JP2001515138A - Iron and steel making - Google Patents

Abstract

(57) [Summary] (1) Prepare iron oxide and a carbonaceous reducing agent, (2) manufacture a molded body from the carbonaceous reducing agent and iron oxide, and (3) obtain a metallization rate from the molded body. (4) producing a solid reduced iron having at least 60%, a specific gravity of at least 1.7 or more, and containing 50% or more of carbon relative to a theoretical equivalent required for reducing remaining iron oxide; The molten iron is produced by heating in an arc-heated melting furnace before the solid reduced iron is substantially cooled. Even from an iron ore having a relatively low iron component content, molten iron can be efficiently obtained with high energy efficiency and reduction efficiency without causing erosion of refractories and with simple equipment and operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an iron making method for producing metallic iron by heating and reducing iron oxide (iron ore or the like) together with a carbonaceous reducing agent (carbonaceous material or the like) and an improvement technique of the steel making method. After heat-reducing the iron oxide-containing molded product (pellets, briquettes, etc.) in the solid state, and then further reducing and melting this to produce molten iron, while increasing the thermal efficiency of a series of steps from heat reduction to reduction melting The present invention relates to an improved iron making method and a steel making method capable of efficiently separating gangue components.

[0002]

[Prior art]

As a direct iron-making method for producing reduced iron by directly reducing iron oxide such as iron ore and iron oxide pellets with a carbon material or a reducing gas, a shaft furnace method represented by the Midrex method has been conventionally known. . This type of direct iron making method is a method in which a reducing gas produced from natural gas or the like is blown from a tuyere at a lower portion of a shaft furnace, and the reducing power is used to reduce iron oxide to obtain reduced iron. Recently, a reduced iron production process using a carbon material such as coal as a reducing agent in place of natural gas has been attracting attention. Specifically, a so-called heat reduction of a fired pellet of iron ore together with coal powder in a rotary kiln has been attracting attention. SL / R
The N method has already been put to practical use.

[0003] Further, as another iron making method, US Patent No. 3,443,931 discloses a process of mixing carbonaceous material and powdered iron oxide to form an agglomerate, and reducing it by heating on a rotary hearth to produce reduced iron. It has been disclosed. In this process, fine ore and fine coal are mixed and agglomerated, and this is heated and reduced in a high-temperature atmosphere.

[0004] Reduced iron produced by these methods is used as an iron source as it is or formed into a briquette or the like, and then charged into an electric furnace at room temperature. Since this reduced iron has a low content of an impurity metal component such as a playing card element, in recent years in which recycling of iron scrap has been activated, this reduced iron has attracted attention as a diluent for the playing card element mixed into the scrap. ing.

[0005] However, the reduced iron obtained by the conventional reduction iron making method includes SiO ₂ and Al ₂ O ₃ contained as gangue components in iron oxide (iron ore or the like) or carbonaceous material (coal or the like) used as a raw material. , Slag components such as CaO are directly mixed in, so that the iron quality (purity as metallic iron) of the product is lowered. In practical use, these slag components are separated and removed in the next smelting process, but an increase in the amount of slag not only lowers the yield of smelted molten iron but also has a large adverse effect on the operating cost of the electric furnace Therefore, reduced iron with high iron grade and low slag content is required, but in order to meet such demands with the conventional reduced iron production method as described above, high-grade iron ore is used as a raw material for reduced iron production. Therefore, the range of selection of practical steelmaking raw materials is greatly reduced.

[0006] Further, the conventional method as described above has a final purpose of obtaining a reduced solid product as an intermediate product, and in practical use, forms a briquette, a cooling, and a cooling process before sending it to the next refining process. Processes such as transportation and storage are required, during which a large energy loss occurs and extra equipment and energy are required for briquetting.

On the other hand, as a method of directly reducing iron oxide to obtain pre-reduced iron, a smelting reduction method such as a DIOS method is also known. In this method, iron oxide is preliminarily reduced to an iron purity of about 30 to 50%, and then reduced to metallic iron by a direct reduction reaction with a carbonaceous material and / or carbon monoxide in an iron bath. It is a method of melting after
In this method, since a recycle system for generating a reducing gas necessary for the preliminary reduction step in the melting furnace and introducing the gas into the preliminary reduction furnace is constructed, it is complicated and extremely difficult to balance the process. . In addition, the molten iron oxide (Fe
O) and the refractory are in direct contact with each other in a molten state, so that the problem of severe wear of the refractory is pointed out.

[0008] As still another method, Japanese Patent Publication No. 60883/1991 discloses that a compact formed by mixing powdery iron ore and a carbon material into a nodular shape is preliminarily reduced in a rotary furnace type heating furnace. There is disclosed an iron making method in which an obtained pre-reduced product is charged into a melting furnace without cooling, melted, a carbon material is added thereto, reduction is performed, and refining is performed by blowing oxygen. This method is a method of reducing and refining by sending the pre-reduced product to the melting furnace without cooling, and thus is considered to be an effective method in terms of productivity with little loss of heat energy and capable of continuous operation. .

In this iron making method, oxygen (or air) is blown together with a large amount of carbon material into a melting furnace for heating and refining. And, as described above, since a large amount of gangue components in iron ore and carbonaceous materials are contained as slag forming components in the preliminary reduced product sent to the melting furnace, the molten iron The slag is exposed to a violent stirring state with a large amount of slag floating on the surface of the molten metal, and unreduced iron oxide (FeO)
, A serious problem in practical use that refractory lining is remarkably melted down, so that practical application on an industrial scale is difficult.

In any case, in order to secure a reducing gas having a sufficient reducing potential required in the upstream pre-reduction furnace in the melting furnace, a large amount of oxygen and carbon material [several hundreds kg / tmi (mi: molten iron to be produced)] and burn them, so that the heat load of the melting furnace is very large, and furthermore, due to vigorous stirring of the molten iron and slag, the refractory lining is Receives severe erosion. Furthermore, in order to stably supply a proper composition and amount of reducing gas required in the preliminary reduction furnace, control for balancing the entire facility is very complicated, and an advanced control system is required. .

[0011]

[Problems to be solved by the invention]

The present invention has been made in view of the above-described circumstances, and the purpose thereof is not only from an iron oxide source having a high iron content but also from an iron ore having a relatively low iron content. It is also possible to use the iron making method which can obtain molten iron efficiently with high energy efficiency and reduction efficiency without causing erosion of refractories, with simple equipment and operation, and further with reduced iron obtained by this method. To provide a steelmaking method.

[0012]

[Means for Solving the Problems]

The iron making method according to the present invention that can solve the above-mentioned problems is a method in which a high-temperature solid reduced iron manufactured by a reduced iron manufacturing facility whose main material is an iron oxide-containing molded body containing a carbonaceous reducing agent is substantially used. An iron making method in which a molten iron is supplied to an arc-heating type melting furnace without being cooled and heated in the melting furnace to obtain molten iron.
In addition to the above, the carbon content in the solid reduced iron is 50% or more of the theoretical equivalent required for reducing the iron oxide remaining in the solid reduced iron, and the specific gravity of the solid reduced iron is 1 0.7 or more, and the solid reduced iron is heated in the arc-heating type melting furnace to obtain molten iron having a carbon content of 1.5 to 4.5%.

