JP2008200685A - Cooling method for continuously cast slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method where a slab in high temperature after continuous casting can be cooled at high efficiency without generating shape deformation caused by warpage even in cooling from a high temperature region where surface temperature exceeds 600°C. <P>SOLUTION: Disclosed is a cooling method for a continuously cast slab where a slab in high temperature after continuous casting is periodically repeatedly subjected to water spray treatment and water spray stopping treatment, so as to cool the slab. In the above cooling method, by periodically repeatedly subjecting the side faces in the longitudinal direction of stacked slabs in high temperature to water spray treatment and water spray stopping treatment, large effect can be exhibited. Preferably, water spray time is controlled to 5 to 30 min and water spray stopping time is controlled to 5 to 30 min, and, more preferably, the upper face of the slab in the uppermost stage in the stacked high temperature slabs is subjected to temperature holding treatment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for cooling a high-temperature slab after continuous casting without causing a shape change, and more specifically, a slab after continuous casting mainly with high efficiency without causing a shape change due to warpage. The present invention relates to a method for cooling a continuously cast slab that can be cooled.

  When cooling a hot slab after continuous casting, a temperature deviation occurs in the slab during the cooling process, and due to the difference in thermal shrinkage due to the temperature deviation and expansion due to phase transformation, Shape deformation is likely to occur. In addition, in a material having a relatively low thermal conductivity such as steel, the surface temperature of the material is lowered by cooling, but the temperature inside the material is hardly lowered. When the surface temperature of the material is lowered to less than 100 ° C. in the case of sprinkling cooling, the heat removal effect due to the latent heat of evaporation of water is lost, so the cooling efficiency per sprinkling amount is significantly reduced.

  As a conventional technique for cooling a high-temperature slab after continuous casting, for example, methods disclosed in Patent Document 1 and Patent Document 2 below are known.

  In Patent Document 1, a plurality of high-temperature slabs are stacked, a water droplet adhesion prevention treatment is applied to the upper surface of the slab positioned at the top of the stacked slabs, and cooling water is sprinkled on the longitudinal side surfaces of the high-temperature slabs. Thus, a method of cooling the slab while preventing warping of the slab loaded on the uppermost stage is disclosed. However, in the method disclosed in the same document, it is difficult to completely prevent the slab from being warped, and the deterioration of the cooling efficiency after the surface temperature is lowered cannot be prevented. Takes a long time. Furthermore, handling work such as installation and removal of a water droplet adhesion prevention plate such as a cold cast slab before and after water cooling is required, which increases the number of cooling steps.

  Further, Patent Document 2 describes that the lower part of the laminated slab is left in the air until the surface temperature of the side surface of the laminated slab becomes 600 ° C. or lower, and then the lower part of the lower part except for a range of at least 0.3 m downward from the upper surface of the uppermost slab. The cooling method of the slab sprayed on the longitudinal direction side surface of this slab is disclosed. However, even in this method, it is difficult to completely prevent deformation due to slab warpage, and in particular, when the surface temperature exceeds 600 ° C., it is difficult to suppress the occurrence of slab warpage caused by water spray cooling. It is.

  As described above, when cooling a high temperature slab after continuous casting by sprinkling cooling, even if it is cooling from a high temperature region where the surface temperature of the slab exceeds 600 ° C., shape deformation due to warpage of the slab etc. In order to prevent and cool with high efficiency, there remains a problem that must be improved.

JP 11-286728 A (Claims and paragraph [0004]) JP 2006-55865 A (Claims and paragraphs [0025] to [0027])

  The present invention has been made in view of the above-described problems that occur when cooling a high-temperature slab after continuous casting, and the problem is that the high-temperature slab after continuous casting, particularly sprinkling of laminated slabs. An object of the present invention is to provide a method for preventing the deformation of the slab due to warpage of the slab and cooling the slab with high efficiency even when cooling from a high temperature region whose surface temperature exceeds 600 ° C.

  In order to solve the above-mentioned problems, the present inventors can cool a high-temperature slab after continuous casting under high watering conditions by suppressing shape deformation due to warpage of the slab and with high efficiency. The cooling method which can be performed was examined, the following knowledge (a) to (d) was obtained, and the present invention was completed.

