JPH093515A - Desulfurization process for low silicon concentration hot metal - Google Patents

Abstract

PURPOSE: To provide an economical and extremely high efficiency of desulfurization in low silicon concentration hot metal. CONSTITUTION: At the time of the desulfurization caused by a mixed flux consisting of quicklime and Al ash, a mixture wherein mixing ratio of CaO and Al2 O3 in desulfurizing agent is made so as to be the range of 33-37.7wt.% Al2 O3 , or the mixture wherein the quicklime and Al ash is added so as to be said mixing ratio after addition, is desulfurized. Or further, said flux is made consist of powder not larger than 22 mesh and then is added into the hot metal. Thereby, the highest efficiency of desulfurization not found conventionally is get and cost for process is inexpensive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly efficient desulfurization method for hot metal and is widely used in the field of hot metal pretreatment.

[0002]

2. Description of the Related Art Sulfur in steel has a property of deteriorating the properties of steel by the formation of sulfide inclusions. For example, steel pipes for sour use require a low sulfur concentration of 5 ppm.

In order to meet these demands, desulfurization treatment technology has been developed in iron and steel refining. Among the desulfurization treatments, the treatment at the hot metal stage uses quicklime, carbide, soda ash, and other highly basic oxides and metallic Mg to produce sulfides such as CaS, Na ₂ S, and MgS, and produce slag as slag. The method of separating and removing is adopted. Further, in order to achieve an extremely low sulfur concentration, the crude refined molten steel is further desulfurized by using a CaO-based flux.

Generally, sulfur has a high binding force with alkali metals or alkaline earth metals such as Na, Mg and Ca, and it is desulfurized to react with these elements to form sulfides and remove them by the following formula. Processing. N of these
a, Mg, and Ca have the highest binding strength in this order, but as a material that can be inexpensively and stably supplied on an industrial scale, quick lime and limestone containing CaO as a main component, soda ash containing Na ₂ CO _{3 as a} main component, or That is, calcium carbide mainly containing CaC ₂ and metallic Mg are used. Among these, the lime-based flux containing CaO as a main component has abundant resources, is cheap, and is easy to handle, although it has a weaker binding force to sulfur than Na-based and Mg-based. Widely used. CaO + S → CaS + O (1) Na ₂ CO ₃ + S → Na ₂ S + CO ₂ + O (2) Mg + S → MgS (3)

On the other hand, CaO itself has a very high melting point of 2800 ° C. and remains in a solid state even when it is simply contacted with molten iron.
In this case, the desulfurization reaction proceeds by solid phase diffusion of S in solid CaO, but this process is generally known to be very slow. Therefore, since solid CaO as it is has poor reactivity, it has a drawback that the desulfurization rate is slow when used alone. Therefore, measures such as adding CaF ₂ or the like to a slag, adding an auxiliary agent for increasing the melting property and increasing the reactivity, or lowering the melting point by firing with these in advance are made.

On the other hand, the desulfurization treatment in the hot metal stage is at a lower temperature than that in the desulfurization process in the molten steel stage, and the reaction of the formula (1) tends to proceed to the right as the temperature rises. Although it is disadvantageous, addition of CaF ₂ slag forming aid has the advantage that the wear of refractory progresses more markedly in the molten steel stage and the sulfur content in molten iron increases due to the large amount of carbon contained in the molten pig iron. , Hot metal desulfurization treatment is actively adopted.

[0007]

The lime-based flux used in hot metal desulfurization is disclosed in Japanese Examined Patent Publication No. 55-249.
As disclosed in Japanese Patent Publication No. 25 and Japanese Patent Publication No. 63-195208, there is a description that CaO and Al ₂ O ₃ are mixed and melted in a specific composition. Although these methods are recognized to have an improvement effect on refining, pre-firing requires significant energy and deviates from the feature of quick lime flux that is inexpensive because it causes high flux cost, so some Although it may be used in secondary refining for high-grade steel, it is a method that cannot be widely applied to ordinary steel.

