Dephosphorization method of molten iron

Abstract

To provide a dephosphorization method of molten iron which can simultaneously dissolve a large amount of scrap and improve dephosphorization ability and iron yield.SOLUTION: In a dephosphorization method of molten iron, scrap 2 is charged in a converter type vessel 1 at a predetermined formula scrap ratio RSC of 4.0% or more and 16.5% or less, and then molten iron 3 is charged and the molten iron 3 is dephosphorized. In the dephosphorization method, the interval of time t1 from the vertical return of the converter type vessel 1 to the start of dephosphorization treatment of the molten iron 3 after the completion of charging of the molten iron 3 is set to 0.95 minutes or more, and the interval of time t2 from the start of charging of the molten iron 3 into the converter type vessel 1 from the ladle 4 to the start of dephosphorization treatment of the molten iron 3 is set to 3.05 minutes or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for dephosphorizing the molten iron by charging scrap into a converter-type vessel, followed by charging molten iron, and melting the scrap by top and bottom blowing stirring. [Background technology]

[0002] In a molten pig iron dephosphorization process using a converter-type vessel, scrap (e.g., trimming scraps, plate scraps, coil scraps, etc. generated in steelworks) is first charged into the converter-type vessel, and then molten pig iron is charged from a ladle, a dephosphorization agent (lime, iron oxide) is added, and the scrap is melted by top and bottom blowing stirring while the molten pig iron is dephosphorized. Technologies for dephosphorization of molten pig iron using scrap are disclosed in, for example, Patent Documents 1 to 3.

[0003] Patent Document 1 aims to make it possible to mix scrap of a size that does not completely melt under normal processing conditions when dephosphorizing molten pig iron in a top and bottom blowing converter. Specifically, when dephosphorizing molten pig iron, a charging scrap mixing ratio (SR) including an amount of scrap that does not completely melt is calculated taking into account the temperature of the molten pig iron, and scrap with a specific surface area that is taken into account in the calculated charging scrap mixing ratio (SR) is used as the scrap to be charged together with the molten pig iron without changing its specific surface area, and a part of the charged scrap remains unmelted in the converter after dephosphorization in the converter.

[0004] Patent Document 2 aims to achieve both melting a large amount of iron scrap (hereinafter simply referred to as "scrap") and dephosphorization of molten pig iron. Specifically, dephosphorization is carried out in a first charge with a scrap blending ratio of 10% or more, after which the molten pig iron is tapped while leaving unmelted scrap together with a portion of the molten pig iron and slag in the refining furnace, and then, as the second charge, only the molten pig iron is charged into the refining furnace and dephosphorization is carried out on the molten pig iron, and after this dephosphorization, the refining furnace is tilted over to the tapping hole side to tap the molten pig iron.

[0005] Patent Document 3 aims to make it possible to melt a large amount of iron scrap quickly without extending the processing time. Specifically, when melting press scrap of iron scrap as an iron source, a carbon source is mixed in advance inside the press scrap before melting. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-132809 A [Patent Document 2] Patent No. 5145736 [Patent Document 3] JP 2006-097048 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the dephosphorization blowing of molten iron, it is common to charge solid oxygen (FeO) or scrap into a converter-type vessel. The more scrap used, the higher the Fe content becomes, and the amount of molten iron can be reduced when the amount of molten iron tapped is constant, which further contributes to reducing CO2 emissions.

[0008] On the other hand, since the melting point of scrap is higher than that of molten iron, if a large amount of scrap is charged into a converter-type vessel, the scrap may not completely melt at the start of blowing.

[0009] Scrap has a higher density than molten iron. When this high-density solid exists in the liquid (molten iron), it is known that the stirring strength decreases. In dephosphorization blowing, there is a risk of an increase in phosphorus concentration after processing and an increase in production costs due to a decrease in iron yield.

[0010] In Patent Document 1, a part of the scrap remains unmelted. In other words, Patent Document 1 is technically different. Leaving this scrap unmelted may reduce the stirring efficiency during dephosphorization blowing, which deteriorates the reaction rate. In addition, since the unmelted scrap is discharged outside the system, the sensible heat of the molten pig iron is taken away by the scrap heat rise, resulting in a large loss. Therefore, it is more effective to melt the scrap reliably in terms of reducing CO2 emissions. Furthermore, since the unmelted scrap is discharged outside the system, the iron yield is poor and productivity is extremely low.

