JPH11104711A - Production method for seamless square shaped steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a product; wherein the curvature of the square part is small even if the product is thick, and the sides are plane. SOLUTION: In this method when a cylindrical base pipe obtained by making a fillet bored by a seamless steel pipe manufacturing equipment, is hot rolled to square tube shape by a hot roller for fixed shape rolling, the ratio of D0 which is the external diameter of the cylindrical base metal at the first inlet of a stand for the square tube forming among the stands of fixed shape rolls and 2h1 which is the external diameter of the square tube at the outlet of the stands including above the stand is determined as an external diameter ratio r1 in the formula, r1 =1n(2h1 /D0 ). The cylindrical base pipe is hot rolled to a square tube in a manner that the external diameter ratio rn from the first square forming stand to the square tube of the final stand satisfies 0.15-0.40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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, a rectangular steel pipe having a complicated cross-sectional shape is manufactured by a hot extrusion molding method, and a normal square steel pipe is manufactured by bending a steel plate and joining a butt portion by welding. This welding method is
As disclosed in JP-A-63-220922, first, a steel plate is formed into a circular shape, and a seam is welded to form a circular raw tube (so-called electric resistance welded tube). It is processed gradually into a square cross section by passing through a steel pipe sizer mill. However, since these methods are usually performed by cold working, there are limitations on the thickness, size, and the like of the square steel pipe to be manufactured, and a step of removing working distortion after working is required.

[0003] In recent years, a facility for manufacturing seamless steel pipes (FIG. 7) has been recently developed to enable mass production of large-sized, especially thick, rectangular steel pipes.
Various attempts have been made with a focus on the use of the above. For example, Japanese Patent Application Laid-Open No. 4-41006 discloses that "a raw pipe 1 having a circular cross section is obtained by piercing a material, and then, after reheating, is reduced to a required cross section by a sizer mill 2 composed of a number of rows of stands. A pipe is formed, and then hot-worked by a sizer mill formed of a plurality of rolls 3 and having a rectangular path cross section, which is disposed on at least one or more stands subsequent to the sizer mill 2. A method for manufacturing a square 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 that the dimensions of the corners (S value, defined by the following equation (2)) of the cross section of the steel pipe shown in FIG. 3 are not more than three times the wall thickness t (S ≦ 3.0 t), and Is 0.5% or less of the side length L (P / L ≦
0.005). That is, the corners are as small as possible and the sides are flat. In practice, the size (S value) of the corner is more strictly 1.5 times.
t or less is desired.

S = (１ ／) × (L−L _F ) Equation (2) where L: side length (mm) of the cross section of the square steel pipe L _F : flat of the side of the cross section of the square steel pipe Section length (mm) t: Wall thickness of square steel pipe (mm) If this demand is to be achieved by cold rolling, which is currently the mainstream in Japan, the radius of curvature R of the corner (which has almost the same meaning as the S value) ) Is large, that is, the roundness is large. In particular, t
The thick steel pipe /L≧0.05, becomes R / t> 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, the degree of work was increased, and the area reduction rate due to the rolling of the steel pipe section (described later, 1-
When A ₀ / A _i is increased, R becomes smaller, the length of the flat portion of the side becomes longer, and S
The value has also decreased. In addition, as shown in FIG. 3, the area reduction rate is a value at a solid portion of the cross section, and does not include a space portion.

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 of the cross section of the square steel pipe deteriorates occurs. Japanese Patent Application Laid-Open No. 4-41006 describes that hot rolling is performed by a sizer mill (standard-size rolling mill) using three rolls for one stand. No information on solving such a problem was obtained from the publication.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method of manufacturing a seamless rectangular steel pipe which can obtain a product having a small curvature at a corner and a flat side even if it is thick. It is intended to be.

[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 index of the degree of processing showed a reduction rate of the ratio of the outer diameter of the circular raw pipe to the outer diameter of the formed rectangular tube. (Hereinafter referred to as an outer diameter ratio reduction rate), thereby completing the present invention.

