Welding of stainless steels. Part 2
Stainless steel, depending on its structural state, requires a certain attitude during the welding process.
According to their structure, stainless steels are divided into:
- martensitic
- ferritic
- austenitic
- two-structure. When on
If there are two structural components, steels are named after these structures (so-called duplex steels) - martensitic-ferritic, austenitic-martensitic, austenitic-ferritic.
Welding martensitic stainless steels
Martensitic steels include steels with a chromium content of 10.5-13% and carbon content of -0.2-1.0%. Other elements may also be contained as alloying elements. Martensitic steels are characterized by high strength and hardness, but have low toughness. This group includes steel grades 15x11MF, 20x12VNMF, 20x13 (420 AISI), 20x17N2 (431 AISI), etc.
A significant disadvantage of martensitic chromium steels is their softening when heated. Steels of this group are prone to air hardening, which depends on the carbon concentration in them. The higher the carbon concentration, the greater the likelihood of hardening.
The increased tendency of martensitic steels to brittle fracture in the hardened state complicates their welding technology. Cracks in welded joints can form both during the cooling process and after cooling. To prevent the formation of cold cracks, martensitic steels are recommended to be welded at positive temperatures. To smooth out temperature differences, preliminary and concomitant heating to a temperature of 250-350oC is used.
The heating temperature is assigned for a specific steel depending on the steel’s tendency to harden. It should not be too high, as this can lead, like welding with high heat input, to overheating of the heat-affected zone, grain growth, and accumulation of impurities along the grain boundaries. All this together leads to embrittlement of the welded joint. To eliminate internal stresses, improve the structure and increase corrosion resistance after welding, tempering at a temperature of 650-750oC is desirable.
To obtain ductile and ductile weld metal, it is possible to use welding materials that ensure an austenitic structure in the weld. To obtain such a connection, welding electrodes Lastek 1226 (TsL-25) or Lastek 809 (OZL-6) are used. The strength properties of such compounds are lower than those of the base metal. Equal strength of welded joints is achieved by using welding materials that provide weld metal with a martensitic structure. Such connections can be obtained using Lastek 821 electrodes or Lastek 810 C rods.
Welding of martensitic-ferritic stainless steels
Martensitic-ferritic steels contain 12-18% chromium, which provides them with high corrosion resistance. Steel grades 15x11MF, 12x13 (410 AISI), 14x17, etc. have this structure.
Welding steels of this class requires compliance with a certain technology. Due to the high tendency of these steels to heat up in welded joints, the formation of cold cracks is possible, and due to a sharp decrease in the impact toughness of the metal in the heat-affected zone, the probability of brittle fracture is high. Taking these factors into account, welding of most steels of this class should be carried out with preliminary and concomitant heating (150-200oC), and also subjected to thermal tempering (680-700oC). With accompanying heating, sudden cooling of the heated part is dangerous, since cracks may appear.
How is the weight of each steel sheet calculated, depending on its cutting, thickness, steel grade, etc.: formula.
To obtain ductile and ductile weld metal, it is possible to use welding materials that ensure an austenitic structure in the weld. Such connections can be obtained using welding electrodes Lastek 8003 (ZIO-8), Lastek 809 (TsL-25) or Lastifil 809 G wires (cv-07Х25Н2Г2Т).
The strength properties of such compounds are lower than those of the base metal. To obtain equal-strength welded joints, welding materials are used that provide weld metal with a martensitic structure.
Welded joints of this type can be obtained using Lastek 8312 electrodes or Lastek 810 C welding rods.
Welding of ferritic stainless steels
In ferritic steels, the proportion of chromium is 12-18%, the carbon content is low - less than 0.2%.
Steels of this class include steel grades 10x13SYU, 08x13 (403 AISI), 172x17 (430 AISI), 08x17T (430 Ti AISI), 15x18SYU, 15x25T, etc. The steels have low strength, hardness and toughness, are not hardenable, and have high corrosion resistance. perseverance.
When welding steels of this type, brittle welds are formed and cracks often appear. Welding of steels of this group should be carried out in a heated state. The heating temperature is approximately 200°C. Welding is performed at the highest possible speeds to ensure minimal heating of the metal during welding. After welding, it is recommended to heat the seams to a temperature of 720-780°C and quickly cool them.
Annealing at a temperature of 760°C for 2 hours completely removes residual stresses and increases the deformability of ferritic steels of all grades. For welding steels containing 15-17% chromium, it is recommended to use additives alloyed with titanium or niobium, and for steels containing 13% chromium - 1% aluminum. Welding of steels of this type can be performed using Lastek 8312, Lastek 809 electrodes or Lastek 8003С, Lastek 810С welding rods.
Welding of stainless steels of austenitic-martensitic class
The austenitic-martensitic class includes steels that have a structure consisting of austenite and martensite, the amount of which can vary within wide limits. This class includes steel grades 20x13N4G9, 09x15N8Yu, 07x16N6 (301 AISI), 08x17N7Yu, 08x17N6T, etc. Depending on the heat treatment, these steels have a structure and have properties close to the properties of steels of the austenitic or martensitic classes.
