AU2023255850B2 - Method for producing grained iron, and grained iron - Google Patents

Abstract

Provided is a technology that enables efficient production of grained iron having a low P concentration. The present invention comprises: a first step for melting reduced iron to obtain primary molten iron; a second step for separating the primary molten iron from slag; a third step for subjecting the primary molten iron separated from the slag to dephosphorization to obtain secondary molten iron; and a fourth step for solidifying the secondary molten iron into grains to obtain grained iron. In the third step, an oxygen source and a CaO source are supplied to the primary molten iron for dephosphorization, and the temperature of the secondary molten iron when the dephosphorization is finished is set to be equal to or lower than the temperature of the secondary molten iron when the dephosphorization is started.

Description

22 Dec 2025

Title of Invention: METHOD FOR PRODUCING GRAINED IRON, AND GRAINED IRON 5 Technical Field

[0001] The present invention relates to grained iron with a reduced P 2023255850

concentration, and a method for producing the same. Background Art 10 [0002] In recent years, there has been a growing demand for increased use of cold iron sources (scrap) in the steel industry. To build a recycling society, recycling iron sources is essential. Moreover, increasing the use of scrap is essential from the perspective of preventing global warming and responding to the demand for reducing CO2 emissions. The amount of scrap used can reduce 15 CO2 emissions because the production process for the scrap does not require a reduction step unlike with iron ore which is iron oxide (Fe2O3). Thus, the amount of cold iron sources used is increasing more and more.

[0003] The blast furnace-converter method is a steelmaking process that includes supplying iron ore (Fe2O3) as a raw material into a blast furnace 20 together with coke (a carbon source) as a reducing agent, to obtain molten pig iron with a C concentration of approximately 4.5 to 5%, and then supplying the obtained molten pig iron into a converter to remove C, Si, and P, which are impurities, through oxidation. When molten pig iron is produced in a blast furnace, a reduction process for iron ore and the like require approximately 500 25 kg of carbon source to produce 1 ton of molten pig iron, generating approximately 2 tons of CO2 gas. Meanwhile, when molten steel is produced using iron scrap as a raw material, no carbon source is required for the reduction process for iron ore. When the energy needed to melt iron scraps is considered, replacing 1 ton of molten pig iron with 1 ton of iron scrap leads to a reduction of 30 CO2 emissions by about 1.5 tons. This shows that the amount of scraps used should be increased to reduce greenhouse gas emissions while maintaining production activity.

2

[0004]

[0004] However,the However, thetight tight supply-demand supply-demandbalance balanceforforiron ironscrap, scrap, especially especially high-grade iron scrap, which is essential for producing high-grade steel, has high-grade iron scrap, which is essential for producing high-grade steel, has

increased the increased the need need for for reduced reduced iron iron to toreplace replacescrap. scrap. Reduced iron is Reduced iron is produced produced

by reducing iron ore, and it is not necessary to set the C concentration in the by reducing iron ore, and it is not necessary to set the C concentration in the

55 produced iron to a high level as in the blast furnace-converter method. produced iron to a high level as in the blast furnace-converter method. Thus, Thus, since an since an excessive excessive amount of carbon amount of carbonsource sourceis is not not used, used, CO emissionscan CO22 emissions canbe be reduced by reduced by approximately approximately0.2 0.2tons tonsper per 11 ton ton of of iron. Further, when iron. Further, whena ahydrogen hydrogen gas or a hydrocarbon-based gas, such as a natural gas, is used as a reducing agent gas or a hydrocarbon-based gas, such as a natural gas, is used as a reducing agent

instead of a carbon source, CO emissions can be further reduced. instead of a carbon source, CO2 emissions 2 can be further reduced.

[0005]

[0005] Problemsfaced Problems facedwhen whenreduced reduced ironisisused iron usedinclude includephosphorus phosphorus contained in contained in the the reduced reduced iron. Sincephosphorus iron. Since phosphoruscontained contained inina asteel steel product product would cause a decrease in quality, such as hot brittleness, it is necessary to would cause a decrease in quality, such as hot brittleness, it is necessary to

reduce the P concentration to a level corresponding to the required quality. reduce the P concentration to a level corresponding to the required quality.

However,when However, when molten molten iron iron is isproduced producedby by melting melting reduced reduced iron iron by by an an electric electric

furnace method, a major part of phosphorus in the reduced iron remains in the furnace method, a major part of phosphorus in the reduced iron remains in the

molten iron (which is referred to as rephosphorization). Therefore, the currently molten iron (which is referred to as rephosphorization). Therefore, the currently

available reduced iron is produced using high-grade iron ore with a low P available reduced iron is produced using high-grade iron ore with a low P

concentration (a concentration (a PP concentration concentration of of approximately 0.01 mass%), approximately 0.01 andthe mass%), and thePP concentration in concentration in the the reduced reduced iron iron isisapproximately approximately 0.02 0.02 mass%. mass%.

[0006]

[0006] Meanwhile,high-grade Meanwhile, high-gradeiron ironore orewith withaalow lowPPconcentration concentrationisis predicted to be depleted in the future, and it will be thus required to produce predicted to be depleted in the future, and it will be thus required to produce

molten steel using, as a raw material, reduced iron produced using low-grade iron molten steel using, as a raw material, reduced iron produced using low-grade iron

ore with a high P concentration. The P concentration in iron ore used for the ore with a high P concentration. The P concentration in iron ore used for the

current blast current blastfurnace furnacemethod method is is 0.05 0.05 to to0.10 0.10mass% (or 0.10 mass% (or 0.10 to to0.15 0.15mass% when mass% when

converted into the P concentration in reduced iron), and the P concentration is converted into the P concentration in reduced iron), and the P concentration is

predicted to further increase in the future. Such a P concentration is 5 to 10 predicted to further increase in the future. Such a P concentration is 5 to 10

times or times or more the P more the P concentration concentration in in the the above-mentioned reducediron above-mentioned reduced ironproduced produced using high-grade using high-grade iron iron ore ore with with aa low low P P concentration. Toprevent concentration. To preventthe thequality quality of of a steel product from deteriorating due to phosphorus contained therein, it is a steel product from deteriorating due to phosphorus contained therein, it is

necessary to necessary to remove phosphorusduring remove phosphorus duringthe theproduction productionofofmolten moltensteel steelby bymelting melting reduced iron reduced iron with with aa high high P P concentration, concentration, or or remove phosphorusduring remove phosphorus duringthe the production of production of reduced reduced iron iron from from iron iron ore ore with with aa high high PP concentration. Several concentration. Several

22 Dec 2025

phosphorus removal technologies have been proposed.

[0007] Patent Literature 1 proposes a dephosphorization refining flux for use in an arc furnace for removing phosphorus in molten steel to achieve a low phosphorus concentration in a relatively short time with the arc furnace alone, 5 the flux containing calcium oxide as the main ingredient, and also containing 5 to 15 mass% of aluminum oxide and 25 to 35 mass% of iron oxide, with the balance being unavoidable impurities. 2023255850

[0008] Patent Literature 2 proposes a method of removing phosphorus by bringing iron ore, titanium-containing iron ore, nickel-containing ore, chromium- 10 containing ore, or a mixture containing such ores, each having a CaO content of 25 mass% or less and a ratio of CaO/(SiO2+Al2O3) of 5 or less, as the main ingredient into contact with a gas selected from the group consisting of Ar, He, N2, CO, H2, and hydrocarbon, or a mixture gas thereof at a temperature of 1600C or higher. 15 [0009] Patent Literature 3 proposes a method including crushing iron ore with a high P concentration to have a size of 0.5 mm or less; adding water thereto to achieve a pulp concentration of approximately 35 mass%; adding H2SO4 or HCl to a solvent to allow a reaction to take place at a pH of 2.0 or less, thereby decomposing and eluting phosphorus minerals; collecting a magnetically 20 attracted substance such as magnetite by magnetic sorting to separate therefrom SiO2, Al2O3, and so on, which are magnetically non-attracted substances, as slime by sedimentation separation; and also adding slaked lime or quicklime to thereby neutralize P eluted into the solution at a pH in the range of 5.0 to 10.0 to separate and recover P as calcium phosphate. 25 Citation List Patent Literature

[0010] Patent Literature 1: JP-H8-120322A Patent Literature 2: JP-S54-83603A Patent Literature 3: JP-S60-261501A 30

[0011] However, each of the above-described conventional technologies has the following problems that should be solved.

