Effect of the Roll Surface Profile on Centerline Segregation in Soft Reduction Process

Abstract

This study investigates the effect of roll surface profile on the centerline segregation of the molten metal (bloom) being solidified in the soft reduction process, where the molten metal (bloom) thickness is reduced consecutively by a set of rolls. The roll surface profiles are convex and flat. Finite element analysis was performed to examine the variations in solidus line contour, the phase state across the bloom cross-section and stress state of the bloom in the mushy zone to the casting direction when high carbon bloom (400 mm in thickness and 500 mm in width) was solidified and plastically deformed at the same time. To verify the finite element analysis results, soft reduction test with an actual bloom caster was also carried out.Results reveal that a convex roll surface profile is much more effective than a flat roll surface profile in decreasing the centerline segregation and the internal cracks in the bloom. The convex roll surface profile compresses the mushy zone from both directions (bloom thickness and width) and subsequently compensates efficiently the solidification shrinkage of molten metal. In addition, the convex roll can save energy required in deforming the bloom in the soft reduction process.

Three-Dimensional Numerical Modeling of Macrosegregation in Continuously Cast Billets

“…It can severely degrade material homogeneity and thus affect the final properties and performance of billet-based products. Macrosegregation is also known as the main cause of cup fracture during wire cord drawing due to the formation of martensite and carbide networks [1]. Macrosegregation cannot be eliminated entirely during heat treatment, so preventing it in the casting process is crucial [2].…”

Analysis and Application of Soft Reduction Amount for Bloom Continuous Casting Process

“…At the same time, because of the different trial conditions, the empirical SR amount was significantly different, for example the 7.5±1.5 mm for bloom thickness of 350 mm, 2) 1.54-6.41 mm for bloom thickness of 380 mm, 6) and 20-30 mm for bloom thickness of 400 mm. 9) Therefore, it is difficult to form common criteria from these industrial trail results only.…”

“…[1][2][3][4][5][6][7][8][9][10] The principle of SR is to impose a reasonable reduction rate/ amount on the solidification end of the strand for compensating liquid core shrinkage and preventing the soluteenriched liquid flowing toward the center of the strand without creating internal cracks. 1,2,4) In bloom SR process, the reduction is usually executed by 6-10 withdrawal units which are arranged in the air cooling zone with intervals of 1.0-3.5 m. Therefore the reduction interface is discontinuous, and the SR amount is generally selected as the primary control parameter during the bloom SR process.…”

Work Roll Surface Profile Design and Optimization for Hot-core Heavy Reduction Rolling Process

“…The industry application showed that shrinkage and segregation defects were improved obviously by using the convex roll. 25,26) Understandably, the void closure of HHR 2 should be also affected by the surface profile of roller. The aim of this paper is to design an appropriate roll profile especially for HHR 2 for eliminating the shrinkage cavities of bloom.…”

“…Convex roll can form stress concentration at the middle zone of blooms, which promotes core deformation, and this was also mentioned in MOON Chang Ho's work. 26) Meanwhile the surface temperature of blooms was lower than the core, which amount to forming a hard shell outside the bloom, so the middle zone of blooms was unsubstantial because of the thinner shell. When the convex roll works, the combined action of hard shell and convex roll may form torque taking the corner of convex as the fulcrum.…”