JPH07110427B2 - Method for manufacturing zirconium-based clad material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to zirconium having a base material of steel such as ordinary steel, low alloy steel and stainless steel, or a nickel base alloy, and pure zirconium or zirconium alloy as a composite material. The present invention relates to a method for manufacturing a clad material.

(Prior Art) Zirconium alloys such as pure zirconium and zircaloys (hereinafter collectively referred to as zirconium-based materials) have excellent corrosion resistance and have extremely small thermal neutron absorption cross-sections, so they are used in nuclear reactor materials, especially in light water reactors. It has been mainly used for fuel cladding. Recently, attention has been paid to the excellent corrosion resistance of zirconium, and the use of zirconium-based materials in other applications such as the electronic industry and medical machine materials has begun to be examined, although the zirconium-based materials are relatively expensive.

However, since the zirconium-based material is difficult to be welded to a general-purpose material such as ordinary steel, stainless steel having high corrosion resistance, or nickel-based alloy such as Inconel (trade name of Inco Co.), its field of use has been considerably narrowed.

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

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 welding method.

As examples of diffusion welding for zirconium-based materials, in addition to joining similar materials of zircaloys with steel as an insert material, joining of zircaloy without a insert material and austenitic stainless steel (SUS302) is known. . However, in the latter example of joining dissimilar materials, zircaloy and stainless steel are directly adhered to each other and heated to a temperature of about 1000 ° C. or more, so that a Zr-Fe-based fragile alloy layer is formed on the joint surface. Formation is unavoidable, and the zirconium-based material could not be welded to dissimilar metals such as steel with sufficient joint strength even by the diffusion welding method.

Dissimilar material joints are known to be effective for joining dissimilar materials that are difficult to be directly joined.

That is, as shown in FIG. 1, welding of different materials such as iron-based material and zirconium-based material such as steel is performed by using a clad material made of the same material as the material to be welded (that is, steel and zirconium of the same kind). If there is a clad material consisting of a material, this is used as a joint and the same kind of material is interposed so that the same kind of material faces each other as shown in the figure, and normal welding such as TIG welding is performed. It is possible to weld without causing brittleness of the joint surface.

A zirconium-based clad material that uses steel or a nickel-based alloy as a base material and a zirconium-based material as a composite material as this dissimilar material joint or its material is indispensable. Joining with a material is very difficult as mentioned above. Therefore, the clad material is difficult to manufacture, and even if it can be manufactured, it has many problems.

(Problems to be Solved by the Invention) A clad steel plate having a high melting point metal such as zirconium as a composite material is a rolled clad method in which a base steel and a composite material are superposed and hot rolled, or a plate. Put gunpowder on,
It is most commonly manufactured by the explosive cladding method in which the explosive force is used for joining.

However, when zirconium or a zirconium alloy and ordinary steel, low-alloy steel, stainless steel, and other steels are stacked and hot-rolled, the dissimilar metals are heated as described above, and brittle intermetallic compounds are contained in the joint. Therefore, it is difficult to obtain a joint having sufficient strength because an alloy layer is formed. Further, both zirconium and zirconium alloys have a strong affinity for oxygen, nitrogen, etc., so that when they are heated to a high temperature, they absorb the atmosphere and become brittle. Due to these problems, there is still no clad steel sheet obtained by rolling using a zirconium-based material as a laminated material with sufficient performance.

On the other hand, even in the explosive cladding method, it is common that a zirconium-iron intermetallic compound is formed at the joint, and stable joint strength cannot be obtained. Practical use is being promoted in the form of an insert (Japanese Patent Laid-Open No. 52-46163). However, this clad material also has a problem that titanium, which is an insert material, causes Ti-Fe-based intermetallic compounds to be formed in the joint, and the corrosion resistance of the joint is significantly deteriorated.

The above describes the case where the base material is steel, but the situation is exactly the same when the base material is a nickel-based alloy, and for the same reason, the composite material of the nickel-based alloy base material and the zirconium-based material is also used. There is no satisfactory clad material consisting of.

