JPH07157819A - Method for decoppering and/or detinning in molten iron - Google Patents

Abstract

PURPOSE:To provide a method, by which [C] in molten iron is made to be low at the stability of the operation and also, high removal ratios of copper and tin can be obtd. even in the case of being such a low [C]. CONSTITUTION:In the method for decoppering and/or detinning tin from molten iron, decarburization is executed to the molten iron by oxygen and mixed material of oxidizing material having weaker than iron oxide and carbonaceous agent in vacuum condition of <=20 Torr. By this method, even in the case of being <=0.50% C content, 84% the decoppering ration and 50-56% the detinning ratio can be obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for removing copper and / or tin from molten iron. More particularly, the present invention relates to a method for effectively and practically removing copper and / or tin, such as from scrap, from molten iron containing them.

[0002]

2. Description of the Related Art When scraps such as automobile scraps are melted in an electric furnace, cupola or the like and used in a converter, the content of copper and / or tin in steel increases. This copper is mixed in, for example, from wiring, and tin is mixed in by plating or the like.

Copper and tin thus mixed in are harmful impurities for steel. That is, too much copper causes red heat embrittlement. Therefore, except for some weathering steels, it is important that the copper content be 0.35% to 0.20% or less. On the other hand, tin causes deterioration in hot workability, elongation and drawing, so it is important to make it 0.10% or less.

However, copper and tin are noble metals rather than iron, and therefore cannot be removed by a normal steelmaking process. Regarding decopperization and / or detinization of molten iron, the following methods are currently known from the literature.

(1) Copper removal A. Method of using lead as a metal for purification Molten lead is brought into contact with hot metal and the distribution ratio of copper expressed by the following formula
It is a method of removing copper in hot metal into lead by utilizing 1.1 to 1.5.

[0006]

[Equation 1]

However, since this method requires a large amount of lead due to its weak decoppering power, it is hardly practical.

B. Method Using Sulfide Slag [Metal
Progress] This is a method that utilizes the fact that copper is removed in slag when sodium sulfide or sodium sulfate is added to hot metal. Ten
About 45% is decopperized with 0 kg / ton flux. In this case, copper is presumed to be removed as sulfide.
However, since this method is limited to hot metal, it is possible to decopper molten carbon-saturated iron that occurs when scrap is melted with a cupola etc., but it is difficult to decopper molten steel melted in an electric furnace. is there. Further, if the hot copper decoppering is carried out by this method, the effect may be small if the treatment time is short, but in many cases, there is a problem that the sulfur content is considerably increased.

(2) Detinning A. Method of dissolving by calcium-calcium fluoride flux by electroslag refining (ESR) A method developed mainly for the purpose of dephosphorization. proceed. It is believed that tin is absorbed and removed in the slag in the form of calcium tin. However, since this method is limited to ESR, there is a problem that the processing cost is too high in the case of inexpensively manufacturing steel using scrap.

B. Method Using Calcium Carbide In principle, the method is the same as in the above-mentioned method A, and tin is incidentally removed in the form of calcium stannous.

The difference from the above method A is that in this method,
As shown in the following formula, this is the point where calcium (Ca) generated by decomposition of calcium carbide (CaC ₂ ) reacts with tin. CaC ₂ → Ca + 2 [C] Although this method is highly likely to be realized as a practical method, it still has a problem in that the flux cost is high. Furthermore,
Both of the above methods A and B are reduction refining, so it is necessary to carry out in an argon atmosphere. Further, since dephosphorization proceeds simultaneously with detinization, if the treated slag is left in the atmosphere. However, there is a problem that calcium phosphide in slag reacts with moisture in the atmosphere to generate phosphine, which is a toxic gas with a strong garlic odor.

