JPH08100231A - High corrosion resistance zirconium alloy and method for producing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a zirconium alloy excellent in corrosion resistance, particularly uniform corrosion resistance. [Composition] High-corrosion-resistant zirconium whose f _R value of the (0001) plane on the alloy surface is 0.60 or less when the integration factor in which the texture is oriented in the direction perpendicular to the alloy surface is expressed by the Kearns integration factor f _R alloy. In the method of manufacturing a zirconium alloy in which beta processing is followed by hot working, repeated cold working and intermediate annealing, and final annealing is followed by final annealing, at least the final intermediate annealing before cold working is performed at 750 ° C. The method for producing a high corrosion resistant zirconium alloy as described above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconium alloy having excellent corrosion resistance, particularly uniform corrosion resistance, which is used as a structural member such as an apparatus exposed to high temperature water or high temperature steam environment, for example, a fuel cladding of a light water reactor.

[0002]

2. Description of the Related Art Zirconium alloy is mainly used as a component for fuel cladding of light water reactors, and Zircaloy 4 (ASTM B353 UNS No.R60) for PWRs (pressurized water reactors).
804), but Zircaloy 2 (ASTM B353 UNS No.R60802) has been put to practical use for BWRs (boiling water reactors).
These alloys have already been used for many years and can be said to be materials with satisfactory results in use. recent years,
Further, it is planned to increase the burnup and the life of the fuel, and a zirconium alloy having higher corrosion resistance is required.

Corrosion phenomena of zirconium alloys are mainly due to the nodular corrosion recognized in BWRs and mainly PW.
A typical example is uniform corrosion progressing in R.

Among these, various studies have been made on nodular corrosion. Chun T. Wang et al., Investigation
of Nodular Corrosion Mechanism for Zircaloy Produc
ts, ASTM STP 1132 (1991) p319-344, ASTM STP 754
(1982) p5 and AIME and ASME 3 (1972) p2879, the so-called Kearns integration factor (hereinafter referred to as “f
_R value ”. It is described that the higher the value is, the better the corrosion resistance to nodular corrosion. Also, (0001)
As a method for preferentially orienting the surface, JP-B-60-33891, JP-A-59-232259 and JP-A-60-67648 disclose that a material is cold-worked at a high workability or at a low temperature. A technique for obtaining a zirconium alloy excellent in nodular corrosion resistance by annealing and developing a texture is disclosed.

That is, zirconium, which is the parent phase of a zirconium alloy, is a hexagonal metal and has a limited slip system. Therefore, for example, when a pipe material or a plate material is manufactured by cold working,
As the cross-sectional area of the pipe material and the thickness of the plate material are reduced, the texture develops and becomes (0001) in the radial direction of the pipe and the vertical direction of the plate surface.
The faces are accumulated, and the f _R value is as high as 0.6 to 0.7.

As described above, various studies have been made for nodular corrosion, but no study has been made so far from the crystal orientation for uniform corrosion, which is a problem mainly in PWR applications.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a zirconium alloy having excellent corrosion resistance, particularly uniform corrosion resistance.

[0008]

Means for Solving the Problems The present inventors have studied the relationship between the crystal orientation of the material surface and uniform corrosion, and obtained the following findings.

Contrary to nodular corrosion, the lower the degree of vertical accumulation of the (0001) plane of the zirconium alloy, the more improved the uniform corrosion resistance.

Usually, the degree of integration is increased by repeating cold working in manufacturing, but at least the intermediate annealing before the final cold working is performed in a high temperature region of α phase or α + β phase higher than the conventional annealing temperature. The degree of integration can be lowered by performing the heating at a temperature higher than the temperature.

However, since the material is harder at a higher cooling rate because it is cooled from a higher temperature range than before, cracks may occur on the surface of the material in the cold working in the next step, and the cooling rate after annealing is Is preferably small.

In the present invention, the integration degree in which the texture is oriented in the direction perpendicular to the alloy surface is defined by the Kearns integration factor f.
When expressed by _R value, f _R value of (0001) plane on the alloy surface is
It is a high corrosion resistance zirconium alloy with 0.60 or less.

In the method for producing a zirconium alloy in which hot working is performed after β treatment, cold working and intermediate annealing are repeated, and final annealing is performed after final cold working, at least before final cold working. This is a method for producing a high corrosion resistance zirconium alloy, in which intermediate annealing is performed at 750 ° C or higher.
After heating, it is preferable to cool at a cooling rate up to 500 ° C of 40 ° C / sec or less.

