US3640781A

US3640781A - Two-phase nickel-zinc alloy

Info

Publication number: US3640781A
Application number: US13913*[A
Authority: US
Inventors: Frank Joseph Ansuini; Jacob Schramm; Frank Arthur Badia
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-10-14
Filing date: 1969-10-14
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: DE2050086A1; CA924931A; SE364069B; GB1292504A; FR2064324B1; BE757506A; CH525282A; FR2064324A1

Abstract

Process of heat treating and mechanically working nickel-zinc alloys or copper-nickel-zinc alloys produces products having special alpha-beta microstructure characterized by high strength at room temperature and high deformability at elevated temperatures.

Description

United States Patent Ansuini ct al.

[ Feb. 8, 1972 [54] TWO-PHASE NICKEL-ZINC ALLOY [72] Inventors: Frank Joseph Ansuini, 176 Wayne Ave., Sufiem, N.Y. 10901; Jacob Schramm, 156 Edgecomb Road, Calhoun Lakes, Spartenburg, SC. 29302; Frank Arthur Badia, 41 Kingsley Road, Ringwood, NJ. 07456 [22] Filed: Oct. 14,1969

[21] Appl.No.: 13,913

[52] US. Cl. ..148/12.7, 148/160 [51] Int. Cl. ..C22f 1/08 [58] Field ofsearch .;..148/11.5, 12.7, 160; 75/1575, 75/170,178 R, 178 C [56] References Cited UNITED STATES PATENTS 2,101,625 12/1937 Munson ..75/l57.5

2,101,626 12/1937 Munson... ....75/157.5

2,101,087 12/1937 Munson ..75/157.5

1,680,046 8/ 1928 Homerberg et a1 148/ 1 60 1,680,045 8/1928 Homerberg et al.

3,005,702 10/1961 Chaudron et al.

3,403,997 10/ 1968 Badia 3,046,166 7/1962 Hartmann ..148/ 160 This application filed under Rule 47.

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. W. Stallard Attorney-Maurice L. Pinel [57] ABSTRACT Process of heat treating and mechanically working nickel-zinc alloys or copper-nickel-zinc alloys produces products having special alpha-beta microstructure characterized by high strength at room temperature and high deformability at elevated temperatures.

8 Claims, 3 Drawing Figures O 7O & A9;

] PATENTEUFEB a tan SHEET 2 OF 2 FIG INVENTORS G 3 FRANK JOSEPH ANSUINI JACOB SCHRAMM FRANK ARTHUR BADIA ATTORNEY TWOJIIASENICKEL-ZINC ALLOY The present invention relates to metallurgy of alloys in the copper-nickel-zinc ternary system, including certain nickelzinc alloys at the'boundar-y of the copper-nickel-zinc system, and more particularly relates to thermomechanical processing of copper-nickel-zinc alloys and to wrought copper-nickelzinc alloy products.

A variety of copper-nickeI-zinc alloys have been known for at least severalcenturies and have been known to possess various desirable combinations of malleability, mechanical characteristics (including strength and ductility) and general corrosion resistance. Many metallurgical studies of the copper-nickel-zinc systemhave been reported in the art and certain metallurgical phases in this system e.g., the face-centered cubic alphaandseveral beta-type phases including body-centered cubic beta'and body-centered tetragonal beta types, arewell known. Some of the alloys which have a rich white (silverlike) color are known as nickel silvers or German silvers and both single-phase alpha nickel silvers and dualphased-.alpha-beta nickel silvers are known. While the term nickel silver usually refers to alloys containing about 9 percent to about percent or percent nickel it is known that the alpha and beta phases are also obtained in copper-nickel-zinc alloys withmuch more nickel, .e.g., 40 percent or 60 percent nickel, and even in alloys containing about 7l percent nickel along with about 29 percentzinc in which very little or no copper is present. 0

While known copper-nickel zinc alloys have been used in many articles, including tableware, medical instruments, scientific measuring instruments and electric switches, it has long been desirable to obtain improved combinations of strength and ductility characteristics with these alloys. It has been known that tensile strength, including ultimate tensile strength and yield'strength, can be increased by simply coldworking the'alloys. However the strength increases obtained by cold-workinglhave been accompanied by serious reductions in ductility, particularly tensile elongation. Furthermore, even whentensile strength has been increased by cold-working, fatigue strength characteristics have remained undesirably low. Need for highfatigue strength in combination with a high'yield strength orelastic limit has been particularly great where the alloy is neededformaking vibratory elements and springs.

