Effects of varying temperature irradiation on the neutron irradiation hardening of reduced-activation 9Cr–2W martensitic steels

Abstract

In order to clarify the effects of varying temperature during irradiation on the irradiation hardening of 9Cr–2W steels, tensile tests and positron annihilation lifetime measurements were carried out following the varying temperature irradiation (220/420°C and 340/530°C) utilizing a so called multi-section and multi-division controlled irradiation capsule in JMTR. After the irradiation at 220°C to 0.053 dpa, the steels show irradiation hardening as much as 110 MPa. The hardening was almost completely diminished immediately after the elevation of the irradiation temperature to 420°C. Subsequent irradiation at 420°C up to 0.14 dpa did not cause any hardening. The results of positron annihilation lifetime measurements indicate that microvoids are formed by the irradiation at 220°C but disappear upon elevating the temperature to 420°C and are then formed again by the subsequent irradiation at 420°C up to a total dose of 0.14 dpa. This behavior may be interpreted in terms of decomposition of interstitial loops or migration of small interstitial loops during temperature elevation. There is no good correlation between irradiation hardening and formation of microvoids in neutron-irradiated reduced-activation martensitic steels.