JP2002018592A - Solid wire for circumferential weld of carbon steel pipe and welding method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slid wire for circumferential weld of a carbon steel pipe used for a high efficiency welding system having a narrowed groove, higher speed and the reduction of heat to be inputted, applicable to a carbon steel pipe having strength of API-X<=60, imparting excellent mechanical properties to weld metal and having good welding operability in all attitudes and excellent defect resistance and to provide a welding method using the same solid wire for welding. SOLUTION: This solid wire for girth-welding a steel pipe has components containing, by mass, 0.03 to 0.12% C, 0.35 to 0.60% Si, 1.60 to 2.10% Mn, 0.30 to 0.90% Ni, <=0.015% P, <=0.015% S, <=0.020% Ti, <=0.10% Cr, <=0.01% Al, <=0.01% Nb, <=0.30% Cu and <=0.20% Mo, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid wire for girth welding of steel pipes, which is applied to girth welding of steel pipes constituting a pipeline or the like that carries gas, oil, etc., and a gas shield arc welding method using the same. In particular, in a high-efficiency welding system with a narrow groove and a high speed, it can be applied to a carbon steel pipe having a strength of line pipe API-X60 or less, has good welding workability, and has excellent mechanical performance of a weld metal, Furthermore, the present invention relates to a solid wire for peripheral welding of steel pipe having excellent defect resistance and a welding method using the solid wire for peripheral welding of steel pipe.

[0002]

2. Description of the Related Art A pipeline is a structure that requires extremely high reliability in view of its purpose and application, and a high quality is also required for its welded portion. For example, welded tensile strength indicating static strength, low-temperature toughness indicating brittle fracture,
Many specifications such as a bead shape related to fatigue fracture susceptibility and a maximum hardness related to hydrogen cracking susceptibility are defined according to use conditions.

[0003] Conventionally, the circumferential welding of steel pipe joints for pipelines is often performed on site and the position must be 360 ° in all positions. Therefore, a manual welding method using a coated arc welding rod is mainly used. there were. However, recently, automatic welding has been studied for the purpose of shortening the construction period and reducing cost, and at present, a small welding robot suitable for girth welding has been developed and has achieved results.

In this conventional automatic welding system, a normal welding wire is used as a welding wire. For example, for a carbon steel pipe having a strength equal to or less than that of a line pipe API-X60 steel pipe, a welding wire generally used for low current welding, for example, NKK technical bulletin No. 136
1991 p. JIS (Japane)
se Industrial Standard: YGW12 of Z3312 and ER70S-6 of AWS (American Welding Society: A5.18) C (0.15% by mass or less) -Si (0.7-1% by mass). A welding wire having a composition of (0% by mass) -Mn (1.3 to 1.6% by mass) is used as it is.

[0005] Recently, there has been a further demand for further shortening of the construction period and cost reduction, and a high-efficiency welding system with a narrow groove and a high speed has been developed.

[0006]

However, a high-efficiency welding system (hereinafter, referred to as a high-efficiency welding system) with a narrow groove and a high speed has the following problems. In this high-efficiency welding system, the phenomenon of extremely low heat input, reduction of interpass temperature and acceleration of segregation to the center of the bead due to parallel collision of the solidified surface of the weld metal due to the decrease in groove angle occur, When a normal welding wire is used, excessive strength and hardness of the weld metal and a decrease in toughness are inevitable.

[0007] In the above-described high-efficiency welding system, the weld metal is cooled at a large cooling rate exceeding the normal suitable cooling rate condition. For example, even if a welding material for low-temperature steel specified in JISZ3325 is used, the cooling rate is high and the hardness becomes excessive, and the Charpy absorbed energy does not improve. In addition, the slag removability is inferior, and the bead sags and becomes convex. Further, a problem such as a bead defect due to instability of the arc in a low current region occurs, and welding workability in all positions is significantly reduced. Furthermore, the sensitivity of solidification cracking increases with narrow groove and high speed welding,
Crack resistance higher than that of conventional wires is required. For these reasons, there is a need for a welding wire that can be applied to a high-efficiency welding system, has excellent mechanical performance at the welded portion, and can achieve good all-position workability.

