US2743175A - Precision casting alloy - Google Patents

Description

A ril 24, 1956 A. M. TALBOT 2,743,175

PRECISION CASTING ALLOY Filed Jan. 27, 1953 2 Sheets-Sheet l 1 2 I /o0 Q P67? d/W' 67/980 INVENTOR.

2&1 fi ezfirffadar 742507 BY (2. (am

ATTORNEY United States Patent PRECISION CASTING ALLOY Albert M. Talbot, Fair Haven, N. J., assignor to The International Nickel Company, Inc., N ew .York, N. Y., a corporation of Delaware Application January 27, 1953, Serial No. 333,523

9 Claims. (Cl. 75-128) The present invention relates to improved high temperature heatand stress-resisting precision cast articles suitable for use at elevated temperatures in power plant units of aircraft gas turbine engines, turbojet enginesand the like and to special heatand stress-resisting nickel chromium-iron alloys substantially free from the strategically scarce metals cobalt, columbium and tungsten.

In recent years the art has been earnestly endeavoring to obtain heatand stress-resisting cast alloys capable of withstanding high stresses at high temperatures inthe range from about l200 F. to about 1800 F., particularly alloys suitable for use as blading material in aircraft gas turbine engines, turbojet engines, etc. A major difliculty which has confronted the art has been the modern trend.

to design aircraft engines to operate at higher and higher temperatures. At the higher operating temperatures, i. e., temperatures in excess of 1350 F. and even in excess of 1500 F., the service life of the alloys is greatly reduced. To be assured of a service life of even a few hundred hours, it has been necessary to employ alloys containing substantial amounts of strategically scarce elements, such as cobalt, columbium and/or tungsten, particularly large amounts of cobalt. Cobalt-base alloys containing either columbium or tungsten or both have been found effective in meeting the rigorous operating requirements of aircraft gas turbine engines, turbojet engines, and the like. However, the aforementioned elements are usually found in countries which are not completely accessible during times of international emergency. When such emergency conditions prevail, which interfere with the obtaining of such strategically scarce elements as cobalt, columbium and tungsten, etc., other alloying materials must be resorted to in the making of heat-resisting alloys, particularly alloying materials which are readily available. In cognizance of this situation, many attempts have been made to employ substitute alloys low in or substantially free from strategically scarce elements. However, many of the substitute non-strategic alloys employed have not been generally satisfactory in that these alloys did not always meet the high temperature strength and creep properties required at the high service temperatures and also did not usually meet the service life usually obtained by the cobalt-base alloys.

In producing high temperature articles, it has usually been necessary to produce them by mechanical working operations rather than by casting the alloys directly into their final shape; Many of the alloys which possessed the required high temperature properties, usually very high in strategically scarce elements, did not have the required properties in the as-cast condition to permit their use as castings. Also, some of the alloys which contained large amounts of other alloying materials for the purpose of ice imparting improved resistance to deformation at elevated desired shape for service.

articles. This was particularly true when producing wrought articles having somewhat complicated shapes which usually also required many finishing operations in' producing the final shape. Moreover, in addition to the increased cost due to the mechanical working operation, there was also the problem of increased cost in producing the final article by machining, grinding, polishing, etc. A

further disadvantage of wrought articles was the necessity in many instances of employing special high temperature heat treatments in order to develop the required high temperature properties. Since in many cases the special heat treatments were applied to the finished article prior to use, many of the articles were subject to twisting, warping, etc., due to the thermal stresses set up during heat treatment and, therefore, had to be rejected or discarded. in view of the foregoing, there has been a demand for alloys suitable for producing articles having complicated and intricate shapes for turbine blades, turbine buckets, etc., by employing precision casting methods which are also sometimes referred to as lost-wax processes. Since many of the known wrought alloys did not have the:

necessary casting properties required for precision casting, a demandlias existed for special cast alloys having high temperature properties comparable to those of Wrought alloys and also having the required precision casting properties. While many cast alloys have been developed meeting high temperature requirements, these alloys did not always have the required casting properties in that some of the alloying elements employed oxidized easily or formed scum during melting which appeared to interfere with the fidelity of precision castings. Further more, many of the suitable precision casting alloys required the presence of substantial amounts of the, stra tegically scarce elements mentioned hereinbefore and/ or required special heat treatments in order to develop the desired high temperature properties. Although many attempts were made to overcome the foregoing difficulties and other difiiculties and disadvantages, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

I have now discovered an improved high temperature heatand stress-resisting precision cast article comprised of an alloy which is substantially free from the strate gically scarce alloying elements cobalt, eolumbiulu and tungsten, which possesses the requisite casting properties demanded by precision casting methods and which has the required high temperature properties, including heat resistance, stress resistance, creep resistance, etc.

