JP6645370B2 - Ladle gas spraying device and method for producing low nitrogen steel - Google Patents

Description

  The present invention relates to a ladle gas blowing device for suppressing absorption of nitrogen into molten steel when tapping molten steel to a ladle, and a low-nitrogen steel using the ladle gas blowing device. And a method for producing the same.

In recent years, material properties required for steel materials have become more sophisticated, and there is a demand for improvement in characteristic values such as toughness of steel materials. If steel contains nitrogen, the properties of the steel may be degraded. Therefore, it is required to remove as much as possible from the steel except when intentionally adding nitrogen.
Further, when it is difficult to remove nitrogen from the steel material, alloy elements such as Ti and Nb are added to fix nitrogen as nitride. However, there is a problem that the production cost is increased due to the addition of the alloy element. Furthermore, there is a possibility that the case where coarse nitrides are formed or the added alloy itself may affect the properties of the steel material.
Therefore, in order to suppress the influence of nitrogen without using alloy elements such as Ti and Nb, reducing the nitrogen concentration in steel is a major issue.

Normally, in the blast furnace-converter method, hot metal having a carbon concentration of 4 to 5% (mass ratio; hereinafter, all concentrations are mass ratios unless otherwise specified in the present specification) is produced in the blast furnace. Decarburize in the furnace. In the converter, carbon in the hot metal is removed by a reaction of 2C + O ₂ = 2CO by blowing a large amount of oxygen onto the hot metal. When this reaction occurs, a large amount of CO gas is generated in the converter, and there is also the effect of the inert gas blown from the bottom of the converter to stir the hot metal. The concentration drops to about 10 ppm. However, when tapping molten steel from a converter to a ladle for transport to the next step, the nitrogen concentration in the molten steel increases due to the molten steel coming into contact with the atmosphere.

  In many cases, the molten steel discharged into the ladle is decompressed using a vacuum degassing device in the next step. However, since the denitrification reaction rate at this time is slow, the amount of denitrification is small. Also, it is difficult to completely shut off the air leak from the atmosphere during the processing, and during the vacuum processing, denitrification and nitrogen absorption occur simultaneously, and as a result, the nitrogen concentration in the steel may increase after the vacuum processing. Many attempts have been made to improve the denitrification reaction rate in vacuum degassing equipment, but due to processing time restrictions, it is necessary to produce low-nitrogen steel economically and stably using only vacuum degassing equipment. Not reached.

For this reason, in order to economically and stably produce low-nitrogen steel, molten steel reduced to about 10 ppm in a converter is output to a ladle without nitriding, and the vacuum degassing device suppresses nitriding. Ideally, the state is maintained and the process proceeds to the next step, continuous casting.
In order to solve such a problem, as described below, a method of suppressing nitrogen absorption during tapping has been proposed.

For example, in Patent Literature 1, for stainless steel for which it is difficult to reduce nitrogen, 0.13 × V (from the inside of the ladle to the outside of the ladle from before the tapping to at least completion of tapping) Product) (Nm ³ / min) or more, a technique is characterized in that a sufficient amount of CO ₂ gas generating substance is allowed to remain in or continue to be supplied to the ladle so as to allow a continuous flow of a CO ₂ gas stream having a flow rate of (Nm ³ / min) or more. Proposed.
Patent Document 2 proposes a technique characterized by using argon gas mixed with 3 to 20% by volume of oxygen gas as a gas for shielding molten steel from air during tapping.

Patent Document 3 proposes a technique of tapping Cr-containing low-nitrogen molten steel denitrified in a converter while sealing with inert gas.
In Patent Document 4, the tapping flow is received by the ladle along the inclined wall of the ladle, and an inert gas is supplied to the tapping port of a steelmaking furnace such as a converter to change the tapping flow to the tapping flow. A technique characterized by mixing an inert gas has been proposed.

In Patent Literature 5, a gas ejector that ejects a gas containing no nitrogen gas is provided around a tapping port of a refining furnace, and a Cr-containing molten steel that taps the refining furnace is discharged from the gas ejector. There has been proposed a technique characterized in that the shield is performed by using a shield.
In Patent Document 6, when tapping from a decarburizing furnace to a ladle for stainless steel in the same manner as described above, toward the vicinity of the lower end of the tapping flow, from before tapping of molten stainless steel until tapping is completed, A gas containing 20% by volume or more of oxygen without containing pure oxygen gas or nitrogen is supplied, and the flow rate V (Nm ³ / min) of the gas supplied into the ladle is changed to the ladle internal volume T (m ³ ). On the other hand, a technique of blowing the gas so that V> T is proposed.

