JPH0629478B2 - Method for producing low silicon medium / low carbon ferromanganese - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a low Si that can economically achieve the target C content and Si content without adversely affecting the Mn yield.
The present invention relates to a method for producing medium / low carbon ferromanganese.

[Prior Art] A conventional method for producing medium-low carbon ferromanganese is a so-called silicide method, which utilizes a mutual solubility of C and Si in a Fe-Mn alloy to achieve a target C content. Si-Mn molten metal is manufactured (electric furnace), and Mn oxide such as Mn ore is added to this to produce Si-
The usual method was to oxidize and remove Si in Mn. Since this method uses an electric furnace, it has an economical problem that the specific gravity of electric power cost is high. In addition, a basic oxide (for example, a basic oxide for capturing a large amount of SiO ₂ by-produced by the above-mentioned oxidative removal) is included. It is also necessary to use a large amount of CaO), and there is a problem in operation that the amount of slag becomes excessive.
Moreover, the amount of Mn contained in the slag is not large enough to be collected, but is contained in an amount enough to cause pollution when it is discarded as it is. Therefore, there is a problem in that slag treatment must be performed with extreme caution. ing. Furthermore, when oxidizing and removing Si by adding Mn oxide, it may be necessary to use a considerably large amount of Mn oxide depending on the reduction target of Si amount.
Basic oxides (CaO etc.) added to neutralize O _2.
However, there was a problem that the amount of slag used was considerably large and the cost of auxiliary raw materials soared. On the other hand, regarding low carbonization, if a low carbon ferromanganese equivalent to JIS No. 1 product (C <1.0%, substantially 0.9%) is to be produced by the silicide method, C and S
In view of the mutual solubility of i, it is necessary to use a Si-Mn molten metal containing 21 to 22% of Si as a raw material, and further low carbon, for example, low carbon ferromanganese having a C content of about 0.5% is to be produced. Then, the raw material Si-M
The Si content in the molten n must be increased to 25 to 26%, and there is a drawback that enormous electric power is required to contain such a large amount of Si that is more reduced than Mn. It was In addition, although heat is supplemented by exothermic reaction in the process of removing Si by Mn oxide, the amount of heat is absolutely insufficient. Therefore, it is necessary to supplement heat by arc heating. It was extremely difficult to produce ferro-manganese with even lower carbon and low Si, since the carbon concentration of the carbon may increase.

On the other hand, as a manufacturing method that is different from the silicide method in principle, M
A method for producing low carbon ferromanganese by reducing high Mn slag has been proposed by taking advantage of the fairly low solubility of C in n slag. For example, Japanese Examined Japanese Patent Publication 57-36337
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a method in which Mn-containing slag is placed in a container that performs horizontal eccentric motion and Fe-Si is added to reduce the content.
According to this method, it is possible to produce ferromanganese having a C content of 1% or less. However, in this method, since Fe-Si is added, 0.8 to 0.9% of Si remains and S
It has a drawback that it cannot be used for products in which residual i is a problem. In addition, a large amount of expensive Fe-Si [for example, 27
0-352 kg / t (product ferromanganese)] has the drawback that the cost of the auxiliary raw material rises.

[Problems to be Solved by the Invention] The present invention has been made in view of these circumstances, and economically produces medium-to-low carbon ferromanganese having a low Si content without deteriorating the Mn yield. It is intended to provide a method.

[Means for Solving the Problems] However, the method of the present invention which has achieved the above-mentioned object is intended for a high carbon ferromanganese molten metal having a Si content of 1.5% or more, and the top blowing of oxygen gas and the addition of oxygen and an inert gas are performed. The first step of decarburizing to a predetermined carbon amount by bottom blowing and also burning silicon to decarburize and desiliconize, and the bottom blowing of oxygen gas and the bottom blowing of inert gas are used together, and the bottom blowing oxygen gas amount is 100 parts by volume. It has a gist in that it comprises a second step of decarburizing to a desired carbon amount while controlling the bottom temperature of the inert gas to 20 parts by volume or more and controlling the molten metal temperature to 1650 to 1800 ° C. In the method of the present invention, medium carbon ferromanganese (for example, C concentration: 3.
0 to 2.5%) to reach a medium carbon ferromanganese (for example, C concentration: 1.9 to 1.6%) (second step), and a method of starting from a high carbon ferromanganese as well as a general medium concentration carbon region ( For example, a method of reaching low carbon ferromanganese (for example, C concentration: 0.95 to 0.70% (second step) through C concentration: 2.5 to 1.9%) is included.