[0011] In Patent Document 2, the molten iron is tapped while leaving unmelted scrap in the refining furnace. In other words, Patent Document 2 is technically different. Leaving the scrap unmelted may reduce the stirring efficiency during dephosphorization blowing, which may result in a deterioration in the reaction rate. In addition, leaving the scrap unmelted may result in a deterioration in iron yield, which may result in extremely low productivity.

[0012] In Patent Document 3, since C is added when scrap iron is melted as the iron source, there is a risk that the production cost will be high.

[0013] In view of the above problems, an object of the present invention is to provide a method for dephosphorizing molten iron which enables melting of a large amount of scrap while improving both the dephosphorization ability and the iron yield. [Means for solving the problem]

[0014] In order to achieve the above object, the present invention provides the following technical solutions.

[0015] The method for dephosphorizing molten iron according to the present invention is to deposit a scrap ratio R SCIn a method for dephosphorization of molten pig iron, scrap is charged at a concentration of 4.0% or more and 16.5% or less, and then molten pig iron is charged and dephosphorization treatment of the molten pig iron is performed, the interval of time t1 from returning the converter-type vessel to a vertical position after completion of the charging of the molten pig iron to the start of the dephosphorization treatment of the molten pig iron is set to be 0.95 minutes or more.

[0016]

number

[0017] Preferably, the time t2 from the start of charging the molten iron from the ladle into the converter-type vessel to the start of the dephosphorization treatment of the molten iron is set to 3.05 minutes or more. Effect of the Invention

[0018] According to the method for dephosphorization of molten pig iron of the present invention, it is possible to melt a large amount of scrap while improving both the dephosphorization ability and the iron yield. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of an operation flow chart for dephosphorization of molten iron in a converter-type vessel and an outline of the scope of the present invention (within the frame surrounded by a thick black line). [Figure 2A] FIG. 2 is a schematic diagram showing the state after scrap is charged into a converter-type vessel when the amount of scrap is small, i.e., the bulk is small. [Figure 2B] FIG. 2 is a schematic diagram showing the state after scrap is charged into a converter-type vessel when the scrap is bulky, e.g. in large quantity. [Figure 3A] FIG. 2 is a schematic diagram showing the stirring state when the converter-type vessel is tilted. [Figure 3B] FIG. 1 is a diagram showing a schematic diagram of the stirring state when the converter-type vessel is returned to a vertical position. [Figure 4] FIG. 1 is a diagram showing the relationship between iron yield (%) and time t1 (min) from the end of molten iron charging to the start of blowing (Examples 1 to 6, Comparative Example 7). [Diagram 5] FIG. 1 is a diagram showing the relationship between iron yield (%) and time t2 (min) from the start of molten iron charging to the start of blowing (Examples 1 to 6, Comparative Example 8). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the method for dephosphorizing molten iron according to the present invention will be described with reference to the drawings.

[0021] The embodiment described below is an example of the present invention. However, this does not limit the configuration of the present invention.

[0022] Conventionally, when scrap 2 is used to dephosphorize molten pig iron 3, the thickness and amount of scrap 2 are controlled to prevent any unmelted scrap 2 from remaining. However, using a larger amount of scrap 2 has the advantage that the Fe content is higher and the amount of molten pig iron can be reduced when the tapping rate is kept constant.

[0023] In the method for dephosphorization of hot metal of the present invention, the dephosphorization process is started after waiting for a certain period of time. According to the method for dephosphorization of hot metal of the present invention, the thickness and amount of scrap 2 can be increased. In addition, the present invention is less affected by heat loss.

[0024] The method for dephosphorizing molten iron according to the present invention will be described in detail below.

[0025] In the method for dephosphorizing molten iron according to the present invention, when scrap 2 is charged into a converter-type vessel 1, a scrap ratio R SC is set to 4.0% or more. Then, the molten pig iron 3 is charged. After the charging of the molten pig iron 3 is completed, the time t1 from when the converter-type vessel 1 is returned to the vertical position to when the dephosphorization treatment of the molten pig iron 3 is started is set to 0.95 minutes or more. Then, the dephosphorization treatment of the molten pig iron 3 is performed.

