JPH10263605A - Manufacture of hot rolled steel plate whose surface defect is reduced - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a hot rolled plate whose surface defects are reduced by which the generation of seam flaws is effectively detered more than before by improving on a rouge rolling stage. SOLUTION: When horizontal rolling is executed just after vertical rolling, the target value of the roll gap between the work rolls in the horizontal rolling is set so as to have such a distribution as the gaps on width end sides are larger than that on the width middle side and the actual roll gap is changed in accordance with the target value. In this way, the amount that the initial positions 20 of corner parts of a rolled stock 4 are moved to the surface and back faces 4e, 4d is remarkably reduced (x<y).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet having a small number of surface flaws, and more particularly, to a method of forming a line in the rolling direction near the width end of the front and back surfaces of a steel sheet during hot rough rolling. The present invention relates to a method for manufacturing a hot-rolled steel sheet having few surface flaws, which is effective for suppressing surface flaws (referred to as "seam flaws") that are likely to occur.

[0002]

2. Description of the Related Art A hot-rolled steel sheet is manufactured using, for example, a hot strip mill having the structure shown in FIG. There, 2
After a steel material having a rectangular cross section made of a continuous cast slab or a slab having a thickness of 00 to 300 mm is heated to a predetermined temperature by a heating furnace 10, a vertical rolling mill 1 a to 1 is passed along a pass line 11.
c and coarse rolling through a row of rough rolling mills including horizontal rolling mills 2a to 2c, followed by finish rolling by a finish rolling mill 12 to a hot-rolled steel sheet (hot strip) having a predetermined thickness.
The product is wound up at

In this example, a row of rough rolling mills has three stands (R1 to R1).
R3), and each stand is constituted by a pair of a vertical rolling mill 1 and a horizontal rolling mill 2. In the rough rolling, as shown in FIG.
Immediately after the rolled material 4 is vertically rolled (width-rolled) by a vertical roll 1 shown as a representative by a vertical roll, it is horizontally rolled (thickness rolled) by a horizontal roll 2 shown as a representative by a horizontal work roll. The pass schedule at this stage is, for example, as shown in FIG. 6, three passes (1st pass to 3rd pass) at the coarse first stand R1, three passes (4th pass to 6th pass) at the coarse second stand R2, and a coarse third stand R2.
One pass (7th pass) is set on the stand R3.

The rolled material 4 before the start of rough rolling has a rectangular cross section as shown in FIG. 8 (a), but in the initial stage of rough rolling in which vertical rolling and horizontal rolling are repeated in various pass orders. As shown in FIG. 8 (b), wrinkles are generated on the side surface 4c in the rolling direction, and further rough rolling progresses.
As shown in (c), a part of the side surface 4c wraps around to the front surface 4d and the back surface 4e of the rolled material 4, and the wrapped side surface 4c
Starting from a part of the wrinkle included in c, a linear surface defect called a seam flaw 4f is often generated at the end of the plate width.

If the hot rolled steel sheet contains such a seam flawed width end portion, it cannot be used as a product. Therefore, the width end portion must be finally cut off by strip width trimming. Incurs significant yield loss. In particular,
In the case of a stainless steel plate or the like, which has strict product surface quality requirements, the trimming width is inevitably increased, so that the adverse effect is great.
As means for preventing this seam flaw, a method of chamfering a slab corner (Japanese Patent Laid-Open No. 33803/1985) and a method of applying a lubricant between a rolled material side end and a roll (Japanese Patent Application Laid-Open No. Hei. -150403), a method of preforming the rolled material side end by vertical roll rolling or a sizing press using a convex die to reduce the wraparound of the side portion to the front and back sides (Japanese Patent Laid-Open No. 5-123713). Gazette) has been proposed.

[0006]

However, even with these measures, the occurrence of seam flaws cannot be completely suppressed, and a more effective seam flaw suppression measure is desired. Therefore, an object of the present invention is to propose a method of manufacturing a hot-rolled steel sheet having a small number of surface flaws, which can improve the rough rolling step and suppress the occurrence of seam flaws more effectively than ever.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies and experiments to solve the above-mentioned problems, and as a result, the rolled material immediately after being subjected to the vertical rolling at the rough rolling mill row, particularly at the upstream stand, is reduced. It has been found that by controlling the material flow (metal flow) in the sheet width direction by properly adjusting the gap between the upper and lower work rolls of the horizontal rolling mill, the wraparound of the side surface of the rolled material to the front and back surfaces can be effectively suppressed. The present invention described below has been made based on such knowledge.

