JP3043326B1 - Ladle refining apparatus and ladle refining method using the same - Google Patents

Abstract

The present invention provides a ladle refining apparatus and a ladle refining method using the same, which efficiently suppress molten metal in the tank and stir molten steel, reform slag, and degas efficiently. SOLUTION: In a device for refining molten steel by directly connecting a vacuum / decompression tank 2 to an upper part of a ladle 1 and blowing a stirring gas 6 with an inert gas into the ladle, a vacuum / decompression tank body is provided. The inner diameter is set to be equal to or smaller than the inner diameter of the upper end of the ladle and equal to or larger than the projected sectional diameter D of the molten steel surface rising portion 7 generated by the stirring gas 6 blown into the ladle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladle refining apparatus and a ladle refining method as a secondary refining process for molten steel.

[0002]

2. Description of the Related Art In recent years, the quality requirements for steel materials have become increasingly severe with the sophistication and diversification of their utilization techniques, and the need for high-purity steel production has been increasing. In response to such demands for the production of high-purity steel, the steelmaking process has attempted to expand the hot metal pretreatment or secondary refining equipment. In particular, as a secondary refining facility, for the purpose of degassing molten steel and removing inclusions,
Vacuum refining equipment such as RH and DH, and arc heating slag refining equipment such as LF are generally used. When producing high cleanliness steel such as bearing steel, LF and RH are used together as necessary. The process of processing is also common.

[0003] However, in a facility such as an RH vacuum refining facility in which an immersion pipe is inserted into molten steel in a ladle and the molten steel is sucked into the vacuum tank from the immersion pipe to perform vacuum refining treatment, stirring of the molten steel in the ladle is performed. The slag existing on the surface of the molten steel outside the immersion tube is insufficiently agitated and the slag cannot be sufficiently reformed, and the molten steel is reoxidized by the highly oxidized slag. There was a limit to the refining capacity of inclusions because iron oxide in the metal adhered in the vacuum tank reacted with the molten steel in the vacuum tank and the molten steel was re-oxidized. Further, in order to avoid deterioration of the cleanliness of molten steel due to reoxidation by slag, L
Generally, a method of reducing the degree of oxidation of slag by using an F facility or the like is commonly used. However, this method has a problem in that the processing time is prolonged and the cost increases such as heat loss and refractory wear.

[0004] From such a viewpoint, as a conventional technique, as a method of directly reducing the pressure of the molten steel surface in a ladle and efficiently reacting the slag and the molten steel under vacuum, VOD method, VAD method, S
The S-VOD method and the like have been developed. As a means to directly depressurize the molten steel surface in the ladle, a method of storing the ladle in a decompression container that can accommodate the entire ladle and depressurizing the entire ladle, and using the ladle itself as a lower decompression tank There is a method in which an upper decompression tank is brought into close contact with the upper part of the ladle to depressurize the molten steel surface in the ladle. Both methods have the problem that the equipment is complicated, and because of its structural constraints, it is not possible to flow a large amount of agitation gas to avoid scattering of molten steel or slag, and from the viewpoint of productivity, equipment cost, and maintenance. At present, it is not widely used.

[0005] From such a viewpoint, as an invention in which the ladle is accommodated in a vacuum / decompression vessel capable of accommodating the entire ladle and the entire ladle is depressurized, a sufficient free board is provided in a vacuum tank. Japanese Patent Application Laid-Open No. Hei 9-111331 discloses a method in which an internal pipe is installed to cope with scattering of molten steel and slag forming during vacuum processing, and to shorten the processing time. However, in this method, the vacuum vessel is divided into upper and lower parts, the inner diameter of the vacuum tank is larger than the outer diameter of the upper end of the ladle, and the entire ladle is charged into the vacuum tank for refining. When the lower end is in close contact with the upper end of the ladle or immersed in the slag and molten steel in the ladle, when refining under vacuum, when the internal pipe cannot be attached or detached by the molten metal scattered metal or when immersed in the ladle There is concern about molten steel contamination by metal. There is also a problem from the viewpoint of securing the molten steel temperature when the processing time is extended.

