Tool hardening at home. Metal hardening at home: hardening steel correctly. When do they use an electric oven?

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

One of the types of heat treatment is hardening. It has been successfully used by man in a handicraft 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 of improving the characteristics of metal, not only on an industrial scale, but also at home, mainly for hardening metal household items.

Quenching 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.

Quenching is also used, at which the heating temperature of the metal does not allow the 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.

Quenching technology with polymorphic transformation is used mainly for steel alloy products. Non-ferrous metals are quenched without achieving polymorphic changes.

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

To reduce unwanted embrittlement after polymorphic 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, it is, on the contrary, increased due to the decomposition of a supersaturated solid solution.

Features of steel hardening

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

If such products are heat treated 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 steel products, it is possible to temper the entire object or only that part of it, which should be working and have increased strength characteristics.

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

Cooling medium

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

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

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

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

In addition to the choice of the cooling medium, the mode and rate of cooling are important. The rate of temperature decrease must be at least 150 ° C per second. Thus, in 3 seconds, the alloy temperature 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 fragility! 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 it is completely cooled.
Cooling in two liquid media: oil and water (or brine) for stainless steels. Products made of carbon steel are first cooled in water, since it is a fast cooling medium, and then in oil.
By jet method, when the part is cooled by a jet of water. This is very convenient when you need to harden a specific area of the product.
By the method of stepwise cooling in compliance with temperature conditions.

Temperature regime

The correct temperature regime for hardening stainless products is an important condition for their quality. To achieve good characteristics, they are uniformly 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, sometimes stage-by-stage cooling of products is used, gradually lowering the temperature at each of the heating stages. This technology allows you to completely remove internal stresses and obtain a durable product with the required hardness.

How to temper metal at home

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

Hardening the ax at the stake and in the furnace

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

During the manufacture of axes, a stamp is put by which you can recognize the grade of steel. We will consider the hardening process using the example of U7 tool steel.

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

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

And for beginners, the temperature can be found out with the help of a magnet. If the magnet stops sticking 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 the red-hot ax to the oven door, remove the heat inward, close the door and latch, leave the heated metal in the oven for 10 hours. Let the ax cool down gradually with the stove.

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

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

3. Letting go of the ax blade... Tempering reduces the brittleness of the steel and relieves internal stress. Grind the metal with emery to better distinguish between the colors of the shade.

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

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

Hardening the knife

It is advisable to use furnaces independently for hardening metals. For household items in the form of knives, axes, and others, small muffle furnaces are most suitable. 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.

You can make such a furnace yourself. On the Internet, you can find many simple options for its design. In such ovens, a metal product can be heated up to 700-900 ° C.

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

Our market is flooded with low-quality Chinese instruments. And the point here is not even the manufacturer, but rather the resellers who carry cheap Chinese screwdrivers en masse, passing them off as a brand. There is also an excellent, high quality Chinese instrument, but it can be difficult to find.

We will not argue a lot about what and how, but we will try to improve the quality of a screwdriver or a screwdriver with replaceable bits.
I will do the hardening of the bit. Hardening has the goal of increasing the strength of steel, changing the properties of the metal, making it harder, but more brittle.

How to temper metal with your own hands

The hardening process is extremely simple and does not require any special knowledge or special work techniques from you. But you will have to be extra careful when working with hot metal and a gas burner.
So what do you need for hardening?

- The bits themselves first.
- Heater. Ideally use, but if you don't have one, you can use a gas burner like me.
- Machine oil. Anyone will do, it is even better to use the waste one, since it is thinner.

Let's start hardening the metal. To hold the bat over the torch, you need to make a holding device. I'll do this out of regular steel wire by wrapping a few turns around the bit.

In principle, you can simply hold the thick end of the bit with pliers so that only the part of the bit that interacts with the screws and screws is hardened.
We light the gas burner. We bring the bat and begin to heat up the metal.

Warm up to a bright pinkish color. It is not recommended to heat it to white, although you are unlikely to succeed on such a burner.
As soon as everything is warmed up, quickly dip it into the oil, for 5-6 seconds. Then we take it out.
You can use another process: 4 seconds in oil, and then abruptly in cold water, they say the effect is better, but again, I have not tried it.

