JPH0931600A - Steam turbine rotor material for high temperature use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine rotor material for high temp. use, applicable to high temp. steam conditions, by forming a Cr steel having a composition in which respective contents of C, Si, Mn, Cr, V, Nb, Ta, N, Mo, W, and Co are specified SOLUTION: This steam turbine rotor material for high temp. use has a composition consisting of, by weight ratio, 0.05-0.13% C, 0.005-0.10% Si, 0.01-0.5% Mn, 9-12% Cr, 0.1-0.3% V, 0.01-0.15%, in total, of Nb and Ta, 0.01-0.1% N, 0.05-0.5% Mo, 1.5-3% W, 1-4% Co, and the balance Fe with inevitable impurities. If necessary, a part of Fe is substituted by B and B is incorporated by 0.001-0.03%. B has a function of increasing grain boundary strength and contributes to the improvement of creep rupture strength.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a steam turbine rotor material for thermal power generation.

[0002]

2. Description of the Related Art High-temperature rotor materials used in steam turbine plants for thermal power generation include CrMoV steel and 12C.
r Steel is an example. Of these, CrMoV steel is limited to plants with steam temperatures up to 566 ° C. due to high temperature strength limitations. On the other hand, a rotor material made of 12Cr steel (for example, Japanese Unexamined Patent Publication No.
0-165359, JP-A-62-103345, etc.) has higher high temperature strength than CrMoV steel, so it can be applied to a plant having a steam temperature up to 600 ° C. It is difficult to apply as a steam turbine rotor because the high temperature strength is insufficient for the temperature exceeding the limit.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention provides
It is intended to provide a high temperature steam turbine rotor material which is a Cr-based steel material and can be applied under a steam condition of 600 ° C. or higher and which has excellent high temperature strength.

[0004]

Therefore, as a result of intensive studies, the present inventors have invented the following excellent high temperature steam turbine rotor material. That is, the present invention is (1)
Carbon: 0.05 to 0.13% by weight, silicon: 0.
005-0.1%, manganese: 0.01-0.5%, chromium: 9-12%, vanadium: 0.1-0.3%, total of niobium and / or tantalum: 0.01-0. 15
%, Nitrogen: 0.01 to 0.1%, molybdenum: 0.05
~ 0.5%, tungsten: 1.5-3%, cobalt:
1 to 4% and inevitable impurities and iron, and a high temperature steam turbine rotor material and (2) part of iron is replaced with boron, and a weight ratio of boron: 0.001 to 0.
The high temperature steam turbine rotor material according to the above (1), characterized in that the content is 03%.

(Regarding First High Temperature Steam Turbine Rotor Material) The first high temperature steam turbine rotor material of the present invention is 1
This is a new high temperature steam turbine rotor material having excellent high temperature characteristics, which was made by carefully selecting alloying elements using 2Cr steel as a basic component to improve high temperature strength. About 0.5% of Ni is added to the conventional 12Cr steel turbine rotor material. Ni is essentially an element that lowers the creep rupture strength, but it is effective in suppressing δ ferrite in controlling the matrix structure, and also improves toughness, so that these useful effects are prioritized. It is addition. On the other hand, in the material of the present invention, ensuring the creep rupture strength is given top priority, Ni is completely eliminated except for those which are inevitably mixed, and at the same time, Co, which has a high effect of suppressing δ ferrite like Ni, is positively active. The feature is that it is added. Further, the contents of Si and Mn, which adversely affect the toughness, are reduced as much as possible to secure the toughness. The reasons for limiting the components in the first high temperature steam turbine rotor material of the present invention will be described below.
In the following description,% means% by weight.

C: C forms carbonitrides together with N and contributes to the improvement of creep rupture strength. However, 0.05%
If it is less than 0.1%, a sufficient effect cannot be obtained, and if it exceeds 0.13%, carbonitrides agglomerate and coarsen during use, resulting in deterioration of high-temperature long-term strength. Therefore, the content is set to 0.05 to 0.13%. A desirable component range is 0.09 to 0.11%.

