With the development of the automotive industry, automobiles will continue to develop in the direction of lightweight while meeting safety requirements, [1-3] so as to achieve the goal of energy saving and emission reduction. [4,5] High-manganese steel, with Mn content higher than 12%, has broad application prospects in lightweight vehicles, cryogenic materials, etc. due to its excellent properties. [6] Therefore, it has received extensive attention from researchers in recent years. As regards the study on thermodynamic data for highmanganese steel, Yan [7] studied the activity of MnO in MnO-CaO-SiO 2-Al 2 O 3-MgO system slag. Paek [8-10] used the modified quasichemical model (MQM) to investigate the Al deoxidation equilibrium. Paek [11] studied the thermodynamics of the formation of AlN in high-Mn-Al-alloy liquid steels. Based on the results of Pak's research, Wu [12] further explored the relationship between Mn content and N solubility in Fe-Mn-Al alloy melts. Jang [13] measured the effects of alloy elements on the nitrogen activity coefficient in the Fe-Mn-SiN , Fe-Mn-C-N, Fe-Al-SiN , and Fe-C-SiN systems. These thermodynamic researches have provided effective contributions to the development of highmanganese steel. As for the research on steelmaking and refining of high-manganese steel, Grajcar, [14] Gigacher, [15] and Park [16] investigated the inclusions in Fe-Mn-Al-Si system and Fe-Mn-Al system steels without top slag. Results showed that the inclusions in master high-manganese steels are mainly Al 2 O 3 , AlN, and MnO•Al 2 O 3 , with some Mn(S, Se). Yang [17,18] studied the evolution of inclusions in twinninginduced plasticity steel, which was melted in a vacuum induction furnace without top slag, under different cooling conditions and Al content. Liu [19] investigated the inclusions in Fe-25Mn-3Si-3Al during the industrial production process of induction furnace!AOD!ESR. Kim [20] and Kang [21] focused on the reaction between high-Mn-Al steel and CaO-SiO 2-type molten mold flux in continuous casting and investigated the composition evolution and interface reaction mechanism of mold flux. Yu [22] researched the refining slag used for high-manganese steel by thermodynamic calculation and laboratory experiment. Peymandar [23] studied the interfacial reaction between CaO-SiO 2-Al 2 O 3-MgO flux and steel-containing Mn (17-22 wt.%) and up to 3 wt. % Al, which mainly focused on the kinetics of interfacial reaction, including composition evolution of steel and slag with reaction time, [Al] transfer and [Si] transfer at the slag/metal interface, etc. It is well known that the reaction processes during steelmaking can be greatly influenced by refining slag. However, the research on the reaction between high-manganese steel and refining slag has been seldom reported. Therefore, it is necessary to explore the reaction between high-manganese steel and refining slag. In addition, Al is an important alloy element in high-manganese steel to lower the density and reduce hydrogeninduced delayed fracture. The effect of Al ...

High manganese steel has excellent mechanical properties, which has garnered much attention. Whereas the research on the refining slag used for high Mn steel is very limited. In this study, the metallurgical characteristics of refining slag for high Mn steel were investigated based on thermodynamic calculation with FactSage 6.3 and slag-metal equilibrium reaction in MgO crucible. The calculated liquid zones of T ≤ 1873 K of CaO-SiO2-Al2O3-8%MgO-5%MnO system are located in the middle region of pseudo-ternary CaO-SiO2-Al2O3. For CaO-SiO2-Al2O3-8%MgO-MnO system, the apparent liquid zone at 1873 K enlarges with MnO content in slag increasing, and moves toward the direction of SiO2 and Al2O3 content increasing. For CaO-SiO2-Al2O3-MgO-MnO system, the liquidus zone shrinks with the basicity increasing, and moves toward the direction of Al2O3 content increasing. The measured MnO content in top slag reacted with high Mn steel was much higher than that reacted with conventional steels. In present experiments, the MnO content was around 5% when CaO-SiO2-Al2O3-MgO slag with basicity of 4 was in equilibrium with high Mn steel (Mn = 10, 20%) at 1873 K. The inclusions in master high Mn steel were mainly MnO type. After reaction with top slag, most inclusions transformed to MnO-SiO2 system and MnO-Al2O3-MgO system, in which the MnO content still shared the majority. Thermodynamic calculations show that SiO2 in top slag can be reduced by [Mn] in steel to supply [Si] under present experimental condition, which subsequently reacts with [O] in steel bath to form SiO2.

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Medium- and high-Mn steels have excellent properties but are very difficult to be commercially produced because of the high content of some alloy elements. To enhance the understanding of the reaction between medium/high-Mn steel and refining slag which is significantly different from the conventional steels, steel and slag composition and the inclusions were investigated by equilibrium reaction between Fe-xMn (x = 5, 10, 15, and 20 mass pct) and CaO-SiO2-Al2O3-MgO top slag at 1873 K in the laboratory. Furthermore, the effect of Mn content on inclusion transformation and steel cleanliness was also explored. After slag–steel reaction, both contents of MnO in slag and Si in steel increased. Most MnO inclusions in master steel transformed to MnO-SiO2 and MnO-Al2O3-MgO. With the increase in Mn content, the amount share of MnO type inclusions decreased and that of MnO-Al2O3-MgO type increased. In addition, both the number density of observed inclusions and the calculated oxygen content in inclusions increased. Thermodynamic analysis indicates that the composition change of steel and slag and the transformation of inclusions are mainly the consequence of the reaction between Mn in molten steel and SiO2 and MgO in top slag. The dissolved Mn in medium/high-Mn steel presents a strong reactivity.

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