JP5188766B2 - Molten alloy sealing device and method of air separation at the start of continuous casting - Google Patents

Description

  The present invention relates to a sealing technique for isolating a molten alloy from the atmosphere, and suppresses oxidation and nitridation of the molten alloy using the sealing device. In particular, the present invention relates to a method for cutting air at the start of casting in continuous casting of molten alloy.

  Depending on the type of metal, the molten alloy may be very reactive with the atmosphere. Specifically, molten steel, stainless steel, Fe—Ni alloy, Ni-base alloy, etc. are in a state where the surface of the molten alloy is exposed to the atmosphere in order to maintain a high temperature of 1400 ° C. or higher in the molten state. Easy to oxidize. Further, when active elements such as Si, Mn, Al, and Ti are added to the alloy, they preferentially react with oxygen and nitrogen in the atmosphere to form oxides and nitrides, respectively. These oxides and nitrides become large non-metallic inclusions, and when they are entrained in a molten alloy, they may become wrinkles in a cast product that has undergone a casting process.

  For this reason, various methods have been studied so that the surface of the molten alloy is not exposed to the atmosphere as much as possible, and several tundish sealing techniques have been disclosed in the field of continuous casting of steel. Tundish inert gas sealing technology is already common because it is easy and highly effective because the lid can be installed relatively easily (for example, Patent Documents 1 to 3). reference).

  Also disclosed is a technique for sealing a sliding gate portion of an immersion nozzle for guiding a molten alloy from a tundish to a continuous casting mold (see, for example, Patent Document 4). Furthermore, some techniques for sealing a continuous casting mold with an inert gas have also been shown (for example, see Patent Documents 5 to 7).

  The technique described in Patent Document 5 is a technique in which a steel box is installed on a dummy bar, and then an inert gas is introduced into the box to cut air and start casting. After casting, the box which is an unsteady part is removed, and the defective part is not brought into the product. However, it is necessary to produce a steel box every time in accordance with casting, and a setup work for setting the steel box is also required, which increases the cost and the number of processes, and can be said to be unrealistic.

  The technique described in Patent Document 6 is a technique in which the lower surface of the tundish and the mold are covered with a shielding plate, the gas is cut off by introducing an active gas therein, and casting is started. This technology also has the problem that it takes time to install the shielding plate. Furthermore, since the upper part of the molten alloy is covered by the shielding plate, the molten alloy cannot be monitored directly at the start of casting, and the timing of the start command of the dummy bar (slab) drawing start It was unrealistic because there were many problems such as being difficult to determine and not being able to respond in an emergency.

  The technique described in Patent Document 7 is a technique in which casting is started while an upper surface of a mold is covered with a lid, and then an inert gas is introduced into the mold and gas is cut off. According to this technique, the upper part of the molten alloy is preferably replaced with an inert gas. However, since the molten alloy cannot be directly monitored at the start of casting, it is unrealistic like the technique described in Patent Document 6.

JP-A-6-39505 JP-A-7-204808 JP-A-8-257708 JP 2002-143994 A JP 59-45064 A Japanese Unexamined Patent Publication No. 60-6253 JP-A-10-314901

  As described above, suppression of oxidation and nitridation of a molten alloy by contact with the atmosphere has been a problem for some time, and a sealing method using an inert gas has been adopted. In particular, when the lid is easy to seal and the container is easy to seal, the seal is maintained to some extent by the effect of the combination of the lid and the inert gas.

  However, the casting mold of a continuous casting machine, which is difficult to install due to the structure, has a process of pouring a molten alloy at the start of casting.

  Therefore, the present invention has been made in view of the above situation, and an object of the present invention is to purge the atmosphere in contact with the molten alloy with an inert gas and maintain a seal without a lid. The present invention proposes a sealing device for a molten alloy that makes it possible. Furthermore, the present invention also proposes a method for shutting off air at the start of continuous casting using this sealing device.

