JP3079962B2 - Manufacturing method of welded 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 high quality welded steel pipe using a high-density energy beam as a heat source and having no defects in a weld.

[0002]

2. Description of the Related Art As one of welded steel pipes, an electric resistance welding method (E
RW) is known. The ERW pipe is manufactured by abutting both ends of the carbon steel strip while continuously forming the carbon steel strip into a tubular shape, and heating and pressing the butted ends by electric resistance heating or high frequency induction heating.

[0003] However, in the ERW steel pipe manufactured as described above, a high melting point substance in the oxide generated at the time of heating is not discharged and is called a penetrator which remains on the joint surface of the ERW weld. There is a problem that a planar oxide is generated, and a rising portion of the metal flow is exposed on the surface of the ERW welded portion due to abutting pressure welding of both end portions, thereby deteriorating toughness and workability.

Various means for solving the above-mentioned problems have been studied in the past, for example, Japanese Patent Application Laid-Open No. 58-100982,
JP-A-1-309792 discloses a method for manufacturing a welded steel pipe by high-density energy beam welding (Laser ER) comprising:
W composite welding method). The steel strip is continuously formed into a tube, and the butt end of the formed tube is preheated by electric resistance heating or high frequency induction heating, and then
The butt end is pressurized by a squeeze roll on the preheated tubular molded body, butting the butt end,
A high-density energy beam is irradiated along the groove at the butt end formed by the abutment, and the groove is heated by the high-density energy beam and welded by melting (hereinafter, the prior art). ).

[0005]

However, the above prior art has the following problems. That is, since the preheating temperature by electric resistance heating or high-frequency induction heating with respect to the butt end of the tubular molded body is as high as about 600 to 1200 ° C., the oxygen content in the weld metal of the weld exceeds 300 ppm. As a result, a large amount of oxidized inclusions is present in the weld, and the toughness of the weld deteriorates.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing a welded steel pipe having excellent toughness of a weld joint when manufacturing a welded steel pipe by high-density energy beam welding. It is in.

[0007]

In view of the above, the present inventors have developed a method for manufacturing a welded steel pipe having excellent toughness in a weld joint when manufacturing a welded steel pipe by high-density energy beam welding. We worked diligently to develop it.
As a result, the butt end of the tubular molded body is formed to be inclined at a predetermined angle in the thickness direction, and such butt ends are abutted against the formed inclined butt end.
It has been found that if a high-density energy beam is irradiated and welded along the inclined groove line, the toughness value of the welded portion becomes almost the same as that of the base metal.

[0008] The present invention has been made based on the above-mentioned findings, and the invention according to claim 1 of the present application is to continuously form a steel strip into a tubular shape and to form a butt end of the tubular formed body. The part was preheated by electric resistance heating or high-frequency induction heating, and then the tubular body whose butt end was preheated was pressed by a squeeze roll to abut the butt end and form the butt. Irradiating a high-density energy beam along a groove at the butt end, heating the butt end with the high-density energy beam and welding by melting;
In the method for manufacturing a welded steel pipe, in advance, the width direction both end faces of the steel strip are formed in a slope at a predetermined angle parallel to each other in the thickness direction, and the steel strip in which the both end faces are formed in the slope is formed into the tubular shape. Molded into a compact, preheated butted abutting ends in the thickness direction of the tubular compact and then butted, along an inclined bevel line of the butted ends formed by the butting, The method is characterized in that the high-density energy beam is irradiated at the same inclination angle and the butt ends are welded.

[0009] The invention according to claim 2 is characterized in that the inclination angle of the abutting end of the tubular molded body and the irradiation angle of the high-density energy beam are within a range of 5 to 30 degrees. Claim 3.
In the invention described in the above, the oxygen amount (O) in the weld metal and the inclination angle (θ) of the welded portion in the welded portion welded by the irradiation of the high-density energy beam are represented by the following formula:
It is characterized by satisfying the relationship of [O] = ≦ 6 × [θ] +300 (ppm).

[0010]

Next, the present invention will be described with reference to the drawings. 1 is a schematic perspective view showing one embodiment of the welding method of the present invention, FIG. 2 is an enlarged sectional view taken along line AA of FIG. 1, FIG. 3 is an enlarged sectional view taken along line BB of FIG. 4 is
It is a width direction expanded sectional view of the steel strip before shaping | molding. As shown in FIG. 4, the steel strip 1 has both end faces 2, 2 in the width direction in advance.
It is formed in an inclined shape at a predetermined angle parallel to the thickness direction. As described above, both end faces 2, 2 in the width direction of the steel strip 1 are formed.
Can be easily formed by side trimming.

