JP4459933B2 - How to resume continuous casting of steel by tundish hot water reservoir - Google Patents

Description

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

  In general, the steel manufacturing process includes a primary refining process for adjusting the components of the hot metal in the converter that receives the hot metal discharged from the blast furnace, and for transporting the molten steel output from the converter to a continuous casting machine. It consists of a secondary refining process for adjusting the components of the molten steel in the ladle used, and a continuous casting process for continuously casting the molten steel conveyed to the continuous casting machine by the ladle. More specifically, the molten steel conveyed from the converter to the continuous casting machine by the ladle is temporarily stored in the tundish provided in the continuous casting machine, and the molten steel is cooled at a predetermined flow rate. Thus, the molten metal is poured into a mold for forming a solidified shell having a predetermined shape.

  Conventionally, the above continuous casting has been temporarily interrupted for the purpose of changing the steel type of a cast slab to be cast, and the refractory constituting the inner wall of the tundish has been replaced each time. However, in recent years, the so-called tundish that does not replace the refractory constituting the inner wall of the tundish even when it is temporarily interrupted for the purpose of changing the steel type of the cast slab for the purpose of cost reduction. Reusable operations are common.

  Specifically, this tundish reuse operation is as follows. That is, after the interruption, the tundish is tilted or the slag remaining in the tundish and the remaining steel are positively transmitted from the tundish to the outside by using the molten steel flow path formed at the bottom of the tundish. Will try to discharge. When these slag and remaining steel are mixed with molten steel poured into the tundish when resuming continuous casting, the slab (especially bottom slab (especially in the initial casting) ))) Is significantly deteriorated (for example, inclusions are increased). However, these slags and remaining steels cannot be easily discharged from the tundish to the outside due to their properties, and if they are to be completely discharged, a considerable amount of time is required. Therefore, when the tundish reuse operation introduced for cost reduction is carried out, how to handle these slag and remaining steel that cannot be completely discharged has been a big issue.

  In order to solve this problem, a so-called tundish hot water reservoir operation technique is known. Specifically, this technique is as follows. That is, (p) a mold for cooling the molten steel to form a solidified shell having a predetermined shape, and a tundish having a molten steel flow path at the bottom for pouring the molten steel at a predetermined flow rate into the mold, The continuous casting machine comprising: a ladle for conveying a predetermined amount of molten steel appropriately processed in a converter to the continuous casting machine; Let it be empty. (q) Then, after a predetermined time has elapsed, the molten steel is poured again into the tundish for the purpose of resuming continuous casting of the steel. (r) In this case, the tundish is not heated in the predetermined time, and the molten steel flow path is closed in advance before the pouring of the molten steel to the tundish that is in an almost empty state. The techniques (p) to (r) in which the molten steel flow path is opened when a predetermined amount of molten steel is poured into the tundish that is in an almost empty state.

  According to this, immediately after the start of pouring of molten steel into the tundish that is in an almost empty state, the molten steel flow path is in a closed state, so that it remains at the bottom of the tundish. It is possible to prevent molten slag and remaining steel from being poured into the mold. On the other hand, at the time when the molten steel flow path is opened and pouring of molten steel into the mold is started, a predetermined amount of molten steel is already contained in the tundish, and the slag and remaining steel are molten steel. The slag and the remaining steel are not poured into the mold unexpectedly, and only the molten steel, which is a predetermined component, is poured into the mold. It will be possible to pour hot water.

  However, since this tundish inner hot water reservoir operation technique starts the pouring of molten steel into the tundish and continues the closed state of the molten steel flow path until the molten steel is accumulated by a predetermined amount, During the continuation, the molten steel in the vicinity of the molten steel channel is always cooled by contact with a so-called sliding nozzle provided in the molten steel channel, and as a result, the molten steel is solidified so as to close the molten steel channel. May end up.

  If the molten steel is solidified in the molten steel flow path, the continuous casting cannot be resumed, and the tundish and the molten steel accommodated in the tundish must be discarded. You will suffer a huge loss.

As a technique for trying to prevent the blockage of the molten steel flow path as described above, for example, Patent Document 1 describes a molten steel injection start method for 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 inclusion of slag and the like 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. "

JP-A-1-266951 (Claims, seventh column, lines 13-18)

  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 will cool down unexpectedly, resulting in clogging of the injection nozzle.

  The present invention has been made in view of such various points, and its main purpose is to prevent the blockage of the molten steel channel formed at the bottom of the tundish while adopting the so-called tundish hot water reservoir operation. It is to provide a method for resuming continuous casting of steel.

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 resumed by the following method.

