How to properly harden a knife at home

Hardening a knife - description of the technological process and sequence of actions

There is no need to talk about the indispensability of a knife. It is in every home, and we use this item every day. It is also interesting that this device has been an integral part of human life for thousands of years, despite this, the need for it does not decrease.

Both then and now, people were worried about the same issue - metal processing. Nowadays this is done more when creating blades, but knife hardening is also of interest to owners, although not many.

Peculiarities

The classical process of steel hardening has always been accompanied by high temperatures, in which polymorphic transformation of the steel occurs. At the same time, heating was always accompanied by sudden changes in temperature, because at a certain stage, the steel was always cooled in water.

Temperatures affected the structure of the metal, since when it increased strongly, the structure of the crystal lattice on its surface changed, and the sharp temperature change produced by water strengthened it. In this regard, the technology for hardening knives today is not much different from that which was used for swords and blades a thousand years ago.

This technology has always had one serious drawback. With a sharp change in temperature, the metal became much harder, but at the same time, it suffered greatly in terms of strength.

If this is a problem, you need to still heat the metal, but then gradually reduce its temperature. In this case, the steel will not become brittle enough.

Subtleties

If you have started hardening knives at home, then you should know that not every knife that comes into your hands is suitable for temperature testing.

This method is optimally suited for products in the production of which stainless steel was used. This may be a high content, or it may be an alloy containing stainless steel or nickel, for example. These knives are much stronger than their high carbon steel counterparts.

In addition, hardening can be carried out over the entire area of ​​the blade, or can be used in a separate area that needs increased strength. The first type is called global, the second was called local.

Knife material

All types of steel consist of simple iron to which carbon is added. This is a common alloy for kitchen knives. If you add other metals to it, such as vanadium, chromium or molybdenum, the properties of the knife will change. Photos of hardening knives from a variety of materials can be found on the Internet without any problems. Some people have even used this process on Damascus steel.

The problem here is that hardening is good for types of steel that contain a sufficient amount of carbon. If there is not enough of it in the alloy, the knife after hardening will become stronger and harder, and it will begin to undergo corrosion, for which Damascus steel is so famous for its protection.

Graphite hardening

Graphite cementation is a very simple but effective way of surface hardening a knife with your own hands, which is best suited for strengthening some part of the blade.

To do this, you will need graphite, which can be obtained from simple AA batteries. You need a metal platform on which the hardening process will take place. A simple profile, which is used when working with drywall and other finishing work, is good for this.

We will also need a constant power source. An excellent option would be a welding machine, the power of which should be set to the minimum level. If this is not the case, you can try a similar option that will be able to provide you with about 50 volts of DC voltage. I strongly do not recommend using a 220 volt network.

Any instructions, including those for properly hardening knives, must begin with preparation. Once you have all the necessary components, you need to prepare your workspace.

We take the profile, pour our graphite onto it, it should turn out to be a small mound. You need to connect the positive cable of the power supply to the profile, but the negative cable needs to be connected to the knife.

Before asking the question of how you can harden a knife yourself using graphite, you should know that after turning on the power source, you should not let the knife and the profile come into contact. An arc will form, and in general nothing good will happen.

This method is good for hardening the edge, which gradually comes into contact with graphite. To do this, after everything has been done above, you need to turn on the power source and apply voltage to our parts. The knife must be gradually drawn along the graphite with the edge of the blade.

When this happens, rest assured that you will see the hardening process in person. This needs to be done gradually and carefully. If you touch the profile, the process is ruined. If you keep the edge in graphite for a long time, it will catch fire and the hardening will be ruined again. In both situations, the blade will be damaged beyond repair.

It is correct to conduct hardening with slow, gradual and short movements. Visually, it is very clearly noticeable when graphite begins to heat up strongly and spark. When you see this, you need to raise the knife. The blade should not be dipped very deeply into graphite; it is best to do this only with the cutting edge.

For a small knife you will need about five minutes to harden its edge. This process is delayed precisely due to the burning of graphite, which must always be avoided. As you can see, there is nothing complicated in this process, you just need to follow the instructions and work carefully.

