Method for blowing molten iron and method for producing molten steel

Abstract

To provide a method for blowing molten iron and a method for producing molten steel by which the optimum amount of lime to be charged can be determined in the static control of blowing treatment in a converter type refining furnace.SOLUTION: In a blowing method for producing molten steel by blowing molten iron, a P distribution ratio is calculated from P distribution formula using estimated FeO concentration, CaO concentration and MgO concentration in slag 3 and a set end point molten steel temperature when determining the amount of lime added at the beginning of blowing, and the lime charging amount is determined on the basis of the P distribution ratio, the P concentration in the molten iron and the target end point molten steel P concentration.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for blowing molten iron and a method for producing molten steel.

Background Art

[0002] Conventionally, in the blowing process of a converter-type refining furnace, various methods have been used to determine the amount of lime input for appropriately controlling the P concentration (end-point molten steel P concentration) in the molten steel at the end point, which is the time immediately after the blowing ends. Among them, it is important to optimize the amount of lime input at the initial stage of blowing. When the amount of lime input at the initial stage of blowing is small, lime input by dynamic control is performed in the final stage of blowing after 80% of the blowing time has elapsed. Lime input in the final stage of blowing may result in incomplete slag formation of lime and out-of-specification of the P component. Conversely, when the amount of lime input at the initial stage of blowing is excessive, the lime unit consumption increases, leading to cost deterioration.

[0003] Therefore, Patent Document 1 discloses a method using the hot metal silicon concentration, the end-point molten steel carbon concentration, the end-point molten steel temperature, the hot metal charge rate, and the end-point molten steel phosphorus concentration as an appropriate lime input calculation formula in the static control of the blowing process of a converter-type refining furnace. Static control is a control in which the amount of oxygen and the fluxing agent required for the target temperature and target components are calculated by a model before the blowing process based on hot metal information. Further, in Patent Document 1, the optimal operation regarding the determination of the lime input amount is an operation that increases the end-point molten steel carbon to such an extent that no problems occur in the subsequent process within a range where excessive dephosphorization does not occur.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, the mainstream of the blowing process in the current converter-type refining furnace is a blowing process that utilizes carbon in the hot metal as a heat source for scrap melting by reducing the endpoint carbon concentration. In such a blowing process, since the C concentration of the molten steel at the endpoint is low, FeO is likely to be generated, creating conditions favorable for dephosphorization.

[0006] However, since the blowing method of Patent Document 1 is a blowing condition for ensuring the C concentration of the molten steel at the endpoint for the subsequent process, FeO is difficult to generate, resulting in conditions unfavorable for dephosphorization. That is, the blowing method of Patent Document 1 differs in the ease of FeO generation compared to the current mainstream blowing process, and thus the way of contributing to dephosphorization is different. Therefore, when using the blowing method of Patent Document 1 in a blowing process that reduces the C concentration of the molten steel at the endpoint, there is a problem that lime becomes excessive.

[0007] Therefore, the present invention has been made paying attention to the above problems, and an object thereof is to provide a hot metal blowing method and a molten steel manufacturing method capable of determining an optimal lime input amount in the static control of the blowing process in a converter-type refining furnace.

Means for Solving the Problems

[0008] (1) According to one aspect of the present invention, there is provided a hot metal blowing method for producing molten steel by blowing hot metal, wherein when determining the lime input amount at the initial stage of blowing, the P distribution ratio is calculated from the P distribution formula using the estimated FeO concentration, CaO concentration, and MgO concentration in the slag, and the set endpoint molten steel temperature, and the lime input amount is determined based on the P distribution ratio, the P concentration in the hot metal, and the target endpoint molten steel P concentration.

[0009] (2) In the hot metal blowing method of (1) above, when determining the lime input amount, the lime input amount is further determined based on the amount and P concentration of the residual slag, which is the slag generated in the immediately preceding blowing process.

[0010] (3) In the hot metal blowing method of (1) or (2) above, when calculating the P distribution ratio, the P distribution formula of formula (1) is used.

