US2678894A

US2678894A - Process of making articles of high elastic strength

Info

Publication number: US2678894A
Application number: US745715A
Authority: US
Inventors: Oscar E Harder; Dimon A Roberts
Original assignee: Elgin National Watch Co
Current assignee: Elgin National Watch Co
Priority date: 1947-05-03
Filing date: 1947-05-03
Publication date: 1954-05-18
Anticipated expiration: 1971-05-18

Description

Patented May 18, 1954 UNITED STATES EATE T OFFICE PROCESS OF MAKING-ARTICLESOF HIGH ELASTIC STRENGTH No Drawing. Application May 3, 1947, Serial No. 745,715

'5 Claims. 1

This invention relates to aprocess' ofmaking articles of high elastic strength such as power springs, containers'io'r' materials underhigh variable pressures, etc. The mainsprin of a'watch is an example of practice presenting extreme problems in that space'and'probable life considerations in a watch demand the capability ofbeing able to store a high amount of energy in a small space with assurance that repeated winding and unwinding during the life of the watch will represent the storage and release of substa-ntially identical amounts of energy.

A characteristic of such articlesis that, during their use, they may be under continuous loaded conditions and, by design for"economy,the load at the maximum strain is close to the strength limits of the material, the least feasible factor of safety being allowed.

This application'is a continuation-impartof our parent and copending application SerialNo. 567,894, filed December '12, '1944,'now abandoned on "Cobalt-Chromiuml-lickel-Base Alloys.

Prior to our invention'watch mainsprings have been customarily made of high carbon spring steel as this is the only material which'hasbeen found to have the necessary combinations of high strength properties and toughness to store the required amounts of energy in the small space available. The spring steel currently used in watch mainsprings has a yield strength of around 232,000 10. s. i., and a modulus of elasticity of around 28,400,600 p. s. i.

Two defects of steel watch mainsprings have long been apparent. One of these is'a tendency to corrosion in the presence of moisture. As watch springs are stressed near their ultimate of strength in use, only slight corrosion causes them to break.

A second defect is thetendency to take aipermanent set'which shortens the effective length of the springs and decreases theamount of energy which can be'put into them. This defect results from the fact that spring steel has a proportional limitwell below its yield strength. The propo'rtional limit of excellent watch springsteel strength in the article.

is only about 177,000 pis. i., so that any stressing over this amount leads to a permanent set and, at the least, has the effects of shortening the length of time the watch will run for a single complete winding, and of altering itsaccuracy due to reduction of average torque delivered to the train while unwinding and driving.

We have succeeded in overcoming both of these defects by providing articles of a non-corrosive material which has ayield strength and modulus of elasticity as great as those of spring steel and has aproportionall-imit well above that of spring steel. The procedure of making begins witha :blanlr of a non-corrosive alloy which is solutionannealed to give itthe relative softness and other properties necessary to permit cold-working. A yieldstrength'and elasticity equal to those of spring steel and a proportional limit remarkably higher than that of spring steel is developed in this materiaLby such procedure of elongation by cold-workingfollowed by heat-aging. These two steps have the effect of increasin the hardness and strength of the material and at the same time the effect of causing an increase of as much as percent inthe proportional limit of the material.

The alloys responding to this treatment to produce the articles consist principally of cobalt "which gives strength, chromium which gives strength and corrosion resistance, and a plasticizer including nickel which makes the alloy when in solution-annealed condition sufficiently plastic to be susceptible of a hig-h'percentage of elongation by cold-working. The solution-annealed alloy includes precipitatable components which during aging develop hardness and The steps of cold elongation and then aging at precipitation'tempera- 'ture results not only in hardening the alloy,'but

also in greatly increasing its tensile strength and proportional limit. The strength inherent in the matrix of cobalt and chromium, coupled with the increase of strength resulting from the cold elongation followed by aging, leadto the development recognized that such modified base alloys can demonstrate strengths and hardnesses almost as high as those of high-carbon heat-treated steels, but, so far as we are aware, none of them has been successfully employed as a substitute for springs of carbon steel.

