JPH02268904A - Manufacture of hot rolled steel sheet by line division - Google Patents

Abstract

PURPOSE:To execute rolling of an extra thin hot rolled steel sheet with high efficiency and to suppress the generation of oxide scale by coiling immediately a hot rolled steel sheet coming out of a final stand, after allowing it to pass through a series of measuring machine group, and subsequently, carrying its coil as it is to another line, and thereafter, uncoiling it. CONSTITUTION:A hot rolled steel sheet 10 is rolled finally by a finish rolling mill train 12 consisting of a rolling mill group of 6-7 stands, and thereafter, fed to a run-out table 30 after measuring width, thickness, temperature, sheet crown, etc., of the hor rolled steel sheet by a series of measuring machine group 14. Prior to the foregoing, the sheet is coiled by a coiler 22 contained and provided in a container 20, and the container 20 is in a non-oxidizing atmosphere of inert gas or nitrogen gas, etc., and prevents the surface of the steel sheet from being oxidized. In such a way, by dividing the line, the productivity can be improved by rolling a thin steel sheet at a high speed. Also, by placing a coiler under a protective atmosphere, a steel sheet being free from oxide scale can be manufactured.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for producing hot-rolled steel sheets, in particular, realizes high-efficiency rolling and multifunctional cooling of ultra-thin hot-rolled steel sheets, and prevents the formation of oxide scale on the surface of the steel sheet. Effectively suppressed hot rolling by line division! Regarding AFi manufacturing method (prior art) Figure 3 is a process diagram of the finishing rolling mill row, cooling stage, and winding stage, which are the final steps of a conventional hot rolling line, and it will be easy to understand from now on. In general, a hot-rolled steel sheet lO is finally rolled in a finishing mill row 12 consisting of a group of 6 to 7 rolling mills, and then passed through a series of measuring machines 14 to measure the width, thickness, and temperature of the hot-rolled steel sheet. After measuring the temperature, temporary crown, etc., it is sent to the runout table 30 and cooled.

Usually, this runout table 30 is 150 to 2001
It has a length of 1, and is wound up by a down coiler 32 after being cooled to about 500 to 650°C.

In this way, the hot-rolled steel sheet that has been cooled on the runout table 30, wound up by the down coiler 32, and left to cool in the atmosphere is then treated with an oxide scale film formed on the surface of the steel sheet in the pickling line (not shown). is removed.

However, in such conventional methods, the following two
There are two problems.

That is, the first problem is that when rolling a thin steel plate with a finish thickness of less than 21 mm, when the hot rolled steel plate leaving the finish rolling mill row 12 runs on the runout table 30, the running speed is 80 mm.
When the speed is higher than 0 m/min, the tip of the m plate curls up, causing problems such as the subsequent w4 temporary being folded in (so-called flying), which significantly impedes productivity.

However, in order to ensure a certain level of productivity, it is necessary to maintain a predetermined speed of the hot rolling line, and the current trend is that the line speed tends to increase.

Conventionally, countermeasures have been taken to counter this, such as reducing the pitch of the rollers 31 of the runout table 30 as much as possible, and arranging the disc-shaped rollers 31 in a staggered manner to shorten the actual roller pitch. It has not yet achieved sufficient effect. Of course, the measure of reducing the traveling speed is out of the question in the current situation as described above.

In this way, the 'FJtlJ board with a finished thickness of less than 2mm was
It is very difficult to run on a runout table at a high speed of over 0 m/min, and especially when water cooling is applied during running, the collision force due to this water pressure is also quite large, making smooth threading impossible.

In addition, in some conventional lines, a down coiler (not shown) called a close down coiler is installed close to the exit side of the finishing rolling mill, but in this case, the The distance to the adjacent down coiler is usually 50 to 60 m, and a water cooling device is provided between this distance. In this case as well, water cooling is unavoidable, and the problem of threading the runout table 30 still remains, and the close down coiler cannot be used for coils for which sufficient water cooling is desired.

The second problem is that the steel plate lO leaving the finishing mill row 12 is exposed to the atmosphere while running on the runout table 30, and during this time an oxide scale film inevitably forms on the surface of the steel plate. be. Even if the thickness of such an oxide scale film is constant, the thinner the plate is, the larger the amount per unit weight of the oxide scale film becomes, and this becomes a major cause of a decrease in overall yield. Further, if the oxide scale film thus generated is directly sent to the subsequent cold rolling process, the surface quality of the steel sheet will deteriorate significantly, so it is essential to remove the oxide scale film in advance.

