TWI609839B - Dephosphorization agent, refining agent and dephosphorization method for molten iron - Google Patents

Abstract

A dephosphorizing agent for molten iron, which contains 2-20% by mass of Al ₂ O ₃ , and the remaining part is calcium ferrite and impurities; and, the ratio of (Al ₂ O _{3 by} mass) / (CaO by mass) is 0.04 ~ 0.5. A refining agent containing the dephosphorizing agent is added to the converter to perform dephosphorization treatment of molten pig iron.

Description

Dephosphorizing agent, refining agent and dephosphorizing method for molten iron

FIELD OF THE INVENTION The present invention relates to a method for dephosphorizing molten pig iron using a top-bottom blowing converter, and to a dephosphorizing agent, refining agent and dephosphorizing method for molten iron, which is characterized in that In a short refining step, the low-phosphorus steel can still be melted efficiently.

Background of the Invention In recent years, the demand for steel materials has been heightened, and the demand for low-phosphorus steels is increasing. At present, the dephosphorization treatment of molten pig iron is based on a method of treatment under low temperature conditions of the molten pig iron stage which is thermodynamically favorable, and is generally widely carried out. The top-bottom blowing converter is more suitable as a device for dephosphorization of molten pig iron. This is because, as an oxidant necessary for dephosphorization, it is more likely that a gaseous oxygen with less heat loss will be sprayed on the molten pig iron from the top blowing lance at a high speed than a solid oxidation source.

Dephosphorization of molten pig iron is carried out under low temperature conditions in the stage of melting pig iron, so it is important to promote the slagging of CaO used as a dephosphorization agent. In the slagging of CaO, the use of fluorite (CaF ₂ ) is more effective, but when fluorite is used, the slag generated by the slagging of CaO will contain fluorine, so the object of slag recycling is greatly restricted The disadvantages are great. Therefore, a method for promoting CaO slag formation without using fluorite has been developed.

This method is known from Patent Documents 1 and 2, which is, for example, adding a refining agent containing calcium ferrite to molten pig iron that has been loaded in a top-bottom converter. Calcium ferrite is a dephosphorizing agent composed of compounds of CaO and Fe ₂ O ₃ ; compared with quicklime, which is generally used as a dephosphorizing agent for the dephosphorization process of molten pig iron, its melting rate for dephosphorizing slag is high , And can promote the dephosphorization reaction. In addition, Patent Document 3 discloses a dephosphorizing agent added with Na ₂ O to improve the meltability of calcium ferrite. In addition, Patent Document 4 discloses a slagging accelerator that contains any of alumina powder, iron oxide powder, soda ash, and soda glass powder in a refining flux containing quicklime powder of 50% by weight or more One.

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Publication No. 2013-163844 Patent Literature 2: Japanese Patent Publication No. 2013-064167 Patent Literature 3: Japanese Patent Publication No. 2012-12680 Patent Literature 4: Japanese Patent Publication Gazette 2001-348610

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION However, the general calcium ferrite disclosed in Patent Documents 1, 2 etc., which can be used for dephosphorization, has a liquidus temperature of about 1400 ° C, which is 1200 higher than the molten pig iron temperature in the converter ~ 1350 ℃ is high. This is considered to be the solid calcium ferrite dissolved in the liquid dephosphorization slag produced by the oxidation reaction of the oxygen supplied by the top blowing lance and the Si or Fe in the molten pig iron, in the case where the blowing time is short If the calcium ferrite is not sufficiently melted, dephosphorization will become insufficient, and in the state where [P] (mass% of P dissolved in steel) does not reach the target value, the blowing will be ended.

In addition, Patent Document 2 describes a technique of setting the blowing time to about 10 minutes, starting to add calcium ferrite after 35% of the total blowing time has elapsed, and after the whole blowing time has passed Added before 80%. However, in the case of blowing in a short time, for example, within 4 minutes, if the method of Patent Document 2 is used, there is a possibility that the melting of calcium ferrite is insufficient and the dephosphorization efficiency deteriorates.

In Patent Document 3, although a calcium ferrite containing Na ₂ O is described, a dephosphorization method using the same is not described, and a dephosphorization method suitable for a case where the blowing time is short is unknown. In addition, according to experiments conducted by the present inventors using a top-bottom blowing converter, when the dephosphorizing agent described in Patent Document 3 was used for blowing in a short time of about 4 minutes, calcium ferrite was insufficient. Melting, dephosphorization efficiency is also insufficient, and it is difficult to melt low phosphorus steel with [P] <0.02%.

