Austenitic steel what is it

Austenitic stainless steels: structure and properties

Austenitic stainless steels are corrosion-resistant chromium-nickel austenitic steels, which in world practice are known as steels of type 18-10. This name gives them a nominal content of 18% chromium and 10% nickel.

Chromium-nickel austenitic steels in GOST 5632-72

In GOST 5632-72, chromium-nickel austenitic steels are represented by grades 12Х18Н9Т, 08Х18Н10Т, 12Х18Н10Т, 12Х18Н9, 17Х18Н9, 08Х18Н10, 03Х18Н11.

The role of chromium in austenitic stainless steels

The main element that gives type 18-10 steels high corrosion resistance is chromium. The role of chromium is that it provides the ability of steel to passivate. The presence of chromium in steel in an amount of 18% makes it resistant to many oxidizing environments, including nitric acid over a wide range, both in concentration and temperature.

The role of nickel in austenitic stainless steels

Alloying with nickel in an amount of 9-12% transfers the steel to the austenitic class. This provides the steel with high manufacturability, in particular, increased ductility and reduced tendency to grain growth, as well as unique service properties. Type 18-10 steels are widely used as corrosion-resistant, heat-resistant, heat-resistant and cryogenic materials.

Phase transformations in austenitic stainless steels

The following phase transformations can occur in chromium-nickel austenitic steels:

• release of excess carbide phases and σ-phase when heated in the range of 450-900 ºС;
• formation of δ-ferrite in the austenitic base during high-temperature heating;
• formation of a martensite-type α-phase during cold plastic deformation or cooling below room temperature.

Intergranular corrosion in austenitic stainless steels

The tendency of steel to intergranular corrosion manifests itself as a result of the precipitation of carbide phases. Therefore, when assessing the corrosion properties of steel, the most important factor is the thermokinetic parameters of the formation of carbides in it.

The susceptibility to intergranular corrosion of hardened steel type 18-10 is determined, first of all, by the concentration of carbon in the solid solution. An increase in carbon content expands the temperature range of steel's susceptibility to intergranular corrosion.

Steel type 18-10, when held in the range of 750-800 ºС, becomes prone to intergranular corrosion:

• with a carbon content of 0.084% – within 1 minute;
• with a carbon content of 0.054% - for 10 minutes;
• at a carbon content of 0.021 5 – after more than 100 minutes.

As the carbon content decreases, the temperature simultaneously decreases, which corresponds to the minimum duration of isothermal exposure before the onset of intergranular corrosion.

Welding of austenitic stainless steels

The required degree of resistance of steel against intergranular corrosion, allowing welding of sufficiently thick sections, is ensured by the carbon content in type 18-10 steel of no more than 0.03%.

Intergranular corrosion at 500-600 ºС

Reducing the carbon content even to 0.006% does not ensure full resistance of type 18-10 steels to intergranular corrosion at 500-600 ºC. This poses a danger during long-term service of metal structures in this temperature range.

Stabilization of steel with titanium and niobium

When titanium and niobium, which promote the formation of carbides, are introduced into chromium-nickel steel type 18-10, the conditions for the precipitation of carbide phases change. At relatively low temperatures of 450-700 ºС, carbides of the Cr23C6 type are predominantly released, which give rise to a tendency to intergranular corrosion. At temperatures above 700 ºС, special carbides such as TiC or NbC are predominantly released. When only special carbides are isolated, there is no tendency to intergranular corrosion.

Nitrogen in austenitic stainless steels

Nitrogen, like carbon, has variable solubility in austenite. Nitrogen can form independent nitride phases during cooling and isothermal exposure or be part of carbides, replacing carbon in them.

The effect of nitrogen on the susceptibility to intergranular corrosion of chromium-nickel austenitic steels is much weaker than that of carbon, and begins to appear only when its content is more than 0.10-0.15%. At the same time, the introduction of nitrogen increases the strength of chromium-nickel austenitic steel.

Therefore, in practice, small additions of nitrogen are used in these steels.

Effect of chromium content

With increasing chromium concentration, the solubility of carbon in chromium-nickel austenite decreases, which facilitates the precipitation of the carbide phase in it. This, in particular, is confirmed by a decrease in the impact toughness of steel with an increase in chromium content, which is associated with the formation of a carbide network along the grain boundaries.

At the same time, an increase in the concentration of chromium in austenite leads to a significant decrease in the susceptibility of steel to intergranular corrosion. This is explained by the fact that chromium significantly increases the corrosion resistance of steel. A higher concentration of chromium in steel results in a lower degree of depletion of grain boundaries when carbides are precipitated there.

 Effect of nickel content

Nickel reduces the solubility of carbon in austenite and thereby reduces the impact strength of steel after tempering and increases its susceptibility to intergranular corrosion.

The influence of alloying elements on the structure of steel

According to the nature of the influence of alloying and impurity elements on the structure of chromium-nickel austenitic steels during high-temperature heating, they are divided into two groups: 1) ferrite-forming elements: chromium, titanium, niobium, silicon;

2) austenite-forming elements: nickel, carbon, nitrogen.

Delta Ferrite in Chromium Molybdenum Austenitic Steel

The presence of delta ferrite in the structure of austenitic chromium-nickel steel type 18-10 has a negative effect on its manufacturability during hot plastic deformation - rolling, piercing, forging, stamping.

The amount of ferrite in steel is strictly limited by the ratio of chromium and nickel in it, as well as by technological means. The group of steels most prone to the formation of delta ferrite is the X18N9T type (see also Stainless steels). When these steels are heated to 1200 ºС, the structure can contain up to 40-45% delta ferrite. The most stable are steels of the X18N11 and X18N12 types, which, when heated at high temperatures, retain an almost purely austenitic structure.

Martensite in chromium-nickel austenitic steels

Within the grade composition in steels of the X18N10 type, chromium, nickel, carbon and nitrogen contribute to a decrease in the temperature of the martensitic transformation, which is caused by cooling or plastic deformation.

The influence of titanium and niobium can be twofold. Being in solid solution, both elements increase the stability of austenite with respect to martensitic transformation. If titanium and niobium are bound into carbonitrides, then they can slightly increase the temperature of the martensitic transformation. This happens because austenite in this case is depleted of carbon and nitrogen and becomes less stable. Carbon and nitrogen are strong austenite stabilizers.

Heat treatment of chromium-nickel austenitic steels

For chromium-nickel austenitic steels, two types of heat treatment are possible:

• hardening and
• stabilizing annealing.

Heat treatment parameters differ for unstabilized steels and steels stabilized with titanium or niobium.

Hardening is an effective means of preventing intergranular corrosion and giving steel an optimal combination of mechanical and corrosion properties.

