JP2020125541A - Converter refining method - Google Patents

Abstract

To provide an improved dephosphorization efficiency and reduction in CaO raw unit by increasing a slag discharge amount during an intermediate slag processing after desiliconization and dephosphorization by promoting slag formation and melting of flux solvent by using a high heating efficiency method for converter refining.SOLUTION: In a converter refining method, desiliconization and dephosphorization processes are performed in a converter. By using an upper blowing lance having a burner function, a flux composed of a granular material containing CaO to be sprayed with industrial oxygen gas is heated by combustion flame of the burner, and then blown to a surface of molten iron. The slag generated after the desiliconization and dephosphorization processes is subjected to an intermediate slag processing at a temperature equal to or higher than the molten iron temperature.SELECTED DRAWING: Figure 1

Description

INDUSTRIAL APPLICABILITY The present invention is a converter refining method which is effective in improving melting ability of slag at the time of intermediate slag and reducing the basic unit of the solvent-melting material by promoting melting and melting of the solvent-melting material added in the converter. Regarding

In recent years, in the field of steelmaking refining, so-called hot metal pretreatment, which removes silicon and phosphorus in hot metal tapped from a blast furnace prior to decarburization in a converter, has become widespread. It is known to contribute to the reduction of the amount of steelmaking slag generated. However, this hot metal pretreatment technology involves heat loss associated with hot metal transfer when it is carried out, for example, in a hot metal transfer container such as a blast furnace pan or a tope car, so the proportion of cold iron sources such as iron scrap must be suppressed. This is an obstacle to reducing the emission of greenhouse gases such as CO ₂ .

Conventionally, a technique has been developed that can solve the above-mentioned problems advantageously, that is, both the merit of so-called hot metal pretreatment and the increase of the main raw material selection range can be achieved. For example, as disclosed in Patent Document 1, there is a method of performing both hot metal pretreatment and decarburization treatment using one converter. This method includes the steps of charging scrap iron and hot metal into a converter, adding a medium material (flux) and dephosphorizing by blowing oxygen, tilting and discharging the dephosphorized slag, adding flux and blowing oxygen. Decarburization, dephosphorization treatment, decarburization, tapping with dephosphorization slag left, decarburization, decarburization slag by adding carbonaceous material to reduce iron oxide in slag It is said that six steps are repeated, and the advantages of the hot metal pretreatment described above can be enjoyed without impairing the productivity.

Patent Document 2 discloses a method of performing desiliconization treatment, dephosphorization treatment and decarburization treatment using two converters. In this method, first, in a first converter, a powder containing refining oxygen and a lime-based solvent is sprayed from an upper blowing lance for desiliconization, and then a part of the desiliconized slag is discharged ( Intermediate slag) and dephosphorization treatment by spraying powder containing refining oxygen and lime-based solvent on the hot metal after desiliconization treatment, and then in the second converter, hot metal after dephosphorization treatment Is a method of decarburizing. In this method, a refining oxygen, a powder containing a lime-based solvent, a lance with a burner function capable of spraying a fuel gas and an oxidizing gas are used in either or both of desiliconization and dephosphorization. As a result, there is a feature that hot metal desiliconization and dephosphorization can be performed with a small amount of a medium-soluble material.

JP-A-5-140627 WO2014/113242

"Fundamental study on the influence of various factors on fluid behavior during intermediate slag in MURC (Multi-Refining Converter) method", Kenichiro Naito, 3 others, Iron and Steel, Nippon Steel & Sumitomo Metal Corporation, 2014 Vol. 100, No. 4, p. 522-529 "Slag forming mechanism and its control in metallurgical process", Shigeta Hara, et al., Iron and Steel, Osaka University, 1992, Vol. 78, No. 2, p. 200-208

Among the above-mentioned related arts, in the method described in Patent Document 1, the basicity of the slag is 1.0 to 2.0 in the step of dephosphorizing by adding the medium material (flux) and blowing oxygen described above. By setting the temperature to 1,350° C. or lower, the dephosphorization ability is secured. However, in the case of this technique, the melting point of the slag rises sharply in the range where the basicity exceeds 1.0, so if it is attempted to promote the dissolution of the flux and improve the dephosphorization ability, There is a problem in that the dephosphorization reaction is rather disadvantageous in that the treatment must be carried out at a temperature.

Further, as for Patent Document 2, by using the upper blowing lance with a burner function, it is possible to utilize a high temperature flame exceeding 2000° C., and therefore, there is an advantage that even a high melting point flux can be easily dissolved. However, in this method, hot metal transfer occurs due to the use of two converters. Therefore, heat loss increases and the blending range of the iron scrap is restricted. Therefore, when the blending range of the iron scrap exceeds the proper blending range, a new heat source is required, which may cause a problem that the heat source cost increases.

Further, Non-Patent Document 1 describes an example in which a water model and a numerical analysis simulation for the intermediate slag process of a converter are performed. In this example, the viscosity of slag is large and the density of slag and metal is high. It has been pointed out that the smaller the difference, the easier the metal will flow out, and the less the slag will be. Therefore, in order to increase the discharge amount of desiliconization slag or dephosphorization slag in the intermediate slag process of the converter, and to enjoy the benefits of reducing the amount of medium-melting materials such as lime and the amount of steelmaking slag generated, the decrease in slag viscosity is required. You will need it.

