Microstructural characterization of second phases in X10CrMoVNb9-1 and 12CrMoWCuVNb steels after long steam exposure time at 550 degrees C

Abstract

Microstructural changes in high alloy (9–12% Cr) creep resistant martensitic X10CrMoVNb9–1 and 12CrMoW · CuVNb steels after 100 000 h of steam exposure at 550°C have been studied using scanning transmission electron microscopy. Precipitates were identified using electron diffraction patterns and energy dispersive X-ray spectroscopy analysis. After long time exposure, a significant coarsening of M23C6 carbides, and intensive precipitation of the coarse Laves phase were observed. Moreover, in the 12CrMoW · CuVNb steel, a low amount of the modified Z-phase particles was detected. The microstructures of the X10Cr · MoVNb9–1 and 12CrMoWCuVNb steels after 100 000 h of exposure differ in several aspects.