US2403128A

US2403128A - Heat resistant alloys

Info

Publication number: US2403128A
Application number: US448234A
Authority: US
Inventors: Scott Howard; Robert B Gordon
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1942-06-24
Filing date: 1942-06-24
Publication date: 1946-07-02
Anticipated expiration: 1963-07-02

Description

July 2, 1946- H. scoTT l-rrAL 2,403,128

` "HEAT RESISTANT ALLOYS Filed June 24, 1942.

Harvard .fco and /Eaber E Gordon,

Patented July 2, 1946 2,403,121; v naar RESISTANT mors Howard Scott and Robert B. Gordon, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa.. a corporation of vania Pennsyl Application June 24. 1942, Serial No. 448,234

11 Claims.

1 This invention relates to alloys. and in particular to alloys having highstrength and corrosion resistance at room and elevated temperatures. I

(Ci. 'l5-171) 2 in conjunction with the accompanying drawing, in which:

At the present time there are a number of alloys available which are known to the trade as heat resistant alloys. The known alloys, however, usually have one or more disadvantages in that the strength at elevated temperatures is insutllcient for many modern applications or the oxidation resistance is poor or the-alloy cannot be readily forged. Among the known heat resistant alloys, the iron-nickel-chromium alloys have been generally considered as superior alloys, the chromium imparting `oxidation resistance while the nickel tends to maintainl the alloys austenitic, that is, having a face-centered-cubic crystal structure. Although superior to the ferritic iron-chromium alloys, nevertheless. the strength'of the austenitic iron-nickel-chromium alloys diminishes quite rapidly with an increase in temperature, it being found. for example, that alloys of the iron base type containing 25% chromium and 20% nickel have only half the strength at 650 C. that they have at room temperature. Further, the available alloys are also relatively weak at room temperature, the speciilc 25-20 alloy referred to hereinbefore having a tensile strength of only 82,000 pounds per square inch at room temperature.

Certain alloys have been produced in which the elementsv such as beryllium, titanium and aluminum have been utilized to impart precipitation hardening characteristics. These elements however are not satisfactory since alloys containing and depending only upon such precipitation hardening elements for their hardness do not have the characteristic of permanently retaining such hardness when subjected to 'extended heating at elevated temperatures, such as are contemplated as the working temperatures for the alloy of this invention.

It is an object of this invention to provide an alloy having oxidation resistance and high strength at elevated temperatures.

Another object of this invention is to provide an alloy capable of substantial precipitation hardening and having oxidation resistance and high strength at elevated temperatures.

A further object is to provide an austenitic alloy having high strength at room temperature.

A more specic object of the invention is to provide an austenitic alloy containing nickel, chromium, molybdenum and manganese which can be forged and precipitation hardened.

Another object oi' this invention is to provide a precipitation hardened alloy having the characteristic of retaining its high temperature properties after prolonged or repeated exposure to elevated temperatures.

Other objects of this invention will become apparent from the following description when taken Figure 1 illustrates the maximum hardness ob.-

tained by heat treatment in alloys of this invention with respect to the molybdenum content.

Fig. 2 is a graph, the curve of which illustrates the maximum hardness of the alloys of this invention in terms of a relation between the alloying constituents. l

Fig. 3 is a graph, the curves of which illustrate the hardness obtained in terms of the relation of the constituents of the alloys of this invention after diilerent heat treatments, and A Fig. 4 is a graph, the curves of which illustrate the hardness obtained on a particular alloy of` this invention as heat treated for diierent periods of time.

We have found that alloys of the heat resistant type can be produced having vhigher strength and good corrosion and oxidation resistance at both room and elevated temperatures, the higher strength being imparted to the alloys by precipitation hardening treatment. In general this application is directed tov alloys containing primarily chromium, nickel, molybdenum and manganese which are precipitation hardened by quenching lthem from a. high temperature and thereafter aging them at a somewhat lower temperature to give the alloys high strength at room and elevated temperatures.

In particular, the heat treatment which has been found suitable for developing the desired characteristics in the alloy of this invention comprises quenching the alloy from a temperature between 1000 C. and 1300,o C. and aging it at a temperature between '100 C. and 1000 C., the aging temperature usually being at least 200 below the quenching temperature. Preferably the heat treatment comprises quenching from a temperature between 1040 C. and 1260o C. and aging the quenched alloy at a temperature between 750 C. and 950 C.