The present invention has been made in view of the above problems, and has a narrow groove, a high speed, and a heat input of 15 kJ /.
cm, a high efficiency welding system with low heat input, can be applied to carbon steel pipes having a strength of API-X60 or less, and has excellent mechanical properties such as toughness, strength and hardness of the weld metal, Solid wire for circumferential welding of carbon steel pipes with good weldability in all positions such as arc stability and slag peelability, and excellent defect resistance such as cracking resistance, poor fusion resistance and blowhole resistance. An object of the present invention is to provide a welding method using a solid wire for welding.

[0009]

The solid wire for circumferential welding of a steel pipe according to the present invention is 100% by volume as a shielding gas.
Ar and CO _{2 in} which CO ₂ gas or Ar is 75% by volume or less
C: 0.03 to 0.12% by mass in a solid wire for circumferential welding of carbon steel pipe using a gas mixture of
i: 0.35 to 0.60 mass%, Mn: 1.60 to 2.10 mass%, Ni: 0.30 to 0.90 mass%,
P: 0.015% by mass or less, S: 0.015% by mass or less, Ti: 0.020% by mass or less, Cr: 0.10% by mass or less, Al: 0.01% by mass or less, Nb: 0.01 % By mass, Cu: 0.30% by mass or less, and Mo: 0.2
0% by mass or less, with the balance being Fe and unavoidable impurities.

In the present invention, by limiting the composition of the solid wire to the above range, in a highly efficient welding system by narrowing the groove, increasing the speed, and reducing the heat input, the toughness, strength, hardness and the like of the weld metal are reduced. It is possible to improve mechanical performance, improve defect resistance such as crack resistance and blow hole resistance, and improve welding workability such as spatter generation, arc stability and slag peeling property. In addition, in this invention, low heat input means 15 kJ / cm or less.

[0011] In the method for welding a steel pipe peripheral joint according to the present invention, the solid wire for welding is used, and one wire is used as a shielding gas.
A method of welding a joint of a steel pipe in a circumferential direction by all-position welding using a CO ₂ gas of 00 volume% or a mixed gas of Ar and CO ₂ , wherein the composition of the mixed gas is 75 vol% Ar.
It is characterized by the following.

In the present invention, the penetration depth in the direction of the groove wall is secured by making Ar 75% by volume or less,
In the narrow-groove and high-speed all-position welding method, poor penetration and generation of a pear-shaped solidification crack defect can be prevented. In addition, generation of blow holes can be suppressed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have reported that, regarding the components of a welding wire, Si and Si, which are the main deoxidizing elements that have a great effect on the mechanical properties of the weld metal and on the welding workability such as bead shape and arc stability, are described. By changing the Mn content and their constituent ratios, and further producing a large number of welding wires by combining Mo, Ni, etc. which affect the toughness and strength of the weld metal, the mechanical performance and defect resistance of the weld metal In order to improve welding workability, various experimental studies were conducted.

As a result, in the above-described high-efficiency welding system, since the amount of oxygen in the weld metal becomes larger than in the conventional welding system, coarse ferrite grains develop in the weld metal, and in particular, the toughness tends to decrease. I found that. Therefore, further experimental research was conducted with the main purpose of improving the toughness of the weld metal while maintaining the welding workability equal to or higher than that of the conventional welding system, and the following results were obtained.

The present inventors have found that Si and Mn are:
In order to suppress the growth of ferrite while strengthening the deoxidizing power, it has been found that it is effective to reduce the Si-Mn content compared to a conventional welding wire. FIG. 1 is a graph showing the relationship between the contents of Si and Mn in a welding wire and the mechanical performance and welding workability of a weld metal. As shown in FIG. 1, if the Si content in the welding wire is larger than the range specified in the present invention, the toughness of the weld metal is insufficient, and if the Si content is smaller than the range specified in the present invention, the bead toe shape is reduced. And the arc stability is degraded. Further, when the amount of Mn in the welding wire is larger than the range specified in the present invention, the hardness of the weld metal becomes excessive and the slag removability deteriorates, and the Mn amount is smaller than the range specified in the present invention. The strength and toughness of the weld metal are insufficient, and the shape of the bead becomes convex.

