Saint-Petersburg State Polytechnic University (St. Petersburg, Russia):

V. M. Golod, K. I. Emelyanov, I. G. Orlova

E-mail: cheshire@front.ru

The article (the second part of the overall review) reviews the publications on dependence of secondary 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. By graphical comparison of published empirical models, it is established that the dependence of the dendrite arm spacing of carbon and low alloy steels from carbon content has the contradictory character, that does not allow its unambiguous quantitative evaluation and detection the determining factors. Analysis of this situation shows that improving the quality of statistical models (the exception of insignificant effects caused by certain components, elimination the correlation distortion, etc.) and for ensuring of their adequacy it is reasonably to unify the description of the experimental data on the basis of a polynomial form of the concentration term of the regression equation, obtained by means of orthogonal experimental design. The role of physical-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 of the changes in the composition of the liquid phase and the evolution of interdendritic spacing. It is established that reduction of the secondary dendrite spacing in carbon and low alloy steels with growth of carbon, silicon, manganese, chromium, and nickel content, as well as the increase in the proportion of austenite during solidification, is caused by suppression of diffusion transport of components during coalescence of dendritic branches. A quantitative evaluation of the 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 decreases in the following sequence: C, Si, Mn, Ni, Cr.

(Part 2)
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