Method for melting and refining iron source

Abstract

To provide a technique capable of reducing a nitrogen concentration of molten iron obtained after refining, in melting and refining an iron source using an electric furnace.SOLUTION: A method for melting and refining an iron source includes a step of supplying an iron source into an electric furnace, melting the iron source and refining the iron source. One or more kinds of high carbon iron source and one or more kinds of low carbon iron source are supplied as the iron source. A content of C in the high carbon iron source is 0.5 mass% or more. A content of C in the low carbon iron source is less than 0.5 mass%. In the method, the iron source is supplied so as to satisfy a relation 0<(WA1-WA2) / WT (WA1 is weight (t) of the high carbon iron source supplied at an earlier half of the step, the earlier half of the step is until 50% of gross weight (t) of the iron source is supplied, WA2 is weight (t) of the high carbon iron source supplied at a later half of the step, and WT is the gross weight (t) of the iron source supplied at the step).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present application discloses a method for smelting and refining an iron source. [Background technology]

[0002] Methods for melting and refining an iron source using an electric furnace are known. For example, Patent Document 1 discloses a technique in which, when melting an iron source using an electric furnace, the iron source is sorted according to its composition and the iron source is charged into the electric furnace while comparing the actual composition during melting with the required quality. Furthermore, Patent Document 2 discloses a technique in which solid reduced iron containing a total of 3.0 mass% or more of SiO2 and Al2O3 and 1.0 mass% or more of carbon is melted in an electric furnace to produce molten steel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 4,564,388 [Patent Document 2] Patent Publication No. 2021-080540 Summary of the Invention [Problem to be solved by the invention]

[0004] Molten iron obtained by melting and refining an iron source using an electric furnace has a higher nitrogen concentration than molten iron obtained by melting and refining an iron source using a converter. This is because at least a portion of the nitrogen contained in the iron source is carried into the molten iron without being denitrified, and because nitrogen absorption from the atmosphere is likely to occur due to an open arc, etc. In this regard, the prior art has room for improvement in terms of reducing the nitrogen concentration in molten iron after refining in the melting and refining of an iron source using an electric furnace. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A method for melting and refining an iron source using an electric furnace, comprising: supplying the iron source into the electric furnace, melting the iron source, and refining the iron source; As the iron source, one or more high-carbon iron sources and one or more low-carbon iron sources are supplied, The C content of the high-carbon iron source is 0.5% by mass or more, The C content of the low-carbon iron source is less than 0.5% by mass, and The following relationship (1): 0<(W A1 -W A2 ) / W T …(1) W A1 : Weight (t) of the high-carbon iron source supplied in the first half of the process The first half of the process: until 50% of the total weight (t) of the iron source is supplied W A2 : Weight (t) of the high-carbon iron source supplied in the latter half of the process W T : Total weight (t) of the iron source supplied in the process The iron source is supplied so as to satisfy A method for melting and refining iron sources. <Aspect 2> The method for smelting and refining an iron source according to aspect 1, The following relationship (1-1): 0.05≦(W A1 -W A2 ) / W T …(1-1) The iron source is supplied so as to satisfy A method for melting and refining iron sources. <Aspect 3> The method for smelting and refining an iron source according to aspect 1 or 2, The following relationship (2): 0.05≦(W A1 +W A2 ) / W T ≦0.95 …(2) The iron source is supplied so as to satisfy A method for melting and refining iron sources. [Effects of the Invention]

[0006] According to the method for melting and refining an iron source of the present disclosure, molten iron having a low nitrogen concentration can be easily obtained after refining. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, one embodiment of the method for melting and refining an iron source according to the present disclosure will be described, although the method for melting and refining an iron source according to the present disclosure is not limited to the following embodiment.

