CN113718135B - Ni-based alloy pipe and welded joint - Google Patents

Abstract

The invention provides a Ni-based alloy pipe and a welded joint. A Ni-based alloy tube, the chemical composition of which includes 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%, one selected from Nb and Ta Above, and Sn: 0-0.010%, any element, balance: Ni and impurities, and satisfy [0.0010≤S+2O+0.2Sn≤0.0180] and [2.50≤Nb+Ta≤4.60].

Description

Ni-based alloy pipes and welded joints

technical field

The invention relates to a Ni base alloy pipe and a welded joint.

Background technique

Chemical equipment and power generation equipment are equipped with various equipment such as equipment for exhaust gas treatment and equipment for seawater treatment. The equipment is a harsh corrosive environment, and there are many substances that aggravate corrosion, such as chlorides and hydrogen sulfide. Therefore, in addition to strength, corrosion resistance is also required for materials used in equipment. Therefore, as disclosed in Patent Documents 1 to 8, Ni-based alloys that are supposed to be used in equipment and have improved corrosion resistance are being developed.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 54-110918

Patent Document 2: Japanese Patent Laid-Open No. 63-89637

Patent Document 3: Japanese Patent Application Laid-Open No. 2-156034

Patent Document 4: Japanese Patent Application Laid-Open No. 3-173732

Patent Document 5: Japanese Patent Application Laid-Open No. 5-271832

Patent Document 6: Japanese Patent Application Laid-Open No. 9-87786

Patent Document 7: Japanese Patent Application Laid-Open No. 10-30140

Patent Document 8: Japanese Patent Laid-Open No. 2012-72446

Contents of the invention

The problem to be solved by the invention

Among the equipment devices, there are those manufactured by assembling parts to each other by welding. In such an apparatus, the state of formation of the weld bead at the welded portion may affect the progress of corrosion.

For example, among heat exchangers, there is a heat exchanger manufactured by butt-welding and connecting a plurality of Ni-based alloy tubes serving as flow paths for refrigerant and the like. Also, when used as a heat exchanger, various corrosive fluids flow inside the tubes. At this time, if the height of the weld formed inside the pipe by welding, that is, the weld reinforcement is too high, the corrosive fluid will stagnate and accumulate in the weld toe where the surface of the weld intersects the surface of the base metal. As a result, there is a problem that corrosion tends to intensify at the weld toe.

On the other hand, if the heat input during welding is reduced by excessively pursuing the reduction of weld reinforcement, the butt surfaces of pipes cannot be completely melted, and it is difficult to form a stable weld. As a result, welding defects are generated, and the corrosive fluid stays and concentrates in the welding defects, and the corrosion tends to intensify. However, Patent Documents 1 to 8 have not conducted any studies on these problems.

Therefore, even if the pipe is manufactured from a Ni-based alloy with high corrosion resistance as a raw material, it is difficult to form a weld bead with an appropriate shape in which corrosion is unlikely to progress during butt welding. That is, during welding, there is a problem that it is difficult to obtain a Ni-based alloy pipe in which the weld bead is stably formed on the inner surface side and the weld bead reinforcement is not too high.

Based on the above, an object of the present invention is to solve the above-mentioned problems and to provide a Ni-based alloy pipe and a welded joint which have good usability of the welded part and can stably form an inner surface side weld.

solutions to problems

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

(1) A Ni-based alloy tube, the chemical composition of which contains in mass %

C: 0.005～0.080%,

Si: 0.01 to 0.50%,

Mn: 0.01～0.50%,

P: 0.015% or less,

S: 0.0001～0.0030%,

Cr: 20.0-23.5%,

Mo: 8.0～10.5%,

Ti: 0.01 to 0.40%,

N: 0.0010～0.0400%,

Al: 0.01 to 0.40%,

O: 0.0004～0.0100%,

One 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 is Ni and impurities,

And it satisfies the following formulas (i) and (ii).

