Saint-Petersburg State PolytechnicaL University (Saint-Petersburg, Russia):

Golod V. M., Cand. Eng., Prof., Chair of Physics and Chemistry of Cast Alloys and Processes, E-mail: cheshire@front.ru
Emelyanov K. I., Post-graduate Student
Orlova I. G., Post-graduate Student

The article (the second part of the overall review) observes the publications on dependence of dendrite arm spacing microstructure of industrial iron-based alloys from their chemical composition. It is noted that quantification of this effect obtained by experiments and presented by statistical models, are characterized by significant differences in mathematical form, as well as the sign and magnitude of the regression coefficients which evaluate the contribution of different components of steel. It is established that dependence of dendrite arm spacing of carbon and low alloy steels (under equality of the thermal parameters — local time of solidification or cooling rate), visualized by graphical comparison of published empirical models, has the contradictory character, that does not allow its unambiguous quantification and detection of the determining factors. Analysis of this situation shows that it is reasonably to unify description of the experimental data on the basis of a polynomial form of concentration term of regression equation, obtained via orthogonal experimental design, for improving the quality of statistical models (except insignificant effects caused by some components, eliminating correlation distortion) and for ensuring of their adequacy. The role of physico-chemical and thermal factors in the development of coalescence of secondary arms is quantified by numerical calculation of the dendritic structure produced by computer simulation of non-equilibrium solidification of steel slabs (250 mm thickness) with calculation the changes in the composition of the liquid phase and the evolution of interdendritic spacing. Reduction of the secondary dendrite spacing in carbon and low alloy steels with growth of C, Si, Mn, Cr and Ni content, as well as increase in the proportion of austenite during solidification, due to the suppression of diffusion transport of components during coalescence of dendritic branches, are observed. Quantitative evaluation of intensity of the process defined by the concentrations of components and a number of thermodynamic (a slope of the liquidus, the distribution coefficient) and kinetic (diffusion coefficient in the melt, the Gibbs-Thomson coefficient) parameters decrease in the following sequence: C, Si, Mn, Ni, Cr. In the final part of the review the researching and modeling of microheterogeneity of dendritic structure using the developed computer models are provided.

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