Photo of the knife hardening process

Source: https://tytmaster.ru/zakalka-nozha/

How to harden a knife at home: be sharp

There are such ordinary tools in the everyday life of Homo sapiens, the necessity of which we somehow do not even think about. But this does not always happen: for example, as soon as our knife becomes dull, a feeling of discomfort immediately appears. In order to happily avoid such situations, you need to figure out how to harden a knife at home, because this question is relevant, since without the correct operation, a much-needed tool becomes absolutely ineffective, and therefore completely useless.

If a homemade knife in a past life was, for example, a spring or a file, then it will need hardening in any case, because mechanical processing of a blade always involves heating it. You can check its quality at home. To do this, fix the knife in a vice, and then start bending it. If it breaks when the bend angle passes the 45° mark, then your product was, alas, of high quality.

Temperature conditions: features

They exist, so hardening knives is an operation that cannot be called elementary. The first rule states that heating of the blade should occur gradually and evenly. If this condition is ignored, then very rapid heating will lead to the formation of rather large grains in the metal structure, and the consequence will be excessive fragility of the product. Therefore, for each steel alloy only its own temperature regime is suitable. For example:

• high-carbon alloys can withstand temperatures from 680 to 850°C;
• low-carbon - from 727 to 950°C;
• alloyed alloys can withstand temperatures from 850 to 1150°C.

How can you determine the heating temperature at home? A pyrometer, which can help, unlike knives, is not present in every home, but there is another accessible method - using a simple magnet.

All metals have one interesting property: each of them has its own Curie point: after passing it, it passes from a ferrimagnetic state to a paramagnetic one. Speaking in human language, he simply stops reacting “passionately” to the magnet.

When the heated blade “no longer has attraction” to the magnet, it means that the heating temperature has reached the critical temperature - the Curie point.

How to avoid trouble?

During the home hardening procedure, the biggest problem is the overheating of the metal, which leads to the fact that the fragility of the material increases greatly. If you do not pay close attention to the uniformity of heating, you can get another defect - transverse cracks form on the blade.

However, there is an opportunity to avoid sad consequences - to memorize a rule that allows you to harden knives in the future without any problems. It states that the cutting part of the blade can be heated only once to a yellow color, checking with a magnet, and the part that will not take part in sharpening can be heated three times to a temperature of 280 ° C, which will correspond to a purple color.

Home hardening and its tricks

High-quality hardening can be successfully performed at home, you just need to have the right approach to such a fascinating process and your tool - a folding or hunting knife, a homemade file or a butterfly knife. The problem will become a little more serious if your product is made of stainless steel, but even in this case there is a solution, you just need to get acquainted with the nuances of the procedure and prepare the necessary equipment for heating.

A couple of paragraphs about cooling media

Such a cooling medium can be various substances. The most popular, due to their availability, are oil and water. Therefore, check out the cooling rates of steel products:

1. Water. If its temperature slightly exceeds 20°, then the cooling rate will be 450°/s. When it is icy, the value is higher - 600°/s.
2. Oil. Its room temperature allows you to cool the blade at a rate of 150°, but if it is heated to 200°, this value will double.

It should also be noted that there is such a phenomenon as hardenability. It means the depth of hardening of the layers. If water acts as a cooling medium, the rate of calcination of steel is 1 mm/s, but if oil is used, the rate is almost halved. There is a way out, however, even for a double-edged instrument: first the blade is heated to our point, then it is lowered into water for a couple of seconds, after which it is moved into oil.

Graphite hardening

Hardening in graphite is excellent for hardening the cutting edge of a knife with a fairly thick blade. This technology allows for high-quality processing of a variety of models, and carrying out this procedure at home is not difficult. You can get acquainted with the process, but it is better to do this by watching the video.

Sending the knife on zone vacation

It is also possible to zone harden the knife if you are satisfied with the blades, but you want the middle part to become more elastic. Then the processing algorithm is as follows:

1. Take a rod with a diameter of 10 mm. It is heated “to white heat”, after which it is applied to the middle part of the knife.
2. After this part has thoroughly warmed up, the blade is placed in boiling water, in which it is left for 2 hours.
3. When the exposure time comes to an end, the knife should be immersed in ice water.

