Heat-resistant steels: composition and grades of heat-resistant alloys

The concept of heat resistance

This property of metals determines their resistance to corrosion when exposed to high temperatures. In an aggressive environment, heat-resistant steel does not collapse or deform.

To impart special properties to the metal, silicon, chromium and other substances with similar properties are added to it Source mprokat.ru

This material is used in the production of parts in contact with temperatures above 550 degrees and subject to vibration loads: turbines, heating boilers, compressors, etc. In order to increase the heat resistance, certain substances are added to metal alloys:

• chromium;
• aluminum;
• nickel;
• silicon.

The purpose of such additives is to create a protective layer. These substances, when in contact with metal during heating, form a thin film on it, which reduces oxidation. Depending on the amount of substances added, the level of heat resistance will be adjusted.

With a chromium content of up to 8%, steel will withstand 750 degrees, and increasing the impurity to 25% will raise the temperature to 1100 degrees Source metalloprokat-63.ru

When producing heat-resistant steel, it undergoes certain testing. First of all, the resulting alloy is heated to a specific temperature, and then it is subjected to stretching. After successful testing, the finished products are allowed for sale.

Grades of heat-resistant and heat-resistant steels

Depending on the state of the structure, austenitic, martensitic, pearlitic and martensitic-ferritic heat-resistant metals are distinguished. Heat-resistant alloys are divided into ferritic, martensitic or austenitic-ferritic types.

Pearlitic grades having a chromium-silicon and chromium-molybdenum composition of heat-resistant steel: Kh13N7S2, Kh10S2M, Kh6SM, Kh7SM, Kh9S2, Kh6S. Chrome-molybdenum compounds 12МХ, 12ХМ, 15ХМ, 20ХМЛ are suitable for use at 450-550 °С, chrome-molybdenum vanadium 12Х1МФ, 15Х1М1Ф, 15Х1М1ФЛ - at temperatures 550-600 °С. They are used in the production of turbines, shut-off valves, apparatus casings, steam lines, pipelines, and boilers.

Ferritic steel is made by firing and heat treatment, due to which it acquires a fine-grained structure. These include brands X28, X18SYU, 0X17T, X17, X25T, 1X12SYU. The chromium content in such alloys is 25-33%. They are used in the production of heat exchangers, equipment for chemical production (pyrolysis equipment), furnace equipment and other structures that operate for a long time at high temperatures and are not subject to heavy loads. The more chromium in the composition, the higher the temperature at which the steel retains its performance properties. Heat-resistant ferritic steel does not have high strength or heat resistance, but is characterized by good ductility and good technological parameters.

Martensitic-ferritic steel contains 10-14% chromium, alloying additives vanadium, molybdenum, tungsten. The material is used in the manufacture of machine elements, steam turbines, nuclear power plant equipment, heat exchangers for nuclear and thermal power plants, parts intended for long-term operation at 600 ºC. Steel grades: 1Х13, Х17, Х25Т, 1Х12В2МФ, Х6СУ, 2Х12ВМБФР.

Austenitic steels are widely used in industry. The heat-resistant and heat-resistant characteristics of the material are ensured by nickel and chromium and alloying additives (titanium, niobium). Such steels retain technical properties that are resistant to corrosion when exposed to temperatures up to 1000 ºC. Compared to ferritic steels, austenitic alloys have increased heat resistance and the ability to be stamped, drawn, and welded. Heat treatment of metals is carried out by hardening at 1000–1050 °C.

Austenitic-ferritic steels have increased heat resistance compared to conventional high-chromium alloys. Such metals are used in the manufacture of unloaded products, operating temperature is 1150 ºC. Pyrometric tubes are made from grade X23N13, and furnace conveyors, tanks for cementation, pipes are made from grade X20N14S2, 0X20N14S2

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Features of heat-resistant steel

The advantages of heat-resistant products are obvious:

• With constant and long-term exposure to high temperatures, the performance properties of the metal remain unchanged.
• Increases resistance to mechanical stress. In aggressive environments, the alloy retains its strength.
• Despite the influence of the gas environment and interaction with acids, the steel alloy retains its original chemical composition.
• Substances added to the alloy give it the property of corrosion resistance.

The main classification of heat-resistant steel alloys is built depending on the additional elements included in its composition Source metall-gipermarket.ru Based on
the duration of exposure to an aggressive environment, heat-resistant steel can be divided into types of long-term and short-term heating. Long-term heating steel is characterized by withstanding high temperatures for a long time. However, the temperature value does not reach a critical level. In the case of short-term heating steel, its use is required where sudden temperature changes of up to several thousand degrees occur.

