A martensitic or bainitic structure of low-carbon steel provides its high strength and fracture toughness combined with good weldability. At the same time, the phase composition of such materials depends on the cooling rate in quenching and hence becomes rather non-uniform in case of thick semi-products. Accordingly, to answer a challenging question of how this issue affects the metal properties, relevant methods of local structural analysis are required. To assess martensite fractions in low carbon bainitic steel quenched at different cooling rates, statistics of the crystal curvature in terms of EBSD data is analyzed. Results are verified by independent data on the transformation kinetics recorded by dilatometry and characteristic coupling of the transformation variants admitted by the interphase orientation relationship.