JP2003275805A - Method for hot-rolling high carbon steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot rolling method of high carbon steel by which a high carbon steel sheet having excellent quality is manufactured. <P>SOLUTION: The heating temperature of the whole in the longitudinal direction of a sheet bar 1 is decided on the basis of a speed pattern in finish rolling in order to prevent the crack on the sheet in the finish rolling by securing the temperature on the outlet side of a finishing mill for the sheet bar 1 of high carbon steel in a heating temperature deciding part 41. The heating temperatures in the tip part and the tail end part of the sheet bar 1 of the heating temperatures decided by the heating temperature deciding part 41 are corrected on the basis of the temperature in the tip part of the sheet bar 1 which is measured a thermometer 5 and these corrected temperatures are set to a sheet bar heater 2 by a heating temperature correcting part 42. Heating in accordance with the set heating temperature is performed to the sheet bar 1 while tracking the advancing position of the sheet bar 1 by the sheet bar heater 2. In this way, the crack of the sheet in the finish rolling of the sheet bar 1 of the high carbon steel is prevented. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method for high carbon steel, and more particularly to a heating device (hereinafter referred to as a sheet bar heater) in which a high carbon steel sheet bar is installed on the inlet side of a finishing rolling mill. The present invention relates to a hot rolling method of heating and finish rolling. The high carbon steel referred to in this specification is JIS G
It refers to those specified in 3311, and particularly refers to steel containing 0.3 mass% or more of C.

[0002]

2. Description of the Related Art A hot rolling line is generally composed of a heating furnace 11, a plurality of rough rolling mills 12, a plurality of finish rolling mills 3, a cooling zone 16, a winding device 17, etc., as shown in FIG. In recent years, it is known that the seat bar heater 2 is installed between the rough rolling mill 12 and the finish rolling mill 3. Here, measuring roll 7 for tracking
May be installed.

The hot rolling in which the tip of the sheet bar-shaped material to be rolled is bitten by the finish rolling mill 3 and rolled, and the tail end is rolled is repeated intermittently, in particular, batch rolling and I am calling it. On the other hand, in recent years, for example, patent 3103
As disclosed in Japanese Patent Publication No. 260, a hot rolling line having an equipment structure as shown in FIG. 16 has also appeared. This hot rolling line runs between the rough rolling mill 12 and the finish rolling mill 3 at the most downstream side in the conveying direction of the material to be rolled, for example, while following the movement of the material to be rolled, Of the trailing end of the rolled material and the trailing end of the rolled material (hereinafter,
(Referred to simply as a joining device) 21 is installed, and cutting is performed between the finish rolling mill 3 and the coiler (winding device) 17 to cut the preceding rolled material and the following rolled material and wind them separately. A device (strip shear) 24 is installed.

Between the rough rolling mill 12 and the finish rolling mill 3, the tail end of the preceding sheet bar-shaped material to be rolled and the tip end of the following sheet bar-shaped material to be rolled are joined and continuously finish rolled. This is called as endless rolling. This hot rolling line capable of endless rolling (referred to as a hot endless rolling line) is, as shown in FIG. 16, for joining the tail end of the preceding rolled material and the leading end of the following rolled material, In addition to the joining device 21, a coil box 20, a crop shape meter 13, and a joining crop shear 22 are provided.

Further, in addition to the deburring device 23 and the sheet bar heater 2, an edge heater and a joint cooling device (not shown) may be installed between the joining device 21 and the finish rolling mill 3, and further cutting is performed before the coiler 17. Before the device 24,
The high-speed plate passing device 51 and the like may be installed as appropriate. here,
The joining device 21 may be of the induction heating type disclosed in Japanese Patent Laid-Open No. 62-234679, or of the laser type disclosed in International Publication No. WO94 / 16838.

The high-speed plate passing device 51 is referred to as Japanese Patent Laid-Open No. 7-124.
As disclosed in Japanese Patent No. 624, a device for stabilizing strip passing, which is suitable for use in a thin strip-shaped rolled material having a thickness of less than 2 mm after finish rolling, for example, It prevents the coiler 17 from curling weakly immediately after being cut and being clogged between the auxiliary equipment of the coiler 17 and being unable to be wound. The material to be rolled in the form of a thin strip having a small thickness after finish rolling is generally called because it has a high transport speed. The principle is to suck the thin strip-shaped rolled material being conveyed to the negative pressure portion generated by the air jet and to straighten it along the guide to prevent it from rolling.

