Abstract:To obtain the solute equilibrium distribution coefficient of the full-composition steel system, based on the solidification process of steel, a thermodynamic calculation model for the solute equilibrium distribution coefficient of multi-component system was established. The phase transformation and solute equilibrium distribution coefficient of 20CrMnTi gear steel under the full-composition system were calculated using FactSage thermodynamic software. During the solidification process of 20CrMnTi gear steel, the phase transformations of L→L+δ→L+δ+γ→L+γ→γ occured. In the L+δ coexistence region, the average equilibrium distribution coefficients of C, Si, Mn, P, S, Cr, Ti and Al are 0.167, 0.702, 0.693, 0.267, 0.035 5, 0.889, 0.255 and 1.268, respectively. In the L+γ coexistence region, the average equilibrium distribution coefficients of C, Si, Mn, P, S, Cr, Ti and Al are 0.328, 0.718, 0.723, 0.135, 0.016 5, 0.855, 0.176 and 1.324, respectively. The carbon content has little effect on the equilibrium distribution coefficients of C, Mn, Cr and Al in the L+δ coexistence region. With the mass fraction of carbon increasing from 0.2% to 0.4%, the average value of solute equilibrium distribution coefficient of Si increases from 0.702 to 0.735, the average value of solute equilibrium distribution coefficient of P increases from 0.267 to 0.272, the average value of solute equilibrium distribution coefficient of S increases from 0.035 5 to 0.036 3, and the average value of solute equilibrium distribution coefficient of Ti decreases from 0.255 to 0.236 in δ ferrite. The carbon content has little effect on the equilibrium distribution coefficients of P, S and Al in the L+γ coexistence region. When the mass fraction of carbon increases from 0.2% to 0.4%, the average value of solute equilibrium distribution coefficient of C increases from 0.328 to 0.341, the average value of solute equilibrium distribution coefficient of Si increases from 0.718 to 0.755, the average value of solute equilibrium distribution coefficient of Mn decreases from 0.723 to 0.708, the average value of solute equilibrium distribution coefficient of Cr are 0.855, 0.857 and 0.853, and the average value of solute equilibrium distribution coefficient of Ti decreases from 0.176 to 0.161 in austenite. The calculated results provide accurate parameters for the study of solute segregation.
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