U.S. patent application number 16/637903 was filed with the patent office on 2020-05-28 for gas turbine disk material and heat treatment method therefor.
The applicant listed for this patent is Mitsubishi Hitachi Power Systems, Ltd.. Invention is credited to Yuichi HIRAKAWA, Tomoyuki HIRATA, Kazuharu HIROKAWA, Takayoshi IIJIMA, Yoshikuni KADOYA, Hiroki TANAKA.
Application Number | 20200165709 16/637903 |
Document ID | / |
Family ID | 65810301 |
Filed Date | 2020-05-28 |
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United States Patent
Application |
20200165709 |
Kind Code |
A1 |
TANAKA; Hiroki ; et
al. |
May 28, 2020 |
GAS TURBINE DISK MATERIAL AND HEAT TREATMENT METHOD THEREFOR
Abstract
A gas turbine disk material according to the present invention
contains: C: from 0.05 to 0.15%; Ni: from 0.25 to 1.50%; Cr: from
9.0 to 12.0%; Mo: from 0.50 to 0.90%; W: from 1.0 to 2.0%; V: from
0.10 to 0.30%; Nb: from 0.01 to 0.10%; Co: from 0.01 to 4.0%; B:
from 0.0005 to 0.010%; N: from 0.01 to 0.05%; Mn: 0.40% or less;
Si: 0.10% or less; and Al: 0.020% or less. A balance is of Fe and
unavoidable impurities. Additionally, as a heat treatment method, a
quenching temperature of a forged material having the component
composition is set within a range from 1050 to 1150.degree. C.
Inventors: |
TANAKA; Hiroki; (Tokyo,
JP) ; HIRAKAWA; Yuichi; (Tokyo, JP) ; KADOYA;
Yoshikuni; (Hiroshima-shi, JP) ; HIRATA;
Tomoyuki; (Yokohama-shi, JP) ; IIJIMA; Takayoshi;
(Yokohama-shi, JP) ; HIROKAWA; Kazuharu;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Hitachi Power Systems, Ltd. |
Kanagawa |
|
JP |
|
|
Family ID: |
65810301 |
Appl. No.: |
16/637903 |
Filed: |
September 19, 2018 |
PCT Filed: |
September 19, 2018 |
PCT NO: |
PCT/JP2018/034683 |
371 Date: |
February 10, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 8/00 20130101; C22C
38/52 20130101; C22C 38/46 20130101; C22C 38/54 20130101; C22C
38/04 20130101; C22C 38/48 20130101; C22C 38/44 20130101; C21D
9/0068 20130101; C22C 38/00 20130101; C21D 9/00 20130101 |
International
Class: |
C22C 38/54 20060101
C22C038/54; C22C 38/52 20060101 C22C038/52; C22C 38/48 20060101
C22C038/48; C22C 38/46 20060101 C22C038/46; C21D 9/00 20060101
C21D009/00; C22C 38/44 20060101 C22C038/44; C22C 38/04 20060101
C22C038/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2017 |
JP |
2017-181196 |
Claims
1. A gas turbine disk material comprising, by mass %: C: from 0.05
to 0.15%; Ni: from 0.25 to 1.50%; Cr: from 9.0 to 12.0%; Mo: from
0.50 to 0.90%; W: from 1.0 to 2.0%; V: from 0.10 to 0.30%; Nb: from
0.01 to 0.10%; Co: from 0.01 to 4.0%; B: from 0.0005 to 0.010%; N:
from 0.01 to 0.05%; Mn: 0.40% or less; Si: 0.10% or less; and Al:
0.020% or less, wherein a balance is of Fe and unavoidable
impurities.
2. The gas turbine disk material according to claim 1, wherein a
ratio of N content [N %] to Al content [Al %], [N %]/[Al %], is 2.4
or greater.
3. The gas turbine disk material according to claim 1, wherein a B
equivalent ([B %]+0.5 [N %]) expressed as a sum of content B [B %]
and 0.5 times of content N [N %] is from 0.0055 to 0.030%.
4. The gas turbine disk material according to claim 1, wherein an
absorption energy in a room temperature Charpy impact test is 40 J
or greater.
5. The gas turbine disk material according to claim 1, wherein a
creep rupture time at 596.degree. C..times.310 MPa is 750 hours or
more.