In addition, as in Patent Document 4, the flux for refining mainly composed of quicklime powder cannot be sufficiently melted in a short time of about 4 minutes, and the dephosphorization efficiency is also insufficient. This is because the melting point of quicklime, alumina, iron oxide, etc. contained in the refining flux is high, and the melting speed of the entire refining flux is low.

In recent years, in order to improve the production efficiency of converters, and to shorten the time for dephosphorization of molten pig iron, it is required to melt low-phosphorus steel with a dephosphorization blowing time of, for example, about 4 minutes [P] <0.02%. In this context, everyone expects to develop a dephosphorization agent and dephosphorization method that can melt low-phosphorus steel even in a short period of blowing.

Means for solving the problem In order to solve the above-mentioned problems, the inventors conducted intensive studies and found one thing: to make calcium ferrite contain Al ₂ O ₃ and to further make these concentrations appropriate, so that even In a short period of time, the refining agent will still be fully melted, and the low-phosphorus steel can be efficiently melted. In addition to including Al ₂ O ₃ , it has been further studied to include SiO ₂ and Na ₂ O.

As a result, the following invention was conceived. (1) A dephosphorizing agent for molten iron, which contains 2-20% by mass of Al ₂ O ₃ , and the balance is calcium ferrite and impurities; and, (Al ₂ O _{3 by} mass%) / (CaO by mass%) The ratio is 0.04 ~ 0.5. (2) The dephosphorizing agent for molten iron as described in (1) further contains 1 to 10% by mass of SiO ₂ , and the ratio (SiO _{2 by} mass) / (CaO by mass) is 0.04 to 0.3. (3) The dephosphorizing agent for molten iron as described in any of (1) or (2) further contains (Na ₂ O mass%) / (Al ₂ O ₃ mass%) ratio of 0.1 to 2.0 Na ₂ O. (4) A refining agent containing the dephosphorizing agent as described in any one of (1) to (3). (5) A method of dephosphorization of molten iron, which is a method of adding a refining agent as described in (4) to a converter and performing dephosphorization treatment of molten pig iron; in which (CaO) / (SiO ₂ ) ratio is charged It is 1.3 ~ 2.0. (6) The method for dephosphorizing molten pig iron according to (5), wherein the mass of CaO contained in the calcium ferrite is 20% or more of the mass of CaO contained in the refining agent. (7) The method for dephosphorizing molten pig iron as described in (5), wherein the refining agent is charged into the converter before the molten pig iron is charged.

Further, the compound CaO and Fe ₂ O ₃ as the main component in the present invention is a so-called calcium ferrite, and refer to the ratio of CaO and Fe ₂ O ₃ at a mass ratio of 6: 4 ~ 3: 7, CaO The mass% and Fe ₂ O ₃ mass% total 70 mass% or more. In addition, calcium ferrite is produced by using quicklime and iron ore as raw materials, completely melting this mixture through a melting furnace, and after cooling, the powdery slag is about 1 to 50 mm in block form. In addition, the so-called low-phosphorus steel refers to steel with [P] of 0.02% or less at the casting stage, and the so-called efficient means that the melted calcium ferrite sufficiently contributes to dephosphorization. In addition, unless otherwise specified, the so-called short-term blowing refers to a blowing time of about 2 to 6 minutes.

The following is a description of the reasons and ideas for completing the above invention. The inventors added various compounds to CaO and Fe ₂ O ₃ and made them into various calcium ferrites completely melted by the melting furnace to improve the calcium ferrite in the dephosphorization process of the top-bottom blowing converter The meltability of the body. In addition, CaO, Fe ₂ O ₃ , and / or Al ₂ O _{3 are} mixed and formed into pellets at room temperature (hereinafter referred to as pellets). Next, the calcium ferrite and pellets were heated at a heating rate of 200 ° C./min using a high-temperature microscope equipped with an infrared gold plating furnace (Infrared gold image furnace), and the melting start temperature and the melting end temperature were measured.