Tensile strengths can also :be'increased'by addition of other elements, such as aluminum, titanium or columbium, which enable strengtheningby age-hardening, but age-hardeninghas not satisfied the needfor increased fatigue strength and the heat'treatment requirements-can sometimes introduce manufacturingtdifficultiesr Another-important need has beento obtain highly improved formability-in order to enable production of a greater variety of shapesin'products, Enhanced formability has been especially desirable for increasing the usefulness of the whitecolored'copper-nickel-zinc alloys inasmuch as the rich silverlike colorof these alloys ishighly desirable forarticles that are both ornamental and utilitarian, e.g., tableware such as cream pitchers and gravy boats. It has been very obvious that improved formability characteristics would provide artists, craftsman and engineers'with greater scope for designing to meet esthetic and engineering needs.

Although many attempts were made to overcome the foregoing difficulties and others and providecopper-nickelzinc alloy products having improved combinations of strength and ductility characteristics, none, as far as we are aware, has fully satisfied all of the outstanding needs.

There has now been discovered a thermomechanical process that provides nickel-zinc, including copper-nickelzinc, alloy products with new and enhanced characteristics of strength andductility, including formability, along with good corrosion'resistance.

An object of the present invention-is to provide a wrought and heat-treated nickel-zinc (or copper-nickel-zinc) alloy product having a two-phase microstructure characterized by a useful combination of strength, ductility and corrosion resistance;

A further object of the invention is to provide a process for working and heattreating nickel-zinc alloys to produce strong. ductile and corrosion-resistant products thereof.

Other objects and advantages of the'present invention will be apparent from the following description --taken in conjunction with the accompanying drawing in which:

FIG. I shows an alloy composition diagram pertaining to the copper-nickel-zinc ternary systemf FIG. 2 is a reproduction'of a photomicrograph taken at a magnification of 1,000 diameters (1,000X) illustrating the etched two-phase microstructure of an embodiment of the wrought and heat-treated product of the invention; and

FIG. 3 is a reproduction of a photomicrograph taken at 500X magnification illustrating the etched-two-phase microstructure of another embodiment of thewrought and heattreated product of the invention. The microstructures illustrated by FIG. 2 and FIG. 3 were both produced in accordanc with the process of the invention.

Generally speaking, the present invention contemplates a wrought and heat-treated product made of a special alloy composition containing zinc and nickel, advantageously 8 percent to 40 percent nickel, and in most instances copper, and having a two-phase microstructure comprising a fine-grained alpha matrix with fine beta particles dispersed intergranularly throughout the alpha matrix. Useful room temperature characteristics of the product of the invention particularly include, among other things, high strength that is generally much greater than the normal strengths of conventional copper-nickel-zinc alloys such as nickel silvers, good ductility and formability in combination with the high strength, and generally good corrosion resistance. Additional important characteristics obtained with embodiments of the present product include high fatigue strength at room temperature and extraordinarilyhigh formability at elevated temperatures. The invention also contemplates a thermomechanical metallurgicalprocess, which provides products in accordance with the invention, comprising-coId-working an alloy of the special nickel-zinc compositionin the alpha solidsolution condition (the single-phase condition) and then, while the alloy possesses strain energy from the cold work, heat treating the coldworked single-phase alloy at a temperature at or above the recrystallization temperature and below the'alpha/alphaplusbeta solvus of the alloy and in the range of about 700 F. to about 1,150 F. to recrystallize the alloy into a fine-grained structure and simultaneously. precipitate fine beta particles in an intergranular dispersion throughout the alpha matrix. While the product can also have some beta within the alpha grains, it is to be understood that the beta is dispersed predominately intergranulary.

The special alloy composition of the invention is the range or areaof composition in the copper-nickel-zinc ternary system that is characterized by an alpha/alpha-plus-beta solvus temperature of 800 F. to 1,200 F. Thus, the alloy composition is the area of composition bounded (including the boundary) by the 800 F. and 1,200 F. solvus lines and the nickel-zinc (binary) boundary line on'the copper-nickel-zinc ternary diagram; this area'of composition in accordance with the invention is illustrated by the shaded area bounded by the l,200 F. solvus=line ABCD, the nickel-zinc boundary line DE from about 29 percent to about 33 percent zinc and the 800 F. solvus line EFGA. All alloy composition percentages referred to herein are by weight. The coordinates of the points A through G on the ternary diagram in FIG. lare set forth-in the following coordinate table.

