JPH05500539A - Forming of Zircaloy milled products with good microstructure and physical properties - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Forming of Zircaloy ground product with good microstructure and physical properties From this application 1 to present 8 abandoned petitions (Ryo petition date) August 3, 990; 8 petition number 071562 , 576), which is a partial continuation of the 8 petitions currently pending (Ryo petition date: July 1991) This is a partial continuation of the petition filed on the 8th, petition number 07/726,964).

Clothes craftsman! I Oh my god! The present invention] Tube made of zirconium alloy, fuel rod spacer or boiling Improving the formability of water reactor channels by forming uniform and fine metal crystals Concerning new ways to improve. More specifically, carbide-phosphide-ke Iride beta phase solid solution heat treatment is applied and molded by embossing, and the molded product is cooled at a faster rate. Annealed, given good microstructure and nodule corrosion resistance by This invention relates to a molded product containing Zircaloy.

Zircaloy undergoes allotropic transformation when heated. Its room temperature dense hexagonal α phase is approximately 815℃ It exists until Its body-centered cubic β phase is between 980°C and the melting point of Zircaloy. Exists at temperature. Among the alloying components, iron, chromium, and nickel (in the β phase) Although dissolved, Zr2(Fe, Cr)2 and Zr2(Fe, Cr)2 are basically in the α phase. It precipitates as an intermetallic compound such as Ni). However, this type of particle is They are usually coarse and their influence on the microstructure of the product is small.

As a conventional treatment applied to Zircaloy (lower β phase 980'C to 1040 By solution heat treatment at 'C and/or quenching treatment at an early stage of molding, There are known methods to supersaturate alloying components and improve the corrosion resistance of the final product. ing. On the other hand, 1 table of intervening components such as carbon, phosphorus, and/or silicon, upper β phase These elements precipitate as zirconium compounds in the lower β phase. Let it stagnate (co-authored by C, T, Wang, P, Yi, Daniel Lin, published 1990) Anode for optical microscopy examination of solubility limits for carbon in Zircaloy Utilization of oxidation technology, Characteristics of Materials 24: 87-92). Zircaloy is the upper β phase When heated at ek and quenched at the lower β phase, these precipitates are numerous and minute; The size is sub-micron. In contrast, conventional treatments applied to zirconium alloys In principle, the basic forging process is usually from 980℃ to 1040℃, which is the lower β phase. It is carried out for half an hour to eight hours at °C. In this state, small precipitates are dissolved and large The growth of precipitates is called Ostwald Ripening. (Calvite, M. et al., Ostwalt growth of precipitates, decomposition of alloys, and beer , published in 1983 by Basen and Pergamon, Vol. (Refer to pages 61-69 of the Bulletin of the Japan Society of Metal Science). The precipitate is removed from the matrix during cooling. This is the position where the α phase forms from a certain β phase as a nucleus. Carbide, silicide, and and/or when the phosphide particles are numerous and minute, the α-base may have a variety of orientations. As a result, the growing α substrates collide with each other at high speed. This allows for various orientations. A small cluster of α-based substrates is formed, which is called “basketweave”. This is the most desirable form. No carbide, silicide gas and/or phosphide When added, the α base becomes a nucleus on the β grain boundary. Orientation with grain boundaries (alpha group) Promoting rapid longitudinal growth of the disk, the α base extends until it collides with the β grain boundary on the opposite side. At this time, all the β-crystals have been digested. There are relatively few β grain boundaries. Because there is no diversity of orientations that can contribute to α-base growth (such as carbonized stocks with many bases) It is much more limited than in the case of nucleation at the location of ionization track and/or phosphide. It will be done.

The number of orientations formed when the α base nucleates unevenly on the β grain boundaries is limited. Therefore, with the rapid growth of the α-base orientation in the longitudinal direction, the “parallel base” structure Undesirable microstructures called .

Parallel substrate structures (which are undesirable due to their limited orientational diversity and large size) stomach. According to the experimental results, the elastic compliance coefficient (a measure of material stiffness) The stress orientation with respect to the crystal structure varies by as much as 300%. Therefore, the following forming action There are also orientations that can withstand the deformations that occur during the process.

The parallel basement assemblage is in the direction of high elastic compliance when an external stress is applied. Once the parallel basement community is oriented, the parallel basement community will transfer its stress to the deformation. "brush off" towards the surrounding crystals to better orientate them. As a result, this The specially oriented parallel basement mass 1 remains intact during the deformation process. It exists as it is.

