US2695844A - High-temperature cobalt base alloys - Google Patents

Description

United States Patent HIGH-TEMPERATURE COBALT .BASE ALLOYS -William Charles Clarke, Jr., Dnndalk, -Md., assignorfto ArmcoSteel Corporation, a corporation of Ohio No Drawing. Application SeptemberZS, 1949, Serial No. 118,453

8 Claims. (CL' 75-134) Thisinvention relatesgencrallyto high temperature alloys, and more particularly to alloys having .a high. degreeof resistance to the combined effects of heat and stress.

An object of my invention is the provision of durable and reliable high temperature alloys.

Another object of my invention is that of providinghigh temperature alloys which are highly capable of withstanding the combined .and continuedeffects of elevated temperatures and stress.

A further object of this invention is the provision of alloys. of'the character indicated whichuare amenable to such operations as forging and hot rolling.

.Other. objects .of. my invention. impart .will. the. obvious .and in part pointed out more fully hereinafter.

The invention, accordingly, consists incthe combination ofvelements, composition of materials, in the prod- ..ucts, articles and. manufactures, and in the several method steps and-the relation of each. of thesame to one or more .of the others as described herein, thescope of the appplication-of which is indicated in thefollowing claims.

As conducive ate a clearer understanding of certain features of my inventiongit may 'benoted at this point that many alloys, andarticles and products made of alloy metal, :arentoday in demand for high temperature use. infrequently-occurs that metal products in this general category are needed for use at temperatures above. about 1000 P. which incidentally assure that .the .metal will be intenselyhot, this use sometimes over a long.and.continued periodaof time; There are occasions too wherethe alloy products, in'view of.the;particular use at hand, are subjected to load andstressunderthe prevailing conditions of intense heat.

.A variety of alloys-which perhaps rightfully belong in the low temperature class are highly susceptible to the development of surface scale or heat scale when subject- .ed to intense heat. Of even greatervconsequencelin. cer tain instances, heat causes many of -these;ealloys to--'*be- .come so weak thathigh temperature use is out=of2t-he .question. .The alloys very often. are susceptible to ,creep under'load, especially while hot, and are furthennnreliable forthe reason of ensuing rupture.

.Even many 0 the heretofore known high temperature alloys are extremely limited. in utility forsuch.reasons -.as having a very marked tendency toWard-tcreepand stress rupture while intensely heated. In otherinstanceasome of the conventionalhigh temperatureproductsare objectionable because of. having very low resistanceto the development of heat scale while. heated in the high'temperature range. The alloy metal often is of a kind which aiiordslittle if any resistance to corrosion as'inhot-corrosive atmospheres such as might surround use in .certain high temperature equipment.

, So. many of the conventional high temperature; alloys are notoriously diflicult to work,.as-bytforgingpand hot rolling. For this reason, they are less in demand for.

reduction to particular form for producingxwrought prod- .-ucts.and articles. Thiscondition existsithough working is often regarded as being important for producing a high temperature product or article.

An. outstanding object of my invention accordinglyis 'the provisio-n-of high temperature alloysand wrought products and articles of the same-which reliably resist corrosion andthe development 'of' heat scale and which have "highlyfavorable creep and stress ruptureproperties in high temperatureuse.

Referring. 'now 'morer particularly toithe practice of my invention, .1 provide 'high temperature cobalt base..alloys which :in containing certain elements in critical amounts.inuadditionuto'sthe.cobalt, not only-have good 5 hot-working:properties,high strength, andhighly favorable-resistance:.to: creepcand stress rupture underv intense :heatgbut are:furtherccharacterized by resistance to corrosion and by substantial freedom from heat scale. develcopment when in: high. temperature use. These 'alloys' in 0 accordance with :my invention contain approximately 12% :to 25% :chromium, 1.5% to.3.5% molybdenum, .2i5% x'to ;4.0% vcopper, carbon inamounts up'to about 0.35%, and the remainder substantially cobalt. Iron .usually is:an elementxpresent-in.thealloy composition, 15 this 'being. in quantities-.upto about 10% either as an impurity orotherwise. My alloy composition preferably :includes nickel insubstantial amounts up to about 16%, but on occasionsrnickel may be entirely or substantially absent. Among;otheruconstituents which preferably are 20 in the alloy are upitoabout 3% total titanium and/or .columbium. 'ITPIEIECI xtozintroduce efiective quantities of bothrof the latter for: together they have an especially advantageouseefiect. upon the'high temperature properties. There ares-instances though where I provide the ralloys -withouteithertitanium or columbium, as -where theimmedia-teEh-igh. temperature needs are successfully satisfied withoutntheadd-ition. Only small. quantities of suche'eiements .as;manganese, silicon, sulphur and phos- .phorus: usually are in thexalloys, these preferably being -withzthe manganesein quantities ranging up to about 2%,"thesiliconranging:upto about 1.5 and the sulphur; and phosphorusa-each not exceeding about 0.04%.

