Method of feeding alloy into ladle

Abstract

To suppress erosion of an alumina refractory material in a ladle.SOLUTION: When producing steel having a silicon content of 1.0 mass% or more by charging a silicon alloy into a ladle so that a pure silicon content per ton of molten steel becomes 8.88 kg or more, the ladle has a portion lined with an alumina-based refractory. At the time of tapping into the ladle, one or more kinds of alloys including a silicon alloy are charged into the ladle. If at the time of tapping, a silicon alloy is charged into the ladle into which a substance mainly composed of aluminum is not charged, the alloy is charged so that a silicon concentration in a molten steel in the ladle at the time of tapping is 3.9 mass% or less when the alloy is being charged at the time of tapping.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method of charging an alloy into a ladle when tapping steel from a converter into the ladle.

Background Art

[0002] Patent Document 1 describes a method of melting a high-Si high-Al extra-low carbon steel using a ladle with a refractory brick containing MgO and C as the main components as the slag line brick of the ladle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described in Patent Document 1, a refractory brick containing MgO and C as the main components may be used for the slag line of the ladle, but generally, the bottom and side portions of the ladle, for example, are lined with alumina-based refractories.

[0005] When melting high-Si steel, a large amount of Si alloy is charged into the ladle during tapping. When the Si alloy is charged into the ladle, Si (silicon) contained in the Si alloy reacts with alumina of the alumina-based refractory of the ladle, causing the alumina-based refractory to be eroded. When a large amount of Si alloy is charged into the ladle, the reaction between Si and alumina easily proceeds, so the alumina-based refractory is easily eroded. This causes problems such as a decrease in the number of usable charges of the ladle and an increase in the number of times of relining the refractory.

[0006] An object of the present invention is to provide a method capable of suppressing erosion of the alumina-based refractory of the ladle when melting high-Si steel.

Means for Solving the Problems

[0007] The reaction of the following reaction formula (1) occurs between Si contained in the Si alloy and alumina of the alumina-based refractory. As a result, the alumina-based refractory is eroded. The underline represents the components in the molten steel. Si + Al2O3 → SiO2 + Al ···(1) The inventors of the present application conducted research aiming to suppress the progress of the reaction of the above formula (1) and found the following method.

[0008] The method for charging an alloy into a ladle disclosed in this specification is to charge a Si alloy into the ladle so that the pure Si content per ton of molten steel is 8.88 kg or more. When melting steel with a Si content of 1.0% by mass or more, the ladle has a portion lined with an alumina-based refractory. When discharging the molten steel into the ladle, when charging one or more alloys including the Si alloy into the ladle and when Al-based substances are not being charged into the ladle, the alloy is charged so that the Si concentration of the molten steel in the ladle becomes 3.9% by mass or less when the alloy is being charged during tapping.

[0009] As the Si concentration in the molten steel increases, the reaction of the above formula (1) tends to proceed, so the alumina-based refractory is likely to be eroded. By the method described above, since the increase in the Si concentration in the molten steel can be suppressed, the progress of the reaction of the above formula (1) can be suppressed. Thereby, erosion of the alumina-based refractory can be suppressed. Specifically, erosion of the alumina-based refractory can be suppressed compared to the conventional method.

[0010] When a substance mainly composed of Al is charged into the ladle, the Al concentration of the molten steel in the ladle increases, and the following reaction of alumina is less likely to occur. Therefore, the alumina-based refractory is less likely to be eroded. The underline represents the components in the molten steel. Al2O3 → 2 Al + 3 O On the other hand, at the stage when a substance mainly composed of Al is not charged into the ladle, since the above reaction is likely to occur, the alumina-based refractory is likely to be eroded. The present invention is directed to the case where the Si alloy is charged when a substance mainly composed of Al has not been charged into the ladle, that is, the case where the Si alloy is charged under conditions where the alumina-based refractory is likely to be eroded. According to the above method, the Si alloy is charged under conditions where the alumina-based refractory is likely to be eroded, but erosion of the alumina-based refractory can be suppressed. Note that, at the time of tapping, after charging the Si alloy, a substance mainly composed of Al may be charged. Also, it is not necessary to charge a substance mainly composed of Al at the time of tapping.

