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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 69 (1983), No. 15

  • A Brief History and Some Topics of the Physical Chemistry in the Pretreatment of Hot Metal

    pp. 1699-1713

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    Readers Who Read This Article Also Read

    1. Recent Studies in Process Science of Injection Metallurgy Tetsu-to-Hagané Vol.69(1983), No.15
    2. Study of Optimum Silicon Content between Iron-making and Steel-making Process on the Hot Metal Pretreatment Tetsu-to-Hagané Vol.69(1983), No.15
  • Recent Studies in Process Science of Injection Metallurgy

    pp. 1714-1720

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    1. A Brief History and Some Topics of the Physical Chemistry in the Pretreatment of Hot Metal Tetsu-to-Hagané Vol.69(1983), No.15
  • Oxidation Mechanism of Silicon in Hot Metal

    pp. 1722-1729

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    The kinetics of the silicon oxidation of the hot metal with the iron oxide slag was studied. The experiment was carried out by the high frequency induction furnace using a graphite susceptor and a fused magnesia crucible. Three ratedetermining steps were found depending upon the FeO content in the slag. The rate of silicon oxidation oxidation was controlled by the silicon transfer in the metal phase when FeO content in the slag was more than 40%. In this region, the rate of silicon oxidation was not affected by carbon and manganese oxidations. When FeO in the slag reduced to less than 40 %, the rate of silicon oxidation was controlled by transfers of silicon in the metal and FeO in the slag. In this region the rate of silicon oxidation was suddenly slowed down. Further, it was assumed that under the FeO content less than 10% the rate of silicon oxidation was controlled by the transfer of FeO in the slag phase. In the industrial experiment, these results were also confirmed, and significance of stirring was further recognized.
  • Metallugical Characteristics of Hot Metal Desiliconization by Injecting Gaseous Oxygen

    pp. 1730-1737

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    The metallurgical characteristics and reaction mechanism of hot metal desiliconization by using gaseous oxygen as a desiliconizing agent, which is injected into hot metal through submerged lance, are investigated and following results are obtained:
    1) Desiliconizing reaction is controlled by the rate of oxygen supply until Si content reaches 0.10%, and efficiency of oxygen used for desiliconization is as high as 50-60%. Demanganization reaction is suppressed by the promotion of reduction of MnO with Fe during the floating process from fire spot up to surface. Decarburization reaction is also suppressed with the effect of ferrostatic pressure at fire spot with increasing the depth of submerged lance.
    2) Hot metal temperature after treatment increases in proportion to the amount of desiliconization and thermal flexibility of total process increases extensively.
    3) The reaction by gaseous oxygen injection starts from the formation of Fe-oxide at fire spot and succeeds to the oxidation of Si, Mn and C by Fe-oxide. But MnO is reduced by Fe during floating process.
    4) Hot metal desiliconization technology by gaseous oxygen injection is applied to the stainless steel production process. The production of stainless steel with very low P content and the reduction of production cost of stainless steel are attained by this application.
  • 諸外国の溶銑成分について/精錬分野での改良技術と画期的技術/その他の溶銑の予備処理法/溶銑中のりん,硫黄の変遷

    pp. 1737-1737,1831

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  • Study of Optimum Silicon Content between Iron-making and Steel-making Process on the Hot Metal Pretreatment

    pp. 1738-1745

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    Optimum silicon contents in hot metal are estimated from the data based on the commercial converter operation in this paper.
    Estimations of optimum silicon content are tried in the case with or without the dephosphorization process between blast furnaces and converters. Metallurgical and economical evaluations are also made for several desiliconization methods.
    The results are summarized as follows:
    (1) Optimum silicon content on the process without hot metal dephosphorization treatment at [P] = 0.110%
    If tapping-temperature is 1 700°C, optimum [Si]≅0.40%
    If tapping-temperature is 1 610°C, optimum [Si]≅0.20%
    (2) Optimum silicon content on the process with hot metal dephosphorization treatment by soda ash [Si]≤0.10%
    (3) Economical evaluations for hot metal desiliconization treatment
    (i) In the case of using iron oxide as desiliconization reagent
    If [Si] initial≥040%, BF runner method is better.
    If [Si] initial<0.40%, torpedo injection method is better.
    (ii) In the case of refining a high manganese steel, the largest benefit would be obtained by the desiliconization treatment with manganese are on blast furnace runner, combining the dephosphorization treatment by soda ash and less-slag blowing in top and bottom blowing converter.
    x

