JPH10263626A - Seamless square steel pipe and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiency produce a seamless square steel pipe having small roundness at the corner parts in the cross section and flat sides by hot-rolling a cylindrical base stock so that the reduction rate of area from the round pipe stock to the square pipe satisfies a specific formula. SOLUTION: Calivers for the round cylindrical steel pipe are set to the rolls at No.1-No.4 stands to secure the peripheral length in the cross section of the pipe stock at the time of rolling with two rolls per stand. The rolls having square shaped calivers are used in No.5-No.8 stands to form the pipe stock fixing the peripheral length into the square shape. Then, the round pipe stock is hot-rolled so that the reduction rate of area from the round pipe stock to the square pipe satisfies the formula 0.20>=1-(Ao/Ai)>=0.05. In the formula, Ao is the cross sectional area (mm<2> ) of the material part in the square steel pipe at the outlet side of the finish stand in the shaping rolling mill, and Al is the cross sectional area (mm<2> ) of the material part in the round pipe stock at the inlet side of the square-forming stand in the shaping rolling mill. By this method, even in the case of being the thick pipe, the product having little roundness at the corner parts and flat sides, can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seamless steel pipe having a rectangular cross section and a method for manufacturing the same, and more particularly, to a method in which one stand includes two tubes.
This is a technique of manufacturing the seamless rectangular steel pipe by hot rolling using a sizer mill consisting of a plurality of rows of stands in rolls.

[0002]

2. Description of the Related Art In recent years, rectangular steel pipes have been frequently used for general structures, building materials, and equipment members. Several manufacturing methods are known for these well-known square steel pipes depending on the size, wall thickness, and the like. For example, square steel pipes with complex cross-sections are manufactured by hot extrusion,
Conventional rectangular steel pipes are manufactured by bending a steel plate and joining butted portions by welding. As disclosed in Japanese Patent Application Laid-Open No. 63-220922, first, a steel plate is formed into a circular shape and a joint is welded to form a circular shell (so-called electric resistance welded tube). Is gradually processed into a square cross section by passing through a sizer mill for a square steel pipe composed of a plurality of stands. However, since these methods are usually performed by cold working, there is a limit in thickness, size, and the like, and a step of removing working distortion after working is required.

In recent years, a facility for manufacturing seamless steel pipes (FIG. 6) has been developed so that large-sized, especially thick-walled rectangular steel pipes can be mass-produced.
Various attempts have been made with a focus on the use of the above. For example, Japanese Unexamined Patent Publication No. Hei 4-41006 discloses that "a raw pipe 1 having a circular cross section is obtained by piercing and rolling a material, and then, after reheating, is reduced to a required cross section by a sizer mill 2 comprising a number of rows of stands. The pipe is formed, and then hot-worked by a sizer mill having a rectangular cross section formed by a plurality of rolls 3, which is disposed on at least one or more stands at the subsequent stage of the sizer mill 2 equipment. A method of manufacturing a seamless rectangular steel pipe is disclosed.

By the way, in order to use a square steel pipe for a building structure such as a pillar, Japanese Industrial Standard (JIS G 346) has been adopted.
It is necessary to satisfy 6). One of them is the dimension of the corner of the steel pipe section shown in FIG. 2 (S value, defined by equation (2))
Is not more than three times the wall thickness t (S ≦ 3.0 t), and the flatness P of the side of the steel pipe is 0.5% or less of the side length L (P / L ≦ 0.00).
5). That is, the corners are as small as possible and the sides are flat. In practice,
It is desired that the size (S value) of the corner is stricter and 1.5 t or less.

[0005] If this demand is to be achieved by cold rolling, which is currently the mainstream in Japan, the radius of curvature R (which has substantially the same meaning as the S value) at the corners increases, and the roundness increases. In particular, in a thick steel pipe with t / L ≧ 0.05, R / t
> Becomes 3, as a result, also shortened the length L _F of the flat portion of the side shown in FIG. Therefore, it was considered that this problem would be solved by manufacturing by making it easy to work by hot rolling.
In fact, if the workability is increased and the area reduction rate by rolling the steel pipe cross section (to be described later, expressed by 1-A ₀ / A _i ) is increased, the R becomes smaller, and the length of the flat portion of the side becomes smaller. As the length became longer, the S value also became smaller. Note that, as shown in FIG. 2, the area reduction rate is a value at a solid portion of the cross section and does not include a space portion.

