JPS63130746A - Manufacture of low-silicon medium-or low-carbon ferromanganese - Google Patents

Abstract

PURPOSE:To economically manufacture products without causing deterioration in Mn yield, by carrying out decarburization and desiliconization by means of top blowing of O2 gas and bottom blowing of O2 and inert gases into high-Si high-C ferromanganese and then by carrying out decarburization while specifying the composition of bottom-blown gas and the temp. of molten metal. CONSTITUTION:The top blowing of O2 gas and the bottom blowing of O2 and inert gases are applied to molten high-C ferromanganese of >=1.5% Si content, so that decarburization and desiliconization are carried out by decarburizing until the prescribed C content is reached and also by burning Si. After this primary stage, the top blowing of O2 is stopped and the bottom blowing is continues, so that decarburization is carried out until the desired C quantity is reached by regulating the amount of bottom-blown inert gas to >=20pts.vol. based on 100pts. vol. of the amount of bottom-blown O2 gas and also by controlling the temp. of the molten metal to 1,650-1,800 deg.C. Since decarburization and desiliconization mainly composed of top blowing of O2 is exerted in the primary stage and decarburization is accomplished by the combination of bottom-blown O2 and bottom-blown inert gases in the secondary stage as mentioned above, decarburizing efficiency in the secondary stage can be improved. Accordingly, Mn oxidation is minimized and the necessity of recovering Mn by using expensive reducing agents can be obviated.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a low St.
The present invention relates to a method for producing medium/low carbon ferromanganese.

[Prior Art] The conventional method for producing medium- to low-carbon ferromanganese is the so-called silicide method, in which the target C content is achieved by utilizing the mutual solubility of C and St in Fe-Mn alloy. Electric furnace for producing St-Mn molten metal)
, Mn oxide such as Mn ore is added to this to form St-Mn.
The conventional method was to remove the St contained therein by oxidation. Since this method uses an electric furnace, it has the economical problem of high electricity costs, and it also uses basic oxides (such as Cab) to capture 5i02, which is produced in large quantities by the oxidation and removal process. It is also necessary to use a large amount of
There is also an operational problem that the amount of slag becomes excessive. Moreover, although the amount of Mn contained in the slag is not large enough to be collected, it does contain enough Mn to cause pollution if dumped as is, so there is a problem in that the slag must be treated with great care. ing. Further M
When oxidizing and removing Si by adding n oxide, S
Depending on the target for reducing the amount of i, it may be necessary to use a considerably large amount of Mn oxide, and further reduce the amount of Si produced.
Basic oxide (CaO etc.) added to neutralize 02
There was a problem in that the amount used was also considerably large, and the cost of auxiliary raw materials soared. On the other hand, regarding low carbonization, the silicide method is used to achieve JIS No. 1 product (C < 1.0%, essentially 0.9
%), it is necessary to use a molten 51-Mn containing 21 to 22% Si as a raw material due to the mutual solubility of C and Si, and even more low-carbon ferromanganese, such as In order to produce low-carbon ferromanganese with a C content of approximately 0.5%, the St content in the raw material molten 51-Mn must be increased to 25-26%, which is higher than that of Mn. SL that is difficult to reduce
It has the disadvantage that it requires a huge amount of electric power to contain such a large amount of. In addition, in the process of Si oxidation removal using Mn oxide, although heat is supplied by an exothermic reaction, the amount of heat is absolutely insufficient, so it is necessary to supply heat by arc heating, and the product is produced by picking up C from the electrode. It has been extremely difficult to produce ferromanganese with even lower carbon and lower SL, as there is a risk that the carbon concentration of ferromanganese may increase.

As a manufacturing method that is fundamentally different from the single layer silicide method,
A method has been proposed for producing low-carbon ferromanganese by reducing high-Mn slag by taking advantage of the fact that the solubility of C in n-slag is quite low. For example, Tokuko Sho 57-36337
The publication describes a method in which Mn-containing slag is placed in a container that moves horizontally eccentrically and is reduced by adding Fe-5t.
According to this method, it is possible to produce ferromanganese with a C content of 1% or less. However, this method has the disadvantage that 0.8 to 0.9% of SL remains due to the addition of Fe-3L, and it cannot be used for products in which residual Si is a problem. Furthermore, since a large amount of expensive Fe-3i (for example, 270 to 352 kg/l (product ferromanganese)) is used, the cost of auxiliary raw materials increases.

[Problems to be Solved by the Invention] The present invention has been made with attention to these circumstances, and it is possible to solve the problem in medium- and low-Si content without deteriorating the Mn yield.
The object of the present invention is to provide a method for economically producing low carbon ferromanganese.

