JP6638538B2 - RH type vacuum degassing equipment - Google Patents

Description

  The present invention particularly relates to an RH vacuum degassing apparatus suitable for use in increasing the speed of a degassing reaction.

  Impurity elements in the steel material reduce the strength of the steel material or generate non-metallic inclusions and serve as starting points for destruction. Therefore, the impurity elements are removed in the refining process. In particular, in the secondary refining, the molten steel is subjected to refining treatment in a reduced pressure atmosphere using a vacuum degassing apparatus, so that gas elements such as carbon (hereinafter, C), hydrogen (hereinafter, H), and nitrogen (hereinafter, N) can be obtained. Perform removal. In the vacuum degassing process, a process using an RH type vacuum degassing device is widely performed.

  It is conventionally known that the removal of gas elements using an RH-type vacuum degassing apparatus is effective in reducing the atmospheric pressure, increasing the annular flow rate of molten steel, and increasing the interfacial area where degassing reaction occurs. . Therefore, the evacuation capacity has been enhanced in order to reduce the atmospheric pressure. Also, the circulating gas flow rate has been increased in order to increase the circulating flow rate of molten steel. Furthermore, regarding the increase of the interfacial area where the degassing reaction occurs, the surface area of the molten steel exposed to the reduced-pressure atmosphere has been increased by increasing the size of the vacuum chamber. However, these methods involve a substantial remodeling of the apparatus and are difficult in practice. Therefore, in the RH type vacuum degassing apparatus, the speed of the degassing reaction utilizing bubbles blown into molten steel as reflux gas is considered. Improvement methods have been proposed.

  Patent Document 1 proposes a vacuum degassing method for molten steel in which the temperature of a gas supplied to a tuyere into which a reflux gas is blown is heated to 200 to 1200 ° C. It is stated that when this method is used, the expansion of bubbles of the reflux gas when heated to the temperature of molten steel is suppressed, and the bubbles become finer.

  Patent Literature 2 proposes an immersion pipe of an RH degassing apparatus provided with an ultrasonic vibrator at an inner peripheral portion of an immersion pipe near a tuyere into which a reflux gas is blown. By using this immersion tube, it is described that bubbles can be miniaturized by ultrasonic vibration.

  Patent Literature 3 proposes a method of refining by selecting whether the gas bubbles to be blown into the molten metal in the riser are uniform or concentrated at the center according to each refining time. According to this method, bubbles are miniaturized by blowing high-pressure reflux gas through a tuyere of a tuyere in order to concentrate the bubbles at the center of the riser.

JP-A-6-17114 JP-A-2-173205 JP-A-1-168809

  However, the method described in Patent Literature 1 has a problem in that the recirculation gas is heated and blown, which promotes the erosion of refractory, especially around the tuyere, and increases the frequency of repair of the refractory. Further, the immersion tube described in Patent Document 2 has a problem that the life of the ultrasonic vibrator is short in molten steel, and the frequency of replacing the ultrasonic vibrator increases. Furthermore, the method described in Patent Document 3 has a problem that the pressure of the gas needs to be increased in order to concentrate the circulating gas bubbles at the center of the immersion tube, and the equipment needs to be largely remodeled.

  Therefore, the present invention provides an RH-type vacuum degassing apparatus capable of accelerating the degassing reaction by reducing the frequency of repair and replacement, minimizing the frequency of repair and replacement, and obviating the need for major remodeling of the apparatus. The purpose is to do.

  In order to solve the above problems, the present inventors collided high-speed bubbles ejected from adjacent reflux gas tuyeres, and molten steel droplets entrained in the bubbles through the collision interface collided with the surface of the bubbles. In doing so, we studied a method of generating fine bubbles by disrupting the bubble surface and breaking them up.

  In order for the bubbles ejected from the tuyere that injects the circulating gas to collide with each other and the molten steel droplet to be caught in the bubbles, molten steel exists between the bubbles immediately before the collision between the bubbles. It is necessary. In addition, it is necessary to make the collision angle between the bubbles appropriate.

  Bubbles blown into the molten steel in the riser tube through the tuyere are due to poor wettability between the refractory and the molten steel, high interfacial tension with the molten steel, and rapid heating to the molten steel temperature and rapid expansion. The area in contact with the refractory increases. Therefore, if the linear distance between the tuyere outlets of the adjacent tuyere pairs (the linear distance connecting the centers of the tuyere outlets) is small, the bubbles coalesce immediately after leaving the tuyere, and the molten steel droplet Do not get involved. If the straight line distance between the tuyere outlets is large, the bubbles will not collide with each other.