Stabilizing annealing of hardened steel converts chromium carbides:

• to a state that is not dangerous for intergranular corrosion for non-stabilized steels;
• into special carbides for stabilized steels.

Hardening of austenitic chromium-nickel steels

In steels without titanium and niobium additives, hardening means heating above the dissolution temperature of chromium carbides and fairly rapid cooling, which fixes a homogeneous gamma solution. The heating temperature for quenching increases with increasing carbon content. Therefore, low-carbon steels are hardened at lower temperatures than high-carbon steels. In general, the heating temperature range is from 900 to 1100 ºС.

The duration of exposure of steel at the hardening temperature is quite short. For example, for sheet material, the total heating and holding time when heated to 1000-1050 ºС is usually selected at the rate of 1-3 minutes per 1 mm of thickness.

Cooling from the quenching temperature must be rapid. For unstabilized steels with a carbon content of more than 0.03%, cooling in water is used. Steels with a lower carbon content and small cross-sections of the product are cooled in air.

Stabilizing annealing of austenitic chromium-nickel steels

In unstabilized steels, annealing is carried out in the temperature range between the heating temperature for hardening and the maximum temperature for the manifestation of intergranular corrosion. The value of this interval primarily depends on the chromium content in the steel and increases with increasing its concentration.

In stabilized steels, annealing is carried out to transfer carbon from chromium carbides to special titanium and niobium carbides. In this case, the released chromium goes to increase the corrosion resistance of steel. The annealing temperature is usually 850-950 ºС.

Resistance of austenitic chromium-nickel steels to acids

The ability to passivate provides chromium-nickel austenitic steels with fairly high resistance to nitric acid. Steels 12Х18Н10Т, 12Х18Н12Б and 02Х18Н11 have the first resistance rating:

• in 65% nitric acid at temperatures up to 85 ºС;
• in 80% nitric acid at temperatures up to 65 ºС;
• 100% sulfuric acid at temperatures up to 65 ºС;
• in mixtures of nitric and sulfuric acids: (25% + 70%) and 10% + 60%) at temperatures up to 70 ºС;
• in 40% phosphoric acid at 100 ºС.

Austenitic chromium-nickel steels also have high resistance to solutions of organic acids - acetic, citric and formic, as well as alkalis KOH and NaOH.

Source: https://steel-guide.ru/klassifikaciya/nerzhaveyushhie-stali/austenitnye-nerzhaveyushhie-stali-struktura-i-svojstva.html

Austenite - what is it?

Heat treatment of steel is a powerful mechanism for influencing its structure and properties. It is based on modifications of crystal lattices depending on temperature changes. Under various conditions, ferrite, pearlite, cementite and austenite may be present in an iron-carbon alloy. The latter plays a major role in all thermal transformations in steel.

Definition

Steel is an alloy of iron and carbon, in which the carbon content is up to 2.14% theoretically, but technologically applicable contains it in an amount of no more than 1.3%. Accordingly, all the structures that form in it under the influence of external influences are also types of alloys.

The theory presents their existence in 4 variations: solid solution of penetration, solid solution of exclusion, mechanical mixture of grains or chemical compound.

Austenite is a solid solution of carbon atom penetration into the face-centric cubic crystal lattice of iron, referred to as γ. The carbon atom is introduced into the cavity of the iron γ-lattice. Its dimensions exceed the corresponding pores between Fe atoms, which explains their limited passage through the “walls” of the main structure. It is formed in the processes of temperature transformations of ferrite and pearlite when the heat rises above 727˚C.

Iron-carbon alloys diagram

The graph, called the iron-cementite phase diagram, constructed experimentally, is a visual demonstration of all possible transformation options in steels and cast irons. Specific temperature values ​​for a certain amount of carbon in the alloy form critical points at which important structural changes occur during heating or cooling processes, and they also form critical lines.

The GSE line, which contains points Ac3 and Acm, displays the level of carbon solubility as the heat level increases.

Table of dependence of carbon solubility in austenite on temperature
Temperature, ˚С	900	850	727	900	1147
Approximate solubility of C in austenite, %	0,2	0,5	0,8	1,3	2,14

Features of education

Austenite is a structure that forms when steel is heated. When the critical temperature is reached, pearlite and ferrite form an integral substance.

Heating options:

1. Uniform, short holding, cooling until the required value is reached. Depending on the characteristics of the alloy, austenite can be either fully formed or partially formed.
2. Slow increase in temperature, long period of maintaining the achieved heat level in order to obtain pure austenite.

Properties of the resulting heated material, as well as that which will occur as a result of cooling. A lot depends on the level of heat achieved. It is important to prevent overheating or overheating.

Microstructure and properties

Each of the phases characteristic of iron-carbon alloys has its own structure of lattices and grains. The structure of austenite is lamellar, having shapes close to both needle-like and flake-like. When carbon is completely dissolved in γ-iron, the grains have a light shape without the presence of dark cementite inclusions.

Hardness is 170-220 HB. Thermal and electrical conductivity is an order of magnitude lower than that of ferrite. There are no magnetic properties.

Variations of cooling and its speed lead to the formation of various modifications of the “cold” state: martensite, bainite, troostite, sorbitol, pearlite. They have a similar needle-like structure, but differ in particle dispersion, grain size and cementite particles.

Effect of cooling on austenite

Austenite decomposition occurs at the same critical points. Its effectiveness depends on the following factors:

1. Cooling rate. Affects the nature of carbon inclusions, grain formation, the formation of the final microstructure and its properties. Depends on the medium used as a coolant.
2. The presence of an isothermal component at one of the stages of decomposition - when lowered to a certain temperature level, stable heat is maintained for a certain period of time, after which rapid cooling continues, or it occurs together with a heating device (furnace).

Thus, continuous and isothermal transformations of austenite are distinguished.

Features of the nature of transformations. Diagram

A C-shaped graph that displays the nature of changes in the microstructure of a metal in a time interval, depending on the degree of temperature change, is a diagram of the transformation of austenite. Real cooling is continuous. Only certain phases of forced heat retention are possible. The graph describes isothermal conditions.

The nature can be diffusion or non-diffusion.

At standard rates of heat reduction, the change in austenite grain occurs by diffusion. In the zone of thermodynamic instability, atoms begin to move among themselves. Those that do not have time to penetrate the iron lattice form cementite inclusions. They are joined by neighboring carbon particles released from their crystals.

Cementite forms at the boundaries of disintegrating grains. Purified ferrite crystals form corresponding plates. A dispersed structure is formed - a mixture of grains, the size and concentration of which depend on the rapidity of cooling and the carbon content in the alloy. Perlite and its intermediate phases are also formed: sorbitol, troostite, bainite.

