METHOD FOR PRODUCING GRAINED IRON, AND GRAINED IRON

Abstract

A method capable of efficiently producing grained iron with a low P concentration includes a first step of melting reduced iron to obtain primary molten iron, a second step of separating the primary molten iron from slag, a third step of subjecting the primary molten iron separated from the slag to dephosphorization to obtain secondary molten iron, and a fourth step of solidifying the secondary molten iron into a grained form to obtain grained iron, in which 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 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.

Claims

1. A method for producing grained iron, comprising: a first step of melting reduced iron to obtain primary molten iron; a second step of separating the primary molten iron from slag; a third step of subjecting the primary molten iron separated from the 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, 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 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. The method for producing grained iron according to claim 1, wherein a temperature T.sub.f of the secondary molten iron at the end of the dephosphorization is set higher than a solidifying temperature T.sub.m of the secondary molten iron at the end of the dephosphorization by 20 C. or more.

3. The method for producing grained iron according to claim 1, 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 SiO.sub.2 concentration (% SiO.sub.2) on a mass basis.

4. The method for producing grained iron according to claim 1, wherein 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 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 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.

5. Grained iron produced from reduced iron with a P concentration of 0.050 mass % or more as a raw material, 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.

6. The method for producing grained iron according to claim 2, 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 SiO.sub.2 concentration (% SiO.sub.2) on a mass basis.

Description

DESCRIPTION OF EMBODIMENTS

[0027] An embodiment of the present invention will be specifically described 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.

[0028] The inventors have considered as follows to implement the present invention.

[0029] 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 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 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 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 SiO.sub.2, 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, 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.

TABLE-US-00001 TABLE 1 Ingredient composition (mass %) T. Fe M. Fe SiO.sub.2 Al.sub.2O.sub.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 Reduced iron C 79.0 61.5 5.0 1.9 5.0 0.12

[0030] In response, the inventors have arrived at a process of producing 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 oxygen source and a lime source to the obtained molten iron to effect dephosphorization, and further solidifying the dephosphorized molten iron into a grained form.

[0031] An embodiment of the present invention will be specifically described below.

[0032] As a first step, reduced iron is heated and melted in an electric furnace to produce primary molten iron. The reduced iron to be used herein may be the one transferred as is at a high temperature from an adjacent plant for producing reduced iron, for example. Of course, reduced iron that has been once cooled to room temperature may also be used. The electric furnace may be an arc furnace, submerged arc furnace, or induction melting furnace. The 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, 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 metallic Al or Si, for example. Such energy is preferably renewable from the perspective of reducing CO.sub.2 emissions.

[0033] As a second step, slag, which is a gangue portion of the reduced iron, and the primary molten iron are separated from each other. For example, the molten metal is tapped into a vessel for transport and then transported to a facility for performing dephosphorization. When dephosphorization is performed in the following step, a CaO source is added to produce slag for dephosphorization. To secure the amount of the slag and adjust the ingredient composition thereof, at least a part of the slag containing a large amount of SiO.sub.2 produced with the melting of the reduced iron may be carried over. The slag may also be removed from a vessel for heating and melting the reduced iron used in the first step, for example, by means of a slag dragger.

[0034] As a third step, the molten metal is subjected to dephosphorization to produce secondary molten iron. A dephosphorization reaction requires an oxygen source and a CaO source as represented by the following Expression (1).

[00001]$\begin{array}{cc}2\left[P\right]+5/2.Math.O_2\left(g\right)+3\mathrm{CaO}\left(s\right)=3\mathrm{CaO}.Math.P_2{O}_5\left(s\right),& \left(1\right)\end{array}$ [0035] where [P] represents phosphorus in the molten iron.

[0036] A pure oxygen gas is normally used as the oxygen source for dephosphorization. The inventors have come to the conclusion that it is advantageous to perform dephosphorization at a low temperature, since a dephosphorization reaction is an exothermic reaction, and also to reduce the temperature of the molten iron within the range that does not adversely affect dephosphorization, taking into account that the resultant is solidified to form grained iron in the following step.