(3) Simultaneous decopperization / detinization method Ultra-high vacuum treatment method This is a method of evaporating and removing copper and tin under ultra-high vacuum by utilizing the fact that the vapor pressure of copper and tin is higher than that of iron. However, this method requires a vacuum degree of 10 ^-3 to 10 ^-6 mmHg, which is higher than the vacuum degree of 0.1 to 200 Torr that is usually used in the vacuum treatment of molten iron. Very high,
In addition, the evaporation rate is low, so it is not practical, and only experiments on a crucible scale have been successful.

As described above, regarding copper removal and tin removal, even if they are removed separately or simultaneously, there are successful examples on a crucible scale, but due to cost or technical problems, There is no practical method, and therefore, in the past, in order to bring the content of copper and tin in the molten iron obtained by melting scrap into the target value or less, it relied solely on the selection of scrap.

However, in developed countries such as Europe and the United States, the amount of scrap generated is large due to the large accumulation of social capital, and the ratio of steelmaking using this is high. Steelmaking, which is the main raw material, is likely to become violent. In this sense, the copper removal and / or tin removal technology of molten iron is considered to become more important in the future.

Therefore, the inventors of the present invention have disclosed in Japanese Patent Laid-Open No. 61-119612.
As disclosed in the publication, as a decoppering method and / or a tin removing method of molten iron, "in a method of simultaneously removing copper and tin from molten iron, the molten iron is oxidized by oxygen and iron oxide under a vacuum of 20 Torr or less. Method characterized by decarburization with a weak oxidizer of

According to this method, it has been found that the following excellent operational effects can be obtained. When [C] in molten iron = 4%, decoppering rate = 80 to 90%, detinning rate = 70 to 80% [C] in molten iron = 0.5%, decoppering rate = 60 to 70%, Detinization rate = 30-40%

[0017]

As described above, in the decoppering and / or detinning method of molten iron disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-119612, in the molten iron from the viewpoint of the decoppering rate and the detinning rate.
It was found that the higher [C] was, the more advantageous it was, but as a result of further studies, the following problems were found.

Since decoppering / detinizing in the above method utilizes the evaporation reaction of copper and tin, the higher the molten iron temperature, the more advantageous for decoppering and detinning. For example, the processing temperature is 1600 ℃
The above is desirable.

On the other hand, when the [C] content of the molten iron is high, the melting point of the molten iron is low, and therefore when the molten iron temperature is high, there is a possibility that the molten iron will penetrate into the refractory material, which may cause operational troubles. is there.

When scrap is smelted as a raw material in an electric furnace, its [C] is 0.5% to 2% at most, and carburization may be considered to increase the decoppering / tintin removal rate. Considering the decarburization in the subsequent step, it is more efficient to treat at a low [C], and a method capable of obtaining a high decopperization / detinization rate at a low [C] has been desired.

[0021] Therefore, conventionally, there is a contradictory requirement that it is necessary to have a high [C] in order to increase the decoppering rate and the tin removal rate, while a low [C] is required for stable operation. To be

Thus, the object of the present invention is to provide a method for lowering the [C] content in molten iron from the standpoint of operational stability and realizing a high decoppering / detinization rate even at such a low [C]. It is to be.

[0023]

DISCLOSURE OF THE INVENTION Here, in the decoppering and / or detinning method of molten iron disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-119612, the decoppering rate and the tin removal rate are From the viewpoint, it was found that the higher [C] in the molten iron, the higher the ratio of 4 to 5%. Therefore, the present inventors have found that C: 2.0% or less in molten iron
In order to obtain the same effect without raising [C], it was conceived to use an oxidizing agent weaker than oxygen and iron oxide as a refining agent to be added, and to use a refining agent in which a carbonizing agent is mixed with this. As a result, it was thought that the low amount of [C] in molten iron could be compensated by the carbonizing agent in the refining agent, and when it was applied to the actual operation, unexpectedly, it was thought that the low [C] that had been contradictory until now. The inventors have completed the present invention knowing that a high decopperization / detinization rate can be achieved even if ≦ 2.0%.

