WO2020208768A1 - 効率の高い溶融鉄合金の精錬方法 - Google Patents
効率の高い溶融鉄合金の精錬方法 Download PDFInfo
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- WO2020208768A1 WO2020208768A1 PCT/JP2019/015737 JP2019015737W WO2020208768A1 WO 2020208768 A1 WO2020208768 A1 WO 2020208768A1 JP 2019015737 W JP2019015737 W JP 2019015737W WO 2020208768 A1 WO2020208768 A1 WO 2020208768A1
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- WIPO (PCT)
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- slag
- iron alloy
- molten iron
- refining
- current
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/36—Processes yielding slags of special composition
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/30—Regulating or controlling the blowing
- C21C5/32—Blowing from above
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/42—Constructional features of converters
- C21C5/46—Details or accessories
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
- C21C5/5229—Manufacture of steel in electric furnaces in a direct current [DC] electric arc furnace
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
- C21C5/5264—Manufacture of alloyed steels including ferro-alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/52—Manufacture of steel in electric furnaces
- C21C5/54—Processes yielding slags of special composition
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D15/00—Handling or treating discharged material; Supports or receiving chambers therefor
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C2250/00—Specific additives; Means for adding material different from burners or lances
- C21C2250/06—Hollow electrode
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C2300/00—Process aspects
- C21C2300/08—Particular sequence of the process steps
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/42—Constructional features of converters
- C21C5/46—Details or accessories
- C21C5/48—Bottoms or tuyéres of converters
Definitions
- the present invention relates to a method for refining a molten iron alloy by a converter.
- the present invention particularly relates to a refining method capable of reducing the content of metallic iron in slag and reducing the variation in the content of metallic iron in slag for each charge, thereby improving the efficiency of slag treatment.
- converter slag Slag (hereinafter also referred to as "converter slag") produced when molten iron alloys such as molten pig iron (hereinafter also referred to as “hot metal”) are refined in a converter contains free CaO, which is water. Volume stability is low because it expands by causing a sum reaction.
- the slag is related to the treatment method, it usually contains about 1 to 40% by mass of iron oxide and has a black appearance, which makes the appearance uncomfortable when used as an aggregate for concrete.
- slag is discharged from the converter into a reaction vessel, and a reforming treatment such as coal ash is added to the molten converter slag in the vessel to reduce free CaO.
- a reforming treatment such as coal ash is added to the molten converter slag in the vessel to reduce free CaO.
- It is used for upper roadbed materials and aggregates for concrete, which are more advanced applications.
- the converter slag contains tens of mass% of granular iron as metallic iron in a suspended state. Carbon is present in the suspended granular iron, and when the molten slag is modified, the carbon of the granular iron reacts with iron oxide in the molten slag and oxygen gas for stirring, so that the molten slag There is a problem that bubbles of CO gas are generated (forming) inside, which causes various adverse effects. Further, when the slag is reused due to the presence of the grain iron, the slag strength varies due to the uneven distribution of the grain iron and the oxidative expansion of the grain iron. Further, the grain iron in the slag is a factor of yield loss when focusing on converter blowing, and the lower the content, the more preferable.
- Patent Document 1 discloses a method in which granular iron in molten slag taken out from a converter is settled in a reaction vessel and then subjected to a slag reforming treatment.
- the amount of iron grains in the slag varies, the settling time also varies, making it difficult to perform stable treatment.
- the reaction vessel performs a treatment to reduce the metallic iron content in the slag. Therefore, if there is a variation in the amount of grain iron in the slag, the slag treatment is performed. There was a problem that the time varied.
- Non-Patent Document 1 in converter refining, an acid feed lance is used as one electrode, and a voltage is applied between the electrode and the other electrode provided on the bottom of the furnace for blowing. Attempts have been made to obtain information such as the distance between the tip of the lance and the molten metal bath surface and the thickness of the slag layer by measuring changes in the current, voltage, and resistance value on the way.