Si: Si has an effect as a deoxidizing agent, but is an element that embrittles the matrix. Since the vacuum carbon deoxidizing method is applied in the production of the rotor material of the present invention,
The addition amount is limited to the minimum amount necessary for steel making, and the component range is 0.005 to 0.1%. A desirable range is 0.005 to 0.05%.

Mn: Mn is an element which acts as a deoxidizer and is useful for preventing hot cracking during forging. It also has the effect of suppressing the formation of δ ferrite.
However, when Mn is added, the creep rupture strength deteriorates according to the amount, and since it is also an element that essentially promotes embrittlement of steel, in the present invention, importance is attached to ensuring the creep rupture strength. The large amount was 0.5%. Also, especially 0.
If the content is suppressed to 15% or less, the creep rupture strength is further improved. Therefore, it is necessary to suppress the addition to 0.15% or less as needed. However, in order to control the content to less than 0.01%, careful selection of the raw material steel and an excessive refining process are required, resulting in high cost. Therefore, the minimum amount is set to 0.01%. A desirable component range is 0.01 to 0.15%.

Cr: Cr forms a carbide and contributes to the improvement of creep rupture strength. It also dissolves in the matrix to improve the oxidation resistance and strengthens the matrix itself, thereby contributing to the improvement of the creep rupture strength. 9%
If it is less than the above range, the effect is not sufficient, and if more than 12% is added, δ ferrite is likely to be formed, resulting in a decrease in strength and a deterioration in toughness. Therefore, the component range is set to 9 to 12%. A desirable range is 10.5-11.
5%.

V: V becomes a carbonitride to improve creep rupture strength. If it is less than 0.1%, a sufficient effect cannot be obtained. Conversely, if the amount exceeds 0.3%, the creep rupture strength is rather lowered. Therefore, the component range is 0.1 to 0.3%.

Nb and / or Ta: Nb and / or T
a forms carbonitrides and contributes to improvement of high temperature strength. Further, the carbide (M ₂₃ C ₆ ) precipitated at a high temperature is made finer, which contributes to improvement in long-time creep rupture strength. If the total amount of both elements is less than 0.01%, there is no effect, and
%, The amount of Nb generated during steel ingot production
And / or Ta carbonitride cannot be sufficiently solid-dissolved in the matrix during heat treatment (solution treatment), and coarsens during use to reduce long-term creep rupture strength. Therefore, the component range is limited to 0.01% to 0.15%.

N: N forms carbonitrides together with C and alloy elements and contributes to improvement of high temperature strength. If it is less than 0.01%, sufficient carbonitride cannot be formed.
Sufficient creep rupture strength cannot be obtained. Also, 0.1%
If it is added in an amount exceeding the above range, the carbonitride will be agglomerated and coarsened over a long period of time, and sufficient creep rupture strength cannot be obtained. Therefore, it is set to 0.01 to 0.1%. A desirable amount is 0.02 to 0.05%.

Mo: Mo forms a solid solution with W in the matrix to improve the creep rupture strength. Although it is possible to add about 1.5% if Mo is added alone, when W is added as in the present invention, W is more effective in improving the high temperature strength, and Mo and W When a large amount of is added, δ ferrite is formed and the creep rupture strength is deteriorated. Therefore, from the balance with the amount of W added, 0.0
It is added in the range of 5 to 0.5%.

W: W improves the creep rupture strength by forming a solid solution in the matrix together with Mo as described above. W
Is an element that has a stronger strengthening function by solid solution than Mo and is effective. However, when a large amount is added, δ ferrite and a large amount of Laves phase are generated, and conversely, creep rupture strength is deteriorated. Therefore, in consideration of the balance with the addition amount of Mo, the addition amount is set to 1.5 to 3%.

