JP2003193121A - Hot metal refining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for refining hot metal in which a manganese yield can be increased to an extreme in a converter decarburization step, and thereby a manganese alloy iron added to molten steel can be reduced to a minimum. . SOLUTION: In a hot metal refining method in which hot metal is preliminarily treated in a converter and then decarburized in a converter, the phosphorus concentration in the hot metal is reduced to [phosphorus concentration of product + 0.015] by dephosphorization performed as hot metal pretreatment. mass% or less,
Then, in the decarburization step, manganese ore is added to perform decarburization blowing, and at least a partial period of the latter half of blowing in the decarburization blowing or / and after the completion of blowing, the powdery or granular carbon source or / and / or in the slag. By adding an aluminum source, the degree of oxidation of slag in the latter half of blowing is reduced, and the manganese yield is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environment-friendly method for refining molten pig iron, which saves resources and energy and can minimize the amount of slag generated.

[0002]

2. Description of the Related Art In order to manufacture steel products from hot metal produced in a blast furnace, it is necessary to reduce the impurity components contained in the hot metal to a predetermined concentration in the refining process and then adjust them to the components required for the steel products. Is. Impurity components contained in the hot metal include phosphorus and sulfur in addition to carbon contained in an amount of 4 mass% or more, and required components for steel materials include manganese and silicon which enhance strength and toughness.

In order to remove phosphorus and carbon from the hot metal of the blast furnace, a refining method in which the hot metal is reacted with dephosphorization slag or a large amount of oxygen is added to promote the oxidation reaction is used. In contrast to the conventional method of simultaneously removing phosphorus and phosphorus at the same time, hot metal pre-dephosphorization treatment for removing only phosphorus in advance at the hot metal stage has been performed recently. By performing this hot metal preliminary dephosphorization treatment, it is possible to reduce the slag required for dephosphorization in the converter decarburization process, and at the end of the decarburization blowing that is performed by adding manganese ore. The manganese reduction rate from the slag can be increased, and the amount of manganese alloy iron added during or after tapping can be reduced as compared with the conventional method.

[0004]

However, even when converter decarburization blowing is performed after such hot metal preliminary dephosphorization treatment, part of the added manganese remains in the slag at the end of blowing. ,
It was difficult to raise the manganese yield sufficiently. In particular, in order to increase the manganese yield at the end of decarburization blowing,
From the reaction principle, it is necessary to lower the manganese distribution ratio between slag and metal (molten steel), but in reality it is extremely difficult. This is because at the end of converter decarburization blowing, the carbon concentration in the metal decreases and the degree of oxidation of the slag increases, so the amount of manganese that turns into manganese oxide increases in the slag. is there. For this reason, conventionally, the amount of acid fed at the end of decarburization is made smaller than that at the peak of decarburization so as not to increase the degree of oxidation of slag, or the agitation by top-blown jet or bottom-blown gas is strengthened. However, the effects of these measures are limited. Also, a method of controlling the slag basicity to a higher level is used to lower the manganese distribution ratio, but due to the balance of manganese in the slag and metal, the amount of slag in the decarburization process should be reduced to increase the manganese yield. It is also necessary to do.
However, since manganese ore originally contains a gangue mainly composed of silicon oxide (SiO ₂ ), it is necessary to add lime for adjusting the basicity thereof, and further, the phosphorus concentration in the dephosphorization step in advance does not decrease. When the amount is sufficient, it is necessary to add lime as a dephosphorizing agent, so that the amount of lime added further increases, and thus it is difficult to reduce the amount of slag. In this case, even if the concentration of manganese oxide in the slag is decreased, the amount of slag itself is increased, and thus the amount of manganese present in the slag is not decreased so much.

Therefore, the object of the present invention is to solve the problems of the prior art and to increase the manganese yield to the limit in the converter decarburization process, whereby the manganese alloy iron added to the molten steel can be minimized. It is to provide a refining method of hot metal that can be reduced.

[0006]

[Means for Solving the Problems] Since a large amount of oxygen is blown into the molten metal in the converter decarburization step, the oxygen content of the slag is reduced especially at the final stage of the blowing when the carbon concentration in the metal (molten steel) decreases. As described above, it is very difficult to reduce the potential (oxidation degree). With respect to such a problem, the present inventors have performed sufficient dephosphorization in the step of pretreating the blast furnace hot metal (preferably completed the substantial dephosphorization), and the converter decarburization step has as few amounts as possible. Performing blowing with a slag amount and selectively reducing the oxygen potential of the slag by adding a reducing agent such as a carbon source or an aluminum source into the slag in the latter half of the blowing (particularly the latter half of the blowing). I found that I can do it.