- An object of the present invention is to provide a highly efficient method for refining a molten iron alloy, which makes it possible to simplify the process of reducing slag.
- the gist of the present invention is as follows.
- the first aspect of the present invention is a method of refining a molten iron alloy while sending acid to a molten iron alloy bath in a converter, wherein the molten iron alloy bath is arranged above the molten iron alloy bath. and the electrode, a direct current between the second electrode which are arranged so as to be in contact with the molten iron alloy bath supplies, the average of the magnitude of the DC current in the energization time energizing the direct current I P [a ], wherein the average size of I P of the DC current in the energization time of the last minute to stop the oxygen-flow '[a], the amount of molten steel of the rolling furnace W s [t], the furnace abdomen the furnace cross-sectional area when the a s [m 2], a refining method of molten iron alloy satisfies at least one of the following (1) to (4) below.
- the converter may have a bottom blowing tuyere.
- the content of granular iron in the slag and its variation can be reduced, and the efficiency of subsequent slag reforming and metal recovery processing can be improved. Can be improved.
- the present inventors have studied a method for reducing the content of ferroalloys in slag and its variation when refining a molten iron alloy in a converter, and focused on energizing a slag bath and a metal bath. Then, it was found that the amount of granular iron contained in the slag and its variation are reduced when a specific amount of electric charge is applied during energization.
- the converter equipment used in the refining method of the present invention will be described with reference to FIG.
- “%” represents “mass%”
- “current” represents “direct current”.
- the "average direct current” indicates the magnitude of the average value of the direct current during the time when the direct current is applied. Strictly speaking, the "average of direct current” is a value obtained by averaging the current values at 10 or more time points at regular time intervals during the time when the direct current is applied.
- converter refining hot metal from the blast furnace is poured into the converter, slag raw material containing CaO as the main component is added, and blowing for the purpose of desiliconization and / or dephosphorization, and finish dephosphorization. Blasting is performed for the purpose of decarburization and temperature adjustment.
- the converter facility 1 used in the present invention is installed above the molten iron alloy bath (hereinafter, also referred to as “iron bath”) 12 at a position where the first electrode 21 frequently contacts the slag 11. .. Further, the second electrode 22 is arranged so as to be in contact with the iron bath 12.
- iron bath molten iron alloy bath
- an electric circuit is formed by the slag 11, the iron bath 12, the first electrode 21, and the second electrode 22.
- a voltage can be applied between the electrodes to supply an electric current to the slag 11 and the iron bath 12.
- the first electrode 21 may also serve as a top-blown acid feed lance 31.
- Blowing of converters is usually carried out by 1) conventional blowing methods in which desiliconization, dephosphorization and decarburization are performed, 2) blowing for the purpose of desiliconization and / or dephosphorization, and finish dephosphorization.
- a blowing method that separates the blowing for the purpose of decarburization and temperature adjustment, and 3) after performing desiliconization in a separate process, blowing for the purpose of dephosphorization, finish dephosphorization and decarburization, and There is a separate blowing method for the purpose of adjusting the temperature.
- the time to energize is either smelting for the purpose of desiliconization and / or dephosphorization, or smelting for the purpose of finish dephosphorization, decarburization and temperature adjustment.
- smelting for the purpose of desiliconization and / or dephosphorization
- smelting for the purpose of finish dephosphorization, decarburization and temperature adjustment.
- One or both are preferable.
- a larger effect can be obtained especially when applied at the end of the smelting.
- desiliconization is performed in a separate process, and then the blowing for the purpose of dephosphorization and the blowing for the purpose of finish dephosphorization, decarburization, and temperature adjustment are separated. The results of the method are shown.
- FIGS. 2A and 2B show a 400-ton converter in which the first electrode 21 on the side in contact with the slag 11 is placed on the furnace belly and the second electrode 22 on the side in contact with the iron bath 12 is placed on the bottom of the furnace. Then, in the case of dephosphorization, a current of 350 A or less is supplied between the electrodes for 24 seconds immediately before the stop of blowing, and in the case of decarburization, a current of 350 A or less is supplied between the electrodes for 24 seconds immediately before the stop of blowing. It is a figure which showed the relationship between the average current value, the amount of grain iron, and the variation between the case of blowing (ON) and the case of not energizing between electrodes (OFF).
