Method for melting and refining iron source
By strategically supplying high- and low-nitrogen iron sources with controlled ratios and timing, the method addresses the high nitrogen concentration issue in molten iron from electric furnace refining, achieving reduced nitrogen levels through managed nitrogen absorption and reaction.
Patent Information
- Application Number
- JP2024011933
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-01-30
- Publication Date
- 2025-08-12
AI Technical Summary
Molten iron obtained by melting and refining an iron source using an electric furnace has a higher nitrogen concentration due to nitrogen absorption from the atmosphere and incomplete denitrification, necessitating a method to reduce this concentration.
A method involving the supply of both high-nitrogen and low-nitrogen iron sources, with specific weight ratios and timing adjustments during the refining process, to manage nitrogen absorption and reduce the overall nitrogen concentration in molten iron.
The method effectively reduces the nitrogen concentration in molten iron by temporarily increasing it in the early stage of refining, thereby minimizing the nitriding reaction caused by the arc, resulting in lower nitrogen levels post-refining.
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Abstract
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-nitrogen iron sources and one or more low-nitrogen iron sources are provided; the N content of the high-nitrogen iron source is 0.005% by mass or more, The N content of the low-nitrogen iron source is less than 0.005% by mass, and The following relationship (1): 0<(W A1 -W A2 ) / W T …(1) W A1 : Weight (t) of the high-nitrogen 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-nitrogen 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-nitrogen iron sources and one or more low-nitrogen iron sources are supplied as the iron sources. The high-nitrogen iron source has an N content of 0.005% by mass or more. The low-nitrogen iron source has an N content of less than 0.005% 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-nitrogen 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-nitrogen 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-nitrogen iron sources and one or more low-nitrogen iron sources are supplied as the iron sources.
[0010] 1.1 High-nitrogen iron source As described below, the high-nitrogen iron source temporarily increases the nitrogen 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 reducing the driving force of the nitriding reaction caused by an arc or the like. This effect is easily achieved when the N content of the high-nitrogen iron source is 0.005% by mass or more. The N content of the high-nitrogen iron source may be 0.005% by mass or more and 0.050% by mass or less, 0.005% by mass or more and 0.025% by mass or less, 0.005% by mass or more and 0.010% by mass or less, 0.006% by mass or more and 0.010% by mass or less, or 0.007% by mass or more and 0.010% by mass or less.
[0011] The high-nitrogen iron source may contain elements other than nitrogen and iron. For example, the high-nitrogen iron source may contain one or both of Si and Al as other elements. The total content of Si and Al in the high-nitrogen iron source may be 0% by mass to 7.0% by mass, 0% by mass to 4.5% by mass, 0% by mass to 3.0% by mass, 0% by mass to 2.0% by mass, 0% by mass to 1.7% by mass, 0% by mass to 1.5% by mass, 0% by mass to 1.3% by mass, 0% by mass to 1.0% by mass, 0% by mass to 0.8% by mass, 0% by mass to 0.6% by mass, or 0% by mass to 0.4% by mass. When the high-nitrogen 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-nitrogen 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-nitrogen iron source is 0.4% by mass or more. In this regard, the total content of Si and Al in the high-nitrogen 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. Furthermore, the high-nitrogen iron source may contain carbon as another element. The carbon content of the high-nitrogen iron source may be, for example, 0% by mass to 15.0% by mass, 0% by mass to 10.0% by mass, 0% by mass to 7.5% by mass, or 0% by mass to 5.0% by mass. Examples of elements other than carbon, Si, and Al include phosphorus, sulfur, manganese, calcium, magnesium, and oxygen.
[0012] The high-nitrogen iron source may be a nitrogen-containing iron alloy or a mixture of a nitrogen-containing material and an iron-containing material. Furthermore, the N contained in the high-nitrogen iron source may be present in a solid solution state or in the form of a compound such as a nitride. The high-nitrogen iron source may be at least one of scrap, reduced iron, and pig iron. Specifically, scrap, reduced iron, and / or pig iron may be measured for their nitrogen concentration and confirmed to have a nitrogen concentration of 0.005% by mass or more. These can be used as the high-nitrogen iron source.
