JP2001181724A - Hot metal refining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten iron refining method, in which the occurrence of slag can be reduced as far as possible, the manufacturing cost of the molten steel can be reduced, and the efficient and stable dephosphorizing treatment and decarburizing treatment can be carried out by using the slag containing substantially no fluorine. SOLUTION: This molten iron refining method comprises carrying out at least the dephosphorizing process and the decarburizing process in this order to the molten iron having <=0.2 wt.% silicon concentration. In the dephosphorizing process, raw material consisting substantially of no fluorine and essentially of lime stone powder, is granulated. By using a reforming agent obtained by carrying out the heating treatment to the granulated raw material, the phosphorus concentration in the molten iron is substantially lowered to a phosphorus concentration level of a product with the slag amount having <=30 kg/T and thereafter, the decarburizing process is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environment-friendly hot metal refining method which is resource-saving, energy-saving and generates less slag than conventional methods.

[0002]

2. Description of the Related Art Conventionally, in the process of refining hot metal using a converter, oxygen is blown to the hot metal to cause carbon and silicon in the hot metal to react with oxygen, thereby converting them into CO and S, respectively.
Separated and removed from the hot metal as iO ₂ , and by adding quick lime (CaO) into the furnace to combine sulfur and phosphorus in the hot metal with CaO, these are separated and removed from the hot metal, and thereby carbon, It has been practiced to reduce silicon, sulfur, and phosphorus to predetermined concentrations that are acceptable for steel products.

[0003] In contrast to the conventional method in which carbon, silicon, phosphorus and the like are simultaneously removed using such a converter, phosphorus has been recently removed in advance in a hot metal stage (hot metal preliminary dephosphorization treatment). ing. In such a process, the amount of slag required for dephosphorization in converter blowing can be significantly reduced, and as a result, manganese ore is charged during blowing and It has become possible to increase the manganese reduction rate from slag and reduce the amount of manganese alloy iron added during or after tapping. In addition, such a process not only reduces the amount of manganese alloy iron used, but also facilitates the production of high-quality steel such as low-phosphorus steel.
The effect of reducing the amount of slag generated in the total steelmaking can be obtained.

[0004] Various measures have also been taken to further enhance the above-mentioned effects, such as reducing the silicon concentration in the hot metal before the dephosphorization treatment and reducing the phosphorus concentration in the hot metal after the dephosphorization treatment. For example, it is being reduced to the phosphorus concentration level of steel products. By these reducing the hot metal in the silicon concentration before dephosphorization process as in the former, it is possible to produce a high slag of high basicity dephosphorization capacity (CaO / SiO ₂₎ with a small amount of lime addition In addition, efficient dephosphorization can be performed with a small amount of slag. In order to reduce the silicon concentration in the hot metal before the dephosphorization treatment, a technique for reducing the silicon content of the hot metal in a blast furnace and an oxidative desiliconization treatment after tapping can be used. Conventionally, molten iron from a blast furnace has a silicon concentration of 0.1.
Although it was 35 to 0.45 wt% or more, it has been reported that hot metal having a silicon concentration of about 0.2 wt% can be produced by the technique for reducing the silicon content of hot metal. In addition, in the oxidative desiliconization treatment after tapping, a solid oxygen source is added to the blast furnace cast floor to perform desiliconization treatment, or oxygen-containing gas is blown and blown into a vessel such as a hot metal ladle or a mixed iron cart (hereinafter referred to as a blast furnace). By carrying out the desiliconization while adding a solid oxygen source), it is possible to reduce the silicon concentration in the hot metal to 0.1 wt% or less.

On the other hand, by lowering the phosphorus concentration in the hot metal after the dephosphorization treatment to the phosphorus concentration level of the steel product as in the latter, slag for dephosphorization is not required in the subsequent decarburization step, and a small amount of slag is required. Decarburization refining can be performed with slag,
Manganese can be recovered from manganese ore at a high yield. At present, it is relatively easy to reduce the phosphorus concentration in hot metal to 0.015 wt% or less, which is the required level of steel products, by a dephosphorizing agent and a dephosphorizing treatment with a limited treatment condition.

[0006]

However, the above-described refining process of hot metal is effective for reducing the amount of slag, but has the following problems with respect to dephosphorization conditions. That is, in order for CaO such as added quicklime to efficiently react with phosphorus or sulfur in the hot metal, Si
It is necessary to melt CaO by reacting with O ₂ or FeO. In order to produce a melt having a high dephosphorizing ability in a CaO—SiO ₂ —FeO system, the weight ratio of CaO / SiO _{2 in} the composition needs to be 3.0 or more. Is determined.

Conventionally, measures have been taken to promote the melting by appropriately adding fluorite (CaF ₂ ) to increase the amount of CaO melt produced. However, the slag to which fluorite is added contains CaF _{2 even} though it is in a small amount, and in particular, recently, the elution of fluoride ions from the slag is undesirable from the viewpoint of environmental conservation. There is a trend to tighten the regulation of quantity, and this is becoming one factor that restricts the use of converter slag.

When the concentration of silicon in the hot metal before the dephosphorization treatment is reduced in order to reduce the amount of slag as described above, the melting action of the CaO source by SiO ₂ generated during the dephosphorization treatment may be reduced. In addition, when a slag substantially containing no fluorine is used for the above-described reason, a countermeasure for compensating for a decrease in the melting action due to the slag not containing fluorine is required. In particular, when dephosphorization is performed in a hot metal pot or mixed iron wheel with a small amount of acid supply and a low stirring capacity, it is generated as compared to a case where a large-scale acid supply equipment or exhaust equipment such as a converter is used. The amount of FeO and the amount of melt produced by stirring tend to be insufficient, and the necessity of measures for accelerating the melting is increased. .

Also, in the dephosphorization step using a converter capable of supplying a large amount of acid, if the amount of decarburization by the acid supply increases, the heat margin in the subsequent decarburization step decreases, and the amount of scrap used and the amount of manganese ore are reduced. Is limited. Therefore, in the dephosphorization step in the converter, if dephosphorization can be efficiently performed with a small amount of acid supply, an improvement in heat balance and manganese yield can be expected. Also, in the decarburization step in the converter, it is necessary to increase the basicity of the slag in order to sufficiently reduce the manganese ore added under the condition that the amount of generated SiO ₂ is small, and when fluorite is not added. Similarly, it is necessary to ensure the melting action.

Incidentally, in order to promote the melting of the granular CaO source added into the furnace in the dephosphorization treatment, for example,
NIRogovtsev et al. Have shown that refining CaO particles coated with iron oxide on the surface of the particles at the stage of manufacturing in a rotary kiln are effective for rapid dephosphorization (St.
eel in the USSR, July (1972), p518-520). Also, Ma
rk Lee et al. also reported that a similar refining agent obtained by a similar process was extremely effective for dephosphorization and desulfurization in a converter (Electric Furmace Conference).
(1996), p539-549). Also, Japanese Patent Application Laid-Open No. 61-217513
In the publication, calcium ferrite (2CaO—Fe ₂
A method for dephosphorizing hot metal using a low melting point sintered ore having a composition of O ₃ , CaO—Fe ₂ O ₃ , and CaO-2Fe ₂ O ₃ is disclosed.

However, these refining agents have not been put to practical use because it is extremely difficult to mass-produce them industrially and the production cost is high. In other words, since the calcium ferrite refining agent has a low melting point, when manufactured using a packed bed type heating furnace, the melting of the filler and the sintering of the filler occur, which hinders the flow of the filler. As a result, the operation of the heating furnace itself becomes difficult. Also, when a rotary kiln is manufactured using a rotary kiln, a large amount of melt adheres to the inner wall of the kiln in a layered manner, so that the operation must be interrupted frequently to remove the melt. It becomes possible. Furthermore, when manufactured using a sintering machine, as described above, the calcium ferrite-based refining agent has a low melting point, so that the permeability of the sintered layer is very poor, and even in this case, stable production is impossible. is there.

[0012] Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to improve the efficiency by using a slag substantially containing no fluorine which adversely affects the environment even under the condition that the amount of generated SiO ₂ is small. It is an object of the present invention to provide a hot metal refining method capable of performing efficient and stable dephosphorization refining and decarburization refining and reducing the amount of generated slag.

[0013]

The refining method for achieving the above object is a refining method capable of reducing the amount of slag generated as much as possible, reducing the energy lost by slag, and reducing the amount of manganese alloy used. And
It is necessary that the refining method uses a refining agent that easily melts even under the condition that the amount of generated SiO ₂ is small and does not contain fluorine, and that has high dephosphorization ability. In other words, instead of a low melting point calcium ferrite-based dephosphorizing agent, which was conventionally difficult to produce stably at low cost, a refining agent that can be produced at a low production cost using inexpensive raw materials is used. It is necessary to stably exert phosphorous ability.

[0014] The refining agent should not be hindered by the adhesion of the refining agent to the wall of the production container or the bonding of grains during the production, and can be rapidly melted during use. is necessary. Furthermore, it is necessary that the refining agent be capable of dephosphorization using a hot metal transfer vessel such as a hot metal ladle or a mixed iron wheel, which is currently the mainstream of the dephosphorization process.

The present invention has been made as a result of studying optimum refining conditions from such a viewpoint, and has the following features. [1] In a method for refining hot metal in which at least a dephosphorization step and a decarburization step are performed in this order with respect to hot metal having a silicon concentration of 0.20 wt% or less, the dephosphorization step contains substantially no fluorine, In addition, a raw material mainly composed of limestone powder is granulated, and a refining agent obtained by heat-treating the granulated material is used.
A method for refining hot metal, comprising reducing the phosphorus concentration in hot metal substantially to the phosphorus concentration level of a product with a slag amount of g / T or less, and then performing a decarburization step.

[2] In the method for refining hot metal according to the above [1], the amount of newly generated slag is 20 kg in the decarburization step.
/ T or less. [3] In the hot metal refining method of the above [2], in the decarburization step, a raw material substantially containing no fluorine and mainly composed of limestone powder is granulated and obtained by heat-treating the raw material. A method for refining hot metal, comprising using a refining agent.

[4] In the method for refining molten iron according to any one of the above [1] to [3], the refining agent is used as a pretreatment for calcining limestone powder having a particle size of less than 5 mm and limestone generated during limestone mining. A refining agent obtained by granulating one or more types of limestone powder selected from limestone powder having a particle size of less than 5 mm generated in a washing step of a raw limestone, and subjecting the granulated limestone powder to heat treatment. Hot metal refining method. [5] In the method for refining hot metal according to any one of [1] to [4], the refining agent is obtained by heat-treating the granulated raw material in a solid furnace, a rotary kiln, a fluidized bed furnace or a moving bed furnace. A method for refining hot metal, characterized in that the refining agent is a refiner.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below together with the reasons for limiting the same. In the method for refining hot metal of the present invention, the silicon concentration is 0.20 wt% or less, preferably 0.10 wt%.
This is a refining method in which at least the dephosphorization step and the decarburization step are performed in this order on the following hot metal. Silicon concentration is 0.20w
In order to obtain hot metal of not more than t%, the hot metal discharged from the blast furnace is usually desiliconized in a desiliconization step. However, when the silicon concentration of the hot metal spouted from the blast furnace is 0.20% by weight or less, the dephosphorization treatment described later can be performed without performing the desiliconization treatment. In this case, a desiliconization step described later can be omitted. On the other hand, even when the silicon concentration of the hot metal spiked from the blast furnace is 0.20% by weight or less, it can be further desiliconized to further reduce the silicon concentration.

By reducing the silicon concentration in the hot metal to 0.20% by weight or less, the amount of high basicity slag required for dephosphorization in the subsequent dephosphorization step can be sufficiently reduced. Here, it is easier to make slag of high basicity in the dephosphorization step, and it is advantageous to reduce the amount of slag generated in the dephosphorization step, since the silicon concentration of the hot metal is reduced as much as possible. Preferably, it is reduced.

Generally, hot metal from a blast furnace is poured and stored in a hot metal transfer vessel such as a hot metal ladle or a mixed iron wheel via a blast furnace casting bed. It may be carried out in either the silicification treatment or the desiliconization treatment in the hot metal transport container, or both. In addition, the desiliconization treatment may be performed in the process of pouring the hot metal from the blast furnace cast floor into the hot metal transport container. According to the required amount of desiliconization and the desiliconization processing capability at each processing position, the desiliconization processing of the processing form selected from these is performed.

In the desiliconization treatment, an oxygen source is added as a desiliconizing agent, and if necessary, a medium such as quicklime or the like may be used as a medium solvent.
The aO content is added to adjust the basicity of the slag. As a desiliconizing agent, a solid oxygen source such as iron ore or mill scale,
Alternatively, any of a gaseous oxygen source such as oxygen or an oxygen-containing gas may be used, or both may be used in combination.

In the desiliconization treatment, it is effective to sufficiently stir the hot metal by gas stirring or the like and to forcibly mix the desiliconizing agent and the hot metal in order to increase the desiliconization efficiency. In this regard, the desiliconization treatment performed in a container such as a hot metal pot is more efficient than other methods, such as desiliconization treatment in a blast furnace cast floor, because the shape of the container can stir the hot metal. Therefore, in order to obtain particularly excellent desiliconization efficiency, perform desiliconization in a vessel such as a hot metal pot, or desiliconization in a blast furnace cast bed, and then desiliconization in the vessel. Is preferably performed. Such a container may be any one provided with a supply means of a medium solvent and a desiliconizing agent and a function of a stirring means for hot metal, such as a ladle such as a hot metal ladle described above, a mixed iron wheel, and other desalting machines. Any of the containers dedicated to silicon may be used.

The addition of a desiliconizing agent or a solvent is carried out by placing the molten metal on a hot metal bath or by pouring the molten metal into the bath. For example, in the desiliconization process using a hot metal pot, a gaseous oxygen source is sprayed on the hot metal bath surface through a lance for acid supply, and a medium solvent such as stirring gas and quicklime powder is blown into the hot metal through an immersion lance. The solid oxygen source is placed above the hot metal bath surface and charged according to the temperature.

[0024] In the dephosphorization step, the molten iron having a silicon concentration of 0.20 wt% or less as described above is treated with a refining agent (dephosphorizing agent) substantially containing no fluorine to obtain 30 kg / mol.
T (T: per ton of hot metal; the same applies hereinafter) The dephosphorization treatment is performed with an amount of slag of less than or equal to, and the phosphorus concentration in the hot metal is substantially reduced to the phosphorus concentration level of the product. The refining agent does not substantially contain fluorine, and therefore does not prevent the refining agent from containing a small amount of fluorine as an unavoidable impurity.

In the dephosphorization step, it is effective to reduce the amount of slag that the hot metal to be dephosphorized is a low silicon hot metal having a silicon concentration of 0.20 wt% or less, but it is effective to reduce the amount of slag efficiently. To perform the phosphorus treatment, it is necessary to generate a slag having a high dephosphorization ability. For this purpose, it is necessary to increase the basicity of the slag. Therefore, it is preferable to minimize the mixing of desiliconized slag and the like. Therefore, in the dephosphorization step, hot metal from which the slag of the previous step has been separated and removed is used. Separation / removal of the slag can be performed by a mechanical waste disposal device or a manual operation.

There is no particular limitation on the container used in the dephosphorization step, and the dephosphorization treatment can be performed using a ladle type container such as a hot metal ladle, a mixed iron wheel, a converter type container or the like. Further, the dephosphorization treatment may be performed in the same vessel subsequent to the desiliconization treatment, or may be performed by transferring to another vessel such as a converter.

In the dephosphorization step in the refining method of the present invention,
As a refining agent, a raw material substantially containing no fluorine and mainly composed of limestone powder is granulated, and dephosphorization is performed using a refining agent obtained by heat-treating the raw material. This refining agent can be mass-produced inexpensively and stably, and has a high porosity due to granulation of limestone powder, even though it does not substantially contain fluorine. In this case, the porosity becomes higher and the contact area with the slag increases, so that the slag easily melts and has a high dephosphorization ability. For this reason, the dephosphorization reaction can be efficiently promoted even in a dephosphorization process having a low acid-supplying capacity, such as a dephosphorization treatment performed in a hot metal transport container. Among them, the refining agents described below are particularly excellent in production cost and dephosphorization ability.

Limestone powder, which is the main raw material of the refining agent, may be procured from any source, but is used as a pretreatment for limestone powder having a particle size of less than 5 mm generated during limestone mining and for calcination of limestone. It is preferable to use one or more kinds selected from limestone powder having a particle size of less than 5 mm generated in the washing step of the raw limestone. Such limestone powder can be obtained relatively inexpensively, and can lead to effective use of fine limestone that is treated as waste, thereby conserving resources and reducing raw material costs. It is also available at a much lower cost than grinding limestone.

If the particle size of the limestone powder is 5 mm or more, the porosity of the refining agent produced from the limestone powder is reduced, and rapid slag formation is inhibited, and sufficient dephosphorization ability is not exhibited. For such rapid slag making, it is necessary to finely granulate the limestone powder, but it is not necessary to excessively finely granulate the limestone powder. Unless fine particles are naturally obtained in the process of collecting from the mine, even if crushed with a crusher, there are economical problems such as crushing energy and yield. is there.

The refining agent is obtained by mixing and granulating limestone powder,
It is manufactured by heating at an appropriate temperature. For mixing limestone powder, a conventional mixer such as a drum mixer can be used, and for granulation, a conventional granulator such as a pelletizer can be used. The heat treatment after granulation can be performed using a general hard furnace, rotary kiln, fluidized bed furnace or moving bed furnace, etc., with the purpose of drying or drying / drying and decarbonating the granulated material by any of these. Heat treatment is performed.

The heating temperature ranges from a relatively low temperature treatment of about 200 to 400 ° C. for drying attached moisture to a relatively high temperature treatment of 1100 ° C. or more for decarbonation treatment in a short time. It can be selected as appropriate. This is because, when the phosphorus concentration of the hot metal before the dephosphorization treatment is low or the gangue content in the manganese ore is small, the dephosphorization treatment and decarburization treatment can be performed with a small amount of refining agent. Even if the heating temperature is lowered within a range that does not cause problems such as powdering at the time, the amount of heat absorbed by decomposition of carbonic acid is small even if carbonic acid remains, and thermal problems such as temperature effects during processing are small. It is. Here, the decarboxylation treatment is a treatment for removing carbonic acid (CO ₂ ) in calcium carbonate, which is a main component of limestone, by heating.

By performing the heat treatment under the above-described conditions, for example, the flow of the filling material is hindered when the heat treatment is performed using a fluidized bed furnace, or the inner wall of the kiln is melted when the heat treatment is performed using a rotary kiln. It is possible to appropriately prevent manufacturing troubles such as a substance adhering in layers.

In the dephosphorization step in the refining method of the present invention,
The dephosphorization treatment is performed at a slag amount of 30 kg / T or less. However, since the above-described refining agent having a high dephosphorization ability is used, the dephosphorization reaction can proceed promptly.
Even at 0 kg / T or less, the phosphorus concentration in the hot metal is substantially reduced to the phosphorus concentration level of the product, specifically 0.00% depending on the product type.
It can be reduced to about 5 to 0.015 wt%.

The dephosphorization treatment is carried out by adding the above-mentioned refining agent on the surface of the hot metal bath, adding it by blowing into the hot metal bath, or using both together. Then, in order to make the dephosphorization reaction between the slag and the hot metal proceed more quickly, it is preferable to carry out acid supply to the hot metal bath surface and blowing of a stirring gas into the bath. Generally, in the dephosphorization process using a ladle-type vessel such as a hot metal ladle or a converter-type vessel, the acid supply is performed through an upper blowing lance, and the stirring gas is supplied through an immersion lance or a tuyere provided at a furnace bottom (blowing nozzle). ) Through the bath.

When performing the dephosphorization treatment in a converter type vessel, the amount of acid supply is preferably 2.0 Nm ³ / min · T or less in terms of pure oxygen. From the viewpoint of iron oxide generation, which is one of the purposes of acid transfer, an increase in the amount of acid transfer can be expected to increase the amount of iron oxide generated. However, the amount of acid transfer is 2.0 Nm ³ / min ·
If it exceeds T, it becomes difficult to control the action of oxygen on the bath, and the amount of reduction of the iron oxide once generated increases. In addition, since the decarburization of the hot metal proceeds due to an increase in the amount of reduction of the iron oxide, the heat retained in the bath is consumed, and problems such as a loss of heat margin in the subsequent decarburization step are likely to occur. In other words, iron oxide generated by acid transfer is useful for slag making,
If the amount of acid transfer exceeds 2.0 Nm ³ / min · T, adverse effects such as decarburization occur, so the amount of acid transfer is 2.0 Nm ³ / m.
It is preferable to be in · T or less.

FIG. 1 schematically shows an example of a dephosphorization process using a converter type vessel. In this example, oxygen is blown into a converter 1 through an upper blowing lance 2 and installed at the furnace bottom. Stirring gas is blown into the hot metal 5 from the tuyere 4 and the raw material 7 such as a refining agent and a solid oxygen source is
Is added from the raw material input device 3 above the slag 6
Is formed. In addition, when performing dephosphorization treatment in a container other than a converter type container such as a hot metal transfer container (for example, a ladle type container such as a hot metal ladle, a mixed iron wheel, etc.)
The stirring power is weaker than that of the converter type container, and the reaction between the hot metal and the slag is slow. It is preferable to be 1.0 Nm ³ / min · T or less in terms of pure oxygen.

In the decarburization step, the amount of slag for newly generating low silicon and low phosphorus hot metal is increased to 20 kg /
Blowing is performed below T. In the decarburization step in the refining method of the present invention, since the phosphorus concentration in the hot metal has substantially decreased to the phosphorus concentration level of the product in the prior dephosphorization step, substantial dephosphorization is necessary in the decarburization step. Not done. For this reason,
A small amount of slag is required as a diluent for iron oxide generated during blowing and as a cover slag to suppress scattering and heat radiation of droplets from the bath surface, but slag for dephosphorization is required. do not do.

Therefore, it is important that the slag in the decarburization step in the method of the present invention has a function of efficiently promoting the reduction reaction of the manganese ore. A small amount of only the basicity adjustment according to the gangue content from the added iron ore and manganese ore is sufficient, and the amount of slag generated for the treated hot metal is 20 k.
g / T or less. It is preferable to use the above-described refining agent as a medium solvent in order to rapidly generate high basicity slag and promote reduction of manganese. In addition, the refining ability of the slag is not essential, and there is no problem with a slight variation in the slag composition. Therefore, the slag can be used repeatedly by, for example, operating the slag in a furnace.

In the decarburization step in the refining method of the present invention, the amount of slag during the decarburization treatment is small, and therefore, when the amount of acid supply is large, the decarburization reaction becomes intense, and the slag is not trapped by the slag, and is not collected as slag. Since the amount of iron discharged to the outside increases and the iron yield decreases, in order to prevent this, the amount of acid transported in the decarburization step is preferably set to 4 Nm ³ / min · T or less in terms of pure oxygen.

[0040]

EXAMPLES Hot metal refined from a blast furnace was refined in a series of steps including de-siliconization of a blast furnace, desiliconization of a hot metal ladle, dephosphorization of a converter, and decarburization of a converter. In this embodiment, molten iron having a silicon concentration of about 0.35 wt% from a blast furnace is subjected to a desiliconization treatment in a blast furnace casting bed and a molten iron pot to obtain a silicon concentration of 0.20 wt%.
It was desiliconized to the following. In the desiliconization step in the hot metal pot, nitrogen gas is blown into the bath at a supply rate of about 0.01 Nm ³ / min · T from a lance immersed in the hot metal while stirring the hot metal,
Add gaseous oxygen or iron oxide according to the required amount of desiliconization,
The desiliconization reaction was allowed to proceed.

After the desiliconization treatment, the generated slag was discharged, and the hot metal was charged into a converter for dephosphorization treatment. The hot metal temperature before the dephosphorization treatment was 1310 to 1355 ° C. As a dephosphorizing agent, a limestone powder having a particle size of 5 mm or less generated in a washing step of limestone rough stone which is performed as a pretreatment for calcining limestone is mixed with a drum mixer, and then 20 to 30 mm with a pelletizer.
A refining agent obtained by subjecting the mixture to heat treatment with a rotary kiln was used. The heating temperature in a rotary kiln is 1100 ° C as standard, 400 ° C, 900 ° C,
And 1200 ° C.

