[en] A dual phase micro-alloyed steel was investigated by atom probe tomography (APT) highlighting boron and carbon co-segregation at dislocations in ferrite and martensite phases. Segregation levels were measured by an original method allowing quantification of the solute excess numbers associated to a dislocation. Applying this method to our APT results, it was observed that the segregation level of boron is higher in martensite than in ferrite. In the martensitic phase, 30% of all boron atoms in the analyzed volume are segregated to the dislocation. - Highlights: • Direct observation of boron and carbon co-segregation at dislocation in ferrite. • A method for quantifying the segregation levels at dislocations is proposed. • The co-segregation level of B and C at dislocations in martensite and in ferrite.