0.0010≤S+2O+0.2Sn≤0.0180···(i)

2.50≤Nb+Ta≤4.60···(ii)

Here, the element symbols in the above formulas represent the content (mass %) of each element contained in the Ni-based alloy, and are set to 0 when not included.

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

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

0.01≤Cu+Co≤1.50···(iii)

Here, the element symbols in the above formulas represent the content (mass %) of each element contained in the Ni-based alloy, and are set to 0 when not included.

(4) The Ni-based alloy tube according to any one of the above (1) to (3), wherein the aforementioned chemical composition contains, in mass %, 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 to 0.0030%,

Mg: 0.0001～0.0030%,

B: 0.0002 to 0.0100%, and

REM: 1 or more of 0.0001 to 0.0100%.

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

The effect of the 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 usability of the welded portion

Description of drawings

FIG. 1 is a diagram showing the shape of a groove in an example.

detailed description

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

(a) At the time of butt welding, the shape of the formed inner surface side weld of the pipe is affected by the contents of S and O contained in the Ni-based alloy pipe. Furthermore, the inventors of the present invention have found that when the contents of S and O are small, the weld seam on the inner surface side cannot be stably formed, and an unmelted butt joint surface remains locally.

On the other hand, when the S and O contents are too high, the above-mentioned weld bead is stably formed, but the weld reinforcement of the weld bead becomes too high. Therefore, when used as an alloy pipe, the corrosive fluid stays near the weld, and the corrosion is easy to aggravate. Therefore, in order to form a weld bead stably and prevent the weld bead reinforcement from becoming excessively high, it is necessary to adjust the S content and the O content to a predetermined range.

(b) The reason why S and O affect the formation of the weld can be considered as follows. S and O are surface active elements, thereby enhancing inward convection in the weld pool during welding. As a result, welding heat is easily transmitted in the depth direction, and a weld bead can be stably formed. On the other hand, when S and O are excessively contained, the surface tension of the molten metal decreases excessively, and the molten metal tends to sag. As a result, the shape of the weld bead becomes an excessively raised convex shape (hereinafter simply referred to as "convex shape"), and the weld bead reinforcement becomes high.

(c) In addition, the shape of the weld bead on the inner surface side of the pipe is affected by the surface roughness in the longitudinal direction of the inner surface of the pipe. The inventors of the present invention have found that when the above-mentioned surface roughness is large, the weld reinforcement becomes high and tends to be convex. Therefore, it is desirable to control the surface roughness within a prescribed range. In particular, when the surface roughness in the longitudinal direction of the pipe inner surface is large, the spread of molten metal in the width direction is suppressed, the shape of the weld bead becomes convex, and the weld bead reinforcement tends to become high.

(d) Furthermore, the inventors of the present invention also found out that the shape of the weld bead on the inner surface side is also affected by the Sn content. When Sn is contained, the depth of penetration becomes large, and the weld bead on the inner surface side tends to be stably formed. On the other hand, when it is contained excessively, the penetration depth becomes excessive, and the weld bead on the inner surface side tends to become convex. The reason for this is considered to be that Sn evaporates from the surface of the molten pool during welding to increase the concentration of the arc. Therefore, in the case where Sn is contained, in order to obtain a suitable shape of the inner surface side weld, the Sn content needs to be controlled within 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 was made based on the above findings. Next, each feature of the present invention will be described in detail.

1. The chemical composition of the alloy tube

The reason for limitation of each element is as follows. In addition, in the following description, "%" concerning content means "mass %".

C: 0.005～0.080%

C has the effect of stabilizing tissue. Therefore, the C content is made 0.005% or more. The C content is preferably 0.008% or more, more preferably 0.010% or more, and still more preferably 0.012% or more. However, if C is contained in excess, it bonds with Cr due to welding heat cycles, and carbides are formed at the grain boundaries in the weld heat-affected zone. As a result, a Cr deficient layer is formed in the vicinity of the grain boundary, which lowers the corrosion resistance. Therefore, the C content is made 0.080% or less. The C content is preferably 0.050% or less, more preferably 0.030% or less, more preferably 0.025% or less.

