US3663213A

US3663213A - Nickel-chromium-iron alloy

Info

Publication number: US3663213A
Application number: US36420A
Authority: US
Inventors: Herbert Louis Eiselstein; Edward Frederick Clatworthy
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1970-05-11
Filing date: 1970-05-11
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16

Abstract

A strongly age-hardenable alloy having low annealed base hardness, high strength in the aged condition, excellent weldability and unexpectedly good machinability contains about 35 percent to about 46 percent nickel, about 12 percent to about 20 percent chromium, about 1.25 percent to about 2.5 percent titanium, about 2.25 percent to about 3.5 percent columbium, up to about 0.08 percent carbon, about 0.0005 percent to about 0.006 percent boron, about 0.05 percent to about 1 percent aluminum and the balance essentially iron.

Description

United States Patent Eiselstein et al.

[ 1 May 16,1972

1541 NICKEL-CHROMIUM-IRON ALLOY [72] Inventors: Herbert Louis Eiselstein; Edward Frederick Clatworthy, both of Huntington, W. Va.

The lnternational Nickel Company, Inc., New York, N.Y.

[22] Filed: Mayll,1970

[21] Appl.No.: 36,420

[73] Assignee:

Related U.S. Application Data [63] Continuation-in-part of Ser. No 10,004, Feb. 9, 1970, which is a continuation-in-part of Ser. No. 766,611,

Oct. 10, 1968.

[52] U.S. Cl ..75/l24, 75/128 R, 75/128 G, 75/128 T [51] Int. Cl ..C22c 39/20 [58] Field of Search ..75/124, 1286 [56] References Cited UNITED STATES PATENTS 3,212,884 10/1965 Soler ..75/124 2,801,916 8/1957 Harris... ....75/128 G 3,540,881 11/1970 White ..75/128 G Primary Examiner-l-lyland Bizot Attorney-Maurice L. Pinel 57 ABSTRACT 7 Claims, No Drawings NICKEL-CHROMlUM-IRON ALLOY The present application is a continuation-in-part of our co pending US. application Ser. No. 10,004 filed Feb. 9, 1970, which in turn is a continuation-in-part of US. application Ser. No. 766,611, filed Oct. 10,1968.

The art pertaining to age-hardenable nickel-chromium and nickel-chromium-iron alloys having high strength and ductility at atmospheric temperatures and at temperatures up to say l,300 F. is now at a well-developed state. However, despite intensive development work over perhaps the past 30 years, problems still remain in this area. These problems include the provision of big ingots of satisfactory quality for conversion into sheet and other forms by rolling, hot and cold workability, transverse ductility, machinability, weldability, etc. Alloys of the type under consideration generally contain substantial quantities of elements such as titanium, aluminum, columbium, etc., to confer hardenability thereto. Many other elements including molybdenum, tungsten, etc., may also be included for the purpose of raising elevated temperature properties of the alloys. One result of the high alloy content employed is that the alloys at the ingot stage are stiff even at the high soaking temperatures employed prior to hot working so that it becomes an extremely difficult problem to reduce the ingots by hot working in conventional equipment. Another problem encountered in producing large ingots is that of difficulty in melting, a condition with is attributable to segregation in cooling and is evident as freckles in the macrostructure of the ingot. In a number of alloys currently being used, this problem cannot be solved by homogenizing heat treatments and hot working and can be sufficiently severe to cause rejection of ingots. The problem is particularly acute in relation to big slab ingots of sufficient width for conversion into plate and sheet.

Alloys of the type under consideration are frequently required to be provided in the form of sizable forgings which are then machined into product forms such as turbine wheels, shafts, rings, etc. Good machinability thus is highly important since, in many cases, substantial quantities of metal are removed by machining. Difficulties frequently have been encountered by way of high tool wear, poor surface finish, etc., in machining many of the stronger alloys currently being used. These difficulties have led to high costs and unsatisfactory results in machining.

Another problem frequently encountered with the stronger alloys currently used is that of weldability, particularly as ap plied to sheet form. Thus, weld cracking has been encountered both in connection with the welding operation itself and also when the weldment was age hardened to restore high strength after welding. In some alloys, the problem is so severe that the alloys are not considered commercially weldable.

