JPH07115188B2 - High corrosion resistant dissimilar material joint - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high corrosion resistant dissimilar material joint which enables welding and joining general-purpose materials such as iron-based materials and zirconium-based materials.

[0002]

2. Description of the Related Art Zirconium alloys such as pure zirconium and zircaloys (hereinafter collectively referred to as zirconium-based materials) have excellent corrosion resistance and have a very small thermal neutron absorption cross-section, so that they are used in nuclear reactor materials, especially in light water reactors. It is mainly used as a fuel cladding tube. Recently, attention has been paid to the excellent corrosion resistance of zirconium, and the use of zirconium in other applications such as the electronic industry and medical machine materials has begun to be examined.

However, zirconium-based materials are more expensive than general-purpose highly corrosion-resistant materials such as stainless steel or nickel-based alloys such as Inconel (trade name of Inco). Therefore, for example, in a piping system, it can be said that it is economical to use a tube made of this material only in a portion requiring a zirconium-based material and replace the other portions with a tube made of a general-purpose material.

When the zirconium-based material is partially used in a piping system or the like, it is necessary to join the zirconium-based material and a general-purpose material, and welding is first considered as a joining method.

However, it is difficult to weld zirconium-based materials and general-purpose materials. The reason why this welding is difficult is that direct fusion welding of dissimilar metals generally produces a very fragile alloy layer on the joint surface, Zr and Fe or Zr and Ni are no exception, and it is also suitable for these welding. There is no brazing material.

On the other hand, one of welding techniques developed for joining dissimilar metals such as iron and zirconium, which are hard to be directly fused, is a diffusion bonding method.

As an example of diffusion bonding to a zirconium-based material, in addition to the bonding of similar materials of zircaloys having steel as an insertion material, bonding of zircaloy without an insertion material and austenitic stainless steel (SUS304) is known. ing. However, in the latter example of joining dissimilar materials, since Zircaloy and stainless steel are directly brought into close contact with each other and heated to a temperature of about 1000 ° C. or more, a Zr—Fe-based fragile alloy layer is formed on the joint surface. Inevitable formation, diffusion
Even with the joining method, the zirconium-based material could not be joined to a dissimilar metal such as steel with sufficient joining strength.

As described above, conventionally, it has been difficult to metallurgically bond a zirconium-based material and a general-purpose material. Therefore, a mechanical joint is used for the joining.
In addition, metallurgical joining is Metallurgical b
With the meaning of "ouded", a bond in which metal atoms are metal-bonded.
Welding and diffusion bonding described above, and further described below.
Both metallurgical and non-melt welding are metallurgical welds.
include. On the other hand, what is not included in this metallurgical joining
Then, there are the above-mentioned mechanical joints and adhesion.

[0009]

However, the mechanical joint is bulky, and the resulting joint is airtight.
There is a problem in reliability, and highly reliable metallurgical joining of zirconium-based materials and general-purpose materials is desired.

An object of the present invention is to provide a dissimilar material joint capable of metallurgically joining a zirconium-based material and a general-purpose material.

[0011]

The dissimilar joint Means for Solving the Problems] As shown in FIG. 1, the first member a and the second member b made of different materials A and B the same <br/> kinds of materials respectively to be joined It is a joint that has both ends on both sides. By using this, joining of dissimilar materials (joining of A and B)
Instead of joining (joining of A and a and joining of B and b) , metallurgical joining of dissimilar materials, which is difficult to metallurgically join, becomes possible.

[0012] Such dissimilar material joints are difficult to metallurgically bond
Used for metallurgical joining of dissimilar materials A and B
From the dissimilar material constituting the joint, that is, the first member
a and the second member b are also the metal bonds between the metal atoms described above.
Sufficient joint strength as a joint due to metallurgical joining involving welding
Must be integrated in. However, if different materials of the general-purpose materials such as zirconium-based material and steel, since its <br/> metallurgical bond is difficult, it is difficult to manufacture itself of the dissimilar joint.

