US3436214A - Columbium base alloy - Google Patents

Description

United States Extent 6 3,436,214 COLUMBIUM BASE ALLOY Mortimer Schussler, Mundelein, 111., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Continuation-impart of application Ser. No.

353,252, Mar. 19, 1964. This application Mar. 22, 1967,

Ser. No. 625,026

Int. Cl. C22c 27/00 US. Cl. 75-174 3 Claims ABSTRACT OF THE DISCLOSURE A columbium base alloy is provided which consists essentially of, by weight, about 5 percent vanadium, about 1 percent zirconium, from about .005 to about .04 percent carbon with the balance being columbium and incidental adventitious impurities. The resultant alloy is both cold rollable and ductile.

This is a continuation-in-part application of Ser. No. 353,252, filed Mar. 19, 1964, now abandoned.

This invention relates to a novel columbium base alloy, and more particularly to an alloy of columbium, vanadium and zirconium which contains beneficiating amounts of carbon.

Columbium base alloys in recent years have been proposed for use in applications where severe service conditions are encountered such as exposure to high temperatures, highly corrosive environments and/or unusual amounts of mechanical wear. These conditions are commonly encountered by certain critical components in nuclear power systems and aerospace vehicles.

Unfortunately, only a relatively limited number of well established columbium-base alloys are available commercially, and generally speaking, they are suitable for only a specific use. As a result, whenever a new use or different set of severe service conditions is encountered, an attempt is made to develop a new columbium base alloy having an optimum set of properties for such use.

Illustrative of the present state of the art are the problems encountered with a binary alloy consisting of one percent zirconium balance columbium which has been successively employed in nuclear applications. This particular alloy has acceptable fabricating and welding properties, but certain of the other mechanical and physical, as Well as chemical properties are, at best, marginal. With the advent of larger and more efficient nuclear installations, the property requirements of certain components became more critical and the particular alloy under discussion failed to meet the new and more severe requirements. In general, it was discovered that each modification of the alloy for the purpose of improving a particular property to meet a necessary need resulted in an undesirable corresponding eifect on another critical property. For example, a modification in the alloy to increase mechanical strength resulted in a reduction in fabricability and weldability. Similarly, an improvement in hardness was accompanied by a reduction in ductility, and an improvement in thermal shock properties was accompanied by a lowered resistance to corrosion.

Accordingly, the principal object of the invention is to provide a columbium base alloy suitable for general industrial use and which is characterized by an optimum combination of physical, mechanical and chemical properties.

Another object of the invention is to provide a columbium base alloy which may be employed in components which will encounter severe service conditions.

A more specific object of the invention is to provide Patented Apr. 1, 1969 a columbium base alloy which is particularly suitable for use in aerospace and nuclear applications.

An additional object of the invention is to provide a columbium base alloy which is both cold rollable and exceptionally ductile.

The objects of the invention are accomplished by an alloy consisting of, in weight percentages, about 5 percent vanadium, about 1 percent zirconium, between about .005 to about .04 percent carbon with the balance being columbium and adventitious impurities. A higher vanadium content than indicated as within the scope of the invention adversely affects the required high temperature strength properties while excess zirconium content adversely aifects the ductility of the alloy.

An unavoidable impurity usually associated with columbium base alloys is tantalum and it may be tolerated up to a maximum of about 5% although it is preferred to be maintained below 1%, if the alloy is to be used in nuclear applications.

Oxygen, nitrogen and hydrogen are harmful to the alloy of the invention and their presence should be kept as low as possible although they can be tolerated in an amount of no more than .03, .02 and .01 percent, respectively.

The total of all other impurities must be kept as low as possible, and in any event should not exceed about 0.1 percent.

The preferred alloy fashioned according to the teachings of the instant invention should contain in excess of 92 Weight percent columbium.

With respect to the other undesirable impurities, the following will be of interest.

