Critical parameters that affect both the ferrite grain size and the precipitation kinetics during hot rolling Nb-bearing steel were studied. Accelerated cooling was applied after the last pass of finishing rolling. In all cases the Nb(C,N) precipitation was strongly retarded, increasing the precipitation hardening by the formation of fine precipitates. Moreover a non-negligible amount of Nb remained in solution. Nb(C,N) precipitation occurred during annealing cold rolled steel, causing secondary hardening.