JP 08-041525 A JP-A-06-025730 JP-A-60-026611 JP-A-61-166911 JP 2010-138446 A JP 2012-207272 A

Nagaro, Katsuyoshi Iwata, Michio Inoue, "Estimation of Oxygen and Nitrogen Absorption of Molten Steel at Converter Startup", Iron and Steel, 69 (1983), p. 767-774

However, the above techniques have problems. As described in Non-Patent Document 1 above, the place where the nitriding occurred, when molten steel was tapped from the converter into the ladle, was stored in the tapping flow and the ladle. It is considered to be a waterhole that is a collision area with the molten steel surface.
In view of this, a large amount of gas is required to fill the entire atmosphere in the ladle with non-nitrogen gas, as in Patent Literature 1, which is not economical.
Even if argon is blown to the molten steel flow passing near the upper part of the ladle as in Patent Document 2, since the vicinity of the molten steel flow is high heat and an updraft is generated, the vicinity of the basin only by being involved in the tapping flow is generated. It is difficult to reduce the nitrogen concentration of the steel.

Patent Document 3 describes that tapping is performed while blowing Ar gas on a ladle in which the inside of the ladle has been replaced with Ar, but it is not clear what specific flow rate and which portion was blown.
Even if an inert gas is involved in the tapping flow from the vicinity of the tapping hole as in Patent Document 4, it is not possible to efficiently reduce the nitrogen concentration in the bubbles of the waterfall pot caused by the entrainment of air from the atmosphere. .

As in Patent Document 5, when a non-nitrogen gas is blown from a tapping hole, since the distance from the tapping hole to the inside of the ladle is usually about 3 to 5 m, the non-nitrogen gas diffuses before reaching the waterhole. Would.
For this reason, it is considered that a method of directly blowing gas toward a waterhole using a nozzle as in Patent Document 6 is efficient. However, a ladle in which high-temperature molten steel is tapped and an updraft is generated. This document does not describe how far and at what flow rate the spraying should be performed.

  The present invention has been made in view of such a point, and a gas spraying device for a ladle capable of suppressing absorption of nitrogen from the atmosphere during tapping into a ladle, and the ladle It is an object of the present invention to provide a method for producing low-nitrogen steel using a gas blowing device for industrial use.

  The present inventors have studied the nitrogen absorption behavior during tapping from the converter to the molten steel in order to solve the above-mentioned problems. As a result, it was found that nitridation occurred mostly in the tapping flow. It was a waterhole that entered the molten steel in the pot, and it was found that nitriding could be suppressed by reducing the nitrogen concentration around this part. Furthermore, as a result of further studying a method for reducing the nitrogen concentration around the waterhole, a certain amount of non-nitrogen gas was blown at a certain flow velocity from a position close to the waterhole using a Laval nozzle. It was found that the surrounding nitrogen concentration could be reduced, and that nitrogen absorption during tapping could be suppressed.

  By using this method, it is possible to suppress nitrogen absorption during tapping without using equipment such as a lid with high sealing properties and a large amount of non-nitrogen gas, and it is possible to economically and stably produce low-nitrogen steel. it can. The present invention contemplates a gas spraying device that can blow non-nitrogen gas toward a waterhole where molten steel in a ladle is in contact with a tapping flow during tapping, and a gas blower for suppressing nitrogen absorption. The present invention has been completed by clarifying the nozzle position adjusting means to be provided in the spraying device, the nozzle shape, and the method of spraying non-nitrogen gas.

  The present invention has been completed based on the above findings, and a gas spraying device for a ladle according to the present invention is a gas spraying device for a ladle provided above a ladle for receiving molten steel. A lance that blows out non-nitrogen gas, a Laval nozzle provided at the tip of the lance, and a nozzle position adjusting unit that adjusts a tip position of the Laval nozzle, and the nozzle position adjusting unit includes: When the molten steel is tapped toward the ladle, the distance from the waterfall, which is the collision region between the tapping flow and the molten steel surface of the molten steel stored in the ladle, is within 2.0 m. In addition, the tip position of the Laval nozzle can be adjusted.

