CN113718135B

CN113718135B - Ni-based alloy pipe and welded joint

Info

Publication number: CN113718135B
Application number: CN202110557676.0A
Authority: CN
Inventors: 平田弘征; 吉泽满; 小薄孝裕; 照沼正明
Original assignee: Nippon Steel and Sumitomo Metal Corp
Current assignee: Nippon Steel Corp
Priority date: 2020-05-22
Filing date: 2021-05-21
Publication date: 2022-12-09
Anticipated expiration: 2041-05-21
Also published as: EP3913102A1; CN113718135A; JP2021183720A

Abstract

The invention provides a Ni-based alloy pipe and a welded joint. A Ni-based alloy pipe whose chemical composition contains, 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%, 1 or more selected from Nb and Ta, and Sn:0 to 0.010 percent, any element and the balance: ni and impurities, and satisfies [0.0010 is more than or equal to S +2O +0.2Sn is more than or equal to 0.0180] and [2.50 is more than or equal to Nb + Ta is more than or equal to 4.60].

Description

Ni-based alloy pipe and welded joint

Technical Field

The present invention relates to a Ni-based alloy pipe and a welded joint.

Background

Chemical plants and power generation plants are provided with various facilities such as a flue gas treatment facility and a seawater treatment facility. The equipment is in a severe corrosion environment, and a plurality of substances such as chloride, hydrogen sulfide and the like which aggravate corrosion exist. Therefore, the raw materials used for the equipment and devices are required to have corrosion resistance in addition to strength. Therefore, as disclosed in patent documents 1 to 8, a Ni-based alloy is being developed which is supposed to be used for equipment and has improved corrosion resistance.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. S54-110918

Patent document 2: japanese laid-open patent publication No. 63-89637

Patent document 3: japanese laid-open patent publication No. 2-156034

Patent document 4: japanese patent laid-open publication No. 3-173732

Patent document 5: japanese laid-open patent publication No. 5-271832

Patent document 6: japanese laid-open patent publication No. 9-87786

Patent document 7: japanese laid-open patent publication No. 10-30140

Patent document 8: japanese patent laid-open publication No. 2012-72446

Disclosure of Invention

Problems to be solved by the invention

Among the equipment devices, there are equipment devices manufactured by assembling parts to each other by welding. In such an apparatus, the state of formation of a bead in the welded portion 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 are flow paths for a refrigerant or the like. Also, when used as a heat exchanger, various corrosive fluids flow inside the tubes. In this case, if the height of the weld formed inside the pipe by welding, that is, the weld margin, is too high, corrosive fluid remains and is concentrated in the weld toe where the weld surface and the surface of the base material intersect. As a result, corrosion tends to progress in the weld toe.

On the other hand, if the reduction of the weld margin is excessively pursued to reduce the heat input amount during welding, the abutting surface between the pipe and the tube cannot be completely melted, and it is difficult to form a stable weld. As a result, there is a problem that a weld defect occurs, and corrosive fluid is accumulated and concentrated in the weld defect, so that corrosion is likely to progress. However, these problems have not been examined at all in patent documents 1 to 8.

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

In view of the above, an object of the present invention is to solve the above problems and to provide a Ni-based alloy pipe and a welded joint that have excellent workability of a welded portion and can stably form an inner surface-side weld.

Means for solving the problems

The present invention has been made to solve the above problems, and its gist lies in the following Ni-based alloy pipe and welded joint.

(1) A Ni-based alloy pipe having a chemical composition comprising, in mass%

C：0.005～0.080％、

Si：0.01～0.50％、

Mn：0.01～0.50％、

P: less than 0.015%,

S：0.0001～0.0030％、

Cr：20.0～23.5％、

Mo：8.0～10.5％、

Ti：0.01～0.40％、

N：0.0010～0.0400％、

Al：0.01～0.40％、

O：0.0004～0.0100％、

1 or more selected from Nb and Ta, and,

Sn：0～0.010％、

Fe：0～5.50％、

Cu：0～1.50％、

Co：0～1.50％、

W：0～1.00％、

V：0～0.40％、

Ca：0～0.0030％、

Mg：0～0.0030％、

B：0～0.0100％、

REM：0～0.0100％，

the balance of Ni and impurities,

and satisfies the following formulae (i) and (ii).