[0013] The shape of the high-nitrogen iron source is not particularly limited as long as it can be supplied as an iron source into an electric furnace. The high-nitrogen iron source may be, for example, in the form of a lump or powder. The high-nitrogen iron source may also be molded.
[0014] 1.2 Low-nitrogen iron sources The low-nitrogen iron source has an N content of less than 0.005% by mass. The N content of the low-nitrogen iron source may be 0% by mass or more and less than 0.005% by mass, more than 0% by mass and less than 0.005% by mass, or more than 0% by mass and 0.004% by mass or less.
[0015] The low-nitrogen iron source may contain elements other than nitrogen and iron. For example, the low-nitrogen iron source may contain one or both of Si and Al as other elements. The total content of Si and Al in the low-nitrogen 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-nitrogen iron source may be greater or less than the total content of Si and Al in the high-nitrogen iron source. The low-nitrogen iron source may also contain carbon as another element. The carbon content of the low-nitrogen iron source may be, for example, 0% by mass or more and 15.0% by mass or less, 0% by mass or more and 10.0% by mass or less, 0% by mass or more and 7.5% by mass or less, or 0% by mass or more and 5.0% by mass or less. Examples of elements other than carbon, Si, and Al include phosphorus, sulfur, manganese, calcium, magnesium, and oxygen.
[0016] The form and type of the low-nitrogen iron source are not particularly limited as long as the N content is less than 0.005% by mass. The low-nitrogen iron source may be, for example, at least one of scrap, reduced iron, and pig iron. That is, scrap, reduced iron, and / or pig iron whose nitrogen concentration is measured and confirmed to be less than 0.005% by mass can be used as the low-nitrogen iron source.
[0017] The shape of the low-nitrogen iron source is not particularly limited as long as it can be supplied as an iron source into an electric furnace. The low-nitrogen iron source may be, for example, in the form of a lump or powder. The low-nitrogen 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 relationship (1). That is, if the refining process is divided into two parts, a first half (from 0% to 50% of the total weight (t) of the iron source is supplied) and a second half (from 50% to 100% of the total weight of the iron source is supplied), the amount of high-nitrogen 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-nitrogen iron source in the first half of the refining process, the nitrogen concentration of the molten iron can be temporarily increased and the driving force for the nitriding reaction due to the arc can be reduced. That is, 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, despite the use of a high-nitrogen iron source.
[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-nitrogen iron source and the low-nitrogen 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-nitrogen iron source and the timing and period for supplying the low-nitrogen iron source do not necessarily have to coincide.
[0023] 3.2 Average carbon concentration of iron source As described above, the high-nitrogen iron source and the low-nitrogen iron source may contain carbon. The carbon contained in the iron source can contribute to slag foaming, etc., and the greater the carbon content of the iron source, the easier it is to increase the slag thickness. That is, a high carbon concentration in the iron source supplied in the first half of the refining process is believed to ensure the slag thickness earlier. Ensuring the slag thickness in the first half of the refining process is believed to further suppress nitrogen absorption due to open arcs. 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-nitrogen iron source to low-nitrogen iron source The proportion of the high-nitrogen iron source and the proportion of the low-nitrogen 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-nitrogen 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. Furthermore, when an iron source with a low carbon content is used, a carbonaceous material may be supplied as an auxiliary material to promote forming. Known means such as a conveyor, a chute, or 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 In the melting and refining of iron sources using an electric furnace, even when only a low-nitrogen iron source is used as the iron source, it is difficult to reduce the nitrogen concentration of the molten iron obtained after melting and refining due to the nitriding reaction caused by the open arc as described above. Furthermore, low-nitrogen iron sources are expensive and have limitations on their usage, so it may be necessary to use a high-nitrogen iron source in addition to a low-nitrogen iron source. However, the use of a high-nitrogen iron source in the melting and refining of iron sources has been considered disadvantageous from the perspective of reducing the nitrogen concentration of the molten iron obtained after melting and refining. In contrast, according to the method disclosed herein, by adjusting the timing of the supply of such a high-nitrogen iron source during the refining process, which is considered to be disadvantageous in reducing the nitrogen concentration after refining, the nitrogen concentration of the molten iron can be temporarily increased in the early stage of the refining process when the amount of molten iron in the electric furnace is small, thereby reducing the driving force of the nitriding reaction caused by the open arc. As a result, it is easier to reduce the nitrogen concentration of the molten iron after refining, even when a high-nitrogen iron source is used. [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 type of iron source was first introduced into an electric arc furnace via a horizontal conveyor. The grades of the iron sources are shown in Table 1 below. Along with the introduction of the iron source, quicklime and silica stone were continuously introduced from above the furnace as auxiliary materials. While the iron source and auxiliary materials were being introduced, an arc was generated in the electric furnace to melt the iron source. 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 amount of oxygen supply and the amount of carbonaceous material injection were appropriately adjusted so that the carbon concentration of the molten steel at the end of the refining process would be approximately 0.05% by mass. The seed molten metal described above 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] The contents of elements other than N in the iron sources A1, B1, and B2 are almost the same among the iron sources A1, B1, and B2.
