KR102406956B1 - How to dephosphorize a chartered boat - Google Patents

Abstract

The method of dephosphorization of molten iron according to an aspect of the present invention includes a step of measuring the Si content in the initial component of the molten iron, a step of putting a first dephosphorization agent into the molten iron, and a step of dephosphorizing the molten iron In the process of dephosphorization and blow tempering, a powdery second dephosphorization agent is further thrown into the molten iron, and the start of the input of the second dephosphorization agent is 0.10 mass% or less by the dephosphorization blow and tempering of the Si content of the molten iron. It is set as after the time of setting it as , and before making into 3.0 Nm<3>/t the blowing-in amount of the said oxygen with respect to the said molten iron|metal after the said time.

Description

How to dephosphorize a chartered boat

The present invention relates to a method of dephosphorization of molten iron.

This application claims priority based on Japanese Patent Application No. 2018-040784 for which it applied to Japan on March 7, 2018, The content is used here.

Since P (phosphorus) contained in molten iron adversely affects various properties of steel such as strength, toughness and elongation, it is necessary to reduce it as much as possible in the steel refining step.

The process of removing P from molten iron is called dephosphorization refining, and in this dephosphorization refining, a dephosphorization agent, a compound containing CaO (or CaCO ₃ ) as a main component, is used. A dephosphorization agent contributes to dephosphorization by producing|generating the slag which has dephosphorization ability in dephosphorization refining. The more the amount of the dephosphorization agent used, the higher the basicity of the slag, the better the dephosphorization ability of the slag. However, if the amount of the dephosphorization agent used is large, the amount of slag also increases. Slag has a high environmental load, and its treatment increases refining costs. Therefore, it is desired to reduce the amount of the dephosphorization agent used by making the dephosphorization process efficient.

Patent Document 1 discloses a method for dephosphorizing molten iron that can reduce the amount of spitting and make the [P] concentration in the molten iron into 0.020% or less. In this dephosphorization method, after gas-stirring the molten iron in which the CaO-containing material which is a 1st dephosphorization agent was injected|thrown-in from the top of a converter, and oxygen-containing gas was taken up and cover slag was produced|generated, molten iron|metal preliminary|backup dephosphorization was performed, and further, molten iron|metal is 2nd Let the CaO containing dephosphorization agent which is a dephosphorization agent be sprayed using oxygen-containing gas as a carrier gas. However, in patent document 1, reducing the amount of slag is not made into a subject, and there is also no indication of the method.

Patent Document 2 discloses a converter refining method capable of stably smelting very low tough steel with particularly strict P standards while enjoying the advantages of performing dephosphorization refining and decarburization refining in the same converter. In this converter refining method, after the first dephosphorization refining and subsequent slag removal, flux is added to perform a second dephosphorization refining before decarburization refining, followed by slag removal, and then decarburization refining It is considered that the P concentration in the molten steel after completion of the decarburization refining can be sufficiently reduced to a very low P steel level. However, in patent document 2, improving the dephosphorization efficiency in each dephosphorization refining is not examined, and there is also no indication of the method.

Patent Document 3 discloses a method of efficiently performing preliminary dephosphorization for molten iron using a solvent containing no F source such as CaF ₂ in the dephosphorization treatment performed as a preliminary treatment for molten iron. This method is a manufacturing method of low phosphorus molten iron, and in the dephosphorization treatment performed as a preliminary treatment for molten iron, by supplying an oxygen source to the molten iron before adding the masonry agent that is the source of CaO to the molten iron, the iron oxide concentration in the slag is raised, and then, the mason agent that is the source of CaO is added to the molten iron It is characterized in that it is added. However, in the technique of patent document 3, it is essential to make a maeyong agent into a lump, and to add this little by little. That is, in the technique of the patent document, since the maeyong agent is added intermittently, the basicity of slag cannot be stabilized. Moreover, in the technique of patent document 3, since it is essential to make the Si concentration of molten iron|metal into 0.10 wt% or less before starting a dephosphorization process, the desiliconization process of molten iron|metal becomes essential prior to a dephosphorization process, and manufacturing efficiency is bad.

