Converter steelmaking process

Abstract

This invention provides a converter steelmaking method that prevents melting residue of the chilled iron source and increases the amount of chilled iron source used in the refining process of the chilled iron source and molten iron contained in a converter-type vessel, without impairing productivity. The converter steelmaking method involves dephosphorizing molten iron to obtain dephosphorized molten iron, and then decarburizing the obtained dephosphorized molten iron to obtain molten steel. In the dephosphorization process, before loading the undephosphorized molten iron into the first converter-type vessel, a first chilled iron source in an amount satisfying the following formula (1) is loaded into the first converter-type vessel at once. Then, the undephosphorized molten iron is loaded, and dephosphorization is performed. The obtained dephosphorized molten iron is tapped to a molten iron receiving vessel and held there. A second chilled iron source is loaded at once into the first converter-type vessel that has undergone dephosphorization, or a second converter-type vessel different from the first converter-type vessel. Then, the dephosphorized molten iron held in the molten iron receiving vessel is loaded, and decarburization is performed. s0 ≤0.1186T-134(%W) s0 ≥0)···(1), where %W s0 The ratio (%) of the first chill source to the sum of the first chill source and the amount of molten iron charged before dephosphorization, and T is the temperature of the molten iron before dephosphorization (°C).

Description

Technical Field

[0001] This invention relates to a converter steelmaking method for preventing melting residues of chills and increasing the amount of chills used in the refining process of molten iron contained in a converter-type vessel. Background Technology

[0002] In recent years, from the perspective of global warming, the steel industry has also called for reducing CO2 emissions, making the reduction of fossil fuel consumption an urgent priority. In the steel industry, molten iron is produced by reducing iron ore with carbon. The carbon source required to produce this molten iron is approximately 500 kg per ton of molten iron. On the other hand, when steel is produced using scrap iron or other cold iron sources as raw materials in a converter, the carbon source necessary for iron ore reduction is not required. In this case, even considering the energy required to melt the cold iron source, replacing 1 ton of molten iron with 1 ton of cold iron source can reduce CO2 emissions by approximately 1.5 tons.

[0003] In a converter, to increase the amount of chills such as scrap iron used, sufficient heat is required to fully melt them. If the heat is insufficient, the chills cannot be completely melted during processing and remain at the bottom of the furnace after tapping. In this case, during the next batch of converter processing using the same furnace charge, the hot metal ratio must be increased to reliably melt the remaining chills, without increasing the amount of chills used. Furthermore, this leads to operational problems such as the need to replenish hot metal during decarburization due to insufficient tapping, and reduced refining capacity due to blocked bottom tuyeres caused by the presence of chills adhering to the furnace bottom.

[0004] Typically, in converter processing, the heat of reaction from carbon and silicon, which are impurities in the molten iron, is used to compensate for the endothermic reaction caused by the melting of the chill. However, with an increased chill ratio, relying solely on the carbon / silicon components of the molten iron becomes insufficient. Furthermore, the temperature change of the molten iron during the melting process, especially in the first half, is crucial. In the initial stage of chill melting, the surrounding molten iron loses heat due to the chill's rising temperature, causing a rapid drop in temperature. If the amount of chill increases, the initial temperature drop in the molten iron becomes more pronounced, making chill melting difficult. Moreover, there is a risk of forming large chill blocks (hereinafter referred to as "icebergs") around the chill, which solidify and are called "steel icebergs" or "ferrobergs." Icebergs have a small heat transfer area relative to their volume, thus requiring time to melt, which can be considered a cause of residual chill melting and prolonged processing time.

[0005] To compensate for insufficient heat when only the carbon / silicon components in molten iron are used, for example, a heat compensation technology is proposed in Patent Document 1, which supplies heating agents such as ferrosilicon, graphite, and coke into the furnace and supplies oxygen.

[0006] Furthermore, Patent Document 2 proposes a technique to promote the melting of the chilled iron source by supplying bottom-blown gas to enhance the stirring of the molten iron in the converter. This technique promotes heat transfer between the molten iron and the chilled iron source and the movement of carbon (due to the decrease in the melting point of the chilled iron source caused by carburization from the molten iron to the surface of the chilled iron source) by enhancing stirring.

