JP2009148788A - Method for restarting continuous casting of steel using pouring basin in tundish employing steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for restarting continuous casting of steel using a pouring basin in tundish, which prevents clogging of a nozzle, improves the quality of the bottom of a casting piece and is easily operated. <P>SOLUTION: Prior to restart of pouring of molten steel to a tundish 3, a steel pipe 12 is provided above a sliding nozzle 5. The steel pipe 12 has a thickness t [mm] meeting formula (1) and formula (2), and a length L [mm] of 350-550. Before completion of blocking of the molten steel by the steel pipe 12, the sliding nozzle 5 is brought into a closed state in advance. In this case, T<SB>LL</SB>denotes a liquidus temperature [°C], ΔT denotes a molten steel overheat temperature [°C] and äΔT} denotes a target value [°C] of the molten overheat temperature ΔT[°C]. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for resuming continuous casting of steel by a tundish hot water reservoir using a steel pipe.

  In general steel continuous casting, the molten steel in the ladle is temporarily held in the tundish and poured into the mold at a predetermined flow rate. When changing the type of steel to be cast, The inside of the dish was once emptied, and the refractory constituting the inner wall of the tundish was replaced. However, in recent years, to reduce costs, the mainstream is the “tundish reuse operation” where the tundish is temporarily emptied and new molten steel is admitted to the tundish without replacing the refractory when changing the steel grade. Is done.

  When this tundish reuse operation is adopted, after the tundish is emptied, the tundish is tilted or the molten steel flow path formed in the inner bottom of the tundish is used. It is necessary to discharge the remaining slag and refractory pieces to the outside of the tundish as much as possible. This is because if the above slag or refractory piece is mixed with molten steel at the start of the next continuous casting, the quality of the bottom slab (meaning the slab at the beginning of casting) will be significantly reduced. . However, as is well known, slag and refractory pieces cannot be completely eliminated. Thus, how to handle slag and refractory pieces has become a major issue.

  In order to solve this problem, a technique called “tundish indoor hot water reservoir operation” is known. In this technology, the slide valve is closed after the tundish is emptied, the molten steel is poured into the tundish, and the slide valve is opened only after the molten steel reaches a predetermined height. is there. According to this operation, when the molten steel begins to be poured into the mold, the slag and refractory pieces are floating at a predetermined height in the tundish due to the difference in specific gravity. It is possible to prevent the molten steel from flowing into the mold.

  However, in this tundish hot water reservoir operation technique, the molten steel may solidify in the closed molten steel flow path. In such a case, the molten steel flow path is not opened even if the slide valve is opened thereafter. There was a problem.

  As this type of technology, for example, Patent Literature 1 describes a method for injecting molten steel in a tundish for continuous casting. In this method, a steel start pipe provided with a thin portion at an intermediate portion in the height direction is installed on the injection nozzle. According to this, “the molten steel level necessary for the inclusions such as slag to sufficiently float can be ensured, and slag mixing into the mold 3 due to slag overflow from the upper end of the steel start pipe 2 can be prevented. It can be done. "

  Patent Document 2 describes a procedure in which a metal cylindrical member surrounding a tundish melt outlet is placed on the tundish bottom, and then the melt is poured into the tundish. And about 3-4 mm is illustrated as thickness of this cylindrical member.

JP-A-1-266951 (Claims, seventh column, lines 13-18) JP-A-63-40651 (2nd page, 2nd column, lines 13-15, 3rd page, 1st column, 19th line)

  However, in the fifth column of the above-mentioned Patent Document 1, “use an inner diameter of 270 mmφ and a length of 1000 mm”, “and the thickness of the lower thick portion 11 and the upper thick portion 13 are set to 15 mm”, etc. As described above, the steel start pipe used in this technology is extremely large and not easy to handle, and furthermore, the heat capacity of the steel start pipe itself is extremely large, so the molten steel poured into the tundish However, it may cool down unexpectedly, and as a result, the injection nozzle may become clogged.

  In addition, as described in the third page, first column, lines 16 to 18 of Patent Document 2, the molten steel is poured into the mold after the molten metal surface position exceeds the upper end of the steel tube. The slag floating on the molten metal will also be poured into the mold and the quality of the bottom slab will not be expected.

