JP3067636B2 - Copper removal from molten iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing copper and / or tin in molten iron.

[0002]

2. Description of the Related Art In recent years, along with an increase in the amount of generated iron scrap, a process of recycling iron scrap using various remelting methods or a process of mixing iron scrap with hot metal or molten steel has been generally performed. ing. By the way, these iron scrap grades tend to decrease year by year. For example, copper and tin are mixed in scraps from automobile demolition and copper wire and tin-plated waste materials contained in scrap motor cores, so the content of copper and tin in steel materials from scrap is reduced. It has increased.

[0003] Since copper and tin in steel are generally harmful impurities to steel quality, it is desired to control them to a low concentration. Since red-hot embrittlement occurs in steel containing a large amount of copper, the copper concentration is generally required to be 0.35 wt% to 0.20 wt% or less except for some steel types such as weathering steel. ing. On the other hand, if the tin concentration in the steel is high, the hot workability, extensibility and drawability of the steel are reduced, so that the tin concentration in the steel must be 0.1 wt% or less.

However, copper and tin are more noble metals than iron, and have a low affinity for oxygen, so that it is difficult to remove copper and tin from molten iron in a normal steel making process, and these are industrially used. A method that can be effectively removed is desired.

One of the present inventors is disclosed in Japanese Unexamined Patent Application Publication No.
In Japanese Patent Publication No. 12 and Japanese Patent Publication No. 3-72129, copper removal from molten iron and / or
Or the method of performing tin removal was shown. These methods remove and evaporate by utilizing the difference in vapor pressure between molten iron and copper and tin in the molten iron. Remove molten iron to increase removal rate
A method in which an oxidizing agent such as iron oxide is sprayed on a powder and decarburized by placing the powder under a reduced pressure of 0 Torr or less, thereby increasing an evaporation interface caused by decarburization and removing copper and / or tin. is there. As a result, a practical method capable of treating a relatively large amount of molten iron has been realized.

The present inventors have further disclosed in JP-A-7-1267.
In Japanese Patent Publication No. 28, when decopperizing and / or detinning simultaneously with decarburization under reduced pressure, a decarburization reaction interface in which a powder oxidizing agent such as iron oxide is blown upward is heated with an inert gas plasma. A method has been disclosed.

However, in any of the above methods, the rate of copper removal and tin removal from molten iron is not sufficient from the viewpoint of more efficient processing of a large amount of scrap, so that the processing time and the copper removal rate are reduced. There is a limit to the improvement of the tin removal rate.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. An object of the present invention is to increase the rate of copper removal and / or tin removal from molten iron and to carry out the treatment with high efficiency in a short time, specifically, to reduce the copper in the molten iron to 0.1% in a treatment time of about 30 minutes. It is an object of the present invention to provide a method capable of reducing tin to 35 wt% or less and tin to 0.10 wt% or less.

[0009]

The gist of the present invention resides in the following copper removing and / or tin removing method.

Decarbonizing the molten iron by spraying an oxidizing agent comprising iron oxide powder and / or an oxide powder having a lower oxidizing power than iron oxide on the surface of the molten iron containing carbon under a reduced pressure of 10 Torr or less. By this, copper in this molten iron and / or
Or a method of removing tin, wherein the spray amount per spray and per unit time is 5 in terms of the endothermic amount of the oxidizing agent.
A method for removing copper and / or tin from molten iron, which is performed at a rate of 00 to 1500 kJ / min.

In the above method, the desired number of spraying points of the oxidizing agent is two or more on the molten iron surface. The upper limit of the number of spraying points is determined by whether or not the distance between the centers of the spraying points on the molten iron surface can be separated by 100 mm or more.

Following the above invention, the present inventors have set forth the following:
Under a reduced pressure of 0 Torr or less, intensive research has been conducted on a method of removing copper and / or copper from molten iron by spraying the above-mentioned oxidizing agent onto the surface of the molten iron containing carbon to remove carbon. As a result, the following new findings were obtained.

Since the reaction of copper removal and tin removal from molten iron is an evaporation reaction, it is necessary to increase the reaction interface area and maintain the reaction interface temperature as high as possible in order to promote the reaction.

As a method of further increasing the reaction interface area, it has been considered that a larger amount of a powder oxidizing agent is sprayed on the molten iron surface to more actively cause the decarburization reaction. However, even if the spraying speed of the powder oxidizing agent is excessively increased, the reaction of copper removal and / or tin removal may stagnate or decrease.

