Harden a kitchen knife. Hardening of the cutting edge of the knife with graphite

There are several ways to harden a knife at home, and you can resort to both the most primitive method, which involves the use of an ordinary fire, and a more complex one. technological process giving truly effective result. In any case, regardless of the selected hardening option, it is necessary to take into account such important indicator like steel grade.

Core Processes

Usually, home-made blades made of steel or available improvised tools that have lost their relevance (files, valves, etc.) are subjected to home hardening.

It is important to understand that only a blade that has gone through the correct hardening process will be as strong and durable as possible.

Weak hardening is fraught not only with the appearance of cracks on the blade, but also with its rapid blunting. If the knife was hardened according to all the rules, then it will break only when deformed, the angle of which exceeds 45 degrees. At the same time, the key to success is a properly selected temperature regime, which must correspond to the selected steel grade.

Temperature selection

You should not assume that in order for the knife to harden well, it must be held at maximum heat, because more does not always mean better. You can determine the optimal temperature range for hardening using special summary tables that indicate the marking of alloys. There are more a simple determination method that does not require knowledge of the exact characteristics of the metal being processed:

To determine the degree of heating of the blade, a special measuring device called a pyrometer is used. But even if a novice master does not have such an auxiliary device, this is not at all a reason to abandon the idea of ​​​​hardening the metal for a knife, because the degree of heating can also be determined using an ordinary magnet.

So, according to physical laws, a steel blade ceases to attract a magnet if it is heated to the so-called Curie point - the peak mark when high-quality hardening of the metal occurs. If you neglect this rule and overexpose the blade on fire, then it will become too fragile and the chances of breaking or stabbing it when used in everyday life will be much higher.

Technology and features of home heating

In order to harden the knife correctly, not only without damaging its blade, but also making it stronger and sharper, it is recommended that you familiarize yourself with the basic rules and nuances of this process. And the first recommendation is that instead of the blade, it is necessary to process another fragment made of the same alloy, conducting all kinds of experiments on it. Such a simple technique will help you choose the optimal temperature regime for heating and cooling without damaging the blade of a kitchen or hunting knife.

In addition, it is highly recommended to pre-bake the metal blade by placing it in a special furnace (muffle). Such heating is recommended to be carried out for as long as possible while observing the lowest temperature regime, which will ensure uniform heating of the steel and protect it from the appearance of surface chips and cracks during further processing.

Correctly harden a knife from a file and any other element at home You can use the following handy tools and tools:

• A heat source, which can be an open flame (bonfire or gas burner), a muffle furnace, special hardening equipment (forge), and an ordinary blowtorch. It is worth recognizing that hardening in a muffle furnace is the most productive, as it allows you to achieve maximum uniformity of steel heating.
• Quite wide containers with water and special mineral oil, which are necessary for proper cooling of a hot blade.
• Blacksmith's iron tongs with long handles, which will allow you to hold the part above an open flame. In order not to damage the knife handle when heated, especially if it is made of plastic or wood, it is recommended to temporarily release the blade from it.

The hardening procedure should begin only after the flame acquires a rich crimson hue. If white fire is used, then there is a risk of overheating due to the fact that the temperature of such a flame is the highest. At the same time, it is necessary to ensure that black or blue foci do not form on the surface of the metal product (not to be confused with tint, which is a thin oxide layer with characteristic iridescent tints).

Carrying out the procedure

The hardening process itself is so simple that, if desired, even the most inexperienced craftsman can handle it, using his own house as a mini-workshop. A It is done in the following two ways:

It is possible to determine the heating temperature of steel by its appearance directly during the hardening procedure. So, there are 4 main groups of shades of hardened steel, by which you can understand to what temperature it has warmed up:

1. Orange group - from 950 to 1000 degrees.
2. The red group, which includes 4 subgroups - from 720 to 950 degrees.
3. Burgundy - from 650 to 720 degrees.
4. Red-brown and its 2 subgroups - from 530 to 580 degrees.