The present invention has been made based on the above findings, and its features are as follows. [1] In the refining method of hot metal, in which the hot metal is preliminarily treated in the blast furnace and then decarburized in the converter, the phosphorus concentration in the hot metal is changed to [the phosphorus concentration of the product +
0.015] mass% or less, and then decarburization blowing is performed by adding manganese ore in the decarburizing step, and at least a part of the latter half of the blowing and / or powder in the slag after the blowing is completed. A method for refining hot metal, which comprises adding a granular carbon source and / or an aluminum source. [2] In the refining method of the above [1], at least 2/3 of the total decarburization amount of the hot metal in the decarburization step has been completed, and at the latter stage of blowing after the completion of blowing, powdery or granular carbon source or /
And a method of refining hot metal, which comprises adding an aluminum source.

[3] In the refining method of the above [1] or [2],
A method for refining hot metal, which comprises performing decarburization treatment after the phosphorus concentration in the hot metal is substantially reduced to the product phosphorus concentration level by the dephosphorization treatment. [4] In the refining method according to any one of the above [1] to [3], after desiliconizing the blast furnace hot metal to reduce the silicon concentration in the hot metal to 0.2 mass% or less, dephosphorization treatment A method of refining hot metal, characterized in that the amount of slag in the phosphorus step is 30 kg / ton of hot metal or less. [5] In the refining method according to any one of the above [1] to [4], the phosphorus concentration in the hot metal after dephosphorization treatment is 0.02 mass% or less, and the amount of slag in the decarburization step is 20 kg / hot metal ton or less. The method for refining hot metal is characterized by the following.

[6] In the refining method according to any one of the above [1] to [5], the pure manganese in the manganese ore added in the decarburization step is 2 kg / ton hot metal ton or more. Refining method. [7] In the refining method according to any one of the above [1] to [6], the addition of the carbon source and / or the aluminum source in the decarburization step is performed through a top-blown acid-feeding lance that mainly feeds acid. Method for refining hot metal. [8] The refining method of any of the above-mentioned [1] to [7], wherein the carbon source added in the decarburization step is coke or / and coal.

[9] In the refining method according to any one of the above [1] to [8], the carbon source added in the decarburization step has a sulfur content of 0.1% mass or less and a nitrogen content of 0.1%. A method for refining hot metal, which is characterized by having a carbon source of not more than% mass. [10] In the refining method of [9] above, the carbon source added in the decarburization step is one or more carbon sources selected from artificial graphite, soil graphite and plastics. Refining method of hot metal. [11] In the refining method according to any one of [1] to [10] above, the aluminum source added in the decarburization step is aluminum dross containing 20 mass% or more of metallic aluminum.

According to the method of the present invention as described above, the oxygen potential of the slag increases with the decrease of the carbon concentration in the metal (molten steel) in the latter half of blowing (particularly preferably in the latter half of blowing) of the converter decarburization step. It can be suppressed appropriately. That is, the added carbon source or aluminum source selectively reduces iron or manganese in the slag, and thus manganese loss can be reduced to the utmost even though the oxygen potential of the metal is high. In the present invention, adding a powdery carbon source or / and an aluminum source to the slag means that the carbon source or / and the aluminum source is a metal phase in addition to directly charging the carbon source or / and the aluminum source into the slag. Or after being added to the metal-slag mixed phase,
Including cases where it is taken into the slag phase. Although such an addition form has a slightly lower efficiency than the form in which it is directly added to the slag, the carbon source and / or the aluminum source that are added are immediately incorporated into the slag phase according to the flow of the metal slag. Therefore, the desired effect according to the present invention can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention is a method for refining hot metal in which hot metal is preliminarily treated in a blast furnace and then decarburized in a converter, and the phosphorus concentration in the hot metal is determined by the dephosphorization treatment performed as hot metal pretreatment. Is reduced to a level of [phosphorus concentration of product + 0.015] mass% or less (preferably a substantial phosphorus concentration level of product), and then manganese ore is added in the decarburization step to perform decarburization blowing. The refining method is characterized by adding a powdery carbon source and / or an aluminum source to the slag after at least a part of the latter half of the blowing or / and after the completion of the blowing.

In the method of the present invention, it is desirable that the concentration of silicon in the hot metal to be dephosphorized is as low as possible. Therefore, depending on the concentration of silicon in the hot metal of the blast furnace, it is desirable to desiliconize the hot metal of the blast furnace before the dephosphorization step. Generally, the hot metal discharged from the blast furnace is poured and stored in the hot metal transfer container such as a hot metal ladle or a mixed pig car via the blast furnace cast bed, but the desiliconization treatment is stored in the blast furnace cast bed or the hot metal transfer container. Either or both may be performed. Desiliconization may be performed in the process of pouring the hot metal from the blast furnace casting floor into the hot metal carrier. Depending on the required amount of silicidation and the silicidation treatment ability at each treatment position, the silicidation treatment of a treatment form selected from them can be performed.

