Methods for hardening knife steels. Hardening a knife at home. How to harden metal at home

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.

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.

Hardening methods

To calcinate the simplest blades made of structural steel, you can use a regular fire. It is impossible to raise the temperature above the required 900 °C when processing high-carbon alloys over an open fire. For this purpose you will need a special muffle furnace (chamber), you can make it yourself.

In the cell

If you want to make your own knives, it is better to use a stove made of refractory clay with a nichrome winding for these purposes. Heat treatment will take place under ideal conditions, at a sufficiently high temperature according to a given schedule. The size of this design is 200x100x77 mm.

First, a blank is made from cardboard, which is coated with paraffin. Next, clay is used - it is applied to the paper in a layer of sufficient thickness so that there are no cracks left. The joints are coated especially carefully. The door is made separately.

The clay will gain the necessary strength after thorough drying and further calcination in the oven at 90-110 °C. The final firing is carried out in a kiln over an open fire at 900 °C. The structure should be cooled slowly, so it should not be opened ahead of time. After the clay chamber has completely cooled, the doors are attached to it: they do this so that they swing open horizontally.

The well-dried workpiece is wrapped with nichrome wire, which will serve as a heating element. It will need about 18 meters. The turns should go tightly. To avoid interturn short circuits, the wire should be pre-coated with wet clay. We must not forget about making 2 holes in the oven. One is necessary to insert a thermocouple, a measuring device with which you can control the heating process. The second hole will be needed to control the process.

Scheme: 1 - nichrome wire; 2 - inner part of the chamber; 3 - outer part of the chamber; 4 - rear wall with spiral leads

Making a clay casing

Ready-made camera

You can harden the blade of a blade made of metal grades 45 and 50 over a regular fire or using a gas burner. To carry out the work, you will need fuel for the fire (coals), as well as a couple of large containers. One will contain machine oil, the second will contain water. Blacksmith's tongs are used to hold the hot blade.

Since prolonged observation of an open fire can affect vision, eyes should be protected with special glasses. It also doesn’t hurt to wear cotton workwear – synthetics can quickly ignite when hit by a spark.

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.

Heating source

In the open air, part of the heat emanating from the fire evaporates - the resulting temperature, especially when heat treating high-carbon steel, may not be enough. In these cases, it is better to use a muffle furnace, cutter, blowtorch, forge, even a regular electric or gas stove. When making a batch of knives, it is better to determine the hardening time experimentally using a test. To do this, several metal plates are heated: one to the maximum, the other a little less.

The fuel is coals, which are heated to a maximum white color. The shade of the flame is yellow-orange or crimson. The fire should be distributed evenly over the entire area of ​​the fire. After heat treatment, the hot object is dipped into the oil three times for a few seconds. The last stage is immersion in a container of water. The liquid should be thoroughly mixed (shaken) beforehand.

Gas stove

Temperature

There are several methods for hardening steel with different heating temperatures, holding times and cooling rates. Each grade of metal requires a certain temperature regime:

• for knives made of low-carbon steel, the temperature range should be 757-950 ° C;
• blades made from high-carbon grades are hardened at 680-850 °C;
• alloying alloys will require heating to 850-1150 °C.

In production conditions, to determine the degree of heating, a non-contact measuring device is used - a pyrometer; in everyday life, an ordinary magnet is used. With a significant increase in temperature, the magnetic properties of the metal decrease: if the steel workpiece is not attracted to it, the temperature is optimal.

Experienced craftsmen are able to determine the quality of hardening by the color of the steel: the lighter it is, the stronger the heating. The metal should not be overheated, otherwise it will turn black and it will be impossible to clean it. The sharpened part of the blade is heated 3 times to an almost purple color, that is, to a temperature of 285 ° C. The cutting part is processed on fire only once, but heated more strongly, until a yellow-orange tint appears, that is, up to 950-1000 ° C.

Red color indicates heating to 720-950 °C. Raspberry or light cherry shades of steel mean that the heating temperature corresponds to 800-850 °C. The appearance of a burgundy color in the flame indicates that the blade is not heated enough, only to 650-720 °C, brown - the temperature is not higher than 530-580 °C.