It is an object of the invention to provide an improved non-strategic, nickel-chromium-iron precision cast article foruse at high temperatures in gas turbines, turbojet engines, and the like.

Another object of the invention is to provide a special cobaltfree, columbium-free, tungsten'free, nickel-chrornium-iron, heatand stress-resisting article for use at high temperatures in gas turbines, turbojet engines, and the like, made of an alloy containing a novel and synergistic combination of relatively non-strategic elements within critical ranges.

It is a further object of the present invention to provide an improved casting alloy free. from strategically scarce elements and having high temperature properties sub- Pal tente d Apr. 24, 1956 stantially comparable to cast alloys containing substantial amounts of strategically scarce elements.

The invention also contemplates providing an improved non-strategic, nickel-chromium-iron alloy for use at high temperatures, said alloy being characterized by good heatand stress-resisting properties at high temperatures.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which;

I igure l depicts comparative rapture life curves which illu trate the synergistic effects of thecritical combination of elements employed in the'noyelalloy. V

Fig. 2 illustrates curves showing the l-hour and IQOO-hotir rupture strengths of an alloy within the scope ofthe invention.

M Fig. 3 depicts curvesillu'strat'ing stress rupture life prop erties of thej alloy contemplated by the invention at various high temperatures. I p p Gen eral lyspeakin'g, he presnt invention contemplates novel high temperature, heatand stress-resisting cast articles adapted for use in aircraft gas turbines, turbojet engines, and the like, comprising a special 'n'ickelchromium-iron alloy substantially free from the strategically scarce element s, cobalt, columbium and/or tungsten. The present invention is'based on the discovery that nickel-chrominm-iron alloys having improved high temperature strength properties can be produced by incorporating in the alloy critical and controlled amounts'of the relatively noil-strategic alloying elements, molybdenum, boron, and carbon. The alloy'employ'ed in producingarticles in 'accorda nce with the inventionis amenable to precision castingmethods and is particularly'applicable to the fabrication by pre cisionjcasting methods of cast articles of complicated shape, including aircraft turbine blades, for service at high temperatures under high stresses ingas turbines, turbojeten'gin'es, etc. The alloy is also amenable to fabrication powder 7 metallurgy. In general, the alloycon tains as critical and. essential elements about 19% t o 50:% nickel, 118% to 30% chromium, 8% to l2 rnolybdenum, 0.03% to 0.8% boron, 0.5% to l.5 oarbon andthe balance essentially iron which constitutes at least about 10% but may be as high as about 55 of the alloy. In producing cast nickel-chrom'ium-iron articles having high fracture life a elevated temperaturescomparable to cast articles made of alloys containing substantial amounts of strategically scarce elements t is preferrdthzit thealloy composition of the articles be maintained within the range of about to 40% nickel, 20% to chromium, 8% to 10% molybdenum, 0.05% to 0.3% boron and 0.6% to 12% carbon, The balance of the preferred alloy composition is essentially iron which constitutes about 15% to 50%of the alloy.

It is an essential feature of the invention that the amounts of nickel, chromium and iron be correctly proportioned Within the ranges specified hereinbefore and be employed in combination with critical and controlled amounts of molybdenum, boron and carbon. It has been fonnd thatthe changes in the amount of nickel have a more important effect upon the properties :than corresponding changes in the amount of chromium. I Increasing the nickel content toabout results in optimum rupture life propertieswhich falloff rapidly when the nickel content of the alloy exceeds 50%. For'this reason, the maximum nickel content of the alloys contemplated by the invention is about 50%. Too low a nickel content endangers the austenite stability andthe high properties of the alloys contemplated by the invention. For this reasomthe nickel content should not the. less than about 20% or 19%. Stress rupture test s conductedf on the novel alloy at elevated temperatures have indicated that the elements molybdenum boron and carbon are critical and are synergistic in efiecting the improved results provided by the invention when the three elements are controlled within the specified ranges. When one 4 or more .of the, elements molybdenum, boron and carbon are absent from the cast alloy or are not within the ranges prescribed hereinbefore, the final properties of the alloy are greatly affected in that the results contemplated by the invention are not obtained.

