JPH0558050B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing medium- and low-carbon ferromanganese by blowing high-carbon ferromanganese molten metal. Specifically, the Mn yield is improved by controlling the progress of decarburization in two stages. The present invention relates to a method for producing medium- to low-carbon ferromanganese that can efficiently achieve a target C content without adversely affecting the carbon content. [Prior art] The conventional method for producing medium- to low-carbon ferromanganese is the so-called silicide method, which uses the mutual solubility of C and Si in Fe-Mn alloy to achieve the target C content. amount of Si−Mn
Molten metal is produced (electric furnace), and Mn such as Mn ore is added to it.
The conventional method was to add an oxide to oxidize and remove the Si in Si-Mn. Since this method uses an electric furnace, it has the economical problem of high electricity costs, and it also requires the use of basic oxides to capture SiO ₂ , which is produced in large quantities by the above oxidation removal process. It is also necessary to use a large amount of (for example, CaO), and 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 it is simply dumped, so the problem is that great care must be taken when disposing of the slag. I also have [Problems to be Solved by the Invention] Therefore, the oxygen gas blowing method as disclosed in Japanese Patent Publication No. 57-27166, in which oxygen gas is blown into the high carbon ferromanganese molten metal, is decarburized by oxygen. A method has been proposed in which ferromanganese is converted into medium- to low-carbon ferromanganese. Examining this method in more detail, it is found that prior to performing oxygen blowing, high carbon ferromanganese is
Heat it to a temperature above ℃ (using a furnace gas jacket nozzle), and when blowing oxygen,
The structure is such that decarburization is promoted by raising the temperature to a high temperature close to 1900°C, while Mn oxides formed by oxygen blowing are reduced and recovered by adding lime and silicon alloy. However, Mn
Since Mn has a relatively low boiling point and high vapor pressure, it is necessary to consider not only the loss due to oxidation but also the loss due to evaporation, and the cost increase cannot be avoided due to the low Mn yield in exchange for the electricity cost. It is considered. On the other hand, JP-A-60-
In No. 56051, a reaction vessel configured to perform top-bottom blowing in parallel was used, and decarburization by top-blowing oxygen gas was promoted using the stirring effect of bottom-blowing inert gas. A method of blowing high-carbon ferromanganese at a freezing temperature has been proposed. According to this method, since decarburization is performed by upward blowing of oxygen gas, a high decarburization oxygen efficiency (ratio of oxygen consumed for decarburization reaction out of supplied oxygen) can be expected in the high carbon region, but in the medium carbon region In the low-carbon region, carbon diffusion becomes rate-limiting, so the decarburization oxygen efficiency decreases, and the blowing time until the target C concentration is reached becomes longer. The disadvantage was that oxidation loss increased. Furthermore, in JP-A No. 60-67608, part of the bottom blowing gas was changed to oxygen gas (the rest remained inert gas).
By using a combination of oxygen blowing from the top and the bottom, decarburization is promoted in the initial stage, and when the oxygen has been rapidly lowered to the specified medium/low carbon range, the oxygen blowing is changed from top blowing to bottom blowing. After that, the molten metal is stirred by bottom-blown inert gas, and the molten metal formed in the decarburization process is removed.
A method has been proposed in which Mn oxide is reduced (Mn is recovered) by adding a reducing agent such as Si alloy or Al to produce medium- to low-carbon ferromanganese. However, the amount of bottom-blown oxygen gas used in this method is only 6 to 7% of the top-blown oxygen gas amount, so if you are trying to lower the carbon concentration to a medium-low carbon range, it is necessary to In view of the low carbon-oxygen efficiency, top-bottom blowing must be carried out over a considerable period of time. Therefore, the problem of an increase in the total amount of oxygen injection and an accompanying increase in Mn oxidation loss has become significant, and following the decarburization process,
Even if the process of recovering Mn oxide using a Si alloy or the like is added, the reducing agent itself, such as a Si alloy, is expensive, so it must be said that this is an extremely uneconomical method when considered as a whole. The present invention was made in consideration of the above-mentioned drawbacks of the prior art, and although it follows the point of blowing using inexpensive high-carbon ferromanganese as a raw material, it is necessary to suppress Mn oxidation during blowing as much as possible. The purpose of the present invention is to provide a method for economically producing medium- to low-carbon ferromanganese.