When welding these steels, structural transformations in the heat-affected zone and the precipitation of carbides lead to a decrease in ductility, impact toughness and a decrease in corrosion resistance and resistance to intergranular corrosion of the heat-affected zone.
Complete heat treatment (quenching, cold treatment, tempering) allows you to obtain an optimal ratio of austenite and martensite, which allows you to increase toughness and maintain strength characteristics.
It is advisable to make welded joints of steels of the austenitic-martensitic class using an argon arc; the use of manual arc and mechanized arc is allowed.
The choice of filler material is carried out based on the strength requirements of the welded joint.
In the absence of high strength requirements for welds, austenitic wires Lastifil 802, Lastifil 803, electrodes Lastek 809, Lastek 802, rods for welding stainless steel 802C, Lastek 8003C can be recommended as additives.
Welding of stainless steels
In this article we will consider the welding technology of some alloyed chromium-nickel austenitic steels, namely: — corrosion-resistant steels (also known as stainless steel or simply “stainless steel”); — heat-resistant and heat-resistant steels. Welding technology of chromium-nickel austenitic steels. All procurement operations on austenitic steels, performed by cold or hot working methods, are carried out mainly by the same methods and on the same equipment as for carbon structural steels. Preparation of the edges of parts for welding must be done mechanically (milling, gouging, turning). It is allowed to prepare the edges with a compressed arc or gas-flux cutting, which requires subsequent mechanical cleaning of the fire-cutting edges to a depth of at least 0.8 mm. When assembling parts before tacking and welding, in order to avoid the formation of cuts and cracks on the surface of the base metal where molten metal splashes, areas near the seam must be covered with one of the types of protective coatings. In the manufacture of welded structures from austenitic steels, all methods of electric fusion welding can be used. The choice of welding method is made taking into account the thickness of the metal being welded, the size and shape of the structure, the location of the seams in space and their accessibility, requirements for welded joints, etc. The main feature of manual arc welding of austenitic steels is the need to ensure the required chemical composition of the weld metal for various types welded joints and spatial welding positions, taking into account changes in the share of the base and electrode metal in the weld metal. This forces the coating composition to be adjusted in order to ensure the required ferrite content in the weld and thereby prevent the formation of hot cracks in the weld. This also achieves the necessary heat resistance and corrosion resistance of the seams. By using electrodes with calcium fluoride coating, which reduces the loss of alloying elements, it is possible to obtain weld metal with the required chemical composition and structures. Maintaining a short arc without transverse vibrations of the electrode also helps to reduce the waste of alloying elements. The latter also reduces the likelihood of defects forming on the surface of the base metal as a result of the adhesion of splashes. The composition of the electrode coating determines the need to use direct current of reverse polarity (with alternating current or direct current of direct polarity, the arc is unstable), the value of which is determined by the formula Iсв=kde, and the coefficient k, depending on the diameter of the electrode, is taken to be no more than 25-30 A/mm. In the ceiling and vertical positions, the welding current is reduced by 10-30% compared to the current selected for the lower welding position. It is recommended to weld with coated electrodes using beads of small cross-section and to increase resistance to hot cracks, use electrodes with a diameter of 3 mm with minimal penetration of the base metal. Careful calcination of the electrodes before welding, the mode of which is determined by their brand, helps reduce the likelihood of the formation of pores and cracks caused by hydrogen in the seams. Some grades of electrodes recommended for various austenitic steels, depending on the operating conditions of the structure, are given in Table 1, and their mechanical properties are given in Table 2. Table 1. Some brands of electrodes and operating conditions for high-alloy steels and alloys| Electrode type | α-phase content (%) and weld structure | |||
| Corrosion-resistant steels | ||||
| 08Х18Н10 | Aggressive environments; resistance to intergranular corrosion | TsL-11 | E-04Х20Н9 | 2,5-7,0 |
| 12Х18Н10Т 08Х22Н6Т | Temperature up to 600oC; liquid media; resistance to intergranular corrosion | L38M | E 07Х20Н9 E-08Х19Н10Г2Б E-02Х10Н9Б | 3 — 5 |
| 10Х17НМ2Т 08Х18Н19Б 08Х21Н6М2Т | Temperature up to 700 °C; resistance to intergranular corrosion | SL-28 | E-08Х19Н10Г2МБ E-09Х19Н10Г2М2Б | 4 — 5 |
| 10Х17Н13МЗТ | Resistance to intergranular corrosion | NZh-13 | E-09Х19НУГ2М2Б | 4-8 |
| Heat-resistant steels | ||||
| 12Х18Н9 12Х18НУТ 08Х18Н12Т | Temperature up to 800 °C | TsT-26 | E-08Х16Н8М2 E-08Х17Н8М2 | 2 — 4 |
| 10Х23Н18 | Temperatures above 850 °C | OZL-4 OZL-6 | E-YUH25N13G2 | Over 2.5% |
| Heat-resistant steels | ||||
| 20Х20Х14С2 20Х25Н20С2 30Х18Н25С2 | Temperatures up to 900-1100°C Temperatures up to 1050°C; heat resistance and heat resistance | OZL OZL-9-1 | E-12Х24Н14С2 E-28Х24Н16Г6 | 3-10% Austenitic-carbide |
| Х25Н38ВТ ХН75МБТУ | Heat | EA-981-15 | E-09Х15Н25М6Г2Ф | Austenitic |
| Table 2. Typical mechanical properties at a temperature of 20 ° C of weld metal made on high-alloy corrosion-resistant and heat-resistant steels |
| Electrode brand | σт | σв | δ, % | KCU, J/cm3 |
| MPa/mm2 | ||||
| Corrosion-resistant steels | ||||
| TsL-11 | 360 | 600 | 24 | 70 |
| OZL-7 | 400 | 640 | 25 | 100 |
| L-38M | 300 | 600 | 30 | 90 |
| SL-28 | — | 600 | 38 | 120 |
| 11Zh-13 | 450 | 600 | 26 | 100 |
| Heat-resistant steels | ||||
| OZL-5 | 350 | 600 | 25 | 60 |
| OZL-6 | 350 | 570 | 33 | 100 |
| OZL-9-1 | 500 | 650 | 12 | 50 |
One of the main methods of welding high-alloy steels with a thickness of 3-50 mm, used in chemical, petrochemical equipment, nuclear engineering and some other industries, is submerged arc welding.
