Recovery of tensile properties in helium implanted EUROFER97 by post-implantation annealing

Reduced activation martensitic stainless steel EUROFER97 was homogeneously implanted at 250 °C with 0.25 at.% helium, and was subsequently annealed in vacuum for 10 h at 550 °C and 750 °C, respectively. Tensile testing at room temperature and at 250 °C showed increase in strength and decrease of ductility by the implantation. Both changes recovered during annealing: While the strength was reduced by annealing to values between unimplanted and implanted condition, ductility was increased even beyond that of virgin material. This means, the implanted plus annealed material showed improved behaviour even when compared to the virgin material: higher strength and greater ductility. Including the results on fracture surface and microstructural investigations, a tentative model is presented.