Si: 0.01 to 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 excessively contained, the structural stability of the alloy will be reduced, and the susceptibility to welding cracks will be increased. In addition, it may be difficult to stably form the weld bead on the inner surface side. Therefore, the Si content is made 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 similarly to Si. In addition, it has the effect of improving the stability of the structure, and contributes to the stable formation of the weld seam on the inner surface side to a large extent. 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 will be reduced. Therefore, the Mn content is made 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 contained in the Ni-based alloy as an impurity will significantly increase the susceptibility to welding cracks. Therefore, the P content is made 0.015% or less. The P content is preferably 0.013% or less, more preferably 0.012% or less. It is preferable to reduce the P content as much as possible, but an excessive reduction leads to an increase in production cost. Therefore, the P content is preferably 0.001% or more, more preferably 0.002% or more.

S: 0.0001～0.0030%

S is usually contained in Ni-based alloys as an impurity, but in the alloy tube of the present invention, it has the effect of improving the weld bead formation ability on the inner surface side during welding 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 seam on the inner surface side of the pipe becomes convex and increases the susceptibility to weld cracking. Therefore, the S content is made 0.0030% or less. The S content is preferably 0.0025% or less, more preferably 0.0020% or less. It should be noted that the relationship between S, O and Sn needs to satisfy the following formula (i).

Cr: 20.0-23.5%

Cr is an element essential for securing corrosion resistance. In particular, Cr 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 still more preferably 21.2% or more. However, if Cr is contained in excess, the tissue stability will decrease. 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, even more preferably 22.8% or less.

Mo: 8.0-10.5%

Mo improves corrosion resistance in an environment where non-oxidizing acids and chlorides exist. 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 still more preferably 8.7% or more. However, if Mo is contained in excess, the structure stability will decrease. Further, since Mo is an expensive element, the production cost increases. Therefore, the Mo content is made 10.5% or less. The Mo content is preferably 10.3% or less, more preferably 10.0% or less, still more preferably 9.8% or less.

Ti: 0.01 to 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 still more preferably 0.10% or more. However, if Ti is excessively contained, a large amount of Ti carbides and carbonitrides will precipitate, and the ductility will decrease. Therefore, the Ti content is made 0.40% or less. The Ti content is preferably 0.38% or less, more preferably 0.35% or less, and still more preferably 0.32% or less.

N: 0.0010～0.0400%

N has the effect of contributing to structure stability and improving pitting 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 still more preferably 0.0040% or more. However, if N is excessively contained, nitrides are precipitated to lower the ductility. Therefore, the N content is made 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. In addition, it contributes to the improvement of oxidation resistance at high temperature. Therefore, the Al content was 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 will be formed with Ni, and hot workability will fall. In addition, it may be difficult to stably form the weld bead on the inner surface side. Therefore, the Al content is made 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 usually contained as an impurity in Ni-based alloys, but in the alloy pipe of the present invention, it has the effect of improving the weld bead formation ability on the inner surface side of the pipe together with S during welding. Therefore, the O content is made 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 weld bead on the inner surface side of the pipe becomes convex, and the hot workability decreases. Therefore, the O content is made 0.0100% or less. The O content is preferably 0.0080% or less, more preferably 0.0060% or less. It should be noted that the relationship between O and S and Sn needs to satisfy the formula (i) described later.

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

Like Ti, both Nb and Ta bond to carbon to form carbides, contribute to strengthening, suppress the formation of Cr carbides, and reduce the deterioration of the corrosion resistance of grain boundaries. Therefore, at least one selected from Nb and Ta is included, and the total content of these elements needs to satisfy the following formula (ii).