Elements with relatively low melting points such as titanium and aluminum, if present, tend to weaken the alloy of the invention at high temperatures above about 1800 to 2200 F. Tungsten and molybdenum, if present, in the subject alloy tend to impair its working and welding properties. Further, the inherent high densities of tungsten and molybdenum disturb the desired strengthto-weight ratio of the alloy. Other elements, such as boron, chromium, silicon, iron, cobalt, etc., if present, form secondary phases in the grain boundaries resulting in undesirable working and welding properties. Further, certain elements, especially cobalt, boron, hafnium and tungsten, have a high neutron absorption cross section when compared to the specified elements of the subject alloy (see Table 1) and therefore are harmful if present in the subject alloy, if the alloy is exposed to nuclear radiation.

Table 1.Neutron absorption cross section, in barns Carbon 0.0045 Columbium 1.1 Vanadium 5.1 Zirconium 0.1 8 Cobalt v 37.0 Tungsten 19.0 Boron 750.0 Tantalum 21.0 Hafnium 115.0

3 4 Test results further indicate that the alloy of this invention was both cold rollable and also evidenced suitable duchas good resistance to corrosion in hot water, steam or tility characteristics. other similar environments found in thermal reactors. Alloy 8 was prepared as a 30 pound heat by the well- From the data tabulated below in Table 2, it will be known consumable electrode arc-melting process in an appreciated that the vanadium, zirconium and carbon conargon plus helium atmosphere. The alloy was cold retents of the alloy of the invention act in a synergistic man- 5 duced to 0.030 inch sheet for further testing and evaluanet and that the excellent properties of the alloys of the tion of the fabricability of the inventive alloys.

invention are not due merely to the presence of vanadium Towards this end, Olsen Cup tests and Bend Tests plus zirconium. were run on the sheet material which had been subjected TABLE 2.EFFECT OF ALLOYING ELEMENTS IN COLUMBIUM ALLOYS Composition, w/o 2,200 F. tensile properties Bend ductility, bend radius Workability Alloy v Hardness factor, IT (deg) to 0.02-iuch No. V Zr Yield Ultimate El0ng., Rockwell B-.-- thick sheet XLOOO p.s.i. X1,000 p.s.i. Percent Transverse Longitudinal 19 26 22 96 0 90 Excellent. 2 1 8 16 14 47 180 180 Do. 5 1 30 31 29 92 98 180 Do. 5 1 98 Poor. 5 1.5 Do. 5 3 Do. 5 5 Do. 5. 23 1. 13 Excellent.

1 0.03 inch thick sheet.

Referring to Table 2, Alloy 1 with 5 percent vanadium to a vacuum anneal of 1 hour at 2100 F. to determine the and Alloy 2 with 1 percent zirconium are both relatively ductility of the alloy. The Olsen Cup tests showed the alweak alloys at 2200 F. The addition of .1 percent carbon 25 loy to be very ductile and formable; a cup depth of 0.390

in the alloys tends to embrittle the alloys as noted in inch was obtained under a load of 5120 pounds. The cup Alloys '4 and 5. Alloys 6 and 7 which contain 5 percent test failures were ductile in nature, i.e., deep cups with vandium and 3 and 5 percent zirconium, respectively, and half-moon type features.

which are outside the limits of the invention, are unsuited Bend test results of 180 degrees over a IT radius were because they lack sufficient ductility and workability rop achieved at both room and liquid nitrogen (-321" F.) erties. Inventive Alloy 8 which contains a carbon amount temperature with the annealed sheet bent both longitudi which is within the allowable limits illustrates that such an nally and transversely to the final sheet rolling direction. addition of carbon does not embrittle the alloys as does In addition, two welded bend specimens were prepared the addition of carbon outside the allowable limits (AllOYS by straight line Heliarc fusion welding of small strips 4 and 5). The data in Table 2 clearly show that best of the annealed sheet in an evacuated dry box. The bend results are obtained when the alloy contains about 5 perte ts wer ru with th ld b d perpendicular t the cent vanadium, about 1.0 percent zirconium, less than 0.1 b d i ith th ot f th ld i compression B d percent carbon and the balance essentially columbium and angles of 180 d 90 degrees o a IT radius w re incidental impurities. Additional data has shown that the achieved at room and liquid nitrogen temperature, recarbon content should not exceed .04 weight percent. spectively.

