JPH0569141A - Gas shielded arc welding method for pipes - Google Patents

Abstract

PURPOSE:To improve the selective corrosion resistance, toughness and cracking resistance of a welded metal in the circumferential welding of pipes exposed to a corrosive environment incorporating CO2. CONSTITUTION:This method is a gas shielded arc welding method where the chemical composition of a base metal and a welding material (a gas shielded arc welding wire) and the chemical composition range of the welded metal obtained thereby, the difference DELTA (Cu+Ni) and DELTAMo in Cu, Ni and Mo between the welded metal and the base metals, especially and welding conditions are regulated.

Description

Detailed Description of the Invention

[0001]

The present invention relates to oil and gas containing CO ₂ or circumferential welding method for line pipe for transporting CO _2, especially resistance to preferential corrosion resistance and low-temperature toughness of the weld metal,
The present invention relates to a circumferential welding method having excellent crack resistance.

[0002]

2. Description of the Related Art Conventionally, there are the following publications regarding selective corrosion of welded parts of low alloy steel. 1) It is said that the difference in the amount of Ni added between the base metal and the weld metal affects local corrosion of welded joints in the ice sea (Takashi Abe et al., Iron and Steel Vol.72, s1266, 1988). 2) Similarly, localized corrosion of welded steel in ice-sea steels, where Ni and Cu influence and 3.8 ΔCu + 1.1 ΔNi + 0.3 influences selective corrosion (Kametaro Ito et al .;
Iron and Steel Vol.72, s1265, 1989). 3) Use of low alloy welding rods containing Cu and Ni is effective for preventing selective corrosion of carbon steel pipe circumferential welds (Yuki Hideaki; Material Vol.38, No.424, p62-p68, 1989). 4) Addition of Ni and Mo is effective for preventing selective corrosion of welded steel pipe vertical seam welds (Suga et al .; Japanese Patent Application No. 1-260271).

As described above, as a method for improving the selective corrosion of the weld metal in a corrosive environment such as seawater containing oxygen such as ice sea, a method of adding Ni and Cu and an improvement of the selective corrosion characteristic of the welded steel pipe vertical seam. A method of adding Ni and Mo has been found, but it has been found that addition of Ni and Mo is effective in suppressing selective corrosion of the circumferential welded portion of a line pipe used in a corrosive environment containing CO _2. , A gas shielded arc welding method considering practicality such as hardness and crack resistance of weld metal has not been obtained. Further, no specific method for solving this problem has been found in relation to the base material component.

[0004]

The welded steel pipe or seamless steel pipe INVENTION SUMMARY is], using the inclusive of oil and natural gas or CO ₂ transport CO _2, circumferential weld metal is selectively corroded, so-called weld-alloying May occur.
This is because the chemical composition and structure of the weld metal and the base material are different and the weld metal part becomes electrochemically base, and the weld metal part is selectively corroded. In the case of the line pipe used in the environment as described above, the circumferential welding method considering the selective corrosion has not been studied so far. However, in a real environment, this type of selective corrosion often poses a problem, and this examination is awaited.

Therefore, the inventors of the present invention have variously changed the chemical composition of the circumferential weld metal and the composition values thereof, so that the selective corrosion characteristic of the welded portion and its mechanical property resistance in a corrosive environment containing CO ₂ and seawater. Thorough investigations were conducted on crackability. The present invention is based on the findings obtained as a result of this investigation,
By adjusting the base metal, welding material and welding method to adjust the chemical composition of the weld metal part, while preventing selective corrosion of the circumferential weld metal part, it has sufficient strength, toughness and crack resistance. An object of the present invention is to provide a gas shielded arc welding method for pipes to obtain a circumferential weld metal.

