JP2004195497A - Method of heating steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of heating a steel sheet by which an arbitrary region in the width direction of a steel sheet (steel strip) is heated and the temperature distribution in the width direction of the steel sheet is controlled. <P>SOLUTION: A plurality of bar heaters arranged in the longitudinal direction of the steel sheet are shifted in the width direction of the steel sheet. The amount of the shift is determined by measuring the temperature distribution in the width direction of the steel sheet with width-direction thermometers arranged upstream from the bar heaters and on the basis of the measured temperature distribution. In the concentrated heating in the middle part in the width direction, for example, the plurality of bar heaters are moved to the middle of the width direction of the steel sheet and, in overall heating in the width of the steel sheet, the plurality of bar heaters are moved so as to be spaced at a fixed interval over the entire in the width direction. Each of the shifted bar heater is then operated for heating, and the temperature distribution in the width direction of the steel sheet is controlled. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５４】
図１１に４種類の鋼板をバーヒータで加熱昇温（バーヒータの鉄心間距離＝２１０ｍｍ）させたそれぞれの仕上圧延機前でのバーヒータによる昇温量（ＢＨ昇温量）と仕上圧延機出側の板幅方向の温度分布の比較（バーヒータの加熱の有無の比較）結果を示す。図１１に示すように、粗圧延された各鋼板はアルファベットＭ型の温度偏差を有する点線で示す温度分布であったが、３台のバーヒータによる細い実線で示す温度分布の合計昇温量により昇温された。その結果、太い実線で示すように鋼板幅方向温度分布はほぼ均一化された。
【００５５】
このように幅方向温度分布を有する鋼板を仕上圧延することにより、鋼板幅方向に材質特性が均一化された熱延鋼板が得られる。
【００５６】
【発明の効果】
本発明によれば、鋼板幅方向の任意の領域を加熱昇温することができるので、熱間圧延において、鋼板（粗バー）幅方向の温度分布の均一化することができ、その結果熱延鋼板幅方向の材質特性の均一化を達成することができる。また、鋼板（粗バー）幅方向の温度分布を意図的に異ならしめることもでき、熱間圧延によって幅方向材質特性の異なるテーラード鋼板を得ることができる。
【図面の簡単な説明】
【図１】熱間圧延工程を示す模式図である。
【図２】連続熱間圧延工程を示す模式図である。
【図３】粗圧延した粗バー及び仕上圧延した鋼板の幅方向温度分布を示す図である。
【図４】（ａ）は、エッジヒーターによる昇温を行った鋼板幅方向温度分布を示す図で、（ｂ）はソレノイド型誘導加熱装置によって昇温された鋼板幅方向温度分布を示す図である。
【図５】（ａ）は６００ＭＰａ級高張力鋼板の熱間仕上温度（℃）と穴広げ率（％）との関係を示す図で、（ｂ）は６００ＭＰａ級高張力鋼板の熱間仕上温度（℃）と伸びＥＬ（％）との関係を示す図である。
【図６】トランスバース型バーヒータの概要を示す図である。
【図７】複数台のバーヒータを鋼板幅方向にシフトして、鋼板を加熱する際の幅方向昇温量を示す模式図である。
【図８】バーヒータによる幅方向昇温分布及び鋼板の幅方向温度偏差改善を示す図である。
【図９】実施例におけるバーヒータの幅方向シフトを説明するための図である。
【図１０】実施例におけるバーヒータによる昇温量及び昇温量差の規定を説明するための図である。
【図１１】実施例における鋼板幅方向温度偏差改善を示す図である。
【図１２】実施例における（ａ）〜（ｅ）の加熱試験に対応する幅方向シフトの状態を示す図である。
【符号の説明】
１ 加熱炉
２ スラブ
３ 粗圧延機
４ 粗バー
５ クロップシャー
６ エッジヒーター
７ 連続仕上圧延機
８ 冷却スタンド
９ コイラー
１０ コイルボックス
１１ 接合シャー
１２ 溶接装置
１３ 放冷大
１４ 低温部
１５ エッジヒーターによる昇温量
１６ ソレノイド型誘導加熱装置による昇温量
１７ トランスバース型誘導加熱装置
１８ 鉄心
１９ コイル
２０ 鋼板
２１ 鋼板（粗バー）
２２ バーヒータ
２３ 昇温量分布[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for heating a steel sheet, and more particularly to a method for heating a steel sheet that controls the temperature distribution in the width direction of the steel sheet.
