Evaluation of particle size distributions of precipitates in a 9% chromium steel using energy filtered transmission electron microscopy

Energy filtered transmission electron microscopy (EFTEM) has been used to evaluate particle size distributions of different phases in the creep resistant 9% chromium steel P92, aged at 600 or 650 degreesC for up to 26,000 It. Precipitates of type VN, M23C6 and Laves phase were visualised by forming so-called jump ratio images of the elements vanadium, chromium and tungsten. Digital image analysis was used to measure the size of the precipitates at different ageing times. As a complement to EFTEM, atom probe field ion microscopy (APFIM) has been used to monitor the composition of the ferritic matrix. This indirectly gives information about precipitated volume fraction of different phases. In the case of VN precipitates the volume fraction was also determined from EFTEM images and the result was in good agreement with the data obtained with APFIM. The high-temperature stability of the secondary phases present in steel P92 and their relation to creep properties are discussed. To further study the applicability of EFTEM, steel P122 (with a composition similar to steel P92, but with an addition of Cu) was investigated and a Cu-rich phase was found. (C) 2001 Elsevier Science Ltd. All rights reserved.