Development of novel multi-element low-activation Fe-based alloys for nuclear and fusion reactor applications

• Two low-activation iron-based alloys (Fe-(10, 20)Mn-15Cr-0.7V-2.0Al-0.5C) were developed for applications to nuclear reactors and high-power accelerators. • The alloys do not contain elements such as Ni, Co, Mo, and Nb, which will bring high radio activations in nuclear environment and high energy accelerators and are also designed with aiming high entropy alloys . • Fe-10Mn-15Cr-0.7V-2.0Al-0.5C was composed of two BCC phases, while Fe-20Mn-15Cr-0.7V-2.0Al-0.5C was mainly composed of BCC and FCC . • Fe-20Mn-15Cr-0.7V-2.0Al-0.5C had better strength and ductility than that in some of conventional ferritic steels . • The ion irradiation response was very good, and the irradiation hardening was about 1.5 GPa at 30 dpa at 573 K at the damage peak, and it was comparable or much better than that of fusion structural materials and pressure vessel steels. Microstructures, mechanical properties and irradiation hardening of novel multi-element iron-based alloys (Fe-(10 and 20)Mn-15Cr-2.0Al-0.7V-0.5C (at %)) were investigated. The alloys do not contain high activation elements, such as, Co, Ni and Mo. The alloy samples were hot-rolled at 1323 K and air-cooled, followed by heat treatment at 1073 K for 0.5 h and quenching in to water. After the heat-treatment, the Fe-10Mn-15Cr-2.0Al-0.7V-0.5C (10Mn) sample consisted mainly of body-centered cubic (BCC) structure with two distinct microstructures, i.e., fine lath-martensite-like structures and recrystallized grains. Meanwhile, the Fe-20Mn-15Cr-2.0Al-0.7V-0.5C (20Mn) sample were a mixture of fine lath-martensite like BCC phase and face-centered cubic (FCC) phases. The 10Mn sample exhibits very high tensile strength of 960 MPa but low elongation, while the 20Mn sample exhibits lower tensile strength of 620 MPa but much improved elongation over 60 %. The samples were simultaneously triple-irradiated with 10.5 MeV Fe 3+ ions, 1.05 MeV He + ions and 0.38 MeV H + ions to a depth of 1 μm from the sample surface. The irradiation hardening in average was only about 1.5 GPa in the alloys irradiated with 10.5 MeV Fe 3+ ions up to 30 dpa at 573 K at the damage peak, measured by nano-indentation. The irradiation hardening resistance of the alloys was better than that of other fusion structural materials and fission reactor pressure vessel steels. Combined analysis with electron-backscattered diffraction and nanoindentation revealed that the irradiation hardening is less significant in lath BCC phase than in recrystallized BCC (10Mn) and in FCC (20Mn). These results suggest that the alloys with good combination of irradiation resistance and mechanical properties can be developed by further tailoring the phase stability of the alloys and combining the high-entropy effects, aiming for the application for components in nuclear reactors, fusion reactors and high-power large accelerator facilities.