JPS6033891B2 - Corrosion-resistant zirconium alloy and its manufacturing method - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a corrosion-resistant zirconium alloy used as a structural material that requires corrosion resistance, such as a saponification material for a nuclear reactor or a structural material for a chemical device, and a method for manufacturing the same. .

Technical background of the invention and its problems Generally, Zircaloy-2,
Zirconium alloys such as Zircaloy 4 are used in nuclear reactors because of their small thermal neutron absorption cross section, excellent corrosion resistance in the atomic environment, and sufficient mechanical properties as structural materials. It is often used as a structural material inside the furnace.

However, as these zirconium alloys are used for a long time, white corrosion products due to a corrosion reaction called so-called nodular corrosion are formed in spots on the surface of the zirconium alloys.

This is because the zirconium alloy reacts with high-temperature water, and the generated hydrogen accumulates between the alloy base material and the oxide film on the surface, forming corrosion products. These corrosion products accumulate on the surface over time and may eventually cause the surface to peel off, leading to a decrease in the strength of the structural material. In addition, a zirconium hydride is formed in which the generated hydrogen penetrates into the interior of the alloy.
When this is formed in a direction perpendicular to the surface, there is a problem of so-called hydrogen embrittlement due to the continuous hydride. In order to solve these problems, alloys containing potassium, yttrium-ursium as a zirconium alloy (see US Pat. No. 3,261,682), or inert materials such as gold, silver, platinum, nickel, chromium or niobium have been developed. A structure in which the surface of a zirconium alloy structural material is coated with a dissimilar metal layer to prevent hydrogen from penetrating has been proposed (see Tokusei No. 52-562y).

However, these methods are technically complicated and economically expensive, and in particular, the latter structure in which dissimilar metal layers are present causes new problems such as contact corrosion, and is not a satisfactory solution.

OBJECTS OF THE INVENTION The present invention was made in view of the conventional problems, and provides a corrosion-resistant zirconium alloy that has excellent nodular corrosion resistance and prevents formation of hydrogen arms, and a method for producing the same.

Summary of the Invention The present inventors have developed a zirconium alloy with nodular corrosion resistance.
In order to improve corrosion resistance, we researched the corrosion state of the surface of alloy members in a water vapor environment and found that the state of generation of white corrosion products differs depending on the crystal plane orientation of the member surface. It was made by

That is, the present invention has a weight ratio of Snl. 7% or less, Feo. 2
4% or less, Cro. 15% or less, Nio. 08% or less,
and at least one selected from Nb2.5% or less
Zirconium lattice 0001 located at least near the surface of a zirconium alloy whose seeds and remainder are Zr
A first aspect of the present invention is a corrosion-resistant zirconium alloy characterized in that the zirconium alloy is oriented in a direction perpendicular to the surface of the alloy.

Moreover, the present invention has a weight ratio of Snl. 7% or less, Feo. 2
4% or less, Cro. 15% or less, Njo. A zirconium alloy consisting of at least one selected from 08% or less and 2.5% or less Nb, and the remainder being Zr, is given a thickness T before cold rolling and a finished cold rolling thickness t (T-
After cold rolling so that the working rate expressed as t)/T x 100% is 10% or more, competitive slowing is performed at a temperature above the crystallization temperature of the zirconium alloy and below the 8-phase formation temperature, at least near the surface. Zirconium 60,000 lattice located 000
1> is oriented in a direction perpendicular to the surface of the alloy.

Furthermore, the present invention provides a weight ratio of Snl. 7% or less, Feo. 2
4% or less, Cro. 15% or less, Nio. 08% or less,
and at least one selected from Nb2.5% or less
A zirconium alloy whose seed and remainder are Zr has a cross-sectional area D before compression processing and a cross-sectional area d after compression processing, (D-
d) Compression processing is performed so that the processing rate expressed by /D x 100% is 2% or more, and the zirconium 60,000 lattice located at least near the surface is processed in a direction perpendicular to the surface of the alloy. The third gist is a method for manufacturing a corrosion-resistant zirconium alloy characterized by orientation.

The present invention will be explained in detail below.

For example, the zirconium alloy having the above composition range used in the present invention has a weight ratio of 1.2 to 1.7% tin and 0.07% iron.
-0.20%, chromium 0.05-0.15%, nickel 0.03-0.08%, balance zirconium, which is called Zircaloy-2, tin 1.2-1.7
%, iron 0.18-0.24%, chromium 0.07-0.1
It can be applied to zirconium alloys such as Zircaloy-4, which is composed of 3% zirconium and the balance is zirconium, or zirconium alloys such as zirconium-2.5% niobium series, zirconium-1% niobium series, or ausenite.

In the alloy of the present invention, the zirconium 60,000 lattice cells located at least near the surface thereof are oriented perpendicularly to the alloy surface.

Figure 1 is a schematic diagram showing the conventional texture of Zircaloy-4, in which arrows indicate 0001〉, which is not perpendicular to the (0001) plane of the hexagonal zirconium core, and
1) has a relatively random orientation.