[0006] The ladle itself is used as a lower vacuum tank,
As a method of depressurizing the molten steel surface in the ladle by closely contacting the upper decompression tank with the upper part of the ladle, "Materials and Process Vol.
No. 1, 1990 p250 "(issued by the Iron and Steel Institute of Japan), an inner lid is provided at the upper part of the ladle, and the splash generated on the molten steel surface by the gas blown from the bottom of the ladle directly contacts the ladle and the upper decompression tank. In addition to preventing splashing to the (ladle sealing portion), a shielding plate is provided at the upper portion of the ladle to prevent splash from jumping over the upper portion of the inner lid and scattering to the ladle sealing portion. But,
In this method, there is a problem that the inner cover cannot be attached or detached due to the molten steel splattered metal, and since the molten steel also adheres to the shield plate, there is a problem of the refractory cost of the shield plate itself. Furthermore, since the inner lid and the shielding plate are attached and detached every time vacuum processing is performed, there is a problem that workability is deteriorated.

[0007]

SUMMARY OF THE INVENTION The present invention provides a ladle refining apparatus and a ladle refining method using the same, which can easily solve the problems of the conventional method. In other words, the present invention is a method for refining ladle refining, which is a problem in the conventional ladle refining method. And a ladle refining apparatus and a ladle refining method capable of efficiently producing high-cleanliness steel and further improving the heat allowance.

[0008]

According to the present invention, a vacuum / decompression tank 2 having no dipping tube for dipping the molten steel 4 in the ladle below is directly connected to the upper part of the ladle 1 to reduce the pressure in the tank. A device for refining the molten steel in the ladle by stirring the molten steel in the ladle by blowing inert gas into the ladle.
The vacuum and decompression tanks are in close contact with each other to form a sealed structure.
Has a body portion, the inner diameter of the body portion is smaller than the inner diameter of the ladle upper end, Ri projected cross-sectional diameter or on der the raised part 7 of the ladle the molten steel surface caused by the stirring gas blown into the ladle, true
The height to the top of the empty / decompression tank 2 is from the molten steel surface in the ladle
Der Rukoto least 5m is a vacuum-reduced pressure refining apparatus according to claim.

Further, a cylindrical portion 9 is provided at the lower end of the vacuum / decompression tank 2, and the cylindrical portion has a diameter equal to or less than the projected cross-sectional diameter of the raised portion of the molten steel in the ladle.
Having an upper inner diameter, and having an outer diameter equal to or less than the ladle upper end inner diameter,
A vacuum / decompression device characterized in that the lower end position of the cylindrical portion is lower than the upper end of the ladle 1 and is not immersed in the molten steel in the ladle.

In the present invention, a burner 10 which burns fuel and oxygen gas from the lower end of the vacuum / decompression tank 2 to blow out a flame is installed in the vacuum / decompression tank 2 to heat the molten steel 4 and keep the temperature in the vacuum / decompression tank. It is a vacuum / decompression device that can perform Further, there is provided a refining method using the vacuum / decompression device, wherein the temperature of the inner wall of the vacuum / decompression tank is constantly maintained at 1000 ° C. or more in a state of continuous use by a flame ejected from the lower end of the heating burner 10. .

Next, the present invention is a ladle refining method characterized by refining the amount of slag on the molten steel surface in the ladle so as to satisfy the following conditions when applying the vacuum refining apparatus. 0.010 ≦ H / h ≦ 0.025 H: Slag thickness in the ladle, h: Molten steel bath depth in the ladle Further, Al is added to the molten steel, and the added Al is burned by supplying oxygen gas. A ladle refining method characterized in that the pressure in a vacuum / decompression tank is set to 760 Torr to 500 Torr when raising the temperature of molten steel.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments will be described below in detail with reference to the drawings. FIG. 1 shows a specific example of the ladle refining apparatus of the present invention. The apparatus comprises a ladle 1 and a vacuum / decompression tank 2, and the ladle is provided with a stirring gas blowing device 3 at the bottom. In the present invention, the method of stirring the molten steel 4 in the ladle is not limited to this. The inner diameter of the body of the vacuum / decompression tank is smaller than the inner diameter of the upper end of the ladle, and is set to be equal to or larger than the projected cross-sectional diameter D of the molten steel surface rising portion 7 in the ladle. Here, the projected sectional diameter of the raised portion of the molten steel surface can be represented by the following equation when stirring gas is blown from the bottom of the ladle.