In FIG. 16, 7 is a measuring roll and 9 is a cropper. Conventionally, as a method of heating a sheet bar using a sheet bar heater, for example, a method of heating a sheet bar and performing finish rolling at a constant speed has been proposed, as described in JP-A-9-225517. There is. Further, as described in JP-A-10-230313, there has been proposed a method of keeping the exit side temperature of the finish rolling mill constant in the longitudinal direction of the steel strip after rolling.

Regarding the sheet bar joining of high carbon steel and the endless rolling, JP-A-2000-27160 is used.
No. 5 is disclosed. Japanese Patent Laid-Open No. 11-169910 discloses the compensation heating of the local low temperature portion of the inner and outer windings of the coil box, which is a problem in endless rolling.

[0009]

By the way, in the case of batch rolling, the speed in ordinary finish rolling of a sheet bar is
As described below, it changes depending on the positional relationship between the sheet bar and the finish rolling mill. That is, the speed is suppressed from the biting of the tip of the sheet bar to the stand of the finishing rolling mill until it is wound on the winding device, and then the sheet bar is accelerated to roll at a predetermined maximum speed, and the tail of the sheet bar is When the end leaves the finishing mill, the rolling speed is slowed down again.

Here, the reason why the rolling speed at the leading end and the tail end of the sheet bar is slow is as follows. Tip: When turning on each stand of the finishing mill one after another, if the speed is high, slip may occur when the tip of the sheet bar is caught in the roll, or after it is caught, it may appear on the exit side of each stand. When it comes out, it may bounce up or warp and hit the side guide of the next stand, making it impossible to continue rolling.

Tail end: When winding is completed, the coil is taken out from the winding device in a stopped state. If the tail end is fast,
When it leaves the finishing rolling mill group, it jumps up and pierces the cooling nozzle in the cooling zone, damaging the nozzle and its header. Therefore, deceleration is started while the tail end is still inside the finishing mill. After the tip winding device is turned on, which stand is turned off to start deceleration is appropriately determined according to the level of the intermediate speed before passing through the tail finishing rolling mill. Incidentally, in the middle part, in order to increase the production efficiency, the rolling is accelerated to the above-mentioned maximum speed.

By the way, when the sheet bar is heated so as to obtain a uniform temperature distribution in its longitudinal direction,
In the subsequent descaling or finish rolling, the finishing mill passing speed (that is, finishing mill passing time) will be different between the tail end part and the central part of the material due to the effect of acceleration and deceleration of the rolling speed as described above. However, there is an inconvenience that the temperature on the delivery side of the finish rolling mill is not constant. This affects the subsequent control of the winding temperature and becomes a factor of making the material properties of the material in the longitudinal direction non-uniform.

In this respect, if the method of keeping the finish rolling temperature constant as described in Japanese Patent Laid-Open No. 9-225517, the material properties in the longitudinal direction of the material become uniform, which is a temporary solution. , There are the following inconveniences. It is an inconvenience that the production efficiency is limited because the acceleration is not performed. Therefore, even in the case of accelerated rolling, the temperature on the exit side of the finishing rolling mill is kept constant in the longitudinal direction.
Although a method as described in Japanese Patent No. 230313 has been proposed, the electric power consumed for heating the sheet bar originally reaches a considerable amount, and operating conditions such as fluctuations in the in-furnace time of the slab in the heating furnace. In some cases, even if the slab does not need to be heated by the sheet bar heater too much, it may be heated unnecessarily in the heating furnace for a long time.

Therefore, in view of the above points, the Applicant, in order to make the material of the seat bar uniform in the longitudinal direction and to optimize the heating of the seat bar, the applicant has designed the tip and tail of the seat bar. A method of determining the heating temperature of the end portion based on a predetermined finish rolling speed pattern of the sheet bar was devised, and an experiment of the method was conducted. However, in hot rolling of high carbon steel, it was later found out that the above method was insufficient, and there was room for improvement.

This is because even when the material to be rolled is a sheet bar of high carbon steel, the surface layer portion becomes martensite and the hardness is extremely increased due to the cooling during hot rolling even by the above method. The high carbon steel having a high hardness in the surface layer portion may cause plate cracking in finish rolling, which is a disadvantage. Plate cracking is likely to occur locally at the edge of the plate width in a hump-like manner. As a result, the product width and surface quality of the product become defective.

In endless rolling, it has been found that the inward and outer winding of the sheet bar wound in the coil box becomes low in temperature, so that the inconvenience easily occurs in the same portion. Then, in view of the above-mentioned point, an object of the present invention is to provide a hot-rolling method of high carbon steel which can manufacture a high quality high carbon steel plate.

