JP2012007225A - Method for producing molten steel using particulate metallic iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing molten steel that can melt more efficiently, when particulate metallic iron produced in a reducing-melting furnace, is continuously charged and melted in an arc-furnace for steel-making to produce the molten steel.SOLUTION: In the method for producing the molten steel G by melting the whole charging iron raw materials composed of the particulate metallic iron A, in which raw materials containing carbonaceous reducing material and iron oxide- contained substance, are heated in a rotary-hearth furnace 1 as the reducing-melting furnace and after solid-reducing the iron oxide in this raw material, the produced metallic iron is further heated, melted and aggregated while separating the iron from the slag composition B and produced, and scrap D being the other iron raw material, with the arc-furnace 2; the carbon-content in the particulate metallic iron A is made to be 1.0-4.5 mass% and the carbon in the particulate metallic iron A is burnt by using together with the oxygen-blown refining and also, the using ratio of the particulate metallic iron A to the whole iron raw material, is made to be 40-80 mass%, and after producing molten iron F by charging the scrap D into the arc-furnace 2 at the initial-stage, the particulate metallic iron A is continuously charged into this molten iron F.

Description

  The present invention relates to a method for producing molten steel by melting granular metallic iron produced in a reduction melting furnace such as a rotary hearth furnace in an electric arc furnace.

  Conventionally, in steel arc furnaces, iron materials such as scrap, pig iron (cold iron), and reduced iron are batch charged into the furnace with scrap buckets from the top of the furnace, and after melting, the furnace lid is opened and the iron materials are removed. Additional charging was performed in batches and the method of melting was taken. For this reason, there has been a problem of deterioration of the working environment in which heat loss and time loss and a large amount of dust are scattered outside the furnace during opening of the furnace lid and charging of the iron material.

  As a countermeasure to this, continuous feeding of reduced iron having a relatively uniform component and size has been performed (see, for example, Patent Documents 1 to 3), but reduced iron contains gangue and unreduced iron oxide. Therefore, there is a problem that more melting energy is required than scrap and pig iron (cold iron).

  On the other hand, pig iron (cold iron) has a restriction that the size cannot be reduced due to a manufacturing problem, and large-scale charging and melting cannot be realized by continuous charging.

  In addition, with the aim of improving the productivity of electric arc furnaces for steelmaking, oxygen addition operations have become established, the amount of oxygen used has increased, and the amount of carbon source used commensurate with the amount of oxygen input has also increased.

  As the carbon source, carbon content in hot metal or cold iron, lump coke, powder coke and the like are used.

  However, when hot metal is used, there is a problem that a dedicated manufacturing facility for hot metal and a dedicated charging equipment for the electric arc furnace are required on the upstream side of the steel arc furnace.

  On the other hand, in the case of using refrigeration, since the size is large as described above, there is a problem that the amount of use is restricted because it is limited to charging in a batch and it takes time to dissolve.

  In addition, when using coke batter and coke breeze, the amount of use is restricted depending on the total sulfur and ash composition, and it is trapped by slag when it is inserted into the electric arc furnace, or it is discharged outside the furnace together with the exhaust gas. Therefore, there was a problem that the addition yield was lowered.

  Here, after the raw material containing the carbonaceous reducing material and the iron oxide-containing material is heated in a reduction melting furnace such as a rotary hearth furnace, the iron oxide in the raw material is solid-reduced, and then the produced metallic iron is further heated. In addition, a method for producing high-purity granular metallic iron by agglomerating while being separated from the slag component has been developed (for example, see Patent Documents 4 and 5).

  Compared with reduced iron, this granular metallic iron has slag components removed in advance and can increase the carbon content, so it can be used together with oxygen blowing by continuously charging into an electric arc furnace instead of reduced iron. Thus, it is expected that the melting energy in the electric arc furnace can be greatly reduced and the productivity of molten steel can be greatly improved.

  However, in the electric arc furnace for steel making, a technique for continuously melting such granular metallic iron and melting it more efficiently has not been established yet.

Japanese Patent Laid-Open No. 50-64111 Japanese Patent Laid-Open No. 51-65007 JP 58-141314 A JP 2002-339909 A JP 2003-73722 A

  Therefore, the present invention is a molten steel production that can be more efficiently melted when producing molten steel by continuously charging and melting granular metal iron produced in a reduction melting furnace such as a rotary hearth furnace into a steel arc furnace. It aims to provide a method.

