JP3345988B2 - Steam turbine rotor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel heat-resistant steel, and more particularly to a steam turbine rotor having a high creep rupture strength at 621 ° C. or higher, a high toughness at low temperature, and a uniform tempered martensite structure. It relates to the manufacturing method.

[0002]

2. Description of the Related Art A conventional steam turbine has a maximum steam temperature of 56.
The temperature is 6 ° C and the steam pressure is 246 atg. This rotor material is 1C
r-1Mo-1 / 4V low alloy steel and 11Cr-1Mo-V-Nb-N steel disclosed in Japanese Patent Publication No. 40-4137 are used.

[0003] However, from the viewpoint of depletion of fossil fuels such as petroleum and coal and energy saving, it is desired to increase the efficiency of thermal power plants. Raising the steam temperature of the steam turbine is the most effective means to increase the power generation efficiency. As these high-efficiency turbine materials, the strength of the current rotor material is insufficient, and a material having a higher strength is required.

However, in all of the above-mentioned alloys, high-temperature steam turbine rotors having a steam temperature of 621 ° C. or higher have insufficient high-temperature strength.

[0005]

As the materials having higher high-temperature strength than the above-mentioned conventional materials, Co-base heat-resistant alloys and Ni-base heat-resistant alloys are known. However, although these alloys are excellent in high-temperature creep rupture strength, there is a problem that a large thermal stress is generated when the turbine is started and stopped because of high cost and high thermal expansion coefficient.

An object of the present invention is to provide a steam turbine rotor having a coefficient of thermal expansion equivalent to that of a conventionally used material, having a high creep rupture strength at 621 ° C. or higher, and a high low-temperature toughness, and a method of manufacturing the same.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method wherein C
0.06 to 0.16%, Si less than 0.2%, Mn less than 1%,
Cr 8-13%, Ni 0.2-0.9%, V 0.05-0.5.
3%, Nb 0.01 to 0.20%, N 0.005 to 0.03
In alloy steels containing 5%, less than 0.5% Mo, and more than W2 and less than 3%, B and 2% of more than 0.001 and less than 0.03%
It has been found that high-temperature strength and high-temperature toughness can be obtained by adding less than Co.

[0008] Further, C in a weight ratio of 0.06-0.14%, S
i less than 0.1%, Mn less than 1%, Cr 8 to 12%, Ni
0.2 to 0.9%, V 0.05 to 0.3%, Nb 0.01 to
The alloy steel containing 0.20%, N 0.005 to 0.055%, Mo less than 0.5%, and W2 more than 3% contains 0.01%.
It has been experimentally determined that the addition of B of less than 0.025% and Co of less than 2% provides higher high-temperature strength and high-temperature toughness than the rotor.

[0009] Further, the weight ratio of C 0.09 to 0.14%,
Si less than 0.07%, Mn less than 0.7%, Cr 9.5 to 1
2%, Ni 0.3 to 0.7%, V 0.15 to 0.25%, N
b 0.04 to 0.08%, N 0.015 to 0.025%, M
o To an alloy steel containing less than 0.4% and W 2.3 to 2.7,
B over 0.01 and less than 0.02% and 2% over 0.5
It has been experimentally determined that by adding less than Co, higher high-temperature strength and high-temperature toughness can be obtained than in a rotor.

In the 12Cr heat-resistant steel of the present invention, a steam turbine rotor having high high-temperature strength and low-temperature toughness can be obtained by adjusting the contents of C and N to be within the following ranges.

[0011]

C + 2N = 0.13 to 0.2 (1) In the 12Cr heat-resistant steel of the present invention, Ta is 0.2% or less,
By adding at least one of 0.1% or less and Zr 0.1% or less, a steam turbine rotor having high low-temperature toughness can be obtained.

In the 12Cr heat-resistant steel rotor material of the present invention, in order to obtain high high-temperature strength, low-temperature toughness and high fatigue strength,
It is necessary to adjust the Cr equivalent calculated by the following formula to 4 to 10 and to completely temper the metal structure to martensite.

[0013]

## EQU4 ## Cr equivalent = Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C-30N-30B-2Mn-4Ni-2Co (2) Since the 12Cr heat-resisting steel of the present invention is used in steam at 621 ° C. or higher, it is 650 ° C., 10 ° C. ⁵ h creep rupture strength 10
kgf / mm ² or more and room temperature impact absorption energy 1.5 kgf-m or more.