[0017]

In order to solve the above problems and to achieve the object of the present invention, the invention described in claim 1 is
A high-carbon steel sheet bar is a hot-rolling method for high-carbon steel, which is heated by a sheet bar heater installed on the inlet side of a finishing rolling mill, and is finish-rolled by the finishing rolling machine, which is a predetermined sheet bar. The target temperature at the conveyance position is previously determined, and the compensation heating of the sheet bar is performed so as to be equal to or higher than the target temperature.

According to a second aspect of the present invention, in the hot rolling method for high carbon steel according to the first aspect, the target temperature at the predetermined conveying position is the temperature of the sheet bar on the inlet side of the finish rolling mill. It is characterized by being. A third aspect of the present invention is the hot rolling method for high carbon steel according to the first aspect or the second aspect, wherein the compensation heating of the high carbon steel is measured at the entrance side of the seat bar heater. It is characterized in that the correction is made based on the actual temperature of the tip portion.

According to a fourth aspect of the present invention, there is provided a seat bar heater in which a tail end of a preceding sheet bar and a tip of a following sheet bar of high carbon steel are joined, and the joined sheet bar is installed on the entrance side of the finishing rolling mill. After heating, finish rolling with the finish rolling machine, cutting, hot rolling method of high carbon steel to be wound, the target temperature at a predetermined transport position of the joined sheet bar is predetermined, Compensation heating of the seat bar is performed so that the temperature becomes equal to or higher than a target temperature.

As described above, according to the present invention, in the hot rolling of the high carbon steel sheet bar, the sheet bar is heated to a temperature higher than the temperature sufficient to prevent the plate cracking. Can manufacture steel sheets.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) A schematic configuration of a part of a hot rolling line to which the first embodiment of the present invention is applied will be described with reference to FIG. This hot rolling line, as shown in FIG.
A rough rolling machine (not shown) for roughly rolling a slab obtained by continuous casting to obtain a sheet bar 1 of high carbon steel, and a sheet for heating the sheet bar 1 roughly rolled by this rough rolling machine A bar heater (heating device) 2 and a finish rolling machine 3 for finish rolling the sheet bar 1 heated by the sheet bar heater 2.
And a heating temperature generation device 4 for generating a heating temperature when the sheet bar heater 2 heats the sheet bar 1 as described below in order to secure the temperature of the sheet bar 1 on the exit side of the finish rolling mill.
And a thermometer 5 arranged on the entrance side of the seat bar heater 2 to measure the temperature (actual temperature) of the tip of the seat bar 1 when passing through the tip.

The heating temperature generator 4 determines the heating temperature of the entire sheet bar 1 heated by the sheet bar heater 2 in order to secure the temperature of the sheet bar 1 on the exit side of the finish rolling mill. The heating temperature of the front end portion and the tail end portion of the seat bar 1 is corrected among the heating temperatures determined in advance by the heating temperature determining unit 41 based on the temperature measured by the portion 41 and the thermometer 5, and the corrected final temperature is obtained. And a heating temperature correction unit 42 that sets a different heating temperature to the seat bar heater 2.

Next, an outline of the operation of the first embodiment configured as described above will be described with reference to FIG. Now, when the sheet bar 1 rolled by a rough rolling machine (not shown) is conveyed to a position before the sheet bar heater 2, at this time, the heating temperature determining unit 41 determines the heating temperature of the entire longitudinal direction of the sheet bar 1 as described later. Is determined in advance. When the tip of the seat bar 1 reaches directly under the thermometer 5, the thermometer 5 measures the temperature of the tip and supplies the measured temperature to the heating temperature correction unit 42.

The heating temperature correction unit 42 corrects the heating temperature of the leading end portion and the tail end portion of the seat bar 1 among the heating temperatures determined by the heating temperature determination unit 41 based on the measured temperature, and this correction is performed. The heated temperature is set to the seat bar heater 2
Set to. The seat bar heater 2 heats the seat bar 1 according to the set heating temperature while tracking the traveling position of the seat bar 1. The tracking is preferably performed by the measuring roll 7 shown in FIG. 15, for example. The measuring roll 7 is a mechanism that is pressed against the seat bar 1 to rotate, and is produced so as to generate a pulse each time it rotates a predetermined angle (for example, 0.025 mm when converted to the circumferential length). This is done by counting the pulses emitted by the measuring roll with a controller. After that, the sheet bar 1 is rolled into a predetermined size by the finish rolling mill 3.

Next, the method of determining the heating temperature by the heating temperature determining unit 41 will be described in detail with reference to FIGS. First, the heating temperature determination unit 41 takes in a finish rolling speed pattern as shown in FIG. 2, which is a result of calculation of the finish rolling schedule, from another determination unit (not shown), and based on this, a representative of the sheet bar (material) 1. The passing time of the finish rolling mill 3 at the point is obtained as shown in FIG. Here, the representative points are the positions X1 and X2 of the seat bar 1 existing on the inlet side and the outlet side of the finish rolling mill 3 at respective times of the acceleration start, acceleration completion, deceleration start, and deceleration completion of the seat bar 1. (See FIG. 5).

