JP2015218391A - Desulfurization method of molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desulfurization method of molten iron, capable of efficiently desulfurizing molten iron to an extremely low level by mechanical agitation type desulfurization.SOLUTION: In desulfurization by mechanical agitation of molten iron tapped from a blast furnace before the decarbonization step in a revolving furnace, a flux having a composition which satisfies the conditions described in the following is used.

Description

  The present invention relates to a hot metal desulfurization method for desulfurizing hot metal in a stage prior to a decarburization process in a converter.

  Currently, in order to meet the demand for low-sulfur steel production with low sulfur content, it is common practice to perform desulfurization treatment on the hot metal discharged from the blast furnace in the hot metal stage before the decarburization process in the converter. In recent years, there has been an increasing need for so-called ultra-low sulfur steels having a sulfur concentration in steel of 0.003 wt% or less, such as high-tensile steels for automobiles. In order to produce such steel, desulfurization treatment is performed not only in the hot metal stage but also in the hot steel stage after the converter steel, but the desulfurization treatment in the molten steel is higher than the cost required for the desulfurization treatment of the hot metal. It is desirable to reduce the desulfurization load in the molten steel treatment by reducing the sulfur concentration as much as possible in the hot metal stage.

In addition, there exists a technique disclosed by patent documents 1-3 as a technique of the desulfurization process in a hot metal stage.
The hot metal desulfurization method disclosed in Patent Document 1 is a method in which hot metal desulfurization is performed using a refining agent mainly composed of CaO and MgO, and the Al concentration of the hot metal is adjusted to 0.005 to 0.1% by mass. Thus, the production of calcium-aluminate is suppressed. This is a method of injecting flux from an immersed lance (so-called injection desulfurization).

In the desulfurization method of the low silicon concentration hot metal disclosed in Patent Document 2, the mixing ratio of CaO and Al ₂ O _{3 in} the desulfurizing agent is Al when the hot metal is desulfurized with a mixed flux of quick lime and Al ash. ₂ O ₃ at 33 to 37.7 of a mixture such that the weight percent range, or the mixing ratio of CaO and _Al 2 _{O 3} after the addition and the range of 33 to 37.7 wt% in _Al 2 _{O 3} An amount of quicklime and Al ash are added.

Moreover, the hot metal desulfurization agent disclosed in Patent Document 3 is a desulfurization agent comprising a mixture of quicklime and an aluminum-based deoxidizer having a metal aluminum content of 10% by mass or more and the balance being substantially alumina. The mixing ratio of the aluminum-based deoxidizer in the desulfurizing agent is 7% by mass or more in terms of alumina.
In addition to this desulfurization treatment technique, as disclosed in Patent Document 4, a flux is placed on hot metal contained in a container, and a refractory stirring blade (impeller) is immersed and rotated. There is also a mechanical desulfurization method (so-called KR desulfurization) in which a placed flux is desulfurized by being wound into hot metal.

  The hot metal desulfurization method disclosed in Patent Document 4 is a hot metal desulfurization method using a mechanical stirring type desulfurization apparatus, in which an alumina-metal Al mixture containing 10 to 50 mass% of metal Al with respect to CaO powder is used. A desulfurizing agent added in the range of X mass% or more and X + 15 mass% or less obtained by the following formulas (2), (3) and (4) according to the temperature before desulfurization treatment of the hot metal to be desulfurized, It is added to the bath surface of the hot metal being stirred by the stirring blade, and the hot metal is desulfurized. When the hot metal temperature is 1250 ° C. or lower, X (mass%) = 20 (2), when the hot metal temperature is higher than 1250 ° C. and lower than 1340 ° C., X (mass%) = 295-0.22 × T (3), hot metal When the temperature is 1340 ° C. or higher, X (mass%) = 0.2 (4), where T is the hot metal temperature (° C.) before the desulfurization treatment.

