The solute element micro segregation behavior during the solidification of medium manganese wear-resistant steel has been systematically studied by means of directional solidification, electron probe microanalysis (EPMA), Factsage and other experiments combined with theoretical calculation. The results showed that the solidification structure of Fe-8.5Mn-2.1Cr-0.95C medium manganese steel was dendrite, and there exist no interconversion between cell and dendrite. Besides, the avera ge secondary dendrite arm spacing of medium manganese steel was 59.77μm when the pulling speed was 50 μm/s during the directional solidification experiment. The results calculated by Factsage showed that the microstructure transformation of medium manganese steel during solidification was L → L + γ → γ, which belonged to the austenite solidification mode, and there is no peritectic reaction and no δ phase and other phase appeared. Based on the “equilibrium cooling” and “IF” modes, the liquidus temperature and solids temperature of medium manganese steel which calculated by Factsage were 1422.93 ℃ and 1280.98 ℃ respectively. In addition, The EPMA experiments indicated that the content of Mn and Cr at the edge of secondary dendrites were significantly higher than those at the center of secondary dendrites. Specifically speaking, the content of Mn decreased from 9.13% to 7.49%, and the content of Cr declined from 2.03% to 1.68% at the same time. Which suggested that the positive segregation behavior of Mn and Cr elements occured during directional solidification of medium manganese steel. By solving the characteristic parameters during the solidification process, the micro segregation model of Mn and Cr elements in medium manganese steel was established. It can be found that the segregation index of Mn calculated by Scheil mode was much higher than the experimental value of EPMA when the solidification fraction was close to 1. However, the results obtained by lever-ruler, Brody-Flemings, Clyne-Kurz, Ohnaka and Won-Thomas models were closer when the solidification fraction was lower than 0.5. Besides, when the solid fraction was less than 0.7, the segregation index of Cr calculated by Scheil model were lower than experiments by EPMA. However, with the solidification process continued, the results of Cr from Scheil model were much higher than experiments. It should be noted that the segregation index of Cr from Brody-Flemings models showed the opposite trend to Scheil model. And there exist little difference among Lever-ruler, Clyne-Kurz, Ohnaka and Won-Thomas models. On the whole, the segregation index of Mn was in good agreement with the Brody-Flemings model. On the whole, the segregation index of Mn is in good agreement with the Brody-Flemings model, while the Cr segregation index was in good agreement with the Clyne-Kurz model.
DownLoad: