JPH11104885A - Fe-ni low thermal expansion coefficient alloy made welding structure and welding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Fe-Ni low thermal expansion coefficient alloy made welding structure having excellent low temperature toughness and a sound weld zone without any crack and a Fe-Ni alloy made welding material having excellent weldability which is usable in all positioned welding. SOLUTION: In the Fe-Ni low temperature expansion coefficient alloy made welding structure, all parts of a weld metal are composed of a Fe base alloy of 30-45% Ni, <=0.5% Si, <=0.8 % Mn, 0.1-3.0 % Nb, whose content of Nb and C is satisfied by -0.01 (% Nb) +0.04<=(% C) <=0.04 (% Nb) +0.40, or the same is composed of a Fe base alloy of 30-45% Ni, 0.08-0.5% C, <=0.5 % Si, <=0.8 % Mn, 0.3-4% Nb, <=0.01 % Al, moreover whose content of Si and Mn is satisfied by 0.1<=(%, Si)/(% Mn)<=1.0, whose content of S and O (oxygen) is satisfied by (% S)+(%, O)<=0.015% and whose content of Al and O (oxygen) is satisfied by (% Al)+(%, O) <=0.015.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquefied natural gas (LN)
G) pipes and storage tanks used for transporting and storing low-temperature substances, such as pipes, storage tanks and various equipment attached to them by butt-welding and joining the pipes, and are Fe-Ni-based The present invention relates to an object made of a low-thermal-expansion alloy and having at least a part of a welded portion (here, these are collectively referred to as “welded structure”). The present invention also relates to a welding material (wire) excellent in welding workability suitable for use in manufacturing the above-described welded structure.

[0002]

2. Description of the Related Art Conventionally, SUS is used as a material for piping and storage tanks for transporting low-temperature substances such as liquefied natural gas (LNG).
Austenitic stainless steels such as 304 have been used. However, austenitic stainless steel,
Since the coefficient of thermal expansion is large, it is necessary to take measures to absorb the deformation caused by expansion and contraction, for example, by interposing the loop pipe at every fixed length in the pipe. If the pipe can be made of a material with a very low coefficient of thermal expansion that makes the loop pipe unnecessary, the elbow pipe required for the loop pipe becomes unnecessary, the diameter of the tunnel through which the pipe passes can be reduced, and heat insulation of the pipe, etc. Maintenance work is also reduced, resulting in significant savings in construction and maintenance costs.

[0003] From the viewpoint of mechanical and chemical properties, among materials that can be used as materials for transporting and storing low-temperature substances such as LNG, Fe-Ni alloys having a specific component ratio are very small. It is known to have an expansion coefficient. Representative examples of such alloys include Fe-36% Ni and Fe-42% Ni, which are collectively referred to as Invar (in the present specification, the percentage with respect to the component content means weight%). These materials are used as materials for devices that do not like expansion and contraction due to temperature changes, taking advantage of their small thermal expansion coefficients.

[0004] When a structure made of the above-mentioned Fe-Ni-based alloy having a low coefficient of thermal expansion is assembled by welding, it is desirable to use a welding material having a linear expansion coefficient equivalent to that of the base metal. for that reason,
Co-metallic welding materials as disclosed in JP-A-4-231194 and JP-A-7-267272 have been proposed.

[0005] The welding material disclosed in the above-mentioned Japanese Patent Application Laid-Open No. Hei 4-231194 is characterized in that, in addition to Ni (Co) and Fe, C: 0.05-0.5%, Nb:
0.5-5%, and if necessary, Mn, Ti, Al, C
This is a welding material that can prevent welding cracks during welding by selectively containing e, Mg, and the like. Also, disclosed in Japanese Patent Application Laid-Open No. 7-267272 is Ni: 30 to 45%, C: 0.03 to 0.3%.
%, Nb: 0.1-3%, P: 0.015% or less, S: 0.005% or less, Si:
0.05-0.6%. Mn: 0.05-4%, A1: 0.05% or less and 0: 0.
015% or less, and further, the relationship between Nb and C is (% Nb) × (%
C) By defining ≧ 0.01, it is a welding material that can achieve both reheat cracking and toughness during multi-layer welding.