Subsequently, the heating temperature determining unit 41 indirectly multiplies the obtained passage time of the seat bar 1 by a predetermined constant to determine the temperature decrease amount at each point from the front end to the rear end of the seat bar 1. Is determined as the heating temperature, and the height of the figure drawn by connecting the points is stored in a memory (not shown) as a virtual heating temperature over the entire length of the sheet bar 1. FIG. 4 shows the virtual heating temperature of the sheet bar 1 obtained in this way. The temperature of the finish rolling mill 3 at a long passage time is large because the temperature drop is large. Since the temperature drop is small, the heating temperature is low.

The constants used above can be easily obtained in advance by temperature calculation using a difference method usually used for off-line analysis and the like, and can be determined for each material, each finished plate thickness or sheet bar. It is preferable to determine the thickness for each layer. As a result of the above method,
The temperature of the sheet bar (rolled material) 1 during finish rolling or on the exit side of the finish rolling mill can be made substantially uniform over the entire length. However, in the case where the sheet bar 1 is a high carbon steel, as described above, the surface layer portion becomes martensite and the hardness is extremely increased by the cooling during the hot rolling, so that the plate crack may occur in the finish rolling. Therefore, the following measures will be taken.

That is, for the entire length of the material to be rolled of high carbon steel, a sufficiently high temperature that does not cause plate cracking is set in advance for each unit of the high carbon steel sheet bar, and the temperature is insufficient for that. The idea is to compensate and heat the minutes. This high carbon steel sheet bar is set for each unit (for each material) and has a sufficiently high temperature that does not cause plate cracking. In addition to the material according to each steel type or other classification specified in JISG3311, the finish plate It is preferable to determine the thickness for each layer or the sheet bar thickness for each layer.

Next, a method of correcting the heating temperature at the leading end portion and the tail end portion of the seat bar by the heating temperature correction unit 42 will be described in detail with reference to FIGS. 6 to 8. When the thermometer 5 measures the temperature of the tip portion of the seat bar 1, the heating temperature correction unit 42 compares the measured temperature with the reference temperature (target temperature) at the thermometer installation position that is predicted or set in advance. The difference is obtained, and the final heating temperature from the front end portion to the tail end portion of the seat bar 1 is calculated based on the obtained temperature difference.

That is, when the actual temperature obtained by measuring the temperature of the tip portion of the seat bar 1 by the thermometer 5 is higher than the reference temperature, the heating temperature is reduced or corrected so as not to be heated. If the actual temperature is lower than the reference temperature, the heating temperature is increased. here,
The reference temperature of the seat bar will be described. In order to prevent sheet cracking of high carbon steel sheet bars during finish rolling, the temperature of the sheet bar during finish rolling should be set to a sufficiently high temperature so that sheet cracking does not occur. Where it is preferable to keep it constant over the entire length of the bar, it is difficult to keep the finish rolling temperature strictly constant for each stand individually over the entire length of the sheet bar.

Therefore, the following fact known empirically, that is, the temperature at the exit side of the finish rolling mill at the tip of the sheet bar is determined for each high carbon steel sheet bar.
The fact that plate cracking does not occur if the allowable lower limit value above which plate cracking does not occur is used. That is, it is empirically known that the sheet bar tip temperature at the entry side of the finishing rolling mill, which is necessary to keep the temperature at the exit side of the finishing rolling mill at the tip of the sheet bar above the allowable lower limit value that does not cause plate cracking, Is the seat bar reference temperature. That is, only when the sheet bar tip temperature on the entry side of the finish rolling mill is lower than this reference temperature, the sheet bar temperature on the exit side of the finish rolling mill may fall below the permissible lower limit value determined by the metallurgy. It suffices to heat certain tip and tail portions to a temperature above that temperature.

Further, the reference temperature of the seat bar is set separately for the tip end and the tail end, and the reference temperature of the tail end of the seat bar is set to be slightly smaller than the reference temperature of the tip end (for example, 10). It is preferable that the temperature is set to a low value (about ℃). Because the tail end of the sheet bar is slightly lower than the tip at the entry side of the finish rolling mill, the passing time of the finish rolling mill is slightly shorter than the tip, so the sheet bar at the exit side of the finish rolling mill is This is because it is empirically known that it is relatively easy to secure the temperature.

