JP4419594B2 - Hot metal refining method - Google Patents

Description

  The present invention relates to a hot metal refining method in which oxygen gas is blown onto the hot metal bath surface, and more specifically, the total iron concentration conversion of the iron oxide concentration in the slag floating on the hot metal being refined is within a predetermined range. The present invention relates to a refining method that can be controlled.

  The hot metal discharged from the blast furnace contains impurities such as silicon, sulfur, phosphorus, and vanadium. In recent years, after removing these impurities to some extent, the hot metal is charged into the converter and converted into the converter. Steelmaking methods for decarburizing and refining have been developed. In this case, as a method for removing silicon, phosphorus and vanadium in the hot metal, an oxygen source such as oxygen gas and solid iron oxide is supplied to the hot metal, and these impurities are oxidized and removed.

  In such a treatment step of oxidizing and removing impurities in the hot metal, in order to efficiently oxidize the impurities in the hot metal, the oxygen potential in the slag is increased, that is, iron such as FeO in the slag. Increasing the oxide concentration is very important. However, since the hot metal contains a large amount of carbon and the iron oxide in the slag is reduced by the following formula (1), the concentration of iron oxide in the slag floating on the hot metal is increased. It is extremely difficult.

For example, Patent Document 1 discloses that in hot metal dephosphorization, oxygen gas is blown up, and the slag composition has an iron oxide concentration of 30 mass% or more in terms of total iron (hereinafter referred to as “T.Fe”) concentration. A method of dephosphorization without using fluoride or chloride has been proposed by controlling the Al ₂ O ₃ concentration to be ₂ to 16 mass% and the SiO ₂ concentration to be 12 mass% or less. T.Fe is the total iron content of all iron oxides (FeO, Fe ₂ O ₃ etc.) in the slag.

However, Patent Document 1 does not particularly specify a method for increasing the T.Fe concentration in the slag to 30 mass% or more. In Examples, iron oxide-containing materials such as iron ore and mill scale are used as Fe ₂ O _3. There is only a description that it should be blended in the flux so as to be 55 to 85 mass% in terms of.

  The method of controlling the oxygen potential of the slag using a large amount of such a solid oxygen source lowers the hot metal temperature. To induce problems. Furthermore, even if a solid oxygen source is blended in the flux, there is no guarantee that they will be effectively utilized for the intended reaction such as desiliconization or dephosphorization, and there is a possibility of reacting with carbon in the hot metal. If the carbon concentration in the hot metal is reduced at the stage of hot metal pretreatment, the heat margin for melting Mn ore, scrap, etc. is insufficient at the time of decarburization refining in the converter of the next process. Further, if the T.Fe concentration in the slag is increased more than necessary, the fluidity of the slag is increased, and as a result, there is a risk of causing operational disturbance such as slag forming.

Thus, an effective method has not been proposed for controlling the T.Fe concentration in the slag, and various problems have been encountered.
JP-A-11-269522

  The present invention has been made in view of the above circumstances, the purpose of which is to refine the hot metal performed by blowing oxygen gas to the bath surface of the hot metal without using a solid oxygen source such as iron ore, To provide a refining method capable of quickly adjusting the T.Fe concentration in slag to an optimum range for dephosphorization reaction, desiliconization reaction, devanadium reaction and the like.

  In order to solve the above-mentioned problems, the present inventors use a refining facility equipped with an upper blowing lance, and perform oxygen removal treatment or desiliconization treatment by blowing oxygen gas from the upper blowing lance onto the hot metal surface. A test was conducted to investigate the effect on the T.Fe concentration in the slag by changing the gas supply amount, the stirring gas flow rate, the slag mass, etc. to various conditions. The test results will be described below.

  By spraying oxygen gas on the hot metal, iron oxide is generated according to the following equation (2). That is, by increasing the supply rate of oxygen gas, the reaction of the formula (2) is further facilitated, the iron oxide concentration in the slag, that is, the T.Fe concentration is increased, and the oxygen potential is increased.

  Therefore, the influence of the oxygen gas supply rate on the T.Fe concentration in the slag was investigated. However, when the stirring gas flow rate is too high, the hot metal and slag are stirred, and the carbon in the hot metal reduces the iron oxide in the slag by the above-described equation (1), and T.Fe in the slag. Concentration may not increase. In other words, in order to increase the T.Fe concentration in the slag efficiently, the top blown oxygen is used so that the iron oxide generation reaction of the formula (2) efficiently proceeds while the reduction reaction of the formula (1) does not proceed. It is necessary to adjust the gas supply rate (also referred to as “acid feed rate”) and the flow rate of the stirring gas to appropriate ranges.