  According to the first aspect of the present invention, a raw material containing a carbonaceous reducing material and an iron oxide-containing substance is heated in a reduction melting furnace, and after the iron oxide in the raw material is solid-reduced, the produced metallic iron is further heated. The molten metal is produced by agglomerating and separating the slag component while separating the granular metallic iron and other iron raw materials in an electric arc furnace and melting the charged iron raw material. The carbon content in the granular metallic iron is set to 1.0 to 4.5% by mass and used in combination with oxygen blowing to burn the carbon in the granular metallic iron, and the granular metal with respect to the total charged iron raw material. The amount of iron used is 40 to 80% by mass, the molten iron is made by initially charging the other iron raw material into the electric arc furnace, and then the granular metallic iron is continuously charged into the molten iron. A feature is a method for producing molten steel using granular metallic iron.

  Invention of Claim 2 is a molten steel manufacturing method using the granular metal iron of Claim 1 which makes the charging speed of the said granular iron per input electric power 1MW be 40-100 kg / min / MW.

  Invention of Claim 3 is a molten steel manufacturing method using the granular metal iron of Claim 1 or 2 which makes the charging position in the molten iron surface of the said granular metal iron be in an electrode pitch circle.

  Invention of Claim 4 is a molten steel manufacturing method using the granular metal iron of any one of Claims 1-3 which makes the average particle diameter of the said granular metal iron 1-50 mm.

  The invention according to claim 5 continuously charges the granular metal iron into the molten iron while forming a molten slag layer formed on the molten iron to always cover the lower end of the electrode. It is a molten steel manufacturing method using the granular metallic iron of any one of 1-4.

  The invention according to claim 6 continuously charges the granular metallic iron produced in the reduction melting furnace into the molten iron in the electric arc furnace at 400 to 700 ° C. without cooling to room temperature. It is a molten steel manufacturing method using the granular metallic iron of any one of -5.

  According to the present invention, the carbon in the granular metal iron is burned by using the granular metal iron produced in a reduction melting furnace and having a carbon content of 1.0 to 4.5% by mass in combination with oxygen blowing. 40-80% by mass of the total charged iron raw material was used, and this was melted by continuously charging it into molten iron made by initially charging other iron raw materials into the arc furnace. It has become possible to greatly reduce the energy and raise the energy efficiency of the electric arc furnace, and to greatly improve the productivity of molten steel.

It is a flowchart which shows schematic structure of the molten steel manufacturing equipment which concerns on embodiment of this invention. It is a graph which shows the relationship between the usage-amount of granular metallic iron with respect to all the charging iron raw materials, and a melting energy in an electric arc furnace. It is a graph which shows the relationship between the usage-amount of granular metal iron with respect to all the charging iron raw materials, and a molten steel production rate in an electric arc furnace. It is a fragmentary longitudinal cross-section which shows schematic structure of a dissolution test apparatus. It is a graph which shows the relationship between the charging speed of granular metal iron and reduced iron, and input electric power in a dissolution test apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
In FIG. 1, schematic structure of the molten steel manufacturing equipment which concerns on one Embodiment of this invention is shown. The facility according to the present embodiment is an example of a case where a rotary hearth furnace 1 and an electric arc furnace 2 as a reduction melting furnace are installed in close proximity.

  And the granular metal iron M used by this invention is manufactured as follows, for example.

  First, a raw material containing a carbonaceous reducing material such as coal and an iron oxide-containing substance such as iron ore is agglomerated into pellets or briquettes. Then, this agglomerated material is placed on a hearth (not shown) on which carbon material C is laid, and is heated to, for example, about 1350 to 1400 ° C. in the rotary hearth furnace 1 to reduce iron oxide in the raw material to solid reduction. After that, the metallic iron to be produced is further heated to about 1400 to 1550 ° C. to be melted, and agglomerated while being separated from the slag component. Then, the mixture of solidified granular metal iron A and slag B is obtained by cooling to about 1000-1100 degreeC in the chill part in a furnace. And after discharging this mixture from the rotary hearth furnace 1 together with the flooring carbonaceous material C, the granular metal iron A is formed by separating and removing the slag B and the flooring carbonaceous material C using the screen 3 and the magnetic separator 4. Obtained (for example, see the above-mentioned patent documents 1 to 3).