However, according to the concept described in Non-Patent Document 1, when desiliconization and dephosphorization are performed in one conversion in one converter, SiO ₂ is generated at the time of desiliconization. It is indispensable to control the decrease of the dephosphorization ability by adding the slag with the basicity of 1.0 to 2.0. However, in the region where the basicity exceeds 1.0, the melting point of the slag sharply rises, so that the slag viscosity becomes high and the slag waste property deteriorates. That is, in the case of performing desiliconization and dephosphorization treatment in a converter, there is a problem that it is difficult to simultaneously secure both improved dephosphorization capacity and slag viscosity due to a decrease in slag viscosity.

Moreover, according to the research conducted by the inventors, when the slag produced by the desiliconization and dephosphorization treatment is subjected to the intermediate slag after the desiliconization and dephosphorization treatment in the converter, the slag is formed in a state of being formed. It was found that the intermediate slags lead to improvement of slag waste.

On the other hand, Non-Patent Document 2 describes a mechanism of slag forming in a metallurgical process including a converter and a control method thereof. According to it, "the forming phenomenon depends on the composition of the slag, and especially on the surface tension. Therefore, a clear relationship cannot be obtained regarding the viscosity of the melt.” Therefore, under conditions where the slag composition is limited to secure the dephosphorization ability, it is necessary to study the surface tension of the slag that promotes slag forming in order to improve the intermediate slag slag removal property. I understand.

Therefore, the present invention is a method developed in view of the above-mentioned problems of the prior art, and the purpose thereof is to increase the slag discharge amount during the intermediate slag treatment to improve the dephosphorization efficiency after the intermediate slag. Another object of the present invention is to propose an advantageous refining method capable of improving the production efficiency and reducing the basic unit of solvent material such as CaO powder.

The present invention is a method for solving the above problems and achieving the above object, wherein in the same converter, when producing molten steel from molten pig iron, before the intermediate slag is blown from the top blowing lance to industrial Granules containing oxygen gas for use and CaO (solvent) are sprayed onto the hot metal in the converter to perform desiliconization and dephosphorization treatment (hereinafter referred to as desiliconization/dephosphorization treatment), then intermediate slag As a method to promote slagging and melting of the medium material before the intermediate slag by adopting a method with high heating efficiency, which is decarburization and dephosphorization treatment (hereinafter referred to as decarburization/dephosphorization treatment). To heat and supply the medium-melting material, and further to improve the intermediate slag removal property while the slag composition is limited to secure the dephosphorization ability, so that the forming of the slag is promoted, It is characterized by adopting a means for changing the surface tension of the slag.

Further, in the present invention, it is also effective when refining using slag having a high viscosity with a slag basicity exceeding 1.0, specifically, a slag having a viscosity of 0.05 Pa·s or more at 1,400° C. If the surface tension of the slag after the desiliconization/dephosphorization treatment is set to 400 mN/m or less and the intermediate slag treatment is performed, the amount of slag discharged during the intermediate slag treatment can be further improved. it can.

That is, the first method of the present invention is, in a converter refining method for producing molten steel from molten iron by the same converter, after charging scrap and molten iron into the converter, industrial oxygen gas is supplied from a top blowing lance. When the desolvation/dephosphorization treatment is carried out by spraying a solvent material composed of powdery particles containing CaO on the surface of the hot metal, by using an upper blowing lance having a burner function, the solvent material is provided with a burner function. It is a converter refining method characterized by heating with a combustion flame and then spraying it on the surface of a hot metal bath, and then producing the desiliconized and dephosphorized slag that has been heated to a temperature above the hot metal temperature and then subjected to intermediate slag treatment.

In the second method of the present invention, the same converter is used first to perform desiliconization and dephosphorization treatment of hot metal by using slag having a viscosity of 0.05 Pa·s or more at 1,400°C, and then to perform dephosphorization. In a converter refining method for producing molten steel by performing charcoal and dephosphorization treatment, after charging scrap and molten pig iron into the converter, a medium consisting of powdery particles containing CaO together with industrial oxygen gas from an upper blowing lance. When performing desiliconization and dephosphorization treatment by spraying the molten material on the hot metal bath surface, by using an upper blowing lance having a burner function, the medium soluble material is heated by the combustion flame of the burner, and then the hot metal bath is heated. It is a converter refining method characterized in that the slag is sprayed on the surface and the resulting slag after desiliconization and dephosphorization treatment is heated to a temperature of the hot metal temperature or higher and then subjected to intermediate slag treatment.

