Background of the Invention
[0001] The present invention relates to a novel heat resisting steel, a gas turbine using
the steel, and various members of the gas turbine.
[0002] At present, a Cr-Mo-V steel, and 12Cr-Mo-Ni-V-N steel have been used in a disc for
a gas turbine. In recent years, from a standpoint of energy saving, there has been
a demand for enhancement of a thermal efficiency of the gas turbine. When power is
generated with a high efficiency, a fossil fuel can be saved, an emission amount of
an exhaust gas can be reduced, and this can contribute to global environment preservation.
Most effective means for enhancing the thermal efficiency is to raise a gas temperature
and pressure. When the gas temperature is raised to an order of 1500°C from an order
of 1300°C, a great efficiency enhancement can be anticipated. Even when a combustion
temperature does not rise, a part of an amount of compressed air for use in cooling
the members is saved, and accordingly the efficiency enhancement can be anticipated.
[0003] However, with the increase of the temperature/pressure, the conventional Cr-Mo-V
steel and 12Cr-Mo-Ni-V-N steel have insufficient strength, and materials having higher
strengths are required. As the strength, a creep rupture strength which influences
high-temperature characteristics most is required. Moreover, for a gas turbine disc,
a high tensile strength and high toughness are also required as well as the creep
strength, and especially embrittlement has to be inhibited from occurring at the high
temperature during the use.
[0004] As a structural material having a high creep rupture strength, austenitic steel,
Ni-base alloy, Co-base alloy, martensitic steel, and the like have generally been
known. The Ni-base alloy and Co-base alloy are not preferable from the standpoint
of hot workability, machinability, and vibration damping property. The austenitic
steel does not have a very high strength at around 400 to 450°C, and is not preferable
in a whole gas turbine system. On the other hand, the martensitic steel has satisfactory
matching with another corresponding component, and also has a sufficient high-temperature
strength.
[0005] In JP-A-2001-49398, a heat resisting steel having high strength and toughness has
been disclosed as a high/low pressure integral type steam turbine rotor. Further in
JP-A-11-209851, PCT/JP97/04609, and JP-A-10-251809, a heat resisting steel for a gas
turbine disc material has been disclosed.
[0006] However, the heat resisting steels disclosed in the publications cannot satisfy especially
the high creep rupture strength and embrittlement reduction at the same time among
the characteristics such as the high creep rupture strength, high tensile strength,
high toughness, and embrittlement reduction, and are not sufficient as the gas turbine
disc having a higher efficiency. Only with the use of the conventional material simply
having the high strength against the high temperature/pressure of the gas turbine,
the gas temperature cannot further rise. When a high-temperature portion is cooled
by a large amount of cooling air, further rise of the gas temperature can be anticipated,
but thermal efficiency remarkably drops. Therefore, cooling air needs to be saved
in order to prevent the drop of the thermal efficiency, but the saving is impossible
until the above-described high material characteristics are obtained. Moreover, in
general, when the high-temperature strength is enhanced, the toughness is lowered,
and it is therefore difficult to achieve both the characteristics at the same time.
Brief Summary of the Invention
[0007] An object of the present invention is to provide a heat resisting steel which has
high creep rupture strength to be capable of handling a higher temperature and which
has high toughness even after heating at a high temperature for a long time, a gas
turbine using the heat resisting steel, and various components of the gas turbine.
[0008] According to one aspect of the present invention, there is provided a heat resisting
martensitic steel comprising, by weight, 0.05 to 0.30% C, not more than 0.50% Si,
not more than 0.60% Mn, 8.0 to 13.0% Cr, 0.5 to 3.0% Ni, 1.0 to 3.0% Mo, 0.1 to 1.5%
tungsten (W), 0.5 to 4% Co, 0.05 to 0.35% vanadium (V), 0.02 to 0.30% in total of
one or two elements selected from the group consisting of Nb and Ta, and 0.02 to 0.10%
nitrogen (N), wherein a value of the square of a difference between the Ni amount
and the Co amount, and the Ni amount are not more than values determined by a straight
line drawn on a point A (1.0, 2.7%) and a point B (2.5, 1.0%) in the orthogonal coordinates
shown in the attached drawing of Fig. 2 which represents a relationship between the
above square value and the Ni amount, and wherein an amount ratio of Mo/(Mo + 0.5W)
is not less than 0.5. Preferably, the above square value is not more than 1.8.
[0009] According to one feature of the martensitic steel of the invention having the above
chemical composition, an amount ratio of W/Mo, and the Mn amount are not more than
values determined by a straight line drawn on a point C (1.3, 0.15%) and a point D
(2.5, 0.37%) in the orthogonal coordinates shown in the attached drawing of Fig. 4
which represents a relationship between the amount ratio and the Mn amount.
[0010] According to another feature of the martensitic steel of the invention having the
above chemical composition, an amount ratio of Mo/(Mo + 0.5W), and the Mn amount are
not less than values determined by a straight line drawn on a point E (0.25, 0.4%)
and a point F (0.7, 0.15%) in the orthogonal coordinates shown in the attached drawing
of Fig. 6 which represents a relationship between the amount ratio and the Mn amount.