  The present invention has been made in view of such various points, and its main purpose is to prevent clogging of the nozzle, improve the quality of the bottom slab, and further facilitate the operation of the steel by the tundish hot water reservoir. It is to provide a method for resuming continuous casting.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to the aspect of the present invention, the continuous casting of steel is interrupted to make the inside of the tundish almost empty, and when the molten steel is poured again into this tundish and the continuous casting is resumed, a predetermined amount is placed in the tundish. The resumption of continuous casting of steel by the hot water reservoir in the tundish, in which hot metal is poured after the molten steel is accumulated, is performed by the following method. The tundish to be reused contains molten steel for 3 hours or more from when it is not used. The tundish to be reused is not heated, and pouring of molten steel is started again within 3 hours from the time when the tundish becomes substantially empty. Before starting to pour molten steel again into the tundish to be reused, a steel pipe is provided at the top of the sliding nozzle. This steel pipe has a thickness t [mm] satisfying the following formulas (1) and (2) and a length L [mm] of 350 to 550. Before the squeezing of the molten steel by the steel pipe is completed, the sliding nozzle is opened in advance.

Here, T _LL is the liquidus temperature [° C.], ΔT is the molten steel superheat degree [° C.], and {ΔT} is the target value [° C.] of the molten steel superheat degree ΔT [° C.].

  According to the above method, (1) nozzle clogging can be prevented, and (2) the molten steel surface dammed up in the steel pipe rises so that the slag and the refractory pieces float, and the molten metal surface becomes the steel pipe. Since the molten steel begins to be poured into the mold through the molten lower part of the steel pipe before reaching the upper end of the slag, slag and refractory pieces do not flow into the mold, so that the quality of the bottom slab can be improved, (3) Furthermore, since the steel pipe is small, operation is easy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partially cutaway front view of a tundish to which the present invention is applied.

  As shown in this figure, the continuous casting equipment for steel has a role as a buffer for temporarily holding the molten steel that has been transported batchwise by the ladle 1 shown in the figure before pouring into the mold 2. Equipped with a tundish 3 to carry.

  The tundish 3 is configured as a bottomed container having a U-shaped cross section that opens vertically upward, and its side wall and bottom have a two-layer structure including a refractory 10 and an iron skin 11 in order from the inside to the outside. . In the bottom of the tundish 3, a hole 4 having a substantially drum-shaped cross section is formed as a flow path for pouring molten steel accommodated in the tundish 3 into the mold 2.

  The hole 4 is provided with a sliding nozzle 5 for adjusting the amount of pouring water into the mold 2. The sliding nozzle 5 includes a first sliding nozzle 6 fixed to the tundish 3 and a second sliding nozzle 7 that can move relative to the first sliding nozzle 6 in the horizontal direction.

  The first sliding nozzle 6 has a cylindrical shape and is formed thinner toward the upper end. The first nozzle 6a is inserted into and fixed to the hole 4 from below, and is attached to the upper nozzle 6a from below. And an upper slide plate 6b having a perforated plate shape. Similarly, the second sliding nozzle 7 is attached to the lower slide plate 7a from below with a perforated flat plate-like lower slide plate 7a configured to be slidable relative to the upper slide plate 6b. The lower nozzle 7b to which the immersion nozzle 8 is connected. With the above configuration, the opening degree of the sliding nozzle 5 can be freely adjusted by sliding the lower slide plate 7a relative to the upper slide plate 6b in the horizontal direction.

  A large number of microcavities (porous) (not shown) are uniformly formed on the inner peripheral surface 6c of the upper nozzle 6a. If an inert gas such as Ar gas is injected from this microcavity through a path not shown, the molten steel flowing in the molten steel flow path 9 formed by the holes 4 and the upper nozzle 6a can be suitably stirred. The specific dimensions of the sliding nozzle 5 described above are illustrated in FIG. 2 as a reference. FIG. 2 is a partially enlarged view of FIG. Reference numeral 3 a indicates the inner bottom of the tundish 3.

  With the above configuration, the operation during continuous casting will be briefly described. Please refer to FIG. 1 again. A predetermined amount of molten steel is held in the tundish 3 during continuous casting. Molten steel is supplied from the ladle 1 to the tundish 3 at a predetermined flow rate, and molten steel is poured from the tundish 3 to the mold 2 through the molten steel passage 9 at a predetermined flow rate. The flow rate of the molten steel from the tundish 3 to the mold 2 is adjusted by increasing or decreasing the opening degree of the sliding nozzle 5. When the remaining molten steel in the ladle 1 is reduced, a new ladle 1 containing a sufficient amount of molten steel is conveyed to the tundish 3. Eventually, when the ladle 1 becomes empty, the ladle 1 is replaced with another ladle 1 that has been waiting, and this time, the molten steel begins to be supplied from the alternate ladle 1 to the tundish 3.

