JPH09104911A - Method for smelting low-p concentration chromium-containing molten metal by smelting reduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smelt low-P concn. chromium-containing molten metal without being accompanied by the oxidation loss of chromium by specifying the charging amt. of carbon, molten iron temp. and the stirring driving power density by a bottom blowing gas at the time of smelting reduction of chromium oxide. SOLUTION: The smelting reduction of the chromium oxide is executed by charging the chromium oxide, carbon source and flux into a steel bath charged into a top and bottom blown refining vessel. At this time, the ratio (the amt. of the carbon/the amt. of the chromium oxide) of the charging amt. of the carbon to the chromium oxide is adjusted to 1.0 to 3.0 and the molten iron temp. is adjusted to <=1500 deg.C. The operation is executed under such conditions under which the stirring driving power density ε by the bottom blowing gas determined by the equation satisfies 5 to 30kW/t. In the equation, Q denotes the flow rate (Nm<3> /min) of the gas, T denotes the temp. (K) of the molten metal, Wm denotes the weight (t) of the molten metal, h denotes the blowing depth (cm) of the gas, P denotes the pressure (Torr) of the atmosphere. The low-P concn. chromium-containing molten metal is smelted without the need for using a flux for dephosphorization, etc., according to this method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for smelting a chromium-containing molten metal having a low P concentration by smelting reduction, and when chrome-melting and reducing chromium oxide to obtain a chromium-containing molten iron, the molten iron is also de-Ped. It is the one to try.

[0002]

2. Description of the Related Art As a method for obtaining a chromium-containing hot metal having a low P concentration, molten iron having a low P concentration and a high C concentration obtained by a method such as de-Ping in advance, and an alloy containing a high chromium content such as Fe-Cr. A method of mixing and dissolving is known, but in this case, all P in the raw material is transferred to the chromium-containing hot metal.

On the other hand, as a method for dephosphorizing molten iron containing chromium, two types of methods have been proposed: reduction de-P and oxidation de-P. Regarding the former, for example, Japanese Patent Publication No. 58-52539 discloses a method using a CaO—CaF ₂ —CaC ₂ system flux. Regarding the latter, for example, JP-A-3-247717 discloses a method of injecting a CaO—CaF ₂ —iron oxide-based flux. Further, Japanese Patent Laid-Open No. 63-223112 discloses a method of obtaining low P hot metal by adjusting the slag composition in the smelting reduction method of iron ore.

[0004]

However, all of the above-mentioned conventional methods have the following problems. That is, the method disclosed in Japanese Examined Patent Publication No. 58-52539 has problems that not only the flux is expensive, but also the treatment of the reaction product is difficult. In addition, JP-A-3-247717
The method disclosed in Japanese Patent Laid-Open Publication No. 1994-29242 not only inevitably causes a loss due to oxidation of chromium, but also has a disadvantage of requiring a special flux although it is relatively inexpensive. Further, the method disclosed in JP-A-63-223112 has a problem that it cannot be applied to hot metal containing chromium which is more easily oxidized than Fe.

The present invention advantageously solves the above-mentioned problems, that is, the smelting reduction operation is performed under a predetermined condition without using a special flux, and the low P content does not occur with the oxidation loss of chromium. It is an object of the present invention to propose a method for producing a low P-concentration chromium-containing molten metal by smelting reduction, which enables obtaining hot metal with a high concentration.

[0006]

That is, the present invention provides:
In the iron bath charged in the refining container with the top and bottom blowing function,
When the chromium oxide, carbon source and solvent are added to perform the smelting reduction of chromium oxide, the ratio of the amount of carbon to chromium oxide (carbon amount / chromium oxide amount) is 1.0 to
After adjusting to 3.0, the molten iron temperature is 1500 ° C or lower, and the stirring power density obtained from the following equation (1) by the bottom-blown gas

[Outside 2] Is a process for producing a chromium-containing molten metal having a low P concentration by smelting reduction, which is characterized in that the operation is carried out under the condition that the ratio of 5 to 30 kw / t. Record

(Equation 2)

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The production of a chromium-containing molten metal by smelting reduction is carried out by utilizing the reduction reaction of chromium oxide with carbon. Since this reaction is an endothermic reaction, the higher the temperature of molten iron, the more the reduction of chromium oxide occurs. Is advantageous to On the other hand, mixing of P from the raw material occurs in the form of an oxide of P ₂ O ₅ , but if the molten iron temperature is high, the reaction of the following equation P ₂ O ₅ + 5C = 2P + 5CO ↑ occurs and P is contained in the molten iron. It is captured. Therefore,
In the conventional smelting reduction method, dephosphorization was practically impossible.

The inventors have reviewed the operating conditions so as to manage to remove P by the smelting reduction method.
First, the inventors have found that when the molten iron temperature is lowered,
The state of reduction reaction of chromium oxide and phosphorus oxide was investigated.
As a result, if the temperature is reduced to 1500 ° C. or lower, the reduction reaction of phosphorus oxide (P ₂ O ₅ ) as shown in the above formula does not occur. In other words, the P reaction from the raw material into the molten iron is reduced. It turns out that it can stop the intrusion.