That is, the present invention relates to a method of forming a cylindrical tube obtained by piercing a billet in a seamless steel pipe manufacturing facility into a rectangular tube by hot rolling with a regular rolling mill and forming the rectangular tube into a rectangular tube. of the outer diameter D ₀ of the cylindrical blank tube in the first corner molding stand entry side, outside the ratio of the outer diameter 2h _i of the rectangular tube in the stand, including the subsequent stand delivery side by the following equation diameter ratio defined as r _i, an outer diameter ratio r _n from the first corner molding stand (i = 1) to the square tube of the final stand (i = n) is 0.15
A method for producing a seamless rectangular steel pipe, characterized in that the cylindrical raw pipe is hot-rolled into a rectangular tube so as to satisfy 0.40.

R _i = ln (2h _i / D ₀ ) (1) In the present invention, the hot rolling is performed by a square forming stand including two rolls per one stand and three or more stands. A method of manufacturing a seamless rectangular steel pipe characterized by performing. Furthermore, the present invention is interstand difference [Delta] r _i of the outer diameter ratio r _i
Is a method for manufacturing a seamless rectangular steel pipe characterized in that the size of the upstream stand is larger than that of the downstream stand.

[0011] In addition, the present invention is also a method for producing a seamless rectangular steel pipe, wherein the temperature of the material to be rolled in the square forming stand is set to 600 to 1100 ° C. In the present invention, since the degree of reduction of the outer diameter ratio is used as an index, and the degree of reduction of the cylindrical tube is hot-rolled so as to suppress it to 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.

[0012]

1 and 2 show 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 rolls 3 from # 1 to # 5 stand.
Is provided with a caliber 4 (hole type) for manufacturing a normal cylindrical steel pipe in order to secure a circumferential length of a cross section of the raw pipe at the time of rolling. Then, the cylindrical elemental tube 1 having the determined circumference is # 6.
In order to form into a square shape in 〜8 stands, a roll 3 having a square caliber 4 is used for those stands. Thereby, the inner corner is determined corresponding to the outer corner. In the calibers 4 of the # 6 and # 7 stands, the radius of curvature R of the corner is reduced to prevent the side from being dented at the time of the fixed 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 reduced within the range of 0.15 to 0.40 from the first square forming stand to the last stand. According to the study of the inventor, even if it is hot working, if the reduction ratio of the outer diameter ratio is less than 0.15, the S value becomes 1.
If it exceeds 5t, the desired roundness of the corner cannot be obtained, and if it exceeds 0.40, the flatness P / L of the side deteriorates, and a product of desired quality cannot be obtained. A specific means of achieving 0.15 to 0.40 is to appropriately set the cross-sectional area of the caliber 4 of the roll 3. In particular, in FIG. 1, the # 5 stand exit side, that is, the first square forming stand The cross-sectional area of the raw tube at the entry side of the # 6 stand is important.

Further, in the present invention, it is preferable that one stand of the square forming stand is formed of two rolls, and three or more stands are formed for a desired square forming. This is for the following reason. In order to improve the symmetry of the cross-sectional shape of the prism,
Heretofore, there has been a problem that a complicated roll structure is required, such as rolling down four rolls from up, down, left and right. In the present invention, by using two rolls, it becomes possible to form a rectangular cylinder having a simpler structure and excellent symmetry in cross-sectional shape. Note that at least three stands are required to obtain a rolling force for forming a cylinder into a rectangular cylinder.

Further, in the present invention, as shown in FIG.
Interstand difference [Delta] r _i of the outer diameter ratio r _i has a large upstream stand from the downstream stand. That is, in order to set the flatness (P / L) of the side of the cross section of the rectangular tube to a desired value, it is better to initially decrease the degree of processing in one stand without increasing the degree of processing irregularly. In addition, in the present invention, the material to be rolled is preferably rolled at a temperature of 600 to 1100 ° C. at the square forming stand. If the temperature is lower than 600 ° C., it is difficult to process the material 1 to be rolled.
This is because t cannot be achieved. 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.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various outer perforated by the piercer mill of FIG.
The production method according to the present invention is applied to a cylindrical raw tube 1 having a diameter.
And set the dimensional accuracy target to 2.0 or less in s / t.
A square steel pipe 11 was manufactured. The steel type of the raw tube 1 is J
It is STK490 of IS G 3466.
Reheating temperature after elongation rolling is 850 to 1050
It is within ° C. The sizer mill 2 used was
There are 8 stands with 2 rolls and each stand rolls
3 has a caliber 4 as shown in FIG.
used. In other words, # 1 to # 5 stands are circular calipers
4, the # 6 to # 8 stands have a square caliber 4
Rules. Table 1 shows the rolling of each manufactured square steel pipe.
Occasionally reduced outer diameter ratio at # 6 to # 8 stand obtained by formula (1)
Small fraction r _i (I is 1, 2, 3), the difference between each stand
Minute Δr_i , Tube temperature, corner roundness (s / t) and flatness
Degree (P / L).

