Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 76 (1990), No. 11

  • Advance and Prospect of Technologies on Converter

    pp. 1765-1769

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  • Q-BOP導入の頃の思い出

    pp. 1770-1774

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  • Development History of Combined Blowing Converter

    pp. 1775-1778

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  • II.新日本製鉄(株)の場合

    pp. 1778-1781

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  • III.川崎製鉄(株)の場合

    pp. 1781-1783

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  • IV.(株)神戸製鋼所の場合

    pp. 1783-1786

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  • V.NKKの場合

    pp. 1786-1788

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  • VI.日新製鋼(株)の場合

    pp. 1788-1790

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  • Metallurgical Characteristics of Combined Blowing Converter

    pp. 1791-1800

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  • Establishment of Steel Making Process with High Productivity and High Efficiency by Use of Hot Metal Pretreatment

    pp. 1801-1808

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    In Nippon Steel Corporation, various types of hot metal pretreatment processes were developed to fit in the condition of each works. In Kimitsu and Yawata Works, simultaneous dephosphorization and desulfurization treatment by lime base flux injection with torpedo car has been put into practical use. In Oita Works, this treatment was modified to make high productivity by high rate injection with snorkel immersed ladle. In Nagoya Works, by use of top-and-bottom blowing converter, highly productive simultaneous dephosphorization and desiliconization treatment was developed.
    By the use of coupled reaction model, based on equilibrium relation at interface and mass transfer equations of each element, the characteristics of these processes were analysed. It was clarified that about the dependence of the efficiency of CaO and oxygen for dephosphorization on the ratio of CaO to oxygen content in flux, the tendency of calculation based on small scale experiment was in good agreement with that of industrial values. The differences amoung each treatment type were caused only by the difference of hot metal composition.
    In addition, some new blowing methods of converter by the use of dephosphorized hot metal were introduced.
  • Dephosphorization of Hot Metal in a Top and Bottom Blowing Converter with BOF-slag-based Flux

    pp. 1809-1816

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    To improve the mass production process of both low-phosphorus and conventional grade steels more economically, a new hot metal dephosphorization process in a top and bottom blowing converter, called SRP, has been developed. In this process, BOF slag generated by the blowing of the dephosphorized hot metal is used as a dephosphorization agent of hot metal, implementing a two-stage slag-metal counter flow tank operation.
    1. In a 2t laboratory scale test, phosphorus content of hot metal was lowered to less than 0.010% using BOF slag of 25 kg/t.
    2. When silicon content of hot metal is less than 0.1%, CaO consumption necessary for producing normal phosphorus steels is calculated to be about 10 kg/t, and even low phosphorus steels can be obtained with calculated CaO of about 15 kg/t.
    3. In this process, even non-desiliconized hot metal containing silicon of 0.2 0.4% can be dephosphorized with calculated CaO of 1218 kg/t for the production of normal phosphorus steels.
  • Development of Effective Refining Process Consisting of both Hot Metal Pretreatment and Decarburization in Two Top and Bottom Blown Converters

    pp. 1817-1822

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    To improve the mass production process of both low-phosphorus and conventional-grade steels more economically, a new refining process, called SRP ( Simple Refining Process), has been developed at Kashima Steel Works. In this process, two 250t capacity top and bottom blown converters are used as reactors, namely one dephosphorization furnace and one decarburization furnace. Low P2O5-content lumpy slag, obtained from the decarburization furnace, is used as a dephosphorization agent in the dephosphorization furnace, minimizing total lime consumption and achieving stable and quick refining. In addition, scrap can be used in the dephosphorization furnace due to bottom blowing. On the other hand, by the reduction of slag volume in the decarburization furnace, manganese ore can be effectively smelted. Therefore manganese alloy consumption can be reduced. SRP made it possible not only to produce extra low phosphorus steels but also reduce the total cost of the steel-making process.
  • Simultaneous Removals of Silicon and Phosphorous in Hot Metal and Temperature Control by CaO-based-flux Injection Using "Solid" and "Gaseous" Oxygen

