JPS59126763A - Production of zirconium alloy member - Google Patents

Abstract

PURPOSE:To improve corrosion resistance to water and steam having a high temp. and high pressure in the stage of forming a Zr alloy by >=2 stages of cold plastic working to a pipe or bar shape by subjecting the alloy to a specific heat treatment during course of the cold plastic working or after the final cold plastic working. CONSTITUTION:A Zr alloy material is worked to a pipe material or bar material by >=2 times of cold plastic working in the stage of producing a pipe or bar material of a corrosion resistant Zr alloy to be used in water or steam having a high temp. and high pressure as a structure of a nuclear plant. A part 2 made of the Zr alloy is put into a heating furnace 1 during the course of the cold plastic working stage or after the final cold plastic working, then the top and bottom ends thereof are fixed by restraining parts 7 and electricity is conducted thereto to heat the part in a temp. region of the beta phase or (alpha+beta) phase of the Zr alloy. Cooling water is thereafter ejected from many cooling nozzles 13 provided to the outside cylinder 12 of the heating furnace and in the case of the pipe material, inert gas such as Ar is passed in the pipe to cool quickly the pipe, whereby the corrosion resistance of the part 2 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for manufacturing a zirconium alloy member, and in particular to a method suitable for improving the corrosion resistance of a tube or rod made of a zirconium alloy used in the structure of an atomic couplant. The present invention relates to a method for manufacturing a zirconium alloy member.

[Prior art]

Zirconium alloys have excellent corrosion resistance and a very small neutron absorption cross section, so they are used in atomic couplet structures, especially fuel cladding tubes, channel spacers, and the like. These members are irradiated with neutrons for a long period of time in the furnace and exposed to high temperature, high pressure water or steam, which leads to oxidation, which tends to have a serious effect on plant operation. Therefore, measures to improve the corrosion resistance of zirconium alloys are important. Recently, as the burnup of fuel rods has been increasing, it has become necessary to further improve the corrosion resistance of these members.

The zirconium alloy used in the structure of the atomic couplant is Zircaloy-2 (about 1.5% Sn and 0.5% Sn on the Zr basis).
1% PE, 0.1% Cr and 0.05% Ni) and Zircaloy-4 (approximately 1.5% Sn, 0
．． 2% Fe and 0.1% Cr) is known. Manufacturing methods have also been proposed for the purpose of improving the corrosion resistance and strength of these zirconium alloys. For example, JP-A-55-10
0947 and JP-A No. 55-100967, a laser beam device is used for the final material or product of zirconium alloy to undergo β-quenching treatment (quenching from the β phase and α+β phase of the zirconium alloy). ) has been proposed.

This method has an optical point where the surface is rapidly heated with a laser beam and then hardened by self-cooling. However, this method has the following drawbacks.

First, since only a small portion of the surface layer is hardened, the unhardened interior (area where corrosion resistance is not improved) is exposed during the subsequent finishing process, and the hardening effect cannot be sufficiently achieved. Second, a reheating region is formed near the surface layer,
Precipitation of intermetallic compounds harmful to corrosion resistance occurs. Thirdly, it is difficult to control heating and cooling, which tends to cause uneven quenching, resulting in a non-uniform material.

Further, Japanese Patent Publication No. 55-100947 discloses a β-quenching method in which a product shaped into a product is heated to β phase and α+β phase and then rapidly cooled. This heating method performs a "zone heat treatment" in which the material is heated by a high-frequency heating device and then rapidly cooled by water spray. However, this manufacturing method has the disadvantage that long pieces require a lot of time for β-hardening, and the hardening tends to be uneven.

[Purpose of the invention]

An object of the present invention is to provide a method for producing a zirconium alloy member with excellent corrosion resistance, particularly a method for producing a zirconium alloy member (material or product) with excellent corrosion resistance against high temperature and high pressure water or steam.

[Summary of the invention]

The present invention provides a method for manufacturing a zirconium alloy member that includes at least two or more cold plastic working steps, in which the zirconium alloy is subjected to an intermediate step of the cold plastic working or after the final cold plastic working is completed. After heating with electricity until reaching the β phase and α + β phase temperature range of the alloy,
It is characterized by rapid cooling.

