The bake-hardening behaviour of intercritically annealed, dual-phase (DP) and transformation induced plasticity (TRIP) steels was studied using X-ray diffraction, transmission electron microscopy (TEM) and three-dimensional atom probe tomography (APT). The DP steel showed an increase in the yield strength and the appearance of the upper and lower yield points after a single bake-hardening treatment compared with the as-received condition, while the mechanical properties of the TRIP steel remained unchanged. This appears to be due to the formation of plastic deformation zones with high dislocation density around the “as-quenched” martensite and segregation of carbon along these dislocations in the DP steel. Moreover, APT showed that the carbon content of polygonal ferrite in the DP steel was higher than in the TRIP steel. The carbon atom map of the DP steel after bake-hardening treatment also revealed the formation of Fe3C carbides within the martensite crystal. APT of the TRIP steel showed the segregation of carbon around the dislocations in the retained austenite crystals.