Method for melting iron sources

Abstract

Disclosed is a technique for melting iron sources using an electric furnace while generating slag at an early stage and promoting slag formation of auxiliary raw materials. A method for melting iron sources according to the present disclosure comprises a step for supplying iron sources into an electric furnace while generating an arc to dissolve the iron sources. In the method for melting iron sources according to the present disclosure, at least one first iron source and at least one second iron source are supplied as the iron sources. The first iron source has an Fe content of at least 50.0 mass% and a total content of Si and Al of at least 0.4 mass%, and the second iron source has an Fe content of at least 50.0 mass% and a total content of Si and Al of less than 0.4 mass%. In the method for melting iron sources according to the present disclosure, the iron sources are supplied so as to satisfy 0<(WA1-WA2) / WT (WA1: weight (t) of the first iron source supplied in the first half of the process, WA2: weight (t) of the first iron source supplied in the latter half of the process, and WT: total weight (t) of the iron sources supplied in the process).

Description

Method for dissolving iron source

[0001] The present application discloses a method for dissolving an iron source.

[0002] Methods for melting 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 grade. Also, Patent Document 2 discloses a technique in which, in an electric furnace, SiO ２ and Al ２ O ３ and 1.0 mass % or more of carbon, to produce molten steel.

[0003] US Patent No. 4,564,388 JP 2021-080540 A

[0004] In order to improve the efficiency of melting iron source in an electric furnace, it is effective to lengthen the arc and maintain a high arc power. However, if the arc is lengthened, the arc will not be covered by slag (a so-called open arc), and the furnace wall refractory will be excessively heated by the radiant heat of the arc, resulting in a shortened refractory life. If the refractory life is shortened, downtime for repairs and furnace construction will increase, which may reduce productivity.

[0005] In melting an iron source using an electric furnace, early generation of slag and promotion of slag formation of auxiliary materials make it difficult for an open arc to occur even if the arc is long. In the prior art, early generation of slag and promotion of slag formation of auxiliary materials when melting an iron source using an electric furnace have not been sufficiently studied.

[0006] The present application discloses the following multiple aspects as means for solving the above problems. <Aspect 1> A method for melting an iron source using an electric furnace, comprising the steps of supplying the iron source into the electric furnace and generating an arc in the electric furnace to melt the iron source, wherein one or more first iron sources and one or more second iron sources are supplied as the iron sources, the first iron source has an Fe content of 50.0 mass% or more and a Si and Al total content of 0.4 mass% or more, the second iron source has an Fe content of 50.0 mass% or more and a Si and Al total content less than 0.4 mass%, and the following relationship (1) is satisfied: 0<(W Ａ１ -W Ａ２ ) / W Ｔ …(1) W Ａ１ W: weight (t) of the first iron source supplied in the first half of the process W: weight (t) of the first iron source supplied in the first half of the process Ａ２ W: Weight (t) of the first iron source supplied in the latter half of the process Ｔ The method for melting an iron source according to Aspect 1, wherein the iron source is supplied so as to satisfy the total weight (t) of the iron source supplied in the step. <Aspect 2> The method for melting an iron source according to Aspect 1, wherein the iron source supplied in the first half of the step has an average carbon concentration of 0.75 mass% or more. <Aspect 3> The method for melting an iron source according to Aspect 1 or 2, wherein the following relationship (1-1) is satisfied: 0.05≦(W Ａ１ -W Ａ２ ) / W Ｔ ...(1-1). <Aspect 4> The method for melting an iron source according to any one of Aspects 1 to 3, wherein the iron source is supplied so as to satisfy the following relationship (2): 0.05≦(W Ａ１ +W Ａ２ ) / W Ｔ The method for dissolving an iron source, wherein the iron source is supplied so as to satisfy the following condition: ≦0.95 (2).