[0011] The invention steel may comprise, by weight, at least one element of not more than
1.5% Re and 0.001 to 0.015% boron (B). The invention steel may comprise, by weight,
at least one element selected from the group consisting of not more than 0.5% Cu,
not more than 0.5% Ti, not more than 0.2% Al, not more than 0.1% Zr, not more than
0.1% Hf, not more than 0.01% Ca, not more than 0.01% Mg, not more than 0.01% yttrium
(Y), and not more than 0.01% of a rare earth element.
[0012] Preferably, the invention heat resisting steel is adjusted to have such a chemical
composition that the Cr-equivalent, as defined by the following equation, is not more
than 10, and the steel does not essentially contain the δ ferrite phase:
the Cr-equivalent = Cr+6Si+4Mo+1.5W+11V+5Nb-40C-30N-30B-2Mn-4Ni-2Co+2.5Ta (where each
element is of a content, by weight %, of the heat resisting steel).
[0013] The invention steel preferably has not less than 1180 MPa of tensile strength at
room temperature, more preferably not less than 1200 MPa, not less than 420 Mpa of
creep rupture strength at 510°C for 10
5 hours, more preferably not less than 430 Mpa, and not less than 19.6 J/cm
2 of a V-notch Charpy impact value at 25°C after heating at 530°C for 10
4 hours.
[0014] According to another aspect of the present invention, there is provided a gas turbine
comprising:
a turbine stub shaft;
a plurality of turbine discs connected to the turbine stub shaft by turbine stacking
bolts via turbine spacers;
turbine blades each implanted in the respective disc to rotate by high-temperature
combustion gas generated in a combustion device;
a distant piece connected to the turbine discs;
a plurality of compressor rotors connected to the distant piece;
compressor blades which are implanted to compressor discs constituting the respective
compressor rotor, and which compress air; and
a compressor stub shaft connected to the compressor rotors, wherein
at least one of the turbine discs, the distant piece, the turbine spacers, the compressor
disc at a last stage, and the turbine stacking bolts is made of the above heat resisting
steel.
[0015] According to still another aspect of the present invention, there is provided a disc
for a gas turbine, which is a disc member comprising a circumferential implanting
section for a turbine blade, and a plurality of bores receiving a plurality of stacking
bolts by which a plurality of the disc members are integrally fastened to one another,
wherein the disc is made of the heat resisting steel having the above chemical composition
and properties. The disc member may have optionally a central bore.
[0016] The gas turbine disc should have high fatigue strength as well as high tensile strength
in order to bear high centrifugal stress and vibration stress due to high-speed rotation.
If the gas turbine disc has a metal structure containing the detrimental delta (δ)
ferrite, the fatigue strength is excessively deteriorated. Therefore, the Cr-equivalent
is so adjusted to be not more than 10 that the steel has an entire temper martensite
structure.
[0017] According to still another aspect of the present invention, there is provided a gas
turbine distant piece which is a cylindrical member comprising protrusions provided
at both opposite ends of the cylindrical member; a plurality of bores in one of the
protrusions, which receive a plurality of stacking bolts by which the cylindrical
member is integrally fastened to turbine discs, and a plurality of other bores in
the other protrusion, which receive a plurality of other stacking bolts by which the
cylindrical member is integrally fastened to compressor discs, wherein the gas turbine
distant piece is made of the above heat resisting steel having the same properties
as mentioned above.
[0018] According to still another aspect of the present invention, there are provided gas
turbine compressor discs each of which is a disc member comprising a circumferential
implanting section for compressor blades, and a plurality of bores receiving a plurality
of stacking bolts by which a plurality of the disc members are integrally fastened
to one another, wherein the gas turbine compressor discs are made of the above heat
resisting steel having the same properties as mentioned above.
[0019] According to still another aspect of the present invention, there is provided a gas
turbine stacking bolt which is a bar member comprising a screw portion at one end
thereof, and a polygonal head portion at the other end, wherein the gas turbine stacking
bolt is made of the above heat resisting steel having the same properties as mentioned
above.
[0020] Other objects, features and advantages of the invention will become apparent from
the following description of the embodiments of the invention taken in conjunction
with the accompanying drawings.
Brief Description of the Several Views of the Drawings
[0021]
FIG. 1 is a graph showing a relationship between creep rupture strength and a value
of the square of a difference between the Ni amount and the Co amount;
FIG. 2 is a graph showing a relationship between the Ni amount and the square value,
in which the line represents a steel having not less than 420 MPa of creep rupture
strength at 510°C for 105 hours on the basis the relationship shown in FIG. 1;
FIG. 3 is a graph showing a relationship between a V-notch Charpy impact value at
25°C and an amount ratio of W/Mo after an embrittle treatment;
FIG. 4 is a graph showing a relationship between the ratio of W/Mo and the Mn amount,
in which the line represents a steel having not less than 19.6 J/cm2 of a V-notch Charpy impact value at 25°C after the embrittle treatment;
FIG. 5 is a graph showing a relationship between the V-notch Charpy impact value at
25°C and an amount ratio of Mo/(Mo + 0.5W) after the embrittle treatment;
FIG. 6 is a graph showing a relationship between the amount ratio of Mo/(Mo + 0.5W)
and the Mn amount, according to which line not less than 19.6 J/cm2 of the V-notch Charpy impact value at 25°C is obtained after the embrittle treatment;
FIG. 7 is a sectional view of a rotary section of a gas turbine according to the present
invention.
Detailed Description of the Invention
[0022] Reasons for limitations on component range of heat resisting steel of the present
invention will be described.