    pp. 1823-1830

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    A side-blown submerged injection with a downward entry tuyere angle was conducted in a 5t pilot plant scale : where both of oxygen gas and CaO-based powders containing iron oxides were injected in order to control the temperature during the dephosphorization. Ceramic tuyeres were used for their good wear resistance against iron oxides. The results obtained are as follows : (1) Simultaneous removals of silicon and phosphorous were obtained effectively. And the final phosphorous content less than 0.010 percent was gained even with the initial silicon content of as high as 0.50 percent. (2) When the gaseous oxygen ratio to the total oxygen consumption was varied from 30 to 70 percent, the changes in bath temperature were range from - 120 to + 50°C, respectively. (3) The analysis of the mushroom showed that the dephosphorization reaction was proceeded just near by the tuyere tip.
  • Smelting Reduction Process of Manganese Ore for [Mn] Increase both in Hot Metal Dephosphorization and Decarburization

    pp. 1831-1838

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    The smelting reduction process of Mn ore both in a dephosphorization and a decarburization converter has been examined in order to increase [Mn] at blow end of BOF. The new hot metal dephosphorization process in a top and bottom blowing converter (SRP : Simple Refining Process), in which BOF slag is used as a dephosphorization agent, is applied for the present study.
    The following results are obtained with the experiments in a 2 kg crucible and a 2 t laboratory scale converter :
    1. 1.5%[Mn] at blow end of BOF can be achieved without [S] increase by the following features of the present process :
    (1) Simultaneous treatment of Mn ore reduction, dephosphorization and desulphurization of hot metal in a dephosphorization converter. (Coke is charged and combusted in some minutes to supply energy for the reduction of Mn ore.)
    (2) MnO-rich slag from a decarburization converter is used as a dephosphorization agent in a dephosphorization converter.
    (3) Less slag operation in a decarburization converter with large amount of Mn ore charge.
    2. The yield of Mn is increased by about 10% by the recycle of BOF slag ; such high yield of Mn as 63% can be achieved in the present process.
  • Fundamental Study on Rapid Reduction of Chromium Ore in Basic Oxygen Furnace

    pp. 1839-1846

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    Experiments have been carried out on smelting reduction of chromium ore to find out the conditions to get rapid reduction speed by 1 kg and 40 to 120 kg scale equipments. And by introducing a rate control model, reduction speed have been investigated.
    The following results were obtained;
    (1) Hard agitation, high temperature, fine ore size and low (MgO + Al2O3) content slag were efficient in getting rapid reduction speed.
    (2) As an ore charging method, top blowing of ore, flux and coal mixture through oxy-coal lance were most effective.
    (3) By using a mixed rate control model consisting of dissolution of ore into slag phase and reaction at the interface of carbonaceous substances and (Cr) in molten slag, contributions of several conditions to reduction speed were explained.
  • Pilot Plant Experiment of Smelting Reduction Using Fine Chromium Ore

    pp. 1847-1854

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    Experiments of smelting reduction of chromium ore by using 5 t test converter have been made to produce chromium containing hot metal for stainless steelmaking. Special interest was focused on usage of fine chromite to the smelting process. Laboratory scale experiments have been also made with 20 kg induction furnace to clarify the mechanism of smelting behavior of fine ore. Following results were obtained :
    (1) When raw chromite was injected with oxygen gas from a bottom tuyere, chromium recovery ratio of 70 93% was obtained. This high recovery ratio was caused by heating and smelting of chromite sand in the high temperature region near the tuyeres. This phenomena was simulated by dipping a sintered chromite into Fe-Cr-C melt in the induction furnace with supplying oxygen.
    (2) Addition of chromite sand through a top blown "oxy-coal burner" was also tried and the same high recovery ratio was obtained. Thermal cracking of chromite sand by the oxy-coal burner was confirmed by experiments of model burner.
    (3)Unsteady heat conduction analysis shows that the chromite sand can be heated up to almost the same temperature of environment during very short time (<0.01 s ).
    (4)Ratio of transitory reaction rate of ascending chromite sand with Fe-C melt was studied.
  • Production of High Carbon Ferrochrome by Smelting Reduction

    pp. 1855-1862

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    As a process for the production of ferrochrome without electric energy as heat source, a new smelting reduction process with the top-and-bottom blowing converter was developed.
    The special feature of this process is to separate the metal bath from top-blown oxygen jet by the thick molten slag layer.
    The pilot plant test of 2 t/h production scale was conducted by the Research Association for New Smelting Technologies.
    The results are summarized as follows ;
    ( 1 ) The operation of this process was stable. Scaling up of about 30 times in oxygen blowing rate was done without any problem.
    ( 2) Suppressing the erosion of lining (MgO-C brick) and accelerating reduction of chrome ore can be satisfied, at the same time, by controlling the slag composition ( (%MgO+%Al2O3) : 4647%).
    ( 3 ) The method for using fine chrome ore without agglomeration was devised.
    ( 4 ) The composition of product is lower in S and Si, higher in C and Cr (about 1%), than conventional EF product.
    P content of the product depends mainly on the carbonaceous materials used. As the process for producing low P ferrochrome with cheap carbonaceous materials ( e.g. green oil coke), a process composed of rotary kiln and smelting reduction furnace was proposed.
    Compared with conventional EF process, the advantages of this process are low energy cost, direct use of fine ore and low impurity in product.
    This process can be applied for the production of other metals and alloys.
  • Production of Stainless Steel with Smelting Reduction of Chromium Ore by Two Combined Blowing Converter