In carrying out the present invention, in order to efficiently promote smelting reduction while minimizing erosion of the refractory lining of the arc-heating type melting furnace, the solid reduced iron is
The molten slag is charged into the arc-heating type melting furnace and heated and melted, and the basicity of the molten slag is preferably controlled in the range of 1.0 to 1.8. It is desirable that the content of the iron oxide component is controlled to 9% or less, more preferably 5% or less in terms of Fe.

In the above-mentioned arc-heating type melting furnace, when the insufficient amount of the carbonaceous reducing agent is additionally charged, by adding the carbonaceous reducing agent toward the addition position of the solid reduced iron, This is desirable because the smelting reduction can proceed more efficiently.

The amount of the carbonaceous reducing agent additionally charged in the arc-heating type melting furnace is as follows:
The carbon content in the reduced iron obtained by smelting reduction is 1.5 to
It is important to keep the content within the range of 4.5%. As a method of adjusting the additional charge of the carbonaceous reducing agent, the molten iron in the arc heating type melting furnace is sampled, and the molten iron is directly collected. Analyze and adjust the addition amount of the carbonaceous reducing agent so that the carbon content is within the above range, or measure the composition and amount of exhaust gas discharged from the arc-heating type melting furnace, and calculate the It is recommended that a method of calculating the carbon content of the molten iron based on the calculated oxygen equivalent of the exhaust gas and adjusting the addition amount of the carbonaceous reducing agent be a preferable method.

Further, in the present invention, there is a great technical feature in that the carbon content of the molten iron is controlled so as to be within the above range, as will be described in detail later.
Si content 0.05% or less, Mn content 0.1% or less, P content 0.1%
In the following, the content of S can be obtained as 0.20% or less, and when this is subjected to desulfurization and dephosphorization treatment by the method described later, the S content is about 0.050% or less, and the P content is Can be reduced to about 0.040% or less, and can be obtained as molten iron with a low impurity content useful as a steelmaking raw material such as an electric furnace (hereinafter abbreviated as EAF) or a converter (hereinafter abbreviated as BOF). .

The following method is recommended as the desulfurization and / or phosphorus removal method employed here. The molten iron melted in the arc-heating type melting furnace is transferred to another container, and a lime-based flux for deflow is added (or injected with a gas) to desulfurize, and / or
Alternatively, a method of removing phosphorus by blowing gaseous oxygen and a lime-based flux containing a solid oxygen source (such as iron oxide).

[0018] Note that the method of the present invention, low reduction potential when reducing iron oxide sources such as iron ore as compared to blast furnace iron making method, SiO ₂ gangue component as Si O ₂ without being reduced Slag. Therefore, since the Si content of the obtained molten iron is low (less than 0.05%), no special desiliconization treatment is required. Moreover, since the Si content in the molten iron is low, low P molten iron can be easily obtained by the above-mentioned dephosphorization treatment without any need for preliminary desiliconization.

The thus obtained molten iron having a reduced impurity content can be put to practical use as an integrated steelmaking / steelmaking method by supplying it as a steelmaking raw material to an adjacent EAF or BOF in a molten state. Alternatively, the produced molten iron may be once discharged outside the furnace, and the cooled and solidified metallic iron may be supplied to EAF or BOF as a steelmaking raw material. In particular, if a method is used in which high-temperature molten iron with a low impurity content produced by the above method is supplied to EAF or BOF as a raw material for steelmaking in a molten state and steelmaking is performed, the thermal energy held by the molten iron is refined. It is recommended as a very economical method because it can be effectively used as a heat source for the process.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an overall configuration of the present invention will be outlined with reference to an overall flowchart showing one embodiment. The reason why conditions and the like are determined for each process will be described in detail.

FIG. 1 is a schematic flow chart showing an iron making method and an integrated iron / steel making method according to the present invention. In the figure, a raw material forming unit 1, reduced iron manufacturing equipment 2, and an arc heating type melting furnace 3 are shown. And the steelmaking furnace 4 are shown. A series of steps indicated by an arrow A corresponds to an iron making (production of reduced iron) method, and a step indicated by an arrow B corresponds to a steel making method.

First, in the iron making method, a raw material molded body manufacturing unit 1 uses a carbonaceous material-containing iron oxide-containing molded body using an iron oxide source such as iron ore and a powder of a carbonaceous reducing agent such as coal powder and coke powder as raw materials. (Pellets, briquettes, etc.) are produced, and the produced compacts are successively sent to the reduced iron production facility 2. The reduced iron production facility 2 is configured to heat a carbonaceous material-containing iron oxide-containing molded body (hereinafter, sometimes simply referred to as a molded body), and to reduce the reducing power of the interior carbonaceous material while maintaining a substantially solid state. What is necessary is just to have a function of promoting the reduction of the iron oxide content in the compact by the reducing power of the CO gas generated by the combustion. For example, a product having an arbitrary structure such as a rotary kiln type or a rotary hearth type can be used. The equipment 2 is provided with a means for transferring the compact, a heating source such as a burner, an oxygen supply section for combustion, a reducing gas supply section if necessary, and a thermometer or temperature control means. A structure in which the progress state can be appropriately controlled is used. In FIG. 1, a rotary hearth type is used, in which the compact charged from the charging portion 2a is heated and reduced while moving along with the movement of the rotary hearth, and is sequentially discharged when a predetermined reduction rate is reached. This shows a configuration in which the liquid is discharged from the portion 2b in a solid state.

The solid reduced iron discharged after being reduced in the reduced iron production facility 2 is continuously sent to the arc-heating type melting furnace 3 without being substantially cooled, and is formed into a compact in the melting furnace 3. The heat reduction of the iron oxide remaining in the unreduced state proceeds, and the dissolution of the reduced iron is performed simultaneously. Note that the solid reduced iron discharged from the reduced iron manufacturing facility 2 generally has heat of about 700 to 1300 ° C., and this heat is used as it is as a heat source of the arc heating type melting furnace 3. This can contribute to a reduction in energy consumption for arc heating.

The arc-heating type melting furnace 3 used here heats the molten iron using the arc heat without forcibly stirring, and reduces the melting loss of the refractory lining as much as possible while efficiently reducing and melting. The arc has a function to advance well, and the arc includes a submerged arc generated by charging the electrode 3a into the slag floating on the molten iron in the melting furnace 3 and energizing the slag. Then, an arc heating unit (that is, the electrode 3a) is provided so that the solid reduced iron charged into the arc heating melting furnace 3 is quickly reduced and melted by receiving the arc heat.
The raw material (solid reduced iron) charging portion 3b is provided near the (insertion portion). Further, the additional charging section 3c for the carbonaceous reducing agent is provided toward the charging position of the solid reduced iron.

In the arc-heating type melting furnace 3, molten iron (sometimes referred to as molten metal or molten iron) is generated by reduction and melting of the charged solid reduced iron A, which has already been generated before. The gangue component that is sequentially taken into the generated and retained molten iron and coexisting in the solid reduced iron A becomes molten slag and joins with the molten slag floating on the molten metal surface. Therefore, when a predetermined amount of molten iron or molten slag accumulates in the arc-heating type melting furnace 3, molten iron or molten slag is appropriately extracted sequentially from a position below the side wall of the melting furnace 3 or an interface position between the molten slag and the molten iron. The molten slag may be appropriately extracted from slightly above.

