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Strong electromagnetic stirring enables promotion of interfacial reaction between slag and metal in ladle refining processes. This study elucidates the interfacial phenomena through plant scale experiments by using stationary alternative current (AC) electromagnetic field, cold models to make clear the hydrodynamic behavior of fluids, and the numerical simulation of the magnetohydrodynamic (MHD) and chemical reaction analyses. They revealed that the enhancement of the interfacial reaction is strongly related to the state of the slag-metal interface and that there exist critical values of the intensity of electromagnetic power supply, which govern the reaction rate.

The effects of top blowing and bottom stirring conditions during steelmaking in a 6 t basic oxygen furnace (BOF) were investigated in studies with the aim of suppressing excessive oxidation. With low oxygen feed rate and high stirring energy, the apparent partial pressure of CO P′CO was calculated from the equilibrium of carbon and oxygen in molten steel as being

In Japan, the hot metal pretreatment process has been developed to refine hot metal under conditions where each impurity can be removed most efficiently. At Nippon Steel, three types of hot metal pretreatment process, using torpedo car, hot metal ladle, or LD converter, are employed, that make a great contribution to the reduction of slag volume. Recently, Nippon Steel has developed a new hot metal pretreatment called the multirefining converter (MURC) process, in which dephosphorisation and decarburisation are carried out continuously in the same converter. Nevertheless, since the dephosphorisation efficiency of CaO is less than 30%, CaO is now being used in far greater quantities than that stoichiometrically required to make 3CaO.P2O5. As hot metal dephosphorisation is a non-equilibrium reaction, in which hot metal is in contact with slag whose oxygen activity differs greatly from that of hot metal, it is important to increase the interfacial oxygen activity. From the results of a fundamental ex...

The authors propose a new refining process, by which hot metal is dephosphorized and decarburized continuously in the same basic-oxygen furnace, with intermediate deslagging following dephosphorization. After decarburization, slag is kept inside the furnace and reused to dephosphorize the next charge so as to minimize the quantity of slag discharge. Experiments were made to clarify the properties of this process, using an 8-ton experimental converter. The results confirmed high productivity or a higher rate of dephosphorzation achievable with an increased rate of oxygen blowing and the addition of iron o?e. Because of the dephosphorization by low-basicity slag and the ho - recycling of decarburization-slag to dephosphorize the next charge, line consumption was relatively low. The proper conditions of this process, such as the slag composition for dephosphorization rate of oxygen supply, bottom agitation, and rate of intermediate deslagging, are also discussed, based on the experimental results.

It is important to know the behavior of jets from a top-blown lance in order to control the reactions in the converter. However, there are few studies on the jet characteristics under incorrect expansion and the interference behavior of multiple jets. In this study, the characteristics of jet under incorrect expansion and the interference behavior of multiple jets were investigated by experiments using a cold model. Furthermore, hot model experiments using a 6 t converter were conducted in order to investigate the correlation between the velocity of jet and dust generation. There is good correlation between dust generation and the velocity of jet, and dust decreases by utilizing incorrect expansion for soft-blow.

The formation of bubbles at a nozzle and subsequent rising behavior of them in a molten iron bath at 1250°C were observed using a high-voltage X-ray fluoroscope and a high-speed video camera. The frequency of bubble formation at the nozzle exit, the mean bubble diameter and the mean bubble rising velocity were obtained for a side range of injected argon gas flow rate. Empirical correlations of these quantities were proposed and compared with previously published experimental data and empirical correlations.It has been commonly believed that the frequency of bubble formation at a nozzle placed in a molten metal bath depends solely on the gas flow rate and the outer diameter of the nozzle when the gas flow rate is relatively high and the wettability between the nozzle material and the molten metal is bad. The present experimental results, however, revealed that the frequency of bubble formation has a close relationship not with the outer diameter but with the inner diameter of the nozzle for a higher gas flow rate. Furthermore, the bubble frequency depended on the gas flow rate and the physical properties of gas and molten metal. The critical gas flow rate for the initiation of small bubbles due to disintegration of large bubbles coming from the nozzle exit was approximately 60 cm3/s under the present experimental conditions. The bubble behavior near the bath surface also was made clear.

Physical model of slag foaming was developed by using results of cold and hot model experiments. The bubble size at the slag/metal interface, the void fraction of foam and the film life of a bubble at the top surface of slag were calculated. The governing factors of slag foaming have been clarified with this model. It was confirmed that the bubble size at the slag/metal interface is determined basically by the static balance between the buoyancy force and the adhesive force to the slag/metal interface. It was resulted that the slag/metal interfacial tension and the surface tension of metal also affect the foam height besides the surface tension and the viscosity of slag because they change the bubble size.

In the smelting reduction process of the thick slag layer type, it is important to keep slag height stably without abnormal slag foaming. This study investigated the mechanism of slag foaming control with carbonaceous materials by experiments using a 1-ton smelting reduction furnace and by X-ray fluoroscopic observation of phenomena occurring in a small graphite crucible. As the carbonaceous material was not wettable with slag, small bubbles coalesced on its surface. Because the large bubbles due to the coalescence of small bubbles rise through the foaming slag layer at a relatively high speed, the foaming of slag may be restrained. It was found that the smaller the size of the carbonaceous material was, the more effective was the carbonaceous material in controlling the foaming of slag. A certain extent of relative motion between carbonaceous material and slag was necessary to promote the coalescence of small bubbles. It was experimentally confirmed that the smelting reduction in 100-ton scale furnace can stably operate under the condition that the carbonaceous material is present in a sufficient amount in the slag.