JP5866790B2 - Laser welded steel pipe manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a steel pipe (hereinafter referred to as a laser welded steel pipe) in which an edge portion of an open pipe is welded using a laser beam, and in particular, extraction and transportation of oil and natural gas such as an oil well pipe or a line pipe. The present invention relates to a method for manufacturing a laser welded steel pipe suitable for the above.

Steel pipes used as oil well pipes or line pipes are roughly classified into welded steel pipes (for example, ERW steel pipes, UOE steel pipes, etc.) and seamless steel pipes. Among these steel pipes, ERW steel pipes are economically advantageous because they can be manufactured at low cost by using hot-rolled strip-shaped steel plates (so-called hot coils) as raw materials.
However, in general, ERW steel pipes are formed by forming steel plates into a cylindrical shape using forming rolls, and open pipes (here, open pipes are pipe-shaped steel strips that are formed by multi-stage forming rolls and not joined at the ends. Hereinafter, it is referred to as an open pipe), and electric resistance welding (also referred to as high-frequency resistance welding) is performed while pressing the edges of the open pipe (that is, both ends of the steel strip formed into a cylindrical shape) with a squeeze roll. Therefore, there is a problem that a seam by welding (so-called seam) inevitably exists, and the low temperature toughness of the seam deteriorates. Therefore, oil well pipes and line pipes of electric resistance steel pipes have problems in use in cold regions. The reason why the low temperature toughness of the seam deteriorates is that when the edge portion is welded, the high temperature molten metal reacts with oxygen in the atmosphere to generate an oxide, and the oxide tends to remain in the seam.

In addition, the ERW steel pipe has a problem that the corrosion resistance of the seam tends to deteriorate because the alloy elements are easily segregated in the molten metal when the edge portion is welded. For this reason, oil-well pipes and line pipes of ERW steel pipes have problems in use in severe corrosive environments (for example, sour environments).
On the other hand, laser beam welding (hereinafter referred to as laser welding) has been attracting attention as a welding method that does not deteriorate the low temperature toughness and corrosion resistance of the seam. Laser welding makes it possible to reduce the size of the heat source and concentrate the heat energy at a high density, thereby preventing the formation of oxides and segregation of alloy elements in the molten metal. Therefore, when laser welding is applied to the production of a welded steel pipe, it is possible to prevent the low temperature toughness and corrosion resistance of the seam from being deteriorated.

Therefore, in the process of manufacturing a welded steel pipe, a technique for manufacturing a steel pipe (that is, a laser welded steel pipe) by irradiating the edge portion of the open pipe with a laser beam for welding has been put into practical use.
However, in laser welding, welding is performed by condensing a laser beam, which is a high-density energy beam, with an optical component and irradiating the welded portion, so that rapid melting of the metal is involved during welding. Therefore, molten metal scatters as spatter from the formed molten pool. The scattered spatter adheres to the laser-welded steel pipe and degrades the quality of the steel pipe, and also adheres to the welding apparatus, optical components, and the pipe making machine, and the welding work becomes unstable. Further, since laser welding is performed by concentrating heat energy at a high density, a large amount of spatter is generated, and welding defects such as undercut and underfill (that is, depressions) are generated. When undercut or underfill occurs, the strength of the welded portion decreases.

  Therefore, various techniques for preventing the adhesion of spatter by laser welding and for preventing the occurrence of spatter have been studied. For example, a technique for preventing the occurrence of sputtering by reducing the laser output, or a technique for preventing the occurrence of sputtering by largely shifting the focal position (so-called defocusing) has been put into practical use. However, the reduction in laser output and defocus not only cause a reduction in welding speed (that is, a reduction in welding efficiency), but also have the problem that penetration defects are likely to occur.