That is, the method for resuming continuous casting of steel targeted by the present invention is as follows: “A mold for cooling molten steel to form a solidified shell of a predetermined shape, and pouring molten steel at a predetermined flow rate into the mold. And a tundish having a molten steel flow path at the bottom thereof, and a ladle for conveying the molten steel appropriately treated in the converter to the continuous casting machine by a predetermined amount. When the continuous casting of steel is interrupted to make the tundish almost empty, and after a predetermined time has elapsed, when the molten steel is poured again into the tundish for the purpose of resuming continuous casting of steel, The tundish is not heated during the time of the above, and the molten steel flow path is previously closed before the pouring of the molten steel with respect to the tundish that has been substantially emptied, and is substantially emptied. The tundish To it a solution steel channel and open state "ones at the time of pouring the molten steel by a predetermined amount.
(a) A sliding nozzle including a first sliding nozzle fixed to the tundish and a second sliding nozzle slidable with respect to the first sliding nozzle is provided in the molten steel flow path of the tundish.
(b) The molten steel flow path is switched to an open state or a closed state by sliding the second sliding nozzle with respect to the first sliding nozzle.
(c) The first sliding nozzle is configured to be able to supply Ar gas from the inner peripheral surface thereof to the molten steel channel.
Furthermore, it has the following process characteristics (1) to (5).
First, (1) The tundish used for the continuous casting of steel to be interrupted contains molten steel for at least 3 hours.
Next, (2) at the bottom of the tundish that is in an almost empty state, the wall thickness t [mm] is 4 to 7, the extension length L [mm] is 350 to 550, and the mass M [kg ] Is 8 or less, and a cylindrical steel pipe having an inner diameter D larger than a hole diameter d of the opening end of the molten steel passage on the inner wall surface of the tundish is set up so as to surround the opening end of the molten steel passage. .
Next, (3) the predetermined time from the time when the continuous casting of the steel is interrupted to make the tundish almost empty until the time when the molten steel starts to be poured into the tundish again is long. Also within 3 hours.
Next, (4) the molten steel having a molten steel superheat degree ΔT [° C.] of 25 to 50 starts to be poured into the tundish, and 180 ° from the inner peripheral surface of the first sliding nozzle to the molten steel passage. Ar gas is supplied at a supply rate Q _Ar [NL / min] of ~ 250.
Finally, (5) when the molten steel depth Y [mm] in the tundish exceeds the extended length L [mm] of the cylindrical steel pipe by at least 50 [mm] or more, Open.

  According to this, since the molten steel flow path is not blocked, continuous casting of steel can be resumed without any problem.

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

  First, a continuous casting machine 100 used for continuous casting of steel in this embodiment will be outlined with reference to FIG. FIG. 1 is a partial cross-sectional view of a tundish used for continuous casting of steel (note that contour lines that should originally be drawn in the partial cross-sectional view are omitted as appropriate for convenience of explanation). In the present embodiment, the continuous casting machine 100 includes a simplified mold 2 for cooling the molten steel to form a solidified shell having a predetermined shape, and pouring the molten steel into the mold 2 at a predetermined flow rate. The tundish 3 having a molten steel flow path 4 at the bottom and a plurality of roll pairs (not shown) arranged side by side along a predetermined casting path starting from directly below the mold 2.

  The configuration of the tundish 3 will be described in detail with reference to FIG. In the present embodiment, the tundish 3 is configured as a bottomed container having a U-shaped cross section that opens vertically upward. The side wall and bottom of the tundish 3 has a two-layer structure including a refractory 9 on the inner wall side and an iron skin 10 on the outer wall side.

  As described above, the bottom of the tundish 3 is formed with a molten steel passage 4 having a substantially drum-shaped cross section for pouring molten steel accommodated in the tundish 3 into the mold 2.

  The molten steel flow path 4 is provided with a sliding nozzle 7 comprising a first sliding nozzle 5 fixed to the tundish 3 and a second sliding nozzle 6 slidable with respect to the first sliding nozzle 5. ing. More details are as follows.

  That is, the first sliding nozzle 5 is inserted into the lower portion of the substantially drum-shaped molten steel flow path 4 from the lower side (iron side) of the tundish 3 and fastened by an appropriate fastening means or the like. As a result, it is fixed to the tundish 3.

  The first sliding nozzle 5 is attached from the opposite side of the insertion direction to the upper nozzle 5a, and the upper nozzle 5a is thinned toward the insertion direction of the first sliding nozzle 5 into the molten steel flow path 4. And a perforated disc-shaped upper slide plate 5b.

  On the other hand, the second sliding nozzle 6 includes a lower nozzle 6b to which a not-shown immersion nozzle for gently pouring molten steel into the mold 2 can be attached, and the flowing direction of the molten steel with respect to the lower nozzle 6b. And a perforated disc-shaped lower slide plate 6a attached to the opposite side.

  With the above configuration, the upper slide plate 5b and the lower slide plate 6a face each other, and both the slide plates 6a and 5b are configured to be relatively slidable. Therefore, the second sliding nozzle 6 is slidable relative to the first sliding nozzle 5, and by sliding the second sliding nozzle 6 relative to the first sliding nozzle 5, The molten steel flow path 4 can be switched to an open state or a closed state. Of course, the opening degree of the molten steel channel 4 can be freely adjusted by appropriately adjusting the amount of movement of the second sliding nozzle 6 relative to the first sliding nozzle 5.

  In the present embodiment, a large number of porous (micro cavities) 5c are uniformly formed over the entire inner peripheral surface of the first sliding nozzle 5 (upper nozzle 5a). Thereby, the first sliding nozzle 5 can supply Ar gas to the molten steel channel 4 from the inner peripheral surface thereof.

