JP3243665B2 - Manufacturing method of coiled 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 producing a coiled steel pipe for use in automobile or industrial machine parts, geothermal, chemical plants, oil well natural gas, and general piping.

[0002]

2. Description of the Related Art A coiled steel pipe is produced by drawing a forged steel pipe, an electric resistance welded steel pipe, a seamless steel pipe, or the like as a raw pipe by a hot stretch reducer, and then winding it into a coil. Thereafter, the coiled steel pipe is subjected to secondary processing such as drawing, cold forging, rolling, and screw cutting, and is used for various pipes and machine parts.

[0003] With respect to the coiled steel pipe,
As disclosed in Japanese Patent No. 125326, the coiled steel pipe is subjected to rolling at a temperature of at least Ar ₁ point in reduction rolling by a stretch reducer, and is rolled and allowed to cool. It is disclosed that since annealing is completed, a completely annealed structure can be obtained and secondary processing can be performed without annealing. On the other hand, as materials for automobiles and industrial machine parts that require a high degree of cold workability, materials whose surface flaw depth is strictly controlled are generally used, but conventional coiled steel pipes are used. When cold forging or rolling is performed, if there is a surface flaw on the inner surface of the coiled steel pipe, a work crack occurs.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems by remarkably reducing the surface flaws on the inner surface of the coiled steel pipe and making it harmless when manufacturing the coiled steel pipe. .

[0005]

SUMMARY OF THE INVENTION According to the present invention, when a coiled steel pipe is manufactured by hot drawing and rolling using an ERW welded steel pipe, a weld abutting portion on the inner surface of the ERW welded steel pipe is centered. 0.3 x wall width or more in the circumferential direction and 20 in the wall thickness direction
A region having a depth of μm to 200 μm is melt-solidified to produce a hot-drawing raw tube, subsequently, the hot-drawing raw tube is heated to a predetermined temperature, and then hot-rolled to form a coil. And roll it up.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method of manufacturing a coiled steel pipe according to the present invention and a coiled steel pipe manufactured by this method will be described. The method for manufacturing a coiled steel pipe according to the present invention uses the electric resistance welded steel pipe 1 formed by the electric resistance weld mill 1 as shown in FIG.
After the inner bead No. 1 is cut by the inner surface cutting device 4, the width and thickness are each 0.3 mm or more in the circumferential direction around the weld abutting portion A of the inner surface B of the ERW welded steel pipe 12. 20 μm in the direction
After melting and solidifying the region having a depth of ~ 200 μm as shown in FIG. 1, the ERW welded steel pipe 12 is heated from 900 ° C. to 1200 ° C. in the heating furnace 5, and the ERW welded steel pipe 12 is heated by the stretch reducer 6. Hot-tube drawing rolling. Subsequently, the coiled steel pipe 14 is manufactured by winding the ERW welded steel pipe 12 into a coil shape.

The ERW welded steel pipe 11 formed by the ERW mill 1 can be made of carbon steel, low alloy steel, or stainless steel. 0.3 × each in the circumferential direction of the welded portion A on the inner surface B of the ERW welded steel pipe 12 in which the inner bead has been cut.
As a means for melting a region having a width of not less than the thickness and a depth of 20 μm to 200 μm in the thickness direction, a method such as a TIG welding torch C or a laser beam can be used. As the heating furnace 5 for heating the electric resistance welded steel pipe 12 whose inner bead has been cut, a barrel furnace, a walking beam furnace, an induction heating furnace, or the like can be used.

The stretch reducer 6 is a rolling mill in which a roll housing of 2 rolls or 3 rolls is continuously arranged in 10 to 30 stands, and the ERW welded steel pipe 12 in which the inner bead is cut is rolled while the outer diameter is sequentially rolled. It is stretched in the axial direction by the difference in peripheral speed between adjacent stands,
The rolled tube 13 has a desired outer diameter and wall thickness.
Is guided by a pinch roller 7 and wound by a winder 8 to form a coiled steel pipe 14.

The reasons for limiting the structure of the present invention are as follows. When hot-rolled to produce a coiled steel pipe, the width of 0.3 × wall thickness or more in the pipe circumferential direction, centering on the weld joint on the inner surface of the ERW welded pipe, and in the wall thickness direction 20 μm-2
The reason for limiting the area of 00 μm to melt solidification is as follows.