  In this test, slag was sampled during top blowing acid, and the time-dependent change in T.Fe concentration in the slag was investigated from the analytical value of the collected slag. It has been found that the temperature rises by about 2 to 4 minutes after the start of acid delivery, and becomes almost constant during the subsequent acid delivery. In other words, it became clear that the settings of the top blowing acid speed, the stirring gas flow rate, etc. until 2 to 4 minutes after the start of acid feeding are very important in controlling the T.Fe concentration in the slag. .

  Further, as the test was repeated, it was found that the method of spraying the top blowing acid onto the hot metal was also important. That is, when the so-called hard blow acid feeding method in which the top blown oxygen gas is strongly blown against the hot metal bath surface, the oxidation reaction of the above-described formula (2) does not proceed so much and the following (3 From the formula, it became clear that oxidation of carbon in hot metal occurs preferentially.

When the carbon in the hot metal is oxidized according to the equation (3), a heat margin is insufficient in the decarburization refining in the converter in the subsequent process, which causes an increase in steelmaking cost. Accordingly, there is a need for an upper blowing acid method that allows the expression (2) to proceed without causing the expression (3) to proceed. From various tests, the ratio (L / L) of the depth (L: mm) of the hollow portion generated on the bath surface of the hot metal during oxygen gas blowing to the bath depth (L ₀ : mm) of hot metal ₀ ) was found to be in an appropriate range. The depth L (mm) of the dent can be measured from the reflection time of sound waves or the like, but can also be calculated using the following equations (4) and (5). In the equations (4) and (5), h is the distance (mm) between the tip of the top blowing lance and the hot metal bath surface, θ is the nozzle angle (deg) of the top blowing lance, and n is the nozzle hole of the top blowing lance. The number, d is the nozzle diameter (mm) of the top blowing lance, W is the hot metal mass (t) to be treated, and F is the acid feed rate (Nm ³ / min · t) from the top blowing lance per ton of hot metal.

  In addition, in controlling the T.Fe concentration in the slag at the time when 2 to 4 minutes have passed since the start of acid delivery, the mass of the slag existing at the time when 2 to 4 minutes have passed after the start of acid delivery is controlled by further testing. I also found it important. For example, if a large amount of smelting flux is added until 2 to 4 minutes after the start of acid feeding, even if the conditions are optimized and the amount of iron oxide produced is controlled, the iron oxide concentration decreases as a result. It becomes difficult to control the T.Fe concentration in the slag. On the other hand, when the mass of slag is extremely small when 2 to 4 minutes have elapsed after the start of acid delivery, the T.Fe concentration in the slag increases, and this is also difficult to control. Moreover, if the mass of the slag is extremely small, there is a possibility of affecting various refining processes. Thus, it became clear that there is an appropriate range for the mass of slag in order to control the T.Fe concentration in the slag. The mass of slag here is a mass calculated from auxiliary materials such as refining flux and scrap and hot metal components.

From the above results, the present inventors have succeeded in finding a necessary condition for controlling the T.Fe concentration in the slag to 10 to 40 mass% when 2 to 4 minutes have elapsed after the start of the acid delivery. And its condition, the top-blown oxygen-flow-rate is 0.5~3.0Nm ³ / min · t, the stirring gas flow rate 0.01~0.30Nm ³ / min · t, the depth of the recess is (L) The ratio (L / L ₀ ) of the hot metal bath depth (L ₀ ) is 0.03 to 0.30, and the slag mass is 5 to 50 kg / t when 2 to 4 minutes have elapsed after the start of acid feeding. It is to be. It became clear that the T.Fe concentration in the slag can be controlled in the range of 10 to 40 mass% by satisfying all of these conditions.

The present invention has been made on the basis of the above test results, and the hot metal refining method according to the present invention blows oxygen gas up toward the bath surface of the hot metal accommodated in the refining vessel. when refining, top-blown oxygen gas 0.5~3.0Nm ³ / min · t the feed rate of the flow rate of stirring gas in the molten iron 0.01~0.30Nm ³ / min · t, the oxygen gas The ratio (L / L ₀ ) between the depth (L) of the depression formed on the hot metal bath surface during top blowing and the bath depth (L ₀ ) of the hot metal is 0.03 to 0.30, and oxygen When the mass of slag in the refining vessel is 2 to 4 minutes after the start of gas supply, 5 to 50 kg / t, and the T.Fe concentration of the slag when 2 to 4 minutes have elapsed after the start of oxygen gas top blowing range was controlled in the range of 10~40mass%, the T.Fe concentration in slag 10～40Mass% to refining End It is characterized in that to maintain.

