The presence of carbon in the composition of steels of this type increases the possibility of tempering and hardening, which is why the material acquires better wear resistance and hardness. Such properties make it possible to manufacture axle shafts, sprockets, equipment frames, gears and other elements in which such parameters are important. But often welding is the only way to produce parts and repair them.

This technology for carbon steels has some problems because there is carbon in the material. It causes the possibility of cracks appearing both in the seam itself and in the heat-affected zone, as well as non-plastic formations. Carbon negatively affects the stability of the seam, this is also facilitated by harmful impurities of the material - sulfur and phosphorus. Today it is customary to consider this procedure separately for each group of material: welding technology for medium carbon steels, high carbon and low carbon.

Main problems and methods for their solution

The concept of "critical carbon content in a weld" was formed. Quantitative indicators depend on the following parameters:

• features of the nodal design;
• weld configuration;
• the presence of chemical elements in the weld;
• preheating of the zone of the future weld.

Methods for stopping the risks of crack formation consider the following actions:

• limiting chemical elements that increase the risk of cracking;
• reduction of stresses that contribute to the formation of defects;
• in the process of welding, the most homogeneous seam of an optimized shape with a normal composition is formed.

Non-ductile structures, which also tend to form during the welding process of carbon steels, increase the risk of cracking under loads. The risks of their occurrence are solved by eliminating the factors that contribute to their formation.

It is imperative that carbon steel products be cleaned of rust, scale, dirt, oil inclusions and other foreign matter before welding. The work area and at least 10 millimeters of the near-weld section are subject to cleaning. These elements can be sources of hydrogen, which will cause the formation of cracks and pores in the seam. This forms a smooth transition and structural strength to loads.

Features of steel welding

Features of welding carbon steels are usually considered by material groups:

Selection of electrodes

When welding carbon steels, it is necessary to take into account not only the characteristics of a particular material, but also its interaction with various types of electrodes. The latter have a variety of properties, and work with them is regulated by various requirements. It is important to choose the right electrode, adequate steel grade. Since there are more than 2 thousand grades of carbon steels, a large number of electrodes are also produced for them. There are electrodes for welding low carbon steels and high carbon iron alloys and so on. When making a choice, you should use the following criteria:

• choose electrodes designed only for carbon steels;
• choose products that reduce the hydrogen content;
• it is better if the product characterizes good re-ignition of the arc;
• the electrode must ensure minimal splashing of the liquid metal.

By following these rules, you form a guaranteed optimal result of welding work on carbon steels.

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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 spatter 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

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 is currently 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.

Increased parameters of 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.

The melting point of carbon steel is 1535°C. Most often, argon-arc welding with a non-consumable electrode is used to weld steels used in thermal power engineering.

Carbon and low alloy steels

DIFFICULTY IN WELDING. Basic - it is difficult to avoid the formation of pores due to insufficient deoxidation of the base metal. The means of combating pore formation is to reduce the proportion of the base metal in the deposited weld metal

Preparation for welding. For cutting steels, as well as preparing edges, gas, plasma or air-arc cutting is used. After it, the areas of metal heating are cleaned with a cutting or abrasive tool until traces of heat treatment are removed. Immediately before assembling the joint, the edges are cleaned to a width of 20 mm to a metallic sheen and degreased.

Joints are assembled in assembly conductors or with the help of tacks, which are performed with full penetration and their remelting when applying the main seam. Tacks with unacceptable defects should be removed mechanically. It is not recommended to apply tacks to the ceiling sections of the seam, since there they are more difficult to melt when making the main seam. On steels 10 and 20, tacking is performed only with filler wire. Its surface must be clean, free of scale, rust and dirt. The wire can be cleaned both mechanically and by chemical etching in a 5% hydrochloric acid solution.

1-5 - the order of installation of tacks A, B - output strips for starting and finishing welding

Select mode options. Welding is carried out on a direct current of direct polarity. Welding current is assigned: for single-pass welding - depending on the thickness of the structure, and for multi-pass welding - based on the height of the seam. The height of the seam (bead) for manual argon-arc welding should be 2-2.5 mm. Approximately the welding current is selected at the rate of 30-35 A per 1 mm of the diameter of the tungsten electrode.

The arc voltage should be as low as possible, which corresponds to short arc welding.

The welding speed is chosen taking into account the guaranteed penetration of the edges and the formation of the required convexity of the weld.

Welding technique. When performing the first (root) weld, welding without filler wire is possible, but all tack welds must be melted. Structural carbon steel grades 10 and 20 cannot be welded without filler wire, as pores may appear in the weld metal. Welding is carried out at an angle forward. The filler wire is fed towards the movement of the burner, and the angle between them should be 90 °. Sudden movements with the wire should be avoided - they will lead to splashing of the filler metal or oxidation of the end of the wire.

The additive must always be in the argon protection zone.

The root seam is welded without transverse vibrations. When applying subsequent layers, the burner performs oscillatory movements, the amplitude of which depends on the shape of the cutting edges.

In the absence of a system for smoothly reducing the welding current, the weld crater is welded by introducing a drop of filler metal into the crater, while smoothly increasing the arc to its natural break. The gas shield is removed by retracting the burner 10-15 s after the arc breaks.

