What is metal hardening

What is cold-worked aluminum?

Aluminum sheet is a semi-finished product that is made from aluminum or its alloys by hot deformation and further cold rolling.

For the production of sheets, modern manufacturers use different grades of technical aluminum, in particular: A0, AD0, A5, A6, duralumin alloys of grades D1, D12, D16, wrought alloys AD31, aluminum-manganese and aluminum-magnesium - AMts and AMg, respectively. To increase corrosion resistance, sheets of most alloys are coated with a film of high-purity aluminum using cladding (layering). Its thickness is up to 5 percent of the total thickness of the workpiece.

Characteristics of aluminum sheets

It is characterized by high anti-corrosion properties, low weight, and ease of machining. All these qualities make it a worthy competitor to analogues of stainless steel rolled metal.

According to some characteristics, sheet aluminum even occupies a leading position, combining ductility and resistance to low temperatures, as well as chemical inertness.

The material lends itself well to stamping, thanks to which three-dimensional products are formed from it through significant plastic deformation. By stamping sheet aluminum, dishes, some machine parts and much more are produced.

Rolled sheets for general and special purposes are manufactured in accordance with GOST 21631-76:

- chem. the composition of grade A5 is determined by GOST 11069-74;

— according to GOST 1131-76 it is controlled by chemicals. composition of VD1;

— the chemical composition of rolled sheets of technical grades of aluminum is determined according to GOST 4784-97.

Advantages of aluminum sheets:

- light weight;

— high electrical and thermal conductivity;

— pliability to any type of processing;

— high corrosion resistance;

- non-toxic;

— immunity to magnetization;

- bactericidal properties.

The only significant drawback of this range is the low strength of sheet aluminum, but to increase this indicator, copper and magnesium additives are introduced into the metal at the production stage.

Thickness and weight of aluminum sheets

The thickness of aluminum sheets most often ranges from 0.3 millimeters to 10.5 millimeters. The most popular dimensions are: 1200x3000 and 4000, 1500x3000 and 4000 millimeters.

The weight of an aluminum sheet is controlled by GOST 21631-76 and depends not only on its thickness and dimensions, but also on the composition of the alloy. The weight of a rolled aluminum sheet can range from 2.8 to 180 kilograms. If the product is of non-standard size, naturally, the weight will be different, depending on the size. For example, the weight of rolled aluminum sheets 10x1500x6000 millimeters is 247.5 kilograms.

Types of aluminum sheets

Aluminum sheets differ not only in the use of various grades of alloys, production method, but also in the method of additional processing. According to the condition of the material, the following types can be distinguished:

— annealed sheet (M);

— cold-worked (H);

— semi-hardened (H2);

— refined (P);

— naturally aged and hardened (T);

- without heat treatment.

Also, aluminum sheets are distinguished by standard size - increased and normal thickness accuracy, which is indicated in the marking by the letter “P”. And according to the production method: aluminum sheet with technological (B), normal plating (A) and without plating.

Depending on the type of surface, sheet aluminum can be: standard, anti-slip, profiled, perforated, corrugated foil.

Standard Aluminum Sheet (General and Special Purpose)

Standard rolled products have a smooth surface with a raised, high or regular finish. It is mainly used for the production of stainless steel structures used in the fuel, food and chemical industries, construction, and mechanical engineering. It is made of aluminum and its alloys of the following grades: A5, 1105, AD, AMg1, AMg3, A6M, AMg2, AMg5, AMts, AMg6, AD1, VD1, D16 and others.

Aluminum sheet A5

The A5 food sheet has a matte surface, a thickness of 0.5 to 10 millimeters, and a standard finishing quality. The chemical composition of A5 grade aluminum corresponds to GOST 11069-74. A5 aluminum sheet can be purchased in rolls and sheets.

Characterized by high thermal conductivity and corrosion resistance. Due to its high plastic properties, rolled metal of grade A5 is easily formed in different ways and processed. The material welds well.

