JP4743078B2 - Method for improving slag evacuation after dephosphorization and method for dephosphorizing hot metal using the slag - Google Patents

Description

  The present invention relates to a method for improving the slag exhaustability after dephosphorization treatment when dephosphorizing hot metal using a dephosphorization agent substantially free of fluorine using a converter type furnace. Further, the present invention relates to a hot metal dephosphorization processing method that suppresses the growth of ingot in the furnace and enables stable operation by using the method for improving the exhaust property.

  Compared to the conventional steel refining method in which carbon and phosphorus in the hot metal were refined at the same time using a converter, a hot metal spare that removes phosphorus in advance in the hot metal stage using a hot metal ladle, torpedo, etc. Dephosphorization treatment is performed, and hot metal preliminary dephosphorization using a converter is actively performed among them.

Generally, in converter refining, a method of adding lime is performed in order to appropriately control the phosphorus concentration in molten steel, and a method of adding fluorite (CaF ₂ ) as a lime solvent is known. It has been. However, when fluorite is used as a hatching accelerator, since the slag after blowing contains fluorine, there is a problem that fluorine elution is a concern when slag is used as a civil engineering material.

  Thus, in consideration of the influence of fluorine on the environment, it is required to reduce the amount of fluorine-containing material as much as possible even in the hot metal preliminary dephosphorization treatment. For this reason, various techniques for reducing the phosphorus concentration after dephosphorization have been proposed in the preliminary dephosphorization of hot metal in which fluorine-containing materials are reduced as much as possible.

  For example, Patent Document 1 discloses a method in which oxygen is used as a carrier gas and a dephosphorization agent containing CaO and manganese oxide is sprayed onto hot metal in order to compensate for the decrease in hatchability of slag accompanying the decrease in fluorine-containing materials. Has been. According to this method, since the hatchability is improved by supplying manganese oxide to the hot spot, the dephosphorization efficiency can be increased and the Mn yield can be improved without using a fluorine-containing material. Can do.

  However, in the method disclosed in Patent Document 1, when oxygen gas is used as a carrier gas and manganese oxide is sprayed onto the bath surface, due to wear of the powder supply line or flexible hose due to manganese oxide having high hardness, There may be a situation where a hole is opened in the pipe or hose and oxygen and powder are ejected to the outside. Further, since such leakage of oxygen gas is not preferable for disaster prevention, a special preventive measure is required.

Further, in Patent Document 2, the CaO source is sprayed onto the hot metal bath surface through an upper blowing lance, and the slag basicity after dephosphorization is set to more than 2.5, or in addition thereto, the hot metal before dephosphorization. A method for stably producing a low phosphorus hot metal even when the amount of CaF ₂ added is reduced by setting the temperature of the steel to 1280 ° C. or higher is disclosed.

As described above, when the slag basicity is increased and the temperature is further increased, a low phosphorus hot metal can be obtained even if the amount of CaF ₂ added is reduced. However, in the method disclosed in Patent Document 2, since the melting point of the slag is increased, the fluidity of the slag is reduced by the temperature drop between the hot water after dephosphorization and the process of discharging the remaining slag. Since it falls, it becomes difficult to discharge | emit all the remaining slag.

  For this reason, the method disclosed in Patent Document 2 has a problem that the dephosphorization ability at the next blowing is reduced due to the influence of residual slag, and slag adheres to the refractory surface of the converter. In order to remove slag, there is a problem that the operation rate decreases. Furthermore, if slag adheres to the refractory surface, scrap may not be charged into the converter.

JP 2001-192724 A JP 2003-328025 A

  As described above, in the preliminary dephosphorization treatment of hot metal, it is required to reduce the amount of fluorine-containing material used for the purpose of reducing the burden on the global environment, and at the same time to reduce the phosphorus concentration of the product. Moreover, in order to enable stable dephosphorization operation, it is necessary to improve the discharge of residual slag after dephosphorization and reduce the amount of slag adhesion in the converter.

  The present invention has been made in view of the above problems, and maintains an efficient dephosphorization treatment even when the hot metal is dephosphorized using a dephosphorization agent substantially free of fluorine. However, an object of the present invention is to provide a method for improving the slag exhaustability after dephosphorization, which enables stable operation, and a method for dephosphorizing hot metal using the same.

