Many are interested in how to properly temper metal at home and in what cases is this process required? Hardening of products from this material is carried out if necessary to increase its strength. For example, to harden edges for cutting kitchen utensils (knife, pruner) or tools (chisel, chisel, etc.) In addition, the metal acquires a certain amount of ductility, which facilitates the processing of the material. Blacksmiths are well acquainted with this rule. The article will describe how to harden metal at home.
What is hardening for?
Hardening of the metal increases the hardness of the product by about 4 times. In this case, an object of this material can easily cut the glass surface. Hardening is required due to insufficient strength of the item or vice versa. In the first case, metal products will jam, and in the second - crumble.
Checking the level of hardening of a metal product
To check the level of hardening of a metal product, you should take a file and run a tool along the edge of the object for cutting, for example, an ax or knife. If you feel that the file is starting to stick or stick to the metal, then this indicates that the product is not hardened enough. At the same time, its edge will be soft and supple.
If the instrument easily moves away from the object and the feeling is created that it is stroking it, and the hand does not feel unevenness, then this means that the metal is hardened too much.
It is possible to temper metal at home. At the same time, you should not turn to complex technologies. The process is done with your own hands.
It should be remembered that low-carbon steels are not subject to the process. But to achieve an increase in the strength of products made of carbon or tool materials is real.
How is hardening carried out?
Quenching technology involves two processes - heating a metal product to a high temperature and subsequent cooling.
Thermal surface treatment is advisable if:
- there is a need to give the metal extra strength;
- An increase in the level of ductility is required, for example, for subsequent hot forging.
The price of hardening a metal product at a professional level is 200 rubles. for 1 kg. Processing small parts with fire is cheaper. The price for this service is 20 rubles.
How to temper metal at home? It is necessary to familiarize yourself with some of the nuances of this case.
Heating should be even. Black or blue spots should not appear on the metal. Do not heat the product to the extreme temperature. The fact that the process is proceeding correctly is indicated by the appearance of a bright red color.
What equipment is used for hardening?
For example, in order to harden metal at home in the form of a drill, an electric or thermal furnace, a lamp for soldering, or a bonfire are used. What is suitable in a particular case depends on what temperature indicator is required for the material being processed.
Cooling different tools
Instrument cooling rules may vary. The process can be carried out in one or more steps. It all depends on the type of metal.
How to harden the metal not over the entire surface, but only in a certain place? In this case, an inkjet type of hardening is used. It implies the direction of a jet of cold water at an object pointwise.
If the action is carried out with one cooler, then specialized devices are required in the form of a barrel or bucket. For this purpose, even a bath is used. This cooling method is suitable for items based on carbon or alloy steel.
If a cooling circuit comprising two stages is required to lower the temperature of the product, then different media are used. This process provides metal tempering. Initially, drills or discs are cooled by water, then by machine or mineral oil. Cooling with it is the second stage of the process, as there is a risk of ignition under the influence of high temperature.
The use of water for cooling
The main cooling fluid is water. If you add a little salt or soap to it, then the cooling rate will change. Therefore, the hardening tank cannot be used for washing hands. To ensure the same hardness indicator on a metal surface, a liquid temperature of 20-30 ° C should be maintained. You can not often change it in the tank. It is forbidden to cool the product in running water.
The disadvantage of hardening with water is the appearance of many cracks on the metal surface. In this way, objects of simple shape or cemented should be subjected to the process.
What is used for hardening parts of complex shape?
How to temper metal of complex shape? For alloy steel , a fifty percent solution of caustic salt is used in cold form or heated to 50-60 ° C. Parts heated in a salt bath and hardened in it come out bright. It is impossible that the temperature of the solution was above 60 ° C.
Vapors that occur during hardening are harmful to health, so the bath must be equipped with a ventilation hood.
How is alloy steel tempered?
How to temper metal? At home, alloy steel is subjected to a process in a bath with mineral oil. Thin carbon steel items are quenched in the same way. The advantage of oil baths is that the cooling rate is not dependent on the temperature of the oil. It will flow equally fast at any rate.
How to temper metal in oil correctly? Water should not get into such a bath, as this can cause cracks to appear on the surface of a metal object. It is noted that if the oil is heated to a temperature of 100 ° C, then the ingress of water will not cause cracking of the product.
Cons of an oil bath
- Hardening produces toxic gases.
- A plaque forms on the subject.
- Oil may ignite.
- The quality of quenching in an oil bath gradually decreases.
How is metal tempering carried out?
All hardened parts are subjected to vacation. This relieves internal stress. As a result of this process, hardness decreases and the ductility of the material increases.
How to release tempered metal? Depending on the desired temperature, the process is carried out:
- in bathtubs with oil;
- in bathtubs with nitrate;
- in air circulation furnaces;
- in alkaline baths.
What determines the choice of vacation temperature?
