The dependence of the transformation kinetics of an HSLA steel and related C-Mn steels on the austenitisation conditions have been investigated using calorimetry and dilatometry. It is observed that the ferrite-start temperature depends both on the manganese content and on the amount of niobium in solution. Calculations of the transformation kinetics based on an interface-mobility model applied in a tetrakaidecahedron austenite-grain geometry are used to investigate the background of the observed changes in transformation kinetics.