The propagation of ultrasound is very sensitive to texture, size and shape of grains and phase composition. Laser-ultrasound is a non-contact method that provides a continuous view of the ultrasonic properties of steel samples during thermal processes. It allows high sample throughput for different process parameters after a short calibration phase for a specific steel grade. We will present the application of existing and new models that establish correlations between changes in microstructure and ultrasonic quantities for isothermal recrystallization processes on cold-rolled steel. We conducted the experiments on inductively heated samples, adapting the chamber of a quenching dilatometer, with lasers for ultrasound generation and detection directed through windows onto the 5 x 5 cm sheet samples. The results were compared with Vickers hardness measurements and micrographs on samples quenched at individual points on the temperature curve.