JPH04228204A - Manufacture of hot rolled steel strip through controlled scale formation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to a method for manufacturing hot-rolled steel strip that suppresses scale formation, particularly in the run-out table of the hot-rolled steel strip manufacturing process, which suppresses the formation of oxide scale on the surface of the hot-rolled steel strip. This invention relates to a method for producing hot rolled steel strip.

0002

[Prior Art] In hot rolling using a hot strip mill, after passing through a finishing stand, a hot rolled steel strip is cooled with water on a runout table to obtain the desired material, then wound into a coil and left to cool. Ru. However, since all of these steps are performed in the atmosphere, an iron oxide film called scale is formed on the surface of the hot-rolled steel strip. This usually has a thickness of 5 to 15 μm, and is thicker than the iron surface of the base material.
wustite), Fe304 (magnetite), Fe
It has a laminated structure of three layers in the order of 203 (hematite). The scale generated as described above in the final process of the hot rolling line does not have an opportunity to be removed in subsequent processes, and remains as it is on the surface of the hot rolled steel strip. When the hot-rolled steel strip with this scale still attached is then cold-rolled, some of it is detached, and the detached scale is crimped onto or embedded in the steel strip surface, resulting in the cold-rolled steel strip after cold rolling. causing scale flaws. The cold-rolled steel strip thus obtained has a poor surface condition and cannot be used for high-grade applications.

[0003] For this reason, conventionally, before producing cold-rolled steel strip, the base metal, hot-rolled steel strip, has been treated by pickling, etc., to remove surface scale, and then cold-rolled. This method requires a long pickling facility, which increases the cost of the facility.Furthermore, it consumes acids such as hydrochloric acid, and requires a waste liquid treatment facility, which requires a large amount of cost. By the way, the following methods have been proposed as methods for suppressing scale formation in hot rolled steel strips. In the method disclosed in Japanese Patent Application Laid-open No. 53-43661, as shown in FIG.
Nozzles 83a and 83 after exiting the final stand of No.2
It is cooled on a roller table 84 by cooling water 83 from b and then wound up by a winder 85. After winding, the coiled hot rolled steel strip 86 is sent to a cooling water tank 88 by a conveyor 87, and after being immersed, it is taken out and stocked in a coil yard 90. In this method, immediately after the final stand of the finishing mill 82, a vast area including the winding machine 85 and after winding is covered and sealed with a compartment 110, and the inside thereof is filled with a non-oxidizing gas 89. , isolates the hot rolled steel strip from the atmosphere and suppresses scale formation in the steel strip after hot rolling. However, in this method, the cooling water tank 8
Not only is it necessary to cover a vast area including a part of 8 with the compartment 110, but also to inactivate the interior of the compartment 110,
A large amount of non-oxidizing gas such as

Next, in the method disclosed in Japanese Patent Application Laid-Open No. 61-123403, as shown in FIG.
After leaving the measuring device installation area 94, the sheet is conveyed on a runout table 96 through a container 95 containing various measuring instruments, and after exiting a cooling device 97, it is wound up by a winding machine 98. In this method, the finishing mill final stand 93
A measuring device installation area 94 for measuring the width, thickness, temperature, shape, etc. of the steel strip located immediately near the exit side of the steel strip is covered with a container 95.
The container is maintained in an inert or reducing atmosphere by filling the container with an inert gas or reducing gas through a gas supply pipe 99, and the container is heated by spraying cooling water onto the hot rolled steel strip in a cooling device 97. It is water-cooled from the exit temperature to a temperature of 500°C or less and wound up. In this method, since the sealing area is only inside the container 95, the amount of inert gas used may be small. There is a possibility that the hot rolled steel strip 92 may be oxidized. Furthermore, a large amount of water is required to cover the entire surface of the hot-rolled steel strip on the run-out table 96 with water, and furthermore, rapid cooling may impair the mechanical properties of the steel strip.

