JPS59159917A - Adding method of additive in degassing treatment of molten steel - Google Patents

Abstract

PURPOSE:To improve the yield of addition with an additive having a high vapor pressure as well and to reduce the time for treatment in a method for adding an additive simultaneously with a degassing treatment by feeding under pressure the additive, which is preliminarily melted, to the descending flow in the RH degassing treatment. CONSTITUTION:A molten additive 18 which is melted in a melting furnace is preliminarily contained in a hermetic vessel 17, and the connecting pipe part 16C of a hollow member 16 is connected to a joint 15 on the outside of the adding port 13 of a downcomer 8 provided to an RH degassing treatment tank 1. Gaseous Ar is then blown into a riser 7 to circulate the molten steel between a ladle 5 and the tank 1. The open-shut device 14 of the port 13 is opened and at the same time a valve 19 is opened to supply the pressurized gas into the vessel 17, by which the inside of the vessel 17 is pressurized and the additive 18 is fed under pressure into the descending flow 4A of the molten steel in the pipe 8 through the member 16. The purpose is attained by the above-mentioned method and in addition, the erosion of the refractory in the tank 1 is decreased and the need for washing the treating tank is eliminated in the case of treating continuously different kinds of steels.

Description

Detailed Description of the Invention This invention provides a method for degassing molten steel tapped from a refining furnace such as a converter using an RH degassing device, and simultaneously adjusting components, deoxidizing, desulfurizing, etc. The present invention relates to a method of adding additives for molten steel.

As is well known, in the refining process of high-grade steel, etc., molten steel that has undergone primary refining (decarburization refining) in a refining furnace such as a converter is degassed using an RH degassing device or a DH degassing device. is often applied. On the other hand, to molten steel tapped from a refining furnace such as a converter, A7, A7 alloy, and Mn alloy are often added for deoxidation or composition adjustment, and Ti alloy is mainly used for composition adjustment. In addition, CaSi 'P was added to remove S.
In some cases, Ca alloys such as CaA1 are added.Recently, methods for adding unnecessary additives such as deoxidation, component adjustment, and removal of S are performed simultaneously with degassing treatment, and the process time is separated, for example. As shown in Fig. 1, a hot spring (-2) for adding additives is provided in the RH degassing treatment tank 1.
A method is known in which solid additives 3 in the form of shots or caramel blocks are added from the hopper 2 onto the bath surface of molten steel 4 in a degassing tank.However, conventional methods of adding There are various drawbacks as follows.

°That is, first of all, the inside of the RH degassing treatment tank is 10~
Since the pressure is reduced to about 50 torr and the condition is close to vacuum, there is a disadvantage that when adding substances with high vapor pressure such as Mn or Ca, the evaporation loss is large and the addition yield is inevitably low. be. In addition, when adding small-density additives that have a large specific gravity difference with the molten steel, such as AA, the additives tend to remain floating on the molten steel bath surface and may not be uniformly mixed into the molten steel. In general, it takes a long time for uniform mixing, and therefore the treatment time is long, resulting in a large drop in temperature of the molten steel, and furthermore, there is a drawback that the amount of erosion of the refractory lining of the RH degassing tank becomes large.

Furthermore, in the conventional method, R
The refractory lining of the H degassing treatment tank is severely damaged, and the refractory lining of the treatment tank is still contaminated by these additives, so it is necessary to clean the inside of the tank when processing different steel types continuously. This invention was made in view of the above circumstances, and even when adding substances with high vapor pressure such as Ca and Mn, the addition yield is high and it is possible to uniformly mix the additives ( It can be done quickly and requires only a short treatment time, and there is little erosion of the refractories in the RH degassing treatment tank, and cleaning of the treatment jl'! is not required even when continuously treating three different fA types. It is an object of the present invention to provide a method for adding nil and no additives in a molten steel degassing device.

That is, the addition method of the present invention has four features: melting the additive in advance in a bath, and injecting the molten additive under pressure into the downward flow of the molten steel in the RH degassing process V.

The addition method of the present invention will be explained in more detail below.

