WO2020208768A1

WO2020208768A1 - Highly efficient molten iron alloy refining method

Info

Publication number: WO2020208768A1
Application number: PCT/JP2019/015737
Authority: WO
Inventors: 佐々木　直人; 充高松尾; 憲一郎内藤; 崇一新野; 浩二森田; 藤　健彦; 昌光若生; 大貫　一雄; 平田　浩; エスアイセミキン; V. F. Polyakov (ポラコフブイエフ)
Original assignee: 日本製鉄株式会社; ゼットアイネクラゾフアイロンアンドスチールインスチチュートオブナショナルアカデミーオブサイエンスオブウクライナ
Priority date: 2019-04-11
Filing date: 2019-04-11
Publication date: 2020-10-15
Also published as: EP3954787A4; KR20210127986A; EP3954787A1; CN113631729B; JP7158570B2; KR102483106B1; UA128009C2; JPWO2020208768A1; CN113631729A

Abstract

This molten iron alloy refining method is for refining a molten iron alloy while blowing oxygen to a molten iron alloy bath in a converter, wherein when a direct current is supplied between a first electrode disposed above the molten iron alloy bath and a second electrode disposed in contact with the molten iron alloy bath, at least one of formulas (1)-(4) is satisfied, where I_P [A] represents the magnitude of the average of the direct current during a current passage period in which the current is passed, I_P' [A] represents the magnitude of the average of the direct current during a current passage period within one minute immediately before the blowing of oxygen is stopped, W_s [t] represents the amount of molten steel in the converter, and A_s [m²] represents the area of the internal cross-section of the furnace at the belly thereof. (1): I_P≥0.125×W_s. (2): I_P≥1.5×A_s. (3): I_P'≥0.125×W_s. (4): I_P'≥1.5×A_s.

Description

Highly efficient method for refining ferroalloys

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.

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.

Furthermore, although 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.

Therefore, the use of slag is limited to low-grade applications such as road ground improvement materials and lower roadbed materials, and it is difficult to use it for upper roadbed materials, concrete aggregates, stone raw materials, etc.

Therefore, conventionally, 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. , It is used for upper roadbed materials and aggregates for concrete, which are more advanced applications.

Further, 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.

If the amount of iron grains in the slag varies, it is difficult to measure the amount of iron grains in the slag directly and instantly. Therefore, when processing molten slag or recovering iron grains from the cooled slag, the heavy treatment side There is no choice but to select the processing of, and the efficiency deteriorates. In addition, the forming time during the melt reforming process also varies, making it difficult to perform a stable process.

Further, for example, 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. However, even in this case, if the amount of iron grains in the slag varies, the settling time also varies, making it difficult to perform stable treatment.

In this way, conventionally, after discharging the converter slag into the reaction vessel, 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.

By the way, as recently reported in 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.

However, the effect of energization on the properties of molten slag has not been particularly investigated.

Japanese Patent Application Laid-Open No. 2006-199984

According to the present invention, when refining a molten iron alloy in a converter, a slag having a smaller content of metallic iron in the slag and its variation than before is obtained, and in the subsequent reforming treatment of the slag, the iron content in the slag is obtained. 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.

(1) 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.
_{_{I P ≧ 0.125 × W s ···}} (1) formula _{_{I P ≧ 1.5 × A s ···}} (2) Formula _{_{I P '≧ 0.125 × W s}} ··· (3) formula I _{_{P '≧ 1.5 × a s ···}} (4) equation (2) in the refining method of molten iron alloy according to (1), the slag composition used for refining of the molten iron alloy, basicity: 0 It may be .5 or more and iron oxide concentration: 5% or more.
(3) In the method for refining a molten iron alloy according to (1) or (2) above, even if the silicon concentration of the molten pig iron before being treated by the refining of the molten iron alloy is 0.25% by mass or less. Good.
(4) In the method for refining a molten iron alloy according to any one of (1) to (3) above, even if the density of slag used for refining the molten iron alloy is 1.0 kg / m ³ or less. Good.
(5) In the method for refining a ferroalloy according to any one of (1) to (4) above, the slag is energized for 10 seconds or more out of 1 minute before the end of the preset blowing time. May be good.
(6) In the method for refining a molten iron alloy according to any one of (1) to (5) above, a hollow top-blown lance is used as the first electrode, and the height of the top-blown slag is determined. It may be controlled based on 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.
(7) In the method for refining a molten iron alloy according to any one of (1) to (6) above, the converter may have a bottom blowing tuyere.

According to the present invention, when refining a molten iron alloy in a converter, 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.

It is a figure which shows the outline of an example of the converter equipment which concerns on this invention. It is a figure which shows the relationship between the average current value and the content of medium-grain iron of slag in the hot metal dephosphorization period. It is a figure which shows the relationship between the average current value and the content of medium grain iron of slag in a decarburization period. It is a figure which shows the outline of another example of the converter equipment which concerns on this invention.