[0006]

The first aspect of the present invention is that the chemical composition of the weld metal (% by weight) is C: 0.01 to 0.15% Si; 0.20 to 1.00% Mn; 0.40 to 2.00% Cu; ≤ 2.50% Ni; 0.50 to 2.50% ΔCu + ΔNi; ≥ 0.50% (Δ: weld metal content-
Base material content) P _CM ; ≤0.25% (P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 +
Cr / 20 + Mo / 15 + V / 10 + 5B (1)) The balance consists of Fe and unavoidable impurities, and the unavoidable impurities are the gas shield arc welding method for pipes satisfying the following range. P; ≤0.030% S; ≤0.030% Al;
≤0.05% N; ≤0.050% Nb; ≤0.10% V;
≤0.10% Cr; ≤1.00% Ca; ≤0.0025% O;
≤0.10% Zr; ≤0.05% B; ≤0.002%

A second aspect of the present invention is that the chemical composition (% by weight) of the weld metal is in addition to the above chemical composition, Mo or Ti.
The gas shielded arc welding method for pipes is characterized by containing either one or both of the above. Mo; ≤1.05% ΔMo; ≥0.03% Ti; ≤0.25%

The chemical components and welding conditions of the pipe base material and the welding wire applied to the first and second inventions are as follows. Chemical composition (% by weight) of base material C; 0.03 to 0.15% Si; 0.05 to 0.50% Mn; 0.50 to 2.00% Al; 0.005 to 0.10% Contained, or in addition to the above chemical components, further contains one or more of the following components: Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cr; 0 .05 to 2.0% Mo; 0.05 to 1.0% Nb; 0.005 to 0.20% V; 0.005 to 0.20% Ti; 0.005 to 0.20% B; 0.0005 to 0.0020% Ca; 0.0005 to 0.0050% The balance contains Fe and unavoidable impurities. Chemical composition of welding wire (% by weight) C; 0.01 to 0.15% Si; 0.20 to 1.20% Mn; 0.60 to 2.50% Cu; ≤ 3.00% Ni; 50 to 3.00%, or in addition to the above chemical components, 1
One or two or more kinds are contained, Mo; ≤ 1.10% Ti; ≤ 0.30% The balance consists of Fe and unavoidable impurities, and the content of the unavoidable impurities should satisfy the following range. P; ≤0.030% S; ≤0.030% Al;
≤0.05% N; ≤0.01% Nb; ≤0.02% V;
≤0.02% Cr; ≤0.05% Zr; ≤0.05% O 2;
≤0.02% B; ≤0.002% Welding conditions Shield gas: 100% CO ₂ or Ar + (5-4
0%) CO ₂ wire diameter: 0.8 to 1.6 mm Welding current: 100 to 500 A Arc voltage: 15 to 45 V Welding speed: 5 to 150 cm / min. Welding posture: All postures

[0009]

As described above, the present invention limits the chemical composition of the weld metal by limiting the chemical composition of the base metal and the welding wire and the range of welding conditions, and provides sufficient strength and high toughness with rich selective corrosion resistance. It is a circumferential welding method that has excellent crack resistance.

