JPH0417917A - Manufacture of single seamless tube - Google Patents

Abstract

PURPOSE: To increase the bonding strength of an associated surface by creating a bonding state between metallic layers by a hot equilibrium press under sufficient pressure and adequate temp. and promoting diffusion in the bond boundary part at and for a sufficiently high temp. and time. CONSTITUTION: A single seamless tube consisting of at least the two concentric metallic layers is produced by associating at least two concentric cylindrical elements and forming a billet assembly for extrusion. For example, this billet consists of zircaloy 6 on the outer side and zirconium 7 on the inner side. The billet assembly described above is treated by the hot equilibrium press under the sufficient pressure and adequate temp., by which the bonding state is created between the metallic layers. The billet is further heated at and for the sufficiently high temp. and time to promote the diffusion in the bond boundary part. As a result, the single seamless tube which is increased in the bonding strength and is adapted to obviate the occurrence of the defect in the bounding boundary part of the tube may be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a multilayer tube suitable for nuclear/chemical processing and other industrial uses.

(Prior Art) When manufacturing seamless tubes made of multilayer metal, coextrusion is usually used. A metal cylinder consisting of multiple layers, one inside and the other concentric, is formed into an extruded billet. The annular opening at each end is sealed by vacuum welding.

The billet is preheated to a suitable temperature and pressed to form a metallurgical bond between adjacent layers. During the extrusion step or after further shrinking of the tube, defects are sometimes found at the bond interface.

The main reason for such problems is that during extrusion molding,
This is because there is insufficient time for bonding to occur at that temperature and time for diffusion to occur at the bonding boundary.

In the conventional method of making two-layer zirconium-zirconium alloy billets, the outer cylindrical zirconium alloy part is first heated to 980-1200°C and water quenched to undergo beta heat treatment to improve the corrosion resistance of the final tube. It improves the grain size and creates a fine grain structure.

After combining with the inner zirconium liner, the billet is extruded into a tube shell and reduced by a tube reducer to a final size suitable for nuclear fuel cladding. Inspection methods such as ultrasonic technology are used to rigorously inspect bonding boundaries for defects measuring a few tenths of a centimeter.

(Problems to be Solved by the Invention) A first object of the present invention is to provide a method for manufacturing a tube made of multilayer metal in which bond boundary defects do not occur on concentric meeting surfaces of the tube.

A second object of the present invention is to provide a method for imparting strong bonding force by diffusion to the interface between an inner metal layer and an outer metal layer.

According to the present invention, in order to achieve the above-mentioned objects, at least two concentric cylindrical elements are combined to form a billet assembly for extrusion. A method of manufacturing a single seamless tube consisting of metal layers, the method comprising: processing the billet assembly by hot isostatic pressing under sufficient pressure and temperature to create a bond between the metal layers; heating the billet at a high temperature for a sufficient period of time to promote diffusion at the bond interface, thereby increasing the bond strength and preventing bond interface defects from forming in the tube. A method of manufacturing a single seamless tube is provided.

In the method of the invention, bonding at the interface between concentric cylindrical tubes is achieved by hot isostatic pressing the billet assembly at a relatively low temperature with a pressure high enough to cause bonding at the interface. be done.

The billet assembly is heat treated at a higher temperature under atmospheric pressure to cause diffusion across the bond and thereby strengthen the bond between the associated metal layers.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in Figure 2, the billet has an outer surface of Zircaloy (
6), the inside is made of zirconium (7).

Both cylindrical elements are cleaned, assembled and vacuum welded so that no gas or other foreign substances can be detected between the different metal layers.

The temperature for subsequent hot equilibrium pressing is 600-800°C.
range, argon pressure is 1055-3164 kg/c
m2 (15,000 to 45,000 psi). Argon is commonly commercially available.

After the hot isostatic pressing (HIP) step, the billet is heated for a short time in the temperature range of 1000-1200° C. so that diffusion occurs at the joints. However, the degree of diffusion.

There should be no diffusion that would change the properties of the metal on either side of the joint.

The billet is quenched in a quenching agent. The quenching agent is preferably a rapid refrigerant. Water is preferably used as the quenching medium, but salt water or other quenching agents can be used if desired.

The preheating and quenching conditions are such that secondary phase particles precipitate, which serve as nucleation sites for recrystallization and provide good corrosion resistance to one or all of the metal layers.

In this way, when the billet is prepared, extruded or even reduced into a tube, the bonds remain diffused and free from defects. FIG. 1 shows typical bond defects produced by conventional methods for comparison and contrast with those produced by the method of the present invention.

The method of the present invention will become clearer from the following examples.

After assembly and vacuum welding, zirconium-zircaloy 2, (Zrl-1,5%5n-0,2%
Fe-0, lCr-0,05Ni) billet, outer diameter 15
．． 2c+a (6 inches) x inner diameter 4.2cm (1,650
inches)
Treat for 2 hours.

After removal from the container, the billet is preheated in an induction furnace and held at 1150°C for 3 minutes, then quenched in 20°C water.

Figure 3 shows the quenched billet at a distance of 12.7 cm (5 cm
FIG. The sample undergoes stain corrosion such that the Zircaloy 2 appears dark gray and the zirconium becomes bright.