  Next, the entire operation including the start, interruption, and resumption of continuous casting will be described in detail with reference to FIG. 3 and other drawings. FIG. 3 is a diagram showing the entire operation of continuous casting in time series. 4-7 is a figure similar to FIG. 1, Comprising: It is the figure showing the mode of resumption of continuous casting. Hereinafter, the time T (x) in the description corresponds to the content of FIG.

<T (0) to T (1): Re-seat>
In general, the refractory 10 of the tundish 3 is melted by use. In order to make up for the melted refractory 10 and maintain the thickness of the refractory 10 to a predetermined thickness or more, the refractory 10 needs to be replaced every 18 charges, for example. That is, a semi-solid refractory is sprayed on the inner wall surface of the tundish 3 and dried for a predetermined time. At time T (1), the temperature of the tundish 3 is approximately room temperature (25 ° C.) by natural heat dissipation.

<T (2) to T (3): Burner heating>
When the reworking is completed, the tundish 3 is heated using a predetermined burner until the temperature of the tundish 3 reaches 900 to 1000 [° C.]. The “predetermined burner” corresponds to, for example, one that uses the reaction heat of CO and oxygen as a by-product gas generated at a steel mill. The “temperature of the tundish 3” corresponds to a value obtained by measuring the temperature of the inner bottom 3a of the tundish 3 using, for example, a radial surface thermometer.

<T (4) to T (6): Start of casting>
When the above-described burner heating is completed, it is confirmed that the sliding nozzle 5 is closed, and then pouring from the ladle 1 to the tundish 3 is started as soon as possible (time T (4)). When the molten steel in the tundish 3 reaches a predetermined amount, the sliding nozzle 5 is opened, and pouring from the tundish 3 to the mold 2 is started (time T (5)).

During continuous casting, Ar gas is injected from the inner peripheral surface 6c of the upper nozzle 6a at a flow rate of approximately 20 [NL / min] to force inclusions such as Al ₂ O ₃ present in the molten steel. It floats and prevents the inclusions from adhering to the immersion nozzle 8. As described above, the ladle 1 is replaced whenever it becomes empty.

  If it is necessary to change the steel type, the ladle 1 is not replaced, and the molten steel supplied into the tundish 3 is waited for being almost empty. Time T (6) indicates the time when the molten steel supplied into the tundish 3 becomes substantially empty. For convenience of explanation, one unit of continuous casting of steel (CC) is defined as “from the time when pouring into the mold 2 is started until the time when the molten steel in the tundish 3 becomes substantially empty”. Time T (5) to time T (6) corresponds to this.

<T (7) to T (8): Cleaning>
At this stage, since a considerable amount of metal, slag, and refractory pieces still remain on the inner bottom 3a of the tundish 3, etc., these are scraped out to the outside as much as possible through the molten steel channel 9.

<T (9) to T (11): Resumption of casting>
When the above cleaning is completed (time (8)), continuous casting of steel is resumed.

  (B) The resumption of continuous casting according to the present embodiment, as a first premise, first, at time T (9), the tundish 3 to be reused contains molten steel for 3 hours or more from when it is not used. You need to have been there. “When the tundish is not used” means “any time between the completion of the refilling operation and the start time of pouring the tundish 3”. An arbitrary time between time T (1) and T (4) corresponds to this. As described above, the reason why the molten steel has been accommodated since it was not used is based on the heat quantity of the tundish 3 that dramatically increases due to the accommodation of the molten steel. In the present embodiment, the first premise is satisfied if the period from time T (4) to time T (6) is 3 hours or more. Although the amount of heat of the tundish 3 can be increased even if a burner is used, it cannot be said that the increase is technically significant as compared to housing molten steel.

