JP2021183720A - Ni-BASED ALLOY TUBE AND WELDED JOINT - Google Patents

Abstract

To provide an Ni-based alloy tube that allows stable formation of an internal bead having good usability of its weldment, and a welded joint.SOLUTION: An Ni-based alloy tube includes a chemical composition containing, in mass%, C: 0.005 to 0.080%, Si: 0.01 to 0.50%, Mn: 0.01 to 0.50%, P: 0.015% or less, S: 0.0001 to 0.0030%, Cr: 20.0 to 23.5%, Mo: 8.0 to 10.5%, Ti: 0.01 to 0.40%, N: 0.0010 to 0.0400%, Al: 0.01 to 0.40%, O: 0.0004 to 0.0100%, one or more elements selected from Nb and Ta, and Sn: 0 to 0.010%, with the balance: Ni and impurities, and satisfying [0.0010≤S+2O+0.2Sn≤0.0180] and [2.50≤Nb+Ta≤4.60].SELECTED DRAWING: None

Description

The present invention relates to Ni-based alloy pipes and welded joints.

In chemical plants and power plants, various plant equipment such as flue gas treatment equipment and seawater treatment equipment are installed. The inside of the plant is a harsh corrosive environment where many substances that promote corrosion such as chloride and hydrogen sulfide are present. Therefore, the materials used for plant equipment are required to have corrosion resistance in addition to strength. Therefore, as disclosed in Patent Documents 1 to 8, Ni-based alloys having improved corrosion resistance have been developed assuming use in plant equipment.

Japanese Unexamined Patent Publication No. 54-110918 Japanese Unexamined Patent Publication No. 63-89637 Japanese Unexamined Patent Publication No. 2-156034 Japanese Unexamined Patent Publication No. 3-173732 Japanese Unexamined Patent Publication No. 5-271832 Japanese Unexamined Patent Publication No. 9-87786 Japanese Unexamined Patent Publication No. 10-30140 Japanese Unexamined Patent Publication No. 2012-72446

Some plant equipment is manufactured by assembling members by welding. In such equipment, the bead formation state of the weld may affect the progress of corrosion.

For example, some heat exchangers are manufactured by butt-welding and joining a plurality of Ni-based alloy pipes that serve as flow paths for refrigerants and the like. When used as a heat exchanger, various corrosive fluids flow inside the tube. At this time, if the height of the bead formed inside the pipe by welding, that is, the surplus height is too high, the corrosive fluid stays at the toe where the bead surface and the surface of the base metal intersect. Thicken. As a result, there is a problem that corrosion is likely to proceed at the toe.

On the other hand, if the excess height is too low to reduce the amount of heat input during welding, the butt surface between the pipes is not completely melted, and it becomes difficult to form a stable bead. As a result, there is a problem that welding defects are generated, and corrosive fluid stays and concentrates in the welding defects, so that corrosion easily progresses. However, Patent Documents 1 to 8 do not examine these problems at all.

Therefore, even if a pipe is manufactured using a Ni-based alloy having high corrosion resistance as a material, it is difficult to form a bead having an appropriate shape in the pipe, which is less likely to cause corrosion during butt welding. That is, there is a problem that it is difficult to obtain a Ni-based alloy pipe in which a bead is stably formed on the inner surface side at the time of welding and the surplus height is not too high.

Based on the above, it is an object of the present invention to solve the above-mentioned problems and to provide a Ni-based alloy pipe and a welded joint capable of stably forming an inner bead having good use performance of a welded portion.

The present invention has been made to solve the above problems, and the gist of the present invention is the following Ni-based alloy pipes and welded joints.

(1) The chemical composition is mass%.
C: 0.005-0.080%,
Si: 0.01-0.50%,
Mn: 0.01-0.50%,
P: 0.015% or less,
S: 0.0001 to 0.0030%,
Cr: 20.0 to 23.5%,
Mo: 8.0-10.5%,
Ti: 0.01-0.40%,
N: 0.0010 to 0.0400%,
Al: 0.01-0.40%,
O: 0.0004 to 0.0100%,
Including one or more selected from Nb and Ta,
Sn: 0 to 0.010%,
The rest is Ni and impurities,
A Ni-based alloy tube satisfying the following equations (i) and (ii).
0.0010 ≦ S + 2O + 0.2Sn ≦ 0.0180 ・ ・ ・ (i)
2.50 ≤ Nb + Ta ≤ 4.60 ... (ii)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero.

