PHASE EVOLUTION DURING NEUTRON-IRRADIATION OF COMMERCIAL FE-CR-MN ALLOYS

Earlier irradiation studies on simple Fe-Mn and Fe-Cr-Mn alloys in the annealed condition showed that these alloys exhibited a higher level of phase instability than do comparable Fe-Cr-Ni alloys. Contributing to this instability was the tendency of iron to segregate at microstructural sinks due to the operation of the inverse Kirkendall effect. This segregation, combined with the addition of various solutes and the application of typical thermomechanical treatments to produce the commercial alloys, added complexity to the phase evolution of Fe-Cr-Mn alloys. This complexity included the intergranular and intragranular precipitation of M23C6 carbide, alpha ferrite, and sigma. These phases can have detrimental effects on mechanical and corrosion properties. Provided that the phase transformations to sigma and carbides can be controlled, the commercial austenitic Fe-Cr-Mn alloys appear to be suitable starting compositions for the development of low activation alloys for service in fusion reactors.