JP 2012-260212 A JP-A-9-3515 JP 2010-229439 A JP 2011-132666 A

For each of the above-mentioned patent documents, Patent Document 1 and Patent Document 2 describe only expensive metal Al as a desulfurization agent, and do not consider inexpensive AlN having a similar deoxidation effect. As a desulfurization agent, there is a disadvantage that it becomes expensive. Further, when the mechanical desulfurization method is assumed, the techniques of Patent Document 1 and Patent Document 2 are based on the premise of injection / blasting desulfurization. It is difficult to use as a guideline.

  In Patent Document 3, there is no description regarding the hot metal temperature that greatly affects the desulfurization reaction, which is insufficient as a guideline for realizing an efficient desulfurization treatment. In addition, since the mechanical desulfurization method is not assumed in the description of Patent Document 3, the stirring power that greatly affects the desulfurization reaction cannot be calculated. It is difficult to use it as a guideline.

Furthermore, in Patent Document 4 that presupposes a mechanical desulfurization method, it is limited to an ideal CaO—Al ₂ O ₃ —M.Al system, but Al ash disclosed in the examples includes MgO and SiO. Impurities such as ₂ are included, and the influence of these impurities is not considered. Therefore, the technique disclosed in Patent Document 4 is insufficient as a guideline for efficiently and extremely low-sulfurizing hot metal in the first place. In addition, the stirring power that plays an important role in the desulfurization reaction efficiency cannot be calculated only by the content disclosed in Patent Document 4, and a guideline for efficiently and extremely low-sulfurizing hot metal by the mechanical stirring desulfurization method It is difficult to do.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide means capable of extremely low-sulfurizing hot metal efficiently by a mechanical stirring type desulfurization method.

In order to solve the above problems, the hot metal desulfurization method of the present invention employs the following technical means.
That is, the hot metal desulfurization method of the present invention has a composition satisfying the following conditions when the hot metal discharged from the blast furnace is desulfurized by mechanical stirring in the hot metal stage before the decarburization process in the converter. It is characterized by using a flux.

  According to the hot metal desulfurization method of the present invention, the hot metal can be efficiently extremely low-sulfurized by the mechanical stirring type desulfurization method.

It is a figure which shows typically the refining process of the hot metal extracted from the blast furnace by embodiment of this invention. It is a figure which shows typically the composition of the hot metal ladle and impeller by this embodiment. It is a figure which shows the graph showing the result of the multiple regression analysis which made the desulfurization rate the dependent variable, the hot metal temperature, and conversion M.Al as an independent variable about the hot metal desulfurization experiment. It is a figure which shows the graph showing the desulfurization result of the Example by this embodiment, and the desulfurization result of the comparative example 1. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically illustrating an example of a refining process of hot metal discharged from the blast furnace 1.
As shown in FIG. 1, the hot metal discharged from the blast furnace 1 is received by the kneading vehicle 3 and then transported to the steelmaking factory, where it is discharged from the kneading vehicle 3 to the hot metal ladle 4. This hot metal ladle 4 is moved to a removal position by a crane, and after removing (steaming) blast furnace slag present on the hot metal surface in the ladle, it is carried to the converter front by the crane. The molten iron removed and transported to the front of the converter is charged into the converter from the hot metal ladle 4. The empty hot metal ladle 4 that has finished charging the hot metal into the converter is returned again to the discharge position by the crane, and the hot metal of the next charge is discharged from the kneading wheel 3 to the hot metal hot pot 4.

  In this embodiment, in such a refining process, the desulfurization process by the mechanical stirring (KR stirring) mentioned later is performed in the hot metal ladle 4. Specifically, in the hot metal ladle 4, a desulfurizing agent (desulfurized flux or simply referred to as flux) is added to the hot metal after the blast furnace slag has been removed (removed), and mechanical stirring is performed on the hot metal to which the flux has been added. To advance the desulfurization reaction. And after removing the slag produced by the desulfurization reaction again at the removal position, the molten iron after desulfurization is discharged from the hot metal ladle 4 to the converter.

Here, as shown in FIGS. 1 and 2, the mechanical stirring means that the impeller 5, which is a blade made of a refractory material, is immersed in the hot metal in the hot metal pan 4 and rotated to add the flux. This is a treatment for promoting the desulfurization reaction while forcibly stirring.
FIG. 2 is a view showing a configuration of a hot metal ladle 4 for storing hot metal and an impeller 5 immersed in the hot metal stored in the hot metal pan 4. If mechanical agitation is performed with the configuration shown in FIG. 2, sulfur in the hot metal is effectively transferred to the desulfurizing agent to form desulfurized slag. By removing the formed desulfurized slag, “the sulfur content is removed. Can be obtained.

