JP4036167B2 - Molten steel heating method and molten steel heating device - Google Patents

Description

  The present invention relates to a method and apparatus for heating molten steel by blowing oxygen under reduced pressure and, more particularly, to a molten steel heating method and a molten steel heating apparatus using an RH vacuum degassing apparatus. .

  As a main method for degassing and secondary refining of steel, a vacuum refining method using an RH vacuum degassing apparatus is now widely used. The main technologies of this vacuum refining method are the following (a) to (d).

  (B) "Base technology": Molten steel is processed in a vacuum, and degassing such as decarburization, deoxidation, and dehydrogenation is performed.

  (B) “Oxygen blown heating technology”: Al, Si, etc. are added to the molten steel, and oxygen is supplied to raise the temperature of the molten steel.

  (C) “Oxygen blown decarburization technology”: Oxygen is blown during decarbonization of molten steel to promote decarburization.

  (D) “Flux addition technology”: Desulfurization of molten steel is performed by adding a desulfurizing agent to the RH vacuum chamber.

  The RH vacuum degassing apparatus is, as schematically shown in FIG. 1, two dip pipes, that is, a riser pipe 4 (a dip pipe in which molten steel flows upward, Tube) and a downcomer 5 (a dip tube in which molten steel flows downward, also referred to as a “discharge tube”), and an inert gas such as Ar gas is circulated into the ascending tube 4 6 is a device that continuously degass the molten steel 3 from the ascending pipe 4 and sucks the molten steel 3 back to the ladle 2 via the descending pipe 5.

  As a technology related to the vacuum refining process, Patent Document 1 discloses a technique for heating the molten steel using an exothermic reaction between Al and oxygen, specifically, a heat generating agent (Al) at the end of the decarburization process. A method of decarburizing while increasing the temperature by adding is disclosed. Further, in Patent Document 2, from the viewpoint of suppressing refractory melting of the refractory in the vacuum chamber, the ratio of the lance height to the bath depth of the molten steel in the vacuum chamber is defined, thereby damaging the bottom refractory in the vacuum chamber. A technology that can realize efficient molten steel heating without incurring heat is disclosed. Further, in Patent Document 3, a lance hole having an angle of 20 to 50 ° is provided at the tip of the lance of the top blow lance device, and the secondary combustion zone is arbitrarily adjusted by adjusting the direction of blowing oxygen. In addition, a technique for preventing a temperature drop of molten steel and suppressing a refractory melt is disclosed.

  However, among the techniques disclosed in each of the above patent documents, in the case of the techniques proposed in Patent Documents 1 and 2, the side wall brick in the vacuum chamber generated when oxygen is blown from the top blowing lance to the molten steel surface. No consideration is given to the erosion damage. For this reason, it is difficult to avoid the occurrence of large melting damage of the side wall bricks that greatly affects the running cost.

  The technique proposed in Patent Document 3 is based on the premise that the CO gas generated during decarburization is burned above the molten steel. For this reason, when assuming Al heating with good heating efficiency, the angle of the lance hole of “20 to 50 °” is excessive, and in order to allow oxygen to reach the molten steel without reaching the side wall, It is necessary to significantly reduce the distance between the steel surface and the molten steel surface (hereinafter referred to as “lance-to-molten steel surface distance”), but in this case, the adhesion of the metal to the lance due to splash increases and damage to the lance is reduced. In some cases, the operation was actually hindered. Furthermore, when the distance between the lance and the molten steel surface is remarkably reduced, oxygen reaches the bottom of the vacuum chamber and the refractory at the bottom of the vacuum chamber may be melted.

JP-A-7-138633

JP 2001-158910 A JP 7-41825 A

  The present invention has been made in view of the above situation, and a first object of the present invention is to melt the side wall brick of the vacuum tank in vacuum refining in which oxygen gas is blown up in the vacuum tank of the RH vacuum degassing apparatus. The present invention is to provide a molten steel heating method capable of suppressing loss and an apparatus therefor, and a second object is to efficiently heat molten steel while suppressing the melting of side wall bricks in a vacuum chamber. It is to provide a method and apparatus therefor.