That is, the lighter the iron becomes, the hotter it is at that moment and vice versa. When processing a smooth steel surface by heating it, a thin iridescent layer of oxidation begins to form, which is called tint among specialists. The color of this layer can also determine the temperature regime in the alloy, however, in this case, light shades will indicate a lower temperature in it.

The color of the tarnish changes in a certain sequence, starting from light straw, brown and lilac and ending with dark blue, light blue and graphite gray. Along with this process undergoes certain changes and temperature conditions, varying in the range from 220 to 350 degrees.

Things will be a little different when hardening chromium steel, which has a higher temperature regime (from 300 to 700 degrees) while maintaining the same colors and the sequence of changing shades of tarnish.

Cooling and graphite hardening

The most important role in the issue of blade hardening is played by the cooling process, the correct implementation of which ensures the strength and elasticity of the processed metal product. For these purposes, water and mineral oil are used, the immersion of the heated metal into which is accompanied by its cooling with different speed. So, in water, the cooling rate of steel is about 1 millimeter per second, while when the blade is immersed in oil, this figure doubles.

It is impossible to harden a stainless steel knife at home without a quality cooling procedure. A For its implementation, such effective methods are used:

Hardening of the knife with graphite proved to be no less effective, which is ideal for processing homemade knives with a thick blade. This technique, based on the heating of blades through a layer of graphite shavings, is most often used to improve home-made knives made from broken springs, beams, soldering irons and other help that has lost its relevance.

Centuries ago, master smiths questioned the hardness of a blade. And many of them understood that steel, after heating, must be quickly cooled. Damascus craftsmen tempered steel in the 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 of the cutting edge of the knife.

A little more history

Some blacksmiths used ram urine collected for three days for this purpose. And others used the urine of a boy for such a process, and he must certainly be red. These are the tricks used by the masters of the past. By the way, the use of urine can be partially justified, since the presence of salts in it accompanied the rapid intake of heat from the hot metal.

There were even rather barbaric hardening methods, a red-hot blade was thrust between the ribs of a slave, and it was believed that his strength passed 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 ways were done to achieve 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 tests, completely got rid of marriage and this person can be called the progenitor of modern metallurgy. Today, any student, having a wealth of knowledge accumulated over the centuries, can cope with steel hardening.

The choice of steel for hardening the knife

As you know, steel is nothing more than an alloy of carbon and iron. Supplements are added to them in small doses. They do not play a big role in 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, it is necessary to know the composition of the future blade. It is best to carry out a carbon analysis of steel.

Perfect hardened knife blade.

If the future product will be, for example, from a file or a car spring. Hardening in this case it 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”. It is necessary to tighten the finished blade in a vice and begin to gradually bend it, and if the blade breaks at about 45 degrees. We can safely say that the hardening was carried out correctly. But this should be done, after your first self-hardening of the blade, you need to remember the whole process well and repeat it again.

hardening methods

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

In the cell

1. We heat the furnace to the desired temperature, in this case 1070 degrees, and immerse the blades in the furnace.
2. Having loaded the blade into the furnace, we heat the furnace again to 1070 degrees, and at this temperature the time 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 a slight pressure.
4. Then the metal is tempered in an oven at 200 degrees.

Tempering a knife in a chamber made at home.

At this process steel gets 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, has been 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 careful and be patient. The only way to check can be a magnet. When the metal reaches a certain point of incandescence, the so-called Curie point, it ceases to interact with the magnet.

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

What will be required:

• mineral oil in a container (you can work out);
• bucket with water;
• well prepared coals;
• long metallurgical tongs.

Tempering a knife on an open fire.

After the part has acquired the desired shade and is not magnetized, you need to carefully take it with pliers and lower it into the oil for 3 seconds, and you need to do this several times. Each time holding the workpiece in the oil a little longer. And in the final stage, we immerse it in water.