[0026] In addition, the time t2 from the start of charging the molten iron 3 from the ladle 4 into the converter-type vessel 1 to the start of the dephosphorization treatment of the molten iron 3 is set to 3.05 minutes or more.

[0027] In detail, when dephosphorization of molten iron 3 is performed, a scrap ratio R SC Scrap 2 is charged with a melting point of 4.0% or more and 16.5% or less. Then, molten iron 3 is charged.

[0028]

number

[0029] For the definition of the parameters in formula (1), please refer to Table 1 described later.

[0030] Generally, in the operation of a converter, scrap 2 is charged into a converter-type vessel 1, and then molten pig iron 3 is charged for dephosphorization. In this case, lime containing a CaO source necessary for the dephosphorization reaction and an iron oxide source (FeO) that contributes to the melting of the lime are added to the molten pig iron 3 containing the scrap 2 into the furnace.

[0031] In order to uniformly mix the molten pig iron 3 and the slag 7, gaseous oxygen is blown toward the molten pig iron 3 from a top blowing lance 5 inserted into the throat of the converter-type vessel 1, and an inert gas (bottom blown gas) is blown from a bottom blowing tuyeres 6 arranged at the bottom of the converter-type vessel 1 to stir the molten pig iron 3 (see FIG. 1). The temperature of the molten pig iron 3 during the dephosphorization treatment is 1300 to 1400°C. The refining vessel of this embodiment is the converter-type vessel 1.

[0032] Since the molten iron 3 tapped from the blast furnace contains phosphorus as an impurity, it is generally subjected to a dephosphorization treatment in a converter-type vessel 1 before the decarburization blowing. For the dephosphorization treatment in the converter-type vessel 1, lime and solid oxygen (iron oxide) are added as auxiliary materials to the molten iron 3. The dephosphorization reaction is expressed by the following formula.

[0033] 3(CaO)+2[P]+5FeO→3(CaO P2O5)+5Fe(l) Furthermore, when scrap 2 is used as the main raw material in addition to the molten pig iron 3, the dephosphorization blowing is different from the decarburization blowing in that the processing temperature is low, and therefore there is a possibility that some of the scrap 2 may remain unmelted from the viewpoint of promoting the melting of the scrap 2. In order to prevent any unmelted scrap 2, it is common to use thin scrap 2 in the dephosphorization process.

[0034] In this embodiment, for example, trimming scraps, plate scraps, coil scraps, etc. generated in a steelworks may be used as the scrap 2 having a comparatively thin thickness. Also, looking at the standards set forth by the Japan Steel Recycling Association for reference, the heavy (variety) carbon steel scraps of H2 to H4 (grades) are the subject of the present invention.

[0035] However, if a large amount of thin scrap 2 is used, the volume inside the converter-type vessel 1 increases, In terms of the contact time between the molten iron 3 and the scrap 2 when the molten iron is charged, if the bulk becomes large, it is disadvantageous for melting the scrap 2.

[0036] As one of the measures to promote the above reaction, stirring of the molten iron 3 is important. However, it is known that the uniform mixing time deteriorates when a solid heavier than the liquid specific gravity is added to the liquid, such as scrap 2-molten iron 3 (for example, reference: "Higuchi et al., CAMP-ISIJ, Vol.32, 2019, 141, etc.), the mixing power density decreases.

[0037] This decrease in stirring power density leads to a decrease in desiliconization oxygen efficiency, a decrease in dephosphorization ability due to a decrease in dephosphorization oxygen efficiency, and a decrease in iron yield due to increased slag foaming. For example, a decrease in dephosphorization ability increases the amount of oxygen required in the subsequent process, which increases the amount of CO2 generated and the amount of auxiliary materials required, which are disadvantages in terms of costs. In addition, a decrease in iron yield not only reduces production volume, but also increases the unit cost of CO2 generation, which is a major disadvantage.

