JP2852317B2 - Square steel pipe and method for manufacturing square steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention eliminates the residual stress of the corner R member of a large-diameter rectangular steel pipe, for example.
The present invention relates to a highly accurate square steel pipe and a method for manufacturing a square steel pipe, which recover deterioration of a steel sheet material, and in particular, improve remarkable reduction in elongation and increase in yield point ratio of the steel material.

[0002]

2. Description of the Related Art Conventionally, the following method is known as a method for mass-producing a thick-walled, large-diameter rectangular steel pipe, which is in growing demand as a column of a steel structure. First conventional method A single steel sheet is bent a plurality of times in parallel with its longitudinal axis direction by cold pressing, and each of the four places is bent to almost 90 ° to form a right-angle cross section in the longitudinal axis direction of the steel sheet. It is formed into an approximate pentagonal shape that is partially open.

[0003] The pentagonal approximate steel material is charged into a rectangular steel tube forming roll composed of a plurality of steps, and the cross-section thereof is formed into a rectangular shape by cold working, and a longitudinal joint is formed by high frequency welding, arc welding or gas welding. Butt-welded to form a one-seam square steel pipe with a square cross section according to the standard dimensions.
Next, the bending in the axial direction is corrected. Second conventional method One thick steel plate, multiple times in parallel with the longitudinal axis direction,
Each part is bent 90 ° by cold pressing.
The cross section is formed into a substantially U-shaped cross section.

A square approximate steel pipe is formed by facing the U-shaped cross-section steel materials in a pair, and the mutually grooved leg ends are butt-welded to form a roughly formed steel pipe, which is then mounted on a plurality of stages of square forming rolls. Then, by cold plastic working, the cross section is formed into a rectangular steel pipe shape as specified in the standard. Third conventional method A strip-shaped steel sheet is passed through a plurality of forming rolls and formed into a cylindrical shape by cold bending first. (Also called a tubing).

[0005] The round steel pipe is passed through a plurality of stages of square forming rolls, and each portion is bent at 90 ° by cold working to form a flat surface on each side. Mold into

Thereafter, the steel pipe is cut to form a large-diameter rectangular steel pipe having a standard length. In the first to third conventional rectangular steel pipe forming methods described above, in any case, a flat thick steel plate is bent by cold plastic working to form a steel pipe corner R portion, and a press die and / or a forming roll are used. Almost 90 by processing such as
° bending process is included. By the way, when a thick steel plate is cold and sharply bent at almost 90 °,
Since the plastic deformation is remarkably performed while a tensile force or a compressive force acts on the neutral surface in the steel plate cross section at the corner R portion, the mechanical properties of the deformed portion, particularly the corner R portion steel material, deteriorate, Conditions for brittle fracture to occur.

[0007] For example, a steel pipe corner R formed by cold bending may have strain hardening, reduced toughness,
In combination with the presence of high residual stress, etc., welding cracks due to welding in winter low sound, cracks during hot-dip galvanizing, and the like may occur. Also, the presence of these cracks,
In addition, there is a possibility that brittle fracture may occur when used at a low temperature and a large load is applied due to minute defects in the base material. In order to solve this kind of material problem in which thick-walled large-diameter rectangular steel pipes formed by cold forming are included, conventionally, manufacturers have used prefabricated round steel pipes, seamless pipes, etc. to convert fossil fuels such as oil and gas or It was proposed to make a rectangular cross section by heating with a heating device using electric energy as a heat source and hot plastic working through a multi-stage compressor. When the above method is used, the quality of the product is good, but the amount of deformation at the time of heat molding is large, and both ends of the steel pipe tend to be inferior in shape and the yield of material is poor, or distortion generated during heating and cooling is reduced. There are problems that cannot be ignored and that production is low due to the processing of one piece of steel pipe.

[0008] A separately formed large-diameter rectangular steel pipe is charged into an annealing furnace, and is heated to a temperature at which residual stress in the material is substantially eliminated, thereby improving the toughness of the material at the corner R. Also, a slow cooling method is known. In this case as well, there may be similar problems as described above. Further, the amount of plastic deformation at the time of cold working is large, and it takes time to produce the effect of improving the material by heating, which is not economical.

Alternatively, after the hot-rolled coil is formed into a round steel pipe by cold plastic working, the steel pipe is charged into a heating device using a fossil fuel such as electric energy, gas or oil, and heated, and Through a multi-stage forming roll device,
After hot plastic forming into a square section steel pipe, it is gradually cooled to produce a product (for example, Japanese Patent Application Laid-Open No.
-71720) has also been proposed.

