Effect of Tempering on Structure and Properties of Plasma Surfacing of R2M9U High-Speed Tool Steel

Using the methods of advanced materials science, the structural-phase states and properties of multiple plasma-surfaced layers of the R2M9U steel formed in a shielding-alloying nitrogen environment on the 30HGSA steel are studied after its subsequent triple high tempering. It is found out that a framework-type structure is formed in the surfaced layer, wherein the base element is iron and the atoms of Mo, N, Cr, and V are localized in lengthy interlayers of the skeletal network formed by the carbide phase of different compositions. The atoms of Al are concentrated in the globular particles chaotically distributed in the surface layer volume. Both in the layer surface and in the zone of its contact with the substrate there are microcracks located along the phase boundaries. After the triple high tempering, the framework material structure is retained. A significant increase (a factor of 1.4) in the surfaced layer microhardness is revealed, which is attributed to the formation of a martensitic structure in the grain bulk, implying substructural strengthening of the material. The tempering is accompanied by a decomposition of the solid solution, followed by the formation of submicron-sized second-phase particles, indicating a dispersion strengthening mechanism.