U.S. patent application number 09/776721 was filed with the patent office on 2001-08-16 for trinickel aluminide-base heat-resistant alloy.
This patent application is currently assigned to KUBOTA CORPORATION. Invention is credited to Takahashi, Makoto, Torigoe, Takeshi.
Application Number | 20010013383 09/776721 |
Document ID | / |
Family ID | 26585040 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013383 |
Kind Code |
A1 |
Takahashi, Makoto ; et
al. |
August 16, 2001 |
Trinickel aluminide-base heat-resistant alloy
Abstract
An Ni.sub.3Al-base heat-resistant alloy containing, in % by
weight, 6.0 to 9.0% of Al, 2.0 to 15.0% of Cr and 0.5 to 3.0% of
Zr, the balance being Ni and inevitable impurities, the alloy
having a metal structure comprising Ni.sub.3Al as the main phase
thereof. When required, the alloy may further contain over 0% to
not more than 5.0% of W, over 0% to not more than 3.0% of Mo, over
0% to not more than 3.0% of Nb, over 0% to not more than 0.003% of
B, over 0% to not more than 0.3% of C and 0.003 to 0.03% of N,
wherein the combined amount of W, Mo and Nb is up to 5.0% if at
least two of these elements are present.
Inventors: |
Takahashi, Makoto; (Osaka,
JP) ; Torigoe, Takeshi; (Soraku-gun, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
KUBOTA CORPORATION
Osaka-shi
JP
|
Family ID: |
26585040 |
Appl. No.: |
09/776721 |
Filed: |
February 6, 2001 |
Current U.S.
Class: |
148/428 ;
420/445 |
Current CPC
Class: |
C22C 19/056 20130101;
C22C 19/058 20130101; C22C 19/057 20130101 |
Class at
Publication: |
148/428 ;
420/445 |
International
Class: |
C22C 019/05 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 8, 2000 |
JP |
2000-030493 |
Feb 8, 2000 |
JP |
2000-030494 |
Claims
What is claimed is:
1. A heat-resistant alloy excellent in creep rupture strength at
high temperatures and in weldability and consisting of, in % by
weight, 6.0 to 9.0% of Al, 2.0 to 15.0% of Cr and 0.5 to 3.0% of
Zr, the balance being Ni and inevitable impurities, the alloy
having a metal structure comprising Ni.sub.3Al as the main phase
thereof.
2. The heat-resistant alloy according to claim 1 which contains one
element selected from the group consisting of over 0% to not more
than 5.0% of W, over 0% to not more than 3.0% of Mo and over 0% to
not more than 3.0% of Nb.
3. The heat-resistant alloy according to claim 1 which contains up
to 5.0%, in a combined amount, of at least two elements selected
from the group consisting of over 0% to not more than 5.0% of W,
over 0% to not more than 3.0% of Mo and over 0% to not more than
3.0% of Nb.
4. The heat-resistant alloy according to claim 1 which contains
over 0% to not more than 0.3% of C and/or 0.003 to 0.03% of N.
5. The heat-resistant alloy according to claim 2 which contains
over 0% to not more than 0.3% of C and/or 0.003 to 0.03% of N.
6. The heat-resistant alloy according to claim 3 which contains
over 0% to not more than 0.3% of C and/or 0.003 to 0.03% of N.
7. The heat-resistant alloy according to claim 1 which contains
over 0% to not more than 0.003% of B.
8. The heat-resistant alloy according to claim 2 which contains
over 0% to not more than 0.003% of B.
9. The heat-resistant alloy according to claim 3 which contains
over 0% to not more than 0.003% of B.
10. The heat-resistant alloy according to claim 4 which contains
over 0% to not more than 0.003% of B.
11. The heat-resistant alloy according to claim 5 which contains
over 0% to not more than 0.003% of B.
12. The heat-resistant alloy according to claim 6 which contains
over 0% to not more than 0.003% of B.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to Ni.sub.3Al-base
heat-resistant alloys having desired high-temperature strength
(tensile strength and proof stress) and excellent in creep rupture
strength and weldability.
BACKGROUND ART
[0002] Trinickel aluminide (Ni.sub.3Al) is an intermetallic
compound (about 1390.degree. C. in melting point) having a
face-centered cubic crystal structure and possesses the peculiar
property that the yield strength thereof, which is indicative of
the strength of the material, increases with a rise in
temperature.