With respect to Ni, the addition of 0.3% by mass or more significantly improved the toughness of the weld metal.
It has been found that when added in excess of 0.9% by mass, cracks occur in the above-described high-efficiency welding system. FIG.
FIG. 3 is a graph showing the relationship between the Ni content in the welding wire, the Charpy absorbed energy (vE0 ° C.) of the weld metal, and the solidification cracking occurrence rate. As shown in FIG. 2, the Charpy absorbed energy increases as the Ni content in the welding wire increases, but cracks occur when the Ni content exceeds 0.9% by mass, and the cracking rate increases as the Ni content increases. Found to be higher.

Hereinafter, the reasons for limiting the chemical components contained in the gas-shielded arc welding wire according to the present invention will be described in detail.

C: 0.03 to 0.12% by mass C is an element necessary for securing the strength of the weld metal. Further, in all-position welding, it is necessary to transfer a short-circuit droplet in order to prevent the bead from sagging. However, if the C content is large, the number of short-circuits increases and the arc is stabilized. The effective amount of C for ensuring the strength and arc stability of the weld metal is 0.03% by mass or more. On the other hand, if the amount of C exceeds 0.12% by mass, the explosion of CO becomes excessive and the amount of spatter generated increases, so that the welding workability decreases. Further, the hardenability of the weld metal is increased, so that the strength becomes excessive. In addition, hot cracking susceptibility and hydrogen cracking susceptibility also increase. Therefore, the upper limit of the amount of C is set to 0.12% by mass.

Si: 0.35 to 0.60 mass% Si is a main deoxidizing element and is an essential element for a welding wire. However, in a low heat input construction with a heat input of 15 kJ / cm or less, the amount of Si required for deoxidation may be smaller than usual. 1. As shown in FIG.
If it exceeds 60% by mass, coarse ferrite grains are easily formed in the weld metal, and the toughness is reduced. In addition, the amount of slag increases, and the time and effort for removal increase. However,
If the amount of Si is less than 0.35% by mass, the conformity of the bead toe becomes poor and the appearance is deteriorated. In addition, since deoxidation is insufficient, arc stability is reduced, and blow holes may be generated. Therefore, the amount of Si is 0.35 to 0.60% by mass.
And

Mn: 1.60 to 2.10% by mass Mn is also a major deoxidizing element like Si, and has the effect of improving the hardenability of the weld metal and increasing the strength and toughness. In addition, an element that lowers crack resistance such as S is fixed,
It also has the effect of improving crack resistance. As shown in FIG.
If the n content is less than 1.60% by mass, deoxidation is insufficient, and the strength and toughness of the weld metal cannot be secured. In addition, the bead easily sags in all position welding, and the bead shape is deteriorated.
Furthermore, crack resistance is also poor. Conversely, the Mn content is 2.10% by mass.
If it exceeds, the hardness of the weld metal becomes excessive, the amount of slag increases, and the trouble of removal increases. Therefore, the upper limit of the amount of Mn is set to 2.10% by mass.

Ni: 0.30 to 0.90% by Mass Ni is effective for improving toughness. However, if the amount of Ni in the welding wire is less than 0.30% by mass, the above effect is not sufficiently exhibited. Further, if Ni is added in excess of 0.90% by mass, arc stability is reduced and solidification cracks are easily generated. In addition, it significantly increases the hardness of the weld metal. Therefore, the upper limit of the amount of Ni is set to 0.90% by mass.

P: 0.015% by mass or less P significantly deteriorates the hot crack resistance and the low temperature toughness of the weld metal. Therefore, it is preferable that the amount of P in the welding wire is as small as possible. Practically, up to 0.015% by mass is permissible, so the upper limit of the P content is 0.015% by mass.