According to the ladle gas spraying device having this configuration, since the Laval nozzle is used, a sufficient flow velocity can be secured, and the ladle nozzle is not disturbed by the rising air currents in the ladle and is not directed toward the waterhole. Nitrogen gas can be blown.
Nozzle position adjustment for adjusting the tip position of the Laval nozzle such that the distance from the waterfall, which is the collision area between the tapping flow and the molten steel surface of the molten steel stored in the ladle, is within 2.0 m. Since the means is provided, a sufficient amount of non-nitrogen gas can be supplied around the waterhole, and the absorption of nitrogen into molten steel can be suppressed.

The method for producing low-nitrogen steel according to the present invention is a method for producing low-nitrogen steel using the above-described ladle gas blowing device, wherein the distance from the waterhole is within 2.0 m. The tip position of the Laval nozzle is adjusted, the gas flow rate at the outlet of the Laval nozzle is set to 350 m / s or more, and the gas flow rate is set to 5 Nm ³ / min or more. It is characterized by suppressing nitrogen absorption.

According to the method for producing low-nitrogen steel having this configuration, the tip of the Laval nozzle is located within 2.0 m from the waterhole, and the gas flow rate is 350 m / s or more, which is sufficiently fast, and the gas flow rate is 5 Nm ³ / min. As described above, since there is a sufficient amount, non-nitrogen gas can be sufficiently supplied to the periphery of the waterhole, and absorption of nitrogen into molten steel can be suppressed.

Here, in the method for producing low-nitrogen steel according to the present invention, it is preferable to use one or more of CO ₂ , Ar, and O ₂ as the non-nitrogen gas.
In this case, the nitrogen gas can be sufficiently removed around the waterhole, and the absorption of nitrogen into the molten steel can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the gas spraying apparatus for ladle which can suppress nitrogen absorption from air at the time of tapping to a ladle, and the low nitrogen steel using this gas spraying apparatus for ladle Can be provided.

It is a figure showing a calculation result of gas diffusion behavior at the time of injecting gas from a nozzle. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explanatory drawing of the tapping equipment to a ladle provided with the gas spraying apparatus for ladles which is one Embodiment of this invention. (A) is a front view, (b) is a side view. It is a graph which shows the relationship between the elapsed time from the start of tapping to a ladle and the amount of nitrogen absorption. It is explanatory drawing which shows operation | work of the tapping operation | work from a converter to a ladle and the gas spraying apparatus for ladles. It is a graph which shows the relationship between the gas flow velocity V of the nozzle outlet in Example, and the blowing gas flow volume Q.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

When smelting low-nitrogen steel with a low nitrogen concentration (for example, nitrogen concentration of 0.0035 mass% or less), molten iron with a high carbon concentration transported from a blast furnace or an electric furnace is charged into a refining furnace such as a converter, and oxygen is removed. It is decarbonized to a predetermined carbon concentration by blowing to form molten steel. During the oxygen blowing, a reaction of 2C + O ₂ = 2CO occurs, so that a large amount of CO gas is generated in the converter, so that the nitrogen concentration in the gas phase in contact with the molten iron is significantly reduced. In addition, by blowing non-nitrogen gas from the furnace bottom by stirring, the molten iron is vigorously stirred, resulting in a denitrification reaction in which nitrogen is released from the molten steel, and the nitrogen concentration in the molten steel after the converter treatment is reduced to about 10 ppm. descend. The molten steel after the converter processing is output from the converter to a ladle, and thereafter the components and temperature are adjusted by secondary refining and the like, and then subjected to a casting process. After that, it is shipped as a product through processes such as heating, rolling, heat treatment, and surface treatment.

  At the time of tapping from a refining furnace such as a converter, the furnace body is tilted, and molten steel is poured into the ladle from the side of the furnace body, the furnace port, or the furnace bottom. During tapping, the furnace body gradually tilts, and the ladle position moves accordingly. Also, during tapping, part or all of the alloy or slag-making agent required for component adjustment is introduced from the chute. At this time, in a portion where the tapping stream contacts the molten steel in the ladle, the surrounding gas phase is involved in the falling tapping stream, forming a so-called waterhole. Since the bubbles forming this waterhole contain a large amount of nitrogen in the atmosphere, the nitrogen concentration in the molten steel, which has dropped to 10 ppm after oxygen blowing, must increase to 400 ppm or more, which is in equilibrium with the nitrogen concentration in the atmosphere. become.