But still, these parameters are not decisive for the classification of heat-resistant steel by type. The main factor here is additional impurities that give the alloy special properties.

Stainless steel markings

In Russia, alloying alloys are produced in accordance with GOST 5632-2014. Marking is a combination of numbers and letters. The number at the beginning indicates the carbon content of the alloy. The numbers located after the letters indicate the average mass fraction of the alloying element, which is indicated in the form of letters of the Russian alphabet.

The composition of foreign brands is standardized by the standards existing in the country of origin. AISI, named after the American research institute “The American Iron and Steel Institute,” has become popular in the Russian Federation. The first digit indicates the type of alloy, the next two indicate the serial number in the entire group of this class. The reduced amount of carbon in the AISI system is indicated by an additional letter L.

Correspondence table of popular foreign brands with Russian analogues

Types of heat-resistant steel

There are several types of steel depending on its internal structure:

• martensitic;
• pearlite;
• austenitic;
• martensitic-ferritic.

An enlarged photograph of a piece of martensitic steel allows you to see the needle-like structure of the metal Source gendocs.ru
Heat-resistant steel is divided into two more types:

• ferritic;
• austenitic-ferritic.

The determining factor here is the ferrite included in the composition.

Grades of martensitic heat-resistant steel

The most popular brands:

• X5. Intended for pipes used at temperatures of 650 degrees. This brand is not designed for high temperatures.
• 1Х8ВФ. Used for the manufacture of steam turbine parts. Withstands temperatures of 500 degrees. Moreover, their service life is 10,000 hours.
• Several brands are combined into one group because they have similar characteristics: X5M, X5VF, 1 X8VF, X6SM, 1 X12N2VMF. Intended for elements manufactured for operation at temperatures from 500 to 600 degrees. The service life of the parts varies from 1000 hours to 10,000 hours.
• Two more brands are combined according to general indicators: 3Х13Н7С2, 4Х9С2. Valves of transport engines are made from them. Able to withstand temperatures from 850 to 950 degrees.

Stainless steel is a durable material that is resistant to corrosion and high temperatures Source 90zavod.ru
Martensitic steels contain pearlite. As the level of chromium in the alloy increases, it changes its state. Grades of steel containing pearlite and chromium:

• Х13Н7С2.
• X6SM.
• X6S.
• X10S2M.
• X7SM.
• X9S2.

The principle of producing martensitic steels is to combine the constituent elements and further harden them at a temperature of 1000 degrees. To increase the level of heat resistance, the alloy is tempered at a temperature of 8100 degrees. It is this procedure that allows the steel to withstand prolonged heating.

Application of heat-resistant stainless steels

The use of heat-resistant alloys of one grade or another is determined by the characteristics of the operating environment and loads:

• 20Х20Н14С2 (AISI 309) – parts and assemblies of thermal furnaces, conveyors, and boxes for cementation are produced from steel of this grade;
• 20Х23Н18 (AISI 310) is used for the manufacture of parts for conveyor belts, furnace conveyors, heat treatment units, fuel combustion chambers (including internal combustion engines), motors, gas turbines, doors;
• 10Х23Н18 (AISI 310S) is used mainly in mechanisms, installations and units for transporting hot gases - turbines, methane conversion devices, exhaust systems, high-pressure gas pipelines, heating elements;
• 20Х25Н20С2 (AISI 314) is used in the field of furnace construction - metal products made from stainless heat-resistant steel of this grade are used for the manufacture of furnace screens, rollers, and boiler hangers.

Ferritic alloy grades

Such compounds contain about 30% chromium. The fine-grained structure of the metal is acquired by annealing. These steels include:

• X28.
• 1Х12СУ.
• X25T.
• X17.
• 0Х17Т.
• X18SYU.

The production of ferritic steel goes through the stages of hardening, firing, and subsequently tempering. Due to the fine-grained structure, the alloy can only be heated at a temperature of 180 degrees. An increase in temperature will damage the integrity and make the alloy brittle. Such alloys are used mainly for heat exchange devices.

Welding features

Modern welding methods make it possible to obtain strong welds that are resistant to the formation of hot cracks on parts made of heat-resistant stainless steels. However, alloys of this type are prone to softening and fracture of the cold weld. To eliminate the disadvantage, general or local heating of the material is carried out in order to minimize the temperature difference at the periphery and at the welding points to reduce stress. After welding, the finished products are tempered for several hours at temperatures up to 2000 °C. As a result of tempering, the main part of the hydrogen dissolved in the structure is removed, and the residual austenite is transformed into martensite.

