Experimental study of thermal degradation in ferritic Cr–Ni alloy steel plates using nonlinear Lamb waves

The thermal degradation in ferritic Cr–Ni alloy steel plates is measured using the nonlinear effect of Lamb wave propagation. Experiments were carried out to introduce controlled levels of thermal damage to determine the nonlinear response of Lamb waves. A “mountain-shape” change in the normalized acoustic nonlinearity of Lamb wave versus the level of thermal degradation in the specimens has been observed. The variation in the measured acoustic nonlinearity reveals, based on metallographic studies, that the normalized acoustic nonlinearity increases due to the second phase precipitates in the early stage and it decreases as a combined result of dislocation change and micro-void initiation in the material. The results show a potential application of the nonlinear Lamb waves for the quantitative assessment of thermal damage in metallic plates or pipes. ► Thermal degradation in ferritic Cr–Ni alloy measured using nonlinear Lamb waves. ► A mountain-shape change in nonlinear Lamb waves versus the level of thermal degradation observed. ► Variation in the measured acoustic nonlinearity interpreted based on microstructure evolution.