A method of determining the heating temperature of the front end portion and the tail end portion of the seat bar 1 from the reference temperature will be described with reference to FIGS. 6, 7 and 8 in order. As shown in FIG. 6, based on the sheet bar heating pattern previously obtained from the finish rolling speed pattern and the reference temperature, the final heating temperature of the tip and tail ends is determined so as to exceed the reference temperature. The heating temperature of the tip and tail end of the sheet bar is the temperature corresponding to the height of the portion drawn by enclosing the tip reference temperature and tail reference temperature or higher, and the length of the enclosed portion. Is heated in the region in the longitudinal direction of the seat bar (FIG. 6).
(See (B)).

FIG. 7 is an explanatory view of a method of correcting the heating temperature when the temperature measured by the thermometer 5 is lower than the reference temperatures of the tip end portion and the tail end portion of the seat bar 1. For example, thermometer 5
Is 970 ° C., the reference temperature of the tip of the seat bar 1 is 1000 ° C., and the reference temperature of the tail end of the seat bar 1 is 9 ° C.
This is the case at 90 ° C. In this case, the correction value a on the leading end side of the seat bar 1 is a = (970-1000) =-30.
C., and the tip side needs to be heated by 30 degrees higher, and the correction value b on the tail side is b = (970-990).
= −20 ° C., and it is necessary to heat the tail end side by 20 ° C. higher.

Therefore, the correction reference temperature shown by the solid line in consideration of the 30 ° C. is obtained from the tip reference temperature shown by the one-dot chain line in FIG. 7A, and the heating temperature corresponding to the region above the correction reference temperature is obtained. The final heating temperature of the tip is as shown in FIG. Similarly, a correction reference temperature shown by a solid line in consideration of the 20 ° C. portion is obtained from the tail end reference temperature shown by the one-dot chain line in FIG. 7A, and the heating temperature corresponding to the upper side of the correction reference temperature is shown in FIG. The final heating temperature of the tail end is as shown in (B).

Here, in the case of FIG. 7, the correction value a = -3.
0 ° C., correction value = −20 ° C., and based on this, heating compensation of 30 ° C. for the tip end side of the sheet bar 1 and 20 ° C. for its tail end side was performed. However, further heating compensation, that is, heating compensation such that the temperature of the seat bar 1 exceeds the reference temperature may be performed. FIG. 8 is an explanatory diagram of a method of correcting the heating temperature when the temperature measured by the thermometer 5 is higher than the reference temperatures of the tip end portion and the tail end portion of the seat bar 1.

For example, the measured temperature of the thermometer 5 is 1030
C., the reference temperature at the tip of the seat bar 1 is 1000.degree. C., and the reference temperature at the tail of the seat bar 1 is 990.degree. In this case, the correction value a on the leading end side is a = (1
030-1000) = 30 ° C, 30 ° C on the tip side
It may be heated by a lower amount, and the correction value b on the tail end side is b =
(1030-990) = 40 ° C., 40 on the tail end side
It may be heated at a low temperature of ℃.

Therefore, the correction reference temperature shown by the solid line in consideration of the temperature of 30 ° C. is obtained from the tip reference temperature shown by the one-dot chain line in FIG. 8A, and the heating temperature corresponding to the size above this correction reference temperature. Is the final heating temperature on the tip side as shown in FIG. Similarly, the correction reference temperature indicated by the solid line in consideration of the 40 ° C. portion is obtained from the tail end reference temperature indicated by the one-dot chain line in FIG. 8A, and the heating temperature corresponding to the upper side of the correction reference temperature is calculated in the same figure. The final heating temperature on the tail end side is set as shown in (B), but in this case, the heating temperature on the tail end side becomes zero and heating is not performed.

In the above description, the reference temperatures of the tip end and the tail end of the seat bar 1 are made different, but if the reference temperatures are made different, the correction value a is made at the tip end and the tail end. , B can be changed, and the final heating temperature according to the tip end and the tail end can be obtained, which is preferable. But,
Even if both reference temperatures are the same, there is no particular problem. As described above, in the method according to the first embodiment, the heating temperature of the tip end portion and the tail end portion of the sheet bar 1 to be heated by the sheet bar heater 2 is set to a predetermined finish rolling speed of the sheet bar 1. Based on the pattern, the determined heating temperature is corrected based on the temperature measured by the thermometer 5, and the corrected heating temperature is set in the seat bar heater 2.

