JPH07126728A - Decupperizing and detinning method from molten iron - Google Patents

Abstract

PURPOSE:To provide the technique of enabling treatment of iron scrap in a large amt. CONSTITUTION:The oxide consisting of one or >=2 kinds selected from a group consisting of oxygen, steam, carbon dioxide, iron oxide and oxide having the oxidizing powder weaker than the oxidizing powder of the iron oxide under a reduced pressure of <=10Torr is blown to molten iron to decarburize this molten iron, by which copper and/or tin is removed from the molten iron. The surface of the molten iron is heated by plasma, by which the decopperizing and detinning are accelerated. As a result, Cu: <=0.30% and Sn: <=0.040% are attained by the treatment within 30 minutes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing copper and / or tin from molten iron.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of iron scrap produced, a process of reusing the iron scrap by various remelting methods and a process of using the iron scrap mixed with hot metal or molten steel are generally performed. ing.

By the way, the quality of these iron scraps tends to decrease year by year. For example, since copper or tin is mixed in from copper wiring in automobile scraps, copper wires contained in a motor core, or tin plating, the content of copper or tin in steel materials made from scrap is increasing.

Since copper and tin in steel are generally harmful impurities, it is desired to control the concentration to be low. In other words, since red-heat embrittlement is unavoidably seen in steel containing a large amount of copper, it is generally 0 except some weathering steels.
It is required to be 35% to 0.20% or less.
On the other hand, tin causes a decrease in hot workability and a decrease in extensibility and drawability in steel, so the tin concentration in steel is 0.10%.
It is necessary to do the following.

As is well known, copper and tin have a lower affinity for a noble metal than iron, that is, oxygen, and are difficult to remove in a normal steelmaking process. However, it is possible to remove copper and / or tin from molten iron by utilizing the high vapor pressure of copper and tin in molten steel as compared with the vapor pressure of molten iron.

[0006] Therefore, some of the inventors of the present invention disclosed in Japanese Unexamined Patent Publication No.
The method disclosed in Japanese Patent Publication No. 119612 and Japanese Patent Publication No. 3-72129 was invented. In these methods, by utilizing the difference in vapor pressure between iron in the molten iron and copper and tin, when decarburizing the molten iron placed under a reduced pressure of 10 Torr or less using an oxidizing agent such as oxygen or iron oxide. The method was a method of simultaneously performing copper removal and / or tin removal, which was a practical method capable of treating a large amount of molten iron. In other words, in the reaction utilizing the vapor pressure difference between the components as in this method, securing the reaction interface is advantageous for increasing the reaction rate, and oxygen or iron oxide is supplied to the molten iron to cause the decarburization reaction. This is a method of increasing the volatile interface due to the generation of CO bubbles due to this decarburization reaction and utilizing the disturbance of the interface to dramatically increase the reaction interface, thereby promoting decopperization and / or detinization.

By the way, another method of increasing the reaction rate of decopperization and detinization from molten iron by utilizing the vapor pressure difference of such components is a method of keeping the reaction temperature high. That is, the decopperization and detinization reaction rates are based on the normal steelmaking temperature.
It is considered that the temperature becomes even higher at a high temperature of 1700 ° C or higher, which is higher than (around 1600 ° C). However, when the practical steelmaking temperature is exceeded, the energy cost required for heating and the melting loss of refractory materials become problems.

However, in either method,
When considering the mass batch treatment of further iron scrap, the decoppering rate and the tinning rate are not sufficient, which shortens the processing time,
There is a limit to the improvement of copper removal rate and tin removal rate, and at present,
For example, the initial concentration Cu: 0.5% by the molten steel treatment of 2 tons scale,
Sn: 0.06% Cu: Cu:
It is difficult to reduce to 0.4% and Sn: 0.05%.