  In this embodiment, as will be described later, a cylindrical steel pipe 8 having a predetermined size is erected / placed so as to surround the open end of the molten steel flow path 4 on the inner wall surface of the tundish 3.

  Here, the shape of the steel pipe 8 in the present embodiment will be described in detail with reference to FIG. FIG. 2 is an enlarged view of part A of FIG. 1 (note that in the enlarged view of part A, contour lines that should originally be drawn are appropriately omitted for convenience of explanation). In the present embodiment, the steel pipe 8 is formed in a hollow cylindrical shape, and its inner diameter D is at least larger than the hole diameter d of the open end of the molten steel flow path 4 on the inner wall surface of the tundish 3. Thereby, the steel pipe 8 can be stably erected on the bottom of the tundish 3. The steel pipe 8 has a wall thickness t [mm] of 4 to 7, an extension length (cylinder length) L [mm] of 350 to 550, and a mass M [kg] of 8 or less.

  Next, a method for resuming continuous casting of steel in an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 3 to 7. FIGS. 3 to 6 are views similar to FIG. 1, and are for continuously explaining the resumption of continuous casting of steel according to an embodiment of the present invention. FIG. 7 is a time-series representation of the resumption of continuous casting of steel in one embodiment of the present invention. Hereinafter, a method for resuming continuous casting of steel will be described with reference to FIG. 1 and FIGS.

  In FIG. 7, immediately after time T (1) corresponds to “start of continuous casting of steel” as illustrated, and immediately after time T (3) corresponds to “resumption of continuous casting of steel” as illustrated. It shall be. That is, “resumption” means “starting” “continuous casting of steel” using a tundish in which the refractory is not restretched. In addition, “continuous casting of steel (abbreviation: CC)” is equivalent to pouring molten steel into a mold. (Thus, “starting continuous casting of steel” and “begin pouring molten steel into the mold” can be said to be synonymous.)

<~ Time T (0)>
As described above, the tundish 3 used for continuous casting of steel has a two-layer structure composed of the refractory 9 and the iron skin 10 (see also FIG. 1), of which the refractory 9 is used. It is a part that melts and wears away. Therefore, as is well known, the refractory 9 needs to be re-tensioned periodically according to the degree of melting. Therefore, for convenience of explanation, the time T (0) in FIG. 7 is a time point when the work of replacing the refractory of the tundish 3 is completed.

  Specifically, the refractory re-covering is performed by spraying a predetermined (solid or liquid) refractory on the inner wall of the tundish 3 whose inner wall has been scraped by melting and drying for a predetermined time. It is to let you. Therefore, at the time T (0), the tundish 3 is in a state of being naturally radiated until reaching the room temperature (25 ° C.).

<Time T (0) to Time T (1)>
If molten steel is poured into the tundish 3 cooled to about room temperature in this way, the poured molten steel will be rapidly cooled and solidified by contact with the tundish 3, so avoid such pouring. There is a need to. Therefore, in the present embodiment, as shown in FIG. 7, the tundish 3 is heated by a predetermined burner for a predetermined time from the time T (0) when the above-described rehanging is completed. Specifically, the tundish 3 is heated by a burner until the temperature of the tundish 3 reaches 900 to 1000 ° C. For the convenience of explanation, the time point at which this burner heating was completed sufficiently and necessary was designated as time T (1).

The “predetermined burner” refers to, for example, a tundish 3 from a predetermined hole drilled in the lid of the tundish 3 while reacting CO and oxygen as by-products generated at a steel mill with each other. It is a device that heats the inside of the tundish 3 using the reaction heat generated by this reaction.
The “temperature of the tundish 3” refers to, for example, a radial surface thermometer or the like inserted through a predetermined hole drilled in the lid of the tundish 3, and the temperature of the bottom of the tundish 3 is measured. Value obtained.

<Time T (1)-Time T (2)>
When the tundish 3 is burner heated up to a predetermined temperature as described above, the molten steel flow path 4 is closed and the molten steel appropriately processed in the converter is transferred to the continuous casting machine 100. The molten steel accommodated in a ladle (not shown) for conveying a predetermined amount is poured into the tundish 3 (time T (1)). When a predetermined amount of molten steel is poured into the tundish 3 from the ladle, the molten steel channel 4 is opened to start pouring the molten steel into the mold 2. Thereby, continuous casting of steel is started.

In the above continuous casting of steel, Ar gas is supplied from the inner peripheral surface of the first sliding nozzle 5 to the molten steel passage 4 at a supply rate Q _Ar [NL / min] of about 250. And According to this, the immersion nozzle is blocked by the inclusion of deposits such as Al ₂ O ₃ dissolved in the molten steel on the inner peripheral wall surface of the immersion nozzle (not shown) described above. Can be prevented.

  In the present embodiment, the tundish 3 used for continuous casting of steel contains molten steel for at least 3 hours.

