JPH03165925A - Method for cooling thin hot rolled coil - Google Patents

Abstract

PURPOSE:To reduce the greatest temperature difference in the direction of plate width in a cooling process and to prevent ununiform plastic distortion from generation by specifying and arranging the distance between plate with end parts of an adjacent thin hot rolled coil. CONSTITUTION:A thin hot coil 1 having a plate thickness 3.5mm or under coiled at a coiling temperature 400 deg.C or higher, after hot rolling is carried into a coil cooling yard C within 40 min after it is coiled. A thin hot rolled coil 1 carried into a cold yard of the coil 1 is adjoined successively to the thin hot rolled coil carried in previously at the end faces of plate width in a down end state and arranged so that the distance between the plate width end parts of the adjacent thin hot rolled coil 1 is not greater than 300 mm. Thus, the max, temperature difference in the plate thickness direction during process is reduced, the ununiform plastic distortion is prevented from generation, and a bot rolled steel sheet excellent in flatness in obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION 1 [Field of Industrial Application] The present invention relates to a method for cooling a thin hot-rolled coil that has been wound up after hot rolling.

(Seira's technology and its problems) After hot rolling to 1g, the coiled hot-rolled coil was transported to a coil cooling yard, where it was stacked in one or two layers with the down end and cooled in the atmosphere. After that, it is transported to the next process such as pickling line, skin bath line, shear line, and slinter line.

By the way, the hot-rolled coils in the coil cooling yard are arranged so that the circumferential direction of the coils is adjacent to the hot-rolled coil 6 as shown in FIG.
The coils are placed close to each other, and the spacing in the width direction of the coil is usually 1 m or more. When the hot-rolled coil 6 cooled in this arrangement is unwound in the next process, the thickness of the coil 6 is particularly reduced to 3. In a thin hot-rolled coil of 5 m+n or less, the flatness of the plate may change after hot rolling and before being wound. In this way, if a flatness defect occurs in the thin hot-rolled coil after cooling, it not only causes problems such as threading trouble in the next process, but also may result in poor quality of the product.

2 In view of the above-mentioned problems, the present invention was made in order to prevent threading troubles and product quality defects in the next process after cooling a thin hot-rolled coil. It is an object of the present invention to provide a method for cooling a thin hot-rolled coil that prevents a change in flatness.

[Means to solve the problem]

In order to achieve the above object, the method for cooling a thin hot-rolled coil according to the present invention is such that the coiling temperature is 400°C after hot rolling.
The thin hot-rolled coil with a thickness of 3.5 mm or less that has been wound in the above manner is transported to the coil cooling yard within 40 minutes after winding, and the incoming thin hot-rolled coil is down-ended in the coil cooling yard. In this state, the thin hot-rolled coils brought in earlier are sequentially placed so that their width end surfaces are adjacent to each other, and the distance between the sheet width ends of adjacent thin hot-rolled coils is 3001III1 or less.

When installing coil transport equipment in the coil cooling yard, the high temperature thin hot-rolled coils brought in are sequentially heated from the input side of the coil transport equipment, and at the time of unloading the coils at the exit side of the coil transport equipment. The temperature is kept below 250°C.

The present invention will be explained in detail below.

After discovering the above-mentioned problem, the present inventors conducted intensive research on changes in flatness during the cooling process of thin hot-rolled coils.

The third factor is the plate thickness of 3.5n, which is placed as shown in Fig. 9 above.
FIG. 2 is a diagram showing the results of examining the flatness change tendency of a thin hot-rolled coil having a diameter of less than 100 nm after hot rolling, before being wound up, and when it is unwound after cooling.

As is clear from this figure, the flatness of many of the thin hot-rolled coils after cooling changes in a wave-like manner.

Figure 4 shows the central part of the sheet width and the end part of the sheet width (201Ill from the edge) of the thin hot rolled coil during the cooling process after hot rolling and coiling.
It is a figure which shows the result of measuring the temperature distribution of the area|region inside l1. As is clear from this figure, the temperature difference in the width direction of the coil plate immediately after winding is around 50°C, but in the coil cooling process, the cooling rate at the edge of the plate width is fast, so it is
After some time, the temperature difference in the width direction of the coil plate becomes 100°C or more, and then this temperature difference gradually decreases.

Figure 5 is a diagram showing the relationship between the temperature difference in the width direction of a steel plate wound as a thin hot-rolled coil (hereinafter referred to as steel plate) and the thermal stress generated thereby. It is a figure showing the result of measuring the yield stress of a steel plate in the vicinity.

As is clear from these figures 5 and 6, 400
In the vicinity of C, the thermal stress generated by a temperature difference of around 100°C exceeds or approaches the yield stress of the steel plate.

