JPS62116752A - Manufacture of low-or medium-carbon ferroalloy - Google Patents

Abstract

PURPOSE:To easily manufacture a low- or medium-carbon ferroalloy from a high-carbon ferroalloy by feeding an oxidative gas mixed optionally with a nonoxidative gas to the high-carbon ferroalloy in a molten state so as to carry out decarburization under reduced pressure. CONSTITUTION:A ladle 7 contg. a molten high-carbon ferroalloy 5 is placed in a vacuum vessel 1. Three porous plugs 4 in the bottom of the ladle 7 are connected to a pipe for feeding gaseous Ar. A top blowing lance 3 is inserted into a hole pierced in the lid 2 of the vessel 1 so that the tip of the lance 3 is positioned above the surface of the molten high-carbon ferroalloy 5. The vessel 1 is evacuated through a duct 6 and the molten high-carbon ferroalloy 5 is decarburized by feeding gaseous oxygen from the lance 3 and gaseous Ar from the bottom porous plugs 4.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing low- and medium-carbon ferroalloys, and in particular to a method for decarburizing high-carbon ferroalloys, such as high-carbon ferromanganese and high-carbon ferrochrome. We propose an advantageous method for producing low- and medium-carbon ferroalloys.

(Prior art) Ferromanganese (hereinafter referred to simply as rFeMnJ)
There are high carbon, medium carbon, and low carbon (rHC-, MC-, and LC-J, respectively) types of ferroalloys such as It is classified into

Among such ferromanganese, rHC-FeMnJ has a saturated carbon concentration, has a low melting point, and can be produced at a relatively low cost. However, rMc-FeMn j, rL
C-FeMn J uses a large amount of electrical energy,
After producing a silicon manganese (SiMn) molten metal, silicon (Si) is removed from the molten metal to form rFeMnJ, which is expensive and requires a large amount of energy.

Conventionally, the carbon content of rHc-FeMn J was removed by oxygen blowing to produce rMc-FeMn J and rLc-FeMn J.
Several methods have been proposed for manufacturing. For example, Japanese Patent Publication No. 60-56051, Japanese Patent Publication No. 57-27166
The publication discloses a method for decarburizing by blowing oxygen into molten HC-FeMn from a top blowing lance or a bottom blowing tuyere. These known decarburization methods are characterized by the need to prioritize the decarburization reaction in equation (1) below over the manganese oxidation in equation (2), which makes it necessary to carry out oxygen blowing at a fairly high temperature from a thermodynamic point of view. be.

For example, a high temperature of 1700°C to 1800°C is required.

In addition, Japanese Patent Application Laid-open No. 54-97521 discloses that oxygen, water vapor, and argon can be simultaneously mixed with hydrogen in order to be thermodynamically advantageous.
A method for preferential decarburization by blowing into a C-FeMn molten metal and diluting CO gas with a non-oxidizing gas to lower the CD partial pressure on the right side of equation 1) is disclosed. However, this method still requires high temperatures.

This method also has the disadvantage of requiring a large amount of non-oxidizing gas, as will be described later.

(Problems to be solved by the invention) Each of the above methods requires high temperature,
In addition, since oxygen is blown into the furnace through the bottom tuyeres, the refractories in the reaction vessel are subject to significant erosion. It is known from experience that the amount of refractory erosion is more than five times that of molten steel production by normal decarburization of hot metal. Furthermore, due to the high temperature, manganese evaporates significantly, causing a decrease in manganese yield during production. For example, pure oxygen is converted into HC-FeMn
When sprayed from above the molten metal bath surface, the initial amount of manganese is 13
There are also reports that % was lost through evaporation.

The purpose of the present invention is to overcome the disadvantages of high-temperature blowing that the conventional technology has, and to convert HC-FeMn to MC-FeMn with a high Mn yield.
The purpose is to propose a method for manufacturing FeMn and LC-FeMn at low cost.

(Means for solving the problem) As is clear from the above known techniques, HC-FeMn
In order to prioritize decarburization of carbon over manganese oxidation, it is effective to lower the CD partial pressure.

Therefore, the present invention aims to reduce the partial pressure by HC-FeM.
Focusing on carrying out the decarburization reaction of n under reduced pressure, we developed the method described below. By operating under reduced pressure when supplying oxidizing gas or a mixed gas of oxidizing gas and non-oxidizing gas to the HC-FeMn molten metal,
The 00 partial pressure at the reaction interface between the gas and the molten HC-FeMn was lowered to allow the reaction of equation (1) above to proceed efficiently to the right.

