The Significance of Central Segregation of Continuously Cast Billet on Banded Microstructure and Mechanical Properties of Section Steel

The solidification structure and segregation of continuously cast billets produced by different continuous casting processes are investigated to elucidate their effect on segregated bands in hot-rolled section steel. It suggested that segregated spots are mainly observed in the equiaxed crystal zone of a billet. The solidification structure is directly related to superheating and the intensities of secondary cooling. To a certain extent, the ratio of the columnar crystal increases with the increase of superheating and secondary cooling. Moreover, the number of spot segregations decreases with the decrease of the equiaxed crystal ratio. After hot rolling, the segregation spots are deformed to form segregated bands in steels. The severe segregation of Mn in segregated bands corresponds with that in the segregation spots. The elongation ratio and low temperature toughness deteriorate significantly by a high fraction of degenerate pearlite caused by central segregation. With a decrease of central segregation, the total elongation is increased by 10% and the ductile–brittle transition temperature (DBTT) is also reduced from −10 to −40 °C. According to the experimental results, columnar crystal in billets is preferred to effectively reduce the degree of central segregation and further improve low temperature toughness and the elongation ratio.

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Quantitative Correlation and Control Strategy for Element Content Fluctuation along Casting Direction in Central Area of Continuous Casting Billet

Metals ◽

10.3390/met11030452 ◽

2021 ◽

Vol 11 (3) ◽

pp. 452

Author(s):

Dongwei Guo ◽

Zibing Hou ◽

Zhiqiang Peng ◽

Qian Liu ◽

Jianghai Cao

Keyword(s):

Control Strategy ◽

Central Area ◽

Solidification Structure ◽

Equiaxed Crystal ◽

Correlation Relationship ◽

Zone Formation ◽

Zone Width ◽

Quantitative Correlation ◽

Central Segregation ◽

And Control

The statistical correlation was applied to analyze the specific and quantitative correlation relationship between the solidification structure and central segregation along the casting direction in carbon steel billet. On this basis, the segregation formation mechanism of the solute element and related control strategy were investigated. It is found that the equiaxed crystal zone fluctuation along the casting direction determines the fluctuation degree of central segregation. At the same time, the central segregation at a certain position is mostly affected by the equiaxed crystal zone width at the hysteretic position. Moreover, the casting speed can influence the columnar to equiaxed transition (CET) fluctuation along the casting direction by affecting the flow of molten steel in the billet. Overall, the segregation mechanism of solute elements along the casting direction can be summarized into two aspects: First, with the growth of columnar crystals in the initial stage, the segregated solutes are continuously enriched and distributed in the equiaxed crystal zone after CET. The fluctuation of the equiaxed crystal zone will affect the distribution of the enriched solute in the billet and cause the fluctuation of the central segregation. Second, due to the solidification shrinkage at the end of solidification, the solute-enriched liquid phase at the hysteretic position is pumped to the solidification endpoint and forms the central V-shaped segregation. Meanwhile, the stable solidification structure (columnar crystal length or equiaxed crystal zone width) along the casting direction and control measures preceded equiaxed crystal zone formation are beneficial to reduce the central V-shaped segregation.

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Rational Distribution of Surface Cooling Intensity for a Round Continuously-Cast Billet in Secondary Cooling Zone

Metallurgist ◽

10.1007/s11015-021-01121-0 ◽

2021 ◽

Vol 64 (11-12) ◽

pp. 1315-1321

Author(s):

A. B. Biryukov ◽

A. A. Ivanova

Keyword(s):

Cast Billet ◽

Cooling Zone ◽

Secondary Cooling ◽

Surface Cooling ◽

Rational Distribution ◽

Secondary Cooling Zone ◽

Cooling Intensity ◽

Continuously Cast Billet ◽

Continuously Cast

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Influence of Secondary Cooling Mode on Solidification Structure and Macro-segregation Behavior for High-carbon Continuous Casting Bloom

High Temperature Materials and Processes ◽

10.1515/htmp-2016-0022 ◽

2017 ◽

Vol 36 (7) ◽

pp. 741-753 ◽

Cited By ~ 2

Author(s):

Kun Dou ◽

Zhenguo Yang ◽

Qing Liu ◽

Yunhua Huang ◽

Hongbiao Dong

Keyword(s):

Continuous Casting ◽

Casting Process ◽

Coupling Model ◽

Solidification Structure ◽

Secondary Cooling ◽

Characteristic Parameters ◽

High Carbon ◽

Cooling Mode ◽

Gcr15 Steel ◽

Continuously Cast

AbstractA cellular automaton–finite element coupling model for high-carbon continuously cast bloom of GCr15 steel is established to simulate the solidification structure and to investigate the influence of different secondary cooling modes on characteristic parameters such as equiaxed crystal ratio, grain size and secondary dendrite arm spacing, in which the effect of phase transformation and electromagnetic stirring is taken into consideration. On this basis, evolution of carbon macro-segregation for GCr15 steel bloom is researched correspondingly via industrial tests. Based on above analysis, the relationship among secondary cooling modes, characteristic parameters for solidification structure as well as carbon macro-segregation is illustrated to obtain optimum secondary cooling strategy and alleviate carbon macro-segregation degree for GCr15 steel bloom in continuous casting process. The evaluating method for element macro-segregation is applicable in various steel types.