0.0010≤S+2O+0.2Sn≤0.0180···(i)

2.50≤Nb+Ta≤4.60···(ii)

In the above formula, the element symbol represents the content (mass%) of each element contained in the Ni-based alloy, and is 0 when not contained.

(2) The Ni-based alloy pipe according to the item (1), wherein an arithmetic mean deviation Ra in a longitudinal direction of the pipe on an inner surface side of the Ni-based alloy pipe is 7.0 μm or less.

(3) The Ni-based alloy pipe according to the item (1) or (2), wherein the chemical composition contains 1 or more selected from Cu and Co and satisfies the following formula (iii).

0.01≤Cu+Co≤1.50···(iii)

(4) The Ni-based alloy pipe according to any one of (1) to (3) above, wherein the chemical composition contains, in mass%, (iii) a chemical composition selected from

Sn：0.001～0.010％、

Fe：0.01～5.50％、

W：0.01～1.00％、

V：0.01～0.40％、

Ca：0.0001～0.0030％、

Mg：0.0001～0.0030％、

B:0.0002 to 0.0100%, and

REM: more than 1 of 0.0001-0.0100%.

(5) A welded joint using the Ni-based alloy pipe according to any one of (1) to (4) above.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to obtain a Ni-based alloy pipe capable of stably forming an inner surface-side weld having good use properties of a weld

Drawings

Fig. 1 is a diagram showing a groove shape in the example.

Detailed Description

The present inventors have studied the weld of the Ni-based alloy pipe and obtained the following findings (a) to (d).

(a) In the butt welding, the shape of the inner surface-side weld of the formed pipe is affected by the contents of S and O contained in the Ni-based alloy pipe. The present inventors have also clarified that: when the contents of S and O are small, the inner surface side weld cannot be stably formed, and an unmelted butt surface remains locally.

On the other hand, when the S and O contents are too large, the bead is stably formed, but the bead height of the bead becomes too high. Therefore, when used as an alloy pipe, corrosive fluid stays in the vicinity of the weld, and corrosion is likely to progress. Therefore, in order to stably form a bead and prevent the bead height from excessively increasing, it is necessary to adjust the S content and the O content to predetermined ranges.

(b) The reason why S and O affect the formation of the weld seam is as follows. S and O are surface active elements, whereby inward convection is enhanced in the weld pool at the time of welding. As a result, the welding heat is easily transferred in the depth direction, and the weld can be stably formed. On the other hand, if S and O are contained excessively, the surface tension of the molten metal decreases excessively, and the molten metal tends to sink. As a result, the shape of the bead becomes a convex shape (hereinafter simply referred to as "convex shape") which is excessively raised, and the bead height becomes high.

(c) Further, the shape of the inner surface side bead of the pipe is affected by the surface roughness in the longitudinal direction of the pipe inner surface. The present inventors have clarified that: when the surface roughness is large, the bead height becomes high, and the bead tends to be convex. Therefore, it is desirable to control the surface roughness to a predetermined range. In particular, when the surface roughness in the longitudinal direction of the inner surface of the pipe is large, the molten metal is suppressed from spreading in the width direction, the shape of the weld bead becomes convex, and the weld bead height tends to increase.

(d) Further, the present inventors have clarified that: the shape of the inner surface-side weld is also affected by the Sn content. When Sn is contained, the penetration depth becomes large, and the inner surface-side weld is easily and stably formed. On the other hand, if the content is excessively large, the penetration may be excessive, and the inner surface side bead may easily become convex. The reason is considered to be that Sn evaporates from the surface of the molten pool during soldering, and the concentration of the arc increases. Therefore, when Sn is contained, in order to obtain an inner surface-side bead having an appropriate shape, the Sn content needs to be controlled to a predetermined range, and the relationship between the S content, the O content, and the Sn content needs to satisfy the predetermined range.

The present invention has been made based on the above findings. The features of the present invention will be described in detail below.

1. Chemical composition of alloy pipe

The reasons for limiting each element are as follows. In the following description, "%" relating to the content means "% by 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, if C is contained excessively, it bonds to Cr by a welding heat cycle, and carbides are formed at grain boundaries in the welding heat affected zone. As a result, a Cr-deficient layer is generated in the vicinity of the grain boundary, 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 still more preferably 0.025% or less.