An object of the present invention is to solve these problems and to provide a method for producing a zirconium-based clad material having excellent bonding strength and corrosion resistance of the bonded portion.

(Means for solving the problem) The deterioration of the bondability between the steel or nickel-based alloy and the zirconium-based material is due to the formation of Zr-Fe-based or Zr-Ni-based intermetallic compounds at the bonding interface. The embrittlement of the joint is the cause. Therefore, in order to prevent the embrittlement of the joint, it is firstly necessary not to form an intermetallic compound at the joint interface. Also, when inserting an insert material between both materials, the insert material must show sufficient bonding strength to both materials, and titanium that deteriorates the corrosion resistance of the joint is not suitable. In addition, the insert material itself is required to have corrosion resistance comparable to that of nickel-based alloys and zirconium materials. Furthermore, ease of manufacture is also important as a practical material.

The present inventors repeated research and study to develop a zirconium-based clad material that satisfies these requirements comprehensively, and as a result, tantalum was inserted between the steel or nickel-based alloy and the zirconium-based material under appropriate conditions. It was found that rolling joining is effective.

The intermetallic compound generated between titanium and the steel or nickel-based alloy has a low eutectic temperature of about 940 to 1000 ° C., so that it is easily generated during the cladding process, and the compound itself has poor corrosion resistance. On the other hand, tantalum produces Ta-Fe-based and Ta-Ni-based intermetallic compounds with steel or nickel-based alloys, but its eutectic temperature is as high as 1300 ° C or higher, which makes it easy to perform during clad processing. Does not occur. Even if it occurs, it does not affect the bonding strength and corrosion resistance as much as titanium does.

However, even if the formation of Ta-Fe-based and Ta-Ni-based intermetallic compounds is suppressed, it is necessary to avoid locally connecting the base material and the laminated material with the above compounds. That is, when the compound produced between the base material made of steel or nickel-based alloy and tantalum locally reaches the laminated material made of zirconium-based material,
Zr-Fe-based and Zr-Ni-based intermetallic compounds are formed and the joint strength and corrosion resistance are significantly deteriorated.

However, Ta-Fe-based and Ta-Ni-based intermetallic compounds should be formed to a thickness of at most about 10 μm, even if they occur, as long as the ordinary clad method such as hot rolling and explosion deposition is adopted. Has been confirmed by the experiments of the present inventors. Therefore, when inserting tantalum, if the thickness is set to 10 μm or more at the product stage, even if an intermetallic compound is produced between the tantalum and the base material, the tantalum layer does not have a discontinuity on the entire surface with the mating material. Is formed, which guarantees the bonding strength and corrosion resistance between the two materials.

Even if tantalum having a sufficient thickness is inserted, Ta-Fe and Ta-Ni intermetallic compounds grow remarkably at the time of joining depending on the joining conditions, and the corrosion resistance of the joining interface deteriorates. Therefore, in joining, it is necessary to limit the conditions in terms of not only the joining strength but also the corrosion resistance of the joined portion.

Further, tantalum is not inferior in performance to steel and nickel-based alloys, and therefore, tantalum itself does not cause the strength of the joint portion to deteriorate or the corrosion resistance to deteriorate.

The method for producing a zirconium-based clad material of the present invention is based on the above findings, and contains an iron-based material or a nickel-based material to be a base material, containing 5% by weight or more of one or more of Fe and Ni in total. Alloy with a thickness of 10μ at the product stage
A first frame member that covers the upper surface of the zirconium-based material and a second frame that covers all the side surfaces of the tantalum and the zirconium-based material are added to the laminated body in which the zirconium-based material that is to be the laminated material is stacked through the tantalum having a thickness of m A frame material is attached by welding to produce an assembly material in which tantalum and a zirconium-based material on an iron-based material or a nickel-based alloy are enclosed in the frame material, and a pressure of 1 torr ( Torr)
Hold the assembly in the following vacuum or 95% or more inert gas atmosphere to reduce the assembly ratio to 2 or more and the rolling start temperature 800 to 1
It is characterized in that the material is rolled at 300 ° C in the material polymerization direction and hot-rolled.