[0005]

[Problems to be Solved by the Invention] As described above, in the conventional method, in order to eliminate the harmful effects of scale formation in hot-rolled steel strips, hot-rolled steel strips, which are the base material, are prepared before producing cold-rolled steel strips. The material was treated with pickling to remove surface scale before cold rolling, but the equipment costs for the lengthy pickling equipment were high.
Furthermore, since waste acid treatment equipment is also required, there is a problem in that a large amount of cost is required. As a countermeasure against this problem, a method has been proposed in the past in which the area after the exit of the final stand of a finishing mill in the hot rolling process is appropriately sealed and a non-oxidizing gas such as N2 is filled inside. It is said that a hot-rolled steel strip with a scale thickness of approximately 0.5 μm can be obtained by this method. However, since the sealing area is vast, a large amount of non-oxidizing gas is required, which is not an economical method, and the effect of suppressing scale formation is not necessarily satisfactory. Thus, an object of the present invention is to effectively suppress scale generated on the surface of a hot-rolled steel strip during hot rolling using a hot strip mill, and to simplify or omit the pickling process. The object of the present invention is to provide an economical method for manufacturing hot-rolled steel strip that can be realized.

[0006]

[Means for solving the problem] Therefore, the present inventors
After conducting various studies to achieve this goal, we found that a series of adjacent rollers like table rollers were installed in two stages above and below the hot-rolled steel strip, and the rollers in the lower stage were used as table rollers, and the rollers in the upper stage were used as table rollers. The present invention was completed based on the knowledge that by using the roller group as sealing rollers, the sealing action of the hot rolled steel strip from the atmosphere can be sufficiently ensured through contact between the rollers. Here, the gist of the present invention is that, in the hot-rolled steel strip manufacturing process, a table roller and a roller installed above the hot-rolled steel strip are used between the exit side of the final rolling mill and the winder. A method for producing a hot rolled steel strip in which scale formation is suppressed, characterized by sealing the hot rolled steel strip.

[0007] Regarding the arrangement of the table roller and the roller installed above it, each roller may be placed in contact with the hot-rolled steel strip, or the table roller and/or the roller installed above it may be placed in contact with the hot rolled steel strip. At least every other one may be spaced apart from the hot-rolled steel strip, and the remaining ones may be arranged in contact with the hot-rolled steel strip. In one embodiment of the present invention, a non-oxidizing atmosphere may be created by supplying a non-oxidizing gas to the area sealed by the roller.

Furthermore, it is effective to suppress the generation of scale between finishing rolling mill stands. For example, a seal box is provided between the finishing rolling mill groups, and non-oxidizing gas or non-oxidizing A non-oxidizing atmosphere may be created between the finishing rolling mill groups by supplying bubbles containing gas. Furthermore, the roller and the steel strip may be cooled by passing water through the roller and draining the water from the outer periphery of the roller. Furthermore, the roller cooling water may be applied from the outside of the roller, and this may be combined with the above-described structure in which water is discharged from the outer circumference of the roller.

[0009]

[Operation] Next, the production of the hot rolled steel strip according to the present invention will be explained in more detail with reference to the attached drawings. Figure 1 shows
FIG. 2 is an explanatory diagram of the cooling process in the method for producing a hot rolled steel strip according to the present invention, in which a hot rolled steel strip 1 is placed above a series of sealing rollers 3 after exiting the final stand of a finishing mill row 2; and the table roller 4 below. After passing through a cooling area 5 of a predetermined length, it passes through an area equipped with measuring instruments such as a thickness gauge 6 and a width gauge 7, and then is wound up by a winding machine 8. In addition, these thickness gauges 6
Measuring devices such as the width gauge 7 may be provided on the entrance side of the final stand of the finishing rolling mill, if necessary.

[0010] In the present invention, the hot rolling process before the final stand is not particularly limited, and may be a conventional one, for example. Furthermore, it would be more effective to suppress scale formation between finishing rolling mill groups. The method of suppressing scale formation between finishing rolling mill groups is not limited in any way, and any known means may be used as appropriate. For example, there is a method in which a seal box is provided between the finishing rolling mill groups and a non-oxidizing gas or bubbles containing the non-oxidizing gas is supplied into the sealing box to create a non-oxidizing atmosphere between the finishing rolling mill groups.

