INFLUENCE OF THE CHI-PHASE ON THE TENSILE PROPERTIES OF ODS STEELS

The influence of both intermetallic chi-phase and oxide dispersion on the mechanical properties of ODS Fe-Cr steels was investigated by tens ile tests performed in the 20 to 700 degrees C temperature range. Comp aring two materials, DT and DY alloys, this study shows that the stren gth of ODS steels is mainly governed by the oxide dispersion in the ma trix rather than by the chi-phase precipitation. The chi-phase acts es sentially as a brittle inclusion responsible for the damage of the mat erial. The final failure results from the initial chi-phase cracking, followed by ductile tearing of the ferritic matrix assisted by the str ess concentrations ahead of the cracks. This interpretation of ductili ty loss attributed to the chi-phase precipitation is demonstrated by i n-situ tensile tests performed in the chamber of a scanning electron m icroscope, as well as by suppressing chi-phase precipitation using an appropriate thermal treatment.