  This continuous casting of steel is interrupted when the pouring of molten steel into the mold 2 is completed. At the same time, the Ar gas supply is terminated. At this time, the tundish 3 is in an almost empty state, and for convenience of explanation, this time is indicated by a symbol T (2) in FIG. (Of course, since the tundish 3 is almost empty, the pouring of molten steel into the mold 2 is finished.)

  When this symbol T (2) is used, the above-mentioned “in this embodiment, the molten steel is accommodated in the tundish 3 used for continuous casting of steel for at least 3 hours”. In other words, “ΔT (1-2) as a time zone between time T (1) and T (2) in FIG. 7 shall be at least 3 hours or more”.

  Thereafter, the slab remaining in the continuous casting machine 100 is pulled out by an appropriate means and discharged.

<Time T (2) to Time T (3)>
After the above “pulling” is completed, or in parallel therewith, the substantially empty tundish is cleaned. Specifically, as shown in FIG. 1, slag and remaining steel (metal) slightly remaining on the bottom of the tundish 3 are discharged to the outside as much as possible through the molten steel channel 4 and the like. At this time, it is desirable that slag and remaining steel remaining on the bottom of the tundish 3 can be completely discharged, but it is technically impossible to completely discharge.

  Then, as shown in FIG. 1, the steel pipe 8 described above is erected (placed) on the bottom of the tundish 3 so as to surround the open end of the molten steel flow path 4 (see also FIG. 2). . According to this, “the slag remaining on the bottom of the tundish 3 flows into the first sliding nozzle 5 and the inside of the upper nozzle 5a as a component of the first sliding nozzle 5 The problem of adhering to the peripheral surface and closing a large number of porous 5c formed on the inner peripheral surface can be prevented.

Now, the molten steel flow path 4 is closed at the same time as or before or after the above-described standing installation. Thereafter, after a lapse of a predetermined time from the time T (2), the molten steel starts to be poured again into the tundish 3 for the purpose of restarting continuous casting of the steel, and the inside of the first sliding nozzle 5 Ar gas is supplied from the peripheral surface to the molten steel flow path 4 at a supply amount Q _Ar [NL / min] of 180 to 250. This pouring start time is defined as time T (3) in FIG.

  In the present embodiment, ΔT (2-3) as the time from the time T (2) to the time T (3) is set to 3 hours or less. In other words, the predetermined time (ΔT () from the time when the continuous casting of the steel is interrupted to make the tundish 3 substantially empty until the time when the molten steel starts to be poured into the tundish 3 again. 2-3)) shall be within 3 hours at the longest.

  The tundish 3 is not heated during the predetermined time (ΔT (2-3)). The so-called molten steel superheat degree ΔT [° C.] of the molten steel poured into the tundish 3 is set to 25-50. Note that this molten steel superheat degree ΔT [° C.] is obtained by immersing a temperature measuring device equipped with a thermocouple at the tip of the molten steel at least 50 mm or more (the distance between the tip of the temperature measuring device and the molten steel surface is 50 mm or more ).

<Time T (3) to Time T (4)>
As shown in FIG. 3, by pouring the molten steel accommodated in the ladle after properly setting up the steel pipe 8 on the bottom of the tundish 3 as described above, as shown in FIG. In the initial stage of the molten steel pouring, the molten steel to be poured does not flow into the molten steel flow path 4. As shown in the figure, impurities such as slag slightly remaining in the tundish 3 float on the upper layer of the molten steel due to the difference in specific gravity.

  If the pouring of the molten steel in FIG. 3 is continued, as shown in FIG. 4, the molten steel whose molten metal surface rises while avoiding the standing steel pipe 8 will eventually straddle the upper end of the steel pipe 8. It flows toward the molten steel flow path 4 (so as to overflow from the upper end).

  In the present embodiment, as described above and as shown in FIG. 5, since Ar gas is supplied from the inner peripheral surface of the first sliding nozzle 5 to the molten steel flow path 4, the molten steel flow The molten steel flowing into and stored in the passage 4 is appropriately stirred. More specifically, as the Ar gas discharged from the inner peripheral surface of the first sliding nozzle 5 rises, the molten steel in the vicinity of the inner peripheral surface is lifted, while the molten steel channel 4 near the center of the channel Thus, the molten steel in the molten steel flow path 4 is appropriately refluxed and agitated. By such a stirring action, "the molten steel in the molten steel flow path 4 is solidified so as to close the molten steel flow path 4 as a result of continuing to be cooled by contact with the sliding nozzle 7". The problem can be prevented beforehand.

  The above reflux / stirring can be ensured for the following reason. That is, (a) the inflow of the slag remaining on the bottom surface of the tundish 3 into the first sliding nozzle 5 is reliably prevented by the steel pipe 8 erected as described above, and (b) the Blocking of a large number of porous 5c formed on the inner peripheral surface of the first sliding nozzle 5 is prevented. (C) As a result, the molten steel channel 4 can be used as a stirring gas without problems through the porous 5c. This is because Ar gas could be supplied.

