized both in the ladle and in the mold, where the interaction of carbon and iron oxide continues in them.

If steel production involves introducing pure metals or ferroalloys into the melt, the result is alloyed iron-carbon alloys.

If in steel of this category it is necessary to add elements that have a lower affinity for oxygen than iron (cobalt, nickel, copper, molybdenum), then they are introduced during the smelting process without fear of them oxidizing.

If the alloying elements that need to be added to steel have a greater affinity for oxygen than iron (manganese, silicon, chromium, aluminum, titanium, vanadium), then they are introduced into the metal after its complete deoxidation (at the final stage of smelting or during ladle).

Necessary equipment

Steel production technology involves the use of the following equipment in steel mills.

Oxygen converter section:

• argon supply systems;
• converter vessels and their supporting rings;
• dust filtration equipment;
• system for removing converter gas.

Electric furnace section:

• induction furnaces;
• arc furnaces;
• containers with which it is performed;
• scrap metal storage area;
• converters designed to provide induction heating.

Secondary metallurgy site where:

• cleaning steel from sulfur;
• steel homogenization;
• electroslag remelting;
• creation of a vacuum environment.

Boiling steel

Area for implementation of bucket technology:

• LF equipment;
• SL equipment.

The bucket facility providing steel production also includes:

• bucket covers;
• casting and pouring ladles;
• gate valves.

Steel production also requires equipment for continuous casting of steel. Such equipment includes:

• rotating frame for manipulating pouring ladles;
• equipment for continuous casting;
• trolleys on which intermediate buckets are transported;
• trays and vessels intended for emergency situations;
• tundishes and storage areas;
• plug mechanism;
• mobile mixers for cast iron;
• cooling equipment;
• areas where continuous casting is performed;
• internal rail-type vehicles.

Source: https://hub-bs.ru/na-2019/proizvodstvo-nerzhaveyushhej-stali-tehnologiya-kak-delayut-dlya-2019.html

Stainless steel products of different brands: production, advantages of stainless steel

Stainless steel is a product that is not subject to corrosion, oxidation, or destruction by aggressive environments. Stainless steel products have an aesthetic appearance, practicality, environmental safety and durability. The metal lends itself well to polishing and grinding. The surface can be matte, mirror, chrome, colored.

The physical and technical characteristics of the product depend on the percentage of chromium. The standard alloy contains 12−20% of the component. Under the influence of oxygen, the additional component is converted into chromium oxide, which creates an inert protective film of insoluble oxides on the surface of the rolled product. In addition to chromium, stainless steel may contain C, Mn, P, Si, S. To increase the physical and mechanical properties, Ni, Mo, Nb, Ti, Co may be present in the alloy.

Rolled metal is produced in different grades that can satisfy the requirements of almost all areas of human activity: from construction to the manufacture of decorative elements.

Depending on the percentage of additives, stainless steel is divided into several types:

1. chromium;
2. chromium-nickel;
3. chromium-manganese-nickel.

Easy processing, high melting point, resistance to ultraviolet radiation, mechanical damage and moisture allow the metal to be used for the production of products for various purposes . The alloy, resistant to chemicals, is used in the manufacture of pipes , parts, and components for various objects:

1. chemical and electronic industries;
2. mechanical engineering;
3. production of food products, medicines, cosmetics;
4. surgical instruments and cutlery;
5. decorative designs;
6. fencing.

Manufacturing of products to order

Based on the client’s sketches, stainless steel products are produced to order after the design of the future product has been developed. According to individual sizes, specialists can quickly and at an affordable cost produce:

1. containers;
2. entrance groups;
3. awnings;
4. fencing;
5. racks;
6. elements of office and home furniture;
7. handrails;
8. gratings;
9. benches;
10. countertops;
11. supply and exhaust systems.

Products are manufactured to order from different grades of steel , the choice of which depends on the purpose and operating conditions. For products intended for indoor installation, inexpensive alloy AISI 430 is suitable, which has a pleasant appearance and durability. Rolled metal combines well with plastic, wood, glass and stone.

Interior and exterior items made of stainless steel combine aesthetics, reliability and environmental friendliness. According to the customer's drawings, it is possible to manufacture barbecues, heating and water supply pipes, smokehouses, stair railings, and decorative grates for the fireplace. Austenitic stainless steel is used for storage tanks, mirror frames, car brackets, table tops, vacuum chambers, and shoe stands.

The main positive properties of alloy steel varieties are light weight, the ability to paint, bend, drill, laser cutting, turning, rolling, casting and welding. According to the project of the enterprise, a range of goods is produced from stainless steel , among which the following can be noted:

1. roof rails;
2. columns;
3. flagpoles;
4. bicycle parking;
5. lamps;
6. tables;
7. chairs;
8. floor coverings;
9. fastenings;
10. accessories;
11. heat screens.

A unique project for a home, restaurant, cafe and other organizations can be the production of a stainless steel aquarium of the appropriate size and shape. The design can fit into any interior, provide access to maintenance systems for an artificial reservoir, and allow you to replace the glass bowl without dismantling the frame.

Popular brands

The most popular grades of metal for production purposes are steel 300 and 400 series. The 300 series includes austenitic, austenitic-ferritic and austenitic-martensitic steel. AISI 304 alloy grade is produced for the food and pharmaceutical industries; the material is easy to weld and is resistant to aggressive environments.

AISI 316 stainless steel for the chemical, shipbuilding and oil and gas industries can withstand high temperatures and retain its properties when in contact with an acidic environment and sea water. AISI 316 T steel contains titanium, which increases the strength characteristics and resistance of the metal to chlorine ions. Stainless steel is used in the manufacture of equipment and components for the chemical and food industries, and welding of gas turbine blades.

AISI 321 alloy metal can withstand heating up to 800 C, and is used in the production of seamless pipes, elbows, tees and adapters from stainless steel in hot water supply systems, sewage systems, as well as in pipelines for transporting mildly aggressive chemicals.

From ductile steel 400 series AISI 430, the customer can order decorative elements for the interior or exterior , as well as parts intended for use in the oil and gas industry. In special cases, specialists can select a cheaper “analogue” with chemical and mechanical properties in accordance with technological conditions.

