Influence of refining process and utilization of different slags on inclusions, titanium yield and total oxygen content of Ti-stabilized 321 stainless steel

Ti-stabilized 321 stainless steel was prepared using an electric arc furnace, argon oxygen decarburization (AOD) furnace, ladle furnace (LF), and continuous casting processes. In addition, the effect of refining process and utilization of different slags on the evolution of inclusions, titanium yield, and oxygen content was systematically investigated by experimental and thermodynamic analysis. The results reveal that the total oxygen content (TO) and inclusion density decreased during the refining process. The spherical CaO–SiO2–Al2O3–MgO inclusions existed in the 321 stainless steel after the AOD process. Moreover, prior to the Ti addition, the spherical CaO–Al2O3–MgO–SiO2 inclusions were observed during LF refining pro-cess. However, Ti addition resulted in multilayer CaO–Al2O3–MgO–TiOx inclusions. Two different samples were prepared by conventional CaO–Al2O3-based slag (Heat-1) and -TiO2-rich CaO–Al2O3-based slag (Heat-2). The statistical analysis revealed that the density of inclusions and the -TiOx content in CaO–Al2O3–MgO–TiOx inclusions found in Heat-2 sample are much lower than those in the Heat-1 sample. Furthermore, the TO content and Ti yield during the LF refining process were controlled by using -TiO2-rich calcium aluminate synthetic slag. These results were consistent with the ion–molecule coexist-ence theory and FactSage?7.2 software calculations. When -TiO2-rich CaO–Al2O3-based slag was used, the -TiO2 activity of the slag increased, and the equilibrium oxygen content significantly decreased from the AOD to LF processes. Therefore, the higher -TiO2 activity of slag and lower equilibrium oxygen content suppressed the undesirable reactions between Ti and O.

Experimental Investigation on Viscosity of CaO-MgO(-Al_2O_3)-SiO_2 Slags and Solid-liquid Mixtures

The viscosities for the selected CaO-MgO-SiO2 and CaO-MgO Al2 O3-SiO2 slags were measured by rota- ting cylinder method in a wide temperature range from 1608 K to 1 823 K. The effects of temperature, slag basicity and Al2 O3 content were studied. The results indicated that the viscosity decreased with increasing the slag basicity at the same temperature. And the viscosities of the slag initially increased linearly with increasing Al2 O3 content in the slags and then decreased as the Al2 O3 content in the slags continued to increase. Al2 O3 addition has a more signifi- cant effect on the viscosity than slag basicity in the selected slags. Based on the experimental data and the fraction of solid phases calculated by the thermodynamic software, the effect of solid phases on slag viscosity was evaluated. The results indicated that the relationship between the relative viscosity and the volume fraction of solid phases esti- mated from the slag composition can be reasonable by allowing the inverse maximum fraction of solid particles to vary.

高磷铁水用CaO-Fe2O3-Al2O3渣系脱磷的实验研究

以CaO-Fe2O3-Al2O3渣系为研究对象,利用Factsage热力学软件计算渣系组成对其熔点、粘度及组元活度的影响,通过热态实验研究渣系钙氧比及渣中w(Al2O3)对高磷铁水脱磷的影响。结果表明:CaO-Fe2O3-Al2O3渣系熔化温度随渣系钙氧比的增大而升高,随w(Al2O3)的增大而降低;渣系粘度随渣系钙氧比增大而升高;渣系中CaO组元活度随着w(Al2O3)增大而降低,随钙氧比增大先大幅度升高后略有降低;渣系中Fe2O3组元活度随钙氧比增大先大幅度降低后略有降低,随w(Al2O3)增大略有波动。渣系的脱磷能力随着钙氧比的逐渐增大先略有增大后快速降低;钙氧比为0.45,w(Al2O3) = 1%~5%时,渣系脱磷率维持在90%以上。C2S-C3P固溶体相是熔渣中磷的主要富集相,C3P以扩散和析出的形式与熔渣中的2CaO·SiO2结合生成C2S-C3P固溶体。