  According to the present invention, in the refining of hot metal performed by spraying oxygen gas onto the hot metal bath surface, the T.Fe concentration in the slag is in the range of 10 to 40 mass% without using a solid oxygen source such as iron ore. Therefore, it is possible to efficiently perform refining that oxidizes and removes the impurity elements in the hot metal, such as desiliconization treatment or dephosphorization treatment. In addition, since the T.Fe concentration in the slag does not become excessively high, there is no risk of causing an operational hindrance such as slag forming, and the carbon in the molten iron is not excessively reduced. Since it does not have to be used, it is possible to prevent the temperature drop of the hot metal when using a solid oxygen source, and it is possible to secure a sufficient heat margin in decarburization refining in the next converter. The industrially beneficial effect is brought about.

  Hereinafter, the case where the present invention is applied to hot metal dephosphorization treatment in a hot metal ladle will be described as an example with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view showing an example of a dephosphorization treatment facility used when carrying out the hot metal refining method according to the present invention, and FIG. 2 is a schematic enlarged cross-sectional view of the top blowing lance shown in FIG. .

  In FIG. 1, a hot metal ladle 5 containing hot metal 2 discharged from a blast furnace (not shown) is mounted on a carriage 6 and carried into a dephosphorization processing facility 1. An upper blowing lance 7 and an injection lance 8 are installed in the dephosphorization processing equipment 1, and the upper blowing lance 7 and the injection lance 8 can move up and down in the hot metal ladle 5. From the top blowing lance 7, oxygen gas as a dephosphorizing agent can be blown onto the hot metal 2. The oxygen gas used is industrial pure oxygen, and may contain impurities such as nitrogen gas in a volume percentage of several percent.

  The injection lance 8 is connected to the storage tank 9 and the storage tank 10, and the solid oxygen source 3 made of iron oxide such as iron ore accommodated in the storage tank 9, and the dephosphorization flux accommodated in the storage tank 10. The quicklime 4 can be blown into the hot metal 2 using nitrogen or Ar gas as a carrier gas. The solid oxygen source 3 functions as a dephosphorizing agent similarly to the oxygen gas. However, the temperature of the hot metal 2 is lowered by adding the solid oxygen source 3. The quicklime 4 is a flux for dephosphorization, and reacts with the phosphorous oxide produced by the dephosphorization reaction to fix the phosphoric oxide in the slag 15 and adjust the basicity of the produced slag 15. In this case, another flux may be mixed with the quicklime 4 or another flux may be used instead of the quicklime 4. Incidentally, the solid oxygen source 3 in the storage tank 9 and the quick lime 4 in the storage tank 10 can be blown independently by controlling the addition amount and the addition time. It is also possible to stir the molten iron 2 by blowing only an inert gas such as gas or Ar gas.

  The dephosphorization processing facility 1 is further provided with a raw material supply facility including hoppers 11 and 12, a raw material transfer device 13, and a chute 14. Using this raw material supply facility, solid oxygen in the hopper 11 is installed. The quick lime 4 in the source 3 and the hopper 12 can also be added to the hot metal ladle 5 and added.

  As shown in FIG. 2, the upper blowing lance 7 is composed of a cylindrical lance main body 16 and a lance nozzle 17 connected to the lower end of the lance main body 16 by welding or the like. The pipe 18, the middle pipe 19, and the inner pipe 20 are made of three concentric steel pipes, that is, a triple pipe, and the copper lance nozzle 17 is provided with a nozzle 21 in a vertically downward direction or a vertically obliquely downward direction. .

  The gap between the outer pipe 18 and the middle pipe 19 and the gap between the middle pipe 19 and the inner pipe 20 serve as a flow path for cooling water for cooling the upper blowing lance 7. This is a supply flow path for oxygen gas to the nozzle 21. Oxygen gas supplied into the inner pipe 20 from the upper part of the upper blowing lance 7 passes through the inner pipe 20 and is jetted from the nozzle 21 toward the bath surface of the hot metal 2. In FIG. 2, a plurality of nozzles 21 are provided, but only one nozzle may be provided. In FIG. 2, the nozzle 21 is a so-called Laval nozzle composed of two cones, a portion whose cross section is reduced and a portion where the cross section is enlarged. However, the nozzle 21 may be a straight nozzle. The nozzle opening angle θ shown in FIG. 2 is referred to as a nozzle angle, and the nozzle diameter (d) of the nozzle 21 is the diameter at the position where the cross section is the smallest.