[0011] Further, in the above-described method, when the alloy is a plurality of types of alloys including a Si alloy and other alloys other than the Si alloy and the Al alloy, the substance mainly composed of Al includes an Al alloy. For example, at the time of tapping, after charging the other alloy, the Si alloy is charged into the ladle in which the substance mainly composed of Al has not been charged.

[0012] At the time of tapping, the amount of molten steel in the ladle increases while other alloys are being charged. Since the Si alloy is charged when the amount of molten steel in the ladle has increased to a certain extent, an increase in the Si concentration in the molten steel in the ladle can be suppressed. Thus, when charging a plurality of types of alloys into the ladle, by changing the charging order of the alloys, the timing of charging the Si alloy can be delayed, so an increase in the Si concentration in the molten steel in the ladle can be suppressed. Thereby, erosion of the alumina-based refractory can be suppressed.

Advantages of the Invention

[0013] When melting high-Si steel, erosion of the alumina-based refractory of the ladle can be suppressed.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described.

[0016] In this embodiment, high-Si steel is melted. The "high-Si steel" in this embodiment refers to steel having a Si content of 1.0 mass% or more. In order to melt high-Si steel, an Si alloy is charged into the ladle so that the pure Si content is 8.88 kg or more per 1 ton of molten steel in the ladle. In this specification, the "Si alloy" is an alloy containing 14 mass% or more of Si.

[0017] The ladle used in this embodiment has a portion lined with an alumina-based refractory on the operating surface side. The "operating surface side" is the side where the molten steel enters. The alumina-based refractory is lined, for example, on the bottom and side portions of the operating surface side of the ladle. The ladle may be partially lined with a refractory other than the alumina-based refractory. For example, an MgO-C-based refractory may be used at the slag line and its vicinity. By repeatedly using the ladle, the lined alumina-based refractory is eroded. In order to prevent leakage of molten steel due to erosion of the alumina-based refractory, when the number of uses of the ladle reaches a predetermined number, the alumina-based refractory is replaced.

[0018] The "alumina-based refractory" is, for example, a refractory containing about 85 mass% or more of alumina (Al2O3). Examples of the "alumina-based refractory" include alumina-magnesia castables. Alumina-magnesia castables are those based on alumina, into which an alumina cement mainly composed of MgO, SiO2, and CaO·Al2O3 is poured and dried before use.

[0019] When melting high-Si steel, the molten steel is tapped from the converter into the ladle, and an alloy for component adjustment is charged into the ladle during tapping. "Tapping" refers to the operation of transferring the molten steel from the converter to the ladle. "During tapping" refers to the period from the start of the transfer of the molten steel from the converter to the ladle (start of tapping) to the end of the transfer of the molten steel (end of tapping). By charging the alloy into the ladle during tapping, the molten steel and the alloy can be stirred using the tapping stream.

[0020] When melting high-Si steel using the above ladle, as described above, due to Si contained in the Si alloy and alumina in the alumina-based refractory, the reaction of formula (1) occurs. As a result, the alumina-based refractory of the ladle is eroded. Si + Al2O3 → SiO2 + Al ···(1)

[0021] The inventors of the present application aimed to suppress the erosion of the alumina-based refractory and conducted research to suppress the progress of the reaction of the above formula (1). As a result, it was found that by charging the alloy during tapping so that the Si concentration of the molten steel in the ladle becomes 3.9 mass% or less when the alloy is being charged during tapping, the increase in the Si concentration in the molten steel can be suppressed, and the progress of the reaction of the above formula (1) can be suppressed. Thus, it was found that the erosion of the alumina-based refractory can be suppressed compared to the conventional method.