Another method for suppressing the formation of scale between stands of a finishing mill is to utilize rolling oil, which is used primarily to reduce wear on the rolling rolls. This method transfers the rolling oil on the roll surface onto the steel strip when rolling the steel strip, creating a film of rolling oil on the front and back surfaces of the steel strip to isolate it from the atmosphere and suppress the formation of scale. . In addition to this, the generation of scale can also be suppressed by installing a high-pressure water descaling device between the stands of the finishing mill or by applying an antioxidant to the steel strip between the stands of the finishing mill. The above method or a combination thereof prevents or suppresses the formation of scale between the stands of the rolling mill, and by sealing the exit side of the finishing rolling mill with rollers, the effect of suppressing scale formation becomes greater.

FIGS. 2(a) and 2(b) are a partial plan view and a side view illustrating the arrangement of rollers constituting the cooling area according to the present invention. A side seal plate 2 is attached to the side surface of a series of rollers 3 and 4 that are arranged almost close to each other.
4 is provided, and by providing a bearing or the like between the roller side surface and the roller side surface, side sealing is performed. Inert gas, that is, non-oxidizing gas, is appropriately supplied to the area defined by each roller row via a supply pipe (not shown), and by applying positive pressure to the internal area, some imperfections may occur. Even with a seal, an inert atmosphere can be maintained inside. each adjacent roller 3, 3 or each roller 4,
4 may be in contact with each other, and some gap is allowed. In particular, by cooling the roller with water from the outside and applying positive pressure inside the sealing area, the allowable gap can be increased.

FIGS. 3(a) and 3(b) are schematic cross-sectional views of examples of the rollers 3 and 4 used in the present invention, and in both figures, a cooling water conduit 2 is provided at the center of the rollers.
5 are provided, and four branch pipes 26 for cooling water are provided in approximately perpendicular directions at points at appropriate distances,
It continues to the nozzle port 27. Note that the arrangement and other aspects of the nozzle ports 27 can be changed as appropriate. Next, an example of the arrangement of the sealing roller 3 and the table roller 4 used in the present invention is partially enlarged and shown in FIG. Each of them is provided with a cooling water supply conduit similar to that shown in FIGS. 3(a) and 3(b). The area defined by each roller is filled with inert gas and is constantly supplied with cooling water.

FIG. 5 is an explanatory diagram showing another modification of the arrangement of these rollers, in which at least every other roller (in the illustrated example, every other roller) is made of hot-rolled steel. The rollers are spaced apart from the belt, and this corresponds to the arrangement in which idle rollers are provided between each adjacent roller in FIGS. 1 and 2. When the rollers are placed in contact with each other in a line as shown in FIGS. 1 and 2, the rotation directions of the adjacent rollers are opposite to each other, and when the rollers are in close contact with each other, each adjacent roller is constantly subjected to friction due to rotation in the opposite direction. It will rotate while
The energy loss caused by this is large. Therefore, Figure 5
Such energy loss can be eliminated by arranging the rollers as shown in FIG.

Note that such a roller arrangement may be provided on either the sealing roller 3 or the table roller 4, or both as shown in the figure. Regarding the material of each roller 3, 4, the table roller 4 may be made of a conventional material, and the roller 3 may be made of the same material, but the upper sealing roller 3
is preferably made of a lightweight, heat-resistant material, such as hollow cast alloy steel. As described above, according to the present invention, compared to the conventional method, the hot-rolled steel strip is covered with the table roller 4 and the sealing roller 3 without any gaps after the final finishing mill, and the area surrounded by the rollers is free from defects. Scale formation is suppressed by filling in active gas, but according to this method, the area to be filled with inert gas is considerably narrower than in the conventional example.

[0016] As described above, by sealing the hot-rolled steel strip after the final finishing mill with a non-oxidizing gas atmosphere, scale formation can be suppressed. The present invention is characterized in that sealing is performed using rollers, and scale formation is suppressed by filling a non-oxidizing gas inside the area surrounded by the upper and lower rollers. Further, the side surface of the roller is sealed using a side seal plate 24 as shown in FIGS. 2(a) and 2(b). When the steel strip is sealed using rollers and side seal plates, the internal volume of the seal can be reduced, and the amount of non-oxidizing gas sealed inside can be reduced, which is economical.

