JP2015098032A - Manufacturing method for butt-welded steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an excellently workable butt-welded steel tube having a butt-welded joint part of an excellent quality having no surface streak and having no crack caused even if applied to a machine work (e.g., expanded or pushed holding).SOLUTION: In a butt-welded steel tube manufacturing method for forming a continuously heated steel strip 1 into a tubular shape and making two edge parts of the steel strip face each other, then abutting and butt-welding the two edge parts at butt-welding rolls 4 thereby to manufacture a butt-welded steel tube 10, on the downstream side of the butt-welding rolls 4, the butt-welded joint parts on the inner face and/or the outer face of the butt-welded steel tube are irradiated with lasers 7a and 7b thereby to reduce the surface streaks of the butt-welded joint parts.

Description

  The present invention relates to a method for manufacturing a forged steel pipe suitable for a processed product (for example, a mechanical joint or the like) obtained by performing machining such as pipe expansion or push expansion, and in particular, in workability that allows easy machining. The present invention relates to a method of manufacturing a forged steel pipe that is excellent in quality of a forged contact portion.

FIG. 3 is a layout diagram schematically showing an example of a conventional forged steel pipe manufacturing facility. An arrow A in FIG. 3 indicates the traveling direction of the steel strip 1.
As shown in FIG. 3, a forged welded tube is conventionally formed into a tubular shape with a forming roll 3 after charging a steel strip 1 having a predetermined width into a heating furnace 2 and continuously heating it to a temperature range of 1100 to 1300 ° C. It is manufactured by forming and making the edge portions on both sides of the steel strip 1 face each other, and then joining both of the high-temperature edge portions by butting them with the forge welding roll 4 (hereinafter referred to as “abutting forge welding”). The general method for manufacturing the forged steel pipe 10 is to arrange the spray nozzle 5 on the entrance side of the forge roller 4 and perform the abutting forge welding while blowing oxygen or air from the spray nozzle 5.

The forged steel pipe 10 produced in this way can be produced with high efficiency forged steel pipes of various dimensions by continuously reducing the diameter to a predetermined outer diameter and thickness with a stretch reducer (not shown).
However, in the forged steel pipe 10, a portion 8 (hereinafter referred to as a forged welded joint) joined by abutting forge welding exists in the longitudinal direction, and the surface (inner surface and outer surface) of the forged steel pipe 10 extends along the forged welded joint 8. As a result, streaks 9a and 9b (hereinafter referred to as surface streaks) having a depth of about 0.1 to 0.3 mm are likely to occur. The forged welded steel pipe 10 in which the surface lines 9a and 9b are generated has a problem of causing cracks along the forged welded contact portion 8 by performing machining (for example, expanding, pushing and expanding).

The surface streaks that occur at the forging contact 8 are
(a) slitting the hot-rolled coil to cut out a steel strip 1 having a predetermined width;
(b) The steel strip 1 is conveyed by a roller conveyor or formed into a tubular shape.
(c) It is considered that the sag generated at the edge portion of the steel strip 1 is caused by spraying oxygen or air from the spray nozzle 5 immediately before the abutting forge welding. In other words, the wrinkles remaining in the streak form after the edge forging contact is the surface streaks 9a and 9b. In addition, when performing collaborative forging,
(d) The occurrence of a level difference (so-called misunderstanding) between both edge portions also causes the surface lines 9a and 9b.

Improving the quality of the forged joint 8 of the forged steel pipe 10 and preventing the surface streaks 9a, 9b will have great effects such as improving the yield of processed products such as mechanical joints, improving productivity, and improving deformation performance. It is done. Therefore, various techniques have been studied in order to prevent the surface lines 9a and 9b.
For example, Patent Document 1 discloses a technique for preventing surface streaking by cutting and removing the outer surface of a forging contact portion between a forging roll and a stretch reducer. Although this technique can remove the surface streaks on the outer surface of the forged steel pipe, it is inevitable that the surface streaks remain on the inner surface.