  Then, when a predetermined amount of molten steel is poured into the tundish 3 that is in an almost empty state, the molten steel channel 4 is opened. More specifically, it is as follows. That is, when the molten steel depth Y [mm] in the tundish 3 exceeds the extended length L [mm] of the steel pipe 8 by at least 50 [mm] as shown in FIG. As shown, the molten steel channel 4 is opened. That is, the pouring of the mold 2 is started at this point. In other words, continuous casting of steel (abbreviation: CC) is started at this point (see FIG. 7).

As shown in the figure, after the molten steel channel 4 is opened, Ar gas is supplied to the molten steel channel 4 at a supply rate Q _Ar [NL / min] of about 250. This supply is mainly intended to prevent adhesion / deposition to the immersion nozzle such as Al ₂ O ₃ described above.

<Time T (4) ~>
In FIG. 7, the time when the continuous casting of the steel is finished (that is, the time when the tundish 3 is almost empty (in other words, when the pouring of the mold 2 is finished)) This is illustrated by T (4).

  Hereinafter, tests (first, second, and third) for confirming the technical effect of the method for resuming continuous casting of steel according to the present embodiment will be described. Each numerical range described above is reasonably supported by the following confirmation test.

<First confirmation test>
This first confirmation test is mainly for confirming the relationship between the shape of the steel pipe 8 and the technical effect. Hereinafter, the evaluation method of the first confirmation test will be described.

  That is, in the “nozzle clogging” column of Tables 1 to 4 below, the evaluation “◯” means that the molten steel flow path 4 can be opened, and the evaluation is also “x”. This means that the molten steel channel 4 could not be opened. Here, the following points can be exemplified as reasons why the molten steel channel 4 cannot be opened. (A) As a result of solidification of the molten steel so as to connect the upper slide plate 5b and the lower slide plate 6a in the state shown in FIG. 5, the lower slide plate 6a is moved with respect to the upper slide plate 5b. When the relative sliding was not possible, the relative sliding described in (b) and (a) was possible, but the molten steel was solidified in the vicinity of the inner peripheral surface of the upper slide plate 5b to form a blocking factor such as a bag shape. If you do.

On the other hand, in the “deformation collapse” column of the following Tables 1 to 4, the evaluation is “◯” because the steel pipe 8 is deformed and does not tilt or fall from the state of FIG. 1 to the state of FIG. It means that the standing state could be maintained, and the evaluation of “x” means that the standing state could not be maintained from the state of FIG. 1 to the state of FIG. More specifically, the determination point of the standing state is immediately before reaching the state of FIG. That is, the time when the standing steel pipe 8 is completely immersed in the molten steel accommodated in the tundish 3.
The reason why the “deformation collapse” is used as an evaluation item is as follows. That is, unless the standing state of the steel pipe 8 is continued sufficiently and sufficiently, the function of the steel pipe 8 cannot be fully exhibited.

  Next, FIG. 8 illustrates the dimensions of a part of the tundish used in this test and the dimensions of the sliding nozzle attached to the tundish. FIG. 8 is a diagram illustrating the dimensions of a part of a tundish used for continuous casting of steel.

The test conditions of the confirmation test and the test results are shown in Tables 1 to 4 below. In each table below, refer to FIG. 2 for “inner diameter D mm”, “wall thickness t mm”, and “extended length L mm”. Further, “mass M kg” is calculated based on the dimensions of the steel pipe 8 described in the same row. At that time, the specific gravity of the steel pipe was 7.61 g / cm ³ .

Other test conditions for the above confirmation test are as follows. That is, the Ar gas supply amount Q _Ar [NL / min] is 150, the molten steel superheat degree ΔT [° C.] of the molten steel poured into the tundish 3 is 30, and immediately after time T (3). At the time when the molten steel starts to be poured into the mold 2, “the depth of the molten metal—the extension length YL [mm] of the steel pipe” is set to 400 (these other test conditions will be examined later in the second confirmation test). .

  Although not described in the above tables, the inner diameter D of the steel pipe 8 is made larger than the hole diameter d (95 mm) of the open end of the molten steel flow path 4 on the inner wall surface of the tundish 3 (see FIG. 2). The steel pipe 8 was able to be stably placed on the bottom surface of the tundish 3 (that is, without tilting or falling).

  Moreover, when the wall thickness t [mm] was less than 4 as described in the above tables, the evaluation regarding “deformation collapse” was not good. This is presumably because the steel pipe 8 was heated by the tundish 3 to reduce its strength and could not withstand its own weight.

  On the other hand, even when the wall thickness t [mm] was set to 8 or more as described in the above tables, the evaluation regarding “deformation collapse” was not good. This is thought to be because the wall thickness t [mm] was excessive and was more susceptible to the influence of the unevenness at the bottom of the tundish 3.

  In addition, when the extension length L [mm] is less than 350 as described in each table above, the evaluation regarding “nozzle clogging” was not good. This is because the slag remaining in the tundish 3 flows into the sliding nozzle 7 because the height as the weir in the standing state of the steel pipe 8 is not sufficient, and the slag is sliding. It is thought that this is because adhesion and solidification to the inner peripheral surface of the nozzle 7 and as a result, distribution of the molten steel to the molten steel channel 4 could not be ensured.