[0023] A carbon (C) content is set to not less than 0.05% in order to obtain high tensile
strength and yield strength. However, if the C amount exceeds 0.30%, the metal structure
becomes unstable when exposed to high temperature for a long time, a creep rupture
strength and toughness are deteriorated. Therefore, the content is set to not more
than 0.30%, especially preferably 0.07 to 0.23%, more preferably 0.10 to 0.20%.
[0024] Si is a deoxidizer, and Mn is a desulfurizing/deoxidizing agent. These are added
at the time of melting of heat resisting steel, and are effective even in small amounts.
Si is a δ ferrite generating element. When a large amount of this element is added,
detrimental δ ferrite is generated to lower fatigue strength and toughness. Therefore,
the content is set to 0.50% or less. It is to be noted that Si does not have to be
added in a carbon vacuum deoxidizing process and electro slag remelting process, and
no Si is preferably added. The content is especially preferably 0.10% or less, more
preferably 0.05% or less.
[0025] When a small amount of Mn is added, the toughness is enhanced. However, when a large
amount is added, the toughness is lowered. Therefore, the content is set to 0.60%
or less. Especially, since Mn is effective as the desulfurization agent, the content
is preferably 0.30% or less, especially preferably 0.25% or less, further preferably
0.20% or less from the standpoint of enhancement of the toughness. The content of
0.05% or more is preferable from the standpoint of the toughness.
[0026] Cr enhances corrosion resistance and tensile strength, but with an addition amount
exceeding 13%, a δ ferrite structure is generated. When the amount is smaller than
8%, the corrosion resistance and high-temperature strength are insufficient, and therefore
the content of Cr is set to 8 to 13%. The content is especially preferably 10.0 to
12.8%, more preferably 10.5 to 12.5%.
[0027] Mo is effective in improving the creep rupture strength by virtue of solid-solution
strengthening and precipitation strengthening with carbide/nitride. When the Mo content
is not more than 1.0%, Mo has an insufficient effect of enhancing the creep rupture
strength. When the Mo content is not less than 3%, delta (δ) ferrite is generated.
Therefore, the Mo content is set to 1.0 to 3.0%, preferably 1.2 to 2.7%, more preferably
1.3 to 2.5%.
[0028] W has an effect similar to that of Mo. For a higher strength, the content may be
equal to that of Mo. With a content of 0.1% or less, W has an insufficient effect
of enhancing the creep rupture strength. With a content exceeding 1.5%, the toughness
is lowered, and therefore the content is set to 0.1 to 1.5%. The content is preferably
0.2 to 1,4%, more preferably 0.3 to 1.3%.
[0029] Since Co enhances the strength at a higher temperature, the content is preferably
increased with the increase of the temperature. With a content less than 0.5%, the
effect is not sufficient. With a content exceeding 4.0%, heating embrittlement is
promoted, and therefore an upper limit is set to 4%. The content is preferably 0.8
to 3.5%.
[0030] V and Nb precipitate carbide, enhance the tensile strength, and further have an effect
of enhancing the toughness. With not more than 0.05% V, or not more than 0.02% Nb,
the effect is insufficient. From the standpoint of reduction of δ ferrite generation,
not more than 0.35% V, and not more than 0.3% Nb are preferable. Especially, the content
of V is preferably 0.15 to 0.30%, more preferably 0.20 to 0.30%. The content of Nb
is 0.04 to 0.22%, more preferably 0.10 to 0.20%. Instead of Nb, Ta can be added in
the same manner, and a total amount is similar to the content even in composite addition.
[0031] Ni enhances low-temperature toughness, and also has an effect of preventing δ ferrite
from being generated. This effect is preferable with not less than 0.5% Ni, and the
effect is saturated with an addition amount exceeding 3.0%. When a large amount of
Ni is added, the creep rupture strength is lowered. The content is preferably 0.5
to 2.5%, more preferably 0.7 to 2.3%.
[0032] N is effective in enhancing the creep rupture strength and in preventing δ ferrite
from being generated. However, the effect is insufficient with a content less than
0.02%, and the toughness is lowered with a content exceeding 0.10%. Especially, superior
properties are obtained in a range of 0.04 to 0.080%.
[0033] Re is effective in improving the creep rupture strength by virtue of solid-solution
strengthening. Since an excess addition promotes the embrittlement, an addition amount
of not more than 2% is preferable. However, since Re is a rare element, a content
of not more than 1.5% is preferable in a practical use, more preferably not more than
1.2%.
[0034] B has a function of enhancing a grain boundary strength, and has an effect of enhancing
the creep rupture strength. This effect is insufficient with a content of not more
than 0.001%, and the toughness drops with an addition amount exceeding 0.015%. The
content is especially preferably 0.002 to 0.008%.
[0035] The reduction of P and S has an effect of enhancing the low-temperature toughness
without impairing the creep rupture strength, and the reduction to the utmost is preferable.
From the standpoint of the enhancement of the low-temperature toughness, not more
than 0.015% phosphor (P), not more than 0.015% sulfur (S) are preferable. Especially,
not more than 0.010% phosphor (P), not more than 0.010% sulfur (S) are preferable.