[0008] A method for melting and refining an iron source using an electric furnace according to one embodiment includes a step of supplying the iron source into the electric furnace, melting the iron source, and refining the iron source (hereinafter, may be referred to as a "refining step"). In the method for melting and refining an iron source according to one embodiment, one or more high-carbon iron sources and one or more low-carbon iron sources are supplied as the iron sources. The high-carbon iron source has a C content of 0.5% by mass or more. The low-carbon iron source has a C content of less than 0.5% by mass. Furthermore, in the method for melting and refining an iron source according to one embodiment, the following relationship (1): 0<(W A1 -W A2 ) / W T …(1) W A1 : Weight (t) of the high-carbon iron source supplied in the first half of the process The first half of the process: until 50% of the total weight (t) of the iron source is supplied W A2 : Weight (t) of the high-carbon iron source supplied in the latter half of the process W T : Total weight (t) of the iron source supplied in the process The iron source is supplied so as to satisfy the following.

[0009] 1. Iron Source In one embodiment of the method for melting and refining an iron source, an iron source is supplied into an electric furnace, and the iron source is melted and refined. Specifically, the iron source is supplied into the electric furnace, an arc is generated in the electric furnace to melt the iron source, and the iron source is refined by blowing gas into the molten iron source, for example. In the method for melting and refining an iron source according to one embodiment, one or more high-carbon iron sources and one or more low-carbon iron sources are supplied as the iron sources.

[0010] 1.1 High-carbon iron source As will be described later, the high-carbon iron source temporarily increases the carbon concentration of molten iron in the first half of the refining process when the amount of molten iron in the electric furnace is small, thereby increasing the thermodynamic activity of N through an interaction and reducing the driving force of the nitriding reaction due to the arc or the like. This effect is easily achieved when the C content of the high-carbon iron source is 0.5% by mass or more. The C content of the high-carbon iron source may be 0.5% by mass or more and 7.0% by mass or less, 0.5% by mass or more and 6.5% by mass or less, 0.5% by mass or more and 6.0% by mass or less, 0.5% by mass or more and 5.5% by mass or less, or 0.5% by mass or more and 5.0% by mass or less.

[0011] The high-carbon iron source may contain elements other than carbon and iron. For example, the high-carbon iron source may contain one or both of Si and Al as other elements. The total content of Si and Al in the high-carbon iron source may be 0% by mass or more and 7.0% by mass or less, 0% by mass or more and 4.5% by mass or less, 0% by mass or more and 3.0% by mass or less, 0% by mass or more and 2.0% by mass or less, 0% by mass or more and 1.7% by mass or less, 0% by mass or more and 1.5% by mass or less, 0% by mass or more and 1.3% by mass or less, 0% by mass or more and 1.0% by mass or less, 0% by mass or more and 0.8% by mass or less, 0% by mass or more and 0.6% by mass or less, or 0% by mass or more and 0.4% by mass or less. When the high-carbon iron source contains one or both of Si and Al, the formation of CaO into slag is promoted along with the generation of SiO2 and Al2O3 when the high-carbon iron source is melted, and slag, which is the source of foaming, is produced early. According to the findings of the present inventors, such effects are easily achieved when the total content of Si and Al in the high-carbon iron source is 0.4% by mass or more. In this regard, the total content of Si and Al in the high-carbon iron source may be 0.4% by mass to 7.0% by mass, 0.4% by mass to 4.5% by mass, 0.5% by mass to 3.0% by mass, 0.5% by mass to 2.0% by mass, or 0.6% by mass to 1.7% by mass. Examples of elements other than Si and Al include phosphorus, sulfur, manganese, calcium, magnesium, nitrogen, and oxygen.

[0012] The high-carbon iron source may be an iron alloy containing carbon, or a mixture of a carbon-containing material and an iron-containing material. Furthermore, the carbon contained in the high-carbon iron source may be contained in a solid solution state or in the form of a compound such as a carbide. Various iron sources can be used as the high-carbon iron source. The high-carbon iron source is preferably one or both of reduced iron and pig iron. Alternatively, scrap with a high carbon concentration can also be used as the high-carbon iron source.