When assembling a welded structure, for example, a pipe for transporting LNG or a storage tank, it is desirable to be able to perform automatic welding in all positions by TIG welding or plasma welding in view of work efficiency and quality of a welded portion. It is. However, when the above-mentioned pipes and tanks are made of a Fe-Ni-based low thermal expansion alloy, it is difficult to perform the welding assembly by automatic welding using the above-mentioned welding materials proposed so far.
This is because, in the above-mentioned welding materials, performances such as solidification crack resistance and toughness of a welded portion are taken into consideration, but no consideration is given to welding workability that enables circumferential welding. Further, in the invention of Japanese Patent Application Laid-Open No. Hei 4-231194, although welding solidification cracking is considered,
Reheat cracking that occurs during multi-layer welding of thick materials such as pipes is not considered, and reheat cracks cannot be prevented with the welding material in practice. Furthermore, the toughness of the weld metal at cryogenic temperatures is not sufficient.

[0007] In the invention of Japanese Patent Application Laid-Open No. 7-267272,
Reheat cracking is also considered. However, in practice, the effect of preventing reheat cracking is not always sufficient depending on the welding method at the time of welding, the dilution ratio caused by the groove shape, and the like.
In addition, since the improvement of welding workability is not considered,
Actually, it is difficult to automatically weld a pipe made of a low thermal expansion coefficient alloy or the like using this welding material.

[0008] Reheat cracking refers to a crack-free weld metal (bead) formed initially in multi-layer welding.
Are cracks that are reheated when the weld metal is further piled thereon, and are generated in the initial weld metal by the thermal effect. This reheating crack is particularly likely to occur in welding of an Fe-Ni alloy, and measures to prevent the reheat cracking are the key to the practical application of a welded structure of an Fe-Ni alloy having a low coefficient of thermal expansion.

[0009]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a welded structure made of a Fe-Ni-based low thermal expansion alloy,
Excellent low-temperature toughness, crack-free sound welds (welded joints)
It is to provide what has. A second object of the present invention is a welding material that is excellent in welding workability, can obtain the above-mentioned sound welded portion by all-position welding, and can efficiently manufacture the welded structure by automatic welding. (Wires).

[0010]

The gist of the present invention is a welding structure of the following (1) and (3) and a welding material of (2).

(1) All parts of the weld metal are
Ni: 30-45%, Si: 0.5% or less, Mn: 0.8% or less, N
b: 0.1 to 3.0%, P: 0.015% or less, S: 0.004% or less Fe
A welded structure made of a Fe-Ni-based low thermal expansion coefficient alloy, wherein the content of Nb and C satisfies the following formula.

−0.01 (% Nb) + 0.04 ≦ (% C) ≦ −0.04 (% Nb) +0.40 (2) Ni: 30 to 45% by weight, C: 0.08 to 0.5%, Si: 0.5%
Below, Mn: 0.8% or less, Nb: 0.3 to 4%, A1: 0.01% or less is a welding material made of a Fe-based alloy, and the impurity P is 0.015%
Hereinafter, S is 0.004% or less, and the content of Si and Mn satisfies the following equation. The content of S, 0 (oxygen) is represented by the following equation.
A1 and O (oxygen) contents satisfy the following formulas, respectively, and are welding materials for Fe-Ni-based alloys with a low coefficient of thermal expansion that are excellent in welding workability.

0.1 ≦ (% Si) / (% Mn) ≦ 1.0 (% S) + (% O) ≦ 0.015% (% A1) + (% 0) ≦ 0.015%・ ・ (3) A weld metal obtained by using the welding material of the above (2), wherein all parts thereof are 30% to 45% by weight of Ni,
i: 0.5% or less, Mn: 0.8% or less, Nb: 0.1 to 3.0%, P: 0.
A welded structure made of an Fe-Ni-based low thermal expansion coefficient alloy, which is an Fe-based alloy with 015% or less and S: 0.004% or less, and whose Nb and C contents satisfy the above-mentioned formula.

The above-mentioned welded structures (1) and (3) include a pipe manufactured by welding (welded pipe), a pipe connected by circumferential welding, and a vessel having a weld at least partially. Tank) and other equipment. An Fe-Ni-based low thermal expansion coefficient alloy is an alloy in which the basic components are approximately 30 to 45% Ni and the remaining Fe, or approximately 1% each.
The following Co, Nb, and Ti, Ta, and C, respectively, of approximately 0.5% or less
It means an Fe-Ni-based alloy containing secondary alloy components such as r and Mo.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

1. Regarding the welded structure of the present invention The welded structure of the present invention is characterized in that the weld metal has the above chemical composition. First, the reason for determining the chemical composition will be described.

Ni: 30-45% Ni is a main element constituting the low thermal expansion alloy. In order to obtain a sufficiently low linear expansion coefficient even for weld metal, Ni
Should be 30-45%. A desirable lower limit is 32%, and a more desirable lower limit is 34%. A desirable upper limit is 43%.