FIG. 2 schematically shows an example of a situation in which the method of the present invention is implemented, in which an RH degassing tank 175E is arranged above the ladle 5 containing the molten steel 4. The lower portions of the ascending pipe 7 and the descending pipe 8 hanging down from the treatment tank 1 are immersed in the melt@brown 4. A gas inlet 9 is provided in the middle of the riser pipe 7, and an Ar gas supply source (not shown) is connected to the inlet 9 through a valve 10 and a gas self-pipe 1.
1. Further, an exhaust port 12 is formed in the upper part of the processing tank 1, and this exhaust port 12 is connected to a vacuum pump (not shown). Such R1 (in a degassing treatment device, the inside of the treatment tank 1 is evacuated and 1O~5
By reducing the pressure to about 0 torr, the molten steel 4 is sucked up into the processing tank 1 and is passed from the gas inlet 9 to the riser pipe 7.
By blowing Ar gas into the tank at a flow rate of about 1300 to 20004/min, the melt/A4 is destroyed by the principle of an air lift pump. That is, the solution 4 in the ladle 5 rises in the riser pipe 7 and is introduced into the treatment tank 1,
Furthermore, it descends from the processing tank 1 into the downcomer pipe 8 and returns to the inside of the ladle 5.

On the other hand, an addition port 13 is formed in the wall of the downcomer pipe 8, and an opening/closing device 14 such as a sliding gate is provided on the outside of the addition port 13. Detachably connected. This hollow member 16 is for guiding molten additive 18 such as molten Ad into the addition port 13 from inside a closed container 17 arranged on the side of the processing tank 6, as will be described later. A closed container 17 contains a molten additive 1 such as molten A1 that has been melted in a separate melting furnace in advance.
8, and a pressurized gas supply source (not shown) for pressurizing the inside of the sealed container is located above the first solenoid valve 1.
9 and pressurized gas piping 20, and one end (stoke portion) 16B of the hollow member 16 is connected to the molten additive 18 in the closed container 17 from above the bath surface.
is immersed. The hollow member 16 is formed by an inverted U-shaped portion 16A located above the bath surface in the closed container 17, and is extended to hang down from one end of the inverted U-shaped portion 16A, either integrally or separately, and melted as described above. The stalk part 16'B immersed in the additive 18 is connected to the other end 1111 of the inverted U-shaped part 16A via a joint 21, and the addition port 1 of the downcomer pipe 8 is connected to the other end 1111 of the inverted U-shaped part 16A.
A connecting pipe portion 16C connected to the outside of 3 via a joint 15.
It consists of.

A gas inlet, for example, a porous plug 22, is provided at the top of the hollow member 16, that is, on the upper surface side of the top of the inverted U-shaped portion 16A.
A gas supply source (not shown) that supplies a blowing gas such as r gas is connected via a blowing gas pipe 23 and a second electromagnetic valve 24 .

Note that the sealed container 17 is placed on a load cell 25 for detecting the weight of the molten additive 18.

When carrying out the method of the present invention using the above-mentioned apparatus configuration, the melted additive 18, which is melted in a melting furnace (not shown), is stored in a closed container 17 in advance, and the opening/closing device is installed. 14 is initially closed and the connecting pipe portion 16C of the hollow member 16 is connected to the joint 15 on the outside of the addition port 13 of the downcomer pipe 8.

And the melt in the ladle 5 at the upper part of the rising pipe 7 and the descending pipe 8 @
4, the pressure inside the processing tank 1 is reduced and Ar gas is blown into the riser pipe 7, and the ladle 5-
Molten steel is circulated between treatment tanks 1.

Immediately before starting addition of the molten additive, the first solenoid valve 19 is closed and the second solenoid valve 24 is opened, thereby injecting Ar into the hollow member 16 via the porous plug 22.
A gas such as gas is blown into the porous plug 22 so that the pressure P2 at the tip thereof is approximately equal to the pressure P+ in the closed vessel 17 and is also set to be greater than the pressure P3 near the addition port 13 in the downcomer pipe 8. By setting in this way, when the switchgear 14 is opened, the molten steel in the downcomer pipe 8 is prevented from entering the hollow member 16 from the addition port 13 12 , and moreover, the gas blown into the porous plug 22 seals the hollow member 16 . container 1
It is possible to prevent the molten additive 18 in the molten additive 7 from forming. Note that the flow rate Q, 2 of the gas blown from the porous plug 22 at this time needs to be set to a smaller value than the flow rate Q+ of the gas blown into the riser 7. That is, if Q2 is equal to or larger than Ql, the molten steel will be prevented from descending in the downcomer pipe 8, and the molten steel will stagnate or flow backwards.