At low temperatures, the technical characteristics remain virtually unchanged.

Based on the state of the metal, aluminum sheets are divided into hard-worked (A5H) and soft or annealed (A5M).

Heat treatment has a significant impact on the physical and mechanical properties and changes the structure of the alloy. A5M aluminum sheets acquire ductility and malleability as a result of annealing; products are easier to cut.

In order to partially restore hardness, the metal is subjected to rolling with 2-5% compression - tempering.

High-strength aluminum sheets A5H are produced by cold working, but this reduces impact strength and ductility.

A5 sheets are used in various industries for the production of structures and equipment. They are used to make food containers, cladding, and decorative elements.

Aluminum sheet A6M

Annealed aluminum sheet A6M is manufactured in accordance with GOST 21631-76, suitable for use in the food industry. The composition of A6 aluminum is controlled by GOST 11069-74.

Aluminum sheet 1105

Rolled aluminum 1105 is a flat product made of wrought aluminum with alloying additives of magnesium and copper. Dural is indicated by the first two digits (11), and the serial number of the alloy is indicated by the last.

Welded structures and parts that are operated at low temperatures are made from sheet aluminum 1105.

The products are characterized by high fracture toughness, ductility, and are easy to machine.

Aluminum sheet 1105N is cold-worked steel strengthened by plastic deformation. Properties and structure change under the influence of pressure on its surface. As a result, impact strength and ductility are reduced, and strength and hardness are increased. Cold-worked aluminum sheet with normal cladding is distinguished by significant indicators of chemical passivity and is marked 1105AN.

Depending on the requirements for the finished product, thicker cladding can be used, which will significantly affect the security of the material.

Aluminum sheet 1105M is a ductile, malleable and soft sheet metal product, annealed at high temperatures. Rolling on a rolling mill with 2-5% reduction (training) helps to partially restore hardness. An aluminum sheet with a thickened cladding layer is marked 1105UM, and with a normal one - 1105AM. Characterized by increased stability in aggressive operating conditions.

Aluminum sheet 1105T is a naturally aged, hardened aluminum range that is in demand in many industries. With normal plating it is designated 1105AT.

Aluminum Sheet AD

It is characterized by high ductility and resistance to corrosion. The material used for the production of sheets is technical aluminum with a low content of impurities. It is divided into soft (ADM) and cold-worked (ADN). AD aluminum sheet is widely in demand as a semi-finished product in many industries.

Sheet aluminum AD1

Available in rolls and sheets. Manufactured from aluminum grade AD1 in accordance with GOST 21631-76, chemical composition in accordance with GOST 4784-74. They are characterized by ease of molding and machining, and high resistance to corrosion processes. Digital marking determines the purity of the alloy as a percentage, and letter marking indicates the deformable metal.

According to the condition of the material, AD1 aluminum sheet is usually classified into AD1M (soft) and AD1N (cold-hardened). A sheet hardened to one half is marked as AD1N2. It combines high mechanical and strength properties. Soft and cold-worked products are used for the production of capacitors, decorative finishes, containers in the chemical industry, and various types of parts.

Aluminum sheet AMg1

Magnesium alloyed wrought alloy. The number determines the amount of the main alloying additive, in this case 1% magnesium. Characterized by excellent weldability, ductility, and corrosion resistance. Used for the manufacture of industrial parts and structures in construction. There are soft and cold-worked sheets AMg1.

Aluminum sheet AMg2

Its characteristics are similar to AMg1, but contains 2% magnesium. Good for cutting. A distinction is made between cold-worked, annealed and semi-hardened rolled metal AMg2. Aluminum sheets AMg2NR are produced from refined and cold-worked alloy. Due to the low content of foreign impurities, semi-finished products have good electrical conductivity.

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The surface is unclad, grooved or matte.

Annealed and cold-worked aluminum sheets AMg2 are used to make truck skins, hydraulic equipment, chemical tanks that operate under pressure, industrial pipelines, transport parts and various building structures.

