EFFECT OF MO AND SI ON PRECIPITATION BEHA VIOR OF LAVES PHASE IN FE-10-PERCENT-CR ALLOYS

9-12%Cr-Mo ferritic heat resisting steels are widely used as high-temp erature materials in the steam-power or chemical plants. It is reporte d, however, that the degradation of ductility is caused by the Caves p hase (Fe2Mo) formed during a long-term service at high temperature and that Si has an effect to enhance the precipitation of the Caves phase . In the present research, a detailed study of the precipitation behav ior of the Caves phase has been made using simple Fe-10%Cr-Mo-Si ferri tic alloys, and the quantitative analysis of the effects of Mo and Si on the bulky Caves phase formation has been performed. Very fine disk like precipitates are formed on the {100} planes of the matrix before the bulky Caves phase formation and these fine precipitates cause a ha rdening peak except for the hardening due to the bulky Caves phase. Th e large effect of Si to enhance the precipitation of the Caves phase h as been confirmed for the Fe-1O%Cr-0 to 5%Si-2 to 10%Mo alloys.