  (B) As a second premise, the tundish 3 to be reused is melted again within 3 hours from the time when the tundish 3 becomes substantially empty without heating the tundish 3 with a burner or the like. You need to start pouring. “When the tundish 3 is substantially empty” means that the pouring amount to the mold 2 is reduced and the pouring is finished. That is, time T (6) corresponds to it. The time T (9) corresponds to the point of time at which “the molten steel starts to be poured again”. Therefore, what should be within 3 hours as the second premise is from time T (6) to time T (9). As described above, the reason for not taking much time for the above-mentioned cleaning is because attention is paid to the amount of heat of the tundish 3 lost due to natural heat dissipation. In the present embodiment, the second premise is satisfied if the period from time T (6) to time T (9) is within 3 hours.

  (C) Further, as shown in FIG. 4, a steel pipe 12 is provided on the upper part of the sliding nozzle 5 before the molten steel is poured again into the tundish 3 to be reused. The steel pipe 12 has a thickness t [mm] satisfying the following formulas (1) and (2) and a length L [mm] of 350 to 550. Hereinafter, the steel pipe 12 will be described in detail.

  The steel pipe 12 is formed in a cylindrical shape, and its inner diameter is larger than the diameter of the upper end of the hole 4 drilled in the inner bottom 3 a of the tundish 3. The steel pipe 12 has the same component as the steel type to be cast as much as possible. Therefore, even if the steel pipe 12 melts and mixes with the molten steel, there is little influence on the quality of the bottom slab. The steel pipe 12 is erected in advance on the sliding nozzle 5 before the molten steel is again poured into the tundish 3 to be reused. Specifically, the steel pipe 12 is placed on the inner bottom 3 a so that the steel pipe 12 and the molten steel flow path 9 are coaxial so that the steel pipe 12 surrounds the hole 4.

In the above formulas (1) and (2), T _LL is the liquidus temperature [° C.], ΔT is the molten steel superheat degree [° C.], and {ΔT} is the target value of the molten steel superheat degree ΔT [° C.] ° C].

The liquidus temperature T _LL [° C.] is calculated, for example, by substituting the components of the steel type into the following formula (3) or (4) called “Hirai formula”. In the following formulas (3) and (4), the units of the element symbols C, Si, Mn, Cr, and Ni are all [wt%].

  The molten steel superheat degree ΔT [° C.] is the molten steel poured from the ladle 1 to the tundish 3 at a very early stage, and is the molten steel superheated degree before being received by the tundish 3. It refers to ΔT [° C.]. “Extremely initial” refers to, for example, within 10 seconds from the time T (9) when pouring from the ladle 1 to the tundish 3 is started. However, when restarting the continuous casting of steel, actual measurement of the molten steel superheat degree ΔT [° C.] is not necessarily required.

  The target value {ΔT} [° C.] of the molten steel superheat degree ΔT [° C.] is, for example, 30 [° C.]. The molten steel superheat degree ΔT [° C.] is about 20 to 45 [° C.] in actual measurement when the target value {ΔT} [° C.] is 30 [° C.]. According to the above formulas (1) and (2), it is understood that a suitable range of the thickness t [mm] is set for the first time after the target value {ΔT} [° C.] of the molten steel superheat degree ΔT [° C.] is determined. Let's be done.

  As described above, in (i) to (c), several points when resuming continuous casting of steel are listed. Next, the state in the tundish 3 when pouring from the ladle 1 to the tundish 3 in the state shown in FIG. 4 will be described.

  First, a state immediately after starting pouring from the ladle 1 to the tundish 3 will be described. Please refer to FIG. As shown in the figure, the molten steel poured from the ladle 1 to the tundish 3 is blocked by the presence of the steel pipe 12 placed in advance, and the molten steel surface rises. At this time, the slag and refractory pieces (indicated by reference numeral 13) remaining on the inner bottom 3a of the tundish 3 float on the molten steel surface due to the effect of the specific gravity difference from the molten steel. On the other hand, the remaining steel adhered on the inner bottom 3 a of the tundish 3 is dissolved in the molten steel poured from the ladle 1.

  Next, the state before and after the damming of the molten steel by the steel pipe 12 will be described. See FIG. The lower part of the steel pipe 12 placed on the inner bottom 3a of the tundish 3 is heated in a short time due to contact with the extremely high temperature tundish 3 and contact with the molten steel whose molten metal surface is rising. And partially melts out. Then, a space is formed between the inner bottom 3a of the tundish 3 and the steel pipe 12, and the molten steel in the tundish 3 begins to flow into the molten steel channel 9 from this space (time T (10)).

