JPH05117739A - Method for melting and secondary-refining steel - Google Patents

Abstract

PURPOSE:To improve the energy efficiently of temp. rising in a secondary refining furnace and to reduce the cost in a melting and secondary refining method for steel by tapping the molten steel into a primary ladle after melting the steel with an electric furnace, and successively, pouring into the secondary refining furnace and heating to rise the temp. and flowing into a secondary ladle in which gas bubbling is executed. CONSTITUTION:The secondary refining furnace 2 is formed as a trough type, and storing basin parts 4a, 4b are arranged in both ends and iron-made electrodes 5 are arranged at these both storing basin parts 4a, 4b and the molten steel flows down into the one side of the storing basin part 4a from the primary ladle, and further when the molten steel flows down into the secondary ladle 3 from the other storing basin part 4b, by conducting the electric powder from both electrodes 5 dipped into the molten steel, the molten steel is heated by resistance heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to melting of steel in an electric furnace and subsequent refining of molten steel by a ladle, and more particularly to efficient heating means in a secondary refining furnace.

[0002]

2. Description of the Related Art As a conventional technique relating to the melting of steel by an electric furnace and the secondary refining method, there is one disclosed in JP-A-2-34715. This method will be described with reference to FIG. First, in the electric furnace 30, while melting the steelmaking raw material, oxygen is blown in and lime is added to perform oxidation and decarburization. As a result, the dephosphorization reaction proceeds. After smelting, the molten steel is heated to a predetermined temperature within 50 ° C. above the liquidus temperature, the above treatment is completed by then, and the primary ladle 21 is quickly tapped together with the basic slag. At this time, most of phosphorus is adsorbed on the basic slag. While injecting the above-mentioned low-temperature molten steel into the crucible-shaped secondary refining furnace 22, temperature rise, deoxidation, desulfurization, degassing, and demetallic non-inclusions are performed in parallel. At this time, the high phosphorus slag 36 in the primary ladle 21 is removed from the secondary refining furnace 2 by the gate nozzle 35 at the bottom.
It is not injected into 2 and is discarded outside the system. The low temperature molten steel injected into the secondary refining furnace 22 is heated by the induction heating unit 28 and discharged from the gate nozzle 27 at the bottom through the vacuum cover 31 to the secondary ladle 23. These injection, heating, and discharge are performed almost simultaneously. The secondary ladle 23 is configured to be airtight, and in parallel with the injection of the molten steel, an inert gas such as argon gas is blown from the bottom plug nozzle 32 to perform a gas bubbling process. At this time, the evacuation system 33 depressurizes the inside of the secondary ladle 23 in parallel with the injection of the molten steel and maintains the low pressure. In addition, a slag forming agent, a deoxidizing agent, an alloy and the like necessary for refining are appropriately inserted into the secondary ladle 23 through the vacuum hatch 34. When the molten steel has finished flowing into the secondary ladle, the refining is stopped and immediately supplied to the continuous casting facility 37. According to this method, low phosphorus steel can be mass-produced extremely efficiently.

[0003]

However, since the above method uses the induction heating system as the heating means in the secondary refining furnace, it has the following problems. The temperature rise by induction heating in the secondary refining furnace is insufficient in terms of energy efficiency. This energy efficiency is about 6
It stops at around 0%. High-grade refractories are required, resulting in high cost. In addition, since the undeoxidized molten steel is treated, the molten steel reacts with the refractory material, and the refractory material is largely damaged. This repair further increases the cost. The present invention has been made to solve such a problem, and provides a steel melting and secondary refining method capable of improving the energy efficiency of the temperature rise in the secondary refining furnace and reducing the cost. The purpose is to do.

[0004]

In order to achieve the above-mentioned object, the method of the present invention is to directly perform resistance heating on molten steel in a secondary refining furnace. That is, a secondary refining furnace is formed in a gutter shape, and storage portions are provided at both ends of the secondary refining furnace, iron electrodes are arranged in both storage portions, and molten steel flowed down from the primary ladle into one storage portion When flowing down from the reservoir to the secondary ladle, electricity is applied from both electrodes immersed in the molten steel to heat the molten steel by resistance heating.