As a result, it was found that calcium iron composed of CaO, Fe ₂ O ₃ and Al ₂ O ₃ is more common than calcium ferrite composed of CaO and Fe ₂ O ₃ (hereinafter sometimes referred to as CF). Oxygen (hereinafter sometimes referred to as CFA) has significantly lower melting start temperature and melting end temperature. This is believed to be due to the effect of Al ₂ O _{3 on} lowering the solidus temperature and liquidus temperature of calcium ferrite. In addition, in an experiment using pellets composed of the same composition as the above-mentioned CFA, it was confirmed that even with the same composition, the melting start temperature and melting end temperature of the pellets are higher than that of CFA.

In the above experiment, the liquidus temperature of CFA was estimated to be below 1350 ° C from the end temperature of melting, which is lower than the liquidus temperature of CF (about 1400 ° C). CFA is used in the dephosphorization blowing of the converter. Compared with the case where CF is used, the melting rate is increased to promote dephosphorization. In addition, we think that in the process of manufacturing CFA, melting the raw materials in advance is also very important in increasing the melting speed. On the other hand, Al ₂ O ₃ will increase the viscosity of the converter slag. Therefore, when the Al ₂ O ₃ concentration of the converter slag becomes too high, a sharp slag forming (slag forming) occurs in the converter. The frequency of the converter furnace mouth flying (hereinafter referred to as splashing) becomes higher, and the blowing has to be interrupted. The present inventors investigated the appropriate Al ₂ O ₃ concentration to prevent such a situation, and found that by making the Al ₂ O ₃ in the calcium ferrite less than 20% by mass to suppress the sputtering frequency, the blowing can be carried out without interruption operating.

In addition, when the Al ₂ O ₃ concentration is too low, the melting rate of calcium ferrite is low, and it is difficult to melt the low-phosphorus steel in a short period of time, so the Al ₂ O ₃ concentration is set to 2% by mass or more. Furthermore, the present inventors confirmed that by setting the Al ₂ O ₃ concentration to 4 to 12% by mass, a higher effect can be exhibited.

In addition, although the Al ₂ O ₃ concentration in calcium ferrite becomes higher, the melting rate of calcium ferrite will increase accordingly, but the CaO concentration in calcium ferrite required for dephosphorization will be relatively low, so We believe that for dephosphorization, there is a proper composition in the Al ₂ O ₃ concentration and CaO concentration of calcium ferrite. The inventors conducted intensive studies on this appropriate composition and confirmed that the (Al ₂ O ₃ mass%) / (CaO mass%) ratio is set to 0.04 to 0.5, whereby low-phosphorus steel can be melted. When the (Al ₂ O ₃ mass%) / (CaO mass%) ratio is less than 0.04, the melting rate of calcium ferrite is low, and dephosphorization will be insufficient. In addition, when the (Al ₂ O ₃ mass%) / (CaO mass%) ratio is greater than 0.5, the CaO concentration is too low and the dephosphorization situation will deteriorate. Furthermore, the present inventors confirmed that by controlling the (Al ₂ O ₃ mass%) / (CaO mass%) ratio to 0.1 to 0.3, a higher effect is exhibited, and dephosphorization is further promoted.

What's more, the present inventors clearly showed that those containing CaO, Fe ₂ O ₃ , Al ₂ O ₃ and Na ₂ O through the aforementioned experiment using a high-temperature microscope equipped with an infrared gold image furnace (Infrared gold image furnace) Calcium ferrite (hereinafter sometimes referred to as CFAN) has lower melting start temperature and melting end temperature than CFA. We believe that this is because Na ₂ O has the effect of lowering the liquidus temperature and solidus temperature of CFA, and it is estimated that the liquidus temperature of CFAN is 1330 ° C or lower from the melting end temperature.

In addition, it was confirmed that in the dephosphorization process of the top-bottom converter, CFAN shows higher dephosphorization efficiency than CFA and can melt steel with lower [P]. The reason is presumed that Na ₂ O has the effect of increasing the phosphate capacity of the slag, and Na ₂ O reduces the viscosity of the converter slag, and has the effect of promoting the migration of phosphorus substances on the slag side.