Japanese Patent Laid-Open No. 2001-64713 Japanese Patent Laid-Open No. 2011-144415 Japanese Patent Laid-Open No. 2002-309310

In order to sufficiently dephosphorize the molten iron without increasing the amount of dephosphorization agent used and the amount of slag generated, the sludge rate of the dephosphorization agent is high and the dephosphorization method of the molten iron is excellent in dephosphorization efficiency.

The gist of the present invention is as follows.

(1) The method of dephosphorization of molten iron according to an aspect of the present invention comprises a step of measuring the Si content in an initial component of the molten iron, a step of introducing a first dephosphorization agent into the molten iron, and oxygen to the molten iron The process of dephosphorizing the said molten iron by blowing is provided, During the process of dephosphorizing and blowing, a powdery 2nd dephosphorizing agent is further thrown into the said molten iron|metal, and the injection start of the said 2nd dephosphorization agent is the said Si content of the said molten iron|metal. Let it be after the time of making 0.10 mass % or less by the said dephosphorization blow temper, and before making into 3.0 Nm<3>/t the blowing amount of the said oxygen with respect to the said molten iron|metal after the said time.

(2) In the method of dephosphorization of molten iron according to (1) above, the ratio of the CaO equivalent amount of the first dephosphorization agent and the SiO ₂ equivalent amount of the Si content in the initial component of the molten iron may be 0.60 to 2.00. .

(3) In the method of dephosphorizing molten iron according to (1) or (2), the input amount of the second dephosphorization agent is adjusted such that the charged basicity of the slag at the end of the dephosphorization and refining of the molten iron is 1.3 to 4.0 You can control it.

(4) In the method of dephosphorization of molten iron according to any one of (1) to (3) above, one or both of the first dephosphorization agent and the second dephosphorization agent are added to quicklime, limestone, calcium ferrite, and dolomite-based lime , and converter slag or secondary refining slag, containing at least one selected from the group consisting of CaO, and the total content of CaO, CaCO ₃ and CaF ₂ equivalent to CaO may be 30 to 100% by mass. .

(5) In the dephosphorization method of molten iron|metal in any one of said (1)-(4), it is good also considering the said 1st dephosphorization agent as a bulk dephosphorization agent.

(6) In the method of dephosphorizing molten iron according to any one of (1) to (5), the second dephosphorization agent is at least one carrier selected from the group consisting of Ar, N ₂ , CO ₂ and O ₂ You may blow into the said molten iron|metal using gas.

(7) In the dephosphorization method of molten iron|metal in any one of said (1)-(6), 0.25 mass % or more may be sufficient as Si content in the said initial component of the said molten iron|metal.

ADVANTAGE OF THE INVENTION According to this invention, since the sludge rate of a dephosphorization agent is high and it is excellent in the dephosphorization efficiency of molten iron|metal, the dephosphorization method of molten iron|metal which can fully dephosphorize without increasing slag amount can be provided.

1 is a CaO—SiO ₂ —Fe _t O ternary phase diagram.
It is a schematic diagram which shows the change of Si content of molten iron|metal in dephosphorization refining, and the injection|throwing-in time of a 2nd dephosphorization agent.
It is a figure which shows an example of the injection|throwing-in location of a 2nd dephosphorization agent.
4 is a graph showing the relationship between the input timing of the second dephosphorization agent and the dephosphorization rate.
5 is a graph showing the relationship between the input timing of the second dephosphorization agent and the sludge rate.
6 is a graph showing the relationship between the input timing of the second dephosphorization agent and the sludge formation rate.

The present inventors repeated examination about improving the dephosphorization ability of dephosphorization refining (that is, improving the dephosphorization efficiency of dephosphorization refining) without increasing the amount of slag. Specifically, the present inventors studied means for improving the sludge rate of the dephosphorization agent injected into the molten iron during dephosphorization refining. In addition, in this embodiment, the sludge _- ization of a dephosphorization agent means that CaO and/or CaCO3 of a dephosphorization agent melt and become slag. In this embodiment, the sludge formation rate refers to the basicity after dephosphorization (value obtained by measuring the basicity of the slag collected after completion of the dephosphorization blow) to the charging basicity (the molten iron and Si of the additive are all SiO ₂ , and CaO of the dephosphorization agent introduced ( Or CaCO ₃ ) is a value defined as a value divided by slag basicity) in the case where it is assumed that all of it is molten CaO. In addition, "actual charging basicity" is a value obtained by measuring the component of slag, ie, an actual value. The sludge formation rate is an index indicating the degree of melting of CaO and/or CaCO ₃ in the dephosphorization agent. The basicity of slag is ratio of the amount of molten CaO in slag and _the amount of molten SiO2, and is computed by following formula A.

