Surface Electric Arc Hardening of Low-Carbon Steels

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.