D = d + 2htan12 ° D; diameter of the projected section of the molten metal rising part d; diameter of the gas blowing plug h; depth of the molten steel bath in the ladle The upper part of the ladle and the vacuum / decompression tank are brought into close contact with each other to maintain the desired degree of vacuum. Provide a seal structure as possible. Stirring gas 6 is blown from the bottom of the ladle to stir the molten steel in the vacuum / decompression tank at normal pressure or vacuum. Under the high vacuum, the molten steel surface rises and the molten steel and the slag 5 are scattered. However, in the apparatus of the present invention, since the inside diameter of the body of the vacuum / decompression tank is smaller than the inside diameter of the ladle, the conventional VOD has been a problem. It is possible to minimize the adverse effects of molten steel and slag scattering on the ladle and the seal of the vacuum / decompression tank. The splash of the molten steel and slag due to the splash first scatters upward from the swelling portion 7 of the molten steel surface, then turns downward and reaches the ladle seal portion. In the present invention, since the vacuum / decompression tank body having an inner diameter smaller than the inner diameter of the ladle upper end part is present at the upper part of the ladle, the splash that has jumped upward collides with the inner surface of the vacuum / decompression tank body, and the ladle is left as it is. Falls on the molten steel surface inside. Therefore, the splash does not reach the ladle seal. In addition, when using the shield plate, most of the splash collides with the shield plate, and a part of the solidifies on the shield plate surface and adheres to the metal, but since the shield plate is not used in the present invention, In the absence of this phenomenon, and in the case of a vacuum / decompression tank having a small inner diameter, it is easy to keep the inner surface temperature high, so that the splash colliding with the body of the vacuum / decompression tank solidifies and grows as a base metal. The speed is also very small and the yield loss is small. Since the evacuation volume is small due to the narrowed shape of the vacuum / decompression tank body, the initial evacuation time until reaching vacuum can be shortened. Furthermore, there is no complicated work and cost reduction such as installation of a shield plate. Here, the reason why the inner diameter of the body of the vacuum / decompression tank is set to be equal to or larger than the projected sectional diameter of the raised portion of the molten steel surface is that molten steel and slag are mainly scattered from the raised portion of the molten steel surface.

Further, FIG. 2 shows an example in which a cylindrical portion 9 having a lower end position below the upper end of the ladle and not immersed in the molten steel 4 and the slag 5 in the ladle is provided below the vacuum / decompression tank according to the first aspect of the present invention. Is shown. This cylindrical portion 9 is a raised portion 7 of molten steel in a ladle.
It has an inner diameter greater than or equal to the cross-sectional diameter of the projection and an outer diameter less than or equal to the inner diameter of the upper end of the ladle, and is manufactured using a refractory or by coating the surface of a core metal with the refractory. When the cylindrical portion 9 is provided, the adverse effects of molten steel and slag scattering on the ladle and the seal portion of the vacuum / decompression tank can be further reduced as compared with the system shown in FIG. (T / CH), and the refining efficiency can be further improved by increasing the amount of gas blown into the molten steel. Here, the reason why the cylindrical portion 9 is not immersed in the slag 5 or the molten steel 4 is that if the lower end of the cylindrical portion is not more than the upper end of the ladle, a sufficient effect can be exhibited. It is to invite. Also, from the viewpoint of producing clean steel, it is desirable that the entire slag on the surface of the molten steel in the ladle be stirred and slag reforming occurs by a sufficient reaction between the slag 5 and the molten steel 4. In the immersion method, the stirring force outside the immersion tube is small. The non-immersion method is advantageous because the slag reforming becomes insufficient.