It should be noted that by inserting tantalum between zirconium and carbon steel or low alloy steel, the joining strength of the clad material is improved, and that the clad material can be manufactured by rolling joining. JP-A-59-47078 It is shown in the official gazette. However, the technique shown here was made by paying attention only to the joint strength, no consideration was given to the corrosion resistance of the joint, and no specific conditions for rolling joining were shown. From the point of view of strength and corrosion resistance of the joint portion, the present invention is significantly different from the present invention in which specific conditions for roll-joining are strictly defined. Further, in the present invention, since the tantalum and zirconium-based materials stacked on the iron-based material or the nickel-based alloy are enclosed in the frame material, not only the bonding interface but the entire tantalum and zirconium-based material is isolated from the outside air. This also contributes to securing the joint strength and the corrosion resistance of the joint.

Hereinafter, the present invention will be described in detail.

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

The base material of the clad material generally means a cheaper material, and thus the laminated material is not always thinner.

According to the results obtained by the present inventors, when a metal material containing one or both of Fe and Ni in a total amount of 5 wt% or more is brought into close contact with the zirconium-based material and heated to a high temperature, Fe and Zr
Alternatively, an alloy layer of Ni and Zr is formed, and the joint surface becomes weak. Therefore, the present invention is not limited to the case where the base material is steel or a nickel-based alloy, but a zirconium-based base material containing any metal material containing 5% by weight or more of one or more of Fe and Ni in total. It can be applied to clad materials.

Steels particularly suitable as a base material are ordinary steel, low alloy steel and austenitic stainless steel from the viewpoint of hot workability and usefulness as a clad steel, and heat-resistant steel containing Cr and Mo is also used as a base material. it can. Examples of nickel-based alloys suitable as base materials are Alloy 600 (75Ni-15Cr-Fe), Alloy 6
25 (60Ni-20Cr-9Mo 3.5Nb-Fe).

The composite material is a zirconium-based material, that is, pure zirconium or a zirconium alloy. Zircaloy-2 (1.5Sn-0.12Fe) is one of the readily available zirconium alloys.
-0.1Cr-0.05Ni) 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 50% or more of Zr.

The types of the base material and the laminated material are appropriately selected according to the application. For example, if the application of the clad material is a joint, it is advantageous to select a base material and a mating material that are similar to the materials to be welded.

In the present invention, tantalum is inserted as an insert material between the base material and the laminated material, which occurs at the bonding interface when the base material and the laminated material are directly bonded as described above.
This is to prevent the joint from becoming brittle due to a Zr-Fe-based or Zr-Ni-based intermetallic compound. However, depending on the joining conditions, Ta-Fe, T may be added at the joining interface between the base material and the insert material.
An a-Ni intermetallic compound may be formed. According to the investigation by the present inventors, it has been confirmed that this metal compound is formed only to a thickness of about 10 μm, but in the unlikely event that this intermetallic compound reaches zirconium on the side of the laminated material, Since the Zr-Fe-based and Zr-Ni-based intermetallic compounds are formed and the bonding strength and corrosion resistance are deteriorated, the thickness of the tantalum layer must be 10 μm or more at the product stage.

The upper limit of the thickness of the tantalum layer does not have to be set, but it is preferable that it is thin from the economical point of view, usually 10 mm.
It only needs to be high.

