US3522112A - Process for treating copper base alloy - Google Patents

Description

July 28, 1970 c, 0, c m 3,522,112-

PROCESS FOR TREATING COPPER BASE ALLOY Filed June 26, 1967 2 Sheets-Sheet 1 ALLOY-6 ROCKWELL l5 7' HARDNESS AS RECE/VED TEMPERATURE FIG-l INVENTORI CHARLESD. McLA/N BY )y ATTORNEY July 28, 1970 c. o. M LAIN PROCESS FOR TREATING COPPER BASEALLOY 2 Sheets-Sheet 2 Filed June 26, 1967 TENS/L5 sms/vcm TENS/LE STRENGTH A: RECEIVED TEMPERA rum: -F

HG mm va wzzw BY g 0% ATTORNEY US. Cl. 14812.7 28 Claims ABSTRACT OF THE DISCLOSURE The present disclosure teaches a process for treating a copper base alloy containing iron and optionally other additives. The process is characterized by hot rolling followed by cold rolling with numerous process variation.

As is well known, copper is an excellent conductor of electricity. However, it is deficient in strength for many applications.

It is known to increase the strength of copper by adding small amounts of various elements. While this effectively increases the strength the electrical conductivity of the copper is often markedly reduced.

Since high conductivity combined with increased strength is highly desirable for many applications, optimum combination of high strength and high conductivity has long been subject to extensive research.

Accordingly, it is a principal object of the present invention to provide a process for obtaining high conductivity, high strength copper base alloys.

It is a further object of the present invention to provide a process as aforesaid which is simple and convenient to utilize and is readily susceptible to commercial operations.

It is a still further object of the present invention to provide a process as aforesaid which enables the attainment of high strength and high conductivity While retaining other desirable characteristics in alloys of this type.

It is a still further object of the present invention to provide a process as aforesaid which provides copper base alloys having the ability to attain various strength levels as a result of different annealing treatments, even when small amounts of impurities are present.

It is an additional object of the present invention to provide a copper base alloy which is inexpensive and wherein the excellent physical properties are easily obtainable.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily attained and a high strength, high conductivity, iron bearing copper base alloy readily provided;

The process of the present invention comprises:

(A) providing a copper base alloy containing from 1 to 3.5% iron and the balance essentially copper;

(B) hot rolling said alloy at a metal temperature of from 800 C. to 1050 C., preferably from 875 to 975 C.; (C) cold rolling said alloy with a reduction of at least 30% and preferably at least 50%;

(D) annealing said alloy for at least 30 minutes at a metal temperature of from 400 to 550 C.;

(E) cold rolling with a reduction of at least 30%; and (F) annealing said alloy at a metal temperature of from 400 to 550 C. for at least 5 seconds.

Variations in the foregoing process will appear from the ensuing specification.

In accordance with the findings of the present inven- Unitcd States Patent Office 3,5ZZ,1 l2. Patented July 28, 1970 tion, the foregoing process results in an unexpected combination of high strength and high electrical conductivity. For example, there is readily obtained an IACS electrical conductivity in excess of IACS, and a range of to 82% IACS is readily attained. Furthermore, the annealing characteristics are predictably excellent, with the ability to attain various strength levels. The present process enables the attainment of various electrical conductivity levels up to 82% IACS independently of ability to control strength levels. Also, the alloys attain high rolled temper strength levels. The high electrical conductivity of the alloys is coupled with excellent annealed tensile strength properties of approximately 65,000 psi. and higher. The strength and physical properties of the alloys are not significantly variable if small amounts of impurities are present. In addition, the alloys resist softening during soldering 700800 F. In addition to the foregoing, the process of the present invention is inexpensive and readily enables the attainment of alloys having excellent physical properties.

In the preparation of the alloy of the present invention, the particular method of casting is not critical and any method used for alloys of this type may be conveniently employed. It should be noted that since iron is used as an alloying addition higher temperatures should be used in order to solutionize the iron. It is preferred to cast the alloy into billets of conventional size and thereafter subject them to hot working in the conventional manner.

The particular alloys utilized in accordance with the present invention are, as stated hereinabove, any copper base alloy containing from 1 to 3.5% iron, preferably 1.5 to 2.9% iron, and preferably containing certain additional additives. For example, the process of the present invention may readily utilize an alloy containing one or more of the following: silicon in an amount from 0.01 to 0.5%; phosphorus in an amount from 0.01 to 0.5%; and zinc in an amount from 0.01 to 0.5%. In addition, small amounts of one or more additional additives may be utilized, for example, 0.01 to 0.5% of the following: manganese, tin, aluminum, nickel, calcium, titanium, chromium, tungsten and vanadium. Also, small amounts of impurities may, of course, be tolerated.

