Identification and quantification of microstructural damage. Final report

In this research project a quantitative metallographic investigation of cavity damage was performed on longitudinal cross sections of creep samples. These samples were taken either from new material or from service-exposed material of the steels 14 MoV 6 3, 13 CrMo 4 4 and 10 CrMo 9 10. The aim of research was to find a relationship between cavity damage and residual lifetime. Nearly no cavity damage could be detected in both conditions of steel 10 CrMo 9 10 and in the service-exposed material of steel 13 CrMo 4 4. The latter had a totally different microstructure compared with the microstructure of the corresponding new material. Samples of that new material showed typical cavity damage as well as samples of steel 14 MoV 6 3, in that case for both conditions. For the latter three casses the cavity damage was quantitatively studied by optical miroscopy. Altogether, four damage parameters were investigated, where always two of them were evaluated either by a manual or by an automatic technique. In all cases scattering of the results did not allow a precise correlation between cavity damage and residual lifetime. The least scatter was found for the parameters evaluated by the more elaborate automatic technique. (orig.)