How to properly harden steel at home

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If you know how to harden 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 is required, in particular, if the metal needs to be given hardness sufficient for it to cut glass. Hardening metal at home Most often, a 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 a tool is too low, its cutting part will jam during operation, but if it is high, the metal will crumble under the influence of mechanical loads. Few people know that there is a simple way to check how well a steel tool is hardened, not only in industrial or home conditions, but also in the store, when purchasing. In order to perform this test, you will need a regular file. It is passed 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 easily move away from the tool being tested, while the hand in which the file is located will not feel any irregularities on the surface of the product. Dependence of steel hardness on the heat treatment mode If it turns out that you have at your disposal a tool whose hardening quality does not suit you, there is no need to worry about this. This problem can be solved quite easily: you can harden metal even at home, without using complex equipment and special devices. However, you should know that low-carbon steels cannot be hardened. At the same time, the hardness of carbon and tool steel alloys can be easily increased even at home.

Technological nuances of hardening

Hardening, which is a type 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 their heat treatment modes do not coincide. Heat treatment modes for some non-ferrous alloys Heat treatment of metal (quenching, tempering, etc.) may be required for:

• its strengthening and increasing hardness;
• improving its ductility, 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 yourself, especially since you can do it even at home.

If you decide to harden the metal on your own, it is very important to correctly carry out such a procedure as heating. This process should not be accompanied by the appearance of black or blue spots on the surface of the product. The bright red color of the metal indicates that heating is occurring correctly. This video demonstrates this process well, which will help you get an idea of ​​the degree to which to heat the metal subjected to heat treatment.

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

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

Hardening a knife on open coals

The choice of 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 a separate section of it, then cooling is also carried out pointwise, for which a stream of cold water can be used.

The technological scheme by which metal is hardened may include instant, gradual or multi-stage cooling.

Rapid cooling, which uses one type of coolant, is optimal for hardening steels classified as carbon or alloy. To perform such cooling, you need one container, which can be a bucket, barrel, or even an ordinary bathtub (it all depends on the size of the item being processed).

Cooling the knife blank in oil

In the event that steels of other categories need to be hardened or if, in addition to hardening, tempering is required, a two-stage cooling scheme is used. With this scheme, a product heated to the required temperature is first cooled with water and then placed in mineral or synthetic oil, in which further cooling occurs. Under no circumstances should an oil-based cooling medium be used directly, as the oil may ignite.

In order to correctly select the hardening modes of various steel grades, you should focus on special tables.

Heat treatment modes for high-speed steels

Heat treatment modes for alloy tool steels

Heat treatment modes for carbon tool steels

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 begin by starting a fire, in which a lot of hot coals should form. You will also need two containers. You need to pour mineral or synthetic oil into one of them, and ordinary cold water into the other.

In order to remove hot iron from a fire, you will need 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 number of hot coals have formed in the fire, objects that need to be hardened can be placed on them.

The color of the formed coals can be used to judge the temperature of their heating. Thus, coals whose surface has a bright white color are hotter. It is also important to monitor the color of the fire’s flame, which indicates the temperature regime in its interior. It is best if the fire flame is colored crimson rather than white. In the latter case, indicating that the flame temperature is too high, there is a risk of not only overheating, but even burning the metal that needs to be hardened.

Heated steel colors

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

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

Steel tarnish colors

When cooling metal with water on the surface of which droplets of hot oil remain, care should be taken, as they may burst into flames. After each dive, the water must be agitated to ensure it remains cool at all times. A training video will help you get a clearer idea of ​​the rules for performing such an operation.

There are certain subtleties when cooling hardenable drills. So, they cannot be lowered flat into a container with coolant. If you do this, then the lower part of the drill or any other metal object that has an elongated shape will cool sharply first, which will lead to its compression. That is why it is necessary to immerse such products in coolant from the wider end.

For heat treatment of special grades of steel and smelting non-ferrous metals, the capabilities of an open fire are not 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 expensive to make an electric furnace at home, then with muffle-type heating equipment this is quite feasible.

Self-production of a chamber for hardening metal

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

Diagram of a chamber for hardening metal: 1 - nichrome wire; 2 - inner part of the chamber; 3 — outer part of the chamber; 4 - rear wall with spiral leads

In order to give the future furnace the required configuration and desired dimensions, it is best to make a mold from cardboard impregnated with paraffin, onto which fireproof clay will be applied.

Clay, mixed with water to a thick, homogeneous mass, is applied to the wrong side of the cardboard form, from which it will peel off after complete drying.

Metal products heated in such a device are placed into it through a special door, which is also made of refractory clay.

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

Clay heater with a walled nichrome spiral

Nichrome wire is wound onto the surface of the 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 around the camera, you should leave a certain distance between its turns, which also needs to be filled with fireproof clay to eliminate the possibility of a short circuit.

After the layer of clay applied to provide insulation between the turns of 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 filled with asbestos chips. In order to provide access to the inner chamber, doors, lined with ceramic tiles on the inside, are hung on the metal body of the oven. All existing gaps between structural elements are sealed using refractory clay and asbestos chips.

Ready homemade camera

The ends of the nichrome winding of the camera, to which electrical power must be supplied, are brought out from the rear side of its metal frame.