In other words, we decided to suppress the amount of Mn burned during blowing as much as possible, so even if the reduction in the amount of Mn is compensated for by adding Mn oxide or a reducing agent, the cost of raw materials for this can be kept to a minimum. The purpose is to establish a method of blowing that can be used. [Means for solving the problems] The present inventors analyzed the drawbacks of the above-mentioned prior art, and
The present invention is based on controlling the blowing method during the early stage when the decarbonizing oxygen efficiency is high and the latter stage when the decarburizing oxygen efficiency is low. That is, the method for producing medium/low carbon ferromanganese according to the present invention is a first step in which a high carbon ferromanganese molten metal is decarburized to a predetermined carbon content by top blowing with oxygen gas and bottom blowing with oxygen and inert gas. The blowing process is divided into a second step of decarburizing to a desired carbon content using a combination of oxygen gas bottom blowing and inert gas bottom blowing, and during the implementation of the first and second steps, The gist is that the amount of Mn in the molten metal is adjusted (increasing the Mn content of the product) by adding Mn oxide and a reducing agent after the completion of the second step. . Therefore, the present invention starts from high carbon ferromanganese, passes through a relatively high carbon concentration region (for example, C concentration: 3.0 to 2.5%), and then reaches medium carbon ferromanganese (for example, C concentration: 1.9 to 1.7%) (first step). (2nd step) Similarly, starting from high carbon ferromanganese, a general medium carbon concentration range (e.g. C concentration: 2.5~
1.9%) (first step) to reach low carbon ferromanganese (e.g. C concentration: 0.95-0.70%) (second step).
process). In order to compensate for the amount of Mn, Mn oxide and a reducing agent are added at any point in time to reduce the Mn oxide formed during blowing and the additionally added Mn oxide, which is then added to the molten metal as metallic Mn. I decided to keep it. If Mn oxide is added during blowing to increase the activity of MnO,
This has the effect of somewhat suppressing the tilting of the Mn oxidation reaction equilibrium toward the oxidation direction, and rather promoting decarburization. [Effect] If we consider thermodynamically the oxidation reaction when trying to decarburize high carbon ferromanganese by oxygen blowing, we find that MnO + C = CO + Mn K = P _CO・a _Mo /a _MoO・a _C logK It is known that the relationship expressed as =-12853/T+7.91 holds true. Therefore, there is a tendency that oxidation of Mn takes priority at low temperatures, and oxidation of C takes priority at high temperatures. However, if we look at the influence of CO generated by the oxidation of C and present on the surface of the molten metal from the perspective of P _CO (partial pressure of CO), we can see that even at low temperatures, if P _CO is low, then C
There is also a tendency for oxidation to take precedence. Regarding temperature, there is a relationship in which the higher the temperature, the more significant the evaporation loss of Mn becomes. Also
The higher the activity of MnO, the more easily the above reaction equation proceeds in the right direction, promoting decarburization. Furthermore, the higher the activity of C, the more decarburization is promoted. To summarize these trends, decarburization blowing of high carbon ferromanganese
This suggests that it is safer to carry out the process at low temperatures, and that it is advantageous to eliminate the stagnation of C oxidation in low temperature blowing by reducing P _CO and adding Mn oxide. Note that Mn ore is generally used as the Mn oxide added here. However, the type thereof is not limited, and any material containing Mn oxide may be used. For example, Mn slag, which is produced as a by-product when producing high-carbon ferromanganese or silicon manganese, or waste from Mn batteries can also be used. When adding materials containing SiO ₂ such as Mn ore or Mn slag, it is necessary to keep the slag layer basic in order to increase the activity of Mn oxide. It is recommended to increase the By the way, the temperature of high carbon ferromanganese, which is a raw material, depends on the temperature at which the hot water is discharged when manufactured in a reduction electric furnace or shaft furnace, or the melt-through temperature when manufactured by remelting in an induction furnace or arc furnace. However, 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 the temperature is about 1300 to 1400°C. Therefore, at the beginning of blowing, the temperature of the molten metal is low and the activity of C 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 in the first step of the present invention, upper and lower blowing of oxygen gas is used together, so in the initial blowing, oxidation of C and oxidation of Mn are performed. progresses significantly in both cases. 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%. As the decarburization reaction progresses and the C concentration in ferromanganese falls to around 2%, the decarburization oxygen efficiency begins to decrease despite the high temperature of the molten metal, and the oxidation reaction of Mn becomes relatively slow. progresses noticeably. Therefore, in the present invention, the top blowing of oxygen is stopped at this stage, and the main role of the 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 a relative or absolute increase in the amount of inert gas blown into the inert gas ratio, and the decarburization oxygen efficiency is maintained at a relatively high level.