That's all. The process is complete. All that remains is to wipe off the oil from the bit and start using it.

It looks darker.

Let me add that not all bits are hardenable. I do not know what is mixed in them, but there are specimens, hardening which not only does not affect, but even destroys them, and they become like plasticine after heat treatment.
I would also like to add that this method does not lie next to the factory hardening, so there is no need to wait for the same hardness of the metal. Since even the metal is not the same as the factory one. But the effect of increasing the hardness, and hence the operating time, is still there.

May appear at any time. A large number of different tools are sold on the market, which could not be hardened during manufacture, or, conversely, overdosed with the temperature during heat treatment. For example, we can recall the well-known drills for a drill. If the steel is not hardened to normal, it will bend. If the steel is hardened too hard, the drill will likely start to crumble.

This description applies to all steel materials. Of course, you won't be able to check the metal in the store. In this case, there is only one option, we are talking about steel hardening at home.

Checking metal for quality at home

The first step after buying a metal item is to check its quality. This can be done with a simple soldering iron. The end of the soldering iron is held over metal to find out defects in tool design. If the soldering iron sticks to the surface, then the steel is not hardened, and with frequent use, the tool will deform. If, on the contrary, the end of the soldering iron runs smoothly over the steel and almost bounces off it, then the metal is too hardened. In this case, it is necessary to heat-treat the steel tool to increase its strength.

Quenching technique

On the Internet you can find a large number of methods and videos for hardening metal objects, but most of them provide for the presence of special equipment, but there are ways that help to improve the quality of steel with improvised means.

First, you need to determine what constitutes steel hardening. The main process is divided into two parts, or rather, speaking, heating the metal to a high temperature and subsequent cooling. The process looks simple only at first glance, but have to take into account the structure and characteristics of the metal... If you start heating it without analysis, the material will most likely be deformed. Deformation occurs especially often with mild steel, so if the structure of the metal is unknown, it is better not to use heat treatment.

Tempering is only justified in some cases.

The need to increase the strength of the tool... For example, it can be a regular kitchen utensil, a chisel, or a chisel.
Increasing the ductility of the metal also requires heat treatment to further simplify hot forging.

You can also order a steel hardening service from specialists, especially since the cost is acceptable. For 1 kg of metal of a large structure, blacksmiths usually take no more than 100–150 rubles. If you temper small parts, then the prices are about 6–20 rubles. This will not guarantee the quality of the instruments, which is why many try apply heat treatment at home to monitor the process yourself.

The first thing to remember when heating steel is to remember some rules. Steel can also be damaged if the temperature of the metal is raised above normal. In this case the instrument may take on a black or blue tint, which in the end will not even be able to grind off with sandpaper. In order for such a defect to be absent, the metal must have a sufficient amount of carbon in its structure, and also one cannot overdo it with an increase in temperature. Steel is usually considered hot when a red tint appears.

For heat treatment of steel tools, a torch, blowtorch, electric or gas stove may be suitable. In some cases heating the metal can also be done over a fire... In fact, there is no difference in where it is better to heat up a metal product. Just outdoors, when heated with a fire, there may not be enough heat energy to reach the required temperature. Therefore, it is important to check in advance the melting and quenching temperatures of the material.

It is also necessary to decide on a cooler during heat treatment. Any container with water is suitable for this, the main thing is that the tool fits completely. If the steel of consumables is hardened, then a simple cut bottle can also be used. In the case of heat treatment of an ax, scrap and other similar tools, you need to choose a container with a large volume. In some cases, even a bathtub may be suitable, especially since there is no risk of its deformation.

The cooler is selected not only taking into account the size of the steel object, but also the method of heat treatment. Sometimes only a certain area needs to be hardened, in which case only jet cooling can be used. More precisely, simple water is poured onto the material in drops into the area that requires quenching. This method is especially often used when heat treating drills for drills or on nails to improve the quality of the tip. The hardening technique can be divided into several levels.