Basicity of slag = amount of molten CaO in slag / amount of molten SiO ₂ in slag: formula A

_A dephosphorization agent is a compound which has CaO (or CaCO3 etc.) as a main component. CaCO ₃ contained in the dephosphorization agent is decomposed within a short time by the heat of molten iron to become CaO and CO ₂ . Examples of the dephosphorization agent include quicklime, limestone, and absence of dolomitic lime, converter slag, secondary refining slag, and the like and containing CaO and the like, and mixtures thereof. The following chemical reactions occur during dephosphorization blow tempering (blowing oxygen into molten iron for dephosphorization) by CaO (including CaO derived from CaCO ₃ etc., the same hereinafter) contained in the dephosphorization agent.

2[P]+5(FeO) → (P ₂ O ₅ )+5[Fe]: formula B

(P ₂ O ₅ )+3(CaO) → (3CaO·P ₂ O ₅ ): Formula C

The formulas enclosed in brackets, described in formulas B and C, are the formulas of the components in the molten iron, and the formulas enclosed in parentheses are the formulas of the components in the slag. In dephosphorization blow tempering, as shown in Formula B, [P], ie, P in molten iron, is oxidized by (FeO), ie, FeO in slag, and becomes P ₂ O ₅ . Next, as shown in Formula C, this P ₂ O ₅ is fixed to (CaO), that is, molten CaO in the slag to form a stabilized compound (3CaO·P ₂ O ₅ ). As shown in Equations B and C, (CaO) is very important for dephosphorization.

As a means for increasing the amount of molten CaO in the slag, it is conceivable to increase the amount of the dephosphorization agent added to the molten iron. However, an increase in the input amount of the dephosphorization agent causes an increase in the amount of slag, thereby increasing the environmental load of the dephosphorization refining. In order to increase the amount of molten CaO in the slag while suppressing the input amount of the dephosphorization agent, it is necessary to increase the sludge rate of the dephosphorization agent to be charged as much as possible. The higher the sludge rate, the higher the ratio of the amount of molten CaO in the slag to the input amount of the dephosphorization agent, so that the dephosphorization can be performed with high efficiency.

As a result of repeated studies, the present inventors put the first dephosphorization agent into the molten iron before the start of the dephosphorization blow tempering, and after a certain period of time after the start of the dephosphorization blow tempering, the second dephosphorization agent is put into the molten iron. The sludge formation rate of the dephosphorization agent was found to be significantly improved. This phenomenon is presumed to be caused by the following mechanism.

1 is a CaO—SiO ₂ —Fe _t O ternary phase diagram. CaO of the dephosphorization agent is initially CaO located at the lower left of the ternary phase diagram of FIG. 1 . Since this CaO has a comparatively high melting|fusing point, it exists in an unmelted state in slag. However, in dephosphorization refining, when dephosphorization blow tempering is performed, Si in molten iron|metal will be oxidized _and SiO2 density|concentration in slag will rise. As the SiO ₂ concentration increases, CaO of the dephosphorization agent becomes a ternary compound of CaO-SiO ₂ -Fe _t O. That is, CaO of the dephosphorization agent moves from the lower left to the center of FIG. 1 along the arrow. The melting point of the compound located in the center of FIG. 1 is lower than the melting point of CaO. Therefore, it becomes easy to melt|dissolve CaO of a dephosphorization agent with a raise _of SiO2 density|concentration.

At the time of the start _of dephosphorization blow tempering, SiO2 hardly exists in slag. Therefore, it is estimated that the first dephosphorization agent is hardly melted at the time of the start of dephosphorization blow tempering, and if the second dephosphorization agent is added at this stage, the first dephosphorization agent is not sufficiently melted. After that, even if the amount of SiO ₂ in the slag increases with the progress of the dephosphorization blow, it is considered that the unmelted product of the first dephosphorization agent remains in the slag and the sludge formation rate is lowered. On the other hand, when the input of the second dephosphorization agent is waited until SiO ₂ is sufficiently generated, the second dephosphorization agent is added in a state in which the sludge of the first dephosphorization agent is advanced, so that both the first and second dephosphorization agents are sufficiently sludge. I think it will be pissed off.