Even if a dissimilar material joint can be manufactured, unlike a cladding plate, the dissimilar material joint is required to have excellent corrosion resistance at the joint portion of different materials. That is, in the case of a clad material, since the material on the side with excellent corrosion resistance is exposed to a corrosive environment, it is only necessary to consider the corrosion resistance of the material itself, but in the case of a dissimilar joint, when it is a pipe, the inner surface side Since the corrosive fluid flows through the joints and the joints of different materials are exposed to the corrosive environment, the corrosion resistance of the joints is also important. Further, in the case of a rod-shaped dissimilar material joint, its outer surface is exposed to a corrosive environment, so that the corrosion resistance of the joint is also important.

Therefore, the dissimilar material joint is required to have not only the joint strength but also the corrosion resistance of the joint portion. In the dissimilar material joint using a zirconium-based material, the material is applied to an extremely harsh corrosive environment. Therefore, particularly excellent joint corrosion resistance is required.

In order to develop a dissimilar material joint satisfying such requirements, the present inventors have paid attention to an insert clad material in which an insert material is interposed between a zirconium-based material and a general-purpose material, and have various insert clad materials. The joint strength and the corrosion resistance of the joint were investigated. As a result, they have found that a clad material using an insert material made of tantalum is effective as a material for a dissimilar material joint of steel or a nickel-based alloy and a zirconium-based material.

The intermetallic compound formed between titanium and the steel or nickel-based alloy has a eutectic temperature of 940 to 100.
Since it is as low as 0 ° C., it is easily generated during the cladding process, and the compound itself has poor corrosion resistance. In contrast,
Tantalum is Ta-F between steel and nickel-based alloys.
Although an e-based or Ta-Ni-based intermetallic compound is produced, its eutectic temperature is as high as 1300 ° C. or higher, and it does not easily occur during clad processing. Even if it occurs, it does not affect the bonding strength and corrosion resistance as much as titanium does.

Further, even if the formation of Ta-Fe-based or Ta-Ni-based intermetallic compounds is suppressed, it is necessary to avoid locally connecting the materials with the above compounds. That is, when the above-mentioned compound produced between steel or a nickel-based alloy and tantalum locally reaches the zirconium-based material locally, a Zr-Fe-based or Zr-Ni-based intermetallic compound is formed to bond strength. , The corrosion resistance is significantly deteriorated.

However, the Ta-Fe-based and Ta-Ni-based intermetallic compounds have a thickness of about 10 μm at most even if they are generated as long as the ordinary clad method such as hot rolling and explosion deposition is adopted. It is confirmed by the experiments of the present inventors that they are not formed. Therefore, in the case of using the tantalum insert material, if the thickness thereof is 10 μm or more, even if an intermetallic compound is generated between the tantalum insert material and the steel or Ni-based alloy, a gap between the zirconium-based material and the intermetallic compound is formed. No tantalum layer is formed, which guarantees the bond strength and corrosion resistance between both materials.

Further, tantalum is not lower in performance than steel and nickel-based alloys, and therefore, tantalum itself does not reduce the strength of the joint or deteriorate the corrosion resistance.

The present invention has been made based on the above findings. As shown in FIG. 1, a tubular or rod-shaped first joint member a made of an iron-based material or a nickel-based alloy, and a tubular or rod-shaped zirconium-based material. A tubular or rod-shaped dissimilar material joint in which a rod-shaped second joint member b is butt-joined, and an insert made of tantalum having a thickness of 10 μm or more between the first joint member a and the second joint member b. The material c is interposed, and the first joint member a and the insert material c are non-melt-bonded, and the second joint member b and the insert material c are non-melt-bonded or melt-bonded. The main feature is a high corrosion resistant dissimilar material joint.

A steel and zirconium-based clad material using tantalum as an insert material is disclosed in JP-A-59-470.
Although disclosed in Japanese Patent Publication No. 78, its clad material is a plate material, and its corrosion resistance at the joint has not been clarified, so its suitability as a dissimilar joint is unknown.

[0022]

The present invention will be described in detail below.

In the present invention, the iron-based material constituting the first joint member means steel, low alloy steel and high alloy steel.