How to loosen hardened metal correctly, what should be considered? An important factor is the temperature of the vacation. It depends on the type of steel and the required hardness indicator of the product. For example, a product for which HRC 59-60 is required is tempered at a temperature of 150-200 ° C. In this case, the internal stress decreases, and the hardness practically does not change.
High-speed steel is lowered at a temperature of 540 - 580 ° C. This process is called secondary hardening. Its result is an increase in the hardness of the product.
The metal is tempered by the color of discoloration. It is heated on an electric stove, in stoves or in hot sand. The oxide film that appears when heated is painted in different colors. In this case, the surface of the metal product is cleaned of scale, carbon and oil.
After tempering, the metal is usually cooled in air. Nickel-chromium products are cooled in water or oil, since the slow cooling of these grades leads to temper brittleness.
How to temper steel over an open fire?
How to temper metal on fire? To easily carry out the process of metal hardening at home, a fire should be built and two large-capacity containers prepared. A lot of hot coals should be present in the fire.
Diesel or motor oil should be poured into one container, and clean water into another. Better if it is a well. Initially, a tool is prepared with the help of which the hot metal will be held to the limit. They use blacksmith mites. But if they are not, then you can use something similar.
After doing the preliminary work, metal drills or other tools are placed in the center of the flame on hot coals. Coals of white are much hotter than the rest. The hardening process must be observed carefully. The flame of the fire should be crimson. If the fire becomes white, then there is a risk of overheating and even combustion of the metal.
It is necessary to ensure that the raspberry color is distributed evenly over all areas of the fire. Black spots should not appear on the edge of a metal product. If blue spots appear on the material, this indicates excessive softening of the material and its excessive ductility. This must not be allowed.
After calcining a metal product in a fire, it should be removed from the hot spot. A hot object is lowered into a container of oil many times at intervals of 3 seconds. The time interval is gradually increased. You can not delay at this stage. The operation is carried out soon and abruptly. The product is dipped in oil until its color ceases to be bright and saturated.
Then the item is immersed in a bucket of water, which must be shaken a little. At this stage, one should be extremely cautious, since drops of oil on a knife or ax can be drained when immersed in an aqueous medium. Drills should be lowered into the fluid with a thick tip.
How to harden the metal, you already know. If you follow all the recommendations, the process will bring the desired effect.
In what cases resort to the use of an electric furnace?
At home, it is necessary to harden products from non-ferrous metals or steel. In this case, a very high temperature of up to 900 º and higher will be required.
Only a electric or muffle stove is able to preheat a metal product to such an indicator. The latter can be made with your own hands, but it is impossible to make an electric one.
How to make a muffle furnace?
How to temper metal at home using a do-it-yourself muffle furnace? Such an adaptation will become very necessary in the household. It will allow heat treatment of metal products without unnecessary manipulation. To make a do-it-yourself kiln, refractory clay used for coating is required. From this material a camera is created with a thickness of not more than 1 cm. Its dimensions should be 210x105x75mm.
Carrying out the molding of a muffle furnace with their own hands, they resort to using a pre-prepared form of cardboard. So that it does not stick, it is impregnated with paraffin.
Clay is spread on the inside out. In this case, during drying, it will not shrink. When hardening, the material itself moves away from the edges of the form. Refractory clay can become the basis of the oven door.
A homemade muffle furnace should be allowed to dry in the open air. Then it is dried to the end in an oven at 100 º. Doors and a chamber are fired gradually with an increase in temperature to an indicator of 900 º.
Parts should be allowed to cool without removing them from the oven. Then the door joins it. Its surface is ground with a file.
18 m of nichrome wire is wound around the camera. Its thickness should be 0.75 mm. The first and last turns must be twisted. So that there is no short circuit, the distance between the turns is coated with clay. On a dry layer of material it is necessary to spread another layer with a thickness of 12 cm.
A self-made muffle furnace consists of a metal frame, the size of which is 270x200x180 mm.
For easy assembly of the housing, it should be designed with two removable covers fixed by screws.
A door is hinged to the front cover. It should open in a horizontal direction. On this door with bolts and gaskets you need to install a ceramic part.
All gaps are smeared with clay, and the edges of the wire are removed on the back cover of the frame.
Then a connector and a standard cord with a plug are made. All openings between the heating parts and the frame are filled with asbestos chips.
To install a thermocouple and to be able to track the process of metal quenching in the chamber, two holes must be drilled. The diameter of the first should be 1 cm, and the second 2 cm. Closing shutters made of metal are attached to them.
The weight of a homemade muffle furnace is 10 kg. She heats up to a temperature of 900 º for an hour. With its help, the process of hardening drills, files, dies and many other metal products can be facilitated.
Muffle equipment for metal hardening is not the only device. For this purpose, a chamber device, an electric or thermal furnace, and a bath furnace are used. Doing a muffle furnace with your own hands is more profitable than purchasing finished equipment. For example, the average price of such a device on the market is 40,000 rubles.