Heat-resistant steel grades, types and features

Ferrite (C interstitial solid solution in α-iron with a body-centered cubic lattice) Austenite (C interstitial solid solution in γ-iron with a face-centered cubic lattice) Cementite (iron carbide; Fe3C metastable high-carbon phase) Graphite stable high-carbon phase

Ledeburite (eutectic mixture of cementite and austenite crystals, which turns into pearlite upon cooling) Martensite (highly supersaturated solid solution of carbon in α-iron with a body-centered tetragonal lattice) Pearlite (eutectoid mixture consisting of thin alternating plates of ferrite and cementite) Sorbitol (dispersed perlite) Troostite (highly dispersed pearlite) Bainite (ustar: acicular troostite) - an ultradispersed mixture of crystals of low-carbon martensite and iron carbides

White cast iron (brittle, contains ledeburite and no graphite) Gray cast iron (graphite in plate form) Ductile cast iron (graphite in flakes) Ductile iron (graphite in the form of spheroids) Half cast iron (contains both graphite and ledeburite)

Heat-resistant (scaling-resistant) steel

- steel that is resistant to corrosion damage to the surface in gas environments at temperatures above 550 °C, operating in an unloaded or lightly loaded state.

Characteristics [edit | edit code]

Heat resistance (scale resistance) of steel is characterized by resistance to oxidation at high temperatures. To increase scale resistance, steel is alloyed with elements that change the composition and structure of scale. As a result of introducing into steel the required amount of chromium (Cr) or silicon (Si), which have a greater affinity for oxygen (O) than iron (Fe), dense oxides based on chromium or silicon are formed on the surface during the oxidation process. The resulting thin film of these oxides hinders the process of further oxidation. To ensure scale resistance up to a temperature of 1100 °C, the steel must contain at least 28% chromium (for example, steel 15Х28). The best results are obtained by simultaneously alloying steel with chromium and silicon.

What is the difference between AISI 304 and 430 stainless steels?

Information article
There are many different models on the sauna stove market that use stainless steel, but not all stainless steel is equally good. Let's try to figure out how stainless steels differ from each other. Let's take as an example the most common steels AISI 430 (17X18 according to GOST) and AISI 304 (12X18H10 according to GOST).

Many manufacturers of sauna stoves use AISI 430 steel in their production, since according to the heat resistance table it is higher.

The use of this steel is also justified by its relatively low price compared to AISI 304 steel.

AISI 304 steel has slightly less heat resistance compared to AISI 430, but this is its only minor difference. Since there are more important indicators that directly affect the performance and durability of the product.

First, let's find out in more detail what kind of steel it is.

Stainless heat-resistant (austenitic) steel AISI 304 (INOX)

Heat resistance

is the ability of a metal to resist plastic deformation and fracture at high temperatures.

The main heat-resistant austenitic steels are chromium-nickel steels. Steels contain 15...20% chromium and 10...20% nickel. They have heat resistance and heat resistance, are plastic, and weld well.

Steel grade AISI 304 (INOX) - belongs to the chromium-nickel class of low-carbon high-alloy steels. High chromium and nickel content

determines excellent strength and anti-corrosion properties, which are in demand everywhere - they are defined as universal. That is why this alloy is one of the most used.

In the GOST system, this grade corresponds to 12X18H10 steel.

The main qualities that give advantages to AISI 304 are: resistance to oxidation and elevated temperatures, increased reliability of welds due to good weldability.

AISI 304 has the following performance properties:

• Acid resistance.
  Resistance to aggressive influences of a man-made or natural nature.
• Heat resistance.
  The ability of a metal to resist plastic deformation and fracture at high temperatures.
• Heat resistance.
  The ability of metals and alloys to resist gas corrosion at high temperatures for a long time (up to 850oC).
• Weak magnetic properties.
  They are achieved due to the structure of the material and the method of its processing.
  AISI 304 steel is not magnetic.
• Environmentally friendly.
  Manufacturers of AISI 304 position this material, also called Inox, as food grade stainless steel. It does not contain toxic substances.

Stainless heat-resistant (ferritic) steel AISI 430

Heat resistance (scale resistance)

is the ability of metals and alloys to resist gas corrosion at high temperatures for a long time.