    pp. 1863-1870

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    Kawasaki Steel Chiba Works has developed the new stainless steel making process by two combined converter with smelting reduction of chromium ore.
    Saving energy by replacing electric power, enlarging flexibility of material choice, and high productivity were considered to be the basic concept of stainless steel making.
    Chromium ore are specially pretreated for pelletizing and prereduced with rotary kiln. Prereduced chromium pellet and coke are fed into combined blowing converter, K-BOP, with top charging method. As for Austenitic stainless steel grade, stainless steel scrap are charged into the K-BOP for smelting reduction prior to the blowing. Scrap can be melted during the first stage blowing. Hence, there is no disturbance for the smelting reduction operation.
    The utilization of the new smelting reduction process have succeeded in the improvement of productivity and energy cost for stainless steel without electric arc furnace.
  • Smelting Reduction of Iron Ore with Top-and-Bottom Blowing Converter

    pp. 1871-1878

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    Smelting reduction of iron ore was studied with 5 t and 170 t top-and-bottom blowing converter in the condition that stirred metal bath was separated from oxygen jet by the thick layer of slag.
    The results obtained in the experiments using coke as carbonaceous materials were as follows :
    (1) Heavy slag increased the rate constant of reduction per area of the geometrical slag-metal interface.
    (2) The effect of bath temperature on the rate constant is small in 170 t furnace compared with 5 t furnace. Smelting reduction about 1 400°C was stably carried out in 170 t furnace.
    (3) The ratio of reduction of iron oxide in three kinds of reaction sites ; bulk metal-slag, metal dropletsslag and coke-slag interfaces was calculated as, for example, 0.55 : 0.27 : 0.18 in the 5 t furnace and 0.34 : 0.33 : 0.33 in the 170 t furnace.
    (4) High post combustion (about 60%), high heat efficiency (about 90%) and suppression of dust formation were achieved in both of 5 and 170 t furnace.
    Hot metal was produced at the rate of 42.7 t-HM/h from ore in 170 t furnace (oxygen blow rate ; 30 000 Nm3/h).
  • Relation between Post-combustion, Heat Efficiency and Coal Consumption in Smelting Reduction of Iron Ore with Top-and-Bottom Blowing Converter

    pp. 1879-1886

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    Factors affecting the coal consumption in the smelting reduction of iron ore with top-and-bottom blowing converter were investigated.
    (1) According to the results of 5 t and 100 t scale experiments, coal consumption increased with the Volatile Matter (VM) content in coal and with the degree of contact of O2 and metal. The decrease of heat loss unexpectedly resulted in the drop, not of coal consumption, but of post combustion ratio.
    (2) Coal consumption did not drop monotonously with post combustion ratio, but increased again in the region of high post combustion.
    (3) Experimental results were explained by introducing the concept of "the necessary amount of fixed carbon".
    (4)One route for decreasing the consumption of high VM coal is to decrease the amount of fixed carbon burned directly or indirectly by O2. The degree of combustion of fixed carbon by O2 was defined as J value (kg-fixed carbon burned/Nm3 - O2). The minimum J value obtained in experiments was 0.25 kg-C/Nm3 - O2.
    It was ascertained by fundamental experiment that transport of oxygen in slag through iron ions limits the minimum J value.
    Therefore, in order to decrease the consumption of high VM coal, it is necessary to combine pretreatment of coal and ore with smelting reduction process.
    x