Si: 0.5% or less Si is an element added as a deoxidizing element at the time of melting the alloy, and is also added to the welding material in order to secure welding workability, as described later. However, Si does not necessarily need to remain in the weld metal. Si in the weld metal is 0.
If it exceeds 5%, the impact characteristics will be degraded, so it must be suppressed to 0.5% or less. Desirable is 0.3% or less, and more desirable is 0.2% or less.

Mn: 0.8% or less Mn is added as a deoxidizing element at the time of alloy smelting similarly to Si. In addition, since it affects welding workability, it is added to the welding material. However, Mn does not necessarily need to remain in the weld metal. Not only excess Mn exceeding 0.8%
In this case, the toughness of the weld metal is reduced to cause deterioration of impact characteristics, so the content of Mn is set to 0.8% or less. Desirable
0.5% or less, more preferably 0.4% or less.

Nb: 0.1-3.0% Nb is an element necessary for securing the strength of the weld metal as it is solidified, and is an essential element for preventing reheat cracking. If the Nb content in the weld metal is less than 0.1%, the effect of preventing reheat cracking does not appear. On the other hand, if it exceeds 3.0%, the impact characteristics are deteriorated. The desirable amount of Nb in the weld metal required for preventing reheat cracking is 0.15 to 2.8%, and more desirably 0.2 to 2.5%. Appears for the first time. Therefore,
The contents of Nb and C in the weld metal must satisfy the above equation as described below.

C: a range satisfying the formula C is an element for stabilizing austenite, which is a matrix of the base material, and has an effect of preventing reheat cracking by coexisting with Nb in the weld metal. But C
Also, Nb has an upper limit of the content in terms of the toughness of the weld metal.

FIG. 1 shows that Ni: 36%, Si: 0.2%, Mn: 0.4
%, Balance: A 2 mm square shirring filler was made from an alloy plate with the basic composition of Fe and the contents of C and Nb varied, and all weld metals were made by manual TIG welding to prevent reheat cracking. The results of examining the tendency of occurrence and the toughness of the weld metal at -196 ° C are shown in order by Nb and C contents. The basic conditions such as the heat input of welding are the same as in Example 2 described later.
Based on the example of TIG welding, the detection of reheat cracking and the impact test were also performed in the same manner as in Example 2, and those showing an impact value of 30 J / cm ² or more at -196 ° C were regarded as having good toughness. Note that the Nb and C contents of the weld metal are actual analysis values, and since they are all weld metals, the Nb and C contents were the same at any position regardless of the lamination position.

The straight line yellow in FIG. 1 is C = −0.04 (% Nb) +
It is expressed by the equation of 0.40. In addition, the straight line honeycomb is C = −0.01.
(% Nb) + 0.04. ○ in the figure indicates N of all weld metals.
b The content is in the range of 0.1 to 3.0% and satisfies the above expression. On the other hand, ● indicates that the Nb content is out of the above range or the Nb and C contents do not satisfy the above formula.

The area below the straight honeycomb in FIG. 1 is an area where reheat cracking occurs. On the other hand, the region above the linear yellow is a region having poor toughness. Also, as described above, when the Nb content is less than 0.1%, reheat cracking occurs, and when it is more than 3.0%, toughness is reduced. After all,
It is a region that satisfies the above formula, and the content of Nb is
The range from 0.1% to 3.0% (shaded area in Fig. 1) is C and Nb
Is in an appropriate range.

P: 0.015% or less P is an unavoidable impurity and needs to be 0.015% or less in order to increase the susceptibility to solidification cracking during welding. Desirable is 0.012% or less, more preferably 0.010% or less.

S: 0.004 or less S is an unavoidable impurity like P, and enhances the solidification cracking susceptibility during welding and the reheat cracking susceptibility during multilayer welding.
In order to eliminate these adverse effects, the content needs to be suppressed to 0.004% or less.

In addition to the above alloying elements and impurities, the balance of the weld metal is substantially Fe, or, like the base metal, approximately 1% or less of Co, approximately 0.5% each.
The following secondary components such as Ti, Ta, Cr, and Mo may be contained. Even if these components are contained, the effect of the present invention is not lost.

Usually, the chemical composition of the weld metal is less likely to be uniform over the entire weld metal because of the dilution effect from the base metal. In particular, in the case of multi-layer welding, a great difference tends to occur between the chemical composition of the bead formed at the beginning and the bead formed thereafter.

