Carbon steels ion-nitrided under various conditions were examined with respect to the microstructure, hardness, phase and thickness of the compound layer, and the depth of the diffusion layer. Furthermore, the wear resistance of ion-nitrided carbon steels was investigated under the unlubricated condition by means of an Ogoshi rapid wear testing machine. The following results were obtained.
(1) The amounts of the ε-Fe
2−3N and γ′-Fe
4N phases which constituted the compound layer were affected by the gas composition in the N
2-H
2 gas mixture atmosphere and also by the carbon content of specimens. In the specimens of higher carbon contents, γ′-Fe
4N monophase was formed in the lower N
2 gas atmosphere.
(2) In the 20% N
2 gas atmosphere, the thickness of the compound layer was hardly influenced by the carbon content, but, in the 80% N
2 gas atmosphere, the thickness increased with an increase in carbon content.
(3) The depth of the diffusion layer decreased with an increase in carbon content.
(4) The wear characteristic of the ion-nitrided carbon steels little depended on the phase of the compound layer, the thickness of the compound layer (about 7∼16 μm) and the carbon content, and the ion-nitrided carbon steels showed far better wear resistance than the normalized carbon steels.
(5) In the carbon steels, the compound layer contributed greatly for wear resistance.
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