Nitriding for increase of corrosion firmness of details of the aviation industry

In article one of processes of himiko-thermal processing - nitriding which is widely applied in aviation, automobile and tool industries to hardening and increase in corrosion firmness of details is investigated. It is one of resource-saving, adjustable processes low temperature processings, allowing to receive a demanded complex of physicomechanical properties, in particular, for the aviation details working in the conditions of raised deterioration and excited environments.

Are investigated a new way of nitriding - in conditions gazo- and thermocyclic influences. Alternating processes of nitriding (saturation) at the first stage and denitriding (resorption of a layer) at the second stage of a cycle, changing diffusion factor at a thermocycle and defining optimum time of half-cycles of saturation and resorption on a surface it is economic and it is easily possible to receive pore-free ε - a phase possessing high corrosion firmness.

Kinetic laws of growth of a diffusive layer on ARMCO - iron are defined at Gazo-thermocycle nitriding (at temperatures cycling 520º С and 620ºС). It is established that in short duration half-cycles of saturation and resorption (0,5 hour and 1) nitriding process prevails over process denitriding, that is the nitrid zone does not have time to resolve. In long duration half-cycles, on the contrary, process resorption proceeds more intensively, than saturation process.

The new technological parameter - duration of a half-cycle (time of saturation and time resorption the nitrated layer), and the quantity of such half-cycles are needed for regulation of phase structure and, accordingly, of reception of a various set of mechanical characteristics is investigated. It is established that the diffusive layer received as a result of the first half-cycle of saturation, i.e. flowing nitriding, in the course of the subsequent denitriding undergoes essential changes, and changes occur both in superficial to a nitrid zone, and in a zone of internal nitriding.

It is established that at end of process by a saturation stage (the quantity of cycles - 7) on a product surface is formed ε - a phase possessing hardness and corrosion firmness. For increase only wear resistances are recommended to be finished nitriding process by a stage resorption (quantity of cycles - 6) at which on a surface of the strengthened zone it is formed firm and wear-resistant γ׳ ? a phase.