  (A) When the high-temperature slab after continuous casting is sprinkled and cooled, the water spray is likely to be applied to the upper surface of the slab, and due to the generated water vapor, the cooling on the upper surface of the slab proceeds more rapidly than the lower surface. For this reason, an upward warp (a warped convex shape) occurs due to a difference in thermal shrinkage due to a temperature difference between the upper surface and the lower surface of the slab. In addition, since the phase transformation from the upper surface of the slab to ferrite proceeds during the cooling process, the slab is warped downward (convex in a convex shape) due to expansion in the vicinity of the upper surface. In particular, when the longitudinal side surfaces of the stacked high-temperature slabs are sprinkled and cooled, the slab located in the uppermost stage is greatly affected by the above.

  (B) In order to relieve the shape deformation due to warping of the slab described in (a) above, a watering method that periodically repeats the watering treatment and the watering stop treatment is effective. This is because the temperature deviation between the upper and lower surfaces of the slab generated during the watering period is relaxed by the reheat from the high temperature portion inside the slab during the watering stop period, and the warpage of the slab is reduced.

  (C) According to the above method (b), the surface temperature of the slab rises due to recuperation during the watering stop period, so that the surface temperature of the slab can be maintained at a relatively high temperature. As a result, the cooling efficiency per unit cooling water volume can be increased, so that the cooling efficiency per sprinkling cooling time can be made the same level as when continuously sprinkling water, and cooling water can be saved and energy can be saved. It is also possible to plan.

  (D) In the method (b), the watering time and the watering stop time are preferably in the range of 5 to 30 minutes, respectively. In addition, by applying a heat retaining treatment to the upper surface of the slabs positioned at the uppermost stage of the stacked slabs, the occurrence of warpage of the slabs due to sprinkling cooling can be almost eliminated.

  This invention is completed based on said knowledge, The summary exists in the cooling method of the continuous cast slab shown to following (1)-(4).

  (1) A cooling method for a continuous cast slab (hereinafter referred to as “first”), wherein the slab is cooled by periodically subjecting a high-temperature slab after continuous casting to water spraying treatment and water spray stop treatment. Also referred to as “invention”).

  (2) After laminating high-temperature slabs after continuous casting, the slabs are cooled by periodically repeating watering treatment and watering stop treatment on the side surfaces in the longitudinal direction of the laminated high-temperature slabs. And a method for cooling a continuous cast slab (hereinafter also referred to as “second invention”).

  (3) The watering time is 5 to 30 minutes, the watering stop time is 5 to 30 minutes, and watering treatment and watering stop processing are periodically repeated. A method for cooling the continuous cast slab described above (hereinafter also referred to as “third invention”).

  (4) The method for cooling a continuously cast slab according to any one of (2) and (3), wherein a heat treatment is applied to the upper surface of the slab located at the uppermost stage of the stacked high-temperature slabs ( Hereinafter, also referred to as “fourth invention”).

  In the present invention, “high temperature slab” or “high temperature slab” means a slab or slab having a surface temperature in the range of 100 ° C. to 800 ° C. The surface temperature is preferably represented by the average surface temperature of the side surface in the longitudinal direction of the slab or slab or the surface temperature of the central portion in the longitudinal direction.

  According to the method for cooling a slab of the present invention, a surface temperature of 600 ° C. is obtained by periodically subjecting a high-temperature slab after continuous casting, particularly a laminated slab, to repeated watering treatment and watering stop treatment. Even if it is cooling from the high temperature area | region exceeding this, shape deformation by the curvature of a slab etc. can be prevented, and a slab can be water-cooled with high cooling efficiency.

  As described above, the present invention is a continuous casting slab cooling method for cooling a slab by periodically subjecting a high-temperature slab after continuous casting to watering treatment and watering stop treatment, and in particular, continuous casting. This is a method of cooling the slab by periodically repeating the watering treatment and the watering stop treatment on the side surface in the longitudinal direction of the high-temperature slab laminated later. In the following description, a cooling method in which watering treatment and watering stop processing are periodically repeated is also referred to as “intermittent watering cooling”, and is distinguished from a conventional cooling method by continuous watering.

  When the high temperature slab after continuous casting is sprinkled and cooled, the water spray is likely to be applied to the upper surface of the slab, and the upper surface of the slab is cooled more than the lower surface due to the influence of the generated water vapor. As a result, a temperature deviation occurs between the upper surface and the lower surface of the slab, causing an upward warpage due to a difference in thermal shrinkage rate, or expansion due to a phase transformation from near the upper surface of the slab to ferrite during the cooling process. Along with this, the slab is warped.

