Annealing behavior of irradiation hardening and microstructure in helium-implanted reduced activation martensitic steel

Post-implantation annealing behavior was investigated for a reduced activation martensitic steel (RAMS), which was homogeneously implanted with 580 at.ppm of helium by cyclotron utilizing energy degrader at below 429 K. Post-implantation isochronal annealing caused no age hardening but the gradual recovery of the hardening even above 673 K, while the neutron irradiated specimen showed a complete recovery of the hardening by the annealing above 673 K. Two-component analysis of positron lifetime measurements along with hardness measurements indicated that long lifetime component (τ2) in the helium-implanted steel still existed after annealing up to 873 K. Evolution of helium bubbles during annealing was examined by TEM and it was revealed that helium bubbles tend to be formed at lath boundaries by the annealing above 723 K. Helium desorption was observed by the annealing above 773 K where recovery of the hardening began.