EVALUATION TECHNIQUES FOR AUSTENITIC STAINLESS-STEELS THROUGH TENSILE DEFORMATION BY ANALYZING ULTRASONIC PULSE WAVES IN THE FREQUENCY-DOMAIN

This paper describes a technique for evaluating the structural variations that tensile deformation induces in austenitic stainless steels.By using fast Fourier transform processing to analyze the spectral distributions of ultrasonic pulse waveforms, I qaantitatively investigate the relationship between the spectral distributions of pulse echoes and the internal structures of SUS304 and SUS310 stainless steel. The spectral distributions are obtained by the zero-crossing method and the relationship between the spectral distributions and ultrasonic attenuation caused by grain scattering are discussed. With increasing elongation, the spectral peak frequency and Q value increase for SUS304 steel and are nearly constant for SUS310 steel. The results for SUS304 steel are attributed to martensite transformation, which results in smaller grain size and a corresponding reduction of the attenuation coefficient due to the ultrasonic scatterings.