Effects of relative thickness of the duplex-treated layer on surface properties or AlSl H13 steel

A duplex surface treatment technique based on calorizing and plasma nitriding was developed to improve the wear and oxidation resistance of H13 steel at high temperatures, The effects of the relative thickness of the calorized layer to the depth of plasma nitriding on the wear and oxidation properties at temperatures up to 900 degrees C were investigated in this work. High-temperature wear tests were performed at 500 degrees C with dry conditions in open air using a ball-on-disk type tribotest machine. Isothermal oxidation tests were performed at 900 degrees C far up to 100 h under controlled atmosphere, The results indicated that the specimens with a calorized layer as an intermediate phase between the surface duplex layer and the base metal showed higher wear and oxidation resistance than the specimens with a nitrided layer alone. During exposure to elevated temperatures, the aluminum in the calorized layer diffused to the surface and formed an aluminum oxide layer. This oxide layer protected the specimens from further oxidation and prevented the nitrogen from diffusing out of the surface, thus resulting in the retention of surface hardness even after exposure to high temperatures. (C) 1997 Elsevier Science S.A.