Specialized equipment is not always necessary to ensure that the metal hardening at home is flawless. Everyone can easily cope with this task. If you wish, having a set of basic knowledge, a simple bonfire as a furnace for heating, as well as a bit of free time, you can get an excellent blade with good hardening. And if you can use professional equipment for hardening, the results will exceed all expectations. The hardening of the knife at home first of all begins with the clarification of the grade of steel from which the blade is made. Only after that the method of hardening is chosen.
Features of quenching
To solve the question of how to properly harden a knife at home, you need to choose the necessary material, depending on what is at hand, whether it be a metal plate, a car spring or old tools that for some reason have become unnecessary . In any case, this once faceless piece of metal, having passed the correct hardening, will become a first-class blade that will last for many more years.
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 has not been sufficiently heated above the flame, then its blade will be covered with microcracks and will become dull in an instant.
Excessive hardening of the knife will have the exact opposite result, because it will become not only cracked, but also brittle, and will chip at any opportunity.
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 conditions
Many people mistakenly think that the best hardening will be the maximum heating of 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 the hardening of steel. Not everyone will deal with so much new information. Moreover, not everyone has sufficient knowledge of the steel grade of which the blade is made, so you can resort to a simpler method:
- Low carbon steel products must be tempered at 800 degrees. But at home it is almost impossible to achieve such an accurate result. Therefore, a temperature of approximately 750 degrees and a maximum of up to 950 is allowed.
- Steels that have a high carbon content are quenched at a temperature of 850 degrees. The lower limit is at 680.
- It is much more difficult to work with alloy steels, because for good hardening they need to be warmed up properly, or rather at least to 850 degrees, and to a maximum of 1150.
Temperature Methods
For correct heating of the blade, a device for non-contact temperature determination will be required. Not every home has such a tool, because in everyday life it is practically nowhere to use it.
For such cases, there are tricks. Everyone can apply them, because you always want to get a good result at minimal cost. Curie's law states that when the steel is heated to the required quenching temperature, it loses some of its properties, or rather it ceases to be magnetized. Therefore, in this case, you only need a magnet 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 a step-by-step instruction:
- Do not immediately take the finished product for hardening. First you need to get a small piece of exactly the same steel. Alternatively, you can saw off a bit from the side of the handle. This is necessary in order to verify the correctness of all actions, and in the end it is necessary to conduct tests for strength, as well as on how the steel holds the sharpening after hardening.
- Before hardening begins, in order to obtain a better result, it is necessary to warm the knife properly in an clay furnace, bringing it to the hardening temperature. The principle of operation of such a furnace is that the blade does not come in contact with a fire source, but is uniformly heated by the furnace. An alternative can be a homemade stove made of brick. In this case, the hardening of the knife will not bring unforeseen costs.
- It is necessary to prepare a source of steel heating for hardening, for this a blowtorch, a bonfire, an impromptu furnace are quite suitable. You can simply buy a gas burner, which is publicly available and has a relatively low price. Naturally, if it is possible to use the blacksmith's forge, then this will be the best option, but not everyone has access to such highly specialized equipment.
- Prepare mites in advance, with which the blade will be held during heating. An important factor is the sufficient length of the mite handles, 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 cooler, as a rule, mineral oil is used. The fact is that it is oil that is able to cool a preheated workpiece with sufficient speed without causing damage.
What next?
Only after all the above conditions have been met can heating of the workpiece begin. If we are talking about preparation, then the procedure starts immediately, and if the knife is quenched in an already assembled state, then before you start, you need to remove the handle, otherwise it will simply become unusable and burn out, which will once again cause unnecessary trouble.
The process of hardening at home
We have already found out that the procedure will not bring special costs, as it does not require academic knowledge. You can perform all the hardening procedures in a personal workshop or on a house plot, since all this is done not in mass production, but in a single case. For home conditions, the quenching methods described below are quite acceptable.
Heating certain areas
This hardening method is based on the fact that the various parts of the knife are heated individually. Conventionally, you can divide the workpiece into two parts. This is the cutting part and the handle. The handle does not need hardening, which allows you to hold sharpening or increases strength. As a rule, the handle of the knife does not receive sufficiently strong loads, so it can be heated up to 300 degrees three times with subsequent cooling. But such hardening is not suitable for the working part of the knife. It needs to be heated once to a suitable temperature, after which, using a magnet, make sure that the temperature regime is chosen correctly. Only making sure you can dip the workpiece in a container with oil.
Uniform heating
When using this technique, repeated use of the coolant will be required, therefore not one capacity but several is needed. The whole process is based on uniform heating of the workpiece in the furnace. If you periodically dip a part in oil, it will heat up over time, and therefore you will have to change the capacity. After fully heating to the required temperature, you need to sharply place the product in oil in order to cool it as quickly as possible.
It was repeatedly noted that during the heating process, the hardened billet noticeably changes color, temperatures were measured in the process, which led to certain conclusions. The longer the workpiece is heated, the higher its temperature, and in the color scheme this was expressed as an 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 hue flowed into burgundy, and the temperature was 650-720 degrees when measured. Over time, the burgundy turned into red, with measurements already results in 720-950 degrees. And only after the mark of 950 the metal began to acquire a bright orange hue.
These measurements help to extract another trick that will undoubtedly help the home master in hardening, especially if such an experience was not previously.
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, you will have to spend a little more effort and time.
Hardening the cutting edge of the knife with graphite and cooling
Workpiece cooling is the most important thing in hardening. Only in this way will the blade get 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 directly depends on the liquid that is used. For many years, various fluids were tested, but truly impressive results were achieved only using water and mineral oil. Water is able to cool the blade at a sufficiently 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 billet made of stainless steel, which is often used in the manufacture of knives because of its properties, then in the process of heating the billet, it is necessary to lower it three times in a container with oil. And only after the workpiece acquires a bright red hue, it must be immersed in 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 of the container with water immediately before immersing the workpiece.
Only when the hardening process has been completely disassembled can we pay attention to hardening in graphite. Where is it used? This method is especially effective in hardening homemade knives. The procedure is practically no different, except for the heating stage. All heating takes place in graphite shavings, which allows warming up thick workpieces as evenly as possible.