  The carbon content in the granular metallic iron A is 1.0 to 4.5% by mass. The reason why the lower limit of the carbon content is set to 1.0% by mass is to secure a necessary C amount according to the type of steel to be manufactured and to enhance versatility as an iron raw material. On the other hand, the reason why the upper limit of the carbon content is 4.5% by mass is that the carbon content is used without weighting the load of additional processing such as decarburization processing. The preferable range of the carbon content in the granular metallic iron A is 1.5 to 3.5% by mass. The carbon content in the granular metallic iron A can be easily adjusted by adjusting the blending amount of the carbonaceous reducing material in the agglomerate and the atmosphere in the rotary hearth furnace 1.

  Here, when the granular metallic iron A is in a molten state in the rotary hearth furnace 1, the carbon in the granular metallic iron A is likely to gather near the surface of the granular metallic iron A. A also has a higher carbon concentration near the surface. For this reason, the granular metallic iron A charged in the molten iron F of the electric arc furnace 2 starts to be easily melted from the vicinity of the surface having a high carbon concentration and a low melting point. The carbon in the molten high carbon concentration molten iron is combusted with oxygen by using it together with oxygen blowing, that is, by blowing oxygen into the electric arc furnace 2, and the heat of combustion in the granular metal iron A The high melting point portion with a low carbon concentration is also easily dissolved.

  The granular metallic iron A and the scrap D as another iron raw material are combined to make the total charged iron raw material, and the use ratio of the granular metallic iron A to the total charged iron raw material is 40 to 80% by mass.

  First, the scrap D is initially charged (batch charged) into the electric arc furnace 2 and is arc-heated and melted at the electrode 7 to make molten iron F.

  Then, while continuing the arc heating, while blowing oxygen (further blowing pulverized coal if necessary), by continuously charging and melting the granular metallic iron A in the molten iron F, the energy of the electric arc furnace 2 The productivity of the molten steel G can be improved while increasing the efficiency, and the molten steel G can be obtained more efficiently.

  Here, the reason why the use ratio of the granular metallic iron A to the total charged iron raw material is 40 to 80% by mass is as follows.

  That is, taking the actual electric arc furnace (internal capacity: 90t, transformer capacity: 74MVA) as an example, the melting energy required to dissolve all the charged iron raw material due to the difference in the usage rate and charging method of granular metallic iron And the influence on the production rate of molten steel was calculated.

  Here, the carbon content of the granular metallic iron was 2.5% by mass. The temperature of the granular metallic iron when the granular metallic iron is “batch charged” and “continuous charged” is room temperature (25 ° C.), and the temperature of the granular metallic iron when “high temperature continuous charged” is 400 ° C. It was. Further, by changing the granular metallic iron from “batch charging” to “continuous charging”, the heat loss of the furnace is 870 Mcal per additional charging (here, 1 Mcal = 4.186605 MJ. The same applies hereinafter). ) The power stoppage time was reduced by 2 minutes, and the boring time was also reduced by 2 minutes.

  The results of the trial calculation are shown in FIGS. FIG. 2 shows the change in dissolution energy required to dissolve the entire charged iron raw material due to the difference in the usage rate of granular metallic iron and the charging method. Moreover, FIG. 3 shows the change of the molten steel production rate by the difference in the usage rate of granular metal iron, and the charging method.

  When the usage rate of the granular metallic iron A is less than 40% by mass, that is, when the usage rate of the scrap D, which is another iron raw material, exceeds 60% by mass, the scrap due to the capacity restriction of a scrap bucket (not shown) for batch charging It becomes necessary to perform the initial charging of D in two steps, and as shown in FIG. 3, even if the granular metallic iron A is continuously charged, the molten steel production rate is greatly reduced.

  On the other hand, if the usage rate of the granular metallic iron A exceeds 80% by mass, the decarburization time is determined by the input power capacity of the arc furnace 2 when the granular metallic iron A is “high-temperature continuous charging”. Since it becomes longer than time and this decarburization time will determine the productivity of molten steel, as shown in FIG.

  From the above results, the ratio of the granular metallic iron A to the total charged iron raw material was 40 to 80% by mass.

  Moreover, it is preferable that the charging speed | rate of the granular metallic iron A per input electric power 1MW shall be 40-100 kg / min / MW for the following reasons.

  That is, in order to grasp the dissolution characteristics of granular metallic iron during continuous charging, a dissolution test was conducted using granular metallic iron having physical and chemical properties shown in Table 1 below as a molten iron raw material and reduced iron as a comparative material. Carried out.

  As a dissolution test apparatus, as schematically shown in FIG. 4, a 500 kg high frequency induction furnace (rated: 350 kW, 1000 Hz), a raw material supply apparatus (hopper capacity: 200 kg, raw material charging speed: 0 to 15 kg / min), A monitor camera for observing the melting state and a data recording device for recording the molten metal temperature and the raw material charging speed were used.