The main principle of refining the metal microstructure is to uniformly modify the individual crystals of the metal matrix. It is to form. During the next heating or annealing process, the deformed crystals are recrystallized. new, finer crystals are formed in a process known as However, deformation Parallel substrates that do not recrystallize and therefore remain at their original size during the annealing process. It does not change. In this case, from a large parallel base surrounded by relatively fine equiaxed α crystals A double microstructure is formed.

Such double microstructures (which are undesirable as they tend to fracture during further deformation) stomach. This can be achieved by properly controlling carbide and silicide particles in the early process. The occurrence of a double structure can be suppressed.

Tomo Gomi Zircaloy-2 and Zircaloy-4 are molded from β-phase quenched billets. Current zirconium alloys (such as There are regular ASTM (American Society for Testing and Materials) crystal sizes from 7 to 10.

Moreover, the process takes a long time. Example (Dai) The process for forming a tube shell Current annealing process: 1 to 4 nominal times in a vacuum furnace at 600°C to 750”C It will be held for a while. The total furnace load is usually 7000-8000 bond, and the annealing L5 The process is approximately 24 hours for 1+1 cycles. In such processing, the Materials placed may be heated above soo’c for more than 12 hours. (See Figure 1). In addition, heat slowly in the range of 500°C to 600°C. In particular, the stress in the material is reduced because the force that promotes recrystallization when it reaches high temperatures is small. The material cannot be completely recrystallized. Heated ingots, hot forged and formed billets A stepwise process is known in which the material is machined to the desired length and then hollowed out. There is. The billet is rapidly heated to the β phase (〕O15°C to 1200'C), and then It is hardened, then crushed and molded into molds. For induction heating below 650°C Therefore, the Zircaloy billet is softened before being stamped into a tube shell. Ru. By vacuum annealing at 620°C to 700'C for 1 to 3 hours, crystallization is achieved. Although the size of the crystals varies widely, it has a structure with good nodule corrosion resistance. Conium alloys can be formed.

To form more uniform and smaller crystals (mechanical production of ingots and heating to β phase) Before rolling, the ingot may be rolled to a larger diameter. however , quenching a larger one, i.e. cooling it slowly, improves the corrosion resistance of the It has been found that it deteriorates. In addition, by additionally heating after quenching, However, it has been proven that nodule corrosion resistance is impaired.

Conventional technology requires hot processing, annealing, and cold processing to obtain the final product. Various stepwise treatments such as machining and annealing are performed.

1'L intermediate annealing according to U.S. Patent 4,775,428 (Sheezus patent) After the cold deformation treatment, the final annealing treatment only affects 20 to 40% of the area. This is done to obtain a partially recrystallized material and an elongated structure. Similarly, US special 4,238,251 and those large particles that also have an adverse effect formation (Williams patent) (partial deformation of α phase to β phase before quenching) The claimed scope of the patent is that processing above the α-β phase has no particular advantage. It is also said that the cost of supplying large amounts of energy associated with processing is unnecessary. .

According to the patent of Matsukuiwen et al. (U.S. Patent No. 4,000,013), solid solution Chemical heat treatment is used to dissolve alloying components such as Nb, Mo, N1, or C. This is a heat treatment. In the case of Zircaloy, the lower limit of the β phase is 980°C, but Z In r-2,5Nb, the lower limit of the β phase is 850°C. As an alloying component on top of carbides, phosphides and/or silicides present as impurities instead of There is no mention of solution heat treatment in the β phase.

The melting and redistribution of alloying components takes place in the lower β phase, and the holding time is the same as the above melting time. It takes a shorter time than it takes for impurities to precipitate.

In the present invention (in contrast to Tomoji's prior art), the upper β phase is 1075℃~13 Heat treatment is performed between 00°C. This treatment eliminates intervening impurities such as carbon, silicon, and phosphorus. important for dissolving substances and precipitating them as many fine particles; The intervening impurities improve the basketweave microstructure and uniformity for the final product. This is to form an equiaxed α crystal structure. This upper β-phase heat treatment also Form of carbide, silicide and/or phosphide inclusions (larger than 1 μm) hinder growth. Such large inclusions impair formability in the next step. . The crystal structure of the inclusions is not a problem. The present invention (only improves steam corrosion resistance) This invention forms finely dispersed carbonized particles, silicide and/or phosphide particles without These and other advantages of In particular, it makes it possible to improve the moldability of objects.

