US3188207A - Cold workable columbium base alloy - Google Patents

Description

United States Patent 3,188,207 COLD WORKABLE COLUMBIUM BASE ALLGY Mortimer Schnssler, Kolromo, Ind, assignor to 7 Union Carbide Corporation, a corporation of New York No Drawing. Filed Mar. 8, 1963, Ser. No. 263,721 1 Claim. (Cl. 75174) The present invention relates to columbium base alloys. More particularly, the present invention relates to strong, workable columbium base alloys which can be readily cold Worked into large sheets and foil.

Up to the present, known columbium base alloys have not been widely used because of various seemingly inherent limitations. For example, columbium base alloys are generally considered to be brittle at sub-zero temperatures. Also, those colurnbium base alloys which are duetile have relatively low strength whereas the high strength alloys have been found to be brittle.

Known high strength columbium base alloys are diificult to work and as a result sheet products are limited to experimental size specimens of about 'two to four square feet. That is to say, up to the present, strong, cold workable columbium base alloys have not been known to the art.

The production of large thin sheets of strong columbiurn base alloys is of high significance, particularly as regards advanced aeronautical applications, since such products are required for the commercial manufacture of articles by forming, cladding, bending, welding and other techniques. A further application is in honeycomb construction.

It is therefore an object of the present invention to provide a high strength, columbium base alloy capable of being cold rolled into thin sheet having an excellent combination of ductility, fabricability, weldability and strength.

It is another object of this invention to provide a columbium base alloy capable of being cold-rolled into thinsheet having high strength in the temperature range of 325 F. to 3000 F.

-'It is a further object to provide a strong colurnbium base alloy having good properties at welded areas.

It is another object to provide a high strength columbium base alloy which can be cold rolled into thin sheet as large as 8 feet by 3 feet.

It is another object to provide a high strength columbium base alloy which can be cold rolled to produce sheet having a smooth surface and uniform thickness.

It is another object to provide a high strength columbium base alloy that can be cold rolled into foil as thin as 0.0005 inch.

Other objects will be apparent from the following description and claim.

A strong, cold rollable alloy in accordance with this invention is a columbium base alloy having 9 to 11 percent tungsten, 2 to 4 percent zirconium, and a maximum carbon content of 0.03 percent. This alloy has several outstanding advantageous characteristics not provided by previously known columbium alloys.

For example, the foregoing alloy can be cold-rolled into thin sheet having an excellent combination of strength, ductility, fabricability, and Weldability. Also, the alloy, in sheet form, is machinable by conventional methods.

Further, the foregoing alloy can be cold-rolled into thin sheet having high strength throughout the temperature range of 325 F. to 3000 F.

By way of example, the foregoing alloy has been coldrolled into a smooth sheet over 8 feet x 3 feet having a smooth surface and a uniform thickness of 0.016 inch.

Also, the alloy has been cold-rolled into foil 0.0005 inch thick.

In the present low carbon alloy, 9 to 11 percent tungsten is necessary to provide high temperature strength; also, the zirconium range of 2-4 percent is critical. At values of zirconium lower than 2 percent, the strength of the alloy is very low, and-at higher values, the alloy is very difiicult to roll into thin sheets and is also considerably less ductile after welding. The preferred range for zirconium in 2-3 percent to provide optimum high temperature strength and ductility in addition to workability. At zirconium levels above 3 percent, increased care must be used in cold-rolling operations.

The effect of zirconium in Cb-W-Zr alloys is shown in Table I.

TABLE I Efiect of zirconium in a c0lumbium-10 percent tungsten alloy having a carbon content of less than 0.03%

In the present alloy, in order to obtain the improved workability the carbon content is kept below 0.03 percent. At the same time however, the zirconium content 7 must be maintained no lower than 2 percent and in the range of 2 to 4 percent in order to provide satisfactorily high strength.

Incidental impurities usually associated with columbium base alloys, such as tantalum and molybdenum may be present in small amounts up to about 2 and 3 percent respectively but it is preferred that their contents be held to a minimum to obtain optimum ductility and strength. For example, it is desirable to keep the molybdenum content below 0.5 percent.

Impurities such as oxygen, nitrogen and hydrogen should be as low as possible and are limited to maximum values of 0.04 percen't',-0.01 percent and 0.01- percent, respectively. The total oxygen, nitrogen and hydrogen content should not exceed about 0.04 percent.

