Slightly nitrided iron samples are quenched from the α or γ phase at different cooling rates. After quenching from the α phase, tensile and internal friction experiments show respectively a decrease of the lower yield stress and an increase of the Köster peak height, when the cooling rate is varied from 300 to 4000 K s−1. Quenching from the γ phase also makes the Köster peak higher. In both cases, the number of dislocations increases. Dislocation densities are estimated by means of the Schoeck theory.