Hitachi's European patent (patent number O○71193) also mentions solution heat treatment. However, the desirable temperature range is 860°, which is the overlapping range of α and β. C to 930'C and 1000C to 1100C which is the lower β phase. This conventional Purpose of the technique (i.e. supersaturation of alloying components to increase steam corrosion resistance of the final product) The goal is to create a state of harmony. This is a multiple cold plastic processing process (“at least (2 times), and has a fine crystalline final structure with high corrosion resistance, high strength, and high toughness. form a product.

The present invention (which has a substantially uniform microcrystalline structure and thereby has a zircaloid structure) Forming zirconium alloy products with improved formability into blanks The purpose is to provide law.

Furthermore, the present invention (orientation of metal crystals in zirconium alloy products such as pipe materials) It also aims to provide ways to improve

In addition, due to the present invention (rapid cooling treatment that generates stress), the metal microstructure is substantially To improve the method of forming uniformly recrystallized Zircaloy tube shells in is also aimed at.

In addition, the present invention (i.e., the use of zirconium alloys in tube shells and other fractured products) It is also aimed at eliminating heat treatment in the temperature range where the α and β phases overlap for forming. It has been the target.

It will be further clear to those skilled in the art by reference to the examples.

Congratulations on your skin 1 Pursuant to the above objectives, and as will be explained in more detail later, the following was unexpectedly discovered. 9. It also has a uniform crystalline microstructure, and has good formability and nodule corrosion resistance. Superior Zircaloy tube shells with Zircaloy billets such as Obtained by heat treatment. This Zircaloy billet has a cross section of approximately 100 to 1 60 square inches, with carbonized gas, phosphorous and/or silicified ruts, or a mixture thereof. At a temperature of about 075°C to about 1300°C, the temperature of the upper β phase is sufficient to dissolve the substance. Processed for 0.5-8 hours. This treatment is followed by either water quenching or air cooling. temperature range from 75°C to 980’C] Rapid cooling treatment. At this cooling rate, carbide gas silicide and/or phosphorus Chemical agriculture precipitates as a large number of fine particles that serve as nucleation sites for the α-base. This process (The basket weave structure and subsequent uniform equiaxed crystal structure in the product are It is essential to the method because it is important for the formation of Also, large (more than 1 μm) (also large) carbide, silicide and/or phosphide particles increase stress and Impairs the formability of Zircaloy during processing. Such large particles (friends) Formed when cooled at a rate slower than substantially 3°C per minute at 3°C. Jill Caloy may be cooled with air or water from 9800C to ambient temperature.

Next step (upper: reducing the cross section of the Zircaloy billet to approximately 30 square inches) It is. And the lower β plate, for example, between 980°C and 1040°C or Heat treatment is performed in advance to a temperature higher than 100℃, and then the temperature is heated at a rate of 1°C per minute or higher, preferably per second] by water quenching at a rate of 0°C to 600°C. maintain supersaturation in the alloy. Pay particular attention to the second β-phase heat treatment, and Avoid heating for more than a few minutes in the beta phase. Because if it gets too hot, Because the number of particles decreases and the precipitates of carbides, phosphides and/or silicides become coarser. It is.

If the product is tubular in shape, the billet is usually mechanically or Formed hollow by other means. After quenching, the hollow billet will melt in less than 10 minutes. Preheat to 00℃ to approx. Shaped.

The formed tube shell is then heated to about 550° C. to about 790° C. for about 5 to about 60 minutes. The annealing treatment may be performed by rapidly heating to a temperature range of C. It is shown below This heat treatment is performed only in the α phase in air or in argon, helium or This is an annealing process performed in an inert atmosphere such as nitrogen.

Ward Wataru Ω solid line Wanderer Figure 1 shows the high and low speeds of conventional vacuum annealing at 621°C for 2 hours. This is a curve showing the results of heating/cooling treatment.

Figure 2 shows a Zircaloy tube shell vacuum annealed at 643°C for 2 hours. is a micrograph showing the double microstructure of .

Figure 3 shows a Zircaloy tube shell that has been air annealed at 670°C for 50 minutes. 2 is a micrograph showing the uniform microstructure of .

A suitable husband! I friend Zirconium alloy is solution heat treated only in the upper β phase and then rapidly cooled in the α phase. As a result, a uniform microcrystalline structure is formed and the precipitates are finely dispersed in the metal matrix. As a result, a zirconium alloy with excellent formability and corrosion resistance can be obtained. 9. This solution heat treatment is performed at an intermediate stage of processing. This treatment 1 coarse carbide and Precipitation of carbides and silicides to dissolve the silicide particles back into the β-phase matrix. It is carried out at a higher temperature than the solvus for the lees. Controlled to be lower temperature than Solvus The core shape of fine, well-distributed carbide and silicide particles is growth is promoted. Zircaloy is further cooled and reaches the upper β phase transition point (transus ) (980°C), a large number of finely distributed carbide and silicide particles An α-base nucleates at the position. As a result, many clusters of α-based substrates with diverse orientations An α-phase structure, for example, a desirable basketweave transformation structure, is formed.

