JP6888492B2 - Molten steel refining equipment and molten steel refining method - Google Patents

Description

The present invention relates to a molten steel refining apparatus and a method for refining molten steel for spraying a single gas or a powder mixed gas from a lance arranged in a vacuum chamber onto the surface of the molten steel in the vacuum chamber in vacuum refining of molten steel.

The molten steel that has undergone primary refining in a converter or electric furnace is stored in a ladle. Vacuum refining of molten steel is performed as secondary refining for the molten steel in the ladle. In the vacuum refining process of molten steel, a wide range of refining such as component adjustment, impurity removal, temperature adjustment, etc. is performed. When performing these refining, the molten steel may be sprayed with a single gas or a refining powder mixed gas in which the gas and the refining powder are mixed from a lance installed above the molten steel housed in the vacuum chamber. A refining reaction proceeds between the sprayed gas and molten steel, or between the refining powder and molten steel. By increasing the speed of this refining reaction, it is possible to reduce the processing cost such as shortening the time required for the vacuum refining process and reducing the amount of gas or refining powder used.

As a vacuum refining device for molten steel, an RH vacuum degassing device is preferably used. As shown in FIG. 3, the RH vacuum degassing device has a vacuum tank 1, and two immersion tubes 2 are provided at the bottom of the vacuum tank 1. By immersing the immersion pipe 2 in the molten steel 24 in the ladle 5 containing the molten steel and depressurizing the inside of the vacuum chamber by the vacuum exhaust system 23, the molten steel in the ladle is sucked up and the molten steel is introduced into the vacuum chamber. To. For one of the two immersion pipes 2 (rising pipe 3), the molten steel is raised by blowing Ar gas as the reflux gas 22 from the inner wall. The molten steel that has flowed into the vacuum chamber 1 from the ascending pipe 3 flows out into the ladle via another immersion pipe (lowering pipe 4). Since the rising pipe 3 blows the recirculation gas 22 from the side surface, the refractory material is severely worn. For the purpose of leveling the refractory life of the two immersion pipes 2, the immersion pipes into which the recirculation gas is blown are replaced. Therefore, the riser pipe 3 is replaced.

Patent Document 1 is an upper blowing lance device that is inserted through the upper lid of a vacuum chamber and is provided so as to be movable up and down, and is provided at the tip of the lance of the upper blowing lance device downward with respect to the shaft core. A top-blowing lance device provided with a lance hole having an angle of 20 to 50 degrees, a mechanism for rotating the lance about the center of the axis, and a mechanism for stopping the rotation at an arbitrary position is disclosed. In order to spray powder from the lance hole onto the surface of the molten steel to promote the desulfurization reaction, etc., the lance is rotated and the rotation is stopped at an arbitrary position so as to expand the powder dispersion zone to just above the rising pipe. However, in order to provide a rotating mechanism on the lance, a large-scale equipment modification is required, resulting in high cost.

In Patent Document 2, in an oxygen-containing gas top-blowing device that blows oxygen-containing gas onto molten steel in a vacuum tank via a water-cooled top-blowing lance inserted into the vacuum tank in an RH degassing facility, a vacuum tank is provided at the tip of the water-cooled lance. We are proposing a method of blowing gas in a direction intersecting the oxygen-containing gas ejection direction on the inner surface of a nozzle installed so as to blow oxygen-containing gas toward the internally molten steel. However, this lance is only used for spraying gas only, and when the refining powder is mixed with gas and sprayed, the powder is clogged in the gas blowing hole.

In Patent Document 3, an oxygen-containing gas top blower in an RH degassing facility, a top blow lance that blows oxygen onto molten steel in a vacuum chamber, and a circular opening for injecting oxygen is the tip of the top blow lance. A method has been proposed in which a plurality of portions are provided to disperse the oxygen flow sprayed on the molten steel. In a conventional lance nozzle that blows gas onto molten steel in a vacuum chamber, gas at a flow velocity exceeding the speed of sound is blown from a lance provided with one Laval nozzle. The sprayed gas concentrates on one place on the surface of the molten steel, and the molten steel scatters, causing the metal in the vacuum chamber to adhere. By using the lance described in Patent Document 3, it is said that the gas flow can be dispersed and the amount of droplets generated can be suppressed. However, since the gas is separated in this lance, the flow velocity of the gas ejected from one opening becomes small, and the ratio of gas dissipating to the vacuum exhaust system before reaching the molten steel increases. It ends up.

Japanese Unexamined Patent Publication No. 7-41825 Japanese Unexamined Patent Publication No. 2004-156083 Japanese Unexamined Patent Publication No. 2005-60801

As described above, in the vacuum refining using the RH vacuum degassing device, when the gas is sprayed on the surface of the molten steel in the vacuum chamber, it is preferable to spray the gas on the surface of the molten steel directly above the riser pipe. This is a method of blowing gas toward a strong stirring region where the stirring gas bubbles blown from the side wall of the rising pipe burst on the surface of the molten steel. On the other hand, since the two immersion pipes are alternately replaced to form a rising pipe, it is necessary to change the gas blowing position when the rising pipe is replaced. In the method described in Patent Document 1, in order to provide the rotation mechanism in the lance, a large-scale equipment modification is required, resulting in high cost. In the method described in Patent Document 2, when the refining powder is mixed with gas and sprayed, the powder is clogged in the gas blowing holes.