[0038] Therefore, it is necessary to melt the scrap 2 without reducing the stirring efficiency during blowing. For example, as a measure to inexpensively suppress the reduction in stirring efficiency due to the remaining scrap 2, it is considered to sufficiently dissolve the scrap 2 in the molten iron 3 before starting the dephosphorization process.

[0039] In addition, the scrap ratio R SC Since the temperature remains above the liquidus temperature up to 16.5%, it is expected that the melting of scrap 2 will be promoted by maintaining the temperature. However, the scrap ratio R SC If the scrap ratio R exceeds 16.5%, the molten iron temperature will be below the liquidus temperature, and the molten iron 3 will solidify, which may cause operational problems. SC :16.5% or less.

[0040] From the viewpoint of the above-mentioned practical operation and equipment constraints, in this embodiment, the scrap ratio R SC The upper and lower limits are set at 4.0% or more and 16.5% or less.

[0041] In the present invention, in order to melt the scrap 2 before the dephosphorization treatment, the time t1 from when the converter-type vessel 1 is returned to the vertical position after the charging of the molten iron 3 is completed until the start of the dephosphorization treatment is set to be 0.95 minutes or more and 14.95 minutes or less.

[0042] In general, when performing dephosphorization, gas stirring is performed from a bottom blowing nozzle 6. In addition, the process of charging the molten iron 3 involves tilting the converter-type vessel 1, charging the molten iron 3 from a ladle 4 (molten iron ladle), and returning the converter-type vessel 1 to the vertical position after charging.

[0043] While the molten iron 3 is being charged, gas is circulated at a flow rate that does not cause splashing of the molten iron 3 while preventing the molten iron 3 from entering the bottom nozzle 6. In other words, while the molten iron 3 is being charged, a small amount of gas is blown out from the bottom nozzle 6.

[0044] In order to maximize the height from the position of the bottom blowing nozzle 6 to the molten iron surface 3 and the stirring power density while keeping the converter-type vessel 1 vertical, it is necessary to ensure this time t1, which allows the scrap 2 to melt before the dephosphorization treatment, and thus prevents a decrease in the stirring power during the dephosphorization treatment.

[0045] As a result of investigating the above influence, it was found that the interval between when the converter-type vessel 1 is returned to the vertical position and when blowing is started, that is, the time t1, needs to be 0.95 minutes (57 seconds) or more.

[0046] Regarding the lower limit of the time t1, if it is below 0.95 minutes, the stirring efficiency decreases due to the influence of the unmelted scrap 2, and the iron yield also decreases.

[0047] On the other hand, it is efficient to set the upper limit of time t1 within the permissible range of the cycle time (for example, 14.95 minutes or less) because the cycle time will be extended and there is a concern of an increase in costs due to a decrease in the dephosphorization rate of the molten iron 3. The upper limit of time t1 is set to 14.95 minutes or less based on the specification of time t2 described later.

[0048] In view of the above-mentioned practical operation and equipment constraints, the time t1 from when the converter-type vessel 1 is returned to the vertical position after the charging of the molten iron 3 is completed until the dephosphorization process is started is specified to be 0.95 minutes or more and 14.95 minutes or less.

[0049] In the present invention, the time t2 from the start of charging the molten iron 3 from the ladle 4 into the converter-type vessel 1 to the start of the dephosphorization treatment is set to 3.05 minutes or more and 18.00 minutes or less.

[0050] In addition, securing time during the charging of molten iron 3 also contributes to the melting of scrap 2. It is known that the influence of the scrap 2 on the stirring efficiency is minimized by securing the total time t2 between the charging of the molten iron 3 and the start of blowing.

[0051] Therefore, when the effect of this time t2 was evaluated, it was found that 3.05 minutes (3 minutes 3 seconds) or more was necessary.

[0052] In addition, the upper limit of the time t2 is set to a maximum of 18 minutes in JP 2006-97048 A, for example, and those skilled in the art consider it appropriate to set the time to the aforementioned time at most. Thus, the upper limit of the time t2 is set to 18.00 minutes or less from the viewpoint of actual operation and equipment constraints.

