US2977223A - Stabilized and precipitation-hardened nickel-base alloys - Google Patents

Description

March 28, 1961 J. T. BROWN STABILIZED AND PRECIPITATION-HARDENED NICKEL-BASE ALLOYS Filed Dec. 10, 1957 000- OO O 000 9 M. m mmv 1 IX ga m a; s Q *om 8 A s I cw cage 3 *1 a o 58 5S v cozoocofi 6961 P6 INVENTOR Jack T. Brown BY MTOR Y United States Patentr 2,977,223. smnruznn AND PRECIPITATION-HARDENED NICKEL-BASE ALLOYS Jack T. Brown, Monroeviile, Pa., assignor to Westing:

house Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 10, 1957, Ser. No. 701,755 Claims. (Cl. 75-171) The present invention is directed to a novel nickel-base alloy which can be forged into massive-shapes from large ingots and aprocess for dually hardening the same.

Material problems connected with the development of aviation gas turbines, land gas turbines, and steam turbines include the need for an alloy for discs which must operate efiiciently in the temperature range offrom 13005 to 1500 and at th ame t me ha e relat sl hi ductility. Dependable operation is required for long times in steam turbines operating at the lower endof this temperature range and for shorter times for aviation gas turbines perat ng a he uppe and Of he nightmare range. Another criteria for a good high temperature alloy is its ability to be economically fabricated frornlarge ingots into various shapes of turbine discs.

Previously known alloys somewhat similar to that of the present invention, have been limited in production to. small precision castings which arenot worked and are put into use without any subsequent heat treatment.

.An object of this invention is to provide a nickel-base alloy comprising predetermined proportions of chromium,

2,977,223 Patented Mar. 28, 1

substituting for each two parts by weight of molybdenum one part by weight of tungsten. If the'alloy is not vacuum melted, silicon will-usually be added ina'range of from 0.2% to 0.7%. However, this amount of silicon may be present in the vacuum melted alloy, and it usually is pres; ent asa component of the metals being melted.

One of the important elements used in the alloy of this invention is vanadium. amounts of from 0.2% to 1%, it aids in refining the grain structure of the ingot so that the ingot may be wrought into massive shapes. The reason for employing such relatively large percentages of onm' numxrem 7% to 25% alone, orin combinatio'n with tungsten, is to impart strength to .the solid solution" inatrix whereby the full strengthof the du allyhardenedallo'y member may'be attained. Manganese also, adds 'to good hot working characteristics by combining with the extraneous s nar molybdenum, aluminum, boron, vanadium, manganese,

and iron, the alloy being characterized by its ability to be worked or forged from large igots into various mas sive shapes and then hardened to provide properties of high strength and ductility over a temperature range of from 1300" F. to 1500 F.

Aturther object-of this invention is'to provide a process for dually hardening'a member of a nickel-base alloy comprising predetermined, proportions 1 of chromium, molybdenum, manganese, aluminum, boron, vanadium and iron, by first hot workingan ingot ofthe alloy to disperse hardening components therein and thereafter solution treating the member at a temperature of from 1850 F. to2250 R, cooling, and aging said'member at a temperature of from 1*200'F'. to 1700 F. for a period oi from five hours to 200 hours so that the desiredproperties ofistrength and ductility are retained in the wrought member when employed in the temperature range of from 1300 F. to 1500" F.

Other objects of the invention will in part appear hereinafter. v I v r The figure is a graph of schematic curvesillustrating the stress rupture properties of the different heats of-the alloy. The alloy of this invention is a nickel base alloy and contains a minimum, of strategic materials. It combines exceptional stress rupture properties at temperaturesup v to 1500 F. with good ductility. It-can be hot worked to desired shape. The alloy can bereadily preparedito be I notch insensitive.v K 1 mi ht; j-

be. obvious andwill The high temperature alloyin accordance with our in and other impurities.

