Treatment method of molten metal

Abstract

To provide a technique for reducing abnormal reaction during charging molten metal.SOLUTION: In a treatment method of molten metal, when a powdery solid including a lower oxide is charged into a reaction vessel and thereafter or simultaneously, C-containing molten metal is charged into the reaction vessel, at least one or more among an average grain size of the powdery solid, a ratio of contained oxygen and a charging quantity of the powdery solid into the reaction vessel are adjusted to suppress abnormal reaction at the time of charging the molten metal. In the treatment method, when the powdery solid containing a lower oxide is charged into the reaction vessel, and thereafter or simultaneously, a C-containing molten metal is charged into the reaction vessel, an index value A of abnormal reaction obtained from a relational expression between a reaction surface area per unit volume in consideration of an oxygen content in a lower oxide and a charging amount of the powdery solid into the reaction vessel is set to a predetermined value or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating molten metal by charging a powdery solid containing lower oxides into a reaction vessel, and then or simultaneously charging a C-containing molten metal into the reaction vessel. Specifically, the present invention relates to a method for charging molten pig iron after or simultaneously charging a powdery solid cold iron source. In this specification, the unit of mass "t" means 10 3 kg. "x~y" representing a range of values ​​means "greater than x and less than y" and includes the boundary value. "Moltane" refers to molten metal primarily composed of Fe, and includes "molten pig iron" and "molten steel" which contain C. "Pig iron" has a C content of 3-5% by mass, and "steel" has a C content of 2.1% by mass or less. [M] indicates that the element M is contained in the molten iron. (R) indicates that a substance with the chemical formula R is contained in the slag. [Background technology]

[0002] In the steelmaking process, scrap or other cold iron sources are added before or after charging molten pig iron into a converter, and the cold iron sources are melted using the heat of combustion of carbon generated during converter blowing. This reduces the hot metal ratio (HMR) of the converter, enabling increased steel production and reduced CO2 emissions. Here, the hot metal ratio is calculated as the ratio of the amount of hot metal to the total amount of charged molten pig iron and cold iron sources.

[0003] Scrap used as a source of cold iron in converters includes chunks and sheets of slabs and coil cuttings, as well as powdery solid scrap that is magnetically separated slag and dust, which is fine-grained, contains low-grade oxides, and is prone to absorbing moisture.

[0004] The abnormal reaction that occurs when hot metal is charged into a converter after or at the same time as scrap is charged is thought to be caused by the following three factors. The first is a reaction that generates CO gas between carbon [C] in the hot metal and oxygen in the powdered solid scrap. The second is a steam explosion caused by the evaporation of water in the powdered solid scrap. The third is a dust explosion caused by the powdered solid scrap floating in the air.

[0005] Various technologies have been developed to prevent abnormal reactions. For example, Patent Document 1 discloses a method for preventing smoke generation during tapping of molten iron without using metallic aluminum. In Patent Document 1, when molten iron with a carbon content of 2% by mass or more is tapped into a molten iron vessel, powdered material such as MgO-C bricks with a median particle size of 1.0 to 5.0 mm is introduced into the molten iron vessel during tapping.

[0006] Patent Document 2 discloses a method for melting a cold iron source, in which a cold iron source is charged into a receiving vessel that receives molten iron produced in a blast furnace before the molten iron is received, and the molten iron is then charged into the receiving vessel into which the cold iron source has been charged. Patent Document 2 states that abnormal reactions can be suppressed by limiting the moisture and oxygen contents of the cold iron source.

[0007] Patent Document 3 discloses a method for producing crude molten steel using an iron bath smelting reduction furnace with molten pig iron, scrap, and various ores as the main raw materials and coal as the solid reducing agent. In Patent Document 3, the effect of moisture content is reduced by adding coal that passes a 3.5 mesh sieve, i.e., coal with an average particle size of 5.6 mm or more.

[0008] Patent Document 4 discloses a technique for effectively utilizing the dust contained in converter exhaust gas, in which a mixture of dust and mill scale is dried to a moisture content of 2 to 10% and then charged into a converter for refining.