  Patent Document 1 discloses a technique for preventing the occurrence of sputtering by splitting a laser beam to generate a plurality of spots. However, the technique of performing laser welding by dispersing it in a plurality of spots is equivalent to the technique of performing laser welding by reducing the laser output, not only causing a decrease in welding efficiency, but also causing poor penetration. There is a problem of becoming. In addition, since optical components that split the laser beam are expensive, it is inevitable that the welding construction cost will increase.

  Patent Document 2 discloses a technique for preventing underfill using a filler wire when performing laser welding. However, in this technique, the composition of the weld metal changes depending on the filler wire components. Therefore, a filler wire must be selected according to the component of the open pipe, and the load of filler wire inventory management and laser welding work management increases.

Patent Document 3 discloses a technique for preventing welding defects by using a combination of laser welding and arc welding. However, with this technique, the structure of the welding apparatus becomes complicated and the load of maintenance increases, and the load of work management for welding also increases.
Patent Document 4 discloses a method using two circular beam spots. However, with this technique, welding defects are not suppressed in laser welding under conditions in which stress is applied to the welded portion, and in particular, the amount of spatter generated on the back surface of the steel sheet increases.

Japanese Patent No. 2902550 JP 2004-330299 A Japanese Patent No. 4120408 JP 2009-178768

In manufacturing a laser-welded steel pipe, the present invention keeps the laser beam irradiation angle and spot diameter properly, arranges two or more laser beams properly, and controls the laser welding conditions. suppressing undercover Tsu with or underfill parts, and with obtaining the welds of good quality without lowering the welding efficiency, and to provide a method of manufacturing a laser welded steel pipe with good yield stably .

The inventors have investigated and studied a laser welding technique for forming a welded portion having no welding defect when laser welding is performed on an edge portion of an open pipe to manufacture a laser welded steel pipe.
FIG. 1 is a perspective view schematically showing an example in which a welding point of the edge portion 2 of the open pipe 1 is laser-welded using one laser beam when manufacturing a laser-welded steel pipe. An arrow A in FIG. 1 indicates the traveling direction of the open pipe. A deep cavity 4 (hereinafter referred to as a keyhole) 4 generated by irradiation with the laser beam 3 and a molten metal 5 formed in the periphery thereof are shown as perspective views.

  When the laser beam 3 is irradiated, as shown in FIG. 1, the edge portion 2 is melted by heat energy concentrated at high density, and the molten metal 5 is evaporated by the evaporation pressure and reaction force generated by evaporation of the molten metal 5. A keyhole 4 is generated at 5. It is considered that the laser beam 3 enters the inside of the keyhole 4 and high temperature plasma generated by ionizing the metal vapor by the energy of the laser beam 3 is filled.

  The keyhole 4 indicates a position where the thermal energy of the laser beam 3 is most converged. A laser welded steel pipe can be stably manufactured by disposing the joining point of the edge portion in the keyhole 4. However, in order to make the joint point of the edge part 2 and the keyhole 4 correspond, a highly accurate groove processing technique is required. If the processing state and the butting state of the edge portion 2 are unstable, the molten metal 5 becomes unstable. As a result, spatter frequently occurs, and welding defects such as undercut and underfill tend to occur.

Further, even if the setting conditions for laser welding and steel pipe production are changed in order to suppress spatter, spatter from the back surface of the steel sheet cannot be suppressed at the same time, and the amount of spatter generated may be increased.
Furthermore, in a situation where stress is exerted on the weld pool due to the upset applied to the welded portion, it is necessary to further increase the energy of the irradiated laser beam in order to maintain the keyhole. As a result, spatter increases, the groove does not melt sufficiently, and welding defects such as undercut and underfill occur.

  Therefore, the inventors focused attention on a technique for irradiating two or more laser beams to the junction of the edge portion 2. As a result, it was found that the occurrence of spatter can be suppressed by properly arranging the irradiation positions of the laser beams and controlling the irradiation angle and spot diameter of each laser beam. It was also found that a laser welded steel pipe can be stably produced with a good yield while suppressing the undercut and underfill of the weld and obtaining a good quality weld without reducing the welding efficiency.