The production of stainless steel products is carried out on modern equipment by high-class specialists, since working with the material requires professional training. In the production workshop the following is carried out: perforation, bending, cutting, engraving, grinding, polishing of sheet material before or after cutting to the size and configuration of a pipe, profile, angle. At the installation site of the part, the weld seam is additionally cleaned, polished and painted.

Steel structures in combination with other building and finishing materials will help emphasize the style of the room. Computer graphics processing or 3D imaging will help produce products in the correct proportions, allowing you to create an image of the future part and make the necessary changes.

Food-grade steel does not oxidize, does not allow pathogens to multiply, and lends itself well to sanitary and heat treatment. The cost of custom-made products depends on the steel grade, purpose, operating conditions and complexity of the work process.

Source: https://tokar.guru/metallicheskie-izdeliya/proizvodstvo-izdeliy-iz-nerzhaveyki-marki-stali-osobennosti.html

Stainless steels

It is impossible to imagine modern life without anti-corrosion steel. The development of such an alloy has made it possible to make a qualitative breakthrough not only in metallurgy, but also in many other areas. Stainless steels differ from classical ones in that in addition to iron and carbon, they also contain chromium. It is the addition of chromium that gives the alloy anti-corrosion properties.

Stainless steel products are very diverse. You can find a wide selection of products from any manufacturer. For example, high-quality products, as confirmed by numerous reviews, can be ordered in the BSM - Metal online store.  

Stainless steels

Physical properties

Stainless steel has gained high popularity not only due to its anti-corrosion properties, but also due to its variety of physical properties. Modern corrosion-resistant steels are produced by adding various impurities to the steel.

The physical properties of the finished steel depend on the amount and type of impurity. It should be noted that some grades of stainless steel are susceptible to corrosion after a long period of use. This is due to the composition, that is, the addition of this or that metal. Such an alloy has other advantages that eliminate susceptibility to oxidation.

It is necessary to highlight the main physical properties of stainless steel, which qualitatively distinguish it from a number of other metals. These properties include:

1. High strength. Products made from stainless steel are characterized by increased strength in comparison with analogues. Due to its resistance to physical stress, the products are not damaged and do not lose their original shape. High-quality steel remains reliable for more than ten years.
2. Resistance to aggressive external environment. Such steel is practically not subject to changes due to environmental conditions. This allows you to maintain the performance properties of the product for a long time.
3. Heat resistance. Stainless steel products are resistant to high temperatures, even when exposed to open fire. Also without changing shape, size and properties under significant temperature changes.
4. Environmental friendliness. Anti-corrosion properties prevent the oxidation process. In addition, the material does not contain harmful components, therefore it is widely used in the food industry.
5. Anti-corrosion properties. The main property that such steel has is that it prevents rust. Moreover, the alloy does not corrode even after exposure to acids or alkalis.
6. Appearance. The appearance of stainless steel products is qualitatively different from items made of other materials. Steel has a clean, shiny appearance that does not change after a long period of use.
7. Compliance. Such an alloy is easy to process, and making an object of the desired shape from it is not difficult.

The choice of stainless steel with certain physical properties depends on the purpose of its use. Today, a variety of components for the production of stainless steel allows you to create a material with the necessary characteristics.

Chemical composition

The chemical composition of stainless steel depends on the type and grade of the alloy. The main features that characterize stainless steel are the presence of at least 10.5% chromium and low carbon content. Carbon is very important in steel making as it gives the required strength. The percentage component of which in the anti-corrosion alloy should not exceed 1.2%.

Stainless steel may also contain Titanium, Phosphorus, Molybdenum, Sulfur, Nickel and Niobium. Depending on the chemical composition, stainless steel is divided into several types.

The most widely used is stainless steel of group A2. Group A2 contains 10% nickel, 18% chromium and 0.05% carbon. Most of it is occupied by the base, namely iron with accompanying components.

The composition of steels in this group includes 0.05% carbon, 2% molybdenum, 12% nickel and 17% chromium. Due to the presence of molybdenum in the composition, the alloy is resistant to acid, so the name “acid-resistant” is often applied to it.

Anti-corrosion steels of group A, due to their chemical composition, are easy to weld. That is why this type is widely used in industry. From such steel it is possible to produce parts of almost any shape, with a strong connection of the component parts.

Particular attention in production is paid to steel for the food industry. In this case, corrosion-resistant steel should not contain foreign components that can negatively affect the taste of products, as well as impurities hazardous to human health.

The resistance of steel to corrosion depends on the amount of chromium. The larger its component, the more stable the alloy. Classic stainless steel used under normal conditions contains no more than 13% chromium. To withstand an aggressive environment, the proportion of chromium must exceed 17%. This corrosion-resistant alloy is suitable for use in acidic environments.

Highly resistant alloys retain their properties even in nitric acid of 50% saturation. For resistance against stronger acids, the percentage of nickel in the composition is increased and other components are added in small quantities.

Classification of stainless steels

The classification of stainless steels varies among countries, but has common principles. Stainless steel marking is carried out depending on the chemical composition, properties and internal structure of the finished material. Based on this, steel is divided into the following types:

1. Ferritic. This group of steels is characterized by a high chromium content, usually more than 20%. Therefore, this type is sometimes called chromium. This chemical composition contributes to high resistance to aggressive external environments. Alloys of this group have magnetic properties. Ferritic steels are relatively cheap and are widely used in industry, second only to austenitic steels.
2. Austenitic. A group of anti-corrosion alloys that are characterized by a high content of chromium and nickel. Due to this, they are distinguished by increased strength and flexibility in comparison with analogues. Also easy to weld and resistant to corrosion. Most widely used in industry. They belong to non-magnetic metals.
3. Martensitic. A special type of stainless alloy. It is characterized by increased strength and wear resistance. They are not exposed to high temperatures, and at the same time contain a minimal part of harmful components that do not emit vapors during intense heating. This group includes heat-resistant, corrosion-resistant steel.
4. Combined. A special type of steel that combines the properties of the above groups. Such innovative steels are developed individually depending on the properties required by the customer. Today, austenitic-ferritic and austenitic-martensitic steels are distinguished.