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  • Key Factors to Improve Post-combustion in Pressurized Converter Type Smelting Reduction Vessel

    pp. 1887-1892

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    Improving the heat efficiency in converter is very important for the development of high scrap ratio operation and scrap melting process in BOF and also in-bath smelting reduction processes.
    Essential conditions to improve heat efficiency in an in-bath smelting reduction furnace, SRF, are described, based on the integrated operation with 5t scale SRF directly connected to a pre-reduction furnace, PRF, in NKK Fukuyama Works. Control method of the SRF operated under the high level of post-combustion and the performance of the bubbling bed type PRF are also mentioned.
    Under post-combustion in the SRF, slag is considered to be a major heat transfer medium. To obtain high heat transfer efficiency from hot gas to slag,
    (1)the height adjustment of a top blowing lance.
    (2)intensive stirring of slag layer by bottom blowing are essentially important.
    For the sake of high post-combustion degree, operation should be carried out under ultra soft blowing of oxygen through a double flow lance. Pressurized operation of the SRF is also effective to increase post-combustion degree.
    As the result, post-combustion degree of 50% with high heat transfer efficiency of more than 85% was attained.
  • Scrapmelting Process in Steelmaking Converter Using Coke Bed

    pp. 1893-1899

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    A steel production process with 100% scrap using a combination-blown converter was developed to utilize small converters, which tend to be out of operation under recent economical situations, and to improve flexibility of steel production. This process does not use hot metal. Instead of hot metal, it utilizes coke bed, which is formed initially on the bottom of a converter. It uses only coke as fuel, and uses nearly the same facilities as an ordinary steelmaking converter.
    Experimental results in a converter for a 10t melt were as follows:
    (1) Bottom blow equipment for oxygen was indispensable for this process. However, requisite ratio of bottom blow oxygen was 15%. The same facilities as a steelmaking converter were confirmed to be usable.
    (2) The ratio of initially charged coke to the total amount of coke affected the whole heat efficiency of this process. When the ratio increased, perfect burning of coke promoted naturally. The higher the ratio, the lower the consumption of coke.
    It was thought that the bottom blow oxygen was necessary to improve the reaction ratio of oxygen with coke, and that the effect of the initially charged coke was in agreement with thermodynamical conditions.
  • Improvement of the Refining Process around Combined Blowing Converter in Kobe Works

    pp. 1900-1907

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    A new steelmaking process composed of hot metal pretreatment, combined blowing converter and ladle refining has been developed at Kobe Works. This process has been successfully applied to mass production of high-grade steel since November 1983. Hot metal pretreatment is performed in the H furnace, which was an originally developed process using modified converter and has the ability of sequential desiliconization, dephosphorization and desulphurization within 15 minutes. In combined blowing converter, high speed and highly-accurate blowing is realized by the automatic blowing control system with sensors to detect slag condition. Ladle refining has the functions of arc heating, degassing and powder injection.
    The high application ratio of hot metal pretreatment and ladle refining led to establish a highly productive, accurate and efficient refining process. In this process consistently scheduled production from blast furnace to continuous caster is assured with its highly accurate controllability of each refining station.
    This paper described the improvements of combined blowing converter operation in this refining process. These improvements consist of the following items,
    (1) Decrease of flux consumption
    (2) Reduction of manganese ore and chromium ore
    (3) Refining control by the automatic blowing control system
    (4) Slag cut technique at tapping
    (5) Production of super-clean steel and realized combined blowing converter operation with high productivity, high quality and low cost.
  • Operation Technique of BOF Using Dephosphorized Hot Metal

    pp. 1908-1915

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    A new process of hot metal pretreatment has been in operation since April 1984 at Kure Works. The process has made the mass-production of low phosphorous steels possible.
    Until now, investigations of metallurgical characteristics in a top and bottom blowing converter using dephosphorized hot metal have been carried out, and the efficient operational techniques have been established. The results obtained are as follows ;
    1) The oxygen utilization efficiency for decarburization at the last stage of oxygen blowing and Fe yield in the converter are increased by use of dephosphorized hot metal.
    2) The OG dust is mainly composed of iron fume, the dust can be reduced by decreasing the area of hot spot by top blowing oxygen.
    3) Manganese yield and chromium yield are increased and the life of refractories is developed by use of dephosphorized hot metal.
    4) The continuous use of dephosphorized hot metal makes the slag basicity in the converter decreased. Consequently the refining cost of special steels was able to be reduced considerably.
  • Manganese Partition Equilibrium in Less Slag Blowing at BOF Linked to High Speed Dephosphorization of Hot Metal

