New evaluation techniques of segregation in continuously cast steel.

Miyamura, Ko; Taguchi, Isamu; Soga, Hiromu

doi:10.2355/isijinternational1966.24.883

Cited by 10 publications

(6 citation statements)

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“…Macroscopic examination of the centreline segregation across the entire width of a c.c. slab is achieved by warm etching in hydrochloric acid or by sulphur print [7][8][9][10]. These methods are reliable, reproducible and easy applicable, but they are nowadays not sensitive enough with respect to modem casting machines.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…For this reason a new electrolytic macro etching system followed by image processing of the etched pattern was applied in an ECSC-project [ll]. The application of the computer-aided micro-probe analyser is highly sensitive with respect to microsegregation and semi-macroscopic segregation or spot segregation [7][8][9][10]12,13]. The fundamental understanding of solidification principles has been much enhanced by this highly accurate method.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Investigation of Centreline Segregation and Centreline Porosity in CC - Slabs

Jacobi

2003

steel research international

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Improvements of solidification processing in conventional or near net shape casting depend on sophisticated methods of macroscopic examination of central unsoundness and inhomogeneity of the cast material. As long as remarkable deviations referring to the quality features exist between the slab centre and the bulk material such methods should be looked after. Two semi‐macroscopic methods of segregation analysis are discussed in this paper: firstly, the potential of the emission spectral analysis combined with sectioning of a sample and secondly, the computer aided micro‐probe analysis. Both methods are restricted to small local areas. The proneness of elements and steel grades with respect to micro‐ and macrosegregation as well as distribution‐ and segregation coefficients are determined. The effect of a diffusion anneal on homogenisation of segregation is studied. Last not least the precipitation of sulphides, phosphides or carbonitrides is estimated. Ultrasonic detection of the central unsoundness of conventional slabs or thin slabs is a new approach towards a quantitative macroscopic examination. The sample size is 400 mm x 300 mm x 30 mm. To achieve a low ultrasonic noise using a 5 MHz‐transducer the samples are heat treated for grain refinement. “Dog bone porosity”, macroscopic topographical misfit between the upper and lower solidifying shells, periodical corner cracks or systematic transverse centre cracks are detected. Obviously, segregations do not reflect the ultrasonic beam. However, it can be presumed that an interrelation exists between porosity and segregation, although these might be locally apart from each other. This new ultrasonic test of the central unsoundness of continuous cast (c.c.) slabs gives valuable arguments to machine builders and maintenance people to decide on the right concepts for strand guidance, support rollers and secondary cooling. Soft reduction can be optimized and variations in casting speed counteracted by dynamic means. R&D service of this kind can help steelmakers when decisions are impending to build new casting machines or revamp old ones.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Investigation of Centreline Segregation and Centreline Porosity in CC - Slabs

Jacobi

2003

steel research international

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“…The secondary dendrite arm spacing, S 2 , was evaluated by the linear intercept method, by counting the numbers of arms over a given length of the primary arm, using the optical microscopic observation in the L section. The micro-segregation mapping image 22,23) for solutes such as P and Mn was given by EPMA (at 15 kV-0.5 mA) for an area of 2.56 mmϫ2.56 mm in the analyses region. Data sets of point analysis with every 5 mm beam scanning for both x and y directions yielded 512 pixelsϫ512 pixels images.…”

Section: Macro-and Micro-structural Characterizationmentioning

confidence: 99%

Influence of Phosphorus on Solidification Structure in Continuously Cast 0.1 mass% Carbon Steel.

