Effect of Refining Conditions for Ultra Low Carbon Steel on Decarburization Reaction in RH Degasser.

Yamaguchi, Koji; Kishimoto, Yasuo; Sakuraya, Toshikazu; Fujii, Tetsuya; Aratani, Makoto; Nishikawa, Hiroshi

doi:10.2355/isijinternational.32.126

Cited by 61 publications

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“…The CO gas fractions decrease as time passes. This CO fraction is much smaller than the value reported by M. Takahashi et al 5) In their report, the fraction is more than half near the surface at 5 min later after the process started. This difference may come from the difference of size expansion during the ascent of bubble.…”

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confidence: 53%

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A New Numerical Model for Predicting Carbon Concentration during RH Degassing Treatment

Park

2003

ISIJ International

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A new decarburization model for the RH system was constructed to calculate the decarburization reaction using a three-dimensional fluid dynamics program. The behavior of Ar gas and the entire fluid flow in the RH process were considered. On the basis of this fluid flow, the decarburization reaction could be calculated by establishing the decarburization reaction model, which considers thermodynamics, reaction kinetics, and the decarburization sites (Ar bubble surface, bath surface, and the CO bubble formation at inner sites). The model showed good agreement with two RH operation results. Using this numerical model, the contributions of each reaction were investigated.KEY WORDS: decarburization; reaction model; reaction site; reaction area; reaction rate.where g is the acceleration due to gravity (m/s 2 ), r l and r g are the densities of the Ar gas and the melt (kg/m 3 ), V p is the volume of the plume (m 3 ) and a is the average volume fraction of the gas. The plume volume was calculated from the plume shape, which is affected by the pressure of the vacuum vessel, nozzle number and position, gas flow rate etc.. The average volume fraction is the total volume ratio of gas in the plume realm. In addition, gas bubble expansion due to the pressure drop and heat transfer from melt during rising was calculated and this effect was considered when calculating the total buoyancy force. In the Ref. 9), the bubble expansion due to only pressure drop was considered. In this study, the numerical model was modified to consider both the thermal expansion and pressure drop, Szekely's model 11) is modified as In Eq. (2), r l is the density of the melt, R b is the radius of the bubble, T is temperature in the bubble, R b and T 0 are radius and temperature at the nozzle respectively, P V is the pressure of the vacuum vessel and H is the height of the melt. To solve Eq. (2), the temperature should be known. ) and C is the heat capacity (J/kg · K). h is the heat transfer coefficient (J/m 2 · s · K) and the value can be derived from the penetration theory with the assumption of gas phase control. Komarove et al. derived heat transfer coefficient from experiments.12) Because the analysis in the Ref. 12) was based on spherical and constant size bubble, there should be some difference in the value of h and further study should be necessary to derive more realistic h value.The buoyancy force calculated by Eq. (1) was inserted as the external force for the velocity components (u, v, w) in the three dimensional Navier-Stokes equation to calculate fluid flow. The numerical model can predict the effects of the operational conditions and shapes of the RH system on fluid flow. 13) Calculation of Decarburization ReactionIn this study, the decarburization reaction was simulated by calculating the dissolved carbon concentration during the RH process. The numerical model included mass transport of dissolved carbon and oxygen due to convection and diffusion and the reaction rate at the reaction sites. The reaction rate was calculated respectively...

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confidence: 53%

“…[4][5][6][7][8] However, the previous studies considered gas behavior only for decarburization reaction and the fluid flow was calculated by assuming the circulation flow rate. Therefore, the effects of parameters, which affect both the fluid flow and decarburization rate, could not be evaluated properly.…”

Section: Introductionmentioning

confidence: 99%

A New Numerical Model for Predicting Carbon Concentration during RH Degassing Treatment

Park

2003

ISIJ International

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“…Assumptions concerning decarburization process 1,[27][28][29][30][31] (12) The contents of carbon and oxygen at the gas-liquid interface are in equilibrium with CO partial pressure in gas phase.…”

Section: Mathematical Modelmentioning

confidence: 99%

Effect of Traveling Magnetic Field on Flow, Mixing, Decarburization and Inclusion Removal during RH Refining Process

Geng¹,

Lei²,

He³

2012

ISIJ Int.