The method of sealing between the ladle 1 and the vacuum / decompression tank is not particularly limited in the present invention. Alternatively, in consideration of heat resistance in a case where slag flows out, a sealing material having excellent heat resistance such as asbestos or metal Al is preferably used. When a rubber-based sealing material is used, it is desirable to take heat treatment such as a double seal using asbestos or the like on the ladle side. In addition, the sealing position is not limited to the upper end of the ladle, the sealing position is set to a position slightly lower than the upper end of the ladle outside the ladle, as a structure to avoid that the seal member directly receives radiant heat from molten steel Such a structure is also included in the present invention.

It is desirable that the vacuum / decompression tank 2 has a sufficient height against the scatter of molten steel and slag during the vacuum treatment. In the present invention, the height of the vacuum / decompression tank is specified to be 5 m or more.
If the height of the vacuum / decompression tank is lower than 5 m, metal sticks to the canopy of the vacuum / decompression tank, blocks the body of the vacuum / decompression tank, and intrudes into the exhaust duct. Deterioration and increase in equipment maintenance costs. The upper limit of the height of the vacuum / decompression tank is not particularly specified, but care must be taken if the height is excessively high, because the increase in the exhaust volume will increase the initial evacuation time.

FIG. 3 shows an example in which a heating burner 10 for injecting and burning fuel gas and oxygen gas into a vacuum / decompression tank is arranged. The heating burner 10 heats the refractory in the vacuum / decompression tank during processing and during non-treatment, and keeps the temperature of the refractory in the tank at a high temperature to further suppress the adhesion of metal to the refractory in the tank. However, it is possible to avoid the contamination of molten steel due to the adhesion of the ingot, the restriction in the continuous treatment of different types of steel, and the reduction in productivity for removing the ingot. Here, in order to obtain a sufficient effect of preventing the adhesion of the metal, the temperature of the refractory of the inner wall of the tank is always set to 100 ° C.
It is necessary to be 0 ° C. or higher. Further, by heating the inside of the vacuum / decompression tank to a high temperature during processing and during non-processing by the heating burner, the temperature drop of molten steel during processing can be reduced.

When refining molten steel using the apparatus of the present invention, it is possible to perform efficient refining by adjusting the amount of slag on the molten steel surface in the ladle within the following condition range.

0.010 ≦ H / h ≦ 0.025 H; slag thickness in ladle h; molten steel bath depth in ladle The reason for limiting the range of H / h is as follows. . When the slag thickness is large and H / h is 0.025 or more, the molten steel surface is covered with slag even during vacuum refining and the surface area of the molten steel exposed to vacuum is small, so that sufficient dehydrogenation efficiency can be obtained. Can not. On the other hand, when the slag thickness is small and H / h is 0.010 or less, the contact area between the slag and the molten steel is reduced, the ability to adsorb inclusions of the slag is reduced, and sufficient deoxygenation efficiency cannot be obtained. Therefore, in refining clean steel, it is desirable to adjust the slag thickness within the above range.

Further, in the apparatus of the present invention, it is possible to burn only Al in the molten steel by supplying only oxygen from the heating burner 7 disposed in the upper part of the tank, and to heat the molten steel by the reaction heat. By the way, in the conventional RH oxygen top blowing method, at least 200 torr is required to introduce molten steel into the reaction tank.
It is necessary to set the pressure in the tank below, so that the oxygen gas whose volume has increased under reduced pressure scatters the molten steel, or the CO gas generated by the reaction between oxygen and carbon in the molten steel scatters the molten steel. The problem was that the splash was large. Here, in the apparatus of the present invention, since the pressure in the tank at the time of performing the process of supplying oxygen to the molten steel can be as low as the atmospheric pressure or less, the pressure is not less than 500 torr and not more than 760 t.
Splash generation can be suppressed to a minimum by performing Al heat-up by blowing oxygen over at a tank pressure of orr or lower. The reason why the pressure in the tank is set to 760 torr or less is that when the inside of the tank is pressurized to a pressure equal to or higher than the atmospheric pressure, the sealing material is burned out by blowing out the high-temperature gas in the tank to the vacuum seal portion.

