Abstract
The metastable R-phase precipitated in the early stage of aging in the Fe-Mo binary alloys is also observed in the Fe-Cr-Mo ternary alloys before the stable μ-phase, the Laves-phase, the χ-phase or the σ-phase is precipitated depending on the Cr and Mo contents and the aging temperature. The crystallographic structure and orientation relationship between the R-phase and matrix α-phase is quite similar to that in the Fe-Mo alloys. The replacement of Cr with Fe causes no effect on the precipitation process of the metastable R-phase but accelerates the transformation from the metastable R-phase to the χ-phase and delays the transformation to the stable σ-phase. The Mo content in the metastable R-phase, which is about 48 mass% in the case of the Fe-Mo binary alloy, decreases slightly with the increase of Cr content in the ternary alloys and shows 40 mass% in a Fe-10Mo-30Cr alloy. But no marked difference is observed in the Cr/Fe ratio between the metastable R-phase and as-quenched alloys.