Which describes in CFA, the concentration of Al ₂ O ₃ Al ₂ O ₃ is set to 2 to 20% by mass, and (Al ₂ O ₃ mass%) / (CaO mass%) ratio to 0.04 to 0.5, by The melting speed of this calcium ferrite increases, and this effect promotes dephosphorization. On the other hand, the addition of Al ₂ O ₃ increases the viscosity of the slag, and has the effect of retarding the movement of the phosphorus substance on the slag side. Na ₂ O has the effect of reducing the viscosity of the converter slag that is increased by the addition of Al ₂ O _3. From this point of view, we believe that the Al ₂ O ₃ concentration and Na ₂ O concentration of calcium ferrite are used to promote dephosphorization There is an appropriate mass ratio.

In view of this mass ratio, the inventors conducted incisive discussions and confirmed that the method of setting (Na ₂ O mass%) / (Al ₂ O ₃ mass%) ratio to be greater than 0.1 can be melted relative to CFA, [ P] Lower steel. In addition, when the (Na ₂ O mass%) / (Al ₂ O ₃ mass%) ratio is greater than 2.0, the dephosphorization situation deteriorates. This is presumed to be because the mass ratio of Al ₂ O _{3 to} Na ₂ O in the converter slag is reduced, so the activity of Na ₂ O becomes larger, and because the gasification of Na ₂ O proceeds, it is impossible to dephosphorize Na ₂ O is supplied to the dephosphorization slag.

In addition, it was confirmed that by setting the (Na ₂ O mass%) / (Al ₂ O ₃ mass%) ratio to 0.2 to 1.8, dephosphorization can be promoted, and a high Na ₂ O yield to the slag can be maintained. In addition, it is known that CFAN suppresses the formation of slag in the converter relative to CFA, and contributes to the stabilization of operations such as suppressing the adhesion of the base metal to the converter mouth or lance. This is considered to be because the viscosity of the converter slag is reduced due to Na ₂ O, whereby the formation or splashing of the converter slag is suppressed.

In addition, the present inventors clearly showed that the calcium ferrite composed of CaO, Fe ₂ O ₃ , Al ₂ O ₃ and SiO ₂ (the following Sometimes referred to as CFAS), the melting start temperature and melting end temperature are also lower than CF. This is considered to be because SiO ₂ has the effect of lowering the liquidus temperature and solidus temperature of CF. On the other hand, SiO ₂ reduces the basicity of the converter slag, so when the SiO ₂ concentration of the converter slag becomes too high, the progress of the dephosphorization reaction is suppressed, and the target [P ] Level. The present inventors investigated the appropriate SiO ₂ concentration to prevent such a situation, and confirmed that the target [P] level can be satisfied by making SiO ₂ in calcium ferrite less than 10% by mass.

In addition, when the SiO ₂ concentration is too low, the effect of lowering the melting temperature cannot be confirmed, so the SiO ₂ concentration should be 1% by mass or more. Furthermore, the present inventors also confirmed that by setting the SiO ₂ concentration to 2 to 5% by mass, a higher effect can be exerted.

In addition, the present inventors conducted in-depth studies on the appropriate composition of SiO ₂ and CaO in CFAS, and confirmed that the ratio of (SiO ₂ mass%) / (CaO mass%) is 0.04 to 0.3, whereby low melting can be achieved Phosphorus steel. When the (SiO ₂ mass%) / (CaO mass%) ratio is less than 0.04, the melting rate of calcium ferrite is low, and dephosphorization will be insufficient. In addition, when the (SiO ₂ mass%) / (CaO mass%) ratio is greater than 0.3, the CaO concentration is too low and the dephosphorization situation is deteriorated. Furthermore, the present inventors confirmed that by controlling the (SiO ₂ mass%) / (CaO mass%) ratio to 0.1 to 0.3, a higher effect is exhibited, and dephosphorization is further advanced.

What's more, the present inventors clearly showed that calcium ferrite containing CaO, Fe ₂ O ₃ , Al ₂ O ₃ , SiO ₂ and Na ₂ O through the aforementioned experiment using a high-temperature microscope equipped with an infrared gold-plating focusing furnace (Hereinafter referred to as CFASN), compared with CFAS, the melting start temperature and melting end temperature are lower. This is considered to be because Na ₂ O has the effect of lowering the liquidus temperature and solidus temperature of CFAS.

In addition, it was confirmed that in the dephosphorization process of the top-bottom blowing converter, CFASN showed higher dephosphorization efficiency than CFAS and could melt steel with lower [P]. The reason is presumed that Na ₂ O has the effect of increasing the phosphate capacity of the slag, and Na ₂ O reduces the viscosity of the converter slag, and has the effect of promoting the migration of phosphorus substances on the slag side.