In order to control the processes occurring in the inside of the muffle furnace, as well as measure the temperature in it using 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 part 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 metalworking and cutting tools, working elements of stamping equipment, etc. at home.

Self-manufacturing of such a furnace (as well as other types of hardening equipment) allows you not only to get at your disposal a device that fully meets your needs, but also to save a lot of money, since serial models are quite expensive.

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Source: https://pellete.ru/stal/kak-pravilno-zakalit-stal.html

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Hardening a knife at home



Many centuries ago, master blacksmiths wondered about the hardness of the blade. And many of them understood that steel must be cooled quickly after heating. Damascus craftsmen hardened steel in gorges where strong winds blew. They believed that the force of the wind was transferred to the blade, and it became elastic, hard and did not break.

Hardening the cutting edge of a knife.

A little more history

Some blacksmiths used sheep urine collected for three days for this purpose. And others used the boy’s urine for such a process, and he had to be red-haired. These are the tricks the masters of the past used. By the way, the use of urine can be partially justified, since the presence of salts in it accompanied the rapid absorption of heat from the hot metal.

There were even quite barbaric methods of hardening, a red-hot blade was stuck between the ribs of a slave, and it was believed that his strength was transferred into a metal blank. It's good that those days are over. But people gradually noticed that if, after heating the metal, it was placed in a salty environment, its quality and characteristics improved.

Time passed, and thousands of methods were tried before achieving a positive result. The young scientist metallurgist D.K. Chernov, who worked on this problem in 1866, achieved considerable success in determining certain values ​​for each metal.

The plant where Mr. Dmitry Konstantinovich Chernov conducted the tests completely got rid of defects and this man can be called the progenitor of modern metallurgy. Today, any student, having a wealth of knowledge accumulated over centuries, can cope with the hardening of steel.

Choosing steel for knife hardening

As you know, steel is nothing more than an alloy of carbon and iron. Additives are added to them in small doses. They do not play a big role on the quality of the future blade. The most important element is carbon.

Additives can be such as zinc, chromium, molybdenum, calcium, etc. But the less carbon in steel, it acquires high strength, but wears out faster and corrosion develops faster. For proper hardening, you must know the composition of the future blade.

It is best to carbon analyze the steel.

Ideal hardening of a knife blade.

If the future product is, for example, made from a file or a car spring. Hardening in this case is simply necessary, especially since forging such a metal implies its mandatory heating. You can check the quality of hardening at home, but it is quite “cruel”.

You need to tighten the finished blade in a vice and begin to gradually bend it, and if the blade breaks at around 45 degrees. We can safely say that the hardening was carried out correctly.

But this should be done after your first independent hardening of the blade, you need to remember the whole process well and repeat it again.

Hardening methods

There are essentially 2 types of hardening methods. On an open fire and in the oven. But, unfortunately, in an ordinary fire it will not be possible to raise the temperature above 900 degrees. Then the oven comes to the rescue. You can make it yourself. This is a rather difficult process, but once you make it once, it will serve you for a long time. Moreover, if you are a beginner master, you simply need it.

In the cell

Next we will talk about how to make your own muffle furnace for proper heat treatment of workpieces, and now we will simply and briefly describe the hardening process in it; the blade steel will be used 50Х14МФ:

1. We heat the oven to the desired temperature, in this case 1070 degrees, and immerse the blades in the oven.
2. Having loaded the blade into the oven, we heat the oven again to 1070 degrees, and at this temperature the countdown begins. The principle is simple: 1 minute 40 seconds for every millimeter of blade thickness.
3. After the required time has passed, the blade is pulled out and cooled in air for 15 minutes under light pressure.
4. Then the metal is tempered in the oven at 200 degrees.

Hardening a knife in a chamber made at home.

With this process, the steel gains a hardness of 56 HRC.

But keep in mind that in this case, hardening took place without immersion in liquid. Each steel has its own hardening conditions. And the result you want to achieve will depend entirely on the process itself.

On an open fire

The method, one might say, was tested by our ancestors and has been around for many years. To properly harden steel, without any precise measuring instruments, so to speak “by eye”, you need to be attentive and patient. The only way to check is with a magnet. When a metal reaches a certain incandescent point, the so-called Curie point, it stops interacting with the magnet.

And one more sign is the color of the workpiece itself, it should turn dark red. But you also need to make sure that no blue or black spots appear during the process, this indicates overheating. The workpiece should be placed in the coals when the color of the flame from them is crimson.

What you will need:

• mineral oil in a container (can be worked off);
• bucket with water;
• well prepared coals;
• long metallurgical pliers.

Hardening a knife over an open fire.

After the part has acquired the desired shade and is not magnetic, you need to carefully take it with pliers and lower it into the oil for 3 seconds, and this must be done several times. Keep the workpiece in the oil a little longer each time. And at the final stage we immerse it in water.

How to make a chamber for hardening metal

It is clear that when making such a camera, it is better to take the process seriously, since you will not be making it for one day or once. Let's try to briefly describe the manufacturing process of such a chamber; it is also called a muffle furnace.