[0037] As a result of examination, the inventors have found that sufficient dephosphorization can be achieved while cooling the molten iron, by supplying 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 contained in the air, achieving a better cooling effect than when a pure oxygen gas is used. Meanwhile, when an iron oxide source is used, an endothermic 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 a better cooling effect than when a pure oxygen gas is used.

[0038] Next, using limestone as the CaO source can cool the molten iron because calcium carbonate contained in limestone absorbs heat as it decomposes into CaO and CO.sub.2. A similar cooling effect is achieved by supplying carbonate, such as raw dolomite. However, if the proportion of CaO in an auxiliary 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 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 material to be added by taking into consideration the required cooling effect and a stable operation.

[0039] 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 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 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 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 furnace or by immersing an injection lance in the molten iron. Regarding the composition of the slag at the end of the dephosphorization, slag basicity, which is the ratio of the CaO concentration (% CaO) to the SiO.sub.2 concentration (% SiO.sub.2) 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.sub.2 that is 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.sub.2 source, such as silica stone or ferrosilicon, and a CaO source, such as quicklime, as appropriate.

[0040] 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 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 after dephosphorization and causes problems such that an abnormal reaction may 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.

[0041] 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 possible to recover the exhaust heat using a boiler, for example.

[0042] As a fourth step, the secondary molten iron after the dephosphorization is solidified into a grained form to obtain grained iron. Examples of a method for producing grained iron include a method of flowing 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 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 solidified grained iron. At this time, since the diameter of grained iron varies in 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 falling speed can be kept constant.

[0043] The temperature of the molten iron decreases while the molten iron is being transported after the dephosphorization to be supplied to a grained iron 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 before the molten iron is entirely supplied to the grained iron production apparatus, resulting in reduced production yields. Meanwhile, if the 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 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 temperature of the molten iron decreases and grained iron is obtained may become long. As described above, considering forming into grained iron after the dephosphorization, there is a suitable range of the temperature of the molten iron after the dephosphorization. Specifically, the temperature T.sub.f of the molten iron after the dephosphorization is set to the temperature T.sub.i of the molten iron at the start of the dephosphorization or lower, from the viewpoint of increasing productivity. In addition, if the temperature T.sub.f at the end of the dephosphorization is set higher than the solidifying temperature T.sub.m of the secondary molten iron at the end of the dephosphorization by 20 C. or more, the molten iron can be supplied to the grained iron producing apparatus in a high yield, which is preferable.

[0044] Note that the solidifying temperature T.sub.m ( C.) may be determined by 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 from a liquidus temperature in an FeC state diagram, based on the C concentration in the molten iron subjected to dephosphorization that is estimated from past records of operation (the C concentration and the temperature before dephosphorization, and the type and supply conditions of the oxygen source).

[0045] The grained iron producing apparatus includes a granulation device 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 water. At least one cooling water pipe which supplies cooling water is 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 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 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 water-flow control vessel has an inclined surface which is inclined such that the horizontal cross-sectional area of the vessel becomes narrower in a downward direction, and a discharge port is provided below the inclined surface. Setting 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 without accumulation of grained iron on the inclined surface.

[0046] 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 accordance with the proportion of the grained iron used can be achieved. This can reduce the load in dephosphorization and ease restrictions on the raw materials to be used in the blast furnace and converter.

[0047] Note that when the grained iron obtained in this embodiment is used 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 grain sizes, it is preferable to adjust the flowing-down speed in the tundish. It is also preferable to perform classification as required. Typically, grained iron with a grain size in the range of 1 to 50 mm is convenient to use. When grained 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 preferable to perform classification so as to obtain grained iron with a grain size of 1 mm or more for use. On the other hand, if grained iron with a grain size of more than 50 mm is used, there is a higher risk of wear damage that may occur to a facility, such as the conveyor for transport or the hopper, when collision due to 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 50 mm or less. It is also possible to perform classification as appropriate to remove grained iron with a grain size of more than 50 mm. Herein, the grain size in the range of 1 to 50 mm may include particles on a sieve with an opening of 1 mm to particles that have passed through a sieve with an opening of 50 mm.