Therefore, since it is possible to prevent the temperature of the leading end and the tail end of the sheet bar having a slow passing speed of the finish rolling mill 3 from being lowered, it is possible to prevent the plate cracking of the entire length of the high carbon steel sheet bar. Further, since the heating temperature is corrected based on the temperature measured by the thermometer 5, it is possible to suppress variations in the temperature reached by heating among the individual sheet bars and make them uniform. Incidentally, in the example described above, by keeping the finish rolling mill inlet side temperature above a predetermined allowable lower limit value, the temperature of the sheet bar during finish rolling is set to a sufficiently high temperature that does not cause plate cracking. Although the alternative method of individually fixing the length of the sheet bar by the stand has been described, the present invention is not limited to this, and the exit side temperature of the finishing rolling mill may be used instead. (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

The hot rolling line applied to this second embodiment, as shown in FIG. 9, is a rough rolling machine 12 for roughly rolling a slab to obtain a sheet bar 1 made of high carbon steel,
A coil box (winding and rewinding device) 20 for winding and rewinding the sheet bar 1, a crop shape meter 13 for detecting the shape of the crop portion at the leading and trailing ends of the sheet bar 1, and a conveyance position of the sheet bar 1 are sometimes set. It is provided with a measuring roll 7 for momentary detection, a joining cropper 22, and a joining device 21 for joining the leading end of the sheet bar rewound by the coil box 20 and the tail end of the preceding sheet bar.

Further, this hot rolling line is heated by a deburring device 23, a sheet bar heater (heating device) 2 for heating the sheet bar 1 as described later, a cropper 9 and a sheet bar heater 2. A finish rolling mill 3 for finish rolling the sheet bar 1, a cooling zone 16 for cooling the sheet bar 1 finish rolled by the finish rolling mill 3, and a strip shear 2
4, a winding device 17 for winding the cooled sheet bar 1, and a high-speed plate passing device 51.

Further, in this hot rolling line, a computer (not shown) for determining a heating pattern for the sheet bar heater 2 to control the heating of the sheet bar 1 in a certain pattern according to its longitudinal position, A control device 14 for controlling heating of the seat bar heater 2 so that the heating pattern is determined by the computer, and a coil box 20.
Between the seat bar 1 and the seat bar heater 2
The thermometer 5 for measuring the temperature before heating in the longitudinal direction and supplying the measured temperature to the control device 14.

In the second embodiment, the coil box 2 is used in the hot rolling line having the structure shown in FIG.
The thermometer 5 installed between 0 and the seat bar heater 2
The temperature of the seat bar 1 is measured in the longitudinal direction, a local change in the measured temperature is captured, and particularly the locally low temperature portions of the inner winding portion and the outer winding portion when wound by the coil box 20, It is characterized by the point that compensation heating is performed. Of course, the skid mark portion or the like formed on the material to be rolled during heating in a heating furnace (not shown) may be compensated and heated.

Here, the coil box 20 is originally
It serves as a timing buffer for endless rolling, that is, for joining the sheet bars together.
If the coil bar 20 holds the seat bar 1 in a wound state for a certain period of time, the temperature drop of the seat bar can be suppressed considerably and the temperature lowering speed can be reduced as compared with the case where the seat bar 1 is not wound. From this, when the sheet bars to be unwound in order in order to catch up with each other and join the sheet bars need to wait for a certain time in timing, the coil bars 20 wind the sheet bars. Try to hold it for some time.

However, even if the sheet bar 1 is wound up by the coil box 20, the state shown in FIG.
As shown in, the inner and outer winding portions of the coiled sheet bar 1 are likely to locally have a low temperature. Therefore, as described above, the temperature of the material to be rolled in the form of a sheet bar is measured in the longitudinal direction by the thermometer 5, the local change in the measured temperature is captured, and the inner winding portion when wound by the coil box 20 is taken. Also, the locally low temperature part of the outer winding part is compensated and heated.

Next, an outline of the operation of the hot rolling line having the above structure will be described with reference to FIG. The coil box 20 winds up the sheet bar 1 rolled by the rough rolling machine 12 and then rewinds it. The shape of the rewound sheet bar coil 1 is detected by a crop shape meter 13. When the sheet bar coil 1 is the leading one, the tail end is cropped, and when the sheet bar coil 1 is the trailing one. The crop at the tip is cut by the joining cropper 22.

The joining device 21 joins the leading end portion of the succeeding sheet bar 1 whose tip crop is cut by the cropper 22 and the tail end portion of the preceding seat bar 1. The thermometer 5 measures the temperature of the conveyed sheet bar 1 in the longitudinal direction, and the measured temperature is supplied to the control device 14. Here, as described above, the seat bar 1 includes the coil box 20.
It is temporarily held in the state of being wound up, and then rewound to be unfolded and conveyed along with finish rolling. The temperature in the longitudinal direction of the seat bar 1 (temperature before heating by the seat bar heater 2) when unfolded and conveyed is, for example, as shown in FIG.
As shown in (A). Here, this figure shows the temperature distribution in the longitudinal direction of the intermediate product among a plurality of continuous sheet bar-shaped materials to be subjected to a group of endless rolling, and shows the case where the finishing rolling speed is constant.