In the silicon removal treatment, an oxygen source is added as a silicon removal agent, and if necessary, Ca such as quick lime is used as a solvent.
O content is added to adjust the basicity of the slag. As the desiliconizing agent, either a solid oxygen source such as iron ore or mill scale, or 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 to forcibly mix the desiliconizing agent and the hot metal to enhance the desiliconization efficiency. In this respect, the desiliconization treatment performed in a container such as a hot metal ladle is more efficient than other methods, such as desiliconization treatment in a blast furnace cast bed, because the hot metal can be stirred due to the shape of the container. Therefore, in order to obtain a particularly excellent desiliconization efficiency, desiliconization should be performed in a container such as a hot metal ladle, or desiliconization should be performed in the blast furnace casting floor before desiliconization in the container. Is preferably carried out. Such a container may be provided as long as it has a supply means such as a solvent or a desiliconizing agent and a stirring means for the hot metal, such as a ladle such as the hot metal ladle described above, a mixing pig wheel, and other Either of the containers for silica may be used.

The addition of the desiliconizing agent and the solvent medium is carried out by placing it on the surface of the molten metal or on the surface of the hot metal bath or by blowing it into the bath. For example, in the desiliconization treatment using a hot metal ladle, a gaseous oxygen source is blown to the hot metal bath surface through an acid-feeding lance, and a stirring gas or a solvent medium such as quick lime powder is blown into the hot metal through an immersion lance. According to the above, a solid oxygen source is placed on the hot metal bath surface.

FIG. 1 schematically shows an example of the state of desiliconization treatment using the hot metal ladle 1, in which the acid feeding lance 2 is placed in the hot metal ladle 1.
A gaseous oxygen source is blown in through the bath, stirring gas or a solvent is blown into the bath through the immersion lance 3, and if necessary, a solid oxygen source (for example, iron ore or mill scale) is placed above the pot. It is designed to be placed on top of item 4 from above.

In the desiliconization step, the hot metal is added to a silicon concentration of 0.2 mass%
It is preferable to desiliconize to the following. By desiliconizing to such a low silicon concentration, the phosphorus concentration can be sufficiently reduced in the subsequent dephosphorization step, and it is also effective in reducing the amount of slag in the dephosphorization step. From this point of view, it is more desirable to desiliconize the hot metal to a silicon concentration of 0.1 mass% or less. When the silicon concentration of the blast furnace hot metal is sufficiently low, for example, when the silicon concentration is 0.2 mass% or less, preferably 0.1 mass% or less, the following dephosphorization treatment is performed without performing the above-mentioned desiliconization treatment. You can go. Even if the silicon concentration of the blast furnace hot metal is 0.2 mass% or less, the silicon concentration is further deoxidized as described above to further reduce the silicon concentration (for example, 0.1 mass% or less). Good.

The low silicon hot metal which has been desiliconized as described above or which has been tapped from the blast furnace is subjected to a dephosphorization step. In this dephosphorization step, the phosphorus concentration in the hot metal is reduced to [phosphorus concentration of the product (hot metal after decarburization blowing) +0.015] mass% or less, preferably substantially to the phosphorus concentration level of the product. In order to efficiently dephosphorize the hot metal in the dephosphorization step, it is necessary to perform refining with a slag amount as small as possible, and for this purpose, it is necessary to generate slag with a high dephosphorization ability. In order to enhance the dephosphorization ability of slag, it is necessary to increase the basicity of slag. Therefore, it is preferable to suppress the inclusion of desiliconized slag as much as possible. Therefore, in the dephosphorization step, the hot metal from which the slag in the previous step has been separated and removed is used. Separation and removal of slag can be done by mechanical slag device or manual work.

There is no particular restriction on the container used in the dephosphorization step, and the dephosphorization treatment can be carried out using a ladle type container such as a hot metal ladle, a mixed piggy wheel or a converter type container. Further, the dephosphorization treatment may be performed in the same vessel after the desiliconization treatment, or may be performed by transferring it to another vessel such as a converter.

In this dephosphorization treatment, in general, in order to effectively enhance the dephosphorization reaction, gaseous oxygen (oxygen gas or oxygen-containing gas) and / or solid oxygen source (such as sintered powder or (Iron oxide such as mill scale) is added together with a solvent. Of these, for gaseous oxygen by any method such as top blowing with a lance or injection into the hot metal or bottom blowing, for solid oxygen source and solvent, any method such as top-up charging and injection, respectively. To be supplied during hot metal. Further, as a more basic condition for efficient dephosphorization, it is necessary to appropriately stir the hot metal. For this stirring,
Generally, gas agitation is performed using a dipping lance or a tuyere provided below the bath surface of the furnace body.

In the dephosphorization step, it is preferable to efficiently carry out the treatment with a slag amount of 30 kg / mol ton or less. Therefore, the appropriate silicon concentration of the hot metal and the amount of solvent medium are set accordingly. Further, it is most preferable that the phosphorus concentration in the hot metal after the dephosphorization treatment is substantially at the phosphorus concentration level of the product,
[Phosphorus concentration of product +0.015] If it is mass% or less, the amount of slag in the decarburization step can be sufficiently reduced,
In the method of the present invention, the phosphorus concentration in the hot metal is reduced to [phosphorus concentration of product +0.015] mass% or less by dephosphorization treatment. From this point of view, the phosphorus concentration in the hot metal after the dephosphorization treatment is preferably [phosphorus concentration of product +0.005] mass% or less.

