JPH11169910A - Manufacture of hot rolled steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regulate the finished outlet-side temp. in the target range over the entire length of a material by heating at least a part in the longitudinal direction of a sheet bar over the entire width before finish rolling after joining, with a high frequency induction heating device. SOLUTION: The heating with a high frequency induction heating device is executed so that the finished outlet-side temp. of the part to be heated becomes the target temp. The finished outlet-side temp. of the middle part in the longitudinal direction of a coil is set so as to be in the target temp. range, the part including at least one side of the outermost turn and innermost turn is heated with the high frequency induction heating device and it is preferable to execute finish rolling while regulating the temp. in the range of the target temp. over the entire length of the coil. Finish rolling is possible by regulating the finished outlet-side temp. so as to be not lower than the transformation point Ar3 or not higher than that. By drastically relaxing the restriction of the heating temp. of the slab and rolling speed, the finished outlet-side temp. and material are secured over the entire length of products in the target range, manufacture is executed in high yield and also the cost of energy required for heating is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet, and more particularly to a method for producing a hot-rolled steel sheet that can advantageously adjust a sheet bar temperature after rough rolling and before finish rolling.

[0002]

2. Description of the Related Art In the production of hot-rolled steel sheets, in the conventional batch rolling in which rough rolling and finish rolling are performed for each slab as a material, when a product becomes thinner, a sheet bar (after rough rolling) is used. Materials) Loops, meandering, squeezing, and the like are likely to occur during the finish rolling at the tip and tail ends, and stable production becomes difficult. In order to overcome this difficulty, a process called endless rolling has been developed in which a plurality of sheet bars are sequentially joined in series and finish rolling is continuously performed while applying a certain amount of tension between finishing stands and a run-out table. . In this process, a sheet bar coiler is used as a buffer for absorbing a difference in the material feed speed between the rough rolling and the finish rolling. The standby time of the material in the sheet bar coiler is about several tens of seconds.

[0003] The coiled material in the sheet bar coiler cools the outermost and innermost portions (corresponding to the leading and trailing end portions of the sheet bar) which are always exposed to the atmosphere, and the temperature on the finishing side is low. Easy to come off. For this reason, when manufacturing a product by endless rolling using a sheet bar coiler, the slab heating temperature is raised in order to compensate for a temperature drop in the sheet bar coiler at the tail end. For example, in the case of a thin material with a finished plate thickness of 1.2 mm or less and a target finish side temperature (FDT) target value set to the Ar ₃ transformation point or higher, the slab heating temperature is set to 1260 ° C., which is higher than in the case of batch rolling. doing.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. S61-119327, a heating device is provided on the inside of a sheet bar coiler or on the entrance / exit side to solve the problem that the front and rear end portions are easily cooled in the sheet bar coiler. There is also a method of installing and heating the outermost winding portion of the coil-shaped material to prevent the temperature of that portion from lowering.

[0005]

As described above, in the endless rolling, the coiled material waits for several tens seconds in the sheet bar coiler. For this reason, as shown in FIG.
In the meantime, the outermost winding part and the innermost winding part are allowed to cool to the atmosphere, and the temperature on the finishing side is lower by 50 to 100 ° C. than the stationary parts other than these parts. Therefore, for materials with a finishing output temperature target of at least the Ar ₃ transformation point, especially thin materials,
Except for the minimum necessary descaling at the tail end,
Although water cooling was not performed in the finishing mill, the target finish-side temperature could not be secured, the desired material could not be obtained, and the yield was poor.

[0006] There is a plan to increase the finish rolling speed at the end of the tail end to secure the finish output side temperature. However, in order to stably cut the coil after finish rolling and switch the winding machine, cutting is performed. Speed at a certain speed or less (eg 1000mpm or less)
, And the finish rolling speed of the tail end portion is also controlled by this. Therefore, there is a limit in increasing the finishing temperature on the leading and trailing end portion by increasing the speed.

