An objective of this article is to evaluate deformation-induced martensite and reversed austenite of a metastable austenitic stainless steel sheet with scanning acoustic microscopy. The sheet was elongated up to 40% at and below the room temperature to produce martensite, followed by annealing for reversion. First, martensite content was measured by a Feritscope. Second, using a complex V(z) curve technique with a spherically focused ultrasonic beam of frequency at 600MHz, surface acoustic wave (SAW) velocity of a specimen was measured. We found that the measured SAW velocity was dependent on the elongation, ambient temperature in elongation, and the annealing temperature. There was a trend in the correlation between the measured SAW and the content measured by the Feritscope. The measured value of the SAW velocity was compared with the theoretical one which was calculated by Young’s modulus, Poisson’s ratio, and the density of the material. The measured SAW velocity agreed well with the theoretical one. Third, using high frequency (i.e., 800MHz) acoustic imaging technique, the deformed and annealed grain structures were observed. Furthermore, the acoustic images were compared with the optical images. We found that deformed grains shown in the acoustic images were clearer than those shown in the optical images.

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