Evaluation of Secondary Steelmaking Slags and Their Relation with Steel Cleanliness

Rocha, Vinicius Cardoso da; Pereira, Julio Aníbal Morales; Yoshioka, Ayumi; Bielefeldt, Wagner Viana; Vilela, Antônio Cezar Faria

doi:10.1007/s11663-017-0935-7

Cited by 16 publications

(21 citation statements)

References 24 publications

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“…This study was performed by taking a total of 16 (sixteen) samples divided evenly before and after vacuum degassing treatment, considering (8) steel samples and (8) slag samples. Steel samples were collected using Samp-O-Line (from Heraeus Electro-Nite) without deoxidizer and analyzed by ASPEX equipment 13,[18][19][20][21] model Explorer, equipped with SEM/EDS system. The analyzed area for all steel samples composes the range of 54.3-83.6 mm 2 .…”

Section: Materials and Methodologymentioning

confidence: 99%

“…Also, these works briefly present an approach regarding the thermodynamics of slags, pointing out the viscosity and driving force of slags in relation to inclusion removal. Some studies [13][14][15] have been developed focusing on the thermodynamic analysis of slags, showing the capacity of slag in the removal of inclusions also as a pertinent topic in the search for steels of better quality. In this context, computational thermodynamics has gained application.…”

Section: Introductionmentioning

confidence: 99%

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Effective Viscosity of Slag and Kinetic Stirring Parameter Applied in Steel Cleanliness During Vacuum Degassing

Rocha

Pereira

Yoshioka³

et al. 2017

Mat. Res.

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The process of vacuum degassing occurs during the secondary refining of special steels. Its main function is to remove undesirable gases. However, during this process, flotation phenomenon and inclusions absorption are reported. The aim of the present work was to study the slag viscosity and vacuum degassing (tank type) capacity in steel cleanliness from an industry perspective. To achieve this objective, slag and steel samples were taken before and after the vacuum stage. The results in steel cleanliness were related to a kinetic stirring parameter (β s ) of the vacuum station and to the effect of slag viscosity. The removal of inclusions during the vacuum stage reached 64, 75 and 78% in the diameter ranges of 2.5-5, 5-15 and ≥ 15 µm, respectively. After the degassing process, the composition of non-metallic inclusions seemed to approach the slags' chemical compositions. The stirring process in the vacuum degassing station promotes a significant decrease in the inclusion densities for the 2.5-15 µm diameter range and also in the sulfur content in liquid steel. Regarding the effective viscosities of slags, it was concluded that lower values (0.20 Pa.s) increased slag capacity in inclusion removal, whereas higher values (> 0.40 Pa.s) were detrimental to steel cleanliness.

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Section: Materials and Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effective Viscosity of Slag and Kinetic Stirring Parameter Applied in Steel Cleanliness During Vacuum Degassing

Rocha

Pereira

Yoshioka³

et al. 2017

Mat. Res.

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“…Through the Viscosity module, the viscosity values of the liquid slag were determined. Finally, the effective viscosity (η e ) was calculated using the Roscoe-Einstein model (Equation 1), which takes into account the solid fraction present in the slag 3,4,6,13,29 (1) where: η o = viscosity of liquid slag; f = fraction of precipitated solid phases; a and n are empirical parameters, which are equal to 1.0 and 2.5, respectively, for rigid spherical particles of different sizes and uniformly dispersed.…”

Section: Thermodynamic Calculationsmentioning

confidence: 99%

Analysis of Secondary Refining Slag Parameters with Focus on Inclusion Cleanliness

et al. 2018

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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.

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“…The data obtained from this equipment was used in a MS Excel spreadsheet developed at Ironmaking and Steelmaking Laboratory (LaSid/UFRGS). Their functions are described in previous works, which used this same spreadsheet for inclusion analysis . This spreadsheet provided the information about inclusion density, size, and chemical composition.…”

Section: Methodsmentioning

confidence: 99%

“…The values for oxygen varied from 0 to 80 ppm, since the increase in this element indicates an increase in the reoxidation level. FactSage has been used by LaSid's research group throughout the past years in works related to thermodynamic properties of steel and slag, showing good results …”

Section: Methodsmentioning

confidence: 99%

Laboratorial Analysis of Inclusions Formed by Reoxidation in Tundish Steelmaking

Alves

Pereira

Rocha

et al. 2018

steel research int.

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In order to investigate the formation of inclusions by reoxidation in the tundish, an MgO-CaO gunning mass (GM1), an MgO gunning mass (GM2), a calcium aluminate tundish slag (TS), and a rice husk ash (RHA) silica based are evaluated. The interaction between the steel and these materials is analyzed under laboratory conditions. The experimental results for the chemical composition of steel and the types of inclusions formed satisfactory reach the thermodynamic equilibrium calculated by FactSage. GM1 presents better results for inclusion density and average size of inclusions compared to GM2. The experiment with TS presents a good steel cleanliness despite the formation of numerous alumina inclusions, caused by the reaction between the slag and the alumina crucible. The addition of RHA increases the inclusion density and average size of inclusions, and also the formation of CaO-Al 2 O 3 -SiO 2 oxides inclusions is favored. RHA has harmful effects concerning reoxidation events, deteriorating the good cleanliness obtained with the TS. The experiments with GM1 and TS are less reoxidative and presents a better steel cleanliness. Thus, the usage of this gunning mass and a calcium aluminate slag without RHA is preferable in order to diminish reoxidation during the tundish steelmaking.

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Evaluation of Secondary Steelmaking Slags and Their Relation with Steel Cleanliness

Cited by 16 publications

References 24 publications

Effective Viscosity of Slag and Kinetic Stirring Parameter Applied in Steel Cleanliness During Vacuum Degassing

Effective Viscosity of Slag and Kinetic Stirring Parameter Applied in Steel Cleanliness During Vacuum Degassing

Analysis of Secondary Refining Slag Parameters with Focus on Inclusion Cleanliness

Laboratorial Analysis of Inclusions Formed by Reoxidation in Tundish Steelmaking

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