GB2086945A - Nitrogen Annealing of Zirconium or Titanium Metals and Their Alloys - Google Patents

Abstract

A method of continuously nitrogen annealing zirconium and titanium metals and their alloys at temperatures at from 1000 DEG F to 1600 DEG F (525 DEG to 875 DEG C) for from1 DIVIDED 2 minute to 15 minutes.

Description

SPECIFICATION Nitrogen Annealing of Zirconium and Titanium Metals and Their Alloys The present invention relates to a continuous process for annealing zirconium and titanium metals and their alloys. More specifically, the present invention deals with the use of a nitrogen atmosphere which allows the process to be continuous.

The idea of continuous annealing of metals is old in the art. Even the idea of continuous annealing in a nitrogen atmosphere has been used in annealing steel and certain metals, as may be seen from U.S. Patent No. 4,183,773, Kawasoko et al, wherein a hydrogen-nitrogen atmosphere is used.

It has also been known to nitride metals including zirconium for the purpose of producing hardness. This hardness, however, is produced at the expense of ductility.

The usual way of annealing zirconium or titanium is by vacuum annealing since these metals are very reactive and considerably more reactive than steel. This vacuum annealing is extremely expensive not only with regard to equipment, but also with regard to operation. There is a need for a continuoous process for annealing zirconium and titanium for economic purposes. However, a nitrogen atmosphere, which would be an inexpensive atmosphere, has been avoided because of the reactivity of these metals. This is also recognized in U.S. Patent No. 4,000,013, MacEwen et al, where a vacuum atmosphere is stated as preferred over helium or argon which have been treated to remove all traces of deleterious substances such as oxygen, nitrogen, etc.

The inventive concept of the present invention is to continuously anneal zirconium and titanium metals and their alloys in the presence of a nitrogen atmosphere. Although the idea of using a nitrogen atmosphere with such highly reactive metals has been unthinkable in the past, it has now been found that it is not only possible, but that it produces a product having better properties than that produced by vacuum annealing. The reason this is possible is because the continuous process is so much faster than the batch vacuum annealing process that the metals are exposed to the heat and atmosphere for comparatively very short periods of time. Specifically, what takes about two hours to vacuum anneal now can be performed in a continuous process in less than three minutes.It has further been found that the reaction between these metals and nitrogen is slow enough to make this nitrogen annealing not only possible, but desirable.

The nitrogen annealing process of the present invention produces less grain growth because of the limited exposure to heat. This finer grain size is responsible for increased yield strength and ultimate tensile strength.

This nitrogen annealing process is also much more economical than vacuum annealing in that the product is produced much faster, the apparatus for continuous annealing is less expensive than that for vacuum annealing, and the production cost for maintaining a nitrogen atmosphere versus a vacuum atmosphere is considerably less.

The following examples were made and tested for strength and formability, the results of which are illustrated in the tables set forth below. A Zircaloy-4 strip having the following composition was prepared in the following manner: Zircaloy-4 (nominally) 1.5% Sn 0.2% Fe 0.1% Cr balance Zr This material was produced by hot forging in the beta phase, hot rolling in the alpha phase, and cold rolling at least 50% reduction with alpha phase intermediate anneals following each 30 to 40% reduction.

A titanium alloy having the following composition was treated in a similar manner as the Zirconium alloy above: Grade II Titanium (nominally) O. 1 4% 02 0.12% Fe balance Ti These alloys were both vacuum annealed and nitrogen annealed and subsequently tested for yield strength, ultimate tensile strength, elongation, ductility or formability, and finally for nitrogen and oxygen pickup. The results of these tests are set forth in the following tables.

The above zirconium and titanium alloys were nitrogen annealed for 3 minutes at 1 3000F (70000). These were then tested both transversely and longitudinally for elongation, ultimate tensile strength, and yield strength. The results are shown in Table Table I Ultimate Tensile Yield Strength Strength Example Elongation psi psi 1.Ti lI,Trans. 27 73,800 61,600 2. Ti ll, Trans. 27 73,800 61,000 3. Ti II, Trans. 27 74,100 60,200 4. Ti II, Long. 27 76,800 58,800 5. Ti II, Long. 27 76,900 59,200 6. Ti II, Long. 27 76,900 58,900 7. Zr-4, Trans. 32 64,700 51,100 8. Zr-4, Trans. 31 64,700 50,700 9. Zr-4, Trans. 32 63,300 49,300 10. Zr-4, Long. 32 63,800 47,500 11.Zr-4, Long. 31 63,500 47,900 12. Zr-4, Long. 31 63,800 48,600 Trans.=transverse testing Long.=longitudinal testing A comparison between the average of the results in Table I and the same alloys treated by vacuum annealing was made. This comparison is shown in the following Table II where there is also shown a comparison of grain sizes.