6. A heat treatment method for a gas turbine disk material, wherein
when a heat treatment of heating and quenching a forged material
having the component composition according to claim 1 and then
tempering the forged material is implemented, a quenching heating
temperature is set within a range from 1050 to 1150.degree. C.
7. The gas turbine disk material according to claim 1, wherein a Ni
content is 0.79 to 1.50% by mass.
8. The gas turbine disk material according to claim 1, wherein a Cr
content is 10.17 to 12.0% by mass.
9. The gas turbine disk material according to claim 1, wherein a
content of the unavoidable impurities is 0.015% or less by mass.
Description
TECHNICAL FIELD
[0001] The present invention relates to a gas turbine disk material
and a heat treatment method therefor.
[0002] This application claims priority based on JP 2017-181196
filed in Japan on Sep. 21, 2017, of which the contents are
incorporated herein.
BACKGROUND ART
[0003] In the related art, so-called I2Cr heat-resistant steel that
contains approximately from 8 to 12% of Cr has been widely used as
a gas turbine disk material. This type of gas turbine disk material
contains Ni to ensure toughness and contains Mo, V, and the like in
addition to Cr to achieve solid solution strengthening of a base
structure and dispersion strengthening by carbide and carbonitride,
thus improving creep strength.
[0004] As an example, Patent Document 1 describes a gas turbine
disk material containing: C: from 0.05 to 0.15%. Si: 0.10% or less,
Mn: 0.40% or less, Cr: from 9.0 to 12.0%, Ni: from 1.0 to 3.5%. Mo:
from 0.50 to 0.90%, W: from 1.0 to 2.0%, V: from 0.10 to 0.30%, Nb:
from 0.01 to 0.10%, and N: from 0.01 to 0.05%, and the balance is
Fe and unavoidable impurities. Contents of Ni, Mo, and W meet a
relationship of -1.5%.ltoreq.Mo W/2-Ni.ltoreq.0.5%. In addition to
the above-described respective components, one kind or two kinds of
Co: from 0.01 to 4.0% and B: from 0.0001 to 0.010% are
contained.
CITATION LIST
Patent Document
[0005] Patent Document 1: JP 1111-209851 A
SUMMARY OF INVENTION
Technical Problem
[0006] Recently, in accordance with an improved performance of a
gas turbine, a temperature of a gas turbine disk has been a usage
temperature greater than 500.degree. C. and further improvement in
creep strength is required. From a perspective of the creep
strength, Ni base alloy is excellent but substantially increases a
cost. Therefore, improving the creep strength while maintaining
toughness of the 12Cr heat-resistant steel of Patent Document 1 has
been desired.
[0007] The present invention has been made in the context of the
circumstances described above, and an object of the present
invention is to provide a gas turbine disk material having an
excellent creep property and sufficient toughness, and a heat
treatment method for manufacturing the same.
Solution to Problem
[0008] The present inventors have conducted diligent experiments
and studies to solve the problems described above. An amount of Ni
is set to be within an appropriate range lower than a conventional
12C heat-resistant steel, and further effective component ranges of
N, Al, and B have been revealed. Thus, it has been found that while
toughness as a gas turbine disk material is ensured, a creep
property can be significantly improved compared with that of a
conventional one. Thus, a gas turbine disk material has been
invented.
[0009] Furthermore, the present inventors have found that the creep
property and the toughness can be reliably ensured by optimizing a
quenching temperature of a forged material as heat treatment in a
production of the gas turbine disk material, and thus a heat
treatment method for manufacturing the gas turbine disk material
has been invented.
[0010] Specifically, a gas turbine disk material of a fundamental
aspect (first aspect) of the present invention includes, by mass
%:
[0011] C: from 0.05 to 0.15%;
[0012] Ni: from 0.25 to 1.50%;
[0013] Cr: from 9.0 to 12.0%;
[0014] Mo: from 0.50 to 0.90%;
[0015] W: from 1.0 to 2.0%;
[0016] V: from 0.10 to 0.30%;
[0017] Nb: from 0.01 to 0.10%;
[0018] Co: from 0.01 to 4.0%;
[0019] B: from 0.0005 to 0.010%;
[0020] N: from 0.01 to 0.05%;
[0021] Mn: 0.40% or less;
[0022] Si: 0.10% or less; and
[0023] Al: 0.020% or less.
[0024] A balance is of Fe and unavoidable impurities.
