JP2005177781A - Hot rolling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a method which is advantageously suitable to the manufacture of a product especially a grain oriented electrical steel sheet to which high-temperature heating of a slab is indispensable by uniformly performing the heating of the slab in the width direction of the slab in hot rolling method by which rolling is performed with a hot-rolling equipment train in which vertical electric heating furnaces are incorporated. <P>SOLUTION: In the hot rolling method by which rolling is performed by passing a material to be rolled through the hot-rolling equipment train in which a gas heating furnace, roughing mill and a continuous finishing mill are successively connected through roller tables and at least one vertical electric heating furnace is arranged on one side of the roller table and at least two furnaces are arranged on both sides, the material to be rolled is inserted into the vertical electric heating furnace arranged on either side of the roller table before starting the rolling with the continuous finishing mill after extracting the material to be rolled from the gas heating furnace and, next, before starting the rolling with the continuous finishing mill and, next, when inserting the material to be rolled into the vertical electric heating furnace arranged on the either other side of the roller table, the material to be rolled is inserted under arrangement by which an end part in the width direction of the material to be rolled on a side near to the vertical electric heating furnace is on the side of the furnace bed in the inside of the vertical electric heating furnace and, after that, the continuous finish rolling is performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is suitable for hot rolling of slabs for directional electrical steel sheets that are used for continuous rolling of continuous cast slabs, particularly directional slabs for high-temperature heating in continuous manufacturing slabs in the manufacturing process of steel sheets. The present invention relates to a hot rolling method that makes it possible to obtain a grain-oriented electrical steel sheet that is excellent in productivity and magnetic properties while improving the uniformity.

A grain-oriented electrical steel sheet used as a core material for transformers and generators is required to have high magnetic flux density and low iron loss as the most important characteristics.
To date, various measures have been taken to achieve low iron loss in grain-oriented electrical steel sheets. Among them, the crystal orientation of the steel sheet after final finish annealing is referred to as the Goss orientation {110} <001> Accumulating highly in the direction is one of the development goals that has been most emphasized. This is because the crystal orientation <001>, which is the easy axis direction of the iron crystal, is highly accumulated in the rolling direction, so that the magnetization force required for magnetization in the rolling direction is reduced and the coercive force is reduced, resulting in hysteresis. This is because the loss is reduced and the iron loss is reduced.

Another important required characteristic of grain-oriented electrical steel sheets is that noise when magnetized is small. This problem is also greatly improved by aligning the crystal orientation to the Goth orientation.
In other words, the magnetostrictive vibration and electromagnetic vibration of the iron core material are known as the cause of the noise generated from the transformer, but the 90 degree magnetic domain causing the magnetostrictive vibration is improved by improving the degree of integration of the crystal orientation in the Goss orientation. At the same time, the excitation current is reduced and electromagnetic vibration is suppressed, resulting in noise reduction.

As described above, it can be said that the accumulation of the crystal orientation <001> in the rolling direction is the most important issue for grain-oriented electrical steel sheets.
Here, in many cases, the value of B ₈ (magnetic flux density at a magnetizing force of 800 A / m) is used as an index of the degree of integration of crystal orientation, and the development of grain-oriented electrical steel sheets is promoted with a major goal of improving B _8. ing. As a typical value of the iron loss, W _17/50, which is an energy loss when the excitation magnetic flux density is 1.7 T and the excitation frequency is 50 Hz, is used.

The secondary recrystallized grain structure of the above-mentioned grain-oriented electrical steel sheet is formed through a phenomenon called secondary recrystallization during the final finish annealing, and this secondary recrystallization preferentially grows goss-oriented crystal grains. To obtain a product with the desired magnetic properties.
In order to effectively promote the accumulation of the secondary recrystallized grains, it is important to form a precipitated dispersed phase called an inhibitor that selectively suppresses the growth of primary recrystallized grains with a uniform and appropriate size. is there. The presence of this inhibitor suppresses the normal grain growth of primary recrystallized grains, maintains the state of fine primary recrystallized grains up to high temperatures during final finish annealing, and increases the selectivity for the growth of grains with good orientation. Therefore, a high magnetic flux density is realized. In general, it is considered that a higher degree of orientation accumulation can be obtained as the inhibitor is stronger and the inhibition of normal grain growth is stronger.

As such an inhibitor, MnS, MnSe, Cu _2-x S, Cu _2-x Se, AlN, BN or the like is used. In order to dissolve such an inhibitor, heating at a high temperature of, for example, 1300 ° C. or more is required. Here, in recent years, vertical electric slab heating has been introduced to slab heating, and heating at a high temperature in a short time is possible. However, the vertical electric slab heating furnace has a disadvantage that heating in the width direction cannot be performed uniformly. This is due to the essential structure of the vertical electric slab heating furnace in which the slab is heated with the side face on one side down and the side face on the other side up. That is, the amount of heat removed from the lower side of the slab to the hearth is different from the amount of heat removed from the side of the upper surface toward the ceiling, and the atmosphere temperature is higher in the upper part of the furnace. Is a problem.

