JPH0136546B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This specification describes an advantageous decarburization method of high carbon ferromanganese molten metal with regard to a manufacturing method for removing carbon from high carbon ferromanganese to medium carbon ferromanganese or low carbon ferromanganese to make products with higher utility value. The results of the development research on processing are described below. Manganese (Mn), which is useful as an alloying component in steel products, is produced at the end of converter smelting, which uses blast furnace hot metal as the main raw material, and after molten steel in the case of electric furnace steelmaking, which uses scrap as the main raw material. Both are Fe−
It is generally added in the form of Mn alloy. This Fe-Mn alloy depends on its carbon concentration.
It is classified into HCFeMn, MCFeMn, and LCFeMn, and the component values specified by the Japanese Industrial Standards (JIS) are listed in Table 1.

【table】

[Table] HCFeMn has a high C concentration and a low melting point, so it is relatively easy and economical to manufacture. (Conventional technology) MCFeMn and LCFeMn are usually made of expensive Si-
Manufactured using Mn alloy and large amount of electricity
It is a much more expensive ferroalloy than HCFeMn. In addition to using an electric furnace as a method for producing MCFeMn, a method of decarburizing molten HCFeMn using oxygen (O ₂ ) has also been proposed;
In all of the methods described in Publication No. 54-97521, molten HCFeMn is charged into a converter-shaped reaction vessel,
This method blows pure O ₂ or a mixed gas of O ₂ and steam through the tuyeres at the bottom of the furnace to remove carbon from 6.5 to 7.5% to about 1 to 1.3%. The structure requires cooling gas to flow around the _O2 tuyeres. Further, JP-A-60-56051 discloses a method in which a non-oxidizing gas is blown into and stirred from the bottom tuyeres of a reaction vessel, and at the same time pure O ₂ gas is blown into the reactor from a top blowing lance. (Problem to be solved by the invention) In conventional decarbonization refining of ferroalloy,
The reason why O ₂ supply was necessary is that O ₂ supply from above the molten metal bath surface promotes Mn oxidation rather than decarbonization. That is, since the molten metal is not sufficiently stirred when O ₂ is supplied from above the melt surface, C in the molten metal is difficult to move to the O ₂ supply point (flame point), and Mn is oxidized, making it difficult to proceed with decarbonization. The decarbonization reaction and the oxidation of Mn are expressed by the following formulas (1) and oxidation, respectively.
Since (2) is followed, of course, if the partial pressure of CO is lowered, the reaction of (1) will take priority over Equation (2) and will be advantageous for decarbonization. C+1/2O ₂ = CO (1) Mn+1/2O ₂ = (MnO) (2) However, since the above method uses O ₂ or a mixed gas of O ₂ and water vapor, a preferential decarbonization reaction cannot be obtained. Therefore, Mn oxidation was more advanced. In such conventional methods, it is necessary to supply O ₂ or a mixed gas of O ₂ and steam from the tuyeres at the bottom of the furnace, and the problems can be summarized as follows. First of all, the reaction vessel for removing carbon has a complicated structure in which a bottom tuyere of two types of tubes is installed, and advanced operating technology is required to prevent leakage of molten metal. Therefore, both equipment costs and operating costs became high. Next, since a mixed gas of pure O ₂ or O ₂ and water vapor is used, a preferential decarbonization reaction cannot be expected as mentioned above, and the loss due to Mn oxidation is large, which is not an economical method. It was not possible to reduce the O ₂ flow rate from the bottom tuyeres below a certain level to prevent molten metal from leaking. Furthermore, at the end of the decarbonization reaction, the O ₂ supply rate is reduced,
Although it is desirable to suppress Mn oxidation, such operation was not possible as long as O ₂ was supplied from the bottom tuyere. On the other hand, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-6051, if non-acidic gas is blown from the bottom tuyere and pure O ₂ is blown from the top blowing lance throughout the refining period, pure O ₂
When using , the CO partial pressure in the atmosphere at the flashing point is always close to 1 atm, and the decarburization reaction shown in equation (1) above does not proceed preferentially, resulting in significant oxidation of Mn, resulting in a low Mn yield and silicon It was necessary to add manganese, HCFeMn, etc. as a coolant and recover Mn. Furthermore, since spraying pure O ₂ causes the temperature of the reaction interface to rise and become higher than the temperature of the molten metal, there is also the problem that Mn, which has a particularly high evaporation pressure, evaporates and becomes a factor in reducing the yield. (Means for solving the problem) O ₂ is not supplied from the bottom tuyere, but instead the minimum amount of non-oxidizing gas is supplied from the tuyere, which has a simple structure, to ensure sufficient agitation of the molten metal. What to do: O ₂ is sprayed onto the molten metal surface as a mixed gas with a non-oxidizing gas to reduce the partial pressure of CO at the reaction interface with the non-oxidizing gas while preferentially proceeding with _{decarbonization} . Basically, Mn loss is suppressed by diluting with non-oxidizing gas, but at the beginning of blowing, the O ₂ concentration of the mixed gas is increased and decarbonized.