We have found that by proper and correlated selections of conditions of composition, mechanical working and heat treatments, alloys which have cobalt and chromium in proportions to confer original strength can be so worked and treated that their strength properties can be increased until the same are equal to or greater than those which can be developed with excel- Table I Alloy No. Go Cr+Mo Cr Mo NH-Fe-l-Mn Ni Fe Mn Be 45. O 29. 22. 5 7. 0 25. 5 15.0 8. 5 2.0 09 40. 0 32. 0 25.0 7. 0 28.0 15. 0 10. 0 2.0 16 .04 40. 0 27. 0 20.0 7. 0 33. 0 15. 5 15. 0 2.0 11 40. 0 27.0 20. 0 7. 0 33.0 15. 5 15.0 2.0 02 35. 0 32. 0 25.0 7. 0 33. 0 20.0 11. 5 1. 5 10 03 35.0 32.0 25.0 7. O 33.0 30.0 1. 5 1. 5 13 03 34. 0 31. 0 25.0 (S. 0 35.0 32.0 2.0 0.14 08 30.0 32.0 26.0 6.0 38.0 31.0 6.0 1. 0 .23 02 31. 0 29.0 23.0 6. 0 40. 0 35.0 4. 5 0.80 09 40. 0 37.0 30. 0 7. 0 23.0 16. 0 5.0 2. 0 13 20. 0 32.0 25. 0 7. 0 48. 0 35.0 10.0 2.0 .06 03 40. 0 25. 0 25.0 35.0 22.0 10.0 2.0 04 .03

Norm-The numerals for Ni+Fe+Mn are herein set out for ternary diagram purposes.

Of these, alloys Nos. 1-7 inclusive have been found to give final articles highly satisfactory under the great demands on mainsprings for watches and alloys Nos. 8 to 10 inclusive are usable for such purpose. For comparison, the behavior of the following alloys, unsatisfactory for the purpose, will also be described.

lent watch mainspring steels; and in this fashion horological power springs can be made with original properties at least equal to those of a steel spring of the same size, and with capability of avoiding corrosion and set so that its probable life is far greater than that of the replaced steel spring.

Table I-A C'o Cr-l-Mo Cr Mo N i-l-Fe-l-Mn Ni Fe Mn 0 Be In the above and other tables, the cobalt, chromium, nickel, molybdenum, iron and manganese are the computed amounts by weight (found closely accurate upon analysis), while the carbon is the analytic value.

Alloys Nos. 4 and 4A have the same ternary" composition; in No. 4, there is Ni with 11.5% Fe; in No. 4A there is Ni with 1.5% Fe. Alloy No. 8 is usable but inferior to alloys Nos. 1 to '7, because of high Crlvlo content with low NiFeMn plasticiser. Alloy No. 9 has minimum Co with only 0.06%C: it is usable, but a modification by increasing the carbon content to 0.20% is desirable. Alloy No. 10 has no Mo and is low in tensile strength.

Alloys are known, which are based upon cobalt and chromium and are employed as castings for dental work, for non-corrosive cutting tools, for parts which must retain shape and strength at elevated temperatures as in combustion engine valves, etc.: the final shaping being by hot-forging or grinding.

Further, it is known to introduce other elements as ingredients in such basic alloys; for example, molybdenum has been introduced in such alloys which are used for dental parts, and tungsten has been used in such alloys which are used for cutting tools, valve facings, etc., to improve the hardness and wear resistance. It is It is preferred to melt the cobalt, nickel, and iron in a high-frequency induction furnace, and then add the chromium as ferrochromium and the molybdenum as ferromolybdenum. The manganese is preferably added as a ferroalloy containing about percent of manganese. After melting and being brought to proper temperature, a small addition of aluminum and then a small addition of calcium-silicon alloy are made for deoxidation. Slag is skimmed, and the ingot cast: in practice, ingots from 5 to pounds have been made.

The ingot is then hot-forged and hot-rolled down to a slab or bar thickness at which hotworking becomes uneoonomical. Forging is satisfactorily done at about 2100 degrees F. to 2200 degrees F., and the hot-rolling at like temperature, and can be continued down to a temperature as low as 1800 degrees F. Thus as hot working progresses the temperature can be decreased, but it is preferred to heat to around 2100 to 2200 degrees for the operation. It is feasible to hot Work the alloys into slabs or strips from about 0.250 to 0.200 inch in economical practice, and hot reductions to 0.050 inch have been made.