Maximum Minimum Nickel: 4%

Zinc:

From 471 to 20% Ni 7Zn=390.375 (1ND From 20% to 35% Ni 1Zn=34.20.l33 (ZNU From 35% to 71% Ni From 471 to Ni %Zn=36+8. I415 (2 Ni) From 10% to Ni A'Zn=40 From 15% to 40% Ni Copper: Balance Balance An advantageous range of composition is included by percentages in accordance with the following:

Minimum Maximum Nickel: 8'1 40% Zinc: 1Zn=380.23 (/z Ni) '7rZn=42-0.23 (1 Ni) Copper: Balance Balance While the alloy may be referred to as having a balance of copper or zinc, this does not exclude small amounts of auxiliary elements, such as deoxidizers, desulfurizers, etc., and incidental elements or impurities. Accordingly, the alloy can contain up to about 0.1 percent titanium up to about 0.03 percent aluminum, up to about 0.5 percent magnesium and up to about 1 percent manganese. lron, carbon and silicon are undesirable and should be restricted to not more than about 0.15 percent iron, about 0.05 percent carbon and about 0.5 percent silicon and more desirably not more than 0.05 percent, 0.01 percent and 0.01 percent of each, respectively. Elements such as bismuth, phosphorus, sulfur and tellurium can be detrimental and should be limited to not more than 0.005 percent each. Although lead is not required, up to 1 percent or higher, e.g., 2 percent, lead can be added to improve machinability. However, where it is desired to obtain especially good formability at elevated temperatures, lead should be controlled to low levels such as up to about 0.05 percent or advantageously not more than 0.015 percent.

In view of the foregoing description pertaining to the alpha/alpha-plus-beta solvus relationships and the shaded area in FIG. 1, it is apparent that the nickel, zinc and any copper in the alloy are within the ranges of about 4 percent to about 71 percent nickel, about 29 percent to about 40 percent zinc and up to about 59 percent copper.

It is also important to note that the controlled composition provides a required cold workability characteristic that enables cold-working the alloy into a condition having a recrystallization temperature below the alpha/alpha-plus-beta solvus temperature, advantageously 50 F. to 200 F. below the solvus, ofthe alloy.

The alpha component of the microstructure referred to herein is the face-centered cubic structured alpha phase in the copper-nickel-zinc system and the beta component is one or more of the beta-type phases which have body-centered cubic or body-centered tetragonal structures in the copper-nickelzinc system. Finely divided alpha-beta microstructures in accordance with the invention are illustrated (etched with potassium dichromate) by FIGS. 2 and 3 of the accompanying drawing. FIG. 2 shows an especially good, fully recrystallized, balanced two-phase microstructure with equiaxed beta uniformly distributed in a fine-grained alpha matrix in a product of an alloy containing about 10 percent nickel, 38.3 percent zinc and essentially balance copper (about 51.7 percent copper by difference) which was processed by hot extrusion, solution annealing for 1 hour at l,200'F. and'water quenching, thereafter cold-rolling to 85 percent reduction, and then recrystallization-precipitation treating for 17 hours at 900 F. followed by air-cooling. FIG. 3 shows a marginally acceptable, satisfactory, fine alpha-beta microstructur'e that is about percent recrystallized (thus predominately although not completely recrystallized) with some beta not equiaxed in a product which is also of an alloy containing about 10 percent nickel, 38.3 percent zinc and balance essentially copper and which was processed by hot extrusion, solution annealing fro 1 hour at l,200 F. and water quenching, cold-rolling to 72 percent reduction and recrystallization-precipitation treating for 2 hours at 900 F. followed by air cooling.

The fine alpha-beta microstructure has a fine-grained alpha matrix with average grain-size diameter not greater than the order of about 10 microns. It is advantageous that the alpha grain size be not greater than about 5 or 6 microns, such as 1 to 5 microns, in order to obtain unifon'nly high strength and ductility characteristics and especially good hot formability.

