JP2017124411A - Heating method and heating facility of continuously cast slab after cut - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a method capable of performing a hot-rolling at a next step just after a continuous casting slab was cut, and a thermal compensation with a little thermal energy.SOLUTION: A continuous casting slab, from which a cast piece was cut out, is hot-rolled immediately after cut from the casting slab, to manufacture a hot-rolled steel band. When the temperature compensation of the slab is induction-heated before the coarse rolling of the hot rolling is executed, the production is characterized in that the induction heating of the slab section entirety is performed immediately after the induction eating of the slab edge part was performed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method and equipment for manufacturing a hot-rolled steel sheet, and more particularly, a direct-rolling method in which a continuous cast slab obtained by cutting a continuously cast slab is hot-rolled immediately after cutting from the slab to form a hot-rolled steel sheet. The present invention relates to a heating method and heating equipment after cutting a continuous cast slab used for (HDR).

  Direct feed rolling is an energy-saving method for producing hot-rolled steel sheets that uses the heat of continuous cast slabs and eliminates the step of heating the slabs in a reheating furnace in order to perform hot rolling.

  In the conventional direct rolling, the slab edge portion (end portion in the slab width direction) where the temperature is lowered by continuous casting has been compensated for temperature by a reheating facility. For example, Patent Document 1 describes providing a heating device that heats the slab edge portion after reaching the cutter outlet after continuous casting. Patent Document 2 describes that an apparatus for heating a slab edge portion with a burner is installed in the vicinity of a slab heating furnace for hot rolling.

  Further, Non-Patent Document 1 discloses a method of heating a slab edge portion by induction heating. Further, in Patent Document 3, a continuously cast slab is put into a soaking furnace with a long length, the temperature is soaked, and a slab obtained by cutting the slab into a predetermined length is induction-heated before the start of rolling. Facilities are listed.

JP 60-018201 A Japanese Patent Laid-Open No. 55-041902 Japanese Unexamined Patent Publication No. 06-198302

Steelmaking Research No.313, Nippon Steel Corporation 1984, page 6

  By the way, in the method using the combustion gas, which is a commonly used heating method, the time required to heat the slab edge portion is about 10 minutes. On the other hand, since the speed of continuous casting is several meters per minute, it takes several minutes to finish casting a single slab. Therefore, as described in Patent Document 1, a heating device is installed at a plurality of locations along the continuous casting equipment. It is possible to heat the slab edge near the continuous casting facility.

  However, as shown in FIG. 2 of Patent Document 1, when a heating device is installed in the vicinity of the cutter of the continuous casting equipment, it takes a long time to transport the slab to the roughing mill, and it is heated and temporarily re-dissolved in Al—N. When the temperature of the slab edge part exceeding the temperature falls again to about 1000 ° C., it is rolled. Compared with the central part in the width direction, which is rolled at about 1200 ° C., in recent years, from the viewpoint of strict quality control, The material is not good enough. In addition, the heating time for the temperature compensation of the edge portion is spent about 10 minutes to keep the temperature necessary for the re-dissolution of Al-N, and the heat radiation due to the temperature difference from the outside air is accumulated for a long time. There is a problem that the heat energy necessary for the heat generation becomes enormous if the loss of heat radiation is added.

  An apparatus for compensating the temperature of the edge portion before rolling the steel slab is also described in Patent Document 2, but heating is often performed by a burner, and the above-described method is used to heat a large heat capacity such as a slab. It takes about 10 minutes. In the process from casting to hot rolling, the heating time of about 10 minutes is long, and there is a problem that this heating becomes a rate-limiting step for stopping the flow of the material. And since the apparatus described in patent document 3 heats a long slab with a soaking furnace, it requires a lot of space for installation of continuous casting equipment, and this also requires enormous heat energy for heating. There is a problem.

  While heating with a burner requires a long time and heat dissipation loss is large, according to the example of the method by induction heating in Non-Patent Document 1, heating at a conveyance speed of 4 m / min is possible, for example, a length of 10 m. If the slab has, the heating at 116 ° C. is completed in 2.5 minutes, so that the heat dissipation loss can be remarkably reduced and the production rate-limiting step can be prevented.