  On the other hand, when the extension length L [mm] is larger than 550 as described in the above tables, the evaluation regarding “deformation collapse” was not good. This is because the heating by the tundish 3 and the own weight of the tundish 3 act on the lower part of the steel pipe 8 in a superimposed manner, so that it is easily deformed regardless of whether molten steel is injected into the tundish 3 or not. / It is thought that it was because the situation was easy to fall down.

  In addition, when the mass M [kg] was larger than 8 as described in the above tables, the evaluation regarding “nozzle clogging” was not good. This is because the refractory in the vicinity of the open end of the molten steel flow path 4 on the inner surface of the tundish 4 has been considerably removed by contact with the steel pipe 8 placed on the refractory, so that it is cooled. It is considered that the molten steel in contact with the refractory solidified and as a result, the molten steel flow path 4 could not be opened.

<Second confirmation test>
Next, the second confirmation test will be described. This second confirmation test is mainly for confirming the relation between the other test conditions and the technical effect. Below, the evaluation method of a 2nd confirmation test is demonstrated.

  That is, the evaluation of “◯” or “×” in the “nozzle blockage” column of Table 5 below is the same as the evaluation method in the first confirmation test.

  On the other hand, in the “bubble defect” column of Table 5 below, the evaluation is “◯” because “(1) Continuous casting under the conditions described in the corresponding row, (2) A steel piece with a cross section of 155 x 155 mm and a length of 10 m was formed in the batch rolling process, and (3) the surface (outer surface: 4 surfaces) of the steel piece was visually observed, and (4) the length in the rolling direction was 5 mm. None of the above linear defects were observed per surface ”. On the other hand, the evaluation “x” means that “(4) one or more linear defects having a length of 5 mm or more in the rolling direction were observed per surface”.

The test conditions of the confirmation test and the test results are shown in Table 5 below. In the table below, “molten steel superheat degree ΔT ° C.” refers to the molten steel superheat degree ΔT of molten steel that begins to be poured into the tundish 3 at time T (3), and its measuring method is as described above. Further, “the depth of the molten metal—the extension length Y-Lmm of the steel pipe” is the molten metal depth Y of the molten steel in the tundish 3 when the molten steel flow path 4 is opened in the state of FIG. It is a value obtained by subtracting the extended length L [mm] of the steel pipe 8 erected at a predetermined location of the tundish 3 from [mm]. In addition, “Ar gas supply amount Q _Ar [NL / min]” is determined from the time T (3) in FIG. 7 until the time when the molten steel passage 4 is opened. This is the supply amount Q _Ar [NL / min] of Ar gas supplied from the peripheral surface to the molten steel channel 4.

In Table 5, other test conditions are as follows.
That is, the inner diameter D [mm] of the steel pipe 8 was 100, the wall thickness t [mm] was 4, the extension length L [mm] was 400, and the mass M [kg] was 3.84.

  According to Table 5 above, when the “molten steel superheat degree ΔT [° C.]” was less than 25, the evaluation regarding “nozzle clogging” was not good. This is thought to be because the molten steel was easily solidified in or around the molten steel flow path 4 because the molten steel superheat degree ΔT was not sufficiently ensured.

  On the other hand, although not described in Table 5 above, when the molten steel heating degree ΔT [° C.] is higher than 50, solidification of the molten steel in the mold 2 is delayed and the thickness is not sufficient on the downstream side of the mold 2. Another problem of so-called breakout has occurred in which the solidified shell is broken and the molten steel in the solidified shell flows out to the outside.

  Also, according to Table 5 above, when “bath depth−extended length Y-L [mm] of the steel pipe” was less than 50, the evaluation regarding “nozzle blockage” was not good. This is considered to be due to the following reasons.

  That is, the second sliding nozzle 6 is slid relative to the first sliding nozzle 5 to open the molten steel flow path 4, and the molten steel is poured from the tundish 3 to the mold 2. When starting, it is assumed that a thin coagulated film is generated on the relative sliding surface (the boundary surface between the upper sliding plate 5b and the lower sliding plate 6a).

  In such a case, since the molten steel flow path 4 is blocked by the solidified film and maintained in the closed state even by the relative sliding, the molten steel pouring from the tundish 3 to the mold 2 may not be started. . However, it is considered that this solidified film can be cleaved by the static pressure of the molten steel acting on the solidified film.

  And, when the second sliding nozzle 6 is relatively slid, the larger the amount of molten steel accommodated in the tundish 3 (the larger the hot water depth Y [mm] is ensured), Since the static pressure becomes large, even if the solidified film is formed, the solidified film is cleaved by the action of the molten steel static pressure, and the molten steel flow path 4 can be completely opened without any problem. Can be estimated.

  Based on the above considerations, the evaluation regarding “nozzle blockage” was not good when “bath depth−extended length YL [mm]” in Table 5 was less than 50. At this time, the above-mentioned solidified film has been formed, and since the above-mentioned molten steel static pressure was not sufficient, the solidified film could not be cleaved, so the closed state of the above-mentioned molten steel flow path 4 was maintained. It is thought that it was because it was done.