Myncoha-lt base: alloys; derive beneficial high temperature effects .from :the cobalt constituent. Also, the 5 amountsiof Chromium:.and-'other elements used are re- :garded.zasnbeingccritioal. With any appreciable lowering .ofwthevchromiumcontent to outsidethe range hereinbeforernoted, scaling. resistance and general corrosion resis-ta-ncev of ithe alloy suffer, and with appreciable in- .crease beyond the range, hot working difiiculties appear, the :alloy furthertending'to lose: ductilityin high temperature use. :In general, I findthat carbon in exwCCSS ofiia-hout 0.36% is not favorable. 'Where the amounts .of copper; and molybdenum in my'alloys are appreciably lowered. to-outside thealowends'of the ranges given here- .inbefore'forithese elements,-the high temperature load- .carryingcapacity decreases, or where the amounts appreciablyexceed the-upper limits of the ranges, the hot work-mg properties'suifer. Too rnuch molybdenum also .seems.to.impair=scaling resistance. If-nickel is used at .alliin my. alloy, I :keep the nickelbelow about 15% and ,preferably; below-about.l0% for best stress rupture prop- .ertres. 'Onzthoseroccasions :where one or 'both'elements rofrthetgroup.consisting-of titanium and columbium are 'inr'the-alloy, I findt-hat best'advantages are had by using nabout up to 8% total titanium and/or columbium. 'Largeramounts seem: tozdecrease. the stress rupture properties. Where manganese is in. excessof. about 2% and 'silicon'more tha-n about 1.5%, this is detrimental tothe hot-working properties.

My high temperature .alloys, especially where the .rnanganese, silicon, sulphur and phosphorus are within .the,percentage.ranges just noted, are amenable to hot workingas byforgingx-and hot'rolling. I, therefore, fre- .q.uently.resortt-to-such: operations as hot Working in producing.wroughtproiducts andarticles of. the alloy metal, as for example turbine .parts such as wheels, rotors, blades,"buclcetsor nozzles. :Among other high tempera- :turezproducts and articles whichl produce of the alloy emetal'are supercharger pa-rts,. chemical equipment parts, tubesfor any or" a variety-of uses such asfor carrying high temperaturefluids-under pressure. Still furthersexamples of my high temperature alloy. articles are bolts,

rivets-and fasteners. The-products and articles of manufacture are'strong, durable and reliable- They resist creep and stress rupture .suchas attemperatures ranging fromrabout .1000" .F. to 19.00 F. and whileeither in- ,termittently.or.continuo.usly.under mechanical stress or load. .Themetal resists-form.ing.heat-scale nnderathe conditions of intense heat and possesses a valuable degree of corrosion resistance.

In certain instances, I provide products of my cobalt base alloy in such form as sheet, strip, wire, rods, or the like, which are readily useful for fabrication as by cutting, punching or bending into shape, or welding as by means of oxy-acetylene or arc welding equipment. Sometimes I use the sheet, wire, or the like directly in high temperature applications without appreciable fabrication.

The cobalt base alloy articles and products which I provide often are useful without particular heat treatment or after annealing, and thus are often so used. I achieve a remarkable increase though in the high temperature load-carrying ability by employing a heat treatment in the nature of an annealing and precipitation treatment. In the annealing operation, I heat the alloy metal to a sufficiently high temperature and for long enough time to put at least part of the copper, and at least some of the titanium and columbium when present, into solid solution. Where desired, advantage is taken of annealing temperatures to achieve hot working or other operations for producing my products and articles of the metal. A preferred temperature range for annealing is that of about 2050 F. to 2250" F.

