Features of the Decomposition of Delta Ferrite in Nitrogen-Containing Austenitic Steels

Features of the decomposition of the ferromagnetic δ ferrite with the formation of nonferromagnetic constituents (γ and σ phases) at temperatures of 900–1200°C in a nitrogen-containing austenitic steel have been determined. The transformation of δ ferrite at high temperatures (1100–1200°C) occurs with the formation of Widmanstäatten austenitic crystals in the ferritic matrix. At lower temperatures (900–1000°C), the transformation of δ ferrite develops by discontinuous decomposition with the formation of colonies of alternating plates of paramagnetic γ and σ phases. In the course of formation of the nonferromagnetic state as a result of the decomposition of δ ferrite at 900–1000°C (for 1 h), a subgrain structure with an increased density of dislocations, which is typical of thermomechanical treatment, is retained in the steel previously strengthened by high-temperature deformation.