INDUSTRIAL APPLICABILITY According to the present invention, gas can be sprayed on the surface of molten steel directly above the riser pipe even if the position of the riser pipe is changed, and further, it is possible to spray a powder mixed gas for refining with inexpensive equipment. The first object is to provide a molten steel refining apparatus and a method for refining molten steel.

In vacuum refining of steel, it is important to increase the refining reaction rate when refining by spraying a single gas or a powder mixed gas for refining on the surface of molten steel in a vacuum chamber. As a result, in the impurity-removing refining, the refining can be advanced to a lower impurity concentration, or the refining time can be shortened.

In order to increase the refining reaction rate, it is effective to increase the boundary area where the reaction occurs and to reduce the concentrated region of the gas component dissolved in the molten steel or the retention region of the refining powder landed on the molten steel. For that purpose, a method of injecting the gas alone or the gas and the refining powder from a lance at a wide angle, or a method of constantly changing the position where the gas is sprayed on the surface of the molten steel can be mentioned as effective means. In the invention described in Patent Document 3, the gas flow is dispersed by blowing gas from a plurality of openings (nozzles), but in the invention described in the same document, the vacuum exhaust system is reached before reaching the molten steel. The rate of dissipation will increase.

The present invention is a method capable of increasing the boundary area where a reaction occurs without dissipating the sprayed gas, and further, a molten steel refining apparatus capable of constantly changing the position where the gas is sprayed on the surface of the molten steel. A second object is to provide a method for refining molten steel.

That is, the gist of the present invention is as follows.
[1] A molten steel refining apparatus having a vacuum chamber for accommodating molten steel.
The vacuum chamber has a lance for spraying a single gas or a powder mixed gas for refining on the surface of molten steel in the vacuum chamber.
There are 2 to 4 nozzles for gas discharge at the end of the tip of the lance, and the positions of the nozzles are arranged so as to be rotationally symmetric with respect to the central axis of the lance, and the gas flow rate from each nozzle is independent. Can be determined in
Toward the downstream side of the gas discharge flow from the end portion, and the outward side of the nozzle outer periphery when viewed from the lance center axis, have a skirt portion, the lance center axis in the cross section including the lance center axis wherein the inclination angle of the skirt portion and theta, the angle of inclination theta is refining apparatus of the molten steel characterized by zero or a positive value der Rukoto at any position of said skirt portion against.
However, when the inclination angle θ is a positive value, the distance between the lance central axis and the skirt portion becomes wider toward the downstream side.
[2] The nozzle diameter is d ₀ , the shortest distance between adjacent nozzles on the outer circumference of the nozzle is d ₁ , the shortest distance between the skirt and the outer circumference of the nozzle _{at the end is d 2} , and the distance from the end to the tip of the skirt is h. The molten steel according to the above [1], wherein the inclination angle of the skirt portion with respect to the lance central axis is θ in the cross section including the lance central axis, and the following equations (1) to (4) are satisfied. Smelting equipment.
0 ° ≤ θ ≤ 8 ° ・ ・ ・ (1)
0.1 ≤ d ₁ / d ₀ ≤ 0.4 ... (2)
2.5 ≤ h / d ₀ ≤ 4.0 ... (3)
0.1 ≤ d ₂ / d ₀ ≤ 2.0 ... (4)
[3] A method for refining molten steel using the molten steel refining apparatus according to the above [1] or [2], wherein the gas alone or the powder mixed gas for refining is discharged from the nozzle to the surface of the molten steel in the vacuum chamber. A method for refining molten steel, characterized in that the gas flow rate of some nozzles is larger than the average gas flow rate of all nozzles (hereinafter referred to as "large flow rate discharge").
[4] The molten steel refining device is an RH vacuum degassing device, the number of the nozzles is two, the nozzle for performing the large flow rate discharge is selected, and the discharge flow from the lance is applied to the surface of the molten steel in the vacuum chamber. The method for refining molten steel according to the above [3], wherein the arrival position is set to the ascending pipe position.
[5] The method for refining molten steel according to the above [3], wherein during refining, the nozzles that discharge the large flow rate are sequentially replaced with the passage of time.

According to the present invention, in vacuum refining of molten steel, when a single gas or a powder mixed gas is sprayed onto the surface of the molten steel in the vacuum chamber from a lance arranged in the vacuum chamber, the molten steel directly above the ascending pipe is changed even if the position of the ascending pipe is changed. It is possible to spray gas on the surface, and further, it is possible to spray a powder mixed gas for refining with inexpensive equipment. Further, the position where the gas is blown on the surface of the molten steel can be constantly changed.

It is a figure which shows the lance tip part of this invention which has a two-hole nozzle, (A) is a view seen from the bottom, (B) is a side sectional view. The lance tip portion of the present invention is viewed from below, where (A) has a 3-hole nozzle and (B) has a 4-hole nozzle. It is sectional drawing which shows the RH vacuum degassing apparatus provided with the lance of this invention. It is a figure which shows the relationship between the inclination angle of a skirt part and N density | concentration after spraying. It is a figure which shows the relationship between the height of a skirt part and N density | concentration after spraying. It is a figure which shows the relationship between the interval between nozzles and N density | concentration after spraying. It is a figure which shows the relationship between the distance between a nozzle and a skirt part, and N density | concentration after spraying. It is a figure which shows the relationship between the number of nozzles and N density | concentration after spraying. Regarding the gas ejection situation at the nozzle outlet of the two-hole nozzle, (A) is a diagram showing a case where the right nozzle is a large flow rate discharge nozzle and (B) is a diagram showing a case where the left nozzle is a large flow rate discharge nozzle. It is a figure which shows the gas ejection state at the nozzle outlet of a 1-hole nozzle, (A) is the case without a skirt part, (B) is the case with a skirt part.