22 Dec 2025

That is, the technology disclosed in Patent Literature 1 is based on the premise of using an iron source with a low P concentration, such as scrap. Specifically, 350 g of flux is added to 7000 g of molten steel to reduce the P concentration in the molten steel from 0.020 mass% to 0.005 mass%. Assuming 5 that the P concentration in reduced iron is 0.15 mass%, the amount of flux required to reduce the P concentration to 0.01 mass%, which is approximately the same level in a steel product, is 230 kg per 1 ton of molten steel. This results in 2023255850

a high proportion of the flux volume in the arc furnace, which is problematic in that the amount of molten steel processed would decrease, reducing production 10 efficiency.

[0012] In the method disclosed in Patent Literature 2, the treatment temperature is 1600C or higher. Further, the specification of Patent Literature 2 describes that "the temperature is preferably 1800C or higher to allow more effective dephosphorization, and such a high temperature range is difficult to 15 achieve by an ordinary heating method, but can be achieved by using a plasma arc or high-frequency induced plasma, for example." Therefore, the method requires more energy, and thus is not suitable for large-scale dephosphorization, which is problematic.

[0013] The method disclosed in Patent Literature 3 is problematic in that it 20 involves wet processing using acid, requiring a long time and high cost to dry the collected magnetically attracted substance for use as the main raw material. The method is also problematic as it requires a long time and high cost to crush iron ore into particles of 0.5 mm or less in advance.

[0014] The present invention has been made in view of the circumstances 25 described above and aims to provide a technology capable of efficiently producing grained iron with a low P concentration even when reduced iron obtained from low-grade iron ore with a high P concentration is used as a raw material. Summary of the Invention 30 [0015] The present invention provides a method for producing grained iron, comprising: a first step of melting reduced iron having P concentration of 0.050

22 Dec 2025

mass% or more to obtain primary molten iron having C concentration of 2 mass% or less; a second step of separating the primary molten iron from slag; a third step of subjecting the primary molten iron separated from the 5 slag to dephosphorization to obtain secondary molten iron; and a fourth step of solidifying the secondary molten iron into a grain form to obtain grained iron, 2023255850

wherein: in the third step, the dephosphorization is performed by supplying an 10 oxygen source and a CaO source to the primary molten iron, and a temperature of the secondary molten iron at the end of the dephosphorization is set to a temperature of the primary molten iron at the start of the dephosphorization or lower. Also described is a method for producing grained iron that includes a first step of melting reduced iron to produce primary molten iron, a second step of 15 separating the primary molten iron from slag, a third step of subjecting the primary molten iron separated from the slag to dephosphorization to produce secondary molten iron, and a fourth step of solidifying the secondary molten iron in a grain state to form grained iron, characterized in that in the third step, the dephosphorization is performed by supplying an oxygen source and a CaO source 20 to the primary molten iron, and a temperature of the secondary molten iron at the end of the dephosphorization is set to a temperature of the primary molten iron at the start of the dephosphorization or lower.

[0016] Note that for the method for producing grained iron according to the present invention, it is considered that the following can be more preferable 25 solution means, for example. (a) A temperature Tf of the secondary molten iron at the end of the dephosphorization is set higher than a solidifying temperature Tm of the secondary molten iron at the end of the dephosphorization by 20C or more. (b) A composition of the slag at the end of the dephosphorization is 30 set to have a slag basicity in a range of 1.0 to 4.0, wherein the slag basicity is a ratio of a CaO concentration (%CaO) to a SiO2 concentration (%SiO2) on a mass basis.

22 Dec 2025

(c) The fourth step is performed using a grained iron producing apparatus including a granulation device that forms the secondary molten iron into droplets, a water-flow control vessel that is disposed at a position for receiving the droplets and accommodates cooling water, and at least one cooling 5 water pipe that is connected to the water-flow control vessel and supplies cooling water to the water-flow control vessel. The water-flow control vessel includes an inclined surface that is inclined such that a horizontal cross-sectional area of 2023255850

the water-flow control vessel becomes narrower in a downward direction, and a discharge port is provided below the inclined surface. 10 [0017] The present invention also provides a method for producing grained iron of the invention, wherein a P concentration of the grained iron is 0.030 mass% or less, and size grain of the grained iron is in the range of 1 mm to 50 mm inclusive. There is further 15 described grained iron which is produced from reduced iron with a P concentration of 0.050 mass% or more as a raw material, characterized in that a P concentration of the grained iron is 0.030 mass% or less, and grain size of the grained iron is in the range of 1 mm to 50 mm inclusive.

20 [0018] The method for producing grained iron according to the present invention can efficiently produce grained iron with a low P concentration from reduced iron obtained from low-grade iron ore with a high P concentration. Furthermore, the grained iron according to the present invention satisfies the P concentration required for most steel products, i.e., 0.030 mass% or less. Thus, 25 molten iron with a P concentration corresponding to the level in a steel product can be obtained simply by re-melting the grained iron according to the present invention.

[0019] Further, since the grained iron is produced by solidifying molten iron into a grained form once after the dephosphorization, it is possible to produce 30 iron and steel not in a large-scale iron-making plant but in such a manner that a plant for producing an iron source is separated from a place where iron source is demanded. For example, such a production method can be considered in which

22 Dec 2025

a process up to the production of dephosphorized grained iron is performed in a raw material-producing country, and iron or steel is produced in an iron steel- producing country, using the dephosphorized grained iron as a raw material.

[0020] When the production of reduced iron and the production of grained 5 iron according to the present invention are both performed in an iron ore- producing country, it is possible to separate a gangue portion, as slag, contained in iron ore, which is a raw material. Thus, by transporting only grained iron, the 2023255850

amount of transportation per unit of Fe can be reduced, thus reducing the transportation cost to a place where grained iron is demanded, as well as energy 10 consumption. Furthermore, when considering the transport of grained iron to the place where grained iron is demanded, the storage of grained iron therein, the supply of grained iron to a facility in the place where grained iron is demanded, and so on, the degree of freedom of facilities used for the transport, storage, and supply can be increased by setting the grain size of grained iron in the range of 1 15 to 50 mm. There is another advantage that a risk such as bridging in a feed hopper can be reduced.

Detailed Description of the Invention

[0021] An embodiment of the present invention will be specifically described 20 below. Note that the following embodiment only describes examples of an apparatus (or a device) and a method for embodying the technical idea of the present invention. Thus, the configuration of the present invention is not limited thereto. That is, the technical idea of the present invention can be modified in various ways within the technical scope described in the claims. 25 [0022] The inventors have considered as follows to implement the present invention. Reduced iron produced using iron ore as a raw material has different properties, such as a metallization rate and composition, depending on the brand of the iron ore used, the type and unit consumption of a raw material composition 30 adjusting agent to be mixed, the type and unit consumption of a reducing agent, a reduction temperature, and a scheme adopted for a facility for producing the reduced iron. Table 1 shows examples of the ingredient compositions of

- 7a - 22 Dec 2025

reduced iron. In the examples in Table 1, the P concentration converted to the P concentration in molten iron, which is obtained by dividing the P concentration by the T.Fe (total iron) concentration, is 0.057 to 0.152 mass%. Therefore, if such reduced iron is melted as is, it will be difficult to reduce the P concentration 5 to the level required for a steel product (0.030 mass% or less). In addition, if such reduced iron is simply melted to be subjected to dephosphorization, the amount of slag produced will become huge due to gangue, such as SiO2, 2023255850

contained in the reduced iron, and the proportion of the slag to the volume of a processing facility will become high, resulting in reduced productivity, and also, 10 the amount of a CaO source required to secure the amount of phosphorus to be removed from the molten iron will increase, resulting in an increase in cost, which are problematic.