2.50≤Nb+Ta≤4.60···(ii)

Here, the element symbols in the above formulas represent the content (mass %) of each element contained in the Ni-based alloy, and are set to 0 when not included.

(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 effect of improving the strength and reducing the deterioration of the grain boundary corrosion resistance cannot be obtained. Therefore, the value of the intermediate formula of the formula (ii) is set to 2.50% or more. The value of the intermediate formula of the formula (ii) is preferably 2.70% or more, more preferably 3.00% or more.

On the other hand, when the value of the intermediate formula 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 susceptibility to weld cracking also increases. Therefore, the value of the intermediate formula of the formula (ii) is 4.60% or less, preferably 4.40% or less, more preferably 4.20% or less.

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

Sn: 0～0.010%

Sn has the effect of increasing the depth of penetration during welding and improving the ability to form a bead on the inner surface side of the pipe. Therefore, it can also be contained as needed. However, if Sn is contained excessively, the hot workability will be reduced and the susceptibility to weld cracking will be increased. In addition, the inner surface side bead tends to be convex. Therefore, the Sn content is made 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 effects, the Sn content is preferably 0.001% or more, more preferably 0.002% or more, and still more preferably 0.003% or more. It should be noted that the relationship between Sn and S and O needs to satisfy the formula (i) described later.

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

0.0010≤S+2O+0.2Sn≤0.0180···(i)

Here, the element symbols in the above formulas represent the content (mass %) of each element contained in the Ni-based alloy, and are set to 0 when not included. In addition, in the above formula, when the Sn content is less than 0.001%, it is treated as Sn=0.

S and O are interface active elements, which have the effect of enhancing inward convection in the molten pool during welding. In addition, Sn has the effect of contributing to the formation of the arc conduction path and improving the concentration of the arc. And, the welding heat is sent along the depth direction of the center of the molten pool. As a result, these elements have the effect of stably forming the weld on the inner surface side, but this effect cannot be obtained when the value of the intermediate formula of the formula (i) is less than 0.0010%. Therefore, the value of the intermediate formula of (i) formula shall be 0.0010% or more. The value of the intermediate formula of the formula (i) is preferably 0.0012% or more, more preferably 0.0015% or more.

On the other hand, when the value of the intermediate formula of the formula (i) exceeds 0.0180%, the surface tension of the molten metal decreases, or the melting at the center of the molten pool is accelerated to cause sinking. 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 of (i) formula shall be 0.0180% or less. The value of the intermediate formula 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-mentioned elements, Fe may be further contained within the range shown below.

Fe: 0～5.50%

Fe is effective for improving hot workability. Moreover, it also contributes to reducing the cost of the alloy. Therefore, it can also be contained as needed. However, if Fe is contained in excess, the tissue stability will be reduced. Therefore, the Fe content is made 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 still more preferably 1.50% or more.

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

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

Cu and Co have the effects of improving structural 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. In addition, when contained, it is preferable that the chemical composition satisfies the following formula (iii).

0.01≤Cu+Co≤1.50···(iii)

Here, the element symbols in the above formulas represent the content (mass %) of each element contained in the Ni-based alloy, and are set to 0 when not included.

(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%, it is difficult to obtain the above-mentioned effect. Therefore, the value of the intermediate formula of the formula (iii) is preferably 0.01% or more, more preferably 0.02% or more, and still more preferably 0.03% or more. However, when the value of the intermediate formula of the formula (iii) exceeds 1.50%, the hot workability decreases and the production cost increases. Therefore, the value of the intermediate formula of the formula (iii) is preferably 1.50% or less, more preferably 1.30% or less. The value of the intermediate formula of the formula (iii) is more preferably 1.00% or less.

In the chemical composition, in addition to the above-mentioned elements, one or more selected from W, V, Ca, Mg, B, and REM may be further contained within the range shown below. The reason for limitation of each element is demonstrated.

