Origins of tertiary creep in high chromium steels

摘要

The development of particulate microstructure and dislocation substructure of two high Cr martensitic steels during long term ageing and creep testing are characterised and the observations related to the strengthening mechanisms to account for tertiary creep behaviour. Particular attention is paid to the role of refractory elements (Mo and W) and of their sluggish redistribution from solid solution to precipitate Laves phase. The tertiary creep behaviour of both allooys is dominated by the effect of creep strain; however, time dependent microstructural changes must also be taken into account in modelling the creep behaviour. An earlier model by Dyson has been modified to incorporate the effects of particle coarsening and depletion of the solid solution hardening elements (Mo and W) during Laves phase precipitation.