[0002]
[Prior art]
As shown in FIG. 1, hot rolling of a steel sheet is performed by charging a low-temperature slab 2 into a heating furnace 1 and reheating the slab 2 to a predetermined temperature. The coarse bar 4 is rolled into a coarse bar 4, and the leading and trailing ends of the coarse bar are cut off using a crop shear 5. After the part is heated and finish-rolled to a predetermined hot-rolled steel sheet by a continuous finishing rolling mill 7 comprising a plurality of stands, it is cooled by a cooling stand 8 on a run-out table and wound up by a coiler 9. I have.
[0003]
Further, when endless rolling is performed in which rough bars are joined and finish rolling is performed before finish rolling, a low-temperature slab 2 is charged into a heating furnace 1 as shown in FIG. The slab 2 which has been reheated to the temperature and is reheated is rolled to a predetermined thickness by the rough rolling mill 3 to form the rough bar 4, which is wound up by the coil box 10 and the tip of the coarse bar unwound from the coil box is removed. It is cut by the joining shear 11, and the rear end of the preceding coarse bar and the front end of the following coarse bar are joined by the welding device 12, and the edge heater 6 is used to recover the temperature drop at both edges in the width direction of the coarse bar 4. After heating both edge portions with a continuous finishing mill 7 consisting of a plurality of stands and finish rolling to a predetermined hot-rolled steel sheet, the resultant is cooled in a cooling stand 8 on a run-out table and wound up by a coiler 9. Is being done.
[0004]
In the hot rolling or endless rolling process of such a hot-rolled steel sheet, in order to reheat the low-temperature slab in the heating furnace, the occurrence of uneven heating is inevitable, and the heat release from the heating furnace and the rolled material are rolled. During the rough rolling, a temperature drop occurs at both edges of the rough bar due to the fact that the plate thickness becomes smaller than the plate width during the rolling. These temperature decreases cause unevenness of the temperature distribution in the width direction of the rough bar, which causes unevenness of the finishing temperature.
[0005]
If the temperature distribution in the width direction of the rough bar becomes uneven, the eaves and middle elongation occur in the hot-rolled steel sheet during finish rolling, and the material properties such as the mechanical properties in the width direction of the hot-rolled steel sheet become uneven. And other problems arise.
[0006]
In order to prevent such a problem caused by non-uniform temperature distribution in the width direction of the rough bar, a heating device and an edge heater are provided between the rough rolling mill and the finishing rolling mill, and the rough rolling is performed by the rough rolling mill. It is known to heat a roughened bar. Conventionally, between a rough rolling mill and a finishing rolling mill, a solenoid-type induction heating device for heating the rough bar over its entire width direction and an edge heater for heating both edges of the rough bar are provided. It has been proposed to heat a coarse bar on the entry side of a finishing mill to a uniform temperature in the width direction by using a solenoid-type induction heating device and an edge heater (for example, Patent Document 1).
[0007]
The characteristic of the solenoid type induction heating device used here is that it has a magnetic field characteristic that a coil is wound around the plate and a magnetic field is generated in parallel with the plate. Therefore, the temperature is increased over the entire width by a uniform temperature while the temperature distribution in the plate width direction is substantially constant.
[0008]
That is, the coarse bar is uniformly heated in the width direction by the solenoid type induction heating device so as to reduce the rolling load, and the both edge portions (edge portions) where the temperature drop is large are heated by the edge heater, so that the temperature in the width direction is uniform. It is intended to be distributed.