Normally, this oxide scale film is removed in a pickling line, but even in this process there are problems in that the running cost increases and the yield decreases especially as the steel sheet becomes thinner.

If the generation of oxide scale film could be completely prevented, the cost would be significantly reduced by omitting the pickling process, but even if part of it was suppressed, it would be possible to improve the threading speed of the pickling line, and that alone would result in a significant cost reduction. Productivity is improved, scale loss is reduced, and yield is improved.

Indeed, various studies have been conducted regarding the generation of this oxide scale film, and it has been found that almost no oxide scale film is generated near the exit of the final stand roll bite of the finishing mill row 12, and that immediately after It is known that the thickness of the oxide scale film rapidly increases to about 6 to 10 - while the steel plate is air-cooled in the atmosphere, especially when the steel plate is in a high temperature range of 700° C. or higher. Therefore, an attempt has been made to suppress the development of the oxide scale film by rapidly cooling the steel plate to about 600° C. near the exit of the final stand, and this makes it possible to reduce the thickness of the oxide scale film by half (3 μm).

However, the problem in this case is that it cannot be applied to materials that do not want to be rapidly cooled near the exit of the finishing mill row, and that an oxide scale film thickness of about 3 μm is still insufficient, and 1 μm
There are cases where it is desired to set the oxide scale film thickness to the following.

Therefore, as shown in, for example, JP-A-61-123403, a method has been proposed in which the exit side of the hot rolling finishing stand, including the runout table, is sealed with an inert gas or a reducing gas. However, although this method may be effective, it requires large-scale equipment and is therefore impracticable.

(Problems to be Solved by the Invention) Thus, the first object of the present invention is to provide hot rolled steel sheets, especially 2 m
It is an object of the present invention to provide a method for preventing the occurrence of flying on a runout table when hot-rolled steel sheets having a thickness of less than m are rolled at high speed.

A second object of the present invention is to provide a method for simply and effectively preventing the formation of an oxide scale film on the surface of a hot-rolled steel sheet, especially after finish rolling, during the production of a hot-rolled steel sheet.

The overall purpose of the present invention is to reduce running costs by high-efficiency high-speed rolling of thin hot-rolled steel sheets, and to completely omit the pickling process by suppressing the formation of oxide scale films, or even if pickling is performed. It is an object of the present invention to provide a method for manufacturing hot rolled steel sheets that can improve process efficiency and yield.

(Means for Solving the Problems) Therefore, the inventors of the present invention have conducted various studies to achieve the above object, and have obtained the following findings.

■Considering that it is not possible to reduce the threading speed of conventional continuous hot rolling lines, and that threading failures occur on the runner out table due to such high-speed threading, it is possible to The plate is required up to the finishing rolling mill, and it is preferable to use the slowest possible speed for the runner out table after that. Therefore, if the parting line after the final finishing rolling mill is used, It becomes possible to achieve that goal.

■Installing a down coiler near the finish rolling mill line will allow the hot-rolled steel sheet to be coiled at high temperature and then cooled under predetermined cooling conditions using a cooling device installed on the side line. Even if slow cooling with one cooling condition takes time, another cooling device can be used during that time, so operations will not be stagnant.

■In addition, during winding, conveyance, and unwinding, the hot-rolled steel sheet is placed in a non-oxidizing atmosphere from the end of the final hot rolling until the winding, so that, for example, a box-shaped steel sheet with a non-oxidizing atmosphere The hot-rolled steel plate is wound into a coil within the conveying device, and the entire conveying device is conveyed to the above-mentioned separate line,
Furthermore, by unwinding the hot rolled steel sheet as it is, the formation of an oxide scale film on the surface of the hot rolled steel sheet is effectively prevented.

The present invention was completed based on the above-mentioned knowledge, and aims to achieve the above object with a simple means.The present invention is aimed at realizing the above-mentioned object with a simple means. For example, the film is rewound for cooling using a cooling device. This allows the equipment to be made more compact. On the other hand, hot-rolled steel sheets of medium thickness or thicker, which have no problem in running on the runout table and do not require oxide scale film suppression, can be processed as they are on conventional lines, which can improve productivity.

Therefore, the gist of the present invention is to change the width, thickness, and
This is a hot rolled steel sheet manufacturing method using line division, which is characterized in that the coil is immediately wound after passing through a group of measuring machines for temperature, plate crown, etc., and then the wound coil is conveyed as it is to another line and then unwound.

