U.S. patent application number 12/541200 was filed with the patent office on 2011-02-17 for powder metal mold.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Timothy Eden Channel.
Application Number | 20110038748 12/541200 |
Document ID | / |
Family ID | 43067051 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110038748 |
Kind Code |
A1 |
Channel; Timothy Eden |
February 17, 2011 |
POWDER METAL MOLD
Abstract
Described is a process of producing a component from a gamma
prime or gamma double prime precipitation-strengthened nickel-base
superalloy. The process includes forming a powder of the superalloy
and filling a can with the powder wherein the can includes
nickel-chromium-molybdenum-niobium alloy. The can is evacuated and
sealed in a controlled environment. The can and the powder are
consolidated at a temperature, time, and pressure to produce a
consolidation. The consolidated billet is forged at a temperature
and strain rate to produce a forging with a uniform fine grain
throughout. A further aspect described is a mold including a
nickel-chromium-molybdenum-niobium alloy can.
Inventors: |
Channel; Timothy Eden;
(Simpsonville, SC) |
Correspondence
Address: |
Hoffman Warnick LLC
75 State Street, Floor 14
Albany
NY
12207
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
43067051 |
Appl. No.: |
12/541200 |
Filed: |
August 14, 2009 |
Current U.S.
Class: |
419/8 ;
249/135 |
Current CPC
Class: |
C22C 1/0433 20130101;
B22F 2998/10 20130101; C22C 19/056 20130101; B22F 3/15 20130101;
B22F 2003/248 20130101; B22F 3/1216 20130101; B22F 2003/247
20130101; C22F 1/10 20130101; B22F 3/17 20130101; C22C 19/055
20130101; B22F 2998/10 20130101 |
Class at
Publication: |
419/8 ;
249/135 |
International
Class: |
B22F 7/04 20060101
B22F007/04; B22F 3/12 20060101 B22F003/12; B22F 3/17 20060101
B22F003/17 |
Claims
1. A process of producing a component from a gamma prime or gamma
double prime precipitation-strengthened nickel-base superalloy, the
process comprising: forming a powder of the superalloy; filling a
can with the powder wherein the can comprises
nickel-chromium-molybdenum-niobium alloy; evacuating and sealing
the can in a controlled environment; consolidating the can and the
powder therein at a temperature, time, and pressure to produce a
billet; and forging the billet at a temperature and strain rate to
produce a forging.
2. A process according to claim 1, wherein the nickel-base
superalloy has a composition of, by weight, about 19 to about 23%
chromium, about 7 to about 8% molybdenum, about 3 to about 4%
niobium, about 4 to about 6% iron, about 0.3 to about 0.6%
aluminum, about 1 to about 1.8% titanium, about 0.002 to about
0.004% boron, about 0.35% maximum manganese, about 0.2% maximum
silicon, about 0.03% maximum carbon, a balance of nickel and
incidental impurities.
3. A process according to claim 1, wherein the
nickel-chromium-molybdenum-niobium alloy has a composition of, by
weight, about 55.0 to about 59.0% nickel, about 19.0 to about 22.5%
chromium, about 7.0 to about 9.5% molybdenum, about 2.75 to about
4.00% niobium, about 1.0 to about 1.7% titanium, about 0.35%
maximum aluminum, about 0.03% maximum carbon, about 0.35% maximum
manganese, about 0.20% maximum silicon, about 0.015% phosphorous,
about 0.010% maximum sulfur, a balance of iron and incidental
impurities.
4. A process according to claim 1, wherein the billet formed by the
consolidation step has a density of at least 99.9% of
theoretical.
5. A process according to claim 1, wherein the component is a rotor
component of a gas turbine engine.
6. A process according to claim 5, wherein the billet weighs about
1.8 to about 4 times the weight of the component.
7. A process according to claim 1, further comprising solution heat
treating the forging.
8. A process according to claim 7, wherein the solution heat
treating comprises: solution heat treatment at a temperature of
about 900.degree. C. for approximately four hours; aging at a
temperature of about 760.degree. C. for approximately eight hours;
cooling at a rate of about 56.degree. C. per minute to about
620.degree. C.; holding for approximately eight hours; and air
cooling.