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    1. A Brief History and Some Topics of the Physical Chemistry in the Pretreatment of Hot Metal Tetsu-to-Hagané Vol.69(1983), No.15
  • Phosphorus Distribution between CaO-containing Slag and Carbon-saturated Iron at Hot Metal Temperatures

    pp. 1747-1754

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    In order to thermodynamically understand the dephosphorization behavior of hot metals, the equilibrium distribution of phosphorus between a solid iron strip and CaO-bearing slag was measured in the temperature from 1200°C to 1400°C as a function of slag composition, avoiding the possible violent CO evolution if carbon-saturated iron were used. The obtained result was then converted to the value for the hot metal system using available thermodynamic data of phosphorus in solid and liquid irons.
    The results are summarized as follows:
    1) The CaO-SiO2-FeO system has very high dephosphorizing capacity when it is saturated with 2CaO·SiO2.
    2) The CaO-CaF2-FeO system containing a large amount of CaO and CaF2 has high Lp values, where Lp denotes the distribution ratio of phosphorus between slag and carbon-saturated iron.
    3) When FeO content is low, the CaO-SiO2-CaF2-FeO system containing a large amount of CaO has very high phosphate capacity.
    4) Iron oxide decreases the phosphate capacity of basic slags.
    5) From the laboratory equilibration test of the CaO-bearing slags used in the practical hot-metal treatment, the partial pressure of oxygen at the slag-metal interface is estimated at 10-1410-15 atm, which is ten it Ines as high as that in the soda-ash treat mem. This lies between the one determined by the reaction Fe+1/2O2= FeO and the one by C+1/2O2=CO.
  • Thermodynamics and Kinetics of Hot Metal Dephosphorization by CaO based Slag Containing CaF2

    pp. 1755-1762

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    Thermodynamics and kinetics of hot metal dephosphorization reaction have been studied for the slags containing 10 to 50% CaF2 in the quasi-ternary CaO-SiO2-CaF2 system.
    From the fundamental experiments, an equation with respect to phosphorus partition equilibrium was derived and the thermodynamic effect of CaF2 addition was discussed. It was indicated that the increase in the activity of (FeO) was one of the main reasons of achieving high phosphorus partition ratio by CaF2-containing slag.
    The rate controlling step of dephosphorization reaction was determined to be the supply of oxygen, in the form of (FeO), to the reaction interface.
    Based on the result of the fundamental experiments, 250 t scale test has been carried out, and it is considered that the hot metal dephosphorization treatment with the slag in CaO-SiO2-CaF2 system is beneficial for the production of high quality steel with less phosphorus content.
    In terms of the mass production, the process is likely to be more promising, with the improvement of the acceleration of dephosphorization reaction rate.
  • Dephosphorization Kinetics of Hot Metal by Lime Injection with Oxygen Gas

    pp. 1763-1770

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    To improve the dephosphorization of hot metal by lime injection process, it is necessary to clarify the dissolution mechanism of blown-in CaO in hot metal and the mechanism of dephosphorization reaction. For the purpose, a single-crystal lime immersion test and a lime powder injection testare conducted. Limes after immersion test and the reaction products adhered to Al2O3 tubes submerged into hot metal are analyzed by EPMA.
    In hot metal, CaO starts to dissolve due to penetration of FetO and MntO. Then, dephosphorization reaction initiates between {CaO-Fe (Mn)tO}1 and phosphorus, and it is fixed as (CaO-SiO2-P2O5)s in the reaction layers. Dephosphorization reaction takes place mainly in the vicinity of the oxygen blowing nozzle.
    The slagging rate of solid CaO decreases by increasing distance between the nozzle and the suspension position of CaO since carbon in the hot metal consumes oxygen. The dephosphorization rate decreases also by increasing the distance since FetO in CaO-FetO-MnO is reduced by the carbon.
    In order to improve the dephosphorization rate, it is concluded that both of the slagging rate of solid lime and oxygen potential in the bath have to be increased with the injection of oxygen.
  • Effect of Oxygen Potential on Simultaneous Dephosphorization and Desulfurization of Hot Metal by Injecting CaO Base Flux