EXAMPLES

Example 1

[0048] The reduced iron A shown in Table 1 was melted in an electric furnace with a capacity of 250 tons, and, after adjusting the temperature of the resultant, transferred to a ladle. Among the slag produced due to the gangue 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 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 perform dephosphorization while changing the types and amounts of an oxygen source and a lime source supplied. The dephosphorization facility included a gas top-blowing lance, an auxiliary material feeding hopper, and a bottom-blowing porous plug. The gas top-blowing lance was capable of supplying gas containing pure oxygen or air at a rate of approximately 1 Nm.sup.3/minute per 1 ton of molten iron. Three auxiliary material feeding hoppers, each filled with iron ore, quicklime (CaO), and calcium carbonate (CaCO.sub.3), can feed them at a rate of approximately 10 kg/minute. The bottom-blowing porous plug can supply gas. In this example, a pure Ar gas was supplied at a rate of approximately 0.1 Nm.sup.3/minute per 1 ton of molten iron.

[0049] The melting temperature in the electric furnace was adjusted to allow the temperature of the molten iron before dephosphorization to be approximately 1590 C. Before dephosphorization refers to the time before the gas top-blowing lance is lowered, while after dephosphorization refers to the time when the gas top-blowing lance has been completely raised after the dephosphorization. At each timing, temperature measurements and sampling were conducted using a sublance. The obtained samples were cut and polished and subjected to an emission spectrochemical analysis to evaluate the C concentration [C] and the P concentration [P] in the molten iron from calibration curves determined in advance. It was possible to measure the solidifying temperature of the molten metal at the timing when the temperature measurement and sampling were performed using the sublance, and the solidifying temperature T.sub.m of the molten iron subjected to the dephosphorization was actually measured.

[0050] The start of the dephosphorization was defined as when the gas top-blowing lance started to be lowered. After the top-blowing lance reached a predetermined height, the supply of an oxygen gas source and the addition of auxiliary materials were started. The dephosphorization was terminated when the supply of predetermined amounts of oxygen gas source and auxiliary materials was completed and the top-blowing lance was raised to a standby position. The duration of the period was determined as a processing time t.sub.f (minutes).

[0051] After the dephosphorization, the ladle was tilted to remove the slag on the molten iron with a slag dragger. Part of the removed slag was collected and subjected to a chemical analysis. The ladle was lifted and tilted using a crane to transfer the molten iron to the tundish. The molten iron was caused to flow 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 vessel and solidified to produce grained iron. The grain sizes of the obtained grained iron ranged from 0.1 to 30 mm. The grain size distributions were: +0.1 mm to 1 mm: 17.2 mass %, +1 mm to 10 mm: 31.3 mass %, +10 mm to 20 mm: 38.8 mass %, and +20 mm to 30 mm: 12.7 mass %. Herein, +N to M means particles on a sieve with an opening of N to particles that have passed through a sieve with an opening of M.

[0052] Table 2 shows, as Test Nos. 1 to 5, the temperatures T.sub.i and T.sub.f ( C.), the C concentrations [C].sub.i and [C].sub.f (mass %), and the P concentrations [P].sub.i and [P].sub.f (mass %) of the molten iron before and after the dephosphorization, respectively; the types and the amounts of the oxygen source and the CaO source supplied; the processing time t.sub.f (minutes); and the basicity of the slag after the process ((% CaO)/(% SiO.sub.2), i.e., the ratio of the CaO concentration (% CaO) to the SiO.sub.2 concentration (% SiO.sub.2) on a mass basis; hereinafter referred to as C/S).

[0053] As shown in Table 2, in all the invention examples, the temperature T.sub.f of the molten iron after the process was lower than the temperature T.sub.i of the molten iron before the process, and the P concentration [P].sub.f after the process was sufficiently lowered. In the comparative example, the temperature T.sub.f after dephosphorization increased higher than the temperature T.sub.i before dephosphorization, and consequently the P concentration [P].sub.f after the process was high, and a waiting time was caused during the grained iron production step, resulting in decreased productivity. In Test No. 4, compared with Test Nos. 1 to 3, the temperature T.sub.f of the molten iron after the process decreased to reduce the P concentration [P].sub.f sufficiently. However, part of the molten iron solidified in the tundish during the production of grained iron, resulting in a reduced yield. In each of Test Nos. 1 to 3, the temperature T.sub.f of the molten iron after the process was lower than the temperature T.sub.i of the molten iron before the process, and the temperature T.sub.f of the molten iron after the process was higher than the solidifying temperature T.sub.m of the molten iron by 20 C. or more. Also, the P concentration [P].sub.f after the process was sufficiently low, and the whole molten iron was formed into grained iron in a high yield with no decrease in productivity.