[Means for Solving the Problems] The method of the present invention, which has achieved the above object, targets a high carbon ferromanganese molten metal with a St content of 1.5% or more, and uses top blowing of oxygen gas and oxygen and inert gas. The first step is to decarburize to a predetermined amount of carbon by bottom blowing gas, and also burn silicon to decarburize and desiliconize it, and the bottom blow of oxygen gas and bottom blowing of inert gas are combined to produce a bottom blowing oxygen gas amount of ioo. The gist of this method is that it consists of a second step in which the bottom blowing amount of inert gas is 20 parts by volume or more, and the temperature of the molten metal is controlled at 1650 to 100° C., while decarburizing to a desired carbon content. In addition, in the process of progressing decarburization, the method of the present invention uses medium carbon ferromanganese in a relatively high carbon region (e.g. C concentration:
3.0 to 2.5%) to reach medium carbon ferromanganese (e.g. C concentration = 1.9 to 1.6%) (second step), and also starting from high carbon ferromanganese and medium carbon concentration region (e.g. C concentration: 2.5-1.9
%) to low carbon ferromanganese (e.g. C concentration: 0
．． 95 to 0.70%) (second step).

[Function] The present invention uses inexpensive high carbon ferromanganese, especially with a St of 1.5.
% or more of high-Si, high-carbon ferromanganese is used as a raw material, and decarburization and Si removal are promoted by rationally utilizing an oxidation blowing method while suppressing oxidative consumption of Mn. That is, in the present invention, a high-Si, high-carbon ferromanganese molten metal is charged into a reaction vessel equipped with top and bottom blowing functions, and in regions where carbon activity is high and decarburization is relatively easy, stirring is performed by inert gas bottom blowing. At the same time, sufficient oxygen gas is supplied by top and bottom blowing to advance decarburization and oxidize SL to remove St. As a result, the carbon activity decreases and the decarburization reaction becomes controlled by the carbon diffusion rate in the molten metal. In the area where the target C content is reached, the top blowing of oxygen is stopped and the bottom blowing of oxygen gas and inert gas is carried out at a predetermined ratio to advance decarburization to the target C content. In de-St in the steelmaking field, it is common to perform a preparatory film St before decarburization, but in the present invention, a sufficient amount of oxygen is supplied in the first step where carbon activity is high, and decarburization is simultaneously performed. Since Si is removed, there is no need to perform the preliminary film St operation, and the process can be carried out economically using high-carbon ferromanganese, which is inexpensive but has a high Si content, as a raw material.

The present invention will be explained in more detail below.

When we consider thermodynamically the oxidation reaction when high carbon ferromanganese is decarburized by oxygen blowing, we find that the oxidation of Mn takes priority at low temperatures, and the oxidation of C takes priority at high temperatures. It will be done.

There is also a tendency for oxidation of C to take precedence in cases where C has a high activity. Incidentally, since St is quite easily oxidized, the oxidation proceeds prior to the oxidation of Mn regardless of the temperature. Therefore, we will mainly consider the oxidation of C and Mn here. On the other hand, the influence of Co generated by the oxidation of C and existing on the surface of the molten metal can be considered, for example, by PC.

From the viewpoint of (partial pressure of co), there is also a tendency that oxidation of C takes precedence if p co is low even at low temperatures. Regarding temperature, there is a tendency that the higher the temperature, the more significant the evaporation loss of Mn becomes. Summarizing these trends, it is safer to perform decarburization blowing of high St, high carbon ferromanganese at low temperatures, and it is advantageous to eliminate the stagnation of C oxidation in low temperature blowing by reducing Peo. You can get a guideline that .

By the way, the temperature of the high St, high carbon ferromanganese used as a raw material is the temperature at which the molten metal comes out when manufactured in a reduction electric furnace or shaft furnace, or the temperature at which the molten metal falls when manufactured by remelting in an induction furnace or arc furnace. Although each can be seen by
In any case, higher temperatures than necessary will result in evaporation loss of Mn, so it is desirable to keep the temperature as low as possible, and generally 1
It will be carried out at about 300 to 1400°C. Therefore, in the early stage of blowing, the molten metal temperature is low and the carbon activity is high, so in this respect there is an advantage that the above guideline is met. However, the oxidation reaction of Mn in low-temperature blowing is not necessarily sufficiently low, and since the first step of the present invention uses both upper and lower blowing of oxygen gas, the oxidation of C and the oxidation of Mn occur in the initial blowing. Both cases progress markedly. Of course, the oxidation of St also progresses. The heat generated by these oxidation reactions causes the temperature of the molten metal to rise, and the oxygen decarburization efficiency increases accordingly to 60 to 90%.

In this way, the decarburization reaction progresses, and the C concentration in ferromanganese drops to around 2% (the activity of C decreases).
Then, even though the molten metal temperature is high, the decarburization oxygen efficiency begins to decrease, and the oxidation reaction of Mn progresses relatively significantly.

