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Thermo-Calc can be used to predict thermophysical and phase-based properties of slags and slag-metal equilibria for steel and non-ferrous metals processing. The Process Metallurgy Module additionally allows the calculation of heat balance and uses an Effective Equilibrium Reaction Zone model to consider kinetic aspects of the process.

Solutions for Slags

Slags are of central importance for a wide range of pyrometallurgical processes from iron making, steelmaking, steel refining, but also for the production of many non-ferrous metals such as copper, ferro-alloys, nickel, aluminium, and so on. Slags most commonly consist of oxides, but can also contain sulfides, fluorides, carbides, or other metallic or non-metallic components that are also covered by the Oxide database. Non-metallic inclusions formed in liquid steel or other metals can also be thought of as slag and can be accurately calculated with Thermo-Calc and the Metal Oxide Solutions database.

Calculate the following based on your actual oxide chemistry:

  • Liquidus / solidus temperatures of slags, phases formed on solidification
  • Binary, ternary, or multicomponent phase diagrams as a function of oxygen partial pressure
  • Stability diagrams or predominance diagrams as a function of oxygen and sulfur partial pressure
  • Thermophysical properties (as a function of temperature):
    • Specific heat, enthalpy, latent heat, density, coefficients of thermal expansion, and more
      • Predict electrical conductivity, electrical resistivity, viscosity, and surface tension for any slag composition

Application Examples

Thermo-Calc has many applications to slags. Below are two such examples.

Multicomponent Slag Phase Diagrams and Physical Properties

The important advantage of CALPHAD-type calculations is that slag phase diagrams and slag properties can be calculated for multicomponent industrial slag systems containing 10 or more elements over a wide range of composition, temperature, and oxygen partial pressure. Properties that can be calculated include solidus and liquidus temperatures, phases forming on solidification, MgO saturation for refractory wear prediction, sulfur and phosphorous capacity, electrical conductivity, electrical resistivity, and physical properties such as density, viscosity, and more. The results can be tabulated or plotted in many different ways.

In this example the CaO-rich side of the CaO-Al2O3-SiO2 (CAS) phase diagram is plotted at 1590 °C and air oxygen partial pressure. Liquid slag viscosities and fractions of liquid slag in the 2- and 3 phase regions are plotted as contour lines that are superimposed onto the phase diagram.

Plot showing a CaO-Al2O2-SiO2 phase diagram with fraction liquid and slag viscosities superimposed as contour lines.

CaO-Al2O3-SiO2 phase diagram with fraction liquid and slag viscosities superimposed as contour lines.

Liquid Steel Composition in Equilibrium with a Slag Phase

The TCOX database not only contains solid oxide phases (refractory materials, non-metallic inclusions, and so on) and the oxide and sulfide liquid phase (often termed slag and matte phase respectively), but -very importantly- it also contains the full description of the metallic liquid phase, and also the most important solid metal phases, such as FCC_A1, BCC_A2 (austenite and ferrite, respectively) and a comprehensive collection of carbides. This means that full process metallurgical calculations involving metallic, non-metallic, and the gas phase can be performed using one single database.

In this example, the composition of 100t of liquid steel that is in equilibrium with about 3t of a CaO-rich slag phase at 1600 °C is plotted as a function of oxygen partial pressure. The important result is that the Phosphorous partitions to the slag phase at high oxygen partial pressures, whereas the Sulfur partitions to the slag at low oxygen partial pressures. This result has far reaching consequences in steelmaking and -refining and explains why it is extremely difficult to simultaneously desulfurize and dephosphorize steel and why the two are performed in separate processing steps.  

A plot showing the composition of 100t of liquid steel in equilibrium with a CaO-rich slag phase at 1600°C, showing desulfurization at low oxygen partial pressure and dephosphorization at high oxygen partial pressure.

Composition of 100t of liquid steel in equilibrium with a CaO-rich slag phase at 1600°C, showing desulfurization at low oxygen partial pressure and dephosphorization at high oxygen partial pressure.

Process Metallurgy Module for Steel and Slag

In addition to the calculations discussed above, we also offer an Add-on Module that makes it easy to set up calculations for steel and slag interactions, the Process Metallurgy Module. The Process Metallurgy Module includes kinetic models that simulates the evolution of the steel, slag, and inclusion compositions as a function of time based on the actual steelmaking process. Process parameters such as blowing of gases into the steel, heating by electric arc, and slag additions can be considered.

Learn more about Applications to Slags

A video tutorial demonstrating how to calculate a phase diagram for the oxide system Al2O3-MgO.

Simulating the Steelmaking and -Refining Process using Thermo-Calc’s Process Metallurgy Module

Steelmaking and Steel Refining using Thermo-Calc and the TCOX9 Database

Accurate Viscosity Prediction for Molten Slags: A New Model and Database

Calculating Steel Making and Steel Refining Processes using Thermo-Calc’s New Process Metallurgy Module and the CALPHAD Database TCOX9

Improving Steel and Steelmaking—an Ionic Liquid Database for Alloy Process Design

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