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.

Hereinafter, the present invention made based on the above findings will be described with reference to the drawings.

First, the converter equipment used in the refining method of the present invention will be described with reference to FIG. In this specification, unless otherwise specified, "%" represents "mass%" and "current" represents "direct current". Further, 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.

In 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.

By arranging the electrodes in this way and connecting them to the power supply device 40 provided outside the converter, an electric circuit is formed by the slag 11, the iron bath 12, the first electrode 21, and the second electrode 22. During refining, 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.

In the case of 2) and 3) above, 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. One or both are preferable. In each of the above 1) to 3), a larger effect can be obtained especially when applied at the end of the smelting.

In FIGS. 2A and 2B, 3) 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.

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).

In each case, 5 charges of slag after blowing were taken out and sampled by the reduction method to examine the total amount of grain iron and the amount of variation.

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, and 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. Here, 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.

As shown in Tables 1 and 2, it can be seen that the higher the current value, the smaller the average value of the iron content, the sample standard deviation, and the relative error, as compared with the case where the current value is OFF. However, it can be seen that the reduction effect is particularly remarkable when the current value is 50 A or more.

Normally, the slag after the reforming treatment is crushed and the metallic iron content is recovered by magnetic force sorting. The results shown in Tables 1 and 2 above show that the magnetic iron content itself is reduced by supplying an electric current to the slag 11, and the variation in the metallic iron content is reduced, resulting in stable magnetic selection. , It is shown that there is a great effect that the metallic iron content in the slag can be further reduced.

The reason why the above-mentioned effect can be obtained by supplying an electric current to the slag 11 during blowing is unknown, but the coagulation coarsening of the grain iron by energizing the grain iron staying in the slag. It is presumed that this is because the grain iron settles due to its own weight.

Based on the test results, the present inventors have diligently studied the necessary conditions. As a result, in order to obtain a sufficient reduction effect of the granulated metallic iron, the average magnitude of the current supplied to the slag 11, that is, the magnitude of the DC current in the energization time energized direct current I _{P [A} ] 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.

When the average magnitude of the current satisfies the above conditions, the amount of iron grains in the slag is reduced and the variation is stabilized. For example, in the case of a 400-ton converter, the value of W _s is 400, so when I _p is 0.125 × 400 = 50 A or more, the variation in the amount of grain iron in the slag is the sample standard deviation. About 9 points or less during the dephosphorization period shown in 2A (here, 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.

When the variation in the amount of iron grains became small to about 9 points during the dephosphorization period, it was possible to recover iron stably in the subsequent process. Further, in the decarburization period, the distribution of granular iron is different from that in the dephosphorization period, but when it is about 1.6 points or less, iron can be stably recovered in the subsequent process.

When I _P is less than 0.125 × _{W s,} granulated metallic iron the amount of variation is increased beyond 1.1%, the variation of the granulated metallic iron content of the slag becomes unstable. Further, when the _{I P} is less than 1.5 × _{A s,} similarly granulated metallic iron the amount of variation becomes large.

As mentioned above, 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.

In addition, 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.

As mentioned above, 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)).

Further, 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.

As a result of experimentally investigating a preferable slag composition before starting energization, it is possible to further reduce the variation in grain iron by setting the basicity of the slag to 0.5 or more and the iron oxide concentration to 5% or more. Do you get it.

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. When the amount of Si is high, the 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.

Further, 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. In the present specification, the slag density means the weight per unit volume of slag when energized in a converter.

In the method for refining a molten iron alloy of the present invention, it is preferable that 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. ..

Therefore, 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).
_{_{I P '≧ 0.125 × W s}} ··· (3) the formula _{_{I P' ≧ 1.5 × A s}} ··· (4) formula

That is, 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).

Further, it is preferable that the electrode arranged above the molten iron alloy bath in the converter is a hollow top-blown lance.
In this case, in order to obtain stable energization, 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 ))

Here, 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.

Since 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. 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. In addition, 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. In order.
At this time, one or both of the oxygen-flow time of the first step and the third step, for more than at least 10 seconds and energized, the average magnitude of the DC current in the energization time energized the DC current I _P [ a], 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 in the converter in W _{s [t],} the furnace abdomen when the furnace cross-sectional area was a _{s [m} ^2], it is effective to control so as to satisfy at least one of the following (1) to (4) below.
_{_{I P ≧ 0.125 × W s ···}} (1) formula _{_{I P ≧ 1.5 × A s ···}} (2) Formula _{_{I P '≧ 0.125 × W s}} ··· (3) formula I _{_{P '≧ 1.5 × A s ···}} (4) formula

This is because 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. As a result, 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. In particular, since the amount of grain iron is large in the first step, the variation of grain iron can be effectively reduced.

As the first electrode 21 of the converter equipment 1, for example, an electrode made of carbon-containing bricks such as MgOC bricks can be arranged on the furnace belly of the converter. As the first electrode 21, 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.

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.

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. ..

Immediately after the start of blowing, there is no reaction product and the input auxiliary material is not dissolved, so slag is not formed, and therefore the situation where the current flows stably in the slag 11 is not prepared. However, current may flow without passing through the slag due to deposits in the furnace, disturbance of the iron bath, or leakage of electricity in the part that should be insulated due to equipment malfunction. In such a case, depending on the current value, heat generation may damage the equipment. By providing a mechanism for cutting off the supply of current, it is possible to cut off the current and avoid an accident in such a case.

In order to determine whether the current is flowing in the slag or not, it is necessary to consider the time when the current flows and the resistance value at that time. As described above, if it is within 10 to 30 seconds after the start of blowing and the resistance between the electrodes is in the range of 1Ω to 0.1Ω, it is highly possible that the current is applied without passing through the slag. It is desirable to provide a mechanism to cut off the circuit when a current commensurate with the above is observed.

In addition, even if a stray current flows out of the converter due to some trouble, the current supply can be cut off, so the equipment can be operated safely.

It is even more preferable if the power supply device 40 has a function of controlling so that a current of a certain magnitude or more does not flow.

Further, it is preferable that 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.

It is preferable that 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. Further, 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.

Hereinafter, the refining method using the converter equipment of the present invention will be described with a more specific example.

A total of 300 tons of hot metal and cold iron source were smelted in the upper blowing converter facility having a bottom blowing function. 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. After the start of smelting, energization started and the current began to rise at the timing when it could be estimated from the acoustic state in the furnace that slag in the molten state was generated. After that, electricity was applied until the end of blowing.
As Experimental Examples 1 to 15, the energization timing was changed and blowing was performed based on the above experimental conditions. The smelting was not interrupted even once in the middle, and the steel was discharged by controlling the predetermined composition and temperature, and the steel was discharged. Moreover, in each experimental example, the acid feeding time was set to 20 minutes in total.
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.

In Experimental Examples 1 to 4 according to the invention examples, refining was performed under appropriate conditions, so that the standard deviation of the amount of iron grains could be reduced.
In Example 5 according to the comparative example, the current I _p, in order 'current I _p' were both low, the (1) to (4) both can not be satisfied in the formula, reducing the standard deviation of the granulated metallic iron weight Couldn't.

According to the present invention, 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. As a result, it is possible to obtain slag used not only for road ground improvement materials and lower roadbed materials, but also for upper roadbed materials, aggregates for concrete, stone raw materials, etc., so that it has great industrial applicability.

1 Converter equipment 11 Slag 12 Iron bath 21 First electrode 22 Second electrode 31 Top blown acid lance 40 Power supply device 41 Current detection means 42 Control device 50 Bottom blown tuyere

Claims

It is a method of refining a molten iron alloy while sending acid to a molten iron alloy bath in a converter.
A direct current is supplied between the first electrode arranged above the molten iron alloy bath and the second electrode arranged so as to be in contact with the molten iron alloy bath.
Wherein the average of the magnitude of the DC current in the energization time energized the DC current I P [A], the average size of the DC current in the energization time of 1 minute immediately before stopping the oxygen-flow I P '[a], the molten steel quantity W s of the rolling furnace [t], when the furnace cross-sectional area of the furnace abdomen was a s [m 2], the following (1) to (4) of at least a A method for refining a molten iron alloy, which is characterized by satisfying one of the above conditions.
I P ≧ 0.125 × W s ··· (1) formula I P ≧ 1.5 × A s ··· (2) Formula I P '≧ 0.125 × W s ··· (3) formula I P '≧ 1.5 × A s ··· (4) formula
The method for refining a molten iron alloy according to claim 1, wherein the slag composition used for refining the molten iron alloy has a basicity of 0.5 or more and an iron oxide concentration of 5% or more.
The method for refining a molten iron alloy according to claim 1 or 2, wherein the silicon concentration of the molten pig iron before being treated by the refining of the molten iron alloy is 0.25% by mass or less.
The method for refining a molten iron alloy according to any one of claims 1 to 3, wherein the density of the slag used for refining the molten iron alloy is 1.0 kg / m 3 or less.
The method for refining a molten iron alloy according to any one of claims 1 to 4, wherein the slag is energized for 10 seconds or more out of 1 minute before the end of the preset smelting time.
A hollow top-blown lance was used as the first electrode.
The height of the top-blown lance is controlled based on the weight of the residual slag in the furnace, the weight of the input auxiliary raw material, the weight of the reaction product, the slag density, and the cross-sectional area of the furnace belly. Item 8. The method for refining a molten iron alloy according to any one of Items 1 to 5.
The method for refining a molten iron alloy according to any one of claims 1 to 6, wherein the converter has a bottom blowing tuyere.