Si：0.01～0.50％

Si has a deoxidizing effect. Therefore, the Si content is set to 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 excessively, the structural stability of the alloy is lowered and the weld crack sensitivity is increased. In addition, the weld bead on the inner surface side is sometimes difficult to form stably. 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：0.01～0.50％

Mn has a deoxidizing effect similar to Si. In addition, there is an effect of improving the structure stability, and it contributes to a large extent to stably forming the weld of 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 excessively, hot workability is degraded. 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: less than 0.015%

P is contained as an impurity in the Ni-based alloy, and the weld crack sensitivity is significantly increased. 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 an excessive reduction leads to an increase in manufacturing costs. Therefore, the P content is preferably 0.001% or more, and more preferably 0.002% or more.

S：0.0001～0.0030％

S 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 improving the forming ability of the inner surface-side weld when welded together with O. Therefore, the S content is set to 0.0001% or more. The S content is preferably 0.0002% or more, more preferably 0.0003% or more. However, if S is contained excessively, the weld bead on the inner surface side of the pipe becomes convex and weld crack sensitivity increases. 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. The S, O and Sn should satisfy the following expression (i).

Cr：20.0～23.5％

Cr is an element necessary for ensuring corrosion resistance. Cr forms a passive film particularly 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 further preferably 21.2% or more. However, if Cr is contained excessively, the structure stability is lowered. Therefore, the Cr content is 23.5% or less. The Cr content is preferably 23.3% or less, more preferably 23.0% or less, and further 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 8.0% or more. The Mo content is preferably 8.2% or more, more preferably 8.5% or more, and further preferably 8.7% or more. However, if Mo is contained excessively, the structure stability is lowered. Further, since Mo is an expensive element, the manufacturing cost may increase. Therefore, the Mo content is 10.5% or less. The Mo content is preferably 10.3% or less, more preferably 10.0% or less, and further preferably 9.8% or less.

Ti：0.01～0.40％

Ti forms carbides, contributes to strengthening, and reduces deterioration of corrosion resistance at grain boundaries by suppressing the formation of Cr carbides. 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 further preferably 0.10% or more. However, if Ti is contained excessively, ti carbides and carbonitrides precipitate in large amounts, 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 further preferably 0.32% or less.

N：0.0010～0.0400％

N has the effect of contributing to tissue stability and improving 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 further preferably 0.0040% or more. However, if N is contained excessively, nitrides precipitate, 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：0.01～0.40％

Al has a deoxidizing effect. And contributes to an improvement in oxidation resistance at high temperatures. Therefore, the Al content is set to 0.01%. The Al content is preferably 0.02% or more, more preferably 0.03% or more. The Al content is more preferably 0.05% or more. However, if Al is contained excessively, a brittle compound is formed with Ni, and hot workability is deteriorated. In addition, the weld bead on the inner surface side is sometimes difficult to form stably. 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 still more preferably 0.28% or less.

O：0.0004～0.0100％

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 improving the formability of a weld bead 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, more preferably 0.0008% or more. However, if O is contained excessively, the inner surface side weld of the pipe becomes convex and hot workability is degraded. Therefore, the O content is 0.0100% or less. The O content is preferably 0.0080% or less, more preferably 0.0060% or less. The following expression (i) is required to be satisfied between O, S and Sn.

1 or more selected from Nb and Ta: 2.50% or more and 4.60% or less in total

Both Nb and Ta are bonded to carbon to form carbide, similarly to Ti, and contribute to strengthening, while suppressing the formation of Cr carbide and reducing deterioration of corrosion resistance of grain boundaries. Therefore, 1 or more selected from Nb and Ta are contained, and the total content of these elements needs to satisfy the following formula (ii).

2.50≤Nb+Ta≤4.60···(ii)

(ii) When the value of the intermediate formula, which is the total content of Nb and Ta in the formula, is less than 2.50%, the effects of improving strength and reducing deterioration of grain boundary corrosion resistance cannot be obtained. Therefore, the value of the intermediate formula in the formula (ii) is 2.50% or more. (ii) The value of the intermediate formula in the formula (iv) is preferably 2.70% or more, more preferably 3.00% or more.

On the other hand, if the value of the intermediate formula of formula (ii) exceeds 4.60%, a large amount of Nb and Ta carbides and carbonitrides precipitate, resulting in a decrease in ductility. Further, the weld crack sensitivity is also increased. Therefore, the value of the intermediate formula in the formula (ii) is 4.60% or less, preferably 4.40% or less, and more preferably 4.20% or less.

In addition to the above elements, sn may be further contained in the following ranges in the chemical composition.