If the product operates in an oxidizing gas environment at a temperature of 500..550 oC without heavy loads, then it is enough that they are only heat-resistant (for example, individual parts of heating furnaces).

Being low-alloy and corrosion-resistant, AISI 430 steel has good resistance to scale formation up to temperatures of 850-900
o C
, maintaining its useful performance properties.

To increase heat resistance, elements are introduced into the steel that form oxides with a dense crystal lattice structure (chromium, silicon, aluminum) with oxygen.

In the GOST system, this grade corresponds to steel 17Х18.

AISI 430 has the following performance properties:

• Heat resistance.
  The ability of metals and alloys to resist gas corrosion at high temperatures for a long time (up to 900oC).
• Environmentally friendly.
  It does not contain toxic substances.

Comparison of AISI 304 and 430 stainless steels

AISI 430 steel, although more heat resistant, is more brittle and difficult to weld. In order to weld it efficiently, a special complex technology and its exact observance at all stages of work are required. This steel is mainly used for decorative purposes. Welded structures made from it are very fragile and the weakest point will always be the welding seam.

This AISI 430 steel has lower acid resistance compared to 304 stainless steel, and when working in harsh conditions of water, soot and condensate, it gradually becomes unusable, so, for example, chimney pipes made of such steel still burn out.

They are simply corroded by the acid produced as a result of the operation of the furnace. Also, AISI 430 steel is magnetic, which easily gives it away during any magnetic test.

This way you can easily determine which stainless steel is in front of you - AISI 430 or real non-magnetic stainless steel AISI 304.

AISI 304 (INOX) steel is a heat-resistant steel and is not afraid of high temperatures when operating a sauna stove. It is perfectly weldable due to the higher quality steel composition and high nickel content.

Nickel is a very expensive metal, but with its high content in stainless steel, it acquires increased strength and resistance to temperature changes, and also acquires excellent weldability.

It is thanks to nickel that this steel loses its magnetic properties.

Also, AISI 304 stainless steel is resistant to chemical and acid influences and does not emit harmful or toxic substances. Therefore, this steel is mainly used in the food and medical industries and is classified as food grade stainless steel.

AISI 304 steel is more expensive compared to AISI 430 steel due to the use of higher quality and more expensive nickel and chromium alloys in large quantities.

Stoves made of such stainless steel can be used constantly and will last almost forever. Therefore, such stoves are recommended by the manufacturer ERMAK for use even in commercial baths with a guarantee of up to 5 years.

Summary

Not all stainless steel stoves are the same, as you already understand. And before you make a choice in favor of one stove or another, check what stainless steel your sauna stove will be made of. Its quality and service life will greatly depend on this.

The Ermak plant also produces sauna stoves from AISI 430 steel, following all welding technology. This is a classic series of Ermak-Elite sauna stoves made of stainless steel.

But in the new line of ERMAK stainless steel sauna stoves in the “Premium” and “Lux” series, AISI 304 (INOX) stainless steel is already used in the manufacture of the firebox and all smoke ducts, which is why the price of the stoves is very different.

Having installed such a stove made of real stainless steel, you will be able to forget about your problems forever and just enjoy the quality of your bath procedures and relax.

How to choose a sauna stove made of real stainless steel? How to distinguish it from ordinary heat-resistant steel? Just use a magnet. The furnace firebox is made of real heat-resistant stainless steel and will not be magnetic! Up to 90% of stoves on the market disguised as stainless steel are sold from ordinary heat-resistant steel. Don't be fooled!

Classification [edit | edit code ]

Heat-resistant steels are divided into several groups:

• chromium steels of ferritic class;
• chromium-silicon steels of the martensitic class;
• chromium-nickel steels of the austenitic-ferritic class;
• chromium-nickel austenitic steels.

Ferritic chromium steels [edit | edit code]

Can be used for the manufacture of welded structures that are not exposed to shock loads at operating temperatures not lower than –20 °C; for the manufacture of pipes for heat exchange equipment operating in aggressive environments; equipment, parts, thermocouple covers, spark plug electrodes, pipes of pyrolysis plants, heat exchangers; for joints with glass. Heat resistance - up to 1100 °C. Example: 15Х25Т, 15Х28.

