U.S. patent application number 10/806439 was filed with the patent office on 2004-09-30 for nickel base heat resistant cast alloy and turbine wheels made thereof.
Invention is credited to Noda, Toshiharu, Shimizu, Tetsuya, Takahata, Noritaka, Ueta, Shigeki.
Application Number | 20040187973 10/806439 |
Document ID | / |
Family ID | 32829031 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040187973 |
Kind Code |
A1 |
Takahata, Noritaka ; et
al. |
September 30, 2004 |
Nickel base heat resistant cast alloy and turbine wheels made
thereof
Abstract
Disclosed is a nickel-base super heat resistant cast alloy, from
which turbine wheels of automobile engines can be manufacture by
casting. The alloy consists essentially of, by weight %, C:
0.02-0.50%, Si: up to 1.0%, Mn: up to 1.0%, Cr: 4.0-10.0%, Al:
2.0-8.0%, Co: up to 15.0%, W: 8.0-16.0%, Ta: 2.0-8.0%, Ti: up to
3.0%, Zr: 0.001-0.200% and B: 0.005-0.300% and the balance of Ni
and inevitable impurities, provided that, [%Al]+[%Ti]+[%Ta], by
atomic %, amounts to 12.0-15.5%, that it contains
.gamma./.gamma.'-eutectoid of, by area percentage, 1-15%, that it
contains carbides of, by area percentage, 1-10%, and that the
"M-value" determined by the alloy composition is in the range of
93-98. The turbine wheels withstand temperature increase of exhaust
gas.
Inventors: |
Takahata, Noritaka;
(Nagoya-shi, JP) ; Ueta, Shigeki; (Nagoya-shi,
JP) ; Noda, Toshiharu; (Nagoya-shi, JP) ;
Shimizu, Tetsuya; (Nagoya-shi, JP) |
Correspondence
Address: |
VARNDELL & VARNDELL, PLLC
106-A S. COLUMBUS ST.
ALEXANDRIA
VA
22314
US
|
Family ID: |
32829031 |
Appl. No.: |
10/806439 |
Filed: |
March 23, 2004 |
Current U.S.
Class: |
148/428 ;
420/442 |
Current CPC
Class: |
F01D 5/28 20130101; C22C
19/057 20130101 |
Class at
Publication: |
148/428 ;
420/442 |
International
Class: |
C22C 019/05 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2003 |
JP |
2003-080844 |
Jan 22, 2004 |
JP |
2004-014921 |
Claims
1. A nickel-base heat resistant cast alloy, which consists
essentially of, by weight %, C: 0.02-0.50%, Si: up to 1.0%, Mn: up
to 1.0%, Cr: 4.0-10.0%, Al: 2.0-8.0%, Co: up to 15.0%, W:
8.0-16.0%, Ta: 2.0-8.0%, Ti: up to 3.0%, Zr: 0.001-0.200% and B:
0.005-0.300% and the balance of Ni and inevitable impurities,
provided that, [%Al]+[%Ti]+[%Ta], by atomic %, amounts to
12.0-15.5%, that it contains .gamma./.gamma.'-eutectoid of, by area
percentage, 1-15%, that it contains carbides of, by area
percentage, 1-10%, and that the "M-value" defined by the formula
below (in which % is atomic %) is in the range of 93-98:
M=0.717[%Ni]+1.142[%Cr]+2.271
[%Ti]+1.9[%Al]+2.117[%Nb]+1.55[%Mo]+0.777
[%Co]+3.02[%Hf]+2.224[%Ta]+1.65- 5[%W]+2.994[%Zr].
2. The nickel-base heat resistant cast alloy according to claim 1,
wherein the alloy further contains at least one of the group
consisting of Mg: up to 0.01%, Ca: up to 0.01% and REM: up to
0.1%.
3. The nickel-base heat resistant cast alloy according to claim 1,
wherein the contents of the impurities are regulated to be up to
the following respective upper limits: Fe: 5.0%, Mo: 1.0%, Cu:
0.3%, P: 0.03%, S: 0.03% and V: 1.0%
4. The nickel-base heat resistant cast alloy according to claim 1,
wherein the alloy further contains at least one of the group
consisting of Mg: up to 0.01%, Ca: up to 0.01% and REM: up to 0.1%,
and wherein the contents of the impurities are regulated to be up
to the following respective upper limits: Fe: 5.0%, Mo: 1.0%, Cu:
0.3%, P: 0.03%, S: 0.03% and V: 1.0%.