Here, the gist of the present invention resides in a method for removing copper and / or tin from molten iron.
A decoppering method and / or detinning method for molten iron, which comprises decarburizing molten iron under a vacuum of Torr or lower with a refining agent composed of a mixture of an oxidizing agent weaker than oxygen and iron oxide and a carbonizing agent. In the present invention, decarburization may be performed under a vacuum of 5 Torr or less.

According to a preferred embodiment of the present invention, the main component of the refining agent is at least one selected from the group consisting of magnesium oxide and carbon, silicon dioxide and carbon, magnesium oxide, silicon dioxide and carbon.

[0026]

As described above, according to the present invention, by adding a refining agent composed of a mixture of an oxidizing agent having a weaker oxidizing power than oxygen and iron oxide and carbon to molten iron under a practical vacuum of 20 Torr or less, for example, [ By setting C] ≦ 1.0%, it is possible to achieve a high decopperization / detinization rate while ensuring operational stability.

There is no particular limitation on the type of molten iron to which the method of the present invention is applied. For example, molten steel or hot metal of carbon steel, which is usually obtained by melting scrap, or molten iron of stainless steel containing a large amount of nickel or chromium may be used. However, as disclosed in JP-A-61-119612, the higher the carbon content of the molten iron, the higher the efficiency of decoppering and / or detinning. However, if the temperature is high [C], the melting point of the molten iron will be low, so when the molten iron temperature is raised, there are operating problems such as the molten iron penetrating into the refractory, but such a problem is [C] ≤ 1.0 %, The molten iron used in the present invention is preferably [C] ≦ 2.0%, more preferably [C] ≦ 1.0%.

Further, the lower the sulfur content, the decopperization and //
Alternatively, the efficiency of detinning is high, but there is no particular problem as long as it is 0.05% or less, which is a level usually found in scrap.
The oxidizing agent used in the method of the present invention may be any oxidizing agent weaker than oxygen and iron oxide. When an oxidizing agent having a stronger oxidizing power than oxygen or iron oxide is used, the amount of oxygen atoms localized at the interface of the decarburization and decopperization and / or detinization reaction is increased, and the number of atoms of copper and / or tin is increased. It is considered that this is because the migration to the reaction interface is hindered and decopperization and / or detinization is inhibited.

Thus, for example, magnesium oxide, silicon dioxide, etc. or mixtures thereof can be used. Magnesium oxide and silicon dioxide are inexpensive, and magnesium, which is a reduction product, evaporates, while silicon enters molten iron, but since it is harmless to molten iron, both oxidizers should be the main components of the oxidizer. Is preferred. Examples of other oxidizing agents include aluminum oxide and zirconium oxide.

Even when the silicon content of molten iron is so large that it becomes a problem, desiliconization can be easily performed by adding quicklime and oxygen or iron oxide after decoppering and / or detinning. . As described above, it is advantageous that the copper removal rate and the tin removal rate are high in molten iron [C].

This is because of the following reasons. The concentration of oxygen, which is surface active, can be reduced, and the mass transfer of copper and tin on the molten steel side at the molten steel-gas interface can be promoted. The decarburization reaction itself can be accelerated and the total gas bubble surface area can be increased. The activity coefficients of copper and tin can be increased by the interaction between Cu-C and Sn-C.

However, in the case of the present invention, particularly low
In order to meet the demand for high decopperization and detinning efficiency in the [C] region (= 0.5 to 2%), the high [C] in molten iron is not increased.
To obtain the same efficiency as in the [C] range, a refining agent in which a carbonizing agent is mixed with an oxidizing agent weaker than oxygen and iron oxide is used as a refining agent to be added.

Therefore, according to the present invention, the low content of [C] in molten iron can be compensated by the carbonizing agent in the refining agent, and the oxygen concentration at the evaporation reaction interface can be locally reduced by the carbonizing agent, and It is considered that the decarburization reaction represented by the formula (2) described later is promoted and the evaporation decoppering detinization can be promoted.

