How to heat metal to red. How to harden metal yourself at home. Electric and temperature field

Heat treatment of metals is one of the main ways to improve their mechanical and physico-chemical characteristics: hardness, strength, and others.

One type of heat treatment is hardening. It has been successfully used by man in an artisanal way since ancient times. In the Middle Ages, this method of heat treatment was used to improve the strength and hardness of metal household items: axes, sickles, saws, knives, as well as military weapons in the form of spears, sabers and others.

And now they use this method to improve the characteristics of the metal, not only on an industrial scale, but also at home, mainly for hardening metal household items.

Hardening is understood as a type of heat treatment of a metal, consisting of heating it to a temperature at which a change in the structure of the crystal lattice occurs (polymorphic transformation) and further accelerated cooling in water or an oil medium. The purpose of this heat treatment is to increase the hardness of the metal.

Hardening is also used, at which the heating temperature of the metal does not allow polymorphic transformation to take place. In this case, its state is fixed, which is characteristic of the metal at the heating temperature. This state is called a supersaturated solid solution.

Polymorphic transformation hardening technology is mainly used for steel alloy products. Non-ferrous metals are subjected to hardening without achieving a polymorphic change.

After such processing, steel alloys become harder, but at the same time they acquire increased brittleness, losing ductility.

To reduce unwanted brittleness after polymorph heating, a heat treatment called tempering is applied. It is carried out at a lower temperature with a gradual further cooling of the metal. In this way, the stress of the metal after the hardening process is removed, and its fragility is reduced.

When quenching without polymorphic transformation, there is no problem with excessive brittleness, but the hardness of the alloy does not reach the required value, therefore, during repeated heat treatment, called aging, on the contrary, it is increased due to the decomposition of a supersaturated solid solution.

Features of steel hardening

Mainly stainless steel products and alloys intended for their manufacture are hardened. They have a martensitic structure and are characterized by increased hardness, leading to the fragility of products.

If heat treatment of such products is carried out with heating to a certain temperature, followed by rapid tempering, then an increase in viscosity can be achieved. This will allow the use of such products in various fields.

Types of steel hardening

Depending on the purpose of stainless products, it is possible to harden the entire object or only that part of it, which must be working and have increased strength characteristics.

Therefore, the hardening of stainless products is divided into two methods: global and local.

Cooling medium

Achieving the required properties of stainless materials largely depends on the choice of their cooling method.

Different grades of stainless steels undergo cooling in different ways. If low-alloy steels are cooled in water or its solutions, then for stainless alloys for these purposes, oil solutions are used.

Important: When choosing a medium in which the metal is cooled after heating, it should be borne in mind that cooling in water is faster than in oil! For example, water at 18°C can cool an alloy by 600°C in a second, but oil by only 150°C.

In order to obtain high hardness of the metal, cooling is carried out in a flow cold water. Also, to increase the quenching effect, a brine solution is prepared for cooling by adding about 10% sodium chloride to the water, or an acidic medium is used in which at least 10% acid (usually sulfuric acid) is used.

In addition to the choice of the cooling medium, the mode and speed of cooling are also important. The rate of temperature decrease must be at least 150°C per second. Thus, in 3 seconds the temperature of the alloy should drop to 300°C. A further decrease in temperature can be carried out at any rate, since the structure fixed as a result of rapid cooling at low temperatures will no longer collapse.

Important: Too fast cooling of the metal leads to its excessive brittleness! This should be taken into account when self-hardening.

There are the following cooling methods:

Using one medium, when the product is placed in a liquid and kept there until completely cooled.
Cooling in two liquid media: oil and water (or salt solution) for stainless steels. Products made of carbon steels are first cooled in water, since it is a rapidly cooling medium, and then in oil.
The jet method, when the part is cooled with a jet of water. This is very convenient when you want to harden a specific area of the product.
The method of stepwise cooling in compliance with temperature conditions.

Temperature regime

Correct temperature regime hardening of stainless products is important condition their qualities. For achievement good performance they are evenly heated to 750-850°C, and then quickly cooled to a temperature of 400-450°C.

Important: Heating the metal above the recrystallization point leads to a coarse-grained structure that worsens its properties: excessive brittleness, leading to cracking!