5. A turbine wheel for automobile engines made of the nickel-base
heat resistant cast alloy according to claim 4.
6. A turbine wheel for automobile engines made of the nickel-base
heat resistant cast alloy according to claim 2.
7. A turbine wheel for automobile engines made of the nickel-base
heat resistant cast alloy according to claim 3.
8. A turbine wheel for automobile engines made of the nickel-base
heat resistant cast alloy according to claim 4.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field in the Industry
[0002] The present invention concerns a nickel base heat resistant
cast alloy and turbine wheels made from the alloy for automobile
engines. The invention provides turbine wheels having the strength
higher than that of the conventional ones with substantially the
same cost.
[0003] 2. Prior Art
[0004] Because turbine wheels for automobile engines are the parts
subjected directly to high-temperature exhaust gas, requirements
for heat resistant property and enough strength at high temperature
thereof are severe. To date, as the material for turbine wheels of
ordinary passenger cars INCONEL 713C (hereinafter abbreviated as
"713C") has been used. The alloy has a long history of practical
use (Japanese Patent Publication Sho.42[1967]-11915). On the other
hand, as the material for the turbine wheels used under severer
conditions, such as for engines of rally cars, there has been used
Mar-M 247 (hereinafter abbreviated as "MM-247") having the strength
higher than that of 713C. This alloy also has been known and used
for many years (Japanese Patent Disclosure Sho.47[1972]-13204).
[0005] While it is anticipated that exhaust gas temperature will be
much higher in the near future due to increase of output of
passenger car engines, 713C may not meet the demand due to its
insufficient high temperature strength. On the other hand, MM-247
contains hafnium, which is expensive, as one of the components of
this alloy and the material cost is thus high. Moreover, HIP
process is often used at manufacturing the wheels so that voids may
not occur in the cast products and therefore, manufacturing cost is
high.
[0006] The efforts for solving these problems have been continued
for years and resulted in proposing turbine wheels made of nickel
base heat resistant cast alloy which achieved the creep rapture
strength higher than that of 713C (Japanese Patent Disclosure
Hei.11[1998]-131162 and 2000-169924). These materials have,
however, alloy compositions comprising niobium (the former contains
0.5-3.5% and the latter, 6.0-8.0%), which brought about a new
problem of easy segregation of Nb. Furthermore, these alloys
contain molybdenum (both 1.0-5.0%) and therefore, high temperature
oxidation resistance is not so high. As the conclusion, from the
viewpoints of balanced cost-saving and merits of improvement, it
cannot be said that fully satisfactory, low-cost Ni-base heat
resistant cast alloy have been developed.
SUMMARY OF THE INVENTION
[0007] The object of the present invention is to provide a
nickel-base heat resistant cast alloy used as the material for
turbine wheels of automobile engines having the high strength at
high temperature to meet the tendency of increasing exhaust gas
temperature, and with respect to the material cost, though a little
higher, with substantially the same cost, while the heat resistance
property and the high temperature strength are about the same as
those of MM-247. To provide turbine wheels made of this material is
also the object of this invention.
[0008] The nickel base heat resistant cast alloy of the invention
consists essentially of, by weight %, C: 0.02-0.50%, Si: up to
1.0%, Mn: up to 1.0%, Cr: 4.0-10.0%, Al: 2.0-8.0%, Co: up to 15.0%,
W: 8.0-16.0%, Ta: 2.0-8.0%, Ti: up to 3.0%, Zr: 0.001-0.200% and B:
0.005-0.300% and the balance of Ni and inevitable impurities,
provided that [%Al]+[%Ti]+[%Ta], by atomic %, amounts to
12.0-15.5%, that it contains .gamma./.gamma.'-eutectoid of, by area
percantage, 1-15%, that it contains carbides of, by area
percentage, 1-10%, and that the "M-value" defined by the formula
below (in which % is atomic %) is in the range of 93-98:
[0009]
M=0.717[%Ni]+1.142[%Cr]+2.271[%Ti]+1.9[%Al]+2.117[%Nb]+1.55[%Mo]+0.-
777[%Co]+3.02[%Hf]+2.224[%Ta]+1.655[%W]+2.994[%Zr]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] The Ni-base heat resistant cast alloy according to the
present invention may contain, in addition to the above mentioned
basic alloy components, at least one of the group consisting of Mg:
up to 0.01%, Ca: up to 0.01% and REM: up to 0.1%.