Chrome-silicon steels of the martensitic class [edit | edit code]

Used for the manufacture of valves for aircraft engines, automobile and tractor diesel engines, and engine fasteners. Example: 40Х10С2М.

Chromium-nickel steels of the austenitic-ferritic class [edit | edit code]

Used for the manufacture of parts operating at high temperatures in a lightly loaded state. Heat resistance up to 900-1000 °C. Example: 20Х23Н13.

Chromium-nickel austenitic steels [edit | edit code]

They are used for the manufacture of sheet parts, pipes, fittings (at reduced loads), as well as parts of furnaces operating at temperatures up to 1000-1100 °C in air and hydrocarbon atmospheres. Example: 10Х23Н18, 20Х25Н20С2.

By ordering heat-resistant steel from us now, you receive:

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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.

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

Definition and types of heat resistance

Heat-resistant stainless steel is an alloy that, due to its physical and chemical properties, is resistant to aggressive chemicals and mechanical wear at temperatures above 500 °C. Such high performance properties are achieved due to the inclusion of a large number of alloying elements in the material composition. Chromium, nickel, titanium help strengthen the metal crystal lattice and prevent the active spread of oxidation processes. Heat-resistant material does not undergo plastic deformation at high temperatures and does not form rust or scale.

The division of heat-resistant stainless steel into types is due to the different content of alloying elements, differences in alloying methods, and the final purpose of the steel. There are 4 groups of stainless heat-resistant alloys:

• austenitic with chromium content up to 26%, nickel up to 25%, molybdenum up to 6%;
• ferritic, which contain no more than 0.2% carbon and up to 27% chromium;
• ferritic-austenitic (mixed, or duplex) steels with the inclusion of 18-28% chromium and up to 8% nickel;
• martensitic contain 10-13% chromium and no more than 1% carbon.

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

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.

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

Table of stainless steel grades used in the food industry

Stainless steel grades and their characteristics, 5.0 out of 5 - total: 5

Brands of heat-resistant stainless steel

The main grades of heat-resistant stainless steels produced by the domestic and foreign metallurgical industry include:

• 20Х20Н14С2, also known under the name EI211 (imported analogue of AISI 309) is a type of high-alloy chromium-nickel alloy containing chromium and nickel up to 22% and 15%, respectively;
• 20Х23Н18 or EI417 (analogue of Western European and American manufacturers AISI 310) - austenitic refractory steel, products from which are used in reducing environments with temperatures up to 1000 °C and oxidizing operating conditions up to 1100 °C;
• 10Х23Н18 or EI417 (AISI 310S) – a low-carbon modification of the AISI 310 alloy, the need for use of which is due to the presence of a corrosive environment due to the influence of condensates and high-temperature gases;
• 20Х25Н20С2 or EI283 (analogue of foreign steel under the brand AISI 314) is a non-magnetic, non-hardening, austenitic alloy, resistant to ultra-high temperatures.

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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.

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.

Content:
1. Which brand of steel is best for a sauna stove?
2. Optimal metal thickness for a bathhouse stove
3. What electrodes should be used to cook a sauna stove?

Homemade sauna stoves cost on average 3-5 times cheaper than factory products. The savings will be even greater if you do the welding yourself. When making it yourself, you will need to decide on the following:

1. What metal to make a sauna stove from?
2. What metal thickness will be optimal?
3. What type of electrodes should be used to ensure maximum weld strength.

The speed of heating of the steam room, the duration and intensity of operation of a self-made stove depend on the answer to all these questions.

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.

Which brand of steel is best for a sauna stove?

Direct exposure to fire causes the steel to burn through. Of course, you can simply use metal with a thickness of 10 mm or more, but then you will have to heat the steam room for a long time and spend a large amount of fuel to warm it up. Due to the use of thick-walled steel sheets, a durable furnace will become economically unprofitable.

The task facing the master is to make the structure strong enough to prevent deformation, burnout and at the same time have good thermal conductivity. In the factory, for the manufacture of sauna stoves, metal with a high degree of heat resistance is used.