[Operation] The present invention is an inexpensive high carbon ferromanganese, in particular Si containing 1.5%.
The above-mentioned so-called high Si high carbon ferromanganese is used as a raw material and the decarburization and Si removal are advanced by rationally utilizing the method of oxidative blowing while suppressing the oxidative consumption of Mn. That is, in the present invention, a high-Si high-carbon ferromanganese melt is charged into a reaction vessel having top and bottom blowing functions, and stirring is performed by bottom blowing with an inert gas in a region where carbon activity is high and decarburization is relatively easy. On the other hand, oxygen gas is sufficiently supplied by top and bottom blowing to promote decarburization and at the same time, Si is deoxidized by deoxidizing Si, the carbon activity decreases, and the decarburization reaction is controlled by the carbon diffusion rate in the molten metal. In the controlled region, the top blowing of oxygen is stopped, and the oxygen gas and the inert gas are bottom blown at a predetermined ratio to advance decarburization to the target C content. In the field of desiliconization in the field of steelmaking, it is general to carry out preliminary desiliconization prior to decarburization. However, in the present invention, sufficient oxygen is supplied in the first step with high carbon activity to simultaneously perform decarburization. Since Si removal is performed, it is not necessary to perform a preliminary Si removal operation, and the treatment can be economically performed using high carbon ferromanganese, which is inexpensive but high in Si, as a raw material.

The present invention will be described in more detail below.

Considering the thermodynamics of the oxidation reaction when decarburizing high carbon ferromanganese by oxygen blowing, the tendency is that the oxidation of Mn has priority at low temperature and the oxidation of C has priority at high temperature. To be It is also recognized that the higher the activity of C, the higher the priority of oxidation of C. Since Si is easily oxidized, it progresses prior to the oxidation of Mn regardless of the temperature. Therefore, the oxidation of C and Mn will be mainly considered here. On the other hand the effect of CO on the surface of the produced molten metal by oxidation and C, for example, P _CO (partial pressure of CO)
From this point of view, there is also a tendency that the oxidation of C takes precedence if the P _CO is low even at a low temperature. Regarding the temperature, there is a tendency that the evaporation loss of Mn becomes more remarkable as the temperature becomes higher. Summarizing these trends, it is safer to carry out decarburization blowing of high Si high carbon ferromanganese on the low temperature side, and it is advantageous to eliminate the stagnation of C oxidation in low temperature blowing by reducing P _CO. The guideline is that

By the way, the temperature of the high Si high carbon ferromanganese used as a raw material depends on the tapping temperature from the reduction electric furnace or the shaft furnace when it is manufactured, or the melt-through temperature when it is manufactured by remelting with an induction furnace or an arc furnace. Although each is set,
In any case, since an excessively high temperature causes Mn evaporation loss, it is desirable that the temperature be as low as possible.
It will be conducted at about 00 to 1400 ° C. Therefore, since the molten metal temperature is low and the carbon activity is high at the initial stage of blowing, there is an advantage that the above guidelines are met in this respect. However, the oxidation reaction of Mn in low temperature blowing is not necessarily sufficiently low, and in the first step of the present invention, the upper and lower blowing of oxygen gas is used in combination, so in the initial blowing, C
And Mn are significantly oxidized. Of course S
Oxidation of i also progresses. The heat generated by these oxidation reactions raises the temperature of the molten metal, and accordingly the decarboxylation efficiency also rises to 60 to 90%.

In this way, the decarburization reaction proceeds, and the C concentration in ferromanganese falls to around 2% (the C activity decreases).
As a result, the efficiency of decarboxylation will start to decrease even though the temperature of the molten metal is high, and the Mn oxidation reaction will significantly proceed.

