The temperature dependence of fracture toughness in HT9 steel irradiated to 3–145 dpa at 380–503 C
was investigated using miniature three-point bend (TPB) fracture specimens. A miniature-specimen
reuse technique has been established: the tested halves of subsize Charpy impact specimens with dimensions
of 27 mm 3mm 4 mm were reused for this fracture test campaign by cutting a notch with a
diamond-saw in the middle of each half, and by fatigue-precracking to generate a sharp crack tip. It
was confirmed that the fracture toughness of HT9 steel in the dose range depends more strongly on
the irradiation temperature than the irradiation dose. At an irradiation temperature <430 C, the fracture
toughness of irradiated HT9 increased with the test temperature, reached an upper shelf of
180—200 MPa ffiffiffiffiffi m
p
at 350–450 C, and then decreased with the test temperature. At an irradiation temperatureP430
C, the fracture toughness was nearly unchanged up to about 450 C and decreased slowly
with test temperatures in a higher temperature range. Such a rather monotonic test temperature dependence
after high-temperature irradiation is similar to that observed for an archive material generally
showing a higher degree of toughness. A brittle fracture without stable crack growth occurred in only
a few specimens with relatively lower irradiation and test temperatures. In this discussion, these TPB
fracture toughness data are compared with previously published data from 12.7 mm diameter disc
compact tension (DCT) specimens.