[0007] In the case of a material whose finishing output side temperature target is equal to or lower than the Ar ₃ transformation point, it is relatively easy to set the slab heating temperature so that the finishing output side temperature of the tail end portion is within the target range. When the finishing temperature at the center in the longitudinal direction increases the top speed (the finishing rolling speed at the central portion in the longitudinal direction), even if water cooling is performed using all the cooling equipment in the finishing mill, the temperature falls outside the target range. So the top speed cannot be increased.
Furthermore, in the endless rolling, the slab heating temperature is higher than in the batch rolling, so that the top speed is limited, and there is a problem that productivity of thin materials is particularly poor.

Further, if the slab heating temperature is increased, the fuel cost is increased, and equipment such as refractories in the heating furnace is severely damaged. If the equipment deteriorates, the operation must be stopped and repairs must be performed, so that the operating time of the equipment is shortened, and problems such as a reduction in production capacity occur. Therefore, in order to maintain the facility maintainability of the heating furnace at a high level, it is important to set the slab heating temperature as low as possible, and desirably, 1200 ° C. or less.

On the other hand, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-119327, the material in the sheet bar coiler is heated to secure the finish-out side temperature at the leading end when it is employed in an endless rolling process. However, there is a problem that the heating efficiency is low. That is, for example, in a sheet bar coiler, FIG.
In the case of performing heating as indicated by the hatched portion in FIG. 2B, heat must be input so as to fill the temperature difference when the temperature difference is large, and furthermore, the innermost winding portion and the outermost winding portion of the coiled material. A large amount of heat escapes to other parts (inside the coiled material). In addition, such a method is difficult to apply to endless rolling without using a sheet bar coiler, and furthermore, a sheet bar portion which is clamped at the time of joining or held down by a pinch roll (the outermost winding portion, the outermost portion in the sheet bar coiler). (It does not necessarily correspond to the winding part).

In view of the above problems of the prior art, the present invention provides:
An object of the present invention is to provide a method for manufacturing a hot-rolled steel sheet efficiently by reducing a temperature difference generated in a longitudinal direction of a sheet bar by an efficient heating means, and further by relaxing restrictions on a slab heating temperature and a finish rolling speed. And Another object of the present invention is to provide the above-mentioned method which is suitable particularly when endless rolling and furthermore endless rolling using a sheet bar coiler are applied.

Another object of the present invention is to provide the above-mentioned method suitable for keeping the finishing temperature within a target range over the entire length of the material.

[0012]

SUMMARY OF THE INVENTION According to the present invention, a slab heated to a predetermined temperature is roughly rolled, and the leading end of the roughly rolled sheet bar is joined to the tail end of the preceding sheet bar. A method for producing a hot-rolled steel sheet, comprising: heating at least a portion of the sheet bar in the longitudinal direction over the entire width by a high-frequency induction heating device after joining and before finish rolling. 1).

[0013] The present invention also provides a slab that has been heated to a predetermined temperature, is roughly rolled, and the roughly rolled sheet bar is wound and rewound, and the leading end is joined to the tail end of the preceding sheet bar to finish the slab. A method for producing a hot-rolled steel sheet by rolling to produce a hot-rolled steel sheet, wherein at least a part of the sheet bar in the longitudinal direction is heated by a high-frequency induction heating device over the entire width before joining and before finish rolling. (Method 2).

Further, the present invention is a method (method 3) in which the high-frequency induction heating device is heated in the above method 1 or 2 such that the finish-side temperature of a heated portion becomes a target temperature. . Further, the present invention provides a method according to the above method 2, wherein the predetermined temperature for heating the slab is set so that the finishing temperature at the center in the longitudinal direction of the coil is within a target temperature range, and the sheet bar is wound. A method (method 4) in which a portion including at least one of the outermost winding and the innermost winding is heated by a high-frequency induction heating device, and finish-rolling is performed over the entire length of the coil such that the finish-side temperature is within a target temperature range. The predetermined temperature for heating the slab is set so that the finishing temperature at the center in the longitudinal direction of the coil is within the target temperature range, and at least one of the outermost winding and the innermost winding when the sheet bar is wound up. This is a method (method 5) in which the part containing the slab is heated by a high-frequency induction heating device and finish-rolled over the entire length of the coil so that the finish-side temperature is equal to or higher than the Ar ₃ transformation point, and the slab is heated. The predetermined temperature is set so that the finish-side temperature at the center in the longitudinal direction of the coil is within the target temperature range, and a portion including at least one of the outermost winding and the innermost winding when the sheet bar is wound is subjected to high frequency. This is a method (method 6) of heating by an induction heating device and finish-rolling the entire length of the coil such that the finish-side temperature is equal to or lower than the Ar ₃ transformation point (method 6).
In any one of (1) and (2), the slab heating temperature is 1200 ° C. or lower, and the thickness of the plate after finish rolling is 0.8 to 1.1 mm (method 7).

