JP3211764B2 - Joining method of heat-resistant Ni-based alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining a Ni-base heat-resistant alloy having excellent strength and corrosion resistance at a high temperature of about 1000 ° C., and more particularly to a method for joining a heat-resistant pressure-resistant pipe of a petrochemical plant.

[0002]

2. Description of the Related Art Austenitic stainless steel satisfying one or both of a high Cr content and a high Ni content has conventionally been used for heat-resistant pressure-resistant piping of a petrochemical-related plant. Recently, a number of Ni-based alloys have been proposed in which the Al content is increased and the high-temperature strength and the corrosion resistance are improved so as to withstand even more severe use conditions (JP-A-4-358037, JP-A-4-58037). 5-33090, JP-A-5-3
No. 3091, JP-A-5-33092, etc.). When assembling such an alloy containing a large amount of Al as a structure, gas tungsten arc welding (GTAW (Gas Tungsten Arc Welding)
lding) welding method: the so-called TIG welding method) causes problems such as high temperature cracking and reheat cracking during heat treatment after welding. Also, when the brazing method is applied, sufficient wettability on the surface to be bonded cannot be obtained due to the formation of the Al ₂ O ₃ film, and a bonding defect occurs. For this reason, even if joining can be performed, a brittle intermetallic compound phase is formed as a different phase in the joining layer, so that sufficient high-temperature strength cannot be obtained.

When the solid-phase diffusion bonding method is applied, sufficient contact between the bonding surfaces cannot be obtained due to the Al ₂ O ₃ film formed on the surfaces to be bonded, and bonding defects easily occur. Therefore, sufficient high-temperature strength cannot be obtained, and application to an actual structure cannot be achieved. On the other hand, the liquid phase diffusion bonding method is known as a method for preventing the formation of a fragile intermetallic compound phase at a bonding portion (Japanese Patent Publication No. 3-71950). However, high Al
Since an Al ₂ O ₃ film is formed on the alloy as in the case of brazing, the liquid phased insert material does not spread uniformly on the joint surface, and a sound joint cannot be obtained.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a diffusion bonding method using a Ni-based alloy having a high Al content as a material to be joined, which can ensure a creep strength similar to that of a base material at a high temperature of about 1000 ° C. It is an object of the present invention to provide a method for joining a heat resistant Ni alloy.

[0005]

The present inventors have conducted studies to establish a liquid phase diffusion bonding technique for a Ni-base heat-resistant alloy having a high Al content, and have confirmed the following items.

(A) Chemical composition of insert material The insert material is made of Ni to ensure strength and corrosion resistance at high temperatures.
Base alloy.

[0007] B has a remarkable effect of lowering the melting point of the insert material and is an essential element.

[0008] Ti raises the melting point of the insert material, but improves the wettability between the surface to be joined and the melted insert material and lowers the joint defect rate.

[0009] Cr is essential for ensuring strength and corrosion resistance at high temperatures. However, it hardly affects the melting point of the insert material and the bonding defect rate.

Based on the above, Cr: 1 to 18%, B: 1 to 5%,
An insert material containing Ti: 0.01 to 6% and the balance being a Ni-based alloy was selected.

(B) Joining conditions Atmosphere, joining time and joining pressure during joining were investigated, and joining conditions having sufficient performance without joining defects were grasped.

(C) Optimization of Post-Heat Treatment Conditions When the post-heat treatment is performed on the obtained joint which satisfies the above conditions (a) and (b), the creep strength at a high temperature can be further improved.

The present invention has been completed through on-site trial production based on the above matters, and its gist lies in the following method for manufacturing a joint.

(1) A joining method using a Ni-base alloy containing 1.5 to 15% by weight of Al and having excellent high-temperature strength and corrosion resistance as a material to be joined. : 1-18
% B: 1 to 5% and Ti: butt through the insert material of the Ni-based alloy containing from 0.01 to 6 percent, shea with inert gas containing 0～5Vol% of H ₂ - In field atmosphere, in the butting direction 0.1 ~
2.0 kgf / mm pressure ² addition, the abutting portion more than the melting point of the insert material, at least below the melting point of the bonding material 12
Bonding method for heat-resistant Ni alloy which is held for 0 seconds and diffusion bonded (referred to as [Invention 1]).

(2) The material to be joined is, by weight%, C: 0.1% or less, Si: 5% or less, Mn: 0.2% or less, Cr: 1 to 18%, Al: 1.5 to 15%
%, Fe: 0-5%, B: 0-0.05%, Zr: 0-0.5%, Hf: 0-1%, T
i: 0-1%, Mg: 0-0.05%, Mo: 0-6%, W: 0-12%, V: 0-3.5
%, Nb: 0 to 5.5%, Ta: 0 to 11%, Y: 0 to 0.25%, La: 0 to 0.25%
And (1) a Ni-based alloy containing 0 to 0.25% of Ce (referred to as [Invention 2]).

