A Novel Investigation of Initial Solidified Shell Thickness of Continuously Cast Slab Based on Solidification Structure

Abstract

Considering the big deviation of the measured initial shell thickness obtained by directly measuring the breakout shell in previous works, a new method has been proposed in this study in a microscopic and mesoscopic view. This innovative measuring method is based on the transformation point of the solidification structure of the initial solidified shell before and after the breakout occurs, which avoids the deviation induced by the attachment of the residual liquid steel. Due to the different heat transfer conditions along the casting direction of the mold, causing different segregation behaviors of the solute elements at the different positions, the micromorphology of solidified shell cannot be revealed just through the same etchant. In the present work, the appropriate etchants for the breakout shell at different positions along the casting direction have been explored through dendrite and grain etching experiments, and a black solute enrichment region appearing in the solidified structure after being etched is chosen to determine the shell thickness, therefore, the solidified structure of the initial solidified shell has been investigated in detail based on the experimental results. The result shows that solidification coefficient within the mold obtained by fitting the change curve of the initial shell thickness with the empirical equation is more competitive than the previous works.

Insight into Breakout Shell of a Bloom Casting by Its Dendritic Morphology and a New Mathematical Model

“…As discussed in the former parts, a white band can always be observed in the dendritic morphology of the breakout shell. Feng and Zhu made observations on the microstructure of a breakout sample from slab casting, and a white band can also be found in their investigation. Before the happening of breakout, the heat transfer and liquid flow in the mold were relatively stable.…”

“…It has been widely accepted that the total shell thickness from the breakout shell is always larger than that in the steady state . There are two factors resulting in the above difference .…”

“…It has been widely accepted that the total shell thickness from the breakout shell is always larger than that in the steady state. [12][13][14] There are two factors resulting in the above difference. [12] On one hand, the leakage of liquid steel during breakout lasts for seconds or even tens of seconds, and the shell keeps thickening until the level drops below.…”

“…Iwasaki employed the fluid mass balance to reconstruct the transient events that occurred during the breakout, explaining why the thickness of breakout shell was greater than the steady state shell. In the latest research, Feng has proposed that a white line and a black line can be observed in the microstructure of a slab breakout shell, while the latter one can be used to determine the initial shell thickness.…”

Evolution of Austenite Grain Size in Continuously Cast Slab during Hot‐Core Heavy Reduction Rolling Process Based on Hot Compression Tests

“…More stringent quality characteristics such as higher toughness, higher strength, and larger plate thickness are required for such heavy steel plates. However, the coarse microstructure always remains at center position of the slabs due to weak heat transfer, sometimes may lead to local stress concentration in soft phase and even fracture during solidification process or reheating process prior to hot rolling, which significantly reduce the rolling yield and the welding property of the final products . Therefore, the demands of producing continuously cast slabs with consistent quality and high productivity make it crucial to ensure excellent mechanical properties of the final products.…”