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 delta/gamma and gamma/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. (C) 2004 Kluwer Academic Publishers.