In situ Observation of Calcium Oxide Treatment of Inclusions in Molten Steel by Confocal Microscopy

Abstract

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...

Modification of Alumina Inclusions in SWRS82B Steel by Adding Rare Earth Cerium

“…However, the addition amount of aluminum has a great influence on the quality of the molten steel, which is likely to cause nozzle clogging. Calcium treatment is used to modify alumina inclusion, decreasing the detrimental effect of alumina [6]. Many scholars have proposed that calcium treatment can transform high-melting alumina inclusions into low-melting liquid composite inclusions.…”

Significance of Nonmetallic Inclusions for the Clogging Phenomenon in Continuous Casting of Steel––A Review

“…Second, inclusions adhere to the refractory wall due to interfacial forces, potentially leading to a cavity formation around the Reproduced under terms of the CC-BY license. [89] Copyright 2017, The Authors, published by Springer Nature. contact point (see Detail A in Figure 9).…”

“…Figure 8. Change in inter-inclusion distance with time for a pair of inclusion particles observed a) Before Ca-treatment and b) After Ca-treatment.Reproduced under terms of the CC-BY license [89]. Copyright 2017, The Authors, published by Springer Nature.…”

Kinetics Study on the Modification Process of Al2O3 Inclusions in High-Carbon Hard Wire Steel by Magnesium Treatment

“…The alumina nonmetallic inclusions in hard wire steel have an important influence on the fatigue resistance of wire breaking or hard wire products during cold drawing, resulting in early fracture of steel in practical application [1][2][3]. The number, size, type and distribution of alumina inclusions are very important for the properties of hard wire steels [4][5][6][7][8]. The solubility of magnesium in molten steel is relatively high.…”