Table II Ultimate Tensile Yield Strength Strength Grain Example Elongation psi psi Size 13. Ti II, Long. 27 72.6 52.1 9-1/2 14. Ti II, Trans. 26 69.2 55.8 15.Ti II, Long. 27 68.7 48.1 9 16. Ti II, Trans. 26 67.8 54.6 17. Zr-4, Long. 34 60.6 48.9 9-1/2 18. Zr-4, Trans. 34 60.5 49.3 19.Zr-4, Long. 31 58.3 56.9 10 20. Zr-4, Trans. 32 59.5 48.2 21.*Ti II, Long. 27 76.9 59.0 11-1/2 22.* Ti II, Trans. 27 73.9 60.9 23* Zr-4, Long. 31.3 63.7 48.0 10-1/2 24.* Zr-4, Trans. 31.7 64.2 50.4 *Nitrogen annealed for 3 minutes at 1 3000F (700 C) In Table II, Examples 13 to 20 were vacuum - annealed and can be compared to Examples 21 to 24 which have been nitrogen annealed as set forth above.

Table Ill Ultimate Tensile Yield Strength Strength Example Temp. Elongation psi Psi 25.*Zr-4,Trans. 600"F 42 31,100 20,700 26.*Zr-4,Trans. 600"F 43 31,100 20,400 27.*Zr-4,Trans. 6000F 41 31,300 21,000 28. * Zr-4, Long. 6000F 46 35,300 18,300 29. * Zr-4, Long. 6000F 46 35,400 18,600 30. * Zr-4, Long. 6000F 46 35,300 18,200 31. Zr-4,Trans. 6000F 43 26,900 17,500 32. Zr-4, Trans. 6000F 43 27,000 17,500 33. Zr-4, Trans. 6000F 44 27,200 17,600 34. Zr-4,Long. 6000F 51 29,300 16,500 35 Zr-4, Long.- 6000F 51 30,100 15,900 36.Zr-4, Long. 6000F 52 28,900 15,700 37. * Zr-4, Trans. R.T. 31 69,400 61,200 38.*Zr-4,Trans. R.T 31 68,700 61,000 39.*Zr-4,Trans. R.T. 31 69,100 60,600 40. * Zr-4, Long. R.T. 32 72,900 51,200 41. * Zr-4, Long. R.T. 28 73,700 50,900 42.*Zr-4,Long. R.T. 29 74,100 51,200 43. Zr-4,Trans. R.T. 30 65,500 56,200 44. Zr-4,Trans. R.T. 31 65,400 56,000 45. Zr-4,Trans. R.T. 31 65,100 56,500 46. Zr-4, Long. R.T. 32 69,600 49,400 47. Zr-4, Long. R.T. 31 69,300 49,400 48. Zr-4, Long.R.T. 30 70,200 50,600 *Nitrogen annealed for 3 minutes at 1 3000F (7000 C) R.T.=Room Temperature Table Ill further illustrates comparatively properties of Zircaloy-4 metal which has been nitrogen annealed versus the same Zircaloy-4 metal which has been vacuum annealed.

Two strips of Zircaloy-4 were separately treated by nitrogen annealing and vacuum annealing and then tested for ductility and formability. The result of this test is represented in Table IV where 2T and 1.6T represent the bending of the metal around a mandrel having a radius two times and 1.6 times the thickness of the material, respectively.