[0013] The shape of the high-carbon iron source is not particularly limited as long as it can be supplied as an iron source into an electric furnace. The high-carbon iron source may be, for example, in the form of a block or powder. The high-carbon iron source may also be molded.

[0014] 1.2 Low-carbon iron sources The low-carbon iron source has a C content of less than 0.5% by mass. The C content of the low-carbon iron source may be 0% by mass or more and less than 0.5% by mass, more than 0% by mass and less than 0.4% by mass, more than 0% by mass and less than 0.3% by mass, more than 0% by mass and less than 0.2% by mass, or more than 0% by mass and less than 0.1% by mass.

[0015] The low-carbon iron source may contain elements other than carbon and iron. For example, the low-carbon iron source may contain one or both of Si and Al as other elements. The total content of Si and Al in the low-carbon iron source may be, for example, 0% by mass or more and 7.0% by mass or less, 0% by mass or more and 4.5% by mass or less, 0% by mass or more and 3.0% by mass or less, 0% by mass or more and 2.0% by mass or less, 0% by mass or more and 1.7% by mass or less, 0% by mass or more and 1.5% by mass or less, 0% by mass or more and 1.3% by mass or less, 0% by mass or more and 1.0% by mass or less, 0% by mass or more and 0.8% by mass or less, 0% by mass or more and 0.6% by mass or less, or 0% by mass or more and 0.4% by mass or less. The total content of Si and Al in the low-carbon iron source may be greater or less than the total content of Si and Al in the high-carbon iron source. Examples of elements other than Si and Al include phosphorus, sulfur, nitrogen, manganese, calcium, magnesium, and oxygen.

[0016] The form and type of the low-carbon iron source are not particularly limited as long as the C content is less than 0.5% by mass. Various iron sources can be used as the low-carbon iron source. The low-carbon iron source is preferably scrap. Alternatively, reduced iron produced without undergoing carburization after hydrogen reduction can also be used as the low-carbon iron source.

[0017] The shape of the low-carbon iron source is not particularly limited as long as it can be supplied as an iron source into an electric furnace. The low-carbon iron source may be, for example, in the form of a lump or powder. The low-carbon iron source may also be molded.

[0018] 2. Relationships (1) In the refining process, the iron source is supplied so as to satisfy the above-mentioned relationship (1). That is, if the refining process is divided into two parts, a first half (until 0% to 50% of the total weight (t) of the iron source is supplied) and a second half (until 50% to 100% of the total weight of the iron source is supplied), the amount of high-carbon iron source supplied in the first half is greater than that in the second half.

[0019] Immediately after the start of melting and refining an iron source using an electric furnace, slag is still being generated, which tends to result in an open arc state in which the arc length exceeds the slag thickness, causing a nitriding reaction due to the arc, which tends to increase the nitrogen concentration in the molten iron. In contrast, in the method disclosed herein, by supplying a relatively large amount of high-carbon iron source in the first half of the refining process, the carbon concentration in the molten iron is temporarily increased, and the thermodynamic activity of N can be increased through interaction, thereby reducing the driving force for the nitriding reaction due to the arc. In other words, by supplying the iron source in the refining process so as to satisfy the above relationship (1), molten iron with a low nitrogen concentration is likely to be obtained after refining.

[0020] The lower limit of the above relationship (1) is greater than 0, and may be 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.06 or greater, 0.07 or greater, 0.08 or greater, 0.09 or greater, or 0.10 or greater. In particular, the following relationship (1-1): 0.05≦(W A1 -W A2 ) / W T …(1-1) By supplying the above iron source so as to satisfy the above requirement, a higher effect can be expected.

