METHODOLOGICAL BASES FOR INVESTIGATION OF THE GRAIN-BOUNDARY STRUCTURE IN STEELS WITH α, γ AND α + γ PHASE STATE

A promising direction of improving the complex of properties of metal products of polycrystalline materials constitutes the use of the grain boundary engineering (GBE) principle in the manufacturing operations of their production. Its essence consists in a combination of temperature-deformation processes that contribute to the formation of a structure with a maximum possible content of special grain boundaries (SGB) of Σ3n type in the concept of lattices of coincident site lattice (CSL). To date, certain results have been achieved, development of this direction is constrained by the lack of scientific methodology and reliable methods of identification, quantification and determination of the energy level of the large-angle homophase and heterophase boundaries in steels with α, γ and α+γ phase states. This work objective is creation of new and improved procedures for studying and determining the complex of characteristics of special homophase and heterophase boundaries in low-alloy and high-alloy steels. Conclusions. New metallographic and electron diffraction methods for recognizing and estimating the energy level of the special boundaries of the Ʃ3n family in steels with α, γ and α+γ phase states have been developed and existing methods modified. The SGBs in ferrite of low-alloy ferritic-pearlitic steels and in the γ-phase of high-alloy austenitic and ferritic-austenitic steels were identified. For the first time, the α-γ interphase boundaries were found in ferritic-pearlitic steels and their specific surface and energy spectrum were estimated. The developed methods can be used in fundamental studies of the grain-boundary structure of polycrystalline materials and in development of innovative technologies.