How to make a metal hardening chamber

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

1. The main thing is to correctly make the "body" of such a camera; here they resort to a simple process. The future neck is made of any hard paper material (such as cardboard), coated with refractory clay thick layer. Do not forget to make a thin layer of paraffin between the shaping paper material and clay.
2. The second stage, at least a day, the future chamber is dried, and then placed in an 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 takes place on an open fire at a temperature of about 900 degrees, then it is cooled under natural conditions. You need to wait for the chamber to cool completely.
4. After the workpiece is cooled, it acquires the properties of a stone, it becomes very rigid 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 avoid a short circuit during winding, it is better to immediately coat with raw clay. We make two holes in the case, one for the thermocouple (to measure the temperature), and the second for visual control.

A self-made chamber for hardening a knife.

On this, we can say that the metal furnace is ready. As you can see, there is nothing complicated in making a muffle furnace for the home.

Hardening a knife at home

It is very good if there is a furnace for hardening steel. It can even be purchased at 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, not 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 an already real part.

Such a tricky technique will help you to "fill your hand" on small workpieces and acquire the skills of heating and cooling the 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, there are several sources of heating the workpiece. Muffle furnace, it is better to exclude, since for all expert opinion- She's the best in the business. But we will try to evaluate other fairly common heating devices.

The forge, quite well, copes with the incandescence of workpieces. A blowtorch or a propane torch may be suitable for this purpose, by trial and error, the desired result can be achieved. By the way, for these two options, you can build a small refractory brick oven, and the process will be easier, and the result is positive.

Refractory brick kiln for hardening a knife.

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

Temperature regime

As has been said many times that each 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).

Should not be allowed dark spots, 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 sharpened part of the blade is heated three times to a temperature of 285 degrees, and the cutting part only once, and up to the limiting 950-1000 degrees.

Heating modes for each brand are different:

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

There is a whole table of colors, heat colors. 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 vacation

For proper hardening, it is necessary to maintain the correct temperature during cooling. Stainless alloys are preferably cooled in mineral oil with additives. And low-alloy steels, aqueous solutions with salt and other additions.

Knife cooling with mineral oil with additives.

There are many cooling options:

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

With all these manipulations, it should be borne in mind that the metal cools down twice as fast in oil. The blank, which 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 above stages, I would like to know what will come of it. How to check the quality of the work done is quite simple:

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

Remember that real skill comes with experience. And experience, as you know, is the son of difficult mistakes.

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

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

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

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

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

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

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

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

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

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

Features of steel hardening

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

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

Types of steel hardening

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

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

Cooling medium

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

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

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

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

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

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

Distinguish the following ways cooling:

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

Temperature regime

The correct temperature regime for hardening stainless products is an important condition for their quality. To achieve good performance, they are evenly heated to 750-850°C, and then quickly cooled to a temperature of 400-450°C.

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

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

How to harden metal at home

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

Tempering an ax on a fire and in a furnace

If you want 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.

On the axes, during the manufacture, a brand is put, by which you can recognize the grade of steel. We will consider the hardening process using the U7 tool steel as an example.

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

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

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

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

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

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

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

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

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

Knife hardening

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

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

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

Illustrative video:

For a long time, hardening has been shrouded in a veil of mystery, and there are many legends, which simply do not have enough time and paper to list. They tempered swords and daggers in the urine of a red-haired three-year-old child and in the urine of a goat that had been starving for a week, and then ate only burdock for three days.

They were hardened by piercing the body of a fat slave, poetically describing the color of a red-hot sword: "The colors of the sun when it rises a third above the edge of the desert." They were hardened in spring water, while for darkness they closed the doors in the forge, drove out strangers and at the same time chopped off the hands of excessively curious apprentices who were trying to find out the temperature of this water ahead of time. We also need to harden, we need an excellent result, but there is no time to repeat all these experiments, and it is expensive to buy a slave and fatten him - you will go around the world yourself.