Therefore, in the present invention, the top blowing of oxygen is stopped at this stage, and the main role for further decarburization is caused by the bottom blowing oxygen. In other words, decarburization in a state where the activity of C is reduced progresses at a rate controlled by diffusion of C, so in the second step, gentle decarburization is performed by bottom blowing of oxygen and bottom blowing of inert gas. The oxygen ratio (oxygen gas amount/inert gas amount) is decreased as the process progresses. The process may end with a single bottom blow of inert gas. The decrease in the oxygen ratio appears as an increase in the inert gas ratio due to a relative or absolute increase in the amount of inert gas blown in, and the decarburization oxygen efficiency is maintained at a relatively high level, resulting in a reduction in Mn oxidation. Decarburization is promoted in low carbon conditions, and blowing continues to reach the target carbon level. The inert gas used in the present invention is generally Ar.
and N2 are commonly used, but from the viewpoint of protecting the bottom blowing nozzle, hydrocarbon gases can also be used, and the type thereof does not limit the present invention. Oxygen bottom blowing and inert gas bottom blowing may be performed through a single pipe nozzle, but a multilayer nozzle with double or more pipes is used to blow oxygen gas from the inner pipe and inert gas from the outer pipe. If the configuration is such that the nozzles are blown into each other, good results can be obtained in terms of preventing heat loss to the nozzle.

By the way, the amount of bottom-blown inert gas in the second step of decarburization must be at least 20 parts by volume per 100 parts by volume of bottom-blown oxygen gas, and if it is less than 20 parts by volume, the stirring effect will be insufficient. An increase in the decarburization oxygen efficiency cannot be expected, and as a result, the progress of decarburization is suppressed, and as a result, the oxidation loss of Mn increases.

Therefore, a more preferable amount is 50 parts by volume or more.

However, when the amount of inert gas becomes excessive, the temperature of the molten metal is lowered, and the oxidation of <Mn as described above is promoted.

Therefore, a preferable upper limit is 400 parts by volume, and a more preferable upper limit is 200 parts by volume. The above is a general description of the present invention, and it is desired that the amount be increased or decreased depending on the target amount of C in the ferromanganese. For example, medium carbon ferromanganese (for example, C concentration: 1.9 to 1.6%)
If the target C concentration is 3.0 to 2.5%, the target C concentration in the first step is, for example, 3.0 to 2.5%, and the bottom blowing amount of inert gas in the second step is 20 to 100 parts by volume (with respect to oxygen bottom blowing amount 10
On the other hand, when aiming at low carbon ferromanganese (for example, C concentration: 0.95 to 0.70%), the target C? ! For example, 4 degrees is 2.5
-1.9%, and controlling the amount of inert gas blown in the second step to 50 to 200 parts by volume (same).

Next, control of the temperature of the molten metal leading to the second step will be explained. In the present invention, the target C concentration is controlled to be blown down in two stages, and in the first step, the carbon concentration is decarburized all at once to a predetermined amount of carbon concentration, which is set as an intermediate target. The load to blow down to the carbon concentration is reduced. Therefore, in the second step, there is no need to increase the temperature of the molten metal more than necessary, and a temperature of 1800° C. or lower is sufficient.

If the temperature exceeds 1800°C, the evaporation of Mn will increase, so it must be avoided. However, if the temperature becomes too low, the oxidation of Mn will easily proceed as described above, so the temperature should be kept as high as possible, specifically 1650°C or higher, to maintain decarburization oxygen efficiency and contribute to the progress of decarburization. Should.

In the above explanation, the point of switching from the first step to the second step is that the C concentration reaches a predetermined value, but the change in decarburization oxygen efficiency during blowing in the first step is checked. It is also within the technical scope of the present invention to perform control in such a manner that the temperature is increased, and when the value falls below a certain value (for example, 40 to 25%), the control is switched to the second step.

As mentioned above, in the first step, decarburization and Si removal are performed mainly using top-blown oxygen, and in the second step, a method is adopted in which decarburization is performed using the cooperation of bottom-blown oxygen and bottom-blown inert gas. The decarburization oxygen efficiency in the second step was set at a level of 40-50% (
It is also possible to maintain the decarburization to the final target concentration in one stage as in the past (decarburization oxygen efficiency = 5).
decarburization can be carried out more efficiently than the conventional method (~15%). Therefore, there is little oxidation of Mn, and there is no need to take the uneconomical and complicated effort of recovering Mn using an expensive reducing agent. However, this does not exclude the addition of alloying elements for the purpose of final component adjustment.