Still another problem is that of providing ductility in the direction transverse to the working direction in such alloys. This problem is particularly severe in rotating parts such as shafts, rotors, rings, etc., which are highly stressed in service at temperatures over the range from about room temperature to about l,400 F. Many present alloys which are strong at room temperature and at elevated temperatures develop low ductility, e.g., a room temperature tensile elongation of 2 percent or less, whenmeasured in a direction transverse to the working direction. Such parts are usually hot worked to rough shape by processes such as forging, pressing, rolling, etc., and are then machined to finish dimensions, and the low transverse ductility which characterizes prior alloys has been a source of concern to designers.

It is to the solution of the foregoing and other problems that the invention is principally directed.

It is an object of the present invention to provide a strongly age-hardenable nickel-chromium-iron alloy which can be produced in large ingot forms by conventional melting and ingot casting.

It is another object of the present invention to provide an improved age-hardenable nickel-chromium-iron alloy having improved machinability and weldability both in the annealed and in the age-hardened condition.

it is a further object of the invention to provide a strongly age-hardenable nickel-chromium-iron alloy which is relatively soft in the annealed condition and is readily hot workable.

Still another object of the invention is to provide an alloy which develops good transverse ductility in the hot worked and age-hardened condition.

Other objects and advantages of the invention will become apparent from the following description.

Generally speaking, the present invention is directed to an age-hardening alloy having good melting characteristics, a low base hardness in the annealed condition together with good machinability, good transverse ductility, and weldability comprising about 35 percent to about 45 percent or 46 percent nickel, about 12 percent to about 18 percent or 20 percent chromium, about 1.25 percent to about 2.5 percent titanium, about 2.25 percent to about 3.5 percent columbium, with the sum of the percentages of columbium and titanium being at least equal to about 4 percent, at least about 0.05 percent or 0.07 percent to about 1 percent aluminum, not more than about 0.08 percent carbon, 0.0005 percent to about 0.006 percent boron and the balance essentially iron. Preferably, the alloy contains about 14.5 percent to about 17.5 percent chromium, about 39 percent to about 44 percent nickel, about 1.5 percent to about 2 percent titanium, about 2.5 percent to about 3 percent columbium, at least about 0.001 percent boron, and about 0.1 percent to about 0.4 percent or 0.5 percent aluminum.

In the alloy, the nickel and iron contents are highly important and the nickel content is controlled within the range of about 35 percent to about 45 percent with the balance of the alloy being iron so as to secure a strong age-hardening effect despite the fact the alloy contains relatively small amounts of age-hardening ingredients. Chromium imparts oxidation resistance. Chromium at a level of about 15 percent or about 15.5 percent maintains the alloy in an essentially non-magnetic condition, i.e., maintains permeability below about 1.02. The principal age-hardening ingredients in the alloy are titanium and columbium which are employed in amounts of about 1.25 percent to about 2.5 percent and about 2.25 percent to about 3.5 percent, respectively, with the total content of these elements being at least about 4 percent to obtain good strength in the age-hardened alloy. Aluminum is employed in amounts not exceeding about 1 percent since paradoxically it is found that aluminum tends to reduce yield strength of the age-hardened alloy in some age-hardened conditions. Preferably, the aluminum does not exceed about 0.4 percent in order to mitigate the effect of this element in reducing strength of the age-hardened alloy and further to avoid the possibility of strain age cracking in welds. However, aluminum plays an important role in the alloy and must be present in a small significant amount of at least about 0.05 percent or about 0.07 percent or 0.1 percent in order to confer transverse ductility to the alloy in the hot worked and aged condition. In this respect, aluminum appears to cooperate with the controlled boron content employed in the alloy. Titanium is preferably employed in amounts of at least about 1.5 percent to about 2 percent and columbium in amounts of about 2.5 percent to about 3 percent. Such amounts of the primary agehardening ingredients confer strong age-hardenability to the alloy, minimize the possibility of undesirable segregation in the production of large ingots and provide a low base hardness in the annealed alloy. Tantalum may be substituted for columbium in equi-atomic amounts, but is less preferred because of the high atomic weight of tantalum. The carbon content of the alloy does not exceed about 0.08 percent, preferably not more than 0.06 percent. As a result, only a small amount of carbide is found in the microstructure of the alloy. Boron in the alloy contributes to stress-rupture ductility, but can lead to undcrbead cracking in welds and acts toward reduction of transverse ductility. Accordingly, the boron content does not exceed about 0.006 percent and is present in amounts of about 0.0005 percent to about 0.005 percent.