(3) The shielding atmosphere is set to a vacuum atmosphere of 8 × 10 ^-1 torr or less. The bonding method of (1) or (2) (referred to as [Invention 3]).

(4) The joined joints are further
At a temperature of 1350 ° C, (T + 273) × (log (t / 3600) +20) × 10
Time t that satisfies ^-3 ≤ 33 (T: temperature [° C], t: time [s])
(1), (2) or (3) (referred to as [Invention 4]).

In the above description, the Ni-based alloy as the material to be joined corresponds to a pipe, a thick plate, a thin plate, a forged product or the like. The chemical composition of the Ni-based alloy of the material to be joined in Invention 1 may be any Ni-based alloy containing 1.5 to 15% Al and having excellent high-temperature strength and corrosion resistance. The insert material may be a thin strip having a thickness of about 5 to 500 μm. In the case of joining pipes, it is preferable to form concentric rings so as to cover joints of cross sections where the pipes abut, and to reduce unnecessary parts. The inert gas corresponds to a gas that does not mainly promote the oxidation reaction, such as Ar and N ₂ .

[0019]

Next, the reason why the limited range of the present invention is set as described above will be described. In the following description, “%” for the alloy element indicates “% by weight”.

1. Insert materials Insert materials are commercially available (trade name "Glassme
t ") can be used. Further, it can be manufactured by dropping a molten metal (Ni-based alloy) whose composition has been adjusted onto a rotating roll surface by a twin roll method or a single roll method. The chemical composition is in the following range.

Cr: 1 to 18% Cr is an element effective for improving strength and corrosion resistance at high temperatures.
1% or more is necessary. However, if it exceeds 18%, the upper limit is 18% because it deteriorates the microstructure stability and high temperature creep strength.
And The more desirable Cr content in terms of corrosion resistance and strength is 2% to 16%.

B: 1 to 5% B is an element effective for lowering the melting point of the insert material, and 1% or more is necessary. However, if it exceeds 5%, the formation of borides is promoted in the joining layer and the ductility of the joint is reduced, so the upper limit is made 5%. Still more desirable B content is 1.5% to 4.5%
It is.

Ti: 0.01 to 6% Ti has a strong affinity with O (oxygen), so that it can destroy the Al ₂ O ₃ film. For this reason, it is effective in improving the wettability and lowering the bonding defect rate, and 0.01% or more is necessary. However, if it exceeds 6%, it reacts with Al in the base metal to form an Al-Ti intermetallic compound, which reduces the ductility and strength of the joint. Also, Ti
If it exceeds 6%, it becomes difficult to manufacture the insert material itself, so the upper limit is made 6%. A more desirable range is from 0.1% to 5%.

In addition, a Ni-based alloy containing a commonly used alloy element without deteriorating the strength and corrosion resistance at high temperatures is also included in the scope of the present invention. Inevitable impurities are also covered by the present invention as long as they are within the usual range.

2. Chemical Composition of Joined Material In Invention 1, the reason why the Ni-based alloy having excellent high-temperature strength and corrosion resistance is used as the material to be joined is that it is used in a chemical plant or the like exposed to a high-temperature environment. The reason for using a Ni-based alloy is that an alloy having a high Ni content is excellent in high-temperature strength and high-temperature corrosion resistance.

Al: 1.5 to 15% Al is necessary for improving carburization resistance and coking resistance at high temperatures. Therefore, the Ni-base alloy targeted by the present invention contains 1.5% Al.
It is necessary to include the above. However, if it exceeds 15%, ductility and toughness at room temperature and high temperature deteriorate, so the content is made 15% or less. A desirable range is 4 to 13%.

Any Ni-based alloy containing 1.5 to 15% of Al and having excellent high-temperature strength and corrosion resistance corresponds to the material to be joined of the present invention. Further, a Ni-based alloy in which the chemical composition of the material to be joined is further specified as follows also falls under the present invention as in Invention 2. The following description of the alloy elements is for Invention 2 and the like.

C: 0.1% or less C is an element that is effective in securing a strength at room temperature and high temperature in a trace amount. However, if it exceeds 0.1%, ductility and toughness decrease, so it is set to 0.1% or less. From the viewpoint of ensuring strength, the C content is
It is desirable to set it to 0.003% or more. Usually, C content is 0.0
It cannot be less than 03%.