9. A process according to claim 1, further comprising machining the
forging.
10. A process according to claim 1, wherein the billet has a grain
size of no larger than about ASTM 8.
11. A process according to claim 1, further comprising ultrasonic
testing of the forging.
12. A process according to claim 1, further comprising ultrasonic
testing of the billet.
13. A mold comprising: a nickel-chromium-molybdenum-niobium alloy
can.
14. The mold of claim 13, wherein the
nickel-chromium-molybdenum-niobium alloy has a composition of, by
weight, about 55.0 to about 59.0% nickel, about 19.0 to about 22.5%
chromium, about 7.0 to about 9.5% molybdenum, about 2.75 to about
4.00% niobium, about 1.0 to about 1.7% titanium, about 0.35%
maximum aluminum, about 0.03% maximum carbon, about 0.35% maximum
manganese, about 0.20% maximum silicon, about 0.015% phosphorous,
about 0.010% maximum sulfur, a balance of iron and incidental
impurities.
15. The mold of claim 13 wherein sides of the can are substantially
square.
Description
TECHNICAL FIELD
[0001] This invention relates to powder metal molds and processes
for producing forgings using metal powders as the starting
material. More particularly, this invention is directed to a mold
and process for producing components with improved properties.
BACKGROUND OF THE INVENTION
[0002] A process for manufacturing very large nickel-base alloy
rotor forgings, generally in excess of 5000 pounds (about 2300 kg),
using powder metallurgy (PM) techniques is discussed in US Pub.
2007/0020135. Powder metal alloys are used to produce nickel-base
consolidations and subsequently forged into large turbine wheels,
spacers, or other rotating components of a size suitable for large
gas turbine engines used in the power generating industry. A
particularly suitable alloy is the commercially available 725
INCONEL.RTM. Alloy 725, hereinafter referred to as Alloy 725.
SUMMARY OF THE INVENTION
[0003] An aspect discussed herein is a process of producing a
component from a gamma prime or gamma double prime
precipitation-strengthened nickel-base superalloy. The process
includes forming a powder of the superalloy and filling a can with
the powder, wherein the can includes a
nickel-chromium-molybdenum-niobium alloy. The can is evacuated and
sealed in a controlled environment. The can and the powder are
consolidated at a temperature, time, and pressure to produce a
consolidation. The billet is forged at a temperature and strain
rate to produce a forging.
[0004] A further aspect shown is a mold including a
nickel-chromium-molybdenum-niobium alloy can.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] These and other features of this invention will be more
readily understood from the following detailed description of the
various aspects of the invention taken in conjunction with the
accompanying drawings that depict various embodiments of the
invention, in which:
[0006] FIG. 1 shows a mold;
[0007] FIG. 2 shows a mold after loading with powder metal and HIP
processing; and
[0008] FIG. 3 shows a mold machined square after loading with
powder metal and HIP processing.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Alloy 725 PM billets are created by first filling a welded
metal can or mold with powder prior to the hot-isostatic pressing
(HIP) process. These cans or molds are typically manufactured from
low-cost mild steel or stainless steel. However, cans or molds
produced from low-cost mild steel or stainless steel create an
elementally different diffusion layer between the contents of the
can and the can itself. The dissimilar steel layer and diffusion
layers interfere with ultrasonic testing (UT) of the billet after
the HIP process. The diffusion layer should be machined away prior
to forming of a part from the billet to maximize the risk of
cracking during the billet forging process. Finally, elimination of
the diffusion layer would allow for UT inspection without removal
of the can.