FIG. 2 schematically shows an example of a dephosphorization process using a converter-type vessel. In this example, oxygen is blown into the converter 5 through an acid-feeding lance 6 and installed at the bottom of the furnace. The stirring gas is blown into the bath from the tuyere 7 (bottom blowing nozzle), and raw materials such as refining agent and solid oxygen source are further added from above the raw material feeding device 8 above the converter 5. ing.

Low silicon after dephosphorization treatment as described above
The low phosphorus hot metal is supplied to a decarburizing process in a converter. In this converter decarburization step, since the phosphorus concentration in the hot metal has been sufficiently reduced in the previous dephosphorization step, decarburization blowing can be performed with a sufficiently small amount of slag. Further, when the phosphorus concentration in the hot metal has been substantially reduced to the phosphorus concentration level of the product in the dephosphorization step, substantial dephosphorization is not required in the decarburization step. Therefore, a small amount of slag is required as a diluent for iron oxide produced during blowing and as a cover slag for suppressing the scattering and heat dissipation of droplets from the bath surface, but the slag for dephosphorization is not do not need. Therefore, in the decarburization blowing in this case, the amount of slag generated by the solvent may be a small amount of the basicity adjustment amount according to the gangue content of the manganese ore. Further, the slag refining ability is not essential, and since there is no problem with some fluctuations in the slag composition, the slag can be repeatedly used by the slag leaving operation in the furnace.
Depending on the amount of manganese ore used, it is usually 20 k during the converter decarburization step of the method of the present invention (particularly when the phosphorus concentration in the hot metal is substantially reduced to the phosphorus concentration level of the product in the dephosphorization step).
It is possible to carry out decarburization blowing with an amount of slag of g / mol pig ton or less, and being able to perform decarburizing blowing with such a small amount of slag contributes to improvement of the manganese yield.

In the converter decarburization step, oxygen or an oxygen-containing gas is supplied (acid feed) through a top blowing acid lance or a bottom blowing nozzle to perform decarburizing blowing. Deoxidization of the hot metal progresses due to the acid transfer, and at the same time, iron oxide is also produced and the temperature of the molten metal rises. Manganese ore and lime are added from the early stage to the middle stage of blowing, and the melting of the manganese ore and the reduction by the carbon in the hot metal proceed.

It is preferable that the manganese ore added in the converter decarburization step has a pure manganese content of 2 kg / mol of hot metal or more. This amount of addition corresponds to about 0.2 mass% of the amount of Mn in the hot metal, and in the method of the present invention, the amount of Mn remaining on the slag side (manganese loss content) is small, so that it is a normal dephosphorized hot metal. Which is the amount of Mn contained in.
Addition of 1 to 0.3 mass% can secure a sufficient amount of Mn as a molten steel component.

As described above, in the converter decarburization step, manganese migrates into the slag in the form of MnO in accordance with the increase in the oxidation degree of the slag accompanying the progress of decarburization of metal (molten steel). Will remain in the slag at the end of blowing, so
In order to suppress the residual manganese in the slag as much as possible, in the converter decarburization step of the method of the present invention, at least a part of the latter half of the blowing or / and after the blowing is completed, the slag is powdered or granular. A carbon source and / or an aluminum source (reducing agent) is added to reduce iron oxide (mainly FeO) and manganese oxide in the slag. As a result, the amount of manganese remaining in the slag at the end of blowing can be reduced to a minimum. Further, the effect of the addition of such a reducing agent is further enhanced by performing decarburization blowing with the slag amount being 20 kg / hot metal ton or less.

Here, the latter half of decarburization in which a powdery and granular carbon source and / or an aluminum source (hereinafter collectively referred to as "reducing agent") is added to the slag means the entire blowing period ( (Time) means the period after the midpoint. The above-mentioned reducing agent can be added during the whole period or a part of the latter half of the blowing in the converter decarburization step, and the addition period depends on the degree of progress of decarburization (carbon concentration in metal), etc. It is selected appropriately. As described above, in the latter half of decarburization blowing, the degree of oxidation of slag increases with the decrease of carbon concentration in the metal, leading to an increase in manganese loss. By adding, the increase in the oxidation degree of the slag is appropriately suppressed, and the manganese loss can be reduced to the limit. On the other hand, the addition of the reducing agent in the stage before the latter half of blowing (that is, the first half of blowing) has the effect of reducing the degree of slag oxidation at the start of the latter half of blowing, but adding a large amount of oxygen This is not preferable because it causes an increase in the amount and oxygen blowing time.

It is preferable that the reducing agent is added to the slag at least in the latter half of the latter half of blowing. The latter stage of blowing is a period after the decarburization of 2/3 of the total decarburizing amount of the hot metal in the decarburizing step is completed. For example, if the carbon concentration [C] in the metal is 3.
In the blowing process of decarburizing from 7 mass% to 0.1 mass%, the period after the carbon concentration in the metal [C] becomes about 1.3 mass% is the latter stage of blowing, and at least the latter stage of blowing. It is preferable to add the reducing agent to the slag.