[0011] The main impurities which may be contained in the present
Ni-base heat resistant cast alloy of the invention are Fe, Si, Mn,
P and S, originated from the raw materials. Depending on the cases,
Cu and Mo may also be contained. It is preferable to regulate the
contents of the impurities at highest up to the following
respective upper limits:
[0012] Fe: up to 5.0%, Mo: 1.0%, Cu: 0.3%, P: 0.03%, S: 0.03%, and
V: 1.0%.
[0013] The effects of the alloy components and the reasons for
limiting the alloy compositions as defined above will be explained
below together with the significance of the limitations of the
above-mentioned [%Al]+[%Ti]+[%Ta], area percentage of
.gamma./.gamma.'-eutectoid, area percentage of carbides and the
"M-value".
[0014] C: 0.02-0.50%, preferably 0.05-0.30%, more preferably
0.05-0.20%
[0015] Carbon contributes to strengthening of grain boundaries by,
in case of an element of the group of Ti, Zr and Hf, or an element
of the group of Nb, Ta and V, combining with it to form carbide or
carbides thereof. A carbon content less than 0.02% may not give
sufficient effect, while a content exceeding 0.50% will cause
formation of excess carbide or carbides, which results in decreased
corrosion resistance and ductility. Preferable C-content is in the
range of 0.05-0.30%, and more preferable range is 0.02-0.20%.
[0016] Si: up to 1.0%
[0017] Silicon is usually used as a deoxidizing agent at the time
of melting and refining the alloy. Though content of a small amount
of Si effective as the deoxidizing agent may cause no problem, too
much addition will lower the ductility of the alloy. Thus, 1.0% is
set as the upper limit. Preferable Si-content is up to 0.5%.
[0018] Mn: up to 1.0%
[0019] Manganese is, like silicon, also added as a deoxidizing
agent. Addition in a small amount effective as the deoxidizing
agent may cause no problem, however, too much addition will lower
the strength and the ductility of the alloy. The upper limit, 1.0%,
is thus set.
[0020] Cr: 4.0-10.0%
[0021] Chromium is the most important element for improving the
corrosion resistance of the alloy. It also contributes to increase
of the strength by solid solution in the matrix phase. Addition
amount less than 4.0% will give little effect, while more than
10.0% lowers the phase stability and the strength and the ductility
of the turbine wheel after operation at a high temperature for a
long period of time. Preferable range of Cr-content is
6.0-10.0%.
[0022] Al: 2.0%-8.0%
[0023] Aluminum is an important element forming .gamma.'-phase, and
is useful for improving high temperature corrosion resistance.
These effects may be week at such a small amount as less than 2.0%.
On the other hand, addition exceeding 8.0% causes deposition of
much amount of eutectic .gamma.'-phase in casting, and as the
result, creep rapture strength will decrease. Preferable range of
Al-content is 4.5-5.5%.
[0024] Co: up to 15.0%
[0025] Cobalt strengthens .gamma.-phase by solid solution. It also
dissolves in .gamma.'-phase, which is effective for increasing the
strength of the alloy, and strengthens the .gamma.'-phase. Co
increases deposition amount of the .gamma.-phase. However, because
Co is an expensive material, addition in a large amount is
disadvantageous from the viewpoints of the cost. Choosing an
addition amount up to 15.0% is recommended. In order to ensure
sufficient high temperature properties at 900.degree. C. or higher,
it is desirable to add Co in an amount of 5.0% or higher.
[0026] W: 8.0-16.0%
[0027] Wolfram contributes greatly to solution strengthening of the
.gamma.-phase and increase of the strength. An amount less than
8.0% will give insufficient effect, while an amount exceeding 16.0%
lowers the phase stability. The lowered phase stability causes
deposition of .alpha.-Cr in the alloy after using for a long while
and damages the strength of the wheels. A preferable range of
addition is 10.0-14.0%.