Si: 5% or less It may be effective as a deoxidizing element and also for improving oxidation resistance and carburization resistance. However, if it exceeds 5%, ductility and toughness are remarkably deteriorated. The target of the lower limit of Si is around 0.05%, which is the content remaining after deoxidation.

Mn: 0.2% or less Mn has a deoxidizing effect, but promotes the formation of a spinel-type oxide film that degrades coking resistance. A more desirable range is 0.1% or less.

Cr: 1 to 18% Cr must be at least 1% in order to secure oxidation resistance and coking resistance. However, it is not necessary to include a high concentration in a Ni-based alloy or the like having a high Al content, such as a material to be joined, which is an object of the present invention.If the content exceeds 18%, the stability of the structure at high temperatures is deteriorated. In addition, since carbides are precipitated unevenly and deteriorate toughness, the content is made 18% or less. A more desirable range is 3 to 15%.

Fe: 0 to 5% In the invention (2) (hereinafter, “in the invention (2)” is omitted), Fe may not be contained. Fe substitutes for a part of Ni, and does not have the effect of positively replacing Ni to improve the performance, but does not cause any deterioration. However, if the content exceeds 5%, the heat resistance deteriorates. Therefore, the content is set to 5% or less in consideration of economy.

B: 0-0.05% B may not be contained. B strengthens grain boundaries and improves creep strength. Since this effect becomes apparent at 0.001% or more, it is desirable to make it 0.001% or more when it is included. On the other hand, if the content exceeds 0.05%, the creep strength is rather reduced, so that the content is set to 0.05% or less.

Zr: 0 to 0.5% Zr may not be included. Zr is effective for strengthening the crystal grain boundary and improving the creep strength.When Zr is 0.01% or more,
Since this effect becomes apparent, it is desirable that the content be 0.01% or more when it is included. On the other hand, if it exceeds 0.5%, coarse carbides are formed and creep strength is lowered, so that
0.5% or less.

Hf: 0 to 1% Hf may not be included. Hf has the effect of strengthening the crystal grain boundary to increase the creep strength, and this effect becomes remarkable at 0.05% or more. Therefore, when Hf is contained, it is desirable that the content be 0.05% or more. However, if it exceeds 1%, coarse carbides are generated and the creep strength is deteriorated.

Ti: 0-1% Ti may not be contained. Ti refines crystal grains in a very small amount,
It has the effect of improving the creep strength, this effect being 0.05
%, The content clearly appears, so if it is included, it is preferable to be 0.05% or more.

Mg: 0 to 0.05% Mg may not be contained. Mg, like the above-mentioned elements, strengthens the crystal grain boundaries in a very small amount and contributes to the improvement in creep strength.
Since this effect becomes remarkable at 0.001% or more, when it is included, it is desirable to make it 0.001% or more. On the other hand, 0.05%
If more, the cleanliness is deteriorated and the ductility and toughness are deteriorated.

Mo: 0 to 6%, W: 0 to 12% Mo and W may not be contained. However, Mo and W mainly dissolve in the austenite phase to strengthen the austenite phase and improve the creep strength. This effect becomes apparent at 0.2% or more in the case of Mo, and 0.5% or more in the case of W.
It is desirable to make the above. On the other hand, Mo exceeds 6%
If W exceeds 12%, an intermetallic compound that deteriorates toughness is generated, so that the content of W is set to 6% or less and 12% or less, respectively.

V: 0 to 3.5% V may not be included. V forms a solid solution in the austenitic phase and Cr carbide to enhance the creep strength. This effect is 0.1%
Since it becomes clear from the above, it is desirable that the content be 0.1% or more when it is included. On the other hand, if it exceeds 3.5%, the toughness deteriorates, so the content is made 3.5% or less.

Nb: 0 to 5.5% Nb may not be contained. Nb improves the creep strength with a very small amount of about 0.3%. Therefore, when Nb is contained, it is desirable that the content be 0.3% or more. On the other hand, if it exceeds 5.5%, ductility and toughness deteriorate, so the content is made 5.5% or less.

Ta: 0 to 11% Ta may not be contained. However, Ta improves the creep strength at a content of about 0.5%, so if it is included, it should be 0.1%.
It is desirable to make it 5% or more. On the other hand, if it exceeds 11%, the ductility and toughness are remarkably deteriorated.