This operation is called low release. What needs to be taken into account for a high-quality result:

1. A small volume of liquid will not be able to provide the desired result: the liquid will quickly heat up, and because of this, both a change in the required cooling rate and a violation of the temperature regime will occur. The minimum amount of water in this case is 20 liters.
2. The position of the blade in the cooling environment must be fixed, otherwise problems will arise with the uniformity of heat transfer, which will lead to disappointing consequences for the knife.

A few rules that can change a knife

They are quite simple, but will allow you and your knife to get out of a difficult “scrape” with honor.

Any hardening of a product of a certain brand must begin with preliminary tests, for which several plates made of a similar material are used. The first test sample is used to select the optimal heating temperature: one part is heated to the maximum, and the other to the minimum.

Then the plate is placed in a cooling medium, which is either oil or water. When the sample has completely cooled, it is fixed in a vice and broken, after which the fracture site is examined with a magnifying glass. When quenching is carried out ideally, the metal should acquire a coarse-grained structure.

Now the next prototype is taken. His role will be to check the coolant. You need to use several of them; you can add liquid lead to our “heroes”. After the hardened plate breaks when it is deflected by 30°, you can continue experiments - both with temperature conditions and with coolants. The result will be achieved if after these manipulations the plate breaks precisely at an angle of 45°.

To protect cutting tools from cracks, they require pre-annealing. This operation must be carried out on certain equipment - in a muffle furnace equipped with a temperature controller. We must remember that the heating process must be slow and uniform.

In the matter called “How to harden a knife at home,” you need to deal with it thoroughly, then your knives will remain intact, and their blades will always be sharp.

Watch a video related to this process:

Source: https://dom-i-remont.info/posts/obshhie-voprosy/kak-zakalit-nozh-v-domashnih-usloviyah/

How to harden a knife at home

A well-tempered knife in the house is a must. Often we don’t even think about how important this tool is until one day it becomes dull - and now we can no longer solve some simple everyday problems. Of course, you can simply give preference to purchased knives that are already properly hardened, but if you decide to make your own, for example, from a spring or a file, then in principle you cannot do without hardening. I'll tell you how to do this as simply as possible.

Determining the temperature

Do not forget to take into account how to heat the knife and to what temperature. The main rule is that rapid heating will lead to increased fragility of the metal, so this is not necessary. As for the maximum, it all depends on the composition.

For example, a high-carbon alloy can withstand up to 850 degrees, low-carbon alloys can withstand up to 950 degrees, while alloy alloys can heat up to 1150 degrees. It is also important to remember about uniform heating, otherwise completely unwanted transverse cracks may form.

How to easily understand what temperature to heat to

Remember a couple of simple rules about how to harden knives without consequences, without complex measurements:

• the part of the blade that is sharpened needs to be heated only once until it turns yellow;
• after that you need to check it with a magnet, make sure that it has stopped being attracted to it;
• The part that is not involved in cutting must be heated until purple three times.

Looking at the colors a blade takes on is much easier than measuring temperatures and doesn't require any equipment.

What to harden in

For hardening, it is necessary to prepare a special small oven chamber, approximately 30 by 20 by 10 centimeters. It is made from fireproof (required!) clay and brick. A flammable material, such as coal, is placed in the oven. Typically, hardening occurs over an open fire, which should be in color from bright orange to crimson, which means that it is approximately the right temperature.

On average, the duration of a knife's exposure to fire should be from 5 to 15 minutes, depending on the material, but still watch how it changes color after heating.

What to cool in

There are two main options for cooling a knife. Often cooled with either water or oil. Water cools faster, and it also helps increase the depth of hardening of the layers. But it is recommended to use a combined approach, when the knife is first heated to the required temperature, then literally dipped in water for a couple of seconds, and only then moved into oil for a longer period of time until it cools down adequately.

This is often done - the knife is heated five times to a bright red color and immersed in oil, after which it is heated and placed in water to consolidate the properties. There are different approaches, focus on what the knife is made of and what effect you want to achieve.

