A study has been carried out to understand the modification of alumina inclusions in an Al-Killed high sulphur steel with calcium treatment in 150 tonne steel ladle. To avoid abnormalities during casting, inclusions chemistry needs to be controlled so that these inclusions are in liquid phase during continuous casting of steel. For calcium treatment to be effective, general practice is to desulphurise the steel so as to reach sulphur levels below 0.010% to prevent formation of solid CaS inclusions that are harmful to steel quality and final properties. To avoid this additional desulphurising step which involves cost and is time consuming, the authors have developed a new approach of calcium treatment of steel at an industrial scale. This approach involves treating the liquid steel with calcium treatment at low aluminium levels which enables formation of liquid calcium aluminate inclusions (C 12 A 7 ) in the melt and then addition of sufficient aluminium for achieving grade requirement (i.e.

Calcium treatment of aluminum killed steel was observed in situ using high-temperature confocal scanning laser microscope (HT-CSLM). This technique along with a novel experimental design enables continuous observation of clustering behavior of inclusions before and after the calcium treatment. Results show that the increase in average inclusion size in non-calcium-treated condition was much faster compared to calcium-treated condition. Results also show that the magnitude of attractive capillary force between inclusion particles in non-treated condition was about 10 À15 N for larger particles (10 lm) and 10 À16 N for smaller particles (5 lm) and acting length of force was about 30 lm. In the case of calcium-treated condition, the magnitude and acting length of force was reduced to 10 À16 N and 10 lm, respectively, for particles of all sizes. This change in attractive capillary attractive force is due to change in inclusion morphology from solid alumina disks to liquid lens particles during calcium treatment. The demand for clean steel production is increasing in engineering industries to produce ultra-clean steels with superior mechanical and performance properties for various structural applications. Non-metallic inclusions in steel are harmful as they cause nozzle clogging during steel processing and also deteriorate the mechanical and performance properties of the final product. [1][2][3] During secondary steel making process, steel is de-oxidized with aluminum which results in the formation of alumina inclusions in steel. While small inclusions are less harmful, large inclusions can often be detrimental. They are sites for crack initiation. They also hinder performance in final products through reduced mechanical strength, toughness, corrosion resistance, and surface quality. In general, inclusions are removed by absorption into ladle slag during secondary steel making process. Since removal of all inclusions is not possible, residual inclusions are treated with calcium wire injection in molten steel which results in transforming solid alumina inclusions to liquid calcium aluminate inclusions, which helps in preventing the nozzle clogging. [4][5][6] Further, the mechanical properties of calcium-treated steel are improved in comparison to non-treated steels. Understanding inclusions morphology, distribution, and their agglomeration behavior is essential to further improve steel cleanliness and mechanical properties of the steel. However, several research studies were performed in the past to understand the effect of calcium treatment on morphological changes of oxide inclusions in steels, but still there is lack of information on understanding of clustering behavior and kinetics agglomeration of inclusions before and after calcium treatment. [6][7][8] Since steel is a high-temperature material, studying the clustering behavior of non-metallic inclusions in molten steel is a very challenging task. Confocal microscopy is an excellent technique which enables in situ observation of phase transformations at high t...

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Samples from calcium-treated liquid steel at Visakhapatnam Steel Plant (VSP), Visakhapatnam are studied under scanning electron microscope to understand the inclusion evolution under various operating parameters. The compositions of inclusions are plotted in ternary Ca-Al-S diagram to evaluate the efficiency of inclusion modification and stable casting operation. Process parameters such as amount of calcium addition, bath superheat, and the speed of wire injection are studied for calcium treatment of steel. Both CaFe and CaSi addition are studied, and calcium recovery for CaFe addition is always found to be less than CaSi addition for the same operating conditions. For CaSi addition, the recommended ranges in terms of bath superheat, wire speed, and the amount of calcium addition are identified for the operating conditions studied for VSP, Visakhapatnam.

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