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Features of carbon steel welding

Carbon steels have good casting properties. They enhance its hardening qualities, have high strength and wear resistance. They are mainly used in mechanical engineering and shipbuilding for the manufacture of housings and various parts: shafts, gears, axles. Welding of such steels has a number of features. Due to the carbon content, the tendency to cracking in welded structures increases. To avoid this, special welding elements are used - UONI electrodes and SV08G2S welding wire, which allow increasing strength and improving the quality of welds.

Types of carbon steel

According to the amount of carbon contained, steels are divided into:

1. Low carbon (carbon content up to 0.25%). They have good weldability, give high-quality seams of the desired chemical composition and strong joints.
2. Medium carbon (carbon content 0.25-0.6%). With an increase in the amount of carbon, the properties of steel deteriorate, and a tendency to form cracks and pores appears. To avoid this, when welding, electrodes with a reduced carbon content (UONI electrodes) and additional alloying of the deposited metal with silicon or manganese are used. Welding wire SV08G2S is also used.

Technological features of carbon steel welding

When welding steel with a high carbon content, the following points must be considered:

• a minimum amount of carbon should pass into the seam from the base metal;
• optimal weld shape and reduction of its chemical heterogeneity;
• additional introduction of chemical elements into the weld zone that enhance its strength (calcium, manganese);
• use of low carbon electrodes.

Electrodes for welding carbon steel

Each brand of electrode or welding wire must meet certain requirements and have a specific set of properties. The main characteristics of welding electrodes are the mechanical properties of the seam, tear resistance, bending angle, impact strength and elongation of the welding arc. When choosing a specific brand, you need to consider the electrode coating:

1. The basic (carbonate and fluoride coating), which, due to the low content of gases and impurities, gives an excellent seam that is not prone to cracking.
2. Acidic (contains oxides of silicon, magnesium and iron) - the tendency to cracking is increased, the seam is not strong enough.
3. Rutile (based on titanium dioxide) - ensures stable arc burning, the metal does not splash much, the slag crust is easily separated.
4. Cellulose - has a high hydrogen content, but provides additional convenience in the welding process.

Based on site materials

Welding of carbon steel 45 has some features, accompanied by certain difficulties, due to the fact that the main alloying component in it is carbon.

Steels, in which carbon is 0.1-2.07 percent, are carbon steels. Alloys with a content of this chemical element in the range of 0.6-2.07 percent are considered high-carbon, with a carbon capacity of 0.25 to 0.6 percent - medium-carbon, and if there is less than 0.25 percent carbon in the alloy - low-carbon.

Welding of carbon steels for each of the above categories differs in the technology of its implementation. But there are also General requirements that must be observed in the process of welding:

• When using semi-automatic welding with flux-cored wire, gas welding, welding in a protective environment and welding workpieces manually with coated electrodes, welds are most often carried out by weight.
• When using automatic welding, it is necessary to choose welding methods that provide the necessary penetration of the weld root, as well as excluding material burn-through.
• Welded structures for reliable fixation of their constituent elements are recommended to be assembled using specialized tacks, various assembly devices. Tacks are usually used for semi-automatic welding in carbon dioxide protective atmosphere, and for carbon alloy steels using coated electrodes.

For various welding technologies, there are individual standards that indicate the requirements for the dimensions of welds, the procedure for preparing the edges of the welded products.

Recommendations for the use of tacks when performing welding work

• The length of the tacks is determined depending on the thickness of the metal to be welded.
• The cross-sectional area of ​​the tacks is 2.5-3 cm (approximately 1/3 of the cross-sectional area of ​​the weld).
• It is recommended to apply tacks on the reverse side of the workpiece relative to the single-pass main seam. If multi-pass welds are assumed, then the overlay is carried out on the opposite side of the first layer.
• Tacks must be thoroughly cleaned and visually inspected before starting welding. If cracks are found, they are removed without fail.

Important point! When performing welding, it is necessary to achieve complete remelting of the tacks, since there is a possibility of cracking due to fairly rapid heat removal. Cracks, in turn, can affect the quality of welding work.