  The problem is that the temperature is lowered at the edge of the slab due to heat removal from the side surface of the slab. It is known that this temperature drop at the slab edge portion appears as deterioration of the magnetic properties of the product edge portion particularly in the electromagnetic steel sheet. In addition, because the temperature difference in the slab width direction becomes asymmetric due to asymmetric heating on the top and bottom of the slab, the shape after rolling becomes bowed due to the difference in hot strength due to temperature, and in severe cases, rolling becomes impossible, etc. Was the cause of operational troubles.

  In order to correct this uneven heating in the width direction of the slab, Patent Document 1 proposes a method of heating the edge portion before inserting into the vertical electric slab heating furnace. This method requires special heating devices such as edge heaters, and since these heating devices are installed on a roller table, other rolling cannot be performed during edge heating, which is economically disadvantageous. is there.

Moreover, in the method described in Patent Document 2, in a vertical induction heating furnace, a heating element by induction heating is disposed in the vicinity of the upper layer surface of the refractory heat insulating material between the support beams supporting the steel material. A method for preventing heat dissipation from the lower surface of the steel material due to heat generation is disclosed. Similarly, Patent Document 3 discloses a method in which a heat-resistant hearth metal of the hearth is once preheated, and then a slab is placed thereon and heated.
With these methods, the side surface temperature on the lower surface side of the slab can be raised, but it is difficult to improve the asymmetry of the upper and lower sides.

  Further, in Patent Document 4, the temperature in the slab width direction is measured before and after insertion of the induction heating furnace, and the temperature is measured by a control computer having a feed forward and feedback function for correcting the setting power and time setting power. A method for controlling the temperature of an induction heating furnace is disclosed. However, even with this method, it is difficult to eliminate the temperature difference in the width direction of the slab, and it is effective for local temperature drops such as the temperature drop part of the slab upper surface support device that prevents the slab from toppling during heating. It was poor.

  Patent Document 5 discloses a method of preventing heat removal from the support device as much as possible by installing a plurality of the upper support devices and supporting the slab by alternately raising and lowering the slab support devices. Thus, although heat removal by the slab support device can be suppressed to some extent, there is a possibility that new steel piece scratches may be generated on the slab side surface by alternately supporting the slab side surface at a high temperature.

As described above, the vertical electric heating furnace has the disadvantage of asymmetric heating in the slab width direction due to its structure, and various measures described above have been taken to eliminate this drawback. It was difficult to completely eliminate the drawbacks.
Japanese Patent Laid-Open No. 5-117753 JP-A-3-110380 JP-A-6-136434 JP 62-16526 A JP 2000-273534 A

  The present invention relates to a hot rolling method in which rolling is performed in a hot rolling equipment row incorporating a vertical electric heating furnace, and by performing the slab heating uniformly in the width direction of the slab, the high temperature of the product, particularly the slab The purpose is to propose a method that is advantageously adapted to the production of grain-oriented electrical steel sheets in which heating is essential.

In order to achieve the above object, the present invention is summarized as follows.
(1) A gas-type heating furnace, a rough rolling mill and a continuous finishing rolling mill are sequentially connected via a roller table, and at least two vertical electric heating furnaces are provided on one side of the roller table. In the hot rolling method that performs rolling through the material to be rolled to the arranged hot rolling equipment row,
After extracting the material to be rolled from the gas heating furnace, prior to starting rolling in a continuous finishing rolling mill, the material to be rolled is placed in a vertical electric heating furnace arranged on either side of the roller table. Then, when the material to be rolled taken out from the vertical electric heating furnace is inserted into the vertical electric heating furnace disposed on the other side of the roller table, the vertical electric heating furnace is inserted into the vertical electric heating furnace. It is characterized by inserting the material to be rolled under the arrangement in which the width direction end of the material to be rolled is the hearth side in the vertical electric heating furnace, and then performing continuous finish rolling. Hot rolling method to do.

(2) A gas heating furnace, a rough rolling mill and a continuous finishing rolling mill are sequentially connected via a roller table, and at least two vertical electric heating furnaces are provided on one side of the roller table. In the hot rolling method that performs rolling through the material to be rolled to the arranged hot rolling equipment row,
After extracting the material to be rolled from the gas heating furnace, prior to starting rolling in the continuous finish rolling mill, the material to be rolled is placed in a vertical electric heating furnace arranged on either side of the roller table. Then, when the material to be rolled taken out from the vertical electric heating furnace is inserted into the vertical electric heating furnace disposed on the other side of the roller table, the vertical electric heating furnace is inserted into the vertical electric heating furnace. Under the arrangement in which the end in the width direction of the material to be rolled is the ceiling side in the vertical electric heating furnace, the material to be rolled is inserted, and then continuous finish rolling is performed. Hot rolling method.

(3) Hot rolling equipment in which a gas heating furnace, a rough rolling mill and a continuous finishing rolling mill are sequentially connected via a roller table, and at least one vertical electric heating furnace is disposed in the vicinity of the roller table. In the hot rolling method in which rolling is performed through the material to be rolled in a row,
After extracting the material to be rolled from the gas heating furnace, before starting rolling in the continuous finish rolling mill, the material to be rolled is inserted into the vertical electric heating furnace, and then from the vertical electric heating furnace. The rolled material taken out is rotated to reverse the width direction of the rolled material by 180 degrees, and then the rolled material is inserted again into the vertical electric heating furnace, and then continuous finish rolling is performed. Hot rolling method.