It has a great advantage over manual arc welding with coated electrodes due to the stability of the composition and properties of the metal along the entire length of the seam, when welding with and without groove edges. This is achieved by the absence of frequent craters formed when changing the electrode, arc breaks, uniform melting of the electrode wire and the base metal along the length of the seam (in manual welding, due to a change in the electrode extension, the rate of its melting at first will be less than at the end, which periodically changes the proportion of the base metal metal in the weld, and hence its composition) and more reliable protection of the welding zone from oxidation of alloying components by atmospheric oxygen. Good formation of the surface of the welds with fine scaling and a smooth transition to the base metal, the absence of splashes on the surface of the product significantly increases the corrosion resistance of welded joints. This method reduces the complexity of the preparatory work, since the cutting of edges is carried out on metal with a thickness of more than 12 mm (for manual welding, more than 3-5 mm). Welding with an increased gap and without cutting the edges of steel up to 30-40 mm thick is possible. Reducing losses due to waste, spattering and cinders of electrodes by 10-20% reduces the consumption of expensive welding wire. When welding under submerged arcs, it is much more difficult to ensure the required content of the ferrite phase in the weld metal only through the selection of welding fluxes and wires, which within the same brand have significant fluctuations in the chemical composition. The content of the ferrite phase in the metal is also affected by its thickness and different cutting forms, leading to a change in the proportion of the base metal in the weld metal. The technique and modes of submerged arc welding of high-alloy steels differ from welding of conventional low-alloy steels. To prevent overheating of the metal and the associated enlargement of the structure, the possibility of cracks and a decrease in the operational properties of the welded joint, it is recommended to weld with small cross-section beads, using wire with a diameter of 2-3 mm, and due to the high electrical resistance of austenitic steels, the electrode stickout should be reduced by 1.5-2 times.
The weld can be alloyed using flux (Table 3) or wire (Table 4), the latter is preferable, as it provides the necessary stability of the weld metal. Table 3. Fluxes for electric arc and electric slag welding of high-alloy steels
| Type of welding | Flux brand |
| Automatic electric arc austenitic-ferritic welds | ANF-14; ANF-16; 48-OF-Yu; K-8 |
| Automatic electric arc austenitic-ferritic welds with a small reserve of austenite | AN-26 |
| Automatic electric arc welding with purely austenitic welds with a large supply of austenite | ANF-5; FCC |
| Automatic electric arc and electroslag welding with purely austenitic welds with a large supply of austenite | 48-OF-6 |
| Electroslag with purely austenitic welds with a large supply of austenite | ANF-1; ANF-6; ANF-7; AN-29; AN-292 |
Table 4. Some grades of welding wire for submerged arc welding and electroslag welding of high-alloy steels
| steel grade | Working conditions | Wire grade (GOST 2246 - 70) |
| Corrosion-resistant steels | ||
| 12Х18Н9 08Х18Н10 12Х18Н10Т 12Х18Н9Т | Resistance to intergranular corrosion | Sv-0.1Х19Н9 Sv-0.4Х19Н9 Sv-07Х18Н9ТУ Sv-04Х19Н9С2 Sv-05Х19Н9ФЗС2 |
| 12Х18Н10Т 08Х18Н10Т 08Х18Н12Т 08Х18Н12Б | Temperature above 350°C; resistance to intergranular corrosion | Sv-07Х19Н10Б Sv-05Х20Н9ФБС |
| 10Х17Н13МЗТ 08X18Н12Б | Resistance to intergranular corrosion | Sv-08Х19Н10МЗБ; Sv-06Х20Н11МЗТБ |
| 08Х18Н10; 12Х18Н10Т 12Х18Н9Т | Welding in carbon dioxide; resistance to intergranular corrosion | Sv-08Х25Н13БТУ |
| Heat resistant steel | ||
| 12Х18Н9 | Temperature up to 800 °C | Sv-04Х19Н19 |
| 12Х18Н9Б 08Х18Н12Т | Temperature up to 800-900 °C | Sv-08Х18Н8Г2Б |
| Х15Н35В4Т | Heat | Sv-06Х19Н10МЗТ |
| Heat-resistant steels | ||
| 20Х23Н13 08Х20Н14С2 20Х23Н18 ХН35ВУ 20Х25Н20С2 | Temperature 800-900°C Temperature 900-1100°C Temperature up to 1200°C | Sv-07Х25Н13 Sv-07Х25Н12Г2Т Sv-06Х25Н12ТУ Sv-08Х25Н13БТУ Sv-08ХН50 |
