Peculiarities of the Surface Structure of High-Speed Steel After Pulse-Plasma Treatment

The work studied the patterns of structure formation and its influence on the properties of the surface layers of high-speed steel P6M5 (preliminarily heat-treated) under different modes of pulse plasma surface treatment (PPT). Mode I - direct impact of the pulsed arc (the distance from the plasmatron to the sample is 60 mm); Mode II - indirect impact (distance from the plasmatron - 30 mm). Using the methods of light, analytical raster and transmission electron microscopy (TEM), the following were studied: phase transformations; concentration changes of chemical elements; grain and subgrain structures, dislocation density, sizes and volume fraction of phase separations. On the basis of complex studies, experimental data were obtained and an analytical assessment of the contribution of structural-phase components and their parameters formed in the surface layers of P6M5 steel during PPT to the level of structural strengthening of the metal was performed. It was established that pulse plasma treatment of the surface of P6M5 steel in mode II leads to dispersion (by 1.5…2 times) of the austenitic-martensitic structure along the depth of the modified layer up to 40 μm (from the surface) with a 20% increase in microhardness (HV up to 9200 MPa). The formed substructure is crushed to 120…160 nm at the density of dislocations in austenite
$\rho=4\times 10^{9} \mathrm{cm}^{-2}$
and martensite
$\rho=2\times 10^{11} \mathrm{cm}^{-2}$
. Carbides of a complex chemical composition were found in the hardened layer: Me
6
C globular type (FeCr)
3
(W, Mo)
3
C mainly with tungsten. Impulse-plasma processing of the indirect impact of an impulse arc (mode II) improves the structural-phase state of the surface and leads to such structural changes that provide a significant increase in the operational properties of high-speed steel P6M5.