  According to the hot rolling method of the present invention, the material to be rolled can be heated uniformly in the width direction using a vertical electric heating furnace. Therefore, if this hot rolling method is applied particularly to the production of grain-oriented electrical steel sheets, high-temperature heating of the slab can be realized evenly in the width direction, resulting in stable production of products having uniform magnetic properties in the width direction. In addition, productivity can be improved.

Below, the hot rolling method of this invention is demonstrated in detail with reference to drawings.
FIG. 1 is a diagram showing a typical example of a continuous hot rolling equipment line used in the hot rolling method of the present invention. In the figure, reference numeral 1 denotes a gas heating furnace, and 2, 3, and 4 denote rough rolling mills. , And 5 are continuous finish rolling mills which are connected to each other via a roller table denoted by reference numeral 6 to constitute an equipment row. In addition, a rough rolling mill and a continuous finishing rolling mill can be increased / decreased as needed.

  Reference numeral 7 denotes an edge heating device, which is provided between the rough rolling mill 4 and the continuous finishing mill 5, and performs heat retention or heating of the rough-rolled sheet bar, while reference numeral 8 indicates continuous. This is a semi-finished product processing apparatus that is provided in front of a finishing mill and cuts crops and the like, and each is installed as needed. Furthermore, a vertical rough rolling mill for width reduction may be installed on each entry side of the rough rolling mills 2, 3 and 4 as necessary.

In this hot rolling equipment row, there are at least two longitudinal rollers on both sides of the rough rolling mills 2, 3 and 4 and the gas heating furnace 1 (including the upstream side) and at least one on one side of the roller table 6. It is important to arrange a type electric heating furnace.
That is, in the example of FIG. 1, a vertical electric heating furnace 9 is disposed on one side of the roller table 6 on the entry side of the rough rolling mill 2 and between the rough rolling mills 2 and 3 and the roller table. The vertical electric heating furnace 9 is arranged on the opposite side of the vertical electric heating furnace 9, and the vertical electric heating furnaces 9 and 10 are installed so as to sandwich the roller table 6.

  In the hot rolling equipment row having the above-described configuration, first, the slab as the material to be rolled is heated to 1000 to 1250 ° C. in the gas heating furnace 1, then moves on the roller table 6, and the vertical electric heating furnace 9 is inserted. Here, the slab width direction end (side surface) close to the vertical electric heating furnace 9 is rotated by 90 degrees, for example, through the slab insertion device described later, and then inserted into the vertical furnace. . The inserted slab is heated to a desired temperature of 1300 ° C. or higher in the vertical electric heating furnace 9 and then returned to the roller table 6 in the reverse order of insertion.

Next, the slab on the roller table 6 is moved to the front of the vertical electric heating furnace 10 and inserted into the vertical furnace so that the side surface of the slab close to the vertical electric heating furnace 10 faces down. Heat to a desired temperature of 1300 ° C or higher. Here, for example, about 3 to 20% of preliminary rolling may be performed using the rough rolling mill 2.
As described above, by heating the slab in the vertical electric heating furnaces 9 and 10 arranged on each side sandwiching the roller table 6, the same side surface of the slab becomes the hearth side and the ceiling side of the vertical electric heating furnace. As a result of the sequential heating under the arrangement, the slab is heated uniformly in the width direction.

  Here, the slab may be inserted into a vertical electric heating furnace after being pre-rolled by about 3 to 20% using a roughing mill after being heated in the gas heating furnace 1, as described above. After slab heating in the vertical electric heating furnace 9, 3-20% pre-rolling may be performed prior to insertion into the vertical electric heating furnace 10. The purpose of this pre-rolling is to prevent the grain size from becoming larger than necessary in the slab by crimping internal defects peculiar to continuous cast slabs or introducing dislocations into the slab.

  The slab after the second electric heating is finished is extracted in the reverse procedure of insertion, transferred to the roller table 6, transported on the roller table 6, and then rolled by a roughing mill. Thereafter, rough rolling of 2 to 5 passes is performed in accordance with a regular method to form a sheet bar of 20 to 60 mm, and then rolled with a continuous finishing rolling mill 5 and finally wound on a coil for a grain-oriented electrical steel sheet. It becomes a hot-rolled sheet. And if this hot-rolled steel sheet is processed in accordance with a normal grain-oriented electrical steel sheet manufacturing process such as cold rolling and annealing, a final product having a uniform surface texture and magnetic properties in the width direction can be stably obtained.

  The vertical electric heating furnaces 9 and 10 installed with the roller table 6 interposed therebetween are not limited to the arrangement shown in FIG. 1, but may be the arrangement shown in FIG. 2 or FIG. In short, it is only necessary to install a vertical electric heating furnace on one side and the other side across the roller table 6, and it is also possible to install a plurality of vertical electric heating furnaces on one or both sides. It is.

Here, in order to insert the slab into the vertical electric heating furnace as described above, a slab insertion device for inserting the slab is provided on the roller table 6 side for each of the vertical electric heating furnaces. It is preferable to do. An example of this slab insertion device is shown in FIG.
That is, the slab insertion device 11 provided on the roller table 6 side of each vertical electric heating furnace includes a support arm 13 that rotates with the base shaft 12 as a fulcrum and a gantry 14 that also serves as a hearth that rises in the vertical direction.