[0014]

The zirconium alloy of the present invention is a zirconium alloy used as a structural member for equipment exposed to high temperature water or high temperature steam environment, for example, fuel cladding of a light water reactor.

From the viewpoint of chemical composition, it is a zirconium alloy in which the hexagonal α phase accounts for 80% or more by volume, and if the α phase is 80% or more, the corrosion resistance can be improved by controlling the texture. Is. For example, alloy elements Sn, Fe,
Examples include zirconium alloys containing Cr, Ni, etc. and Zr-Nb binary alloys, but the content of each alloying element is% by weight.
The following range is preferable.

Sn: 0.4 to 1.7% Sn is an element effective in improving the corrosion resistance and also has a function of ensuring mechanical strength. If the Sn content is 0.4% or more, the effect is obtained, and if it exceeds 1.7%, the corrosion resistance deteriorates.
1.7% is preferable.

Fe: 0.4% or less Fe is contained as necessary for securing corrosion resistance and strength, but if a large amount of Fe is added, cold workability is deteriorated, so 0.4% or less is preferable.

Cr: 0.2% or less Cr is also contained as necessary to secure corrosion resistance and strength like Fe, but addition of a large amount deteriorates cold workability.
0.2% or less is preferable.

Ni: 0 to 0.10% Ni is an element that greatly contributes to the improvement of corrosion resistance and may be contained if necessary. When Ni is positively contained, the content is preferably 0.005% or more. Further, since it also has a function of promoting hydrogen absorption, excessive content adversely affects the mechanical properties, so the content is preferably 0.10% or less.

Nb: 15% or less Nb may be contained in a Zr--Sn alloy for improving the corrosion resistance. Alternatively, a Zr-Nb alloy may be used. In the case of Zr-Nb alloy, it is less than 15% that the α phase is formed and the improvement of corrosion resistance due to the texture is observed.

In the present invention, when the integration degree in which the texture is oriented in the direction perpendicular to the alloy surface is expressed by the Kearns integration factor f _R value, the zirconium alloy surface is
It is important that the f _R value of the (0001) plane is 0.60 or less.

As the f _R value decreases, the corrosion resistance against uniform corrosion improves, and when the f _R value of the material surface is 0.60 or less, excellent corrosion resistance can be obtained. The material surface as used herein means at least 5 μm from the material surface, and the f _R value may be 0.60 or less over the entire thickness.

This finding is the opposite of the conventional corrosion resistance against nodular corrosion. The reason why uniform corrosion resistance is improved when the f _R value is 0.60 or less is that nodular corrosion is corrosion in which the surface oxide film grows partially, whereas uniform corrosion is the oxide film formed on the material surface. It is thought that this is because the corrosion uniformly grows, and the growth of the oxide film is suppressed by reducing the texture in the vertical direction in which the diffusion of oxygen is fast on the material surface.

FIG. 1 shows a manufacturing process of a zirconium alloy pipe by taking a pipe material as an example. Zirconium alloy tube is β processing,
It is manufactured in a process of repeating hot working, cold working, halfway annealing, and final annealing.

Since the texture is accumulated in the direction perpendicular to the (0001) plane by subjecting the material to cold working, the f _R value can be lowered by reducing the workability of cold working.

However, if the workability of cold working is lowered and the f _R value is set to 0.60 or less, the mechanical properties, particularly the tensile strength, are lowered. Therefore, it is preferable from the viewpoint of not only the corrosion resistance but also the mechanical properties. It's hard to say how.

Therefore, in the present invention, a preferable manufacturing condition is that at least the intermediate annealing before the final cold working is performed at 750 ° C. or higher. That is, in order to reduce the degree of accumulation of texture, it is necessary to reduce the degree of accumulation of texture by heating the texture accumulated by cold working up to a temperature range in which phase transformation once occurs, that of α + β phase or higher. it can. Further, even in the α phase at 750 ° C. or higher, which is slightly lower than the temperature range of the α + β phase, the degree of accumulation of the texture formed up to that time is lowered due to the growth of crystal grains and the re-dissolution of the precipitated intermetallic compound. Therefore, the heating temperature was 750 ° C or higher, preferably 830 ° C or higher, which is the temperature range of the α + β phase. The upper limit of the heating temperature is not particularly set, but it is preferably 1100 ° C. or lower because the growth of crystal grains deteriorates the cold workability.