Further, a third method of the present invention is a converter refining method for producing molten steel by first performing desiliconization/dephosphorization treatment of hot metal and then decarburizing/dephosphorization treatment in the same converter. ,
First, after scrap and hot metal are charged into the converter, a desolvation/dephosphorization treatment is performed by spraying a medium-soluble material consisting of industrial oxygen gas and powder containing CaO from the top blowing lance onto the hot metal bath surface. Then, while discharging a part of the slag generated after this desiliconization/dephosphorization treatment to the outside of the furnace, the inside of the furnace is degassed/dephosphorized hot metal and the slag remaining after the desiliconization/phosphorus treatment And the demolition and dephosphorization-treated hot metal in the furnace are sprayed with the refining oxygen gas together with the refining oxygen gas from the top blowing lance to remove the hot metal. Performs charcoal/dephosphorization treatment, and then taps the decarburized/dephosphorized molten steel remaining in the furnace into a molten steel ladle, while removing a portion of the decarburized/dephosphorized slag remaining in the furnace or When manufacturing the molten steel by discharging the whole outside the furnace,
In performing the desiliconization/phosphorus removal treatment, the industrial oxygen gas and the medium-dissolving material are heated by the combustion flame of the burner for the medium-dissolving material by using an upper blowing lance having a burner function. It is a converter refining method characterized in that the slag generated after the desiliconization/dephosphorization treatment is sprayed onto the hot metal bath surface and the slag is heated to a temperature of the hot metal temperature or higher for intermediate slag treatment.

The fourth method of the present invention is to perform desiliconization and dephosphorization treatment of hot metal by using the same converter and slag having a viscosity of 0.05 Pa·s or more at 1,400°C, and then degassing. A converter refining method for producing molten steel by performing charcoal and dephosphorization treatment,
First, after scrap and hot metal are charged into the converter, a desolvation/dephosphorization treatment is performed by spraying a medium-soluble material consisting of industrial oxygen gas and powder containing CaO from the top blowing lance onto the hot metal bath surface. Then, while discharging a part of the slag generated after this desiliconization/dephosphorization treatment to the outside of the furnace, the inside of the furnace is degassed/dephosphorized hot metal and the slag remaining after the desiliconization/phosphorus treatment And the demolition and dephosphorization-treated hot metal in the furnace are sprayed with the refining oxygen gas together with the refining oxygen gas from the top blowing lance to remove the hot metal. Performs charcoal/dephosphorization treatment, and then taps the decarburized/dephosphorized molten steel remaining in the furnace into a molten steel ladle, while removing a portion of the decarburized/dephosphorized slag remaining in the furnace or When manufacturing the molten steel by discharging the whole outside the furnace,
In performing the desiliconization/phosphorus removal treatment, the industrial oxygen gas and the medium-dissolving material are heated by the combustion flame of the burner for the medium-dissolving material by using an upper blowing lance having a burner function. It is a converter refining method characterized in that the slag generated after the desiliconization/dephosphorization treatment is sprayed onto the hot metal bath surface and the slag is heated to a temperature of the hot metal temperature or higher for intermediate slag treatment.

Regarding each of the above methods of the present invention, a converter refining method characterized by subjecting the slag after the desiliconization/dephosphorization treatment to a surface tension of 400 mN/m or less for the intermediate slag treatment is more preferable. It is a form.

According to the converter refining method of the present invention configured as described above, desiliconization/dephosphorization treatment is first performed using one converter, then intermediate slag treatment is performed, and then decarburization/dephosphorization is performed. In refining to perform treatment, by adopting a method with high heating efficiency, that is, by heating the medium material composed of powdery particles containing CaO by a combustion flame by an upper blowing lance having a burner function utilizing combustion gas, By supplying the medium-melting material into the hot metal of the combustion flame and then supplying it into the hot metal to be treated, it is possible to promote the melting and melting of the medium-melting material. Moreover, when the surface of the desiliconization/dephosphorization-treated slag is brought into a state where the surface tension is lowered at a high temperature by each of the methods of the present invention, slag foaming is promoted, and the slag after the desiliconization/dephosphorization treatment is treated. It becomes possible to improve the efficiency of intermediate waste treatment. As a result, the unit consumption of CaO can be reduced.

Further, according to each of the methods of the present invention, the amount of slag remaining in the furnace can be reduced by adopting the above-described treatment.

FIG. 3 is a schematic view of a converter equipment equipped with an upper blowing lance with a burner function, which is used for performing desiliconization/dephosphorization and decarburization/dephosphorization. Whether or not fuel gas is used (a, b) and CaO powder is sprayed (b) when the CaO-based powder and granules are sprayed together with the refining oxygen gas onto the hot metal bath surface using the top-blowing lance with burner function. , C) is a diagram in which slag heating characteristics (melted slag temperature-hot metal temperature) during desiliconization/dephosphorization treatment are evaluated. About the presence or absence of fuel gas (a, b) and the presence or absence of CaO powder (b, c) when CaO powder is sprayed together with refining oxygen gas onto the hot metal bath surface using a top blowing lance with burner function It is a figure which evaluated the intermediate slag ratio of the slag after desiliconization and dephosphorization processing. When spraying refining oxygen gas and CaO powder onto the hot metal bath surface using a top lance with a burner function, the presence or absence of fuel gas and the total used during desiliconization/dephosphorization and decarburization/dephosphorization It is a figure which shows the relationship with the medium solvent (CaO containing powder) basic unit of. It is a figure which shows the relationship between the surface tension of slag and the slag calming time.