You can learn more about this topic by watching the video below:

Let's sum it up

Of course, this is a very simplified process of hardening a knife, but several conclusions can still be drawn:

• be sure to prepare a good chamber in which you can simply harden the knife;
• Don't heat too quickly, and don't cool too quickly;
• focus on the colors that the blade acquires during the heating process, this will make it easier to understand when to stop;
• Follow safety precautions and be extremely careful when working with high temperatures.

When using materials from thebestvideo.ru, a link to the source is required.

Source: https://thebestvideo.ru/fun/poleznosti/zakalit-nozh/

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 properly harden knives at home, useful tips

Even if the knife blade is made of high quality steel, it will still be weak without pre-hardening. Such a blade can break with just a little pressure, and sharpening it will be problematic.

It is not for nothing that many users are interested in the question of how to harden a knife at home, because it is after heat treatment that the physical and mechanical properties of the metal are significantly improved.

There is nothing complicated in the procedure, however, if it is performed incorrectly, the cutting part of the tool will quickly become dull, which will make operation ineffective.

Features of working with steel

The main purpose of hardening a metal is to change its structure and rearrange the atomic lattice. When the temperature rises above the peak point, called the Curie point, the steel becomes especially strong and wear-resistant.

Subsequent rapid cooling reduces the fragility of the metal resulting from internal stress and increases its ductility. It will not be easy to break well-hardened steel - cracks will appear on it only when bent at an angle of more than 45°.

However, violation of the hardening technology can lead to the transition of the atomic lattice to an intermediate state. In this case, the strength of the material, on the contrary, will decrease.

Properly hardening a knife at home is not that difficult. The main thing is to accurately observe the time, heating and cooling temperatures. In the absence of special equipment, not every type of steel can be hardened. Only metals with a high carbon content are suitable for this purpose. You can find out what type of steel was used to make the blade by the marking - the mark on the blade.

It is easiest to work with products from the structural variety of grades 45, 50, heat-resistant 40´13 or instrumental. Moreover, the higher the carbon content, the stronger the blade will be, but it will be more difficult to process (sharpen) it. Blades made of high-carbon steel and alloy alloys are hardened at fairly high temperatures in special chambers. Low-carbon steels containing the numbers 10, 20 and 25 in the markings, and cast iron are not subjected to this procedure.

A liquid medium, machine oil (waste) or water is used as a coolant. A too rapid decrease in temperature is undesirable - it can lead to cracks. Therefore, it is important to observe the exact time of not only hardening, but also further cooling.

To determine how well the steel is hardened, you should run a file along the cutting edge of the blade. The tool should move smoothly, effortlessly, easily move away from the surface, without sticking to the metal.

How to carry out the procedure yourself

To do this, you do not need to have any experience - just follow the instructions exactly, which will tell you how to harden knives at home on your own. The procedure can be used for any type of blade - an ax, scissors, and other cutting tools.

Source: https://posuda-gid.ru/nozhi/obsluzhivanie/315-kak-zakalit-v-domashnih-usloviyah

Quality knife: indicators

Having a knife or planning to make one yourself, it is important to know the characteristics that you should pay attention to. The quality of a product is determined by its blade. Since it is he who is responsible for the product performing its main function - cutting. The blade must meet certain requirements.

The first and most important indicator is hardness, since it is responsible for the ability of the blade to be resistant when interacting with other materials. If the hardness is high enough, then the blade holds an edge well and does not break or deform. Thus, the service life is significantly increased.

Another equally important indicator is strength. It determines the preservation of the appearance of the product throughout the entire period of its operation. Also, do not forget about the plasticity of the blade, which allows the metal to take the necessary shape and return to its own without difficulty. But here it is worth noting that it will be low with high hardness.

The service life of a knife is determined by its wear resistance, as it implies the ability of the blade to resist wear during operation. It determines the time of its use. As practice shows, some products can be used for more than ten years. In many ways, this indicator depends on the main characteristics of the product.

Knife hardening: what is it?

To provide a knife with these characteristics, various manipulations are performed during its production. But the most important thing is hardening. It helps make the metal strong. And as mentioned above, this is an important indicator that determines the quality of the product.