The present invention will be described with reference to FIGS. 1 to 10.
In the present invention, in vacuum refining of molten steel, as shown in FIG. 3, when the gas blown from the nozzle 7 at the tip of the lance 6 is blown onto the molten steel surface 25 in the vacuum tank 1, a gas alone or a powder mixed gas for refining is used. The following objectives are achieved by using simple equipment that can be used and does not require large-scale equipment modification. That is, first, in the vacuum tank 1 of the RH vacuum degassing device, even if the position of the riser pipe 3 is changed, the blowing direction can be changed so that the gas to be blown becomes the riser pipe position 26. Second, it increases the gas sprayed area on the molten steel surface without dissipating the gas. Thirdly, it is possible to constantly change the position where the gas is blown on the surface of the molten steel.

The inside of the vacuum chamber 1 of the vacuum refining apparatus has a reduced pressure atmosphere. When the gas is blown into the vacuum chamber from the nozzle 7 at the tip of the lance 6, when the pressure at the nozzle outlet is higher than the atmospheric pressure in the vacuum chamber, that is, in a so-called insufficient expansion state, the blown gas is shown in FIG. 10 (A). As shown in, it spreads at the outlet of the nozzle 7 to form an expansion wave 34. When the shape of the nozzle 7 is a straight pipe, or when the underexpansion condition is used even for a Laval nozzle, an underexpansion state occurs and an expansion wave 34 is formed at the nozzle outlet, and a jet near the outlet of the nozzle 7 is formed. The boundary 35 will be widened as shown in FIG. 10 (A). Further, regarding the shape of the discharge flow 31 downstream of the nozzle 7, since the atmosphere is depressurized, the straightness of the gas is high, and the spread angle of the jet boundary 35 of the blown gas is large regardless of whether the gas is a single gas or a powder mixed gas for refining. (See FIG. 10 (A)). When a single nozzle is provided at the tip of the lance to blow out the gas as in the conventional case, the spread angle of the blown out gas is small, so that the surface area of the gas blown when reaching the surface of the molten steel in the vacuum chamber is small, and the present invention Could not achieve the purpose of.

As shown in FIG. 10B, when a wall (skirt portion 8) is provided on one side near the jet at the end of the outlet of the nozzle 7 for discharging gas, the expansion wave of the jet ejected from the nozzle is generated. It was confirmed that the discharge flow 31 collided with this wall, and as a result, the discharge flow 31 changed its course to the opposite side of the wall (skirt portion 8) installation direction, and the jet spread angle also increased (see FIG. 10 (B)). ). Then, by utilizing this phenomenon, it was possible to find a method for achieving the object of the present invention.

As shown in FIGS. 1 and 2, the lance for blowing gas onto the surface of molten steel in a vacuum chamber of the present invention has 2 to 4 gas discharge nozzles 7 at the end 12 of the tip of the lance 6. have. The position of the nozzle is arranged so as to be rotationally symmetric with respect to the lance central axis 29. Further, the skirt portion 8 having a shape surrounding the nozzle 7 is provided on the downstream side of the gas discharge flow 31 from the end portion 12 and on the outer side of the nozzle outer circumference 11 as viewed from the lance central axis 29. Regarding the relationship between each of the 2 to 4 nozzles 7 and the skirt portion 8, the wall of the skirt portion 8 is located on one side of the discharge flow 31 discharged from the nozzle 7, that is, the skirt portion. 8 serves as a wall that changes the course of the discharge flow 31 and increases the spread angle of the discharge flow 31.

For the 2 to 4 nozzles 7 provided at the tip of the lance, the device configuration is such that the gas flow rate from each nozzle 7 can be determined independently. Therefore, as shown in FIG. 3, a gas supply pipe 13 for supplying gas to each nozzle 7 is provided for each nozzle, and a flow rate adjusting device 14 is provided for each gas supply pipe 13. As a result, instead of blowing gas from each nozzle 7 at the same flow rate, the gas flow rate for one specific nozzle is higher than that for the other nozzles. Increasing the gas flow rate compared to other nozzles is referred to as "large flow rate discharge", and the nozzle that discharges a large flow rate is named "large flow rate discharge nozzle 9". As a result of such a flow rate configuration, the gas flow rate of the large flow rate discharge nozzle 9 becomes larger than the average gas flow rate of all the nozzles. Then, the discharge flow 31 from the large flow rate discharge nozzle 9 leads the direction of the gas jet from the lance 6 provided with the 2 to 4 nozzles 7.