As will be described in detail in Example 2 to be described later, a weld metal free of reheat cracking and having excellent low-temperature toughness must have the above-described chemical composition at all positions. However, it is not necessary that the chemical composition be exactly the same at all positions. Within the range of the above chemical composition, the composition may be different depending on the position of the weld metal.

The structure of the present invention having a weld metal as described above can be obtained by using a welding material having a chemical composition determined in consideration of a dilution ratio according to welding conditions. As shown in Example 2, different types of welding materials are used in combination, and the initially formed weld metal layer has a composition that is particularly resistant to reheat cracking, and the subsequently formed weld metal layer is particularly tough. The welding construction method of making the composition excellent in the above can also be adopted. It is desirable to use the material of the present invention described below as the welding material.

2. Welding materials The contents of the components constituting the welding materials of the present invention are determined as described above for the following reasons.

Ni: 30 to 45% As described above, Ni is a main element constituting the low thermal expansion alloy, and Ni of the welding material transfers to the weld metal as it is. Therefore, the reason for limiting the content is the same as in the case of the aforementioned weld metal.

C: 0.08-0.5% C stabilizes the austenite of the weld metal,
As described above, coexistence with Nb prevents reheat cracking of the weld metal. The welding material must contain at least 0.08% C to ensure C to provide these effects.
However, if it exceeds 0.5%, C in the weld metal exceeds the upper limit defined by the above equation. Therefore, the appropriate content of C in the welding material is 0.08 to 0.5%.

Si: 0.5% or less Si in the welding material affects the physical properties of the molten metal and affects the welding workability, but if it exceeds 0.5%, the amount of Si in the welding metal increases and the toughness decreases. In addition, the workability of the welding material itself is deteriorated, and it becomes difficult to manufacture a wire. Therefore, the upper limit is set to 0.5%, but preferably 0.3%. On the other hand, in order to ensure sufficient welding workability, it is necessary to satisfy the expression in relation to the Mn content as described later.

Mn: 0.8% or less Mn also affects the physical properties of the molten metal and affects the welding workability. However, if the Mn content in the welding material exceeds 0.8%, the Mn content in the weld metal becomes excessive, causing a decrease in toughness as described above. Therefore, the upper limit is set to 0.8%, but a desirable upper limit is 0.5%.

In order for the welding material to have sufficient welding workability, the content of Mn must satisfy the above expression in relation to Si.

The welding workability of the welding wire is closely related to the contents of Si and Mn in the welding wire. That is, 0.1
Within a range satisfying ≦ (% Si) / (% Mn) ≦ 1.0, a flat welded portion which is the most difficult to weld and has no burn-through even in an upwardly welded portion can be obtained. The reason is considered as follows.

If the Si / Mn ratio is less than 0.1, the slag composition generated on the surface of the molten pool becomes Mn-rich, and the arc tends to concentrate there. . On the other hand, if the Si / Mn ratio exceeds 1.0, the viscosity of the molten metal becomes small, so that the molten metal sags during upward welding.

FIG. 2 shows the range of the appropriate contents of Si and Mn (shaded area). The reasons for limiting the upper limits of Si and Mn are as described above. Nb: 0.3 to 4% As described above, Nb is an essential element for securing the strength of the weld metal as it is solidified and preventing reheat cracking, and 0.1 to 3.0% is contained in the weld metal. Need to be. In consideration of the dilution of the components, the Nb content in the welding material required to secure the Nb content in the weld metal is 0.3 to 4%. In addition, Nb exceeding 4% impairs the hot workability of the welding material and causes an increase in wire manufacturing cost.

P: 0.015% or less P, which is an inevitable impurity in the welding material, migrates to the weld metal as it is, and increases the solidification cracking susceptibility during welding.
Therefore, as in the case of the weld metal, the content is suppressed to 0.015% or less, preferably 0.012% or less, and more preferably 0.010% or less.

S: 0.004% or less As described above, it is an impurity that increases the susceptibility to solidification cracking during welding and the susceptibility to reheat cracking during multi-layer welding. . S is an element that strongly affects the welding workability, and in order to secure good welding workability, the relationship with 0 (oxygen) must satisfy the above expression, as described later.

A1: 0.010% or less A strong deoxidizing element, added during melting of an alloy. Excessive addition increases the amount of inclusions, degrades the hot workability of the welding material, and further reduces the toughness of the weld metal. Therefore, the content is set to 0.010% or less. A1 affects welding workability in relation to 0 (oxygen). Therefore, as described below, the contents of Al and O (oxygen) must satisfy the above equation. Note that Al does not necessarily need to be contained in the welding material. However, some residual added as a deoxidizer is inevitable. The lower limit of the actual content is about 0.0005%.

