JPH07126726A - Decupperizing and detinning method from molten iron - Google Patents

Abstract

PURPOSE:To enhance the treatment efficiency by heating the surface of molten iron with hydrogen-contg. plasma at the time of subjecting the molten iron to decopperizing and detinning treatment under a reduced pressure. CONSTITUTION:Copper and/or tin is removed from the molten iron by blowing an oxidizing agent consisting of one or >=2 kinds selected from an iron oxide and oxide group having the oxidizing power lower than the oxidizing power of the iron oxide under a reduced pressure of <=10Torr, thereby decarburizing the molten iron. The surface of the molten iron is heated by the hydrogen-contg. plasma at the time of this decarburization to accelerate the decopperizing and detinning. More specifically, the molten iron in an MgO refractory vessel 5 in a vacuum chamber 1 is maintained under the reduced pressure and while the molten iron is kept stirred by blowing gaseous Ar from a porous brick tuyere 7 in the bottom, powders of the iron oxide, silicon dioxide, magnesium oxide, etc., are blown from a lance 3 disposed in an upper cap 2 of the vacuum furnace. The surface of the molten iron is irradiated with the gaseous hydrogen- contg. plasma from a non-migration type gaseous Ar plasma torch 4 and is thereby heated to a high temp. after the start of the blowing of the oxidizing agent.

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. Is starting to appear.

By the way, the quality of these iron scraps tends to decrease year by year. For example, copper and tin are mixed in from copper wiring in automobile scraps, copper wires contained in motor cores, and tin plating, so the content of copper and tin in steel products made from iron 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 0.35 except some weathering steels.
% To 0.20% or less is required. On the other hand, tin causes a decrease in hot workability, a decrease in progressability, and a decrease in drawability in steel. Therefore, it is also necessary to suppress the tin concentration to 0.1% or less.

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 iron as compared with the vapor pressure of molten iron.

Therefore, some of the inventors of the present invention have disclosed in Japanese Patent Laid-Open No. 61-11.
The method disclosed in Japanese Patent Publication No. 9612 and Japanese Patent Publication No. 3-72129 was invented. In these methods, the difference in vapor pressure between iron and copper and tin in the molten iron is used to decarburize the molten iron placed under a reduced pressure of 10 Torr or less by supplying and adding an oxidizing agent such as oxygen and iron oxide. At this time, copper removal and / or tin removal are performed simultaneously due to an increase in the volatile interface that accompanies decarburization, and it was a practical method capable of batch-processing molten iron in a large amount.

That is, in the reaction utilizing the vapor pressure difference between the components as in these methods, it is advantageous to secure the reaction interface for increasing the reaction rate. Therefore, the oxidizing agent is supplied to the molten iron for decarburization. A method of causing a reaction and dramatically increasing the reaction interface by increasing the volatile interface due to the generation of CO bubbles generated by this decarburization reaction and disturbing the interface, thereby promoting decopperization and / or tin removal Met.

However, even in this method, the copper removal rate and the tin removal rate are not sufficient when further large-scale processing of iron scrap is assumed, so that the processing time can be shortened and the copper removal rate and the tin removal rate can be improved. There was a limit.

On the other hand, as a method for accelerating decopperization and detinization from molten iron, Japanese Patent Publication No. 3-75603 discloses a decoppering / detinizing method from molten iron by irradiation with plasma containing hydrogen. According to this method, when the surface of molten iron is heated by using a plasma gas containing hydrogen, copper heating / detinization from the molten iron is promoted by local heating. However, even in this method, the copper removal rate and the tin removal rate are not sufficient when further large-scale processing of iron scrap is assumed,
There was a limit to shortening the processing time and improving the copper removal rate and the tin removal rate.

The Metallurgical Society of Japan, 22, (1983) P412-42
0, Masahiro Uda's paper "New method for producing fine metal particles" describes the effect of hydrogen-containing plasma on molten metal, and shows that the reactivity of hydrogen-containing plasma is promoted.

Another means of increasing the reaction rate of decoppering and detinning from molten iron by utilizing the vapor pressure difference of such components is a method of keeping the evaporation reaction temperature high.
That is, the copper removal and tin removal reaction rates are
It is considered that it becomes more advantageous at a temperature (1700 ° C or higher) higher than (around ℃). This method does not necessarily mean increasing the bulk temperature, but it is sufficient if the temperature at the reaction interface where decopperization / detinization occurs is high. In fact, the bulk temperature
It is clear that if the temperature is kept above 1700 ° C, not only will the energy cost rise, but also the melting of refractory and the shortening of the furnace life.

By the way, in order to recycle iron scrap, which has become a social problem in recent years, it is necessary to construct a mass scrap batch processing process. In particular, in order to remove copper and tin whose concentrations are increasing yearly as impurities in iron scrap from molten iron, increasing the decoppering rate and the tin removal rate from molten iron is an indispensable technique.

