US2018520A - High strength alloy - Google Patents

Description

Patented Oct. 22,1935 v I 1 520 UNITED STATES PATENT OFFICE HIGH STRENGTH ALLOY George P. Halliwell, Wilkinsburg,'I-a.,' assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application March}, 1932, Serial No. 596,565

' 4 Claims. (01. 148-13) My invention relates to alloys and more par- 1 other machines or apparatus which are operticularly to alloys having a comparatively high ated at comparatively high temperatures. Its

strength at elevated temperatures. high tensile strength and resistance to oxidation The principal object of my invention is to proat comparatively high temperatures also renders 5 vide an alloy containing nickel, cobalt, iron and it especially valuable for use in springs and other 5 titanium which is characterized by having a high apparatus. proportional limit and a high tensile strength at My improved alloy comprises nickel, cobalt, normal and elevated temperatures. iron and titanium in various proportions and Another object of my invention is to provide may also contain chromium, although satisfacan alloy containing nickel, cobalt, iron and titantory results have been obtained when the chrol0 ium which has been subjected to a specific agemium is omitted. The respective proportions of ing process whereby the characteristics of the iron, nickel and cobalt which are present in the alloy are substantially changed and an alloy havalloy may be Varied over wide ranges if d ing greatly improved physical properties is prosired, either the cobalt, nickel or iron may be enduced.

A still further object of my invention is to istics of the alloy will not be as satisfactory as provide alloys and a process of producing alloys when all the elements are present. containing cobalt, iron and titanium; nickel, cm In order that the alloy may be forgeable, it is balt and titanium; nickel, iron and titanium; or also essential that the titanium should be mainnickel, cobalt, iron and titanium, which comta ed b w d p f ra ly b w A 20 prises quenching the alloy from a comparatively a rule I prefer to utilize amounts ranging from high temperature and then subjecting it to an 2% to 5%. I also find it very desirable to have ageing process at a lower temperature for a sufiinickel present in substantial amounts to minicient length of time to improve its physical mi oxidation- I also fi that nickel a y properties. improves the physical properties of the alloy at 26 It has heretofore been customary to utilize anormal and elevated temperaturesmetal, such as iron or steel, for the component In general, it y be Stated that nick', H parts of power plant apparatus, such as supermay range from more than incidental impurities heaters, steam boilers, turbines, and .turbine up to 7 the cobalt from 10% to 80%. h

30 blades. Since the limiting temperatures and iron f om 1 0 6 a the titanium from pressures at which such apparatus can be operto 10%, and chromium may be present in Y ated, however, are governed largely by the tenamounts ranging from more than incidental imsile strength and proportional limit of the matepurities up to 25%. Carbon may also be present rial of which they are composed, it is essential in limited amounts but is preferably maintained that the metal or alloy utilized shall have a high below 1%.

tensile strength and retain its initial dimensions Better results may be obtained when the under stress. nickel is maintained in amounts ranging from I have made the discovery that if alloys con- 20% to 70%, co in amounts ng rom taining cobalt, nickel, iron and titanium are 10% to 60%, iron in amounts ranging from 5% quenched from a comparatively high temperato 50%, and titanium ranging in amounts from ture, such as 900 C. to 1000 C., and then sub- 2% t0 5%.

jected to an ageing process at a lower temper- In the preferred embodiment of my invention, ature for varying lengths of time, the proporthe base of nickel plus cobalt constitutes the tional limit and tensile strength of the alloy at major proportion of the alloy, and the amount of normal and elevated temperatures will be subnickel is greater than the amount of cobalt. 45 stantially improved. For example, the nickel is preferably maintained My improved alloy has a proportional limit and in amount from 40% to 60%, cobalt in amount an ultimate tensile strength that is far superior ranging from 20% to 35%, iron in amount rangto that of steel or of ferrous or non-ferrous aling from 5% to 20%, and the titanium in amount loys which have heretofore been utilized for such ranging from 2% to 5%. I have also found it purposes. The fact that these physical propervery desirable to have chromium present in ties are maintained at elevated temperatures also amounts ranging from 1% to 25%, renders it especially suitable for use as the con- In preparing my improved alloy, the nickel tacting portions of valves and. valve seats for and cobalt are first melted together in a reducinternal combustion engines or for valves of ing or inert atmosphere and the additional altirely omitted, although the physical character- 15 loying ingredients are then added. 1 preier to add the iron and titanium in the form 01 a termtitanium alloy containing approximately 75% iron and 25% titanium, though to-obtain'desired percentage of iron or titanium, additional amounts of either one of these metals may be added in the elementary form. After the melt is completed and Just bei'ore casting, a small amount, say iromone to two grams, of a deoxidizer, such asalumin is attached to a rod composed of nickel or of a cobalt-nickel base allo and plunged into the molten bath. Care troducing the deoxidizer as it causes a rapid reaction of almost explosive violence.