In addition, in parallel with the melting of the steelmaking raw material, the molten steel is oxidized and decarburized, and when it is burnt, this is almost finished.
After smelting, the liquidus temperature was raised to a temperature within 50 ° C., the steel was tapped into the primary ladle, and then the primary ladle was injected into the secondary refining furnace. It is the same as the above-mentioned conventional example in that the gas is allowed to flow down to the secondary ladle, and in parallel with this, gas bubbling is continuously performed in the secondary ladle under a slag interposed vacuum.

A specific example of the present invention will be described below with reference to FIG. FIG. 1A is an explanatory view of the method of the present invention, and the outline of the apparatus will be described first. The apparatus using the method of the present invention mainly comprises a primary ladle 1, a secondary refining furnace 2 and a secondary ladle 3. Among them, the primary ladle 1 and the secondary ladle 3 are the same as those in the conventional example. That is, the primary ladle 1
Is for storing the steelmaking raw material melted in the electric furnace 10 and flowing it down to the secondary refining furnace 2 described later.
In addition, the secondary ladle 3 has a vacuum cover 1 that can be attached to and detached from the upper portion.
1 has a plug nozzle 1 for blowing gas into the bottom
2 is provided and the internal pressure of the vacuum exhaust system 13 can be maintained at a predetermined reduced pressure state. Then, gas bubbling is performed on the molten steel flowed down from the secondary refining furnace 2 described below, and the slag forming agent and the like can be appropriately charged from the vacuum hatch 14.

On the other hand, as shown in FIG. 1B, the secondary refining furnace 2 is formed in a trough shape, and storage portions 4a and 4b are provided at both ends thereof. Molten steel from the primary ladle 1 is injected into one of the reservoirs 4a,
The other side 4b is provided with a gate nozzle 7, which is arranged so that molten steel can flow down to the secondary ladle 3. Further, iron electrodes 5 are installed on both of the reservoirs 4a and 4b. Then, these electrodes 5 are connected to a power source 6, molten steel is injected from the primary ladle 1 into one storage portion 4a, and is flowed down from the gate nozzle 7 of the other storage portion 4b to the secondary ladle 3. At this time, the molten steel can be directly resistance-heated by being immersed in the molten steel and passing a predetermined current.

Using such an apparatus, the melting and secondary refining of steel are performed by the following steps. First, while melting the steelmaking raw material in the electric furnace 10, oxidation and decarburization are performed by blowing oxygen and adding lime. As a result, the dephosphorization reaction proceeds. After the smelting, the molten steel is heated to a predetermined temperature within 50 ° C. above the liquidus temperature, the above treatment is completed by then, and the steel is rapidly tapped to the primary ladle 1 together with the basic slag. At this time, most of the phosphorus is adsorbed on the basic slag. While injecting the above-mentioned low temperature molten steel into one of the storage parts 4a of the secondary refining furnace 2, the temperature rise, deoxidation, desulfurization, degassing, and denonmetallic inclusions are performed in parallel. At this time, the high phosphorus slag 16 in the primary ladle 1 is not injected into the secondary refining furnace 2 by the bottom gate nozzle 15 and is discarded outside the system. The low temperature molten steel injected into the secondary refining furnace 2 is stored in both storage parts 4
While being directly energized and heated through the iron electrodes 5 provided on a and 4b, it is discharged to the secondary ladle 3 through the vacuum cover 11 from the gate nozzle 7 provided at the bottom of the other storage section 4b. These injection, heating, and discharge are performed almost simultaneously. The secondary ladle 3 is airtightly configured, and in parallel with the injection of the molten steel, argon gas is blown from the plug nozzle 12 at the bottom to perform gas bubbling treatment. At this time, the evacuation system 13 is operated in parallel with the injection of molten steel to reduce the pressure in the secondary ladle 3 and maintain it at a low pressure.
It should be noted that the secondary ladle 3 is appropriately inserted with a slag forming agent, a deoxidizing agent, an alloy and the like necessary for refining through the vacuum hatch 14. When the molten steel has finished flowing down to the secondary ladle 3, the refining is stopped and immediately supplied to the continuous casting facility 17.