S: 0.015% by mass or less S significantly deteriorates the hot crack resistance and the low temperature toughness of the weld metal. Therefore, the S content in the welding wire is preferably as small as possible. Since practically, up to 0.015% by mass is permissible, the upper limit of the amount of S is set to 0.015% by mass.

Ti: 0.020% by mass or less Ti has the effect of improving the arc stability in a high current range, but the arc stability in a low current range is more important in all-position welding. When a large amount of Ti is added, the arc stability in a low current region decreases. Further, when Ti is added, the amount of slag increases, and the work of removing the slag increases. Therefore, it is preferable that the amount of Ti is small. Since there is no problem if the Ti content is 0.020% by mass or less, the upper limit of the Ti amount is set to 0.020% by mass.

Cr: 0.10% by mass or less Cr has the effect of improving the corrosion resistance of the weld metal, and Cr is added to steel pipes and welding wires for pipelines for the purpose of improving carbon dioxide gas corrosion resistance. There is something. However, in the case of general carbon steel pipes in which carbon dioxide corrosion does not pose a problem, the improvement of corrosion resistance by adding Cr to the welding wire not only results in excessive quality and high price, but also
It is preferable that the amount of Cr is small, because it leads to a decrease in slag peelability, toughness and arc stability and an increase in the strength of the weld metal. If the Cr content is 0.10% by mass or less, these adverse effects do not appear, so the upper limit of the Cr amount is set to 0.10% by mass.

Al: 0.01% by mass or less Al greatly increases the strength of the weld metal and lowers the toughness. In addition, the amount of spatter generated is greatly increased, and the amount of slag is also increased. Therefore, it is preferable that the amount of Al is as small as possible. Considering economics, the upper limit of the amount of Al is 0.01
% By mass.

Nb: 0.01% by mass or less Nb greatly increases the strength of the weld metal and lowers the toughness. In addition, the amount of spatter generated is greatly increased, and the amount of slag is also increased. Therefore, the Nb content is preferably as small as possible. Considering economics, the upper limit of the Nb amount is 0.01
% By mass.

Cu: 0.30% by mass or less Cu is said to have the effect of improving the corrosion resistance of the weld metal like Cr, but has the problem of lowering toughness and crack resistance. Therefore, when the corrosion resistance is not important, the Cu content is preferably as small as possible. C
If the u content is 0.30 mass% or less, the above problem does not occur. Therefore, the upper limit of the Cu content is set to 0.30 mass%. In the present invention, when the welding wire is a plated wire, the amount of Cu is the sum of the amount of Cu contained in the core wire and the amount of Cu contained in the plating.

Mo: 0.20% by mass or less Mo has the effect of improving the hardenability of the weld metal and increasing the strength and toughness. However, in a high-efficiency welding system, a sufficient heat-strength is ensured by a low heat input construction by high-speed welding, so that a steel pipe of API-X60 or less can be used without intentionally adding Mo. Higher strength than material can be obtained. Mo content in welding wire is 0.20
If the amount is less than or equal to% by mass, the strength of the weld metal will not be excessive, so the upper limit of the amount of Mo is set to 0.20% by mass.

Next, the reasons for limiting the composition of the shielding gas will be described.

In a mixed gas of Ar and CO ₂ , Ar:
75% by volume or less The shielding gas used in the welding method of the present invention is 1
It is necessary to be a mixed gas of Ar and CO _{2 of} 00 vol% CO ₂ or 75 vol% or less. When the Ar mixing ratio exceeds 75% by volume, the penetration state becomes sharp and shallow, and the penetration depth in the direction of the groove wall becomes small. Therefore, in a high-efficiency welding system with a narrow groove and a high speed, penetration is performed. Defective and pear-shaped solidification cracking defects are likely to occur. Therefore, the Ar mixing ratio in the shielding gas is set to 75% by volume or less.

