JPH10146601A - Manufacturing method of thin-scale hot-rolled steel sheet using hot-rolling continuous process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate descaling of a primary scale and to be formed on the surface of a steel sheet so that a hot-rolled steel sheet can be manufactured by a hot-rolling continuous process with high productivity. It is an object of the present invention to manufacture a steel sheet having a thin scale by continuous hot rolling. SOLUTION: In a hot-rolling continuous step of cutting a trailing end portion of a leading material of a rough bar and a leading end portion of a trailing material, joining the leading material and the trailing material and continuously rolling, After inverting the front and back and the front and rear ends of the steel strip, joining and performing high-speed rolling at a final rolling speed of at least 800 m / m using a high-speed roll while utilizing ORG in the subsequent stage in the subsequent finishing rolling, 550-360 ° C after quenching after rolling
A method for producing a thin-scale steel sheet, comprising:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing a hot-rolled steel sheet by hot-rolling a slab in a continuous hot-rolling line extending from a heating furnace to a winding machine.
In particular, the present invention relates to a method for producing a thin-scale steel sheet in which primary scales present on both front and rear surfaces of a steel sheet are effectively removed and finish rolling is performed by high-speed rolling.

[0002]

2. Description of the Related Art In a conventional hot-rolling line, slabs (slabs) heated in a heating furnace are subjected to rough rolling and finish rolling one by one. It is difficult to control the temperature and cooling at the time of hot rolling, and the material tends to fluctuate.Moreover, this part moves in the cooling zone from finish rolling to winding in the absence of tension, causing unstable flapping. As a result, flaws are likely to occur and the yield is reduced. In recent years, in order to solve this problem, slabs (slabs) heated in a heating furnace are roughly rolled into coarse bars, and the rear end of the preceding material of the rough bar and the rear end of the rough bar at the entrance of the finishing mill. After cutting the tip of the row material straight with a shear, butting both end faces, joining the butted faces with a rough bar welding machine, etc., and descaling by spraying high pressure water on the rough bar surface, finish rolling is performed. Then, a method of winding a steel sheet by a winder has been adopted.

[0003] However, inspection of the surface of a steel sheet produced by such continuous hot rolling reveals that there are scale flaws and there is a problem in the quality of the steel sheet, or that the rough bar surface has There is a problem that it is difficult to continue continuous hot rolling due to flaws formed on the surface of the finish rolling roll due to the existing scale. In particular, in such continuous hot rolling, repair of the rolling roll, etc. Therefore, when the rolling line is stopped, there is a problem that the loss of the work-in-process material is much larger than that of a normal rolling line that is discontinuous rolling.

[0004] In addition, when the finishing rolling speed is low or the winding temperature is increased in continuous hot rolling, a thick scale is formed on the surface of the steel sheet. In order to remove the scale formed on the steel sheet surface in the subsequent pickling process, it is necessary to reduce the pickling speed, and there is a disadvantage that the pickling time becomes long. Furthermore, in applications where steel is used as it is as hot rolled, poor surface scale adhesion may cause problems such as stains due to peeling scale during steel material processing, glaring surfaces, and uneven coating. Are required to have good steel materials.

As described above, in continuous hot rolling, continuous hot rolling cannot be effectively performed unless the scale existing on the surface of the rough bar is removed. It is important for the effect of the subsequent pickling process and the production of scale adhesion of the used material as it is to reduce the scale of the steel sheet surface to be formed.

[0006]

Accordingly, the present invention solves the above-mentioned problems and aims at producing a hot-rolled steel sheet having high applicability in a hot-rolling continuous process of high productivity.
It is an object of the present invention to facilitate the descaling of the next scale and to manufacture a steel sheet in which the scale formed on the steel sheet surface is a thin scale by continuous hot rolling.

[0007]

Means for Solving the Problems The present inventor conducted an inspection on the surface of a steel sheet manufactured by continuous hot rolling, and found that there was almost no scale biting flaw on the back surface of the steel sheet.
It was found that scale biting flaws existed only on the surface of the steel sheet. When investigating the cause, the coarse bar is transported on a roll table for rolling by a finish rolling mill, and the lower surface scale of the scale formed on both surfaces of the coarse bar due to the impact on the roll table during the transport is It was found that there was no scale biting flaw on the back surface of the steel plate produced by the removal. Furthermore, it was found that the scale on the surface of the steel sheet adhered to the finishing rolls, causing biting flaws, damaging the finishing rolling rolls, and deteriorating the adhesion of the secondary scale to the base steel.