[0007] Furthermore, Patent Document 3 proposes a method for adding the total amount or a portion thereof of the chill source to the molten iron from the furnace during the first half of the blowing process when using a converter-type furnace with top-blowing and bottom-blowing functions for dephosphorization treatment of molten iron.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2011-38142

[0011] Patent Document 2: Japanese Patent Application Publication No. 63-169318

[0012] Patent Document 3: Japanese Patent Application Publication No. 2005-133117 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, in the method described in Patent Document 1, the processing time in the converter is prolonged and productivity is reduced due to the supply of oxygen required for the oxidation and combustion of carbon and silicon. Furthermore, there are the following problems: if ferrosilicon is used, SiO2 is generated due to the combustion of silicon, thus increasing the amount of slag produced; if graphite or coke is used, the amount of CO2 gas produced increases due to the combustion of carbon.

[0015] Furthermore, the bottom-blowing stirring enhancement method described in Patent Document 2 has a smaller effect compared to thermal compensation. Considering the thermal balance and carbon mass balance near the molten iron-cold iron source interface, the melting rate of the cold iron source can be expressed as a linear function of the interfacial heat transfer coefficient or the molten iron mass transfer coefficient. Here, it is known that the interfacial heat transfer coefficient or the molten iron mass transfer coefficient is proportional to the 0.2 to 0.3 power of the stirring energy. Therefore, even if the stirring power energy is set to 1.5 times, the melting rate only increases by about 10%.

[0016] Furthermore, the method described in Patent Document 3 avoids the stagnation of chilled iron source melting and the formation of icebergs caused by the drop in molten iron temperature during the first half of the dephosphorization process. However, to avoid melting residue, the timing of chilled iron source input is limited to the first half of the blowing process, thus limiting the amount that can be input during actual blowing time. In the method described in Patent Document 3, the upper limit of chilled iron source usage ratio is approximately 10%.

[0017] The present invention was made in view of the following circumstances, and its object is to provide a converter steelmaking method that prevents melting residue of the chill source and increases the amount of chill source used in the refining process of the chill source and molten iron contained in a converter-type vessel without impairing productivity.

[0018] Problem Solving Methods

[0019] To solve the aforementioned problems, the inventors conducted various experiments. As a result, by setting an upper limit on the amount of chilled iron source charged before the dephosphorization process begins, and by studying the conditions for further adding chilled iron source during the dephosphorization or decarburization processes, they discovered a new converter steelmaking method that can solve the existing problems. This invention is based on the above insights, and its main points are as follows.

[0020] The converter steelmaking method of the present invention, which advantageously solves the above-mentioned problems, has the following advantages:

[0021] The process involves adding auxiliary materials to the cold iron source and molten iron before dephosphorization contained in a converter-type vessel, and supplying oxidizing gas to perform dephosphorization treatment on the molten iron before dephosphorization, obtaining dephosphorized molten iron, and then tapping the obtained dephosphorized molten iron into a molten iron receiving vessel and maintaining it in the molten iron receiving vessel; and...

[0022] The dephosphorized molten iron, held in the aforementioned molten iron receiving container, is then transferred to a first converter-type container that has undergone the aforementioned dephosphorization treatment, or to a second converter-type container different from the first converter-type container. Oxidizing gas is supplied to perform decarburization treatment, thereby obtaining molten steel.

[0023] In the above dephosphorization process, a first chill source in an amount satisfying the following formula (1) is loaded into the first converter-type vessel at once, and then the molten iron before dephosphorization is loaded to perform the dephosphorization process. In the above decarburization process, a second chill source is loaded into the first converter-type vessel that has undergone the above dephosphorization process, or a second converter-type vessel different from the first converter-type vessel, and then the molten iron after dephosphorization, which is held in the molten iron receiving vessel, is loaded to perform the decarburization process.

[0024] %W s0 ≤0.1186T-134(%W) s0 ≥0)···(1)

[0025] In the formula, %W s0 The ratio (%) of the first chill source charge to the sum of the first chill source charge and the molten iron charge before dephosphorization.

[0026] T: Temperature of molten iron before dephosphorization (°C).

[0027] It should be noted that, for the converter steelmaking method of the present invention, the following 1 to 4 are considered to be more preferred solutions.

[0028] 1. In any one or both of the above-mentioned dephosphorization treatment and decarburization treatment, a third cold iron source is introduced from the furnace of the above-mentioned converter-type vessel into the converter-type vessel.