Sn：0～0.010％

Sn has the effect of increasing the penetration depth during welding and improving the ability to form a weld on the inner surface side of the pipe. Therefore, it may be contained as necessary. However, if Sn is contained excessively, hot workability is lowered and solder crack sensitivity is increased. Further, the inner surface side bead is likely to be convex. Therefore, the Sn content is 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-described effects, the Sn content is preferably 0.001% or more, more preferably 0.002% or more, and still more preferably 0.003% or more. Sn, S, and O should satisfy the following expression (i).

As described above, S, O and Sn effectively contribute to the formation of a weld bead on the inner surface side of the tube, and therefore, the Ni-based alloy tube of the present invention needs to satisfy the following expression (i) of the relational expression between the S content, the O content and the Sn content.

0.0010≤S+2O+0.2Sn≤0.0180···(i)

In the above formula, the element symbol represents the content (mass%) of each element contained in the Ni-based alloy, and is 0 when not contained. In the above formula, when the Sn content is less than 0.001%, the treatment is performed with Sn = 0.

S and O are interface active elements, and have a function of enhancing inward convection in the molten pool during welding. In addition, sn contributes to the formation of an arc conduction path and has an effect of increasing the concentration of an arc. Then, the welding heat is transferred in the depth direction of the center of the molten pool. As a result, these elements have an effect of stably forming the inner surface side bead, but when the value of the intermediate formula of formula (i) is less than 0.0010%, the effect cannot be obtained. Therefore, the value of the intermediate formula in the formula (i) is 0.0010% or more. (i) The value of the intermediate formula in the formula is preferably 0.0012% or more, more preferably 0.0015% or more.

On the other hand, if the value of the intermediate formula of the formula (i) exceeds 0.0180%, the surface tension of the molten metal becomes small, or melting at the center of the molten pool is promoted to cause a dip. As a result, the weld bead becomes convex, and the weld bead cannot be stably formed on the inner surface side of the pipe. Therefore, the value of the intermediate formula in the formula (i) is 0.0180% or less. (i) The value of the intermediate formula in the formula (iv) is preferably 0.0175% or less, and more preferably 0.0170% or less.

In addition to the above elements, the chemical composition may further contain Fe within the following ranges.

Fe：0～5.50％

Fe is effective for improving hot workability. And also contributes to the reduction of alloy cost. Therefore, it may be contained as necessary. However, if Fe is contained excessively, the tissue stability is lowered. 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 effects, the Fe content is preferably 0.01% or more, more preferably 0.50% or more, and further preferably 1.50% or more.

In addition to the above elements, the chemical composition may further contain Cu and Co within the ranges shown below.

1 or more selected from Cu and Co: 1.50% or less in total

Cu and Co have the effect of improving the structural stability and corrosion resistance in non-oxidizing acid and chloride environments. Therefore, 1 or more species selected from Cu and Co may be contained as necessary. When contained, the chemical composition preferably satisfies the following formula (iii).

0.01≤Cu+Co≤1.50···(iii)

(iii) When the value of the intermediate formula, which is the total content of Cu and Co in the formula, is less than 0.01%, the above-described effect is difficult to obtain. Therefore, the value of the intermediate formula in the formula (iii) is preferably 0.01% or more, more preferably 0.02% or more, and further preferably 0.03% or more. However, if the value of the intermediate formula in the formula (iii) exceeds 1.50%, hot workability is deteriorated and production cost is increased. Therefore, the value of the intermediate formula in the formula (iii) is preferably 1.50% or less, more preferably 1.30% or less. (iii) The value of the intermediate formula in the formula (iv) is more preferably 1.00% or less.

In the chemical composition, 1 or more selected from W, V, ca, mg, B and REM may be further contained in the range shown below in addition to the above elements. The reason for limiting each element will be described.

W：0～1.00％

W improves corrosion resistance in the presence of non-oxidizing acids and chlorides. Therefore, it may be contained as necessary. However, if W is contained excessively, the tissue stability is lowered. Also, since it is an expensive element, the manufacturing cost may increase. Therefore, the W content is 1.00% or less. The W content is preferably 0.90% or less, more preferably 0.80% or less. On the other hand, in order to obtain the above effects, the W content is preferably 0.01% or more, more preferably 0.02% or more.

