JP2003205302A - Method for hot-rolling bar steel and wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-rolling method of bar steel and a wire rod for reducing dents of pressed-in scale defects and wrinkles furthermore, surface flaws which are generated on the surface of a material to be rolled. <P>SOLUTION: In a method for hot-rolling a billet into the bar steel and the wire rod by using a rolling device having a grooved roll train at least in a finishing train, after forming a square billet after heating into an approximately an octagonal shape or an approximately circular shape by reducing its four apex angles from four directions, it is rolled by the grooved roll train. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method for steel bars and wire rods, and more particularly to a method for hot rolling a billet using a rolling facility having a hole roll row at least in a finishing row.
The present invention relates to a method of hot rolling a wire rod.

[0002]

PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION
Hot-rolled products of wire rods are usually manufactured by rolling a billet heated in a heating furnace by a rolling facility having a row of hole rolls from a rough row to a finishing row. Surface defects are a serious problem in the hot-rolled products of steel bars and wires produced in this manner. The surface flaws include scale indentation flaws generated by pushing the primary scale produced in a heating furnace and secondary scale produced during rolling into rolling, and the cross-section of the rolled material produced by the rolling rolls during rolling. There are wrinkles due to compressive strain in the circumferential direction.

As a means for improving the former scale indentation flaw, for example, Japanese Patent Application Laid-Open No. 58-110117 discloses.
A method of descaling a steel material has been proposed in which, when the steel material is deformed by the upper and lower rolls, high-pressure water or compressed air or both of them are blown to the steel material between the upper and lower rolls to remove the scale.

According to this embodiment, this steel material descaling method employs the above-described configuration in addition to the descaler on the rolling mill entrance side, so that both sides of the descaler on the rolling mill entrance side and the upper and lower rolls are arranged. It is possible to easily remove the scale on the surface of the steel material by setting the spray pressure of the descaler arranged in the same to a low pressure. However, this method only removes scales and cannot be expected to have an effect on wrinkle defects caused by deformation described later. Further, in such a method of removing scales using high-pressure water or the like, although a scale removal effect can be expected, fine scales, high-pressure water, compressed air, etc. are scattered and the work environment is poor. Further, a suction device or the like is required to improve this.

On the other hand, in Japanese Unexamined Patent Publication No. 4-356302, in a steel strip rolling method in which a material cross section is surface-reduced by a flat roll (flat) and then form-rolled by a hole-type roll, it is reduced in the final pass of the flat roll rolling. There has been proposed a steel strip rolling method in which an obtuse angle surface of 5 to 40 degrees is formed at four corners of a material to be rolled while performing a reduction of an area ratio of 10% or more. Further, according to this method for rolling a rolled steel, after rolling with a flat pass, a reduction of area of 10% or more and
Since rolling (box pass) that forms an obtuse angle surface of 5 to 40 degrees is provided at one corner, rotation of the material to be rolled is prevented by subsequent hole roll rolling, and folding flaws in this hole roll rolling are also provided. It is possible to prevent the occurrence of.

Therefore, the present inventors have paid attention to the box path adopted in the above-mentioned proposed method for rolling steel strips, which eliminates the sharp corners of the material to be rolled, and adopt this box path. Therefore, we investigated and considered that it might be possible to prevent wrinkle defects. However, even if it is formed so as to have an obtuse angle surface of 95 to 130 degrees in the corner portion of the material to be rolled, it is a quadrangular shape as a whole. It was found that the local compressive strain in the cross section, which is the cause of wrinkle defects, could not be reduced. Further, when a flat path is used for the rough row, the rate of contact between the material to be rolled and the roll on the surface becomes large, so that the scale peeling property during rolling deteriorates and scale indentation is likely to occur.

The present invention has been made in order to improve the above-mentioned circumstances, and its object is to reduce the scale indentation flaws, the wrinkle flaws and the surface flaws generated on the surface of the material to be rolled. -A method for hot rolling a wire rod is provided.

[0008]

In order to achieve the above object, a hot rolling method for steel bars and wire rods according to a first aspect of the present invention is a method for rolling a billet having a hole type roll row from a rough row to a finishing row. In the method of hot rolling to steel bars and wire rods using equipment, after heating the square billet to reduce its 4 apexes from 4 directions to form an approximately octagonal shape or an approximately circular shape, then roll it with a hole-type roll row. To do.