  However, due to improved performance of the induction heating device and strict quality control in recent years, it has become necessary to compensate the temperature of the slab edge portion to about 200 ° C. While the edge portion is being heated, the temperature of the portion other than the heated edge portion, for example, the central portion in the width direction, continues to drop due to cooling. For this reason, there existed a problem that rolling start temperature fell below predetermined temperature and the slab which cannot perform direct feed rolling generate | occur | produces with a certain probability.

  Therefore, an object of the present invention is to solve the problem that the cross-sectional average temperature of the slab is lowered when the temperature compensation of the slab is performed by induction heating before the hot rolling is performed on the continuously cast slab.

  The heating method after cutting a continuous cast slab according to the present invention that advantageously solves the above-mentioned problem is a hot-rolled steel obtained by hot rolling a continuous cast slab obtained by cutting a continuously cast slab immediately after cutting from the slab. In the production of the strip, when performing the slab temperature compensation by induction heating before performing the hot rolling rough rolling, the induction heating of the entire slab cross section should be performed immediately after the induction heating of the slab edge part. It is a feature.

  Moreover, the heating equipment after cutting the continuous cast slab of the present invention for carrying out the above heating method is to hot-roll the continuous cast slab obtained by cutting the continuously cast slab immediately after cutting from the slab. In the production of hot-rolled steel strip, in the heating equipment that performs temperature compensation of the slab by induction heating before performing the hot rolling, the induction heating device of the slab edge part and the induction heating device of the entire slab cross section are provided. The slabs are arranged adjacent to each other in this order in the slab feed direction.

  In the present invention, the arrangement length of the induction heating device in the slab edge portion is preferably 0.8 times or more of the slab length, and the arrangement length of the induction heating device in the entire slab cross section is not less than the slab length. It is preferable that it is 3 times or less of the slab length.

  Furthermore, it is preferable that each induction heating apparatus completes the heating within 5 minutes.

  According to the heating method of the present invention and the heating equipment of the present invention for carrying out the method, the slab edge portion that requires sufficient heating is first heated, and then the entire slab, which requires only slight heating, is then heated. Therefore, it is possible to heat a part other than the edge part where the temperature falls while heating the slab edge part, and immediately perform hot rolling in the next process, and furthermore, heat compensation can be performed with less heat energy. .

  In addition, it can prevent that a slab melt | dissolves by rapid heating by arrange | positioning the apparatus which induction-heats the slab edge part heated previously to 0.8 or more times the slab length.

  Also, by arranging the induction heating device that heats the entire slab cross section in the section of the slab length or more, when the tail end of the slab finishes heating the edge part, the entire cross section heating of the slab tip is completed, The cumulative heating time of the entire cross section becomes shorter from the slab tip to the tail end, and the slab disappears this temperature gradient when the tip is coldest and the tail end is coldest with casting. However, the cumulative heating time that decreases toward the tail end is preferred.

  In the case where the temperature at the tail end is insufficient, the induction heating device for the entire slab cross-section may be arranged longer, but the length for arranging the induction heating device is not more than three times the length of the slab. If it does so, the installation space of an induction heating apparatus can be suppressed. And the electric power which compensates the heat | fever lost by standing_to_cool can be made small by making time to heat within 5 minutes.

(A), (b) is a side view which shows typically the structure of the direct feed rolling line of the continuous casting slab provided with the heating equipment of one Example of this invention used for implementation of the heating method of one Example of this invention. FIG. It is explanatory drawing which shows the continuous casting state of the slab in the direct feed rolling line of the said continuous casting slab. It is explanatory drawing which shows the heating equipment of the said Example in the direct feed rolling line of the said continuous casting slab. It is a relationship diagram which shows the difference in the cool-down time of each part along the longitudinal direction from the tail end of the slab shown in FIG. 2 to a front-end | tip. It is a relationship diagram which shows the difference in the cross-section whole heating time of each part along the longitudinal direction from the tail end of the continuous casting slab by the heating equipment shown in FIG. 3 to a front-end | tip.