The preferred alloy composition of this invention is 10 percent W, 2.5 percent Zr, balance Ob with a carbon content of less than 0.01 percent. This alloy has been found to be highly workable and to have excellent strength and ductility.

The alloy of this invention, which can be prepared and processed by methods known to the art, is coated or canned during hot working operations and heat treatments are conducted in a vacuum atmosphere.

in practice, the alloy is melted and alloyed in an arc melting furnace or preferably an electron beam furnace and formed into an ingot. The ingot breakdown may be accomplished by (1) forging to about percent reduction, (2) extruding to about 4 to 1 reduction and/or (3) directly rolling to about 20 to 1 reduction. The initial ingot breakdown is performed Within the range 2150 to 2350 F.

Following the ingot breakdown, the resulting slabs are heat treated within the range of 2400 F. to 3000 F., preferably about 2700 F., for about 1 hour. intermediate working, in which the slabs are rolled to about inch thick plate, is subsequently performed within the range 2000 to 2300" F. and preferably at about 2150 F. Following the intermediate working, the plates are heat treated at a temperature lower than the first heat treatment, within the range 2200 to 2800 F. and preferably about 2500 F. The plates are then given the final working to the desired thickness at relatively low temperatures. For products up to about A inch thick, the rolling is conducted at about 400 F. For products less than about 12 inch thick, the final rolling is conducted at room temperature. Foil of the alloy of this invention has been cold reduced as thin as .002 inch thick in coils over 12 inches wide.

Sheet product may be given a final heat treatment at temperatures between 2150 and 2300 F. for one hour to obtain from about 75 to 100 percent recrystallization.

The foregoing processing schedule for the alloy of this invention may be applicable to pure colurnbium or columbium with a low alloy content. For previously known high strength columbium alloys, processing temperatures of about 200 to over 400 F. are required at each processing step previously described. Processing at these higher temperatures is disadvantageous in that it increases the cost of production and yields .a rough uneven surface as compared to the very smooth surface of cold-rolled product of the present invention.

Aserious problem usually associated with columbiumbase alloys relates to the ductile-to-brittle transition temperature. This is especially true for weldments of high strength columbium-base alloys. Previously known high strength columbium alloys are characterized by high transition temperatures and are generally, unsuited for service at sub-zero temperatures such as encountered in aeronautical applications. However, in a series of tests it was found that the. alloy of this invention exhibited excellent bend ductility by sustaining a 90-degree bend angle at temperatures down to and including 320 F. In addition, Welds were made on 0.030-inch cold-rolled sheet by electron beam and TIG (tungsten inert gas) processes. These weldments also exhibited excellent bend ductility by sustaining a 90-degree bend angle at temperatures from -230 to -320 F. Minus 320 F. Was the lowest temperature of the test and not the transition limit of the alloy. The alloy used in the foregoing test had a composition of 10.02 percent tungsten, 2.46 percent zirconium, and the balance columbium and a total of .0226 percent oxygen, nitrogen, carbon and hydrogen.

An alloy having a similar composition except for Zr, which was 5 percent, had a bend transition temperature above room temperature and weldments had a transition temperature above 200 F. The small sheet samples containing 5 percent Zr which were used in this test Were fabricated only with great difficulty.

The following tables II, III. and IV show the result of tests performed with 0.030 in. sheet. The composition ii of the sheet was 10 W, 2.5 Zr, balance Ob. The carbon content was less than 0.02 and the total of oxygen, nitrogen and hydrogen was less than 0.04 percent.

TABLE II 1 Ultimate Yield Elonga- Tcmp., F. Tensile Strength at tion, per- Strength, 0.2% offset. cent in p.s.i. p.s.i. 1 in.

1 All tests were conducted at a strain rate of 0.005 in./in./min. to failure.

TABLE III Average Initial Stress (p.s.i.) for Rupture at- Temp., I

1 hour 10 hours 100 hours Rupture Minimum Temp, F Stress, Time, Creep p.s.i hours in./in./hr.

What is claimed is:

A colurnbiurn base alloy consisting essentially of about 10 percent tungsten, 2.5 percent zirconium, a maximum of 0.01 percent carbon, a maximum of 0.04 percent in the aggregate of oxygen, nitrogen and hydrogen, balance columbium.

References Cited by the Examiner UNITED STATES PATENTS 2,973,261 2/61 Frank 75l74 3,056,672 10/62 Clark 75l74 OTHER REFERENCES Metal Progress, June 1960 (pp. 6974 relied upon).

DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.