The beta particles are generally about the same size or smaller than the alpha grains. The beta is dispersed atthe alpha grain boundaries and, importantly, are in finely divided discontinuous pattern and do not form grain boundary networks, films or stringers.

At the start of cold-working in the process of the invention, the alloy is in an essentially homogeneous solid-solution condition free from coarse structures, such as coarse dendritic or other segregation or precipitates. Accordingly, where the alloy is prepared by usual procedures of melting and casting into ingot form, the as-cast structure should be well broken up by hot working, e.g., extrusion or forging. Moreover, inasmuch as the alloy usually precipitates beta when normally cooled, for instance, when air cooled in section thicknesses of about one-half inch or greater, it is important that the alloy be solution-treated prior to the cold-working. Solution treatment to place the alloy in the required solid-solution condition can be accomplished by solution-annealing the alloy at a temperature above the solvus (alpha/alpha-plus-beta) for a time sufficient to dissolve any second phase and then cooling the alloy rapidly enough to prevent any diffusion-based reactions, such as precipitation. Advantageously, for solution treatment, the alloy is heated to a temperature of 50 F. to 200 F. above the solvus for about 10 minutes to 2 hours and then cooled in the solid-solution condition; when the alloy contains 4 percent or 8 percent to 20 percent nickel, normal air-cooling is sufficiently rapid for section thicknesses up to one-half inch, but for thicker sections, or when the alloy contains more than 20 percent nickel, the alloy should be cooled more rapidly such as by water quenching.

With the alloy in the solid-solution condition, the alloy is cold-worked an amount effective to depress the recrystallization temperature to below the solvus, advantageously at least about 50 F. below the-solvus and more advantageously 100 F. to about 200 F. below the solvus. Although, in some instances, as little as 30 percent cold worked (30 percent reduction in cross section area) or possibly less may be satisfactory the alloy is advantageously cold-worked at least about 60 percent or better 72 percent or percent, in order to provide sufficient strain energy for recrystallization into a good finegrained two-phase structure.

Following the cold working, the alloy while in the coldworked, alpha-phase solid-solution condition is subjected to a recrystallization-precipitation treatment by heating the coldworked alloy to, and advantageously, above the recrystallization temperature of the alpha phase and yet below the solvus in order to precipitate sufficient beta phase to control the recrystallized alpha grain size. Advantageously, the recrystallization-precipitation treatment is at 50 F. to about 200 F. below the solvus for a period of one-quarter hour to about 24 hours. The recrystallized and precipitated structure provided by the invention has good stability and, accordingly, the heating time may be longer than 24 hours and the cooling rate may be either fast or slow, e.g., air-cooling.

For carrying the invention into practice, an especially advantageous processing cycle, especially for alloys containing 8 percent to 40 percent nickel, is to solution treat the alloy by heating at l,150 F. to 1,300 F. for 30 minutes to 2 hours and thereafter water quenching, or air cooling if the alloy contains 20 percent or less, e.g., 18 percent, nickel, cold working the solution-treated alloy at least about 80 percent and then heattreating the cold-worked alloy to not higher than 50 F. below the solvus-and in the range 750 F. to 1,050 F. for 1 hour to 24 hours, advantageously at least 24 hours in order to ensure full recrystallization.

The invention provides products, which can be produced by the use of the process of the invention, having high yield strengths of 60,000 pounds per square inch (p.s.i.) and higher in combination with very good toughness and ductility, e.g., tensile elongations of percent or greater. Yield strengths referred to herein are by the 0.2 percent offset method unless otherwise noted. Advantageously, the product is made with about 20 percent to about 40 percent nickel, more advantageously, 24-percent to 38 percent nickel, in order to obtain very high yield strengths of 90,000 p.s.i. and higher, e.g., 100,000 or 105,000 p.s.i. with 25 percent nickel. In connection with obtaining very high yield strength along with good ductility and other characteristics, e. g., fatigue strength, it is to be understood that the balanced two-phase structure is especially advantageous for these objects. For most practical commercial production purposes and in order to achieve good control'of the zinc content, the product is produced with about 8 percent to about 40 percent nickel. With less than 8 percent nickel, the tolerance for variation in zinc is very low, only about plus or minus 1.2 percent, and such close control may be very difficult in commercial production. With more than about 40 percent nickel in the alloy, control of the zinc content is difficult due to volatilization at the high melting points of such alloys and special techniques, e.g., powder metallurgy or pressure'rnelting, may be necessary in order to prepare the alloy.