In order to accelerate the reaction and further suppress the unavoidable Mn loss in the latter half of decarbonization, the O ₂ supply rate is gradually reduced or, more preferably, the ratio of the non-oxidizing gas supply rate to the O ₂ supply rate is increased. The key to solving the problem is to gradually increase the amount and maintain conditions favorable to the decarbonization reaction. This invention decarburizes molten high carbon ferromanganese in a top-bottom blowing reaction vessel to produce medium-carbon or low-carbon ferromanganese. A mixed gas of oxygen and a non-oxidizing gas that dilutes the oxygen is supplied onto the molten metal bath surface, and the oxygen supply rate is gradually decreased during the period from the initial stage of blowing until a predetermined carbon concentration is reached. This is a method for producing medium carbon or low carbon ferromanganese, which is characterized by spraying an oxidizing gas while gradually increasing its concentration. Note that the top blowing may be completed and the mixed gas may be sprayed from a single lance, or the mixed gas may be sprayed using a lance having separate flows of oxygen and non-oxidizing gas, or separate lances. Now, an example of equipment suitable for carrying out the above method is shown in FIG. 1, and the case of decarbonization refining of HCFeMn will be explained below according to the figure. In the figure, 1 is a reaction vessel that can supply gas below the surface of the molten metal bath (a top-bottom blowing converter in the illustrated example), and 2
is molten HCFeMn, 3 is slag, 4 is a lance that blows a mixed gas of O ₂ and non-oxidizing gas from above the molten metal bath surface, 5 is a tuyere that guides non-oxidizing gas below the bath surface, 6 is tuyere 5 Gas piping that leads non-oxidizing gas to
7 is a non-oxidizing gas pipe for top blowing, 8 is a pipe for O ₂ , and 9 is a flow rate control valve. A molten HCFeMn is first charged into the reaction vessel 1, but an appropriate amount of non-oxidizing gas is flowed through the tuyeres 5 before this charging. Next, lower the lance 4 from above and connect the O ₂ pipe 8 and the non-oxidizing gas pipe 7 at an appropriate position above the bath surface.
Begin blowing a mixed gas of O ₂ and non-oxidizing gas delivered via. When decarbonization is completed to a predetermined concentration, the lance 4 is raised and the blowing of O ₂ or non-oxidizing gas is also stopped. However, in order to protect the tuyere 5, the non-oxidizing gas from the tuyere 5 is kept flowing. Here, rare gases (Ar,
He, Ne, etc.), N ₂ , converter exhaust gas, coke oven gas, etc. are suitable, and one or more of these gases can be used. The non-oxidizing gases used may be of the same type or different types. In addition, the non-oxidizing gas pipes 6 and 7 may be switched to other types of non-oxidizing gas during refining, for example, N ₂ gas may be used in the initial stage and Ar gas may be used in the latter stage. In any case, these piping 6,
The non-oxidizing gas supplied into the container 1 through 7 is
Helps reduce CO partial pressure and temperature at the reaction interface. The tuyere 5 may be a general tuyere with a simple structure,
For example, one or more steel pipes with a diameter of 4 to 6 mm are installed on the bottom wall of the container 1. The lance 4 may be similar to a lance used in the converter steel manufacturing method. The flow rate of gas supplied from the tuyere 5 is HCFeMn
It is desirable that the minimum amount is enough to stir the molten metal. Bottom-blown gas flow rate per ton of molten metal when HCFeMn is decarbonized and smelted to [%C]≒1.2
Figure 2 shows the relationship between Mn yield. At low flow rate,
Mn yield decreases due to insufficient stirring. Furthermore, even if the flow rate is increased unnecessarily, no improvement in Mn yield is observed, and because the flow rate is high, the molten metal is directly exposed to the atmosphere in the furnace, which causes Mn vapor to become intense and tends to reduce the Mn yield. So,
As shown in the shaded area in the figure, 0.05~
A gas flow rate of 0.8Nm ³ /min is a necessary and sufficient bottom-blown gas amount. As the C-refining reaction progresses further and the C concentration decreases,
Mn oxidation progresses rapidly, but in order to suppress this, the O ₂ flow rate of the top blowing gas is lowered. It is clear that by simultaneously increasing the flow rate of the non-oxidizing gas at this time, it is possible to lower the CO partial pressure at the decarburization reaction interface and advance preferential decarbonization. The method of changing the gas flow rates for both cannot be unconditionally determined depending on the constraints of refining time and the tolerance for decreasing the concentration of Mn.
An example will be shown in the Examples described below. (Operation) The reason why by using the means according to the present invention, a Mn yield higher than that obtained by conventional pure O ₂ gas bottom blowing or pure O ₂ gas top blowing methods can be obtained will be described below. First, as explained above using equations (1) and (2), the partial pressure of CO gas at the decarbonization reaction interface can be lowered by mixing a non-oxidizing gas.
Priority can be given to decarbonization up to the concentration. Furthermore, since the top-blown gas has a lower O ₂ concentration than when using only pure O ₂ gas, Mn loss due to oxidation can be suppressed. Furthermore, the top-blown gas is diluted with non-oxidizing gas.
Since the O ₂ concentration is low, the temperature at the reaction interface is lower than in the case of pure O ₂ spraying, and therefore Mn loss due to evaporation is also reduced. (Example) An example of an operation carried out using a 5-ton scale top-bottom blowing converter will be explained according to what is shown in FIG. For the tuyeres 5, four stainless steel pipes each having an inner diameter of 4 mm were installed distributed at the bottom of the furnace. _N2 as non-oxidizing gas,
Using Ar gas, heat all _N2 (,) all Ar (), and initially _N2
In the case of switching to Ar in the second half (), we carried out each case. Here, the mixing ratio of O ₂ and N ₂ (or Ar) was changed depending on the C concentration, and the ratio is as shown in FIG. 3 showing the operation results for producing LCFeMn. The bottom blowing gas flow rate is 0.5Nm ³ /min・t (2.5N
m ³ /min) was used as the standard. As a comparative example, according to the conventional technology, from tuyere 4
5 so that O ₂ gas can be injected at approximately 2.5Nm ³ /min・t.
The ton converter was modified and four double pipes through which propane gas could flow were installed to protect the tuyeres, and the operation was started. Table 2 shows the amounts of various gases used, the Mn yield, the melting rate of the bottom tuyeres, and the amount of slag forming agent (quicklime) used for Examples of the present invention in which MCFeMn and LCFeMn were produced.