Martensite and ferrite - steel grades

It is worth noting that steel can be martensitic-ferritic. This material is used in mechanical engineering. A distinctive feature is resistance to temperatures of 600 degrees. With such exposure, even long-term, the performance properties of steel do not change.

Steel grades of the following composition:

• 2Х12ВМБФР;
• X6SYU;
• 1Х12В2МФ;
• 1Х13;
• 1Х12ВНМФ;
• 1 X11MF.

A characteristic of the composition of martensitic-ferritic alloys is the presence of chromium no more than 14% and no less than 10%. Tungsten, vanadium and molybdenum are used as additional metals.

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%).

For reference! Alloying elements serve to increase resistance to the appearance and development of corrosion and improve other properties:

• chromium – hardness;
• titanium and molybdenum - strength;
• nickel – strength, plastic properties;
• manganese – hardness, wear resistance, impact resistance.

Austenitic and austenitic-ferritic steel

The peculiarity of such alloys is the presence of nickel, which forms the structure of the material, as well as chromium, which provides heat resistance. Some steel grades in this category contain the presence of titanium and niobium.

Austenitic steel is stainless. It is resistant to scale formation when exposed to a working environment up to 1000 degrees.

The marking indicates the composition of the steel: 12 - percentage of carbon, X18 - percentage of chromium, H10 - percentage of nickel, T - presence of titanium (no more than 1%) Source tehenergomash.ru

Heat-resistant compounds are divided into two categories:

• homogeneous;
• dispersion-hardening.

Homogeneous steels are used for the manufacture of fittings and pipes for operation under increased loads. The impact on the structure occurs not only at the temperature level, but also with high pressure and shock loads. Brands of this type of steel include:

• 1Х14Н16Б.
• Х25Н20С2.
• 1Х14Н18В2Б.
• X25N16G7AR.
• Х18Н12Т.
• Х23Н18.
• Х18Н10Т.

Dispersion-hardening compositions are used for the manufacture of turbine equipment and motor valves. They are characterized by long and regular heating, as well as frequent cooling. Temperature changes do not affect the performance characteristics of the alloy. Grades of dispersion-hardening steel:

• 0Х14Н28В3Т3УР.
• Х12Н20Т3Р.
• 4Х14Н14В2М.
• 4Х12Н8Г8МФБ.

Austenitic steel belongs to the category of dispersion-hardening compositions. For high quality performance, carbide is added to them, as well as an intermetallic sealant. This type of heat-resistant steel is used for the furnace. The composition can withstand temperatures of 700 degrees.

Austenitic and austenitic-ferritic metals are divided into three categories:

• with a reduced content of additional metals;
• alloys with a high carbide content;
• steel with the presence of intermetallic hardening.

Kamintherm pipes

AISI 304 steel is a high-alloy chromium-nickel stainless steel. In addition, it is an austenitic steel with a low carbon content. Unlike other steel grades, AISI 304 steel is in demand due to its high quality and reasonable price. In the production of chimneys, this steel is indispensable as an outer casing. In particular, the outer shell of insulated Schiedel ICS chimneys and Russian-made chimneys is made from this steel.

AISI 316 steel is an improved analogue of AISI 304 due to the addition of molybdenum. This steel has good corrosion resistance in most aggressive environments and excellent acid resistance. In addition, it is not critical to high temperatures. AISI 316 steel is the best option for diesel and gas appliances. This steel is used to make the inner pipe in Schiedel ICS chimneys.

AISI 444 steel is an acid-resistant steel, similar to AISI 316. It can be used in aggressive environments subject to strict temperature requirements. The inner pipe in Schiedel Permeter chimneys is made of this grade of steel

AISI 321 steel is a corrosion-resistant, heat-resistant, heat-resistant stainless steel with a long service life. The recommended temperature for using steel is from 600 to 800°C. It is used for the manufacture of chimneys with high flue gas temperatures - sauna stoves, coal boilers, domestic boilers, sauna stoves and heat exchangers.

AISI 310 steel is a heat-resistant, high-temperature steel that has excellent oxidation resistance, good strength at high temperatures and good weldability, which is why it is widely used. Used for resistance heating elements and devices with high combustion temperatures.

Steel grades used in the production of chimneys

Steel grades AISI 409 and AISI 430 are heat-resistant stainless steels for general use with fairly low performance. They find application in areas with mildly corrosive environments, or where resistance at moderate temperatures is required. It is used in the automotive industry, architecture and for the manufacture of decor.