[0009]
However, as a result of the present inventor's research on the material properties of the hot-rolled steel sheet in the width direction, the rough bar on the entrance side of the finishing mill was heated by an edge heater with a large temperature drop by an edge heater to obtain a temperature distribution in the width direction. It has been found that even when the steel sheet is made uniform, the width direction material properties of the steel sheet obtained by finish rolling are not uniform. That is, the heating method of uniformly heating the entire rough bar in the width direction between the rough rolling mill and the finishing rolling mill, and heating both edges having a large temperature drop by the edge heater, is obtained by finish rolling. It was difficult to make the width direction material properties of the hot rolled steel sheet uniform. Various experiments were conducted to determine the cause, and it was found that there was a cause during slab heating in a heating furnace. That is, since the heating furnace heats the slab in a high-temperature atmosphere, the temperature at the center of the slab is inevitably low, and this temperature distribution is maintained even if the sheet thickness is reduced by rolling. The center temperature is lower than the average temperature, and the width of the letter M in the width direction increases toward the edge.
[0010]
Therefore, it is impossible to make the temperature distribution in the width direction uniform and to make the material properties in the plate width direction uniform by a heating method using an edge heater or a bar heater that raises the temperature in the width direction by a constant value.
[0011]
Also, tailored blanks having different strengths in the width direction of the board are manufactured as press blanks (blanks) for body parts of automobiles and the like. When this tailored blank is press-formed into a vehicle body part, it becomes possible to make the mechanical properties of a predetermined portion of the vehicle body part different.
[0012]
Conventionally, a method of welding a plurality of steel strips to form a tailored blank material is generally used. In recent years, when a hot-rolled steel strip is water-cooled with a run-out table (ROT), a cooling rate in a width direction of the steel strip is changed. Various methods have been proposed for producing tailored blanks without welding by varying the mechanical properties of the steel strip in the width direction (for example, Patent Documents 2 and 3).
[0013]
However, rather than changing the cooling rate in the width direction of the steel strip, by changing the temperature difference in the width direction of the steel strip before finish rolling, and making it a tailored blank material, the mechanical properties, especially the hole expansion rate and elongation properties It was found that tailored blanks excellent in quality can be manufactured. In this method, a method and an apparatus for heating a steel strip for effectively changing the temperature difference in the width direction of the steel strip are required.
[0014]
[Patent Document 1]
JP-A-3-314216 [Patent Document 2]
JP-A-11-192501 [Patent Document 3]
JP 2000-11541 A
[Problems to be solved by the invention]
In view of the above circumstances, the present invention provides a steel sheet heating method capable of heating an arbitrary region in the width direction of a steel plate (steel strip) and controlling the temperature distribution in the width direction of the steel plate. The task is to do so.
[0016]
[Means for Solving the Problems]
In order to obtain a hot-rolled steel sheet having no variation in the material properties in the width direction, the present inventor needs to make the temperature distribution in the width direction of the rough bar on the entry side of the finishing mill uniform, but for that purpose, the slab is used. Heating and raising the temperature of the center low temperature part of the rough bar due to the low temperature of the center part of the slab during heating, and changing the temperature difference in the width direction of the steel sheet (rough bar) before finish rolling to obtain a tailored blank material For this purpose, it is required to heat and raise an arbitrary region in the coarse bar width direction. For this reason, bar heaters composed of a plurality of transverse induction heating devices are arranged in the longitudinal direction of the steel plate (coarse bar), and there is a portion where each bar heater overlaps in the longitudinal direction of the steel plate (the total amount of temperature rise is large). The present invention has been found to be possible by controlling the widthwise temperature distribution by controlling the widthwise temperature distribution by shifting the width of the steel sheet in the width direction and performing a heating operation on each bar heater so that an arbitrary region in the width direction of the steel sheet can be heated and heated with a temperature difference. Was completed.
[0017]
The gist of the present invention is as follows.
[0018]
(1) A method for heating a steel sheet, comprising shifting a plurality of bar heaters arranged in the longitudinal direction of the steel sheet in the width direction of the steel sheet, performing a heating operation on each bar heater, and controlling a temperature distribution in the width direction of the steel sheet.
[0019]
(2) The temperature distribution in the steel sheet width direction is controlled by shifting a plurality of bar heaters arranged in the steel sheet longitudinal direction in the steel sheet width direction so that the overlapping part exists in the steel sheet longitudinal direction and controlling the amount of the overlapping part. A method for heating a steel sheet.
[0020]
(3) The method for heating a steel sheet according to the above (1) or (2), wherein, in the centralized central heating in the steel sheet width direction, a plurality of bar heaters are moved to the center in the steel sheet width direction to perform a heating operation.