    pp. 1771-1778

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    Plant scale experiments have been carried out to dephosphorize and desulfurize hot metal with injecting pulverized CaO base flux in a charging ladle (100t). It has been reveraled from oxygen potential, PO2, measured by oxygen probes that dephosphorization takes place near lance nozzles where P>O2 is kept high (=10-1410-13 atm), whereas desulfurization at the top slag/hot metal boundary where PO2 is made lower (_??_10-15 atm).
    The injection treatment which forms the above distribution of PO2>in hot metal can provide the separation of reaction sites for dephosphorization and desulfurization. Thus, the simultaneous removal of phosphorus and sulfur is possible in one step operation.
    Phosphate capacity of the CaO base slag with CaO/SiO2 of 2.5 has been evaluated as 1026.5 at 1 200-1 300°C. Since the value of PO2near the lance nozzles has been measured as 10-1410-13 atm, the calculated phosphorus destribution ratio between ascending slag particles and hot metal increases up to ca. 104. This high value is sufficient to dephosphorize hot metal.
    Rate of dephosphorization by the slag particles has been studied. The rate-determining step has been shown to be phosphorus transfer in the slag particles at the early stage and halfway of the treatment and in the hot metal boundary layer at the last stage. Observed decrease of phosphorus content in hot metal has agreed well with calculated one.
    x

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  • Dephosphorization of 40% Iron Melt with CaO-based Flux Containing CaF2-CaCl2 and CaCl2

    pp. 1779-1786

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    Iron melt of 4% C was treated with CaO based flux containing CaF2-CaCl2 and CaCl2 additives by using a rotating crucible containing 1 kg metal at 1 350°C, and the dephosphorization reaction and its important donimant factors were studied. The transport of phosphorous occurred between slag and metal.
    The experimental results were explained by assuming the following equation of dephosphorization reaction :
    [P]+3/2 (O2-)+5/4 O2=(PO43-)
    Apparent distribution ratio, Lp(≡(P)/[P]), was strongly dependent on oxygen partial pressure, PO2, slag basicity, B, and additive contents.
    Lp in air was given experimentally as follows :
    B≤1.2 logLp=2.04+8.69 logBi·NAdd.
    less than or ezualB>1.2 logLp = 2.75+εi·NAdd.
    where B=NCaO/(2NSiO2+3NP2O5)
    NAdd: mole fraction of additive
    NAdd=0.150.5
    εCa(F, Cl)2=0.74, andεCaCl2= 2.91
    Lp and overall reaction rate constant of phosphorous, kp, increased as PO2 increased.
  • Dephosphorization and Desulphurization of Hot Metal by CaO-based Flux Containing MnO2

    pp. 1787-1794

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    Experiments have been performed to study dephosphorization and desulphurization of desiliconized hot metal (Si=0.12%) by CaO-based flux containing MnO2 (CaO-CaF2-MnO2-Fe2O3 system) in a magnesia crucible at 1 350°C
    It is found that the flux is more effective for dephosphorization and desulphurization that the CaO-CaF2-Fe2O3 system and that manganese content in hot metal can also be increased. In the slag, as the activity of lime is unity, further addition of CaO content is ineffective for dephosphorization and desulphurization. The increase in MnO content, however, may be effective for them by behaving as a basic oxide. Namely, the addition of manganese oxide increases phosphate capacity by increasing ao2- (NMnO<0.12) and increases sulphide capacity by decreasing fs2-. The slag, however, becomes partially solidified by excessive addition of manganese oxide (NMnO>0.12) and dephosphorization reaction rate becomes slow. The optimum flux composition has been found as follows: CaO(30%)-CaF2(15%)-MnO2(1020%)-Fe2O3(3545%)
  • Dephosphorization of Molten Chromium-containing Pig Iron by CaO-CaF2-FeO Flux with Addition of Li2CO3

    pp. 1795-1801

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    An investigation has been made in order to search for effective fluxes for dephosphorization of molten chromium-containing pig iron on a laboratory scale. By treating molten pig iron containing 18%Cr and 8%Ni using 70 g(per kg of metal) of, for example, 10% Li2CO3-14%CaO-47%CaF2-29%FeO flux, F, S and N in metal were removed by about 70%, 90% and 85%, respectively. High degree of dephosphorization was obtained with low silicon content and high carbon content near the carbon saturation in metal, and in the slag composition containing more than 1% of lithium, with (%CaO)/ (%SiO2)≥3 and (%CaF2)≥30. Even relatively low contents of SiO2, Al2O3 and MgO in slags had unfavorable effects on the dephosphorization. The temperature range suitable for the dephosphorization treatment was about 140°C. By X-ray diffraction analysis of the solidified sample Ca5F(PO4)3 (fluorapatite) was identified as a compound containing phosphorus and LiCrO2 as a compound containing chromium in the phosphoruse-nriched Li2CO3-CaO-CaF2-FeO-Cr2O3 slag. On the other hand, Ca(CrO2)2 was identified as a compound containing chromium in the slags without the addition of Li2CO3 or with the addition of Na2CO3 or K2CO3 instead of Li2CO3.
  • Dephosphorization of Hot Metal with Injection of Lime Bearing Fluxes in a Ladle