1. The main thing is to correctly manufacture the “body” of such a camera; here they resort to a simple process. The future neck is made from any hard paper material (such as cardboard) and coated with a thick layer of fireproof clay. Don't forget to make a thin layer of paraffin between the form-building paper material and the clay.
2. In the second stage, the future chamber is dried for at least a day, and then placed in the oven and calcined at a low temperature of about 90-110 degrees Celsius. After this stage, the paper component can already be removed.
3. The final firing of the structure occurs over an open fire at a temperature of about 900 degrees, then it is cooled under natural conditions. You need to wait until the camera cools down completely.
4. After the workpiece has cooled, it acquires the properties of stone and becomes very hard, like a brick. Doors that open horizontally are attached to it.
5. The final stage can be called wrapping the future furnace with nichrome wire, with a cross-sectional diameter of about 0.75 mm. The entire structure will require about 18 meters. To prevent short circuits during winding, it is better to immediately coat it with raw clay. We make two holes in the housing, one for a thermocouple (to measure temperature), and the second for visual control.

A self-made chamber for hardening a knife.

At this point, we can say that the furnace for heating metal is ready. As you can see, there is nothing difficult in making a muffle furnace for your home.

It is very good if there is a furnace for hardening steel. You can even purchase it in a specialized store, but the pleasure is not cheap. So how to harden a knife at home without a special muffle furnace? There is a way out, and to be honest, there is more than one.

But first, you need to conduct small experiments and remember in detail all your actions. If the result is positive, then the same manipulations can be performed with a real part.

This tricky technique will help you get better at working on small workpieces and acquiring the skills to heat and cool a blade. We must not forget that different alloys require different temperatures and cooling methods, otherwise cracks and brittleness of the workpiece cannot be avoided.

Source: https://VashNozh.ru/izgotovlenie/zakalka-nozha

How to harden a knife or other steel at home: types of hardening, their features and instructions



How to harden a knife at home? This question arises for many home craftsmen. Metal hardening is a type of heat treatment that allows you to deform and change the state of a substance.

This method of improving the properties of weapons has been used since ancient times. For example, in the Middle Ages, hardening was used to increase the strength and hardness of various objects: from ordinary knives to axes and sickles.

Thanks to the development of technology, this heat treatment is now available not only at industrial enterprises where there is special equipment, but also at home. We will talk about this in detail in this article.

Features of steel hardening

As mentioned earlier, hardening is one of the types of heat treatment of metals. It involves heating the body temperature to such an extent that a change in its crystal lattice becomes possible. After such treatment, a knife or other metal object becomes somewhat harder and stronger, plus its ductility is completely lost until the next hardening.

There is also the concept of vacation. This is another type of heat treatment, which reduces the stress the metal acquires during the hardening process.

It is worth knowing that hardening is carried out exclusively on stainless steel bodies, as well as the alloys from which they are made. Due to its structure, the product has a high hardness index, which affects its fragility . With proper heat treatment and subsequent rapid tempering, the fragility of the object can be reduced and can be used in a variety of applications.

Proper cooling (holiday)

In order to achieve the necessary properties of the metal, you need to responsibly choose the cooling medium in which this process will take place.

The list of cooling media that are suitable for our business is as follows:

• One medium with liquid. Cold water is best. The body is placed inside and remains there until it cools completely.
• Two environments with different liquids. As in the first case, water is placed in the first medium, and the product is sent there first. After initial cooling, it is placed in oil or saline solution.
• Next comes standard jet cooling. There is nothing complicated or special here: the product is simply placed under running cold water until cooled. Perfect for cases when it is necessary to heat a separate element of the entire product.
• A special staged cooling method that uses several different temperature conditions.

Correct temperature

Before starting the process of hardening steel at home, it is necessary to understand the temperature regime, which must be observed to achieve a high-quality result. The product must be uniformly heated to a temperature of about 700−850 degrees Celsius, and then quickly released to 400−500 using one of the methods described above.

There are a large number of methods, involving various techniques and other devices. However, in this article we will look at the two most popular ones, which are best suited for home use: in a stove or oven and over a fire.

There is no fundamental difference between these methods. The main thing is to place the knife or other product in the oven or fire and monitor its temperature.

The first step is annealing, that is, the main step of heat treatment. It is important to monitor the temperature of the steel and prevent overheating. If there is no special device that can be used to measure its current indicator, you can evaluate it by the color of the heat:

• Orange - from 950 to 1000 degrees;
• Red-orange - from 900 to 950;
• Red - from 800 to 900;
• Darkish red - from 750 to 800 degrees;
• Red-burgundy - from 700 to 750;
• Burgundy - from 650 to 700;
• Brown-red - from 550 to 650;
• Reddish brown - 500 to 550 degrees.

You can also check the readiness of hardening using a regular magnet. If it stops “sticking” to the metal, then its temperature is about 760 degrees, and it is necessary to proceed to cooling as quickly as possible.

For a more convenient holiday, you can also check the color of the product, thus:

• Gray - 350 degrees;
• Blue - 300−350 degrees;
• Blue - 300 degrees;
• Purple - 280 degrees;
• Red-brown - 260 degrees;
• Yellow-brown - 250 degrees;
• Straw yellow - 240 degrees;
• Light yellow - 200−240 degrees.

So, as you can see, it is quite easy to harden a steel product at home. However, you should always remember safety precautions and also keep in mind the instructions described in this article.

