Secondary Cooling Pattern for the Prevention of Surface Cracks of Continuous Casting Slab

Nozaki, Tsutomu; Matsuno, Jun-ichi; Murata, Kenji; Ooi, Hiroshi; Kodama, Mutsuo

doi:10.2355/tetsutohagane1955.62.12_1503

Cited by 35 publications

(41 citation statements)

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“…(1) Typical values of the maximum heat-transfer coefficient measured by different researchers [65,67,77] lie between 2.0 and 3.0 kW m Ϫ2 K Ϫ1 at the burnout temperature of ϳ500 °C to 700 °C. (2) Within the desired surface temperature range of 900°C to 1200 °C for spray cooling, the surface temperature of the strand has little impact on the spray heat-transfer coefficient.…”

Section: B Secondary Coolingmentioning

confidence: 99%

“…This relative lack of dependence clearly indicates that the heat-transfer mechanism is dominated by the convective heat transport occurring between the surface of the casting and a stable film of steam adhering to it (film boiling). (3) Within the film boiling regime, the spray heat-transfer coefficient has a strong correlation with the water flow rate, as represented by the following empirical relationship: [67] [2]…”

Section: B Secondary Coolingmentioning

confidence: 99%

“…Experiments have been conducted to quantify heat transfer from water cooling and to establish boiling water curves (refer to Figure 10) in controlled laboratory experiments on small steel [48,[63][64][65][66][67][68] and aluminum [21,50,[69][70][71][72][73][74][75][76] samples, in plant measurements of secondary cooling in the continuous casting of steel [77] , and in DC casting of aluminum [78][79][80][81] . Generally, empirical relationships are developed by applying inverse heat-transfer analysis to the measurements recorded by d Fig.…”

Section: B Secondary Coolingmentioning

confidence: 99%

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The use of water cooling during the continuous casting of steel and aluminum alloys

Sengupta

Thomas

Wells

2005

Metall Mater Trans A

105

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In both continuous casting of steel slabs and direct chill (DC) casting of aluminum alloy ingots, water is used to cool the mold in the initial stages of solidification, and then below the mold, where it is in direct contact with the newly solidified surface of the metal. Water cooling affects the product quality by (1) controlling the heat removal rate that creates and cools the solid shell and (2) generating thermal stresses and strains inside the solidified metal. This work reviews the current stateof-the-art in water cooling for both processes, and draws insights by comparing and contrasting the different practices used in each process. The heat extraction coefficient during secondary cooling depends greatly on the surface temperature of the ingot, as represented by boiling water-cooling curves. Thus, the heat extraction rate varies dramatically with time, as the slab/ingot surface temperature changes. Sudden fluctuations in the temperature gradients within the solidifying metal cause thermal stresses, which often lead to cracks, especially near the solidification front, where even small tensile stresses can form hot tears. Hence, a tight control of spray cooling for steel, and practices such as CO 2 injection/pulse water cooling for aluminum, are now used to avoid sudden changes in the strand surface temperature. The goal in each process is to match the rate of heat removal at the surface with the internal supply of latent and sensible heat, in order to lower the metal surface temperature monotonically, until cooling is complete.

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Section: B Secondary Coolingmentioning

confidence: 99%

Section: B Secondary Coolingmentioning

confidence: 99%

Section: B Secondary Coolingmentioning

confidence: 99%

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The use of water cooling during the continuous casting of steel and aluminum alloys

Sengupta

Thomas

Wells

2005

Metall Mater Trans A

105

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“…The water distribution coefficients in each secondary cooling zone in Eq. (14) are shown in Table 4. The verified model has already been applied to adjust the operation parameters to improve the strand quality and the productivity.…”

Section: Resultsmentioning

confidence: 99%

Applying of Real-time Heat Transfer and Solidification Model on the Dynamic Control System of Billet Continuous Casting

