2024 年 64 巻 1 号 p. 134-141
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.