Somehow it so happened that traditionally by hardening they try to achieve maximum hardness with miserable remnants of strength. But after all, the cutting resistance of the blade is important for a knife, and this parameter is directly related to the strength of the edge and to a much lesser extent depends on hardness. A heavily hardened knife will chip along the edge and become dull quickly. It turns out to be absurd: they achieve hardness at the expense of cutting qualities, although the durability of the blade is a practical value, and one can only abstractly boast of superhardness: “You have a knife of 58 units?! And I have 72 units!!!”, completely losing sight of the fact that this super-hard one is sharpened only with diamond bars and this has to be done 4 times more often.

To begin with, let's understand that a knife works in completely different conditions than a chisel or an electric planer knife, even a saber cannot be compared in working with a knife. It has a large mass and speed, so the structure of the blade edge can be rougher and harder for better work. Comparing a saber and a knife is like comparing two saws: one for felling - with large teeth, and the second for fine carpentry work.

The working knife must be thin and strong. When cutting a carcass, you can drop a knife on a cobblestone and immediately step on it - the knife must withstand such a test. Therefore, during hardening, strength is given priority over hardness. I affirm that a knife is normally hardened if it can be bent from 45° to 90° from the vertical in a vise. A very hardened knife breaks at a deviation of up to 45 ° from the vertical. So you can heat a large and thick knife in the butt, strength will be achieved by thickness. It is unacceptable that the knife breaks at deviations less than 45 ° from the vertical - this is an obvious overheating and such a product has a place on the carpet as an ornament, and in work it will let the owner down: the blade will crumble, the tip of the knife will break off.

It is impossible to temper one thing perfectly (even if you were told the steel grade, having distorted it over the years). The Technological Handbook is not an assistant; it does not provide hardening of steel, but of products. Those. the bearing is heated for hardness, the spring for elasticity, the valve for heat resistance. The knife also heats up like a product, i.e. the knife can be zone or surface hardened, but not uniform.

All this was a preface, and the practice of hardening is as follows. It is necessary to make several plates from the metal that you intend to heat. We heat the first plate unevenly from max to min t ° and kalim in water to make it easier to break. The unevenness of heating depends on the steel grade, which must be determined by spark breakdown, analysis.

The temperature range is:
Low carbon steels: 727° to 950°
High carbon steels: 680° to 850°
Alloy steels: from 850° to 1150°

So, the first strip from max to min in length, we harden it in water and break it in a vice, we look for the grain we need in size at the break. The fracture should not be coarse-grained, but not smooth (paraffin), the lack of grain is poor cutting properties. If you break a large file, then around the perimeter it will have a smooth break, and in the center - about the grain you need.

Check back often finished goods on the cut and you will soon know which grain works best. So, the desired temperature is found. Now on the second strip we check our eye: we heat the tip to the desired temperature, harden and break, the grain should be the same.

Now you need to choose a quenching medium. In the 19th century, up to 12 quenching media were used at any plant: from calm air to copper drums with mercury or nitrogen. We cannot afford such luxury, alas! I get by with half: still air, air jet, oil +20°, oil +90°, oil +200°, water +25°.

Quenching media differ only in the cooling rate. You can create a table:

Calm air - 50 ° per sec.
Fan or rider on horseback - 70° in sec.
Room temperature oil - 150° per sec.
Oil at 200° - 300° per sec.
Water +27° - 450° per second
Ice water - 600° per second

If quenching in water does not contradict common sense - the colder, the stronger, then quenching in oil at first confuses immature minds. And everything is simple - with increasing temperature, the oil is less viscous and cools faster. If that gives the right grain and strength, then smoking oil quenching is one of the best. Heating the product, then into oil t-200 °, exposure from 15 minutes to 2 hours, then into water - immediately hardening and tempering. The same hardening in liquid lead, but more rigid.

Alternation of media is possible, double hardening is possible, as well as zone hardening - that's all. Any wrestler will say that it is better to know three moves well than three hundred - badly. We continue our research. We take a plate, heat it to the t° that we have already determined, successively harden it in different media to such a degree of strength that it breaks in a vice at a deviation of 30° from the vertical, and by tempering we achieve that the plate breaks at 45°. That's the whole technique. We got maximum strength, with maximum cutting properties.