[0011] [Number] Here, L P : P distribution ratio (%T.Fe): FeO concentration in slag (mass%) (%CaO): CaO concentration in slag (mass%) (%MgO): MgO concentration in slag (mass%) T: End-point molten steel temperature (°C) a0, a1, a2, a3: Constants

[0012] (4) In the method for blowing molten iron as described in (3) above, perform multiple regression analysis using past performance values to set the constants a0, a1, a2, a3 in the above formula (1).

[0013] (5) In the method for blowing molten iron as described in (4) above, according to the end-point molten steel P concentration, a plurality of the constants a0, a1, a2, a3 in the above formula (1) are set respectively.

[0014] (6) In the method for blowing molten iron as described in (5) above, when the end-point molten steel P concentration is 10×10 -3 mass% or less, when the end-point molten steel P concentration is more than 10×10 -3 mass% and 20×10 -3 mass% or less, and when the end-point molten steel P concentration is more than 20×10 -3 mass%, set the constants a0, a1, a2, a3 in the above formula (1) respectively.

[0015] (7) In the method for blowing molten iron as described in (3) above, when the end-point molten steel P concentration is 10×10 -3 mass% or less, use formula (7), and when the end-point molten steel P concentration is more than 10×10 -3 mass% and 20×10 -3 mass% or less, use formula (8), and when the end-point molten steel P concentration is more than 20×10 -3 mass%, use formula (9).

[0016] [Number]

[0017] According to one aspect of the present invention, there is provided a method for producing molten steel using the method for blowing molten iron according to any one of (1) to (7) above. [Advantages of the Invention]

[0018] An object of the present invention is to provide a method for blowing molten iron and a method for producing molten steel, which can determine an optimal amount of lime input in the static control of the blowing process in a converter-type refining furnace according to one aspect of the present invention. [Brief Description of the Drawings]

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

[0020] In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals, and redundant descriptions are omitted. Each drawing is schematic and may include cases where it is different from the actual one. Further, the following embodiments illustrate devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the materials, structures, arrangements, etc. of the components as the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

[0021] [Device Configuration] Referring to FIG. 1, the apparatus configuration of the converter-type refining furnace 1 in an embodiment of the present invention will be described. The converter-type refining furnace 1 is a converter facility that produces molten steel by performing blowing treatment using hot metal and scrap as raw materials. As shown in FIG. 1, it includes a furnace body 10, an oxygen lance 11, a hopper 12, and a control device 13. In this embodiment, hot metal and molten steel are collectively referred to as molten iron 2.

[0022] In the furnace body 10, a tapping port 100 is provided at the upper part of the side surface, and a plurality of bottom blowing tuyeres 101 are provided at the bottom. Bottom blowing gas 5 is blown into the molten iron 2 from the bottom blowing tuyeres 101 to stir the molten iron 2. The oxygen lance 11 is a lance that injects oxygen-containing gas 4 from the lower tip, and supplies oxygen to the molten iron 2 by injecting the oxygen-containing gas 4 in a state of being inserted into the furnace body 10 from above. The hopper 12 is a container for storing auxiliary raw materials, and cuts out the stored auxiliary raw materials from the lower part and inputs the auxiliary raw materials into the molten iron 2 through the connected chute 120. In the example shown in FIG. 1, lime 6, which is one of the auxiliary raw materials, is stored in the hopper 12. Note that a plurality of hoppers 12 are provided in the converter-type refining furnace 1, and different auxiliary raw materials are stored in each hopper 12.

[0023] The control device 13 is an electronic computer that controls the blowing treatment of the converter-type refining furnace 1, and has a control unit 130 and a lime input amount calculation unit 131. The control unit 130 controls a series of operations of the converter-type refining furnace 1 related to the blowing treatment, such as the tilting of the furnace body 10, the lifting and lowering operation of the oxygen lance 11, the adjustment of the injection amount (oxygen supply amount) of the oxygen-containing gas 4, and the cutting and input operations of auxiliary raw materials such as lime 6. The lime input amount calculation unit 131 calculates the lime input amount (the input amount of lime 6) at the initial stage of blowing. Details of the method for calculating the lime input amount will be described later.

