Abstract: In this paper two die steels 7Cr7Mo3V2Si and 4Cr3Mo3W4 VNb were chemically heat-treated by means of conventional soft nitriding and RE(Rare Earth)-soft nitriding, in which La, Ce and special solvent were added. The results of impact wear tests showed that the impact toughness and impact wear-resistance of the RE nitriding layers are better than the conventional nitriding layers'. The life time of a RE-nitrided hot die for screw of bicycles was increased about 1 and 3 times than that of conventionally nitrided dies. It has been also found through observation of impact wear surfaces on SEM that the larger wear debris are often flaked off from the conventional nitriding layers, whereas that from RE-nitriding layers are much smaller. Finally, the impact wear mechanism of RE-nitriding layers was discussed.