Go-Gi Lee

Prediction and control of subsurface hooks in continuous cast ultra-low-carbon steel slabs

Abstract Subsurface hook formation during initial solidification in the continuous casting mould degrades the quality of steel slabs owing to the associated entrapment of argon bubbles and non-metallic inclusions. To minimise hook depth and to improve slab quality, extensive plant experiments were performed and analysed to quantify the effect of casting parameters on hook characteristics using the no. 2-1 caster at POSCO Gwangyang Works, Korea. The results reveal that meniscus heat flux plays an important role in controlling hook characteristics. Hook depth correlates with oscillation mark depth, hook shell thickness, and hook length. Based on regression analysis, this paper proposes an equation to predict hook depth in ultra-low-carbon steels as a function of casting speed, superheat, oscillation frequency, surface level fluctuations, and mould flux properties. Use of this quantitative equation enables improved control of subsurface quality in the continuous casting of steel slabs.

Novel approach to Zr powder production by smooth ZrCl4 bubbling through molten salt

A reduction process using ZrCl4 bubbles as a reactant was investigated to produce zirconium metals. ZrCl4 vapor was bubbled through the lance in the bath, in which Mg melt and MgCl2 salt were separated. Zr powder was formed by a reduction of ZrCl4 bubbles in magnesium layer. However, the lance was clogged by the aggregate of zirconium occurred during ZrCl4 vapor injecting leading to interruption of ZrCl4 supply into the bath. This phenomenon could be caused by the presence of magnesium at the lance tip, which passes through MgCl2 salt during bubbling, and then zirconium was formed in the forms of intermetallic compounds with aluminum. In this study, the effect of molten salt on the troubled phenomena was investigated and it was verified that CaCl2 with relatively low Weber number meaning relatively high surface tension as molten salt is effective in inhibiting the lance clogging phenomena. Then, a few micrometer-sized Zr powder with the high purity of 91.6 wt% was obtained smoothly without the formation of intermetallic compound.