For some types of service however, where the creep rate at operating temperatures must be very low, the alloys of this invention may be utilized in either the as quenched or under aged state. By under aged is meant the aging to less than ymaximum hardness for the aging time interval chosen. We have found that in this incompletelyaged condition the rate of creep is lower than as aged to maximum hardness prior to service.

Generally the period of time of aging the alloy depends upon the aging temperature. Practically, however, the aging temperature for any ing, referred to hereinafter, higher hardness canbeobtainedonanyofihealloysiftheyare aged orlongerperiodsoftimeatlowertemperatures. The of the constiulents of the alloyrnaybcvairlcdoverwider-angesinapte-` determined manner as will be explained more fullyhereinafter Mtinorderthattheresulting alloy may be foxgeableit is essential that the molybdenum coniznt should be maintained at not more than 20%. lnxgeneral, the alloy comf position may range fromliil. to 28% chromium. from20%to80% nickel.from4%to20% of molybdemmimm-upto3% of manganese withthebalanceirmandnotmorethan 1% of impurities auch as carbon and the deoxidizers, silicon, vanadium, titanium and/or aluminum. The 4manganese is included to improve workibility. l In the alloy of this invention. the molybdenumeontentismaintainedatnotlessthan4% in order to insure precipitation hardening characteristics, it being found that molybdenmn in the range 4% to 20% is a 'very active precipitation hardening agent in the alloy. While molybdenumis employed as the precipitation hardening agent the other alloying elements have an elect on the characteristics of the alloy and thereiationofthealloying consiituentsinthe alloymust be carefully controlled asP will be explained hereinafter. i It is preferred to maintain the carbon content of the valloy at less than 0.2%. This is because ithasbeenfmindthat carbonio amounts above 0.2% is harmful in that it forms carbides with chromium and molybdenum. thereby lowering both oxidation resistance and response to precipitation hardening treatment.

nickel content is given as 20% inorderthattheresultingalloywillhavean entirely anstenitic strnctine. Alloys having lower nickel contents and containing chromium and molybdenum in varying elective amounts may contain the ferritic or sigma phases after having been subjected to precipitation hardening heat treatment whereas the alloys of this invention are free of the sigma phase. Although the upper g5 to or is greater than [2T-0.2 Nll.

inbefore as 60%. because of metallurgical economies it is preferred to utilize 52% as the upper limit of nickel where the chromium and molybdenum are introduced rinto the alloy in the form of ferro-alloys. This, however. is not a limiting factor as it may be desirable to form the `alloys of this invention from pure chromium and molybdenum.-

The chromium is primarily utilized for imlo partingr corrosion and oxidation resistance to thealloy, it being found that not less than v16% chromium is necessary in the present alloy for giving the required corrosion and oxidation resistance to the alloys which will permit its use l5 at temperatures up to 870 C. (1600 FJ. The

upper limit of 28% is established for the chromium content since it has been found that no advantagev in tensile strength and other desirable characteristics can be obtained by increasgo ing the chromium content beyond this point. In

general, from our investigation it can be said that the chromium content required for imparting a high degree of corrosion and oxidation resistance to the alloy of this invention is equal The actualchromium content needed for a particular application will depend. in addition to the nickel,

on the service temperature and the life desired at that temperature.

30 The chromium and molybdenum are readily introduced into the melt in forming the alloy by utilizing a 70% ferro-molybdenum and a '10% 5 ferro-chromium alloy. Such alloys are available and are a more economical medium for obtaining a5 a given molybdenum and chromium content than 40 parent the cost of the alloy is decreased as the iron content is increased. However, it has been found that the best physical properties are obtained with a low iron content.

As representative of alloys within the broad 45 range given hereinbefore. reference may yhe had limit -of the nickel range has been given here,- to.` the following table: f

Table I f Cmnponhon; weight percent Hardnessl l om ailoyNo. sqxrhm tegn Fonbility N1 cr M0 Mn 150 C 850 c. we.

:a5 124 5.0 1.5 10o m0 000 Good. :as 20.2 14.8 1.a zn 25s 1100 D0. aai 11.4 15.4 111 250 34o 20o am Fair. 3.0 25.0 15.0 0.1 Nogood.

