US2772964A - Zirconium alloys - Google Patents

Description

Un ed S emen ZIRCONIUM. ALLOYS; Donald E. Thomas, Kenneth M. Goldman, Robert B.

Gordon, andWilliam A. Johnson, Pittsburgh, 21., as signors to WestinghousaEle'ctric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application March 15, 1954,

. Serial No. 416,396

6 Claims, (Cl. 75- 177) This invention relates to zirconium alloys having high resistance to corrosion and characterized by being readily hot and cold Worked or -wrought to desired strips, sheets and the like shapes.

It has been proposed heretofore to alloy zirconium With small quantities of tin. We have found, however, that such alloys have a number of-undesirable characteristics. Thus, for example, an alloy comprising zirconium and 2.5% of tin when subjected to temperatures of the order of 600 F. in the presence of water forms heavy oxide films. Furthermore, such Zirconium-tin alloys, when exposed to temperatures in a range above 500". F.' at first corrode slowly for a brief period of time, and then the corrosion rate'rather abruptly increases 'm-any fold. After reaching such breakraway conditions, the oxidation rate is so great that the alloys are not suitable for numerous possible applications.

Typical impurities in low hafnium zirconium sponge Element Al 0 Hi M11 N 02 Si Ti All Others Weight Percent. 005 1 It will be understood that our invention can be applied to normal zirconium containing up to 3% by weight of hafnium, which is naturally present in ordinary zirconium ores. 1 r V In preparing the alloy, the zirconium and tin, and the iron or nickel or chromium individually, or any com- 7 bination of two or all three of the latter, in weighed increments are charged into an arc melting furnace which,

In addition, in order to produce members fromzi-rconium-tin alloys, it is desirable to work the alloy to desired shape by suitable rolling, extrusion, forging and similar metal working procedures in order to produce tubing, wire, sheet and bars of the alloys. Binary alloys of zirconium with 2.5% of tin, for example, have been found 'to be subject to serious cracking with consequent high scrap losses under hot rolling operations.

alloy. T

The object of this invention is to provide for a zirconium alloy characterized by a lowfcorrosion rateat elevated temperatures when'in the presence of water or steam, such alloys having good hot and cold working properties. j

Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter.

We have discovered novel alloys characterized by a low corrosion rate and good hot and cold working properties, such alloys consisting essentially of from 0.1% to 2.5 by weight of tin, a total of at least 0.1%, but not exceeding 2% by weight of at least one metal from period 3 (and particularly series 4) of the periodic table selected from the group consisting of iron, nickel and chromium, less than 0.5% by weight of incidental impurities, and the balance being zirconium. We have found that the alloys of our invention will function satisfactorily even when containing relatively large amounts of such impurities as nitrogen, oxygen, and carbon. It is well known that nitrogen and carbon, in particular; result in injurious effects on the corrosion resistance of zirconium when exposed to water at moderately elevated temperatures. We have discovered that the alloys of our invention will tolerate a higher percentage of nitrogen and carbon with less adverse effects than has been heretofore considered possible in zirconium base metals and alloys. For example, our alloys will function satisfactorily with up to 0.01% nitrogen being present, and even with 0.025% nitrogen present, the corrosion rate appeared to be only slightly increased.

In preparing the alloys of this invention, the zirconium used may be crystal bar zirconium characterized by high purity and extremely low proportions of nitrogen, carbon and other impurities. We have found, however, that the alloys of the present invention may be successfully pre- Similar difficulties have arisen when forging and cold-rolling this aslab. The zirconium alloy slab is hot rolled at a temexamples illustrate alloys in perature of 1550 F. into a sheet or strip which may b employed as desired.