Source: https://tokar.guru/metally/sovety-po-zakalke-stali-v-domashnih-usloviyah.html

How to properly harden a knife at home: step-by-step instructions

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

One type 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.

Expert advice

Experts advise hardening stainless steel over an open fire. The flame of a fire is best suited for these purposes. It is recommended to use ready-made coals. They maintain the desired temperature for quite a long time.

If the product requires partial hardening, a blowtorch should be used. It is suitable for working with cutting edges and other small parts. It is important not to overexpose the parts to the fire.

Beginners often ask how to harden stainless steel according to instructions. It is also important to know what safety precautions should be followed when working with it. If the cooling phase uses oil, you must keep a distance from the container to avoid burns.

Hardness test

The hardness of metals is determined by two methods:

1. According to Brinell, a metal ball is pressed into the metal.
2. According to Rockwell, it consists of pressing a small cone from a strong pyramid (diamond).

When determining Brinell hardness, the size of the mark left by a ball when pressed with a force is measured, the magnitude of which depends on the expected hardness and the ball used. The tests use balls of different diameters (1.10 mm). Recalculation of readings is performed according to the formula:

Where F is the force applied on the device, N; D – diameter of the ball used to test hardness, mm; d – imprint diameter. It is measured under a microscope that has a special ruler. Measurement accuracy up to 0.01 mm.

This method is recommended for determining hardness of no more than 300320 units. If it is necessary to determine harder objects, then use the Rockwell device. On this scale, information is indicated by HRC and numerical value.

Based on numerous studies, it has been established that for knife steel, HRC 5563 will be quite high. When designing gears and manufacturing gears, hardening of the tooth surface is also performed. Designers set the hardness to HRC 5258. Metal-cutting tools (cutters, drills, cutters, milling cutters) have a hardness of HRC 6065.

How to harden metal at home

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

Hardening an ax at the stake and in the oven

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 manufacture, axes are stamped with a mark by which you can identify the grade of steel. We will look at the hardening process using U7 tool steel as an example.

The technology must be performed 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 is 720-780°C). More advanced craftsmen recognize the temperature by the color of the heat.

And beginners can find out the temperature using a magnet. If the magnet stops sticking to the metal, it means the ax has heated up above 768°C (red-burgundy color) and it’s time to cool down.

Use a poker to move the hot ax to the oven door, remove the heat deeper, close the door and valve, leave the heated metal in the oven for 10 hours. Let the ax gradually cool down with the stove.

2. Hardening of steel . Heat the ax over a fire, potbelly stove or stove until dark red - temperature 800-830°C (the magnet has stopped magnetizing, wait another 2-3 minutes).

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

Next, place the ax in a container with oil; if the oil catches fire, cover the container with a thick cloth. Keep in oil until completely cool.

3. Release of the ax blade . Tempering reduces the brittleness of steel and relieves internal stress. Sand the metal with sandpaper to better distinguish the colors of the paint.

Place the ax in the oven for 1 hour at a temperature of 270-320°C. After standing, remove and cool in air.

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

Common media for self-heating

For hardening steel at home, the following cooling media are usually used: air, water and aqueous solutions, mineral oil. 10-15% sodium chloride (table salt) is usually used as aqueous solutions, and mineral oil in home workshops is most often used as a regular engine oil.

To harden individual parts of a product with different hardness, hardening with sequential cooling in two environments is used. Each of these quenching media is characterized by its own cooling rate, which directly affects the structure of the metal being processed.

For example, air cools steel at a rate of 5÷10 °C per second, oil - 140÷150 °C, and water (depending on temperature) - 700÷1400 °C.

In order to properly and without problems harden your product, you need to know the brand of metal from which it is made, since both the heating temperature and the cooling method depend on this. For their products, craftsmen most often use used products made from high-speed and tool steels, which can be hardened in a home workshop, as starting materials. The table below shows the recommended temperature conditions and cooling environments for various steels.

Source: https://instanko.ru/drugoe/kak-zakalit-nozh.html

How to harden metal at home

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 because the hardness of the steel or other alloy is low. This is why many people wonder how to harden metal at home?

Hardening metal at home

Methodology

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

Heat treatment at home is justified in the following cases:

1. If necessary, strengthen the material, for example, at the cutting edge. An example is the hardening of chisels and chisels.
2. If it is necessary to increase the plasticity of an 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 surface hardness costs approximately 200 rubles. It is possible to organize hardening of steel at home only taking into account all the features of increasing surface hardness.

Process Features

Steel can be hardened taking into account the following points:

1. Heating should occur evenly. Only in this case the structure of the material is homogeneous.
2. The steel should be heated without the formation of black or blue spots, which indicates severe overheating of the surface.
3. The sample cannot be heated to an extreme state, since changes in the structure will be irreversible.
4. The bright red color of the metal indicates that the steel has been heated correctly.
5. Cooling must also be carried out evenly, for which a water bath is used.

Temperature of the workpiece depending on the color when heated

It is recommended to take these points into account when considering how to harden at home.

Modes of hardening and tempering of steels

Equipment and features of the process

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

1. electric oven;
2. blowtorch;
3. thermal oven;
4. a large fire that is surrounded to redirect the heat.