[0003] Because of this property, Ni.sub.3Al-base heat-resistant
alloys, i.e. alloys containing precipitating Ni.sub.3Al dispersed
therein are capable of retaining a high stress level in a
temperature range of up to high temperatures. Such Ni.sub.3Al-base
heat-resistant alloys heretofore proposed include the
following.
[0004] Japanese pre-examination publication 62-93334 discloses an
alloy which comprises, in atomic %, 0.2 to 1.5% of a Group IVb
element (Zr or Hf), 17 to 20% of Al, 4.5 to 8% of Cr, 0.05 to 0.2%
of B, 9 to 16% of Fe, 0.001 to 0.004% of a rare-earth element (such
as Ce) and the balance Ni and which is improved in strength at high
temperatures, ductility and hot workability.
[0005] Japanese post-examination publication 63-66374 discloses an
Ni-Al alloy consisting mainly of Ni.sub.3Al, containing, in wt. %,
0.01 to 2.0% of Mo, 0.05 to 3.0% of B, 0.5 to 4.0% of Zr, etc. and
improved in ductility at room temperature and strength.
[0006] Japanese pre-examination publication 63-266036 discloses an
Ni-base alloy having a metal structure wherein Ni.sub.3Al is its
main phase, containing, in atomic %, 75.4 to 79% of Ni, 7 to 12% of
Al, up to 0.5% of B, up to 0.9% of C, 0.5 to 4% of Hf, 4.5 to 11%
of Fe, up to 3% of Mo, W, Nb or Zr and improved in ductility at
room temperature, strength, etc.
[0007] Japanese national phase publication 4-501440 discloses an
alloy containing, in atomic %, 15 to 18.5% of Al, 6 to 10% of Cr,
0.05 to 0.35% of Zr, 0.08 to 0.30% of B and the balance Ni, and
improved in ductility at high temperatures, workability and
strength.
[0008] Japanese Patent No. 2599263 discloses an Ni-Al alloy
comprising Ni.sub.3Al as its main phase, containing, in wt. %, less
than 1% of a Group IVb element (Hf or Zr), 14.5 to 17.5% of Fe, up
to 0.01% of a rare-earth element (such as Ce, Y or La), 0.01 to
0.05% of B and up to 4% of Mo and improved in workability.
[0009] However, since Ni.sub.3Al exhibits almost no elongation, the
conventional Ni.sub.3Al-base heat-resistant alloys have the problem
of becoming markedly impaired in creep rupture strength in a
high-temperature range exceeding 1050.degree. C., and are therefore
limited in application to high-temperature use from the viewpoint
of strength.
[0010] Further because the intermetallic compound Ni.sub.3Al is
highly susceptible to weld cracking, such alloys are not usable for
structural bodies which require welding for assembling. Thus, the
conventional alloys are limited in use as heat-resistant
alloys.
[0011] An object of the present invention, which has been
accomplished in view of the foregoing problems, is to provide an
Ni.sub.3Al-base heat-resistant alloy having a high creep rupture
strength in a high-temperature range in excess of 1050.degree. C.
and excellent weldability.
SUMMARY OF THE INVENTION
[0012] The present invention provides a heat-resistant alloy
containing, in % by weight, 6.0 to 9.0% of Al, 2.0 to 15.0% of Cr
and 0.5 to 3.0% of Zr, the balance being Ni and inevitable
impurities, the alloy having a metal structure comprising
Ni.sub.3Al as the main phase thereof.
[0013] The expression "Ni.sub.3Al as a main phase" as used herein
means that the proportion by volume of Ni.sub.3Al in the metal
structure the main phase of which is an Ni solid solution is larger
than 50%. To assure the desired high-temperature strength (proof
stress and tensile strength), the proportion of Ni.sub.3Al by
volume is preferably at least 70%.
[0014] When required, over 0% to not more than 5.0% of W, over 0%
to not more than 3.0% of Mo, over 0% to not more than 3.0% of Nb,
over 0% to not more than 0.003% of B, over 0% to not more than 0.3%
of C and 0.003 to 0.03% of N can be incorporated into the
heat-resistant alloy of the present invention. When at least two of
W, Mo and Nb are present, the combined amount of these elements is
up to 5.0%.