[0021] 3.Other matters In the refining process, known refining conditions can be adopted, except that the iron source is supplied so as to satisfy the above relationship (1). In melting and refining of an iron source using an electric furnace, the start time of melting the iron source using an arc and the start time of refining the iron source using gas injection are usually approximately the same. Furthermore, refining of the iron source usually ends after the end time of melting the iron source. Furthermore, the start time of refining the iron source using gas injection is the same as or later than the start time of supplying the iron source to the electric furnace. However, this embodiment is premised on the premise that refining using gas injection starts in the first half of the refining process. In other words, if the start time of refining the iron source using gas injection is later than the start time of supplying the iron source to the electric furnace, refining using gas injection starts when the amount of the iron source supplied to the electric furnace is less than 50% of the total amount of the iron source. Refining of the iron source using gas injection may also start when the amount of the iron source supplied to the electric furnace is 40% or less, 30% or less, or 20% or less of the total amount of the iron source. In the refining process, for example, an iron source is supplied into an electric furnace, and an arc is generated in the electric furnace to melt the iron source into molten iron. The molten iron is then arc-heated, and auxiliary materials such as a dephosphorizing agent, a desulfurizing agent, and a carbon material are supplied, while an oxygen-containing gas is blown into the molten iron. This controls the temperature of the molten iron within a predetermined range and adjusts the composition of the molten iron. The molten iron (molten steel) after refining can be tapped from the tap hole of the electric furnace.

[0022] 3.1 Iron source supply The supply form of the iron source in the refining process is not particularly limited. The iron source may be supplied continuously or intermittently into the electric furnace. "Continuously" means that there is no interruption of 10 seconds or more between the start and end of the supply of the iron source into the electric furnace. In other words, the time between the start and end of the supply of one iron source into the electric furnace and the start and end of the supply of another iron source is less than 10 seconds. "Intermittently" means that there is an interruption of 10 seconds or more between the start and end of the supply of the iron source into the electric furnace. The means for supplying the iron source is also not particularly limited. For example, the iron source can be supplied into the electric furnace via known supply means such as a conveyor, a chute, or a lance. The supply rate and supply amount of the iron source are also not particularly limited, and the optimal supply rate and supply amount may be selected depending on the size of the electric furnace, etc. In addition, the high-carbon iron source and the low-carbon iron source may be supplied into the furnace separately or in the form of a mixture. Furthermore, the timing and period for supplying the high-carbon iron source and the timing and period for supplying the low-carbon iron source do not necessarily have to coincide.

[0023] 3.2 Average carbon concentration of iron source As described above, the iron source melting and refining method disclosed herein uses a high-carbon iron source and a low-carbon iron source. The carbon contained in the iron source not only reduces the driving force of the nitriding reaction caused by the arc but also contributes to slag foaming and other processes. The higher the carbon content of the iron source, the easier it is to increase the slag thickness. In other words, a high carbon concentration in the iron source supplied in the first half of the refining process is believed to ensure a sufficient slag thickness more quickly. In this regard, the average carbon concentration of the iron source supplied in the first half of the refining process may be 0.30% by mass or more to 6.00% by mass or less, 0.30% by mass or more to 5.00% by mass or less, 0.30% by mass or more to 4.00% by mass or less, 0.30% by mass or more to 3.00% by mass or less, 0.30% by mass or more to 2.75% by mass or less, or 0.30% by mass or more to 2.50% by mass or less.

[0024] 3.3 Ratio of high-carbon iron source to low-carbon iron source The proportion of the high-carbon iron source and the proportion of the low-carbon iron source in the entire iron source supplied in the refining step are not particularly limited. For example, in a method for melting and refining an iron source according to one embodiment, the following relationship (2) is satisfied: 0.05≦(W A1 +W A2 ) / W T ≦0.95 …(2) That is, the proportion of the high-carbon iron source in the entire iron source supplied in the refining step may be 5% by mass or more and 95% by mass or less, 10% by mass or more and 95% by mass or less, 10% by mass or more and 90% by mass or less, or 10% by mass or more and 85% by mass or less.

[0025] 3.4 Auxiliary raw materials In the refining process, auxiliary materials such as a dephosphorization agent, a desulfurization agent, and a carbonaceous material may be supplied into the electric furnace. The auxiliary materials may be supplied together with the iron source or separately from the iron source. In one embodiment, the auxiliary materials may be, for example, a Ca-containing material such as quicklime, a Si-containing material such as silica stone, or a combination thereof. To promote forming, a carbonaceous material may be supplied as an auxiliary material. Known means such as a conveyor, a chute, and a lance may be used to supply the auxiliary materials.