The method of dephosphorization of molten iron according to this embodiment based on the technical idea described above includes a process of measuring the Si content of molten iron, a process of injecting a first dephosphorization agent into the molten iron, and a process of dephosphorizing and blowing the molten iron, In the process of dephosphorization blow tempering, a 2nd dephosphorization agent is further thrown into molten iron, and, at the start time of the input of the 2nd dephosphorization agent, after the Si content of molten iron becomes 0.10 mass % or less by dephosphorization blow tempering, the oxygen blowing amount with respect to molten iron|metal It should be between 3.0Nm3/t and 3.0Nm3/t. Hereinafter, the dephosphorization method of the molten iron|metal which concerns on this embodiment is demonstrated in detail.

In the dephosphorization method of molten iron|metal which concerns on this embodiment, Si content of the initial stage component of molten iron|metal is measured first. The measured value of the Si content of the initial component of molten iron|metal is considered necessary in order to determine the injection|throwing-in timing of the 2nd dephosphorization agent. In addition, the measured value of Si content of the initial stage component of molten iron|metal may be used in order to determine the input amount of a 1st dephosphorization agent. You may measure content of elements other than Si of molten iron|metal for estimation of slag basicity at the time of the completion|finish of dephosphorization blow tempering mentioned later. In addition, the initial component of molten iron means the component of molten iron|metal before dephosphorization blow temper. Measurement of Si content of molten iron|metal, etc. may be performed, after inserting molten iron|metal into a furnace, and may be performed before that. Furthermore, carrying out the above-mentioned measurements when the molten iron is in a solidified state (ie in the form of pig iron) is of course not impeded.

Although Si content in the initial stage component of molten iron|metal is not specifically limited, It is preferable to set it as 0.25 mass % or more. As mentioned above, CaO of _a dephosphorization agent becomes easy to melt|melt with SiO2 density|concentration rising during dephosphorization blow temper. That is, in the dephosphorization method of molten iron|metal which concerns on this embodiment, it is preferable to raise _the SiO2 concentration in slag from a viewpoint of further promoting sludge formation. Therefore, it is preferable that a certain amount of Si is contained in the initial component of molten iron|metal before the start of dephosphorization blow temper. Therefore, it is preferable that Si content of molten iron|metal before blowing in oxygen is 0.25 mass % or more. It is good also considering Si content in the initial stage component of molten iron|metal as 0.27 mass % or more, 0.30 mass % or more, or 0.32 mass % or more.

Next, the first dephosphorization agent is put into the molten iron. The form and input amount of the first dephosphorization agent are not particularly limited, and may be appropriately set according to the target values of the component of molten iron and the component of steel. It is preferable that the form of a 1st dephosphorization agent is a lump form from a viewpoint of preventing input loss.

In addition, the input amount of the first dephosphorization agent is the ratio of the CaO equivalent amount of the first dephosphorization agent and the Si equivalent amount of the Si content in the initial component of molten iron (that is, CaO equivalent amount of the first dephosphorization agent/Si content of the initial component of molten iron) of SiO ₂ equivalent) is preferably controlled to be 0.60 to 2.00. CaO equivalent of a dephosphorization agent is CaO content of a dephosphorization agent at the time of assuming that all Ca in a dephosphorization agent forms CaO. _The SiO2 equivalent of Si content in the initial stage component of molten iron|metal is SiO2 quantity at the time _of assuming that all Si _of molten iron|metal became SiO2. When the above conditions are satisfied and the first dephosphorization agent is added, the basicity of the slag is approximately 0.60 to 2.00 at the time when Si in the molten iron is substantially all SiO ₂ due to the progress of the dephosphorization blow.