INDUSTRIAL APPLICABILITY The present invention, as described above, is used when performing desiliconization/dephosphorization treatment using a single converter and, subsequently, a refining method in which further decarburization/dephosphorization treatment is performed, particularly during desiliconization/dephosphorization treatment. The refining method was developed by focusing on a new method of using a medium-soluble material that is CaO-containing powder and granules and heating it into a heat medium state and then spraying it onto the surface (bath surface) of hot metal or the like. is there. That is, the present invention proposes a refining method having excellent slag removal properties even in a state where the slag viscosity is high, and, while the slag composition is limited in order to secure dephosphorization ability, the intermediate slag slag is removed. In order to improve the property, it was decided to adopt a means for changing the surface tension of the slag so as to promote the forming of the slag.

In carrying out the refining method, it is recommended to use a converter as shown in FIG. 1, for example, a so-called upper-bottom blowing converter capable of top-blowing oxygen gas and bottom-blowing gas for stirring hot metal. It Moreover, this top-bottom blowing converter can burn not only oxygen gas and the solvent but also hydrocarbon-based fuel gas such as natural gas, city gas, propane gas or vaporized liquid fuel through the top-blowing lance. A furnace equipped with a top-blowing lance with a burner is preferable, and a furnace capable of forming a combustion flame due to combustion of the burner immediately below the top-blowing lance. In addition, in the case of such a converter, since the medium-dissolving material composed of powder particles or the like containing CaO can be passed through the combustion flame due to the action of the upper blowing lance, particularly the burner, the medium-dissolving material is After being in the state of the heat medium, it is sprayed into the molten iron (in the hot metal or molten steel), and high energy efficiency is obtained.

Then, as described above, the medium-solvent sprayed in the state of the heat medium acts on the surface of the desiliconization/dephosphorization-treated slag at a high temperature, and further acts to reduce the surface tension of the slag, so that the forming of the slag is performed. It is promoted and shows a good intermediate waste property.

Generally, in refining of a converter, first, iron scrap and hot metal are charged into the upper-bottom blowing converter, and then oxygen gas and a medium-melting material are top-blown to perform desiliconization and dephosphorization treatment. It usually starts with.

The desiliconization and dephosphorization treatment means that, at the same time as the start of the blowing using the upper blowing lance that is attached to the converter, the [Si] in the hot metal is the upper blowing oxygen or It is oxidized by a part of the bottom-blown oxygen and is transferred in the form of (SiO ₂ ) in the slag generated at this time (desiliconization treatment) to proceed. Then, excess oxygen that was blown into the converter during the desiliconization process but was not consumed oxidizes [P] and [C] in the hot metal, resulting in decarburization and dephosphorization. In addition, the iron content in the hot metal is further oxidized to generate (P ₂ O ₅ ) and (FeO), which are transferred to the slag (dephosphorization treatment). All of these oxidation reactions are exothermic reactions, and the reaction heat contributes to the melting of the iron scrap and, at the same time, the hot metal temperature rises. In the present specification, [Si], [P], and [C] represent Si, P, and C as components contained in molten iron (hot metal or molten steel). Further, (SiO ₂ )(P ₂ O ₅ ), (FeO) represent SiO ₂ , P ₂ O ₅ , and FeO as components contained in the slag. Hereinafter, the same applies to (CaO) in the present specification.

The decarburization/dephosphorization treatment, which is performed subsequent to the desiliconization/phosphorus removal treatment, is carried out at the same time as the start of the blowing using the upper blowing lance provided with the converter and the [C ] Is oxidized by part of top-blown oxygen or bottom-blown oxygen, and is transferred to the exhaust gas as CO gas (decarburization treatment) to proceed. Then, the excess oxygen that was blown into the converter during the decarburization process but was not consumed is used for the dephosphorization by the oxidation of [P] in the hot metal and for the oxidation of the iron content in the hot metal. It becomes (P ₂ O ₅ ) and (FeO) and moves into the slag (dephosphorization treatment).

The basicity (CaO/SiO ₂ ) of the slag after desiliconization and dephosphorization generated in the furnace under such a reaction also changes depending on the dissolution rate of (CaO) and the production rate of (SiO ₂ ). Further, properties such as melting point and viscosity of the desiliconized/dephosphorized slag vary greatly depending on the basicity of the desiliconized/dephosphorized slag and the composition ratio of other oxides such as (FeO) in the slag. Therefore, the basicity of these desiliconization/dephosphorization slags and the ratio of (FeO) in the slag are important operational control items for ensuring the fluidity of the slag in the intermediate slag after the desiliconization/dephosphorization treatment. Become. For example, if the basicity is too high, or conversely, it is too low, the melting point and viscosity will increase, so the composition and physical properties of the slag within the temperature range of the above-mentioned desiliconization/dephosphorization treatment will be intermediately removed. It is preferable to make adjustments so as to be suitable for.

In the method of the present invention, the CaO-containing powder or granular material (solvent material) sprayed on the hot metal bath surface is heated by the combustion flame of the upper blowing lance having a burner function with the progress of the desiliconization and dephosphorization treatment, and the heating medium Since it is in the state of (3), it rapidly moves into the slag in the form of (CaO). Further, since the medium solvent heated and sprayed also has the effect of increasing the temperature of the slag surface, it is possible to change the physical properties of the slag by both the composition change of the slag and the temperature increase of the slag. That is, the surface tension of the slag can also be changed.

Therefore, the inventors of the present invention, by spraying industrial oxygen gas or the like on the hot metal bath surface in the converter, influences the slag temperature when performing desiliconization and dephosphorization treatment of the hot metal, The effects of heating and non-heating, and the presence or absence of CaO-containing powder, that is, CaO powder spraying, were examined. Specifically, it is equipped with a top-blowing lance with a burner function that can blow industrial oxygen gas, CaO powder (solvent material), and burner combustion flames onto the molten iron bath surface, and a stirring gas from the bottom-blowing tuyere at the bottom of the furnace. A test operation was performed using a converter having a capacity of 300 tons capable of blowing in, and the molten slag temperature and the hot metal temperature during this test operation were measured. The temperatures of the molten slag and the hot metal were estimated from the change in thermoelectromotive force by a thermocouple with a temperature measuring probe attached to the tip of the sensor lance (sublance).

FIG. 1 is a schematic view of the converter equipment used in this test operation, that is, the converter equipment having an upper blowing lance with a burner function that uses a fuel gas such as natural gas. In FIG. 1, reference numeral 1 is an overall view of converter equipment, 2 is a converter (main body), 3 is a top blowing lance, 4 is a bottom blowing tuyere, 5 is hot metal, and 6 is injected from a top blowing lance. Oxygen gas jet, 7 is a CaO powder jet passing through the combustion flame of a burner using fuel gas (natural gas) as fuel, 8 is an oxygen gas supply pipe for supplying oxygen gas to the upper blowing lance 3, and 9 is A powder conveying pipe for supplying CaO powder to the upper blowing lance, 10 is a fuel gas supplying pipe for supplying natural gas or the like to the upper blowing lance, and 11 is for supplying cooling water for cooling the upper blowing lance. A cooling water supply pipe 12 is a cooling water discharge pipe for discharging the cooling water that has cooled the upper blowing lance.

The upper blowing lance 3 is a Laval type having 5 refining nozzles installed at its tip and an injection angle of 15°, and has a single-hole straight type powder blowing nozzle at the center. It has a burner function in which an annular fuel gas supply nozzle is arranged around it.

Table 1 shows the specifications of the 5-hole Laval nozzle type injection nozzle having the burner function arranged on the upper blowing lance 3. The injection angle of the injection nozzle is the relative angle between the axial direction of the oxygen gas jet of the injection nozzle and the axial direction of the upper blowing lance.

In the test operation, the basic conditions are a top-blown oxygen gas flow rate of 850 Nm ³ /min, a lance height of 3.0 m, and a bottom-blown gas flow rate of 50 Nm ³ /min. The speed is 600 kg/min, and when blowing natural gas, 40 Nm ³ /min, the slag basicity at the end of the desiliconization/dephosphorization treatment is 1.9, and the viscosity of the slag is 0.05 Pa·s at 1400°C. Aggregated CaO was added from the upper part of the furnace so as to be s or more.

In this test operation, the desiliconization and dephosphorization treatment was started from the time when the [Si] concentration in the hot metal was 0.3 mass% and was performed until the [Si] concentration in the hot metal became 0.01 mass%. .. Then, in this test operation, in order to investigate the difference in the molten slag temperature depending on the presence or absence of a burner and the presence or absence of powder spray,
(B) When fuel gas (natural gas) is not supplied and only refining oxygen gas and CaO powder are sprayed,
(B) When CaO powder is not sprayed and only refining oxygen gas and natural gas are sprayed,
(C) When all of the refining oxygen gas, natural gas and CaO powder are sprayed,
The three levels were compared and investigated.

FIG. 2 shows whether or not the fuel gas is used and whether CaO is sprayed or not when the CaO-based powder and granules are sprayed onto the hot metal bath surface together with the refining oxygen gas by using the above-mentioned top blowing lance with burner function. It shows the difference between the molten slag temperature and the hot metal temperature at the end of the desiliconization/phosphorus removal treatment. “(A) projection” in FIG. 2 is a case where the refining oxygen gas and CaO powder are injected without injecting natural gas, and “(B) burner” in FIG. 2 is CaO powder injection. 2 is a case where the refining oxygen gas and the natural gas are injected, and “(c) Burner+projection” in FIG. 2 is a case where the refining oxygen gas, the natural gas and the CaO powder are all injected. ..

As is clear from FIG. 2, the result was obtained that the temperature of the molten slag was higher than the hot metal temperature at any level. Above all, the levels of (b) and (c) above are higher than the level of (a) (when only the refining oxygen gas and CaO powder are sprayed), and the temperature of the molten slag is particularly high ( The effect of raising the temperature of the molten slag was conspicuous in the case of burner+projection. In this case, since the hot metal temperature at the end of the desiliconization/dephosphorization treatment was in the range of 1,300°C to 1,340°C at any level, the molten slag temperature at the level of (c) Was found to be about 1,600°C or higher.

Next, the above-mentioned desiliconization/phosphorus removal treatment was followed by intermediate slag treatment. The result is shown in FIG. In addition, the value defined by the following formula (1) was used as the intermediate waste ratio in FIG.

As is clear from FIG. 3, the intermediate slag ratio (%) is the case where the molten slag temperature becomes high at the end of the desiliconization/phosphorus removal treatment, that is, the case where the refining oxygen gas and natural gas are injected (b). It was found that the improvement was obtained at the level of the case (C) in which oxygen gas for refining, natural gas and CaO powder were injected. The surface tension of the sample having the same slag composition as that at this time was measured at 1,400° C., and it was about 490-530 mN/m, and at 1,500° C., it was reduced to about 400 mN/m.

After that, following the desiliconization/phosphorus removal treatment and the subsequent intermediate slag treatment, decarburization/phosphorus removal treatment was performed using the same converter. The top-blown lance 3 used in these treatments has the same burner function as that used in the above-mentioned desiliconization/phosphorus removal treatment, the top-blown oxygen gas flow rate is 1,200 Nm ³ /min, and the lance height is 2 The molten steel temperature at the end of decarburization and dephosphorization was 1,650 to 1, with 0.5 m, a bottom blowing gas flow rate of 50 Nm ³ /min, a CaO powder blowing rate of 600 kg/min, and a natural gas amount of 40 Nm ³ /min. 670° C., [C] concentration in molten steel is 0.03 to 0.06 mass%, [P] concentration in molten steel is 0.010 to 0.014 mass%, and slag basicity is 3.4 to 3.6. The amount of CaO powder blown in and the amount of iron ore added were adjusted. The natural gas was stopped when the CaO powder was blown in.

Figure 4 shows the total of the basic unit of the solvent material (CaO powder) used during desiliconization/dephosphorization treatment and decarburization/dephosphorization treatment. When only refining oxygen gas and CaO powder are sprayed (a), when CaO powder is not sprayed and when refining oxygen gas and natural gas are sprayed (b), refining oxygen gas, natural gas and It is a comparison of three levels of (C) when all of the CaO powder is sprayed.

As shown in Table 4, the basic unit of total solvent solution (CaO) used in desiliconization/dephosphorization treatment and decarburization/dephosphorization treatment decreases according to the intermediate slag ratio after desiliconization/dephosphorization treatment. Was there. In particular, it was found that when the refining oxygen gas, natural gas, and CaO powder were all sprayed from the top-blown lance during the desiliconization/phosphorus removal treatment (C), it was the lowest.

As described above, in addition to the spraying of the medium-melting material composed of the fine particles of oxygen gas for refining and CaO powder and the like, from the top-blowing lance 3 to the hot metal in the converter, fuel gas such as natural gas is simultaneously injected. In the case of the converter refining method according to the present invention in which desiliconization and dephosphorization are carried out by means of this, the medium-melting material becomes a heat medium and is sprayed onto the hot metal. As a result, by carrying out such refining, the hot metal or molten steel can be more effectively heated and the mixing ratio of iron scrap can be improved, and the temperature of the molten slag during desiliconization/dephosphorization treatment can be improved. You will also be able to increase. Therefore, even if the composition of the medium-melting material has a relatively high melting point, it can be surely dissolved. As a result, not only does the slag discharge rate increase due to the decrease in the viscosity of the slag after desiliconization/phosphorus treatment, but the surface tension decreases due to the increase in the molten slag temperature, making it easier to maintain the desired state of slag forming. Therefore, it becomes possible to remarkably improve the efficiency of waste during intermediate waste.

In the present invention, the desired surface tension of the slag after desiliconization/dephosphorization treatment, that is, the surface tension for promoting slag foaming and improving the intermediate slag removal property is preferably as low as possible, specifically 400 mN/ It is preferably m or less. The reason for this is that when the surface tension of this slag exceeds 400 mN/m, the slag is calmed down (the formed slag shrinks) as shown in FIG. 5, so the slag calms before the end of the intermediate slag. This is because the slag cannot be discharged sufficiently due to this. The more preferable surface tension of the slag is 200 mN/m or less.

As the method for measuring the surface tension of the molten slag, methods such as the static drop method and the maximum bubble pressure method are known, and these methods can be applied as the method for measuring the slag surface tension in the present invention. Further, a method of estimating the value of the surface tension by analyzing an image of the formation of an oxide drop and its dropping process is also known, and this method is also applied to the measurement of the surface tension of the slag targeted by the present invention. can do.

As a more preferred embodiment of the method of the present invention,
a) A model for estimating the slag composition from the amount of the solvent input, the amount of SiO ₂ produced, etc., and the hot metal temperature is prepared in advance.
b) Given the surface tension of the slag as a function of slag composition and temperature, based on the data measured or estimated in advance for the slag composition estimated by the model,
c) Adjusting the heat quantity of the burner so that the value of the surface tension of the slag in the treatment is in a suitable range,
There is a method such as.

This example is an example in which converter refining was performed using a top-bottom blowing converter (oxygen gas top blowing, stirring gas bottom blowing) as shown in FIG. 1 having a capacity of 300 tons. The upper blowing lance 3 used in this example is a Laval type with 5 holes for refining nozzles installed at its tip and an injection angle of 15°, and a single-hole straight type powder blown into the center. It has a burner function by disposing a fuel gas supply nozzle and an annular fuel gas supply nozzle around it. The refining nozzles were arranged at equal intervals on the same circumference with respect to the axial center of the upper blowing lance, the throat diameter (d _t ) was 76.2 mm, and the outlet diameter (d _e ) of the injection nozzle was 80. It is 0 mm.