As described above, in the present invention, efficient decarburization is performed in two stages while considering changes in carbon concentration or changes in decarburization oxygen efficiency, so that oxidation loss of Mn can be suppressed as much as possible. However, Mn oxidation loss during the blowing process cannot be completely prevented. In addition, a coolant (generally medium/low carbon ferromanganese ingot) may be added to adjust the blowing temperature, but if the amount of Mn in the coolant is small, the Mn content at the end of blowing will naturally be low. In some cases, the amount of Mn oxide after blowing is quite large. Therefore, in the present invention, it is also possible to introduce a reducing agent (generally preferably after oxygen blowing) to reduce Mn oxides in the slag and increase the amount of Mn in the molten metal. The reducing agent may include, without limitation, ferrosilicon, metal Si, silicon manganese, metal Ca, metal A1, etc., but ferrosilicon is generally often used. If ferrosilicon or the like is used to reduce the Mn slag, excess St may sometimes remain, but as mentioned above, St is easily oxidized, so the sample after the reduction treatment is analyzed and By supplying the necessary amount of oxygen through bottom blowing and/or bottom blowing, it is possible to easily remove St and produce the desired low S content.
i Medium to low carbon ferromanganese can be produced.

[Example] Example I A double tube nozzle installed at the center of the bottom of a reaction vessel with an inner diameter of 600 mm lined with Mgo-C bricks was used to blow Ar at a total rate of 0.5 Nm3/min into the inner and outer tubes while high-carbon 500 kg of ferromanganese molten metal (see Table 1) was charged. The temperature of the molten metal after charging was 1400°C. Afterwards, Ar is blown at a rate of 0.2 Nm3/min from the outer tube of the bottom blowing nozzle, and oxygen is blown at a rate of 0.3 Nm3/min from the inner tube, and at the same time, oxygen is blown at a rate of 1.3 Nm3/min from the water cooling lance installed at the top of the container. Blowing was carried out for 25 minutes including blowing the rice. Thereafter, the top blowing oxygen was stopped and only the bottom 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 it was possible to produce a low-St medium carbon ferromanganese with a high Mn content. The cast metal is 325K.
g, and the yield was 72%.

Example 2 In performing decarburization n-refining using the same reaction vessel as in Example 1, the high carbon ferromanganese molten metal shown in Table 1 was blown with Ar of 0.48 m3/min from a bottom blowing double tube nozzle. 500Kg was charged into the container. The temperature of the molten metal after charging was 1340°C.

After that, 0.25Nm37 of Ar was applied from the outer tube of the bottom blowing nozzle.
At the same time, oxygen was blown into the inner tube at a rate of 0.5 Nm3/min, and at the same time oxygen was blown in at a rate of 1.5 Nm3/min from the water-cooled lance installed at the top of the container.
Blowing was continued for 26 minutes by blowing at a rate of 5 Nm for 37 minutes. During this time, 45 kg of Mn ore and 22.5 g of quicklime were added. After that, the top blowing oxygen was stopped and the oxygen was 0.5Nm3.
The blowing continued for 22 minutes at a rate of 1/min.

During this time, 15 kg of Mn ore and 7.5 g of quicklime were added in divided amounts. After blowing, 15 kg of fluorite was blown into the inner and outer tubes with Ar only at a total of 0.4 Nm for 37 minutes from the bottom blowing nozzle.
When 60 kg of ferrosilicon and 91 kg of quicklime were added in portions, samples were taken and analyzed before tapping [S i
] = 0.7%, so pre-blowing was carried out for 8 minutes under bottom blowing conditions after top blowing was stopped, and after sludge removal, the melt was tapped and cast. The metal components at the end of casting were as shown in Table 1, and low carbon ferromanganese with a high Mn content was obtained. The weight of the cast metal was 472 kg, and the Mn yield was 97.5%.

The ingredients of the additives are also listed in Table 2.

Table 1 (wt%) Table 2 [Effects of the invention] Since the present invention is configured as described above, it is possible to effectively control the progress of decarburization and control the Si concentration. It has become possible to produce low-Si medium and low-carbon ferromanganese more economically than the silicide method or other oxygen decarburization methods.

Claims (1)

[Claims] Targeting high-carbon ferromanganese molten metal with a Si content of 1.5% or more, it decarburizes to a specified carbon content by top blowing oxygen gas and bottom blowing oxygen and inert gas, and also burns silicon to decarburize. The first step of desiliconization is combined with bottom blowing of oxygen gas and bottom blowing of inert gas, and the amount of bottom blowing oxygen gas is 10.
A low-silicon medium characterized by comprising a second step of decarburizing to a desired carbon content while controlling the molten metal temperature to 1,650 to 1,800° C. and controlling the bottom blowing amount of inert gas to 0 parts by volume to 20 parts by volume or more.・Production method of low carbon ferromanganese.