ROLE OF HIGH-TEMPERATURE TEMPERING IN FORMATION OF STRUCTURAL-PHASE STATES OF PLASMA-DEPOSITED MOLYBDENUM HIGH-SPEED STEEL

The technology of plasma surfacing in nitrogen on 30HGSA grade steel with a powder wire of the MoCrCoC system with a diameter of 4 mm formed a deposited layer with a thickness of approximately 9 ‒ 10 mm Argon of the highest grade was used as the plasma-forming gas. The structural and phase states and defective substructure of the surface of a plasma-deposited layer in a nitrogen medium with high-speed molybdenum steel on a substrate subjected to double tempering at a temperature of 560 ‒ 580 °C for 1 hour have been studied by methods of modern physical materials science. It is shown that the deposited layer has a polycrystalline structure and contains layers of eutectic. The formation of a multiphase structure in the deposited layer was revealed, represented by an α-phase (solid solution based on the BCC crystal lattice Fe), a γ-phase (solid solution based on the FCC crystal lattice Fe), carbides of complex composition Me₂₃C₆ and Me₆C, iron carbides Fe₃C and chromium Cr₃C₂. It was established that tempering of the deposited layer does not lead to a change in the morphology of the structure formed by grains of eutectic and a solid solution based on α-iron (BCC crystal lattice). The main phases are α-Fe (85 wt. %) and carbides of complex composition Me₂₃C₆ (9 wt. %) and Me₆C (6 wt. %) forming eutectic grains. It has been established that the tempering of the deposited layer is accompanied by the pre-transformation of residual austenite with the formation of nanoscale particles of iron and chromium carbides along the boundaries of martensite crystals. Microcracks have been identified along the interfacial interfaces and in the volume of the plates of the carbide phase of eutectic grains, which can initiate the destruction of the deposited layer material during operation.