[0007] According to the method of the present disclosure, when melting an iron source using an electric furnace, slag can be generated early and the formation of slag from auxiliary materials can be promoted. Therefore, for example, even when the arc is lengthened, an open arc is less likely to occur.

[0008] Hereinafter, one embodiment of the method for dissolving an iron source according to the present disclosure will be described, although the method for dissolving an iron source according to the present disclosure is not limited to the following embodiment.

[0009] A method for melting an iron source according to one embodiment is a method for melting an iron source using an electric furnace, and includes a step of supplying the iron source into the electric furnace and generating an arc in the electric furnace to melt the iron source (hereinafter, this may be referred to as a "melting step"). In the method for melting an iron source according to one embodiment, one or more first iron sources and one or more second iron sources are supplied as the iron sources. The first iron source has an Fe content of 50.0 mass% or more and a Si and Al total content of 0.4 mass% or more. The second iron source has an Fe content of 50.0 mass% or more and a Si and Al total content less than 0.4 mass%. In addition, in the method for melting an iron source according to one embodiment, the following relationship (1): 0<(W Ａ１ -W Ａ２ ) / W Ｔ …(1) W Ａ１ W: weight (t) of the first iron source supplied in the first half of the process W: weight (t) of the first iron source supplied in the first half of the process Ａ２ W: Weight (t) of the first iron source supplied in the latter half of the process Ｔ The iron source is supplied so as to satisfy the total weight (t) of the iron source supplied in the step.

[0010] 1. Iron Source In one embodiment, a method for melting an iron source includes supplying an iron source into an electric furnace and generating an arc in the electric furnace to melt the iron source. Here, one or more types of first iron sources and one or more types of second iron sources are supplied as the iron sources.

[0011] 1.1 First Iron Source The first iron source is an iron source that contributes to the early generation of slag and the promotion of slag formation of auxiliary materials. When the first iron source contains a predetermined amount or more of Si and Al, SiO ２ and Al ２ O ３ The formation of Si promotes the formation of slag from CaO, resulting in the early production of slag, which is the source of foaming. According to the findings of the present inventors, such an effect is achieved when the total content of Si and Al in the first iron source is 0.4% by mass or more. The total content of Si and Al in the first iron source may be 0.4% by mass or more and 7.0% by mass or less, 0.4% by mass or more and 4.5% by mass or less, 0.5% by mass or more and 3.0% by mass or less, 0.5% by mass or more and 2.0% by mass or less, or 0.6% by mass or more and 1.7% by mass or less. Alternatively, it is believed that the higher the total content of Si and Al in the first iron source, the more effective the slag formation promotion effect. In this regard, the total content of Si and Al in the first iron source may be 0.6% by mass or more and 7.0% by mass or less, 0.8% by mass or more and 6.0% by mass or less, or 1.0% by mass or more and 5.0% by mass or less.

[0012] The first iron source contains a sufficient amount of Fe to function as an iron source. Specifically, the Fe content of the first iron source is 50.0% by mass or more. The Fe content of the first iron source may be 50.0% by mass or more and 99.6% by mass or less, 65.0% by mass or more and 99.3% by mass or less, 75.0% by mass or more and 99.0% by mass or less, 85.0% by mass or more and 98.8% by mass or less, 88.0% by mass or more and 98.5% by mass or less, or 90.0% by mass or more and 98.0% by mass or less. In this application, the "Fe content" of the first iron source and the second iron source refers to so-called total Fe (the iron content contained in the iron source, including not only metallic iron but also Fe in Fe compounds).

[0013] The first iron source may contain elements other than Si, Al, and Fe. For example, the first iron source may contain carbon as the other element. The carbon content of the first iron source may be, for example, 0% by mass or more and 15.0% by mass or less, 0.2% by mass or more and 10.0% by mass or less, 0.4% by mass or more and 7.5% by mass or less, or 0.5% by mass or more and 5.0% by mass or less. Examples of elements other than carbon include phosphorus, sulfur, manganese, calcium, magnesium, and oxygen.