At significant rates of temperature decrease, the decomposition of austenite does not have a diffusion nature. Complex distortions of crystals occur, within which all atoms simultaneously shift in the plane without changing their location. The lack of diffusivity promotes the nucleation of martensite.

The influence of hardening on the characteristics of austenite decomposition. Martensite

Quenching is a type of heat treatment, the essence of which is rapid heating to high temperatures above the critical points Ac3 and Acm, followed by rapid cooling. If the temperature decreases with the help of water at a rate of more than 200˚C per second, then a solid needle-shaped phase called martensite is formed.

It is a supersaturated solid solution of carbon penetration into iron with an α-type crystal lattice. Due to powerful movements of atoms, it is distorted and forms a tetragonal lattice, which is the cause of hardening. The formed structure has a larger volume. As a result of this, crystals confined to a plane are compressed, and needle-shaped plates are born.

Martensite is durable and very hard (700-750 HB). Formed exclusively as a result of high-speed hardening.

Hardening. Diffusion structures

Austenite is a formation from which bainite, troostite, sorbitol and pearlite can be artificially produced. If cooling of the hardening occurs at lower rates, diffusion transformations occur; their mechanism is described above.

Troostite is perlite, which is characterized by a high degree of dispersion. Formed when heat decreases by 100˚C per second. A large number of small grains of ferrite and cementite are distributed over the entire plane. “Hardened” cementite is characterized by a lamellar form, and troostite obtained as a result of subsequent tempering has a granular visualization. Hardness – 600-650 HB.

Bainite is an intermediate phase, which is an even more dispersed mixture of crystals of high-carbon ferrite and cementite. In mechanical and technological properties it is inferior to martensite, but superior to troostite. It is formed in temperature ranges when diffusion is impossible, and the force of compression and movement of the crystalline structure is not enough to transform it into martensitic.

Sorbitol is a coarsely dispersed needle-shaped variety of pearlite phases when cooled at a rate of 10˚C per second. Mechanical properties are intermediate between perlite and troostite.

Pearlite is a combination of grains of ferrite and cementite, which can be granular or lamellar in shape. It is formed as a result of the smooth decomposition of austenite with a cooling rate of 1˚C per second.

Beitite and troostite are more related to hardening structures, while sorbitol and pearlite can also be formed during tempering, annealing and normalization, the features of which determine the shape of the grains and their size.

Effect of annealing on the features of austenite decomposition

Almost all types of annealing and normalization are based on the reciprocal transformation of austenite. Complete and partial annealing is used for hypoeutectoid steels. The parts are heated in a furnace above the critical points Ac3 and Ac1, respectively. The first type is characterized by the presence of a long holding period, which ensures complete transformation: ferrite-austenite and pearlite-austenite. This is followed by slow cooling of the workpieces in the oven.

The output is a finely dispersed mixture of ferrite and pearlite, without internal stresses, ductile and durable. Incomplete annealing is less energy-intensive; it only changes the structure of pearlite, leaving ferrite practically unchanged. Normalization implies a higher rate of temperature decrease, but also a coarser-grained and less plastic structure at the output.

For steel alloys with a carbon content of 0.8 to 1.3%, upon cooling, within the framework of normalization, decomposition occurs in the direction: austenite-pearlite and austenite-cementite.

Another type of heat treatment, which is based on structural transformations, is homogenization. It is applicable for large parts. It implies the absolute achievement of an austenitic coarse-grained state at temperatures of 1000-1200˚C and exposure in an oven for up to 15 hours. Isothermal processes continue with slow cooling, which helps to align the metal structures.

Isothermal annealing

To simplify understanding, each of the listed methods of influencing metal is considered as an isothermal transformation of austenite. However, each of them has characteristic features only at a certain stage. In reality, changes occur with a stable decrease in heat, the speed of which determines the result.

One of the methods that is closest to ideal conditions is isothermal annealing. Its essence also consists in heating and holding until all structures completely disintegrate into austenite. Cooling is carried out in several stages, which contributes to a slower, longer and more thermally stable decomposition.

1. A rapid decrease in temperature to a value 100˚C below point Ac1.
2. Forced retention of the achieved value (by placing it in a furnace) for a long time until the formation of ferrite-pearlite phases is completely completed.
3. Cooling in still air.

The method is also applicable to alloy steels, which are characterized by the presence of retained austenite in the cooled state.

Retained austenite and austenitic steels

Sometimes incomplete decomposition is possible when retained austenite occurs. This may happen in the following situations:

1. Cooling too quickly and complete disintegration does not occur. It is a structural component of bainite or martensite.
2. High-carbon or low-alloy steel, for which the processes of austenitic disperse transformations are complicated. Requires the use of special heat treatment methods, such as homogenization or isothermal annealing.

For highly alloyed ones, there are no processes of the described transformations. Alloying steel with nickel, manganese, and chromium promotes the formation of austenite as the main strong structure that does not require additional influences. Austenitic steels are characterized by high strength, corrosion resistance and heat resistance, heat resistance and resistance to complex aggressive operating conditions.

Austenite is a structure, without the formation of which no high-temperature heating of steel is possible and which is involved in almost all methods of its heat treatment in order to improve mechanical and technological properties.

Source: https://FB.ru/article/281801/austenit---eto-chto-takoe

What is austenitic stainless steel: description and features

Austenitic steels have a number of special advantages and can be used in working environments that are highly aggressive. It is impossible to do without such alloys in power engineering, oil and chemical industries.

Austenitic steels are steels with a high level of alloying; upon crystallization, a single-phase system is formed, characterized by a crystalline face-centered lattice. This type of grating does not change even when exposed to very low temperatures (about 200 degrees Celsius). In some cases, there is another phase (the volume in the alloy does not exceed 10 percent). Then the lattice will be body-centered.

Description and characteristics

Steels are divided into two groups regarding the composition of their base and the content of alloying elements such as nickel and chromium:

• Compositions based on iron: nickel 7%, chromium 15%; total number of additives - up to 55%;
• Nickel and iron-nickel compositions. In the first group, the nickel content starts from 55% and more, and in the second - from 65 and more percent of iron and nickel in a ratio of 1:5.

Thanks to nickel, it is possible to achieve increased ductility, heat resistance and manufacturability of steel, and with the help of chromium, it is possible to impart the required corrosion and heat resistance. And the addition of other alloying components will make it possible to obtain alloys with unique properties. The components are selected in accordance with the service purpose of the alloys.

For alloying it is mainly used:

• Ferritizers that stabilize the structure of austenites: vanadium, tungsten, titanium, silicon, niobium, molybdenum.
• Austenizers represented by nitrogen, carbon and manganese.

