JPH0154427B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION This invention relates to a continuous process for annealing zirconium and its alloys. Furthermore, the invention specifically deals with the use of a nitrogen atmosphere, which allows the process to be continuous. [Prior Art] The concept of continuous annealing of metals is old in the art. US patent where hydrogen/nitrogen atmosphere is used
Even the idea of continuous annealing in a nitrogen atmosphere has been implemented for annealing steel and certain metals, as seen in 4183773. It is also known to nitride zirconium-containing metals to create hardness. However, this hardness comes on top of the loss of ductility. This metal is highly reactive;
The conventional method of annealing zirconium is by vacuum annealing because its reactivity is significantly greater than that of steel. This vacuum annealing is very uneconomical not only in terms of equipment but also in terms of its operation. A continuous method of zirconium annealing for economical purposes is needed. However, nitrogen atmospheres, which are inexpensive, are avoided due to the reactivity of this metal. This is covered by US Patent 4000013
It is also recognized that a vacuum atmosphere is preferable to helium or argon, which has been treated to remove all traces of harmful substances such as oxygen and nitrogen. Means for Solving the Problems The inventive concept of this invention is to continuously anneal zirconium metal and its alloys in the presence of a nitrogen atmosphere. In the past, the use of a nitrogen atmosphere with such highly reactive metals would have been unthinkable, but this is not only possible, but is more effective than those produced by vacuum annealing.
It has been found that it yields a product with better properties. This is possible because the continuous process is much faster than the batch vacuum annealing process due to the relatively short time period in which the metal is exposed to heat and atmosphere. Specifically, what currently takes about two hours with vacuum annealing can be accomplished in less than three minutes with a continuous process. Additionally, it has been found that the reaction between the metal and nitrogen is sufficiently slow to make nitrogen annealing not only possible, but desirable. The nitrogen annealing process of this invention results in slower grain growth due to limited exposure to heat. This finer grain size is responsible for the increased yield strength and fracture tensile strength. Furthermore, the product is produced much more slowly, the equipment for continuous annealing is less expensive than that for vacuum annealing, and the cost for maintaining a nitrogen atmosphere versus a vacuum atmosphere is considerably lower, and this nitrogen annealing method is less expensive than the vacuum annealing method. It is much more economical than EXAMPLES The following examples were performed to test strength and formability, and the results are shown in the table below. Zircaloy-4 strips having the following composition were prepared in the following manner. Zircaloy-4 (nominally) 1.5% Sn 0.2% Fe 0.1% Cr balance Zr The material is hot forged in the beta phase and hot rolled in the alpha phase, then 30 to 40% each
At least by alpha phase intermediate annealing accompanied by deformation.
Manufactured by cold rolling with 50% deformation. The alloy was vacuum annealed and nitrogen annealed and subsequently tested for yield strength, fracture tensile strength, elongation, ductility or formability, and finally nitrogen and oxygen adsorption/absorption. The results of these tests are shown in the table below. The above zirconium alloy was heated at 1300〓 for 3 minutes.
Nitrogen annealed at (704℃). These were then tested for elongation, tensile strength at break, and yield strength in both the transverse and longitudinal directions. The results are shown in the table. A comparison was made between the average values of the results in Table 1 and the same alloys treated by vacuum annealing. This comparison is shown in the table, where the grain sizes are also shown. Grain size is the ASTM grain size number, which is defined by the formula N = 2 ^2n-1 , where N is the number of grains per square inch at magnification (x100) and n is the grain size.・This is the number of sizes.

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[Table] Examples 7 to 10 in the table were vacuum annealed, and Example 11 was nitrogen annealed as described above.
12 can be compared. Furthermore, Table 1 shows nitrogen annealed Zircaloy-4
vs. the same vacuum annealed Zircaloy-4
This comparatively shows the characteristics of Two strips of Zircaloy-4 were separately treated with nitrogen and vacuum annealing and then tested for ductility and formability. The results of this test are shown in the table, where 2T and 1.6T indicate the bending of the metal about a core axis with a radius of twice and 1.6 times the thickness of the specimen, respectively.

[Table] Range peel = Satin finish Zircaloy-4 was used as an attempt to measure the depth and amount of adsorption and absorption of oxygen and nitrogen derived from the annealing process.
An Auger analysis was performed on each of these, and the results are shown in Table 1. The examples are as-received, unannealed specimens. Examples are at 1250°C (675°C) in pure nitrogen.
Examples are annealed for 10 minutes at 1250 °C in nitrogen.
(675°C) for 5 minutes. However, during these examples it was discovered that the furnace leaked. Therefore, there was a considerable amount of air in the furnace during annealing. Most of the nitrogen annealing mentioned above was performed for 3 minutes at 1300°C.
(704° C.), but nitrogen annealing can be performed at lower and higher temperatures that are inversely proportional to the residence time of the material in the furnace. For this reason, the accepted products can be produced at temperatures between 977° and 1607° (525°C to 875°C) and processing times between 0.5 minutes and 15 minutes.
It can be up to a minute. Therefore, the parameters range from 1 minute at 1250〓 (677℃) to 5 minutes at 1200〓 (649℃).
It can be varied for up to 15 minutes at 1100㎓ (593℃). What is important is that the temperature and time correspond to a time sufficient for complete recrystallization to occur, but not longer. It was found that at temperatures above 1607°C (875°C) nitrogen diffuses into the material even for a short time, causing contamination problems. Similarly, within 0.5 minutes there may not be enough treatment to obtain complete recrystallization. In summary of this disclosure, the present invention provides an economical method for continuous annealing of zirconium and its alloys to produce superior products. Modifications are possible within the scope of this invention.

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Claims (1)

[Claims] 1. A continuous annealing method for zirconium metal and its alloys, in which zirconium or its alloys are continuously passed through an annealing furnace containing nitrogen and heated at 525°C to 875°C for 0.5 to 15 minutes. 1. A continuous annealing method for zirconium metal and its alloy, characterized by maintaining the zirconium metal or its alloy at a temperature within a range. 2. The method of claim 1, wherein the metal is in the form of a zirconium alloy strip.