To relieve stress after heating to the desired metal hardening temperature, stage-by-stage cooling of products is sometimes used, gradually lowering the temperature at each stage of heating. This technology allows you to completely remove internal stresses and get a durable product with the desired hardness.

How to harden metal at home

Using basic knowledge, you can harden steel at home. Metal heating is usually carried out using a fire, electric muffle furnaces or burners using gas.

Tempering an ax on a fire and in a furnace

If additional strength is required household tools, for example, to make an ax more durable, then the easiest way to harden it can be done at home.

Axes are stamped during manufacture, by which you can recognize the grade of steel. We will consider the hardening process using the U7 tool steel as an example.

The technology must be carried out in compliance with the following rules:

1. Annealing. Before processing, dull the sharp edge of the blade and place the ax in a burning brick oven to heat. The heat treatment procedure must be carefully monitored to prevent overheating (permissible heating 720-780°C). More advanced masters recognize the temperature by the color of heat.

And beginners can find out the temperature with a magnet. If the magnet no longer sticks to the metal, then the ax has heated up over 768 ° C (red-burgundy color) and it's time to cool down.

With a poker, move a red-hot ax to the furnace door, remove the heat deep into, close the door and valve, leave the heated metal in the furnace for 10 hours. Let the ax gradually cool down with the stove.

2. Steel hardening. Heat the ax on a fire, potbelly stove or stove to a dark red color - temperature 800-830 ° C (the magnet has stopped magnetizing, wait another 2-3 minutes).

Hardening is carried out in heated water (30°C) and oil. Lower the ax blade into the water by 3-4 cm, moving it intensively.

3. Ax blade release. Tempering reduces the brittleness of steel and relieves internal stress. Sand the metal with sandpaper to better distinguish the colors of the whiteness.

Keep the ax for 1 hour in the oven, at a temperature of 270-320°C. After exposure, take out and cool in the air.

Video: heat treatment of an ax at home, three stages: annealing, hardening, tempering.

Knife hardening

It is advisable to use furnaces independently for hardening metals. For household items in the form of knives, axes, and others, the most suitable are muffle furnaces small size. In them, it is possible to achieve a hardening temperature much higher than on a fire and it is easier to achieve uniform heating of the metal.

Such an oven can be made independently. On the Internet you can find many simple options her designs. These ovens can be heated metal product up to 700-900°C.

Consider how to harden a stainless steel knife at home using a muffle electric furnace. For cooling, instead of water or oil, melted sealing wax is used (you can get it in a military unit).

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

Here, a hacksaw, of course, can help out, but a disproportionate amount of time and effort will be spent. And this means that a more radical approach is needed, and in this article we will talk about how to cut metal and what is the best way to do it.

We cut metal with a grinder

It is not known for certain why this instrument was so named. The main version is that Bulgaria was the first producing country, but in fact this is just a version.

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

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

In working with metal, there can be no trifles at all, and the whole cutting tool metal poses a certain danger. The safety instructions for working with a cutting tool are relevant both for large angle grinders with a power 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 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.

We will not talk about the importance of safety in this article. This is always a priority issue, 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.

A few important points

So:

For safety reasons, the rotation of the disk should occur in the direction of the cut, that is, in the direction of the one who cuts the metal, but, as a rule, this position is not very convenient, and it is 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 appropriate discs. Discs on stone or wood have a lower density, and upon contact with a steel surface, they quickly scatter, and fragments can damage you or others.

Don't work without protective cover. It directs the sparks to the side, and they will not fly in your face. Also, it is the only salvation in case the disc bites and shatters.
Do not cut metal away from you. So it is much more likely that a disk bite will occur. The direction of the cut must always be in the direction of the cutter.
Keep the tool straight. Cutting at an angle will cause the disc to warp and break, and fragments flying out at such a speed can cause significant harm to health.

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

Never use discs of a different size. Each size is designed for a tool with a certain number of revolutions. So, if you put a disk of small or medium size on a large grinder, it will simply burst.
Don't save. If a crack appears on the disc, or you did not notice it when buying, immediately throw it into 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 at the time of work. Sparks flying out from under the grinder can ignite wood, plastic, and other combustible materials. Moreover, you can’t work as a grinder near gasoline or gas.
Before cutting metal with a grinder, make sure it is properly positioned. When cutting, the cut off part must be overhanging, otherwise the disc may be bitten.

