Microstructural changes in steel 10Kh9V2MFBR during creep for 40000 hours at 600°C

In this work, we have investigated microstructural changes in steel 10Kh9V2MFBR (analog of P02 steel) after long-term creep tests at a temperature of 600A degrees C under an initial stress of 137 MPa. Time to rupture was found to be more than 40000 h. It has been established that, in the zone of grips and in the neck region of the sample, the size of the particles of the M C-23(6) carbides increases from 85 nm to 152 nm and 182 nm, respectively. In addition, large particles of the Laves phase with an average size of 295 nm are separated. The particles of these phases are located along high-angle boundaries. During prolonged aging and creep, the transformation of the M(C,N) particles enriched in V into the Z phase occurs. The average size of particles of the Z phase after prolonged ageing was 48 nm; after creep, it reached 97 nm. The size of M(C,N) particles enriched by Nb increases from 26 nm after tempering to 55 nm after prolonged aging and creep. It has been established that, in spite of an increase in the transverse size of the laths of tempered martensite from 0.4 to 0.9 A mu m in the neck of the sample, the misorientation of the lath boundaries does not increase. No recrystallization processes were found to develop in the steel during creep.