[0024] <Blowing method of molten iron> The method for blowing molten iron in this embodiment will be described. In the blowing process of the converter-type refining furnace 1, first, hot metal and scrap as raw materials are charged into the furnace body 10 (charging step). In this embodiment, as an example, the hot metal conditions for the blowing process are as follows. Note that each component concentration in the following hot metal conditions is the component concentration in the hot metal before the blowing process. The hot metal used may have been subjected to preliminary treatments such as de-siliconization treatment and de-phosphorization treatment after being tapped from the blast furnace, or it may not have been subjected to preliminary treatments. In this embodiment, the unit of t (ton) is the metric ton.

[0025] (Hot metal conditions) Hot metal amount: 170 t or more and 300 t or less Scrap amount: 0 t or more and 45 t or less C concentration: 250×10 -2 mass% or more and 500×10 -2 mass% or less Si concentration: 0×10 -2 mass% or more and 100×10 -2 mass% or less P concentration: 10×10 -3 mass% or more and 200×10 -3 mass% or less Mn concentration: 1×10 -2 mass% or more and 100×10 -2 mass% or less S concentration: 1×10 -3 mass% or more and 50×10 -3 mass% or less

[0026] After the charging step, oxygen-containing gas 4 is injected from the oxygen lance 11 into the hot metal in the furnace, thereby performing oxidative refining of the hot metal (blowing step). In the blowing step, the molten iron 2 is agitated by blowing bottom-blown gas 5 from the bottom-blown tuyere 101. Note that an inert gas or an oxygen-containing gas may be blown as the bottom-blown gas 5 from the bottom-blown tuyere 101.

[0027] Also, in the blowing process, lime 6 with a predetermined input amount is added to the molten iron 2 at the initial stage of blowing. Lime 6 is cut out from the hopper 12 by the required input amount and introduced into the molten iron 2 in the furnace body 10 through the chute 120. The added lime 6 forms slag 3 by slagging. In addition, auxiliary raw materials other than lime 6 (for example, auxiliary raw materials containing Si and Mg) may be added to the molten iron 2 as required.

[0028] In the blowing process, the molten iron 2 is oxidatively refined to remove C in the molten iron 2 by oxidation, and the hot metal becomes molten steel with a low C concentration. Also, when the molten iron 2 is oxidatively refined in a state where slag 3 is formed, P in the molten iron 2 is removed by oxidation. In this embodiment, the end-point molten steel C concentration, which is the C concentration of the molten iron 2 after the blowing treatment (after the blowing process), is preferably 10×10 -2 mass% or less. By reducing the end-point molten steel C concentration, carbon in the molten iron 2 can become a heat source to promote the melting of scrap. Also, by performing oxidative refining in a state where the carbon in the molten iron 2 is low, FeO is likely to be generated, which is also an advantageous condition for the dephosphorization reaction. Furthermore, in the case of steel grades with a large amount of alloying elements such as Mn and Cr, since an alloy is added to the molten steel after the blowing treatment, it is necessary to increase the end-point temperature. Even in such a case, by reducing the end-point molten steel C concentration and promoting the oxidation reaction of C, the molten iron 2 can be heated and the end-point temperature can be increased.

[0029] The blowing process ends when the amount of acid supplied to the molten iron 2 (the blowing amount of the oxygen-containing gas) reaches the set total amount. In the blowing process, during the initial stage of blowing and the middle stage of refining until 80% of the blowing time has elapsed, the treatment is carried out under the blowing conditions (the total amount of acid supply and the lime input amount) set before the blowing treatment (static control). On the other hand, in the final stage of blowing after 80% of the blowing time has elapsed, the acid supply amount is adjusted and auxiliary raw materials are additionally added according to the estimated or measured components and temperature of the molten iron 2 (dynamic control).

[0030] When the blowing process is completed, the furnace body 10 is tilted, and molten steel is discharged from the tapping hole 100 provided at the upper part of the side surface of the furnace body 10 (tapping process). At this time, the slag 3 floats on the molten iron 2, and by tilting the furnace body 10 back before the slag 3 is discharged from the tapping hole 100, mainly the slag 3 remains in the furnace body 10 after the tapping process.

