US2412447A - Working and treating be-cu alloys - Google Patents

Description

Patented Dec. 19, 1 946 WORKING AND TREATING BE-CU ALLOYS Matthew J. Donachie, Holyoke, Mass, assignor, by mesne assignments, to Berks County Trust Company, Reading, Pa., a banking institution of Pennsylvania No Drawing. Application July 31,1942 Serial No. 453,039

9 Claims.

This invention relates to metal working and heat-treating methods and more particularly to an improved method of working and heat-treating beryllium-copper alloys of the type known in the art as cold workable and precipitation hardenable beryllium-copper alloys.

Alloys of the type known as cold workable and precipitation hardenable beryllium-copper alloys are those copper base alloys which contain beryllium not in excess of that amount which may be put into solid solution at temperatures within the range 1400-1500 F. but in excess of that amount which is retained in solid solution at temperatures within the range 300-750 F. Ordinarily, such alloys are essentially binary beryllium-copper alloys containing from about 1.0% Be to about 2.40% Be with only substantially residual amounts of associated metal and metalloid impurities. However, frequently such alloys contain from .10 to 50% of at least one of the metals Fe, Co and Ni for the purpose of promoting the formation of relatively small sized and more uniformly dispersed cast beta particles, in which case the total Be and iron group metal may be as high as 3%. Silicon also may be present in the alloy in amounts up to 1% without detriment to the cold working and precipitation hardening properties of the alloy. Other metals in small fractional percentages also may be present without substantially altering the essential phase change reactions on which the cold workability and precipitation hardenable properties of the binary beryllium-copper alloy depends.

The term cold workable and precipitation hardenable beryllium-copper alloys, as it may hereinafter appear in the specification and claims, is to be construed as defining that group of essentially binary beryllium-copper alloys which contain beryllium in an amount within the range 1 to 3% with or without small amounts of other metals and metalloids in total amount insuificient to suppress the essential phase change reactions on which the workability and precipitation hardening of the binary alloy is predicated.

The cold workability of the beryllium-copper alloys hereinabove defined is predicated upon the ductility of a so-called alpha or solid solution phase which is formed therein at temperatures within the range 1400-1500 F. and which may be stabilized at atmospheric temperatures by rapid cooling, as by quenching in water.

The precipitation hardening properties of the alloy is predicated upon the decomposition of this alpha phase at temperatures within the range 300-750 F. into a mixture of alpha and gamma phases, wherein the gamma phase is finely di vided and uniformly dispersed throughout the alpha phase and present on grain boundaries as membranes.

When the beryllium-copper alloy is in the cast condition, however, a considerable proportion'of the beryllium content thereof is present as a hard brittle constituent known as cast beta as a result of the relatively slow rate of cooling a castis assigned to the same assignee as the present application.

The present invention has for its object the provision of an improved method of working and heat-treating the beryllium-copper alloy of the type hereinabove described after it has been conditioned for cold working by any of the prior art methods.

Another object is to provide an improved method of cold working and annealing berylliumcopper alloys of the type hereinabove described to avoid the production of lar e grain sized material and surface impoverishment of beryllium content in the alloy.

Still another object is to provide a method of working and annealing which provides a control over the ultimate grain size of the alloy and for. a more uniform and consistent control over the physical properties and hardenability of the alloy. A further object is to provide an improved method of forming relatively thin sheet and strip material and relatively small gauged wire from beryllium-copper alloys of the type hereinabove described.

Other objects and advantages will be apparent as the invention is more fully hereinafter disclosed.

In accordance with these objects, I have observed that when cold worked beryllium-copper alloys of the type hereinabove described are subjected to a precipitation hardening heat-treatment without prior solution-anneal heat-treatment at l4001500 F., extremely variable hardening results are obtained and that in many instances the metal becomes softened instead of being hardened.

After considerable investigation, I discovered that these variable results and the loss in hardness was caused by recrystallization of the coldworked solid solution alpha phase which offsets the hardness induced by gamma phase precipitation and that to avoid such loss in hardness and to obtain the maximum hardness as a result of gamma precipitation, the time of heating a cold worked beryllium-copper alloy within the precipitation hardening range must be limited to be less than the time interval required at the temperature of heating to obtain any substantial recrystallization of the cold worked alpha. For example, I found that the heat-treating time at 650 F. for a beryllium-copper alloy containing about 2% Be which has been cold worked to the extent indicated by a 40-45% reduction in area, must be not over 2 hours in contrast to 2 to 8 hours usually employed in precipitation hardening the same alloy in the unstrain-hardened condition.

