How and how to cut metal correctly. Heating of metal with welding current Intrinsic resistance of the part

Have you ever faced the need to cut or cut something metal with your own hands? If so, then you probably faced the question of how to do this. Of course, you can always use a good old hacksaw for metal, but what if we are talking not about a thin galvanized sheet, but, for example, a thick-walled pipe?

Here a hacksaw, of course, can help out, but a lot of effort and time will be spent. This means that a more radical approach is needed, and in this article we will talk about how to cut metal and how to do it better.

We cut metal with a grinder

It is not known for certain why this instrument was named that way. The main version is that Bulgaria was the first producer country, but in reality this is only a version.

When choosing what to cut metal, most people prefer the grinder, since, unlike gas equipment, its price is much lower, and no specific skills are needed to work with it.

On the other hand, many are very afraid to work with a grinder, because of its high power and danger. In fact, there is nothing complicated, the main thing is to strictly observe safety measures and not neglect even the smallest details.

In working with metal, there can be no trifles at all, and all metal cutting tools pose a certain danger. Safety instructions for working with a cutting tool are relevant both for large grinders with a capacity of more than two kilowatts, and for very small ones, which, despite their compact size, can cause considerable harm to health.

This tool cuts metal by rotating the abrasive disc, the thickness of which may vary depending on the metal to be cut. The thinner the wall of the steel product, the thinner the metal cutting disc will be used.

In this article, we will not talk about how important safety precautions are. This is always a priority question, but if you do not have experience with a grinder, then especially for you we will give a few subtleties that you need to know about so as not to harm your health.

Several important points

So:

For safety reasons, the rotation of the disk should occur in the direction of the cut, that is, towards the one who cuts the metal, but, as a rule, this position is not very convenient, and much easier when the flow of sparks is directed forward. In principle, there are no significant restrictions here, it all depends on the personal convenience of the tool operator.
When cutting metal, use only suitable blades. Discs for stone or wood have a lower density, and when they come into contact with a steel surface, they quickly scatter, and fragments can damage you or others.

Do not work without a protective cover. He directs sparks to the side, and they will not fly in your face. Also, he is the only salvation in case the disc bites and scatters.
Do not cut metal away from you. So it is much more likely that disc biting will occur. The direction of the cut must always be in the direction of the cutter.
Keep the tool level. Cutting at an angle will lead to curvature of the disc and its breakage, and fragments flying out at such a speed can cause significant harm to health.

Never scrape the surface with a cutting blade. For stripping, there are special discs that differ in thickness and density.
Some types of grinders use only their own branded wheels. This is due to the difference in the number of revolutions, so if you are the owner of a branded tool, use only discs under this brand.

Never use discs of any other size. Each size is designed for a tool with a certain number of revolutions. So, if you put a small or medium-sized disc on a large grinder, it will simply burst.
Don't skimp. If a crack appears on the disc, or you did not notice it when buying, immediately throw it in the trash. Accidental cracking at the time of cutting can end very badly for you. Remember, the price of a disc is not worth your life and health.

Always keep a close eye on what is ahead of you when you work. Sparks emitted from under the grinder can ignite wood, plastic, and other combustible materials. Moreover, you cannot work with a grinder near gasoline or gas.
Before cutting metal with a grinder, make sure it is correctly positioned. When cutting, the part to be cut must be in a canopy, otherwise the disc may bite.

Important! Never be afraid of an instrument, no matter how dangerous it looks or how loud it sounds. Knowing how to cut metal correctly, you are guaranteed not to get injured.

So, we figured it out with the grinder, but this is far from the only tool for cutting metal. And below we will consider other options, but for now we recommend that you watch the video in this article, which tells about cutting metals and cutting tools. In the meantime, we move on.

Other metal cutting tools

Of course, you can cut off anything with a grinder, the main thing is to choose the right disc for it. But this option is not always the most convenient and practical. Here are just a few points when it is more expedient to cut metal with another tool.

If the material is zinc coated. Due to the high speed, the grinder simply burns the coating, and no trace remains of it.

Painted material, it is also better to cut metal with scissors. They will preserve the coating and will not burn it.

