JPH01298111A - RH degassing refining method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides an R
This invention relates to an H degassing refining method.

[Prior art] After steel is tapped from a converter, R is used to adjust the molten steel composition.
So-called out-of-furnace refining such as H vacuum degassing is performed. In the RH vacuum degassing method, the pressure inside the degassing tank is reduced to about 1 to 20 torr, so when the molten steel in the tank is strongly stirred, gases such as [N], [0], [H], etc. components are removed and reduced. In other words, the RH degassing tank has a removable 1
The molten steel is immersed in the molten steel in the ladle, the molten steel is sucked up into the tank under reduced pressure, and then gas is blown into one of the tubes to remove the molten steel from the ladle. The molten steel is raised to the degassing tank, while the molten steel in the tank is recycled down to the ladle through the other pipe. In this way, while stirring the molten steel, a predetermined component and a predetermined amount of alloy material are added to the molten steel to adjust the composition.

[Problems to be Solved by the Invention] Recently, when aluminum-killed steel is produced, the molten steel is not deoxidized when it is tapped from a converter, and metal aluminum, etc. is added to the undeoxidized molten steel in the next degassing process. is added to deoxidize the molten steel in a degassing tank. When molten steel is deoxidized in a degassing tank, aluminum oxide A, f? . 03
occurs in large quantities. The melting point of pure A, l'203 is 200
Since the temperature is 0°C or higher, this precipitates in the molten steel and adheres to the inner wall of the reflux pipe as it flows together with the molten steel. In an RH degassing tank, due to differences in molten steel flow conditions, the ascending pipe is usually subject to melting damage and the descending pipe is likely to be clogged. Therefore, when the number of times of processing reaches a predetermined number, the ascending pipe and the descending pipe are used interchangeably. However, when aluminum guild steel is treated, due to the large amount of deoxidized products, the amount of aluminum oxide deposited increases compared to normal treatment, the inner diameter of the reflux pipe decreases in a short period of time, and the reflux speed of molten steel decreases. do. Therefore, there are problems in that the dissolution rate of the alloy material decreases, the processing time becomes longer, and the processing cost increases.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide an RH degassing refining method that can prevent aluminum oxide from adhering to the inner wall of the downcomer pipe and prevent an extension of processing time. purpose.

[Means for resolving the division report] The RH degassing refining method according to the present invention involves immersing a pair of pipes at the bottom of the degassing tank in the molten metal in the container, sucking up the molten metal into the tank, and injecting the molten metal into one pipe. In an RH degassing refining method in which gas is blown into the tank and the molten metal is supplied together with the gas into the tank, the molten metal in the tank is circulated down into the container through the other pipe. It is characterized by the presence of a melting point depressant that produces a low melting point compound.

In this case, it is preferable to add a melting point depressant to the already deoxidized molten metal and to flow this together with the molten metal into the downcomer pipe.

[Function] In the RH degassing refining method according to the present invention, the molten metal is sucked up into the degassing tank, and while the molten metal is circulated between the molten metal container and the degassing tank, a deoxidizing agent containing aluminum is added to the molten metal. do. When the molten metal is deoxidized, aluminum oxide is generated in the molten metal, and this adheres or tries to adhere to the inner wall of the downcomer pipe, but since a melting point depressant is present in the molten metal, the high melting point aluminum oxide depresses the melting point. The aluminum oxide reacts with the agent to produce a low melting point compound, the aluminum oxide is completely or partially melted, and this low melting point compound is suppressed by the flowing molten metal and leaves the inner wall of the downcomer pipe.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

As shown in FIG. 1, the RH degassing tank 10 is a vertical cylindrical container with a diameter of about 2.2 m, and the inside thereof is lined with a refractory material. The degassing tank 10 is fixed upward in the building so as not to move substantially, and a rail is laid directly below it so that the ladle 2 can be carried in. A lift table (not shown) is provided directly below the degassing tank 10,
When ladle 2 is brought into the building and placed on the table, will it degas? ! It increases by 1 towards 10.

An exhaust hole 20 is formed in the upper part of the degassing tank 10, and the hole 20
is communicated with an exhaust blower (not shown) via a duct 21, so that the gas inside the tank is exhausted. rising pipe 1
2 and a downcomer pipe 16 are installed side by side at the lower part of the degassing tank 10, and the molten steel 4 in the ladle is sucked up into the tank under reduced pressure through these pair of pipes. The rising pipe 12 and the descending pipe 16 each have short pipes 14 and 18 connected to a pipe 13° 17 on the tank body side, respectively, so that only the short pipes 14 and 18 are immersed in the molten steel. There is. That is, when the number of treatments reaches a predetermined number, the short pipes 14 and 18 are removed from the tank body, and by replacing them and using them, the erosion of the refractory lined in the pipes is averaged out. It is supposed to be done. A thin tube 15 for blowing gas is attached to the main body side tube 13 of the riser tube. That is, the base end side of the thin tube 15 is connected to a nitrogen gas supply source and an argon gas supply source (
(not shown) and a mixed gas of N2 and Ar is blown into the molten metal passage of the tube 13 through the thin tube 15, the apparent specific gravity of the molten steel decreases and the molten steel rises in the riser tube 12. It is supposed to be done.

Further, the molten steel raised in this way is transferred from the tank to the downcomer pipe 16.
It is designed to be returned to the ladle 2 via. In this case, the initial inner diameter of the riser pipe 12 and the downcomer pipe 16 is approximately 45 mm.
0 to 580fflI11.