  In order to insert the slab 15 on the roller table 6, when the roller table 6 is transported to the front of the vertical electric heating furnace, the support arm 13 waiting at a position lower than the upper surface of the table 6 is moved upward. The slab 15 on the roller table 6 is scooped up by rotating it to 90 °, and further rotated to a 90 ° position to transfer the slab 15 from the support arm 13 onto the gantry 14, and the gantry 14 can be raised in the slab loading state. That's fine.

  If the above slab insertion device is used, the slab width direction end (side surface) on the side close to the vertical electric heating furnace is placed below the arrangement in which the slab width side becomes the hearth side in the vertical electric heating furnace, or If the end portion (side surface) in the slab width direction is placed on the ceiling side in the vertical electric slab heating furnace, the above-described uniform heating in the slab width direction is realized.

Furthermore, another hot rolling method according to the present invention will be described with reference to FIGS.
In the figure, the same equipment configurations as those shown in FIGS.
That is, in the hot rolling equipment row shown in FIG. 5, the vertical electric heating furnace 9 is arranged on the upstream side of the roughing mill 2, and the slab is placed in the roller table 6 on the upstream side of the vertical electric heating furnace 9. A turning device 20 is installed.

  In this hot rolling equipment row, the slab is first heated to 1000 to 1250 ° C. in the gas heating furnace 1, then moved on the roller table 6 and inserted into the vertical electric heating furnace 9. Here, the slab width direction end portion (side surface) close to the vertical electric heating furnace 9 is erected, for example, downward via the slab insertion device, and then inserted into the vertical furnace. The inserted slab is heated to a desired temperature of 1300 ° C. or higher in the vertical electric heating furnace 9 and then returned to the roller table 6 in the reverse order of insertion.

Next, the slab on the roller table 6 is moved to the front of the slab turning device 20, and the slab is turned so that the width direction of the slab is reversed by 180 degrees, and then the slab is moved to the front of the vertical electric heating furnace 9. Then, it is inserted into the vertical furnace so that the side surface of the slab close to the vertical electric heating furnace 9 faces down, and heated again to a desired temperature of 1300 ° C. or higher. Here, you may perform pre-rolling of about 3 to 20%, for example, using the rough rolling mill 2.
As described above, by heating the slab twice using the vertical electric heating furnace 9 and the slab turning device 20 arranged on one side of the roller table 6, the same side surface of the slab becomes the hearth side of the vertical electric heating furnace. As a result of the sequential heating under the arrangement on the ceiling side, the slab is uniformly heated in the width direction.

  Here, the slab may be inserted into the vertical electric heating furnace after being pre-rolled by about 3 to 20% using a roughing mill after being heated in the gas heating furnace 1, as described above. Then, after slab heating in the vertical electric heating furnace 9, it may be pre-rolled 3 to 20% before being rotated 180 degrees and inserted into the vertical electric heating furnace 9 again. The purpose of this pre-rolling is to prevent the grain size from becoming larger than necessary in the slab by crimping internal defects peculiar to continuous cast slabs or introducing dislocations into the slab.

  The slab after the completion of the second electric heating is extracted in the reverse order of insertion, transferred by the roller table 6, transported on the roller table 6, and then rolled by a roughing mill. Thereafter, rough rolling of 2 to 5 passes is carried out in accordance with a regular method to form a sheet bar of 20 to 60 mm, and then rolled with a continuous finish rolling mill 5 and finally wound on a coil for a grain-oriented electrical steel sheet. Use hot-rolled sheet. And if this hot-rolled steel sheet is processed in accordance with a normal grain-oriented electrical steel sheet manufacturing process such as cold rolling and annealing, a final product having a uniform surface texture and magnetic properties in the width direction can be stably obtained.

The vertical electric heating furnace 9 and the slab turning device 20 installed around the roller table 6 are not limited to the arrangement shown in FIG. 5 but may be the arrangement shown in FIG. 6 or 7.
That is, in FIG. 6, the vertical electric heating furnace 9 is installed facing the roller table 6 on the upstream side of the gas heating furnace 1, and the roller table between the gas heating furnace 1 and the roughing mill 2 is installed. The slab turning device 20 is installed outside the table 6 facing 6.

In FIG. 7, the vertical electric heating furnace 9 is installed facing the roller table 6 between the gas heating furnace 1 and the roughing mill 2, and the vertical electric heating furnace 9 and the roller table 6 are A slab turning device 20 is installed between them.
In short, it is only necessary to install at least one vertical electric heating furnace 9 and one slab turning device 20 around the roller table 6, and further install a plurality of vertical electric heating furnaces on one or both sides. It is also possible to do.

Here, FIG. 8 shows an example of the slab turning device 20 that is used when the slab after being heated once in the vertical electric heating furnace 9 is turned 180 degrees and heated again.
That is, the slab turning device 20 of this example is formed by arranging a plurality of turning rolls 21 in parallel. The turning rolls 21 have different diameters at the center in the roll axial direction, and the large diameter part and the small diameter part are alternately arranged, and the alternately arranged turning rolls 21 rotate in reverse with each other. By doing so, the slab 15 on the turning roll 21 can be turned 180 degrees.