[Table] As is clear from the table, good yields of 92 to 96% were obtained in Examples ~ according to the present invention. Note that although the amount of N ₂ (Ar) used increases, the amount of O ₂ gas used is less than the comparative example. Additionally, the bottom tuyere erosion rate has been significantly improved. In addition, as a comparison, when blowing was performed using only O ₂ gas without mixing Ar gas to a C concentration of around 1% at the end of blowing, the Mn yield deteriorated, and this experiment
Mn yield was in the range of 84-88%. Table 3 shows a comparison of the final N concentrations of Examples.

[Table] From the same table, it can be seen that if you switch from N ₂ to Ar in the latter half, the N concentration will be the same as when only Ar was used from the beginning. Since Ar is more expensive than N ₂ , it is an economical method to use cheaper N ₂ halfway and then switch to Ar. The timing of switching differs depending on the bottom blowing gas flow rate, but the appropriate timing is when [%C]=2 or more, and when it is less than this, the N concentration at the end point increases. (Effects of the invention) This is an effective method for economically decarbonizing HCFeMn, and allows McFeMn and LCFeMn to be easily produced with high yields using simple equipment and without using special operating technology. Moreover, since the reaction vessel can be used for a long period of time, work efficiency is greatly improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the implementation procedure of this invention, Fig. 2 is a graph showing the relationship between bottom blowing gas flow rate and Mn yield, and Fig. 3 is a graph showing an example of the operation results of decarburization to low carbon ferromanganese. It is. 1...Top-bottom blowing converter, 2...High carbon ferromanganese molten metal, 3...Slag, 4...Lance for top-blown gas, 5...Tuyere, 6, 7...Non-oxidizing gas piping, 8... ...Top blowing _O2 piping, 9...Flow control valve.

Claims (1)

[Scope of Claims] 1. When molten high carbon ferromanganese is decarburized in a top-bottom blowing reaction vessel to produce medium-carbon or low-carbon ferromanganese, non-oxidizing material is added under the surface of the molten metal bath by bottom blowing. While supplying a stirring gas of A method for producing medium carbon or low carbon ferromanganese, which comprises blowing the gas while gradually increasing the concentration of a non-oxidizing gas.