JPH05287354A - Method for refining molten steel at tapping and method for preventing mixture of slag at tapping steel - Google Patents

Abstract

PURPOSE:To efficiently execute decarburization in molten steel by utilizing steel tapping from a converter to a ladle. CONSTITUTION:At the time of tapping a molten steel 2 from a steel tapping hole 4 arranged in the converter 1, inert gas is blown during the steel tapping from blowing holes 6 arranged in the inner wall of a steel tapping hole. The gas becomes fine bubbles to cause the decarburizing reaction in the steel receiving ladle 5. Further, at the end stage of the steel tapping, by a rotating magnetic field generator arranged at the outer periphery of the steel tapping hole 4, molten steel is rotated, and by utilizing the static pressure gradient, the blown gas is concentrated to the center and floated up in the converter, and recessed deformation of the interface between the slag 3 and the molten steel 2 is prevented and the mixture of the slag 3 into the steel receiving ladle is simply and efficiently prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently carrying out a secondary decarburizing refining reaction at the time of tapping after the refining is completed in a converter.

[0002]

2. Description of the Related Art In response to the recent increase in demand for ultra-low carbon steel, decarburization is carried out to 500 to 200 ppm [C] in a converter and, after tapping, 50 ppm or less [C] in a secondary refining furnace such as RH and DH. ] The method of decarburizing up to the area has become common.

A large amount of slag is generated during converter refining. However, this slag is harmful after refining, and we want to avoid mixing it in the ladle. When the residual amount of molten steel in the converter furnace decreases, a dent is generated at the interface between the molten steel and the slag at the top of the tapping mouth, and the slag becomes caught in the molten steel, and the slag is mixed. In order to prevent this, hitherto, refractory balls have been thrown in to suppress the generation of dents and suppress the inclusion of slag as much as possible. On the other hand, as a method that does not use this refractory material, there are JP-A-51-81708 and JP-A-58-1.
There is a method for preventing the slag in the converter furnace from being mixed into the pan by blowing bubbles as described in Japanese Patent No. 1716.

[0004]

When the conventional secondary refining method as described above is carried out, a large amount of capital investment and operating personnel are required, resulting in a large fixed cost load. In addition, since different steps of the reaction container are sequentially performed,
The amount of various materials (refractory, etc.) in each process increased, and the energy released was too large, resulting in a large total refining cost.

The first object of the present invention is to provide a technique for consolidating the secondary refining process in a converter in order to solve such problems. On the other hand, regarding the prevention of slag inclusion, when a refractory ball is thrown in, there are costs such as refractory cost, throwing workability, and environmental problems. In addition, JP-A-51-81708 and JP-A-58
Although the method for preventing the mixture of slag in the converter furnace by the bubble blowing as described in JP-A-11716 is noted compared to the method for preventing mixture by the refractory described above, the tapping speed is usually easy. It is extremely fast at a few m / sec as calculated in the above, and the levitation speed of bubbles does not exceed several tens cm / sec, so most of the bubbles are discharged from the tapping hole by the molten steel flow and inside the converter furnace. It does not float and does not bring the effect of preventing slag contamination. Secondly, the present invention also provides a technique for solving this point.

[0006]

Means for Solving the Problems The present invention is to solve the above-mentioned problems, and when molten steel is tapped from a tapping port provided in a converter, a gas blow-in port provided in the tapping port inner wall is used. A method for refining molten steel is characterized in that an inert gas is blown into the molten steel during tapping. Further, it is also characterized in that it is carried out after decarburizing and refining to a range of 0.02 to 0.05% [C] in a converter before this steel tapping. Furthermore, it is characterized in that an electromagnetic stirrer is provided on the outer circumference of the tapping hole to carry out the stirring while giving the tapped stream.

Further, when the molten steel is tapped from the tapping port provided in the converter, an inert gas is blown into the molten steel during tapping from the gas blowing port provided on the inner wall of the tapping port, and the molten steel is rotated. This is a method for preventing slag inclusion during tapping of molten steel, which is characterized in that a magnetic field is applied to cause air bubbles of the inert gas concentrated in the center of the tapping port to naturally float in the converter.

Further, in each of the above methods, a porous refractory (porous plug) or a plurality of tuyere are provided as the gas blowing port.

[0009]

First, a concrete method of the molten steel decarburizing and refining method of molten steel which is the first part of the present invention will be described below with reference to the operation and the sectional view of the converter and the ladle shown in FIG. .. According to this method, when the molten steel in the converter is tapped from the tapping port provided in the converter furnace body, an inert gas is blown into the molten steel being tapped from a gas blowing port provided on the inner surface of the tapping port. At this time, the inert gas is mixed with the molten steel flowing out as bubbles, and a decarburization reaction occurs in the ladle that receives the flowing molten steel. As the inert gas blowing port, a porous refractory material (porous plug) or a plurality of tuyere is provided.