Therefore, in the present invention, the slab or the rough bar is turned over at least once during the transport process on the roll table from the exit side of the heating furnace to the entrance side of the finishing mill, and formed on both sides thereof. The peeled scale is separated from the base steel by an impact with a roll table, and then, at a finish rolling mill entering side, at least 150 kg / cm ^{2 as} usual.
For example, descaling is performed by jetting high-pressure water of 250 kg / cm ² , and finish rolling is performed. Also,
By using high-speed rolls while utilizing an online roll grinder (ORG) in the finish rolling, damage to the finish rolling rolls caused by scale adhesion is prevented, and finish rolling is performed by high-speed rolling. The scale formed on the surface of the steel sheet is made uniform by reducing the removal temperature to make magnetite (Fe ₃
O ₄ ) thin scale.

The specific solution of the present invention is as follows.

(1) In a method for producing a steel sheet by continuous hot rolling, in a process from the exit side of a heating furnace to the entrance side of a finish rolling mill, after the slab and / or the coarse bar are turned at least once, Finish rolling is performed, and in the subsequent stage of the finish rolling, an online roll grinder (OR
A method for producing a thin-scale steel sheet, comprising rolling with a high-speed roll while utilizing G).

(2) In a method for producing a steel sheet by continuous hot rolling, in the process from the exit side of the heating furnace to the entrance side of the finishing rolling mill, the front and back, the front end and the rear end of the rough bar are reversed, and then the finish rolling is performed. And rolling at a high-speed roll while utilizing an online roll grinder (ORG) in the subsequent stage of the finish rolling.

(3) After cutting the trailing end of the leading material of the rough bar and the leading end of the trailing material, the leading material and the trailing material are joined,
In a continuous hot rolling process in which rolling is continuously performed, the front and back, front and rear ends of a rough bar before joining are inverted, then joined, and an on-line roll grinder (ORG) is provided at a later stage in a subsequent finish rolling. A method for producing a thin-scale steel sheet, characterized in that high-speed rolling is performed at a final rolling speed of 800 / m or more while using a high-speed roll while being utilized, followed by rapid cooling after rolling and winding at 550 to 360 ° C.

Hereinafter, matters constituting the present invention will be described in detail.

In the present invention, it is preferable to use a known coil box in order to reverse the front and back of the coarse bar before joining and remove the scale on both the front and back surfaces by impact with the roll table. Regarding the coil box, for example, “Stahl unt Eisen (steel and iron)” (1
1. April. 1983. pp. 295-305).

In the present invention, the reason why the leading and trailing ends of the rough bar before the joining are reversed is that when the slab is hot-rolled by a rough rolling mill to form a rough bar, the leading and trailing ends of the rough bar are different. Finishing temperature is different. That is, the temperature at the front end of the rough bar is low, and the temperature at the rear end increases. Such a temperature difference is caused by the fact that the leading end, which is rolled first and becomes thinner, has a higher cooling rate, and thus has a lower temperature than the trailing end which is later rolled and becomes thinner, and cannot be avoided. is there.
In addition, the temperature difference generated between the front end and the rear end causes a difference in material between the front end and the rear end of the rough bar. Therefore, according to the present invention, the material of the finished rolled steel sheet is homogenized by inverting the leading and trailing ends of the rough bar and performing finish rolling.

[0016] Further, by using a high-speed roll in the latter stage of the finish rolling, the steel plate finally rolled can have a smooth and clean surface as a result of the transfer of the surface of the high-speed roll. The scale formed in the step (1) can be made uniform and excellent in adhesion.
The high-speed roll is made of a high-speed tool steel (hi) such as tungsten containing W or molybdenum containing Mo.
gh speed tool steel), the hardness is high, and even if the scale adheres to the roll, the roll is hardly damaged and can withstand continuous hot rolling for a long time. For this reason, when the conventional roll is used continuously, the surface is severely damaged, the surface of the transferred base iron and the scale / base iron interface formed thereon are roughened, and the adhesion of the secondary scale is reduced. It became possible to avoid. In addition, since the surface of the high-speed roll is ground using an on-line roll grinder (ORG) that enables grinding with checks except during bearing inspection and maintenance, the rough surface of the roll and the heat affected zone Thus, the fatigue layer is removed and the roundness of the roll is maintained. The use of this online roll grinder (ORG)
Efficient continuous hot rolling is indispensable for efficient execution, and the use of ORG has solved the problem of hot rolling line downtime caused by scale problems caused by roll damage due to continuous rolling. This is because in the conventional method of removing the roll check and grinding, the continuous hot rolling cannot be performed efficiently because the downtime of the rolling line is too long.