Since the amount of the refining agent added as a dephosphorizing agent is determined according to the phosphorus concentration of the hot metal to be treated, the amount of the refining agent added is small in the hot metal having a low silicon concentration. There was a difference in the amount of slag. In this example, the amount of the refining agent was adjusted so that the basicity of the slag generated was 4 or more. In addition, while supplying a nitrogen gas of about 0.7 Nm ³ / min · T from the tuyere at the bottom of the furnace and stirring the hot metal, acid is supplied from the upper blowing lance, and oxygen is supplied in accordance with the oxygen amount of the iron oxide placed above. The amount is about 12 Nm ³ / T
It was adjusted to become. The dephosphorization treatment was constant for 8 minutes, and the hot metal temperature at the end of the dephosphorization treatment was 1320 to 1340 ° C. Further, in order to lower the degree of oxidation of the slag at the end of the dephosphorization treatment, T.P. Fe
The concentration was adjusted to 2% by weight or less.

The hot metal after the dephosphorization treatment in the converter was once discharged into a charging pan and then re-charged into another converter, and subjected to a decarburization treatment mainly for final decarburization. . In this decarburization treatment, nitrogen gas or argon gas is blown in from the tuyere at the bottom of the furnace at a supply rate of about 0.12 Nm ³ / min · T to stir the hot metal while 3.2 Nm ³ / min ·
The acid was fed with the amount of T fed.

In this decarburization step, the above-mentioned refining agent was added as a solvent so that the basicity of the slag was about 3.3 with respect to SiO ₂ mixed from manganese ore or the like. After the decarburization treatment, the entire amount of slag in the furnace was discharged, and the decarburization treatment was continued in a state where no slag remained except for the amount adhered to the furnace wall in the furnace. In this decarburization process, slag is formed a refining agent to be added according to the SiO ₂ which is mixed manganese ore mainly, residual manganese to the slag became manganese loss. In this decarburization step, the carbon concentration in the molten steel at the end of the treatment was 0.09 wt%, and the molten steel temperature was 164.
The temperature was controlled to be 5 ° C.

Further, for comparison, Comparative Example 1 in which the other conditions were the same as those of the present invention, the slag amount in the decarburization step was out of the conditions of the present invention, and the silicon concentration of the hot metal was out of the conditions of the present invention, Comparative Example 2 in which the amount of slag in the dephosphorization step was out of the conditions of the present invention, while using massive quicklime having a particle size of 20 to 30 mm in the dephosphorization step and the decarburization step, the amount of slag in the decarburization step was out of the conditions of the present invention. Comparative Example 3, a dephosphorization step using a massive quicklime having a particle size of 20 to 30 mm in the dephosphorization step and the decarburization step, and a dephosphorization step using a massive quicklime having a particle size of 20 to 30 mm in the dephosphorization step and the decarburization step Comparative Example 5 in which the amount of slag was outside the conditions of the present invention was also carried out. Table 1 shows processing conditions and processing results of a series of steps in the present invention examples and comparative examples.

[0046]

[Table 1]

FIG. 2 shows the relationship between the silicon concentration in the hot metal before the dephosphorization treatment and the phosphorus concentration in the hot metal after the dephosphorization treatment among the results shown in Table 1. As shown in Table 1 and FIG. 2, in Comparative Examples 3 and 4 using massive quicklime, the hot metal phosphorus concentration after the treatment was high, and it was not possible to dephosphorize to the phosphorus concentration level of the product. In Comparative Example 5, the concentration of hot metal phosphorus could be reduced to the phosphorus concentration level of the product, but in this case, a large amount of massive quicklime was required. In Comparative Example 2 in which the silicon concentration of the hot metal was high, the phosphorus concentration of the hot metal could not be reduced to the product phosphorus concentration level even though a large amount of the refining agent was used. On the other hand, in the present invention example, since the used refining agent is easily melted, it was possible to reduce the phosphorus concentration level of the product in a short time. In addition, it was found that substantially the same dephosphorizing effect can be obtained even when the heating temperature after granulation was changed as shown in Examples 9 to 11 of the present invention.