Throughout the instant specification percentages designate percentages by weight.

Throughout the present specification the terms hot rolling and cold rolling are utilized as these are the preferred modes of operation. It should be understood, however, that hot or cold working may be utilized, e.g., forging, extrusion, the piercing of billets for seamless pipe or tubes and wire drawing, etc.

Subsequent to the casting, the alloys are hot rolled at an elevated temperature. The hot rolling temperature may vary from 800 to 1050 C., i.e., the material may enter the hot rolling mill within the foregoing temperature range. The hot rolling finishing temperatures are not particularly critical. It is preferred to utilize a hot rolling temperature range of from 875 to 975 C.

One high temperature treatment in the range of 800 to 1050 C. is required to develop optimum electrical conductivity. The high temperature treatment may be combined with hot rolling, but if not convenient may be before or after hot rolling and should be before the cold rolling and annealing. The high temperature solution treatment will enable a lower hot rolling temperature, provided it is followed by a high temperature treatment within the range of 800 to 1050 C. Accordingly, the material is preferably subjected to a high temperature holding step, namely at a temperature of from 800 to 1050 C., and preferably 875 to 975 C. for at least minutes and preferably for minutes or more before rolling. Naturally, if desired, it may be convenient to combine this high temperature holding step with the hot rolling step, or perform the high temperature holding step following hot rolling.

The amount of reduction taken in the hot rolling step is not particularly critical, being dictated by gage requirements.

Following the hot rolling and high temperature holding steps, the material is cooled to a holding temperature of 400 to 550 C. and held at metal temperature for at least 30 minutes. The manner of cooling to holding temperature is not critical, but preferably the material is slowly cooled following holding. The material should be cooled slowly at a rate less than 200 C. per hour to a temperature of at least 350 C., and preferably at a rate less than 75 C. per hour, and optimally less than C. per hour. Controlled cooling rates following holding at temperatures below 350 C. are not particularly critical. Although the holding step is not essential, it results in some improvement in final properties. In fact, when the material is held as above, improved results are obtained even with one cycle of cold rolling and annealing. Indeed, quite surprisingly, this enables the elimination of annealing and the attainment of good properties by cold rolling directly to finish gage. For example, conventionally hot rolled, water-cooled metal cold rolled 90% will develop about 80,000 p.s.i. tensile strength and about IACS electrical conductivity; whereas, a holding step from hot rolling in the foregoing manner and cold rolling 90% can develop about 80,000 p.s.i. tensile strengh and about 65% IACS electrical conductivity.

The material is then cold rolled, followed by low temperature anneals. In accordance with the present invention, there is utilized two cycles of cold rolling and annealing and preferably three cycles for maximum conductivity. That is, after solution treatment or hot rolling the material is cold rolled, annealed, cold rolled, and annealed, preferably with an additional cold rolling and annealing cycle. Additional cycles may be used, if desired. Generally, more than four (4) cycles of cold rolling and annealing are not necessary.

The annealing steps should be in the temperature range of 400 to 550 C., preferably 440 to 520 C. and the cold rolling reduction should be reductions of at least and preferably at least 50% in each cold reduction step. The preferred annealing temperatures are as follows. The first anneal utilizes preferably a temperature of 470 to 510 C., the second anneal utilizes preferably a temperature of from 400 to 5 00 C. and the last anneal utilizes preferably a temperature range of from 400 to 500 C. The annealed tensile strength properties can be controlled from about 40,000 to 70,000 p.s.i. within these temperature ranges for the last anneals.

If it is desired to utilize a cold reduction step after the final anneal, cold reductions of less than 60% should preferably be utilized, i.e., reductions greater than 70% result in a slight decrease of electrical conductivity after the final anneal.

The time at annealing temperature for the first anneal should be at least 30 minutes, preferably at least 3 hours, and preferably for economic reasons under 8 hours, although, longer annealing times may be utilized, if desired. The longer the time at temperature the higher is the resulting electrical conductivity. However, the improvement becomes a very modest improvement at very long holding times. Therefore, a 24 or 48 hour soak provides only marginal, but measurable improvement in electrical conductivity over a 6 to 8 hour soak. Thus, economics will naturally determine the optimum soak time.