[0023] [Table 1] Ingredient composition (mass %)

T.Fe M.Fe SiO 2 Al 2 O 3 CaO P

Reduced iron A 88.8 68.5 1.8 1.0 1.0 0.10

Reduced iron B 87.5 78.9 4.0 2.0 0.9 0.05

8

Reducediron Reduced ironCC 79.0 79.0 61.5 61.5 5.0 5.0 1.9 1.9 5.0 5.0 0.12 0.12

[0024]

[0024] In response, the inventors have arrived at a process of producing In response, the inventors have arrived at a process of producing

grained iron by melting reduced iron once to obtain molten iron, and also grained iron by melting reduced iron once to obtain molten iron, and also

removing at least a part of the slag derived from gangue, and then supplying an removing at least a part of the slag derived from gangue, and then supplying an

oxygen source and a lime source to the obtained molten iron to effect oxygen source and a lime source to the obtained molten iron to effect

dephosphorization, and further solidifying the dephosphorized molten iron into a dephosphorization, and further solidifying the dephosphorized molten iron into a

grained form. grained form.

[0025]

[0025] Anembodiment An embodimentof of thethepresent presentinvention inventionwill willbebespecifically specifically described described

below. below.

As a first step, reduced iron is heated and melted in an electric As a first step, reduced iron is heated and melted in an electric

furnace to furnace to produce primary molten produce primary molteniron. iron. TheThe reduced reduced iron iron to to bebe usedherein used herein may be the one transferred as is at a high temperature from an adjacent plant for may be the one transferred as is at a high temperature from an adjacent plant for

producingreduced producing reducediron, iron, for for example. example. OfOf course, course, reduced reduced iron iron thathas that hasbeen been once cooled once cooled to to room temperaturemay room temperature may alsobebeused. also used.TheThe electric electric furnace furnace maymay be be an arc an arc furnace, furnace, submerged arc furnace, submerged arc furnace, or or induction induction melting melting furnace. The furnace. The

thermal energy to be supplied in the first step to heat and melt the reduced iron, thermal energy to be supplied in the first step to heat and melt the reduced iron,

which is a solid iron source, can be not only electrical energy but also, which is a solid iron source, can be not only electrical energy but also,

supplementally, the combustion heat of gaseous fuel such as a natural gas or a supplementally, the combustion heat of gaseous fuel such as a natural gas or a

propane gas, liquid fuel such as heavy oil, or combustible solid such as coal or propane gas, liquid fuel such as heavy oil, or combustible solid such as coal or

metallic Al metallic Al or or Si, Si,for forexample. Suchenergy example. Such energyisis preferably preferably renewable renewablefrom fromthe the

perspective of perspective of reducing reducing CO emissions. CO2 2 emissions.

[0026]

[0026] As a second step, slag, which is a gangue portion of the reduced iron, As a second step, slag, which is a gangue portion of the reduced iron,

and the and the primary molteniron primary molten iron are are separated separated from each other. from each other. For Forexample, example, the the molten metal is tapped into a vessel for transport and then transported to a molten metal is tapped into a vessel for transport and then transported to a

facility for facility forperforming performingdephosphorization. When dephosphorization. When dephosphorization dephosphorization is is

performed in the following step, a CaO source is added to produce slag for performed in the following step, a CaO source is added to produce slag for

dephosphorization. To To dephosphorization. secure secure thethe amount amount of of thethe slag slag and and adjustthe adjust theingredient ingredient composition thereof, at least a part of the slag containing a large amount of SiO2 composition thereof, at least a part of the slag containing a large amount of SiO2

producedwith produced withthe the melting melting of of the the reduced iron may reduced iron be carried may be carried over. over. The Theslag slag mayalso may also be be removed removedfrom from a a vesselfor vessel forheating heatingand andmelting meltingthe the reduced reducediron iron used used

in the first step, for example, by means of a slag dragger. in the first step, for example, by means of a slag dragger.

[0027]

[0027] As a third step, the molten metal is subjected to dephosphorization to As a third step, the molten metal is subjected to dephosphorization to

9

producesecondary produce secondarymolten molteniron. iron.AAdephosphorization dephosphorization reactionrequires reaction requiresananoxygen oxygen source and source and aa CaO sourceasasrepresented CaO source representedby bythe the following following Expression Expression(1). (1). 2[P] + 2[P] + 5/2 O 2(g) ++ 3CaO(s) 5/2.02(g) 3CaO(s) ==3CaOP2O5(s)...(1), 3CaO P2O5(s) ...(1), where [P] represents phosphorus in the molten iron. where [P] represents phosphorus in the molten iron.

[0028]

[0028] A pure A pure oxygen oxygengas gasisis normally normallyused usedasasthe the oxygen oxygensource sourcefor for dephosphorization. The dephosphorization. The inventors inventors have have come come to the to the conclusion conclusion that that it itisis

advantageoustoto perform advantageous performdephosphorization dephosphorizationatata alow lowtemperature, temperature,since sinceaa dephosphorization reaction is an exothermic reaction, and also to reduce the dephosphorization reaction is an exothermic reaction, and also to reduce the

temperature of the molten iron within the range that does not adversely affect temperature of the molten iron within the range that does not adversely affect

dephosphorization, taking into account that the resultant is solidified to form dephosphorization, taking into account that the resultant is solidified to form

grained iron in the following step. grained iron in the following step.

[0029]

[0029] As a result of examination, the inventors have found that sufficient As a result of examination, the inventors have found that sufficient

dephosphorizationcan dephosphorization canbe beachieved achievedwhile whilecooling coolingthe themolten molteniron, iron, by by supplying supplying air or an iron oxide source such as iron ore or mill scale, as the oxygen source. air or an iron oxide source such as iron ore or mill scale, as the oxygen source.

When air is used, heat removal proceeds as sensible heat of a nitrogen gas When air is used, heat removal proceeds as sensible heat of a nitrogen gas

contained in the air, achieving a better cooling effect than when a pure oxygen contained in the air, achieving a better cooling effect than when a pure oxygen

gas is gas is used. Meanwhile, used. Meanwhile, when when an an iron iron oxide oxide source source is is used,ananendothermic used, endothermic reaction occurs as the iron oxide source is reduced to form metallic Fe, or heat reaction occurs as the iron oxide source is reduced to form metallic Fe, or heat

absorption occurs as a molten slag is formed in the form of iron oxide, achieving absorption occurs as a molten slag is formed in the form of iron oxide, achieving

a better cooling effect than when a pure oxygen gas is used. a better cooling effect than when a pure oxygen gas is used.

[0030]

[0030] Next, using Next, using limestone limestone as as the the CaO sourcecan CaO source cancool cool the the molten molteniron iron because calcium because calciumcarbonate carbonatecontained containedininlimestone limestoneabsorbs absorbsheat heatas as it it decomposes decomposes

into CaO into CaO and CO 2.A similar andCO2. A similar cooling cooling effect effect isisachieved achievedbybysupplying supplying carbonate, carbonate,

such as such as raw dolomite. However, raw dolomite. However, if theproportion if the proportionofofCaO CaO in in an an auxiliary auxiliary

material is low, the amount of the auxiliary material to be added will increase, material is low, the amount of the auxiliary material to be added will increase,

and the amount of the produced slag will thus increase, and the time required to and the amount of the produced slag will thus increase, and the time required to

add the auxiliary material will also increase, which is problematic in operation. add the auxiliary material will also increase, which is problematic in operation.