Alloys provided in accordance with the invention contain not more than 0.35 percent manganese, not more than about 0.35 percent silicon, not more than 0.3 percent copper, and not more than about 1 molybdenum. Molybdenum in amounts exceeding about 1 percent significantly stiffens the alloy matrix both at room temperature and at metal hot working temperatures and increases processing difficulties particularly in large sections. Impurities such as sulfur and phosphorus are kept to low levels not exceeding about 0.015 percent each. Cobalt does not contribute to useful properties in the alloy and is not deliberately added thereto. This element, like molybdenum, raises cost and cobalt is objectionable for uses in which radiation may be encountered.

The alloy is readily workable both hot and cold and can be aged either directly in hot or cold worked product forms or after an anneal in the temperature range of about 1,700 F. to about 1,950 F. or about 2,000 F. Annealing times of about 1 hour per inch of section are satisfactory. The alloy responds to aging treatments over the temperature ranges of about 1,l F. or 1,200 F. to about 1,400 F. which may be carried out for periods of time of about 4 hours to about 16 hours, e.g., about 8 hours. It is found that material annealed at temperatures above 1,750 F. develops better 1,200 F. stress-rupture ductility if an intermediate aging step in the temperature range of about l,500 F. to about 1,600 F., e.g., 1,550 F., for a time period of about 1 to about 8 hours, e.g., 3 hours, is also employed, thereby providing a three-stage aging treatment. A preferred aging treatment comprises a heating in the temperature range of about 1,300" F. to about 1,400 F. for about 8 hours followed by furnace cooling at a rate of about 100 F. per hour to 1,200 F. and holding at about 1,150 F. to 1,200 F. for about 8 hours. In the annealed condition, the alloys are quite soft and ductile, generally having room temperature yield strengths as determined in wrought material in the range of about 35,000 to about 50,000 pounds per square inch (p.s.i.). In the aged condition, wrought products made of the alloy will have in sections ranging up to about 3 inches a room temperature yield strength of about 140,000 p.s.i. or 150,000 p.s.i. or higher together with substantial ductility.

The low annealed base hardness and high strength in the aged condition provide substantial advantages in the alloy from the standpoints of mill production, component fabrication and end use. In addition, the alloy demonstrates excellent weldability in both annealed and aged conditions, and weldments can be aged without encountering weld cracking. Furthermore, the alloy provides unexpectedly good machinability in both the annealed and aged conditions. When compared on an equal strength basis with prior age-hardenable nickel-chromium alloys intended for elevated temperature service, the machinability of the alloy is very good indeed.

In order to give those skilled in the art a better understanding and/or appreciation of the advantages of the invention, the following illustrative examples are given:

EXAMPLEI A series of 15 kilogram vacuum melted heats was prepared and cast into 4 inch X 4 inch ingots. The ingots were homogenized at about 2,100 F. to 2,150 F. for 12 to 16 hours and air cooled. The material was reheated and forged to 2-% inch square bars. Transverse slices prepared from the forgings demonstrated that the material was sound and devoid of segregation. The analyses of nine heats prepared as aforedescribed are set forth in the following Table I:

TABLEI Percent Alloy No. 0 Ni 01' A1 Cb Ti 13 Fe 14.91 0.22 3.06 1.24 N.d. Bal. 14.64 0.21 2.91 1.45 0.001 Bel. 15.00 0.18 2.77 1.42 0.0012 Bal. 14.82 0.10 2.78 1.42 0.0013 Ba]. 15.12 0.20 2.41 1.86 0.0012 Bal. 15.27 0.19 2.54 1.90 0.001 Bal. 14.07 0.10 2.52 1.83 0.001 Bal. 15.88 0.22 2.71 1.68 0.0006 Bal. 15.82 0.19 2.71 1.63 0.0043 Ba].

NOTE.Ihe alloys in Table I contained about 0.01% manganese,

about 0.04% to 0.07% silicon, not more than 0.03% copper, and not more than 0.006% sulfur.

1V .d iotdgtermined.

material from the 244 inch square forgings was subjected to room temperature tensile testing in various conditions of heat treatment with the results set forth in the following Table II:

TABLE 11 Yield strength (0.2% Tensile I offset), strength, EL, R.A., Alloy No Condition K s.1 K s.i. percent percent 1 As forged, aged 156.0 174.0 13. 0 21. 0 Annealed 1,000 F 34. (i 03. 3 51. 0 57. 0 Annealed 1,000 F., aged 154.0 178.0 16.0 27.0 Annealed 1,050 F 46. 5 100. 0 44. 0 48. 0 Annealed 1,050 F., aged 153. 5 176.0 16. 0 24. 5 Annealed 1,050 F., aged 3 151.5 178.0 15.0 25. 8 2 As forged, aged 2 161.0 170. 5 16. 0 20. 5 Annealed 1,000 F 34. 8 01. 7 48. 0 54. 7 Annealed 1,000 F., aged 151. 5 178.0 19. 0 26. 2 Annealed 1,950 F 36. 4 92. 7 45. 0 45. 8 Annealed 1,950 F., aged I55. 0 175. 5 l. 0 17. 5 Annealed 1,950 F., aged 3 152. 5 177. 5 19. 0 80. 0

