Duplex plasma surface treatment process on mild steel and high alloyed tool steel

Duplex plasma surface treatment by calorizing and plasma nitriding was carried out on mild steel and high alloyed tool steel to improve their elevated temperature wear properties. Effects of calorizing on the plasma nitriding behavior of the steels and the characteristics of the duplex-treated specimens were analyzed using SEM, EDS, XRD, and a microhardness tester. Calorizing on mild steel created a FeAl compound layer of approximately 120 mu m thickness, resulting in the improvement of the surface hardness by a factor of 2. Subsequent plasma nitriding increased the surface microhardness above 1200 Hv (0.1 kgf) and the nitriding depth was of the order of 80 mu m. The high alloyed tool steels showed a decrease in microhardness in the Al-diffused layer upon calorizing. The subsequent plasma nitriding, however increased the hardness up to 1280 Hv and the nitriding depth of over 80 mu m was obtained. The room temperature wear resistance of the duplex-treated steels was slightly better than that of the nitrided one, but there was considerable improvement in the high temperature wear resistance at 500 degrees C in the duplex-treated steels when both the wear volume and the weight change due to oxidation were considered.