JP3969008B2 - Structure of vacuum degassing tank - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a vacuum degassing tank, particularly an RH vacuum degassing tank, used for vacuum degassing treatment of molten steel.
[0002]
[Prior art]
Conventionally, RH degassing tanks and DH degassing tanks have been used to melt steel with a low carbon (C) content. Since molten steel is repeatedly introduced into these degassing tanks, the lining refractories of the tanks are exposed to severe thermal conditions, and the parts in contact with the molten metal at the bottom of the tank are directly eroded by the molten metal. As a refractory that can withstand such severe conditions, magnesia carbon bricks with a C content of 3 to 9 mass% are used as lining refractories for vacuum degassing tanks, extending the life of the tank and further melting extremely low carbon steel. It is possible.
[0003]
For example, Japanese Patent Application Laid-Open No. 9-104915 discloses an RH degassing container in which a magnesia carbon brick having a thickness of 5 mm or less after being exposed to an air atmosphere at 1400 ° C. for 4 hours is partially or entirely lined. A refractory lining for RH degassing tanks has been proposed, in which one or more bricks are lined with metal plates or magnesia carbon bricks partially or entirely on one side, which contributes to the extension of the life of the tank. JP-A-9-41031 contains 80 to 98.5 wt% MgO, 0.3 to 5 wt% CaB ₆ and 1 to 10 wt% carbon raw material, and 1 to 8 wt% in this carbon raw material. % of expanded graphite are contained, the balance has been proposed a vacuum degassing vessel used as a lining refractory brick consisting of impurities, allowing the melting of ultra-low carbon steel.
[0004]
[Problems to be solved by the invention]
However, these conventional proposals can extend the life of the vacuum degassing tank or melt ultra-low carbon steel, but cannot satisfy both of them. Moreover, there is a problem that the refractory cost is not necessarily lowered. The present invention aims to solve these problems of the prior art, and provides a vacuum degassing tank structure that does not become an obstacle to the decarburization reaction and that has a long tank life and is economical. With the goal.
[0005]
[Means for Solving the Problems]
In the present invention, the structure of the vacuum degassing tank is a magnesia carbon brick having a C content of 2 to 4 mass% in the molten steel contact portion of the lower tank constituting the vacuum degassing tank, and the remaining portion is C. content to solve the above problems by a 6 ~ 8 mass% of magnesia carbon bricks.
[ 0006 ]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on the embodiments. Figure 1 is a cross-sectional view schematically showing an overall configuration of the applied vacuum degassing apparatus of the present invention. Thus, the vacuum degassing tank comprises an upper tank A, a middle tank B, and a lower tank C. The middle tank B may be omitted and the upper tank A and the lower tank C may be used. A reflux pipe 20 is attached to the lower shell C, and a dip pipe 30 is attached to the lower part of the reflux pipe 20. Accordingly, the molten steel is introduced into the lower tank C through the dip tube 30 and the reflux tube 20, and the lower portion thereof becomes the molten steel contact portion 10B that is directly exposed to the rising molten steel. In contrast, the upper part of the lower tank C and the upper tank A are not directly exposed to the molten steel, but are exposed to the radiant heat of the molten steel.
[ 0007 ]
In the vacuum degassing tank having such a structure, in the present invention, as shown in FIG. 2, the molten steel non-contact part 10A of the lower tank C and the lining refractories 14 and 15 of the molten steel contact part 10B are selectively used. That is, the inner refractory 15 of the molten steel contact portion 10B is magnesia carbon brick with a C content of less than 5 mass% by mass ratio, and the inner refractory 14 of the molten steel non-contact portion 10A is 5-9 mass% by mass ratio. It is a magnesia carbon brick. The lining bricks of the upper tank A and the middle tank B need not be specified as long as they can withstand rapid temperature changes due to the radiant heat of the molten steel, but the refractory lining 14 of the molten steel non-contact part 10A of the lower tank C From the viewpoint of heat-resistant spalling, it is preferable to use a magnesia carbon brick having the same C content of 5 to 9 mass%.
[ 0008 ]
The molten steel non-contact portion 10A and the molten steel contact portion 10B of the lower tank C have a common iron skin 11 , and permanent refractories 12 and 13 are stuck inside the iron skin 11 . The lining refractories 14 and 15 are lined inside the permanent refractories 12 and 13 and are directly affected by the molten steel. Of these, the molten steel non-contact portion 10A is a portion exposed mainly to radiant heat from the molten steel and splash generated from the molten steel during vacuum degassing operation, and is not directly washed by the molten steel flow. On the other hand, the molten steel contact portion 10B is a portion that is directly washed by the molten steel flow, although it depends on the magnitude of the reflux energy.
[ 0009 ]
The reason why the magnesia carbon brick whose C content is less than 5 mass% is used as the lining refractory 15 of the molten steel contact portion 10 B is that the ultra low carbon steel is melted by vacuum degassing. In other words, when the C content exceeds 5 mass%, the spalling resistance when exposed to molten steel is improved, but C in the refractory reacts with oxygen in the molten steel to become CO and deteriorates while decarburizing the molten steel. On the other hand, if C is too low, spalling is likely to occur when washed directly in the molten steel flow, and the amount of refractory wear increases. From such a viewpoint, the lining refractory 15 of the molten steel contact portion 10B is preferably a magnesia carbon brick having a C content of 2 to 4 mass%.
[ 0010 ]
The molten steel contact portion refers to a portion of the lower tank C constituting the vacuum degassing tank that is directly washed by the molten steel raised by the vacuum degassing operation, but the molten steel component, the type of degassing operation (so-called killing treatment) In the present invention, the maximum height is taken. Then, at least the inner refractory 15 of the molten steel contact portion 10B in the lower tank C is made of magnesia carbon brick having a C content of less than 5 mass%, thereby suppressing carbon pickup during the melting of the ultra-low carbon steel.