The present invention has been made based on these findings.
That is, in the present invention, a steel plate having a thickness of 4 mm or more is formed into a cylindrical open pipe with a forming roll, and the edge portion of the open pipe is irradiated with a laser beam from the outer surface side while being pressed with a squeeze roll. In a laser welded steel pipe manufacturing method that uses laser welding, a spot in just focus that is transmitted using different fibers while adding 0.2-1.0mm upset using a squeeze roll to the edge forming the I groove. Two or more laser beams having a diameter of 0.32 to 0.64 mm are classified into a preceding laser beam and a succeeding laser beam, and the preceding laser beam precedes the succeeding laser beam in the welding line direction and is melted by the preceding laser beam. When the pond is formed and the center line interval of the preceding laser beam and the following laser beam in the steel plate is 1.0 to 2.5 mm In both cases, the energy density of the surface of the steel plate of the preceding laser beam is made smaller than that of the succeeding laser beam, and laser welding is performed at a welding speed where the laser output of two or more laser beams exceeds 16 kW in total and exceeds 7 m / min. It is a manufacturing method of a laser welded steel pipe.

In the laser welded steel pipe manufacturing method of the present invention, it is preferable to perform laser welding by making the spot diameter or spot length of the preceding laser beam on the surface of the steel plate larger than that of the subsequent laser beam. Further, it is preferable that the above line laser beam and the trailing laser beam is arranged so as not to intersect with the steel plate is performed with the laser welding. Further, it is preferable to perform through welding by setting the advance angle of the preceding laser beam to 5 to 50 ° and the receding angle of the following laser beam to 0 to 50 °.

In the method of manufacturing a laser welded steel pipe of the present invention performs the preheating of the steel sheet prior to the record over laser welding, and it is preferable to process the weld bead is subjected to cutting or grinding after the laser welding.

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing a laser-welded steel pipe, a weld part of favorable quality can be obtained, without suppressing the undercut and underfill of a weld part, and reducing a welding efficiency. As a result, the laser welded steel pipe can be manufactured stably with a high yield. The obtained laser welded steel pipe has excellent seam low-temperature toughness and corrosion resistance, and is suitable for oil well pipes and line pipes used in cold regions and corrosive environments.

It is a perspective view which shows typically the example which welds the junction of the edge part of an open pipe with one laser beam. In addition, it shows as a perspective view which showed the keyhole and the molten metal formed in the circumference | surroundings. It is a top view which shows the example of the irradiation position of two or more laser beams by applying this invention. It is sectional drawing which shows typically the example of arrangement | positioning of the preceding laser beam and subsequent laser beam which are shown to Fig.2 (a).

  In the present invention, two or more laser beams are transmitted using different fibers, and the edge portion is irradiated with the preceding laser beam and the subsequent laser beam from the outside of the open pipe. When two or more laser beams are transmitted by a single fiber, a spot diameter, a spot length, an energy density, an irradiation angle, etc., which will be described later, cannot be individually set. Therefore, it is necessary to transmit two or more laser beams using different fibers.

One or more laser oscillators may be used. When one laser oscillator is used to transmit two or more laser beams, the laser light may be divided into each fiber.
The spot diameter at the just focus of two or more laser beams must exceed 0.3 mm in diameter. Here, the spot diameter at the just focus refers to the beam diameter of the focal parallel portion of the laser beam by optically condensing the laser beam. That is, at the just focus position, since the laser beam is optically focused, the energy density of the laser beam is the highest.

In less than the laser beam spot diameter is 0. 32 mm in a just focus, the width of the weld bead during welding becomes narrow, undissolved groove occurs. Furthermore, since in order to increase the amount of melting of the steel sheet, it is necessary to increase the laser output, and 0. 32 mm or more. On the other hand, if the spot diameter exceeds 0.64 mm, the keyhole becomes difficult to stabilize. Therefore, the spot diameter at the just focus of the laser beam is not more than 0.64 mm.

