Analysis of the technical state of heat-resistant steel of thermal power equipment components

Mechanical properties and structure of the steel of the control valve stem and rivets after operation in a steam turbine were investigated. It was found that the values of relative elongation and impact toughness determined on transverse samples of the stem were lower than the regulatory requirements. The mechanical properties of the metal of the stem and rivets obtained by tensile testing of axial samples met the regulatory requirements. Metallographical analysis revealed the structure of highly tempered martensite in the metal of the stem and rivet. Complex alloyed chromium carbides were recorded along the grain boundaries. Accumulations of large (up to 10 mkm) phases of niobium carbide were also detected, which were located along the grain boundaries, mainly in the form of ribbon-like colonies that were stretched in the longitudinal direction. Such their arrangement in the steel structure facilitated the fracture of the stems. The technical state of the metal was assessed by the quantitative and morphological parameters of niobium carbide inclusions in the steel structure.