[0021]
(4) The heating of the steel sheet according to the above (1) or (2), wherein the heating operation is performed by moving a plurality of bar heaters so as to have a constant interval in the entire width direction in the entire heating in the width direction of the steel sheet. Method.
[0022]
(5) The method for heating a steel sheet according to any one of the above (1) to (4), wherein heating is performed by a plurality of bar heaters installed upstream of a finishing final stand of the hot rolling line.
[0023]
(6) The temperature distribution in the width direction of the steel sheet is measured by a width direction thermometer disposed upstream of the bar heater, and the shift amount of each bar heater is determined based on the measured temperature distribution. ) The method for heating a steel sheet according to any one of (1) to (5).
[0024]
(7) The method for heating a steel sheet according to any one of the above (1) to (6), wherein the shift is possible by in-coil.
[0025]
(8) The method for heating a steel sheet according to any one of the above (1) to (7), wherein the heating amount of each bar heater is independently varied by an in-coil.
[0026]
(9) The method for heating a steel sheet according to any one of the above (1) to (8), wherein the distance between the iron cores of each bar heater is independently varied by in-coil.
[0027]
(10) The method for heating a steel sheet according to any one of the above (1) to (9), wherein the edge in the sheet width direction is heated by an edge heater.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0029]
FIG. 3 is a diagram showing a temperature distribution in a width direction of a rough bar obtained by roughly rolling a slab heated in a heating furnace.
[0030]
Since the heating furnace heats the slab in a high-temperature atmosphere, it is inevitable that the heated slab has a high temperature around its periphery and a low-temperature portion in the center. For this reason, as shown in FIG. 3A, the temperature of the rough bar obtained by roughly rolling the heated slab is lowered because the edge of the rough bar 4 is a large cooling portion 13, and the center portion is at the low temperature portion of the slab. As shown in FIG. 3B, for example, as shown in FIG. 3 (b), the temperature of the central part of the plate width is 1033 ° C., the maximum temperature is 1056 ° C. from the central part toward the edge, and the edge is 1002 ° C. The temperature distribution in the width direction is M-shaped. When the rough bar having such a temperature distribution in the width direction is finish-rolled, as shown in FIG. 3 (c), the temperature at the center of the plate width is 852 ° C., the maximum temperature from the center to the edge is 865 ° C., and the edge is at the edge. Is 800 ° C. and a finish-rolled steel sheet exhibiting the letter M shape, so that the hot rolled steel sheet obtained after cooling has non-uniform material properties such as mechanical properties in the width direction.
[0031]
In the conventional hot rolling method, as shown in FIG. 4A, only the edge portion of the rough bar is cooled by cooling, and it is considered that the temperature distribution in the width direction becomes uniform when heated by the edge heater. However, even if the edge heater is heated and heated (1056 ° C.) by a heating amount 15 indicated by oblique lines in the edge portion, the central low-temperature portion (1033 ° C.) cannot be heated. Also, in the method of heating and raising the temperature in the entire coarse bar width direction by using the solenoid-type induction heating device, as shown in FIG. Is raised, and the M-type widthwise temperature distribution is maintained. Therefore, uniform heating in the width direction cannot be achieved by heating with an edge heater or a solenoid-type induction heating device.
[0032]
In addition, to manufacture tailored steel sheets having different mechanical properties in the width direction of the steel strip, particularly, different properties of hole expansion properties and elongation properties by hot rolling, if the temperature difference in the width direction of the steel sheet is different before finish rolling, It has been found that when finish rolling is performed, the hole expanding properties of the steel sheet are effectively improved by the hot finishing temperature.
[0033]
For example, C: 0.09 to 0.11%, Si: 1.30 to 1.50%, Mn: 1.25 to 1.45%, P: 0.010% or less, S: 0.002% or less When applying a 590 MPa class high-strength steel strip composed of the following components to automotive parts such as cross members, parts are removed in the width direction of the steel strip, and from the part shape, stretch flange processing is performed near the center of the coil width, and steel is removed. At the quarter width to the width edge portion of the band, processing mainly involving overhanging processing is performed.