V：0～0.40％

V forms carbide by bonding with carbon, suppresses the generation of Cr carbide, and reduces deterioration of corrosion resistance at grain boundaries. Therefore, it may be contained as necessary. However, if V is contained excessively, V carbides and carbonitrides precipitate in a large amount, and ductility is lowered. Therefore, the V content is set to 0.40% or less. The V content is preferably 0.35% or less, more preferably 0.30% or less. On the other hand, in order to obtain the above-described effects, the V content is preferably 0.01% or more, more preferably 0.02% or more.

Ca：0～0.0030％

Ca has an effect of improving hot workability. Therefore, it may be contained as necessary. However, if Ca is contained excessively, it bonds with oxygen, and the cleaning property is remarkably reduced. As a result, hot workability is rather deteriorated. 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 effects, the Ca content is preferably 0.0001% or more, and more preferably 0.0003% or more.

Mg：0～0.0030％

Mg has the effect of improving hot workability in the same manner as Ca. Therefore, it may be contained as necessary. However, if Mg is contained excessively, it bonds with oxygen, and the cleaning property is significantly reduced. As a result, 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 effects, the Mg content is preferably 0.0001% or more, more preferably 0.0003% or more.

B：0～0.0100％

B is segregated in the grain boundary at high temperature, thereby strengthening the grain boundary and improving hot workability. Therefore, it may be contained as necessary. However, if B is contained excessively, the weld 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-described effects, the B content is preferably 0.0002% or more, more preferably 0.0005% or more.

REM：0～0.0100％

REM has the effect of improving hot workability during production, similarly to Ca and Mg. Therefore, it may be contained as necessary. However, when REM is contained excessively, it is bonded to oxygen, and the cleaning property is remarkably lowered. As a result, hot workability is rather lowered. Therefore, the REM content is set to 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 effects, the REM content is preferably 0.0001% or more, more preferably 0.0003% or more. Wherein REM represents Sc, Y and lanthanoid elements, and the REM content represents the total amount of the contents of these elements.

In the chemical composition of the Ni-based alloy of the present invention, the balance is Ni and impurities. The "impurities" are components that are mixed in due to various factors such as raw materials and production steps in the industrial production of Ni-based alloys, although not intentionally added elements, and are allowed within a range that does not adversely affect the present invention.

2. Surface roughness of alloy pipe

The weld is formed when welding the ends of the alloy tube. In order to form a good weld, it is preferable to control the arithmetic mean deviation Ra in the longitudinal direction on the inner surface side of the alloy pipe. The surface roughness of the alloy pipe is the surface roughness after the final step in the production process. That is, although the surface roughness of the alloy pipe varies during the production process, the surface roughness in the longitudinal direction of the pipe after the final step may satisfy the range specified in the present invention in order to obtain the effect of the present invention, and is not dependent on the surface roughness during the production.

When the arithmetic mean deviation Ra in the longitudinal direction of the tube exceeds 7.0 μm on the inner surface side of the Ni-based alloy tube, wetting of the weld metal on the inner surface of the tube is inhibited, and the weld metal is less likely to spread in the width direction, i.e., the tube circumference. As a result, the bead is likely to be convex, and the bead height is likely to be high. Therefore, the arithmetic mean deviation Ra in the longitudinal direction of the tube is preferably 7.0 μm or less on the inner surface side of the Ni-based alloy tube. The arithmetic mean deviation Ra is preferably 5.0 μm or less, more preferably 3.0 μm or less. The lower limit of the arithmetic mean deviation Ra is not particularly limited, but is usually 0.1 to 1.0 μm or more in most cases when the production method described later is used.

Wherein the arithmetic mean deviation Ra is in the range of JIS B0601: 2001, a contact surface roughness measuring device can be used for the measurement.

3. Welded joint

The welded joint of the Ni-based alloy pipe can be obtained by butt-welding the pipe ends of the Ni-based alloy pipe to each other under predetermined conditions. The welded joint of the Ni-based alloy pipe has: the molten metal solidifies to become the weld metal of the joint portion, and the base portion. The base material portion includes: a welding heat affected part affected by heat input due to welding. The base material portion other than the welding heat affected zone is subjected to the chemical composition, surface roughness, and other properties of the Ni-based alloy pipe described in the above items 1 and 2. The weld portion refers to a weld metal and a weld heat affected zone.

4. Manufacturing method

A preferred method for producing the Ni-based alloy pipe of the present invention will be described. The Ni-based alloy pipe of the present invention can obtain its effects as long as it has the above-described structure, regardless of the production method, and can be stably produced by, for example, the following production method.

