JPH08109408A - Steelmaking by electric furnace - Google Patents

Abstract

PURPOSE: To improve the steelmaking method for melting scrap by using an electric furnace. CONSTITUTION: In the electric furnace, molten iron in an amount of 30-85% ratio per the whole charged material is charged together with the raw material of the scrap, etc., into a part surrounded by the solid raw material of the scrap, etc., at the center part of the furnace from the furnace top in the stage of 30-40% scrap melting ratio in the charging time of the molten iron. Further, in the case of charging the molten iron in an amount of 72-85% ratio per the whole charging material, the quick reaction is restrained by blowing carbonaceous powder and Al shots. By this method, even if the efficient utilization of the latent heat of the molten metal is executed, the quality of the molten steel is not deteriorated, and the productivity is further improved by utilizing the exothermic decarburized reaction. Further, the lowering of impurities in the steel is attained, and even the low grade scrap, can efficiently be reused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a steelmaking method for melting scrap by using an electric furnace.

[0002]

2. Description of the Related Art A steelmaking method in which a solid raw material such as scrap is charged and melted in an electric furnace is widely practiced. Since such a steelmaking method starts operation from a cold raw material such as scrap, the time required for melting and the electric power energy are large. Therefore, it is required to reduce the time and energy required for this melting, and in recent years, in addition to scraps of solid raw materials, hot metal is charged into the furnace to improve productivity and save energy. The mixing ratio of the hot metal at this time is 20 to 30% according to JP-A-6-41627.
It is said that a higher mixing ratio of hot metal reduces the melting efficiency of solid raw materials such as scrap. Further, according to JP-A-57-47815, the molten iron is charged into the electric furnace by blowing a stirring gas from the lower part of the furnace to keep the molten surface in a bubbling state and smoothly stir the molten iron.
A method for uniformly mixing is disclosed. In this method, the hot metal is charged so that the ratio does not exceed 70% of the total charge. When the amount of hot metal exceeds 70%, the furnace wall refractory is gradually melted and a recess is formed. When hot metal having a high carbon content infiltrates into the recessed portion of the furnace wall, refining such as decarburization is difficult to perform, and the quality of the final molten steel deteriorates.

[0003]

DISCLOSURE OF THE INVENTION According to the present invention, even if the mixing ratio of the hot metal is further increased to efficiently utilize latent heat of the hot metal,
The quality of molten steel is not deteriorated, and the heat generated during decarburization is used to improve productivity. Further, it is intended to reduce the steel impurities so that the low-grade scrap can be effectively reused.

[0004]

According to the present invention, 30 to 85% of the total amount of molten iron is charged in an electric furnace together with raw materials such as scrap.
Scrap dissolution rate of 30 to 40
%, A steelmaking method using an electric furnace in which a portion surrounded by solid raw materials such as scrap in the center of the furnace is charged from the top of the furnace. That is, according to the present invention, the amount of hot metal charged is 3
By increasing it from 0 to 85%, the electric power consumption of the electric furnace is reduced by the latent heat of the hot metal, and by using oxygen, carbon dioxide and CO
_Use the reaction heat of ₂ to further improve productivity. By increasing the amount of hot metal, the level of impurities in the molten steel can be lowered, so that the amount of low-grade scrap can be increased. By loading the hot metal into the electric furnace from the furnace top to the center of solid raw materials such as scrap in the center of the furnace, damage to the furnace wall due to hot metal can be eliminated and consequently impurities can be reduced. .

If the amount of hot metal charged is less than 30% of the total amount charged, the amount of electric power used is not sufficiently reduced, and the effect of reducing impurities is not sufficient. If the amount exceeds 85%, the purpose of recycling scrap becomes insufficient. The most effective range is 40-72%. Further, the inventors of the present invention have found that even when the amount of hot metal is 72 to 85% at a high compounding ratio, the [C] difference of the hot metal and the rapid reaction due to the temperature difference cause the deoxidation by cutting carbon powder into scrap molten steel and blowing Al shot. We have found a technology to suppress it by measuring. It is preferable that the molten iron is charged at a stage where the dissolution rate of solid raw materials such as scrap is 30 to 40%. If the hot metal is charged at the stage where the dissolution rate of the solid raw material is less than 30%, the scrap dissolution efficiency and the latent heat recovery of the hot metal will be reduced and the productivity will be reduced. , A rapid reaction occurs due to the temperature difference between the hot metal and molten steel, and the difference in [C], making it difficult to top-charge the hot metal.
Neither is preferred.