Features of welding products from high-alloy steels

Welding of high-alloy steels differs from welding of low-carbon steels in a higher coefficient of linear expansion (exceeds 1.5 times), and a lower coefficient of thermal conductivity (at high temperatures it is almost 2 times less).

• An increased coefficient of expansion in the process of performing welding operations leads to significant deformations of the welded samples, with high rigidity of products to the formation of cracks (large workpieces, large metal thickness, rigid fastening of the welded elements, the absence of gaps between them).

• The low coefficient of thermal conductivity in the process of welding leads to heat concentration, respectively, the depth of penetration of the metal increases. To avoid this, it is necessary to reduce the value of the welding current by approximately 15 percent (+/-5%).

Crack formation

Steels alloyed with aluminum, unlike low-carbon steels, are more prone to cracking. Most often, hot cracks form in austenitic steels, cold cracks - in hardened martensitic, martensitic-ferritic steels. The presence of eutectic mesh along the grain boundaries makes the welds brittle.

Materials resistant to corrosion, alloyed with vanadium, not containing niobium, titanium, if heated above 500 °, lose their anti-corrosion properties. This occurs as a result of precipitation of iron, chromium carbides.

heat treatment

With the help of heat treatment (hardening is usually carried out), the anti-corrosion characteristics of the metal can be renewed. When the product is heated to a temperature of 850 degrees, the precipitated chromium carbides dissolve again in austenite, with instant cooling they no longer stand out. Such heat treatment is called stabilization, but it leads to a decrease in the value of toughness, ductility of steel.

To ensure high viscosity, corrosion resistance, plasticity of the material, it is necessary to heat it up to 1000-1150 degrees, instantly harden it (cool it in water).

Features of Friction Stir Welding Technology

The technological process of friction stir welding involves heating the parts to be joined by friction (one of the welded elements is in motion).

Operating principle

Friction welding of reinforcing steel parts involves welding, during which the mechanical energy of one of the welded elements, which is constantly moving (rotating), is converted into thermal energy. Usually, either one of the parts to be welded, or an insert between them, rotates. Metal blanks connected in this way are simultaneously pressed against each other under a set or gradually increasing pressure. Heating in this case is carried out directly at the welding site.

Basic steps in the friction welding process

• Destruction by friction of oxide films, their removal.
• Heating of the edges of the parts to be welded to a plastic state, destruction of the temporary contact.
• Extrusion of the most ductile volumes of steel from the joint.
• Stopping the movement (rotation) of the welded element, the formation of a monolithic joint.

Upon completion of the procedure for welding blanks from reinforcing steel, sedimentation occurs, an instant cessation of movement (rotation) of the connected product. The contact surfaces of the parts in the welding zone in the process of increasing the rotational speed, under compressive pressure, rub against each other.

Contact, fatty films on the connected products are destroyed. After that, the boundary friction is converted into dry friction. Separate microprotrusions begin to contact each other, respectively, deformation occurs. Juvenile zones are formed, in which the surface atoms do not have a saturated bond - metal bonds are instantly formed between them, which are instantly destroyed due to the relative motion of the surfaces.

Conclusion

Considering the complexity of the technological process of welding structures made of high-alloy steels, only professional welders should perform welding work.

Steel is an alloy of iron and carbon, which is used more than all other metals and their alloys combined. Without the use of steel structures and parts, the existence of a modern technogenic civilization is unthinkable.

A special place in modern industry is occupied by welding of low-carbon steels, as the most widely used joining method. Steel has excellent weldability - this led to the emergence of a number of methods and methods of welded joints.

Modern technologies allow to achieve high quality welding seams. Thus, welded joints almost replaced the previously used ones - riveted ones. Heavy-duty welding methods have been developed, such as underwater welding.

Definition of the concept - carbon steel

If the carbon capacity in the alloy does not exceed 2.07%, then such a material can be safely called steel . Anything above 2.14 is cast iron. An increase in the percentage of carbon in the alloy leads to an increase in its hardness and brittleness.

• Low carbon steels contain up to 0.25% carbon.
• Medium carbon steels contain from 0.25 to 0.6% carbon.
• High carbon steels contain from 0.6 to 2.07% carbon.