In the continuous hot rolling, it is desired to increase the rolling speed. In the case of using a conventional finish rolling roll, the speed cannot be increased due to problems such as durability of the roll. However, in the present invention, high-speed rolling at a final rolling speed of 800 m / m or more, which cannot be conventionally achieved by continuous hot rolling, is ensured by using a high-speed roll in the subsequent stage of finish rolling, and quenching is performed immediately after rolling. By doing so, it became possible for the first time to suppress the generation of scale. In addition,
The upper limit of the final rolling speed is determined by the durability of the device.

The steel sheet after the finish rolling is immediately quenched, for example, cooled at 30 ° C./s or more within 1 second to 550-360.
C., preferably at 500-400.degree. The shorter the time from rolling to cooling, the better. However, to measure the temperature, thickness, and width during final finishing rolling, it is necessary to set
An interval of about m is required. 800 m / m or more, preferably 1000 m / m or more is required to secure the effect of the scale generation within 1 second. If the winding temperature is 550 to 360 ° C., wustite (FeO) formed on the surface of the steel sheet immediately after rolling is easily transformed into magnetite (Fe ₃ O ₄ ) having good consistency with the base iron, and scale growth This is because a thin scale having good adhesiveness can be obtained in order to suppress the occurrence of the problem. Then, outside the range of the winding temperature, a uniform thin scale with stable and good adhesion cannot be obtained.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an outline of a rolling line when the continuous hot rolling of the present invention is performed.

As shown in FIG. 1, a steel slab (slab) 2 obtained by continuous casting is converted into a heating furnace 1 such as a walking beam furnace.
And heated to a temperature equal to or higher than the hot rolling temperature, conveyed to the rough rolling machine 4 on the roll table 3, and hot rolled by the rough rolling machine 4 to form a rough bar. The coarsely-rolled coarse bar is rolled up to form a coarsely-rolled coil 5, and then the coarse-rolled coil 5 is rewound by inverting the front and back, the front end, and the rear end.

A known coil box can be applied as an apparatus for performing the winding and rewinding. FIG. 2 is a diagram showing an outline of the coil box. As shown in FIG. 2, the rough-rolled coarse bar is transported by a roll table and guided to a coil box. That is, the leading end of the coarse bar is introduced into the coil box by the bottom roll 21 and the deflector roll 22, is bent into a coil by the upper bending roll 23 and the lower bending roll 24, and is wound by the action of the forming roll 25. 26 is wound as a coil. The coil of the coarse bar is transferred by a transfer device 27 to a rewind station 28. In the transfer in the coil box, the coil wound around the coarse bar is transferred to the rewinding station 28 such that the front and rear ends and the upper and lower surfaces of the coil are inverted. The coil of the rewind station 28 is drawn by a pinch roll 29 and sent out to the line to the finishing mill.

Next, as shown in FIG. 1, the unwound coarse bar is conveyed to a cutting machine 6 by a roll table 2 and its tip is cut by a cutting machine 6 such as a shear cutting machine to form a tip suitable for welding. A groove is formed. Similarly, the rear end of the preceding rough bar, whose rear end has been cut by the cutting machine 6, is brought into contact with the rear end of the preceding rough bar, and joined from the upper surface to the lower surface of the steel plate by a welding device 7 such as laser or arc welding. The joined coarse bar is transported to the descaling device 8 by the roll table 2.

During the transfer process from the heating furnace, the scale formed on the lower surface of the lower side of the rough bar by the winding process is removed by the impact with the roll table and the subsequent deske device. Since the coarse bar is inverted, the scale formed on the opposite surface of the coarse bar is removed by impact with the roll table.