  In one embodiment of the heating method of the present invention, a hot-rolled steel strip is produced by hot rolling a continuous cast slab obtained by cutting a continuously cast slab immediately after cutting from the slab. When performing slab temperature compensation by induction heating before performing the rough rolling, induction heating of the entire slab cross section is performed immediately after induction heating of the slab edge portion. In an embodiment of the heating equipment of the present invention for carrying out this heating method, an apparatus for performing induction heating of the slab edge portion and an apparatus for performing induction heating of the entire slab are arranged in the slab feed direction. They are placed next to each other in order. The reason for this arrangement is that the slab edge portion requires a long induction heating, while the entire slab including the edge portion requires a shorter induction heating time. In this order, the continuous casting slab is heated. By carrying out, hot rolling can be started immediately when induction heating of the entire slab is completed.

  If this order is reversed, since the part other than the edge part of the slab is allowed to cool until the heating of the edge part is completed after the entire heating is finished, the temperature raised by heating the whole is increased. , Will fall again. That is, in the case of the reverse arrangement, it is necessary to increase the temperature at which the temperature is increased by heating, including the decrease in temperature, which is inefficient.

  Moreover, in one Embodiment of the heating equipment of this invention, the length of the area which arrange | positions the induction heating apparatus of an edge part shall be 0.8 times or more of the length of a slab. By doing in this way, the temperature fall of the edge accompanying casting can be eliminated, preventing melting of a slab. On the other hand, when the section of the induction heating apparatus is short, heating is performed while conveying the slab in order to heat the edge part of the entire length of the slab, and the slab may be melted by rapid heating.

  In one embodiment of the heating equipment of the present invention, an induction heating device for heating the entire slab is disposed adjacent to the induction heating device at the edge portion. In this induction heating device, the entire heating of the slab tip is first performed. And the tail end is heated at the end. When the entire heating device is arranged in the section of the same length as the slab, the tail end enters the induction heating device when the tip finishes heating, but the cross-sectional average temperature of the tail end where casting is late is sufficient In the case where the slab is too high, induction heating of the entire cross section of the tail end may not be performed, and the slab may be carried out from the induction heating device at high speed and hot rolling in the next process may be performed.

  On the other hand, when the cross-sectional average temperature of the tail end after casting is insufficient for the next hot rolling, the entire induction heating device section is extended to about twice the length of the slab. If so, the tail end can be heated as much as the tip. However, if it exceeds 3 times the slab length, the installation space becomes long, so 3 times or less is preferable.

  Further, it is desirable that the heating time be within 5 minutes. The reason is that the induction heating device itself does not reach a high temperature as in a furnace, so heat continues to escape from the surface of the slab due to radiation. Because it is uneconomical.

  Hereinafter, the present invention will be described more specifically with reference to the drawings. 1 (a) and 1 (b) are side views schematically showing a configuration of a direct feed rolling line of a continuous cast slab including a heating facility of an example of the present invention that further embodies the heating facility of the above embodiment; In the figure, reference numeral 1 denotes a continuous casting machine, 2 denotes a cutting machine, 3 denotes a continuously cast slab, and S denotes a continuous casting slab obtained by cutting the slab 3.

  That is, in this direct feed rolling line, the high-temperature slab 3 is continuously manufactured by the continuous casting machine 1, and when the slab 3 is manufactured for a predetermined length of the slab, the slab 3 is converted to the predetermined length by the cutting machine 2. The continuous casting slab S is formed by being cut into pieces, and the continuous casting slab S is sent to the hot rolling process immediately after being cut by the cutting machine 2.

  In the hot rolling process, the continuous cast slab S is composed of a rough rolling mill group 7 and a finishing rolling mill group 8, and a sizing press (not shown) that adjusts the width of the slab, and the edge temperature of the rough bar for several minutes by rough rolling. The steel sheet is cooled by the run-out cooling equipment 9 after it is appropriately hot-rolled by an edge heater (not shown) that heats the temperature reduction to reduce the thickness to a thickness of several millimeters to form a hot-rolled steel strip. It is wound up by a coiler (not shown) and becomes a hot rolled coil as a cold rolled material for a product or the next process.