This hot-working is followed by a solutionannealing at 2100 to 2200 degrees F., for a time at temperature of about 20 to 30 minutes. It is convenient to water quench this stock. The alloys Hardness Alloy No. (Vickers) The term solution-annealing, as employed herein, defines the-operation of heating the mass to a temperature at which apparent homogenizationoccurs, that is, at which precipitation components are brought into solution; and the cooling of the homogenized mass in order to fix this condition. This cooling must be rapid enough to prevent precipitation of such components, or premature ageing, as such would lead to an undesirable hardness and resistance to cold-working. In practice, the alloy should be given an initial solution-annealing. at and from a temperature of 2000 to 2300 degrees F., and preferably from 2100 to 2150 degrees F.; and thereafter the intermediate and final solution annealings can.

be conducted at and from temperatures as low as 1800 degrees F., with commercial practice of 1900 degrees F. The cooling by quenching is necessary; sections thicker than 0.200 inch require water-quenching, while thinner sections can be effectively and more conveniently cooled in air.

The strip is then cold-rolled at room temperature to 0.100 inch, and a. further solution-annealing' performed, followed by further cold-rolling to 0.040 or 0.060 inch. A final solution-annealing was performed from. 2100 degrees F.; and then the final cold-rolling reduced. the tape to 0.0044 inch. The most desirable cold-rolling resulted in reductions of about 85% to 93% in section or an elongation of eight times or more. At this stage, the strength properties were:

Table III Alloy No. ggggg 'IS PL YS Mod VHN 89.2 295 122 165 25.9 520 92.0 294 142 173 23.6 497 92.7 252 132 155 24.5 551 211.0 294 117' 142 27.6 535 22.7 272 155 172 22.3 515 92.7 284 135 164 25.2 421 89.0 sec 259 150 184 21.2 485 89,0 (9 (9 78.5. 202 153 174 25.6 535 92.7 251 I 141 177 22.5 475 92.7 263 1-42 175 24.1 455 57.0 221" 113 152 22.2" 542 1 (9 8 :0 0)

(N'ofiz-Alloys Nos. 11, 15 and 16 were difficult to cold-roll due to low amount oi plasticising. material, and the. stated reductions are practicable-limits.)

1 Not determined.

Couldnot be hot rolled.

In the above and other tables and data, TS represents tensile strength, PL proportional limit, YS yield strength, Mod modulus of elasticity, and VHN the Vickers Hardness Number. TS, PL and Y are in thousands of pounds per square inch (p. s. 1.); and Mod is in millions p. s. i. YS is given with 0.02 percent offset. Bend tests, which are an index of toughness, were 180 around the arborsshown.

The tapes were then subjected to aging at 900 degrees F. for 5 hours: and, upon test, had the following properties:

Table IV Bend Test-Diameter, inches TS PL YS Mod VHN' All Part All Bend Break Break (N ote.-Alloy No. 13 is of low strength and hardness, alloys Nos. 15 and 16 were too brittle to test. The satisfactory materials exhibit strength values above thoseof excellent carbon steel.)

The illustrated alloy compositions are of the group which basically contains about 20 to 50 percent of cobalt and about 15 to 30 percent of chromium, along with 20 to'50 percent of softening or plasticizing component including nickel. In general, these components are present as 20 to50 percent of cobalt, 20 to 37 percent of chromium and molybdenum combined (the molybdenum being 1 to 10 percent of the alloy), and 20 to 50 percent of nickel, iron and manganese combined (the percentage of nickel being greater than that of the iron, with negligible traces to" a maximum of 15 percent of iron, and the percentage of manganese being from a residual fraction to 5), and with a carbon content of 0.05 to 0.30 percent. Beryllium may be present in low amounts, specifically from 0.01 to 0.09 percent having been found of benefit for watch mainsprings. The remainder consists of impurities concurrent with the metals introduced and those resulting from melting procedures. They should not comprise in excess of 0.05 percent of sulphur, 0.05 percent of phosphorus, and 0.05 percent of nitrogen (the nitrogen being effective as a partial substitute for carbon). Residual silicon from deoxidation during melting can be tolerated up to 0.50 percent, and in some alloys up to 1 percent when the iron content is high. Thus the total of concurrent and residual minor elements is less than about 1.2 percent.

The presently preferred range of compositions, in which. the ratios have been selected to permit optimum conditions of softness in solution-annealed. condition, strength development during cold-working and subsequent aging, and properties superior to. watch mainspring steel. in the final article, comprise 28 to 45 percent cobalt, 24 to 35 percent of chromium and molybdenum combined (of which 6 to '7- percent is molybdenum and 25 to 42 percent of nickel, iron and manganese combined (of which the iron is less than the nickel, and about 0.5 to 2 percent is manganese). For the remainder, the alloy has 0.08 percent to 0.22. percent of carbon: 0 to 0.09 percent beryllium; less than about 0.15 to 0.25 percent silicon being preferred; less than 0.05 percent each of sulphur and phosphorus; other elements being present in non-significant traces. Thus the total of concurrent and residual elements is less than about 0.50percent.