[0022] As described above, when a substance mainly composed of Al is charged into the ladle, the Al concentration of the molten steel in the ladle increases, and the following reaction of alumina is less likely to occur. Therefore, the alumina-based refractory is less likely to be eroded. Al2O3 → 2 Al + 3 O On the other hand, at the stage when a substance mainly composed of Al is not charged into the ladle, since the above reaction is likely to occur, the alumina-based refractory is likely to be eroded. In this embodiment, the case where the Si alloy is charged when a substance mainly composed of Al has not been charged into the ladle is targeted, that is, the case where the Si alloy is charged under conditions where the alumina-based refractory is likely to be eroded is targeted. In this specification, the "substance mainly composed of Al" is a substance containing 40% by mass or more of Al. Examples of the "substance mainly composed of Al" include, but are not limited to, Al alloys and alumina dross. The purpose of charging the "substance mainly composed of Al" into the ladle is not particularly limited, and may be, for example, for adjusting the components of the molten steel, or for other purposes (such as deoxidizing the molten steel).

[0023] Hereinafter, the experiments and the like conducted to obtain the above findings will be described.

[0024] When melting steel, generally, a plurality of types of alloys for component adjustment are sequentially charged into the ladle one by one. For charging the alloy into the ladle, for example, a container such as a hopper is used. A plurality of types of alloys are put into a container such as a hopper one by one in order, and the alloy is charged into the ladle from the discharge port at the bottom of the container.

[0025] When melting high-Si steel, a large amount of Si alloy is charged into the ladle. Conventionally, when melting high-Si steel, first, the Si alloy was put into a container such as a hopper, and then other alloys were put into the container one by one in order. In the container, the Si alloy was present at the bottom, and other alloys were stacked on top of it in the order of charging. When the discharge port at the bottom of the container was opened, the Si alloy at the bottom of the container was first charged into the ladle, and then other alloys at the lower side in the container were sequentially charged into the ladle.

[0026] The inventors of the present application decided to change the charging order of the alloys when melting the high-Si alloy. Conventionally, the Si alloy was charged first, but in the following experiment, the Si alloy was charged last. The high-Si alloy was melted by each of the conventional charging method and the charging method different from the conventional one, and the following experiment was conducted to examine the effect of suppressing the erosion of the alumina-based refractory.

[0027] (Experiment) Under the conditions shown in Table 1 and Table 2, high-Si steel as the target component shown in Table 1 was melted. In this experiment, at the time of tapping, Si alloy, Mn alloy and Cr alloy were put into the ladle for component adjustment. Regarding the Si alloy, the Si alloy was put into the ladle so that the pure Si content would be 8.88 kg or more per 1 ton of molten steel in the ladle. As the ladle, a ladle with alumina-based refractories lined on the bottom and side on the operating surface side was used. Alloys were charged under the conditions shown in each charge, Table 1 and Table 2.

[0028]

Table 1

[0029]

Table 2

[0030] The experimental conditions shown in Table 1 and Table 2 and the like will be described.

[0031] The Si alloy used in this experiment is mainly composed of FeSi. In the Si alloy, in addition to FeSi, a small amount (2 mass% or less) of Al and the like is contained. The Mn alloy used in this experiment is mainly composed of FeMn. The Mn alloy generally contains 60 mass% or more of Mn. The Cr alloy used in this experiment is mainly composed of FeCr. The Cr alloy generally contains 65 mass% or more of Cr.

[0032] Three types of alloys (Si alloy, Mn alloy, Cr alloy) were put into the hopper one by one in the "alloy charging order" shown in Table 1. At the time of tapping, the three types of alloys were put from the hopper into the ladle in the "alloy charging order" shown in Table 1. Also, the alloys were charged into the ladle at the alloy charging rate shown in Table 2.

[0033] Twenty-one seconds after the start of tapping, the charging of the alloys was started. Table 1 shows the "tapping timing of Si alloy". The "tapping timing of Si alloy" is the time from the start of tapping to the start of Si alloy charging. Due to the "alloy charging order" and "alloy charging amount at tapping" shown in Table 1, etc., the "tapping timing of Si alloy" for Experiment Nos. 1 to 4 was different.

[0034] When the Si alloy is charged into the ladle, the Si concentration of the molten steel in the ladle increases. As a result, Si in the molten steel reacts with alumina in the alumina-based refractory of the ladle (see the above formula (1)), and the alumina-based refractory of the ladle is eroded. The inventors of the present application focused on the Si concentration of the molten steel in the ladle when the alloy is being charged during tapping, and investigated the relationship between the Si concentration of the molten steel in the ladle and the amount of erosion of the refractory.