  In order to solve the above-described problems of the prior art, the present inventors have studied optimum operating conditions. As a result, in order to improve the discharge of residual slag after dephosphorization and to suppress the adhesion of slag to the refractory surface in the converter, it is necessary not to leave unreacted CaO content in the residual slag. I knew it was important.

  Furthermore, by controlling the chemical composition of the residual slag, lowering the melting point of the residual slag improves the discharge of the residual slag after dephosphorization and prevents slag from adhering to the refractory surface in the converter. I found it necessary to suppress.

  On the other hand, it is well known that slag basicity needs to be 2.5 or more in order to stably produce low phosphorus steel in dephosphorization without using fluorine-containing materials. It is also well known that increasing the iron oxide concentration in the slag is effective for reducing the melting point.

  However, the present inventors have found that it is difficult to increase the iron oxide concentration in the slag because the carbon concentration in the hot metal is high. That is, in the dephosphorization process, the carbon concentration in the hot metal is generally about 3 to 4% by mass, and it is possible to increase the iron oxide concentration in the slag during blowing, but it is between the end of blowing and the hot water. Since the iron oxide is reduced by the carbon in the hot metal, it was found that the iron oxide concentration in the slag decreases and the melting point of the slag increases at the stage of discharging the slag.

  For this reason, as a result of various studies to reduce the melting point of slag, a method is known that can increase the iron oxide concentration in the slag as much as possible and keep the iron oxide concentration in the slag high even when slag is discharged. Got. In other words, in order to make it difficult for the hot metal carbon and iron oxide in the slag to react, it is effective to weaken the stirring of the hot metal, and the input iron oxide should be hatched at a rate according to the conditions in the furnace. Thus, it was found that adjusting the timing of charging is effective in controlling the iron oxide concentration in the slag.

  Further, these findings have been found to be more effective in combination with the effect of promoting the hatching of CaO by adopting a method of spraying a CaO source from the top blowing lance to the molten iron together with oxygen.

The present invention has been completed on the basis of the above-mentioned findings. The following (1) and (3) to (5) are methods for improving the slag rejection after dephosphorization, and (2) and (6) )) The hot metal dephosphorization method.
(1) When dephosphorizing the hot metal using a dephosphorization agent that does not substantially contain fluorine using a converter type furnace, it is defined by the mass concentration ratio of CaO and SiO ₂ after dephosphorization. The slag basicity is 2.5 or more and 3.5 or less, and the hot metal temperature in the pan after the dephosphorization treatment is 1320 ° C. or more and 1380 ° C. or less, and before 60% of the total blowing time has elapsed. From bottom to end of blowing, the bottom blowing gas flow rate is kept below 0.18 Nm ³ / min (hereinafter also referred to as “0.18 Nm ³ / min / t”) per 1 ton of molten iron, T. T. et al. A method for improving the slag rejection after dephosphorization, wherein the Fe concentration is 5% by mass or more.
(2) A method for dephosphorizing hot metal, which comprises using the method for improving the slag exhaustability after dephosphorization described in (1) above.
(3) In the method for improving the slag rejection after dephosphorization described in (1) above, the molten iron is stirred by setting the distance between the top blowing lance and the hot metal stationary hot water surface to 3 m or more. Since it weakens, the reduction | restoration reaction of the iron oxide by the carbon in hot metal becomes slow, and since the iron oxide density | concentration in slag can be kept high, it is desirable.
(4) In the method for improving the slag rejection after dephosphorization described in (1) or (3) above, 10 kg / t or more of iron oxide is added during blowing, and the timing of the addition is determined to be the same as that of de-Si outside O. _{2 After the} basic unit becomes ³ Nm ³ / t or more, it is desirable because the iron oxide concentration in the slag at the end of blowing can be kept high.
(5) In the method for improving slag rejection after dephosphorization described in (1), (3) and (4) above, of the CaO source used as the dephosphorizing agent, 50 mass% or more of CaO It is desirable to spray together with a gaseous oxygen source on the hot metal bath surface through an upper blowing lance.
(6) A method for dephosphorizing hot metal, which uses the method for improving the slag exhaustability after dephosphorization described in (3) to (5) above.