It is desirable that the carbonizing agent to be mixed with the refining agent, for example, carbon, is sufficiently mixed in fine particles so as to easily react with the oxidizing agent. The ratio of the oxidizing agent and the carbon in the refining agent is not particularly specified, but as a range in which the effects of the oxidizing agent and the carbon sufficiently appear, as the mixing ratio of carbon in the refining agent,
A weight percentage of 5-50% is recommended.

The oxidizer used need not be pure,
Any of these may be used as long as they are the main components. For example, if magnesium oxide or silicon dioxide is to be used as an oxidizing agent, brick waste or silica sand may be used. Further, in order to further increase the reactivity, fluorspar (CaF ₂ ) may be supplementarily added to slag these oxidizing agents.

From the viewpoint of increasing the reaction rate, it is desirable that the oxidizing agent used be as fine as possible within the range where it does not scatter. Practically, it is preferably used as particles having a particle size in the range of 0 to 0.5 mm.

These oxidizing agents and carbonizing agents can be added to the molten iron by any method. For example, it is sufficient to simply add them to the surface. However, in order to increase the reaction rate, it is preferable to use argon gas, nitrogen gas or the like as a carrier gas to inject it into the molten iron or to spray it onto the surface of the molten iron. The addition rate is preferably a rate commensurate with the decarburization rate, but may be faster or slower,
Alternatively, all the necessary amount may be added first.

The treatment temperature is preferably as high as possible in order to increase the reaction rate, but in principle, it may be higher than the temperature at which decarburization proceeds. The means for obtaining the degree of vacuum necessary for carrying out the present invention is not particularly limited. For example, ladle degassing method, VAD
Or LFV method, DH vacuum degassing method, RH vacuum degassing method, ASEA
Any of the SKF degassing methods can be used.

In the method of the present invention, since decarburization is an endothermic reaction, the temperature gradually decreases as the reaction progresses. Therefore, it may be desirable to perform heating on the way if necessary. The heating method in this case is not particularly limited, and may be any method such as electric heating using an arc or the like and oxygen blowing by adding aluminum or the like.

In the method of the present invention, stirring is performed in order to increase the decarburization reaction rate. The stirring method may be any method such as bubbling with argon, mechanical stirring with an impeller or the like, or electrical stirring with an induced current or the like.

In carrying out the method of the present invention, a vacuum degree of 20
It needs to be Torr or less, preferably 5 Torr or less. This is because the higher the degree of vacuum is, the more the evaporation decoppering and the evaporation detinning are promoted, and the decarburization itself is more likely to occur.

The reason is that in the method of the present invention, the following equation (1)
According to (2), carbon reacts with magnesium oxide and carbon reacts with silicon dioxide to generate carbon monoxide, so if the carbon monoxide partial pressure becomes low under high vacuum, the following reaction proceeds to the right and the decarburization itself Because it is promoted.

[C] + MgO → Mg ↑ + CO (1) [C] + 1/2 SiO ₂ → 1/2 [Si] + CO (2) The higher the degree of vacuum, the decoppered amount relative to the decarburized amount, The following two points can be considered as the reason why the proportion of the amount of detinning becomes large.

(1) In the method of the present invention, copper and / or tin is evaporated and removed, and vapor of copper and / or tin enters the carbon monoxide gas produced by decarburization,
It is considered that it is removed together with this carbon monoxide gas. Therefore, it is considered that the progress rate of decopperization and / or detinization is determined by the degree of vacuum and the vapor partial pressure of copper and / or tin in the carbon monoxide gas. It is believed that copper and / or detinning is promoted.

(2) Decarburization proceeds according to the above formulas (1) and (2), but it can also be said that oxygen supplied by magnesium oxide and silicon dioxide dissolves in the vicinity of the decarburization reaction interface of molten iron and decarburizes. .