The spot shape of the laser beam is preferably circular, but may be elliptical. If the spot shape of an ellipse, the minor axis needs Ru der than 0. 32 mm. Also for the same reason as the case of the circular mentioned above, minor axis is not more than 0.64 mm.
When irradiating two or more laser beams in substantially the same vertical direction with respect to the weld line, a part of each spot shape of the region in the steel plate through which the laser beam passes (hereinafter referred to as the steel plate) overlaps. Alternatively, it is relatively easy to place the joint points in the molten pool by irradiating the laser beams so that they do not overlap and by setting the spot length of each laser beam on the steel sheet surface (perpendicular to the weld line) to 0.4 mm or more Easy to do. Here, the inside of a steel plate includes the steel plate surface. The spot length refers to the length of the widest part in the vertical direction of a spot-shaped weld line in which a part of the laser beam is overlapped and connected. If the laser beam does not overlap, the spot length is vertical. It refers to the sum of the widest widths of each spot shape in the direction.

And the centerline space | interval of the laser beam in a steel plate shall be 1.0-2.5 mm in a weld line direction. In other words, the center lines of the laser beams that are classified into the preceding laser beam and the following laser beam and arranged in the welding line direction (that is, the center line in the optical axis direction to be irradiated) are spaced by 1.0 to 2.5 mm in the welding line direction. By arranging and arranging, it becomes possible to perform laser welding in one molten pool extending in the weld line direction.

When using a plurality of laser beams for the preceding laser beam and a plurality of laser beams for the following laser beam, the center line of the preceding laser beam closest to the following laser beam and the preceding laser beam among the following laser beams are used. The distance in the weld line direction from the center line of the closest object is set to 1.0 to 2.5 mm .
Further, for two or more laser beams, an arrangement of irradiation positions as shown in FIGS. 2 (a) to 2 (d) can be considered. 2A to 2D are plan views showing examples of irradiation positions of two or more laser beams. An arrow A in FIG. 2 indicates the traveling direction of the open pipe. FIG. 2A shows the arrangement of the irradiation positions of two laser beams. The preceding laser beam 3-1 preceding the welding direction and the succeeding laser beam 3-2 are arranged on the welding line. This is an example. FIG. 2B shows the arrangement of the irradiation positions of the three laser beams. The preceding laser beam 3-1 is arranged on the weld line, and the subsequent laser beams 3-2 and 3-3 are weld lines. It is the example arrange | positioned on both sides. FIG. 2 (c) shows an arrangement of irradiation positions of three laser beams. The preceding laser beams 3-1 and 3-2 are arranged on both sides of the weld line, and the subsequent laser beam 3-3 is arranged. It is the example arrange | positioned on a weld line. FIG. 2 (d) shows the arrangement of the irradiation positions of the four laser beams. The preceding laser beams 3-1, 3-2 and the succeeding laser beams 3-3, 3-4 are arranged on both sides of the weld line. It is the example which has each arranged.

Note that the arrangement of two or more laser beams is not limited to that shown in FIGS. 2A to 2D, and the arrangement can be appropriately set according to the purpose. The number of laser beams used in the present invention is preferably 2 to 4. Five or more laser beams are not preferable because the equipment cost, manufacturing cost, and laser beam position control are complicated.
In order to place the junction of the edge part at a predetermined position while irradiating two or more laser beams to the positions as shown in FIGS. is necessary. In view of this, laser welding may be performed while controlling so as to arrange the joining point of the edge portion in the molten metal formed by the two or more laser beams. Since the length of the molten metal is larger in the circumferential direction of the pipe (perpendicular to the weld line) than the spot length of the laser beam, it can be controlled by a relatively easy technique.

