physical properties, in particular, the hardness of any material not only depends on its chemical composition, but also the bulk of the molecular structure.A striking example is the diamond, composed of the same carbon atoms as ordinary pencil lead.Iron may also become softer or harder, depending on how it is formed crystal lattice.It is his property is known to people for a long time, and as often happens, initially became widespread in weapons technology.
metal hardening practiced since ancient times in the manufacture of swords and sabers.Art of the gunsmith was that to create a blade that will not break in the battle will be as long as possible to maintain their sharpness.Sword Knight, Saracen scimitar, kladenets Russian knight or samurai katana meet these requirements, and their production technology are brought to the level of high art.
hardening metal is produced by heating it to a temperature called critical.Its value corresponds to the state of the material in which the increase in entropy occurs, leading to crystalline changes.To fix this situation, the subject should be fast enough to cool.Of course, this description of the process is extremely simplistic, in fact, technology is usually much more difficult.However, it is in this way made metal hardening in the home in cases where the purchased tool such as an ax, too quickly blunts.Keep in mind that repeat this procedure many times you can not, or metal "tired", its internal molecular bonds weakened, and besides, he melted down for nothing amiss.
As in any other case, you can not rely on the principle of "the more, the better."To obtain the desired properties of the object, it should be heated to the desired temperature.Thermometer, unfortunately, can not be used.The method used for temperature control are also very ancient.The temperature is determined by the color of light, and when it is reached, the hardening of metal moves into the next phase - cooling, which uses water or oil.
Comprehension scientists induction effect opened a new page in metalworking technologies.It was found that the depth of the heated layer depends on the current frequency.
Scheme arrow shows the heating zone and the details of the passage of pickup lines.
became possible surface hardening metal.Before the white-hot piece is brought not by dipping into the center of the flame, as it was in the Middle Ages, and by resistance heating currents induced coil having no direct contact with it.This technology provides unique, seemingly contradictory properties: outside the product may be solid, but inside the plastic.Surface induction hardening is used in cases when you need strength and fragility is unacceptable.
author of the theoretical foundation and the practical methods of application of this technology began in 1936, our compatriot - a professor VPVologdin.In addition to physical advantages, this development is beneficial and economically, since the preform is heated almost all the energy radiated by the inductor.