It is preferred when producing articles made of alloys within the foregoing ranges of composition by precision casting that boron be employed in amounts ranging from about 0.10% to about 0.3%. Silicon may be present in the alloy up to about 2% but is not essential. However it is desirable that silicon be present as it improves the castability of the alloy. Man anese likewise may be optionally employed up toaboiit 3% in producing the alloy provided by the invention. When the two foregoing elements are employed in the alloy, they are usually present in amounts ranging from about 0.1% to 2% silicon and from about 0.1% to 3% manganese. It is preferred to employ manganese in amounts ranging from about 1.5% to 2%. Ir 1 tl 1is range, manganese, is effective in improving the castabilit'y of "the may. The expression the balance or the balance essentially iron does not exclude silicon and manganese in the foregoing amounts. Other elements maybe present in the alloy in incidental amounts without 'deleteriously affecting the properties of the alloy. Such incidental elements may be present as the :result of scrap contamination, as a result of the use of master addition alloys, from the use of deoxidizers, dega's'ifierspurifiers and the'like, during processing, etc. The incidental elementswhich may be present in the alloy include up to about 0.1% aluminum, up to about 0.03% magnesium, up to about0.03% calcium, up to about 0.1% copper, etc. 'It is to be understood that certain gases may be picked up from the atmosphere during melting and as a result are unavoidably present in small amounts. Thus, nitrogen may be picked up in this Way and may be present in amounts up to about 0.15% and is not detrimental eve n.,'when intentionally added in amounts up -to 'about 0.2'%.' However, the presence of nitrogen iin-g'reater amounts leads to porosity of the c'asting. The rare earth elements, lanthanum and cerium, may be present in amounts of less than about 0.1% to counteract the detrimental effects of any sulfur present andto 'i rnp rovethe surface condition of castings. The total per cent of all the incidental'elements together should not exceedabout one pe'r cent. Impurities, such as sulfur and phosphorus, should bekept as low as is commercially feasible. While'the alloy is characterized as being cobaltfree, smallamounts of cobalt may be present in incidental amounts upto about one per cent and may be introduced into th nm imdemarto the addition of other elements. For enampl cobalt may be introduoed in the alloy 'along with commercial nickel which often contains small amounts of cobalt up to about 1% or 2% or evenin'ore. Likewise, small amountsof titanium maybe present incidental to the'maniifactur'e of the 'alloy.

A composition range which has been found to be particularly adaptable 'for commercial use comprises about 30% to 34% nickel, 23% to 27% ehrornium, 8% to 10% molybdenum, 0.05% to 10.3% 'boi'on, ,0.'6% to 1% carbon, up 2%.maiiga'n'es'e, up to l..5% silicon and the balance essentially iron, including tlie usual amounts of incidental elements ,and impurities, In the foregoing composition it is preferred that the boron content be at least 0.10%. Anominalcompositiou "of such an alloy would'comprise about'32'% iiic'keLfabout 25% chromium, about 9% molybd enum, about 0.8% carbon, about0.15% boron, aboiit l .5 'mangane'sefabout 0.4% silicon and are names essentially ash.

. ln'evaluating heat resistant alloys forns'e in gas turbine jengines, turbojet engines andthe like, high temperatur'eruptu rehr'e usually employed. One such test,

which is usually referred to "thoseskilled in art as 'a stressrupture test, comprises subjecting-an alloyspecimen to a given stress 'at an elevatedternperature and maintaining thestress until ihe'alloy fractures. The time mining the 100-hour or 1000-hour rupture life of the alloy,

which is the stress which will produce rupture in 100 hours or 1000 hours, respectively, at the temperature of test. A cast alloy is usually considered adequate when it has a 100-hour rupture life at a temperature of about 1350 F. when subjected to a rupture stress of about 34,000 p. s. 1'. The alloy produced in accordance with the invention generally has a 100-hour rupture life at v about 1350 F. when subjected to a rupture stress of at least about 37,000 or 38,000 p. s. i. and may attain as high as 46,000 p. s. i. under certain conditions.

For the purpose of giving those skilled in the art a better understanding of the invention and a better appreciation of the advantages of the invention, the following illustrative examples are given:

Example I An alloy embodying the present invention was produced having the following composition:

Per Per Per Per For For Per Per Alloy N0. cent cent cent cent cent cent cent cent Ni Or Mo B Mn S1 Fe The procedure followed in producing the aforementioned alloy comprised melting proper proportions of alloy ingredients, such as ingot iron, metallic nickel, high-carbon ferro-chrome, ferro-molybdenum, ferro-manganese and ferro-boron, in a high-frequency induction furnace. All of the foregoing materials, except ferro-boron, were melted and the melt deoxidized with either ferro-silicon or silico-rnanganese and wherever necessary carburized with washed pig iron. The boron addition was made immediately before casting the metal which was cast into sand molds in the shape of miniature pigs suitable for remelting in an indirect arc furnace customarily used for precision casting. The miniature pigs were remelted in the indirect are furnace and poured into an investment mold produced by the lost-wax process to produce precision cast test bars measuring about 0.25 inch in diameter and having a one-inch gauge length.