  Here, during tapping, a non-nitrogen gas is blown toward the waterhole at a certain speed or higher and at a certain flow rate or higher. When the sprayed non-nitrogen gas reaches the vicinity of the waterhole, the nitrogen concentration in the vicinity of the waterhole is reduced, so that the nitrogen concentration in the bubbles forming the waterhole is also reduced. At this time, when the nitrogen concentration in the vicinity of the waterhole becomes approximately half that in the air, the equilibrium nitrogen concentration also becomes approximately half, so that a large nitrogen absorption suppression effect can be obtained. On the other hand, when the non-nitrogen gas is blown at a speed lower than a certain speed, the non-nitrogen gas will reach It diffuses and cannot reduce the nitrogen concentration around the basin.

Therefore, assuming that non-nitrogen gas is blown near the waterhole during tapping, we tried to reproduce the behavior of non-nitrogen gas blown from the nozzle by flow calculation. The calculation region was filled with N ₂ , and a non-nitrogen gas was blown from the ceiling to reproduce the diffusion. The gas species to be sprayed were Ar, CO ₂ , and O _2, and these were appropriately mixed. The atmosphere pressure was set to 1 atm, the atmosphere temperature was set to 1000K, and the gas temperature was set to 300K at the nozzle outlet, assuming the inside of the ladle. Also, it was assumed that an upward airflow of 10 m / s was generated upward in the ladle.
FIG. 1 shows an Ar gas concentration distribution when the Ar gas flow rate is 5.0 Nm ³ / min and the gas flow rate at the nozzle outlet is 384 m / s. When the gas is about 2 m away from the nozzle outlet, the Ar gas concentration is reduced to about 50%. It can be seen that the Ar gas concentration decreases to 20% or less when the ladle height is assumed to be 4 m away. From the results of these flow calculations, the flow velocity and flow rate of non-nitrogen gas blown near the waterhole were estimated, and the effect of preventing nitrogen absorption during tapping was estimated by actual machine tests.

  In order to ensure that the non-nitrogen gas reaches the waterhole, the gas flow rate at the nozzle outlet is preferably 350 m / s or more. If the gas flow rate is insufficient, even if the non-nitrogen gas is blown, the non-nitrogen gas is pushed back by the upward airflow generated around the waterhole, so that the non-nitrogen gas does not reach the waterhole. Obtaining such a gas flow rate is difficult with a normal straight nozzle, and requires the use of a Laval nozzle. The gas flow rate at the nozzle outlet is preferably at least 380 m / s, more preferably at least 400 m / s.

Further, in order to reduce the nitrogen concentration around the waterhole, the gas flow rate of the non-nitrogen gas to be blown is preferably 5 Nm ³ / min or more. When the flow rate of the non-nitrogen gas is small, even if the gas reaches the vicinity of the waterhole, the gas is immediately diffused, and the nitrogen concentration in the bubbles entrained by the tapping flow cannot be sufficiently reduced. The gas flow rate of non-nitrogen ^gas, is preferably 7 Nm 3 / min or more, more preferably 10 Nm ³ / min or more.
When the gas flow rate of the non-nitrogen gas is determined, the gas flow rate is determined by the shape and pressure of the Laval nozzle. Therefore, the inner diameter and shape of the Laval nozzle may be determined according to the required gas flow rate and gas flow rate.

  In addition, in order to further reduce the nitrogen concentration around the basin, the distance from the tip of the Laval nozzle to the basin must be within 2.0 m. Assuming that the distance at which the Ar degree is 50% is considered as one criterion for the flow calculation result, the condition where the distance from the tip of the Laval nozzle to the waterhole is greater than 2.0 m is a condition where the gas flow velocity is increased. However, the Ar gas is diffused, and the position where the Ar concentration becomes 50% does not extend extremely beyond 2.0 m. On the other hand, by increasing the gas flow rate, the position where the Ar concentration becomes 50% extends beyond 2.0 m. However, in order to increase the gas flow rate while maintaining the gas flow rate, the nozzle diameter is kept the same. However, there is a limit to increasing the gas pressure, and increasing the pressure of a large amount of gas is costly.