(2) The Ni-based alloy pipe according to (1) above, wherein the arithmetic average roughness Ra in the longitudinal direction of the pipe is 7.0 μm or less on the inner surface side of the Ni-based alloy pipe.

(3) The chemical composition is, instead of a part of the Ni, by mass%.
The Ni-based alloy tube according to (1) or (2) above, which contains Fe: 5.50% or less.

(4) Any of the above (1) to (3), wherein the chemical composition contains one or more selected from Cu and Co instead of a part of the Ni, and satisfies the following formula (iii). The Ni-based alloy tube described.
0.01 ≤ Cu + Co ≤ 1.50 ... (iii)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero.

(5) The chemical composition is, in mass%, instead of a part of the Ni.
W: 1.00% or less,
V: 0.40% or less,
Ca: 0.0030% or less,
Mg: 0.0030% or less,
B: 0.0100% or less, and REM: 0.0100% or less,
The Ni-based alloy tube according to any one of (1) to (4) above, which contains one or more selected from the above.

(6) A welded joint using the Ni-based alloy pipe according to any one of (1) to (5) above.

According to the present invention, it is possible to obtain a Ni-based alloy tube capable of stably forming an inner bead having good use performance of a welded portion.

FIG. 1 is a diagram showing a groove shape in an embodiment.

The present inventors examined the beads of the Ni-based alloy tube and obtained the following findings (a) to (d).

(A) The shape of the inner bead of the pipe formed during butt welding is affected by the content of S and O contained in the Ni-based alloy pipe. Then, the present inventors have clarified that when the contents of S and O are small, the inner bead is not stably formed, and a part of the unmelted butt surface remains.

On the other hand, when the S and O contents are excessive, the bead is stably formed, but the excess height of the bead becomes excessively high. Therefore, when used as an alloy pipe, the corrosive fluid stays in the vicinity of the bead, and the corrosion easily progresses. Therefore, in order to stably form beads and prevent the excess height from becoming excessively high, it is necessary to adjust the S content and the O content within a predetermined range.

(B) The following are possible reasons why S and O affect the formation of beads. S and O are surface active elements, which enhance inward convection in the weld pond during welding. As a result, the welding heat is easily transferred in the depth direction, and the bead can be stably formed. On the other hand, if S and O are excessively contained, the surface tension of the molten metal is excessively lowered, and the molten metal tends to hang down. As a result, the shape of the bead becomes a convex shape (hereinafter, simply referred to as "convex shape") in which the bead is excessively raised, and the extra height becomes high.

(C) In addition, the shape of the bead on the inner surface side of the pipe is affected by the surface roughness of the inner surface of the pipe in the longitudinal direction. The present inventors have clarified that when the surface roughness is large, the surplus height becomes high and the shape tends to be convex. Therefore, it is desirable to control the surface roughness within a predetermined range. In particular, when the surface roughness of the inner surface of the pipe in the longitudinal direction is large, the spread of the molten metal in the width direction is suppressed, the shape of the bead becomes convex, and the extra height tends to increase.

(D) Furthermore, the present inventors have also clarified that the shape of the inner bead is also affected by the Sn content. When Sn is contained, the penetration depth becomes large, and the inner bead is likely to be stably formed. On the other hand, if it is contained in an excessive amount, the penetration becomes excessive and the inner bead tends to have a convex shape. It is considered that the reason for this is that Sn evaporates from the surface of the molten pool during welding and the concentration of the arc is increased. Therefore, when Sn is contained, the Sn content is controlled within a predetermined range in order to obtain an inner bead having an appropriate shape, and the relationship between the S content, the O content, and the Sn content is within a predetermined range. Must be met.

The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.

1. 1. Chemical composition of alloy tube The reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%".

C: 0.005-0.080%
C has the effect of stabilizing the tissue. Therefore, the C content is set to 0.005% or more. The C content is preferably 0.008% or more, more preferably 0.010% or more, and further preferably 0.012% or more. However, when C is excessively contained, it is combined with Cr by the welding heat cycle to form carbides at the grain boundaries at the weld heat affected zone. As a result, a Cr-deficient layer is formed in the vicinity of the grain boundaries, and the corrosion resistance is lowered. Therefore, the C content is set to 0.080% or less. The C content is preferably 0.050% or less, more preferably 0.030% or less, and even more preferably 0.025% or less.