By making ratio of CaO equivalent amount of a _1st dephosphorization agent and SiO2 equivalent amount of Si content in the initial stage component of molten iron|metal into 0.60 or more, dephosphorization can be performed at a high level. This is considered to be because the dephosphorization ability of the slag can be improved by sufficiently supplying molten CaO in the slag. On the other hand, by making the ratio of the CaO equivalent amount of the first dephosphorization agent and the SiO ₂ equivalent amount of the Si content in the initial component of molten iron into 2.00 or less, the sludge rate of CaO can be maintained high, and the dephosphorization efficiency can be maintained even higher. More preferably, ratio of CaO equivalent amount of a _1st dephosphorization agent and SiO2 equivalent amount of Si content in the initial stage component of molten iron|metal is 0.80 or more, 0.85 or more, or 0.90 or more. More preferably, ratio of CaO equivalent amount of a _1st dephosphorization agent and SiO2 equivalent amount of Si content in the initial stage component of molten iron|metal becomes 1.50 or less, 1.20 or less, 1.15 or less, or 1.10 or less.

In addition, when Si is separately added to molten iron before the start of dephosphorization blow tempering, and when Si is included in the first dephosphorization agent, etc., when the SiO ₂ source of slag is not limited to molten iron, Si derived from other than molten iron is also 1 This should be taken into account when determining the dosage of dephosphorization agent. For example, in the case of recycling use of the slag produced by dephosphorization refining in another dephosphorization refining for reduction of dephosphorization agent usage _- amount, the SiO2 source derived from molten iron|metal arises other than molten iron|metal. In this case, what is necessary is just to include Si derived other than molten iron|metal in "the SiO2 equivalent _of Si content in the initial stage component of molten iron|metal". That is, the charging amount of the first dephosphorization agent and other additives may be controlled so that the estimated value of basicity based on the charging amount of the slag at the end of the Si oxidation reaction in dephosphorization blow tempering becomes 0.60-2.00.

Next, the molten iron is dephosphorized and blown. Dephosphorization blow tempering is performed by blowing in oxygen to molten iron|metal. This dephosphorization blow temper WHEREIN: A 2nd phosphorus dephosphorization agent is thrown in to molten iron|metal. This dephosphorization blow temper WHEREIN: The timing of the injection|throwing-in start of a 2nd dephosphorization agent is controlled so that it may demonstrate below.

After the start of the input of the second dephosphorization agent to the molten iron, the Si content of the molten iron is made 0.10 mass% or less by dephosphorization blowing, and the amount of oxygen blown into the molten iron after this time is 3.0 Nm 3 /t do it between Here, "Nm3/t" is the amount of oxygen blowing per ton of molten iron (Nm3). The input start time of the 2nd dephosphorization agent with respect to molten iron|metal is shown in FIG. 2 : is a graph which shows typically a mode that Si content of molten iron|metal falls as blowing of oxygen in dephosphorization blow tempering advances, The vertical axis of the graph shows Si content (mass %) of molten iron|metal, and the horizontal axis shows oxygen represents the blowing amount (Nm3/t) for molten iron. The hatched area|region of FIG. 2 is the injection|throwing-in start timing of the 2nd dephosphorization agent with respect to the molten iron|metal in the dephosphorization method of the molten iron|metal which concerns on this embodiment.

It is necessary to make the injection|throwing-in start timing of the 2nd dephosphorization agent with respect to molten iron|metal after the time when Si content of molten iron|metal fell sufficiently by dephosphorization blow tempering, ie, the time when Si content of molten iron|metal fell to 0.10 mass % or less. When the input of the second dephosphorization agent is started before the Si content of the molten iron is sufficiently reduced, SiO ₂ in the slag is insufficient, and the second dephosphorization agent is introduced before the first dephosphorization agent is sufficiently melted, so that the dephosphorization agent is melted Due to this disturbance, the sludge formation rate is lowered, and the dephosphorization efficiency is impaired. You may do it after the time when Si content of molten iron|metal fell to 0.05 mass % or less, or 0.01 mass % or less, as for the injection|throwing-in start timing of the 2nd dephosphorization agent with respect to molten iron|metal.

On the other hand, the injection of the second dephosphorization agent to the molten iron is carried out after the time when the Si content of the molten iron is reduced to 0.10 mass% or less, and continues to blow oxygen until the blowing amount becomes 3.0 Nm 3 /t have to start If the input of the second dephosphorization agent to the molten iron is delayed, the dephosphorization efficiency is impaired. This is presumed to be because dephosphorization blow tempering proceeds in a state in which molten CaO in the slag having an action of stabilizing unstable P ₂ O ₅ is insufficient. Preferably, the input of the second dephosphorization agent to the molten iron is 2.5Nm3/t, 2.0Nm3/t, or 1.5Nm3/t of oxygen from the point in time when the Si content of the molten iron is reduced to 0.10 mass% or less. is started in between. In addition, the time when the Si content of molten iron fell to 0.10 mass % or less is estimated by a conventional method from the initial component of molten iron, the components and amounts of additives such as the first dephosphorization agent, and the amount of oxygen injected into the molten iron. can do. Moreover, although it is generally difficult, if it is possible to measure in real time the change of Si content of molten iron|metal during dephosphorization blow tempering, the measurement of Si content of the initial stage component of molten iron|metal can also be abbreviate|omitted.