Within the range of 8 percent to 40 percent nickel and with zinc and copper in accordance with the solvus relationships and/or the shaded area on the drawing, the low-nickel alloys containing 8 percent to about 20 percent are characterized by good tensile and fatigue strengths, e. g., 65,000 to 90,000 p.s.i. yield strength, while also being soft and highly malleable at normal hot-working temperatures, such as employed in brass mills, and not requiring'a rapid quench after solution annealing. The 'medi'um-nickel alloys containing at least about 20 percent, e.g., 21 percent, to 33 percent nickel, are characterized by higher strengths, e.g., yield strengths of about 90.000 to 105,000 p.s.i., although being somewhat stiffer at hot-working temperatures and requiring rapid cooling from the solution annealing temperature. Higher nickel alloys containing at least 33 percent, e.g., 34 percent, to 40 percent nickel, are advantageous from the viewpoint of corrosion resistance and have very good strengths of the order of 95,000 p.s.i. to 100,000 p.s.i. yield strength. Control of the composition of these high-nickel alloys becomes more difficult as the nickel content approaches 40 percent.

Further advantageous embodiments and advantages will become apparent hereinafter, inter alia, from the following illustra tive examples which are given for the purpose of giving those skilled in the art a better understanding and appreciation of the advantages of the invention.

A number of copper-nickel-zinc alloys, including the alloys referred to as alloy Nos. 1 through 7, having compositions in accordance with the invention were prepared by air-melting electrolytic copper and electrolytic nickel together and adding zinc pellets, or a zinc-nickel master alloy in the higher nickel compositions, with the melt at a temperature a little above the liquids. When all the zinc was added, the melt temperature was raised to the pouring temperature, about l50 F. above the lit nidns, tinishcd with 0 l percent titanium addition and pooled into ingot molds. ('hcluiral compositions olalloys l to law set forth in the following 'l'aldc l. the ingots ot' the alloys were hot worked to reduce the cross-section size and break up the as-cast structure; alloys 1, 2 and 4 being extruded to 3/4- inch-diameter rod; alloys 5, 6 and 7 being extruded to L5- inch-diameter rod; alloy 3 was forged and hot-rolled to A-inch plate. Generally, hot-working temperatures were about l,400 F. to 1,600 F. with the lower temperatures being used for the lower nickel contents in order to minimize grain growth. Prior to hot working the alloys were homogenized by soaking about 2 hours to 4 hours at 1,500 F. to l,600 F.

Wrought and heat-treated alpha-beta microstructured products in accordance with the invention were prepared from alloys Nos. l through 7 by the following processes Pl and Pll in accordance with the invention as follows. in P-l, applied to alloys 1 through 4, the alloy was solution-treated by heating at l,l50 F. for 1 hour and water quenching, then cold-rolling to percent reduction in area and thereafter heating the cold-rolled alloy at 900 F. for 24 hours followed by air cooling. in process PIl, applied to alloys 5, 6 and 7, the alloy was solution-treated by heating to l,200 F. for 1 hour and water quenching, then cold-rolling to '82 percent reduction in area and thereafter recrystallization-precipitation treating by heating at 1,020 F. for 4 hours followed by air cooling. The resulting products were in the form of 0.080- inch-thick rolled strip. Mechanical characteristics of the products produced by processes P-l and P-ll were confirmed by tests of standard strip tensile specimens with a l-inch by 5- inch gauge section and the thus-obtained room-temperature tensile test results are set forth in the following Table I.

TABLE I Composition Product characteristics (percent) 0.2% Y UTS Elong. Ni Cu Zn Process (ksi.) (ksi.) (percent) 10.0 51.7 38.3 P-I 67.7 89.6 32 14. 7 49. 2 36. 1 P-I 69:4 94. 2 29 15. 4 48. 3 36. 3 P-I 81. 5 99. 9 24 19.2 45.8 "35.0 P-I 90.1 101.3 21 25.5 Bal 34.4 P-II 105.5 118.0 17 30.2 Bel. 33.1 P-II 98.1 121.1 26 38.1 *Bal. 31.7 P-II 98.2 129.4 28