  As melting conditions, C: 0.2 to 0.3% by mass, Si <0.03% by mass, Mn: 0.05% by mass, temperature: 250 kg of an initial molten metal at 1550 ° C., and a molten metal temperature of 1550 to The raw material charging speed was sequentially changed while maintaining the temperature at 1600 ° C., and the power input was adjusted while confirming that the continuously charged iron raw material was smoothly dissolved with a monitor camera.

  The results of the dissolution test are shown in FIG.

  As shown in these charts, the granular metal iron has a maximum dissolution rate of 2.5 to 3.0 times per 1 MW of input power, compared with the reduced iron.

  In addition, that the maximum dissolution rate of granular metallic iron was 2.5 to 3.0 times the maximum dissolution rate of reduced iron in this way, the amount of slag component contained in the reduced iron compared to granular metallic iron. However, it is thought that the reason is that high-frequency induction heating was used instead of arc heating as a heating source for the dissolution test.

  That is, since the apparent density of the granular metallic iron is almost equal to that of the molten iron, the granular metallic iron is melted in a floating state in the molten iron, and the molten iron is sufficiently heated by the high frequency induction heating, so that the dissolution rate of the granular metallic iron is sufficiently increased. On the other hand, reduced iron has almost the same density as molten slag, so it melts in a floating state in molten slag. Unlike arc heating, molten slag cannot be heated sufficiently by high-frequency induction heating. This is considered to be due to the fact that the dissolution rate of reduced iron is greatly reduced compared to granular metallic iron.

  Here, since the melting test apparatus is as small as 500 kg, the heat loss is remarkably larger than that of a 90t electric arc furnace in actual operation. Therefore, the maximum melting per unit input power of granular metal iron obtained in the melting test is as follows. The speed is expected to be even greater when used in an actual arc furnace. Accordingly, the melting rate per 1 MW of the input power of the granular metal iron was estimated as follows when the granular metal iron was continuously charged into the 90t electric arc furnace in actual operation.

  As shown in Table 3 below, when the melting power basic unit of the granular metallic iron in this melting test apparatus is determined, it is 714 kWh / t when the charging speed is 4 kg / min, and 584 kWh when the charging speed is 7 kg / min. / T was obtained. On the other hand, in the actual operation 90t electric arc furnace, there is an actual value of the melting power basic unit in the case where reduced iron is continuously charged. 366 kWh was obtained when the melting power basic unit of granular metallic iron was calculated in consideration of the difference in composition from iron. Therefore, as shown in the table, the charging power efficiency of the melting test apparatus for the actual 90t electric arc furnace is 366/714 = 51.3% when the charging speed is 4 kg / min, and the charging speed is 7 kg. In the case of / min, 366/584 = 62.7%.

  Therefore, in the present dissolution test apparatus shown in Table 2, the maximum dissolution rate [R] per 1 MW of the input power of granular metallic iron is corrected by dividing by the input power efficiency [C] / 100, and the actual operation of 90 t In the electric arc furnace, the maximum dissolution rate per 1 MW of the input power of granular metallic iron was estimated (see the column of “Maximum dissolution rate after correction” in Table 2 above).

  The estimation results are summarized and shown in the “continuous charging” column of Table 4 below. Also, in the same table, when the carbon content of granular metallic iron is 2.5% by mass and this carbon is burned by oxygen blowing to give energy, the granular metallic iron is further charged at 600 ° C. at a high temperature. For each of the cases, the power consumption rate in the above-mentioned 90t electric arc furnace in actual operation was estimated, and the results of estimating the maximum melting rate per 1 MW of the input power of granular metallic iron are also shown.

  From the estimation results shown in Table 4 above, the maximum dissolution rate per 1 MW of input power of the granular metallic iron varies depending on the carbon content of the granular metallic iron and the charging temperature, but in the range of 40 to 100 kg / min / MW. I know that there is. Therefore, it is recommended that the charging speed of granular metallic iron A per 1 MW of input power is 40 to 100 kg / min / MW.

  Moreover, it is preferable that the charging position on the molten iron F surface of the granular metallic iron A is within the electrode pitch circle.

  That is, as described above, since the apparent density of conventional reduced iron is almost the same as that of molten slag, the reduced iron introduced into the molten metal of the electric arc furnace stays in the molten slag layer for a relatively long time. Melting proceeds by arc heating through the molten slag layer. For this reason, there was no restriction | limiting in particular in the charging position of reduced iron.

