Quantification of precipitates in advanced creep resistant 9-12% Cr steels

In this paper a procedure is introduced for the quantification of precipitates appearing in 9-12°Cr-steels. Results gained from conventional transmission electron microscopic (TEM) investigations are compared with results from energy filtering transmission electron microscopic (EFTEM) investigations. The study was performed on a creep rupture specimen of the cast material G-X12CrMoWVNbN10-1-1 exposed at 600°C and ruptured after 33000 h. The size distribution of M₂₃C₆ carbides, MX phase and Laves phase were measured for both the un-stressed head and the stressed shank (gauge length) part of the investigated specimen. In particular, problems and sources of uncertainty concerning the quantitative determination of particle parameters in this type of steel are discussed. It is shown that quantification of the MX-particles by means of TEM bright field images is hardly possible. The size distributions of M₂₃C₆ carbides and MX phase overlap significantly which makes a separation based only on their size nearly impossible. Only Laves phase occupies a different size range. The difference between the size distributions of head and shank is pronounced only for M₂₃C₆ carbides. The measured particle distributions obey more closely a log-normal distribution rather than a normal distribution.