  As shown in FIG. 2A, when one preceding laser beam and one following laser beam are arranged on the weld line, the spot diameter of the preceding laser beam 3-1 is set to the spot of the following laser beam 3-2. Laser welding is preferably performed with a diameter larger than that. As shown in FIG. 2B, when the preceding laser beam (one) is arranged on the weld line and the succeeding laser beams (two) are arranged on both sides of the weld line, the preceding laser beam 3-1 Laser welding is preferably performed with the spot diameter larger than the spot length of the subsequent laser beams 3-2 and 3-3. As shown in FIG. 2 (c), when the preceding laser beams (2) are arranged on both sides of the welding line and the succeeding laser beam (1) is arranged on the welding line, the preceding laser beams 3-1, Laser welding is preferably performed with the spot length 3-2 being larger than the spot diameter of the subsequent laser beam 3-3. As shown in FIG. 2 (d), when the preceding laser beams (2) are arranged on both sides of the weld line and the succeeding laser beams (2) are arranged on both sides of the weld line, the preceding laser beam 3- Laser welding is preferably performed by setting the spot lengths 1 and 3-2 to be larger than the spot lengths of the following laser beams 3-3 and 3-4. That is, in order to form a molten pool with the preceding laser beam and irradiate the subsequent laser beam into the molten pool, the spot diameter or the spot length of the preceding laser beam is larger than the spot diameter or the spot length of the subsequent laser beam. To do.

  Irradiate three or more laser beams on almost the same vertical line as the preceding laser beam, and irradiate three or more laser beams on the almost identical vertical line as the following laser beam. In this case, it is preferable to perform laser welding by setting the spot length of the preceding laser beam in the direction perpendicular to the welding line on the surface of the steel plate to be larger than that of the subsequent laser beam. That is, in order to form a molten pool with the preceding laser beam and irradiate the subsequent laser beam into the molten pool, the spot length of the preceding laser beam is made larger than that of the subsequent laser beam.

  As shown in FIGS. 2 (c) and 2 (d), when the preceding laser beams (2) are arranged on both sides of the weld line, the spot length of the preceding laser beam on the surface of the steel plate should be more than 0.4 mm. preferable. When the spot length of the preceding laser beam is 0.4 mm or less, it is difficult to irradiate the subsequent laser beam into the molten pool, spatter frequently occurs, and welding defects such as undercut and underfill occur.

As shown in Fig. 2 (b) and (d), when two subsequent laser beams are arranged on both sides of the weld line, the spot length of the subsequent laser beam on the surface of the steel plate exceeds 0.3 mm. It is preferable to do. When the spot length is 0.3 mm or less, the width of the weld bead at the time of welding becomes narrow, and the unmelted groove is generated.
When three or more laser beams are used for the preceding and succeeding laser beams, the spot length in the direction perpendicular to the welding line of each laser beam on the surface of the steel plate is set to exceed 0.4 mm for the preceding laser beam, The trailing laser beam is over 0.3 mm. In this way, the joining points can be arranged relatively easily in the molten pool. When two or more laser beams are used for each of the preceding and succeeding laser beams, the laser beam transferred by a single fiber may be divided by optical system components.

In the present invention, the energy density of the preceding laser beam on the surface of the steel sheet (when two or more beams are irradiated, the total laser output divided by the total laser irradiation area) is calculated as the energy density of the subsequent laser beam on the surface of the steel sheet. (when irradiating two or more sum divided by the laser irradiation area that total laser output) will rows of laser welding with less than. In other words, when the molten pool is formed by the preceding laser beam and the subsequent laser beam is irradiated into the molten pool, the energy of the preceding laser beam is suppressed in order to suppress the occurrence of spatter from the molten pool formed by the preceding laser beam. Reduce the density. When the energy density of the preceding laser beam is increased, spatter from the molten pool increases and the fluctuation of the molten pool increases. As a result, spatter is further increased by the subsequent laser beam, and a large amount of welding defects such as undercut and underfill occur.