[0025] In a gas turbine disk material according to a second aspect
of the present invention, which is in the gas turbine disk material
of the first aspect, a ratio of N content [N %] to Al content [Al
%], [N %]/[Al %], is 2.4 or greater.
[0026] In a gas turbine disk material according to a third aspect
of the present invention, which is in the gas turbine disk material
of the first or the second aspect, a B equivalent ([B %]+0.5 [N %])
expressed as a sum of content B [B %] and 0.5 times of content N [N
%] is from 0.0055 to 0.030%.
[0027] In a gas turbine disk material according to a fourth aspect
of the present invention, which is in the gas turbine disk material
of any one of the first to the third aspects, an absorption energy
in a room temperature Charpy impact test is 40 J or greater.
[0028] In a gas turbine disk material according to a fifth aspect
of the present invention, which is in the gas turbine disk material
of any one of the first to the fourth aspects, a creep rupture time
at 596.degree. C..times.310 MPa is 750 hours or more.
[0029] Further, in a heat treatment method for a gas turbine disk
material according to a six aspect of the present invention, when a
heat treatment of heating and quenching a forged material having
the component composition according to any one of the first to the
third aspects and then tempering the forged material is
implemented, a quenching temperature is set within a range from
1050 to 1150.degree. C.
Advantageous Effect of Invention
[0030] According to the gas turbine disk material according to the
first aspect of the present invention, a balanced material property
achieving both of high creep strength and high toughness can be
ensured.
[0031] In addition, according to the minor component specification
according to the second aspect or the third aspect and the heat
treatment method according to the sixth aspect of the present
invention, it is further possible to reliably and stably obtain the
gas turbine disk material having the high toughness while improving
creep strength.
BRIEF DESCRIPTION OF DRAWINGS
[0032] FIG. 1 includes graphs illustrating a relationship between
Ni content and an evaluation score of toughness (absorption
energy), and between Ni content and an evaluation score of
high-temperature creep property (creep rupture time) of a gas
turbine disk material.
[0033] FIG. 2 is a graph illustrating a relationship between a
ratio of Ni content [N %] to Al content [Al %], [N %]/[Al %], and
the evaluation score of the high-temperature creep property (creep
rupture time) of the gas turbine disk material.
[0034] FIG. 3 is a graph illustrating preferred ranges of the ratio
of the N content [N %] to the Al content [Al %], [N %]/[Al %], in
the gas turbine disk material and a B equivalent expressed by a sum
of B content [B %] and 0.5 times of the N content [N %] ([B
%]+0.5[N %]).
DESCRIPTION OF EMBODIMENTS
[0035] First, reasons for limiting a component composition of a gas
turbine disk material according to one aspect of the present
invention will be described.
Reasons for Limiting Component Composition
[0036] C: from 0.05 to 0.15%
[0037] C is an element that ensures a quenching property, forms
fine and high-hardness carbide and carbonitride through bonding
with Cr, Mo, Nb, V, Nb, and the like in a tempering process, and
greatly affects high-temperature strength. However, the content of
less than 0.05% fails to produce sufficient amounts of carbide and
carbonitride and fails to obtain a uniform martensite structure. In
other words, the C content of less than 0.05% generates a mixed
structure of martensite, delta ferrite, and the like, significantly
decreasing the high-temperature strength and high-temperature
fatigue strength. On the other hand, when the content exceeds
0.15%, not only toughness is decreased but an aggregation of
carbide and carbonitride in use at a high temperature becomes
significantly coarse, causing decrease in creep rupture strength.
Therefore, the C content is set to be from 0.05 to 0.15%.
Ni: from 0.25 to 1.50%
[0038] Ni is an element that can improve hardenability and
toughness at normal temperature, and can satisfy the desired
toughness at 0.25% or greater. On the other hand, when the amount
of Ni increases exceeding 1.50%, the toughness is improved;
however, the creep rupture strength is significantly decreased, and
the gas turbine disk material becomes inappropriate as a gas
turbine disk material used at a high temperature exceeding
500.degree. C. Therefore, the Ni content is designed to be from
0.25 to 1.50%. Thus, Ni is an element that affects the toughness
and the creep property in the opposite direction, and therefore the
amount of Ni has been defined within a range from 0.25 to 1.50% as
an appropriate Ni amount range that can achieve both of the
high-temperature creep property and the toughness. Thus, a fact
that from 0.25 to 1.50% is appropriate as the amount of Ni has been
newly found by experiments by the present inventors, and the
experiments will be described later again.