In the manufacturing method of the present invention, the bonding atmosphere in the frame material is maintained at a high vacuum degree of 1 torr or less or an inert gas atmosphere of 95% or more because the Zr in the laminated material is at the interface during heating at high temperature. This is to prevent the atmosphere from being absorbed and react with the atmosphere, particularly nitrogen and oxygen to weaken, and to prevent the oxidation of the bonding interface. Zr is a high temperature environment, for example
Since it is deteriorated by a very small amount of nitrogen such as 100 ppm, it is necessary to keep the voids in such a high vacuum to eliminate the atmosphere. If the pressure exceeds 1 Torr or the inert gas purity becomes 95% or less, the above brittleness becomes remarkable, and the bonding strength of the obtained clad material decreases. For this purpose, the higher the degree of vacuum or the higher the purity of the inert gas is, the more desirable it is. It is observed that the bonding strength tends to increase to some extent as the degree of vacuum becomes higher even under a high vacuum of 1 torr or less. However, since the increase is slight, and the higher the degree of vacuum, the higher the cost, the atmosphere pressure at the bonding interface may be selected within the range of 1 Torr or less in consideration of economic efficiency.

In the same method, the laminated body is heated for hot rolling while maintaining the joining interface atmosphere at the high vacuum degree or the high-purity inert gas atmosphere, and then the rolling is started. In order to produce a strong clad material, it is necessary to metal bond the base material and the laminated material at the interface during rolling, so the rolling temperature should be 800 ° C or higher at the rolling start temperature, and the reduction ratio should be sufficient for atomic diffusion. 2 or more in order to cause. When rolling at 800 ° C to 900 ° C, a nickel foil with a thickness of about 10 μm may be inserted between the base material, tantalum, and the combined material to stabilize the metal bonding at the interface. Corrosion resistance is lower than that without insertion.

However, the insertion of the nickel foil is not particularly necessary in high temperature rolling at 1000 ° C. or higher, and rather, it is preferable not to perform it because it causes Zr—Ni-based eutectic and causes embrittlement.

Regarding the upper limit of rolling temperature, when the rolling start temperature exceeds 1300 ° C, Ta-Fe-based or Ta-Ni-based intermetallic compound is 10 μm.
Since it is formed to have the above thickness and causes deterioration of corrosion resistance at the joint interface, it is necessary to set the temperature to 1300 ° C or lower. The thickness of the intermetallic compound is preferably suppressed to 2 μm or less, and from this point, the rolling temperature is particularly preferably 1100 ° C. or less.

The upper limit of the rolling reduction ratio is not particularly specified, but if the rolling reduction ratio is too large, both the base material and the laminated material become too thin.

Next, an example of a specific procedure of the manufacturing method of the present invention will be described with reference to FIG.

Prepare a base material (strictly speaking, its material) 1 with an appropriate thickness, and a mating material (strictly speaking, its material) 2 with an appropriate thickness whose size is slightly smaller than that of the base material, and set the pressure to 1 Torr or less. In a vacuum chamber for electron beam welding that has been decompressed to a vacuum degree of, a tantalum plate (strictly speaking, a plate having the same planar shape as the mating material and having an appropriate thickness between the base material 1 and the mating material 2 as shown in FIG. (Material) 3 is sandwiched and stacked.

Next, as shown in the drawing, the side surface frame member 4 is placed along the edges of the four sides of the base material, and the upper surface frame member 5 is placed on the side surface frame member 4 to surround the laminated material. The frame material is SS41 steel,
It can be manufactured from SUS304 stainless steel, and it is preferable to have a considerably strong structure in consideration of scale loss.

Instead of performing the assembly in the vacuum chamber which has been depressurized from the beginning, the assembly may be performed externally and transferred to the vacuum chamber after the assembly is completed to depressurize, or the assembly may be depressurized after assembling in the vacuum chamber before depressurizing.

Next, in the depressurized vacuum chamber, as shown in the figure, the contact portion between the base material and the side surface frame material and the contact portion between the side surface frame material and the top surface frame material are temporarily attached from the outer surface by electron beam welding, Seal the container consisting of the base material. This allows
The void between the base material and the laminated material and the surrounding space of the laminated material are shielded from the outside, and a high degree of vacuum inside the space can be maintained regardless of the ambient pressure.