In addition, in the present invention, the above-mentioned gas is supplied to the molten metal by using a combination of top blowing and bottom blowing methods, and in the present invention, the degree of pressure reduction is gradually increased within the range of 400 to 10 Torr as decarburization progresses. It is desirable to do so.

(Function) Comparing the method of the present invention, which lowers the CD partial pressure by decompression, with the conventional blowing method using a mixed gas, it is found that the method using a mixed gas requires a large amount of non-oxidizing gas to lower the CD partial pressure. need to use. For example, in the case of a low carbon concentration region, the ratio of oxidizing gas to non-oxidizing gas should be increased to 1:2 to 1.
I set it to about 6. However, in this method, argon (Ar) is generally used as the non-oxidizing gas, but Ar is an expensive gas and the refining cost increases, making it uneconomical.

Moreover, when a large amount of non-oxidizing gas is supplied to the molten metal, the amount of splash and dust increases, resulting in a decrease in the Mn yield.

In contrast, the depressurization method of the present invention reduces the CD partial pressure by reducing the pressure, so decarburization and refining can be performed even at low temperatures, and the above-mentioned problem is solved.

An example of the decarburization process according to the present invention will be explained below in order.

First, HC-FeMn molten metal is charged into a decarburization reaction vessel.

As the decarburization reaction vessel, a vacuum decarburization device (VOD) is suitable, but a converter having a pressure reduction function may be used, or a device in which a pressure reduction function is added to an induction heating furnace may be used. In either case, the required functions are a pressure reduction function and a lance or tuyere below the bath surface for supplying oxidizing gas for decarburization. Additionally, it is desirable to have an electric heating device for molten metal and equipment for adding auxiliary materials under reduced pressure.

Oxygen (0□) and carbon dioxide (Co□) are added as oxidizing gases to the HC-FeMn molten metal charged in the container.
, water vapor (H2O), air, etc. In order to suppress Mn evaporation from the high-temperature part where the oxidizing gas hits the molten metal, the non-oxidizing gas may be supplied in a mixed manner or may be supplied separately toward the fire point.

The vacuum in the container is started before or at an appropriate time after the gas supply starts. As for the degree of depressurization, low pressure is more efficient for decarburization, but considering the cost of decompression, it is 400%
It is desirable to have a pressure of about 400 mmHg to 10 mmHg. Further, it is desirable to reduce the degree of pressure reduction in a region of high carbon concentration and gradually shift to a lower pressure as decarburization progresses, thereby reducing the cost of pressure reduction.

The method of supplying oxidizing gas for refining is shown in Figure 2 (a).
Although various methods such as those in (C) to (C) are possible, the general method is (a), in which the oxidizing gas is supplied from the top blowing lance and the non-oxidizing gas for stirring is supplied from the bottom blowing tuyere. The combination is
It is simple in terms of equipment, and maintenance costs and operating costs are low.

Even in decarburization under reduced pressure, high temperatures are advantageous, but there is no need to raise the temperature to as high as 1,700 to 1,800 degrees Celsius as in conventional methods.
0 to 1500°C), which is very advantageous in terms of Mn loss due to melting and evaporation of the refractory.

Once a predetermined amount of decarburization is completed, the pressure is returned to atmospheric pressure and the product is poured into a mold.

FIG. 1 shows the relationship between the degree of pressure reduction and the overall economic efficiency such as operating cost and equipment cost when carrying out the present invention. 40
If it is 0 torr or more, the decarburization efficiency will be poor and the refining time will be long. Furthermore, even if the pressure is lower than 10 torr, the decarburization efficiency does not improve significantly, but the cost for reducing the pressure increases, and the loss of Mn due to evaporation also increases. Therefore, the optimum degree of pressure reduction is 400 to 10 torr.

Furthermore, if the molten HC-FeMn is not stirred, the uniformity within the bath will deteriorate and decarburization will proceed only in the upper part of the bath.

Therefore, stirring is performed by blowing gas under the bath surface to ensure uniform decarburization.

This type of gas may be the same as that sprayed onto the bath surface, or since stirring is the main purpose, a non-oxidizing gas may be used alone.