The obtained molten metal iron is subjected to a purifying treatment such as desulfurization or dephosphorization if necessary, and then sent to the steelmaking furnace 4 as a steelmaking raw material. EAF4a or B as steelmaking furnace 4
OF4b or the like is used, and refining is performed in this portion by mixing with iron scrap, pig iron, or the like. At this time, if the steelmaking furnace 4 is arranged adjacent to the arc-heating type melting furnace 3, high-temperature molten reduced iron can be supplied as a raw material of the steelmaking furnace 4 without substantially lowering the temperature. This is most preferable in terms of thermal efficiency because the retained heat of the molten reduced iron can be used as it is as a heat source for refining. Depending on the case, the molten reduced iron obtained in the arc-heating type melting furnace 3 may be once received in a mold or the like, cooled and solidified, and commercialized as an intermediate steelmaking raw material, or may be sent as a steelmaking raw material to a remote steelmaking furnace. It is possible.

As described above, the molten reduced iron obtained by the present invention has an extremely small amount of mixed foreign metal elements as compared with scrap. Therefore, by using an appropriate amount of scrap together with the scrap, it is possible to dilute the impurity metal elements in the scrap. It can be effectively used as an agent.

Although the basic steps in the present invention are as described above, in order to carry out such steps efficiently on an industrial scale, the metallization ratio of the solid reduced iron in the reduced iron production facility, the solid reduced iron It is extremely important to adjust the carbon content in the steel, the specific gravity of the solid reduced iron, and the like, and it is necessary to appropriately control the carbon content of the molten iron produced by smelting reduction using the arc-heating type melting furnace 3. It is extremely important. Hereinafter, they will be described in detail.

First, in forming the iron oxide-containing compact supplied to the reduced iron production facility 2,
Each powder of an iron oxide source such as iron ore and a carbonaceous reducing agent such as coal or coke is kneaded with an appropriate amount of a binder as necessary, and the kneaded material is optionally mixed using a granulating device or a pelletizer. What is shape | molded in the shape of and the pre-baked as needed is used. In the production of the compact, in order to promote the reduction in the reduced iron production facility 2 efficiently, the theoretical equivalent required to reduce the iron oxide with respect to the iron oxide contained in the iron oxide source and the reduced iron production facility In view of the reduction reaction characteristics of the above, it is desirable to mix a carbonaceous reducing agent necessary for obtaining a target residual carbon amount with an iron oxide source. In addition, in order to obtain solid reduced iron having a “metallization ratio of 60% or more” which is important in performing the stable operation of the method of the present invention, it is necessary to obtain reduced iron having a predetermined target metallization ratio. What is necessary is just to mix a carbon material, and to appropriately control the atmospheric temperature of the reduction furnace, the reaction time, and the like.

Next, in the present invention, it is an important requirement to advance the metallization rate of the solid reduced iron obtained in the preliminary reduction step in the reduced iron manufacturing facility 2 to 60% or more as described above. That is, in order to carry out the smelting reduction by the arc heating type melting furnace 3 in the next step from the preliminary reduction by the reduced iron manufacturing equipment 2 stably and efficiently as an integrated process, the reduced iron manufacturing equipment 2 is transferred to the arc heating type melting furnace 3. It is important to minimize the variation in the metallization rate of the supplied solid reduced iron. If the metallization ratio fluctuates greatly, it becomes difficult to control the operating conditions such as the amount of the carbonaceous reducing agent added in the melting furnace 3 and the heating conditions, and it is difficult to rapidly reduce the smelting of solid reduced iron. In addition to this, it becomes difficult to control the carbon content in the molten reduced iron.

That is, when the metallization ratio of the solid reduced iron supplied to the arc heating type melting furnace 3 is less than 60%, the heat of reaction (endothermic reaction) required for the reduction of the unreduced iron oxide remaining in the solid reduced iron ), A large amount of heat must be supplied in the melting furnace 3. Specifically, a large amount of electric power must be supplied to the electrode for arc heating, and not only the reduction load of the melting furnace is remarkably increased, but also the erosion of the refractory lining of the melting furnace 3 becomes severe, This is because this extremely shortens the life of the melting furnace 3 and makes it difficult to put it to practical use on an industrial scale. However, if the metallization rate of the solid reduced iron is increased to 60% or more, preferably 70% or more, an excessive reduction load does not occur in the arc-heating type melting furnace 3 and the above-described problem is avoided. Thus, smooth smelting reduction can be performed.

The specific means for increasing the metallization ratio of the solid reduced iron obtained in the reduced iron manufacturing facility 2 to 60% or more is not particularly limited, and the amount of the carbonaceous reducing agent when the raw material molded body is manufactured (Equivalent ratio to iron oxide content) may be appropriately adjusted, and pre-reduction conditions (temperature, reduction potential, processing time, etc.) in reduced iron production facility 2 may be appropriately controlled. Regarding these conditions, the relationship between these conditions and the metallization ratio is checked in advance in a preliminary experiment, and if this is applied to actual operation, a predetermined metallization ratio can be easily secured without causing significant variation. be able to.

The solid reduced iron supplied to the arc-heating type melting furnace 3 has the specific gravity of the solid reduced iron of 1.7 or more in addition to the above-mentioned metallization ratio, and has a carbon content in the solid reduced iron. It is important that the content is 50% or more of the theoretical equivalent required for reducing the iron oxide remaining in the solid reduced iron.

The reasons for defining the above requirements are as follows. That is, as shown in FIG. 2 (schematic diagram), for example, as shown in FIG. 2 (schematic diagram), the solid reduced iron A charged into the arc-heating type melting furnace 3 is molten slag that has already been generated in the melting furnace 3 and floated on the molten iron. It is thrown on S. In order to efficiently heat the solid reduced iron A by the arc heat and promptly carry out the reduction, it is necessary that the solid reduced iron A sinks into the molten slag S and receives heat from the entire surface.
As a result of various experiments, in order to promptly reduce the solid reduced iron A into the molten slag S and promptly promote the reduction, the specific gravity of the solid reduced iron A is set to 1.7 or more.
In addition, it was confirmed that the carbon content in the solid reduced iron A should be 50% or more with respect to the theoretical equivalent necessary for reducing the iron oxide remaining in the solid reduced iron A.

The general specific gravity of the molten slag is about 2.4 to 2.7, but the reason why the solid reduced iron A having a specific gravity of about 1.8 gets into the molten slag S is considered as follows. . That is,
The solid reduced iron A charged on the molten slag S in the melting furnace 3 receives heat from the surface of the molten slag S, and undergoes a reduction reaction generated by a carbonaceous reducing agent remaining inside, thereby causing the solid reduced iron A to undergo solid reduction. CO gas and a small amount of CO ₂ gas are mainly generated around the iron A, and these are foamed and mixed into the molten slag S to foam (see FIG. 2A), and the specific gravity of the molten slag S decreases. I will do it. Then, when the solid reduced iron A further sinks into the molten slag S (FIG. 2B), the gas generated from the solid reduced iron A further increases, and the foaming of the molten slag S becomes more intense. The specific gravity of the solid reduced iron A
Further sinks into the molten slag S, and after the entire solid reduced iron A sinks,
The reduced iron A receives heat from the molten slag S from the entire surface (FIG. 2C), and the solid reduced iron A is rapidly reduced and melted. Then, the molten iron is sequentially taken into the molten iron Fe, and the by-product slag component is sequentially taken into the molten slag S.