The present invention is a sealing device for sealing a molten alloy with an inert gas, and includes a jet nozzle having a flat jet slit for supplying an inert gas to one end of an opening of a mold for holding the molten alloy. A suction nozzle having a flat suction slit for sucking the inert gas having a suction amount of 0.7 to 0.9 times the ejection amount at a position facing the ejection nozzle, and a flow rate of the inert gas There 100~2000L / min der is, the jet nozzle and the suction nozzle, is characterized in that it is divided into two each with a mold center near a position opposite to the immersion nozzle of the molten alloy.

The present invention is also a sealing device for sealing a molten alloy with an inert gas, and 0.2: 0.8 to 0.5: 0 at opposite ends of a mold opening for holding the molten alloy. Each having an ejection nozzle having a flat ejection slit for supplying an inert gas at a quantity ratio of .5, the flow rate of the inert gas is 100 to 2000 L / min, and the ejection nozzle is immersed in a molten alloy It is characterized by being divided into two parts in the vicinity of the mold center, which is a position facing the nozzle .

  Further, the method for shutting off air at the start of continuous casting according to the present invention is characterized in that the above molten alloy sealing device is used at the start of casting for continuous casting, and the molten alloy held in the mold is vented from the atmosphere.

  By using the sealing device of the present invention at the start of casting of continuous casting of the alloy, non-metallic inclusion physical defects due to oxidation and nitriding of the molten alloy can be prevented, so that the yield of unsteady parts at the initial casting can be improved, and the quality can be improved. Contributes to improvement and reduction of manufacturing costs.

Preferred embodiments of the present invention will be described below with reference to the drawings.
1. Continuous Casting Process A schematic diagram of a CCM (Continuous Casting Machine, continuous casting machine) to which the sealing device of the present invention can be applied is shown in FIG. The casting machine shown in FIG. 1 is a vertical casting machine in which a molten alloy is supplied from above and a slab is sent downward. Since the present invention is a starting sealing technique at the start of casting, the type of continuous casting machine, ie, vertical type, curved type, vertical bending type, etc., is not limited.

  First, the raw material is melted in an electric furnace or the like (not shown). Then, as a refining process, decarburization, deoxidation, and desulfurization are performed, and the temperature is adjusted by ladle refining. Next, a molten alloy is cast with the CCM shown in FIG. 1 to produce a slab. In FIG. 1, reference numeral 10 denotes a ladle, and the molten alloy 20 that has undergone the melting process and the refining process is put into the ladle 10. Subsequently, the molten alloy 20 is supplied to the mold 15 through the tundish 11 provided on the downstream side of the ladle 10 and is put into the mold. The molten alloy 20 poured into the mold is solidified by passing through a spray cooling zone 17 provided on the lower side of the mold, and is drawn by the pinch roll 18 to obtain a slab 21 having a predetermined thickness. . The slab 21 is cut by the torch 19 at a predetermined position. The above is the steady state of casting after a certain time has elapsed since the start of casting.

  Next, the start of continuous casting will be described. FIG. 2 is an enlarged view showing the tundish 11 and the mold 15 in more detail, showing the starting setting state of the continuous casting machine. The molten alloy 20 held by the tundish 11 is supplied into the mold 15 from the discharge hole 13 via the immersion nozzle 12 by controlling the stopper 14. Reference numeral 16 denotes a sealing material, which is a member for sealing so that the molten alloy does not leak. After a predetermined amount of molten alloy 20 is poured into the mold 15, the dummy bar 22 (set up to the pinch roll 18) is pulled out in the casting direction (vertically downward in the figure) to start casting. The slab is continuously cast by continuously supplying the molten alloy 20 together with the drawing.

  Before the start, the mold 15 is filled with air, and when the molten alloy 20 is poured into the mold 15, the molten alloy 20 entrains oxygen and nitrogen. In addition, since the liquid level of the molten alloy 20 continues to be exposed to the atmosphere from the start of pouring until the dummy bar 22 starts to be drawn and the mold powder is charged, the quality of the slab after production is generated. As described above, it is aggravated. The present invention suppresses contact between the molten alloy and the atmosphere by providing a sealing device at the top of the mold 15 at the start of casting. Hereinafter, the sealing device of the present invention will be described in detail.

