Determination of the Fe-Cr-Mo Phase Diagram at Intermediate Temperatures using Dual-Anneal Diffusion Multiples

Abstract

A recently developed dual-anneal diffusion-multiple approach is employed to the determination of the Fe-Cr-Mo phase diagram at intermediate temperatures. Diffusion multiples of Fe-Cr-Ni-Co-Mo were first annealed at 1200 °C for 500 h to create wide ranges of solid solution compositions. Subsequent annealing of the diffusion multiples at individual intermediate temperatures induced various precipitate phases. Electron probe microanalysis (EPMA) across the interface between large precipitates and the matrix phase provided local equilibrium information for the establishment of equilibrium tie-lines which are utilized to construct the Fe-rich part of the Fe-Cr-Mo isothermal sections at 900 and 800 °C. The Mo-rich part of the isothermal sections at intermediate temperatures was not obtained due to the sluggish kinetics of precipitation and growth, resulting in too small precipitates for reliable EPMA composition evaluation. A complete 1200 °C isothermal section of the Fe-Cr-Mo system is also established from EPMA data on a water quenched diffusion multiple that was annealed at 1200 °C for 500 h only without a second anneal.