JP3209061B2 - Method for producing carbon steel pipe excellent in toughness by high energy density beam welding - 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 carbon steel pipe having excellent toughness by high energy density beam welding.

[0002]

2. Description of the Related Art As a conventional technique for producing a carbon steel pipe, there are known an electric resistance welding (ERW) method and a method for producing a steel pipe by high energy density beam composite welding described below.

[0003] ERW (ERW): ERW (ER)
W), while forming the carbon steel sheet into a cylindrical shape, butts the ends of both sides of the carbon steel sheet, heats by applying an induced current to the butted part, welds the butted part, and welds the carbon steel pipe. (ERW)
It has been widely practiced conventionally. In this method, a heat treatment such as heating and cooling (referred to as seam heat treatment) may be performed on the welded portion and its periphery by means such as high-frequency induction heating.

[0004] In this method of manufacturing an electric resistance welded tube, the oxygen content of the electric resistance welded portion reaches several hundred ppm. These oxygens are present in the form of oxide inclusions in the weld and degrade the toughness represented by the Charpy transition temperature. In addition, the shape of the oxide inclusions in the welded portion is as large as 10 to 30 microns or more, and the large inclusions also cause deterioration in toughness. For this reason, Japanese Patent Application Laid-Open No. 3-264171 discloses a method for shielding the ERW welded portion by a non-oxidizing gas such as nitrogen gas during ERW welding as a means for reducing the oxygen content. (Hereinafter referred to as prior art 1).

A method of manufacturing a steel pipe by high energy density beam composite welding: A method of manufacturing a carbon steel pipe by high energy density beam composite welding is to form a metal plate (steel plate or the like) into a cylindrical shape while forming a cylindrical shape on both sides of the steel plate. In this method, a metal (steel pipe) pipe is manufactured by butt-joining the ends, passing an induced current through the butt, and irradiating the butt with a beam having a high energy density to melt-weld the butt. Japanese Patent Publication No. Hei 4-18954 discloses that a metal member in the form of a cylinder is formed while being conveyed in the longitudinal direction while being formed into a cylindrical shape so that both ends are sequentially opposed to each other. A frequency at which the depth of heat penetration to the metal member by the induction heating coil wound around the metal member at a predetermined distance upstream of the V convergence point where both side end portions first contact the metal member is about the thickness of the metal member And supplying a high-frequency current to such an extent that melting of the metal member hardly occurs to preheat the metal member, and furthermore, a joint portion of the metal member downstream of the V convergence point is subjected to heat with respect to the metal member. In a method for manufacturing a metal pipe to be welded by a laser welding means whose output is set so that the depth of influence becomes the thickness of the metal member, the metal portion is provided between the convergence point and a molten portion in laser welding. Clamping the metal member from both sides in the amount tightening a degree that both ends of the simply contacted,
Further, there is disclosed a method for manufacturing a metal pipe, characterized in that the metal member is tightened from both sides with a tightening amount such that both end portions of the metal member are merely in contact with each other on the downstream side of the melting portion. Further, it is disclosed that about 10 to 100 kHz is used as a high-frequency current flowing through the induction heating coil (hereinafter, referred to as Conventional Technique 2).

[0006] As a technique similar to the prior art technique 2, opposing edges of an open pipe are preheated by a first heating source based on a high-frequency induction or high-frequency resistance method, and are melted by a second heating source near a squeeze roll. Japanese Patent Laid-Open No. 3-29 discloses a method of joining a composite heat source made of pipes in which a preheating temperature of a first heating source is set to 200 to 600 ° C.
No. 1176 (hereinafter referred to as prior art 3).

[0007] Japanese Patent Publication No. 61-29830 discloses that when a steel pipe is manufactured by high energy density beam welding, oxides remain in a welded portion depending on welding conditions and adversely affect mechanical properties. (Hereinafter referred to as prior art 4). It is needless to say that also in the prior arts 2 to 4, the seam heat treatment described in the prior art 1 may be performed after the seam welding.

[0008]

However, the prior arts 1 to 4 have the following problems.

In the prior art 1, although the effect of improving the toughness by reducing the amount of oxygen is slight, the improvement in toughness is limited because nonmetallic inclusions are not reduced.

The prior art 2 states that preheating is effective as a means for increasing the welding speed, but does not mention at all how the preheating affects the mechanical properties of the metal pipe. .

