CA1169269A - Iron-nickel/chromium alloy having improved swelling resistance and low neutron absorbence - Google Patents

Abstract

9 48,082 ABSTRACT OF THE DISCLOSURE
An iron-nickel-chromium age-hardenable alloy suitable for use in fast breeder reactor ducts and clad-ding which utilizes the gamma-double prime strengthening phase and characterized in having a delta or eta phase distributed at or near grain boundaries. The alloy con-sists essentially of about 33-39.5% nickel, 7,5-16% chrom-ium, 1.5-4% niobium, .1-.7% silicon, .01-.2% zirconium, 1-3% titanium, .2-.6% aluminum, and the remainder essen-tially all iron. Up to .4% manganese and up to .010%
magnesium can be added to inhibit trace element effects.

Description

1 48,082 IRON-NICKEL-CHROMIUM ALLOY HAVING
IMPROVED SWEI,LING RESISTANCE AND
- LOW NE~TRON ABSORBENCE
GOVERNMENT CONTRACTS
The invention described herein was made during the course of or in performance of work under U.S. Govern-ment Contract No. EY-76C-14-2170 under the auspices of i 5 ERDA.
BACKGROUND OF THE INVENTION
While not limited thereto, the present invention is particularly adapted for use as a fast breeder reactor duct and fuel rod cladding alloy. Such an alloy requires strong mechanical properties at high temperatures and at the same time must have both swelling resistance under the influence of irradiation and low neutron absorbence. Al-loys such as those described in U.S. Patent No. 3,046,108 to Eiselstein disclose age-hardenable nickel-chromium base alloys which have high strength and good ductility over a wide temperature range up to about 1400F. The aforesaid patent discloses a nickel-base alloy having a nominal com-position consisting essentially of about 53% nickel, 19%
chromium, 3% molybdenum, 5% niobium, .2% silicon, .2%
manganese, .9% ~i~anium, .45% aluminum, .G4% carbon and the balance essentially iron. The alloy is characterized in the age-hardened condition by a yield strength (0.2%
offset) of at least 100,000 pounds per square inch at room temperature and by a 100-hour rupture strength of at least 90,000 psi at 1200F.
rt is known that nickel-base alloys containing ~f;~

2 ~8,082 titanium and aluminum, such as those described in U.S.
Patent No. 3,046,108, are strengthened by precipitation of a gamma-prime phase. It has also been found that by adjusting the amounts of titanium, aluminum and niobium in such alloys, a morphology can be obtained wherein precipi-tated gamma-prime particles are coated on their six faces with a shell of gamma-double prime precipitate. The resulting microstructure is very stable on prolonged aging and has good thermal stability characteristics.
In ~. S. Patent No. 4,236,943, issued December 2, 1980 and assigned to the assignee of the present appli-cation, an iron-nickel-chromium alloy is described which incorporates the gamma-prime and gamma-double prime phases to achieve high strength mechanical properties at elevated 15 temperatures as well as good swelling resistance in response to irradiation. The alloy described in the aforesaid U. S. Patent No. 4, 236,943 contains about 0. 3%
aluminum, about 1.7% titanium, about 45% nickel, about 10% chronium and about 1~7V/o niobium.
SUM~ARY OF THE INVENTION
The present invention resides in the discovery that the desirable properties of the alloy described in the aforesaid U. S. Patent No. 4,236,943 can be further enhanced by reducing the nickel content to about 35% and 25 critically limiting the aluminum content. Specifically, the improved alloy of the invention has a lower neutron absorption cross section than alloys containing higher amounts of nickel; has less tendency to form aulted dis-locations; has higher post irradiation ductility; and, at the 30 same time, has high swelling resistance in response to irradiation. The alloy of Patent No. 3, 046,108 has a neutron absorption cross section which is 56% higher than that of AISI 316. The alloys of this disclosure have cross sec-tions on the order o~ 27% higher than that of AISI 316--a significant improvementl Furthermore, the ductility of the alloy can be improved by an appropriate heat treat-/
/ ,.