Further, according to Table 5 above, when “Ar gas supply amount Q _Ar [NL / min]” was set to 180 or less, the evaluation regarding “nozzle clogging” was not good. This is considered to be due to the following reasons.

That is, as shown in FIG. 5, by supplying Ar gas to the molten steel flow path 4, the above-mentioned reflux is formed in the molten steel flow path 4, so that high temperature molten steel is continuously guided to the molten steel flow path 4. The molten steel in the molten steel flow path 4 is appropriately stirred. According to this, solidification of the molten steel in the vicinity of the inner peripheral surface of the first sliding nozzle 5 can be prevented. However, when the above-mentioned “Ar gas supply amount Q _Ar [NL / min]” is 180 or less, the above reflux is not sufficiently formed, so the degree of stirring in the molten steel flow path 4 is weak, As a result, it is considered that the molten steel has solidified in the vicinity of the inner peripheral surface of the first sliding nozzle 5. In other words, the supply of heat to the inner peripheral surface of the first sliding nozzle 5 may not have been sufficiently achieved by the reflux.

On the other hand, according to Table 5 above, when “Ar gas supply amount Q _Ar [NL / min]” was greater than 250, the evaluation regarding “bubble defects” was not good. This is because a large amount of Ar gas bubbles are trapped in the molten steel, the trapped Ar gas bubbles flow into the mold 2, and the molten steel is solidified while containing the Ar gas bubbles. This is thought to be due to the surface defects of the slab in the rolling process.

<Third confirmation test>
This third confirmation test is to confirm the relationship between the characteristics related to the setting of ΔT (1-2) and ΔT (2-3) and the technical effect. Hereinafter, the evaluation method of the third confirmation test will be described.

  FIG. 9 is a diagram showing test conditions and test results of the third confirmation test. In the drawing, the evaluation regarding the “nozzle blockage” is “x” (that is, indicated by “♦: black diamond”), and the evaluation is also “◯” (that is, “◇: The meaning of the plot (indicated by the white diamonds) is the same as that in Tables 1-5 above.

  Other test conditions for this third confirmation test are as follows. That is, the inner diameter D [mm] of the steel pipe 8 was 100, the wall thickness t [mm] was 4, the extension length L [mm] was 400, and the mass M [kg] was 3.84.

  According to FIG. 9, it can be seen that ΔT (1-2) is preferably at least 180 minutes (3 hours) or more from the viewpoint of evaluation regarding “nozzle blockage”. This is considered to be due to the following reasons.

  That is, in the case of repeatedly using the tundish 3 (without changing the refractory 9) as in the above-described embodiment, in order to stably and safely accommodate the molten steel by the tundish 3 From the viewpoint of preventing solidification of the molten steel, it can be said that it is important to secure a sufficient amount of heat of the tundish 3. On the other hand, in the above embodiment, the tundish 3 to which the refractory 9 has been replaced is heated in advance by a predetermined burner before casting. Nevertheless, in order to ensure a large amount of heat of the tundish 3, it is most effective to actually contain molten steel. Considering the above, if the ΔT (1-2) as the time during which the tundish 3 actually contains the molten steel before the resumption of continuous casting of steel is 180 minutes or more, “nozzle” It is possible to reasonably explain that the main reason is the large amount of heat stored in the tundish 3 due to the containment of molten steel. Like.

  Further, according to this figure, it can be seen that ΔT (2-3) is preferably 180 minutes (3 hours) or less at the longest from the viewpoint of evaluation related to “nozzle blockage”. This is considered to be due to the following reasons.

  That is, even if the tundish 3 can secure a large amount of heat by housing the molten steel, it takes time to start pouring the molten steel into the tundish 3 again (in other words, the tundish 3 This is because, if the substantially empty state of 3 is maintained for a long time), the stored heat amount is released to the atmosphere.

  As described above, in the above embodiment, the method for resuming continuous casting of steel is performed by the following method.