A case where the number of nozzles 7 arranged at the end portion 12 of the lance 6 is two will be described with reference to FIG. As shown in FIG. 1, the two nozzles 7 are arranged at positions that are 180 ° rotationally symmetric with respect to the lance central axis 29. The skirt portion 8 is provided on the downstream side of the gas discharge flow from the end portion 12 and on the outer side of the nozzle outer circumference 11 as viewed from the lance central axis 29. The nozzle on the left side of FIG. 9 is named the first nozzle 7A, and the nozzle on the right side is named the second nozzle 7B. First, as shown in FIG. 9B, the first nozzle 7A on the left side is a large flow rate discharge nozzle 9. When the gas flow rate from the second nozzle 7B on the right side is 1, the gas flow rate from the first nozzle 7A is set to 3, and the gas is discharged from the first nozzle 7A and the second nozzle 7B. The discharge flow from the first nozzle 7A having a large flow rate forms an expansion wave immediately after exiting the nozzle, the expansion wave on the skirt portion side collides with the skirt portion, and the discharge flow from the first nozzle 7A is shown in FIG. At the same time that the discharge direction is bent to the right side of B), the spread angle of the gas also increases. Since the gas flow rate is small, the discharge flow from the second nozzle 7B merges with the jet flow from the first nozzle 7A and flows mainly in the discharge direction of the first nozzle 7B as shown in FIG. 9B. It becomes. Next, when the gas flow rate for each nozzle is changed and the second nozzle 7B is a large flow rate discharge nozzle 9 as shown in FIG. 9 (A), the discharge flow from the second nozzle 7B is shown in FIG. 9 (A). It is bent to the left, and the discharge flow of a small flow rate from the first nozzle 7A merges with the discharge flow of the second nozzle 7B. As described above, the jet direction of the gas from the lance 6 can be changed by providing the plurality of nozzles 7 and the skirt portion 8 and replacing the large flow rate discharge nozzles 9. In addition, the action of the skirt portion 8 can also exert the effect of widening the spread angle of the jet stream.

First, a point of achieving the first object of the present invention will be described. In vacuum refining using the RH vacuum degassing device, by using the lance 6 having two nozzles 7 of the present invention, when the ascending pipe 3 is replaced, the gas blowing position is changed, and which immersion pipe 2 is used. Even when used for the riser pipe 3, gas can be sprayed on the riser pipe position 26 on the molten steel surface 25. This point will be described with reference to FIGS. 1, 3, and 9.

At the tip of the lance shown in FIG. 1, the nozzles so that the plane including the central axes (28A, 28B) of the two nozzles is the same plane as the plane including the central axes of the two immersion tubes 2 shown in FIG. To place. In FIG. 3, when the immersion pipe (first immersion pipe 2A) on the left side is the rising pipe 3, the nozzle on the right side (second nozzle 7B) in the lance 6 is a large flow rate discharge nozzle as shown in FIG. 9 (A). Let it be 9. The discharge flow 31 from the lance is bent to the left side in FIGS. 9 (A) and 3 (A). By adjusting the distance between the tip of the lance and the molten steel surface in the vacuum chamber, and adjusting the gas flow rate of the large flow rate discharge nozzle 9 (second nozzle 7B) and the other nozzle (first nozzle 7A), the gas flow rate from the lance can be adjusted. Allow the discharge flow rate 31 to reach the surface of the molten steel just above the first immersion pipe 2A (see FIG. 3). Next, when the immersion tube to be the rising tube 3 shifts from the first immersion tube 2A to the right immersion tube (second immersion tube 2B), the gas flow rate from each nozzle is changed, and FIG. 9B is shown. As shown in, the large flow rate discharge nozzle 9 is changed from the second nozzle 7B to the first nozzle 7A. As a result, the discharge flow 31 from the lance is bent to the right side in FIG. 9B so that it can reach the molten steel surface 25 just above the second immersion tube 2B.

Next, the second and third objects of the present invention are the effect of increasing the gas spraying area on the molten steel surface without dissipating the gas, and making it possible to constantly change the position where the gas is sprayed on the molten steel surface. The verification of the effect was performed as follows. That is, in an RH type vacuum degassing device that processes 300 tons of molten _{steel, a test was conducted in which N 2} gas was sprayed onto the molten steel from a lance 6 installed above the molten steel in the vacuum chamber, and a change in the N concentration in the molten steel was performed. Therefore, the refining reaction efficiency was investigated.

The number of nozzles 7 provided at the end 12 of the tip of the lance was set to 2 to 4 for the present invention (see FIGS. 1 and 2). In the case of one nozzle in the comparative example, there are a comparative example in which a wall is provided as a substitute for the skirt portion on one side of the nozzle (see FIG. 10B) and a conventional example without a skirt portion (see FIG. 10A). Two types were used. The total gas flow rate per lance was the same for all lances. The nozzle diameter was selected so that the total opening cross-sectional area of the nozzle was 5000 to 8000 mm ^2. In the same lance, the inner diameters of 2 to 4 nozzles are the same. Further, in each nozzle, the nozzle shape near the outlet is not a Laval nozzle but a cylindrical shape having the same diameter in the nozzle axis direction, and the nozzle central axis is arranged so as to be the same direction as the lance central axis. For 2 to 4 nozzles, the position where the central axis of the nozzle passes through the end is arranged at a position that is rotationally symmetric with respect to the central axis of the lance, and the gas flow rate from each nozzle can be determined independently. The device configuration is such that it can be used.

Upon testing, a common condition of the lance, the skirt portion the inclination angle θ = 5~7 °, h / d 0 = 3.5~4.0, d 1 / d 0 = 0.20~0.30, d 2 / D ₀ = 0.2 to 0.8 and the number of lance holes = 2 were adopted. Then, a lance having a nozzle and a skirt portion in which one of the conditions was changed was prepared, and a gas blowing test was conducted.