  (D) In the present embodiment, the molten steel is dammed by the steel pipe 12 so that the molten steel that has started to flow into the molten steel channel 9 is smoothly poured into the mold 2 without staying in the molten steel channel 9. Before stopping, the sliding nozzle 5 is opened in advance. For example, if the sliding nozzle 5 has never been switched to the closed state after time T (5), going back to a long time, “Before the damming of the molten steel by the steel pipe 12 is completed, the sliding nozzle 5 has already been If the sliding nozzle 5 is switched to the closed state during cleaning (time T (7) to time T (8)), there is no delay after the cleaning is completed. It is sufficient to switch the sliding nozzle 5 to the open state. Further, the sliding nozzle 5 may be kept closed until just before the molten steel damming by the steel pipe 12 is completed.

  In addition, before the damming of the molten steel by the steel pipe 12 is completed, not only the sliding nozzle 5 is opened in advance, but also at a flow rate of approximately 20 [NL / min] from the inner peripheral surface 6c of the upper nozzle 6a. It is preferable that gas is injected. This is because the molten steel flowing into the molten steel flow path 9 is agitated to prevent the molten steel from sticking to the upper nozzle.

  Next, how the steel pipe 12 is completely dissolved in the molten steel will be described. Please refer to FIG. If the melting of the steel pipe 12 further proceeds, the steel pipe 12 will eventually disappear and shift to a steady state of continuous casting of steel.

During continuous casting, Ar gas is supplied from the inner peripheral surface 6c of the upper nozzle 6a at a flow rate of approximately 0 to 20 [NL / min] to force inclusions such as Al ₂ O ₃ mixed in the molten steel. The inclusions are prevented from adhering to the immersion nozzle 8. As described above, the ladle 1 is replaced whenever it becomes empty.

  If it is necessary to change the steel type, the ladle 1 is not replaced, and the molten steel supplied into the tundish 3 is waited for being almost empty. Time T (11) indicates the time when the molten steel supplied into the tundish 3 becomes substantially empty.

<T (12) to T (13): Cleaning>
Cleaning is performed in the same manner as at times T (7) to T (8).

<T (14)-: Resume casting>
When the above cleaning is completed (time (13)), continuous casting of steel is resumed.

  (A) As described above, at time T (14), the tundish 3 to be reused needs to contain molten steel for 3 hours or more from when it is not used. “When the tundish is not used” means “any time between the completion of the refilling operation and the start time of pouring the tundish 3”. An arbitrary time between time T (1) and T (4) corresponds to this. In this embodiment, the “total” of the time from time T (4) to time T (6) and the time from time T (9) to time T (11) is 3 hours or more. If so, the first premise is satisfied. Since others are as above-mentioned, the description is omitted.

  The overall operation including the start, interruption, and resumption of continuous casting has been described above. In particular, the method for resuming continuous casting of steel by a tundish hot water reservoir using the steel pipe according to the present embodiment has been described in detail.

  Hereinafter, the test for confirming the technical effect of the restarting method of the continuous casting of steel by the tundish hot water reservoir using the steel pipe according to the present embodiment will be described. Each numerical range described above is reasonably supported by the following confirmation test.

[Test 1]
This confirmation test is for confirming the technical effect obtained by setting the thickness t [mm] and the length L [mm] of the steel pipe 12 within a predetermined range.

[Test 1.1] Index First, an index used for evaluation of each confirmation test will be described. “Nozzle clogging” is an index related to whether or not the sliding nozzle 5 is clogged. A test in which the amount of pouring into the mold 2 was remarkably small or no pouring itself was recognized at all after about 30 seconds from the start of pouring from the ladle 1 to the tundish 3 was “nozzle clogging occurred: × On the other hand, a test in which a pouring amount of about 0.5 [t / min], for example, was confirmed within about 30 seconds after starting pouring from the ladle 1 to the tundish 3 was “nozzle clogging occurred. “None: ○”.

[Test 1.2] Common Test Method Next, a test method common to each confirmation test will be described. That is, in any test, it operated according to the operation procedure shown in time series in FIG. Then, it was confirmed whether the nozzle clogging occurred at the time of “first restart” in which nozzle clogging is most likely to occur. “Restart for the first time” refers to the resumption of continuous casting for the first time after the unused tundish is used once for continuous casting and the continuous pouring is interrupted to change the steel grade. means.

