JPH0739009B2 - Method for manufacturing rectangular steel pipe with low yield ratio using circular steel pipe - Google Patents

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 low yield ratio rectangular steel pipe used for a column of a steel structure building in the field of construction and the like, and particularly for a large structure or artificial ground in the future. The present invention relates to a method for manufacturing a large diameter low yield ratio rectangular steel pipe which is expected to be used as a member.

[0002]

2. Description of the Related Art Conventional rectangular steel pipes are mainly small-diameter rectangular steel pipes used for automobile chassis and truss structures of buildings. Bending rolls are used for large-diameter steel pipes with a diameter of 600 mm or more. There was almost no demand except for the small amount of production. However, in recent years, a large-scale building or a large erected artificial ground has been developed, and a large demand for a large-diameter square steel pipe has come to be expected.

As a method of manufacturing a rectangular steel pipe, there is a method of rolling with a forming roll such as a method of manufacturing in an electric resistance welded steel pipe manufacturing process. Further, as a method of molding with a press, Japanese Patent Laid-Open No.
There is a method disclosed in Japanese Patent Publication No. 144339. This method consists of three steps. In the first step, the cross section is formed into a rhombic shape, in the second step, the blank tube is rotated by 90 ° to form the cross section into a rhombic shape in the same manner, and in the third step, the blank tube is further formed into 90 pieces. It is rotated to form a square steel tube with a square cross section. However, in the example, the outer diameter is 165.2 mmφ and the wall thickness is 4.5 mm.

[0004]

Most of the conventional methods for manufacturing a rectangular steel pipe as described above are intended for a small-diameter rectangular steel pipe, and these methods are applied to a large-diameter rectangular steel pipe having completely different manufacturing methods. Is difficult to do. That is, the method of forming a rectangular steel pipe each time by a bending roll or the like is suitable for small-quantity / multi-product production, but is not suitable for mass production. Furthermore, the method described in JP-A-55-144339 discloses
Although there is a point to be referred to when forming a rectangular steel pipe using a large-diameter pipe as a raw pipe, it is not suitable for mass production because it takes three steps and is formed into a rhombic cross section. Further, there is a possibility that problems such as the accuracy of R at the corner portion and the buckling of the four side portions may occur only by pressing.

Further, in any of the above-mentioned methods, if the steel pipe is still formed into a rectangular steel pipe, the workability of the corner portion is particularly large, and the yield ratio remarkably increases due to work hardening. recent years,
Due to earthquake resistance, it is required for building structural members to have a low yield ratio with high plastic deformability, and rectangular steel pipes as formed cannot meet the demand. An object of the present invention is to overcome the conventional technical problems in manufacturing a low yield ratio rectangular steel pipe using a circular steel pipe as a raw pipe, and to provide a method for manufacturing a large yield and reliable low yield ratio rectangular steel pipe. And

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a method of forming a circular steel pipe into a rectangular shape by using a circular steel pipe as a raw pipe.
After heating to a temperature of 00 ° C or higher and less than Ac _1, the temperature of the blank tube is 400 ° C or higher, and a jig with a tapered die that expands and contracts in four directions centering on the pipe axis through a taper inclination is placed in the pipe axis direction. By the reciprocating movement, the jig slides through the taper inclination, the tapered die expands and contracts in the radial direction of the circular steel pipe, and pushes and expands the circular steel pipe in four directions from the inner surface to complete the forming into a rectangular shape. Is a manufacturing method of a low yield ratio rectangular steel pipe having a circular steel pipe as a base pipe.

[0007]

1 is a schematic view showing a longitudinal section of a circular steel pipe corner forming machine according to the present invention, and FIG. 2 is a schematic view showing a cross section in the direction perpendicular to the machine, wherein a is a work piece, b is a tapered die, and c is a die.
Indicates a jig. The shape of the tapered die b differs depending on the material and size (outer diameter, wall thickness, length) of the raw pipe, and the R of the tip must be changed according to the requirement for the corner R of the rectangular steel pipe. Normally, the radius R at the tip is 1 to 3 of the wall thickness of the raw pipe.
About twice the length of the parallel part in the longitudinal direction of the tube is 300 to 1200
The taper angle θ shown in FIG. 1 is about 55 to 87 ° in mm.

The molding is carried out from the end of the raw pipe, the jig is pushed to a predetermined degree of molding, and then slightly pulled back, the tapered die is moved in the longitudinal direction of the raw pipe, and the pushing jig is pushed to the predetermined degree of molding again. repeat. The forming degree at this time is expanded by about 0.5 to 3% in order to secure the corner portion R, but as a result, sufficient tension is applied to the four side portions, which is also preferable in terms of securing the flatness. .

Further, it is preferable that the weld bead of the raw pipe does not come to the corner portion of the square steel pipe at the time of forming the square pipe. The reason for this is to avoid bead cracking that can occur if the weld bead is at a corner. Therefore, as the raw pipe, a spiral steel pipe or the like can be used as long as the outer weld beads are removed by cutting. Further, there is no problem even if the inner weld beads are removed by cutting.