The N ₂ gas spray test was conducted as follows. The refining process of 300 tons of molten steel contained in the ladle was started by the RH type vacuum degassing device. The molten steel composition is C concentration = 0.10 to 0.30%, Si concentration = 0.1 to 0.4%, Mn concentration = 0.6 to 1.2%, Al concentration = 0.010 to 0.050%. , S concentration = 0.001 to 0.003%, N concentration = 0.0033 to 0.0037%. The atmospheric pressure in the vacuum chamber was 1330 to 4000 Pa, and Ar was introduced as the reflux gas at 4.5 to 7.4 Nm ³ / (t · min) per ton of molten steel.

After confirming the stability of the atmospheric pressure in the vacuum chamber and the flow rate of the circulating gas, install the lance 6 at a height of 3.0 m from the surface of the molten steel in the vacuum chamber, and pass the nozzle 7 at the tip of the lance through the nozzle 7 to the total of N ₂ gas Was sprayed at a flow rate of ^{0.11 to 0.15 Nm 3} / (t · min) per ton of molten steel. The flow rate ratio of each nozzle is 1: 3 when the number of nozzles = 2, 1: 1: 4 when the number of nozzles = 3, 1: 1: 1: 4 when the number of nozzles = 4, and 1: 1: 1 when the number of nozzles = 5. The flow rate was 1: 5, and the flow rate of each nozzle was changed in 10 to 40 seconds. The spraying time was 8 minutes. A sample was taken after spraying and the N concentration in the molten steel was analyzed.

The result when the nozzle hole is one hole is shown in FIG. In the comparative example (white circle) with one nozzle hole and no skirt, the amount of increase in nitrogen concentration increased slightly, but was insufficient, as opposed to the conventional example (black triangle) with one nozzle and no skirt. It is presumed that the effect of the skirt portion is the effect of increasing the spread angle of the discharge flow. In each of the examples of the present invention (white circles) having 2 to 4 nozzles, the amount of increase in nitrogen concentration is larger than that of the conventional example and the comparative example having one nozzle hole.

From the relationship between the inclination angle θ of the skirt portion shown in FIG. 4 and the N concentration after spraying, the N concentration increased when θ was 0 to 8 °. _{From the relationship between h / d 0 obtained} by dividing the height of the skirt portion shown in FIG. 5 by the nozzle diameter and the N concentration after spraying, the N concentration became high when _{h / d 0 was 2.5 to 4.0.} .. _{From the relationship between d 1} / d ₀ obtained by dividing the distance between adjacent nozzles shown in FIG. 6 by the nozzle diameter and the N concentration after spraying, the N concentration becomes high when _{d 1} / d _{0 is 0.10 to 0.40.} It was. _{From the relationship between d 2} / d ₀ obtained by dividing the closest contact distance between the nozzle and the skirt connection portion shown in FIG. 7 by the nozzle diameter and the N concentration after spraying, d ₂ / d ₀ is 0.1 to 2.0. Sometimes the N concentration was high. From the relationship between the number of nozzles shown in FIG. 8 and the N concentration after spraying, the N concentration was high when the number of nozzles was 2-4.

From the above results, in the present invention having 2 to 4 nozzles and a skirt portion, the amount of increase in nitrogen concentration is increased as compared with the conventional example in which the nozzle has one hole and does not have a skirt portion. It was confirmed that the refining reaction rate was increased by increasing the gas spraying area on the molten steel surface without dissipating the gas and constantly changing the position where the gas was sprayed on the molten steel surface. Further, it was confirmed that an excellent refining reaction rate increasing effect can be obtained by arranging the nozzle and the skirt portion satisfying the above equations (1) to (4).

The lance provided with the nozzle of the present invention is used in a vacuum degassing apparatus that processes molten steel under reduced pressure conditions. In particular, the RH type vacuum degassing treatment device performs processing such as alloy component adjustment, degassing, desulfurization, removal of non-metal inclusions, and temperature adjustment in a short time, so that the gas alone from the lance or a mixture of gas and refining powder It is desirable because it has a large effect of shortening the spraying process time.

The gas blown from the lance includes O ₂ , N ₂ , CHO ₄ , Ar, etc., regardless of the type. Examples of the refining powder sprayed from the lance include powders for desulfurization mainly containing CaO, powders for decarburization such as FeO and MnO, and carbonaceous materials for adjusting the carbon concentration, and the types are not limited. However, the particle size of the powder is preferably 0.5 mm or less. This is because when the size is larger than 0.5 mm, the inertial force of the powder becomes stronger, so that the spraying angle does not increase without being accompanied by the rapid expansion immediately after the gas is ejected from the nozzle.

The atmospheric pressure at the time of spraying the gas alone or the mixed spraying of the gas and the refining powder is preferably 133 to 13300 Pa. If it is less than 133 Pa, the degree of expansion of the gas ejected from the nozzle becomes too large, and the jet becomes unstable. This is because when the value is larger than 13300 Pa, the degree of expansion of the gas ejected from the nozzle is small, and collision and reflection on the inner wall of the skirt hardly occur.

