JPH02133510A - Vacuum treating apparatus - Google Patents

Abstract

PURPOSE:To prevent splash from molten metal surface and to enable hard blow refining by setting a shading body at the specific height position from molten metal surface in a submerged tube in inner part of a vacuum vessel providing a submerged tube submerged into the molten metal in a ladle. CONSTITUTION:The lower end of the submerged tube 4 at the lower part of the vacuum vessel 3 is submerged into the molten metal 2 charged in the ladle 1. Successively, by evacuating through a gas exhaust pipe 8 connecting with a vacuum source, the pressure in the vacuum vessel 3 is reduced. Further, while blowing inert gas from a porous plug 9 at the bottom part of the ladle 1, oxidizing gas is blown on the molten metal surface in the submerged tube 4 from a top blowing lance 10 to execute refinings of degassing, decarburizing, etc. In the above vacuum treating apparatus, the shading body 12 is set in the vacuum vessel 3 at 2-5m height from the molten metal surface in the submerged tube 4. By this shading body 12, spattering of the splash from the molten metal surface caused by blow is prevented and sticking and depositing to inner walls of the vacuum vessel 3 and gas exhaust pipe a, etc., are prevented. By this method, the hard blow suiting to the vacuum treatment of chromium-containing steel, etc., can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for performing vacuum processing such as degassing of molten steel and vacuum decarburization of chromium-containing molten steel.

[Conventional technology]

The VOD method is a method for degassing molten steel and vacuum decarburization of chromium-containing molten steel in a vacuum open atmosphere.

There are RH method, R)(-OB method, etc.).

The present invention is also a vacuum processing apparatus of this type, and one having the structure shown in FIG. 4 is introduced in Japanese Patent Publication No. 59-19967. In this device, a dipping tube 54 provided at the lower end of a vacuum chamber 53 is immersed in molten metal 52 housed in a ladle 51. Then, by evacuating the inside of the vacuum IW 53 through the exhaust pipe 55, the molten metal 52 flows up the vacuum chamber 53. In this state, ladle 5
While blowing an inert gas into the molten metal 52 from a gas blowing pipe 56 opening below the dipping tube 54 in the molten metal 52, an oxidizing gas is blown onto the molten metal surface in the vacuum tank 53 through an upper lance 57.

At this time, when the comparison between the inner diameter D1 of the dipping tube 54 and the inner diameter D0 of the ladle 51, /Do is maintained in the range of 0.4 to 0.8, the melting between the ladle 51 and the dipping tube 54 Gold @52
circulation is carried out smoothly. Further, when the ratio H,/H, between the depth H of the molten metal 52 in the ladle 51 and the inert gas injection depth iL is maintained in the range of 0.5 to 1.0, the molten metal 52 is given sufficient stirring power. therefore,
The refining reaction of the molten metal 52 by the oxidizing gas ejected from the upper lance 57 proceeds smoothly.

[Problem to be solved by the invention]

In the scouring method proposed in the above-mentioned prior application, when a large amount of oxidizing gas is blown into the molten metal, CO gas bubbles are actively generated on the surface of the molten metal 52 in the immersion tube 54.

Bubbles that emerge from the hot water surface into the vacuum atmosphere burst and cause splash generation, which is further aggravated by the strength of the top-blown gas jet.

Then, the splash scattered from the surface of the molten gold@52 adheres to and accumulates on the inner wall and ceiling of the vacuum chamber 53, the inner wall of the exhaust pipe 55, etc., and adversely affects the operation. Therefore, it is necessary to operate with soft blowing in which the depth of the depression in the hot water surface due to the oxidizing gas is approximately 180+++ m.

By the way, when chromium-containing molten steel such as stainless steel is subjected to double-blow oxygen blowing, the oxygen gas oxidizes the chromium and iron in the molten steel, and the generated oxides react with the carbon in the molten steel, resulting in a decarburization reaction. It is generally said that the process progresses. Therefore, when soft blowing is performed to reduce splash, the force of the oxidizing gas jet ejected from the upper lance 57 is reduced, and the generated oxide floating in the scene is removed from the molten metal 52.
The force of pushing inside becomes weaker. As a result, decarburization of the molten steel is inhibited, and the amount of generated oxides, that is, chromium oxides in the molten steel increases.