[0014] The 12Cr heat-resistant steel rotor of the present invention comprises 12Cr
An alloy material with a target composition of heat-resistant steel rotor material is melted and refined in an electric furnace, then deoxidized by vacuum carbon deoxidation, an electrode is made, and an ingot is made by electroslag remelting using this electrode. By forming the steel ingot by hot forging, a sound product can be produced.

[0015] The rotor material of 12Cr heat-resistant steel is 950-
After hot forging at 1200 ° C., it is heated to 950 to 1150 ° C., cooled to 660 to 750 ° C., annealed at this temperature, and further quenched by heating to 1000 to 1150 ° C.
By performing tempering twice at -650 ° C and 650-750 ° C, a steam turbine rotor usable in steam at 621 ° C or higher can be manufactured.

[0016]

[Function] C is an element required at least 0.06% in order to obtain high tensile strength, but if it exceeds 0.16%, the metal structure becomes unstable when exposed to high temperatures for a long time, and Since the creep rupture strength is reduced, the content is limited to 0.06 to 0.16%. In particular, 0.09 to 0.14% is preferable.

N is effective in improving the creep rupture strength and preventing the formation of a δ ferrite structure. However, if the content is less than 0.005%, the effect is not sufficient, and if it exceeds 0.035%, the toughness is reduced and the creep rupture is reduced. It also reduces strength.
Particularly, 0.015 to 0.03% is preferable.

It has been experimentally determined that the proper range of C and N satisfies the following equation.

[0019]

C + 2N = 0.13-0.2 (1) Mn is added as a deoxidizing agent, and its effect is achieved by adding a small amount, and creep rupture strength is obtained by adding a large amount exceeding 1%. Lower. In particular, it is preferably 0.7% or less.

Although Si is also added as a deoxidizing agent, according to steelmaking techniques such as vacuum C deoxidizing method, Si deoxidizing is unnecessary. Also, lowering Si has an effect of preventing formation of a harmful δ ferrite structure. Therefore, when it is added, it needs to be suppressed to 0.2% or less, and especially 0.2%.
Less than 07% is preferred.

V has the effect of increasing the creep rupture strength, but if it is less than 0.05%, its effect is insufficient, and if it exceeds 0.3%, δ ferrite is formed and the fatigue strength is reduced. In particular, 0.15 to 0.25% is preferable.

Nb is a very effective element for increasing the high-temperature strength. However, if it is added in an excessively large amount, coarse eutectic Nb carbides are generated, especially in large steel ingots, so that the strength is reduced and the fatigue strength is reduced. Must be suppressed to 0.2% or less because it causes δ ferrite to precipitate. On the other hand, if the content of Nb is less than 0.01%, the effect is insufficient. Particularly in the case of a large steel ingot, the content is preferably 0.03 to 0.1%, more preferably 0.04 to 0.08.

Ni is a very effective element for increasing the toughness and preventing the formation of δ ferrite.
%, The effect is not sufficient, and the addition exceeding 0.9% is not preferable because it lowers the creep rupture strength.
Particularly, it is preferably from 0.3 to 0.7%.

Cr has the effect of improving high strength and high temperature oxidation. If it exceeds 13%, a harmful δ ferrite structure is formed, and if it is less than 8%, the oxidation resistance to high-temperature and high-pressure steam becomes insufficient. Further, the addition of Cr has the effect of increasing the creep rupture strength, but the excessive addition causes the formation of a harmful δ ferrite structure and a decrease in toughness. In particular,
It is preferably 9.5 to 11%, more preferably 10.5 to 11.5%.

W has the effect of significantly increasing the high-temperature long-time strength. If W is less than 2%, the effect is insufficient for heat-resistant steel used at 621 to 650 ° C. If W exceeds 3%, the toughness decreases. 2.1-2.8% is preferred,
In particular, it is preferably 2.3 to 2.7%.

Conventionally, about 1% of Mo has been added to high-Cr martensitic heat-resistant steel in order to improve high-temperature strength. However, when the content of W exceeds 2% as in the steel of the present invention, the addition of Mo of 0.5% or more lowers the toughness and the fatigue strength, so that it is limited to less than 0.5%.

Addition of Ta, Ti and Zr has an effect of increasing toughness, and a sufficient effect can be obtained by adding Ta 0.2% or less, Ti 0.1% or less and Zr 0.1% or less alone or in combination. When 0.1% or more of Ta is added, N
The addition of b can be omitted.

The heat-resistant steel rotor material of the present invention must have a substantially fully tempered martensitic structure. If a δ ferrite structure is mixed, the fatigue strength and toughness are reduced, so that the structure has a uniform tempered martensitic structure. There is a need to. In order to obtain a fully tempered martensite structure, the Cr equivalent calculated by equation (1) must be reduced to 10 or less by adjusting the composition. If the Cr equivalent is too low, the creep rupture strength decreases, so it must be 4 or more. In particular, a Cr equivalent of 6 to 8 is preferable.

Although the addition of B significantly increases the high temperature (621 ° C. or higher) creep rupture strength, the effect is insufficient when the B content is less than 0.01%. If the B content exceeds 0.04%, the high-temperature hot workability deteriorates, so the upper limit is 0.0.
Limited to 4%. The B content of the large rotor is 0.01
-0.03%, particularly preferably 0.01-0.02%.

The addition of Co has the effects of preventing precipitation of the δ ferrite phase, which is a harmful structure, and increasing creep rupture strength and toughness. Addition of 2% or more has the disadvantage of lowering toughness. In particular, it is preferably 0.5 to 1.9%.

Since the rotor is rotated at a high speed (3000 or 3600 rpm) in steam at 621 ° C. or higher, a high stress acts on the dovetail portion and the center hole portion supporting the blade. From a viewpoint, 10kgf
/ Mm ² or more 10 ⁵ h creep rupture strength is required. In addition, at the time of startup, when the metal temperature is low, tensile thermal stress acts on the center hole, so from the viewpoint of preventing brittle fracture,
Room-temperature impact absorption energy of 1.5 kgf-m or more is required.

In order to homogenize the entire rotor, a steel ingot weight of around 80 tons (rotor → diameter: 1200 mm, length: about 8 m)
Therefore, advanced manufacturing technology is required. The rotor of the present invention melts the alloy raw material having the target composition in an electric furnace, refines it, deoxidizes it by a vacuum carbon deoxidation method, produces an electrode, and produces an ingot by electroslag remelting using this electrode. The steel ingot can be manufactured by molding by hot forging. By repeating melting twice with an electric furnace and an electroslag remelting method, a homogeneous rotor with less component segregation can be manufactured.

The hot forging of the steel ingot is performed at a high temperature because the deformation resistance is small and the forging is easy, but when it is performed at an excessively high temperature, the steel is broken. Therefore, it must be performed in a temperature range of 950 to 1200 ° C. 950-1150 after hot forging
C., cooled to 660-750.degree. C., annealed at this temperature, isothermally quenched at 1000-1150.degree. C., and then tempered twice at 550-650.degree. C. and 650-750.degree. / mm ² or more of the 650
° C., 10 ⁵ h creep rupture strength and 1.5 kgf-m or more at room temperature impact absorption energy can be obtained, the steam turbine rotor manufacturing method available in 621 ° C. or higher in the vapor. In the above heat treatment, the constant temperature annealing refines crystal grains and increases toughness.
In addition, the twice tempering completely decomposes the retained austenite and makes it possible to form a uniform whole tempered martensitic structure.

[0034]

EXAMPLES Examples of the steel of the present invention will be described below.

Table 1 shows the chemical composition of a representative sample.

[0036]

[Table 1]

As a sample, a steel ingot was prepared using a high-frequency induction melting furnace, and then hot forged into a 35 mm square bar at 950 to 1150 ° C. Sample Nos. 8 to 13 are invention materials, and Sample Nos.
1 and 2 are conventional materials. Samples No. 1 and No. 2 were made of Cr-Mo-V steel and 11
Cr-1Mo-V-Nb-N steel. No.3 to No.7
Is a comparative material.

