JP2017171975A - Dephosphorization agent for molten pig iron and dephosphorization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dephosphorization agent for molten pig iron capable of producing low phosphorus steel effectively even by short term blowing and a dephosphorization method.SOLUTION: A dephosphorization agent consists of calcium ferrite which mainly contains CaO and FeO, has an SiOconcentration of 2 to 10 mass%, an (SiOmass%)/(CaO mass%) ratio of 0.05 to 0.3 and the balance inevitable impurities. The input base degree (CaO)/(SiO) is 1.3 to 2.0 while conducting dephosphorization treatment of molten pig iron 4 by adding a refining agent 3 containing the dephosphorization agent into a converter 1.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a hot metal dephosphorization method using an upper bottom blowing converter, and relates to a hot metal dephosphorization method and a dephosphorization method that can efficiently produce low phosphorus steel even in a refining process with a short blowing time. It is.

  In recent years, the demand for steel materials has increased, and the demand for low phosphorus steel has increased. At present, hot metal dephosphorization is widely performed by a method in which the hot metal is treated under low temperature conditions in a hot metal stage which is thermodynamically advantageous. As the hot metal dephosphorization apparatus, an upper bottom blowing converter is suitable. This is because, as an oxidant necessary for dephosphorization, gaseous oxygen with less heat loss than a solid oxidation source can be blown from the top blowing lance to the hot metal at high speed.

Since hot metal dephosphorization is performed under low temperature conditions in the hot metal stage, it is important to promote the hatching of CaO used as a dephosphorizing agent. The use of fluorite (CaF ₂ ) is effective for the hatching of CaO. However, when fluorite is used, the slag generated by the hatching of CaO contains fluorine. Detrimental effects such as significant restrictions are significant. Therefore, CaO hatching promotion methods that do not use fluorite have been developed.

For example, Patent Documents 1 and 2 are known in which a refining agent containing calcium ferrite is added to the hot metal charged in the top-bottom blow converter. Calcium ferrite is a dephosphorization agent composed of a compound of CaO and Fe ₂ O ₃ , and has a higher dissolution rate in dephosphorization slag as compared with quick lime generally used as a dephosphorization agent for hot metal dephosphorization process. Dephosphorization reaction can be promoted. Patent Document 3 discloses a dephosphorizing agent to which Na ₂ O is added in order to improve the meltability of calcium ferrite.

JP 2013-163844 A JP 2013-064167 A JP 2012-12680 A

  However, the normal calcium ferrite used in the dephosphorization treatment disclosed in Patent Documents 1 and 2 has a liquidus temperature of about 1400 ° C., which is higher than 1200 to 1350 ° C., which is the temperature of the hot metal in the converter. high. This means that solid calcium ferrite dissolves in the dephosphorization slag of the liquid generated by the oxidation reaction between oxygen supplied from the top blowing lance and Si or Fe in the hot metal, and if the blowing time is short, It is conceivable that calcium ferrite does not melt sufficiently, dephosphorization becomes insufficient, and blowing is completed in a state where [P] (mass% of P dissolved in steel) does not reach the target value.

  In Patent Document 2, the blowing time is about 10 minutes, and after 35% of the total blowing time has elapsed, calcium ferrite starts to be added, and the addition is completed until 80% of the total blowing time has elapsed. The technology to do is described. However, for example, when blowing in a short time of 4 minutes or less, there is a concern that the method of Patent Document 2 may cause insufficient melting of calcium ferrite and deteriorate the dephosphorization efficiency.

Patent Document 3 describes calcium ferrite containing Na ₂ O, but does not describe a dephosphorization method using the same, and a dephosphorization method suitable for a short blowing time is unknown. is there. Further, according to experiments using the top-bottom blow converter of the present inventors, when the dephosphorization agent described in Patent Document 3 is used for a short time of about 4 minutes, calcium ferrite is not sufficient. It did not melt, the phosphorus removal efficiency was insufficient, and it was difficult to produce low phosphorus steel with [P] <0.02%.

  Recently, in order to improve the production efficiency of converters, the hot metal dephosphorization process has been shortened. For example, [P] <0.02% low phosphorus steel with a dephosphorization blowing time of about 4 minutes. It is required to melt. In such a background, it is desired to develop a dephosphorizing agent and a dephosphorizing method capable of melting low phosphorus steel even when short-time blowing is performed.