Stainless steel parts

In turn, grades of stainless steel of the austenitic group are divided into 4 types:

1. A1 is steel that contains a significant amount of sulfur, which is why it is more susceptible to corrosion than others.
2. A2 is the most widely used grade. Easily weldable without loss of physical properties. Frost-resistant, but susceptible to corrosion in an aggressive acidic environment.
3. A3 is a derivative of A2, but with the addition of stabilizing components. It is characterized by increased resistance to high temperatures and acidic environments.
4. A4 – alloy with the addition of molybdenum (up to 3%). Characterized by resistance to acidic environments. Widely used in shipbuilding.
5. A5 – similar to the A4 brand. It differs only in the ratio of stabilizing components. Manufactured for increased resistance to high temperatures.

Types of stainless steel are not limited to the above types. Since even the slightest changes in the percentage of components can significantly affect the properties of steel.

Scope of application of stainless steels

Since their development, corrosion-resistant steels have been used only in high-tech production in such areas as aircraft manufacturing, nuclear energy, petrochemical production and mechanical engineering. Today, stainless steels are widely used in various areas of our lives.

Stainless steel car detail

Let us highlight the main areas of use of stainless alloys:

1. Mechanical engineering. Stainless steel is widely used for the production of cars, industrial machines and various units. Ferritic and austenitic types are commonly used.
2. Chemical industry. The chemical industry is accompanied by the use of aggressive substances, the maintenance of which requires special equipment. Austenitic alloys are used for its production. Production tanks, pipes and vessels are not exposed to chemicals and do not lose their performance properties.
3. Energy. In the electrical power industry, only high-strength materials are used, since the strength and reliability of working units are of particular importance.
4. Pulp and paper industry. Almost all equipment in this area is made of high-quality stainless steel.
5. Food industry. There are increased requirements for the production, storage and transportation of food products. Therefore, in the manufacture of equipment, you can only use glass, several types of plastic and stainless steel. This ensures an increased level of hygiene.

In the food industry, an alloy containing a small number of components is usually used, since the equipment is not exposed to ultra-high temperatures and aggressive substances. Frost-resistant materials are used for refrigeration units.

1. Aerospace sector. Special types of stainless steel began to be used to build airplanes, rockets and spaceships.
2. Construction. Stainless steel is widely used in construction and design. Such sheets are scratch-resistant and do not leave hand marks.

Corrosion-resistant steels are also used in many fields, due to the variety of types and properties.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/nerzhaveyushhie-stali.html

Stainless steel grades and their characteristics

Corrosion-resistant (stainless) steels are steels that, in addition to iron, carbon and standard impurities, contain alloying elements. These additives provide resistance to corrosion - the destruction of metal under the influence of negative factors (air, water, acidic and alkaline environments). One of the dangers of corrosion is the likelihood of a sharp deterioration in the technical characteristics of the metal without external changes. The main component in the corrosion-resistant alloy is chromium (content not less than 12%).

Decoding stamps

The marking of alloy steels consists of letters and numbers. At the beginning there is a two-digit number that characterizes the amount of carbon in hundredths of a percent. The following are letters of the Russian alphabet, denoting a specific element:

• X – chromium;
• N – nickel,
• T – titanium;
• B – tungsten;
• G – manganese;
• M – molybdenum;
• D – copper.

After the letter designation of the alloying element in the decoding there is a number indicating its content in stainless steel, rounded to the nearest whole percent. If there is no such figure, then the additive in the alloy is in the range of 1-1.5%.

Grades of heat-resistant and heat-resistant stainless steels

Heat resistance, otherwise called “scale resistance,” is the property of a metal to resist gas corrosion at high temperatures in an unloaded or lightly loaded state.

Definition! To improve this characteristic, chromium, silicon and aluminum are introduced into the composition of stainless steels. These elements, combining with oxygen, form dense structures that increase the resistance of steel to temperatures above +550°C. Nickel by itself does not affect heat resistance, but in combination with Cr, Al and Si it increases their efficiency.

Heat-resistant steels are steels that function at high temperatures and loads without a tendency to short-term and long-term creep.

Table of areas of application of scale-resistant and heat-resistant steels

Type	Brand	Temperature at which active reaction with air begins, °C	Areas of use
Chromium, scale resistant	X18	+850+900	Equipment, products and structures operated at T up to +900°C without load
High chromium, scale resistant	Х25 Х25ТХ28	+1100+1150	Metal products intended for operation without load up to T +1150°C, Х25Т – for the production of thermocouples
Silchrome, scale-resistant	Х25С3Н	+1100	For heating units and heaters operating at temperatures up to +1100°C
Highly alloyed, scale resistant and heat resistant	Х23Н18	Loaded products and structures intended for operation at T up to +1000°C
Х20Н35	Metal products operated at T +1000°C

Stainless steel grades for the manufacture of chimneys

When purchasing modular chimney systems, you need to find out what kind of steel they are made of. On sale you can find chimneys that are about one and a half times cheaper than other products in this category. In their production, AISI 201 steel (12X15G9ND) is used.

According to international standards, it is necessary to use steel grade AISI 321 (08Х18Н12Т), the cost of which is approximately 2 times higher than the cost of AISI 201. It is impossible to visually distinguish AISI 201 from AISI 321, moreover, both alloys are non-magnetic.

They can only be distinguished by chemical analysis.

Differences in chemical composition

Brand	WITH	Mn	P	S	Si	Cr	Ni	Cu	Ti
AISI 201	Up to 0.15%	7-9,5	Up to 0.1%	Up to 0.03%	Up to 1.0%	13-18	0,3-3,0	0,5-2,5	—
AISI 321	Up to 0.08%	Up to 2.0	Up to 0.05%	Up to 0.03%	Up to 1.0%	17-19	9,0-12,0	—	Min 0.5%

AISI 201 steel has low anti-corrosion characteristics, instability of the structure, and the risk of cracks during drawing. Its use will lead to rapid failure of the chimney due to rapidly developing corrosion. This steel is mainly distributed in China and India.