Next, the reason why each chemical component in the weld metal is limited will be described. C: 0.01 to 0.15% C is 0.01 to 0.15% in the weld metal in order to obtain good workability and mechanical properties of the weld metal. 0.01
If it is less than%, the ferrite grains in the weld metal become coarse, so that the strength and toughness decrease, and the mechanical performance becomes insufficient with respect to the base metal. If it exceeds 0.15%, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness. Furthermore, since the hardness increases, the susceptibility to welding cracks and stress corrosion cracking increases. Si; 0.20 to 1.00% Si is 0.20 to 1.00% in the weld metal in order to obtain good workability and mechanical properties of the weld metal. 0.2
If it is less than 0%, the familiarity of the molten metal with respect to the base material is lowered, so that the bead shape becomes defective, causing defects such as fusion failure. Especially when the content is extremely low, deoxidation becomes insufficient and blowholes occur. Further, in terms of mechanical performance, the strength of the weld metal is insufficient with respect to the base metal. 1.0
If it is added to the weld metal in an amount of more than 0%, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness.
Further, since hardness increases, susceptibility to welding cracks and stress corrosion cracking increases. Mn: 0.40 to 2.00% Mn is also set to 0.40 to 2.00% in the weld metal in order to obtain good welding workability and mechanical properties. If it is less than 0.40%, the amount of slag increases as the value of Mn / Si approaches 1 or falls below 1, causing slag entrainment and the like. Particularly when the content is extremely low, blowholes are generated due to insufficient deoxidation. Regarding the mechanical performance, the strength of the weld metal is insufficient with respect to the base metal, and the hardenability deteriorates, so that the toughness deteriorates. If it exceeds 2.00% and is added to the weld metal, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness. Further, since hardness increases, susceptibility to welding cracks and stress corrosion cracking increases. Cu; ≤ 2.50% Ni; 0.50 to 2.50% Cu and Ni are 2.50% in the weld metal in order to improve the toughness and selective corrosion characteristics of the weld metal (see Fig. 1).
Hereinafter, (Cu) and 0.50 to 2.50% (Ni) are added. Cu has the effect of improving the selective corrosion characteristics of the weld metal, but if it exceeds 2.50%, the susceptibility to hot cracking increases. Ni is also effective in improving the selective corrosion property. When Cu is not added, it is necessary to add 0.50% or more in order to obtain good selective corrosion characteristics by adding Ni.
If it is added in excess of 2.50%, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness. Further, since hardness increases, susceptibility to welding cracks and stress corrosion cracking increases. Moreover, especially in order to suppress the occurrence of stress corrosion cracking, the Ni content is set to less than 1.00%. The method of adding Cu and Ni to the wire may be either plating or melting. Further, in order to obtain better selective corrosion characteristics, it is desirable that the difference Δ (Cu + Ni) in the content between the weld metal of Cu and Ni and the base metal is 0.5% or more as shown in FIG. .. FIG. 1 is a graph showing the effect of Δ (Cu + Ni) on the selective corrosion characteristics, where the vertical axis represents the selective corrosion current (μA) flowing between the base metal and the weld metal, and the horizontal axis represents Δ ( It is shown by taking Cu + Ni) (%). When the selective corrosion current is positive, the selective corrosion of the weld metal does not occur. Δ (Cu + Ni) is 0.5
%, The selective corrosion current turned positive. P _CM ; ≦ 0.25% When the P _CM value represented by the formula (1) exceeds 0.25%, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness. Further, since hardness increases, susceptibility to welding cracks and stress corrosion cracking increases.

Next, in the second aspect of the present invention, in addition to the above-mentioned components, the above-mentioned optional components and their compositions are limited. Mo: 0.03 to 1.05% Mo is 0.03 to 1.03% in the weld metal so that ΔMo is 0.03% or more in order to prevent selective corrosion of the weld metal.
Add 1.05%. As shown in FIG. 2, if the difference ΔMo in Mo content between the weld metal and the base metal is 0.03% or more,
Selective corrosion of the weld metal can be prevented in a corrosive environment containing CO ₂ . However, if added in excess of 1.05%, the hardness of the weld metal increases and the susceptibility to cold cracking and stress corrosion cracking increases. Note that FIG. 2 shows Δ that affects the selective corrosion characteristics.
6 is a graph showing the effect of Mo, in which the vertical axis represents the selective corrosion current (μA) flowing between the base metal and the weld metal, and the horizontal axis represents ΔMo (%). When the selective corrosion current is positive, the selective corrosion of the weld metal does not occur. Δ
When Mo becomes 0.03% or more, the selective corrosion current turns to a plus. Ti; ≤0.25% Ti may be added to the weld metal in a range of 0.25% or less as needed for the purpose of toughness of the weld metal due to the refinement of proeutectoid ferrite. If it exceeds 0.25%, the amount of slag increases, which causes defects such as slag inclusion. In addition, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness. Further, since hardness increases, susceptibility to welding cracks and stress corrosion cracking increases. Inevitable impurities;
When the content of unavoidable impurities is within the above range, the selective corrosion resistance and mechanical performance of the weld metal are not impaired. When the content of each component exceeds the above range, welding workability is deteriorated (Al), welding defects are generated (P, S, B, N), mechanical performance is deteriorated (Al, Cr, Nb, V). , O, N) and the like occur.

