The Microstructures and Wear Resistance of Gas-Nitrided and Ionically Nitrided AISI H10 Dies with Narrow Gaps Designed for the Hot Extrusion of Aluminium

Abstract

Dies made from AISI H10 die steel with narrow and deep gaps were nitrided by various manufacturers of equipment for ionic and gas nitriding. The manufacturers chose the optimum nitriding parameters themselves, based on their experience with extrusion dies. The resulting microstructures showed differences in terms of the presence or absence of a compound layer, the thickness of the layer and its ε/γ′ phase ratio (XRD), the nitriding depth and the microhardness values. The obtained nitriding depths, the maximum microhardness of the nitrided surfaces and the ε /γ′ phase ratio were usually similar for dies from the same manufacturer, while the dies from different manufacturers tended to have different values. Samples with various nitrided microstructures were laboratory tested for wear resistance with a newly designed test rig that provided a simulation of the tribological conditions for the hot extrusion of aluminium. The results of the study indicate that dies with a greater nitriding depth in combination with a compound layer composed primarily of just one phase (in our case the ε phase) exhibited better wear resistance than those dies with a small nitriding depth and with an equal share of the two phases.