To investigate delectability of thermal embrittlement, SUS329J and two simulated CF8M samples were used as the materials to be tested. The modulated microstructure and composition alteration in ferrite phase due to spinodal decomposition were observed in these specimens. This alteration was confirmed by Mossbauer measurement, which shows the increase in the hyperfine field with aging time. The hyperfine field which was dependent on spinodal decomposition and was determined by Mossbauer measurement showed the linear correlation with micro-Vickers hardness in aphase in process of thermal aging. The linear relationship between the changes in sound velocity and the changes in micro-Vickers hardness was also obtained. Consequently, it is suggested that the thermal aging embrittlement can be evaluated by measuring sound velocity in materials.

To investigate delectability of IGSCC, we were trying to apply surface acoustic wave technique which is very sensitive to characteristics of material surface. As the result of experiment for SUS304 test specimens which contain IGSCC in various degrees, it is clear that velocity of surface wave is remarkably dependent on degrees of IGSCC. The change in the velocity of surface wave can be estimated effectively by pich-catch technique. It is also clear that leaky surface acoustic wave by immersion technique is more effective to detect IGSCC.