  For example, in the equipment row shown in FIG. 5, when the slab 15 returned from the vertical electric heating furnace 9 onto the roller table 6 is conveyed onto the slab turning device 20 by the roller table 6, the slab turning is performed. The slab 15 is rotated 180 degrees by rotating the rotating rolls 21 of the apparatus 20 in the opposite directions, and thereafter, the slab 15 is again conveyed to the vertical electric heating furnace 9 by the roller table 6 and the slab 15 is heated again.

  When the above slab turning device is used, both ends (side surfaces) in the slab width direction are heated in the vertical electric furnace under the arrangement on the hearth side and the arrangement on the ceiling side, respectively. Uniform heating in the slab width direction is realized.

  By mass%, C: 0.065%, Si: 3.50%, Mn: 0.065%, Al: 0.023%, N: 0.0090%, S: 0.027%, Sn: 0.00. Ten continuous cast slabs for a grain-oriented electrical steel sheet having a thickness of 230 mm containing 20%, Cu: 0.12%, and Cr: 0.01% and the balance being substantially Fe were manufactured.

  Five of these slabs were heated in a gas heating furnace 1 at 1190 ° C. for 2 hours using the hot rolling equipment array shown in FIG. 2, and then a vertical electric (induction) heating furnace 9 was used. And heated to 1380 ° C. in 20 minutes, soaked for 5 minutes and extracted outside the furnace. Next, the temperature was increased to 1420 ° C. in a vertical electric (induction) heating furnace 10 in 10 minutes, soaked for 10 minutes, extracted from the furnace, and then transported to a roughing mill to perform three-pass hot rolling. The sheet bar was 50 mm thick. In any slab, the end (side surface) in the slab width direction on the side close to the vertical electric (induction) heating furnace was set as the hearth side of the furnace. Next, a hot rolled steel sheet for directional electrical steel sheets having a thickness of 2.2 mm is obtained by performing hot finish rolling and winding with a coiler while performing edge heating for heat retention at the end of the sheet bar width direction. (Invention example).

  On the other hand, the remaining five slabs were heated at 1190 ° C. for 2 hours in a gas heating furnace using the hot rolling equipment row shown in FIG. 2 and then inserted into an electric (induction) heating furnace 9. It was heated to 1420 ° C. for 30 minutes, soaked for 15 minutes, extracted outside the furnace, and then hot-rolled for 3 passes to obtain a 50 mm thick sheet bar. Next, a hot rolled steel sheet for directional electrical steel sheets having a thickness of 2.2 mm is obtained by performing hot finish rolling and winding with a coiler while performing edge heating for heat retention at the end of the sheet bar width direction. (Comparative Example).

  FIG. 9 shows the results of investigation on the temperature distribution in the sheet bar width direction on the entry side of the hot finish rolling mill in the above two hot rolling processes. As shown in FIG. 9, in the inventive example, the temperature distribution in the width direction is symmetric, while in the comparative example, the temperature distribution is asymmetric because it is inserted only in the vertical electric furnace.

Subsequently, the hot-rolled sheet for grain-oriented electrical steel sheets obtained under these different slab heating conditions was processed into a final product by processing according to a conventional method. That is, hot-rolled sheet annealing was performed at 1130 ° C. × 60 seconds, cooled to 200 ° C. at 30 ° C./s, and cold-rolled to a thickness of 0.27 mm after pickling at a reduction rate of 88%. Thereafter, this cold-rolled sheet was subjected to decarburization annealing at 820 ° C. for 120 seconds in an atmosphere of 60 vol% hydrogen and 40 vol% nitrogen, and a dew point of 60 ° C., and an annealing separator mainly composed of MgO was applied to 1180 ° C. A final finish annealing for 15 hours was performed, and then the unreacted separating agent was removed, followed by coating and flattening annealing to obtain a product.
FIG. 10 shows the average value of the magnetic characteristics (magnetic flux density) in the width direction of the product thus obtained. As shown in FIG. 10, it can be seen that the product according to the invention example has uniform magnetic characteristics in the width direction as compared with the comparative example.

  In mass%, C: 0.075%, Si: 3.25%, Mn: 0.080%, Al: 0.023%, N: 0.0090%, Se: 0.027%, Sn: 0.00. Ten continuous cast slabs for a grain-oriented electrical steel sheet having a thickness of 240 mm including 20%, Cr: 0.12%, and Bi: 0.0010% and the balance being substantially Fe were manufactured.

  Five of these slabs were heated at 1100 ° C. for 2 hours in the gas heating furnace 1 using the hot rolling equipment array shown in FIG. . Subsequently, it was inserted into a vertical electric (induction type) heating furnace 9, heated to 1410 ° C. in 25 minutes, soaked for 5 minutes and extracted outside the furnace. Furthermore, after heating to 1405 ° C. for 12 minutes in a vertical electric (induction) heating furnace 10 and heating for 10 minutes, the material is extracted from the furnace and conveyed to a roughing mill, subjected to 4 passes of hot rolling and 40 mm thick. The sheet bar. In either case, the end (side surface) in the slab width direction on the side close to the vertical electric heating furnace was the ceiling side of the furnace. Next, hot finish rolling was performed, and the steel sheet was wound with a coiler to obtain a 2.4 mm thick hot rolled steel sheet for grain-oriented electrical steel sheet (the present invention).