  Patent Document 2 discloses a technique for performing an abutting forge welding while spraying a high-speed combustion flame and heating both edge portions. Patent Document 3 discloses a technique for performing abutting forging while irradiating a laser and heating both edge portions. Patent Document 4 discloses a technique in which both edge portions are heated with a plasma arc, and further, forcibly forging while spraying oxygen. These are all techniques for preventing surface streaks due to the above (c), but it is difficult to prevent surface streaks caused by other causes.

Patent Document 5 discloses a technique in which an edge portion of a steel strip is cut and further abutting forge welding is performed while maintaining a predetermined upset rate. This technique can prevent surface streaks due to the above (a), but it is difficult to prevent surface streaks caused by other causes.
Although patent document 6 is not the manufacturing technology of a forge-welded steel pipe, the technique which cuts and removes a bead after high-frequency resistance welding, heats the obtained electric resistance welded steel pipe, and restrict | squeezes it to a predetermined dimension with a stretch reducer is disclosed. Since the removal of the bead of the ERW steel pipe is performed at room temperature, it is not necessary to ensure the heat resistance of the equipment. Therefore, when the cutting technique disclosed in Patent Document 6 is applied to a forged steel pipe and a high-temperature forged joint portion is cut, the equipment is exposed to a high-temperature environment, and failure tends to occur. This interferes with the manufacture of forged steel pipes.

  In other words, since surface streaks are caused by various causes, a technique for obtaining a forged steel pipe having no surface streaks at the forging and abutting portions on both the inner surface and the outer surface has not been established.

Japanese Unexamined Patent Publication No. 3-248715 JP-A-10-277636 Japanese Unexamined Patent Publication No. 7-32034 JP 57-4319 JP 2007-152430 A JP-A-60-15082

  The present invention eliminates the problems of the prior art, has a superior quality forged contact portion without surface streaks, and consequently does not crack even when subjected to machining (for example, pipe expansion, expansion, etc.) It aims at providing the method of manufacturing the forge-welding steel pipe excellent in property.

The present inventor studied the cause of surface streaks. And since the generation | occurrence | production cause of the surface streak was various, it turned out that it is difficult to suppress the generation | occurrence | production of a surface streak in the upstream of a forge roll. Therefore, the technology for removing the surface streaks generated by the abutting forging on the downstream side of the forging roll was examined in detail. As a result, when removing the surface streaks of the high temperature forging contact portion with a cutting tool (for example, a bite, etc.) on the downstream side of the forging contact roll for abutting and forging the high temperature steel strip formed into a tubular shape,
(A) Since it is necessary to maintain heat resistance in order to prevent failure of equipment, the construction of equipment becomes large and complicated.
(B) Since the seizure of the cutting tool to be used is likely to occur, it has been found that there is a problem that the life of the cutting tool is short and the productivity and yield of the forged steel pipe are adversely affected.

  From these research results, the present inventor has focused attention on a technique for irradiating a laser to dissolve the surface layer portion of the forging contact portion and then solidifying it again to eliminate the surface streaks. That is, since it is not necessary to use a cutting tool by irradiating a laser, the problem (B) described above can be solved. Furthermore, the laser can be transferred to a predetermined position inside and outside the forged steel pipe through a highly heat-resistant material such as glass fiber, and further irradiated to the forged joint area. The problem can be solved.

Since the depth of the surface streaks is about 0.1 to 0.3 mm, the surface streaks disappeared by irradiating a laser to melt the surface streaks by melting the surface layer part of the forging contact area and then solidifying again. Forging contact area can be formed.
The present invention has been made based on such knowledge.
That is, according to the present invention, a continuously heated steel strip is formed into a tubular shape, both edge portions of the steel strip are made to face each other, and then both edge portions are abutted and forged by a forging roll to produce a forged welded steel pipe. In the method of manufacturing a forged steel pipe, a laser beam is irradiated on the inner surface and / or the outer surface of the forged steel pipe at the downstream side of the forged roll to reduce the surface streaks of the forged steel welded part. is there.

  In the method for producing a forged steel pipe according to the present invention, it is preferable to irradiate a laser to heat the surface temperature of the forged joint portion to the melting point of the steel strip or higher. The beam width of the laser is preferably 5 mm or more.