[0029] 2. In any one or both of the above-mentioned dephosphorization treatment and decarburization treatment, the third chill source is successively added from the furnace of the converter-type vessel into the converter-type vessel in an amount satisfying the following formula (2).

[0030] W sadd ≤2.4t add ···(2)

[0031] In the formula, W sadd Input volume of chilled iron source (t)

[0032] T add The first feeding into the furnace refers to the time (in minutes) from the start of blowing to the start of the first feeding.

[0033] For subsequent investments, the time (in minutes) from the completion of the previous investment to the start of the next investment is used.

[0034] 3. The longest dimension of the third cold iron source fed into the furnace of the above-mentioned converter-type vessel is 100 mm;

[0035] 4. When the third cold iron source is introduced into the converter-type vessel from the furnace in the above-mentioned dephosphorization treatment, one or both of the following conditions are met: the carbon concentration in the third cold iron source is 0.3% by mass or more, and the temperature of the dephosphorized molten iron after the above-mentioned dephosphorization treatment is 1380°C or more.

[0036] The effects of the invention

[0037] According to the present invention configured as described above, dephosphorization is performed by setting an upper limit on the amount of chilled iron source charged before the start of the dephosphorization process. The resulting dephosphorized molten iron is then charged into a converter for decarburization. At this time, the chilled iron source is charged all at once before the dephosphorized molten iron is charged for decarburization. This suppresses the temperature drop of the molten iron at the beginning of the dephosphorization process, and inhibits the stagnation of chilled iron source melting and the formation of icebergs. As a result, residual melting of the chilled iron source can be prevented, and the amount of chilled iron source used can be increased in a series of processes, including dephosphorization and decarburization. Furthermore, since it prevents the blockage of the bottom tuyeres due to the adhesion of the chilled iron source raw material metal to the furnace bottom, which would lead to poor stirring and reduced dephosphorization capacity, it also has the effect of enabling stable implementation of the dephosphorization process.

[0038] Furthermore, a portion of the chills added during dephosphorization and decarburization is introduced from the converter itself during the process. This suppresses the initial drop in molten iron temperature, inhibits stagnation in chill melting and the formation of icebergs, and allows for the melting of more chills during dephosphorization or decarburization. By setting the chills fed from the furnace to a maximum size of 100mm, malfunctions in conveying equipment such as furnace hoppers and conveyors are avoided, thus stabilizing the supply of chills from the furnace. Attached Figure Description

[0039] Figure 1 Figures (a) to (g) illustrate one embodiment of the converter steelmaking method of the present invention.

[0040] Figure 2 Figures (a) to (g) illustrate other embodiments of the converter steelmaking method of the present invention.

[0041] Symbol Explanation

[0042] 1. First converter-type container

[0043] 2. Scrap iron chute

[0044] 3 First Cold Iron Source

[0045] 4. Ingredient Packet

[0046] 5. Molten iron (before dephosphorization)

[0047] 6 Top-blown spray guns

[0048] 7 Bottom air outlet

[0049] 8. Molten Iron

[0050] 9 (After dephosphorization) molten iron

[0051] 10 Molten Iron Receiving Container

[0052] 11 Second converter type container

[0053] 12 Second Cold Iron Source

[0054] 13. Furnace hopper

[0055] 14. Add a cold iron source to the furnace. Detailed Implementation

[0056] The embodiments of the present invention will now be described in detail. It should be noted that the accompanying drawings are schematic diagrams and may sometimes differ from reality. Furthermore, the following embodiments exemplify apparatus and methods for embodying the technical concept of the present invention and are not limited to the following configuration. That is, the technical concept of the present invention can be modified in various ways within the scope of the claims.

[0057] <Description of one embodiment of the converter steelmaking method of the present invention>

[0058] Figure 1 Figures (a) to (g) illustrate one embodiment of the converter steelmaking method of the present invention. Hereinafter, reference will be made to... Figure 1 (a) to (g) describe one embodiment of the converter steelmaking method of the present invention.