The hardness depends on the steel. Attempts to squeeze hardness out of any steel lead to a loss of strength and cutting properties. If you hardened two steels correctly (with priority to strength), for example: Kh12FM and U-8A, then Kh12FM will have 60-61 HRC units, and U-8A - 56-58 units. True, the U-8A will cut four times longer, but the X12FM cuts even after opening a can of canned food - so choose. By the way, I did not say that these two steels should be hardened in the same way, no - all the conditions are different, but the result is the same: they have the same grain and break in a vice at 45 °.

A few general words: before hardening, anneal the blade - there will be less twist and fewer cracks. Heating should be done slowly, not higher than the desired temperature - this gives uniform heating without unnecessary grain growth. Heating for vacation is better for a long time. Well, if there is a muffle furnace with adjustment. If, for example, steel is kept heated at 190 ° for about two hours, then it will be twice as strong as that which you heated in a furnace for 10 minutes. until golden (190°). Cooling after tempering is usually done in the same medium as hardening, although this rule is not always observed, it is better to experiment on the same plate.

Try to make heating for hardening as uniform as possible, otherwise you will get cracks across the blade, and you can make uneven tempering. You can heat the butt three times to violet (285 °), while the tip only once heats up to yellow color- this is easily done in the forge.

Such hardening gives more stable results than experiments with coating. One must always remember about the hardenability (the depth of the hardened layer). In water - this figure is 1 mm per second, and in oil - half as much. If you need to harden a double-edged blade (double-edged, as people say), and the temperature and medium, for example, water, have already been found, then you heat it very evenly without spots, to the desired temperature, lower it into water for two seconds, and then transfer it to oil. The edges with a thickness of two millimeters were calcined through, and the core remained elastic.

Leave is balanced. On a double-edged blade, it is very difficult to heat the middle to a high temperature without overheating the edges. But if you still need uneven tempering, then we heat the middle of the blade with a bar with a diameter of 10 mm, heated to a thousand degrees. If a low vacation is required (up to 190 °), then they use boiling water, stearin, and rosin. The blade can be boiled in water for a couple of hours, then dipped in ice water - this will be a low vacation. A piece of rosin (candle) is placed on the blade and heated in a flame, as soon as it melts, the temperature is reached (130 ° -150 °).

If a greater hardness is suddenly needed, then it is achieved by lowering the heating temperature (grain reduction) and a sharp decrease in the temperature of the medium. Usually they do everything the other way around: they heat it up a lot, get a large grain and the blade crumbles. First, we find at what temperature this steel gives a “paraffin” fracture, and harden it in the coldest possible environment: salt + snow + water gives approximately -4 °; acetone + dry ice gives approximately -70°. Harden for 2 seconds, transfer to water, release on the butt. Do not make the edge thinner than 0.5 mm, sharpening angle 45 °.

Such a knife easily opens a tin can, cuts all the knives of the neighbors in the bunks in the winter hut, after that it even cuts paper. But besides this, it doesn’t cut anything: it glides over the fat (on the table) and along the elk skin too. But sometimes it is useful to have such a product with you. If you are tempering a chisel or a saber, then look for the temperature that gives the paraffin break. This is max hardness at min strength. The so-called point "B" Chernov. Each has its own, but basically it is a transition from red to scarlet. Those. from dull to luminous. In a chisel, strength is achieved by thickness, partial hardening (only the edge); in a long length - also by partial hardening: coating in the Japanese manner, or shallow hardenability (coal, sand, sealing wax). Vacation with such hardening is selected very carefully.
The blade is lowered into the liquid vertically, sometimes with the tip down - this is a tougher hardening, with the tip up - this one is softer, and they are held motionless. If you pull the blade, the cooling will be uneven - the blade will lead and twist into a pig tail, cracks may appear. If you want consistent results, keep the blade still and allow the fluid to pick up the heat.