I have further found that as the temperature of heating the cold worked alloy increases above the precipitation hardening range to a temperature approximating but below the so-called transition temperature which in binary Be-Cu alloys approximates 1060 F., the time interval required for recrystallization of the cold worked alpha decreases rapidly and that at a temperature of about 1000' F. the time interval is relatively short as compared to the time interval at 650 F. and becomes a matter of seconds with as high as 90-95% reduction in area and a few minutes with as low as 20-25% reduction in area.

After considerable experimentation, I have found that by subjecting the cold worked beryllium-copper alloy to an extended heat-treatment at a temperature within the range 750- 1060 F. but preferably at a temperature approximating 1000 F., a heterogeneous crystal structure, consisting of recrystallized alpha and uniformly dispersed substantially agglomerated and spheroidized gamma, may be produced which has a cold workability closely approximating that of the solid solution alpha phase which is formed by extended heat-treatment at 1400-1500 F. and stabilized at atmospheric temperatures by quenching in water as heretofore practiced in the art.

Moreover, I have found that this new structure may be repeatedly cold worked and the alpha phase content thereof repeatedly annealed or recrystallized by heat-treatment within the temperature range 750-1040 F. without substantial alteration of the gamma phase and hence restored to its original cold workability and that by an appropriate regulation of the time and temperature of heating with respect to the percent reduction in area the grain size of the alpha phase constituent of the final product may be controlled and regulated as heretofore possible with other metals but not heretofore possible with beryllium-copper alloys.

Further, I have found that by the practice of the present invention that the elimination of certain detrimental effects attending high temperature annealing heretofore experienced in the art can be effected. Among these are such things as excessive surface oxidation, beryllium impoverishment from the surface and excessive grain growth. I have also found that the physical properties and mechanical characteristics of the alloy are stabilized and rendered consistent and reproducible.

Finally, I have found that only a relatively short time of heating at a temperature within the range 1400-l500 F. is required to convert the heterogeneous alpha-gamma structure of the 4 present invention into solid solution alpha to condition the alloy for subsequent precipitation hardening heat-treatment, and that the rain size of the final solid solution alpha phase after resolution of the gamma phase thereby may be maintained relatively small.

The present invention is adapted for wide util ity in the art of working and treating berylliumcopper alloys, as one skilled in the art will recognize, and the particular point in the cold working stage at which it may be applied may vary widely without departure from the present invention and depends as much upon available equipment and desired final size as upon the desired physical properties and grain size of the final product.

As one specific embodiment of the present invention, but not as a limitation of the same, an adaptation which facilitates the cold rolling of a beryllium-copper alloy containing 2% Be and 20% Co, balance copper, to relatively thin strip material will be described. The alloy, per se, forms no part of the present invention.

The alloy in cast or ingot form is first subjected to hot working in accordance with prior art practice, preferably by the practice of the alternate heat-treating at 1450 F. and hot working method described and claimed in Martin Patent No. 2,266,056, to an elongated strip having a thickness of about .250 inch. At this thickness the strip is usually substantially free from cast beta particles and is in a condition permitting some cold reduction, at least a cold reduction to about .100 inch in a plurality of passes.

In accordance with the present invention, instead of annealing the cold worked metal at 1400-1500 R, as heretofor practiced in the art, to condition the metal for further cold reduction, I anneal at a temperature of about 1000 F. for an elxtended time interval approximating 4 to 8 hours, to impart to the alloy a thermally stabilized heterogeneous crystal structure consisting of recrystallized alpha and substantially agglomerated and spheroidized gamma phases, following which the metal is allowed to cool slowly to atmospheric temperatures to obtain a final stabilized crystal structure at atmospheric temperatures.

The resultant heat-treated product after surface cleaning, as by pickling, is then subjected to alternate cold working and annealing operations, the annealing temperature approximating 1000 F. and the time interval of annealing being relatively short as compared to the first anneal time interval, the particular time varying with variation in the extent of cold working imparted to the metal between anneals, and the total number of such alternate cold working and annealing operations depending upon the desired final thickness.

In general, I prefer to work harden the strip between anneals at least an amount equivalent to a 40-45% reduction in area, although greater or lesser amounts of strain-hardening may be employed without essential departure from the present invention. When the thickness of the strip approximates th desired final thickness, I have found it preferable to subject the alloy to a short time heating at 1400-1500 F. followed by rapid cooling, to condition the same for subsequent precipitation hardening, and then to cold roll the metal to the desired final size. The extent of such final cold deformation, however, should not exceed 10 to 20% allowing for further strainhardening of the strip by cutting, stamping and In general, I prefer to anneal for a time inter-- val of 2 hours at 1000 F. following a 40-50% reduction in area where the thickness of the strip does not permit continuous annealing operations so that the time at temperature may be more closely controlled. Thinner gauge strip material may be annealed at time intervals as short as 15 seconds where grain refinement of the cold worked alpha is desired.