Next, the reasons for limiting the chemical composition of the steel pipe base material will be described. C: 0.03 to 0.15% Carbon in steel is an element effective in increasing the strength of steel, but excessive addition causes deterioration of toughness. Therefore,
The upper limit of the carbon content is 0.15% in order to manufacture a steel pipe having both good strength and toughness. The reduction of the carbon amount improves the toughness, but if it is 0.03% or less, the toughness deteriorates. Further, 0.03% of carbon is required to effectively utilize stable precipitation hardening of Nb, V, Ti, etc., so the lower limit of the amount of carbon is set to 0.03%. The reasons for limiting the other components are as follows. Si: 0.05 to 0.50% Si is necessary for deoxidation, but if added in excess, it deteriorates toughness, so the lower limit is made 0.05% and the upper limit is made 0.5%. Mn: 0.50 to 2.00% Mn is required to be 0.50% or more for deoxidation, but 2.0
If it exceeds 0%, the weldability deteriorates, so the upper limit is 2.00.
%. Al: 0.005-0.10% Al is necessary for deoxidation, but if it is less than 0.005%, deoxidation is insufficient, so the lower limit is made 0.005%. On the other hand, if it exceeds 0.10%, the cleanliness of the steel and the HAZ toughness deteriorate, so the upper limit is made 0.10%. Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cu and Ni improve the strength and toughness of the base material without adversely affecting the HAZ toughness, but when it exceeds 2.0%. Since the HAZ hardenability and toughness are adversely affected, the upper limit is 2.0%. Cr: 0.05 to 2.0% Cr increases the strength of the base material and the welded portion, but if it exceeds 2.0%, the hardenability and toughness of the HAZ are deteriorated, so the upper limit is made 2.0%. Mo: 0.05-1.0% Mo improves the strength and toughness of the base material, but 1.0%
If it exceeds 0.1%, the hardenability of the HAZ increases and the weldability deteriorates, so the upper limit is made 1.0%. The lower limit of the amount of addition of these elements is the minimum required amount to obtain the effect on the material, and 0.05
%. Nb; 0.005 to 0.20% V; 0.005 to 0.20% Nb and V are found to have an effect on strength and toughness.
If it exceeds 20%, the toughness of the base material and the welded part deteriorates, so the upper limit is made 0.20%. The lower limit is set to 0.005% at which improvement in material is recognized. Ti: 0.005 to 0.20% Ti has the effect of preventing coarsening of austenite during slab heating by adding 0.005% or more, so the lower limit is made 0.005%, and if added excessively, the weld zone Since the toughness is deteriorated, the upper limit is made 0.10%. B: 0.0005 to 0.0020% B is effective in increasing the strength of the base material, but excessive addition causes deterioration of weldability and HAZ toughness, so the upper limit is 0.002.
0%, the lower limit is 0.00, which is effective in increasing strength.
05%. Ca: 0.0005 to 0.0050% Addition of Ca improves hydrogen-induced cracking resistance, and the lower limit is made 0.0005% at which the effect is recognized. Excessive addition forms an oxide and is harmful, so the upper limit is made 0.005%.

The reasons for limiting the chemical composition (% by weight) of the welding wire in the present invention are as follows. C: 0.01 to 0.15 in order to secure good welding workability and to obtain appropriate strength, toughness and hardness for the base material.
%Added. Si: Add 0.20 to 1.20% in order to suppress the generation of blowholes by a deoxidizing action and to obtain good welding workability and appropriate mechanical properties of the weld metal. Mn; 0.60 to 2.50% for the same reason as Si
Added. Cu: 3.00% is added as an upper limit in order to improve the selective corrosion resistance of the weld metal while suppressing the occurrence of welding cracks. Ni: 0.50 to 3.00% is added to improve the selective corrosion resistance of the weld metal while ensuring appropriate toughness, strength and hardness with respect to the base material. For the same reason as for Mo; Ni, 1.10% is added as the upper limit. Ti: 0.30% is added as an upper limit in order to improve the toughness of the weld metal within a range that does not impair the welding workability. Inevitable impurities; when the content of each component exceeds the above range, welding defects occur (P, S, B, N), welding workability decreases (Al, Cr, Nb, V, O, N), etc. The problem occurs.

The reason for limiting the welding conditions in the present invention is as follows. Shielding gas: The composition of the shielding gas generally used for CO ₂ welding or MAG welding. Wire diameter: Welding wire diameter generally used according to the groove shape and welding position. Welding current, arc voltage, welding speed: welding current generally used according to groove shape, welding position, and wire diameter,
Arc voltage and welding speed. Welding position: All positions All positions should be set considering the circumferential welding of the pipe.