The present invention relates to a method for producing a hot-rolled steel sheet in which a hot slab is subjected to rough rolling by combining vertical rolling and horizontal rolling, and then finish-rolled into a hot-rolled steel sheet. When performing, according to the width cross-sectional shape of the rolled material immediately before the horizontal rolling, the target value of the roll gap of the work roll of the horizontal rolling is set such that the width end side has a distribution that is larger than the width center side. A method for producing a hot-rolled steel sheet having a small number of surface flaws, wherein the actual roll gap is changed in accordance with the target value.

The roll gap can be changed by the following methods:
Or a combination thereof. Method: Both taper rolls having tapered tapered portions at both ends in the body length direction and having a tapered shape corresponding to the target value are used as work rolls. Method: A single taper roll having a tapered portion tapered at a predetermined position on one side in the body length direction is used as a work roll, and the work rolls are arranged vertically so that the tapered portions are opposite to each other with respect to the center of the rolled material sheet width. The shift is performed in the roll axis direction by a shift amount corresponding to the target value. Method: The roll axes of the upper and lower work rolls and / or backup rolls are rotated upside down in the rolling plane by a cross angle corresponding to the target value. Method: The work roll is bent with the bending force corresponding to the target value in the direction in which the upper and lower roll ends expand.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the deformation behavior of a cross section in the width direction of a rolled material during rough rolling (vertical rolling and horizontal rolling). The present invention will be described in more detail with reference to FIG. The rolled material 4 before vertical rolling has a rectangular cross section as shown in FIG. In addition, in FIG.
Reference numeral 20 denotes a corner position (initial corner position) of the initial rectangular cross section. When the rolled material 4 is vertically rolled, a thickened portion (usually called "dog bone") 19 is generated at the end of the plate width as shown in FIG. However, the initial corner portion position 20 is restrained by the vertical roll and stopped at the width end, and the rolled material 4 has a small wraparound to the front and back surfaces.

For the rolled material 4 immediately after the vertical rolling,
Conventionally, when horizontal rolling is performed with the entire width of the roll gap constant, since the thickness in the width direction is distributed in the shape of the dogbone 19, the rolling reduction of the horizontal rolling increases toward the width end rather than the width center. . As a result, the metal flow in the rolling direction tends to flow more at the width end and less at the width center, so that a compressive stress acts on the end of the width cross section and a tensile stress acts on the center. For this reason, as shown in FIG. 1B, a metal flow 21 outward in the width direction is generated, and FIG.
As a result, the side surface 4c protrudes outward, and as a result, the amount of turn (y) of the initial corner portion position 20 to the front surface 4e and the back surface 4d increases.

On the other hand, in the present invention, the target value of the work roll gap in horizontal rolling immediately after vertical rolling is defined as:
The width of the rolled material 4 immediately before the horizontal rolling was set so that the width was widened at the end of the width and narrowed at the center of the width, and the actual roll gap was changed in accordance with the target value. Horizontal rolling can be performed with a roll gap according to the cross-sectional shape, so that the difference in the horizontal rolling reduction ratio depending on the width direction position is reduced, and the distribution of the stress acting on the width cross section in the width direction is equalized. Metal flow 21 outward in width direction shown
Becomes smaller. Therefore, as shown in FIG.
c is less protruding to the outside than before, and the surface 4
e Wrapped amount of initial corner position 20 to back surface 4d (x)
Is also smaller than before. That is, x <y.

As described above, according to the present invention, the seam flaw of the hot-rolled steel sheet can be limited to a very narrow range at the end of the sheet width, so that the product yield can be remarkably improved as compared with the related art.

[0014]

EXAMPLE An example of the present invention in the production of a hot-rolled steel sheet by a hot strip mill having the structure shown in FIG. 6 will be described below. In rough rolling, 3 passes (1st
2nd pass, 3rd pass), 3rd pass (4th pass to 6th pass) in the second rough stand R2, 1 pass (7th pass) in the 3rd coarse stand R3, 2nd pass which is the reverse pass,
Except for the 5th pass, vertical rolling is performed in each of the first, third, fourth, sixth and seventh passes. Therefore, in this embodiment, the width distribution of the work roll gap is changed for horizontal rolling in each of these passes.

In each of these horizontal rolling passes, a target value of the work roll gap S (w) at the position w in the width direction of the rolled material is set in the following procedure. First, a width direction thickness distribution Δh (w) generated by vertical rolling (width rolling) immediately before each horizontal rolling.
Is obtained by actual measurement or simulation calculation. For the simulation calculation, the width reduction of the vertical rolling (= the width of the side plate entering the vertical rolling mill−the distance between the vertical rolls) is used.