As is clear from the examples below, uniform equiaxed α in Zircaloy-containing products In order for the crystal to grow throughout the microstructure, tL ZrC and Z r3 (S i, P) It is important to control the particles and their size and density.

Dando A forged log-shaped Zircaloy-2 with a diameter of 14" and a length of 30" is made of carbide. Heating at a higher temperature than Solvus at about 1100℃ for about 2 hours removes all the pre-existing coarse particles. Promotes dissolution of carbide and silicide particles. This is then air cooled to room temperature.

This cooling process (top) allows the temperature to drop by exactly 3.6°C in about 1 minute. All subsequent processing, including processing, is conducted at temperatures well below the 1040°C temperature of the carbide solvus. finely distributed carbides and silicides as a result of "ostwalt growth" Prevents inadvertent coarsening of particles.

The final β-phase quenching treatment is performed on intermetallic compounds Zr-Fe, Zr-Cr, Zr -N is done to dissolve particles and give good corrosion resistance in water vapor . This β phase hardening treatment is carried out within a temperature range of about 980°C to 1040°C.

Zircaloy to this humidity range but again on a reduced cross section (approximately 6-8” diameter) Heat it and put it in water. By preheating the lower β phase in this way, the holding time can be reduced to several minutes. By limiting the initial upper β phase formed by heat treatment/cooling treatment in the melting range. nucleation position can be maintained. Also, Z　r-F　e, Z　r　-C It is certain that the intermetallic compounds of r, Zr-Ni will be completely dissolved, and this It is also believed that these intermetallic compounds will be finely and uniformly distributed. why If (Dai) these intermetallic compounds (like This is because it forms the outline of the finely separated α-based grain boundaries that serve as the core.

Example” Following the treatment described in Example I, the Zircaloy-2 was Machined from a solid billet at 650°C to 2.5" outside diameter x 0.430" width x length Press the mold into the tube shell, and then leave it for 50 minutes at 670'C Zircaloy, which undergoes air annealing, has a typical crystal size of ASTM No. It was completely recrystallized in 10 to 1/2 times, as shown in FIG. Vacuum at 643°C for 2 hours Comparison of micrographs of conventional annealed Zircaloy-2 tube shells This is shown in Figure 2. Although the crystal sizes in the conventional technology are similar, Note that there is a non-recrystallized portion extending diagonally across.

``Kauni''- Samples of Zircaloy-2 tube shells were incubated at temperatures between 620°C and 643°C. One is air annealed and the other is air annealed at a temperature of 643°C to 732°C. The samples were examined under a microscope and the results are shown in Table 1. Vacuum at 620℃ for up to 2 hours One is annealed, and the other is vacuum annealed at 643°C for up to 1 hour ( It exhibited a band of non-recrystallized part or a partially forged structure (the part marked with * in the table ). On the other hand, those that have been air annealed at 643°C for one hour, or those that have been annealed at a higher temperature. After being air annealed for less time, the product is basically completely recrystallized. Disadvantages of vacuum annealing treatment (when processing for nominally 2 hours, the Materials may be heated for more than 12 hours at temperatures above 600°C. Yes (see Figure 1). Furthermore, slowly in the temperature range of so　o=c~600'C When heated, the stress in the material is reduced, and the force that causes recrystallization when it reaches higher temperatures is small. Therefore, complete recrystallization cannot be achieved even if the nominal time is increased.

Table 1 Zirconium has a very high affinity for oxygen. Vacuum used in industry Conventional method by annealing treatment Table 1 Possibility of introducing oxygen during air annealing It is something to avoid. Oxygen easily cracks zirconium and makes it hard, so remove oxygen. This would adversely affect the physical properties of the product. Table 2 shows the burrs of Zircaloy-2. The results of an oxygen analysis of a sample of Atube shell are shown. (barrier tube shell) Made of zirconium metallurgically deposited into an alloy by hot stamping and molding. It has an internal liner. ) Zircaloy-2 barrier tube shell is , air annealed at a temperature range of 643°C to 750°C for several minutes to several hours. Barrier tube of simply extruded sample or ingot Compared to the shell, there is no appreciable effect on both the outer shell and the liner. No oxygen uptake is observed.