The alloys are next cast, homogenized (at 1000 C. for 8 hours), forged and annealed at a temperature 01' from 900 C. to 1000 C. for approximately one hour and quenched from that temperature. The quenching may be accomplished by any suitable cooling medium, such as air, oil or water. The alloys are then subjected to an ageing process at temperatures 01' from 500 C. to 800 C. for a period of time ranging from to 2,000 hours. In general, it may be statedthat the greatest improvement in the char- 7 acteristics of the alloy'which is effected by the ageing process takes place within the first few hours, and that about 80% or the maximum increase in hardness is efiected after 72 hours. The'time of ageing is also dependent upon the ageing temperature. At higher temperatures the ageing. takes place in a shorter period or time. After the alloy has aged for a sumcient time 5, to produce the maximum hardness, the alloy is cooled.

The increase in hardness that. may be imparted to my improved alloys and their ability to retain their initial dimensions under stress at high temperatures will be better understood by relere'nce to the accompanying drawings, in which Figure 1 is a graph showing the increased hardness that may be imparted to my improved alloys by ageing at a temperature of 600 0.;

5 Figs. 2 and 3 are similar graphs showing the effects of ageing at temperatures of 650 C. and

;,time of ageing in hours.

750 C., respectively;'

Fig. 4 is a graph showing the resistance to strain of my improved alloysas compared to carbon steel containing approximately .5% carbon; and

. Fig. is a. graph similar to Fig. 4 showing the resistance to strain oi! my improved alloys as compared to a nichrome alloy containing ap- ;proximately 60% nickel, 20%

um, and 2% manganese. In Figs. 1, 2 and 3 of the drawings, the ordinates represent hardness as measured in Vickers Pyramid Numerals and the.abscissaa represent In these figures the numerals 1 to 12, inclusive, are representative alloys having approximately the following compositions:

' more] Cobalt Iron Titanium Chromium Carbon be obtained at ageing silicon or manganese,

should be exercised in in-' desired temperature.

iron, 18% chromi-"' 17% iron and a small The increase in hardness of the alloy is imdoubtedly caused at least partially by the precipitation oi titanium elther alone or as a com-- pound of oneor more or the alloying ingredients 'i'rom solid solution during'the' ageing process. g

My experiments indicate, however, that unless substantial quantities of iron and-cobalt are prescut, a pronounced increase in-hardness will not I temperatures. From Figs. 1, 2 and 3 of the drawings, it will also 10 be apparent that when the nickel and cobalt constitute the major proportion oi the alloy, the ageing will be very rapid and the hardness attained will be comparatively high. This is indicated from alloys designated by the curves I, I, 0 and u l 0. I, therefore, prefer that the nickel plus cobalt content shall constitute at least a major pro- 7 portion of the alloy. Itwill be noted, however, that the alloy represented by curve 1 does not contain any nickel which indicates that my proc- I ess is also applicable to alloys containing cobalt. iron and titanium. The physical properties of such alloys, however, are not as good as when nickel is present.

In Figs. 4 and 5 01' the drawings, in which the Q ordinates designate percentage 0! maximum deflection and the abscissae represent the temperature, curves illustrative 01' representative alloys indicate the superiority of my improved alloys over medium carbon steel and tainlng their initialdimensions under stress. This property is highly important in alloys employed for service at high temperatures.

In making tests to determine this characteristic, the alloys were first rolled down to a thick- U ness of about .017 of an inch, cut into'strips 5% inches in length, heated at a temperature of 950 C. for a period of minutes, and cooled rapidly. The alloys were next subjected to my improved ageing process at a temperature of 650 C. for a 40 period of 72 hours. v

The flat strips were then placed in a form oi known radius and maintained 30 minutes at the After-cooling, the strips were removed from the form and laid across two 6 pivots placed four inches apart. The bend produced was measured by determining the radius of curvature oi the strip by means of a fixed micrometer at a point midway between the pivots. Since the curvature of the form is fixed, the vertical displacement'in a four inch chord can bereadily calculated. In the graphs shown in Figs.

4 and 5, the percentage of maximum deflection equals the vertical displacement of the strip, after being constrained for the period and at the temperature indicated and then cooled, divided by the vertical displacement of the form, and multiplied by 100.

Curves I, 2, 3, 4, 5 and 1 in Figs. 4 and 5 des-- ignate alloys having the same composition as the '2 corresponding curves in Figs. 1, 2 and 3.