[0034]
In such processing, the steel strip needs to have a hole expansion ratio of 70% or more, preferably 80% or more for the stretch flanged portion, and the elongation ratio of the steel sheet is 31% or more for the overhanging process, and desirably. 34% or more is required.
[0035]
Consider the conditions for obtaining the above mechanical properties.
[0036]
FIG. 5A is a diagram showing the relationship between the hot finishing temperature (° C.) and the hole expansion rate (%) of the 590 MPa class high tensile steel strip, and FIG. It is a figure which shows the relationship between finishing temperature (degreeC) and elongation EL (%). As shown in FIG. 5A, the hole expansion ratio of the steel strip is improved in response to the increase in the hot finishing temperature, but as shown in FIG. As a result, the elongation of the steel strip decreases. In other words, the hole expanding property and the elongation property show a tendency to be contradictory to the hot finishing temperature.
[0037]
Therefore, the hot finishing temperature is required to be 878 ° C. or more as shown by the arrow in order to make the hole expansion rate 70% or more from FIG. 5A, and the elongation is 31% or more from FIG. 5B. Is required to be 860 ° C. or lower as indicated by an arrow, and it can be seen that the required temperature ranges are different between the two. However, in order to obtain a steel strip having both properties, it is possible to obtain a steel strip by controlling the hot finishing temperature to a very narrow range of 860 to 880 ° C. (the range indicated by oblique lines). There is a problem that the deviation from the given condition occurs, and even if the temperature condition is hit, the target deviation due to the variation of the material occurs, thereby lowering the yield.
[0038]
In the present invention, the hot finishing temperature in the steel strip width direction is varied, and the hot finishing temperature in the vicinity of the center of the steel strip width is 870 ° C or higher, and the １ ／ width to width edge portion of the steel strip is 860 ° C or lower. By applying a hot finishing temperature condition in which the central portion of the steel strip width is heated by 20 ° C. or more so that the width of the central portion of the steel strip is increased by 70% or more, and the width of the central portion of the steel strip is reduced to 1/4 width or more. It was found that a tailored steel strip having an elongation of 31% or more at the width edge portion and having different mechanical properties in the width direction can be easily manufactured.
[0039]
However, a heating device necessary to manufacture a steel sheet having uniform material properties in the width direction or a tailored steel sheet having different material properties in the width direction, that is, arbitrarily controlling the temperature distribution in the width direction of the steel sheet, and controlling the temperature in the width direction. There has not been proposed a heating device capable of making the distribution uniform or effectively changing the temperature in the width direction.
[0040]
The inventor of the present invention has conducted intensive studies on a method and an apparatus for heating a steel sheet that can arbitrarily control the temperature distribution in the width direction of the steel sheet. Then, it has been found that the widthwise temperature distribution can be arbitrarily controlled by shifting each bar heater in the width direction, controlling the overlapping portion amount of the bar heaters in the steel plate longitudinal direction, and performing the heating operation of each bar heater.
[0041]
As shown in FIG. 6, unlike the solenoid induction heating device, the transverse induction heating device 17 is configured by winding a coil 19 around an iron core 18. Has the property that it can be uniformly heated.
[0042]
In addition, since the steel sheet can be used by being arranged at the upper and lower positions of the steel sheet, it can be easily shifted in the width direction of the steel sheet, and has a characteristic that the surface of the steel sheet is not flawed.
[0043]
FIG. 7A is a diagram showing the arrangement of one bar heater in the width direction of the steel sheet and the amount of temperature rise. FIGS. 7C to 7E show three bar heaters arranged in the longitudinal direction of the steel sheet. It is a figure which shows the amount of temperature rise of the steel plate width direction at the time of shifting the bar heater by a predetermined amount in the width direction.