For welding, low-silicon fluoride fluxes are used, which create non-oxidizing or low-oxidizing environments in the welding zone, which leads to minimal waste of alloying elements. To reduce the likelihood of pores forming in the welds, fluxes for high-alloy steels must be calcined immediately before welding at 500-800°C for 1-2 hours. Residues of slag and flux on the surface of the welds, which can serve as sources of corrosion of welded joints on corrosion- and heat-resistant steels , must be carefully removed. A feature of electroslag welding is its reduced sensitivity to the formation of hot cracks, which is explained by the low speed of movement of the heating source and the nature of crystallization of the metal of the weld pool, as a result, conditions are created for obtaining purely austenitic welds without cracks. However, prolonged exposure of the weld metal and heat-affected zone at elevated temperatures increases its overheating and the width of the heat-affected zone, and prolonged exposure of the metal at temperatures of 1200-1250°C leads to a change in its structure and reduces strength and plastic properties. As a result, welded joints of heat-resistant steels are prone to failure during heat treatment or operation at elevated temperatures. Overheating during welding of the heat-affected zone of corrosion-resistant steels can lead to the formation of knife corrosion in it, therefore, to prevent these defects, heat treatment of welded products (hardening or stabilizing annealing) is necessary. When choosing flux and welding wire, it is necessary to take into account the penetration of air oxygen through the surface of the slag bath, which leads to the loss of easily oxidized elements (titanium, manganese, etc.). This makes it necessary in some cases to protect the surface of the slag bath by blowing with argon. Electroslag welding of high-alloy steels can be performed with wire or plate electrodes (Table 5). It is advisable to weld thick products with short seams using a plate electrode; their manufacture is much simpler. But wire welding allows, within wide limits, by varying the mode, to change the shape of the metal pool and the nature of crystallization of the seam, and this is one of the effective factors ensuring the production of seams without hot cracks. Table 5. Typical mode of electroslag welding of high-alloy steels and alloys
| Metal thickness, mm | Electrode | Diameter, (dimensions), mm | Flux brand | Gap, mm | Electrode feed speed, m/h | Welding current strength, A | Voltage, V | Slag bath depth, mm |
| 100 100 200 200 | Wire Plate » » | 3 10X100 12X200 12X200 | ANF-7 ANF-7 ANF-1 ANF-6 | 28-32 28-32 38-40 38-40 | 330 2,4 1,9 1.9 | 600-800 1200-1300 3500-4000 1800-2000 | 40-42 24-26 22-24 26-28 | 25-35 15-20 15-20 15-20 |
However, the rigidity of the welding wire makes it difficult for long-term and reliable operation of the current supply and supply units of welding equipment. When welding in carbon dioxide, an oxidizing atmosphere is created in the arc due to the dissociation of carbon dioxide, causing increased (up to 50%) burnout of titanium and aluminum. Manganese, silicon and other alloying elements burn out less, therefore, when welding corrosion-resistant steels in carbon dioxide, welding wires containing deoxidizing and carbide-forming elements (aluminum, titanium, niobium) are used. The disadvantage of welding in carbon dioxide is the intense spattering of the metal and the formation of dense films of oxides on the surface of the weld, firmly adhered to the metal, which can reduce the corrosion resistance and heat resistance of the welded joint. To reduce the adhesion of splashes, emulsions are applied to the base metal, and to combat the oxide film, a small amount of ANF-5 fluoride flux is fed into the arc. Welding with a consumable electrode in carbon dioxide is carried out using semi-automatic and automatic machines. At the same time, for welding steel grade 12Х18Н10Тyu, Sv-07Х18Н9ТУ, Sv-08Х20Н9С2БТУ wire is recommended; for steel grades 12Х18Н12Т - wire Sv-Х25Н13БТУ, and for chromium-nickel-molybdenum steels - wire grades Sv-06Х19Н10МЗТ and Sv-06Х20Н11МЗТБ. Welding in carbon dioxide is carried out in all spatial positions, which makes it possible to mechanize welding work on structures made of high-alloy steels in installation conditions. Approximate modes of arc welding in carbon dioxide of high-alloy steels without cutting edges with a consumable electrode in carbon dioxide are given in Table. 6. Table 6. Modes of arc welding of high-alloy steels without cutting edges with a consumable electrode in carbon dioxide
| Metal thickness, mm | The seam | Wire diameter, mm | Electrode extension, mm | Urgent current strength, A | Arc voltage, V | Welding speed, m/h | Carbon dioxide consumption, l/min |
| 1 3 6 8 10 | Single-sided » Double-sided » » | 1 2 2 3 2 3 2 | 10 15 15 15 15 — 20 20 — 25 25 — 30 | 80 230-240 250-260 350-360 380-400 430-450 530-560 | 16 24-28 28-30 30-32 30-32 33-35 34-36 | 80 45-50 30 — 30 — — | 10-12 12-15 12-15 — 12-15 12-15 12-15 |
When welding in inert gases, the stability of the arc increases and the waste of alloying elements decreases, which is important when welding high-alloy steels.