[0059] First, using a converter-type furnace with top-blowing and bottom-blowing functions (hereinafter referred to as the first converter-type container 1), scrap iron, which serves as the first cold iron source 3, is loaded into the first converter-type container 1 through the scrap iron chute 2. Figure 1 (a)). Then, using the charging bag 4, molten iron 5 (hereinafter also referred to as molten iron before dephosphorization 5) is loaded into the first converter-type vessel 1. Figure 1 (b)). Next, oxygen is supplied from the top-blown lance 6, and inactive gases such as N2 are supplied from the bottom-blown tuyeres 7 located at the bottom of the furnace. Heating agents, slagging agents, and other auxiliary materials are added, and the molten iron 8 in the first converter-type vessel 1 undergoes dephosphorization treatment to obtain dephosphorized molten iron 9. Figure 1 (c)). Then, the obtained dephosphorized molten iron 9 is discharged into the molten iron receiving container 10 and held in the molten iron receiving container 10. Figure 1 (d)).

[0060] Then, the second chill source 12 is loaded into the second converter-type container 11, which is different from the first converter-type container 1, in one go. Figure 1 (e)). Subsequently, the dephosphorized molten iron 9, which was held in the molten iron receiving container 10, was loaded into the second converter-type container 11. Figure 1(f)). Here, the second converter vessel 11 may be omitted, and the first converter vessel 1, which has undergone dephosphorization treatment, may be used instead. Finally, oxygen is supplied from the top-blown lance 6, and inactive gases such as N2 as stirring gases are supplied from the bottom-blown tuyeres 7 located at the bottom of the furnace. Additional raw materials such as heating agents and slagging agents are added, and decarburization treatment is performed on the dephosphorized molten iron 9 within the second converter vessel 11. Figure 1 (g) It should be noted that, for the amount of chilled iron source loaded before dephosphorization and decarburization, the total amount loaded before the two treatments (total chilled iron source loading predetermined amount) can be predetermined, and the loading amount of the second chilled iron source 12 can be determined as the amount equivalent to the difference between the total chilled iron source loading predetermined amount and the amount of the first chilled iron source 3.

[0061] According to this embodiment, by setting the amount of the first chill source 3 loaded during the dephosphorization process to a quantity that satisfies the following formula (1), it is possible to suppress the decrease in the temperature of the molten iron in the initial stage of the dephosphorization process, suppress the stagnation of the melting of the chill source, and suppress the formation of icebergs:

[0062] %W s0 ≤0.1186T-134(%W) s0 ≥0)···(1)

[0063] In the formula, %W s0 The ratio (%) of the first chill source charge to the sum of the first chill source charge and the molten iron charge before dephosphorization.

[0064] T: Temperature of molten iron before dephosphorization (°C).

[0065] It should be noted that, since it can prevent the agitation from deteriorating and the dephosphorization capacity from being reduced due to the adhesion of the cold iron source metal to the bottom of the furnace and the blockage of the bottom tuyeres, it also has the effect of stably carrying out the dephosphorization treatment. In addition, when the obtained dephosphorized molten iron 9 is loaded into the second converter-type vessel 11 or the first converter-type vessel 1 for decarburization treatment, by loading the second cold iron source 12 at once before loading the dephosphorized molten iron 9 for decarburization treatment, it is possible to prevent the melting residue of the cold iron source and increase the amount of cold iron source used in the series of treatments from dephosphorization treatment to decarburization treatment. Here, the amount of the second cold iron source 12 loaded during decarburization treatment can exceed the upper limit obtained from the above formula (1). This is because the temperature of the molten iron is higher in decarburization treatment than in dephosphorization treatment, so even if the amount of the second cold iron source 12 loaded is large, melting residue is not likely to occur.

[0066] <Description of other embodiments of the converter steelmaking method of the present invention>

[0067] Figure 2Figures (a) to (g) illustrate other embodiments of the converter steelmaking method of the present invention. Hereinafter, refer to... Figure 2 (a) to (g) describe other embodiments of the converter steelmaking method of the present invention.

[0068] First, using a first converter-type container 1 with top-blowing and bottom-blowing functions, scrap iron, serving as the first cold iron source 3, is loaded into the first converter-type container 1 through a scrap iron chute 2. Figure 2 (a)). Then, using the charging bag 4, molten iron 5 before dephosphorization is loaded into the first converter-type vessel 1. Figure 2 (b)). These Figure 2 (a) and Figure 2 (b) shows the process as described in the first embodiment. Figure 1 (a) and Figure 1 The procedures described in (b) are the same.