At the same time, the work roll gap S ₀ at the center position of the sheet width is calculated based on a sheet thickness schedule given from a host computer. Δ thus obtained
The target value (target distribution) of S (w) is calculated by substituting h (w) and S ₀ into the following equation (1). Note that the coefficient g in the equation (1) is called an adjustment gain, and is a positive real number representing a correction factor in consideration of the influence of a steel type, a rolling load, a pass rank, and the like, and is experimentally determined so as to reduce the edge seam. However, in this example, the upstream path has a larger value, and the seventh path has a value of zero.

S (w) = g × Δh (w) + S ₀ (1) Match the actual work roll gap to the target distribution (target roll gap) of the roll gap obtained by Expression (1). In this embodiment, the above-described method is used.
As shown in FIG. 2, the method is such that both tapered rolls 2DT having tapered tapered portions 9 at both ends in the body length direction are used as work rolls 2W, and among them, a work roll 2W having a tapered shape corresponding to the target roll gap is formed. This is a method of selecting and using a roll, in which a so-called “roll exchange method” in which a roll is replaced with a roll having a shape suitable for a desired rolling index at any time is applied to the present invention.

However, if the horizontal pass by the same mill, such as the 1st pass, the 3rd pass, the 4th pass and the 6th pass, is replaced with a roll having a shape corresponding to the individual target roll gap each time, the equipment cost will be reduced. Therefore, the average value of the target roll gap was used as the target value. Also, it is assumed that the target roll gap becomes a complicated curve, and it is difficult to accurately match the taper shape of the tapered portion 9 from the viewpoint of roll processing accuracy. Or, even if approximated by a simple curve represented by a power series at the width direction position w,
There is no problem in practical use.

In FIG. 2, 15 is the center of the roll width,
Numeral 16 denotes a mill width center (a plate width center). In FIG. 2, the two taper rolls are tapered with a taper whose diameter becomes narrower with a slope of 0.02 / radius / work roll body length direction starting from a position 350 mm from the work roll center and moving toward the end of the work roll. This was applied to the first stand, and hot rolling of stainless steel having a width of 1000 mm was performed.

In the example of the present invention, the work roll diameter changes at 150 mm at both ends of the rolled material, and the amount of reduction at the end of the plate becomes smaller by 3 mm above and below the center of the plate. The rolling schedule used a slab thickness of 200 mm and both tapered rolls above 1
st, 2nd, 3rd pass exit side thickness is 179mm, 147mm,
118mm, 4th, 5th, 6th, using flat rolls
The 7th pass exit side thickness was rolled to be 72 mm, 66 mm, 46 mm, and 35 mm, respectively. As a result, the average of the distance of the seam flaw from the edge of the sheet width in the rolling longitudinal direction was 10 mm. When the work roll of the rough first stand was rolled in the same manner without providing a taper as in the past, the average value of the distance from the end of the sheet width of the seam flaw in the rolling longitudinal direction was 15 mm. Therefore, according to the example of the present invention, the distance of the seam flaw from the end of the plate width is reduced by 5 mm.

In the above embodiment, both taper rolls are applied only to the first rough stand, but they may be applied to other rough mill stands in consideration of the rolling schedule of the rolled material. In addition, as a means for changing the roll gap in the plate width direction, in addition to the roll exchange method applied by the method,
“Work roll shift method”, “roll cross method”, and “roll bending method” are well known, and all of them can be applied to the present invention either alone or in appropriate combination.

In the above method, a work roll shift method is applied to the present invention, and as shown in FIG. 3, a single taper roll 2 having a tapered portion 9 tapered at a predetermined position on one side in the body length direction.
ST is a work roll 2W, which is vertically tapered 9
Are arranged so as to be opposite to each other with respect to the mill width center 16 and shifted in the roll axis direction by a shift amount η according to the target roll gap. The shift amount η is a shift amount of the roll width center 15 from the mill width center 16 as illustrated. A rolling mill capable of performing the work roll shift method is generally called a “shift mill”.

In the above method, the roll cloth method is applied to the present invention. As shown in FIG. 4, the upper and lower work rolls 2W and / or the roll shaft 17 of a backup roll (not shown) are vertically moved in the rolling plane. This is a method of rotating in the opposite direction by the cross angle α corresponding to the target roll gap. The cross angle α is a tilt angle of the roll shaft 17 with the rolling perpendicular direction 18 as a base line as shown in the figure. A rolling mill capable of performing the roll cloth method is generally called a “cross mill”.

