U.S. patent application number 12/507885 was filed with the patent office on 2011-01-27 for heavy austempered ductile iron components.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Gregory Keith Bouse, Junyoung Park, Jason Robert Parolini, Sujith Sathian.
Application Number | 20110017364 12/507885 |
Document ID | / |
Family ID | 43496256 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110017364 |
Kind Code |
A1 |
Park; Junyoung ; et
al. |
January 27, 2011 |
HEAVY AUSTEMPERED DUCTILE IRON COMPONENTS
Abstract
A component for wind turbines includes cast austempered ductile
iron containing about 3.0 to about 3.8 weight percent carbon, about
1.9 to about 2.8 weight percent silicon, up to about 0.3 weight
percent manganese, up to about 0.8 weight percent copper, up to
about 2.0 weight percent nickel, up to about 0.3 weight percent
molybdenum, about 0.03 to about 0.06 weight percent magnesium, less
than about 0.05 weight percent chromium, less than about 0.02
weight percent vanadium, and less than about 0.01 weight percent
sulfur. The component is preferably a drive shaft or gearbox
component having a mass of more than about 3 tons. A method of
manufacturing the component is also provided.
Inventors: |
Park; Junyoung; (Greer,
SC) ; Bouse; Gregory Keith; (Greer, SC) ;
Parolini; Jason Robert; (Greer, SC) ; Sathian;
Sujith; (Zachary, LA) |
Correspondence
Address: |
Hoffman Warnick LLC
75 State Street, Floor 14
Albany
NY
12207
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
43496256 |
Appl. No.: |
12/507885 |
Filed: |
July 23, 2009 |
Current U.S.
Class: |
148/544 ;
148/321; 148/545 |
Current CPC
Class: |
C21D 9/32 20130101; Y02E
10/722 20130101; C21D 2211/005 20130101; F05B 2240/60 20130101;
F05C 2201/0439 20130101; C21D 2211/001 20130101; C22C 37/10
20130101; Y02P 10/32 20151101; Y02E 10/72 20130101; F05B 2230/21
20130101; C22C 37/04 20130101 |
Class at
Publication: |
148/544 ;
148/545; 148/321 |
International
Class: |
C21D 5/00 20060101
C21D005/00; C22C 37/10 20060101 C22C037/10 |
Claims
1. A component comprising: cast austempered ductile iron containing
about 3.0 to about 3.8 weight percent carbon, about 1.9 to about
2.8 weight percent silicon, up to about 0.3 weight percent
manganese, up to about 0.8 weight percent copper, up to about 2.0
weight percent nickel, up to about 0.3 weight percent molybdenum,
about 0.03 to about 0.05 weight percent magnesium, less than about
0.05 weight percent chromium, less than about 0.02 weight percent
vanadium, and less than about 0.01 weight percent sulfur wherein
the component comprises a mass of more than about 3 tons.
2. The component of claim 1, wherein the component comprises a mass
of more than about 6 tons.
3. The component of claim 1, wherein the component comprises a
drive shaft.
4. The component of claim 1, wherein the component comprises a
heavy gearbox component.
5. The component of claim 1, wherein the austempered ductile iron
comprises acicular ferrite and austenite.
6. A method of manufacturing a component, the method comprising:
melting ductile iron containing about 3.0 to about 3.8 weight
percent carbon, about 1.9 to about 2.8 weight percent silicon, up
to about 0.3 weight percent manganese, up to about 0.8 weight
percent copper, up to about 2.0 weight percent nickel, up to about
0.3 weight percent molybdenum, about 0.03 to about 0.06 weight
percent magnesium, less than about 0.05 weight percent chromium,
less than about 0.02 weight percent vanadium, and less than about
0.01 weight percent sulfur; casting the component; austenitizing
the component; quenching the component; and austempering the
component.
7. The method of claim 6, wherein the quenching comprises immersing
the component in a medium kept at a temperature of from about 230
to about 400.degree. C.