[0036] The reduction of Sb, Sn, and As also has the effect of enhancing the low-temperature
toughness, and the reduction to the utmost is preferable, but from the standpoint
of an existing steel making technique level, the content is limited to not more than
0.0015% Sb, not more than 0.01% Sn, and not more than 0.02% As. Especially, not more
than 0.001% Sb, 0.005% Sn, and not more than 0.01% As are preferable.
[0037] At least one of MC carbide forming elements such as Ti, Al, Zr, Hf, Ta is preferably
contained by not more than 0.5% in total. The content of Al, which is used as a deoxidizer
and a grain refiner, is set to not less than 0.0005%. If the Al content exceeds 0.2%,
nitrogen, which is effective for improving the creep strength, is fixed to deteriorate
the creep rupture strength. Thus, the Al content is preferably not more than 0.2%.
[0038] The present inventors turned their attention to a content balance of additive Ni
and Co. Accordingly, a value of the square of a difference between the Ni amount and
the Co amount, and the Ni amount have been set to be not more than values determined
by a straight line drawn on a point A (1.0, 2.7%) and a point B (2.5, 1.0%) in the
orthogonal coordinates shown in the attached drawing of Fig. 2 which represents a
relationship between the above square value and the Ni amount, and an amount ratio
of Mo/(Mo + 0.5W) is set to be not less than 0.5, whereby the above properties can
be obtained. Especially, remarkable properties can be obtained when the tungsten (W)
amount is not more than 1.5%. Further, the above square value is preferably set to
be not more than 1.8. If the tungsten (W) amount exceeds 1.5%, the high creep strength
mentioned above can be obtained, but the toughness is deteriorated after heating at
high temperature for a long time. Thus, more than 1.5% tungsten (W) is not preferable.
[0039] Ni and Co contribute to improving martensitic steel in toughness. Ni is effective
for improving the toughness, but deteriorates the creep strength. Co is effective
for improving the creep strength, but promotes embrittlement of the steel during operation,
and deteriorates the toughness. Therefore, since the toughness and creep strength
are kept and the heating embrittlement is inhibited, it has been found that the difference
between the Ni amount and the Co amount is an effective index indicating a preferable
balance between the additive amounts of Ni and Co in the present invention.
[0040] Further, in the present invention, an amount ratio of W/Mo, and the Mn amount are
set to be not more than values determined by a straight line drawn on a point C (1.3,
0.15%) and a point D (2.5, 0.37%) in the orthogonal coordinates shown in the attached
drawing of Fig. 4 which represents a relationship between the amount ratio and the
Mn amount. Accordingly, a high toughness is obtained even after the heating at high
temperature for the long time.
[0041] Further, in the present invention, an amount ratio of Mo/(Mo + 0.5W), and the Mn
amount are set to be not less than values determined by a straight line drawn on a
point E (0.25, 0.4%) and a point F (0.7, 0.15%) in the orthogonal coordinates shown
in the attached drawing of Fig. 6 which represents a relationship between the amount
ratio and the Mn amount. Accordingly, the high toughness is obtained especially even
after the heating at high temperature for the long time.
[0042] That is, in the present invention, also for the addition of Mo and W, it has been
found that a specific ratio of both the addition amounts is an effective index indicating
a preferable balance. As the elements contributing to improvement of high-temperature
strength of martensitic steel, Mo and W function as a solid-solution strengthening
element, respectively, and the effect is represented by the Mo-equivalent = (Mo(%)+0.5W(%))
or the amount ratio of W/Mo. However, these elements lower the toughness after the
heating at high temperature for the long time, but a small amount of Mn performs an
important function of enhancing the toughness after the heating at high temperature
for the long time, and the effect is remarkably obtained by a composite addition with
a specific content from the relation with the Mn amount. Mo and W are different from
each other in the effect, the addition of W is more effective in enhancing the strength
at the high temperature. However, when a ratio of W is large, the toughness tends
to drop as described above.
[0043] Especially, the addition of W is effective under a use environment at a temperature
exceeding 600°C, but a use temperature of the gas turbine disc is lower, and the high
toughness is required. Therefore, the Mo addition is more preferable in the present
invention. Therefore, when the amount ratio of (Mo/(Mo + 0.5W) is set to 0.5 or more,
preferably 0.6 to 0.95, more preferably 0.75 to 0.95, the high toughness is obtained
even after the heating at high temperature for the long time.
[0044] In a preferable thermal treatment of the material of the present invention, first
the material is uniformly heated at a temperature sufficient for transformation to
complete austenite, 1000°C at minimum, 1150°C at maximum, quenched (preferably oil
cooling or water spraying), and subsequently heated/retained and cooled at a temperature
of 540 to 600°C (primary tempering). Subsequently, the material is heated/retained
and cooled at a temperature of 550 to 650°C (secondary tempering) to form an entirely
tempered martensitic steel. The temperature of the secondary tempering is set to be
higher than a primary tempering temperature. When quenching, it is preferable to stop
cooling just above an Mf point in order to prevent occurrence of cracks. Specifically,
the above cooling-stop temperature is preferably not lower than 150°C. When conducting
a primary tempering, the material is heated from the above temperature.
EMBODIMENTS
Example 1
[0045] Table 1 indicates a chemical composition (weight %) of heat resisting 12% Cr steel
for a gas turbine disc material, and the balance is Fe. Each specimen was subjected
to vacuum arc melting at 150 kg, heated at 1150°C, and forged to form a raw material.
