[Show abstract][Hide abstract] ABSTRACT: Properties of steel depend also on its internal structure. In practice, one can distinguish between primary structure (obtained during solidification) and secondary structure (being a result of the γ phase transition into the α phase during hot working or heat treatment). The grain refinement degree obtained is assessed with microscopic examination. In this work an alternative method is proposed in the determination of the steel microstructure refinement degree. The method is based on the dependence between the high frequency sound attenuation coefficient and the average grain diameter. Sound in steel increases when the average steel grain diameter approximates the ultrasonic wave length, because of the scattering of waves on grain boundaries.