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The diffusion model of nitrogen and carbon during carbide phases transformation into nitrocarbides

Dariusz Siniarski ,  Leszek Klimek 

Technical University of Łódź, Institute of Materials Engineering, Stefanowskiego 1/15, Łódź 90-924, Poland


The model of diffusion of nitrogen and carbon during nitriding of NC11 steel, which demonstrates phenomena occurring during chromium carbides of type Cr7C3 transformation, is shown in this paper.
The determination method of diffusion coefficient, of nitrogen in steel, basing on chemical profiles researches by means of EDS is also presented.
The method is based on results coming from carbon concentration profiles determination on the cross section of the layer in areas free from carbides precipitations and in areas of their presence. The diffusion coefficient was calculated by converse problem solution.
The diffusion equation was solved by means of finite difference method. The simulation of nitriding process of NC11 steel was performed, thanks to that the model of diffusion controlled transformation: chromium carbide-nitrocarbide, was obtained.
The numerical model verification was made on the base of researches with use of X-Ray microanalysis.
The carried out experiments allowed developing a model of transformation kinetics of chromium carbide into nitrocarbide in dependence from nitrogen flow.
The mathematical model of nitrogen diffusion both in steel NC11 and chromium carbide of type Cr7C3 is presented in this paper. The details of 1D, preliminary numerical model were also presented. The detailed visualization and analysis were done in 2D space. The calculations realized in 2D space allowed precise description of diffusion mechanism of nitrogen around carbides and accurate determination of process kinetics in dependence from nitrogen diffusion direction. The 2D model was applied only in small areas (nearby carbide) because of high calculation complexity. The nitrogen diffusion in areas free from precipitations was calculated in 1D space.


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Presentation: poster at E-MRS Fall Meeting 2004, Symposium H, by Dariusz Siniarski
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-27 14:12
Revised:   2009-06-08 12:55