Therefore, it is preferable to adjust the type and the amount of the auxiliary Therefore, it is preferable to adjust the type and the amount of the auxiliary

material to be added by taking into consideration the required cooling effect and material to be added by taking into consideration the required cooling effect and

a stable operation. a stable operation.

[0031]

[0031] It is preferable to adjust the supply rate of pure oxygen or air and the It is preferable to adjust the supply rate of pure oxygen or air and the

height of a top-blowing lance in accordance with the operation condition of height of a top-blowing lance in accordance with the operation condition of

10

dephosphorization, as the behavior of the occurrence of spitting differs dephosphorization, as the behavior of the occurrence of spitting differs

depending on the height of a freeboard (the height from the surface of the molten depending on the height of a freeboard (the height from the surface of the molten

iron to the upper end of a vessel) of a vessel in which dephosphorization is iron to the upper end of a vessel) of a vessel in which dephosphorization is

performed and the nozzle shape of the lance. In addition, an inert gas is performed and the nozzle shape of the lance. In addition, an inert gas is

preferably blown into the molten iron to agitate it. The inert gas is preferably preferably blown into the molten iron to agitate it. The inert gas is preferably

blown into the molten iron via a porous plug disposed at the bottom of the blown into the molten iron via a porous plug disposed at the bottom of the

furnace or furnace or by by immersing aninjection immersing an injection lance lance in in the themolten molten iron. Regardingthe iron. Regarding the composition of the slag at the end of the dephosphorization, slag basicity, which composition of the slag at the end of the dephosphorization, slag basicity, which

is the is theratio ratioofof thethe CaOCaOconcentration concentration(%CaO) to the (%CaO) to the SiO SiO22 concentration concentration (%SiO (%SiO2)2 )

on a mass basis, is preferably in the range of 1.0 to 4.0. The slag basicity is on a mass basis, is preferably in the range of 1.0 to 4.0. The slag basicity is

adjusted based on the amount of slag containing a large amount of SiO that is adjusted based on the amount of slag containing a large amount of SiO2 that is 2

carried over to the second step, and the type and the amount of the CaO source carried over to the second step, and the type and the amount of the CaO source

added. It is also possible to add a SiO source, such as silica stone or added. It is also possible to add a SiO2 source, 2 such as silica stone or

ferrosilicon, and a CaO source, such as quicklime, as appropriate. ferrosilicon, and a CaO source, such as quicklime, as appropriate.

[0032]

[0032] If the slag basicity is low, the amount of phosphorus to be removed in If the slag basicity is low, the amount of phosphorus to be removed in

dephosphorization will be small. Meanwhile, if the slag basicity is high, a part dephosphorization will be small. Meanwhile, if the slag basicity is high, a part

of the slag will solidify and thus become attached to a refractory when the of the slag will solidify and thus become attached to a refractory when the

temperature of the molten iron drops. This makes it difficult to remove the slag temperature of the molten iron drops. This makes it difficult to remove the slag

after dephosphorization after dephosphorization and causes problems and causes problemssuch suchthat that an an abnormal abnormalreaction reactionmay may

occur the next time molten iron is charged, or the residual slag may be mixed occur the next time molten iron is charged, or the residual slag may be mixed

into the produced slag, causing the composition to fall out of range. into the produced slag, causing the composition to fall out of range.

[0033]

[0033] Further, since a large amount of an exhaust gas at a high temperature Further, since a large amount of an exhaust gas at a high temperature

is generated through such dephosphorization that involves the use of air, it is also is generated through such dephosphorization that involves the use of air, it is also

possible to recover the exhaust heat using a boiler, for example. possible to recover the exhaust heat using a boiler, for example.

[0034]

[0034] As a fourth step, the secondary molten iron after the As a fourth step, the secondary molten iron after the

dephosphorization is solidified into a grained form to obtain grained iron. dephosphorization is solidified into a grained form to obtain grained iron.

Examplesofofaamethod Examples methodfor forproducing producinggrained grainediron ironinclude includea amethod methodofof flowing flowing

down molten iron subjected to dephosphorization to cause it to collide with a down molten iron subjected to dephosphorization to cause it to collide with a

surface plate of a refractory, and a method of causing water to collide with the surface plate of a refractory, and a method of causing water to collide with the

molten iron, which has flowed out, to obtain molten iron droplets, and then molten iron, which has flowed out, to obtain molten iron droplets, and then

dropping the molten iron droplets into a water-flow control vessel to obtain dropping the molten iron droplets into a water-flow control vessel to obtain

solidified grained iron. At this time, since the diameter of grained iron varies in solidified grained iron. At this time, since the diameter of grained iron varies in

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accordance with the flowing-down speed of the molten iron, it is preferable to accordance with the flowing-down speed of the molten iron, it is preferable to

transfer the molten iron subjected to dephosphorization, to a tundish where a transfer the molten iron subjected to dephosphorization, to a tundish where a

falling speed can be kept constant. falling speed can be kept constant.

[0035]

[0035] The temperature of the molten iron decreases while the molten iron is The temperature of the molten iron decreases while the molten iron is

being transported after the dephosphorization to be supplied to a grained iron being transported after the dephosphorization to be supplied to a grained iron

producing apparatus. If the temperature of the molten iron after the producing apparatus. If the temperature of the molten iron after the

dephosphorization is too low, part of the molten iron in the vessel will solidify dephosphorization is too low, part of the molten iron in the vessel will solidify

before the molten iron is entirely supplied to the grained iron production before the molten iron is entirely supplied to the grained iron production

apparatus, resulting apparatus, resultingininreduced reducedproduction production yields. Meanwhile,ifif the yields. Meanwhile, the

temperature of the molten iron after the dephosphorization is high, the heat load temperature of the molten iron after the dephosphorization is high, the heat load

when the molten iron is solidified by the grained iron production apparatus will when the molten iron is solidified by the grained iron production apparatus will

increase, increasing the amount of cooling water to be used, so that the increase, increasing the amount of cooling water to be used, SO that the

productivity may decrease due to the cooling rate, or the waiting time until the productivity may decrease due to the cooling rate, or the waiting time until the

temperature of temperature of the the molten iron decreases molten iron decreases and and grained grained iron iron is isobtained obtainedmay may

becomelong. become long.As As described described above, above, considering considering forming forming intointo grained grained iron iron after after

the dephosphorization, there is a suitable range of the temperature of the molten the dephosphorization, there is a suitable range of the temperature of the molten

iron after the dephosphorization. Specifically, the temperature T of the molten iron after the dephosphorization. Specifically, the temperature Tf of the molten f

iron after the dephosphorization is set to the temperature T of the molten iron at iron after the dephosphorization is set to the temperature Ti of the i molten iron at

the start of the dephosphorization or lower, from the viewpoint of increasing the start of the dephosphorization or lower, from the viewpoint of increasing

productivity. In addition, if the temperature T at the end of the productivity. In addition, if the temperature Tf at the f end of the

dephosphorization is set higher than the solidifying temperature T of the dephosphorization is set higher than the solidifying temperature Tm of the m

secondarymolten secondary molteniron ironat at the the end end of of the the dephosphorization dephosphorization by 20 Cor by 20°C or more, more, the the molten iron can be supplied to the grained iron producing apparatus in a high molten iron can be supplied to the grained iron producing apparatus in a high

yield, which is preferable. yield, which is preferable.

