JP2000218391A - Gas shield arc welding wire for line pipe, and gas shield arc welding method of line pipe perimeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas shield arc welding wire and a welding method, by which a welding metal with good crack resistance, good welding workability, excellent strength, excellent low temperature toughness, and excellent selective corrosion resistance at a line pipe circumferential welding part for transporting oil, natural gas and the like, can be obtained and high performance welding can be performed. SOLUTION: This gas shield arc welding wire for a line pipe comprises, against total weight of the wire, 0.02-0.20 wt.% C, 0.20-1.50 wt.% Si, 0.50-2.0 wt.% Mn, 0.030 wt.% or less P, 0.015 wt.% or less S, 0.003-0.050 wt.% O, 0.10-2.00 wt.% Cr, 0.10-5.50 wt.% Ni, 0.005-0.200 wt.% one or more kinds of La, Ce, Zr and Ti in total, and the balance of Fe and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a welded portion having excellent crack resistance, strength and low-temperature toughness of a weld metal in circumferential welding of a line pipe used as a means of transporting oil and natural gas. An object of the present invention is to provide a gas shielded arc welding wire and a method for automatically welding a gas line around a line pipe, which have good welding workability in all postures and enable high-speed and high-efficiency welding.

[0002]

2. Description of the Related Art In recent years, fluid transportation by line pipes worldwide has rapidly developed both at sea and on land, and at present, long-distance mass transportation piping for gas and liquid such as oil and natural gas, city gas piping, and water transportation. It is used for transportation of industrial piping, district heating and cooling piping, etc., and tends to increase in the future. On the other hand, for circumferential welding, which is one of the important technologies that affect the quality and cost of line pipes, there is a demand for a welding material from which a weld metal having excellent strength and low-temperature toughness can be obtained.
Furthermore, since the welding is performed in all positions, it is required to secure a highly accurate welded joint with few welding defects.

[0003] On the welding side, the butt weld is narrowed in order to improve the efficiency, and the welding speed is increasing. Especially in the case of the first-layer joint weld metal, it is rapidly cooled during the solidification process of the molten metal. There is a problem that welding cracks occur due to the melting and the shape of penetration. Furthermore, in recent years, it has become a problem that transport of oil, gas, and the like by these line pipes causes selective corrosion of the pipe circumferential weld metal portion, and it is necessary to consider corrosion resistance.

Japanese Patent Application Laid-Open No. 10-216934 also discloses a method of welding a pipe circumferential joint, but a solution for straight welding has been proposed. In addition, JP
Japanese Patent Publication No. 240193 discloses a steel wire for TIG welding used for Uranami welding, which is intended to obtain a good Uranami bead in non-fusing electrode type TIG welding using an inert gas as a shielding gas. The purpose is not considered for CO2 corrosion resistance and selective corrosion resistance. Further, Japanese Patent Application Laid-Open No. 5-57478 proposes a gas shielded arc welding wire for a pipe, but little consideration is given to welding workability.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and relates to welding of a line pipe for transporting oil and natural gas, etc., and has excellent crack resistance of a weld metal portion of a circumferential joint. Gas-shielded arc welding wire and welding that provide a weld metal part with excellent strength, low-temperature toughness and selective corrosion resistance, good welding workability in all positions, and high-speed and high-efficiency welding It concerns the method.

[0006]

The gist of the present invention is that C: 0.02% by weight based on the total weight of the wire.
０．２0.20%, Si: 0.20 to 1.50%, Mn:
0.50 to 2.0%, O: 0.003 to 0.050%,
Cr: 0.10 to 2.00%, Ni: 0.10 to 5.5
0%, one or more of La, Ce, Zr, and Ti, containing 0.005 to 0.200% in total;
A gas shielded arc welding wire for line pipes, characterized in that the content is 0.030% or less, S: 0.015% or less, and the balance consists of Fe and unavoidable impurities.