It is more expedient to cut the metal with a hacksaw if it is in tension, for example, if it is a heating pipe, closed in the system circuit.

Metal with a thickness of more than 10 millimeters, it is better to cut it with a gas cutter, since the grinder may simply not be able to cope with it.

Important! We intend not to tell in this article how to cut metal with a cutter, since this requires special knowledge and experience. Never try to start the torch yourself. This could cause a propane explosion or fire.

This is not a complete list of moments when it is better to refuse to use a grinder, but all of the above situations are very common in everyday life. So what do you use for work?

Let's take a look at the most popular and affordable alternative metal cutting tools:

Gas cutter... It is difficult to call this tool affordable, but we could not ignore it, since in some cases, this is the only tool that is able to cope with the task. For example, when cutting thick metals, only a laser can be an alternative to a cutter, and such a tool is not available for domestic needs.

Hacksaw for metal... This tool, as a rule, is in the arsenal of any home craftsman. Cutting metal with a hacksaw is long and problematic, but in some hard-to-reach places it is possible to crawl only with it.

Metal scissors... Of course, you won't cut the pipe with such a tool, but if it is necessary, for example, to bite off a profile for drywall, then you simply cannot find a better option. They are simple and safe to work with, and they do not destroy zinc or paint.

Press shears... This tool is intended for cutting wire or rebar. Depending on the size, scissors can separate a bar up to 20 millimeters in diameter, and they are much more convenient to work with than a grinder.

As you can see, the choice is very rich, and the tool should be chosen depending on the specific situation. Of course, it is difficult to compete with a grinder, but it is not always possible to use it, and then alternative options will come to the rescue.

And in conclusion, I would like to remind you once again - always follow safety precautions and use personal protective equipment. No job is worth risking your health or even your life.

Heating the metal with welding current. Joule-Lenz law. Electrical resistance of the metal.

All current-carrying elements are heated by an electric current, and the amount of heat released in any section of an electric circuit with an active resistance R \u003d R (t), which is a function of t and τ at a current I \u003d I (t), depending on time t, is determined by Joule's law -Lenza:

This is a general formula that does not show or determine specific temperatures in the joint zone when it is heated by welding current.

However, it must be remembered that the value of R and I largely depends on the duration of this current.

Contact machines are constructed so that the greatest amount of heat is released between the electrodes.

Seam spot welding has the largest number of electrode-electrode sections, the total amount of resistance is the sum of the resistance electrode - part + part - part + part + electrode - part

Ree \u003d 2Red + Rdd + 2Rd

All components of the total resistance Ree are continuously changing during the thermal cycle of welding.

Contact resistance - Rdd is the largest in value, because contacting is carried out along microprotrusions and the area of \u200b\u200bphysical contact is small.

In addition, oxide films and various contaminants are present on the surface of the part.

Because we weld mainly steels and alloys with significant strength, then complete crushing of micro-irregularities occurs only when they are heated with a welding current to temperatures of about 600 degrees C

The resistance at the electrode-workpiece contact is much less than Rdd, because a softer and more highly thermally conductive material of the electrodes is actively embedded between the protrusions of microroughness of parts.

The increased resistance in the contacts is also due to the fact that there is a sharp curvature of the current line in the contact areas, which determines a higher resistance due to an increase in the current path.

Contact resistance Rdd and Red largely depends on surface cleaning for welding.

By measuring 2 plates, 3 mm thick, very strongly compressed 200N according to the ammeter-voltmeter scheme, the following values \u200b\u200bwere obtained:

Surface cleaning by grinding and grinding: 100μOhm

Conclusion: grind

In practice, they use etching (when welding large surfaces), surface treatment with metal brushes, sandblasting and shot blasting.

In resistance welding, they try to use cold-rolled steel on the surface of which there may be oil residues.

If there is no rust on the surface, then it is enough to degrease the surfaces to be welded.

The contact resistance of clean, but oxide-coated parts decreases with increasing compression forces. This is explained by the greater deformation of the microprotrusions.

We turn on the current, the highest density of the streamline is concentrated on the juvenile surfaces. The current through the contacts formed during the deformation of the microprotrusions.