3 As forged, aged 156. 0 178. 5 15. 0 26. 8 Annealed l,800 F-.. 39. l) 96. 8 39. 0 39. 0 Annealed 1,800 F., ag 153. 0 181.0 21. 0 30. 1 Annealed 1,000 F 35. 6 04. 0 50. 0 60. 3 Annealed 1,900 F., aged 152.0 170. 5 21.0 37. 8 Annealed 1,950 F 35. 6 03. 3 54. 0 58. 3 Annealed 1,950 F., aged 2 154. 5 178. 0 10. 0 33. 5

4 As forged, aged 2 157.0 178.5 17.0 31. 1 Annealed 1,900 F 35. 3 93. 4 40. 0 50. 3 Annealed 1,900 F., aged 152. 5 170. 5 22.0 38. 0 Annealed 1,950" F 37. 1 95. 3 53. 0 53. 3 Annealed 1,950 F., aged 2 153. 5 178. 0 20.0 34. 0 Annealed 1,950 F., aged 3 154. 5 178. 5 17. 0 25. 0

5 Annealed 1,950 F 35. 8 95. 8 52. 0 57. U Annealed 1,050 F., aged 151. 5 180. 5 20. 0 34. 0 Annealed 1,950 F., aged 156.0 182. 5 18. 0 33.5 Annealed 1,050 F., aged 4 152.5 182. 0 18. 0 30. 7

6 Annealed 1,1100" F 36. 6 07. 3 50. 0 57. Annealed 1,I00 F., aged 3 155. 5 183. 5 10. 0 .28. 0 Annealed 1,050 F 47. 6 04. 7 40. 0 57. 3 Annealed 1,050 F., aged 155. 0 180. 5 16.0 2-1. 0 Annealed 1,050 F., 1111011 157. 5 183. 5 l6. 0 33 0 Table ll- Continued 1 Aged 1,825 F./8 hours, furnace cool 100 F./hr. to 1,200 F., hold 8 hours, air cool. 2 Aged 1,350 F./8 hours, furnace cool 100 F./hrs. to 1,200 F., hold 8 hours, air cool. 3 Aged 1,375 F./8 hours, furnace cool 100 F./l1r. to 1,200 F., hold 8 hours, air cool.

4 Aged 1,400 F./8 hours, furnace cool 100 F./hr. to 1,200 F., hold 8 hours, air cool.

K s.i.=thousands of pounds per square inch. El.=elongation. R.A. =reduction in area.

NorE.Annealing times one hour, followed by air cool.

Forged material from Alloys Nos. 8 and 9 were subjected to stress-rupture resting at 1,300 F. and 75,000 p.s.i. with the about 0.08 percent manganese, about 0.11 percent silicon, 39.73 percent nickel, 15.99 percent chromium, 0.24 percent results set forth in the following Table III. aluminum, 1.61 percent titanium, 2.83 percent columbium, TABLE n 0.0026 percent boron and the balance essentially iron. The ingot was press forged to a 15% inch octagon which was then Life to machined to a 14 inch diameter round. Three inch slices were Alloy Rupture along" RA" cut from the head and toe ends of the forgingand were excondition hours ammed 1n the transverse and longltudmal directions. Ex-

amination demonstrated that the material was devoid of 8 Annealed "50F" segregatlon, and indicated that large slab ingots could be aged (3) 156.9 155 produced from the alloy usmg conventlonal vacuum-melting 8 Annealed 1850F., techniques without encountering melting difficulties. Three aged (3) 0 156-8 7 inch square material was forged to 2V8 inch square bars with 9 gzii g 166 5 23 5 46 forging temperatures of 1,900 F. and 2,050 F. Tensile, im- 9 Annealed 50F pact and stress-rupture properties of the two forgings were aged (3) 154.4 16.5 28.6 determined with the results set forth in the following Tables 1V and V: 35

TABLE IV Y.S. (0.2% CVN, ft. ll)s. ofi'set), I.S., El., R.A., Condition s.i. K s.i. percent percent Room 320 F.