W: 0～1.00%

W improves corrosion resistance in the presence of non-oxidizing acids and chlorides. Therefore, it can also be contained as needed. However, if W is contained in excess, the tissue stability will be reduced. And, since it is an expensive element, the manufacturing cost will increase. Therefore, the W content is made 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 carbides by bonding with carbon, suppresses the generation of Cr carbides, and reduces deterioration of corrosion resistance at grain boundaries. Therefore, it can also be contained as needed. However, when V is contained in excess, a large amount of carbides and carbonitrides of V are precipitated, and the ductility is lowered. Therefore, the V content is made 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 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 can also be contained as needed. However, if Ca is contained in excess, it will bond with oxygen and detergency will be remarkably reduced. As a result, hot workability will rather fall. Therefore, the Ca content is made 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, more preferably 0.0003% or more.

Mg: 0～0.0030%

Mg has the effect of improving hot workability similarly to Ca. Therefore, it can also be contained as needed. However, if Mg is contained excessively, it will bond with oxygen, and the detergency will fall remarkably. As a result, hot workability will rather fall. Therefore, the Mg content is made 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 has the effect of segregating at grain boundaries at high temperatures to strengthen grain boundaries and improve hot workability. Therefore, it can also be contained as needed. However, when B is contained in excess, the susceptibility to weld cracking increases. Therefore, the B content is made 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 effects, the B content is preferably 0.0002% or more, more preferably 0.0005% or more.

REM: 0～0.0100%

Like Ca and Mg, REM has the effect of improving hot workability during production. Therefore, it can also be contained as needed. However, if REM is contained in excess, it will bond with oxygen and significantly reduce the cleaning performance. As a result, hot workability will rather fall. Therefore, the REM content is made 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 lanthanide 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. Here, "impurities" refer to elements that are not intentionally added, but are mixed in due to various factors such as raw materials and manufacturing processes during the industrial production of Ni-based alloys, and are within the range that does not adversely affect the present invention. allowed substances.

2. Surface roughness of alloy tube

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. Here, the surface roughness of the alloy pipe refers to the surface roughness after the final process in the manufacturing process. That is, although the surface roughness of the alloy pipe changes during the manufacturing process, in order to obtain the effect of the present invention, as long as the surface roughness in the longitudinal direction of the pipe after the final process satisfies the range specified in the present invention, it is different from that in the middle of manufacture. Surface roughness is irrelevant.

On the inner surface side of the Ni-based alloy tube, when the arithmetic mean deviation Ra in the length direction of the tube exceeds 7.0 μm, the wetting of the weld metal on the inner surface of the tube is hindered, and the weld metal is difficult to spread in the width direction, that is, the circumference of the tube. As a result, the weld bead tends to become convex, and the weld bead reinforcement tends to become high. Therefore, on the inner surface side of the Ni-based alloy tube, the arithmetic mean deviation Ra in the longitudinal direction of the tube is preferably 7.0 μm or less. The arithmetic mean deviation Ra is preferably 5.0 μm or less, more preferably 3.0 μm or less. In addition, although the lower limit of the said arithmetic mean deviation Ra is not specifically limited, When using the manufacturing method mentioned later, it is usually 0.1-1.0 micrometers or more.

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

3. Welded joints

The welded joint of the Ni-based alloy pipe can be obtained by butt-welding the pipe ends of the above-mentioned Ni-based alloy pipe under predetermined conditions. The welded joint of the Ni-based alloy pipe has a weld metal which becomes a joint part by solidification of molten metal, and a base metal part. It should be noted that the base metal portion includes a welding heat-affected portion that is affected by heat input due to welding. The base metal portion other than the welded heat-affected zone inherits the chemical composition, surface roughness, and other characteristics of the Ni-based alloy tube described in items 1 and 2 above. In addition, the welded part refers to a weld metal and a weld heat-affected zone.