- FIG. 2A shows the effect of the average current value on the metallic iron concentration in the slag after the hot metal dephosphorization treatment in the converter
- FIG. 2B shows the influence on the metallic iron concentration in the slag after the decarburization treatment. .. In both cases, the higher the current value, the lower the iron content and the variation in the iron content.
- Tables 1 and 2 show the average value (mass%) of the iron grain content (mass%) contained in the slag shown in FIGS. 2A and 2B, the sample standard deviation, and the relative error.
- the sample standard deviation is the square root of the variance value obtained by the sum of the squares of the distances between the values of each sample and the mean value.
- the relative error is a value obtained by dividing the standard deviation by the average value.
- the average magnitude of the current supplied to the slag 11 is the amount of molten steel in the converter in W s [t], the furnace cross-sectional area of the furnace abdomen as a s [m 2], I p ⁇ 0.125 ⁇ W s [ A] ⁇ (1) formula I p ⁇ 1.5 ⁇ A s [ A] ⁇ (2) type to be controlled to satisfy at least one It turned out to be important.
- the amount of iron grains in the slag is reduced and the variation is stabilized.
- the point is the standard deviation of the amount of iron grains and is synonymous with "%" as a unit representing the content), and during the decarburization period. It will be about 1.6 points or less.
- the required current to flow through the slag is considered to be related to the weight of the molten steel. This is because the weight of the slag inevitably increases as the weight of the molten steel increases, so unless the current value is increased, the amount of iron grains in the slag cannot be reduced within the blowing time, and as a result, the required energization is required. This is because the amount is proportional to the weight of the molten steel.
- the required current to flow through the slag is considered to be related to the cross-sectional area of the furnace belly of the converter.
- the controlling factor that actually reduces the current density in the slag is the density of the current flowing in the slag (current density). Since the slag is conductive, current flows through the entire slag. Therefore, the current density flowing in the slag is the value obtained by dividing the current value flowing by the cross-sectional area As in the furnace belly of the converter, and this value becomes the required current density. That is, the current density required will I p / A s. Assuming that the required current density is a constant value, the required current value is proportional to the cross-sectional area of the furnace belly.
- the required current flowing through the slag is considered to be proportional to the weight of the molten steel and the cross-sectional area in the furnace. Therefore, in order to reduce the amount of iron grains in the slag and further stabilize the variation, the required current derived from the weight of the molten steel (formula (1) above) or the required current derived from the cross-sectional area in the furnace (formula 1) It is preferable to select the smaller current of the above equation (2)).
- the slag composition before starting energization preferably has a basicity of 0.5 or more and an iron oxide concentration of 5% or more. Since SiO 2 in the slag has a strong bonding force with each other, it inhibits conductivity. On the other hand, CaO has an action of breaking the bond of SiO 2 , so that the conductivity is improved. Iron oxide also improves conductivity.
- the basicity can be estimated by calculating from the ratio of the charged material.
- the iron oxide concentration can be calculated from the amount of acid sent, the amount of oxygen contained in the exhaust gas, and the amount of oxygen contained in the molten steel. Since these values are stored as actual values, these values can be estimated before blowing.
- the composition of the molten iron alloy to be treated is not limited to a specific composition, but it is preferable to treat the molten pig iron having a silicon concentration (Si amount) of 0.25% or less.
- Si amount silicon concentration
- SiO 2 concentration in the slag increases. Since SiO 2 is a factor that deteriorates conductivity, it becomes difficult for current to flow through the slag, and it acts in a direction that hinders the reduction of the amount of iron grains.
