U.S. patent application number 13/123001 was filed with the patent office on 2011-08-11 for ductile iron having cobalt.
Invention is credited to Stefan Janssen, Shilun Sheng.
Application Number | 20110194969 13/123001 |
Document ID | / |
Family ID | 41138731 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110194969 |
Kind Code |
A1 |
Janssen; Stefan ; et
al. |
August 11, 2011 |
Ductile Iron Having Cobalt
Abstract
Known cast iron alloys have application limits with regard to
temperature. A cast iron including cobalt is provided. Through the
use of cobalt, an optimal ferritic microstructure is achieved such
that with an alloy having silicon 2.0-4.5 wt %, cobalt 0.5-5 wt %,
carbon 2.0-4 wt %, molybdenum 0.3-1.48 wt %, manganese .ltoreq.0.5
wt %, nickel .ltoreq.0.5 wt %, the remainder iron, wherein the
proportion of silicon, cobalt, and molybdenum is preferably less
than 7.5 wt %, the application limits are shifted to high
temperatures.
Inventors: |
Janssen; Stefan; (Essen,
DE) ; Sheng; Shilun; (Oberhausen, DE) |
Family ID: |
41138731 |
Appl. No.: |
13/123001 |
Filed: |
September 4, 2009 |
PCT Filed: |
September 4, 2009 |
PCT NO: |
PCT/EP2009/061457 |
371 Date: |
April 7, 2011 |
Current U.S.
Class: |
420/27 |
Current CPC
Class: |
C22C 37/10 20130101;
C22C 37/04 20130101 |
Class at
Publication: |
420/27 |
International
Class: |
C22C 37/10 20060101
C22C037/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2008 |
DE |
10 2008 051 042.4 |
Claims
1-34. (canceled)
35. An alloy comprising (in % by weight): silicon 2.0%-4.5%; cobalt
0.5%-5.0%; carbon 2.0%-4.5%; and molybdenum 0.5%-0.8%.
36. The alloy as claimed in claim 35, further comprising (in % by
weight): manganese .ltoreq.0.5%, nickel .ltoreq.0.5%, magnesium
.ltoreq.0.09%, phosphorus .ltoreq.0.07%, sulfur .ltoreq.0.04%,
chromium .ltoreq.0.1%, and remainder iron.
37. The alloy as claimed in claim 35, wherein a proportion of
silicon, cobalt and molybdenum is less than 7.5% by weight.
38. The alloy as claimed in claim 35, comprising 0.5% by weight to
1.5% by weight cobalt.
39. The alloy as claimed in claim 36, wherein the alloy comprises
at least 0.005% by weight manganese.
40. The alloy as claimed in claim 36, wherein the alloy comprises a
manganese content .ltoreq.0.07% by weight.
41. The alloy as claimed in claim 36, wherein the alloy comprises
no manganese.
42. The alloy as claimed in claim 36, wherein the alloy comprises
at least 0.01% by weight nickel.
43. The alloy as claimed in claim 36, wherein the alloy comprises
no nickel.
44. The alloy as claimed in claim 35, wherein the alloy comprises
2.8% by weight--3.2% by weight silicon.
45. The alloy as claimed in claim 36, wherein the alloy comprises
at most 0.007% by weight phosphorus.
46. The alloy as claimed in claim 36, which comprises at least
0.005% by weight phosphorus.
47. The alloy as claimed in claim 36, wherein the alloy comprises
at most 0.008% by weight sulfur.
48. The alloy as claimed in claim 36, wherein the alloy comprises
at least 0.001% by weight sulfur.
49. The alloy as claimed in claim 36, wherein the alloy comprises
at most 0.05% by weight magnesium.
50. The alloy as claimed in claim 36, wherein the alloy comprises
at least 0.01% by weight magnesium.
51. The alloy as claimed in claim 36, wherein the alloy comprises
no chromium.
52. The alloy as claimed in claim 36, wherein the alloy comprises
at most 0.03% by weight chromium.
