Remanent life assessment of creep-resistant modified 12% chromium steels: microstructural analysis and microstructural development models

This paper presents the current status of the development work of 9-12% chromium steels intended for use in the power generation industry. To meet the need for reliable remanent life assessment of these steels, a co-operation between research groups specialised at microanalysis and modelling of 9-12% chromium steels was initiated. The microstructure of several alloys was studied in detail using different methods of microscopy and microanalysis including atom-probe field-ion microscopy, TEM and AES. Concurrently, different kinetic models describing microstructural changes models were tested. It was shown that many microstructural observations could be explained using thermodynamic and kinetic models, e. g., the occurrence of Laves phase at the aging temperature and the replacement of M7C3 by M23C6 during tempering. The currently developed models can be used for predictions of the effects on microstructure of small changes in alloy composition and heat treatment. (C) Munksgaard, 1997.