In addition, the present inventors conducted in-depth research on the appropriate composition of SiO ₂ and Na ₂ O in CFASN, and confirmed that by making the ratio of (Na ₂ O mass%) / (SiO ₂ mass%) greater than 0.1, For CFAS, melt [P] lower steel. In addition, if the (Na ₂ O mass%) / (SiO ₂ mass%) ratio is greater than 3.0, the dephosphorization situation will be worsened. This is presumed to be because the mass ratio of SiO _{2 to} Na ₂ O in the converter slag is reduced, so the activity of Na ₂ O becomes larger, and because the gasification of Na ₂ O proceeds, the Na required for dephosphorization cannot be ₂ O is supplied to the dephosphorization slag. In addition, the appropriate composition of SiO ₂ , Al ₂ O ₃ and Na ₂ O in CFASN was studied, and it was found that the ratio of (Na ₂ O mass%) / (SiO ₂ mass% + Al ₂ O ₃ mass%) was better It is 0.1 ~ 2.5.

As sources of Al ₂ O ₃ when manufacturing CFA, there are aluminum ash, alumina-based refractory and steel slag containing Al ₂ O ₃ , etc .; as sources of SiO ₂ when manufacturing CFAS, there are peridotite , Pumice, and steel-making slag containing SiO ₂ etc. In addition, as Na ₂ O sources of CFAN and CFASN, there are Na ₂ CO ₃ , soda lime glass, sodium metasilicate, and the like.

Effect of the Invention According to the present invention, in the dephosphorization treatment of the top-bottom blowing converter, calcium ferrite containing Al ₂ O ₃ at an appropriate concentration is used, whereby the refining agent will be sufficiently dissolved even after a short time of blowing, and Can efficiently melt low-phosphorus steel. Furthermore, in addition to Al ₂ O ₃ , by adding an appropriate amount of Na ₂ O and / or SiO ₂ , dephosphorization can be further promoted.

Forms for Carrying Out the Invention Next, the form when dephosphorization treatment is performed using the dephosphorization agent of the present invention will be described. The refining furnace used in the steel-making refining step generally uses a converter, and in the steel-making step according to the converter method, molten pig iron and scrap are charged as main raw materials to produce molten steel. Figure 1 shows a summary of the refining steps using a top-bottom converter.

First, as shown in FIG. 1 (a), scrap 2 is loaded into the converter 1. Then, while loading the waste material 2, the refining agent 3 is put into the furnace. The refining agent contains at least any one of the dephosphorizing agent of the present invention, that is, CFA, CFAN, CFAS, and CFASN. The particle diameters of CFA, CFAN, CFAS, and CFASN are 1-50 mm, and those with a particle diameter of about 5-35 mm are preferably used.

In addition, from the point of view of reducing the amount of steel slag produced and manufacturing costs, when using CFA, CFAN, CFAS, and CFASN, the basicity of converter slag charging should be 1.3 to 2.0. The loading alkalinity is the instruction "total mass of CaO contained in the auxiliary raw material supplied to the converter" as a molecule, and to make "total mass of SiO ₂ contained in the auxiliary raw material supplied to the converter" and "melted pig iron The sum of the SiO ₂ mass when all the Si contained in the waste material has been oxidized to SiO ₂ is calculated as the denominator. In addition, in order to fully obtain the effect of the dephosphorizing agent of the present invention, the amount of CaO supplied from calcium ferrite is preferably 20% or more of the total CaO mass contained in the refining agent 3 supplied into the converter.

After loading the waste material 2 and the refining agent 3, the molten pig iron 4 is charged into the furnace (FIG. 1 (b)), and then, blowing is carried out by blowing oxygen from the spray gun 5 into the molten pig iron 4 (FIG. 1 (c)) ).

Through blowing, the phosphorus in the molten pig iron 3 will react with oxygen and CaO in the slag and move to the slag side. Generally, quicklime as a source of CaO has a high melting point. Although its melting rate is low at the temperature of molten pig iron during refining, the dephosphorization agents of the present invention, namely CFA, CFAN, CFAS and CFASN, melt due to melting at the temperature of molten pig iron The high speed can increase the CaO concentration in the slag early, thereby promoting the dephosphorization of molten pig iron.