Y: 0 to 0.25%, La: 0 to 0.25%, Ce: 0 to 0.25% Y, La and Ce may not be contained. However, these elements mainly improve the adhesion of the SiO ₂ or Al ₂ O ₃ film under the thermal cycle conditions of shutdown and start of the chemical plant, and excellent carburization resistance even when used under temperature fluctuations And coking resistance is maintained. This effect is
Since it becomes remarkable at about 0.01%, when it is included, it is preferable to be 0.01% or more. On the other hand, if each element exceeds 0.25%, the cleanliness deteriorates, the workability decreases, and the product may not be manufactured.

3. To suppress the oxidation film generated during the bonding atmosphere bonding performs joining the H ₂ 0~5vol% containing inert gas atmosphere or 8 × 10 ^-1 torr time in a vacuum atmosphere (Invention 3). When joining the former in an inert gas atmosphere, an oxide film is reduced, in order to increase the bondability further, it is desirable to include of H ₂ at least 0.5% or more. As the inert gas, as described above, Ar,
It is preferable to use N ₂ gas or the like.

4. Joining time If the joining holding time is too short, the joint and the base material are not sufficiently homogenized, and a joint having sufficient high-temperature strength cannot be obtained. Therefore, it is necessary to hold for at least 120 seconds. More preferably, the time is 240 seconds or more. The upper limit is not particularly limited, but about 1800 seconds is a guideline in consideration of construction efficiency and the like.

5. Pressing force If the pressing force is less than 0.1 kgf / mm ² , the Al ₂ O ₃ oxide film on the surface to be bonded does not break down and sufficient wettability cannot be obtained. 2.0kgf
/ mm large deformation at the time of bonding occurs at ² or more. Therefore, the pressing force at the time of joining is 0.1 to 2.0 kgf / mm ² as a pressure on a surface perpendicular to the butting direction. A more desirable range is 0.3-1.
It is a 5kgf / mm ^2.

6. Post-Heat Treatment Conditions By using the insert material defined in Invention 1 and satisfying the joining conditions within the defined range of Invention 1, a joint having a sufficient high-temperature strength can be obtained. It is effective to perform a post-heat treatment as defined in Invention 4. The post heat treatment is performed in a temperature range of 1100 to 1350 ° C. If the temperature is lower than 1100 ° C., it takes a long time to obtain the effect of the post heat treatment, and the efficiency is reduced. On the other hand, when the temperature exceeds 1350 ° C., the base material deteriorates, and the creep strength deteriorates. Also the temperature
In relation to T and time t, (T + 273) x (log (t / 3600) + 20) x 1
0 ^-3 is more than 33 large amount of intermetallic compound is precipitated deteriorating the toughness and the like. Therefore, (T + 273) × (log (t / 3600) +
20) ^x10-3 shall be 33 or less. There is no particular lower limit, but if it is less than 25, the tissue may not be sufficiently homogenized. Log is
Logarithm with base 10.

[0047]

EXAMPLES The effects of the present invention will be described with reference to examples.

Table 1 shows the chemical compositions of the materials to be joined (high-Al-content Ni-based alloys). The chemical compositions of these alloys are all materials to be joined within the scope of the invention defined as invention 2.

[0049]

[Table 1]

Table 2 shows the values of these materials to be joined at 1000 ° C.
It shows a creep rupture strength of 0000h. Steel number and creep rupture strength of 1.3, 1.4 or 1.5k respectively
It is a gf / mm ^2.

[0051]

[Table 2]

Table 3 shows the chemical compositions of the 15 types of insert materials used in this example.

[0053]

[Table 3]

Using the material to be joined and the insert material, joining was performed under various joining conditions, and joint performance was evaluated.

Tables 4 to 7 are tables showing the joining conditions of each test number.

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[0059]

[Table 7]

In the above table, Table 4 shows the invention example of Invention 1. Of these, test numbers AJ24 to AJ27 are both examples of invention 1 and examples of invention 4. As shown in Table 1, all three types of materials to be joined fall within the definition range of Invention 2. In contrast, Table 5 shows a comparative example for Invention 1. Table 6 shows Examples and Comparative Examples of Invention 3. Table 7 shows Comparative Example of Invention 4 (which is an example of Invention 1).
Is shown.

For evaluation of the joint performance, a cross section of the joint portion of the joint was revealed, and the joint defect (void) rate was measured. here,
The joint defect (void) rate is a value defined as {(occupied length of void) / (joint length)} × 100%. Only joints having a joint defect rate of 0% were judged to be acceptable.

FIG. 1 is a view showing the shape of a creep test piece. A test piece having the shape shown in FIG. 1 was collected from the joint joined under the above conditions, and a creep rupture test was performed at a temperature of 1000 ° C. and a stress of 1.5 kgf / mm ² . Joints that reached 80% or more of the creep rupture time of the base metal were judged to be acceptable. Note that the creep rupture time of the base material, the temperature 1000 ° C., so was 10 ⁴ h or more in terms of stress 1.5 kgf / mm ^2, and a reference for determining the 10 ⁴ h,
Pass if the rupture time is 8000h or more.