[0015] Most preferably, the heat-resistant alloy of the present
invention contains Al, Cr, Zr, W, B, C and/or N as effective
elements in the respective ranges described, the balance being
substantially Ni.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a photograph showing sample No. 12 as subjected to
a weldability test involving a dye check, and
[0017] FIG. 2 is a photograph showing sample No. 102 as subjected
to a weldability test involving a dye check.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The components of the Ni.sub.3Al-base heat-resistant alloy
of the invention are limited for the reasons given below.
[0019] In the following description, the percentages are all by
weight.
[0020] Al: 6.0-9.0%
[0021] Al is a basic element for forming the intermetallic compound
of Ni.sub.3Al along with Ni. If the content of Al is less than
6.0%, an insufficient quantity of Ni.sub.3Al phase will result,
failing to afford the desired high-temperature strength. If the
content is over 9.0%, on the other hand, the alloy is lower in
creep rupture strength. Accordingly, the Al content should be 6.0
to 9.0%.
[0022] Cr: 2.0-15.0%
[0023] Cr contributes to an improvement in tensile strength at high
temperatures. This effect is available when the Cr content is at
least 2.0%. However, the presence of more than 15.0% of Cr entails
an excessively increased hardness to result in impaired ductility
at room temperature. For this reason, the Cr content should be 2.0
to 15.0%, preferably 4.0 to 8.0%.
[0024] Zr: 0.5-3.0%
[0025] Zr is effective for giving remarkably improved weldability.
Since the Ni.sub.3Al-base heat-resistant alloy comprising
Ni.sub.3Al as its main phase is highly susceptible to weld
cracking, the alloy is liable to develop weld cracks when welded.
However, the presence of Zr forms Ni.sub.5Zr in the base phase,
affording improved resistance to cracking at the grain boundary. Zr
further contributes to improvements in strength (tensile strength
and proof stress) and creep rupture strength at high temperatures
in excess of 1050.degree. C. Accordingly, at least 0.5%, preferably
at least 1.0%, of Zr should be present. However, if the content is
over 3.0%, the effect levels off, so that this value is the upper
limit.
[0026] The heat-resistant alloy of the present invention comprises
Ni and inevitable impurities providing the balance. With the
Ni.sub.3Al-base heat-resistant alloy of the invention, the
impurities include, for example, Fe in addition to S, P, etc.
Preferably, the alloy of the invention should be minimized in Fe
content since this element produces an impaired strength at high
temperatures. If the content exceeds 3.0%, an unnegligible
influence will result, so that the content should be limited to not
greater than 3.0%, preferably to not greater than 1.0%.
[0027] When required, the following elements can be incorporated
into the Ni.sub.3Al-base heat-resistant alloy of the present
invention.
[0028] W: over 0% to not more than 5.0%
[0029] W is an element effective for giving a higher creep rupture
strength at high temperatures. However, the presence of an excess
of this element not only leads to lower tensile ductility at high
temperatures but also conversely entails an impaired creep rupture
strength while producing the influence of lower weldability. The W
content should therefore be up to 5.0% if highest and is preferably
0.5 to 5.0%, more preferably 1.0 to 4.0%.
[0030] Mo, Nb: over 0% to not more than 3.0%
[0031] Like W, Mo and Nb are elements effective for giving a higher
creep rupture strength at high temperatures. Mo and Nb can
therefore be made present in place of or along with W. Like W,
however, an excessive Mo or Nb content not only leads to lower
tensile ductility at high temperatures but also conversely entails
an impaired creep rupture strength while producing the influence of
lower weldability. For this reason, the Mo and Nb contents should
each be up to 3.0%.
[0032] W, Mo and Nb are similar in effect, so that when at least
two of these elements are used, the combined amount of these
elements should be limited to not greater than 5.0%.
[0033] C: over 0% to not more than 0.3%
[0034] When C is present conjointly with Cr, Cr carbide
precipitates at the grain boundary to fortify the boundary, giving
improved ductility at high temperatures. This effect is available
when a trace quantity of C is present. If the C content exceeds
0.3%, impaired ductility will result in the range of ordinary
temperatures along with lower weldability. Accordingly, the C
content should be limited to not greater than 0.3% and is
preferably 0.1 to 0.2%.