- the amount of Si when the amount of Si is 0.25% or less, the amount of slag required for blowing is reduced. Since the amount of iron granules generated is determined by the energy input into the furnace (heavy top blowing) and the amount of decarburization, when the amount of slag is small, the concentration of iron grains in the slag is relatively high. If the concentration of granular iron in the slag increases before energization, the effect of reducing the energization increases, so that the amount of sedimentation of the granular iron increases. Therefore, when the silicon concentration of the molten pig iron is 0.25% or less, a remarkable effect can be obtained.
- the slag density when energized is preferably 1.0 kg / m 3 or less, and more preferably 0.8 kg / m 3 or less. This is because when the density of the slag is lowered, the sedimentation rate of the grain iron increases, and the effect of the present invention can be further obtained.
- the slag density means the weight per unit volume of slag when energized in a converter.
- the slag is energized for 10 seconds or more out of 1 minute before the end of the preset blowing time. That is, it is desirable that the time during which no current is flowing at the end of blowing (after 1 minute before the stop of acid feeding) is set to 50 seconds or less. Furthermore, the shorter the interval between the end of energization and the stop of blowing, the better.
- the reason for this is as follows. 1) If the power is turned off before the end of slag, the grain iron may be mixed again and the grain iron in the slag may increase. 2) Before the end of blowing, the density of slag is often 1.0 kg / m 3 or less, and the slag tends to settle. 3) The amount of iron granules in the slag tends to increase at the end of the slag when the input auxiliary materials are sufficiently dissolved and the reaction products are sufficiently produced, and if energization is started in this state, the amount of iron granules tends to decrease. ..
- the size of I P of the average of the DC current in the energization time of the last minute to stop the oxygen-flow '[A] is the amount of molten steel in the converter in W s [t], the furnace abdomen the furnace cross-sectional area as a s [m 2], it is important to be controlled to satisfy at least one of the following (3) and (4).
- the effect of the present invention can be obtained by controlling the current so as to satisfy at least one of the above equations (1) to (4).
- the electrode arranged above the molten iron alloy bath in the converter is a hollow top-blown lance.
- the height of the top-blown lance is determined by the weight of the residual slag in the furnace, the weight of the input auxiliary material, the weight of the reaction product, the slag density, and the cross-sectional area of the furnace belly. It is preferable to control based on. Specifically, it is preferable to control the height H of the top blowing lance between 0.1 times and 10 times the slag height.
- the slag height (H) can be calculated by the following formula.
- H (m) (total weight of residual slag in the furnace, input auxiliary materials and reaction products (kg)) / (slag density (kg / m 3 ) x cross-sectional area of the furnace abdomen (m 2 ))
- the amount of residual slag in the furnace can be obtained from the past operation data, and the input auxiliary raw material and the reaction product can be appropriately obtained by using the weighed value and the component value.
- the slag density is not limited to 1.0 kg / m 3 or less, and a value of 2.0 to 3.0 kg / m 3 may be used depending on the composition.
- the slag is considered to expand about 10 times including the generated gas, there is a possibility that energization can be obtained even if the lance position is about 10 times the slag height required by the above equation. On the other hand, if there is no problem of metal adhesion to the lance or cooling, lowering the lance to about 0.1 times the slag height stabilizes the energization.
- the degree of expansion of the selection from the range of 0.1 to 10 times changes depending on the blowing conditions and the progress of blowing, so theoretically or empirically depending on the time when the effect is desired. Can be decided.
- the lance height By setting the lance height in this way, it is possible to adjust the current to flow in the slag only when the slag density is about 1.0 kg / m 3 or less, so that the reduction of the amount of iron grains can be promoted. it can.
- stable operation is possible because the lance does not come into contact with molten steel during operation.
- the converter is preferably a converter having a bottom blowing tuyere. Since bottom blowing strengthens the agitation of the slag, the reduction of the amount of iron grains in the slag is promoted. In addition, the chances of contact between the slag and the molten steel are increased, which promotes the transfer of grain iron from the slag to the molten steel.
- the flow rate of the bottom blowing gas is preferably in the range of 0.01 to 0.2 Nm 3 / min / ton in the case of an inert gas and 0.1 to 0.4 Nm 3 / min / ton in the case of oxygen blowing.
