It is not always necessary to have specialized equipment to make metal hardening at home with your own hands flawless. Anyone can do this task. If desired, with a set of basic knowledge, a simple fire as a furnace for heating, as well as a little free time, you can get an excellent blade with good hardening. And if it is possible to use professional equipment for hardening, then the results will exceed all expectations. Hardening a knife at home first of all begins with finding out the grade of steel from which the blade is made. Only after that the method of hardening itself is chosen.
Hardening features
To resolve the issue of how to properly harden a knife at home, you need to choosethe necessary material, depending on what is at hand, whether it be a metal plate, an automobile spring, or old tools that for some reason are no longer needed. Either way, this once featureless piece of metal, when properly tempered, will become a first-class blade that will last for years to come.
Hardening a homemade knife will not bring any result and even harm if you do not follow all the necessary rules. So, if the knife was not heated enough over the flame, then its blade will be covered with microcracks and will become blunt in an instant.
Excessive hardening of the knife will have exactly the opposite result, because it will become not only cracked, but also brittle, and will chip off whenever possible.
Really good hardening will allow the blade to bend up to 45 degrees, but without load, and then such a blade will return to its original state. Also, the knife will gain strength, sufficient even for extreme use, up to cutting wood.
How to make a knife with your own hands? Knife hardening and temperature control
Many mistakenly think that the best hardening will be the maximum heating of the steel and then its sharp cooling. Only with the help of tables and other reference materials can you find out the required temperature. This is the weakness of steel hardening. Not everyone will deal with so much new information. Moreover, not everyone has sufficient knowledge of the steel grade from which the blade is made, so you can resort to a simpler method:
- Steel products with low carbon content must be hardened at a temperature of 800 degrees. But at home it is almost impossible to achieve such an accurate result. Therefore, a temperature of about 750 degrees and a maximum of 950 is allowed.
- Steels that have a high carbon content are hardened at a temperature of 850 degrees. The lower limit is 680.
- It is much more difficult to work with alloyed steels, because for good hardening they need to be properly heated, or rather, at least up to 850 degrees, and up to a maximum of 1150.
Temperature detection methods
To correctly heat the blade, you will need a device for non-contact temperature detection. Not every home has such a tool, because in everyday life there is practically nowhere to use it.
There are tricks for such cases. Everyone can apply them, because you always want to get a good result at minimal cost. Curie's law states that when steel is heated to the required hardening temperature, it loses some of its properties, or rather, ceases to be magnetized. Therefore, in this case, only a magnet is required to check the heating temperature of the product.
Knife hardening at home: technology
In order not to harm the blade, but to make it stronger, sharper and more resistant to external influences, you should use step-by-step instructions:
- Do not immediately take the finished product for hardening. To get started, you need to purchasea small piece of exactly the same steel. Alternatively, you can saw off a little from the side of the handle. This is necessary in order to check the correctness of all actions, and at the end it is necessary to test for strength, as well as for how the steel holds sharpening after hardening.
- Before hardening, to obtain a better result, it is necessary to properly warm the knife in a clay oven, bringing it to the hardening temperature. The principle of operation of such a furnace is that the blade does not come into contact with the source of fire, but is evenly heated by the furnace. An alternative may be a homemade stove made of bricks. In this case, the hardening of the knife will not bring unexpected costs.
- It is necessary to prepare a steel heating source for hardening, a blowtorch, a fire, an impromptu furnace are quite suitable for this. You can just buy a gas burner, which is widely available and has a relatively low price. Naturally, if it is possible to use a forge, then this will be the best option, but not everyone has access to such highly specialized equipment.
- Prepare in advance the tongs that will hold the blade during heating. An important factor is the sufficient length of the handles of the tongs, since during heating and cooling there is a high probability of burns, so you should protect yourself in advance.
- Stock up on metal containers for coolant. As a coolant, as a rule, mineral oil is used. The fact is that it is oil that is capable of sufficient speedcool the heated workpiece without causing damage.
What's next?
Only after all the above conditions have been met, you can start heating the workpiece. If we are talking about a workpiece, then the procedure starts immediately, and if the knife is hardened in an already assembled state, then before starting it is necessary to remove the handle, otherwise it will simply become unusable and burn out, which will once again cause unnecessary trouble.
Tempering process at home
We have already found out that the procedure will not bring any special costs, nor does it require academic knowledge. You can perform all the hardening procedures in a personal workshop or on a house adjoining site, since all this is not done in mass production, but in a single case. For home conditions, the hardening methods described below are quite acceptable.
Heating specific areas
This hardening method is based on the fact that different parts of the knife are heated separately. It is conditionally possible to divide the workpiece into two parts. This is the cutting part and the handle. The handle does not need hardening, which will keep sharpening or increase strength. As a rule, the knife handle does not receive strong enough loads, so it can be heated up to 300 degrees three times, followed by cooling. But for the working part of the knife, such hardening is not suitable. It must be heated once to a suitable temperature, after which, using a magnet, make sure that the temperature regime is correctly selected. Only after making sure, you can dip the workpiece into a container with oil.
Even heating
Using this technique will require repeated use of the coolant, so you need not one container, but several. The basis of the whole process is the uniform heating of the workpiece in the furnace. If you periodically dip the part in oil, over time it will heat up, so you will have to change the container. After fully heating to the required temperature, you need to abruptly place the product in oil to cool it as quickly as possible.
It has been repeatedly observed that during the heating process, the workpiece being hardened noticeably changes color, temperatures were measured during the process, which led to certain conclusions. The longer the workpiece is heated, the higher its temperature, and in the color scale this was expressed as the acquisition of a lighter shade. At the moment when the metal had a red-brown color, the temperature of the workpiece was approximately 530-580 degrees, then its shade flowed into burgundy, and the temperature readings were 650-720 degrees. Over time, the burgundy turned into red, the measurements already show results of 720-950 degrees. And only after the mark of 950 did the metal begin to acquire a bright orange hue.
The measurement data helps to extract another trick that will undoubtedly help the home master when hardening, especially if there was no such experience before.
It is also worth noting that when using steel with a chromium content, the heating temperature changes more slowly. Therefore, in order to achieve the same results, one has tospend a little more effort and time.
Knife edge hardening with graphite and cooling
Cooling the workpiece is the most important thing in hardening. Only in this way the blade will receive the necessary properties. If the cooling is not correct, then the workpiece will simply be sent for recycling, as re-hardening reduces the properties of metals.
Speed
In the cooling process, speed plays an important role. The cooling rate itself depends on the liquid that is used. Various fluids have been tested over the years, but only water and mineral oil have been used to achieve truly impressive results. Water is able to cool the blade at a fairly high speed, or rather 1 mm / sec. But when using oil, it was noticed that the workpiece cools down twice as fast.
If we consider the cooling of a workpiece made of stainless steel, which is quite often used in the manufacture of knives due to its properties, then in the process of heating the workpiece, it is necessary to lower it three times into a container with oil. And only after the workpiece acquires a bright red hue, it must be lowered into the water. It is important that there is circulation in the water tank. This can be achieved by a constant influx of water or a good shake up the container with water just before immersing the workpiece.
Only when the steel hardening process is completely disassembled, one can pay attention to hardening in graphite. Where is sheused? This method is especially effective when hardening homemade knives. The procedure is practically no different, except for the heating stage. All heating takes place in graphite shavings, which allows you to heat thick workpieces as evenly as possible.