The input amount of the second dephosphorization agent is not particularly limited, and may be appropriately set according to the target value of the component of the molten iron and the component of the steel. The form of the second dephosphorization agent is in powder form. By making a 2nd dephosphorization agent into a powder phase, it becomes possible to inject|throw-in a 2nd dephosphorization agent continuously in molten iron|metal through the carrier gas injected from a lance. It becomes possible to suppress the rapid change of slag basicity by continuous injection|throwing-in of a 2nd dephosphorization agent. By stabilizing the basicity of the slag, the operation can be stabilized by preventing the occurrence of a sudden slag forming phenomenon. Moreover, by making a 2nd dephosphorization agent into a powder phase, the sludge formation rate of a 2nd dephosphorization agent can be improved, and it can also make it easy to control the composition of slag. In this case, it is preferable that a powdery 2nd dephosphorization agent is blown into molten iron|metal using carrier gas.

It is preferable that the input amount of the second dephosphorization agent is controlled so that the charged basicity of the slag at the end of the process of dephosphorizing and refining molten iron is 1.3 to 4.0. More preferably, the input amount of the second dephosphorization agent is controlled so that the charged basicity of the slag at the end of the process of dephosphorizing and refining the molten iron is 1.3 to 3.0.

A linear relationship is seen between the charged basicity of the slag after the second dephosphorization agent is added, and the slag basicity and the dephosphorization rate after dephosphorization. There exists a tendency for slag basicity and dephosphorization rate to improve after dephosphorization, so that this charging basicity is large. When the input amount of the second dephosphorization agent is controlled so that the charged basicity of the slag at the end of the dephosphorization refining process is 1.3 or more, the dephosphorization ability of the slag can be further improved and dephosphorization of molten iron can be performed at a high level. The input amount of the second dephosphorization agent may be controlled so that the charged basicity of the slag at the end of the dephosphorization refining process becomes 1.5 or more, 2.0 or more, or 2.5 or more. On the other hand, when the input amount of the second dephosphorization agent is controlled so that the charged basicity of the slag at the end of the dephosphorization refining process is 4.0 or less, the increase in the amount of slag is suppressed to maintain the dephosphorization efficiency even higher, and the dephosphorization process environment The load can be further reduced. The input amount of the second dephosphorization agent may be controlled so that the charged basicity of the slag at the end of the dephosphorization refining process becomes 3.5 or less, 3.0 or less, 2.8 or less, or 2.3 or less. In addition, the input amount of the second dephosphorization agent at which the charged basicity of the slag becomes 1.3 to 4.0 at the end of the dephosphorization refining process of the molten iron is the initial component of the molten iron, the component of the second dephosphorization agent, and the first dephosphorization agent by a conventional method. It can be estimated from the components and input amount of additives such as phosphorus, and the amount of oxygen blown into the molten iron. The optimal input amount of the second dephosphorization agent is affected by the various conditions described above, and it is considered that it is often 1.0 to 5.0 t under normal conditions.

The types of the first dephosphorization agent and the second dephosphorization agent are not particularly limited as long as the basicity of the slag can be controlled as described above. For example, quicklime, limestone, calcium ferrite, dolomitic lime, and converter slag or secondary refining slag and containing at least one selected from those containing CaO, in CaO equivalent amounts of CaO, CaCO ₃ and CaF ₂ What is 30-100 mass % of total content of can be used as one or both of a 1st dephosphorization agent and a 2nd dephosphorization agent.

As long as the above requirements are satisfied, the method of dephosphorizing the molten iron according to the present embodiment may include an additional step. For example, the molten iron after dephosphorization may be further subjected to decarburization refining, and this decarburization refining may be performed continuously in a furnace subjected to dephosphorization refining, or may be performed in a furnace different from the dephosphorization refining furnace.