[0069] Next, oxygen is supplied from the top-blown lance 6, and inactive gases such as N2 are supplied from the bottom-blown tuyeres 7 located at the bottom of the furnace as stirring gases. Heating agents, slagging agents, and other auxiliary materials are added, and the molten iron 8 in the first converter-type vessel 1 undergoes dephosphorization treatment to obtain dephosphorized molten iron 9. Figure 2 (c)). Here, in this other embodiment, any of the following steps are performed: in Figure 2 In stage (a), before the dephosphorization treatment, the total amount of cold iron source used in the dephosphorization treatment is loaded into the first converter-type container 1 at one time as the first cold iron source 3 (C-2); and in the case where a portion of the cold iron source used in the dephosphorization treatment is loaded into the first converter-type container 1 from the scrap iron chute 2 as the first cold iron source 3 before the dephosphorization treatment, while the remaining cold iron source 14 is fed into the first converter-type container 1 from the furnace via the furnace hopper 13 as the third cold iron source 14 (C-1, C-3).

[0070] Then, the obtained dephosphorized molten iron 9 is discharged into the molten iron receiving container 10 and kept in the molten iron receiving container 10. Figure 2 (d)). Then, the second chill source 12 is loaded into the second converter-type container 11, which is different from the first converter-type container 1, in one go. Figure 2 (e)). Then, the dephosphorized molten iron 9 held in the molten iron receiving container 10 is loaded into the second converter-type container 11 ( Figure 2 (f)). Here, the second converter vessel 11 can also be omitted, and the first converter vessel 1, which has undergone dephosphorization treatment, can be used instead. Figure 2 (d) Figure 2 (e) and Figure 2 The process shown in (f) is the same as that described in the first embodiment. Figure 1 (d) Figure 1(e) and Figure 1 The process described in (f) is the same. It should be noted that, for the amount of chills used before or after dephosphorization, the total amount used in the two processes (the total chills used is predetermined) can be determined in advance, and the amount of the second chill 12 can be determined to be the amount equivalent to the difference between the total chills used and the amount of the first chill 3.

[0071] Finally, oxygen is supplied from the top-blown lance 6, and inactive gases such as N2 are supplied from the bottom-blown tuyeres 7 located at the bottom of the furnace as stirring gases. Heating agents, slagging agents, and other auxiliary materials are added, and the decarburization treatment of the dephosphorized molten iron 9 is carried out in the second converter-type vessel 11. Figure 2 (g)). Here, for in Figure 2 In stage (e), the case where the total amount of the second chill source 12 is loaded into the second converter-type container 11 at once is described (G-1). However, in this other embodiment, any of the following steps (G-2, G-3) is performed: a portion of the chill source used in the decarburization process is loaded into the second converter-type container 11 from the scrap iron chute 2 as the second chill source 12, while the remaining chill source 14 is fed into the second converter-type container 11 from the furnace via the furnace hopper 13.

[0072] It should be noted that, in Figure 2 (c) shows the dephosphorization process and Figure 2 In the decarburization process shown in (g), process G-1 is performed when process C-1 has been performed, process G-2 is performed when process C-2 has been performed, and process G-3 is performed when process C-3 has been performed. Thus, in either or both of the dephosphorization and decarburization processes, a chill source is introduced from the furnace of the converter-type vessel into the converter-type vessel.

[0073] Here, in Figure 2 (c) shows the dephosphorization processes (C-1, C-3) and Figure 2 In the decarburization process (G-2, G-3) shown in (g), when the chill source 14 is added from the furnace hopper 13 all at once or in multiple additions, in order to minimize the drop in molten iron temperature, it is preferable to set the amount of chill source added from the furnace hopper all at once to the amount that satisfies the following formula (2):

[0074] W sadd ≤2.4t add ···(2)

[0075] In the formula, W sadd Input volume of chilled iron source (t)

[0076] T addThe first feeding into the furnace refers to the time (in minutes) from the start of blowing to the start of the first feeding.

[0077] For subsequent inputs, the time (in minutes) from the completion of the previous input to the start of the next input is considered.

[0078] Furthermore, when adding chills from the furnace multiple times, by setting the timing of adding the chills (the timing of adding them after the second time) to the moment when the temperature of the molten iron rises after the chills that have already been added to the furnace have melted, it is possible to suppress the stagnation of the melting of the chills and the formation of icebergs, and to melt the chills efficiently.