Si: 0.01-0.50%
Si has a deoxidizing effect. Therefore, the Si content is 0.01% or more. The Si content is preferably 0.02% or more, more preferably 0.03% or more. The Si content is more preferably 0.05% or more. However, if Si is contained in an excessive amount, the structure stability of the alloy is lowered and the welding crack sensitivity is increased. In addition, it may be difficult to stably form the bead on the inner surface side. Therefore, the Si content is set to 0.50% or less. The Si content is preferably 0.48% or less, more preferably 0.45% or less. The Si content is more preferably 0.43% or less.

Mn: 0.01 to 0.50%
Mn has a deoxidizing effect like Si. In addition, it has the effect of enhancing the tissue stability and contributes not a little to the stable formation of the bead on the inner surface side. Therefore, the Mn content is set to 0.01% or more. The Mn content is preferably 0.03% or more, more preferably 0.05% or more. The Mn content is more preferably 0.08% or more. However, if Mn is contained in an excessive amount, the hot workability is deteriorated. Therefore, the Mn content is set to 0.50% or less. The Mn content is preferably 0.48% or less, more preferably 0.45% or less. The Mn content is more preferably 0.40% or less.

P: 0.015% or less P is contained in the Ni-based alloy as an impurity and significantly increases the welding crack sensitivity. Therefore, the P content is set to 0.015% or less. The P content is preferably 0.013% or less, more preferably 0.012% or less. The P content is preferably reduced as much as possible, but excessive reduction increases manufacturing costs. Therefore, the P content is preferably 0.001% or more, and more preferably 0.002% or more.

S: 0.0001 to 0.0030%
S is generally contained in the Ni-based alloy as an impurity, but in the alloy pipe of the present invention, it has an effect of enhancing the ability to form the inner bead at the time of welding together with O. Therefore, the S content is set to 0.0001% or more. The S content is preferably 0.0002% or more, and more preferably 0.0003% or more. However, when S is excessively contained, the bead on the inner surface side of the pipe becomes convex and the welding crack sensitivity is increased. Therefore, the S content is set to 0.0030% or less. The S content is preferably 0.0025% or less, more preferably 0.0020% or less. It should be noted that S needs to satisfy the equation (i) described later between O and Sn.

Cr: 20.0 to 23.5%
Cr is an essential element for ensuring corrosion resistance. Cr particularly forms a passivation film on the surface and improves corrosion resistance in an oxidizing acid environment. Therefore, the Cr content is set to 20.0% or more. The Cr content is preferably 20.5% or more, more preferably 21.0% or more, and even more preferably 21.2% or more. However, if Cr is contained in an excessive amount, the tissue stability is lowered. Therefore, the Cr content is set to 23.5% or less. The Cr content is preferably 23.3% or less, more preferably 23.0% or less, and even more preferably 22.8% or less.

Mo: 8.0-10.5%
Mo improves corrosion resistance in the presence of non-oxidizing acids and chlorides. Therefore, the Mo content is set to 8.0% or more. The Mo content is preferably 8.2% or more, more preferably 8.5% or more, and even more preferably 8.7% or more. However, if Mo is contained in an excessive amount, the tissue stability is lowered. Further, since Mo is an expensive element, the manufacturing cost increases. Therefore, the Mo content is set to 10.5% or less. The Mo content is preferably 10.3% or less, more preferably 10.0% or less, and even more preferably 9.8% or less.

Ti: 0.01 to 0.40%
Ti forms carbides, contributes to strengthening, and suppresses the formation of Cr carbides, thereby reducing deterioration of corrosion resistance at grain boundaries. Therefore, the Ti content is set to 0.01% or more. The Ti content is preferably 0.05% or more, more preferably 0.08% or more, and even more preferably 0.10% or more. However, if Ti is contained in an excessive amount, a large amount of carbides and carbonitrides of Ti are precipitated, and the ductility is lowered. Therefore, the Ti content is set to 0.40% or less. The Ti content is preferably 0.38% or less, more preferably 0.35% or less, and even more preferably 0.32% or less.

