US3615906A

US3615906A - Process for fabricating threaded elements from the age-hardenable alloys

Info

Publication number: US3615906A
Application number: US811201A
Authority: US
Inventors: Marvin C Vanwanderham; John A Harris Jr; James J Campbell
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1969-03-27
Filing date: 1969-03-27
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26

Abstract

Threaded elements having improved mechanical properties for high-temperature service are fabricated from the age-hardenable superalloys in a process comprising: solution heat treating the alloy and establishing a grain size corresponding to ASTM 2-6, or more preferably ASTM 4-5; forming the threads; stabilization heat treating the threaded alloy; and aging.

Description

United States Patent Inventors Marvin C. Vanwanderhnm;

John A. Harris, Jr., Palm Beach, Fla.; James J. Campbell, Cincinnati, Ohio 811,201

Mar. 27, 1969 Oct. 26, 1971 United Aircraft Corporation East Hartford, Conn.

Appl. No. Filed Patented Assignee PROCESS FOR FABRICATING THREADED ELEMENTS FROM THE AGE-HARDENABLE ALLOYS 6 Claims, No Drawings U.S. Cl. l48/l2.7, 148/1 2.3 Int. Cl C221 1/00, C22f 1/10, C2ld 9/00 Field ol'Search 148/12.3, 11.5, 12.7

[56] References Cited UNITED STATES PATENTS 2,637,672 5/1953 Losco et a1. 148/12.3 2,957,790 10/1960 Metcalfe 148/1 2.3 3,357,868 12/1967 Tanczyn.... 148/12.3 3,376,780 4/1968 Tanczyn 148/12.3

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. W. Stallard Attorney-Richard N. James BACKGROUND OF THE INVENTION The present invention relates to the production of threaded elements from the age-hardenable superalloys.

1n gas turbine engines, a number of threaded elements, such as bolts and compressor tie rods, are utilized in environments involving exposure under stress to elevated temperatures. As manufactured by conventional techniques, these elements are prone to failure with time, due primarily to poor stress relaxation resistance and insufficient thread strength.

Two alloys, Waspaloy and Astroloy, are widely used in applications of this nature, although other age-hardcnable alloys such as lnco 901, lnconel x 750 and Udimet 700, are also available for this type of service. Waspaloy, which is suitable for this type of service up to temperatures of about 1,200 F. has the following nominal composition by weight: 19.5% Cr, 13.5% Co, 0.07% C, 3% Ti, 1.4% A1, 4% Mo, 0.005% B, 0.08% Zr, bal. Ni. For service over 1,200 F., Astroloy is commonly used at a nominal composition, by weight of: 15.5% Cr, 17% Co, 0.07%C, 3.3% Ti, 4.5% a], 5.3% Mo, 0.03% B, bal. Ni.

The conventional threading practice involves rolling of the threads in barstock after the stablization heat treatment but prior to aging. Threaded elements so formed, however, exhibit poor stress relaxation and thread failure resistance and, hence, are prone to thread failure in service.

SUMMARY OF THE INVENTION The present invention describes a fabrication technique for providing threaded elements from the age-hardenable alloys characterized by improved mechanical properties in elevated temperature applications.

The improved properties are achieved by first establishing a grain size of ASTM 2-6 by appropriate heat treatment and, then, by altering the conventional thread forming procedure to provide rolling of the threads prior to stabilization and aging. The process thus involves:

solution heat treating the alloy to establish a grain size of ASTM 2-6 or more preferably ASTM 4-5; forming the threads; stabilizing heat treating the threaded alloy; and aging.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For service to temperatures up to about 1,200 F., suitable stock is formed from an alloy consisting of, by weight,: 18-21 percent chromium, 12-15 percent cobalt, 0.04-0.10 percent carbon, 3.5- percent molybdenum, 2.75-3.25 percent titanium, 1.2-1.6 percent aluminum, 0.02-0.08 percent zirconium, 0.003-0.01 percent boron, balance essentially nickel. The stock is solution heat treated at a temperature of about 1 ,825-l ,900 F. for 2-4 hours and cooled at a rate equivalent to air cool or faster the conditions being selected to establish a grain size of ASTM 2-6, preferably ASTM 4-5. Any machining of boltheads, etc., may be done either before or after the solution heat treatment. Threads are formed by a single rolling process. After thread rolling, the parts are stabilization heat treated by heating to about 1,550 F; holding at heat for about 4 hours; and cooling in air. After stabilization, the parts are precipitation heat treated by heating to about 1,400 F.; holding at heat for about 16 hours; and cooling in air.