[Test 1.3] Common Test Conditions Next, test conditions common to each confirmation test will be described. The above-mentioned conditions (a) and (b) were sufficiently satisfied. That is, in all the tests, the “cumulative usage time ΔT (4 to 6) from when not in use”, which is the time between time T (4) and time T (6), was approximately 6 hours. One charge is completed in approximately 60 minutes, and 6 hours corresponds to 6 charges. In all the tests, the “tundish free time ΔT (6-9)”, which is the time between time T (6) and time T (9), was approximately 0.5 hours. Moreover, the open state of the sliding nozzle 5 was continued from time T (1).

[Test 1.4] Individual Test Conditions and Test Results Next, individual test conditions and test results of each confirmation test are shown in Tables 1 and 2 below. Table 2 is a continuation of Table 1. In Tables 1-2 below, the column title variables correspond to the variables used in this specification.

As can be seen from Tables 1 and 2, the above confirmation test was performed uniformly within and outside the predetermined ranges of thickness t [mm] and length L [mm] suitable in the above embodiment. FIG. 8 is a graph of Tables 1 and 2 above. FIG. 8 is a graph showing the results of a test for confirming the technical effect of the present invention. The vertical axis in FIG. 8 is the thickness t [mm] of the steel pipe 12, and the horizontal axis is “liquidus temperature T _LL [° C.] plus target value [° C.] of molten steel superheat degree ΔT [° C.]”. is there. However, the graph of FIG. 93-98 test results are not shown. That is, in FIG. 8, please confirm whether there is a technical effect by setting the thickness t [mm] within a predetermined range.

According to FIG. 8, the range of the thickness t [mm] of the steel pipe 12 is strongly related to “the liquidus temperature T _LL [° C.] plus the target value [° C.] of the molten steel superheat degree ΔT [° C.]”. It will be understood that a clear technical effect can be achieved in the presence or absence of nozzle clogging. In other words, the thickness t [mm] is 3 to 6 depending on the liquidus temperature T _LL [° C.] derived from the steel type plus the target value [° C.] of the molten steel superheat degree ΔT [° C.]. If the steel pipe 12 is properly used, nozzle clogging does not occur.

  In addition, according to Tables 1 and 2, it is understood that when the range of the length L [mm] of the steel pipe 12 is appropriately set, a clear technical effect is exhibited in the presence or absence of occurrence of nozzle clogging as described above. Let's be done.

  Hereinafter, the reason why nozzle clogging occurs when it deviates from the above-mentioned preferable numerical value range has been considered through visual observation and the like, and will be described in detail below.

(A) According to visual observation, when the thickness t [mm] of the steel pipe 12 is insufficient and the above formula (2) is not satisfied, pouring from the ladle 1 to the tundish 3 is started, and the molten steel level is The pouring of the mold 2 had already begun while it was almost not rising. This is because the bottom of the steel pipe 12 has already melted shortly after the pouring from the ladle 1 to the tundish 3 or before the pouring from the ladle 1 to the tundish 3 is started, This is considered to be because a gap was formed between the inner bottom 3 a of the tundish 3 and the steel pipe 12. The slag adhering to the inner bottom 3a of the tundish 3 flows into the sliding nozzle 5 because the pouring of the mold 2 has started before the molten steel surface sufficiently rises. The slag blocks the microcavity formed in the inner peripheral surface 6c of the upper nozzle 6a, the Ar gas injection is inhibited, the stirring of the molten steel in the molten steel channel 9 is inhibited, and the molten steel is in the molten steel channel 9 It is thought that nozzle clogging occurred because it stuck to the inner periphery.

(B) According to visual observation, when the thickness t [mm] of the steel pipe 12 is ensured too much and the above formula (1) is not satisfied, pouring from the ladle 1 to the tundish 3 is started, Even when the surface was raised sufficiently, pouring into the mold 2 did not start, and the molten steel blocked by the steel pipe 12 overcame the upper end of the steel pipe 12 and flowed into the molten steel flow path 9. This means that the slag floating on the surface of the molten steel has flowed into the sliding nozzle 5 without being removed. The causal relationship between the slag flowing into the sliding nozzle 5 and the nozzle clogging is as shown in FIG.