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hot-rolled steel sheet by finish-rolling a sheet bar at a predetermined temperature to produce a hot-rolled steel sheet. The gist of the invention is that the whole is heated by a high-frequency induction heating device. FIG. 1 is a schematic view showing an example of an embodiment of the present invention. FIG. 1A shows a state in which a sheet bar 1 before finish rolling is heated by a high-frequency induction heating device 6 including a high-frequency coil 62 and a high-frequency power supply 61. (B) shows the path of the coil current and the induced current in the cross section of the sheet bar, and (c) shows the current distribution in the sheet bar thickness direction. As shown in FIGS. 2B and 2C, the induced current flows in a direction around the width end to the surface layer to the width end of the sheet bar due to a skin effect, an edge effect, and the like, and Joule heat generated instantaneously. Causes the material temperature to rise rapidly. According to such a heating method, since the portion generated in the longitudinal direction of the sheet bar can be uniformly and rapidly heated over the entire width, uneven temperature in the longitudinal direction of the sheet bar can be quickly eliminated. .

In order to apply the present invention to endless rolling and further to endless rolling using a sheet bar coiler, it is preferable to apply the high frequency heating to the sheet bar after joining and before finish rolling. Above all, the outermost winding portion and the end portion of the sheet bar corresponding to the innermost winding portion, which are wound in a coil shape in the sheet bar coiler and cooler than the stationary portion during standby, are heated after joining and before finish rolling. Is preferred.

According to the conventional method of heating the coiled material in the sheet bar coiler, the middle winding portion (corresponding to a constant portion of the sheet bar) which does not require heating is heated more than necessary. Since the plate-like material is heated, heat can be supplied to necessary portions without waste, and the heating efficiency is excellent. As a result, even in the case of a thin material, the finish-side temperature can be kept within a target range over the entire length of the steel sheet coil, the desired material can be secured, and the yield is improved.

The slab heating temperature at this time may be set so that the finishing temperature at the central portion in the longitudinal direction of the steel sheet coil is within the target range. Therefore, the setting of the slab heating temperature can be lower than before, and the heating energy cost can be greatly reduced. Further, the top speed can be set higher than before. Further, since the setting of the slab heating temperature can be reduced, deterioration of the refractory in the heating furnace becomes relatively difficult to progress, the frequency of the heating furnace repair is reduced, and the repair cost can be greatly reduced. In addition, since the surface temperature of the slab in the heating furnace also decreases, the scale loss in the heating furnace is reduced, and the yield is improved. Further, since the slab life time can be shortened, the processing capacity of the heating furnace is improved. Generally, the processing capacity of finish rolling by endless rolling exceeds the processing capacity of a heating furnace, so that the production capacity of the entire line is also improved.

Further, according to the present invention, since the heating is performed after joining by the joining device located downstream of the sheet bar coiler, instead of heating in the sheet bar coiler, the leading and trailing ends from the sheet bar coiler to the high frequency induction heating device entrance side. Can be conveyed while the temperature of the section is kept low, as shown in the shaded area in FIG.
Due to the radiation heat radiation difference during the conveyance, the leading end portion in a state where the temperature difference from the stationary portion is reduced as compared with the conventional example of FIG. 2B can be heated. This shaded portion corresponds to the amount of energy required for heating. In the example of the present invention shown in FIG. 2C, this is only about 2/3 of the conventional example shown in FIG. 2B, so that the energy cost can be reduced. In addition, equipment costs can be reduced because the size of the heating device can be reduced.