For the manufacture of tool alloys of increased strength, low-carbon alloy steels are used. Chromium, nickel, molybdenum, vanadium, tungsten, niobium, titanium serve as alloying additives. Minor impurities of sulfur and phosphorus, up to 0.035%, also increase the characteristics of alloys, high purity of steel is indicated by the letter "A" in the marking.

Carbon also plays an important role in the composition of steel. Thanks to him, hardening and tempering is possible, service life is increased, and hardness is increased. Such characteristics are important for the manufacture of parts of increased wear resistance of gears, sprockets, housings, center shafts, gears.

The presence of various impurities in alloys determines the use of various methods and flux additives in welding high-alloy steels. But weldability is mainly affected by the amount of carbon. The higher its percentage, the less durable the weld becomes.

Types and technologies of welding carbon steels

One of the main criteria for achieving the optimal quality of the weld is the maximum approximation of its physical and chemical characteristics to those of the base alloy. Equal strength and one-component nature of the welded steel and filler components make it possible to obtain the most durable joints.

Since the quality of weldability decreases with increasing percentage of carbon content, the main steel grades can be divided into two groups:

• Alloys with good weldability– St10, St20, 15GS, 12MH, 15HM
• Alloys with satisfactory weldability- 15G2S, 12X1MF, 15X1M1F, 12X2M1, 12X2MFSR, 12X2MFB.

To overcome the problems that arise when welding steel, welding technologies have been developed to create the necessary conditions. Below are the main directions of development on this topic.

• Arc welding

This method involves the use of an electric arc to heat the metal to a liquid state. The technology originated more than 100 years ago and during this period has taken a dominant place, almost completely replacing some types of connections, such as riveting.

The use of a high-temperature welding arc significantly narrows the required heating zone, which preserves the quality of the parts to be joined. The stability of combustion and the speed of heating the electric arc made it possible to create a number of directions in the development of welding equipment.

• Electric arc welding with consumable electrodes (MMA)

Welding occurs due to the burning of the arc between the tip of the electrode and the workpiece, while the electrode melts, filling the weld pool. To prevent oxidation of the molten metal, the electrodes are covered with a coating, which, when melted, covers the seam with a protective layer of slag. After cooling, the slag is removed by tapping.

Welding machines of this type successfully operate both from a 220 W network and from a 380 W network. Low requirements and compact dimensions of modern welding machines allow them to be used from the most inaccessible places, at high-rise objects, to household use.

The type of welding arc can be either constant or variable. DC welding machines have more functionality due to the higher characteristics of the welding arc.

For different types of welded metal, electrodes are used for welding carbon and low alloy steels. The main criterion for selecting the brand of electrodes is the formation of an equal-strength weld, without internal cracks and brittle intermetallic zones.

To perform arc welding of carbon steels with satisfactory weldability, it is advisable to use a constant welding current.

MMA welding on this moment is the most common and frequently used type of welding in general.

• Electric arc welding with a non-consumable (tungsten) electrode in an inert gas environment (TIG)

The heating of the metal with this method occurs due to the burning of the arc between the tungsten electrode and the workpiece. The filling of the weld pool with metal occurs due to the supply of filler wire directly into the melting zone.

The torch of this type of welding machine supplies argon to the heating zone. This inert gas not only protects the molten metal from oxidation, but due to its ionizing properties, it leads to stable arc burning.

Elevated Options welding characteristics allow you to perform work that requires special strength and accuracy. TIG welding is especially justified when used to join alloyed tool steels.

• Electric arc semi-automatic welding in shielding gases (MIG-MAG)

Welding occurs due to the burning of the arc between the supplied wire and the part. The wire is fed automatically and fills the weld pool. The burner is designed in such a way as to supply a protective or inert gas to the melting zone.

Semi-automatic welding, thanks to its high productivity and accuracy of welding seams, has firmly taken its place in the industry.

• Electric arc gas-plasma welding

The arc at the tip of the tungsten electrode ionizes the flow of argon atoms, which forms a plasma torch that melts the metal. Thanks to the plasma effect, a deeper penetration of steel occurs, the quality and strength of the seams increase.

Equipment for gas-plasma welding is usually produced in an industrial format. Often, these are fully automatic systems controlled exclusively by software.