In such mechanical stirring, the desulfurization effect changes depending on the stirring power P and the stirring power density ε described later.
The stirring power P is obtained by using the following Nagata formula (see, for example, Chemical Engineering Handbook, Maruzen (1998), P893-897).

  In the above Nagata equation, A, B, and p are constants, and the meanings of the other symbols are shown in Table 1 and FIG.

Based on the stirring power P thus obtained, the stirring power density ε [kw / t] can be obtained by dividing the stirring power P (for example, kw) by the hot metal weight (t) in the hot metal pan 4. .
As described above, the desulfurization treatment according to the present embodiment is performed by adding mechanical treatment to the hot metal in the hot metal ladle 4 to which the flux as a desulfurizing agent is added and the hot metal in the hot metal pan 4 to which the flux is added. And a stirring process to be applied. Specifically, the desulfurization treatment according to the present embodiment is characterized by the definition of the components of the flux used for the addition treatment, and also by the definition of the stirring power density ε in the stirring treatment.

Below, an addition process is demonstrated, and the stirring process with respect to the hot metal which finished the addition process is demonstrated.
Since the desulfurization reaction in the above-mentioned desulfurization process is an endothermic reaction, there is a characteristic depending on the temperature of the hot metal such that the high temperature is easy to proceed and the low temperature is difficult to proceed. Therefore, the conditions required for the flux vary depending on the hot metal temperature, and the desulfurization efficiency with the same flux varies greatly depending on the hot metal temperature.

The reason for this is that when the hot metal temperature is low, the efficiency of the desulfurization reaction itself is worsened, and the hatching of lime in the added flux is remarkably slowed, and the utilization efficiency of lime in the flux is greatly reduced. It is.
In this embodiment, the lower limit of the hot metal temperature is not set. However, if the hot metal temperature is too low, the adhesion of the metal to the hot metal ladle 4 becomes significant before desulfurization. Can be considered.

Therefore, in consideration of the hot metal temperature before the desulfurization treatment and the concentration of silicon Si contained in the hot metal, a flux satisfying the composition described below is added as a desulfurizing agent. The reason for considering the hot metal Si concentration which is the concentration of silicon Si contained in the iron will be described later.
First, the flux satisfies the conditions shown in the following formula (1) for converted M.Al.

M.Al is metallic aluminum (metal Al), and the total of this M.Al and aluminum contained in Al nitride (AlN) represents the amount of metallic aluminum contained in the flux “converted M.Al. " In the present embodiment, the unit [kg / t] represents the weight (kg) of metal aluminum or flux per 1 t (ton) of hot metal.
Here, the desulfurization reaction is represented by [S] + (O) = (S) + [O]. The symbol [] indicates that it is dissolved in the hot metal, and the symbol () indicates that it is dissolved in the slag. As can be seen from this equation (a), in order to advance the desulfurization reaction efficiently, it is first necessary to reduce the oxygen potential in the hot metal (first condition), and secondly, sulfur in the slag. It is necessary to reduce the activity of (second condition).

  The conditions for the converted M.Al shown in Formula (1) relate to the first condition described above, and the amount of converted M.Al added to the hot metal satisfies the condition shown in Formula (1). The oxygen potential of the hot metal can be lowered to a level at which the desulfurization reaction proceeds efficiently. On the contrary, if the amount of converted M.Al added to the hot metal does not satisfy the condition shown in the formula (1), the oxygen potential of the hot metal cannot be sufficiently lowered, and the desulfurization reaction does not proceed efficiently.

Here, since the metal Al introduced as a flux is for reducing the oxygen potential in the hot metal, Al in Al ₂ O ₃ already bonded to oxygen has no effect. As a form of Al that can reduce the oxygen potential, metal Al (M.Al) is common, but Al in Al nitride (AlN) reacts with oxygen to become Al ₂ O ₃ , so Al, like metal Al, contributes to the reduction of oxygen potential.