  In the present invention, the “converter type furnace” means a converter having a sufficient free board (upper space) capable of performing dephosphorization treatment by spraying powder such as a dephosphorizing agent on the hot metal with an upper blowing lance. It means a type of dephosphorization furnace, and it is desirable to have a bottom blowing mechanism for gas stirring the hot metal.

  In addition, “substantially free of fluorine-containing dephosphorization agent” means a dephosphorization agent that does not use high-concentration fluorine-containing substances such as fluorite, for example, less than 1% by mass as a gangue component Even when using fluorine-containing substances, converter slag and ladle slag generated in the steelmaking process, the fluorine concentration in the slag will ultimately be less than 0.4% by mass. Applicable to dephosphorizing agents using substances.

  The “component concentration (mass%) in the slag after dephosphorization treatment” means the slag component analysis value after the molten iron after dephosphorization is discharged (that is, at the time of discharge). “T.Fe concentration” means the concentration (mass%) of the Fe component present as iron oxide in the slag.

Further, “O ₂ basic unit out of Si removal” means that it is stoichiometrically required to oxidize all the Si contained in the molten iron to SiO ₂ from the amount of oxygen gas supplied during blowing. This means the oxygen gas intensity after removing oxygen.

  According to the present invention, even when a dephosphorization agent that does not substantially contain fluorine is used when the hot metal is dephosphorized using a converter type dephosphorization furnace, the slag after the dephosphorization treatment is used. Can be improved. Furthermore, while improving the discharge | emission property of the residual slag after dephosphorization refining, the low phosphorus hot metal can be obtained stably by suppressing the growth of the adhesion metal in the furnace.

  Therefore, according to the exhaustability improving method and the dephosphorization method of the present invention, the operation of the dephosphorization furnace capable of reducing the burden on the global environment and at the same time obtaining a low phosphorus hot metal is stably and continuously performed. It becomes possible to do.

  In the method for improving the slag exhaustability and the hot metal dephosphorization method of the present invention, a dephosphorization agent substantially free of fluorine is used by using a converter type dephosphorization furnace for 200 to 350 tons of hot metal. Use to dephosphorize hot metal. In particular, it is a method for producing low phosphorus hot metal (the P concentration in the hot metal after dephosphorization is 0.020% by mass or less) by spraying powdered quicklime onto hot metal together with oxygen from an upper blowing lance, and the degassing after the treatment. In this method, phosphorus slag is easily discharged out of the furnace, and the growth of bare metal that tends to adhere around the furnace port of the dephosphorization furnace is suppressed. Below, the reason and preferable range which prescribed | regulated this invention as mentioned above are demonstrated. Table 1 shows the components of the hot metal before and after the dephosphorization treatment of the hot metal targeted for the investigation.

(1) Method for Improving Excretion In the present invention, the slag basicity after dephosphorization treatment is 2.5 or more and 3.5 or less. By setting the Fe concentration to 5% by mass or more and the hot metal temperature in the pan after dephosphorization to 1320 ° C. or higher and 1380 ° C. or lower, the slag exhaustability after dephosphorization is improved, Promotes dephosphorization stably.
(1) -1. The slag basicity after dephosphorization treatment is 2.5 or more and 3.5 or less. The method for improving the slag rejection and the dephosphorization treatment of the hot metal of the present invention uses a dephosphorization agent substantially free of fluorine. According to the value of the silicon concentration in the hot metal so that the slag basicity defined by CaO / SiO ₂ after dephosphorization is in the range of 2.5 to 3.5, quick lime or limestone A CaO-containing substance such as

  As a result of investigating and examining hot metal 200 to 300 t shown in Table 1 above, the present inventors have found that when the slag basicity is less than 2.5, the slag dephosphorization ability decreases, and the dephosphorization treatment is performed. Not only is it not possible to stably obtain low phosphorus hot metal having a phosphorus concentration of 0.020% by mass or less later, but the viscosity of the slag during blowing increases, so slag forming occurs, In some cases, it was confirmed that slag overflowing outside the furnace, slag overflowing from the furnace outlet during hot water, etc. occurred.

