JPH0924417A - Producing method of bott welded steel tube having highly strong butt welded part and high quality - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a butt welded steel tube having a highly strong butt welded part and high quality by providing with a rotary cutting device and a tension roll between a forming roll and a butt welding roll to completely eliminate scale bitings, outer surface stripes and edge butt defect. SOLUTION: The tension roll 8 is provided with between the rotary cutting device 10 and the butt welding roll 6 in addition to the rotary cutting device 10 in order to completely restrain vibrations just before butt welding and to directly cut an edge part. Vibrations are completely restrained owing to tension acting on an edge part of a skelp before and after cutting by providing with the tension roll 8. As a result of that, the edge part of the skelp is linerly cut, rugged parts in the butt welded surface are eliminated and the occurrence of outer surface stripes and edge butt defect are completely eliminated. By this way, scale bitings in the butt welded part, outer surface stripes and edge butt defect are completely eliminated, whereby the butt welded steel tube having the strong butt welded part and high quality is produced.

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 forged steel pipe having a high strength and high quality forged portion.

[0002]

2. Description of the Related Art A conventional forged steel pipe manufacturing process is shown in FIG. The forged steel pipe is made by continuously heating a steel strip 1 as a material in a heating furnace 2
Then, it is heated to 1200 ° C. to 1300 ° C., molded by the molding rolls 3 and 4, and oxygen is blown to the edge portion from the nozzle 7 of the welding horn 5 just before forging to forge welding. After that, it is successively drawn by a drawing roll and rolled to continuously produce a forged steel pipe having a predetermined outer diameter and thickness. At this time, the oxygen blowing direction is the same as the traveling direction of the tubular skelp, and the position where oxygen is blown from the oxygen nozzle to the edge is just before forging, so the scale of the forged surface that has not been removed and the blown forged surface The invading scale bites into the forged surface and the strength of the forged part decreases.

Further, the forged steel pipe is formed by hot forming a soft material, and the pipe forming speed in the vicinity of forging is as high as about 100 m / min, so that the vicinity of the skelp edge is unstable and vibration occurs.
Such a phenomenon that occurs during molding is one of the factors that cause defective edge butting, and the strength of the forged portion decreases. In order to prevent the outer surface line of the forged portion of the forged steel pipe during the production of the forged steel pipe, the outer surface of the forged portion is cut off between the forging roll and the drawing roll to prevent the outer surface line of the forged portion as disclosed in JP-A-3-248715. Method and Japanese Patent Laid-Open No. 2-3421
There is a manufacturing method for preventing buckling that occurs at the edge of the skelp by applying a tension to the skelp formed up to the forming roll as in Japanese Patent Laid-Open No. 4).

[0004]

As shown in FIG. 5, in the conventional manufacturing process, the position where oxygen is blown is from the nozzle 7 of the welding horn 5 immediately before forging, and the oxygen blowing direction is the same as the traveling direction of the tubular skelp. Same direction. For this reason, the scale of the forged surface that has not been removed and the scale that has been blown off and that has entered the forged surface are caught in the forged surface, and the strength of the forged portion is reduced. As shown in FIG. 4, there are two types of skelp edge shapes when the hot-rolled coil is sheared by a slitter to a predetermined width of the steel strip, that is, bar-up (a) and bar-down (b). When the forged welded surfaces having such a shape are butted against each other, an inner bead and a streak are generated in the forged welded portion, and the strength and quality of the forged welded portion deteriorate.

Since the forged steel pipe is hot formed by soft material and the pipe forming speed in the vicinity of forged welding is as high as 100 m / min, unstable and vibration occurs in the vicinity of the skelp edge, and such a phenomenon occurred during forming. Is one of the factors that cause the edge butting failure. By applying the method of the present invention, scale entrapment, outer surface streaks, and edge butting defects in the forged portion are completely eliminated, and a forged steel pipe with high strength and high quality in the forged portion can be manufactured.

[0006]

According to the present invention, a steel strip 1 as a material shown in FIG. 5 is heated in a heating furnace 2, and the heated steel strip is hot-formed into a tubular shape and then forged to an edge portion of a tubular skelp. In the production of a forged steel pipe in which oxygen is blown from the nozzle 7 of the immediately preceding welding horn 5 in the same direction as the advancing direction of the tubular skelp, the shape of the forged surface of the edge of the tubular skelp is adjusted to be flat and the outer surface line and the edge abutment defect In order to completely eliminate the generation, a rotary cutting device 10 and a tension roll 8 are provided between the forming rolls 3 and 4 and the forging roll 6.
Is a method for manufacturing a high-strength forged welded steel pipe with high strength.