  Therefore, in order to economically reduce the nitrogen concentration around the waterhole, the distance from the tip of the Laval nozzle to the waterhole must be within 2.0 m. Further, it is more desirable that the distance from the tip of the Laval nozzle to the waterhole is within 1.5 m. On the other hand, if the Laval nozzle tip is deformed by heat when it is too close to the molten steel surface, the distance from the Laval nozzle tip to the waterhole is desirably 1.0 m or more.

  Since the place where the nitrogen absorption occurs is a waterfall that occurs at the part where the tapping flow and the molten metal surface are in contact, the gas spraying device has a lance for blowing non-nitrogen gas and moves with tapping. It is necessary to provide nozzle position adjusting means capable of adjusting the tip position of the Laval nozzle in accordance with the movement of the waterhole. At this time, in order to surely reduce the nitrogen concentration around the basin as described above, the distance from the tip of the Laval nozzle to the basin must be within 2.0 m. At the time of tapping, since the distance between the lance tip and the molten steel is short, it is preferable to use a water-cooled structure.

Here, FIG. 2 shows a tapping facility for a ladle 20 provided with the ladle gas blowing device 10 according to the present embodiment.
In the present embodiment, as shown in FIG. 2, the ladle 20 is provided below the converter 30, and the molten steel is tapped from the converter 30 to the ladle 20. . In addition, the ladle 20 is arrange | positioned on the movable cart 21.

  The ladle gas blowing device 10 according to the present embodiment includes a support base 11 disposed at a height substantially equal to a work floor 32 on which the trunnion 31 of the converter 30 is installed. A lance 12 supported by the lance 12, a Laval nozzle 13 disposed at the tip of the lance 12, and nozzle position adjusting means 15 for adjusting the position of the tip of the Laval nozzle 13 are provided.

The nozzle position adjusting means 15 is capable of moving the lance 12 up to about 10 m in its length direction and adjusting the elevation angle of the lance 12. Further, the support base 11 can be rotated in the horizontal direction.
In this way, by adjusting the longitudinal position and the elevation angle of the lance 12, the height position of the tip of the Laval nozzle 13 is adjusted according to the rise of the waterfall pot accompanying the rise of the molten metal level in the ladle 20 during tapping. It is configured to be able to. Furthermore, by combining the longitudinal position and the horizontal rotation of the lance 12, the tip position of the Laval nozzle 13 can be adjusted in accordance with the tapping flow 2 that moves back and forth during tapping.
Therefore, during tapping, it is possible to adjust the tip position of the Laval nozzle 13 within a range of 2.0 m or less from the waterhole.

  Here, the period during which the non-nitrogen gas is blown around the waterhole is preferably continuous from before tapping to after tapping. However, nitriding occurs at the time of tapping mainly at the waterfall basin. Immediately after the start of tapping, the ladle is not yet sufficiently filled with molten steel, so that a sufficient waterfall basin has not been generated. As shown in FIG. 3, the temporal change of the nitrogen absorption during tapping increases rapidly when the ladle is filled with molten steel to some extent.

  For this reason, the effect of the invention can be sufficiently obtained even when the start time of blowing the non-nitrogen gas around the waterhole is 15 seconds to 20 seconds after the start of tapping. Thereafter, the ladle is filled with molten steel just enough to create a large waterhole, and the fall distance from the converter to the ladle is still large, showing the maximum value in the first half of tapping, but from the middle to the end, As the ladle is filled with molten steel, the amount of nitrogen absorption decreases as the falling distance decreases. However, since nitrogen absorption still occurs even during the middle to late stages, it is desirable to continuously blow a non-nitrogen gas until the end of tapping. In particular, it is desirable to blow a non-nitrogen gas until the end of tapping, since after the addition of the alloying element, nitrogen absorption may occur easily.