After the annealing and before precipitation heat treatment, I quench the cobalt base alloy metal preferably to about room temperature, this, for example, by using air, oil or water as the quenching medium. By subsequently heating the quenched metal preferably to Within a temperature range of about 1000 F. to 1400 F. and by maintaining the same at temperature for long enough time, a critically finely divided precipitate is believed to come out in the metal lattice along the slip planes in the matrix. The copper is thought to precipitate in fine form, or possibly as an intermetallic compound including one or more of the group consisting of nickel, titanium or columbium, depending upon which if any of the nickel, titanium and columbium are present in the alloy composition. Although not immediately visible with the ordinary light microscope, the precipitates become visible after a very long period of time at high temperatures is allowed for coalescing. When titanium and/or columbium are present in the alloy, some portion thereof is thought to come out in the form of carbides. Regardless of theory, however, I find that my high temperature alloys, and articles and products thereof, have excellent properties. Upon quenching or cooling the metal as in air from the precipitation treating temperature, I find that it has a fine grain structure and is further characterized by enhanced load-carrying capacity in view of the precipitation treatment. I often work the metal in this heat-treated condition, or subject the same to fabricating and finishing operations, thus providing high temperature products or articles. During high temperature use of the cobalt base alloy, the precipitates remain critically dispersed, uncoalesced and effective against creep and stress rupture, for long periods of time. Any heating of the metal to as high as solution temperature, of course, tends to put the precipitates back into solution.

For optimum results, I provide cobalt base alloys of the character indicated, but which more specifically contain approximately 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, 0.08% to 0.20% carbon, and the remainder substantially cobalt. Should nickel be used in the alloy composition, the amounts of this element preferably range up to about maximum. I prefer to use quantities of both titanium and columbium in the alloy, but, on occasions, either or both are omitted. Where used, the titanium ranges in amount up to about 0.35% and the columbium up to about 0.70%, alone or together. Iron usually is present in the alloy in permissible amounts up to about 10%. Where manganese, silicon, sulphur and phosphorus are in the alloy, as usually is the case, these preferably are with the manganese in quantities ranging up to about 2%, the silicon ranging up to about 1.5 and (ghg/jfsyulphur and phosphorus each not exceeding about A few examples of the high temperature cobalt base alloys which I provide are noted in Table I. In this, it will be observed that Alloys A, B and C respectively have increased carbon contents within the permissible carbon range. Also, it will be seen that the Alloy B has a higher nickel content and a lower chromium content as compared with either Alloy A or Alloy C.

TABLE I Cobalt base alloys Alloy A, Alloy 13, Alloy 0,

Percent Percent Percent Carbon 0. 11 0. 23 0.30 Chromium 19. 25 16. 39 19.00 Molybdenunr- 1. 92 1. 2. 25 Copper 3. 19 3. 08 3. 25 Nickel"... 5. 33 15. 40 5.00 Titanium 0. 17 0. 23 0. 20 Columbim 0. 56 0. 53 0. 50 Manganese 0. 86 Low 0. 50 Silicon 0.31 0. 55 0. 60 Sulphur 0. 029 0.012 Low Phosphorus. 0.02 018 0. 02 Cobalt c 58. 7 52. 8 58. 0 Iron Bal. Bal. Bal.

The several alloys identified in Table I all were subjected to annealing at about 2250 F. for one-half hour, followed by quenching in water and precipitation heat treatment at about 1350 F. for five hours. The alloys then were given stress rupture tests, the conditions and results of which appear in Table II.

TABLE II Stress rupture tests of Alloys A, B and C Test Load Time for Elong. Bed. of A Temp., S i Rupture (2 per-) Area y F. (hrs.) eent (percent) 1, 500 30, 000 40 8. 1 26.0 1, 500 25, 000 239 6. 5 7. 0 A 1, 500 21, 500 492 6. 0 8. 2 1,500 20,000 1, 281 4. 0 2. 5 1, 700 10, 000 183 4. 3 3. 3 1, 700 7, 500 532 2. 5 1. 0 1, 500 28, 000 44 9. 0 13. 2 B 1,500 25,000 116 4. 0 6. 0 1, 500 23,000 162 4. 3 4. 5 C 1,500 30, 000 36 2.0 1.0 1, 500 24, 000 70 1. 0 1.0

My cobalt base alloys have many vaulable high temperature properties, including resistance to stress rupture whether or not the alloys or products and articles thereof are in the precipitation heat-treated condition. The precipitation heat treatment though enhances a number of the properties. Despite the high temperature properties, my cobalt base alloys are capable of reduction as by forging and hot rolling and of fabrication in a simple, direct and economical manner by virtue of the inherent ease of working. In view of the excellent working properties, I often resort to the production of wrought articles and products of the metal. I find too, though, that my high temperature alloys are thoroughly amenable to casting or molding as in a fixed mold or centrifugally to desired form. Because of this, I often provide cast high temperature products and articles of the alloy metal.