[0035] 2. Iron source supply conditions 2.1 Example A1 The proportion of iron source A1 in the total iron sources was set to 92 mass%. A relatively larger amount of iron source A1 was supplied in the first half of the refining process than in the second half. Specifically, only 50 mass% of iron source A1 was supplied in the first half of the refining process, and 42 mass% of iron source A1 and 8 mass% of iron source B1 were supplied in the second half of the refining process. The iron sources were supplied continuously.
[0036] 2.2 Comparative Example a1 The proportion of iron source A1 in the total iron sources was set to 92 mass%. The supply amount of iron source A1 was constant in the first and second halves of the refining process. Specifically, 46 mass% of iron source A1 and 4 mass% of iron source B1 were supplied in the first half of the refining process, and 46 mass% of iron source A1 and 4 mass% of iron source B1 were supplied in the second half of the refining process. The iron sources were supplied continuously.
[0037] 2.3 Example B1 The proportion of iron source A1 in the total iron sources was set to 68 mass%. A relatively larger amount of iron source A1 was supplied in the first half of the refining process than in the second half. Specifically, 35 mass% of iron source A1 and 15 mass% of iron source B1 were supplied in the first half of the refining process, and 33 mass% of iron source A1 and 17 mass% of iron source B1 were supplied in the second half of the refining process. The iron sources were supplied continuously.
[0038] 2.4 Example B2 The proportion of iron source A1 in the total iron source was set to 68 mass%. A relatively larger amount of iron source A1 was supplied in the first half of the refining process than in the second half. Specifically, 38 mass% of iron source A1 and 12 mass% of iron source B1 were supplied in the first half of the refining process, and 30 mass% of iron source A1 and 20 mass% of iron source B1 were supplied in the second half of the refining process. The iron sources were supplied continuously.
[0039] 2.5 Comparative Example b1 The proportion of iron source A1 in the total iron sources was set to 68 mass%. A relatively larger amount of iron source A1 was supplied in the latter half of the refining process than in the first half. Specifically, 32 mass% of iron source A1 and 18 mass% of iron source B1 were supplied in the first half of the refining process, and 36 mass% of iron source A1 and 14 mass% of iron source B1 were supplied in the latter half of the refining process. The iron sources were supplied continuously.
[0040] 2.6 Example C1 The proportion of iron source A1 in the total iron source was set to 12 mass%. A relatively larger amount of iron source A1 was supplied in the first half of the refining process than in the second half. Specifically, 9 mass% of iron source A1 and 41 mass% of iron source B1 were supplied in the first half of the refining process, and 3 mass% of iron source A1 and 47 mass% of iron source B1 were supplied in the second half of the refining process. The iron sources were supplied intermittently.