Co: Co forms a solid solution in the matrix, strengthens the matrix itself, and suppresses the formation of δ ferrite. Therefore, when Co is added, it becomes possible to add more strengthening elements such as Mo and W having a stronger tendency to form ferrite than those without Co. As a result, high creep rupture strength can be obtained. Similarly, Ni is a general element that has an effect of suppressing the formation of δ ferrite, but Ni deteriorates the creep rupture strength as the amount of addition increases. In the conventional 12Cr steel turbine rotor material, about 0.5% of Ni is added in order to suppress the formation of δ ferrite and to secure the toughness, but in the present invention, importance is attached to the securing of creep rupture strength, and Ni is particularly important. Is characterized in that it is not added. However, the addition of Co completely suppresses the formation of δ ferrite. C
The effective effect of o addition appears when the addition amount is 1% or more, but if Co amount exceeding 4% is added, the precipitation of carbides is promoted, so that the creep rupture strength on the long side is deteriorated. Will end up. In addition, since Co itself is an expensive material, addition of a large amount leads to high cost. Therefore, the component range is set to 1 to 4%. A desirable range is 2.5 to 3.5%.

(Regarding the Second High-Temperature Steam Turbine Rotor Material of the Present Invention) The second high-temperature steam turbine rotor material of the present invention contains 0.001% by weight of a part of the first Fe.
The steam turbine rotor material for high temperature is characterized by being replaced by 0.03% of B. The reasons for limiting the components will be described below, but since C, Si, Mn, Cr, Mo, W, V, Nb and / or Ta, Co, N are the same as those of the first high temperature steam turbine rotor material, The explanation is omitted,
Only the new additive element B will be described.

B: B has the function of increasing the grain boundary strength. This contributes to improvement in creep rupture strength. However, if added in a large amount, the hot workability deteriorates and the toughness decreases. Therefore, 0.001% of the minimum amount that can actually control the addition amount is set as the lower limit value and the upper limit value is set as 0.03% at which no adverse effect appears. A desirable range is 0.01 to 0.02%.

[0018]

EXAMPLES The effects of the present invention will be clarified by giving specific examples of the first and second high temperature steam turbine rotor materials of the present invention.

Example 1 First High Temperature Steam Turbine Rotor Material ◯ (Structure of Example 1) Table 1 shows the chemical components of the materials used in the test. Sample numbers 1 to 9 correspond to the material of the present invention, and sample numbers 10 to 18 correspond to the comparative material. All materials were melted in a 50 kg vacuum induction melting furnace and forged at a heating temperature of 1200 ° C. The heat treatment of the test materials used in various tests was a quenching process simulating the center part when a rotor with a body diameter of 1200φ was oil-cooled, and then tempering was performed with a 0.2% proof stress of about 63 to 67 kgf / m.
The tempering temperature of each material was determined so as to be m ² .

(Effect of Example 1) Table 2 shows the mechanical properties and creep rupture properties of the material of the present invention and the comparative material. The Charpy impact value (at room temperature test) of the material of the present invention shows a high value of 9.0 kgf-m or more, and it can be seen that a sufficiently high impact value can be secured even if Ni is excluded. Focusing on the creep rupture time when a load of 15 kgf / mm ² is applied at 650 ° C., it is found that the material of the present invention has a significantly longer rupture time than the comparative material. Subsequently, among the materials of the present invention, 650 ° C.-15
For kgf / mm ² creep rupture time longest 650 ℃ -15kgf / mm ² creep rupture time longest sample 14 in the sample 8 and the comparative material, further 650 ° C. in a variety of stresses, the creep rupture test at 700 ° C. The creep rupture strength at 105 ° C. for 10 ⁵ hours was estimated from the obtained data. Sample 8 is 12.1 kgf /
mm ² and Sample 14 are 8.2 kgf / mm ² , and it can be seen that the material of the present invention is also very excellent in long-term creep rupture strength. The above suggests that the component design based on the exclusion of Ni and the positive addition of Co is effective in improving the creep rupture strength.