[0013]

Therefore, an object of the present invention is to carry out decoppering and / or detinning when deoxidizing molten iron by supplying and adding an oxidizing agent consisting of an oxide under reduced pressure. In the method, the rate of decopperization / detinization from molten iron is increased,
It is an object of the present invention to provide a method capable of highly efficiently removing copper and tin from molten iron in a short time. Specifically, an object of the present invention is to provide a decoppering / detinizing method from molten iron which can reduce Cu: 0.30% or less and Sn: 0.040% or less.

[0014]

DISCLOSURE OF THE INVENTION The inventors of the present invention relate to a method of decopperizing and detinizing molten iron at the same time as decarburizing by spraying oxidizing agents made of various oxides onto the surface of molten iron under reduced pressure. As a result of intensive research, it was found that a higher reaction temperature was more advantageous for the decopperization reaction and the tin removal reaction, and further research led to the following findings.

To further promote the copper removal / tin removal reaction,
It is important to keep the temperature of the reaction interface where decopperization and detinization occur as high as possible, and in particular to maintain a sufficiently high temperature near the surface of the molten iron generated during the decarburization reaction.

If plasma heating, which is a high-energy heat source, is used as the heating source for the molten iron surface, sufficient heat can be applied to the molten iron surface, and the decoppering / detinization reaction can be further promoted.

When the surface of molten iron is heated by using hydrogen-containing plasma for this plasma, the decoppering / detinization reaction from the molten iron is further effectively promoted by the effect of hydrogen plasma.

The present invention has been completed on the basis of such findings, and the gist of the present invention is that iron oxide and silicon dioxide, which has a weaker oxidizing power, and oxides are oxidized under a practical reduced pressure of 10 Torr or less. In a method of removing copper and / or tin from molten iron by spraying an oxide consisting of one or more oxides such as magnesium as an oxidant on the surface of molten iron to decarburize, it is possible to more effectively remove copper and / or deoxidize copper. In order to perform tin, the method of decoppering and / or detinizing from molten iron is characterized in that the surface of molten iron serving as a reaction interface is heated by plasma containing hydrogen.

[0019]

Next, the operation of the present invention will be described in more detail by comparing it with that of the prior art. As described above, in the method of decarburizing by adding an oxidizing agent or blowing it into molten iron, the decarburizing reaction occurs under the surface of molten iron, so that the reaction interface increases and the interface is disturbed. It is thought that due to the endotherm associated with the dissociation reaction of slag and the heat capacity of the oxidizer itself, a temperature drop occurs locally near the interface that actually occurs in the decarburization reaction, which is a disadvantageous situation for the decopperization / detinization reaction. To be Therefore, it is considered that some thermal compensation at the reaction interface is effective for promoting the decopperization / detinization reaction.

Therefore, in order to effectively perform decopperization and detinization from molten iron by utilizing the decarburization reaction, the increase of the interface near the free surface caused by the decarburization reaction is maintained and the temperature of this reaction interface is increased. It is thought that it is important to locally keep the value as high as possible. In such a method, a local heating method having a sufficient energy density is suitable for maintaining a high reaction interface temperature near the molten iron free surface, and plasma heating is considered to be the most suitable as such a method. .

If a hydrogen-containing gas is used as the plasma gas at this time, deoxidization and tin removal are further promoted by the reaction promoting effect of hydrogen plasma. In other words, the present invention uses a hydrogen-containing plasma to heat the molten iron surface where decarburization has occurred when decarburizing by supplying oxide powder, which is an oxidizer, to the molten iron surface by spraying or the like. The decoppering / detinizing reaction is further promoted by maintaining the reaction interface where the decoppering / detinizing reaction is performed at a high temperature and further increasing the decarburizing reaction interface by using the hydrogen-containing plasma. Of.

The reason why decopperization / detinization is promoted by heating with hydrogen-containing plasma is not only the formation of a high-temperature reaction interface in the irradiation region, but also the easy reactivity caused by hydrogen plasma and the molten iron surface due to hydrogen absorption / desorption. It is considered that the disturbance phenomenon etc. act. In the present invention, a decarburization reaction is caused by supplying an oxidizer made of a solid oxide to molten iron, etc.,
At this time, the basic reaction is to remove copper and tin from molten iron.