A light iris can also form due to the appearance of an oxidizing layer. In this case, the situation is the opposite: the lighter this thinnest top layer, the lower the temperature.

Cooling and holiday

Depending on the heat treatment method and the type of blades, different cooling methods are used, for example, in mineral oil (waste oil) or ordinary water with added salt. Options:

• if the blades to be hardened are heated red-hot, they are cooled in oil, dipping into it three times, so that each subsequent cooling is longer than the previous one; the last stage is immersion in pre-mixed water;
• for knives with double-sided blades, to give them greater sharpness and elasticity, the blades, on the contrary, are first dipped in water for a couple of seconds and then used for sharpening;
• To make the middle of the blade as elastic as possible, you can first warm it up with a metal rod, then immerse the knife in boiling water for a couple of hours, then in ice water.

It should be taken into account that metal cools 2 times faster in oil (working oil). To determine the cooling rate of a material in different solutions, you can refer to the summary table.

Steel that has been quenched and cooled is still too brittle. To further increase the characteristics of plasticity and viscosity, it should be heated again for an hour, but only to 150-200 ° C (this procedure is called tempering). For alloyed metal, the temperature should be in the range of 270-320 °C, for high-speed metal – even higher. To prevent the blade from bending during rapid cooling, it must be lowered into the liquid strictly vertically, the cutting edge must be at the bottom, and the blade must remain motionless.

Cooling in oil

Determining the quality of work

The quality of a properly hardened knife is determined by the following parameters:

• the blade must maintain strength when in contact with other materials;
• The hardness of the metal also ensures the quality of sharpening - it should last for a long time;
• The service life of a knife also determines its wear resistance, that is, the duration of use without loss of cutting properties. A good tool with regular sharpening can last up to 10 years.

An equally important indicator is plasticity. The material should bend fairly easily and, when unbent, return to its previous shape without any problems. Only if the above requirements are met will the blade last a long time.

The lifespan of a knife is determined by the quality of sharpening

The blade must remain hard during use

Video

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

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.

Hardening a knife at 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.

Heating source

Basically, several sources of heating the workpiece can be distinguished. It is better to exclude the muffle furnace, since according to all expert estimates, it is the best in this matter. But we will try to evaluate other fairly common heating devices.

The forge copes quite well with heating workpieces. A blowtorch or propane torch may be suitable for this purpose; by trial and error, you can achieve the desired result. By the way, for these two options, you can build a small oven from refractory bricks, and the process will be simpler and the result will be positive.

Fireproof brick furnace for hardening a knife.

Well, the last, one might say, completely unacceptable source of heating is a gas stove. If you want to spoil something, use this option.

Temperature

As has been said many times, every steel requires a certain temperature. In production, special thermometers are used for control, but in everyday life you can use a magnet (also mentioned above).

Dark spots should not be allowed; this is overheating, which will subsequently ruin the entire workpiece. If the master has enough experience, then he can determine by eye by the color of the hot metal whether the workpiece is heated enough or not. There is also such a hardening method: the part of the blade that is sharpened three times is heated to a temperature of 285 degrees, and the cutting part is heated only once, and to the maximum 950-1000 degrees.

The heating modes for each brand of steel are different:

• low-carbon steel requires heating in the range of 757-950 °C;
• steel with a high carbon content is sufficient at 680-850 °C;
• but alloying grades require from 850 to 1150 °C.

There is a whole table of colors, colors of incandescence. For example: brown-red 580-650 °C, dark red 780-830 °C or orange 950-1000 °C. So be careful and do not overheat the workpiece.

Cooling and holiday

For proper hardening, you need to maintain the correct temperature during cooling. It is preferable to cool stainless alloys in mineral oil with additives. And low-alloy steels, in aqueous solutions with salt and other additions.

Cooling the knife with mineral oil with additives.

There are many cooling options:

• blades with double-sided blades are dipped first into oil and then into an aqueous solution;
• Red-hot workpieces are dipped into the oil three times, each immersion taking a little longer than the previous one. And only then they lower it into the water;
• To give elasticity to the middle of the blade, this part is heated, then dipped in boiling water for 2 hours, and then in ice water.