Thus it will be seen that there are provided in my invention cobalt base alloys, and products and articles thereof, in which the various objects noted together with many thoroughly practical advantages are successfully achieved. It will be seen that the metal is strong, durable and tough, corrosion-resistant and heat-resistant and serves well at high temperatures over long periods of time under any of many conditions of actual practical use.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiment hereinbefore set forth, it will be understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

I claim:

1. High temperature cobalt alloy having good hot working properties and great high temperature strength and resistance to creep, consisting of about 12% to 25 chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, manganese up to about 2%, silicon up to 1.5%, carbon up to about 0.35%, and the remainder cobalt.

2. High temperature cobalt alloy having good hot working properties and great high temperature strength and resistance to creep, consisting of about 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, nickel up to about 16%, carbon up to about 0.35 up to about 3% in total amount of at least one element of the group consisting of titanium and columbium, manganese in quantities up to about 2%, silicon in quantities up to 1.5 and the remainder cobalt.

3. High temperature cobalt alloy having good hot working properties and great high temperature strength and resistance to creep, consisting of about 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, manganese up to about 2%, silicon up to about 1.5%, from about 0.08% to 0.20% carbon, at least one element of the group consisting of titanium up to about 0.35% and columbium up to about 0.70%, and the remainder cobalt.

4. High temperature cobalt alloy having good hot working properties and great high temperature strength and resistance to creep, consisting of about 12% to 25 chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, nickel 5% up to about 16%, manganese up to about 2%, silicon up to about 1.5%, from about 0.08% to 0.20% carbon, at least one element of the group consisting of titanium up to about 0.35% and columbium up to about 0.70%, and the remainder cobalt.

5. High temperature cobalt alloy having good hot working properties and great strength and great resistance to creep at high temperatures, consisting of about 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5 to 4.0% copper, manganese up to about 2%, silicon up to about 1.5%, from 0.08% to 0.20% carbon, up to about 0.35% titanium, columbium up to 0.70%, up to about 10% iron, and the remainder cobalt.

6. High temperature cobalt alloy having good hot working properties and great strength and great resistance to creep at high temperatures, consisting of in approximate amount 0.08% to 0.20% carbon, 19% chromium, 2.25% molybdenum, 3.25% copper, 5% nickel, manganese up to about 2%, silicon up to about 1.5%, titanium up to about 0.35%, columbium up to about 0.70%, and the remainder cobalt.

7. High temperature cobalt alloy wrought metal arti- Cir cles or products having great strength and great resistance to creep while hot, said articles or products consisting of about 12% to 25 chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, manganese up to 2%, silicon up to 1.5%, carbon up to about 0.35%, nickel up to about 16%, iron up to about 10%, and the remainder at least about 52.8% cobalt.

8. High temperature cobalt base alloy wrought metal articles or products having great strength and great resistance to creep while hot, said articles or products consisting of about 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, manganese up to 2%, silicon up to 1.5%, carbon up to about 0.35%, titanium and columbium up to 3% total, nickel up to about 16%, iron up to about 10%, and the remainder at least about 52.8% cobalt.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,115,239 Parr Oct. 27, 1914 1,587,992 Apotzley et al. June 8, 1926 1,685,570 Masing et al Sept. 25, 1928 1,945,679 Corson Feb. 6, 1934 2,072,911 Touceda Mar. 9, 1937 2,081,392 Touceda May 25, 1937 2,108,051 Egeberg et al. Feb. 15, 1938 2,246,078 Rohn et al. June 17, 1941 2,309,136 Neiman Jan. 26, 1943 2,495,063 Hood et al. Jan. 17, 1950 2,509,800 Blackwood May 30, 1950 2,509,801 Blackwood May 30, 1950 2,536,034 Clarke Jan. 2, 1951 FOREIGN PATENTS Number Country Date 832,391 France June 27, 1938

Claims (1)

1. HIGH TEMPERATURE COBALT ALLOY HAVING GOOD HOT WORKING PROPERTIES AND GREAT HIGH TEMPERATURE STRENGTH AND RESISTANCE TO CREEP, CONSISTING OF ABOUT 12% TO 25% CHROMIUM, 1.5% TO 3.5% MOLYBDENUM, 2.5% TO 4.0% COPPER, MANGANESE UP TO ABOUT 2%, SILICON UP TO 1.5%, CARBON UP TO ABOUT 0.35%, AND THE REMAINDER COBALT.