[0032]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples that fall outside the scope of the present invention. 3A and 3B are diagrams illustrating a welding method in the present embodiment, in which FIG. 3A is a schematic diagram illustrating a steel pipe peripheral joint, and FIG. 3B is a cross-sectional view illustrating a shape of a groove of a welded portion. As shown in FIGS. 3A and 3B, a peripheral joint of a steel pipe was automatically welded using a welding robot dedicated to a high-efficiency welding system. Table 1 shows the welding conditions at this time. This steel pipe is an API-X60 carbon steel pipe, and the plate thickness is 12.7 mm. Table 2 shows the chemical composition of this steel pipe. Further, Tables 3 and 4 show the components of the tested welding wires.

A welding test was carried out by combining the welding wires shown in Tables 3 and 4 and the shielding gas having different compositions. As the evaluation of the mechanical performance of the weld, a full thickness joint tensile test, a weld Charpy impact test, and a weld Vickers hardness test were performed. In the full-thickness joint tensile test, a case where the fracture mode was a base material fracture was regarded as acceptable. In the Charpy impact test of the weld, a test piece was sampled from the center of the plate thickness of the weld so that the notch of the test piece was at the center of the groove, and the absorbed energy (vE0 ° C.) was measured. The measurement was performed on three test pieces, and a case where the average value was 100 J or more was regarded as a pass. In the Vickers hardness test for welds, HIC resistance
From the viewpoint of (Hydrogen Induced Cracking), a position 1 mm below the surface was measured at a 0.5 mm pitch, and a case where the maximum value of the hardness (Hv) was 220 or less was determined to be acceptable. In addition, as an evaluation of the defect resistance, cracks, poor fusion (LF) and blowholes (B
The presence or absence of H) was confirmed, and the case where these defects were not recognized was evaluated as ○, the case where some of them were generated was evaluated as 多量, and the case where a large amount was generated was evaluated as ×. Further, as the evaluation of the welding workability, the arc stability, the bead shape, and the removability of the slag (the amount of the slag, the releasability) were evaluated based on the sensory characteristics of the operator. Was rejected (x). Table 5 shows the results of this welding test.

[0034]

[Table 1]

In the welding directions in Table 1, 12:00 indicates the uppermost portion of the steel pipe, 3 o'clock indicates the side of the steel pipe, and 6 o'clock indicates the lowermost portion of the steel pipe. Therefore, 12: 00 → 3: 00 → 6: 00 means that welding is started from the uppermost part of the steel pipe, welding is performed toward the lower part of the steel pipe, and welding is completed at the lowermost part. In the present embodiment, half the circumference of the steel pipe was welded in this manner, and then the opposite side of the steel pipe was similarly welded from the top to the bottom, and the entire circumference was welded.

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

Hereinafter, the results of the welding test will be described in detail. No. in Table 5 above. T1 to T18 are embodiments of the present invention. Example No. T1 to T18 are
Since the components of the welding wire and the composition of the shielding gas were within the scope of the present invention, the mechanical properties, defect resistance and welding workability of the weld metal were excellent. Therefore, in these examples, good welding was realized by the high-efficiency welding system.

On the other hand, no. T1
9 to T44 are comparative examples. Comparative Example No. In T19, since the C content in the welding wire is low, the strength of the weld is insufficient,
The arc stability at the short circuit transfer was poor. Comparative Example No. T
On the other hand, No. 20 had an excessive C content, so that the strength of the weld was too high and the maximum hardness exceeded 220. In addition, cracking resistance was deteriorated, cracking occurred, and the amount of spatter generated was large.
Comparative Example No. In T21 and T22, since the amount of Si was lower than the range of the present invention, the beads were easily sagged, the bead shape was deteriorated, and blowholes were generated due to insufficient deoxidation. In particular, in Comparative Example No. 1 in which the amount of Mn in the welding wire was close to the lower limit. T21 also lacked strength.