Source: https://varimtutru.com/nagartovannyy-alyuminiy-chto-eto/

Traducción - cold rolling - de ingles -

  • 321 Sendzimir mill Metallurgy: Sendzimir mill, Sendzimir mill Universal English-Russian Dictionary > Sendzimir mill
  • 322 corrugation [ˌkɒrə'geɪʃ(ə)n]1) General vocabulary: waviness, pothole, wrinkle, corrugation, fold, wrinkling, pothole, wrinkle 2) Technique: corrugation, boxiness, ring corrugation of rigidity 3) Construction: flute, bead, waves for rigidity, ribs for rigidity, corrugation, bump4) Automotive term: pothole of the road surface5) Road engineering: buckling 6) Forestry: formation of a wavy road surface7) Metallurgy: buckling Printing: corrugation8) 11) Tengizchevroil: pothole 12) Gas turbines: corrugation Universal English-Russian dictionary > corrugation
  • 323 rolling oil English-Russian combinatory dictionary > rolling oil
  • 324 Sendzimir mill English-Russian dictionary of metal rolling > Sendzimir mill
  • 325 double-reduced tinplate English-Russian Dictionary of Metal Rolling > double-reduced tinplate
  • 326 double-reduced tinplate ROLLING OF METALLS TERMS TNT No. 108 New terms dictionary > double-reduced tinplate
  • 327 thermomechanical treatment deformation-heat treatment DTO A set of operations of hot pressure treatment and heat treatment of steels and alloys, combined in one continuous technological cycle, for example, in a hot rolling mill line. DTO differs in that the density of crystal lattice defects, which increases as a result of plastic deformation, is inherited in one form or another by the metal structure formed during subsequent cooling. Therefore, DHT provides a higher level of strength properties of the metal, and also significantly reduces the energy intensity of its production. With all the variety of DTT, three main types are distinguished (in relation to steel processing): thermomechanical high-temperature and low-temperature processing, including deformation of austenite at t - fpp of austenite and subsequent quenching and tempering; hot rolling of a predominantly thick sheet with the end of austenite deformation with large single reductions at ? < / kr and subsequent uncontrolled (in air) or regulated accelerated cooling, hot rolling with the end of austenite deformation above (or slightly below) t and subsequent accelerated (up to 25-50 °C/s) cooling, mainly to obtain a fine-grained metal structure .[https://metaltrade.ru/abc/a.htm]
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EN

  • thermomechanical treatment

mechanical-thermal treatment
MTO Processing of steels and alloys, combining two methods of hardening - phase transformations as a result of heat treatment and cold plasticity. deformation (hardening), i.e. carrying out these technological operations in the reverse order than during TMT.

Thus, a small deformation of steel with a martensite structure by 3-5% (due to its reduced ductility) makes it possible to further increase its strength characteristics by 10-20% while reducing plastic properties and impact toughness. MHT of steel, including hardening to martensite, slight plastic deformation mainly under conditions close to uniform compression, and low tempering, has found industrial application.

MTO is sometimes called marforming (martensite is subjected to deformation) in contrast to austenite forming (AMF), when austenite is deformed. MTO is also widely used in the production of semi-finished products from aging copper, aluminum and austenitic alloys, which are first subjected to conventional supersaturated solid solution quenching and then cold deformation before aging. For example, MHT of beryllium bronze increases its yield strength by 20%.

Long semi-finished products (profiles, panels, pipes, strips) made of aluminum alloys after hardening are subjected to straightening with tension with a degree of deformation of 1-3%, and subsequent aging, which increases the yield strength by ~ 50 MPa.

[https://metaltrade.ru/abc/a.htm]

Cold-worked metal is

The task of strengthening the surface layer of a metal product is quite relevant in many cases, because most machine parts and various mechanisms operate under the influence of significant mechanical loads. This problem can be solved by both cold hardening and cold hardening, which, despite their similarity, still have certain differences.