In the above-mentioned hot rolling method for steel bars and wire rods, the square billet after heating is shaped into a substantially octagonal shape or a substantially circular shape by pressing down its four apex angles from four directions, so that the scale can be sufficiently removed. In addition, since rolling is then performed with a row of rolls, rolling with less surface flaws such as scale-indented flaws can be performed, and steel bars and wire rods with less surface flaws can be manufactured.

According to a second aspect of the present invention, there is provided a method of hot rolling a steel bar and wire rod according to the first aspect of the present invention, wherein the rolling roll rows from the rough row to the finishing row are provided with an oval hole type and a round hole type. This is a type roll sequence. As described above, the hole type roll row including the oval hole type and the round hole type is adopted as the preferable hole type roll row, because the square billet which has already been heated has a substantially octagonal shape by pressing down its four apex angles from four directions. Or, it is formed into a substantially circular shape, and the same action and effect as the round-to-oval pass rolling adopted in the case of high-grade steel as described below is expected in addition to the action and effect of the invention of claim 1 above. This is because.

That is, in the case of high-grade steel, the round → oval → round pass is generally repeated after the middle row →
Oval pass rolling is adopted. The reason is
As shown in Fig. 2, unlike the round → oval pass rolling, the corner → oval pass rolling contacts the roll from the apex angle of the material to be rolled (corner), resulting in a large circumferential compression that causes wrinkle flaws on the free surface. Since the strain acts and the scale in the pressure lower part cannot be peeled off, scale indentation flaws are easily generated. On the other hand, the round-to-oval pass rolling is a pass in which large circumferential compressive strain does not act and the surface is uniformly deformed, and it is said that it has the effect of shallowing the surface flaws generated up to the rough row. It is because it is done.

According to a third aspect of the present invention, in the hot rolling method for steel bars and wire rods according to the first or second aspect, the square billet after heating has a ratio (D / d) of the longest diameter D and the shortest diameter d. 1 to
It is molded into a substantially octagonal shape or a substantially circular shape within the range of 1.2. With such a shape, the above-mentioned claim 1
Alternatively, the effect of reducing scale indentation flaws and wrinkle flaws of 2 can be more effectively obtained.

The method of hot rolling a steel bar / wire rod according to claim 4 is a method of hot rolling a billet into a steel bar / wire rod by using rolling equipment from a rough row to a finishing row. Is rolled into a square cross-sectional shape, the intermediate material of the square cross-sectional shape is subsequently rolled down to form a substantially octagonal shape or a substantially circular shape by rolling down the four apex angles from four directions, and thereafter, an oval hole shape and a round hole shape are formed. Rolling is carried out by a hole type roll row of intermediate and finishing rows. The rolling to the square cross-sectional shape in this method is not particularly limited as long as it is in the middle of the rough row or the intermediate row, but the rolling equipment from the rough row to the finishing row is a rolling equipment having a hole-type roll row. From the standpoint of scale peeling, it is preferable to perform rolling to a square sectional shape with a rough row provided with square hole type rolls.

Conventionally, in the hot rolling of steel bars and wire rods, square billets are generally used. Therefore, in rough row rolling, a square billet is used as a starting material, and rhomboid-pass rolling that repeats rhombic → square → rhomboid pass, box-pass rolling that repeats box-pass, or flat-pass rolling that repeats flat-pass is performed, and an intermediate material with a rectangular cross-section is formed. In addition to the above-mentioned forming, the intermediate material is subsequently subjected to the oval → round → oval pass repeated round → oval rolling in the intermediate row and thereafter, and hot rolling of the steel bar and wire rod is performed.

As described above, in the rolling of wire rods and bar steels, the material to be rolled is rolled while being shaped into various shapes.
A portion with a large circumferential compressive strain is created, and this portion becomes a wrinkle flaw. According to the experiments by the present inventors, the wrinkle flaws are generated from the rough row, and the frequency of the flaw is highest in the vicinity of the corner-shaped corner on the rough row exit side, and further, the corner on the rough row exit side → Oval path It was clarified that the surface compressive strain was maximized and the surface flaws generated in the rough row were further deepened. In the subsequent round->oval-> round passes after the middle row, the surface is deformed almost uniformly, and the surface flaws that are generated and promoted in the oval pass from the coarse row to the first stand in the middle row are shallowed.