[0035] [Si concentration of molten steel in ladle] The Si concentration of the molten steel in the ladle (hereinafter sometimes referred to as "Si concentration") is represented by the following formula (2). [Number] In the above formula (2), M is the tapping amount (molten steel amount in the ladle) (kg) m is the amount of alloy charged into the ladle at the time when the tapping amount is M (for example, at M = 10 kg) (hereinafter sometimes referred to as "alloy charging amount") (kg) m si is the total amount of Si contained in the alloy charged into the ladle at the time when the tapping amount is M (for example, at M = 10 kg) (hereinafter sometimes referred to as "Si amount") (kg). Here, since M ≫ m, the Si concentration is represented by the following formula (3). [Number]

[0036] Figure 1 shows a schematic diagram of the change over time of "M" (tapping amount), the change over time of "m Si " (Si amount), and the change over time of "m si / M" (Si concentration). As shown in Figure 1, "M" (tapping amount) increases from the start of tapping to the end of tapping and then remains constant. "m Si " (Si amount) increases from the start of charging the Si alloy into the ladle to the end of charging and then remains constant. "m siThe "(Si concentration)" of " / M" increases from the start to the end of the Si alloy input into the ladle, and then gradually decreases.

[0037] For example, at the time of tapping, when the three types of alloys shown in Table 3 are input in the amounts shown in Table 3, the "Si concentration of the molten steel in the ladle" (Si concentration (mass%)) is represented by the following formula (4).

Table 3

Number

[0038] In this experiment, as shown in Table 2, a Si alloy containing 75 mass% Si is input into the ladle. For example, when inputting a Si alloy into the ladle, the "Si concentration of the molten steel in the ladle" (Si concentration (mass%)) at the time when the Si alloy input amount is m (kg) is represented by the following formula (5). M (kg) in formula (5) is the tapping amount (molten steel amount in the ladle) at the time when m (kg) of the Si alloy is input into the ladle. Note that in this experiment, since the amount of Si contained in alloys other than the Si alloy is extremely small compared to the Si amount of the Si alloy, the amount of Si contained in alloys other than the Si alloy is not considered.

Number

[0039] According to the above, the "Si concentration" at the time of tapping for Experiment Numbers 1 to 4 was calculated.

[0040] Table 4 shows a part of the "Si concentration" of Experiment Number 1 (conventional). The tapping speed of Experiment Number 1 (conventional) is 694 kg / s, and the alloy input speed is 65 kg / s. The tapping speed is calculated from the tapping amount (ladle tapping amount) and the tapping time (see Table 2). The alloy input speed can be adjusted with a hopper.

Table 4

[0041] In Experiment No. 1 (conventional) shown in Table 4, the maximum Si concentration was 5.5% by mass. In Experiment No. 1 (conventional), the Si alloy was charged first among the plurality of alloys. When the charging of the Si alloy was completed (90 seconds after the start of tapping), the Si concentration reached its maximum. In Table 4, in order to show the maximum Si concentration, the Si concentrations at 90 seconds and 91 seconds after the start of tapping are shown to four decimal places, and the others are shown to two decimal places. After 92 seconds from the start of tapping, the Si concentration decreased. In Table 4, the Mn alloy and the Cr alloy are described together, but describing the Mn alloy and the Cr alloy together does not affect the calculation of the Si concentration.

[0042] Table 5 shows a part of the "Si concentration" of a certain charge of Experiment No. 4. The tapping rate of Experiment No. 4 is 694 kg / s, and the alloy charging rate is 65 kg / s.

Table 5

[0043] From Table 5, in Experiment No. 4, the maximum Si concentration was 3.9% by mass. In Experiment No. 4, the Si alloy was charged last among the plurality of alloys. When the charging of the Si alloy was completed (127 seconds after the start of tapping), the Si concentration reached its maximum. In Table 5, the Si concentration is shown to two decimal places in order to show the maximum Si concentration. After 128 seconds from the start of tapping, the Si concentration decreased. In Table 5, the Mn alloy and the Cr alloy are described together, but describing the Mn alloy and the Cr alloy together does not affect the calculation of the Si concentration.

