Structural-Phase Transformations in the Diffusion Zone Nitrooxidiation of Alloy Steels

Abstract

Abstract. Increasing the corrosion resistance and wear resistance of cutting tools used under conditions of dynamic wear and shock loads requires the formation on their surface of a high-strength diffusion zone with damping properties. In the process of oxidation of the nitrided layer, the creation of a barrier oxide film on its surface due to the dissociation of high nitrogen nitrides deep into the matrix, as a result of which structural and phase changes occur in the diffusion zone. In the process of oxidation of the nitrided layer, the creation of a barrier oxide film on its surface due to the dissociation of highnitrogen nitrides deep into the matrix, as a result of which structural and phase changes occur in the diffusion zone. The process of resorption of the nitride layer at the nitride-matrix interface due to volumetric and reaction diffusion is accompanied by the formation of a transition zone with intermediate low-nitrogen nitrides and an increase in the diffusion zone in the matrix. As a result of phase changes in the transition zone with low-nitrogen nitrides with the achievement of the maximum concentration of nitrogen solubility at the “nitride-matrix” boundary, stable and metastable phases of solid solutions, both base metal and alloying elements, are released in the diffusion zone. Corrosion tests and determination of the surface gradient properties of the composite layer have proposed compositions for surface hardening of cutting tools, consisting of combined layers “oxide-nitride-diffusion zone”, providing a double damping effect of the high-strength diffusion zone.