  Regarding the collision angle between the bubbles, when the angle is small, the bubbles are united and the molten steel droplet is not caught in the bubbles. When the angle is large, the area where the bubbles contact the refractory wall surface becomes too large, and the number of fine bubbles generated by the collision decreases.

  Thus, it can be seen that in a tuyere pair having a pair of adjacent tuyeres, there is an appropriate range for the linear distance between the tuyere outlets and the angle at which the tuyees face each other. The appropriate range was examined by experiments using molten steel. The experiment was performed by the following method.

  First, the tuyere of a stainless steel pipe with an inner diameter of 0.0015 m was placed 0.3 m above the bottom of a MgO crucible (inner diameter 0.75 m, height 2.0 m) installed in a chamber capable of controlling the atmosphere. Two pieces of Ar gas were installed on the upper side so as to eject the gas horizontally, and the straight distance between the tuyere outlets and the facing angle between the tuyeres were arranged in several ways.

  The molten steel is heated to 1600 ° C. in a crucible, and an alloy is added so that the C concentration is 0.005 to 0.10% by mass, the Al concentration is 0.020 to 0.10% by mass, and the S concentration is 0.0010%. The concentration of N was adjusted to 0.0038 to 0.0042% by mass. After adjusting the component concentration, the chamber was evacuated to a vacuum and the pressure was controlled to 133 to 4000 Pa under an Ar atmosphere. After the pressure was stabilized, Ar gas was passed through the tuyere. The Ar gas flow rate was 80 NL / min in total. The gas was flowed for 10 minutes, the bubbles floating on the surface of the molten steel were photographed, and the bubble diameter was measured. In addition, the N concentration of the samples collected before and after gas injection was quantified by analysis.

  The bubbles having a diameter of 0.01 m or less are defined as fine bubbles, and the relationship between the ratio of the fine bubbles to the total number of bubbles (hereinafter referred to as the fine bubble presence ratio) and the angle at which the adjacent tuyere pairs face each other is shown in FIG. When the straight-line distance between the tuyere outlets was 0.07 m or less, the fine bubble existence rate was low regardless of the angle at which the tuyere pairs faced each other. This is because the linear distance between the tuyere outlets was small, and the bubbles expanding at the tuyere outlets came into contact with each other, so that the molten steel droplets were not involved and fine bubbles were not generated.

  On the other hand, when the straight-line distance between the tuyere outlets was 0.08 to 0.29 m, the microbubble abundance significantly increased when the tuyere pairs faced each other at an angle of 70 to 120 °. This is because at 69 ° or less, the collision angle between the bubbles was small, the molten steel droplet was not involved at the interface of the collision, and fine bubbles were not generated, and at 121 ° or more, the bubbles always contacted the wall surface, This is because the generated fine bubbles are absorbed by the large-diameter bubbles.

  When the straight-line distance between the tuyere outlets was 0.30 m or more, the microbubble abundance ratio was low regardless of the angle at which the tuyere pairs faced each other. This is because the straight-line distance between the tuyere outlets is large, and no collision between bubbles occurs.

  FIG. 1B shows the relationship between the denitrification amount obtained by subtracting the N concentration after the gas injection from the N concentration before the gas injection and the angle at which the adjacent tuyere pairs face each other. When the linear distance between the tuyere outlets where the fine bubble abundance ratio was high was 0.08 to 0.29 m and the angle at which the tuyere pairs faced was 70 to 120 °, the denitrification amount also became high. This is because the interface area where the denitrification reaction occurs due to the fine bubbles has increased.

  FIG. 2A shows the relationship between the fine bubble existence rate and the linear distance between the tuyere outlets. As described above, the facing angle of the tuyere pair is 70 to 120 °, the linear distance between the tuyere outlets is 0.08 to 0.29 m, and the fine bubble existence rate is high, When the linear distance was 0.08 to 0.20 m, the fine bubble existence ratio was particularly high.

  FIG. 2B shows the relationship between the amount of denitrification and the linear distance between the tuyere outlets. The amount of denitrification increases when the tuyere pair with a high microbubble abundance ratio is 70 to 120 ° and the linear distance between the tuyere outlets is 0.08 to 0.20 m. The angle at which the tuyere pairs face each other was 70 to 120 °, and the linear distance between the tuyere outlets was particularly large at 0.08 to 0.20 m.