[0010] An aspect of the disclosure is a can or mold suitable for
hot isostatic pressing (HIP). Shown in FIG. 1 is a can 10 suitable
for hot isostatic pressing (HIP) of a powder metal. After filling
the can 10 with the powder metal and subjecting it to HIP, the can
deforms as shown in FIG. 2. The deformed sides of can 10 and the
processed metal form a layer 12 that has a composition that is a
combination of the powder metal and the material of the can. The
next step in the process is to machine the sides of the can 10 so
that they are smooth and square for UT inspection. In FIG. 3 a
machined can 10 is shown where some of the layer formed from the
powder metal and the can is shown in an exaggerated manner by
residual layer 13. Once the sides are machined smooth and square,
the resulting billet is inspected with ultra sonic testing to
detect defects.
[0011] When using a steel can to form a billet of Alloy 725, layer
12 (can plus diffusion layer) shown in FIG. 2 needs to be
completely removed, or there is a potential for cracks. If the
layer is not fully removed by machining, a residual layer 13 (can
and diffusion layer or diffusion) results, as shown in FIG. 3. This
boundary layer attenuates the UT signal and counteracts the
improved inspection sensitivity brought about by using fine grain
Alloy 725 material.
[0012] In one aspect, the can is made from a
nickel-chromium-molybdenum-niobium alloy, such as INCONEL.RTM.
alloy 725. INCONEL.RTM. alloy 725 has a composition of, by weight,
about 55.0 to about 59.0% nickel, about 19.0 to about 22.5%
chromium, about 7.0 to about 9.5% molybdenum, about 2.75 to about
4.00% niobium, about 1.0 to about 1.7% titanium, about 0.35%
maximum aluminum, about 0.03% maximum carbon, about 0.35% maximum
manganese, about 0.20% maximum silicon, about 0.015% phosphorous,
about 0.010% maximum sulfur, the balance iron and incidental
impurities.
[0013] A particularly suitable alloy for illustrating the
advantages of this mold or can is a gamma-prime precipitation
strengthened nickel-base superalloy based on the commercially
available Alloy 725. The superalloy, identified herein as
INCONEL.RTM. alloy 725, has a composition of, by weight, about 19
to about 23% chromium, about 7 to about 8% molybdenum, about 3 to
about 4% niobium, about 4 to about 6% iron, about 0.3 to about 0.6%
aluminum, about 1 to about 1.8% titanium, about 0.002 to about
0.004% boron, about 0.35% maximum manganese, about 0.2% maximum
silicon, about 0.03% maximum carbon, the balance nickel and
incidental impurities.
[0014] Properties of conventionally cast plus wrought Alloy 725 as
discussed in U.S. Pat. No. 6,315,846 to Hibner et al. and U.S. Pat.
No. 6,531,002 to Henry et al. render the alloy particularly well
suited for producing very large forgings from powder metal. These
properties include room and elevated temperature tensile strength
and ductility.
[0015] While described in reference to the Alloy 725, the teachings
herein are applicable to other gamma prime and gamma double prime
precipitation-strengthened nickel-based superalloys, such as Alloy
625.
[0016] For the applications of interest to the invention, optimum
processibility and mechanical properties are achieved by uniform
grain sizes of not larger than American Society for Testing and
Materials (ASTM) about 8, or preferably about 10. Grain sizes
larger than ASTM 8 are undesirable in that the presence of such
grains can significantly reduce the low cycle fatigue resistance of
the component, can have a negative impact on other mechanical
properties of the component such as tensile and high cycle fatigue
(HCF) strength, can increase hot working load requirements, and can
inhibit the thorough ultrasonic inspection of billets and thick
section forgings. Therefore, a preferred aspect is to achieve a
uniform grain size within a nickel-base superalloy, in which random
grain growth is prevented so as to yield a maximum grain size of
ASTM 8 or finer. Such a process is discussed in US Pub.
2007/0020135.
[0017] The powder is placed in a suitable
nickel-chromium-molybdenum-niobium alloy can, whose size will meet
the billet size requirement after consolidation. This can is shown
in FIG. 1. Loading of the can is performed in a controlled
environment (inert gas or vacuum), after which the can is evacuated
while subjected to moderate heating (e.g., above about 200.degree.