The reason for the above-mentioned stagnation or decrease is that when a powder oxidizing agent is sprayed on a molten iron surface to carry out a decarburizing reaction, the amount of the oxidizing agent (oxide) is smaller than the amount of heat generated by the decarburizing reaction itself.
The endotherm associated with the dissociation of is much larger,
This is because the temperature at the interface where the decarburization reaction occurs is rather lowered.

When the powder oxidizing agent is sprayed upward at two or more locations on the molten iron surface, the effect of significantly increasing the reaction interface area can be obtained.

By optimizing the amount of powder oxidizing agent sprayed at one location and per unit time, the reaction interface temperature can be maintained as high as possible.

In order to increase the reaction interface area without locally lowering the reaction interface temperature, the spraying amount of the powder oxidizing agent is increased by using the above-mentioned means, and the spraying amount per one place is set as described above. In the means, the amount may be such that the reaction rate of copper removal and / or tin removal becomes the maximum.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method for producing an oxide powder having lower oxidizing power than one or more iron oxides at one or more sites on the surface of a molten iron containing carbon under a reduced pressure of 10 Torr or less. The molten iron is decarburized by spraying an oxidizing agent consisting of the following under appropriate conditions to remove copper and / or tin in the molten iron.

The apparatus required for carrying out the method of the present invention is capable of spraying powder on the molten iron surface and having an atmospheric pressure of 10
It is not particularly limited as long as it is a vacuum refining facility capable of obtaining Torr or less. For example, out-of-pile refining equipment such as RH vacuum degassing equipment commonly used for molten steel processing, VOD and V
Vacuum refining equipment which is equipped with a powder top blower in addition to currently used equipment such as a ladle vacuum degassing equipment such as AD and a VIM equipment capable of heating by high frequency.

The type of molten iron to be used in the present invention is not particularly limited as long as it contains carbon. For example, the method of the present invention can be applied to carbon steel or hot metal usually obtained by melting scrap, since decarburization with an oxidizing agent is possible. Further, the present invention is also applicable to stainless steel molten steel or high alloy molten steel containing a large amount of nickel or chromium. Depending on the type of steel, it is also possible to supply and add an oxidizing agent after carburizing as needed to remove copper and remove tin. Since the decarburization reaction is used in the method of the present invention, the higher the carbon content of the molten iron, the higher the efficiency of copper removal and tin removal.

An example of the configuration of an apparatus to which the method of the present invention is applied will be described with reference to FIG. FIG. 1 is a schematic vertical sectional view showing a vacuum high-frequency induction heating and melting apparatus. The apparatus comprises a vacuum chamber 1 having a vacuum exhaust hole 6, a container 9 of molten iron 8 having a refractory 5 and an induction heating coil 7, and two vertically movable powders provided on a top lid 2 of the vacuum chamber 1. It is composed of blowing lances 3 and 4.

In the above-described apparatus, the pressure in the vacuum chamber 1 is maintained at 10 Torr or less while holding the molten iron 8 and spraying the powder oxidizing agent by a steam ejector pump (not shown) through the exhaust hole 6. Has been made possible.

The powder oxidizing agent is sprayed from the powder blowing lances 3 and 4 together with the carrier gas onto the molten iron 8 surface.

As the carrier gas, an argon gas which is generally inert to the molten iron is preferably used. However, there is no particular limitation. For example, nitrogen gas can be used for molten iron having no limitation in nitrogen concentration. The amount of the carrier gas is not particularly limited because the pressure difference generated by the reduced pressure is used for spraying the powder oxidizing agent. However, for example, the range of the carrier gas amount per one spraying is 100 to 10
If it is 00 Nl / min, the spraying stability is improved.

According to the method of the present invention, the conditions for copper removal and / or tin removal in the above-described apparatus and method are as follows: the pressure in the vacuum chamber (hereinafter referred to as the degree of vacuum) is blown under a reduced pressure of 10 Torr or less. The agent is an oxidizing agent composed of iron oxide or an oxide powder having a lower oxidizing power than iron oxide,
And the range of the spray amount per unit time and the spray time per unit time is 500 to 1500 kJ in terms of the endothermic amount of the oxidizing agent.
/ Min. Hereinafter, the reasons for limiting the above conditions will be described in detail.

When the degree of vacuum deteriorates beyond 10 Torr,
Even when decarburizing by spraying a powder oxidizer, copper removal,
Since detinning is an evaporation reaction in nature, the reaction speed thereof decreases.

Next, the type of the powder oxidizing agent and the spraying conditions thereof will be described.