3 ~,082 ment.
The above and other objects and features of thein\7ention will becomc apparen~. from the following de~ailed description of exempLary embodiments of the invention:
_ESCRIPTION OF THE P~EEERRED EMBODIMEMTS
: The broad and preferred compositions of the a].loy of the invention are listed in the following Table 1: :
; TABLE I
_oad - % Preferred - /O
Nickel 33-39.5 37 Chromium 7.5-16 12 Niobium 1.5-4 2.9 Silicon .1-.7 .2 Zirconium .01-0.2 0.05 ; Titanium 1-3 1.75 Aluminum .2-.6 .3 Carbon .02-.l .03 Boron .002-.015 .005 ,'(l Manganese .05-.4 .2 Iron Bal Bal Additionally, up to 1.5% molybdenum and/or up to 0.010 magnesium can be added to improve long-term mechani-cal properties.
Normally, alloys containing less than 40% nick-el, rega`rdless of heat treatment, will not form the gamma-double prime phase, and thus the alloy will not achieve its ultimate characteristics. It has been found, however, that the nickel content can be less than 40% where other considerations are taken into account. In this respect, it has been found that the aluminum content is critical and cannot exceed 0.6% where the nickel content is below 40%; for example, 37% nickel, and still obtain the gamma-double prime precipitate. While at first blush it may appear that a corresponding increase is also required in the zirconium content, it is not seen wherein zirconium content effects the transformation characteristics of this alloy. Moreover, a detrimental effect can be foisted upon ~l~c~

~ 48,082 the alloy where the zirconium content is too high since the alloy will no~ be able to be fabricated, for example, by ~ welding.
The foregoing alloys are characterized in having both the gamma-prime and gamma-double prime phases. At the same time, by virtue of the fact that the nickel content is beneath 40% by weight, the alloy is character-ized by low neutron absorbence and at the same time has good swelling resistance under irradiation.
lo In order to derive the optimized alloy of the invention, a number of alloys were examlned, the composi-tions of these alloys being listed in the following Table II:
TABLE II
Alloy Fe Ni Cr M~ Nb Ef Si Mn Mg D32 Bal 37 12 - 4.G - - - -D33 Bal 45 12 - 4.0 D66 Bal 45 12 3.0 - - 0.5 - -D31-M-5 Bal 37 12 - 3.0 0.03 0.5 D31-M-6 Bal 37 12 - 3.0 - 0.5 D31-M~7 Bal 37 12 2.0 4.0 - 0.5 - -D31-M-8 Bal 37 12 4.5 4.0 - 0.5 D31-M-9 Bal 37 15 3.0 4.0 - O.S 0.2 0.02 D31-M-10 Bal 45 12 - 4.0 - O.S 0.2 0.02 D31-M-ll Bal 45 12 - 4.0 - 0.5 0.2 0.02 D31-M-12 Bal 45 12 - 4.0 - 0.5 0.2 0.02 D31-M-13 Bal 45 12 2.0 4.0 - 0.5 0.2 0.02 D31-M-14 Bal 45 12 2.0 4.0 - 0.5 0.2 0.02 D68 Bal 45 12 - 3.6 - 0.350,2 0.01 D68-Bl Bal 45 12 - 3.0 - 0.3 0.2 D68-B2 Bal 37 12 - 2.9 - 0.3 0.2 D68-C4 Bal 34 12 - 2.9 - 0.5 0.2 i.~