A specific operation will be described with reference to FIG.
First, as shown in FIG. 4 <1>, at the time of the start of tapping, the lance 12 is arranged at the standby position, and the non-nitrogen gas is not sprayed.
Next, as shown in FIG. 4 <2>, 15 to 20 seconds after the start of tapping, molten steel 1 is stored in ladle 20, and tapping flow 2 is brought into contact with the molten metal surface of molten steel 1. A colliding waterhole is formed. By this time, the converter 30 has been sufficiently tilted, and a gap is formed that does not interfere with the converter steel bar even when the lance 12 is lowered from the standby position into the ladle 20. Then, the lance 12 is moved by the nozzle position adjusting means 15 so that the tip of the Laval nozzle 13 is located within 2.0 m from the waterhole, and the blowing of non-nitrogen gas is started.
Next, as shown in FIG. 4 <3>, when tapping is continued, the molten metal level of the molten steel 1 in the ladle 20 rises. As the molten metal surface of the molten steel 1 in the ladle 20 rises, the lance 12 is moved by the nozzle position adjusting means 15 to spray the non-nitrogen gas while maintaining the tip of the Laval nozzle within 2.0 m from the waterhole. Is carried out.

  Thus, according to the ladle gas spraying device 10 of the present embodiment, the Laval nozzle 13 is used, and the Laval nozzle 13 is positioned such that the distal end of the Laval nozzle 13 is within 2.0 m from the waterhole. Since the nozzle position adjusting means 15 for adjusting is provided, a non-nitrogen gas can be blown toward the waterfall at a sufficient flow rate, and by sufficiently removing nitrogen around the waterfall, nitrogen in the molten steel can be reduced. Absorption can be suppressed. Therefore, it is possible to manufacture high-quality low-nitrogen steel with a sufficiently reduced nitrogen concentration.

Furthermore, according to the method for producing low-nitrogen steel according to the present embodiment, the position of the tip of the Laval nozzle 13 is adjusted so that the distance from the waterhole is within 2.0 m, and the gas flow rate at the outlet of the Laval nozzle 13 is set to 350 m. / S or more, the gas flow rate is 5 Nm ³ / min or more, and the non-nitrogen gas is blown toward the waterfall, so that the non-nitrogen gas can be sufficiently supplied around the waterfall and the nitrogen in the molten steel can be supplied. Absorption can be suppressed.

Note that the non-nitrogen gas is desirably one or a mixed gas of two or more of CO ₂ , Ar, and O ₂ .

Although the embodiments of the present invention have been specifically described above, the present invention is not limited thereto, and can be appropriately modified without departing from the technical idea of the present invention.
For example, non-nitrogen gas blown around the waterhole diffuses near the waterhole, so even a single lance can provide the effect of preventing nitrogen absorption. However, two or more lances must be used within a range that does not interfere with the chute for alloy addition. There is no problem even if it is installed and non-nitrogen gas is blown.
The present invention is very effective for carbon steel, but is also effective for melting stainless steel and alloy steel other than carbon steel.
Further, although the operation mode in the converter has been described, the present invention is also applicable to an operation mode in which steel is tapped from a furnace opening to a ladle like AOD.

Under the conditions of the method of the present invention and the comparative method described below, an evaluation test of nitrogen absorption behavior at the time of tapping was performed to confirm the effects of the invention.
First, hot metal (equivalent to a carbon content of 4.5%) transported from a blast furnace was charged into a converter, and oxygen blowing was performed. The components after converter blowing are [C] = 0.03 to 0.15%, [Si] = 0.01 to 0.05%, [Mn] = 0.1 to 0.4%, [P] = 0.01 to 0.03%, [N] = 8 to 12 ppm, the balance being Fe and unavoidable components.

The throughput is 300 ton and the tapping time is 5 minutes. The height from the bottom of the ladle for receiving molten steel to the top of the ladle is 3.9 m and is preheated in advance. In the tapping flow, when the furnace mouth of the tilted converter is viewed from the front from the start to the end of tapping, it moves back and forth, so the ladle trolley is moved according to the tapping flow to receive steel. .
In addition, the lance which blows non-nitrogen gas is arrange | positioned toward the waterhole from the side surface of the tapping flow, and can be moved back and forth according to the movement of the tapping flow. The tip of the lance is a straight nozzle or a Laval nozzle, and is configured so that it can be moved up and down in accordance with the level of molten steel filling the ladle.