On the other hand, the alloy of the present invention has <000
1> are aligned in the direction perpendicular to the surface. The fR value of the texture is used as an index to express the proportion of 0001> oriented perpendicularly to the alloy surface, and the fR value of the alloy of the present invention is 0.66 or more, making it economical. In the practical range, 0.66 to 0.70 is desirable.

Next, a method for producing the alloy of the present invention will be explained.

When producing a plate material using the alloy of the present invention, the plate material is produced by repeatedly cold rolling and annealing a material obtained by hot working an ingot to a predetermined finished thickness. In the present invention, in the step of cold rolling the material after hot processing, the total rolling rate of each cold rolling process, that is, the hot processed material (
The processing rate expressed as (T-t)/T x 100% is 10% or more, preferably 15 to 98%, as the plate thickness T of the material before cold rolling and the finished plate thickness t of cross-rolling. do.

The reason for this is that if the processing rate is less than 10%, it becomes difficult to orient the zirconium hexagonal lattice 0001〉 located near the surface of the zirconium alloy in a direction perpendicular to the surface of the alloy. . Furthermore, the annealing performed after the cold rolling process is performed at a temperature above the recrystallization temperature of the zirconium alloy (approximately 550°C) and below the 8-phase formation temperature (about 8400°C), preferably in the range of 700 to 8400°C, and then Air cool. The reason for limiting the temperature conditions during annealing is that if the temperature range is exceeded, the zirconium hexagonal lattice located near the surface of the zirconium alloy
1> is difficult to align in a direction perpendicular to the surface of the alloy. As a result, the hexagonal zirconium lattice (0001), which was oriented in a slightly inclined state with respect to the surface during cold rolling, can be aligned vertically by this annealing. The conventional sintering process for forming zirconium alloys into plates is carried out simply to soften the plates that have been work-hardened by cold rolling, and is heated for a short period of time to approximately 620 qo, which is slightly higher than the recrystallization temperature. Ta. However, in the present invention, the <0001> of the zirconium hexagonal lattice is positively regulated by heating the sintered body at a high temperature or for a long time, in practice, at a high temperature of 700° or higher for about 1 to 5 hours. This is intended to improve corrosion resistance. Next, the second manufacturing method of the present invention will be described. A zirconium alloy is compressed and the zirconium hexagonal lattice at least near the surface is
001> is oriented perpendicularly to the alloy surface.

This compression processing is performed so that the processing rate expressed as (D-d)/D x 100% is 2% or more, preferably 3 to 85%, where the cross-sectional area D before compression processing and the cross-sectional area d after compression processing are expressed as (D-d)/D x 100%. go to The reason for this is that if the processing rate is less than 2%, it becomes difficult to orient the <0001> of the zirconium hexagonal lattice located near the surface of the zirconium alloy in a direction perpendicular to the surface of the alloy. Examples of this compression processing method include peening processing such as shot blasting, shot peening, grit blasting, and sandblasting, swaging processing such as extrusion swaging and rotary swaging, and pressing processing. In this case, the peening process is a mechanical compression process performed only on the surface of the alloy member, and involves cutting a material such as a rod into a predetermined shape,
By peening the surface of an alloy member that has been given a finished shape by swaging, the <0001> of the zirconium 60,000 lattice near the surface can be oriented perpendicularly to the surface. By performing light swaging or pressing, it is possible to align the orientation of the surface near the surface of the machine. Furthermore, since some unevenness remains on the surface of an alloy member that has been subjected to compression processing, it is preferable to finish the surface by cutting it lightly to the extent that the compression processing surface layer remains. Alternatively, the entire alloy material may be strongly compressed to align the <0001> of the zirconium hexagonal lattice to the inside. For example, after strongly compressing an alloy rod by swaging, this alloy rod is cut into a predetermined member shape. Any method is fine.

Further, the present invention may be performed not only by compression processing but also in combination with cold rolling processing.

Alternatively, a method may be used in which compression and rolling proceed simultaneously, such as in extrusion processing or drawing processing, and <0001> is directed in a predetermined direction. Alternatively, a method in which a sintering process is added after the compression process in the same manner as described above may also be used. The corrosion-resistant zirconium alloy of the present invention thus obtained has excellent resistance to Dural corrosion because the <0001> of the hexagonal zirconium lattice located at least near the surface is oriented perpendicularly to the alloy surface. There is.

This is because when the zirconium 60,000 lattice 0001> is oriented perpendicular to the alloy surface, hydrogen generated by contact with high-temperature water enters the interior along the orientation direction, and the zirconium lattice on the surface It is thought that the accumulation of hydrogen in the oxide film portion is prevented or suppressed, and as a result, the generation of white corrosion products is prevented and corrosion resistance is improved. In addition, the plate-shaped zirconium hydride produced by hydrogen penetrating into the alloy along <0001> is formed parallel to the alloy surface and is not continuous in the vertical direction, reducing the risk of hydrogen arm formation. can. Although the present invention has been described with respect to alloys, it can be similarly applied to titanium, hafnium, or alloys thereof to improve corrosion resistance.