    pp. 1916-1923

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    In Keihin Works low phosphorous hot metal has been obtained stably in large quantities, after improving operational conditions at hot metal dephosphorizing station.
    Optimum conditions of less slag blowing at BOF using pretreated hot metal, were also studied, in particular, on Mn partition between slag and metal. Total process of hot metal dephosphorization and less slag blowing which contributed to cost saving was established.
    The following results were obtained by the study of metallurgical charactarization of hot metal dephosphorization and less slag blowing.
    (1) ( %T. Fe) depends on top oxygen flow rate and bottom stirring. Reduction of top oxygen flow rate and increase of bottom stirring are important for reducing (%T. Fe).
    (2) Comparing slag oxygen potential with metal oxygen potential, the former is higher than the later. But its difference becomes to be small as decreasing the carbon content in metal. Mn partition ratio between slag and metal apparently depends on intermediate oxygen potential between those of slag and metal.
  • Refining Technology of High Cr Steel by Mixed Gas Top Blowing in Combined Blowing Converter

    pp. 1924-1931

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    Decarburization behavior of high Cr steel by mixed gas top blowing was investigated in experiments with a 5t inert gas stirred converter.
    Results obtained are summarized as follows :
    1) Preferential decarburization characteristics in low carbon region are obtained with mixed gas top blowing better than those with oxygen top blowing.
    2) A new index, ( CROI ), is introduced to attain good correlation between the operational conditions and the decarburization characteristics in low carbon region.
    3) The new index can reasonably explain the difference in the decarburization characteristics in several kinds of the combined blowing converters.
    Based on the above results, the refining process for high Cr steel has been commercialized in the 180t combined blowing converter (LD-KGC) at Mizushima Works.
    x

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  • Development of Refining Process for Production of High Purity Ultra-low-carbon Steel

    pp. 1932-1939

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    In steelmaking process, the refining technology are progressed greatly by the introduction of combined blowing converter and the spread of the process of hot metal pretreatment. At Mizushima Works, the top-and-bottom blowing converter (K-BOP) were introduced in April 1980 and the hot metal pretreatment facilities had the capacity of pretreating all hot metal in November 1988. For the purpose of the development of best K-BOP only for decarburization practice, we made the experiments of reducing the bottom oxygen flow rate. As a result, it was able to reduce to 0.25 Nm3/min·t from 0.8 Nm3/min·t (conventional way) with same metallurgical characteristics, when the inert gas is used at final stage of blowing at the rate of 0.35 Nm3/min·t or above using pretreated hot metal. Based on this principle, we changed the K-BOP's tuyeres and obtained the prolongation of converter life and the reduction of process gas cost. Furthermore, by using the pretreated hot metal and controlling the converter slag basicity to more than 5 and the (%MgO) to around 10% and deoxidizing the ladle slag, the quality and cleanliness of ultra low carbon steel for cold-rolled sheet is able to be improved drastically.
    x

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  • Improvement of Refining Technologies in Bottom Blowing Converter

    pp. 1940-1947

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    Hot metal pretreatment system has recently established applicable to virtually all hot metal produced in Chiba Works. Several developments have been made for establishing an optimum and cost-efficient Q-BOP operations with dephosphorized metal.
    The main features of the developments are as follows :
    1) Final dephosphorization in Q-BOP is possible by non slag-off blowing method with the use of only a slight amount of dolomite used for coating. By this method, reduction of lime consumption in Q-BOP is achieved.
    2) By lowering oxygen flow rate at the final stage of blowing, excess oxidation of steel melt is prevented. Figures of ( T. Fe) in slag and [O] in steel at tapping are lowered by 4% and 100 ppm, respectively.
    3) Newly introduced post combustion lance is effective for heat compensation and mouth skull melting.
    4) Tapping temperature is successfully decreased by 26°C in manufacturing process of ultra low carbon steel with the aid of the development of KTB, the technology of oxygen blowing through top lance in the vacuum vessel. This technology is effective not only for heat compensation during RH treatment but also for enhancing a decarburization rate in higher carbon region.
  • Production Technology of High Purity Steel for High Class Line Pipes and Cold Sheets

    pp. 1948-1955

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    Following purification technology for line pipes or cold sheets has been developed and put to practical use in some works of Nippon Steel Corporation.
    (1) Synthetic refining system of hot metal pretreatment, top and bottom blowing converter and multi-functional secondary refining, namely ladle injection under reduced pressure (V-KIP), flux injection during RH treatment (RH-Injection, RH-PB) are successfully in operation. Consequently final product of [P] ≤ 50 ppm, [S] ≤ 10 ppm and [H] ≤ 1.5 ppm can be stably produced.
    (2)Ar injection into RH vacuum vessel or DH snorkel and vacuum vessel drastically improved decarburization rate of ultra low carbon level.
    Technology of nitrogen removal during top and bottom blowing in converter and protection of molten steel from nitrogen adsorption between the end point of converter and casting have been operated. Consequently final product of [C] _??_ 10 ppm, [N] _??_ 10 ppm can be produced.
  • Development of Refining Control System in Combined Blowing Converter Based on Exhaust Gas Information