Mobile forge for heating parts

When choosing a heat source, you should take into account the fact that the part must be completely placed in the oven or fire on which the heating is carried out. It will also be correct to select equipment based on 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 cases where only part of the part needs to be hardened, jet hardening is used. It provides for a jet of cold water to hit only a certain part of the part.

A water bath or barrel or bucket is often used to cool steel. It is important to take into account the fact that in some cases gradual cooling is carried out, in others it is rapid and abrupt.

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

All work can be divided into several stages:

1. First you need to make a fire;
2. at the time of lighting the fire, two large containers are prepared that will correspond to the size of the part;
3. In order for the fire to produce more heat, you need to provide a large amount of coals. they give a lot of heat for a long time;
4. one container should contain water, the other should contain motor oil;

Source: https://stankiexpert.ru/spravochnik/materialovedenie/kak-zakalit-metall-v-domashnikh-usloviyakh.html

How to harden a knife or other steel at home: types of hardening, their features and instructions - Machine

Surface hardening of the knife provides additional strength to the cutting base. Heat treating a steel billet significantly improves the mechanical and physical properties of that item.

If you neglect this requirement, then the risk of quickly erasing the metal plate increases. In simple terms, the knife will constantly become dull, which will affect its performance.

In our material we will talk about how to harden a knife at home. Here are recommendations from professionals who know all the intricacies of working with metal.

What material are knives made of?

An alloy of carbon and iron is used to produce knives. When these components are heated, high carbon steel is formed.

This material is able to cope with sudden changes in temperature. In addition, it is characterized by high density and resistance to various mechanical influences.

Products made from pure carbon steel are quite expensive. To reduce the cost of materials and components, many craftsmen prefer to add special additives.

To do this they use the following substances:

• Molybdenum;
• Vanadium;
• Zinc;
• Tungsten;
• Calcium.

If the workpiece contains a minimum amount of carbon steel, then which products are elastic? They require proper hardening, which will provide them with additional strength.

We make a chamber for hardening metal

Before you begin processing the metal base, you need to prepare the appropriate equipment. It is recommended to pay special attention to the oven in which high-temperature processing will be carried out.

The oven chamber should have dimensions of 30 cm x 20 cm x 10 cm. It is made of refractory clay and brick. The clay composition should not contain any impurities.

The design of the furnace is a rectangle. The walls and back panel are on the same level. A metal door on hinges is installed in front. This will maintain the temperature inside the furnace structure.

To harden steel you will need from 300 to 900 degrees. This parameter directly depends on the material from which the metal product is made. For example, to harden a knife from a file, you will need a temperature of 500 degrees.

The composition of this material contains a high steel content and a minimal amount of tungsten. The finished item is quite strong and durable.

The process of hardening steel at home

The easiest way to harden a workpiece is an open fire. Our ancestors used a similar method more than 100 years ago. The processing process is carried out “by eye”.

For the work process you will need the following materials and tools. These include:

• Fire;
• Large container with oil;
• Bucket of cold water;
• Metal pliers with long handles. They will help you carefully remove and lower the iron for further heating.

The first step is to achieve the desired temperature. We send combustible material in the form of firewood and coal to the oven. The flame begins to change its hue from bright orange to crimson.

At this time, wood and combustible material are added to the fire. When the flames change their color to white, you can proceed to hardening the metal product.

Place the base of the knife on burning coals and leave until the metal turns red. On average, this will take from 5 to 15 minutes. When the product acquires a bright red hue, it is immersed in oil.

Tempering a knife with oil helps add ductility and strength. After the first dive, similar manipulations are carried out 5 more times. Next, he sends the metal blade back to the heating furnace

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The next step is cold water quenching. This procedure is final. It adds strength to the metal product. The hot workpiece is placed in ice water for 20 minutes. A photo of knife hardening shows this manipulation.

We present to your attention a detailed video of knife hardening. Here is presented all the regular actions and manipulations with carbon steel.

Photo of knife hardening

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Source: https://regionvtormet.ru/beton/kak-zakalit-nozh-ili-druguyu-stal-v-domashnih-usloviyah-vidy-zakalki-ih-osobennosti-i-instruktsiya.html

Hardening metal at home: hardening steel correctly

If you know how to harden 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 is required, in particular, if the metal needs to be given hardness sufficient to enable it to cut glass.

Hardening metal at home

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

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 a store when purchasing. In order to perform this test, you will need a regular file.

It is passed 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 easily move away from the tool being tested, while the hand in which the file is located will not feel any irregularities on the surface of the product.

Dependence of steel hardness on heat treatment mode

If it turns out that you have at your disposal a tool whose hardening quality does not suit you, there is no need to worry about it.

This problem can be solved quite easily: you can harden metal even at home, without using complex equipment and special devices. However, you should know that low-carbon steels cannot be hardened.

At the same time, the hardness of carbon and tool steel alloys can be easily increased even at home.

How to harden steel at home

Hardening the metal increases the hardness of the product by 3-4 times.

The need for this procedure arises when you need a metal object to cut glass without effort.

It happens that the need to harden a metal tool arises due to the fact that it is either not hardened to the required degree, or, conversely, it was overdone in hardening it.

In the first case, metal objects, such as drills, become jammed, in the second they literally crumble.

It is unlikely that you will be able to check in the store how well a metal tool is hardened.

