Compound surface-modification technique combined DLC film coating and martensitic trasnformation with dispersed-precipitated carbonitrides

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A hybrid surface-modification technique with a combination of vacuum carbonitrided martensitic-transformation and a DLC film coating was investigated using Cr-Mo steel designed for carbonitriding to high nitrogen content.Very fine martensite having solute-nitrogen, retained austenite, dispersed-precipitated CrN, Fe4N and Fe3C, was obtained by vacuum-carbonitrided-quenching of the Cr-Mo steel.The results of a roller-pitting fatigue test show that each of a DL film (deposited by linear-ion-source:LIS method), a Si-doped DLC film coating and nitrogen-implantation (performed by plasma-based ion implantation; PBII, and deposition; PBIID methods) improve the pitting endurance of the steel vacuum carbonitrided with a nitrogen content of 0.41-0.55%, especially under a Hertz's pressure (Pmax) of more than 4.2GPa.