It is easy to check the strength of the product. This can be done using a vice. In them you need to bend the knife in a vertical position. If hardening is carried out correctly, it will be stable and only when it reaches a slope of 45 degrees can it break. If this happened earlier, then the technology was violated and the product was of low quality.

You need to know how to harden a knife. Especially if the product is formed at home. This process is simple, but requires a responsible approach, as it determines the quality of the resulting product.

Hardening should be carried out after certain work has already been done with the blade. It has the required shape. After annealing, it is much more amenable to other procedures.

The importance of the knife hardening process is enormous. Especially if it will be used for various tasks. Since the knife should not only have a beautiful appearance, but also be durable and hard. And only hardening will help make it like this.

How to harden a knife at home?

To harden a knife at home, you can use several plates. It will be as an experience. So, the first one can be heated unevenly. In this case, the temperature starts from the minimum and rises to the maximum.

Then the plate is lowered into a liquid, which is water or oil. After that it is installed in. Now you need to examine the fracture site. Depending on the grain size, the quality of metal processing is determined.

They must be large.

As you can see, the specific heating temperature is not indicated. Since it is better to determine it empirically for a specific case. This processing method will have the result that needs to be achieved.

The next thing you need for hardening is a medium. This procedure can be carried out in nitrogen and other conditions. But the most popular option is oil. It heats up to a temperature of two hundred degrees. Then the plate is lowered into it and left for a while. It can be either twenty minutes or two hours. Its choice depends on what metal is used. After this, plunge into cold water, as shown in the video.

At this stage you can also experiment. By alternating the medium, double hardening is achieved. It makes the product very durable with excellent cutting properties. This technique consists of heating the plate to a certain temperature. Then it is tested for strength in a vice. At the same time, it should break at thirty degrees. Then it is tempered so that the fracture occurs at forty-five degrees, as shown in the photo.

Tempering a knife at home: tips

When hardening a knife at home, you should take into account the recommendations of specialists. They relate to the pre-treatment of the blade, which consists of annealing it. This will result in a minimum of cracks. In this case, the procedure is carried out slowly and evenly. It is better to do this using a muffle furnace, which is adjustable. The procedure can also be carried out for hardened steel.

If hard hardening is carried out, the blade is lowered vertically into the liquid. In this case, you cannot move it, it must be motionless. This will allow you to get a product with a long service life.

You can see how knives are hardened in the video below. The whole process is clearly shown here with its features and subtleties that will certainly help.

Source: http://metall.trubygid.ru/obrabotka/nozh-v-domashnih-usloviyah

How to harden a knife?

The technology for obtaining a durable, strong, reliable knife is impossible without hardening. In essence, this is the same technological process of metal processing as sharpening, milling and grinding. Only instead of an emery wheel, a graver and a cutter, high temperature is used. And if polishing gives the blade a mirror shine, emery gives the sharpness of the blade, and engraving gives an irresistible design, then hardening makes it durable, which is very important even for a home kitchen knife.

What steel to choose for making a knife?

Today, a brand of steel and alloys can offer metal in several thousand names and grades. In addition to iron, the steel alloy may contain tungsten, nickel, vanadium, and zinc.

The physical and chemical properties of the metal depend on this; with tungsten it becomes hard and durable, zinc makes it soft, and the aluminum component allows it to be drawn. But this is not important for a knife; the determining factor here is how much carbon the metal contains.

The higher the carbon component, the stronger it is, but it is also more fragile. But the less carbon, the more ductile the metal, no, not softer, but more ductile.

Therefore, when choosing a metal for a knife, it is recommended to pay attention to high-grade steels and high-alloy grades; a blade made of such metal will be both durable and flexible, remaining sharp for a long time.

What is the purpose of the hardening process?

High-temperature processing of a metal allows you to change its internal structure - when heated to a certain temperature, the carbon content in it changes, and when it cools sharply, the metal retains the acquired structure. When alternating the heating and cooling process, the metal acquires strength. But heating at a certain temperature allows you to maintain the elasticity of the metal.