  The gist of the present invention resides in the molten steel heating method shown in the following (1) to (3) and the molten steel heating device shown in (4) to (6).

  (1) A molten steel heating method in which oxygen gas is blown from an upper blowing lance in a vacuum tank of an RH vacuum degassing apparatus, wherein the center position of an oxygen fire point is located on the riser side in the vacuum tank. How to heat up molten steel.

  (2) The center position of the oxygen fire point is a position of 0.5 to 0.9 in terms of the ratio (r / r0) between the distance r from the side wall on the riser side of the vacuum chamber and the inner radius r0 of the vacuum chamber. The molten steel heating method according to (1) above.

  (3) The molten steel heating method according to the above (1) or (2), wherein a lance having an angle of 3 to 10 ° downward with respect to the vertical direction is provided in the lance hole at the tip of the lance nozzle as the upper blowing lance.

  (4) A molten steel heating device for blowing oxygen gas from an upper blowing lance in a vacuum chamber of an RH vacuum degassing device, characterized in that the center position of the oxygen fire point is located on the riser side in the vacuum chamber. Molten steel heating device.

  (5) The center position of the oxygen fire point is 0.5 to 0.9 in terms of (r / r0), which is the ratio of the distance r from the side wall on the riser side of the vacuum chamber to the inner radius r0 of the vacuum chamber. The molten steel heating apparatus as described in said (4) in the position of.

  (6) The molten steel heating apparatus according to (4) or (5), wherein the upper blowing lance is a lance having an angle of 3 to 10 ° downward with respect to the vertical direction in the lance hole at the tip of the lance nozzle.

  In the present invention, the “center position of the oxygen fire point” refers to the center of the region where the top-blown oxygen gas jet reaches the molten metal bath surface.

  The “rising pipe side in the vacuum chamber” means that the distance from the rising tube in the vacuum chamber is smaller than the distance from the descending tube.

  The “distance r from the side wall on the riser side” of the center position of the oxygen fire point is “the distance r from the inner surface of the riser side wall”, that is, on the horizontal plane including the center position of the oxygen fire point. Assuming a circle formed by the inner wall of the vacuum chamber, it indicates the distance r between the center position of the oxygen fire point on the diameter of the circle passing through the center position of the oxygen fire point and the circumference corresponding to the riser side. . Accordingly, the relationship between the distance r from the side wall on the riser side and the inner radius r0 of the vacuum chamber is such that “r <r0” when the center position of the oxygen fire point is on the riser side, If the position is on the downcomer side, “r> r0”, and if the center position of the oxygen fire point coincides with the center of the circle, that is, the center position of the oxygen fire point is from the riser pipe and the downcomer pipe, etc. When the distance is present, “r = r0”.

  The angle provided downward in the lance hole at the tip of the lance nozzle with respect to the vertical direction refers to an angle θ formed by the vertical direction indicated by the two-dot chain line shown in the “A section enlarged” diagram of FIG. 1 and the central axis of the lance hole. .

  Hereinafter, the invention related to the molten steel heating method of (1) to (3) and the invention related to the molten steel heating device of (4) to (6) are referred to as inventions of (1) to (6), respectively.

  According to the method of the present invention, in the vacuum refining in which oxygen gas is blown up in the vacuum chamber of the RH vacuum degassing apparatus, the refractory constituting the side wall brick of the vacuum chamber can be prevented from being melted. Furthermore, it is possible to efficiently heat the molten steel. For this reason, running cost can be reduced significantly. Moreover, if the molten steel heating apparatus of this invention is used, the method of this invention can be implemented easily.

  In order to solve the above-mentioned problems, the present inventors investigated the state of erosion of side wall bricks when oxygen gas was blown up in a vacuum tank of an RH vacuum degassing apparatus, and the following (a) to (a) to The knowledge of (d) was obtained.

  (A) The amount of side wall brick erosion increases as the average amount of oxygen supplied per charge increases.