Moreover, the apparatus for implementing the dephosphorization method of molten iron|metal which concerns on this embodiment is not specifically limited, either. From what the present inventors discovered, the top-bottom blow converter 1 which has a lance for blowing in the powdery 2nd dephosphorization agent 5 using carrier gas illustrated in FIG. 3, for example in this embodiment It is preferable to carry out the dephosphorization method of the molten iron according to the When performing dephosphorization refining of molten iron using the top-bottom odor converter 1, it is to inject the 2nd dephosphorization agent 5 into and near the lance 4 which blows the top-blowing oxygen 6 into molten iron|metal. desirable. Immediately below and in the vicinity of the lance 4 is a region which is extremely high due to oxidation heat of Si and C in the molten iron, that is, the ignition point 7 . By injecting the second dephosphorizing agent 5 into this region, the second dephosphorizing agent 5 can be melted more efficiently. In addition, in FIG. 3, although the embodiment which blows in the 2nd dephosphorization agent 5 using the lance 4 which blows in the upper breath oxygen 6 is shown, for blowing in the 2nd dephosphorization agent 5 You may provide another lance in the top-bottom odor converter 1 . In addition, the total refining time is shortened by using a top-bottom odor converter and converter refining in which dephosphorization refining, slag removal and decarburization refining are performed in the same converter, thereby further reducing the amount of dephosphorization agent used, and heat loss in refining It becomes possible to reduce

The kind of carrier gas used when the powdery second dephosphorization agent is blown into the molten iron is also not particularly limited, and for example, one or more gases selected from the group consisting of Ar, N ₂ , CO ₂ and O ₂ may be used as carrier gas. can be used as Considering cost, stability of equipment, etc., it is considered that blowing of the second dephosphorization agent using N ₂ gas is preferable. In the molten iron in the stage of dephosphorization blow tempering, since the content of C having an action to prevent the introduction of N into the molten iron is high, even if the second dephosphorization agent using N ₂ is blown into the molten iron, the amount of N introduced into the molten iron is negligible. I think it would be small enough.

Example

In the dephosphorization step, the powdery second dephosphorization agent was blown in at any of the following steps. Hereinafter, the time when Si content of molten iron|metal became 0.10 mass % or less by dephosphorization blow tempering is called "at the time of Si desorption completion|finish".

Step 1 (Comparative Example): 40 seconds before completion of deSi

2nd step (comparative example): 20 seconds before completion of deSi

3rd step (invention example): immediately after completion of deSi

4th step (invention example): 20 seconds after completion of deSi

In addition, in the above-described fourth step, before the amount of oxygen blown into the molten iron after Si deSi is completed is set to 3.0 Nm 3 /t.

In addition, operating conditions other than the timing of blowing in of a 2nd dephosphorization agent are as follows.

・Form of the first dephosphorization agent: a mixture of bulk, quicklime, limestone and converter slag (CaO equivalent: 25% by mass or more)

・Form of the second dephosphorization agent: powdered quicklime

-Ratio of CaO equivalent amount of a 1st dephosphorization agent, and SiO2 equivalent amount of Si content in the initial stage component of molten iron|metal: In the range _of 0.60-2.00

・Carrier gas type: N ₂

The experimental results are shown in Tables 1 to 4 and FIGS. 4 to 6 . The values shown in Tables 1 to 4 are experimental results in each of the first to fourth steps. The column "Lump CaO" and the column "powder CaO" show the input amount of each of the first dephosphorization agent and the second dephosphorization agent. "Initial component Si content" is Si content in the initial stage component (component before a dephosphorization blow tempering start) of molten iron|metal. 4 to 6 are graphs of data shown in Tables 1 to 4.

The horizontal axis of the graph shown in FIG. 4 is the charging basicity (slag basicity when it is assumed that all Si of the molten iron and the additive becomes SiO ₂ and the Ca of the first and second dephosphorization agents are all molten CaO), The vertical axis is the dephosphorization rate. The dephosphorization rate is the amount of decrease in the P content by dephosphorization blow tempering (the value obtained by subtracting the measured value of the P content of the molten iron after dephosphorization blow tempering from the measured value of the P content of the molten iron before dephosphorization blow tempering), the measured value of the P content of the molten iron before dephosphorization blow tempering It is the value divided by , that is, the calculated value in the following formula.

