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| Řeháčková L., Kalousek J., Dobrovská J., Stránský K., Dobrovský L. |
| ON METHODOLOGY OF CONCENTRATION DATA PROCESSING AT MATHEMATICAL MODELLING OF SUBSTITUTION ELEMENT DIFFUSION IN THE ZONE OF WELDED JOINT OF STEELS |
Abstract
The paper deals with methodology of processing of original results from measurement of redistribution of substitution elements (Cr, Si, Mo, Ni) in welded joint of steels made from low-alloy steel CrNiMoV and low-alloy silicon steel. The steels forming the given welded joint are of same structural type, both of them have ferritic structure. The measurement was made in temperature interval 500 - 1000°C. Distribution of selected elements perpendicularly across welded boundary was determined with use of energy dispersive (ED) X-ray micro-analysis. This analysis was made in the individual points, along three line segments perpendicularly to the welded boundary. Overall length of each line segment was approx. 180 ?m and distance between individual points was 3?m; the centre of each line was the boundary of welded joint. In one measured segment there was obtained a concentration set containing 61 values of concentration of measured elements. It was established that during diffusion annealing there occurs measurable redistribution of all elements. Redistribution of substitution elements has character of mutual diffusion.
Solution of the 2nd Fick’s law on one-dimensional diffusion with suitable boundary conditions was theoretical basis for evaluation of concentration profiles. Parameters of diffusion equation were determined by method of non-linear regression. Three sets of measured concentration data lead to calculation of diffusion coefficients of analysed substitution elements and other parameters of diffusion equation. Processing of data can be made by various manners and they can be subjected to a detailed statistical evaluation. It was established that calculated values of diffusion coefficient and their accuracy are very sensitive to selected calculation method, that’s why individual calculation methods were mutually compared and the best method was chosen, i.e. the method with the smallest error. The results are important for evaluation of chemical and structural nonhomogeneity of welded joint and usability of the model of molecular diffusion.
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| Keywords: redistribution of substitution elements, diffusion|welded joint of steels| |
| No 4 (2006), p. 388-398 |
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