For service in excess of about 1,200 F., the stock is formed from a preferred composition consisting of, by weight: 14-16 percent chromium, 16-18 percent cobalt, 0.03-0.09 percent carbon, 4.5-5.5 percent molybdenum, 3.35-3.65percent titanium 3.85-4.15 percent aluminum, 002-003 percent boron, balance essentially nickel. The stock is solution heat treated at a temperature of 1,975 F. or higher; held at temperature to establish a grain size corresponding to ASTM 2-6, preferably 4-5; and cooled at a rate equivalent to air cool or faster. Threads are formed in a single rolling process. After thread rolling, parts are stabilizing heat treated by: holding the part at a temperature of about 1,600 F., for about 8 hours; and cooling at a rate equivalent to aircooling. The parts are subsequently precipitation heat treated at about 1,200 F. for 24 hours and air cooled; and heat treated at about 1,400 F. for about 8 hours and air cooled.

A number of specimens were prepared with varying heat treatments as affecting grain size and were subjected to a variety of tests comparing the effect of both grain size and the processing sequence. The results of a number of these tests are summarized in the following tables.

TABLE I Specimen Grain Size/Threading Practice Room Temperature Tensile Results and Specimen Data CKB Grain YS, UTS, EL, RA, Failure Part Size K s.i. K s.i. k '2 Location Number Range 9561 Coarse 133 210 21 16 Threads 130 208 21 I9 Shank 123 180 15 13 Shank 9562 Coarse I25 192 ll 16 Shank 122 188 II 16 Shank 121 I83 l8 l6 Shank 9563 Coarse 160 10 9 Threads 122 163 I0 9 Threads I65 8 8 Threads 9564 Coarse 119 179 17 14 Threads 122 I77 l5 12 Threads 126 168 I5 13 Threads 9565 Coarse 121 178 15 11 Threads 129 191 l7 13 Threads 127 180 14 11 Thread: 9571 Fine 141 208 25 29 Shank 141 215 24 27 Shank 143 216 24 J1 Shank 9572 Fine 141 214 25 J2 Shank 149 223 23 2! Shank 156 220 24 51 Shank 9573 Fine I49 200 I2 9 Threads 153 201 ll 9 Threads 162 209 ll 9 Thread: 9574 Fine 151 206 14 15 Threads 157 218 22 27 Shank 160 224 23 3| Shank 9575 Fine 158 221 16 15 Threads 148 214 16 12 Threads 224 24 32 Shank TABLE III l,400 F. Tensile Results and Specimen Data CKB Grain YS, UTS, EL, RA. Failure part Size K s.| K a.i. k L gi Number Range 956I Coarse l I 8 154 I I9 Shank I17 I51 22 34 Shank I20 160 l9 2! Shank 9562 Coarse I08 I46 13 $3 Shank I08 I48 28 36 Shank I I8 154 26 30 Shank 9563 Coarse I I4 147 18 31 Shank I08 I49 21 32 Shank I07 I51 26 32 Shank 9564 Coarse I I6 154 21 26 Shank I06 I50 24 30 Shank I07 I50 23 25 Shank 9565 Coarse I I7 I54 22 25 Shank I07 150 21 29 Shank I l I 153 24 24 Shank 957l Fine I22 I52 16 I6 Shank I30 I50 I3 19 Shank I30 157 l1 l5 Shank 9572 Fine I28 I55 21 52 Shank I28 I49 23 55 Shank I38 154 29 54 Shank 9573 Fine 136 I50 34 58 Shank I40 I51 23 53 Shank I59 I69 30 52 Shank 9574 Fine I32 26 55 Shank I3I 147 23 S9 Shank 142 141 :9 s7 Shank 9575 Fine I32 l5] l0 14 Threads l 32 149 I4 Threads I37 154 31 57 Shank TABLE IV I400 Fl85l0 ksi stress rupture results and specimen data Root Radius, Area Ratio. in. (Thousandths) CKB Grain El, RA;