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

So, we figured out 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 talks about cutting metals and cutting tools. And in the meantime, we're moving on.

Other metal cutting tools

Of course, you can cut anything with a grinder, the main thing is to choose the right disk for it. But this option is not always the most convenient and practical. Here are just a few moments 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 there is not a trace of it left.

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

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

Metal with a thickness of more than 10 millimeters, it is better to cut with a gas cutter, as a 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. Under no circumstances should you try to start the cutting torch yourself. This could result in a propane explosion or fire.

This is far from full list moments when it is better to refuse to use a grinder, but all of the situations listed 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:

Cutting torch . It is difficult to call this tool affordable, but we could not leave it unattended, 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 master. Cutting metal with a hacksaw is long and problematic, but in some hard-to-reach places it is possible to crawl only to her.

Metal shears. Of course, you won’t cut the pipe with such a tool, but if you need, for example, to bite off a drywall profile, then better option just can't be found. They are easy and safe to work with and will not attack zinc or paint.

Press scissors. This tool is designed for cutting wire or rebar. Depending on the size, scissors can cut a bar with a diameter of up to 20 millimeters, and it is much more convenient to work with them than with 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.

The process of hardening steel allows you to increase the hardness of the product 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 the steel or other alloy is low. That is why many are wondering how to harden metal at home?

Methodology

In order to carry out work on hardening steel, it is necessary to take into account how such a process is performed correctly. Hardening is the process of increasing the hardness of the surface of an iron or alloy, which involves heating the sample to high temperature and its subsequent cooling. Despite the fact that at first glance the process under consideration is simple, various groups metals differ in their peculiar 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 hardening of steel is an expensive process. The cost of 1 kg of increasing the surface hardness 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

It is possible to carry out hardening of steel, taking into account the following points:

Heating must be even. Only in this case the structure of the material is homogeneous.
Heating of steel should take place without the formation of black or blue spots, which indicates a strong overheating of the surface.
The sample must not be heated to the extreme state, since the changes in the structure 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 quite difficult to heat steel to the melting point. At home, the following equipment is often used:

electric furnace;
blowtorch;
thermal furnace;
a large bonfire that is built around to redirect the heat.

When choosing a source of heat, one should take into account the fact that the part must be completely placed in the furnace 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 plasticity.

In the case when it is necessary to harden only part of the part, jet hardening is used. It provides for a jet of cold water to hit only a certain part of the part.

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

Increasing hardness on an open fire

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

All work can be divided into several stages:

first you need to make a fire;
at the time of making a fire, two large containers are prepared that will correspond to the size of the part;
in order for the fire to give more heat, you need to provide a large number of coals. they give a lot of heat for a long time;
one container should contain water, the other - engine oil;
special tools should be used with which the hot workpiece will be held. on the video you can often find blacksmith tongs, which are most effective;
after preparation necessary tools you should put the object in the very center of the flame. at the same time, it is possible to bury the part in the very depths of the coals, which will ensure that the metal is heated to a melting state;
embers that have bright White color- hotter than others. the process of melting metal must be monitored closely. the flame should be crimson, but not white. if the fire is white, then there is a possibility of overheating of the metal. in this case, the performance is significantly degraded, and the service life is reduced;
the correct color, uniform over the entire surface, determines the uniformity of heating of the metal;
if darkening occurs of blue color, then this indicates a strong softening of the metal, that is, it becomes excessively ductile. this should not be allowed, since the structure is significantly violated;
when the metal is fully heated, it should be removed from the hotbed;
after that, the red-hot metal should be placed in a container with oil with a frequency of 3 seconds;
the final stage can be called immersion of the part in water. At the same time, shaking of water is periodically carried out. This is due to the fact that the water quickly heats up around the product.

When performing work, attention should be paid to caution, as hot oil can harm the skin. In the video, you can pay attention to what color the surface should be when the desired degree of plasticity is reached. But for hardening non-ferrous metals, it is often necessary to exert a temperature 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 is the use of an electric furnace, which is capable of heating the surface up to 800 degrees Celsius.