FIG. 3 shows the relationship between the silicon concentration in the hot metal before the dephosphorization treatment and the manganese yield in the decarburization step among the results shown in Table 1. As shown in Table 1 and FIG. 3, the manganese yield is low in Comparative Example 1 in which the amount of slag is out of the range of the present invention and Comparative Examples 3 to 5 using massive quicklime. In particular, Comparative Example 3 in which the amount of slag was out of the range of the present invention and using massive quicklime had the worst manganese yield. On the other hand, in the present invention example, the used refining agent is easily melted, and a high basicity slag suitable for the reduction of manganese ore can be produced with a small amount of the refining agent, so that a high manganese yield can be obtained. I have.

FIG. 4 shows the relationship between the silicon concentration in the hot metal before the dephosphorization treatment and the total amount of slag generated in the dephosphorization step and the decarburization step in the results shown in Table 1. As shown in Table 1 and FIG. 4, in the refining method according to the present invention, in the steps from the decarburization step to the decarburization step, 50 kg / T
It is found that it is possible to smelt steel having a desired composition with a small amount of slag as follows, and it is also possible to reduce the amount of slag generated by selecting processing conditions to 20 kg / T or less. Call

[0050]

As described above, according to the method of the present invention, the amount of slag generated can be reduced as much as possible to contribute to resource saving and energy saving, the production cost of molten steel can be reduced, and moreover, the environment can be reduced. Efficient and stable dephosphorization can be performed using a slag substantially containing no adversely affecting fluorine.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an example of a dephosphorization process using a converter type container.

FIG. 2 is a graph showing the relationship between the concentration of silicon in hot metal before dephosphorization and the concentration of phosphorus in hot metal after dephosphorization.

FIG. 3 is a graph showing the relationship between the concentration of silicon in hot metal before dephosphorization and the manganese yield in the decarburization step.

FIG. 4 is a graph showing the relationship between the concentration of silicon in hot metal before the dephosphorization treatment and the total amount of slag generated in the dephosphorization step and the decarburization step.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Converter, 2 ... Top blowing lance, 3 ... Raw material input device, 4 ...
Tuyere, 5: Hot metal, 6: Slag, 7: Raw material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Shimizu 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Ryo Kawabata 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Yoshiaki Tabata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Inventor Tadaaki Hino 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan In-house F term (reference) 4K013 AA00 BA02 BA03 DA03 DA06 DA08 DA13 EA12 FA05 4K014 AA00 AA01 AA03 AB04 AB12 AB28 AC03 AC14 AC16 AC17 AD01 AD23

Claims (5)

[Claims] 1. A method for refining hot metal in which at least a dephosphorization step and a decarburization step are performed in this order with respect to hot metal having a silicon concentration of 0.20 wt% or less, wherein substantially no fluorine is contained in the dephosphorization step. By using a refining agent obtained by granulating a raw material mainly composed of limestone powder and subjecting it to a heat treatment, the phosphorus concentration in the hot metal can be substantially reduced at a slag amount of 30 kg / T or less. A method for refining molten iron, comprising reducing the concentration of phosphorus to a phosphorus level and then performing a decarburization step. 2. The hot metal refining method according to claim 1, wherein in the decarburization step, a newly generated slag amount is set to 20 kg / T or less. 3. The decarburizing step is characterized in that a refining agent obtained by granulating a raw material containing substantially no fluorine and mainly containing limestone powder and heat-treating the raw material is used. The method for refining hot metal according to claim 2. 4. A refining agent comprising: a limestone powder having a particle size of less than 5 mm generated at the time of limestone mining; and a particle size of 5 mm generated at a washing stage of a limestone rough stone performed as a pretreatment for calcining limestone.
The hot metal according to claim 1, 2 or 3, wherein the refining agent is obtained by granulating one or more limestone powders selected from limestone powders having less than or equal to, and subjecting the granulated powder to heat treatment. Refining method. 5. The refining agent according to claim 1, wherein the refining agent is a refining agent obtained by subjecting the granulated raw material to heat treatment in a solid furnace, a rotary kiln, a fluidized bed furnace or a moving bed furnace. ,
3. The method for refining hot metal according to 3 or 4.