[0014] The first iron source may be an alloy containing Si and / or Al and Fe, or a mixture of Si and / or Al and an Fe-containing material. The Si, Al, and Fe contained in the first iron source may be contained in the form of a pure metal or an alloy, or in the form of a compound such as an oxide. However, when Si or Al is contained in the form of a compound such as an oxide, the compound is preferably physically or chemically integrated with other substances contained in the first iron source. For example, the compound is preferably physically or chemically integrated with an oxide such as iron oxide or calcium oxide contained in the first iron source. The first iron source is preferably in at least one of the following four forms. More preferably, the first iron source is one or both of reduced iron and pig iron. Form 1: An iron source containing an alloy of Fe with one or both of Si and Al (e.g., pig iron, ferrosilicon, etc.); Form 2: An iron source containing Fe and a pure metal or alloy of one or both of Si and Al (e.g., a mixture of an iron-containing material with one or both of elemental Si and elemental Al); Form 3: An iron source in which a compound containing one or both of Si and Al is physically integrated with Fe or an Fe alloy (e.g., reduced iron); Form 4: An iron source in which a compound containing one or both of Si and Al is physically or chemically integrated with an Fe-containing compound

[0015] The shape of the first iron source is not particularly limited as long as it can be supplied as an iron source into an electric furnace. The first iron source may be, for example, in the form of a block or powder. The first iron source may also be molded.

[0016] 1.2 Second Iron Source The total Si and Al content of the second iron source is relatively lower than that of the first iron source. That is, the second iron source is an iron source that has less of an effect on the early formation of slag and the promotion of slag formation of auxiliary materials compared to the first iron source. Specifically, the total Si and Al content of the second iron source is less than 0.4 mass%. The total Si and Al content of the second iron source may be 0 mass% or more and less than 0.4 mass%, more than 0 mass% and less than 0.4 mass%, more than 0 mass% and less than 0.3 mass%, more than 0 mass% and less than 0.2 mass%, or more than 0 mass% and less than 0.1 mass%.

[0017] The second iron source contains a sufficient amount of Fe to function as an iron source. Specifically, the Fe content of the second iron source is 50.0% by mass or more. The Fe content of the second iron source may be 50.0% by mass or more and 100% by mass or less, 65.0% by mass or more and 99.7% by mass or less, 75.0% by mass or more and 99.4% by mass or less, 85.0% by mass or more and 99.2% by mass or less, 88.0% by mass or more and 98.9% by mass or less, or 90.0% by mass or more and 98.4% by mass or less.

[0018] The second iron source may contain elements other than Si, Al, and Fe. For example, the second iron source may contain carbon as another element. The carbon content of the second 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, 0% by mass or more and 5.0% by mass or less, 0% by mass or more and 3.0% by mass or less, 0% by mass or more and 1.0% by mass or less, 0% by mass or more and 0.5% by mass or less, 0% by mass or more and 0.3% by mass or less, or 0% by mass or more and 0.1% by mass or less. Examples of elements other than carbon include copper, tin, zinc, chromium, titanium, niobium, vanadium, boron, phosphorus, sulfur, manganese, calcium, magnesium, and oxygen.

[0019] The form of the second iron source is not particularly limited as long as the total content of Si and Al is less than 0.4 mass %. The second iron source may be, for example, scrap.

[0020] The shape of the second iron source is not particularly limited as long as it can be supplied as an iron source into an electric furnace. The second iron source may be, for example, in the form of a block or powder. The second iron source may also be molded.