In practice, iron scrap was charged into the upper-bottom blown converter, and then desulfurized hot metal at 1,310 to 1,360° C. that had been desulfurized beforehand was charged into the upper-bottom blown converter. Then, while blowing nitrogen gas into the hot metal from the bottom blowing tuyere 4 as a stirring gas, a combustion flame of natural gas is blown from the top blowing lance 3 through industrial oxygen gas, CaO powder and a burner. Desiliconization and dephosphorization treatment was performed by spraying toward the furnace, and then the generated desiliconization and dephosphorization slag was discharged to the outside of the furnace (intermediate slag). Next, while part of the desiliconization/dephosphorization slag and the hot metal after desiliconization/dephosphorization treatment are left in the furnace, while blowing argon gas into the hot metal from the bottom blowing tuyere 4 as a stirring gas. Then, industrial oxygen gas, natural gas and CaO powder were continuously sprayed from the top blowing lance 3 toward the hot metal bath surface for decarburization and dephosphorization. Table 2 shows the chemical components of the hot metal used at this time, and Table 3 shows the conditions of top blowing-bottom blowing during the desiliconization/dephosphorization treatment and the decarburization/dephosphorization treatment.

Under these conditions, the [Si] concentration in the hot metal at the end of the desiliconization/dephosphorization treatment is 0.01 mass%, the molten steel temperature at the end of the decarburization/dephosphorization treatment is 1650°C, and the [C] concentration in the molten steel is 0%. Each treatment time and the amount of iron ore added were adjusted so as to be 0.04 mass %.

In addition, a part of CaO added during the desiliconization/phosphorus removal treatment and the decarburization/phosphorus removal treatment is charged from a furnace hopper (not shown), and the rest is blown from the upper blowing lance 3. Add the total so that the basicity (mass% CaO/mass% SiO ₂ ) of the slag generated in the furnace will be 1.9 during desiliconization/dephosphorization treatment and 3.5 during decarburization/dephosphorization treatment. The amount was adjusted.

In order to confirm the effect of the present invention, in order to maximize the heating effect of the in-furnace slag, the blowing of the natural gas for fuel and CaO powder from the upper blowing lance 3 is perfectly synchronized, and the CaO powder is blown in. At the end of the process, the blowing of natural gas should be stopped and the blowing of natural gas and CaO powder from the top blowing lance 3 should be performed only during desiliconization and dephosphorization treatment along with the addition of massive CaO from the hopper on the furnace. Regarding the carried out example (Invention Example 1) and the example (Invention Example 2) in which natural gas and CaO powder were blown from the top blowing lance 3 in all of the processing steps of desiliconization/dephosphorization, decarburization/dephosphorization It is summarized in Table 4. In Table 4, with respect to Inventive Examples 1 and 2, and Comparative Examples 1 to 5, the surface tension of the slag at the end of the desiliconization/dephosphorization treatment in each example is 400 mN/in both of the inventive examples 1 and 2. Although it was m or less, it was confirmed that Comparative Examples 1 to 5 were all over 400 mN/m. In addition, in Invention Examples 1 and 2 and Comparative Examples 1 to 5, the slag having a viscosity of 0.05 Pa·S or more at 1,400° C. is used so that the dephosphorization ability is not hindered.

In addition, in the comparative example shown in Table 4, the natural gas and the CaO powder were not simultaneously blown from the upper blowing lance 3. That is, an example in which only a burner flame was formed during decarburization/dephosphorization treatment (Comparative Example 2), a CaO powder alone was blown without forming a burner flame during decarburization/dephosphorization treatment, An example in which only a burner flame was formed during the phosphorus treatment (Comparative Example 3), only the burner flame was formed in the initial stage of the desiliconization/dephosphorization treatment, and the burner flame was extinguished in the latter stage of the desiliconization/dephosphorization treatment to CaO. An example in which only the powder was blown and only a burner flame was formed during decarburization/dephosphorization treatment (Comparative Example 4), and both during desiliconization/dephosphorization treatment and decarburization/dephosphorization treatment It is an example (Comparative Example 5) in which only CaO powder was blown in without forming a burner flame. However, the converter equipment and the operating method other than the above were in accordance with the above-mentioned invention examples.

As can be seen from the results shown in Table 4, the refining times (the time required from the charging of the iron scrap to the tapping and the end of the slag) of the invention examples 1 and 2 and the comparative examples 1 to 5 were almost the same. However, in the comparative example, the CaO unit consumption increased and the iron yield decreased as compared with the invention example. On the other hand, in the case of refining (Invention Examples 1 and 2) to which the method of the present invention is applied, particularly in the case of desiliconization/phosphorus dephosphorization slag having a surface tension of 400 mN/m or less due to a solvent medium by a burner flame and a slag heating effect, It was confirmed that not only the improvement of slag discharge capacity but also the reduction of CaO intensity and the improvement of iron yield can be achieved by the operation of the converter.

The converter refining method according to the present invention can be applied to steel refining techniques other than the converter.