According to the research conducted by the present inventors, Fe and N
When a metal material containing 5% by weight or more of one or both of i in total is brought into close contact with a zirconium-based material and heated to a high temperature, an alloy layer of Fe and Zr or Ni and Zr is formed and the joint surface becomes brittle. . Therefore, the iron-based material or the nickel-based alloy forming the first joint member means any metal material containing at least 5 wt% of Fe and Ni in total.

Steels particularly suitable as the first joint member are ordinary steel, low alloy steel and austenitic stainless steel, and Cr, Mo containing heat resistant steel can also be used as the first joint member.

Suitable nickel-based alloys for the first joint member are Alloy 600 (75Ni-15Cr-Fe),
Alloy 625 (60Ni-20Cr-9Mo3.5Nb-
Fe) and the like.

The second joint member is a zirconium-based material,
That is, it is pure zirconium or a zirconium alloy, and zircaloy-2 (1.5Sn-0.12Fe-0.1Cr-0.05N) is one of the zirconium alloys that are currently easily available.
i) and Zircaloy-4 (1.5Sn-0.18Fe-0.
1 Cr). Zircaloy has improved corrosion resistance in high-temperature water and in a nitrogen-containing atmosphere compared to pure zirconium. The zirconium alloy is not limited to zircaloy, and other zirconium alloys can be used in the present invention. The zirconium alloy preferably contains Zr in an amount of 50% or more.

The material combination of the first joint member and the second joint member is appropriately selected according to the application. It is advantageous to use the same kind of combination as the materials to be welded.

In the present invention, the first joint member and the second joint member
Tantalum is inserted as an insert material between the joint member and the joint member, which is caused by the Zr-Fe system and the Zr-Fe system which are generated at the joint interface when the both members are directly joined as described above.
This is to prevent the joint from becoming brittle due to the Ni-based intermetallic compound. However, depending on the joining conditions, Ta- may be formed at the joining interface between the first joint member and the insert material.
Fe, Ts-Ni based intermetallic compounds may be formed. According to the investigation by the present inventors, it was confirmed that this metal compound was formed only to a thickness of about 10 μm, but in the unlikely event that this intermetallic compound reached zirconium on the second joint member side. In case of Zr-Fe system, Zr-N
Since the i-type intermetallic compound is formed and the joint strength and corrosion resistance are deteriorated, the thickness of the tantalum layer is 10 at the product stage.
At least μm must be secured.

The upper limit of the thickness of the tantalum layer does not have to be set, but it is preferably thin from the economical point of view, and usually about 10 mm.

In the dissimilar material joint of the present invention, the first joint member and the insert material are joined by non-melt welding, and the second joint member and the insert material are joined by fusion welding or non-melt welding. To be done.

Here, the term "melt welding" refers to welding in which a molten pool is formed, and specifically, electron beam welding, TIG welding, MIG welding and the like.

On the other hand, the non-melt welding means welding performed without forming a molten pool, and specifically includes explosion welding, friction welding, diffusion welding, hot pressure welding and the like.

Since there is a risk of formation of intermetallic compounds between the first joint member and the insert member, non-melt welding is essential, but between the insert member and the second joint member. Since there is little danger of producing a malicious intermetallic compound, either non-melt welding or melt welding may be adopted.
However, since fusion welding is less laborious, fusion welding will usually be used.

In the case of joining from either the first joint member and the insert member or between the insert member and the second joint member, melting occurs between the insert member and the second joint member. In the case of adopting welding, if the non-melt welding is completed first, that is, if the first joining member and the insert material are joined together, there is a danger that the heat accompanying the melt welding adversely affects the non-melt welding portion. , Insert material and second
It is desirable to join the joint members in advance. However, this risk is avoided if the thickness of the insert material is 10 mm or more.

The conditions of the fusion welding and the non-fusion welding can be set as appropriate depending on the relation between the joining means to be employed and the materials to be joined, and therefore detailed description will be omitted.

In the dissimilar material joint of the present invention, the first joint member made of an iron-based material or a nickel-base alloy and the second joint member made of a zirconium-based material are joined with sufficient strength through tantalum, and Excellent corrosion resistance at the joint.