Therefore, in order to recycle iron scrap, which has become a social problem in recent years, it is necessary to construct a more efficient mass batch processing process for scrap.
In particular, in order to remove copper and tin, which are increasing in concentration as impurities in iron scrap from year to year, from molten iron, increasing the decoppering and detinning rates from molten iron is an indispensable technique.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for decarburizing and / or detinizing a molten iron at the same time when decarburizing molten iron with an oxidizing agent under a high reduced pressure as described above. It is an object of the present invention to provide a method capable of increasing the decopperization / detinization rate from molten iron and performing it with high efficiency in a short time.

[0011]

[Means for Solving the Problems] The inventors of the present invention have been earnestly researching a method of simultaneously producing decopperization / detinization when decarburizing with an oxidizing agent under the above-mentioned high reduced pressure. It was found that it is advantageous to raise the reaction temperature above the ordinary holding temperature of molten steel for the copper removal reaction and the tin removal reaction, and as a result of further research, the following findings were obtained.

(1) In order to further promote the decopperization / detinization reaction, the temperature of the reaction interface where decopperization and detinization occur is kept high, and in particular, the temperature near the molten steel surface generated by the decarburization reaction is locally It is effective if it is raised. (2) For such localized heating of the molten steel surface, it is effective to apply a temperature by plasma irradiation.

The present invention has been completed based on such findings, and the gist of the invention is to provide oxygen, water vapor, carbon dioxide, nickel oxide, iron oxide, and iron oxide under a practical vacuum of 10 Torr or less. In the method of removing copper and / or tin from molten iron by supplying one or more oxidizing agents selected from the group consisting of oxidants having a weaker oxidizing power to molten iron for decarburization, more effective deoxidization is performed. It is a decoppering / detinizing method from molten iron, characterized in that the surface of the molten iron is heated by plasma in order to perform copper and / or detinning.

[0014]

Next, the operation of the present invention will be described in more detail. According to the present invention, the reaction interface where decopperization and / or detinization takes place is an interface which is dramatically increased by the decarburization reaction in the vicinity of the free surface.
It is sufficient if even the temperature of this reaction interface can be kept high.

Therefore, in order to promote the decoppering and detinning reactions utilizing the decarburization reaction, it is not always necessary to raise the bulk temperature, and if only the reaction interface is locally kept at a high temperature,
It turned out to be efficient.

According to the present invention, a local heating method having a sufficient energy density is suitable for heating only the reaction interface temperature near the free surface of molten iron to the molten iron temperature or higher,
Especially, it was confirmed that the plasma heating method is advantageous for local heating of the reaction interface. Thus, the operational characteristic of the present invention is to further increase the reaction interface by locally heating the decarburization reaction interface using plasma heating.

As described above, according to the present invention, when decarburizing is performed by spraying oxygen or iron oxide onto the surface of molten steel,
Since it is intended to increase the reaction interface near the free surface,
The plasma heating may be performed by irradiating the surface of the molten steel with thermal plasma, and therefore the method of generating thermal plasma is not particularly limited based on this idea.

By the way, in the present invention, the decarburization reaction can be utilized by using various oxidizing agents. It should be noted that the form of supplying the oxidizing agent may be blowing into molten iron like a gaseous oxidizing agent, placing a solid oxidizing agent on the surface of molten iron, or blowing with a carrier gas. ".

For example, a refining gas containing an oxidizing gas (oxygen, water vapor, carbon dioxide, etc.) may be sprayed onto the surface of the molten iron to cause a decarburization reaction. Further, as a solid oxide, iron oxide may be added to or sprayed on the surface of molten iron to cause decarburization, and by utilizing this, decopperization and detinization may be performed from molten iron. At this time, iron oxide not only serves as an oxygen supply source, but also contributes as a site for the decarburization reaction and becomes a part of the molten iron after the oxygen is consumed by the decarburization reaction. Other oxides that are similar to iron oxide and have a similar oxidizing power include manganese oxide, chromium oxide, nickel oxide, etc., all of which are molten iron after oxygen is consumed in the decarburization reaction. Since it melts into the steel and becomes a steel component, it can be selected according to the target component of molten iron. In addition, SiO ₂ , MgO or the like can be used.