In Japanese Patent Publication No. 2-305913, Al ₂ O ₃ is added to quick lime as a molten slag forming aid,
There is a description that the flux is melted by spraying it onto hot metal to accelerate the sulfur reaction. CaO-A
In the case of the l ₂ O ₃ binary system, the composition having the lowest melting point is known when the mixing ratio is 1: 1 by weight, and the melting point is known to be about 1400 ° C. However, this method imposes restrictions on the temperature on the hot metal side. For example, 1 after hot metal preliminary dephosphorization
There is a problem that it cannot be used at temperatures around 350 ° C.

Furthermore, Japanese Patent Publication No. 5-78723 discloses C
There are aO-Al ₂ O ₃ mixed effect of describing the SiO ₂ or CaF ₂ for improving the slag formation meltability by system. Although SiO ₂ is easy to use as a slagging agent as a secondary material that can be obtained in large quantities at low cost in the form of silica stone, etc., it reduces the desulfurization ability of slag, so it is essentially preferable to use SiO ₂ as a slagging aid. Absent. CaF ₂ is one of the auxiliary materials that can be industrially used in iron and steel refining, and is known to best assist the quick lime slag formation and not reduce the desulfurization ability of slag. Since it corrodes significantly, a mixed flux of CaO and CaF ₂ is only used in the secondary refining, for example, for some high-grade steels that require extremely low sulfur concentrations.

On the other hand, it is well known that the diffusion distance of S in solid quick lime can be shortened and the desulfurization rate can be increased by blowing CaO as fine powder without completely slagging and melting CaO. Therefore, for example, Japanese Patent Publication Sho 54
JP-A-37020 describes that the particle size of CaO blown into the hot metal is 0.4 mm or less. On the other hand, handling problems such as quick lime particle size scattering, blowing hopper, blow tank,
There is a problem such that adhesion to the inside of the pipe occurs and operation becomes impossible, and there is a limit to the industrial use of pulverization as a matter of course.

On the other hand, it is known that coexisting elements greatly affect the desulfurization efficiency even when fine powder is blown. For example, iron and steel vol.61 (1975), p. Two
As described in No. 9, when the hot metal contains silicon, silicon is oxidized by free oxygen generated by the formula (1), and 3CaO.Si which is a high melting point oxide on the surface of quick lime.
It is known that O ₂ (melting point: 2150 ° C.) and 2CaO · SiO ₂ (melting point: 2180 ° C.) are generated to inhibit the diffusion of S into the quicklime particles and reduce the desulfurization rate. As a means for avoiding this, Japanese Patent Publication No. 56-23220 discloses that powder Al is blown into hot metal together with Al ₂ O ₃ and CaO to adjust the Al concentration in the hot metal in advance, and then Ca
There is a description that blows O and CaC ₂ to desulfurize. A
It is described that l is added for the purpose of suppressing the oxidation reaction of silicon by oxygen, and the amount of Al added is defined by the equation (4). [% Al] = (0.01 to 0.1) [% Si] + (0.2 to 1.0) × Δ [% S] (4) where [% Si]: Silicon concentration in hot metal (% by weight) Δ [% S]: Desired desulfurization width (% by weight)

Further, Japanese Patent Publication No. 55-110711 discloses that Al is blown in the same way as CaO from the viewpoint of suppressing the oxidation of silicon. With respect to this point, the present inventors have made detailed studies leading to the present invention. It is desirable to desulfurize with hot metal having a low silicon concentration when Al is added. Under such conditions, a very high desulfurization efficiency can be obtained. However, there is a problem that the effect of Al added is not maximized in the hot metal having a high silicon concentration.

As a similar technique, Japanese Patent Publication No. 56-58912
The publication describes a desulfurizing agent containing 20 to 90% calcium carbide, 75 to 5% quicklime, and 1 to 5% Al residual ash, but the technical basis for its composition is ambiguous.