Decarburization is promoted in a state with little Mn oxidation, and blowing continues to the target carbon level. It goes without saying that adding Mn oxide during the second step can also contribute to the progress of decarburization. In addition, the inert gas used in the present invention generally includes Ar and _N2 .
is commonly used, but if the purpose is to protect the bottom blowing nozzle, it is also possible to use hydrocarbon gas, and the type thereof does not limit the present invention.
Oxygen bottom blowing and inert gas bottom blowing may be performed through a single tube nozzle, but a double layer nozzle or more may be used to supply oxygen gas from the inner tube and inert gas from the outer tube. If the nozzle is configured to be injected intermittently, good results can be obtained in terms of preventing heat loss to the nozzle. As described above, in the present invention, efficient decarburization is performed in two stages while taking into account changes in carbon concentration or 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 cold blocks) is sometimes 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. death,
On the other hand, in the present invention, where the addition of Mn oxide is an essential requirement as described above, the amount of Mn oxide after blowing is quite large. Therefore, in the present invention, a reducing agent is introduced (generally preferably after oxygen blowing) to reduce Mn oxides in the slag and increase the amount of Mn in the molten metal. In addition, examples of the above-mentioned reducing agent include ferrosilicon, metal Si, silicomanganese, gold-plated Ca, metal Al, etc., without limitation. It is recommended that Mn oxide be added during the progress of blowing, but if there is little Mn oxide during decarburization, it may be added after blowing is completed. The important points of the present invention have been explained above, and next, suitable conditions for carrying out the present invention will be explained. First, the amount of bottom-blown inert gas in the second step of decarburization is preferably 20 parts by volume or more per 100 parts by volume of bottom-blown oxygen gas, and if it is less than 20 parts by volume, the stirring effect may be insufficient. Therefore, the increase in decarburization oxygen efficiency is reduced, 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 is promoted as described above. 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, when targeting medium carbon ferromanganese (for example, C concentration: 1.9 to 1.7%), the target C concentration in the first step is, for example, 3.0 to 2.5%,
The bottom blowing amount of inert gas in the second step is 20 to 100.
part by volume (bottom blowing amount relative to oxygen: 100 parts by volume), while low carbon ferromanganese (for example, C concentration: 0.95
0.70%), the target C concentration in the first step is set to 2.5 to 1.9%, and the amount of inert gas blown in the second step is controlled to 50 to 200 parts by volume (same). be done. Next, control of the molten metal temperature in 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 raise the temperature of the molten metal more than necessary, and a temperature of 1800°C is sufficient. If the temperature exceeds 1800°C, the evaporation of Mn will increase and must be avoided. However, if the temperature becomes too low, the oxidation of Mn will easily progress as mentioned above, so it is necessary to maintain the decarburization oxygen efficiency by keeping it as high as possible, specifically at 165°C or higher, to contribute to the progress of decarburization. is recommended. The point of switching from the first step to the second step in the above explanation is based on the fact that the C concentration reaches a predetermined value. 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 is carried out mainly using top-blown oxygen, and in the second step, a method is adopted in which decarburization is carried out by the cooperation of bottom-blown oxygen and bottom-blown inert gas, and Mn oxide is decarburized. Since the structure was designed to create conditions suitable for decarburization through input, it is possible to maintain the decarburization oxygen efficiency in the second step at a level of 40 to 50% (dashed line), as shown in Figure 1. This means that decarburization is more efficient than the conventional case where decarburization is carried out to the final target concentration in one stage (the final stage shown by the solid line in Figure 1, decarburization oxygen efficiency: 5 to 15%). I can do it. [Example] Example 1 High-carbon ferromanganese was blown from a double tube nozzle installed at the center of the bottom of a reaction vessel lined with MgO-C bricks with an inner diameter of 600 mm while blowing Ar at a total rate of 0.4 Nm ³ /min. 450 kg of molten metal (see Table 1) was charged. The temperature of the molten metal after charging was 1325°C.
