The key parts of ferromagnetic materials that have served in high temperature environment for a long time are prone to cracks, and the growth of cracks seriously threatens the safe operation of the components. Aiming at the surface crack defects of ferromagnetic materials, based on numerical simulation, this study uses wideband ultrasonic surface waves to carry out nondestructive evaluation of surface crack defects. The wideband ultrasonic surface waves are generated and received by the wideband ultrasonic surface waves transducers. Based on time-frequency analysis method, the interaction law between ultrasonic surface wave with different frequency components and surface crack defects is studied. Ultrasonic characteristic parameters with different frequency components are extracted, and a neural network model with ultrasonic characteristic parameters as input and surface crack defects information as output is constructed to evaluate surface cracks defects. The results show when the crack length is between the wavelength depth of high-frequency ultrasonic surface waves and the wavelength depth of low-frequency ultrasonic surface waves, the prediction error of crack length is large. The prediction error of crack length can be reduced and the ability of nondestructive evaluation of surface crack defects can be improved when using wideband ultrasonic characteristic parameters for crack nondestructive evaluation.

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