[0015]

EXAMPLES Examples of the present invention will be described. Table 1 shows the chemical composition (% by weight) of the test base metal. After manufacturing a welded steel pipe having an outer diameter of 38 inches and a total length of 12 m using the steels A to D shown in Table 1, circumferential welding is performed by gas shield arc welding to obtain the strength, toughness, seawater environment (CO ₂ bubbling) of the weld metal. ), The selective corrosion rate was measured. Table 2 and Table 3
Shows the selective corrosion rate of weld metal, strength, toughness, and the presence of cracks. Strength YS is JIS Z2201 No. 3 (6 mm
φ) test piece and toughness were evaluated by the absorbed energy at 0 ° C. using a JIS Z3128 No. 4 test piece. The presence or absence of weld cracking is determined by observing 5 cross-sections after welding, and the selective corrosion rate is 50 cm long steel pipe including circumferential welds, artificial seawater is put inside, and CO ₂ gas is blown into it to form a base metal. It is a value measured by obtaining the difference in plate thickness of the weld metal part.

As shown in Tables 2 and 3, the yield strength (350 N / mm ² or more), toughness (50 J or more), and selective corrosion are found in the circumferential welded portion where the chemical composition of the weld metal satisfies the claims. Property (welded metal part does not selectively corrode, 0 in Table 2)
It was confirmed that the circumferential welded portion has excellent hardness, low hardness (Hv 300 or less), and excellent crack resistance.

[Table 1]

[Table 2]

[Table 3]

[0017]

As described above, according to the present invention, since the chemical composition of the weld metal portion is adjusted by the base material, the welding material and the welding method, it is exposed to a corrosive environment such as a seawater environment containing CO _2. In the selective corrosion of the circumferential welded portion, by specifying the Cu, Ni, Mo difference between the weld metal portion and the base metal as described above, it has sufficient strength and high toughness, and has weld crack resistance. It is possible to obtain a circumferential weld metal part having excellent selective corrosion resistance.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a selective corrosion current (μA) flowing between a base material and a weld metal and Δ (Cu + Ni).

FIG. 2 is a graph showing the relationship between the selective corrosion current (μA) flowing between the base metal and the weld metal and ΔMo.

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[Procedure amendment]

[Submission date] September 22, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Conventionally, there are the following publications regarding selective corrosion of welded parts of low alloy steel. 1) Local corrosion of welded joints in ice seas is affected by the difference in the amount of Ni added to the base metal and weld metal (Abe et al .; “Iron and Steel” Vol.72, No.12 , s1266, 19 86
Year ). 2) Similarly, localized corrosion of welded steel in ice-sea steels, where Ni and Cu influence and 3.8 ΔCu + 1.1 ΔNi + 0.3 influences selective corrosion (Kametaro Ito et al .;
"Iron and Steel," Vol.72, No. 12 , s1265 , 1986 ). 3) Use of low alloy welding rods containing Cu and Ni is effective for preventing selective corrosion of carbon steel pipe circumferential welds (Yuki Hideaki; “Materials” Vol.38, No.424, p62- p68,1989
Year). 4) to select corrosion of welded steel pipe longitudinal seam weld, which addition of Ni and Mo is assumed to be effective (Suga addition, JP
(Head 3-170641 ).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Next, in the second aspect of the present invention, in addition to the above-mentioned components, the above-mentioned optional components and their compositions are limited. Mo; ≦ 1.05% ΔMo ≧ 0.03 % Mo 1.05% or the weld metal as DerutaMo to prevent preferential corrosion of the weld metal is 0.03% or more
It is added at the bottom. As shown in FIG. 2, M of the weld metal and the base metal
o If the difference in content ΔMo is 0.03% or more, CO ₂
Selective corrosion of the weld metal can be prevented in a corrosive environment including. However, if added in excess of 1.05%, the hardness of the weld metal increases and the susceptibility to cold cracking and stress corrosion cracking increases. Note that FIG. 2 is a graph showing the effect of ΔMo on the selective corrosion characteristics. The vertical axis represents the selective corrosion current (μA) flowing between the base metal and the weld metal, and the horizontal axis represents ΔMo.
(%) Is shown. When the selective corrosion current is positive, the selective corrosion of the weld metal does not occur. When ΔMo is 0.03% or more, the selective corrosion current turns to a plus. Ti; ≤0.25% Ti may be added to the weld metal in a range of 0.25% or less as needed for the purpose of toughness of the weld metal due to the refinement of proeutectoid ferrite. If it exceeds 0.25%, the amount of slag increases, which causes defects such as slag inclusion. In addition, the strength of the weld metal becomes excessive with respect to the base metal, resulting in insufficient toughness. Further, since hardness increases, susceptibility to welding cracks and stress corrosion cracking increases. Inevitable impurities; When the content of unavoidable impurities is within the above range, the selective corrosion resistance and mechanical performance of the weld metal are not impaired. When the content of each component exceeds the above range,
Welding workability deterioration (Al, Zr, Ca ), Welding defect occurrence (P, S, B, N), Mechanical performance deterioration (Al, C)
Problems such as r, Nb, V, O, N) occur.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