  (B) An oxygen gas is blown up in the vacuum chamber by using an upper blowing lance that is inserted straight down from the center position of the upper portion of the vacuum chamber and is provided with a lance nozzle that injects the oxygen gas straight down. In the case of tempering, melting of the side wall brick on the downcomer side becomes significant. This is because the molten steel flows from the riser side to the downcomer side in the vacuum chamber, so even if oxygen gas is blown straight down, a lot of splash is generated at the downcomer side. It is because of melting.

  (C) When Al, Si, or the like is added to molten steel and oxygen gas is supplied to raise the temperature of the molten steel, if oxygen gas is supplied to the downcomer side, the melting loss of the downside pipe side wall bricks becomes extremely large. This is a process in which the above heat treatment is performed by adding Al, Si, etc. to the vacuum chamber and supplying oxygen gas. When oxygen gas is supplied to the downcomer, the heated steel is sufficiently heated. It passes through the vicinity of the downcomer pipe in a high temperature state without a time margin for mixing and averaging the temperature, and for this reason, the melting loss of the side wall brick on the downcomer pipe side becomes extremely large.

  (D) In order to suppress the melting of the side wall brick on the downcomer side, the splash generated on the downcomer side is reduced, and the molten steel in a sufficiently mixed state with the temperature averaged passes through the downcomer. What should I do?

  The present inventions (1) to (6) have been completed based on the above findings.

  Hereinafter, each requirement of the present invention will be described with reference to FIG.

  The lower part of the vacuum chamber 1 has an ascending pipe 4 and a descending pipe 5, and an inert gas is allowed to flow through the ascending pipe 4 as a reflux gas 6, and the molten steel 3 is sequentially sucked up from the ascending pipe 4. The oxygen gas 8 is supplied from an upper blowing lance 7 inserted from the upper center position of the vacuum chamber 1 into the vacuum chamber 1 of the RH vacuum degassing apparatus that continuously performs degassing processing by returning the 3 to the ladle 2. When top blowing is performed, if oxygen gas 8 is supplied to the central portion, that is, a portion equidistant from the ascending pipe 4 and the descending pipe 5, the side wall bricks on the downcomer pipe 5 side are significantly melted.

  Further, when the oxygen gas 8 is blown up from the top blowing lance 7, if the oxygen gas 8 is supplied to the downcomer 5 side, the side wall bricks on the downcomer 5 side are extremely damaged.

  On the other hand, when the oxygen gas 8 is blown upward from the top blowing lance 7, when the oxygen gas 8 is supplied to the rising pipe 4, the oxygen jet moves in the direction against the flow of the molten steel 3 in the vacuum chamber 1. Therefore, the splash splashing toward the downcomer 5 by the oxygen jet is significantly reduced. Furthermore, the splash jumping direction is also dispersed, and the melting of the side wall brick on the downcomer pipe 5 side is suppressed. That is, in order to suppress melting of the side wall brick on the downcomer pipe 5 side, supply of the oxygen gas 8 when the oxygen gas 8 is blown up from the top blowing lance 7 inserted from the upper center position of the vacuum chamber 1 is supplied. May be on the riser 4 side.

  Therefore, in the invention of (1), in order to suppress melting of the side wall brick on the downcomer pipe 5 side in the vacuum chamber 1 of the RH vacuum degassing apparatus, the center position 9 of the oxygen fire point is set to RH vacuum degassing. It was decided to be located on the ascending pipe 4 side in the vacuum chamber 1 of the apparatus.

  In the apparatus according to the invention of (4), it is defined that the center position 9 of the oxygen fire point is located on the riser 4 side in the vacuum chamber 1.

  Note that the “center position of the oxygen fire point” refers to the center of the region where the top-blown oxygen gas jet reaches the molten metal bath surface, and the “rising tube side in the vacuum chamber” is the distance from the rising tube in the vacuum chamber. As already mentioned, is a position smaller than the distance to the downcomer.