  In the dephosphorization treatment of the hot metal 2 using the dephosphorization treatment equipment 1 having such a configuration, the refining method according to the present invention is carried out as follows.

  An inert gas such as nitrogen gas or Ar gas is blown from the injection lance 8 as a stirring gas, and quick lime 4 is placed on the hot metal 2 via the chute 14 as a dephosphorization flux, or via the injection lance 8. While blowing into the hot metal 2, oxygen gas is continuously blown from the upper blowing lance 7 toward the hot metal 2 accommodated in the hot metal ladle 5, and the dephosphorization treatment of the hot metal 2 is started.

At that time, the oxygen gas sending rate from the top blowing lance 7 is adjusted within the range of 0.5 to 3.0 Nm ³ / min · t, and the stirring gas flow rate from the injection lance 8 is set to 0.01 to The ratio of the depth (L) of the recess formed on the hot metal bath surface when oxygen gas is blown up to the bath depth (L ₀ ) of the hot metal 2 is adjusted within the range of 0.30 Nm ³ / min · t. (L / L ₀ ) is adjusted within the range of 0.03 to 0.30, and the mass of the slag 15 generated at the time when 2 to 4 minutes have elapsed after the start of acid delivery is within the range of 5 to 50 kg / t. Adjust in.

In this case, the oxygen gas feeding rate and the stirring gas flow rate can be adjusted by adjusting the opening of a flow meter (not shown). The ratio (L / L ₀ ) can be adjusted by adjusting the distance (h) between the tip of the top lance 7 and the hot metal bath surface while observing the hot metal bath surface. It is preferable to adjust using the formulas (4) and (5).

Specifically, the number of nozzle holes (n), nozzle diameter (d), acid feed rate (F), and hot metal mass (W) to be processed are substituted into the equation (4) for the upper blowing lance 7 being used. By defining L _h and substituting the determined L _h , the nozzle angle (θ) of the upper blowing lance 7 and the distance (h) between the tip of the upper blowing lance 7 and the hot metal bath surface into the equation (4), The depth (L) of the depression can be calculated. On the other hand, since the bath depth (L ₀ ) of the hot metal 2 can be obtained from the hot metal mass (W) and the inner diameter of the hot metal ladle 5, the ratio (L / L ₀ ) can be calculated from these. In the equations (4) and (5), the factor that can be easily changed online is the distance (h). Therefore, the ratio (L / L ₀ ) is adjusted by adjusting the distance (h). Since the ratio (L / L ₀ ) also changes by changing the oxygen gas delivery rate (F), the acid delivery rate (F) is within the range of 0.5 to 3.0 Nm ³ / min · t. If so, the ratio (L / L ₀ ) may be adjusted by adjusting the acid feed rate (F). Further, the ratio (L / L ₀ ) may be adjusted by replacing the upper blowing lance 7 with an upper blowing lance having a different shape of the nozzle 21.

  The adjustment of the mass of the slag 15 takes into account the amount of slag generated from easily oxidizable components (for example, silicon) in the hot metal 2 and the amount of slag generated from auxiliary materials such as charged scrap, This can be done by adjusting the amount of quicklime 4 added.

  The hot metal 2 to be used can be processed with any composition, and T.Fe in the slag can be controlled without any problem if the temperature of the hot metal is in the range of 1250 to 1450 ° C. . Furthermore, as an oxygen source, not only oxygen gas but also solid oxygen source 3 is added if the amount of oxygen gas converted to solid oxygen source 3 is within 20% or less of the total oxygen source. It can be used without causing any inconvenience in controlling the Fe concentration. However, from the viewpoint of reducing heat loss, it is preferable not to use the solid oxygen source 3 but to control the T.Fe concentration only with oxygen gas.

  By dephosphorizing the hot metal 2 in this manner, the T.Fe concentration in the slag can be quickly controlled in the range of 10 to 40 mass% without using the solid oxygen source 3, so that Phosphorus treatment can be performed efficiently. Further, since the T.Fe concentration in the slag does not become excessively high, there is no risk of causing an operation hindrance such as forming of the slag 15, and the carbon in the hot metal is not excessively reduced. 3 does not need to be used, so the temperature drop of the hot metal 2 when the solid oxygen source 3 is used can be prevented in advance, and a sufficient thermal margin is secured in the decarburization refining in the converter of the next process. It becomes possible.