Forging temperature: 1,900 F.

Annealed 1,700 F., aged 15s. 0 174.0 11.0 19. 0 Annealed l,750 F., aged 152.0 179. 0 16. 0 21. O 27. 5 26 Forging temperature: 2,050" F.

As forged, aged 3 156. 0 182. 5 18.0 29. 0 Annealed 1,700 F., aged 159.0 187. 5 16. 0 22. 5 Annealed 1,750 F., aged 156.5 183. 5 17.0 31.8 22. 5 20 Y.S.=yield strength. T.S.=tensile strength. CVN, ft.-lbs.=Charpy V-notch, foot-pounds.

TABLE V Stress rupture test Life, El., R.A., Co ditio conditions hours percent percent Forging temperature: 1,900 F.

Annealed 1,700 F., aged 1,200" F./100 K s.i 160. 2 3.0 3.0 Do.3 1,300 F./75 K s.i 104. 5 2. 5 4. 5 Annealed 1,750 F., aged 3 1,300 F./75 K s 71. 2 4. 0 7. 5

, Forging temperature: 2,050" F.

Annealed 1,700 F., aged 3 1,3o0 F./75 K s.i 101. 3 8. 5 11.5

EXAMPLE I1 Portions of the remainder of the ingot were converted into A 24 inch diameter vacuum-arc ingot was prepared from a composition which contained about 0.01 percent carbon,

inch diameter hot rolled bar stock and to 0.062 inch diameter cold rolled sheet. The tensile properties, Charpy V-Notch impact and stress-rupture properties of the material in the bar stock and sheet product forms are set forth in the following Tables VI, VII, VIII, IX and X:

were then welded in the holes using the manual argon-shielded tungsten-arc process, with matching filler metal being used in TABLE VI Hot rolled -inch diameter bar Y.S. T.S., K 5.1. Test (0.2

temp., offset) Smooth Notched EL, R.A., Condition F. K s.i. bar bar percent percent As rolled Room 78. 3 41 64. 5 As rolled aged 3 Room 164. 5 22 43. 2 Annealed 1,750 F Room 68. 45 50. 7 Annealed 1,750 I11, aged Room 158. 0 100. 0 256. 0 21 42 0 3 -320 180. 0 235. 0 281. 0 22 37. Do 3 1, 200 133. 0 147. 0 218. 0 23 48 Ii-r of notched b:tl'=li.3.

TABLE VII the case of the 1,950 F. annealed specimen. The welds were Hot rolled inch diameter bar aged at l,375 F. for 8 hours, furnace cooled at 100 F. per hour to 1,200 E, held for 8 hours at 1,200 F., air cooled. XQBA L 333, f-g gfg Simulated repair welds were then made over about 90 of arc C nditi Room 108 cycles at opposite sides of the disc within the initial weld using the AS rolled 135 5 239. 5 70 same welding technique and the welds were again aged using As rolled, aged 26.5-27.5 30-305 80 the same aging cycle. No weld cracks were detected at any I H280 'ijjjij 1%,, ig 98 stage of the operation, indicating good weldability for the alloy in this severely restrained test.

Machinability tests were conducted on a 3 /4 inch diameter TABLE VIII forging as annealed at l,850 F. for 1 hour, air cooled, and in Hot rolled %-ineh diameter bar the annealed and aged condition (aged l,375 F. for 8 hours, Life hours furnace cooled 100 F. per hour to 1,200 F., held 8 hours at 1,200" F., air cooled). In the machinability tests, an instrugfi gx gggi gg}. fi g g, mented variable speed lathe was employed using single point D h carbide tools. Each test tool was ground with a 0 back rake i'ggo igg' ,5 2 angle, a 5 side rake angle, a 5 end clearance angle, a 5 side 1I300 F./75 K s.i.: 39. 6 218.1 in 37. 5 clearance angle, 15 end cutting edge angle, a 15 side cutting NOTE.The material was annealed at 1,750 F. for one hour, aged 3. edge angle and a U3? Inch nose radlus' Tool pomt D=disc0ntinued; KT of notched bar=6.3. was taken as 0.015 inch flank wear. The cutting site was TABLE IX Cold rolled 0.062 inch sheet Y.S. 'I S., K s 1 Test 0.2% temp, oll'set), Smooth Notch EL, Condition F. K s.i. specimen specimen" percent As rolled Room 110.0 137. 5 u As rolled, aged 3 Room 187. 5 210. 5 Annealed 1,750 F Room 45. 0 111. 5 Annealed 1,750 F., aged 3 Room 176. 5 200.5 D0 3 1, 200 144. 5 168. 5 Annealed 1,850 F Room 44. 3 115. 5 Annealed 1,850 F., aged 3 Room 175.5 100. 5 D0 3 320 206. 0 260. 0 D0 3 1, 200 140 162. 5 Annealed 1,950 F Room 42. 0 111.0 Annealed 1,950 F., aged 3 Room 170.0 193.5 D0 3 320 195. 0 254. 5 1, 200 137. 5 160. 0

K of notched specimen=20.