All of the listed components are located not only in excess phases, but also in a solid solution of steel.

Alloys resistant to corrosion and temperature changes

A wide range of additives allows you to create special steels that will be used for the manufacture of structural components and will work in cryogenic, high-temperature and corrosive conditions. Therefore, compositions are divided into three types:

• Heat-resistant and heat-resistant.
• Corrosion resistant.
• Resistant to low temperatures.

Heat-resistant alloys are not destroyed by chemicals in aggressive environments and can be used at temperatures up to +1150 degrees. They are made from:

• Elements of gas pipelines;
• Furnace fittings;
• Heating components.

Heat-resistant grades can resist stress at elevated temperatures for a long time without losing high mechanical characteristics. When alloying, molybdenum and tungsten are used (up to 7% can be allocated for each addition). Boron is used to grind grains in small quantities.

Austenitic stainless steels (resistant to corrosion) are characterized by a low content of carbon (no more than 0.12%), nickel (8−30%), chromium (up to 18%). Heat treatment is carried out (tempering, hardening, annealing). It is important for stainless steel products, because it makes it possible to hold up well in a variety of aggressive environments - acidic, gas, alkaline, liquid metal at temperatures of 20 degrees and above.

Cold-resistant austenitic compositions contain 8–25% nickel and 17–25% chromium. They are used in cryogenic units, but the cost of production increases significantly, so they are used very limitedly.

Heat-resistant and heat-resistant grades can be subjected to different types of heat treatments to increase beneficial properties and modify the existing grain structure. We are talking about the number and principle of distribution of dispersed phases, the size of blocks and grains themselves, and the like.

Annealing such steel helps reduce the hardness of the alloy (sometimes this is important during operation), as well as eliminate excessive brittleness. During the processing process, the metal is heated to 1200 degrees for 30-150 minutes, then it must be cooled as quickly as possible. Alloys with a significant amount of alloying elements are usually cooled in oils or in open air, while simpler alloys are cooled in ordinary water.

Double hardening is often carried out. First, the first normalization of the compositions is performed at a temperature of 1200 degrees, followed by a second normalization at 1100 degrees, which allows for a significant increase in plastic and heat-resistant properties.

Increased heat resistance and mechanical strength can be achieved through the process of double heat treatment (hardening and aging). Before operation, artificial aging of all heat-resistant alloys is carried out (that is, they are dispersion hardened).

Source: https://tokar.guru/metally/stal/austenitnaya-stal-osobennosti-i-harakteristiki.html

Which steels are classified as austenitic steels

Austenite is a solid single-phase solution of carbon up to 2% in y-Fe. its peculiarity lies in the sequence in which the atoms are arranged, i.e., in the structure of the crystal lattice. It comes in 2 types:

1. BCC a-iron (volumetric - centered - one atom is located in 8 vertices of the cube and 1 in the center).
2. fcc y-iron (face-centered, one atom is located in the 8 vertices of the cube and one is located on each of the 8 faces, 16 atoms in total).

In simple words: austenite is the structure or state of a metal that determines its technical characteristics, which cannot be obtained in another state, because By changing its structure, the metal also changes its properties. Without austenite, such a technology as hardening is impossible, which is the most common, cheapest, technically accessible, and in some cases the only technology for strengthening metal.

Properties of austenitic steels and where they are used  

The very state of iron in the Y-phase (austenite) is unique, thanks to which the metal is heat-resistant (+850 ºC), cold-resistant (-100 ºC and below t), capable of providing corrosion and electrochemical resistance and other important properties, without which many would be unthinkable technological processes in:

• oil refining and chemical industries;
• medicine;
• space and aircraft construction;
• electrical engineering.     

Heat resistance is the property of steel not to change its technical properties at critical temperatures over time. Fracture occurs when the metal is unable to resist dislocation creep, i.e., the displacement of atoms at the molecular level.

Softening gradually occurs, and the aging process of the metal begins to occur faster and faster. This occurs over time at low or high temperatures.

So, the extent to which this process extends over time is the metal’s ability to resist heat.

Corrosion resistance is the ability of a metal to resist destruction (dislocation creep) not only over time and at cryogenic and high temperatures, but also in aggressive environments, that is, when interacting with substances that actively react with one or more component elements. There are 2 types of corrosion:

1. chemical - oxidation of metal in environments such as gas, water, air;
2. electrochemical - dissolution of a metal in acidic environments containing positively or negatively charged ions. When there is a potential difference between the metal and the electrolyte, inevitable polarization occurs, leading to partial interaction of the two substances.   

Cold resistance - the ability to maintain structure at cryogenic temperatures over a long period of time.

Due to the distortion of the crystal lattice, the structure of cold-resistant steel is capable of taking on the structure inherent in ordinary low-alloy steels, but at very low temperatures.

But these steels have one drawback - they can have full properties only at subzero temperatures; t - ≥ 0 is unacceptable for them.

Methods for obtaining austenite

Austenite is a metal structure that occurs in low-alloy grades in the temperature range of 550-743 ºC.

How can this structure and, accordingly, properties be preserved beyond the boundaries of these t? — Answer: by alloying method.

When the austenite lattice is filled with atoms of other elements, structural distortions are formed, and the process of restoration of the bcc lattice (natural structure at normal temperatures) shifts by hundreds of degrees. 

How these properties manifest themselves and in what state depends on the additional, i.e., alloying elements and the heat treatment of the part, which it can additionally receive. Moreover, it is not only the elements that influence, but their ratio, so austenitic steel is divided into:

• chromium-manganese and chromium-nickel-manganese (07Х21Г7АН5, 10Х14АГ15, 10Х14Г14H4T);
• chromium-nickel (08Х18Н12Б, 03Х18Н11, 08X18H10T, 06X18Н11, 12X18H10T, 08X18H10;
• high-silicon (02Х8Н22С6, 15Х18Н12C4Т10);
• chromium-nickel-molybdenum (03Х21Н21М4ГБ, 08Х17Н15М3Т, 08Х17Н13M2T, 03X16H15M3, 10Х17Н13М3Т).