The prior art 3 has been proposed as a means for increasing the welding speed of a high-strength steel pipe or a stainless steel pipe. Although it is stated that sound welds can be obtained without defects, no consideration is given to the toughness of the welds.

Further, the content of the prior art 4 is merely a general description, and no mention is made of the amount and shape of the oxide that does not adversely affect the toughness of the weld.

As described above, in the prior arts 1 to 4, there is a problem in the toughness of the welded portion. Therefore, it is desired to develop a method of manufacturing a carbon steel pipe having excellent toughness in the welded portion. No method has been proposed yet.

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

According to the first aspect of the present invention, both ends of the carbon steel sheet are butted against each other while the carbon steel sheet is formed into a tubular shape, and the butt is preheated. Then, a beam having a high energy density is applied to the butt. In the method for manufacturing a carbon steel pipe in which the butt portion is melt-welded by irradiation, a preheating temperature for preheating the butt portion is 400 to 90.
The butt portion to be melt-welded within a range of 0 ° C.
The oxygen content in the weld metal and has a feature in this <br/> and to 300ppm or less.

[0016]

According to the present invention, as a method for welding carbon steel sheets,
Since high energy density beam welding with preheating is adopted,
The size of the oxide at the weld can be reduced, and the toughness is improved.

The reasons for limiting the preheating temperature are as follows. The preheating is performed for the purpose of compensating for insufficient heat input when welding the butt portion with a beam having a high energy density. However, in high energy density beam welding of carbon steel pipes, if the preheating temperature is lower than 400 ° C. , a sufficient preheating effect cannot be obtained to compensate for insufficient welding heat input. Therefore, the welding speed becomes extremely low and the welding cost is extremely low, or the cost of equipment is increased, such as preparing a large-capacity power supply to significantly increase the energy density of the beam. On the other hand, when the preheating temperature is 9
When the temperature exceeds 00 ° C., in the process from the preheating of the butt portion to the welding, the butt portion is oxidized intensely, the oxygen content of the weld metal increases drastically, and the toughness of the weld portion is deteriorated. Therefore,
Preheating temperature should be limited within the range of 400 to 900 ° C..

The reasons for limiting the oxygen content in the weld metal at the butt portion to be melt-welded are as follows. In a carbon steel pipe welded with a high energy density beam, when the oxygen content in the weld metal exceeds 300 ppm, the toughness rapidly deteriorates. Therefore, the oxygen content was limited to 300 ppm or less.

[0019]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a welding method according to an embodiment of the present invention. In FIG. 1, 1 is a carbon steel pipe (1a is a carbon steel plate), 2 is a power supply device for supplying an induced current for preheating a butt portion, 5 is a beam having a high energy density, 6 is a portion where welding has been completed (welding point). ), 3a and 3b are squeeze stands, 4a and 4b are top rolls, and 7 is a welding line.

As shown in FIG. 1, while forming the carbon steel sheet 1a into a tubular shape (in this embodiment, a cylindrical shape), the ends on both sides of the steel sheet 1a are butted, and an induction current is passed through the butted portion to preheat by induction heating. Then, the butt portion is irradiated with a beam 5 having a high energy density to melt-weld the butt portion, and the test steel pipe Nos. 1 to 6 of the carbon steel pipe having the chemical composition shown in Table 1 are welded as follows. Manufactured according to conditions. Table 1 does not describe the balance of Fe, S, P, and the like, which are contained as impurity elements. Welding conditions: Steel pipe dimensions: 72.0 mm (outer diameter) x 9.7
mm (pipe thickness) Welding speed; 2 m / min Beam energy density; 25 kW / mm ² Gas shield; none In addition, these test steel pipes are provided immediately after welding with a seam heat treatment device (not shown) arranged on the rear surface of the welding line. For seam heat treatment. The method uses a welding line outer surface temperature of 10
After heating until reaching 50 ° C., the mixture was cooled in air. Here, performing the seam heat treatment is not essential to the present invention, but by performing an appropriate seam heat treatment, the weld toughness can be further improved as compared with the case where no heat treatment is performed.