We have obtained particularly satisfactory alloys from the standpoint of low corrosion rate and good workability by limiting the total alloying content added to zirconium to a maximum of 3%. For certain critical applications, it has been found desirable to limit the-total content of tin, iron, nickel and chromium to approximately 2.0%. We have produced a substantial amount of hot-rolled strip having a Rockwell B hardness of'approximately 91, from an alloy consisting of from 1.3% to 1.6% by weight of tin, from 0.07% to 0.12% by weight of chromium, 0.04% to 0.08% by weight of nickel, from 0.09% to 0.16% by weight of iron, less than 0.3% by weight of incidental impurities being present, and the balance being zirconium. This last alloy was readily fabricated by both hot and cold forming operations into numerous types of members. In water or steam at temperatures of up to and including 750 F., its corrosion resistance was outstanding. A sample of annealed hot rolled strip of this last analysis had a0,2% yield strength of 22,700 pounds per square inch in a tensile test conducted at 500 F.

It will be appreciated that other methods of producing the alloy may be employed such, for example, as by initially melting zirconium in an arc melting furnace and then adding pellets prepared by alloying tin, iron, nickel and chromium in the desired proportions. The following tion:

TABLE II Typical alloy analyses Alloy Sn Cr Ni Fe N2 accordance with the inven- The carbon content of all of the above alloys was less than 0.05%.

We have prepared a series of alloys in which tin was maintained at 1.5%, the total' of nickel, iron and chromium in nearly equal proportions being varied from 0.1% to 0.5%, the balance being zirconium and incidental impurities, and tested strips of each of these alloys in water at 680 F. for 98 days. The average corrosion in milligrams of absorbed oxygen per square decimeter of surface dropped from 50 at 0.1% total iron nickel and chromium to 32 at 0.3% and then increased slowly to 38 at 0.5%. These data indicate a minimum amount of corrosion for alloys having approximately 0.3% by weight of combined iron, nickel and chromium.

We have prepared a number of alloys within the following range of compositions: Chromium 0.01% to- 2%, tin 0.5 to 2.5%, and zirconium and incidental impurities balance. Numerous samples of these ternary alloys were prepared by arc melting procedures. For example, ternary alloys comprisingta) 2.5% tin, 0.75% chromium and the balance zirconium, and (b) 1.5% tin, 1.00% chromium, and the balance being zirconium, were prepared. Strips Were hot rolled from these alloys and they were readily fabricated into desired shapes. When exposed to elevated temperatures of 500 F. and higher, in the presence of water or steam, the alloys all exhibited an adherent black temper film. In tests running for over a hundred days, in no case did these alloys exhibit a break-away corrosion tendency.

We have tested numerous samples of a ternary alloy comprising up to 1% nickel, from 0.5 to 2.5% tin, and the balance being zirconium. Alloys containing (a) 1.5 tin, and 0.25% nickel, balance zirconium, and (b) 2.5% tin, 0.25 nickel and the balance zirconium were readily hot formed and hot rolled, and cold worked into many desired shapes. When exposed to elevated temperatures in contact with steam, these members all exhibited black temper films and the corrosion proceeded at a uniform rate even after many days exposure to temperatures of 600 F. and higher.

A ternary alloy wasprepared from 0.25% iron, 1.8% tin and the balance being zirconium and incidental impurities. The alloy was readily forged and hot rolled into sheets. These sheets could be readily cold worked and fabricated. Samples of members of these ternary alloys were exposed to both water and steam at 650 F.-

for over 100 days. These samples exhibited adherent black temper films and the corrosion rate was extremely low. No break-away corrosion was found.

The following alloy was prepared: Nickel 0.25%, iron 0.25%, tin 0.5%, the balance being zirconium and incidental impurities. melting twice as disclosed in the Gordon and Hurford application referred to previously. The resulting ingot was readily hot formed and hot rolled into strip. Samples of the alloy when exposed to elevated temperatures of 600 F. and higher in the presence of water and steam had an extremely low corrosion resistance and showed no break-away point over long periods of test.

We have found that the tin content of our alloys may be varied within the range of 0.5% to 1.5% without any significant change in corrosion properties. Therefore, the mechanical properties of our alloys can be varied appreciably, as desired, by appropriate changes in tin content without sacrificing high corrosion resistance.