The distance between the end portion 12 of the tip of the lance and the surface 25 of the molten steel is preferably 2.0 to 4.5 m. If it is less than 2.0 m, the spread will be insufficient even by spraying a single gas or a mixed spray of gas and refining powder. If it is larger than 4.5 m, the speed of the gas or the refining powder will be attenuated, and the rate of dissipation to the vacuum exhaust system without reaching the surface of the molten steel will increase.

As shown in FIGS. 1 and 2, the end portion 12 of the tip of the lance has 2 to 4 nozzles 7 for gas discharge, and the nozzle positions are rotationally symmetrical with respect to the lance central axis 29. Place in. The number of nozzles of the lance needs to be 2 to 4 holes. With one hole, the gas blowing direction cannot be changed over time. If the number of holes is 5 or more, the flow rate of gas flowing through one nozzle becomes small, the speed of gas or refining powder does not increase, and the ratio of gas or refining powder not reaching the surface of molten steel and dissipating into the vacuum exhaust system increases.

The nozzle diameters may all be the same or different. However, in order to control the flow rate, it is desirable that they are all the same. The device configuration is such that the gas flow rate from each nozzle can be determined independently. Specifically, as shown in FIG. 3, a gas supply pipe 13 is connected to each nozzle 7, each of which has a flow rate adjusting device 14, and the flow rate adjusting device 14 for each nozzle 7 to the gas supply pipe 13 in the lance. The device configuration is such that each has a flow path to each nozzle via the above.

_{The shortest distance d 1 on the} outer circumference of the nozzle between the closest nozzles is preferably 0.1 to 0.4 times the diameter d _{0 of the nozzle.} If it is less than 0.1 times, the gas jets ejected from the adjacent nozzles interfere with each other during the rapid expansion, and the flow is disturbed. If it is larger than 0.4 times, the influence of the negative pressure portion generated between the gas jets ejected from the adjacent nozzles becomes strong, and the direction of the jets is rectified vertically downward.

The skirt portion 8 is provided on the downstream side of the gas discharge flow from the end portion and on the outer side of the nozzle outer circumference 11 as viewed from the lance central axis 29. It is preferable that the skirt portion 8 is configured to surround all the nozzle central shaft portions. The skirt portion may be provided only in a part near the nozzles instead of surrounding the entire circumference of all the nozzles. For example, when the nozzle has two holes, a wall may be provided on the opposite side of the lance central axis when viewed from the nozzle central axis, and two walls corresponding to the two-hole nozzle may be used as the skirt portion. The inclination angle θ of the skirt portion is preferably 0 to 8 °. It is difficult to manufacture a lance below 0 °. If it is larger than 8 °, collision of gas or refining powder with the inner wall of the skirt is less likely to occur.

The height h of the skirt portion is preferably 2.5 to 4.0 times _{the diameter d 0 of the nozzle.} If it is less than 2.5 times, the colliding area of the gas or the refining powder becomes insufficient. If it is larger than 4.0 times, the direction in which the reflected gas or the refining powder is sprayed is rectified vertically downward.

_{The shortest distance d 2} between the skirt portion and the outer circumference of the nozzle at the end portion is preferably 0.1 to 2.0 times the diameter d _{0 of the nozzle.} If it is less than 0.1 times, the gas or refining powder ejected from the nozzle expands along the inner wall of the skirt. If it is larger than 2.0 times, the collision with the inner wall of the skirt hardly occurs.

The gas spraying direction may be changed by adjusting the gas flow rate with the passage of time for introduction into each nozzle, and in the case of the RH type vacuum degassing treatment device, the gas is fixedly sprayed toward the rising pipe. Is also good. However, it is desirable to observe the ejection behavior of gas or refining powder from a window that allows observation of the inside of the device, which is obtained in advance by numerical fluid calculation for the spraying direction.

As shown in FIG. 3, while the molten steel 290 to 310t is being subjected to the RH type vacuum degassing treatment, a lance 6 having the nozzle 7 of the present invention or the comparative example is applied to the surface of the molten steel from the upper part of the vacuum tank 1. The distance between the 25 and the end 12 at the lower end of the lance was 2.5 to 4.0 m. The ability to add nitrogen to the molten steel was evaluated by blowing nitrogen gas from the nozzle 7 onto the surface 25 of the molten steel in the vacuum chamber and evaluating the degree of increase in the N concentration in the molten steel.

Nozzles with 1 to 5 holes were prepared as the nozzles 7 to be arranged at the end of the tip of the lance. For the nozzles 7 having 2 to 4 holes, the device configuration is such that the gas flow rate from each nozzle can be determined independently. The nozzle 7 was a straight nozzle, and the nozzle diameter was determined so that the total nozzle cross-sectional area was the same for the nozzles having 1 to 5 holes. In the lance 6 having a plurality of nozzles 7, the nozzle diameters were the same. As the lance 6 having a single-hole nozzle 7, a lance 6 having no skirt portion (No. 11) and a lance 6 having a skirt portion 8 concentric with the nozzle on the entire circumference of the nozzle (Comparative Example No. 12) were prepared. For the lance 6 having the nozzles 7 having 2 to 5 holes, the nozzle arrangement and the skirt portion arrangement as shown in Table 1 were adopted.