    pp. 1802-1809

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    Experiments have been made in a 270 t transfer ladle. The reaction of dephosphorization proceeds coupled with the oxidation of manganese; the lower the manganese content in the hot metal, the higher the rate of dephosphorization. Gaseous oxygen accelerates the removal rate of manganese and retards that of phosphorus. Although from the industrial point of view, some amounts of gaseous oxygen are required to suppress the temperature drop of hot metal, it should be kept at minimum during treatment. The preferential oxidation of manganese over phosphorus is interpreted in terms of the difference of free energy change of oxidation between the two. To suppress the manganese oxidation the basicity of the slag is a key factor and should be kept higher than 3.0. In comparison with gaseous oxygen, oxide source such as ore, mill scale, etc. provides a better dephosphorization. The rates of dephosphorization and demanganization are approximated as the first order reaction and the apparent rate constants have been experimentally obtained.
    The apparent rate constants for dephosphorization were compared between Q-BOP, LD, K-BOP and the present ladle injection. A comprehensive understanding has been made in terms of modified feeding rate of total oxygen.
    x

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    1. Thermodynamics and Kinetics of Hot Metal Dephosphorization by CaO based Slag Containing CaF2 Tetsu-to-Hagané Vol.69(1983), No.15
  • The Influence of Operating Condition on Dephosphorization and Desulphurization Reactions of Hot Metal with Lime-based Flux

    pp. 1810-1817

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    In order to estimate the improvement of dephosphorization and desulphurization of hot metal by adding lime-based flux, 100 t scale tests are conducted. Two kinds of stirring methods, mechanical stirring by impeller and that by injection, are adopted. Injection method is more practical than mechanical stirring method because of higher reaction efficiency. Dephosphorization ratio of about 85% and desulphurization ratio of about 60% can be achieved on a commercial scale by adding 15 kg/t of CaO, 34 kg/t of CaCl2+CaF2 and a certain amount of oxygen source, oxygen gas and/or iron oxide. One of the most important techniques is fluid slag formation of high basicity and low FeO content. Dephosphorization reaction is strongly affected by several kinetic factors, for example, dissipation energy of bath ε. The relationship between ε and apparent rate constant of dephosphorization k'P can be expressed as k'P=0.14ε0.58.
  • Investigation of Dephosphorization Reaction by Injecting Lime-based Fluxes and Iron Oxides into Hot Metal in Torpedo Ladle

    pp. 1818-1824

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    Dephosphorization by injecting lime-based fluxes and iron oxides into hot metal has been investigated extensively including water model test. The followings have been obtained through thermodynamic, kinetic and fluid dynamic studies.
    (1) The dephosphorization behavior can be divided consistently in terms of consumption of dephosphorization reagent or oxygen supplied into three stages which are controlled by silicon content in metal, basicity of slag and so forth. The three stages are characterized as stagnant stage, proceeding stage and retarding stage in dephosphorization.
    (2) The equation of dephosphorization reaction between molten iron and slag at temperatures of 1 200 to 1 400°C can be expressed by the conventional method available in LD process on the basis of stoichiometric reaction equation.
    (3) A dynamic model considering both transitory reaction and permanent reaction is proposed to explain the dephosphorization behavior to quite a good agreement with experimental data based on mass-balance during oxidizing process. This has made it clear that the three stages are controlled by rate-determining factors such as basicity, silicon content, consumption of oxygen and phosphorus distribution ratio between slag and metal.
  • Dephosphorization and Desulfurization of Hot Metal by Lime Based Flux Injection-Oxygen Top Blowing Method