- the refining method includes the first step of performing smelting for the purpose of desiliconization and / or dephosphorization in the same converter, the second step of discharging a part of slag, finish dephosphorization, decarburization and temperature.
- the third process of refining for the purpose of adjustment the fourth process of discharging the steel that has been adjusted to the target components and temperature, and the fifth process of discharging part of the slag remaining in the furnace.
- the acid feeding time in the first step and the third step is a state in which the density of grain iron in the slag is increased, and the amount of grain iron is reduced.
- the ferroalloys are likely to settle in the molten iron alloy layer, so that the metallic iron content in the slag can be easily reduced.
- the amount of grain iron is large in the first step, the variation of grain iron can be effectively reduced.
- first electrode 21 of the converter equipment for example, an electrode made of carbon-containing bricks such as MgOC bricks can be arranged on the furnace belly of the converter.
- an upper blown acid lance 31 may be used as shown in FIG.
- a carbon-containing brick or the like can be used for the second electrode 22.
- the second electrode 22 is preferably provided on the bottom or belly of the converter equipment 1.
- the first electrode 21 When the first electrode 21 is arranged on the furnace belly, it is preferably provided 200 to 4000 mm above, preferably 200 to 400 mm above, with reference to the static molten metal surface of the iron bath 12 estimated from the volume of the converter. It is more preferable to provide.
- the tip When the upper blown acid lance 31 is used as the first electrode 21, the tip may be moved up and down, and the position may be moved up and down by the current flowing between the electrodes so that the magnitude of the flowing current can be controlled. ..
- the power supply device 40 supplies a current when the resistance value between the first electrode 21 and the second electrode 22 is equal to or greater than the preset current value for a preset time after the start of blowing. It is preferable to provide a mechanism for blocking the current.
- the current value is obtained by inputting a signal from the current detecting means 41 to the control device 42. Then, if the obtained current value is equal to or higher than the preset current value within the preset time after the start of blowing, the output of the power supply device 40 is stopped and the current supply is cut off. ..
- the power supply device 40 has a function of controlling so that a current of a certain magnitude or more does not flow.
- the carbon concentration at the refining end point of the dephosphorization treatment is 2.5% by mass or more. This is because refining in such a region is often performed with a relatively low basicity, and since the treatment is completed at a low temperature, the viscosity of the slag before energization is high and the amount of iron grains contained in the slag is large. This is because the amount of iron grains can be easily reduced when energized.
- the bottom blowing tuyere 50 made of porous brick is provided on the bottom of the furnace, and the iron bath 12 is agitated by blowing gas into the iron bath 12 from the bottom of the furnace during refining.
- the number of bottom blowing tuyere 50 may be one, but it is preferable to provide a plurality of bottom blowing tuyere 50s.
- FIG. 1 shows an example in which the bottom blowing tuyere 50 is provided at two locations.
- the gas flowing from the tuyere is not particularly limited, and any single gas such as oxygen, carbon dioxide, nitrogen, Ar, LPG, or a mixed gas of two or more types can be selected, and the piping itself can be a single tube, a multiple tube, You can use a collecting pipe or the like.
- the electrode 22 can also be used as the tuyere. However, in that case, it is necessary to properly insulate the tuyere and piping of the conductive path to eliminate the possibility of a large current flowing through the iron shell of the furnace body or the trunnion shaft.
- the inner diameter of the furnace belly of the converter was 6 m. That is, the value of 0.125 ⁇ W s 37.5, the value of 1.5 ⁇ A s is 42.4.
- MgOC electrodes are installed on the furnace belly and bottom, and conductor connecting mechanisms are provided on the furnace body side and the operating floor side so that they can be connected at the furnace hanging position, and a current of 500 A or more does not flow to the operating floor.
- a power supply that can be controlled is installed.
- the electrode of the furnace belly was set 250 mm above the static molten metal surface when 300 tons of the main raw material was inserted.