Curve l4 designates medium carbon steel andcurve IS a nickeHrQn-chmmium alloy containing approximately nickel, 21% chromium.

percentage oi manganese, commonly referred to as nichrome.

From the drawings it will be noted that myimproved alloy is far superior to carbon steel in maintaining its initial dimensions under stress and is considerably better than nichrome in this balt, iron, titanium, and in some instances chromium, were present in amounts ranging from" nichrome in re- I 20% to 70% nickel, to 60% cobalt, to 60% iron, 2% to 5% titanium, and 1% to 20% chromium. The alloys after being aged at 650C. for a period of 72 hours had a proportional limit ranging from 45,000 to 80,000 pounds per square inch at room temperature and a proportional limit ranging from 30,500 to 66,250 pounds per square inch at a temperature of 600 C. The tensile strength ranged from 135,000 to 170,250 pounds per square inch at room temperature, and 92,000 to 120,200 pounds at a temperature of 600 C. The ductility of the alloy varies considerably in accordance with the composition.

The following specific examples represent the preferred embodiment of my invention in which the proportions of nickel, cobalt, iron, titanium and chromium are within the range of 40% to 60% nickel, 20% to 35% cobalt, 5% to 20% iron, 2% to 5% titanium and 1% to 20% chromium.

The above alloys were aged at a temperature of 650 C. for a period of 72 hours and their physical properties at room temperature and at a temperature of 600 C. were determined. The following table shows their physical properties at room temperature and a temperature of 600 C.

vious value that had been attained in cobaltnickel base alloys which had not been subjected to an ageing process was 33,750 pounds per square inch. The marked improvement imparted to the alloys by my improved process will therefore readily be appreciated. From Figs. 4 and 5 of the drawings, it will also be apparent that my improved alloy is superior to nichrome or medium carbon steel in retaining its initial dimensions under stress.

While I have described my invention in considerable detail and have given numerous examples, it will be understood that the present invention is not limited to the specific details set forth in the foregoing examples which should be construed as illustrative and not by way of limitation, and in view of the numerous modifications which may be effected therein without departing from the spirit and scope of this invention, it is desired that only such limitations be imposed as are indicated in the appended claims.

I claim as my invention:

l. The process of improving the physical properties of an alloy containing essentially from to 70% nickel, 60% to 10% cobalt, 5% to 85 50% iron, and 0.5% to 10% titanium, which com- Tensile strength lbs. Proportional Limit per Sm inch Percent elongation Alloy lbs. per sq. inch number room tem- 600 C perature Room tem- 0 Room tem- C pei'ature perature From the foregoing tables it will be noted that in the preferred embodiment of my invention, the nickel plus cobalt content constitutes the major proportion of the alloy and that the amount of nickel is greater than the amount of cobalt. I do not desire, however, to be limited to an alloy in which such a ratio exists as alloys have been produced in which either the nickel or cobalt has been omitted. For example, alloy No. 7, previously referred to, does not contain any nickel and in my investigation of this subject, I have produced alloys in which the cobalt has been entirely omitted. For example, an alloy containing approximately 70% nickel, 27.5% iron and 2.5% titanium was prepared, quenched from a high temperature and aged for 72 hours at a temperature of 650 C. Upon testing the alloy at room temperature and 600 C. it was found that it had a proportional limit and tensile strength of 65,000 and 150,250 pounds per square inch at room temperature, respectively, and a proportional limit and tensile strength at 600 C. of. 49,500 and 100,000 pounds per square inch, respectively.

The high proportional limit of my improved prises quenching the alloy from temperatures of at least 900 C. and ageing it at temperatures of from 500 to 800 C. for a period of at least onehalf hour.

2. The process of improving the physical properties of an alloy containing essentially from 40% to 60% nickel, 20% to 35% cobalt, 5% to 20% iron, 0.5% to 10% titanium, which comprises quenching the alloy from a temperature of at least 900 C. and ageing at temperatures ranging from 500 to 800 C. for at least one-half hour.

3. An alloy comprising essentially 20% "to 70% nickel, 60% to 10% cobalt, 5% to iron and 0.5% to 10% titanium, which has been quenched from a temperature of at least 900 C. and aged at a temperature of 500 to 800 C. for a period of at least one-half hour.

4. An alloy comprising essentially 40% to nickel, 20% to 35% cobalt, 5% to 20% iron and 0.5% to 10% titanium, which has been quenched from a temperature of at least 900 C. and aged at a temperature of 500 to 800 C. for a period of at least one-half hour.

GEORGE P. HALLIWELL.

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