At this time, when the specific gravity of the solid reduced iron is less than 1.7, the solid reduced iron A put on the molten slag S in the arc heating type melting furnace 3 as shown in FIG. As it floats on the molten slag S, it does not sink into the molten slag S, the contact area with the molten slag S decreases, the heating efficiency decreases, the reduction reaction speed decreases, and the processing time increases. As a result, productivity is remarkably reduced, and industrial and economical practical use becomes difficult.

However, when the specific gravity of the solid reduced iron A is 1.7 or more, more preferably 1.8 or more, and still more preferably 1.9 or more, on the molten slag S as shown in FIGS. 2B and 2C. The solid reduced iron A charged into the slag sinks into the molten slag S within a very short time due to a specific gravity difference, and receives heat of the molten slag S over the entire surface, so that the heating and reduction proceeds rapidly, so that the reduction efficiency is reduced. The reduction reaction is remarkably improved and the reduction reaction is completed promptly. On the other hand, the amount of iron oxide dissolved in the molten slag S is also minimized, and the erosion of the refractory lining is also minimized.

As described above, the heat transfer efficiency of the arc heat transmitted through the molten slag S is extremely important for the reduction efficiency of the solid reduced iron A. Even if the specific gravity is proper, if the amount of the carbonaceous reducing agent contained in the solid reduced iron A is insufficient, a satisfactory reduction efficiency cannot be obtained. In the melting furnace 3, it is possible to additionally add the carbonaceous reducing agent necessary for reduction separately from the solid reduced iron A. However, the additional carbonaceous reducing agent is only added around the solid reduced iron A. Is not supplied to the inside of the solid reduced iron A, but the reducing power is not effectively exerted unless the solid reduced iron A is melted. Depends on the amount of the carbonaceous reducing agent present in the solid reduced iron A.

From such a viewpoint, as another requirement for efficiently promoting the heat reduction of the solid reduced iron A charged into the melting furnace 3 in a short time, the carbonaceous reducing agent contained in the solid reduced iron A is required. As a result of examining the amount, the carbon content in the solid reduced iron A was set to 50% or more, more preferably 70%, with respect to the theoretical equivalent required for reducing the iron oxide remaining in the solid reduced iron A. By doing so, it has been found that reduction of unreduced iron oxide in solid reduced iron A proceeds promptly by receiving heat from the outside, and high reduction melting efficiency is obtained.

It is best that the carbon content is 100% or more. However, even if there is a shortage of about 50% in the carbon content, the carbon content of the shortage is separately reduced by carbonaceous reduction. It has been confirmed that by adding an additional agent, the iron oxide in the unreduced state flowing out due to the melting of the solid reduced iron A is rapidly reduced, and practically no obstacle is caused. Therefore, the carbon content in the solid reduced iron A supplied to the arc-heating type melting furnace 3 is 1 to the theoretical equivalent required for the reduction of the iron oxide remaining in the unreduced state.
If it is less than 00%, the shortage of carbon may be additionally charged as a carbonaceous reducing agent in the vicinity of the input portion of the solid reduced iron A.

The specific gravity of the solid reduced iron produced in the above-mentioned reduced iron production facility depends on the properties and the mixing ratio of the raw materials supplied to the reduced iron production facility, and also on the reduction conditions (particularly the ambient temperature and time) in the reduced iron production facility. ), The relationship between these conditions and the specific gravity may be confirmed in advance by a preliminary experiment, and appropriate conditions may be set in accordance with them.

In addition, in order to adjust the amount of residual carbon in the solid reduced iron, the reduction characteristics in the reduced iron production facility should be sufficiently understood, and their reduction reaction characteristics should be considered from the brand and composition of the blended raw materials. , The amount to be blended is determined, and the heating and reducing conditions (temperature, time, atmosphere gas composition, etc.) may be appropriately controlled.

Next, the reason why the oxygen content of the molten reduced iron A obtained by the arc heating type melting furnace 3 is set in the range of 1.5 to 4.5% will be described.

In the case of the reduced iron manufactured from the iron oxide-containing molded body in which the carbonaceous reducing agent is provided, about 70% of the sulfur contained in the carbonaceous reducing agent such as coal usually remains in the reduced iron. I do. And when this reduced iron is melted in a melting furnace, desulfurization in the melting furnace can hardly be expected, especially when dissolving reduced iron with a low metallization rate, and therefore, it was brought into the melting furnace. Most of the sulfur content migrates into the molten iron, resulting in the production of high S molten iron.

The sulfur content in the molten iron can be desulfurized using a lime-based flux in a ladle after tapping from a melting furnace. However, the carbon content [C] in the molten iron is 1.
If it is less than 5%, the oxygen concentration [O] existing in the molten iron in an equilibrium state becomes high, so that the subsequent desulfurization efficiency is significantly impaired. Therefore, in order to increase the desulfurization efficiency and facilitate the production of low S molten iron, it is necessary to increase the [C] of the molten iron produced by the arc-heating type melting furnace 3 to 1.5% or more. Required. However, the [C] in the molten iron becomes almost saturated at about 4.5%, and a considerably excessive amount of the carbonaceous reducing agent is introduced into the melting furnace to stably obtain the saturated [C] molten iron. However, it is necessary that the carbonaceous reductant is always present in the slag in the furnace at about 10% or more, which not only increases the cost of the carbonaceous reductant but also increases the decarburization load during the subsequent refining. Is not preferred. A particularly preferable lower limit of the carbon content of the molten iron is 2.0%, and a preferable upper limit is 3.5% in order to enhance the operation stability.

The amount of carbon in the molten iron produced by the arc-heating type melting furnace 9 is adjusted to 1.5 to 4
. The specific method for controlling the content to the range of 5% is not particularly limited, and the optimal conditions for securing such carbon amount (the amount of interior carbon material when manufacturing a raw material molded article, the preliminary The reduction conditions, the additional amount of the carbonaceous reducing agent in the arc-heating type melting furnace, the operation conditions, and the like) can be set in advance by preliminary experiments, and the operation can be performed under the set conditions. The quality of the iron oxide source and carbonaceous reducing agent used as raw materials for the body is not always stable, and usually fluctuates considerably. In order to obtain molten iron, it is desirable to employ, for example, the following method.

The molten iron in the arc-heating type melting furnace is sampled, the molten iron is analyzed, and the amount of the carbonaceous reducing agent is adjusted while measuring the amount of carbon in the molten iron. A method of adjusting the carbon content to an appropriate range.

The composition and amount of exhaust gas discharged from the arc-heating type melting furnace are measured, and the carbon content in the molten iron is calculated from the oxygen equivalent of the exhaust gas calculated from the measured values. A method of adjusting the amount of a carbonaceous reducing agent to be additionally charged according to the amount.

Meanwhile, when the solid reduced iron is reduced and melted in the above-mentioned arc-heating type melting furnace, molten slag generated from the gangue component in the solid reduced iron floats on the molten metal surface. Appropriately controlling the basicity and the iron oxide content of the molten slag increases the reduction efficiency and the separation efficiency of the molten slag in the melting furnace, and suppresses the melting damage of the refractory lining of the melting furnace. It is extremely effective in practical use. In carrying out the present invention, the basicity of the molten slag is adjusted to a range of 1.0 to 1.8 (a more preferred lower limit is 1.1, and a more preferred upper limit is 1.5), and the molten slag is also adjusted. Total iron (T.
Fe), (total amount of iron present as iron oxide) is preferably controlled to 9% or less, more preferably 5% or less.