The raw material was heated at 1050°C for two hours and subsequently oil-cooled, heated
at 560°C for five hours and subsequently air-cooled to be subjected to the primary
tempering, and next heated at 580°C for five hours and furnace-cooled to be subjected
to the secondary tempering. After the thermal treatment, a creep rupture specimen,
tensile specimen, and V-notch Charpy impact specimen were sampled from the raw material,
and used in experiments. An impact test was conducted with respect to the thermally
treated material and a heated/embrittled material at 530°C for 10,000 hours. The embrittled
material has conditions equal to those of a material heated at 510°C for 100 thousand
hours on the basis of the Larson-Miller parameter.
[0046] Table 2 shows mechanical properties of these specimens. Specimen Nos. 7 to 13 are
of the invention steel exhibiting not less than 1180 MPa of tensile strength at room
temperature which is required for a high-temperature/high-pressure gas turbine disc
material, not less than 420 MPa of creep rupture strength at 510°C for 10
5 hours, and not less than 19.6 J/cm
2 of the V-notch Charpy impact value at 25°C after embrittle treatment. It has been
confirmed that the specimens are sufficiently satisfactory. On the other hand, Specimen
Nos. 1 to 6, which are of comparative steel, cannot simultaneously satisfy mechanical
properties required for the high-temperature/pressure gas turbine disc material. For
any one of Specimen Nos. 1, 3, 4, and 5 which are of comparative steel, the above
square value increases, and this indicates that the addition amount of one of Ni and
Co is large. For Comparative Specimen Nos. 1 and 5 having a large Ni addition amount,
the tensile strength and the V-notch Charpy impact value at 25°C before/after the
heating embrittlement are satisfied, but the creep strength cannot be satisfied. For
Comparative Specimen Nos. 3 and 4 having a large Co addition amount, the creep rupture
strength is satisfied, but the V-notch Charpy impact value at 25°C after the heating
embrittlement is remarkably deteriorated.
[0047] Specimen Nos. 3 and 6 in which the amount ratio of Mo/(Mo + 0.5W) of an Mo-equivalent
is less than 0.5 have a low impact value. Specimen No. 2 to which Mo alone is added
(the W amount = 0) has a low creep rupture strength.
[0048] Furthermore, the specimens of the chemical compositions shown in Table 3 were manufactured
by the melting and forging, and subjected to the same thermal treatment for use in
the experiments. The test results are shown in Table 4. As shown in Table 4, for Specimen
Nos. 17 to 19 which are the present invention materials, it has been confirmed that
the properties are obtained so as to sufficiently satisfy the room temperature tensile
strength required for the high-temperature/pressure gas turbine disc material of not
less than 1180 MPa, the creep rupture strength at 510°C for 10
5 hours of not less than 420 MPa, and the V-notch Charpy impact value at 25°C after
the embrittle treatment of not less than 19.6 J/cm
2. On the other hand, for Specimen Nos. 14 and 15 of the comparative materials to which
B is excessively added, elongation and impact value of the tensile test are low, and
the mechanical properties required for the high-temperature/pressure gas turbine disc
material cannot simultaneously be satisfied. Specimen No. 14 of the comparative material
to which Mo is added alone (the W amount = 0) has a slightly low creep strength. The
Specimen No. 16 of the comparative material to which Re is excessively added has a
sufficient creep strength, but a value of drawing is low.
[0049] FIG. 1 is a diagram showing a relation between the creep rupture strength and the
square of (difference between Ni amount and Co amount). As shown in FIG. 1, the creep
rupture strength remarkably drops as the value of the square of a difference between
the Ni amount and the Co amount increases. Especially, the relation with the Ni amount
is large. When the Ni amount is 1.0 to 1.2%, the creep rupture strength is high as
compared with an amount of 2.2 to 3.2%. However, with high Ni, when the square value
increases, the creep rupture strength rapidly drops.
[0050] Especially, when the Co amount is larger than the Ni amount, the creep strength drops
slightly, and an influence by the square value is small.
[0051] FIG. 2 is a linear diagram showing a relationship between the square value and the
Ni amount having a creep rupture strength at 510°C for 10
5 hours of not less than 420 MPa from the relation of FIG. 1. As described above, for
the creep rupture strength, the above square value has a close relation with the Ni
amount. When the value represented by the relation between the square value and the
Ni amount is set to be not more than the value determined by a straight line drawn
on a point A (1.0, 2.7%) and a point B (2.5, 1.0%) in the orthogonal coordinates shown
in the attached drawing of Fig. 2 which represents a relationship between the above
square value and the Ni amount, a creep rupture strength of 420 MPa or more is obtained.
[0052] FIG. 3 is a linear diagram showing a relation between the V-notch Charpy impact value
at 25°C and an amount ratio of W/Mo after the embrittle treatment. As shown in FIG.
3, the impact value rapidly drops with an increase of the ratio of W/Mo. The impact
value is high with a large Mn amount of 0.32 to 0.4% as compared with an amount of
0.15%, and is further high with a large C amount. Furthermore, the impact value remarkably
drops with any Mn amount, when the ratio of W/Mo increases.