[0021] 2. Relationship (1) In one embodiment of the method for melting an iron source, the iron source is supplied so as to satisfy the relationship (1). That is, if the melting process is divided into 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 the first iron source supplied in the first half is greater than that in the second half. By supplying a relatively large amount of the first iron source in the first half of the melting process, slag can be generated early and the slag formation of the auxiliary materials can be promoted. That is, a sufficient slag thickness can be ensured early in the melting process, and open arcs are less likely to occur even if the arc is lengthened. By suppressing open arcs, dimensional reduction of the refractory can be suppressed. In other words, the arc can be lengthened and high arc power can be maintained from an early stage of the melting process, thereby improving the melting efficiency of the iron source.

[0022] (W Ａ１ -W Ａ２ ) / W Ｔ The lower limit of is greater than 0, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.1 or more. In particular, the following relationship (1-1): 0.05≦(W Ａ１ -W Ａ２ ) / W Ｔ By supplying the iron source so as to satisfy the following condition (1-1), a higher effect can be expected.

[0023] In addition, in the melting of iron sources, the first iron source is often subject to greater limitations on its usage amount than the second iron source due to factors such as cost. The method of the present disclosure can be said to achieve the aforementioned effect of accelerating slag generation and the effect of promoting slag formation of auxiliary materials by devising a way to supply the first iron source, which is subject to a limited usage amount, to an electric furnace. That is, according to the method of the present disclosure, the supply amount of the first iron source is relatively increased in the first half of the melting process, and the supply amount of the first iron source is relatively decreased in the second half of the melting process, thereby achieving the aforementioned effect of accelerating slag generation and the effect of promoting slag formation of auxiliary materials without increasing the total supply amount of the first iron source in the melting process.

[0024] 3. Other Matters 3.1 Iron Source Supply Form The iron source supply form in the melting process is not particularly limited. The iron source may be continuously or intermittently supplied 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 first iron source and the second iron source may be supplied into the furnace separately, or in the form of a mixture. Furthermore, the timing and period for supplying the first iron source and the timing and period for supplying the second iron source do not necessarily have to coincide.

[0025] 3.2 Carbon Concentration of Iron Source As described above, the first iron source and the second iron source may contain carbon. The carbon contained in the iron source can contribute to slag foaming and other effects. The greater the carbon content of the iron source, the easier it is to increase the slag thickness. In this regard, a high carbon concentration in the iron source supplied in the first half of the melting process allows the slag thickness to be secured more quickly, making it easier to achieve the open-arc suppression effect described above. According to the inventors' findings, this effect is more pronounced when the average carbon concentration of the iron source supplied in the first half of the melting process is 0.75% by mass or more. The average carbon concentration of the iron source supplied in the first half of the melting process may be 0.75% by mass or more and 5.00% by mass or less, 0.75% by mass or more and 4.00% by mass or less, 0.75% by mass or more and 3.00% by mass or less, 0.75% by mass or more and 2.75% by mass or less, or 0.75% by mass or more and 2.50% by mass or less.

[0026] 3.3 Ratio of First Iron Source and Second Iron Source The ratio of the first iron source and the ratio of the second iron source to the total iron source supplied in the melting step are not particularly limited. For example, in a method for melting an iron source according to one embodiment, the following relationship (2) is satisfied: 0.05≦(W Ａ１ +W Ａ２ ) / W Ｔ The iron source may be supplied so as to satisfy the relationship (2) below. That is, the proportion of the first iron source in the entire iron source supplied in the melting 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. When the iron source is supplied so as to satisfy the relationship (2) above (that is, when the proportion of the first iron source in the entire iron source supplied in the melting step is 5% by mass or more and 95% by mass or less), the effect of promoting slag formation by the first iron source tends to become more pronounced.

[0027] 3.4 Auxiliary Materials In the method disclosed herein, auxiliary materials may be supplied into the electric furnace. The auxiliary materials may be supplied together with the iron source or separately from the iron source. The auxiliary materials may be, for example, Ca-containing materials such as quicklime, Si-containing materials such as silica, or a combination thereof. As described above, in the melting process, a relatively large amount of the first iron source is supplied in the first half of the process, which tends to promote the formation of slag from the auxiliary materials. By promoting the formation of slag from the auxiliary materials, the slag thickness can be secured more quickly, and the open arc suppression effect can be achieved more quickly. Furthermore, in the refining process described below, auxiliary materials such as a dephosphorizing agent, a desulfurizing agent, and a carbonaceous material may be supplied into the electric furnace. Known means, such as a conveyor, a chute, or a lance, may be used to supply the auxiliary materials.