The energy density of the laser beam can be adjusted by controlling the laser output and controlling the spot diameter by the optical system.
Further, in the present invention, it is preferable to perform laser welding by arranging so that the preceding laser beam and the succeeding laser beam do not intersect in the steel plate (that is, the region in the steel plate through which the laser beam passes). The reason is that when the preceding laser beam and the following laser beam intersect in the steel plate, the energy density at that portion increases, the amount of spatter generated on the back surface of the steel plate increases, and undercut or underfill is formed on the back surface side. This is because a welding defect occurs.

  It is preferable to provide an irradiation angle for each of two or more laser beams. As shown in FIG. 3, the laser beam irradiated to the rear of the welding progress direction is defined as an advancing angle θa, which is an irradiation angle formed between the laser beam irradiated in the forward direction of the welding and the vertical line on the surface of the steel plate. The irradiation angle made with the vertical line on the surface is defined as the receding angle θb. The arrow B in FIG. 3 shows the progress direction of welding, and is the reverse direction of the arrow A in FIG.

For example, when each of the preceding laser beam 3a and the succeeding laser beam 3b is irradiated (see FIG. 2 (a)), as shown in FIG. 3, the preceding laser beam 3a is tilted forward in the welding direction. It is preferable to irradiate with the advancing angle θa and to irradiate the subsequent laser beam 3b with the receding angle θb by inclining the backward laser beam 3b backward in the welding traveling direction.
The advance angle θa of the preceding laser beam 3a is preferably 5 to 50 °. By applying a forward angle of 5 ° or more to the preceding laser beam, the amount of spatter generated from the steel sheet surface is reduced. However, if the advance angle exceeds 50 °, the effect cannot be obtained.

When there are two or more preceding laser beams (see FIGS. 2C and 2D), it is preferable that the advance angle θa of each preceding laser beam is 5 to 50 °. It is more preferable that the advance angles of the preceding laser beams are aligned at a predetermined angle within a range of 5 to 50 ° so that the preceding laser beams are parallel.
The receding angle θb of the trailing laser beam 3b is preferably 0 to 50 °. By applying a receding angle of 0 ° or more to the subsequent laser beam, the amount of spatter generated from the back surface of the steel sheet is reduced. However, if the receding angle exceeds 50 °, the effect cannot be obtained.

When there are two or more subsequent laser beams (see FIGS. 2B and 2D), the receding angle θb of each subsequent laser beam is preferably set to 0 to 50 °. It is more preferable that the backward laser beams are made parallel by aligning the receding angles of the subsequent laser beams to a predetermined angle within the range of 0 to 50 °.
When performing laser welding, Ru added upsets 0.2~1.0mm the weld. If the amount of upset is less than 0.2 mm, the blowhole caused by laser welding cannot be eliminated. On the other hand, if it exceeds 1.0 mm, laser welding becomes unstable and the amount of spatter generated increases.

In order to stabilize the keyhole during laser welding in such a situation where stress is applied to the laser welded portion, it is preferable to use two or more laser beams, for example, as shown in FIG. .
In general, spatter generated during laser welding decreases as the laser output decreases and the welding speed decreases. However, reducing the laser output and the welding speed in order to suppress the occurrence of spatter means reducing the productivity of the laser welded steel pipe. In this invention, the laser output of two or more laser beams is greater than the sum 16 kW, and will rows of laser welding at a welding speed of greater than 7m / min. If the laser output is 16 kW or less in total, the welding speed will be 7 m / min or less, resulting in a decrease in productivity of the laser welded steel pipe.

  FIG. 1 is a perspective view schematically showing an example in which a joint point of an edge portion of an open pipe is welded with one laser beam, but also when two or more laser beams are irradiated as in the present invention, While pressurizing the edge 2 of the open pipe 1 with a squeeze roll (not shown), a laser beam is irradiated from the outer surface side of the open pipe 1. The joining point of the edge part 2 of the open pipe 1 may be anywhere as long as the average interval G in the thickness direction of the edge part 2 is narrowed by a squeeze roll and becomes 0.5 mm or less.