Although the possibility of such verification exists. You need to take a file and run it along the edge of a cutting object - a knife or an ax.

The fact that the file sticks and sticks to the metal means that the product has not been hardened enough.

In this case, its edge will be too soft and pliable.

If the file moves away from the object with ease and seems to be stroking it, and the hand does not feel any uneven places while pressing, then the product has become overloaded on the face.

If you still have metal equipment in your hands that needs additional hardening, then it’s okay.

You can harden a knife with your own hands, even without resorting to complex technologies, that is, at home.

The only thing you need to remember: it is forbidden to harden low-carbon steels.

But it is quite possible to increase the strength of carbon and tool steels.

Hardening technique

Simply put, hardening technology consists of two actions - heating the sample to a high temperature and cooling it.

Just don’t assume that everything is elementary, because groups of metals differ in their unique structure and characteristics.

Do-it-yourself heat treatment of metal is justified if:

• there is an urgent need to strengthen the material, for example, to “strengthen” the cutting edges of kitchen utensils or tools, such as a chisel or chisel;
• it is necessary to increase the ductility of the object, which makes it easier to work with metal, for example, the hot forging process.

The price of professional hardening of 1 kg is 100-200 rubles. Hardening small parts will cost less. The price for this service ranges from 6 to 20 rubles.

If you harden equipment at home, it is important to know some of the subtleties of this process.

Heating requires uniformity; it must occur without the appearance of black or blue spots on the object. Under no circumstances should the sample be heated to extreme levels.

The fact that the product is heating up correctly will be indicated by its coloring in a bright red color.

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For hardening a metal object such as a drill, equipment such as an electric furnace or thermal oven, as well as a blowtorch and a large fire are suitable.

What is more suitable - a furnace, an electric furnace or an open fire depends on the temperature required by the type of metal being processed.

When it is necessary to harden not the entire surface of a metal object, but only a certain place, jet hardening is used. It assumes that a stream of cold water is directed at the object pointwise.

The cooling method for a drill, screwdriver, chisel or crimp may vary. It can be carried out in several stages, one-time and abruptly, or gradually. It all depends on the type of metal.

If you plan to carry out an operation with one cooler, then special equipment, such as a bucket or barrel, is prepared. Even a bath is suitable for this.

This cooling method is ideal for products made from carbon or alloy steel.

When a two-stage cooling scheme is needed to lower the temperature of a metal object, two different media are used. This procedure also ensures the tempering of the metal.

So, first, drills or disk parts are cooled with water, then with oil, which can be machine or mineral.

Temperature conditions and other hardening indicators are reflected in the table below.

Hardening steel over an open fire

It is possible to harden metal at home. For an easy and useful hardening process, you need to light a fire and prepare two large containers. There should be a lot of hot coals in the fire.

Diesel or motor oil is poured into one container, clean water, preferably from a well, is poured into the other. You should first prepare a tool with which you will need to hold the hot product.

It is advisable to find blacksmith pliers, but if they are not among the tools, you can arm yourself with something else similar to pliers.

When the preliminary work is done, metal drills or other objects are placed in the very center of the flame, that is, on hot coals.

The rich white coals are hotter than the rest. It is important to watch the hardening process - the flame should be crimson, not white. If the fire is painted in the latter color, there is a risk of overheating and even burning of the metal.

It is necessary that the color is distributed evenly across the entire area of ​​the fire. Black spots should not appear on the edge of the product that is being hardened.

And if the metal turns blue in places, this indicates that the material has softened too much and become too plastic. This should not be allowed under any circumstances.

Therefore, the process requires increased care, because you can overdo it and heat the ax blade white-hot.

When the metal equipment is heated in the fire, it is time to remove it from the high heat.

A hot object must be lowered into a container of oil many times with a frequency of 3 seconds, gradually increasing this period of time.

You cannot hesitate with these actions; you need to carry out operations to harden the metal edge quickly and sharply.

When working with your own hands, the element should be dipped into a container with liquid until the color loses its saturation and brightness.

Next, the object is immersed in a bucket filled with water, which will have to be shaken a little.

At this stage, do not forget to be careful, as oil droplets on a knife or ax may burst into flames if they end up in water.

The table shows how to correctly and incorrectly immerse various parts, including drills and disc cutters, in water:

Very often there is a need to harden drills. It is not recommended to immerse thin long elements flat into water, otherwise the lower layer of metal, cooled first, will shrink.

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Drills should be lowered into the liquid with the thicker end.

If you follow all the rules and precautions, then hardening yourself will not seem like a complicated and dangerous procedure. It will bring the desired guaranteed effect.

But sometimes at home you have to harden steel equipment or melt non-ferrous metal. Such operations require extremely high temperatures, 700-900 degrees.

And only a muffle furnace or an electric furnace can heat metal objects to this level. You can make a muffle furnace yourself. It is unlikely that you can make an electric oven at home.

How to make a chamber for hardening metal?

A homemade muffle furnace is a must-have in the household today. It allows you to heat treat the product without unnecessary steps.

To make a stove with your own hands, you will need fireproof clay, which is used to cover boilers. A chamber no more than 1 cm thick is created from this material.

And its dimensions must fit into the following parameters of length, height and width - 210 * 105 * 75 mm.