  According to the present invention, it is possible to manufacture a forged welded steel pipe having an excellent quality forged contact portion having no surface streaks, and thus excellent workability in which cracking does not occur even when machined. There is a remarkable effect.

It is an arrangement figure showing typically an example of the manufacture equipment of a forge welded steel pipe to which the present invention is applied. It is sectional drawing which shows typically the example of the irradiation position of the laser in FIG. It is a layout view schematically showing an example of a conventional forged steel pipe manufacturing facility. It is sectional drawing which shows the example of a surface stripe typically. It is an arrangement figure showing typically other examples of manufacturing equipment of a forged steel pipe to which the present invention is applied. It is sectional drawing which shows typically the example of the irradiation position of the laser in FIG.

FIG. 1 is a layout diagram schematically showing an example of a forged steel pipe manufacturing facility to which the present invention is applied. An arrow A in FIG. 1 indicates the traveling direction of the steel strip 1.
In the present invention, lasers 7a and 7b are transferred from a laser oscillator (not shown) to predetermined positions inside and outside the forged steel pipe 10 on the downstream side of the forge welding roll 4 as shown in FIG. The surface (inner surface and outer surface) of the abutting portion 8 is irradiated (see FIG. 2). The transfer optical devices 6a and 6b for transferring the lasers 7a and 7b can be made of a glass wire (eg, glass fiber) for guiding the lasers 7a and 7b, or can be reflected, spectroscopically or condensed. Conventionally known means such as glass mirrors, prisms, and lenses are used. Laser irradiation is possible by protecting these optical devices from heat with a cylindrical material having a heat insulating structure (for example, an internal water-cooled multilayer structure).

By irradiating the lasers 7a and 7b, the surface of the forging contact portion 8 is heated and further melted to dissolve the surface stripes. Therefore, it is preferable that the surface temperature of the forging contact portion 8 is heated to the melting point of the steel strip 1 or higher.
Thereafter, the melted surface layer portion is solidified again to form the forging contact portion 8 in which the surface streaks disappear.

In the present invention, it is necessary to stably maintain the depth and shape of the molten pool of the forging contact 8 melted by the irradiation of the lasers 7a and 7b. When the energy density of the lasers 7a and 7b is too large, a keyhole is generated in the molten pool of the forging contact portion 8 and the shape of the molten pool is likely to fluctuate. On the other hand, if the energy density is too small, it is difficult to melt the surface layer portion of the forging contact portion 8. Therefore, the energy density of the lasers 7a and 7b is preferably in the range of 10 ⁴ to 10 ⁶ W / cm.

The energy density distribution of the laser beam varies depending on the focusing method such as a circular beam having a normal Gaussian intensity distribution (so-called Gaussian focusing beam) or a square beam having a top hat shape (so-called top-hat focusing beam). . Therefore, the energy density I is not particularly limited.
The condensing method is preferably a top hat type. Further, the variation (= 100 × [I _MAX −I _MIN ] / [I _MAX + I _MIN ]) between the maximum energy density I _MAX and the minimum energy density I _MIN in the top hat region is preferably 30% or less. The reason is that by using a top-hat type focused beam, irradiation with a uniform energy density is possible, the depth of the molten pool can be kept substantially constant, and the molten pool can be made shallower and wider. . As a result, the surface streaks of the forged steel pipe that is piped at a high speed can be reduced.

  If the beam widths of the lasers 7a and 7b are too large, not only the forging contact portion 8 but also the periphery thereof is melted over a wide range, so that the dimensional accuracy (particularly the thickness) of the forging steel pipe 10 is deteriorated. On the other hand, if the beam width is too small, a narrow molten pool is formed, so when the forging contact portion 8 is twisted in the circumferential direction, the forging contact portion 8 comes off from the laser irradiation region, and as a result, There is a possibility that the surface streak does not disappear and remains as it is. Therefore, the beam width of the lasers 7a and 7b is preferably in the range of 5 to 30 mm. If the depth of the molten pool at the surface layer portion of the forging contact portion 8 is too large, the forging contact portion 8 after solidifying again may be depressed. On the other hand, if the depth is too small, the surface streaks (about 0.1 to 0.3 mm) may not disappear and remain as they are. Therefore, the depth of the molten pool is preferably within the range of 0.1 to 0.4 mm.

