The creep crack growth ratio and AE count rate of Cr-Mo-V cast steel for steam turbine casting, were measured, and the applicability of AE method to the monitoring of creep crack growth was examined. The results obtained are summarized as follows;
(1) AE event count has no good correspondence to AE energy intensity, so that the relation between the stress intensity factor KI and the creep crack growth rate da/dt or AE count rate dN/dt is not linear in the range of high KI.
(2) AE ringdown count has a good correspondence to AE energy intensity, so that the relation between KI and da/dt or dN/dt is linear. Accordingly, it is possible to predict the creep crack growth rate of high temperature materials by measuring dN/dt.
(3) Frequency spectra of AE during creep crack growth indicate peaks in the range of 110∼300kHz. Accordingly, it is possible to distinguish AE of creep crack growth from steam noise in a steam turbine by analyzing frequency of output or by adapting a high-pass filter of about 120kHz.
(4) According to the facts described above, it is found that AE method is adaptable for the fracture mechanical evaluation of creep cracks and the measurement of creep crack growth in high temperature materials.