The following levels of cooling are distinguished:

sharp;
one-time;
gradual.

For single cooling, a simple container with water is most often used. If cooling is used in two stages, then two different means are used in the process. This, in turn, improves not only the quality, but also the tempering of steel material appears. First of all, the steel is immersed in plain water, and then transferred for further cooling in engine oil or mineral oil... The process is quite dangerous, because you need to cool the product in water so that the oil does not ignite.

Tempering steel over an open fire

How to temper metal at home over an open fire? The question is quite common, and there are a lot of techniques. Conducting heat treatment on an open fire may not be so effective, but at the same time reduces the risk of fire especially when using oil while cooling the steel material.

The first step is to prepare the tools. It is necessary to take a steel material that will be heat treated, a forge pliers or an analog tool and two containers. Water should be poured into one container, and machine or diesel oil is added to the other container.

After that, a fire should be made, while using a large amount of coal. Unlike most methods of heating metal, here the material must be put directly on the coals and it is desirable that they be white, because they are the ones that give out the highest temperature. The fire that will envelop the steel must be crimson. If a white fire appears, then we can assume that steel material started to burn... In this case, it is impossible to save it, therefore, it is better not to bring hardening to such a melting stage.

It is also impossible to allow black or blue spots to appear on a metal product. A blue color indicates that the steel has softened too much and has begun to deform, so it is worth checking the shade of the material from time to time. Complete deformation of the metal occurs when the object turns white.

After the steel material has warmed up, you need to pull it out of the fire and dip it into the oily liquid. The metal should be dipped several times at intervals of three seconds, gradually increasing this time. The main thing is to do everything without haste, but you can't hesitate either, because you can dip steel only if the material has a suitable heating shade... After that, the metal product is placed in plain water, but here you should be extremely careful, since the remaining drops from the oil can simply flare up. If the procedure is carried out taking into account all the recommendations, the metal product can simply be left in water until it cools completely.

It is also important to remember that unlike conventional tools, elongated objects, such as drills or nails, must not be dipped sideways into the water, since the lower part, due to the high temperature and sharp contact with water, may simply flatten. Such elongated objects descend the water vertically, with an end that has a larger diameter.

Tempering steel at home on a stove or fire is only suitable in cases where a simple type of material is used. When quenching non-ferrous metal, too high a temperature is required, which equals 600-900 degrees. This can be achieved with blast furnaces, but not at home.

Conclusion

Using metal heat treatment can improve the quality of the tools or consumable. When hardening steel at home, it is important to remember the basic recommendations so as not to deform the material.

Many are interested in how to properly harden metal at home and in what cases is this process required? Hardening of products from this material is carried out when it is necessary to increase its strength. For example, for strengthening the edges for cutting kitchen utensils (knife, pruning shears) or tools (chisel, chisel, etc.) In addition, the metal acquires a certain amount of plasticity, which makes it easier to process the material. Blacksmiths are familiar with this rule. The article will describe how to harden metal at home.

What is hardening for?

Hardening of the metal increases the hardness of the product by about 4 times. In this case, an object made of this material can easily cut the glass surface. Hardening is required due to insufficient strength of the object, or vice versa. In the first case, metal products will be jammed, and in the second, they will crumble.

Checking the level of hardening of a metal product

To check the hardening level of a metal product, take a file and run the tool along the edge of the object to be cut, for example, an ax or a knife. If you feel that the file starts to stick or stick to the metal, then this indicates that the product is not sufficiently hardened. At the same time, its edge will be soft and pliable.

If the instrument easily moves away from the object and creates the feeling that it is stroking it, and the hand does not feel irregularities, then this means that the metal is too tempered.

It is possible to harden the metal at home. In this case, one should not turn to complex technologies. The process is done by hand.

It should be remembered that mild steels are not subject to the process. But to achieve an increase in the strength of carbon products or really.

How is hardening carried out?

The hardening technology involves two processes - heating a metal product to a high temperature and subsequent cooling.

Heat treatment of the surface is advisable if:

there is a need to give the metal additional strength;
an increase in the level of ductility is required, for example, for subsequent hot forging.