Due to the above-mentioned problems, the hot metal desulfurization treatment with a lime-based flux is still widely practiced by a method in which the lime itself, which has been pulverized to some extent, is blown into the hot metal. In view of such a situation, an object of the present invention is to provide a lime-based desulfurizing agent that enables inexpensive and highly efficient desulfurization treatment of hot metal.

[0015]

Means for Solving the Problems The present invention is as follows: (1) In the desulfurization treatment of hot metal with a mixed flux of a flux containing lime as a main component and Al ash, C in a desulfurizing agent is used.
The mixing ratio of aO and Al ₂ O ₃ is Al ₂ O ₃ and 33 to 37.
7 a mixture such that the weight percent range, or the mixing ratio of CaO and Al ₂ O ₃ after addition with Al ₂ O _3. 33 to
A method for desulfurizing hot metal having a low silicon concentration, which comprises adding quick lime and Al ash in an amount in the range of 37.7% by weight. (2) The desulfurizing agent for hot metal according to the above item (1), in which a flux composed of powder having a raw material particle size of 22 mesh or less is blown.

[0016]

When the metallic Al is present, the desulfurization reaction is represented by the following equation.

3CaO (solid) + 3S + 2Al = 3CaS (solid) + Al ₂ O ₃ (solid) (5) When the equilibrium constant of this reaction is used, the equilibrium reaching sulfur concentration is CaO on the slag side as shown in equation (6). , Al ₂ O ₃ , C
Activity of aS aCaO, aAl ₂ O ₃ , aCaS, Al in hot metal
Expressed using concentration. Equilibrium reached [% S] = {(aCaS aAl ₂ O ₃ ) / (KaCaO [% Al] ² )} ^1/3 (6)

Since the slag is in a solid state at the experimental conditions of 1350 ° C., the reaction between the solid slag and the hot metal may be taken into consideration. That is, the equilibrium sulfur concentration if the ratio of the same CaO-Al ₂ O ₃ becomes to be reduced in inverse proportion to 2/3 power of the Al concentration in the molten iron. Therefore, from the viewpoint of increasing the Al concentration in the hot metal, it is better to add Al ash as much as possible.
The activity of CaO and Al ₂ O ₃ at 1350 ° C. is estimated as shown in FIG. That is, aCaO is kept at the maximum value of 1 and the activity of aAl ₂ O ₃ is at the minimum value up to the theoretical Al ₂ O ₃ concentration of tricalcium aluminate (3CaO.Al ₂ O ₃ ) of 37.7% by weight. Stays in. However, when the Al ₂ O ₃ concentration exceeds 7%, aCaO decreases,
aAl ₂ O ₃ rises. From this result and equation (6), Al
Figure 2 shows the relationship between the ash mixture ratio and the sulfur concentration at equilibrium. Here, the use of lower grade Al ash, which is an industrial waste having the composition shown in Table 1, is considered as the Al ash. The Al ash mixing ratio at which the ultimate sulfur concentration becomes the minimum value is the point at which tricalcium aluminate (3CaO.Al ₂ O ₃ ) is produced. Therefore, it is concluded that the desulfurization efficiency with a large mixed flux of quicklime and Al ash is obtained when the mixing ratio of Ca ₂ O and Al ₂ O _{3 in} Al ash is 3: 1 in molar ratio. It was

[0019]

[Table 1]

Next, the present inventors conducted a test confirming the present theory. That is, quick lime was mixed with low-grade Al ash, which is an industrial waste having the composition shown in Table 1, to perform desulfurization treatment of hot metal, and the results shown in FIG. 3 were obtained. It was clarified that the maximum desulfurization rate was obtained when the weight mixing ratio of quicklime and Al ash was about 1: 1, but this optimum composition is in good agreement with the composition with the lowest sulfur concentration reached in the results of FIG. did.

On the basis of these results, a test was conducted in which quick lime and Al ash were mixed in advance at a weight ratio of 1: 1 in a torpedo car, and a test was carried out. In the case of low silicon hot metal, the Al concentration on the hot metal side increased. Together with flux desulfurization efficiency K
The result of FIG. 4 that the value increases is obtained.