However, if the temperature of the molten iron is set to 1500 ° C. or lower, the reduction reaction of chromium oxide will naturally occur and the production efficiency will be lowered. So, next, the inventors
Even if the temperature of molten iron is 1500 ° C or less, intensive research was conducted to prevent deterioration of the reduction reaction of chromium oxide. as a result,
The ratio of carbon input to chromium oxide (weight ratio)
1.0 to 3.0, and stirring power density by bottom blowing of 5 to 3
It was clarified that the intended purpose could be advantageously achieved at 0 kw / t.

FIG. 1 shows the ratio of carbon to chromium oxide and the stirring power density by bottom blowing at a molten iron temperature of 1490 ° C.

[Outside 3] The result of having investigated about the P removal rate when variously changed is shown. However, the P removal rate as used herein means the degree of P remaining in the metal when P contained in all the input raw materials is 100%, and all the input P remains in the metal. In this case, the P removal rate is 0%. . As is clear from the figure, the carbon content / chromium oxide ratio is 1.0 to 3.
0 and agitation power density

[Outside 4] Was 5 to 30 kw / t, an excellent P removal rate of 60 to 70% could be obtained.

On the other hand, the bottom blowing agitation power density

[Outside 5] When the carbon content was 3 kw / t, the dephosphorization rate was as low as around 20% even when the carbon content / chromium oxide content ratio was 3.0 or less. It is considered that this is because the reaction between the slag and the metal does not proceed sufficiently due to the insufficient stirring force. on the other hand,
Even at 40 kw / t, the P removal rate was as low as around 15%. It is considered that the reason is that the stirring power is too large, so that the chromium oxide concentration in the slag becomes too low, and the P oxide concentration also decreases accordingly.

Therefore, the stirring power density by bottom blowing

[Outside 6] Was limited to the range of 5 to 30 kw / t. The carbon content / chromium oxide content ratio was limited to the range of 1.0 to 3.0.

Next, in FIG. 2, the hot metal temperature is 30 ° C. higher than in FIG.
The results of the survey were shown at a high temperature of 1520 ° C.
When the temperature rises 30 ° C and exceeds 1500 ° C, the stirring power density

[Outside 7] Regardless of the above, the P removal rate is significantly reduced. It is considered that the reason for this is that the reduction tendency becomes stronger as the temperature rises, and the reduction of phosphorus oxide proceeds accordingly. Therefore, the molten iron temperature is set to 1500 ° C. or lower, but if it is too low, the reduction of chromium oxide is deteriorated and the Cr yield is lowered. Therefore, the lower limit temperature is preferably set to about 1450 ° C.

Further, FIG. 3 shows the chromium yield when operating under the same conditions as in FIG. When the stirring force by bottom blowing is weak, the chromium yield decreases, but this is because the stirring of the slag is insufficient and the reduction does not proceed sufficiently. In this respect, stirring power density by bottom blowing

[Outside 8] If it is 5 kw / t or more, a chromium yield of about 80% can be obtained.

[0015]

According to the present invention, the ratio of carbon to chromium oxide is 1.0 to 3.0, the iron bath temperature is 1500 ° C or less, and the stirring power density by bottom blowing is 5 to 30 kw / t. As a result, a chromium-containing hot metal having a low P concentration can be obtained. The reason for this is that the concentration of chromium oxide in the slag does not hinder the recovery into molten iron by its reduction,
Moreover, it is considered that the range can be maintained in an appropriate range for P removal. The proper range here is the minimum amount of slag saturated with chromium oxide, which is CaO / Si.
_{O 2 = 2~4, (% Al} 2 O 3) = 10~30%, (% MgO) = 10~30
% Of slag is usually estimated to be around 1%.

The reason why the above chromium oxide concentration is optimum can be considered as follows. The de-P reaction in the present invention is an oxidation reaction, and oxygen necessary for this oxidation reaction is supplied from a chromium oxide. Therefore, it is considered that the higher the chromium oxide concentration is, the more advantageous it is to remove P. However, in reality, chromium oxide is a compound with a high melting point, and even if it exists as a simple substance, it hardly contributes to the dephosphorization reaction, and is not dissolved in the slag until the dephosphorization reaction occurs within the operating time. Contribute. That is, it is considered that there is no effect on P removal even if chromium oxide having a saturation solubility or higher is present. On the other hand, from the viewpoint of the yield of chromium, the lower the chromium concentration in the slag, the more preferable. From the above two points, it is considered that the slag is just saturated with the oxide of chromium in order to keep the yield of chromium high and to promote the de-Ping at the same time.

