Research on Laser Ultrasonic Testing of 316l Stainless Steel Mean Grain Size Based on Wavelet Threshold Denoising

Abstract This paper investigated a mean grain size characterization method base on laser ultrasonic. The 316L stainless steel samples with different mean grain size were conducted with different heat treatments and times, and each sample was observed by SEM and tested by laser ultrasonic. Due to the state of the sample surface, complexity of equipment and environment, the ultrasonic signal contain a lot of noise. Proposes a method to calculate the ultrasonic attenuation coefficient based on the signal after wavelet threshold denoising. Using db3 as the wavelet basis function, the signal is decomposed and denoised 5 times and then recombined. The attenuation coefficients of the amplitudes in the time domain and frequency domain of the original signal and the denoised signal are calculated. The results show that wavelet threshold denoising can improve the signal-to-noise ratio of the signal and the calculation accuracy of the average grain size.