[0053] For this reason, the upper limit of the time t1 is set to 18.00 min-3.05 min (the lower limit of the time t2)=14.95 min or less. In other words, from the viewpoint of not decreasing the ratio of dephosphorization blowing, it is preferable to set the time until the start of dephosphorization blowing within the ranges of t1 and t2 specified in the present invention.

[0054] Table 1 shows the parameters used in equations (1) and (2).

[0055] [Table 1]

[0056] Here, the operational steps of dephosphorization of the molten iron 3 in the converter-type vessel 1 will be described.

[0057] FIG. 1 shows an operation flow chart for dephosphorization of molten iron 3 in a converter-type vessel 1 and the scope of the present invention (enclosed in a frame surrounded by a thick black line).

[0058] As shown in FIG. 1, in the charging process of the molten iron 3, in this embodiment, a state where the molten iron 3 starts to enter the converter-type vessel 1 is defined as the start of charging of the molten iron 3.

[0059] The converter-type vessel 1 is tilted, scrap 2 is charged, and then charging of molten iron 3 is started. Charging of molten iron 3 is continued while tilting the converter-type vessel 1.

[0060] The converter-type vessel 1 is returned from the tilted state to a vertical state. The time when the converter-type vessel 1 is returned to the vertical state is defined as the end of charging of the molten iron 3.

[0061] Next, the problems that arise when thin scrap 2 is charged will be described.

[0062] FIG. 2A shows the situation after scrap is charged into a converter-type vessel when the amount of scrap 2 is small, i.e., the bulk is small.

[0063] As shown in FIG. 2A , when the amount of scrap 2 is small, or when the scrap 2 is bulky, for example, when a thick piece of scrap 2 is charged, the scrap 2 is dispersed in the converter-type vessel 1 over a narrow range, and the scrap 2 is easily brought into contact with the molten iron 3.

[0064] FIG. 2B shows the state after the scrap 2 has been charged into the converter-type vessel 1 when the scrap 2 is bulky, i.e., the amount of the scrap 2 is large.

[0065] As shown in FIG. 2B, when the amount of scrap 2 is large, or when the scrap 2 is bulky, for example, when thin scrap 2 is charged, the scrap 2 is dispersed over a wide area in the converter-type vessel 1, and it takes a long time for the surface of the scrap 2 to come into contact with the molten iron surface 3.

[0066] The present invention is a technology that targets the above, and is characterized in that it ensures a contact time t1 between the molten iron 3 that has reached the surface layer of the scrap 2 and the scrap 2.

[0067] The stirring power density in the converter-type vessel 1 will now be described.

[0068] FIG. 3A shows the state of stirring when the converter-type vessel 1 is tilted.

[0069] As shown in Fig. 3A, the bottom nozzle 6 is generally attached to the bottom of the furnace. When the converter-type vessel 1 is tilted, the depth from the position of the bottom nozzle 6 to the surface of the molten iron is shallow, and the stirring power density is low.

[0070] FIG. 3B shows the state of stirring when the converter-type vessel 1 is returned to the vertical position.

[0071] As shown in Fig. 3B, when the converter-type vessel 1 is in a vertical state, the depth from the bottom blowing nozzle 6 to the molten iron surface 3 is the deepest, and therefore the stirring power density is the maximum. In other words, one of the effective factors for melting the scrap 2 is a high stirring power density. Therefore, it is important to keep the converter-type vessel 1 in a vertical state for a long time.

[0072] Here, the definition of the vertical state of the converter-type vessel 1 will be described.

[0073] The vertical state of the converter type vessel 1 generally has an error of about 3°. For this reason, in this embodiment, the vertical state of the converter type vessel 1 may be defined as 87 to 103°. Also, for example, although the vessel is different, reference may be made to JP 2015-34346 A (which defines the inclination as 3 to 8°). [Example] Examples carried out according to the method for dephosphorizing molten iron of the present invention and comparative examples carried out for comparison with the present invention will be described below.

[0074] The conditions for carrying out this embodiment are as follows.

[0075] [Table 2]

[0076] It should be noted that the embodiments described in this specification are merely examples of the present invention and the present invention is not limited to these.

[0077] [Table 3]

[0078] Table 4 shows examples and comparative examples carried out according to the method for dephosphorizing hot metal of the present invention. Table 4 shows only the implementation conditions. Table 5 shows the implementation results.