With all these manipulations, it is worth considering that metal cools twice as fast in oil. A workpiece that has undergone hardening is subjected to a special process called tempering to restore the crystal lattice of the metal structure. There is nothing complicated in this procedure: the blade needs to be warmed up for a couple of hours. For alloy steel 270-320 degrees, for plain steel 150-200 degrees.

Determining the quality of work

Having gone through all the stages described above, I would like to know what will come of it. How to check the quality of the work done is quite simple:

• sharpening should last for a long time;
• the blade should not wrinkle or crumble when in contact with dense materials;
• the blade must have plasticity, bending and restoring its previous shape;
• a normal tool, with regular sharpening and constant use, should last at least 10 years.

Don't forget that true mastery comes with experience. And experience, as we know, is the son of difficult mistakes.

If you didn’t succeed the first time, or the second, then be persistent - the tenth time it will turn out no worse than others. Study the material, practice and sculpt true beauty.

I will tell you and show you a simple way to harden any knife at home. And then, I will not harden the entire knife, but only its cutting edge, which greatly simplifies the task.

If we go into detail, it will most likely not be hardening, but carburization, which aims to increase the hardness and wear resistance of the metal.

Hardening the cutting edge of a knife

We take a knife.

We go along the edge with a file, while paying attention to the dull sound and slight grinding of the metal. Everything indicates that the knife is made of ordinary steel and has not been previously hardened.

For hardening you need graphite. It is best to obtain graphite from graphite brushes of a generator or brushed electric motor. Of course, I haven’t tried it, but you can also get graphite rods from AA batteries or simple pencils.
In general, we grind this graphite into powder in any way. There is no need to grind it too much, without fanaticism.

Next, I need a metal base on which the graphite powder will lie. I took a piece of galvanized drywall profile.

The knife edge hardening process also requires a power source. Ideally, this is a pulsed DC welding machine set to minimum. You can also try to repeat the process using another source, 30-60 volts AC or DC. There is another dangerous option: using a 220 V network directly, in series with an incandescent lamp, but this is already fraught, so I do not recommend it.

Pour in graphite. We connect the plus of the welding machine to the base of the substrate, and the minus to the knife.
We set the inverter to minimum settings and turn it on.
We begin the process of hardening the edge. To do this, very carefully run the edge of the knife along the graphite pile.
Our task is: first, to prevent the blade from touching the base. And the second thing is to prevent the graphite from burning. In both cases the blade will be damaged.

Ideally, the blade should be moved slowly, and the graphite should sparkle and flicker. Naturally, you don’t need to lower the knife too much.
As soon as you notice the contact area heating up, immediately lift the knife.

The whole process does not last long, about 5 minutes. During this time I managed to walk along the entire length of the blade several times.

Knife hardening result

We take the file and shuffle the blade like the first time. A ringing sound is immediately audible, indicating the high hardness of the metal. Plus, the edge is practically impossible to process.

We cut a glass jar.

Leaves notches, be healthy!
We knock on a steel nail.

The result is excellent - not a scratch on the knife.

Finally, I cut the nail with a knife by hitting it with a hammer.

The knife was not damaged!
I'm not a big expert in steel hardening, but the method really clearly works. Local craftsmen say that such hardening increases the hardness of a section of metal to almost 90 units. I can’t disagree or refute, since I don’t have a hardness tester. If you have questions or suggestions, as well as comments, write in the comments. Good luck to all!

For many people, edged weapons are a symbol of strength and masculinity. This is what sometimes pushes home craftsmen to independently produce some of its types. The most common option is a knife. Making this product with a small list of electric tools is quite simple.

Knife manufacturing technology

Work should begin with the selection of suitable material. The blade blade must meet some mandatory requirements:

• Be convenient to use for certain purposes (a mushroom picker’s knife and a hunter’s knife are completely different tools);
• Be durable, withstand possible shock loads without destroying the blade;
• Be sharp and maintain an edge for as long as possible;
• Be as resistant to corrosion as possible.

There are a lot of options for blanks for the home craftsman. One of the most accessible is the flat file. Even a tool with a worked notch can easily be turned into a convenient, practical, durable knife.