In production, the problem of hardening metal surfaces is solved using special equipment

The essence of cold hardening and cold hardening

Metal hardening is one of the ways to harden a metal product. This occurs due to plastic deformation, which such a product is subjected to at a temperature below the recrystallization temperature.

Deformation during cold hardening leads to changes in both the internal structure and the phase composition of the metal. As a result of such changes in the crystal lattice, defects appear that appear on the surface of the deformed product.

Naturally, these processes also lead to changes in the mechanical characteristics of the metal. In particular, the following happens to him:

  • increases hardness and strength;
  • ductility and toughness decrease, as well as resistance to deformations of the opposite sign;
  • corrosion resistance deteriorates.

The hardening of a metal surface can be assessed by changes in microhardness, which decreases with distance from the surface

The phenomenon of hardening, if it relates to ferromagnetic materials (for example, iron), leads to the fact that the value of a parameter such as coercive force increases in the metal, and its magnetic permeability decreases.

If the work-hardened area was formed as a result of slight deformation, then the residual induction that characterizes the material decreases, and if the degree of deformation is increased, then the value of this parameter increases sharply.

Among the positive consequences of cold hardening, it should be noted that with its help it is possible to significantly improve the performance characteristics of more ductile metals that create significant friction during use.

The hardened layer on the surface of a metal product can be formed either intentionally, in which case such a process is useful, or unintentionally, in which case it is considered harmful.

Most often, unintentional surface hardening of a metal product occurs during cutting, when significant pressure is applied to the metal being processed from the cutting tool.

Hardening (hardening) during cutting

An increase in strength leads to the fact that the metal surface becomes more brittle, which is a very undesirable consequence of processing.

If the formation of cold hardening can occur as a result of both conscious and unconscious actions, then cold hardening is always performed specifically and is, in fact, a full-fledged technological operation, the purpose of which is to surface harden the metal.

Deformation compaction of the edge of this valve occurred as a result of operation, which means ˜ is work hardening

Types of cold hardening

There are two main types of cold hardening, which differ in the processes that occur during its formation in the material.

If new phases in the metal, characterized by a different specific volume, are formed as a result of phase changes, then this phenomenon is called phase hardening.

If the changes that occurred in the crystal lattice of the metal occurred due to the influence of external forces, they are called strain hardening.

Deformation hardening, in turn, can be centrifugal ball or shot peening. To perform cold hardening of the first type, the surface to be treated is impacted by balls, initially located in the internal sockets of a special rim.

When the rim rotates (which is performed as close as possible to the surface being processed), the balls, under the influence of centrifugal force, are thrown to its periphery and have an impact on the part.

The formation of hardening in shot blasting plants occurs due to the impact on the surface being treated of a flow of pellets moving through the internal chamber of such equipment at a speed of up to 70 m/s.

Cast iron, steel or ceramic balls can be used as such pellets, the diameter of which can be 0.4–2 mm, for hardening.

Scheme of traditional strain hardening and graph of increasing material hardness

In order to understand why cold hardening or cold hardening leads to hardening of the metal, you should understand the processes that occur in the material when performing such procedures. During cold plastic deformation, which occurs under the influence of a load whose magnitude exceeds the yield strength of the metal, stresses arise in its internal structure.

Thus, the metal will become stronger or, as experts say, will go into a hard-worked state.

Even one pair of moving defect lines formed in a crystal lattice can lead to the formation of more and more similar locations, which ultimately increases the yield strength of the material.

Change in the structure of the surface layer as a result of cold deformation

The internal structure of the metal, when it is deformed during cold hardening or hardening, undergoes serious changes. In particular, the configuration of the crystal lattice is distorted, and the spatial position of crystals, which are randomly oriented, is ordered.

This ordering leads to the fact that the axes of the crystals, in which they have maximum strength, are located along the direction of deformation. The more active the deformation is, the more crystals will take on a similar spatial position.

