Computational thermodynamics as tool to study microstructural evolution of EAF duplex stainless steelmaking slags

Abstract

Computational thermodynamics was used as a tool to study and determine the microstructural evolution of the electrical arc furnace (EAF) slag during and at the end of the refining period in the production of duplex stainless steel. At all the process stages, the slag contains magnesiochromite spinels. Before FeSi addition to the furnace, the slag can also contain calcium chromite crystals. After FeSi addition, the amount of magnesiochromite spinels decreases considerably from ∼15 to ∼6 wt-%. In addition, dependent on the basicity and the temperature, the slag may contain solid dicalcium silicate. More specifically, during the refining stage of the EAF duplex steelmaking process, a slag basicity of >1·55 leads to the precipitation of the dicalcium silicate phase. It has been shown that computational thermodynamics can be used as a powerful and relative reliable tool to study the slag (or slag/steel) equilibriums for different stainless steelmaking processes.

Keywords:

• EAF
• Slag
• Microstructural evolution
• Computational thermodynamics
• Duplex stainless steel
• Basicity

The authors wish to thank the Swedish Energy Agency (Energimyndigheten), the Swedish Steel Producers Association (Jernkontoret, project no. JK23028) and also the ITM foundation for financial support to this study. The authors are also grateful to the Thermo-Calc software AB and especially to Dr L. Kjellqvist and Dr J. Bratberg for the great help with modifying and developing the TCMSI1 slag/steel database.