TABLE-US-00002 TABLE 2 Slag Molten iron Oxygen source Molten iron Solidi- before process Iron Pure CaO source after process fication T.sub.i [C].sub.i [P].sub.i ore oxygen Air CaO CaCO.sub.3 t.sub.f T.sub.f [C].sub.f [P].sub.f T.sub.m C/S Present/ No. C. mass % mass % kg/t Nm.sup.3/t Nm.sup.3/t kg/t kg/t minute C. mass % mass % C. Absent Remarks 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 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 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 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 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

Example 2

[0054] Dephosphorization and a production of grained iron were conducted using a method similar to that of Example 1. Table 3 shows the temperatures T.sub.i and T.sub.f ( C.), the C concentrations [C].sub.i and [C].sub.f (mass %), and the P concentrations [P].sub.i and [P].sub.f (mass %) of the molten iron before and after the dephosphorization, respectively; the types and amounts of the oxygen source and CaO source supplied; the processing time t.sub.f (minutes); 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 basicity C/S of the slag was low compared with Test Nos. 6 to 10, and thus the P 10 concentration after the process was high. Meanwhile, in Test No. 12, the basicity C/S of the slag was high, and the solidification of the slag was confirmed.

TABLE-US-00003 TABLE 3 Slag Molten iron Oxygen source Molten iron Solidi- before process Iron Pure CaO source after process fication T.sub.i [C].sub.i [P].sub.i ore oxygen Air CaO CaCO.sub.3 t.sub.f T.sub.f [C].sub.f [P].sub.f T.sub.m C/S Present/ No. C. mass % mass % kg/t Nm.sup.3/t Nm.sup.3/t kg/t kg/t minute C. mass % mass % C. Absent Remarks 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 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 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 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 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 11 1599 0.010 0.110 5 0.5 0 11 0 7.7 1573 0.010 0.084 1535 0.9 Absent Invention Example 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

Example 3

[0055] The reduced iron A shown in Table 1 was melted with anthracite in an electric furnace with a capacity of 250 tons to produce molten iron with a C concentration of approximately 2.0 mass %. After adjusting the temperature of the molten iron, the molten iron was transferred to a ladle, where dephosphorization and a production of grained iron were conducted by a method similar to those of Examples 1 and 2. Table 4 shows the temperatures T.sub.i and T.sub.f ( C.), the C concentrations [C].sub.i and [C].sub.f (mass %), and the P concentrations [P].sub.i and [P].sub.f (mass %) of the molten iron before and after the dephosphorization, respectively; the types and amounts of the oxygen source and CaO source supplied; the processing time t.sub.f (minutes); and the basicity C/S of the slag after the process, as Test Nos. 13 to 19. As shown in Table 4, the basicity C/S of the slag in Test No. 18 was low compared with Test Nos. 13 to 17, and thus the P concentration [P].sub.f after the process was high. Meanwhile, in Test No. 19, the basicity C/S of the slag was high, and the solidification of the slag was confirmed.

TABLE-US-00004 TABLE 4 Slag Molten iron Oxygen source Molten iron Solidi- before process Iron Pure CaO source after process fication T.sub.i [C].sub.i [P].sub.i ore oxygen Air CaO CaCO.sub.3 t.sub.f T.sub.f [C].sub.f [P].sub.f T.sub.m C/S Present/ No. C. mass % mass % kg/t Nm.sup.3/t Nm.sup.3/t kg/t kg/t minute C. mass % mass % C. Absent Remarks 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 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 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 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 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 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 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

[0056] 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 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 17, and 19 could be used in an electric furnace, a blast furnace, or a converter without any problem.

[0057] In this specification, the unit t of a mass represents 103 kg. In addition, the symbol N added to the unit Nm.sup.3 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.

INDUSTRIAL APPLICABILITY

[0058] 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 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.