  On the other hand, the remaining five slabs were heated at 1100 ° C. for 2 hours in the gas heating furnace 1 using the hot rolling equipment row shown in FIG. Inserted into a vertical electric (induction type) heating furnace 9, heated to 1420 ° C. in 30 minutes, soaked for 15 minutes, extracted outside the furnace, then subjected to 4 passes of rough rolling, and a 40 mm thick sheet bar did. Hot finish rolling was performed, and the steel sheet was wound with a coiler to obtain a hot rolled steel sheet for a grain-oriented electrical steel sheet having a thickness of 2.4 mm (comparative example).

  FIG. 11 shows the result of investigation on the temperature distribution in the sheet bar width direction on the entry side of the hot finish rolling mill in the above two hot rolling processes. As shown in FIG. 11, in the inventive example, the temperature distribution in the width direction is symmetric, whereas in the comparative example, the temperature distribution is asymmetric because it is inserted only in the vertical electric furnace.

  Subsequently, the hot-rolled sheet for grain-oriented electrical steel sheets obtained under these different slab heating conditions was processed into a final product by processing according to a conventional method. That is, hot-rolled sheet annealing was performed at 1000 ° C. for 60 seconds, cooled to 200 ° C. at 20 ° C./s, and cold-rolled to a thickness of 1.7 mm after pickling. Then, this cold-rolled sheet was cooled at 35 ° C./s to 150 ° C. after intermediate annealing at 1120 ° C. for 120 seconds in an atmosphere with a dew point of 60 ° C. with 50 vol% hydrogen and 50 vol% nitrogen. Thereafter, it was rolled to a thickness of 0.22 mm at a reduction ratio of 87%. Next, this cold-rolled sheet was subjected to intermediate annealing at 1120 ° C. for 120 seconds in an atmosphere with a dew point of 60 ° C. with 60 vol% hydrogen and 40 vol% nitrogen, and then cooled to 150 ° C. at 35 ° C./s. Thereafter, this cold-rolled sheet was subjected to decarburization annealing at 840 ° C. for 100 seconds in an atmosphere of 60% hydrogen, 40% nitrogen, and 60 ° C. dew point, and an annealing separator mainly composed of MgO was applied to 1180 ° C. × 15 h. The final finish annealing was performed, and then the unreacted separating agent was removed, followed by coating and flattening annealing to obtain a product.

The average value of the magnetic characteristics (magnetic flux density) in the width direction of the product thus obtained is shown in FIG. As shown in FIG. 12, it can be seen that the product according to the invention example has more uniform magnetic characteristics in the width direction than the comparative example.
Further, FIG. 13 shows a plate thickness profile in the width direction of the final product plate. As shown in FIG. 13, in the comparative example, the plate thickness profile is asymmetrical, and a large problem arises when a large number of sheets are laminated to form a transformer.

  In mass%, C: 0.065%, Si: 3.50%, Mn: 0.065%, Al: 0.023%, N: 0.0090%, S: 0.027%, Sn: 0.20%, Cu: 0.12% and Cr: 0.01% Ten continuous cast slabs for a grain-oriented electrical steel sheet having a thickness of 23 Omm, the balance being substantially made of Fe, were manufactured.

  Five of these slabs were heated in a gas heating furnace 1 at 1190 ° C. for 2 hours using the hot rolling equipment row shown in FIG. 6, and then placed in a vertical electric (induction) heating furnace 9. It was inserted, heated to 1380 ° C. in 20 minutes, soaked for 5 minutes and extracted outside the furnace. Next, after turning 180 degrees with the slab turning device 20, the temperature was raised to 1420 ° C in 10 minutes in a vertical electric (induction) heating furnace 9, soaked for 10 minutes, extracted from the furnace, and then transferred to the roughing mill Then, hot rolling of 3 passes was performed to obtain a sheet bar having a thickness of 50 mm. In any slab, the end portion (side surface) in the slab width direction in the example close to the vertical electric (induction) heating furnace was the hearth side of the furnace. Next, a hot rolled steel sheet for directional electrical steel sheets with a thickness of 2.2 mm is obtained by performing hot finish rolling and winding with a coiler while performing edge heating for heat retention at the end of the sheet bar width direction. Obtained (Invention Example).

  On the other hand, the remaining five slabs were heated in a gas heating furnace at 1190 ° C. for 2 hours using the hot rolling equipment row shown in FIG. 6 and then inserted into an electric (induction) heating furnace 9. It was heated to 1420 ° C. for 30 minutes, soaked for 15 minutes, extracted outside the furnace, and then hot-rolled for 3 passes to obtain a 50 mm thick sheet bar. Next, a hot rolled steel sheet for directional electrical steel sheets with a thickness of 2.2 mm is obtained by performing hot finish rolling and winding with a coiler while performing edge heating for heat retention at the end of the sheet bar width direction. Obtained (comparative example).

  FIG. 14 shows the results of investigation on the temperature distribution in the sheet bar width direction on the entry side of the hot finish rolling mill in the above two hot rolling processes. As shown in FIG. 14, in the inventive example, the temperature distribution in the width direction is symmetric, while in the comparative example, the temperature distribution is asymmetric because it is inserted only once into the vertical electric furnace.

