Structural and Phase States and Properties of Plasma Coating of High-Speed Molybdenum Steel After Tempering

This article presents a comprehensive analysis of the structural and phase states, as well as the properties of plasma coatings on high-speed molybdenum steel after tempering. Advanced techniques, including scanning and transmission electron microscopy, X-ray diffractometry, and microcomposition analysis, were employed to investigate the impact of heat treatment on the microstructure and phase composition of the coating. Using methods of modern physical materials science, the structure, mechanical and tribological properties of the surface of a plasma deposited layer in a nitrogen medium with high-speed molybdenum steel on a substrate made of CSN 14331 medium carbon steel subjected to two times tempering at a temperature of 560-580°C for 1 hour have been studied. It was found that tempering of the deposited layer does not lead to a change in the morphology of the polycrystalline structure formed by eutectic grains and grains of a solid solution based on α-iron (BCC crystal lattice). The main phases are α-Fe (85% wt.) and carbides of complex composition Me<sub>23</sub>C<sub>6</sub> (9% wt.) and Me<sub>6</sub>C (6% wt.), forming eutectic grains. The formation of nanoscale particles of iron and chromium carbides along the boundaries of martensite crystals formed during the transformation of residual austenite during tempering has been revealed. The hardness of the deposited layer is 4.3 times higher than the hardness of the substrate, the wear parameter is 1.5 * 10-6mm<sup>3</sup>/ N*m, and the coefficient of friction is 0.66.