In the above method, the roll bending method is applied to the present invention, and as shown in FIG. 5, the work roll 2W is bent in a direction in which the upper and lower roll ends expand with a bending force 6 corresponding to a target roll gap. Is the way. This method is performed using a well-known roll bending device (roll bender). FIG. 5 shows an example in which the method is used in combination with the work roll shift method.

In the above methods (1) to (4), it is not necessary to change the rolls one by one, so that the actual roll gap can reach the target roll gap several steps faster than the method, and it is possible to respond quickly to changes in rolling conditions. There are advantages. In addition,
The embodiment in which the work roll shift method, the roll cloth method, and the roll bending method described here are simply replaced with other roll gap changing means not disclosed here and applied to the present invention has the same seam flaw reduction as the present invention. It is obvious that the effect can be obtained, and thus such a simple replacement embodiment also belongs to the scope of the present invention.

It is clear from the operation results so far that the more the vertical rolling pass ranks, the larger the amount of edge seam wrap around the front and back surfaces. Therefore, for example, there may be a case where the vertical rolling is not intentionally performed in the forward pass (1st pass, 3rd pass) in the first rough stand R1, but in this case, the rough rolling in the second rough stand R2 and thereafter is not performed. It is an object of the present invention.

[0027]

As described above, according to the present invention,
Since the seam flaws of the hot-rolled steel sheet can be limited to a very narrow range at the end of the sheet width, there is an effect that the product yield can be remarkably improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a deformation behavior of a rolled material during rough rolling (vertical rolling and horizontal rolling).
(B) shows the thickness distribution after the vertical rolling, (c) shows the horizontal rolling of (b) according to the present invention, and (d) shows the thickness distribution in the width direction after horizontal rolling of (b) by the conventional method.

FIG. 2 is an explanatory diagram of a method for changing a roll gap.

FIG. 3 is an explanatory diagram of a method of changing a roll gap.

FIG. 4 is an explanatory diagram of a method of changing a roll gap.

FIG. 5 is an explanatory diagram of a method of changing a roll gap.

FIG. 6 is a configuration diagram of a hot strip mill.

FIG. 7 is a conceptual diagram of a rough rolling mill.

FIG. 8 is an explanatory diagram of a seam flaw generation process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical rolling mill 2 Horizontal rolling mill 2W Work roll 2DT Double taper roll 2ST Single taper roll 4 Rolled material 4c Side surface 4d Back surface 4e Surface 4f Seam flaw 9 Tapered part 10 Heating furnace 11 Pass line 12 Finishing rolling mill 14 Coiler 15 Roll width Center 16 Mill width center (Sheet width center) 17 Roll axis 18 Rolling perpendicular direction 19 Thickened part (dog bone) at end of sheet width 20 Initial corner position 21 Metal flow outward in width direction

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B21B 31/20 B21B 31/20 D (72) Inventor Haruhiko Ishizuka 1 Kawasaki-cho, Chuo-ku, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works ( 72) Inventor Ryosuke Oikawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Chiba Works, Ltd. (72) Inventor Hideya Furusawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Chiba Works, Chiba

Claims (5)

[Claims] In a method for manufacturing a hot-rolled steel sheet, in which a heated slab is subjected to rough rolling by combining vertical rolling and horizontal rolling, and then finish-rolled into a hot-rolled steel sheet, horizontal rolling is performed immediately after vertical rolling. Setting the target value of the roll gap of the horizontal rolling work roll so that the width end side has a distribution that is larger than the width center side, and changing the actual roll gap according to the target value. A method for producing a hot-rolled steel sheet with few characteristic surface flaws. 2. The roll gap is changed by using both tapered rolls as work rolls having tapered tapered portions at both ends in the body length direction and having a tapered shape corresponding to the target value. The method of claim 1. 3. A work roll having a single tapered roll having a tapered portion tapered at a predetermined position on one side in a body length direction, and the work roll is vertically arranged such that the tapered portion is opposite to the center of the width of the rolled material sheet. The method according to claim 1, wherein the roll gap is changed by shifting the roll gap in the roll axis direction by a shift amount corresponding to the target value. 4. The roll gap is changed by rotating the roll axes of upper and lower work rolls and / or backup rolls upside down in a rolling plane by a cross angle corresponding to the target value. 3. The method according to any one of 3. 5. The method according to claim 1, wherein the roll gap is changed by bending a work roll with a bending force corresponding to the target value in a direction in which upper and lower roll ends expand.