  In addition, although the said description demonstrated in the example of the dephosphorization process of hot metal, this invention is not restricted to the dephosphorization process of hot metal, The hot metal accommodated in the refining container is not restricted to the desiliconization process of hot metal. The present invention can be applied to all cases where oxygen gas is blown up and hot metal is oxidized and refined. In addition, the dephosphorization process is not limited to the hot metal ladle described above. For example, instead of the injection lance 8, a hot metal ladle or a torpedo car having a bottom blowing tuyere, or an upper bottom blowing converter type refining vessel. Also, the present invention can be implemented.

When the hot metal was dephosphorized using the dephosphorization equipment shown in FIG. 1, a test operation to which the present invention was applied was carried out. In the test operation, the hot metal ladle containing about 150 tons of hot metal discharged from the blast furnace was transported to the dephosphorization treatment facility shown in FIG. 1, and oxygen gas was blown onto the hot metal bath surface through an upper blowing lance, This was carried out by blowing nitrogen gas into the molten iron as a stirring gas through an injection lance. The mass of the slag was changed by adjusting the amount of quicklime added as a dephosphorization flux. Further, the ratio (L / L ₀ ) is obtained from the above-mentioned formulas (4) and (5), and the bath depth of the hot metal from the inner diameter of the hot metal pan and the hot metal density (L / L ₀ ). L ₀₎ and seeking to calculate a ratio (L / L _0), and adjusted the ratio of (L / L ₀₎ in the range of 0.03 to 0.30. During oxygen blowing, a slag sample was collected from the hot metal ladle and analyzed for the T.Fe concentration in the slag.

  FIG. 3 shows two representative examples in which the change with time in the T.Fe concentration in the slag was investigated. As shown in FIG. 3, the behavior of the T.Fe concentration in the slag under oxygen blowing is increased until about 2 to 4 minutes after the start of the acid transfer, and thereafter, the behavior of the T.Fe concentration may change to a substantially constant value. I understood. Therefore, in order to raise the oxygen potential in slag, it turned out that the refining conditions of the period until 2-4 minutes pass after the start of acid sending are very important.

  Table 1 shows the test conditions and test results in the examples of the present invention. The time in Table 1 represents the elapsed time from the start of acid delivery, and T.Fe in Table 1 is the analytical value of the slag sample collected at that time. The slag mass is obtained by adding the dephosphorization flux introduced up to that time and the amount of slag generated by calculation from the component value of the hot metal.

As the present invention example of Table 1, the oxygen-flow-rate 0.5~3.0Nm ³ / min · t, the stirring gas flow rate 0.01~0.30Nm ³ / min · t, the ratio (L / L ₀ ) is 0.03 to 0.30, and the slag mass at the time when 2 to 4 minutes have elapsed after the start of acid delivery is within the range of 5 to 50 kg / t, 2 to 4 minutes after the start of acid delivery It turned out that the T.Fe density | concentration in the slag in the time of progress can be controlled in the range of 10-40 mass%.

  On the other hand, the test conditions and test results of Comparative Examples 1 to 4 performed for verifying whether these four conditions are essential are also shown in Table 1 described above.

Comparative Example 1 is a case where the acid feed rate, the ratio (L / L ₀ ), and the slag mass are in the proper range, but the stirring gas flow rate is outside the proper range. In the test No. 10 in which the gas flow rate for stirring was 0.003 Nm ³ / min · t, which is much less than the appropriate range, the T.Fe concentration in the slag was a very high value. This is considered to be because the hot metal and slag were not stirred because the stirring gas flow rate was small and the stirring power was weak, and the reduction of iron oxide by carbon in the hot metal did not occur. As described above, it is not preferable to increase the T.Fe concentration in the slag more than necessary, and in the test No. 10, severe slag forming was confirmed. On the other hand, in the test No. 11 in which the stirring gas flow rate was 0.40 Nm ³ / min · t, which was larger than the appropriate range, the T.Fe concentration in the slag was very small. This is presumably because iron oxide was reduced by carbon in the hot metal because stirring was strong.