Based on the measured temperature, the control device 14 determines the boundary between the inner winding portion and the outer winding portion when the sheet bar 1 is wound by the coil box 20 and the other stationary portion, and The heating temperature is set to the seat bar heater 2 so that the locally low temperature portions near the front end and the tail end from the determined boundary are heated compensatively.
The sheet bar heater 2 tracks the conveyance position of the sheet bar 1 on the line as in the first embodiment,
The seat bar 1 is heated based on the heating temperature set as described above.

The sheet bar 1 thus heated by the sheet bar heater 2 is cut to a predetermined length by the cropper 9 at the crop portion, and then the finish rolling mill 3 is used.
It is finish-rolled by, is cooled in the cooling zone 16, and is further wound by the winding device 17. Here, specific methods of the above-described boundary determination, tracking, and heating control are as described below.

First, the thermometer 5 measures the temperature in the longitudinal direction of the seat bar 1 at a constant pitch (for example, 1 mm pitch), and supplies each measured temperature to the controller 14. Next, based on the respective measured temperatures of the thermometer 5, connecting the respective measured temperatures with a straight line to obtain the temperature gradient (temperature gradient) at each point in the longitudinal direction of the seat bar 1, for example, FIG. As shown. FIG. 11B is an enlarged view within the circle of FIG. The obtained change in the absolute value of the temperature gradient in the longitudinal direction of the seat bar 1 becomes a polygonal line as shown in FIG.

Therefore, the polygonal line is examined from the upstream side to the downstream side in the conveying direction of the sheet bar 1, and the position corresponding to the point immediately downstream where the polygonal line intersects with the threshold value is located in the coil box 20. It is determined to be the boundary between the inner winding portion and the outer winding portion when wound in step (4) and the other stationary portion (see FIG. 12). Note that, here, for example, a smoothing process is performed as appropriate, in which the temperature gradient at a certain point is the center and the average value of the three points of the temperature gradient and the temperature gradients before and after that are represented as the temperature gradient at the certain point. You can

In addition, the polygonal line in FIG.
Looking from the downstream side to the upstream side of the sheet bar 1 in the transport direction, the position corresponding to the point on the upstream side where the polygonal line intersects the threshold value is located at the inner winding portion and the outer portion when wound by the coil box 20. You may make it determine with the boundary of a winding part and a stationary part other than that. In this way, the control device 1
When the above-mentioned boundary is determined by 4, the downstream side (the outer winding portion side when winding the coil box: the sheet bar tip side) in the sheet bar conveying direction and the upstream side (the winding of the coil box) from the boundary are determined. The control device 14 controls the seat bar heater 2 so that the seat bar heater 2 heats the inner winding part side: the tail end side of the seat bar (FIG. 13).
(See (B)).

At this time, with respect to the sheet-bar-shaped material to be rolled of high carbon steel, a temperature sufficiently high so as not to cause plate cracking is set in advance for each unit of the material to be rolled of high carbon steel. On the other hand, compensate for the insufficient temperature. Although the thermometer 5 is separated from the seat bar heater 2 by a certain distance, the control for accurately heating the portion corresponding to the outer winding portion or the inner winding portion when winding the coil box 20 is a major measure. This is performed by tracking the change in the position of the sheet bar 1 due to the conveyance by a tracking means such as a ring roll 7 every moment.

For example, taking the case where the measuring roll 7 is used as the tracking means, the tracking is performed as follows. That is, when the distance from the thermometer 5 to the seat bar heater 2 is measured in advance and stored as a constant in the control device 14 and the control device 14 determines the above boundary, the measuring roll is determined from the timing of the determination. Start counting pulses from 7. next,
When counting the pulses corresponding to the distance to the seat bar heater 2, the control device 14 recognizes that the boundary has reached the position of the seat bar heater 2 (correctly, the seat bar heater inlet position).

When the controller 14 recognizes that the boundary has reached the position of the seat bar heater 2, the coil box 20
The seat bar heater 2 performs compensating heating so that the portion corresponding to the outer winding portion or the inner winding portion at the time of winding is at a temperature on the extension line of the heating temperature pattern of the other steady portion (Fig. 13 (B) (C)). Therefore, the control device 14 controls the seat bar heater 2 so as to reliably perform the compensation heating.

