| Solidification technology under outfield mainly refers to the solidification process of liquid metal applied electric field, magnetic field or ultrosonic to control the microstructure and properties of metal materials. Under existing conditions, electric field is divided into direct current electric field and pulse electric field, magnetic field is divided into direct current magnetic field, alternating magnetic field and pulsed magnetic field. A large number of experimental results show that the outfield applied during solidification process does change the distribution of impurity elements in metal and to refine the crystal grain. However, most studies focus on the low melting point melt, for the high-melting-point melt, such as steel, iron alloy there is still at an initial stage of research, the effect mechanism is unclear.The solidification of Fe-C-i melt is studied in the role of pulsed electric and steady magnetic field respectively. In the experiments, for the molten metal with different content of elements Si, Mn, P and S, by changing the outfield conditions, a systematic study on migration and distribution of impurity for different elements are carried out with metallographic analysis, OPA analysis and scanning electron microscopy analysis. Finally the impact of impurity elements and their inclusion in the migration and distribution mechanism are put out, while the theoretical explanation is also given in which the outfield improves the Fe-C-i melt solidification.The pulsed electric field experimental results show that the effect of pulse electric field on different impurity elements is not the same, but a whole it can improve solute segregation, and refine the crystal grain. In various melts treated by pulse electric field C-elements have been improved uniformity, in which the treatment effect is the most obvious for Fe-C-Si melt. Under the experimental conditions, it is more advantageous to uniform the melt's composition and improve the C segregation for 8V pulse voltage. Pulse voltage makes the migration of impurities in different directions and form some different segregation bands, in which P, Si negative segregation in the center, Mn segregation in the center is formed, in which Mn, P, S have migrated trend to the negative, there are a similar migration laws for element C and Mn, C and P. Treated by pulsed electric field, the distribution of inclusions in Fe-C-P and Fe-C-S system is different, the former mainly concentrated in the central region, the latter are more scattered. The inclusions formed in Fe-C-P system are mainly MnS and Al2O3, and in Fe-C-S system the inclusions are mainly FeS and MnS.The experimental results treated by steady magnetic field shows that the effect of magnetic field on the solidification of Fe-C-S, Fe-C-P, Fe-C-Si melt is more obvious, there is an obvious grain boundaries arrangement direction; on the Fe-C-Mn melt it is significantly different. Magnetic field reduced the solute segregation and even the crystal grain size, After applying magnetic field, the distribution of elements in melt change which leads to a change of partition coefficient, in this experimental conditions with increasing magnetic field (<1T) the migration direction of elements is different. and the distribution of inclusions in Fe-C-P system treated strong magnetic field is oppsite to that in Fe-C-S system melt, for the former it gathered at the edge of the region, and for the latter it concentrated in the central region. the inclusions formed in Fe-C-P system are mainly Fe of phosphide and MnS, and in Fe-C-S system the inclusions are mainly FeS and MnS. In this experimental conditions, the migration of elements and C impurities in the ternary iron-based melt of elements are similar. The results show that magnetic field can increase uniformity; with increasing of magnetic field strength the degree of uniformity decreases. So that the greater the magnetic field strength is not more favourable to the solidification structure, there should be one of the best worth to the most appropriate undercooling, to get the most refinement grains, and segregation can be best improved. |
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