[0044]
As shown in FIG. 7 (a), when one bar heater (transverse induction heating device) 22 is disposed in the center of the steel plate 21 and the bar heater is operated for heating, the temperature rise distribution 23 in the width direction of the steel plate becomes the bar heater. Corresponding to the width (iron core width). Three bar heaters having such a temperature increasing characteristic are arranged in the longitudinal direction of the steel sheet, and each bar heater is shifted by a predetermined amount in the width direction of the steel sheet (the center of the width direction is used as a reference for the shift amount. 7B, for example, FIG. 7B shows an example in which the shift amount is zero and all three bar heaters overlap each other, and the temperature rise amounts of the three bar heaters are summed up and shown in the lower diagram. As shown in FIG. 7 (c), the temperature distribution in the central portion in the width direction of the steel sheet is high, and the two bar heaters on the upstream side and the downstream side are shifted in the opposite direction without shifting one bar heater in the center. In the example where the overlapping portions of the bar heaters are slightly reduced, the amounts of temperature rise of the three bar heaters are added in a state of being shifted according to the shift amount, and are added in the width direction of the steel sheet as shown in the lower figure. As a result, the distribution of the temperature rise becomes a broad mountain shape, and FIG. FIG. 7D is an example in which the shift amount of the two bar heaters on the upstream side and the downstream side is made larger than that in FIG. 7C, and the overlapping portion of the bar heaters is further reduced. The temperature distribution is a mountain-shaped temperature rise distribution that is wider than that in FIG. 7C. FIG. 7E shows an example in which the bar heater is moved so as to have a constant interval in the entire width direction to eliminate the overlapping portion of the bar heater and to heat the entire width. A wider mountain-shaped temperature rise distribution is obtained.
[0045]
The bar heater to be shifted is not limited to the downstream side, and the same temperature distribution can be achieved by shifting any bar heater. In the above example, an example of three bar heaters is shown. However, if the number of bar heaters is further increased, the total temperature increase can be increased, and the distribution of the temperature increase in the steel sheet width direction can be controlled accurately. It becomes possible. That is, a plurality (two or more) of bar heaters can be shifted in the width direction of the steel sheet, and the shift can make the distribution of the temperature increase of the steel sheet in the width direction variable. Can be raised, and the temperature distribution in the width direction can be controlled. The bar heaters can be shifted in-coil, and the bar heaters can be used in combination with bar heaters having the same width and / or different widths. Further, the temperature controllability can be further improved by independently varying the heating amount of each bar heater and the distance between the iron cores with the in-coil of the plurality of bar heaters.
[0046]
For example, an example will be described in which the temperature deviation in the width direction is improved by using three bar heaters having the same width when the temperature of the central portion of the steel plate (rough bar) is low.
[0047]
As shown in FIG. 8A, the temperature distribution in the width direction of the coarse bar having a width of 1500 mm was a letter M type (shown by a dotted line) whose central portion was lower by 40 ° C. Then, in order to raise the temperature of the central part of the steel sheet to 40 ° C. in an inverted M-shape to make the temperature distribution in the width direction uniform, the temperature was raised using three bar heaters (the hatched area indicates the amount of temperature increase). It is necessary that the total temperature rise amount (indicated by a solid line) of the three bar heaters be a gentle mountain-shaped temperature rise amount distribution (inverted M type) whose central part is higher by 40 ° C. As shown in FIG. 8 (b), the three bar heaters have the same distance between the iron cores and the same amount of temperature rise, and the three bar heaters having a width of 600 mm (No. 1) are used. The heating operation was performed by shifting two of the bar heaters (No. 1 and No. 3) in (1) to (3) ± 150 mm with respect to the center in the width direction (the distance in the plate width direction is 750 mm). That is, the position where the distance in the plate width direction is 600 mm to 900 mm (± 150 mm based on the center in the plate width direction) is No. No. 1 to No. 3 are provided at positions where the iron cores of all three bar heaters overlap each other, and the distance in the plate width direction is 450 mm to 600 mm (-300 mm to -150 mm based on the center in the plate width direction). The iron cores of the two bar heaters No. 1 and No. 2 have a distance of 750 mm to 900 mm in the plate width direction (+150 mm to +300 mm based on the center in the plate width direction). There were portions where the iron cores of the two bar heaters 2 and 3 overlapped each other. As a result, the heating amount distribution of each of the bar heaters (No. 1 to No. 3) becomes a shifted gentle mountain shape, and the total heating amount of the three units is the same as the mountain-shaped heating amount distribution in which the central part is higher by 40 ° C. became.