  When the oxygen gas 8 is blown up from the top blowing lance 7, even if the oxygen gas 8 is supplied to the riser 4 side, the center position 9 of the oxygen fire point becomes the side wall brick on the riser 4 side. When approaching too much, splash to the ascending pipe 4 side increases, and the melting damage of the side wall brick on the ascending pipe 4 side may increase. In this case, the center position 9 of the oxygen fire point is set to 0.5 to 0 in the ratio (r / r0) between the distance r from the side wall on the riser 4 side of the vacuum chamber 1 and the inner radius r0 of the vacuum chamber 1. .9, it is possible to stably and reliably suppress melting of the side wall bricks even on the ascending pipe 4 side.

  Therefore, in the invention of (2), the center position 9 of the oxygen fire point is determined by the ratio (r / r0) between the distance r from the side wall on the riser 4 side of the vacuum chamber 1 and the inner radius r0 of the vacuum chamber 1. The value of 0.5 to 0.9.

  In the apparatus according to the invention of (5), the center position 9 of the oxygen fire point is the ratio of the distance r from the side wall on the riser 4 side of the vacuum chamber 1 to the inner radius r0 of the vacuum chamber 1. The value of (r / r0) was defined to be 0.5 to 0.9.

  As already described, the “distance r from the side wall on the riser side” of the center position of the oxygen fire point is “the distance r from the inner wall surface of the riser side wall”, that is, the center of the oxygen fire point. Assuming a circle formed by the inner wall of the vacuum chamber on the horizontal plane including the position, the circumference corresponding to the center position of the oxygen fire point on the diameter of the circle passing through the center position of the oxygen fire point and the riser side And the distance r.

  When the oxygen gas 8 is blown upward from the top blowing lance 7, if a lance having an angle downward with respect to the vertical direction is used in the lance hole at the tip of the lance nozzle, the lance is located at the upper center position of the vacuum chamber 1. The oxygen gas 8 can be supplied to the ascending pipe 4 side even when it is inserted straight down. Then, a downward angle with respect to the vertical direction provided in the lance hole and the distance from the molten steel 3 of the upper blowing lance 7 when the oxygen gas 8 is blown (that is, the distance between the lance and molten steel surface) or the vacuum of the upper blowing lance 7. By controlling the distance from the tank bottom 10 (hereinafter referred to as the lance height), the oxygen gas 8 can be sprayed at an arbitrary position. In this case, if the angle provided in the lance hole at the tip of the lance nozzle is less than 3 ° downward with respect to the vertical direction, the oxygen gas 8 is supplied to the riser 4 side. In order to set the position 9 to a position of 0.5 to 0.9 in terms of the ratio (r / r0) of the distance r from the side wall on the riser 4 side of the vacuum chamber 1 to the inner radius r0 of the vacuum chamber 1. In this case, it is necessary to increase the distance between the lance and the molten steel surface and the height of the lance, the reaction efficiency with Al may decrease, and the heating efficiency of the molten steel may decrease. On the other hand, when the angle provided in the lance hole at the tip of the lance nozzle exceeds 10 ° downward with respect to the vertical direction, the oxygen gas 8 is supplied to the riser 4 side. Is set to a position of 0.5 to 0.9 in the ratio (r / r0) of the distance r from the side wall on the riser 4 side of the vacuum chamber 1 to the inner radius r0 of the vacuum chamber 1. It may be necessary to reduce the distance between the lance and the molten steel surface and the height of the lance, which may cause adhesion of metal to the lance and damage to the refractory at the bottom of the vacuum chamber.

  Therefore, in the invention of the above (3), as the upper blowing lance, a lance provided with an angle of 3 to 10 degrees downward with respect to the vertical direction in the lance hole at the tip of the lance nozzle is used.

  In the apparatus according to the invention of (5), the upper blowing lance is defined as a lance having an angle of 3 to 10 degrees downward with respect to the vertical direction in the lance hole at the tip of the lance nozzle.