In the apparatus of the present invention, it is also possible to provide a wire adding apparatus for adding an element having a high vapor pressure such as Ca using a wire coated with a steel shell, if necessary. Is preferably carried out at atmospheric pressure after vacuum and reduced pressure refining.

[0022]

EXAMPLE After converter decarburization and refining, at the time of tapping, 6.8 kg / t of Mn alloy, 2.7 kg / t of Si alloy,
The molten steel to which 0.45 kg / t of aluminum was added and 3.0 kg / t of CaO was added for slag composition control was refined using the apparatus of the present invention shown in FIG.
A comparison with the conventional RH processing was performed. Table 1 shows the production conditions and production results of the present invention, and Table 2 shows the production conditions and production results of the comparative example.

[0023]

[Table 1]

[0024]

[Table 2]

The value of hydrogen after the treatment is the same good level in both the present invention example and the comparative example. The oxygen after the treatment was 1 in the comparative example.
In contrast to 8 ppm, the example of the present invention was 8 ppm, which was a very good result. T. of slag component after treatment Fe is
In contrast to the comparative example having a high value of 1.40%, in the example of the present invention, the reaction between the slag in the ladle and the molten steel sufficiently progressed,
T. A very low value of Fe of 0.24% could be realized, so that the degree of slag oxidation was reduced and the oxygen concentration in the molten steel could be reduced. By using the device of the present invention,
It was possible to obtain steel having a low hydrogenation equivalent to that of the conventional RH method and a higher degree of cleanliness than the conventional RH method.

FIG. 4 shows the relationship between the ratio (H / h) of the slag thickness H in the ladle and the molten steel bath depth h (H / h) and the dehydrogenation efficiency and deoxygenation efficiency when vacuum refining is performed using the apparatus of the present invention. FIG. In the region of H / h> 0.025, the surface of the molten steel is covered with slag even during vacuum processing, and a sufficient dehydrogenation efficiency cannot be obtained because the surface area of the molten steel exposed to vacuum is small. Further, in the range of H / h <0.010%, the amount of slag is small and a sufficient reaction surface area between slag and molten steel cannot be obtained, so that sufficient deoxidation efficiency cannot be obtained.

FIG. 5 is a comparison of the total oxygen content of the bearing steel obtained by refining using the LF-RH method conventionally used for obtaining high-purity steel and the apparatus of the present invention. By using the apparatus of the present invention, even in the production of high-grade steel such as bearing steel, it is possible to obtain a high degree of cleanliness equal to or higher than the conventional one, and it is possible to reduce the production cost by omitting the LF step.

FIG. 6 is a diagram showing the effect of the in-tank heating burner on the apparatus of FIG. By maintaining the refractory temperature of the inner wall of the vacuum / decompression tank at 1000 ° C. or higher by using the in-tank heating burner, the amount of metal ingot was significantly reduced.

FIG. 7 shows the pressure and splash in the tank when only oxygen is supplied to the molten steel from the heating burner using the apparatus shown in FIG. 3 to burn Al in the molten steel to increase the heat of the molten steel. It is the figure which showed the relationship of the reaching height. 5 tank pressure
By setting the pressure to 00 torr or more, the height at which the splash reached can be reduced as compared with the conventional RH, and the amount of the ingot in the tank could be reduced.

[0030]

According to the apparatus of the present invention and the refining method using the same, it is possible to avoid the adverse effect of molten steel scattering on the ladle seal portion, which is a problem in the conventional ladle refining method, and
The amount of metal in the tank can be reduced, and the temperature drop of molten steel during processing can be reduced. Further, in the production of steel requiring high cleanliness, the efficiency of the production process can be improved by performing the process of reforming the slag by reducing the degree of oxidation of the slag and the process of degassing with the same refining device. .

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of the apparatus of the present invention.