[0041] 2.7 Comparative Example c1 The proportion of iron source A1 in the total iron sources was set to 12 mass%. A relatively larger amount of iron source A1 was supplied in the latter half of the refining process than in the first half. Specifically, 5 mass% of iron source A1 and 45 mass% of iron source B1 were supplied in the first half of the refining process, and 7 mass% of iron source A1 and 43 mass% of iron source B1 were supplied in the latter half of the refining process. The iron sources were supplied intermittently.
[0042] 2.8 Example D1 The proportion of iron source A1 in the total iron sources was set to 55 mass%. A relatively larger amount of iron source A1 was supplied in the first half of the refining process than in the second half. Specifically, 35 mass% of iron source A1 and 15 mass% of iron source B2 were supplied in the first half of the refining process, and 20 mass% of iron source A1 and 30 mass% of iron source B2 were supplied in the second half of the refining process. The iron sources were supplied continuously.
[0043] 2.9 Comparative Example d1 The proportion of iron source A1 in the total iron sources was set to 55 mass%. A relatively larger amount of iron source A1 was supplied in the latter half of the refining process than in the first half. Specifically, 25 mass% of iron source A1 and 25 mass% of iron source B2 were supplied in the first half of the refining process, and 30 mass% of iron source A1 and 20 mass% of iron source B2 were supplied in the latter half of the refining process. The iron sources were supplied continuously.
[0044] 2.10 Reference example The above-mentioned refining process was carried out using only iron source B1 as the iron source. The iron source was continuously supplied.
[0045] 3. Evaluation Method For each of the Examples, Comparative Examples, and Reference 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 graded according to the following criteria: Example A1 was graded based on Comparative Example a1, Examples B1 and B2 were graded based on Comparative Example b1, Example C1 was graded based on Comparative Example c1, Example D1 was graded based on Comparative Example d1, and the Reference Example was graded based on Comparative Example c1.
[0046] Rating 1: 20% or more improvement over the base 2: 10% to 20% improvement from the base 3: Bass
[0047] 4. Evaluation Results The evaluation results for each of the Examples, Comparative Examples, and Reference Examples are shown in Table 2. In Table 2, the "value of formula (I)" refers to a value determined by formula (I) below.
[0048] (W A1 -W A2 ) / W T …(I) W A1 : Weight (t) of high-nitrogen iron source supplied in the first half of the refining process W A2 : Weight (t) of low-nitrogen iron source supplied in the latter half of the refining process W T: Total weight of iron source supplied in the refining process (t)
[0049] [Table 2]
[0050] As is clear from the results shown in Table 2, when an iron source is supplied to 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). It is believed that the satisfaction of the following requirements (A) to (D) temporarily increases the nitrogen 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 reducing the driving force for the nitriding reaction caused by the arc. Furthermore, a comparison of Example C1 and the Reference Example shows that when only a low-nitrogen iron source is used as the iron source, there is no significant difference in the nitrogen concentration in molten iron after refining compared to when a high-nitrogen iron source and a low-nitrogen iron source are used. Even if a low-nitrogen iron source is supplied throughout the entire refining process, it is believed that a nitriding reaction caused by the arc occurs in the first half of the refining process, increasing the nitrogen concentration in the molten iron.
[0051] (A) One or more high-nitrogen iron sources and one or more low-nitrogen iron sources are supplied as iron sources. (B) The N content of the high-nitrogen iron source is 0.005 mass% or more. (C) The N content of the low-nitrogen iron source is less than 0.005% 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-nitrogen iron source supplied in the first half of the refining process W A2 : Weight (t) of high-nitrogen iron source supplied in the latter half of the refining process W T : Total weight of iron source supplied in the refining process (t)
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-nitrogen iron sources and one or more low-nitrogen iron sources are provided; the N content of the high-nitrogen iron source is 0.005% by mass or more, The N content of the low-nitrogen iron source is less than 0.005% by mass, and The following relationship (1): 0<(W Ａ１ -W Ａ２ ) / W Ｔ …(1) W Ａ１ : weight (t) of the high-nitrogen 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-nitrogen 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.
Citation Information
Patent Citations
Production method of molten steel
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Method for continuous steelmaking
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