    pp. 1956-1963

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    Mass spectrometer for analyzing the exhaust gas was mounted at No. 2 BOF shop in NKK Fukuyama Works, and the level-up of refining under the computer control system using the exhaust gas information has been achieved. As the result, the continuous estimations of bath temperature, [O] and [C] etc. have been enabled, and the accuracy of end point control has been much improved. Moreover, rationalizing such as reductions of flux and steel making time has been achieved.
    Especially the productivity has been remarkably improved and the production amount has reached to 330 000 t month under one vessel operation with two vessels.
  • Phosphorus and Manganese Control Technologies in Basic Oxygen Furnace and Their Future View

    pp. 1964-1971

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    Phosphorus and manganese content control technologies in Basic Oxygen Furnace (BOF) are focused to materialize the accurate refining control. The feature of three technologies conducted at Sakai steelmaking shop are discussed.
    (1) Phosphorus and manganese content control method based on the analysis of off-gas data
    (2) Expert system for BOF refining control
    (3) Real time manganese determinating technology
    Taking account of labor saving, the refining control technologies of BOF should be more accurate and quick in near future. New technologies should analyse properties and compositions of slag and metal in real time and continuously, and control their metallurgical and physical conditions by the proper devices.
  • Estimation Technique of Blow-end Compositions

    pp. 1972-1977

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    The accurate estimation method of the end-point composition of the steel in BOF is indispensable to the quick tapping operation of the converter. The two estimation methods were studied in Kobe Steel. One is so-called the [O]F method which is based on the free-oxygen content of the steel at the blow-end-point. The other is so-callled a QV method which is based on the spectroscopic analysis data of the steel sample obtained by the sublance in the blowing period.
    The results of the study are as follows.
    1) As the [O]F method is based on material balance and the slag-metal equilibrium, the accuracy of the method is not sufficient and the method is not applicable to high carbon steel.
    2) The QV method supplements the weak points of [0] F method. The accuracy of the QV method is so high that it has been applied to the highest specifications of the steel. In addition, the method is applicable to high carbon steel.
  • Development of Automatic Blowing Control System in Combined Blowing Converter

    pp. 1978-1985

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    The LD-converter process has a great influence on the cost and productivity of the overall steelmaking process. Therefore it is very important to establish a "Just in Time" LD-converter process which can punctually supply molten steel to the continuous casting machine. At Kakogawa Works, Kobe Steel, through the installation of hot metal Pre-treatment and a ladle-arc refining furnace, we have reduced the burden of the LD-converter. In addition we have been developing and improving blowing control models ; techniques which detect reactions in the vessel such as the measurement of hot metal level and slopping prediction, along with the quick tapping technique. However there was still room for improvement in establishing a "Just in Time" process, particularly, because all the decisions for blowing control depended on the individual operator and there was variation because of this. So based on the above mentioned techniques, we have decided to apply a fully-automatic blowing system to our converters by which we can produce a wide range of carbon steel. In the system, a DDC (Digital Direct Controller) automatically controls blowing following the commands of the process computer. As a result of its implementation. Steelmaking time and variation have improved remarkably, and has made it possible for a single man to operate both blowing and the OG exhaust gas recovery system.
  • Steelmaking Reactions and Their Modelling

    pp. 1986-1995

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  • The Mechanism of the Back-attack Phenomenon on a Bottom Blowing Tuyere Investigated in Model Experiments

