On the microstructural development of the tempered martensitic Cr-steel P 91 during long-term creep - a comparison of data

Microstructural data for creep of the tempered martensitic 9 wt.%CrMoV stee l P 91 at 873 K were analyzed. It was found that the variation of the subgr ain size with strain conforms to an exponential change from the initial to the stress dependent steady-state value. Analysis of the size distributions of precipitated particles confirmed the previous result that in P 91 there is a superposition of growth of particles with the dynamic precipitation o f new particles mostly of type MX. From the distributions the numerical fra ctions of two types of particles, a predominating population of M23C6 carbi des and a population of fine particles representing mostly carbonitrides of type MX, and their sizes could be deduced. The variation of the creep rate with strain is in qualitative agreement with these microstructural changes . (C) 1999 Published by Elsevier Science S.A. All rights reserved.