Slag basicity is one of the basic and representative characteristics that characterize slag properties.
A typical component contained in the molten slag CaO and SiO ₂ ratio, represented by words _{(Ca O) / (SiO 2} ). When the basicity of the molten slag exceeds 1.8, the melting point of the slag rises sharply and the fluidity decreases, and unless the molten iron temperature is intentionally raised, reduction and melting in the melting furnace become difficult to proceed smoothly. If the basicity is less than 1.0, the erosion of the refractory lining becomes severe. Further, the melting damage of the refractory lining of the melting furnace increases as the amount of iron oxide in the molten slag increases. This tendency is due to the
T. When Fe) exceeds 9%, it appears remarkably. Accordingly, in order to efficiently promote the reduction and melting of the solid reduced iron in the melting furnace in a short time and to extend the life of the melting furnace by minimizing the erosion of the refractory lining, it is necessary to use a solid-state furnace using an arc heating melting furnace. In the reduction / dissolution step of reduced iron, a molten slag is appropriately collected, its basicity and (T.Fe) amount are measured, and a slag basicity modifier (CaO or SiO ₂ ) is added to adjust the basicity of the slag to an appropriate range. Or the additional amount of the carbonaceous reducing agent is adjusted so that (T.
It is desired to reduce the amount of Fe).

As described above, by reducing and melting in the arc heating melting furnace 3, molten iron having a carbon content of 1.5 to 4.5% and a Si content of about 0.05% or less is obtained. As described above with reference to FIG. 1, this is slightly different depending on the amount of [C] in the molten iron, but it is possible to obtain EAF or B in a molten state having heat of about 1350 ° C. or more.
It can be used as an intermediate product for steelmaking after being supplied to a steelmaking furnace such as OF, or once taken out into a mold and cooled and solidified. However, since a large amount of sulfur and phosphorus is contained in the molten iron obtained above, it is preferable to remove these sulfur and phosphorus before sending to the steelmaking process.

As a preferable desulfurization method employed for this purpose, the molten iron produced in the melting furnace 3 is poured into a ladle or the like, and a new lime-based flux is added thereto for desulfurization. A method of injecting a lime-based flux into molten iron together with an inert gas using a blowing lance immersed in water, trapping sulfur with the flux and separating and removing it as slag on the surface of the molten metal is exemplified. As a preferable dephosphorization method, a solid oxygen source (eg, iron oxide) or a gaseous oxygen source (eg, oxygen or air) is supplied to the molten iron discharged from a ladle or the like, together with a lime-based flux, so that the phosphorus component is given priority. Oxidized to the flux, trapped by the flux, and floated and separated on the molten iron. These desulfurization methods and dephosphorization methods are not limited, and it is of course possible to employ other known desulfurization and dephosphorization methods. However, if the latter dephosphorization method is adopted, unlike the known blast furnace hot metal, the [Si] of the molten iron produced in the melting furnace is as low as 0.05% or less as described above, and special desiliconization treatment is performed. This is preferable because a high dephosphorization rate can be ensured at least.

When these desulfurization and dephosphorization treatments are performed, [C]: 1.5 to 4.5%, [Si]: 0.
[Mn]: about 0.1% or less, [S]: about 0.05% or less,
[P]: At about 0.04% or less, the balance can be obtained as high-purity reduced iron substantially composed of Fe, and can be used very effectively as a steelmaking raw material. In particular, the molten iron obtained by this method has a high iron purity and a very low content of other impure metal components. Therefore, using this as a raw material for steelmaking, for example, about 20 to 50% of another iron source (scrap, pig iron, etc.) is used. When used in combination, it acts as a diluent for the impurity metal element mixed in from the scrap or the like, and it is possible to obtain steel with a low impurity metal element content. Of course, depending on the content of the impurity metal element in the scrap used in combination, the combined ratio of the reduced iron can be selected from a range other than the above range, or the production of steel having a high iron purity by using 100% of the reduced iron. It is also effective to perform
At the end of the steelmaking process using F or BOF, other metal elements can be positively added to produce an alloy steel.

In any case, the above-mentioned reduced iron obtained by the method of the present invention has a great feature that the content of an impurity metal element is very small. Can be widely used in the manufacture of

Next, the “metallization rate of the solid reduced iron: 60% or more” defined in the present invention, “the carbon content in the solid reduced iron: reducing the iron oxide remaining in the solid reduced iron” 50% or more of the theoretical equivalent (hereinafter sometimes referred to as FeO equivalent carbon amount) necessary for the above, "specific gravity of the solid reduced iron: 1.7 or more", "molten iron produced in an arc heating type melting furnace" The basis determined for carbon content of 1.5 to 4.5 "will be described in more detail.

The metallization rate curve of the solid reduced iron produced by the reduced iron production facility defined in the “metallization rate of solid reduced iron: 60% or more” indicates that the iron oxide raw material and the carbonaceous reducing agent to be blended are It varies depending on the composition and blending ratio, and furthermore, the reducing conditions. The metallization ratio curve shows, for example, a tendency as shown in FIG.

That is, the point A in the curve of FIG. 3 indicates a point where the metallization ratio is 76% and the residual carbon amount is 4.8%, and the point B is a point where the metallization ratio is 85% and the residual carbon amount is 1.6%. Is shown. The residual carbon content was 142% at the point A and 63.5 at the point B with respect to the FeO reduced equivalent carbon amount.
%, And the amount of residual carbon decreases as the reduction time elapses. The curve in FIG. 3 is an example in which the metallization rate of the solid reduced iron is suppressed to a low level by changing the raw material composition and the like. In any case, the metallization rate rises sharply at first as the reduction time progresses, and the rising curve becomes gentler as the metallization rate increases with time.

Meanwhile, in the continuous process of producing and reducing and dissolving solid reduced iron employed in the present invention, the metallization rate of the solid reduced iron produced in the reduced iron production facility is controlled by an arc-heating type melting furnace (hereinafter, referred to as a melting furnace). This has a significant effect on the operability of the arc melting furnace. For example, FIG.
Is a graph showing the relationship between the metallization ratio of solid reduced iron and the basic unit of electric power consumed for reduction and melting of unreduced iron oxide in an arc melting furnace. When performing continuous operation of the reduced iron production facility and the arc melting furnace, it is important to ensure stable operation of the arc melting furnace, and as the power supplied to the arc melting furnace increases, the And the heat shock applied to the refractory lining of the melting furnace increases. For this reason, in order to reduce the thermal shock to the electrode device and the furnace wall, the furnace body must be large, which is economically and practically inferior.

[0059] In a normal arc melting furnace, such a problem is remarkably exhibited when the power consumption unit is 800
kWh / tmi is exceeded. Therefore, in order to obviate the above-mentioned obstacles beforehand, the metallization ratio of the solid reduced iron supplied to the arc melting furnace is set to 60% or more, more preferably 70% or more. Should be suppressed.

The variation in the metallization ratio of the solid reduced iron produced by the reduced iron production facility is greatly affected by the absolute value of the metallization ratio. The lower the metallization ratio, the greater the variation. FIG. 5 is a graph showing the results of examining the variation in the metallization rate for the solid reduced iron having an average metallization rate of 62.8% and 80.2%.
It can be confirmed that the lower the metallization ratio, the more the variation becomes significant. In actual operation, the target metallization ratio itself becomes unstable if the variation in the metallization ratio becomes large. Therefore, in order to secure a stable target metallization ratio, the metallization ratio needs to be set higher. As a result of various experiments, it was confirmed that the average value of the metallization ratio should be 60% or more, more preferably 70% or more, in order to suppress the variation of the metallization ratio to a level at which practical operation is possible.