In addition, from another aspect, the present invention is arranged very close to the exit side of the finishing rolling machine so that the coiler axis position is within 10 m in the exit side direction from the final stand roll axis position of the hot finishing rolling mill. The hot-rolled steel sheet is wound up by the down coiler, and then the wound coil is conveyed to a multi-function cooling device provided as a separate line, and the hot-rolled steel sheet is supplied to the multi-function cooling device by unwinding. This is a method for manufacturing hot rolled steel sheets by line division, characterized by performing scheduled processing.

Here, the multifunctional cooling device is a heat treatment device that is appropriately equipped with heat retention, heating, and cooling means.

In a preferred embodiment of the present invention, when winding the hot rolled steel sheet,
The wound coil may be placed in a non-oxidizing atmosphere during coil transportation and unwinding.

In addition, the hot-rolled steel sheets before being wound up from the final stand of the hot finishing mill, the hot-rolled steel sheets during winding and unwinding, and the hot-rolled steel sheets during coil transfer were each tested at an oxygen concentration of 0. It may be placed under a non-oxidizing gas atmosphere of 5% by volume or less.

Further, the wound coil may be kept warm within a certain temperature range, and the temperature of the coil within the moving device may be controlled using a predetermined temperature change pattern when the coil is moved.

Therefore, according to the present invention, ultrathin hot rolled steel sheets, oxidation scale suppressed hot rolled steel sheets, and various other cooling controlled hot rolled steel sheets are manufactured.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings. Note that the same members are represented by the same symbols.

In FIG. 1, a hot-rolled steel sheet lO is finally rolled in a finishing mill row 12 consisting of a group of 6 to 7 rolling mills, and then a series of measuring machines 14 are used to measure the width of the hot-rolled steel sheet lO. , thickness, temperature, plate crown, etc., before being sent to the run-out table 30. According to the present invention, for example, in the case of thin steel having a plate thickness of 21 mm or less, the plate is placed in the container 20 and provided. The coiler 22 coils the container 2.
0 is a non-oxidizing atmosphere such as inert gas or nitrogen gas to prevent oxidation of the steel plate surface as much as possible. When the winding temperature is as high as 700 to 600°C, surface oxidation progresses significantly, so it is preferable to adjust the atmosphere in the container Fi20.

A shutter 24 is provided at the entrance of the container 20, and when winding of the hot rolled steel sheet 10 is completed, the entrance is closed to protect the internal atmosphere. The main function of this container 20 is:
The purpose is to prevent surface oxidation of the hot-rolled steel sheet that has been wound up and to use the hot rolling line as a dividing line, and as long as this is the case, the specific structure thereof is not particularly limited.

The hot-rolled steel plate 10 does not cause a problem of surface oxide scale film formation, and has a considerable plate thickness, so that the lunch-out table 30 can be used.
If there is no problem with flying, for example, in the case of the steel plate 10 having a medium thickness or more, the steel plate 10 may be brought to the down coiler 32 via the runout table 30 and then wound up as in the conventional method.

After leaving the finish rolling mill row 12, subsequent processing can be carried out using a dividing line method.

Here, as described above, the coil wound up in the container 20 and kept warm may be transported to another line by appropriate means, during which time heat treatment may be performed at a predetermined temperature pattern if necessary. .

Container 2 transported to a line equipped with another heat treatment equipment
From 0, the hot rolled steel sheet 10 is now unwound as an unwinding coiler. At this time, the shatter 24 is opened again, and the hot-rolled steel sheet 10 passed through the fully sealed multifunctional cooling device 28 is wound up on a winding coiler 29 after prescribed cooling and heat treatment. In this case, if a long period of time or many times of processing is required, the winding recoiler 29 may also include a container 20° similar to the container 20 to enable heat retention and atmosphere adjustment.

In this way, while the coils are being processed in another line, the hot rolling line is continuously operated, and if there is a failure in the cooling device 28 that would cause the sheet rolling to stop. Even if this occurs, it will only occur on the parting line and will not cause the hot rolling line to stop.

Another preferred embodiment of the present invention will be described below with reference to FIG.