[0044] In the same way as above, the Si concentrations of Experiment No. 2 (conventional) and Experiment No. 3 in Table 1 were calculated. The maximum Si concentration of Experiment No. 2 (conventional) was 5.4% by mass. The maximum Si concentration of Experiment No. 3 was 3.5% by mass. The maximum Si concentrations of Experiments 1 to 4 are shown in Table 7 described later.

[0045] Figure 2 shows the change over time in the Si concentration for Experiment No. 2 (conventional) and Experiment No. 4. Also shown for reference is the change over time in the amount of molten steel tapped. Experiment No. 2 (conventional) and Experiment No. 4 are of the same steel type. The maximum Si concentration in Experiment No. 4 is lower than the maximum Si concentration in Experiment No. 2 (conventional). From Figure 2, it can be seen that in Experiment No. 4, the increase in Si concentration is suppressed compared to Experiment No. 2 (conventional). Although not shown in the figure, similar trends to those of Experiment No. 2 (conventional) and Experiment No. 4 were also observed in Experiment No. 1 (conventional) and Experiment No. 3. In Experiment No. 3, the increase in Si concentration was suppressed compared to Experiment No. 1 (conventional).

[0046] [Amount of erosion of alumina-based refractories] The amount of erosion of the alumina-based refractory of the ladle was calculated from the alumina balance in the ladle during the melting of high-Si steel. Details will be described below.

[0047] Figure 3 shows a diagram related to the process of melting high-Si steel and subsequent analysis. Figure 4 shows the alumina balance in the process of melting high-Si steel. As shown in Figure 3, high-Si steel was melted by performing tapping, slag skimming, addition of slag-forming agent, and LF treatment in sequence. In this experiment, LF treatment was performed as ladle refining. After LF treatment, the analysis described below was carried out.

[0048] (Tapping) At the time of tapping, three types of alloys (Si alloy, Mn alloy, Cr alloy) for composition adjustment were charged into the ladle in the order shown in Table 1. (1) In this experiment, the Si alloy contains Si. The Si contained in the Si alloy reacts with the alumina of the alumina-based refractory of the ladle, causing the alumina-based refractory to erode. As a result, alumina is mixed into the molten steel in the ladle (''C'', ''c'' in Figure 4). (2) In this experiment, the Si alloy contains a trace amount of Al (aluminum). The Al contained in the Si alloy generates alumina (''F'', ''f'' in Figure 4).

[0049] (Slag skimming) After tapping was completed, the slag on the molten steel was removed.

[0050] (Adding slag-making agent) After slow slagging, a slag-making agent was added to the ladle. The slag-making agent contains alumina (''B'' and ''b'' in Fig. 4).

[0051] (LF treatment) (1) During LF treatment, the alumina-based refractory of the ladle is eroded due to the flow of molten steel, etc. As a result, alumina is mixed into the molten steel in the ladle (''D'' and ''d'' in Fig. 4). (2) A lance is used for gas blowing during LF treatment. The lance may use an alumina-based refractory. During LF treatment, the alumina-based refractory of the lance is eroded due to the flow of molten steel, etc. As a result, alumina is mixed into the molten steel in the ladle (''E'' and ''e'' in Fig. 4). Note that during LF treatment, an alloy for component adjustment may be added to the ladle. However, since the amount of alloy added during LF treatment is very small, the generation of alumina and the erosion of the alumina-based refractory due to this alloy do not need to be considered.

[0052] The above is the alumina generated in the ladle and the alumina mixed into the ladle during the melting of high-Si steel (''B'' to ''F'' and ''b'' to ''f'' in Fig. 4).