At the initial moment of time, the current density in the material of the part is less, because streamlines are distributed relatively evenly, and in the part-part contact, the current flows only through the conduction zones, therefore, the current density is higher than in the bulk of the part and heat generation and heating in this area are more significant.

The metal in contact will become ductile. It deforms under the action of the welding force, the area of \u200b\u200bthe conducting contacts will increase and when t \u003d 600 degrees C (in hundredths of a second) the micro protrusions are completely deformed, the oxide films partially break down, partially diffuse into the mass of the part, and the role of the contact resistance Rdd will cease to be of primary importance in the heating process ...

However, by this time the temperature in the part-part contact area will be the highest, the material resistivity ρ is the highest, and the heat release will be more intense anyway in this zone.

With sufficient current densities for the duration of its flow, it is there that the metal begins to melt.

The appearance of a melting isotherm in the part-part contact will be promoted by the least heat removal from this area, the part's own resistance.

Intrinsic resistance of the part

S-conductor section

Coefficient A increases the spreading of the streamline into the mass of the part, while the actual spreading area increases

dk - spreading diameter

A \u003d 0.8-0.95, depends on the hardness of the material, and to a greater extent on the resistivity.

From the ratio dk / δ \u003d 3-5 A \u003d 0.8

Obviously, the resistance of the part depends on the thickness, this is taken into account by the coefficient A and on the specific electrical resistance of the material of the part ρ, it depends on the chemical composition.

In addition, the resistivity depends on temperature.

ρ (t) \u003d ρ0 * (1 + αp * T)

In the process of welding with current flow t is measured from contact to tp and above

Tm \u003d 1530 degrees C

When tmelt is reached, the resistivity increases abruptly.

αρ - temperature coefficient

αρ \u003d 0.004 1 / degC - for pure metals

αρ \u003d 0.001-0.003 1 / degC - for alloys

The αρ value decreases with an increase in the degree of ligation.

With an increase in temperature, the metal both in the contact and in the bulk under the electrodes is deformed, the contact area increases, and if the working surface of the electrodes is spherical, the contact area can increase by 1.5-2 times.

Resistance change graph during welding.

At the initial moment of time, the resistance of the part grows due to an increase in temperature and an increase in electrical resistivity, then the metal becomes plastic and the contact area begins to increase due to the pressing of electrodes into the surface of the part, as well as an increase in the size of the contact area between the part and the part.

The total resistance will decrease as the welding current is turned off. However, this is true for welding carbon and low alloy steels.

For welding creep resistant Ni and Cr alloys, the resistance may even rise.

Electric and temperature field.

The Joule-Lenz law Q \u003d IRt shows heat release in current-carrying elements, and heat removal processes also take place.

Thanks to the active cooling of the electrodes and an increase in heat removal in them, we obtain a lenticular shape of a cast core.

But such a shape is not always possible to obtain, especially when welding dissimilar materials of different thickness and thin parts.

Knowing the nature of the temperature field in the welding zone, you can analyze:

1) Dimensions of the cast core.
2) Size of HAZ (structure)
3) The magnitude of the residual stresses, i.e. properties of connections.

Temperature field is a set of temperatures at various points of the part at a certain point in time.

Points with the same temperature connected by a line are called an isotherm.

The size of a clean core on a microsection refers to the melting isotherm along the boundaries of the cast core.

Ultimately, the temperature and size of the melting isotherm, i.e. cast core, it mainly affects the resistance of the part.

Founder - Gelman, took two parts 2 + 2mm, sanded, etched and got a cast core; took the parts and got the same cast core.

However, difficulties arising in welding of dissimilar thicknesses force us to investigate the distribution of thermal fields in the welding zone.

The current density is the number of charges passing within 1 second through a small area perpendicular to the direction of movement of the charges, referred to the length of its surface.

Basic methods and methods of converting electrical energy into heat classified as follows. Distinguish between direct and indirect electrical heating.

When direct electric heating the conversion of electrical energy into heat occurs as a result of the passage of an electric current directly through the heated body or medium (metal, water, milk, soil, etc.). When indirect electric heating an electric current passes through a special heating device (heating element), from which heat is transferred to a heated body or medium through conduction, convection or radiation.

There are several types of conversion of electrical energy into heat, which determine methods of electric heating.