The temporarily attached assembly material is taken out of the vacuum chamber, and the temporarily attached electron beam welded portion is main welded by, for example, covered arc welding, MIG, TIG welding, etc., and the welded portion is strengthened so that the internal vacuum can be maintained during heating. In the figure, 6 indicates a welding point.

As a method other than the above, after assembling the assembly material shown in FIG. 2 by welding outside the chamber, make a hole in the frame material 4 and attach a nozzle, and seal pure Ar inside the assembly material in an Ar atmosphere. There is also a method in which the nozzle is closed and the assembly material for rolling is used after the gas replacement is performed.

Then, put this assembly into the normal heating furnace as it is,
After heating to a predetermined temperature, the entire assembled material together with the frame material is hot-rolled according to the rolling schedule according to the present invention.

The frame material is removed after rolling, but if a scale or the like is attached to the surface of the frame material, the clean surface is less likely to come into direct contact, so the frame material does not bond to the base material and the laminated material by rolling, and it is easy Can be removed.

The clad material produced by the method of the present invention is such that the base material Zr-based composite material containing at least one of Fe and Ni is bonded with sufficient strength through Ta, and has good corrosion resistance at the bonded portion. Become.

This clad material can be used as the original application of the clad material, for example, zirconium on the surface on the side where the corrosive environment is severe, and steel on the other surface as a structural material having high corrosion resistance with strength secured by an iron-based material. As an example, if a tank for a highly corrosive liquid such as nitric acid is manufactured with a clad material so that the inner surface is Zr, a tank having a high corrosion resistance can be obtained at a relatively low cost.

Also, since it has excellent corrosion resistance of the joint, it is useful as a material for dissimilar material joints used for welding steel or nickel-based alloys and zirconium-based materials, and this joint makes zirconium-based materials ordinary steel, which is a general-purpose structural material, It becomes possible to weld to stainless steel or nickel-based alloy, which contributes to expanding the applications of zirconium-based materials. In addition,
Welding of zirconium-based materials of the same type can be performed by TIG welding, electron beam welding, or the like.

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

As shown in Table 1, mild steel (SS41), 21 /
4Cr-1Mo steel, austenitic stainless steel (SUS304L) and nickel-based alloy (Alloy625), pure zirconium (ASTM grade R60702) and zirconium alloy (ASTM grade R60802) are used as materials for the laminated material,
In addition, as the material for insert material, industrial pure tantalum (JISH47
01, TaP and TaH) and pure titanium for comparison (JIS No. 1
Seed) and pure nickel were used to produce a clad material by a rolling method under various conditions shown below.

The clad material using zircaloy as a composite material was manufactured only when the base material was austenitic stainless steel.

As for the dimensions of the material used, the thickness for the base material is 50 mm thick × width 200 mm × length 3
00mm, 35mm thickness x 140mm width x 240mm length for laminated material, 140mm width x 240mm length with various thickness for insert material
I used the one.

After using these materials to assemble the assembly material having the configuration shown in FIG. 2 by welding, a hole was made in the frame material and a nozzle was attached, and the vacuum degree inside the assembly material was adjusted with a vacuum pump.
Further, instead of evacuating, argon gas was sealed from the nozzle to make the inside of the assembly material a predetermined inert gas atmosphere.

Next, these assembled materials were put into a heating furnace, kept at various temperatures, and then hot rolled at a reduction ratio of 2.5 or less. The rolling monitoring temperature was 700 to 1400 ° C including the meaning of comparison.

According to the shear strength test method specified in JIS G 0601, the obtained clad material was measured for shear strength at the joint interface when the base material and the laminated material were separated in the parallel direction, and the joint strength was evaluated. did. In addition, the corrosion resistance of the joint interface is 8NHNO ₃ aqueous solution,
The corrosion depth at the interface after immersion at 100 ° C for 300 hours was evaluated. The shape of the test piece is as shown in FIG.