[0039] Note that, considering the high-temperature creep property,
the Ni content may be designed to be from 0.25% to 0.99% or from
0.25% to 0.90%.
Cr: from 9.0 to 12.0%
[0040] Cr improves an oxidation-resisting property and the creep
rupture strength. However, the Cr content of less than 9.0% fails
to obtain sufficient oxidation-resisting property and creep rupture
strength. On the other hand, containing Cr in excess of 12.0% does
not decrease the creep rupture strength as much, but delta ferrite
deposits and the toughness and the high-temperature fatigue
property are decreased. Therefore, the Cr content is designed to be
from 9.0 to 12.0%.
Mo: from 0.50 to 0.90%
[0041] Mo improves the high-temperature strength and the creep
rupture strength through both actions of solid solution
strengthening and precipitation quenching. However, when the Mo
content is less than 0.50%, the effects are small, and when the Mo
content is greater than 0.90%, delta ferrite is produced, which
possibly degrades the toughness and the creep rupture strength.
Therefore, the Mo content is designed to be from 0.50 to 0.90%.
W: from 1.0 to 2.0%
[0042] W is an element that improves the high-temperature strength
and the creep rupture strength. However, the W content of less than
1.0% fails to sufficiently obtain the effects. In addition, the W
content in excess of 2.0% possibly precipitates delta ferrite,
which is harmful to the high-temperature property. Therefore, the W
content is designed to be from 1.0 to 2.0%.
V: from 0.10 to 0.30%
[0043] V is an element that forms carbide (V.sub.4C.sub.3) and
nitride (VN), also forms composite carbonitride with Nb (Nb, V) (C,
N), and increases the high-temperature strength and the creep
rupture strength. However, when the V content is less than 0.10%,
the effects are not sufficient, and when the V content exceeds
0.30%, the carbide and the carbonitride form coarse aggregate
during use over a long period, decreasing the creep rupture
strength. Therefore, the V content is designed to be from 0.10 to
0.30%.
Nb: from 0.01 to 0.10%
[0044] Nb is an element that forms carbide (NbC), forms composite
carbonitride with V (Nb, V) (C, N), and increases the
high-temperature strength and creep rupture strength. However, when
the Nb content is less than 0.01%, the effects are small, and when
the content exceeds 0.10%, the carbide and the carbonitridc are not
sufficiently dissolved even at a high quenching temperature of
1100.degree. C. or more, the precipitated carbide and carbonitride
form coarse aggregate during creep, and the creep rupture strength
decreases. Therefore, the Nb content is designed to be from 0.01 to
0.10%.
Co: from 0.01 to 4.0%
[0045] Co is an element that increases amounts of solid solution of
carbide and carbonitridc to a matrix. Co itself exhibits solid
solution strengthening action and has an effect of improving the
high-temperature strength and the creep rupture strength. However,
when the Co content is less than 0.01%, the effects are small, and
when Co exceeds 4.0%, the toughness and the creep rupture strength
are decreased. Therefore, the Co content is designed to be from
0.01 to 4.0%.
B: from 0.0005 to 0.010%
[0046] B is an element that increases the high-temperature strength
and the creep rupture strength. However, when the B content is less
than 0.0005%, the effects are small, and when B is contained in
excess of 0.010%, eutectic Fe2B and BN are generated when B is
heated to 900 to 1200.degree. C. during forging, which adversely
affects hot workability and a mechanical property. Therefore, the B
content is set to be from 0.0005 to 0.010%. As will be described
later again, it is desirable that the B content be adjusted so that
a B equivalent (B+0.5 N) expressed by a sum of the B content [B %]
and 0.5 times of the N content [N %] becomes 0.030% or less.
N: from 0.01 to 0.05%
[0047] N is an element that contributes to improvement in
high-temperature strength and creep rupture strength through
precipitation of carbonitrides of Nb and V by appropriate heat
treatment, and exhibits an effect of reducing the generation of
delta ferrite. However, when the N content is less than 0.01%, the
effects do not sufficiently appear, and when the N content exceeds
0.05%, the toughness is decreased. Therefore, the N content is
designed to be from 0.01 to 0.05%. Note that when Al is contained
in a steel, N is fixed as AlN; therefore, an amount of N (amount of
effective nitrogen) contributing to produce the carbonitrides of Nb
and V is reduced. Therefore, as will be described later again, it
is desirable to adjust the N content according to the amount of Al
in the steel such that a ratio of the N content [N %] to the Al
content [Al %] in the steel becomes 2.4 or greater.