For subsequent anneals one may if desired utilize strip annealing as an in process and/or as the final anneal, i.e., subsequent anneals may be for at least 5 seconds at a metal temperature of from 400' to 550 C. However, for

4 preferred electrical conductivity properties it is preferred to utilize longer holding times for the final anneal, optimally for all subsequent anneals, e.g., a bell anneal for at least 30 minutes and preferably at least 3 hours.

Alternatively, one may utilize strip annealing prior to the final anneal, i.e., at 400 to 800 C. for at least 5 sec onds. In this case, the final anneal should be a bell anneal at from 400 to 500 C. for at least 30 minutes as hereinabove described.

The cooling rate from low temperature anneals should be less than 200 C. per hour down to at least 375 C. and preferably be less than 75 C. per hour and optimally less than 20 C. per hour down to a temperature of 350 C. for optimum electrical conductivity. Below 350 C. the cooling rate is not critical. In addition, it has been found to be highly advantageous to slowly cool in the foregoing manner following low temperature anneals, particularly with one cycle of cold rolling and annealing. If the long soak time and slow cooling rate can only be controlled on one anneal of a multiple anneal process, it is best for the last anneal to be controlled for development of maximum electrical conductivity.

In an alternative embodiment the present invention comprehends within its scope an improved thermal treatment for obtaining high electrical conductivity in cast parts. In accordance with this embodiment a casting or forging may be treated in the following manner:

(A) providing copper base alloy containing from 1 to 3.5% iron, balance essentially copper;

(B) holding said alloy at a metal temperature of from 800 to 1050 C. for at least 10 minutes; and

(C) transferring said alloy to a hold at a metal temperature of from 400 to 550 C. for at least 30 minutes.

The foregoing steps are as discussed hereinabove. It should be noted that after step (B) the material should be immediately transferred to a furnace and held at metal temperature as indicated in step (C). Subsequent cool down rates are not critical.

The present invention will be more readily understandable from the consideration of the following illustrative examples.

EXAMPLE I Alloys were prepared in the following manner. High purity copper and high purity iron were melted together in a low frequency, slot type induction furnace under a charcoal cover at approximately 1200 C. About 10% of the copper charge was held back and the melt was slightly overheated to about 1300" C. in order to put the iron into solution. High purity alloying additions were added when the molten mass was at about 1300 C. The balance of the copper was added and the melt brought to the pouring temperature of about 1200 C. The melt was then poured into a water-cooled ingot mold of 28%" x 5" x 96" at a pouring rate of 21.3 per minute.

The alloys thus prepared had the following composition.

Alloys 1, 2 and 3 prepared in Example I were processed as follows. The alloys were hot rolled at from 900 to 940 C. in eleven passes to 0.350", followed by a water spray quench to room temperature. The materials were then milled to 0.300" and cold rolled to 0.100", bell annealed at 480-600 C. (1 to 4 hours at temperature), cold rolled to 0.050", bell annealed at 460 to 480 C. (l to 3 hours at temperature), and cold rolled to 0.02 gage and bell annealed at 440 to 480 C. (1 to 3 hours at temperature).

The alloys were then tested for physical properties with the results being shown in the following table.

were slow cooled to about 200 C. at a rate of about 75 C. per hour. The alloys were milled to 0.300", cold TABLE H rolled to 0.100", annealed for two hours at 490 C., cold E I rolled to 0.050", annealed at 440 C. for two hours and Yield Tensile Elonlectrica u strength, Strength gation, Conductivity, 5 cold rolled to 0.025 and annealed for two hours at Alloy p.s.i. p.s.i. percent percent IACS 440 C 26,900 53,400 27 gm After each anneal the tensile strength and electrical 23,100 50,100 27.5 73.5 27, 000 59,500 24 7M conductivity of each sample was determined and the re sults are shown in the following table.

TABLE v First Anneal Second Anneal Third Anneal Tensile Electrical Tensile Electrical Tensile Electrical Strength, Conductivity, Strength, Conductivity, Strength, Conductivity, p.s.i. percent IACS p.s.i. percent IACS p.s.i. percent IACS EXAMPLE III EXAMPLE V In this example three alloys were prepared in a manner after Example I, wherein the alloys had the following composition:

The alloys were then processed in a manner after Example II with an additional cold rolling to increase strength level. The alloys were then tested for softening temperature in the following manner. The alloys were immersed in a salt bath at elevated temperatures at 600, 700 and 800 F. for periods of time of 3 and 4 minutes. The samples were then tested for Rockwell 1ST hardness, yield strength and tensile strength, the results are shown in FIGS. 1 and 2. FIG. 1 is a curve of Rockwell 1ST hardness versus temperature and FIG. 2 is a curve of strength versus temperature. In FIGS. 1 and 2, the solid lines represent the data after 3 minutes immersion in the salt bath and the dashed lines represent the data after 4 minutes 5 immersion in the salt bath.