Next, the reasons for limiting the chemical composition of the steel pipe base material will be described. C: 0.03 to 0.15% Carbon in steel is an element effective in increasing the strength of steel, but excessive addition causes deterioration of toughness. Therefore,
The upper limit of the carbon content is 0.15% in order to manufacture a steel pipe having both good strength and toughness. The reduction of the carbon amount improves the toughness, but if it is 0.03% or less, the toughness deteriorates. Further, 0.03% of carbon is required to effectively utilize stable precipitation hardening of Nb, V, Ti, etc., so the lower limit of the amount of carbon is set to 0.03%. The reasons for limiting the other components are as follows. Si: 0.05 to 0.50 % Si is necessary for deoxidation, but if added in excess, it deteriorates toughness, so the lower limit is 0.05% and the upper limit is 0.50 %.
And Mn: 0.50 to 2.00% Mn is required to be 0.50% or more for deoxidation, but 2.0
If it exceeds 0%, the weldability deteriorates, so the upper limit is 2.00.
%. Al: 0.005-0.10% Al is necessary for deoxidation, but if it is less than 0.005%, deoxidation is insufficient, so the lower limit is made 0.005%. On the other hand, if it exceeds 0.10%, the cleanliness of the steel and the HAZ toughness deteriorate, so the upper limit is made 0.10%. Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cu and Ni improve the strength and toughness of the base material without adversely affecting the HAZ toughness, but when it exceeds 2.0%. Since the HAZ hardenability and toughness are adversely affected, the upper limit is 2.0%. Cr: 0.05 to 2.0% Cr increases the strength of the base material and the welded portion, but if it exceeds 2.0%, the hardenability and toughness of the HAZ are deteriorated, so the upper limit is made 2.0%. Mo: 0.05-1.0% Mo improves the strength and toughness of the base material, but 1.0%
If it exceeds 0.1%, the hardenability of the HAZ increases and the weldability deteriorates, so the upper limit is made 1.0%. The lower limit of the amount of addition of these elements is the minimum required amount to obtain the effect on the material, and 0.05
%. Nb; 0.005 to 0.20% V; 0.005 to 0.20% Nb and V are found to have an effect on strength and toughness.
If it exceeds 20%, the toughness of the base material and the welded part deteriorates, so the upper limit is made 0.20%. The lower limit is set to 0.005% at which improvement in material is recognized. Ti: 0.005 to 0.20% Ti has the effect of preventing coarsening of austenite during slab heating by adding 0.005% or more, so the lower limit is made 0.005%, and if added excessively, the weld zone The toughness deteriorates, so the upper limit is made 0.20 %. B: 0.0005 to 0.0020% B is effective in increasing the strength of the base material, but excessive addition causes deterioration of weldability and HAZ toughness, so the upper limit is 0.002.
0%, the lower limit is 0.00, which is effective in increasing strength.
05%. Ca: 0.0005 to 0.0050% Addition of Ca improves hydrogen-induced cracking resistance, and the lower limit is made 0.0005% at which the effect is recognized. Excessive addition forms an oxide and is harmful, so the upper limit is 0.0050 %.
And