As described above, in the conventional method, when a large amount of iron scrap is to be treated, the speeds of copper removal and tin removal are not sufficient, so that the processing time is reduced and the copper removal rate and the tin removal rate are improved. Has limitations. That is, even if the spraying speed of the powder oxidizing agent is simply increased excessively in order to increase the reaction rate of copper removal and tin removal, the copper removal and tin removal reactions stagnate or decrease. The reason is that when a powder oxidizing agent is sprayed on the surface of molten iron to perform a decarburizing reaction, the amount of heat absorbed by the dissociation of the oxidizing agent (oxide) is much larger than the amount of heat generated by the decarburizing reaction itself. This is because, when the oxidizing agent is sprayed excessively, the temperature of the interface where the decarburization reaction occurs is rather lowered locally.

In order to solve the above problem, the number of reaction sites where decarburization occurs is increased as much as possible at one or more, preferably at least two sites where the powder oxidizing agent is sprayed, so that the reaction interface area is dramatically increased. It is necessary to gain an increase. By dispersing the spraying locations at two or more locations, it is possible to further suppress a local decrease in temperature at the reaction interface where the evaporation reaction occurs, and to improve the copper removal and tin removal rates.

The type of the powder oxidizing agent and the amount of the powder oxidizing agent sprayed per one spraying can be considered as follows.

The reason why the oxidizing agent is iron oxide and / or an oxide having a lower oxidizing power than iron oxide is to cause a decarburization reaction having an effect of increasing a reaction interface area under a lower oxygen potential. is there. Under such a low oxygen potential, oxygen, which is a surface active element, is reduced at the reaction interface, so that the copper removal and tin removal reactions, which are evaporation reactions, are less likely to be inhibited.

As such an oxidizing agent, iron oxide (Fe ₂ O ₃ ) capable of dissociating and supplying oxygen for decarburization or / and an oxide having a lower oxidizing power than this iron oxide, for example, chromium oxide (Cr ₂ O ₃ ), manganese oxide (MnO),
Silicon dioxide (SiO ₂ ) and magnesium oxide (Mg
It is appropriate to use a metal oxide such as O).

When the molten iron containing carbon is decarburized by spraying a metal (Me) powder oxide Me _x O _y , the reaction per mole of carbon is represented by the following formula (1).

(1 / y) Me _x O _y + [C] → (1 / y) [Me] + CO (g) (1) The metal oxide is Fe ₂ O ₃ , Cr ₂ O ₃ , MnO, SiO
_In the case of ₂ and MgO, the change in the free energy of the reaction at 1873K and the endothermic amount per mole of carbon when the carbon in the molten iron: 1 wt% and the Me in the molten iron: 1 wt% were calculated. Become like Where F
With e ₂ O ₃ , 99% by weight
Calculated as Fe.

[0036]

[Table 1]

As shown in Table 1, iron oxide (Fe ₂ O ₃ )
In the oxide having a larger free energy change in the formula (1), the reaction in the formula (1) proceeds more actively when the partial pressure of CO is reduced under reduced pressure. The “oxidizing agent having a lower oxidizing power than iron oxide” in the method of the present invention is an oxide having such properties.

Such a decarburization reaction under reduced pressure using an oxidizing agent having a weaker oxidizing power than iron oxide has a sufficiently high rate, while the oxygen potential at the reaction interface is sufficiently low. As a result, the effect of not hindering the evaporation of copper and tin from the molten iron is obtained.

For the above reasons, the oxidizing agent used in the method of the present invention is at least one selected from iron oxide or an oxide having lower oxidizing power than iron oxide, or a mixture thereof.
When one or more mixtures are used, the ratio of each oxide is not particularly limited.

The oxide having a lower oxidizing power than iron oxide is not limited to the above-described examples, as long as it has a higher reaction free energy in the above formula (1) than iron oxide. Both naturally occurring and synthetic ones can be used. It is preferable that the amount of impurities contained in each oxide is small in determining the supply amount of the powder oxidizing agent. For example, if the oxide content is less than 10 wt%, the method of the present invention can be applied as it is.

The particle size of the powder oxidizing agent is not particularly limited, but for example, an average particle size in the range of 10 μm to 1 mm is desirable for handling.

Further, as shown in Table 1, since each oxide requires a large amount of energy for the dissociation reaction, it can be seen that each reaction is also a large endothermic reaction. By this endothermic reaction,
The temperature near the reaction interface where decarburization occurs decreases locally, and if this decrease is large, it exceeds the effect of increasing the reaction interface area, and the reaction rates of copper removal and tin removal decrease rather.