[0028] Ta: 2.0-8.0%
[0029] Tantalum not only combines with carbon to form the carbide,
but also dissolves in the .gamma.'-phase to strengthen it. The
effect is low at addition amount less than 2.0%. Because Ta is an
expensive material like Hf, from the viewpoint of the cost, it is
desirable to use it in an amount as small as possible. The upper
limit, 8.0%, is thus set.
[0030] Ti: up to 3.0%
[0031] Titanium reacts Ni to form the .gamma.'-phase which is
effective in increasing the strength of the alloy. Ti has further
effect of replacing Al to contribute to solution strengthening of
the .gamma.'-phase, and thus, further improves the strength of the
alloy. However, addition of Ti exceeding 3.0% tends to cause
deposition of .eta.-phase (Ni.sub.3Ti), which gives disadvantage to
the high temperature strength and the ductility of the alloy.
Preferable amount of addition is 2.0% or less.
[0032] Zr: 0.001-0.200%
[0033] Zirconium has both the effect of combining with carbon to
form the carbide and the effect of segregating at the grain
boundaries to strengthen. These effects are observed at even such a
small amount of addition as 0.001%. Due to decrease of the
ductility at addition of a large amount the upper limit is set to
be 0.200%. An optimum amount of addition may be found in a range up
to 0.1%.
[0034] B: 0.005-0.300%, preferably 0.050-0.200%
[0035] Effects of adding B are suppressing formation of the
.eta.-phase to prevent decrease of the high temperature strength
and the ductility, and further, enhancing the high temperature
creep rapture strength. Also, B forms borides with Cr and some
other elements. Because melting points of the borides are low, the
temperature range of solid-liquid coexisting is board, and thus,
castability of the alloy will be improved. To seek these effects,
it is necessary to add a suitable amount of B in the range of
0.005% or more. Addition in an excess amount, however, results in
decrease of the strength and the ductility of the alloy. Thus, the
upper limit of addition is set to 0.300%. Favorable balance of the
castability and strength-resilience can be achieved in the range
from 0.050 to 0.200%.
[0036] One or more of Mg: up to 0.01%, Ca: up to 0.01% and REM: up
to 0.1%
[0037] Both Magnesium and calcium segregate at the grain boundaries
to strengthen. REM has the same effect. Large amount addition of
any element or elements is not advisble due to decrease of the
strength and the ductility of the alloy. The upper limits of
addition are thus set to be 0.01% for Mg and Ca, and 0.1% for
REM.
[0038] Regulation on the contents of the impurities to the
following upper limits:
[0039] Fe: 5.0%, Mo: 1.0%, Cu: 0.3%, P: 0.03%, S: 0.03% and V:
1.0%.
[0040] In the case where iron scrap, a cheep raw material, is
intended to use for the purpose of decreasing the manufacturing
cost, various impurities will come into the product alloy. The
element which may get mixed with the highest possibility is Fe,
which is harmful to all the properties of the strength, the
corrosion resistance at room- and high temperature. Allowable limit
of Fe-content is 5.0%, and 3.0% or less is preferable. Phosphor
segregates at the grain boudaries to cause lowered strength, and
therefore, content of a large amount of P is undesirable. However,
it is inevitable that a certain amount exists in the alloy. The
allowable limit of P is 0.03%. Sulfur is also an element decreasing
the strength like P, and the S-content is preferably limited to be
0.03% or less. Molybdenum, though it dissolves in the matrix of the
alloy to contribute to increasing the strength, content at a large
amount damages the high temperature oxidation resistance, and thus,
the Mo-content should be such amount as up to 1.0%. Copper is also
the cause of decreased strength, and therefore, existence of Cu in
a large amount is not desirable. The allowable upper limit is 1.0%,
and Cu-content of 0.3% or less is preferable. Vanadium brings about
the disadvantage of decreased high temperature strength, and the
V-content should be limited to less than the upper limit, 1.0%.
[0041] [%Al]+[%Ti]+[%Ta]: 12.0-15.5 atomic %
[0042] In order to ensure sufficient strength and workability of
the alloy this condition must be met. Outside this range there are
the following disadvantages. If the amount is less than 12.0%, the
lower limit, then satisfactory strength may not be obtained, and if
the amount is more than 15.5%, the upper limit, then cracks tend to
occur in the cast products.