  FIG. 1 is a diagram schematically showing cooling of a laminated slab by the sprinkling cooling method of the present invention. When sprinkling and cooling the longitudinal side surface 2 of the laminated high temperature slab 1 (shaded portion in the figure), the upper surface 4 and the lower surface 5 of the slab as described above in the uppermost slab 3 The temperature deviation during this period is remarkably generated, and therefore, the shape deformation due to the slab warpage caused by the temperature deviation also becomes large.

  The present invention improves the sprinkling cooling method to alleviate the temperature deviation in the above slab that causes shape deformation of the slab, and suppresses the shape deformation due to warping while cooling with high efficiency. Is the method. Hereinafter, the reason why the configuration of the present invention is defined as described above and preferred embodiments will be described in detail.

(1) Periodic repetition of sprinkling treatment and sprinkling stop processing The present invention is characterized by periodically repeating sprinkling treatment and sprinkling stop processing on a high-temperature slab. In order to suppress the occurrence of warpage of the slab, a watering method that periodically repeats the watering process and the watering stop process as described above is effective. The reason for this is that the temperature deviation between the upper and lower surfaces of the slab generated during the watering period is alleviated by the recuperation phenomenon based on the heat conduction from the high-temperature part inside the slab during the watering stop period. This is because the warpage of the sheet is reduced.

  Further, in the case of the conventional method in which water spray cooling is continuously performed, the surface temperature of the slab is lowered, but the temperature inside the slab is hardly lowered, and when the surface temperature is lowered to 100 ° C. or lower, the cooling water Since heat removal due to the latent heat of evaporation does not occur, the amount of heat taken away from the slab by sprinkling is only heat transfer based on the temperature difference between the surface temperature of the slab and the cooling water temperature, so cooling efficiency per unit water volume Will be significantly reduced.

  On the other hand, in intermittent sprinkling cooling that periodically repeats the sprinkling treatment and the sprinkling stop treatment, the surface temperature of the slab rises due to the recuperation phenomenon during the sprinkling stop period, so the surface temperature of the slab is relatively high. Can be maintained. As a result, the effect of heat removal due to the latent heat of vaporization of the cooling water can be secured over a long period of time, and the heat transfer rate based on the temperature difference between the slab surface and the cooling water can be maintained at a high level. Efficiency can be increased. Therefore, the cooling effect per sprinkling cooling time can be set to the same level as in the case of continuous sprinkling cooling, and cooling water can be saved and energy can be saved.

  When water spray cooling is applied to the stacked high-temperature slabs, the side surfaces in the longitudinal direction of the stacked slabs are designed to minimize the difference in cooling effect between the upper and lower surfaces of each slab and to increase the cooling efficiency. It is preferable to periodically and repeatedly perform the watering treatment and the watering stop treatment. In addition, in order to prevent the occurrence of lateral warping (lateral warping) parallel to the ground due to temperature deviation in the width direction of the slab, water spraying treatment and water spray stopping treatment are periodically performed on both sides in the longitudinal direction. It is preferable to apply repeatedly.

(2) Sprinkling time and sprinkling stop time As prescribed in the third invention, the sprinkling time is preferably 5 to 30 minutes, and the sprinkling stop time is preferably 5 to 30 minutes.

  The reason is as follows. That is, when the watering time is less than 5 minutes, the cooling rate of the slab per unit time decreases, while when the watering time exceeds 30 minutes, the surface temperature of the slab decreases too much, This is because, in addition to the cooling efficiency per unit amount of water being lowered, the temperature deviation inside the slab is enlarged, and shape deformation such as warpage caused by the temperature deviation is promoted. In addition, when the watering stop time is less than 5 minutes, the surface temperature of the slab is not sufficiently reheated, and thus the cooling efficiency per unit water amount is lowered, while the watering stop time is longer than 30 minutes. This is because although the cooling efficiency per unit amount of water does not decrease, the time required for cooling the slab becomes longer and the sprinkling cooling capacity decreases.

(3) Upper surface heat retention treatment of the uppermost slab of the laminated slab As defined in the fourth invention, it is preferable to apply a heat retention treatment to the upper surface of the uppermost slab of the laminated slab. The reason for this is that the top surface of the uppermost slab is particularly susceptible to cooling sprinkling, and the cooling of the upper surface of the slab proceeds rapidly due to the influence of the generated water vapor, causing warpage and ferrite due to differences in the heat shrinkage rate. This is because the downward warping caused by the phase transformation to is likely to occur.