0.2% Y ksi.=Yield strength at 0.2% offset in 1000 p.s.i. units. UTS ksi.=Ultimate tensile strength in 1,000 p.s.i. units. Elong. percent=Tensile elongation in percent. Bal.=Balance. *=By difierence. *=0.8% Mn and 0.1% Ti added to melt.

it is to be understood that the strengths of the two-phase products of the invention are much greater than the strengths obtained with alloys of corresponding compositions in he solid-solution condition. For instance, alloys 1 and 7 when in the solid-solution condition had 0.2 percent yield strengths of 26,400 p.s.i. and 52,000 p.s.i., ultimate tensile strengths of 64,000 p.s.i. and 108,400 p.s.i. and elongations of 65 percent and 24 percent, respectively. It is notable that with compositions having nickel contents of about 30 percent and 37 percent, the ductility of the high-strength two-phase products of the invention, as evidenced by tensile elongations, was as good as or better than the ductility of the solution-treated alloys of the corresponding compositions.

Fatigue testing confirmed that the alloy has high fatigue testing confirmed that the alloy has high fatigue strength that is substantially enhanced over the fatigue strength of conventional copper-nickel-zinc products such as nickel silvers. A fatigue specimen machined from the strip product of alloy 3 produced by processP-l successfully survived, or ran out," without fracture when subjected to cyclically applied reversed bending stresses of 40,000 p.s.i.

Of further advantage, the product of the invention has been found to exhibit desirable high ratios of the 0.01 percent and the 0.02 percent offset yield strengths to the 0.2 percent offset yield strength, for example, 0.01 percent yield: 0.2 percent yield ratios of 0.682l and 0.87zl, and 0.02 percent yield: 0.2 percent yield ratios of 0851i and 0.96:], were obtained with alloys 0 and 7. respectively. These results are illustrative of high elastic limit characteristicsthat are beneficial for springs and other articles subjected to high elastic strain in use.

The wrought and heat-treated two-phase product can be cold-worked, if desired, to reduce the cross section or change the shape of the product or to further harden the product. A highly useful feature of the two-phase product is that the product can be heavily cold-worked and then given a second recrystallization-precipitation heat treatment without causing any serious degradation of tensile characteristics. The following Table ll shows tensile characteristics and hardness test results obtained with strip products made by processing alloy 3 in accordance with the process of the invention, both without and with additional cold work, and in the fourth instance with a second heat treatment, after the first recrystallization-precipitation heat treatment.

TAB LE 11 ST=Solution treatment at 1,150 F. for 1 hour and air cool.

Percent CR=Percent reduction by cold rolling.

RPHT=Recrystallization-precipitation heat treatment at 900 F. for 24 hours and air 0001.

Hard. R30T=Rockvirell superficial hardness, 301 scale. 7

The two-phase product has also been produced in form of wire by cold-drawing the alloy in the solution-treated condition and then recrystallization-precipitation (RP) heat-treating the wire; also, the RP heat-treated wire has been again drawn and again RP heat-treated with good results, thus confirming the utility of the process for multiple-pass drawing of wire.

The electrical conductivity of the product is of the general order of that of commercial nickel silvers of similar nickel levels. Examples of products of the invention containing 10 percent. percent and percent nickel had electrical conductivities of 7.9 percent, 6.8 percent and 5.9 percent lACS (international Annealed Copper Standard). it will be understood that the conductivity will generally decrease with increasing nickel.

lt is understood that temperatures and times required for recrystallization are codependent with alloy composition and degree of cold work. Accordingly, it is understood that the process of the invention is controlled, within the ranges set forth herein, with regard to alloy composition, degree of cold work and heat-treating time and temperature to result in simultaneous recrystallization and precipitation. The techniques for the required control are apparent from the foregoing examples and other disclosures. As an additional guide to facilitate controlling the process, the following results of microstructures obtained with various processing of alloys l, 2 and 3 are set forth in Table III which illustrates many satisfactory procedures which provided satisfactory microstructures A, B, C and D, and also illustrates other procedures resulting in unsatisfactory microstructures E, F and G, which are to be avoided. in this connection, it is noted that particularly consistently good results were obtained when alloys 1, 2 and 3, containing 10 percent to 20 percent nickel, were coldworked at least 85 percent and heat-treated at 800 F. to 900 F. for 24 hours; longer heat treatments, e.g., l00 hours or more, would not be detrimental. it should be further noted that as the nickel is increased, it is beneficial to increase the degree of cold working, the heat-treat temperature and/or the heat-treat time.