As the types of lasers 7a and 7b, conventionally known lasers such as a YAG laser, a semiconductor laser, and a CO ₂ laser are used.

<Example 1>
The steel strip 1 was continuously supplied to the production facility shown in FIG. The procedure will be described below.
A steel strip 1 having a predetermined width is charged into a heating furnace 2 and continuously heated (1300 ° C.), and then formed into a tubular shape with a forming roll 3 so that the edge portions on both sides of the steel strip 1 face each other. Further, both the high-temperature edge portions were subjected to collision forging with forging rolls 4. The abutting forging contact was performed while blowing oxygen from the spray nozzle 5 disposed on the entrance side of the forging roll 4.

  On the exit side of the forging roller 4, the surface (inner surface and outer surface) of the forging contact portion 8 is irradiated with lasers 7a and 7b (see FIG. 2) to melt the surface layer portion of the forging contact portion 8 (that is, the surface streaks are dissolved). And then solidified again to eliminate surface streaks. The beam widths of the lasers 7a and 7b and the depth of the molten pool are as shown in Table 1. Forge welding No. 8 is an example in which laser irradiation is not performed (hereinafter referred to as a conventional example).

  The forged welded steel pipe (100 for each forged weld No.) was observed on the inner and outer forged joints to determine the presence or absence of surface streaks. For forged steel pipes with surface streaks, the depth of the surface streaks was measured. The maximum and minimum values are shown in Table 1. Of the invention examples disclosed in Table 1, the depth of the surface streaks of the forged welds No. 1 to 5 is 0 mm. It means that it was not recognized.

  In the forged welding Nos. 6 and 7 of the invention example, the lower limit of the surface streak depth is 0 mm because there are at least one of the 100 forged steel pipes in which no surface streak is observed. Means that. Forging weld No. 6 has a beam width of lasers 7a and 7b of less than 5 mm, so that surface streaks occur in some of the forged steel pipes. The quality of the parts is inferior. Forged weld No. 7 has a weld pool depth of less than 0.10 mm, so that some of the forged welded steel pipes have surface streaks, and the weld welded abutting part is more than forged welded No. 1-5, which is another invention example. The quality of is inferior.

The quality of the forging joint No. 8 which is a conventional example is the worst.
Next, these forged steel pipes (100 for each forged weld No.) were subjected to flare processing (a tube expansion ratio of 1.5), which is one form of tube expansion processing. The surface of the obtained processed product (particularly corresponding to the forging contact portion) was observed to determine the presence or absence of cracks. Table 1 shows the occurrence rate (%) of the cracks. The occurrence rate of cracks is a value calculated by the following equation (1).
Crack occurrence rate (%) = 100 x number of forged steel pipes with cracks / number of forged steel pipes subjected to flare processing (1)
Of the invention examples shown in Table 1, the crack occurrence rate of forged welds Nos. 1 to 5 is 0%. All forged steel pipes (100 pipes) are cracked in any forged weld number. It means no. Forge welding No. 6 of the invention example has a beam width of less than 5 mm of lasers 7a and 7b, so that cracks are generated from the surface streaks due to flare processing, and it is processed more than forge welding No. 1 to 5 of the other invention examples. Inferior. Forging weld No. 7 has a depth of the molten pool of less than 0.10 mm, so that cracks are generated from the surface streaks due to flare processing, and the workability is inferior to that of other welding examples No. 1 to 5.

It can be seen that the crack occurrence rate of the forged No. 8 which is the conventional example is the highest, and the workability is inferior to that of the invention example.
<Example 2>
The steel strip 1 was continuously supplied to the production facility shown in FIG. The procedure will be described below.