In the above-described rough row pass rolling, box pass rolling and flat pass rolling have poor scale releasability because the material to be rolled and the roll are in surface contact with each other, and wrinkle flaws are generated by pushing the scale during rolling. This is an easy path. On the other hand, the rhomboid pass rolling is used for rolling high-grade steel because the material to be rolled and the roll are in convex contact with each other and the scale releasability is relatively good. As described above, the rough row pass having the best scale releasability and rolling stability is the rhomboid pass rolling, and it is difficult to further improve the pass schedule. Therefore, the present inventors intend to improve surface corner-side oval pass rolling, which is a pass that easily causes surface flaws because the surface compression strain becomes the largest, and increases the flaws in the rough row. The invention described in claim 4 is completed.

Therefore, in the hot rolling method for steel bars and wire rods according to the fourth aspect, the billet after heating is rolled into a square cross-sectional shape, and the intermediate material having the square cross-sectional shape is continuously rolled down from its four apex angles in four directions. To form a substantially octagonal shape or a substantially circular shape, and then roll with a hole type roll row of intermediate and finishing rows provided with an oval hole type and a round hole type, so that scale indentation flaws, wrinkle flaws and other surface flaws It is possible to perform rolling with a small amount and to manufacture steel bars and wire rods with few surface defects. This method improves wrinkle flaws in corner-to-oval pass rolling, and the hole shape of the rolling roll up to the square cross-sectional shape is not particularly limited (flat pass is also acceptable), but scale indentation flaws In order to effectively improve, it is preferable to use rhomboid pass rolling with a square hole roll, which can be expected to cause scale peeling.

According to a fifth aspect of the present invention, in the hot rolling method for steel bars and wire rods according to the fourth aspect of the invention, the ratio of the longest diameter D to the shortest diameter d of the intermediate material after being rolled into a square cross section in a coarse row is used. (D /
d) is formed into a substantially octagonal shape or a substantially circular shape within the range of 1 to 1.2. With such a shape, it is possible to more effectively obtain the action and effect of reducing the scale indentation flaws and the wrinkle flaws according to the fourth aspect.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 2 to 4 are schematic views showing a hole shape of a reduction roll for reducing the four apex angles of a square billet or an intermediate material having a square cross section according to the present invention from four directions to form a substantially octagonal shape or a substantially circular shape. is there.

The reduction roll 1 shown in FIG. 2 is formed so that the cross-sectional shape in the roll axial direction is hourglass-shaped and the roll surfaces 2 and 3 form 90 degrees at the central portion. By providing a pair of the pressing rolls 1 facing each other and applying pressure from two directions, the rolled material 4 having a square cross section can be pressed from four directions. By this reduction, the material to be rolled 4 is formed into a substantially octagonal shape or a substantially circular shape in cross section as shown in FIG. 2b. The ratio (D / d) of the longest diameter D and the shortest diameter d of the cross section in FIG. 2b is about 1.
It is 1.

When the above-mentioned forming is carried out on a square billet after heating, the scale can be sufficiently removed by the forming, and thereafter, by rolling with a hole-type roll row, the surface such as scale indentation flaws can be removed. Rolling with few flaws can be performed, and steel bars and wire rods with few surface flaws can be manufactured. Also,
When the above-mentioned forming is performed on the intermediate material after the billet after heating is rolled into a square cross-sectional shape by the coarse row provided with the square hole type rolls, then the intermediate piece having the oval hole type and the round hole type is formed. Also, by rolling with a hole-type roll row in the finishing row, rolling with less surface flaws such as scale-indented flaws and wrinkle flaws can be performed, and steel bars and wire rods with less surface flaws can be manufactured.

The reduction roll 5 shown in FIG. 3 is a flat roll having a flat roll surface 6. By providing two pairs of the pressing rolls 5 facing each other and applying pressure from four directions, the rolled material 4 having a square cross section can be pressed from four directions.
By this reduction, the rolled material 4 is formed into a substantially octagonal shape or a substantially circular shape in cross section as shown in FIG. 3b. The ratio (D / d) of the longest diameter D and the shortest diameter d of the cross section in FIG. 3b.
Is about 1.1.

The reduction roll 7 shown in FIG. 4 is an hourglass roll whose roll surface 8 has a roundness (arc). By providing two pairs of the pressing rolls 7 facing each other and applying pressure from four directions, the rolled material 4 having a square cross-sectional shape can be pressed from four directions. By this reduction, the material to be rolled 4 is formed into a substantially octagonal shape or a substantially circular shape in cross section as shown in FIG. 4b. The ratio (D / d) of the longest diameter D and the shortest diameter d of the cross section in FIG. 4b is about 1.0.