Welding of austenitic steels in inert gases is performed with a non-consumable (tungsten) or consumable electrode. It is usually used for welding material up to 7 mm thick, but it is especially effective for small thicknesses (up to 1.5 mm), when burns are observed when using other methods. However, in some cases it is used when welding non-rotating butt pipes of large thickness, and welding root welds in grooves in the manufacture of particularly critical thick-walled products. Welding is carried out without filler material or with filler material using direct current of direct polarity. But when welding steel or an alloy with a high aluminum content, alternating current is used to destroy the surface film of oxides through cathode sputtering. Plasma welding is also used for high alloy steels. Its advantages are extremely low consumption of protective gas, the ability to obtain plasma jets of various cross-sections (round, rectangular, elliptical, etc.). It can be used for welding very thin metal thicknesses and for metal up to 12 mm thick. Approximate welding modes of high-alloy steels with a tungsten electrode at direct current of reverse polarity with filler wire with a diameter of 1.6 - 2.0 mm are given in Table. 7. Table 7. Modes of welding with a tungsten electrode in argon of high-alloy steels
| Metal thickness, mm | Connection type | Welding current strength, A | Argon consumption, l/min | Speed, m/h |
| Manual welding | ||||
| 1 2 3 | With flange | 35-60 65-120 100-140 | 3,5-4 5-6 6-7 | |
| 1 2 3 | Butt without groove with additive | 40-70 75-120 120-160 | 3,5-4 5-6 6-7 | |
| Automatic welding | ||||
| 1 2,5 4 | Butt without additive | 60-120 110-200 130-250 | 4 6-7 7-8 | 35-60 25-30 25-30 |
| 1 2 4 | Butt joint with additive | 80-140 140-240 200-280 | 4 6-7 7-8 | 30-60 20-30 15-30 |
Welding with a consumable electrode is carried out in inert as well as active gases or a mixture of gases. When welding high-alloy steels containing easily oxidized elements (aluminum, titanium, etc.), inert gases, mainly argon, should be used and the process should be carried out at current densities that ensure jet transfer of the electrode metal. Thus, when welding in argon, a butt joint is made on steel type 18-9 with a thickness of 5-6 mm at direct current of reverse polarity with a wire with a diameter of 1.2 mm at a welding current of 230-300 A, voltage of 16-20 V, gas flow rate of 16-20 V. 20 m/min, jet transfer of the electrode metal will take place. At the same time, the arc has high stability, and metal spattering is practically eliminated, which has a beneficial effect on the formation of seams in various spatial positions and eliminates the likelihood of the formation of corrosion centers associated with spattering when welding corrosion-resistant and heat-resistant steels. However, jet transfer in argon occurs at critical currents, when burn-throughs are possible when welding thin sheet metal. A decrease in the critical current can be achieved by adding 3-5% oxygen to argon, which reduces the likelihood of pore formation caused by hydrogen, or by using a mixture of argon with 15-20% carbon dioxide for welding, which reduces the consumption of expensive argon. But the presence of carbon dioxide can cause waste of alloying elements. An approximate mode of argon-arc butt welding with a consumable electrode of high-alloy steels in the lower position is given in Table. 8. Table 8. Mode of argon-arc butt welding with a consumable electrode of high-alloy steels
| Metal thickness, mm | Edge preparation | Number of layers | Welding wire diameter, mm | Welding power current, A | Welding speed, m/h | Argon consumption, l/min |
| Semi-automatic welding | ||||||
| 4 | Without cutting | 1 | 1,0-1,6 | 160-300 | — | 6-8 |
| 8 | V-cut | 2 | 1,6-2,0 | 240-360 | — | 11-15 |
| Automatic welding | ||||||
| 2 | Without cutting | 1 | 1 | 200-210 | 70 | 8-9 |
| 5 | V-groove at 50° angle | 1 | 1 | 260-275 | 44 | 8-9 |
| 10 | Same | 2 | 2 | 330-440 | 15-30 | 12-17 |
How and where 20x23n18 steel is used, its characteristics
Due to the fact that recently there has been a strong increase in interest in energy, and also in the technology that deals with gas turbines, heat-resistant steel is becoming popular. And there are several explanations for this. Thus, not only has interest in the industry increased recently, but also the possibility of using high temperature to manufacture some parts that have been in demand recently.