Table 2 Problems with air annealing using methods other than oxygen (possibility of incorporating hydrogen) It is. Hydrogen also adversely affects the physical properties of the product. Even if the density of hydrogen is very Even at low temperatures, precipitation of zirconium hydroxide compounds occurs, making the product susceptible to cracking.

Table 3 (Table: External shell Zircaloy-2 and Zircaloy of air annealed samples Hydrogen analysis of the conium liner was performed simply on a sample of the as-molded material. This is shown together with hydrogen analysis. Air annealed samples have a No significant increase in hydrogen was observed.

Table 3 *These samples were tried again, so three numbers may be written on the same sample. It is.

Table 4 (Results of autoclave tests on the above air annealed samples showed that the alloy No nodules were observed on the outer or inner diameter of the tube shell7':,) The present invention can be implemented in various forms without departing from its spirit or basic characteristics. Therefore, this embodiment is merely an example, and the present invention is not limited to this embodiment.

This is because the scope of the present invention depends on the description written before the scope of the claims. However, changes within the scope of the claims shall not be limited by the scope of the appended claims. or changes from their functionally and cooperatively equivalent equivalents are within the scope of the claims. shall be included.

Figure 22. Zircaloy-2 tube shell with 5" outer diameter x 43o width x length, Typical microstructure F2 when conventional vacuum annealing treatment is performed at 643℃ for 2 hours Shown at 00x magnification. Exhibits non-recrystallized parts.

Figure 3 Zircaloy 2-inch L-Bunel with 25” OD x 0430” width x length, empty Typical microstructure after air annealing at 670"C for 50 minutes Shown at double magnification. ASTM crystal size is 10.5.

) 4 years old Upper β-phase heat treatment and/or lower β-phase quenching treatment is performed to form the molded material or the main component. Excellent formability due to rapid cooling and/or air annealing treatment after shaping. Forms Zircaloy milled product free of large carbide (silicide or phosphide) particles This is a new method. The final product formed by this method also has a uniform It has an equiaxed α crystal structure and excellent water vapor corrosion resistance.

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Claims (1)

[Claims] The scope of the claims is: 1. It has a fine and uniform crystal structure, and contains carbides, silicides, phosphides, or their There are no particles larger than 1 μm in the substance selected from the mixture, and the particles are fine. Jill characterized by having intermetallic particles dispersed in it and having good nodule corrosion resistance. A method of forming a conium-based alloy milled product comprising: a) a zirconium-based alloy; A billet or hollow billet having a cross section of about 100 to 160 square inches, consisting of heat-treated at 1075°C to 1300°C, which is the upper β phase, for about 0.5 to about 8 hours. and then air cooling or Rapid cooling by water quenching reduces billet cross-section to approximately 30 to 90 square inches and then reheated to about 980℃ to about 1050℃ for several minutes, and heated at 10 to 60℃ per second. water quenching at a cooling rate of b) billet or hollow billet into rod, sheet or tube shell, approximately 500 Extrusion molding at a temperature of ℃~800℃, c) The extruded product is heated to about 550°C to 790°C for about 5 minutes to about 60 minutes. A method characterized in that it includes the step of annealing by rapid heating at . 2. The zirconium-based alloy pulverized product is a tube shell. The method according to claim 1. 3. characterized in that the annealing treatment is carried out in air or an inert atmosphere 4. Method according to claim 1. It has a fine and uniform crystal structure, and contains carbides, silicides, and silicon. particles larger than 1 μm in a substance selected from compounds or mixtures thereof; No grains, good nodule corrosion resistance, fine precipitates in the metal matrix A method for forming a zirconium-based alloy milled product characterized by diffusion. a) consisting of a zirconium-based alloy with a cross section of approximately 100 to 160 square inches; A certain solid billet or hollow billet is heated to about 1075°C to 13°C, which is the upper β phase. 00°C for about 0.5 to about 8 hours, followed by a temperature range of about 1075°C to 980°C. The billet is rapidly cooled by air cooling or water quenching at a rate higher than 3°C per minute. The cross-section is reduced to about 30 to 90 square inches and then heated to about 980°C to about 1 Reheat to 050℃, water quenching at a cooling rate of 10 to 60℃ per second, b) Billet or hollow billet into rod, sheet or tube shell, approximately 500 Extrusion molding at a temperature of ℃~800℃, c) The extruded product is heated to about 550°C to 790°C for about 5 minutes to about 60 minutes. A method characterized in that it basically includes the step of annealing by rapid heating at . 5. The method according to claim 1, characterized in that the crushed material is a tube shell. .