  As the top surface heat treatment of the uppermost slab of the laminated slab, for example, a non-combustible fibrous refractory such as glass wool or rock wool, or a board or porous brick made of refractory is combined and placed on the top surface of the slab. Therefore, almost no slab warpage due to sprinkling cooling can be achieved.

  In order to confirm the effect of the water spray cooling method of the slab according to the present invention, the test described below was performed and the result was evaluated.

  Test conditions and test results are shown in Table 1.

  As shown in the table, slab dimensions, number of slabs, initial surface temperature of slab, water spray pattern, water spray amount, heat treatment on top surface of top slab, etc. are changed as test conditions, and the amount of warpage of slab and the number of days required for cooling are changed investigated.

(1) Test method Using a high-temperature slab cast by continuous casting and having a thickness of 227 mm, a width of 950 mm or 1250 mm, and a length of 9 to 10 m and an initial surface temperature of 500 to 760 ° C. A cooling test in which water was sprayed on the upper surface of the slab and a cooling test in which water was sprayed on the side surfaces of the stacked slabs of 8 sheets (8 stages) or 9 sheets (9 stages) were performed. For sprinkling cooling, water was sprayed on the surface of the slab using a full cone type nozzle arranged in one or more rows until the surface temperature of the upper surface of the slab or the side surface of the laminated slab decreased to a predetermined temperature.

  The “watering pattern” described in Table 1 indicates the distinction between continuous watering cooling or intermittent watering cooling according to the method of the present invention, and A, B and C in the watering pattern are watering time, watering stop time, and Represents total sprinkling cooling time. In order to clarify these relationships, FIG. 2 shows a conceptual diagram of the change over time in the watering amount in the watering cooling method. In intermittent sprinkling cooling during the cooling test, the sprinkling time (A), sprinkling stop time (B) and total sprinkling cooling time (C) from the start of sprinkling cooling to the end of sprinkling cooling shown in FIG. Each value of A, B, and C shown was adopted and tested.

  In addition, “average watering amount” described in the table is (total watering amount (L) sprayed within the total watering cooling time) / (time from the start of watering cooling to the end of watering cooling (min)) / (cooling The value calculated by the total mass (t) of the slab.

  The “top slab heat treatment” in the table indicates the presence or absence of heat treatment, and “present” indicates non-flammable fibrous refractories such as glass wool and rock wool as heat treatment on the top surface of the slab. , Or a combination of refractory boards, porous bricks, etc., placed on the top of the slab to indicate that it has been kept warm, and the indication “none” did not take any action Represents that.

  After sprinkling cooling, the slab was allowed to cool until the surface temperature became 40 ° C. or less, and the “warping amount” was measured. The amount of warpage was measured in terms of warpage in the direction perpendicular to the ground (longitudinal warpage), and indicated by the amount of warpage (mm) per unit length (m) in the longitudinal direction of the slab.

  “Cooling days” is indicated by the required days from the end of continuous casting until the surface temperature of the slab drops to 40 ° C.

  The surface temperature of the slab was measured as follows. That is, for the surface temperature of one slab, the surface temperature at the center of one side surface in the longitudinal direction of the slab was measured and used as the surface temperature. Regarding the surface temperature of the laminated slabs, the surface temperature at the central portion of one side surface in the longitudinal direction of the fifth slab from the bottom of the laminated slab was measured and used as the surface temperature. In addition, the surface temperature before watering was measured with the radiation type thermometer, and the surface temperature after watering was measured with the contact-type thermometer after drying the surface.

(2) Test results Test Nos. 1 to 4 are tests on comparative examples in which continuous watering cooling that does not satisfy the requirements defined in the present invention is performed, and test numbers 5 to 12 are intermittent water cooling defined in the present invention. This is a test for an example of the present invention that satisfies the above requirements. Test numbers 1 and 5 are tests in which water is cooled on the upper surface of one slab, and test numbers 2 to 4 and test numbers 6 to 12 are water sprays on both side surfaces in the longitudinal direction of the stacked slabs. This is a test with cooling. Test numbers 4 and 10 to 12 are tests in which heat treatment was performed on the upper surface of the uppermost slab, and test numbers 1 to 3 and test numbers 5 to 9 were tests in which heat treatment was not performed. It is.