The cobalt is matrix ingredient to give strength. In general, increase of strength follows with increase of cobalt, but excessive amounts produce such hardness that :cold-working characteristics are unsatisfactory, so that the desired final strengths cannot be built up. The cobalt is furthermore believed to form an intermetallic compound with chromium which provides a hardening and strengthening component during aging.

The chromium contributes most importantly to the corrosion resistance, and cooperates with the molybdenum in that increase of one or the other or both, above the lowest values stated, lead to increased strength and hardness, so that the sum of the chromium and molybdenum is determinative when both are present.

The molybdenum is a very effective strengthening element both for its effect in the matrix and upon aging.

The plasticizing metals of the group consisting of nickel, iron and manganese are regarded as softeners of the composition in solution-annealed condition. That is, a mixture having good ratios of cobalt and chromium for development of strength upon aging, in accordance with our studies, is too hard to be cold-worked sufficiently to build up its strength so that the present superior strength values can be attained upon aging: but upon addition of such plasticizers, the hardness of the solution-annealed alloy is reduced so that cold-worked strengths can be developed before the hardness has been increased by the cold-rolling to values which render further cold-working impracticable. In general, nickel by itself is effective; and it can be used without significant amounts of iron or manganese. In practice, iron can be used as a minor replacement for nickel with a saving in cost of iron as compared with nickel and also with the great saving in that the chromium, molybdenum and manganese can be introduced as the corresponding ferro alloys which are cheaper per weight of chromium or molybdenum and also have lower melting points and thus facilitate the mixing. Iron is not permissible as a total replacement, however, due to scaling trouble upon heating; and its amount should be kept below that of the nickel. Manganese is a good deoxidizer during mixing, and also acts to overcome any harmful effect of sulfur: in the final alloy, the residual manganese cooperates with the nickel in giving the softness or workability desired: up to percent can be present without harmful effect, but no specific advantage appears with more than about 2 percent.

The preference for carbon contents of 0.10 to 0.20 percent has been indicated by the above satisfactory compositions. The effect of carbon in otherwise identical alloys is illustrated by the following, in which alloy No. 3 was made in two melts, of which alloy No. 33 had 0.05 percent and alloy No. 30 had 0.09 percent. The cold-rolled condition is that given by soution-annealing and cold-rolling, while the aged condition is same followed by aging for 5 hours at 900 degrees F.

Table V Condition 'lS PL YS Mod VHN Cold-rolled." 259 x34 169 22.4 519 .do 262 135 165 23.4 531 Aged 326 193 243 29.5 635 do 341 219 258 29.4 081 Thus, a most significant improvement in proportional limit is attained, being the property of a power spring which determines whether or not the spring will set in service and how much it 5 will set.

Intermediate and final solution-annealings can be accomplished at temperatures below 2100 to 2300 degrees F. as low as 1800 degrees F.; but it is preferred to use temperatures of at least 2000 degrees F. The effect of the heating is to soften the alloy to suitable condition for cold working, to put certain secondary constitutents into solution and to tend to produce a homogeneous structure having a face-centered cubic arrangement, and to put the alloy into condition for good response to the age-hardening treatment. The quenching can be done in water while thin stock can be satisfactorily cooled in air.

The effect of the temperature during solutionannealing is illustrated by alloy No. 3 which before cold-rolling had a Vickers hardness of 240 and. which was then reduced 50 percent by coldrolling, and was then quench-annealed.

Table VI Time Hardness as cold-rolled, reduction.--

From this, it will be noted that cold-rolling raised the hardness from 240 to 468, and this was further increased by treatment at 1200 and at 1300 degrees F., and is softened very little at 1400 degrees F. At the successively higher temperatures, softening occurs wherewith a satisfactory softening is obtained at 2100 degrees and a usable softening at 1800 degrees F. With alloys harder than alloy No. 3, it is recommended to use a temperature higher than 2100 degrees F., but excessive temperature should be avoided, in order to minimize scaling and roughening the surface of the stock.