[0028] 3.5 Gas Injection In the method disclosed herein, gas may be injected into the electric furnace. For example, an oxygen-containing gas may be injected into the iron source or molten iron in the electric furnace. While the above-mentioned effects of slag generation and promoting slag formation of auxiliary materials can be achieved by the oxygen atmosphere in the electric furnace alone, these effects become more pronounced by supplying oxygen into the electric furnace. In addition, gas injection also enables slag foaming. There are no particular limitations on the gas injection means, and known means such as a lance may be used.

[0029] 3.6 Carry-Over Slag When melting an iron source using an electric furnace, some or all of the slag at the end of charging (at the end of the refining process described below) may be left in the furnace and carried over to the next charge. Such carry-over slag can also contribute to ensuring the amount of slag in the first half of the melting process. According to the inventors' findings, when the amount of carry-over slag (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 carry-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 means installed in the electric furnace, or may be measured by a weight measuring means separate from the electric furnace, or may be calculated from the slag discharge time, slag discharge angle, etc.

[0030] 3.7 Slag Removal When melting an iron source using an electric furnace, slag may be removed as needed. However, in the first half of the melting process, it is preferable not to remove slag in order to ensure a sufficient slag thickness. Slag removal is preferably performed in the second half of the melting process or later.

[0031] 3.8 Electric Furnace The configuration of an electric furnace for melting an iron source is not particularly limited and may be a known configuration. The electric furnace, for example, has a melting furnace for melting the 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 a cathode and the lower electrode may be an 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.

[0032] 4. Refining Process In one embodiment, the iron source (molten iron) melted as described above may be refined. The refining process of molten iron in an electric furnace may be the same as conventional processes. In the refining process, the temperature and composition of the molten iron are adjusted. For example, arc heating is performed on the molten iron, and a dephosphorizing agent, a desulfurizing agent, a carbon material, etc. are supplied. Furthermore, for example, by blowing an oxygen-containing gas into the molten iron, the temperature of the molten iron is controlled within a predetermined range and the composition of the molten iron is adjusted. The refined molten iron (molten steel) is tapped from the tapping port of the electric furnace. Note that the refining process may be started before the end of the melting process.

[0033] 5. Effects As described above, according to the method of the present disclosure, the supply amount of the first iron source in the first half of the process of melting the iron source using an electric furnace is relatively greater than that in the second half, which allows for the early generation of slag and promotes the slag formation of the auxiliary materials. Therefore, for example, even when the arc is lengthened, an open arc is less likely to occur, and size reduction of the refractory material can be suppressed.

[0034] 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.

[0035] 1. Common conditions The melting and refining processes of the iron source were carried out using an electric arc furnace. The tapping amount per charge was 110 t (65 t of hot heel from the previous charge, furnace volume 175 t).

[0036] In the melting process, at least one of scrap, reduced iron, and pig iron was first introduced into an electric arc furnace as an iron source via a horizontal conveyor. The grades of the iron sources are shown in Table 1 below. Simultaneously 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. Oxygen was supplied into the electric furnace during the melting of the iron source. The operating conditions (electrode height control, amount of auxiliary material introduced, oxygen supply conditions, etc.) other than the supply of the iron source were the same in all examples and comparative examples. Specifically, the electrode height and other factors were adjusted so that the arc voltage was 440 V to 540 V (note that in the open arc state at the beginning of current application, the voltage fluctuates to some extent even if there is residual molten metal from the previous charge).

