Properties of duplex treated (gas-nitriding and PVD-TiN, -Cr2N) low alloy steel

Gas-nitriding of low-alloy steel as a pretreatment for hard-coating deposition by hollow cathode discharge evaporation is well established. Above all, the produced nitrided case leads to a distinct increase in the resistance of the coating towards mechanical and chemical stress. Gas-nitrided samples of 31CrMoV9 coated with TiN and Cr2N were objects of extensive investigations to characterize their properties. The description of coating-substrate adhesion and the behaviour of the sample surface under tribological stress were the main subject of the experiments. The investigation of rolling wear with different geometries of contact and slips confirms the statement at the beginning. It was found that the bearable Hertz'ian contact stress is within the known range of bearing steels. The results are discussed from the viewpoint of stress field parameters (geometry of contact, slip) and case structure (for example, residual stress and the gradient of hardness). (C) 1998 Elsevier Science S.A.