N: 0.0010 to 0.0400%
N has the effect of contributing to tissue stability and enhancing pitting corrosion resistance. Therefore, the N content is set to 0.0010% or more. The N content is preferably 0.0020% or more, more preferably 0.0030% or more, and even more preferably 0.0040% or more. However, if N is contained in an excessive amount, a nitride is precipitated and the ductility is lowered. Therefore, the N content is 0.0400% or less. The N content is preferably 0.0350% or less, more preferably 0.0300% or less. The N content is more preferably 0.0250% or less.

Al: 0.01 to 0.40%
Al has a deoxidizing effect. It also contributes to the improvement of oxidation resistance at high temperatures. Therefore, the Al content is set to 0.01% or more. The Al content is preferably 0.02% or more, and more preferably 0.03% or more. The Al content is more preferably 0.05% or more. However, if Al is contained in an excessive amount, a brittle compound is formed with Ni, and the hot workability is deteriorated. In addition, it may be difficult to stably form the bead on the inner surface side. Therefore, the Al content is set to 0.40% or less. The Al content is preferably 0.35% or less, more preferably 0.30% or less, and even more preferably 0.28% or less.

O: 0.0004 to 0.0100%
O is generally contained as an impurity in the Ni-based alloy, but in the alloy pipe of the present invention, it has an effect of enhancing the bead forming ability on the inner surface side of the pipe at the time of welding together with S. Therefore, the O content is set to 0.0004% or more. The O content is preferably 0.0006% or more, and more preferably 0.0008% or more. However, if O is contained in an excessive amount, the bead on the inner surface side of the tube becomes convex and the hot workability is deteriorated. Therefore, the O content is 0.0100% or less. The O content is preferably 0.0080% or less, more preferably 0.0060% or less. It should be noted that O needs to satisfy the equation (i) described later between S and Sn.

A total of one or more selected from Nb and Ta, 2.50% or more and 4.60% or less Nb and Ta, like Ti, both combine with carbon to form carbides and contribute to strengthening. It suppresses the formation of Cr carbides and reduces the deterioration of corrosion resistance at grain boundaries. Therefore, it is necessary to include one or more selected from Nb and Ta, and the total content of these elements must satisfy the following formula (ii).

2.50 ≤ Nb + Ta ≤ 4.60 ... (ii)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero.

When the middle value of the formula (ii), which is the total content of Nb and Ta, is less than 2.50%, the above-mentioned strength is improved and the effect of reducing the deterioration of the grain boundary corrosion resistance cannot be obtained. Therefore, the middle value of equation (ii) is set to 2.50% or more. The middle value of the formula (ii) is preferably 2.70% or more, and more preferably 3.00% or more.

On the other hand, when the middle value of the formula (ii) exceeds 4.60%, a large amount of carbides and carbonitrides of Nb and Ta are precipitated, and the ductility is lowered. Furthermore, the sensitivity to weld cracks is also increased. Therefore, the middle value of equation (ii) is preferably 4.60% or less, preferably 4.40% or less, and more preferably 4.20% or less.

In the chemical composition, in addition to the above elements, Sn may be further contained in the range shown below.

Sn: 0 to 0.010%
Sn has the effect of increasing the penetration depth during welding and enhancing the ability to form the bead on the inner surface side of the pipe. Therefore, it may be contained as needed. However, if Sn is contained in an excessive amount, the hot workability is lowered and the weld cracking sensitivity is increased. In addition, the inner bead tends to have a convex shape. Therefore, the Sn content is set to 0.010% or less. The Sn content is preferably 0.009% or less, more preferably 0.008% or less. On the other hand, in order to obtain the above effect, the Sn content is preferably 0.001% or more, more preferably 0.002% or more, and further preferably 0.003% or more. In addition, Sn needs to satisfy the equation (i) described later between S and O.

As described above, since S, O, and Sn effectively contribute to the formation of beads on the inner surface side of the pipe, the Ni-based alloy pipe according to the present invention contains S content, O content, and Sn. It is necessary to satisfy the following equation (i), which is a relational equation with the quantity.

0.0010 ≦ S + 2O + 0.2Sn ≦ 0.0180 ・ ・ ・ (i)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero. Further, in the above formula, when the Sn content is less than 0.001%, it is treated as Sn = 0.