The strong and weak "oxidizing power" is understood as the dissociated oxygen partial pressure of pure oxide (equilibrium oxygen partial pressure). That is,

[0021]

[Equation 1]

The oxygen partial pressure (Po ₂ ) when the pure substance M reacts with oxygen as represented by the following reaction formula, and can be expressed as a function of temperature. For example, typical steelmaking temperatures
At 1600 ° C., Po ₂ is 10 ^-8 atm iron oxide, Po ₂ of CO ₂ is 10
It is about ^-11 atm. The above-mentioned manganese oxide and chromium oxide, which are oxides similar to iron oxide, have slightly low Po ₂ values of about 10 ⁻¹⁴ atm. Further, nickel oxide has a value of about 10 ⁻⁴ atm, which is higher than iron oxide.

Further, as a method of causing decarburization and promoting decopperization and detinization by using a solid oxidizing agent, there is a method of using silicon dioxide or magnesium oxide, which has a weaker oxidizing power than iron oxide. Here, the equilibrium oxygen partial pressures of silicon dioxide and magnesium oxide are 10 ^-16 atm and 10 ^-18 atm, respectively, which are considerably small values at 1600 ° C.

When a method of spraying molten iron with an oxide powder containing SiO ₂ or MgO having a lower oxidizing power than oxygen and iron oxide as described above is used, the oxidant does not dissolve in molten iron and disappear. Since a decarburization reaction site is formed on the surface of molten iron,
The combined use with the local heating of the molten iron surface by plasma as in the present invention is more effective.

Further, the advantage of using an oxidizing agent having a weaker oxidizing power than iron oxide as the oxidizing agent is to reduce the localization of oxygen atoms at the decarburizing reaction interface and facilitate the transfer of copper / tin to the reaction interface. This is because it is possible to promote decopperization / detinization.

When the oxidizer is a solid, its particle size is not particularly limited, but generally has an average particle size of 0.002 to 1 mm,
It is more preferable to use the one having a thickness of 0.05 to 0.3 mm in order to sufficiently secure the reaction interface and to handle it practically. The supply amount of the oxidizing agent may be based on so-called decarburization, and it is sufficient to add the amount used in the conventional operation.

Means having a refining function by vacuum treatment of molten iron necessary for carrying out the present invention is not particularly limited. For example,
When considering molten steel as molten iron, an out-of-furnace refining method such as the RH process that is generally used for molten steel treatment, ladle vacuum degassing method such as VOD and LFV, VIM that can be heated by high frequency
The present invention is applicable to any vacuum process currently used, such as a process.

The reason why the degree of vacuum is set to 10 Torr or less is that the degree of vacuum is practically easily realizable, and it is advantageous to remove copper and tin by evaporation in association with decarburization.
It can also be expected that the generation of gas will reduce the localization of oxygen atoms at the decarburization reaction interface and promote decopperization and detinization.

The type of molten iron to which the present invention is applied is not particularly limited. For example, carbon steel and hot metal obtained by normally melting scrap are applicable because they can be decarburized with an oxidizing agent. It is also applicable to stainless steel and high alloy steel containing a large amount of nickel and chromium. Depending on the type of steel, it is also possible to decarburize and detinize by supplying and adding an oxidizing agent after carburizing as required. Since the decarburization reaction is used in the present invention, it can be said that the higher the carbon content of the molten iron, the higher the decoppering / detinizing efficiency. Next, the operation and effect of the present invention will be described more specifically by way of examples.

[0030]

Example In this example, molten steel was used as molten iron, and decarburization was performed by blowing an oxidant while heating the molten steel surface by Ar gas plasma irradiation. Copper removal and tin removal from molten steel according to the present invention were performed using the vacuum melting apparatus shown in FIG.