The foregoing alloy was subjected in the as-cast condltion to a stress rupture test at 1350 F. at various stresses. The following schedule sets forth the results and demonstrates the markedly high rupture lives exhibited by this alloy.

Stress, p. s. i. Rupture Life, hours Example II Other embodiments of the present invention which have given good results are illustrated by the following alloys:

, Per Per Per Per Per Per Per Per Alloy N0. cent cent cent cent cent cent cent cent N1 Cr M0 B 0 Mn 1 Fe 26. 1 8. 1 0. 12 0. 93 1. 52 0. 42 Bel. 27. 4 8. 1 0. 13 0. 93 1. 66 0. 48 Bal. 26.0 8. 1 0.18 0.90 1.52 0.42 Bal. 28 8 O. 18 0. 2 0. 4 Ba]. 28 8 0. 13 0. 98 2 0. 4 Bel 28 8 0. 21 0. 96 2 0. 4 Bel. 28 8 0. 24 0. 95 2 0.4 B81- 28 9. 2 0. 24 0. 53 0. 42 0. 47 Bal. 28. 1 9. 3 0. 27 0.58 0. 41 0. 46 B8,]. 28 9 0. 1 0. 62 0. 4 0. 5 B01. 28 9. 2 0. 12 0. 72; 0. 42 0. 50 Bal. 27. 5 9. 1 0. 17 0. 86 0. 44 0. 63 Ba]. 27. 3 9. 3 0. 17 1. 02 1. 48 0. 48 Bal. 28 9 0.1 1. 11 0.4 0. 5 Hal. 28 11. 8 0.08 0. 03 0.4 0. 5 Ba]. 28 11.5 0.10 0.93 0.4 0. 5 Bal.

1 Both Alloy N o. 11 and Alloy No. 15 contained about 0.2% nitrogen.

' being essentially iron including such other ingredients as manganese, silicon, nitrogen, etc.

The foregoing alloys, when subjected in the as-cast condition to a stress rupture test at 1350 F. at various stresses gave the following rupture lives:

Rupture Life at 1850 F. in hours under stress of Alloy No.

35,000 p. s. i. 40,000 p. s. i. 45,000 p. s. l.

1 Under rupture stress of 28,000 p. s. 1.

2 Under rupture stress of 33,000 p. s. 1.; extrapolated rupture life under stress of 28,000 p. s. l. is about 1300 hours.

3 Under rupture stress of 33,000 p. s. i.; under rupture stress of 37,000 p. s. 1., rupture life is 261 hours. The foregoing alloys after fracture under the aforementioned test conditions exhibited ductility values ranging from about 4% to 17% measured as per cent elongation over a gauge length of one inch.

The stress to give a rupture life of hours at 1350 F. for each of the above alloys is given inthe following table:

100-hour Rupture Stress in p. s. l.

Example III 511 st rs; registrants the saint. the rea s of the invention "and produced in accordance with the procedure of Example I are as follows:

Per Per Per 7 Per Per 4 Per 7 Per Per Alloy No eent cent cent cent cent cent cent cent Ni Gr 1 M0 Y B Mn Si Fe 9:24 0. 18 0. 91 1. 19 0.39 Bai.

The foregoing alloys were subjected in the ns-cast condition to a stress rupture test at 1350" F. and 'at 1500" F. As a result of this test the following high rupture lives at stresses of 35,000 p. s. i. and 20,000 p. s. i., respectively, were obtained:

'AlloyNO.

at 1350 F. under 0101500" I .,under 05,0001). i. 20,000 p. szi.

Temperature, Stress, 'Rri tili'e Life, A1103 F. p. s. 1 hours 1500 25, 000 75 1500 25. 000 as 1500 24, 000 122 11500 24, 000 107 1500 22, 000 2 13 1500 22, 000 185 .1500 20, 000 278 1500 20 000 180 11500 18, 000 "400 1500 18, 000 350 I500 10, 000 1035 1800 1 0, 000 10 1200 s; 000 as 1800 0. 000 250 I 55 In the foregoing schedule, alloy No. 22contained about 33% nickel, 29.5% chrdmium, 1.0% carbon, 2% mangatiese, 053% silicon, 8.8% molybdenum, 0.25% boron, and the balance essentially iron. and alloy No. 23 contained about nickel, 28% chromium, 1.06% carbdn, 2% manganese, 0.3% silicon, 9% molybdenum, 0.23 'boron'andthe balance essentially'iron.