S and O are surfactant elements and have an action of strengthening inward convection in the molten pool during welding. Further, Sn contributes to the formation of the arc energization path and has the effect of increasing the concentration of the arc. Then, the welding heat is transported in the depth direction of the center of the molten pool. As a result, these elements have an effect of stably forming the inner bead, but this effect cannot be obtained when the middle value of the formula (i) is less than 0.0010%. Therefore, the middle value of the formula (i) is set to 0.0010% or more. The middle value of the formula (i) is preferably 0.0012% or more, and more preferably 0.0015% or more.

On the other hand, when the middle value of the formula (i) exceeds 0.0180%, the surface tension of the molten metal becomes small, or the melting of the center of the molten pool is promoted, and the molten metal hangs down. As a result, the bead becomes a convex shape, and the bead cannot be stably formed on the inner surface side of the pipe. Therefore, the middle value of the formula (i) is set to 0.0180% or less. The middle value of the formula (i) is preferably 0.0175% or less, more preferably 0.0170% or less.

In the chemical composition, in addition to the above elements, Fe may be further contained in the range shown below.

Fe: 5.50% or less Fe is effective for improving hot workability. Furthermore, it also contributes to the reduction of alloy cost. Therefore, it may be contained as needed. However, excessive inclusion of Fe reduces tissue stability. Therefore, the Fe content is set to 5.50% or less. The Fe content is preferably 5.30% or less, more preferably 5.00% or less. On the other hand, in order to obtain the above effect, the Fe content is preferably 0.01% or more, more preferably 0.50% or more, and further preferably 1.50% or more.

In the chemical composition, in addition to the above elements, Cu and Co may be further contained in the range shown below.

A total of 1.50% or less selected from one or more of Cu and Co Cu and Co have the effect of enhancing tissue stability and improving corrosion resistance in non-oxidizing acid and chloride environments. Therefore, one or more selected from Cu and Co may be contained as needed. Further, when it is contained, it is preferable that the chemical composition satisfies the following formula (iii).

0.01 ≤ Cu + Co ≤ 1.50 ... (iii)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero.

If the middle value of the formula (iii), which is the total content of Cu and Co, is less than 0.01%, it becomes difficult to obtain the above effect. Therefore, the middle value of the formula (iii) is preferably 0.01% or more, more preferably 0.02% or more, and further preferably 0.03% or more. However, when the middle value of the formula (iii) exceeds 1.50%, the hot workability is lowered and the manufacturing cost is increased. Therefore, the middle value of the formula (iii) is preferably 1.50% or less, and more preferably 1.30% or less. The middle value of the equation (iii) is more preferably 1.00% or less.

In the chemical composition, in addition to the above elements, one or more selected from W, V, Ca, Mg, B, and REM may be further contained in the range shown below. The reason for limiting each element will be described.

W: 1.00% or less W improves corrosion resistance in the presence of non-oxidizing acids and chlorides. Therefore, it may be contained if necessary. However, excessive inclusion of W reduces tissue stability. Moreover, since it is an expensive element, the manufacturing cost increases. Therefore, the W content is set to 1.00% or less. The W content is preferably 0.90% or less, and more preferably 0.80% or less. On the other hand, in order to obtain the above effect, the W content is preferably 0.01% or more, more preferably 0.02% or more.

V: 0.40% or less V combines with carbon to form carbides and suppresses the formation of Cr carbides, thereby reducing the deterioration of corrosion resistance at the grain boundaries. Therefore, it may be contained if necessary. However, if V is contained in an excessive amount, a large amount of carbides and carbonitrides of V are precipitated, and the ductility is lowered. Therefore, the V content is set to 0.40% or less. The V content is preferably 0.35% or less, and more preferably 0.30% or less. On the other hand, in order to obtain the above effect, the V content is preferably 0.01% or more, more preferably 0.02% or more.

Ca: 0.0030% or less Ca has an effect of improving hot workability. Therefore, it may be contained as needed. However, if Ca is contained in an excessive amount, it binds to oxygen and significantly reduces the cleanliness. As a result, the hot workability is rather lowered. Therefore, the Ca content is set to 0.0030% or less. The Ca content is preferably 0.0020% or less, more preferably 0.0010% or less. On the other hand, in order to obtain the above effect, the Ca content is preferably 0.0001% or more, and more preferably 0.0003% or more.

Mg: 0.0030% or less Mg has the effect of improving hot workability like Ca. Therefore, it may be contained as needed. However, if Mg is contained in an excessive amount, it will be combined with oxygen and the cleanliness will be significantly reduced. As a result, the hot workability is rather lowered. Therefore, the Mg content is set to 0.0030% or less. The Mg content is preferably 0.0020% or less, more preferably 0.0010% or less. On the other hand, in order to obtain the above effect, the Mg content is preferably 0.0001% or more, more preferably 0.0003% or more.