When beta-quenching a zirconium alloy using a laser beam device or high-frequency heating device to straddle the final shape of the material or the final shape of the product, the beta-quenching treatment involves solution treatment of only the surface layer of the material. The interior will retain the same properties as before β-quenching.

Therefore, the intermetallic compounds (for example, ZrCr2, z 1 x p e 5 Cr 2, etc.) precipitated during hot plastic working or normalizing in the step before β-quenching remain in the interior. Furthermore, since the internal precipitates are reheated to a high temperature during β-quenching, coarsening is promoted. Such precipitation and coarsening of intermetallic compounds tends to cause nodular corrosion, resulting in an unstable oxide film, which significantly reduces corrosion resistance.

Therefore, in the β-quenching method of only the surface layer, the surface layer, which is effective for corrosion resistance, is scraped away during the removal of the oxide film after β-quenching or during refining, and the internal parts with low corrosion resistance are exposed.

The present invention provides that the material to be treated is directly energized to rapidly heat the entire material and then rapidly cooled to perform β-quenching treatment. Here, the direct current heating may be performed either after intermediate cold plastic working or after final cold plastic working, and either method may be used.

In the direct current heat treatment, the material to be treated is uniformly and rapidly heated until it reaches the temperature range of the β phase and α+β phase of the zirconium alloy, but a heating rate of 20 c/in or higher is desirable. On the other hand, when the material to be treated is a long object such as a pipe or a rod, the rapid cooling operation is preferably carried out by spraying water or inert gas to uniformly cool the material immediately after heating with electricity. Furthermore, when the material is being disposed of, it is preferable to restrain both ends of the material, such as a pipe or a long rod, to prevent bending due to heating and cooling.

In addition, the annealing treatment after direct current heating treatment is corrosion resistant (+) %: raw material sponge zirconium and additive elements (Sn, p
e, Cr, Ni) and compression molded using a press to make a cylindrical briquette.

This was welded under an inert atmosphere to form an electrode, which was melted twice in a vacuum consumable electrode arc melting furnace to form an ingot.

(11) β-forging: The ingot was forged in the β-phase temperature range (approximately 1 ooo C) of a zirconium alloy for forming.

(ill) Solution treatment: The β-forged material was held in the β-phase temperature region of the zirconium alloy for about 3 hours, and then subjected to solution treatment in which it was rapidly cooled (water-cooled). This treatment homogenizes the alloying elements and improves the structure.

(1v) α forging: After removing the surface oxide film produced by solution treatment, forging is performed within the temperature range of the α phase region around 700 t:' for dimension adjustment.

(V) Machining, copper coating: The solution-treated material is machined into a hollow billet, which is then protected against oxidation.

Copper coating was applied to prevent gas absorption and improve lubricity during hot extrusion.

(vl) Hot plastic working (hot extrusion) near 00t? The copper-coated billet was extruded through a die with a press at a similar temperature to produce an extruded blank tube.

(Vii) Annealing: The annealing was maintained at a temperature of about 6,500 ℃ for about 3 hours under high vacuum to remove distortion due to processing. Note that the temperature of annealing Vii)' after conductive electrical heating was suppressed to a range of 400 to 550C. This is from the viewpoint of not reducing corrosion resistance.

(ViiD cold plastic working: The outer diameter was reduced and the wall thickness was reduced by rolling at room temperature, and rolling was repeated three times with annealing until the specified dimensions were reached. The degree of working in each rolling was approximately 70%. Before and after.

(1x) β-quenching treatment by direct current heating 2 This treatment was carried out using the apparatus shown in FIGS. 1 to 4.

In FIG. 1, the upper end of the material to be treated (zirconium alloy tube) 2 in the heating furnace 1 is fixed by a restraint part 7, and the restraint part 7 on the upper end side is used as a current-carrying terminal. An energizing circular terminal 11 is fixed on the lower side of the screen. A large number of cooling nozzles 13 are provided on the circumferential surface of the heating furnace outer cylinder 12, and these cooling nozzles 13 are connected to the cooling pipe 9, and on the upper end surface side and the lower end surface side of the heating furnace outer cylinder 12, respectively. Bellows 14 are attached, and the restraining portion 7 is housed within these bellows 14. As shown in FIGS. 2 and 3, the restraint section 7 is equipped with a large number of fixing jigs 15, and the workpiece 2 is
A core 16 is fitted into the lower part of the core 16, and gas is introduced into the hollow part of the material to be treated 2 from the gas introduction pipe 17 through the hollow part inside the core 16.