Well-known foreign and conscientious Russian manufacturers, in addition to AISI 321 steel, use high-alloy alloys stabilized by Ti. They are acid and heat resistant. The use of cheaper steels (AISI 409, AISI 430) for gas exhaust pipes that do not meet acid resistance requirements leads to their failure soon after the start of the heating season.

Stainless steels for the food industry

Corrosion-resistant steels are indispensable for industries producing equipment, tools and utensils intended for contact with food products. Their advantages:

• Resistance to various types of corrosion - chemical and electrochemical. In each specific case, it is necessary to select brands that are resistant to the environments with which they will come into contact during operation. These are normal atmospheric conditions, water, salt water, acidic, alkaline, chloride solutions.
• Good machinability. Modern tools make it possible to weld, cut, form and process corrosion-resistant alloys on lathes, milling and drilling machines in the same way as “ferrous” steels.
• Compliance with sanitary and hygienic standards. Thanks to various processing methods - grinding, polishing to a mirror finish - a surface is obtained that is practically free of pores and cracks into which dirt and pathogenic microorganisms can penetrate.
• Good mechanical characteristics. Thanks to them, it is possible to produce products and structures of smaller thickness and weight without compromising technical properties. Austenitic steels are more resistant to low temperatures compared to general purpose metals.
• Aesthetics. Electropolishing, satin finishing and other surface treatment methods provide a stylish look to stainless steel products.

Table of properties and areas of application of food grade stainless steels

Steel grade according to GOST	AISI	Characteristics	Areas of use
304	08Х18Н10	It welds well, can be electropolished, retains high strength at normal and low temperatures, and is resistant to intercrystalline corrosion.	Equipment, tools, technological pipelines of food, petrochemical, pharmaceutical and medical industries, for utensils intended for high-temperature processing of products are not used
316	03Х17Н14М2	The presence of molybdenum increases the technical characteristics of the alloy at high temperatures	Installations, technological equipment, containers for the food and chemical industries
321	12Х18Н10Т	Good weldability, maintaining performance characteristics at temperatures up to +800°C	Equipment for the chemical and oil refining industry
409	08Х13	Characteristics are satisfactory	Crockery and cutlery
410	12Х13	Heat resistance, resistance only to mildly aggressive environments	Winemaking equipment, alcohol containers
420	20Х13-40Х13	Versatility, ductility, wear resistance, increased corrosion resistance	Dishes, kitchen sinks
430	08Х17	Strength, thermal conductivity, good machinability, corrosion resistance	Utensils for heat treatment of products, including steam
439	08Х13	Possibility of use in various operating conditions	Alloy for mass use - production of refrigerators, sinks, washing machines

Table of stainless steel grades used in the food industry

Industry	Stamps
Dairy products – product sterilization and storage, cheese making, transportation tanks, ice cream and milk powder production	Austenitic steels – 304, 316, 321
Fruit canning, juice production. In such industries, steel comes into contact with an environment containing sulfur dioxide	Grades containing molybdenum
Preparation of soups and sauces (these are aggressive mixtures with high acidity, containing chlorides)	Molybdenum-containing grades
Bakery, requirements - hygienic, smooth surfaces of tables and mixing equipment	Austenitic steels – 304, 316, 321

Source: https://www.navigator-beton.ru/articles/marki-nerzhaveyushhej-stali.html

How to identify stainless steel: methods and materials

Stainless steel is the name of a group of iron alloys that contain corrosion-resistant metals. Carbon, titanium, copper are used as additives, and the composition also includes from 12 to 25% chromium and nickel. Alloy steel alloys are not susceptible to corrosion and are resistant to moisture, aggressive environments, alkalis and acids.

Stainless steel is used to produce dishes, knives, elements of machine tools, cars and industrial equipment, especially in the chemical and oil industries. Such scrap is accepted at a high price, which depends on the composition. The most expensive alloys are those with a high nickel content (from 10%). To get maximum profit from scrap metal, it is important to know how to identify stainless steel?

Metals and alloys that are often confused

The silver alloy of iron and chromium is suitable for the production of kitchen utensils, medical instruments, bearings, cutting elements, etc. But these items are also made from the following materials:

• nickel-plated brass (a white copper alloy with a zinc content of more than 25%);
• cupronickel (silver-white metal made from an alloy of copper and nickel);
• white copper (an alloy containing at least 25% nickel).

Polished aluminum, nichrome, nickel silver and other alloys used for the production of cookware, knives, and jewelry can easily be confused with alloy steel. Despite their similar composition and high nickel content, they are easily distinguished at a scrap metal collection point and will not be accepted at the desired price. There are several ways to determine whether aluminum or stainless steel has fallen into your hands: chemical, mechanical, etc.

Analysis using a magnet

In the laboratories of large collection points, a spectrometer is installed - an optical device for spectroscopic research. It is equipped with an interferometer to evaluate the intensity of spectral lines and measure wavelengths. The received data is processed by a computer, giving an accurate conclusion about the composition of the alloy.

If you need to identify stainless steel at home, use improvised but relatively reliable means. One of them is a magnet: it is generally accepted that stainless steel is not magnetic. However, this diagnostic method is not accurate enough, because martensitic and ferritic alloys have magnetic properties.

Using a magnet, only austenitic and austenitic-ferritic alloys with a high content of chromium and nickel can be detected. They are used to produce dishes, plumbing and refrigeration equipment, containers for food liquids, etc. Contrary to popular belief, it is impossible to accurately determine stainless steel with a magnet, but you can roughly identify its type.

Defining food grade stainless steel

As stated above, a magnet helps to identify food grade stainless steel at home. Alloys with a low carbon content and a large amount of nickel in the composition do not react to contact with it. Stainless steel with a high carbon content (more than 0.9%) has magnetic properties and is prohibited for use in the food industry.

Also, to determine food grade stainless steel, various acids are used (citric, tartaric, acetic, etc.). Alloys for food applications contain more alloying additives, so their surface film is stronger and contains almost no iron.

For additional protection against corrosion, passivation is used - a method of treating the surface of a metal, as a result of which its activity is reduced and it does not enter into oxidative reactions.

Under the influence of these acids, stainless steel may become covered with a light patina, which indicates its non-food purpose.