[0053] When the total amount of alumina (in the ladle) after LF treatment is designated as ''A'' and ''a'', as shown in Fig. 4,[[]]END]] In Experiment No. 1 (conventional) and Experiment No. 2 (conventional) in Table 1,[[]]END]] A = B + C + D + E + F and In Experiment No. 3 and Experiment No. 4 in Table 1,[[]]END]] a = b + c + d + e + f are true.[[]]END]]

[0054] The above ''A'', ''B'', ''E'', ''F'', ''a'', ''b'', ''e'' and ''f'' are calculated from the calculation methods shown in Table 6. The ''A'', ''B'', ''F'', ''a'', ''b'' and ''f'' per charge were calculated. Note that hereinafter, ''ch'' means ''charge''. In this specification, ''charge'' (one charge) is defined as from the start of tapping to the end of casting.[[]]END]]

Table 6

[0055] "C + D" for Experiment No. 1 (conventional example) and Experiment No. 2 (conventional example) was obtained from the following formula (6), and the average value of "C + D" for all charges was taken as the "amount of corrosion of the alumina-based refractory in the ladle". C + D = A - B - E - F ···(6) Also, "c + d" for Experiment No. 3 and Experiment No. 4 was obtained from the following formula (7), and the average value of "C + D" for all charges was taken as the "amount of corrosion of the alumina-based refractory in the ladle". c + d = a - b - e - f ···(7) Table 7 described later shows the "amount of corrosion of the alumina-based refractory in the ladle" for Experiment Nos. 1 to 4.

[0056] Table 7 shows the "maximum Si concentration" and the "amount of corrosion of the alumina-based refractory in the ladle" for Experiment Nos. 1 to 4. Table 7 also shows the experimental conditions of Table 1. Further, Table 7 also shows the "frequency of replacement of the alumina-based refractory" obtained using the "amount of corrosion of the alumina-based refractory in the ladle".

[0057]

Table 7

[0058] The "alumina-based refractory loss amount of the ladle" shown in Table 7 is "C + D" or "c + d" calculated from the above formula (6) or formula (7). As shown in Figure 3, "C" and "c" are the alumina mixed in due to the loss of the alumina-based refractory of the ladle during tapping. "D" and "d" are the alumina mixed in due to the loss of the alumina-based refractory of the ladle during LF treatment. Since the LF treatment conditions (treatment time, treatment method, etc.) of Experiment Nos. 1 to 4 are the same, "D" and "d" of Experiment Nos. 1 to 4 are almost the same. Therefore, the difference in the "alumina-based refractory loss amount of the ladle" of Experiment Nos. 1 to 4 shown in Table 7 can be considered as the difference in "C" and "c" shown in Figure 3, that is, the difference in the loss amount of the alumina-based refractory of the ladle melted by the reaction with the Si alloy charged during tapping.

[0059] The "frequency of replacement of alumina-based refractory" shown in Table 7 was determined by the following method. From the "alumina-based refractory loss amount of the ladle" and the "specific gravity of the alumina-based refractory" shown in Table 8 below, the "volume of the melted alumina-based refractory" (= alumina-based refractory loss amount of the ladle / specific gravity of the alumina-based refractory) was calculated. From the "volume of the melted alumina-based refractory" and the "molten steel contact area of the ladle", the "alumina-based refractory loss rate" (= volume of the melted alumina-based refractory / molten steel contact area of the ladle) was calculated. The "molten steel contact area of the ladle" is the area where the molten steel contacts the ladle after tapping. From the "alumina-based refractory loss rate" and the "usable loss thickness", the "usable number of charges" (= usable loss thickness / alumina-based refractory loss rate) was calculated. From the "usable number of charges" and the "number of ladle uses per year", the "frequency of replacement of alumina-based refractory" (= number of ladle uses per year / usable number of charges) was calculated. Note that the "usable loss thickness" and the "number of ladle uses per year" shown in Table 8 are examples.

[0060]

Table 8

[0061] The following was found from Table 7. In Experiment No. 3 and Experiment No. 4, the "maximum Si concentration" is lower, the "amount of alumina-based refractory wear in the ladle" is less, and the "frequency of replacing the alumina-based refractory" is less than in Experiment No. 1 (conventional) and Experiment No. 2 (conventional).

[0062] In Experiment No. 3 and Experiment No. 4, by charging the Si alloy last, the "charging timing of the Si alloy" was delayed. Since the "charging timing of the Si alloy" was delayed, the Si alloy was charged when the amount of molten steel in the ladle had increased to a certain extent. Therefore, it is considered that the increase in the "maximum Si concentration" was suppressed. As a result, in Experiment No. 3 and Experiment No. 4, it is considered that the wear of the alumina-based refractory was suppressed and the frequency of replacing the alumina-based refractory decreased.