[0048] Furthermore, to suppress the generation of BN, which is
harmful to the hot workability and the mechanical property, it is
desirable to adjust the amount of N according to the B content such
that the B equivalent (B+0.5N) expressed by the sum of the B
content [B %] and 0.5 times of the N content [N %] becomes 0.030%
or less.
Mn: 0.40% or less
[0049] Mn is an element often used as a deoxidizer while the steel
is smelted and often contained as an impurity in steel. An effect
as a deoxidation material is sufficiently achieved with the Mn
content of 0.40% or less. Additionally, because Mn is an element
that promotes embrittlement, the content is desirably small.
Therefore, the Mn content is regulated to be 0.40% or less.
Si: 0.10% or less
[0050] Si is an element often used as a deoxidizer when the steel
is smelted similarly to Mn, and often contained as an impurity. At
the Si content exceeding 0.10%, segregation in a large steel ingot
becomes significant and the toughness after use over a long period
is decreased. Therefore, the Si content is regulated to be 0.10% or
less.
Al: 0.020% or less
[0051] A trace amount of Al is contained as an impurity derived
from Al used as the deoxidation material when the steel is smelted.
Since Al fixes N as AlN to reduce the amount of effective nitrogen
and decreases the high-temperature strength and the creep rupture
strength by reducing an amount of produced carbon nitride, such as
Nb and V, the amount of Al is desirably reduced as much as
possible. Therefore, the amount of Al is regulated to be 0.020% or
less. Note that the amount of N is associated with the amount of
produced carbon nitride, as described later, the ratio of [N %]/[Al
%] is preferably designed to be 2.4 or greater.
[0052] The balances of the respective elements described above are
Fe and unavoidable impurities. Examples of the impurities include
P, S, and the like. However, these elements make the material
brittle and adversely affect an impact property; therefore, the
content is desirably small as much as possible. The content is
preferably designed to be 0.015% or less.
[0053] Furthermore, the appropriate ranges of the amount of Ni and
the ratio of [N %]/[Al %] described in the above-mentioned reasons
for limiting components will be described next on the basis of the
experiments by the present inventors.
Appropriate Range of Amount of Ni
[0054] The 12Cr heat-resistant steel of the turbine disk material
described in Patent Document 1 contains Ni within a range from 1.0
to 3.5%. However, with such a turbine disk material, the creep
rupture strength is insufficient at a usage temperature greatly
exceeding 500.degree. C., and the creep strength needs to be
improved further.
[0055] Therefore, as results of detailed experiments and studies,
the present inventors have found the following. Designing an amount
of Ni within a range from 0.25 to 1.50%, which is lower than that
of the turbine disk material of Patent Document 1, allows further
improving a high-temperature creep property while ensuring
toughness desired as a gas turbine disk material and allows the gas
turbine disk material to be used at a usage temperature greatly
exceeding 500.degree. C.
[0056] Note that, considering the high-temperature creep property,
the Ni content according to the present invention may be designed
to be from 0.25% to 0.99%, which is a range lower than the Ni
content of the turbine disk material of Patent Document 1, or may
be designed to be from 0.25% to 0.90%.
[0057] That is, the present inventors investigated toughness and a
high-temperature creep property under high stress of forged
materials after heat treatment of 12Cr heat-resistant steels where
amounts of Ni were variously changed, and results such as
illustrated in FIG. 1 are obtained. Here, components in the 12Cr
heat-resistant steels provided to the experiment are test materials
J1 to J3 of examples and test materials C1, C4, AL15, and AL20 of
comparative examples in Table 1. The forged material was heated to
1050.degree. C. or 1090.degree. C., held for 3.5 hours, quenched by
oil cooling, and then tempered at 670.degree. C. for material
test.
[0058] Table 2 shows results of a room temperature tensile test and
a room temperature Charpy impact test. Table 3 shows a creep
rupture time under test conditions of 596.degree. C..times.310 MPa.
The test results in the tables are organized with amounts of Ni in
the test materials, and the results are illustrated in FIG. 1.
[0059] From Table 2 and FIG. 1, although both of proof stress at
0.2% and tensile strength are similar, absorption energy changes
greatly. As the amount of Ni becomes large, the absorption energy
increases and the toughness increases. The amount of Ni of 0.25% or
greater allows obtaining the absorption energy of 40 J or more
required for the gas turbine disk material.