[0031] After the tapping process, the furnace body 10 is tilted to the side opposite to the tapping process, and the slag 3 remaining in the furnace body 10 is discharged from the upper part (furnace mouth) of the furnace body 10 (slag discharging process).

[0032] Through the above processes, the blowing treatment of the molten iron 2 in the converter-type refining furnace 1 is completed. Note that a series of blowing treatments from the charging process to the slag discharging process are performed by the control device 13. In addition, by repeatedly performing a series of blowing treatments from the charging process to the slag discharging process, the blowing treatment is continuously performed. Here, the unit of the blowing treatment in the converter-type refining furnace 1 is also referred to as a charge. Furthermore, the charge for which the lime input amount is calculated and in which the blowing treatment will be performed next is referred to as the current charge, and the charge that was subjected to the blowing treatment immediately before the current charge is referred to as the previous charge.

[0033] <Method for determining lime input amount> Next, a method for determining the lime input amount in the blowing treatment will be described. In the present embodiment, as described above, before the blowing treatment, more specifically, before the charging process, the lime input amount calculation unit 131 determines the lime input amount at the beginning of the blowing.

[0034] The lime input amount calculation unit 131 first calculates the P distribution ratio L using the FeO concentration, CaO concentration, and MgO concentration in the estimated slag, which are parameters affecting P removal, and the set end-point molten steel temperature, from the P distribution formula. P (P distribution ratio calculation step). The P distribution ratio L P is the ratio of the P concentration in the slag 3 to the P concentration in the molten iron 2 in a state close to apparent equilibrium. Specifically, the lime input amount calculation unit 131 calculates the P distribution ratio L from the P distribution formula of the following formula (1). P

[0035] [Number] Here, L P : P distribution ratio (%T.Fe): FeO concentration in slag 3 (mass%) (%CaO): CaO concentration in slag 3 (mass%) (%MgO): MgO concentration in slag 3 (mass%) T: End-point molten steel temperature (°C) a0, a1, a2, a3: Constants

[0036] In formula (1), the FeO concentration, CaO concentration, and MgO concentration in slag 3 are estimated by the following estimation method.

[0037] (FeO concentration in slag) The FeO concentration in slag has a strong correlation with tapping oxygen (end-point molten steel O concentration), end-point molten steel temperature T, and calculated basicity. Therefore, by using the preset tapping oxygen, end-point molten steel temperature T, calculated basicity, and the following formula (2), the FeO concentration in slag can be estimated. Note that the tapping oxygen and end-point molten steel temperature are preset according to the steel grade, treatment process, etc. Also, basicity is the ratio of CaO concentration to SiO2 concentration in slag 3 ((%CaO) / (%SiO2)), and calculated basicity is the basicity preset considering dephosphorization reaction, etc.

[0038] [Number] Here, [O]: Tapping oxygen (mass%) B cal : Calculated basicity b0, b1, b2, b3: Constants

[0039] The constants b0, b1, b2, and b3 can be determined by performing multiple regression analysis using Equation (2) on past actual operation data (actual values). For example, in the case of a general top-bottom blown converter-type refining furnace 1 with a charge amount of about 300 t as in the present embodiment, Equation (3) below can be used.

[0040] [Number]

[0041] (CaO concentration in slag) The CaO concentration in slag 3 can be estimated using the estimated FeO concentration in slag 3 and the calculated basicity. Specifically, the CaO concentration in slag 3 can be estimated using Equation (4) below.

[0042] [Number]

[0043] (MgO concentration in slag) The MgO concentration in slag has a strong correlation with the estimated FeO concentration in slag 3 and the tapping molten steel temperature T. Therefore, the MgO concentration in slag can be estimated using the estimated FeO concentration in slag 3, the preset tapping molten steel temperature T, and Equation (5) below.

[0044] [Number] Here, c0, c1, c2: constants

[0045] The constants c0, c1, and c2 can be determined by performing multiple regression analysis using Equation (5) on past actual operation data (actual values). For example, in the case of a general top-bottom blown converter-type refining furnace 1 with a charge amount of about 300 t as in the present embodiment, Equation (6) below can be used.

