Ural Federal University, Nizhny Tagil Institute of Technology (branch), Nizhny Tagil. Russia

E. N. Safonov, Dr. Eng., Director of the School of Master’s Degree, Senior Researcher, e-mail: E.N.Safonov@urfu.ru
M. V. Mironova, Cand. Eng., Associate Prof., Deputy Director for Education and Science, e-mail: maria.mironova@urfu.ru
G. E. Trekin, Cand. Eng., Associate Prof., Laboratory Assistant-Researcher, e-mail: trekin1963@yandex.ru

An important problem of increasing the operational resistance of machine parts and technological tools is to obtain a hardened working layer with a given hardness distribution in depth corresponding to its functional purpose. The most technologically advanced method is surface plasma hardening. Among the advantages of such technology are accessibility, low cost and prevalence of equipment, a wide range of regulation of heat input in various ways, and sufficiently high productivity. Under the influence of a concentrated flow of thermal energy released in the plasma arc heating spot, a directional modification of the structure of the surface layer of the workpiece occurs due to phase transformations. By adjusting the speed, temperature and depth of heating, it is possible to change the state of austenite during the phase transformation and, ultimately, to form various products of its decomposition during cooling. The paper analyzes the hardness distribution over the depth of the thermal impact zone during plasma surface treatment of steels. It is revealed that it is possible to form three characteristic variants of the hardness gradient in depth of the hardened layer. A smooth change in hardness was observed on low hardenability steel. High calcinability steels are characterized by a stepwise hardness distribution or mixed - smooth with a stepwise one. Martensitic steels are characterized by a mixed hardness distribution. The probable processes leading to the formation of each of the characteristic hardness gradients are determined. Recommendations are given on the choice of processing modes based on the functional purpose of the gradient hardened layer.

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