  The direct feed rolling line further includes an induction heating device 4 for heating the slab edge portion and an induction heating device 5 for heating the entire slab cross section, which constitute the heating equipment of the above embodiment, as shown in FIG. Are arranged adjacent to each other in this order in the feed direction of the continuous cast slab S directed from the side to the right, and the induction heating device 4 for heating the slab edge portion is at least 0.8 times the slab length. The edge part of the continuous casting slab S is induction-heated over the section. The induction heating device 4 includes an induction heating device that applies a magnetic flux in a direction perpendicular to the side surface of the continuously cast slab S, or a C-type core type induction heating device that normally heats the edge of a coarse bar. Etc. can be used.

  By the way, as shown in FIG. 2, the continuous casting machine 1 continuously casts the slab 3 at a speed of several meters per minute. Therefore, the edge portion of the continuous casting slab S obtained by cutting the slab 3 with the cutting machine 2. In this case, a temperature drop occurs due to cooling for several tens of minutes in the continuous casting machine 1, and the temperature of the edge part is too low as it is, and cracking or material deterioration of the edge part occurs due to rolling. End up. For this reason, it is necessary to compensate for the temperature of the edge portion. However, in order to compensate for the temperature drop due to long-time cooling, it is necessary to increase the temperature of the edge portion by about 200 ° C.

  Table 1 below shows the results of a heating test in which the temperature of the edge portion is increased by about 200 ° C. with various heating section lengths for a continuous cast slab S having a length of 10 m. Heating section lengths of 5 m and 7 m are comparative examples, and heating section lengths of 8 m and 10 m are examples.

  As apparent from Table 1, in the case of the comparative example in which the edge portion was subjected to induction heating with a short section length of 5 m and 7 m, a melted portion was generated in the continuous cast slab S. However, in the example in which the edge portion was subjected to induction heating with a long section length of 8 m and 10 m which is 0.8 times or more the slab length, the continuous cast slab S did not melt.

  This is because, in induction heating in which the surface is heated, if an attempt is made to perform rapid heating at 200 ° C. in a short section, the plate thickness average temperature near the edge is about 1000 ° C., whereas the temperature near the surface is 1600 ° C. Because it will exceed. On the other hand, if this heating is performed in a section of 0.8 times or more of the slab length, the continuous casting slab S is not melted in order to prevent the vicinity of the surface from becoming hot.

  Following the heating of the edge portion in the induction heating device 4 for heating the slab edge portion, the continuous casting slab S is heated in its entire cross section by the induction heating device 5. As the induction heating device 5 for heating the entire slab cross section, for example, a solenoid type induction heating device can be used. When heated by the solenoid type induction heating device 5, the surface of the continuous cast slab S is heated and the cross section is increased. The overall average temperature rises.

  Since the induction heating device 5 is a solenoid type cylinder, it is necessary to divide and install the induction heating device 5 in order to provide the transport roll 6 that supports the continuous casting slab S as shown in FIG. At this time, the slab edge portion is also heated by the induction heating device 5, but since the required temperature rise of the entire cross section is small compared to the edge portion, it can be heated to such an extent that no melting occurs in all cross sections, In the induction heating with the induction heating device 5 for heating the entire slab cross section, the edge portion is not heated to such a temperature that it melts.

  The induction heating of the entire cross section of the slab in the induction heating device 5 is performed in order to compensate for the temperature drop of the cross section average temperature of the slab 3 and the continuous casting slab S accompanying the continuous casting in the continuous casting machine 1. This is because the continuous casting speed of the slab 3 is about 2 m / min. In the 10 m continuous casting slab S, as shown in FIG. 4, after the slab tip completes casting, the slab tail end casts. By the time it is finished, the tip of the slab is caused to cool for a long time of about 5 minutes from the tail end, resulting in a temperature drop. The cooling time at this time linearly increases from the tail end toward the tip end as shown in FIG.