At this time, the atmosphere becomes a reducing atmosphere due to the hydrogen plasma, but this oxide powder is not easily reduced in the atmosphere in which it is being supplied. An oxide having a weak oxidizing property under reduced pressure is more desirable because it reacts with medium carbon to cause a decarburization reaction. Here, strong and weak "oxidizing power" is understood as the dissociated oxygen partial pressure (equilibrium oxygen partial pressure) of pure oxide. That is,

[0024]

[Equation 1]

The oxygen partial pressure (Po ₂ ) when the pure substance M reacts with oxygen as expressed by the following reaction formula, and can be expressed as a function of temperature. For example, typical steelmaking temperatures
At 1600 ℃, iron oxide Po ₂ is about 10 ^-8 atm. Oxides having an oxygen partial pressure lower than that of iron oxide include manganese oxide, chromium oxide, silicon dioxide, magnesium oxide, etc., and their Po ₂ are 10 ^-14 atm and 10 ^-14 atm at 1600 ° C, respectively.
m, 10 ^-16 atm, 10 ^-18 atm. Also, nickel oxide is 10 ^-4 atm higher than iron oxide.

Therefore, the oxidizer used for decarburization is iron oxide or one of oxides having an oxidizing power weaker than that of iron oxide.
They may be used alone or in combination of two or more. Some examples of such weakly oxidizable oxides are described above, but particularly suitable oxides cannot be limited, but they are relatively stable in a hydrogen reducing atmosphere and are not melted in molten iron under reduced pressure. In particular, silicon dioxide and magnesium oxide, which can be a decarburizing agent, are particularly suitable.

When these oxides are mixed with oxides such as iron oxide, chromium oxide and manganese oxide and used, oxygen can be supplied more efficiently. If the mixing ratio is too high, hydrogen in the plasma gas may be consumed for the reduction of these oxides.

The particle size of the oxidizer is not particularly limited, but in general, those having an average particle size of 0.003 to 1 mm are used, and desirably, a powder having an average particle size of 0.05 to 0.3 mm has a sufficient reaction interface, It is suitable because it is easy to handle.

The method of generating plasma for heating the surface of the molten iron is not particularly limited in principle, but non-transferred plasma is suitable from the viewpoint of generating stable thermal plasma under reduced pressure. The hydrogen content of the plasma gas at this time is
20% volume or more, more preferably 30 volume% or more
The effect on tin removal is remarkable, but the effect is saturated when the hydrogen content exceeds 60% by volume.

The method for heating the surface of molten iron by plasma is not particularly limited, but a positional relationship is preferably such that the supplied oxide powder is not reduced by the plasma flame. It is desirable that the surface of the molten iron is heated at an angle of about 30 degrees with respect to the powder flow supplied vertically.
From this point of view, the non-transfer type plasma flame also has a high degree of freedom in the device configuration.

The means having a refining function by vacuum treatment of molten iron necessary for carrying out the present invention is not particularly limited. For example,
The vacuum refining methods currently used such as out-of-pile refining methods such as the RH process generally used for molten iron treatment, ladle vacuum degassing methods such as VOD and LFV, and VIM processes that can be heated by high frequency are essential Any of the inventions can be applied.

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 melting ordinary iron 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 steel type, oxidizer is supplied after carburizing as necessary,
It is also possible to add and perform copper removal and tin removal. 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.

[0033]

EXAMPLE In this example, an example in which decopperization / detinization from molten iron was performed using oxide powder and non-migrating hydrogen-containing plasma will be described. The decopperization / detinization method from molten iron according to the present invention was carried out using an apparatus as shown in FIG.

In the figure, a vacuum furnace 1 of a high frequency induction heating system capable of melting up to 2.5 tons of molten iron is used, and a powder 2 such as iron oxide, silicon dioxide or magnesium oxide, which serves as an oxidant, is used for the upper lid 2 of the vacuum furnace. A liftable lance 3 capable of spraying molten iron and a non-transfer type hydrogen-Ar gas plasma torch 4 capable of heating the molten iron surface are attached. Molten iron is held in a refractory container 5 whose main component is magnesium oxide.

In this vacuum furnace, the degree of vacuum can be maintained at 1 Torr or less while the molten iron is held by the steam ejector pump through the exhaust hole 6. Further, the furnace bottom has a porous brick tuyere 7 for stirring the molten iron, and the molten iron can be stirred 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 molten steel used as an example has a composition of wt%.
And contained Cu: 0.5%, Sn: 0.06%, carbon: 0.6
%, Si: 0.03%, Mn: 0.01%, P: 0.012-0.018%,
The molten steel consisted of the balance iron and unavoidable impurities.

First, 1.5 tons of this molten steel is placed in the above vacuum furnace for 16
After the solution was held at 50 ° C., the pressure was reduced to about 1 Torr. next,
In order to cause the decarburization reaction under this reduced pressure, various oxidizing agents were blown into the molten steel to decopper and detinize the molten steel. After the start of blowing the oxidant, the surface of the molten steel was irradiated and heated with hydrogen-containing plasma for about 30 minutes.