The sample was heat-treated (quenched and tempered) under the following conditions, assuming the center of a large steam turbine rotor shaft. Even if the center of the large rotor is quenched with water or oil, the cooling rate is not so high, and is at most 100 ° C./h.
It is.

Sample No. 1: 970 ° C. × 20 h 100 ° C.
/ H cooling 675 ° C × 20h air cooling Sample No.2: 1050 ° C × 20h 100 ° C / h
Cooling 570 ° C x 20h Air cooling 675 ° C x 20h Air cooling Sample Nos. 3 to 13: 1050 ° C x 20h 100 ° C
/ H Cooling 570 ° C × 20h Air cooling 700 ° C × 20h Air cooling Sample No. 10 ′ was subjected to constant temperature annealing treatment (heated to 1050 ° C. and held for 10 hours before quenching / tempering
The sample was cooled to 00 ° C., kept at this temperature for 50 hours, transformed at a constant temperature, and cooled in a furnace.

Table 2 shows the tensile properties at room temperature and the V at 20 ° C.
Notch Charpy impact absorption energy and 650 ° C, 10
⁵ h shows the creep rupture strength.

[0041]

[Table 2]

The material of the present invention to which appropriate amounts of N, B and Co are added
Creep rupture strength and impact absorption energy of (No.8~10) are characteristics required for the ultra supercritical pressure turbine rotor (650 ℃, 10 ⁵ h strength ≧ 10kgf / mm ^2, 20 ℃ absorbed energy ≧ 1.5 kg -M) is sufficiently satisfied. Also,
The toughness of the samples (Nos. 11, 12, and 13) to which Ta, Ti, and Zr are added are quite excellent.

The toughness of the sample 10 'subjected to the constant temperature annealing treatment is remarkably improved as compared with the sample No. 10 not subjected to this treatment.

FIGS. 1 and 2 show the effect of the amount of C + N on impact absorption energy and creep rupture strength. C
The material of the present invention (No. 9) having a + N amount of 0.14% is a comparative material (N
o.6: C + N = 0.07, No. 4: C + N = 0.18)
As compared with the above, the creep rupture strength and the impact absorption energy are remarkably excellent, and the required values are sufficiently satisfied. The material of the present invention has 6
Even in a temperature range of 50 ° C. or lower (525 to 625 ° C.), the material exhibited significantly higher creep rupture strength than the comparative material.

The alloy composition raw material of the present invention was melted and refined in an electric furnace, and then deoxidized by a vacuum carbon deoxidation method to produce an electrode. Using this electrode, a 10 ton steel ingot was produced by an electroslag remelting method. This ingot was formed by hot forging at 950 to 1200 ° C. After hot forging, heating to 1050 ° C, 70
After cooling to 0 ° C., constant temperature annealing at this temperature, and heat quenching to 1050 ° C., tempering was performed twice at 570 ° C. and 700 ° C. to produce a steam turbine rotor. FIG. 2 shows the shape. The cutting survey result this prototype rotor, characteristics (650 ° C. required for ultra supercritical pressure turbine rotor, 10 ⁵ h
Strength ≧ 10 kgf / mm ² , shock absorption energy at 20 ° C. ≧ 1.5
kg-m), which proved to be a homogeneous rotor.

[0046]

According to the present invention, a martensitic heat-resistant steel having a high creep rupture strength at 650 ° C. and a high room temperature toughness can be obtained. Instead of superalloy steel, it can be made of martensitic heat-resistant steel (steel of the present invention).

By using the steel of the present invention for a high-temperature member instead of the conventional superalloy steel, material costs can be significantly reduced. Further, since the steel of the present invention has a smaller thermal expansion coefficient than that of superalloy steel, it has advantages in that it is easy to start the turbine quickly and is less susceptible to thermal fatigue damage.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the influence of the amount of C + N on shock absorption energy.