53. The alloy as claimed in claim 36, wherein the alloy comprises
at least 0.01% by weight chromium.
54. The alloy as claimed in claim 35, wherein the alloy consists of
iron, silicon, cobalt, molybdenum and carbon.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2009/061457, filed Sep. 4, 2009 and claims
the benefit thereof. The International Application claims the
benefits of German application No. 10 2008 051 042.4 DE filed Oct.
9, 2008. All of the applications are incorporated by reference
herein in their entirety.
FIELD OF INVENTION
[0002] The invention relates to a cast iron comprising cobalt as
claimed in the claims and to a component as claimed in the
claims.
BACKGROUND OF INVENTION
[0003] The known cast iron alloys now employed (so-called GJS
nodular cast iron alloys) primarily use silicon and molybdenum to
increase the creep strength, scaling resistance and endurance
strength. Over time, however, these elements lead to a significant
decrease in the toughness.
[0004] Molybdenum furthermore exhibits a very high susceptibility
to segregation.
SUMMARY OF INVENTION
[0005] It is therefore an object of the invention to specify an
alloy and a component, which overcome the aforementioned
disadvantages and have better mechanical strengths over the service
life.
[0006] The object is achieved by an alloy as claimed in the claims
and a component as claimed in the claims.
[0007] The dependent claims list further advantageous measures
which may advantageously be combined with one another in any
desired way.
[0008] The invention consists in the fact that cobalt can partially
replace molybdenum. The working limitations presented by the
previous GJS alloy can therefore be overcome. The alloy according
to the invention has high elongations for the application field in
the temperature range of 450.degree. C.-550.degree. C., and has the
following composition (in % by weight):
silicon 2.0%-4.5% cobalt 0.5%-5% carbon 2.0%-4.5% molybdenum
0.3%-1.48%, remainder iron.
[0009] Advantageously, the proportion of silicon, cobalt and
molybdenum is .ltoreq.7.5% by weight, in particular .ltoreq.6.0% by
weight.
[0010] Preferably, the proportion of cobalt in the alloy lies
between 0.5% by weight and 1.5% by weight cobalt.
[0011] Advantageous mechanical values are achieved for the alloy
respectively when the cobalt content is 0.5% by weight, 1.0% by
weight cobalt, 1.5% by weight cobalt and 2.0% by weight cobalt.
[0012] The addition of molybdenum to the alloy (preferably
0.5%-0.8%) has a positive influence on the high-temperature
strength (Rp0.2 and Rm in the elevated temperature range) and the
endurance behavior (creep strength).
[0013] Magnesium increases the castability and is preferably
present in an amount of at least 0.02% by weight, at most 0.07% by
weight.
[0014] Depending on the application, chromium is preferably present
in an amount of at least 0.01% by weight, but at most 0.05% by
weight, and this increases the oxidation resistance.
[0015] The alloy may contain further elements.
[0016] Preferably, however, the alloy consists of iron, silicon,
cobalt and carbon.
[0017] Particular advantages are also achieved when the alloy
consists of iron, silicon, cobalt, carbon and manganese.
[0018] Further advantages are obtained with an alloy which consists
of iron, silicon, cobalt, carbon and optional admixtures of
molybdenum, manganese and/or nickel.
[0019] The alloy optionally contains small minimum admixtures of
phosphorus 0.005% by weight, sulfur 0.001% by weight, magnesium
0.01% by weight,
[0020] which have a positive influence on the castability and/or
the formation of the nodular graphite, but also must not be
excessively high since otherwise the negative influences
prevail.
[0021] Furthermore, there is preferably no chromium (Cr) in the
alloy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Exemplary embodiments of the invention will be explained in
more detail with reference to the following figures:
[0023] FIG. 1 shows a cast part in a micrograph,
[0024] FIG. 2 shows a steam turbine,
[0025] FIG. 3 shows a gas turbine.