[0053] FIG. 4 is a linear diagram showing a relationship between the ratio W/Mo and the
Mn amount having a V-notch Charpy impact value at 25°C of 19.6 J/cm
2 or more after the embrittle treatment. As shown in FIG. 4, when the value represented
by the relation between the (W amount/Mo amount) ratio and the Mn amount is set to
be not more than the value determined by a straight line drawn on a point C (1.3,
0.15%) and a point D (2.5, 0.37%) in the orthogonal coordinates shown in the attached
drawing of Fig. 4 which represents a relationship between the amount ratio and the
Mn amount, a 25°C V-notch Charpy impact value of not less than 19.6 J/cm
2 is obtained. It is to be noted that FIG. 4 is applied with a C amount of not more
than 0.17%.
[0054] FIG. 5 is a linear diagram showing a relationship between the V-notch Charpy impact
value at 25°C and an amount ratio of Mo/Mo + 0.5W) after the embrittle treatment.
As shown in FIG. 5, when the ratio is further increased, the high toughness is obtained
even after the heating at high temperature for the long time. The impact value is
high with a large Mn amount of 0.32 to 0.4% as compared with an amount of 0.15%, and
further with a large C amount, and increases as the ratio of Mo/(Mo + 0.5W) increases.
When the Mn amount is 0.15%, a carbon amount is not more than 0.15%. When the Mn amount
is 0.32 to 0.4%, the carbon amount is 0.11 to 0.17%.
[0055] FIG. 6 is a linear diagram showing a relationship between the amount ratio of Mo/(Mo
+ 0.5W) and the Mn amount in which a V-notch Charpy impact value at 25°C after the
embrittle treatment of not less than 19.6 J/cm
2 is obtained. When the value represented by this relation is set to be not less than
the value determined by a straight line drawn on a point E (0.25, 0.4%) and a point
F (0.7, 0.15%) in the orthogonal coordinates shown in the attached drawing of Fig.
6 which represents a relationship between the amount ratio and the Mn amount, the
above-described impact value is obtained. It is to be noted that FIG. 6 is applied
with a carbon amount of 0.17% or less.
Example 2
[0056] FIG. 7 is a sectional view of a turbine upper half of an air compression type three-stage
turbine including an air cooling system. As shown in FIG. 7, a gas turbine of the
present example is constituted of a casing 80, a compressor including a compressor
rotor 2 and a blade array of an outer peripheral portion, a combustion unit 84, alternately
arranged turbine nozzles 81 to 83 and turbine blades 51 to 53, a turbine rotor 1,
and the like. The turbine rotor 1 includes three turbine discs 11, 12, 13 and a turbine
stub shaft 4, and is closely bonded as a high-speed rotating member. The turbine blades
51 to 53 are disposed on the outer periphery of each turbine disc, connected to the
compressor rotor 2 and turbine stub shaft via a distant piece 3, and rotatably supported
by a bearing. In this constitution, air compressed by the compressor is used, and
a high-temperature/pressure working gas generated by the combustion unit 84 expands
while flowing. Accordingly, the turbine rotor 1 is rotated to generate a motive energy.
A combustion gas flowing out of the turbine section is fed to an exhaust heat recovery
boiler (HRSG) to produce steam.
[0057] Although there are also portions not shown, in addition to the above-described constitution,
a main constitution of the gas turbine in the present embodiment includes the turbine
stub shaft 4, turbine stacking bolts 5, turbine spacers 18, the distant piece 3, compressor
discs 17 constituting a compressor rotor, compressor blades, compressor stacking bolts,
and a compressor stab shaft. The compressor discs 17 are of not less than seventeen
stages, and the turbine blades are of three stages. The constitution can similarly
be applied also with respect to four stages.
[0058] In the present embodiment, air compressed by the compressor is used to cool each
component by a flow of air shown by an arrow in FIG. 7. Air flows in via an outer
side wall in the first-stage turbine nozzle 81 and the second-stage turbine nozzle
82, and is exhausted from a blade section. The second-stage turbine nozzle 82 is cooled
over an inner side wall. In the third-stage turbine nozzle 83, air flows in via the
outer side wall, flows out of the inner side wall, and is exhausted to the outside
via the spacer section. For the first-stage turbine blade 51, compressed air passes
through the side wall from a central portion of the turbine disc 11. The air passes
through a spacer 18 section and through cooling bores provided in the blade, and is
exhausted via the tip end of the blade and a trailing portion of a blade section to
cool both the blade and disc. In the blade, the combustion gas is sealed not to flow
inside by a seal fin disposed in a shank portion. Similarly, in the second-stage turbine
blade 52, air passes through the spacer 18 and the cooling bore provided in the blade
from the turbine disc 12, and is exhausted via the tip end, and cooled. The third-stage
turbine blade 53 does not include any cooling bore, but air passes through the side
wall from the central portion of the turbine disc 13, passes through the seal fins
to cool these fins, and enters the exhaust heat recovery boiler together with the
combustion gas. In the boiler, steam is formed as a power source of a steam turbine.
[0059] As the material for use in the turbine discs 11, 12, 13 in the present embodiment,
a large-sized specimen including composition No. 1 shown in Table 1 of Example 1 was
melted, heated at 1150°C, and forged to form an experiment material. The material
was heated at 1050°C for eight hours and cooled with a blast air, and the cooling
temperature was stopped at 150°C. The material was heated at 580°C for 12 hours and
air-cooled to perform the secondary tempering. Next, the material was heated at 605°C
for five hours, and furnace-cooled to perform the secondary tempering. A creep rupture
specimen, tensile specimen, and V-notch Charpy impact test specimen were sampled from
the material after the thermal treatment, and used in the experiments. The impact
test of the thermally treated material was conducted with respect to the heated/embrittled
material in the same manner as in Example 1. These properties in the present embodiment
are equivalent to those of Example 1.
