A rapid method was used to study the effect of carbon content on the kinetics of post-deformation softening, t50, in Nb-steels. The hot deformation behaviour of austenite was not affected by carbon. However, the t50 was influenced by the carbon with different effects in different temperature regimes. At deformation temperatures above the non-recrystallization temperature, Tnr, carbon produced a small change in the softening behaviour. However, the t50 was significantly retarded with increasing carbon content at deformation temperatures lower than Tnr, due to Nb(C,N) precipitates.