[C] + [O] ---> CO (3) Therefore, the higher the degree of vacuum, the lower the partial pressure of carbon monoxide, and the above reaction (3) proceeds to the right, at the decarburization reaction interface. Decarburization proceeds with a small amount of oxygen. Oxygen is a surface-active element. Therefore, as described above, when the amount of oxygen is high, the amount of oxygen localized at the interface of decarburization and decopperization and / or tin removal reaction increases, and the transfer of copper and / or tin to the reaction interface is prevented. , Copper removal and / or tin removal are inhibited. Therefore, it is considered preferable for decoppering and detinning that the degree of vacuum becomes high and the amount of oxygen at the reaction interface becomes small accordingly. Hereinafter, the method of the present invention will be described more specifically with reference to Examples.

[0047]

【Example】

(Example 1) Molten steel of the composition shown in Table 1 obtained by melting 1.5 tons of scrap in a high frequency furnace (C: 0.50%)
Is agitated with high-frequency power of 300 kW and 1 kHz, and the processing temperature is 16
The temperature was adjusted to 50 ° C. and the degree of vacuum was 1 Torr. And Mg shown in the table
A powder refining agent consisting of a mixture of O and carbon was sprayed little by little on a molten steel surface through a pipe using 500 Nl / min of Ar gas as a carrier gas. After 90 minutes, as shown in the table, a copper removal rate of 84% and a tin removal rate of 56% were achieved.

In Table 1, [C] i represents the C content in the starting molten iron, and [C] f represents the C content in the molten steel after the decarburizing treatment. The same applies to other components. same as below.

Comparative Example 1 Under the same conditions as in Example 1, 500 Nl / min Ar gas as a carrier gas was used as a carrier gas through a pipe with a refining agent consisting only of MgO shown in Table 1 little by little to form a molten steel surface. Sprayed. After 90 minutes, as shown in the table, a copper removal rate of 64% and a tin removal rate of 33% were achieved, but they were inferior to those of Example 1.

(Example 2) Under the same conditions as in Example 1, with respect to high C hot metal (C: 4.3%) having the components shown in Table 1,
The powdery refining agent consisting of a mixture of SiO ₂ and carbon shown in the same table was dispensed. After 120 minutes, as shown in the table, a copper removal rate of 95% and a tin removal rate of 85% were achieved.

(Example 3) 80 tons of scrap was melted in an electric furnace. Molten iron having the components shown in Table 1 (C: 0.43%)
Is adjusted to 1650 ° C and then 5 Nl /
A min of Ar gas was flown and stirred to adjust the vacuum degree to 1 Torr. Then, a powdered refining agent composed of a mixture of MgO, SiO ₂ and carbon shown in the same table was pipetted at a rate of 2000 Nl / mi.
The n 2 Ar gas was used as a carrier gas and sprayed onto the surface of the molten steel. After 120 minutes, as shown in the table, a copper removal rate of 84% and a tin removal rate of 50% were achieved.

[0052]

[Table 1]

As can be seen from the results in Table 1, according to the present invention, even if [C] ≦ 2.0%, the decoppering rate is 84% and the detinning rate is 50%.
% Can be achieved, which is also a conventional example [C]
= 0.43%, which is excellent compared to the comparative example. The decoppering rate improved by about 30%, and the tin removal rate improved by 52%.
The effect is remarkable.

[0054]

As described above, according to the present invention,
Copper and tin can be efficiently removed from molten iron under a practical vacuum of 20 Torr or less, and considering that the blending ratio of scrap will increase in the future, there are great benefits in practical use.

Claims (3)

[Claims] 1. A method for removing copper and / or tin from molten iron, wherein the molten iron is decarburized under a vacuum of 20 Torr or less with a refining agent consisting of a mixture of oxygen and an oxidizing agent weaker than iron oxide and a carbonizing agent. A decoppering and / or detinning method for molten iron, which is characterized in that 2. The method according to claim 1, wherein decarburization is performed under a vacuum of 5 Torr or less. 3. The method according to claim 1, wherein the main component of the refining agent is at least one selected from the group consisting of magnesium oxide and carbon, silicon dioxide and carbon, magnesium oxide, silicon dioxide and carbon.