There is a misconception that the grains that make up the internal structure of the metal are crushed when it is deformed. In fact, they are only deformed, and their surface area remains unchanged.

From all of the above, we can conclude that during the process of cold hardening or cold hardening, the crystal structure of steel or other metal changes, as a result, the material becomes harder and stronger, but at the same time more brittle. Work-worked steel is therefore a material that has been specifically subjected to plastic deformation to improve its strength characteristics.

Hardening and equipment for it

Cold hardening of steel products is especially important in cases where there is a need to increase their resistance to surface cracking, as well as to prevent fatigue processes from occurring in it. Industries in which cold-worked products have proven themselves particularly well include aircraft and automotive manufacturing, oil production, oil refining and construction.

Industrial shot blasting machine for pipe processing

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Methods of metal hardening, such as controlled cold hardening or cold hardening, can be implemented using various equipment, the quality and functionality of which determines the result of the operations performed.

Equipment for hardening of products made of steel or other alloys, which today is represented by a wide variety of models, can be general purpose or special - in order to process parts of a certain type (bolts, springs, etc.).

On an industrial scale, cold hardening is performed on automated devices, all operating modes of which are established and controlled through the use of electronic systems. In particular, on such machines, both the quantity and the feed rate of the shot used to perform the processing are automatically adjusted.

Shot blasting machine for processing sheet and profile metal products

Hardening, in which the process of its formation is controlled, is used in cases where a steel product cannot be strengthened by heat treatment.

In addition to cold hardening and cold hardening, other methods of cold plastic deformation can also increase the strength of the surface layer of a metal product.

This includes, in particular, drawing, knurling, cold rolling, shot blasting, etc.

In addition to steel, the carbon content of which should not exceed 0.25%, this method of hardening is necessary for copper products, as well as some aluminum alloys. Stainless steel tape is also often subjected to cold hardening. Cold-worked tape is used in cases where ordinary stainless steel tape is not able to cope with the perceived loads.

Source: https://steelfactoryrus.com/nagartovannyy-metall-eto/

Cold hardening and cold hardening: features and differences between types of metal hardening

The task of strengthening the surface layer of a metal product is quite relevant in many cases, because most machine parts and various mechanisms operate under the influence of significant mechanical loads. This problem can be solved by both cold hardening and cold hardening, which, despite their similarity, still have certain differences.

In production, the problem of hardening metal surfaces is solved using special equipment

Cold-worked steel is

In the Russian-language technical literature, there is a certain confusion in the definition and application of the terms “hardening” and “hardening” . Most often, these terms are identified, used one instead of the other, or both at once. Usually cold hardening (hardening) refers to both the physical process of changing the crystalline structure of a metal during its plastic deformation, and the result of this process, that is, an increase in the strength and hardness of the metal.

The essence of metal hardening

Metals and their alloys, including aluminum and its alloys, have a crystalline structure and consist of a large number of grains. These grains have irregular shapes and different sizes. In each grain, the atoms are ordered, but adjacent grains are oriented differently relative to each other. During cold deformation, the grain structure changes due to grain fragmentation, atomic movement, and distortion of the atomic lattice.

When a material is subjected to mechanical stress, microscopic defects known as dislocations form in its crystal structure. If the loads continue to increase, these dislocations begin to move and interact with each other.

In this way they form a new internal structure that resists further plastic deformation. This structure increases the yield strength of the material, that is, its ability to resist applied forces. In this case, the plastic properties of the material are reduced.

One of the most well-known ways to intentionally create cold hardening is cold forming of parts and products.

Reduction of metal density during cold hardening

When a metal is hardened, its density decreases. This occurs because plastic deformation leads to disruption of the order in the arrangement of atoms, an increase in the density of defects and the formation of micropores. A decrease in density means an increase in specific volume - the volume of a unit of mass.