Annealing the knife blank

The main difficulty associated with giving the rasp plate the required blade shape is associated with the high hardness of the part. Of course, you can process the workpiece on an emery machine, but you will have to spend a lot of time and use up several stones. An alternative is to reduce the hardness of the file. For this purpose, one of the types of heat treatment of steels (temperature treatment), called annealing, is used. It consists of heating the part to relatively high temperatures (about 650 - 700 C), holding it at these temperatures for several hours and slowly cooling.

At home, you can anneal a workpiece for a knife by heating it in a wood fire, in an oven, in a fireplace or in a stove, heating them properly together with the workpiece placed in the firebox and leaving the metal until the heating device cools completely. With this procedure, the hardness of the metal is significantly reduced, and it can be processed with both hand and electric tools.

Having achieved an optimal reduction in hardness, use a grinder to make a blank for the future knife.

Knife design and shaping

One of the most difficult tasks in making a knife is designing its shape. The simplest solution for a novice knife maker would be to copy the outlines from any product you like. It is best to pay attention to models with simple forms, since it will be problematic to repeat complex elements, which most often negatively affect functionality, at home.

Having some experience in fine arts, you can draw a unique author’s project. In this case, you should pay attention to the harmony of the lines and the combination of shapes of the handle and blade. The most common design mistake is a “break” along the butt line at the point where they join. If the specific application (such as a boning or skinning knife) does not require just such an articulation, then it would be best to make the transition along a straight line or a smooth arc.

The next point is the length of the handle. For most manufacturers, this parameter is 110 - 120 mm and almost does not depend on the length of the blade. In any case, even if the knife is made to suit your own hand, it is advisable to comply with such tolerance.

You should also not get carried away with the number and depth of finger grooves and stops. This reduces the convenience of working with a reverse grip and may well transform the product into the category of edged weapon.

To match the chosen shape, first make a simple cardboard template and check the correctness of the work by checking it.

One of the essential parts of a knife is the handle. For its manufacture, various types of wood are most widely used. Our version uses oak overlays, which will be connected with brass rivets. To install them, three holes must be drilled in the tail part of the workpiece. This work will not be difficult with annealed metal.’

Selecting the shape of the slopes

The geometry of the bevels or the cross-sectional shape of the blade are selected based on the purpose of the knife and the intended scope of application. The most common profiles are:

1. Straight wedge from the butt. The section is an isosceles triangle. The most universal form, combining the resistance of the cutting edge to impacts of moderate force and low resistance during cutting.
2. Concave slopes. This profile is typical for straight razors: a very delicate cutting edge that does not tolerate impacts or lateral loads, and high cutting qualities. Knives with this profile are convenient with a small cutting depth; as it increases, the resistance increases significantly.
3. Convex lens. The easiest profile to learn. Lenticular blades are designed for heavy duty work and are especially popular with hikers and survivalists. One of the most famous examples is the Swedish Fallkniven “F1”

There are also asymmetrical bevels, for example, on traditional Japanese knives used by professional chefs. Removing them requires some experience and special equipment.

Hardening steel at home

Before assembling, sharpening and polishing the knife blade, it is necessary to return the metal to its former hardness. For these purposes, another type of heat treatment is used - hardening. Many have heard about it, but not many have done it in practice, so we will discuss hardening steel with our own hands in more detail.

Technologically, steel hardening consists of heating it to high temperatures (about 900 C) and rapid cooling, usually in a liquid coolant. The most commonly available options are machine oil (waste) or water.

Secrets of hardening: heat source

There are several options for devices that can bring the heating of a steel part to the desired temperature threshold. The ideal option is industrial or self-made.

In the absence of such a tool, you can use another home assistant - a blowtorch.

A fairly powerful jet of flame makes it easy to heat parts of small thickness to the required temperature. Remember to move the torch along the plate being hardened to achieve even heating.

In addition, it is possible to use ordinary charcoal together with a blowtorch. To do this, dig a small hole in the soil, pour coal into it, and place the hardened blades of the knives on the edge. Heat the coal together with the plates with a lamp until the latter reaches the required heating. This method prevents the rapid cooling of the unheated part of the workpiece and its overheating.