The price of hardening a metal product at a professional level is 200 rubles. for 1 kg. Fire treatment of small parts is cheaper. The price for this service is 20 rubles.

How to harden metal at home? It is necessary to familiarize yourself with some of the nuances of this case.

Heating should be uniform. There should be no black or blue stains on the metal. Do not heat the product to the extreme temperature. The fact that the process is proceeding correctly is evidenced by the appearance of a bright red color.

What equipment is used for hardening?

For example, in order to harden metal at home in the form of a drill, an electric or a lamp for soldering or a fire is used. What is suitable in a particular case depends on what temperature is required for the material being processed.

Cooling of various instruments

Instrument cooling rules vary. The process can be carried out in one or more steps. It all depends on the type of metal.

How to harden the metal not over the entire surface, but only in a certain place? In this case, jet hardening is used. It involves directing a stream of cold water to an object pointwise.

If the action is carried out with one cooler, then specialized devices are required in the form of a barrel or bucket. For this purpose, even a bath is used. This cooling method is suitable for items based on carbon steel or alloy steel.

If a two-stage cooling circuit is required to lower the product temperature, different media are used. This process provides metal tempering. Initially, drills or discs are cooled with water, then with machine or mineral oil. Cooling with it is the second stage of the process, since there is a risk of ignition under the influence of high temperatures.

Application of water for cooling

The main cooling liquid is water. If you add a little salt or soap to it, then the cooling rate will change. Therefore, the hardening tank cannot be used for hand washing. To ensure the same hardness on the metal surface, the temperature of the liquid should be maintained at 20 - 30 ° C. Do not change it frequently in the tank. Do not cool the product in running water.

The disadvantage of hardening with water is the appearance of many cracks on the metal surface. In this way, objects of simple shape or cemented objects should be subjected to the process.

What is used for hardening parts of complex shapes?

How to temper complex metal? For using a fifty percent solution of caustic salt cold or heated to 50 - 60 ° C. Parts heated in a salt bath and hardened in it come out bright. The temperature of the solution must not be higher than 60 ° C.

The vapors that arise during hardening are harmful to health, so the bathtub must be equipped with a ventilation hood.

How is alloy steel hardened?

How to temper metal? At home, alloy steel is subjected to the process in a mineral oil bath. Thin carbon steel objects are hardened in the same way. The advantage of oil baths is that the cooling rate does not depend on the oil temperature. It will proceed equally quickly for any indicator.

How to quench metal in oil correctly? Water should not get into such a bath, as this can provoke the appearance of cracks on the surface of a metal object. It is noticed that if the oil is heated to a temperature of 100 ° C, then the ingress of water will not cause cracking of the product.

Cons of oil bath

Quenching produces poisonous gases.
A plaque forms on the subject.
The oil can catch fire.
The quality of the oil bath quenching is gradually decreasing.

How is metal tempering carried out?

All hardened parts are tempered. This relieves internal stress. As a result of this process, the hardness decreases and the plasticity of the material increases.

How to release hardened metal? Depending on the required temperature, the process is carried out:

in baths with oil;
in baths with saltpeter;
in ovens with air circulation;
in alkaline baths.

What determines the choice of the tempering temperature?

How to loosen hardened metal correctly, what should be considered? An important factor is the tempering temperature. It depends on the type of steel and the required hardness of the product. For example, a product that requires an HRC of 59 - 60 is tempered at a temperature of 150 - 200 ° C. In this case, the internal stress decreases, and the hardness practically does not change.

It is lowered at a temperature of 540 - 580 ° C. This process is called secondary hardening. Its result is an increase in the hardness of the product.

The metal is tempered to a tarnish color. It is heated in ovens or hot sand. The oxide film that appears when heated turns into different colors. At the same time, the surface of the metal product is cleaned of scale, carbon deposits and oil.

After tempering, the metal is usually air-cooled. Nickel-chromium products are cooled in water or oil, since the slow cooling of these grades leads to temper brittleness.

on an open fire?