The reason for this will be described below from the reaction mechanism of decarburization blowing. That is, when decarburizing by adding oxygen (sending acid) in decarburization blowing, almost all of the added oxygen is consumed for decarburization as the final reaction when the metal is still in the high carbon region. The generated oxygen does not increase the production amount of iron oxide (FeO). On the other hand, when decarburization progresses and the metal enters the low carbon region, a part of the added oxygen is consumed for producing FeO. That is, at this stage, the reduction of FeO by C in the metal is delayed with respect to the amount of FeO generated by the added oxygen, so that FeO increases. In the reduction reaction of FeO by C, it is said that diffusion transfer of C in the metal to FeO in the slag is rate-determining. In this case, the decarburization rate (or FeO reduction rate) depends on the C concentration in the metal. Since the proportion is proportional, the FeO accumulation amount increases as the C concentration in the metal decreases. Although the C concentration at the time of transition from the oxygen supply rate-determining rate to the movement rate-determining rate of C in the metal as described above also varies depending on the stirring rate of the metal and the acid transfer rate, normally the carbon concentration in the hot metal [C] is 1 ma.
It is ss% or less (in many cases, 0.3% mass or less). That is, since FeO starts to increase sharply when the concentration becomes lower than this C concentration, if the addition of the reducing agent is started at least before or at the time when the C concentration becomes FeO,
It is possible to suppress the sudden increase of. Here, the time when the decarburization of approximately 2/3 of the total decarburization amount in the decarburization step is completed is the stage at which the rapid increase of FeO starts due to the above-mentioned decrease in the C concentration or a stage immediately before that. ,
By adding the reducing agent to the slag at least in the latter stage of blowing after that time, it is possible to suppress a rapid increase in FeO due to a decrease in the C concentration of the metal.
In addition, by intensively adding the reducing agent in the latter stage of blowing, there is an advantage that FeO that has already been generated can be reduced and the degree of oxidation of the slag can be further reduced. By suppressing the degree of oxidation of the slag in this way, manganese in the metal is suppressed from migrating into the slag as MnO, and manganese loss can be effectively reduced. In addition, the reducing agent added during decarburization blowing does not mean that the entire amount is consumed for the reduction at the same time as the addition, and normally, a part of the reducing agent added before the end of blowing is added to the slag. It stays and the reducing action continues even after the end of blowing.

Further, in the method of the present invention, in addition to the addition of the reducing agent during the blowing period (second half of blowing) described above, or in place of the addition of the reducing agent during the blowing period (second half of blowing), blowing is performed. A reducing agent may be added to the slag at the stage after the end. However, in this case, it is preferable to stir the bath in order to accelerate the reduction reaction. In this way, by adding the reducing agent to the slag at the stage after the end of blowing, the iron oxide that has already been generated can be reduced. In particular, when the reducing agent is added after the end of the blowing in addition to the addition of the reducing agent during the blowing period (the latter half of the blowing), in addition to the above-mentioned action, the reducing action of the iron oxide once generated is Since it is strengthened, the effect of reducing iron oxide as a whole is great.

Since the reducing reaction after the end of the blowing with the reducing agent added as described above does not supply the acid at this stage, the reducing agent is mixed with oxygen or an oxide whose formation by oxygen is in progress. Since the amount consumed in the direct reaction is small, there is an advantage that the reduction efficiency becomes high. However, when a carbon source is used as a reducing agent, the reaction of reducing the FeO by the carbon source is an endothermic reaction, and there is no problem because there is thermal compensation due to an oxidative exothermic reaction due to oxygen during blowing. Since there is no such heat compensation after the end of blowing, it may be necessary to raise the hot metal temperature in advance or raise the temperature in a later process so as not to cause a problem due to a decrease in metal temperature. When the aluminum source is used as the reducing agent, the reaction of reducing the FeO by the aluminum source is an exothermic reaction, so that it is not necessary to consider the thermal problem as described above.

Since the carbon source and the aluminum source have substantially the same functions as the deoxidizing agent, either the carbon source or the aluminum source may be added, or both may be added in combination. There is no particular limitation on the supply amount of these reducing agents,
Supply in accordance with the amount of iron oxide and manganese oxide that is or is expected to be accumulated in the slag, which is determined by the conditions of acid supply and stirring in the latter half of blowing and the end point conditions such as C concentration in metal. Is desirable.