The atmospheric pressure in the vacuum chamber when the gas is blown from the nozzle 7 is 3000 to 7000 Pa, and Ar is used as the recirculation gas 22 in the ascending pipe 3 at a flow rate of ^{0.0040 to 0.0060 Nm 3 / (t ・ min) per ton of molten steel.} It was blown into the molten steel from the provided tuyere 21. _{After the lance was lowered, N 2} gas was sprayed onto the molten steel through the nozzle 7 in order to increase the N concentration in the molten steel. N ₂ gas was sprayed at a flow rate of ^{0.13 Nm 3} / (t · min) per ton of molten steel for 8 minutes. Samples were taken before and after N ₂ gas spraying, and the N concentration was analyzed.

Table 1 shows the test conditions and changes in N concentration before and after gas injection. Numerical values and items outside the scope of the present invention are underlined.

In the conventional example (Test No. 11) with one nozzle and no skirt, the increase in nitrogen concentration was the smallest. In the comparative example (test No. 12) in which the skirt portion was provided on the entire circumference of the nozzle with a one-hole nozzle, the gas blowing direction was in the center of the vacuum chamber, and the test No. 12 was used. Nitrogen concentration increased from 11 but was slight.

Test No. using the suitable conditions of the present invention. In 1 to 10, _{the N concentration after spraying N 2} gas was 0.0048 to 0.0052%, and the above test No. Good results could be obtained as compared with 11 and 12. When the ascending pipe is fixed with a 3-hole nozzle, when the arrangement of the ascending pipe is changed, the test No. 5 and test No. It can be dealt with by switching with 7.

Test No. which is an example of the invention using a nozzle outside the suitable range of the present invention. In 13 to 22, _{the N concentration after spraying N 2} gas was the above-mentioned test No. The amount of nitrogen increase was smaller than that of 1 to 10. Test No. This is because in No. 13, since the gas was blown toward the position of the descending pipe where the molten steel flow was relatively gentle, the N concentration was locally increased and the absorption efficiency of N from the gas was decreased. Test No. This is because the inclination angle θ of the skirt in No. 14 was too large to exceed the preferable range, and the reflection of the expanded gas jet due to the collision with the skirt did not occur so much. Test No. In 15 and 21, the distance d ₁ / d ₀ between the nozzles was smaller than the preferable range, and the gas jets ejected from the adjacent lances merged in the process of rapid expansion, and the jet flow became unstable. Is. Test No. _{This is because in No.} 16, the distance d 1 / d ₀ between the nozzles is larger than the preferable range, the influence of the negative pressure portion generated between the adjacent gas jets becomes large, and the jet flow becomes unstable. Test No. This is because the height of the skirt portion in No. 17 was lower than the preferable range, and the reflection of the jet occurred only in a limited manner. Test No. In No. 18, the height h / d _{0 of the} skirt portion is higher than the preferable range, and even if the jet is reflected, the spraying direction is rectified vertically downward. Test No. This is because in No. 19, the distance d ₂ / d ₀ between the nozzle and the skirt connection portion was closer than the preferable range, and the gas jet expanded along the skirt and did not reflect. Test No. In 20 and 22, the distance d ₂ / d ₀ between the nozzle and the skirt connection portion was far from the preferable range, and the expanded jet did not collide with the skirt portion.

Test No. This is because the number of nozzles in 22 is too large and the gas jet ejected from one nozzle is weakened.

Similar to the first embodiment, a lance having 1 to 5 hole nozzles is prepared, and as shown in FIG. 3, a vacuum is applied to the molten steel 290 to 310 t during the RH type vacuum degassing treatment. The lance 6 of the present invention was lowered from the upper part of the tank 1 so that the distance between the molten steel surface 25 and the end portion 12 at the lower end of the lance was 2.5 to 4.0 m. At this time, the atmospheric pressure in the vacuum chamber was 133 to 3990 Pa, and Ar was used as the recirculation gas at ^{a flow rate of 0.0040 to 0.0060 Nm 3} / (t · min) per ton of molten steel. Was blown into molten steel. After the lance was lowered, Ar gas and FeO powder were mixed and sprayed onto the molten steel through the nozzle 7 in order to cause a decarburization reaction. The FeO powder was supplied from the powder supply device 15. The flow rate of Ar gas was 0.02 Nm ³ / (t · min), and the supply rate of FeO powder was 0.18 to 0.20 kg / (t · min) for 7 to 8 minutes. Samples were taken before and after the mixed spraying of Ar gas and FeO powder, and the C concentration was analyzed. In the case of the comparative example (test No. 3) in which the ascending pipe is fixed by the 3-hole nozzle, when the arrangement of the ascending pipe is changed, the gas flow rate ratio is changed to the test No. 3 in Table 2. It can be dealt with by switching from "1: 1: 4" shown in 3 to "2: 2: 1".

Table 2 shows the test conditions and changes in C concentration. Numerical values and items outside the scope of the present invention are underlined.

In the conventional example (Test No. 7) with one nozzle and no skirt, the decrease in C concentration was the smallest. In the comparative example (test No. 8) in which the skirt portion was provided on the entire circumference of the nozzle with a one-hole nozzle, the gas blowing direction was in the center of the vacuum chamber, and the test No. 8 was used. The C concentration was lower than that of 7, but it was slight.

Test No. using the suitable conditions of the present invention. In 1 to 6, the C concentration after the mixed spraying of Ar gas and FeO powder was 0.0007 to 0.0011%, and the above test No. The concentration could be reduced compared to 7 and 8.