In Comparative Example 2, the gas flow rate for stirring, the ratio (L / L ₀ ), and the slag mass are in the proper range, but the acid feed rate is outside the proper range. In Test No. 12, where the acid feed rate was 0.30 Nm ³ / min · t, which was less than the appropriate range, the T.Fe concentration in the slag was a low value. This is thought to be due to a lack of acid-feeding capacity for producing iron oxide. On the other hand, in the test No. 13 in which the acid feed rate exceeds 3.20 Nm ³ / min · t and the appropriate range, the T.Fe concentration in the slag becomes higher than necessary, and it is in the range of 10 to 40 mass%. I couldn't control it.

In Comparative Example 3, the acid feed rate, the stirring gas flow rate, and the slag mass are in the proper ranges, but the ratio (L / L ₀ ) is outside the proper range. In the test No. 14 in which the ratio (L / L ₀ ) was 0.02 smaller than the appropriate range, the T.Fe concentration in the slag was a low value. This is because although the distance (h) between the top lance tip and the hot metal bath surface was increased to direct soft blow, the distance (h) between the lance tip and the hot metal bath surface was made too large. This is thought to be because the molten iron did not reach the hot metal bath surface sufficiently. Also in Test No. 15 where the ratio (L / L ₀ ) is 0.35 which is larger than the appropriate range, the T.Fe concentration in the slag was a low value. This is thought to be because the oxidation of carbon in the hot metal takes precedence over the oxidation of iron due to hard blow.

Comparative Example 4 is a case where the acid feed rate, the stirring gas flow rate, and the ratio (L / L ₀ ) are in the proper range, but the slag mass is outside the proper range. In the test No. 16 in which the slag mass was 3 kg / t, which is less than the appropriate range, the T.Fe concentration in the slag was high, and it was impossible to control it in the range of 10 to 40 mass%. On the other hand, in the test No. 17 in which the slag mass was 61 kg / t which was larger than the appropriate range, the generated iron oxide was thinned, and as a result, the T.Fe concentration in the slag was low.

As mentioned above, from the result of this invention example and Comparative Examples 1-4, the T.Fe density | concentration of the slag in the time of 2 to 4 minutes having passed since the start of acid feeding is controlled in the range of 10-40 mass%, and until the completion of oxygen blowing In order to maintain the concentration, the oxygen feed rate of the top blown oxygen gas is 0.5 to 3.0 Nm ³ / min · t, and the stirring gas flow rate of the hot metal is 0.01 to 0.30 Nm ³ / min · t. The ratio (L / L ₀ ) is set to 0.03 to 0.30, and the slag mass at the time when 2 to 4 minutes have elapsed after the start of acid feeding needs to be adjusted within the range of 5 to 50 kg / t. I understood. Moreover, it was confirmed that the dephosphorization reaction was efficiently performed by performing the dephosphorization treatment under these conditions.

It is a schematic sectional drawing which shows the dephosphorization processing equipment used when implementing the hot metal refining method which concerns on this invention. It is a general | schematic expanded sectional view of the upper blowing lance shown in FIG. It is a figure which shows the result investigated about the time-dependent change of the T.Fe density | concentration in slag.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dephosphorization processing equipment 2 Hot metal 3 Solid oxygen source 4 Quicklime 5 Hot metal pan 6 Bogie 7 Top blowing lance 8 Injection lance 9 Storage tank 10 Storage tank 11 Hopper 12 Hopper 13 Raw material conveyance device 14 Chute 15 Slag 16 Lance main body 17 Lance nozzle 18 Outer pipe 19 Middle pipe 20 Inner pipe 21 Nozzle

Claims (1)

When refining the hot metal by blowing up oxygen gas toward the bath surface of the hot metal contained in the refining vessel, the supply rate of the upper blown oxygen gas is set to 0.5 to 3.0 Nm ³ / min · t , The flow rate of the hot metal stirring gas is 0.01 to 0.30 Nm ³ / min · t , the depth (L) of the recess formed on the hot metal bath surface when the oxygen gas is blown up, and the hot metal bath depth (L ₀ )) (L / L ₀ ) is set to 0.03 to 0.30, and the mass of the slag in the refining vessel is 5 to 50 kg / t when 2 to 4 minutes have elapsed after the start of oxygen gas supply. As described above , the T.Fe concentration of the slag at the time when 2 to 4 minutes have elapsed after the start of the top blowing of oxygen gas is controlled to a range of 10 to 40 mass%, and the T.Fe concentration of the slag is set to 10 to 40 mass% until the end of refining. A method for refining hot metal, characterized by maintaining the range .

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