Low temperature nitriding enables the corrosion and wear resistant layers to be formed on austenitic steel due to presence of so-called S-phase. It was found that depending on the process parameters and nitrogen contents this phase exhibits magnetic or non-magnetic properties. The previous investigations shows that the layers with different morphology can be produced depending on the nitriding parameters as well as on the plasma parameters used for activation before gas nitriding. Especially when nitrogen was used as sputtering gas, the additional subsurface layer was produced, which has non-magnetic properties. The main aim of the paper was to investigate nitrded layers structure with the special attention paid to application of magnetic force microscopy, which enable that specific morphology of these layers can be revealed. The investigation were performed on the layers obtained in various conditions of the treatment. Additionally to AFM/MFM studies, X-ray diffraction (XRD and GXRD) together with CEMS, XPS and EBSD techniques was used to evaluate the phase composition of the layers. Elements content and distribution were determined by means of EMPA and SIMS methods. The mirostructure was investigated using scanning and transmission electrons microscopy. The results confirmed complex microstructure of the layers formed during low temperature nitriding of austenitic steel, and nanocrystalline structure of subsurface non-magnetic zone. This particular characteristic of the latter is discussed in terms of increased oxygen content in subsurface area.

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1. Investigation of mechanical properties of thin nitrided layers produced on stainless steel 
2. Microstructural changes in upper surface of austenitic steel under low energy plasma