The flow of electric current through electrically conductive solids or liquid media is accompanied by the release of heat. According to the Joule-Lenz law, the amount of heat Q \u003d I 2 Rt, where Q is the amount of heat, J; I - silatoka, A; R is the resistance of a body or medium, Ohm; t - current flow time, s.

Resistance heating can be carried out by contact and electrode methods.

Contact method It is used for heating metals both according to the principle of direct electric heating, for example, in electric contact welding devices, and according to the principle of indirect electric heating - in heating elements.

Electrode method It is used to heat non-metallic conductive materials and media: water, milk, succulent feed, soil, etc. The heated material or medium is placed between electrodes, to which an alternating voltage is applied.

Electric, current, flowing through the material between the electrodes, heats it up. Ordinary (non-distilled) water conducts an electric current, since it always contains a certain amount of salts, alkalis or acids, which dissociate into ions, which are carriers of electric charges, that is, electric current. The nature of the electrical conductivity of milk and other liquids, soil, succulent feed, etc. is similar.

Direct electrode heating is carried out only with alternating current, since direct current causes electrolysis of the heated material and its deterioration.

Electric resistance heating has found wide application in production due to its simplicity, reliability, versatility and low cost of heating devices.

Electric arc heating

In an electric arc that occurs between two electrodes in a gaseous medium, electrical energy is converted into heat.

To ignite the arc, the electrodes connected to the power source are briefly touched and then slowly pulled apart. The resistance of the contact at the time of dilution of the electrodes is strongly heated by the current passing through it. Free electrons, constantly moving in the metal, accelerate their motion with increasing temperature at the point of contact of the electrodes.

As the temperature rises, the speed of free electrons increases so much that they break away from the metal of the electrodes and fly out into the air. When moving, they collide with air molecules and split them into positively and negatively charged ions. The air space between the electrodes is ionized and becomes electrically conductive.

Under the influence of the voltage of the source, positive ions rush to the negative pole (cathode), and negative ions - to the positive pole (anode), thereby forming a long discharge - an electric arc, accompanied by the release of heat. The arc temperature is not the same in its various parts and is at metal electrodes: at the cathode - about 2400 ° C, at the anode - about 2600 ° C, in the center of the arc - about 6000 - 7000 ° C.

Distinguish between direct and indirect electric arc heating. The main practical application is found in direct electric arc heating in electric arc welding installations. In indirect heating installations, the arc is used as a powerful source of infrared rays.

If a piece of metal is placed in an alternating magnetic field, then a variable e will be induced in it. d. s, under the action of which eddy currents will arise in the metal. The passage of these currents in the metal will cause it to heat up. This method of heating the metal is called induction. Some induction heaters are based on surface and proximity effects.

For induction heating, currents of industrial (50 Hz) and high frequency (8-10 kHz, 70-500 kHz) are used. The most widespread is the induction heating of metal bodies (parts, workpieces) in mechanical engineering and in the repair of equipment, as well as for hardening metal parts. The induction method can also be used to heat water, soil, concrete and pasteurize milk.

Dielectric heating

The physical essence of dielectric heating is as follows. In solids and liquid media with poor electrical conductivity (dielectrics), placed in a rapidly changing electric field, electrical energy is converted into heat.

Any dielectric contains electric charges connected by intermolecular forces. These charges are referred to as bonded charges as opposed to free charges in conductive materials. Under the influence of an electric field, bound charges are oriented or displaced in the direction of the field. The displacement of bound charges under the action of an external electric field is called polarization.

In an alternating electric field, there is a continuous movement of charges, and, consequently, of the intermolecular forces of molecules associated with them. The energy expended by the source to polarize the molecules of non-conductive materials is released as heat. Some non-conductive materials have a small amount of free charges, which, under the influence of an electric field, create a small conductivity current, which contributes to the release of additional heat in the material.

With dielectric heating, the material to be heated is placed between metal electrodes - capacitor plates, to which a high-frequency voltage (0.5 - 20 MHz and higher) is supplied from a special high-frequency generator. The dielectric heating unit consists of a high frequency lamp generator, a power transformer and a dryer with electrodes.

