Surface Modification of AISI H13 Tool Steel via Atmospheric-pressure Plasma Nitriding and Superheated Steam Treatment

Abstract

Samples treated using conventional plasma nitriding have good surface hardness, wear resistance, corrosion resistance, and fatigue strength, but their friction coefficients are not low enough. This study presents a novel method of reducing the friction coefficient of AISI H13 tool steel through a hybrid treatment consisting of atmospheric-pressure plasma nitriding and superheated steam treatment. The surface structures and tribological and mechanical properties of a hybrid-treated sample were investigated. Results showed that atmospheric-pressure plasma nitriding had no effect on the formation of Fe3O4, which improves the corrosion and tribological properties of tool steel. The surface of the hybrid-treated sample had an oxide layer separated into two layers. The nitrided and non-nitrided samples had nearly the same thickness of the oxide layer.The outermost layer of the hybrid-treated sample contained almost no Cr, a large amount of nitrogen, and small amounts of Fe and O. From its outermost surface to its base material, this sample had a three-layer structure consisting of a nitride layer, a Fe3O4 layer, and a Cr-rich oxide layer. The depth of the diffusion layer of the hybrid-treated sample was greater than that of a sample treated using atmospheric-pressure plasma nitriding only. The outermost surface of the hybrid-treated sample was softer than its inner part, and the hybrid-treated sample had the lowest friction coefficient among all samples. Overall, the hybrid treatment reduced the friction coefficient and improved the wear resistance of AISI H13 tool steel.