In addition to the above-mentioned method, there is also a four-sided box method in which a large-diameter thick-walled square steel pipe is manufactured by combining four strip-shaped thick steel plates into a combined rectangular section and butt-welding the respective corners. It is known that this includes welding time,
Materials and inspections are labor intensive, inefficient and not economical.

[0011]

SUMMARY OF THE INVENTION The present invention is an improvement of the above-mentioned "method for improving the material of the corner R of a large-diameter rectangular steel pipe". In this method, a round shape formed by cold plastic working is used. Since a steel pipe is hot-formed to produce a square steel pipe having sharp corners R as specified, the deformation of the cross section of the steel pipe during hot is relatively large, and it is difficult to improve the processing accuracy. Also, there is a problem that the forming of the end face of the steel pipe becomes unstable. Further, severe temperature control and heating time control are required to maintain the heating temperature of the corner R formed by cold plastic working.

Therefore, the invention according to claim 1 of the present invention is sharper and thicker than the conventionally known corner portions of a large-diameter rectangular steel pipe, and the present invention is characterized in that It is an object of the present invention to provide a square steel pipe having a uniform corner R portion in which the toughness of a steel material is improved and the residual stress is suppressed below an allowable limit.

The invention according to claim 2 improves the toughness of the rectangular steel pipe material by minimizing the amount of hot deformation of the rectangular steel pipe as much as possible, makes the residual stress below the allowable limit, and reduces the material of the corner part. It is an object of the present invention to provide a method for manufacturing a high quality square steel pipe that is uniform and stable without deterioration.

[0014]

In order to achieve the above-mentioned object, in the present invention, a square steel pipe according to the first aspect of the present invention is obtained by heating a roughly formed square steel pipe larger than a product.
It is characterized by being obtained by hot drawing with a regular outer diameter and a radius of curvature at a corner R.

Therefore, according to the first aspect of the present invention, the corner R portion (corner portion) is sharpened and the thickness is increased.
In addition, it is possible to provide a square steel pipe having improved uniformity by improving the toughness of the steel material and suppressing the residual stress below an allowable limit.

According to a second aspect of the present invention, there is provided a method of manufacturing a square steel pipe, comprising: a roughly formed square having a diameter larger than a regular outer diameter of a product and a larger radius of curvature at a corner R portion than a regular corner R portion curvature radius; After the steel pipe is put in a heating furnace and heated as a whole, it is passed through a hot forming roll and hot drawn into a square steel pipe having a regular outer diameter and a regular corner R radius of curvature. is there.

According to the second aspect of the present invention, by inserting the roughly formed rectangular steel tube into the heating furnace and heating the whole as uniformly as possible, the residual stress and the material of the steel material based on the remarkable cold plastic deformation are obtained. Deterioration can be recovered, and residual strain due to heat of the steel material near the welded joint can be eliminated. Furthermore, by passing the rough-formed square steel pipe in the heated state through a hot forming roll and hot-drawing the square steel pipe having a regular outer diameter and a regular corner R radius of curvature, the corner where stress is concentrated after construction is formed. By increasing the thickness of the steel sheet in the R portion, the mechanical strength, particularly the yield ratio, of the steel pipe can be improved.

According to a third aspect of the present invention, there is provided a method for manufacturing a square steel pipe according to the second aspect of the present invention, wherein the temperature of the heated roughly formed square steel pipe is not lowered below the A ₃ transformation point. It is characterized by being passed through a forming roll.

[0019] Therefore, according to the invention of claim 3, by rough shaping RHS is hot molded before cools below A ₃ transformation point, kept to a minimum processing amount of hot, allowed the hot pressing step It can be shortened as much as possible to increase the accuracy of the cross section of the steel pipe, and can correct distortion, torsion, bending and the like generated in the rough formed steel pipe due to heat treatment.

According to a fourth aspect of the present invention, there is provided a method for manufacturing a square steel pipe according to the second or third aspect, wherein the rough-formed square steel pipe is formed by passing a round steel pipe through a square forming roll. It is a characteristic.

Therefore, according to the fourth aspect of the present invention, it is possible to manufacture a square steel pipe without performing bending by a press or the like.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
The state adopted in the production line for large diameter square steel pipes will be described with reference to the drawings. Since a partial modification is possible, it is not allowed to restrictively interpret the constituent elements of the manufacturing method of the present invention based on only the specific structure described in the present embodiment without special reason. .

