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Abstract: The goal of this paper is to present a new microsegregation model for multicomponent steels designed to be coupled with a macrosegregation code, which takes into account the thermodynamic equilibriums between phases and the peritectic transformation. Among the great diversity of microsegregation models available in literature, very few can fulfil all these requirements. If it is the case, some simplifying assumptions must be adopted to increase the time efficiency of the microsegregation model but this often results in the restriction of its validity. In the model presented in this paper, a numerical approach is used to solve the diffusion equation in each phase, which implies the definition of a microsegregation mesh, whose number of nodes must be limited to have realistic calculation time by the resulting micro–macro code. To keep the number of nodes low and ensure mass conservation during calculation, an original algorithm is presented in this paper to ensure the stability of the solution, which is not a trivial problem because of the sharp solute gradients at the / interface during the peritectic transformation. [Copyright &y& Elsevier]

Abstract: Paper I of this series was dedicated to the theoretical formulation of a new algorithm to calculate microsegregation in macrosegregation computation. This paper aims to prove that the microsegregation model is particularly well adapted to be coupled with a macrosegregation code. The application of the model to Fe–Ni–C alloys shows that it provides reliable microsegregation results with a very limited number of nodes in non trivial cases (coexistence of two different solid phases during the peritectic transformation, multicomponent systems with very different solute diffusion coefficients). The model predicts that ferrite regression during the peritectic transformation occurs in false paraequilibrium conditions. It is not coherent with the assumptions made to simplify the complex treatment of ferrite regression in macrosegregation computation. It is shown that certain assumptions, which are often employed, can significantly modify the calculated value of the liquid density in the mushy zone. [Copyright &y& Elsevier]

Micro-macro segregation models are based on the multi-scale approach of the segregation, i.e., on the coupling of a macrosegregation model, which describes transport phenomena at the ingot scale, with a microsegregation model, which describes solidification at the scale of the primary or secondary dendrite arm spacing. The goal of this work is to illustrate the influence of the microsegregation phenomena on the macrosegregation. A microsegregation model for multicomponent steel alloys has been developed which takes into account solutal diffusion in solid and liquid phases, a correct description of the multicomponent phase diagram, and the variation of the local average solute concentration (open system). The peritectic transformation has been tackled and specific attention has been drawn on the accurate determination of the δ/γ and γ/liquid interface movements during solidification. Examples of micro-macro calculations obtained with this microsegregation model on ingot cases are presented and original results which illustrate specific effects of the peritectic transformation on macrosegregation are discussed. [ABSTRACT FROM AUTHOR]