Physical properties, in particular, hardnessany material, depend not only on its chemical composition, but also on the bulk molecular structure. A striking example is a diamond, consisting of the same carbon atoms as a conventional pencil lead. Iron can also become softer or harder, depending on how its crystal lattice is formed. This property is known to people for a long time, and, as often happens, it was initially spread in weapon technologies.
Hardening of metal from ancient times was practiced atmaking swords and sabers. The art of the gunsmith was to create such a blade, which will not break in battle, will remain as sharp as possible for as long as possible. The sword of a knight, a saber of a Saracen, a klendzen of a Russian knight or a katana samurai met these requirements, and the technology of their production was brought to the level of high art.
Hardening of the metal is done by heating it up totemperature, called critical. Its value corresponds to a material state at which an increase in entropy occurs, leading to crystal changes. To fix this position, the object must be cooled quickly enough. Of course, this description of the process is extremely simplistic, in fact, technology is usually much more complicated. However, it is this method that makes hardening of the metal at home in those cases when the purchased instrument, for example, an ax, is too quickly blunt. It should be remembered that it is impossible to repeat this procedure many times, otherwise the metal will "get tired", its internal molecular bonds will be weakened, and except for melting it will not do anything.
As in any other case, one can not rely onon the principle "the more, the better." To obtain the desired properties of the object, it should be heated to the desired temperature. Unfortunately, the thermometer can not be used. The method used for thermocontrol is also very ancient. The temperature is determined by the color of the glow, and when it is reached, the hardening of the metal passes into the next phase - cooling, for which water or oil is used.
Comprehension of the effect of induction scientists opened a new page in the technology of metalworking. It turned out that the depth of the heated layer depends on the frequency of the current.
In the diagram, the arrows show the heating zones of the part and the passage of the lines of guidance.
A surface hardening of the metal has become possible. Until the white heat, the detail is brought not by immersion in the source of the flame, as it was in the Middle Ages, but due to resistive heating by currents induced by a coil that does not have direct contact with it. This technology provides unique, at first glance, contradictory properties: from the outside the product can be hard, and inside it is plastic. Surface induction hardening is used in cases where strength is required and brittleness is unacceptable.
The author of theoretical justification and methodologyThe practical application of this technology was in 1936, our compatriot - Professor VP. Vologdin. In addition to physical advantages, this development is also economically advantageous, since practically all the energy emitted by the inductor is used to heat the workpiece.