How to harden metal on fire? For an easy process of metal hardening at home, you should make a fire and prepare two large containers. A lot of hot coals should be present in the fire.

Diesel or engine oil should be poured into one container, and clean water into the other. Better if it is well. Initially, a tool is prepared, with the help of which the metal, red-hot to the limit, will be held. Use blacksmith tongs. But if they are not there, then you can use something similar.

After completing the preliminary work, metal drills or other tools are placed in the center of the flame on hot coals. The white coals are much hotter than the rest. The hardening process must be monitored carefully. The flame of the fire should be crimson. If the fire turns white, then there is a threat of overheating and even combustion of the metal.

It is necessary to ensure that the crimson color is evenly distributed over all areas of the fire. Black stains should not appear on the edge of a metal product. If blue spots appear on the material, this indicates excessive softening of the material and its excessive plasticity. This should not be allowed.

After the metal product has been ignited in a fire, it should be removed from the high temperature center. The red-hot object is lowered into a container of oil many times at intervals of 3 seconds. The time span is gradually increased. It is impossible to hesitate at this stage. The operation is carried out quickly and abruptly. The product is dipped in oil until its color ceases to be bright and saturated.

Then the object is immersed in a bucket of water, which must be shaken a little. At this stage, you should be extremely careful, as oil droplets on a knife or ax may dry out when immersed in an aquatic environment. The drills should be dipped into the liquid with the thick end.

You already know how to properly harden the metal. If you follow all the recommendations, then the process will bring the desired effect.

When do you use an electric oven?

At home, you have to harden products made of non-ferrous metals or steel. In this case, a very high temperature up to 900 ºС and higher will be required.

Only an electric or muffle stove can heat a metal product to such an indicator. The latter can be made by hand, but it is impossible to make an electric one.

How to make a muffle furnace?

How to harden metal at home using a handmade muffle furnace? Such a device will become very useful in the household. It will allow heat treatment of metal products without unnecessary manipulations. To make a furnace with your own hands, you need refractory clay used for coating. A chamber no more than 1 cm thick is created from this material. Its dimensions should be 210x105x75mm.

Carrying out the modeling of the muffle furnace with their own hands, they resort to using a pre-prepared form made of cardboard. So that it does not stick, it is soaked in paraffin.

Clay is smeared on the mold from the inside out. In this case, during drying, it will not shrink. When solidified, the material will itself move away from the edges of the form. Refractory clay can form the basis of the kiln door.

The homemade muffle furnace must be allowed to dry in the open air. Then it is dried to the end in an oven at 100 ° C. The doors and the chamber are fired gradually as the temperature rises to 900 ºС.

The parts should be allowed to cool without removing them from the oven. Then a door joins it. Its surface is sanded with a file.

The camera is wound with 18 m of nichrome wire. Its thickness should be 0.75 mm. The first and last turns must be twisted. To avoid a short circuit, the distance between the turns is coated with clay. On a dry layer of material, you need to spread another layer 12 cm thick.

A self-made muffle furnace consists of a metal frame, the size of which is 270x200x180 mm.

For easy assembly of the case, it should be designed with two removable covers fixed by screws.

A door is hinged to the front cover. It should open horizontally. A ceramic piece must be installed on this door using bolts and gaskets.

All gaps are covered with clay, and the edges of the wire are removed to the back cover of the frame.

Then a connector and a standard cord with a plug are made. All openings between the heating parts and the frame are filled with asbestos chips.

To install the thermocouple and be able to track the metal hardening process in the chamber, two holes must be drilled. The diameter of the first one should be 1 cm, and the second 2 cm. Closing metal curtains are attached to them.

The homemade muffle furnace weighs 10 kg. It heats up to a temperature of 900 ºС within an hour. With its help, you can facilitate the process of hardening drills, files, dies and many other metal products.

Muffle equipment for metal hardening is not the only device. For this purpose, a chamber device, an electric or thermal oven, and a bath oven are used. Making a muffle furnace with your own hands is more profitable than purchasing ready-made equipment. For example, the average price of such a device on the market is 40,000 rubles.