[0008]

As described above, by using resistance heating as the heating means of the secondary refining furnace, the design of the power source can be facilitated and the cost can be reduced. That is, since the commercial frequency can be used as it is as the power source, the power source can be designed only by determining the voltage and the power source capacity matching the load. In addition, energy efficiency can be improved. Direct heating is performed while the electrode of the reservoir is immersed in molten steel,
The refractory lining does not reduce efficiency like induction heating.

Further, since the secondary refining furnace is shaped like a gutter having a simple structure, general lower refractories can be used. As a result, the refractory cost can be reduced and the repair time can be shortened. Further, since the electrode material is made of iron, which is the same quality as the molten steel, the molten steel will not be contaminated even if the electrode melts to some extent during contact with the molten steel. Due to the circuit resistance, heat is generated only in the trough portion, and the electrode portion outside the reservoir does not generate heat and melt.

[0010]

EXAMPLES According to the method of the present invention and the conventional method described above,
Table 1 shows the heating conditions and results when 30 tons of steel were continuously heat-treated and their energy efficiencies were compared.

[0011]

[Table 1]

As shown in the table, the method of the present invention was able to remarkably improve the energy efficiency. Further, as compared with the conventional method by induction heating, it was possible to raise the temperature to the target molten steel temperature after finishing the refining with electric power which is 11 KWH / ton less. In addition, the refractory cost was reduced and the lining repair time was shortened.

[0013]

As described above, according to the method of the present invention, the molten steel is directly resistance-heated, so that the treatment can be performed with high energy efficiency. Moreover, since the commercial frequency can be used as a power source as it is, the equipment cost is reduced. Further, since the secondary refining furnace is a gutter type having a simple structure, a general low-grade refractory can be used and its repair can be easily performed, so that the refractory cost can be reduced.

[Brief description of drawings]

1A is an explanatory view of the method of the present invention, and FIG. 1B is a plan view of a secondary refining furnace used in the method of the present invention.

FIG. 2 is an explanatory diagram of a conventional method.

[Explanation of symbols]

 1, 21 Primary ladle 2, 22 Secondary refining furnace 3, 23 Secondary ladle 4a, 4b Storage part 5 Electrode 6, 26 Power supply 7, 27 Gate nozzle 8 Opening cylinder 9 Opening / closing stopper 10, 30 Electric furnace 11, 31 Vacuum cover 12, 32 Plug nozzle 13, 33 Vacuum exhaust system 14, 34 Vacuum hatch 15, 35 Gate nozzle 16, 36 High phosphorus slag 17, 37 Continuous casting equipment 28 Induction heating part 29 Processing unit 40 Radiation thermometer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location F27B 3/20 7727-4K F27D 11/04 8825-4K

Claims (1)

[Claims] 1. A method of oxidizing molten steel in parallel with melting of a steelmaking raw material,
Decarburization is performed, and when it is burnt out, it is almost finished. After the burnout, the temperature is raised to within 50 ° C above the liquidus temperature, steel is tapped into the primary ladle, and then injected into the secondary refining furnace from the primary ladle. The secondary ladle is heated and heated in the secondary refining furnace while flowing down to the lower secondary ladle, and in parallel with this, the secondary ladle continuously performs gas bubbling under slag-containing vacuum. In the refining method, the secondary refining furnace is formed in a gutter shape, storage portions are provided at both ends of the secondary refining furnace, iron electrodes are arranged in both storage portions, and molten steel flowed down from the primary ladle to one storage portion. The method for melting and secondary refining of steel, characterized in that, when the molten steel is flowed down from the other storage portion to the secondary ladle, electric current is applied from both electrodes immersed in the molten steel to resistance-heat the molten steel.