TABLE X Cold rolled 0.062 inch sheet Stress-rupture test Life, El., Condition conditions hours percent Annealed 1,750 F., aged 3 1,200 F./100 K s.l 196.6 7 Annealed 1,850 F., aged 1,200 F./100 K s.i 113. 0 4 Annealed 1,950 F., aged 3 1 200 F./100 K s i 123. 5 2 Annealed 1,760 F., aged 3 1 300 F./75 K s 1 03.1 14 Annealed 1,850 F., aged 3 1,300 F./75 K s. 123.5 6 Annealed 1,950 F., aged 3 1,300 F./75 K 5.1 85. 8 5

Test specimens from the sheet material were subjected to the severe restrained welding test identified as the Pierce Miller patch weld test. In this test, a specimen of 0.062 inch cold rolled sheet of the alloy 4 inches square and with a central 2 inch diameter hole was welded symmetrically to a face of an age-hardenable nickel-chromium alloy strong-back made of Va inch thick plate 6% inches square and with a 3 inch diameter central hole so as to leave the hole in the sheet specimen unsupported. Two such assemblies were made which were annealed at l,750 F. for 1 hour and l,950 F. for 1 hour, respecflooded with coolant. A cobalt-bonded general purpose carbide tool of the WTiC type having a hardness of 91 on the Rockwell A" scale was employed. Data were obtained with 0.050 inch depth of cut at two feed rates and with two wearland conditions on the carbide tool point. Using a feed rate of 0.00825 inch per revolution with an 0.015 inch wearland, the cutting velocity for a 30 minute tool life (V30) was determined as being l68 surface feet per minute for annealed material and 182 surface feet per minute for annealed and aged material. With the heavier 0.01175 inch per revolution tively. Two inch diameter discs of matching sheet material feed rate and with an 0.030 inch wearland on the tool point,

the cutting velocity for a 30 minute tool life was determined to be 164 surface feet per minute for annealed material and 168 surface feet per minute for annealed and aged material. The machinability index for the material was determined on a comparative basis with other nickel-chromium alloys converted to a machinability index factor using the formula Machinability index (Mi) Material tested (V30) X100 10 Standard material (V30) Using as the standard material the forged alloy of the present invention in the'annealed condition, M, values were determined in comparison with five other nickel-chromium alloys (of which Alloys A, B and E are age-hardenable, while Alloys C and D are not) with the results set forth in the following Table X1:

TABLE XI Material Condition M, Alloy of this invention Annealed 100 Alloy of this invention Annealed and aged I08 Alloy A Hot rolled or hot rolled 50 and aged B Annealed 39 C Annealed 229 D Hot rolled 250 D Annealed 230 E Hot rolled 47 E Hot rolled and equalized 72 E Hot rolled and equalized 66 and aged Alloy A 52.5% Ni, 19% Cr, 0.5% Al, 0.9% Ti, 5% Cb, 3% Mo, balance Fe. Alloy B= 73% Ni, 15.5% Cr, 0.7% A1, 2.5% Ti, 0.95% Cb, balance Fe. Alloy C= 76% Ni, 15.5% Cr, balance Fe.

Alloy D= 32.5% Ni, 21% Cr, 0.38% Al, 0.38% Ti, balance Fe.

Alloy E= 42.7% Ni, 13.5% Cr, 2.5% Ti, 0.25% Al, 6.2% Mo, balance Fe.

percent carbon, 42.46 percent nickel, 14.33 percent chromi um, 2.09 percent titanium, 2.95 percent columbium, 0.06 percent aluminum, 0.009 percent boron, balance iron. Alloy H with a high boron content of 0.009 percent outside the invention was thus found to have poor machinability. However, from machinability tests using the 0.025 inch depth of cut to conserve material, it was found that good machinability was obtained which was relatively unaffected by variations in aluminum content and boron content over the ranges set forth hereinbefore for alloys within the invention. The improved machinability which characterizes alloys within the invention has not been explained from a theoretical point of view. It was determined that about one horsepower per cubic inch per minute was required in cutting the alloy of the invention and this further demonstrated the excellent, quite unexpected, level of machinability provided in the alloy.