WELDING MODES FOR LOW CARBON AND LOW ALLOY STEELS

The most consumed metal in the world is steel, in fact steel is not a metal, but an alloy of iron and carbon. At the moment, the total amount of steel produced in the world exceeds one and a half billion tons per year. Steels are divided into carbon and alloyed, alloyed differ in that during the production process, various elements are added to the steel (for example, nickel to increase corrosion resistance, manganese to increase strength characteristics, and so on), giving it special properties. Carbon steels are most often used for welding, there are low-carbon steels containing less than 0.3% carbon, they lend themselves well to any welding, medium-carbon steels with a content of 0.3 to 0.6% lend themselves to the welding process worse, but stronger, but less ductile, high-carbon steels are the strongest, but have a small relative elongation, and are the worst to be welded. They differ in carbon content, and, consequently, in chemical and physical properties.

Low carbon steel belongs to a large group of structural steels. The carbon content in it is not more than 0.3%, due to such a low percentage, it has the following properties:

• High plasticity and elasticity;
• It lends itself well to the welding process;
• High impact strength.

This brand has found wide application in construction due to the fact that it is very easy to weld, since there is very little carbon in its structure, which has a bad effect on the welding process, since fragile structures and porosity can form in the metal seam, which then lead to breakage. Also, due to its high softness, parts are made from it by cold stamping.

Welding of carbon steels

It is possible to weld absolutely all grades of steel. However, each type of metal has its own technology for welding. The technology for welding carbon steels must meet the requirements, which include:

• Uniform distribution of the strength of the seam along the entire length;
• The absence of weld defects, the seams should not have various cracks, pores, rifling, and so on;
• The dimensions and geometric shape of the seam must be made in accordance with the standards prescribed in the relevant GOST 5264-80;
• Vibration stability of the welded structure;
• The use of electrodes with a reduced content of hydrogen and carbon, which can have a negative impact on the quality of the weld;
• The structure must be strong and rigid.

Thus, the technology should be as efficient as possible, that is, give the highest process productivity while ensuring high strength and reliability.

The mechanical properties of the weld metal and the welded joint are completely dependent on the microstructure, which is the chemical composition, and is also determined by the welding mode and heat treatment, which is carried out both before and after welding.

Low carbon steel: welding technology

As mentioned above, low carbon steels lend themselves best to the welding process. They can be welded using oxy-acetylene flame gas welding without additional fluxes. Metal wires are used as an additive. Hydrogen, which is capable of forming pores, can adversely affect the welding process. To prevent this problem, it is recommended to carry out the welding process with a filler metal containing a small amount of carbon.

After the welding process has been carried out, the structure must be thermally treated in order to improve the mechanical properties - ductility and strength will be the same. Heat treatment of welded structures is carried out by the normalization operation, which consists in heating the product to a certain temperature, approximately 400 degrees, holding and further cooling in air. As a result, the structure is equalized, carbon in the form of cementite in the metal diffuses into the grains, due to which the structure becomes uniform.

Gas welding is carried out in the presence of argon, which creates a neutral environment. Structures that are welded in an argon environment have a more responsible purpose.

Welding of low carbon steels can be done manually, arc welding of such material requires the correct choice of electrode. When choosing an electrode, the following factors must be taken into account, due to which a uniform weld structure without defects is ensured. Before carrying out the welding process, it is necessary to ignite the electrodes in order to prepare them for further work, remove hydrogen. Welding of low-carbon iron alloys must be accurate and fast, and metal parts must be prepared before starting the process.

Welding of medium carbon

The procedure for welding steel parts with medium carbon content, from 0.3% to 0.55%, is more difficult compared to low carbon, since more carbon can adversely affect the weld. Carbon reduces the cold brittleness limit - that is, destruction at low temperatures, increases strength and hardness, but reduces the ductility of the seam.

For welding, electrodes with a reduced carbon content are used, which provide a strong connection.

Welding of high carbon steels

Steels with a high percentage of carbon content, from 0.6% to 0.85%, are very difficult to weld. Gas welding cannot be used in this case, since in the process carbon burns out in large quantities and hardening structures are formed that degrade the quality of the seam. It is best to use arc welding in this case.

Requirements

When welding carbon steels, in order to achieve maximum parameters, the following requirements must be observed:

• Welded electrodes and wires should have a low percentage of carbon to avoid unnecessary defects;
• It is necessary to ensure that carbon from the metal does not pass into the weld under the action of high temperature; for this, a wire is used for welding steels with an average carbon content and higher, for example, Forte E71T-1, Bars-71. These types are excellent for welding steels with a carbon content above 0.3%;
• When carrying out the welding process, fluxes should be added that contribute to the formation of refractory formations;
• Reduce the chemical heterogeneity of the weld by subsequent heat treatment;
• Reduce the hydrogen content by baking the electrodes, using electrodes with a low hydrogen content, and so on.

Peculiarities

The following features of the welding of carbon steels should also be noted:

• Before carrying out this operation, it is necessary to thoroughly clean the welded material from rust, mechanical irregularities, dirt, scale. These contaminants contribute to the formation of cracks in the weld;
• It is necessary to cool welding structures made of carbon steels slowly, in air, so that the structure normalizes;
• When carrying out the welding process, critical parts need preheating, up to about 400 degrees, with the help of heating, the required strength of the seam will be ensured, and in this case, welding can be carried out in several approaches.

Thus, the welding process of carbon steels depends mainly on their carbon content. Therefore, it is necessary to consider what content and choose the right technological scheme in order to obtain a high-quality durable product that can last a long time.