Microstructure and Mechanical Properties of G17CrMoV5 – 10 Cast Steel After Regenerative Heat Treatment

Abstract

The paper presents results of research on the influence of regenerative heat treatment on microstructure and properties of a cast steel after long term operation at the elevated temperature. The material under investigation was G17CrMoV5 – 10 cast steel taken out (in the form of a section) from an internal frame of steam turbine serviced for about 250 000 hours. Performed research has proved that, through the structure degradation, long-term service contributes to an increase of brittleness and decrease of mechanical properties — higher in the case of yield strength than tensile strength. The heat treatment, however, contributes to an increase of impact energy, regardless of the applied parameters. Is has also been proved that the optimum combination of mechanical properties and impact energy is ensured by the structure of high tempered bainite. Low mechanical properties and impact energy, however, were obtained for the structure which was slowly cooled from the austenitizing temperature, i.e. the ferritic – bainitic – ferritic structure.