J. Granacher et al., LONG-TERM CREEP CRACK BEHAVIOR OF TYPICAL POWER-PLANT STEELS, Materialwissenschaft und Werkstofftechnik, 24(10), 1993, pp. 367-376
The creep crack behaviour of the steels was investigated in a wide loa
ding range up to a test duration of 40 000 h and down to a creep crack
growth rate of 2 . 10(-5) mm/h with specimens of different shape and
size. For steels of type 1%Cr-1%Mo-0.6%Ni-0.3%V, 1%Cr-0.9%Mo-0.7%Ni-03
.%V, 12%Cr-1%Mo-0.3%V-0.22%C and 12%Cr-1%Mo-0.3%V-0.20%C tested at 550
-degrees-C, the creep crack growth rate could be described by the para
meter C2 with significantly smaller scatter bands than by the paramet
er C1 or the stress intensity factor K(I). For steel 12%Cr-2%Ni-1%Mo
tested at 450-degrees-C, parameter K(I) leads to the smallest scatter
band. The creep crack initiation can be described in a two-criteria di
agram based on nominal stress and stress intensity factor. However the
method is assumed to be over-conservative in case of increasing speci
men size. As a result of several aperiodic creep fatigue crack tests,
precracking under fatigue conditions gave a weak increase of the creep
crack growth rate whereas by precracking under creep conditions the f
atigue crack rate was strongly decreased.