[0036]

[0036] Note that Note that the the solidifying solidifyingtemperature temperature TTm m ((°C) C) may be determined may be determinedby by either of the following methods. First, it may be directly measured as the either of the following methods. First, it may be directly measured as the

solidifying temperature of a sample. Alternatively, it can be a temperature read solidifying temperature of a sample. Alternatively, it can be a temperature read

from a liquidus temperature in an Fe-C state diagram, based on the C from a liquidus temperature in an Fe-C state diagram, based on the C

concentration in the molten iron subjected to dephosphorization that is estimated concentration in the molten iron subjected to dephosphorization that is estimated

from past records of operation (the C concentration and the temperature before from past records of operation (the C concentration and the temperature before

dephosphorization, dephosphorization, and and the the typetype and supply and supply conditions conditions of thesource). of the oxygen oxygen source).

[0037]

[0037] The grained The grained iron iron producing producingapparatus apparatusincludes includes aa granulation granulation device device

12

which forms the molten iron into droplets, and a water-flow control vessel which which forms the molten iron into droplets, and a water-flow control vessel which

is disposed at a position for receiving the droplets and accommodates cooling is disposed at a position for receiving the droplets and accommodates cooling

water. AtAtleast water. leastone onecooling coolingwater waterpipe pipewhich whichsupplies suppliescooling coolingwater waterisis connected to the water-flow control vessel into which the molten iron is dropped connected to the water-flow control vessel into which the molten iron is dropped

to solidify. As the cooling water is discharged from the cooling water pipe to to solidify. As the cooling water is discharged from the cooling water pipe to

form a water flow, the formation of a stagnation region of the cooling water form a water flow, the formation of a stagnation region of the cooling water

within the vessel is suppressed. This can suppress a local temperature rise of within the vessel is suppressed. This can suppress a local temperature rise of

the cooling water and efficiently cool grained iron to suppress the fusion of the cooling water and efficiently cool grained iron to suppress the fusion of

grained iron caused by insufficient cooling of grained iron. In addition, the grained iron caused by insufficient cooling of grained iron. In addition, the

water-flow control vessel has an inclined surface which is inclined such that the water-flow control vessel has an inclined surface which is inclined such that the

horizontal cross-sectional horizontal cross-sectionalarea areaofofthe vessel the becomes vessel becomesnarrower narrower in ina adownward downward

direction, and a discharge port is provided below the inclined surface. direction, and a discharge port is provided below the inclined surface. Setting Setting the inclination angle of the inclined surface to be the angle of repose of grained the inclination angle of the inclined surface to be the angle of repose of grained

iron in water or more allows grained iron to be directed to the discharge port iron in water or more allows grained iron to be directed to the discharge port

without accumulation of grained iron on the inclined surface. without accumulation of grained iron on the inclined surface.

[0038]

[0038] By using the thus-obtained grained iron as a part of an iron source in a By using the thus-obtained grained iron as a part of an iron source in a

blast furnace or a converter, the effect of diluting the P concentration in blast furnace or a converter, the effect of diluting the P concentration in

accordancewith accordance withthe the proportion proportion of of the the grained grained iron iron used used can can be be achieved. This achieved. This

can reduce the load in dephosphorization and ease restrictions on the raw can reduce the load in dephosphorization and ease restrictions on the raw

materials to be used in the blast furnace and converter. materials to be used in the blast furnace and converter.

[0039]

[0039] Note that Note that when the grained when the grained iron iron obtained in this obtained in thisembodiment is used embodiment is used

as an iron source in an electric furnace, blast furnace, or converter, there is a as an iron source in an electric furnace, blast furnace, or converter, there is a

range of grain sizes that are convenient to work with. To obtain the desired range of grain sizes that are convenient to work with. To obtain the desired

grain sizes, it is preferable to adjust the flowing-down speed in the tundish. grain sizes, it is preferable to adjust the flowing-down speed in the tundish. It is It is

also preferable to perform classification as required. Typically, grained iron also preferable to perform classification as required. Typically, grained iron

with aa grain with grain size sizeininthe range the rangeofof 1 to 50 50 1 to mmmmisisconvenient convenienttoto use. use. When grained When grained

iron with a grain size of less than 1 mm is included, there is a higher possibility iron with a grain size of less than 1 mm is included, there is a higher possibility

of clogging a conveyor for transport or bridging in a hopper. Therefore, it is of clogging a conveyor for transport or bridging in a hopper. Therefore, it is

preferable to perform classification so as to obtain grained iron with a grain size preferable to perform classification SO as to obtain grained iron with a grain size

of 11 of mm mm oror more more for for use.use. On theOn thehand, other otherifhand, if grained grained iron withiron withsize a grain a grain of size of morethan more than 50 50mm mmisisused, used,there there is is a higher higher risk riskofofwear weardamage that may damage that occur to may occur to a facility, such as the conveyor for transport or the hopper, when collision due to a facility, such as the conveyor for transport or the hopper, when collision due to

13

falling of grained iron occurs, for example. Therefore, it is preferable to reduce falling of grained iron occurs, for example. Therefore, it is preferable to reduce

the flowing-down speed in the tundish to obtain grained iron with a grain size of the flowing-down speed in the tundish to obtain grained iron with a grain size of

50 mm or less. It is also possible to perform classification as appropriate to 50 mm or less. It is also possible to perform classification as appropriate to

removegrained remove grainediron ironwith with aa grain grain size size of of more more than than 50 50 mm. Herein, mm. Herein, thethe grain grain

size in the range of 1 to 50 mm may include particles on a sieve with an opening size in the range of 1 to 50 mm may include particles on a sieve with an opening

of 11 mm of to particles mm to particles that thathave have passed passed through through aa sieve sievewith withan anopening opening of of50 50 mm. mm.

Examples Examples

[0040]

[0040] (Example 1) (Example 1)

The reduced The reducediron iron AAshown shownininTable Table1 1was was melted melted in in anan electric electric

furnace with a capacity of 250 tons, and, after adjusting the temperature of the furnace with a capacity of 250 tons, and, after adjusting the temperature of the

resultant, transferred resultant, transferredtoto a ladle. a ladle.Among the slag Among the slag produced due to produced due to the the gangue gangue

content in the reduced iron during the melting of the reduced iron in the electric content in the reduced iron during the melting of the reduced iron in the electric

furnace, approximately 10 kg of slag per 1 ton of molten iron was transferred to furnace, approximately 10 kg of slag per 1 ton of molten iron was transferred to

the ladle together with the molten iron, and the rest of the slag was transferred to the ladle together with the molten iron, and the rest of the slag was transferred to

a slag vessel. The ladle was transferred to a dephosphorization facility to a slag vessel. The ladle was transferred to a dephosphorization facility to

perform dephosphorization perform dephosphorizationwhile whilechanging changing thetypes the typesand andamounts amounts of of an an oxygen oxygen

source and source and aa lime lime source supplied. The source supplied. Thedephosphorization dephosphorization facilityincluded facility includeda a gas top-blowing lance, an auxiliary material feeding hopper, and a bottom- gas top-blowing lance, an auxiliary material feeding hopper, and a bottom-

blowingporous blowing porousplug. plug.TheThe gasgas top-blowing top-blowing lance lance was was capable capable of supplying of supplying gas gas

containing pure oxygen or air at a rate of approximately 1 Nm3/minute 3per 1 ton containing pure oxygen or air at a rate of approximately 1 Nm /minute per 1 ton of molten iron. Three auxiliary material feeding hoppers, each filled with iron of molten iron. Three auxiliary material feeding hoppers, each filled with iron

ore, quicklime ore, quicklime (CaO), and calcium (CaO), and calciumcarbonate carbonate(CaCO3), (CaCO3),can canfeed feedthem them at ata arate rate of of approximately1010kg/minute. approximately kg/minute.TheThe bottom-blowing bottom-blowing porous porous plug plug can supply can supply gas. gas. In this example, a pure Ar gas was supplied at a rate of approximately 0.1 In this example, a pure Ar gas was supplied at a rate of approximately 0.1

Nm3/minuteper Nm3/minute per1 1ton tonofofmolten molteniron. iron.