[0021]

[Table 1]

[0022]

[Table 2]

(Example 2) Second High Temperature Steam Turbine Rotor Material O (Structure of Example 2) Table 3 shows the chemical components of the materials used in the test. All materials are melted in a 50kg vacuum high frequency melting furnace and heating temperature:
Forging was performed at 1200 ° C. The heat treatment of the test materials used in various tests was a quenching process simulating the center of a rotor with a cylinder diameter of 1200φ when it was oil-cooled, and then tempering was performed at 0.
The tempering temperature of each material was determined so that the 2% proof stress was about 65 to 67 kgf / mm ² . Sample number 19
-21 correspond to the material of the present invention, and sample numbers 22 and 23 correspond to the comparative materials. Sample Nos. 19, 20 and 22 are materials with the amount of B added varied based on the components of Sample No. 8 used in Example 1 above, and Sample Nos. 21 and 23 are Sample No. 6 used in Example 1 above. It is a material in which the addition amount of B is changed based on the component of. Strictly speaking, sample number 1
The component bases of 9, 20 and 22 have a slight difference from the sample number 8 and the sample numbers 21 and 23 have a slight difference from the sample number 6 of the component base, but in reality, such a variation in the component base is controlled. Difficult, so sample numbers 19, 20 and 22
It can be said that the sample number 8 is based on the component, and the sample numbers 21 and 22 are sample number 6 based on the component.

(Effect of Example 2) Table 4 shows the mechanical properties and creep rupture properties of the material of the present invention and the comparative material. The Charpy impact value (at room temperature test) of the material of the present invention shows a high value of 10.0 kgf-m or more, which is comparable to the base material (Sample Nos. 6 and 8). This means that within the range of addition in the material of the present invention, B
It has been shown that the addition of at least has no adverse effect on the impact value. 15kgf / m at 650 ° C
Focusing on the creep rupture time when a load of m ² is applied, it can be seen that the material of the present invention has a longer rupture time than the base materials (sample numbers 6 and 8). On the other hand, the comparative materials (Sample Nos. 22 and 23) containing a large amount of B have a shorter fracture time than the base materials (Sample Nos. 6 and 8). Next, among the materials of the present invention, 650 ° C.-15 kgf / mm ²
The creep rupture test at 650 ° C. and 700 ° C. was further conducted on Sample 20 having the longest creep rupture time at various stresses.
0 ⁵ hours creep rupture strength was estimated. The estimated breaking strength of Sample 20 is 12.7 kgf / mm ² , and it can be seen that the long-term creep breaking strength is also superior to that of the base material (Sample No. 8). The above suggests that by replacing a part of Fe in the turbine rotor material shown in Example 1 with B in the component range shown in Example 2, the creep rupture strength is further improved.

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

The high temperature steam turbine rotor material of the present invention has excellent high temperature strength, so that the steam temperature is 600 ° C.
It is useful as a high temperature steam turbine rotor material for ultra-supercritical power generation plants exceeding 100. According to the present invention, it can be said that the present ultra-supercritical power plant is useful for further raising the temperature, contributing to the saving of fossil fuels, and keeping the amount of generated carbon dioxide low.

Front Page Continuation (72) Inventor Ikujiro Kitagawa, 59, Nakahara Sakinohama, Tobata-ku, Kitakyushu, Fukuoka, Japan 59, Nippon Cast & Forged Steel Co., Ltd. Nohama 46 Address 59 Nippon Cast and Forged Steel Co., Ltd.

Claims (2)

[Claims] 1. Carbon: 0.05 to 0.13% by weight,
Silicon: 0.005-0.1%, Manganese: 0.01
~ 0.5%, chromium: 9-12%, vanadium: 0.1
~ 0.3%, total of niobium and / or tantalum: 0.0
1 to 0.15%, nitrogen: 0.01 to 0.1%, molybdenum: 0.05 to 0.5%, tungsten: 1.5 to 3
%, Cobalt: 1 to 4%, and inevitable impurities and iron. A high temperature steam turbine rotor material. 2. A high temperature steam turbine rotor material according to claim 1, wherein a part of iron is replaced by boron, and the content of boron is 0.001 to 0.03% by weight.