[0017]

[Table 1]

The change of the s / t value and the edge flatness (P / L) of each manufactured square steel tube with respect to r _n (horizontal axis) is as follows:
As shown in FIG. As shown in FIG. 5, the square steel pipe manufactured according to the present invention has the desired values of s / t value and (P / L) (1.5 and 0.005 or less). And the desired value cannot be satisfied. Further, the angular steel pipe of the present invention examples (Experiment No.4), was prepared according to the conditions of the present invention the [Delta] r _i, to produce a square steel pipes of Comparative Examples (Experiment No.5) under the conditions of conventional. As a result, as shown in FIG. 6, it was also confirmed that a large difference occurred in flatness (P / L).

[0019]

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 and inexpensively 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 perspective view of FIG.

FIG. 3 is a cross-sectional view illustrating the size of each part of a rectangular steel pipe.

FIG. 4 is a diagram showing a difference in an outer diameter ratio r _i between square forming stands.

FIG. 5 is a diagram showing the results of the implementation of the present invention, wherein (a) shows s / t;
The value (b) is the side flatness (P / L).

FIG. 6: Change in difference in outer diameter ratio r _i and side flatness (P / L)
FIG.

FIG. 7 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)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takuya Nagahama 1-1, Kawasaki-cho, Handa-shi, Aichi Kawasaki Steel Corp. Chita Works (72) Inventor Takaaki Toyooka 1-1-1, Kawasaki-cho, Handa-shi, Aichi Kawasaki (72) Inventor Hideo Sato 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Nobuhiko Morioka 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Inside Chita Works, Steel Works (72) Inventor Masaharu Kita 1-1-1, Kawasaki-cho, Handa City, Aichi Prefecture Inside Chita Works, Kawasaki Works (72) Kenichi Yamamoto 1-1-1, Kawasaki-cho, Handa City, Aichi Prefecture Kawasaki Inside the Chita Works of Iron and Steel Corporation

Claims (4)

[Claims] When a cylindrical tube obtained by perforating a billet in a seamless steel pipe manufacturing facility is subsequently hot-rolled in a fixed rolling mill and formed into a rectangular tube, the first corner of the fixed rolling mill is used. the outer diameter D ₀ of the cylindrical blank tube at a molding stand inlet side defines an outer diameter ratio r _i the ratio between the outer diameter 2h _i by the following equation of the rectangular tube in the stand delivery side of the stand, including later , The outer diameter ratio r _n from the first square forming stand (i = 1) to the square tube of the last stand (i = n) is:
A method for producing a seamless rectangular steel pipe, wherein the cylindrical raw pipe is hot-rolled into a rectangular tube so as to satisfy 0.15 to 0.40. r _i = ln (2h _i / D ₀ ) (1) 2. The method for producing a seamless rectangular steel pipe according to claim 1, wherein the hot rolling is performed by a square forming stand having three rolls or more and one stand having two rolls. 3. A stand between the difference Δr _i of the outer diameter ratio r _i
3. The method for producing a seamless rectangular steel pipe according to claim 1, wherein the diameter of the pipe is larger at the upstream stand than at the downstream stand. _{Here, Δr i = r i -r i} + 1 4. The method according to claim 1, wherein the temperature of the material to be rolled at the square forming stand is set to 600 to 1100 ° C.
The method for producing a seamless rectangular steel pipe according to any one of claims 1 to 3.