The hardness at the beginning of final coldrolling should be below about 300 Vickers (note Table II), and alloys as low as 200 Vickers have been found competent of attaining final strengths of satisfactory values. The hardness and strength increase quite rapidly in the first stages of cold-reduction and then less rapidly. For ex ample, alloy No. 3 at reductions of '75, 80, 85 and 90 percent showed hardness values of about 510, 5'70, 580 and 590 respectively. For watch mainsprings, the cold-reduction should be carried as far as practicable, and the hardness should be at least 450 Vickers (note Table III). The thickness reduction for such mainsprings should be at least 70 percent, and it is preferred to have reduction of at least 80 percent, and reductions in excess of 90 percent have been found of value.

The aging treatment has as its principal function the increasing of the proportional limit, the yield strength, the ultimate strength, and the modulus of elasticity. The response in the aging temperature depends to some extent upon the composition of the alloy; and is a function of the amount of the cold reduction, the final thickness of the article, the aging time and the aging temperature.

This aging treatment is particularly advantageous after material which has been coldworked to the stated reductions. For example, in Table VI it is shown that alloy No. 3 with a solution-annealed hardness of 240 Vickers underwent increase of hardness to 468 Vickers, and then was reduced to original hardness upon a subsequent solution-appealing at 2100 degrees F. Such alloy No. 3, subjected to solution-annealing to hardness 216-233 Vickers and then to aging at 900 degrees F. for 5 hours, without intermediate cold-rolling, increased in hardness to only about 260 to 270 Vickers, or around to percent. By comparison, as appears in Table IV above, a cold-rolling with 92.7 percent reduction (to a hardness of 530 to 550 Vickers) followed by identical aging, gave a hardness of 690-695 Vickers' or around 30 percent. That is, the increase by successional cold-rolling and aging is striking not only in the absolute hardness values but also in the relative percentages. The tensile strength increases similarly; while an even more striking result is in the gain of proportional limit and yield strength.

The temperature and time for aging are interrelated. A lower temperature requires a longer time while permitting a wider latitude in control. The maxima of effects upon strength and upon ductility may occur at different temperature/time conditions. The general useful range of aging temperature is 500 to 1200 degrees F., 1

with usual practice from 600 to 1000 degrees F.; the presently preferred range is 750 to 900 degrees F. As an example of selective practice, one alloy treated under the conditions stated for annealing and cold-rolling may have a peak or maximum of strength values at 900 degrees F. in 5 hours, but its ductility may have been reduced below a desirable value for forming into a spiral spring of short minimum radius; in such a case,

an aging at 800 or even 700 degrees F. for the same or a longer time is desirable. A time of 5 hours at 900 degrees F. has been found to give a desirable coordination of increased strength values for alloys Nos. 1 to 7.

The effects of thickness of stock at final solution-annealing, and of percentages of coldreduction, upon specimens of alloy No. 3 and of different aging temperatures upon the hardness is shown in:

As a matter of comparison of properties before and after aging of stock which has been solutionannealed and cold-rolled as stated, the increase of tensile strength and hardness may be about to percent, and in general these properties increase similarly to one another. The increase of proportional limit may be from '70 percent up; alloy No. 2 showing an increase of 135 percent, and alloy No. 3 an increase of 01 percent. The yield strength increases from 60 percent upward. The modulus of elasticity increases about 16 to percent, usually being less than the increase in tensile strength.

In particular, over-aging must be avoided be-.

cause heating for such a period of time as 5 hours at temperatures of above 1200 F. causes a marked decrease in the strength properties with inadequate, if any, compensation and ductility. It may be theorized that a condition of solid solution supersaturated in precipitatable components, produced by solution-annealing, is modified by aging, in that the precipitation particles come out in submicroscopic size and in total amount corresponding to the difference in solubilities at solution temperature and at aging temperature, and when the supersaturation has essentially ceased :by formation of the submicroscopic particles, a maximum of strength properties has been attained; while higher temperatures will cause more rapid precipitation but also more rapid agglomeration. In practice, 1200 degrees F. is the maximum useful temperature: but it is preferred to use lower temperatures, for the reason that the time factor is then not so critical.

In general, lengthy exposure at temperatures between 1200 and 1800 degrees F. should be avoided after the final solution-annealing. If the material is slowly dropping in temperature from solution-annealing conditions, premature precipitation with agglomeration occurs so that the material becomes too hard for cold-working and incapable of developing the strength values which can be induced by proper cold-rolling and aging; if the material is slowly increasing in temperatures within this range, agglomeration occurs and then re-solution, but the homogenization does not proceed to the necessary reduction of hardness for proper cold-working or to the condition for eifective precipitation during aging.