Molten steel 2 is placed in the converter 1 after the predetermined refining is completed.
And molten slag 3 is present. Molten steel 2 after this refining is completed
Is transported to the next step, and is generally tapped into the ladle 5 through the tapping port 4. In the present invention, at the time of tapping, the inert gas 7 is blown from the porous plug or the tube nozzle 6 on the inner wall of the tapping port 4. Then, the gas blown in the tap steel flow 8 is made into fine bubbles and is transported into the pan together with the tap steel flow 8. Utilizing these fine bubbles, the C + O → CO reaction between C and O in the molten steel is efficiently caused, and the generated C
O gas is taken into the inert gas to accelerate the decarburization reaction. At that time, the bubbles are miniaturized to increase the interfacial area between the gas and the molten steel. As described above, the atomized bubbles are transported and float in the ladle together with the tapping flow.
In the case of the present invention, the bubbles are miniaturized, and the staying time in the ladle increases as compared with the case of blowing from the bottom of a normal ladle, and becomes saturated with CO gas during the rise. Blow-in from the bottom of the pan gives a saturation level of 100%, which is five times as high as that at a saturation level of at most 20%.

The above method may be carried out by providing an electromagnetic stirrer on the outer circumference of the tapping hole and stirring the tapped steel stream. Thereby, the bubble diameter of the inert gas blown from the blowing port can be further reduced.

In particular, the omission of the current secondary refining process has a great cost implication as described above.
It is significant that decarburization refining in the converter furnace is limited to 0.02 to 0.05% [C], and decarburization to 0.005% [C] or less after tapping.

Next, the second part of the present invention, which is the method for preventing the mixing of slag in the converter furnace into the molten steel to be tapped, the concrete method will be described together with the action and the cross section of the converter and ladle shown in FIG. Shown below with reference to the figures. In this method, when molten steel is tapped from the tapping port provided in the converter, an inert gas is blown into the molten steel during tapping from the gas blowing port provided on the inner surface of the tapping port, and a rotating magnetic field is applied to the molten steel. Inert gas bubbles concentrated in the central part of the tap hole are naturally floated in the converter. This can prevent the slag existing on the molten steel in the furnace from being mixed into the tapped steel flow. As in the case of the above-mentioned 1, a porous refractory (porous plug) or a plurality of tuyere is provided as the gas blowing port.

As the tapping is continued, the molten steel 2 in the converter 1
Decreases and the state becomes as shown in FIG. At this time, when the depth 9 of the molten steel 2 becomes a certain value determined by the surrounding conditions such as the tapping diameter and the molten steel / molten slag interface tension, for example, 50 cm or less, the deformation of the interface between the molten steel 2 and the slag 3 starts and A dimple is formed above the mouth 4 to start mixing slag into the molten steel 2. In the present invention, the inert gas 7 is blown from the inner wall of the tap hole 4 through the porous plug or the pipe nozzle 6. Further, a centrifugal force is applied to the molten steel 2 by using a rotating magnetic field generator 13 that produces a swirling flow 12, and a part of the bubbles of the inert gas 7 blown in the opposite direction is collected in the center, and the upward flow created by this is used. It is intended to prevent the formation of dents at the interface above the tapping hole 4 and prevent the inclusion of slag.

[0015]

[Example] In a test using 300 tons of molten steel, 12 Nm ³ / min (0.4 Nm ³ / t) was blown in during a tapping time of 10 minutes, and 0.02% [C], 0 in the furnace. 0.07%
What was [O] gave a value of 0.005% [C] in the ladle. In addition, in this test, for 1 minute at the end of tapping,
When the peripheral speed of 1 m / min was theoretically given to the molten steel by the rotating magnetic field generator arranged on the outer circumference of the tapping hole having a diameter of 20 cm,
The amount of slag flowing out into the ladle was able to be kept below 10% of the conventional level.

[0016]

As described above, when the method of the present invention is used, the secondary refining step can be omitted, the steelmaking cost can be significantly reduced, and the outflow of converter slag into the ladle can be improved. It is possible to prevent it well.

[Brief description of drawings]

FIG. 1 is a sectional view of a converter and a ladle showing a steel refining method of the present invention.

FIG. 2 is a sectional view of a converter and a ladle showing a method for preventing slag inclusion during tapping according to the present invention.

[Explanation of symbols]

 1 Converter 2 Molten Steel 3 Molten Slag 4 Steel Tap 5 Ladle 6 Porous Plug or Tube Nozzle 11 Rotating Magnetic Field Generator

Claims (6)

[Claims] 1. When the molten steel is tapped from a tap hole provided in a converter, an inert gas is blown into the molten steel during tapping from a gas blowing port provided on the inner wall of the tap port. Method for refining molten steel. 2. The method for refining molten steel according to claim 1, wherein a porous refractory (porous plug) or a plurality of tuyere are provided as the gas blowing port. 3. 0.02 to 0.05% in a converter before tapping
A method for refining molten steel, comprising carrying out the method according to claim 1 after performing decarburization refining to the range of [C]. 4. The molten steel tapping refining method according to claim 1, wherein an electromagnetic stirrer is provided on the outer circumference of the tapping tap while stirring the tapped steel flow. 5. When the molten steel is tapped from a tapping port provided in a converter, an inert gas is blown into the molten steel during tapping from a gas blowing port provided on the inner wall of the tapping port, A method for preventing slag inclusion during tapping of molten steel, characterized by applying a rotating magnetic field and allowing air bubbles of inert gas concentrated in the center of the tapping hole to naturally float in the converter. 6. The method for preventing slag inclusion at the time of tapping of molten steel according to claim 5, wherein a porous refractory (porous plug) or a plurality of tuyere are provided as the gas blowing port.