Toward On-Line Slag Composition Analysis: Optical Emissions from Laboratory Electric Arc

Electric arc furnaces and ladle furnaces have an important role in the future of steelmaking where $$\hbox {CO}_2$$ CO 2 emissions have to be mitigated to an acceptable level. One way to address this goal is to optimize and improve the current practices by adjusting the chemistry and reactions with material additions or gas injections. These procedures would greatly benefit from on-line slag composition analysis. Since the electric arcs radiate throughout the melting, optical emission spectroscopy is a potential method for such analysis. In this study, optical emissions from the electric arc are measured in a laboratory environment. Dozens of atomic emission lines were correlated with $$\hbox {Cr}_2\hbox {O}_3$$ Cr 2 O 3 , $$\hbox {Fe}_2\hbox {O}_3$$ Fe 2 O 3 , $$\hbox {Al}_2\hbox {O}_3$$ Al 2 O 3 , $$\hbox {SiO}_2$$ SiO 2 , MnO, MgO, CaO, $$\hbox {CaF}_2$$ CaF 2 , $$\hbox {V}_2\hbox {O}_5$$ V 2 O 5 , and Ni content of the slag together with correlation between $$\hbox {CaF}_2$$ CaF 2 and molecular optical emission bands of CaF. Optimal spectral resolution for industrial applications was deducted to be between 0.022 and 0.179 nm.

Factors Influencing Dephosphorization of Low Carbon Steel in Converter

A 300-metric ton converter in a steel plant in China was studied. The influence of factors such as slag composition and temperature in the smelting process on the dephosphorization effect was statistically analyzed. The dephosphorization ability of slag increased firstly and then decreased with the increase of temperature, basicity and FeO content. Low-temperature, high-basicity and high-oxidizing slag are thermodynamically beneficial to promote the dephosphorization reaction, but the basicity is higher than 4.0, and the temperature is higher than 1640 °C are not conducive to the slag to obtain better fluidity. At the same time, too high FeO content will increase the activity coefficient of P2O5, thereby increasing its activity, which is not conducive to the progress of the dephosphorization reaction. As the end point content of carbon decreases, the oxygen content increases and the phosphorus content decreases. A very low carbon content is not conducive to metal yield and temperature control.

Effect of Mn Content on the Reaction between Fe-xMn (x = 5, 10, 15, and 20 Mass Pct) Steel and CaO-SiO2-Al2O3-MgO Slag

Medium- and high-Mn steels have excellent properties but are very difficult to be commercially produced because of the high content of some alloy elements. To enhance the understanding of the reaction between medium/high-Mn steel and refining slag which is significantly different from the conventional steels, steel and slag composition and the inclusions were investigated by equilibrium reaction between Fe-xMn (x = 5, 10, 15, and 20 mass pct) and CaO-SiO2-Al2O3-MgO top slag at 1873 K in the laboratory. Furthermore, the effect of Mn content on inclusion transformation and steel cleanliness was also explored. After slag–steel reaction, both contents of MnO in slag and Si in steel increased. Most MnO inclusions in master steel transformed to MnO-SiO2 and MnO-Al2O3-MgO. With the increase in Mn content, the amount share of MnO type inclusions decreased and that of MnO-Al2O3-MgO type increased. In addition, both the number density of observed inclusions and the calculated oxygen content in inclusions increased. Thermodynamic analysis indicates that the composition change of steel and slag and the transformation of inclusions are mainly the consequence of the reaction between Mn in molten steel and SiO2 and MgO in top slag. The dissolved Mn in medium/high-Mn steel presents a strong reactivity.

Experimental Determination of the MnO Activity Coefficient in High-Manganese Slags Using the Chemical Equilibrium Method

The thermodynamics of manganese oxide in high-MnO-containing slags was investigated using the chemical equilibrium method in the temperature range of 1623 to 1723 K. MnO-SiO2-Al2O3 slags were brought into equilibrium with molten silver (Ag) under controlled CO/CO2 gas atmosphere. The equilibrium Mn concentration in the silver was measured by ICP-AES (inductively coupled plasma atomic emission spectroscopy) analysis after the experiment. Slag samples were analyzed by EPMA (electron probe microanalyzer) analysis. The obtained activity aMnO and activity coefficient γMnO were derived as a function of the slag composition and temperature. The activity coefficient of MnO within the investigated slag system increased with an increasing MnO/SiO2 ratio. The derived temperature dependence of the activity coefficient and partition ratio of Mn between the metal and the slag was strongly influenced by the slag composition. The thermodynamic assessment of the activity and activity coefficient of MnO was carried out by applying the regular solution model (RSM) on the basis of interaction energies of the cations and with FactSageTM 7.3. The theoretical calculations were compared with the experimentally derived values.

Study on Slag Forming Route of Dephosphorization in Combined Blown Converter

In order to achieve the purpose of high-efficiency dephosphorization by single-slag method during the combined blown converter steelmaking process, the CaO-SiO2-FetO-MgO-MnO-P2O5 slag system was taken as the research object, and the slag-forming route of dephosphorization was studied. The effects of slag compositions on the liquidus and the contour map of phosphorus distribution ratios (recorded as Lp) were calculated by thermodynamics software FactSage, and then the theoretic slag-forming route of dephosphorization was obtained. The effects of slag compositions on dephosphorization rate and Lp were studied by a high-temperature experiment. Based on the results of the theoretic calculation and high-temperature experiment, the actual slag-forming route of dephosphorization by the single-slag process in the combined blown converter was obtained: The initial slag composition should be around 15.0%CaO-44.0%SiO2-41.0%FetO. The composition of high-efficiency dephosphorization slag should be around 50.8%CaO-24.2%SiO2-25%FetO. The final slag composition should be around 65.6%CaO-28.3%SiO2-6.1%FetO. After using the actual slag-forming route in the production, the dephosphorization rate was increased by 3.6%, and the consumption of slagging materials was reduced by 3.78 kg/t.