In the figure, 18 is a hydraulic two-cylinder case.

FIG. 4 shows a control system for the heating furnace shown in FIG. In FIG. 4, the material to be treated 2 is set in the heating furnace 1 (the current-carrying terminal 11 at the lower end is fixed and the lower part is not restrained), and the controller 3 issues an energization command to the energizing heating power source 5. The material 2 to be treated is energized and heated. Material to be treated 2
The heating state of the material to be processed 2 is detected by the temperature sensor 4, and after the temperature of the material to be processed 2 reaches a predetermined temperature, the lower end side and the restraint part 7 are activated immediately based on the restraint controller 6, and at the same time, the lower end side and the restraint part 7 are activated. Water is spouted from the cooling nozzle 13 based on the command. When an inert gas is used instead of cooling water, the inert gas is introduced into the heating furnace based on a command from the atmosphere adjustment device 10. In addition, based on the command from the controller 3, the heating furnace drive device 19
The heating furnace 1 rotates at the same time as the cooling water and inert gas are spouted from the cooling nozzle, thereby achieving a uniform cooling effect and a uniform hardening effect.

In this example, after the material to be treated 2 is brought to the temperature range of β phase and α+β phase of the zirconium alloy (xoooc in this example) by heating with electricity, the lower end of the material to be treated 2 is restrained, and at the same time, the cooling nozzle is Water was spouted from No. 13 to rapidly cool the container. Further, during rapid cooling, argon was fed through the gas introduction pipe 7. In this embodiment, since the material to be treated 2 is a thin-walled tube, it can withstand compression during restraint by the core 16, and oxidation of the inner surface of the tube can be prevented by introducing argon gas.

The effect of restraint cooling on the material to be processed is to restrain the shrinkage in the longitudinal direction due to temperature drop, which prevents bending and significantly improves oxidation on the inner surface, significantly reducing the number of steps required for finishing. The energization heating conditions were determined from the relationship between the heating time and the load current and voltage shown in FIG. 5, and this example is a master curve with a heating temperature of 1000 t:'.

(x) Precision machining: After the final normalization, precision machining was performed for the purpose of removing 9 curves of the cladding tube, removing the oxide film, and adjusting the dimensions.

The structure of the cross section of the Zircaloy coated tube manufactured by the above method was observed. Comparative cladding tubes were a sample in which the above step (1x) was omitted (a manufacturing method that is currently widely used), and a sample in which the above step (IX) was β-quenched with a laser beam (Japanese Patent Application Laid-Open No. 55-100947. 55-100
967). The results of tissue observation are schematically shown in FIG. As shown in FIG. 6(a), the cross-sectional structure of the conventional method (a) exhibits a relatively coarse α-phase single structure, and intermetallic compounds are considerably large and coarse. Conventional method (b)
As shown in FIG. 6(b), only the surface layer of the cross-sectional structure exhibits an α phase with extremely fine crystal grains, and intermetallic compounds are also finely precipitated (this structure is effective for corrosion resistance). on the other hand,
The inside shows a composite structure exhibiting the structure of conventional method (a). However, this composite structure does not exist uniformly throughout the cross section of the tube, and in some cases, the effective fine structure formed on the surface layer is lost, leaving a single structure inside. The reason for this is thought to be that the surface layer portion was cut during the tiv manufacturing process in the above step (x) and the β quenching unevenness. The cross-sectional structure of (C) obtained by the method of the present invention exhibits a single structure of α phase with extremely fine crystal grains, as shown in FIG. 6(C). In addition, the intermetallic compounds are finer and more uniformly distributed, and the amount of precipitation is smaller than in conventional materials. As described above, it has been found that the structure of the cladding tube produced by the method of the present invention exhibits a fine α phase suitable for corrosion resistance, and also exhibits a uniform single structure throughout the tube cross section.