Therefore, in the present invention, the upper blowing of oxygen is stopped at this stage, and further decarburization causes bottom blowing oxygen to play a major role. That is, since decarburization in a state where the activity of C is lowered progresses at a rate-controlling rate of C, the second step is to perform gentle decarburization by bottom blowing of oxygen and bottom blowing of an inert gas.
The oxygen ratio (oxygen gas amount / inert gas amount) is reduced according to the progress of decarburization. At the end, the bottom of the inert gas may blow up. The decrease in the oxygen ratio appears as an increase in the inert gas ratio due to the relative increase or absolute increase in the amount of inert gas blown in, and the decarboxylation efficiency is maintained at a relatively high level. Decarburization is promoted in a small amount, and blowing is continued to the target carbon level. The inert gas used in the present invention is generally A
Although r and N ₂ are commonly used, a hydrocarbon-based gas can be used from the viewpoint of protecting the bottom blowing nozzle, and naturally the type does not limit the present invention. The bottom blowing of oxygen and the bottom blowing of inert gas may be performed through a single-tube nozzle, but a double-layer or more multi-layer nozzle is used to supply oxygen gas from the inner tube and inert gas from the outer tube. If each of them is configured to blow, good results can be obtained in the sense of preventing heat loss of the nozzle.

By the way, the bottom blowing amount of the inert gas in the second step of decarburization needs to be 20 parts by volume or more relative to 100 parts by volume of the bottom blowing oxygen gas, and if it is less than 20 parts by volume, the stirring effect is insufficient. An increase in decarboxylation efficiency cannot be expected, and as a result, the progress of decarburization is suppressed, resulting in an increase in Mn oxidation loss. Therefore, a more preferable amount is 50 parts by volume or more. However, when the amount of the inert gas becomes excessive, the temperature of the molten metal is lowered, and the oxidation of Mn is promoted as described above. Therefore, the preferable upper limit is 400 parts by volume, and the more preferable upper limit is 200 parts by volume. The above is the case where the present invention is described as a whole, and it is desired to increase or decrease according to the target C amount in the target ferromanganese. For example, when targeting medium carbon ferromanganese (for example, C concentration: 1.9 to 1.6%), the target C concentration in the first step is, for example, 3.0.
To 2.5% and the bottom blowing amount of the inert gas in the second step is controlled to 20 to 100 parts by volume (100 parts by volume against oxygen bottom blowing amount), while low carbon ferromanganese (for example, C concentration: 0.
95 to 0.70%), the target C concentration in the first step may be set to 2.5 to 1.9%, and the amount of the inert gas blown in the second step may be controlled to 50 to 200 parts by volume (the same). It is illustrated.

Next, the control of the molten metal temperature in the second step will be described. According to the present invention, the target C concentration is controlled so as to be blown down in two steps, and in the first step, the carbon concentration of a predetermined amount, which is set as an intermediate target, is decarburized all at once. The load to blow down to the carbon concentration of is reduced. Therefore, it is not necessary to raise the temperature of the molten metal more than necessary in the second step, and 1800 ° C. or lower is sufficient. 1
If the temperature exceeds 800 ° C., Mn will be vaporized so much that it must be avoided. However, if the temperature becomes too low, the oxidation of Mn easily proceeds as described above.
Specifically, it should be maintained at 1650 ° C. or higher to maintain the efficiency of decarboxylation and contribute to the progress of decarburization.

The point of switching from the first step to the second step in the above description was that the C concentration reached a predetermined value, but the transition of the decarboxylation efficiency was checked during blowing in the first step. Every other time, when the value becomes equal to or less than a certain value (for example, 40 to 25%), the control is switched to the control in the second step.

As described above, in the first step, decarburization centering on top blown oxygen and Si removal are performed, and in the second step, a method of performing decarburization operation in cooperation with bottom blown oxygen and bottom blown inert gas is adopted. It is also possible to maintain the decarboxylation efficiency in the second step at a level of 40 to 50% (broken line), and when decarburizing to the final target concentration in one stage as in the conventional case (decarboxylation efficiency:
Decarburization can be performed more efficiently than that of (5 to 15%). Therefore, Mn is less oxidized, and it is not necessary to uneconomically and complicatedly recover Mn by using an expensive reducing agent. However, the addition of alloying elements for the purpose of final component adjustment is not excluded.