K, 20:5 214 ma 111 20a 341 :a4 81o Fair.

aan 2.0 lsov 0.1 Pour. 53.9 13.0 11.9 es 240 :451 an 925 Good. 45.8 v5.0 18.0 0.7 Nogood. m5 25.2 13.8 0.1 24o :n1 :no 1100 Fair. :1.5 zio 1112 0.1 m4 :421 20s M5 Good.

:a2 24.2 10.1 0.1 210 290 24o 000 Do.

- 51.8 21.3 a9 0.1 200 290 215 nooA D0.

2115 24s 1.1 0.1 241 15: 335 050 Fair. 4119 252 1.6 0.1 11s :so 255 000 Good. aus 242 1.6 01 19s `A:112 205 045 Dn. :|14 24.1 4.0 0.1 115 an 225 050 Do. :0.5 24.5 6.0 0.1 104 :104 29o am Do. :|15 21.3 5.9 0.1 224 aas 315 050 Do. :0.4 24.1 0.2 25 212 m :|01 Do. 40.5 21a so 1.1 171 25s Do. 41.5 25:0 13.0 0.1 2110 544 Fair. 411s m0 11.0 0.1 245 :44o dood. :5.0 245 0.a 0.1 25o 325 Do. :n1 21.1 13.2 00 211 sas Do. 35.0 :a5 11.4 0.1 255 :a5 Fair. a1.: 11.8 c4 0.1 m m0 Good. 25.1 22s 3.0 21 au Do. :n.0 242 1.0 21 215 1 Do. :no 2110 15.0 2o 231 Do. 50.0 10.0 111s 20 214 Do. 411.4 19.0 14.8 0.1 225 :425 20o 950 Do.

In the foregoing table each of the alloys listed contain about 0.4% silicon and about 0.1% carbon with the balance of the alloying constituent being iron with negligible amounts of the deoxidizers and other impurities. The heat treatment applied is indicated as comprising quenching the.- alloys from 1150 C. and subjecting them to different ing treatments consisting of aging them at 850 C. and at 950 C.

Referring to Fig. 4 of the drawing, there is illustrated typical hardness curves for a representative alloy of this invention. These curves are based on alloy #4111 given in Table I and which has been quenched from 1150 C:, curves Il, I3 and I5 representing the hardness of the alloy as aged at 850 C., 900 C. and 950 C, respectively for different periods of time. As illustrated the maximum hardness for this particular alloy as aged at 950 C. is obtained after 20 hours of aging.

In aging the alloysan accurate record was kept of the aging temperature at which maximum hardness is reached in 20 hours and this temperature is listed in the table as the characteristic temperature. Such characteristic temperature indicates the relative thermal stability of the group of alloys as a whole and also measures the relative stability of the individual alloys.

As is evident, the variable nickel,`chromium, molybdenum constituents have an effect on the hardness of the resulting alloys. In order to relate these elements with respect to the hardness, an empirical formula has been derived, the terms of which must be satisfied in producing the alloy of this invention having the desired degree of precipitation hardening and required forging characteristics. In this formula, the respective contributions of molybdenum, chromium, manganese and nickel to the precipitation hardening are evaluated quantitatively, and from it a number, called for convenience, the percent effective molybdenum content, is calculated. This formula is effective molybdenum=% Mo+0.8 Cr) +0.75

(% Min-0.25 rin-1.5]

From the formula, it is evident that the elements chromium and manganese act to increase the molybdenum hardening efl'ect While nickel decreases such effect.

The following Table II gives the percent effective molybdenum content found in accordance with the foregoing formula for the alloys of Table I.

Table II .muy No f Forgenbility 13.3 N 2001i 12.8 D0. l2. l Poor. l1. l Fair. 10. 4 Do. 10.`4 Do. 10.2 Do. l0. 2 Do. 10.0 Do. 10.0 Good. l0. 0 Do. 10.0 Do.

9. 9 Do. 9. 9 Do. 9. 8 Do. 9. 8 Do. 9. Do. 9. 4 Do. 9. 2 Do. 9. 1 Do. 8. 9 Do. 8. 8 Do. 8. 6 Do. 8. 4 Do. 8. 3 Do.

Percent n.Mo, Foraenbuny tween hardness as aged and actual molybdenum' content, the scatter being the result of the effects of the variable nickel, chromium and manganese contentsA on the precipitation hardening. However, by utilizing the empirical formula given for the effective molybdenum content a well defined relation between maximum hardness and the effective molybdenum content is obtained -as illustrated by curve I0 of Fig. 2.