Types and grades of non-magnetic steels

If the origin of the product is known, the reaction with a magnet can roughly determine the type of stainless steel. The following brands are not magnetic:

• AISI 409 (analogue 08X13) - containers for cargo transportation, parts for the exhaust system of a car, etc. are made from this ferritic steel. (plasticity and lack of magnetic properties are due to the extremely low C content - less than 0.03%);
• AISI 304 (analogous to 8-12X18H10) - household items are made from it, as well as utensils and equipment for the food and pharmaceutical industries;
• 12Х21НБТ (ЭИ8П) – austenitic-ferritic steel for use in medium-aggressive environments, from which containers and equipment for the chemical and pharmaceutical industries are produced.

Stainless steel grades AISI 402–420, which contain from 11 to 14% chromium and less than 0.07% carbon, are not magnetic.

Magnetic stainless steel

AISI 430 steel (analogous to 08X17, which contains 15% chromium) has magnetic properties. It is used to produce wire mesh, pipes for transporting petroleum products, and elements of gas and oil refining process plants. Steel grade AISI 630 contains up to 5% nickel and chromium, as well as a large number of additives: copper, titanium, molybdenum. It is used in instrument making and metallurgy.

Stainless steel can be identified even if it is magnetic. To do this, place a sample of the material in 2% vinegar or another aggressive medium for 1–2 days. Corrosion-resistant alloys will pass this test without visible changes, but metals that are susceptible to corrosion will darken.

Copper sulfate will also help determine magnetic stainless steel at home. First clean the metal surface with sandpaper, and then apply a few drops of a concentrated substance (rusting alloys are covered with a red film).

Spark test

Testing metal for spark color is a common method of sorting scrap metal, which is used even by specialists. The grade of stainless steel can be determined by the following factors:

• the number of sparks and flashes, which is directly proportional to the volume of carbon in the alloy;
• the color of the sparks, which indicates the composition of the metal (the lighter it is, the higher the likelihood that this is low-carbon steel);
• the presence of shiny white sparks, which indicates a high titanium content in the composition.

To carry out the test, an angle grinder (grinder) is required. Start grinding the surface of the steel and observe the reaction. The color, length and shape of the sparks will help you accurately determine metal or stainless steel.

"Yellow flow" or "white fork"

There are many types of sparks: “fork”, “twig”, “arrow”, etc. You learn to distinguish them with experience, but even an untrained person will be able to distinguish a dense and short stream of flashes from the long and rare sparks characteristic of stainless steel. The presence of dark red sparks coming out from under the grinding wheel indicates a high content of nickel, tungsten carbide and cobalt.

If a medium-density stream appears during the grinding process, and the sparks are straw-yellow at the base and white at the end, you have stainless steel. A long stream of sparks, reaching 1.5 meters, indicates the presence of nitrogen in the composition. In this case, it is not difficult to determine the grade of stainless steel: nitrogen alloys are quite rare and there are only a few of them (Nitrobe 77, Sandvik™ 14C28N, Böhler N680, etc.).

What does the price depend on?

Low-carbon, corrosion-resistant alloys are used to produce a wide variety of products: blades, profiled sheets, roofing materials, medical supplies. Scrap stainless steel can be collected when dismantling an old fence, dismantling an old refrigerator, throwing away unnecessary kitchen utensils, etc. In this case, potential income will depend on the following factors:

• type of steel (austenitic, ferritic, martensitic, etc.);
• steel grade (AISI 304, AISI 630, 12Х21НБТ);
• type of rolled metal (sheet, section, pipe);
• sheet thickness;
• compound;
• quality.

You can determine the stainless steel brand and composition in a laboratory setting by contacting a reliable collection point. We have the necessary equipment to analyze the composition, assess the quality and test the radiation activity of non-ferrous scrap. But you can pre-evaluate scrap metal at home.

How to evaluate quality?

The quality of stainless steel depends on various factors - from the amount of additives to the joining method. In places where welds are formed, the anti-corrosion properties of the metal deteriorate significantly, which over time leads to the appearance of rust and gradual destruction of the material.

Painted profiled sheets will have to be cleaned of the coating and sanded, damaging the protective layer on the surface. Accordingly, the metal will become less resistant to moisture, its quality will deteriorate, and therefore the price of such scrap will be lower. You can preliminary evaluate the properties of steel using a salt solution.

It should not leave stains on the surface of high-alloy steel. And water will leave yellowish stains on low-quality stainless steel.

The most expensive types of stainless steel

The cost is affected by the amount of nickel in the alloy: in the cheapest types its content does not exceed 5%. The most expensive are high-alloy alloys containing nickel from 12%. The expensive scrap includes plumbing fittings and rings, wire and various electrical connectors (connectors, adapters, etc.). Matte (a by-product of non-ferrous metallurgy) with a nickel content of over 35% is also highly valued, although it is classified as slag.

But the most common steel grade is A2, containing approximately 10% nickel and 18% chromium. It is usually used to make household items. To find out the exact price, visit our collection point: to evaluate scrap, specialists must inspect the metal, assess the degree of contamination, composition and properties.

Source: https://blog.blizkolom.ru/kak-opredelit-nerzhavejku

Categories and technical specifications

The constant increase in the use of stainless steel in many industries is due to its unique characteristics:

• high corrosion resistance,
• high strength,
• good weldability,
• excellent processability by cold stamping.

There are five main categories of stainless steel based on their microstructure: Austenitic, Ferritic, Duplex, Martensitic, Heat Resistant.

Austenitic is non-magnetic and contains nickel in addition to chromium, which increases corrosion resistance. Austenitic stainless steels are the most widely used group of stainless steels. With increased chromium content up to 20% - 25% and nickel up to 10% - 20%, austenitic stainless steels better resist oxidation at high temperatures and can be used for the manufacture of furnace elements exposed to high temperature heating.