2003

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In 0.1 mass% carbon steels with phosphorus contents ranging from 0.01 to 0.2 mass%, slabs were continuously cast to a thickness of 100 mm with a laboratory scale caster. Their macro-and micro-structures were characterized, focusing on the effects of phosphorus addition on the structural evolution during solidification and subsequent cooling. Cast slabs of high phosphorus steels have a fine columnar-g-grain structure. The mean width of the columnar grain was approximately half of that in the cast slabs without the phosphorus addition. Dispersed globular a grains were observed in the a grain structure of high phosphorus steels. The globular grains evolved at the phosphorus-rich spots in the prior-g grain. The micro-segregation of phosphorus results in these structural evolutions. Since the phosphorus enrichment stabilizes bcc (d or a) phase locally at the inter-dendritic region, the phosphorus-rich spot makes d phase retained to lower temperature for the d/g transformation, and provides a predominant site for the g/a transformation. In the high phosphorus casts, therefore, the dispersed d phase are thought to pin the g grain growth more effectively in the dϩg region when the completion of the d/g transformation is remarkably suppressed by the phosphorus segregation.

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“…In medium-high carbon steels' production, elements' segregation can occur easily as the solidifying range is relatively wide; thus, it has called more attention to be improved [1][2][3]. Usually, the micro-segregation can be reduced in the subsequent processing; however, macro-segregation [4][5][6][7][8][9], which may cause inconsistent transformation products, leading to failure of the finished products in service [10][11][12][13][14], is more harmful. Therefore, it is vital to control the macro-segregation at a desired level.…”

Section: Introductionmentioning

confidence: 99%

Effect of Solidifying Structure on Centerline Segregation of S50C Steel Produced by Compact Strip Production

Liu

Cheng

et al. 2021

Coatings

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Medium-high carbon steels having a high quality are widely used in China. It is advantageous to produce high value-added hot-rolled plates with the crystal refined and chemical composition homogenized in the casting slabs. However, element segregation occurs easily during high-medium carbon steels’ production. Generally, the centerline segregation is improved by enlarging the equiaxed zone with low-superheat casting and electromagnetic stirring (EMS). Studies were conducted on centerline segregation of S50C steel slabs with a thickness of 52 mm produced by the compact strip production (CSP) process in China without EMS equipped. By sampling along the width at different position, the secondary dendrite arm spacing (SDAS) was measured after etching and picture processing, based on which the cooling rate was calculated. It was found that the cooling rate increased from the center to the surfaces of the slabs ranging in 1~20 K/s, 10 times faster than that of a conventional process. The faster cooling rate led to a refined solidifying structure and columnar dendrite through the center of the slabs. The SDAS tended to increase from surfaces to the center, ranging only 32~120 μm smaller than that of a conventional process in 100~300 μm, indicating a finer solidifying structure by the CSP process. Results by EPMA indicated that elements C, Si, and Mn distribute in dispersed spots, increasing towards the center, and the centerline segregation changed in a narrow range: for C mainly in 1.0~1.1, Si in 0.98~1.08, Mn in 0.96~1.02, respectively, meaning a more chemical homogenization than that of thick slabs. Elements’ segregation originated from solute redistribution between solid and liquid. According to thermodynamic calculation, δ region of S50C is so narrow that the solute redistribution mainly occurred between γ-Fe and liquid during solidification. As the equilibrium partition coefficient of element C was the smallest, it was easy for C to be rejected to the residual liquid in the inter-dendritic space, leading to obvious segregation, relatively. Besides, as a result of high-cooling intensity, the solidifying structure became so fine that the Fourier number increased and the volume of the residual liquid decreased, making centerline segregation alleviated effectively both in volume and degree. Although bulging was observed during the industrial experiment, the centerline segregation was still inhibited obviously as the refining solidifying structure with permeability ranged only in 0.1~2.3 μm2 from the surfaces to centerline, which showed a good resistance on the residual flow towards the centerline.

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New evaluation techniques of segregation in continuously cast steel.

Cited by 10 publications

References 0 publications

Investigation of Centreline Segregation and Centreline Porosity in CC - Slabs

Investigation of Centreline Segregation and Centreline Porosity in CC - Slabs

Influence of Phosphorus on Solidification Structure in Continuously Cast 0.1 mass% Carbon Steel.

Effect of Solidifying Structure on Centerline Segregation of S50C Steel Produced by Compact Strip Production

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