DETAILED DESCRIPTION OF INVENTION
[0026] The alloy has an almost optimal ferritic microstructure with
nodular graphite (FIG. 1).
[0027] The table shows exemplary alloys which have improved
mechanical properties.
TABLE-US-00001 Cobalt 0 0.56 0.99 1.44 Carbon 3.63 3.67 3.65 3.67
Silicon 2.45 2.42 2.49 2.41 Manganese 0.067 0.036 0.03 0.029
Phosphorus 0.007 0.006 0.007 0.007 Sulfur 0.009 0.006 0.008 0.008
Magnesium 0.044 0.04 0.05 0.049 Molybdenum 0.87 0.5 0.3 0.3
[0028] Even small proportions of cobalt and molybdenum improve the
mechanical characteristics.
[0029] FIG. 2 shows a steam turbine 300, 303 having a turbine shaft
309 extending along an axis of rotation 306.
[0030] The steam turbine comprises a high-pressure turbine part 300
and a medium-pressure turbine part 303, each with an inner housing
312 and an outer housing 315 enclosing the latter. The
high-pressure turbine part 300 is, for example, configured in pot
design. The medium-pressure turbine part 303 is, for example,
configured to be twin-streamed. It is likewise possible for the
medium-pressure turbine part 303 to be configured to be
single-streamed.
[0031] A bearing 318 is arranged along the axis of rotation 306
between the high-pressure turbine part 300 and the medium-pressure
turbine part 303, the turbine shaft 309 comprising a bearing region
321 in the bearing 318. The turbine shaft 309 is mounted on a
further bearing 324 beside the high-pressure turbine part 300. In
the region of this bearing 324, the high-pressure turbine part 300
comprises a shaft seal 345. The turbine shaft 309 is sealed
relative to the outer housing 315 of the medium-pressure turbine
part 303 by two further shaft seals 345. Between a high-pressure
steam intake region 348 and a steam outlet region 351, the turbine
shaft 309 in the high-pressure turbine part 300 comprises the
high-pressure rotor blading 357. With the associated rotor blades
(not shown in more detail), this high-pressure rotor blading 357
constitutes a first blading region 360.
[0032] The medium-pressure turbine part 303 comprises a central
steam intake region 333. Associated with the steam intake region
333, the turbine shaft 309 comprises a radially symmetric shaft
shield 363, a cover plate, on the one hand to divide the steam flow
into the two streams of the medium-pressure turbine part 303 and
also to prevent direct contact of the hot steam with the turbine
shaft 309. In the medium-pressure turbine part 303, the turbine
shaft 309 comprises a second blading region 366 with the
medium-pressure rotor blades 354. The hot steam flowing through the
second blading region 366 flows from the medium-pressure turbine
part 303 out of a discharge port 369 to a low-pressure turbine part
(not shown) connected downstream.
[0033] The turbine shaft 309 is composed for example of two turbine
shaft parts 309a and 309b, which are connected firmly to one
another in the region of the bearing 318. Each turbine shaft part
309a, 309b comprises a cooling line 372 formed as a central bore
372a along the axis of rotation 306. The cooling line 372 is
connected to the steam outlet region 351 via a feed line 375
comprising a radial bore 375a. In the medium-pressure turbine part
303, the coolant line 372 is connected to a cavity (not shown in
more detail) below the shaft shield. The feed lines 375 are
configured as a radial bore 375a, so that "cold" steam from the
high-pressure turbine part 300 can flow into the central bore 372a.
Via the discharge line 372 also formed in particular as a radially
directed bore 375a, the steam passes through the bearing region 321
into the medium-pressure turbine part 303 and there onto the
lateral surface 330 of the turbine shaft 309 in the steam intake
region 333. The steam flowing through the cooling line is at a much
lower temperature than the temporarily superheated steam flowing
into the steam intake region 333, so as to ensure effective cooling
of the first rotor blade row 342 of the medium-pressure turbine
part 303 and the lateral surface 330 in the region of this rotor
blade row 342.