  In order to confirm the effect of the present invention, the molten steel in the converter before the start of tapping and in the ladle after tapping was completed was sampled, and the amount of change in nitrogen concentration Δ [N] (ppm) before and after tapping was determined by nitriding. It was evaluated as an amount. Table 1 shows the tapping conditions. Since it was difficult to actually measure the gas flow velocity V at the nozzle outlet in Table 1, the flow velocity at the nozzle outlet position obtained by the flow calculation was used.

  Before tapping, when the lance was extended, it interfered with the furnace body of the converter, so the lance was raised to the upper limit position and kept on standby. Start tilting the converter to tap, and if the converter tilts to a certain extent, it will not interfere with the converter body even if the lance is extended, so extend the lance from this point until the molten steel comes out from the tap hole. I waited with the lance tip in the ladle. At the start of tapping, the position of the basin was investigated, and the lance length, elevation angle and horizontal rotation angle were adjusted so that the tip of the lance was directed toward the basin, and at the same time the distance between the lance and the basin was adjusted appropriately. The distance between the nozzle and the basin was adjusted by adjusting the length of the lance, the elevation angle, and the horizontal rotation angle with reference to the previously determined rate of rise of the molten metal level during tapping.

  At the time of tapping, an alloy containing Al was fed in such a manner that it was involved in the tapping flow two minutes after tapping. The C and Al concentrations shown in Table 1 are components of the molten steel in the ladle after tapping is completed. Hereinafter, when Δ [N] is 15 ppm or less, it is determined that the effect of the present invention is obtained. When Δ [N] is 12 ppm or less, it is determined that an excellent effect is obtained. When there was, it was judged that there was a particularly excellent effect.

Test No. In 1 (conventional method), Δ [N] = 23 ppm as a result of tapping the steel from the converter to the ladle as usual.
Hereinafter, Test No. 2 to No. 2 Up to 23, non-nitrogen gas was sprayed from the gas spray lance toward the waterhole during tapping. In addition, the distance between the nozzle and the waterhole in the table indicates the distance from the initial stage to the end stage of tapping. In the last stage, the distance was 1.2 m, which is the upper limit of the lance lifting device.

Test No. 2 to No. 2 In No. 4 (Comparative method), a non-nitrogen gas was blown toward the waterhole at a nozzle outlet flow rate of 305 to 422 m / s and a gas flow rate of 8 to 12 Nm ³ / min. At this time, the test No. 2 and No. In No. 3, since the lance was sprayed with the lance fixed to the upper part of the ladle, the distance between the nozzle and the waterhole was 5.0 m immediately after tapping, and became shorter according to the level of the molten metal during tapping. At the completion, it was 1.2 m, but Δ [N] was 22 ppm, and the effect of the invention was not recognized. Test No. No. 4 was moved up and down during tapping so that the distance between the nozzle and the basin became 2.5 to 3.0 m, and when tapping was completed, it was 1.2 m, but Δ [N] was 21 ppm, No effect of the invention was observed.

Test No. 5 to No. 5 No. 9 (Comparative method) shows that the gas flow rate is 5 to 10 Nm ³ / min while the distance between the nozzle and the waterhole is maintained at 1.5 to 2.0 m during tapping, and the nozzle outlet is formed using a straight nozzle at the tip of the lance. As a result of spraying a non-nitrogen gas toward the waterhole at a flow rate of 72 to 310 m / s, [N] was 17 to 22 ppm, and the effect of the invention was not recognized.

Test No. 10 to No. No. 12 (Invention method), the nozzle exit flow rate is 386 m / s or more and the gas flow rate is 3 using a Laval nozzle at the tip of the lance while maintaining the distance between the nozzle and the basin at 1.5 to 2.0 m during tapping. As a result of spraying a non-nitrogen gas toward the waterhole under the condition of ４4 Nm ³ / min, Δ [N] became 13 to 15 ppm, and the effect of the invention was recognized.
Test No. From the results up to 12, the nitrogen-absorbing effect can be obtained by blowing a non-nitrogen gas to the tip of the lance using a Laval nozzle while maintaining the distance between the nozzle and the waterfall at 1.5 to 2.0 m during tapping. You can see that.