Microstruetures, heat treatment in cold worked condition Percent 700 F. 800 F. 900 F.

(Git Alloy work 3 .M 3 t- M J a at his. Ins lu'shis his his in: has ms t n It ll (1 i I". A A l it A H A A A A A A A E l) l) l" l I" F) A I) ii A (l E E A A A A A Percent cold work=pcrccut reduction in cross-sectional area by cold working.

A=Very good-Balanced two-phase microstructure; alpha fully recrystallized; coring minimal or nonexistent; beta finely divided, equlaxed and uniformly intergranularly distributed throughout alpha matrix.

B Satisfactory-Two-phase microstructure; alpha fully recrystallized; minor coring a parent by moderate beta concentration.

C=Margina ly satistactory-Two-phase microstructure; about alpha recrystallized; some beta not equiaxed.

D=Marginally satisfactory-alpha fully recrystallized but beta not completely equiaxed.

E=Not satisfactory-alpha fully recrystallized; substantial beta-iree cored areas.

F=Not Satisfactory-alpha not recrystallized; beta on slip lines and on grain boundaries.

G Not satisiactoryalpha not recrystallized; heavy beta concentration on slip lines and on grain boundaries.

The fine alpha-beta structured product of the invention provides extraordinarily high formability at elevated temperature. For example, an ingot of alloy 3 was hot rolled from 4-inch thickness to /2-inch plate at l,500 F. The hot-rolled plate was solution-annealed at 1,250 F. for one-half hour, air-cooled, than cold-rolled at room temperature to 0.10-inch-thick strip (80 percent cold work) and thereafter recrystallizationprecipitation heat-treated at 950 F. for 4 hours and aircooled. The product produced by this process of the invention had a balanced two-phase microstructure typical of the microstructure illustrated in FIG. 2 of the drawing. Tensile specimens with a 2-inch by /z-inch gauge portion (0.10 inch thick) were machined from the recrystallization-precipitation treated strip. Straining such a tensile specimen of the thusproduced product of alloy 3 in tension at a constant elongation rate starting from an initial strain rate of 0.025 inch per inch per minute at 900 F. resulted in neck-free elongation of 305 percent and thus demonstrated that the product had very high formability of a superplastic nature. Moreover, metallurigical inspection of the product after being elongated over 300 percent showed that no grain growth occurred during the elongation. Another tensile specimen of the fine alpha-beta alloy 3 product was likewise, stretched at 900 F., except that the elongation rate was gradually increased from 0.002 to 0.05 inch per minute and resulted in a neck-free elongation of about 300 percent without fractfief fhe unusuaTly hi gh formability of the product at elevated temperatures, such a tensile elongation of 200 percent or greater at temperatures of about 750 F. to about l,000 F., provides special utility for hot-forming the product into articles having special shapes of highly elongated or deep-drawn, or other greatly stretched, configurations by forming methods such as press-forging, drawing, blow or vacuum forming and others. Furthermore, the hot fonnability characteristics of the product enable hotworking the product at desirable low working loads, e.g., low tensile-stretching loads or low roll-separation forces.

The product has generally good corrosion resistance providing utility in fresh water, salt water and other environments. However, the good corrosion resistance of the product does not generally extend to cover resistance to stress-corrosion cracking in ammonia and if the product is to be used under stress while in contact with ammonia, the product should contain at least about 33 percent nickel and advantageously, for protection against stress-corrosion cracking, should contain 37 percent or more nickel.

The present invention is applicable in the production of strong and ductile corrosion-resistant wrought products including sheet strip, plate, bar, wire and rolled or extruded shapes, e.g., channels, T-sections, etc. Moreover, the invcntion is particularly applicable in the production of usefully and/or ornamentally shaped articles, including tableware, e.g., forks, spoons, butter knives, gravy boats, cream pitchers, and other items commonly referred to as holloware, and including springs, e.g., barometer springs, diaphragm springs and electrical contactor springs, musical instrument keys, surgical and medical instruments, and also costume jewelry. Furthermore, the product is also desirable for use as the underbody of an article cladded with another metal, especially as an underbody for cladding with silver as certain of the compositions have a color close to that of silver.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

I. A process for producing a wrought and heat-treated metal product comprising cold-working an alpha-phase solidsolution structured alloy of the copper-nickel-zinc alloy system characterized by an alpha/alpha-plus-beta solvus temperature of about 800 F. to about l,200 F. and heating the cold-worked alloy to recrystallize the alpha phase into a finegrained alpha-phase matrix and simultaneously precipitate beta-phase particles in a fine intergranular dispersion in the alpha-phase matrix.