However, hardening is only the first part of the metal heat treatment process. The second part is the gradual cooling of the metal after heating. Tempering is necessary to relieve internal stress that arises in the crystal lattice of the metal and makes it brittle. Thus, in order to harden a knife, it is necessary to perform a complete hardening technology and complete it with a metal tempering process.

What is needed for hardening?

The key point in the blade processing process is the process of heating and maintaining the metal at a high temperature for a certain time. For this we use:

• Muffle furnace;
• Gas-burner;
• Forge;
• Blowtorch.

Each method has its pros and cons. The advantages of the burner and lamp include their mobility, which cannot be said about the forge and furnace, but the burner and lamp do not make it possible to maintain the temperature for the required time. On the other hand, it is possible to adjust the heating temperature with an accuracy of up to 50 degrees only in an oven, and the process of working with it is more convenient.

Hardening in the classic form is carried out by heating to 700-1000 degrees, after which cooling is done in a container with mineral oil. Therefore, it is recommended to work in a specially prepared room where it is possible to install both a stove and an oil container.

Heating a workpiece in a forge is quite simple - when air is supplied, the coals become hot and the workpiece can reach the desired temperature. The main thing here is not to overheat the blade. It is better to navigate using a special temperature scale, in which the temperature corresponds to a certain color of the metal. True, in order not to make a mistake, the scale must be studied thoroughly, since when overheated, the steel loses its properties and becomes soft.

The cooling process of the workpiece is carried out in a container with mineral oil, without access to oxygen. The container needed is quite large - the blade should be completely immersed in the oil, but the oil should not boil.

To work with a red-hot workpiece, you will need blacksmith pliers with long handles and canvas or leather gloves. At home, for work, you need to provide clothing made of non-flammable material and a mask to protect your face.

 The process of hardening a blade at home

When working with a forge or burner, the workpiece should lie on the coals when the flame acquires a crimson hue. A white or blue flame is not suitable for hardening - with a white color the temperature reaches 1000-1100 degrees, and the metal quickly overheats, and with a blue color of 500-600 it simply does not have time to warm up to the required temperature.

When the blade is uniformly painted purple-red and then yellow, and visible dark spots on the surface disappear, the workpiece can be removed and dipped in oil.

The workpiece is first dipped in a container with oil for 3-4 seconds, after which it is again sent for firing in a furnace or forge. When the metal reaches a dark red color, it is removed again and lowered for 4-5 seconds. The process is repeated 4-6 times, with the time increasing by 1-2 seconds.

The last time the workpiece is lowered into a container of water for cooling - you need to be especially careful here, since water can cause the droplets of oil remaining on the blade to splash.

To what temperature should the workpiece be heated?

Depending on the steel grade, heating is carried out in the following temperature ranges:

• Low carbon alloys and steels – 730-945 degrees;
• High carbon steels 678-851 degrees;
• Alloy steels – 850-1150 degrees;

Release of blanks

High temperature treatment creates internal stress in the metal. This negatively affects the flexibility and strength of the metal. The workpiece becomes fragile - if the pressure is incorrect or skewed, it begins to crumble or burst.

In order for the metal to become more ductile, a tempering procedure is carried out - bringing the temperature of the workpiece to the point of maximum ductility of the metal and its gradual, natural cooling. To do this, the metal is heated in a muffle furnace to the required temperature, and then, with the door closed, it is gradually cooled for 2-3 days.

It is quite simple to check whether the blade has been properly hardened - just run a file over the blade - if the blade slides, the hardening was successful, but if it touches the metal, then the procedure will have to be repeated.

Source: https://1nerudnyi.ru/kak-zakalit-nozh-10/

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

Hardening a knife at home: video, instructions, tips

It is no coincidence that the question of how to harden a knife yourself at home is so relevant, because it is this technological operation that allows you to give the blade of a cutting tool the required strength and hardness. If you neglect this procedure or perform it incorrectly, the cutting part of your knife will quickly become dull, which will make its use ineffective.

The durability and cutting ability of a knife are determined by the hardness of the blade.

Even if a homemade knife is made of a solid metal product (file, spring, valve, etc.), it still requires hardening, since during the manufacturing process the blade was subjected to intense mechanical processing and, accordingly, heating.

