JPH01275715A - Vacuum degassing treatment of molten steel by rh type degassing device - Google Patents

Abstract

PURPOSE:To prevent the intrusion of ladle slag into a molten steel and to improve the cleanliness of the molten steel by blowing an inert gas out of the outside circumference in the outside part of an immersion pipe to the outside. CONSTITUTION:Plural pieces of gas supply openings 7 are arranged circumferentially to the outside circumference in the lower part of a downcomer 11 and are provided to face upward. The inert gas is blown out of the openings 7 into the molten steel 12 through a gas supply system 5 and a gas passage 6 embedded into the refractories of the downcomer 11. The downward flow generated when the gas is sucked toward the outside circumference of the downcomer 11 is, therefore, blocked by utilizing the buoyancy of the inert gas and the intrusion of the slag 4 in a ladle 1 into the molten steel is prevented even if the flow rate of the molten steel 12 flowing down in the downcomer 11 is high. This method is, therefore, effective for the degassing treatment intended to improve the cleanliness of the molten steel.

Description

[Detailed description of the invention]

<Industrial Field of Application> The present invention relates to a method for vacuum degassing treatment of molten steel, and particularly to a method for preventing slag from being entrained in a ladle around the ascending side immersion pipe and the descending side immersion pipe of an RH degassing device. The present invention relates to a method for vacuum degassing treatment of molten steel using an RH type degassing apparatus. <Prior art> As shown in FIG. 2, the RH type degassing device has a rising side immersion pipe 10 (hereinafter referred to as the rising pipe) and a descending side immersion pipe 11 (hereinafter referred to as the downcomer pipe) provided at the lower end of the degassing tank 1. ) immersed in the molten steel 12 in the ladle 2 and sucked up the molten steel 12 by reducing the pressure in the degassing tank 1, and the inert gas supplied from the gas injection system 3a was provided in the riser pipe 10. The gas is blown in from the gas blowing port 3. The molten w412 is raised using a gas flotation blade of inert gas blown into the riser pipe 10 and guided to the degassing tank 1, and then lowered through the downcomer pipe 11 which is not equipped with a gas supply port to remove the molten steel 1.
2 is circulated to perform degassing treatment. Therefore, the amount of molten steel that passes through the degassing tank 1 per unit time (hereinafter referred to as the recirculation flow rate) has a large effect on the time required for degassing treatment, that is, on the degassing treatment capacity. As the amount of gas increases, efforts have been made to increase the degassing reaction rate by increasing the flow rate of molten steel. It has been believed that increasing the flow rate of the recirculation gas and increasing the inner diameter of the immersion pipe are effective ways to increase the recirculation flow rate.
For example, as disclosed in Japanese Unexamined Patent Publication No. 51-6103, an inert gas is blown vertically into the riser pipe from a gas inlet provided near the center of the horizontal section at the lower end of the riser pipe to increase the amount of blown gas. An increase in flow rate has been achieved. <Problems to be Solved by the Invention> However, as the recirculation flow rate increases, the flow velocity due to the rise of the molten steel 12 into the riser pipe 10 or the fall of the molten steel 12 from the downfall pipe inevitably increases, and the slag in the ladle 2 increases. 4 is molten steel 12
In particular, a downward flow of molten steel 12 as shown by the white arrow occurs near the outer periphery on the downcomer pipe 11 side compared to the riser pipe 10 side, and the slag 4 is easily sucked into this downward flow. . Conventionally, as a measure to prevent such slag entrainment, the downcomer pipe 11
The diameter of the descending pipe 11 is increased to increase the immersion depth h (see Fig. 2) into the molten steel 12, thereby entraining the slag 4. Although measures have been taken to prevent this, all of them have the disadvantage that they increase the cost of the refractory material for the downcomer pipe 11 and are not economical. The present invention solves the above-mentioned conventional problems and is capable of vacuum degassing of molten steel using an RH type skin degassing device that prevents slag from being caught in the ladle even when the molten steel flow velocity increases with an increase in the recirculation flow rate. The purpose is to provide a processing method. Means for Solving the Problems> The present inventor has conducted extensive research on the ladle slag entrainment phenomenon caused by the downward flow of molten steel from the downcomer pipe, where slag entrainment is particularly significant among the riser pipe and the downcomer pipe. FIG. 4 shows the state of the flow near the downcomer pipe 11' in a water model experiment. When the flow velocity of the water 12' flowing down in the direction of the arrow in the downcomer pipe 11' increases, a flow shown by a white arrow is generated near the surface of the water 12' stored in a container (not shown), causing pseudo slag 4'. It was found that a portion of the water was caught in this flow and guided downward along the outer periphery of the downcomer pipe 11'. It was discovered that the entrainment of the pseudo slag 4' occurs depending on the conditions of the water flow, that is, it occurs when the flow is sucked up to the outer periphery of the downcomer pipe 11', but does not occur when the flow leaves the outer periphery of the downcomer pipe 11'. Ta. Therefore, in a water model experiment, as shown in FIG. 3, a gas blowing lower 'is provided outward at the bottom of the downcomer pipe 11', and the argon gas supplied from the gas supply system 5a' is blown out to reduce the buoyancy caused by the rise of the argon gas. It has been found that the downward flow generated near the outer periphery of the downcomer pipe 11' can be reduced as shown in FIG. 4, or can be made to rise as shown in FIG. 3. As a result of a series of water model experiments as described above, we found that the negative pressure region around the outer circumference of the downcomer pipe can be eliminated by blowing inert gas toward the outer circumference of the downcomer pipe, and the present invention was achieved. This is what I came to do. The present invention provides a method for vacuum degassing treatment of molten steel using an RH type skin degassing device equipped with an ascending side immersion pipe and a descending side immersion pipe at the lower end of the degassing tank. A plurality of gas outlets are arranged in the circumferential direction on one or both of the outer peripheries of the lower part of the pipe and are provided facing outward, and inert gas is blown out from the gas outlets to direct the circulating molten steel into the ladle. This method is characterized by performing vacuum degassing treatment while preventing slag entrainment on the internally molten steel. The structure of the present invention will be described based on FIG. 1 with a gas outlet 3 provided on the downcomer pipe 11 side. Components in the figure that are the same as those in FIG. 2 above are given the same reference numerals to facilitate explanation. In FIG. 1, a plurality of gas blowing lowers are arranged circumferentially on the outer periphery of the lower part of the downcomer pipe 11 and are provided facing outward, and a gas passage 6 is buried in the gas supply system 5 and the refractory material of the downcomer pipe 11.
Inert gas is blown into the molten steel 12 from the gas blowing lower through the gas blowing lower. <Function> The present invention blows inert gas outward from the lower outer periphery of the downcomer pipe 11 by the above-described means, so that even if the flow velocity of the molten steel 12 flowing down in the downcomer pipe 11 is high, it is attracted to the outer periphery of the downcomer pipe 11. The buoyancy of the inert gas is used to block the downward flow of molten steel around the downcomer pipe 11, rather than turning it upward as shown by the white arrow. This prevents crowding. In addition, in FIG. 1, a case in which a gas blowing lower is provided only in the descending pipe 11 has been explained, but when slag entrainment occurs due to the suction flow accompanying the rise of molten steel on the rising pipe 10 side, the gas blowing lower is provided in the upper pipe 10 in the same way. It is preferable to install a lower pipe, and depending on the equipment and operating conditions, it is preferable to install a lower pipe.
It is also possible to provide a gas blowing lower only on the 0 side. <Embodiment> A preferred embodiment of the present invention will be described below based on the drawings. In the RH type skin degassing apparatus shown in FIG. 1, a rising pipe 10 and a descending pipe 11 each having an inner diameter of 550 φ are placed at the lower end of a degassing tank 1, and a molten steel (chemical composition C: 0.04%, Si: 0.01%, Mn
: Q, 20%. A1: Immersion depth 40 in molten steel 12 (0.040%)
After being immersed at a depth of 0 mm, the pressure was reduced and the molten steel 12 was sucked into the degassing tank 1. Then, gas inlets 3 to 1 for circulation provided in the riser pipe 10
500 f 7 minutes of argon gas is blown in to circulate the molten steel 12 and from the gas blowing lower installed in the downcomer pipe 11 to prevent slag entrainment.2004! Vacuum degassing was performed while blowing argon gas at a rate of 1/2 min. For comparison, a vacuum degassing process was carried out under the same conditions with the amount of inert gas from the gas blowing lower for slag entrainment in the downcomer pipe 11 being zero. Figure 5 shows the RHH gas treatment time and the molten steel oxygen in ladle 2 when performing vacuum degassing treatment under the above treatment conditions.