B: 0.0100% or less B has the effect of segregating at the grain boundaries at high temperatures, strengthening the grain boundaries, and enhancing hot workability. Therefore, it may be contained as needed. However, if B is contained in an excessive amount, the welding crack sensitivity increases. Therefore, the B content is 0.0100% or less. The B content is preferably 0.0080% or less, more preferably 0.0060% or less. On the other hand, in order to obtain the above effect, the B content is preferably 0.0002% or more, more preferably 0.0005% or more.

REM: 0.0100% or less REM, like Ca and Mg, has the effect of improving hot workability during manufacturing. Therefore, it may be contained if necessary. However, if REM is contained in excess, it binds to oxygen and significantly reduces cleanliness. As a result, the hot workability is rather lowered. Therefore, the REM content is 0.0100% or less. The REM content is preferably 0.0050% or less, more preferably 0.0030% or less. On the other hand, in order to obtain the above effect, the REM content is preferably 0.0001% or more, and more preferably 0.0003% or more. Here, REM refers to Sc, Y and lanthanoids, and the REM content indicates the total content of these elements.

In the chemical composition of the Ni-based alloy according to the present invention, the balance is Ni and impurities. Here, the "impurity" is not an element that is intentionally added, but is a component that is mixed by various factors such as a raw material and a manufacturing process when a Ni-based alloy is industrially manufactured. It means something that is acceptable as long as it does not have an adverse effect.

2. 2. The surface roughness bead of the alloy tube is formed when the end of the alloy tube is welded. In order to form a good bead, it is preferable to control the arithmetic mean roughness Ra in the longitudinal direction on the inner surface side of the alloy tube. Here, the surface roughness of the alloy tube refers to the surface roughness after the final step in the manufacturing process. That is, the surface roughness of the alloy tube changes in the manufacturing process, but in order to obtain the effect of the present invention, the surface roughness in the longitudinal direction of the tube after the final step is irrelevant regardless of the surface roughness during the manufacturing process. , The scope specified by the present invention may be satisfied.

When the arithmetic mean roughness Ra in the longitudinal direction of the pipe exceeds 7.0 μm on the inner surface side of the Ni-based alloy pipe, wetting of the weld metal is hindered on the inner surface of the pipe, and the weld metal is inhibited in the width direction, that is, along the circumference of the pipe. Is hard to spread. As a result, the bead tends to have a convex shape, and the extra height tends to increase. Therefore, on the inner surface side of the Ni-based alloy pipe, the arithmetic average roughness Ra in the longitudinal direction of the pipe is preferably 7.0 μm or less. The arithmetic average roughness Ra is preferably 5.0 μm or less, and more preferably 3.0 μm or less. The lower limit of the arithmetic mean roughness Ra is not particularly determined, but it is usually 0.1 to 1.0 μm or more when the manufacturing method described later is used.

Here, the arithmetic mean roughness Ra is defined in JIS B 0601: 2001, and can be measured by using a contact-type surface roughness measuring device.

3. 3. Welded joints Welded joints for Ni-based alloy pipes can be obtained by butt-welding the pipe ends of the above Ni-based alloy pipes under predetermined conditions. The welded joint of the Ni-based alloy pipe has a welded metal formed by solidifying the molten metal and forming a joint portion, and a base metal portion. The base metal portion includes a welding heat-affected zone that is affected by heat input due to welding. The base metal portion excluding the weld heat-affected zone inherits the chemical composition, surface roughness, and other characteristics of the Ni-based alloy pipe described in items 1 and 2 above. Further, the welded portion refers to the weld metal and the weld heat affected zone.

4. Manufacturing Method A preferred manufacturing method for the Ni-based alloy tube according to the present invention will be described. The Ni-based alloy tube according to the present invention can obtain the effect as long as it has the above-mentioned configuration regardless of the manufacturing method, but for example, it can be stably manufactured by the following manufacturing method. can.

