Several heat treatment were applied to on HSLA steel of type StE47 (German standard) to produce five ferrite microstructures of different strength and at least two different grain sizes respectively. Whereas the ferrite microstructure had a strong influence on yield strength the effect of grain size was negligible. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbide particles, and their mutual interaction. Specimens tranformed at $600^{circ}C$ showed the highest strength levels. In this case precipitation has occured after the $gamma$- $alpha$ transformation. Very small VC particles are arranged mostly along dislocation lines. Increasing both, grain size and pearlite volume fraction leads to a remarkable shift of transition temperature which was further enhanced by increasing ferrite strength.