[0026] 3.5 Gas injection In the refining process, gas is injected into the electric furnace. For example, an oxygen-containing gas may be injected into the molten iron in the electric furnace. Furthermore, slag foaming may be performed by gas injection. There are no particular limitations on the gas injection means, and known means such as a lance may be used.

[0027] 3.6 Dregs Removal In the refining process, slag may be removed as needed. However, in the first half of the refining process, it is preferable not to remove slag in order to ensure a sufficient slag thickness. It is preferable to remove slag in the second half of the refining process or later.

[0028] 3.7 Slag carryover In the melting and refining of iron sources using an electric furnace, some or all of the slag at the end of charging (the end of the refining process) may be left in the furnace and carried over to the next charge. Such carried-over slag can contribute to ensuring the amount of slag in the first half of the refining process. According to the findings of the present inventors, when the amount of carried-over slag (the mass per ton of molten steel in the furnace at the end of the refining process) is 25 kg / t-steel or more, high effectiveness can be expected regardless of scale in the electric furnace. However, when the amount of carried-over slag exceeds 120 kg / t-steel, impurities such as phosphorus may concentrate in the slag, which may cause rephosphorization and other problems in the refining process. The amount of slag carried over may be 25 kg / t-steel to 120 kg / t-steel, 25 kg / t-steel to 100 kg / t-steel, 25 kg / t-steel to 80 kg / t-steel, 25 kg / t-steel to 60 kg / t-steel, or 25 kg / t-steel to 40 kg / t-steel. The amount of slag carried over may be measured by a weight measuring device installed in the electric furnace, or by a weight measuring device separate from the electric furnace, or may be calculated from the slag draining time, slag draining angle, etc.

[0029] 3.8 Electric furnace The configuration of the electric furnace is not particularly limited and may be a known configuration. The electric furnace, for example, has a melting furnace for melting an iron source. The melting furnace may be defined by a furnace lid, an inner wall, and a furnace bottom. The planar shape of the melting furnace may be circular. The melting furnace may have a constant bath depth or a constant furnace diameter. The bath depth and diameter of the melting furnace are not particularly limited. Means for generating an arc in an electric furnace are also known. For example, a direct current type using an upper electrode and a lower electrode may be used, or an alternating current type may be used. In the case of a direct current type, the upper electrode may be the cathode and the lower electrode may be the anode. The upper electrode is installed so as to be inserted into the furnace through the furnace lid. The lower electrode is installed at the furnace bottom. In the case of a direct current type, the number of upper electrodes and the number of lower electrodes are at least one. The positions of the upper electrode and the lower electrode are not particularly limited.

[0030] 4.Effects As described above, according to the method for melting and refining an iron source disclosed herein, by adjusting the timing of supplying a high-carbon iron source in the refining process, it is possible to temporarily increase the carbon concentration of molten iron in the first half of the refining process when the amount of molten iron in the electric furnace is small, and this interaction can increase the thermodynamic activity of N and reduce the driving force of the nitriding reaction caused by the open arc. As a result, it becomes easier to reduce the nitrogen concentration of molten iron after refining. [Example]

[0031] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention.

[0032] 1. Common conditions The iron source was melted and refined using an electric arc furnace. The amount of steel tapped per charge was 110 t (65 t seed molten metal, 175 t furnace volume).