Further, according to the present invention, since the temperature of the sheet bar dispensed from the sheet bar coiler is actually measured, the amount of heating that the high-frequency induction heating device gives to the end of the sheet bar can be set. By setting the heating amount according to the difference between the measured temperature and the target temperature on the finishing side, it is easier to control the temperature on the finishing side than before. Furthermore, since the finish output side temperature and the finish input side temperature can predict one from the other through the finish rolling history, in the present invention, the heating amount is set according to the finish output side temperature target, that is, Heating by the high-frequency induction heating device can be adopted as the most preferable embodiment in terms of operation, so that the finish-side temperature of the heated portion is the target temperature.

[0021]

FIG. 3 is a schematic view showing an example of a hot rolling line suitable for carrying out the present invention. In FIG. 3, after a material (slab) 1 is extracted from a heating furnace, the material (slab) 1 is roughly rolled by a rough rolling mill 3. Thereafter, when the sheet is wound around the sheet bar coiler 4 and is further discharged and passed through the joining device 5, the leading end is joined to the trailing end of the preceding material, and the tail end is joined to the leading end of the succeeding material.
After the joining, the leading end portion of the material (sheet bar) 1 is induction-heated by the high-frequency induction heating device 6 and finish-rolled by the finish-rolling machine 7. After the finish rolling, the temperature of the material (steel plate) 1 is measured by the finishing-side thermometer 8, and temperature information relating to securing the material quality of the product is managed by a calculator (not shown). (Embodiment 1) The high-frequency induction heating apparatus shown in FIG. 3 was installed in Embodiment 1 and not installed in the conventional example, but using a hot rolling line, the finish plate thickness was 1.1 mm, and the finish delivery temperature was Ar ₃ transformation. For products whose target range is set to 850 ° C or higher so that the temperature exceeds the point, Conventional Example 1 without sheet bar heating, Conventional Example 2 with sheet bar heating in a sheet bar coiler, and finishing with sheet bar heating Manufactured under three conditions of Example 1 performed on the side,
Table 1 shows the results of comparing the operation factors with each other. Table 1
The temperature shown in the graph is the measured value of the temperature at the tip of the material at each position of the hot rolling line.
It is indicated by point A in (a) to (c). The temperature at the tail end was almost equal to the temperature at the tip.

[0022]

[Table 1]

According to Table 1, in Conventional Example 1 in which sheet bar heating is not performed, the maximum temperature at which the slab can be set in a heating furnace is 1260 ° C.
Until heated. The temperature of the sheet bar after rough rolling is 1100 ° C, but the outermost and innermost windings (the end of the sheet bar) of the coiled material in the sheet bar coiler cool down. The target temperature could not be obtained because the side temperature dropped to 980 ° C and the finishing temperature reached 830 ° C, which was lower than the target of 850 ° C. Also, the slab heating temperature is 1260 ° C
Therefore, the heating cost was high and the refractory in the heating furnace deteriorated quickly, so the heating furnace had to be repaired once a week. Production capacity remained at 450 tons / hour.

In the conventional example 2 in which sheet bar heating is performed in the sheet bar coiler, even if the slab heating temperature is lowered to 1200 ° C.
Heating the leading and trailing ends of the coiled material in the sheet bar coiler and easing the water cooling of the unheated part in the finishing mill ensure the finishing target temperature target of 850 ° C over the entire longitudinal direction. Was. Since the slab heating temperature was lower than that of the conventional example 1, the heating furnace was repaired only once a month.
Production capacity increased to 600 tons / hour. However, the required heating cost at the end of the material inside the sheet bar coiler is as large as 90 ° C, which requires a large-scale heating device, which requires high equipment costs, and reduces the heating cost because the sheet bar heating energy is large. The effect was not enough.

On the other hand, in Embodiment 1 in which sheet bar heating is performed on the finishing inlet side, the finishing outlet temperature target can be secured over the entire longitudinal direction, and the slab heating temperature, heating furnace repair frequency,
The production capacity is the same level as that of the conventional example 2, and the required heating allowance at the end of the material is reduced to 60 ° C., and the equipment scale of the heating device can be reduced. / 3, and the heating cost was sufficiently reduced. (Embodiment 2) The high-frequency induction heating apparatus of FIG. 3 was not installed in the conventional example, but the hot-rolling line installed in the embodiment 2 was used, and the finishing side temperature was 1.1 mm and the finishing delivery temperature was Ar ₃ transformation point. For the products whose target range is below 820 ° C as follows, Conventional Example 3 without sheet bar heating, Conventional Example 4 with sheet bar heating in a sheet bar coiler, Sheet bar heating on the finishing side Manufactured under three conditions of Example 2 performed in
Table 2 shows the result of comparing the operation factors with each other. Table 2
The temperature shown in the graph is the measured value of the temperature at the tip of the material at each position of the hot rolling line.
It is indicated by point A in (a) to (c). The temperature at the tail end was almost equal to the temperature at the tip.