  The present invention has been made in view of such a viewpoint, and provides a hot metal dephosphorizing agent and a dephosphorizing method capable of efficiently producing low phosphorus steel even in a short time of blowing. With the goal.

In order to solve the above-mentioned problems, the inventors of the present invention have sufficient SiO ₂ or SiO ₂ and Na ₂ O in calcium ferrite, and by optimizing these concentrations, it is sufficient for short-time blowing. It has been found that the refining agent dissolves and low phosphorus steel can be efficiently produced.

The present invention comprises CaO and Fe ₂ O ₃ as main components, the SiO ₂ concentration is 2 to 10% by mass, and the (SiO ₂ mass%) / (CaO mass%) ratio is 0.05 to 0.3, There is provided a hot metal dephosphorizing agent characterized in that the balance is made of calcium ferrite which is an inevitable impurity.

Further, the present invention is mainly composed of CaO and Fe ₂ O ₃ , SiO ₂ concentration is 2 to 10% by mass, (SiO ₂ mass%) / (CaO mass%) ratio is 0.05 to 0.3, A hot metal dephosphorization agent characterized in that the ratio of (Na ₂ O mass%) / (SiO ₂ mass%) is 0.1 to 3.0, and the balance is calcium ferrite which is an inevitable impurity. provide.

Further, a refining agent containing the hot metal dephosphorizing agent is added to the converter, and the hot metal dephosphorization treatment is performed, and the basicity of charge (CaO) / (SiO ₂ ) is 1.3-2. The present invention provides a method for dephosphorizing hot metal, which is characterized by being 0.0.

  In the hot metal dephosphorization method, the mass of CaO contained in the dephosphorization agent is preferably 20% or more of the mass of CaO contained in the refining agent. The refining agent is preferably charged into the converter before the hot metal is charged.

According to the present invention, the dephosphorization treatment in the upper bottom blown converter, SiO _2, or by using a dephosphorization agent containing a proper concentration and SiO ₂ and Na ₂ O, a short time of blowing However, the refining agent is sufficiently dissolved, and low phosphorus steel can be efficiently produced.

It is explanatory drawing which shows the outline of the dephosphorization process using the top bottom blowing converter which concerns on this invention.

  Embodiments of the present invention will be described below.

In the present specification, the calcium ferrite, a compound mainly composed of the CaO and Fe ₂ O _3, 4 in a ratio mass ratio of CaO and Fe ₂ O _3: 6~3: a 7, The total of CaO mass% and Fe ₂ O ₃ mass% refers to those of 70 mass% or more. Further, low phosphorus steel refers to steel having [P] of 0.02% or less at the slab stage, and efficient means that dissolved calcium ferrite sufficiently contributes to dephosphorization. Unless otherwise specified, short-time blowing refers to blowing with a blowing time of about 2 to 6 minutes.

The present inventors added various compounds to CaO and Fe ₂ O ₃ in order to improve the meltability of calcium ferrite as a dephosphorizing agent in the dephosphorization process of the top-bottom blow converter, Various molten calcium ferrites were prepared. Next, these calcium ferrites were heated using a high-temperature microscope equipped with an infrared gold image furnace, and the melting end temperature was measured.

As a result, calcium ferrite composed of CaO, Fe ₂ O ₃ , and SiO ₂ (hereinafter referred to as CFS) is compared with normal calcium ferrite composed of CaO and Fe ₂ O ₃ (hereinafter sometimes referred to as CF). Has found that the melting end temperature is low. This is presumably because SiO ₂ has the effect of lowering the liquidus temperature of calcium ferrite.

In the above experiment, the CFS liquidus temperature is estimated to be 1350 ° C. or less from the melting end temperature and is lower than the CF liquidus temperature (about 1400 ° C.). It is considered that the use of CFS increases the dissolution rate with respect to the case of using CF and promotes dephosphorylation. However, since SiO ₂ lowers the phosphate capacity of converter slag, if the SiO ₂ concentration in the calcium ferrite becomes too high, the dephosphorization efficiency deteriorates. The present inventors investigated an appropriate SiO ₂ concentration for preventing such a situation, and found that a large deterioration in dephosphorization efficiency can be suppressed by making SiO _{2 in} calcium ferrite 10% by mass or less. .

In addition, when the SiO ₂ concentration is too low, the dissolution rate of calcium ferrite is low, and it is difficult to melt the low phosphorus steel by short-time blowing, so the SiO ₂ concentration is set to 2% by mass or more. Furthermore, the present inventors have confirmed that a higher effect can be exhibited by setting the SiO ₂ concentration to 3 to 6% by mass.