0 (oxygen): Formula and range satisfying the formula O is an unavoidable impurity, but is an element that strongly affects welding workability. 0 acts as a surface activating element of the molten metal similarly to S, affects the stability of the arc, and affects the uniformity of the beads during circumferential welding. (% S) + (% 0) ≦ 0.015% is required in order to obtain a bead with excellent uniformity without removing the target position during all-position welding. That is, if it exceeds 0.015%, the stability of the molten pool is impaired, the weld bead becomes uneven, and defects such as poor fusion are caused. Accordingly, the range satisfying the above equation, that is, the hatched region in FIG. 3 is the range of the appropriate O and S contents. However, since extremely low O and S increase production cost, the lower limit of desirable (% S) + (% 0) is
0.001%.

The contents of Al and O are within a range satisfying the following equation:
That is, it must be in the hatched area in FIG. 0
Is easily combined with A1 and easily generates welding slag. Therefore, if (% A1) + (% 0) exceeds 0.015%, a large amount of slag is generated, and the heat input from the arc is not sufficiently input to the base material, and no Uranami is formed in the first layer. And poor fusion at the time of upward welding and poor fusion are likely to occur.

The welding material of the present invention may be composed of the above-mentioned alloying elements and the balance substantially consisting of Fe, and the sub-components that may be contained in the welding metal, that is, about 1% each. % Or less of Co, each about 0.5% or less of Ti, Ta, C
It may contain components such as r and Mo.

The welding method for producing the welded structure of the present invention is optional. Regardless of the welding method used, if the formed weld metal is within the above-mentioned chemical composition range at all positions and satisfies the formula, there is no cracking and low temperature toughness. It will be excellent.

The welding material of the present invention is desirably used for TIG welding or plasma welding. In these welding methods, the wear of the alloy elements in the welding material is small, and a low-oxygen weld metal is obtained, so that the effect of further improving low-temperature toughness can be obtained.

As described above, the welding material of the present invention is capable of obtaining a sound weld metal by all-position welding. Therefore, if this material is used, girth welding for connecting pipes can also be automated. Further, it is easy to produce a pipe (welded pipe) by seam welding a Fe-Ni-based alloy having a low coefficient of thermal expansion molded using this welding material.
Since the pipe has a weld with the above-mentioned excellent properties, LN
It is extremely suitable as a pipe for transporting cryogenic substances such as G.

[0048]

【Example】

(Example 1) Using 9.5 m of the chemical composition shown in Table 2, using 29 kinds of welding wires (diameter: 1.2 mm) whose chemical composition is shown in Table 1.
An m-thick alloy plate was welded. The welding method was TIG welding and plasma welding, and the base material was an alloy plate having a groove as shown in FIGS. 5 and 6, respectively.

[0049]

[Table 1]

[0050]

[Table 2]

In the TIG welding, the welding is performed in each of the downward and upward welding positions, and the back-wave forming ability in the first layer weld bead is obtained.
The uniformity of the weld bead and the flatness of the weld bead were evaluated. In addition, the plasma welding was performed in a downward position, and the backwashing ability and the uniformity of the weld bead were evaluated. With respect to the ability to form a backside bead, one having a backside bead formed over the entire welding line (100% backside formation rate) was regarded as acceptable. Regarding the uniformity of the weld bead, the width of the weld bead was measured at regular intervals, and the difference (△ W) between the maximum width and the minimum width and the average value (Wave) were calculated.
Those whose ratio (△ W / Wave) did not exceed 0.2 were judged as acceptable.

Regarding the flatness of the weld bead, as shown in FIG. 7, the extra height (H) and the width (W) of the weld bead were measured from the cross section of the weld bead, and the ratio (H / W) was 0.5. Those that did not exceed were passed. Tables 3 and 4 show the evaluation results. In addition, TIG in the column of “Welding method” in Tables 3 to 6 is TIG.
Welding method, PAW means plasma arc welding method.

[0053]

[Table 3]

[0054]

[Table 4]

As is clear from Table 3, it was confirmed that the test numbers AW1 to AW19 using the welding materials A1 to A15 having the chemical compositions defined in the present invention had excellent welding workability.

On the other hand, when the welding materials of symbols B1 to B14 which do not satisfy the conditions of the chemical composition defined in the present invention were used, as shown in Table 4, no satisfactory welding workability was obtained. . That is, in the test number BW1, the Si / Mn ratio of the welding material B1 used was 2.083, which exceeded 1, and therefore, the viscosity of the welding metal was small, and the welding metal dropped in the upward welding. Also in test number BW2, since the Si / Mn ratio of the welding material B2 used in the same manner exceeded 1.01 and 1, the sagging occurred in the upward welding.