[0046] [Number]

[0047] Further, in the present embodiment, the constants a0, a1, a2, and a3 in the formula (1) can be determined by performing multiple regression analysis using the formula (1) based on past actual operation data (actual values). In this case, as the FeO concentration, CaO concentration, and MgO concentration in the slag 3, the results of chemical analysis of the actual slag 3 may be used, or the estimated values as described above may be used.

[0048] Furthermore, due to the difference in the mass balance between the P concentration in the slag 3 and the P concentration in the hot metal 2 depending on the P concentration of the molten steel at the end point, this difference in the mass balance also affects the P distribution ratio. For this reason, it is preferable that a plurality of the constants a0, a1, a2, and a3 are set respectively according to the target P concentration of the molten steel at the end point. Also, when the target P concentration of the molten steel at the end point is 10×10 -3 mass% or less, 10×10 -3 mass% and more than 20×10 -3 mass% or less, and more than 20×10 -3 mass%, it is preferable to set the constants a0, a1, a2, and a3 separately for the three cases. In this way, by dividing the target P concentration of the molten steel at the end point into three ranges and providing a P distribution formula for each range, the behavior of the actual P distribution ratio can be accurately reproduced.

[0049] When using a general top-bottom blown converter type refining furnace 1 with a charge of about 300 t as in the present embodiment and setting the P distribution formula by dividing the target P concentration of the molten steel at the end point into three as described above, the P distribution formula can be the following formulas (7) to (9). When the target P concentration of the molten steel at the end point is 10×10 -3 mass% or less, formula (7) is used; when it is more than 10×10 -3 mass% and 20×10 -3 mass% or less, formula (8) is used; when the P concentration of the molten steel at the end point is more than 20×10 -3 mass%, formula (9) is used respectively.

[0050]

Number

[0051] After the P distribution ratio calculation step, the lime input amount calculation unit 131 determines the lime input amount at the initial stage of blowing (lime input amount determination step) based on the calculated P distribution ratio, the P concentration in the hot metal (P concentration in the molten iron 2 before the blowing process), and the target final molten steel P concentration. In the lime input amount determination step, specifically, the lime input amount is calculated according to equation (10).

[0052]

Number

[0053] Note that the unidentified P in equation (10) is a numerical value indicating the influence of the P contained in the slag 3 of the previous charge remaining in the furnace body 10 before the charging process of this charge. The unidentified P can be calculated by the following equation (11) based on the amount of the residual slag, which is the slag 3 of the previous charge remaining in the furnace body 10, and the P concentration of the residual slag. Note that the P concentration (%P)1 in the slag 3 of the previous charge may be a measured value obtained by analyzing the slag 3 of the previous charge, or an estimated value estimated from the P distribution ratio. The P concentration (%P)2 in the slag 3 of this charge is related to the P distribution ratio L P and the lime input amount W T.CaO and the P concentration P in the hot metal before the blowing process HM and the final molten steel P concentration P f and can be obtained therefrom. Note that since the unidentified P and the lime input amount W T.CaO are mutually related, that is, equations (10) and (11) are mutually related, the unidentified P and the lime input amount W T.CaOso that the convergence or the amount of lime input W T.CaO It is preferable to repeat the calculations according to equations (10) and (11) so that it becomes smaller.

[0054]

Equation

[0055] According to the blowing method according to this embodiment, by determining the amount of lime input using the estimated P distribution ratio, in the static control of the blowing process, the optimal amount of lime input can be determined.

[0056] <Modification Example> The present invention has been described above with reference to specific embodiments, but it is not intended to limit the invention by these descriptions. By referring to the description of the present invention, those skilled in the art will also be clear about other embodiments of the present invention including various modification examples together with the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the claims also cover embodiments including these modification examples described herein alone or in combination.

[0057] For example, in the above embodiment, the top-bottom blown converter as shown in FIG. 1 is used as the converter type refining furnace 1, but the present invention is not limited to such an example. The converter type refining furnace 1 may be a converter of other types such as a top blown type or a bottom blown type. Also, the hot metal conditions may be different from those in the above embodiment.