Also, when soft blowing the molten gold [Ha 52], the CO gas contained in the exhaust gas rising from the molten metal surface reacts with the oxygen contained in the oxidizing gas from the upper lance 57. , the degree of secondary combustion increases. As a result, the temperature inside the furnace becomes high and the heat load applied to the refractory increases, shortening the life of the refractory. Moreover, since the oxidizing gas blown from the upper lance 57 is consumed in secondary combustion, the molten metal 5
The decarburization efficiency and decarburization speed of No. 2 decrease.

Therefore, the present invention is particularly suitable for vacuum treatment of chromium-containing molten steel by providing a shield inside the vacuum chamber to prevent soubranonite scattered from the hot water surface from adhering to the inner wall of the vacuum chamber or exhaust pipe. [1] To provide a vacuum processing apparatus f2 capable of 1-dry blowing.

[Failure to solve the problem]

In order to achieve the purpose, the vacuum processing apparatus of the present invention has the following features:
a ladle for containing molten metal; a vacuum tank having a dip tube at its lower end to be immersed in the molten metal; an exhaust pipe connected to a vacuum source for reducing pressure inside the vacuum tank; and an inside of the vacuum tank. The method is characterized in that the shielding body is maintained at a height of 2 to 5 m above the hot water level in the immersion pipe.

[Effect]

Hereinafter, the features of the present invention will be specifically explained along with its operation with reference to the drawings.

Also in the vacuum processing apparatus of the present invention, as shown in FIG. 1, a dipping tube 4 provided at the lower end of a vacuum chamber 30 is immersed in molten metal 2 housed in a ladle 1. This dip tube 4 is
It is detachably attached to the vacuum chamber 3 by a flange 5. Further, an upper lid 7 is detachably attached to the upper part of the vacuum chamber 3 via a gasket 6. The inside of the dip tube 4 is
It is connected to a vacuum evacuation device (not shown) via an exhaust pipe 8, and the molten metal 2 in the ladle 1 is sucked out according to the degree of vacuum.

A porous plug 9 is provided on the bottom wall of the ladle l,
The molten metal 2 is stirred by an inert gas such as argon that is blown into the porous plug 9. Alternatively, instead of the porous plug 9, the gas blowing pipe described in FIG. 4 may be used. In addition, a top-blowing lance) 0 is inserted into the vacuum tank a3 through an insertion hole provided in the top lid 7, and oxidizing gas is blown from the top-blowing lance 10 onto one side of the molten metal 2 in the vacuum tank 3. I can roll.

Inside the vacuum chamber 3, a shield 12 is suspended from the upper lid 7 by a chain 11. A lance insertion hole 13 is formed in the center of the shield 12, and the tip of the top-blowing lance 10 faces the inside of the vacuum chamber 3 through this lance insertion hole 13. Further, inside the shielding body 12, there is a cavity 14 to reduce the weight. This shield 12 is guided by a guide tube 15 provided on the upper lid 7, and is held at a predetermined height within the vacuum chamber 3 by adjusting the length of the chain 11. The guide tube 15 also has the function of protecting the chain 11 from the heat released from the molten gold @2 in the vacuum chamber 3.

Furthermore, 'i! , a recessed space 16 may be formed on the lower surface of the shield 12 as shown in the figure. This hollow space 16 acts as a reservoir for the splash that has risen from the hot water level in the immersion pipe 4, and the splash flows out into the exhaust pipe 8 after passing between the shield 12 and the inner wall of the immersion pipe 4 or the vacuum pipe 3. suppress things. At this point, the inner wall surface of the recessed space 16 corresponds to the dip tube 4.
It is preferable to determine the size of the recessed space 16 so that it does not protrude inwardly from the inner wall surface of the recessed space 16.

Further, it is preferable that the outer diameter of the lower part of the shield 12 be larger than the inner diameter of the immersion tube 4. As a result, the splash generated within the immersion tube 4 travels up the immersion tube 4 and then collides with the lower surface of the shield 12. This prevents the air from directly flowing into the vacuum If3 and the exhaust pipe 8.