The articl thus formed and constituted is a power spring capable of withstanding service conditions at which a spring of high-carbon steel, but of identical size and use will fail. It demonstrates a tensile strength and proportional limit exceeding those of the steel spring, and under preferred conditions (Table IV) has a proportional limit in excess of about 200,000 p. s. i.; a yield strength in excess of about 250,000 p. s. i.; and a modulus of elasticity of above about 29,000,000; as compared with high-quality carbon steel mainsprings which may have a proportional limit of 177,000 p. s. i., a yield strength around 232,000 p. s. i. and a modulus of elasticity around 28,400,00 p. s. i. It is non-corrosive to atmospheric conditions, to perspiration, and is highly resistant to strong acid and alkaline solutions. It is non-magnetic and non-magnetizable. The effects of the procedure of preparation are apparent in the article: in that such a spring, when heated to 2100 degrees F. and quickly cooled undergoes severe loss of strength and hardness; in particular, the hardness will drop to below 300 Vickers, and the tensile strength falls below 200,- 000 p. s. i., and the article is no longer competent of use, for the reason that no known method will restore the desired values without a high coldreduction as stated above, that is, without reducing its section and increasing its length so that it no longer is the same article. In this respect, the article is strikingly difierent from a carbon steel spring, which can be repeatedly hardened and tempered if care be taken to avoid scaling and decarbonization.

The practical limit of cold Working our alloy, as by cold rolling, is fixed by that degree of cold working which causes damage to the material such as excessive edge cracking and surface cracking; by the degree of cold working beyond which further cold working gives little or no improvement in the strength properties of the material as cold worked or in the enhancement of the strength properties on aging; and also to some extent by the plant equipment available, but the cold working should give at least the minimum reduction disclosed hereinbefore in this specification.

The illustrative preparation of a watch mainspring is not restricted, as the procedur is obviously applicable to the preparation of other articles where all or part of the stated combinations of properties is desirable.

The watch mainspring referred to illustratively herein is set out and claimed in our co-pending application No. 745,714, filed May 3, 1947, now Patent No. 2,524,660: and some of the illustrative alloys upon which the process may b employed are set out and claimed in our co-pending application Serial No. 745,716, now Patent No. 2,524,661, filed May 3, 1947.

We claim:

1. The process of producing a metal of high elastic strength which comprises providing an alloy consisting essentially of 20 to 50 per cent cobalt, 15 to 30 per cent chromium, molybdenum in amount up to per cent, the combined chromium and molybdenum being 20 to 37 per cent, manganese in amount not exceeding 5 per cent, not exceeding per cent iron, not exceeding 0.09 per cent beryllium, 0.05 to 0.30 per cent carbon, and nickel in amounts greater than the amount of iron, the combined nickel, iron and manganese being to 50 per cent of the alloy, and the remainder of the alloy consisting of not to exceed 1.2 per cent of elements concurrent with the aforesaid elements in commercial purities thereof and elements residual from deoxidation of the melted alloy, said alloy having a hardness of 200 to 300 Vickers in solution-annealed condition and being capable in solution-annealed condition of cold reduction by at least 50 per cent, forming a blank from said alloy having a cross-section at least twice that of the article to be produced, solution-annealing by heating the blank at a temperature of from 1800 to 2300 degrees F., quickly cooling the blank, cold-working the solution-annealed blank to the intended cross-section of the article and until the hardness is at least 450 Vickers, and then heating the cold-worked blank at a temperature above 500 degrees F. and below 1200 degrees F. until the hardness of the cold-worked blank has increased to at least 486 Vickers without development of perceptible aggregations of precipitation components, and terminating said heat treatment of the cold-worked blank when the proportional limit is at least 190,000 p. s. i., the yield strength (0.02 per cent offset) is at least 225,000 p. s. i., and the modulus of elasticity is at least 28,400,000 p. s. i.