Furthermore, in the present invention, by adding water cooling, the rollers can be cooled while flowing cooling water through the center of the rollers, as shown in enlarged views in FIGS. 3(a) and 3(b). Furthermore, the hot rolled steel strip can be cooled by jetting this cooling water from a nozzle port 27 provided on the outer periphery of the roller. With such additional cooling,
If the temperature of the steel strip on the exit side of the roller seal part is kept below 400°C, scale formation will not be a problem even if no atmosphere sealing is performed thereafter. In other words, the area sealed by the roller can be shortened. Next, the effects of the present invention will be explained in more detail with reference to Examples.

[0018]

[Example 1] In this example, a model rolling equipment approximately 1/4 the size of the actual hot-rolled steel strip production equipment shown in FIG. was manufactured. In FIG. 6, members similar to those in FIG. 1 are designated by the same reference numerals. In Figure 6, steel strip 1 has a thickness of 1.2 mm and a width of 300 mm.
It was a low carbon material of mm. 2a and 2b are rolling mills, 3 is a sealing roller, 4 is a table roller, 8 is a winding machine, and 9 is a furnace coiler. The length of the roller seal section 5, which is the cooling area, is 15 m, and the diameter of each roller is 200 m.
It was m. Further, 10 and 11 are seal boxes, the inside of which is filled with atmospheric gas (Ar). As steel strip 1, a hot-rolled steel strip descaled by pickling was used.

In carrying out the process, first, the coiled descaled steel strip 1 is installed in the winder 8 and passed between the table roller 4 and the sealing roller 3. At this time, the sealing roller 3 is moved above the sealed position to increase the gap between the table roller 4 and the sealing roller 3 and pass the sheet through the sheet. Next, after passing through the rolling mills 2b and 2a,
Steel strip 1 in furnace coiler 9 sealed in Ar atmosphere
is rolled up while being heated in a non-oxidizing state. In the furnace coiler 9, the steel strip 1 was heated to 1000°C. In the above method,
The heated steel strip 1 in a non-oxidized state is wound around the furnace coiler 9, and preparation for the test is completed.

[0020] At the time of testing, the top of furnace coiler 9
(Bottom of the cold coiler) is first passed through the rolling mill 2a and then passed through the rolling mill 2b. Up to this point, the steel strip 1 is covered with atmospheric gas Ar in the seal boxes 10 and 11.
does not oxidize. Thereafter, the tip of the steel strip 1 was wound around a winder 8 by passing it between a sealing roller 3 made of material SS41 and a table roller 4 made of the same material. At this time, there is a large gap between the table roller 4 and the sealing roller 3, and no atmospheric gas is passed therethrough, so the steel strip 1 is oxidized between the rolling mill 2b and the cold coiler.

The following is a scale suppression test. First, the sealing roller 3 is lowered to a height corresponding to the thickness of the steel strip 1 (in contact with the steel strip 1), and the sealing roller 3 is lowered to a height corresponding to the thickness of the steel strip 1 (contacting the steel strip 1). shall be in a sealed state. The gap between each adjacent roller is such that they are in close contact with each other, and the side surfaces are as shown in Figures 2(a) and 2.
It was sealed with a side seal plate as shown in (b). Next, Ar gas was passed through the sealed portion between the rollers 3 and 4 to maintain an internal pressure of 0.5 kg/cm2, and at the same time cooling water was passed through the rollers 3 and 4 as shown in FIGS. 3 and 4. A total of 12 holes, 3 holes per roller in the width direction and 4 holes in the circumferential direction, were made to allow water to gush out.

In this embodiment, the rollers 3 and 4 are both in contact with the steel strip 1. In this state, the gap between the work rolls of the rolling mill 2a is set to 0.8 mm, and the gap between the work rolls of the rolling mill 2b is set to 0.6 mm, and while rolling the steel strip 1, the steel strip is passed between the sealing roller 3 and the table roller 4, and the steel strip is rolled at the same time. 1 was also cooled. The amount of Ar used at this time was approximately 400 Nm<3>/h for the entire sealed portion by rollers 3 and 4. The winding temperature in the winder 8 can be set to 400 °C or 400 °C by changing the amount of cooling water.
The temperature was set at 500°C.