Further, when the hot metal containing 0.25% or more of silicon was desulfurized with this flux, the Al concentration was 0.015.
%, The effect of Al addition tends to be saturated, which is different from the case of low silicon concentration. When 0.25% or more of silicon was melted on the hot metal side, even if the same flux was used, a great effect of improving desulfurization efficiency was not obtained, but this was due to the high melting point of Gehlenite (2CaO · SiO ₂ · Al ₂
This is because O ₃ and melting point: 1600 ° C.) are generated and the diffusion of sulfur into the solid raw stone part is hindered.

The present inventors conducted detailed experiments and studies on the reaction mechanism in the course of reaching the present invention. That is, a lump of quick lime made by burning limestone at 1000 ° C. using a rotary kiln is polished, a spherically shaped lime having a diameter of about 20 mm is immersed in hot metal, reacted with the hot metal for 120 minutes, and then quick lime is polished. Then, the vicinity of the contact surface of the quick lime cross section with the hot metal was analyzed with an X-ray microanalyzer.

FIG. 5 shows that 0.5 mol of silicon is added to the hot metal at the initial stage of the reaction.
%, Aluminum 0.07% and sulfur 0.05% are observed by an X-ray microanalyzer. In this case, the secondary electron beam image (SEM image)
Quantitative analysis was performed at the positions indicated by d ₁ , d ₂ , d ₃ , and d ₄ . Shows a plot of the quantitative results in CaO-SiO ₂ -Al ₂ O ₃ ternary system phase diagram on. Pole to d ₂ near the surface generation of _{Gehlenite (2CaO · Al 2 O 3} · SiO 3) was observed. Further, from the qualitative photograph, it is clear that the penetration depth of sulfur and aluminum into the interior of the quick lime is only about 10 microns.

On the other hand, in FIG. 6, silicon is not contained in the initial stage of the reaction,
It is the X-ray microanalyzer qualitative analysis result in the vicinity of the surface of the cross section of the quick lime after the spherical quick lime was immersed in the hot metal containing 0.021% of aluminum for 120 minutes to cause the reaction. In this case, it is apparent that the penetration depth of sulfur and aluminum into the quicklime is large and the sulfur is also concentrated at a high concentration in comparison with the results of FIG.

Considering the above results, in the case of hot metal containing silicon, not only the reaction of the formula (5) but also the reaction of the formula (7) occur at the initial stage of the reaction, and together with CaO and Al ₂ O _3.
It is presumed that Gehlenite (2CaO · Al ₂ O ₃ · SiO ₂ ) is generated and the penetration of sulfur and Al into the quick lime is hindered in order to form a dense protective film. Therefore,
In the case of hot metal having a high silicon concentration in FIG. 4, the desulfurization efficiency is improved up to an Al concentration of 0.02%, but above this, even if the aluminum concentration is increased to some extent, the desulfurization efficiency is not so much improved. Therefore, in order to promote the desulfurization reaction of the formula (5) more effectively, the condition of low silicon concentration is desirable, and the present inventors have made clear that the silicon concentration is desirably 0.25% or less. 2CaO (solid) + 2S + Si = 2CaS (solid) + SiO ₂ (solid) (7)

The following conclusions can be made by summarizing the above examination results. (A) As a condition on the slag side, the mixing ratio of CaO and Al ₂ O ₃ is up to ₃ CaO · Al ₂ O _{3 which is} a chemical equivalent.
₂ O ₃ may be mixed, but if it exceeds this, CaO
This leads to a decrease in activity and is not preferable. (B) The higher the Al concentration in the hot metal, the higher the desulfurization efficiency can be. However, when silicon is present in an amount of 0.25% or more, dense Gehlenite with a high melting point is generated on the surface of the raw coal to form sulfur in the quicklime particles. It is not preferable because it can prevent penetration.