  As described above, the angle provided downward in the lance hole at the tip of the lance nozzle with respect to the vertical direction is the vertical direction indicated by the two-dot chain line shown in the “A section enlarged” diagram of FIG. 1 and the central axis of the lance hole. This refers to the angle θ formed.

  Note that the position of the oxygen fire point in the vacuum chamber is, for example, when the top blow lance is inserted straight down from the center of the upper portion of the vacuum chamber with respect to the vertical direction in the lance hole at the tip of the lance nozzle. It can be adjusted by using a lance that is angled downward, and when using an upper blow lance that does not provide the above angle in the lance hole at the tip of the lance nozzle, it is necessary to remove from the upper center position of the vacuum chamber. When the upper blowing lance is inserted straight down, or when the upper blowing lance is inserted from the upper part of the vacuum chamber, it can be adjusted by inserting it at an angle rather than in the vertical direction (that is, in the straight downward direction).

  And the method of the said (1)-(3) invention can be easily implemented, for example using the apparatus which concerns on the said (4)-(6) invention, respectively.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Degassing treatment was repeated for the molten steel primarily refined in a 210-ton converter using an RH vacuum degassing apparatus having a circulation rate of 150 tons per minute. In order to heat the molten steel using the exothermic reaction between Al and oxygen, 0.17 m ³ (Normal) / min of oxygen gas per ton of molten steel is supplied from the top blowing lance into the vacuum chamber. It was tempered, and about 100 charges were taken as one cycle.

  During one cycle, blowing was performed with the center position of the oxygen fire point fixed when oxygen gas was blown from the top blowing lance. In addition, the center position of the oxygen fire point was set to three types: the center in the vacuum chamber, the downcomer side, and the upcomer side. When adjusting the center position of the oxygen fire point to the ascending pipe side and the descending pipe side, an upper blowing lance having an angle of 5 ° downward with respect to the vertical direction was used for the lance hole at the tip of the lance nozzle.

The maximum amount of erosion of the side wall bricks in the vacuum chamber when the oxygen gas was blown up under the above conditions was investigated. In addition, as already described as knowledge (a), since the amount of erosion is proportional to the amount of supplied oxygen, comparison was made with respect to an average supplied oxygen amount per charge of about 200 m ³ (Normal).

  Table 1 shows the results of the investigation of the top blowing condition of oxygen gas and the maximum amount of erosion of side wall bricks. FIG. 2 shows the relationship between the center position of the oxygen fire point and the maximum amount of erosion loss of the side wall bricks. In Table 1 and FIG. 2, “the center position of the oxygen fire point” is represented as “fire point position”, and “the maximum amount of erosion” of the side wall brick is represented as “the amount of erosion”.

  From Table 1 and FIG. 2, it is clear that the maximum amount of erosion of the side wall brick in the vacuum chamber can be reduced by positioning the center position of the oxygen fire point on the riser side.

As in the case of Example 1, the degassing treatment was repeated for the molten steel primarily refined in the 210-ton converter using an RH vacuum degassing apparatus having a circulation rate of 150 tons per minute. Also in the case of this example, in order to raise the temperature of the molten steel using the exothermic reaction between Al and oxygen, oxygen gas of 0.17 m ³ (Normal) / min per 1 ton of molten steel was put into the vacuum chamber. Supplied from the top blowing lance and blown, and about 100 charges were taken as one cycle.

  During one cycle, blowing was performed with the center position of the oxygen fire point fixed when oxygen gas was blown from the top blowing lance. In addition, the center position of the oxygen fire point uses an upper blow lance having an angle of 1 to 10 ° downward with respect to the vertical direction in the lance hole at the tip of the lance nozzle, and the distance between the lance and the molten steel surface is 2.0 to As a value of 3.9 m, the ratio (r / r0) of the distance r from the side wall on the riser side of the vacuum chamber to the inner radius r0 of the vacuum chamber was arbitrarily adjusted in the range of 0.20 to 0.94.