The present invention has been made as a result of such studies, and its gist lies in the following RH type vacuum degassing apparatus.
(1) The straight-line distance between the tuyere outlets of a pair of tuyere pairs adjacent to each other into which an inert gas is blown is 0.08 to 0.29 m, and the facing angle between the tuyeres is 70. An RH-type vacuum degassing apparatus comprising a dip tube provided with one or more tuyere pairs of up to 120 °.
(2) The RH type vacuum degassing apparatus according to the above (1), wherein a linear distance between the tuyere outlets is 0.08 to 0.20 m.

  According to the present invention, there is provided an RH-type vacuum degassing apparatus capable of accelerating the degassing reaction by reducing the frequency of repair and replacement, minimizing bubbles of recirculation gas, and obviating the need for extensive remodeling of the apparatus. can do.

It is a figure which shows the relationship between the microbubble presence ratio and the amount of denitrification, and the angle which the adjacent tuyere pair faces. It is a figure which shows the relationship between the fine bubble existence rate and denitrification amount, and the linear distance between tuyere exits. It is a figure which shows the example of a schematic structure of the RH type vacuum degassing apparatus of this invention.

  Hereinafter, the RH type vacuum degassing apparatus of the present invention will be described by taking as an example a case where the apparatus is used in secondary refining of molten steel.

(1) Apparatus configuration FIG. 3 is a view showing a schematic configuration example of an RH type vacuum degassing apparatus of the present invention, and FIG. FIG. 3B is a longitudinal sectional view. As shown in FIG. 3 (b), the RH type vacuum degassing apparatus includes a vacuum tank 1, and an ascending pipe 2 and a descending pipe 3 provided at the bottom thereof. The riser 2 has a tuyere 4 into which a reflux gas is blown. The upper part of the vacuum chamber 1 is connected to a vacuum exhaust device 5. When performing the refining process of molten steel, the riser pipe 2 and the descender pipe 3 are immersed in the molten steel 7 in the ladle 6. Slag 8 covers the surface of molten steel 7 in the ladle.

  The RH type vacuum degassing apparatus of the present invention may be the same as a normal RH type vacuum degassing apparatus except for the tuyere for injecting the reflux gas. However, the tuyere into which the reflux gas is blown must satisfy the requirements of the present invention. That is, the linear distance between the tuyere exits of the adjacent tuyere pairs (the linear distance connecting the centers of the paired tuyere) must be 0.08 to 0.29 m, and the facing angle must be 70 to 120 °. is there. Further, as can be seen from the above experimental results, it is more desirable that the straight line distance between the tuyere exits of adjacent tuyere pairs is 0.08 to 0.20 m.

  The number of tuyeres is desirably 8 to 24 holes (4 to 12 tuyere pairs). If the number of tuyeres is less than 8, the uneven distribution of the circulating gas in the immersion tube is likely to occur, causing poor mixing due to a decrease in the circulating flow rate, which may lower the processing efficiency. On the other hand, if the number of tuyeres is more than 24 holes, the pressure loss of the reflux gas in the tuyere piping will increase, and the gas flow required for the refining process may not be able to be blown. May be affected by the reflux gas.

  The inner diameter of the tuyere is desirably 2 to 7 mm. If the inner diameter of the tuyere is smaller than 2 mm, the pressure loss of the circulating gas in the tuyere pipe becomes large, and the gas flow required for the refining process may not be able to be blown. If the inner diameter of the tuyere is larger than 7 mm, molten steel may enter the tuyere, causing the tuyere to melt.

(2) Treatment method After the decarburization treatment is performed in the converter and the steel is output to the ladle, the ladle is transferred to the RH type vacuum degassing apparatus shown in FIG. 3 (b), and the refining treatment is started. Refining by gas bubbling in a ladle for the purpose of reducing and desulfurizing FeO and MnO in the slag may be performed before degassing after tapping.
The immersion tubes (the riser tube 2 and the downcomer tube 3) are immersed in the molten steel 7 in the ladle 6, and at the same time, the reflux gas is blown into the riser tube 2 through the tuyere 4, and the inside of the vacuum tank 1 is further depressurized by evacuation. The molten steel 7 is sucked into the tank 1. As the reflux gas, for example, an inert gas such as an Ar gas is used.