  In addition, when the slag basicity is higher than 3.5, it becomes difficult to reduce the unreacted CaO content in the slag (hereinafter also referred to as “free CaO”), and the slag basicity is reduced. This will increase the amount of inner slag adhesion.

FIG. 1 is a graph showing the relationship between free CaO concentration and residual slag discharge. As shown in the figure, the slag dischargeability in the converter has a good correlation with the free CaO concentration in the slag. For this reason, it is desirable that the entire amount can be discharged. However, if the residual slag remains in the furnace by 20% by mass or more, the operability is remarkably deteriorated. Therefore, the ratio of dephosphorization treatment in which the residual slag in the furnace exceeds 20% by mass. In practice, refining operations that reduce as much as possible are important. When the free CaO concentration was 2 to 3% by mass, the ratio of the residual slag in the furnace exceeding 20% by mass was as low as 2%. However, when the free CaO concentration was 3 to 4% by mass, the ratio was 9%. It was as high as about%. From this, it is effective that the free CaO concentration in the slag is 3% by mass or less.
(1) -2. T. in slag Fe concentration is 5% by mass or more. Free CaO concentration and T.I. The result of investigating the relationship with the Fe concentration is shown in FIG. Table 2 shows the relationship with the Fe concentration.

  Here, the total amount non-dischargeable ratio is a charge ratio at which it can be clearly recognized that dephosphorization slag remains in the furnace after the discharge process.

  FIG. 2 shows the free CaO concentration and T. slag. It is a figure which shows the relationship of Fe density | concentration. As shown in FIG. When the Fe concentration was 5 to 6%, the ratio of the free CaO concentration exceeding 3% by mass was 15%. When the Fe concentration was 4-5%, the ratio increased to 46%.

  Thus, T.W. By setting the Fe concentration to 5% by mass or more, the ratio of the free CaO concentration exceeding 3% by mass decreased. As a result, as shown in Table 2, the total amount non-removable ratio decreased to 13.8% or less. This “total amount non-removable ratio” includes the charge of “less than 20% by mass of residual slag in the furnace” shown in FIG. 1, so the slag basicity is simply set to 2.5 to 3.5. In addition to slag T. It can be seen that by setting the Fe concentration to 5% or more, the total amount rejection impossible ratio can be greatly reduced.

If the total amount of undischargeable ratio exceeds 20%, furnace bottom tuyere is clogged with residual slag and the operability is significantly deteriorated. It is important to set the Fe concentration to 5% by mass or more. In addition, T. If the Fe concentration exceeds 15% by mass, the cost increases due to the deterioration of the iron yield, so it is desirable to make it 15% by mass or less.
(1) -3. When the hot metal temperature in the pan after dephosphorization treatment is 1320 ° C. or higher and 1380 ° C. or lower, when the hot metal temperature in the pan after dephosphorization treatment is lower than 1320 ° C., hatching of slag is inhibited, and free CaO is To increase. Further, when the hot metal temperature exceeds 1380 ° C., poor dephosphorization occurs due to high temperature. Therefore, the hot metal temperature in the pan after the dephosphorization treatment needs to be controlled to 1320 ° C. or higher and 1380 ° C. or lower.

  As a method of controlling the hot metal temperature in the pan after the dephosphorization process, based on the hot metal composition and temperature information before blowing, the amount of cold material corresponding to the temperature rise calculated from the amount of oxygen blown into the hot metal is set. A method of obtaining by calculation is common.

In the hot metal dephosphorization method of the present invention, the hot metal temperature is regulated by the hot metal temperature in the pan after dephosphorization, instead of the temperature in the dephosphorization furnace after dephosphorization. The reason for this definition is that it is not preferable to measure the hot metal temperature after the dephosphorization treatment in the dephosphorization furnace because the operating efficiency of the dephosphorization furnace is lowered. As described above, the present invention uses the hot metal temperature immediately after completion of the hot metal tapping after the dephosphorization process, which is measured from the necessity in the decarburizing and refining process of the next step, thereby defining the scope of the present invention. An improvement in the operating efficiency of the phosphorus furnace can also be achieved.
(2) T. in slag. Method for increasing Fe concentration (2) -1. Bottom blowing gas flow rate As described above, in the present invention, the bottom blowing gas flow rate is maintained at 0.18 Nm ³ / min / t or less before 60% of the total blowing time has elapsed until the end of blowing. T. in the slag after treatment. One of the features is that the Fe concentration is controlled to 5 mass% or more.