In the welding using the above wire,
A gas shield arc welding method for a line pipe circumference, wherein a gas obtained by mixing at least CO2 gas and Ar gas among CO2 gas and O2 gas as a shielding gas is used. Here, it is also characterized in that the number of wire swings is regulated to 0.1 to 50 Hz, and gas shielded arc automatic welding is performed in one layer per pass.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the circumferential welding of a line pipe, the inventors of the present invention have conducted various studies on various wire components for gas shielded arc welding in order to solve the above-mentioned problems. We have found a gas shielded arc welding wire that has excellent crack resistance, strength, low temperature toughness, good selective corrosion resistance, good welding workability, and high-speed, high-efficiency welding. The reasons for limiting the chemical components of the gas shielded arc welding wire of the present invention are as follows.

C: 0.02 to 0.20% C is added in an appropriate amount mainly for adjusting the strength. However, the arc length varies depending on the amount of C added, which affects the quality of welding workability. Increasing the C content tends to shorten the arc length, increase the number of short circuits, improve the droplet transfer characteristics, and improve the arc stability to improve welding workability. However, a large amount of C significantly hardens the weld metal, not only deteriorating the crack resistance, but also lowering the ductility and impact toughness, as well as causing more spatters. . In addition, 0.02%
If it is less than 30%, effects such as securing strength and improving workability are not recognized, so the range is set to 0.02 to 0.20%.

Si: 0.20 to 1.50% Si is an indispensable component as a main deoxidizing agent for a weld metal.
It is added to clean the weld metal, adjust the strength and ensure toughness. However, if it is less than 0.20%, deoxidation becomes insufficient and the soundness of the weld metal cannot be ensured. Further, if it is contained excessively, it causes solid solution hardening of ferrite at the time of solidification of the weld metal, lowers the toughness, increases the amount of slag generated and deteriorates welding workability, so the range is 0.20 to 1.5.
0%.

Mn: 0.50 to 2.0% Mn is an element effective in improving the strength and low-temperature toughness of the weld metal in addition to acting as a deoxidizing agent together with Si.
If it is less than 0%, the soundness of the weld is impaired due to insufficient deoxidation.
On the other hand, if the content exceeds 2.0%, the hardenability increases, the hardness of the weld metal increases, thereby deteriorating the cracking resistance. In addition, the increase in the amount of spatter and the amount of slag increase the occurrence of welding defects and deterioration in welding workability. Therefore, the range was set to 0.50 to 2.0%.

O: 0.003 to 0.050% O is necessary for improving the bead formability in high-speed welding and the dripping property of the molten metal in each position, and has the effect of reducing the generation of spatter. In the configuration of the present invention, 0.00
When the content exceeds 3%, the effect becomes remarkable. When the content exceeds 0.050%, not only the effect is saturated, but also the arc becomes unstable and spatter occurs frequently.
0%.

Cr: 0.10 to 2.00% Cr improves the resistance to CO2 and selective corrosion of the weld metal, improves the hardenability, and obtains good mechanical properties by forming fine carbides. In particular, the effect of corrosion resistance is small when the Cr content is less than 0.10%, whereas when it exceeds 2.0%, the strength of the weld metal becomes excessive and the weld cracking sensitivity increases, so that the Cr content is 0.10%. To 2.00%.

Ni: 0.10% to 5.50% Ni has the effect of improving the resistance to CO2 and selective corrosion with Cr and also has the effect of precipitating nitride and suppressing pore formation. However, if it is less than 0.15%, these effects are insufficient, and if it exceeds 5.50%, the strength of the weld metal becomes excessive and the crack susceptibility increases.
It was 5.50%.

La, Ce, Zr, and Ti are sulfide-forming elements, and form sulfides such as La 2 S 3, CeS, ZrS, and TiS. These sulfides are stable and have a freezing point of Fe
It is an element that is higher than the above and reduces the cracks due to S by fixing S. In addition, it has the effect of improving droplet transferability, increasing arc stability, increasing penetration depth and penetration into the groove wall surface, and preventing welding defects such as poor fusion, bead shape and bead toe end. The familiar state can be improved. However, when contained in a large amount, not only does the amount of slag increase, but also the amount of spatter increases remarkably, and the arc becomes unstable and welding workability deteriorates. Therefore, La, Ce, Zr, and Ti are used alone or in combination of two or more. To 0.005 to 0.200%.