EXAMPLES OF THE INVENTION Example 1 Commercially available Zircaloy-4 was melted using a consumable electrode type vacuum arc melting furnace, and the obtained coin coins were hot forged to form a plate shape with a thickness of 3 mm.

This material was subjected to repeated cold rolling and annealing three times to finally obtain a plate material with a thickness of 2. The total rolling rate in this tin cold rolling process was 93%, and the bran dulling condition was 7.
After heating at 5,000° C. for 3 hours, it was air cooled. The obtained zirconium alloy plate was subjected to X-ray diffraction to examine the whale orientation state of <0001), and the fR value was 0.689. A test piece was cut out from this alloy plate, and the surface was polished with diamond powder having a particle size of about 25 m.
It was maintained in a water vapor environment of 0.07k9/c. In the above test, no speckled white product was observed on the surface even after a holding time of 4 feeding hours.

We also investigated the change in weight increase due to corrosion.
This is now shown by the solid line a in the graph of FIG. In addition, for comparison with the present invention, annealing was performed at 620 qo in the above method.
After heating for 2 hours, the secondary zirconium alloy plate was air-cooled and rolled.

When this alloy plate was subjected to X-ray diffraction to examine the orientation state of 0001), the fR value was found to be 0.623. In addition, in a corrosion test in a hydrogen atmosphere, white speckled corrosion products were generated after several hours and grew larger over time. When the change in weight increase due to this corrosion was investigated, it became as shown by the broken line b in the graph of FIG. Example 2 Zircaloy-2 was melted using a consumable electrode type vacuum arc melting furnace,
The obtained mirror ingot was forged using a forging press machine, and then machined to produce a hollow billet.

Next, after hot extruding this hollow billet, a pilger
A tube was produced by cold rolling three times using a rolling mill. This tube was subjected to impact vibration by swaging and compressed at a cross-sectional competitive processing rate of 6%. When the resulting zirconium alloy tube was examined for <0001> orientation by X-ray diffraction, the fR value was 0.701.

In addition, a test piece was cut out from this tube and subjected to a corrosion test in high-pressure steam in the same manner as in Example 1. As a result, no white corrosion products were observed even after 24 hours had passed, and there was no increase in weight due to corrosion. As shown by the solid line a in the graph of FIG. 4, the corrosion weight increase was as low as about 70 9/dm2, and it was confirmed that it had excellent nodular corrosion resistance. In addition, for comparison with the present invention, the fR value of an alloy tube that was not compressed by swaging was measured and was 0.620, and the corrosion test in high-pressure steam was shown in the graph in Figure 4. As shown by the broken line b, the corrosion weight increase was about 650 9/dn2.

Effects of the Invention As explained above, according to the corrosion-resistant zirconium alloy and the manufacturing method thereof according to the present invention, the (0001) plane of the zirconium 60,000 lattice near the alloy surface is oriented perpendicularly to the surface, thereby achieving excellent corrosion resistance. It has Jufu corrosion properties and can prevent the risk of hydrogen arm formation.
It is particularly effective as a structural material for nuclear reactors and chemical equipment that come into contact with high-temperature water.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the conventional texture of Zircaloy-4, Figure 2 is a schematic diagram showing the texture of the corrosion-resistant zirconium alloy of the present invention, Figure 3 is an example of the present invention, and Figure 4 is an example of the present invention. 2 is a graph showing weight changes due to corrosion of a corrosion-resistant zirconium alloy and a conventional zirconium alloy. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. Sn 1.7% or less, Fe 0.24% or less in weight ratio,
Cr 0.15% or less, Ni 0.08% or less, and Nb2
．． <0001> of the zirconium hexagonal lattice located at least near the surface of a zirconium alloy consisting of at least one selected from 5% or less and the remainder Zr is oriented in a direction perpendicular to the surface of the alloy. Corrosion-resistant zirconium alloy featuring: 2 Weight ratio of Sn 1.7% or less, Fe 0.24% or less,
Cr 0.15% or less, Ni 0.08% or less, and Nb2
．． A zirconium alloy consisting of at least one element selected from 5% or less and the balance being Zr, the thickness T before cold rolling and the finished cold rolling thickness t, (T-t)/
After cold rolling so that the processing rate expressed by T x 100% is 10% or more, the zirconium hexagonal lattice located at least near the surface is annealed at a temperature higher than the crystallization temperature of the zirconium alloy and lower than the β-phase formation temperature. <0001> of
A method for producing a corrosion-resistant zirconium alloy, which comprises orienting the alloy in a direction perpendicular to the surface of the alloy. 3 Sn 1.7% or less, Fe 0.24% or less in weight ratio,
Cr 0.15% or less, Ni 0.08% or less, and Nb2
．． A zirconium alloy consisting of at least one type selected from 5% or less and the remainder Zr has a cross-sectional area D before compression processing and a cross-sectional area d after compression processing, (D-d)/D
Compression processing is performed so that the processing rate expressed as ×100% is 2% or more, and the <0001> of the zirconium hexagonal lattice located at least near the surface is oriented in the direction perpendicular to the surface of the alloy. A manufacturing method for a characteristic corrosion-resistant zirconium alloy.