Microstructural Aspects on the Creep Behaviour of Advanced Power Rant Steels

摘要

There is a world-wide substantial demand toincrease the application temperature and design stresses ofadvanced creep resistant ferritic-martensitic 9-12 percent Crsteels to increase the efficiency of thermal power plants. Thesealloys show during service conditions pronouncedmicrostructural changes in the aged as well as in the stressedconditions. Therefore an intensive investigation and modellingof the microstructure of the cast steel material G-X12CrMoVWNbNl0-1-1, was applied to understand themechanisms. Hardness tests, optical microscopy, TEM methodsand thermodynamic equilibrium phase diagram calculationswere performed. By means of the EFTEM (Energy filteringTEM) method a quantification of the precipitation sequence ofM_(23)C_6, MX, Laves Phase and Z -Phase could beestablished at 600 deg C as a function of exposure time.A new approach ("Graz Model") was proposed for theimprovement of the creep resistant alloys in terms of the#alpha#/#gamma# - transformation temperature and diffusionbehaviour respectively, which influence the microstructuralstability. Both were found as important influencing factors.