FIG. 2 is a characteristic diagram showing the effect of the amount of C + N on creep rupture strength.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeyoshi Nakamura 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hiroshi Fukui 7-1-1, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd., Hitachi Research Laboratory (72) Inventor Toshio Fujita 4-6 Kanda Surugadai, Chiyoda-ku, Tokyo Hitachi, Ltd. (56) References JP-A-59-232231 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (5)

(57) [Claims] (1) 3000 rp in high-temperature steam of 621 ° C. or more.
A steam turbine rotor which is rotated at a high speed of 3 m or 3600 rpm and has a weight ratio of C 0.06 to 0.16%,
Si less than 0.2%, Mn less than 1%, Cr 8-13%, N
i 0.2 to 0.9%, V 0.05 to 0.3%, Nb 0.01
~ 0.20%, N 0.005 ~ 0.03%, Mo less than 0.5%, over W2 and less than 3%, B over 0.001 and 0.03%
Less than and less than Co2%, the balance being Fe and unavoidable impurities, the sum of the C amount and the N amount is in the range of [Equation 1] , and the Cr equivalent calculated by [Equation 2] is 4-10. ,
Has a fully tempered martensitic structure, 650 ° C, 10
A steam turbine rotor comprising a 12Cr heat-resistant steel having a ⁵ h creep rupture strength of 10 kgf / mm ² or more and a room temperature shock absorption energy of 1.5 kgf-m or more. (1) C + 2N = 0.13 to 0.2 (1) Cr equivalent = Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C-30N-30B-2Mn-4Ni-2Co (2) (2) 3000 rp in high-temperature steam of 621 ° C. or higher.
A steam turbine rotor which is rotated at a high speed of 3 m or 3600 rpm, and has a weight ratio of C 0.06 to 0.14%,
Si less than 0.1%, Mn less than 1%, Cr 8-12%, N
i 0.2 to 0.9%, V 0.05 to 0.3%, Nb 0.01
~ 0.20%, N 0.005 ~ 0.03%, Mo less than 0.5%, more than W2 less than 3%, more than B0.01 more than 0.025%
Less than and less than Co2%, the balance being Fe and unavoidable impurities, the sum of the C amount and the N amount is in the range of [Equation 1] , and the Cr equivalent calculated by [Equation 2] is 4-10. ,
Has a fully tempered martensitic structure, 650 ° C, 10
A steam turbine rotor comprising a 12Cr heat-resistant steel having a ⁵ h creep rupture strength of 10 kgf / mm ² or more and a room temperature shock absorption energy of 1.5 kgf-m or more. [Number 1] C + 2N = 0.13~0.2 ... (1 ) Equation 2] Cr equivalent = Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C -30N-30B-2Mn-4Ni-2Co ... (2) (3) 3000 rp in a high temperature steam of 621 ° C. or more.
A steam turbine rotor which is rotated at a high speed of 3 m or 3600 rpm and has a weight ratio of C 0.09 to 0.14%,
Si less than 0.07%, Mn less than 0.7%, Cr 9.5 to 1
2%, Ni 0.3 to 0.7%, V 0.15 to 0.25%, N
b 0.04 to 0.08%, N 0.015 to 0.025%, M
o less than 0.4%, W 2.3-2.7%, B more than 0.01 and less than 0.02%, and Co more than 0.5 and less than 2%,
The balance consists of Fe and unavoidable impurities, the sum of the C content and the N content is in the range of [Equation 1] , and Cr calculated by [Equation 2]
Equivalent weight is 4-10, fully tempered martensite structure, 650 ° C, 10 ⁵ h Creep rupture strength of 10 kg
A steam turbine rotor made of 12Cr heat-resistant steel having f / mm ² or more and room-temperature impact absorption energy of 1.5 kgf-m or more. [Number 1] C + 2N = 0.13~0.2 ... (1 ) Equation 2] Cr equivalent = Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C -30N-30B-2Mn-4Ni-2Co ... (2) 4. The method according to claim 1, 2 or 3, wherein Ta0.
A steam turbine rotor containing at least one of 2% or less, Ti 0.1% or less and Zr 0.1% or less. 5. The method for manufacturing a steam turbine rotor according to claim 1, wherein the alloy material is melted in an electric furnace, refined, and then deoxidized by a vacuum carbon deoxidation method. A steel ingot is produced by an electroslag remelting method using this electrode, and the steel ingot is subjected to hot forging at 950 to 1200 ° C., and then heated to 950 to 1150 ° C.
After cooling to 50 ° C, annealing at this temperature,
A method for manufacturing a steam turbine rotor, comprising: heat quenching at 0 to 1150 ° C., tempering at 550 to 650 ° C., and then tempering at 650 to 750 ° C.