[0006] However, when the area reduction rate is increased as described above, buckling occurs in the steel pipe during rolling, and another problem that the flatness of the side is deteriorated occurs. JP-A-4-
Japanese Patent No. 41006 discloses that hot rolling is carried out by a three-roll sizer mill (fixed rolling mill). However, since there is no description of specific conditions to be implemented, there is no information on solving the problem from the publication. Could not be obtained.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method of manufacturing a seamless rectangular steel pipe capable of obtaining a product having a small rounded corner and a flat side even if it is thick. The purpose is to provide the steel pipe itself.

[0008]

Means for Solving the Problems In order to achieve the above object, the inventor has used a sizer mill of a seamless steel pipe manufacturing facility,
We worked diligently to find out the rolling conditions to reduce the roundness of the corners and flatten the sides of the square steel pipe. As a result, it was found that the object could be achieved by adjusting the degree of processing from the raw tube to the product, and the area reduction rate was adopted as an index of the degree of processing, thereby completing the present invention.

That is, the present invention provides a method for producing a cylindrical tube obtained by piercing a billet in a seamless steel pipe manufacturing facility, and then hot rolling the same into a rectangular tube by using a regular rolling mill. A method for producing a seamless rectangular steel pipe, comprising hot rolling the cylindrical raw pipe so that a reduction in area from the pipe to the square tube satisfies the following formula (1). 0.20 ≧ 1− (A ₀ / A _i ) ≧ 0.05 Expression (1) where A _{0 is} the cross-sectional area (mm ² ) of the square steel pipe on the exit side of the final stand of the fixed rolling mill. A _i : cross-sectional area (mm ² ) of the cylindrical tube at the entrance of the square forming stand of the fixed-size rolling mill. Or a temperature of the cylindrical tube of 600 to 1100 is used.
C. and a method for producing a seamless square steel pipe.

[0010] Further, the present invention provides a seamless square tube manufactured by forming a cylindrical tube obtained by perforating a billet in a seamless steel tube manufacturing facility and then hot-rolling the same into a square tube using a fixed-size rolling mill. A seamless tubular steel pipe, wherein an outer corner portion of the rectangular tube has an S value defined by the following equation (2) satisfying equation (3). S = (１ ／) × (L−L _F ) Equation (2) S ≦ 1.5 × t Equation (3) where L: side length (mm) of the steel pipe cross section L _F : Length of flat part of the side of steel pipe cross section (mm) t: Wall thickness of steel pipe (mm)
Since hot rolling is performed so as to keep it within a certain range, the roundness of the corners is reduced in the cross section of the product steel pipe, and the flatness of the side also satisfies a desired value. Further, since two horizontal rolls are used as a set in the sizer mill to be used, square steel pipes can be mass-produced at low cost simply by replacing only the rolls in the conventional seamless steel pipe facility.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows three examples of rolls of a fixed rolling mill (sizer mill) 2 used for manufacturing a seamless rectangular steel pipe according to the present invention. In FIG. 1, the sizer mill 2 has eight stands, and the rolls 3 from # 1 to # 4 stand are two rolls per stand. In order to secure the circumferential length of the tube section during rolling, a normal cylindrical steel pipe is used. Caliber 4 for manufacturing
(Hole type) is provided. The rolls 3 having the square calibers 4 are used for these stands only for forming the base tube 1 having the determined circumference into a square shape at the # 5 to # 8 stands. Thereby, the inner corner is determined corresponding to the outer corner. In the calibers 4 of the # 5 and # 6 stands, the radius of curvature R of the corners is reduced in order to prevent the side from being dented at the time of the standard form.

According to the present invention, the cylindrical tube 1 is shaped into a rectangular tube by hot rolling using such a sizer mill 2. At this time, as described above, during the rolling of the cross section of the tube 1, Is to be suppressed to 0.20 or less and 0.05 or more (see the equation (1)). According to the research of the inventor, even if it is hot working, when the reduction in area is out of this range, the roundness (R value) of the corner exceeds 2t, and as a result, the S value becomes 1.5t.
(See equations (2) and (3)), or the flatness P / L of the side is deteriorated, and a product of desired quality cannot be obtained. A specific means for satisfying the expressions (1) to (3) is to appropriately set the cross-sectional area of the caliber 4 of the roll 3. In particular, in FIG. The cross-sectional area of the tube at the entry side of the # 5 stand, which is a square forming stand, is important.