In a general decarburization blowing operation, the amount of acid fed cannot be extremely reduced during blowing. This is because the oxygen jet is significantly weakened when the amount of oxygen fed is extremely reduced during blowing (for example, the flow rate is less than half of the normal flow rate), and a lance height is secured that does not damage the lance. This is because, under the operating conditions of No. 2, the arrival rate of oxygen to the metal surface decreases, and efficient decarburization blowing cannot be performed. Therefore, even in the latter stage of blowing, it is not possible to extremely reduce the amount of acid fed, and it is necessary to carry out an amount of acid fed that exceeds the amount of acid fed that complies with the decarburization rate limit in the reaction.
Excess oxygen is consumed in addition to decarburization, and the amount of iron oxide produced increases. Generally, the amount of iron oxide accumulated in the slag in the latter stage of blowing is as high as several kg / hot metal ton or more, and it is necessary to add about 1 kg / hot metal ton or more of the reducing agent to reduce the total amount of iron oxide. However, since the acid is actually sent at the same time, it cannot be expected that the reducing agent will be consumed for the reduction of 100% iron oxide. Therefore, a larger amount (for example, several times that amount) is added. ) May be required.

Coke and / or coal can be used as the carbon source. Further, from the viewpoint of suppressing the increase in the sulfur concentration and the nitrogen concentration of the metal, the sulfur content as the carbon source is 0.1% mass or less and the nitrogen content is 0.1% ma.
It is preferable to use ss or less, and examples of such a carbon source include artificial graphite, soil graphite, plastics, etc., and it is preferable to use one or more carbon sources selected from these. it can.

As the aluminum source, for example,
Aluminum metal, aluminum ash generated by melting or refining aluminum, or the like can be used. Although aluminum ash often contains about 30 to 70% of metallic aluminum, it can be used regardless of the aluminum content. Also, for example, 20 mass of metallic aluminum
It is also possible to use aluminum dross containing at least%. This aluminum dross is scum generated during aluminum refining or remelting of aluminum ingot or the residue after separating metallic aluminum from it, and in the latter case, the metallic aluminum fraction is separated by processing such as squeezing out from the scum, Use the residue. By using this aluminum dross as an aluminum source, alumina (Al ₂ O ₃ ) that has a strong reducing power for the contained metal aluminum lowers the melting point of the high basicity slag during normal oxidative blowing and accelerates the reduction reaction. It is possible to effectively use aluminum whose purity was originally low and its use was limited.

The particle size of the powdery carbon source or the aluminum source is determined from the viewpoint that the slag can be reliably charged and that iron oxide and manganese oxide in the slag can be rapidly reduced.
It is appropriately selected depending on the charging system, the stirring conditions of the slag, and the like.
That is, if the particle size of the carbon source or the aluminum source is too large, the reduction efficiency decreases, while if it is too small, problems such as scattering at the time of addition occur. Usually, particles having a particle size of several tens of μm to several mm can be used.

In the method of the present invention, there is no particular restriction on the method of adding the reducing agent to the slag as described above, and it may be added by so-called top charging, but it is premised on the existing equipment for decarburization blowing. In this case, particularly preferable is the addition through the top blowing acid lance to carry out the main acid feeding. This is because if the lance is blown up with acid, the reducing agent can be directly and accurately added to the slag, which is the reaction region, and the reaction can be carried out efficiently. In addition, since the spray direction and range can be set arbitrarily by selecting the structure of the nozzle hole of the top blown acid lance, the reducing agent powder is dispersed and added to the entire slag, or a small amount of slag is added. When it tends to be unevenly distributed in, the powder of the reducing agent can be accurately projected toward the place where the slag is present, so it is particularly effective as a means for adding the reducing agent.

When the reducing agent is added through the top-blown acid lance, a perforated nozzle type lance having a plurality of nozzle holes (gas injection holes) is usually used, and some nozzle holes (for example,
Oxygen is supplied from the nozzle hole in the center of the lance tip or the nozzle hole formed in the side wall on the lance tip side),
Using a suitable carrier gas (for example, an inert gas such as argon or nitrogen) other than oxygen from another nozzle hole (for example, the nozzle hole formed in the side wall portion on the lance tip side or the nozzle hole at the center of the lance tip) The reducing agent is supplied.

The existence form of slag in the furnace differs depending on the position of the bottom blown tuyere and the amount of slag. For example, when the bottom blown tuyere is installed mainly in the center of the bottom of the furnace, the slag is the inner wall of the furnace. When the bottom blown tuyere is arranged on the peripheral side of the furnace wall on one side of the furnace bottom or on one side of the furnace bottom, the slag tends to be unevenly distributed on the central part of the furnace or on the one side of the furnace. Therefore, the nozzle hole for supplying the reducing agent of the upper blown acid lance is
The inclination angle (the angle of the nozzle hole axis with respect to the axis of the lance inserted in the vertical direction) is appropriately selected according to the existing form of the slag in the furnace as described above. Normally, the nozzle tilt angle is selected in the range of about 0 to 50 °. Further, the reducing agent may be added by using an addition means such as a dedicated lance instead of the above-mentioned top blowing acid lance.