Subsequently, the hot-rolled sheet for grain-oriented electrical steel sheets obtained under these different slab heating conditions was processed into a final product by processing according to a conventional method. That is, hot-rolled sheet annealing was performed at 1130 ° C. × 60 seconds, cooled to 200 ° C. at 30 ° C./s, and after pickling, cold rolled to a thickness of 0.27 mm at a reduction rate of 88%. After that, this cold-rolled sheet was decarburized and annealed at 820 ° C for 120 seconds in an atmosphere with 60vol% hydrogen and 40vol% nitrogen at a dew point of 60 ° C, and an annealing separator mainly composed of MgO was applied to A final finish annealing for 15 hours was performed, and then the unreacted separating agent was removed, followed by coating and flattening annealing to obtain a product.
The average value of the magnetic properties (magnetic flux density) in the width direction of the product thus obtained is shown in FIG. As shown in FIG. 15, it can be seen that the product according to the invention example has more uniform magnetic characteristics in the width direction than the comparative example.

  In mass%, C: 0.075%, Si: 3.25%, Mn: 0.080%, Al: 0.023%, N: 0.0090%, Se: 0.027%, Sn: 0.20%, Cr: 0.12% and Bi: 0.0010% Ten continuous cast slabs for a grain-oriented electrical steel sheet having a thickness of 240 mm, the balance being substantially made of Fe, were manufactured.

  Five of these slabs were heated at 1100 ° C. for 2 hours in the gas heating furnace 1 using the hot rolling equipment row shown in FIG. Subsequently, it was inserted into a vertical electric (induction type) heating furnace 9, heated to 1410 ° C. in 25 minutes, soaked for 5 minutes and extracted outside the furnace. The slab is turned 180 degrees with the slab turning device 20, and further heated to 1405 ° C for 12 minutes in a vertical electric (induction) heating furnace 9, soaked for 10 minutes, extracted from the furnace, and conveyed to the roughing mill. Four-pass hot rolling was performed to obtain a 40 mm thick sheet bar. In either case, the end (side surface) in the slab width direction on the side close to the vertical electric heating furnace was the ceiling side of the furnace. Next, hot finish rolling was performed, and the steel sheet was wound with a coiler to obtain a hot-rolled steel sheet for a grain-oriented electrical steel sheet having a thickness of 2.4 mm (invention example).

  On the other hand, the remaining five slabs were heated at 1100 ° C. for 2 hours in the gas heating furnace 1 using the hot rolling equipment row shown in FIG. Inserted into a vertical electric (induction type) heating furnace 9, heated to 1420 ° C in 30 minutes, soaked for 15 minutes, extracted outside the furnace, and then subjected to 4 passes of rough rolling to obtain a 40 mm thick sheet bar did. Subsequently, hot finish rolling was performed, and the steel sheet was wound with a coiler to obtain a hot rolled steel sheet for a grain-oriented electrical steel sheet having a thickness of 2.4 mm (comparative example).

  FIG. 16 shows the results of investigation on the temperature distribution in the sheet bar width direction on the entry side of the hot finish rolling mill in the above two hot rolling processes. As shown in FIG. 16, in the inventive example, the temperature distribution in the width direction was symmetric, while in the comparative example, the temperature distribution was asymmetric because it was inserted only once into the vertical electric furnace.

  Subsequently, the hot-rolled sheet for grain-oriented electrical steel sheets obtained under these different slab heating conditions was processed into a final product by processing according to a conventional method. That is, hot-rolled sheet annealing was performed at 1000 ° C. for 60 seconds, cooled to 200 ° C. at 20 ° C./s, and cold-rolled to a thickness of 1.7 mm after pickling. Then, this cold-rolled sheet was cooled at 85 ° C./s to 150 ° C. after intermediate annealing at 1120 ° C. for 120 seconds in an atmosphere of 50 ° C. hydrogen and 50 vol% nitrogen and a dew point of 60 ° C. Thereafter, it was rolled to a thickness of 0.22 mm at a reduction ratio of 87%. Next, this cold-rolled sheet was subjected to intermediate annealing at 1120 ° C. for 120 seconds in an atmosphere of 60 vol.% Hydrogen and 40 vol.% Nitrogen at a dew point of 60 ° C., and then cooled to 150 ° C. at 35 ° C./s. After that, this cold-rolled sheet was decarburized and annealed at 840 ° C for 100 seconds in an atmosphere of 60% hydrogen, 40% nitrogen, and 60 ° C dew point, and an annealing separator mainly composed of MgO was applied. A final finish annealing was performed for a period of time, and then the unreacted separating agent was removed, followed by coating and flattening annealing to obtain a product.

FIG. 17 shows the average value of the magnetic characteristics (magnetic flux density) in the width direction of the product thus obtained. As shown in FIG. 17, it can be seen that the product according to the invention example has a uniform magnetic property in the width direction as compared with the comparative example.
Further, FIG. 18 shows a plate thickness profile in the width direction of the final product plate. As shown in FIG. 18, in the comparative example, the thickness profile is asymmetrical, and a large problem arises when a large number of sheets are laminated to form a transformer.