• Electroslag welding

Thanks to this technology, it became possible to weld thick metal in one pass, which significantly improves the quality of the weld.

The heating of the metal occurs due to the passage of an electric arc through a conductive slag (flux). Metal electrodes are implanted into the slag layer, which, when the slag is melted, take over the current conductivity, thereby extinguishing the arc. Subsequent arcless heating occurs solely due to the resistance of the metal to the electric current.

Welding is usually carried out in the direction from the bottom up, limiting the place of welding with copper cooled sliders. This method is very convenient for filling thick joints of a non-linear configuration.

The melting of the metal is carried out by a high-temperature torch of combustible gas in a pure oxygen environment. Mixing of gases takes place in a special gas-flame burner, which is equipped with handles for controlling the intensity of the supply of a combustible mixture.

The weld pool is filled with metal thanks to the filler wire, which is fed into the melting zone.

For gas welding, not every combustible gas will be acceptable. For example, propane has impurities that oxidize the molten metal, the seam is loose and shapeless.

Gas welding technology for carbon steels involves the use of traditional acetylene or the more modern MAF.

The disadvantage of gas welding is its low productivity, increased labor costs, high cost of consumables. The development of various electric welding technologies has gradually replaced gas welding from widespread use.

The listed number of welding methods is the most popular, but far from complete. This industry is constantly evolving. There are thermite, electrolyzer, laser, chemical welding. Even the method of friction welding has found its place in certain industries. Medium-carbon and low-carbon steel grades are unlikely to lose their popularity in the foreseeable future, rather the opposite. So, the development of promising welding technologies will remain a demanded industry for a long time to come.

Introduction

Welding equipment and technology occupy one of the leading places in modern production. The hulls of giant supertankers and the retina of the human eye, miniature parts of semiconductor devices and human bones during surgical operations are welded together. Many designs of modern machines and structures, for example, space rockets, submarines, gas pipelines and oil pipelines, cannot be made without the help of welding. The development of technology makes ever new demands on production methods and, in particular, on welding technology. Today, materials are being welded that until relatively recently were considered exotic. These are titanium, niobium and beryllium alloys, molybdenum, tungsten, composite high-strength materials, ceramics, as well as all kinds of combinations of dissimilar materials. Welded parts of electronics with a thickness of several microns and parts of heavy equipment with a thickness of several meters. The conditions under which welding work is carried out are constantly becoming more difficult: you have to weld under water, at high temperatures, in a deep vacuum, with increased radiation, in weightlessness. It is not for nothing that welding has become the second technological process after assembly, tested for the first time in the world by our cosmonauts in space.

Modern technological progress in industry is inextricably linked with the improvement of welding production. Welding, as a high-performance process for the manufacture of permanent joints, is widely used in the manufacture of metallurgical, press-forge, chemical and power equipment, various pipelines, in agricultural and tractor engineering, in the production of building and other structures.

Brief information about carbon steels

Carbon steels are iron-carbon alloys containing up to 2.14% carbon (C) with a low content of other elements. They have high plasticity and are well deformed. Carbon strongly affects the properties of steel even with a slight change in its content. Carbon steels can be classified according to several parameters:

1) By quality.

2) By the method of deoxidation.

By quality

Standard quality steel

Are made in accordance with GOST 380-71. They are denoted by the letters St and conditional numbers from 0 to 6, for example: St 0, St 1, ..., St 6. The degree of deoxidation is indicated by the letters cn (calm steel), ps (semi-calm), kp (boiling), which are put at the end designations of the steel grade.

Depending on the purpose, three groups of steels of ordinary quality are distinguished: A, B and C. Only groups B and C are indicated in the grades, group A is not indicated.

Group A is supplied only in terms of mechanical properties, the chemical composition of steels in this group is not regulated, it is only indicated in the manufacturer's certificates. Steels of this group are usually used in products in the delivered state without forming and welding. The larger the number of the conditional number of steel, the higher its strength and less ductility.

Group B is supplied only with a guaranteed chemical composition. The larger the number of steel reference number, the higher the carbon content. These steels can later be subjected to deformation (forging, stamping, etc.), and in some cases, heat treatment. However, their original structure and mechanical properties are not preserved. Knowing the chemical composition of steel allows you to determine temperature regime hot working pressure and heat treatment.