In addition, the SiO ₂ concentration in calcium ferrite increases, so that the dissolution rate of calcium ferrite increases. However, the CaO concentration in calcium ferrite necessary for dephosphorization becomes relatively low. It is considered that there is an appropriate composition for the SiO ₂ concentration and the CaO concentration of calcium ferrite. This proper composition, the present inventors, the ratio of the mass% of SiO ₂ mass% and CaO (SiO ₂ mass%) / (CaO mass%)
It was confirmed that the low phosphorus steel can be melted by setting 0.05 to 0.3. When the ratio (SiO ₂ % by mass) / (CaO% by mass) is less than 0.05, the dissolution rate of calcium ferrite is low and dephosphorization is insufficient. On the other hand, when the ratio (SiO ₂ mass%) / (CaO mass%) is larger than 0.3, the CaO concentration is too low and the dephosphorization efficiency deteriorates. In addition, the present inventors express a higher effect by controlling the (SiO ₂ mass%) / (CaO mass%) ratio to 0.1 to 0.2, and further promote dephosphorization. confirmed.

Furthermore, the present inventors conducted an experiment using a high-temperature microscope equipped with the above-described infrared gold image furnace, and obtained calcium ferrite containing CaO, Fe ₂ O ₃ , SiO ₂ , and Na ₂ O (hereinafter referred to as CFSN). Revealed that the end-of-melting temperature is lower than that of CFS. This is thought to be because Na ₂ O has the effect of lowering the liquidus temperature of CFS, and the liquidus temperature of CFSN is estimated to be 1320 ° C. or less from the melting end temperature.

In addition, in the dephosphorization process of the top-bottom blow converter, it was confirmed that CFSN showed higher dephosphorization efficiency than CFS, and steel with lower [P] could be produced. This can have the effect of Na ₂ O increases the phosphate capacity of the slag, Na ₂ O is lower the viscosity of the converter slag, and because it has the effect of promoting mass transfer of phosphorus slag side Presumed.

In CFS, the dissolution rate of calcium ferrite is increased by setting the SiO ₂ concentration to 2 to 10 mass% and the (SiO ₂ mass%) / (CaO mass%) ratio to 0.05 to 0.3. It has been mentioned above that dephosphorization is promoted by. On the other hand, the addition of SiO ₂ has the effect of lowering the phosphate capacity of the slag and dephosphorizing efficiency. Na ₂ O is from having the effect of increasing the phosphate capacity was reduced by the SiO ₂ addition, SiO ₂ concentration and the concentration of Na ₂ O Calcium ferrite exists proper mass ratio in promoting dephosphorization I think that.

With respect to this mass ratio, the present inventors set a (Na ₂ O mass%) / (SiO ₂ mass%) ratio of 0.1 or more to dissolve steel having a lower [P] relative to CFS. It was confirmed that it could be manufactured. Further, when the (Na ₂ O mass%) / (SiO ₂ mass%) ratio was larger than 3.0, the dephosphorization efficiency was deteriorated. This is because the mass ratio of SiO ₂ to Na ₂ O of the converter slag is lowered, the greater the activity of Na ₂ O, Na ₂ by O gasification has proceeded, dephosphorizing the required Na It is estimated that ₂ O could not be supplied to the dephosphorization slag.

In addition, by maintaining the (Na ₂ O mass%) / (SiO ₂ mass%) ratio to 0.2 to 2.0, the yield of Na ₂ O to the slag is maintained higher while promoting dephosphorization. I confirmed that I can do it. In addition, it was found that CFSN contributes to operational stability, such as suppression of slag forming in the converter, and suppression of metal adhesion to the converter furnace opening and lance, compared to CFS. This is considered to be because the forming and slopping of the converter slag were suppressed by the reduction of the viscosity of the converter slag by Na ₂ O.

Examples of the SiO ₂ source for producing CFS include soft silica, peridotite, and steelmaking slag containing SiO ₂ . Further, as the Na ₂ O source of CFSN, there are Na ₂ CO ₃ , soda lime glass, sodium metasilicate, and the like, and soda lime glass and sodium metasilicate are also SiO ₂ sources.

  Next, an embodiment when performing a dephosphorization process using the dephosphorizing agent according to the present invention will be described.