Boron is essential to provide the first stage of hardening of thedually hardenable alloy. When the solution treating temperature is attained, boron is dispersed in the matrix as aboride present'as a finely dispersed stable second phase. The higher amounts of boron, that is from 0.4% up to 0.8%, increase the inherent matrix strength without decreasing ductility to an undesirable level; For example, in a heat of the alloy'containing' 0.78% boron, a specimen tested at 45,000 p.s.i. and 1400 F. lasted 1108 hours and ruptured with 22% elongation."

The carbon content, on the other hand, is limited to a maximum value of 0.08% owing to the 'fact that carbides may be formed'which are soluble in the solid solution matrix, therefore, imparting a loss of ductility. The iron, while it may be present in amounts upto 20%, need not be added in elemental form. Thus, iron m'ay'be'added incombination with the other elementsheretofore men tioned, such as ferrochromium and ferromanganese, etc.

These last additions are-more economical than'the use of the pure separate elements.

Aluminum is employed as the primary precipitation hardening constituent in the second or aging'stage of the dual hardenirig process. The aluminum precipitates at relatively high aging temperatures and enables the alloy to be used at higher temperatures than with other hardeners such as titanium. The invention further relates to a dual hardening process for membersfrom ingots of a nickel-base alloy comprising essentially by weight from 12% to 28% chromium, from 7% to 25% molybdenum, from .'2% o' l vanadium, from .2%' t'o"2% manganes e, from'lto 6% "aluminum, from .2.% tof.8,% boron,

ay max imumfof .08% carbon, up to 20% iron and, the

balance substantially, all nickelaexcept' for minor amounts of impurities, l ngots of the alloy' are characteriid by abilityft o be readily forged into lawsuits-nearest, shafts and similar parts required for high temperature use. Wrought; and :dually hardened members exhibitproperties of high strength and ductility inthe temperature rangeof from 1300. F. to 1500. F.. A preferred Balan'ce L 0 range of composition of ,said alloy which has given oiuti standing properties comprises'by weight from 12% to. 16%chromium, from 12% to 16% molyb denum,from

3% to .6%J-vanadium, from 7% to 1% manganese, ram 2.%;. .5.% .tll lminl ill f om to .8.% boron. a

of impurities.

sir ns. .Qoha t canreplacea par of the nickel. 1 s 1 I Particularly, the invention relatesto thereindually hardening-the hightemperature nickel base-alloy of thislinventionwhich ,comprisesforging; or

aherwis'e e was: easie trials: na

When added in substantial finely dispersed boride in a matrix. then heating the wrought member to a solution treating temperature of from 1850 F. to 2250" F. for a period of time suitable to produce a matrix cf a finely dispersed second phase, cooling the material to room temperature, then aging said alloy at a temperature of from 1200 F. to 1700 F. for a period of from five hours to 200 hours, and coolingin air to room temperature, said aged forgings having properties of high strength and ductility when used at'a temperature range of from 1300" F. to 1500 F. A convenient procedure for preparing alloy members in accordance with the teachings of the invention is the following. Predetermined proportions of the components of the alloy are preferably melted in a vacuum-cold hearth arc furnace at a temperature sufficient to melt the components. The alloy can be also melted in a vacuum induction furnace or in an open air induction furnace. The alloy melt is then cast in a large ingot mold. The alloy ingot is then heated in a soaking furnace and hot forged at a temperature of from 2000 F. to 2300 F. into the desired shape. Other hot working processes can be applied to produce massive wrought shapes. The forgings may then be machined or ground to specification. The forgings, or machined members, are solution treated in the temperature range of from 1850 F. to 2250 F. During the hot working operation, the boride phase is dispersed in the matrix and, a phenomenon called dispersion hardening results. This dispersion hardening comprises a fine dispersed stable second phase which increases the matrix hardness of the solution treated alloy from about RC" (Rockwell fC scale) to about RC. The alloy members may be then further secondarily hardened by a precipitation hardening process. Precipitation hardening is obtained by aging the solution treated members at a temperature of from 1200 F. to 1700 F. for a period of from about five hours to 200 hours and longer, thereby increasing the hardness to a maximum of approximately 41 RC. The aging can be carried out at a uniform temperature, or the temperature changed to a higher or lower value in the range of from 1200 F. to 1700 F.