[0009] Patent Document 5 discloses a method for using ingots generated in the steelmaking process, in which the ingots are placed in a refining vessel while there is little reoxidation, and molten pig iron is then charged into the vessel to melt them. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-059234 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-277670 [Patent Document 3] Japanese Patent Application Publication No. 09-143525 [Patent Document 4] Japanese Patent Application Publication No. 61-238908 [Patent Document 5] Japanese Patent Application Laid-Open No. 2002-371312 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the above-mentioned conventional techniques have the following problems to be solved. In other words, to reduce the molten iron content, it is effective to add powdered scrap recycled from dust and slag generated during the steel production process to a reaction vessel such as a converter. However, recycled powdered scrap is highly reactive with molten iron, and abnormal reactions can lead to disasters and operational problems. The techniques described in Patent Documents 1 to 4 were insufficient as measures to suppress abnormal reactions between powdered scrap and molten iron. Furthermore, the technique described in Patent Document 5 determines the degree of reoxidation based on the number of days elapsed since the pulverization of the molten iron, and abnormal reactions are determined only by slag foaming. Although thresholds for the degree of oxidation and particle size are indicated, adding already oxidized powdered iron source is insufficient to effectively suppress abnormal reactions that pose a fire risk, such as flame damage.

[0012] The present invention has been made to solve the above-mentioned problems, and aims to provide a technology for reducing abnormal reactions during the charging of molten metal when a powdery solid containing lower oxides is charged into a reaction vessel and then, or simultaneously, C-containing molten metal is charged into the reaction vessel. [Means for solving the problem]

[0013] The method for treating molten metal according to the present invention, which advantageously solves the above-mentioned problems, is characterized in that, first, a powdered solid containing lower oxides is charged into a reaction vessel, and then or simultaneously, C-containing molten metal is charged into the reaction vessel, and at least one of the average particle size of the powdered solid, the oxygen content, and the amount W(t) of the powdered solid charged into the reaction vessel is adjusted to suppress abnormal reactions when the molten metal is charged.

[0014] Secondly, the method for treating molten metal according to the present invention, which advantageously solves the above-mentioned problems, is characterized in that when a powdery solid containing lower oxides is charged into a reaction vessel and then or simultaneously, a C-containing molten metal is charged into the reaction vessel, the index value A of abnormal reaction calculated by the following formulas (1) to (4) is set to 60 or less. (1) Formula A=ln(σ3)×W Equation (2) σ3 = σ2 × [%FeO × {M O / (M Fe +M O )}+%MnO×{M O / (M Mn +M O )}] Equation (3) σ2=σ1 / {4π / 3·(d / 2) 3} (4) Formula σ1=4π·(d / 2) 2 where: σ1: Reaction surface area (m 2 ), σ2: Reaction surface area per unit volume of powder solid (m 2 / m 3 ), σ3: Reaction surface area per unit volume (m2) taking into account the oxygen content in the lower oxides 2 / m 3 ), d: average particle size of powder solid (m), %FeO, %MnO: mass percentage (mass%) of FeO and MnO in the powder solid, respectively, and M R : Atomic weight of element R (R is Fe, O, Mn) Represents.

[0015] In the method for treating molten metal in a steelmaking process according to the present invention, it is more preferable to set the index value A of the abnormal reaction to 30 or less. [Effects of the Invention]

[0016] The present invention reduces the risk of abnormal reactions during molten metal charging and improves the safety of the molten metal charging process. Furthermore, when using a new brand of powdered solid metal source, the risk of abnormal reactions can be verified in advance before charging tests, making it possible to prevent disasters and operational problems. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a graph showing correlation coefficients between various converter operating conditions and flame intensity as an abnormal reaction. [Figure 2] 1 is a graph showing the correlation between particle size of a powdered solid and flame strength. [Figure 3] 1 is a graph showing the correlation coefficient between the oxidation degree of a powdery solid and flame strength. [Figure 4] 10 is a graph showing the relationship between index value A, which indicates the risk of abnormal reaction, and frame strength. [Figure 5] FIG. 2 is a schematic diagram showing the reactive surface area of ​​powdered solid scrap. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes in detail the embodiments of the present invention. Note that the following embodiments are merely examples of methods for realizing the technical idea of ​​the present invention, and are not intended to limit the configuration to the following. In other words, the technical idea of ​​the present invention can be modified in various ways within the technical scope described in the claims.