Chemical elements and their effect on austenite  

Austenite has few accomplices; they can be used both jointly and partially, depending on what properties need to be obtained:  

• Chromium - when its content is more than 13%, it forms an oxide film on the surface, 2-3 atoms thick, which prevents corrosion. In austenite, chromium is in a free state, subject to a minimum carbon content, since it immediately forms Cr23C6 carbide, which leads to chromium segregation and depletes large areas of the matrix, making it available for oxidation; Cr23C6 carbide itself promotes intergranular corrosion of austenite.
• Carbon (its maximum value is not more than 10%). Carbon in austenite is in a combined state, its main task is the formation of carbides, which have extreme strength.
• Nickel is the main element that stabilizes the desired structure. A content of 9-12% is sufficient to transfer the steel to the austenitic class. Grinds and inhibits grain growth, which ensures high plasticity;
• Nitrogen replaces carbon atoms, the presence of which in electrochemically resistant steels is reduced to 0.02%;
• Boron - already in thousandths of a percent increases plasticity in austenite, crushing its grain;
• Silicon and manganese are not listed as the main alloying elements in the labeling, but they are the main or essential alloying elements of austenite that impart strength and stabilize the structure.
• Titanium and niobium - at temperatures above 700 °C, chromium carbide decomposes and stable TiC and NiC are formed, which do not cause intergranular corrosion, but their use is not always justified in cold-resistant steels, because it increases the limit of austenite decomposition.

Heat treatment

Austenite is processed only when necessary. The main operations are high-temperature annealing (1100-1200 °C for 0.5-2.5 hours), which eliminates brittleness. Next is quenching with cooling in oil or air.

Austenitic steel alloyed with aluminum is subjected to double hardening and double normalization:

1. at t 1200 °C;
2. at t 1100 °C.

Mechanical finishing is carried out before hardening, but after annealing.

Products made of ausnitic steels

Semi-finished products in which steel is supplied are:

• Sheets 4-50 mm thick with guaranteed chemical composition and mechanical properties.
• Forgings. Due to the complex processing of these steels by welding, the production of some parts involves the production of almost finished products already at the casting stage. These are rotors, disks, turbines, engine pipes.  

  How to make a loop on a steel cable

Austenite joining methods:

• Solder greatly limits the use of metal at temperatures above 250 °C;
• Welding is possible in a protective atmosphere (gas, flux), with subsequent heat treatment.
• Mechanical connection - bolts and other fasteners made of similar material.

Austenitic steels are one of the most expensive technical steels, the use of which is limited to a narrow specialization of equipment. 

Source: https://steelfactoryrus.com/kakie-stali-otnosyatsya-k-austenitnym-stalyam/

What is austenitic stainless steel: description and features – Machine

Stainless steels, which contain iron, chromium and nickel, are the most important category of special structural materials that are used in many industries. In this article we will talk about one of the types of stainless steel - chromium-nickel steel with an austenitic structure. And a little about the properties and application of stainless steel 12Х18Н10Т.

Corrosion and its features

I noticed that while describing the qualities of stainless steels and noting their need and usefulness for industry, I have not yet focused on why they are so important. The main property of stainless steels is the ability to resist corrosion, so a few words about what it is.

Corrosion is the process of destruction of the surface of metals as a result of purely chemical or electrochemical action of the external environment, usually aggressive.

In general, metal corrosion is accompanied by the formation of destruction products on the surface, such as rust, but there are also destructions without external manifestations. The intensity of corrosion depends on the properties of the metal and the degree of aggressiveness of the environment.

Corrosion is a fairly broad concept and is characterized by various manifestations:

• continuous (uniform) corrosion, when the entire surface of the metal is destroyed;
• point (local, crevice, pitting) corrosion, when individual areas of the metal surface are destroyed;
• intergranular corrosion, when corrosion spreads deep into the product along the grain boundaries;
• stress corrosion (corrosion cracking), when cracks develop on the metal surface due to the simultaneous influence of tensile stresses and an aggressive environment.

A separate type is electrochemical corrosion, when electrochemical processes at the interface are added to the purely chemical processes of interaction between the metal and the environment. This is the most destructive type of corrosion.

In the process of electrochemical corrosion, the destruction of metals occurs under the influence of electrolytes and is accompanied by the transition of atoms. In practice, most often electrolytes are aqueous solutions of salts, acids and alkalis.

Thus, metal containers, pipelines, machine parts and parts of structures in contact with sea and river water, as well as groundwater, are subject to intense destruction by electrochemical corrosion.

From the theory of electrochemical corrosion it follows that very pure metals have the greatest resistance. But in real life, the use of pure metals is practically impossible, so there is a need to ensure a homogeneous structure of the solid solution in alloys.

Increased resistance to uniform corrosion in a wide range of corrosive environments of varying degrees of aggressiveness is a distinctive feature of stainless steels and alloys. Many types of stainless steels are also resistant to intergranular and pitting corrosion and corrosion cracking.

General information about chromium-nickel stainless steels

The main alloying elements that give chromium-nickel steel corrosion resistance in oxidizing environments are Cr (chromium) and Ni (nickel). Chromium promotes the formation of a protective dense passive film of Cr2O3 oxide on the surface of stainless steel. The concentration of chromium in steels of this group required to impart corrosion resistance to stainless steel is 18%.

Nickel belongs to metals that are or easily pass into the so-called “passive” state. In a passive state, a metal or alloy has increased corrosion resistance in an aggressive environment. Although, of course, this ability of nickel is less than that of chromium or molybdenum.

Chromium and iron form a solid solution in the alloy, and nickel in an amount of 9-12%, in addition, contributes to the formation of an austenitic structure. Due to their austenitic structure, chromium-nickel stainless steels are distinguished by high processability during hot and cold deformation and resistance at low temperatures.

Chromium-nickel austenitic stainless steels are the most widespread group of corrosion-resistant steels. They are also known in world practice under the general name of steels of type 18-10.

In our country, the most common grades of chromium-nickel stainless steels are: 12Х18Н10Т, 08Х18Н10Т (EI914), 08Х18Н10, 12Х18Н9Т, 03Х18Н11, 12Х18Н12Т, 08Х18Н12Б (ЭИ402), 02Х18Н11, 03Х19AG 3H10.

These stainless steels exhibit corrosion resistance in many oxidizing environments at varying concentrations and over a wide range of temperatures. They also have heat resistance and heat resistance, but at moderate temperatures.

Resistance of stainless steel against intergranular corrosion

The ability to resist intergranular corrosion in chromium-nickel austenitic stainless steels primarily depends on the carbon content of the solid solution. Carbon promotes the release of carbide phases in the solid solution, thereby accelerating the manifestation of intergranular corrosion with increasing temperature.

Chromium-nickel austenitic stainless steels, when held in the range of 750-800 ºС, lose their ability to resist intergranular corrosion:

• with a carbon content of 0.084% - within 1 minute;
• with a carbon content of 0.054% - within 10 minutes;
• at a carbon content of 0.021 5 – after more than 100 minutes.

nitrogen in the composition of chromium-nickel austenitic stainless steels also affects the susceptibility to intergranular corrosion, but to a much lesser extent. the presence of nitrogen in the composition may even be useful for increasing strength.