A number of heats of the alloys of this invention as set forth in the following Table I, which gives the chemical analysis thereof were prepared.

Table 11 sets forth tensile test data made on forged bars from heat number 993, while Table III sets forth thetensile tests made on forged bars produced from heat numbers 1303 and 1304.

Table 11 0.27 Percent Percent: Duall Testing Ultimate Yield Elong in Redue- Hardend. Temp, F Strength Strength 1.4 tlon of' Hardness,

- Area RC" Heat Treatment: Solution treat, 2100 Rio! iane hour.

Age: One day, 1400 F.

o'lnleeoio caucus Table III Testing 0.2% Percent Percent Heat No. Temp, Yield Ultimate Elong. Reduc- 1*. Strength Strength in 1.4 tron of Area R.T. 125, 000 191, 000 9 11 R.T. 133. 000 196.000 7 10 1, 200 111. 000 159.000 6 1, 200 139.000 182. 000 10 12 1, 400 104, 000 115. 000 19 30 1, 400 133,000 21 41 1, 600 46. 000 47, 000 37 67 1, 600 59, 000 61, 000 26 61 5 Heat Treatment: Solution treat, 2100 F. for one hour.

Age: 48 hours, 1400 F.

Table IV gives the stress rupture results on combination (Notch and Plain) bars from heat number 1182.

Table IV Plain Bar Notched Testing Temp., Stress Rupture Percent Bar Rup- Hardness,

F. (p.s.i.) Time Elong. ture Time RO" (Hrs) (Hrs) For a further showing of the excellent properties ex- 0 hibited by the alloys of the present invention, reference may be made to Fig. 1. Forgings of alloys of Heats 993, 1303 and 1304 were subjected to rupture tests at 1300 F., 1400 F. and 1500 F. as indicated. The excellent ductility is indicated by the figures in the drawing 5 in parentheses.

It will be obvious that the above description is illustrative and not limiting.

I claim as my invention: V v 1. A high strength high temperature nickel'base alloy comprising by weight from 12 to 28% chromium, from 45 except for minor amounts of impurities said alloy exhibiting good workability characteristics so that the final ingot casting may be forged or wrought into massive shapes at temperatures of from 2000 F. to 2300 F., and having properties of high strength and ductility in 0 the temperature range of from 1300" F; to '1500" F.

2. The alloy of claim 1 wherein from .2 to .7% of silicon is present. 7 V

3. A high strength high temperature nickel-base alloy comprising by weight from 12% to 16% chromium, from 12% to'l6% molybdenum, from 2 to 5% aluminum,

from 0.4 to 0.8% boron, from 0.3 to 0.6% vanadium, from 0.7 to 1% manganese, a maximum of 0.03% car'- bon, up to'13% iron, and the balance substantially all nickel except for minor amounts of impurities, said alloy exhibiting good workability characteristics so that the.

final ingot casting may be forged or wrought into mas-. sive shapes at temperatures of from 2000 F. to 2300 F., and having properties .of high strength and ductility in the temperature range; of from 1300 F. to 1500 F.

4.-The alloy of claim 3 wherein .2 to .4% silicon is num, from .2 to .8%, boron, from .2 to1% vanadium,- from .2'to 2% manganese, a maximum of 08% carbon,

used. a s. A wrought high strengt .hi hl mp eni base alloy member comprising'by weight 12 to 28%- chromium, .7 to 25 molybdenum, from 1 to 6% alumiup to 20% .iron, anda balancesubstantially allnickel except, for .minoramoun H berhaving. been, hot worked ,t o shapes and dually hard- '4 ened by dispersion hardening and precipitation harden tsof impurities, said alloy meming to a hardness of at least a Rockwell C value of 20, so that the final wrought member exhibits properties of high strength and ductility within a temperature range of from 1300 F. to 1500 F.