[0079] In addition, Figure 2 (c) shows the dephosphorization processes (C-1, C-3) and Figure 2 In the decarburization processes (G-2, G-3) shown in (g), considering the handling in the furnace hopper 13 and conveying equipment such as conveyors, it is preferable to cut the chill source 14 fed into the furnace hopper 13 to a maximum size of 100mm or less (the size for a box with internal dimensions of 100mm×100mm×100mm) by means of cutting. In the dephosphorization process, as the dephosphorization process proceeds, at the moment when the first chill source 3 fed from the scrap iron chute melts and the temperature of the molten iron rises, the third chill source 14 is fed from the furnace. At this time, it is preferable that the carbon concentration contained in the third chill source 14 fed from the furnace is 0.3% by mass or more, and that the temperature of the molten iron after dephosphorization is 1380°C or more after the above-mentioned dephosphorization process, or both. This can suppress the melting residue of the third chill source 14 fed from the furnace. During the decarburization process, as the decarburization treatment proceeds, the second cold iron source 12, which is loaded from the scrap iron chute, melts, and as the temperature of the molten iron rises, the third cold iron source 14 is added from the furnace.

[0080] Furthermore, the molten iron is not limited to molten iron tapped from a blast furnace. The present invention can also be applied to molten iron obtained through a blast furnace, induction melting furnace, electric arc furnace, etc., or to molten iron obtained by mixing such molten iron with molten iron tapped from a blast furnace.

[0081] Example

[0082] (Example 1)

[0083] The amount of cold iron source used in the dephosphorization process was investigated. Molten iron from the blast furnace and cold iron source (scrap iron) were used for dephosphorization in a top-blown and bottom-blown converter (first converter type vessel). The temperature and phosphorus concentration of the molten iron before dephosphorization were 1230–1263℃ and 0.130–0.134%, respectively. Various variations were made in the amount of molten iron charged before dephosphorization and the amount of scrap iron charged from the scrap iron chute, and the temperature of the molten iron after dephosphorization was controlled at 1350℃. It should be noted that no cold iron source was added from the furnace during this dephosphorization process. The results are shown in Table 1.

[0084]

[0085] According to the results in Table 1, as shown in Tests No. 1 to 6, when the amount of scrap iron loaded from the scrap iron chute exceeds the upper limit obtained from the above formula (1), that is, when the ratio of the amount of scrap iron to the total loading amount (the amount of molten iron before dephosphorization + the amount of scrap iron loaded from the scrap iron chute) exceeds 0.1186T-134 (T: the temperature of molten iron before dephosphorization, °C) (Tests No. 4 to 6), scrap iron melting residue occurred. In addition, it was confirmed that the dephosphorization capacity was reduced, which can be attributed to the poor stirring caused by the blockage of the bottom blow vent due to the adhesion of scrap iron raw material metal.

[0086] (Example 2)

[0087] For the molten iron after dephosphorization treatment in Example 1, the phased addition of cold iron source (scrap iron) in the decarburization treatment was studied. In the dephosphorization treatment using the first converter-type vessel in Example 1, the ratio of scrap iron amount to total charge (molten iron before dephosphorization + scrap iron charged from the scrap iron chute) was set below the upper limit obtained by the above formula (1), and scrap iron was also used in the top-blown and bottom-blown converter (second converter-type vessel) for decarburization treatment. In order to minimize the decrease in molten iron temperature caused by the use of scrap iron and to efficiently melt the scrap iron, the scrap iron was added in phases in the second converter-type vessel (decarburization furnace). Specifically, scrap iron was charged from the scrap iron chute before molten iron was charged, and then scrap iron was added from the furnace during the decarburization treatment. It should be noted that there was no melting residue in the dephosphorization furnace, and the temperature of the molten iron before decarburization in the decarburization furnace was 1360–1380℃, while the temperature of the molten steel after decarburization was 1640–1650℃. The results are shown in Table 2.

[0088]

[0089] The results in Table 2 confirm that by adding scrap iron from the furnace hopper in stages, below the upper limit obtained from equation (2) above, the amount of scrap iron used can be steadily increased. It should be noted that the same effect was observed not only in decarburization but also in dephosphorization.

[0090] (Example 3)

[0091] The size of the scrap iron fed from the furnace in Example 2 was investigated. In Example 2, the size of the scrap iron fed from the furnace was changed, and the results are shown in Tests No. 21 to 23 in Table 3 below. It can be seen that by setting the scrap iron size to a maximum size of 100 mm or less (the size of a box with an internal size of 100 mm × 100 mm × 100 mm), it is possible to stably feed the scrap iron from the furnace without causing malfunctions in the conveyor system or other transport systems.

