JPH06145765A - Efficient oxygen blowing decarburization refining method of molten steel using plasma - Google Patents

Abstract

PURPOSE:To execute the refining without lowering the decarburization oxygen efficiency to low carbon range at the time of executing the top-blowing decarburization blowing in a refining furnace such as converter. CONSTITUTION:At the time of executing top-oxygen-blowing decarburization refining in the refining furnce 1 such as the converter, VOD, etc., by supplying bottom-blowing gas 11 in the range of 0.01-0.5Nm<3>/min.ton, the molten steel 7 is stirred, and by supplying 1-50% of the energy generated at a firing point part 9 by irradiating plasma energy 6 to the oxygen blowing firing point part 9 formed on the molten steel by the top-blowing oxygen 5, the temp. at the firing point part is made to be an ultrahigh temp. and the firing point range is activated. By this method, the decarburization oxygen efficiency can be kept at a high degree till the low carbon range without lowering the oxygen speed and causing problems, such as the wearing of a nozzle 10 for blowing bottom- blowing gas and the erosion of the refractory in the furnace.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a refining method for producing molten steel without lowering the efficiency of decarbonation to a low carbon region when carrying out decarburization of blown acid in a refining furnace such as a converter or VOD. Regarding

[0002]

2. Description of the Related Art Conventionally, as a method of improving decarbonation efficiency in a refining furnace such as a converter and efficiently performing decarburization refining to a low carbon region, a bottom blowing function is added to the converter to remove a steel bath. Agitation is performed vigorously to accelerate the supply of carbon in molten steel to the hot spot of the acid spray, which is the most active reaction area (Japanese Patent Publication No. 62-14602).
Gazette), the critical carbon concentration ([% C ^* ]) that shifts from the oxygen supply rate controlling region that maintains the decarboxylation efficiency to a high level to the carbon diffusion rate controlling region that reduces the decarboxylation efficiency shifts to the low coal side. In order to prevent the decrease of decarboxylation efficiency (iron and steel, by controlling the blowing acid rate such as lowering the blowing acid rate in the carbon diffusion controlled region at the final stage of decarburization)
68th year (1982), p1946).

Further, as a method of performing thermal compensation for molten steel in converter blowing, as shown in Japanese Patent Laid-Open No. 62-60807, supersonic oxygen is injected into a steel bath in the converter. During refining, subsonic oxygen containing plasma is separately injected into the steel bath to react the oxygen with CO gas in the furnace, and the high temperature reaction product gas collides with the steel bath. A converter operating method has been proposed in which the heat is transferred to the steel bath.

[0004]

[Problems to be Solved by the Invention] As shown above,
As a method for improving the efficiency of decarboxylation in carrying out decarburization of blown acid in a refining furnace such as a converter, Japanese Patent Publication No. Sho 62-1460
No. 2, the method and iron and steel, 68th year (198)
2) and p1946. However, in these methods, even if the bottom blowing gas flow rate is increased, there is a limit to the shift of [% C ^* ] to the low coal side, and if the bottom blowing gas flow rate is excessively increased, the gas blowing nozzle is greatly worn. There was a difficulty such as becoming. Furthermore, the improvement of decarboxylation efficiency is insufficient by controlling the blowing acid rate in the carbon diffusion controlled region. If the blowing acid rate is reduced too much, the blowing time increases and the melting loss of the refractory of the converter becomes severe. There was such a problem. In addition, as a method of using plasma energy when carrying out the decarburization of blown acid in a converter, there is disclosed in JP-A-62-60.
Although there is a method disclosed in Japanese Patent Publication No. 807, this method promotes heat transfer to a steel bath and improves heat deposition efficiency, but the injected oxygen plasma is consumed for reaction with CO gas in the furnace. Since it hardly contributes to the reaction at the blowing acid hot spot, it was not sufficient to improve the efficiency of decarboxylation, and the reaction between oxygen containing plasma and CO gas occurs excessively. And the temperature inside the furnace rises, and the life of the converter refractory is significantly impaired. Also, since oxygen gas is used as a gas body for plasma generation, there is also a problem with the life of the plasma generator (torch). .

Therefore, it is an object of the present invention to use an excessive amount of bottom-blown gas, to extend the blowing time, and to further refine the refining resulting from the excessive reaction between the blowing oxygen gas and the CO gas. An object of the present invention is to enable efficient decarburization refining without lowering the efficiency of decarbonation to the low carbon region without causing a problem of impairing the refractory life of the container.