When fashioning a muffle furnace with your own hands, you need to have a mold made from cardboard in advance. It is better to soak it in paraffin so that it does not stick.

The clay is spread on the mold from the wrong side, because this way it will not shrink during drying. When the clay hardens, it will move away from the edges of the mold on its own.

The same refractory clay will serve as the material for making the oven door. Then the homemade muffle furnace in the form of two parts should dry in the open air.

Then it is completely dried in an oven at a temperature of one hundred degrees.

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Then the door and chamber are fired, gradually increasing the temperature to 900 degrees. These parts should then gradually cool in the oven itself.

  U-shaped steel profile

Then the door is attached to the oven, carefully using a file and sanding the surface with sandpaper.

You need to wind 18 meters of nichrome wire around the camera. Its thickness should be 0.75 mm. The first and last turns are twisted.

A homemade muffle furnace made by yourself is placed in a metal frame measuring 270*200*180 mm.

To make the case easy to assemble, it is better to make it with two removable covers, which are secured with screws.

A door is attached to the front lid on a hinge; it should open horizontally. It is necessary to install a ceramic part on this door using bolts and gaskets.

The remaining gaps are again filled with clay, and the edges of the wire are removed onto the back cover of the frame.

Then a connector and a standard cord with a plug are prepared. All holes between the heating elements and the frame must be filled with asbestos chips.

To install a thermocouple and be able to monitor the heating process, it is advisable to make two holes in the chamber.

The first is 1 cm in diameter, the second is 2 cm. Closable metal curtains need to be attached to these holes.

The homemade stove design weighs 10 kg and can heat up to 950 degrees within an hour.

Its presence facilitates the process of hardening a drill, file, matrix and many other metal products. How a homemade stove hardens metal equipment is shown in the video.

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Although muffle equipment that hardens metal is not the only option. Heat treatment can be performed by chamber and flame equipment, electric furnace, thermal furnace, as well as bath furnaces.

In any case, making a hardening device yourself is more profitable than buying it. For example, the average price of a muffle furnace is 40 thousand.

An electric furnace is used to harden metal at a temperature of about 1300 degrees and the electric furnace costs much more.

Source: https://steelfactoryrus.com/kak-zakalit-stal-v-domashnih-usloviyah/

Features of steel hardening

Heat treating a metal changes its characteristics. Tempering steel makes it harder and stronger. In some cases, heat treatment is carried out to refine the grain and level the structure. A simple heating and rapid cooling technology for small parts can be done at home. It is necessary to know the grade of steel and its heating temperature for hardening.

What is metal hardening?

One type of heat treatment is metal hardening. It consists of several stages performed in a certain sequence:

1. Heating metal to a certain temperature. Dwell time for leveling over the entire depth of the part.
2. Fast cooling.
3. Tempering to relieve stress and correct hardness to a specified value.

During the manufacturing process, complex parts can undergo several different types of hardening.

Based on the depth of treatment, hardening is divided into two types:

Basically, in mechanical engineering, volumetric heat treatment is used, when the part is heated to its entire depth. As a result of sudden cooling, after the completion of heat treatment, the hardness inside and outside differs by only a few units.

Surface hardening is used for parts that must be hard on top and ductile on the inside. The inductor heats the steel to a depth of 3–20 mm and immediately behind it there is a sprayer that pours water on the hot metal.

The steel is heated to austenite state. Each brand has its own temperature, determined from the table of the state of iron-carbon alloys. During sudden cooling, carbon remains inside the grain and does not enter the intercrystalline space. The transformation of the structure does not have time to occur, and the internal structure contains pearlite and ferrite. The grain becomes finer, the metal itself becomes harder.

What steels can be hardened?

When heated and rapidly cooled, internal changes in structure occur in all steels. Hardness increases only with carbon content greater than 0.4%. St. 35 according to GOST has it 0.32 - 0.4%, which means it can “get hot” - slightly change the hardness if the carbon is located at the upper limit.

Steels starting from CT45 and higher in carbon content are considered hardenable. At the same time, hardening of stainless steel with low carbon content, type 3X13, is possible. Chromium and some other alloying elements replace it in the crystal lattice and increase the hardenability of the metal.

High-alloy carbon steels contain substances that accelerate the cooling process and increase the steel's ability to harden. They require a complex step cooling system and high temperature tempering.

Temperature and heating rate

The heating temperature for hardening increases with the content of carbon and alloying substances in the steel. For St45 it is, for example, 630–650⁰, St 90HF - more than 800⁰.

High-carbon and high-alloy steels, when heated quickly, can “crack” - form small cracks on the surface and inside. They are heated in several stages. At temperatures of 300⁰ and 600⁰, exposure is done. In addition to equalizing the temperature throughout the depth, there is a structural change in the crystal lattice and a transition to other types of internal structure.

Properties of steel after hardening

After hardening of parts, structural changes occur that affect the technical characteristics of the metal:

• increases hardness and strength;
• grain decreases;
• flexibility and ductility decreases;
• fragility increases;
• abrasion resistance increases;
• fracture resistance decreases.

It is easy to obtain a high class of cleanliness on the surface of a hardened part. Raw steel is not polished, it drags on and on.

Types of steel hardening

The main parameters for hardening steel: heating temperature and cooling rate. They completely depend on the grade of steel - carbon content and alloying substances.