part size Life, perper- Failure End End End End number range hr cent cent location One Two One Two 9561 Coarse 50 8 8 Threads 93 93 8 8 58 21 24 Threads 93 93 8 8 43 9 l2 Shank 93 93 8 8 62 l4 l4 Shank 93 93 8 8 9562 Coarse 44 I6 24 Shank 93 93 8 K 50 I9 Shank 93 93 8 8 57 25 26 Shank 93 93 8 8 S3 23 29 Shank 93 93 8 8 9563 Coarse 40 I6 27 Shank 93 93 I0 IO SI I3 20 Shank 93 92 l0 I0 52 I8 I9 Shank 92 92 l0 IO 69 l4 l5 Shank 92 92 l0 I0 9564 Coarse 68 14 I6 Shank 93 93 l0 I0 48 I9 25 Shank 92 92 l0 ll) 52 I6 22 Shank 93 93 l0 l0 6] I7 l8 Shank 92 92 10 I0 9565 Coarse 54 I5 20 Shank 95 95 5 5 45 I9 23 Shank 95 95 5 6 62 l5 l7 Shank 95 95 5 5 53 I7 22 Shank 95 95 5 6 9571 Fine I3 3 3 Threads 93 93 9 9 8 6 8 Shank 92 92 8 8 I5 I 1 Threads 92 92 9 9 l9 3 3 Threads 92 92 9 9 9572 Fine 29 41 64 Shank 92 93 8 8 34 37 5] Shank 92 92 8 S l i 3| 42 51 Shank 92 92 8 8 9573 Fine 22 35 55 Shank 93 93 l0 I0 36 28 48 Shank 92 92 I0 10 39 34 52 Shank 92 92 l0 l0 I6 45 58 Shank 93 93 I0 10 9574 Fine 20 37 51 Shank 92 93 l0 I0 22 53 65 Shank 92 93 l0 I0 45 60 Shank 92 92 10 H) I8 42 7O Shank 92 92 I0 I0 9575 Fine 63 29 44 Shank 95 95 7 6 30 36 60 Shank 96 95 7 6 44 48 Shank 96 96 6 5 47 45 55 Shank 96 96 5 6 TABLE V l,300 F./65.0 K s.i./I 00 hr. Stress Relaxation Results and Specimen Data CKB Grain Part Size Relaxation. Number Range 1:

956l Coarse 4 7 9562 Coarse 3 8 9563 Coarse 2 6 9564 Coarse 3 9 9565 Coarse 3 0 7I Fine 6 I0 9572 Fine l2 8 9573 Fine I3 I2 9574 Fine 14 9 9575 Fine I0 TABLE VI Relative Influence of Grain Size on Mechanical Properties D Detrimental Influence B Beneficial Influence N No Influence The results confirm that both grain size and threading practice exert an influence on mechanical properties. The finergrained specimens produced results equal or superior to the coarser-grained specimens in tenns of all mechanical properties except stress rupture life and stress relaxation resistance. Unfortunately, the influence on grain size can be seen to exert contradictory effects in terms of the physical properties required of a threaded element. The choice of a grain size of ASTM 2-6 or more preferably ASTM 4-5 represents the best compromise for threaded elements, recognizing also the problems of precise grain size control in production processes.

Basically, the solution-roll-stabilize-age threading sequence improves the ability of the threads to resist stress relaxation and failure. It must, however, be considered in combination with the selection of the required grain size for optimum results. Clearly, the program has demonstrated that, as opposed to conventional processing techniques, the improved process described herein may be utilized to provide threaded elements which are not susceptible to thread failure.

While the invention has been described in connection with certain examples and preferred embodiments, these are illustrative only. It will be understood that the invention is not to be limited to the exact details described, for obvious modifications will occur to those skilled in the art.

We claim:

I. The process of fabricating threaded elements from the age-hardenable alloys which comprises:

forming the threads on solution heat treated, age-hardenable alloy stock having a grain size corresponding to about ASTM 2-6;

subjecting the threaded alloy to a stabilization heat treatment; and

aging the alloy.

