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      Nanosized precipitates in H13 tool steel low temperature plasma nitriding

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          Abstract

          A comprehensive study of pulsed nitriding in AISI H13 tool steel at low temperature (400{\deg}C) is reported for several durations. X-ray diffraction results reveal that a nitrogen enriched compound (Epsilon-Fe2-3N, iron nitride) builds up on the surface within the first process hour despite the low process temperature. Beneath the surface, X-ray Wavelength Dispersive Spectroscopy (WDS) in a Scanning Electron Microscope (SEM) indicates relatively higher nitrogen concentrations (up to 12 at.%) within the diffusion layer while microscopic nitrides are not formed and existing carbides are not dissolved. Moreover, in the diffusion layer, nitrogen is found to be dispersed in the matrix and forming nanosized precipitates. The small coherent precipitates are observed by High-Resolution Transmission Electron Microscopy (HR-TEM) while the presence of nitrogen is confirmed by electron energy loss spectroscopy (EELS). Hardness tests show that the material hardness increases linearly with the nitrogen concentration, reaching up to 14.5 GPa in the surface while the Young Modulus remains essentially unaffected. Indeed, the original steel microstructure is well preserved even in the nitrogen diffusion layer. Nitrogen profiles show a case depth of about ~43 microns after nine hours of nitriding process. These results indicate that pulsed plasma nitriding is highly efficient even at such low temperatures and that at this process temperature it is possible to form thick and hard nitrided layers with satisfactory mechanical properties. This process can be particularly interesting to enhance the surface hardness of tool steels without exposing the workpiece to high temperatures and altering its bulk microstructure.

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          Most cited references 20

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          Structure and properties of plasma-nitrided stainless steel

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            The nitriding kinetics of iron-chromium alloys; the role of excess nitrogen: Experiments and modelling

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              Nitride precipitation and coarsening in Fe–2.23at.% V alloys: XRD and (HR)TEM study of coherent and incoherent diffraction effects caused by misfitting nitride precipitates in a ferrite matrix

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                Author and article information

                Journal
                28 August 2012
                Article
                10.1016/j.surfcoat.2012.05.081
                1208.5662

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                Custom metadata
                Surface and Coatings Technology, Volume 207, 2012, 72-78
                16 pages, 12 figures, 65 references, in press
                cond-mat.mtrl-sci

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