[0043] Area percentage of .gamma./.gamma.'-eutectoid: 1-15%
[0044] Keeping the lower limit, 1%, is necessary for ensuring the
workability, particularly, castability of the alloy. In case where
the area percentage is less than 1%, voids may occur at the last
stage of casting, and the liability of the product wheels will
become low. On the other hand, in case where the area percentage
exceeds 15%, the eutectoid may become the starting points of
fracture.
[0045] Area percentage of carbides: 1-10%, preferably 1-5%
[0046] Formation of a suitable amount of carbides is useful for
strengthening the grain boundaries and enhance the high temperature
strength at 1000.degree. C. or higher. When the area percentage of
the carbides is 1% or more, this effect can be obtained, and when
the area percentage exceeds 10%, it is lost. Preferable range of
the area percentage of the carbides is 1-5%.
[0047] M-value: 93-98
[0048] The M-value defined by the formula above is a measure for
the phase stability. The M-value in the range of 93-98 guaranties
the durability of the product turbine wheels. Because the alloy of
this invention is used for automobile parts, a higher M-value is
advantageous to give longer durability of the parts. However, at an
M-value exceeding 98, harmful phases such as .sigma.-phase tend to
occur after using for a long period of time, and the durability
will decrease.
[0049] Though the Ni-base heat resistant cast alloy according to
the invention contains no expensive Hf, which is effective for
strengthening the alloy, it has creep rapture strength much better
than that of 713C alloy which is used most widely as the material
for the turbine wheels, and the creep rapture strength of the
invented alloy is substantially the same as that of MM-247
containing Hf. Based on the alloy composition, the material cost
may be a little higher than that of 713, but still lower than that
of MM-247. Because of high castability of the present alloy HIP
process is not necessary to apply, and thus, the cost for
manufacturing the turbine wheels may not be high. The present
invention thus makes it possible to provide turbine wheels, which
can meet the anticipated increase of exhaust gas temperature in the
near future, at lower prices.
EXAMPLES
[0050] Nickel-base heat resistant alloys having the alloy
compositions shown in Table 1 (Working Examples) and Table 2
(Control Examples) were produced and cast into ingots weighing
50kg. No.A of the Control Examples is the conventional 713C alloy,
and No.B corresponds to MM-247. Properties of these alloys such as
[%Al]+[%Ti]+[%Ta] are shown in Table 3 (Working Examples) and Table
4 (Control Examples). Test pieces were taken from the ingots by
machining, and they were subjected to creep rapture tests at the
conditions of 1000.degree. C. and 180 MPa. The determined creep
properties are shown in Table 3 and Table 4.
[0051] In regard to the alloys of the Working Examples No.8 and
No.9 the area percentages of .gamma./.gamma.'-eutectoid were
adjusted to be 3.2% (No.8 and No.9) and 18.5 (No.8A and No.9A) by
regulating the cooling rates after casting. The samples were also
