The metal heat treatment is a required process in metallurgy. Thanks to a properly conducted heat treatment of steel can improve those or other mechanical characteristics of the product. On this subject I can speak long enough. Let's see you, what is hardening of steel, why it is needed and what is the technology. At first glance, it may seem extremely difficult, however, to understand in more detail, it is not.
A bit of background information
Annealing is the process of altering the crystal lattice of steel and its alloys by reaching a critical temperature, which for each material its own. As a rule, upon reaching the desired temperature threshold followed by a sharp cooling. As the coolant can be water or oil, but about this in more detail we will discuss later.
It is worth noting that tool steel often used incomplete quenching. Its essence is that temperature is reached, at which are formed the excess phase. For other steel grades are used for full annealing. In this case, the temperature increases by 50 degrees. Non-ferrous metals are subjected to heat treatment without polymorphic transformation, and the steel with polymorphic transformation.
The removal of the quenching
Vacation – the process of cooling products, the essence of which is to obtain more plastic and less brittle material. At this strength try to keep at the same level. This product was placed in an oven with a temperature of from 150 to 650 degrees, where it gradually cools. There are three types of leave:
- Low-temperature – processed product gives high wear resistance, but such steel is worse perceive dynamic loads. The process takes place under the temperature of 260 degrees. Are subjected to low-temperature release of products from low-alloyed and carbon steels (cutting tools and measuring tools).
- Medium temperature - flows at a temperature of 350 to 500 degrees. The most common use is the release of springs, springs, dies, etc. Such a product will have good elasticity and endurance.
- High temperature the holiday proceeds at a temperature of 500-680°. After the process the product will have high strength and ductility. High temperature vacation suitable for further manufacture of parts, perceiving heavy loads (gear, shaft, etc.).
Hardening steel in the home
If you have a need to increase the strength home tool, it is not necessary to run to the blacksmith, because you can do on their own. For this you will need a minimum of equipment and knowledge. As an example, let's take the axe. If the product has been manufactured in the USSR, you can be sure that it is made to last. However, the current axes are not distinguished quality. The jam or chipping indicates that the quenching was not observed. But nothing prevents us not to do everything yourself.
For this kindle a fire with coals. The latter should be whiter. It speaks to their high temperature. Pre-prepare two containers. One fill the oil, you can testing machine, the second clean, cold water. When edge turns crimson, the axe needs to get. For hold you can use blacksmith tongs or something like that. Quickly dip the axe into the oil and hold for three seconds, then the same amount again and get dipping. So you need to do to the loss of bright colors. After you dip the axe into the water, do not forget to stir. At the same time hardening steel in the home is finished. And now we go on.
Details on the heating of metal
The whole process of quenching can be conditionally divided into three stages:
- heat steel
- extract is necessary to the completion of all structural transformations and end-to-end warm-up
- cooling (speed adjustable).
If we talk about products made of carbon steels, the hardening is carried out in chamber furnaces. It does not require pre-heating, due to the material's resistance to warping and cracking. Complex products, for example sharp transitions and fine line, require preheating. Do this:
- in the salt furnaces with 3-fold dip for 3-4 seconds
- in individual ovens at a temperature of 400-500 degrees Celsius.
You need to understand that technology means even heating. If one approach is not to provide, the necessary shutter speed for through warming up. The more products is in the oven, the longer they must be warm. For example, one disk cutter with a diameter of 2.4 cm requires an exposure of 13 minutes and a dozen of the same product must be heated for 18 minutes.
Methods of steel quenching
Currently actively used:
- Hardening in one cooler. Its essence lies in the fact that the product is placed in the quench liquid, where it is before it completely cooled. This hardening can be realized at home.
- Hardening in two environments – a method suitable for processing carbon steel. The essence of the method lies in the fact that the part is first immersed in water (fast cooling medium), and then into the oil.
- Wavy – the essence of the method is that the workpiece spraying with water. This method of hardening is used when it is necessary to harden only a portion of the part. In addition, steam is not formed shirt, which increases the efficiency.