    pp. 1825-1831

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    Dephosphorization and desulfurization of hot metal with lime based fluxes were studied. The experiment was carried out by the flux injection-oxygen top blowing method. By this method the dephosphorization rate was excellently improved and the high phosphorus distribution ratio, (%P2O5)/[%1p]=5001500, was constantly attained when CaO/SiO2 in slag was more than 3.0. And by mixing fluxes with soda ash, the dephosphorization rate was kept at higher level and the desulfurization rate was remarkably improved.
    In this method, many reactions concurrently proceed at various sites. A large portion of dephosphorization occurred at the oxygen fire spot. The desulfurization reaction mainly proceeded during the flotation of injected flux. At the oxygen fire spot, however, resulfurization and gaseous desulfurization reactions also occurred. The contribution of top slag which is called "permanent reactor reaction" was little. Effects of (%Na2O) on the phosphorus distribution and the sulfur distribution were 1.75 and 5.62 times as much as those of (%CaO), respectively.
  • Dephosphorization and Desulfurization of Molten Pig Iron by Injection of CaO-based Fluxes

    pp. 1832-1836

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    Dephosphorization and desulfurization of molten pig iron by CaO-based fluxes were investigated at 1 370°C. The results indicated that simultaneous dephosphorization and desulfurization of pig iron were possible by a selection of flux composition for CaO-based system. By injection of fluxes containing iron oxide, oxidation state at flux-iron interface seemed to be locally controlled. This fact strongly suggested that simultaneous dephosphorization and desulfurization process could be achieved by a selection of flux composition and that of method on flux-metal contact for CaO-based fluxes.
  • Phosphorus Distribution between Na2O-SiO2-FeO Slag and Carbon-saturated Iron at Hot Metal Temperatures

    pp. 1838-1840

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  • Analysis of Dephosphorization Reaction in the Hot Metal Treatment by Use of Soda Ash

    pp. 1841-1848

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    A new process for the hot metal dephosphorization is examined. It is done in the 200 t hot metal ladle, soda ash being top charged, oxygen gas being top blown and nitrogen gas being injected through a submerged lance. Dephosphorization reaction is analyzed in terms of its reaction equilibrium and stirring intensity or energy involved.
    Equation for the dephosphorization equilibrium is established by the extrapolation of the laboratory data at 1 600°C :
    logK=(P2O5)/[P]2=1873/T[9.49+8.41log{(CaO)+2.32(Na2O)} - 4.78log(SiO2)] + 5logao+0.26[C] +
    36 850/T-25.32
    This equation is found to well describe the hot metal dephosphorization all through the treatment. Thus, the reaction is found to proceed very close to the equilibrium.
    The effect of the oxygen blow and the stirring upon the dephosphorization is clearly demonstrated. The optimum stirring energy is found to exist for the maximum dephosphorization attainment: between 0.6 to 1.5 MJ/t.
  • Optimization of the Hot Metal Pretreatment Method in the Ladle by Use of Soda Ash

    pp. 1849-1855

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    Process performances of various dephosphorization methods are compared in terms of their chemical reactions and other operational items.
    Among the various ladle hot metal treatments, (1) quick Na2CO3 top charge method, (2) Na2CO3 injection method, and (3) snorkel(specially designed lid) method are examined, and the following results are obtained:
    (i) Injection method is unfavorable for the stable operation, since it enlarges the slopping and hot metal temperature drop.
    (ii) In the Na2CO3 top charge method, treatment time can be shortened to the level of 15 to 20 min. (quick method)
    (iii) By the quick method, same dephosphorization is secured as the slow one, the desulfurization being greatly improved, and the unit refractory consumptions being reduced to the half.
    (iv) Snorkel is found to be beneficial, since it can increase the hot metal carrying capacities of the ladle and reduce the ladle lining wear and temperature drop of hot metal, keeping the dephosphorization and desulfurization same as the non-snorkel method.
  • Some Phenomena during Dephosphorization of Hot Metal by Soda Ash in 400 t Torpedo Car

    pp. 1856-1862

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    The new refining process which includes the desiliconization, dephosphorization and desulfurization was started at Kashima Steel Works in 1982. In this paper some phenomena during dephosphorization of hot metal by injection of soda ash in 400 t torpedo car are discussed. Followings are main results,
    (1) The phosphorus partition (P2O5)/[P] is larger than 1 000 when the temperature is lower than 1 250°C and the basicity (Na2O)/(SiO2) is larger than 3.
    (2) The vaporization of Na injected increases rapidly when phosphorus content becomes lower than 0.040%. But this vaporization is suppressed by increasing of (SiO2) content in slag and injection rate of soda ash and O2 blowing onto hot metal.
    (3) It is effective for increasing of dephosphorization reaction and repressing of temperature drop of hot metal to blow oxygen onto hot metal during dephosphorization by soda ash.
    (4) The loss of phosphorus and sulfer into the gas phase is less than 5% respectively.
  • Comparison of Refining Characteristics in Hot Metal Treatment by Bottom Injection with Top Blowing Using Soda Ash