4. Manufacturing method

A preferable manufacturing method of the Ni-based alloy tube of the present invention will be described. The Ni-based alloy tube of the present invention can achieve the effect as long as it has the above structure regardless of the production method, and can be stably produced, for example, by the following production method.

4-1. Ni-based alloy tube

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

Specifically, it is preferable to perform cold rolling or cold drawing after hot extrusion of the billet. During processing, softening heat treatment and intermediate pickling can also be performed if necessary. Then, as heat treatment, it is preferable to perform solution treatment on the alloy pipe. After the solution treatment, pickling or processing may be performed as necessary.

Among them, in order to make the arithmetic mean deviation Ra in the longitudinal direction of the tube 7.0 μm or less, it is preferable to perform the following steps. Specifically, it is preferable to perform solution treatment under 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 subject the inner surface of the tube to any treatment such as grinding treatment, machining such as grinding, and sandblasting or shot blasting.

It should be noted that although the arithmetic mean deviation Ra changes during the manufacturing process, the effect of the present invention is only affected by the surface roughness in the longitudinal direction of the tube after the final process, and has nothing to do with the surface roughness in the mid-process.

4-2. Welded joints of Ni-based alloy pipes

A 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, for example, welding may be performed by arc welding. Moreover, it is preferable that the conditions at the time of performing arc welding set heat input into the range of 4-20 kJ/cm, for example. In addition, it is preferable to use Ar gas as a shielding gas and a shielding back gas during welding. It is preferable to properly adjust the flow rate of the gas flowing through the weld.

Also, the chemical composition of the solder material (filler metal) to be used is not particularly limited, but is preferably the composition shown below. That is, 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 in mass % , Co: 15.0% or less, Cr: 14.0 to 26.0%, Mo: 17.0% or less, W: 4.5% or less, a total of at least one of Nb and Ta of 4.20% or less, 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%, and the balance is Ni and impurities. The relationship between the contents of S and O satisfies the following formula (a).

0.0010≤S+2O≤0.0180···(a)

However, the element symbols in the above formulas indicate the content (mass %) of each element contained in the welding material, and it is set to 0 when not contained.

Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

Example

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

Next, the above-mentioned alloy plate was subjected to a solution treatment in which the alloy plate was kept at 1150° C. for 10 minutes in a hydrogen furnace, and then cooled with water. Then, a plate material having a width of 50 mm and a length of 100 mm was cut out of the alloy plate. Then, as shown in Table 2, as shown in Table 2, a part of the plate material was assumed to be the inner surface side of the alloy pipe, and shot blasting was performed on only one side. For the plate without shot blasting, grind one side, or use a grinding stone with a particle size of No. 40 or No. 60 to grind for 1 to 5 times. In Table 2, for example, grinding (#40×1 time) means grinding once with a No. 40 grindstone.

[Table 1]

[Table 2]

Table 2

* indicates that it is outside the scope specified by the present invention.

** indicates deviation from the preferred range of the present invention.

The arithmetic mean deviation was measured for each plate using a contact roughness meter. In addition, two produced plate materials of each type of alloy were prepared, and groove processing as shown in FIG. 1 was performed on the end faces in the rolling direction. The beveled end faces of these plate materials were butted together, and root welding was performed using a filler metal having an outer diameter of 1.0 mm having the chemical composition shown in Table 3 to obtain welded joints. The heat input during welding is about 5kJ/cm, Ar gas is used as shielding gas and shielding back gas, and flows to the welding place at a flow rate of 10L/min.

[table 3]

table 3

For the obtained welded joints, those in which the rear side weld was formed over the entire length of the weld line were judged to have no problem in the formation ability of the inner surface side weld of the alloy pipe, and were rated as "pass". Among them, the width of the back side weld in the entire length of the welding line is 2 mm or more is rated as "excellent", and the width of the back side weld is formed is less than 2 mm but 1 mm or more is rated as "possible". It should be noted that, in this embodiment, the back side weld seam corresponds to the inner surface side weld seam formed when welding is performed from the outer side of the alloy pipe.