Other nicliel-chrornium-iron alloy compositions which have been found to give the results provided by the invention are given in the following schedule:

Alloy N0. 24,1ivhich contained high'nrolybdenumand-high 1.101600011151118 1 1 5% MO Ziiid 11.77% 8), exhibited a high 100 hoin nrpmre stress 'of "46;000 p. s. i. at -'a tempera-ture er 1350 F. while al-10y No. -25, which had a high -'nickel "content of 48.4%; exhibited a high rupture -life of 1453 hours 'nnde'r a "stress of 28,000 'p. s. i. at 1350" For the purpose'of better illustrating the 'advairtage'sof the 'inveintion, a s'eries'of comparative tests wefeconduct'ed with a group "of alloys having compositions outside the scope of theinven'tibn. The compositions of these alloys are illustrated in the following schedule:

Per -Per Ier Per Per Per Tor Per Alloy N0. cent cent cent cent cent cent cent cent Ni Cr M0 B 0 Mn Si Fe A.... 35.3 15.2 0.34 0.39 0.36 Hal.

34.8 27.0 0.35 0.46 0. 29 Del.

' .7 26.6 0.38 1.94 0.8 Bal.

. 20. 8 0. 52 0. 53 0. 3 Hal.

28 0.23 1.80 0.4 0.0 Hal.

20 9 0. 082 0. 25 2 0. 4 Del.

The foregoingalloys were producedby procedures similar to those employed in producing the alloys described hereinbefore. Thestress rupture results obtained on the foregoing alloys 'at elevated temperatures are as follows:

LUnder a stress 0020.000 p. s. 1.

2 Under a stress of 35,000 p. s. i. It willbe noted from the foregoing schedule that all of the alloys outside the scope of the invention had low stress rupture values and were markedly inferior to the alloys provided by the'invention.

As has been stated hereinbefore, it is important in carrying out the invention that the alloy contain carbon, boron and'molybdenumin order to obtain the desired improved properties in cast articles made of the alloy iirovided'by the invention. The three elements cooperate toproduce a' synergisticefiect in the relatively non-strategiccast alloy to produce-good rupture life at elevated temperatures. This effect can be illustrated by Fig. l

Iwhichcomp'ares'the influence of carbon on the rupture lifeof alloys containing about 35% nickel, 28% chromium and both 'molybdenum and boron in proper amounts (curve A) with th'e'influence of carbon in similar nickelchromium alloys containing molybdenum but devoid of boron (curve B) or "containing boron but devoid of molybdenum (curve 'C) 'or devoid of both boron and molybdenum (curve-D). The curves depicted in Fig. 1 are based on rupture tests conducted under a stress -of 9 28,000 p. s. i. at'1350 F. In Fig. 1, curves .B,"C and D show the inferior rupture lives which are obtained with varying carbon contents in alloys containing molybdenum but devoid of boron, containing boron but devoid of molybdenum and devoid of both molybdenum and boron, respectively, while curve A illustrates the markedly improved results which are obtained when synergistic proportions of carbon arepresent in accordance with the invention in the nickel-chromium alloys containing both molybdenum and boron in critical amounts. Thus, at a carbon level of 0.6%, the alloy devoid of both molybdenum and boron (curve D) would have an inferior stress rupture life of less than 25 hours, the alloy devoid of molybdenum but containingboron (curve C) would have an inferior stress rupture life-of less than 50 hours, while the alloy containing molybdenum but devoid of boron (curve B) would have a lowstress rupture life of close to 100 hours. In contradistinction, the alloy Within the scope of the invention having the same carbon content of 0.6% would have the remarkably improved rupture life of over about 500 hours (curve A). Likewise, at a carbon level of 0.7%, it will also be noted from the curves of Fig. 1 that the alloy devoid of both molybdenum and boron (curve D) would have an inferior stress rupture life of less than 25 hours, the alloy devoid of molybdenum but containing boron (curve C) would have an inferior stress rupture life of less than 50 hours, while the alloy containing molybdenum but devoid of boron. (curve B) would have a low stress rupture life of less than.150 hours. On the other hand, it will be noted that the alloy within the scope of the invention and having the same carbon level of 0.7% would have the remarkably high stress rupture life of over about 1000 hours (curve A). It will also be noted from Fig. 1 (curve A) that the carbon appears to have its most critical effect when it is presentin the alloy provided by the invention in amounts above about 0.5%. s

The importance of carbon as an essential element is also shown by the following schedule which illustrates the marked critical effect of carbon on the 100-hour rupture stress of the alloy at 1350 F.

R1113pt6igreFSttressat Y 0 give Alloy 1\0. Percent O mrhour me, p.