When irradiating the molten steel surface with hydrogen-containing plasma, care was taken so that the powder blown from the upper lance 3 was not directly exposed to the plasma flame. The reason for this is to prevent as much as possible the reduction of the decarburization rate due to the hydrogen plasma reducing the oxidant in the atmosphere.

The oxidizing agent used was blown into molten iron in the following manner. (1) Silicon dioxide (average particle size 100
(2) The method of blowing powder from the lance 3 using Ar carrier gas at a rate of 0.4 kg / min.t, (2) Magnesium oxide powder (average particle size 100 μm) from the lance 3 at a rate of 0.4 kg / min. Blowing into molten steel using Ar carrier gas at a ratio of min ・ t, (3) Silicon dioxide powder (average particle size 100 μ
m) mixed with 10% by mass of iron oxide powder (average particle size 100 μm) into the molten steel at a feed rate of 0.4 kg / min · t from the lance 3 into the molten steel using an Ar carrier gas,
(4) Arsenic powder mixed with 25 mass% iron oxide powder (average particle size 100 μm) to silicon dioxide powder (average particle size 100 μm) was supplied from lance 3 at a rate of 0.4 kg / min · t Ar. Blowing into molten steel using a carrier gas.

The molten steel was stirred by using both high frequency stirring and Ar gas stirring from the furnace bottom. Oxidizing agent blowing conditions
In the case of (1), an oxidizer was further blown in the following manner, and the decoppering behavior and the detinning behavior were compared for each. The H ₂ content is expressed in volume%.

(A) Ar-40% H ₂ plasma heating (output about 200
kW), (b) Ar-25% H ₂ plasma heating (output about 200 kW), (c) Ar-20% H ₂ plasma heating (output about 200 kW). And (d) Ar 100%
Plasma heating (output about 200 kW) was performed (comparative example), (e) Ar plasma heating was not performed (conventional example).

Further, oxidant blowing conditions (2), (3),
In each case of (4), as shown in the table below, (b) above
Comparison was carried out under the plasma condition of (e). Table 1 shows the changes in the molten steel components before and after the treatment.

[0043]

[Table 1]

From the results shown in Table 1, when the silicon dioxide powder was blown into the molten steel (1), the examples of heating the molten steel surface with hydrogen-containing plasma were (a), (b) and (c). It can be seen that the decopperization / detinization reaction is much accelerated as compared with the example (d) in which the heating is performed by the method and the example (e) in which the plasma heating is not performed.

Further, it is recognized that the higher the hydrogen content in the plasma gas, the better the results of decopperization and detinization. Furthermore, even when the magnesium oxide powder was blown into the molten steel (2), the example (b) in which hydrogen-containing plasma heating was performed was better in both decopperization and detinization than the comparative example (e). I'm getting results.

When iron oxide is mixed with silicon dioxide powder (3) and (4), iron oxide is 10% (3)
In the case of decopperization and detinization, the decarburization reaction and the promotion effect by hydrogen plasma are seen to be the same, and there is no great difference. The decarburization reaction, which is considered to indicate the reduction of iron oxide in the gas phase, was observed, and the decopperization and detinization reaction were considered to be reduced. Moreover, it is considered that the consumption of hydrogen in the gas phase also stagnates the reaction promoting effect of hydrogen plasma. In the case of 10% iron oxide (3)
Is considered to be particularly effective when it is desired to sufficiently supply oxygen.

[0047]

As described above, the present invention is a method of decoppering and / or detinizing molten iron when blowing an oxidizing agent made of an oxide for decarburization. According to this, by heating the molten iron surface where decoppering and detinning occur with a hydrogen-containing plasma to apply heat, the decoppering rate and the tinning rate can be further increased, and a considerably large amount can be obtained.
Even scraps containing Cu and Sn can be decopperized and detinized to Cu: 0.30% or less, Sn: 0.040% or less by treatment for 30 minutes. It is particularly effective for a large amount of molten iron and a large amount of molten iron for copper removal and tin removal treatment.

[Brief description of drawings]

FIG. 1 is a schematic view of a high frequency induction heating furnace according to the present invention.

[Explanation of symbols]

1: Vacuum furnace chamber 2: Vacuum furnace top cover 3: Lance 4: Non-transfer type Ar gas plasma torch 5: MgO refractory container 6: Exhaust hole 7: Porous brick tuyere

Claims (1)

[Claims] 1. Decarburization of molten iron by spraying molten iron with an oxidizing agent consisting of one or more selected from the group consisting of iron oxide and oxides having an oxidizing power weaker than iron oxide under reduced pressure of 10 Torr or less. In the method for removing copper and / or tin from the molten iron by carrying out, the decoppering and the detinning are promoted by heating the surface of the molten iron by hydrogen-containing plasma during the decarburization.
Copper removal and tin removal from molten iron.