[0060] From Table 3 and FIG. 1, the smaller the amount of Ni is,
the longer the creep rupture time becomes and the high-temperature
creep property is improved. In addition, the higher the quenching
temperature is, the longer the creep rupture time becomes. In
quenching at 1090.degree. C., even when the amount of Ni is
designed to be the maximum of 1.5%, the creep rupture time of more
than 750 hours required for the gas turbine disk material can be
obtained. On the other hand, in quenching at 1050.degree. C.,
designing the amount of Ni to be 0.25%, which is the lowest value
required to ensure the toughness described above, allows obtaining
the creep rupture time of 750 hours or more required for the gas
turbine disk material.
[0061] From the test results described above, from 0.25 to 1.50%
has been defined as the appropriate range of the amount of Ni at
the quenching temperature of 1050.degree. C. or higher as a range
in which both of the toughness required for the gas turbine disk
material (absorption energy by the room temperature Charpy impact
test of 40 J or greater) and the creep strength (creep rupture time
at 596.degree. C..times.310 MPa of 750 hours or more) are
achieved.
[N %]/[Al %] Ratio
[0062] To improve the creep rupture strength on the high
temperature and low stress side, an increase in an amount of
precipitation of fine precipitates mainly containing carbonitrides
of Nb and V is effective. To do so, a sufficient amount of N
effective to contribute to the production of carbonitride needs to
be dissolved in a matrix in the steel during quenching.
[0063] On the other hand, when this type of steel is smelted, Al is
often used as the deoxidation material, and therefore Al is often
present in the steel. The Al bonds with N to fix N as AlN.
Therefore, when the amount N is too small relative to the amount of
Al, the amount of N (amount of effective nitrogen) effective to
produce the carbonitrides of Nb and V is reduced, and the
sufficient amount of carbonitride is not precipitated.
[0064] The present inventors investigated an effect of the ratio of
the N content [N %] to the Al content [Al %] in the steel [N %]/[Al
%] given to the creep strength and have found that, as illustrated
in FIG. 2, the creep rupture time is decreased dramatically in a
material quenched at 1090.degree. C. at [N %]/[Al %] of less than
2.4. Therefore, in order to sufficiently ensure the amount of
effective nitrogen not fixed as AlN, sufficiently precipitate the
carbon nitrides of Nb and V, and ensure the high creep rupture
strength, [N %]/[Al %] is preferably 2.4 or greater.
[0065] In order to produce 2.4 or greater of [N %]/[Al %], a method
that increases the amount of N or regulates the amount of Al to be
a small amount is considered. However, when the amount of N becomes
an overabundance exceeding 0.05%, as described above, there is a
possibility that BN, which is harmful to the hot workability and
the mechanical property, is generated and therefore means to
restrict the amount of Al is desirably applied.
B Equivalent ([B %].+-.0.5 [N %])
[0066] When large amounts of B and N are added, eutectic Fc2B and
BN are produced during heating to 900 to 1200.degree. C. during
forging, adversely affecting the hot workability and the mechanical
property. Therefore, as described in JP 2948324 B, it is desirable
to adjust the amount of N according to the B content such that the
B equivalent (B+0.5N) expressed by the sum of the B content [B %]
and 0.5 times of the N content [N %] becomes 0.030% or less. On the
other hand, since B and N are elements effective for improving the
high-temperature strength. B needs to be contained by 0.0005% or
greater and N needs to be contained by 0.01% or greater.
Accordingly, a lower limit value of the B equivalent ([B %]+0.5 [N
%]) was set to be 0.0055%.
[0067] FIG. 3 illustrates preferred ranges of [N %]/[Al %] and the
B equivalent ([B %]+0.5 [N %]) in the present invention.
Manufacturing Method (Heat Treatment Method)
[0068] The method for manufacturing the gas turbine disk material
is described next, including the heat treatment method according to
another aspect of the present invention.
[0069] The alloy with the above-described component composition is
smelted in accordance with a usual method, and is casted to produce
an ingot. After the resulting ingot is homogenized as needed, the
ingot is heated to, for example, to 900 to 1200.degree. C. and hot
forging is performed. The resulting forged material is subjected to
a heat refining treatment from quenching through tempering. This
step of the heat refining treatment is a heat treatment method as
another aspect of the present invention.