All the alloys in the foregoing schedule contained, in addition to the specified amounts of carbon, approximately 35% nickel, approximately 28% chromium,.about 8% to 9% molybdenum, about 0.08% to 0.13% boron and the balance essentially iron plus theusual incidental elements and impurities. It will be noted that the alloys containing above about 0.5% carbon exhibit marked improved 100-hour rupture stress of the order of 38,000 p s. i. orbetter whereas the alloys containing less than about 0.5 carbon exhibit inferior rupture stress values of the order of 29,000 to 30,000 p. s. i.,

Similar alloys having higher boron content, c. g., 0.16% to 0.27% boron, also show the critical effect of carbon on the 100-hour rupture stress ofv the alloy at 1350" F. as illustrated by the data in the following schedule:

Rupture Stress at 1350 F. to give 99. 9 (DO! N man o:

It will be noted from the foregoing schedule that alloys within the scope of they invention and containing above about 0.5 of carbon exhibit a 100-hour rupture stress value of at least about 37,000 p. s. i. On the other hand, when the carbon content is below about 0.5%, e. g., 0.26% carbon, the alloy exhibits a low 100-hour rupture stress value, e. g., 27,000 p. s. i.

The two foregoing schedules illustrate the marked critical effect which carbon has been found to exert in combination with the remainder of the composition in improving the 100-hour rupture life when it is present in the alloy provided by the present invention in amounts of about 0.5% carbon and higher. Likewise, similar data have indicated that the minimum content of boron should be 0.03% and the minimum content of molybdenum should be 8% in order to obtain the results provided by the invention.

The high temperature properties exhibited by the relatively non-strategic cast alloy provided by the invention compare very favorably with prior art cast alloys.

containing a large amount of such strategicallyscarce elements cobalt, columbium, and/or tungsten. For example, the following schedule compares the 100-hour and the 1000-hour rupture strengths (as stress in pounds per square inch) of the novel alloys at 1350" F. and 1500 F. with two prior art alloys referred to in the art as Stellite 21 (or Vitallium) and 8-816" which contain large amounts of at least one strategically scarce element.

At 1350" I At 1500 F.

Alloy Load Load Load Load (p. s. i.) (p. s. i.) (p. s. i.) p. s. 1. to fracture to fracture to fracture to fracture in 100 hrs. in 1,000 hrs. in 100 hrs.. in 1,000 hrs.

Present Alloy 41, 000 32, 000 24, 000 16, 000 Stellite 21- .I 34, 000 21, 000 22, 000 14, 000 S-816 40, 000 20, 000 26, 000 21, 000

In making the foregoing comparison, the alloy of the present invention had a composition of about 35% nickel, 28% chromium, 9% molybdenum, 0.15% boron, 1.0% carbon, 1.5% manganese, 0.5% silicon and the balance essentially iron. The alloy referred to in the prior art Stellite 21 contained about 2% nickel, 27% chromium, 6% molybdenum, 0.25% carbon, 0.6% manganese, 0.6% silicon and the balance cobalt, while the prior art alloy referred to as 8-816 contained about 20% nickel, 18% chromium, 4% tungsten, 4% colunn bium, 4% molybdenum, 0.4% carbon, 0.6% manganese, 0.3% silicon and the balance cobalt. As illustrative of the temperature range over which the aforementioned composition of the present alloy exhibits good l00-hour and 1000-hour rupture strengths, attention is directed to Fig. 2 which depicts the rupture strengths of the alloy at temperatures from about 1300 up to about 1800 F.

A further illustration of the high rupture properties which can be obtained without the use of strategically scarce elements by compositions within the preferred range at various high temperatures is shown graphically in Fig. 3 which depicts stress rupture curves obtained as a result of many tests at temperatures of 1350 F., 1500 F., 1650 F.', and 1800 F. The alloys employed in the tests ranged in composition from about 33.8% to 35.4% nickel, about 26% to 28% chromium, about 8% to 9% molybdenum, about 0.86% to 1.06% carbon, about 0.1% to 0.25% boron, about 1.5% to 2% manganese, about 0.3% to 0.5 silicon and the balance essentially iron plus incidental elements.

The improved properties of the cast alloy provided by the invention, which are obtained when the three aforementioned elements molybdenum, boron and carbon are properly employed in the alloy, appear to be associated with a type of metallographic structure which 'is different horn that normally obtained in the usual heat resisting cast alloy. The meta-llographie structure of the present alloy in the as-east condition comprises a matriir of structureless austenite, containing massive, primary carbide as an *almost continuous interdendritic phase with portions 'ofthe-earbide having a e'u'tectiferous structure.

The high properties which are provided by the relatively-non-st'rategic novel alloy contemplated by the presentinvention 'are'obtained the as-cast condition without resorting to the usual high temperature heat trcatments, age-hardening treatments, etc. However, if it is desired to improve the room temperature ductility of the alloy provided by the invention, the alloy can be subjected to a high temperature heating comprising heating the cast alloy to a temperature range of about 1900 F. to about 2250 F. for a period of the order of about o'ne hal'f to one hour or more followed by a normal rate of cooling similar to that obtained when 'eoo'ling'in air.