F. (about 93.degree. C.)) to drive off moisture and any volatiles,
and then sealed. Thereafter, the can and its contents are
consolidated at a temperature, time, and pressure sufficient to
produce a consolidation having a density of at least about 99.9% of
theoretical. Consolidation is accomplished by hot isostatic
pressing (HIP). The can be any shape, such as a cylinder or cube
but is preferable that the sides are square.
[0018] As shown in FIG. 2, the can is deformed post HIP. The
deformed can and processed powder exist as a slightly deformed
billet having a layer 12 on the outer edges. The outer edges are
machined square as shown in FIG. 3. By eliminating the difference
in composition between the can and the powder metal layer that
occurs when a can of mild steel or stainless steel is used, less
machining is required as removal of the entire layer 12 is not
essential. The residual layer 13 (FIG. 3) does not impart any
detrimental effects on the resulting billet. In addition,
inspection through ultrasonic testing is easier.
[0019] The billet is then forged using known techniques, such as
those currently utilized to produce Alloy 706 and Alloy 718 rotor
forgings for large industrial turbines, but modified to take
advantage of fine grain billet techniques. Forging is performed at
temperatures and loading conditions that allow complete filling of
the finish forging die cavity, avoid fracture, and produce or
retain a fine uniform grain size within the material of not larger
than ASTM 8. Notably, because chemical and microstructural
segregation are virtually eliminated and a very fine grain size can
be achieved through use of the powder metal starting material, the
ratio of input (billet) weight to final forging weight can be
significantly reduced. For example, it is believed the starting
billet weight can be as little as about 1.2 to about 1.5 times the
weight of the finished forging, and about 1.8 to about 4 times the
weight of the finish-machined rotor component. This weight
reduction and resulting cost savings are enabled by the improved
processibility of fine-grained billet as well as the enhanced sonic
inspectibility thereof.
[0020] The resulting rotor forging preferably undergoes ultrasonic
inspecting for potential life-limiting defects. However, since the
input billet lacks a diffusion layer, improved inspection is
possible as there is less material and time wasted in prepping the
billet for UT inspection.
[0021] Inspection is followed by finish machining by any suitable
known method to produce the finish-machined rotor component. In
order to achieve required mechanical properties of the rotor
component, prior to machining the forging is solution heat-treated
and aged at temperatures and times, which achieve the preferred
balance of properties for industrial gas turbine service. An
illustrative example of an appropriate heat treatment process for
the Alloy 725 entails a solution heat treatment at a temperature of
about 900.degree. C. (about 1650.degree. F.) for approximately four
hours, followed by two step aging at a temperature of about
760.degree. C. (about 1400.degree. F.) for approximately eight
hours, then cooling at a rate of 56.degree. C. (about 100.degree.
F.) per minute to about 620.degree. C. (about 1150.degree. F.) and
holding for approximately eight hours, followed by air cooling.
[0022] The terms "first," "second," and the like, herein do not
denote any order, quantity, or importance, but rather are used to
distinguish one element from another, and the terms "a" and "an"
herein do not denote a limitation of quantity, but rather denote
the presence of at least one of the referenced item. The modifier
"about" used in connection with a quantity is inclusive of the
stated value and has the meaning dictated by the context, (e.g.,
includes the degree of error associated with measurement of the
particular quantity). The suffix "(s)" as used herein is intended
to include both the singular and the plural of the term that it
modifies, thereby including one or more of that term (e.g., the
metal(s) includes one or more metals). Ranges disclosed herein are
inclusive and independently combinable (e.g., ranges of "up to
about 25 w/o, or, more specifically, about 5 w/o to about 20 w/o",
are inclusive of the endpoints and all intermediate values of the
ranges of "about 5 w/o to about 25 w/o," etc).
[0023] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations or improvements therein may be made by those
skilled in the art, and are within the scope of the invention. In
addition, many modifications may be made to adapt a particular
situation or material to the teachings of the invention without
departing from essential scope thereof. Therefore, it is intended
that the invention not be limited to the particular embodiment
disclosed as the best mode contemplated for carrying out this
invention, but that the invention will include all embodiments
falling within the scope of the appended claims.
* * * * *