That is why heat-resistant steel is precisely the necessary discovery that allows us to produce the necessary parts at temperatures that were previously beyond the control of humans. And despite the fact that such a material is immediately exposed to high temperatures and the most unpredictable weather conditions , steel still continues to retain all its properties, which are precisely necessary for the manufacture of sought-after parts.
Classification of heat-resistant steels
Typically, heat-resistant material is used to make parts that are simply impossible to produce in any other way. First of all, we are talking about blades for engines such as gas turbines. Typically, this material goes through several operations that help produce the necessary parts.
Operations used for the manufacture of gas turbine engine parts:
- Forging.
- Grinding.
- Mechanical restoration.
- Polishing.
- Precision casting.
All these and many other technical tasks must go through the metal called steel. There are many different types of this metal, but steel 20x23n18 its characteristics prove that it is not only the most common, but also adapted to work and perform all necessary technical operations in any climatic conditions.
20 x23n18 characteristics
It is worth reading the characteristics of the metal very carefully to understand how and why such steel can be used. So, first of all, it is a metal that is resistant to heat and the hottest temperature changes . It is manufactured according to all standards, so there are no complaints about its quality. Most often it can be found at enterprises involved in mechanical engineering.
The metal contains iron and nickel, which are not afraid of heat, and oxidation resistance is provided by chromium, which is also part of steel. But there should be little chromium in the metal, otherwise such a property as heat resistance may gradually deteriorate. Steel also contains , but it is small. Approximately two tenths of a percent of carbon indicates that its increased content is harmful to the metal. Let's summarize what a metal like steel consists of.
Steel composition:
- Iron.
- Nickel.
- Chromium.
- Carbon.
- Manganese.
- Silicon.
- Phosphorus.
- Sulfur.
This metal composition allows not only to withstand extreme heat, but also not to react in any way to increased moisture content. In addition, due to the increased nickel content, we can say that steel is also a ductile metal.
How is this type of steel produced? It is simply impossible to obtain such metal at home, since special equipment is required . For example, arc furnaces, in which steel is smelted.
Welding heat-resistant steels and alloys: ensure quality fasteners
Representing a special category, heat-resistant alloys, among which austenitic materials and stainless steel are used in welding, all require careful selection of electrode brands. Correctly selected elements will help:
- The entire structure can be assembled more efficiently and accurately.
- Ensure guaranteed durability of welded fasteners without cracks or tears.
- It firmly holds not only stainless steel together, but also sublayers.
If you are interested in welding heat-resistant steels and alloys, pay special attention to the fact that stainless steel can be bonded to both low-alloy metal and unalloyed bases. By qualitatively welding layers and sublayers, craftsmen often use more advanced thermomechanical technology, covering all kinds of metal products with layers of other metals. This is called cladding, which is carried out during the assembly of: metal plates, sheets, pipes and wires.
Hot rolling or pressing cannot be used everywhere. Difficulties may arise when the process involves heat-resistant alloys or stainless steel.
Difficulties encountered during welding
Being compositions based on iron, heat-resistant steels and alloys are distinguished by a large number of alloying elements. In terms of total volume, such additives can reach a limit of 65%. In order for welding of heat-resistant stainless steel to be carried out at the highest level, it is necessary to know special nuances about working with this alloy.
Heat resistance is understood as the resistance of stainless steel to destruction processes occurring under high exposure temperatures. But this property depends not only on the selected temperature regime, but also on time factors. When a particularly strong metal or alloy is destroyed, when long-term high-temperature loading is observed, this is characterized by a diffusion nature, where dislocation creep develops.
In order to prevent creep and ensure the required level of heat resistance of stainless steel, it is customary to use several methods.
Among the main methods of preventing creep and increasing the heat resistance of iron alloys are:
- Formation of dispersed heat-resistant barriers. Such inclusions will prevent dislocations from sliding and crawling into free spaces. Both intermetallic compounds and carbides are used in the work. Heat-resistant steels are usually divided into subcategories - heterogeneous and homogeneous, which are not subject to thermal hardening, as well as those that are strengthened during heat treatment.
- The mobility of vacancies where doping is carried out, increasing the technical characteristics of the γ-solid solution with the help of tungsten, molybdenum or other elements.
Heat-resistant and heat-resistant alloys from the category of heat-resistant stainless steel and austenitic steel are not subject to transformation both when heated and when cooled.
Heat treatment is not applicable to hardening austenitic steels!
Heat resistance and increased anti-corrosion resistance of such alloys are provided by chromium. Thanks to the presence of nickel, the entire structure is stabilized, and the indicators of heat resistance, manufacturability and ductility increase. This contributes to the widespread use of austenitic steel, used as a universal structural material.
Distinguished by increased resistance to corrosion and distinguished by heat and cold resistance, austenitic alloys are used for welding not only at high and low temperatures, but also for reliable installation in aggressive environments.
Welding technology
The welding of heat-resistant steels and alloys is often carried out using arc welding, which uses tungsten electrodes and a shielding gas environment. The process of assembling structures takes place both in argon and using helium. Not only manual argon arc welding can be performed, but also a more productive method using mechanized argon arc welding, where both consumable and non-consumable electrodes are purchased in advance.