2. Sealing device Figure 3 is a schematic sectional view showing a state in which a sealing device to the mold of a continuous casting machine according to an embodiment of the present invention. 3 is a view as seen from the direction A in FIG. One side of the upper end opening of the mold 15 is provided with a flat ejection nozzle 31 connected to a pipe, and a flat suction nozzle 32 connected to the pipe is provided at an opposite position. . As shown by arrows in FIG. 3, after the inert gas is ejected from the ejection nozzle 31, most of the inert gas is sucked into the suction nozzle 32 as it is, and part of the inert gas enters the mold 15. At this time, since both nozzles 31 and 32 have a flat shape, the inert gas blown out and sucked flows in a flat shape, functions as an inert gas curtain, and seals the inside and the outside of the mold 15. it can. In addition, a part of the inert gas that has entered the mold 15 can expel the atmosphere and replace the mold 15 with an inert gas atmosphere.

  Here, the amount (exhaust amount) of the inert gas sucked by the suction nozzle 32 is preferably 0.7 to 0.9 times the ejection amount from the ejection nozzle 31. By setting it within this range, the inert gas remaining without being sucked can be retained in the mold, and the molten alloy can be sealed from the atmosphere. An exhaust gas ratio of less than 0.7 is not preferable because the inert gas does not sufficiently enter the mold. On the other hand, when the exhaust gas ratio exceeds 0.9, most of the supplied inert gas is exhausted, and a sufficient amount of inert gas for staying in the mold and sealing the atmosphere cannot be secured.

  The ejection nozzle 31 and the suction nozzle 32 may be integrated or divided into the mold width and full width. An example of the mode is shown below.

  FIG. 4A is a view of FIG. 3 as viewed vertically from below (direction B), and shows a case where the nozzle is integrated with the entire width of the mold. Inert gas is supplied from the ejection nozzle 31 and exhausted by the opposing suction nozzle 32.

  FIG. 4B is a view of FIG. 3 as viewed from above vertically downward (direction B). The ejection nozzle 31 and the suction nozzle 32 are each divided into two near the center of the mold 15. Inert gas is blown out and sucked by a pair of opposed members. This type is different from that shown in FIG. 4A, and it is suppressed that the inert gas hits the immersion nozzle 12 arranged near the center of the mold 15. Since the immersion nozzle 12 holds the high-temperature molten alloy, the immersion nozzle 12 itself is at a high temperature. When the immersion nozzle 12 is cooled by an inert gas, the molten alloy in the immersion nozzle 12 is solidified or immersed by a rapid temperature change. The nozzle 12 itself is prevented from being damaged.

  FIG. 5 is a schematic cross-sectional view showing a state in which a sealing device according to another embodiment of the present invention is provided in a mold of a continuous casting machine. FIG. 5 shows a form in which the ejection nozzle 31 is used instead of the suction nozzle 32 in FIG. In this embodiment, as shown by the arrows in FIG. 5, since the inert gas collides with each other after being ejected from the opposed ejection nozzles 31, the inert gas functions as an inert gas curtain to evacuate the atmosphere. Can be sealed. In addition, a part of the colliding inert gas diffuses above the mold 15 and a part enters the mold 15 and drives out the air, so that the inside of the mold 15 can be replaced with an inert gas atmosphere. In the drawing, the supply amount of the inert gas is a preferred embodiment in which the total amount is 1 and the balance is between 0.2: 0.8 and 0.5: 0.5, as the left and right balance.

  The ejection nozzle 31 may be integrated or divided into the mold width and full width. An example of the mode is shown below.

  FIG. 6A is a view of FIG. 5 as viewed from above vertically downward (direction C), and is a case of integral type in the entire width. An inert gas is supplied from the opposed ejection nozzle 31.

  FIG. 6B is a view of FIG. 5 as viewed from above vertically downward (direction C), in which the ejection nozzle 31 is divided into two near the center of the mold 15, and each pair is opposed to each other. Inert gas is ejected. By changing in this way, it is suppressed that an inert gas hits the immersion nozzle 12, and it prevents that the molten alloy in the immersion nozzle 12 solidifies or the immersion nozzle 12 itself is damaged. Same as b).