- Step – cooling were performed in a quenching medium at a temperature above the martensitic. After that comes the shutter speed. At this stage, the item must have the same temperature in all sections, which should correspond to the temperature of the quenching bath.
Protection of the product against external influences
Quite often there is a need to protect items from the harmful effects such as oxidation and loss of carbon. To achieve this we often use special gases which serves the furnace, where it is treated in detail. Of course, this is only possible if a complete sealing of the furnace. In most cases, the source of gas is a special generator that runs on hydrocarbon gases (methane, ammonia, etc.).
In any case, full hardening steel should be protected. If the gas to bring does not work, then it makes sense to use a sealed container. As the sealant used is clay, which does not allow air inside. Before doing this, it is desirable to overwhelm the detail of the cast iron shavings.
Full or surface hardening of steel must take place in salt baths. They protect the workpiece from oxidation, but not from decarburization. For this simple reason they are subjected to deoxidation brown or black salt several times for 8-12 hours. Salt bath operating at a temperature of 760-1000 degree, effectively rastilayutsya charcoal. This requires the glass has a lot of holes to fill dried charcoal. Then a glass lid to prevent the ascent of the coal and fall to the bottom of the salt bath. Over time the number of flames is gradually reduced. In fact, the more raskisleniya have on a single product, the better the protection against decarburization.
Periodically check the degree of deoxidation. To do this, take a regular steel blade and put it on 5-7 minutes in the tub. If it will break, not bend, the bath is considered to be sufficiently deoxidized. It is worth noting that some types of hardening steel do not require such measures.
It is easy to guess that, as a basic liquid for cooling steel products use water. In this case, adding salt or soap, you can change the cooling rate of the part. There were cases when the quenching tank is used for other purposes, for example for washing hands. The number of trapped soap was enough to make the cooling process was not so, and the product obtained the required properties.
The part was cooled uniformly over the entire surface, the temperature in the tank should not be less than 20 and above 30 degrees. In addition, you cannot use running water. There are significant disadvantages of such cooling, which consist in cracking and warping of the product. Therefore, water cooling is most often used for simple non-critical parts and tools, or having cemented floors. Water is cooled in quenching carbon steel.
Cooling of structural and alloy steel
Structural steel of higher quality, and most of the products has a complex configuration. For cooling use 50% caustic soda solution, which was pre-heated to a temperature of 50-60 degrees. After hardening in this solution the items will have a bright color that suggests that the technology was observed. It is important not to overheat the solution of caustic soda above 60 degrees.
Alloy steel is tempered in mineral oil. The same applies to very thin products made of carbon steel, such as edge cutting tools. A key feature of this method is that the rate of cooling depends on the temperature of the oil. So, the process will be the same as at 20, and at 120 degrees.
About tempering temperature
Structure of steel after quenching can be different, depending on the tempering temperature of. But you need to understand that the temperature should be chosen depending on the grade of steel. For example, if you want to obtain a product of a hardness of 60 HRC, the vacation is carried out at a temperature of 200 degrees. In this case, the observed slight decrease in hardness and a decrease of internal stress. But high-speed steel should be dispensed at a temperature below 540 degrees. It is possible to talk about a significant increase in the hardness of the product.
The quenching temperature of steel should never exceed 1300 degrees, which is considered a critical threshold. The color of the product when it reaches this point will be white and normal – usually red or crimson. Minimum temperature for hardening steel parts 550 degrees. The product is bright red in color.
By the way, it is worth noting that quenching stainless steel is held under the temperature of 1050-1080 ° C in the water. Mechanical properties of the product at the end of the process are characterized by the fact that several reduced strength and hardness, but significantly increases the ductility and toughness. This can end the conversation on this topic. As you can see, to obtain the required mechanical properties, it is important to adhere to the technology, because the slightest deviations lead to undesirable results. If all is done correctly, even in the home, you will notice a significant change in a positive way.