The opening/closing device 14 of the addition port 13 is opened with the pressure and gas flow rate of each part set as described above. Simultaneously with or immediately after the opening, the first solenoid valve 19 is opened to pressurize the inside of the sealed container 17, and the second solenoid valve 24 is closed. As a result, the molten additive 18 in the closed container 17 passes through the hollow member 16 and is injected under pressure into the molten steel descending flow 4A in the downcomer pipe 8 from the addition port 13.

When it is detected by the signal from the load cell 25 that the addition of a predetermined amount of molten additive has been completed, the second electromagnetic valve 24 is opened and the first electromagnetic valve 19 is closed. Gas is blown into the hollow member 16 and the supply of pressurized gas into the closed container 17 is stopped. At this time, the pressure P2 at the tip of the porous gelag 22 is almost equal to the pressure P inside the closed container 17, and the pressure P2 at the tip of the porous gelatinous 22 is almost equal to the pressure P inside the closed container 17.
3, and the blowing gas flow rate Q1 from the porous plug 22 is set to a value larger than the condition pressure P3 in the vicinity of the riser pipe 7.
The amount is sufficiently smaller than the blown gas flow rate Q2 in . The molten additive 18 thus flows through the hollow member 16 by blowing gas into the hollow member 16.
The flow of the molten additive 1 in the hollow member 16 remaining between the porous plug 22 and the addition port 13 is blocked.
8 is extruded into the molten steel F descending stream 4A through the addition port 13,
The addition of the molten additive 18 to the molten steel descending flow 4A is completed.

Even after all the molten additives remaining in the hollow member 16 are extruded, molten steel can be effectively prevented from entering the hollow member 16 from the addition port 13.
Just close 4.

In some cases, the porous plug 22 may be added before the addition of the molten additive 18 as described above and at the end of the addition.
It is also possible to start and stop the addition only by opening and closing the opening/closing device 14 without blowing gas into the hollow member 16. In this case, the porous plug 22 can be omitted from the hollow member 16. .

Furthermore, in the above explanation, the porous plug 22 is provided on the wall surface of the downcomer pipe 8, and the molten additive 18 is added inside the downcomer pipe 8, but in this invention, the point is that the molten steel reflux is lowered in the RH degassing process. It is sufficient to add it to stream 4 A, so that it can be added to the lower end of downcomer pipe 8 or to the downcomer pipe 8.
It may be added in the downward flow of molten steel above the upper end.

As mentioned above, in the method of the present invention, the additives are directly added to the molten steel without being exposed to RH degassing or the reduced pressure atmosphere in the treatment tank 1 before being added to the molten steel. Since the additives are added during the downward flow of molten steel from the treatment tank 1 into the ladle 5, there is no risk of them floating up and being exposed to the reduced pressure atmosphere in the treatment tank 1.
Even when adding additives containing substances with high vapor pressure such as, there is little risk of evaporation loss occurring. Still, as mentioned above, since it is added during the downward flow of molten steel, even when adding a substance whose specific gravity is significantly lower than that of Al4+, it will not float up but will be caught up in the downward flow of molten steel and will be added to the molten steel. On the other hand, it is quickly and uniformly mixed. Furthermore, in the method of this invention, since the additives are added in a molten state, they are diffused and mixed with the molten steel through a liquid-group reaction, and therefore uniformly dispersed and mixed much more quickly than when conventional solid additives are added. will be done.

On the other hand, since the additives are added during the downward flow of molten steel,
Additive components such as high concentrations of A7 and Ca do not remain in the treatment tank, so there is no risk that the refractories in the treatment tank will be damaged by high concentrations of A7 and Ca. Since there is no risk of contamination by concentrated additive components, there is no need to clean the inside of the treatment tank even when different steel types are continuously degassed.

Next, an example will be described in which an additive addition experiment was conducted using the method of the present invention and a conventional method.

In other words, the present inventors conducted 1 in the RH degassing treatment of molten steel.
When adding Fe-Mn alloy to 00 tons of molten steel, an experiment was carried out in which the molten Fe-Mn alloy was injected into the descending flow of molten steel using the apparatus shown in Fig. 2 (method of the present invention), and Fig. 1 As shown in RH
An experiment (conventional method) was conducted in which steel was dropped onto the surface of a molten steel bath in a degassing treatment tank. However, in both cases, the degassing treatment time was 10 minutes. And Mn of Fe-Mn alloy added in each method
Basic unit (Mn of added Fe-Mn alloy based on weight of molten steel)
Weight) W and Mna of molten steel by adding Fe-Mn alloy
The relationship with the degree increase amount ΔMn is shown in FIG. The straight line A in FIG. 3 corresponds to the case where the Mn yield is 100%, and therefore, in the case of the method of the present invention, the Mn yield is 100%, compared to the case of the conventional method.
It is clear that the n addition yield is stable and high.

