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The geometric characteristics, microhardness and features of structure formation were studied in the heat-affected zone during the surface hardening of 09Г2, 20ФЛ, 45XHM, 65Г steels with direct current electric arc in argon. It is shown that the depth of zone with thermally modified structure is 0.7–1.2 mm with a tendency to decrease at maximum values of arc speed. Reheating of previously formed local hardening zone is accompanied by certain decrease in surface hardness, however, by changing the overlapping, the hardness of treated surface can be optimized with achieving of formation of regular structure. A regular gradient structure with periodically changing phase composition and microhardness is formed in the surface layer of steel that has been thermally treated with an electric arc. By changing the parameters of the processing conditions (electric arc current, speed of its movement, overlap of local hardening zones), it is possible to purposefully form a certain structural-phase state of the steel surface with properties that meet the operating conditions.

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Examined geometric characteristics, microhardness and features of structure formation in the heat affected zone of steels 09G2, 20L, 20FL. These studies were carried out after surface quenching by a magnetically controlled (scanning) DC electric arc in a protective argon atmosphere. It is shown that electric arc hardening forms on the treated surface of the steel a thin layer of martensitic-austenitic structure with varying composition and hardness. A ferrite-austenitic structure is formed in the region of transition from the base metal to the heat-strengthened metal. This structure contains crushed ferrite grain and winding boundaries between the structural components. On the periphery of austenitic grains martensitic layer is observed. Repeated heating, occurring during heat treatment of the adjacent surface area, is accompanied by a partial decay of martensite and austenite of a pre-hardened structure with the formation of bainite-and sorbitol-like tempering structures. On the surface, experienced repeated heating, the volume fraction of austenite increases. The dependences allowing to control the structural state and depth of the hardening zone are established.