[0041]

[0041] The melting temperature in the electric furnace was adjusted to allow The melting temperature in the electric furnace was adjusted to allow

the temperature the of the temperature of the molten molten iron iron before before dephosphorization to be dephosphorization to be approximately approximately

1590 C. "Before 1590°C. “Before dephosphorization” dephosphorization" refers refers to the to the timetime before before the the gasgas top- top-

blowing lance is lowered, while “after dephosphorization” refers to the time blowing lance is lowered, while "after dephosphorization" refers to the time

whenthe when thegas gas top-blowing top-blowinglance lancehas hasbeen beencompletely completelyraised raisedafter after the the dephosphorization. dephosphorization. At At each each timing, timing, temperature temperature measurements measurements and and sampling sampling

were conducted were conductedusing usingaasublance. sublance.TheThe obtained obtained samples samples werewere cut and cut and polished polished

14

and subjected to an emission spectrochemical analysis to evaluate the C and subjected to an emission spectrochemical analysis to evaluate the C

concentration [C] concentration [C] andand the the P concentration P concentration [P] in[P] thein the molten molten iron iron from from calibration calibration

curves determined curves determinedin in advance. advance. It was possible to measure the solidifying It was possible to measure the solidifying

temperature of temperature of the the molten metal at molten metal at the the timing timing when the temperature when the measurement temperature measurement

and sampling and samplingwere wereperformed performed using using thesublance, the sublance,and andthe thesolidifying solidifying temperature temperature Tm of Tm of the the molten iron subjected molten iron subjected to to the thedephosphorization dephosphorization was actually measured. was actually measured.

[0042]

[0042] The start of the dephosphorization was defined as when the gas top- The start of the dephosphorization was defined as when the gas top-

blowinglance blowing lance started started to to be be lowered. Afterthe lowered. After the top-blowing top-blowinglance lancereached reacheda a predeterminedheight, predetermined height, the the supply of an supply of an oxygen gas source oxygen gas source and and the the addition addition of of

auxiliary materials auxiliary materials were were started. The dephosphorization started. The dephosphorizationwas wasterminated terminatedwhen when the supply the supply of of predetermined amountsofofoxygen predetermined amounts oxygengas gassource sourceand andauxiliary auxiliary materials was materials completedand was completed andthe thetop-blowing top-blowinglance lancewas wasraised raisedtotoaa standby standby position. The position. Theduration durationofofthe the period period was wasdetermined determinedasasa aprocessing processingtime timetft f (minutes). (minutes).

[0043]

[0043] After the dephosphorization, the ladle was tilted to remove the slag on After the dephosphorization, the ladle was tilted to remove the slag on

the molten the iron with molten iron with aa slag slag dragger. Part of dragger. Part of the the removed slag was removed slag wascollected collected and and subjected to a chemical analysis. The ladle was lifted and tilted using a crane to subjected to a chemical analysis. The ladle was lifted and tilted using a crane to

transfer the transfer themolten molten iron irontotothe tundish. the tundish. The The molten iron was molten iron caused to was caused to flow flow down from the tundish so as to collide with a surface plate of a refractory, and down from the tundish SO as to collide with a surface plate of a refractory, and

the resulting molten iron droplets were dropped into the water-flow control the resulting molten iron droplets were dropped into the water-flow control

vessel and solidified to produce grained iron. The grain sizes of the obtained vessel and solidified to produce grained iron. The grain sizes of the obtained

grained iron grained iron ranged ranged from 0.1 to from 0.1 to 30 30 mm. mm. TheThe grain grain size size distributionswere: distributions were:+0.1 +0.1 mmtoto--1-1mm: mm mm: 17.2 17.2 mass%, +1mmmm mass%, +1 to to -10 -10 mm: mm: 31.3 31.3 mass%, mass%, +10 +10 mm tomm -20tomm: -20 mm: 38.8 mass%, 38.8 and+20 mass%, and +20mmmm to -30 to -30 mm:mm: 12.712.7 mass%. mass%. Herein,Herein, "+N to "+N to -M" -M" means means

particles on a sieve with an opening of N to particles that have passed through a particles on a sieve with an opening of N to particles that have passed through a

sieve with sieve with an an opening of M. opening of M.

[0044]

[0044] Table 2 shows, as Test Nos. 1 to 5, the temperatures T and T ( C), Table 2 shows, as Test Nos. 1 to 5, the temperatures Ti and Tfi (°C), f

the C concentrations [C] and [C] (mass%), and the P concentrations [P] and [P] f the C concentrations [C]i and i [C]f (mass%), f and the P concentrations [P]i and [P]fi

(mass%) of the molten iron before and after the dephosphorization, respectively; (mass%) of the molten iron before and after the dephosphorization, respectively;

the types the types and and the the amounts of the amounts of the oxygen source and oxygen source andthe the CaO CaOsource sourcesupplied; supplied;the the processing time t (minutes); and the basicity of the slag after the process processing time tf (minutes); f and the basicity of the slag after the process

((%CaO)/(% SiO2),i.e., ((%CaO)/(% SiO2), i.e., the the ratio ratioof ofthe theCaO CaO concentration concentration (%CaO) to the (%CaO) to the SiO2 SiO 2

15

concentration (%SiO ) on a mass basis; hereinafter referred to as C/S). concentration (%SiO2) on2 a mass basis; hereinafter referred to as C/S).

[0045]

[0045] As shown in Table 2, in all the invention examples, the temperature T f As shown in Table 2, in all the invention examples, the temperature Tf

of the molten iron after the process was lower than the temperature T of the of the molten iron after the process was lower than the temperature Ti of the i

molten iron before the process, and the P concentration [P] after the process was molten iron before the process, and the P concentration [P]f after fthe process was

sufficiently lowered. sufficiently In the lowered. In the comparative comparativeexample, example,the thetemperature temperatureTfT fafter after dephosphorization increasedhigher dephosphorization increased higher than than the the temperature temperature Ti Ti before before

dephosphorization, dephosphorization, and and consequently consequently the P concentration the P concentration [P]the

[P]f after f after the process process

was high, and a waiting time was caused during the grained iron production step, was high, and a waiting time was caused during the grained iron production step,

resulting in resulting indecreased decreased productivity. In Test productivity. In Test No. No. 4, 4, compared withTest compared with Test Nos. Nos.11 to to

3, the temperature T of the molten iron after the process decreased to reduce the 3, the temperature Tf of f the molten iron after the process decreased to reduce the

P concentration P concentration[P]f

[P]sufficiently. f sufficiently. However, However, part ofpart the of the iron molten molten iron solidified in solidified in the tundish during the production of grained iron, resulting in a reduced yield. the tundish during the production of grained iron, resulting in a reduced yield.

In each of Test Nos. 1 to 3, the temperature T of the molten iron after the In each of Test Nos. 1 to 3, the temperature Tf of the f molten iron after the

process was lower than the temperature T of the molten iron before the process, process was lower than the temperature Ti of the i molten iron before the process,

and the temperature T of the molten iron after the process was higher than the and the temperature Tf off the molten iron after the process was higher than the

solidifying temperature solidifying temperature T of the Tmm of the molten molten iron iron by by 20 C or 20°C or more. Also,the more. Also, theP P concentration [P] after the process was sufficiently low, and the whole molten concentration [P]f after f the process was sufficiently low, and the whole molten

iron was formed into grained iron in a high yield with no decrease in iron was formed into grained iron in a high yield with no decrease in

productivity. productivity.