By heating to the above temperature range, f _R
The value can be set to 0.60 or less, but since the texture is accumulated again by the subsequent cold working, this annealing needs to be performed at least in the intermediate annealing before the final cold working. The non-final intermediate annealing before cold working is 750
The annealing may be performed at a temperature of not less than 0 ° C., or may be performed in the α phase at a lower temperature than that of the present invention for the purpose of pretreatment of the cold working which has been conventionally performed.

From the viewpoint of texture, the f _R value and the corrosion resistance are not affected by the cooling conditions after heating to a high temperature, but from the viewpoint of cold working after annealing, the material strength increases due to rapid cooling, and after that, Rapid cooling is not preferable because cracks may occur on the product surface during cold working. Also, 500
Since the rapid cooling effect disappears at a temperature of not higher than 0 ° C, the cooling condition after heating is preferably a cooling rate up to 500 ° C of 40 ° C / sec or less, more preferably 20 ° C / sec or less.

[0030]

The present invention will be described below in detail with reference to examples.

A zirconium alloy having the composition shown in Table 1 was melted and, as shown in FIG. 1, β-treated and hot-tube extruded, followed by two cold rolling steps and an intermediate annealing, followed by a third cold rolling step. Final annealing was performed to produce a 10 mm diameter x 0.8 mm thick zirconium alloy tube.

[0032]

[Table 1]

Regarding the zirconium alloy tube of each composition, 3
The intermediate annealing before the second cold rolling (final cold rolling) was performed by changing the conditions as shown in Table 2.

Condition a is a conventional example, conditions b to e are examples of the present invention,
Condition F is a comparative example. Condition b: After the second cold rolling, 900 ° C x 10 minutes continuous annealing was performed by the high frequency heating device, and a cooling chamber was installed immediately after the high frequency heating device to control the cooling rate up to 500 ° C at 20 ° C / sec. did. Condition c: continuous anneal at 770 ℃ for 60 minutes in an ordinary electric furnace at 5 ℃ / sec.
It was cooled to 00 ° C. Condition 2 was continuous annealing at 770 ° C for 20 minutes and cooling at 35 ° C / sec. Condition E was subjected to continuous annealing at 900 ° C for 10 minutes and then cooled at 50 ° C / sec. Under the conditions, heating was performed at 730 ° C., which is lower than in the present invention.

The texture of the obtained zirconium alloy tube within the range of 100 μm from the outer surface portion in the thickness direction was measured by the X-ray diffraction method to obtain the f _R value.

Also, a test piece was taken from the tube and the temperature was changed to 360 ° C (200
After performing an autoclave test in pure water (kgf / cm ² ) for 350 days, the cross-section of the tube was observed with a microscope to measure the film thickness on the outer surface. Furthermore, the workability during cold working was evaluated by observing the presence or absence of cracks on the outer surface of the pipe. f
Table 2 also shows the test results of _R value, film thickness, and workability.

In the evaluation of workability, "⊚" was given when no cracks were found on the product surface, and "○" was given when minute cracks were found.

[0038]

[Table 2]

From Table 2, the coating thickness is reduced when the f _R value is 0.6 or less, and the corrosion resistance of uniform corrosion is improved by making the f _R value lower than that of the conventional zirconium alloy. Also,
Under the condition (e) where the cooling rate after annealing is high, the film thickness is reduced but the workability is deteriorated, and it is understood that it is preferable to lower the cooling rate.

[0040]

INDUSTRIAL APPLICABILITY The zirconium alloy according to the present invention has very good corrosion resistance in an environment exposed to high temperature water or high temperature steam environment and can be applied to equipment such as structural members such as fuel cladding of light water reactors.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a zirconium alloy.

Claims (2)

[Claims] 1. When the integration degree in which the texture is oriented in the direction perpendicular to the alloy surface is expressed by the Kearns integration factor f _R value,
A high corrosion resistance zirconium alloy having an ( _R ) value of the (0001) plane of the alloy surface of 0.60 or less. 2. A method for producing a zirconium alloy in which hot working is performed after β treatment, cold working and intermediate annealing are repeated, and final annealing is performed after final cold working, at least before final cold working. The method for producing a highly corrosion resistant zirconium alloy according to claim 1, wherein the intermediate annealing is performed at 750 ° C or higher.