Metanographic Studies of the aHQYS listed in Tabla 2 Finally tensile properties over a temperature range of ind cat t 11116 inventive 3 8 has a Single Phase from room temperature to 2400 F. were determined and structure while Alloys 6 and 7, with higher zirconium are reported in Table 3 below.

contents, appear to have a secondary phase at the grain boundaries. It appears, by correlation, that the microstruc- TABLE L PR P RTIE OF (mac-INCH THICK ture of the alloy influences the working properties of this L OY N0 8 SHEET KNNEALED 1 HOUR AT 2900 01M alloys as Sherwin Table a sat are time Five examples of each composition listed in Table 2 3 F: 5 5 psi i P inch (except Alloy 8) were made to obtain average results for 75 6',000 84 100 2 the table. Commercially pure columbium, vanadlum and 63,600 3 zirconium were used in preparing the alloys. The process- 75 71,200 9 0 7 75 73,100 90, 200 24 mg steps *dCSCIlbBd herein are withm the sk1lls of the pres- 700 54' 800 86, 20 ent art to produce best results. Each charge was tungsten- 61,100 .000 19 1, 100 49, 500 87, 600 14 are melted under one-half atmosphere of argon. Each 100- 1,100 57,100 101,300 15 gram button ingot was melted a total of four times and m- 55 83g ggg 600 :3 verted between remelts to achieve alloy homogeneity. The 200 500 263600 74 h -in h reduc- D0 2 200 25 600 27 400 79 as cast in ots were rolled at 400 F wit 0 01 c Transversem 2:400 171900 18:70) 72 tion per pass to 0.125-inch thickness. The specimens were Do 2,400 then cfurther cold rolled at room temperature to final thicknesses ranging from about 0.10 inch to about 0.01 60 inch.

The initial reduction step at about 400 F. is, metallurgically, a cold-rolling process because the temperature is below the recrystallization point of the alloy. Through experimentation, it was found that excellent results are 5 obtained when rolling at about 400 F., thus avoiding the harmful effects of hot rolling and eliminating the attendant procesin g steps required in hot rolling. Considering surface condition and physical-mechanical properties, cold-rolled alloys are superior to hot-rolled alloys. Alloy 3 was readily 7 processed to less than 0.02-inch thickness as described im- The alloy of claim 1 wherein the weight Percent of niedlately above H w m Tabie Alloy vanadium is 5.23, the weight percent of zirconium is 1.13 did not possess suitable ductihty characteristics as ev1- and the Wei ht cream of carbon is 005 denced by bend test results. Alloys 4, 5, 6 and 7 were g p difiicult to cold roll, but may be hot rolled at temperatures 7 above about 2000 F. It is t0 be noted that only Alloy 8 Registered trademark of Union Carbide Corporation.

As will be appreciated from the foregoing data, the alloy of the subject invention as typified by Alloy 8 in Table 2, has overcome the strength problem associated with the binary columbium-zirconium alloy previously discussed, without impairing producibility.

What is claimed is:

1. A cold rollable, ductile alloy consisting essentially of about 5 weight percent of vanadium, about 1 weight percent of zirconium, about .005 weight percent of carbon with the balance being columbium and adventitious impurities.

5 6 3. The alloy of claim 1 wherein the Weight percent of 3,206,305 9/1965 Begley et a1. 75174 columbium is at least 92. 3,236,638 2/1966 Clark 75174 References Cited OTHER ERENCES UNITED STATES PATENTS Columbium Metallurgy,;lnterscience Publishers Inc.,

5 N.Y., 1961, relied on p. 239. 3,012,883 12/1961 Allen 7s 174 3,188,207 6/1965 Schussler 75-474 CHARLES N. LOVELL, Primary Examiner.