The third option is to make a small forge. It can be either coal or gas. The main structural elements of the device are the housing and the source of forced air. The base of the coal hearth can be made of a steel sheet 10 mm thick with a piece of pipe with a diameter of about 20 cm welded at the bottom and an outlet from it for connecting a hose from the outlet of a household vacuum cleaner.

Do not forget to drill several holes in the sheet of sufficient diameter to supply air. Wood (barbecue) or coal is used as fuel.

Hardening secrets: heating temperature

One of the most important points when hardening steel yourself is achieving the optimal heating temperature for the workpiece. In production conditions, this value is controlled by special high-temperature thermometers. In everyday life, it is better to use old, grandfatherly methods.

The first of them is determining the temperature by the glow color of the workpiece. It has been noticed that when heated, the metal changes its color depending on the achievement of a particular temperature. For hardening steel, the most optimal color is light cherry or crimson, which corresponds to heating at 800-850 C.

The second way is to change the magnetic properties. Another property of steel when heated is a change in its magnetic properties. It is enough to lean the heated workpiece against a strong magnet and the absence of “attraction” between them will also give a signal that the workpiece has been sufficiently heated.

Secrets of hardening: cooling

To cool a workpiece heated to the required temperatures, take a container of convenient volume and pour the working material into it. Holding the knife by the shank with long-handled pliers, lower it into the oil and wait a while. The viscosity of the liquid ensures optimal heat transfer. Be careful, the oil on the surface may ignite!

The second method of cooling is using water. In this case, it is better not to use pure liquid. Before work, dissolve a few tablespoons of table salt in it or use brine to cool the metal. In the old days, when salt had a very high price, blacksmiths used their own urine as a brine solution.

One of the unpleasant moments that sometimes arises during hardening is the leash of the blade or its deformation, which occurs due to uneven heating or cooling. To avoid this, it is best to lower the blade into the cooling medium strictly vertically with the cutting edge down.

Secrets of hardening: vacation

Hardening has only a positive property, from the point of view of improving the operational properties of steel, which consists in increasing the hardness several times, but also a negative property, consisting in increasing the fragility of the workpiece. In other words, when a hardened knife hits metal, stone, wood or bone, the blade can easily split. To avoid this, a third type of heat treatment is used, called tempering. The workpiece must be heated to a temperature of 180 - 200°C, kept for an hour and cooled in air. Many home craftsmen temper hardened knives from files in molten lead, however, due to higher temperatures (the melting point of lead is 327 ° C), this can cause a significant decrease in hardness and loss of cutting properties. It is best to use an ordinary gas or electric oven, if you can persuade the owner of the house.

Assembling a homemade knife

Having completed all the above operations and bringing the knife steel to the required hardness, we proceed to assembly. We adjust the shape of the pads to the shank of the knife and cut out two additional leather inserts.

Then we lubricate the parts with glue, install brass inserts on the glue and leave to dry for several hours.

It is better to make the extreme insert not from a rod, but from a tube of the required diameter. This will help attach the finished product to a leather strap during use, which will prevent its loss while hiking, fishing or hunting.

After the glue has dried, carefully sand the handle and blade with sandpaper. To protect the blade from corrosion, it is enough to polish it well after final sharpening and finishing.

Dear readers, if you have any questions, please ask them using the form below. We will be glad to communicate with you;)

To obtain the necessary characteristics of the future knife, a sketch of it is drawn from a file as a blank on paper. It is better to choose an old tool with a worn notch. High-carbon steel provides the future knife with high cutting performance. The production of such a tool will be inexpensive, and its quality will surpass many factory samples.

General characteristics of a homemade knife

Knowing what kind of steel files are made from, it becomes clear why they are used to make knives. The material used is high-carbon steel of such grades as U10A, Kh12M, ShKh15.

Due to its high carbon content, this material can be hardened to 64-66 Rockwell units. This provides it with sufficient hardness. That is why at home they make a knife from a file.

A high-quality homemade knife can be made from:

• A thick drill for metal. It should be taken into account that the hardened part is only working. The shank is raw.
• Engine piston connecting rod.
• Socket wrench.
• Springs.
• File.