For austenitic alloys and stainless steel, it is customary to carry out automatic submerged arc welding. Steels from the austenitic category (type 18-8) are welded quite firmly and without problems.
When preparing for welding parts made of these materials, it is recommended to carry out technological operations that are applicable during preparatory operations when welding of alloy or carbon alloys is planned.
The complexity of this type of fastener is due to the pronounced tendency for cracks to accumulate in the heat-affected sector and in the weld itself, which can be accompanied by microtears. The defect can occur in alloys characterized by coarse grain macrostructures.
Welded joints of austenitic compositions are distinguished by the specificity of crystallization and present a cellular-dendritic structure. This can lead to the formation of fairly massive crystals (columnar type). In order to increase the level of resistance of welds, it is recommended, using advanced technologies, to quickly eliminate defective structures on metals and alloys. The techniques used help:
- Effectively crush crystals.
- Reduce the specific gravity of phosphorus and sulfur in the metal.
- Eliminate hot cracks when the depth of the metal being melted decreases.
For welding I use materials made from steel with electroslag remelting or vacuum smelting. In order to reduce the cracks that form, alloying additives (bromine) are increased to levels that will provide crystallites with abundant eutectic. A more universal way to reduce the formation of cracks is to modify the seams. It is performed using additives, which include alloying components. In addition to molybdenum and chromium, silicon and aluminum are used.
Steel 20x23n18: characteristics, application, types
Heat-resistant steel, which is excellent for the production of gas turbines, has recently begun to be used much more often. This is due to several reasons. The fact is that recently interest in the industrial industry has grown significantly, and methods of high-temperature processing of steel have also begun to be used quite often. Therefore, heat-resistant stainless steel 20x23n18, the characteristics of which are excellent for these purposes, has become popular.
General information about the material
If we take into account the characteristics, this steel boasts such advantages as: manufacturability of the material, increased ductility, high heat resistance. What is important is that the weldability of this metal is quite high. It is also worth noting that steel 20x23n18 belongs to the austenitic class of metal. The basis for this material is made up of two substances such as nickel and iron.
Sheet steel is made from a complex alloy and austenitic alloy. It must be highly resistant to any aggressive environmental influences. Atmospheric and soil moisture should also not have a significant effect on it. The heat-resistant steel sheet of grade 20x23n18 itself is a very multifunctional and convenient material that allows it to be used in a variety of conditions. Often used to make combustion chambers, the main requirement of which is high temperature resistance.
Steel classification
Most often, heat-resistant steels are used to produce parts that are simply impossible to obtain in any other way. One of these parts was a blade for gas turbine engines. Most often, st 20x23n18, the characteristics of which allow it to withstand high temperatures well, is ideal. Other important parts are also made from it.
In the industrial sector today, several operations are used to produce elements for gas turbine engines. These include forging, grinding, machining, polishing and precision casting. In order to go through all these stages of processing, it is necessary to use sufficiently high-quality steel.
You can use a large number of different materials, but the characteristics of steel 20x23n18 indicate that it is most profitable to use it, since it is most suitable for the job. It can also be used in almost any climatic conditions. Thanks to all these qualities, it has become the most common in this field.
This steel is very resistant to high temperatures and also withstands sudden changes in this indicator. Most often it is used in mechanical engineering factories. It is manufactured according to certain state standards, and therefore its quality is guaranteed.
Product composition
The characteristics of 20x23n18 metal are determined by its composition. High resistance to temperatures is provided by iron and nickel, which are included in the composition. Due to the presence of a certain amount of chromium in the composition, it was possible to achieve high resistance to corrosion, which makes it stainless.
Very small, but still there is carbon content in this grade of steel. It is very important to note here that exceeding 0.2% carbon in the composition already indicates that the metal is of poor quality.
In addition to the listed substances that give certain characteristics to 20x23n18 metal, there are also such as phosphorus, sulfur, and manganese.
This composition leads to the fact that it is possible to obtain not only a heat-resistant material, but also steel that tolerates moisture well. Nickel in steel indicates that the material has a certain ductility. To obtain such characteristics for 20x23n18 steel, it must be manufactured in an arc furnace. In order to obtain high-quality material of this brand as a result, it is necessary to carry out a complex production process with temperature control at each stage.
Steel production
The production of this product is quite complex. The initial stage should take place at a temperature of 1180 °C. The closer the process is to completion, the lower the temperature should be. It decreases until it reaches a limit of 900 °C. With this indicator, the operation is completed. At this point the deformation process ends and you can move on to the next stage. There are several ways to heat treat a material. The first method is heating to a temperature of 1100-1150 °C. The steel is hardened and then undergoes a cooling process in water, oil or air.
In the second method, the metal is heated to a temperature of 1160 °C and increases to 1180 °C. Afterwards you also need to cool the material in water. This will take at least four or five hours.
High-alloy heat-resistant steel 20Х23Н18
Substitute
Stainless steel grades – 20Х23Н13, 15Х25Т.
ASTM Standard: 310S AISI.