Alloy steel differs from structural steel in the following characteristics:

• Resistance to moisture – alloy steel used in the manufacture of sauna stoves, stainless steel. There is no tendency to corrosion even with intense heating. Domestic brand of heat-resistant high-alloy stainless steel 08Х17Т. Some sources indicate almost complete identity of the characteristics of heat-resistant steels of this type. Structural iron is not corrosion resistant, which must be taken into account when calculating the thickness of the furnace walls.
• Operating time – the service life of furnaces made of structural steel is 3-4 years. AISI 430 becomes unusable in 5-8 years.
• Possibility of repair work - grades of heat-resistant steel for the manufacture of wood-burning sauna stoves, AISI 430 and 08Х17Т, have a low carbon content, which makes welding work possible. Structural iron contains sulfur and phosphorus compounds, which make it brittle and brittle.
• Heat resistance – grades of heat-resistant steel for bath ovens, AISI 430 and 08Х17Т, can withstand heating up to 850°C without changing the structure of the metal and its crystal lattice. When the temperature rises to 600 °C, the tensile strength remains around 145 MPa. Scale formation occurs only when heated to 8500°C. The metal in a sauna stove with intensive combustion heats up to a temperature of 450-550°C. The structural material has lower heat resistance parameters.

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Features of materials with heat-resistant properties

Heat-resistant steels and alloys, as mentioned above, can be successfully operated under conditions of constant exposure to high temperatures, without showing a tendency to creep. The essence of this negative process, to which ordinary steel grades and other metals are subject, is that the material, which is exposed to constant temperature and constant load, begins to slowly deform, or creep.

Creep, which they try to avoid when creating heat-resistant steels and other types of metals, comes in two types:

• long-term;
• short-term.

To determine the creep of alloys, research centers use a set of testing machines

To determine the parameters of short-term creep, materials are subjected to special tests, for which they are placed in an oven heated to a certain temperature and a tensile load is applied to them. This test is carried out for a limited period of time.

It will not be possible to test a material for its tendency to long-term creep and determine such an important parameter as the creep limit in a short period of time. To do this, the test product placed in the oven must be subjected to prolonged load. The importance of such an indicator as the creep limit of a material lies in the fact that it characterizes the greatest stress, which leads to the destruction of a heated product after exposure for a certain period of time.

Optimal metal thickness for a bathhouse stove

When determining the thickness of the metal, two main characteristics are taken into account that affect the operating parameters of the sauna stove:

• Burnout of steel - if you use a thin-walled sheet of ordinary metal for the firebox, after literally six months of fire the firebox will have to be repaired. Regular steel 4 mm thick will provide quick heating of the steam room, but will not last long. For this reason, manufacturers make the combustion chamber from AISI 430, a heat-resistant chromium stainless steel with a thickness of 4-6 mm.
• Thermal conductivity - the heating temperature of the furnace directly depends on the thickness of the firebox walls. It seems that it would be easier to make the combustion chamber out of metal 10 mm or larger, and thus prevent burnout, but this approach is impractical for several reasons. The thicker the metal, the more thermal energy and time it takes to heat it and maintain the required temperature. Furnace equipment becomes economically unprofitable. The optimal metal thickness for a sauna stove should be 6-8 mm.

The minimum thickness of steel in the combustion chamber is 4 mm, permissible only if AISI 430 and 08Х17Т are used. In other cases, a metal thickness of at least 6 mm is needed. Most craftsmen recommend using 8 mm thick structural steel when making a stove yourself.

What electrodes should be used to cook a sauna stove?

To weld the furnace, you will need electrodes selected depending on the steel used in production. Stainless steel is welded using argon arc welding. Suitable electrodes are TsL 11 and D4.

After welding work, it is necessary to remove scale and etching. This way you can avoid corrosion at the weld.

Electrodes for welding sauna stoves made of structural steel NIAT-5, EA-112/15, EA-981/15 and EA-981/15. The thickness is selected depending on the density of the metal and its heating temperature.

Making a sauna stove with your own hands is not difficult if you have special skills and the right choice of components and consumables.

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.