4-1. Ni-based alloy pipe First, the Ni-based alloy ingot, which is the material of the Ni-based alloy pipe, is manufactured. The Ni-based alloy ingot is preferably produced by melting an alloy having the above-mentioned chemical composition in an electric furnace or the like, removing impurities by refining, and then casting. Subsequently, it is preferable that the obtained ingot is hot forged to form a columnar billet. Then, the obtained billet is processed to form a tube shape.

Specifically, it is preferable to hot-extrude the billet and then perform cold rolling or cold drawing. At the time of processing, softening heat treatment and intermediate pickling may be performed on the way, if necessary. After that, as a heat treatment, it is preferable to perform a solution treatment on the alloy tube. After the solution treatment, pickling or processing may be performed, if necessary.

Here, in order to make the arithmetic average roughness Ra in the longitudinal direction of the pipe 7.0 μm or less, it is preferable to perform the following steps. Specifically, it is preferable to carry out the solution treatment under the conditions of heating in a temperature range of 950 ° C to 1230 ° C for 1 to 15 minutes and cooling with water. Further, it is preferable to perform any of grinding treatment, machining such as grinding, and shot blasting or shot peening treatment on the inner surface of the pipe.

Although the arithmetic mean roughness Ra changes in the manufacturing process, the effect of the present invention is affected only by the surface roughness in the longitudinal direction of the pipe after the final process, regardless of the surface roughness in the middle process. ..

4-2. Welded joints for Ni-based alloy pipes Welded joints can be obtained by using the Ni-based alloy pipes according to the present invention as a material and welding the ends of the alloy pipes. The welding method is not particularly limited, but for example, it may be welded by arc welding. Further, as the conditions for arc welding, for example, the amount of heat input is preferably in the range of 4 to 20 kJ / cm. Further, at the time of welding, it is preferable to use Ar gas as a shield gas and a back shield gas. It is preferable to adjust the flow rate of the gas flowing to the welded portion as appropriate.

Further, the chemical composition of the welding material (filler) to be used is not particularly limited, but the composition shown below is preferable. That is, in terms of mass%, C: 0.150% or less, Si: 1.00% or less, Mn: 3.50% or less, P: 0.030% or less, S: 0.0001 to 0.0100%, Fe. : 38.0% or less, Cu: 3.00% or less, Co: 15.0% or less, Cr: 14.0 to 26.0%, Mo: 17.0% or less, W: 4.5% or less, At least one of Nb and Ta in total is 4.20% or less, Ti: 1.50% or less, V: 0.35% or less, N: 0.0500% or less, Al: 1.50% or less, O: 0 It is preferable that the content is 0004 to 0.0100%, the balance is Ni and impurities, and the relationship between the contents of S and O satisfies the following formula (a).

0.0010 ≤ S + 2O ≤ 0.0180 ... (a)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the welding material, and if it is not contained, it is set to zero.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

An alloy having the chemical composition shown in Table 1 was melted to produce an ingot. Then, hot forging and hot rolling were performed to adjust the thickness to 10 mm. Subsequently, the scale formed on the surface was removed by pickling. At this time, the arithmetic average roughness Ra was about 10 μm for all steel types. Then, assuming the manufacturing process of the alloy tube, a 3 mm alloy plate was obtained by cold rolling while performing softening heat treatment and intermediate pickling on the way.

Subsequently, the alloy plate was subjected to a solution treatment by holding it at 1150 ° C. for 10 minutes in a hydrogen furnace and then cooling it with water. Then, a plate material having a width of 50 mm and a length of 100 mm was cut out from the alloy plate. Then, as shown in Table 2, shot peening was performed on only one side of the cut out plate material, assuming the inner surface side of the alloy tube. For the plate material that was not shot peened, one side was ground or polished 1 to 5 times using a grindstone having a particle size of No. 40 or No. 60. In Table 2, for example, polishing (# 40 × 1 time) indicates that the polishing was performed once with a grindstone having a particle size of No. 40.

Arithmetic mean roughness was measured for each plate using a contact roughness meter. In addition, two plates of each alloy type were prepared, and the end face in the rolling direction was grooved as shown in FIG. The end faces of these plate materials that had been grooved were butted against each other, and an initial layer weld was performed using a filler metal having an outer diameter of 1.0 mm having the chemical composition shown in Table 3 to obtain a welded joint. The heat input during welding was about 5 kJ / cm, Ar gas was used as the shield gas and the back shield gas, and the heat was flowed to the welded portion at a flow rate of 10 L / min.