Group B can be welded. They are supplied with a guaranteed chemical composition and guaranteed properties. The steels of this group are marked with the letter B and a number, for example - B StZps. This steel has the mechanical properties corresponding to its group A number, and the chemical composition to the group B number, corrected for the deoxidation method.

Quality carbon steels

This class of carbon steels is manufactured in accordance with GOST 1050-74. High-quality steels are supplied both in terms of chemical composition and mechanical properties. They are subject to more stringent requirements for the content of harmful impurities (sulfur no more than 0.04%, phosphorus no more than 0.035%).

High-quality carbon steels are marked with two-digit numbers 08, 10, 15, ..., 85, indicating the average carbon content in hundredths of a percent, indicating the degree of deoxidation (kp, ps).

High-quality steels are divided into two groups: with the usual content of manganese (up to 0.8%) and with a high content (up to 1.2%). When designating the latter, the letter G is placed at the end of the grade, for example, 60 G. Manganese increases the hardenability and strength properties, but somewhat reduces the ductility and toughness of steel.

When designating boiling or semi-calm steel, the degree of deoxidation is indicated at the end of the grade: kp, ps. In the case of calm steel, the degree of deoxidation is not indicated.

low-carbon (up to 0.25% C).

medium carbon (0.3-0.55% C).

high-carbon (0.6-0.85% C).

For critical products, high-quality steels with an even lower content of sulfur and phosphorus are used. The low content of harmful impurities in high-quality steels additionally increases the cost and complicates their production. Therefore, usually high-quality steels are not carbon, but alloy steels. When designating high-quality steels, the letter A is added at the end of the grade, for example, U10A steel.

Carbon steels containing 0.7-1.3% C are used for the manufacture of impact and cutting tools. They are labeled U7, U13, where Y means carbon steel, and the number is the carbon content in tenths of a percent.

According to the method of deoxidation

semi-calm

Calm

Contains 0.15-0.35% silicon, deoxidized by silicon, manganese.

Weldability of carbon steels

Mild steels have good weldability. Harmful impurities can reduce weldability if their content exceeds the norm.

Harmful impurities can impair weldability even at an average content that does not go out of the norm, if they form local accumulations, for example, due to segregation. Elements harmful to welding in mild steel can be carbon, phosphorus and sulfur, the latter being especially prone to segregation with the formation of local accumulations.

The contamination of the metal with gases and non-metallic inclusions can also have a negative effect on weldability. Contamination of metal with harmful impurities depends on the method of its production and can be partly judged by the marking of the metal. High quality steel welds better than regular quality steel of the corresponding grade; open-hearth steel is better than Bessemer steel, and open-hearth steel is better than boiling steel. In the manufacture of critical welded products, these differences in the weldability of low-carbon steels must be taken into account and taken into account when choosing the brand of the base metal.

Carbon steels containing more than 0.25% carbon have reduced weldability compared to low-carbon steels, and weldability gradually decreases as the carbon content increases. Steels with a high carbon content are easily hardened, which leads to hard brittle hardening structures in the weld zone and may be accompanied by the formation of cracks. With an increase in the carbon content, the tendency of the metal to overheat in the welding zone increases. An increased carbon content enhances the process of its burnout with the formation of gaseous carbon monoxide, which causes the bath to boil and can lead to significant porosity of the deposited metal.

With a carbon content of more than 0.4-0.5%, steel welding becomes one of the most difficult tasks in welding technology. Carbon steels generally have reduced weldability and, if possible, it is recommended to replace them with low-alloy structural steels, which give the same strength at a much lower carbon content due to other alloying elements. When welding carbon steels by fusion, they usually do not adhere to the correspondence of the chemical composition of the filler and base metal, striving to obtain a deposited metal of equal strength with the base metal due to alloying with manganese, silicon, etc. at a reduced carbon content.

Welding of carbon steels is often carried out with preheating and subsequent heat treatment, and, if possible, in many cases it is sought to combine heat treatment with the welding process, for example, gas welding of small parts, gas pressure welding, spot welding and butt welding. resistance welding etc.