[0026]

[Table 2]

According to Table 2, in Conventional Example 3 in which sheet bar heating was not performed, the slab was heated to 1080 ° C. The sheet bar temperature after the rough rolling is 950 ° C, but the outermost and innermost windings (the end of the sheet bar) of the coiled material in the sheet bar coiler cool down. Side temperature is 87
The temperature drops to 0 ° C, and the finishing temperature reaches 800 ° C,
Although the temperature could be reduced to 0 ° C or less, the slab heating temperature was raised in anticipation of the temperature drop at the leading and trailing ends in the sheet bar coiler.
° C, which is relatively high, and if the speed is greatly accelerated by finish rolling, the finishing speed will exceed the Ar ₃ transformation point.
The production capacity was limited to 550 tons / hour, forced to mpm.

In the conventional example 4 in which sheet bar heating is performed in the sheet bar coiler, even if the slab heating temperature is lowered to 1000 ° C.
Since the leading end of the coiled material was heated in the sheet bar coiler, the finishing temperature of this portion was 800 ° C. The slab heating temperature can be lower than that of Conventional Example 3 and the top speed can be reduced to 12
Even when the pressure was increased to 50 mpm, the temperature on the finishing side of the stationary part could be maintained at 800 ° C, and the production capacity increased to 600 tons / hour. However, the required heating allowance at the end of the material inside the sheet bar coiler is as large as 60 ° C, requiring large-scale heating equipment and high equipment costs, and reducing heating costs due to large sheet bar heating energy. The effect was not enough.

On the other hand, in the second embodiment in which sheet bar heating is performed on the finishing inlet side, the finishing outlet temperature target can be secured, and the slab heating temperature, the top speed, and the production capacity are the same as those of the conventional example 4, In addition, the required heating allowance at the end of the material tip is 40
℃, the equipment scale of the heating device can be reduced, and the heating energy of the sheet bar is reduced to 2/3 of that of the conventional example 2, and the heating cost is sufficiently reduced. (Embodiment 3) The high-frequency induction heating device 6 of FIG.
The target range was set to 850 ° C or higher using a hot rolling line so that the finishing temperature was higher than the Ar ₃ transformation point with a finishing plate thickness of 0.8mm. Products were manufactured under three conditions: Conventional Example 5 in which sheet bar heating was not performed, Conventional Example 6 in which sheet bar heating was performed in the sheet bar coiler, and Example 3 in which sheet bar heating was performed on the finishing side.
Table 3 shows the result of comparing the operation factors with each other. Table 3
The temperature shown in the graph is the measured value of the temperature at the tip of the material at each position of the hot rolling line.
It is indicated by point A in (a) to (c). The temperature at the tail end was almost equal to the temperature at the tip.

[0030]

[Table 3]

According to Table 3, in the conventional example 5 in which sheet bar heating is not performed, the maximum temperature at which the slab can be set in the heating furnace is 1260 ° C.
Until heated. The temperature of the sheet bar after rough rolling is 1100 ° C, but the outermost and innermost windings (the end of the sheet bar) of the coiled material in the sheet bar coiler cool down. Since the side temperature dropped to 970 ° C and the finish side temperature reached 825 ° C, which was below the target of 850 ° C, the target material could not be obtained. The heating temperature of the slab is 1260
Due to the extremely high temperature, the heating cost was high, and the refractory in the heating furnace deteriorated quickly, requiring repair of the heating furnace once a week. Production capacity stayed at 420 ton / hour.