Considering industrial applications, aluminum ash, which is generated as a large amount of industrial waste as aluminum and Al ₂ O ₃ , is inexpensive and has a high utility value. The present invention, which is used as a mixture, is disclosed. In addition, considering the variation in the quality of Al ash that is industrial waste, that is, the variation in the Al ₂ O ₃ content rate, the molar ratio of CaO and Al ₂ O ₃ is strictly 3:
It is quite difficult to set the ratio to 1, but according to the test conducted by the present inventors, the weight ratio of CaO to Al ₂ O ₃ is 1.
It has been clarified that substantially the same effect can be obtained within the range of 65 to 2.0.

In this method, Al having a high metal Al content is used.
Since ash has a higher Al concentration in the hot metal and higher desulfurization efficiency, it is desirable for improving desulfurization efficiency. On the other hand, Al ash having a high metal Al content is valuable as a raw material for Al and is generally expensive. Therefore, it is not preferable in terms of cost.

However, this method can be applied without any problem if Al ash having a high metal Al content is available at a low cost. Further, it is not preferable that the concentration of acidic oxides such as SiO ₂ , P ₂ O ₅ and B ₂ O ₃ that have a deteriorating action on desulfurization is high as impurities. As a guideline, the total concentration of these acidic oxides is 15%. It is desirable to use the following Al ash. Further, when the concentration of metallic Al in the flux is 3% or less, the Al concentration on the hot metal side does not increase so much, so that the desulfurization efficiency does not differ much from the case of using quicklime alone. Therefore, it is desirable that the metal Al content in the flux be 3% or more. Alternatively, CaO and Al ash may be fired in advance.

Since the method of the present invention is based on the reaction in the solid state as described above, the reaction is slow when the desulfurizing agent has a large particle size, and the reaction is slow. As a guide, 22mesh or less is desirable. This is because when the particle size is larger than this, as shown in FIG. 7, even if Al ash is mixed, the desulfurization efficiency is not significantly improved. Most preferably, it should be blown into the hot metal as fine powder. When this is difficult, a so-called blasting method, in which the carrier gas is conveyed from above the hot metal with a high-speed carrier gas and sprayed, can also be used. On the other hand, if it is too fine, the crushing cost will be excessive, and handling problems such as scattering will occur, and there will be problems such as adhesion to the blowing hopper, blow tank, and pipes, making operation impossible. Therefore, there is a limit to the industrial use for fine pulverization, and the particle size may be within a usable range, but fine powder within the range currently industrially used is sufficient.

Further, at present, many steelworks using blast furnace hot metal as a raw material already have desiliconization treatment or dephosphorization treatment equipment as hot metal pretreatment equipment. The high desulfurization efficiency of the method can be easily obtained. Further, when hot metal having a silicon concentration of 0.25% or less is used as a raw material, it is unnecessary to perform these pretreatments only for the purpose of applying the method of the present invention. Further, the reaction vessel may be any of a torpedo car, a hot metal ladle, an induction melting furnace, and the like, which can be sufficiently implemented within the scope of conventional equipment technology such as simply adding a desulfurizing agent blowing device and some equipment accompanying it.

[0033]

【Example】

(Example 1) 291 t of blast furnace hot metal was subjected to desiliconization and dephosphorization treatment in a hot metal pretreatment furnace from a torpedo car, then transferred to a pan and mixed with 52% quicklime and 48% Al ash having the composition shown in Table 2. The desulfurization rack was desulfurized by blowing N ₂ gas as a carrier through an immersion lance. The blowing rate of the desulfurizing agent was about 150 kg / min. The silicon concentration before treatment is 0.01% or less, and the hot metal temperature before treatment is 12%.
90 ° C. The sulfur concentration in the hot metal decreased from 0.020% to 0.002% by the treatment for 15 minutes. At this time, the temperature drop of the hot metal was about 16 ° C. At this time, the basic unit of CaO is 4.0 kg / tp / t of hot metal, and the K value of the desulfurization reaction is 0.1
A value as high as 50 was obtained. However, the K value is an index showing the utilization efficiency of quick lime, which is shown by the equation (8). K = ln ([% S] _i / [% S] _f ) / WCaO (8) where [% S] _i : pretreatment sulfur concentration (%) [% S] _f : posttreatment sulfur concentration (%) ) WCaO: quicklime basic unit (kg / t)