[0037]

[0038] In this example, a mixture of multiple types of scrap was used as the scrap, and the C content, Si content, Al content, and Fe content of the scrap shown in Table 1 above are the average C content, average Si content, average Al content, and average Fe content in the mixture of multiple types of scrap.

[0039] In the refining process, oxygen was supplied to the molten iron in the electric furnace, and a carbon material was injected to promote forming, and the molten iron was refined. The amount of oxygen supplied and the amount of carbon material injected were appropriately adjusted so that the carbon concentration of the molten steel at the end of the refining process was about 0.05 mass%, and the concentrations of Si and Al were each less than 0.01 mass%. Note that the remaining molten steel from the previous charge can be considered to have the same composition as the molten steel at the end of the refining process of the immediately preceding charge.

[0040] 2. Iron Source Supply Conditions 2.1 Example A1 Scrap was used as the second iron source and reduced iron was used as the first iron source. 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 melting 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 melting process, and 48 mass % of scrap and 2 mass % of reduced iron were supplied in the second half of the melting process. The iron source was supplied continuously.

[0041] 2.2 Comparative Example a1 Scrap was used as the second iron source and reduced iron was used as the first iron source. The proportion of scrap in the total iron source was set to 90 mass %. The amount of reduced iron supplied was constant in the first and second halves of the melting process. Specifically, 45 mass % of scrap and 5 mass % of reduced iron were supplied in the first half of the melting process, and 45 mass % of scrap and 5 mass % of reduced iron were supplied in the second half of the melting process. The iron source was supplied continuously.

[0042] 2.3 Example B1 Scrap was used as the second iron source and reduced iron was used as the first iron source. The proportion of scrap in the total iron source was set to 60 mass %. Relatively more reduced iron was supplied in the first half of the melting process than in the second half. Specifically, 27 mass % of scrap and 23 mass % of reduced iron were supplied in the first half of the melting process, and 33 mass % of scrap and 17 mass % of reduced iron were supplied in the second half of the melting process. The iron sources were supplied continuously.

[0043] 2.4 Example B2 Scrap was used as the second iron source and reduced iron was used as the first iron source. The proportion of scrap in the total iron source was set to 60 mass %. Relatively more reduced iron was supplied in the first half of the melting process than in the second half. Specifically, 25 mass % of scrap and 25 mass % of reduced iron were supplied in the first half of the melting process, and 35 mass % of scrap and 15 mass % of reduced iron were supplied in the second half of the melting process. The iron sources were supplied continuously.

[0044] 2.5 Comparative Example b1 Scrap was used as the second iron source and reduced iron was used as the first iron source. The proportion of scrap in the total iron source was set to 60 mass %. The amount of reduced iron supplied was constant in the first and second halves of the melting process. Specifically, 30 mass % of scrap and 20 mass % of reduced iron were supplied in the first half of the melting process, and 30 mass % of scrap and 20 mass % of reduced iron were supplied in the second half of the melting process. The iron source was supplied continuously.

[0045] 2.6 Example C1 Scrap was used as the second iron source and reduced iron was used as the first iron source. The proportion of scrap in the total iron source was set to 15 mass %. Relatively more reduced iron was supplied in the first half of the melting process than in the second half. Specifically, 5 mass % of scrap and 45 mass % of reduced iron were supplied in the first half of the melting process, and 10 mass % of scrap and 40 mass % of reduced iron were supplied in the second half of the melting process. The iron source was supplied intermittently.

[0046] 2.7 Comparative Example c1 Scrap was used as the second iron source and reduced iron was used as the first iron source. The proportion of scrap in the total iron source was set to 15 mass %. Relatively more reduced iron was supplied in the latter half of the melting process than in the first half. Specifically, 10 mass % of scrap and 40 mass % of reduced iron were supplied in the first half of the melting process, and 5 mass % of scrap and 45 mass % of reduced iron were supplied in the latter half of the melting process. The iron source was supplied intermittently.