High-frequency dielectric heating is a promising heating method and is mainly used for drying and heat treatment of wood, paper, food and feed (drying grain, vegetables and fruits), pasteurization and sterilization of milk, etc.

Electron beam (electronic) heating

When a stream of electrons (electron beam), accelerated in an electric field, meets a heated body, electric energy is converted into heat. A feature of electronic heating is a high density of energy concentration, amounting to 5x10 8 kW / cm2, which is several thousand times higher than with electric arc heating. Electronic heating is used in industry for welding very small parts and smelting ultrapure metals.

In addition to the considered methods of electric heating, in production and everyday life is used infrared heating (irradiation).

If you know how to harden the metal correctly, then even at home you can increase the hardness of products made from it two to three times. The reasons why there is a need for this can be very different. Such a technological operation, in particular, is required if the metal needs to be hard enough to cut glass.

Most often, the cutting tool needs to be hardened, and heat treatment is performed not only if it is necessary to increase its hardness, but also when this characteristic needs to be reduced. When the hardness of the tool is too low, its cutting part will be jammed during operation; if it is high, the metal will crumble under the influence of mechanical stress.

Few people know that there is a simple way to check how well a steel tool is hardened, not only in production or at home, but also in the store when buying. In order to perform this check, you will need a regular file. They are guided along the cutting part of the purchased tool. If it is poorly hardened, then the file will seem to stick to its working part, and in the opposite case it will be easy to move away from the tested tool, while the hand in which the file is located will not feel any irregularities on the surface of the product.

If, nevertheless, it so happened that you have at your disposal a tool whose hardening quality does not suit you, you should not worry about this. This problem is solved quite easily: you can harden the metal even at home, without using complex equipment and special devices for this. However, you should be aware that mild steels do not lend themselves to hardening. At the same time, the hardness of carbonaceous and easy enough to increase even at home.

Technological nuances of hardening

Quenching, which is one of the types of heat treatment of metals, is performed in two stages. First, the metal is heated to a high temperature and then cooled. Different metals and even steels belonging to different categories differ from each other in their structure, therefore, the modes of performing heat treatment do not coincide.

Heat treatment of metal (quenching, tempering, etc.) may be required for:

its hardening and hardness increase;
improving its plasticity, which is necessary when processing by plastic deformation.

Many specialized companies harden steel, but the cost of these services is quite high and depends on the weight of the part that needs to be heat treated. That is why it is advisable to do this on your own, especially since you can do this even at home.

If you decide to harden the metal yourself, it is very important to carry out a procedure such as heating correctly. This process should not be accompanied by the appearance of black or blue spots on the surface of the product. The fact that the heating is proceeding correctly is evidenced by the bright red color of the metal. This process is well demonstrated in a video that will help you get an idea of \u200b\u200bhow much to heat the metal being heat treated.

As a heat source for heating to the required temperature of the metal product that needs to be hardened, you can use:

a special oven powered by electricity;
blowtorch;
an open fire that can be made in the yard of your house or in the country.

The choice of a heat source depends on the temperature to which the metal to be heat treated must be heated.

The choice of cooling method depends not only on the material, but also on the results to be achieved. If, for example, it is not necessary to harden the entire product, but only its separate section, then cooling is also carried out pointwise, for which a jet of cold water can be used.

The technological scheme according to which the metal is quenched can provide for instant, gradual or multistage cooling.

Rapid cooling, which uses the same type of coolant, is ideal for hardening steels classified as carbonaceous or alloyed. To perform such cooling, one container is needed, which can be a bucket, barrel or even an ordinary bath (it all depends on the size of the object being processed).

In the event that other categories or if, in addition to hardening, it is required to carry out tempering, a two-stage cooling scheme is used. With this scheme, the product heated to the required temperature is first cooled with water, and then placed in mineral or synthetic oil, in which further cooling takes place. Under no circumstances should an oil cooling medium be used immediately, as the oil may ignite.

In order to correctly select the hardening modes of various steel grades, one should be guided by special tables.

How to harden steel over an open fire

As mentioned above, you can harden steel at home, using an open fire for heating. Naturally, such a process should be started by making a fire, in which a lot of hot coals should form. You also need two containers. In one of them you need to pour mineral or synthetic oil, and in the other - ordinary cold water.