In addition, when adding Al to 100 tons of molten steel in the RH degassing treatment of molten steel, an experiment was conducted in which molten Al was injected into the molten steel in the downward flow using the apparatus shown in Fig. 2 (method of the present invention); Using the apparatus shown in FIG. 2, an experiment (conventional method) was conducted in which Al in the form of a caramole block was dropped onto the surface of a molten steel bath in an RH degassing treatment tank. AI of molten steel before adding A7
! The concentration is more than 0.020W, and the amount of A7 added is 0.7'kg per ton of molten steel. In each experiment, degassing was continued for 10 min after adding All +6, and A
The molten steel in the ladle was sampled from three points at different depths of the molten steel at regular intervals after the addition of l, and the initial AA'78
FIG. 4 shows the results of investigating the variation in the Al concentration increase amount ΔA7 from the temperature. However, in Fig. 4, the sampling point is determined by the ratio of the depth h from the molten steel bath surface to the sampling point and the depth H from the molten steel bath surface to the bottom of the ladle (h/H
) is 0.2 : 0.5 : 0.8, and ΔA7 at the sampling point where h//H is 0.2 is (a
), ΔA7 at the sampling point where h/f( is 05) (b), ΔA7 at the sampling point where h/f is 0.8 In the case of the method of the present invention, the mixture is uniformly mixed in about 4 minutes, and therefore is uniformly mixed. It is clear that the time required for mixing is significantly shorter than before. It is also clear from FIG. 4 that the A7 yield is also improved compared to the conventional method.

Furthermore, as mentioned above, the present inventors found from the experiment shown in FIG.
Based on the fact that the method of the present invention takes about 4 minutes, the degassing treatment with the addition of AA according to the method of the present invention was performed for 100 heats, and the treatment time after adding Al was set to 4 minutes for 100 tons of molten steel. Table 1 shows the results of 100 heats of conventional Al addition degassing treatment for 8 minutes, and the average drop in temperature of molten steel before and after the treatment, and the average amount of erosion of the refractories in the RH degassing treatment tank. The average Al concentration of molten steel before treatment is 0.02%, and the average amount of A added is 0 per ton of molten steel.
It weighs 7 kg. Further, the amount of erosion loss is shown as an average value of 10 locations on the side wall of the RH degassing treatment tank that come into contact with molten steel.

Table 1 From Table 1, it is clear that by shortening the treatment time, it is possible to reduce the amount of molten steel temperature drop, and it is possible to completely prevent the melting damage of the refractories in the RH degassing treatment tank.

As is clear from the above explanation, according to the method of this invention,
The addition yield of additives is high, and especially in the case of additives containing substances with high vapor pressure such as Ca and Mn, evaporation loss is small and high addition yields can be obtained, and it is possible to uniformly mix the additives into molten steel. The process is carried out quickly, and the time required for uniform mixing is short, especially when adding substances with low specific gravity such as A7. Therefore, it is possible to shorten the processing time and reduce the temperature drop of the molten steel, and it is possible to reduce the temperature drop of the molten steel while still in the degassing treatment tank Various effects can be obtained, such as reducing erosion of refractories and eliminating the need to clean the inside of the tank even when processing different steel types continuously.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view showing an example of the situation in which the additive addition method in the conventional molten steel degassing treatment is implemented;
The figure is a schematic cross-sectional view showing the situation in which the additive addition method of the present invention is implemented, and Figure 3 is the Mn basic unit and Mn concentration when Mn alloy is added according to the method of the present invention and the conventional method. Figure 4 is a correlation diagram showing the relationship between the increase amount and the variation in the degassing treatment time after A7 addition and the increase in Al concentration in the ladle when Al is added according to the method of this invention and the conventional method. FIG. 1... RH degassing treatment tank, 4... Molten steel, 4A...
Molten steel descending flow, 8... Downcomer pipe, 13... Addition port, 18
...Melting additive. Applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Takehito Toyota (and 1 other person) 3rd drawing, 1 attachment unit rz w (-#J/-5t-t) 4th drawing 〃゛′入DA3. Diko-shin f: Irne (nin)

Claims (1)

[Claims] A method for adding additives in molten steel degassing treatment, comprising melting the additives in advance and injecting the molten additives under pressure into a downward flow of molten steel in RH degassing treatment.