FIG. 3 shows the T.V. It is a figure which shows the relationship between Fe density | concentration and bottom blowing inert gas flow rate. As shown in FIG. In order to make the average value of the Fe concentration 5% by mass or more, the bottom blowing gas flow rate for stirring needs to be 0.18 Nm ³ / min / t or less. The reason for this regulation is to lower the rate at which the generated iron oxide or the iron oxide charged is reduced by the carbon in the hot metal by lowering the flow rate of the bottom blowing gas for stirring the hot metal and weakening the stirring. This is because the iron oxide concentration in the slag can be kept high.

As the blowing time, if the bottom blowing gas flow rate is a low flow rate of 0.18 Nm ³ / min / t or less from about 50% of the total blowing time until the end of blowing, the flow rate is low during the entire blowing time. It is possible to maintain the same iron oxide concentration as that in the case of the above. Essentially, it is only necessary to set the gas flow rate to a low flow rate as described above from before 60% of the total blowing time has elapsed until the end of blowing. At this time, it is necessary to secure a gas flow rate that can at least prevent the molten iron from entering the bottom blowing tuyere.

Moreover, in the initial stage of blowing, the bottom blowing gas flow rate is set to about 0.20 to 0.40 Nm ³ / min / t because it is necessary to dissolve the scrap and promote initial slag hatching. Is desirable. In the method of the present invention, the acid feed rate from the top blowing lance is about 1.0 to 3.0 Nm ³ / min / t, and the oxygen supply time in the dephosphorization blowing is about 5 to 15 minutes.
(2) -2. In the present invention, the distance between the top blowing lance and the hot metal stationary hot water surface is preferably 3 m or more. The reason for this regulation is that by increasing the distance between the lance and the hot water surface, that is, by weakening the stirring of the hot metal, the generated iron oxide or the iron oxide introduced is reduced by the carbon in the hot metal. This is because it is possible to keep the iron oxide concentration in the slag high by slowing the reaction rate.

  FIG. 4 shows the T.V. It is a figure which shows the relationship between Fe density | concentration and the distance between lance-hot-water surfaces. As shown in FIG. 4, when the distance between the lance and the stationary hot water surface is 3 m or more, the T.I. The Fe concentration can be 5% by mass or more.

  However, if the distance between the lance and the static hot water surface is increased more than necessary, the reaction efficiency of oxygen, refractory melting, and increased slopping will be caused. Is preferably 4.0 m or less. In the initial stage of blowing, it is desirable to reduce the distance between the lance and the stationary hot water surface in order to increase the reaction efficiency of oxygen.

The amount of hot metal used in the survey is 200 to 300 t. However, even when the amount of hot metal reaches 350 t, the hot metal depth is about the same as in the case of 300 t. The preferred range of distances does not change.
(2) -3. During the smelting, 10 kg / t or more of iron oxide is added, and the timing of the addition is after the non-Si-free O ₂ basic unit becomes ³ Nm ³ / t or more. It is a figure which shows the relationship between Fe density | concentration and the input time of the iron oxide in blowing. The input iron oxide is hatched at the hatching rate according to the blowing conditions and is reduced by the carbon in the hot metal. To keep the iron oxide concentration in the slag at the end of blowing, The timing and amount of input are also important factors.

As shown in FIG. 5, regarding the timing of iron oxide input and the input amount, as the iron oxide input amount increases, the T.O. There is a tendency for the Fe concentration to increase. This increase effect is greater when iron oxide is added after the non-Si-excluded O ₂ basic unit becomes ³ Nm ³ / t or more than before.

T. in slag In order to achieve a stable Fe concentration of 5% by mass or more, it is necessary to add 10 kg / t or more of iron oxide while setting the bottom blowing gas flow rate to a low flow rate of 0.18 Nm ³ / min / t or less. It is more desirable that the charging time be after the non-Si-free O ₂ basic unit becomes ³ Nm ³ / t or more. The figure shows the top blown O ₂ basic unit of 1.54 Nm ³ / min / t, the C concentration in the hot metal from 4.7% to 3.5%, and the Si concentration in the hot metal from 0.3% to 0.0%. When dephosphorization blowing is performed under the following conditions.