When making fincas on a professional basis, all these things are pre-forged. It is especially convenient to forge a file that has a suitable shape for this. During the forging process, the metal acquires the desired properties and becomes more elastic.

The thickness of the file is such that it requires removal of a layer of metal in order to properly form the bevel. During forging, the metal is not removed, it takes on a different shape. In order to forge a workpiece it will take much less time than when making it on a machine.

Technology and manufacturing stages

At the first stage, the selection of material is carried out. The better it is, the better the quality of the blade. The blade must meet the requirements:

• be adapted to a specific job;
• withstand shock loads;
• The sharpness of the blade must be maintained for a long time;
• not to be subject to corrosion.

To make a good homemade dagger, you first need to make a design for it. It is better to choose a simple form. Pay attention to the junction of the blade and the handle. There is no need for complications here. It is better to move along a smooth radius.

The DIY process at home consists of several stages. Their order is as follows:

• annealing of the workpiece;
• blade formation;
• hardening;
• vacation;
• making a handle.

Annealing of the original workpiece

The main problem is the high hardness of the file. Sanding iron will take a long time. To reduce hardness, the workpiece is subjected to heat treatment in the form of annealing.

Its essence is to heat the steel to a temperature of 650-700 degrees, hold it for several hours, followed by slow cooling.

To anneal at home, you can use a stove, fireplace or fireplace. The workpiece is placed along with the fuel and is heated during its combustion. Then everything cools down together. After this procedure, the material is ready for further processing. Without annealing, the workpiece cannot be worked with a metalwork tool.

Blade making process

Depending on the application, the cross-sectional shape of the blade is selected. It can be of several varieties:

• Straight wedge in the form of an isosceles triangle. It withstands uniform impacts well and has stable cutting resistance.
• Concave slopes. The sharp cutting edge does not withstand heavy forces and side impacts. As the cutting depth increases, the resistance increases.
• Convex lens - designed for heavy duty work.

After the workpiece has cooled, processing begins. It consists of stages:

Hardening the finished blade

The dimensions of the finished blade are checked with a caliper. In order for the blade to regain its former hardness, you need to know how to properly harden a knife. To do this, it is heated to a temperature of 900 degrees and quickly cooled in liquid.

At home, hardening a knife from a file is carried out using a blowtorch. To do this, a jet of flame is directed along the blade. It is important to ensure uniform heating.

Another option is to use charcoal in which the blade is buried. It is heated using a blowtorch. During the heating process, you need to accurately achieve the desired temperature. This is determined by the color of the metal, which changes depending on the heat. As soon as the temperature reaches 850-900 degrees, the iron acquires a crimson or light cherry color.

Cooling is carried out in waste oil or water:

• The waste is poured into a bucket. The knife is held by the shank and lowered into the liquid. Thanks to the viscosity, an optimal heat transfer process occurs. The holding time is several minutes. Be careful because the oil may ignite.
• When using water, salt or brine is added to it. It is not recommended to use pure liquid. To avoid dragging the metal, the blade should be lowered vertically.

Secrets of releasing a knife

Thanks to hardening, the hardness of the product increases. However, along with this, its fragility also increases. If the steel hits a hard surface, it may break. To prevent this from happening, you need to release the steel. This type of heat treatment is called tempering.

To do this, the blade is heated for an hour to a temperature of 180-200 degrees, and then cooled in air. Gas and electric ovens are used as heating devices. It is allowed to heat in molten lead. However, its melting point is 327 degrees, which leads to a decrease in the hardness of the finca.

Handle manufacturing stage

There are 2 linings on the knife shank made of wood. Exactly according to their shape, 2 leather inserts are cut out as gaskets. 3 holes are drilled in the blade, pads and inserts. 3 brass tubes are cut according to the thickness of the package.

All parts are lubricated with glue, the tubes are inserted and the entire package is clamped with clamps. After a few hours the glue will dry and the clamp can be removed.

At the last stage, all irregularities in both the blade and handle are removed with sandpaper. To protect the product from corrosion, it must be polished.

Making a homemade knife from a file at home is a painstaking process. However, the resulting blade will fully satisfy the necessary requirements for performing a specific job. The steel from which the file is made has high characteristics, which is the key to the high quality of a homemade knife.