An increase in the concentration of nickel in the composition of chromium-nickel austenitic stainless steels helps to reduce the solubility of carbon, but negatively affects the impact strength of chromium-nickel steel after tempering and promotes intergranular corrosion.

The solubility of carbon in the solid solution of chromium-nickel austenitic stainless steels also occurs with increasing chromium content. In this case, the impact toughness of the steel also decreases, but at the same time the resistance to intergranular corrosion increases.

Stainless steel 12Х18Н10Т application, properties

Steel 12Х18Н10Т is an excellent example of chromium-nickel austenitic stainless steel, widely used in the production of welded structures.

It can work in contact with nitric acid and other strong oxidizing agents; in some organic acids of medium concentration, organic solvents, atmospheric conditions, etc.

These are containers, heat exchangers, as well as welded structures using cryogenic technology (up to -269 °C).

Examples of using stainless steel 12Х18Н10Т:

• rolled forged round, square, hexagonal
• the leaf is thick;
• thin sheet;
• cold rolled strip;
• seamless hot-deformed pipes;
• cold- and heat-deformed seamless pipes;
• wire;
• shaped steel profiles.

The corrosion resistance of stainless steel 12Х18Н10Т against intergranular corrosion is determined by testing according to the AM and AMU methods of GOST 6032-89 with a duration of exposure in the control solution of 24 and 8 hours, respectively. Tests are carried out after provoking heating at 650 °C for 1 hour.

During continuous operation, stainless steel 12Х18Н10Т is resistant to oxidation in air and in the atmosphere of fuel combustion products at temperatures up to 900 °C. Stainless steel 12Х18Н10Т has fairly high heat resistance at temperatures of 600-800 °C.

Stainless steel 12Х18Н10Т, having good manufacturability, can be subject to significant plastic deformation. The temperature range for pressure treatment of stainless steel 12Х18Н10Т is 1180-850 °C, the heating and cooling rates are not limited. When cold, they allow high degrees of plastic deformation.

Welding stainless steel 12Х18Н10Т

The main problem when welding austenitic stainless steels is calcination, which causes structural changes in them, leading to a decrease in resistance to intergranular corrosion.

To reduce such risks, titanium or niobium is introduced into the composition of chromium-nickel stainless steels. Stainless steels alloyed with titanium can be welded well, provided that subsequent heat treatment is avoided.

Chromium-nickel stainless steel 12Х18Н10Т can be welded well by all types of manual and automatic welding. Electric welding can be performed by resistance welding, welding with a non-consumable tungsten electrode in a protective atmosphere of argon, semi-automatic welding in a protective atmosphere of a mixture of argon and carbon dioxide, and welding with individual, coated electrons.

For conventional automatic submerged arc welding AN-26, AN-18 and argon arc welding, a special wire for welding “stainless steel” is used, for example Sv-08Kh19N10B, Sv-04Kh22N10BT, Sv-05Kh20N9FBS and Sv-06Kh21N7BT.

For manual welding of stainless steel, electrodes for “stainless steel” type EA-1F2 of brands GL-2, TsL-2B2, EA-606/11 with wire Sv-05Х19Н9ФЗС2, Sv-08Х19Н9Ф2С2 and Sv-05Х19Н9ФЗС2 are used. This ensures the resistance of the seam against intergranular corrosion. Welding electrodes for stainless steel are usually shorter than electrodes for ordinary steel, since their electrical resistance is higher.

It is also possible to weld parts made of stainless steel and ordinary steel, but in this case it is necessary to use the so-called. "transition" electrodes. In this case, it is required that the weld metal be made of stainless steel, which is why transition electrodes containing a high content of alloying elements are used.

Welding electrodes are specially marked for welding stainless steel intended for use in the food industry. The use of the correct welding consumables ensures that high corrosion properties are maintained against both general and intergranular corrosion.

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Source: https://regionvtormet.ru/svarka/chto-takoe-austenitnaya-nerzhaveyushhaya-stal-opisanie-i-osobennosti.html

Austenitic steels

Austenite is a solid single-phase solution of carbon up to 2% in y-Fe. its peculiarity lies in the sequence in which the atoms are arranged, i.e., in the structure of the crystal lattice. It comes in 2 types:

1. BCC a-iron (volumetric - centered - one atom is located in 8 vertices of the cube and 1 in the center).
2. fcc y-iron (face-centered, one atom is located in the 8 vertices of the cube and one is located on each of the 8 faces, 16 atoms in total).

In simple words: austenite is the structure or state of a metal that determines its technical characteristics, which cannot be obtained in another state, because By changing its structure, the metal also changes its properties. Without austenite, such a technology as hardening is impossible, which is the most common, cheapest, technically accessible, and in some cases the only technology for strengthening metal.

Austenitic steel

Austenitic steel is one of the modifications of iron with a high degree of alloying. It has a face-centered crystal lattice. It easily retains its structure even at very low temperatures. Austenites have high strength values. It is resistant to both high temperatures and heavy loads.

Properties of austenitic steels

Austenitic steel forms a 1-phase structure during the crystallization process. Its crystal lattice does not change even with sudden cooling to negative temperatures (–200 °C). The main components of austenitic iron alloys are chromium and nickel. The manufacturability, ductility, strength and heat resistance of the material depend on the proportion of their content. The following materials are used for alloying:

1. Ferritizers: titanium, silicon, molybdenum, niobium. They stabilize the austenite structure and form a body-centered cubic lattice.
2. Austenizers: nitrogen, manganese and carbon. They are present in excess phases formed during heat treatment of iron alloys.

Based on the properties of materials, austenitic modifications of iron are divided into the following types:

1. Corrosion resistant (stainless). They include chromium (18%), nickel (30%) and carbon (0.25%). These high-alloy steels have been used in industrial production since 1910. Their main advantage is their resistance to corrosion. The material retains this property even with strong heating, which is due to its low carbon content. Corrosion-resistant iron alloys are produced in accordance with GOST 5632-2014. They may contain additives from silicon, manganese, and molybdenum.
2. Heat resistant. They have an fcc lattice and are resistant to high temperatures. This material can be heated up to 1100 °C. Heat-resistant austenitic steels are used in the manufacture of furnace devices, power plant rotor turbines and other devices operating with diesel fuel. In the production of this modification of iron, additional additives from boron, niobium, vanadium, molybdenum and tungsten are used. These chemical elements increase the heat resistance of the material.
3. Cold resistant. These high-alloy steels contain chromium (19%) and nickel (25%). The main advantage of the material is its high viscosity and plasticity. This modification of iron is also highly resistant to corrosion. Cold-resistant metals retain these properties even with a sharp drop in temperature. Their main disadvantage is their low strength when operating at room temperature.