The test results are shown in Tables 4 to 7 above.

[Invention 1] As shown in Table 5, test numbers BJ1 and BJ4, which are comparative examples, show that the insert materials
The bonding defect rate was as high as 40% due to the absence of Ti or excess Ti, and the creep rupture strength was about 10% of that of the base metal. In Comparative Examples BJ2 and BJ3, the B content of the insert material was too high or too low, respectively, so that both the bonding defect rate and the creep rupture strength deteriorated. In Comparative Example BJ5, the above two characteristics deteriorated because the Cr content of the insert material was too high. In Comparative Example BJ8 or BJ9, the above two characteristics were degraded because both of the bonding times were short. Comparative Example BJ
In the case of No. 10, the creep rupture strength was extremely deteriorated due to joining without applying pressure. In Comparative Example BJ11, the pressure was too high to obtain a joint, and the creep test could not be performed.

On the other hand, as shown in Table 4, Invention 1
If you apply the insert materials and joining conditions limited by
It was found that a joint having no defect and having a creep rupture time of 80% or more of the base metal was obtained.

[Invention 3] Test No. BJ6, which is a comparative example of Invention 3 shown in Table 6, was bonded in 1 torr of air, and BJ7 was bonded in atmospheric pressure, so that the creep rupture strength and the bonding defect rate were deteriorated. In contrast, AJ15 and AJ according to the third embodiment of the invention
In No. 16, satisfactory results were obtained with the above two characteristics being satisfactory.

[Invention 4] Test No. BJ12, which is a comparative example of Invention 4 shown in Table 7, had an excessive tempering index, and did not give good results in both creep rupture strength and joint defect rate. In Comparative Example BJ13, the post-heat treatment temperature exceeded 1350 ° C., so that the same result as BJ12 was obtained. On the other hand, AJ24 to AJ27, which are examples of Invention 4, had a creep rupture strength of the joint of 90% or more of that of the base material, and extremely good results were obtained.

[0068]

According to the present invention, a heat-resistant Ni-based alloy having a high Al content can be joined without deteriorating properties such as creep strength, and a highly safe petrochemical plant can be manufactured at low cost. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a view showing a shape of a creep test piece used in a creep test of an example.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazuyuki Saida 5-12-17 Izuo, Taisho-ku, Osaka-shi, Osaka (56) References JP-A-1-186290 (JP, A) JP-A-58-159988 ( JP, A) JP-A-53-35655 (JP, A) JP-A-59-16687 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 20/00-20/14

Claims (4)

(57) [Claims] 1. A joining method using a Ni-based alloy containing 1.5 to 15% by weight of Al and having excellent high-temperature strength and corrosion resistance as a material to be joined,
The joining surfaces of the materials to be joined are Cr: 1 to 18% by weight%, B: 1
5% and Ti: butt through the insert material of the Ni-based alloy containing from 0.01 to 6%, shea with inert gas containing 0～5Vol% of H ₂ - 0.1~2.0k in field atmosphere, in the butting direction
gf / mm pressure ² addition, the abutting portion more than the melting point of the insert material, at least 120 seconds less than the melting point of the material to be joined
A method for joining heat-resistant Ni-based alloys, characterized by holding and diffusion-bonding. 2. The material to be joined is, by weight%, C: 0.1% or less, Si: 5% or less.
% Or less, Mn: 0.2% or less, Cr: 1 to 18%, Al: 1.5 to 15%, Fe: 0
~ 5%, B: 0 ~ 0.05%, Zr: 0 ~ 0.5%, Hf: 0 ~ 1%, Ti: 0 ~ 1
%, Mg: 0-0.05%, Mo: 0-6%, W: 0-12%, V: 0-3.5%, Nb:
0 ~ 5.5%, Ta: 0 ~ 11%, Y: 0 ~ 0.25%, La: 0 ~ 0.25% and
2. The joining method according to claim 1, wherein the alloy is a Ni-based alloy containing Ce: 0 to 0.25%. 3. The bonding method according to claim 1, wherein the shield atmosphere during the bonding is a vacuum atmosphere of 8 × 10 ⁻¹ torr or less. 4. The joined joint is further heated at 1100-1350 ° C.
At the temperature of (T + 273) × (log (t / 3600) +20) × 10 ^-3 ≦ 33
4. The bonding method according to claim 1, wherein the holding is performed for a time t satisfying (T: temperature [° C.], t: time [s]).