2. The process of fabricating threaded elements from the age-hardenable nickel-base alloy which comprises:

solution heat treating the alloy to establish a grain size substantially corresponding to ASTM 2-6;

rolling the threads; subjecting the threaded alloy to a stabilization heat treatment and precipitation heat treating the stabilized alloy. 3. The method of fabricating threaded elements for service up to about l,200 F. which comprises:

providing suitable stock from an alloy consisting essentially of, by weight, about l8-2l percent chromium, 12-] 5 percent cobalt, 3.5-5 percent molybdenum, 2.75-3.25 percent titanium, 1.2-1.6 percent aluminum, about 0.07 percent carbon, about 0.005 percent boron, about 0.08 percent zirconium, balance nickel; solution heat treating the alloy at l,800-l,900 F. for a minimum of about 2 hours and establishing a grain size corresponding to about ASTM 2-6; rolling the threads in the stock after cooling; stabilization heat treating the alloy; and precipitation heat treating the alloy at about l,400 F. 4. The process according to claim 3 wherein: the stabilization heat treatment is conducted at a temperature of about l,500 F. 5. The method of fabricating threaded elements for hightemperature service which comprises:

providing suitable stock from an alloy consisting essentially of, by weight, 14-16 percent chromium, 16-18 percent cobalt, 4.5-5.5 percent molybdenum, 3.35-3.65 percent titanium, 3.85-4.l5 percent aluminum, about 0.06 percent carbon, about 0.03 percent boron, balance nickel; solution heat treating the alloy at a temperature of at least l,975 F. and establishing a grain size corresponding to about ASTM 2-6; rolling the threads in the stock after cooling; stabilization heat treating the alloy; and precipitation heat treating the alloy at about l,200 F. 6. The process according to claim 5 wherein: the stabilization heat treatment is conducted at a temperature of about l,600 F.

22 13? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,615,906 Dated October 26, 1971 Patent No.

Inventor) Marvin C. Vanwanderham et a1 It 15 certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 3, column 6, line 13 1800 should read -l82S-- Claim 4, column 6, line 21 l500 should read --l550-- Signed and sealed this 28th day of March 1972.

(SEAL) Attest:

EDWARD M.FLETCHI ]R, JR. ROBERT GOT'ISCHALK Commissioner of Patents Attesting Officer

Claims

2. The process of fabricating threaded elements from the age-hardenable nickel-base alloys which comprises: solution heat treating the alloy to establish a grain size substantially corresponding to ASTM 2- 6; rolling the threads; subjecting the threaded alloy to a stabilization heat treatment; and precipitation heat treating the stabilized alloy.
3. The method of fabricating threaded elements for service up to about 1,200* F. which comprises: providing suitable stock from an alloy consisting essentially of, by weight, about 18-21 percent chromium, 12-15 percent cobalt, 3.5-5 percent molybdenum, 2.75-3.25 percent titanium, 1.2-1.6 percent aluminum, about 0.07 percent carbon, about 0.005 percent boron, about 0.08 percent zirconium, balance nickel; solution heat treating the alloy at 1,800*-1,900* F. for a minimum of about 2 hours and establishing a grain size corresponding to about ASTM 2-6; rolling the threads in the stock after cooling; stabilization heat treating the alloy; and precipitation heat treating the alloy at about 1,400* F.
4. The process according to claim 3 wherein: the stabilization heat treatment is conducted at a temperature of about 1,550* F.
5. The method of fabricating threaded elements for high-temperature service which comprises: providing suitable stock from an alloy consisting essentially of, by weight, 14-16 percent chromium, 16-18 percent cobalt, 4.5-5.5 percent molybdenum, 3.35-3.65 percent titanium, 3.85-4.15 percent aluminum, about 0.06 percent carbon, about 0.03 percent boron, balance nickel; solution heat treating the alloy at a temperature of at least 1, 975* F. and establishing a grain size corresponding to about ASTM 2-6; rolling the threads in the stock after cooling; stabilization heat treating the alloy; and precipitation heat treating the alloy at about 1,200* F.
6. The process according to claim 5 wherein: the stabilization heat treatment is conducted at a temperature of about 1,600* F.