4-1. Ni-based alloy pipe

First, a Ni-based alloy ingot, which is a raw material of the Ni-based alloy pipe, is manufactured. The Ni-based alloy ingot is preferably produced by melting an alloy having the above chemical composition in an electric furnace or the like, removing impurities by refining, and then casting. Next, the obtained ingot is preferably hot forged to form a cylindrical bar-shaped billet. Then, the obtained bar-shaped billet is processed to be formed into a tube shape.

Specifically, it is preferable to perform cold rolling or cold drawing after hot extrusion of the strip. In the processing, softening heat treatment and intermediate pickling may be performed as needed. Then, as the heat treatment, the alloy pipe is preferably subjected to solution heat treatment. After the solutionizing treatment, pickling or processing may be performed as necessary.

Among them, the following steps are preferably performed so that the arithmetic mean deviation Ra in the longitudinal direction of the tube is 7.0 μm or less. Specifically, the solution treatment is preferably performed by heating at 950 to 1230 ℃ for 1 to 15 minutes and water-cooling. Further, it is preferable to subject the inner surface of the tube to any of grinding, machining such as grinding, blasting, and the like.

Although the arithmetic mean deviation Ra varies during 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, and is not related to the surface roughness in the middle process.

4-2. Ni-based alloy pipe welded joint

The welded joint can be obtained by welding the end of the alloy pipe using the Ni-based alloy pipe of the present invention as a raw material. The welding method is not particularly limited, and welding may be performed by arc welding, for example. Further, the conditions for arc welding are preferably set to a heat input amount in the range of 4 to 20kJ/cm, for example. In addition, in the welding, it is preferable to use Ar gas as a shielding gas or a back gas. The flow rate of the gas flowing through the weld is preferably appropriately adjusted.

The chemical composition of the welding material (filler metal) to be used is also not particularly limited, but the following composition is preferred. Namely, it is preferable to contain 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, 4.20% or less in total, and Ti:1.50% or less, V:0.35% or less, N:0.0500% or less, al:1.50% or less, O:0.0004 to 0.0100%, the balance being Ni and impurities, the contents of S and O satisfying the following expression (a).

0.0010≤S+2O≤0.0180···(a)

In the above formula, the element symbol represents the content (mass%) of each element contained in the welding material, and is 0 when not contained.

The present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Examples

Alloys having chemical compositions shown in table 1 were melted to produce ingots. Then, hot forging and hot rolling were performed to adjust the thickness to 10mm. Then, the scale formed on the surface was removed by acid washing. At this time, the arithmetic mean deviation Ra was about 10 μm in all the steel grades. Then, assuming a manufacturing process of the alloy pipe, an alloy sheet of 3mm was obtained by cold rolling while softening heat treatment and intermediate pickling were performed in the middle.

Next, the alloy sheet was subjected to a solutionizing treatment in which the alloy sheet was held at 1150 ℃ for 10 minutes in a hydrogen furnace and then water-cooled. Then, a plate material having a width of 50mm and a length of 100mm was cut out of the alloy plate. Then, as shown in table 2, a part of the cut-out plate material was assumed to be the inner surface side of the alloy pipe, and shot blasting was performed only on one surface. On the other hand, the plate material not subjected to shot blasting was ground on one side or ground 1 to 5 times using a grindstone having a grain size of 40 or 60. In table 2, for example, grinding (# 40 × 1 times) means grinding 1 time with a grindstone having a grain size of No. 40.

[ Table 1]

[ Table 2]

TABLE 2

* Are shown outside the scope specified by the present invention.

* Denotes deviations from the preferred scope of the present invention.

The arithmetic mean deviation was measured for each plate using a contact roughness meter. Further, 2 prepared plate materials of each alloy type were prepared, and the end faces in the rolling direction were subjected to beveling as shown in fig. 1. The beveled end surfaces of these plate materials were butted against each other, and filler metal having a chemical composition shown in table 3 and an outer diameter of 1.0mm was used to perform root welding, thereby obtaining a welded joint. The heat input at the time of welding was set to about 5kJ/cm, and Ar gas was used as a shielding gas and a protective back gas, and the flow rate was 10L/min.

