Electromagnetic Effects on Solidification Defect Formation in Continuous Steel Casting
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https://doi.org/10.1007/s11837-020-04329-8 Ó 2020 The Minerals, Metals & Materials Society
SOLIDIFICATION BEHAVIOR IN THE PRESENCE OF EXTERNAL FIELDS
Electromagnetic Effects on Solidification Defect Formation in Continuous Steel Casting SEONG-MOOK CHO1 and BRIAN G. THOMAS
1,2
1.—Colorado School of Mines, Department of Mechanical Engineering, Brown Hall W470I, 1610 Illinois Street, Golden, CO 80401, USA. 2.—e-mail: [email protected]
Understanding and reducing defects formed during continuous casting of steel are challenging because of the many inter-related, multiscale phenomena and process parameters involved in this complex process. Solidification occurs in the presence of turbulent multiphase flow, transport and capture of particles, superheat transport, and thermal–mechanical behavior. The application of electromagnetic fields provides an additional parameter to control these phenomena to reduce solidification defects. It is especially attractive because the field has the potential to be easily adjusted during casting to accommodate different casting conditions. This article briefly reviews how electromagnetic forces affect solidification defects, including subsurface hooks, particle capture, deep oscillation marks, depressions, cracks, breakouts, segregation, and shrinkage. This includes the related effects on superheat transport, initial solidification, surface quality, grain structure, internal quality, and steel composition distribution. Finally, some practical strategies regarding how to apply electromagnetics to improve steel quality are evaluated.
INTRODUCTION Continuous casting is the most widely used process to manufacture steel, accounting for > 96% of steel in the world.1 Thus, even small improvements to this process can greatly impact the industry. During continuous casting, molten steel flows into the mold cavity through a submerged nozzle and freezes against the water-cooled mold plates in the presence of turbulent fluid flow, argon gas injection, transport and capture of particles, superheat transport, and thermal–mechanical behavior,2–4 and it finally solidifies into a semi-finished solid shape, such as a slab, bloom, or billet.5 Solidification in this process is very complex and is difficult to understand and optimize, owing to the complicated behavior of the steel and slag6,7 and the many process conditions that can be varied, such as nozzle geometry, mold size, casting speed, argon gas injection rate, water cooling conditions, and mold taper, in addition to the electromagnetic systems. Moreover, solidification defects are mainly caused by abnormal transient upsets of the various
(Received May 17, 2020; accepted August 11, 2020)
phenomena during casting. This makes it challenging to quickly detect and adequately respond to defect formation during operation. Recent efforts involving improved sensing capabilities are enabling better monitoring of temperature of the mold plates, top surface, heat flux in the gap between the steel shell and mold, meniscus level variations, and slag consump
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