After winding, the coiler was allowed to cool, and the scale thickness was measured. When the coiling temperature was 400° C., the scale thickness was 0.06 μm, which was very thin and could be cold rolled as is. Also,
At 500°C, it was about 0.1 μm. As a result of changing the conditions and conducting a test in which the steel strip 1 was passed between the sealing roller 3 and the table roller 4 without using Ar gas, the results were as follows.
Cooling was performed by changing the amount of water as described above, and the winding temperature was 400.
A scale of approximately 1.2 μm was generated at 500°C and approximately 2 μm at 500°C. Even with this method, a considerable scale generation suppression effect was observed when compared with the conventional atmospheric cooling method.

[0024]

[Embodiment 2] This embodiment shows an example in which the method according to the present invention is applied to continuous hot rolling technology. An example of a rolling equipment row in that case is shown in FIG. As shown in FIG. 7, in the continuous rolling method, the rough bar 14 coming out of the rough rolling mill 13 is rolled into a coil box 15.
Wind it up. After that, it is pulled out from the coil box 15, and the front end of the coarse bar 14 is cut with a crop shear 16.
It is joined to the rear end of the preceding sheet bar 18 by a joining machine 17. 19 is a looper provided to ensure bonding time. By connecting the rough bars 14 and 18 between the rough rolling mill 13 and the finishing rolling mill 20 as described above, it is possible to continuously produce a steel strip with a thin scale thickness.

In the case of this embodiment, the length of the roller seal portion 21 constructed in the same manner as in Embodiment 1 is sufficient to be about 60 to 80 m when the plate thickness is about 2.3 mm, and when the plate thickness is about 3 mm. In this case, it would be sufficient to increase the length of the roller seal by approximately 30%. Roller diameter is 200~300mm
And so. In addition, in FIG. 7, 21 is a roller seal portion which is a cooling area. A strip shear 22 cuts the steel strip to an appropriate length, and the strip is wound up by a winder 23.

[0026]

[Embodiment 3] FIG. 10 shows an example of hot rolled steel strip manufacturing equipment in which scale formation is suppressed when the model rolling equipment shown in FIG. 6 is applied to an actual machine. In FIG. 10, scale generated on the front and back surfaces of the steel strip 1 between the rough rolling roll and the finishing roll is removed by a high-pressure water desk 30 on the entry side of the finishing mill. Thereafter, the steel strip 1 is rolled in a finishing mill, and at this time, it is more important to prevent or suppress the generation of scale between the finishing mill stands.

As a method for suppressing the generation of scale, as shown in FIG. 10, the passage of the steel strip between the stands of the rolling mill is covered with a seal box 31 in the form of a tunnel, and a non-oxidizing gas is supplied inside to suppress the scale. It shows how to suppress the occurrence of

At this time, as shown in FIG. 11, by putting a bubble 32 made of non-oxidizing gas (for example, N2 gas is contained in the bubble) into the seal box 31,
The gap between the steel strip 1 and the seal box 31, which is absolutely necessary for the steel strip 1 to pass through, can be sealed with foam. Therefore, it is possible to reduce the oxygen concentration inside the seal box 31 to a very low level of 1% or less. Also,
Since non-oxidizing gas is not released directly from the above gap,
It is also possible to reduce the amount of gas used. On the exit side of the finishing mill, it is preferable to install a guide plate 33 in order to improve the threading performance, especially at the leading edge of the steel strip 1. Also,
On the finishing rolling machine side of the roller seal portion, the distance between the upper and lower rollers may be increased to provide a guide roller 34. Note that side seal plates are also installed at the positions of the guide plate 33 and guide roller 34, and a non-oxidizing atmosphere is created inside. 35
is a threaded roll. In this way, by sealing the exit side of the finishing rolling mill with rollers and suppressing the generation of scale between the stands of the finishing rolling mill, a larger effect of suppressing scale generation can be obtained.