Figure 7 is a diagram showing the results of applying a stress equal to 80% of the yield stress of the steel plate to a steel plate in a tensile test at each temperature shown in factor 6, and measuring the plastic strain remaining after unloading. . Generally, it is obvious that plastic strain remains if the applied stress exceeds the yield stress of the steel plate, but according to this figure, even if the applied stress is less than the yield stress of the steel plate, there is a slight plastic strain of about 0.05%. It can be seen that distortion remains.

Further, as described above, in the thin hot-rolled coil during the cooling process, the edge portions of the sheet width are cooled faster than the center portion of the sheet width, so that tensile thermal stress is generated at the edge portions of the sheet width.

From the above findings, the poor flatness of the ear wave tendency during the cooling process shown in Figure 3 is due to the thermal stress caused by the temperature difference in the sheet width direction of around 100°C during the cooling process being close to the yield stress of the steel sheet. It is presumed that this occurs due to non-uniform plastic strain in the width direction of the plate. In other words, this non-uniform plastic strain in the sheet width direction exists as a compressive residual stress at the sheet width end because the shape rigidity is high in the coil state after cooling, and this compressive residual stress is released when the coil is unwound.
The steel plate buckles and forms an ear wave. By the way, according to the well-known conversion formula, the steepness λ of the ear waves produced by a non-uniform plastic strain Δε of 0.05% is approximately 1.4% (wave pitch 1m).
The height of the wave was 14 mm), which is almost the same as the size of the actually observed ear wave.

λ-2/πJΔεXIOO (%) On the other hand, the reason why ear waves are difficult to generate in a thick hot-rolled coil with a plate thickness of more than 3.5 nm is considered to be because the buckling boundary stress of the steel plate is high.

6 The present invention was made based on the above-mentioned knowledge, and the present invention is based on the above-mentioned knowledge, and the present invention is based on the above-mentioned findings. At the same time, in the coil cooling yard, the incoming thin hot-rolled coil is brought in in a down-end state, and the thin hot-rolled coil brought in earlier is sequentially brought in adjacent to the sheet width end face, and the plate of the adjacent thin hot-rolled coil is The coils are arranged so that the distance between the width ends is 300 mm or less to reduce the maximum temperature difference in the width direction of the coil plate during the cooling process and to prevent uneven plastic strain from occurring in the width direction of the coil plate due to thermal stress. This is to prevent changes in flatness during the coil cooling process.

The reason why the delivery time from immediately after winding to the coil cooling yard was set within 40 minutes was because, as shown in Part 4, the temperature difference in the width direction of the coil plate immediately after winding was around 50"C, and this temperature The difference increases as coil cooling progresses, but remains below 70°C within 40 minutes, and as shown in Figures 5 and 6.
As can be seen from the figure, this is because the thermal stress generated at this temperature difference (70° C. or less) is sufficiently smaller than the yield stress of the steel plate.

In addition, in the downent state, the width end faces of the thin hot rolled coils are adjacent to each other, and the distance between the width ends of the adjacent thin hot rolled coils is 3.
The reason why they are arranged so that the width is 00 mm or less is that the hot-rolled coils retain heat from each other due to the radiant heat of the hot-rolled coils placed in front and behind each other at a high temperature of 400°C or more. This is to reduce the temperature by slowing down the wI temperature rate and minimizing the temperature difference in the width direction of the coil plate, and this effect cannot be enjoyed if the distance between the width ends of the thin hot rolled coil exceeds 300lIIIa. Incidentally, FIG. 8 is a diagram showing the results of investigating the relationship between the distance between the width ends of mutually adjacent thin hot-rolled coils during the cooling process and the maximum temperature difference that occurs in the width direction of the coil plates. According to this figure, the smaller the distance between the sheet width ends of adjacent thin hot-rolled coils, the smaller the maximum temperature difference in the sheet width direction that occurs during the cooling process.
When this distance is 300 mm, the maximum temperature difference in the board width direction is about 80°C. The thermal stress generated in the steel plate at this maximum temperature difference of 80°C is well below the yield stress of the steel plate, as determined from Figures 5 and 6 above, and the thin hot-rolled coil is placed in a coil cooling yard. When cooling, the distance between the width edges of adjacent thin hot rolled coils is
If it is 1 or less, excessive thermal stress can be prevented from occurring, and changes in flatness that occur during the coil cooling process can be prevented.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sheet with a thickness of 3.5n+II in a coil cooling yard to which the thin hot-rolled coil cooling method according to the present invention is applied.
FIG. 2 is a diagram showing the arrangement of one or less thin hot-rolled coils.

