Abstract
Secondary refining slag samples with different chemical compositions (45-54 % CaO, 7-13 % Al2O3, 20-29 % SiO2, 9-16 % MgO, 0-5 % CaF2) 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 CaF2 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 CaF2, 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.
Highlights
The DIN 38MnS6 steel, due to its application in the mechanical industry through automotive components, requires that steel-melting shops improve the conditions for clean steel production during the manufacturing process
The objective of this study is to investigate the effects of composition variation of secondary refining slags by analysing the effective viscosity and the control of non-metallic inclusions as a function of the Al2O3 content during the manufacturing process of DIN 38MnS6 steel
The results found in series A did not clarify the effect of the heat sequence on inclusion removal
Summary
The DIN 38MnS6 steel, due to its application in the mechanical industry through automotive components, requires that steel-melting shops improve the conditions for clean steel production (reduction of inclusions) during the manufacturing process. Conditions which can be improved in this context, are those of the secondary steel refining processes, where the chemical composition and effective viscosity of the slag used has a significant effect on the kinetics of the refining reactions These conditions add to the removal and dissolution of inclusions throughout the steel-slag interface, as well as facilitate the removal of gases from liquid steel[1,2,3,4,5,6,7,8,9].
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