subjected to the creep tests of the same conditions, 1000.degree.
C. and 180 MPa. The results are shown in Table 5. For convenience
of comparison the data of the case of area percentage 7.1% is shown
in Table 5 again.
1TABLE 1 Alloy Compositions (Working Examples) No. C Si Mn Cr Co W
Ta Al Ti Zr B Others 1 0.15 0.06 0.08 8.1 11.6 11.9 4.9 5.2 1.1
0.05 0.015 -- 2 0.13 0.11 0.07 4.3 9.1 10.3 5.1 5.0 1.0 0.04 0.015
-- 3 0.16 0.08 0.06 5.9 -- 13.1 4.5 5.2 1.4 0.05 0.013 -- 4 0.11
0.07 0.06 7.4 12.2 8.3 4.7 5.3 1.3 0.04 0.020 -- 5 0.13 0.12 0.04
9.0 10.9 14.2 2.2 5.6 1.2 0.05 0.018 -- 6 0.12 0.42 0.06 7.9 9.2
11.1 7.6 5.1 0.9 0.04 0.016 -- 7 0.14 0.14 0.39 7.3 10.0 13.2 5.1
4.1 2.6 0.05 0.015 -- 8 0.12 0.08 0.08 6.2 13.6 11.2 3.2 6.8 0.4
0.03 0.011 -- 9 0.11 0.07 0.07 6.3 12.8 10.9 7.9 2.1 2.9 0.04 0.013
-- 10 0.05 0.13 0.06 8.2 10.4 12.3 4.6 5.3 0.9 0.03 0.013 -- 11
0.18 0.12 0.08 9.2 11.4 13.0 4.5 5.2 1.0 0.05 0.014 -- 12 0.14 0.12
0.09 7.3 9.1 13.0 4.8 4.9 1.4 0.01 0.015 -- 13 0.13 0.10 0.10 8.2
11.2 9.3 4.6 5.1 0.9 0.18 0.012 -- 14 0.12 0.13 0.06 9.3 10.9 12.2
4.7 5.4 1.1 0.04 0.006 -- 15 0.04 0.12 0.05 8.2 10.1 12.1 4.7 5.3
1.2 0.05 0.14 -- 16 0.10 0.14 0.08 8.2 10.1 11.6 4.3 5.2 0.9 0.04
0.003 Mg 0.005 17 0.11 0.11 0.09 8.3 10.6 12.1 4.6 5.3 1.1 0.05
0.002 Ca 0.006 18 0.13 0.09 0.12 8.2 10.1 12.2 4.6 5.3 1.0 0.05
0.056 -- 19 0.14 0.10 0.11 8.4 10.9 12.4 4.3 5.2 0.9 0.05 0.260 --
20 0.14 0.12 0.09 7.3 9.1 13.0 4.8 4.9 1.4 0.01 0.058 --
[0052]
2TABLE 2 Alloy Compositions (Control Examples) No. C Si Mn Cr Co W
Ta Al Ti Zr B Others A 0.15 0.12 0.08 8.3 10.0 10.0 2.9 5.6 1.1
0.05 0.015 Mo 0.7 Hf 1.5 B 0.12 0.12 0.06 12.0 -- -- -- 5.9 0.8
0.15 0.015 Mo 4.0 Nb 2.3 C 0.19 0.11 0.08 8.4 9.8 9.8 4.7 5.1 1.2
0.16 0.014 -- D 0.11 0.12 0.06 9.5 14.2 14.2 5.8 5.2 2.9 0.05 0.015
-- E 0.12 0.09 0.08 9.1 9.5 9.5 4.7 5.1 1.0 0.04 0.012 Fe 5.3 F
0.10 0.12 0.09 8.6 10.3 10.3 4.5 5.2 1.1 0.05 0.012 S 0.1
[0053]
3TABLE 3 Results (Working Examples) Ti + .gamma./.gamma.'- Al + Ta
Eutectoid Carbide (atomic (area per- (area per- Creep Property No.
%) centage) centage) M-value Life (hr) Elongation 1 12.58 3.9 4.2
94 47 3 2 12.28 2.5 3.8 92 45 4 3 12.45 3.3 4.1 93 48 3 4 12.19 2.0
4.7 94 44 3 5 12.73 4.1 4.3 95 45 4 6 12.89 4.6 4.2 94 44 5 7 12.21
2.7 3.9 94 45 3 8 14.33 12.2 4.0 95 47 4 9 12.16 2.1 4.5 94 42 6 10
12.25 2.4 1.3 93 41 7 11 12.29 2.6 4.2 94 45 4 12 12.30 2.7 3.7 94
43 3 13 12.19 2.5 3.8 93 48 4 14 12.86 9.2 3.6 95 47 4 15 12.76 3.6
1.1 94 43 5 16 12.22 2.7 4.2 94 46 4 17 12.67 3.1 4.4 94 45 4 18
12.52 4.0 4.7 94 52 6 19 12.03 3.9 4.9 94 46 7 20 12.30 2.7 37 94
48 6
[0054]
4TABLE 4 Results (Control Examples) Ti + .gamma./.gamma.'- Al + Ta
Eutectoid Carbide (atomic (area per- (area per- Creep Property No.
%) centage) centage) M-value Life (hr) Elongation A 13.61 8.5 4.7
96 46 3 B 13.63 3.2 3.2 96 14 11 C 12.30 7.3 5.7 95 32 2 D 14.52
6.2 3.9 99 36 4 E 12.15 1.9 4.0 96 34 5 F 12.40 2.3 4.2 95 38 4
[0055]
5 TABLE 5 .gamma./.gamma.'-Eutectoid Creep Property No. (area
percentage) Life (hr) Elongation 8 12.2 47 4 8A 18.1 36 10 9 2.1 42
6 9A 0.4 Many casting defects occurred.
* * * * *