  As the refining furnace used in the steelmaking refining process, a converter is usually used. In the steelmaking process using the converter method, molten steel and scrap are charged as main raw materials to produce molten steel.

  In FIG. 1, the outline of the refining process using an upper bottom blowing converter is shown. First, as shown in FIG. 1A, the scrap 2 is charged into the converter 1. Simultaneously with the charging of the scrap 2, the refining agent 3 containing CFS or CFSN as the dephosphorizing agent according to the present invention is put into the furnace. The particle size of CFS and CFSN may be 1 to 50 mm, preferably about 5 to 35 mm.

Moreover, from the point of steelmaking slag generation amount reduction and manufacturing cost reduction, the charging basicity of the converter slag when using CFS or CFSN is preferably 1.3 to 2.0. The charge basicity refers to “the total amount of CaO contained in the auxiliary raw material supplied into the converter” as a molecule, and “the total amount of SiO ₂ contained in the auxiliary raw material supplied into the converter” and “ Si contained in the molten iron and scrap is a number of the ratio is calculated the sum of the SiO ₂ mass "in the case of the oxidized to the total SiO ₂ as a denominator. Furthermore, in order to sufficiently obtain the effect of the dephosphorizing agent according to the present invention, the amount of CaO supplied from the dephosphorizing agent is 20% or more of the total CaO mass contained in the refining agent 3 supplied into the converter. It is preferable that

  After the scrap 2 and the refining agent 3 are charged into the converter 1, the hot metal 4 is charged into the furnace (FIG. 1 (b)), and then blown by blowing oxygen from the lance 5 into the hot metal 4 ( FIG. 1 (c)).

  By blowing, phosphorus in the hot metal 4 reacts with oxygen and CaO in the slag, and shifts to the slag side. Normally, quick lime as a CaO source has a high melting point, and the dissolution rate at the hot metal temperature during refining is small, but CFS or CFSN, which is a dephosphorizing agent according to the present invention, melts at the hot metal temperature, so the dissolution rate is large, and slag By increasing the CaO concentration inside, the dephosphorization of hot metal can be promoted.

  In the present invention, the introduction of the refining agent 3 containing CFS or CFSN is effective even after the molten iron 4 is charged into the converter, but the refining agent 3 is charged before the molten iron 4 is charged. Is preferred. This is for promoting the dissolution of CFS or CFSN by utilizing the stirring force when the molten iron 4 is charged. Alternatively, only CFS or CFSN of the refining agent may be charged before the molten iron 4 is charged, and other substances of the refining agent may be charged at the time of blowing.

Calcium ferrite composed of CaO and Fe ₂ O ₃ is a compound that has improved the melting property of CaO as described above, and it is well known that it is easily melted to quicklime and exhibits a dephosphorization effect. according a dephosphorization agent, SiO _2, or, by using calcium ferrite containing SiO ₂ and Na ₂ O, lower the further melting point, it is possible to enhance the dephosphorization effect.

  As a form of refining that performs dephosphorization, after dephosphorization, decarburization is performed in another furnace, and after dephosphorization, called the MURC (Multi Refining Converter) method, the converter is tilted. There are cases where slag with high phosphorus concentration is discharged and then decarburization is continued in the same furnace. Although the present invention can be applied to any case, in particular, in the MURC method, the blowing time during dephosphorization is usually as short as 4 minutes or less, and even in such a case, the dephosphorizing agent according to the present invention According to the dephosphorization method using, dephosphorization can be performed efficiently.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  For example, in the above embodiment, the dephosphorizing agent is CFS or CFSN. However, both CFS and CFSN may be used as the dephosphorizing agent.

Using various dephosphorization agents shown in Table 1, dephosphorization treatment in a converter was performed. Here, the composition of each dephosphorizing agent in Table 1 is a value obtained by dividing the chemical analysis values so that the total of the components of CaO, Fe ₂ O ₃ , SiO ₂ , and Na ₂ O becomes 100% by mass. The conditions for the dephosphorization treatment are as follows: [P] before dephosphorization is 0.1%, blowing time is 3 to 4 minutes, charging basicity is 1.8, and the amount of dephosphorizing agent used is 10 kg / t. is there. “Product [P]” in the table is [P] at the slab stage. Further, the “charging timing” is the timing at which the dephosphorizing agent is charged into the converter, and is “before hot metal charging” or “after hot metal charging”.