  Thus, in order to compensate for the average cross-sectional temperature that becomes lower toward the tip, the heating equipment of this embodiment is provided with the induction heating device 5 for the entire cross section immediately after the induction heating device 4 at the edge portion. Thus, at the end of the continuous casting slab S, the entire heating starts when the edge portion is heated, and when the tail end finishes heating the edge portion, the entire cross section heating time from the tip to the tail end, That is, the cumulative heating time by the induction heating device 5 is ideally reduced from the tip to the tail as shown in FIG.

  Therefore, ideally, it is not necessary to compensate the temperature of the entire cross section of the tail end, and therefore, the heating section of the induction heating device 5 for the entire cross section only needs to be the slab length, and when the heating of the tip ends in the heating section of the slab length, the slab The feed rate may be switched from the heating feed rate (5 to 10 m / min) to the rolling feed rate (60 to 120 m / min) and the continuous cast slab S may be conveyed to the rough rolling mill group 7 at a high speed. Since the heating in the heating device 5 is intermittent in the slab conveying direction, it corresponds to the necessity of leveling the temperature and an unexpected tail end temperature drop due to cooling during continuous casting in the continuous casting machine 1. Therefore, it is desirable that the heating section of the induction heating device 5 of the entire cross section is long to at least about twice the slab length. However, if it exceeds 3 times the slab length, the installation space becomes long, and therefore 3 times or less is preferable.

  In this embodiment, in order to finish heating in a shorter time than the gas combustion furnace, the induction heating devices 4 and 5 are used for temperature compensation, and the induction heating devices 4 and 5 themselves are at a high temperature like a gas combustion furnace. Therefore, heat is lost from the continuous casting slab S by cooling at all times. On the other hand, in this example, the energy intensity could be reduced by setting the heating time of each of the induction heating devices 4 and 5 within 5 minutes.

  Although the present invention has been described based on the illustrated example, the present invention is not limited to this example, and can be appropriately changed within the scope of the claims, for example, induction heating of the entire cross section The device 5 may also be a type other than the solenoid type cylindrical one, for example, a C-type core type induction heating device.

  Thus, according to the heating method of the present invention and the heating equipment of the present invention for its implementation, the slab edge portion that requires sufficient heating is first heated, and then the entire slab, which requires only slight heating, is then heated. Therefore, it is possible to heat the part other than the edge part where the temperature falls while heating the slab edge part, and immediately perform hot rolling of the next process, and to perform the thermal compensation with less heat energy. it can.

DESCRIPTION OF SYMBOLS 1 Continuous casting machine 2 Cutting machine 3 Slab 4 Induction heating apparatus of edge part 5 Induction heating apparatus of the whole cross section 6 Conveyance roll 7 Coarse rolling mill group 8 Finish rolling mill group 9 Runout cooling equipment S Continuous casting slab

Claims (5)

In producing a hot-rolled steel strip by hot rolling a continuous cast slab obtained by cutting a continuously cast slab immediately after cutting from the slab,
Continuous casting characterized by performing induction heating of the entire slab cross section immediately after performing induction heating of the slab edge portion when performing temperature compensation of the slab by induction heating before performing hot rolling rough rolling. Heating method after slab cutting. When producing a hot-rolled steel strip by immediately rolling a continuously cast slab obtained by cutting a continuously cast slab after cutting from the slab, the temperature compensation of the slab is performed before the hot rolling rough rolling is performed. In a heating facility that performs induction heating,
A heating facility after cutting a continuous cast slab, characterized in that an induction heating device for a slab edge portion and an induction heating device for the entire slab section are arranged adjacent to each other in this order in the slab feed direction.   The heating equipment after cutting a continuous cast slab according to claim 2, wherein the arrangement length of the induction heating device of the slab edge portion is 0.8 times or more of the slab length.   The heating equipment after cutting a continuous cast slab according to claim 2 or 3, wherein the arrangement length of the induction heating device for the entire cross section of the slab is not less than three times the slab length.   At least one of the induction heating device of the slab edge portion and the induction heating device of the entire slab cross section completes the heating of the continuous cast slab within 5 minutes. Heating equipment after cutting the continuous cast slab according to any one of the above.

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