2! The shield 12 prevents the splash from the molten metal 2 being blown in the immersion pipe 4 from jumping up, and in particular prevents the splash from flowing into the exhaust pipe 8 or clogging the mounting portion of the upper lid 7. disappears. At this point, dip tube 4
It is necessary to maintain the height from the inner hot water level to the shielding body 12 at 2 to 5 m. When the shield 12 is maintained at such a height, the refining reaction and generation of splash occur in a relatively narrow space. As a result, the surface temperature of the refractory in the reaction tank is maintained at a high temperature, and adhesion of one-time splash is prevented.

In other words, the adhesion of splash to the refractory surface is
This process follows the process in which high-temperature liquid splash hits the refractory surface, loses heat, solidifies, and adheres to the surface. Considering the generation mechanism of this splash adhesion, the shielding body 12 and the like of the present invention has a surface temperature of 1200, for example.
It was found that splash adhesion does not occur when the temperature is sufficiently high, above ℃.

In order to maintain the surface temperature of the refractory in this reaction space, that is, the inner wall of the immersion tube 4 and the lower surface of the shielding body 12, at a high temperature, heat reception by high-temperature exhaust gas may be considered. but,
What is most affected is the height from the hot water level in the immersion tube 4 to the shield 12.

By maintaining this height appropriately, the inner wall surface of the immersion tube 4 and the lower surface of the shield 12 are heated by the radiant heat from the molten metal 2, and the temperature is maintained at a high temperature.

Through experiments conducted by the present inventors, it has been found that there is a relationship shown in FIG. 2 between the height of the image body 12 and the surface temperature of the refractory material on the lower surface of the shield 12. From this relationship, in order to maintain the lower surface of the shield 12 at a high temperature of 1200°C or higher without splashing, the height from the hot water level of the immersion tube 4 to the shield 12 should be 5 m or less. is necessary.

Also, when the installation height of the shield 12 is brought closer to the hot water surface,
This is advantageous in that the surface temperature of the refractory material on the lower surface of the B double body 12 increases, and no splash is attached. However, the shield 1
Thermal damage to the refractories No. 2 increases. That is, the splash is made up of a molten metal and its oxides, and the oxides wet the refractories, which progresses the melting loss.

This melting loss increases as the temperature increases, significantly shortening the life of the refractory. In this way, in practice, the oxides contained in the splash can cause corrosion of refractories, molten metal 2
Decreased durability due to increased load due to radiant heat from
Due to the need to secure sufficient space for the forming of molten steel that occurs at the start of vacuum treatment of undeoxidized molten steel, the shielding body 1
2, the lower limit of the installation height is 2 m.

By providing the shield 12 described above in the tank, hard blowing becomes possible compared to conventional methods. As an indicator of hard blowing, the depth of the depression formed on the surface of the molten metal 2 is generally 1. , (+nm) are used. In addition, the following formula, which was obtained as a result of studies on water models, etc., was used for the calculation.

Q = 1.19 xlO-3d (L, +-h) 1 mouth However, Q is the oxygen supply rate (Nm'/hour), d is the nozzle inner diameter of the top-blowing lance lO (mm), and k+ is the temperature above the hot water level. The distance to the blowing lance lO (carp) is shown.

When molten metal is hard-blown, the kinetic energy of the top-blown oxygen jet at the hot point increases, and the Fc generated at the surface of the molten metal increases.
Oxides such as O and Cr 203 are thrown into the bath, and the rate of reduction with carbon (c) dissolved in the molten metal 2 increases.As a result, oxidation 1 of chromium and iron decreases, resulting in decarburization. Efficiency is improved and the amount of ferroalloy (8eSi) consumed for chromium reduction is also reduced.

Furthermore, since the oxidizing gas is blown from the top blowing lance 10 to the inner part of the body at high speed, the proportion of oxygen consumed in secondary combustion is reduced. This secondary combustion is an exothermic reaction in which CO generated in the decarburization reaction is further oxidized to become CO2. When this secondary combustion occurs, not only the efficiency with which oxygen from the top blowing lance 1O is used for refining decreases, but also the temperature in the furnace increases excessively. On the other hand, the oxidizing gas ejected by hard blowing does not react with the CO gas, and the molten metal [
2, the decarburization efficiency increases by 2).