    pp. 1996-2003

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    The "back-attack" phenomenon was suspected to be an important factor in tuyere refractory erosion, so the characteristics of submerged high speed gas jet were investigated in a water model, and the mechanism of the back-attack generation was clarified.
    1) The submerged gas jet forms a cavity in the bath, but occasionally the cavity is constricted close to the tuyere, and collapses, so the jet blows back and attacks the surface of the tuyere. That is named "back-attack" phenomenon. This constriction is thought to be caused by the suction, because the static pressure distribution shows large negative value there. Therefore not only the surrounding gas, but also the liquid is drawn into the negative depression of static pressure.
    2) The velocity of the jet blown in water at the pressure 3.84 bar through the straight type tuyere reached sonic velocity at the exit of the tuyere and increased suddenly to super sonic value after exceeding the tuyere. Mach number distribution showed large up-and-down change and formed supersonic core inZ/D from 0 to 7, and the super sonic region continued to Z/D of 12.8 where Z is distance from the tip of the tuyere along the tuyere centerline and D is inner diameter of the tuyere. The value of Mach number of the gas jet in water showed good agreement with that in air before the exit of the tuyere, but decayed more rapidly than the air jet after leaving the tuyere, because the gas jet in water was pushed in the cavity and cavity collapsed intermittently.
    x

    Readers Who Read This Article Also Read

    1. Elimination of the Back-attack Phenomenon on a Bottom Blowing Tuyere Investigated in Model Experiments Tetsu-to-Hagané Vol.76(1990), No.11
  • Elimination of the Back-attack Phenomenon on a Bottom Blowing Tuyere Investigated in Model Experiments

    pp. 2004-2010

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    Elimination of the back-attack phenomenon in the submerged gas jet, that is expected to decrease the erosion of bottom blowing tuyeres, was investigated in the water model and in the hot iron model. And the following results were obtained.
    1)The back-attack phenomenon causes concave erosion in tuyere refractory.
    2) The sum of impact pressure by the back-attack of a circular tuyere decreased beyond 19.6 bar ( 20 kg/cm2), and the frequency of that in a slit-shaped tuyere disappeared when the circumference ratio was greater than 3 in the water model.
    3)The back-attack of a circular tuyere was observed in the hot iron model, and it was confirmed that the slit-shaped tuyere with the circumference ratio larger than 5 could eliminate the phenomenon completely.
    x

    Readers Who Read This Article Also Read

    1. The Mechanism of the Back-attack Phenomenon on a Bottom Blowing Tuyere Investigated in Model Experiments Tetsu-to-Hagané Vol.76(1990), No.11
  • Kinetic Model for the Reaction between Iron Oxide in Molten Slag and Carbon in Molten Iron via CO-CO2 Bubble

    pp. 2011-2018

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    The kinetic model for the reaction between iron oxide in molten slag and carbon in molten iron was developed, assuming CO and CO2 in the bubble on slag/metal interface was a ferrying medium for oxygen. The overall reaction was combination of two reactions : reduction of FeO by CO and oxidation of the carbon by CO2.
    The slag/gas and gas/metal interfacial area were evaluated by calculating the shape of the bubbles and their occupying area on the slag/metal interface. The shape of the bubble was calculated assuming mechanical balance of surface and interfacial tensions and gravity. The bubble occupancy area was estimated by simulating the growth and detachment of the bubbles on slag/metal interface. The calculated results are that the ratio of the slag/gas interfacial area to gas/metal is greater than 5, and that gas/metal interfacial area is less than 30% of apparent slag/metal interface.
    Assuming the rate limiting step is either of the interfacial reactions, the overall reaction rate was calculated. The calculated rate is slower than published experimental data, as far as using GRAENZDOERFFER et al.'s equation and Sain-Belton's equation for the interfacial reaction rates. It suggests that the two stage reaction mechanism could not be adequate one within this model.
  • Fundamental Study on Post-combustion Technique in Strongly Stirred Iron Bath Reactor

    pp. 2019-2024

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    Post-combustion technique in converter is regarded as an essential measure for high scrap-ratio operation or scrap melting. It is also one of the key technologies to develop smelting reduction process. Effective technique of post combustion, however, has not been completely developed yet. Some factors in obtaining high heat transfer efficiency with high degree of post combustion was investigated by using 40 kg and 400 kg scale converters. As a result it was found essential to carry out post combustion in slag layer. To achieve an aimed high degree of post combustion, oxygen for post combustion or the resultant oxidized gas should avoid the reaction with reducing agents such as C in metal droplets. That requires a proper design of nozzles for post combustion and minimization of droplet generation. Heat transfer efficiency, η, was expressed as a semi-empirical equation of post-combustion ratio, OD, and parameter, P, representing operational conditions. This equation showed that P value should be increased to improve η at an aimed OD. It was found that parameter P had some relation with the ratio of the characteristic length for heat exchange zone in slag layer to superficial velocity.
  • Effect of Slag Volume on the Characteristics of Post-combustion in a Test Decarburization Furnace

