Characterization of Microstructure Variations by Laser-Ultrasound during and after the Heat Treatment of Metals

Abstract

We demonstrate the potential of laser ultrasound for non-destructive testing applications in steel production and processing in two use cases: (1) Imaging of the grain structure transition between the thermally hardened surface and the unaffected core material with a comparison to sectional views by an optical microscope. We found very good correlation between the laser ultrasonic image and the microscopic view at the cross section. (2) In situ monitoring of Poisson’s ratio of steel sheets during thermal processes by evaluation of resonant frequencies of Lamb waves. In our ongoing research the results will be correlated to metallurgical properties of interest.