Application area
High-alloy heat-resistant steel 20Х23Н18 is used in the production of individual parts for combustion chambers, such as clamps, hangers, and fastening parts. This grade of steel is often used to produce seamless pipes, which are operated at high temperatures – up to +1100 °C.
Type of delivery
Stainless steel bars comply with GOST 5949-75, GOST 2590-71, GOST 2591-71, GOST 2879-69. Calibrated rods are made from stainless steel in accordance with GOST 7417-75, GOST 8559-75, GOST 8560-78, and ground rods - in accordance with GOST 14955-77.
Thick sheets produced from steel of this grade must comply with 7350-77, GOST 19903-74, GOST 19904-74, steel strips - GOST 4405-75, GOST 103-76, and strips - GOST 4986-79. When manufacturing forged blanks, there must be compliance with GOST 1133-71.
Chemical composition
| Chemical element | Silicon (Si), no more | Copper (Cu), no more | Manganese (Mn), no more | Nickel (Ni) | Titanium (Ti), no more | Phosphorus (P), no more | Chromium (Cr) | Sulfur (S), no more |
| % | 1.0 | 0.30 | 2.0 | 17.0-20.0 | 0.2 | 0.035 | 22.0-25.0 | 0.02 |
Mechanical properties
| Heat treatment, delivery condition | Rods. Quenching 1100-1150°C, air or water | Sheets are hot-rolled or cold-rolled. Quenching 1030-1130°C, water (transverse samples) | Cold rolled strip. Quenching 1050-1080°C, water or air | Cold rolled strip. Quenching 1050-1080°C, water or air |
| Section, mm | 60 | >4 | <0,2 | 0,2-2,0 |
| 0.2, MPa | 196 | 264 | ||
| B, MPa | 490 | 539 | 580 | 580 |
| 5, % | 35 | 35 | ||
| 4, % | 19 | 38 | ||
| , % | 50 |
Mechanical properties at elevated temperatures
| ttest, °C | B, MPa | KCU, J/m2 | 0.2, MPa | 5, % | , % |
| Rods with a diameter of 38-55 mm. Quenching 1180°C, water. Aging 800°C, 4 hours. | |||||
| 20 | 600-660 | 137-186 | 295-320 | 29-35 | 47-54 |
| 300 | 520-540 | 147-166 | 235 | 25-28 | 45-49 |
| 400 | 540 | 147-166 | 225 | 24-32 | 39-45 |
| 500 | 520-540 | 171 | 210 | 25-31 | 41-45 |
| 600 | 440 | 176 | 195 | 24 | 46 |
| 700 | 315-330 | 171 | 185-195 | 19-24 | 35 |
| 800 | 185-205 | 176 | 165 | 19-27 | 34 |
| Sample with a diameter of 10 mm and a length of 50 mm, rolled | |||||
| Deformation speed 20 mm/min. | |||||
| Strain rate 0.007 1/s. | |||||
| 800 | 255 | 215 | 24 | 67 | |
| 900 | 135 | 135 | 37 | 77 | |
| 1000 | 71 | 64 | 49 | 77 | |
| 1100 | 44 | 39 | 51 | 70 | |
| 1200 | 27 | 22 | 27 | 31 | |
Technological properties
Forging temperature
The initial temperature for forging stainless steel should be +1220 °C, and the final temperature should be about + 900 °C. If the cross-section of stainless steel is less than 350 mm, then cooling is carried out in air.
Weldability
Limited weldability.
Machinability
In the normalized and tempered state at HB 178 and B = 610 MPa, Ku b. Art. = 0.4.
Endurance limit
| Heat treatment, steel condition | Quenching 1100°C, water or air. HB 140-200 | |
| -1, MPa | 255 | 245 |
| B, MPa | 590 | 570 |
| 0.2, MPa | 290 |
Heat resistance
| Wednesday | Air | Air | Air |
| Temperature, °C | 650 | 750 | 800 |
| Test duration, h p> | 4500 | 1500 | |
| Depth, mm/year | 0,0027 | 0,01 | 0,044 |
| Strength group or score | 2 | 3 | 4 |
Physical properties
| Test temperature, °C | Modulus of normal elasticity, E, GPa | Density, kg/cm3 | Thermal conductivity coefficient W/(m °C) | Ud. electrical resistance (p, NΩ m) |
| 20 | 200 | 7900 | 14 | 1000 |
| 100 | 16 | |||
| 200 | ||||
| 300 | 182 | 19 | ||
| 400 | 176 | 7760 | ||
| 500 | 170 | 7720 | 22 | |
| 600 | 160 | 7670 | ||
| 700 | 150 | 7620 | ||
| 800 | 141 | |||
| 900 | 7540 |
| Test temperature, °C | Linear expansion coefficient (10-6 1/°С) | Specific heat capacity (C, J/(kg °C)) |
| 20-100 | 14.9 | 538 |
| 20-200 | 15.7 | |
| 20-300 | 16.6 | |
| 20-400 | 17.3 | |
| 20-500 | 17.5 | |
| 20-600 | 17.9 | |
| 20-700 | 17.9 | |
| 20-800 | ||
| 20-900 | ||
| 20-1000 |