FIG. 1 is a schematic explanatory view showing a process according to an embodiment of the manufacturing method of the present invention, and FIG. 2 shows a state of forming a thick steel plate corresponding to each of the above processes. In this embodiment, the thickness t3 is set to SS400 or SM490.
Using a 5 mm steel material, while transporting one thick steel plate 1 from the left in the figure by the transport device 2,
The width of both side edges is determined, and processing is performed by the groove processing machine 3.

The thick steel plate 1 is applied to a forming press 4 and
Cold plastic working is performed in parallel with the longitudinal direction to form a pentagonal cross-sectional steel plate 5 having a narrowest gap from which a bending die can be extracted in a part of the peripheral surface, sequentially bending four times. At that time, the angle of the steel plate shoulder corner was almost 92
°, the angle of both corners on the bottom is almost 115 °,
It is standard. However, the outer radius of curvature of each corner R portion is formed so as to have a roundness of about 3 to 6 times the thickness t of the steel sheet, and the toughness of local members deteriorates due to cold bending of the thick steel sheet 1 and the yield is reduced. Prevent deterioration of ratio and work hardening as much as possible.

The sectional steel sheet 5 is charged into a tack welding machine 6, and the sectional steel sheet 5 is successively approximated to a square shape through a plurality of forming rolls.
The butted portion is tack-welded with metal touch to form a roughly formed square steel pipe 7. At this time, the outer diameter of the tack-welded rough-formed square steel pipe 7 is a regular outer diameter of 500 × 500 m.
m slightly larger than m (for example, 510 × 510 mm
(525 x 525 mm). The tack welding may be continuous or discontinuous using the butt groove surface as a guide. Tab plates are respectively attached to portions where the tack welding intersects both end surfaces of the roughly formed rectangular steel pipe 7.

The above-mentioned tack-welded rough-formed square steel pipe 7
Is rotated 180 ° about the longitudinal axis to rotate the inner surface welding machine 8.
And apply a metal touch butt tack weld from the inside. As a welding method, a well-known technique at the time of the present application is applied.

The rough-formed square steel pipe 9 to which the above-mentioned inner surface is completely welded is turned into an outer surface welding machine 10 by being rotated by 180 ° about the longitudinal axis, and the butted portion of the metal touch is completely welded from the outside. And rough-formed square steel pipe 11 which has been subjected to internal and external main welding.
And

The roughly formed square steel pipe 11 is charged into a heating furnace 12, and the whole is uniformly heated to approximately 750 ° C. to 950 ° C., thereby deteriorating the material due to cold working at the time of forming the steel pipe. To recover welding distortion. The heating furnace 1
Kerosene, gas, electricity or the like can be used as the heat source.

Before the temperature of the heated roughly formed rectangular steel pipe is cooled to the A ₃ transformation point or lower, the hot formed roll 14
The steel pipe cross section is drawn close to the regular size by successively drawing on a plurality of forming rolls, and the outer radius of curvature of the corner R portion is set to about 1.5 t to 3.0 t of the regular by the final roll. Then, roll forming is performed so that the outer diameter becomes a regular outer diameter dimension of 500 × 500 mm. For example, a roughly formed square steel pipe 7
When the outer radius of curvature of the corner R portion is about 4 to 6 times the plate thickness t, the outer radius of curvature of the same portion in the hot-formed square steel pipe 15 is reduced to about 2.0 t to 3.0 t. Is preferred.

After the hot forming, the steel sheet is cooled to a normal temperature in the cooling floor 16 and the bending generated in the steel pipe is corrected by a straightening machine (straightening roll or press) 17.
By 9, it is carried out as a product (square steel pipe) 20.

The steps from the above-mentioned embodiment, that is, the pre-step of charging the heating furnace 12, are as follows: (a) One thick steel plate, for example, a thick steel plate having a thickness of about 50 mm , Width-adjusted beveling, two places in parallel in the longitudinal direction, bent by cold plastic working to form a U-shaped steel material, and buttocks of both legs with a pair of U-shaped steel materials facing each other A method of forming a two-seam roughly formed square steel pipe 7 by welding.