In the present invention, the input of the refining agent 3 containing any one of CFA, CFAN, CFAS, and CFASN will have an effect even after the molten pig iron 4 is charged into the converter, but it is preferable to charge Before the pig iron 4 is melted, the refining agent 3 is put in advance. This is because the stirring force when the molten pig iron 4 is charged is used to promote the melting of CFA, CFAN, CFAS, and CFASN. Alternatively, CFA, CFAN, CFAS, and CFASN in the refining agent may be added only before the molten pig iron 4 is charged, and other materials of the refining agent may be added during blowing.

Calcium ferrite composed of CaO and Fe ₂ O ₃ is a compound that improves the meltability of CaO as described above, and it is relatively easy to melt compared to quicklime and the like and exerts a dephosphorization effect. It is well known, but by using calcium ferrite containing the dephosphorization agent of the present invention, that is, Al ₂ O ₃ , or further containing SiO ₂ or Na ₂ O, the melting point is further lowered, and the dephosphorization effect can be improved.

The forms of dephosphorization refining include: after dephosphorization, decarburization in other furnaces; and, known as MURC (Multi Refining Converter, Multi Refining Converter) method, that is, after dephosphorization, tilting The converter discharges the slag with a high phosphorus concentration, and then continues to decarburize in the same furnace. The present invention can be applied in any situation, but especially in the MURC method, the blowing time during dephosphorization is usually a short time within 4 minutes, even in this case, as long as the dephosphorization agent of the present invention is used If the dephosphorization method is carried out, the dephosphorization treatment can be carried out efficiently.

The suitable embodiments of the present invention have been described above, but the present invention is not limited by these examples. As long as the person has ordinary knowledge in the technical field to which the invention belongs, within the scope of the technical idea described in the patent application scope, various modifications or amendments are obviously conceivable, and it should be understood that such modifications or amendments belong to this The technical scope of the invention.

Examples Using various calcium ferrites shown in Table 1, dephosphorization treatment using a converter was performed. The dephosphorization treatment conditions are as follows: [P] before dephosphorization is 0.1%; the blowing time is 3 to 4 minutes; the loading alkalinity is 1.8; the amount of calcium ferrite used is 10kg / t. The finished product [P] in the table is the [P] in the casting stage. In addition, the spattering condition from the furnace mouth during dephosphorization blowing was investigated, and the case where the blowing was interrupted halfway due to the spattering was set to "yes", and the case where it was not interrupted was set to "none". In addition, the input time point is the time point at which calcium ferrite is introduced into the converter, and is set to "before the molten pig iron is charged" or "after the molten pig iron is charged".

[Table 1]

The examples 1 to 9 of the present invention achieve finished products [P] <0.02%, in particular, the numbers 3, 4, 8, and 9 are finished products [P] <0.015%, and it can be seen that they show superior desorption Phosphorus capacity. On the other hand, the numbers 10 to 16 of the comparative examples are all finished products [P]> 0.02%, and dephosphorization is insufficient.

No. 1 and No. 2 of the agent of the present invention, the Al ₂ O ₃ is 3-20% by mass, (Al ₂ O ₃ % by mass) / (CaO% by mass) ratio is 0.04 ~ 0.5; through Al ₂ O ₃ will promote calcium The rate at which CaO is supplied to the dephosphorization slag due to the melting of the ferrite is high. Therefore, it is considered that dephosphorization has been promoted. On the other hand, in the case of No. 10, Al ₂ O _{3 is} less than 2% by mass, and the melting of calcium ferrite is insufficient, so dephosphorization is considered insufficient. In addition, No. 11 is considered to be insufficient for dephosphorization because the concentration of Al ₂ O ₃ is greater than 20% by mass, so intense spraying occurs and the blowing is interrupted in the middle; and, (Al ₂ O ₃ % by mass ) / (CaO mass%) ratio is greater than 0.5, and the increase in Al ₂ O ₃ concentration results in a small supply of CaO to the dephosphorization slag.