FIG. 3 schematically shows an example of the implementation of converter decarburization blowing in the method of the present invention. In this example, oxygen is supplied into the converter 9 through the top blowing acid lance 10. Decarburization blowing is performed, and during the latter half of blowing or during a partial period, the reducing agent is an inert gas or the like through the same flow path and nozzle hole different from that for acid feeding of the same top blowing acid lance 10. Is supplied as a carrier gas, and the reducing agent is added to the slag. Also, the tuyere 11 installed on the bottom of the furnace during blowing.
The stirring gas is blown into the bath from the (bottom blowing nozzle).
Further, manganese ore (and a small amount of a solvent if necessary) is placed over the raw material charging device 12 above the converter 9 in the early to middle stages of blowing.

[0042]

[Example] [Example 1] Smelting of hot metal tapped from a blast furnace is performed by a series of steps of casting bed desiliconization-ladle (hot metal ladle) desiliconization-converter dephosphorization-converter decarburization. Was carried out. At the time of desiliconization in the cast bed and the hot metal ladle, about 20 kg / hot metal ton was added to the hot metal through the upper charge of massive iron oxide. In the hot metal ladle, nitrogen gas was supplied through the immersion lance to about 0.01 Nm ³ / mi.
The hot metal was agitated by blowing it into the bath at a supply amount of n / hot metal ton. The silicon concentration in the hot metal after desiliconization was lowered to 0.1 mass% by desiliconization in the cast bed and the hot metal ladle. After removing the slag generated in this desiliconization step, the hot metal was loaded into a converter to carry out the dephosphorization step. This dephosphorization treatment was carried out by adding a total of 9 kg of hot metal ton of lime and fluorite and 10 Nm ³ of oxygen from the top blowing acid lance / oxygen of hot metal ton, and the phosphorus concentration in the hot metal after dephosphorization was It decreased to 0.012 mass%.

The hot metal that had been subjected to the above dephosphorization treatment was once tapped in a pan and re-charged into another converter to decarburize the converter. 3 converters
It has a capacity of 00 tons, and in this decarburization step, a manganese source was added into the furnace by top charging at the beginning of blowing. As a manganese source, manganese content: 48 mass%, silicic acid (Si
O ₂ ) content: 6 mass% of manganese ore was used, and 8 kg of this manganese source was added as a pure manganese content / molton ton. Nitrogen or argon gas from the bottom of the furnace is 0.1 Nm
^The acid was fed through a top-blown acid feeding lance while being blown into the bath at a supply rate of ³ / min / hot metal ton while stirring the bath. The amount of acid fed is 3.5 Nm ³ from the beginning of blowing to 3 minutes.
/ Min / hot metal ton, 2.9 Nm from 3 to 6 minutes
³ / min / hot metal ton, 3.5 from 6 to 11 minutes
Nm ³ / min / hot metal ton, thereafter 1.9 Nm ³ / m
In / hot metal ton. Also, the basicity of the slag is set to 3.
In order to adjust to 5, the required amount of lime source was cut out from the converter upper hopper and added via a shooter.

During a part of the latter half of the decarburization blowing, the carbon source was charged through the top blowing acid lance. The top-blown acid lance used was a quadruple pipe structure (water-cooled type), and the powder was pressure-fed through the carrier gas into the flow path at the center of the lance to eject the powder from the tip injection hole, and outside of it. High-pressure oxygen is made to flow in the flow path of and is injected from the tip injection hole. In this example, the carbon source was injected using argon gas as a carrier gas through the flow path at the center of the lance and the injection hole at the tip thereof.
As the carbon source, granular soil graphite having a particle size of 2 to 5 mm occupying 85 mass% or more and having a particle size of less than 2 mm occupying 15 mass% was used. The carbon source was added at a charging rate of 300 to 900 kg / min from the middle of the blowing (late stage) so that a predetermined amount of the carbon source could be added by the end of the blowing. At the end of decarburization blowing, the carbon concentration in the molten steel is approximately 0.06 mass.
%, The molten steel temperature was controlled to be 1650 ° C.

Table 1 shows the results of examining the slag component, metal component, manganese yield, etc. after the decarburization, together with the decarburizing treatment conditions. According to this, by adding the carbon source to the slag in the latter half of the decarburization blowing according to the method of the present invention, the manganese loss can be significantly reduced as compared with the comparative example in which the carbon source is not added. , It can be seen that the manganese concentration in the metal at the end of blowing can be made sufficiently high. Further, it can be seen that the amount of slag generated can be reduced in the present invention.

[0046]

[Table 1]

Example 2 The steps from tapping from the blast furnace to decarburization of the converter, the treatment conditions in each step, and the blowing conditions in the converter were the same as in Example 1. During a part of the latter half of decarburization blowing, aluminum ash was added through the top blowing acid lance. The top blown acid lance used is a quadruple pipe structure (water cooling type)
And the flow path in the center of the lance is 30 cm from the tip of the lance.
The powder is sprayed from the spray holes that branch into three directions at the upper part and communicate with the lance side wall. Further, high-pressure oxygen is made to flow in the flow passage on the outer side of the flow path and is injected from the tip injection holes (5 holes). In this example, aluminum ash was injected using argon gas as a carrier gas through the flow path in the center of the lance and the injection hole in the side wall of the lance. Aluminum ash has a particle size of 1 to 5 mm and an aluminum content of 30 to
70 mass% was used. 220 to 5 aluminum ash was added between 2 minutes before the end of blowing and the end of blowing so that the pure aluminum content was 1 kg / ton of ton.
The addition rate was 00 kg / min.