[0006]

[Means for Solving the Problems] As a result of the inventors of the present invention, as a method of maintaining the decarboxylation efficiency at a high level even in the low carbon region (carbon diffusion rate-controlling region), the results of the dilute decarburization refining of molten steel It was found that the effect is remarkable by increasing the temperature of the hot spot of the acid spray formed during the decarburization of the acid spray. The present invention is based on this finding.

[0007] The gist of the present invention is that, when performing blown acid decarburization refining in a refining furnace, 1 to 50% of the energy generated at the blown point on the blown acid formed on the molten steel.
Is supplied by irradiating plasma energy, which is an efficient method for decarburizing and refining molten steel using plasma.

[0008]

The present invention is based on increasing the temperature of the blown acid hot spot of molten steel to accelerate the decarburization reaction at the hot spot as described below. FIG. 1 is a schematic view showing the inside of a converter. Reference numeral 1 is a converter, 2 is a lance, 3 is a plasma generation torch, 4 is a supply passage for a gas body (Ar or the like) to be turned into plasma, 5 is an oxygen gas jet for blowing, and 6 is a plasma torch 3 in the lance 2.
Plasma jets such as Ar generated by, 7 is molten steel, 8 is slag, 9 is a sprayed acid fire point, 10 is a gas injection nozzle, and 11 is a bottom blowing gas for stirring (Ar, N ₂ , O _2, etc.)
Is. When the oxygen jet 5 is sprayed from the lance 2 onto the molten steel 7 to carry out decarburization refining, a sprayed acid fire spot 9 is formed. The temperature of this flame spray point is about 2300 in normal blowing.
The temperature is up to 2,500 ° C., which is considerably higher than the temperature of molten steel, and most of the decarburization reaction is carried out at or near the blowing acid hot spot. That is, regardless of ordinary steel or stainless steel, the decarburization mechanism of molten steel by blown acid decarburization is expressed by the following equation (1) by the metal oxide (FeO, Cr ₂
O ₃ ) reacts with the carbon in the molten steel in the hot spot and in the entrained bath (equation (2)), and the oxides that could not contribute to decarburization are trapped in the slag on the molten steel. This causes an increase in the FeO or Cr ₂ O ₃ concentration in the slag. Here, M in the equations (1) and (2)
Indicates a metal atom such as Fe or Cr.

M + 1 / 2O ₂ → MO (1) MO + C → M + CO ↑ (2) C + 1 / 2O ₂ → CO ↑ (3) Further, in the relation between temperature and free energy of formation of various oxides, Fe and In the case of metal oxides such as Cr, the change in free energy of generation shifts to the higher side, that is, becomes unstable as the temperature becomes higher, whereas the CO gas generation reaction represented by the formula (3) becomes lower as the temperature becomes higher. Transition to
In other words, it is known to stabilize. Therefore, the reduction reaction of the metal oxides at and around this hot spot ((2)
Formula) or oxygen jet and direct reaction of carbon in molten steel ((3)
(Equation) is more advantageous as the temperature of the hot spot is higher, but the temperature of the propellant acid hot spot formed by spraying an oxygen jet on the molten steel is 2300 to 2500 as described above.
It is about ℃, and it is thought to increase the temperature of the hot spot by promoting the reaction (secondary combustion) between the oxygen gas jet for blowing acid and the CO gas in the furnace, and increasing the secondary combustion rate. However, if secondary combustion is promoted excessively, the temperature inside the furnace will rise, and there will be problems such as severe melting loss of the refractory in the furnace. With the current equipment, the hot spot temperature will be raised above 2600 ° C. Is impossible.

Therefore, the inventors of the present invention irradiate plasma energy to the blowing acid hot spot as a method of further increasing the temperature of only the blowing acid hot spot and efficiently promoting decarburization.
The inventors have invented a method of significantly improving the temperature of the hot spot while suppressing excessive secondary combustion. According to this method, the Ar-based gas body is turned into plasma by the plasma generation torch 3 built in the lance 2 in FIG. The point area can be activated. Therefore, the flow rate of the bottom blowing gas for stirring is 0.01 to 0.5 Nm ³ / (min ·
It is advantageous to improve the reactions of formulas (2) and (3) by increasing the temperature of the flash point to an extremely high temperature by giving an appropriate stirring force in the range of It is also clear from the relation of the free energy of formation of oxides. Here, the bottom blowing gas flow rate is 0.01 Nm ³ / (min · to
If it is less than n), the carbon supply to the hot spot will be insufficient and the efficiency of decarboxylation will be reduced. Further, if the bottom blowing gas flow rate exceeds 0.5 Nm ³ / (min · ton), the gas blowing nozzle will be worn.