  On the other hand, since the apparent density of the granular metallic iron A according to the present invention is almost equal to the molten iron F, the granular metallic iron A introduced into the molten metal of the electric arc furnace 2 penetrates the molten slag layer E. The molten iron layer F enters the molten iron layer F, and melting proceeds by arc heating through the molten slag layer E and the molten iron layer F. For this reason, when the granular metallic iron A is inserted at a position away from the electrode 7, heat transfer to the granular metallic iron A is insufficient, and there is a possibility that the undissolved residue of the granular metallic iron A is accumulated in the molten iron layer F. Arise. Therefore, it is particularly recommended that the charging position of the granular metallic iron A on the molten iron F surface is within the electrode pitch circle, whereby the arc heat is more directly and efficiently transmitted to the granular metallic iron A and remains unmelted. Is prevented, and the productivity of the molten steel G is further improved.

  Moreover, it is preferable that the average particle diameter of granular metallic iron A shall be 1-50 mm.

  If the particle size of the granular metallic iron A is too small, fine slag components are likely to be mixed at the time of separation and recovery after being discharged from the rotary hearth furnace 1, and the purity of the iron content is lowered, or when the electric arc furnace 2 is charged. It becomes easy to scatter and an additive yield falls. On the other hand, if the particle size of the granular metallic iron A is too large, it takes time to transfer the heat to the inside of the agglomerated material during the production in the rotary hearth furnace 1, and the productivity is lowered or the inside of the furnace hopper 6 is reduced. This is because clogging occurs at the cut-out portion from the hopper 6 or the melting rate is lowered during melting in the electric arc furnace 2. The more preferable average particle diameter of the granular metallic iron A is 2 to 25 mm.

In the present invention, the average particle diameter is a mass average particle diameter calculated from the representative diameter between each sieve mesh and the mass between the sieve meshes after classification by a sieving method. For example, when the sieve is classified by a _{D 1, D 2 ···, D} n, sieve _{D n + 1 (D 1 <} D 2 <··· <D n <D n + 1), and the sieve _{D k} when the mass between D _{k + 1} is _{W k,} mass average particle diameter _{d m} is defined by _{d m = Σ k = 1,} n (W k × d k) / Σ k = 1, n (W k) The Here, d _k is a representative diameter between the meshes D _k and D _{k + 1} , and d _k = (D _k + D _{k + 1} ) / 2.

  Further, when the granular metallic iron A is continuously charged into the molten iron F of the electric arc furnace 2, the molten slag layer E formed on the molten iron layer F is formed to melt while always covering the lower end of the electrode 7. Preferably it is done. Thereby, the heat of the arc can be transmitted to the molten iron layer F more efficiently without escaping to the upper space, and the dissolution rate of the granular metallic iron A is further improved. The forming height of the molten slag layer E can be adjusted, for example, by blowing oxygen into the molten iron layer F and generating CO gas by decarburization reaction of carbon in the molten iron layer F.

  Moreover, it is preferable to continuously charge the granular metallic iron A produced in the rotary hearth furnace 1 into the molten iron F of the electric arc furnace 2 at a high temperature of 400 to 700 ° C. without cooling to the room temperature.

  Thereby, the sensible heat of the granular metallic iron A can be effectively used, and the unit of melting energy in the electric arc furnace 2 can be further reduced, and the productivity (molten steel production rate) of the molten steel G can be improved (described later). See Examples).

  The reason why the preferable temperature range for the granular metallic iron A is set to 400 to 700 ° C. is as follows. That is, since a certain temperature is required from the viewpoint of effective utilization of sensible heat of the granular metallic iron A, the lower limit temperature is set to 400 ° C., and the granular metallic iron A, the slag component B, and the flooring carbon material C are separated by magnetic separation. At this time, since it is necessary to magnetize the granular metallic iron A, the upper limit temperature was set to 700 ° C. lower than the Curie temperature (770 ° C.) of iron.

In order to charge the granular metallic iron A into the electric arc furnace 2 in a high temperature state, a mixture of the granular metallic iron A, the slag B, and the floor covering carbon material C at about 1000 to 1100 ° C. discharged from the rotary hearth furnace 1 After cooling a little to protect the equipment such as the screen 3, the magnetic separator 4 and the conveyor 5, the granular metallic iron A is separated and recovered by the high-temperature specification screen 3 and the magnetic separator 4, and this granular metallic iron A is converted to the high-temperature specification. What is necessary is just to make it the temperature when it conveys to the upper hopper 6 of the electric arc furnace 2 with the conveyor 5, and once stores it and cuts from this upper hopper 6 to 400-700 degreeC. In order to prevent the granular metal iron A from coming into direct contact with the atmosphere and reoxidizing from the discharge duct for discharging the mixture from the rotary hearth furnace 1 to the furnace hopper 6 of the electric arc furnace 2, N ₂ or the like is preferably blown to create an inert gas atmosphere.