In the test number BW3, the welding material B3 used was
Since the Si / Mn ratio is less than 0.09 and 0.1, the slag generated on the molten ground surface becomes Mn-rich, the arc tends to concentrate there, and the melting around the molten pool becomes uneven, and the upward and downward In any welding position
H / W became a convex bead exceeding 0.5. Similarly, for BW4, since the Si / Mn ratio of the welding material B4 used was 0.095, which was smaller than 0.1, the weld bead was a convex bead.

In the test number BW5, the “S + O” amount of the welding material B5 used was 0.016% and exceeded 0.015%, so that the stability of the molten pool was poor. As a result, ΔW / Wave exceeded 0.2,
The uniformity of the weld bead deteriorated. Furthermore, the amount of “Al + O”
Since 0.019% and 0.015% are exceeded, a large amount of welding slag is generated, and the heat input from the arc covering the molten pool is not sufficiently input.
There was a part where no Uranami was formed.

In Test No. BW6, plasma welding was performed using the same welding material as BW5. However, since the “S + O” and “Al + O” amounts of the welding material were out of the ranges specified in the present invention. In addition, the uniformity of the weld bead was inferior, the keyhole was not sufficiently formed, and the part where no swelling was formed remained.

Even in test number BW7, the amount of “S + O” in the welding material B6 used was 0.023%, which greatly exceeded 0.015%.
The uniformity of the weld bead deteriorated. In addition, the amount of “Al + O”
Since it greatly exceeds 0.027% and 0.015%, a large amount of welding slag is generated, and in both the downward and upward welding positions, the penetration rate is 72% and 20%, respectively.
Uranami formation ability was remarkably inferior.

Test No. BW8 is an example in which plasma welding was performed using the same welding material as BW7, but the “S + O” amount and “Al + O” amount of the welding material were within the ranges defined by the present invention. Since it was outside, the uniformity of the weld bead was poor, and a keyhole was not sufficiently formed, leaving a part where no Uranami was formed.

In test numbers BW9 and BW10,
TIG and plasma welding were performed using welding material B7, respectively, and the "S + O" amount of the welding material was 0.016%, which was 0.1%.
Since it exceeded 015%, the uniformity of the weld bead was poor. Test number BW11 is also a welding material with "S + O" amount of 0.016%.
Since B8 was used, the uniformity of the weld bead was poor. In addition, since the S content of the welding material was too high at 0.009%, the occurrence of hot cracks on the surface of the weld bead was also observed.

In the case of BW12, since the amount of “Al + O” was too large as 0.016% and the Al content was as high as 0.014%, a large amount of slag was generated during welding, and sufficient backwashing was formed. No performance was obtained, and the Uranami-unformed portion remained in the upward position. Test No. BW13 is an example in which plasma welding was performed using the same welding material B9, but a sufficient penetration depth was not obtained, and a part where no penetration was formed remained.

In BW14, welding material B10 was used. Since this welding material has a Si / Mn ratio of 0.083 and smaller than 0.1, H / W is 0.5 in both downward and upward welding positions.
It became a convex bead exceeding.

In the test number BW15, the welding material B11 having an "Al + O" amount of too large as 0.016% was used, so that a sufficient penetration depth could not be obtained at the time of upward welding, and there was a part where no penetration was formed. Also, since the Si / Mn ratio of the welding material exceeded 1.105 and 1.0, dripping occurred in upward welding.

In the test number BW16, the amount of “Al + O” was similarly set to 0.
Since the welding material B12, which is too large as 018%, was used, sufficient backwashing ability could not be obtained, and a portion where no backwashing was formed was observed in both the downward and upward welding positions.

In Test Nos. BW17 and BW18, "Al +
This is an example in which welding material B13 with a high O content of 0.017% was used, and TIG welding and plasma welding were performed, respectively. In each case, sufficient backwashing ability was not obtained, and a backwash-unformed portion remained.

In test number BW19, welding material B14 was used. This welding material has "S + O" amount exceeding 0.016% and 0.015%, and "Al + O" amount also exceeding 0.020% and 0.015%.
Since the i / Mn ratio was 1.619, which is higher than the upper limit defined in the present invention, no backwash was formed, the bead was non-uniform, and the sagging in the upward posture occurred at the same time.