In addition, FIG. 3 shows the relationship between the carbon concentration at which manganese oxidation starts and the 00 partial pressure when decarburizing HC-FeMn, determined by thermodynamic calculation. It has also been thermodynamically confirmed that the present invention can efficiently decarburize even at low temperatures.

(Example) Is HC-FeMn melted in a normal electric furnace? is9.
Five tons were received in the ladle 7, and the ladle 7 was placed in the vacuum vessel 1 shown in FIG. Three porous plugs 4 are arranged at the bottom of this receptacle 17 so that they can be connected to argon gas piping. Next, after putting a lid on the vacuum container 1, insert the top blowing gas lance 3 from the center of the lid, and
It was installed so that the lower end 5 was located 700 cm above the FeMn bath surface.

Next, at the same time as the pressure inside the container 1 was reduced, oxygen was started to flow from the top blowing lance 3, and oxygen supply was continued while maintaining the inside of the container at about 300 torr. Further, a total of 6 (1 to 12 ON1/min -t) of argon was continuously supplied from the porous plug 4 at the bottom.

FIG. 5 shows changes over time in the degree of vacuum, top-blown oxygen flow rate, bottom-blown argon flow rate, and changes in carbon concentration during this operation.

Table 2 also shows the molten metal components before and after refining. At this time, in order to keep the molten metal temperature within the range of 1450 to 1500℃, when the temperature is low, a heat generating agent such as Fe-3i or AI is added, and when the temperature is high, a coolant such as crushed MC-FeMn waste or manganese ore is added as appropriate. did. After such refining, the weight of MC-FeMn injected into the mold was 8.6 tons.

Table 2 Example 2 HC-FeMn was decarburized in exactly the same manner as in Example 1. However, from the top blowing lance 3, a mixed gas of oxygen and argon was used instead of pure oxygen, and the mixing ratio was changed as the refining progressed to increase the amount of argon.

The operating conditions during refining in this example are shown in FIG. 6 and the molten metal components are listed in Table 3. At about 52 minutes after the start of refining, the carbon concentration became 2% or less, resulting in MC-FeMn according to the JIS standard shown in Table 1. When the refining was further continued for 85 minutes, the carbon concentration decreased to 1% or less and became a component of LC-FeMn.

5 kg of Cu was added to the molten metal at an appropriate time, and the weight of the molten metal during refining was estimated from the increase in concentration, and this is shown in Table 3. Calculating the yield of manganese from this weight, M
98% when refined to C-FeMn, L C-F
It was 97% at the time of refining to e M n, and the loss due to evaporation, which was originally predicted, was not large enough to be economically disadvantageous.

Table 3 Table 4 compares the manufacturing costs between the vacuum refining of the present invention and the conventional atmospheric pressure refining, and the present invention is more advantageous.

Table 4 (Effects of the invention) As explained above, according to the present invention,! , 4 C-F
E! An.

When manufacturing LC-FeMn, there is no need to use large amounts of expensive electrical energy, and it is relatively inexpensive) IC-
It is economical because it can now be produced by decarburizing FeMn as a raw material. Moreover, compared to conventional methods, smelting can be carried out at low temperatures, reducing the cost of refractories, and there is less oxidation loss of manganese to slag, making it more effective overall.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between the degree of pressure reduction and the cost index in the present invention, Fig. 2 is a diagram showing various aspects of supplying refining gas in the present invention, and Fig. 3 is a graph showing the relationship between the degree of pressure reduction and the cost index in the present invention. Figure 4 is a schematic diagram of the equipment used to carry out the present invention. It is a graph showing operational data when implementing. 1...Reduced pressure container 2...Lid of the reduced pressure container 3...
・0□ Supply lance 4...Porous plug for bottom-blown Ar 5...Molten metal 6...Duct for pressure reduction 7...
・Ladle

Claims (1)

[Claims] 1. A method for producing a low-carbon or medium-carbon ferroalloy by decarburizing a high carbon-containing ferroalloy, wherein the above treatment is carried out by adding an oxidizing gas or A method for producing a low/medium carbon alloy iron, characterized by supplying a mixed gas of an oxidizing gas and a non-oxidizing gas and carrying out the process under reduced pressure. 2. The manufacturing method according to claim 1, wherein the gas is supplied to the molten metal by blowing it onto the surface of the molten metal and also by blowing into the molten metal from below the bath surface. 3. The manufacturing method according to claim 1 or 2, characterized in that the degree of pressure reduction is gradually increased within the range of 400 to 10 torr as decarburization progresses.