Austenitic high-alloy steel is one of the most expensive modifications of iron because it contains a large amount of expensive materials: chromium and nickel. Also, its cost is affected by the number of additional alloying components, which make it possible to create iron alloys with special properties. Additional alloying elements are selected depending on the complexity of the work where austenite is used.

The following types of transformations can occur in austenitic steels:

1. Ferrite formation when heating an iron alloy to high temperatures.
2. When heated to a temperature of 900 °C, excess carbide phases begin to precipitate from austenite. During this process, intercrystalline corrosion forms on the austenitic surface, gradually destroying the material.
3. During cooling of austenite to a temperature of 730 °C, eutectoid decomposition occurs. As a result, pearlite is formed - a modification of iron alloys. Its microstructure is presented in the form of small plates or rounded grains.
4. With a sharp decrease in the temperature of a metal product, martensite is formed - a microstructure consisting of needle-shaped or lath-shaped plates.

The time required to transform austenitic steel into other modifications of iron is determined by the carbon content in the solid solution and the amount of additional alloying components. The lower these indicators, the faster the metal product cools.

Application of alloys

Austenitic steels are used in the manufacture of devices operating at high temperatures, starting from 200 °C: steam generators, rotors, turbines and welding mechanisms. The disadvantage of using austenite in these mechanisms is the low strength of the metal.

With prolonged contact of iron alloys with various hydroxides, additional cracks may form, which will lead to breakage of the working surfaces of devices. This drawback can be eliminated by adding additional chemical elements to the iron solution: vanadium and niobium.

They form a carbide phase, which increases the strength of steel.

Stainless austenitic steels are used in mechanisms operating in difficult conditions and with strong temperature changes. They are most often used when welding corrosion-resistant pipes. During this process, a seam space is created between the fasteners. When stainless austenite pipes are heated to the melting temperature, they acquire a monolithic structure that protects the metal from oxidation processes and high temperature changes.

Austenitic steels are also highly resistant to electromagnetic radiation. Therefore, it is used in the production of individual parts for electronic equipment. Austenite improves the strength of radio mechanisms and does not lose its properties when the structure of the magnetic field changes. For this reason, radio equipment will easily receive the necessary signals.

Austenitic iron alloys are widely used in the production of mechanisms operating in aqueous environments. Stainless steel is resistant to corrosion. It is used as a protective material.

With the correct ratio of chromium and nickel, austenite can form a thin layer, reducing the influence of the aqueous environment on the working surface of the metal device. As a result, wear on the device is reduced.

But with significant leaching of nickel, the material completely loses its resistance to corrosion.

Modern turbine casings also use high-yield austenitic steels. They allow you to avoid warping of this device and improve its strength. Due to its coarse grain structure, high yield strength austenite can also be used to strengthen the turbine rotor structure. The disadvantage of this technology is a significant increase in the cost of mechanisms due to the use of a large amount of expensive austenitic steel.

Austenitic steel grades

The regulations for the production of austenite are defined in GOST 5632-2014. It specifies the following grades of austenitic steels:

• 12Х18Н9Т;
• 08Х18Н10Т;
• 12Х18Н10Т;
• 12Х18Н9;
• 17Х18Н9;
• 08Х18Н10;
• 03Х18Н11.

These names indicate the percentage of chromium, carbon and nickel in austenite. For example, 12Х18Н9 means that in the iron modification the nominal content of chromium is 18%, nickel - 10%, carbon - 0.12%. The marking may also contain the letter “T”. It means that the alloy contains a small amount of titanium.

Austenitic steel grades make it possible to determine the basic properties of the material. The percentage of nickel and chromium describes the heat resistance and rust resistance of austenite. Using carbon concentration, you can calculate the time and temperature range at which intercrystalline corrosion appears on an iron alloy.

Heat treatment features

Austenitic stainless steels are classified as difficult-to-cut materials. To improve the basic properties of austenite and modify its structure, the following methods are used:

1. Annealing. The metal product is heated to 1200 °C for 2–3 hours. After this, the metal is cooled either in an oily liquid or water, or in the open air. Annealing reduces the hardness of the iron alloy and increases its flexibility.
2. Double hardening. The solid solution of austenitic steel is normalized at a temperature of 1200 °C. The iron alloy is then re-quenched to a temperature of 1000 °C. During the heat treatment process, the ductility of austenite and its resistance to high temperatures increase. The effect can be increased by aging the steel before use.

On a production scale, special mechanical machines are used for heat treatment of austenitic steels. Processing of iron alloys should be carried out using powerful equipment. Otherwise, the material may deform or form long chips, which is due to high viscosity.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/austenitnaya-stal.html

Austenitic stainless steel - what is it?

Popular brands of stainless steel of domestic and foreign production.

AISI 304 is the most common and popular steel grade. It is characterized by high strength, elasticity, resistance to oxidation, and is easy to weld.

AISI 316 and 316Ti steel is an improved version of AISI 304,
with increased anti-corrosion resistance and resistance to aggressive environments.

AISI 430 is an economical option for corrosion-resistant material, ideal for stamping, deformation and perforation.

Stainless steel is a type of alloy steel that is resistant to corrosion due to its chromium content of 12% or more. In the presence of oxygen, chromium oxide is formed, which creates an inert film on the surface of the steel, protecting the entire product from adverse influences. The modern market can offer various grades of stainless steel for use in a wide variety of industries.

Not every grade of stainless steel demonstrates the resistance of chromium oxide film to mechanical and chemical damage. Although the film recovers when exposed to oxygen, special grades of stainless steel have been developed for use in aggressive environments.

Popular steel grades

Russia has a developed steel industry and has its own designations for steel grades, but the most popular grades have foreign analogues.

These are steels of the so-called 300 and 400 series, which are distinguished by high characteristics of corrosion resistance, resistance to aggressive environments, ductility and strength.

They are practically universal and are used for the production of a wide variety of products - from medical instruments to large building structures. The 200 series is gradually catching up with them in popularity due to its favorable price-quality ratio.

Types of steel 300 series

Chromium-nickel stainless steel of this group in its chemical composition is austenitic, austenitic-ferritic and austenitic-martensitic, depending on the percentage of carbon, nickel, chromium and titanium. This is the most versatile stainless steel, the properties of which ensure its consistently high demand in the market.

AISI 304 (08Х18Н10)

In demand in all industries, this stainless steel, however, has gained fame as “food grade”. Its chemical composition and properties make it most suitable for use in the food industry. It is easy to weld and shows high corrosion resistance characteristics in aggressive environments. It is also often chosen for the chemical, pharmaceutical, petroleum and textile industries.