Next, a corrosion test was conducted on the cladding tube manufactured by the direct current heating method of the present invention. The cladding tube for comparison was made of the same material as the sample used for the above-mentioned tissue observation. Corrosion test conditions are 520C,
It was held in high temperature, high pressure steam at 105 kg/cm2 for 50 hours. The results are shown in FIG.

Looking at the corrosion state of the material treated according to the present invention, the corrosion weight increase is about 100
mg/d rll, and its surface exhibited a black, glossy appearance, indicating that it had excellent corrosion resistance. On the other hand, the corrosion weight increase of conventionally treated material (b) was 60
The variation is significant at ~800 mg/d mz.

Its surface shows localized nodular corrosion (unstable oxide film) characteristic of Zircaloy alloys. Conventionally treated material (a
) shows a significantly high value. In addition, the surface shows signs of markedly advanced corrosion, with nodular corrosion distributed over the entire surface and becoming coarser.

Thus, the method of the present invention was found to be suitable for producing products with excellent corrosion resistance.

Example 2 The zirconium alloy used has the same chemical composition as in Example 1. The manufacturing process was the same as in Example 1 up to hot plastic working, and after repeating the subsequent cold plastic working twice, the direct current heating treatment of the present invention was performed. The normalizing temperature after direct current heating was 500 C (method in Table 1).
d)).

As a result of the corrosion test, the properties were exactly the same as those of Example 1, and the corrosion resistance was excellent.

Example 3 The zirconium alloy used was 1.4 wt% Sn.

0.25wt%Fe, o, tzwt%Cr and balance Zr
Out. This alloy was melted in the same manner as in Example 1.

After β forging and hot plastic working, cold plastic working was applied to a shape close to that of the product, and then the direct current heat treatment of the present invention was performed. Next, the corrosion of the image processing material was tested in high-temperature, high-pressure steam. As a result, the corrosion resistance was as good as that of the previous example.

〔Effect of the invention〕

According to the present invention, a zirconium alloy, particularly a zircaloy alloy, can be made into fine crystal grains and have a fine and uniformly distributed structure with a small amount of precipitated intermetallic compounds, thereby improving corrosion resistance. Therefore, the performance of equipment made of Zircaloy alloy can be improved and the service life can be extended.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a heating furnace in an electrical heating apparatus for carrying out the present invention, Fig. 2 is an explanatory diagram showing a method of restraining the material to be treated in the heating furnace of Fig. 7, and Fig. 3 is a diagram during cooling. A cross-sectional view showing the structure of the lower part of the material to be treated, FIG. 4 is a block diagram of the current heating device, FIG. 5 is a relationship between heating time, load current and voltage under direct current heating conditions, and FIGS. 6(a) and (b)
6 is a schematic diagram of the cross-sectional structure of a tube manufactured by the conventional method.
Figure (C) is a schematic diagram of the cross-sectional structure of a pipe manufactured by the method of the present invention. Figure 7 shows a bar graph of the results of a corrosion test. 1... Heating furnace, 2... Processed material, 3... Control machine,
4... Temperature sensor, 5... Current heating power supply, 6...
Restraint control machine, 7... Restraint part, 8... Cooling control machine, 9
...Cooling piping, 10...Atmosphere adjustment device, 11...
・Electricity terminal, 12... Heating furnace outer cylinder, 13... Cooling nozzle, 14... Bellows, 15... Fixing jig, 16.
... Core, 17... Gas inlet pipe, 1st eye 4th eye Kaya S eye load - I straight (Electrical 5K

Claims (1)

[Claims] 1. In a method for manufacturing a zirconium alloy member having at least two or more cold plastic working steps, after the intermediate step of the cold plastic working or the subsequent final cold plastic working step, A method for manufacturing a zirconium alloy member, which comprises heating a zirconium alloy with electricity until it reaches the temperature range of the β phase and α+β phase of the alloy, and then rapidly cooling the alloy. 2. The method of manufacturing a zirconium alloy member according to claim 1, wherein the zirconium alloy member is a tube or a rod. 3. A method for producing a zirconium alloy member according to claim 2, wherein the quenching is performed by injecting water or inert gas into the tube or rod. 4. The method of manufacturing a zirconium alloy member according to claim 3, characterized in that both ends of the tube or rod are fixed when the water or inert gas is injected.