As described above, this dissimilar material joint is useful as a joint in welding of steel or nickel-based alloy and zirconium-based material (see FIG. 1),
This joint enables the zirconium-based material to be welded to general-purpose structural materials such as ordinary steel, stainless steel, or nickel-based alloys, and contributes to expanding the applications of the zirconium-based material. The zirconium-based material can be welded by TIG welding, electron beam welding, or the like.

[0039]

EXAMPLES Examples and comparative examples of the present invention will be described below.

As shown in Table 1, mild steel (SS41), 2 1 / 4Cr-1Mo steel, austenitic stainless steel (SUS304L) and nickel base alloy (Alloy 625) were used as materials for the first joint member. Pure zirconium (ASTM grade R60
702) and zirconium alloy (ASTM grade R6
0802) and using pure tantalum for industrial use (JIS H4701, TaP and TaH) as insert materials, and pure titanium (JIS type 1) and pure nickel for comparison, various dissimilar joints were manufactured.

[0041]

[Table 1]

[0042]

[Table 2]

The first joint member and the second joint member are
Tubing material with an outer diameter of 50 mm, wall thickness of 5 mm, and length of 100 mm. The insert material is an annular plate material with an outer diameter of 50 mm, an inner diameter of 40 mm, and a thickness of 10 mm.
m foil was used.

Electron beam welding was adopted as the fusion welding, and friction welding was used as the non-fusion welding.

Electron beam welding is performed in a welding atmosphere at a vacuum degree of 10
^-3 Torr, acceleration voltage 50KV, beam current 200mA, welding speed 80cm / min.
As shown in the figure, one material 1 to be bonded is set to the chuck 3, and the other material 2 to be bonded is set to the chuck 4, respectively, and as shown in FIG. Are rubbed at pressure P _{1 for} time t ₁ ,
The rotation was stopped and the pressure was set to P ₂ and the welding was performed by upsetting in the tube axial direction for the time t ₂ . Where P ₁ is 3-5k
gf / mm ² , t ₁ is 2 to 5 seconds, P ₂ is 10 kgf / m
m ² and t ₂ are 10 seconds.

The joint was evaluated by a joint tensile test using the test piece shown in FIG. 4 and a corrosion resistance test using the corrosion test piece shown in FIG. In the corrosion resistance test, the corrosion depth of the interface was measured after the test piece was immersed in an 8N HNO ₃ aqueous solution at 100 ° C for 300 hours.

The results are shown in Table 2. The dissimilar material joint of the present invention has a very high joint strength and is extremely excellent in the corrosion resistance of the joint.

[0048]

As apparent from the above description, in the dissimilar material joint of the present invention, the first joint member made of an iron-based material or a nickel-based alloy and the second joint member made of a zirconium-based material are sufficient as joints. Since it is joined with various strengths and the corrosion resistance of the joint is remarkably excellent, it enables metallurgical joining of dissimilar materials of this kind, which was difficult to perform metallurgical joining up to now, and greatly contributes to expanding the applications of zirconium-based materials. It is a thing.

[Brief description of drawings]

FIG. 1 is an explanatory view of a structure of a dissimilar material joint of the present invention and a method of using the joint.

FIG. 2 is an explanatory diagram of a friction welding method.

FIG. 3 is a time chart of pressing force in friction welding.

FIG. 4 is a dimensional diagram of a test piece for evaluating the joint strength of a dissimilar material joint and the corrosion resistance of the joint.

[Explanation of symbols]

 a first joint member b second joint member c insert material 1.2 material to be joined 3,4 chuck

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area // B23K 103: 18

Claims (1)

[Claims] 1. A tubular or rod-shaped dissimilar material in which a tubular or rod-shaped first joint member made of an iron-based material or a nickel-based alloy and a tubular or rod-shaped second joint member made of a zirconium-based material are butt-joined to each other. A joint having a thickness of 10 μ between the first joint member and the second joint member.
An insert material made of tantalum of m or more is inserted, and the first joint member and the insert material are non-melt-bonded, and the second joint member and the insert material are non-melt-bonded or melt-bonded. High corrosion resistance dissimilar material joint characterized by being