• Ferritic - magnetic, have a low carbon content and chromium as the main element, usually at the level of 13% - 17%.
• Duplex stainless steels have a mixed, ferritic-austenitic structure. chromium varies from 18% to 28%, and nickel from 4.5% to 8%. Duplex varieties find their use in aggressive chlorine-containing environments,
• Martensitic grades are magnetic and typically contain 12% chromium and medium carbon content. They are hardened by quenching and tempering like simple carbon steels, and are therefore used mainly in the manufacture of cutlery, cutting tools and general mechanical engineering.
• Heat-resistant steels have a chromium content of typically 17% with the addition of nickel, copper and niobium. Because these steels can be hardened and resist aging well, they are ideal for mine pumps, valve spindles and aerospace applications.
• Austenitic and ferritic grades account for approximately 95% of stainless steels used. Of the ferrite grades, the most widely used is grade 430, the so-called. “nickel-free” stainless steel. They have good strength and mechanical characteristics, which is ensured by a high chromium content and low carbon content, and low cost compared to chromium-nickel stainless steels.

Among austenitic grades, grade 304 is widely used, which is the most versatile and widely used of all grades of stainless steels. It is also designated 18-10 (food grade).

In recent years, steels of the 300 series are gradually losing ground to the more cost-effective austenitic steels of the 200 series, in which expensive nickel is partially replaced by manganese and nitrogen.

These grades of stainless steels are actively produced and offered in the market by Indian enterprises. After all, they are given primacy in the development of these brands.

The mechanical properties of stainless steels make it possible to reduce the thickness of the materials used, thus reducing material consumption without reducing strength characteristics. Austenitic and Duplex grades do not lose strength even at low temperatures, and allow the use of smaller thicknesses compared to carbon steels, achieving significant savings.

Sheets offered on the market can have the following types of surfaces:

• matte;
• frosted mirror;
• mirror;
• polished;
• fine grinding;
• covering with a protective film.

 The use of stainless steels in household appliances

The uniqueness of the stainless steel surface is its density; it has no pores or microcracks for the penetration of dirt or bacteria. Ease of care and cleaning, its environmental neutrality and resistance to aggressive substances compared to other materials make it indispensable for the manufacture of household stoves and other kitchen appliances. An important factor is a good and smooth (without kinks, irregularities or scratches) metal surface.

Strict restrictions on the solubility of heavy metals present in food contact equipment are already in place and will certainly be tightened in the future.

According to European standards, the amount of chromium and nickel dissolved from steel during the standard test according to ISO 6486/1 is allowed no more than 2 mg/dm2. For austenitic steels, the amount of dissolved nickel and chromium is less than 0.02 mg/dm2, i.e.

about 1% of the permissible value.

 The following grades are classified as food grade corrosion-resistant steels:

Steel grade according to GOST 5632-72	Analogous to ASTM A240/A 240M-05a
08Х18H10	304
08Х18Н10Т	321
12Х18Н10Э (T)	303

 Steel tarnish colors

Iron alloys, including corrosion-resistant ones, when heated, become covered with a thin film of iron oxides of a wide variety of color shades and tarnish colors appear, which correlate with certain heating temperatures. There are so-called “heat-resistant” alloys, in which the temperature at which oxides begin to form is higher than that of other alloys, but such grades are not food grade and are very expensive due to their high nickel content.

 For carbon steel 

Heating temperature	Tarnish color
220	light yellow
240	dark yellow
255	brown-yellow
265	brown-red
275	purple-red
285	violet
295	cornflower blue
315	light blue
330	grey

  For stainless steels

Temperature	12Х18Н9Т	ХН75МБТУ
300	light straw	—
400	straw	light yellow
500	reddish brown	yellow
600	violet blue	brown
650	blue	blue
750	—	blue

Most importantly, the duration of heating has a significant impact on the color of the surface. Indeed, more or less prolonged processing can cause steel to turn blue at a temperature lower than that required for the appearance of even a straw-yellow color.

Stainless steel manufacturing plants

At the moment, there are actually three sources of supply for consumers and sellers of stainless steel products: Russian-made corrosion-resistant steel, high-quality metal from European and South American manufacturers, and rolled products from India and Southeast Asia.

Due to the instability of nickel prices, manufacturers are currently refocusing on steel grades other than the 300 series. For China, these are primarily ferritic steels that do not contain nickel at all; for India and commercial enterprises in China - the 200th series with a reduced nickel content and additional additives that reduce the hardness of the alloy and increase its corrosion-resistant properties.

Currently, the market is unevenly divided between steel series. The most expensive 300 series is traditionally used most widely (brands such as AISI 304, AISI 316, AISI 321, AISI 310 S, AISI 309 S and others), the use of the 200 series, which is unfamiliar to domestic manufacturers, is most limited.

In recent years, as a result of research and experimentation, steel grades of this series have undergone significant changes in the chemistry and technological rolling process and currently deserve closer attention. Steel 200 groups are cheaper than AISI 304 by approximately 16-17%. AISI 430 (nickel-free) steel is even cheaper - about 50% compared to AISI 304. With rising nickel prices, this difference may increase even more.

However, the use of this grade of steel is still controversial in relation to food products and medical technology.

Manufacturing plants in Russia

• Chelyabinsk Metallurgical Plant",
• Volgograd Metallurgical Plant "Red October"
• Izhora factories

Manufacturing plants in Europe

•    Acerinox, SA Spain,
•    Marcegaglia SpA, Italy,
•    Arcelor Stainless Int. France,
•    Outokumpu Stainless, Finland,
•    ThyssenKrupp, Germany.

Southeast Asia

•    Jindal Stainless, India,
•    Zhejiang Baocheng Stainless Steel Manufacture Co., Ltd. China,
•    Jiangsu Xi'erfa Group Co., Ltd. China,
•    YUSCO(Yieh United Steel Corp.) Taiwan,
•    NISCO (Taiyuan Iron & Steel Group) Company Ltd, China

Source: https://engitime.ru/metallicheske-materiali/nerzhaveyushhie-stali.html

Stainless steel (stainless steel)

Stainless steel is a steel that has high corrosion resistance in aggressive environments (sea and river atmosphere, air, some acids, salt solutions, etc.). Stainless steels are also commonly called “corrosion-resistant”, but this does not mean that they do not corrode at all. Like all metals, stainless steels are also susceptible to corrosion, but to a lesser extent.

Types of stainless steels (classification)

Stainless steels are classified according to GOST 5632 - 72. The main groups can be distinguished: chromium, nickel and chromium-nickel steels, chromium-manganese, chromium-manganese-nickel.