This is a plot of the relationship with [0]. As is clear from Figure 5, when the amount of argon gas to prevent slag entrainment is reduced to zero, the rate of decrease of molten steel [0] is slow (and

The concentration of [0] is high. This is because the molten steel is reoxidized due to the inclusion of ladle slag. On the other hand, when argon gas to prevent slag entrainment is blown into the ladle at 2001/min, there is no slag entrainment, so the deoxidation rate increases, and the oxygen concentration reached

It can be seen that [0] is also decreasing. <Effects of the Invention> As explained above, it is possible to prevent ladle slag from being drawn into molten steel by blowing inert gas outward from the outer periphery of the immersion tube, which aims to improve the cleanliness of molten steel. It is effective for degassing treatment and can easily obtain highly clean molten steel.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a preferred embodiment of the present invention, FIG. 2 is a sectional view showing a conventional example, FIGS. 3 and 4 are partial sectional views showing a water model experiment example, and FIG. Oxygen in molten steel (0)
It is a graph showing the relationship between RHH processing time and RHH processing time. l... degassing tank, 2... ladle, 3...
・Recirculation gas outlet, 4... Ladle slag, 5...
・Gas supply system, 6... Gas passage, 7... Gas outlet for preventing slag entrainment, 10... Rising side immersion pipe,
11... Descending side immersion pipe, 12... Molten steel. Patent applicant: Kawasaki Steel Corporation Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 RH processing time

Claims (1)

[Claims] In a method for vacuum degassing treatment of molten steel using an RH type degassing device equipped with an ascending dip tube and a descending dip tube at the lower end of the degassing tank, the lower outer periphery of the ascending dip tube and the lower outer circumference of the descending dip tube are A plurality of gas outlets are arranged circumferentially and facing outward in one or both of the gas outlets, and by blowing out inert gas from the gas outlets, the circulating molten steel flow is exposed to the surface of the molten steel in the ladle. A method for vacuum degassing treatment of molten steel using an RH type degassing device, characterized in that vacuum degassing treatment is performed while preventing slag entrainment.