As is evident from the above results, when a welding material having no chemical composition defined in the present invention is used, sufficient welding workability cannot be obtained and welding in all positions is impossible.

(Example 2) The following test was conducted to examine the performance of a welded joint. That is, using the grooves shown in FIGS. 5 and 6, the welding materials shown in Table 1 were used, the TIG welding was performed using 12-pass six-layer lamination welding shown in FIG.
Welded one layer of plasma welding and one layer of TIG welding as shown in
Welded joints were made.

A chemical analysis sample was taken from each of the welded metal portions shown in FIG. 9 and FIG. 10 from the manufactured joint, and a chemical analysis was performed. Further, a bending test piece shown in FIG. 11 and a V-notched Charpy test piece shown in FIG. 12 were sampled and subjected to a test for confirming the occurrence of reheat cracking and an impact test at −196 ° C., respectively.

In confirming the reheat crack, the test piece was slightly bent as shown in FIG. 11 to facilitate observation, and if there was a minute reheat crack, the test piece was opened to open it. Using a microscope, the weld metal portion was observed at a magnification of 100 to 500 to confirm the occurrence of cracks. As a criterion, those having no cracks were accepted, and those having at least one crack were failed.

In the pass / fail judgment of the impact test, an impact value of 30 J / cm ² required for practical use as a joint was used as a judgment standard. The impact test was not carried out for those having cracks in the reheat crack confirmation test. Tables 5 and 6 show the results of analysis of the weld metal and the results of evaluating the joint performance. As the analysis results, only the analysis values of the main alloy components other than Fe are shown.

[0074]

[Table 5]

[0075]

[Table 6]

The joint numbers TAJ1 and TAJ2 in Table 5 are examples in which the same welding materials A1 and A3 were used for TIG welding over the entire layers. In these joints, each position of the weld metal
Since the amounts of Nb and C satisfied the above expressions, no reheat cracking was observed in the weld metal, and the impact value was 50 J / cm ² or more.

Similarly, joint numbers PAJ1 and PAJ2 are examples in which plasma welding is performed on all the layers using the same wires A1 and A3, respectively. As in TAJ1 and TAJ2 above, the Nb and C contents at each position of the weld metal satisfied the formula, so no reheat cracking was observed in the weld metal, and the impact value was 50 J / cm.
It was a high value of ² or more.

On the other hand, the joint number TBJ1 shown in Table 6 is an example in which the welding material of A6 is used for all the layers and the TIG welding is performed. −0.04 (% Nb) + 0.40 ”and Nb
Since the amount exceeded 3.0%, reheat cracking did not occur, but the impact value was extremely low at 8 J / cm ² .

Similarly, the joint number TBJ2 in Table 6 is an example in which AIG welding material is used for all layers and TIG welding is performed.
The C content of the weld metal satisfies the relational expression in all positions. However, since the Nb content in the weld metal of the center thickness and the final layer exceeded 3.0%, reheat cracking did not occur, but the impact value was as low as 14 J / cm ² .

The joint number TBJ3 in Table 6 indicates that A1
This is an example of TIG welding using welding material 3
When the C content is 0.02%, the lower limit of the equation "-0.01 (% Nb) + 0.0
4 ", there were many reheat cracks in the first layer. The joint number TBJ4 is obtained by TIG welding using a welding material of A15 for all layers. In this example, since the C content of the weld metal in the center of the thickness and the final layer was larger than the upper limit of the equation, reheat cracking did not occur, but the impact value was as low as 20 J / cm ² .

The joint numbers PBJ1 and PBJ2 in Table 6 were formed by plasma welding using all layers A13 and A15, respectively (strictly speaking,
The final layer is an example of TIG welding. For the same reasons as the above-mentioned joint numbers TBJ3 and TBJ4, reheat cracking occurred in the plasma-welded metal portion in TBJ3 and low toughness in TBJ4.

As described above, the welding materials A6, A
13, the joints obtained by TIG and plasma welding at A15 do not satisfy the conditions of the above equation, and thus have problems of reheat cracking and insufficient toughness. In contrast, the joint number T in Table 5
Like AJ3, TAJ4, PAJ3 and PAJ4, even if these welding materials are used, by properly combining the welding materials so that the chemical composition at all positions of the weld metal satisfies the conditions defined in the present invention, It became clear that a welded joint having no toughness and excellent toughness was obtained.

As described above, it is clear that only the welding material having the chemical composition defined in the present invention has sufficient welding workability and is applicable to all-position welding and automatic welding.
Further, it is clear that when the weld metal obtained using these welding materials is within the composition range defined by the present invention, reheat cracking does not occur and a welded joint having excellent toughness can be obtained. is there.

