FRACTURE PROPERTIES OF NEUTRON-IRRADIATED MARTENSITIC 9CR-WVTA STEELSBELOW ROOM-TEMPERATURE

Fracture properties of the reduced activation martensitic 9Cr-1WVTa an d 9Cr-3WVTa steels were investigated by carrying out instrumented Char py impact tests and tensile tests at temperatures below room temperatu re after irradiation in the Japan Materials Testing Reactor at 493 and 538 K. Modified 9Cr-1MoVNb steel was also examined for comparison. Th e irradiation-induced increase in ductile-to-brittle transition temper ature was 53, 26 and 40 K for the 1/3 size Charpy specimens of 9Cr-1WV Ta, 9Cr-3WVTa and 9Cr-1MoVNb steels, respectively, which resulted prim arily from the irradiation-induced increase in yield stress. The cleav age fracture stress was 1820-1870 MPa for the three steels in unirradi ated conditions, which was scarcely affected by irradiation. The defle ctions to the maximum load and to the brittle fracture initiation were decreased by irradiation. In the tensile test, quasi-cleavage fractur e occurred at 77 K in both unirradiated and irradiated conditions. The cleavage fracture stress was 1320-1380 MPa for the tensile specimens of the three steels, which was about 1.4 times smaller than that for t he Charpy specimens.