(B) Hot rolled coil, for example, plate thickness t9 mm
~ 25mm strip steel sheet is stretched out, put on a forming roll, its cross section is rolled by cold working and the butt surface is welded,
After forming a one-seam round steel pipe, a method of forming a roughly formed square steel pipe 7 through a square forming roll. In any case, the cross-sectional shape of the roughly formed rectangular steel pipe 7 is formed to have a large diameter of about 10 mm to 25 mm with respect to the regular outer diameter. The outer radius of curvature of the portion is formed to a size of about 3 to 6 times the thickness t of the plate, and in part, the amount of deformation of the steel material due to cold working is reduced, and it can be easily recovered by post heat treatment. In addition to allowing a certain degree of deterioration of the steel material, the deformation amount of the steel material due to hot working is reduced as much as possible in forming the product 20 from the rough-formed square steel pipe 7, and the unstable element of the shape due to the hot forming is reduced. It has been excluded.

As described above, the details of other functions and effects according to the present embodiment are as described above.

[0034]

According to the first aspect of the present invention, the corner R is sharpened, the wall thickness is increased, the toughness of the steel material is improved, and the residual stress is suppressed to a permissible limit or less. Can provide a rectangular steel pipe. in this way,
Since the corner R can be formed sharply without deterioration of the material, the usability of the rectangular steel pipe is improved, the appearance is improved and the commercial value is increased, and when the same steel material is used, the section modulus is increased. Can be. Further, the curvature radius of the corner R can be made the same regardless of the thickness of the steel material, which is advantageous in construction.

According to the second aspect of the present invention,
By inserting the roughly formed square steel pipe into the heating furnace and heating the whole as uniformly as possible, it is possible to recover the residual stress of the steel material due to remarkable cold plastic deformation and the deterioration of the material. The residual strain due to the heat of the material can be eliminated. Furthermore, by passing the rough-formed square steel pipe in the heated state through a hot forming roll and hot-drawing the square steel pipe having a regular outer diameter and a regular corner R radius of curvature, the corner where stress is concentrated after construction is formed. The strength can be increased by increasing the thickness of the steel sheet at the R portion, and the mechanical strength, particularly the yield ratio, of the rectangular steel pipe can be improved. In addition, because of the hot roll forming, the flatness, large bend and twist of the four sides of the rectangular steel pipe can be easily removed.

According to the third aspect of the present invention, the rough-formed square steel pipe is hot-formed before cooling to a temperature not higher than the A ₃ transformation point, thereby minimizing the amount of hot working and reducing hot working. The process can be shortened as much as possible to increase the accuracy of the cross section of the steel pipe.
It can correct twisting and bending.

Further, according to the fourth aspect of the present invention, a square steel pipe can be manufactured without bending by a press or the like.

[Brief description of the drawings]

FIG. 1 shows an example of an embodiment of the present invention and is a block diagram of a line in a method for manufacturing a rectangular steel pipe.

FIG. 2 is a cross-sectional view of a steel pipe material corresponding to each step.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thick steel plate 2 Conveyor 3 Groove processing machine 4 Forming press 6 Temporary welding machine 8 Inner surface welding machine 10 Outer surface welding machine 11 Rough forming square steel pipe 12 Heating furnace 14 Hot forming roll 15 Hot forming square steel pipe 16 Cooling floor 17 Straightening machine 20 products (Square steel pipe)

──────────────────────────────────────────────────続 き Continued on the front page (73) Patent holder 598134835 Shin Nakajima 4-26-27 Kichijoji Honcho, Musashino City, Tokyo (72) Inventor Taku Nakajima 3-70 Midorigaoka, Itami City, Hyogo Prefecture (56) References JP Hei 4-100632 (JP, A) JP-A-61-115614 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B21C 37/15

Claims (4)

(57) [Claims] 1. A square steel pipe obtained by heating a whole of a roughly-formed square steel pipe larger than a product, and then hot-drawing it to a regular outer diameter and a radius of curvature at a corner R. 2. A roughly-formed square steel pipe having a diameter larger than a regular outer diameter dimension and a larger radius of curvature at a corner R portion than a regular corner R portion curvature radius is put into a heating furnace and heated as a whole. A method for producing a square steel pipe, wherein the steel sheet is hot drawn into a square steel pipe having a regular outer diameter and a regular corner R radius of curvature through a hot forming roll. 3. The temperature of the heated roughly formed rectangular steel pipe is A ₃
3. The method for producing a rectangular steel pipe according to claim 2, wherein the pipe is passed through a hot forming roll while not being cooled below the transformation point. 4. The method for producing a square steel pipe according to claim 2, wherein the roughly formed square steel pipe is formed by passing a round steel pipe through a square forming roll.