Residual stresses during work hardening

The outer riveted layer tends to expand, but the inner layers “do not allow it” - compressive residual stresses arise in it. These stresses can be very useful, as they can slow down the initiation and growth of surface fatigue cracks.

Useful hardening

Hardening can be desirable and undesirable, useful and harmful. If hardening of a metal is useful, then in its manufacture they tend to use cold plastic deformation operations: cold rolling, drawing, shot processing, tumbling, rolling, and the like.

This is especially important for metals and alloys that are not capable of thermal hardening. These materials include low-carbon steels, some aluminum alloys, and pure copper.

When these materials are subjected to compression, drawing, bending or forging, the stresses that arise lead to the appearance of dislocations in the crystal structure, which strengthen the metal. In this case, both terms are used: cold hardening and hardening.

Standards on cold hardening and work hardening

Domestic, still Soviet, standards - GOSTs - apply only the term “hard-worked” to usefully “cold-worked” metal products, for example, sheets of aluminum alloys and do not use the words “cold-hardened” or “cold-hardened” at all. You can see this, for example, in GOST 21631 for sheets of aluminum and aluminum alloys: “hard-worked sheets”, “semi-hardened sheets”.

Harmful hardening

Undesirable, harmful hardening occurs, for example, when ductile and soft metals and alloys are subjected to mechanical cutting. Excessively deep cuts in one pass at high speed can lead to intense hardening with an undesirable increase in the strength of the metal and its embrittlement.

 This prevents further machining of the part and can lead to damage to the cutting tools. Another example of harmful work hardening is repeated loading of a part beyond the yield strength of the material. Under such loading, the material in critical sections can quickly harden, lose its ductility and collapse.

In such cases, the phenomenon of strain hardening is called work hardening, but is never called work hardening.

When is “hardening” and when is “hardening”?

Taking into account the above, we draw two “bold” but natural conclusions.

Hardening is any manifestation of strain hardening of crystalline materials - useful and harmful , intentional and unintentional .

Cold hardening refers only to useful strain hardening of products, which deliberately applied to products in order to increase their strength properties. Sometimes, perhaps not intentionally, but always consciously.

Cold plastic deformation

Cold plastic deformation of metals is considered to be plastic deformation at a certain temperature, after which hardening occurs in the metal and it remains unchanged for an indefinitely long time.

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Scientifically, it sounds like this: the cold deformation temperature to achieve the cold hardening effect of a metal must be lower than its recrystallization temperature, that is, the temperature at which new, undeformed and rounded grains of metal begin to appear and grow in place of old, deformed and elongated grains. grains

Typically this temperature is half the absolute melting temperature of that metal or alloy. However, in practice, cold hardening of metals is carried out at room temperature or at a temperature not exceeding a third of the melting point.

Hot deformation of metals

In contrast to cold deformation, hot deformation of metals and alloys occurs at a temperature sufficient for recrystallization of the deformed metal structure to occur simultaneously with plastic deformation.

Typically, hot deformation processing (pressure processing) is carried out at a temperature above the recrystallization temperature of the metal (usually from 70 to 90% of the absolute melting temperature).

After such hot treatment, a metal with a favorable fine-grained recrystallized structure is obtained.

Source: https://respect-kovka.com/nagartovannaya-stal-eto/

Cold hardening and cold hardening

In order to increase the strength and hardness of materials, they are subjected to heat treatment: they are heated and kept in a thermal oven and cooled. But this method is not always suitable. In particular, it is not used for metals such as copper and aluminum.

Then cold hardening is used - a technological treatment that involves changing the shape of the product through cold plastic deformation. At the same time, the hardness and strength of the material increases, but its ductility - the ability to deform without destruction - decreases.

For some alloys, cold hardening is the only possible way to increase strength.
Such alloys, for example, include corrosion-resistant alloys of chromium and nickel. The study of a process such as cold hardening (hardening of metal) is one of the important and interesting problems of materials science.

For example, as a result of cold hardening, the hardness of the surface layers of steel increases several times.

