Development and Application of Chrome-free Refractory Materials for RH Degasser

The research progress and industrial application of chrome-free refractories for RH degasser were introduced in the paper.It is proved that unburned magnesia-spinel refractories used for RH throat and snorkel in Baosteel have longer service life compared with traditional direct bonded fused magnesia-chrome materials.The new developed chrome-free unburned magnesia-spinel composite can fully meet the present demand for RH operation and can be applied extensively for RH processing.At present,instead of chrome-containing materials,chrome-free refractories have been applied widely for RH in Baosteel.Super low carbon MgO-C material with high mechanical properties at mild and high temperatures can be an alternative chrome-free material for RH.

Development of RH refining technology at Baosteel

With the strong demand for the development of automobile sheets, tin plates, household appliances, silicon steel, pipeline steel and other products as well as for the quality improvement of steel products, remarkable progress has been made in RH refining technology and equipment design since Baosteel began production more than 20 years ago. The vacuum degassing ratio of Baosteel has jumped from 35% in the initial stage when Baosteel began production, to the current ratio of approximately 60%, and will soon reach 75% in the near future. The independent innovations in RH refming technology in Baosteel, such as RH equipment optimization, vacuum decarburization, inclusion control, deoxidation, desulfurization, rhythm adjustment between primary steelmaking and continuous casting, the high efficiency of the RH refining process, and other aspects of RH technology, have all effectively met the requirements of developing new steel products, quality improvement and logistical control. Complete sets of RH equipment and refining technology have been successfully exported to the domestic steel plants. In the future, Baosteel will make further efforts to improve efficiency, stabilize production and quality, and realize special line production, so that the RH degasser will play a greater role in Baosteel.

Prediction of liquid circulation flow rate in RH degasser:improvement of decarburization at low atmospheric pressure

The two-fluid model coupled with population balance model was used for simulating the gas-liquid flow in the Ruhrstahl-Heraeus(RH)degasser.The predicted circulation flow rate was compared with that measured from a water model experiment to validate the mathematical model.Then,influence of snorkel immersion depth on liquid circulation flow rate was numerically investigated under an atmospheric pressure of 101 and 84 kPa,respectively.Predicted result indicates that the circulation flow rate of the RH degasser in the high-altitude area was severely reduced because of the decrease in atmospheric pressure.However,increasing the snorkel immersion depth from 0.5 to 0.7 m can compensate for the decrease in atmospheric pressure.Industrial test result indicates that decarburization rate is significantly enhanced by increasing the snorkel immersion depth.Through optimization,the percentage of heats with a final carbon content less than 0.002 wt.%is significantly increased from 22.0%to 96.4%.

Slag Corrosion Resistance of MgO-ZrO_2 Refractories

Slag corrosion resistance of MgO -ZrO2 refractories was inrestigated ill this work. The resuhs indicate that in a non-oriented electric steel slag systenl with a high ratio of ealci^t to silica, the slag resistance of MgO - ZrO, refractories can be described as flllows ： ZrO2 reacts with GtO .forming calcium zireonate compound which strengthens the material and blocks the channel of the slag infihration ; however, in an oriented electric steel slag system with a high concentration of silica and the low ratio of calcia to silica, the slag corrosion resistance ofM gO-ZrO： refractories is different ; ZrO2 reaets with CaO forming the ealcium zirconate and simultaneously one more product C2S as well; C2S cam improve corro- sion resistance by blinding pore and enhancing slag viscosity; therefore, it is expected to be the major reason for the enham＇ed corrosion resistance observed for MgO-ZrO2 refractories.

Powder transport behavior in RH degasser with powder injection through up snorkel: a transient numerical model

A transient numerical model was established to predict the dispersion,distribution,and circulation behavior of the powder injected through the up snorkel in a Ruhrstahl–Heraeus(RH)degasser.The effects of the powder diameter,the lifting gas flow rate,and the powder injection rate on the powder transport were investigated.Local powder concentration was measured by a cold model.The results showed that the predicted powder concentration agreed well with the measured.The powder injection process is divided into three periods,named dispersion period,aggregation and circulation period,and dynamically stable period according to the powder transport behavior.The powder diameter has a great effect on the particle dispersion.When the particles size changes from 30 to 500μm,the powder dispersion characteristic index changes from 0.110 to 0.741,and the ladle top zone powder mass ratio changes from 0.118 to 0.685.The powder circulation mass flow rate increases to 101.0 kg min^(-1)(150μm)and then decreases to 46.6 kg min^(-1)(500μm).Powders with a diameter of more than 220μm can change the steel flow mode in the RH degasser.Increasing the lifting gas flow could slightly improve the powder dispersion.Variation in the powder injection rate has almost no effect on the powder dispersion.

Modelling Effect of Circulation Flow Rate on Inclusion Removal in RH Degasser

Based on the similarity principles, a 1 ： 7 scale physical model was established to study the behavior of molten steel flow and inclusion removal in a 145 t Rheinsahl-Heraeus （RH） degasser. On the basis of the quantitative measurements of the circulation flow rate and inclusion removal under various lifting gas flow rates, the effect of circulation flow rate on inclusion removal was investigated in the RH degasser. The inclusion removal rate shows the trend of first increase and then decrease twice with increasing the circulation flow rate when the circulation flow rates are smaller than 104.7 L/min. Whereas, the inclusion removal rate increases again with the further increase in circu- lation flow rate when the circulation flow rate is larger than 104.7 L/min. At lower circulation flow rates, inclusions are mainly removed by Stokes flotation to the slag/steel interface after inclusions are transferred near the slag/steel interface by the circulation flow. At higher circulation flow rates, the collision and aggregation of inclusions improves the inclusion removal efficiency. With the further increase in the circulation flow rate, inclusions are mainly removed by following the turbulent fluctuation （turbulent diffusion） to the slag/steel interface after inclusions are transferred near the slag/steel interface by the circulation flow.

Flow Structure in RH Vacuum Degasser Using Rotating Electromagnetic Field

An innovative steelmaking process is suggested using an electromagnetic driven swirling flow in the up-leg of an RH vacuum degasser.A physical and a mathematical model based on 300t RH vacuum degasser are developed to understand the effect of rotating electromagnetic field on the circulation flow rate and the two phases flow behavior of RH system.Both water model experiments and numerical simulation show the flow pattern and distribution of gas bubbles. The gas bubbles move towards the centre of up-leg under the effect of rotating electromagnetic field,and the accumulation of gas bubbles depends on the magnetic intensity.An optimization value of magnetic intensity was suggested in this paper.

Study of Argon/Molten Steel Two-Phase Flow in Refining of High Clean Steel Using Two-Fluid Model

RH vacuum degasser is a very important secondary refining device in the production of high quality steels. The flow field of molten steel in RH system plays a significant role in determining productivity of the equipment. The homogeneous model and VOF method were often used to predict the flow field in RH system, but these kinds of models simplified the interaction between gas bubbles and molten steel. In the present work, a numerical model of a whole RH system, including vacuum degasser, immersed legs and ladle,was built based on gas-liquid two-fluid model, and it could be used to analyze the interaction between argon bubbles and molten steel, to understand the effect of the bubble size to the flow field.