[ The Carbon Content in the Solid Reduced Iron: The Basis of Setting the Carbon Content in the FeO Reduction Equivalent to 50% or More] FIG. 6 shows that the solid reduced iron produced under various conditions Fe
It is the graph which showed the result of having investigated the relationship between the O reduction equivalent carbon amount and the iron oxide content in molten slag. In this experiment, the iron oxide content in the molten slag obtained by dissolving with 20 tons of EAF using solid reduced iron having a metallization ratio of 78 to 82% and different FeO equivalent carbon amounts was used. T. Fe) was examined. As is clear from this figure, when the FeO reduced equivalent carbon amount (the theoretical equivalent carbon amount required to reduce unreduced iron oxide) is contained in the solid reduced iron, (T .Fe) is suppressed to a low level, but when the amount of carbon falls below 50% of the FeO reduced equivalent carbon amount (that is, FeO reduced equivalent carbon amount × 0.5), (T.Fe) in the molten slag is reduced. It can be confirmed that the refractory has increased sharply, and consequently the refractory of the lining has become remarkably molten. Therefore, in order to minimize the erosion of the refractory lining and ensure stable operation, the carbon content of the solid reduced iron should be 50% or more of the FeO equivalent carbon equivalent.

In this experiment, the carbon content of the molten iron produced in the arc melting furnace was 2.1 to 2.4.
In each case, the missing carbon material was additionally charged in the arc melting furnace so that
Regardless of the amount of the additional carbon material, the residual carbon amount of the solid reduced iron itself is expressed by FeO
Unless it is 50% or more of the reduced equivalent carbon amount, (T.Fe) in the molten slag cannot be sufficiently reduced. Needless to say, if a sufficient amount of carbon material is added to the iron oxide remaining in the solid reduced iron to ensure the reduced equivalent carbon amount and the target carbon content of the molten iron, (T.Fe. ) Seems to be possible. However, in reality, it is very difficult to maintain the carbon content in the molten iron at a constant value equal to or less than the saturated carbon content, and the carbon content in the molten iron gradually increases with the elapse of the treatment time,
It is not preferable because it becomes difficult to obtain molten iron having the target carbon content.

In the case where the method of the present invention for obtaining solid reduced iron by preliminarily reducing in a solid state the iron oxide formed body containing carbon material based on the basis specified in “specific gravity of solid reduced iron: 1.7 or more” is adopted, Since the body is hollowed by the progress of the preliminary reduction by the amount of the carbon material and the like, the specific gravity of the solid reduced iron is considerably smaller than that of the preliminary reduced iron manufactured by, for example, the Midrex method.

On the other hand, as described in FIG. 2, when reducing and melting the solid reduced iron in the arc melting furnace, in order to increase the reduction and melting efficiency of the solid reduced iron, the solid reduced iron is charged into the arc melting furnace. The solid reduced iron should quickly sink into the molten slag on the molten iron so that the entire surface can efficiently receive arc heat. For that purpose, the specific gravity of the solid reduced iron has a great effect. FIG. 7 shows that the specific gravity is 1.65-1.75 (average specific gravity: 1.6).
The effect of the specific gravity of the solid reduced iron on the reduction melting rate when performing the reduction melting in an arc melting furnace using the solid reduced iron of 5) and 1.8-2.3 (average specific gravity: 2.1) was investigated. The horizontal axis is the dissolution rate when each solid reduced iron is charged alone on the molten slag, and the vertical axis is the reduction melting when each solid reduced iron is continuously charged. , Respectively, indicate the critical dissolution rates at which the dissolution can be performed.

As is apparent from this figure, when the average specific gravity of the solid reduced iron is 1.65, even if the solid reduced iron is continuously charged onto the molten slag, the solid reduced iron is not melted. No phenomenon of sinking into the inside is observed, and most of the solid reduced iron undergoes reduction dissolution on the surface of the molten slag. Therefore, the dissolution rate when the solid reduced iron is continuously charged is approximately 100 times the dissolution rate when the solid reduced iron is charged alone. At this level of dissolution rate, reductive dissolution by continuous charging cannot be performed on a practical scale. On the other hand, in the case of the solid reduced iron having an average specific gravity of 2.1, the solid reduced iron charged on the molten slag quickly enters into the slag and the reduction and dissolution proceeds efficiently. The dissolution rate at the time of continuous charging is greatly increased as compared with the case where charging is carried out at a rate of, and a continuous dissolution rate of about 300 times can be obtained. With such a dissolution rate, continuous reduction dissolution can be sufficiently practically used on an industrial scale.

Regarding the influence of the specific gravity of the solid reduced iron, the aspect at the time of dissolution greatly changes around an average specific gravity of 1.7, and the continuous dissolution rate rapidly changes. And the average specific gravity is 1.7
If it is less than 1, a dissolution rate that can withstand continuous operation on an industrial scale cannot be obtained, and the average specific gravity is 1.
When it is 7 or more, more preferably 1.9 or more, it is possible to secure a dissolution rate sufficient for performing continuous operation.

The basis defined in “The carbon content of molten iron produced in an arc-heating type melting furnace: 1.5 to 4.5” Generally, there is a close relationship between the amount of carbon in molten iron and the amount of dissolved oxygen. The amount of dissolved oxygen in the molten iron increases as the amount of carbon in the molten iron decreases. The higher the dissolved oxygen content, the higher the oxygen potential of the molten iron, which is disadvantageous for desulfurization.
As a result, the oxygen potential of the molten slag, which is in equilibrium with the molten iron, also increases, and as a result, the FeO concentration in the molten slag increases, the reactivity with the refractory increases, and the erosion of the refractory lining the melting furnace becomes severe. . Therefore, in order to increase the desulfurization rate during the desulfurization process and to suppress the erosion of the refractory lining of the melting furnace and prolong its life, it is necessary to set the carbon content in the molten iron to a somewhat high level. Become.

FIG. 8 is a graph summarizing the relationship between the carbon content in the molten iron and the desulfurization rate obtained by many experiments. In this experiment, a method in which a CaO-based desulfurizing agent is injected into molten iron in a ladle is adopted, and data when the desulfurizing agent basic unit is fixed is shown. As is clear from this figure, when the carbon content in the molten iron is less than 1.5%, the desulfurization rate is remarkably reduced, and in order to secure the target desulfurization rate, a large amount of desulfurizing agent must be injected. As a result, a large amount of metallic iron is taken into slag generated in a large amount, and iron loss increases. That is, in order to make the present invention practicable on a practical scale, it is necessary to consider additional problems such as the treatment of slag generated with desulfurization, and to efficiently perform ladle desulfurization with a small unit of desulfurizing agent, 1.5% or more, more preferably 2.0% of carbon content in molten iron
That's it.

However, the carbon content in the molten iron reaches a saturation state at about 4.5%, and in order to stably obtain a reduced molten iron having a saturated carbon content, a considerably excessive amount of a carbonaceous reducing agent is used. The carbon content is 4.5% or less, more preferably 3.5 or less.

The basis defined in “Molten slag basicity: 1.0 to 1.8” This basicity (that is, the ratio of CaO / SiO ₂ ) is not an essential requirement in the present invention. Not only has a considerable effect on the reduction and dissolution efficiency of the solid reduced iron, but also has a great effect on the erosion of the refractory lining of the melting furnace.