[0048]
The method of determining the heating amount of the steel sheet is as follows. The heating profile in the width direction of the bar heater is stored in the calculator for each width of the steel sheet (coarse bar), for each shift amount of the bar heater, and for each heating amount of the bar heater, and the upstream side of the bar heater is stored. The temperature distribution in the width direction of the steel sheet is grasped by the width direction thermometer arranged in the direction, and the nearest shift amount and temperature increase amount are selected by a computer so as to heat the difference in the profile of the target width direction temperature distribution, This instruction can be performed by instructing the electric sequencer to set the bar heater shift amount (overlapping portion of the bar heater) and the heating amount. This makes it possible to raise the temperature of an arbitrary region in the width direction of the steel sheet by a predetermined amount.
[0049]
Further, as means for shifting the bar heater, for example, a bar heater is installed on a carriage that can travel on rails so as to be able to move up and down, and the carriage is shifted by a driving device, so that the bar heater can be shifted in the steel sheet width direction. Then, the gap between the bar heaters can be adjusted by raising and lowering the upper and lower bar heaters.
[0050]
【Example】
Hereinafter, the present invention will be described in detail based on examples.
[0051]
In hot rolling, four types of roughly-rolled steel plates of 900 mm width, 1200 mm width, 1500 mm width, and 1800 mm width were produced using three 600 mm width transverse bar heaters (BH1, BH2, BH3). Tests (a) to (e) were conducted in which the (rough bar) was heated by shifting the bar heater in the width direction in front of the finish rolling mill to make the temperature distribution in the width direction of the steel sheet uniform. The distance (gap) between the iron cores of the upper and lower bar heaters was changed by three levels of (1) 210 mm, (2) 160 mm, and (3) 130 mm in each plate width. Then, the temperature rise amount and the temperature rise difference at each level were determined. Further, for the 900 mm width, a test (e) in which heating by an edge heater was further added was also performed.
[0052]
Table 1 shows the test conditions and the temperature rise. As shown in Table 1, as the distance (gap) between the iron cores of the upper and lower bar heaters is smaller, the temperature rise amount and the difference in the temperature rise amount are larger, and as the overlap between the bar heaters is larger, the temperature rise amount and the temperature difference are larger. I was As shown in FIG. 9, each of the three bar heaters (BH1 to BH1) was shifted to the WS (Work Side) side or the DS (Drive Side) side. (A) to (e) of FIG. 12 show the state of the width shift of the bar heater corresponding to each of the heating tests a to e. As shown in FIG. 10 (a), the "heating amount" by the bar heater in Table 1 was defined as the difference between the minimum temperatures in the plate width direction before and after the heating. Similarly, as shown in FIG. 10 (b), the “temperature rise difference” in Table 1 indicates the difference between the temperature rise at the center 150 mm from the steel plate edge and the temperature rise at the center in the steel sheet width direction. And
[0053]
[Table 1]

[0054]
In FIG. 11, the temperature rise amount (BH temperature rise amount) by the bar heater in front of each finishing mill in which four types of steel plates were heated by a bar heater (distance between the iron cores of the bar heater = 210 mm) and the exit side of the finishing mill were shown. The result of comparison of the temperature distribution in the plate width direction (comparison of the presence or absence of heating of the bar heater) is shown. As shown in FIG. 11, each of the rough-rolled steel sheets had a temperature distribution indicated by a dotted line having a temperature deviation of the letter M, but the temperature distribution was increased by a total temperature increase amount indicated by a thin solid line by three bar heaters. Was warmed. As a result, as shown by the thick solid line, the temperature distribution in the width direction of the steel sheet was substantially uniformized.
[0055]
By subjecting the steel sheet having the temperature distribution in the width direction to finish rolling, a hot-rolled steel sheet having uniform material properties in the width direction of the steel sheet can be obtained.
[0056]
【The invention's effect】
According to the present invention, an arbitrary region in the width direction of the steel sheet can be heated and heated, so that in hot rolling, the temperature distribution in the width direction of the steel sheet (rough bar) can be made uniform, and as a result, hot rolling can be performed. Uniformity of material properties in the width direction of the steel sheet can be achieved. Further, the temperature distribution in the width direction of the steel sheet (rough bar) can be intentionally made different, and tailored steel sheets having different material properties in the width direction can be obtained by hot rolling.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a hot rolling step.