It is quite simple to check how correctly the hardening of a homemade knife has been carried out at home. To do this, you need to hold its blade in a vice and begin to bend it vertically. If the knife breaks at a bend angle greater than 45°, it means the hardening was done correctly.

For those who do not like to go into the subtleties and details of the process, you can immediately watch a video with a detailed description and demonstration of one of the methods of hardening a knife at home. If you want to get acquainted with the technology in more detail, we recommend reading the entire article.

Temperature

It may seem that there is nothing complicated in hardening a knife, but, as in any other technological operation, a number of nuances must be taken into account when performing it. The first thing that should be controlled in order to properly harden the blade is the uniformity and gradualness of heating.

If you neglect this requirement and heat the knife too quickly, this will lead to the formation of too large grains in the metal structure, which will make the product brittle.

For steel alloys belonging to different categories, different temperature conditions are used to perform quenching operations:

• steels belonging to the group of low-carbon alloys – 727–950°;
• high-carbon steel alloys – 680–850°;
• steels containing alloying elements – 850–1150°.

Processing modes for corrosion-resistant heat-resistant steels

At home, it is not always possible to use a device such as a pyrometer, which is used to determine the heating temperature of the metal. Meanwhile, you can determine the degree of heating of a steel product if you use an ordinary magnet. The essence of this simple technique is that every metal has a so-called Curie point, at which it turns from ferromagnetic into paramagnetic material, that is, it ceases to be attracted to the magnet.

Consequently, if the blade of a heated knife has ceased to be attracted to the magnet, its heating temperature has reached the Curie point (you can see its value for various metals in special tables).

Features of the technology

At home, if you approach the matter correctly, you can qualitatively harden any knife. This could be a hunting or folding knife, a bayonet-knife or a product in the form of a hook, a blade made of a file or a bearing, a butterfly knife, etc. It is somewhat more difficult to harden products made from stainless steel at home, but this problem can be solved, if you carefully study the process technology and select the appropriate heating equipment.

Various materials are used as a cooling medium when performing hardening, both in production and at home. Thus, the most common cooling media - water and oil - provide the following cooling rates of a heated steel product:

• oil at room temperature – 150°/s;
• oil heated to a temperature of 200° – 300°/s;
• water, the temperature of which is slightly above 20°, – 450°/s;
• ice water – 600°/s.

In some cases, hardening is performed by cooling the product in an intermediate medium, which can be molten lead. This technique, in particular, is used when hardening knives that are made from files.

Annealing a knife over an open fire requires close attention.

The most important problem that you may encounter when trying to harden a knife at home is overheating the metal, which leads to a significant increase in its fragility. It is also necessary to very carefully monitor the uniform heating of the knife being hardened, so as not to encounter the formation of transverse cracks on its blade.

There is a simple rule that should be followed in order not to encounter such a problem: the part of the blade that will not be sharpened is heated three times to a purple color, which corresponds to a temperature of 285 °, and the cutting part is heated only once to a yellow color, after which the degree Its heating is checked using a magnet. You can learn more about this technique by watching the corresponding video.

Colors of heat and tarnish of carbon and low-alloy steels

On stainless steels, tarnish colors appear in the same sequence, but at higher temperatures

Different cooling media also provide different depths of the hardened layer (hardenability). Thus, when cooled with water, steel is calcined at a rate of 1 mm per second, and when oil is used as a cooling medium, this rate is almost halved. To harden a double-edged knife, obtaining hard cutting edges and an elastic core, you need to do the following: the blade, heated to the required temperature, is first dipped in water for two seconds and then placed in oil.

Another technology that allows you to qualitatively harden the cutting edge of a blade with significant thickness is hardening the knife in graphite. Using this technology, the details of which can also be easily studied in the video, you can qualitatively harden knives of various models and configurations (hunting knife, bayonet knife, butterfly knife, etc.). At the same time, such hardening can be performed efficiently at home.

Homemade knife after hardening in graphite

It is often necessary to carry out zone tempering of an already hardened knife in order to make its middle part more elastic, while maintaining the hardness of the cutting blades. At home, such a technological operation is performed according to the algorithm below.