The results are summarized in FIGS. 4 to 7 and Table 2. Second
The thickness of the insert material in the table is the thickness after rolling and joining.

Fig. 4 shows the relationship between the bonding strength and the rolling start temperature reduction ratio. When the rolling reduction ratio is less than 2 or when the rolling start temperature is 700 ° C or less and more than 1300 ° C, the bonding strength decreases, but the reduction ratio is 2 or more. By setting the rolling start temperature to 800 to 1300 ° C, 1
It can be seen that a shear strength of 5 kgf / mm ² ) can be obtained.

FIG. 5 shows the degree of vacuum, and FIG. 6 shows the relationship between the state of an inert gas (argon) atmosphere and the bonding strength.
Good bonding strength can be obtained at a torr temperature of less than torr or at an argon purity of 95% or more in the atmosphere, but if the vacuum degree exceeds 1 torr or a purity of less than 95% in an argon atmosphere, oxidation occurs at the bonding interface, and good bonding cannot be obtained. I understand.

FIG. 7 shows the relationship between the rolling start temperature and the corrosion depth at the joint interface, and it can be seen that good joint corrosion resistance can be obtained at 1300 ° C. or lower, particularly 1100 ° C. or lower.

Table 2 shows the relationship between the bond strength and corrosion resistance of the clad material rolled in the rolling ratio of 2.5, the rolling start temperature of 1100 ° C, and the atmosphere of the bonding interface of 0.1 torr, and the type of insert material. As is clear from the table, when tantalum is used as the insert material, both the joint strength and the corrosion resistance are good, but when the insert material is not used or when titanium or nickel is used as the insert material, the joint strength and the corrosion resistance are the same. A good clad material cannot be obtained.

(Effects of the Invention) As can be understood from the above description, the present invention comprises a base material made of a metal material containing 5% or more of Fe or Ni such as steel or a nickel-based alloy, and pure zirconium or a zirconium alloy. With such a laminated material, a zirconium-based clad material having sufficient bonding strength and excellent corrosion resistance at the bonded portion can be produced, which greatly contributes to expanding the applications of the zirconium-based material.

[Brief description of drawings]

FIG. 1 is an explanatory diagram when a clad material is a dissimilar material joint, FIG. 2 is a structural explanatory diagram of a laminated body according to an embodiment of the present invention, and FIG.
FIG. 4 is a shape and dimension diagram of a test piece for evaluating the bonding strength and corrosion resistance of the rolled clad material, FIG. 4 is a graph showing the influence of the rolling start temperature and the rolling reduction ratio on the bonding strength of the rolled clad material, FIG. FIG. 6 is a graph showing the effect of the bonding interface atmosphere on the bonding strength of the rolled clad material, and FIG. 7 is a graph showing the effect of rolling temperature on the corrosion resistance of the bonded part of the rolled clad material. In the figure, 1: base material, 2: laminated material, 3: insert material, 4: side frame material, 5: upper surface frame material, 6: welded part.

Claims (1)

[Claims] 1. An iron-based material or a nickel-based alloy to be a base material, containing at least 5% by weight of one or more of Fe and Ni in total, through tantalum having a thickness of 10 μm or more at the product stage. Then, the first frame member that covers the upper surface of the zirconium material and the second frame member that covers all the side surfaces of the tantalum and the zirconium material are attached by welding to the laminated body in which the zirconium material that is to be the laminated material is stacked. Then, an assembly material in which tantalum and zirconium-based material on iron-based material or nickel-based alloy is enclosed in the frame material is manufactured, and the inside of the frame material of the manufactured assembly material is vacuumed at a pressure of 1 Torr or less or 95
% In the inert gas atmosphere, and the assembly material is hot-rolled with a reduction ratio of 2 or more and a rolling start temperature of 800 to 1300 ° C. in the material polymerization direction to perform hot rolling. A method for producing a zirconium-based clad material having excellent corrosion resistance.