[0058] In the above-described embodiment, it is assumed that the lime 6 is introduced into the furnace body 10 via the chute 120. However, the present invention is not limited to such an example. The lime 6 may be configured to be injected together with the carrier gas from the acid lance 11 or the bottom blowing tuyere 101 in addition to being added from the chute 120. Further, the supply method of the lime 6 may be a combination of these plurality of supply methods.

[0059] Furthermore, in the above-described embodiment, it is assumed that the lime input amount calculation unit 131 is one of the functions of the control device 13. However, the present invention is not limited to such an example. For example, the lime input amount calculation unit 131 may be configured as a device (such as an electronic computer) independent of the control device 13.

[0060] Furthermore, in the above-described embodiment, it is assumed that the final molten steel C concentration of the produced molten steel is low. However, the present invention is not limited to such an example. The blowing method according to the above-described embodiment can accurately obtain the lime input amount required for dephosphorization by using the estimated P distribution ratio, and can be applied even when the C concentration is higher than 10×10 -2 mass%.

[0061] Furthermore, in the above-described embodiment, the unknown P was estimated using the formula (11). However, the present invention is not limited to such an example. For example, when the blowing treatment is performed under the same steel type and blowing conditions, if the unknown P is considered to be the same, the value of the unknown P used previously may be used. Also, when the influence of the difference in the unknown P on the lime input amount is small, a constant value may be used as the unknown P. Further, when the amount of residual slag is small, etc., it may not be necessary to consider the unknown P. Note that by estimating the unknown P using the formula (11) as in the above-described embodiment and considering the unknown P estimated when estimating the lime input amount as in the formula (10), a more optimal lime input amount can be estimated.

[0062] Furthermore, in the above-described embodiment, as a preferred embodiment, the P distribution ratio was estimated using the P distribution formula of formula (1), but the present invention is not limited to such an example. As the P distribution formula, at least the FeO concentration, CaO concentration, and MgO concentration in the slag may be considered. For example, other factors such as other components in the slag 3 may be further considered.

[0063] Furthermore, in the above-described embodiment, as a preferred embodiment, the P distribution ratio was calculated by dividing the final molten steel P concentration into three ranges, but the present invention is not limited to such an example. For example, the P distribution ratio may be calculated by dividing the final molten steel P concentration into four or more ranges. Note that by dividing the final molten steel P concentration into three ranges as in the above-described embodiment, the P distribution ratio can be estimated accurately and simply.

Example

[0064] Next, the examples implemented by the present inventors will be described. In the examples, the blowing treatment was performed in the same manner as in the above-described embodiment, and the actual results of the lime usage amount and the actual results of the molten steel P concentration were investigated in comparison with the conventional method. The hot metal conditions in the examples were the same as those in the above-described embodiment. Also, for the three cases where the final molten steel P concentration was 25×10 -3 mass%, 15×10 -3 mass%, and 8×10 -3 mass%, investigations were conducted respectively. Furthermore, in the examples, the actual results of the lime usage amount and the actual results of the molten steel P concentration were investigated as the P margin values with respect to the conventional conditions. The P margin is the value obtained by subtracting the actual P concentration in the molten steel from the target molten steel P concentration, and the larger this value is, the more excessive the dephosphorization is.

[0065] FIG. 2 shows the results of the examples with the following sorting conditions when the target molten steel P concentration is 25×10 -3 mass%. Note that in the sorting conditions, HR (Hot Metal Ratio) is the ratio of the weight of hot metal to the total weight of hot metal and scrap as raw materials. Also, in the examples shown in FIG. 2, the P distribution ratio was estimated using formula (7).

[0066] (Sorting conditions) HR: Above 86% and below 90% P concentration in hot metal: 80×10 -3 mass% or more and 90×10 -3 mass% or less Si concentration in hot metal: 20×10 -2 mass% or more and 30×10 -2 mass% or less Final molten steel temperature: 1670°C or more and 1700°C or less B cal : 3.0 or more

[0067] Also, Figure 3 shows the results of examples with the following sorting conditions when the target molten steel P concentration is 15×10 -3 mass%. In the examples shown in Figure 3, the P distribution ratio was estimated using equation (8).