[0034]

[Table 2]

Example 2 Blast furnace hot metal 287t was transferred to a torpedo car while being desiliconized by introducing a desiliconizing agent such as mill scale in a tap iron gutter, and further dephosphorized in a hot metal pretreatment furnace. Then, after transferring to a hot metal ladle, N ₂ gas was used as a carrier gas through a top blowing lance and quick lime 3
Desulfurization treatment was carried out by blasting of a desulfurization flux mixed at a ratio of 3% and 67% of Al ash having the composition shown in Table 3. The silicon concentration before the treatment was 0.10%. The desulfurizing agent supply rate was 130 kg / min. The linear flow velocity at the nozzle outlet was 350 m / sec. The sulfur concentration in the hot metal decreased from 0.022% to 0.003% by the treatment for 15 minutes. At this time, the temperature drop was only 12 ° C. At this time, the basic unit of CaO is 2.24 kg / t, and the K value is 0.
A very high value of 9 was obtained.

[0036]

[Table 3]

(Example 3) 160 t of blast furnace hot metal was received by a torpedo car to remove the mixed blast furnace slag, and then descaling was carried out by blowing mill scale and oxygen gas. Then, after removing the desiliconized slag, a mixed flux of 54% quick lime and 46% Al ash having the composition shown in Table 2 was blown to perform desulfurization treatment. The silicon concentration before the treatment was 0.17%. The desulfurizing agent supply rate was 60 kg / min. At 45 minutes, the sulfur concentration dropped from 0.019% to 0.001%. The temperature drop of the hot metal at this time was 25 ° C. Quicklime basic unit 5.
It was 7 kg and a high K value of 0.5 was obtained.

COMPARATIVE EXAMPLE 1 Blast furnace hot metal 289t was desiliconized and dephosphorized in a hot metal pretreatment furnace from a torpedo car, then transferred to a pan, and fine powder of quick lime and soda ash mixed desulfurizing agent was passed through a dipping lance to obtain N ₂ Gas was used as a carrier to perform desulfurization treatment. The mixing ratio by weight of desulfurizing agent, quicklime and saw ash, was 4: 1. Blowing speed of desulfurizing agent is about 15
It was 0 kg / min. The silicon concentration before the treatment was 0.1% or less. The hot metal temperature before the treatment was 1305 ° C.
The sulfur concentration of 0.020% in the hot metal dropped to 0.003% after the treatment for 30 minutes. At this time, the temperature drop of the hot metal was large at about 50 ° C., and adhesion to the pan occurred. The basic unit of desulfurization agent that combines soda ash and quicklime is 15.6 kg /
t, quicklime alone required a large amount of 12.5 kg / t, and the K value of desulfurized quicklime was as low as 0.15.

(Comparative Example 2) 289 tons of blast furnace hot metal was received from a torpedo car and transferred to a hot metal pretreatment furnace for desiliconization and dephosphorization treatment. Furthermore, it was transferred to a pan and finely powdered quick lime was blown through an immersion lance using N ₂ gas as a carrier for desulfurization treatment. The particle size of the desulfurizing agent was 200 mh or less, and ultrafine powder was used. Blowing speed of desulfurization agent is about 150kg
/ min. The hot metal temperature of the treatment was 1307 ° C.
During the treatment for 30 minutes, the concentration of sulfur in the hot metal, 0.020%, decreased to 0.00%. At this time, the temperature drop of the hot metal was large at about 50 ° C., and adhesion to the pan occurred. The K value was as low as 0.12.