- the slag was received in a slag pan, discharged into a yard and cooled, and then fist-sized lumps were randomly collected from 10 locations and analyzed to obtain the average value of the metallic iron content.
- the slag was subjected to 5 charges, and the average value of the amount of iron grains in the slag at that time was calculated, and the standard deviation of 5 charges was calculated.
- the results of Experimental Examples 1 to 15 are shown in Table 3.
- the granular iron contained in the slag can be coarsened and dissolved in the metal bath, and the slag having a lower metallic iron content than the conventional one can be stably obtained.
- the efficiency of the reforming treatment of slag can be improved.
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Abstract
Description
また、粒鉄が存在することでスラグを再利用する際に、粒鉄の偏在や粒鉄の酸化膨張などが起因となり、スラグの強度のバラツキが生じる。
さらに、スラグ中の粒鉄は、転炉吹錬に主眼をおいた場合は歩留ロスの要因であり、その含有量は低いほど好ましい。
IP≧0.125×Ws・・・(1)式
IP≧1.5×As・・・(2)式
IP’≧0.125×Ws・・・(3)式
IP’≧1.5×As・・・(4)式
(2)上記(1)に記載の溶融鉄合金の精錬方法では、前記溶融鉄合金の精錬に用いるスラグ組成が、塩基度:0.5以上、酸化鉄濃度:5%以上であってもよい。
(3)上記(1)又は(2)に記載の溶融鉄合金の精錬方法では、前記溶融鉄合金の精錬で処理する前の溶融銑鉄の珪素濃度が、0.25質量%以下であってもよい。
(4)上記(1)~(3)のいずれか一項に記載の溶融鉄合金の精錬方法では、前記溶融鉄合金の精錬に用いるスラグの密度が1.0kg/m3以下であってもよい。
(5)上記(1)~(4)のいずれか一項に記載の溶融鉄合金の精錬方法では、あらかじめ設定した吹錬時間の終了前の1分間のうち10秒間以上はスラグに通電してもよい。
(6)上記(1)~(5)のいずれか一項に記載の溶融鉄合金の精錬方法では、中空の上吹きランスを前記第一の電極として用い、前記上吹きランスの高さを、炉内残留スラグの重量、投入副原料の重量、及び反応生成物の重量と、スラグ密度と、炉腹部の断面積とに基づき制御してもよい。
(7)上記(1)~(6)のいずれか一項に記載の溶融鉄合金の精錬方法では、前記転炉が底吹き羽口を有してもよい。
そして、通電の際に特定量の電荷を与えた場合には、スラグ中に含まれる粒鉄量とそのバラツキが減少することを知見した。
Ip≧0.125×Ws[A]・・・(1)式
Ip≧1.5×As[A]・・・(2)式
の少なくとも一方を満たすように制御されることが重要であることが分かった。
IP’≧0.125×Ws・・・(3)式
IP’≧1.5×As・・・(4)式
この場合、安定した通電を得るために、上吹きランスの高さは、炉内残留スラグの重量、投入副原料の重量、及び反応生成物の重量と、スラグ密度と、炉腹部の断面積とに基づき制御することが好ましい。
具体的には、上吹きランスの高さHは、スラグ高さの0.1倍から10倍の間に制御することが好ましい。スラグ高さ(H)は、以下の式で求めることができる。