[0063] Also, from Table 7, it can be seen that as the "charging timing of the Si alloy" is delayed, the maximum Si concentration decreases. From the results of Experiment No. 3 and Experiment No. 4, when the Si alloy is charged 57 seconds after the start of tapping, the maximum Si concentration is 3.9 mass% or less.

[0064] When comparing Experiment No. 1 (conventional) and Experiment No. 3 of the same steel type (Steel Type 1), in Experiment No. 3, the "amount of alumina-based refractory wear in the ladle" is reduced by about 20% compared to Experiment No. 1 (conventional), and the "frequency of replacing the alumina-based refractory" is also reduced by about 20%. When comparing Experiment No. 2 (conventional) and Experiment No. 4 of the same steel type (Steel Type 2), in Experiment No. 4, the "amount of alumina-based refractory wear in the ladle" is reduced by more than 30% compared to Experiment No. 2 (conventional), and the "frequency of replacing the alumina-based refractory" is reduced by more than 30%.

[0065] From the above, it was found that in Experiment No. 3 and Experiment No. 4, the effect of suppressing the wear of the alumina-based refractory was obtained, and as a result, the effect of reducing the frequency of replacing the alumina-based refractory was obtained. From Experiment No. 3 and Experiment No. 4, it is considered that the above effect is obtained by setting the maximum Si concentration to 3.9 mass% or less.

[0066] Table 9 shows the anti-corrosion effect of "maximum Si concentration of 3.9 mass% or less" indexed. The "maximum Si concentration of 3.9 mass% or less" shown in Table 9 is the average (weighted average) of Experiment No. 3 and Experiment No. 4 shown in Table 7 and the like. The "conventional" shown in Table 9 is the average (weighted average) of Experiment No. 1 (conventional) and Experiment No. 2 (conventional) shown in Table 7 and the like.

Table 9

[0067] The "average corrosion loss of the alumina-based refractory of the ladle" in Table 9 was calculated from the following formula using the "corrosion loss of the alumina-based refractory of the ladle" shown in Table 7 and the "number of charges" shown in Table 1. · "Average corrosion loss of the alumina-based refractory of the ladle" with "maximum Si concentration of 3.9 mass% or less" =(17.8 (corrosion loss of the alumina-based refractory of the ladle in Experiment No. 3) × 182 (number of charges in Experiment No. 3) + 20.1 (corrosion loss of the alumina-based refractory of the ladle in Experiment No. 4) × 114 (number of charges in Experiment No. 4)) / (182 (number of charges in Experiment No. 3) + 114 (number of charges in Experiment No. 4)) ≒18.7 · "Average corrosion loss of the alumina-based refractory of the ladle" of "conventional" =(21.9 (corrosion loss of the alumina-based refractory of the ladle in Experiment No. 1 (conventional)) × 291 (number of charges in Experiment No. 1 (conventional)) + 30.0 (corrosion loss of the alumina-based refractory of the ladle in Experiment No. 2 (conventional)) × 201 (number of charges in Experiment No. 2 (conventional))) / (182 (number of charges in Experiment No. 1 (conventional)) + 114 (number of charges in Experiment No. 2 (conventional))) ≒25.2

[0068] The "INDEX of the average corrosion loss of the alumina-based refractory of the ladle" in Table 9 is indexed with the "average corrosion loss of the alumina-based refractory of the ladle" of "conventional" as 1. The smaller this index, the higher the anti-corrosion effect compared to the conventional.

[0069] The index of "maximum Si concentration of 3.9 mass% or less" is significantly smaller than 1. From this, it was found that by setting the maximum Si concentration to 3.9 mass% or less, a higher effect of preventing melting loss than before can be obtained.

[0070] From the above, when melting high-Si steel, when one or more alloys containing Si alloy are charged into the ladle at the time of tapping, and when charging the Si alloy into a ladle into which a substance mainly composed of Al has not been charged at the time of tapping, charge the alloy so that the Si concentration of the molten steel in the ladle becomes 3.9 mass% or less when charging the alloy at the time of tapping. By the above method, although the Si alloy is charged under conditions where the alumina-based refractory is likely to be melted, the melting loss of the alumina-based refractory can be suppressed. As a result, the number of times of relining the refractory can be reduced. Also, the number of times the refractory can be used increases.