Similar results are found when the effective molybdenum content is also plotted against the hardness of the alloys as quenched from 1150 C. and as quenched and then aged at 950 C. Representative curves of such relations are given in Fig, 3 in which curve I2l represents the hardness in terms of the effective molybdenum content of the alloy as quenched from 1150 C., curve M represents the hardness in terms of the effective v molybdenum content for the alloys as quenched from 1150 C. and aged at 850 C. and curve It represents the hardness in terms of the effective molybdenum content for the alloy as quenched from 1150 C. and aged at 950 C. From these curves it is seen that the precipitation hardening effect commences at an effective molybdenum content of about 6% and does not become appreciable until the effective molybdenum content reaches 8%. It is therefore preferred to maintain the lower limit of effective molybdenum con.. tent at not less than 8%.

In Table II, the alloys of Table I are listed in order of decreasing effective molybdenum content so as to illustrate the relation between forge.. ability and effective molybdenum content. We have found that a definite line of division in terms of the effective molybdenum content can be drawn between the alloys having poor and fair forging characteristics at an effective molybdenum content `of 11.5%. However, for the purpose of this invention it is preferred to limit the upper limit of the effective molybdenum content to 11% because alloys with an effective molybdenum content greater than 11% contain an excessive amount of undissolved hardening constituent in the as quenched condition. As may be seen by referring to Fig. 3, the as quenched hardness equation for the effective molybdenum content ,e

have good corrosion resistance and high strength,

it is found that certain of the alloys have an exceptional high strength in excess of 29,000 lbs. per square inch at an elevated temperature of about 870 C. Through numerous experiments it inch per inch per minute on a number of alloys including` the more specific range given herein-L before are given in the following table:

Table III Composition, wt. percent Per Tensile Percent Per-` y ft Strength. elw- Nl or Mo Mn Mo *lm-L 0n area 4090--. 53.9 18.0 17.9 0.8 8.9 36,900 54 84 4111.-- 31.5 23.0 10.2 0.7 9.9 29,100 42 62 4135. 40.9 25.2 7.6 0.7 8.3 3,600 30 35 4161..- 30.4 24.7 4.0 0.7 7.5 24,000 l 20 4162... 30.5 24.6 6.0 0.7 8.5 @,Zl 9 l2 4165.-- 30.4 24.7 6.2 2.5 9.4 25,800 34 58 4189..- 40.5 25.3 6.0 1.1 7.7 272m() 14 14 4219..- 47.6 25.0 y13.0 0.7 10.0 31,500 26 40 4210.-- 40.8 25.0 11.0 0.7 9.9 31,111) 15 18 4211--- 35.9 24.5 i 9.9 0.7 i 9.8 30,000 13 14 4218.-- 39.7 21.7 13.2 0.6 9.8 31,600 18 27 M-l56- 48.4 19.9 14.8 0.7 8.8 35,300 7 `8 The alloys were heat treated to produce maximum hardness in an aging period of( 20 hours and then .stabilized for 20 hours at a temperature of 870 C. (1600 F.) prior to the testing. By referring to Table III, it is apparent that a number ofthe alloys in the specific composition range did not have the required strength' of 29,000 pounds per square inch at 870 C. even though they satisfy the requirement of the formula for effective molybdenum content.

We have found that the tensile strength a .by the solid solution molybdenum formula and the tensile strength at 870 C. are set forth, it is evident that'only those alloys having a relation of the constituents thereof to givea solid solution content equal to or greater than will have the `required strength.

Table 1V l Approximate Tensile scent strength Alloy No. mo ybdenum at 870 C.,

in soli pounds solution per sq. in

l5. 0 36. 900 l2. 0 35, 300 9. 4 3l, 000 9. 0 3l, 600 7. l 31, 100 6. 3 29, 100 -6. l 30, 600 6. 3 28, 600 4. 3 27, 200 3. 5 28. 210 2. 8 Zi. 800 2. 4 24, 000

