Mechanical property change in neutron irradiated Fe-Cr and Fe-Mn alloys, and their defect structures*1

The mechanical property change and defect structures were investigated on Fe-Cr and Fe-Mn alloys irradiated in the JMTR and the FFTF. Dislocation loop density increases much larger with manganese levels than chromium levels in irradiation in the JMTR, while in the FFTF, dislocation density of the Fe-Cr alloys is much larger than in the Fe-Mn alloys. This reverse trend is due to the saturation in the development of dislocation loops. The Fe-0.1 and 0.4% Cr with dislocation density much lower than that of 2% Cr, and that of the Fe-0.1 and 0.4% Mn much lower than that of 2% Mn showed the increment in yield strength almost the same as that of the Fe-2% Cr and rather larger than that of the Fe-2% Mn, respectively, in the JMTR. Yield strength increase without significant variation in strain hardening exponent is observed in the Fe-0.1% Cr and Fe-0.1% Mn irradiated in the FFTF and very small voids are observed in the Fe-0.1% Mn irradiated in the JMTR. These results suggest the existence of invisible defect clusters produced by irradiation.