P: 0.030% or less P is an impurity, and when P increases, it is an element that remarkably promotes cracking of weld metal and lowers toughness. P forms a compound such as Fe3P having a low melting point and deteriorates cracking resistance. Therefore, it is preferable to suppress P as much as possible, particularly in the wire of the present invention to which a large amount of Si and Mn are added.
If the content is 0.030% or less, the purpose is achieved.

S: 0.015% or less S is an element which easily forms a low melting point compound such as FeS and, when segregated, is an element which induces hot cracking particularly at the weld metal solidification stage, and its amount exceeds 0.015%. Not be.

The welding wire of the present invention is constituted as described above. When gas shielded arc welding of the circumference of a line pipe is performed using the wire having such a composition, the shielding gas is Ar gas and CO2 gas. By mixing, a stable arc state and low spatter welding can be achieved even in high-speed welding. The range of this CO2 gas is preferably 5 to 40 vol%. Further, by mixing the O2 gas, the penetration depth and the bead width can be secured. The preferred range of the O2 gas is less than 7 vol%.

Further, in the automatic gas-shielded arc welding using the welding wire of the present invention, a welding method in which the number of wire swings is set to 0.1 to 50 Hz and one pass per layer without sorting is preferable. In other words, the shape of the pipe butt groove joint is narrowed for the purpose of improving welding efficiency,
There is a tendency to improve efficiency by reducing the groove cross section,
If the groove angle is made extremely small, the groove wall becomes nearly vertical, and defective fusion defects are likely to occur. In addition, in a pipe circumferential joint performed in all-position welding, molten metal is easily dripped in a vertical or upward welding position, and various welding conditions have to be changed in accordance with the welding position in order to prevent them.

In order to solve these problems, by setting the frequency of the wire swing to 0.1 Hz or more, the molten metal is less likely to droop even in the welding position of the pipe circumferential joint, and poor penetration of the groove is less likely to occur. Become. In addition, welding conditions such as current, voltage and welding speed can be easily selected, and high-speed welding of one pass and one layer can be performed even in a narrow groove without distribution, so that the welding efficiency can be dramatically improved.

However, when the number of swings is less than 0.1 Hz, if the welding speed is high, poor penetration is likely to occur. In addition, there is a possibility that the molten metal will hang down in the vertical or upward welding position, and that the bead shape becomes extremely convex, making it difficult to weld in the next pass. On the other hand, if the frequency of oscillation exceeds 50 Hz, the generation of spatters will increase significantly, and a large amount of the spatter will adhere to the groove, making it difficult to continue welding. I do. Hereinafter, examples of the present invention will be described.

[0022]

EXAMPLE A steel plate having a chemical composition shown in Table 1 having a plate thickness of 25.4 mm was assumed to have a pipe circumferential joint with a butt groove shown in FIG. 1 and a downward position, a vertical position, and an upward position. Using a 1.2 mm diameter welding wire of the chemical composition shown in Table 3,
Gas shielded arc welding was performed under the welding conditions shown in Table 2.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

Table 4 shows the overall evaluation of the workability of welding and the weld crack, tensile strength, impact toughness, and corrosion resistance of the weld metal, and Table 5 shows the results of the respective investigations based on the composition of the shielding gas. Since welding cracks tend to occur at the time of first-pass one-pass welding, the entire length of the welded portion was examined by a radiation transmission test after one-pass welding.

[0027]

[Table 4]

[0028]

[Table 5]

The tensile strength conforms to JIS Z 3111 and the width of the weld metal portion is narrow. Therefore, the test piece was evaluated as A2 test piece according to JIS Z 2241 tensile test method for metallic materials, and 640 N / mm ² or more was judged to be acceptable. . Impact test is J
JIS based on No. 4 test piece specified in IS Z 3111
According to the impact test method of Z 2242, the test temperature was -3.
The test was carried out at 0 ° C., and a value of 47 J or more was regarded as acceptable. The corrosion resistance was measured by bubbling 1 atm CO2 into a 10% aqueous NaCl solution to adjust the temperature to 80 DEG C. and the pH to 5.0, and the test piece was heated for 96 hours.
r or more, and the corrosion amount was 0.55 mm / y or less. If a weld crack occurred, a normal test specimen could not be collected, so a tensile test and an impact test were omitted.