[0047] 2.8 Example D1 Scrap was used as the second iron source and pig iron was used as the first iron source. The proportion of scrap in the total iron source was set to 60 mass %. Relatively more pig iron was supplied in the first half of the melting process than in the second half. Specifically, 25 mass % of scrap and 25 mass % of pig iron were supplied in the first half of the melting process, and 35 mass % of scrap and 15 mass % of pig iron were supplied in the second half of the melting process. The iron source was supplied continuously.

[0048] 2.9 Comparative Example d1 Scrap was used as the second iron source and pig iron was used as the first iron source. The proportion of scrap in the total iron source was set to 60 mass%. The amount of pig iron supplied was constant in the first and second halves of the melting process. Specifically, 30 mass% of scrap and 20 mass% of pig iron were supplied in the first half of the melting process, and 30 mass% of scrap and 20 mass% of pig iron were supplied in the second half of the melting process. The iron source was supplied continuously.

[0049] 2.10 Example E1 Scrap was used as the second iron source, and a mixture of reduced iron and pig iron was used as the first iron source. The mixing ratio (mass ratio) of reduced iron to pig iron in the first iron source was 50:50. The proportion of scrap in the total iron source was 60 mass%. A relatively larger amount of the first iron source was supplied in the first half of the melting process than in the second half. Specifically, 25 mass% of scrap and 25 mass% of the first iron source were supplied in the first half of the melting process, and 35 mass% of scrap and 15 mass% of the first iron source were supplied in the second half of the melting process. The iron sources were supplied continuously.

[0050] 2.11 Comparative Example e1 Scrap was used as the second iron source, and a mixture of reduced iron and pig iron was used as the first iron source. The mixing ratio (mass ratio) of reduced iron to pig iron in the first iron source was 50:50. The proportion of scrap in the total iron source was 60 mass%. The supply amount of the first iron source was constant in the first and second halves of the melting process. Specifically, 30 mass% of scrap and 20 mass% of the first iron source were supplied in the first half of the melting process, and 30 mass% of scrap and 20 mass% of the first iron source were supplied in the second half of the melting process. The iron source was supplied continuously.

[0051] 3. Evaluation method The thickness of the refractory material on the furnace wall of the electric arc furnace was measured with a laser distance meter before operation and after 100 ch operation, and the average reduction in size per ch was determined and 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, Example D1 was scored based on Comparative Example d1, and Example E1 was scored based on Comparative Example e1.

[0052] 1: 20% or more improvement from the base 2: 10% to less than 20% improvement from the base 3: Base

[0053] 4. Evaluation Results The evaluation results are shown in Table 2 below. In Table 2 below, the "value of formula (I)" refers to the value calculated by the following formula (I). Furthermore, the "average carbon concentration" refers to the average carbon concentration of the iron source supplied in the first half of the melting step.

[0054] (W Ａ１ -W Ａ２ ) / W Ｔ …(I) W Ａ１ W: Weight (t) of the ferrous iron source supplied in the first half of the dissolution process Ａ２ W: Weight (t) of the ferrous iron source supplied in the latter half of the dissolution process Ｔ : total weight (t) of iron source supplied in the melting process

[0055]

[0056] As is clear from the results shown in Table 2, in a method for melting an iron source using an electric furnace, which includes a step of supplying an iron source into the electric furnace and generating an arc in the electric furnace to melt the iron source, it can be said that wear of the furnace wall refractory can be suppressed when the following requirements (A) to (D) are satisfied (Examples A1, B1, B2, C1, D1, and E1). It is believed that this is because, when the following requirements (A) to (D) are satisfied, slag can be generated early in the melting step and the slag formation of the auxiliary materials can be promoted, thereby ensuring a sufficient slag thickness and suppressing open arcs.