In the figure, a high-frequency induction heating type vacuum furnace 1 capable of melting up to 2.5 tons of molten steel is used, and an upper lid 2 of this vacuum furnace has a gas containing oxygen and an iron ore serving as an oxidizing agent.
A liftable lance 3 capable of spraying SiO ₂ and MgO powder onto molten steel, and a non-transfer type Ar gas plasma torch 4 capable of heating the molten steel surface are attached. Further, there is also installed a powder charging device 5 capable of adding the above powder onto the surface of the molten steel. The molten steel is held in a refractory container 8 whose main component is MgO.

In this vacuum furnace, the degree of vacuum can be maintained at 1 Torr or less while the molten steel is held by the steam ejector pump through the exhaust hole 6. Further, the furnace bottom has a porous brick tuyere 7 for stirring molten steel, and stirring can be performed by blowing Ar gas.

Although not shown in the figure, a sampler for collecting a sample during the dissolution is attached to the upper lid. The composition of the molten steel used as an example was as follows: Cu: 0.5%, Sn: 0.06%, carbon: 0.5
%, Si: 0.03%, Mn: 0.01%, P: 0.018%, and a balance of iron and inevitable impurities. Next, an implementation method will be described.

First, 1.5 tons of the molten steel was melt-held at 1650 ° C. and then depressurized to about 1 Torr. Next, in order to cause a decarburization reaction under this reduced pressure, an oxidizing agent was blown into the molten steel in the following manner.

(1) Oxygen + 50 volume% Ar gas is blown from the upper lance at 0.2 Nl / min · t, (2) Iron oxide powder (average particle size 100 μm) and 10 mass% SiO ₂ powder (average particle size) 100 μ
(3) A method of placing 30 kg of oxidizer mixed with m) on the molten steel surface from above, (3) Using the Ar carrier gas at a rate of 0.4 kg / min ・ ton from the lance for the powder used in (2) above. (4) Iron oxide powder (average particle size 100 μ
m), and 10% by mass of MgO powder (average particle size 100 μm) are mixed into the molten steel from the lance at a feed rate of 0.4 kg / min ・ ton using Ar carrier gas to blow the molten steel (5).
10% by mass of Si in manganese oxide powder (average particle size 100 μm)
Oxidizer powder (average particle size 100 μm) mixed with O ₂ powder (average particle size 100 μm) is supplied from the lance at a feeding rate of 0.4 kg / min ・ ton.
(Ar + 50 vol% oxygen) carrier gas is used to blow into molten steel, (6) CO ₂ + 50 vol% Ar gas is blown from the upper lance at 0.4 Nl / min · t, (7) H ₂ O + 50
Blowing volume% Ar gas at 0.4 Nl / min ・ t from the upper lance, (8) Chromium oxide powder (average particle size 100 μm) was made into molten steel using Ar carrier gas at a rate of 0.4 kg / min ・ ton from the lance. Blowing method, (9) Nickel oxide powder (average particle size
100 μm) is blown into the molten steel from the lance at a rate of 0.4 kg / min · ton using Ar carrier gas.

The molten steel was stirred by using both high frequency stirring and Ar gas stirring from the furnace bottom. Under these conditions,
(a) When plasma heating (output about 200 kW) is performed
(b) The copper removal behavior and the tin removal behavior were compared in the case of not performing (comparative example).

(I) Decoppering / detinizing behavior accompanying decarburization with oxygen + Ar mixed gas In decarburizing method (1), when the molten steel surface was plasma-heated (a) and when not (b), A graph of changes in copper concentration in molten steel with time is shown in FIG. 2, and a graph of changes in tin concentration in molten steel with time is shown in FIG. In both figures, comparing Example (a) with Comparative Example (b), it can be seen that when the molten steel surface is plasma-heated (a), the copper and tin concentrations decrease more rapidly.