The present invention will be described in detail with reference to FIGS. 1, 2 and 3. As shown in FIG. 2, a rotary cutting tool 9 is attached to the rotary cutting device 10. The cutting tool is vertical, horizontal and mounting angle θ so that all pipe sizes can be cut.
Can move freely. The cutting tool cuts at a high temperature exceeding 1000 ° C, but it is sufficient to use commercially available high temperature super steel or fine ceramics and water cooling. In the conventional manufacturing process, the oxygen blowing position was just before forging, and the scale of the forged surface was not completely removed because it was in the same direction as the tubular skelp's advancing direction. However, there is a problem in that the strength and quality of the forged portion are deteriorated due to the inclusion of foreign matter.

The shape of the skelp edge when the hot rolled coil is sheared by a slitter to a predetermined width of the steel strip is shown in FIG.
There are two types, bar up (a) and bar down (b), as shown in Fig. 2. When the edges of such a shape are butted against each other, inner beads and outer lines are generated in the forged portion, and the strength and quality of the forged portion deteriorate. There is a problem. In order to solve these problems, as shown in FIGS. 1 and 2, in addition to the blowing of oxygen from the welding horn 5 immediately before forging, the rotary cutting device 1 is provided between the forming rolls 3 and 4 and the forging roll 6.
Set 0. The rotary cutting device 10 is installed for the purpose of adjusting the shape of the forging surface of the edge portion of the tubular skelp to be flat and removing the scale attached to the forging surface of the edge portion of the tubular skelp during the heating furnace and hot forming.

However, when the edge portion of the tubular skelp is cut, the forged steel pipe is hot-formed by a soft material and the pipe forming speed in the vicinity of forging is as high as about 100 m / min, so that the vicinity of the skelp edge is unstable and vibrates. Occurs and it is difficult to cut the edge portion of the tubular skelp linearly. As a result, unevenness is generated on the forged surface, and streaks on the outer surface and defective edge butting occur. In order to completely suppress the vibration just before forging and cut the edge portion linearly, a tension roll 8 is installed between the rotary cutting device 10 and the forging roll 6 as shown in FIGS. 1 and 3 in addition to the rotary cutting device. To do. By installing the tension roll 8 in addition to the rotary cutting device 10, tension acts on the skelp edge portion before and after cutting, and vibration is completely suppressed.

As a result, the edge portion of the skelp can be cut linearly, the unevenness of the forged surface is eliminated, and the occurrence of outer surface streaks and defective edge butting is completely eliminated. From the above, by applying the present invention, it is possible to completely eliminate scale biting, outer surface streaks and edge butting defects in the forged portion, and to manufacture a forged steel pipe with high strength and high quality in the forged portion.

[0011]

EXAMPLES Table 1 shows the results of practical tests, outer streaks, and occupancy ratio of foreign matters in the forged portion in the manufacturing process of the method of the present invention shown in FIG. Table 2 shows the results of the practical tests, the outer surface lines, and the occupancy ratio of the forged portion impurities in the conventional manufacturing process shown in FIG. The following formulas show the calculation methods of the flatness ratio, the expansion ratio, and the occupancy ratio of the forged portion impurities shown in Tables 1 and 2, respectively. Flatness = (1-H / D) × 100 (%) D: Outer diameter of plain pipe H: Flat height Push expansion ratio = D ′ / D D: Outer diameter of plain pipe D ′: Outer diameter of pipe after push expansion Occupancy rate of foreign matter in forged portion = L / t x 100 L: Length of all foreign matter in forged portion t: Pipe wall thickness

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

As described above, scale entrapment, outer surface streaks, and edge butting defects in the forged portion in the manufacturing process of the forged steel tube by the conventional method are completely eliminated, and a forged portion with high strength and high quality is obtained. It has become possible to manufacture.

[Brief description of drawings]

FIG. 1 is a plan view showing a method for manufacturing a forged steel pipe according to the present invention,

FIG. 2 is a cross-sectional view around a rotary cutting device according to the present invention,

FIG. 3 is a sectional view around a tension roll according to the present invention,

FIG. 4 is a diagram showing a skelp edge shape when cut by a slitter,

FIG. 5 is a plan view showing a manufacturing process of a conventional forged steel pipe.

[Explanation of symbols]

 1 Steel Strip 2 Heating Furnace 3 Forming Roll 4 Forming Roll 5 Welding Horn 6 Forging Roll 7 Nozzle 8 Tension Roll 9 Rotary Bit 10 Rotating Cutting Device a Bar Up Material b Bar Down Material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Ogata 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corp. Kimitsu Steel Co., Ltd.

Claims (1)

[Claims] 1. A steel strip heated in a heating furnace is hot-formed into a tubular shape, and then oxygen is blown onto the edge of the tubular skelp from the nozzle of the welding horn just before forging in the same direction as the advancing direction of the tubular skelp. In the manufacture of forged steel pipe,
A method for producing a forged steel pipe having a high-strength and high-quality forged portion, characterized by installing a rotary cutting device and a tension roll between the forming roll and the forging roll.