In FIG. 1, 1a is a tubular formed body of a steel strip 1, and 3 is a pair of squeezes for forming the steel strip 1 into a tubular formed body 1a and abutting its butted ends 2a, 2b. The roll 4 is a power feeding device for preheating the butted ends 2a and 2b of the tubular molded body 1a by electric resistance heating, and 6 is a top roll. The steel strip 1 is formed into a tubular molded body 1a while moving continuously in the direction of the arrow, and the inclined butted ends 2a, 2b of the tubular molded body 1a are preheated by electric resistance heating by the power supply device 4, and Pressed by the pair of squeeze rolls 3, the butted ends 2a, 2b are abutted.

As a result, as shown in FIG.
The butt ends 2a and 2b of 1a are abutted to form a butt groove inclined at an angle θ in the thickness direction. Along the inclined butting groove, a laser beam 5 is irradiated as a high-density energy beam at the same inclination angle θ, and the groove is heated by the laser beam 5. Thus, as shown in FIG. 3, the butted butted ends 2a and 2b of the tubular molded body 1a are welded to form a welded portion 7 inclined at an angle θ in the thickness direction.

According to the present invention, as described above, the butted butted ends 2a and 2b of the tubular molded body 1a are welded by the laser beam 5 to form a welded portion inclined at an angle θ in the thickness direction. 7 is formed. As a result, the toughness value of the welded portion 7 becomes substantially equal to that of the base metal for the following reason.

That is, one criterion of toughness is an impact value in a Charpy impact test, and it depends on how a crack propagates when an impact is applied to a weld.
Toughness is affected. According to a conventional method, as shown in FIG. 6, a butt end portion 2 perpendicular to the thickness direction of the tubular molded body 1a.
When a 'and 2b' are welded by the laser beam 5 'to form a weld 7' perpendicular to the thickness direction, all cracks generated by the impact propagate to the weld 7 '. Therefore, the toughness value of the welded portion 7 'depends on its material, and it is inevitable that the welded portion 7' deteriorates compared to the base material.

On the other hand, according to the method of the present invention, FIG.
As shown in FIG. 5, when the butted butted ends 2a and 2b of the tubular molded body 1a are welded by the laser beam 5 to form a welded portion 7 inclined at an angle θ in the thickness direction, the impact is caused by impact. The crack propagates through the weld 7 to the base material. Therefore, the toughness value of the welded portion 7 becomes almost the same as that of the base material portion and does not deteriorate.

It is desirable that the abutting ends 2a and 2b of the tubular molded body 1a, that is, the inclination angle of the welded portion 7 and the irradiation angle of the high-density energy beam 5 be in the range of 5 to 30 degrees. If the angle is less than 5 degrees, in the Charpy impact test, cracks generated by the impact cannot be sufficiently propagated to the base metal, and therefore, the effect of improving the toughness of the welded portion decreases. On the other hand, if the angle exceeds 30 degrees, the welding distance becomes too long and a large amount of welding heat input is required,
The problem that productivity falls occurs.

The oxygen content (O) in the weld metal and the inclination angle (θ) of the welded portion in the welded portion welded by the irradiation of the high-density energy beam are represented by the following formula: [O] = ≦ 6 × [θ] It is desirable to satisfy the relationship of +300 (ppm).

FIG. 5 is a graph showing the toughness of the welded portion in relation to the angle of inclination of the welded portion and the oxygen content in the weld metal when a welded steel pipe is manufactured by the method of the present invention. The circles and ● in the figure are toughness values,
QT treatment (950 ℃ × 30min, water cooling after holding + 650 ℃ × 30min
Based on the fracture surface transition temperature (vTs) in the Charpy impact test of the weld after holding and air cooling), the following evaluation was made. ：: Fracture transition temperature (vTs) in the Charpy impact test of the weld
When the temperature is below -60 ° C and the toughness is excellent ●: Fracture transition temperature (vTs) in the Charpy impact test of the weld
Is higher than -60 ° C and the toughness is poor

FIG. 5 shows that the fracture surface transition temperature (vTs) is -60 ° C.
In the following region showing excellent toughness, the oxygen amount (O) in the weld metal is (O) = ≦ 6 × (θ) +300 (ppm) in relation to the inclination angle (θ) of the welded portion. It is understood that it is desirable to satisfy the relationship.

