Industrial experimental study on the formation of microbubbles by argon injection into ladle shroud

Using bubbles to remove inclusions in steel is rapidly becoming a popular method for refining. Fine bubbles are thought to be more effective on inclusion removal than big bubbles. The fine bubbles can be formed in molten steel using the argon injection into ladle shroud technology. There are two stages during the formation of fine bubbles in ladle shroud: bubble detachment from wall orifice and detached bubbles splitting into smaller ones in turbulent steel. Many reports have been published on the water model of the argon injection into ladle shroud technology, but industrial experimental research is in its early stage. In this study, high argon flow was injected into a ladle shroud and adopted in continuous casting production to produce fine argon bubbles in a tundish. The bubbles were captured by dipping a cold steel sheet into molten steel. The captured bubbles at the surface of a hot-dipped steel sheet, with a size of 1.0–3.0 mm, characterized the argon bubbles at steel/slag interface and slag phase in the upper part of a tundish rather than those inside molten steel in tundish. The bubbles inside molten steel in tundish were characterized by the captured bubbles in the interior of a hot-dipped steel sheet, and their morphology, size, and number were analyzed using scanning electron microscopy and confocal microscopy. The bubbles inside molten steel in tundish have a spherical shape and occasionally adhere to each other. These bubbles rang in size from 100 to 1000 μm, with an average of 500 μm. They are dispersed at the exit of a ladle shroud in its lower position, with a density of 15.2 cm^–2. Moreover, it was observed that a bubble could adhere to inclusion, even multiple inclusions for part of bubbles. Bubbles adhered more strongly to Al₂O₃ inclusions than that to CaO(‒MgO)‒Al₂O₃‒SiO₂ complex inclusions.