From a great number of tests, we have found that the The alloy was prepared by are 4 inclusion of at least one of the group of iron, nickel and chromium, in the proportions indicated, in zirconium-tin alloys, markedly stabilizes the corrosion resistance of these alloys and there is much less variability in the corrosion rate values of these alloys than of either the binary zirconium-tin alloys, or pure zirconium;

It will be appreciated that numerous uses may be made of alloys prepared in accordance with the present invention. It is intended that the disclosure be construed as illustrative of the invention and not in limitation thereof.

We claim as our invention:

1. An alloy consisting essentially of from 0.1% to 2.5% by weight of tin, and a total of at least 0.1% but not exceeding approximately 2% by weight of at least one metal from period 3 of the periodic table selected from the group consisting of iron, nickel and chromium, carbon not exceeding 0.05 the balance being zirconium and less than 0.5% by Weight of incidental impurities.

2. An-alloy consisting essentially of from 0.5% to 2.5% by weight of tin, a total of at least 0.1% of at least one metal of period 3 of the periodic table selected from the group consisting of iron, nickel and chromium, the total weight of tin, iron, nickel and chromium not exceeding 3%, carbon not exceeding 0.05%, the balance being zirconium and less than 0.5% by weight of incidental impurities.

3. An alloy consisting essentially of from 0.5% to 2.5% by weight of tin, from 0.05% to 1% by weight of chromium, from 0.05% to 0.5% by weight of nickel, from 0.05% to 0.5% by weight of iron, carbon not exceeding 0.05%, less than 0.5% by weight of incidental impurities, and the balance being zirconium.

. 4. An alloy consisting of from 1.3% to 1.6% by weight of tin, from 0.07% to 0.12% by weight of chromium, from 0.04% to 0.08% by weight of nickel, from 0.09% to'0.16% by weight of'iron, carbon not exceeding 0.05 less than 0.5% by weight of incidental impurities, and the balance being zirconium.

' 5 Members comprising a worked and shaped alloy consisting essentially of from 0.1% to 2.5% by weight of tin,.and.,a total of at least 0.1% but not exceeding approximately 2%.by weight of at least one metal from period 3 of the periodic table selected from the group consisting of iron, nickel and chromium, carbon not exceeding 0.05 the balance being Zirconium and less than 0.5% by weight of incidental impurities, the members having high resistance to corrosion when subjected to both water and steam at temperatures above 500 F.

. 6. Members comprising a worked and shaped alloy consisting of from 1.3% to 1.6% by weight of tin, from 0.07% to 0.12% by weight of chromium, from 0.04% to 0.08% by weight of nickel, from 0.09% to 0.16% by 'weightof iron, carbon not exceeding 0.05%, less than 0.5% by Weight of incidental impurities, and the balance being zirconium, the members having high resistance to corrosion when subjected to both water and steam at temperatures above 500 F.

References Cited in the file of this patent Anderson et al.: A Preliminary Survey of Zirconium Alloys. Bureau of Mines Report of Investigations 4658, March 1950, pages 42 and 43.

Hayes: Transactions of Am. Society for Metals, Cleveland, Ohio, vol. 43, 1951, pages 888, 891, 897-899.

.Journal of Metals, November 1952, pages 1138-1140.

Claims (1)

1. AN ALLOY CONSISTING ESSENTIALLY OF FROM 0.1% TO 2.5% BY WEIGHT OF TIN, AND A TOTAL OF AT LEAST 0.1% BUT NOT EXCEEDING APPROXIMATELY 2% BY WEIGHT OF AT LEAST ONE METAL FROM PERIOD 3 OF THE PERIODIC TABLE SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL AND CHROMIUM, CARBON NOT EXCEEDING 0.05%, THE BALANCE BEING ZIRCONIUM AND LESS THAN 0.5% BY WEIGHT OF INCIDENTAL IMPURITIES.