As described above, in the present invention, efficient decarburization is performed in two stages while monitoring the transition of carbon concentration or the change of decarboxylation efficiency, so that the Mn oxidation loss is suppressed as much as possible. However, Mn oxidation loss during the blowing process cannot completely prevent this. A cooling agent (generally, a medium-low carbon ferromanganese cold mass) may be added to adjust the blowing temperature. However, if the amount of Mn in the cooling agent is small, the Mn content at the end of blowing is naturally low. However, the amount of Mn oxide after the completion of blowing may be considerably large. Therefore, in the present invention, it is possible to increase the Mn amount in the molten metal by adding a reducing agent (generally, after oxygen blowing), the Mn oxide in the slag is reduced. As the reducing agent, ferrosilicon, metal Si, silicon manganese, metal Ca, metal Al and the like can be exemplified without limitation, but generally ferrosilicon is often used. If ferrosilicon or the like is used to reduce the Mn slag, excess Si may sometimes remain,
As described above, Si is easily oxidized, so the sample after the reduction treatment can be analyzed, and if the required amount of oxygen is supplied by top blowing and / or bottom blowing, Si can be easily deoxidized. Low carbon ferromanganese can be produced.

[Example] Example 1 High carbon ferromanganese while blowing Ar total 0.5 Nm ³ / min of inner and outer tubes from a double tube nozzle installed in the center of the bottom of a reaction vessel having an inner diameter of 600 mm lined with MgO-C bricks. 500 kg of molten metal (see Table 1) was charged. The temperature of the molten metal after charging was 1400 ° C. Then the Ar from the bottom blown nozzle outer tube 0.2 Nm ³ / min, and at the same time blown from the inner tube with oxygen 0.3 Nm ³ / min, the oxygen from the water-cooled lance installed in the top of the vessel 1.3 Nm ³ / min rate Blowing was performed for 25 minutes. Thereafter, the top-blown oxygen was stopped and only the bottom-blown blowing was continued for 12 minutes. The composition and temperature of the molten metal at the end of blowing were as shown in Table 1, and low Si medium carbon ferromanganese having a high Mn content could be manufactured. The cast metal weighed 325 kg and the yield was 72%.

Example 2 In carrying out decarburization refining using the same reaction vessel as in Example 1, high carbon ferromanganese melt 5 shown in Table 1 was blown while blowing 0.4 Nm ³ / min of Ar from a bottom blowing double tube nozzle.
00 kg was charged into the container. The molten metal temperature after charging is 134
It was 0 ° C. After that, Ar is reduced to 0 from the outer tube of the bottom blowing nozzle.
25 nm ³ / min, the oxygen from the water-cooled lance was placed in a container top with blowing oxygen from the inner tube at 0.5 Nm ³ / min 1.
Blowing at a rate of 5 Nm ³ / min was continued for 26 minutes. During this period, 45 kg of Mn ore and 22.5 kg of quick lime were added. After that, the top blowing oxygen was stopped, and the blowing was completed by continuing the oxygen blowing at 0.5 Nm ³ / min for 22 minutes. During this period, 15 kg of Mn ore and quick lime
7.5 Kg was added in portions. A from bottom blowing nozzle after blowing
Fluorite 1 while blowing only r at a total of 0.4 Nm ³ / min of inner and outer tubes
5kg, ferrosilicon 60kg, quicklime 91kg were dividedly charged, and a sample before tapping was collected and analyzed [Si] =
Since it was 0.7%, it was smelted again for 8 minutes under the bottom blowing condition after the top blowing was stopped, and the molten metal was discharged and cast. The metal components at the end of casting are as shown in Table 1, and low carbon ferromanganese having a high Mn content was obtained. The cast metal was 472 kg and the Mn yield was 97.5%. The components of the additives are also shown in Table 2.

[Advantages of the Invention] Since the present invention is configured as described above, the progress of decarburization can be effectively suppressed and the Si concentration can be controlled. Therefore, the conventional silicide method and other oxygen decarburization methods can be used. It has become possible to economically produce low Si medium / low carbon ferromanganese.

Claims (1)

[Claims] 1. A high carbon ferromanganese melt having a Si content of 1.5% or more is targeted for decarburization to a predetermined carbon amount by top blowing oxygen gas and bottom blowing oxygen and an inert gas, and also burning silicon. The first step of decarburization and desiliconization is used together with the bottom blowing of oxygen gas and the bottom blowing of inert gas, and the bottom blowing amount of inert gas per 100 parts by volume of oxygen gas is 20 parts by volume or more and the molten metal temperature 1650-1800 ° C
A method for producing low-silicon medium / low-carbon ferromanganese, which comprises a second step of decarburizing to a desired carbon amount while controlling the above.