[0068] (Sorting conditions) HR: 90% or more and 94% or less P concentration in hot metal: 65×10 -3 mass% or more and 75×10 -3 mass% or less Si concentration in hot metal: 10×10 -2 mass% or more and 15×10 -2 mass% or less Final molten steel temperature: 1670°C or more and 1700°C or less B cal : 3.0 or more

[0069] Furthermore, Figure 4 shows the results of examples with the following sorting conditions when the target molten steel P concentration is 8×10 -3 mass%. In the examples shown in Figure 4, the P distribution ratio was estimated using equation (9).

[0070] (Sorting conditions) HR: 96% or more and 100% or less P concentration in hot metal: 25×10 -3 mass% or more and 35×10 -3 mass% or less Si concentration in hot metal: 3×10 -2 mass% or more and 8×10 -2less than mass% Final molten steel temperature: 1610 °C or higher and 1640 °C or lower B cal : 3.0 or higher

[0071] As shown in FIGS. 2 to 4, it was confirmed that under any conditions, by determining the amount of lime input using the estimated P distribution ratio, while achieving the target molten steel P concentration, excessive lime input can be suppressed. Therefore, according to the blowing method of the present invention, it was confirmed that the optimum lime input amount can be determined in the static control of the blowing process in the converter-type refining furnace 1.

Explanation of symbols

[0072] 1 Converter-type refining furnace 10 Furnace body 100 Tap hole 101 Bottom blowing tuyere 11 Oxygen lance 12 Hopper 120 Shoot 13 Control device 130 Control unit 131 Lime input amount calculation unit 2 Hot metal 3 Slag 4 Oxygen-containing gas 5 Bottom blowing gas 6 Lime

Claims

1. A method for blowing molten iron to produce molten steel by subjecting hot metal to blowing treatment, comprising: When determining the amount of lime input at the initial stage of blowing, calculating the P distribution ratio from the P distribution formula using the estimated FeO concentration, CaO concentration, and MgO concentration in the slag, and the set end-point molten steel temperature; A method for blowing molten iron, wherein the amount of lime input is determined based on the P distribution ratio, the P concentration in the hot metal, and the target end-point molten steel P concentration.

2. The method for blowing molten iron according to claim 1, wherein when determining the amount of lime input, the amount of lime input is further determined based on the amount and P concentration of residual slag, which is the slag generated in the immediately preceding blowing treatment.

3. The method for blowing molten iron according to claim 1 or 2, wherein when calculating the P distribution ratio, the P distribution formula of formula (1) is used. 【Equation 1】 Here, L Ｐ : P distribution ratio (%T.Fe): FeO concentration in the slag (mass%) (%CaO): CaO concentration in the slag (mass%) (%MgO): MgO concentration in the slag (mass%) T: End-point molten steel temperature (°C) a ０ a １ a ２ a ３ : Constants

4. Performing multiple regression analysis using past performance values to set the constants a ０ a １ a ２ a ３ in the formula (1) according to claim 3.

5. According to the end-point molten steel P concentration, the constants a ０ a １ a ２ a ３The method for blowing molten iron according to claim 4, wherein a plurality of each are set.

6. When the concentration of P in the molten steel at the end point is 10×10 －３ mass% or less, when the concentration of P in the molten steel at the end point is 10×10 －３ mass% and more than 20×10 －３ mass% or less, when the concentration of P in the molten steel at the end point is 20×10 －３ When it is more than mass%, for the constant a in the formula (1) ０ , a １ , a ２ , a ３ The method for blowing molten iron according to claim 5, wherein each is set.

7. When calculating the P distribution ratio, when the concentration of P in the molten steel at the end point is 10×10 －３ mass% or less, the formula (7) is used, and when the concentration of P in the molten steel at the end point is 10×10 －３ mass% and more than 20×10 －３ mass% or less, the formula (8) is used, and when the concentration of P in the molten steel at the end point is 20×10 －３ When it is more than mass%, the formula (9) is used. The method for blowing molten iron according to claim 3. 【Equation 2】

8. A method for producing molten steel, which uses the method for blowing molten iron according to claim 1 to produce molten steel.

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