  The flow rate of the reflux gas is preferably in the range of 4.0 to 14.0 NL / (t · min) per ton of molten steel. When the recirculation gas flow rate is less than 4.0 NL / (t · min), the recirculation flow rate of the molten steel becomes insufficient and the smelting treatment efficiency decreases, and when the recirculation gas flow rate exceeds 14.0 NL / (t · min). In addition, when bubbles of the reflux gas break, the amount of scattered molten steel increases. When the RH-type vacuum degassing apparatus of the present invention is used, it is more preferable to set the number to 7.0 NL / (t · min) or more from the viewpoint of keeping the number of fine bubbles high.

  The pressure in the vacuum chamber is desirably in the range of 67 to 13300 Pa. If the pressure is less than 67 Pa, it takes too much time to evacuate, and the amount of molten steel scattered when bubbles of the reflux gas break. On the other hand, when the pressure in the vacuum chamber exceeds 13300 Pa, the annular flow rate becomes insufficient, and the smelting process efficiency decreases. When using the RH-type vacuum degassing apparatus of the present invention, in order to quickly discharge the gas element removed by the degassing reaction to the outside of the vacuum chamber, it is required to be 67 to 3990 Pa during the period of the degassing reaction. It is more desirable to do.

In the case of using the RH type vacuum degassing apparatus of the present invention, in addition to degassing, component adjustment by addition of an alloy, fine fine particles suspended in molten steel are performed similarly to a normal RH type vacuum degassing apparatus. Refining processes such as floating removal of inclusions, temperature rise utilizing Al oxidation heat generated by blowing O ₂ gas from a lance installed above molten steel in a vacuum chamber, desulfurization by addition of a desulfurization flux, and the like can be performed.

  Hereinafter, an example of the present invention will be described, but the conditions in the example are one condition example adopted to confirm the operability and effects of the present invention, and the present invention is limited to this one condition example. It is not something to be done. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  After the decarburization treatment was performed in the converter, 300 tons of molten steel were tapped into the ladle. At the time of tapping, a deoxidizing element and a flux were added, and the molten steel was transferred to the RH-type vacuum degassing apparatus together with the ladle. After the transfer, the ascending pipe and the descending pipe were immersed in the molten steel in the ladle, and while the reflux gas (Ar gas) was being blown from the tuyere, the inside of the vacuum chamber was evacuated to start degassing. The pressure in the vacuum chamber was 67 to 6700 Pa, and the reflux gas flow rate was 2000 to 3000 NL / min. The degassing process was performed for 15 to 25 minutes, and samples were taken at the start of the process and immediately after the process, and the degassing ability was evaluated based on changes in the H concentration and the N concentration.

  Table 1 shows changes in H concentration and N concentration before and after the treatment.

  Test No. 1 which is an RH type vacuum degassing apparatus of the present invention example In Examples 1 to 4, the H concentration was reduced to 1.5 ppm and the N concentration was reduced to 0.0030% by mass or less. On the other hand, Test No. In No. 5, the straight line distance between the tuyere outlets of the tuyere pair was small, and the bubbles merged immediately after leaving the tuyere, and fine bubbles were not generated. It is considered higher. Test No. In No. 6, it is considered that the H concentration and the N concentration after the treatment increased because the linear distance between the tuyere exits of the tuyere pair was large, the bubbles did not collide with each other, and no fine bubbles were generated. Test No. In No. 7, the angle at which the tuyere pairs face each other was small, and when the bubbles collided, they coalesced without involving the molten steel droplet, and the H concentration and the N concentration after the treatment increased because fine bubbles were not generated. Conceivable. Test No. In No. 8, it is considered that the H concentration and the N concentration after the treatment were increased because the facing angle of the tuyere pair was large, the area where the bubbles contacted the refractory became large, and no fine bubbles were generated.

DESCRIPTION OF SYMBOLS 1 Vacuum tank 2 Rise pipe 3 Down pipe 4 Tuyere 5 Vacuum exhaust device 6 Ladle 7 Molten steel 8 Slag

Claims (2)

  The straight-line distance between the tuyere outlets of two tuyere pairs adjacent to each other into which an inert gas is blown is 0.08 to 0.29 m, and the facing angle between the tuyeres is 70 to 120 °. An RH type vacuum degassing apparatus characterized by having a dip tube provided with at least one tuyere pair.   The RH type vacuum degassing apparatus according to claim 1, wherein a straight distance between the tuyere outlets of the tuyere pair is 0.08 to 0.20m.

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