The main element that makes ordinary steel stainless is chromium. The metal has high corrosion resistance. A protective oxide film is formed on its surface in oxidizing atmospheres.

When added to steel, chromium forms a solid solution with iron, thereby increasing the steel's corrosion resistance. At the same time, the chromium content should not be less than 11.7%. This boundary can be tracked during potential measurements, when at a content of about 12 - 13% Cr, there is a sharp change in the potential of the iron-chromium system. With increasing chromium content, the corrosion resistance of steel increases.

This is inherent in the alloy not only in atmospheric conditions, but also in a number of other aggressive environments. It can also be said that stainless steels better resist corrosion damage with an increase in the content of oxidizing agents in the environment, because the electrode potential of the metal becomes more positive. This does not apply to nitric acid because With an increase in its concentration, chromium steels succumb to corrosion destruction more quickly, and overpassivation occurs.

At low concentrations, steel is highly resistant.

Among the stainless steels, the most common are chromium (with a chromium content from 13 to 30%), chromium-nickel (nickel up to 12%), chromium-nickel-molybdenum and others.

All additives introduced into steel can improve or worsen its properties. For example, carbon, which is present in all steels, binds chromium into particles of carbides (such as Cr23C7, etc.). This removes it from the alloy. Stainless steel loses its corrosive properties. To prevent this from happening, more chromium is introduced into the alloy. If the steel contains 0.15–0.20% carbon, then no less than 13–14% chromium must be added.

Chromium stainless steels

Chromium stainless steels (stainless steel) are widely used in industry and the national economy. Chromium steel is produced in the form of rods, sheets, pipes, castings and parts. It is also the most economical in terms of alloying.

F.F. Khimushin, based on the structure and composition, proposed the following classification:

- heat-resistant chromium steels (semi-stainless), which contain 5 - 10% Cr and are hardened to martensite;

— valve chromium steels (silchrome, etc.);

— stainless steel, with a chromium content of 10–17%;

- complex alloy stainless steels (stainless steels), which contain 12 - 17% Cr and are used as heat-resistant;

- acid-resistant and stainless chromium steels with a chromium content of 16 - 20% (ferritic and semi-ferritic class), ferritic heat-resistant steels with a Cr content of 25 - 33%, nitrogen-chromium heat-resistant and stainless steels;

— heat-resistant chromium steels with additions of aluminum and other elements.

Nickel and chromium-nickel stainless steels

This is the most common and sought after stainless steel. Now about a hundred brands of such stainless steel are produced. This steel is used to produce sheet and long products, cold-rolled and hot-rolled pipes, forgings, all kinds of profiles and much more for various fields of human activity.

Nowadays, there are grades of chromium-nickel stainless steels with intermetallic and carbide hardenings, alloyed with different materials, having intermediate structures.

Nickel and chromium-nickel stainless steels are divided into the following subgroups:

— acid-resistant chromium-nickel austenitic steels with additions of copper and molybdenum;

— austenitic steels with a low carbon content, including those stabilized by niobium or titanium;

— scale-resistant chromium-nickel steels with a high content of chromium and nickel;

— austenitic-ferritic chromium-nickel stainless steels;

— austenitic-martensitic chromium-nickel steels with martensite of unstable shape.

Chromium-manganese and chromium-manganese-nickel stainless steels

Manganese, like nickel, is an austenite-forming element. In addition, manganese helps strengthen steel. Stainless steel, which contains manganese, is used in conditions of increased abrasion. Nickel has better austenite-forming properties, so manganese must be added to the steel in greater quantities than nickel (almost twice as much).

Chromium-manganese and chromium-manganese-nickel steels are usually divided into four subgroups:

— austenitic steel containing 12–14% chromium, with varying contents of nickel and manganese;

- austenitic stainless steel containing about 17 - 19% Cr, as well as nickel, manganese and nitrogen;

- austenitic-martensitic stainless steel with a chromium content of about 12 - 18%, also containing nickel and manganese;

- austenitic-ferritic steel with additions of varying amounts of manganese and 16 - 18% chromium.

Source: https://www.okorrozii.com/nerzhaveika.html

Stainless steel: composition, properties, grades, markings

The high popularity of such a material as stainless steel is explained by its unique characteristics that ordinary carbon steel alloys do not possess. Thanks to the wide variety of stainless steel grades available on the modern market, they can be selected to successfully solve various technological problems.

The appearance of stainless steel structures does not change throughout their entire service life

What is unique about stainless steels?

Stainless steel was patented in England in 1913. The author of this invention, which, without exaggeration, became the most important stage in the development of not only steel, but also other industries, is metallurgist Harry Brearley.

The addition of an element such as chromium to their chemical composition made it possible to endow ordinary steel alloys with unique characteristics and obtain corrosion-resistant steels from them.

It is chromium, which must be at least 10.5% in stainless steel alloys, that provides these materials with such characteristics as:

• exceptionally high corrosion resistance;
• very high strength;
• good weldability;
• ease of processing using cold deformation methods;
• long service life without loss of original characteristics;
• aesthetically attractive appearance of products made from alloys of this category.

Influence of alloying elements on the properties of steels

Stainless steels necessarily contain chromium and iron in their chemical composition. These elements complement each other, which is what gives these materials such unique characteristics. In particular, chromium, combining with oxygen, creates an oxide film on the surface of the stainless alloy, which becomes a reliable obstacle to corrosion processes.

In order to provide stainless steel with additional characteristics and significantly improve existing properties, alloying additives are introduced into its chemical composition - nickel, titanium, molybdenum, niobium, cobalt, etc. This alloying makes it possible to create various types of stainless steel alloys that differ from each other their characteristics and, accordingly, purpose.

We are already so accustomed to corrosion-resistant steel that we don’t even notice how much more comfortable our lives have become due to the presence of stainless steel in it.

Stainless steel contains carbon in its chemical composition, which gives it high hardness and strength. It should be noted that this chemical element is an essential component of any steel alloy and has a serious impact on its properties.

The unique characteristics of stainless steel make it possible to successfully use this metal in a variety of areas related to the operation of products and equipment in conditions of high humidity and constant exposure to aggressive environments.

