A cold rolled DP-grade (TS 600 MPa), coiled at 550°C, was comparedwith a steel of approximately the same analysis but with theaddition of 0.015 wt% Nb, coiled at 520 and 600°C respectively. TheNb-addition refines the ferrite grain size substantially and a moreuniform grain shape is achieved. The smaller grain size of the ferriteand martensite phases, results in a material with better formability.Recrystallization and phase transformations were studied with thelaser ultrasonic technique. This technique could be implemented onindustrial annealing lines.