Then, three cross-sections appeared from the welded joint, and in all the cross-sections, those with a weld bead height on the back side of 1.0 mm or less were judged to have a good shape of the weld bead on the inner surface side of the alloy pipe, and were recorded as "pass". Among them, those whose back side weld bead height was 0.8 mm or less in all cross-sections were rated as "excellent", and those other than that were rated as "possible". The results are summarized in Table 4 below.

[Table 4]

Table 4

* indicates that it is outside the scope specified by the present invention.

Underlines indicate properties that deviate from the object of the present invention.

The test bodies using alloy types A to H and L to N all satisfied the requirements of the present invention, and the formability and shape of welds were good. Among them, the test body N1 using the alloy type N satisfies the prescribed range of the formula (i), and therefore satisfies both the formation ability and the height of the inner surface side weld.

On the other hand, the contents of S, O, and Sn in test bodies I1 and K1 using alloy types I and K did not satisfy the formula (i), and were higher than the specified range. Therefore, the sinking of the molten metal was conspicuous, and the height of the rear side bead did not meet the target. The relationship between the S and O contents in the test body J1 using the alloy type J does not satisfy the formula (i), and is below the specified range. Therefore, the melting in the plate thickness direction was insufficient, and the intended ability to form the weld on the inner surface side was not obtained.

In the test bodies O1 and P1 using alloy types O and P, the Sn content exceeds the specified range, or the S, O, and Sn contents exceed the range specified by the formula (i). Therefore, the sag of the molten metal was large, and the target bead height on the back side was not satisfied. In addition, the contents of S, O, and Sn in the test body Q1 using the alloy type Q did not satisfy the formula (i). Therefore, the melting in the plate thickness direction was insufficient, and the ability to form the weld on the inner surface side did not meet the target.

Industrial availability

According to the present invention, it is possible to obtain a Ni-based alloy pipe in which the weld seam on the inner surface side is stably formed during butt welding and the weld reinforcement is not too high.

Claims (4)

1. A Ni-based alloy tube, the chemical composition of which contains in mass % C: 0.005～0.080%, Si: 0.01 to 0.50%, Mn: 0.01～0.50%, P: 0.015% or less, S: 0.0001～0.0030%, Cr: 20.0-23.5%, Mo: 8.0～10.5%, Ti: 0.01 to 0.40%, N: 0.0010～0.0400%, Al: 0.01 to 0.40%, O: 0.0004～0.0100%, Sn: 0.001～0.010%, One 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 is Ni and impurities, and satisfy the following (i) and (ii) formulas, 0.0010≤S+2O+0.2Sn≤0.0180···(i) 2.50≤Nb+Ta≤4.60···(ii) Wherein, the element symbols in the formula represent the content in mass % of each element contained in the Ni-based alloy, and set to 0 when not included, However, on the tube inner surface side, the arithmetic mean deviation Ra in the longitudinal direction of the tube is 7.0 μm or less. 2. The Ni-based alloy tube according to claim 1, wherein the chemical composition comprises more than one selected from Cu and Co, and satisfies the following formula (iii), 0.01≤Cu+Co≤1.50···(iii) Wherein, the element symbols in the above formula represent the content in mass % of each element contained in the Ni-based alloy, and set to 0 when not included. 3. The Ni-based alloy tube according to claim 1 or 2, wherein the chemical composition contains in mass % selected from Fe: 0.01～5.50%, W: 0.01～1.00%, V: 0.01～0.40%, Ca: 0.0001 to 0.0030%, Mg: 0.0001～0.0030%, B: 0.0002 to 0.0100%, and REM: 1 or more of 0.0001 to 0.0100%. 4. A welded joint using the Ni-based alloy tube according to any one of claims 1 to 3.

Images