  In the present invention, even an open pipe made of a thick material (for example, a thickness of 4 mm or more) can be laser-welded without preheating by high-frequency heating or the like of the edge portion. However, if the edge portion is preheated by high frequency heating or the like, effects such as improved productivity of the laser welded steel pipe can be obtained. If preheating is performed by high-frequency heating, a surplus is formed in the welded portion. However, if the surplus is removed by cutting or grinding after laser welding, the surface properties of the welded portion are further improved.

Oscillator of the laser beam used in the present invention, an oscillator of various forms can be used, a gas (e.g. CO _2, helium - neon, argon, nitrogen, iodine) gas laser is used as a medium, solid (e.g., a rare earth element A solid-state laser using YAG doped with YAG, etc.) as a medium, and a fiber laser using a fiber instead of a bulk as a laser medium are suitable. Alternatively, a semiconductor laser may be used.

You may heat with an auxiliary heat source from the outer surface side of an open pipe. The configuration of the auxiliary heat source is not particularly limited as long as it can heat and melt the outer surface of the open pipe. For example, a means using a burner melting method, a plasma melting method, a TIG melting method, an electron beam melting method, a laser melting method or the like is suitable.
The auxiliary heat source is preferably disposed integrally with the laser beam oscillator. The reason is that if the auxiliary heat source and the laser are not integrated, a large amount of heat is required to obtain the effect of the auxiliary heat source, and it is very difficult to suppress welding defects (such as undercut and underfill). Because it becomes. Further, it is more preferable that the auxiliary heat source is disposed ahead of the laser beam oscillator. The reason is that moisture and oil can be removed from the edge portion.

  Furthermore, the use of an arc is preferred as a preferred auxiliary heat source. As the arc generation source, one that can add electromagnetic force (that is, electromagnetic force generated from the magnetic field of the welding current) in a direction to suppress the molten metal from falling off is used. For example, conventionally known techniques such as TIG welding and plasma arc welding can be used. Note that the arc generation source is preferably arranged integrally with the laser beam. The reason is that, as described above, the influence of the magnetic field generated around the welding current that generates the arc is effectively given to the molten metal generated by the laser beam. Further, it is more preferable that the arc generation source is arranged ahead of the laser beam. The reason is that moisture and oil can be removed from the edge portion.

Furthermore, the effect can be obtained by combining the present invention with conventionally known techniques such as gas shield welding and filler material addition. Such composite welding technology can be applied not only to the manufacture of welded steel pipes but also to the welding of thick steel plates.
As described above, according to the present invention, in manufacturing a laser welded steel pipe, the spot diameter and the spot length are properly maintained, and two or more laser beams are properly arranged, and the irradiation angle of the laser beam, etc. By controlling the laser welding conditions, it is possible to suppress the undercut and underfill of the welded part, and to obtain a welded part of good quality without reducing the welding efficiency, and to stabilize the laser welded steel pipe with high yield Can be manufactured. The obtained laser welded steel pipe is excellent in low temperature toughness and corrosion resistance of the seam by taking advantage of laser welding, and is suitable for oil well pipes and line pipes used in cold regions and corrosive environments.

  A strip-shaped steel plate was formed into a cylindrical open pipe with a forming roll, and a laser welded steel pipe was manufactured by irradiating the edge of the open pipe with a squeeze roll and irradiating a laser beam from the outer surface side. The components of the steel sheet are as shown in Table 1.

  In laser welding, two 10 kW Faber laser oscillators are used, and the welding conditions are as shown in Table 2.

The welded steel pipes Nos. 1 to 4 and 7 to 10 in Table 2 are examples in which a laser beam is arranged as shown in FIG. The arranged examples, welded steel pipe Nos. 6 and 12, are examples in which a laser beam is arranged as shown in FIG.
Inventive examples (welded steel pipe Nos. 1 to 6) shown in Table 2 are examples in which the spot diameter and center line interval at the just focus of the laser beam satisfy the scope of the present invention. The welded steel pipe Nos. 7, 8, 11 and 12 of the comparative examples are examples in which the center line interval of the laser beam is outside the range of the present invention, and the welded steel pipe Nos. 9 and 10 of the comparative example are just focus of the laser beam. This is an example in which the spot diameter is outside the scope of the present invention.