[0017]

【Example】

Example 1 5 tons of hot metal was charged into a top-and-bottom blowing converter, the coke amount was changed to 2.4 tons, and the chromium ore to Cr ₂ O ₃ was added to 0.8 tons. The charging time was 90 minutes, and the charging was continued within this time. At the same time, top-bottom blowing of oxygen (top blowing: 14 N
m ³ / min, bottom blowing: 6 Nm ³ / min). In this case, since oxygen is blown in, most of it becomes CO when it is blown into the hot metal, and this amount of CO becomes the actual blown amount. Therefore, Q is about 12 Nm ³ / min. The temperature of the bath during the treatment was kept in the range of 1480 ° C ± 10 ° C by adjusting the secondary combustion rate by adjusting the lance height. Furthermore, the weight of molten iron (Wm) is 5t, the gas injection depth (h; the depth from the stationary molten metal surface to the tip of the bottom blowing tuyeres) is 45 cm, and the atmospheric pressure (P)
Was 760 Torr, so the agitation power density according to Eq. (1) above.

[Outside 9] The value of is 13 to 14 kw / t. The slag basicity was adjusted to 2.5 by adding CaO. Table 1 shows the chromium yield and the P removal rate after the above-mentioned smelting reduction treatment.

Example 2 The same process as in Example 1 was performed. However, the amount of carbon in the coke was 0.8t, and the rate of top-blown acid was 5 N.
m ³ / min. Table 1 shows the chromium yield and P removal rate after the treatment.

Example 3 The same process as in Example 1 was performed. However, the top blowing acid rate was 5 Nm ³ / min and the bottom blowing acid rate was 12 Nm ³ / min. Therefore, the bottom blowing agitation power density

[Outside 10] Will be 26-27 kw / t. Table 1 shows the Cr yield and P removal rate after the treatment.

Comparative Example 1 The same treatment as in Example 1 was performed. However, the amount of coke added was increased to 3.2 tons. Table 1 shows the chromium yield and P removal rate after the treatment.

Comparative Example 2 The same treatment as in Example 1 was performed. However, the bottom blowing acid rate was 18 Nm ³ / min and the top blowing acid rate was 2 Nm ³ / min. Therefore, the stirring power density by bottom blowing

[Outside 11] Became 39 to 41 kw / t. Chromium yield after treatment, de-P
The rates are shown in Table 1.

Comparative Example 3 The same process as in Example 1 was performed. However, the bottom blowing acid rate was 1 Nm ³ / min and the top blowing acid rate was 19 Nm ³ / min. Therefore, the stirring power density by bottom blowing

[Outside 12] Became 2 kw / t. Table 1 shows the chromium yield and P removal rate after the treatment.

Comparative Example 4 The same treatment as in Example 1 was performed. However, the secondary combustion rate was adjusted by adjusting the lance height of the upper blowing, and the temperature of the bath during the treatment was kept within the range of 1520 ° C ± 10 ° C. Table 1 shows the chromium yield and P removal rate after the treatment.

[0024]

[Table 1]

As is clear from the table, according to the present invention, carbon content / chromium oxide content: 1.0 to 3.0, molten iron temperature:
Stirring power density of 1500 ℃ or less and bottom blowing gas

[Outside 13] Shows a high chromium yield and a good P-removal rate only when the operation is carried out under the condition of 5 to 30 kw / t.

[0026]

As described above, according to the present invention, dephosphorization at the time of smelting reduction, which has not been heretofore desired, does not cause a reduction in the chromium yield, and it is not necessary to use a special dephosphorization flux or the like. This can be effectively realized, and it becomes possible to obtain chromium-containing hot metal having a low P content in the smelting reduction refining.

[Brief description of the drawings]

FIG. 1 is a graph showing the P removal rate when the ratio of carbon to chromium oxide and the stirring power density by bottom blowing were variously changed at a molten iron temperature of 1490 ° C.

FIG. 2 is a graph showing a P removal rate when the ratio of carbon to chromium oxide and the stirring power density by bottom blowing were variously changed at a molten iron temperature of 1520 ° C.

FIG. 3 is a graph showing a chromium yield when the molten iron temperature was 1490 ° C. and the ratio of carbon to chromium oxide and the stirring power density by bottom blowing were variously changed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Nishikawa, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba, Kawasaki Steel Co., Ltd. Chiba Works (72) Soichiro Watanabe, 1 Kawasaki-cho, Chuo-ku, Chiba, Kawasaki Chiba Steel Works, Ltd.

Claims (1)

[Claims] 1. When performing smelting reduction of chromium oxide by introducing chromium oxide, carbon source and solvent into an iron bath charged in a refining vessel having a top-bottom blowing function, chromium oxide After adjusting the ratio of carbon input (carbon amount / chromium oxide amount) to 1.0 to 3.0, the molten iron temperature
Stirring power density of 1500 ° C or less and bottom blowing gas obtained from the following equation (1) [External 1] Is carried out under conditions satisfying 5 to 30 kw / t, and a method for producing a chromium-containing molten metal having a low P concentration by smelting reduction. Note