Hardening in one environment

When hardening steel, the environment determines the cooling rate. The greatest hardness is obtained when the part is dipped in water. This way you can heat medium-carbon low-alloy steels and some stainless steels.

If the metal contains more than 0.5% carbon and alloying elements, then when cooled in water, the part will crack - become covered with cracks or completely collapse.

High-alloy steels increase their hardness even when cooled in air.

When quenching in water, alloy steel is heated to 40–60⁰. The cold liquid will bounce off the hot surface, forming a steam jacket. The cooling rate will be significantly reduced.

Step hardening

Hardening of steels with complex composition can be carried out in several stages. To speed up the cooling of large parts made of high-alloy steels, they are first dipped in water. The residence time of the part is determined by several minutes. After this, quenching continues in oil.

Water quickly cools the metal on the surface. After this, the part is dipped in oil and cools to the critical temperature of structural transformations of 300–320⁰. Further cooling is carried out in air.

If you heat massive parts only in oil, the temperature from the inside will slow down the cooling and significantly reduce the hardness.

Isothermal hardening

It is difficult to harden metal with a high carbon content, especially tools made of tool steel - axes, springs, chisels. When rapidly cooled, strong stresses are formed in it. High temperature tempering removes some of the hardness. Hardening is carried out in stages:

1. Normalization to improve structure.
2. Heating to hardening temperature.
3. Dipping into a bath of saltpeter, heated to 300–350⁰, and soaking in it.

After hardening in a saltpeter bath, tempering is not necessary. Stresses are released during slow cooling.

Light hardening

There is no technical term for “light hardening”. When alloy steels are hardened, including heating, in a vacuum or inert gases, the metal does not darken. Hardening in a protective gas environment is expensive and requires special equipment separately for each type of part. It is used only for mass production of the same type of product.

In a vertical furnace, the part is heated, passing through an inductor, and immediately lowered below - into a salt or nitrate bath. The equipment must be sealed. After each cycle, the air is pumped out of it.

Hardening with self-tempering

During rapid cooling during the hardening process of steel, heat remains inside the part, which gradually leaves and releases the material - relieving stress. Self-tempering can only be done by specialists who know how much the time a part remains in the coolant can be reduced.

Self-tempering can be done at home if you need to slightly increase the hardness of fasteners or small parts. It is necessary to lay them on heat-insulating material and cover with asbestos on top.

Cooling methods during hardening

Methods of cooling metal during water and oil quenching are widely used in industry. The most ancient composition for hardening swords and other thin-walled objects is saline solution. Hardening was carried out by blacksmiths using forging heat and the heat generated by deformation.

Red sabers, swords, knives were dipped into the urine of red-haired guys. In Europe they were simply stuck into the bodies of living slaves. The colloidal composition containing salts and acids made it possible to cool the steel at an optimal speed and not create unnecessary stresses and leads.

Currently, various sodium salt solutions, saltpeter and even plastic shavings are used.

How to harden steel at home

The decision on how to heat metal is made based on several parameters:

• steel grades;
• required hardness;
• operating mode of the part;
• dimensions

Not all heat treatment methods are available to amateurs. You should choose the simplest ones. Most often, at home, you have to harden stainless steel when making knives and other home cutting tools.

The hardening temperature of chromium-containing steels is 900–1100⁰C. Heating should be checked visually. The metal should have a light orange - dark yellow color, uniform over the entire surface.

You can dip a thin stainless steel into hot water, lifting it into the air and lowering it again. The higher the carbon content, the more time the steel spends in air. One cycle lasts approximately 5 seconds.

Plain weldable steels are heated to a cherry color and cooled in water. Medium alloy materials should have a red color before immersion in water. After 10–30 seconds, they are transferred to oil, then placed in the oven.

When hardening, the maximum hardness that steel gives with this technology is obtained. Then it is reduced to the required value by high-temperature tempering.

Hardening at home

Equipment

Metal is heated in various ways. You just need to remember that the combustion temperature of wood cannot provide heating to the metal.

If you need to improve the quality of 1 part, just light a fire. It must be lined with bricks around the perimeter and, after laying the workpiece, partially closed on top, leaving gaps for air access. It's better to burn coal.

A separate area and a small part are heated with a gas and kerosene burner, constantly running the flame and heating it from all sides.

Making a muffle furnace requires a lot of time and resources. It is advisable to build it for constant use.

The coolant can be in a bucket or any other container that will ensure complete immersion of the part with an oil thickness of the 5 largest sections of the part:

• one part under the hardened product;
• two on top.

The part must be moved slowly in the coolant. Otherwise, a steam jacket will form.

Defects during hardening of steel

When hardening steel, 2 groups of defects arise:

The first are associated with uneven, spotty hardening and the discrepancy between the resulting hardness and the requirements in the drawing. Such defects are mainly caused by improper cooling or poorly performed heat treatment.

Uncorrectable items include chips, cracks, and complete destruction of parts. The reason most often lies in low-quality metal.

Hardening significantly changes the structure and performance properties of the metal. You can do it yourself using simple parts. It is necessary to know exactly the grade of steel, its hardening temperature and the cooling medium.

Source: https://metalloy.ru/obrabotka/termo/zakalka-stali

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