[0035] N: 0.003-0.03%
[0036] Like C, N acts to give improved ductility at high
temperatures. This effect appears when at least 0.003% of N is
present. Although an increase in content affords an enhanced
effect, presence of more than 0.03% of N entails impaired economy
in producing the alloy by melting. The N content should therefore
be 0.003 to 0.03% and is preferably 0.004 to 0.02%,
[0037] B: over 0% to not more than 0.003%
[0038] B segregates at the grain boundary, giving enhanced
ductility and contributing to an improvement in creep rupture
strength at high temperatures. However, presence of more than
0.003% of B results in enhanced susceptibility to weld cracking and
seriously impaired weldability. For this reason, the B content
should be limited to not greater than 0.003% and is preferably
0.001 to 0.002%.
[0039] The metal structure of the Ni.sub.3Al-base heat-resistant
alloy of the invention contains an Ni solid solution as its base
phase and has the main phase of Ni.sub.3Al and a small amount of
Ni.sub.5Zr precipitate phase as mixed therewith.
EXAMPLE
[0040] Samples were prepared by the following procedure.
[0041] An alloy was produced by high-frequency melting in an argon
atmosphere using an alumina crucible (145 mm in inside diameter and
256 mm in height). First, Ni was melted by heating, Al was added to
the Ni as melted, and the mixture was heated to a higher
temperature. Specified metal elements were then added to the
mixture, followed by temperature adjustment, and the resulting melt
was poured into a ladle. The melt was 16 kg in weight.
[0042] Next, a tubular sample (137 mm in outside diameter, 19 mm in
wall thickness and 270 mm in length) was prepared by centrifugal
casting in the atmosphere using a metal mold.
[0043] The macroscopic structure of the tubular sample as cast
centrifugally was found to contain columnar crystals on the outer
side and granular crystals locally present on the inner side owing
to directional solidification.
[0044] Specified test pieces were made from each of samples thus
prepared, and subjected to a high-temperature characteristics test,
a high-temperature creep rupture test and a weldability test. The
high-temperature characteristics test was conducted to check for
tensile strength, 0.2% proof stress, elongation or reduction of
area at 1100.degree. C. The high-temperature creep rupture test was
conducted to determine the creep rupture time at 1100.degree. C.
under a load of 30 MPa. For the weldability test, the test piece
was TIG-welded on its outer periphery axially thereof by the
beads-on-plate method (welding current 120 A) and thereafter
checked with the unaided eye for cracks as dyed.
[0045] Table 1 shows the chemical compositions of alloys of the
samples and the results of the tests.
1 TABLE 1 Alloy Chemical Composition High temperature
characteristics Creep (Balance being Ni and inevitable impurities)
Tensile 0.2% Proof Elon- Reduction ruture Sample (wt. %) strength
stress gation of area time No. Al Cr Zr W Mo Nb C N B Fe (MPa)
(MPa) (%) (%) (Hrs.) Weldability 1 7.5 5.0 1.8 -- -- -- -- -- --
0.09 158 95 25.9 30.6 90.2 .largecircle. 2 7.5 2.5 1.0 2.5 -- -- --
-- -- 0.90 233 139 5.1 5.1 70.2 .largecircle. 3 7.5 5.0 1.5 -- 1.5
-- -- -- -- 0.10 194 116 21.2 44.7 69.3 .largecircle. 4 7.5 5.0 1.8
-- -- 1.0 -- -- -- 0.10 245 127 3.2 3.4 66.0 .largecircle. 5 8.0
7.0 1.8 -- -- -- 0.25 -- -- 0.10 191 110 9.4 11.7 71.4
.largecircle. 6 8.0 6.5 1.8 -- -- -- -- 0.0045 -- 0.10 201 114 5.1
6.3 85.2 .largecircle. 7 7.5 5.0 1.2 -- -- -- -- -- 0.0015 -- 149
99 24.0 31.3 113.4 .largecircle. 8 7.5 5.0 1.5 2.5 -- -- -- 0.0057
-- 0.90 225 129 6.1 6.1 110.2 .largecircle. 9 7.5 5.0 1.2 2.5 -- --
0.05 0.0052 -- 0.90 199 112 3.2 9.9 108.6 .largecircle. 10 7.5 5.0
1.5 -- 2.0 -- -- -- 0.0020 0.10 193 113 16.6 29.0 77.0
.largecircle. 11 7.5 5.0 1.5 -- -- -- 0.15 -- 0.0015 0.10 172 104