8. The method of claim 6, further comprising: machining the
component.
9. The method of claim 6, wherein the component comprises a mass of
more than about 3 tons.
10. The method of claim 6, wherein the component comprises a mass
of more than about 6 tons.
11. The method of claim 6, wherein the component comprises a wind
turbine shaft.
12. The method of claim 6, wherein the component comprises a
gearbox component.
13. The method of claim 6, wherein the austenitizing comprises
holding the component at a temperature in a range of about
815.degree. C. to about 985.degree. C. for a time sufficient to
convert a matrix to austenite
14. A wind turbine drive shaft comprising: cast austempered ductile
iron containing about 3.0 to about 3.8 weight percent carbon, about
1.9 to about 2.8 weight percent silicon, up to about 0.3 weight
percent manganese, up to about 0.8 weight percent copper, up to
about 2.0 weight percent nickel, up to about 0.3 weight percent
molybdenum, about 0.03 to about 0.06 weight percent magnesium, less
than about 0.05 weight percent chromium, less than about 0.02
weight percent vanadium, and less than about 0.01 weight percent
sulfur wherein the drive shaft comprises a mass of more than about
3 tons.
15. The wind turbine drive shaft of claim 14, wherein the drive
shaft comprises a mass of more than about 6 tons.
16. The wind turbine drive shaft of claim 14, wherein the
austempered ductile iron comprises acicular ferrite and austenite.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to austempered ductile iron for use in
wind turbine shafts and gearbox components.
[0002] Wind turbines have a main shaft that transmits power from a
rotor to a generator. As wind turbines increase their outputs from
1.5 and 2.5 megawatts (MW) to 3, 4, 5, and 6 MW, the size and
required properties of the wind turbine drive shaft increases. In
addition, the loads gearbox components, such as planet gear
carriers, handle are too high for conventional ductile iron grades
(ferrtitic/pearlitic grades). Forged/hardened steel is the material
of choice for gearbox components and drive shafts having sizes
greater than 3 tons. This shaft is typically machined out of a
steel forging. The material of the shaft is usually
quenched-tempered high-strength low alloy steel with critical
fatigue properties. Examples include nickel chromium steels such as
34CrNiMo6 steel.
[0003] Processing of heavy forged steel wind components from large
ingots is complex, requiring numerous hot working operations
(a.k.a., forging) and heat treatment operations to sufficiently
refine the structure to provide a suitable microstructure
responsive to the subsequent quality heat treatment to develop
desired mechanical properties. Such exhaustive processing paths and
the extensive machining attributed to the limited freedom of
geometry come at a steep cost relative to the straightforward
production of cast ADI counterparts.
SUMMARY OF THE INVENTION
[0004] Embodiments of the invention include a component that is
cast austempered ductile iron containing about 3.0 to about 3.8
weight percent carbon, about 1.9 to about 2.8 weight percent
silicon, up to about 0.3 weight percent manganese, up to about 0.8
weight percent copper, up to about 2.0 weight percent nickel, up to
about 0.3 weight percent molybdenum, about 0.03 to about 0.06
weight percent magnesium, less than about 0.05 weight percent
chromium, less than about 0.02 weight percent vanadium, and less
than about 0.01 weight percent sulfur. The component has a mass of
more than about 3 tons.
[0005] Another embodiment of the invention includes a method of
manufacturing a component. The method includes melting ductile iron
containing about 3.0 to about 3.8 weight percent carbon, about 1.9
to about 2.8 weight percent silicon, up to about 0.3 weight percent
manganese, up to about 0.8 weight percent copper, up to about 2.0
weight percent nickel, up to about 0.3 weight percent molybdenum,
about 0.03 to about 0.06 weight percent magnesium, less than about
0.05 weight percent chromium, less than about 0.02 weight percent
vanadium, and less than about 0.01 weight percent sulfur. The
component is cast. The component is austenitized and quenched to
the austempering temperature. The component is austempered.