Dephosphorization rate = ([P]i-[P]f)/[P]i

In the said formula, [P]i is a measured value of P content of molten iron|metal before dephosphorization blow tempering, and [P]f is a measured value of P content of molten iron|metal after dephosphorization blow tempering.

The horizontal axis of the graph shown in FIG. 5 is the charging basicity, and the vertical axis is the slag basicity after dephosphorization (a value obtained by measuring the basicity of the slag collected after the dephosphorization blow and tempering). 6 : is a graph which shows the average sludge formation rate in a 1st step - a 4th step. As described above, the value obtained by dividing the slag basicity by the charging basicity after dephosphorization is the sludge rate, and the average value of the sludge rate in each of the first to fourth stages is the average sludge rate of each of the first to fourth stages, have.

As shown in FIG. 4 , the dephosphorization rate of the invention example was significantly improved compared to the comparative example by the conventional dephosphorization method. In addition, as shown in Figs. 5 and 6, the sludge formation rate of the invention example was significantly improved compared to the comparative example by the conventional dephosphorization method.

In the dephosphorization method of molten iron|metal which concerns on this invention, the sludge rate of a dephosphorization agent is high, and it is excellent in the dephosphorization efficiency of molten iron|metal. Therefore, the method of dephosphorizing molten iron according to the present invention can sufficiently dephosphorize the molten iron without increasing the amount of slag, so that high-grade steel with a low P content can be manufactured with a low environmental load. For the reasons described above, the present invention has extremely high industrial applicability.

1: converter
2: Charter
3: slag
4: Lance
5: Second dephosphorization agent
6: top breath oxygen
7: fire point

Claims (8)

It is a method of dephosphorization of chartered ships,
a step of measuring the Si content in the initial component of the molten iron;
A step of adding a first dephosphorization agent to the molten iron;
Process of dephosphorizing and blowing the molten iron by blowing oxygen into the molten iron
to provide
In the process of dephosphorization blowing, a powdery second dephosphorization agent is further added to the molten iron,
After the start of the input of the second dephosphorization agent, the Si content of the molten iron was made 0.10 mass% or less by the dephosphorization blow and tempering, and the blowing amount of the oxygen to the molten iron after the time point was 3.0 Nm 3 / before doing t
A method of dephosphorization of molten iron, characterized in that. According to claim 1,
The ratio of the CaO equivalent amount of the said _1st dephosphorization agent and the SiO2 equivalent amount of the said Si content in the said initial component of the said molten iron|metal shall be 0.60-2.00, The dephosphorization method of molten iron|metal characterized by the above-mentioned. 3. The method of claim 1 or 2,
The method of dephosphorization of molten iron characterized in that the input amount of the second dephosphorization agent is controlled so that the charged basicity of the slag at the end of the step of dephosphorizing the molten iron is 1.3 to 4.0. 3. The method of claim 1 or 2,
One or both of the first dephosphorization agent and the second dephosphorization agent include at least one selected from quicklime, limestone, calcium ferrite, dolomite-based lime, and converter slag or secondary refining slag and containing CaO and the total content of CaO, CaCO ₃ and CaF ₂ equivalent in CaO is 30 to 100 mass %, The method of dephosphorization of molten iron characterized by the above-mentioned. 3. The method of claim 1 or 2,
The method of dephosphorization of molten iron, characterized in that the first dephosphorization agent is a bulk dephosphorization agent. 3. The method of claim 1 or 2,
The method of dephosphorizing the molten iron, characterized in that the second dephosphorization agent is blown into the molten iron using at least one carrier gas selected from the group consisting of Ar, N ₂ , CO ₂ and O ₂ . 3. The method of claim 1 or 2,
Si content in the said initial component of the said molten iron|metal is 0.25 mass % or more, The dephosphorization method of molten iron|metal characterized by the above-mentioned. The apparatus according to claim 1 or 2, wherein the apparatus for performing the dephosphorization method of molten iron is a top-bottom blow converter provided with a lance for blowing in the oxygen and a lance for blowing in the second dephosphorization agent,
The method of dephosphorizing the molten iron, characterized in that the second dephosphorization agent is blown into the molten iron using at least one carrier gas selected from the group consisting of Ar, N ₂ and CO ₂ .

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