That is, considering a method of accelerating the decopperization and detinization reactions accompanying the decarburization reaction, the decarburization reaction proceeds as the spraying speed of the powder oxidizing agent increases, and the reaction interface area where the evaporation reaction occurs is reduced. On the other hand, excessive oxidizing agent spraying causes a decrease in the reaction interface temperature due to the endothermic reaction, resulting in a reduction in the copper removal rate and tin removal rate due to evaporation. Therefore,
By optimizing the amount of powder oxidizing agent sprayed per point, and further increasing the number of spray points as much as possible to increase the reaction area, copper removal,
The tin removal speed can be improved.

Experiments were carried out using various powder oxidizing agents. As long as the container can hold 1 ton or more of molten iron, irrespective of the type of oxidizing agent and the number of spraying points, per oxidizing agent is sprayed per unit time and per unit time. When the range of the heat absorption per unit is set to 500 to 1500 kJ / min, while the effect of increasing the reaction interface area by the decarburization is sufficiently enjoyed, the local temperature decrease at the reaction interface is minimized, so that copper removal and / or copper removal can be achieved. Alternatively, the tin removal rate could be improved. That is, 3
0.30 wt% or less of copper in the molten iron in a processing time of about 0 minutes,
Tin could be reduced to 0.10 wt% or less.

As described above, at an endothermic amount of 500 kJ / min or more, the decarburization reaction can be sufficiently caused, and the effect of increasing the reaction interface area can be obtained. On the other hand, the heat absorption 150
At 0 kJ / min or less, the decrease in local temperature at the reaction interface does not hinder the decopperization and tin removal reactions.

[0046] per spot spraying and converted into the supply amount per unit time of the heat absorption amount of each oxide powder within the above range, Fe ₂ in _{O 3 160~482g / min, Cr 2} O
₃ is 90 to 270 g / min, and MnO is 123 to 37 g / min.
0 g / min, 106 to 320 g / min for SiO ₂ , M
In gO, it corresponds to 83 to 249 g / min.

When the amount of molten iron is less than 1 ton, there is a limitation on the heat margin of the molten iron itself.
It is necessary to reduce the amount of oxidizer per site. in this case,
As the oxidizing agent amount, a value obtained by converting the amount of heat absorption and dividing by the amount of molten iron (t) is used. That is, the amount of molten iron α (t) (where α <1)
In this case, the range of the amount of the oxidizing agent is 500 × α to 1
500 x α (kJ / min).

In principle, the larger the number of spraying points, the better. However, the upper limit of the number of spraying points is practically limited by the volume of the molten iron container, its shape, the powder spraying apparatus and its installation method. Be restricted. For example, when a process is performed on molten iron of 1.5 tons in a high-frequency furnace that can be heated from the outside, four places are possible. At this time, it is desirable to arrange the distance between the spraying points such that the spraying center on each molten iron surface is separated by 100 mm or more. That is, as shown in FIG.
4 may be inclined or vertical, but the center is 1
When the diameter is less than 00 mm and the spray point approaches, the spray point becomes substantially the same point, and the effect of increasing the reaction interface area decreases.

If the above conditions can be satisfied, the powder upper blowing lance may have a porous structure.

[0050]

【Example】

(Test 1) Copper removal and tin removal treatment were performed using a vacuum high-frequency induction heating and melting apparatus having the configuration shown in FIG. The conditions are shown below.

Iron composition: Cu = 0.40 wt%, Sn =
0.11 wt%, carbon = 0.5-1 wt%, Si = 0.03
wt%, Mn = 0.01 wt%, P = 0.008-0.0
18 wt%, balance = iron and unavoidable impurities Molten iron content: 1.5 t Molten iron temperature: 1650 ° C Main component of refractory: magnesia chromite Vacuum degree: 1 Torr before starting treatment, 1 to 9 Torr during treatment Oxidizing agent: (1) Iron oxide powder (average particle size 90 μm) (2) Chromium oxide powder (average particle size 120 μm) (3) Manganese oxide powder (average particle size 60 μm) (4) Silicon dioxide powder (average particle size 110 μm) ( 5) Magnesium oxide powder (average particle size 100 μm) Carrier gas: Ar (flow rate is 400 to 700 liters /
min) Spraying location: 1 location Processing time: 30 minutes FIGS. 2 and 3 show the results of the above test.

FIG. 2 shows that when the spraying speed is represented by the endothermic amount of the oxidizing agent per unit time (kJ / min),
It is a figure which shows the influence which [% Cu] has on reduction (%). FIG. 3 is a diagram showing the effect of the amount of heat absorption on the decrease in [% Sn]. In figures and below,% is wt
%.