Most low-alloy structural steels have satisfactory weldability. Due to the increased importance of welding, new grades of structural low-alloy steels are, as a rule, produced with satisfactory weldability.

Carbon structural steels include steels containing 0.1 - 0.7% carbon, which is the main alloying element in the steels of this group and determines their mechanical properties. An increase in the carbon content complicates the welding technology and the production of high-quality welded joints. In welding production, depending on the carbon content, carbon structural steels are conditionally divided into three groups: low-, medium- and high-carbon. The technology of welding steels of these groups is different.

Most welded structures are currently made from low-carbon steels containing up to 0.25% carbon.

Low-carbon steels are well-welded metals by almost all types and methods of fusion welding.

The welding technology for these steels is selected from the conditions of compliance with a set of requirements that primarily ensure the equal strength of the welded joint with the base metal and the absence of defects in the welded joint. The welded joint must be resistant to the transition to a brittle state, and the deformation of the structure must be within limits that do not affect its performance. The weld metal when welding low-carbon steel differs slightly in its composition from the base metal - the carbon content decreases and the content of manganese and silicon increases. However, ensuring equal strength in arc welding does not cause difficulties. This is achieved by increasing the cooling rate and alloying with manganese and silicon through welding consumables. The influence of the cooling rate is largely manifested in the welding of single-layer welds, as well as in the last layers of a multi-layer weld. Mechanical properties The metal of the heat-affected zone undergoes some changes compared to the properties of the base metal - for all types of arc welding, this is a slight hardening of the metal in the overheating zone. When welding aging (for example, boiling and semi-quiet) low-carbon steels in the area of ​​recrystallization of the near-weld zone, a decrease in the impact strength of the metal is possible. The metal of the heat-affected zone is embrittled more intensively in multilayer welding compared to single-layer welding. Welded mild steel structures are sometimes subjected to heat treatment. However, for structures with single-layer fillet welds and intermittent multilayer welds, all types of heat treatment, except for hardening, lead to a decrease in strength and an increase in the ductility of the weld metal. Seams made by all types and methods of fusion welding have quite satisfactory resistance to the formation of crystallization cracks due to the low carbon content. However, when welding steel with an upper limit of carbon content, crystallization cracks can appear, especially in fillet welds, the first layer of multi-layer butt welds, one-sided welds with full penetration of the edges and the first layer of a butt weld welded with a mandatory gap.

In the manufacture of low-carbon steel structures, manual welding with coated electrodes has become widespread. Depending on the requirements for the welded structure and the strength characteristics of the steel being welded, the type of electrode is selected. In recent years, electrodes of the E46T type with a rutile coating have been widely used. For particularly critical structures, electrodes with calcium fluoride and calcium fluoride-rutile coatings of the E42A type are used, which provide increased resistance of the weld metal against crystallization cracks and higher plastic properties. High-performance electrodes with iron powder in the coating and electrodes for deep penetration welding are also used. The type and polarity of the current is chosen depending on the characteristics of the electrode coating.

Despite the good weldability of low-carbon steels, sometimes special technological measures should be provided to prevent the formation of hardening structures in the near-weld zone. Therefore, when welding the first layer of a multilayer weld and fillet welds on thick metal, it is recommended to preheat it to 120-150 ° C, which ensures the resistance of the metal against the appearance of crystallization cracks. To reduce the cooling rate, before correcting defective areas, it is necessary to perform local heating up to 150 ° C, which will prevent a decrease in the plastic properties of the deposited metal.

Low-carbon gas welding steels are welded without much difficulty with a normal flame and, as a rule, without flux. Flame power with the left method is selected based on the consumption of 100-130 dm3/h of acetylene per 1 mm of metal thickness, and with the right method - 120-150 dm3/h. Highly qualified welders work with a high power flame - 150-200 dm 3 / h of acetylene, while using a filler wire of a larger diameter than in conventional welding. To obtain a joint of equal strength with the base metal when welding critical structures, a silicon-manganese welding wire should be used. The end of the wire must be immersed in a bath of molten metal. During the welding process, the welding flame must not be deflected from the pool of molten metal, as this can lead to the oxidation of the weld metal with oxygen. To seal and increase the plasticity of the deposited metal, forging and subsequent heat treatment are carried out.