In order to extract the red-hot iron from the fire, you will need a blacksmith tongs, which can be replaced with any other tool of a similar purpose. After all the preparatory work has been completed, and a sufficient amount of hot coals has formed in the fire, objects that need to be hardened can be laid on them.

By the color of the formed coals, one can judge the temperature of their heating. So, the coals are more red-hot, the surface of which is bright white. It is also important to monitor the color of the fire flame, which indicates the temperature regime in its inner part. It is best if the fire flames are colored crimson rather than white. In the latter case, indicating a too high flame temperature, there is a risk of not only overheating, but even burning the metal that needs to be hardened.

The color of the heated metal must also be closely monitored. In particular, black spots must not be allowed to appear on the cutting edges of the tool being machined. The blue of the metal indicates that it has softened greatly and has become too plastic. It cannot be brought to such a state.

After the product is calcined to the required degree, you can proceed to the next stage - cooling. First of all, it is dipped into a container with oil, and this is done often (at intervals of 3 seconds) and as sharply as possible. Gradually, the intervals between these dives increase. As soon as the red-hot steel loses the brightness of its color, you can start cooling it in water.

When water-cooling a metal with hot oil droplets on its surface, care should be taken as they may flash. Shake the water after each dive to keep it cool at all times. A training video will help you get a better idea of \u200b\u200bthe rules for performing such an operation.

There are certain subtleties when cooling hardened drills. Thus, they must not be placed flat in a container with a coolant. If you do this, the bottom of the drill or any other elongated metal object will cool sharply first, which will cause it to shrink. That is why it is necessary to immerse such products in the coolant from the wider end.

For heat treatment of special grades of steel and smelting of non-ferrous metals, the capabilities of an open fire will not be enough, since it will not be able to heat the metal to a temperature of 700-9000. For such purposes, it is necessary to use special furnaces, which can be muffle or electric. If it is quite difficult and costly to make an electric oven at home, then with muffle-type heating equipment this is quite feasible.

Self-made chamber for metal hardening

A muffle furnace, which is quite possible to make yourself at home, allows you to harden various grades of steel. The main component that will be required to make this heating device is refractory clay. The layer of such clay, which will cover the inside of the oven, should be no more than 1 cm.

The scheme of the metal hardening chamber: 1 - nichrome wire; 2 - inner part of the chamber; 3 - outer part of the chamber; 4 - back wall with spiral leads

In order to give the future furnace the required configuration and the desired dimensions, it is best to make a form of cardboard impregnated with paraffin, on which refractory clay will be applied. Clay, mixed with water to a thick, homogeneous mass, is applied to the seamy side of the cardboard form, from which it will lag behind itself after complete drying. Metal products heated in such a device are placed in it through a special door, which is also made of refractory clay.

After drying in the open air, the chamber and the door of the device are additionally dried at a temperature of 100 °. After that, they are fired in an oven, the temperature in the chamber of which is gradually brought to 900 °. When they have cooled down after firing, they must be carefully connected to each other using locksmith tools and emery cloth.

A nichrome wire is wound onto the surface of a fully formed chamber, the diameter of which should be 0.75 mm. The first and last layers of such winding must be twisted together. When winding the wire onto the chamber, a certain distance should be left between its turns, which must also be filled with refractory clay in order to exclude the possibility of a short circuit. After the layer of clay applied to provide insulation between the turns of the nichrome wire has dried, another layer of clay is applied to the surface of the chamber, the thickness of which should be approximately 12 cm.

After complete drying, the finished camera is placed in a metal case, and the gaps between them are covered with asbestos chips. In order to provide access to the inner chamber, doors are hung on the metal body of the furnace, finished from the inside with ceramic tiles. All existing gaps between structural elements are sealed using refractory clay and asbestos chips.

The ends of the nichrome winding of the chamber, to which it is necessary to supply electrical power, are removed from the rear side of its metal frame. To control the processes occurring in the inner part of the muffle furnace, as well as to measure the temperature in it with a thermocouple, two holes must be made in its front part, the diameters of which should be 1 and 2 cm, respectively. From the front of the frame, such holes will be closed with special steel curtains. The homemade design, the manufacture of which is described above, allows you to harden locksmith and cutting tools, working elements of stamping equipment, etc. at home.