Further, regarding the gas body to be turned into plasma, A
A gas such as O ₂ can be considered based on r, and almost the same effect can be obtained with any gas in terms of the effect of improving the efficiency of decarbonation, but Ar gas is the most effective when considering the life of the plasma generation torch. desirable. Furthermore, if the irradiation energy of the plasma is less than 1% of the energy generated at the fire point due to the oxygen supply, the hot point portion will not be sufficiently heated, that is, will not be activated, so that the improvement of decarboxylation efficiency will be insufficient. turn into. Further, even if an energy of more than 50% is given, the effect of further improving the decarbonation efficiency is small (Fig. 3), and the temperature of the hot spot is excessively increased.
Since the evaporation of metals such as e and Cr occurs, the yield of molten steel deteriorates.

Further, since the plasma irradiation raises the temperature not only in the hot spot but also in the vicinity of the hot spot as compared with normal blowing, the reduction reaction ((2 Formula) will also be promoted. Further, the plasma jet immediately after being irradiated by the plasma generation torch is in a very high temperature state (≧ 5000 ° C.), and this heat is activated by propagating to the oxygen jet for blowing at the same time. , The reaction of formula (3) is also significantly promoted. Therefore, as a whole, as shown in FIG. 2, it is possible to improve the efficiency of decarbonation even in the low carbon region (carbon diffusion control region), that is, without increasing the flow rate of the stirring gas, that is, the wear of the nozzle for the bottom blowing gas. Without causing such a problem, it is possible to maintain a high decarboxylation efficiency in a low carbon region. Further, in the present invention, it is possible to maintain a high decarboxylation efficiency in a low carbon region (carbon diffusion rate controlling region) without performing a conventional operation such as lowering the blowing acid rate. It is possible to decarburize and refine to a low carbon concentration without extending. Further, in the present invention, the blowing oxygen jet is ultrasonically jetted from all the ejection holes, so that the reaction between the CO gas in the furnace and the blowing oxygen is not excessively caused, and almost all plasma energy is burnt. Since the point temperature is increased or consumed for the reaction, the efficiency of the reaction can be increased, and the problem that the refractory material in the furnace is worn away can be solved.

[0013]

EXAMPLE As shown in FIG. 1, a converter 1, a lance 2, a plasma generation torch 3, a gas supply passage 4 for plasmaization, an oxygen gas jet 5 for blowing, a plasma jet 6, a molten steel 7,
When decarburization blowing is performed on general low-carbon Al-K steel using a 175 ton scale converter with slag 8, blowing acid hot spot 9, gas blowing nozzle 10, and bottom blowing oxygen for stirring 11. Examples of are shown in Table 1. In this case, the number of lance holes is 4, and the amount of top-blown oxygen is uniformly 2.7 Nm ³ / (mi
n ・ ton), the bottom flow gas flow rate is uniformly 0.2 N
It was performed as m ³ / (min · ton). Further, Ar is used as a gas body for plasma generation in any case,
The gas flow rate is 0.7 Nm ³ / (min · ton),
Plasma irradiation was performed in the region of [C] ≦ 0.1%.

As is clear from Table 1, it is possible to efficiently carry out the decarburization and refining of blown acid by the present invention without lowering the efficiency of decarboxylation in the low carbon region.

[0015]

[Table 1]

[0016]

EFFECTS OF THE INVENTION By using the present invention, the decarboxylation efficiency is reduced to a low carbon region without extending the blowing time, and without damaging the refractory of the refining vessel or the bottom blowing gas injection nozzle. It has become possible to efficiently carry out the decarburizing and refining of blown acid without doing so.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an embodiment of a blowing acid decarburization refining method according to the present invention.

FIG. 2 is a diagram showing carbon concentration in molten steel and decarbonation efficiency.

FIG. 3 is a diagram showing the relationship between the amount of additional energy by plasma and the decarbonation efficiency with respect to the energy of the fire point.

[Explanation of symbols]

1 Converter 2 Lance 3 Plasma Generation Torch 4 Plasmaization Gas Supply Passage 5 Blowing Oxygen Gas Jet 6 A Generated by Plasma Torch 3 in Lance 2
Plasma jet of r, oxygen, etc. 7 Molten steel 8 Slag 9 Bleaching acid fire point 10 Gas injection nozzle 11 Bottom blowing gas for stirring (Ar, N ₂ , O ₂ etc.)

Claims (1)

[Claims] 1. When performing blown acid decarburization refining in a refining furnace, plasma energy is applied to the blown acid hot spot formed on molten steel at 1 to 50% of the energy generated at the hot spot. An efficient method of decarburizing and decarburizing molten steel using plasma, which is characterized in that