Table IV Example 2T 1.6T 49. * Zr-4, Trans. no cracks no cracks 50. * Zr-4, Trans. no cracks no cracks 51. Zr-4, Trans. slight orange peel slight organge peel 52. Zr-4, Trans. slight orange peel slight orange peel 53. * Zr-4, Long. no cracks no cracks 54. * Zr-4, Long. no cracks no cracks 55. * Zr-4, Long. no cracks no cracks 56. Zr-4, Long. slight orange peel slight orange peel 57. Zr-4, Long. slight orange peel slight orange peel *Nitrogen annealed at 1 3000F (700"0) for 3 minutes Trans.=transverse testing Long.=longitudinal testing In an attempt to determine the depth and amount of oxygen and nitrogen pickup from the annealing process, an Auger analysis was performed on Zircaloy-4, the results of which are shown in Table V.

Table Example Position C O N S Fe Sn Zr F Si Ar 22.1 5.9 .55 .72 .63 - 69.0 1.1 Base(200A) 1.94 .35 - - .19 .83 95.8 - .88 II AR 9.2 12.5 1.7 .42 1.1 - 71.5 - 3.2 100A 11.0 2.2 3.65 - -- .77 82.2 - - Base (500 ) 1.3 .28 - - .27 .93 96.3 - .82 Ill AR 8.7 15.4 .37 .27 .95 .47 70.9 - 2.8 100A 5.9 12.6 .51 - .66 .32 79.1 - .83 7000A 3.3 2.8 - - .24 .92 91.7 7 .96 IV AR 17.5 7.47 .40 - 1.3 .28 69.6 - 2.9 700A 5.5 11.9 .36 - 1.5 .34 78.6 - 1.8 AR=As Received Example I represents unannealed material in the as-received condition. Example II was annealed for 10 minutes at 1 2500F (6750C) in pure nitrogen. Examples Ill and IV were annealed for 5 minutes at 12500F (6750C) in nitrogen; however, it was discovered that the furnace leaked during these examples and therefore there was a considerable amount of air in the furnace during the annealing.

Although most of the above nitrogen annealing was performed at 1 3000 F (7000C) for 3 minutes, the nitrogen annealing can be performed at lower and higher temperatures inversely proportional to the residence time of the material in the furnace. Therefore, it is possible to produce an acceptable product at temperatures from 10000 to 1 6000F (5250 to 8750C) and times of treatment can be from 2 minute to 15 minutes. The parameters therefore, can vary from 1 minute at 1 2500F (6750C) to 5 minutes at 12000F (6500C) to 15 minutes at 11 000F (6000C). The important thing is that the temperature and time coincide for a time sufficient to cause complete recrystallization but no longer. It has been found above 1 6000F (8750C) even for a short time there is diffusion of nitrogen into the material thus causing staining problems. Likewise, at times below T minute, there is not sufficient treatment to obtain complete recrystallization.

In summary of this disclosure, the present invention provides an economical method of continuously annealing zirconium, titanium and alloys thereof, to yield a superior product.

Modifications are possible within the scope of this invention.

Claims (12)

Claims

1. A method of annealing zirconium and titanium metal and their alloys, which comprises effecting annealing continuously in a nitrogen atmosphere.

2. A method as claimed in claim 1, in which the annealing is effected at a temperature in the range of 10000 to 1 6000F (5250 to 8750C).

3. A method as claimed in either of claim 1 or 2, in which the annealing is effected in a temperature-dependent time of from 0.5 to 1 5 minutes.

4. A method as claimed in any one of claims 1 to 3, in which the annealing is effected by passing the metal or alloy through an annealing furnace containing a nitrogen atmosphere.

5. A method as claimed in claim 4, in which the metal or alloy is continuously heated to about 1 2500 F (about 675 OC) for 1 minute while in the furnace.

6. A method as claimed in claim 4, in which the metal or alloy is continuously heated to about 12000F (about 6500 C) for 5 minutes while in the furnace.

7. A method as claimed in claim 4, in which the metal or alloy is continuously heated to about 11 000F (about 600"C) for 1 5 minutes while in the furnace.

8. A method as claimed in claim 4, in which the metal or alloy is continuously heated to about 1 3000F (about 7000 C) for 3 minutes while in the furnace.

9. A method as claimed in any one of claims 1 to 8, in which the metal is a zirconium alloy strip.

10. A method as claimed in any one of claims 1 to 8, in which the metal is a titanium alloy strip.

11. A method of continuous annealing of zirconium and titanium metal and their alloys substantially as hereinbefore described with reference to the Examples.

12. Zirconium and titanium metal and alloys thereof whenever annealed by the method claimed in any one of claims 1 to 11.