That is, the method for resuming continuous casting of steel targeted by the above embodiment is “a mold 2 for cooling molten steel to form a solidified shell of a predetermined shape, and pouring molten steel into the mold 2 at a predetermined flow rate. Therefore, a continuous casting machine 100 provided with a tundish 3 having a molten steel flow path 4 at the bottom thereof, and for transporting molten steel appropriately processed in a converter to the continuous casting machine 100 by a predetermined amount The continuous casting of the steel using the ladle is interrupted to make the tundish 3 almost empty, and after a predetermined time has passed, the molten steel is again added for the purpose of restarting the continuous casting of the steel. When pouring to 3, the tundish 3 is not heated during the predetermined time, and the molten steel flow path 4 is set before starting the pouring of the molten steel to the tundish 3 that is in an almost empty state. Before closing in advance and making it almost empty To the solution steel flow path 4 in an open state at the time of pouring the molten steel by a predetermined amount to the tundish 3 'it is intended.
(a) The molten steel flow path 4 of the tundish 3 includes a first sliding nozzle 5 fixed to the tundish 3, and a second sliding nozzle 6 slidable with respect to the first sliding nozzle 5. A sliding nozzle 7 is provided.
(b) By sliding the second sliding nozzle 6 with respect to the first sliding nozzle 5, the molten steel channel 4 is switched to an open state or a closed state.
(c) The first sliding nozzle 5 is configured to be able to supply Ar gas to the molten steel channel 4 from the inner peripheral surface thereof.
Furthermore, it has the following process characteristics (1) to (5).
First, (1) The tundish 3 used for the continuous casting of steel to be interrupted contains molten steel for at least 3 hours (corresponding to ΔT (1-2), see FIG. 7).
Next, (2) the bottom portion of the tundish 3 in an almost empty state has a thickness t [mm] of 4 to 7, an extension length L [mm] of 350 to 550, and a mass M [ kg] is 8 or less, and an inner diameter D surrounds the open end of the molten steel flow channel 4 with a cylindrical steel pipe 8 having a diameter larger than the hole diameter d of the open end of the molten steel flow channel 4 on the inner wall surface of the tundish 3 Stand up like you do.
Next, (3) the predetermined time ΔT from the time when the continuous casting of the steel is interrupted and the tundish 3 is made almost empty until the time when the molten steel starts to be poured into the tundish 3 again. (2-3) shall be within 3 hours at the longest.
Next, (4) molten steel having a molten steel superheat degree ΔT [° C.] of 25 to 50 starts to be poured into the tundish 3, and from the inner peripheral surface of the first sliding nozzle 5 to the molten steel channel 4 On the other hand, Ar gas is supplied at a supply amount Q _Ar [NL / min] of 180 to 250.
Finally, (5) when the molten steel depth Y [mm] in the tundish 3 exceeds the extended length L [mm] of the cylindrical steel pipe 8 by at least 50 [mm] or more, The channel 4 is opened.

  According to this, since the molten steel flow path 4 is not blocked, continuous casting of steel can be resumed without any problem. From another point of view, the steel pipe 8 can be stably erected on the bottom of the tundish 3. Further, it is possible to realize casting of a slab free of bubble defects.

Partial sectional view of tundish used for continuous casting of steel Part A enlarged view of FIG. Similar to FIG. Similar to FIG. Similar to FIG. Similar to FIG. The figure which expressed resumption of continuous casting of steel in one embodiment of this invention in time series Diagram illustrating the dimensions of a part of a tundish used for continuous casting of steel The figure which shows the test condition and the test result of the third confirmation test

Explanation of symbols

2 Mold
3 Tundish
4 Molten steel flow path
5 First sliding nozzle
5a Top nozzle
5b Upper slide plate
6 Second sliding nozzle
6a Lower slide plate
6b Lower nozzle
7 Sliding nozzle
8 Steel pipe
9 Refractories
10 Iron skin
100 continuous casting machine

Claims (1)

A continuous casting machine comprising: a mold for cooling molten steel to form a solidified shell of a predetermined shape; and a tundish having a molten steel flow path at the bottom for pouring molten steel into the mold at a predetermined flow rate When,
A ladle for conveying the molten steel appropriately processed in the converter to the continuous casting machine by a predetermined amount;
When the continuous casting of steel using is interrupted to make the tundish almost empty, and after a predetermined time has passed, the molten steel is poured again into the tundish for the purpose of restarting the continuous casting of steel. ,
The tundish is not heated at the predetermined time, and the molten steel flow path is closed in advance before starting the pouring of the molten steel to the tundish that has been substantially empty, and is in an almost empty state. In the method for resuming continuous casting of steel, the molten steel flow path is opened when a predetermined amount of molten steel is poured into the tundish.
(a) The molten steel flow path of the tundish is provided with a sliding nozzle comprising a first sliding nozzle fixed to the tundish and a second sliding nozzle slidable with respect to the first sliding nozzle,
(b) By switching the molten steel flow path to an open state or a closed state by sliding the second sliding nozzle with respect to the first sliding nozzle,
(c) The first sliding nozzle is configured to be able to supply Ar gas from the inner peripheral surface to the molten steel flow path,
(1) The tundish used for continuous casting of steel to be interrupted shall contain molten steel for at least 3 hours,
(2) At the bottom of the tundish that is substantially empty, the wall thickness t [mm] is 4 to 7, the extension length L [mm] is 350 to 550, and the mass M [kg] is 8 The inner diameter D is erected so as to surround the open end of the molten steel flow path with a cylindrical steel pipe having a diameter larger than the hole diameter d of the open end of the molten steel flow path on the inner wall surface of the tundish,
(3) The predetermined time from the time when the continuous casting of the steel is interrupted to make the tundish almost empty until the time when the molten steel starts to be poured again into the tundish is at most 3 hours. As within
(4) The molten steel having a molten steel superheat degree ΔT [° C.] of 25 to 50 begins to be poured into the tundish, and 180 to 250 from the inner peripheral surface of the first sliding nozzle to the molten steel flow path. Ar gas is supplied at a supply rate of Q _Ar [NL / min]
(5) When the molten steel depth Y [mm] in the tundish exceeds the extended length L [mm] of the cylindrical steel pipe by at least 50 [mm], the molten steel flow path is opened. To
For resuming continuous casting of steel

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