[0019] To investigate the operating conditions that have a significant impact on the abnormal flame reaction that occurs when molten iron (hot metal) is charged into a converter (reaction vessel), four levels of flame intensity were defined, as shown in Table 1. The correlation coefficients between each operating condition and flame intensity were investigated and are shown in Figure 1. Figure 1 shows the correlation coefficients between flame intensity 4 and each operating condition. The results in Figure 1 indicate that the amount (mass) of powdered solid scrap charged yielded the highest correlation coefficient with flame intensity. High flame intensity poses a disaster prevention and safety risk if it reaches surrounding equipment, particularly the crane cab. Additionally, molten iron splashing can cause fires and equipment damage.

[0020] [Table 1]

[0021] Therefore, the relationship between various physical properties of powdered solid scrap and flame strength was investigated. First, Figure 2 shows a graph of the correlation coefficient between the average particle size of the powdered solid and flame strength. Figure 2 shows that the smaller the average particle size of the powdered solid, the greater the impact on the flame (flame). The symbols "○" and "△" in Figure 2 represent powdered solid scrap with different average particle sizes d (mm). The symbol "×" in Figure 2 represents coil cutting waste. The correlation coefficients are the same as in Table 1. The average particle size was defined as the particle size that passes 50% of the volume of a sieve equivalent to a sphere.

[0022] Next, Figure 3 shows a graph of the correlation coefficient between the oxygen content of lower oxides contained in the powdered solid and flame strength. Figure 3 shows that the higher the oxygen content in the powdered solid, the greater the impact on the flame. The lower oxides were iron oxide and manganese oxide. The correlation coefficients are the same as those in Table 1.

[0023] Based on the above results, the relationship between flame strength and the index value A of abnormal reactions, which takes into account the average particle size of the pulverized solid scrap charged before or simultaneously with the hot metal, and the oxygen content of the low-grade oxides, was analyzed. The index value A of abnormal reactions was calculated using the following equations (1) to (4). Equation (1) calculates the index value A as the natural logarithm of the reaction surface area per unit volume, taking into account the oxygen content of the low-grade oxides, divided by the amount of pulverized solids charged (by mass). First, the powder surface area is calculated from the average particle size d (m) of the pulverized solids using equation (4), and this is defined as the reaction surface area σ1 for the average particle size of the pulverized solids. Next, the number of pulverized solids per unit volume is calculated, and the reaction surface area σ2 per unit volume of the pulverized solids is calculated using equation (3). As shown in Figure 5, pulverized solids 1, which are spheres with a diameter of the average particle size, are arranged at the vertices of a cubic lattice within a cubic frame 2. Taking into account the oxygen content derived from lower oxides such as FeO and MnO as oxygen sources that react with the C contained in the molten iron, the reactive surface area per unit volume, σ3, is calculated from equation (2), taking into account the amount of oxygen in the powdered solids that react with the C contained in the molten iron. The calculated σ3 is then introduced into equation (1). (1) Formula A=ln(σ3)×W Equation (2) σ3 = σ2 × [%FeO × {M O / (M Fe +M O )}+%MnO×{M O / (M Mn +M O )}] Equation (3) σ2=σ1 / {4π / 3·(d / 2) 3} (4) Formula σ1=4π·(d / 2) 2 where: W: powder solid input amount (t), σ1: Reaction surface area (m 2 ), σ2: Reaction surface area per unit volume of powder solid (m 2 / m 3 ), σ3: Reaction surface area per unit volume (m2) taking into account the oxygen content in the lower oxides 2 / m 3 ), d: average particle size of powder solid (m), %FeO, %MnO: mass percentage (mass%) of FeO and MnO in the powder solid, respectively, and M R : Atomic weight of element R (R is Fe, O, Mn) Represents.

[0024] When past operational results were compiled using the index value A, which indicates abnormal reactions, it was found that events with an A value of over 60, such as flame strength 4 (shown in Table 1), frequently occurred, indicating significant abnormal reactions. Therefore, it was decided to determine the average particle size and low-grade oxide content of the pulverized solid scrap in advance, and then adjust at least one of the average particle size, oxygen content, and amount (by mass) of the pulverized solids charged before or simultaneously with the molten iron so that the A value would be 60 or less. When there are multiple brands of pulverized solid scrap, the average of their physical property values ​​may be used, or the A value may be calculated for each brand and the sum may be set to 60 or less. It is more preferable to set the A value to 30 or less.