Stainless steels are actively used for the production of products for both industrial and household purposes.

In particular, it is from this metal that cutlery and knives are most often made, elements of communications and enclosing structures, equipment parts, etc.

Classification methods

The characteristics of stainless steels are determined both by the chemical composition of the alloys and by the characteristics of their internal structure. Depending on these parameters, all steels classified as stainless steel are divided into four groups.

Ferritic (chromium)

The chemical composition of steels of this group contains chromium in a volume of 20% (which is why they are called chromium). Due to the significant chromium content, products made from such steels are able to successfully withstand even very aggressive environments. Steel alloys of this group have good magnetic characteristics.

Chemical composition and mechanical properties of ferritic steels

Large consumers of ferritic steels are enterprises of the heavy and chemical industries; elements of heating equipment are produced from stainless alloys of this type, as well as much more. Alloys of the ferritic group occupy a fairly large share of the stainless steel market and, in terms of their level of demand, are only slightly inferior to materials with an austenitic internal structure, but are much cheaper than the latter.

Austenitic

These are stainless steels, a significant proportion of the chemical composition of which (up to 33%) is chromium and nickel. Consumers prefer these alloys due to the fact that such materials are characterized by high strength and exceptional corrosion resistance.

Chemical composition and applications of heat-resistant austenitic stainless steels (click to enlarge)

Martensitic and ferritic-martensitic

Due to the peculiarities of the internal structure, such alloys have the highest strength among steels. In addition, they are characterized by good wear resistance and a minimal amount of harmful impurities in their composition.

It is this category that includes heat-resistant, corrosion-resistant steel, which can not only successfully withstand oxidative processes, but also be operated under conditions of constant exposure to high temperatures, without losing its original properties.

chemical elements in martensitic and ferritic-martensitic steels (click to enlarge)

Combined

This includes steels with a combined internal structure: austenitic-ferritic and austenitic-martensitic. Such innovative materials optimally combine the best properties of all the above types of stainless steels.

Chemical compositions of corrosion-resistant steels of the austenitic-martensitic class

Possession of information about which group a particular grade of stainless steel belongs to allows you to optimally select alloys for solving certain technological problems.

The most popular brands and areas of their application

To choose the right stainless steel for the manufacture of products for a specific purpose, you can use special reference books that list both all grades of such material and their main characteristics. Meanwhile, in each of these groups there are the most popular brands, which are most often chosen by the consumer. Let's list them.

• 10Х17Н13М2Т and 10Х17Н13М3Т are steels that are characterized by good weldability and excellent corrosion resistance. Thanks to these properties, stainless steel alloys of these grades are successfully used for the production of products that, during their operation, are constantly exposed to high temperatures and aggressive environments. The properties of steels of these grades are formed due to the presence in their chemical composition of the following elements: chromium (16–18%), molybdenum (2–3%), nickel (12–14%), carbon (0.1%), silicon (0 .8%), copper (0.3%), sulfur (0.02%), phosphorus (0.035%), manganese (2%), titanium (0.7%). If there is a need to select stainless steels of these grades, then you should keep in mind that their foreign analogues can also be purchased on the domestic market, namely: SUS316Ti (Japan), 316Ti (USA), OCr18Ni12Mo2Ti (China), Z6CNDN17-12 (France) ).
• 08Х18Н9 and 08Х18Н10 are stainless steel alloys from which pipes of both round and any other cross-section are made. These materials are used for the production of various structures used in the mechanical engineering and chemical industries, as well as for the production of pipeline elements and furnace devices. The chemical composition of these grades of steel contains the following elements: chromium (17–19%), carbon (0.8%), titanium (0.5%), nickel (8–10%).
• 10Х23Н18 - steel of this grade is characterized by a high content of nickel (17–20%) and chromium (22–25%), as well as manganese (2%) and silicon (1%) in its composition. This combination of elements gives the alloy the required characteristics and creates an increased tendency to temper brittleness. It should be noted that the alloy of this grade belongs to stainless steels of the heat-resistant category.
• 08Х18Н10Т - a stainless alloy of this brand is characterized by high resistance to oxidation processes, as well as good weldability, and to obtain a high-quality connection using this technology, the products do not need to be preheated, and they also do not require heat treatment after welding. To improve the strength characteristics of products made from such steel, they must be hardened, as specified in the relevant regulatory document.
• 06ХН28МДТ - an alloy of this grade is optimally suited for creating welded structures that will subsequently be used in aggressive environments. The chemical composition of this steel contains the following elements: chromium (22–25%), nickel (26–29%), copper (2.5–3.5%).
• 12Х18Н10Т – products made from steel of this grade are mainly used to equip enterprises in the chemical, pulp and paper, construction, food and fuel industries. This metal is characterized by thermal resistance, good impact strength and practicality of use.
• 12Х13, 20Х13, 30Х13 and 40Х13 – stainless steel alloys of these grades are practically impossible to weld, but they also have positive properties. The latter lies in the fact that these steels do not have a tendency to temper brittleness, and their internal structure is not affected by defects, which in professional language are called flakes. Cutting and measuring tools, as well as springs and springs for various purposes are made from these grades of stainless steel.
• 08Х13, 08Х17, 08Х18Т1 are stainless steel alloys of the ferritic group, from which products are produced that do not experience shock loads during operation, as well as exposure to low temperatures.

Types of stainless steel surfaces

How to decipher the markings

Marking of stainless steels, the rules for the formation of which are stipulated by the provisions of regulatory documents, carries the following information:

• the number in first place indicates the quantitative content of such a chemical element as carbon in the alloy composition (for example, in steel grade 08Х17 carbon is contained in an amount of 0.08%, and in 40Х13 - 0.4%);
• after the letters in the marking, each of which indicates the corresponding chemical element (X - chromium, H - nickel, M - manganese), numbers are placed indicating its content in whole percentages.

An example of decoding the designation of stainless steel

In general, if we talk about the rules for marking steel alloys classified as stainless, they are practically no different from those adopted for marking steels of any other type.

Source: http://met-all.org/metalloprokat/nerzhaveyushhij/nerzhaveyushhaya-stal-sostav-vidy-svojstva-korrozionnostojkaya.html