The terms cold hardening and cold hardening are often considered almost synonymous, meaning:

  • the process of changing the structure of the material;
  • increasing its hardness and strength as a result of these changes.

But in some literary sources these terms are distinguished: cold hardening is a process that can be either spontaneous or purposeful, while cold hardening is a deliberate process, the purpose of which is to strengthen the metal.

From this point of view, cold hardening can be a process both useful and harmful, and cold hardening is a process that can only be useful.

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As the temperature increases, the cold hardening ability decreases noticeably. For example, cold hardening of aluminum is impossible at temperatures above 200 °C. This temperature (recrystallization temperature) will be different for different substances. For low-melting metals (including zinc, lead, tin), the recrystallization temperature can be negative.

  • Process description
  • Types of hardening
  • Hardening equipment
  • Application

Process description

Let us consider the essence of the phenomenon of cold hardening. As you know, almost all metals and their alloys (for example, aluminum or copper and their alloys) have an ordered crystalline structure. But everything is not so simple. They consist of grains, within which the arrangement of atoms is ordered. But the grains themselves are located chaotically in relation to each other, that is, disordered.

Under mechanical load, dislocations (microscopic defects) appear in the structure of the substance. As the load increases, dislocations move and interact with each other. Another structure is formed. It resists the deformation that remains after the load is removed (plastic deformation). The ability of the metal to resist deformation increases.

But it should be borne in mind that with cold hardening, the plastic properties of the material become worse. For example, the ductility of low-carbon steel decreases by 5-6 times. The resistance to plastic deformation also decreases when its sign changes (the so-called Bauschinger effect).

After hardening, the state of the substance is thermodynamically unstable. If ductility needs to be increased, hardening is removed by recrystallization annealing, heating the material above the recrystallization temperature. In this case, the material goes into a more stable state. The need to remove hardening arises, for example, in metallurgy during the production of wire or tape.

The dislocation density increases during work hardening, which leads to a decrease in bulk density. In this case, the metal grains are stretched in the direction of the forces that act on them. This grain orientation is called deformation texture. Due to texture, anisotropy of the mechanical properties of metals and alloys occurs.

The following conclusions can be drawn:

  • after cold hardening or hardening, the hardness and strength of the material increases;
  • The fragility of the material also increases.

In particular, cold hardening of steel is relevant for products in which it is necessary to prevent surface cracking and such phenomena as metal fatigue, which leads to the accumulation of internal stresses, the occurrence of cracks, and ultimately to the destruction of the material.

Types of hardening

Basically, there are two types of cold hardening:

  • phase, when changes in the crystal lattice are caused by phase changes;
  • deformation, when lattice changes are caused by external forces.

The formation of deformation hardening occurs when the surface being treated is exposed to balls or a stream of pellets.

Hardening equipment

Equipment for the process of cold hardening of aluminum and other metals and alloys is quite diverse. In industry, cold hardening is a fully automated process that is performed on electronically controlled devices.

In particular, when deformation hardening is formed, the number and feed rate of pellets is automatically adjusted.

Application

In industry, cold hardening is used to impart strength to products made of stainless steel, copper, aluminum and its alloys. This is very important for mechanical engineering, since various components and mechanisms often operate in unfavorable conditions and wear out over time.

Cold-worked stainless steel wire has increased hardness and rigidity and is resistant to temperature fluctuations. This wire is used in mechanical engineering in the manufacture of parts for various types of cars. It is also widely used for making very strong ropes, cables and springs. Hardening is also often used for the production of stainless steel strips.

Electrical wires made from cold-worked wire are not subject to corrosion and have a long service life.