[0033] Specifically, at least one of scrap, reduced iron, and pig iron was first introduced into an electric arc furnace via a horizontal conveyor as the iron source. The grades of the iron sources are shown in Table 1 below. In addition, quicklime and silica stone were continuously added as auxiliary materials from above the furnace along with the introduction of the iron source. An arc was generated in the electric furnace while the iron source and auxiliary materials were being introduced, and the iron source was melted. During the melting of the iron source, oxygen was supplied to the molten iron in the electric furnace, and a carbonaceous material was injected to promote forming, thereby refining the molten iron. Refining by oxygen supply and carbonaceous material injection began when the amount of iron source supplied to the electric furnace was 20% or less of the total iron source. The oxygen supply rate and the carbonaceous material injection rate were appropriately adjusted so that the carbon concentration of the molten steel at the end of the refining process was approximately 0.05% by mass. The seed molten steel can be considered to have the same composition as the molten steel at the end of the refining process of the immediately preceding charge. The operating conditions other than the supply of the iron source (control of electrode height, amount of auxiliary raw material input, oxygen supply conditions, refining time, etc.) were the same in all Examples and Comparative Examples.

[0034] [Table 1]

[0035] 2. Iron source supply conditions 2.1 Example A1 The proportion of scrap in the total iron source was set to 90 mass%. Relatively more reduced iron was supplied in the first half of the refining process than in the second half. Specifically, 42 mass% of scrap and 8 mass% of reduced iron were supplied in the first half of the refining process, and 48 mass% of scrap and 2 mass% of reduced iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0036] 2.2 Comparative Example a1 The proportion of scrap in the total iron source was set to 90 mass%. Relatively more reduced iron was supplied in the latter half of the refining process than in the first half. Specifically, 46 mass% of scrap and 4 mass% of reduced iron were supplied in the first half of the refining process, and 44 mass% of scrap and 6 mass% of reduced iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0037] 2.3 Example B1 The proportion of scrap in the total iron source was set to 64 mass%. Relatively more reduced iron was supplied in the first half of the refining process than in the second half. Specifically, 30 mass% of scrap and 20 mass% of reduced iron were supplied in the first half of the refining process, and 34 mass% of scrap and 16 mass% of reduced iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0038] 2.4 Example B2 The proportion of scrap in the total iron source was set to 64 mass%. Relatively more reduced iron was supplied in the first half of the refining process than in the second half. Specifically, 26 mass% of scrap and 24 mass% of reduced iron were supplied in the first half of the refining process, and 38 mass% of scrap and 12 mass% of reduced iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0039] 2.5 Comparative Example b1 The proportion of scrap in the total iron source was set to 64 mass%. The amount of reduced iron supplied was constant in the first and second halves of the refining process. Specifically, 32 mass% of scrap and 18 mass% of reduced iron were supplied in the first half of the refining process, and 32 mass% of scrap and 18 mass% of reduced iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0040] 2.6 Example C1 The proportion of scrap in the total iron source was set to 10% by mass. Relatively more reduced iron was supplied in the first half of the refining process than in the second half. Specifically, only 50% by mass of reduced iron was supplied in the first half of the refining process, and 10% by mass of scrap and 40% by mass of reduced iron were supplied in the second half of the refining process. The iron source was supplied intermittently.

[0041] 2.7 Comparative Example c1 The proportion of scrap in the total iron source was set to 10 mass%. Relatively more reduced iron was supplied in the latter half of the refining process than in the first half. Specifically, 6 mass% of scrap and 44 mass% of reduced iron were supplied in the first half of the refining process, and 4 mass% of scrap and 46 mass% of reduced iron were supplied in the second half of the refining process. The iron source was supplied intermittently.

[0042] 2.8 Example D1 The proportion of scrap to the total iron source was set to 60% by mass. Relatively more pig iron was supplied in the first half of the refining process than in the second half. Specifically, 25% by mass of scrap and 25% by mass of pig iron were supplied in the first half of the refining process, and 35% by mass of scrap and 15% by mass of pig iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0043] 2.9 Comparative Example d1 The proportion of scrap to the total iron source was set to 60% by mass. The amount of pig iron supplied was constant in the first and second halves of the refining process. Specifically, 30% by mass of scrap and 20% by mass of pig iron were supplied in the first half of the refining process, and 30% by mass of scrap and 20% by mass of pig iron were supplied in the second half of the refining process. The iron source was supplied continuously.