EXAMPLE III In order to demonstrate the effects of aluminum and boron on room temperature transverse ductility, four lS-kilogram vacuum melts were prepared, of which Alloys l0 and 11 were within the invention and Alloys F and G were outside the invention, with compositions as shown in the following Table XII:

TABLE XII Cl) Ti 13 1 I 2. .18 2. l0 0. 0014 3. 05 2. 27 0. 0013 2. JD 2. 18 0. 0002 2. 08 2. 21 0. 0034 Bal. Bal.

The ingots of the foregoing alloys were homogenized at 2,100 F. for 16 hours and were forged to 2A-inch square bar. Longitudinal and transverse tensile properties were determined at room temperature and at l,200 F. in the as forged, annealed l,800 F. for 1% hour at temperature), and annealed plus aged conditions. The aging treatment comprised a heating at 1,550F. for 3 hours, air cool, a heating at 1,325F. for 8 hours, a furnace cool at F. per hour to l,l50F., a hold at 1,150F. for 8 hours and an air cool. Stress-rupture properties in the longitudinal direction were determined at 1,200F. and 100,000 psi using combination smooth and notch specimens. The results of the tensile tests are set forth in the following Table XIII:

TABLE XIII Tensile test results Room temperature 1,200" F.

Yield Yield strength strength (0.2% Tensile (0.2% Tensile offset), strength Percent Percent ofiset), strength Percent Percent Alloy No Condltion K s.i. K s.i. elong. R.A. K s.i. K s.i. elong. R.A.

10 A5 for ed 81. 5 32 32 Annea le 43.0 106.5 44 49. 5 Annealed plus aged (L) 141 139 17 21 123 22 48 Annealed plus aged (T) 50 85 8 5 122 142 18 25 11 As for ed 113 167 18 23 Annezfied 50 115. 5 43 44. 5 v Annealed plus aged (L) 158 194 18 25 130 2 43 Annealed plus aged (T) 154. 5 187. 5 8 12 126. 5 145. 5 4 30 5 Astor ed 73 7 28 33 Annea led 41. 5 106 40 40. s Annealed plus aged (L) 144 188 18 27 122. 5 146 24 51 Annealed plus aged ('I) 151 163 2 8 120 5 5 5 g 7 4 A for ed 109 140 16 22 i i i v V g l p (J Anneaigd A 44: 104 34 36. 5 v r r i A A 7 7 7 7 7 V Annealed plus aged (L) 193 18 26 120 14G 24 51 Annealed plus aged (T) 157. 5 173 4 10 124 144 5 21 g 5 EXAMPLE lV An alloy containing about 0.01 percent carbon, about 0.1 percent manganese, about 0.06 percent silicon, about 40.6 percent nickel, about 16.14 percent chromium, about 0.27 percent aluminum, about 1.76 percent titanium, about 2.68 percent columbium, 0.0025 percent boron, and the balance essentially iron, in accordance with the invention was melted in a vacuum induction furnace. Metal from the melt was cast in air into a vertical slab ingot weighing about 5,500 pounds and measuring 1 1 inches by 45 inches by 50 inches using a flux casting procedure. The ingot was heated to 2,050 F. and forged to inches thick, was then soaked for 16 hours at 2,050 F. and rolled to 6 inches thick, reheated to 2,050 F. and rolled to 3 inches thick. The 3 inch thick slab was reheated to 2,050 F. and rolled to a hot band about /4 inch thick. Excellent malleability was evident throughout the procedure. A transverse slice cut just below the head crop of the 3 inch slab was freckle free. The hot band was mill annealed in the temperature range 1,900 F. to 2,000 F. and a portion therefrom was further annealed for 1 hour at 1,750 F. In this condition, the material displayed a yield strength (0.2 percent offset) of 42.7 k.s.i., a tensile strength of 100.5 k.s.i. and an elongation of 49 percent. A portion of the annealed material was then aged by heating at 1,350 F. for 8 hours, furnace cooled to 1,150 F. and held for 8 hours. In the aged condition, the material displayed a yield strength (0.2 percent offset) of 152 k.s.i., a tensile strength of 188 k.s.i. and an elongation of 22 percent. This example illustrates the amenability of the alloy to production of flat rolled products using conventional melting and slab ingot procedures, with the attainment of high strength.