• The middle part of the blade is heated using a metal rod with a diameter of 10 mm, heated to maximum.
• After heating the middle part of the blade, it is dipped in boiling water and kept in it for 2 hours.
• After soaking in boiling water, the blade is dipped into ice water.

After completing all the manipulations described above, you will receive a knife whose middle part of the blade has been subjected to low tempering.

You can determine the tempering temperature by the colors of tarnish - a rainbow film that appears when the cleaned surface of the knife is heated: from light yellow (item 1) to bluish (item 6)

If you are trying to harden your knife at home, you should follow two rules that will allow you to get high-quality results.

• The volume of coolant used must be large enough (minimum 20 liters). Otherwise, the liquid will become very hot, which will change the temperature regime and cooling rate, and this in turn will negatively affect the result of the entire technological operation.
• In order for the heat transfer from the heated knife to be uniform and not to lead during the hardening process, it cannot be moved in the cooling environment - it must be kept motionless.

Rules for quality hardening

There are a few more simple rules that allow you to harden a knife at home to the highest possible quality.

1. Before you begin surface or deep hardening of a knife made of a certain grade of steel, you can select the modes for performing such a technological operation using plates made of the same material. The first plate is used to more accurately select the required heating temperature. To do this, the metal plate must be heated unevenly: one part to the maximum temperature, the second to the minimum. Then the heated plate is dipped in water or oil and, after complete cooling, it is clamped in a vice, broken and the metal is examined for fracture. High-quality hardened metal, if the temperature conditions were selected correctly, should have a coarse-grained structure.
2. The next stage of experiments with metal plates is the selection of the optimal cooling medium. Using various cooling media (water, oil, liquid lead, etc.), harden the plate to such a state that, when clamped in a vice, it breaks at a deflection of 30°. After this, it is necessary to temper the plate, also selecting various cooling media and temperature conditions. As a result of this operation, you should ensure that the plate, clamped in a vice, breaks at an angle of deflection of 45°.
3. To avoid the appearance of surface cracks on the blade of a hardened knife, the product must first be annealed. When performing such a technological operation, for which it is desirable to use a muffle furnace with a temperature controller, the following rules must be adhered to: the knife is heated as long as possible, slowly and evenly.

By following these simple recommendations, you can even harden a knife correctly at home, resulting in a strong and durable tool with excellent cutting properties.

Source: http://met-all.org/obrabotka/termo/zakalka-zakalit-nozh-domashnih-usloviyah-video.html

How to harden a knife

Many home craftsmen are interested in making their own knives. Their products go through a complex process of repeated forging, etching, and machining. But in order for the knife to be durable and serve for a long time, it must be hardened—exposed to high temperatures. After heat treatment, the physical and mechanical properties of the metal are significantly improved.

How to harden a knife

Heating temperature

The temperature regime is of exceptional importance for the high-quality hardening of a knife. If the workpiece is underheated, it will not be hardened, but if it is overheated, it will lose strength, deform or collapse. Alloys with low carbon content should be hardened at a temperature of 730-945 ° C. High carbon ones need to be hardened in the range of 678-851 °C. To harden alloy alloys, they are heated to 850-1150 °C

Cooling

In order to qualitatively harden a metal, it is very important not only to maintain the correct cooling temperature, but also to select a suitable coolant. Stainless alloys must be cooled in mineral oil with certain additives. Low alloy steels are cooled in aqueous solutions containing special additives.

Cooling the knife in mineral oil

The wrong choice of coolant can negate all the work and irreversibly damage the workpiece.

Vacation

After heat treatment, internal stresses accumulate in the workpiece. They reduce the strength, hardness and elasticity of the part. The part becomes brittle and is unable to withstand the design loads. To get rid of internal stresses and bring the mechanical characteristics to the calculated values, a tempering procedure is used.

During tempering, the workpiece is reheated to the plasticity temperature, but, unlike hardening, it cools smoothly, under natural conditions. Different materials have their own individual release schedules. Thus, when hardening a knife, the workpiece is reheated to 250 °C and left to cool in a muffle furnace.

Steel tempering

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