2. The process of producing a metal of high elastic strength which comprises providing an alloy consisting essentially of 28 to 45 per cent cobalt, 24 to per cent chromium and molybdenum together, of which molybdenum is 6 to 7 per cent, 25 to 42 per cent nickel, iron and manganese, the amount of nickel being greater than the amount of iron and the amount of manganese being less than 5 per cent of the total alloy, the amount of iron being not over 15 per cent, and 0.08 to 0.22 per cent carbon, with the remainder consisting of not in excess of 0.5 per cent of elements concurrent with the aforesaid elements in commercial purities thereof and elements residual from deoxidation of the melted alloy, said alloy having a hardness of 200 to 300 Vickers in solution-annealed condition, and being capable in solution-annealed condition of a reduction of at least per cent, forming a blank from said alloy having a cross-section at least five times that of the article to be produced, solution-annealing the blank by heating to from 1800 to 2300 degrees R, quickly cooling the blank, cold-working the blank to the intended crosssection of the article and until the hardness thereof is at least 480 Vickers, and then aging the cold-Worked blank at a temperature between 500 and 1200 degrees F. until the hardness thereof has increased to above 575 Vickers, the proportional limit thereof is at least 200,000 p. s. i., the yield strength (0.02 per cent offset) thereof is at least 260,000 p. s. i., and the modulus of elasticity thereof is at least 28,400,000 p. s. i.

3. The process of producing a metal of high elastic strength properties which comprises providing an alloy consisting essentially of 40 per cent cobalt, 20 per cent chromium, 7 per cent molybdenum, 15.5 per cent nickel, 15 per cent iron, 2 per cent manganese, 0.08 to 0.22 per cent carbon,

and up to 0.09 per cent beryllium, the remainder of the alloy consisting of not to exceed 0.50 per cent of elements concurrent with the aforesaid elements in commercial purities thereof and elements residual from deoxidation of the melted alloy, said alloy having a hardness of from 225 to 240 Vickers in solution-annealed condition, and being capable in solution-annealed condition of reduction by cold-rolling by at least 80 per cent, forming a blank from said alloy having a crosssection at least five times that of the article to be produced, solution-annealing by heating the blank at a temperature of from 1800 to 2300 degrees F., quickly cooling the blank, cold-working the blank to the intended cross-section of the article and until the hardness thereof is 480 Vickers, and then aging the cold-worked blank to a temperature of from 600 to 1,000 degrees F. until the hardness thereof has increased to above 600 Vickers, the proportional limit thereof is at least 220,000 p. s. i., the yield strength (0.02 per cent offset) thereof is above 270,000 p. s. i., and the modulus of elasticity thereof is at least 28,400,000

4. The process of producing a metal of high elastic strengths which comprises forming an alloy consisting essentially of 20 to 50 per cent cobalt, 15 to 30 per cent chromium, molybdenum in amount of 1 to 10 per cent, the combined chromium and molybdenum being 20 to 37 per cent, manganese in amount not exceeding 5 per cent, iron in amount not exceeding 15 per cent, beryllium in amount not exceeding 0.09 per cent, 0.05 to 0.30 per cent carbon, and nickel in amounts greater than the amount of iron, the combined nickel, iron and maganese being 20 to 50 per cent of the alloys, and the remainder of the alloy consisting of not to exceed 1.2 per cent of elements concurrent with the aforesaid elements in commercial purities thereof and elements residual from deoxidation of the melted alloy, said alloy having a hardness of from 200 to 300 Vickers in solution-annealed condition, and being capable in solution-annealed condition of cold-reduction of at least 50 per cent, forming a blank from said alloy, solution-annealing said blank by heat ing at from 1800 to 2300 degrees F. and then quickly cooling the blank, cold-working the blank to reduce the cross-section thereof by at least 50 per cent, and until the hardness of the blank is at least 480 Vickers, and then aging the cold- 13 worked blank at a temperature of about 900 de grees F. for five hours and until the hardness thereof has increased to 575 Vickers, the proportional limit thereof is at least 200,000 p. s. i., and the modulus of elasticity thereof is at least 28,400,000 p. s. i.