Regarding the obtained welded joint, the one in which the bead on the back surface side was formed over the entire length of the weld line was judged to have no problem in the forming ability of the bead on the inner surface side of the alloy pipe, and was judged as "passed". Among them, the one in which the width of the back surface side bead is 2 mm or more over the entire length of the weld line is "excellent", and the one in which the width is less than 2 mm but the back surface side bead of 1 mm or more is formed is "acceptable". In this embodiment, the back surface side bead corresponds to the inner surface side bead formed when welding is performed from the outside of the alloy pipe.

After that, three cross sections were revealed from the welded joint, and if the bead height on the back surface side was 1.0 mm or less in all the cross sections, it was judged that the shape of the bead on the inner surface side of the alloy pipe was good. It was "passed". Among them, those having a bead height on the back surface side of 0.8 mm or less in all cross sections were rated as "excellent", and others were rated as "possible". The results are summarized in Table 4 below.

The test pieces using alloy types A to H and L to N all satisfied the provisions of the present invention, and the forming ability and shape of the bead on the back surface side were good. Of these, the test piece N1 using the alloy type N satisfied the specified range of the formula (i), and therefore satisfied both the forming ability and the height of the bead on the back surface side.

On the other hand, the S, O and Sn contents of the test bodies I1 and K1 using the alloy types I and K did not satisfy the formula (i) and were higher than the specified range. Therefore, the molten metal hangs down remarkably, and the height of the bead on the back surface side does not satisfy the target. In the test piece J1 using the alloy type J, the relationship between the S and O contents did not satisfy the formula (i) and was lower than the specified range. Therefore, the melting in the plate thickness direction was not sufficient, and the target ability to form the back surface side bead could not be obtained.

The test bodies O1 and P1 using the alloy types O and P each have a Sn content exceeding the specified range, or the S, O and Sn contents are higher than the range specified in the formula (i). For this reason, the molten metal hangs down significantly, and the target height of the bead on the back surface side is not satisfied. Further, in the test piece Q1 using the alloy type Q, the contents of S, O and Sn did not satisfy the formula (i). Therefore, the melting in the plate thickness direction was not sufficient, and the ability to form the bead on the back surface side did not satisfy the target.

According to the present invention, it is possible to obtain a Ni-based alloy tube in which the inner bead is stably formed during butt welding and the excess height is not excessive.

Claims (6)

The chemical composition is by mass%,
C: 0.005-0.080%,
Si: 0.01-0.50%,
Mn: 0.01-0.50%,
P: 0.015% or less,
S: 0.0001 to 0.0030%,
Cr: 20.0 to 23.5%,
Mo: 8.0-10.5%,
Ti: 0.01-0.40%,
N: 0.0010 to 0.0400%,
Al: 0.01-0.40%,
O: 0.0004 to 0.0100%,
Including one or more selected from Nb and Ta,
Sn: 0 to 0.010%,
The rest is Ni and impurities,
A Ni-based alloy tube satisfying the following equations (i) and (ii).
0.0010 ≦ S + 2O + 0.2Sn ≦ 0.0180 ・ ・ ・ (i)
2.50 ≤ Nb + Ta ≤ 4.60 ... (ii)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero. The Ni-based alloy pipe according to claim 1, wherein the arithmetic mean roughness Ra in the longitudinal direction of the pipe is 7.0 μm or less on the inner surface side of the Ni-based alloy pipe. The chemical composition is, in mass%, instead of a portion of the Ni.
The Ni-based alloy tube according to claim 1 or 2, which contains Fe: 5.50% or less. The Ni-based alloy tube according to any one of claims 1 to 3, wherein the chemical composition contains one or more selected from Cu and Co instead of a part of the Ni, and satisfies the following formula (iii). ..
0.01 ≤ Cu + Co ≤ 1.50 ... (iii)
However, the element symbol in the above formula represents the content (mass%) of each element contained in the Ni-based alloy, and if it is not contained, it is set to zero. The chemical composition is, in mass%, instead of a portion of the Ni.
W: 1.00% or less,
V: 0.40% or less,
Ca: 0.0030% or less,
Mg: 0.0030% or less,
B: 0.0100% or less, and REM: 0.0100% or less,
The Ni-based alloy tube according to any one of claims 1 to 4, which contains one or more selected from the above. A welded joint using the Ni-based alloy pipe according to any one of claims 1 to 5.

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