(Ii) Decoppering / Detinizing Behavior Following Decarburization by Addition of Oxidizing Agent (Iron Oxide + 10% Silicon Dioxide Mixture) on the Molten Steel Surface by Plasma Heating in Decarburizing Method (2) (a) In the case of (b), the change in copper concentration in molten steel with time is shown in FIG. 4, and the change in tin concentration in molten steel with time is shown in FIG. Comparing Example (a) and Comparative Example (b) in both figures, it can be seen that when the molten steel surface is plasma heated (a) as in (1).
It can be seen that the copper concentration and the tin concentration are rapidly decreasing.

(Iii) Decoppering / detinizing behavior accompanying decarburization by a method of blowing an oxidizing agent (iron oxide + 10% silicon dioxide mixed powder) into molten steel together with a carrier gas. In decarburizing method (3), the molten steel surface was plasma-heated. FIG. 6 shows a graph of changes in the copper concentration in the molten steel with respect to time, and FIG. 7 shows a graph of changes in the tin concentration in the molten steel with respect to time, in the cases (a) and (b). In both figures, comparing Example (a) and Comparative Example (b), (1), (2)
It can be seen that when the surface of the molten steel is plasma-heated as in the case of (a), the copper concentration and the tin concentration decrease more rapidly. In addition, the decarburization method compared to the case of the decarburization method (2)
In the case of (3), both the copper removal rate and the tin removal rate are faster.

(Iv) Oxidizing agent (iron oxide + 10% magnesium oxide mixed powder) decopperization / detinization associated with decarburization by blowing Decarburization method (4), when oxide powder is heated by plasma (a) FIG. 8 shows a graph of changes in the copper concentration in the molten steel with respect to time in the case (b) where there was not, and FIG. 9 shows a graph of changes in the tin concentration in the molten steel with respect to time. Comparing Example (a) and Comparative Example (b) in both figures, copper heating was faster when oxide powder was plasma heated (a) as in the case of decarburization method (1). It can be seen that the concentration and tin concentration have decreased. Further, when iron oxide and magnesium oxide are decomposed to perform the decarburization reaction, a larger endothermic reaction is considered to occur, but when plasma heating is performed, the decoppering / detinizing reaction proceeds sufficiently effectively. From this, it can be seen that the thermal compensation due to the plasma heating works effectively.

(V) Decopperization / detinization associated with decarburization by blowing an oxidizing agent (manganese oxide + 10% silicon dioxide powder) into molten steel with Ar + 50% oxygen carrier gas In the decarburization method (5) from molten steel, Figure 10 shows a graph of the change in the copper concentration in the molten steel with time when the oxide powder was plasma-heated (a) and when it was not heated (b). Shown in. In any of the figures, comparing Example (a) with Comparative Example (b), it was found that when the oxide powder was plasma-heated (a) as in the case of decarburization methods (1) and (2). It can be seen that the copper concentration and the tin concentration are rapidly decreasing. Especially, the reason why decopperization / detinization is delayed without plasma heating is considered to be that the decarburization reaction does not proceed. On the other hand, even if the same oxidant is used, it is considered that the decarburization reaction and the decopperization / detinization reaction are promoted when heat is applied to the oxidant by plasma. Further, if the oxidizing agent is selected according to the composition of the molten steel, more appropriate decoppering and detinning can be performed.

(Vi) Decopperization / detinization associated with decarburization by blowing in an oxidizing gas (CO ₂ +50 vol% Ar gas) and (H ₂ O + 50 vol% Ar gas) When plasma heating was not performed In case (b), changes in copper concentration in molten steel, tin concentration, and changes after approximately 30 minutes of molten steel treatment are summarized in Table 1. In any result,
It can be seen that copper removal and tin removal are more effectively performed in the case of plasma heating (a).