Even in the case of forming by the pressing rolls 5 and 7 shown in FIGS. 3 and 4, the same operational effect as in the case of forming by the pressing roll 1 shown in FIG. 2 can be enjoyed. That is, when the above-mentioned molding is performed on a square billet after heating, the scale can be sufficiently removed by the molding, and by rolling with a hole roll row after that, surface flaws such as scale-indented flaws. It is possible to perform rolling with few defects and to manufacture steel bars and wire rods with few surface defects. Further, when the above-mentioned forming is performed on the intermediate material after rolling the billet after heating into a square cross-sectional shape, the intermediate and finishing row hole-type rolls including the oval hole type and the round hole type thereafter. By rolling in rows, rolling with less surface flaws such as scale-indented flaws and wrinkle flaws can be performed, and steel bars and wire rods with less surface flaws can be manufactured.

[0025]

[Embodiment 1] This embodiment relates to the invention of claim 1. A 150-square billet (SCM435) is heated according to a conventional method, and the billet after the heating is formed into a substantially octagonal shape or a substantially circular shape by the pressing roll having the shape shown in FIGS. Was rolled into a round bar of φ12.0 mm. For comparison, a 150-square billet (SCM4
After heating No. 35) in the usual manner, it was rolled into a round bar of φ12.0 mm under the usual rolling conditions (No. 1 in Table 1). In addition, No. 1 in Table 1. No. 2 is shown in FIG. 3 is N in FIG.
o. 4 corresponds to forming with the reduction roll of FIG. Also,
The billet extraction temperature during heating in this example is 1000 ° C., and the final rolling speed is 30 m / sec.

[0026]

[Table 1]

Round bar (φ12.0 mm) obtained by the above rolling
The surface flaws of No. 1 were examined using an optical microscope (magnification: 400 times). Figure 5 shows the distribution of the maximum surface flaw depth based on the survey results.
Shown in. In addition, a in FIG. 1 (comparative example),
b is No. 2 (invention example), c is No. 3 (invention example), d is No. 4 (invention example).

As is apparent from FIG. 5, in all the examples of the present invention, the surface defects having a depth of 30 μm or more, which have been considered as harmful surface defects in the comparative example, are eliminated.
The maximum is about 10 μm. It should be noted that what remains in the example of the present invention is that the flaw depth is less than 5 μm.
73% in c and c and 75% in d were less than 5 μm, which was a good result.

[Embodiment 2] This is an example of the case according to the invention of claim 4. A 150-square billet (SCM435) was heated in a usual manner, and the billet after heating was subjected to rhomboid pass rolling under the rolling conditions shown in Table 2 in a rough row to be rolled into an intermediate material having a square cross section of 50 mm, and subsequently, After the intermediate material is formed into a substantially octagonal shape or a substantially circular shape by the reduction roll having the shape shown in FIGS. 2 to 4, the intermediate row and subsequent rows shown in Table 2 are subjected to oval pass rolling to obtain a φ15.0 mm circle. It was rolled into a bar. For comparison, a 150-square billet (SCM
435) was heated in the usual manner, and then rolled into a round bar of φ15.0 mm under the usual rolling conditions (No. 1 in Table 2). In addition, in Table 2, No. No. 2 is shown in FIG. 3 is N in FIG.
o. 4 corresponds to forming with the reduction roll of FIG. Also,
The billet extraction temperature during heating in this example is 1000 ° C., and the final rolling speed is 30 m / sec.

[0030]

[Table 2]

Round bar obtained by the above rolling (φ15.0 mm)
The surface flaws of No. 1 were examined using an optical microscope (magnification: 400 times). Figure 6 shows the distribution of the maximum surface flaw depth according to the survey results.
Shown in. In addition, a in FIG. 1 (comparative example),
b is No. 2 (invention example), c is No. 3 (invention example), d is No. 4 (invention example).

As is apparent from FIG. 6, in all of the examples of the present invention, the surface defects having a depth of 30 μm or more, which have been considered as harmful surface defects in the comparative example, are eliminated.
The maximum is about 10 μm. In the example of the present invention, what remains is that the flaw depth is less than 5 μm.
45% in c and c and 49% in d were less than 5 μm, which was a good result.