FIG. 2 is a schematic view showing a continuous hot rolling step.
FIG. 3 is a diagram showing a temperature distribution in a width direction of a rough-rolled rough bar and a finish-rolled steel sheet.
FIG. 4 (a) is a diagram showing a temperature distribution in a width direction of a steel sheet heated by an edge heater, and FIG. 4 (b) is a diagram showing a temperature distribution in a width direction of a steel sheet heated by a solenoid-type induction heating device. is there.
FIG. 5A is a diagram showing a relationship between a hot finishing temperature (° C.) and a hole expansion ratio (%) of a 600 MPa class high strength steel sheet, and FIG. 5B is a diagram showing a hot finishing temperature of a 600 MPa class high strength steel sheet. It is a figure which shows the relationship between (° C) and elongation EL (%).
FIG. 6 is a diagram showing an outline of a transverse bar heater.
FIG. 7 is a schematic diagram showing a widthwise heating amount when heating a steel sheet by shifting a plurality of bar heaters in the width direction of the steel sheet.
FIG. 8 is a diagram showing a widthwise temperature rise distribution by a bar heater and an improvement in a widthwise temperature deviation of a steel sheet.
FIG. 9 is a view for explaining a shift in the width direction of the bar heater in the embodiment.
FIG. 10 is a view for explaining the regulation of the temperature rise amount and the temperature rise amount difference by the bar heater in the embodiment.
FIG. 11 is a diagram showing improvement in temperature deviation in the steel sheet width direction in the example.
FIG. 12 is a diagram showing a state of a shift in the width direction corresponding to the heating tests (a) to (e) in the example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Slab 3 Rough rolling mill 4 Rough bar 5 Crop shear 6 Edge heater 7 Continuous finishing rolling mill 8 Cooling stand 9 Coiler 10 Coil box 11 Joining shear 12 Welding equipment 13 Large cooling unit 14 Low temperature unit 15 Heating by edge heater Quantity 16 Temperature rise by solenoid type induction heating device 17 Transverse type induction heating device 18 Iron core 19 Coil 20 Steel plate 21 Steel plate (coarse bar)
22 Bar heater 23 Heating amount distribution

Claims (10)

A method for heating a steel sheet, comprising shifting a plurality of bar heaters arranged in the longitudinal direction of the steel sheet in the width direction of the steel sheet, performing a heating operation on each bar heater, and controlling a temperature distribution in the width direction of the steel sheet. A plurality of bar heaters arranged in the longitudinal direction of the steel sheet are shifted in the width direction of the steel sheet so as to have an overlapping portion in the longitudinal direction of the steel sheet, and the temperature distribution in the width direction of the steel sheet is controlled by controlling the amount of the overlapping portion. Steel sheet heating method. The method for heating a steel sheet according to claim 1 or 2, wherein in the central heating in the width direction of the steel sheet, a plurality of bar heaters are moved to the center in the width direction of the steel sheet to perform a heating operation. 3. The method for heating a steel sheet according to claim 1, wherein, in the entire heating in the width direction of the steel sheet, the heating operation is performed by moving a plurality of bar heaters at regular intervals in the entire width direction. The method for heating a steel sheet according to any one of claims 1 to 4, wherein the heating is performed by a plurality of bar heaters installed on the upstream side of a finishing final stand of the hot rolling line. The temperature distribution in the width direction of the steel sheet is measured by a width-direction thermometer disposed upstream of the bar heater, and the shift amount of each bar heater is determined based on the measured temperature distribution. The method for heating a steel sheet according to any one of the above. The method for heating a steel sheet according to any one of claims 1 to 6, wherein the shift can be performed by in-coil. The method for heating a steel sheet according to any one of claims 1 to 7, wherein a heating amount of each bar heater is independently varied by an in-coil. The method for heating a steel sheet according to any one of claims 1 to 8, wherein a distance between iron cores of the respective bar heaters is independently varied by an in-coil. The method for heating a steel sheet according to any one of claims 1 to 9, wherein the edge portion in the sheet width direction is heated by an edge heater.

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