In Conventional Example 6 in which sheet bar heating is performed in the sheet bar coiler, even if the slab heating temperature is reduced to 1240 ° C.
Heating the leading and trailing ends of the coiled material in the sheet bar coiler and easing the water cooling of the unheated part in the finishing mill ensure the finishing target temperature target of 850 ° C over the entire longitudinal direction. Was. Since the slab heating temperature was lower than that of the conventional example 5, the heating furnace was repaired twice a month.
Production capacity increased to 470 ton / hour. However, the required heating allowance at the end of the material inside the sheet bar coiler is as large as 105 ° C, which requires a large-scale heating device, which requires high equipment costs, and reduces the heating cost due to the large energy required for heating the sheet bar. The effect was not enough.

On the other hand, in the third embodiment in which sheet bar heating is performed on the finishing inlet side, the finishing outlet temperature can be secured as desired over the entire longitudinal direction, and the slab heating temperature, heating furnace repair frequency, and production capacity are the same as those of the conventional example 6. In addition, the required heating allowance at the front and rear ends of the material is reduced to 70 ° C., and the equipment scale of the heating device can be reduced. Was sufficiently reduced. (Embodiment 4) The high-frequency induction heating apparatus 6 of FIG. 3 is not installed in the conventional example, but uses the hot-rolling line installed in Embodiment 4 and has a finish plate thickness of 0.8 mm and a finish delivery side temperature of Ar ₃ transformation. The products whose target range is 820 ° C or less so that the temperature is below the point, Conventional example 7 without sheet bar heating, Conventional example 8 with sheet bar heating in a sheet bar coiler, and sheet bar heating are finished. Manufactured under three conditions of Example 4 performed on the side,
Table 4 shows the results of comparing the operation factors with each other. Table 4
The temperature shown in the graph is the measured value of the temperature at the tip of the material at each position of the hot rolling line.
It is indicated by point A in (a) to (c). The temperature at the tail end was almost equal to the temperature at the tip.

[0034]

[Table 4]

As shown in Table 4, in Conventional Example 7 in which sheet bar heating was not performed, the slab was heated to 1100 ° C. The temperature of the sheet bar after rough rolling is 970 ° C, but the outermost and innermost coiled portions (the end portion of the sheet bar) of the coiled material in the sheet bar coiler cool down. Side temperature is 88
The temperature drops to 0 ° C, and the finishing temperature reaches 800 ° C,
Although the temperature could be reduced to 0 ° C or less, the slab heating temperature was raised in anticipation of the temperature drop at the end of the tail in the sheet bar coiler.
° C, which is relatively high, and when accelerated significantly in finish rolling, the finishing speed exceeds the Ar ₃ transformation point, so the top speed is increased to 1100.
It had to be reduced to mpm, and the production capacity stayed at 480 tons / hour.

In the conventional example 8 in which the sheet bar is heated in the sheet bar coiler, even if the slab heating temperature is lowered to 1000 ° C., the leading end of the coiled material is heated in the sheet bar coiler. The outlet temperature was 800 ° C. The slab heating temperature can be lower than that of the conventional example 7, and the top speed can be reduced to 13
Even when the pressure was increased to 00mpm, the finishing temperature in the steady part could be maintained at 800 ° C, and the production capacity increased to 520 ton / hour. However, the required heating allowance at the end of the material inside the sheet bar coiler is as large as 80 ° C, which requires a large-scale heating device, which requires high equipment costs, and reduces the heating cost because the sheet bar heating energy is large. The effect was not enough.

On the other hand, in the fourth embodiment in which sheet bar heating is performed on the finishing inlet side, the finishing outlet temperature can be secured as desired, and the slab heating temperature, top speed, and production capacity are the same as those of the conventional example 8.
And the required heating allowance at the end of the material is reduced to 60 ° C, and the equipment scale of the heating device can be reduced.
The heating energy of the sheet bar is 3/4 of that of the conventional example 8, and the heating cost is sufficiently reduced.