[0046] [Table 2]

[0046] [Table 2]

[0046] [Table 2]

before iron Molten before iron Molten Molten iron before process after iron Molten Oxygen CaO source Slag

Oxygen source source Oxygen source CaO source Molten iron after process Slag

process process process

tf tf Remarks

Pure

No. No. Pure Solidification Remarks

Iron Iron ore Air

ore C/S

CaO

Ti CaCO3 Tf Tm

[C]i

[P]f

[C]f

[P]i Ti [C] i [P] i Iron ore Air CaO CaCO 3 Tf [C] f [P] f Tm C/S Solidification

oxygen oxygen oxygen Present/Absent minute -

Nm3/t

Nm3/t

°C °C mass% °C

mass% mass%

mass% kg/t kg/t

kg/t ℃ mass% mass% kg/t Nm3 /t Nm3 /t kg/t kg/t minute ℃ mass% mass% ℃ - Present/Absent Example Invention Absent

14.2 1557

1587 1535 2.4

1.5 0.009

1 0.010 24 0 0.032

0.110 5 0 1 1587 0.010 0.110 5 1.5 0 24 0 14.2 1557 0.009 0.032 1535 2.4 Absent Invention Example Example Invention Absent

14.1

1591 1565 1535 16

0.0 2.4

0.008

0.010 11

0.110 0 24 0 0.034

2 16

2 1591 0.010 0.110 0 0.0 11 24 0 14.1 1565 0.008 0.034 1535 2.4 Absent Invention Example Example Invention Absent

17.7

1587 1558 1535

2.4 2.4

16 0.008

0.010 15 0.032

3 0.110 0 0 3 1587 0.010 0.110 0 2.4 0 15 16 17.7 1558 0.008 0.032 1535 2.4 Absent Invention Example Example Invention Absent

14.1

1593 1543 1535 2.4

0.0 24

0.110

0.010 7 0.009

0

5

4 0.031

4 1593 0.010 0.110 5 0.0 7 24 0 14.1 1543 0.009 0.031 1535 2.4 Absent Invention Example Example Comparative Absent

13.9

1591 1535

1599 2.4

3.0 24

0.010

0.007

0.110 0 0.041

0 0 5 1591 0.010 0.110 0 3.0 0 24 0 13.9 1599 0.007 0.041 1535 2.4 Absent Comparative Example

17

[0047]

[0047] (Example2)2) (Example

Dephosphorizationand Dephosphorization anda aproduction productionofofgrained grainediron ironwere wereconducted conducted using aa method using similar to method similar to that that of ofExample 1. Table Example 1. Table3 3shows shows thetemperatures the temperatures TiTi

and T ( C), the C concentrations [C] and [C] (mass%), and the P concentrations and Tf f(°)), the C concentrations [C]i andi [C]f (mass%), f and the P concentrations

[P]

[P]ii and [P] f (mass%) and [P]f (mass%) of of thethe molten molten iron iron before before and the and after after the dephosphorization, dephosphorization,

respectively; the respectively; thetypes typesand andamounts amounts of of the the oxygen oxygen source source and CaOsource and CaO source supplied; the processing time t (minutes); and the basicity C/S of the slag after supplied; the processing time tf (minutes); f and the basicity C/S of the slag after

the process, as Test Nos. 6 to 12. As shown in Table 3, in Test No. 11, the the process, as Test Nos. 6 to 12. As shown in Table 3, in Test No. 11, the

basicity C/S of the slag was low compared with Test Nos. 6 to 10, and thus the P basicity C/S of the slag was low compared with Test Nos. 6 to 10, and thus the P

concentration after concentration after the theprocess processwas was high. Meanwhile,ininTest high. Meanwhile, TestNo. No.12, 12,the the basicity C/S of the slag was high, and the solidification of the slag was basicity C/S of the slag was high, and the solidification of the slag was

confirmed. confirmed.

[Table 3]

[0048]

[0048] [Table 3]

process before iron Molten process after iron Molten process before iron Molten CaOCaO

Oxygen Oxygen source source

source Slag

source Molten iron before process Oxygen source CaO source Molten iron after process Slag

Iron Pure tf Iron Pure tf Remarks

Air C/S

No. CaCO3 Tf

Ti Tm

[P]f

[P]i

[C]i CaO Solidification

No. Ti [C] i [P] i Air CaO CaCO 3 Tf [C] f [P] f Tm C/S Solidification Remarks

[C]f

ore ore oxygen

oxygen Nm3/t -

Nm3/t mass%

mass% mass%

°C °C

mass% °C

kg/t

kg/t minute

kg/t Present/Absent

℃ mass% mass% kg/t Nm3 /t Nm3 /t kg/t kg/t minute ℃ mass% mass% ℃ - Present/Absent

1535 1.1

1.0 9.7

0.110 0.059

0.009

0.010 15

0

6 0

5 Absent

1603 1574 6 1603 0.010 0.110 5 1.0 0 15 0 9.7 1574 0.009 0.059 1535 1.1 Absent Invention Example Invention Example

12.1 1.8

1.5

0.010 0.110 0.009 0.038

20

7 5 0

0 Absent

1597 1574 1535

7 1597 0.010 0.110 5 1.5 0 20 0 12.1 1574 0.009 0.038 1535 1.8 Absent Invention Example Invention Example 18

3.0

2.5 18

0.010 0.020

0.110 0.008

8 5 30

0 0 Absent

1535

1601 16.9 1573 8 1601 0.010 0.110 5 2.5 0 30 0 16.9 1573 0.008 0.020 1535 3.0 Absent Invention Example Invention Example

1571 3.6

3.0 0.019

0.110 0.007

0.010 36

5 0

0

9 Absent

1600 19.8 1535 Invention Example

9 1600 0.010 0.110 5 3.0 0 36 0 19.8 1571 0.007 0.019 1535 3.6 Absent Invention Example

1597 21.9 1535

1573 0.007

0.010 3.5 4.0

0.110 0.018

40

10 0 0

5 Absent Invention Example

10 1597 0.010 0.110 5 3.5 0 40 0 21.9 1573 0.007 0.018 1535 4.0 Absent Invention Example

1599 1535 0.9

7.7

0.5

0.110 0.010

0.010 0.084

11 0 11

5 0 Absent

11 1599 0.010 0.110 5 0.5 0 11 0 7.7 1573 1573 0.010 0.084 1535 0.9 Absent Invention Example Invention Example

Present

24.5 4.5

4.0 0.006

0.010 0.016

0.110

12 45

5 0 0

1600 1535

1572

12 1600 0.010 0.110 5 4.0 0 45 0 24.5 1572 0.006 0.016 1535 4.5 Present Invention Example Invention Example

19

[0049]

[0049] (Example3)3) (Example

The reduced The reducediron iron AAshown shownininTable Table1 1was was melted melted with with anthraciteininanan anthracite

electric furnace with a capacity of 250 tons to produce molten iron with a C electric furnace with a capacity of 250 tons to produce molten iron with a C

concentration of concentration of approximately 2.0 mass%. approximately 2.0 mass%.After After adjusting adjusting thethe temperature temperature of of

the molten iron, the molten iron was transferred to a ladle, where the molten iron, the molten iron was transferred to a ladle, where

dephosphorizationand dephosphorization andaaproduction productionofofgrained grained iron iron were were conducted conductedbybya amethod method similar to similar to those thoseof ofExamples Examples 1 1 and and 2. Table4 4shows 2. Table showsthethetemperatures temperaturesTiTand i and Tf Tf ( C), the C concentrations [C] and [C] (mass%), and the P concentrations [P]i (°C), the C concentrations [C]i and i [C]f (mass%), f and the P concentrations [P]i

and [P] (mass%) of the molten iron before and after the dephosphorization, and [P]f f (mass%) of the molten iron before and after the dephosphorization,

respectively; the respectively; thetypes typesand andamounts amounts of of the the oxygen oxygen source and CaO source and CaOsource source supplied; the processing time t (minutes); and the basicity C/S of the slag after supplied; the processing time tf (minutes); f and the basicity C/S of the slag after

the process, the process, as asTest TestNos. Nos. 13 13 to to19. As shown 19. As shownininTable Table4,4,the the basicity basicity C/S C/S of the the slag in slag in Test Test No. No. 18 18 was was low comparedwith low compared withTest TestNos. Nos.1313toto17, 17,and andthus thus the the PP concentration [P]f concentration [P]f after after the theprocess processwas was high. Meanwhile,ininTest high. Meanwhile, TestNo. No.19, 19,the the

basicity C/S of the slag was high, and the solidification of the slag was basicity C/S of the slag was high, and the solidification of the slag was

confirmed. confirmed.

