Hardening of metal. Methods from antiquity to modern times

The physical properties, in particular the hardness of any material, depend not only on its chemical composition, but also on the bulk molecular structure. A prime 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 in the manufacture of swords and swords. The art of the gunsmith was to create such a blade, which does not break in battle, will remain as sharp as possible for as long as possible. The knight's sword , the saber of the Saracen, the clown of the Russian Knight or the Katan of the Samurai met these requirements, and the technology of their production was brought to the level of high art.

Hardening of metal is done by heating it to a temperature 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 needs to be cooled quickly enough. Of course, this description of the process is extremely simplistic, in fact the 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 on 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 interference.

A surface hardening of the metal became possible. Until the white heat, the detail is brought not by immersion in 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, but inside it is plastic. Surface induction hardening is used in cases where strength is required and impermissibility of brittleness.

The author of the theoretical justification and methodology of practical application of this technology was in 1936 our compatriot - Professor VP. Vologdin. In addition to physical advantages, this development is also beneficial economically, since virtually all the energy emitted by the inductor is used to heat the workpiece.