[0033]

As described above, according to the hot rolling method for steel bars / wires according to the present invention, scale indentation flaws,
It is possible to reduce not only wrinkle flaws but also surface flaws generated on the surface of the material to be rolled.

[Brief description of drawings]

FIG. 1 is a view for explaining a difference in contact between a rolled material and a roll due to a difference in cross-sectional shape of the rolled material during the oval pass between corner → oval pass rolling and round → oval pass rolling. It is a schematic diagram, a is a case of square-> oval pass rolling, b is a case of round-> oval pass rolling.

FIG. 2 is a schematic diagram showing a hole shape of a reduction roll for reducing the four apex angles of a square billet or an intermediate material having a square cross section according to the present invention from four directions to form a substantially octagonal shape or a substantially circular shape. ,
a is a roll before reduction and a rolling material, b is a roll and reduction material under reduction.

FIG. 3 is a schematic diagram showing a hole shape of a reduction roll for reducing the four apex angles of a square billet or an intermediate material having a square cross section according to the present invention from four directions to form a substantially octagonal shape or a substantially circular shape. ,
a is a roll before reduction and a rolling material, b is a roll and reduction material under reduction.

FIG. 4 is a schematic diagram showing a hole shape of a reduction roll for reducing the four apex angles of a square billet or an intermediate material having a square cross section according to the present invention from four directions to form a substantially octagonal shape or a substantially circular shape. ,
a is a roll before reduction and a rolling material, b is a roll and reduction material under reduction.

FIG. 5 is a graph showing distribution of maximum surface flaw depth in a round bar obtained by the hot rolling method for a steel bar / wire according to the present invention (Claim 1), where a is a comparative example and b is a comparative example. Through d are examples of the present invention.

FIG. 6 is a graph showing distribution of maximum surface flaw depth in a round bar obtained by the hot rolling method for a steel bar / wire according to the present invention (claim 4), where a is a comparative example and b is a comparative example. Through d are examples of the present invention.

[Explanation of symbols]

1,5,7: Roll down 2,3,6,8:
Roll surface 4: Rolled material D: Longest diameter
d: shortest diameter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Fujio Koizumi             2nd Nadahama Higashi-cho, Nada-ku, Kobe City, Hyogo Prefecture Stock Association             Company Kobe Steel Works Kobe Steel Works (72) Inventor Katsuhiko Ozaki             1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture             Kobe Steel Co., Ltd.Kobe Research Institute (72) Inventor Mikako Takeda             1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture             Kobe Steel Co., Ltd.Kobe Research Institute F-term (reference) 4E002 AC12 AC14 BA01 BB01 BC01                       CB03                 4E016 AA04 AA05 BA01 BA08

Claims (5)

[Claims] 1. A method of hot rolling a billet into a steel bar / wire rod using a rolling facility having a row of rolls from a coarse row to a finishing row, wherein a square billet after heating has four vertex angles in four directions. A method of hot rolling a steel bar / wire material, comprising rolling the material into a substantially octagonal shape or a substantially circular shape by rolling from a hole roll roll row. 2. A row of perforated rolls from a coarse row to a finishing row,
The hot rolling method for steel bars and wire rods according to claim 1, wherein the hot rolling method is a hole type roll row including an oval hole type and a round hole type. 3. The heated billet is formed into a substantially octagonal shape or a substantially circular shape having a ratio (D / d) of the longest diameter D and the shortest diameter d in the range of 1 to 1.2. The method for hot rolling a steel bar or wire according to 1 or 2. 4. A method of hot rolling a billet into a steel bar / wire rod using rolling equipment from a rough row to a finishing row,
The billet after heating is rolled into a square cross-sectional shape, and the intermediate material of the square cross-sectional shape is continuously pressed to form four octagons from four directions to form a substantially octagonal shape or a substantially circular shape. A method for hot rolling of steel bars and wire rods, which comprises rolling with intermediate and finishing row hole roll rows each having a round hole shape. 5. A substantially octagonal shape or a substantially circular shape in which the ratio (D / d) of the longest diameter D and the shortest diameter d of the intermediate material after being rolled into a square cross-sectional shape in a rough row is in the range of 1 to 1.2. The method for hot rolling a steel bar and wire rod according to claim 4, wherein the hot rolling method is performed into a shape.