(Comparative Example 3) After receiving 291 t of blast furnace hot metal with a torpedo car and removing blast furnace slag, 31% of quick lime and 69% of Al ash having the composition shown in Table 3 were used as N ₂ gas as a carrier gas and a dipping lance was used. And then desulfurized. The silicon concentration of the hot metal before the treatment was 0.52%.
The blowing rate of the desulfurizing agent was 60 kg / min. 45min
By the treatment of 1, the sulfur concentration only dropped from 0.020% to 0.011%. The K value remained at 0.2.

(Comparative Example 4) 279 t of blast furnace hot metal was desiliconized and dephosphorized in a hot metal pretreatment furnace from a torpedo car and then transferred to a pan to obtain 47% of fine calcified lime and 53% of Al ash having the composition shown in Table 2. Mixed desorbent consisting of N through the immersion lance
_Two gases were used as a carrier to perform desulfurization treatment.
The blowing rate of the desulfurizing agent was about 150 kg / min. The silicon concentration before the treatment was 0.1% or less. The hot metal temperature before the treatment was 1305 ° C. During the treatment for 30 minutes, the sulfur concentration in the hot metal, 0.020%, decreased to 0.012% and could not be reduced to the target of 0.010% or less.
At this time, the temperature drop of the hot metal was about 25 ° C. The K value of desulfurized quicklime was as low as 0.17. This is because the CaO / Al ₂ O ₃ ratio in the desulfurizing agent was 1.5, which was largely deviated from the optimal range of 1.65 to 2.0 to a lower one.

[0042]

As described above, according to the present invention, the conventional lime-based lux containing CaF ₂ which is expensive and has large refractory wear, or soda ash-based flux which has large refractory wear and large temperature drop is used. Further, there is provided an efficient desulfurization method utilizing an inexpensive desulfurizing agent which is obtained by simply mixing inexpensive raw materials such as low-grade Al residual ash which is industrial waste. As a result, the cost is 0.001% at low cost.
The following hot metal with a low sulfur concentration causes less temperature drop and is easily obtained. As described above, the present invention provides a desulfurizing agent which can easily, reliably, and inexpensively produce extremely low sulfur steel on an industrial scale.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the Al ₂ O ₃ weight concentration and the amount of CaO and Al in a mixture of CaO and Al ₂ O ₃ at 1350 ° C.

FIG. 2 is a diagram showing the relationship between the Al ash mixture ratio of CaO and Al ash mixture desulfurization agent and the equilibrium reaching sulfur concentration.

FIG. 3 is a graph showing a relationship between quick lime obtained in the test leading to the present invention by the present inventors and Al ash mixture specific desulfurization rate in terms of Al ₂ O ₃ .

FIG. 4 is a diagram showing a relationship between a desulfurization efficiency K value of quicklime and an Al concentration in hot metal.

FIG. 5 is a diagram showing an electron beam microanalyzer analysis result in the vicinity of the surface of quicklime particles that have been desulfurized with hot metal containing 0.070% Al and 0.50% silicon.

FIG. 6 is a diagram showing an electron beam microanalyzer analysis result in the vicinity of the surface of quicklime particles which has been desulfurized with hot metal containing 0.021% Al and containing no silicon.

FIG. 7 is a graph showing the relationship between desulfurizing agent particle size and desulfurization rate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsutaka Matsuo 5-3 Tokai-cho, Tokai-shi, Aichi Pref.Nippon Steel Works Ltd. (72) Inventor Kunitake Tomo-cho, Tokai-shi, Aichi 5-3 Inside Nippon Steel Works, Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. A flux containing quick lime as a main component and Al
In the desulfurization treatment of the hot metal with the mixed flux of ash, the mixing ratio of CaO and Al ₂ O _{3 in} the desulfurizing agent is 33% as Al ₂ O ₃ .
˜37.7% by weight, or the mixing ratio of CaO and Al ₂ O ₃ after addition is Al ₂ O ₃
In an amount of 33 to 37.7% by weight, quicklime, Al
A method for desulfurizing hot metal having a low silicon concentration, which comprises adding ash. 2. The desulfurizing agent for hot metal according to claim 1, wherein a flux made of powder having a raw material particle size of 22 mesh or less is blown.