[0006] Embodiments of the invention include a wind turbine drive
shaft that is cast austempered ductile iron containing about 3.0 to
about 3.8 weight percent carbon, about 1.9 to about 2.8 weight
percent silicon, up to about 0.3 weight percent manganese, up to
about 0.8 weight percent copper, up to about 2.0 weight percent
nickel, up to about 0.3 weight percent molybdenum, about 0.03 to
about 0.06 weight percent magnesium, less than about 0.05 weight
percent chromium, less than about 0.02 weight percent vanadium, and
less than about 0.01 weight percent sulfur. The drive shaft has a
mass of more than about 3 tons.
DETAILED DESCRIPTION
[0007] Austempered ductile iron (ADI) that is cast is able to
provide high mass and net-shaped components, greater than about 3
tons, more preferably greater than about 6 tons, for heavy wind
turbine shafts and gearbox components. Presently, forge/hardened
steel is used to make large wind turbine shafts and gearbox
components. However, forged/hardened steel, for example 34CrNiMo6,
is a relatively expensive material that requires a complex process
to produce a component, especially a component of greater than
about 3 tons with complex geometries. As size increases to 6 tons
or greater the expense of producing a forged/hardened steel
component is even greater and the worldwide supplier base is very
limited. The typical steps required to produce heavy wind turbine
gearbox components from high strength, low alloy steels include
melting of ingot, cogging of ingot into billet, forging of billet,
forging of part, normalizing, austenitizing, water quenching,
tempering and extensive/complicated machining. The process to
produce gearbox components from high strength, low-alloy steel
requires numerous steps and a large energy requirement when
compared with a conventional casting process. These manufacturing
steps for producing components from high strength, low-alloy steel
increase in cost as the size of the component increases.
[0008] The primary chemical composition of austempered ductile iron
(ADI) used in embodiments of the invention includes about 3.0 to
about 3.8 weight percent (w/o) carbon, about 1.9 to about 2.8
weight percent silicon, up to about 0.3 weight percent manganese,
up to about 0.8 weight percent copper, up to about 2.0 weight
percent nickel, up to about 0.3 w/o molybdenum, less than about
0.05 weight percent chromium, less than about 0.02 weight percent
vanadium, about 0.03 to about 0.06 weight percent magnesium and
less than about 0.01 weight percent sulfur. Primary chemistry is
used to identify the most important elements. Not every element is
identified as there are certain "tramp" elements at low
concentrations in the iron. The term ductile iron means that iron
makes up the remainder of the composition except for "tramp"
elements. ADI provides weight reduction attributed to its lower
density, noise reduction attributed to its higher damping
capability, similar or better mechanical properties than those of
cast/forged steel and the casting processes provide less costly
manufacturing and keeps machining of the component to a minimum.
ADI requires a special isothermal heat treatment, referred to as
austempering, which provides excellent combinations of high
strength and toughness. The strain induced by the final machining
after this heat treatment enhances the fatigue properties.
[0009] Certain properties of ADI are not as good as forged/hardened
steel. ADI possesses 15-20 percent less stiffness than
forged/hardened steel and lower impact resistance. However, by
making the parts slightly larger and/or proper design modifications
this deficiency is mitigated. In comparing ADI with forged/hardened
steel and the chemistry range identified, it is possible to obtain
heavy wind turbine shafts and gearbox components at reduced costs
with comparable properties.
[0010] The preferred primary chemical composition of ADI for use in
embodiments of the present invention includes about 3.0 to about
3.8 weight percent (w/o) carbon, about 1.9 to about 2.8 weight
percent silicon, up to about 0.3 weight percent manganese, up to
about 0.8 weight percent copper, up to about 2 weight percent
nickel, up to about 0.3 weight percent molybdenum, about 0.03 to
about 0.06 weight percent magnesium, less than about 0.05 weight
percent chromium, less than about 0.02 weight percent vanadium, and
less than about 0.01 weight percent sulfur. As mentioned above,
iron is the remaining constituent except for certain tramp
elements.