A typical working schedule according to this specific embodiment is as follows:

(1) Hot roll from ingot to about .250 inch with intermediate 3 hour anneals at 1450" F.

(2) Surface clean to remove scale and surface imperfections.

(3) Cold roll to .100 inch.

(4) Heat-treat at 1000 F. for from 4 to 8 hours, preferably 6 hours, and allow to cool slowly to atmospheric temperature.

(5) Surface clean.

(6) Cold roll to .036 inch in 8 passes.

(7) Anneal 2 hours at 1000 F.

(8) Cold roll to .015 inch in 8 passes.

(9) Anneal 1 hour at 1000 F.

(10) Cold roll to .0063 inch in 8 passes.

(11) Continuous strand anneal at 1000 F., the time interval at temperature being regulated to give a hardness approximating 3.81 Rockwell.

(12) Cold roll to a thickness within 10-20% larger than desired final size.

(13) Continuous strand anneal at 1450 F., the time interval at temperature being regulated to give a hardness approximating B54 Rockwell.

(14) Surface clean.

(15) Cold roll to desired final size.

Alloy strip material processed in the above manner consistently and uniformly develops a grain size within the range .00'7-.011 mm. as contrasted to a grain size of .065.120 mm, normally obtained by prior art methods of cold working and annealing at 1450" R, with materially higher tensile and fatigu strengths and more uniform precipitation hardening properties than heretofore obtainable.

As a guide to the practice of the present invention. I have found that in the forming ofthe cold workable and recrystallizable thermally stabilized heterogeneous alpha-gamma structure of the present invention, the time of treatment at any temperature within th range 7501060 F. at any given percent reduction in area decreases with increase in temperature and that at any given temperature within the range the time at temperature to obtain substantially complete recrystallization of the cold worked alpha decreases with increase in the percent reduction in area;

Recrystallization and the formation of the thermally stabilized heterogeneous structure are each time-temperature reactions, the time factor of each decreasing with increase in temperature. It usually requires from 3 to 5 hours at 1000 F. to obtain substantially complete precipitation of the gamma phase and its agglomeration into the most suitable sized spheroids. It appears necessary to strain-harden the alloy to an extent approximating 40-50% reduction in area in order to obtain during the first heattreatment at 1000 F. substantially complete recrystallization of the alpha hase within the time interval of 3 to 5 hours. However, good results have been obtained on metal strain-hardened with a reduction in area as low as 20% with a time interval of 5 to 8 hours. The most economically practical combination, however, appears to be a cold reduction of from 40 to 50% and heattreatment for 6 hours at 1000 F. for the first heat-treatment. Thereafter the heat-treating time and temperature may be selected with respect to the reduction in area to produce recrystallization of the cold worked alpha constituent of the stabilized heterogeneous structure, as the gamma constituent thereof remains substantially unaltered at all temperatures below the temperature of initial heat-treatment.

My experiments indicate that it is preferable to employ a temperature approximating 1000 F. for all recrystallizing heat-treatments, shortening the time at temperature with increase in reduction in area to be but a few seconds with as high as 90 to 95% reduction in area to a few minutes with as low as 10 to 20% reduction in area. As the rate of grain growth at 1000 F. is relatively low due to the blocking efiect of the gamma phase present, the time at temperature during recrystallization is not as critical as in other metals and alloys and may be widely varied without great variation in actual grain size after the structure has been once thermally stabilized at a temperature that is at least as high as the recrystallizing temperature.

As a second specific embodiment of the practice of the present invention, the adaptation of the same to wire drawing will be described.

In the production of wire from the 2% Be, 20% Co, balance copper alloy hereinabove described, the metal is reduced from ingot size to an elongated rod or wire of about .081 inch diameter by the practice of hot and cold working with intermediate high temperature anneals (at 1450 F.) as heretofore practiced in the art.

At this diameter the cold worked pure alpha structure is subjected to heat-treatment at 1000 F. for a time interval of 6 to 8 hours followed by slow cooling to atmospheric temperatures to obtain a thermally stabilized heterogeneous alpha-gamma structure consisting of recrystallized alpha and substantially spheroidized and uniformly dispersed gamma.

