Speaker
Description
Non-metallic inclusions play an important role in determining the quality of steel products; Thus there have been various researches done in order to study such inclusions. Adequate knowledge about the behavior of nonmetallic inclusions in molten steel and during the solidification stage bas been discovered. However, the effect of non-metallic inclusions on the quality of steel products is determined by its state in the final products after various thermal and mechanical treatments as well as steel making and casting processes. In many cases, the shape and composition of the non-metallic inclusion in the final product would not be able to be prospected from that in the cast sample. Hence, the knowledge on the behavior of steel after solidification is poor as it is an interdisciplinary area between the research field of steelmaking and forming, processing and thermomechanical treatment.
Therefore, in this study, we first investigated the composition of the oxide equilibrated with the molten steel deoxidized by Mn-Si. Based on the results obtained, we determined the initial compositions of bulk oxide and solid steel for the diffusion couple experiment. In the present study, a diffusion couple consisting of the thick bulk oxide and solid alloy deoxidized by Mn-Si was made to simulate the reaction at the interface between oxide inclusion and solid steel in actual process.
Firstly, the oxide composition equilibrated with the molten alloy deoxidized by Mn-Si was investigated to determine composition of bulk oxide and alloy for the diffusion couple experiment. Using this experiment and thermodynamic calculation, it is confirmed that the equilibrium oxide with steel deoxidized by Mn and Si is not a binary oxide of MnO-SiO2, but the ternary oxide of Mn-SiO2-FeO. The equilibrium composition of alloy and slag observed in the experiment correspond approximately with result of thermodynamic calculation.
Secondly, the diffusion couple method was used to understand the solid-state reaction between the Fe-Mn-Si alloy and MnO-SiO2 oxide. The counter diffusion has occurred between Mn and Si in the oxide without FeO and Fe in the alloy. This result indicates the inclusion of manganese silicate after deoxidized Mn and Si is not a binary compound of MnO, SiO2 but a ternary compound of MnO, SiO2 and FeO at high temperature condition.
References
[1] K. KIM et al., "Reaction between MnO–SiO2–FeO Oxide and Fe–Mn–Si Solid Alloy during Heat Treatment", ISIJ International, Vol. 54 (2014), No. 10, pp. 2144–2153
[2] K. KIM et al., "Influence of Sulfur on the Reaction between MnO–SiO2–FeO Oxide and Fe–Mn–Si Solid Alloy by Heat Treatment" ISIJ International, Vol. 54 (2014), No. 12, pp. 2678–2686
| Keywords | steelmaking, heat treatment, inclusion, manganese silicate |
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