Structure Features of the Surface of Structural Alloyed Steel after Pulse-Plasma Treatment

The paper presents the results of a study of the development of one of the technological modes of pulse-plasma treatment of structural alloyed steel 40X. Steel 40X is widely used in mechanical engineering in the production of high-strength parts. After quenching and tempering, this steel has high mechanical properties:
$\boldsymbol{\sigma}_{0,2}=720\ldots 1560$
MPa;
${}_{\boldsymbol{\sigma B}}=860\ldots 1760$
MPa;
$\boldsymbol{\delta}_{5}\geq 8\%;\ \boldsymbol{\psi}\geq 35\%$
. In this experiment, steel 40X was used after preliminary heat treatment (isothermal quenching for bainite in oil at T=850°C). The subsequent pulse-plasma treatment was carried out at a specific heat flux Q=6,5×10
⁸
W/m
²
. Complex of methods for studying samples of 40X steel, including optical metallography, scanning electron analytical microscopy and transmission electron microscopy, showed the following. The base metal is represented by the structure of upper and lower bainite with a small amount of martensite. Base metal microhardness is 4120 … 5090 MPa. As a result of pulse-plasma treatment of the surface of 40X steel, a layer with a dispersed martensitic structure is formed on the metal surface to a depth of 70 µm during the formation of a substructural component. The microhardness of this layer is 6550 … 5160 MPa. The parameters of the substructure directly in the surface layer along the depth of the metal up to 20 µm are 30 … 120 nm. Herewith, a uniform distribution of dislocation density is observed in the forming substructure. The absence of dislocation density gradients predetermines the absence of local internal stress gradients. This will provide crack resistance of the treated surface in this zone.