In the present invention, it is preferable that the temperature of the cylindrical tube 1 at the time of rolling is 600 to 1100 ° C. for rolling. If the temperature is lower than 600 ° C., the processing of the raw tube 1 becomes difficult, and the S value ≦ 1.5t cannot be achieved with a thick product. On the other hand, if the temperature exceeds 1100 ° C., the generation of scale increases, the surface properties of the product steel pipe deteriorate, and flaws also occur.

[0014]

EXAMPLE A seamless square steel pipe 11 was manufactured by applying the manufacturing method according to the present invention to a cylindrical raw pipe 1 having various outer diameters perforated by a piercer mill shown in FIG. The steel type of the raw tube 1 is JISG3466STKR400,
The reheating temperature after piercing-thinning and elongation rolling was 850.
It is within ５０1050 ° C. Sizer Mill 2 used
As for the stand, there were eight stands with two rolls, and a roll 3 of each stand having a caliber 4 as shown in FIG. 1 was used.

Table 1 collectively shows the size, reduction of area, roundness (R / t), flatness (p / L) and S value of the manufactured steel pipe.

[0016]

[Table 1]

The various data shown in Table 1 are arranged according to the area reduction rate and shown in FIGS. According to FIGS. 5 and 5, it is clear that the area reduction rate for achieving the S value of 1.5t or less or the R value of 2.0 or less is 0.05 or more. On the other hand, from FIG. 4, the flatness (P / L) of the side is 0.00
In order not to exceed 5, the area reduction rate needs to be 0.20 or less.

[0018]

As described above, according to the present invention, a seamless rectangular steel pipe having a small rounded corner and a flat side can be efficiently manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a caliber shape of a roll arranged in a sizer mill for forming a seamless rectangular steel pipe according to the present invention.

FIG. 2 is a sectional view illustrating the size of each part of a rectangular steel pipe.

FIG. 3 is a diagram showing a relationship between a reduction in area and a radius of curvature of an outer corner.

FIG. 4 is a diagram illustrating a relationship between a reduction in area and flatness of a side.

FIG. 5 is a diagram showing the relationship between the area reduction rate and the S value length.

FIG. 6 is a flowchart showing a facility for manufacturing a seamless steel pipe.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 raw tube (cylindrical raw tube) 2 fixed rolling mill (sizer mill) 3 roll 4 caliber 5 heating furnace 6 piercer mill 7 elongator 8 plug mill 9 reeler 10 reheating furnace 11 seamless square steel pipe (square tube)

Continued on the front page (72) Inventor Hideo Sato 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Kenichi Yamamoto 1-1-1 Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation (72) Inventor Takaaki Toyooka 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Takuya Nagahama 1-1-1, Kawasaki-cho, Handa City, Aichi Prefecture Chita Works

Claims (4)

[Claims] When a cylindrical tube obtained by perforating a billet in a seamless steel pipe manufacturing facility is subsequently hot-rolled by a fixed rolling mill to form a square tube, the cylindrical tube is converted into a square tube. A method for producing a seamless rectangular steel pipe, wherein the cylindrical raw pipe is hot-rolled so that the area reduction rate before the satisfies the following equation (1). 0.20 ≧ 1− (A ₀ / A _i ) ≧ 0.05 Expression (1) where A _{0 is the} cross-sectional area of the material of the square steel pipe at the exit of the final stand of the fixed rolling mill (mm ² ) A _i : Cross-sectional area (mm ² ) of the material of the cylindrical tube at the entrance of the square forming stand of the fixed form rolling mill 2. The method for manufacturing a seamless rectangular steel pipe according to claim 1, wherein a fixed rolling mill including a plurality of stands and one stand having two rolls is used for the hot rolling. 3. The method for producing a seamless rectangular steel pipe according to claim 1, wherein the temperature of the cylindrical raw pipe in a fixed rolling mill is set to 600 to 1100 ° C. 4. A seamless rectangular steel pipe manufactured by drilling a billet in a seamless steel pipe manufacturing facility and subsequently hot rolling it into a square tube using a fixed rolling mill. A seamless rectangular steel pipe characterized in that the S value defined by the following equation (2) at the outer corner of the rectangular tube satisfies the equation (3). S = (1/2) × (L−L _F ) Equation (2) S ≦ 1.5 × t Equation (3) where L: side length (mm) of steel pipe cross section L _F : Length of flat part of side of steel pipe cross section (mm) t: Wall thickness of steel pipe (mm)