(C) By the way, in the above restarting method, the lower part of the steel pipe 12 needs to be partially dissolved before the molten steel surface rises and reaches the upper end of the steel pipe 12. When L [mm] is short, the molten steel surface reaches the upper end of the steel pipe 12 at an early stage. Therefore, the lower part of the steel pipe 12 must be melted at an early stage. However, if the lower portion of the steel pipe 12 is melted before the molten steel surface is not enough, the distance between the gap formed in the lower portion of the steel pipe 12 and the molten steel surface is shortened, so the slag floating on the molten steel surface is The gap formed in the lower part of the steel pipe 12 is drawn into the flowing molten steel and flows into the molten steel flow path 9. In order to meet this consideration, the test No. in Table 2 above. As shown in 93 to 95, when the length L [mm] of the steel pipe 12 is less than 350, nozzle clogging occurs regardless of how the thickness t [mm] is set.

(D) As described above, the lower portion of the steel pipe 12 placed on the inner bottom 3a of the tundish 3 is first heated by heat input from the molten steel secondly blocked by heat input from the tundish 3. Yield stress decreases early. In such a situation, the longer the length L [mm] of the steel pipe 12 is, the larger the load acting on the lower part of the steel pipe 12 is. Therefore, before the pouring from the tundish 3 to the mold 2 is appropriately started. In addition, the posture of the steel pipe 12 will change. And if the attitude | position of the steel pipe 12 changes, since it will not be able to dam the molten steel normally, the slag of a molten steel surface will flow in into the molten steel flow path 9. FIG. In order to meet this consideration, the test No. in Table 2 above. As shown in 96 to 98, when the length L [mm] of the steel pipe 12 exceeds 550, nozzle clogging occurs regardless of how the thickness t [mm] is set.

[Test 2]
The confirmation test is as follows: (b) “The re-used tundish 3 contains molten steel for 3 hours or more from when it is not used” and (b) “The re-used tundish This is for confirming the technical effect of the fact that, without heating, the molten steel starts to be poured again within 3 hours after the tundish becomes substantially empty.

[Test 2.1] Index Since the index used for the evaluation of this confirmation test is the same as the index in Test 1 described above, its description is omitted.

[Test 2.2] Common Test Method Next, a test method common to each confirmation test will be described. That is, in any test, it operated according to the operation procedure shown in time series in FIG. Then, it was confirmed whether the nozzle clogging occurred at the time of “first restart” in which nozzle clogging is most likely to occur.

[Test 2.3] Common Test Conditions Next, test conditions common to each confirmation test will be described. That is, in any test, the thickness t [mm] of the used steel pipe 12 is the target value {ΔT} of the liquidus temperature T _LL [° C.] and the molten steel superheat degree ΔT [° C.] determined based on the steel type to be cast. Based on [° C.], it was set within the range of thickness t [mm] determined by the above formulas (1) and (2). Specifically, in any test, when the thickness t [mm] was 4 [mm], it seemed that the above formulas (1) and (2) were satisfied, so this thickness t [mm] was always adopted. did. The length L [mm] of the steel pipe 12 was always 400 [mm].

[Test 2.4] Individual Test Conditions and Test Results Next, individual test conditions and test results of each confirmation test are shown in Table 3 below. In Table 3 below, the column title variables correspond to the variables used in this specification.

  FIG. 9 is a graph of Table 3 above. FIG. 9 is a graph showing the results of a test for confirming the technical effect of the present invention. The vertical axis in FIG. 9 is the time Δt (6-9) [min] in which the inside of the tundish is substantially empty when the continuous casting is interrupted, and the horizontal axis is the accumulated use since the tundish is not used. Time Δt (4 to 6) [min].

  According to FIG. 9, if the usage time Δt (4 to 6) [min] accumulated since the tundish is not used is less than 180 [min], the cleaning (Δt (7 to 8)) can be performed in a short time. Even when rounded up, it can be seen that nozzle clogging occurred when restarting. Further, when the time Δt (6-9) [min] during which the inside of the tundish is substantially empty at the time of continuous casting interruption exceeds 180 [min], similarly, nozzle clogging occurs when restarting. You can see that it's gone.

  The inventor of the present application considers the above results as follows. That is, the inventor of the present application considers that the amount of heat of the tundish 3 greatly affects the occurrence of nozzle clogging.