5. The process of producing a metal of high elastic strength which comprises forming a cohalt-chromium alloy consisting essentially of 20 to 50 per cent cobalt, 15 to 30 per cent chromium, molybdenum in amount of 1 to 10 per cent, the combined chromium and molybdenum being 20 to 37 per cent, maganese in amount not exceeding per cent, iron in amount not exceeding 15 per cent, beryllium in amount of 0.01 to 0.09 per cent, 0.05 to 0.30 per cent carbon, and nickel in amounts greater than the amount of iron, the combined nickel, iron and manganese being 20 to 50 per cent, and the remainder of the alloy consisting of not to exiieed 1.2 per cent of elements concurrent with the aforesaid elements in commercial purities thereof and elements residual from deoxidation of the melted alloy, said alloy having a hardness of less than 300 Vickers in solution-annealed condition and being capable in solution-annealed condition of cold-reduction of at least 80 per cent, forming a blank from said alloy, solution-annealing the blank by heating at from 1800 to 2300 degrees F. and coldrolling until the hardness is at least 480 Vickers, aging the cold-worked blank at a temperature of about 900 degrees F. for five hours and until the hardness thereof has increased to above 575 Vickers, the proportional limit thereof is at least 200,000 p. s. i. and the modulus of elasticity thereof is at least 28,400,000 p. s. i.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,698,935 Chesterfield Jan. 15, 1929 1,917,723 Koster July 11, 1933 1,942,150 Rohn Jan. 2, 1934 1,949,313 Koster Feb. 27, 1934 2,174,171 Wasson Sept. 26, 1939 2,245,366 Rohn June 10, 1941 2,419,825 Dinerstein Apr. 29, 194$ OTHER REFERENCES Age Hardening of Metals, 1940, page 322, Transactions American Society for Metals, Cleveland, Ohio, vol. 33, 1944, pages 5085l1.

Age Hardening of Metals, 1940, Am. Soc. for Metals, Cleveland, Ohio, page 321.

Claims

1. THE PROCESS OF PRODUCING A METAL OF HIGH ELASTIC STRENGTH WHICH COMPRISES PROVIDING AN ALLOY CONSISTING ESSENTIALLY OF 20 TO 50 PER CENT COBALT, 15 TO 30 PER CENT CHROMIUM, MOLYBDENUM IN AMOUNT UP TO 10 PER CENT, THE COMBINED CHROMIUM AND MOLYBDENUM BEING 20 TO 37 PER CENT, MANGANESE IN AMOUNT NOT EXCEEDING 5 PER CENT, NOT EXCEEDING 15 PER CENT IRON, NOT EXCEEDING 0.09 PER CENT BERYLLIUM, 0.5 TO 0.30 PER CENT CARBON AND NICKEL IN AMOUNTS GREATER THAN THE AMOUNT OF IRON, THE COMBINED NICKEL, IRON AND MANGANESE BEING 20 TO 50 PER CENT OF THE ALLOY, AND THE REMAINDER OF THE ALLOY CONSISTING OF NOT TO EXCEED 1,2 PER CENT OF ELEMENTS CONCURRENT WITH THE AFORESAID ELEMENTS IN COMMERCIAL PURITIES THEREOF AND ELEMENTS RESIDUAL FROM DEOXIDATION OF THE MELTED ALLOY, SAID ALLOY HAVING A HARDNESS OF 200 TO 300 VICKERS IN SOLUTION-ANNEALED CONDITION AND BEING CAPABLE IN SOLUTION-ANNEALED CONDITION OF COLD REDUCTION BY AT LEAST 50 PER CENT, FORMING A BLANK FROM SAID ALLOY HAVING A CROSS-SECTION AT LEAST TWICE THAT OF THE ARTICLE TO BE PRODUCED, SOLUTION-ANNEALING BY HEATING THE BANK AT A TEMPERATURE OF FROM 1800 TO 2300 DEGREES F., QUICKLY COOLING THE BANK, COLD-WORKING THE SOLUTION-ANNEALED BANK TO THE INTENDED CROSS-SECTION OF THE ARTICLE AND UNTIL THE HARDNESS IS AT LEAST 450 VICKERS, AND THAN HEATING THE COLD-WORKED BANK AT A TEMPERATURE ABOVE 500 DEGREES F. AND BELOW 1200 DEGREES F. UNTIL THE HARDNESS OF THE COLD-WORKED BLANK HAS INCREASED TO AT LEAST 486 VICKERS WITHOUT DEVELOPMENT OF PERCEPTIBLE AGGREGATIONS OF PRECIPITATION COMPONENTS, AND TERMINATING SAID HEAT TREATMENT OF THE COLD-WORKED BLANK WHEN THE PROPORTIONAL LIMIT IS AT LEAST 190,000 P. S. I., THE YIELD STRENGTH (0.02 PER CENT OFFSET) IS AT LEAST 225,000 P. S. I., AND THE MODULUS OF ELASTICITY IS AT LEAST 28,400,000 P. S. I.