[0060] In the present example, any of the entirely tempered martensitic steel Nos. 7 to
13, Nos. 17 to 19 shown in Example 1 is usable in the distant piece 3 and turbine
stacking bolt 5 in addition to the turbine discs 11, 12, 13.
[0061] Moreover, these martensitic steels have a ferrite-based crystalline structure, but
the ferrite-based material has a small thermal expansion coefficient as compared with
an austenite-based material such as Ni-base alloy. When the heat resisting steel of
the present embodiment is used in the turbine disc instead of the Ni-base alloy, the
thermal expansion coefficient of the disc material is further small. Therefore, thermal
stress generated in the disc is reduced, cracks are inhibited from being generated,
and collapse can be reduced. The compressor blade includes 17 stages, and an obtained
air compression ratio is 18.
[0062] Further in the present example, an Ni-base super alloy is used in the first-stage
turbine nozzle 81 and first-stage turbine blade 51 of the gas turbine. Depending on
a combustion gas temperature, a polycrystalline cast material is used in 1300°C class,
and a monocrystalline cast material is used in 1500°C class. In the monocrystalline
cast material, an Ni-base super alloy is used containing, by weight percentage, 4
to 10% Cr, 0.5 to 1.5% Mo, 4 to 10% W, 1 to 4% Re, 3 to 6% Al, 4 to 10% Ta, 0.5 to
10% Co, and 0.03 to 0.2% Hf. The equivalent alloy containing 10 to 15% Cr is used
in the polycrystalline cast material.
[0063] The second-stage turbine nozzle and third-stage turbine nozzle are constituted of
the Ni-base super alloy containing, by weight percentage, 21 to 24% Cr, 18 to 23%
Co, 0.05 to 0.20% C, 1 to 8% W, 1 to 2% Al, 2 to 3% Ti, 0.5 to 1.5% Ta, and 0.05 to
0.15% B. These nozzles include an equiaxed structure obtained by usual casting.
[0064] The Ni-base super alloy is used in the second-stage turbine blade 52 and third-stage
turbine blade 53. Depending on the combustion gas temperature, the polycrystalline
cast material is used in the 1300°C class, and a directionally solidified prismatic
Ni-base super alloy cast material is used in 1500°C class. Either material is constituted
of the Ni-base super alloy containing, by weight percentage, 5 to 18% Cr, 0.3 to 6%
Mo, 2 to 10% W, 2.5 to 6% Al, 0.5 to 5% Ti, 1 to 4% Ta, 0.1 to 3% Nb, 0 to 10% Co,
0.05 to 0.21% C, 0.005 to 0.025% B, 0.03 to 2% Hf, and 0.1 to 5% Re. The blade of
the directionally solidified prismatic Ni-base super alloy is obtained by entire solidification
in one direction toward a dove-tail direction from the tip end.
[0065] In the present exceeding, the toughness is high even with strength enhancement and
heating embrittlement. Accordingly, since especially the material temperature of the
turbine disc can be set to be high, the above-described cooling can be reduced. Furthermore,
the thickness or diameter of the above-described member for use can be reduced, reduction
in weight is achieved, and start properties are enhanced.
[0066] By the above-described constitution, a gas turbine generally balanced with high reliability
is obtained. It is possible to achieve a gas turbine for power generation, in which
a natural gas, light oil, and the like are used as fuels for use, a gas inlet temperature
into the first-stage turbine nozzle is 1500°C, a metal temperature of the first-stage
turbine blade is 900°C, an exhaust gas temperature of the gas turbine is 650°C, and
a power generation efficiency is 37% or more in LHV indication. This also applies
with the gas inlet temperature into the first-stage turbine nozzle of 1300°C.
[0067] Moreover, in the present embodiment, it is possible to constitute a multiaxial combined
cycle power generation system including a combination of one gas turbine and one high/medium/low
pressure integral steam turbine having a steam inlet temperature into the first-stage
turbine blade at 566°C. Each turbine includes a power generator. A higher power generation
efficiency can be obtained.
[0068] According to the present invention, a high-efficiency high-temperature gas turbine
is obtained in which a creep rupture strength and an impact value after heating embrittlement
required especially for a gas turbine in a gas temperature class at 1300 to 1500°C
are high. Furthermore, the present invention can also be applied to a turbine stacking
bolt, turbine spacer, and distant piece exposed at a high temperature in a heating
embrittlement range. Therefore, according to the present invention, since a combustion
temperature and member temperature of a gas turbine power generation plant can be
raised, the cooling in a high-temperature section can be reduced. Further, on the
other hand, a rotation section can be reduced in weight, and therefore further high
efficiency is achieved. Moreover, it is possible to save a fossil fuel and to reduce
a generated amount of exhaust gas and to contribute to global environment preservation.
[0069] It should be further understood by those skilled in the art that although the foregoing
description has been made on embodiments of the invention, the invention is not limited
thereto and various changes and modifications may be made without departing from the
spirit of the invention and the scope of the appended claims.