1 Converter Equipment 2 Converter 3 Top Blowing Lance 4 Bottom Blowing Tuyere 5 Hot Metal 6 Oxygen Gas Jet 7 CaO Powder Jet 8 Oxygen Gas Supply Pipe 9 Powder Transfer Pipe 10 Fuel Gas Supply Pipe 11 Cooling Water Supply Pipe 12 Cooling Water Discharge tube

Claims (6)

In a converter refining method for producing molten steel from hot metal by the same converter,
After performing the desiliconization and dephosphorization treatment by charging scrap metal and hot metal into the converter, and spraying the medium solvent consisting of powdery particles containing CaO together with industrial oxygen gas from the top blowing lance on the hot metal bath surface. By using an upper blowing lance having a burner function, the medium-melting material is heated by the combustion flame of the burner and then sprayed onto the hot metal bath surface, and the generated slag after desiliconization/dephosphorization treatment is at a temperature higher than the hot metal temperature. The method for refining a converter is characterized in that the temperature of the slag is used for intermediate slag treatment. In the same converter, desiliconization and dephosphorization of hot metal is first performed using slag having a viscosity of 0.05 Pa·s or more at 1,400°C, and then decarburization and dephosphorization are performed to produce molten steel. In the converter refining method to
After performing the desiliconization and dephosphorization treatment by charging scrap metal and hot metal into the converter, and then spraying the medium solvent consisting of powdered particles containing CaO together with industrial oxygen gas from the top blowing lance onto the hot metal bath surface. By using an upper blowing lance having a burner function, the medium-melting material is heated by the combustion flame of the burner and then sprayed on the hot metal bath surface to generate slag after desiliconization/dephosphorization treatment, which is higher than the hot metal temperature. The method for refining a converter is characterized in that the temperature of the slag is used for intermediate slag treatment. 3. The converter refining method according to claim 1, wherein the slag after the desiliconization/phosphorus removal treatment has a surface tension of 400 mN/m or less and is subjected to the intermediate slag treatment. A converter refining method for producing molten steel by first performing desiliconization and dephosphorization treatment of hot metal by the same converter, and then performing decarburization and dephosphorization treatment,
First, after scrap and hot metal are charged into the converter, a desolvation/dephosphorization treatment is performed by spraying a medium-soluble material consisting of industrial oxygen gas and powder containing CaO from the top blowing lance onto the hot metal bath surface. Then, while discharging a part of the slag generated after this desiliconization/dephosphorization treatment to the outside of the furnace, the inside of the furnace is degassed/dephosphorized hot metal and the slag remaining after the desiliconization/phosphorus treatment And the demolition and dephosphorization-treated hot metal in the furnace are sprayed with the refining oxygen gas together with the refining oxygen gas from the top blowing lance to remove the hot metal. Performs charcoal/dephosphorization treatment, and then taps the decarburized/dephosphorized molten steel remaining in the furnace into a molten steel ladle, while removing a portion of the decarburized/dephosphorized slag remaining in the furnace or When manufacturing the molten steel by discharging the whole outside the furnace,
In performing the desiliconization/phosphorus removal treatment, the industrial oxygen gas and the medium-dissolving material are heated by the combustion flame of the burner for the medium-dissolving material by using an upper blowing lance having a burner function. A converter smelting method, which comprises subjecting the produced slag after desiliconization/dephosphorization treatment at a temperature equal to or higher than the hot metal temperature to an intermediate slag treatment by spraying on a hot metal bath surface. In the same converter, desiliconization and dephosphorization of hot metal is first performed using slag having a viscosity of 0.05 Pa·s or more at 1,400°C, and then decarburization and dephosphorization are performed to produce molten steel. A converter refining method that
First, after charging scrap and hot metal into the converter, a desolvation/dephosphorization treatment is carried out by spraying a medium-soluble material consisting of powder particles containing industrial oxygen gas and CaO from the top blowing lance onto the hot metal bath surface. Then, while discharging a part of the slag generated after this desiliconization/dephosphorization treatment to the outside of the furnace, the inside of the furnace is degassed/dephosphorized hot metal and the slag remaining after the desiliconization/phosphorus treatment And the demolition and dephosphorization-treated hot metal in the furnace are sprayed with the refining oxygen gas together with the refining oxygen gas from the top blowing lance to remove the hot metal. Performs charcoal/dephosphorization treatment, and then taps the decarburized/dephosphorized molten steel remaining in the furnace into a molten steel ladle, while removing a portion of the decarburized/dephosphorized slag remaining in the furnace or When manufacturing the molten steel by discharging the whole outside the furnace,
In performing the desiliconization/phosphorus removal treatment, the industrial oxygen gas and the medium-dissolving material are heated by the combustion flame of the burner for the medium-dissolving material by using an upper blowing lance having a burner function. A converter smelting method, which comprises spraying a hot metal bath surface and subjecting the produced slag after desiliconization/dephosphorization treatment at a temperature equal to or higher than the hot metal temperature to an intermediate slag treatment. The converter smelting method according to claim 4 or 5, wherein the slag after the desiliconization/phosphorus removal treatment has a surface tension of 400 mN/m or less and is subjected to the intermediate slag treatment.

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