Creep-crack behaviour of typical power plant steels

For design and supervision of high temperature components for power plants the long-term creep-crack behaviour is important. Creep crack tests on different specimens are needed to obtain a description of the initiation and growth of creep cracks which is independent of geometry and load. Such tests were carried out in a wide loading range down to creep crack growth rates of 5.10-5 mm/h and up to test durations of 14 000 h with specimens of different shape and size. As a result of these tests on steels of type 1%Cr-1%Mo-0.6%Ni-0.3%V, 12%Cr-1%Mo-0.3%V-0.22%C and 12%Cr-1%Mo-0.3%V-0.20%C, the 550deg C-creep crack growth rate is described in smaller scatter bands by the parameter C2* than by the parameters C1* or KI. Only in the case of a 12%Cr-2%Ni-1%Mo-steel tested at 450deg C the parameter KI gave a better fit. The creep-crack initiation can be estimated by means of a two-criteria diagram. For larger specimens, this diagram is too conservative and this is presumably also the case for larger components. (orig.)