Test No. 13 to No. 13 No. 21 (Invention method), the gas flow rate is 5 Nm ³ / min or more, and the nozzle outlet flow rate is increased by using a Laval nozzle at the tip of the lance while maintaining the distance between the nozzle and the waterhole at 1.5 to 2.0 m during tapping. As a result of spraying a non-nitrogen gas toward the waterhole under a condition of 350 m / s or more, Δ [N] was 7 to 12 ppm, and an excellent effect of the invention was recognized. In particular, the test No. 19 to No. Up to 21, Δ [N] was 7 to 9 ppm, and particularly excellent effects of the invention were obtained.

Test No. No. 22 to No. 22. No. 23 (invention method) is that the gas flow rate is 5 Nm ³ / min or more and the nozzle outlet flow rate is increased by using a Laval nozzle at the tip of the lance while maintaining the distance between the nozzle and the waterfall at 1.0 to 1.5 m during tapping. As a result of spraying a non-nitrogen gas toward the waterhole under a condition of 350 m / s or more, Δ [N] was 7 to 9 ppm, and a particularly excellent effect of the invention was recognized.
Test No. As can be seen from the results up to 23, the distance between the nozzle and the waterhole during tapping was 2.0 m or less, and the gas flow rate was 350 m / s or more and the gas flow rate was 5 Nm ³ using a straight nozzle at the tip of the lance. It can be seen that an excellent nitrogen absorption control effect can be obtained by spraying a non-nitrogen gas toward the waterhole at a rate of / min or more.

  FIG. 5 shows test No. 2 in which the distance between the nozzle and the waterhole during tapping was maintained from 1.5 m to 2.0 m. 5 to No. 5 The relationship between the gas flow rate at the nozzle outlet up to 21 and the flow rate of the blowing gas is shown. In FIG. 5, crosses indicate conditions under which the effects of the present invention were not recognized, Δ marks indicate conditions under which the effects of the present invention were recognized, 印 marks indicate conditions under which excellent effects were recognized, Is the recognized condition.

Test No. 7, 8 (Comparative method) and Test No. From the comparison between Nos. 18 and 20 (invention method), it is understood that the gas flow velocity V at the nozzle outlet is desirably 350 m / s or more.
Test No. Nos. 11 and 12 (invention method) and Test Nos. 13 to No. 13 From comparison with No. 16 (Invention method), it is understood that the spray gas flow rate Q is desirably 5 Nm ³ / min or more.
Further, the test No. As shown in 11, 14, 15, 16, 19, and 20, even when the gas type is changed, the effect of suppressing nitrogen absorption is recognized, so that one or more of CO ₂ , Ar, and O ₂ are used. It can be seen that even if a mixed gas is used, it can be used as a non-nitrogen gas.

  From the above, it can be seen that it is desirable to satisfy the conditions of the present invention in order to smelt low-nitrogen steel economically (that is, while maintaining the yield).

  Since it is possible to prevent nitrogen absorption during the tapping of molten iron, it is useful in a method for producing low-nitrogen steel.

REFERENCE SIGNS LIST 1 molten steel 2 tapping flow 10 gas blowing device for ladle 12 lance 13 Laval nozzle 15 nozzle position adjusting means 20 ladle 30 converter

Claims (3)

A ladle gas spraying device provided above a ladle that receives tapping molten steel,
A lance that blows out non-nitrogen gas, a Laval nozzle provided at the tip of the lance, and a nozzle position adjusting unit that adjusts a tip position of the Laval nozzle,
The nozzle position adjusting means, when the molten steel is tapped toward the ladle, a distance from a waterhole, which is a collision area between a tapping flow and a molten steel surface stored in the ladle. Characterized in that the tip position of the Laval nozzle can be adjusted so that is within 2.0 m. A method for producing low nitrogen steel using the ladle gas spraying device according to claim 1,
While adjusting the tip position of the Laval nozzle so that the distance from the waterhole is within 2.0 m,
The gas flow rate at the outlet of the Laval nozzle is 350 m / s or more, and the gas flow rate is 5 Nm ³ / min or more. By blowing a non-nitrogen gas toward the waterhole, the absorption of nitrogen into the molten steel is suppressed. And producing a low-nitrogen steel. As a non-nitrogen, CO 2, _Ar, method for producing a low nitrogen steel according to claim 2, one or characterized by the use of two or more of the O _2.

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