FIG. 2 is a cross-sectional view of the apparatus of the present invention when a cylindrical portion is installed inside a vacuum lid.

FIG. 3 is a sectional view in which a heating burner is installed in the apparatus of the present invention.

FIG. 4 is a diagram showing a relationship between a ratio (H / h) of a slag thickness h in a ladle and a molten steel bath depth H (H / h) and various refining efficiencies when performing molten steel refining using the apparatus of the present invention.

FIG. 5: Bearing steel product T. Comparison diagram of the conventional method and the method according to the present invention in O

FIG. 6 is a diagram showing the refractory temperature of the inner wall of the vacuum / decompression tank and the thickness of the metal in the apparatus of the present invention.

FIG. 7 is a diagram showing the pressure in the tank and the height at which the splash reaches when oxygen is blown onto molten steel containing Al using the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 2 Vacuum / decompression tank 3 Stirring gas blowing plug 4 Molten steel 5 Slag 6 Stirring gas 7 Molten steel surface rising part by stirring gas 8 Seal material 9 Cylindrical part 10 Heating burner

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masayuki Arai 12 Nakamachi, Muroran City Nippon Steel Corporation Muroran Steel Works (72) Inventor Jun Aoki 12th Nakamachi, Muroran City Nippon Steel Corporation Muroran Steel In-house (56) References JP-A-47-7301 (JP, A) JP-A-62-63611 (JP, A) JP-A-62-64460 (JP, A) JP-A-3-281720 (JP, A) JP-A-2-101108 (JP, A) JP-A-5-25533 (JP, A) JP-A-61-199559 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21C 7/10 B22D 1/00

Claims (6)

(57) [Claims] 1. A vacuum / decompression tank having no dipping tube for dipping into molten steel in a ladle is connected directly to the upper part of the ladle to depressurize the tank and blow an inert gas into the ladle. the ladle molten steel was stirred for an apparatus for performing the refining ladle molten steel, the ladle top and vacuum and depressurizing snug seal structure
And forming, vacuum-vacuum chamber has a body portion, the inner diameter of the body portion is smaller than the inner diameter of the ladle upper portion, the projection cross-section of the raised part of the ladle the molten steel surface caused by the stirring gas blown into the ladle diameter or less on der is, the height to the top of the vacuum and depressurizing, preparative
Vacuum and pressure reducing refining apparatus according to claim der Rukoto least 5m from the pot in the molten steel surface. Wherein the cylindrical portion is provided in the vacuum and depressurizing the lower, circular
The inner diameter of the cylinder is larger than the projected cross-sectional diameter of the raised part of the molten steel in the ladle
The vacuum device according to claim 1 , wherein the cylindrical portion has an outer diameter less than or equal to the inner diameter of the upper end of the ladle, and the lower end position of the cylindrical portion is lower than the upper end of the ladle and is not immersed in the molten steel in the ladle. Vacuum refining equipment. 3. A vacuum-vacuum refining apparatus according to claim 1 or 2 by burning fuel and oxygen gas from the lower end to the vacuum-vacuum vessel to be characterized in that arranged burners for jetting flame. 4. The vacuum / vacuum refining according to any one of claims 1 to 3 , wherein the amount of slag on the ladle molten steel surface is adjusted so as to satisfy the following conditions. Ladle refining method using equipment. 0.010 ≦ H / h ≦ 0.025 H: Slag thickness in ladle h: Depth of molten steel bath in ladle 5. The temperature of the inner wall of the vacuum / decompression tank is constantly maintained at 1000 ° C. or higher in a state of continuous use by a flame ejected from a lower end of a burner disposed in the vacuum / decompression tank. 4. A ladle refining method using the vacuum / vacuum refining device according to 3 . 6. Addition of Al into molten steel, supply of oxygen gas to burn the added Al, and when raising the temperature of molten steel, increase the pressure in the vacuum / decompression tank to 760 Torr to 500 Torr.
A ladle refining method using the vacuum / vacuum refining apparatus according to any one of claims 1 to 3 .