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Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet

Metals ◽

10.3390/met9050543 ◽

2019 ◽

Vol 9 (5) ◽

pp. 543 ◽

Cited By ~ 4

Author(s):

Yanshen Han ◽

Xingyu Wang ◽

Jiangshan Zhang ◽

Fanzheng Zeng ◽

Jun Chen ◽

...

Keyword(s):

Heat Transfer ◽

Continuous Casting ◽

Surface Temperature ◽

Water Flux ◽

Solidification Structure ◽

Equiaxed Crystal ◽

Secondary Cooling ◽

Cooling Strategy ◽

Crystal Density ◽

Heat Transfer And Solidification

Water flux distribution largely influences the heat transfer and solidification of continuously-cast steel billets. In this paper, a secondary cooling strategy of transverse non-uniform water flux (i.e., higher flux density on billet center), was established and compared with the uniform cooling strategy using mathematical modeling. Specifically, a heat transfer model and a cellular automaton finite element coupling model were established to simulate the continuous casting of C80D steel billet. The water flux was measured using different nozzle configurations to assist the modeling. The mathematical results were validated by comparing the surface temperature and the solidification structure. It is shown that the non-uniform cooling strategy enables the increase of corner temperature and reduction in surface temperature difference, while a higher reheating rate is found on the surface center of the billet. Moreover, the non-uniform cooling strategy can enhance the cooling effect and refine the solidification structure. Accordingly, the liquid pool length is shortened, and the equiaxed crystal density is increased along with the decreased equiaxed crystal ratio. The uniform cooling strategy contributes to reducing internal cracks of billet, and the non-uniform one is beneficial for surface quality and central segregation. For C80D steel, the non-uniform cooling strategy outperforms the uniform one.

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Initial Transfer Behavior and Solidification Structure Evolution in a Large Continuously Cast Bloom with a Combination of Nozzle Injection Mode and M-EMS

Metals ◽

10.3390/met9101083 ◽

2019 ◽

Vol 9 (10) ◽

pp. 1083

Author(s):

Wang ◽

Zhang ◽

Tie ◽

Qi ◽

Lan ◽

...

Keyword(s):

Single Port ◽

Solidification Structure ◽

Internal Quality ◽

Equiaxed Crystal ◽

Injection Mode ◽

Solidification Interface ◽

Nozzle Injection ◽

Continuously Cast ◽

Heat Transfer And Solidification

A three-dimensional numerical model combining electromagnetic field, fluid flow, heat transfer, and solidification has been established to study the effect of nozzle injection mode and mold electromagnetic stirring (M-EMS) on the internal quality of a continuously cast bloom. The model is validated by measured data of the magnetic flux density along the stirrer center line. According to the simulation and experimental results, M-EMS can introduce a horizontal swirling flow ahead of the solidification front, promoting the superheat dissipation of molten steel and columnar to equiaxed transition (CET). As the stirring current increases from 0 to 800 A, the superheat at the mold exit in the bloom center decreases by 1.9 K for the single-port nozzle case and 3.8 K for the five-port nozzle case. The resulting increase in the equiaxed crystal ratio is about 5.65% and 4.06%, respectively. In comparison, the injection mode shows a more significant influence on the heat transfer and solidification structure in the bloom under the present casting conditions. The superheat at the mold exit in the bloom center decreases by 5.1‒7.7 K as the injection mode changes from a single-port nozzle to a five-port nozzle, and the increase in the equiaxed crystal ratio ranges between 14.8% and 17%. It is found that the flow velocity of the molten steel in front of the solidification interface for the five-port nozzle is higher than that for the single-port nozzle regardless of the M-EMS power. The washing effect here reinforces both the heat exchange through the solidification interface and the dendrite re-melting or fragmenting, stimulating the formation of an equiaxed crystal at the bloom center. In addition, it is observed that both the central shrinkage and carbon segregation have decreased with the five-port nozzle plus M-EMS. This suggests that the combined application of a five-port nozzle and M-EMS can effectively improve the internal quality of large bloom castings.

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