Texture analysis of low-carbon steel under annealing conditions using non-contact ultrasound

Abstract

The ability to rapidly and non-destructively detect crystallographic changes in sheet metals under annealing conditions has potential uses in the strip manufacturing industry. Ultrasonic Lamb wave velocity measurements as a function of the in-plane angle were taken on a number of steel sheets and an aluminium sheet of a nominal thickness of I mm. A number of thermal annealing steps in air were performed on all these sheets and subsequent ultrasonic measurements of the same Lamb wave velocities were taken. The first three crystallographic texture orientation distribution coefficients (ODCs) were inferred from the ultrasonic velocity data. These ODCs were used to construct 'simulated pole figures', illustrating crystallographic texture changes that occurred in the steel and aluminium sheets during the annealing processes. The changes (including those relative to the material's melting point) were found to be much more pronounced in the case of the aluminium sheet. The steel sheets showed a gradual shift from fourfold to twofold symmetry under anneals of increasing temperature, whereas the aluminium sheet showed a much more extreme shift, with a reversal of the ultrasonic fast axes implying substantial recrystallisation