A micro-segregation model of solute elements in mushy zone withδ/γtransformation during solidification was established based on the regular hexagon transverse cross section of dendrite shape proposed by finite difference method under the non-equilibrium solidification condition.The model was used to calculate the non-equilibrium pseudo binary Fe-C phase diagram and the strain of steels induced by variation of temperature in brittle temperature range.On the basis of the phase diagram and the strain,the strain curve in brittle temperature range as a function of carbon content for continuously cast strand was introduced and obtained.Solute elements change the position of the strain curve.And cooling rate changes the position and the shape of the strain curve.The comprehensive formula of the strain as functions of solute elements and cooling rate in brittle temperature range has been obtained by nonlinear fitting program. A micro-segregation model of solute elements in mushy zone with δ / γ transmission during solidification was established based on the regular hexagon transverse cross section of dendrite shape proposed by finite difference method under the non-equilibrium solidification condition. The model was used to calculate the non -equilibrium pseudo binary Fe-C phase diagram and the strain of steels induced by variation of temperature in brittle temperature range. On the basis of the phase diagram and the strain, the strain curve in brittle temperature range as a function of carbon content for continuously cast strand was introduced and obtained. Solute elements change the position of the strain curve. And rate of change the position and the shape of the strain curve. The comprehensive formula of the strain as functions of solute elements and cooling rate in brittle temperature range has been obtained by nonlinear fitting program.