In order to develop a non-destructive method to detect the creep damage and estimate the residual life for the machine parts used at high temperatures, the changes in material properties caused by long-term heating and by creep were observed with the test methods of X-ray diffraction, eddy current and hardness. The material tested was the tempered Cr-Mo-V steel.
The results obtained are summarized as follows:
(1) Hardness test was found the most suitable method to detect the material property change for Cr-Mo-V steel.
(2) The change in hardness during long-term heating was able to be expressed by a simple curve in the plotting against Larson-Miller parameter. Softening was caused by the heating above a certain temperature but below the temper temperature.
(3) The softening was accelerated by the stress larger than 11kg/mm2. The change in hardness during creep under the stress of σ (kg/mm2) was correlated with those of long-term heating by the plotting against the parameter of
where T is the test temperature (K) and t is the loading time or heating time (hour).
(4) A method to detect the creep damage and to estimate the residual life was deduced from the above mentioned results.