Two-Step Recovery Process of Irradiation Hardening in 1%Ni Doped 9%Cr-2%W Martensitic Steel

Abstract

The effect of nickel addition on irradiation-induced hardening has been investigated for reduced-activation martensitic steel (RAMS). Specimens were irradiated in the JMTR at 80°C and 220°C up to 0.15 dpa. There was no significant difference in the tensile properties between the steels with and without Ni addition after the irradiation at 220°C, while in the case of the irradiation below 170°C, the Ni-added RAMS showed a more than four times larger irradiation hardening than the steel without Ni addition. The recovery behavior of the irradiation hardening of Ni-added steel on post-irradiation annealing showed two-step recovery behavior; the first step was around 200°C and the second one was around 350°C, while only the single step of recovery was observed around 350°C in the steel without Ni addition. The mechanism of the recovery process of the tremendous irradiation hardening in Ni-added steel is discussed along with the behavior of vacancies, carbon atoms and their complexes investigated by means of positron annihilation lifetime spectrometry.

Effects of Nickel Addition on Microstructural Evolution and Mechanical Properties of Reduced Activation Martensitic Steels Irradiated in the ATR-A1

“…However, post-irradiation annealing recovery behavior of irradiation hardening investigated in the previous work suggested that irradiation induced ''nickel-related phase'' would be produced and be stable only at relatively low temperature less than about 543 K. 10) Further investigation is needed for the invisible factor.…”

“…Furthermore, we pointed out that the irradiation hardening of RAF steel with a nickel addition was much larger than that of RAF steel without nickel addition when the irradiation temperature was relatively low. 9,10) Thus, effects of nickel in itself on the microstructure evolution and the mechanical properties in RAFSs after irradiation should be evaluate for understanding helium effects on embrittlement when the NIT method are applied. In the present study, therefore, we investigated the effect of a nickel addition on the microstructure evolution and the mechanical properties in RAF steel irradiated in the ATR-A1 with low level of helium generation.…”

Current Status of Reduced-Activation Ferritic/Martensitic Steels R&D for Fusion Energy

“…7. 43) Examinations by TEM revealed that the size and number density of dislocation loops were smaller and higher in the steel added with nickel, indicating that the large irradiation hardening observed in the nickel added steel is due to increase in the number density of dislocation loops. It is expected that ironnickel dumbbell is more stable and enhances to form smaller dislocation loops in a high density, which induce larger hardening.…”

Reduced activation martensitic steels as a structural material for ITER test blanket

“…(2) Helium and hydrogen effect Simulation irradiations using B-doping, Ni-doping and 56 Fe-doping have been conducted to investigate He and H effects [11,[14][15][16][17][18][19][20]. In these simulation methods, Ni-doping has some side effects, so that it is difficult to evaluate the helium effect itself [11,16,17].…”

“…In these simulation methods, Ni-doping has some side effects, so that it is difficult to evaluate the helium effect itself [11,16,17]. B-doping results suggest He up to 300 appm does not affect hardening, but it does increase the DBTT.…”