[0079] [Table 4]

[0080] [Table 5]

[0081] As shown in Tables 4 and 5, in this Example 1, the scrap ratio R is set to satisfy the prescribed range of 4.0% to 16.5%. SC was set to 5.1%, and the time t1 from when the converter-type vessel 1 was returned to vertical after the completion of the charging of the molten iron 3 to when the dephosphorization treatment of the molten iron 3 began was 1.80 minutes (1 minute 48 seconds), which satisfied the specified range of 0.95 minutes or more and 14.95 minutes or less, and the time t2 from when the charging of the molten iron 3 from the ladle 4 to the converter-type vessel 1 began to begin the dephosphorization treatment was 3.48 minutes, which satisfied the specified range of 3.05 minutes or more and 18.00 minutes or less, resulting in an iron yield of 98.47%, or more than 98.2%, and thus obtaining good results in terms of improved iron yield.

[0082] In this embodiment, the scrap ratio R SC By setting the value to 7.4%, the time t1 to 1.40 minutes, which satisfies the specified range of 0.95 minutes or more and 14.95 minutes or less, and the time t2 to 3.50 minutes, which satisfies the specified range of 3.05 minutes or more and 18.00 minutes or less, the iron yield was 98.40%, which was 98.2% or more, and good results were obtained in terms of improved iron yield.

[0083] In this embodiment, the scrap ratio R SCBy setting the value of t1 at 4.7%, time t1 at 1.70 minutes, which satisfies the specified range of 0.95 minutes or more and 14.95 minutes or less, and time t2 at 3.73 minutes, which satisfies the specified range of 3.05 minutes or more and 18.00 minutes or less, the iron yield was 98.31%, which was above 98.2%, and good results were obtained in terms of improved iron yield.

[0084] In this embodiment 4, the scrap ratio R SC By setting the value of t1 at 4.7%, time t1 at 0.97 minutes, which satisfied the specified range of 0.95 minutes or more and 14.95 minutes or less, and time t2 at 3.22 minutes, which satisfied the specified range of 3.05 minutes or more and 18.00 minutes or less, the iron yield was 98.24%, which was above 98.2%, and good results were obtained in terms of improved iron yield.

[0085] In this embodiment 5, the scrap ratio R SC By setting the value of t1 at 4.8%, time t1 at 0.95 minutes, which satisfies the specified range of 0.95 minutes or more and 14.95 minutes or less, and time t2 at 3.18 minutes, which satisfies the specified range of 3.05 minutes or more and 18.00 minutes or less, the iron yield was 98.83%, which was 98.2% or more, and good results were obtained in terms of improved iron yield.

[0086] In this Example 6, the scrap ratio R SC By setting the value of 4.5%, the time t1 was 1.15 minutes, which satisfied the specified range of 0.95 minutes or more and 14.95 minutes or less, and the time t2 was 3.08 minutes, which satisfied the specified range of 3.05 minutes or more and 18.00 minutes or less, the iron yield was 98.22%, which was above 98.2%, and good results were obtained in terms of improved iron yield.

[0087] On the other hand, in Comparative Example 7, the time t1 was 0.92 minutes, which did not satisfy the prescribed range of 0.95 minutes or more and 14.95 minutes or less, so the iron yield was 98.10%, which was lower than 98.2%, and the iron yield was deteriorated.

[0088] In Comparative Example 8, the time t2 was 2.93 minutes, which did not satisfy the prescribed range of 3.05 minutes or more and 18.00 minutes or less, and therefore the iron yield was 96.94%, which was lower than 98.2%, and the iron yield was deteriorated.

[0089] In Comparative Example 9, the time t1 was 0.93 minutes, which did not satisfy the specified range of 0.95 minutes or more and 14.95 minutes or less, and the time t2 was 2.93 minutes, which did not satisfy the specified range of 3.05 minutes or more and 18.00 minutes or less, so the iron yield was 97.23%, which was lower than 98.2%, and the iron yield was deteriorated.