[0022]

[Table 1]

FIG. 2 shows a test steel pipe No. 1 prepared according to the method of the present invention.
And by the method (ERW) described in Prior Art 1
It is a graph which showed the relationship between the toughness of a welding part and the oxygen content of a welding metal part about the case where it manufactures by changing the oxygen content of a welding metal part variously. In FIG. 2, the toughness of the welded portion was defined as the fracture surface transition temperature vTs (° C.) in the Charpy impact test performed on the weld metal.

FIG. 2 shows that when manufactured by high energy density beam welding, the oxygen content of the weld metal was 3%.
If it exceeds 00 ppm, the toughness starts to deteriorate rapidly, but if it is less than that, it can be seen that good toughness is maintained.

In FIG. 2, the case of the prior art 1 is indicated by a triangle as a comparative example. However, in the case of the prior art 1 manufactured by ERW, even if the oxygen content is 300 ppm or less, the toughness of the welded portion is reduced. It turns out that it is significantly inferior to the present invention. The reason for this difference is that the size of the oxide at the weld is different. That is, in the present invention, the size of the oxide at the welded portion is as small as 1 micron or less in diameter, whereas in the prior art 1, it is as large as 10 microns or more in diameter.

FIG. 3 is a graph showing the relationship between the preheating temperature and the oxygen content of the welded portion when the test steel pipe No. 1 was manufactured with various preheating temperatures. The preheating temperature shown in FIG. 3 is 50 m of the point irradiated with the high energy density beam.
It is indicated by a value obtained by measuring the temperature at a position m in front.
From FIG. 3, it is understood that the preheating temperature needs to be 900 ° C. or less in order to suppress the oxygen content in the weld metal to 300 ppm or less.

Table 2 shows the test steel pipe Nos. 1 to 6 shown in Table 1.
Are produced by welding with a beam of high energy density, and the results are produced by a method within the scope of the present invention (Examples Nos. 1 to 10 and 8 are missing numbers ) ; (Comparative Examples Nos. 1 to 4) are shown.

[0028]

[Table 2]

As shown in Table 2, in the carbon steel pipe welded by the high energy density beam, if the preheating temperature is within the range of the present invention, the weld toughness (vTs) is as good as −20 ° C. or less. Understand

In this embodiment, the gas shielding of the preheated portion and the welded portion was not particularly performed. However, it is not an essential requirement of the present invention that the gas shield is not performed. It is further reduced, and the weld toughness is further improved.

The oxygen content of the weld is determined by the preheating temperature,
The condition is not determined solely by the gas shield conditions, but also varies depending on conditions such as the welding speed and the energy beam density. Conditions for suppressing the concentration to 300 ppm or less within the scope of the present invention are not unique, and various combinations are possible.

[0032]

As described above, according to the present invention, as a method for welding carbon steel pipes, first, a method using a high energy density beam is used. Second, the welding preheating temperature is set to 400 to
Since the oxygen content in the weld metal is limited to 900 ppm or less and the oxygen content in the weld metal is suppressed to 300 ppm or less, the amount of oxide in the weld metal can be limited. Thus, a carbon steel pipe excellent in quality can be provided, and an industrially useful effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a welding method according to an embodiment of a method for manufacturing a carbon steel pipe of the present invention.

FIG. 2 is a graph showing the relationship between the oxygen content of the weld metal and the toughness of the weld.

FIG. 3 is a graph showing a relationship between an oxygen content of a weld metal part and a preheating temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carbon steel pipe 1a Carbon steel sheet 2 Power supply device for preheating 3a, 3b Squeeze stand 4a, 4b Top roll 5 High energy density beam 6 Welding point 7 Welding line

Continued on the front page (72) Inventor Yukio Sekine 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Masaki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-53-22152 (JP, A) JP-A-3-281078 (JP, A) JP-A-57-106488 (JP, A) JP-A-4-238681 (JP, A) JP-A-60-33890 (JP, A) JP-A-5-23867 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/00 B21C 37/08 B23K 15/00

Claims (1)

(57) [Claims] 1. A method for forming a carbon steel sheet into a tubular shape, butting both ends of said carbon steel sheet, preheating the butted portion, and then irradiating said butted portion with a beam having a high energy density. In the method for producing a carbon steel pipe by melt welding, a preheating temperature for preheating the butt portion is 400 to
Limited to the range of 900 ℃
The oxygen content in the weld metal at the weld
Method for producing a carbon steel pipe excellent in toughness by the high energy density beam welding, characterized in that that.