The difference between medium carbon steels and low carbon steels is mainly in the different carbon content. Medium carbon steels contain 0.26 - 0.45% carbon. The increased carbon content creates additional difficulties in welding structures made of these steels. These include low resistance to crystallization cracks, the possibility of formation of low-plastic hardening structures and cracks in the near-weld zone, and the difficulty of ensuring equal strength of the weld metal with the base metal. An increase in the resistance of the weld metal against crystallization cracks is achieved by reducing the amount of carbon in the weld metal by using electrode rods and filler wire with a reduced carbon content, as well as by reducing the proportion of the base metal in the weld metal, which is achieved by welding with groove edges in modes that provide minimal penetration of the base metal and the maximum value of the weld shape factor. This is also facilitated by electrodes with a high deposition coefficient. To overcome the difficulties that arise when welding products from medium carbon steels, preliminary and concomitant heating, modification of the weld metal and two-arc welding in separate pools are performed. Manual welding of medium-carbon steels is carried out with calcium fluoride-coated electrodes of the UONI-13/55 and UONI-13/45 grades, which provide sufficient strength and high resistance of the weld metal against the formation of crystallization cracks. If high plasticity requirements are imposed on the welded joint, it is necessary to subject it to subsequent heat treatment. When welding, the imposition of wide rollers should be avoided; welding is performed with a short arc, small rollers. The transverse movements of the electrode must be replaced by longitudinal ones, the craters must be welded or brought to technological plates, since cracks can form in them.

Gas welding of medium-carbon steels is carried out with a normal or slightly carburizing flame with a power of 75-100 dm3 / h of acetylene per 1 mm of metal thickness only in the left way, which reduces overheating of the metal. For products with a thickness of more than 3 mm, general heating up to 250 - 350 ° C or local heating up to 600-650 ° C is recommended. For steels with carbon content at the upper limit, it is advisable to use special fluxes. To improve the properties of the metal, forging and heat treatment are used.

High-carbon steels include steels with a carbon content in the range of 0.46 - 0.75%. These steels are generally not suitable for the manufacture of welded structures. However, the need for welding arises when repair work. Welding is carried out with preliminary, and sometimes with concomitant heating and subsequent heat treatment. At temperatures below 5 ° C and in drafts, welding cannot be performed. Other technological methods are the same as for welding medium carbon steels. Gas welding of high-carbon steels is carried out with a normal or slightly carburizing flame with a power of 75–90 dm3/h of acetylene per 1 mm of metal thickness with heating up to 250–300 °C. The left welding method is used, which makes it possible to reduce the overheating time and the residence time of the weld pool metal in the molten state. Fluxes of the same composition as for medium carbon steels are used. After welding, the seam is forged, followed by normalization or tempering.

In recent years, heat-strengthened carbon steels have been used. Steels of increased strength allow to reduce the thickness of products. The modes and technique of welding heat-strengthened steels are the same as for ordinary carbon steel of the same composition. Welding consumables are selected taking into account the equal strength of the weld metal with the base metal. The main difficulty in welding is the softening of the area of ​​the heat-affected zone, which is heated to 400 - 700 °C. Therefore, for heat-strengthened steel, low-power welding modes are recommended, as well as welding methods with minimal heat removal to the base metal.

Steel with protective coatings is also used. The most widely used galvanized steel in the manufacture of various structures and sanitary pipelines. When welding galvanized steel, if zinc gets into the weld pool, conditions are created for the appearance of pores and cracks. Therefore, the zinc coating must be removed from the edges to be welded. Considering that traces of zinc remain on the edges, additional measures should be taken to prevent the formation of defects: in comparison with welding of ordinary steel, the gap is increased by 1.5 times, and the welding speed is reduced by 10–20%, the electrode is moved along the seam with longitudinal vibrations. At manual welding galvanized steel, the best results are obtained when working with rutile-coated electrodes, which provide a minimum silicon content in the weld metal. But other electrodes can also be used. Due to the fact that zinc fumes are extremely toxic, welding of galvanized steel can be carried out with strong local ventilation. After completion of welding work, it is necessary to apply a protective layer on the surface of the weld and restore it in the area of ​​the near-weld zone.