[0092] [Table 3]

[0093]

[0094] (Example 4)

[0095] The on-furnace charging of scrap iron after dephosphorization was studied. The amount of scrap iron charged from the scrap iron chute (pre-charged scrap iron amount) was set below the upper limit obtained from equation (1) above, and then only one on-furnace charging of scrap iron was performed after the start of treatment. The molten iron temperature before dephosphorization was 1250-1260°C, and the upper limit of the pre-charged scrap iron amount obtained from equation (1) above was 14.5-15.6%. The on-furnace charging time of scrap iron was set at 65-75% of the blowing progress. The results are shown in Table 4.

[0096]

[0097] According to the results in Table 4, by meeting any one or both of the following conditions, such as the carbon concentration in the scrap iron fed into the furnace being 0.3% by mass or more, and the temperature of the molten iron after dephosphorization being 1380°C or more, the melting residue of the scrap iron can be suppressed even when the scrap iron is fed into the furnace halfway through the dephosphorization process.

[0098] In the above embodiments, an example of processing using molten iron tapped from a blast furnace and a cold iron source (scrap iron) is shown, but the molten iron is not limited to molten iron tapped from a blast furnace. The present invention is equally applicable to molten iron obtained by a blast furnace, induction melting furnace, electric arc furnace, etc., or to molten iron obtained by mixing such molten iron with molten iron tapped from a blast furnace.

[0099] Industrial applicability

[0100] As for the converter steelmaking method of the present invention, this technology can be applied in any method that uses a cold iron source to refine molten iron in a converter to obtain molten steel, and therefore it is useful in industry.

Claims

1. A converter steelmaking method, comprising: The process involves adding auxiliary materials to the cold iron source and molten iron before dephosphorization contained in a converter-type vessel, and supplying oxidizing gas to perform dephosphorization treatment on the molten iron before dephosphorization, obtaining dephosphorized molten iron, and then tapping the obtained dephosphorized molten iron into a molten iron receiving vessel and maintaining it in the molten iron receiving vessel; and... The dephosphorized molten iron, held in the molten iron receiving container, is then transferred to a first converter-type container that has undergone the dephosphorization treatment, or to a second converter-type container different from the first converter-type container, and oxidizing gas is supplied for decarburization treatment to obtain molten steel. In the dephosphorization process, a first chill source in an amount satisfying the following formula (1) is loaded into the first converter-type vessel at one time, and then the molten iron before dephosphorization is loaded to perform the dephosphorization process. In the decarburization process, a second chill source is loaded into either the first converter-type vessel that has undergone the dephosphorization process, or a second converter-type vessel different from the first converter-type vessel, in one go. Then, the dephosphorized molten iron, which is held in the molten iron receiving vessel, is loaded into the vessel to perform the decarburization process. %IN s0 ≤0.1186T-134 (%W s0 ≥0) ···(1) In the formula, %W s0 The percentage (%) of the first chill source charge relative to the sum of the first chill source charge and the molten hot metal charge before dephosphorization. T: Temperature of molten iron before dephosphorization (°C) In the dephosphorization process, a third chill source is introduced from the furnace of the converter-type vessel into the converter-type vessel, and the timing of the addition of the third chill source is set at the moment when the temperature of the molten iron rises due to the melting of the chill source already added to the furnace, and either or both of the following conditions are met: the carbon concentration in the third chill source is 0.3% by mass or more, and the temperature of the molten iron after dephosphorization is 1380°C or more.

2. The converter steelmaking method according to claim 1, wherein, In either or both of the dephosphorization and decarburization processes, the third chill source is successively introduced from the furnace of the converter-type vessel into the converter-type vessel in an amount satisfying the following formula (2). IN sadd ≤2.4t add ···(2) In the formula, W sadd : Input amount of chilled iron source (t), t add The first feeding into the furnace refers to the time (in minutes) from the start of blowing to the start of the first feeding. From the second time onwards, the time (in minutes) from the completion of the previous feeding to the start of the next feeding is used when feeding is added to the furnace.

3. The converter steelmaking method according to claim 1 or 2, wherein, The longest dimension of the third chill source fed from the furnace of the converter-type vessel is 100 mm.

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