[0057] (A) One or more first iron sources and one or more second iron sources are supplied as iron sources. (B) The first iron source has an Fe content of 50.0 mass% or more and a total Si and Al content of 0.4 mass% or more. (C) The second iron source has an Fe content of 50.0 mass% or more and a total Si and Al content of less than 0.4 mass%. (D) The iron sources are supplied so as to satisfy the following relationship (1): 0<(W Ａ１ -W Ａ２ ) / W Ｔ …(1) W Ａ１ W: Weight (t) of the ferrous iron source supplied in the first half of the dissolution process Ａ２ W: Weight (t) of the ferrous iron source supplied in the latter half of the dissolution process Ｔ : total weight (t) of iron source supplied in the melting process

[0058] Furthermore, it can be said that a higher effect can be obtained when the following requirement (E) is satisfied in the dissolving step.

[0059] (E) The average carbon concentration of the iron source supplied in the first half of the melting step is 0.75 mass% or more.

[0060] 5. Study of the Amount of Carry-Over Slag 5.1 Evaluation Conditions The amount of carry-over slag was adjusted by adjusting the slag removal time during the refining process. The composition and timing of the iron source were the same as in Example A1 above. The electrode height, etc., were adjusted so that the arc voltage was 440 V to 540 V (in the open arc state at the beginning of current application, the voltage fluctuates to some extent even if there is residual molten metal from the previous charge). In this case, the arc length is estimated to be 400 mm to 500 mm. Video footage of the furnace was taken through the slag door, and a situation in which light emitted by the arc was always observed was considered an "open arc." The time from the start of current application to the resolution of the open arc was evaluated based on the following points.

[0061] 1: 10% or more reduction from base 2: Base

[0062] 5.2 Evaluation Results The evaluation results are shown in Table 3 below.

[0063]

[0064] As is clear from the results shown in Table 3, when the amount of carried-over slag is 25 kg / t-steel or more, it can be said that open arcs can be suppressed more significantly.

[0065] 6. Supplementary Information Although the above examples illustrate cases in which one or both of reduced iron and pig iron are used as the first iron source, the form of the first iron source is not limited to this. Iron sources other than reduced iron and pig iron may also be used as the first iron source. Furthermore, the above examples illustrate cases in which a mixture of multiple types of scrap is used as the second iron source, but the form of the second iron source is not limited to this. One type of scrap may be used as the second iron source, or an iron source other than scrap may be used as the second iron source.

Claims

1. A method for melting an iron source using an electric furnace, comprising: a step of supplying the iron source into the electric furnace and generating an arc in the electric furnace to melt the iron source; one or more types of first iron sources and one or more types of second iron sources are supplied as the iron sources; the first iron source has an Fe content of 50.0 mass% or more and a total content of Si and Al of 0.4 mass% or more; the second iron source has an Fe content of 50.0 mass% or more and a total content of Si and Al of less than 0.4 mass%, and the following relationship (1) is satisfied: 0<(W Ａ１ -W Ａ２ ) / W Ｔ … (1) W Ａ１ W: weight (t) of the first iron source supplied in the first half of the process; W: weight (t) of the first iron source supplied in the first half of the process; Ａ２ W: Weight (t) of the first iron source supplied in the latter half of the process Ｔ a step of supplying the iron source so as to satisfy a total weight (t) of the iron source supplied in the step.

2. The method for dissolving an iron source according to claim 1, wherein the average carbon concentration of the iron source supplied in the first half of the process is 0.75 mass % or more.

3. The method for dissolving an iron source according to claim 1 or 2, wherein the following relationship (1-1) is satisfied: 0.05≦(W Ａ１ -W Ａ２ ) / W Ｔ ...(1-1).

4. The method for dissolving an iron source according to any one of claims 1 to 3, wherein the following relationship (2) is satisfied: 0.05≦(W Ａ１ +W Ａ２ ) / W Ｔ The method for dissolving an iron source, wherein the iron source is supplied so as to satisfy the following condition: ≦0.95 (2).

Images