[0070] The heat refining treatment is a step necessary to obtain
the high strength desired for the gas turbine disk material by
making a steel structure into a substantially uniform martensite
structure and to improve the creep strength by precipitating
carbide and carbonitride. That is, the heat refining treatment is a
process necessary to austenize the steel structure through heating
the forged material to a high temperature, to martensize it by
dissolving an element contributing to the formation of the carbide
and the carbonitride in the matrix and then quenching (rapidly
cooling) it, and to finely precipitate the carbide and carbonitride
through tempering by supersaturatedly dissolving the element
contributing to the formation of the carbide and the carbonitride
in the steel.
[0071] Here, as the quenching temperature (heating temperature for
quenching) becomes high, the amounts of solid solution of C, N, Nb,
and V, which contribute to the production of carbonitride, can be
increased. Consequently, the amount of precipitation of the
carbonitrides of Nb and V precipitated by tempering is increased,
thereby ensuring improving the creep strength. On the other hand,
the excessively high quenching temperature coarsens crystal grains,
resulting in decrease in toughness. Therefore, there is an
appropriate temperature range for the quenching temperature to
avoid the decrease in toughness while improving the creep
strength.
[0072] The present inventors investigated an effect of the
quenching temperature given to the toughness and the creep strength
using test materials quenched at a quenching temperature of
1050.degree. C. or 1090.degree. C. and tempered at 670.degree. C.
and obtained results shown in Table 2, Table 3, and FIG. 1.
[0073] Components in the 12Cr heat-resistant steels provided to the
experiment are the respective test materials of the examples and
the respective test materials of the comparative examples of Table
1. The forged material was heated to 1050.degree. C. or
1090.degree. C., held for 3.5 hours, quenched by oil cooling, and
then tempered at 670.degree. C. for material test.
[0074] From Table 2, Table 3, and FIG. 1, the absorption energies
of the test pieces at the quenching temperature of 1050.degree. C.
and 1090.degree. C. are equivalent, and an effect of the quenching
temperature given to the absorption energy is not observed. On the
other hand, the creep rupture time in quenching at 1090.degree. C.
is longer than that in quenching at 1050.degree. C. and the higher
the quenching temperature is, the higher the creep rupture strength
becomes.
[0075] From the results described above, as the quenching
temperature increases, the creep rupture time becomes long and the
high-temperature creep strength becomes high. Additionally, even in
quenching at 1050.degree. C., as long as the amount of Ni is
designed to be 0.25%, which is the lowest value required to ensure
the toughness described above, the creep rupture time of 750 hours
or more required for the gas turbine disk material can be obtained,
and therefore 1050.degree. C. was set to be the lowest temperature.
When the temperature exceeds 1150.degree. C., the temperature
enters a temperature range in which the delta ferrite is
precipitated and the grain size becomes significantly coarse to
reduce the toughness; therefore, the temperature range of quenching
was set from 1050 to 1150.degree. C. The temperature is preferably
around 1090.degree. C.
EXAMPLES
[0076] Examples of the present invention will be described below
together with comparative examples. Note that the following
examples are examples for validating the effects of the present
invention, and obviously, the conditions of the examples do not
limit the scope of the present invention.
[0077] A steel ingot was manufactured by electroslag remelting
method so as to be chemical components shown in the test materials
J1 to J3 of examples and the test materials C1, C4, AL15, and AL20
of comparative examples in Table 1. This was heated to 900 to
1200.degree. C. and forged to produce a disc-shaped forged
material. The forged material was heated to 1050.degree. C. or
1090.degree. C., held for 3.5 hours, quenched by oil cooling, and
then tempered at 670.degree. C.
[0078] A tensile test piece was manufactured from each forged
material after tempered, and a room temperature tensile test was
conducted in accordance with the tensile test method in JIS Z 2241.
Additionally, a piece for Charpy V notch impact test was
manufactured to conduct an impact test in accordance with the
Charpy impact test method in JIS Z 2242. The results are shown in
Table 2.
[0079] In addition, a round-bar-shaped smooth test piece for creep
rupture test was manufactured from the same test piece, and the
creep rupture test was conducted under conditions of 596.degree.
C..times.310 MPa in accordance with the high-temperature creep test
method in JIS Z 2272. The results are shown in Table 3.