After the steel plate 10 rolled by the finishing mill row 12 is measured for thickness, width, temperature, temporary crown, etc. by the measuring machine group 14,
Down coiler 22 installed extremely close to 1510m
After being wound up, the shutter 24 is closed and the container is installed in a separate line in a portable container 20 sealed with a non-oxidizing gas atmosphere of an inert gas or/and a reducing gas with an oxygen concentration of 0.5% by volume or less, for example. After being moved by a coil moving device (not shown) to a multi-functional cooling device equipped with a sealed cooling zone, it is cooled under predetermined cooling conditions. Here, L≦10
The reason for setting m is that when L>Low, it becomes difficult to thread a thin material, and the sealing device for the steel sheet 10 from when it exits the finishing mill until it is wound up becomes large.

The sealing conditions for the container 20 may be such as to prevent oxidation of the surface of the steel plate, but preferably the oxygen concentration is 0.
．． This is because the oxygen concentration is 5% or less, and the oxide scale film thickness increases when the oxygen concentration exceeds 0.5%. The atmosphere at this time is preferably an inert gas (for example, nitrogen gas or argon gas) and/or a reducing gas (for example, hydrogen) atmosphere.

As a cooling method for the seal cooling zone in the multifunctional cooling device 28 in a separate line, in addition to normal laminar spray,
Mist cooling, water film cooling, etc. may be performed in an appropriate combination.

After cooling and winding, the coil is cooled in a sealed atmosphere according to a predetermined cooling pattern to obtain desired material properties such as r value.

Note that even thin steel plates that do not require oxide scale film suppression can be processed using this separate line cooling device without sealing, thereby significantly increasing the overall productivity. Of course, even steel plates of medium thickness or higher may be subjected to cooling processing at such a dividing line.

In an example using the apparatus shown in FIGS. 1 and 2, it was possible to make the oxide scale film thickness of a low carbon steel plate (plate thickness 1.2 #1 1l) 0.6 to 0.8 p thick per side. This was obtained by winding under an argon gas atmosphere.

At this time, in the case of finishing r￥1.0 to 1.2 m-, the finish hot rolling machine exit side *Fi speed was 70011/min or less in the conventional method, but it was increased to 1000 m/min in the method of the present invention. However, continuous operation was possible.

(Effects of the Invention) As explained above, according to the present invention, by using a dividing line, the first effect is that productivity can be improved by high-speed rolling of thin steel sheets, and the second effect is that productivity can be improved by high-speed rolling of thin steel sheets. By placing the wound coil in a protective atmosphere, it is possible to manufacture steel sheets without (or with a significantly thinner) oxide scale film, which can reduce manufacturing costs by omitting the pickling process or improving pickling efficiency. . Furthermore, the overall effect is that multi-functional steel plates can be produced in the same hot rolling line without reducing productivity, which is a great practical effect.

[Brief explanation of drawings]

FIG. 1 is a partial schematic explanatory diagram of a hot rolling line using a split line system according to the present invention; FIG. 2 is a schematic explanatory diagram of processing using a cooling device in a separate line; and FIG. FIG. 2 is a partially schematic explanatory diagram of a hot rolling line. leaves, 3 figures

Claims (5)

[Claims] (1) The hot-rolled steel plate that comes out of the final stand of the hot finishing rolling mill is immediately wound up after passing through a group of machines that measure the width, thickness, temperature, plate crown, etc. of the steel plate, and then the wound coil is transferred to another line as it is. It is characterized by being conveyed to and then rewound.
A hot-rolled steel plate production method using line division. (2) Hot-rolled steel sheets are rolled by a down coiler installed very close to the exit side of the finishing mill so that the coiler axis is within 10 m from the final stand roll axis of the hot finishing mill in the exit direction. The coil is wound up and then transported to a multi-functional cooling device installed as a separate line.
A method for producing a hot rolled steel sheet by line division, characterized in that the hot rolled steel sheet is unwound and then supplied to the multifunctional cooling device to perform a scheduled processing. (3) The coil is placed in a non-oxidizing atmosphere during winding of the hot-rolled steel sheet, during coil transportation, and during unwinding. the method of. (4) The hot-rolled steel sheet from the final stand of the hot finishing rolling mill until it is wound up, the hot-rolled steel sheet during winding and unwinding, and the hot-rolled steel sheet during coil transfer, each with an oxygen concentration of 0. The method according to any one of claims 1 to 3, characterized in that the method is placed under a non-oxidizing gas atmosphere of 5% by volume or less. (5) Any one of claims 1 to 4, characterized in that the wound coil is kept warm within a certain temperature range, and the temperature of the coil in the moving device is controlled in a predetermined temperature change pattern when the coil is moved. Method described.