[0044] 3. Evaluation Method For each of the Examples and Comparative Examples, the nitrogen concentration of the molten iron (molten steel) after refining was measured, and the average value of the nitrogen concentration in 10 channels was scored according to the following criteria: Example A1 was scored based on Comparative Example a1, Examples B1 and B2 were scored based on Comparative Example b1, Example C1 was scored based on Comparative Example c1, and Example D1 was scored based on Comparative Example d1.

[0045] Rating 1: 20% or more improvement over the base 2: 10% to 20% improvement from the base 3: Bass

[0046] 4. Evaluation Results The evaluation results are shown in Table 2. In Table 2, the "value of formula (I)" refers to the value determined by formula (I) below.

[0047] (W A1 -W A2 ) / W T …(I) W A1 : Weight (t) of high-carbon iron source supplied in the first half of the refining process W A2: Weight (t) of low-carbon iron source supplied to the latter half of the refining process W T : Total weight of iron source supplied in the refining process (t)

[0048] [Table 2]

[0049] As is clear from the results shown in Table 2, when an iron source is supplied into an electric furnace, melted, and refined, the nitrogen concentration of molten iron after refining can be reduced if the following requirements (A) to (D) are met (Examples A1, B1, B2, C1, and D1). By meeting the following requirements (A) to (D), the carbon concentration of molten iron can be temporarily increased in the first half of the refining process when the amount of molten iron in the electric furnace is small, and the thermodynamic activity of N can be increased by interaction, which is thought to be why the driving force for the nitriding reaction caused by the arc can be reduced.

[0050] (A) One or more high-carbon iron sources and one or more low-carbon iron sources are supplied as iron sources. (B) The C content of the high-carbon iron source is 0.5 mass% or more. (C) The C content of the low-carbon iron source is less than 0.5% by mass. (D) The iron source is provided so as to satisfy the following relationship (1): 0<(W A1 -W A2 ) / W T …(1) W A1 : Weight (t) of high-carbon iron source supplied in the first half of the refining process W A2 : Weight (t) of high-carbon iron source supplied in the latter half of the refining process W T : Total weight of iron source supplied in the refining process (t)

[0051] 5. Supplementary Information In the above examples, scrap was used as the low-carbon iron source and reduced iron and pig iron were used as the high-carbon iron source, but the form of the iron source is not limited to these. That is, among known iron sources such as scrap, reduced iron, and pig iron, one having a C content of 0.5% by mass or more may be used as the high-carbon iron source, and one having a C content of less than 0.5% by mass may be used as the low-carbon iron source.

Claims

1. A method for melting and refining an iron source using an electric furnace, comprising: supplying the iron source into the electric furnace, melting the iron source, and refining the iron source; As the iron source, one or more high-carbon iron sources and one or more low-carbon iron sources are supplied, the high-carbon iron source has a C content of 0.5% by mass or more, The C content of the low-carbon iron source is less than 0.5% by mass, and The following relationship (1): 0<(W Ａ１ -W Ａ２ ) / W Ｔ …(1) W Ａ１ : weight (t) of the high-carbon iron source supplied in the first half of the process The first half of the process: until 50% of the total weight (t) of the iron source is supplied W Ａ２ : weight (t) of the high-carbon iron source supplied in the latter half of the process W Ｔ : total weight (t) of the iron source supplied in the step The iron source is supplied so as to satisfy A method for melting and refining iron sources.

2. The method for melting and refining an iron source according to claim 1, The following relationship (1-1): 0.05≦(W Ａ１ -W Ａ２ ) / W Ｔ …(1-1) The iron source is supplied so as to satisfy A method for melting and refining iron sources.

3. 3. The method for melting and refining an iron source according to claim 1 or 2, The following relationship (2): 0.05≦(W Ａ１ +W Ａ２ ) / W Ｔ ≦0.95 …(2) The iron source is supplied so as to satisfy A method for melting and refining iron sources.

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