    pp. 1863-1870

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    Hot metal refining using the flux containing Na2CO3 was studied on a laboratory scale by comparison of bottom injection method with top blowing method using argon or oxygen gas as a flux carrier.
    Excellent desulfurization performance could be obtained by the bottom injection method, particularly on using argon gas as a flux carrier. This was due to a increase in flux/metal interfacial reaction area which was estimated about 3 times as large as that of top blowing method. However, efficient phosphorous removal could not be achieved by the bottom injection method because the reaction of Na2CO3 with C took place instead of the reaction of Na2CO3 with P, especially in the region of low phosphorous content level. On the other hand, in the case of top blowing, dephosphorization reaction proceeded to the extreamly low phosphorous content level without remarkable decarburization reaction.
  • Continuous Refining of Hot Metal with Soda Ash in the Trough-type Refining Furnace

    pp. 1871-1877

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    Studies on the continuous refining of hot metal with soda ash were performed using the trough-type continuous refining furnace. The furnace had ability to process the hot metal at the rate of 45 t/h.
    1) [P] and [S] after refining were lowered to 0.015% and less than 0.005% respectively, at the consumption of 20kg·Na2CO3 per ton of hot metal(t·HM).
    2) Oxidized amount of [Mn] in the refining was 0.08% and nitrogen of refined hot metal was also removed to 10 to 20ppm.
    3) Owing to low iron oxide and iron particle content of the Na2CO3 slag, iron loss in the refining was nearly 2.5kg/t·HM.
    4) Temperature drop of hot metal due to the decomposition and evaporation of charged soda ash was estimated as 4.6°C/kg·Na2CO3/t·HM and heat loss in the continuous refining was calculated as 6.5×103 kcal/t·HM.
    Estimation of dephosphorization degree of the refined hot metal by reaction model and the characteristics of continuous refining were discussed.
  • Soda Ash Recovery from Soda Slag

    pp. 1878-1884

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    Recently, the demand for production of high quality steel ([P]≤0.010% and [S]≤0.0010%) and for cost saving of steelmaking has been increasing. Especially, in the new refining process for steelmaking using soda ash, soda recovery from soda slag is an important subject. So, we studied and developed new type soda ash recovery process. Our method is characterized as follows.
    (1) NaHCO3 crystallization is reactionary crystallization with lowering pH 11 to 9 and decreasing temperature 80°C to 40°C.
    (2) Reflux method of Na2O solution can decrease water-slag ratio in extracting stage, and as the result, the new process does not need vaporization stage in soda crystallization.
    (3) Contaminative components Si, P, and S in solution can be removed (simultaneously) by addition of lime and (small quantity of) magnesia in extraction stage.
    (4) Filtrating character of residue is very good by formation of CaCO3.
    (5) The crystal size of recovered sodium bicarbonate is 200μ and over, and its purity is about 97%.
  • Refining Stainless Steel in Top and Bottom Blowing Converter with Dephosphorized Hot Metal

    pp. 1886-1892

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    K-BOP, one of combined blowing processes, is favorable for refining stainless steel by diluting gas practice because of its inherent advantage of preferential carbon oxidation suppressing excessive chromiun oxidation. In K-BOP, application of dephosphorized hot metal to production of stainless steel can realize energy saving.
    One of the application technique is a duplex process in which crude molten metal is produced by mixing dephosphorized hot metal with optimum chromium bearing molten steel from electric melting furnace (EF). This crude molten metal has higher heat energy i.e. sensible heat and heat of oxidation of C, Si, Mn, Cr than that from overall EF practice. Consequently it is possible to refine stainless steel at higher temperature and this leads to the benefits of higher chromium yield.
    The other technique is "Hot Metal Process" in which dephosphorized hot metal are decarburized and all ferro alloys must be charged in converter. Consequently input heat energy is not enough to raise temperature of molten steel to aim point. For the compensation of the shortage of heat, the use of small size coke which is surplus and cheap material in works is found to be beneficial. To countermeasure the sulfur pick up by coke addition, K-BOP practice is associated with remarkable gaseous desulfurization and slag/metal desulfurization reaction. In "Hot Metal Process" production cost is decreased by 3.4% due to saving electric power for EF
  • Characteristics of Refining Process with a Little Quantity of Slag in the Top and Bottom Blowing Converter