When oxygen is used, as described above, C + O ₂
→ The reaction of CO or CO ₂ takes place, and the heat of reaction can be effectively used for melting scraps while decarburizing. It is preferable to supply oxygen into the furnace from the operation port using a manipulator device.

[0007]

【Example】

Example 1 It carried out using the direct-current electric furnace apparatus of the amount of steel output 100t shown in FIG. Reference numeral 1 is an electric furnace, and 2 is a ladle. The furnace lid and electrodes that have been turned off are swung to a predetermined position, charged with hot metal from the blast furnace, and loaded into the electric furnace chamber by a bucket crane 4. Reference numeral 3 is a self-propelled vehicle provided on the crane 4, which moves the ladle 2 to a position near the electric furnace 1 and inclines it at an appropriate position so that the molten pig iron in the solid portion of scrap 5 or the like in the substantially central portion of the electric furnace 1 is slanted. Charge into the area surrounded by raw materials.

60 tons of scrap 5 and 1.8 tons of lime
Was charged into the electric furnace 1, and when the scrap 5 was melted by 30%, 60 t of hot metal was charged from the ladle 2 from the center of the furnace top. The oxygen required for the reaction of C in the hot metal and the oxygen required for the dephosphorization in the slag were introduced into the furnace from the operating port using a manipulator device at an amount of 5000 Nm ³ / Hr of 15 Nm ³
/ T acid was sent. The results of decarbonization and dephosphorization are shown in FIG.
Is shown by a solid line graph. As can be seen from FIG. 2, C2.2% and P0.034% in the hot metal were reduced to C0.2% and P0.01% by supplying oxygen of 15 Nm ³ / T.

Example 2 The same operation as in Example 1 was carried out by using a 100 t steel output DC electric furnace apparatus shown in FIG. After charging 30 t of scrap 5 and 2.4 t of quick lime into the electric furnace 1, electricity was applied, and when 35% of the scrap 5 was melted, 90 t of hot metal was charged from the center of the furnace top. After the scrap 5 is completely melted, carbon powder 5kg / T
And 2 kg / T of Al shot, followed by 750
Although 20 Nm ³ / T was fed with an oxygen feed amount of 0 Nm ³ / Hr and decarburization refining was performed, no sudden decarburization reaction or corrosion of the furnace wall was observed. The results of decarburization and dephosphorization are shown over time in a dotted line graph in FIG. C3.05% of hot metal, P
By supplying oxygen of 20 Nm ³ / T, 0.039% was reduced to C0.2% and P0.010% at the time of tapping.

[0010]

INDUSTRIAL APPLICABILITY According to the present invention, the blending rate of hot metal is further increased to efficiently utilize latent heat of hot metal, and the productivity of heat is generated by decarburization reaction without degrading the quality of molten steel. . In addition, steel impurities can be reduced, and even low-grade scrap can be effectively reused.

[Brief description of drawings]

1 is an illustration of a device suitable for practicing the present invention.

FIG. 2 is a graph showing the effects of decarburization and dephosphorization in Examples.

[Explanation of symbols]

 1 Electric furnace 2 Ladle 3 Self-propelled vehicle 4 Crane 5 Scrap etc.

Claims (2)

[Claims] 1. An electric furnace, together with a raw material such as scrap, contains hot metal at a rate of 30 to 85% of the total charge, and the charging time is set at a stage of a scrap dissolution rate of 30 to 40%. A steelmaking method using an electric furnace, which comprises charging a portion surrounded by solid raw materials such as scrap at the center. 2. When the molten iron is charged at a rate of 72 to 85% of the total amount of the charged material, its rapid reaction is suppressed by blowing carbon powder and Al shot into the scrap molten steel.
A method for producing steel by the described electric furnace.