[ 0011 ]
The lining refractory 14 of the molten steel non-contact part 10A is made of magnesia carbon brick with a C content of 5-9mass%, so this part is not washed directly by the molten steel, so only considering spalling resistance This is because it only has to be done. The most excellent spalling resistance is when the C content is 5 to 9 mass%, particularly about 7 mass%, and this makes it possible to extremely reduce the refractory spalling in the vacuum degassing process. Thereby, while being able to reduce the amount of refractory wear, it is possible to prevent the spalled refractory from falling into the molten steel and carburizing the molten steel. Since spalled magnesia carbon bricks have very little carburizing action, the prevention is very important for the melting of ultra-low carbon steel. Further, the magnesia carbon brick having a C content of 5 to 9 mass% has an extremely low wear rate. Therefore, the thickness of the construction part can be reduced, and the construction cost can be reduced.
[ 0012 ]
FIG. 4 shows the results of determining the relationship between the amount of brick wear and the C content in magnesia carbon brick when the molten steel is rimmed using the RH vacuum degassing tank in the non-contact portion of the molten steel. From this figure, in the non-contact part of the molten steel, if the C content in the magnesia carbon brick is too high or too low, the amount of wear of the brick will increase and the life of the RH vacuum degassing tank will be shortened. However, it is clear that stable melting of low carbon steel and ultra low carbon steel is hindered. In the region where the C content is high, the reaction of MgO + C → Mg + CO is presumed to be caused by deterioration of the brick under high temperature and high vacuum. On the other hand, in the region where the C content is low, the brick is worn due to progress of wear due to thermal spalling It is assumed that the amount will increase. Therefore, it can be said that the magnesia carbon brick used in the non-contact part of the molten steel has a long life in terms of the amount of wear when the C content is 5 to 9%. As can be seen from FIG. 4 , the C content is preferably 6 to 8 mass%.
[ 0013 ]
The magnesia carbon brick used in the present invention is a refractory material obtained by mixing magnesia and a carbon-containing material, and includes phenol resin, pitch, etc. as a binder, and Al, Si, CaB ₆ as a carbon antioxidant. In some cases, metal elements such as C content is the mass ratio of magnesia and graphite used as raw material, that is, (mass of raw material graphite) / (mass of raw material magnesia + mass of raw material graphite)
C included in the binder is excluded.
[ 0014 ]
The features of the RH degassing tank according to the present invention are as described above, and other points are not different from those conventionally known. That is, considering that the refractory 21 of the reflux pipe 20 is a refractory in contact with molten steel, the C content is less than 5 mass% by mass ratio, preferably 2 to 4 mass% magnesia carbon brick, and the dip pipe 30 This refractory may be constructed as magnesia chromite brick, less than 5 mass% magnesia carbon brick, or composite brick of these.
[ 0015 ]
【Example】
As an example of the present invention, one having a lower tank of a vacuum degassing tank having a structure shown in FIG. 2 was prepared. The lining refractory 15 of the molten metal contact portion 10B was a magnesia carbon brick having a C content of 3 mass%, and its construction thickness was 450 mm. On the other hand, the lining refractory 14 of the molten steel non-contact part 10A was a magnesia carbon brick having a C content of 7 mass%, and its construction thickness was 360 mm. As a comparative example, a magnesia carbon brick with a C content of 3 mass% was used as the lining brick in the lower tank for the molten steel contact part and the molten steel non-contact part , and a construction thickness of 450 mm was prepared.
[ 0016 ]
When vacuum degassing operation was carried out for these, in the case of the present invention example, it had a life of 500 charges , whereas in the case of the comparative example, the refractory lining the non-contact portion of the molten steel was worn out by thermal spalling. , 350 charge life. Further, in the case of the present invention example, there was virtually no occurrence of a carburizing accident during the vacuum degassing operation, whereas in the case of the comparative example, carburization occurred every time the magnesia carbon brick was spalled off by spalling. There was also an increase in operating hours.
[ 0017 ]
Although the case where the present invention is applied to the RH degassing tank has been described above, the technical idea of the present invention can also be applied to a DH degassing apparatus. That is, the part of the refractory lining of the DH degasser that is washed by the molten metal is a magnesia carbon brick whose C content is 5% or less, preferably 2 to 4% by mass, and the part where the molten metal does not rise is the C content. The mass ratio may be 5 to 9 mass % magnesia carbon brick.
[ 0018 ]
【The invention's effect】
The present invention has a structure in which the refractory lining the vacuum degassing tank is used separately for the molten metal contact portion, the portion that receives the width of the molten steel, and the non-contact portion of the molten steel, thus extending the life of the refractory In addition, it is possible to effectively prevent carburization when melting ultra-low carbon steel.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the overall configuration of a vacuum degassing apparatus to which the present invention is applied.
FIG. 2 is a cross-sectional view schematically showing the structure of a vacuum degassing tank according to the present invention.
FIG. 3 is a cross-sectional view schematically showing the structure of a vacuum degassing tank which is a comparative example of the present invention.
FIG. 4 is a graph showing the relationship between the amount of brick wear and the C content in magnesia carbon brick when processing molten steel using an RH vacuum degassing apparatus.

Claims (1)

C content of the molten steel contact portions of the refractory lining of the lower vessel constituting the vacuum degassing vessel and 2 ~ 4 mass% of magnesia carbon bricks, the remaining portion C content of 6 ~ 8 mass% magnesia carbon Structure of vacuum degassing tank characterized by being made of brick.

Images