From this table it is apparent that the amount of `molybdenum in solid solution in the alloy has a f ployed attemperatures up to 870 C. have the f denum content in order to have the required these elevated temperatures depends chieny on 1 the molybdenum content of the solid solution matrix, the precipitation hardening being eifective at the lower temperatures. In the as quenched condition, the molybdenum content of the solid solution nearly equals the total molybdenum content of the alloy and during aging'it decreases by the amount of molybdenum which is precipitated. If the aging were carried to a cmplete equilibrium condition, the solid solution would be depleted to the molybdenum content equivalent to 6% effective molybdenum. Practically, however, aging is carried only to the state of maximum hardness, at which point, an estimated 50% of the molybdenum has been precipitated. Hence as aged to maximum hardness the molybdenum content in solid solution can be calculated from th'e equation:

% Mo in s. s. f i

=% Mol/2 Mo available for precipitation) or y % Mo in S. S.=% Mo-(% eff. Mo-6) If in the latter formula, the formula for the effective molybdenum is substituted, then strength and good forgeability.

The alloys in this group which satisfy both the effective molybdenum and solid solution molybdenum formulae have a high resistance to creep. As a specinc example, reference may be had to the alloy identified as M-l56 in Table III which has a minimum creep ,rate of 2.4X 104 inch/inch/ hour at 650 C. under a stress ofy40.000 pounds per square inch. l

v Where consideration must be given to the cost ofthe alloy and the requirements of service are such that the alloy will be subjected to temperatures below 800 C., then the composition is preferably within the range of 20% -to 40% nickel,

classification, reference may be had to the folv lowing Table V:

Table V Composition, wt. Per Alloy percent cent T. S., Percent pement No. l eil. #/Sq. elong. :w

Ni Cr Mo Mn M 4162. 30. 5 24. 6 0 0. 7 8. 5 55, 1m 8 10 4163. 30. 6 27. 3 5. 9 0. 7 9. 5 6l, m0 5 7 4165-.. 30. 4 24. 7 6. 2. 5 9. 4 4s, 9m l5 17 4374. 25. l 22. 8 8.0 2. l 10. 0 56, al) m 30 4375. 30. 0 24. 2 7. 9 2. l 10. 0 56, m) l1 l5 The tensile strength given in the foregoing table is that obtained at 760 C. (1400 F.) and` Silicon and titanium additions within low limits act to increase the precipitation hardening of the alloy. This is because, qualitatively, these elements reduce the solid solubility of molybdenum and serve to increase the amount 'of molybdenum which is precipitated. Through numerous experiments it has been found that additions of silicon and/or titanium in amounts greater than those employed for deoxidizing purposes and preferably up to 2.5% silicon and/or 3% titanium in the resulting alloy, have an eilect on the precipitation hardening which is additive to the effect of the chromium and manganese additions. It is therefore necessary to modify the formula for the effective molybdenumcontent given hereinbefore where the alloy contains either or both silicon and titanium as essential alloying elements to maintain the effective molybdenum content within the limits of 8% to 11% as established hereinbefore. This modied formula is as follows:

In the following table a number of representative alloys containing either or both silicon and titanium are listed together with some of the properties of the alloys, it being understood that the balance of the alloying composition is iron and not more than 1% of impurities.

10 replace a larger amount of the molybdenum, thereby giving a more economical alloy with little or no loss in tensile strength at temperatures of 650 C.

Where expense is no criterion, then an alloy composed of 59% nickel, 20% chromium, 20% molybdenum, 0.6% manganese and the balance deoxidizers plus impurities, can be advantageously employed, it being found that such an alloy can be cast and precipitation hardened by the treatment given hereinbefore to a hardness in excess of 300 DPH. If it is desired to achieve maximum strength at 870 C. in forgeable alloys then a composition such as alloy No. 4545 listed in Table I can be used. In both of these alloys iron is present only as an impurity. In this type of alloy it is preferred to maintain the composition within the ranges of 52% to 60% nickel, 16% to 28% chromium, 8% to 20% molybdenum, from traces up to 3% manganese with less than 1% of impurities including iron, with the alloying components having the relation satisfying the equations for the percent effective molybdenum and percent molybdenum in solid solution.