EXAMPLE V In order further to illustrate the effect of aluminum content in alloys provided by the invention, a series of kilogram vacuum induction heats was produced to essentially the same base composition; namely, about 0.04 percent carbon, about 0.22 percent manganese, about 0.16 percent silicon, about 40.3 percent nickel, about 16.7 percent chromium, about 2 percent titanium, about 3.1 percent columbium, about 0.0028 percent boron, and the balance essentially iron and containing aluminum in varying amounts, i.e., 0.033 percent (Heat 12A), 0.12 percent (Heat 128), 0.2 percent (Heat 12C), 0.44 percent (Heat 12D), 0.65 percent (Heat 12E) and 0.9 percent (Heat 12F). The ingots were forged to 9/16 inch square bar. The bars were annealed at 1,900 F. for one-half hour, air cooled, and then aged at 1,550 F. for 3 hours, at 1325 F. for 8 hours, furnace cooled at the rate of 100 F. per hour to 1, 1 50 F. held at 1,150 F. for 8 hours and then air cooled. The annealed and aged bars were subjected to room temperature and 1,200 F. tensile tests with the results as shown in the following Table XlV:

TABLE XIV Room Temperature Tensile Tests Yield Strength 12 1200F. Tensile Tests 12A 126.5 143.5 25 52.5 12B 128 147 23 49.5 12C 134 148.5 22 43 12D 129 148 21 47 12E 124 146 24 44.5 12F 131.5 153.5 25 54 In addition, annealed and aged bars of the alloy were subjected to stress-rupture testing at 1,200 F. and 100,000 psi stress with the results set forth in the following Table XV:

The data provide further confirmation that best yield strength and rupture life are exhibited in the alloy in the condition of heat treatment employed in this Example V when the aluminum content is between about 0.2 percent and about 0.45 percent.

Products produced from the alloy provided in accordance with the invention include sheet, plate, strip, bar, tubing, extruded shapes, forgings, etc., useful in turbine wheels, shafts, rings, pressure vessels, high temperature piping, bolts, springs, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An age-hardenable alloy having good melting characteristics, a low base hardness in the annealed condition and good machinability consisting essentially of about 35 percent to about 46 percent nickel, about 12 percent to about 20 percent chromium, about 1.25 percent to about 2.5 percent titanium, about 2.25 percent to about 3.5 percent columbium, with the sum of the percentages of titanium and columbium being at least about 4 percent, at least about 0.05 percent to about 1 percent aluminum, about 0.0005 percent to about 0.006 percent boron, up to about 0.08 percent carbon, up to about 0.35 percent manganese, up to about 0.35 percent silicon, not more than about 0.3 percent copper, not more than about 1 percent molybdenum, and the balance essentially iron.

2. An alloy according to claim 1 wherein the nickel content does not exceed about 45 percent and the chromium content does not exceed about 18 percent.

3. An alloy according to claim 1 containing about 14.5 percent to about 17.5 percent chromium, about 39 percent to about 44 percent nickel, about 1.5 percent to about 2 percent titanium, about 2.5 percent to about 3 percent columbium, and not more than about 0.5 percent aluminum.

4. An alloy according to claim 3 wherein the carbon content does not exceed about 0.06 percent.

5. An alloy according to claim 3 wherein the aluminum content is about 0.1 percent to about 0.4 percent.

6. An alloy according to claim 1 wherein the boron content is about 0.001 percent to about 0.005 percent.

'7. An alloy in accordance with claim 3 wherein the aluminum is about 0.2 percent to about 0.45 percent.

Claims

2. An alloy according to claim 1 wherein the nickel content does not exceed about 45 percent and the chromium content does not exceed about 18 percent.
3. An alloy according to claim 1 containing about 14.5 percent to about 17.5 percent chromium, about 39 percent to about 44 percent nickel, about 1.5 percent to about 2 percent titanium, about 2.5 percent to about 3 percent columbium, and not more than about 0.5 percent aluminum.
4. An alloy according to claim 3 wherein the carbon content does not exceed about 0.06 percent.
5. An alloy according to claim 3 wherein the aluminum content is about 0.1 percent to about 0.4 percent.
6. An alloy according to claim 1 wherein the boron content is about 0.001 percent to about 0.005 percent.
7. An alloy in accordance with claim 3 wherein the aluminum is about 0.2 percent to about 0.45 percent.