32 slabs having the same components as in Example 1 were rolled in the same manner as the inventive example of Example 1, and 48 slabs of the same components were rolled in the same manner as in the comparative example of Example 1. . The relationship between the temperature difference in the width direction on the exit side of the roughing mill and the cut-off weight of the crop part after finish rolling (the part where the plate width is insufficient at the leading end of the turn after hot rolling) is shown. It is shown in 19.
As can be seen from FIG. 19, according to the present invention, as a result of the shape of the cropped portion being substantially symmetrical, the weight to be cut off is reduced and the yield is also improved.

  The hot rolling method of the present invention is applicable not only to the production of the above-mentioned grain-oriented electrical steel sheet but also to the production of a general steel sheet, and realizes uniform slab heating in the width direction. This is meaningful in the production of all steel sheets.

It is explanatory drawing which shows the continuous hot rolling equipment row | line | column used for the hot rolling method of this invention. It is explanatory drawing which shows the continuous hot rolling equipment row | line | column used for the hot rolling method of this invention. It is explanatory drawing which shows the continuous hot rolling equipment row | line | column used for the hot rolling method of this invention. It is explanatory drawing which shows an example of the slab insertion apparatus accompanying a vertical type electric heating furnace. It is explanatory drawing which shows the continuous hot rolling equipment row | line | column used for the hot rolling method of this invention. It is explanatory drawing which shows the continuous hot rolling equipment row | line | column used for the hot rolling method of this invention. It is explanatory drawing which shows the continuous hot rolling equipment row | line | column used for the hot rolling method of this invention. It is explanatory drawing which shows an example of the slab turning apparatus in a continuous hot rolling equipment row | line | column. It is a figure which shows the temperature distribution by the side of a finishing rolling mill in a slab width direction position. It is a figure which shows the magnetic flux density in the board width direction position of a product board. It is a figure which shows the temperature distribution by the side of a finishing rolling mill in a slab width direction position. It is a figure which shows the magnetic flux density in the board width direction position of a product board. It is a figure which shows the board thickness distribution in the board width direction position of a product board. It is a figure which shows the temperature distribution by the side of a finishing rolling mill in a slab width direction position. It is a figure which shows the magnetic flux density in the board width direction position of a product board. It is a figure which shows the temperature distribution by the side of a finishing rolling mill in a slab width direction position. It is a figure which shows the magnetic flux density in the board width direction position of a product board. It is a figure which shows the board thickness distribution in the board width direction position of a product board. It is a figure which shows the relationship between the temperature difference of the width direction in a rough rolling mill delivery side, and the cut-off weight of the crop part after finish rolling.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas type heating furnace 2, 3, 4 Rough rolling mill 5 Continuous finishing rolling mill 6 Roller table 7 Edge heating apparatus 8 Semi-finished product processing apparatus 9, 10 Vertical electric heating furnace 11 Slab insertion apparatus 12 Support arm rotating shaft 13 Slab Support arm 14 Slab lifting base 15 Slab 20 Slab turning device 21 Turning roll

Claims (3)

A gas heating furnace, a roughing mill and a continuous finishing rolling mill are sequentially connected via a roller table, and at least two vertical electric heating furnaces are arranged on one side of the roller table. In the hot rolling method of rolling through the material to be rolled,
After extracting the material to be rolled from the gas heating furnace, prior to starting rolling in the continuous finish rolling mill, the material to be rolled is placed in a vertical electric heating furnace arranged on either side of the roller table. Then, when the material to be rolled taken out from the vertical electric heating furnace is inserted into the vertical electric heating furnace disposed on the other side of the roller table, the vertical electric heating furnace is inserted into the vertical electric heating furnace. It is characterized by inserting the material to be rolled under the arrangement in which the width direction end of the material to be rolled is the hearth side in the vertical electric heating furnace, and then performing continuous finish rolling. Hot rolling method to do. A gas heating furnace, a roughing mill and a continuous finishing rolling mill are sequentially connected via a roller table, and at least two vertical electric heating furnaces are arranged on one side of the roller table. In the hot rolling method of rolling through the material to be rolled,
After extracting the material to be rolled from the gas heating furnace, prior to starting rolling in the continuous finish rolling mill, the material to be rolled is placed in a vertical electric heating furnace arranged on either side of the roller table. Then, when the material to be rolled taken out from the vertical electric heating furnace is inserted into the vertical electric heating furnace disposed on the other side of the roller table, the vertical electric heating furnace is inserted into the vertical electric heating furnace. Under the arrangement in which the end in the width direction of the material to be rolled is the ceiling side in the vertical electric heating furnace, the material to be rolled is inserted, and then continuous finish rolling is performed. Hot rolling method. Through a roller table, a gas heating furnace, a rough rolling mill, and a continuous finishing rolling mill are sequentially connected, and further to a hot rolling equipment row in which at least one vertical electric heating furnace is disposed in the vicinity of the roller table, In the hot rolling method of rolling through the material to be rolled,
After extracting the material to be rolled from the gas heating furnace, before starting rolling in the continuous finish rolling mill, the material to be rolled is inserted into the vertical electric heating furnace, and then from the vertical electric heating furnace. The rolled material taken out is rotated to reverse the width direction of the rolled material by 180 degrees, and then the rolled material is inserted again into the vertical electric heating furnace, and then continuous finish rolling is performed. Hot rolling method.

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