In all of the alloys referred vto hereinbefore,

manganese is present in order to improve workability of the alloy. Further, although the nickel content is given within certain specic ranges, the actual nickel content of the specic alloys listed includes incidental cobalt, it being found Table VI e Composition, weight percent Percent Hardness as Mo quenched e from 115o C. N1 Cr Mo Mn S1 Ti 30.0 18.0 10.0 1.3 0.5 2.8 10.6 263. 30. 4 18. 9 10. 1 0. 7 l. l 2. 0 l0. 3 232 30. 4 22. 3 10. 3 0. 7 0. 6 l. 0 l0. 7 265 30.4 24.8 6.2 -0.7 0.6 0.5 9.2 194 31.6 24.7 5.6 0.7 1.9 9.1 225 30.8 25.0 6.2 0.7 0.9 0.9 9. 7 238 30.2 25.5 6.1 2.1 1.2 10.0 205 26.3 22.8 4.1 2.1 2.2 9.0 198 2l. l 21.2 6.3 2.0 1.5 9.6 240 25.1 23.0 6.0 2.0 2.0 10.0 224 30.0 24.1 6.1 2.1 2.1 10.0 221 20.2 17.6 6.0 2.0 2.0 8.5 Y 174 25.2 19.8 8.1 2.1 2.0 9.8 212 30.2 22.0 8.0 2.1 2.0 10.0 234 29.8 25.3 6.1 0.7 0.6 0.3 9.3 200 42. 2 22. 5 11.6 1. 7 1. 6 10. 1 247 In the table the effective molybdenum as calculated by the formula for the alloys containing silicon and/or titanium is given. It is of course apparent that where titanium is not present, that the titanium factor in the formula becomes zero and can be ignored. By utilizing the formula the optimum compositions can be selected from the infinite number which it is possible to form in the broad ranges given for the different alloying elements, thereby reducing the possible combinations to include a relatively small number of correctly balanced compositions.

The tensile strength recorded is that obtained at 6 50" C. (1200 F.) with a strain rate of 0.017 inch per inch per minute. The precipitation hardened alloys containing silicon and/or titanium within thev ranges given are particularly useful at temperatures in the neighborhood of 650 C., where the effects of the precipitation hardening predominate as opposed to those alloys which are to be employed at the higher temperatures in the neighborhood of 870 C. where the amount of molybdenum in solid solution is of primary importance. In these austenitic alloys the relatively small amounts of silicon and/or titanium that the nickel metal contained about 1% cobalt as is usual in the nickelv supplied to the trade.

The alloys of this invention are austenitic, that is, they have a face-centered-cubic crystal structure andl have exceptional corrosion resistance and high strength at elevated temperatures, the composition of the alloy being determined by the temperature to which the alloy will be subjected in industry and the cost that the application can absorb. The alloy having the higher nickel content and illustrated by certain specic compositions in Table III and Whose alloying constituents have a relationwhich will satisfy the formulae for the effective molybdenum content and the solid solution molybdenum content are particularly applicable for use in gas turbines where it is necessary to employ an alloy having relatively high tensile strength and a. high degree of oxidation resistance. Further, these alloys are particularly adapted for use as parts of turbines where the temperature gradients range from the maximum down to as low as room temperature and where the turbine parts may be subjected to stresses which vary inversely with the temperature. These particular alloys have adequate strength at all temperatures up to 870 C. (1000 F.) with the advantage over previous known alloys increasing as the temperature approaches 8"(0I C.

All of the alloys of this invention have an un-l 40ans 12 5.Amechanicale1ementwhichistobesub riectedtoatemperatureof atleast" C.and

considerable stress in normal use consisting of a heat resistant alloy comprising to 60% nickel, 16% to 28% chromium, 4% to20% molybdenum, less than 0.20% carbon, from traces up to 3% manganese, and the balance 'iron except the usual contaminants in common amounts, the alloy being precipitation hardened and havingthe relation among the allcying components that 1/ Mai-0.8 Cr) +0.75 Mn) A.

0.25 iiD-1.5] :3%- t0 11% 2. A mechanical element which is to be subjected to a temperature of at least 650 C. and considerable stress in normal use consisting oi a heat resistant alloy containing 20% to 52% nickel, 16% to 28% chromium, 4% to 20% molybdenum, from traces up to 3% manganese, less than 0.20% carbon, and the balance iron except for .the usual contaminants in common amounts, the alloy being a precipitation hardened austenitic alloy and having the relation among its alloying components that 3. A mechanical element which is to he subjected to a temperature of" at least 650 C. and considerable stress in normal use consisting of an age hardened alloy comprising 20% to 52% nickel, 16% to 28% chromium, 4% to 20% molybdenum, from traces up-to 3% manganese, less than 0.20%

carbon, and the balance iron except from the y usual contaminants in common amounts, which has beenquenched from a temperature between 1040 C. and 1260 C. and aged at a temperature between 750 C. and 950 C. the alloy having the relation among its alloying components that umis greater than27-02 Ni),

t M0+0.8 y 0.25 Ni) -,1.5]=8% |20 11% and g la [et nro-0.a cio-0.15 (a. un)

- 0.25 Ni) is greater than 6%.