That is, the basicity of the molten slag has a great influence on its fluidity. For example, as shown in FIG. 9, as the basicity decreases, the melting temperature of the slag decreases, the fluidity increases, and the reduction and dissolution of solid reduced iron Although this has a positive effect on the efficiency, the reactivity with the refractory increases, and the refractory of the lining refractory becomes severely damaged. On the other hand, when the basicity increases, the melting temperature of the slag rises, and thus the furnace temperature must be excessively increased to melt the slag. The effect of heat on the air also increases. As shown in FIG. 9, such a tendency becomes remarkable when the slag basicity is less than 1.0 or exceeds 1.8, so that the basicity of the molten slag in the arc melting furnace is 1.0 to 1.8, More preferably, it is desirable to adjust to a range of 1.3 to 1.6.

[0072]

【Example】

Next, examples of the present invention will be described. The present invention is not limited by the following examples, and can be appropriately modified and implemented without departing from the scope of the present invention, and they are included in the technical scope of the present invention.

EXAMPLES [0091] Each of the crushed iron ore and coal and a small amount of a binder (bentonite) are used, and these are blended so that the carbon in the coal becomes the theoretical equivalent to the iron oxide in the iron ore.
These were formed into a substantially spherical shape having a diameter of about 13 to 20 mm by a granulator, and the iron oxide-containing formed body containing the carbon material was used as a raw material formed body. An example of the composition of the iron ore and the coal used is shown below.

Composition of iron ore: T.Fe = 65%, FeO = 0.7%, SiO ₂ = 2.5% Al ₂ O ₃ = 2.10%, CaO = 0.04% Coal composition: Total Carbon content = 77.6%, fixed carbon = 71.2%, volatile content = 17.0%, ash content = 11.8%

The above molded product (raw pellet) is supplied to a rotary hearth type reduced iron production facility,
Heat reduction was performed at 50 to 1350 ° C. for an average residence time of 7 to 9 minutes in a rotary furnace to produce solid reduced iron. The amount of unreduced iron oxide and the amount of residual carbon in the obtained solid reduced iron differ depending on the heating and reducing conditions. In this example, the heat reduction conditions were adjusted so that the metallization ratio of iron oxide in the solid reduced iron was 60% or more. Table 1 shows an example of the metallization ratio and component composition of the obtained solid reduced iron. Further, the weight and specific gravity of the solid reduced iron obtained in the same experiment are, for example, as shown in FIG. 10 and are almost irrelevant to the weight per piece, and the average specific gravity is in the range of 1.7 to 2.5. It is.

[0076]

[Table 1]

The solid reduced iron obtained by the above reduced iron production facility is provided as close to the reduced iron production facility as possible so as not to come into contact with the atmosphere and at a high temperature (1000 ° C. in this experiment). It is continuously charged into the obtained arc-heating type melting furnace, and further reduced and melted. At this time, a fixed amount of molten iron is held in the melting furnace, and the basicity of the molten slag floating on the molten iron is adjusted to a range of 1.0 to 1.8, so that the molten iron is heated for arc heating. The electrodes were energized while protruding into the molten slag, and a submerged arc heating method was employed. Then, the solid reduced iron was charged toward the vicinity of the arc heating section, and coal was additionally charged toward the solid reduced iron charging position, and reduction and melting by arc heating were advanced.

The reduced solidified iron in the reduction / melting step contains more SiO ₂ as a slag forming component than other oxides. As the dissolution of reduced iron progresses in the melting furnace, the basicity decreases. Therefore, a flux containing mainly calcined lime and, if necessary, calcined dolomite is added as a basicity adjusting agent to reduce the basicity of the molten slag to 1 It adjusted to the range of 0.0-1.8. According to this method, when the basicity of the molten slag exceeds 1.8 as described above, the molten slag becomes viscous, the solid reduced iron does not easily sink into the molten slag, and the heat reduction efficiency decreases. It was confirmed that the melting of the refractory lining became remarkable when it was less than 0.0.

In this heating reduction / melting step, the solid reduced iron charged on the molten slag contacts the molten slag and receives arc heat, and the unreduced iron oxide is reduced by the carbon remaining inside. Then, CO gas is released to the surface of the solid reduced iron, the solid reduced iron moves around actively, and the molten slag foams violently by the CO gas. Then, as the specific gravity decreases due to the foaming, the solid reduced iron sinks into the molten slag and undergoes further heat reduction, and the unreduced iron is almost completely reduced by the action of the carbonaceous reducing agent additionally charged in the vicinity thereof. As it melts, it is taken in the lower molten iron.

At this time, the specific gravity of the charged solid reduced iron is 1.7 or more, more preferably 1.8.
As described above, more preferably, when it is 1.9 or more, it quickly sinks into the molten slag after being charged from the molten slag, and the heat reduction proceeds efficiently in a short time, but the specific gravity is less than 1.7. At one time, the charged solid reduced iron is unlikely to sink into the molten slag, so heat transfer from the molten slag is insufficient, foaming is reduced, and the time required for heat reduction is greatly delayed, Accordingly, the amount of iron oxide dissolved in the molten slag also increases, and the refractory lining of the melting furnace is easily melted.

Further, when the carbon content in the solid reduced iron is less than 50% of the theoretical carbon amount required for reducing the unreduced iron oxide in the solid reduced iron, the reduction efficiency is insufficient. Thus, even if the carbonaceous reducing agent is additionally charged into the melting furnace, the reduction rate is slow, the iron oxide content in the molten slag is increased, and the refractory lining material is significantly damaged.

In the heating and reducing step, the amount of carbon is measured by periodically sampling molten iron, and the addition of a carbonaceous reducing agent is performed so that the amount of carbon falls within the range of 1.5 to 4.5%. The input amount was adjusted.

When such a heating reduction / melting process is continuously performed, and when a predetermined amount of molten iron has accumulated in the melting furnace, the molten metal is extracted from a tap hole provided at the bottom of the furnace into a ladle, and the melting furnace is melted. An appropriate amount of molten slag is extracted from the slag discharge hole provided in the side wall of the furnace, and the amount of slag remaining in the furnace is adjusted.

The specific conditions and the results when performing such heat reduction / dissolution are exemplified as follows.

(Properties of Reduced Iron) Composition and the like of solid reduced iron: 3 (metallization ratio: 80%) Charging temperature to the arc-heating type melting furnace: 1000 ° C Charging method: continuous charging (Operating conditions of the arc-heating type melting furnace) Basic unit of electric power to the arc-heating electrode: about 565 KWh / Tmi (mi: molten iron to be produced) (Type and amount of auxiliary raw material) Slaked lime: 92.2 kg / tmi, calcined dolomite: 21.5 kg / tmi Additional coal charge: about 20 kg / tmi Use of reduced iron Basic unit: 1227 kg / tmi (composition of obtained molten iron and formed slag) Molten iron: C: 2.0%, Si: 0.03% or less, Mn: 0.05% or less, P: 0.043%, S : 0.137%, temperature 1550 ° C Slag produced: CaO: 36.5%, SiO ₂ : 26.1%, Al ₂ O ₃ : 18.2%, MgO: 10.0%, T.Fe: 6. 3%, basicity: 1.4

As is clear from the above, the Si content of the molten iron has been sufficiently reduced in the reduction / dissolution step, but the S content and the P content are too large for a steelmaking raw material, Desulfurization and dephosphorization were performed using a ladle to obtain a molten metal having the following composition.