On the other hand, the upper side wall of the degassing tank 10 has holes 2 for introducing additives.
2 is formed, and various alloy materials and auxiliary materials are introduced into the tank through this hole 22. That is, a chute 24 is provided from the hole 22 to the plurality of hoppers 23, and when an alloy material etc. is weighed by a weighing machine provided in the hopper 23, it is added to the molten metal in the tank via the chute 24. It has become so. In this case, the hopper 23 contains ferrosilicon, ferromanganese, metal aluminum, wollastonite (CaO-8), and wollastonite (CaO-8).
iO□), fluorite (CaF2), etc. are stored.

Next, a case will be described in which undeoxidized molten steel is degassed and aluminum is deoxidized to produce aluminum killed steel.

Molten steel from a converter is tapped into a ladle 2 without being deoxidized. The [0] concentration of molten steel during tapping is adjusted to a range of 200 to 600 ppm. The ladle 2 containing this molten steel is carried directly below the degassing tank 10, and is lifted by a lift table.
1 to immerse the tube 12.16 into the molten steel 4. Also,
The gas inside the tank is exhausted through the duct 21, and the pressure inside the tank is reduced. When the pipe] 2° 16 is immersed in molten steel, the molten steel 4 is sucked up into the tank. Next, the valves of the nitrogen gas supply source and the argon gas supply source are opened, N2 gas and Ar gas are mixed at a predetermined ratio, and the mixed gas is supplied to the thin tube 15 via the flow rate control valve. When the mixed gas is blown into the molten metal flow path of the tube 13 through the thin tube 15, the apparent specific gravity of the molten steel decreases, the molten steel rises, and the molten metal level in the tank rises. When the gas that rises with the molten steel separates from the molten steel, the surface of the molten metal bubbles violently, causing splash. The molten steel sucked up into the tank descends down the downcomer pipe 16 and is returned to the ladle 2. In this way, since the molten steel 4 is circulated from the degas W110 to the ladle 2, the molten steel circulates between the ladle 2 and the degassing tank 10. As a result, the molten steel is strongly stirred, and [C] and [0] in the molten steel react to generate CO gas, and this CO gas is exhausted from the degassing tank 10, so that decarburization of the molten steel 4 is promoted. Ru.

When about 7 minutes have passed from the start of the treatment, a predetermined amount of metallic aluminum is added to the molten steel, and the molten steel is deoxidized. Immediately after this, wollastonite and fluorspar are added to the molten steel. The amount of these fluxes added is O, 1 to 1 per ton of melt fI.
It is preferable to set it as kg.

Further, the added flux is in the form of a lump with a diameter of 5 to 30111 fil, and the entire amount is quickly dissolved in the molten steel. When metallic aluminum is added to molten steel, it is oxidized into [0] in the molten steel, and aluminum oxide A i203 is precipitated. For example, aluminum oxide adheres to the inner wall of the downcomer pipe 16 and the adhesion layer 8 is likely to be formed. However, since a special flux is added as a melting point depressant to the molten steel immediately after adding the deoxidizing agent, precipitates A and 203 react with the Ca components of wollastonite and fluorite to create a low melting point compound, which is added to the molten steel. It becomes easier to dissolve. As a result, the adhesion force of aluminum oxide is weakened, the already attached aluminum oxide easily separates from the inner wall of the reflux tube, and further adhesion of aluminum oxide is prevented.

In the middle and final stages of treatment, alloy materials of a predetermined amount and composition are introduced into the tank at appropriate times to adjust the molten steel composition to the target composition. After confirming that the molten steel has been adjusted to a predetermined composition, gas injection is stopped and the process is completed. In this case, the average processing time is approximately 15 minutes.

Under the processing conditions of the above examples, aluminum killed steel was
As a result of the charge treatment, the downcomer inner diameter decreased only slightly, and the average treatment time could be maintained at about 15 minutes.

In the above examples, wollastonite and fluorite in the form of flux were used as melting point depressants, but any substance that reacts with aluminum oxide to produce a low melting point compound may be used without limitation. I can do it.

[Effects of the Invention] According to the present invention, the average processing time for aluminum killed steel in the RH degassing method can be shortened, and the processing cost can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view schematically showing a degassing tank during processing. 2; ladle, 4; molten steel, 10; degassing tank, 12; riser pipe,
14, 18; Short pipe, 15; Thin tube for gas injection, 16; Descending pipe, 23; Addition hopper Patent attorney Patent attorney Takehiko Suzue I11 Figure

Claims (3)

[Claims] (1) A pair of pipes at the bottom of the degassing tank are immersed in the molten metal in the container to suck up the molten metal into the tank, and while blowing gas into one pipe to supply the molten metal together with the gas into the tank, An RH degassing refining method in which molten metal in a tank is recycled down into a container through a pipe, characterized in that a melting point depressant that reacts with aluminum oxide to produce a low melting point compound is present near the inner wall of the downcomer pipe. Degassing refining method. (2) The RH degassing refining method according to claim 1, characterized in that a melting point depressant is added to the deoxidized molten metal, and the molten metal is passed through the downcomer pipe together with the molten metal. (3) The RH degassing refining method according to claim 1, characterized in that the inner wall of the downcomer pipe is covered with a melting point depressant.