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In order to improve productivity during RH refining, the traveling magnetic field was imposed around the snorkels. The numerical method was employed to investigate the flow, mixing, decarburization and inclusion removal in RH degasser. Numerical results showed that the predicted results agree well with the experimental data. With the increasing current, the circulation flow rate increases and the mixing time decreases. If the current frequency lies in the range of 10-30 Hz, with the increasing current frequency, the circulation flow rate increases while the mixing time decreases. If the current frequency lies in the range of 30-60 Hz, with the increasing current frequency, the circulation flow rate decreases while the mixing time increases. In order to increase circulation flow rate and shorten mixing time, the most effective measure is to apply the traveling magnetic field around the up snorkel, and the second choice is to apply the traveling magnetic field around the down snorkel if the gas flow rate is smaller than the saturation value. Applying the traveling magnetic field can accelerate the decarburization rate during the process, but can not decrease the final carbon mass concentration. For inclusion removal, the most effective measure is to apply the traveling magnetic field around the up snorkel and down snorkel, and to apply the traveling magnetic field around the up snorkel has the minor effect. Furthermore, the application of traveling magnetic field can decrease the maximum inclusion characteristic radius and the related peak value time.

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“…About rapid decarburization controlling during RH vacuum treatment process, many relevant models were proposed. [7][8][9][10][11] RH-OB heating mode by Al-O reaction always was adopted when temperature of liquid steel was lower than target temperature; oxygen was injection into liquid steel by lance situated in top of vacuum chamber and then aluminum was added into liquid steel to reacted with soluble oxygen; the chemical reaction energy was used to heat liquid steel. Normal treatment mode was suitable for inclusions removal and dehydrogenation; under this mode, free oxygen in liquid steel was killed before RH treatment; and inclusions aggregated sufficiently and easily were removed during vacuum process due to early formation of inclusions.…”

Section: Introductionmentioning

confidence: 99%

Difference Analysis in Steel Cleanness between Two RH Treatment Modes for SPHC Grade

et al. 2015

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This paper studied the steel cleanness' difference of grade SPHC by comparing two RH modes. Experiments were carried out at 210 ton BOF, RH and 60 ton tundish by sampling systematically. Under mode I, free oxygen was killed during BOF tapping; and inclusions had sufficient removal during RH vacuum treatment; under mode II, RH vacuum carbon de-oxidation was adopted firstly; and then residual oxygen was killed by grain aluminum. Results showed that, (1) total generation amount of inclusions in mode II was 1/2 of that in mode I due to low residual oxygen after vacuum carbon de-oxidation, but steel cleanness in mode I was better in tundish due to long inclusions removal time; (2) under mode I, total oxygen in tundish could be controlled below 20 ppm; and cast-ability in continuous casting process reached 15 heats; (3) under mode II, nitrogen could be controlled below <15 ppm, which was 1/2 of that in mode I; (4) by adopting mode II to reduce total generation amount of inclusions and nitrogen picking up, also to prolong 20 to 30 minutes calming time before casting to guarantee inclusions' removal, low nitrogen, low total oxygen and good cast-ability could realize.

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Effect of Refining Conditions for Ultra Low Carbon Steel on Decarburization Reaction in RH Degasser.

Cited by 61 publications

References 0 publications

A New Numerical Model for Predicting Carbon Concentration during RH Degassing Treatment

A New Numerical Model for Predicting Carbon Concentration during RH Degassing Treatment

Effect of Traveling Magnetic Field on Flow, Mixing, Decarburization and Inclusion Removal during RH Refining Process

Difference Analysis in Steel Cleanness between Two RH Treatment Modes for SPHC Grade

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