Following this treatment, the metal is cold drawn to about .057 inch diameter and reannealed at 1000 F. for from 2 to 6 hours and again cooled slowly to atmospheric temperatures.

From this point on the wire may be cold drawn between anneals as much as to reduction in area, and all annealing operations at 1000 1 F. subsequently applied may be short time anneals in continuous annealing furnaces of standard design. The time for recrystallization of the cold worked alpha decreases rapidly with increase in cold working at temperatures approximating 1000 F. and a few seconds exposure to temperature is sufficient to obtain complete softening of the wire when the cold working has proceeded as high as 80 to 90% reduction in area.

A typical working schedule for forming wire from the 2% Be, 20% Co, balance Cu alloy is as follows:

1) The alloy is hot worked in accordance with prior art practice down to wire of approximately .250 inch diameter, the-last few passes being at a cold working temperature sufficient tointroduce strain hardening approximately equivalent to a 40-45 cold reduction in area.

(2) Heat-treated at 1000 F. for from 6 to 8 hours and cooled slowly to atmospheric temperatures.

7 Surface cleaned. Cold drawn to .162 inch. Annealed for 2 hours at 1000 F. S'urface cleaned. Cold drawn to .080 inch.

(8) Annealed for 2 hours at 1000 F.

(9) .Surface cleaned.

(10) Cold drawn to .032 inch.

(11) Annealed for 2 hours at 1000 F.

(12) Surface cleaned.

(13) Cold drawn to .016 inch.

(14) Annealed for 2 hours at 1000 F.

From this point on the drawing process may be widely varied depending upon the desired final size. The wire diameter from .016 inch down is such as to permit continuous annealing with the time interval of anneal shortened to effect recrystallization of the cold worked alpha, the gamma phase being so stabilized as to require no further treatment at temperature. Reductions in area as high as 70 to 75% may be applied to the metal between anneals and the anneal time at temperature with over 70% reduction in area is a matter of a few seconds to obtain substantially complete recrystallization of the cold worked alpha.

The strength and ductility of the thermally stabilized heterogeneous crystal structure of the alloy obtained by reason of the present invention enables the alloy to be drawn to the finest diameter wire with little difficulty.

Where the wire subsequently to drawing to desired final size is to be precipitation hardened, the wire should be subjected to a solution anneal heat-treatment at 1450 F. followed by rapid cooling to convert the heterogeneous structure back to the substantially pure alpha phase. Such treatment may readily be effected in a standard type of strand anneal (or continuous anneal) furnace where the time at temperature may be regulated to accomplish this result. In general, the time at temperature to effect this conversion is a matter of a few seconds as the gamma phase of the heterogeneous structure being uniformly dispersed and of relatively uniform particle size redissolves readily in the alpha matrix at this high temperature.

As an example of this advantage gained in physical properties by the practice of the present invention, the usual tensile strength of cold drawn beryllium-copper wire of the composition above given at a diameter approximating .010 inch (#30 B. & S. gauge) formed in accordance with prior art practice which includes intermediate anneals at 1450 F., approximates 63,000 p. s. i. (elongation 48% in 12") whereas the usual tensile strength of the same alloy processed in accordance with the present invention approximates 75,000 10. s. i. (60-62% elongation in 12").

From the above description of the present invention and the two specific embodimentsgiven it is believed apparent that the invention may be widely varied and variously adapted in the art of cold working beryllium-copper alloys of the type hereinabove identified and all such adaptations of the same are contemplated as may fall within the scope of the following claims:

What I claim is:

].r The method of working and treating beryllium-copper alloys of the cold workable-precipitation hardenable type to impart thereto a cold workable structure capable of being repeatedly cold worked and recrystallized by heating to ternperatures within the range 750-1040" F. without substantial alteration in structure, which comprises cold working the alloy when in its solution-annealed condition to strain harden the same materially, heat-treating the cold worked 5 product at a temperature within the range 750-1060 F. for an extended time interval at least approximating 2 hours and slowly cooling the heat-treated product to atmospheric temperatures.

2. The method of working and treating beryllium-copper alloys of the cold workable-precipitation hardenable type to impart thereto a cold workable structure capable of being repeatedly cold worked and recrystallized by heating to a temperature within the range 750-1040 F. without precipitation hardening and without substantial alteration in structure, which comprises cold working the alloy when in its solution-annealed condition to strain harden the same materially, heat-treating the strain hardened prodnot at a temperature approximating 1000 F. for an extended time interval at least approximating 2 hours and slowly cooling the heat-treated product to atmospheric temperatures.