[0011] Carbide forming elements including but not limited to
chromium and vanadium shall be held to as low a level as possible
to avoid formation of massive carbides in the microstructure.
Chromium and vanadium should be below 0.05 weight percent and 0.02
weight percent respectively.
[0012] The matrix microstructure of ADI includes a fine-scale
dispersion of acicular ferrite with ductile high carbon stabilized
austenite, so called ausferrite. The ausferrite matrix is
responsible for unique properties attainable in ADI components.
[0013] The austenite in ADI is thermally stabilized with carbon
during heat treatment and will not transform to brittle martensite
even at temperatures approaching absolute zero. Stable, carbon
enriched austenite can undergo a strain-induced transformation when
exposed to high, normal forces. This transformation, which gives
ADI its remarkable wear resistance, is more than mere "work
hardening". In addition to a significant increase in flow stress
and hardness, this strain induced transformation of the austenite
to martensite also produces a localized increase in volume and
creates high compressive stresses in the "transformed" areas. These
compressive stresses inhibit crack formation and growth, and
produce significant improvements in the fatigue properties of ADI
when it is machined after heat treatment or subjected to surface
treatments such as shot peening, grinding or rolling.
[0014] Austenitizing is the process of holding the ductile iron
casting above the critical temperature for a sufficient period of
time to ensure that the matrix is fully transformed to austenite.
Both austenitizing time and temperature depend on the
microstructure and composition of the as-cast material. In order to
produce a single phase matrix microstructure (austenite) with a
uniform carbon distribution, austenitizing includes holding the
casting at temperatures in the range of about 815-985.degree. C.
(1500-1800.degree. F.) for a time period that is sufficient to
fully convert the matrix of the thickest section to austenite.
Unlike steels, selection for the austenitizing temperature in cast
irons determines the initial carbon content of the austenite, a
factor crucial in defining the thermodynamic driving force for
ausferrite transformation during subsequent austempering.
Additionally, proper selection of the austenitizing temperature
will help ensure distribution of austenite and ferrite phases
within the fully transformed ausferrite product.
[0015] An isothermal hold is preformed right after a direct quench
from austenitizing to a temperature above the martensitic
transformation. The rate of quench has to be high enough to avoid
ferrite/pearlite formation. Depending upon the desired mechanical
properties of end products, the temperature of the isothermal hold
(a.k.a. austempering) is in the range of about 230 to about
400.degree. C. (450-750.degree. F.) and its duration has to be long
enough to produce a matrix of ausferrite which includes acicular
ferrite and austenite stabilized with about 2 weight percent
carbon. Selection of the austempering temperature also plays a
crucial role in defining the nature and composition of the
ausferrite product and its attendant properties. In general, as the
austempering temperature decreases, the carbon stabilized austenite
will increase in carbon content and decrease in volume fraction,
which is compensated by an increase in volume fraction of ferrite.
Ductile iron austempered at lower temperatures will typically have
a finer matrix microstructure with improved strength compared to
iron transformed at higher temperatures. However, these irons will
typically contain higher levels of carbide at the expense of
ferrite potentially leading to a drop in toughness. Careful
selection of austempering temperature with sufficient hold time is
required to develop the desired properties of ADI components.
[0016] Generally, cast ADI parts provide components that are
net-shaped and require no further machining; however, for some
parts, depending on their geometry machining may be necessary. Gun
drilling or deep hole drilling that is needed to create a center
bore in forged wind turbine shafts can be eliminated with the use
of cores in the casting process described above.
[0017] 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",
is inclusive of the endpoints and all intermediate values of the
ranges of "about 5 w/o to about 25 w/o," etc).
[0018] 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.
* * * * *