[0034] FIG. 3 shows, by way of example, a partial longitudinal
section through a gas turbine 100.
[0035] In the interior, the gas turbine 100 has a rotor 103 with a
shaft 101 which is mounted such that it can rotate about an axis of
rotation 102 and is also referred to as the turbine rotor.
[0036] An intake housing 104, a compressor 105, a, for example,
toroidal combustion chamber 110, in particular an annular
combustion chamber, with a plurality of coaxially arranged burners
107, a turbine 108 and the exhaust-gas housing 109 follow one
another along the rotor 103.
[0037] The annular combustion chamber 110 is in communication with
a, for example, annular hot-gas passage 111, where, by way of
example, four successive turbine stages 112 form the turbine
108.
[0038] Each turbine stage 112 is formed, for example, from two
blade or vane rings. As seen in the direction of flow of a working
medium 113, in the hot-gas passage 111 a row of guide vanes 115 is
followed by a row 125 formed from rotor blades 120.
[0039] The guide vanes 130 are secured to an inner housing 138 of a
stator 143, whereas the rotor blades 120 of a row 125 are fitted to
the rotor 103 for example by means of a turbine disk 133.
[0040] A generator (not shown) is coupled to the rotor 103.
[0041] While the gas turbine 100 is operating, the compressor 105
sucks in air 135 through the intake housing 104 and compresses it.
The compressed air provided at the turbine-side end of the
compressor 105 is passed to the burners 107, where it is mixed with
a fuel. The mix is then burnt in the combustion chamber 110,
forming the working medium 113. From there, the working medium 113
flows along the hot-gas passage 111 past the guide vanes 130 and
the rotor blades 120. The working medium 113 is expanded at the
rotor blades 120, transferring its momentum, so that the rotor
blades 120 drive the rotor 103 and the latter in turn drives the
generator coupled to it.
[0042] While the gas turbine 100 is operating, the components which
are exposed to the hot working medium 113 are subject to thermal
stresses. The guide vanes 130 and rotor blades 120 of the first
turbine stage 112, as seen in the direction of flow of the working
medium 113, together with the heat shield elements which line the
annular combustion chamber 110, are subject to the highest thermal
stresses.
[0043] To be able to withstand the temperatures which prevail
there, they may be cooled by means of a coolant.
[0044] Substrates of the components may likewise have a directional
structure, i.e. they are in single-crystal form (SX structure) or
have only longitudinally oriented grains (DS structure).
[0045] By way of example, iron-based, nickel-based or cobalt-based
superalloys are used as material for the components, in particular
for the turbine blade or vane 120, 130 and components of the
combustion chamber 110.
[0046] Superalloys of this type are known, for example, from EP 1
204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO
00/44949.
[0047] The blades or vanes 120, 130 may likewise have coatings
protecting against corrosion (MCrAlX; M is at least one element
selected from the group consisting of iron (Fe), cobalt (Co),
nickel (Ni), X is an active element and stands for yttrium (Y)
and/or silicon, scandium (Sc) and/or at least one rare earth
element, or hafnium). Alloys of this type are known from EP 0 486
489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1.
[0048] It is also possible for a thermal barrier coating to be
present on the MCrAlX, consisting for example of ZrO.sub.2,
Y.sub.2O.sub.3--ZrO.sub.2, i.e. unstabilized, partially stabilized
or fully stabilized by yttrium oxide and/or calcium oxide and/or
magnesium oxide.
[0049] Columnar grains are produced in the thermal barrier coating
by suitable coating processes, such as for example electron beam
physical vapor deposition (EB-PVD).
[0050] The guide vane 130 has a guide vane root (not shown here),
which faces the inner housing 138 of the turbine 108, and a guide
vane head which is at the opposite end from the guide vane root.
The guide vane head faces the rotor 103 and is fixed to a securing
ring 140 of the stator 143.
* * * * *