3. The method of working and treating beryllium-copper alloys of the cold workable-precipitation hardenable type to impart thereto a cold workable structure capable of being repeatedly cold worked and recrystallized by heating to temperatures within the range 750-1040 F. without precipitation hardening and without substantial alteration in structure, which comprises cold working the alloy when in its solution-annealed condition to strain harden the same an amount within the range 20 to 50% reduction in area, heat-treating the strain hardened product at a temperature approximating 1000 F. for a time interval within the range 2 to 8 hours and cooling the heat-treated product slowly to atmospheric temperatures.

4. The method of working and treating beryllium-copper alloys of the cold workable-precipitation hardenable type to impart thereto a crystal structure having a cold workability at least approximating that of the alloy in the solutionannealed condition but capable of being repeatedly cold worked and recrystallized by heating to temperatures within the range 750-1040 F with- 50 out precipitation hardening and without substantial alteration in structure, which comprises cold working the alloy when in its solution-annealed condition to strain harden the same an amount within the range about 40 to 50% reduction in 5 area, heat-treating the alloy at a temperature approximating 1000 F. for a time interval within the range 2 to 8 hours, and slowly cooling the heat-treated product to atmospheric temperatures.

5. The method of working and treating beryllium-copper alloys of the cold workable-precipitation hardenable type to impart thereto a crystal structure having a cold workability approximating that of the alloy in the solution-amiealed c5 condition but capable of being repeatedly cold worked and recrystallized by heating to temperatures within the range 750-1040" F, without precipitation hardening and without substantial alteration in structure, which comprises cold work- 7 ing the alloy when in its solution-annealed condition to strain harden the same an amount within the range 20 to 50% reduction in area, heattreating the strain hardened product at a temperature approximating 1000 F. for a time in- 75 terval within the range 4 to 8 hours, and slowly 9 cooling the heat-treated product to atmospheric temperatures.

6. A beryllium-copper alloy of the cold workable-precipitation hardenable type, said alloy having a crystal structure consisting of a mixture of alpha and gamma phases in which the gamma phase consists of small sized spheroids dispersed throughout the said alpha phase and the said alpha phase is stabilized with respect to its beryllium content at atmospheric temperatures, said alloy being characterized by being cold workable and capable of repeated cold Working and heat-treating Within the range 750-1040" F. to recrystallize the cold worked structure Without substantial alteration in structure and Without precipitation hardening on heating and cooling during said recrystallization heating.

'7. A beryllium-copper alloy containing about 2% beryllium, balance mainly copper, said alloy having a crystal structure consisting of a mixture of alpha and gamma phases in which the gamma phase consists of small sized spheroids dispersed throughout the said alpha phase and the said alpha phase is stabilized With respect to its beryllium content at atmospheric temperatures, said alloy being characterized by being cold workable and capable of repeated cold working and heattreating Within the range 7504040" F. to recrystallize the cold worked structure Without substantial alteration in structure and without Precipitation hardening on heating and cooling during said recrystallization heating.

8. Wire, rod, sheet and strip material consisting of a beryllium-copper alloy containing about 2% beryllium, balance mainly copper, said alloy having a crystal structure consisting of a mixture of alpha and gamma phases in which the gamma phase consists of small sized spheroids dispersed throughout the said alpha phase and the said alpha phase is stabilized with respect to its beryllium content at atmospheric temperatures, said alloy being characterized by being cold workable and capable of repeated cold working and heat-treating within the range 7501040 F, to recrystallize the cold Worked structur without substantial alteration in structure and without precipitation hardening on heating and cooling during said recrystallization heating.

9. The method of conditioning beryllium-copper alloys of the cold workable precipitation hardenable type for repeated cold working and recrystallization heat-treatings at temperatures approximating 10GO F.,-which comprises cold working the alloy While in its solution-annealed condition to work harden the alpha phase matrix materially and heat-treating the work hardened material at a temperature approximating 1000 F, for an extended time interval of the order of 2 to 8 hours which is at least sufficient to obtain a thermally stabilized structure consisting of a mixture of the alpha and gamma phases wherein the alpha phase is in its recrystallized un-strain hardened condition and the gamma phase consists of finely dispersed spheroid particles uniformly dispersed throughout the recrystallized alpha phase, and cooling the heat-treated product to atmospheric temperatures, said structure thereby obtained being characterized by a ductility and cold workability approximating that of the same alloy in its un-strain hardened solution-annealed condition free of gamma and beta phases.

MATTHEW J. DONACHIE.