[0050] [Table 4]

[0050] [Table 4]

[0050] [Table 4]

before iron Molten before iron Molten Molten iron before process after iron Molten CaO

Oxygen Oxygen CaOsource source Slag

source source Oxygen source CaO source Molten iron after process Slag

process process process

tf tf Remarks

Iron Pure

No. No. Iron Pure Solidification Remarks

Air CaO C/S

CaCO3

Ti Tf Tm

[C]i

[C]f

[P]f

[P] Ti [C] i [P] i Air CaO CaCO 3 Tf [C] f [P] f Tm C/S Solidification

oxygen

ore oxygen ore oxygen Present/Absent minute minute - -

Nm3/t Nm3/t mass%

°C mass%

mass% °C

mass% °C

kg/t kg/t

kg/t ℃ mass% mass% kg/t Nm 3 /t Nm 3 /t kg/t kg/t minute ℃ mass% mass% ℃ - Present/Absent Example Invention Absent

2.06 1430

1473 1458 1.18

27.8

4.0 1.1

15

0.110 0.039

22

13 10 0 13 1473 2.06 0.110 10 4.0 22 15 0 27.8 1458 1.18 0.039 1430 1.1 Absent Invention Example Absent

1434

1478 1459

27.8 1.13

2.00 1.8

4.0

0.110 20 0.020

14 10 22 20

0 20

14 1478 2.00 0.110 10 4.0 22 20 0 27.8 1459 1.13 0.020 1434 1.8 Absent Invention Example Invention Example

Absent

1453

28.3

1492 1427

1.21

2.07 4.0 3.0

0.017

0.110 10 22

15 30 0 15 1492 2.07 0.110 10 4.0 22 30 0 28.3 1453 1.21 0.017 1427 3.0 Absent Invention Example Invention Example

Absent

1456

1497 1434

1.96 28.1 1.13 3.6

4.0

0.110 36 0.017

22

16 10 0 16 1497 1.96 0.110 10 4.0 22 36 0 28.1 1456 1.13 0.017 1434 3.6 Absent Invention Example Invention Example

Absent

1450 1429

1502 1.19

28.1

1.98 4.0 4.0

0.110 0.017

17 10 40

22 0 17 1502 1.98 0.110 10 4.0 22 40 0 28.1 1450 1.19 0.017 1429 4.0 Absent Invention Example Invention Example

Absent

1437

1463 27.8 1454

1.92 1.10

4.0 0.9

0.067

0.110

18 10 11

22 0 18 1463 1.92 0.110 10 4.0 22 11 0 27.8 1454 1.10 0.067 1437 0.9 Absent Invention Example Invention Example

Present

1.26

1448

28.1

1.95

1508 1423 4.5

4.0

0.110 0.017

45

22

19 10 0 19 1508 1.95 0.110 10 4.0 22 45 0 28.1 1448 1.26 0.017 1423 4.5 Present Invention Example Invention Example

22 Dec 2025

[0051] The grained iron produced in each of Test Nos. 8 to 10, 12, 14 to 17, and 19 were found to have a P concentration of 0.030 mass% or less. When the reduced iron of each process was melted in an electric furnace, the obtained molten iron was found to have a P concentration of 0.030 mass% or less. Such 5 a P concentration has reached a level required of a steel product, thus requiring no additional dephosphorization. After being classified based on a grain size of 1 mm or more, the grained iron obtained in each of Test Nos. 8 to 10, 12, 14 to 2023255850

17, and 19 could be used in an electric furnace, a blast furnace, or a converter without any problem. 10 [0052] In this specification, the unit "t" of a mass represents 103 kg. In addition, the symbol "N" added to the unit "Nm3" of a volume represents the standard state of gas. In this specification, the standard state of gas corresponds to 1 atm (= 101325 Pa) and 0C. Symbol [M] in a chemical formula represents that an element M is melted in molten iron or reduced iron. 15 Industrial Applicability

[0053] According to the method for producing grained iron and grained iron of the present invention, it is possible to efficiently produce grained iron with a low P concentration even when reduced iron obtained from low-grade iron ore with a high P concentration is used as a raw material. In addition, only 20 remelting the grained iron according to the present invention can obtain molten iron with a P concentration corresponding to the level in a steel product. Thus, the present invention is industrially advantageous.

[0054] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should 25 not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0055] Throughout this specification and the claims which follow, unless the 30 context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any

22 Dec 2025

other integer or step or group of integers or steps.

Claims (5)

1. 22 Dec 2025

   The Claims Defining the Invention are as Follows:

   [Claim 1] A method for producing grained iron, comprising: a first step of melting reduced iron having P concentration of 0.050 5 mass% or more to obtain primary molten iron having C concentration of 2 mass% or less; a second step of separating the primary molten iron from slag; 2023255850

   a third step of subjecting the primary molten iron separated from the slag to dephosphorization to obtain secondary molten iron; and 10 a fourth step of solidifying the secondary molten iron into a grain form to obtain grained iron, wherein: in the third step, the dephosphorization is performed by supplying an oxygen source and a CaO source to the primary molten iron, and a temperature of 15 the secondary molten iron at the end of the dephosphorization is set to a temperature of the primary molten iron at the start of the dephosphorization or lower.
2. [Claim 2] The method for producing grained iron according to claim 1, wherein a 20 temperature Tf of the secondary molten iron at the end of the dephosphorization is set higher than a solidifying temperature Tm of the secondary molten iron at the end of the dephosphorization by 20C or more.
3. [Claim 3] The method for producing grained iron according to claim 1 or 2, 25 wherein a composition of the slag at the end of the dephosphorization is set to have a slag basicity in a range of 1.0 to 4.0, wherein the slag basicity is a ratio of a CaO concentration (%CaO) to a SiO2 concentration (%SiO2) on a mass basis.
4. [Claim 4] The method for producing grained iron according to claim 1, wherein 30 the fourth step is performed using a grained iron producing apparatus including a granulation device that forms the secondary molten iron into droplets, a water-flow control vessel that is disposed at a position for receiving the

   22 Dec 2025

   droplets and accommodates cooling water, and at least one cooling water pipe that is connected to the water-flow control vessel and supplies cooling water to the water-flow control vessel, and the water-flow control vessel includes an inclined surface that is 5 inclined such that a horizontal cross-sectional area of the water-flow control vessel becomes narrower in a downward direction, and a discharge port is provided below the inclined surface. 2023255850
5. [Claim 5] The method for producing grained iron according to claim 4, 10 wherein a P concentration of the grained iron is 0.030 mass% or less, and size grain of the grained iron is in the range of 1 mm to 50 mm inclusive.