After the coarse bar conveyed to the descaling device is removed from the scale on both sides by descaling by injecting high-pressure water, the rough bar is finally processed by a finishing mill 9 equipped with high-speed rolls utilizing ORG. High-speed finish rolling at a constant rolling speed of 800 m / min or more is performed, and the cooling device 10 provided on the run-out table is quenched at 30 ° C./sec or more within 1 second to suppress scale generation. 550 to transform into magnetite (Fe ₃ O ₄ ) with good adhesion to base iron
After cooling to a winding temperature of up to 360 ° C., preferably 500 to 400 ° C., it is wound up by a winder 12 into a coil.

When the steel sheet is wound into a coil having a predetermined size, it is cut by a cutting machine 11. The cutting position is desirably cut at the joining position.

[0027]

[Examples] Each steel type shown in Table 1 (extreme carbon steel, low carbon steel,
Experiments using medium-carbon steel, high-tensile slabs with different rolling speeds and winding temperatures for the reversal of the front and back and back and forth of the steel material between roughing and finishing, and the effect of using or not using high-speed rolls and ORG. Was done. The results include:
The thickness of the scale was measured with a microscope using 7% HCl at 90 ° C.
It was evaluated as good when the scale passed through the liquid at 160 m / m and no scale remained on the steel sheet, and poor when the scale remained. Also,
A sample was taken while hot-rolled before pickling, and a 90 ° bending tape peeling test was performed. A sample in which no scale peeling was observed in appearance was evaluated as good, and a sample which peeled sparsely was evaluated as poor. Table 2 shows the results.

No. 1 was carried out within the scope of the present invention. With respect to 1 to 6, the scale thickness was 6 μm or less, and the pickling property and the scale adhesion of the hot-rolled material were good. No. No. 7 and No. 7 with a low rolling speed. No. 10, CT is high. Sample No. 11 had a high scale, and was poor in both pickling properties and scale adhesion. In addition, No. No. which did not use ORG and high-speed roll. In Nos. 8 and 9, the scale thickness was relatively thin and the pickling property was good, but the scale adhesion was poor because the roll surface was rolled in a rough state. Also, when CT is low N
o. In No. 12, the pickling property was good but the scale adhesion was poor due to the large amount of FeO in the scale composition.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

As described above, according to the method of the present invention, the descaling of the primary scale is facilitated, and the scale formed on the surface of the steel sheet is a thin scale having good uniform adhesion. Can be continuously manufactured by high-speed rolling without stopping the rolling line for a long time, thereby enabling continuous hot rolling with high productivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a rolling line when performing continuous hot rolling of the present invention.

FIG. 2 is a diagram showing an outline of a main part of a coil box.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Cast piece 3 Roll table 4 Rough rolling machine 5 Rough rolling coil 6 Cutting machine 7 Welding device 8 Descaling device 9 Finishing rolling machine 10 Cooling device 11 Cutting machine 12 Winding machine 21 Bottom roll 22 Deflector roll 23 Bending up Roll 24 Lower bending roll 25 Forming roll 26 Take-up station 27 Transfer device 28 Rewind station 29 Pinch roll

Claims (3)

[Claims] In a method for producing a steel sheet by continuous hot rolling, in a process from the exit side of a heating furnace to the entrance side of a finishing rolling mill, the slab and / or the rough bar are turned over at least once and then finished. A method for producing a thin-scale steel sheet, comprising: performing rolling, and rolling at a high-speed roll while utilizing an online roll grinder (ORG) in a stage subsequent to the finish rolling. 2. A method for producing a steel sheet by continuous hot rolling, wherein during the process from the exit side of the heating furnace to the entrance side of the finish rolling mill, after the front and back, the front end, and the rear end of the rough bar are reversed,
A method for producing a thin-scale steel sheet, comprising: performing finish rolling; and rolling the steel sheet on a high-speed roll while utilizing an online roll grinder (ORG) in a subsequent stage of the finish rolling. 3. A hot rolling continuous process in which a leading end of a rough bar and a leading end of a succeeding material are cut, and then the leading material and the succeeding material are joined and continuously rolled. After reversing the front and back and the front and back ends of the steel strip, joining them, and performing high-speed rolling at a final rolling speed of 800 m / m or more using a high-speed roll while utilizing ORG in the subsequent stage in the subsequent finishing rolling. Quenched after rolling, 550-360 ° C
A method for producing a thin-scale steel sheet, comprising: