Dual-phase (ferrite-martensite) low-carbon sheet steels are produced by annealing in the intercritical temperature range to produce ferrite-austenite mixtures, followed by accelerated cooling to transform the austenite phase into martensite. Dual-phase steels have gained considerable importance over the conventional HSLA steels due to the high strength and formability achieved. A good formability is achieved by high deformation hardening, due to a fine distribution of martensite. A cold rolled DP-grade (TS 600 MPa), coiled at 550 °C, was compared with a steel of approximately the same analysis but with the addition of 0.015 wt% Nb, coiled at 520 and 600 °C respectively. The Nb-addition refines the ferrite grain size substantially and a more uniform grain shape is achieved. The smaller grain size of the ferrite- and martensite phases, results in a material with better formability. It appears that coiling at 520°C results in a slightly better formability than coiling at 600°C. The material shows a lower a?? start temperature, probably due to easier dissolution of finer carbides, compared to the strip coiled at 600°C. The recrystallization and phase transformation behaviour was studied using laser ultrasonics (LUS). Developing the LUS-technique for use in-line during annealing would open new ways of optimising and controlling the mechanical properties of the final strip.