. e stress in normal use consisting of a heat resistant alloy comprising 30%- to 60% nickel, 10% to28% chromium,f8% to.20%lmolyb denum, from traces up to 3% manganese, less than 0.20% carbon, and the balance iron with not more than 1% of impurities, which/has been quched from a temperature between 1040 C.

and 1200' C. and aged at a temperature between 750" C. and 950 C., the alloy having the relation its alloying components that the chromium is greater than 27-,02 0% Ni),

v 0.25 Ni)-| 13.5l is greater than 6%.

8. A mechanical element which is to be subjected to a temperature of at least 650 CC.k and considerable stress in normal use consisting of a precipitation hardened austenitic alloy comprising 20% to 40% nickel, 16% to 28%. chromium, 4% to 10% molybdenum, from traces up to 3% manganese, less than 0.20% carbon, and the balance ironand incidental impuritiesI ,the alloy h avhig the relation among its alioying compoments that t MIM-0.8 (7a Cr) +0.75 Mn) L A mechanical element which is to be suhjected to a temperature of atleast 650 C. and considerable stress in normal use consisting oi' an age hardened alloy comprising 20% to 40% nickel, 16% te 28% chromium, 4% to 10% molybdenum,

from traces up to 3% manganese, less than 020% carbon, and the balance iron. with not more than 1% o impurities, the alloy having the relation among its alloying components that the chromium is greater than 21-02 Ni) and 8. A mechanical elementwhich is to lbel subjected to a temperature oflat least 650 C. and considerable stress in normal use eonsistingof a heat resistant alloy consisting of 20% to 60% nickel, 16% to 28% chromium, 4% to: 20% molybdenum, from traces up to a 3%y \n1anganese from traces up to 2.5% silicon, less than. 0.20% carbon, and the balance iron with not more than 1% of impurities, the alloy being precipitation hardened and having the relation among its alloying conrponents that 9. A mechanical element which. is to be suh- Jected toa temperature of at least 650 Cf. and

considerable stress in normal use consisting of a heat resistant alloy consisting of 20% to 60% nickel, 16% to28% chromium, 4% to 20% molybdenum, from traces up to 3% manganese, from traces up to 2.5% silicon, from traoesuptoait titanium, less than 0.20% carbon, and the iron with not vmore than 1% of impurities, the alloy being a precipitation hardened austenitic alloy and having the relation among its allow ing component: that .la les no+os (a, cr +o`15 @a mii-ry 1.6 (et 'rm-12 ea sac25 e% rui-sham to 11% 10. A mechanical element which is to be subjected to a. temperature of at least 650 C. and considerable stress in normal use consisting of a heat resistant alloy consisting of 20% to 60% nickel, 16% to 28% chromium, 4% to 20% molybdenum, from traces up to 3% manganese, from traces up to 2.5% silicon, from traces up to 3% titanium, less than 0.20% carbon, and the balance iron with not more than 1% of impurities, which has been quenched from a temperature between 10 1040 C. and 1260o C. and aged at a temperature between 750 C. and 950 C., the alloy being austenitic and having the relation among its alloying components that the chromium is greater than 27-0.2 Ni), and that 11. A mechanical element which is'to be subjected to a temperature of at least 650' C. and considerable stress in normal use consisting of a heat resistant alloy consisting of 52% to 60% nickel, 16% to 28% chromium, 8% to 20% molybdenum, from traces up to 3% manganese, less Ithan 0.20% carbon, and less than 1% of impurities including iron, the alloy being precipitation hardened and having the relation among its a1- loying components that 1/2 Mo-|0.8 Cr) +0.75 Mn) 0.25 Ni)-1.5]=8% to 11% and is greater than 6%.

HOWARD sco'rr. ROBERT B. GORDON.