The steel hardening process allows increasing the product hardness by about 3-4 times. Many manufacturers carry out a similar process at the time of production, but in some cases it must be repeated, since the hardness of steel or other alloy has a low level. That is why many are wondering how to harden metal at home?

Methodology

In order to carry out work on steel hardening, you need to take into account how such a process is performed correctly. Hardening is the process of increasing the hardness of the surface of iron or alloy, which involves heating the sample to a high temperature and then cooling it. Despite the fact that at first glance the process under consideration is simple, various groups of metals differ in their own structure and characteristics.

Heat treatment at home is justified in the following cases:

If necessary, harden the material, for example at the cutting edge. An example is the hardening of chisels and chisels.
If necessary, increase the plasticity of the object. This is often necessary in the case of hot forging.

Professional steel hardening is an expensive process. The cost of 1 kg of surface hardness increase costs about 200 rubles. It is possible to organize hardening of steel at home only taking into account all the features of increasing the surface hardness.

Process features

Steel hardening can be carried out taking into account the following points:

Heating should be uniform. Only in this case is the structure of the material homogeneous.
Heating of the steel should take place without the formation of black or blue spots, which indicates a strong overheating of the surface.
The sample should not be heated to an extreme state, since the structural changes will be irreversible.
The bright red color of the metal indicates the correctness of the heating of the steel.
Cooling must also be carried out evenly, for which a water bath is used.

Equipment and features of the process

Special equipment is often used to heat the surface. This is due to the fact that it is rather difficult to heat the steel to the melting point. The following equipment is often used at home:

electric oven;
blowtorch;
thermal oven;
a large fire that is lined around to redirect the heat.

When choosing a source of heat, it should be borne in mind that the part must be completely placed in the oven or fire on which heating is carried out. It will be correct to select equipment also according to the type of metal that will be processed. The higher the strength of the structure, the more the alloy is heated to impart ductility.

In the case when only a part of the part needs to be hardened, jet hardening is used. It provides for the ingress of a jet of cold oxen only on a certain part of the part.

A tub of water or a barrel, as well as a bucket, is often used to cool steel. It is important to take into account the fact that in some cases, stage-by-stage cooling is carried out, in others it is fast and abrupt.

Increasing hardness over an open fire

In everyday life, quenching is often carried out over an open fire. This method is only suitable for a one-time surface hardening process.

All work can be divided into several stages:

for a start, you should make a fire;
at the time of making a fire, two large containers are prepared, which will correspond to the size of the part;
in order for the fire to give more heat, you need to provide a large amount of coals. they give a lot of heat for a long time;
one container must contain water, the other must contain engine oil;
special tools should be used to hold the hot part being processed. in the video you can often find blacksmith tongs, which are most effective;
after preparing the necessary tools, place the object in the very center of the flame. in this case, the part can be buried deep in the coals, which will ensure the heating of the metal to a fusible state;
coals that are bright white are hotter than others. the process of metal melting must be monitored closely. the flame should be crimson, but not white. if the fire is white, then there is a possibility of overheating the metal. in this case, the performance deteriorates significantly, and the service life is reduced;
the correct color, uniform over the entire surface, determines the uniformity of metal heating;
if it darkens to a blue color, then this indicates a strong softening of the metal, that is, it becomes excessively plastic. this should not be allowed, since the structure is significantly violated;
when the metal is fully heated, it should be removed from the high temperature center;
after that, the hot metal should be placed in a container with oil with a frequency of 3 seconds;
the final stage is the immersion of the part in water. In this case, the water is periodically shaken. This is due to the fact that the water quickly heats up around the product.

Care should be taken when performing work, as hot oil can harm the skin. On the video, you can pay attention to what color the surface should be when the desired degree of plasticity is achieved. But for the hardening of non-ferrous metals, it is often necessary to exert an effect of temperatures in the range of 700 to 900 degrees Celsius. It is practically impossible to heat non-ferrous alloys on an open fire, since it is impossible to reach such a temperature without special equipment. An example would be the use of an electric oven that is capable of heating surfaces up to 800 degrees Celsius.