Test No. which is an example of the invention using a nozzle outside the suitable range of the present invention. In 9 to 18, the C concentration after gas blowing was the above-mentioned test No. The amount of C decrease was smaller than that of 1 to 6. Test No. No. 9 was sprayed onto the descending pipe side of the vacuum chamber where the molten steel flow was gentle, and FeO was locally retained in the molten steel, the reaction between the FeO powder and the molten steel did not proceed, and the FeO powder was dissipated into the vacuum exhaust system. This is because of the vacuum. Test No. 10 is because the inclination angle θ of the skirt is larger than the preferable range, and the powder hardly collides with the inner wall of the skirt and is not reflected. Test No. In Nos. 11 and 17, the nozzle spacing d ₁ / d ₀ is too close to the preferable range, and the gas jets ejected from the nozzles coalesce in the process of rapid expansion, resulting in unstable jet flow and FeO powder. This is because the acceleration was insufficient and the molten steel surface was not reached and was dissipated into the vacuum exhaust system. Test No. _{In No.} 12, the distance d 1 / d ₀ between the nozzles was too large than the preferable range, the influence of the negative pressure portion generated between the adjacent gas jets became large, and the spraying direction of the FeO powder was fixed. .. Test No. In No. 13, the height h / d _{0 of the} skirt portion was too lower than the preferable range, and the reflection of the FeO powder occurred only in a limited manner. Test No. This is because in No. 14, the height h / d _{0 of the} skirt portion is too high than the preferable range, and even if the FeO powder is reflected, the spraying direction is rectified vertically downward in the skirt. Test No. _{In No. 15, the distance d 2} / d ₀ between the nozzle and the skirt connection portion was too close to the preferable range, and the gas jet expanded along the skirt and was not reflected, so that the FeO powder was not reflected either. Test No. This is because in 16 and 18, the distance d ₂ / d ₀ between the nozzle and the skirt connection portion was too far from the preferable range, and the FeO powder did not collide with the skirt portion.

Test No. At 19, the number of nozzles is too large, the flow velocity of the gas jet ejected from one nozzle is low, and the acceleration of FeO powder is insufficient, so that it dissipates into the vacuum exhaust system without reaching the molten steel surface. This is because it has been closed.

1 Vacuum tank 2 Immersion pipe 3 Ascending pipe 4 Lowering pipe 5 Topping pot 6 Lance 7 Nozzle 8 Skirt part 9 Large flow rate discharge nozzle 11 Nozzle outer circumference 12 End 13 Gas supply pipe 14 Flow rate adjusting device 15 Powder supply device 21 Tuft 22 Circulating gas 23 Vacuum exhaust 24 Molten steel 25 Molten steel surface 26 Ascending pipe position 27 Down pipe position 28 Nozzle central axis 29 Lance central axis 31 Discharge flow 32 Upflow 33 Downflow 34 Expansion wave 35 Jet boundary

Claims (5)

A molten steel refining device having a vacuum chamber for accommodating molten steel.
The vacuum chamber has a lance for spraying a single gas or a powder mixed gas for refining on the surface of molten steel in the vacuum chamber.
There are 2 to 4 nozzles for gas discharge at the end of the tip of the lance, and the positions of the nozzles are arranged so as to be rotationally symmetric with respect to the central axis of the lance, and the gas flow rate from each nozzle is independent. Can be determined in
Toward the downstream side of the gas discharge flow from the end portion, and the outward side of the nozzle outer periphery when viewed from the lance center axis, have a skirt portion, the lance center axis in the cross section including the lance center axis wherein the inclination angle of the skirt portion and theta, the angle of inclination theta is refining apparatus of the molten steel characterized by zero or a positive value der Rukoto at any position of said skirt portion against.
However, when the inclination angle θ is a positive value, the distance between the lance central axis and the skirt portion becomes wider toward the downstream side. The nozzle diameter is d ₀ , the shortest distance between adjacent nozzles on the outer circumference of the nozzle is d ₁ , the shortest distance between the skirt and the outer circumference of the nozzle _{at the end is d 2} , the distance from the end to the tip of the skirt is h, the above. The molten steel refining apparatus according to claim 1, wherein the inclination angle of the skirt portion with respect to the lance central axis is θ in the cross section including the lance central axis, and the following equations (1) to (4) are satisfied.
0 ° ≤ θ ≤ 8 ° ・ ・ ・ (1)
0.1 ≤ d ₁ / d ₀ ≤ 0.4 ... (2)
2.5 ≤ h / d ₀ ≤ 4.0 ... (3)
0.1 ≤ d ₂ / d ₀ ≤ 2.0 ... (4) The method for refining molten steel using the molten steel refining apparatus according to claim 1 or 2, wherein a single gas or a powder mixed gas for refining is discharged from the nozzle and sprayed onto the surface of the molten steel in a vacuum chamber. A method for refining molten steel, characterized in that the gas flow rate of some nozzles is larger than the average gas flow rate of all nozzles (hereinafter referred to as "large flow rate discharge"). The molten steel refining device is an RH vacuum degassing device, the number of the nozzles is two, the nozzle for performing the large flow rate discharge is selected, and the discharge flow from the lance reaches the surface of the molten steel in the vacuum tank. The method for refining molten steel according to claim 3, wherein the position is a rising pipe position. The method for refining molten steel according to claim 3, wherein during refining, the nozzles that discharge the large flow rate are sequentially replaced with the passage of time.

Images