AISI 201 steel has fairly high strength and excellent deformability. Due to its balanced chemical composition, this steel has good corrosion resistance in organic, acidic and other mildly aggressive environments.

Refractory metals

The refractory metals included in the steel alloy impart additional properties, increasing the heat resistance of the steel. Such metals can withstand temperatures from 1000 to 2000 degrees. Refractory steel is subject to deformation. At high temperatures, its structure is destroyed. In order to maintain the strength of such steel, other substances are added to the alloy. The most common compositions of heat-resistant alloys based on refractory metals:

• tungsten as the base metal and rhenium as the alloying substance (30%);
• iron as a base (48%), and additional substances: niobium - 15%, molybdenum - 5%, zirconium - 1%;
• vanadium (60%) and doping niobium (40%);
• tungsten and tantalum in an equal ratio - 10%.

There are alloys that can withstand enormous temperatures, even over 3000 degrees:

• Tungsten. Does not react to aggressive environments. Its temperature threshold is 3410 degrees.
• Rhenium. The most heat-resistant metal that can withstand temperatures of 3180 degrees.
• Tantalum. No less heat resistant than rhenium. Its maximum strength is determined by a temperature of 3000 degrees.
• Molybdenum. Withstands heating up to 2600 degrees.
• Niobium – 2415 degrees.
• Hafnium. Used in alloys that will subsequently be used at temperatures of 2000 degrees.
• Vanadium. It can be exposed to an environment of 1900 degrees.
• Zirconium. Operates at 1855 degrees maximum.

Special additives oxidize during hardening, which serves as protection from environmental influences Source krepej-metiz.ru
Taking into account the described properties and characteristics of heat-resistant steel, we can conclude that the classification is built depending on the following indicators:

• permissible temperature conditions at which the alloy does not deform;
• metal heating period;
• resistance to acidic environments and high humidity.

Nickel alloys

Heat-resistant steels can be made from nickel containing 55%. It is also possible to use nickel with iron (65%). This composition increases heat resistance and makes the alloy more durable. The alloying component is chromium, which is in a ratio of no more than 23%.

The most popular grades of nickel-based heat-resistant steel are:

• ХН78Т.
• ХН60В.
• ХН78МТУ.
• ХН67ВМТУ.
• ХН77TYU.
• ХН70.
• ХН70МВТУБ.

The admixtures of aluminum and chromium contained in heat-resistant steel based on nickel form an oxide film, which serves as protection from external influences. Source u-metall.ru
Some types of grades are used for specific products:

• KhN35VMT, KhN35VT – rotors as turbine equipment;
• KHN5VMTYu – details of gas communications;
• ХН35ВТУ – components for compressors, for example, disks;
• KhN5VTR – some details of the turbine design.

Heat-resistant grades of steel alloys are ways to work at elevated temperatures. Their performance characteristics depend on the composition of the alloy. Alloying components impart strength to the metal, the limit of which depends on the type of additional substance. Taken together, all indicators influence the scope of application of heat-resistant steel products. Some brands are used only for industrial purposes, while others are suitable for household use.

Heat Resistant Stainless Steel Range

Our warehouse in Moscow offers a wide range of products made from heat-resistant steel of various grades. The high quality of the products sold is confirmed by manufacturer certificates and meets the requirements of international standards. Domestic brands of heat-resistant stainless steel in our catalog include: 08Х13, 08Х17, 08Х18Т1, 10Х23Н18, 12Х13, 12Х17, 14Х17Н2, 20Х23Н18, 20Х13, 30Х13 and 40Х13. Among foreign analogues, AISI 310, AISI 310S and AISI 321 steels should be noted.

Product sizes and prices are constantly updated, so contact our managers to quickly and correctly place your order.

Choosing a steel grade for stoves or baths

Heat-resistant steels for home use differ significantly from industrial options. For a furnace, for example, you should select alloys that can heat up to 500 degrees. Moreover, it is possible to use different alloy options depending on the structural element used. Steel grades, including heat-resistant steel, for individual furnace parts:

• 08Х17Т, AISI430 – suitable for separating the firebox. If difficulties arise in purchasing these grades, then St-10 steel can replace them.
• 08PS, 08Yu - used for heat shields.
• St-3 – suitable for the furnace body.
• Most grades of heat-resistant steel can be used for furnace walls. In some cases cast iron may be used.

To build a sauna stove, steel is used, which contains at least 12% chromium. It is important to consider the thickness of the steel sheet. For such a design it should be 5 mm. Heat-resistant steel is used for equipment that heats a large area.

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

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.