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 ni triding 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 an d oxidation properties at temperatures up to 900 degrees C were invest igated 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 t ribotest machine. Isothermal oxidation tests were performed at 900 deg rees C far up to 100 h under controlled atmosphere, The results indica ted that the specimens with a calorized layer as an intermediate phase between the surface duplex layer and the base metal showed higher wea r and oxidation resistance than the specimens with a nitrided layer al one. During exposure to elevated temperatures, the aluminum in the cal orized layer diffused to the surface and formed an aluminum oxide laye r. This oxide layer protected the specimens from further oxidation and prevented the nitrogen from diffusing out of the surface, thus result ing in the retention of surface hardness even after exposure to high t emperatures. (C) 1997 Elsevier Science S.A.