The absence of sharp bonds indicates that the desired degree of diffusion has occurred between the bonded components.

Billet, outer diameter 6.4C (2.5 inches) x inner diameter 4
．． After extrusion to 2 am (1,650 inches) x (length) and annealing at 663° C. for 2 hours, a sample is taken from one end of the tube for examination of the microstructure.

Figures 4a and 4b show stain-corroded samples.
These are photographs enlarged to 180X and 750X, respectively.

At lower magnification (180x), the bond between zirconium and Zircaloy-2 is visible, but at higher magnification (7x), the bond between zirconium and Zircaloy-2 is visible.
50x), the bond is widened.

Figures 5a and 5b are photographs showing, at the same magnification, the joints of coextruded tubes with billets prepared in the same way, but without hot isostatic pressing and quenching.

As is clear, no diffusion occurs at the bond in that sample.

Figures 6a and 6b are photographs showing the diffusion bond and non-diffusion bond, showing differences in the grain structure near the bond.

Oxygen, Sn, Fe, in pure zirconium liner
The contents of Cr and Ni are generally lower compared to Zircaloy. This gives the zirconium liner high ductility and resistance to stress corrosion cranking caused by iodine when used in nuclear reactors.

A sample of a billet consisting of a Zircaloy-2 outer layer and a Zr liner and treated as described in this example shows that the diffusivity of all the elements mentioned above is 3.74 times the thickness of the liner. % (see Table 1).

Experiments have shown that the desirable properties of zirconium mentioned above are unaffected by the HIP and beta quench treatments, so zirconium treated in this way performs similarly to conventional tube liners in a nuclear reactor environment. You can use it.

Zr-2, which was assembled by shearing and vacuum welded.
5%Nb/Zircaloy 4 (Zr-0,15Sn-0,
2Fe-0, ICr) billet under an argon pressure of 1055
kg/c+++”, hot isostatic pressing at 615°C for 3 hours. The treated billet is then preheated and kept at 1150°C for 3 minutes before being quenched in 20°C water. do.

The billet was extruded at 650°C and the outer diameter was 6.4cm.
m x inner diameter 4.2 cm x (length).

The diffused bond was the same as described in Example 1.

Although the present invention has been described above based on preferred embodiments, devices of various sizes can be manufactured using the techniques disclosed herein and taking advantage of its advantages.

Accordingly, the invention is limited only by the scope of the claims appended hereto.

(yachomu tr) O

[Brief explanation of drawings]

FIG. 1 is a 180X photograph showing typical bond defects between upper Zircaloy-2 and lower Zirconium coextruded from one assembled billet by conventional methods. The specimen is stain-corroded. FIG. 2 is a cross-sectional view of the combined two-layer metal billet. The outer layer is Zircaloy-2 and the inner liner is Zirconium. FIG. 3 is a 180× photograph showing a stain eroded diffusion bond between upper zirconium and lower zircaloy-2 that has been subjected to IIP and quench treatment (according to the present invention). Figures 4a and 4b are photographs showing stain-etched diffusion bonds between upper zirconium and lower zircaloy-2 treated by the method of the present invention after extrusion of the billet assembly. Figure 4a is 180
X, Figure 4b is 750x. Figures 5a and 5b are photographs showing non-diffusion bonding between upper zirconium and lower zircaloy-2 by conventional extrusion methods. Figure 5a is 180x and Figure 5b is 750x. Figures 6a and 6b are photographs showing the granular structure of the specimens shown in Figures 4b and 5b, respectively, after being subjected to corrosion treatment with HNO, -HF-820 and magnified at 750x. (6) Zircaloy (7) No change in the cleaning content of zirconium drawing) rub, i No change in cleaning content of LIFc drawing) F/, 4σ. FIG. 4b. Figure 11
i1's? III) (No change in content) F/, 5a
. F/to, 5b.

Claims (6)

[Claims] (1) A method of manufacturing a single seamless tube consisting of at least two concentric metal layers by combining at least two concentric cylindrical elements to form a billet assembly for extrusion, the method comprising: processing the billet assembly by hot isostatic pressing at a temperature to create a bond between the metal layers; heating the billet at a sufficiently high temperature for a sufficient period of time;
1. A method for manufacturing a single seamless tube, comprising the step of promoting diffusion at the bonding boundary, thereby increasing the bonding force and preventing the tube from having defects at the bonding boundary. (2) Claim (2) wherein the billet consisting of at least one cylindrical element is made of zirconium or a zirconium alloy.
1) The manufacturing method described. (3) Approximately 1055 to 3164 kg/hot equilibrium press
The manufacturing method according to claim 1, wherein the manufacturing method is carried out under a pressure of cm^2. (4) The manufacturing method according to claim (3), wherein the hot equilibrium pressing is performed at a temperature of about 450 to 1250°C. (5) The manufacturing method according to claim (2) or (3), wherein the pressed product is heated to a temperature of about 450 to 1250°C. (6) After the heating step, the product is quenched by immersing it in a quenching agent maintained at a temperature of about 0 to 100°C.
) manufacturing method described.