For example, the secondary combustion rate PCR, which is expressed by the following formula % based on the concentration in exhaust gas, is calculated as follows:
In flffi, PCR was stabilized at a low level of 15%,
-The proportion of L-blown oxygen consumed for oxidation of CO is reduced, and as a result, the decarburization efficiency is improved.

From the above two effects, the relationship shown in FIG. 3 is established between the decarburization oxygen efficiency and the recess depth L. That is, by maintaining the blowing acid condition such that the depression depth L>300ml, it is possible to ensure a high decarburization oxygen efficiency exceeding 80%. Further, the oxygen consumption rate, the alloy iron consumption rate for chromium reduction, etc. are reduced, and benefits such as shortening of the acid blowing time can be obtained.

〔Example〕

In order to process 150 tons of molten steel, the immersion tube 4 with an inner diameter of 1800 seconds was immersed in the molten steel in It. And vacuum chamber 3
The length of the immersion tube 4 and the height of the shield 12 are determined so that when the pressure inside the immersion tube 4 is reduced to 200 torr, the height from the molten steel in the immersion tube 4 to the shield 2 will be approximately 3000 zm. A diameter of 40 m from the lance insertion hole 13 in the center of the shield 12
A single-hole double-blow lance 10 was exposed to the vacuum [3].

I took crude molten stainless steel of 80% CD and 15% Cr melted in a converter. 1 was accepted. The temperature of the crude molten stainless steel after receiving the steel was 1600°C. Then, vacuum decarburization was performed using the apparatus shown in FIG. 1 under the following conditions.

The acid blowing rate was kept constant at 413 ONm'/hr. The degree of vacuum was set to an initial value of 200 Torr, and then continuously controlled to a high vacuum, and set to 50 Torr after 19 minutes. Furthermore, the pressure was maintained at about 50 torr for three minutes before the first blow. In addition, the porous plug 9 at the bottom of the ladle 1
The argon gas injected from the beginning of blowing to 19 minutes was 40ONg/min, and then 500Ng/min until the end of blowing.
/I blew it.

The molten steel thus blown was decarburized as shown in Table 1. Also, almost no oxidation loss of chromium was observed.

Table 1 Changes in composition before and after blowing (%) In addition, when performing blowing in this way, as shown in Table 2,
Compared to the conventional method, the decarburization oxygen efficiency is 20% higher.
'', decarburization reduced the time by 8 minutes.

In Table 2, both the example and the conventional method use a lance with a single hole and a straight nozzle.

Table 2 Blow talk 1 and metallurgical properties [Effects of the invention] As explained above, in the present invention, a shield is placed inside the vacuum chamber to prevent soubranille from jumping up from the hot water surface. At the same time, the wall surface inside the furnace is maintained at a high temperature and the splatter is marked with a V-notch. Therefore,
It is possible to process the molten gold by hard blowing =i
In particular, it is possible to efficiently decarburize chromium-containing molten steel such as crude molten stainless steel. Moreover, since the height of the vacuum chamber can be suppressed by the shield, the entire apparatus can be made low-profile, and an apparatus with good operability can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the vacuum processing equipment of the present invention, Fig. 2 is a graph showing the relationship between the installation height of the shield and the surface temperature of the lower refractory, and Fig. 3 is a graph showing the relationship between the depression depth of the molten metal surface and the removal FIG. 4, a graph showing the relationship with carbon-oxygen efficiency, shows a vacuum processing apparatus previously proposed by the present inventors. 1: Ladle 2: Molten metal 3: Vacuum drilling
4. Dip tube 5: flange 6
: Batskin 7'15 8: Exhaust pipe 9゛Porous plug l〇2 Top blow lance 11:
Chie 7 12' mu body 13: Lance insertion hole 14: Cavity 15 guide tube I-1
: Depth of dent in hot water surface Patent applicant: Nippon Steel Corporation Representative: Masaru Ko
(2 other people) Diagram: Concavity depth L (mm) Diagram 1: Height of shielding body

Claims (1)

[Claims] 1. A ladle for storing molten metal, a vacuum chamber equipped with a dip tube at the lower end to be immersed in the molten metal, an exhaust pipe connected to a vacuum source for reducing the pressure inside the vacuum chamber, and the vacuum chamber. and a shield disposed inside the immersion tube, the shield being maintained at a height of 2 to 5 m above the hot water level in the immersion tube.