17.4 23.3 62.3 .largecircle. 12 7.5 5.0 1.8 2.5 -- -- 0.15 --
0.0015 0.90 184 108 11.2 10.5 147.9 .largecircle. 13 7.5 10.0 1.8
2.5 -- -- 0.15 0.0120 0.0015 0.90 230 158 15.8 24.6 160.5
.largecircle. 14 7.5 12.5 1.5 -- 1.0 1.5 -- 0.0140 -- 0.10 212 111
3.5 3.9 55.9 .largecircle. 15 7.5 5.0 1.5 2.0 1.0 1.5 0.08 0.0060
0.0015 0.90 236 131 3.3 3.7 50.5 .largecircle. 101 7.5 5.0 -- 2.5
-- -- -- -- -- 0.90 83 37 0.5 2.2 0.2 X 102 8.0 5.5 0.2 -- -- -- --
-- -- 0.10 95 62 2.6 2.0 0.3 X 103 7.5 5.0 1.5 2.5 1.5 1.5 -- -- --
0.90 245 135 1.8 1.6 26.0 .DELTA. 104 5.0 5.0 1.8 -- -- -- -- -- --
0.10 54 26 11.9 10.1 0.5 .largecircle. 105 10.0 5.0 1.8 -- -- -- --
-- -- 0.10 169 -- 0 0 2.1 .largecircle. 106 8.0 5.0 1.5 -- -- --
0.35 -- -- 0.10 157 90 12.0 13.6 88.7 X 107 8.0 5.0 1.8 -- -- -- --
-- 0.0045 0.10 207 115 6.0 6.9 93.7 X 108 7.5 5.0 1.2 7.0 -- -- --
-- 0.0015 -- 247 210 1.8 1.1 24.0 .DELTA. 109 7.5 5.0 1.5 2.5 -- --
0.15 -- 0.0015 5.50 166 101 3.1 4.4 8.4 .largecircle.
[0046] In Table 1, samples No.1 to No. 15 are examples of the
invention, and samples No.101 to No. 109 are comparative examples.
Incidentally, Fe is handled as an impurity element in the case of
the alloy of the invention. When the ingredients are melted for the
preparation of the alloy, Fe is liable to become incorporated into
the alloy from the materials, producing an adverse effect on the
strength if present in an increased amount. Accordingly, Table 1
shows Fe contents.
[0047] In the weldability column of Table 1, the circular mark
indicates "no cracking", the triangular mark "slight cracking", and
the cross mark "marked cracking".
[0048] The results of Table 1 reveal that the examples of the
invention are superior to the comparative examples when the
high-temperature characteristics, high-temperature creep rupture
strength and weldability of the samples were evaluated
collectively.
[0049] Among the comparative examples, No. 106 and No. 107 are
satisfactory in creep rupture strength but low in weldability.
Although No. 104 and No. 105 have good weldability, No. 104 is low
in high-temperature strength (tensile strength and proof stress)
and in creep rupture strength, and No. 105 is poor in
high-temperature elongation and creep rupture strength. No value is
given as the 0.2% proof stress of No. 105 because the test piece
ruptured immediately when tested, hence the value was immeasurable.
No. 109 exhibited a low creep rupture strength due to a high Fe
content.
[0050] The test piece of example of the invention, No.1 was
polished by buffing, and corroded with Marble's reagent. When
observed under an electron microscope (magnification: X5000), the
metal structure was found to contain 88% by volume of the
intermetallic compound, Ni.sub.3Al.
[0051] FIGS. 1 and 2 show photographs of the test pieces of the
invention example, No. 12 and comparative example, No. 102, as
tested for weldability and dyed for checking. The dyed portions in
FIG. 2 indicate cracks occurred.
[0052] The Ni.sub.3-Al-base heat-resistant alloy of the present
invention is suitable, for example, as radiant tubes for use in
steel material heating furnaces, hearth rolls for use in heating
furnaces and cracking tubes for use in pyrolysis furnaces in the
field of the petrochemical industry. These products are fabricated
usually by preparing the alloy by the melting process and casting
the alloy. Such products are usable of course as cast, but can be
subjected to a solution heat treatment at a temperature of about
1100 to about 1200.degree. C. when so required. This treatment is
expected to make the product more uniform in structure and further
improved in properties.
[0053] The alloy of the invention is usable in the form of a powder
as a cladding material for forming clad structures. Cladding can be
performed, for example, by the plasma powder welding method (PPW
method).
* * * * *