TABLE-US-00001 TABLE 1 Chemical Component (mass %) B-0.5 Sample
Code C Si Mn Ni Cr Mo W V Al Mb Co B N Fe N/Al N Examples J1 0.12
0.01 0.09 1.42 10.17 0.66 1.73 0.20 0.008 0.04 2.48 0.0030 0.024
Bal. 3.0 0.0150 J2 0.13 0.03 0.06 0.82 10.36 0.66 1.77 0.20 0.010
0.05 2.51 0.0040 0.024 Bal. 2.4 0.0160 J3 0.11 0.06 0.07 0.79 10.26
0.66 1.74 0.20 0.002 0.05 2.47 0.0032 0.025 Bal. 12.5 0.0157 C1
0.12 0.07 0.06 2.24 10.38 0.70 1.76 0.20 0.003 0.05 2.57 0.0039
0.026 Bal. 8.7 0.0169 Comparative C4 0.11 0.08 0.05 0.05 10.60 0.71
1.74 0.20 0.002 0.05 2.57 0.0040 0.025 Bal. 12.5 0.0165 Examples
AL15 0.12 0.03 0.07 0.80 10.30 0.70 1.75 0.20 0.015 0.05 2.50
0.0040 0.028 Bal. 1.9 0.0180 AL20 0.12 0.03 0.07 0.80 10.30 0.70
1.75 0.20 0.019 0.05 2.50 0.0040 0.027 Bal. 1.4 0.0175
TABLE-US-00002 TABLE 2 Quenching Tempering Proof Stress Tensile
Absorption Temperature Temperature at 0.2% Strength Energy Sample
Code .degree. C. .degree. C. MPa MPa J Examples J1 1050 670 817 942
163 1090 670 817 947 140 J2 1050 670 800 939 91 1090 670 837 951
101 J3 1090 670 830 950 90 Comparative C1 1050 670 796 994 170
Examples C4 1050 670 786 937 20
TABLE-US-00003 TABLE 3 Ratio When Creep Rupture Strength of J3 Is 1
(Comparison Only Rupture Time with Material Quenching Tempering at
596.degree. C. .times. with 0.8% Ni Temperature Temperature 310 MPa
Quenched at Sample Code .degree. C. .degree. C. MPa 1090.degree.
C.) Examples J1 1050 670 398 -- 1090 670 794 -- J2 1050 670 564 --
1090 670 1125 0.94 J3 1090 670 1199 1.0 Comparative C1 1050 670 119
-- Examples AL15 1090 670 1028 0.86 AL20 1090 670 991 0.83
[0080] The test materials J1 to J3 of the examples are examples of
the present invention within the range of component composition
defined by the present invention. A room temperature impact
absorption energy satisfied 40 J, which is required for the gas
turbine disk material. Additionally, a material quenched at
1090.degree. C. satisfied the creep rupture time required for the
gas turbine disk material, 596.degree. C..times.310 MPa.times.750
hours or more.
[0081] On the other hand, it has been proved that, in Comparative
Example C1 in which the amount of Ni is high, the creep rupture
time is significantly short and the high-temperature strength is
inferior. This Comparative Example C1 is a comparative example
equivalent to the material described in. Patent Document 1. In
contrast to this, it is clear that in the creep strengths of the
examples of the present invention J1 to J3 are greatly improved.
Furthermore, in Comparative Example C2 in which the amount of Ni is
small, the room temperature absorption energy is low, 20 J, not
satisfying 40 J, which is required for the gas turbine disk
material.
[0082] Furthermore, as illustrated in FIG. 2, it has been seen
that, in Comparative Examples AL15 and AL20, the creep strengths
sharply decrease in a low N/Al region compared with those of
Examples J1 to J3. It is seen that N/Al needs to be increased to
2.4 or more in order to stably ensure the creep rupture
strength.
[0083] While preferred embodiments and examples of the present
invention were described above, these embodiments and examples are
no more than examples within the scope of the spirit of the present
invention, and additions, omissions, substitutions, and other
changes to the configuration may be made only within a scope that
does not deviate from the spirit of the present invention.
INDUSTRIAL APPLICABILITY
[0084] According to the gas turbine disk material according to the
present invention, a balanced material property achieving both of
high creep strength and high toughness can be ensured.
[0085] In addition, according to the minor component specification
and the heat treatment method according to the present invention,
it is further possible to reliably and stably obtain the gas
turbine disk material having the high toughness while improving
creep strength.
* * * * *