  No. which is an example of the present invention. 1-No. 6 achieved the product [P] <0.02%. 5 and No. No. 6 was a product [P] <0.016%, and it was found that it showed a better dephosphorization ability. On the other hand, No. which is a comparative example. 7 to 11 were all products [P]> 0.02%, and dephosphorization was insufficient.

No. which is an example of the present invention. 1 and no. 2, SiO ₂ is 2 to 10 wt%, a (SiO ₂ mass%) / (CaO mass%) ratio of 0.05 to 0.3, melting of the calcium ferrite is promoted by the SiO _2, dephosphorization slag It is considered that dephosphorization was promoted because of the high CaO supply rate. On the other hand, no. In No. 7, SiO ₂ was less than 2% by mass, and dissolution of calcium ferrite was insufficient. No. No. 8 has a SiO ₂ concentration larger than 10 mass% and a (SiO ₂ mass%) / (CaO mass%) ratio is larger than 0.3.

Moreover, No. which is an example of the present invention. 3 and no. 4, SiO ₂ is ₂ to 10 mass%, (SiO ₂ mass%) / (CaO mass%) ratio is 0.05 to 0.3, and (Na ₂ O) / (SiO ₂ ) ratio is 0.1. is 3.0, the melting of the calcium ferrite by SiO ₂ and Na ₂ O is promoted, lowering the viscosity of the converter slag by Na ₂ O was increased phosphate capacity of the slag, the slag side of phosphorus Since the mass transfer was promoted, No. 1 as an example of the present invention. 1 and No. 2 is considered to have further promoted dephosphorylation.

  Moreover, No. which is an example of the present invention. 5 and no. No. 6 had a dephosphorizing agent charged in the converter before the hot metal was charged, and No. 6 in which the dephosphorizing agent was charged after the hot metal was charged. 3 and no. 4 is further promoted to remove phosphorus. This is considered to be because the dissolution of the dephosphorizing agent was promoted by utilizing the stirring force of the hot metal charging to the converter.

On the other hand, no. In No. 9, SiO ₂ was smaller than 2% by mass, the dephosphorization agent was not sufficiently melted, (Na ₂ O) / (SiO ₂ ) was larger than 3.0, and Na ₂ O vaporization caused Na ₂ O to vaporize. Was not sufficiently left in the dephosphorization slag, it is considered that the dephosphorization was insufficient. No. 10 is less than 2% by mass of SiO ₂ and (Na ₂ O) / (SiO ₂ ) is less than 0.1, and Na ₂ O increases the phosphate capacity of slag and the mass transfer rate of phosphorus on the slag side. It was thought that dephosphorization was insufficient because it was not sufficiently large. No. In No. 11, SiO ₂ was smaller than 2% by mass, and (Na ₂ O) / (SiO ₂ ) was larger than 3.0, and Na ₂ O did not sufficiently remain in the dephosphorized slag due to vaporization of Na ₂ O. Therefore, it is considered that dephosphorization was insufficient.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a dephosphorization processing method in which steel-containing scrap and molten iron are charged into a smelting furnace and blown in a steelmaking process to melt the molten steel.

1 Converter 2 Scrap 3 Refining agent 4 Hot metal 5 Lance

Claims (5)

The main component is CaO and Fe ₂ O ₃ , the SiO ₂ concentration is 2 to 10% by mass, the (SiO ₂ mass%) / (CaO mass%) ratio is 0.05 to 0.3, and the balance is inevitable. A hot metal dephosphorizing agent characterized by comprising calcium ferrite which is a major impurity. The main component is CaO and Fe ₂ O ₃ , the SiO ₂ concentration is 2 to 10% by mass, the (SiO ₂ mass%) / (CaO mass%) ratio is 0.05 to 0.3, (Na ₂ O mass%) ) / (SiO ₂ mass%) ratio is 0.1 to 3.0, and the balance is made of calcium ferrite which is an inevitable impurity. A refining agent containing the hot metal dephosphorization agent according to claim 1 or 2 is added to a converter, and the hot metal dephosphorization treatment is performed.
A hot metal dephosphorization method, wherein the basic charge (CaO) / (SiO ₂ ) is 1.3 to 2.0.   The hot metal dephosphorization method according to claim 3, wherein the CaO mass contained in the dephosphorizing agent is 20% or more of the CaO mass contained in the refining agent.   The hot metal dephosphorization method according to claim 3, wherein the refining agent is charged into the converter before the hot metal is charged.

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