As shown in FIG. 2, the decrease of [% Cu]
In any oxidizing agent, the range of the above-mentioned endothermic amount is 500
It became 10% or more at １０1500 kJ / min. As shown in FIG. 3, the amount of reduction of [% Sn] was 10% at 500 to 1500 kJ / min for all oxidizing agents.
That's all.

(Test 2) Copper removal and tin removal treatment were performed using a vacuum high-frequency induction heating melting apparatus having the configuration shown in FIG. 1 while changing the number of spraying points and the spraying speed. The conditions are shown below.

Iron composition: Cu = 0.40%, Sn =
0.11%, carbon = 0.5-1%, Si = 0.03%,
Mn = 0.01%, P = 0.008 to 0.018%,
Balance = iron and unavoidable impurities amount of molten iron: 1.5 t molten iron temperature: 1650 ° C main component of refractory: magnesia chromite Vacuum degree: 1 Torr before treatment, 1 to 9 Torr during treatment Oxidizing agent: (4) silicon dioxide Powder (average particle size: 110 μm) Carrier gas: Ar (flow rate is 400 liters / min per location) Blowing location: (1) One location with one single lance (2) Two single lances Two locations Two lances point vertically downward The distance between the centers of the spraying points is 500 mm (3) Three locations using one single-hole lance and two-hole lance (branch angle 3 °). The distance between the centers of the two lance spray points is 300mm (adjust the height of the lance). (4) The distance between the centers of the spray points is 300mm (adjust the lance height) using two two-hole lances (branch angle 3 °). Processing time: 30 minutes FIGS. 4 and 5 show the results of the above test.

FIG. 4 is a diagram showing the effect of the number of spraying points on the reduction of [% Cu] when the spraying speed is expressed by the amount of heat absorbed per unit time of the oxidizing agent (kJ / min). FIG. 5 is a diagram showing the effect of the number of spraying points on the decrease in [% Sn].

As shown in FIG. 4, the decrease of [% Cu] is
The range of the above-mentioned heat absorption was 500 to 1500 kJ / min, and it became larger as the number of spraying points increased. As shown in FIG. 5, the amount of decrease in [% Sn]
It increased from 00 to 1500 kJ / min and increased as the number of spray points increased.

[0058]

According to the method of the present invention, the rate of copper removal and / or tin removal from molten iron can be increased, and the treatment can be performed efficiently in a short time.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an example of a vacuum high-frequency induction heating / melting apparatus for carrying out the method of the present invention.

FIG. 2 is a diagram showing the effect of the endothermic amount on the reduction amount of [Cu] when the spraying speed is represented by the endothermic amount per unit time (kJ / min) of the oxidizing agent when the number of spraying points is one; It is.

FIG. 3 is a graph showing the effect of the endothermic amount on the decrease in [Sn] when the spraying speed is represented by the endothermic amount per unit time (kJ / min) of the oxidizing agent when the number of spraying points is one; It is.

FIG. 4 shows that the number of spraying points when the spraying speed is represented by the amount of heat absorbed per unit time (kJ / min) of the oxidizing agent is [C
u] is a diagram showing the effect on the amount of decrease.

FIG. 5 shows that the number of spraying points when the spraying speed is represented by the endothermic amount (kJ / min) of the oxidizing agent per unit time is [S
[n] is a diagram showing the effect on the amount of decrease.

[Explanation of symbols]

1: vacuum tank, 2: vacuum tank top lid, 3, 4:
Powder top blowing lance, 5: refractory, 6: exhaust hole,
7: induction heating coil, 8: molten iron,
9: Container

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-126726 (JP, A) JP-A-7-126727 (JP, A) JP-A-1-195241 (JP, A) JP-A-6-126 10026 (JP, A) JP-A-61-190011 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21C 1 / 04,7 / 04 C21C 7 / 068,7 / 10

Claims (1)

(57) [Claims] An oxidizing agent comprising iron oxide powder and / or an oxide powder having a lower oxidizing power than iron oxide is sprayed on the surface of the molten iron containing carbon under a reduced pressure of 10 Torr or less to decarbonize the molten iron. By doing so, the copper and / or
Or a method of removing tin, wherein the spray amount per spray and per unit time is 5 in terms of the endothermic amount of the oxidizing agent.
A method for removing copper and / or tin from molten iron, which is performed at a rate of 00 to 1500 kJ / min.