After that, Ar was applied at 0.25Nm ³ /min from the bottom blowing nozzle outer tube.
Blowing was carried out for 22 minutes by blowing oxygen at a rate of 0.5 Nm ³ /min from the inner pipe and at the same time blowing oxygen at a rate of 1.5 Nm ³ /min from a water-cooled lance installed at the top of the container. After that, the top blowing oxygen was stopped and only the bottom blowing was continued for 19 minutes. During this time, 60 kg of Mn ore and 30 kg of quicklime were added little by little. After blowing, 25 kg of ferrosilicon and 25 kg of quicklime were decomposed and introduced while blowing Ar (0.4 Nm ³ /min) from the bottom, and finally, the slag was removed.
The metal was cast using hot water. The ingredients of the additives are also listed in Table 2. The composition and temperature of the molten metal at the end of Ar rinsing were as shown in Table 1, and low carbon ferromanganese with a high Mn content could be produced. The weight of the cast metal was 369 kg, and the yield was 75.1%. Example 2 When performing decarburization scouring using the same reaction vessel as in Example 1, a bottom blowing double pipe nozzle was used.
While blowing Ar at 0.4 Nm ³ /min, 500 kg of the high carbon ferromanganese molten metal shown in Table 1 was charged into the container. The temperature of the molten metal after charging was 1350°C. After that, Ar was blown at a rate of 0.25Nm ³ /min from the outer pipe of the bottom blowing nozzle, and oxygen was blown at a rate of 0.5Nm ³ /min from the inner pipe.At the same time, oxygen was blown from the water-cooled lance installed at the top of the container.
Blowing was continued at a rate of 1.5 Nm ³ /min for 26 minutes. During this period, 40 kg of Mn ore and 20 kg of quicklime were added. After that, stop the top blowing oxygen and 0.5N oxygen.
The blowing was continued for 22 minutes at m ³ /min. During this time, 20kg of Mn ore and 10kg of quicklime were added in portions. After blowing, 15 kg of fluorite, 55.5 kg of ferrosilicon, and 84 kg of quicklime were added in portions while blowing only Ar into the inner and outer tubes at a total rate of 0.4 Nm ³ /min using a bottom blowing nozzle, and after removing the sludge, the tube was cast and cast. The metal composition at the end of casting was as shown in Table 1, and low carbon ferromanganese with a high Mn content was obtained. The metal that was cast was 474 kg and the yield was 89.4%. The ingredients of the additives are also listed in Table 2.

【table】

[Table] [Effects of the Invention] Since the present invention is configured as described above, it is possible to effectively control the progress of decarburization, and it is more economical than the conventional silicide method or other oxygen decarburization methods. It has become possible to produce medium and low carbon ferromanganese.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in decarburization oxygen efficiency due to top-bottom blowing.

Claims (1)

[Claims] 1 The first step is to decarburize high-carbon ferromanganese molten metal to a predetermined carbon content by top blowing with oxygen gas and bottom blowing with oxygen and inert gas, and bottom blowing with oxygen gas and bottom blowing with inert gas. The process consists of a second step of decarburizing to a desired carbon content by using a combination of A method for producing medium/low carbon ferromanganese, characterized by adjusting the amount of Mn in the molten metal.