When the weld bead of the raw pipe is to be cut and removed from both the inner and outer surfaces, by doing so, it becomes possible to obtain a rectangular steel pipe having a substantially uniform strength over the entire cross section of the steel pipe and good flatness at the four sides. You can In this case, the corner portion of the rectangular steel pipe can be located at any position, and the workability can be significantly improved. In the present invention, a UO steel pipe, a spiral steel pipe, and the like can be used as the raw pipe, but it is most preferable to apply the pipe expansion / straightening process in the UO steel pipe manufacturing process.

The square steel pipe manufactured as described above also has a large degree of workability at the corners as it is, and the yield ratio remarkably increases due to work hardening. Therefore, in the present invention, the material pipe is heated to a temperature of 400 ° C. or higher and lower than Ac ₁ , and thereafter the molding is finished at 400 ° C. or higher. This point will be described below.

Work hardening is caused by the accumulation of strain (dislocation), and in order to lower the yield ratio, the temperature at the time of molding should be increased.
It is necessary to recover the strain (dislocation) introduced by processing. Higher temperature is more effective in terms of recovery of strain (dislocation), but if the heating temperature exceeds Ac ₁ , the steel transforms and the structure of the base metal / material itself changes greatly, so the upper limit of the heating temperature is Ac ₁ The temperature was less than. On the other hand, at a low temperature, the effect of recovering the processing strain (dislocation) is small, so the lower limit of the heating temperature is set to 4
At the same time as 00 ° C., the molding end temperature was set to 400 ° C. or higher for any heating temperature.

By increasing the temperature in this way, the deformation resistance is also reduced, which is preferable in terms of equipment and operation.
It should be noted that the molding after heating may be carried out in the heating furnace or after extraction from the heating furnace as long as the completion temperature can be kept at 400 ° C. or higher.

[0014]

[Example] An outer diameter of 1240 mmφ, a wall thickness of 12 mm,
Using a UO steel pipe having a length of 12 m, it was heated to various temperatures in a heating furnace according to the method of the present invention and then formed into a rectangular steel pipe. In each case, by expanding the pipe by about 2%, it was possible to manufacture a square steel pipe of 1004 mm square with good corner roundness and flatness at the four sides.

Table 1 shows the tensile properties of the corner portion of the rectangular steel pipe together with the heating temperature and the forming end temperature. In Comparative Example 1 formed at room temperature, the yield ratio at the corners is significantly higher than that of the steel sheet before working. Further, in Comparative Example 2 in which the forming end temperature is low, the recovery of the work strain (dislocation) is insufficient and the yield ratio remains high. Furthermore, in Comparative Example 3 in which the heating temperature exceeds Ac ₁ , the structure itself has changed from the structure before processing, and the strength / yield ratio equivalent to that of the steel plate before processing cannot be secured. On the other hand, in each of the examples of the present invention, the work hardening and the increase in the yield ratio due to the work hardening were suppressed, and almost the same characteristics as the mother steel sheet before working were obtained.

[0016]

[Table 1]

[0017]

As described above, according to the present invention, it is possible to easily produce a large amount of a low yield ratio rectangular steel pipe from a large diameter steel pipe, and it is expected to be a large-scale building or a member for artificial ground in the future. It is possible to supply products to be attached.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in the longitudinal direction of a steel pipe of a square steel pipe corner forming machine according to the present invention.

FIG. 2 is a schematic view showing a cross section in the direction perpendicular to the plane.

[Explanation of symbols]

 a Workpiece b Tapered die c Jig

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Hirokawa 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Stock Company Kimitsu Works (56) Reference JP-A-55-144339 (JP, A) Sho 54-161576 (JP, A)

Claims (3)

[Claims] 1. A method for forming a circular steel pipe into a rectangular shape as a raw pipe, wherein the raw pipe is heated to a temperature of 400 ° C. or higher and lower than Ac ₁ and thereafter, the temperature of the raw pipe is 400 ° C. or higher and a taper inclination is centered on the pipe axis. By reciprocating a jig with a tapered die that expands and contracts in four directions through the pipe axial direction, the jig slides through a taper inclination and the tapered die expands and contracts in the radial direction of the circular steel pipe. Round steel pipe from inside 4
A method for producing a rectangular steel pipe having a low yield ratio, which comprises forming a circular steel pipe as a raw pipe, characterized in that the forming into a rectangular shape is finished by expanding in a direction. 2. The element pipe is formed into a rectangular shape after the outer surface weld bead of the circular steel pipe is removed by cutting.
A method for producing a rectangular steel pipe having a low yield ratio, which uses the circular steel pipe as described above as a raw pipe. 3. The production of a low yield ratio rectangular steel pipe using the circular steel pipe as a raw pipe according to claim 1, wherein after the inner and outer weld beads of the circular steel pipe are cut and removed, the raw pipe is formed into a square shape. Method.