[0025] In the above embodiment, the reaction vessel is a converter, but it may also be an electric furnace. The molten metal to be charged may be molten pig iron or C-containing molten iron. The powdered solid may be a cold iron source such as scrap, or a powdered metal source containing, reduced in, or with a low content of lower oxides. [Example]

[0026] Before charging the hot metal, various types of scrap containing powdery solids were added, and the flame strength was observed. Table 2 shows the physical properties of the scrap added. In this example, scrap 1, with an average particle size d1 of 0.4 mm, was added at a charge amount W1 of 4.0 t for all levels. Scrap 2 was made from different brands with different physical properties, and the charge amount W2 was also adjusted as shown in Table 2. In Table 2, W1 and W2 represent the charge amounts (t) of each scrap, d1 and d2 represent the average particle size (mm) of each scrap, and O1 and O2 represent the oxygen content (mass%) of each scrap due to low-grade oxides. The logarithm of the reactive surface area per unit volume, calculated using Equation (2) above and taking into account the oxygen content in low-grade oxides, is also shown for ln(σ3). The index value A of abnormal reactions calculated using Equation (1) is also shown.

[0027] As shown in Table 2, the A value can be reduced to 60 or less by reducing the amount of powdered solid scrap added, increasing the average particle size of the powdered solid scrap, or reducing the oxygen content of the powdered solid scrap.

[0028] [Table 2]

[0029] Powdered solid scrap was charged under various A value conditions, and the flame strength during molten iron charging was judged according to the classification in Table 1. This is plotted as a conventional example in Figure 4 with a "○" mark. The results can be summarized as shown in Table 3.

[0030] [Table 3]

[0031] Figure 4 shows that a flame strength of 4 is observed when the A value is around 70. A flame strength of 4 causes molten iron to splash, which can lead to operational issues such as interrupting molten iron charging and impeding productivity. Furthermore, a flame strength of 2 or less can be achieved within an operationally acceptable range when the A value is 60 or less. Therefore, in the inventive example, the average particle size of the powdered solid scrap was increased to adjust the A value to 60 or less. The results are plotted in Figure 4 as a relationship between the A value and flame strength, marked with a "◆." Table 4 also shows the average (Ave) and standard deviation (σ) of the flame strength for the conventional example and the inventive example. The inventive example showed lower average and standard deviation flame strengths than the conventional example.

[0032] [Table 4] [Explanation of symbols]

[0033] 1. Powdered solid (average particle size) 2 (cubic) frame

Claims

1. A method for treating molten metal, comprising: charging a powdered solid containing lower oxides into a reaction vessel; and subsequently or simultaneously charging C-containing molten metal into the reaction vessel; adjusting at least one of the average particle size of the powdered solid, the proportion of oxygen contained therein, and the amount W(t) of the powdered solid charged into the reaction vessel, thereby suppressing abnormal reactions during the charging of the molten metal.

2. A method for treating molten metal, comprising charging a powdery solid containing lower oxides into a reaction vessel, and subsequently or simultaneously charging a C-containing molten metal into the reaction vessel, so that an index value A of abnormal reaction calculated by the following formulas (1) to (4) is 60 or less: (1) Formula PO(σ ３ 6×6 (2) Formula σ ３ =σ ２ ×[%FeO×{M Ｏ / (M Ｆｅ +M Ｏ )}+%MnO×{M Ｏ / (M Ｍｎ +M Ｏ )}] (3) Formula s ２ =s １ / {4π / 3・(d / 2) ３ } (4) Formula s １ = 4π・(d / 2) ２ where: σ １ : Reaction surface area (m) of the average particle size of the powder solid ２ ), σ ２ : Reaction surface area per unit volume of powder solid (m ２ / m ３ ), σ ３ : Reaction surface area per unit volume taking into account the oxygen content in the lower oxides (m ２ / m ３ ), d: average particle size of the powder solid (m), %FeO, %MnO: mass percentage (mass%) of FeO and MnO in the powder solid, respectively; M Ｒ : atomic weight of element R (R is Fe, O, or Mn) Represents.

3. 3. The method for treating molten metal according to claim 2, wherein the index value A of the abnormal reaction is set to 30 or less.

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