As the above-mentioned substances containing M.Al and AlN, in addition to metal Al, dross generated by aluminum refining (so-called aluminum dross), a material in which the metal Al content is recovered by ash drawing treatment of this aluminum dross (so-called aluminum ash) ), And those obtained by recovering the metal Al content by arc furnace treatment (so-called arc furnace ash) or the like can be used.
As described above, since the desulfurization reaction is an endothermic reaction, there is a feature that the reaction is less likely at lower temperatures. For this reason, as the hot metal becomes colder, it is necessary to increase the amount of Al added and lower the oxygen potential of the hot metal, and the condition for the converted M.Al according to the above formula (1) is the conversion required based on the hot metal temperature. It defines the amount of M.Al.

  In addition, the hot metal generally contains a maximum of about 1% (max 1%) of Si by reducing part of the gangue in the ore and ash in the coke in the blast furnace. Since Si is not as high as Al, but is an element with high oxygen affinity, hot metal having a lower Si concentration has a higher oxygen potential if the equivalent amount of Al is the same. For this reason, in order to efficiently sulphite the hot metal extremely low, it is necessary to define the flux input amount in consideration of the difference in the hot metal Si concentration.

In recent years, as with the desulfurization treatment, it is common to add oxygen and lime to the hot metal in the hot metal stage to perform dephosphorization. The order of the desulfurization treatment and the dephosphorization treatment exists depending on the layout of each steelworks, the owned facilities, etc., but in the dephosphorization treatment, oxygen is added, so the hot metal Si concentration is greatly reduced.
For this reason, when dephosphorization is performed before desulfurization, since the Si concentration in the hot metal is greatly reduced at the start of the desulfurization, the oxygen potential tends to be high and the dephosphorization is not performed in advance. In comparison with the above, a larger amount of converted Al is required.

In view of the characteristics of these desulfurization reactions, the condition shown in the above formula (1) defines the converted M.Al amount necessary for the production of extremely low sulfur hot metal according to the hot metal temperature and hot metal Si concentration.
The calculation process of the formula (1) is shown below.
I. A 300 kg hot metal desulfurization experiment was conducted, and a multiple regression was performed using the desulfurization rate as a dependent variable and the hot metal temperature and converted M.Al as an independent variable, as shown in FIG. 3, and the following equation (A) was obtained. FIG. 3 is a graph showing the results of a multiple regression analysis of the hot metal desulfurization experiment with the desulfurization rate as a dependent variable and the hot metal temperature and converted M.Al as an independent variable.

Desulfurization rate [%] = 126.7 x converted M.Al [kg / t] + 0.189 x T [° C] + 8.44 x [Si] [wt%] -228.77
-(A)
In the hot metal desulfurization experiment, the desulfurization rate [%] was determined by the following equation.

II. Next, as shown in, for example, Japanese Patent Application Laid-Open No. 2011-6761, the above formula (A) is used to achieve a desulfurization rate ≧ 90%, which is a standard as a condition for obtaining extremely low sulfur hot metal. Thus, the following formula (B) is obtained.
Desulfurization rate [%] = 126.7 x converted M.Al [kg / t] + 0.189 x T [° C] + 8.44 x [Si] [wt%] -228.77≥90-(B)
III. By transforming the above formula (B), the above formula (1) defining the converted M.Al amount considering the hot metal temperature T and the hot metal Si concentration before the desulfurization treatment is derived. In other words, in order to effectively produce extremely low sulfur hot metal, a larger amount of converted M.Al than the amount calculated by equation (1) may be added to the hot metal.

  Next, the flux satisfies the condition shown in the following formula (2).

The condition shown in the formula (2) is a condition related to the sulfur activity in the slag corresponding to the above formula (a). Generally, it is known that a basic oxide contained in slag significantly reduces the activity of sulfur (S) in the slag and promotes the desulfurization reaction. Examples of basic oxides include alkali metal oxides such as Na ₂ O and K ₂ O, and alkaline earth metal oxides such as CaO and MgO. However, alkali metal oxides have the problem of being expensive, the problem of large refractory erosion, and the problem of slag treatment after treatment, and are currently not used as the main component of desulfurization agents. .

Usually, oxides of alkaline earth metals such as CaO and MgO are used as the main component of the desulfurizing agent, and the above formula (2) defines the input amount. When the input amounts of CaO and MgO are less than 8 kg / t, even if the oxygen potential is lowered, the desulfurization ability of slag is lowered, and it becomes difficult to produce extremely low sulfur hot metal.
In the formula (2), the unit of the content of CaO and MgO is [kg / t], and represents the weight (kg) of CaO and MgO per 1 t (ton) of molten iron.

It should be noted here that, as described above, M.Al and AlN are oxidized during the desulfurization process, and almost all of them become Al ₂ O ₃ after the process. Since Al ₂ O ₃ decreases the desulfurization ability of slag, the composition of the flux must be designed in consideration of the amount of Al ₂ O ₃ converted from M.Al and AlN.
As a flux satisfying the above formulas (1) and (2), for example, quick lime, metal Al particles, and two types of aluminum ash, a total of four kinds of raw materials can be mixed and used. Of these, the metallic Al particles are substantially 100% M.Al, and the composition of the remaining three raw materials is as shown in the table below.

  In Table 2 below, the aluminum ash (1) is the residue after the aluminum dross generated by aluminum refining is ash-drawn and the contained M.Al is recovered. The aluminum ash (2) is a residue obtained by recovering M.Al from the above-mentioned aluminum dross by arc furnace treatment (see, for example, JP-A-2006-283083), and the content of AlN is It is characterized by being higher than aluminum ash (1).

Since the above-mentioned aluminum ash and arc furnace ash are substances containing all of metal aluminum (M.Al), aluminum nitride (AlN), and Al ₂ O ₃ , the weight of each component can be obtained by the following method. The rate was measured.
First, the M.Al [wt%] of the sample flux is measured by bromine-methanol decomposition-ICP emission analysis. Here, the unit [wt%] represents weight percent.

Next, the nitrogen (N) content in the bromine-methanol decomposed residue is measured by a neutralization titration method, and the detected nitrogen amount N [wt%] is all derived from aluminum nitride (AlN), and AlN [wt%] is calculated. To do.
Further, the total amount of aluminum (Al) T.Al [wt%] was measured for the residue by ICP emission analysis, and the total amount of aluminum (Al) T.Al [wt%] was calculated as shown in the following formula (3). Al ₂ O ₃ [wt%] was calculated assuming that the amount of Al in Al ₂ O ₃ is the amount excluding the amount of Al in AlN.

Next, the stirring process for the hot metal after the addition process will be described. As described above, the stirring process according to the present embodiment is a process of promoting the desulfurization reaction while forcibly stirring the hot metal to which the flux has been added by the impeller 5 immersed in the hot metal of the hot metal pan 4. It is characterized by how to use the stirring power density ε [kw / t].
In the stirring process according to the present embodiment, the stirring power density ε [kw / t] is used as shown in the following formula (4).

In the mechanical stirring process according to the present embodiment, since the atmosphere is entrained simultaneously with the flux in the hot metal, the ratio of M.Al and AlN introduced for deoxidation is important. Both M.Al and AlN added to the hot metal eventually react with oxygen to become Al ₂ O ₃ , but M.Al has a strong reaction with oxygen (the progress of the deoxidation reaction is fast). Therefore, the time until the total amount becomes Al ₂ O ₃ is short, and since the reaction of AlN is slow (the progress of the deoxidation reaction is slow), the time required for the total amount to react is longer. is there.

When the total amount of M.Al is used without using AlN as a component for deoxidation, the oxygen potential rapidly decreases immediately after the addition, but once converted to Al ₂ O _3, it can no longer contribute to deoxidation. Therefore, it cannot react with the oxygen entrained by stirring after that, and the oxygen potential in the hot metal will increase, and the desulfurization ability will decrease.
On the other hand, when the total amount of AlN is used without using M.Al, since the progress of the deoxidation reaction is slow, the oxygen potential does not decrease immediately after the addition and the desulfurization ability is lowered. An optimum range is considered to exist, and in order to advance the desulfurization reaction efficiently, it is necessary to operate after adjusting the ratio of M.Al and AlN to the optimum range.

In addition to the ratio of M.Al and AlN, the amount of atmospheric entrainment in the hot metal is determined by the strength of stirring by the impeller 5, so the optimum range of the ratio of M.Al and AlN is the strength of stirring. It changes depending on the expressed stirring power density ε.
In other words, when the stirring power is large, the amount of entrained air (entrained oxygen amount) is large, so the ratio of slow-acting (slow progress of deoxidation reaction) AlN needs to be high, and when the stirring power is small, the effect is immediate. The ratio of the characteristic M.Al (the progress of the deoxidation reaction is fast) needs to be high.

Therefore, as shown in the above formula (4), the quotient (X / ε) of the ratio X (= AlN / (AlN + M.Al)) of M.Al and AlN and the stirring power density ε (X / ε) yields M.Al and AlN. This represents the relationship between the ratio and the stirring power by the impeller 5. That is, equation (4) can be said to be an index that quantitatively represents the relationship between the ratio of slow-acting AlN in the deoxidation component and the stirring power. Therefore, when the quotient X / ε is smaller than 0.5, the amount of AlN with respect to the magnitude of the stirring power is too small, so that not only M.Al but also AlN is quickly oxidized and consumed by the entrained air. As a result, the desulfurization ability decreases. On the other hand, when the quotient X / ε is greater than 0.8, the amount of AlN relative to the magnitude of the stirring power is too large, so that the progress of the deoxidation reaction becomes too slow and the desulfurization ability is lowered.

As for the absolute amount of AlN, it is desirable that AlN> 0.02 kg / t in order to satisfy the above-mentioned converted M.Al condition, and the stirring power density ε of mechanical stirring desulfurization is generally Is about 0.4 to 1.2 kw / t. The method for calculating the stirring power density ε is as described above.
As explained above, by performing desulfurization treatment with the composition of the flux satisfying the above-mentioned formulas (1), (2) and (4) and the stirring power density ε, the hot metal is effective in accordance with the hot metal temperature before the desulfurization treatment. Can be desulfurized automatically.

Hereinafter, an experimental result (desulfurization result) of the desulfurization treatment in which the above-described addition treatment and stirring treatment are performed will be described.
First, experimental conditions are described. A high frequency melting furnace was used for the experiment. The inner diameter (D) of the furnace is 400 mm, the bath depth (Z) is 340 mm, and the amount of molten iron is 300 kg. The treatment time was 10 minutes (min) from the start of stirring, and the flux was charged all at once from the top of the furnace immediately before the start of stirring. As the flux, a 3 mm under product having a particle size of less than 3 mm was used.

As for the size of the impeller for stirring the hot metal, the height (b) is 90 mm, the width (d) is 140 mm, the number of blades (n _p ) is 4, the twist angle (θ) is 90 °, and the stirring power is the rotation of the impeller Controlled by number control.
Regarding the hot metal component, the hot metal [C], which is the content of carbon C in the hot metal, is 3.69 to 4.65% by weight, and the hot metal [S], which is also the content of sulfur S, is 0.019 to 0.031% by weight. %, The hot metal [Si], which is the content of silicon Si, was 0.01 to 0.52% by weight.

Finally, a threshold for determining whether or not desulfurization has been satisfactorily performed for the treated S (treated iron S), which is the content of sulfur S in the molten iron after the desulfurization treatment, is disclosed in, for example, Japanese Patent Laid-Open No. 2011-2011. As shown in Japanese Patent No. 6761, the desulfurization rate ≧ 90%, which is a standard as a condition for producing extremely low sulfur hot metal and extremely low sulfur steel.
Table 3 below shows the case where all three conditions of conversion M.Al defined by the above formula (1), basicity defined by the formula (2), and deoxidation parameter Z defined by the formula (4) are satisfied. The results of the desulfurization treatment (experimental results) are shown as examples.

According to Table 3 above, since the desulfurization rate is 90% or more in all the experiment numbers, as an evaluation of the experimental results, the symbol “◯” indicating that desulfurization as an extremely low-sulfur steel was successfully performed. "Is attached.
Table 4 below satisfies the two conditions of the basicity defined by the formula (2) and the deoxidation parameter Z defined by the formula (4), but the converted M.Al defined by the formula (1) above. The result (experimental result) of the desulfurization process when not satisfying is shown as Comparative Example 1.

According to Table 4 above, the conversion M.Al defined by the formula (1) is not satisfied, so the desulfurization rate is less than 90%. A symbol “x” indicating that the operation was not performed successfully is added.
FIG. 4 is a graph showing the results of the example shown in Table 3 and the results of Comparative Example 1 shown in Table 4. According to the graph shown in FIG. 3, when the conversion M.Al prescribed | regulated by Formula (1) is not satisfy | filled, that is, when it is less than the lower limit of conversion M.Al, the desulfurization rate is less than 90%. Therefore, it is desirable to perform the desulfurization treatment using a flux of a component in which the converted M.Al specified by the formula (1) does not fall below the lower limit.

  Table 5 below satisfies the two conditions of conversion M.Al defined by the formula (1) and basicity defined by the formula (2), but the deoxidation parameter Z defined by the above formula (4). The result (experimental result) of the desulfurization process when not satisfy | filling these conditions is shown as the comparative example 2. FIG.

According to Table 5 above, the condition of the deoxidation parameter Z defined by the equation (4) is not satisfied, that is, the relationship between AlN / (AlN + M.Al) and the stirring power does not satisfy the condition. Is less than 90%, and as an evaluation of the experimental results, a symbol “x” indicating that desulfurization as an extremely low-sulfurized steel was not performed well is given.
When the deoxidation parameter Z defined by the equation (4) is not satisfied, that is, the deoxidation parameter Z, the ratio X (= AlN / (AlN + M.Al)) of M.Al and AlN and the stirring power density ε When the quotient (X / ε) is not in the range of 0.5 or more and 0.8 or less, the desulfurization rate is less than 90%. Therefore, it is desirable to perform the desulfurization treatment at a deoxidation parameter Z of 0.5 or more and 0.8 or less.

  Table 6 below satisfies the two conditions of the conversion M.Al defined by the formula (1) and the deoxidation parameter Z defined by the formula (4), but is defined by the above formula (2). The result (experimental result) of the desulfurization process when the basicity is not satisfied is shown as Comparative Example 3.

According to Table 6 above, since the basicity defined by the formula (2) is not satisfied, the desulfurization rate is less than 90%, and as an evaluation of the experimental results, desulfurization as an extremely low sulfur steel is satisfactory. A symbol “x” indicating that the operation was not performed is added.
When the basicity defined by the formula (2) is not satisfied, that is, when the ratio of the content of CaO or MgO to the content of SiO ₂ or Al ₂ O ₃ is large, the desulfurization rate is less than 90%. Yes. Therefore, it is desirable to perform the desulfurization treatment using a flux of a component whose basicity defined by the formula (2) is 8 (kg / t) or more.

  According to the hot metal desulfurization method according to the present embodiment described above, it is possible to produce ultra-low-sulfur steel by desulfurizing hot metal very efficiently, but in particular, as little flux as possible depending on the difference in hot metal temperature. The hot metal can be efficiently desulfurized. For this reason, since the usage-amount of expensive fluxes, such as aluminum ash, falls, it is possible to hold down desulfurization processing cost to a low level, and also the amount of generated slag is reduced, leading to reduction in slag processing cost.

  As mentioned above, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. In particular, in the embodiment disclosed this time, matters that are not explicitly disclosed, for example, operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that a person skilled in the art normally performs. Instead, values that can be easily assumed by those skilled in the art are employed.

1 Blast Furnace 3 Chaos Car 4 Hot Metal Pan 5 Impeller

Claims (1)

In carrying out desulfurization treatment of the hot metal discharged from the blast furnace by mechanical stirring at the hot metal stage before the decarburization process in the converter,
A hot metal desulfurization method characterized by using a flux having a composition satisfying the following conditions.

Images