2008

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In this paper, a real-time mathematical heat transfer model for billet continuous casting of low carbon steel has been presented and solved by finite volume method. This model can be used to simulate the casting conditions which vary frequently. As taking the variation of superheat of liquid steel into consideration in the water flow rate distribution, the fluctuation of billet surface temperature has been decreased. Meanwhile the fluctuation of measured temperature has been largely reduced when it is measured with thermal imager. The mathematical model has been validated by measuring shell thickness and surface temperature in industrial caster. The on-line model can monitor surface temperature and shell thickness along the caster machine in the casting process, and it has been applied on the dynamic control system to adjust the operation parameters. The billet defect has been decreased greatly and the quality of billet has been obviously improved.KEY WORDS: real-time model; continuous casting; heat transfer; solidification; secondary cooling; dynamic control.......... (1) where T is the billet temperature, t is the time, x, y are the rectangular coordinates, k is the thermal conductivity of steel, c is the specific heat capacity of steel, r is the density of steel, and q is the latent heat source.Owing to the symmetry of heat transfer in square sections, one quarter of billet cross-section is selected as calculation area. The grid division and boundary conditions for cross-section of the billet are presented in Fig. 1. The P is the control volume, and w, e, n, s are the correspondence interfaces.In the time interval (t, tϩDt), Eq. (2) is obtained by finite volume method and the discrete equation group of complete implied format is formulated. 8,9) ... Thermophysical Properties of SteelThe latent heat is generated during phase change between liquidus and solidus temperatures of steel and is ex- where L is the latent heat of fusion, r is the density of steel, f s is the solid fraction in the mushy zone and it can be expressed in accordance with Eq. (4) Equations (4) and (1) giveThe f s 3) of low carbon steel can be expressed by the following equation:... (6) where T L is the liquidus temperature of steel, T S is the solidus temperature of steel.The convective heat transfer in the liquid pool and mushy zone is quite difficult to be calculated by using differential equations. The effective thermal conductivity is given by the following linear relationship 5) :where k eff is the effective thermal conductivity, k is the thermal conductivity of solid steel, A is a constant, and f s is the solid fraction in the mushy zone.The specific heat capacity and density are expressed by the following equations: where sub-indices S and L, respectively, indicates solid and liquid state. The Boundary Conditions (1) Initial ConditionThe boundary condition to the steady state casting has been assumed to be the same as the pouring or casting temperature (T 0 ) of the steel. (10) where T 0 is the steel casting temperature, which is ...

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“…[1][2][3][4][5][6][7] It is frequently reported that performing the unbending operation at the temperatures below or above the aforementioned thermal region has been moderately successful in improving the incidence of cracking in some problem grades because the temperature range of embrittlement has been avoided. 8) However, recent laboratory studies have shown that the thermal history itself has a pronounced effect on the hot ductility. 9) In these new tests, tensile specimens were subjected to thermal histories typical of the surface of a billet during continuous casting.…”

Section: Introductionmentioning

confidence: 99%

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

Akhlaghi

Yue

2001

ISIJ International

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Many attempts have been made to understand the problem of transverse cracking in continuous casting process. Much of this research has involved the study of hot ductility using 'conventional' isothermal hot ductility testing. In these tests, the specimens were isothermally tensile tested to fracture, at temperatures achieved by cooling from a solutionizing temperature, close to the solidus, or above the liquidus. These studies showed that hot ductility at the test temperature is highly depended on the thermal path followed by the specimens. The thermal histories experienced by strands during continuous casting were found to be quite complex and invariably involve rapid cooling and heating cycles. This may therefore lead to high thermal gradients, which, in turn, can generate strains in the surface of the solidifying strand. This then may alter the microstructural evolution of the strand surface and the corresponding hot ductility, a possibility that has not been addressed in any previous studies. Thus, the purpose of this study was to consider the effect of the thermomechanical history on the hot ductility of steel.After in-situ melting and solidification, Nb-Ti microalloyed tensile specimens were subjected to a thermal history typical of a continuously cast billet. Different degrees of deformation were imposed on the specimens at selected stages of this thermal history, before tensile testing to fracture point at the time and temperature corresponding to the unbending stage of the billet casting. It was found that the hot ductility varied from 1 to 98 %, depending on the stage in the thermal history at which deformation was executed. The microstructural evolution during the thermomechanical profile was followed to study the effect of thermomechanical history on the hot ductility.

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Secondary Cooling Pattern for the Prevention of Surface Cracks of Continuous Casting Slab

Cited by 35 publications

References 0 publications

The use of water cooling during the continuous casting of steel and aluminum alloys

The use of water cooling during the continuous casting of steel and aluminum alloys

Applying of Real-time Heat Transfer and Solidification Model on the Dynamic Control System of Billet Continuous Casting

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

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