Analysis of Secondary Refining Slag Parameters with Focus on Inclusion Cleanliness

Abstract

Secondary refining slag samples with different chemical compositions (45-54 % CaO, 7-13 % Al 2 O 3 , 20-29 % SiO 2 , 9-16 % MgO, 0-5 % CaF 2) were investigated to verify the influence of their effective viscosity on inclusion cleanliness of DIN 38MnS6 in a steelmaking plant. The steel samples were collected during the production process for analysis of inclusions. Using the commercial software FactSage 6.4, thermodynamic calculations were performed to determine the effective viscosity, solid fraction, liquid fraction and MgO saturation point of these slags at 1560ºC. The results showed that all the slags were saturated in MgO, revealing a better protection of the ladle refractory. The addition of 2 to 5 % of CaF 2 reduced the effective viscosity values for the analyzed slags from 0.45 Pa•s to 0.10 Pa•s , in comparison to the slags without the addition of CaF 2 , with an effective viscosity of 0.40 Pa•s, 0.27 Pa•s and 0.22 Pa•s, decreasing the level of non-metallic inclusions for some of the analysed heats. However, it was detected during the manufacturing process that high slag fluidity and re-oxidation events continue to be a challenge associated with reducing the level of non-metallic inclusions.

Influence of synthetic slag added during the tapping on inclusion features of a vacuum degassed LCAK steel grade

“…They observed a higher removal rate for larger inclusions due to their easier flotation characteristics. A similar behavior was observed in a VD route combined with a high stirring LF (Pereira et al, 2018), where virtually no inclusions larger than 15µm were found.…”

Effect of CaF₂ on Viscosity and Refining Ability of Highly Basic Slags for Duplex Stainless Steel

“…Such a phenomenon is consistent with previous studies. [16][17][18][19][20][21][22][23][24][25][26] Physical properties of slags including viscosity intrinsically depend on ionic structure of molten slags. Therefore, to clarify the mechanism of fluorine (F) ions in decreasing slag viscosity, various spectroscopic instruments, such as nuclear magnetic resonance (NMR) spectroscopy, 42) Raman spectroscopy, 25,30) X-ray photoelectron spectroscopy (XPS) 22,43) and Fourier transform infrared (FTIR) spectroscopy, 44,45) as well as molecular dynamics simulation method [45][46][47] have been used to explore the effect of F ions on the structural changes of molten slags.…”

“…Park et al 18) compared the effect of CaF 2 and Al 2 O 3 on the viscosity of low basicity CaO-SiO 2 -10%MgO-CaF 2 /Al 2 O 3 slags and found that CaF 2 is more effective in decreasing viscosity of the slags. Pereira et al 19) reported that addition of 2%-5% CaF 2 in low basicity slags (C/S = 1.62-2.26) containing 7%-13% Al 2 O 3 decreases the viscosity of the slags from 0.45 Pa•s to 0.10 Pa•s. Deng et al 20) revealed that CaF 2 addition not only decreases the viscosity of low basicity SiO 2 -CaO-Al 2 O 3 -MgO silicate melts also changes the crystallization behavior from spherical diopside to plate-like anorthite.…”

Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al₂O₃-Based Inclusions from Liquid Steel

“…These Al 2 O 3 -based inclusions should be removed from liquid steel and this process is commonly affected by slag properties such as the thermodynamic driving force (∆C) and effective viscosity (η e ). 7,10,12,20,21) Thermodynamic driving force (ΔC) has been studied in the past years in order to understand its effect on the dissolution of Al 2 O 3 -based inclusions (Al 2 O 3 and MgO•Al 2 O 3 ). 7,10,20) Once the dissolution of these inclusions is controlled by mass transfer, the difference between the Al 2 O 3 wt.% of the interface and the bulk (ΔC) have a significant influence in this process.…”

“…This property includes slags solid and liquid fraction and shows up as an efficient tool to evaluate steel cleanliness. 12,21) Thermodynamic software such as FactSage 22) and Thermocalc 23) are excellent tools to calculate viscosity of liquid slags. It is important to note that steelmaking slags have both a liquid and a solid fraction, prompting some additional steps to obtain effective viscosity using these programs.…”