Plasma nitriding on simultaneously Al-Cr diffusion-treated AISI H13 and AISI 403 steel was performed and analysis of microstructure, microhardness, cyclic oxidation behavior and high temperature wear resistance of these duplex-treated steels was made. The results were compared with those from steels treated by either plasma nitriding or by duplex treatment of single element (Al) diffusion and plasma nitriding. Both steels showed a FeAl compound layer of approximately 350 μm thickness on the surface after simultaneous diffusion coating and nitrided layer of approximately 70 ～ 80μm formed after the subsequent plasma nitriding process. The microhardness was significantly improved by the duplex surface treatment (approximately 1500 ～ 1600 Hv(0.5N)) more than only by plasma nitriding (approximately 1000 ～ 1100 Hv(0.5N)) by a factor of 1.5 to 1.6. In addition the duplex treated specimens showed a much-improved high temperature wear resistance. Results from the cyclic oxidation test at 1173K showed that much improved oxidation resistance could be observed from the specimens treated by Al-Cr diffusion and plasma nitriding and this could be attributed to formation of a Cr_2O_3 layer as an additional protective layer on the surface.
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