2. A process as set forth in claim 1 which also comprises .llL solution heat-treating the alloy to dissolve any precipitated phases therein and place the alloy in the solid-solution condition prior to commencing the cold working.

3. A process as set forth in claim 2 wherein the alloy is solution-treated by heating at about 50 F. to about 200 F. above the solvus for at least 10 minutes and cooled to room temperature sufficiently rapidly to maintain the alloy in the solid-solution condition.

4. A process as set forth in claim 1 wherein the cold-worked alloy is heated to a temperature of about 50 F. to about 200 F. below the solvus to accomplish the simultaneous recrystallization and precipitation.

5. A process as set forth in claim 1 wherein the alloy has a percentage composition represented by a point within the area included by the line ABCDEFGA on FIG. 1 of the accompanying drawing.

6. A process as set forth in claim 5 wherein the alloy contains 8 percent to 40 percent nickel.

7. A process as set forth in claim 1 wherein the amount of cold working is sufficient to effect at least 60 percent reduction in cross section area. D

8. A process as set forth in claim 6 WhlCh also comprises solution heat-treating the alloy in the range of l,l50 F. to l,300 F. prior to commencing the cold working, wherein the amount of cold working is sufficient to effect at least percent reduction in cross section area and wherein the heating of the cold-worked alloy to recrystallize the alpha-phase and simultaneously precipitate beta-phase particles is in the range of 750 F. to l,050 F.

@ 1 UNITED STATES PATENT QFFKCE CER'EEWCATE GE CQRRECTWN 3,640,781 February 8, 1972 Patent No. Dated It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F Column 3 line 16 under Maximum" for %Zn=36+8.l ll5(%Ni) read --%zn 36 0;.4l5(%Ni)-- Same Column, line 40, second occurrence, for "0.5 per" read -'--0.05% per--.

Column 4 line ll, for "fro" read -for.

Column 5, line 42, insert the word "niokel before the word "are v v Column 6, line 52, for "64,000" read -'64,400. Same column, line 60, delete "testing confirmed that the alloy has high fatigue Signed andsealed this 3rd day of July 1973 (SEAL) Attest:

EDWARD M.FLETCHEQR,JR.

Attesting Officer Rene yer Acting Commissioner of Patents FRANK JOSEPH ANSUINI, JACOB SCI'IRAMM and FRANK ARTHUR BADIA

Claims

2. A process as set forth in claim 1 which also comprises solution heat-treating the alloy to dissolve any precipitated phases therein and place the alloy in the solid-solution condition prior to commencing the cold working.
3. A process as set forth in claim 2 wherein the alloy is solution-treated by heating at about 50* F. to about 200* F. above the solvus for at least 10 minutes and cooled to room temperature sufficiently rapidly to maintain the alloy in the solid-solution condition.
4. A process as set forth in claim 1 wherein the cold-worked alloy is heated to a temperature of about 50* F. to about 200* F. below the solvus to accomplish the simultaneous recrystallization and precipitation.
5. A process as set forth in claim 1 wherein the alloy has a percentage composition represented by a point within the area included by the line ABCDEFGA on FIG. 1 of the accompanying drawing.
6. A process as set forth in claim 5 wherein the alloy contains 8 percent to 40 percent nickel.
7. A process as set forth in claim 1 wherein the amount of cold working is sufficient to effect At least 60 percent reduction in cross section area.
8. A process as set forth in claim 6 which also comprises solution heat-treating the alloy in the range of 1,150* F. to 1, 300* F. prior to commencing the cold working, wherein the amount of cold working is sufficient to effect at least 80 percent reduction in cross section area and wherein the heating of the cold-worked alloy to recrystallize the alpha-phase and simultaneously precipitate beta-phase particles is in the range of 750* F. to 1,050* F.