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

Features of the decomposition of the ferromagnetic delta ferrite with the formation of nonferromagnetic constituents (gamma and sigma phases) at temperatures of 900-1200A degrees C in a nitrogen-containing austenitic steel have been determined. The transformation of delta ferrite at high temperatures (1100-1200A degrees C) occurs with the formation of Widmanstaatten austenitic crystals in the ferritic matrix. At lower temperatures (900-1000A degrees C), the transformation of delta ferrite develops by discontinuous decomposition with the formation of colonies of alternating plates of paramagnetic gamma and sigma phases. In the course of formation of the nonferromagnetic state as a result of the decomposition of delta ferrite at 900-1000A degrees 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.