[0020]

EXAMPLES Next, the method of the present invention will be further described with reference to Examples and Comparative Examples. Using three types of tubular molded bodies A, B, and C having a chemical composition shown in Table 1 and having a thickness of 12 mm and an outer diameter of 406 mm, a specimen of a welded steel pipe (hereinafter, referred to as a specimen) was prepared by the method of the present invention shown in FIG. No. 1)
~ 19 were prepared. For comparison, specimens of welded steel pipes (referred to as comparative specimens) Nos.
Was prepared.

[0021]

[Table 1]

With respect to each of the specimen of the present invention and the comparative specimen, the oxygen content of the welded portion was examined, and the QT treatment (950)
After holding at ℃ × 30min for water cooling and holding at 650 ° C × 30min for air cooling), the Charpy impact test of the welded part was performed and the fracture surface transition temperature (vTs) was examined. Table 2 shows the evaluation of toughness by the welding speed, the inclination angle of the weld, the oxygen content of the weld, the fracture surface transition temperature (vTs), and vTs. The toughness was evaluated as follows. ：: vTs is (−80) ° C. or less and very good toughness ○: vTs is (−60) to less than (−80) ° C. and good toughness ×: vTs is less than (−60) ° C. Poor toughness

[0023]

[Table 2]

As is clear from Table 2, the test sample N of the present invention
o. 1 to 19 have a smaller amount of oxygen in the welded part and are superior in the toughness of the welded part as compared with the comparative specimens Nos. 1 to 6, and in particular, the oxygen amount (O) in the weld metal and the welding Specimens Nos. 1 to 3 and Nos. 6 to 8 of the present invention, in which the inclination angle (θ) of the portion satisfies the relationship of [O] = ≦ 6 × [θ] +300 (ppm)
o.11-14 and No.17-18 showed extremely good toughness. On the other hand, the toughness of the comparative specimens Nos. 1 to 6 were poor.

[0025]

As described above, according to the present invention,
When a welded steel pipe is manufactured by high-density energy beam welding, an industrially useful effect that a welded steel pipe excellent in toughness of a weld portion can be manufactured is provided.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing one embodiment of a welding method of the present invention.

FIG. 2 is an enlarged sectional view taken along the line AA of FIG. 1;

FIG. 3 is an enlarged sectional view taken along the line BB of FIG. 1;

FIG. 4 is an enlarged cross-sectional view in the width direction of a steel strip before forming.

FIG. 5 is a graph showing the toughness of a welded portion in the relationship between the inclination angle of the welded portion and the oxygen content in the weld metal when a welded steel pipe is manufactured by the method of the present invention.

FIG. 6 is an enlarged sectional view showing a butt end portion of a tubular molded body in a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel strip 1a Tubular molded object 2 Both end surfaces 2a Butt end 2b Butt end 3 Squeeze roll 4 Power supply device 5 Laser beam 6 Top roll 7 Welded part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-202385 (JP, A) JP-A-2-147187 (JP, A) JP-A-5-23867 (JP, A) JP-A 8- 252682 (JP, A) Jpn. Sho 62-155980 (JP, U) JP-B 61-29830 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/26 B23K 31 / 00 B23K 33/00 B21C 37/083

Claims (3)

(57) [Claims] 1. A steel strip which is continuously formed into a tubular shape, and a butt end of the tubular body is preheated by electric resistance heating or high-frequency induction heating, and then the butt end is preheated. Is pressed by a squeeze roll to abut the butted ends, and irradiate a high-density energy beam along a groove line of the butted ends formed by the abutting, thereby bringing the butted ends to the high-density energy. In a method for manufacturing a welded steel pipe, which is heated and melted by an energy beam and welded by melting, in advance, the width direction both end surfaces of the steel strip are formed in a slant shape at a predetermined angle parallel to each other in a thickness direction, A steel strip having an inclined end surface is formed into the tubular molded body, and a butt end inclined in a thickness direction of the tubular molded body is preheated, then abutted, and shaped by the abutment. Has been along the inclined groove lines of the butt end, irradiating the high density energy beam at the same angle of inclination as this method of manufacturing a welded steel pipe, characterized in that welding the butt end. 2. The method according to claim 1, wherein an inclination angle of the butt end of the tubular molded body and an irradiation angle of the high-density energy beam are in a range of 5 to 30 degrees. 3. The amount of oxygen (O) in a weld metal in a weld portion welded by irradiation with the high-density energy beam.
3. The method according to claim 1, wherein the inclination angle (θ) of the welded portion satisfies the following equation: [O] = ≦ 6 × [θ] +300 (ppm).