Prope'r'tie'scf the alloy provided by the invention useful in designing articles made thereof include the tensile strength at room temperature and at elevated temperatures and the mean coefiicient of expansion. The

alloy exhibits a tensile strength of about 70,000 p. s. i.

at room temperature and about 60,000 p. s. i. at -1500 F. The meancoeffiecientofexpansion'(inch/inch/ F.) of the alloy over various'temperature ranges from room temperature up to 1800 F. is as follows:

From Room Temperature to- Mean Coefiiclent While the novel alloy provided by the invention is particularly adaptable to the manufacture of articles by precision casting, it is to be understood that the articles made thereof may be produced by other methods, such as other castingmthods, powder metallurgy, etc.

The present invention is particularly applicable to the fabrication of castarticles, e. g., blading material, for use inpower units orturbine engines, turbojet engines, and the like, and also applicable to the fabrication of articles by other conventional methods of casting for use "at elevated temperatures under conditions where a high degree of resistance to deformation under stress is required. Some of the articles which can be made from the 'alloy provided by the invention include turbine blades for use as rotary and-stationary blades, i. e., turbine buckets and nozzle vanes, etc.

Although the present -iriventionhas been described'in conjunction with preferred embodiments, it is to be understood that modificationsand variations may be resorted to without departing-from the spirit and scope of the invention, as those skilled in-theartwill readily understand. Suchmodifications and variations are considered to be within the .purview and scope of the invention and appended claims.

I claim:

l. A substantially cobalt-free, 'columbium-free, tungsten-free, nickel-chromium-iron precision "cast "article of manufacture suitable for use at high temperatures in power plant units of gas'turbines, turbojet engines and the like, -said cast article being comprised of aiprecision -east alloy characterized by a l hour 'ruptur'e stress at l350 Fpof at least about-37', 0O0:p.=s. i. and containing -about 30% 'to34'%-'nickel,:2'3% to"27%-ehromium, 8% to molybdenum,-0=05 %-to-0.3 boron; 016% to 1% 'carbon, 0.1% to 2% silicon, 051% to -3% manganese and the balance except for small amounts of ether ele- 12 inents which do not materially adversely affect the novel and basic characteristics of the alloy.

=2. A substantially cobalt-free, columbium-free, tungsten free, niekel-chromium-iron .preeisio'n 'cast article of manufacture suitable-for use-at-hi'ghtemperatures inpower plant units of gas turbines, turbojet'engines and the :like, said cast article being comprised of a precision 'cast alloy 'characterized by a -100-hourrupture stress at 1350. or at least about 37 00011). -s.-i. and containing about to 10% =nicke1, 20% to chromium, -8% to 10% molybdenum, 0.10 60 0.3% boron, 0.6% to 1.2% carbon, 01% to 2% silicon, 0.1% to 3% manganese and-the balance ironexcept for small amounts of other elements 'which do not materially adversely affect the 'noveland basic characteristics of the alloy, the iron'c'ontent'constituting about 15% to 50% of 'the alloy.

3. A cobalt-free, columbium=free, tungsten-free,-'nickel- 'chromitim i'ron ipreeis'ion cast article or manufacture -suit able for use at high temperatures in .power :plant units 'of gas turbines, =turbojet'engines and the like, sai'd Iprecision cast article being comprised of an alloy characterized by improved =100-hour rupture stress at 1350 'and'co'ntaining:abdut 20% to nickel, 20% '-to 30% chromium, 8% to 10% molybdenum, 0.05% to 0.3% boron, 06% to 4.2% carbon, 01% to 2% :silicon, '0.'-1% to -3% manganese and the balance iron except for srnall amounts of other'eletnents which do not materially adversely 'aifect the 'novel and basic characteristics of the alloyftheiron-content constituting about 15% to of the alloy.

4. 1A substantially cobalt-"free, columbium-free, tungs'te'n-free, DlGkCl-ClillOfl'lllll'lT-ll'Ofl 'preci'sion cast article of manufacture suitable for use at high temperatures :in Lp'oweriplant units of Egas 'turbines, 'turbojet engines and the like, -said .p'recisioncast article being comprised of an alloy characterized by improved 'l00 hour rupture stress at l 350 F. and containingahout 19% to 50% hicke1, 18% to 30% chromium, 8% to 12% molybdenum, 0.03% to 0.8% b'oron, 0.5% to 1.5% carbon, up =to 2% silicon, up to 3% manganese and the balance iron except for small-amounts of other elements which do'not materially adversely affect the novel and basic characteristics offthe lalloy, the iron content constituting about 10% to of the alloy.