As shown in Table 4, the wire No. 1 to N
o. It was confirmed that in the joint welding with the wire of the present invention of No. 7, it was possible to obtain a weld metal part having good welding workability with no welding cracks and little spatter generation, good strength and impact toughness, and excellent corrosion resistance. did.

However, the wire No. of the comparative wire was used. 8 to No. 8 With 19 wire components, the occurrence of welding cracks and poor welding workability, insufficient strength and impact toughness of the weld metal,
A sound welded joint cannot be produced due to deterioration of corrosion resistance and the like. Wire No. In No. 8, since La, Ce, and Zr were out of the range of the present invention, the arc state became unstable, spatter occurred frequently, and welding defects such as poor penetration occurred.

Wire No. No. 9 has excess S, and wire No. 9 In No. 19, welding cracks occurred because La, Ce, Zr, and Ti were not added. Wire No. 10 is Mn
Is no. In No. 18, Si exceeded the range of the present invention, spatter generation increased remarkably, welding workability was inferior, and welding cracks also occurred. Wire No. In No. 11, both Cr and Ni were out of the range of the present invention, and the corrosion resistance was deteriorated.

Wire No. 12, No. 13, No. 1
In No. 4, each of Cr, Ni and C is larger than the range of the present invention,
Cracking occurred because the weld metal was significantly hardened. Wire No. In No. 15, C is less than the range of the present invention, the strength of the weld metal is insufficient, and the arc state fluctuates rapidly, so that good workability cannot be secured. Wire No. No. 16 is Mn, and No. 16 In No. 17, Si is less than the range of the present invention, a blowhole occurs due to insufficient shielding, a healthy weld metal cannot be obtained, and the weld metal strength is also insufficient.

In the tests shown in Table 5, welding conditions other than the shielding gas composition were carried out in accordance with Table 2. 20
-No. The shielding gas composition of 25 is 5 to 40 in Ar gas.
Vol% CO2 gas is mixed, stable arc condition is obtained even in high speed welding, low spatter welding is possible, and workability is good. Further, 5 to 4 in Ar gas
By mixing 0 vol% CO2 gas and less than 7 vol% O2 gas, a penetration depth and a stable bead width can be secured, and welding defects such as poor penetration can be prevented.

However, Test No. 26-No. In No. 29, the amount of CO2 gas mixed with Ar gas is more than 40% by volume, or the amount of O2 gas of 7% by volume or more is mixed. The weldability is also deteriorated, and it is difficult to continue good welding with the method of the present invention having a narrow groove.

[0036]

Industrial Applicability The present invention is used as a means of transporting oil, natural gas, and the like by a high-efficiency welding method in which a wire component is adjusted and a single-layer, single-layer bead is placed without any sorting while oscillating the wire at high speed. Is a gas shielded arc welding method that can provide a weld metal with good crack resistance and workability, excellent strength, low temperature toughness, and excellent selective corrosion resistance in line pipe girth welding. The effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a joint groove shape of a test plate.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/50 C22C 38/50 (72) Inventor Toshio Aoki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Nippon Steel Co., Ltd. F-term (reference) 4E001 AA03 BB06 CC03 DC01 DD02 DD04 DD05 EA05 4E081 AA08 BA27 BB07 CA07 DA11 DA23 DA47 EA32 YQ10

Claims (3)

[Claims] 1. C .: 0.02 to 0.20%, Si: 0.20 to 1.50%, Mn: 0.50 to 2.0%, O : 0.003 to 0.050%, Cr: 0.10 to 2.00%, Ni: 0.10 to 5.50%, 0 in total of one or more of La, Ce, Zr, and Ti A gas shielded arc welding wire for a line pipe, comprising 0.0005 to 0.200%, P: 0.030% or less, S: 0.015% or less, and the balance being Fe and unavoidable impurities. 2. A gas around the circumference of a line pipe, wherein a gas obtained by mixing at least CO2 gas with Ar gas among CO2 gas and O2 gas is used as a shielding gas in welding using the wire according to claim 1. Shield arc welding method. 3. The gas shielded arc welding of a line pipe circumference according to claim 2, wherein the number of wire swings is set to 0.1 to 50 Hz and gas shielded arc automatic welding is performed in one pass and one layer. Method.