(Vii) Solid oxidizer (chromium oxide, nickel oxide) Decoppering due to decarburization by blowing Ar carrier gas
Table 2 summarizes the changes in copper concentration and tin concentration in molten iron before and after the treatment for about 30 minutes, with and without (a) and without (a) plasma heating. In all of these results, decoppering and detinning were effectively performed by performing plasma heating (a) .Therefore, depending on the composition of molten iron such as chromium-containing nickel molten iron, chromium oxide and nickel oxide may also be solid oxidizers. As a result, it can be used for copper removal and tin removal.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

INDUSTRIAL APPLICABILITY As described above, the present invention is a method for decoppering and / or tinning in molten iron when deoxidizing by blowing an oxidizer. A method of increasing the decoppering rate and the detinning rate by heating the surface with plasma to apply heat, and according to the present invention, for example, Cu: 0.30% or less in a treatment time of 30 minutes or less, Sn : It can be reduced to 0.040% or less, and it makes a large-scale scrap processing process practical for the recycling of iron scrap, which has become a social problem in recent years, and its practical significance is great.

[Brief description of drawings]

FIG. 1 is a schematic view of a high frequency induction heating furnace.

FIG. 2 is a graph showing the influence of plasma heating of the molten steel surface on decoppering behavior when decarburizing the molten steel with an oxygen-containing gas.

FIG. 3 is a graph showing the influence of plasma heating of the molten steel surface on the detinning behavior when decarburizing the molten steel with an oxygen-containing gas.

FIG. 4 is a graph showing the influence of plasma heating of the molten steel surface on decoppering behavior when deoxidizing by supplying oxidizing powder to the molten steel surface.

FIG. 5 is a graph showing the influence of the presence or absence of plasma heating of the molten steel surface on the tin removal behavior when deoxidizing by supplying oxidizing powder to the molten steel surface.

FIG. 6 is a graph showing the influence of plasma heating of the molten steel surface on decoppering behavior when deoxidizing by spraying an oxidizing powder onto the molten steel surface.

FIG. 7 is a graph showing the influence of the presence or absence of plasma heating of the molten steel surface on the detinization behavior when deoxidizing by spraying an oxidizing powder on the molten steel surface.

[Fig. 8] (Iron oxide + 10% by mass magnesium oxide powder) A graph showing the effect of plasma heating of oxide powder on decoppering behavior when the molten iron is decarburized by spraying molten iron on the mixed powder. is there.

[Fig. 9] (Iron oxide + 10 mass% magnesium oxide powder) A graph showing the influence of plasma heating of the oxide powder on the detinization behavior when the molten iron is decarburized by spraying the mixed powder on the molten iron. is there.

FIG. 10 shows the influence of plasma heating of oxide powder on decoppering behavior when deoxidizing molten iron by spraying mixed powder of oxidizing agent (manganese oxide + 10 mass% silicon dioxide powder) on molten iron. It is a graph shown.

FIG. 11 shows the influence of plasma heating of oxide powder on detinization behavior when deoxidizing molten iron by spraying mixed powder of oxidizing agent (manganese oxide + 10 mass% silicon dioxide powder) on molten iron. It is a graph shown.

[Explanation of symbols]

1: Vacuum furnace 2: Vacuum furnace top cover 3: Lance 4: Non-transfer type Ar gas plasma torch 5: Powder injection device 6: Exhaust hole 7: Porous brick tuyere 8: Refractory container

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Anezaki 4-533 Kitahama, Chuo-ku, Osaka Sumitomo Metal Industries Co., Ltd.

Claims (1)

[Claims] 1. An oxidizer consisting of one or more selected from the group consisting of oxygen, water vapor, carbon dioxide, nickel oxide, iron oxide, and an oxide having a weaker oxidizing power under a reduced pressure of 10 Torr or less. In the method of removing copper and / or tin from the molten iron by supplying the molten iron to the molten iron to decarburize the molten iron, promoting decoppering and detinning by heating the surface of the molten iron with plasma. The decoppering / detinizing method from molten iron, which is characterized by