The maximum amount of erosion of the side wall bricks in the vacuum chamber when the oxygen gas was blown up under the above conditions was investigated. Since the amount of erosion was proportional to the amount of oxygen supplied, a comparison was made for an average amount of oxygen supplied per charge of about 200 m ³ (Normal). Moreover, the temperature rise was investigated by measuring the temperature of the molten steel before and at the end of oxygen blowing.

Table 2 shows the results of the investigation of the top blowing condition of oxygen gas and the maximum erosion amount of side wall bricks, and the investigation result of the oxygen gas top blowing condition and the temperature rise per 100 m ³ (normal) of oxygen. Show. FIG. 3 shows the relationship between the value of (r / r0) and the maximum amount of erosion of the side wall bricks. In Table 2 and FIG. 3 as well, the “maximum erosion amount” of the side wall brick is expressed as “the erosion amount”. The “lance hole angle” in Table 2 means an angle provided downward in the lance hole at the tip of the lance nozzle with respect to the vertical direction.

From Table 2 and FIG. 3, even when the center position of the oxygen fire point is located on the riser side, the test number 11 in which the value of (r / r0) is in the range of 0.5 to 0.9. It is clear that in the case of .about.26 and test number 32, the maximum amount of erosion of the side wall brick in the vacuum chamber is reduced. In the case of test number 32, since the lance hole angle is as small as 1 °, the distance between the lance and the molten steel surface increases when the value of “r / r0” is set to 0.88. Therefore, the oxygen amount is 100 m ³ (Normal). The heat-up efficiency of molten steel expressed by the amount of temperature rise per hit is inferior.

  According to the method of the present invention, in the vacuum refining in which the oxygen gas is blown up in the vacuum chamber of the RH vacuum degassing apparatus, the refractory constituting the side wall brick of the vacuum chamber can be suppressed. Since it is possible to efficiently heat the molten steel, the running cost can be significantly reduced. Moreover, if the molten steel heating apparatus of this invention is used, the method of this invention can be implemented easily.

It is a schematic diagram explaining the method of this invention which blows up oxygen gas in a vacuum tank using the upper blowing lance inserted from the upper center position of the vacuum tank of RH vacuum degassing apparatus. It is a figure which shows the relationship between the center position of the oxygen fire point investigated in Example 1, and the maximum amount of molten loss of a side wall brick. It is a figure which shows the relationship between the center position of the oxygen fire point in the riser side area | region investigated in Example 2, and the maximum amount of molten loss of a side wall brick.

Explanation of symbols

1: vacuum chamber,
2: Ladle
3: Molten steel,
4: riser,
5: downcomer,
6: reflux gas,
7: Top blowing lance
8: oxygen gas,
9: Center position of oxygen fire point,
10: Vacuum tank bottom.

Claims (6)

  A molten steel heating method in which oxygen gas is blown from an upper blowing lance in a vacuum tank of an RH vacuum degassing apparatus, the center position of the oxygen fire point being located on the riser side in the vacuum tank. Heat method.   The center position of the oxygen fire point is set to a position of 0.5 to 0.9 in terms of the ratio (r / r0) of the distance r from the side wall on the riser side of the vacuum chamber to the inner radius r0 of the vacuum chamber. Item 2. The molten steel heating method according to Item 1.   The molten steel heating method according to claim 1 or 2, wherein a lance in which an angle of 3 to 10 ° is provided downward in a lance hole at a tip of a lance nozzle as a top blowing lance.   A molten steel heating device for blowing oxygen gas from an upper blowing lance in a vacuum tank of an RH vacuum degassing apparatus, wherein the center position of the oxygen fire point is located on the riser side in the vacuum tank. Thermal device.   The center position of the oxygen fire point is at a position of 0.5 to 0.9 in terms of (r / r0), which is the ratio of the distance r from the side wall on the riser side of the vacuum chamber to the inner radius r0 of the vacuum chamber. The molten steel heating apparatus according to claim 4. The molten steel heating apparatus according to claim 4 or 5, wherein the upper blowing lance is a lance having an angle of 3 to 10 degrees downward with respect to the vertical direction in the lance hole at the tip of the lance nozzle.

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