1. A heat resisting martensitic steel comprising, by weight, 0.05 to 0.30 % C, not more
than 0.50 % Si, not more than 0.60 % Mn, 8.0 to 13.0 % Cr, 0.5 to 3.0 % Ni, 1.0 to
3.0 % Mo, 0.1 to 1.5 % W, 0.5 to 4 % Co, 0.05 to 0.35 % V, 0.02 to 0.30 % in total
of at least one of the elements Nb and Ta, and 0.02 to 0.10 % N,
wherein the value of the square of the difference between the Ni amount and the
Co amount, and the Ni amount are not more than values determined by a straight line
intersecting a point A (1.0, 2.7%) and a point B (2.5, 1.0%) in the orthogonal coordinates
shown in Fig. 2 which represents the relationship between the above square value and
the Ni amount, and
wherein the amount ratio of Mo/(Mo + 0.5W) is not less than 0.5.
2. The steel of claim 1, wherein the square value is not more than 1.8.
3. The steel of claim 1, which further comprises, by weight, not more than 1.5 % Re and
0.001 to 0.015 % B.
4. A heat resisting martensitic steel comprising, by weight, 0.05 to 0.30 % C, not more
than 0.50 % Si, not more than 0.60 % Mn, 8.0 to 13.0 % Cr, 0.5 to 3.0 % Ni, 1.0 to
3.0 % Mo, 0.1 to 1.5 % W, 0.5 to 4 % Co, 0.05 to 0.35 % V, 0.02 to 0,30 % in total
of at least one of the elements Nb and Ta, and 0.02 to 0.10 % N,
wherein the amount ratio of W/Mo, and the Mn amount are not more than values determined
by a straight line intersecting a point C (1.3, 0.15%) and a point D (2.5, 0.37%)
in the orthogonal coordinates shown in Fig. 4 which represents the relationship between
the amount ratio and the Mn amount.
5. The steel of claim 4, wherein the amount ratio of Mo/Mo + 0.5W, and the Mn amount
are not less than values determined by a straight line intersecting a point E (0.25,
0.4%) and a point F (0.7, 0.15%) in the orthogonal coordinates shown in Fig. 6 which
represents the relationship between the amount ratio and the Mn amount.
6. The steel of claim 4 or 5, which further comprises, by weight, not more than 1.5 %
Re and/or 0.001 to 0.015 % B.
7. The steel of claim 1, which further comprises, by weight, at least one of not more
than 0.5 % Cu, not more than 0.5 % Ti, not more than 0.2 % Al, not more than 0.1 %
Zr, not more than 0.1 % Hf, not more than 0.01 % Ca, not more than 0.01 % Mg, not
more than 0.01 % Y, and not more than 0.01 % of a rare earth element.
8. The steel of claim 4, which further comprises, by weight, at least one of not more
than 0.5 % Cu, not more than 10.5 % Ti, not more than 0.2 % Al, not more than 0.1
% Zr, not more than 0.1 % Hf, not more than 0.01 % Ca, not more than 0.01 % Mg, not
more than 0.01 % Y, and not more than 0.01 % of a rare earth element.
9. A gas turbine comprising:
a turbine stub shaft (4);
a plurality of turbine discs (11, 12, 13) connected to the turbine stub shaft (4)
by turbine stacking bolts (5) via turbine spacers (18);
turbine blades each implanted in the respective disc to rotate by high-temperature
combustion gas generated in a combustion device;
a distant piece (3) connected to the turbine discs;
a plurality of compressor rotors (2) connected to the distant piece (3);
compressor blades which are implanted to compressor discs (17) constituting the respective
compressor rotor, and which compress air; and
a compressor stub shaft connected to the compressor rotors,
wherein at least one of the turbine discs (11, 12, 13), the distant piece, the
turbine spacers (18), the compressor disc (17) at the last stage, and the turbine
stacking bolts is made of the martensitic steel defined in any preceding claim.
10. A disc for a gas turbine, which is a disc member comprising a circumferential implanting
section for a turbine blade (51, 52, 53), and a plurality of bores receiving a plurality
of stacking bolts (5) by which a plurality of the disc members are integrally fastened
to one another, wherein the disc (11; 12; 13) is made of the martensitic steel defined
in any one of claims 1 to 8.
11. A gas turbine distant piece which is a cylindrical member comprising protrusions provided
at both opposite end of the cylindrical member; a plurality of bores in one of the
protrusions, which receive a plurality of stacking bolts (5) by which the cylindrical
member is integrally fastened to turbine discs (11, 12, 13), and a plurality of other
bores in the other protrusion, which receive a plurality of other stacking bolts by
which the cylindrical member is integrally fastened to compressor discs (17), wherein
the gas turbine distant piece (3) is made of the martensitic steel defined in any
one of claims 1 to 8.
12. A gas turbine compressor disc which is a disc member comprising
a circumferential implanting section for a compressor blade, and a plurality of
bores receiving a plurality of stacking bolts by which a plurality of the disc members
are integrally fastened to one another, wherein the gas turbine compressor disc (17)
is made of the martensitic steel defined in any one of claims 1 to 8.
13. A gas turbine stacking bolt which is a bar member comprising a screw portion at one
end thereof, and a polygonal head portion at the other end, wherein the gas turbine
stacking bolt (5) is made of the martensitic steel defined in any one of claims 1
to 8.