  Generally, it is desirable to use a scale or iron ore having the composition shown in Table 3 as iron oxide.

(3) Synergistic effect with the use of powdered CaO The effect of increasing the Fe concentration appears more clearly in the hot metal dephosphorization method in which 50% by mass or more of CaO is supplied from the top blowing lance to the hot metal from the CaO source supplied as a dephosphorizing agent.

  When the CaO source is sprayed onto the hot metal bath surface together with oxygen from the top blowing lance, the CaO source is supplied to the hot spot of the oxygen fire point, so that the reaction efficiency is further improved and the free CaO concentration can be reduced. . In this case, if the CaO particle size is 2.8 mm or less, there is no significant difference in reaction efficiency, but it is more desirable to be 150 μm or less from the viewpoint of transportability.

  Hereinafter, among the CaO sources used as the dephosphorizing agent, the ratio of CaO supplied as the powdery raw material (CaO mass in the powdery raw material × 100 / CaO mass in the whole CaO source used as the dephosphorizing agent) is expressed as “ "Powder CaO ratio".

  The inventors set the slag basicity after the dephosphorization treatment to 2.5 to 3.5, the hot metal temperature in the pan after the dephosphorization treatment to 1320 to 1380 ° C., and the T.V. Blowing was performed under the condition where the Fe concentration was 5% by mass or more, and the relationship between the powder CaO ratio and the free CaO concentration was investigated.

  FIG. 6 is a diagram showing the relationship between the powder CaO ratio in the CaO source and the free CaO concentration. As shown in FIG. 6, among all the CaO components used for blowing, when the ratio of the CaO component supplied by spraying powdered quicklime having a particle size of 150 μm or less to hot metal is 50% or more, it is stable. It was confirmed that the free CaO concentration in the slag could be 2% by mass or less.

  Furthermore, when the powder CaO ratio is 80% or more, the free CaO concentration in the slag is 1.5 mass% or less, and when the powder CaO ratio is 90% or more, the free CaO concentration in the slag is 0.3 mass%. % Or less, and it was also confirmed that substantially no free CaO remained in the slag. In this way, if free CaO does not remain in the slag, the waste and dephosphorization treatment is stabilized, the CaO component can be used effectively, and the slag can be used as a by-product by suppressing the submerged expansion rate of the slag. It is more desirable when used as a material.

In order to confirm the effect of the hot metal dephosphorization method of the present invention, the following tests were conducted to evaluate the exhaustability, in-furnace slag adhesion, and the like.
(Test conditions)
The hot metal component before dephosphorization was [C]: 4.2 to 4.8% by mass, [Si]: 0.15 to 0.45% by mass, [P]: 0.095 to 0.120% by mass. , [Mn]: 0.20 to 0.35 mass%, and about 264 ton of hot metal and about 29 ton of scrap having a temperature before dephosphorization of 1300 to 1370 ° C. were poured into an upper bottom blowing converter, Smelted.

The hot metal ratio of the dephosphorization furnace was 89 to 91% by mass. The quicklime is about 92% CaO, and is a lump with a particle size of 30 mm or less and a powder of 150 μm or less.
(Evaluation methods)
The evaluation was performed on three items, that is, dephosphorization performance, exhaustability, and in-furnace slag adhesion. In the evaluation of the dephosphorization performance, the case where the phosphorus concentration in the hot metal after dephosphorization was 0.020% by mass or less was evaluated as ◯, and the case where it exceeded 0.020% by mass was evaluated as x. The evaluation of the evacuation property was 1 in the case of complete evacuation, 2 in the case of slight slag remaining, and 3 in the case of incomplete evacuation. In the comprehensive evaluation, the case where all the evaluations of the above three items are ○ (1 for the evaluation of rejection) is ○, and the case other than that is ×.
(Test results)
Table 4 shows test conditions and test results of the examples.