That is, in the region within 0.3 × wall thickness in the circumferential direction of the pipe centering on the welded joint portion on the inner surface of the ERW, the welded joint portion is processed by set-up immediately after ERW welding. 0. In the solidified structure and in the circumferential direction of the pipe centering on the weld joint.
A region within 3 × thickness has a processed structure accompanied by a metal flow. The metal flow of the processing structure including the fusion zone,
When viewed from the end face side of the pipe, it becomes the thickness direction. Therefore, when the ERW welded steel pipe is hot-drawn and drawn, the physical properties such as strength, ductility, drawn value, Poisson's ratio, etc. are different from those of the base material. Wrinkles are generated near the inner surface weld. Further, immediately after the electric resistance welding, the inner surface welded portion from which the inner surface bead is removed has an uneven shape. The irregularities serve as starting points of wrinkles on the inner surface during the hot-rolling rolling process. The inner surface wrinkle flaw becomes a starting point of a working crack during cold forging or rolling.

[0011] Each of the ERW welded steel pipes according to the present invention has a width of at least 0.3 x the wall thickness in the pipe circumferential direction and the depth of 20 µm to 200 µm in the wall thickness direction, centering on the weld-welded portion on the inner surface of the steel pipe. The solidified structure produced by upset processing by melt-solidifying the steel is recrystallized by being heated from 900 ° C. to 1200 ° C. in a heating furnace before hot drawing rolling, and has a metal structure equivalent to the structure of the base metal part. (See FIG. 2).

Further, the irregular shape of the inner surface from which the inner bead has been removed immediately after the electric resistance welding has a width of at least 0.3 × wall thickness in the circumferential direction of the pipe centering on the weld contact portion, and 20 μm or more in the thickness direction. 2
A region having a depth of 00 μm is smoothed by melt-solidification, and the occurrence of wrinkles on the inner surface can be prevented in the hot drawing rolling process. However, the above-described electric resistance welding caused by the upset process even when a region having a width of at least 0.3 × the wall thickness in the circumferential direction of the pipe centering on the weld contact portion and a depth of less than 20 μm in the wall thickness direction is melt-solidified. Physical properties such as strength, ductility, reduction value, Poisson's ratio, etc. of the processed solidification structure of the welded part are different, wrinkles are generated on the inner surface during the hot drawing rolling process, and when the melting depth exceeds 200 μm, the molten metal falls Since the thickness of the fusion zone is insufficient, the fusion depth in the thickness direction is 20 μm to 200 μm.
Area. Using carbon steel and stainless steel, the area of 0.3 x wall thickness or more in the pipe circumferential direction around the weld abutment joint of the electric resistance welded steel pipe and the area of 20 μm to 200 μm in the wall thickness direction are melted and solidified. Table 1 shows the results of evaluating the cold workability of the coiled steel pipe manufactured by hot drawing rolling.

[Table 1] The coiled steel pipe manufactured by the manufacturing method of the present embodiment,
Since there is no internal wrinkle flaw harmful to the cold workability, the compression workability of the coiled steel pipe is good, and the cold workability is greatly improved as compared with the conventional coiled steel pipe.

[0013]

The coiled steel pipe of the present invention is manufactured by using an electric resistance welded steel pipe in which the inner surface welded area and the heat affected zone are re-melted and solidified when the coiled steel pipe is manufactured by hot drawing and rolling. It is possible to prevent the occurrence of wrinkles on the inner surface in the vicinity of the inner surface welded portion during the rolling process. Furthermore, the coiled steel pipe of the present invention is intended to prevent the occurrence of wrinkles on the inner surface in the vicinity of the inner surface welded portion, and has dramatically improved cold workability as compared with the conventional coiled steel pipe. The industrial value is enormous.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram in which a welding abutting portion on an inner surface of an ERW welded steel pipe obtained by cutting an inner bead used in the present invention is melt-solidified by a TIG welding torch.

FIG. 2 is a micrograph showing a metal structure obtained by solidifying an inner bead of the present invention and a metal structure heated at 1000 ° C. after solidification.

FIG. 3 is a diagram showing an example of a method for manufacturing a coiled steel pipe of the present invention.

[Explanation of symbols]

 11 ERW welded steel pipe 12 ERW welded steel pipe after inner surface bead cutting A ERW welded part B Surface cut by inner surface cutting device C TIG welding torch D Fused part

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C21D 9/08 C21D 9/08 F (56) References JP-A-60-125326 (JP, A) JP-A-2-258190 ( JP, A) JP-A-56-99016 (JP, A) JP-A-59-82187 (JP, A) JP-A-6-238488 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) B21C 37/08 C21D 8/10 C21D 9/08

Claims (1)

(57) [Claims] When a coiled steel pipe is manufactured by hot-drawing an ERW welded steel pipe from which an inner bead has been cut, each of the ERW welded steel pipes is circumferentially centered on a weld abutting portion on the inner surface of the ERW welded steel pipe. 0.3
× Width greater than wall thickness and 20 μm to 200 μm in the wall thickness direction
Melt-solidify the region of the depth to produce a hot-rolling raw tube, and then heat the hot-rolling raw tube to a predetermined temperature,
Subsequently, the hot-rolling rolling is carried out to form a coil.