  The obtained laser welded steel pipe was subjected to an ultrasonic flaw detection test and a magnetic particle flaw detection, and a seam was flawed over 20 m in accordance with JIS standard G0582 and JIS standard G0565. Table 3 shows the flaw detection results. In Table 3, for ultrasonic flaw detection, the peak indicated height is superior to 10% or less (◎), and is greater than 10% to 25% or less with respect to the standard N5 inner and outer notch artificial defects. (○), 25% to 50% or less was evaluated as acceptable (△), and 50% was evaluated as unacceptable (×).

  For magnetic particle inspection, the weld defect on the inner surface of a laser welded steel pipe is inspected. Excellent (◎) if no weld defect is found, acceptable (△) if spot weld is found, and linear welding. Those in which defects were recognized were evaluated as impossible (x). The results are shown in Table 3.

As is apparent from Table 3, in the inventive examples (welded steel pipe Nos. 1 to 6), the ultrasonic flaw detection was excellent (◎) or good (○). Also, no welding defects such as undercut and underfill due to the occurrence of spatter were observed.
On the other hand, in the comparative examples (welded steel pipe Nos. 7 to 12), ultrasonic flaw detection was acceptable (Δ) or not possible (×), and magnetic particle flaw detection was also acceptable (Δ) or not possible (×). In addition, welding defects such as undercut and underfill due to the occurrence of spatter were also observed.

  When manufacturing a laser welded steel pipe, the laser welded steel pipe can be manufactured stably with a high yield, so that it has a remarkable industrial effect.

1 Open pipe 2 Edge 3 Laser beam
3a Leading laser beam
3b Trailing laser beam 4 Keyhole (cavity)
5 Molten metal 6 Seam

Claims (5)

A steel plate having a thickness of 4 mm or more is formed into a cylindrical open pipe with a forming roll, and a laser beam is irradiated from the outer surface side of the open pipe while pressurizing the edge portion of the open pipe with a squeeze roll to laser the edge portion. In a method for manufacturing a laser welded steel pipe to be welded, a spot at a just focus that is transmitted using different fibers while adding an upset of 0.2 to 1.0 mm using the squeeze roll to the edge portion forming the I groove. diameter is classified into a prior laser beam and the trailing laser beam two or more laser beams with a diameter 0.32～0.64Mm, the prior laser the preceding laser beam by preceding the weld line direction than the trailing laser beam beam by forming a molten pool, and the medium in the preceding laser beam within the steel sheet of the trailing laser beam The line spacing is 1.0 to 2.5 mm, the energy density of the preceding laser beam on the surface of the steel plate is smaller than that of the subsequent laser beam, the laser output of the two or more laser beams exceeds 16 kW, and A method for producing a laser-welded steel pipe, wherein the laser welding is performed at a welding speed exceeding 7 m / min.   2. The method of manufacturing a laser welded steel pipe according to claim 1, wherein the laser welding is performed by making a spot diameter or a spot length of the preceding laser beam on the surface of the steel plate larger than that of the subsequent laser beam.   The method of manufacturing a laser welded steel pipe according to claim 1 or 2, wherein the laser welding is performed by arranging the preceding laser beam and the subsequent laser beam so as not to intersect in the steel plate.   The laser welding is performed with the advance angle of the preceding laser beam being 5 to 50 ° and the receding angle of the following laser beam being 0 to 50 °. The manufacturing method of the laser welding steel pipe of description.   The laser according to any one of claims 1 to 4, wherein the steel plate is preheated prior to the laser welding, and the welding bead is processed by cutting or grinding after the laser welding. Manufacturing method of welded steel pipe.

Images