  Slag basicity after dephosphorization treatment as defined in the present invention; In the present invention examples T9 to T17 that satisfy the conditions for the Fe concentration and the hot metal temperature, as shown in Table 4, good results were obtained in any of the dephosphorization performance, the exhaust property, and the in-furnace slag adhesion. . Furthermore, in Invention Examples T13 to T17 in which a CaO source used as a dephosphorizing agent was added as a powder, there was an effect of reducing the free CaO concentration in the slag.

  On the other hand, in Comparative Examples T2, T3, and T5 to T8 that did not satisfy any of the conditions defined in the present invention, the evacuation property decreased and the amount of slag adhesion in the furnace increased. In Comparative Example T1, in which the slag basicity after the dephosphorization treatment did not satisfy the conditions specified in the present invention, good results were obtained in terms of the exhaustability and the in-furnace slag adhesion, but poor dephosphorization occurred. It was.

  Further, even in Comparative Example T4 in which the hot metal temperature in the pan after the dephosphorization treatment did not satisfy the conditions specified in the present invention, good results were obtained in terms of exhaustability and in-furnace slag adhesion, Since the hot metal temperature in the pan exceeded 1380 ° C., dephosphorization failure due to high temperature occurred.

  According to the present invention, even when a dephosphorization agent that does not substantially contain fluorine is used when the hot metal is dephosphorized using a converter type dephosphorization furnace, the slag after the dephosphorization treatment is used. Can be improved. Furthermore, while improving the discharge | emission property of the residual slag after dephosphorization refining, the low phosphorus hot metal can be obtained stably by suppressing the growth of the adhesion metal in the furnace.

  As described above, according to the exhaustability improving method and the dephosphorization treatment method of the present invention, the operation of the dephosphorization furnace capable of reducing the burden on the global environment and at the same time obtaining a low phosphorus hot metal can be stably and continuously performed. It becomes possible to carry out. As a result, the present invention can be widely applied in the hot metal treatment process as a hot metal dephosphorization method capable of significantly improving the operation efficiency.

It is a figure which shows the relationship between free CaO density | concentration and discharge property of residual slag. Free CaO concentration and T. in slag It is a figure which shows the relationship of Fe density | concentration. T. in slag It is a figure which shows the relationship between Fe density | concentration and bottom blowing inert gas flow rate. T. in slag It is a figure which shows the relationship between Fe density | concentration and the distance between lance-hot-water surfaces. T. in slag It is a figure which shows the relationship between Fe density | concentration and the input time of the iron oxide in blowing. It is a figure which shows the relationship between the powder CaO ratio in a CaO source, and free CaO density | concentration.

Claims (6)

When dephosphorizing the hot metal using a dephosphorization agent substantially free of fluorine using a converter type furnace,
The slag basicity defined by the mass concentration ratio of CaO and SiO ₂ after dephosphorization treatment is 2.5 or more and 3.5 or less, and the hot metal temperature in the pan after dephosphorization treatment is 1320 ° C. or more and 1380 ° C. In addition, the bottom blowing gas flow rate is maintained at 0.18 Nm ³ / min or less per 1 ton of hot metal from before 60% of the total blowing time has elapsed until the end of blowing, T. T. et al. A method for improving the slag rejection after dephosphorization, wherein the Fe concentration is 5% by mass or more.   A method for dephosphorizing hot metal, which uses the method for improving the slag exhaustability after dephosphorization according to claim 1.   2. The method for improving the slag exhaustability after dephosphorization according to claim 1, wherein the distance between the top blowing lance and the hot metal surface of the hot metal is 3 m or more. The deoxidization according to claim 1 or 3, characterized in that iron oxide is introduced at a rate of 10 kg / t or more during blowing and the timing of the addition is after the O ₂ basic unit outside de-Si becomes ³ Nm ³ / t or more. A method for improving the slag drainage after phosphorus treatment.   5. The CaO source used as the dephosphorizing agent, wherein 50% by mass or more of CaO is sprayed together with a gaseous oxygen source onto a hot metal bath surface through an upper blowing lance. The method for improving the slag evacuation property after the dephosphorization treatment according to claim 1.   A method for dephosphorizing hot metal, which uses the method for improving the slag exhaustability after dephosphorization according to any one of claims 3 to 5.

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