Comparative Example No. In T23, T25 and T27, since the Mn content in the welding wire was lower than the lower limit, the hardenability was insufficient and the Charpy absorbed energy was low. Also, M
Since the effect of improving the hot cracking resistance by n was not obtained, cracking occurred. Furthermore, the arc stability was poor, the beads were easily sagged, and the bead shape was poor. In particular, in Comparative Example No. 1 in which the amount of Si in the welding wire was close to the lower limit. T23 is
The strength of the weld metal was also insufficient. Comparative Example No. T24,
In T26 and T28, since the Mn content in the welding wire was higher than the upper limit of the present invention, the quenchability was excessive and the maximum hardness exceeded 220. In addition, a large amount of slag was generated, and the slag removal property was reduced.

Comparative Example No. In T29, T30, and T31, since the amount of Si in the welding wire was excessive, the maximum hardness of the weld metal exceeded 220, coarse ferrite grains were generated, and the Charpy absorbed energy was low. Also, S
Since a large amount of i-oxide was generated, the amount of slag increased, and the slag removal property was reduced. Comparative Example No. In T32, since the P content in the welding wire was excessive, the hot cracking resistance was reduced, and many cracks occurred. Also, the toughness was reduced. Comparative Example No.
In T33, since the S content in the welding wire was excessive, the hot cracking resistance was lowered and many cracks occurred. Also, the toughness was reduced.

Comparative Example No. T34 is Ni in the welding wire
Since the amount was insufficient, the effect of improving toughness was not obtained, and the Charpy absorbed energy was insufficient. Comparative Example No. In T35, since the Ni was excessively added to the welding wire, the hardenability of the weld metal became excessive and the maximum hardness exceeded 220. In addition, the hot cracking resistance was reduced, and cracking occurred. Comparative Example No. In T36, since the amount of Ti in the welding wire was excessive, the amount of slag generated increased, and the slag removability was poor, and the slag removal property was reduced. In addition, the stability of the transfer of the short-circuit droplet was significantly reduced, and the amount of spatter generated was large.

Comparative Example No. T37 is Cr in the welding wire
Due to the excessive amount, the weld metal became excessively strong and the maximum hardness exceeded 220. Further, the toughness was reduced, and the Charpy absorbed energy was reduced. The arc stability was also inferior, the amount of spatter generated was large, and the slag removal property was also inferior due to an increase in the amount of slag and a decrease in peelability. Comparative Example No. In T38, since the amount of Al in the welding wire was excessive, the strength of the weld metal was excessive, and the maximum hardness exceeded 220. Further, the toughness was reduced, and the Charpy absorbed energy was reduced. The arc stability was also inferior, the amount of spatter generated was large, and the slag removal property was also inferior due to an increase in the amount of slag and a decrease in peelability. Comparative Example No. T3
In No. 9, since the Nb content in the welding wire was excessive, the strength of the weld metal was excessive, and the maximum hardness exceeded 220. Also,
The toughness was reduced and the Charpy absorbed energy was low. The arc stability was also inferior, the amount of spatter generated was large, and the slag removal property was also inferior due to an increase in the amount of slag and a decrease in peelability. Comparative Example No. In T40, since the amount of Cu in the welding wire was excessive, the crack resistance and toughness of the weld metal were reduced, cracks occurred frequently, and the Charpy absorbed energy was low. Comparative Example No. T
In No. 41, since the Mo content in the welding wire is excessive, the hardenability of the weld metal becomes excessive, and the maximum hardness of the welded portion is 220.
Exceeded.

Comparative Example No. T42 is AWS ER70 which is a wire used for general welding of a steel pipe in all positions.
This is a case where a welding wire corresponding to S-6 and JISZ3312 YGW12 is used. This welding wire (W3
In No. 8), since the amount of Si was high and Ni was not added, the Charpy absorbed energy was low and the amount of slag was large. Further, since the amount of Mn was small, the bead was easy to drop, and the effect of crack resistance was not obtained. Further, since the amount of S was large, cracks occurred frequently. Arc stability was also poor.