[ Table 3]

TABLE 3

In the obtained welded joint, the determination that the back-side weld was formed over the entire length of the weld line was no problem in the ability to form the inner-surface-side weld of the alloy pipe, and was regarded as "pass". Here, the width of the back side bead of the entire length of the weld line is 2mm or more and is referred to as "excellent", and the width of the back side bead of less than 2mm but 1mm or more is formed and is referred to as "ok". In the present embodiment, the back-side weld corresponds to an inner-surface-side weld formed when welding is performed from the outside of the alloy pipe.

Then, 3 cross sections were formed from the welded joint, and the shape of the inner surface side bead of the alloy pipe was judged to be good when the height of the back side bead was 1.0mm or less in all the cross sections, and was regarded as "good". Among them, the height of the weld on the back side in all the cross sections is 0.8mm or less and is referred to as "excellent", and the other portions are referred to as "acceptable". The results are summarized in table 4 below.

[ Table 4]

TABLE 4

* Are shown outside the scope specified by the present invention.

Underlining indicates characteristics that deviate from the objectives of the present invention.

The test pieces using alloy types A to H and L to N all satisfy the specification of the present invention, and the weld bead formation ability and shape are good. Among them, the test piece N1 using the alloy type N satisfies the predetermined range of the formula (i), and therefore satisfies both the forming ability and the height of the inner surface side bead.

On the other hand, the contents of S, O and Sn in the test pieces I1 and K1 using the alloy types I and K do not satisfy the formula (I), and are higher than the predetermined range. Therefore, the sagging of the molten metal is significant, and the height of the back side bead does not satisfy the target. The relation between the contents of S and O in the test specimen J1 using the alloy type J does not satisfy the formula (i), and is less than the predetermined range. Therefore, the melting in the plate thickness direction is insufficient, and the formation capability of the intended inner surface side bead is not obtained.

The test pieces O1 and P1 using the alloy species O and P had Sn contents exceeding the predetermined ranges or S, O and Sn contents exceeding the ranges specified by the formula (i), respectively. Therefore, the molten metal has a large sag and does not satisfy the intended back-side bead height. In addition, the contents of S, O and Sn in the test piece Q1 using the alloy type Q do not satisfy the formula (i). Therefore, the melting in the plate thickness direction is insufficient, and the forming ability of the inner surface side bead is not satisfactory.

Industrial applicability

According to the present invention, a Ni-based alloy pipe can be obtained in which an inner surface side weld is stably formed during butt welding and the weld margin is not excessively high.

Claims

1. A Ni-based alloy pipe having a chemical composition comprising, in mass%

C：0.005～0.080％、

Si：0.01～0.50％、

Mn：0.01～0.50％、

P: less than 0.015%,

S：0.0001～0.0030％、

Cr：20.0～23.5％、

Mo：8.0～10.5％、

Ti：0.01～0.40％、

N：0.0010～0.0400％、

Al：0.01～0.40％、

O：0.0004～0.0100％、

Sn：0.001～0.010％、

1 or more selected from Nb and Ta, and,

Fe：0～5.50％、

Cu：0～1.50％、

Co：0～1.50％、

W：0～1.00％、

V：0～0.40％、

Ca：0～0.0030％、

Mg：0～0.0030％、

B：0～0.0100％、

REM：0～0.0100％，

the balance of Ni and impurities,

and satisfies the following formulae (i) and (ii),

0.0010≤S+2O+0.2Sn≤0.0180···(i)

2.50≤Nb+Ta≤4.60···(ii)

wherein the element symbol in the formula represents the content of each element in the Ni-based alloy in mass%, and is 0 when not contained,

wherein the arithmetic mean deviation Ra of the tube in the longitudinal direction is 7.0 μm or less on the inner surface side of the tube.

2. The Ni-based alloy tube according to claim 1, wherein the chemical composition contains 1 or more selected from Cu and Co and satisfies the following formula (iii),

0.01≤Cu+Co≤1.50···(iii)

wherein the element symbol in the formula represents the content of each element in the Ni-based alloy in mass%, and is 0 when not contained.

3. The Ni-based alloy pipe according to claim 1 or 2, wherein the chemical composition contains, in mass%, a chemical composition selected from the group consisting of

Fe：0.01～5.50％、

W：0.01～1.00％、

V：0.01～0.40％、

Ca：0.0001～0.0030％、

Mg：0.0001～0.0030％、

B:0.0002 to 0.0100%, and

REM: more than 1 of 0.0001-0.0100%.

4. A welded joint using the Ni-based alloy pipe according to any one of claims 1 to 3.