MICROSTRUCTURE MECHANICAL-PROPERTIES CORRELATION OF IRRADIATED CONVENTIONAL AND REDUCED-ACTIVATION MARTENSITIC STEELS

Tensile, Charpy, and transmission electron microscopy specimen of two conventional steels, modified 9Cr-1Mo (9Cr-1MoVNb) and Sandvik HT9 (12 Cr-1MoVW), and two reduced-activation steels, Fe-9Cr-2W-0.25V-0.1C (9C r-2WV) and Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa), were irradiated in the Fast Flux Test Facility. Before irradiation, M(23)C(6) was the pr imary precipitate in all four steels, which also contained some MC. Ne utron irradiation did not substantially alter the M(23)C(6) and MC. No new phases formed during irradiation of the 9Cr-2WV and 9Cr-2WVTa, bu t chi-phase precipitated in the 9Cr-1MoVNb and chi-phase and alpha' pr ecipitated in the 12Cr-1MoVW. Irradiation-produced dislocation loops f ormed in the 9Cr-2WV, 9Cr-2WVTa, and 12Cr-1MoVW. The microstructural c hanges caused the steels to harden, as measured by the change in yield stress. Hardening was correlated with a change in the Charpy impact p roperties of the 9Cr-1MoVNb, 12Cr-1MoVW, and 9Cr-2WV. Although irradia tion caused a yield stress increase in 9Cr-2WVTa similar to that for t he 9Cr-2WV and 9Cr-1MoVNb, the change in Charpy properties was conside rably less for the 9Cr-2WVTa. This difference in Charpy behavior of th e 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 ot her two 9Cr steels.