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

The reasons for limiting the chemical composition (% by weight) of the welding wire in the present invention are as follows. C: 0.01 to 0.15 in order to secure good welding workability and to obtain appropriate strength, toughness and hardness for the base material.
%Added. Si: Add 0.20 to 1.20% in order to suppress the generation of blowholes by a deoxidizing action and to obtain good welding workability and appropriate mechanical properties of the weld metal. Mn; 0.60 to 2.50% for the same reason as Si
Added. Cu: 3.00% is added as an upper limit in order to improve the selective corrosion resistance of the weld metal while suppressing the occurrence of welding cracks. Ni: 0.50 to 3.00% is added to improve the selective corrosion resistance of the weld metal while ensuring appropriate toughness, strength and hardness with respect to the base material. For the same reason as for Mo; Ni, 1.10% is added as the upper limit. Ti: 0.30% is added as an upper limit in order to improve the toughness of the weld metal within a range that does not impair the welding workability. Inevitable impurities; When the content of each component exceeds the above range, welding defects (P, S, B, N), deterioration of welding workability (Al, Zr ), deterioration of mechanical performance (Al, C
Problems such as r, Nb, V, O, N) occur.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

As shown in Tables 2 and 3, the yield strength (350 N / mm ² or more), toughness (50 J or more), and selective corrosion are found in the circumferential welded portion where the chemical composition of the weld metal satisfies the claims. Property (welded metal part does not selectively corrode, 0 in Table 2)
It was confirmed that the circumferential welded portion has excellent hardness, low hardness (Hv 300 or less), and excellent crack resistance.

[Table 1]

[Table 2]

[Table 3]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motosei Ito 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Toshihiko Nakano 100-1 Urakawachi, Fujisawa City, Kanagawa Prefecture Incorporated company Kobe Steel, Fujisawa Works (72) Inventor Masato Konishi 100-1 Urakawachi, Miyamae, Fujisawa City, Kanagawa Incorporated, Fujisawa Works, Kobe Steel

Claims (2)

[Claims] 1. A gas shielded arc welding method for a pipe by combining a pipe base material, a welding wire and welding conditions so that a weld metal having the following chemical composition (wt%) can be obtained in circumferential welding of the pipe. C; 0.01 to 0.15% Si; 0.20 to 1.00% Mn; 0.40 to 2.00% Cu; ≤ 2.50% Ni; 0.50 to 2.50% ΔCu + ΔNi; ≥ 0.50% (Δ: weld metal content-
Base material content) P _CM ; ≤0.25% (P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60
+ Cr / 20 + Mo / 15 + V / 10 + 5B) The balance consists of Fe and inevitable impurities, and the inevitable impurities satisfy the following range. P; ≤0.030% S; ≤0.030% Al;
≤0.05% N; ≤0.050% Nb; ≤0.10% V;
≤0.10% Cr; ≤1.00% Ca; ≤0.0025% O;
≤0.10% Zr; ≤0.05% B; ≤0.002% Chemical composition of base material (% by weight) C; 0.03 to 0.15% Si; 0.05 to 0.50% Mn; 0.50 to 2.00% Al; 0.005 to 0.10%, or one or more of the following components in addition to the above chemical components: Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cr; 0.05 to 2.0% Mo; 0.05 to 1.0% Nb; 0.005 to 0.20% V; 005 to 0.20% Ti; 0.005 to 0.20% B; 0.0005 to 0.0020% Ca; 0.0005 to 0.0050% The balance contains Fe and unavoidable impurities. Chemical composition of welding wire (% by weight) C; 0.01 to 0.15% Si; 0.20 to 1.20% Mn; 0.60 to 2.50% Cu; ≤ 3.00% Ni; 50 to 3.00%, or in addition to the above chemical components, 1
One or two or more kinds are contained, Mo; ≤ 1.10% Ti; ≤ 0.30% The balance consists of Fe and unavoidable impurities, and the content of the unavoidable impurities should satisfy the following range. P; ≤0.030% S; ≤0.030% Al;
≤0.05% N; ≤0.01% Nb; ≤0.02% V;
≤0.02% Cr; ≤0.05% Zr; ≤0.05% O 2;
≤0.02% B; ≤0.002% Welding conditions Shield gas: 100% CO ₂ or Ar + (5-4
0%) CO ₂ wire diameter: 0.8 to 1.6 mm Welding current: 100 to 500 A Arc voltage: 15 to 45 V Welding speed: 5 to 150 cm / min. Welding posture: All postures 2. The weld metal, in addition to the chemical composition,
2. The gas shielded arc welding method for a pipe according to claim 1, wherein one or both of Mo and Ti are contained. Mo; ≤1.05% ΔMo; ≥0.03% Ti; ≤0.25%