As for the first and second embodiments described above, as the heating method of the seat bar heater 2, various methods such as induction heating and burner can be applied. In order to perform the localized compensation heating of the low-temperature portion as described above, it is necessary to have a mechanism in which the momentary energy input to the seat bar can be temporarily increased or decreased and easily variably controlled.
For example, in the induction heating method, the coil voltage and coil current can be variably controlled, and the setting values of coil voltage and coil current can be set in the calculator (not shown) for each sheet bar with different thickness and width. Prepare a calculation program for setting.

Specifically, in the case of the induction heating method, the calculation program is, specifically, an equivalent circuit theoretical model, a semi-empirical formula, a table using the thickness and width of the sheet bar as a search key, or a combination thereof. Any of these, or any other type, will not hinder the implementation of the present invention. (Example) A high carbon steel having the composition (mass%) shown in Table 1 was hot-rolled according to the conventional example and the first and second embodiments described above so as to satisfy the conditions shown in Table 2. As a result, plate cracking occurred in the conventional example, but none of the plates according to the first and second embodiments did.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

As described above, according to the present invention,
In the hot rolling of the high carbon steel sheet bar, since heating is performed at a temperature higher than or equal to a temperature that does not cause plate cracking, it is possible to manufacture a high carbon steel plate of good quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a hot rolling line to which a first embodiment of a method of the present invention is applied.

FIG. 2 is a diagram showing an example of a finish rolling speed pattern.

FIG. 3 is a diagram showing an example of a passage time of a finish bar of a sheet bar.

FIG. 4 is an explanatory diagram for obtaining a heating temperature of a seat bar.

FIG. 5 is an explanatory diagram for explaining representative points.

FIG. 6 is a diagram showing a method of determining a heating temperature from a reference temperature.

FIG. 7 is an explanatory diagram illustrating a method of correcting the heating temperature when the temperature measured by the thermometer is lower than the reference temperature of the leading and trailing ends of the seat bar.

FIG. 8 is an explanatory diagram illustrating a method of correcting the heating temperature when the temperature measured by the thermometer is higher than the reference temperature of the leading and trailing ends of the seat bar.

FIG. 9 is a diagram for explaining the overall outline of a hot rolling line to which the second embodiment of the method of the present invention is applied.

FIG. 10 is a diagram showing how local temperatures of inner and outer windings of a coil box decrease.

FIG. 11 is a diagram schematically showing a method of determining a boundary between a local temperature lowering portion of the inner and outer windings of the coil box and a portion not so.

FIG. 12 is a diagram schematically showing a method for determining a boundary between a local temperature lowering portion of inner and outer windings of a coil box and a portion other than the local temperature lowering portion.

FIG. 13 is a diagram illustrating a heating method using a seat bar heater according to a second embodiment of the present invention.

FIG. 14 is a diagram for explaining an overall outline of a conventional hot rolling line.

FIG. 15 is a diagram for explaining the operation and mechanism of the measuring roll.

FIG. 16 is a diagram for explaining an overall outline of another conventional hot rolling line.

[Explanation of symbols]

1 High carbon steel sheet bar 2 seat bar heater 3 finish rolling mill 4 Heating temperature generator 5 thermometer 7 Majoring roll 9 Cropshire 12 rough rolling mill 13 Crop shape meter 14 Control device 16 cooling zones 17 Winding device 20 coil box 21 joining device 22 Crop shear for joining 23 Deburring device 24 Cutting device (strip shear) 41 Heating temperature determination unit 42 Heating temperature correction unit

Claims (4)

[Claims] 1. A hot-rolling method for high-carbon steel, comprising heating a high-carbon steel sheet bar with a sheet bar heater installed on the inlet side of a finish rolling mill, and then finish rolling with the finish rolling mill. A hot rolling method for high carbon steel, characterized in that a target temperature at a predetermined conveyance position of the sheet bar is predetermined and the sheet bar is subjected to compensation heating so as to be equal to or higher than the target temperature. 2. The hot rolling method for high carbon steel according to claim 1, wherein the target temperature at the predetermined conveying position is a temperature at the entrance side of the finish rolling mill for the sheet bar. 3. The compensation heating of the high carbon steel is corrected on the basis of the actual temperature of the tip end portion of the seat bar measured on the entrance side of the seat bar heater. 2. The method for hot rolling high carbon steel according to 2. 4. The tail end of the preceding sheet bar and the tip of the following sheet bar of high carbon steel are joined, and the joined sheet bar is heated by a sheet bar heater installed on the inlet side of the finishing rolling mill, and then the finish rolling is performed. Finishing rolling with a machine, cutting, hot rolling method of high carbon steel to be wound up, a target temperature at a predetermined conveying position of the joined sheet bars is previously determined, and the target temperature is equal to or higher than the target temperature. A hot rolling method for high carbon steel, characterized in that compensation heating of the sheet bar is performed.