    pp. 2025-2032

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    Effects of flux and slag volume on the characteristics of post-combustion were studied by using a 10 t ladle type test furnace with pre-treated molten pig iron. Three kinds of flux were used : CaO, CaO-MgO and SiO2, and amount of flux addition was varied between 3 to 15 kg/t.
    Followings are brief results.
    In the case that the cavity depth by O2 jet was lower than 150 mm deep, the post-combustion ratio decreased in every flux addition as compared with no flux addition. Especially, SiO2 flux addition caused the lowest post-combustion ratio.
    From the results of heat balance, it was made clear that the heat efficiency for heating the bath decresed sharply in SiO2 flux adding heat.
    The reason is considered to be that, in SiO2 flux adding heat, slag foaming was very high.
    Some mechanisms are proposed to explain the decrease of the post-combustion ratio by the addition of SiO2 flux.
  • Analysis of the Scrap Melting Rate in High Carbon Molten Iron

    pp. 2033-2040

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    A mathematical model has been developed for analyzing scrap melting process, considering operation conditions and thermal interaction between molten iron and scrap. This model is composed of a model for single-scrap melting and heat & mass balance model. Furthermore, experiments on melting of rotating steel rod in 300 kg heating furnace and on scrap melting in 5t converter, were carried out to obtain data required for model calculations. The results obtained by model analyses and the experiments, are as follows.
    (1) Nondimensional correlation for mass transfer obtained in melting of rotating steel rod is Sh= 0.163 Re0.78 Sc0.356.
    (2) Correlation between heat and mass transfer coefficients has been obtained. This correlation approximately coincides with Chilton-Colburn's analogies.
    (3) In 5t converter tests, the following value was obtained about heat (h) and mass transfer coefficient (u). h: 20 00040 000 (kcal/m2h°C ), u: 0.30.7 (m/h), [3 500 ≤ε ≤ 12 000 (W/t)]
    Further, the results obtained from model analyses concerning the effect of some operation conditions are summarized as follows:
    (4) Increase of mixing power is effective for reducing melting time and bath temperature, but isn't so effective beyond a certain range.
    (5) For stable operation, melting in the iron with high C is preferable than in the one with low C, in respect to bath solidification.
    (6) Increase of charging rate of scrap improves the productivity of scrap melting process, within the range where excess solidification doesn't occur.
  • Development of a Level Meter for Molten Iron in a Converter Using Microwave

    pp. 2041-2048

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    A precision microwave level meter based on frequency moduration (FM) method has been developed for measuring the molten iron level in a converter. In order to attain as high accuracy as 20 mm in the measurement range of 20 m, new technique has been developed for improving the SN ratio of the received signal and decreasing the quantized error of the conventional FM method.
    The initial phase of the received signal caused by the reflection wave from the surface of molten iron always fluctuates as a result of fluctuation of its level. By averaging the waveform of the received signal, the noise component caused by fixed targets such as an antenna cover is extracted. Thus the SN ratio of the received signal is improved by subtracting the averaged waveform of the received signal from the instantaneous one.
    In order to decrease the quantized error, modulation is applied to the phase fraction of the noise-cancelled signal. During one cycle of the phase moduration, the zerocrossing counts of the signal are averaged, and so the quantized error is reduced.
    These level meters were installed to converters in Kakogawa Works of Kobe Steel, Ltd. and contribute effectively to improving the hitting ratio of blowing.
  • Refractory Technologies Combined Blowing Converters

    pp. 2049-2056

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    Today's combined blowing converters have been lined almost with MgO-C bricks.
    In this paper, wear mechanism of MgO-C bricks particularly for sidewall and tuyere bricks was researched, and then the refractory technologies such as designing of brick qualities, study of brick shapes for tuyeres and of brickwork structure were discussed.
    As the result, a small amount addition of Al-Mg alloy to MgO-C bricks showed a great improvement on the oxidation resistance of the bricks.
    And the investigation results also indicated that the size distribution with fine grains was quite effective for the densification of brick texture.
    Giant vacuum press with super high pressure was introduced to manufacture big size tuyere bricks and bottom bricks.
    On the brickwork structure for body and bottom lining, thermal stresses were calculated and the applicable lining method which could reduce them was studied.
  • 底吹きから上吹きへ,そして上吹きから上底吹きへ/ごまめの歯ぎしり/日本の大学でFaculty Clubは育つだろうか

    pp. 2057-2058

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