Microstructure-mechanical properties correlation of irradiated conventional and reduced-activation martensitic steels

Abstract

Tensile, Charpy, and transmission electron microscopy specimens of two conventional steels, modified 9Cr 1Mo (9Cr 1MoVNb) and Sandvik HT9 (12Cr 1MoVW), and two reduced-activation steels, Fe 9Cr 2W-0.25V-0.1C (9Cr 2WV) and Fe 9Cr 2W 0.25V 0.07V 0.07Ta Ta 0.1C (9Cr 2WVTa), were irradiated in the Fast Flux Test Facility. Before irradiation, M 23C 6 was the primary precipitate in all four steels, which also contained some MC. Neutron irradiation did not substantially alter the M 23C 6 and MC. No new phases formed during irradiated of the 9Cr and 9Cr WVTa, but chi-phase precipitated in the 9Cr 1MoVNb and chi-phase and α′ precipitated in the 12Cr 1MoVW. Irradiation-produced dislocation loops formed in the 9Cr 2WV, 9Cr 2WVTa, and 12Cr 1MoVW The microstructural changes caused the steels to harden, as measured by the change in yield stress. Hardening was correlated with a change in the Charpy impact properties of the 9Cr 1MoVNb, 12Cr 1MoVW, and 9Cr 2WV. Although irradiation caused a yield stress increase in 9Cr 2WVTa similar to that for the 9Cr 2WV and 9Cr 1MoVNb, the change in Charphy properties was considerably less for the 9Cr 2WVTa. This different in Charpy behavior of the 9Cr 2WVTa with that of the 9Cr 2WV and 9Cr 1MoVNb was attributed to differences in the fracture stress-temperature relationship and/or the flow stress-temperature relationship between the 9Cr 2WVTa and the other two 9Cr steels.