3~
48,082 Identl~ied ~_, Zr Ti Al C B
D32 0.03 2.8 0.8 0.03 0.010 ~ ' ~ n D33 0.03 199 0.5 0.03 0.010 1:66 0~05 2~5 2.5 O.~t3 0.005 ~ ' D31-M~5 0~03 1~9 1~9 0.03 1.01 ~ ' D31~M~6 0~05 2.5 2~5 0~03 O~Ot)5 ~ l D~1~M-7 0.05 0.8 0.6 0,.03 0-005 ~ ' D31-M-8 0.05 0.8 0.6 0.03 0.005 `t ' D31~M-9 - 1~0 0.4 0.04 0.005 ~ l I~31-M-10 1).05 1.8 0~,8 0.03 0.005 ~ ' D31-M~11 0.05 1~8 1.0 0.03 O.OC)5 ~' D31-M-12 0.05 1.8 192 0.03 0~005 ~' D31-M-13 0.05 1,8 0.8 0~,03 01~05 ~ ' D31-M-14 0.05 1.8 1dO 0.03 0.005 ~ ' D68 0.05 1.7 0.3 0.0~ 0.005 ~., D68-B1 0 O 05 1 " 6 0 . 50 . 030 . 006 D68-B2 Q.05 1.75 û.3 0.03 0~,005 Y , D68-C4 ~) . 05 1 . 75 0 . 30 . 030 . 005 8 1 ~lloy.s aged in the rarlge of 16-24 hours at about 7600C.
From an examina~io~ of Table II, it can be seen that most aïloys ~e.g~., alloys D31~M~5 to D31-M-9) con-taining less th~n 40% nickel do no~ contain the gamma-double prime phase ~mless the al~ um content is le3s than 0,.6% by weight. I~kewise, 1;he nickel content must be ~sreater than 33 to 35% to obtain the ~ " phase.
Stre~s rupture te~ting con~ that the 100-h~ur ~50C stress rup~ure strength of alloy D68-B2 is about 586 ~pa, which is about the ~ame as -that measured ior alloy D68. In addition, alloy ~68-B2 has approxi-mately a 10% lower n~utron abso~ption cross section th~n alloy D68 which tran~lates into a æigni~ica~t savings ~or ~uel cladding applications.
As was stated previously, the lower nickel range together with the presence o~ the gamma-double prime precipltate is ei~ective ~or showing an impro~d ductil-ity. This ductility is most critical ln the post irradia-6 48,082 tion mode, and therefore any improvement in the bend ductility is highly effective for making such materials eminently suited for use in fast breeder reactors.
In order to demonstrate this phenomenon, the alloys listed hereinafter, whose chemical composition and phase ident:ifica~ion are set forth in Table II, were irradiated to a fluence of 6.9 x 10 neutrons per square cerltimeter at a temperature of 593 ~ 25C, and thereafter tested at 730C. The disc test to which the hereinafter lo specified alloys were subjected is a specially designed microductility test in which an indentor is pushed through a disc onto a mandrel. This has been correlated with tensile testing and found to give identical results to bulk tensile testing. It is used for reactor testing specimens because it permits the utilization of reduced size and configuration samples in or~er to obtain the data. The discs that are normally tested are 1/8" or 3 mm in diameter and approximately 1/12,000" in thickness. The test is only accurate in the range of low ductility in which there is less than 2% ductility because the develop-i mental work has not yet been completed on materials which exhibit higher ductilities. This test has been utilized by most of the major reactor manufacturers and is compati-ble with government testing requirements.
Alloy Designation Bend Ductility (%) D68-~1 0.2 D68~ 0.8 As stated, the use of this material in a nuclear environment requires that the material as irradiated to i 30 normal fluences must demonstrate low swelling of the com-position. In order to demonstrate this outstanding fea-ture in the present invention, reference is had to the following table in which alloy D68-B2 was irradiated to the nominal fluences indicated. For comparison, the table also contains data on the swelling resistance of AISI Type 316 under the same conditions.
;

7 48,082 PERCENT SWELLING (6.9 x 1022 n/cm2) ., ... ~
`rlll ure25~/o Col(l Worked20% Cold Worked "(: D6~-B2 AISI ~16 . . .. . . _ _ . . . _ _ . _ . .

4~7 -0.87 +~.17 48~ -1.19 ~0.79 510 -1.10 +1.9 538 -0.92 +2.47 593 -0.65 +3.20 - 649 -0.92 +0.5 10From the foregoing, it is noted that alloy D68-B2 is still densifying, while AISI Type 316 is well ~: into the void swelling regime regardless of the tempera-tures employed. These data make it clear that the alloys of the present invention are particularly suitable for ,l'j use, for example, in a fast breeder reactor.
,While the invention has been described in con-¦nection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in compositional limits can be made to suit re--20 quirements without departing from the spirit and scope of ``the invention.

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Claims (3)

8 48,082 What is claimed is:

1. An iron-nickel-chromiun age-hardenable alloy characterized in having ? ' and ? " phases present and consisting essentially of about 33 - 39.5% nickel, 7.5 - 16%
chromium, 15 - 4% niobium, 0.1 - 0.7% silicon, 0.01 - 0.2%
zirconium, 1 - 3% titanium, 0.2 - 0.6% aluminum, 0 - 0.1 carbon, 0 - 0.015% boron, 0 - 0.4% manganese and 0 - 0.010%
magnesium and the remainder essentially all iron.

2. An iron-nickel-chromium age-hardenable alloy characterized in having ? ' and ? " phases present and con-sisting essentially of about 33-39.5% nickel, 7.5 16% chromium, 1.5 - 4% niobium, 0.1 - 0.7% silicon, 0.01 - 0.2% zirconium, 1 - 3% titanium, 0.2 - 0.6% aluminum, 0.02 - 0.1% carbon, 0.002 - 0.015% boron, 0.05 - 0.4% manganese and up to 0.010%
magnesium and the remainder essentially all iron.

3. An iron-nickel-chromium age hardenable alloy characterized in having ? ' and ? " phases present and con-sisting essentially of about 37% nickel, 12% chromnium, 2.9%
niobium, 0.2% silicon, 0.05% zirconium, 1.75% titanium, 0.3%
aluminum, and the remainder essentially all iron.