Desulfurizer (lime-based flux) Composition: CaO: 83 to 90%, CaF ₂ : 6 to 10%, C: 4.0% Usage: about 12 kg / tmi Dephosphorizer (lime-based flux + Fe ₂ O) _{3) composition: CaO: 44~45%, CaF 2} : 7~8%, Fe 2 O 3: 47~48% consumption: about 20 kg / tmi molten iron composition after desulfurization and dephosphorization: C: 1.8 2.0%, Si: trace, Mn: 0.02%, P: 0.032% S: 0.038%.

The molten iron (1450 ° C.) after the desulfurization and dephosphorization treatment is charged into an EAF with iron scrap and pig iron in the following composition, and the following auxiliary materials are added thereto and a small amount of oxygen is blown. Electric furnace steelmaking was performed while mixing, to produce molten steel having the following composition. (Electric furnace charging material) Desulfurized and dephosphorized molten iron: 40%, scrap: 50%, pig iron: 10% (auxiliary raw materials) calcined lime: 50.2 kg / tmi, calcined dolomite: 10 kg / tmi, silica stone: 15 0.1 kg / tmi Injection oxygen amount: about 18 Nm ³ / tmi (the obtained molten steel composition) C: 0.10%, Mn: 0.06%, Si: trace, S: 0.022%, P: 0. 018%.

In the above experiment, an example was shown in which molten iron produced in an arc heating type melting furnace and subjected to desulfurization and dephosphorization treatment was supplied to the EAF in a molten state, that is, at a high temperature, and used as an iron making raw material. However, it is also possible to supply the molten iron to the BOF as a raw material for steelmaking, and it is also effective to temporarily take out the molten iron into a mold, cool and solidify it, and use it as an intermediate raw material for steelmaking.

Finally, it is to be understood that the invention is capable of various modifications and implementations in light of the above description and, therefore, is to be understood as falling within the scope of the appended claims. It should be considered that the embodiment can also be implemented.

This application is filed with the Japan Patent Office on Sep. 1, 1997 as Japanese Patent Application No. 9-236.
No. 214, the entire contents of which are included therein.

[0092]

【The invention's effect】

The present invention is configured as described above, and can stably secure a high reduction efficiency, can minimize the erosion of the refractory lining of the processing furnace, can extend the life of the furnace, Along with those effects, the production of reduced iron using iron oxide-containing compacts containing a carbonaceous reducing agent as the main raw material, and the further reduction and melting of solid reduced iron obtained by the production of high-purity molten reduced iron The production can be realized very efficiently on an industrial scale with low energy losses. In addition, the reduced iron obtained by this method has a low content of an impure metal element, so not only by using it as a steelmaking raw material, it is possible to produce a high-purity steel material, but also when producing an alloy steel. Component adjustment is also easy. Further, a steelmaking furnace is provided adjacent to the arc-heating type melting furnace, and the molten reduced iron or the desulfurized / dephosphorized molten metal produced in the melting furnace is used as a steelmaking raw material in a molten state having high heat. If it is supplied to the steelmaking plant, the retained heat of the molten reduced iron can be used effectively as a heat source for steelmaking, so that the heat energy can be further reduced. An extremely efficient method can be established.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a typical example of a continuous process of heat reduction, arc heating melting and steelmaking of a carbonaceous material-containing iron oxide-containing compact according to the present invention.

FIG. 2 is an explanatory diagram showing a state of heating and reducing solid reduced iron charged from above a molten slag of an arc-heating type melting furnace.

FIG. 3 is a graph showing an example of a relationship between a reduction ratio of solid reduced iron and a reduction time obtained in an experiment.

FIG. 4 is a graph showing the relationship between the reduction rate of solid reduced iron and the basic unit of electric power in an arc melting furnace.

FIG. 5 is a graph showing an example of the metallization ratio of solid reduced iron and its variation.

FIG. 6 is a graph showing the relationship between the carbon content in solid reduced iron and iron oxide (T.Fe) in molten slag.

FIG. 7 is a graph showing the relationship between the dissolution rate of solid reduced iron alone and the limit dissolution rate during continuous charging.

FIG. 8 is a graph showing the relationship between the carbon content in molten iron and the desulfurization rate.

FIG. 9 is a graph showing the relationship between slag basicity and melting temperature.

FIG. 10 is a graph showing the weight per piece and the specific gravity of the solid reduced iron.

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission Date] March 1, 2000 (200.3.1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM, HU, ID, IL, IS, JP, KE, KG, KR, KZ , LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW

Claims (20)

[Claims] 1. A carbon content of from 1.5 to 4.
Iron making method to produce 5% molten iron. (a) preparing iron oxide and a carbonaceous reducing agent; (b) producing a molded article from the carbonaceous reducing agent and iron oxide; (c) producing a molded article having a metallization ratio of at least 60% and a specific gravity. Is at least 1.7 and 50% of the theoretical equivalent required to reduce the remaining iron oxide.
(D) heating the solid reduced iron in an arc-heating type melting furnace without substantially cooling the molten iron, the molten iron having a carbon content of 1.5 to 4.5%; Get. 2. The solid reduced iron is placed in the arc-heating type melting furnace at a temperature of 700 to 1
The iron making method according to claim 1, wherein the iron is heated to 300 ° C. 3. The iron making method according to claim 1, wherein a carbonaceous reducing agent is supplied to a supply position of the solid reduced iron in the arc heating type melting furnace. 4. The iron making method according to claim 1, wherein the solid reduced iron is supplied into the molten slag in the arc heating type melting furnace. 5. The iron making method according to claim 4, wherein the pH of the molten slag is 1.0 to 1.8. 6. The iron making method according to claim 4, wherein the iron oxide content of the molten slag is 9% or less. 7. The iron making method according to claim 6, wherein the molten slag has an iron oxide content of 5% or less. 8. The method of claim 1 wherein the carbon content of the molten iron is determined. 9. The iron-making method according to claim 1, wherein the iron-making method is determined by an amount and a composition of an exhaust gas from the arc-heating type melting furnace. 10. The iron-making method according to claim 9, wherein the iron-making method is determined by an oxygen equivalent of the exhaust gas. 11. The iron making method according to claim 1, wherein the molten iron in the arc-heating type melting furnace is transferred to another container and desulfurized. 12. The iron making method according to claim 1, wherein the molten iron in the arc-heating type melting furnace is transferred to another container and dephosphorized. 13. The molten iron according to claim 1, wherein the Si content is 0.05% or less.
The iron making method described in 1. 14. The method according to claim 1, wherein the Mn content of the molten iron is 0.1% or less. 15. The iron making method according to claim 1, wherein the P content of the molten iron is 0.1% or less. 16. The iron making method according to claim 1, wherein the S content of the molten iron is 0.2% or less. 17. A steelmaking method in which molten iron obtained according to claim 1 is supplied to a steelmaking furnace to produce steel. 18. The steelmaking method according to claim 17, wherein the steelmaking furnace is an electric furnace (EAF) or a converter (BOF). 19. (a) cooling the molten iron obtained according to claim 1 to solidify iron,
b) A steelmaking method in which the solidified iron is supplied to a steelmaking furnace to produce steel. 20. The steelmaking method according to claim 19, wherein the steelmaking furnace is an electric furnace (EAF) or a converter (BOF).