The movement of the blade in the air and in solid media is permissible: sealing wax, wet sand, wet charcoal, well, and the fat slave was pierced three times. Wet sand and coal reduce hardenability. If sand and coal are moistened with water, then you will get hardened to a depth of 1.5-2 mm, and steel hardened for elasticity will remain inside.

So practice, make 4 blades from one steel, and determine the parameters in advance, i.e. set goals and accomplish them. This experience will save tenfold time in further work.

When hardening products from one steel in one environment, the cutting properties of these products directly depend on the achieved hardness. Example: 9 x C steel, oil hardened. Cutting took place in a machine with a set pressure, paper was cut. When hardening in different environments, sometimes a softer knife will cut longer, i.e. with one chemical composition- different structure. And the third case, when steel and hardness are different. Here is a prime example from my experience. The test conditions are described above.

That is, a knife made of P18 will easily cut 9 x C, but it will have to be sharpened twice as often in everyday life and hunting. Here, rather, the difference is both in the chemical composition and in the structure. It follows that even when working with one steel, one cannot stupidly achieve some kind of max. HRC, it is necessary to bring the test to field conditions, and then choose the best without looking at the hardness. I want to hint that it is necessary to test on the material that this product will encounter more often on its life path.

All materials with which knives have to work are divided into two groups: soft and hard. But the group of soft materials is incomparably larger, so choose. There is no universal cutting tool.

There is no need to talk about the indispensability of the 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.

And then, and now, a person was worried about the same issue - metal processing. Now they do this more when creating blades, but the hardening of the knife is also of interest to the owners, although not many.

Peculiarities

The classic steel hardening process has always been accompanied high temperatures, in which the polymorphic transformation of steel took place. At the same time, heating was always accompanied by sharp jumps in temperature, because at a certain stage, steel was always cooled in water.

Temperatures affected the structure of the metal, because with its strong increase, the structure of the crystal lattice on its surface changed, and a sharp temperature drop, which was produced by water, strengthened it. In this regard, the technology of hardening knives today has not become much different from that which was applied to 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 are engaged in hardening knives at home, then you should know that not every knife that falls into your hands is suitable for temperature testing.

This method is optimally suited for products during the production of which stainless steel was used. This may be its high content, or it may be an alloy, which will include 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 it can be used on a separate area that needs to increase strength. The first kind is called global, the second was called local.

knife material

All types of steel are made up of simple iron to which carbon is added. This is a common alloy for kitchen knives. If other metals are added 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 even applied this process to Damascus steel.

The problem here is that hardening is good for steels that contain enough carbon. If there is little of it in the alloy, the knife after hardening will become stronger and harder, while it will begin to undergo corrosion, protection against which, damascus steel so famous.

graphite hardening

Graphite carburizing is a very simple but effective way to surface harden a knife by hand, which is best suited for strengthening some part of the blade.

To do this, you 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 is good for this, which is used when working with drywall and other finishing work.

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

Any instruction, including for the correct hardening of knives, should begin with preparation. When you have all the necessary components, you need to prepare the workspace.

We take a profile, pour our graphite on it, it should turn out to be a small slide. The positive cable of the power source must be connected to the profile, but the minus must be connected to the knife.

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

This method is well used for hardening exactly the edge, which gradually comes into contact with graphite. To do this, after all that has been done above, you need to turn on the power source and give voltage to our parts. The knife should be gradually drawn along the graphite with the edge of the blade.

When this happens, be sure - you will see the hardening process in person. This must be done gradually and carefully. If you touch the profile, the process is corrupted. If you keep the edge in graphite for a long time, it will light up and the hardening will be spoiled again. In both situations, the blade will be damaged and beyond repair.

It will be correct to harden with slow, gradual and short movements. Visually, it is very clearly noticeable when the graphite begins to heat up strongly and sparkle. Seeing this, you need to raise the knife. The blade should not be dipped very deep into the graphite, it is best to do this only with a cutting edge.

On small knife you will need about five minutes to harden its edge. This process is delayed, just due to the combustion 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