On heterogeneity of welded joint by modelling of diffusion

Abstract

The paper deals with estimation of chemical heterogeneity by modelling of diffusion of selected substitutive elements across the weld interface of two steels. The work presents proprietary approach in obtaining and evaluation of data set. Heat-resistant low-alloyed CrNiMoV and silicon steel, both of ferrite structure, form welded joint. The welded pairs were isothermally annealed in electric furnace from 500°C to 1,000°C. Concentration profiles in the plane perpendicular to the weld were investigated by energy dispersion X-rays microanalysis (EDX), along three abscissas. Theoretical fundament for evaluation of data was the solution of 2nd Fick's law. Parameters of the diffusion equation were calculated by non-linear regression. The new adaptation of Levenberg-Marquart's algorithm was developed, accompanied by statistic quantities. Differences in position of concentration profiles in three segments can be considered as a measure of heterogeneity. They prove that the parameters of diffusion equation depend on local conditions. The detailed description follows below in the paper. © Springer Science + Business Media B.V. 2009.