These graphs vividly demonstrate that the iron-containing alloys attain improved results (alloys 4 and 5) when processed in accordance with the present invention over In this example an alloy having the following composition was prepared in a manner after Example 1: Alloy 12iron, 2.3%; phosphorous, 0.026%; zinc, 0.10%, balance essentially copper. Two five inch thick slabs were processed in the following manner: both samples were hot rolled from about 940 C. to about 0.350. Sample A was water spray quenched to room temperature immediately after the last hot rolling pass and subsequently cold rolled 90%. Sample B was cooled from hot rolling temperature to 500 C. and held for 30 minutes and was slowly cooled to about 200 C. at a rate of about 75 C.

An alloy was prepared in accordance with Example I having a composition corresponding to Alloy 3. The ma terial was then heated to a temperature in the range of 850 to 975 C. and held with the metal at temperature for 30 minutes. The material was then transferred to a second furnace and held for three (3) hours with the metal at a temperature in the range of 425 to 550 C. The material was then air cooled to room temperature and had the following properties:

a conventional alloy (alloy 6). TABLE v11 EXAMPLE IV Yield strength p.s.i 17,500 Tensile strength p.s.i 46,800 In this example three alloys were prepared in a man- Electrical conductivity Percent IACS 635 ner after Example I, wherein the alloys had the following Elongation percent 320 compositions:

EXAMPLE VII TABLE Iv Two alloys were prepared in a manner after Example I having the following composition. Percent TABLE VIII Alloy Phosphorus Iron Silicon Zinc Copper Percent 0.021 2.3 0.13 0.08 Essentially balance. 0.014 2.4 0. 09 D Alloy Iron Phosphorus Zinc Copper 0. 045 2.4 Do. 0.022 2.1 Do. 13 2.4 0.03 0.12 Essentially balance. 0. 025 2.4 Do. 14 2.4 0. 03 0.13 Do.

The alloys were processed in the following manner. The (five inch thick slabs were hot rolled at 925 C. to 0.350". After the last hot rolling pass, alloys 7, 9 and 11 were water quenched to room temperature and alloys 8 and Both alloys were hot rolled at about 940 C. in eleven passes to 0.350".'Alloy 13 was then held at a temperature of 500 C. for 30 minutes at temperature followed by slow cooling to room temperature at a rate of less than 200 C. per hour. Alloy 14 was water spray quenched after the last hot rolling pass. Both alloys were then cold rolled to 0.070" and strip annealed such that the metal temperature was 485 C., with the metal at this temperature for about 10 seconds, followed by rapid cooling in a continuous strand annealing furnace. The resulting properties were as follows:

This example clearly illustrates the improved electrical conductivity of Alloy 13 when it is subjected to the 500 C. holding step followed by slow cooling.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process for the preparation of high conductivity high strength copper base alloys which comprises:

(A) providing copper base alloy containing from 1 to 3.5% iron, balance essentially copper; (B) hot working said alloy at a temperature of from 800 to 1050 C.;

(C) cold working with a reduction of at least 30%;

(D) annealing said alloy at a metal temperature of from 400 to 550 C. for at least 30 minutes;

(E) cold working with a reduction of at least 30%;

and

(F) annealing said alloy at a metal temperature of from 400 to 550 C. for at least 5 seconds.

2. A process according to claim 1 wherein before the cold rolling step (C), the material is held at a metal temperature of from 800 to 1050 C. for at least minutes.

3. A process according to claim 1 wherein the alloy (A) contains from 0.01 to 0.5% of a material selected from the group consisting of zinc, phosphorus, silicon, manganese, aluminum, tin and mixtures thereof.

4. A process according to claim 1 wherein the material is held for at least 30 minutes at a temperature of from 400 to 550 C. after step (B).

5. A process according to claim 4 wherein the cooling rate from hot working temperature is less than 75 C. per hour down .to 350 C.