Also, cold-worked wire can serve as a material for stainless mesh, from which partitions are made.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/naklep.html

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    The task of strengthening the surface layer of a metal product is quite relevant in many cases, because most machine parts and various mechanisms operate under the influence of significant mechanical loads. This problem can be solved by both cold hardening and cold hardening, which, despite their similarity, still have certain differences. In production, the problem of hardening metal surfaces is solved using special equipment

    Cold-worked steel is a metalworker's guide

    Most common metals cannot be strengthened by heat treatment. However, almost all metals are strengthened—to some degree—by forging, rolling, or bending. This is called cold hardening or hardening of metal.

    Annealing is a type of heat treatment to soften metal that has become hardened so that it can continue to be cold worked.

    Cold working: copper, lead and aluminum

    Ordinary metals vary greatly in their degree and rate of strain hardening - cold hardening or cold hardening. Copper is hardened quite quickly as a result of cold forging, and, therefore, quickly reduces its malleability and ductility. Therefore, copper requires frequent annealing so that it can be processed further without the risk of destruction.

    On the other hand, lead can be hammered into almost any shape without annealing or risk of breaking it. Lead has such a reserve of ductility that allows it to obtain large plastic deformations with a very low degree of strain hardening. However, although copper is harder than lead, it is generally more malleable.

    Aluminum can withstand quite a large amount of plastic deformation through hammer forming or cold rolling before it needs to be annealed to restore its ductile properties. Pure aluminum hardens much more slowly than copper, and some sheet aluminum alloys are too hard or brittle to allow much hardening.

    Cold working of iron and steel

    Industrial pure iron can be cold worked to large degrees of deformation before it becomes too hard for further processing.

    Impurities in iron or steel impair the cold workability of the metal to such an extent that most steels cannot be cold worked, except of course special low carbon steels for the automotive industry.

    At the same time, almost all steel can be successfully processed plastically in a red-hot state.

    Why is metal annealing necessary?

    The exact nature of the annealing process to which the metal is subjected depends largely on the purpose of the annealed metal. There is a significant difference in the method of annealing between annealing in factories where huge quantities of sheet steel are produced, and annealing in a small auto repair shop, where only one part requires such processing.

    In short, cold working is plastic deformation by destruction or distortion of the grain structure of the metal.

    During annealing, a metal or alloy is heated to a temperature at which recrystallization occurs - the formation of new grains - not deformed and round - instead of old - deformed and elongated - grains. Then the metal is cooled at a given speed.

    In other words, crystals or grains within the metal that have been displaced or deformed during cold plastic working are given the opportunity to realign and recover to their natural state, but at an elevated annealing temperature.

    Annealing of iron and steel

    Iron and mild steels must be heated to temperatures of around 900 degrees Celsius and then allowed to cool slowly to ensure they are as "soft" as possible. At the same time, measures are taken to prevent contact of the metal with air in order to avoid oxidation of its surface. When this is done in a small auto repair shop, warm sand is used for this.

    High carbon steels require similar processing except that the annealing temperature for them is lower and is about 800 degrees Celsius.

    Annealing of copper

    Copper is annealed at about 550 degrees Celsius, when the copper is heated to a deep red color. Once heated, the copper is cooled in water or allowed to cool slowly in air. The cooling rate of copper after heating at the annealing temperature does not affect the degree of “softness” of this metal obtained. The advantage of rapid cooling is that it cleans the metal of scale and dirt.

     Annealing aluminum

    Aluminum is annealed at a temperature of 350 degrees Celsius. In factories this is done in suitable ovens or salt baths. In the workshop, aluminum is annealed with a gas torch. They say that in this case a wooden splinter is rubbed over the surface of heated metal.

    When the wood begins to leave black marks, it means that the aluminum has received its annealing. Sometimes a bar of soap is used instead of wood: when the soap begins to leave brown marks, the heating should be stopped.

    The aluminum is then cooled in water or left to cool in air.

    Annealing of zinc

    Zinc becomes malleable again at temperatures between 100 and 150 degrees Celsius. This means that it can be annealed in boiling water. Zinc must be processed while it is hot: when it cools, it loses much of its malleability.

    Source: https://ssk2121.com/nagartovannaya-stal-eto/

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