Discussion on calcium treatment technology for clean steel refining
DENG Zhiyin1,2, ZHU Miaoyong1,2
1. Key Laboratory for Ecological Metallurgy of Multimetallic MineralMinistry of Education, Northeastern University, Shenyang 110819, Liaoning, China; 2. School of Metallurgy, Northeastern University, Shenyang 110819, Liaoning, China
Abstract：Aiming at a better understanding on calcium treatment technology, the physical and chemical properties of metal calcium were summarized, the modification mechanisms of calcium treatment and the related thermodynamic data based on the study results in literature. According to the studies and industrial practice of the present authors, the problems of calcium treatment were discussed, and the principle and control standard for calcium treatment were recommended. Due to the evolution of inclusions in steel during refining process, the object inclusions for calcium treatment change from Al deoxidation products(Al2O3 inclusions) to their evolution products (including MgO·Al2O3 inclusions and CaO-Al2O3-MgO system inclusions, etc.). Although calcium treatment technology can modify the inclusions in steel and improve the castability of steels, it generally declines the removal efficiency of inclusions, enlarges the frequency of macro-inclusions, and leads to reoxidation of liquid steel and corrosion of refractories. Therefore, calcium treatment pollutes liquid steel in most cases. If there are no special requirement on inclusion modification, and no problem with castability of steels, calcium treatment is not recommended to perform. If in need, Ca should be added as little as possible for calcium treatment, and it should be carried out after refining. Accurate measurement of dissolved [Ca] in steel is still a challenge, and large deviations are existed in the thermodynamic data of Ca. In addition, the yield of Ca is unstable as well, so it is difficult to achieve precise control of calcium treatment. Since the measurement of dissolved [Ca] is avoided, and thermodynamic data are not needed, the standard of w(T[Ca])/w(T[O]) can be practical in industry. In order to improve the castability of low-oxygen and low-sulfur steels, the Ca content can be controlled referring to the recommended value (0.91-1.25) of w(T[Ca])/w(T[O]). Nevertheless, the lowest Ca addition is still suggested for higher steel cleanliness. Also, calcium treatment cannot solve all the castability problems due to the various influential factors.
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2023, Vol. 58 