AISI 316 (10Х17Н13М2)

316 stainless steel is obtained by adding molybdenum to 304 stainless steel, which further increases corrosion resistance and the ability to maintain properties in aggressive acidic environments, as well as at high temperatures. This stainless steel is more expensive than 304 and is used in the chemical, oil and gas, and shipbuilding industries.

AISI 316T (10Х17Н13М2Т)

This grade of stainless steel contains a small amount of titanium, which increases the strength of the material, making it resistant to high temperatures, as well as chlorine ions. Used in welded structures, for the manufacture of gas turbine blades, in the food and chemical industries. Affordable price and high technical characteristics make this stainless steel very popular.

AISI 321 (12-08Х18Н10Т)

Stainless steel, the characteristics of which are determined by the increased titanium content. Easily weldable, resistant to temperatures up to 800 o C. Widely in demand for the manufacture of seamless pipes, as well as pipeline fittings - flanges, tees, bends and reducers.

Types of steel 400 series

This series has a narrower range than the 300th. This includes stainless steel with a high chromium content; it contains almost no other alloying elements, which has a positive effect on its cost. The low carbon content makes these stainless steels ductile and easy to weld.

AISI 430 (12Х17)

This is stainless steel with a high percentage of chromium and low carbon. This ratio contributes to high strength and at the same time ductility. AISI 430 bends, welds and stamps well. Retains its properties in corrosive and sulfur-containing environments, and is resistant to sudden temperature changes. It is used in the oil and gas industry, as well as as a decorative material for finishing buildings and premises.

Types of steel 200 series

So far we can only talk about one grade of steel in this series, but it is successfully catching up with its competitors in the 300 and 400 series.

AISI 201 (12X15G9ND)

AISI 201 stainless steel is much cheaper than stainless steel of other series with similar properties. In it, expensive nickel is partially replaced by manganese and nitrogen. The advantageously balanced chemical composition makes the characteristics of AISI 201 stainless steel not inferior to AISI 304 and AISI 321. It has found its application in the medical and food industries. It is also used in the manufacture of round and profile pipes, which are required to create railings, handrails and fences.

Sales of stainless steel throughout Russia and the CIS

The MetPromStar company sells stainless steel of all grades, equipped with quality certificates and meeting international standards.

Flexible pricing and a wide selection of rolled steel attract both large enterprises and small private companies as clients. MetPromStar consultants are ready to answer all questions regarding any brand of stainless steel.

Delivery is carried out throughout Russia and the CIS countries. It is possible to individually manufacture stainless steel products according to customer sketches.

Source: https://crast.ru/instrumenty/austenitnaja-nerzhavejushhaja-stal-chto-jeto-takoe

What steels are austenitic and their properties?

In power engineering, chemical and oil industry enterprises, equipment elements that are in direct contact with aggressive environments must be made of a special material that can withstand negative impacts. According to modern technologies, austenitic steels are used, their grades are selected in accordance with production tasks.

This is a highly alloyed material that forms a 1-phase structure during crystallization. It is characterized by a face-centered crystal lattice, which is preserved even at cryogenic temperatures - below -200 degrees C. The material is characterized by a high content of nickel, manganese and some other elements that contribute to stabilization at different temperatures. Austenitic steels are classified into 2 groups regarding composition:

• material based on iron, in which chromium is up to 15%, and nickel is up to 7%, the total number of alloying elements should not exceed 55%;
• material based on nickel, when its content is 55% and higher, or based on iron-nickel, when the content of these components is 65% and higher, and the ratio of iron and nickel is in the proportion of 1 to 1 ½, respectively.

Nickel in these iron alloys is necessary to increase manufacturability, resistance and strength to heat, and increase ductility parameters. Chrome increases resistance to corrosion and high temperatures.

Other alloying additives can form other unique properties that austenitic stainless steel should have under certain technological conditions.

Unlike other materials, this iron alloy does not undergo transformations when temperatures decrease and increase. Therefore, temperature treatment is not used.

Classification of austenitic steels by groups and grades

What steels belong to austenitic steels are usually classified into three groups:

• Corrosion resistant. In these iron alloys, the chromium content varies from 12 to 18%, nickel from 8 to 30%, carbon from 0.02 to 0.25%. They have been known to modern industry since 1910, when they were developed by German engineer Strauss. Compared to chromium iron alloys, this material is characterized by increased corrosion resistance, which it retains when heated, which is facilitated by the limited carbon content. Corrosion-resistant austenitic steels are produced in accordance with GOST 5632-72. This group includes the following brands: chromium-nickel - 08Х18Н10, 12Х18Н10Т, 06Х18Н11 and others, with manganese additives - 10Х14Г14Н4Т, 07Х21Г7АН5 and others, chromium-nickel-molybdenum - 08Х17Н13М2Т, 03Х16Н16ьЗ and others, high-silicon - 02Х8Н22С6, 15Х18Н12С4Т10 and others.
• Heat-resistant and heat-resistant. These are alloys with a fcc lattice; in comparison with materials with a bcc lattice, they are characterized by more significant heat resistance. They are mainly used for the production of furnace installations. Valves of units operating on diesel fuel, turbine blade elements, rotor modules and disks are made from this material. Some brands are able to withstand temperatures up to 1100 degrees C. To enhance the heat resistance parameters, boron, tungsten, niobium, vanadium or molybdenum are added to the material. This group includes brands such as: 08Х16Н9М2, 10Х14Н16Б, 10Х18Н12Т, 10Х14Н14В2БР and others.
• Cold resistant. This iron alloy is indispensable in technological processes occurring at cryogenic temperatures. In its composition, the chromium content varies from 17 to 25%, and nickel - from 8 to 25%. This material maintains viscosity and ductility over an extended operating temperature range. It is characterized by good manufacturability and high corrosion resistance. The disadvantages of this iron alloy are: reduced strength at normal temperatures, especially at the yield point, as well as significant cost due to the presence of expensive nickel metal in the composition. The most popular brands of this group are: 03X20N16AG6 and 07X13N4AG20.

Features of processing of austenitic steels

Austenitic steels are difficult to machine materials. Thermal effects on them are difficult, so other technologies are used. Machining of these alloys is difficult because the material is prone to work hardening and minor deformations significantly densify the material.

This iron alloy produces long chips because it has high toughness parameters. Mechanical processing of austenitic steels requires energy and consumes 50% more resources compared to carbon alloys. Therefore, their processing must be performed on powerful and rigid machines.

Welding, ultrasonic influence and cryogenic-deformation technology are possible.

Source: http://solidiron.ru/steel/kakie-stali-otnosyatsya-k-austenitnym-i-kakimi-svojjstvami-oni-obladayut.html