In addition, No. 3 and No. 4 of the dephosphorization agent of the present invention are considered to be further promoted relative to No. 1 or No. 2 of the example of the present invention due to the following circumstances: Al ₂ O ₃ is 2 to 20% by mass, (Al ₂ O ₃ mass%) / (CaO mass%) ratio is 0.04 ~ 0.5, and even worse, (Na ₂ O) / (Al ₂ O ₃ ) ratio is 0.1 ~ 2.0; through Al ₂ O ₃ and Na ₂ O promotes the melting of calcium ferrite, Na ₂ O increases the phosphate capacity of the slag; moreover, Na ₂ O reduces the viscosity of the converter slag and promotes the movement of phosphorus substances on the slag side. In addition, the time point when the calcium ferrite is put into the converter in No. 5 is "after the molten pig iron is loaded". Compared with the "before the charged molten pig iron" in the numbers 3 and 4, the reaction time is short, The finished product [P] will rise, but the finished product [P] <0.02% can still be achieved.

On the other hand, in No. 12, it is considered that dephosphorization is insufficient due to the following: Al ₂ O _{3 is} less than 2% by mass, the melting of calcium ferrite is insufficient; and, (Na ₂ O) / (Al ₂ O ₃₎ greater than 2.0, the resulting vaporization of Na ₂ O Na ₂ O is not sufficiently remain in the dephosphorization slag. In addition, because the number 13 (Na ₂ O) / (Al ₂ O ₃ ) is less than 0.1, the phosphate capacity of the slag and the phosphorus substance moving speed on the slag cannot be sufficiently increased through Na ₂ O, so it is considered that dephosphorization is insufficient. Through No. 14 _{(Na 2 O) / (Al} 2 O 3) ratio of greater than 2.0, due to the vaporization of the resulting Na ₂ O Na ₂ O is not sufficiently remain in the dephosphorization slag, dephosphorization is considered insufficient.

In addition, No. 6 and No. 7 of the dephosphorization agent of the present invention, Al ₂ O ₃ is 2 to 20% by mass, (Al ₂ O ₃ % by mass) / (CaO% by mass) ratio is 0.04 to 0.5, and SiO ₂ is 1 ~ 10% by mass, (SiO ₂ % by mass) / (CaO% by mass) ratio is 0.04 ~ 0.3, through Al ₂ O ₃ and SiO ₂ will promote the melting of calcium ferrite, and the speed of supplying CaO to the dephosphorization slag is high Therefore, it is believed that dephosphorization has been promoted. On the other hand, in No. 15, Al ₂ O _{3 is} less than 2% by mass, SiO _{2 is} less than 1% by mass, and calcium ferrite is not sufficiently melted, so dephosphorization is considered insufficient. In addition, No. 16 has a concentration of Al ₂ O _{3 of} less than 2% by mass and SiO ₂ of 10% by mass or more. The basicity of the slag is reduced by SiO ₂ , and dephosphorization is considered insufficient.

INDUSTRIAL APPLICABILITY The present invention relates to a dephosphorization treatment method suitable for melting molten steel. In the steel-making step, iron-containing scrap and molten pig iron are charged into a refining furnace for blowing and melting. Steel dephosphorization treatment.

1‧‧‧Converter
2‧‧‧ Waste
3‧‧‧refining agent
4‧‧‧melted pig iron
5‧‧‧ spray gun

1 (a) to 1 (c) are explanatory views showing the outline of the dephosphorization process using the top-bottom blowing converter of the present invention.

no

Claims (6)

A dephosphorizing agent for molten iron, which contains 2-20% by mass of Al ₂ O ₃ , and the remaining part is calcium ferrite and impurities; and, the ratio of (Al ₂ O _{3 by} mass) / (CaO by mass) is 0.04 ~ 0.5; and, further comprising 1 to 10 mass% of SiO _2, and (SiO ₂ mass%) / (CaO mass%) ratio of 0.04 to 0.3. The requested item of the molten iron dephosphorization agent 1, which further comprises (Na ₂ O mass%) / (Al ₂ O ₃ mass%) is 0.1 to 2.0 of Na ₂ O. A refining agent containing the dephosphorizing agent as claimed in claim 1 or 2. A method for dephosphorization of molten iron, which is a method of adding a refining agent as described in claim 3 to a converter and performing dephosphorization treatment of molten pig iron; wherein, the ratio of (CaO) / (SiO ₂ ) is 1.3 to 2.0 . The method for dephosphorizing molten pig iron according to claim 4, wherein the mass of CaO contained in the calcium ferrite is more than 20% of the mass of CaO contained in the refining agent. The method for dephosphorizing molten pig iron according to claim 4, wherein the refining agent is put into the converter before the molten pig iron is charged.