(Modification)
In the above embodiment, the rotary hearth furnace is exemplified as the furnace type of the reduction melting furnace, but a linear furnace may be used.

  Moreover, in the said embodiment, although the agglomerated material formed by agglomerating a carbonaceous reducing material and an iron oxide containing material was illustrated as a raw material containing a carbonaceous reducing material and an iron oxide containing material, it does not agglomerate. These may be used in powder form.

  Moreover, in the said embodiment, although the conveyor of a high temperature specification was illustrated as a conveyance apparatus of the granular metal iron of a high temperature state, you may make it transfer the heat-retained container using a conveyance trolley, a crane, etc.

  Moreover, in the said embodiment, although the case where a rotary hearth furnace and an electric arc furnace were installed close was illustrated, when a rotary hearth furnace and an electric arc furnace are installed apart, a rotary hearth furnace If the granular metallic iron produced in step 1 is cooled to room temperature, the granular metallic iron is once melted and solidified, so it is denser than reduced iron, so there is no need to take special measures to prevent reoxidation. It can be transported to the electric arc furnace using ordinary transportation means.

  Moreover, in the said embodiment, although the scrap was illustrated as another iron raw material initially charged to an electric arc furnace, reduced iron or granular metal iron may be used, and these 2 or more types may be used together. .

  In addition, even when using granular metallic iron as all or part of the other iron raw material initially charged in the electric arc furnace, the granular material continuously charged in the molten iron made from the other iron raw material initially charged. The use ratio of metallic iron with respect to all the charged iron raw materials needs to be 40 to 80% by mass. In other words, when using granular metallic iron as all or part of other iron raw materials initially charged to the electric arc furnace, the ratio of the total granular metallic iron to the total charged iron raw materials is the initial charged amount. Since it becomes the ratio which totaled the continuous charge, it will be a usage rate higher than 40-80 mass%.

1 ... Smelting reduction furnace (rotary hearth furnace)
2 ... Electric arc furnace 3 ... Screen 4 ... Magnetic separator 5 ... Conveyor 6 ... Furnace hopper 7 ... Electrode A ... Granular metal iron B ... Slag C ... Flooring carbon material D ... Other iron raw materials (scrap)
E ... Molten slag, molten slag layer F ... Molten iron, molten iron layer G ... Molten steel

Claims (6)

A raw material containing a carbonaceous reducing material and an iron oxide-containing substance is heated in a reduction melting furnace, and the iron oxide in the raw material is solid-reduced, and then the resulting metallic iron is further heated to melt and separated from the slag component It is a method for producing molten steel by melting all charged iron raw materials composed of granular metallic iron produced by agglomerating while making other iron raw materials in an electric arc furnace,
Combusting the carbon in the granular metallic iron by using together with oxygen blowing and the content of carbon in the granular metallic iron is 1.0-4.5 mass%,
The use ratio of the granular metallic iron to the total charged iron raw material is 40 to 80% by mass,
After the initial charging of the other iron raw material into the electric arc furnace and making molten iron, the granular metallic iron is continuously charged into the molten iron, and the molten steel production using granular metallic iron Method.   The molten steel manufacturing method using the granular metallic iron according to claim 1, wherein a charging speed of the granular metallic iron per 1 MW of input power is 40 to 100 kg / min / MW.   The molten steel manufacturing method using the granular metallic iron according to claim 1 or 2, wherein a charging position of the granular metallic iron on the surface of the molten iron is within an electrode pitch circle.   The molten steel manufacturing method using the granular metallic iron of any one of Claims 1-3 which makes the average particle diameter of the said granular metallic iron 1-50 mm.   The molten metal slag layer formed on the molten iron is formed and the granular metallic iron is continuously charged into the molten iron while always covering the lower end of the electrode. The manufacturing method of the molten steel using the granular metal iron of description.   The granular metallic iron manufactured by the said reduction melting furnace is continuously charged in the molten iron of the said electric arc furnace at 400-700 degreeC, without cooling to normal temperature. A method for producing molten steel using granular metallic iron.