[0071] The method of charging the alloy so that the Si concentration of the molten steel in the ladle becomes 3.9 mass% or less when charging the alloy at the time of tapping is not particularly limited. As described above, by delaying the charging timing of the Si alloy, the Si concentration can be made 3.9 mass% or less. To delay the charging timing of the Si alloy, for example, the charging order of the alloys may be changed. When charging a plurality of types of alloys, the Si alloy may be charged after other alloys or the Si alloy may be charged last. Note that as long as the charging timing of the Si alloy can be delayed to make the Si concentration 3.9 mass% or less, it is not necessary to charge the Si alloy last. When charging three or more types of alloys, as long as the charging timing of the Si alloy can be delayed to make the Si concentration 3.9 mass% or less, the Si alloy may be charged after the second one. Also, regardless of the charging order of the alloys, it may be simply to delay the charging timing of the Si alloy. For example, after the start of tapping, after a certain period of time has passed, the Si alloy may be charged.

[0072] Also, in the above experiment, a substance mainly composed of Al was not charged into the ladle at the time of tapping. Even when a substance mainly composed of Al is not charged into the ladle at the time of tapping in this way, the melting loss of the alumina-based refractory can be suppressed by the method described above.

[0073] In addition, in the above experiment, a substance mainly composed of Al was not added to the ladle during tapping, but a substance mainly composed of Al may be added to the ladle during tapping. When a substance mainly composed of Al is added to the ladle during tapping, in the present invention, after adding the Si alloy, a substance mainly composed of Al is added. Even when a substance mainly composed of Al is added after adding the Si alloy, the erosion of the alumina-based refractory can be suppressed by the method described above. When a substance mainly composed of Al is added to the ladle during tapping, after adding the Si alloy, other alloys or the like may be added and then a substance mainly composed of Al may be added. After adding the Si alloy, a substance mainly composed of Al may be added without adding other alloys or the like.

[0074] In addition, when the alloy added during tapping includes a Si alloy and other alloys other than the Si alloy and the Al alloy, for example, the timing of adding the Si alloy can be delayed by adding other alloys first and then adding the Si alloy. By changing the charging order of the alloys, the erosion of the alumina-based refractory can be suppressed. However, the method of adding the Si alloy is not limited to this method. For example, as exemplified above, it is also possible to simply delay the timing of adding the Si alloy.

[0075] As described above, the embodiments of the present invention have been described with reference to the drawings. However, the specific configuration should not be considered to be limited to these embodiments. The scope of the present invention is shown not by the above description but by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

[0076] For example, the melting conditions of high-Si steel (for example, tapping amount, tapping speed, alloy addition method, alloy addition speed) can be changed within the scope of the common general knowledge of those skilled in the art.

[0077] Also, as in this experiment, after adding an alloy for component adjustment during tapping, an alloy may be added for fine adjustment of the components by LF treatment or the like. The alloy for fine adjustment of the components is not added during tapping. The alloy for fine adjustment of the components is very small compared to the alloy added for component adjustment during tapping, and it is not necessary to consider the generation of alumina and the erosion of alumina-based refractories due to this alloy.

Claims

1. When melting steel with a Si content of 1.0 mass% or more by charging a Si alloy into a ladle so that the pure Si content per ton of molten steel is 8.88 kg or more, the ladle has a portion lined with an alumina-based refractory, when tapping the molten steel into the ladle, one or more alloys including a Si alloy are charged into the ladle, when charging a Si alloy into the ladle where no substance mainly composed of Al is charged during tapping, the alloy charging method into the ladle is characterized in that the alloy is charged so that the Si concentration of the molten steel in the ladle becomes 3.9 mass% or less when the alloy is charged during tapping.

2. the alloy is a plurality of alloys including a Si alloy and other alloys other than the Si alloy and the Al alloy, the substance mainly composed of Al includes an Al alloy, The alloy charging method into the ladle according to claim 1, characterized in that when tapping, after charging the other alloy, a Si alloy is charged into the ladle where no substance mainly composed of Al is charged.

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