  Subsequently, in order to solve the above-described problem caused by the contact between the molten metal and the atmosphere, an experiment conducted by the present inventors and a calculation simulation performed in combination with the experiment will be described below.

  First, SUS304 (Fe-18 mass% Cr-8 mass% Ni) was dissolved in a laboratory using a 20 kg high-frequency induction furnace. Magnesia was used for the crucible, and 0.1% Al was added to deoxidize the molten alloy. A sealing experiment was conducted in which Ar gas was blown onto a free board (space from the upper surface of the molten alloy to the upper surface of the crucible), and the oxygen concentration in the atmosphere of the free board was continuously measured with an oxygen concentration meter. Here, the top of the crucible was covered to maintain confidentiality. As a result, it was found that when oxygen was reduced to 10 vol% or less, scum (soot oxidized by the molten alloy) formed on the surface of the molten alloy disappeared. However, when the steel ingot after the experiment was investigated, large non-metallic inclusions exceeding 100 μm were present.

  Furthermore, it has been clarified that when the oxygen in the atmosphere is reduced to 5% or less, there is no large non-metallic inclusion exceeding 100 μm. From this preliminary experiment, the target of the sealing technology was determined to be 10% or less essential in oxygen concentration, and the final target was set to 5% or less. Of course, as described above, the precondition is “no lid” in order not to disturb the workability.

  Subsequently, the experiment shifted to a practical level. First, a cold experiment without using a molten alloy was performed. First, the measurement was performed under the conventional conditions and used as a benchmark. In order to seal the inside of the molten alloy holding container and the mold, Ar gas was blown using a straight type nozzle having an inner diameter of 3.17 mm (one minute).

  As a result, it was found that the oxygen concentration in the space to be sealed is 18 to 20%, which is almost the same as the atmosphere. First, sealing was attempted with two straight nozzles, but the oxygen concentration decreased only to about 16%, and the targeted effect was not obtained. As a result of earnest analysis of this reason by computer simulation, it was found that when a strong straight flow was created with Ar, the atmosphere was also drawn by the flow.

  Therefore, when various nozzle shapes were devised and examined, it was found that a flat injection nozzle was placed on one side, and a flat suction nozzle opposite to the other side was placed to achieve a good seal. Furthermore, in order to perform early purging and fill the mold with an inert gas in the cold, the result is that the supply amount of the inert gas needs to be kept high at 10 L / min or higher.

  Also, a good result was obtained in a similar manner even when a flat ejection nozzle was arranged relative to the upper surface of the mold and an inert gas was supplied from both sides. Similarly, the supply amount of the inert gas was 10 L / min or more.

  Subsequently, the experiment shifted to an experiment through a molten alloy in a state closest to the actual machine level. Here, an experiment was conducted on the state of gas shut-off by an inert gas when pouring the molten alloy using a mold of a continuous casting machine for casting a 60 ton scale molten alloy. 60 ton scale NH840 (INCOLOY840 equivalent, UNSS33400 equivalent; Fe-20 mass% Cr-20 mass% Ni-0.4 mass% Ti-0.4 mass% Al) melted in an electric furnace and refined with AOD and VOD It was an alloy. The procedure was the same as for cold, and the mold was sealed with Ar before pouring the molten alloy into the mold via the immersion nozzle. Subsequently, the tundish stopper was opened and pouring of the mold was started. The Ar sealing was continued until the mold was filled with the molten alloy and mold powder was charged onto the molten alloy surface. The experiment was repeated for about 3 charges in this procedure. In this series of experiments, the Ar gas flow rate was changed between 2 and 3000 L / min along the way to study how the oxygen concentration is affected.

  As a result, even if the molten alloy starts to be poured, an oxygen concentration of 10% or less can be achieved if Ar is continuously blown at a supply rate of 100 L / min or more. It has also been found that a flow rate of 200 L / min or more is required to achieve the final target oxygen concentration of 5% or less. As described above, the reason why the supply amount higher than 10 L / min in the cold experiment is required is that the gas expands when it is exposed to a high-temperature molten alloy at 1400 to 1500 ° C. and flows to replace the upper room temperature atmosphere. This is because it occurs.

  As described above, the present invention has been completed through experiments, analysis, and calculation simulations. Specifically, the present invention is as follows. That is, a flat nozzle for having a flat jet slit for supplying an inert gas to one end of an opening of a mold for holding a molten alloy and for sucking the inert gas into a position opposite to the jet nozzle. A sealing device for sealing a molten alloy with an inert gas, comprising a suction nozzle having a suction slit. Or the type which provided the ejection nozzle in the both sides of the opening part of the mold holding a molten alloy may be sufficient.

  Further, the flow rate of the inert gas should be controlled to 100 to 2000 L / min. The inert gas is preferably Ar.

  In any of the above types, it is more preferable that the ejection nozzle and the suction nozzle are each divided into two near the mold center.

  Furthermore, the present invention also proposes a method for cutting off air at the start of casting in continuous casting. That is, in the continuous gas casting method, the molten alloy is gas-isolated from the atmosphere by using the sealing device at the time of continuous casting.

  The reason for limiting the numerical values in carrying out the present invention will be described below. The present invention is a sealing device for sealing a molten alloy with an inert gas, and includes a nozzle and piping for supplying an inert gas thereto. This nozzle is flattened toward the tip, and the tip has a slit through which an inert gas is ejected. The height of the slit is 0.5 to 10 mm.

  If the height is less than 0.5 mm, the flow rate of the inert gas becomes high and the atmosphere is likely to be involved, and the target oxygen concentration cannot be achieved. On the other hand, if it exceeds 10 mm, the gas flow rate is low and the sealing effect is small. Therefore, it was determined as 0.5 to 10 mm. Preferably, it is preferable to divide into two in the width direction so that the gas flow does not hit the casting nozzle in the center of the mold because the heated casting nozzle is difficult to break.

  The flow rate of the inert gas is adjusted to 100 to 2000 L / min. If it is less than 100 mL / min, when a high-temperature molten alloy is poured, a gas expands and a flow that replaces the upper room temperature atmosphere is generated, so that the state of gas separation cannot be maintained and the oxygen concentration exceeds 10%. In order to obtain a high supply rate exceeding 2000 L / min, not only the equipment cost is required, but also the surface of the molten alloy is cooled, and a bare metal is formed, which may lead to the worst breakout. Therefore, it was determined as 100 to 2000 L / min. Preferably, the oxygen concentration in the atmosphere is set to 200 to 2000 L / min that can be reduced to 5% or less. More preferably, it is 200-900 L / min.

  Examples of the inert gas include Ar, carbon dioxide, He, Ne, and Xe. In consideration of cost and handling properties, Ar is a preferred embodiment. Also, considering the gas density along with the cost, Ar has a higher density than the atmosphere, so it tends to accumulate in the mold.

  When the molten alloy is vented from the atmosphere using the sealing device determined as described above at the start of continuous casting, non-metallic inclusion physical defects associated with oxidation or nitridation of the molten alloy can be prevented.

  Alloys to which this method can be applied are not limited to ordinary steel, stainless steel, and cast steel, but can be applied to a wide variety such as Fe-Ni alloys, Ni-base alloys, and Ni-base superalloys. Specifically, NW2201 (99 mass% Ni), UNS S33400 (equivalent to INCOLOY 840, NH840 equivalent; Fe-20 mass% Cr-20 mass% Ni-0.4 mass% Ti-0.4 mass% Al), SUS321 (Fe-18 mass%) Cr-8 mass% Ni-0.3 mass% Ti), NCF825 (Fe-42 mass% Ni-21.5 mass% Cr-3 mass% Mo-2 mass% Cu-1 mass% Ti), NCF625 (Ni-21.5 mass%) Cr-9 mass% Mo-3.5 mass% Fe-3.6 mass% (Nb + Ta)), NCF690 (Ni-30.0 mass% Cr-9.5 mass% Fe), NW6022 (Hastelloy C-22: Ni-21. 3 mass% Cr- 13.5 mass% Mo-4 mass% Fe-3 mass% W), NW0276 (Hastelloy C-276: Ni-15.5 mass% Cr-16 mass% Mo-5.5 mass% Fe-3.8 mass% W), NW4400 (Monel400) : Ni-31.5 mass% Cu), NCF601 (INCONEL 601: Ni-23 mass% Cr-14.4 mass% Fe-1.4 mass% Al), NCF600 (INCONEL 600: Ni-15.5 mass% Cr) -7 mass% Fe), SUH660 (Fe-25 mass% Ni-15 mass% Cr-1.2 mass% Mo-2 mass% Ti-0.2 mass% Al), NCF718 (Ni-18.0 mass% Cr-3.0 mass% Mo) -18.5ma s% Fe-0.9 mass% Ti-0.5 mass% Al-5.1 mass% (Nb + Ta)), NCF750 (Ni-15.5 mass% Cr-7 mass% Fe-2.5 mass% Ti-0. 9 mass% Al-1.0 mass% (Nb + Ta)), NCF800 (30 to 35 mass% Ni-21 mass% Cr-Fe), NCF800H (30 to 35 mass% Ni-21 mass% Cr-Fe), NCF80A ( Ni-19.5 mass% Cr-2.4 mass% Ti-1.5 mass% Al), NW6002 (Ni-21.5 mass% Cr-9 mass% Mo-18.5 mass% Fe-1.2 mass% Co) NW5500 (Monel K500: Ni-29.5 mass% Cu-3 mass% Al-0.5m ss% Ti), Fe-36% Ni, Fe-42% Ni, PB (Permalloy B), PC (Permalloy C), Fe-50.5% Ni, Fe-42% Ni-6% Cr, Fe-47 % Ni-6% Cr and the like.

  By using the sealing device of the present invention described above at the start of continuous casting of an alloy, non-metallic inclusion physical defects due to oxidation and nitridation of the molten alloy can be prevented, so that the yield of unsteady parts at the initial stage of casting can be improved. Contribute to improving quality and reducing manufacturing costs.

Hereinafter, the effects of the present invention will be clarified by showing examples.
A. The nozzles used in the sealing device examples are shown in FIGS. 3, 4 (a), (b), 5 and 6 (a), (b).
i) FIG. 3 and FIG. 4 (a) (b)
A flat jet nozzle was installed at one end of the opening of the mold of the continuous casting apparatus, and a flat suction nozzle opposite to this was installed at the other end. The inside of the mold is separated from the outside by a flat inert gas flow forming an inert gas curtain. Since the exhaust amount from the suction nozzle is 0.7 to 0.9 times the supply amount from the ejection side, a part of the excess amount flows inward to keep the inside of the mold in a non-oxidizing atmosphere. FIG. 4A shows a form in which nozzles are installed over the entire width of the mold. FIG. 4B shows a form in which the nozzle is divided into two at the center of the mold. For comparison, a straight pipe was inserted into the mold and an inert gas was ejected. The straight pipe had an inner diameter of 3.17 mm.

ii) FIG. 5 and FIG. 6 (a) (b)
Flat ejection nozzles were installed at both ends of the mold opening of the continuous casting apparatus. The inside of the mold is separated from the outside by a flat inert gas flow forming an inert gas curtain. The supply amount from each side was blown in the range of 0.2: 0.8 to 0.5: 0.5 when the total amount was 1. FIG. 6A shows a form in which nozzles are installed over the entire width of the mold. FIG. 6B shows a form in which the nozzle is divided into two at the center of the mold. For comparison, a straight pipe was inserted into the mold, and an inert gas was ejected. The straight pipe had an inner diameter of 3.17 mm.

B. Raw materials such as continuously cast iron scrap, stainless steel scrap, Fe—Cr, and Fe—Ni were melted in a 60-ton electric furnace and refined using both or one of AOD and VOD. The molten alloy held in the ladle was cast with a continuous casting machine. The continuous casting machine is a vertical type, and the mold is made of a copper plate and the surface thereof is plated with Ni. The mold sizes are 154 × 700-1500 mm and 200 × 700-1500 mm. The mold height at the start setting is 500 mm excluding the setting of the dummy bar.

Mold sealing was performed with the steel types shown in Table 1. The procedure started sealing the mold with an inert gas before pouring the molten alloy into the mold via the immersion nozzle, and subsequently opening the tundish stopper to start pouring the mold. Sealing was continued until the mold was filled with molten alloy and mold powder was charged onto the molten alloy surface. The inert gas was mainly Ar, but some carbon dioxide (CO ₂ ) was also used.

Each item was evaluated as follows, and the evaluation results are shown in Table 1.
-Oxygen concentration: measured with a zirconia oxygen analyzer.
-Gas flow rate: Measured with a flow meter.
# 1 slab grinding and cutting yield: After penetrating the # 1 slab, which was the slab at the start of continuous casting, a penetration test was conducted. Grinding was performed until the indication due to the foreign object disappeared, and the yield was calculated from the change in weight. If it could not be removed by grinding, cutting was taken into consideration.

  As shown in Table 1, in all of the inventive examples within the scope of the present invention, the oxygen concentration was 10 vol% or less, and the yield of # 1 slab was as good as 90% or more. The reason why the yield is good in this way is that the generation of non-metallic inclusions made of oxides and nitrides formed by reaction with the atmosphere and the inclusion of non-metallic inclusions in the slab are suppressed.

Inventive Examples and Reference Examples 1 to 7 are examples using the model shown in FIG. Specifically, Invention Examples 1, 2, 4, 5, and 7 are the results of casting using the model of FIG. 4B, and Reference Examples 3 and 6 show the results of using FIG. 4A. Yes. Invention Examples and Reference Examples 8 to 13 are examples using the model shown in FIG. Specifically, Invention Examples 8 to 12 are the results using FIG. 6B, and Reference Example 13 is the results using FIG. 6A.

Further, as can be seen from Table 1, examples using a model in which nozzles are arranged over the entire width of the mold, that is, Reference Examples 3 and 6 (FIG. 4 (a)) and Reference Example 13 (FIG. 6 (a)). As noted in the remarks column, although the casting itself was not hindered, the immersion nozzle was cooled. Normally, the immersion nozzle is preheated and heated to about 1000 ° C., and the whole is red hot. However, the portion where the gas hits intensively was darkened, so cracks may occur. For this reason, it has become clear that a type that is divided into two near the mold center and does not cool the nozzle is more preferable.

  On the other hand, in Comparative Example 1, Comparative Example 1 has no seal, and Comparative Examples 2 and 3 both have an inert gas flowed linearly from a conventional straight pipe that does not use the sealing device of the present invention. Did not go down.

  Comparative Examples 4 to 11 used the sealing device of the present invention, but the yield of # 1 slab was low because the gas flow rate was inappropriate. This will be specifically described below. In Comparative Examples 4, 7, 8, 10, and 11, since the flow rate was less than 100 L / min and too low, the oxygen concentration was higher than 10%, and oxidation and nitridation reactions with the atmosphere could not be prevented. Metal inclusions were not formed, resulting in a decrease in yield of less than 90%. In Comparative Examples 5, 6 and 9, on the contrary, the molten alloy was cooled because the flow rate was too high, and a solidified material was formed on the surface of the molten metal. It was also difficult. Therefore, in these comparative examples, the yield of the # 1 slab was as low as less than 90%.

  FIGS. 7 and 8 show images of a slab cross section when a # 1 slab, which is a slab at the start of continuous casting, is cut in a cross section perpendicular to the casting direction and subjected to a penetration flaw detection test. The cast steel type is SUS321, and the sampling position of the slab is located 450 mm from the surface in contact with the dummy bar, which is exactly the casting start point. FIG. 7 is a # 1 slab cross section of Comparative Example 2 cast without using the present sealing device. FIG. 8 is a # 1 slab cross section of Invention Example 4 cast using this sealing device.

  In FIG. 7, it can be seen that many dyed portions of the outer edge, that is, non-metallic inclusions are seen, whereas this is greatly reduced in the slab of FIG. In addition, about the dyeing | staining of the center part of each photograph, since it is the center porosity of the magnitude | size harmless to a product, a comparison should just be performed only about the dyeing part of an outer edge part.

  Moreover, in invention example 5, the graph showing the relationship between the passage of time from the start of sealing and the oxygen concentration in the mold is shown in FIG. Obviously from this graph, if the sealing device of the present invention was used, the oxygen concentration was rapidly reduced, and 4%, which was less than 5% before the start of pouring, could be realized. Furthermore, the low concentration can be maintained even after the start of pouring.

  It prevents non-metallic inclusion physical property defects, improves the yield and quality of the cast alloy, and further contributes to the reduction of manufacturing costs.

It is a schematic diagram which shows the continuous casting machine in this invention. It is an enlarged view of a tundish part and a mold part. It is sectional drawing which shows one Embodiment of the sealing device of this invention. (A) is a top view of the form which provided the ejection nozzle and the suction nozzle over the full width of a mold, and is the figure seen from upper direction (direction B) in FIG. 3, (b) is an ejection nozzle. FIG. 4 is a plan view of a form in which the suction nozzle is provided over the entire width of the mold and divided into two near the center, and is a view seen from above (direction B) in FIG. 3. It is sectional drawing which shows other embodiment of the sealing device of this invention. (A) is the top view of the form which provided the ejection nozzle over the full width of a mold, and is the figure seen from the upper direction (direction B) in FIG. 5, (b) is a figure which shows the ejection nozzle of the mold. FIG. 6 is a plan view of a form provided over the entire width and divided into two near the center, and viewed from above (direction C) in FIG. 5. It is a photograph which shows the penetration flaw test result of the slab cross section produced by the conventional method. It is a photograph which shows the penetration flaw test result of the slab cross section produced with the method of this invention. It is a graph which shows the relationship of the elapsed time from the seal | sticker start in this invention, and the oxygen concentration in a mold.

Explanation of symbols

C continuous casting machine 10 ladle 11 tundish 12 immersion nozzle 13 discharge hole 14 stopper 15 mold 16 sealing material 17 spray cooling zone 18 pinch roll 19 torch 20 molten alloy 21 slab 22 dummy bar 31 ejection nozzle 32 suction nozzle

Claims (6)

A sealing device for sealing a molten alloy with an inert gas, comprising a jet nozzle having a flat jet slit for supplying an inert gas to one end of an opening of a mold for holding the molten alloy, A suction nozzle having a flat suction slit for sucking the inert gas having a suction amount of 0.7 to 0.9 times the ejection amount is provided at a position facing the nozzle, and the flow rate of the inert gas is 100 to 2000 L. / min der is,
The molten alloy sealing device, wherein the jet nozzle and the suction nozzle are each divided into two near the mold center, which is a position facing the immersion nozzle of the molten alloy. The molten alloy sealing device according to claim 1 , wherein the height of the ejection slit of the ejection nozzle and the height of the suction slit of the suction nozzle are 0.5 mm to 10 mm. A sealing device for sealing a molten alloy with an inert gas at a ratio of 0.2: 0.8 to 0.5: 0.5 at opposite ends of an opening of a mold for holding the molten alloy Each having a jet nozzle having a flat jet slit for supplying an inert gas, the flow rate of the inert gas being 100 to 2000 L / min,
2. A molten alloy sealing device according to claim 1 , wherein each of the jet nozzles is divided into two parts in the vicinity of the center of the mold, which is a position facing the immersion nozzle of the molten alloy. 4. The molten alloy sealing device according to claim 3 , wherein a height of the ejection slit of the ejection nozzle is 0.5 mm to 10 mm. The molten alloy sealing device according to claim 1 , wherein the inert gas is Ar. 6. A gas blow-off at the start of continuous casting, wherein the molten alloy sealing device according to claim 1 is used at the start of casting of continuous casting, and the molten alloy held in the mold is cut off from the atmosphere. Method.

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