6. A high strength, high temperature nickel-base alloy comprising by weight from 12 to 16% chromium, from 12 to 16% molybdenum, from 2 to 5% aluminum, from 0.4 to 0.8% boron, from 0.3 to 0.6% vanadium, from 0.7 to 1% manganese, a maximum of .03% carbon, up to 13% iron, and the balance substantially all nickel except for minor amounts of impurities, said alloy, having been hot worked totshape and, dually hardened by dispersion hardening and precipitation hardening to a hardness of at least a Rockwell C value of 20, so that the final wrought member exhibits properties of high strength and ductility within a temperature range of from 1300" F. to 1500" F.

7. In the process of dually hardening a nickel-base alloy forging comprising from 12 to 28% by.weight of chromium, from 7 to 25% by weight of molybdenum, from 1 to 6% by weight of aluminum, from 0.2 to 0.8% by weight of boron, from 0.2 to 1% by weight of vanadium, from 0.2 to 2% by weight of manganese, from 0.2 to 0.7% by weight of silicon, a maximum of 0.8% carbon, up to iron, and the balance substantially all nickel except for minor amounts of impurities, the forging having a first relatively uniform dispersion of hardening components, the step comprising heating the forging to a solution treating temperature of from 1850 F. to 2250 F. for a period of time suitable to produce a matrix of a finely dispersed second phase, cooling the material to room temperature, aging said alloy at a temperature of from 1200 F. to 1700 F. for a period of from about 5 hours to 200 hours and cooling in air to room temperature, said forgings having properties of high strength and ductility in the temperature range of from 1300" F. to 1500 F.

' properties of high strength and ductility in 8. In the process of dually hardening a nickel-base by weight of boron, from 0.3 to 0.6% by weight of vanadium, from 0.7 to 1% by weight of manganese,

from 0.2 to 0.4% by weight of silicon, a maximum of 0.03% carbon, up to 13% by weight of iron, and the balance substantially all nickel except for minor amounts of impurities, the forginghaving a first relatively uniform dispersion of hardening components, the steps comprising heating the forging to a solution treating temperature of from 1850 F. to 2250 F. for a period of time suitable to produce a matrix of a finely dispersed second phase, cooling the material to room temperature, aging said alloy at a temperature of from 1200 F. to 1700 F. for a period of from about 5 to 200 hours and cooling in air to room temperature, said forgings having the temperature range of from 1300 F. to 1500" F.

9. The alloy of claim 5, wherein 0.2% to 0.7%' of silicon is present.

10. The alloy of claim 6 wherein 0.2% to 0.4% of silicon is present.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain May 31, 1950

Claims (1)

1. A HIGH STRENGTH HIGH TEMPERATURE NICKEL-BASE ALLOY COMPRISING BY WEIGHT FROM 12 TO 28% CHROMIUM, FROM 7 TO 25% MOLYBDENUM, FROM 1 TO 6% ALUMINUM, FROM 0.2 TO 0.8% BORON, FROM 0.2 TO 1% VANADIUM, FROM 0.2 TO 2% MANGANESE, A MAXIMUM OF 0.08% CARBON, UP TO 20% IRON, AD THE BALANCE SUBSTANTIALLY ALL NICKEL EXCEPT FOR MINOR AMOUNTS OF IMPURITIES SAID ALLOY EXHIBITING GOOD WORKABILITY CHARACTERISTICS SO THAT THE FINAL INGOT CASTING MAY BE FORGED OR WROUGHT INTO MASSIVE SHAPES AT TEMPERATURE OF FROM 2000*F. TO 2300*F., AND HAVING PROPERTIES OF HIGH STRENGTH AND DUCTILITY IN THE TEMPERATURE RANGE OF FROM 1300*F. TO 1500*F.

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