6. A process according to claim 1 including an additional cold working step after the final anneal.

7. A process according to claim 1 wherein all annealing steps are from 1 hour to 8 hours at temperature.

8. A process according to claim 1 wherein the cooling rate from annealing temperature is less than 200 C. per hour down .to at least 350 C.

9. A process according to claim 5 wherein the cooling rate from annealing temperatures is less than 75 C. per hour down to at least 350 C.

10. A process according to claim 1 wherein the first anneal is for a period of time of at least 3 hours.

11. A process for the preparation of high conductivity high strength copper base alloys which comprises:

(A) providing copper base alloy containing from 1 to 3.5 iron, balance essentially copper;

(B) hot working said alloy at a temperature of from i 800 to 1050 C.;'

(C) holding for at least 30 minutes at a temperature of from 400 to 550 C.;

(D) gold working with a reduction of at least 30%;

(E) annealing said alloy at a metal temperature of from 400 to 550 C. for at least 5 seconds.

12. A process according to claim 11 wherein the annealing step (E) is for a period of time of at least 3 hours.

13. A process according to claim 11 including an additional cold working step after the final anneal.

14. A process according to claim 11 wherein steps (D) and (E) are repeated.

15. A process according to claim 14 wherein both annealing steps utilize a period of time of at least 3 hours.

16. A process for the preparation of high conductivity high strength copper base alloys which comprises:

(A) providing copper base alloy containing from 1 to 3.5% iron, balance essentially copper;

(B) hot working said alloy at a temperature of from 800 to 1050 C.;

(C) cold working with a reduction of at least 30%;

(D) annealing said alloy at a metal temperature of from 400 to 550 C. for at least 30 minutes; and

(E) slowly cooling down to at least 375 C. at a rate less than 200 C. per hour.

17. A process according to claim 16 wherein the alloy (A) contains from 0.01 to 0.5% of a material selected from the group consisting of zinc, phosphorus, silicon, manganese, aluminum, tin and mixtures thereof.

18. A process according to claim 16 wherein the annealing step (D) is for a period of time of at least 3 hours.

19. A process according to claim 16 wherein steps (C), (D) and (E) are repeated.

20. A process according to claim 16 including an additional cold working step after the final anneal.

21. A process for the preparation of high conductivity high strength copper base alloys which comprises:

(A) providing copper base alloy containing from 1 to 3.5% iron, balance essentially copper;

(B) hot working said alloy at a temperature of from 800 to 1050 C.;

(C) holding for at least 30 minutes at a temperature of from 400 to 550 C. followed by slowly cooling at a rate less than 200 C. per hour down to at least 350 C.; and

(D) cold working with a reduction of at least 30%.

22. A process according to claim 21 wherein the alloy (A) contains from 0.01 to 0.5% of a material selected from the group consisting of zinc, phosphorus, silicon, manganese, aluminum, tin and mixtures thereof.

23. A process for the preparation of high conductivity high strength copper base alloys which comprises:

(A) providing copper base alloy containing from 1 to 3.5 iron, balance essentially copper;

(B) hot working said alloy at a temperature of from 800 to 1050 C.;

(C) cold working with a reduction of at least 30%;

(D) annealing said alloy at a metal temperature of from 400 to 800 C. for at least 5 seconds;

(E) cold working with a reduction of at least 30%;

and

(F) annealing said alloy at a metal temperature of from 400 to 550 C. for at least 30 minutes.

24. A process according to claim 23 wherein steps (C) and (D) are repeated prior to steps (E) and (F).

25. A process according to claim 23 wherein the annealing time (F) is for at least 3 hours.

26. A process for the preparation of high conductivity high strength copper base alloys, castings or forgings which comprises:

(A) providing copper base alloy casting or forging containing from 1 to 3.5% iron, balance essentially copper;

(B) holding said alloy at a metal temperature of from 800 to 1050 C. for at least 10 minutes; and

9 10 (C) transferring said alloy to a hold at a metal tem- References Cited 155331;: of from 400 to 550 C. for at least 30 UNITED STATES PATENTS 27. A process according to claim 26 wherein the alloy 3,039,867 6/1962 McClain 75 153 is held in step (B) at a temperature of 875 to 975 C.

28. A process according to claim 26 wherein the alloy 5 DEWAYNE RUTLEDGE Pnmary Exammer is held in step (C) for at least 3 hours. W. W. STALLARD, Assistant Examiner 222 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,522,112 Dated July 28, 1970 Inventor(s) Charles D. McLain It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- IrT Column 4, line 8, "400 to 500C" should read --4oo to 550C".

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