Comparative Example No. In T43 and T44, the composition of the welding wire is within the range of the present invention, but the shielding gas composition at the time of welding is out of the use conditions of the welding wire of the present invention. That is, since the ratio of Ar in the shield gas was too high, the penetration range was narrowed, and poor fusion of the groove surface and blowholes caused by Ar occurred frequently. In addition, the amount of oxygen in the weld metal was reduced and the hardenability became excessive, and the maximum hardness of the welded portion exceeded 220.

The groove shape in the present invention is not limited to the groove shape of this embodiment, and the same applies to a V groove, a U groove and a multi-step groove having a groove angle of up to 40 °. It is effective for Also, the torch rod method in the present invention is not limited to the rotating arc method and the horizontal weaving method,
It is effective in other methods. Further, the method of laminating the welding beads in the above-described embodiment is all-layer downward welding as shown in Table 1, but the present invention is not limited to this, and for example, only the finishing layer may be upward-welding. In this case, upward welding
Refers to the method of welding from the bottom to the top of a steel pipe. Further, in the above embodiment, one layer is used for laminating the weld beads.
Although the lamination is performed in the pass, the present invention is not limited thereto, and the distribution welding in which one layer is laminated in two or more passes may be performed.

[0049]

As described in detail above, according to the present invention,
In the case of introducing a highly efficient welding system by narrowing the gap and increasing the speed in girth welding of pipelines that are difficult to construct because welding is performed in a complicated posture by properly specifying the components of the welding wire and the shielding gas composition However, mechanical properties such as strength, hardness and toughness of weld metal, crack resistance, defect resistance such as poor fusion resistance and blowhole resistance, bead shape, arc stability, low spatter generation and slag removal , Etc., can be improved. As a result, in on-site welding of pipelines,
Improve the efficiency of welding work and the quality of welded products,
Costs can be reduced. The industrial value of these effects is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the contents of Si and Mn in a welding wire and the mechanical performance and welding workability of a weld metal.

FIG. 2 is a graph showing the relationship between the Ni content in a welding wire, the Charpy absorbed energy of a weld metal, and the rate of solidification cracking.

3A and 3B are diagrams showing a welding method in an embodiment of the present invention, wherein FIG. 3A is a schematic diagram showing a steel pipe peripheral joint, and FIG.
FIG. 4 is a cross-sectional view showing a shape of a groove of a welded portion.

[Explanation of symbols]

 1; steel pipe 2; groove 3; copper backing

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naohiro Tamaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Within Nihon Kokan Co., Ltd. Construction Co., Ltd. (72) Inventor Sadafumi Miura 88, Ono-cho, Tsurumi-ku, Yokohama, Japan Kanagawa Pref. (72) Inventor Reichi Suzuki 100-1 Urakawachi, Miyama-ji, Fujisawa-shi, Kanagawa F-term in Kobe Steel, Ltd.Fujisawa Plant (Reference) 4E081 AA03 AA05 BA27 BB04 CA09 CA10 DA05 DA23 DA36 DA40 DA62 EA38

Claims (2)

[Claims] 1. A 100% by volume CO ₂ as a shielding gas
In a solid wire for circumferential welding of carbon steel pipes using a gas or a mixed gas of Ar and CO ₂ in which Ar is 75% by volume or less, C: 0.03 to 0.12% by mass, Si:
0.35 to 0.60 mass%, Mn: 1.60 to 2.
10% by mass, Ni: 0.30 to 0.90% by mass, P:
0.015% by mass or less, S: 0.015% by mass or less, T
i: 0.020% by mass or less, Cr: 0.10% by mass or less, Al: 0.01% by mass or less, Nb: 0.01% by mass
Hereinafter, a solid wire for circumferential welding of carbon steel pipes, characterized by containing Cu: 0.30% by mass or less and Mo: 0.20% by mass or less, and having a balance of Fe and unavoidable impurities. 2. The solid wire according to claim 1, wherein 100% by volume CO ₂ gas or A is used as a shielding gas.
A method of circumferentially welding a steel pipe joint by all-position welding using a mixed gas of r and CO ₂ , wherein the composition of the mixed gas is such that Ar is 75% by volume or less. Steel pipe girth welding method.