(E) That is, if the usage time Δt (4 to 6) [min] accumulated from when the tundish 3 is not used is less than 180 [min], the tundish 3 that was initially at room temperature holds the molten steel. Therefore, the amount of heat of the tundish 3 at the time of resuming continuous casting is not sufficient, and the molten steel channel 9 is formed from the gap formed between the inner bottom 3a of the tundish 3 and the steel pipe 12. It is considered that the molten steel that has flowed into the upper surface is fixed to the cooled upper nozzle 6a, and as a result of growth of the fixed metal, the molten steel flow path 9 is closed and nozzle clogging occurs.

(F) Further, when the time Δt (6-9) [min] during which the inside of the tundish was substantially empty when continuous casting was interrupted exceeded 180 [min], the tundish 3 had The amount of heat is lost due to natural heat dissipation, and the amount of heat of the tundish 3 at the time of resuming continuous casting is not sufficient, and flows into the molten steel flow path 9 from the gap formed between the inner bottom 3a of the tundish 3 and the steel pipe 12. It is considered that the molten steel is fixed to the cooled upper nozzle 6a, and as a result of the growth of the fixed metal, the molten steel passage 9 is closed and nozzle clogging occurs.

  As described above, in the above embodiment, when the continuous casting of steel is interrupted and the inside of the tundish 3 is made almost empty, the molten steel is poured again into the tundish 3 and the continuous casting is resumed. The resumption of continuous casting of steel by the tundish hot water reservoir, in which a predetermined amount of molten steel is stored in 3 and then pouring into the mold 2 is started by the following method. The tundish 3 to be reused contains molten steel for 3 hours or more from when it is not used. The tundish 3 to be reused is not heated, and the molten steel starts to be poured again within 3 hours from when the tundish 3 becomes substantially empty. Before starting to pour molten steel again into the tundish 3 to be reused, the steel pipe 12 is provided on the upper part of the sliding nozzle 5. The steel pipe 12 has a thickness t [mm] satisfying the following formulas (1) and (2) and a length L [mm] of 350 to 550. Before the squeezing of the molten steel by the steel pipe 12 is completed, the sliding nozzle 5 is opened in advance.

Here, T _LL is the liquidus temperature [° C.], ΔT is the molten steel superheat degree [° C.], and {ΔT} is the target value [° C.] of the molten steel superheat degree ΔT [° C.].

  According to the above method, (1) nozzle clogging can be prevented, and (2) the molten steel surface dammed up by the steel pipe 12 rises, so that the slag and the refractory piece float and the molten metal surface Since the molten steel begins to be poured into the mold 2 through the melted lower portion of the steel pipe 12 before reaching the upper end of the steel pipe 12, slag and refractory pieces do not flow into the mold 2, so Quality can be improved. (3) Furthermore, since the steel pipe 12 is small, operation is easy.

Front view of a partially cutout tundish to which the present invention is applied Partial enlarged view of FIG. Diagram showing the overall operation of continuous casting in time series FIG. 2 is a view similar to FIG. 1 and showing the state of resuming continuous casting. FIG. 2 is a view similar to FIG. 1 and showing the state of resuming continuous casting. FIG. 2 is a view similar to FIG. 1 and showing the state of resuming continuous casting. FIG. 2 is a view similar to FIG. 1 and showing the state of resuming continuous casting. The graph which shows the result of the test for confirming the technical effect of this invention The graph which shows the result of the test for confirming the technical effect of this invention

Explanation of symbols

3 Tundish 5 Sliding nozzle 8 Immersion nozzle 12 Steel pipe

Claims (1)

When continuous casting of steel is interrupted to make the inside of the tundish almost empty, and when molten steel is poured again into this tundish and continuous casting is resumed, a predetermined amount of molten steel is accumulated in the tundish and then transferred to the mold. In the method of resuming continuous casting of steel with a tundish hot water reservoir,
The reusable tundish contains molten steel for more than 3 hours from when it is unused.
The tundish to be reused is not heated and begins to pour molten steel again within 3 hours from the time when the tundish becomes substantially empty,
Before starting to pour molten steel again into the tundish to be reused, install a steel pipe at the top of the sliding nozzle,
This steel pipe has a thickness t [mm] satisfying the following formulas (1) and (2), and has a length L [mm] of 350 to 550,
Before the damming of the molten steel by this steel pipe is finished, the sliding nozzle is set in an open state in advance.
Resuming continuous casting of steel by tundish hot water reservoir

Here, T _LL is the liquidus temperature [° C.], ΔT is the molten steel superheat degree [° C.], and {ΔT} is the target value [° C.] of the molten steel superheat degree ΔT [° C.].

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