ホローカソード放電を利用したCr-Mo鋼のプラズマ浸硫窒化

抄録

Cr-Mo steel was plasma-sulfnitrided using hollow cathode discharge between steel and MoS₂ plates. The MoS₂ plate was parallel to the steel plate at an interval of 3-10mm. Treatment was at 823K for 10.8ks in an atmosphere of 30vol% N₂-70vol% H₂ mixing gas at 665Pa. Steel was also ion-nitrided without MoS₂ under the same conditions to compare plasma sulfnitriding. Plasma-sulfnitrided layers formed on the steel were analyzed using EDX, XRD, micrographic structure observation, and hardness measurement.
An iron nitride layer of 4μm and a nitrogen diffusion layer of 400μm were formed on the steel ion-nitrid without MoS₂. A compound layer 8-15μm thick and a nitrogen diffusion layer about 400μm thick were formed on plasma-sulfnitrided steel. The compound layer consisted of FeS containing Mo and iron nitrides. ε-Fe_2-3N and γ′-Fe₄N iron nitrides form beneath the FeS. The compound layer thickness and surface hardness differ with the spacing interval two cathodes in the same sample temperature. Surface hardness in plasma sulfnitriding was distributed from 640 to 830Hv. The hardness of nitrogen diffusion layers was distributed mainly from 600 to 400Hv, gradually decreasing to the base. Surface hardness was higher in plasma sulfnitriding than conventional molten salt sulfnitriding, perhaps due to Mo in the sulfnitriding layer.