  When comparing test number 1 of the comparative example in which water spray cooling was performed on the upper surface of one slab and test number 5 which is the invention example of the first invention, in test number 1 of the comparative example, a large warp occurred in the slab. On the other hand, in the test number 5 of the example of the present invention, the amount of warpage of the slab was suppressed to about 1/5 that in the case of the test number 1, and a cooling slab having a good shape was obtained. Moreover, the average watering amount obtained by dividing the total watering amount sprinkled within the total watering cooling time by the time from the start of watering cooling to the end of watering cooling and the total mass of the cooling slab is the test number compared to the case of test number 1. No. 5 is markedly reduced, and the total water spray amount per unit mass of the slab is also reduced to about 70% in the case of Test No. 5 in the case of Test No. 1.

  In test numbers 6 and 7, which are invention examples of the third invention in which water spray cooling is performed on the side surfaces of the laminated slabs, as compared with test numbers 2 and 3 in the comparative example in which water spray cooling is similarly performed on the side surfaces of the laminated slabs. The amount of warpage of the slab is suppressed to about 40%, and the total amount of water sprayed per unit mass of the slab is also reduced to about ½.

  Test Nos. 7, 8 and 9 increase the watering time (A) from 10 minutes to 25 minutes in response to the initial surface temperature of the slab rising from 700 ° C to 760 ° C, and the watering stop time (B). This is an example of the invention of the third invention shortened from 10 minutes to 5 minutes. Even when water spray cooling is performed from the initial surface temperature of the slab, the amount of warpage of the slab is not significantly changed and is suppressed to a low level, and the total water spray amount per unit mass of the slab is also maintained at a relatively low level. Has been.

  In test number 10 which is the invention example of the fourth invention in which the upper surface of the slab positioned at the uppermost layer of the stacked slabs is subjected to heat insulation treatment, the heat retaining treatment is performed on the upper surface of the slab positioned at the uppermost layer of the stacked slabs. Compared with the test number 4 of the comparative example to which the slab was applied, the warpage of the slab was drastically improved, and a cooling slab having a very good shape with no warpage was obtained. Further, the total water spray amount per unit mass of the slab is also reduced to about 60% in the case of test number 4.

  Although test numbers 11 and 12 are examples of the invention of the fourth invention carried out under conditions where the initial surface temperature of the slab is 740 to 760 ° C., the cooling of a very good shape without any warping of the slab A slab was obtained. In addition, the total amount of water sprayed per unit mass of the slab was significantly lower than the test number 4 of the comparative example.

  In addition, the days required for cooling in Test Nos. 5 to 12 as examples of the present invention are shortened to the same number as or less than the days required for cooling in Test Nos. 1 to 4 as comparative examples.

  According to the method for cooling a slab of the present invention, a surface temperature of 600 ° C. is obtained by periodically subjecting a high-temperature slab after continuous casting, particularly a laminated slab, to repeated watering treatment and watering stop treatment. Even if the cooling is from a high temperature region exceeding 1, it is possible to prevent shape deformation due to warping of the slab and to economically cool with high efficiency. Therefore, the method for cooling a slab of the present invention can be widely applied to a cooling process such as a slab that is required to be cooled with high efficiency by simple equipment.

It is a figure which shows typically cooling of the lamination | stacking slab by the water spray cooling method of this invention. It is a conceptual diagram of the time-dependent change of the watering amount in the watering cooling method of this invention.

Explanation of symbols

  1: Laminated high-temperature slab 2: Longitudinal side surface of the slab 3: Slab located at the top, 4: Upper surface of the slab, 5: Lower surface of the slab

Claims (4)

  A method for cooling a continuous cast slab, characterized in that the slab is cooled by periodically subjecting a high-temperature slab after continuous casting to water spray treatment and water spray stop treatment.   Continuously characterized by laminating a high-temperature slab after continuous casting and then cooling the slab by periodically repeating watering treatment and watering stop treatment on the side surface in the longitudinal direction of the laminated high-temperature slab A method for cooling cast slabs.   The continuous casting slab according to claim 1 or 2, wherein the watering time is 5 to 30 minutes, the watering stop time is 5 to 30 minutes, and the watering treatment and watering stop processing are periodically repeated. Cooling method.   The method for cooling a continuous cast slab according to any one of claims 2 and 3, wherein heat treatment is applied to the upper surface of the slab located at the uppermost stage of the stacked high-temperature slabs.

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