A steel strip 1 having a predetermined width is charged into a heating furnace 2 and continuously heated (1300 ° C.), and then formed into a tubular shape with a forming roll 3 so that the edge portions on both sides of the steel strip 1 face each other. Further, both the high-temperature edge portions were subjected to collision forging with forging rolls 4. The abutting forging contact was performed while blowing oxygen from the spray nozzle 5 disposed on the entrance side of the forging roll 4.
On the exit side of the forging roll 4, the outer surface of the forging contact 8 is irradiated with a laser 7a (see FIG. 6) to melt the surface layer of the forging contact 8 (ie, the surface streaks are melted), and then again. The surface streaks disappeared by solidification. Table 2 shows the beam width of the laser 7a and the depth of the molten pool. Forge welding No. 17 is an example in which laser irradiation is not performed (hereinafter referred to as a conventional example).

  The forged welded steel pipe (100 for each forged weld No.) was observed on the inner and outer forged joints to determine the presence or absence of surface streaks. For forged steel pipes with surface streaks, the depth of the surface streaks was measured. The maximum and minimum values are shown in Table 2. Of the invention examples disclosed in Table 2, the depth of the surface streaks of the forged welding Nos. 11 to 14 is 0 mm. All the forged steel pipes (100 pipes) have surface streaks in any of the forging numbers. It means that it was not recognized.

  In the forge welding Nos. 15 and 16 of the invention example, the lower limit of the surface streak depth is 0 mm because at least one of the 100 forged steel pipes has no surface streak. Means that. Forging weld No. 15 has a weld pool depth of less than 0.10 mm, so that surface streaks occur in some of the forged steel pipes, and the forging junction is more than forge welding No. 11-14, which is another invention example. The quality of is inferior. Forging weld No. 16 has a beam width of laser 7a of less than 5 mm, so that surface streaks occur in some of the forged steel pipes, and the forging joint area is more than the forging weld No. 11 to 14 of the other invention examples. The quality is inferior.

The quality of the forging joint No. 17 which is the conventional example is the worst.
Next, these forged steel pipes (100 pieces for each forge weld No.) were subjected to flattening with a flatness height ratio (= height after flattening / outer diameter of base pipe) of 0.5. The surface of the obtained processed product (particularly corresponding to the forging contact portion) was observed to determine the presence or absence of cracks. Table 1 shows the occurrence rate (%) of the cracks. The occurrence rate of cracks is a value calculated by the following equation (2).
Crack generation rate (%) = 100 x number of forged steel pipes with cracks / number of forged steel pipes used for flattening ... (2)
Of the invention examples shown in Table 2, the crack occurrence rate of forging Nos. 11 to 14 is 0%. In any forging No, cracks are observed in all forged steel pipes (100 pipes each). It means no. Forging weld No. 15 of the invention example has crack depth from the surface streak due to flattening because the depth of the molten pool is less than 0.10 mm, and workability is better than forge welding No. 11 to 14 of the other invention examples Is inferior. Forging weld No. 16 has a beam width of less than 5 mm of laser 7a, so that cracking occurs from the surface streak due to flattening, and the workability is inferior to that of other welding examples No. 11 to 14.

  It can be seen that the crack occurrence rate of the forged No. 17 which is the conventional example is the highest and the workability is inferior to that of the invention example.

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Heating furnace 3 Forming roll 4 Forge welding roll 5 Spray nozzle
6a Transfer optics (outside)
6b Transfer optics (inner side)
7a Laser (external side)
7b Laser (inner side)
8 Forging contact
9a Surface stripe (outside)
9b Surface stripe (inner side)
10 Forged steel pipe

Claims (3)

  A continuously welded steel strip is formed into a tubular shape, both edge portions of the steel strip are made to face each other, and then both edge portions are abutted and forged with a forging roll to produce a forged steel tube. In the manufacturing method, the laser welding is performed on the inner surface and / or the outer surface of the forge welded steel pipe on the downstream side of the forge weld roll to reduce the surface streaks of the forge welded portion. Steel pipe manufacturing method.   2. The method for producing a forged steel pipe according to claim 1, wherein the laser is irradiated to heat the surface temperature of the forged joint portion to a melting point of the steel strip or higher.   3. A method for manufacturing a forged steel pipe according to claim 1, wherein a beam width of the laser is 5 mm or more.

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