In the above embodiment, for comparison with the conventional example, the material portion to be heated by the sheet bar heating device (high-frequency induction heating device) on the entrance side of the finishing mill is formed by the outermost winding of the coiled material in the sheet bar coiler. Although the present invention is not limited to this, the present invention is not limited to this, and any portion of the material on the finishing side that is lower in temperature than other portions in the longitudinal direction of the material may be used. You can heat any part,
The entire part having a relatively low finish rolling speed may be heated. For example, when manufacturing a 0.8mm thick product, Ar
_In order to secure the finishing temperature at the transformation point or higher, the outermost winding portion, a portion deeper than the innermost winding portion, specifically, a portion about 20 to 30 m from the tail end is heated. Is good.

Further, in the above embodiment, the endless rolling using the sheet bar coiler was described. However, according to the present invention, in the endless rolling without using the sheet bar coiler, the portion where the temperature is reduced by the clamp of the joining device is heated. Thus, this temperature drop can be compensated. Further, in the above embodiment, the material for setting the finish output side temperature target based on the Ar ₃ transformation point was shown, but the present invention is also applicable to hot rolling of a material having no transformation point, for example, stainless steel. Applicable.

[0040]

As described above, according to the present invention, since the sheet bar is heated by the high-frequency induction heating device provided at an appropriate position in the line, the finishing temperature at the tail end portion of the sheet bar can be controlled to a desired temperature. The restrictions on slab heating temperature and rolling speed are greatly eased, ensuring the finishing temperature and material within the target range over the entire length of the product, enabling products to be manufactured with a high yield and greatly reducing the energy cost required for heating. It has a remarkable effect that it can be done.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.

2 (a) and 2 (b) show the temperature history in the longitudinal direction of the material from the winding of the sheet bar coiler to the finishing side.
(C) is a graph shown about the example of this invention.

FIG. 3 is a schematic diagram showing an example of a hot rolling line suitable for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Material (slab, sheet bar, steel plate) 2 Heating furnace 3 Rough rolling mill 4 Sheet bar coiler 5 Joining device 6 High frequency induction heating device 7 Finish rolling machine 8 Finishing thermometer 61 High frequency power supply 62 High frequency coil

Claims (7)

[Claims] A slab heated to a predetermined temperature is roughly rolled,
In the method of manufacturing a hot-rolled steel sheet in which the leading end of the roughly-rolled sheet bar is joined to the tail end of the preceding sheet bar, and finish-rolled to produce a hot-rolled steel sheet, the longitudinal direction of the sheet bar after joining and before finish rolling is determined. A method for producing a hot-rolled steel sheet, comprising heating at least a part of the entire width by a high-frequency induction heating device. 2. A slab heated to a predetermined temperature is roughly rolled,
After winding and unwinding the rough-rolled sheet bar, the leading end is joined to the tail end of the preceding sheet bar, and then subjected to finish rolling to produce a hot-rolled steel sheet. A method for producing a hot-rolled steel sheet, wherein at least a part of the sheet bar in the longitudinal direction is heated over the entire width by a high-frequency induction heating device before rolling. 3. The heating by the high-frequency induction heating device,
The method according to claim 1, wherein the finishing temperature of the heated portion is set to a target temperature. 4. A predetermined temperature for heating the slab is set such that a finish-side temperature at a central portion in a longitudinal direction of the coil is within a target temperature range, and an outermost winding and an innermost winding when the sheet bar is wound up. 3. A part including at least one of the turns is heated by a high-frequency induction heating device, and finish-rolled over the entire length of the coil with the finish-side temperature within a target temperature range.
The method described in. 5. A predetermined temperature for heating the slab is set so that a finish-side temperature at a central portion in a longitudinal direction of the coil is within a target temperature range, and an outermost winding and an innermost winding when the sheet bar is wound up. a portion including at least one winding is heated by high-frequency induction heating apparatus, method of claim 2, over coil entire length, to finish rolling finish delivery temperature as a temperature above Ar ₃ transformation point. 6. A predetermined temperature for heating the slab is set so that a finishing temperature at a central portion in a longitudinal direction of the coil is within a target temperature range, and an outermost winding and an innermost winding when the sheet bar is wound up. a portion including at least one winding is heated by high-frequency induction heating apparatus, method of claim 2, over coil entire length, to finish rolling finish delivery temperature as a temperature below the Ar ₃ transformation point. 7. The method according to claim 1, wherein the slab heating temperature is 1200 ° C. or less, and the thickness after finish rolling is 0.8 to 1.1 mm.