[0090] In Comparative Example 10, the time t1 was 0.88 minutes, which did not satisfy the specified range of 0.95 minutes or more and 14.95 minutes or less, and the time t2 was 2.80 minutes, which did not satisfy the specified range of 3.05 minutes or more and 18.00 minutes or less, so the iron yield was 98.07%, which was lower than 98.2%, and the iron yield was deteriorated.

[0091] The effect of the present invention was evaluated using the iron yield, which is defined by the formula (2).

[0092]

number

[0093] For parameter definitions, please refer to Table 1.

[0094] FIG. 4 shows the relationship between the iron yield (%) and the time t1 (min) from the end of charging the molten iron 3 to the start of blowing (Examples 1 to 6 and Comparative Example 7).

[0095] As shown in FIG. 4, the results of this embodiment show that the iron yield is significantly improved if the time t1 from when the converter-type vessel 1 is returned to the vertical position after the completion of the charging of the molten iron 3 to when the dephosphorization treatment of the molten iron 3 is started is 0.95 minutes or more.

[0096] In addition, at time t1, the phosphorus concentration after treatment did not change. In the comparative example, the reduction of FeO in slag 7 was slow due to the decrease in stirring strength caused by scrap 2, but the slag composition became favorable for dephosphorization, and it is considered that the phosphorus concentration did not change significantly.

[0097] FIG. 5 shows the relationship between the iron yield (%) and the time t2 (min) from the start of charging the molten iron 3 to the start of blowing (Examples 1 to 6 and Comparative Example 8).

[0098] As shown in FIG. 5, the results of this embodiment show that if the time t2 from the start of charging the molten iron 3 from the ladle 4 (molten iron ladle) into the converter-type vessel 1 to the start of the dephosphorization process is 3.05 minutes or longer, the iron yield is significantly improved.

[0099] Furthermore, even at time t2, the phosphorus concentration after treatment did not change. In the comparative example, the reduction of FeO in slag 7 was slow due to the decrease in stirring strength caused by scrap 2, but the slag composition became favorable for dephosphorization, and it is considered that the phosphorus concentration did not change significantly.

[0100] In summary, the present invention provides a converter-type vessel 1 with a scrap ratio R SC In a method for dephosphorization of molten pig iron, in which scrap 2 is charged at a content of 4.0% or more and 16.5% or less, and then molten pig iron 3 is charged and dephosphorization of the molten pig iron 3 is performed, the interval of time t1 from when the converter-type vessel 1 is returned to a vertical position after the charging of the molten pig iron 3 is completed to when the dephosphorization of the molten pig iron 3 is started is set to be 0.95 minutes or more and 14.95 minutes or less. In addition, the interval of time t2 from when the charging of the molten pig iron 3 from the ladle 4 to the converter-type vessel 1 is started to when the dephosphorization is started is set to be 3.05 minutes or more and 18.00 minutes or less.

[0101] As described above, the method for dephosphorizing molten iron of the present invention makes it possible to melt a large amount of scrap 2 while improving the dephosphorization ability and iron yield.

[0102] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. In particular, in the embodiments disclosed herein, matters not explicitly stated, such as operating conditions, operating conditions, various parameters, dimensions, weights, volumes of components, etc., do not deviate from the scope of ordinary practice by a person skilled in the art, and values ​​that can be easily assumed by a person skilled in the art are used. [Explanation of symbols]

[0103] 1 Converter-type vessel 2. Scrap 3. Molten iron 4 Ladle 5 Top blowing lance 6 bottom-blown tuyere 7. Slug

Claims

1. In the converter-type vessel, the scrap ratio R SC A method for dephosphorizing molten pig iron, comprising charging scrap having a phosphorus content of 4.0% or more and 16.5% or less, subsequently charging molten pig iron, and carrying out a dephosphorization treatment of the molten pig iron, The time interval t1 from when the converter-type vessel is returned to the vertical position after the charging of the molten iron is completed until the dephosphorization treatment of the molten iron is started is set to 0.95 minutes or more. A method for dephosphorizing molten iron, comprising the steps of: [0010]

2. The time t2 from the start of charging the molten iron from the ladle into the converter-type vessel to the start of dephosphorization of the molten iron is set to 3.05 minutes or more.

2. The method for dephosphorizing molten iron according to claim 1 .

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