H(m)=(炉内残留スラグと投入副原料と反応生成物の合計重量(kg))/(スラグ密度(kg/m3)×炉腹部の断面積(m2))
このとき、第一工程及び第三工程の送酸時間の一方又は双方に、少なくとも10秒以上の間、通電を行い、直流電流を通電した通電時間における直流電流の平均の大きさをIP[A]、送酸を停止する直前の1分間のうちの通電時間における前記直流電流の平均の大きさをIP’[A]、転炉内の溶鋼量をWs[t]、炉腹部の炉内断面積をAs[m2]としたとき、下記(1)式~(4)式の少なくとも一つを満たすように制御すると効果的である。
IP≧0.125×Ws・・・(1)式
IP≧1.5×As・・・(2)式
IP’≧0.125×Ws・・・(3)式
IP’≧1.5×As・・・(4)式
炉腹と炉底にMgO-C電極を設置し、炉垂位置で接続できるように、炉体側と操業床側に導体連結機構を設け、かつ、操業床に、500A以上の電流が流れないように制御することが可能な電源を設置した。
炉腹の電極は、主原料を300t挿入した際の静止湯面から250mm上方とした。吹錬開始後、炉内の音響状態から溶融状態のスラグが生成したことが推定できたタイミングで、通電が開始し、電流が上昇しはじめた。その後、吹錬終了まで通電を行った。
実験例1~15として、上記の実験条件を基に、通電タイミングを変更し、吹錬を行った。吹錬は、途中一度も中断せず、鋼を所定の成分、温度に制御して出鋼し、排滓した。また、それぞれの実験例において、送酸時間は、全体で20分とした。
スラグはスラグパンに受け、ヤードに放流して冷却したのち、ランダムに10か所から、拳大の塊を採取し、それぞれを分析し、金属鉄含有量の平均値を求めた。吹錬は5チャージ行い、その際のスラグ内の粒鉄量の平均値を求め、5チャージの標準偏差を求めた。
実験例1~15の結果を表3に示す。
比較例に係る実験例5では、電流Ip、’電流Ip’のいずれも低かったために、(1)~(4)式のいずれも満たすことができず、粒鉄量の標準偏差を小さくすることができなかった。
11 スラグ
12 鉄浴
21 第一の電極
22 第二の電極
31 上吹送酸ランス
40 電源装置
41 電流検出手段
42 制御装置
50 底吹き羽口
Claims (7)
- 転炉内の溶融鉄合金浴に送酸しながら溶融鉄合金を精錬する方法であって、
前記溶融鉄合金浴の上方に配置された第一の電極と、前記溶融鉄合金浴に接するように配置された第二の電極との間に直流電流を供給し、
前記直流電流を通電した通電時間における直流電流の平均の大きさをIP[A]、前記送酸を停止する直前の1分間のうちの通電時間における前記直流電流の平均の大きさをIP’[A]、前記転炉内の溶鋼量をWs[t]、炉腹部の炉内断面積をAs[m2]としたとき、下記(1)式~(4)式の少なくとも一つを満たす
ことを特徴とする溶融鉄合金の精錬方法。
IP≧0.125×Ws・・・(1)式
IP≧1.5×As・・・(2)式
IP’≧0.125×Ws・・・(3)式
IP’≧1.5×As・・・(4)式 - 前記溶融鉄合金の精錬に用いるスラグ組成が、塩基度:0.5以上、酸化鉄濃度:5%以上である
ことを特徴とする請求項1に記載の溶融鉄合金の精錬方法。 - 前記溶融鉄合金の精錬で処理する前の溶融銑鉄の珪素濃度が、0.25質量%以下である
ことを特徴とする請求項1又は2に記載の溶融鉄合金の精錬方法。 - 前記溶融鉄合金の精錬に用いるスラグの密度が1.0kg/m3以下である
ことを特徴とする請求項1~3のいずれか1項に記載の溶融鉄合金の精錬方法。 - あらかじめ設定した吹錬時間の終了前の1分間のうち10秒間以上はスラグに通電する
ことを特徴とする請求項1~4のいずれか1項に記載の溶融鉄合金の精錬方法。 - 中空の上吹きランスを前記第一の電極として用い、
前記上吹きランスの高さを、炉内残留スラグの重量、投入副原料の重量、及び反応生成物の重量と、スラグ密度と、炉腹部の断面積とに基づき制御する
ことを特徴とする請求項1~5のいずれか1項に記載の溶融鉄合金の精錬方法。 - 前記転炉が底吹き羽口を有する
ことを特徴とする請求項1~6のいずれか1項に記載の溶融鉄合金の精錬方法。
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