[0084]

The welded structure of the present invention has a weld metal which does not generate reheat cracks and has excellent low-temperature toughness. In addition, since the welding material of the present invention has sufficient welding workability, it can be used for circumferential welding and automatic welding in all positions.

The present invention relates to the manufacture of a welded pipe using an Fe—Ni-based low coefficient of thermal expansion alloy, a pipe to which the pipe is joined, and a storage tank and peripheral equipment for handling cryogenic substances such as liquefied natural gas. This greatly contributes to the production of structures.

[Brief description of the drawings]

FIG. 1 is a view showing an appropriate range of Nb and C of a weld metal.

FIG. 2 is a diagram showing appropriate ranges of Mn and Si of a weld metal.

FIG. 3 is a diagram showing appropriate ranges of O (oxygen) and S of a weld metal.

FIG. 4 is a diagram showing appropriate ranges of O (oxygen) and Al of a weld metal.

FIG. 5 is a view showing a groove shape of TIG welding adopted in the embodiment.

FIG. 6 is a view showing a groove shape of plasma welding adopted in the embodiment.

FIG. 7 is a diagram showing a method for measuring flatness of a weld bead.

FIG. 8 is a diagram showing a lamination method of TIG welding adopted in the example.

FIG. 9 is a diagram showing a position at which a chemical analysis sample is collected from a weld metal of TIG welding.

FIG. 10 is a diagram showing a lamination method of plasma welding adopted in the example and a position at which a chemical analysis sample is collected from a weld metal.

FIG. 11 is a diagram showing a reheat crack evaluation method adopted in the examples.

FIG. 12 is a view showing a Charpy impact test piece employed in an example.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masao Shirai 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Inside Osaka Gas Co., Ltd. (72) Inventor Naoshige Kubo 4 Hirano-cho, Chuo-ku, Osaka-shi, Osaka 1-2, Osaka Gas Co., Ltd. (72) Inventor Taku Iwahashi 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Prefecture, Japan Inside (72) Inventor Taketo Yamakawa Niijima, Harima-cho, Kako-gun, Hyogo Prefecture No. 8 in Kawasaki Heavy Industries, Ltd.Harima Plant (72) Inventor Hidehiro Matsushima 8 in Niijima, Harima-cho, Kako-gun, Hyogo Prefecture No. 8 in Harima Plant, Co., Ltd. No. 1-1 Kawasaki Heavy Industries, Ltd. (72) Inventor Masayuki Inuzuka 3-1-1, Higashi Kawasaki-cho, Chuo-ku, Kobe 72) Inventor Hiroyuki Hirata 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Toshinobu Nishihata 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal (72) Inventor Masato Ikebe 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd.

Claims (3)

[Claims] 1. The method according to claim 1, wherein all parts of the weld metal are Ni:
30-45%, Si: 0.5% or less, Mn: 0.8% or less, Nb: 0.1-
Welded structure made of Fe-Ni based low coefficient of thermal expansion alloy, Fe-based alloy with 3.0%, P: 0.015% or less, S: 0.004% or less, and whose Nb and C contents satisfy the following formula: Stuff. -0.01 (% Nb) + 0.04 ≤ (% C) ≤ -0.04 (% Nb) + 0.40 ... 2. Ni: 30 to 45% by weight, C: 0.08 to 0.5% by weight,
Si: 0.5% or less, Mn: 0.8% or less, Nb: 0.3 to 4%, A1: 0.01%
The following welding material made of an Fe-based alloy, wherein P
Is 0.015% or less, S is 0.004% or less, and the content of Si and Mn satisfies the following formula, the content of S, 0 (oxygen) is the following formula, and the content of A1 and O (oxygen) Is a welding material for Fe-Ni-based low thermal expansion alloys with excellent welding workability that satisfies the following formulas. 0.1 ≦ (% Si) / (% Mn) ≦ 1.0 (% S) + (% O) ≦ 0.015% (% A1) + (% 0) ≦ 0.015% 3. A weld metal obtained by using the welding material according to claim 2, wherein all parts thereof are, by weight%,
Ni: 30 to 45%, Si: 0.5% or less, Mn: 0.8% or less, Nb: 0.
1-3.0%, P: 0.015% or less, S: 0.004% or less Fe-based alloy, whose content of Nb and C satisfies the following formula. Welded structures. -0.01 (% Nb) + 0.04 ≤ (% C) ≤ -0.04 (% Nb) + 0.40 ...