At the end of the decarburizing blowing, the carbon concentration in the molten steel was controlled to be approximately 0.05 mass% and the molten steel temperature was controlled to 1650 ° C. Table 2 shows the results of examining the slag component, metal component, manganese yield, etc. after the decarburization, together with the decarburization treatment conditions. According to this, by adding an aluminum source to the slag in the latter half of decarburization blowing according to the method of the present invention, manganese loss can be significantly reduced, and the manganese concentration in the metal at the end of blowing can be reduced. It turns out that it can be made high enough. Further, it can be seen that the amount of slag generated can be reduced in the present invention.

[0049]

[Table 2]

[0050]

According to the method of the present invention described above, a high manganese yield can be obtained in the decarburizing and blowing step, so that the manganese component necessary for the steel material can be reasonably increased in the steelmaking stage,
It can contribute to resource saving and energy saving, and can minimize the generation of slag and the like.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of the status of desiliconization treatment of hot metal in the method of the present invention.

FIG. 2 is an explanatory view schematically showing an example of a dephosphorization treatment state of hot metal in the method of the present invention.

FIG. 3 is an explanatory view schematically showing an example of the implementation status of converter decarburization blowing in the method of the present invention.

[Explanation of symbols]

1 ... hot metal pot, 2 ... top blowing acid lance, 3 ... immersion lance,
4 ... Raw material charging device, 5 ... Converter, 6 ... Top blown acid lance,
7 ... Tuyere, 8 ... Raw material feeding device, 9 ... Converter, 10 ... Top blowing acid lance, 11 ... Tuyere, 12 ... Raw material feeding device

Continued front page    (72) Inventor Hidetoshi Matsuno             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Ryo Kawabata             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F term (reference) 4K014 AA01 AA03 AC03 AD01 AD23                       AD27                 4K070 AB02 AB03 AB06 AC02 AC03                       AC11 AC21 AC24 AC32 BA05                       BA11 BC01 BD00 BD08 EA01                       EA30

Claims (11)

[Claims] 1. A method for refining hot metal in which hot metal is preliminarily treated in a blast furnace and then decarburized in a converter. In the method for dephosphorizing the hot metal, the phosphorus concentration in the hot metal is changed to [phosphorus concentration of product +0.015]. ] To a concentration of not more than mass%, then decarburization blowing is performed by adding manganese ore in the decarburization step, and at least a part of the latter half of the blowing and / or carbon powder in the slag after the blowing is completed. Source and / or aluminum source is added, the method for refining hot metal. 2. Adding at least a powdery carbon source and / or an aluminum source to the slag in the latter stage of blowing after the decarburization of 2/3 of the total decarburization amount of the hot metal in the decarburization step is completed. The method for refining hot metal according to claim 1, characterized in that 3. The refining of hot metal according to claim 1 or 2, wherein the phosphorus concentration in the hot metal is substantially reduced to the phosphorus concentration level of the product by the dephosphorization treatment, and then the decarburization treatment is performed. Method. 4. The blast furnace hot metal is desiliconized to reduce the silicon concentration in the hot metal to 0.2 mass% or less, and then dephosphorization is performed so that the amount of slag in the dephosphorization step is 30 kg / hot metal ton or less. The refining method of hot metal according to claim 1, 2 or 3, characterized in that. 5. The phosphorus concentration in the hot metal after the dephosphorization treatment is 0.02.
The amount of slag in the decarburization step is set to 20 mass% / ton of hot metal or less, and the mass% is set to not more than 20%.
Or the refining method of hot metal according to 4. 6. The method for refining molten iron according to claim 1, wherein the manganese ore added in the decarburizing step has a manganese pure content of 2 kg / ton of hot metal or more. . 7. The carbon source and / or the aluminum source in the decarburization step are added through a top-blown acid feeding lance that mainly feeds acid.
4. The method for refining hot metal according to 4, 5, or 6. 8. The carbon source to be added in the decarburization step is coke or / and coal, 1.
The method for refining hot metal according to 3, 4, 5, 6 or 7. 9. The carbon source added in the decarburization step is a carbon source having a sulfur content of 0.1% mass or less and a nitrogen content of 0.1% mass or less. 2, 3,
The method for refining hot metal according to 4, 5, 6, 7 or 8. 10. The hot metal according to claim 9, wherein the carbon source added in the decarburization step is one or more carbon sources selected from artificial graphite, soil graphite and plastics. Refining method. 11. The aluminum source added in the decarburization step is an aluminum dross containing 20 mass% or more of metallic aluminum.
The refining method of hot metal according to 6, 7, 8, 9 or 10.