Effect of Mo and Si on Precipitation Behavior of Laves Phase in Fe-10%Cr Alloys

9-12%Cr-Mo ferritic heat resisting steels are widely used as high-temperature materials in the steam-power or chemical plants. It is reported, however, that the degradation of ductility is caused by the Laves phase (Fe2Mo) formed during a long-term service at high temperature and that Si has an effect to enhance the precipitation of the Laves phase. In the present research, a detailed study of the precipitation behavior of the Laves phase has been made using simple Fe-10%Cr-Mo-Si ferritic alloys, and the quantitative analysis of the effects of Mo and Si on the bulky Laves phase formation has been performed. Very fine disk like precipitates are formed on the {100} planes of the matrix before the bulky Laves phase formation and these fine precipitates cause a hardening peak except for the hardening due to the bulky Laves phase. The large effect of Si to enhance the precipitation of the Laves phase has been confirmed for the Fe-10%Cr-0 to 5%Si-2 to 10%Mo alloys.