In the figure, reference numeral 1 indicates a thin hot-rolled coil having a thickness of 3.5 mm or less that was wound up at 600°C after hot rolling. This thin hot-rolled coil 1 is transported to the coil cooling yard C approximately 20 minutes after being wound up, and is transported in the order in which the distance l between the sheet width ends is approximately 300 II m, and in the down-end state 2.
0 to 30 coils were placed in rows. The row spacing is approximately 2
m. Further, at least at the front and rear ends of each of the nine rows, thick hot-rolled coils 2 having a thickness of more than 3.5 mm, which were wound in parallel operation, were arranged.

When we investigated the flatness of 50 thin hot-rolled coils 1 cooled in this way when applying them to skin bath lines, all of the coils had a steepness λ of 0.5% or less, indicating that the flatness It was possible to obtain hot-rolled thin steel sheets with good quality.

Incidentally, in the above embodiment, an example was explained in which the thin hot-rolled coils l were placed in a planar manner in rows, but the coils may be stacked in two layers on top of a plurality of rows of coils.

FIG. 2 shows another embodiment of the invention.

In the figure, 3 indicates a coil conveyor installed in the coil cooling yard C, and l indicates a thin hot-rolled coil. The thin hot-rolled coil l is transported to the coil cooling yard C within 40 minutes after being wound up, and the distance Rl between the coil plate width end from the man side 4 of the coil transport conveyor 3 is 3001III1 in the order of delivery.
The coil is placed in the following manner and sent to the exit side 5 of the coil conveying conhair 3. The thin hot rolled coils 1 are then cooled down to 250''C or less on the coil transport conveyor 3, and are sequentially transported to a conventional cooling yard, starting with the cooled thin hot rolled coil 1, where they are cooled to a predetermined temperature and transported to the next process.

By the way, the reason why the cooling temperature of the thin hot-rolled coil l on the coil conveyor 3 is set to 250°C or less is due to the fourth embodiment.
As shown in the figure, after being cooled to below 250°C,
This is because the temperature difference in the width direction of the coil decreases, and the thermal stress caused by the temperature difference is sufficiently smaller than the yield stress of the steel plate.

〔Effect of the invention〕

As detailed above, according to the method for cooling a thin hot-rolled coil according to the present invention, the coiling temperature is 400'C after hot rolling.
The thin hot-rolled coil with a thickness of 3.5 mm or less that has been wound in the above manner is transported to the coil cooling yard within 40 minutes after winding, and the incoming thin hot-rolled coil is down-ended in the coil cooling yard. In this state, the thin hot-rolled coils brought in earlier should be placed so that their width end faces are adjacent to each other, and the distance between the width ends of adjacent hot-rolled coils is 300mlI1 or less. This reduces the maximum temperature difference in the width direction of the coil plate during the cooling process and prevents uneven plastic strain from occurring in the width direction of the coil plate due to thermal stress. It has the effect of obtaining. Furthermore, troubles such as sheet threading in the next process can be reduced, and productivity can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the arrangement of thin hot-rolled coils in a coil cooling yard in an embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG. Figure 4 shows the change in flatness of a thin hot-rolled coil after hot rolling, before winding, and after cooling and unwinding. Figure 5 shows the temperature distribution in the widthwise center and edge of a thin hot-rolled coil during the cooling process, and shows the temperature difference in the widthwise direction of the steel sheet wound as a thin hot-rolled coil and the resulting temperature difference. Figure 6 is a diagram showing the relationship between thermal stress, Figure 6 is a diagram showing the relationship between temperature and yield stress of a steel plate, Figure 7 is a diagram showing the plastic strain remaining after a stress near the yield stress of 12 mm is applied to the steel plate,
FIG. 8 is a diagram showing the relationship between the distance between the width ends of adjacent thin hot rolled coils during the cooling process and the maximum temperature difference that occurs in the width direction of the coil plates. FIG. 3 is a diagram showing the arrangement of hot-rolled coils in a cooling yard. 1 Thin hot rolled coil 2 Thick hot rolled coil 3 Conveyor for conveying coils 4 Inlet side of the conveyor 5 Outlet side of the conveyor C Coil cooling yard l Distance between coil plate width ends

Claims (2)

[Claims] (1) After hot rolling, a thin hot-rolled coil with a thickness of 3.5 mm or less, which was wound at a winding temperature of 400°C or higher, is
In the coil cooling yard, the incoming thin hot-rolled coils are brought in in a down-end state, and the thin hot-rolled coils are successively brought in adjacent to the thin hot-rolled coils brought in earlier, and A method for cooling a thin hot-rolled coil, the method comprising arranging the thin hot-rolled coil so that the distance between the width ends of the thin hot-rolled coil is 300 mm or less. (2) Coil transport equipment is installed in the coil cooling yard, and the high-temperature thin hot-rolled coils brought in are placed one after another from the input side of the coil transport equipment, and when the coils are unloaded at the exit side of the coil transport equipment. The method for cooling a thin hot-rolled coil according to claim 1, characterized in that the temperature is set to 250°C or less.