5. 'A cobalt free, columbium-free, tungsten-free,-nickelchromium-iron casting alloy suitable for use at high temperatures in power plant units of gas'turbines, turbojet engines and the like-said casting alloy being characterized by improved hour rupture'stress'at 1350" F. and being comprised (if-"about 30% to 34% nickel, 23% to 27% chromium, 8% to 10% molybdenum, 0.05% to 0.3% boron, 0.6% to 1% carbon 'and the balance iro'n except'for small amounts of other elements which do notrnaterially adversely affect the novel and basic characteristics of the alloy.

7 6. A cobalt-free, colum biumfree, tungsten-free, nickelchromium'iron casting alloy suitable for use at high temperatures in power .plant units of gas turbines, turbo- .jet engines and the like, said casting alloy'being characteri'zedv by improved "IOU-hour rupture stress at l350 F. and being comprised of about 20% to 40% nickel, 20% to 30% chromium, 18% to 10% molybdenum, 0.10% to 0.3% boron, 0.6% to 1.2% carbon and the balance iron except 'for small amounts of other elements which do not materially adversely afiect the novel and basic characteristics -of the alloy, 'the iron content c'onsti'tuting"ab'out'15% to 50% of the alloy.

7. A substantially cobalt-free, columbium-free, tung- 'sten-free, nickel-chromiurn-iron casting alloy suitable for use at"elevated temperatures in power plant units of .gas turbines, t'urbojet engines and the like, said casting alloy being characterized by improved 100 -hour ruptfiie stress at 1350 F. and being comprised (if abotit-20% to 40% -'nickel, 20% to"3 0% chromium, 8% to 10% molybdenum, 0.05% to 0.3% boron, 0.6%

13 to 1.2% carbon and the balance iron except for small amounts of other elements which do not materially adversely aifcct the novel and basic characteristics of the alloy, the iron content constituting about 15% to 50% of the alloy.

8. A substantially cobalt-free, columbium-free, tungsten-free, nickel-chromimn-iron alloy suitable for use at elevated temperatures in power plant units of gas turbines, turbojet engines and the like, said alloy being characterized. by improved 100-hour rupture stress at 1350 F. and being comprised of about 19% to 50% nickel, 18% to 30% chromium, 8% to 12% molybdenum, 0.10% to 0.3% boron, 0.5% to 1.5% carbon and the balance iron except for small amounts of other elements which do not materially adversely affect the novel 15 and basic characteristics of the alloy, the iron content constituting at least about 10% of the alloy.

9. A substantially cobalt-free, columbium-free, tungsten-free, nickel-chromium-iron alloy suitable for use at elevated temperatures in power plant units of gas turbines, turbojet engines and the like, said alloy being characterized by improved l00-hour rupture stress at 1350 F. and being comprised of about 19% to 50% nickel, 18% to 30% chromium, 8% to 12% molybdenum, 0.03% to 0.8% boron, 0.5% to 1.5% carbon and the balance iron except for small amounts of other elements which do not materially adversely aifect the novel and basic characteristics of the alloy, the iron content constituting at least about 10% of the alloy.

References Citedin the file of this patent UNITED STATES PATENTS 2,403,128 Scott et al. July 2, 1946 2,513,472 Franks et al. July 4, 1950 2,562,854 Binder July 31, 1951

Claims (1)

1. A SUBSTANTIALLY COBALT-FREE, COLUMBIUN-FREE , TUNGSTEN-FREE, NICKEL-CHRONIUM-IRON PRECISION CAST ARTICLE OF MANUFACTURE SUITABLE FOR USE AT HIGH TEMPERATURE IN POWER PLANT UNITS OF GAS TURBINES, TURBOJET ENGINES AND THE LIKE, SAID CAST ARTICLE BEING COMPRISED OF A PRECISON CAST ALLOY CHARACTERIZED BY A 100-HOUR RUPTURE STRESS AT 1350* F. OF AT LEAST ABOUT 37,000 P. S. I. AND CONTAINING ABOUT 30% TO 34% NICKEL, 23% TO 27% CHRONIUM, 8% TO 10% MOLYBDENUM, 0.05% TO 0.3% BORON, 0.6% TO 1% CARBON, 0.1% TO 2% SILICON, 0.1% TO 3% MANGANESE AND THE BALANCE EXCEPT FOR SMALL AMOUNTS OF OTHER ELEMENTS WHICH DO NOT MATERIALLY ADVERSELY AFFECTED THE NOVEL AND BASIC CHARACTERISTICS OF THE ALLOY.

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