    pp. 1893-1900

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    Refining process with a little quantity of slag in the top and bottom blowing converter (LD-OTB) has been found very promising one through the experiments of using low sulfur and low phosphorus hot metal. Desulfurization and dephosphorization of the hot metal was carried out using a 350 t torperdo car after desiliconization practice and phosphorus content was reduced to the level less than 0.02%. The hot metal, charged into 240 t top and bottom blowing converter was refined at a little quantity of slag less than 8 kg/t in burnt line consumption. A little quantity of slag refining process brought us such good features as lowering the critical carbon content (C*) which decarborization rate decreases in the top and bottom blowing converter, increasing manganese content and reducing hydrogen content at turn down.
    However, the increase of iron loss into exhaust gas was observed to some extent in spite of the slag volume decrease and the pretreatment of desiliconization might have a tendency toward the shortage of heat in high temperature heat. One of the countermeasures for these two problems was tested by super soft blowing which was the extreme high lance height practice. The super soft blowing was found out very effective not only for preventing the increase of iron loss into exhaust gas with assistance of bottom stirring, but also for compensating the heat by controlling the post combustion of CO gas.
  • Developments of Refractories for Pre-refining Vessel of Molten Pig Iron

    pp. 1901-1909

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  • Development of Al2O3-SiC-C Brick for Pre-refinement of Molten Iron

    pp. 1910-1916

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    In the past about five years, superduty fireclay or high alumina brick has been applied for torpedo car. Recently, in accordance with the progress of desulphurization and desiliconization of pig iron in torpedo car, its lining material comes into a problem awaiting the solution. Several kinds of brick were developed for this purpose, and tested in laboratory and practically. As a result of these tests, unburned Al2O3-SiC-C brick was excellent in resistance to corrosion, spalling, slag penetration and oxidation. The properties and application for torpedo car of this brick are reported in this paper.
  • Refractories for Hot Metal Pretreatment

    pp. 1917-1923

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    Several rotary slag erosion tests were carried out as a part of study on refractories for desiliconization, dephosphorization, and flux injection lance.
    Al2O3-SiC-C bricks are the most suitable refractories for desiliconization, and low silica spinel-C bricks are the most suitable for dephosphorization. By considering the cost, however, the former are better than the latter in performance. High alumina castable refractories containing 70 to 90% Al2O3 are suitable for lining of flux injection lance. Since lance performance is influenced by deformation, and vertical and horizontal cracks in addition to erosion, strengthening of the inner pipe and proper expansion clearance between the inner pipe and castable refractory are necessary.
  • Corrosion of Refractories by Soda-based Slag for Hot Metal Treatment

    pp. 1924-1930

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    The corrosion of refractories by molten soda-based slag was studied by rotating cylindrical polycrystalline specimens (φ20×35 mm) in a stationary crucible containing the slag melt prepared with mixture of Na2CO3 and SiO2 at 1 400°C.
    Alumina, spinel, and magnesia specimens had good corrosion resistances as compared with other specimens, especially alumina was independent of the composition of melts, while magnesia was affected by that. Zircon, mullite, carbon and silicon carbide specimens were extremely corroded for slags more than Na2CO3/SiO2 mol ratio 2.
    The quantity of dissolution of alumina specimen estimated from the decrease in its diameter was dependent on both the dipped time and the speed of rotation of specimen in the slag of mol ratio 3. It was also remarkably accelerated as the temperature of slag increased. Activation energy for the dissolution was estimated to be about 28 kcal/mol. Its corrosion in ternary slag decreased with increase in P2O5 content of Na2CO3-SiO2-P2O5 melts. Therefore, it is shown that the process of corrosion of alumina specimen in soda-based slag within the range of this experiment is controlled by the diffusion of reaction product in the liquid boundary layer.
  • Recent Progress in Refractories for Hot Metal Handling

    pp. 1931-1937

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  • Interim Report of the Steel Refining Reaction Committee

    pp. 1938-1941

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