[0029]

[Effects of the Invention] According to the present invention, scale formation in hot-rolled steel strips, which was previously thought to be unavoidable, can be prevented in a hot-rolled steel strip manufacturing line by a relatively simple means. This not only makes it possible to reduce the huge cost required for descaling treatment such as pickling prior to the cold rolling process and prevent a decrease in the yield of steel strip, but also improves the productivity of rolled products. The above is of great significance.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of a roller seal in the present invention.

2(a) and 2(b) are a plan view and a side view, respectively, showing aspects of sealing on the side surface of the roller according to the present invention.

3(a) and 3(b) are a side view and a sectional view, respectively, showing an example of the structure of a roller used in the present invention.

FIG. 4 is an explanatory diagram showing an example of arrangement of each roller in the present invention.

FIG. 5 is an explanatory diagram showing an example of arrangement of rollers in another modification of the present invention.

FIG. 6 is a schematic explanatory diagram showing an example using a model rolling facility.

FIG. 7 is a schematic explanatory diagram showing an embodiment in which the roller seal of the present invention is applied to a continuous rolling method.

FIG. 8 is a schematic explanatory diagram of a conventional hot rolling method in which rolled steel is moved while being isolated from the atmosphere.

FIG. 9 is a schematic explanatory diagram of a conventional scale suppression method using atmosphere sealing and water cooling.

FIG. 10 is a schematic explanatory diagram showing an example of hot-rolled steel strip production equipment in which scale formation is suppressed according to the present invention.

FIG. 11 is a schematic explanatory diagram showing an example of a sealing method using bubbles.

[Explanation of symbols]

1: Hot rolled steel strip 2:
Finishing mill rows 3 and 4: Rollers
5: Cooling area 6: Thickness gauge
7: Width total 8: Winding machine
9: Furnace coiler 10, 11: Seal box 12:
Thermometer 13: Roughing mill
14: Rough bar 15: Coil hox
16: Crop shear 17: Splicing machine
18: Seat bar 19
: Looper 20 : Finishing rolling mill 21 : Roller seal part 22
: Strip shear 23 : Winder
24: Side seal plate 25:
Cooling water conduit 26: Cooling water branch pipe 27: Nozzle port
30: High pressure water desk 31: Seal box
32: Foam 33: Guide plate
34: Guide roller 35: Threading roll

Claims (8)

[Claims] 1. In the manufacturing process of hot-rolled steel strip, the hot-rolled steel strip is sealed by a table roller and a roller installed above the hot-rolled steel strip between the outlet side of the final finishing mill and the winder. A method for producing a hot-rolled steel strip that suppresses scale formation. 2. The method according to claim 1, wherein the table roller and the roller installed above the table roller are disposed in contact with the hot rolled steel strip. Law. 3. The method according to claim 1, wherein at least every other table roller and/or a roller installed above the table roller is separated from the hot-rolled steel strip, and the remaining rollers are brought into contact with the hot-rolled steel strip. A method for producing a hot-rolled steel strip that suppresses scale formation, characterized by arranging the hot-rolled steel strip in such a manner that scale formation is suppressed. 4. The method according to claim 1, wherein a non-oxidizing atmosphere is created by supplying a non-oxidizing gas into the area sealed by the roller. A method for manufacturing suppressed hot-rolled steel strip. 5. The method according to any one of claims 1 to 4, wherein the method also suppresses scale generation between finishing rolling mill stands. Manufacturing method. 6. Suppression of scale generation between finishing rolling mill stands is achieved by providing a seal box between the finishing rolling mill groups and supplying non-oxidizing gas or bubbles containing non-oxidizing gas into the seal box. 6. The method for producing a hot rolled steel strip with suppressed scale formation according to claim 5, which is carried out by providing a non-oxidizing atmosphere. 7. In the method according to any one of claims 1 to 6, the roller and the steel strip are cooled by having a structure in which water passes inside the roller and water is discharged from the outer periphery of the roller. A manufacturing method for hot-rolled steel strip that suppresses scale formation. 8. A method for producing a hot-rolled steel strip in which scale formation is suppressed in the method according to any one of claims 1 to 7, characterized in that roller cooling water is applied from the outside of the roller.