How to harden a knife at home

Ever since people learned to process metal, all blacksmiths have constantly been faced with the question of how to give hardness to a blade. Most craftsmen guessed that to do this, the heated steel should be immediately cooled. There are legends that craftsmen from Damascus hardened their blades in mountain gorges, where they were cooled by strong winds. The blacksmiths believed that the weapon would become more elastic, gain hardness and would not break if the force of the wind entered it.

Methods for hardening a knife

There are not many options for such processing. In principle, there are only two varieties. You can harden steel using an open fire or do it in a furnace. However, no matter how hard you try, the fire will not be able to produce a flame temperature higher than nine hundred degrees. And this is where you will need a stove. It is quite possible to fold it even with your own hands. And although this procedure is not entirely simple, it is enough to master it only once and the structure will serve properly for a long time. And for novice craftsmen, such a stove is an essential item.

In the cell

Procedure:

1. The temperature inside the oven should be raised to the required value. Each case is unique, but in ours we need to reach 1070 degrees. After this, the blade can be sent to the oven.
2. It should be heated again to 1070 degrees and the time should be noted. It's quite simple.We hold for one hundred seconds for each millimeter of thickness.
3. We take the blade out into the air and let it cool. It is better to put it under a small press for fifteen minutes.
4. Now the metal should be tempered. To do this, put it in the oven, the temperature of which should be 200 degrees.

If we follow all the technology exactly, we will get a hardness of 56 HRC.

It should be taken into account that the example considers the option when no liquid was involved in the quenching. That is, the object was not immersed in it. Each steel requires special conditions. The final result directly depends on the technology of the hardening process.

On an open fire

Our ancestors processed metal in this way back in the distant past. Without measuring instruments, achieving the correct hardening requires special care and patience. The only thing that will help is a magnet. During heating, the metal gradually reaches a certain state, which in science is called the Curie point. At this temperature, the metal is not attracted to the magnet.

You can also focus on the color of the workpiece. The right moment comes when the metal acquires a dark red tint. The appearance of blue and black spots should be avoided. All this indicates that overheating has occurred. The blade is lowered into the coals as soon as the flames emanating from them acquire a crimson color.

Manufacturing of hardening furnace

The construction of such a structure is a very serious matter. After all, it is not built for a one-time use. How to lay out the furnace for hardening? Let's try to understand this in more detail:

1. First of all, you need to make the base of the camera correctly. The neck is formed from cardboard, which is coated on the outside with a thick layer of fireproof clay. Before applying it, the cardboard is coated with paraffin.
2. Once the mold is ready, it is left to dry for a day. After drying, it must be sent to the oven, which heats up to one hundred and ten degrees. And only then it will be possible to remove the cardboard base.
3. The next stage involves firing the entire structure over a fire. The temperature should be nine hundred degrees. It is necessary that the fire burns out completely and the future oven cools down on its own.
4. When the workpiece cools, it will already have the properties of stone. The former clay will become hard, like a brick. Now you can attach doors that should open horizontally.
5. Now is the time to wrap the entire stove with nichrome wire. The diameter of its cross-section should be approximately 0.75 mm. To cover the entire structure, you will have to spend eighteen meters. The wound wire is covered with raw clay. In this way we prevent the occurrence of a short circuit. The body of the structure must have two openings. One will house a thermocouple for temperature control. And through the second we will visually monitor what is happening.

Now we can say for sure that the production of the structure has been completed.

The procedure for hardening a knife in an oven

To properly process a blade, you should know exactly what is included in the alloy from which it is made:

• if it contains a very low amount of carbon, then it is hardened at temperatures from 750-950 ° C;
• an alloy with a high carbon composition requires 680–850°C;
• if an alloying metal with additional impurities is hardened, it should be heated to 850–1150°C.

The hardening procedure is not very complicated. Even a novice master will not find it difficult to do this. A knife reforged from any obsolete tool is heated three times in a furnace until it takes on a bright red color. After the next time The workpiece should be cooled, but this must be done correctly. Each time the dive time increases.

The heating temperature of steel is determined in various ways. In production there are pyrometers for this purpose. Well, at home you can determine it by color.

How to harden a knife without a furnace

You need to prepare:

• container with mineral oil;
• water tank;
• thoroughly hot coals;
• long-handled pliers.

As soon as it becomes noticeable that the metal has acquired the required color and no longer reacts to the magnet, the workpiece is dipped in oil. You shouldn’t hold it there for a long time—three seconds is enough for the first time. This is repeated several times. Each immersion in oil should be kept a little longer. At the final stage, the blade is lowered into a container of water.

Cooling the knife

Hardened steel is cooled in two different ways. This can be done with water or oil. If a stainless alloy is subjected to hardening, it is cooled in mineral oil, and low-alloy steel is immersed in water to which table salt is added. Cooling is a very important step. If you decide on its option incorrectly, then all the work can go down the drain. It is not advisable to combine water and oil immersion.

How not to make a mistake with the technique? The main thing here is the purpose and method of heating:

1. Steel blanks that are red-hot should be cooled with oil. After which they are heated again and dipped into oil again, for a longer time. Finally, cool them in water.
2. If the blade has an edge on both sides, then there is a different scheme. First you need to immerse it in water, and then cool it in a container with oil.
3. To make the metal as elastic as possible, the heated workpiece is immersed in boiling water for two hours, and then cooled in cold water.

Hardening quality assessment

At the end of the work, a homemade knife that was reforged from an old saw or any other used tool should be checked for quality. To do this, take a file and make circular movements along the blade. If you managed to harden it well, it will slide with ease. But if the knife sticks to its surface and the edge bends, then this is a sign that the process went wrong. It clearly needs to be done again.

Quality is checked according to the following criteria:

• a well-hardened knife retains its sharpness for a long time;
• if the blade comes into contact with hard metals, it does not deform;
• the blade remains durable, but at the same time has flexibility and ductility.

During cooling, the product is lowered into the liquid only vertically, with its back facing straight down. This will prevent thermal deformation.

If the device that is being hardened is forged from steel with a low carbon content, then it is not advisable to cool it in clean water. You need to pour a little regular table salt into it.

Hardening a knife is a responsible procedure and requires a certain skill and attention. But if you follow all the nuances of the technological process, the result will justify itself. In any case, it is not the gods who burn the pots! Having spent some time acquiring a certain skill, you can confidently show your friends and acquaintances the results of your blacksmithing work.