JPH0641678A - Turbine rotor - Google Patents

Abstract

PURPOSE:To inexpensively manufacture a rotor for a steam turbine excellent in creep breaking strength at a high temp. as well as tensile strength and toughness at a relatively low temp. by manufacturing the rotor with a low alloy steel having a specified compsn. CONSTITUTION:The steam turbine rotor is manufactured by the low alloy steel having a compsn. constituted of, by weight, 0.10 to 0.35% C, less than 0.3% Si, less than 1.0% Mn, 1.0 to 2.0% Ni, 1.5 to 3.0% Cr, 0.9 to 1.3% Mo, 0.10 to 0.35% V, 0.01 to 0.15% Nb and 0.1 to 1.5% W, and the balance Fe. The turbine rotor in which the segregation of C on the central part of the rotor is suppressed, and small in brittleness as well as having a high creep breaking strength at a high temp. and high tensile strength even under the steam conditions of a relatively low temp. can be manufactured at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a turbine rotor, and more particularly to a turbine rotor which is excellent in creep rupture strength at high temperatures, tensile strength and toughness at relatively low temperatures, and which reduces segregation of components.

[0002]

2. Description of the Related Art Since the rotor of a steam turbine is used under severe conditions, the selection of its constituent materials is an extremely important matter for improving the life or operating rate of the steam turbine. Rotors made of different materials are used depending on steam conditions.

For example, in a large steam turbine, as a rotor material used on the high temperature / high pressure side (for example, near 566 ° C.), excellent creep rupture at a high temperature as specified in ASTM-A470 (Class 8). CrMoV steel with strength is used and also on the low pressure side (eg 35
As a rotor material for 0 ° C. or lower), ASTM-A470
NiCrMoV steel containing 2.5% or more of Ni as defined in (Class 2 to 7) is used, and rotors made of different materials corresponding to these steam conditions are mechanically joined to each other to form a steam turbine. Are configured. On the other hand, in a relatively small-sized steam turbine, a high-low pressure integrated rotor in which a high-pressure side and a low-pressure side are constituted by a single rotor made of the same material is usually used.

[0004]

However, the conventional steam turbine rotor has the following problems.
That is, in a conventional large-scale steam turbine, a plurality of rotors made of different materials are joined to form a turbine, which complicates the manufacturing process and increases the installation space of the entire turbine, which increases plant cost. There is a problem such as.

On the other hand, as a material for a high-low pressure integrated rotor used in a small steam turbine, usually CrM is used.
Although oV steel and NiCrMoV steel are used, the conventionally used CrMoV steel is not sufficiently satisfactory in terms of tensile strength, so the size of the blade that can be mounted in the low pressure final stage is limited. There was a problem. Also, CrM
oV steel has a very low content of impurity elements to suppress embrittlement caused by long-term use and to improve creep rupture ductility.
When Si and Mn are reduced, there is also a problem that carbon (C) segregation at the center of the rotor is promoted. further,
The conventional NiCrMoV steel has excellent tensile strength but lacks creep rupture strength and toughness.
There is a problem that embrittlement easily progresses in the temperature range of ℃ or more. For this reason, in the conventional rotor material, there has been a large limitation when trying to improve the efficiency of the steam turbine by using high temperature steam and by mounting a long low pressure last stage blade.

Further, as a rotor material excellent in creep rupture strength and toughness, and also in tensile strength in a low temperature range,
Although 12Cr steel has already been developed, this 12Cr steel is expensive, and there is a problem that use of this 12Cr steel as a rotor material causes an increase in manufacturing cost.

The present invention has been made in view of the above-mentioned problems, and has a high tensile strength under a relatively low temperature steam condition, a large creep rupture strength even under a high temperature condition, and a small embrittlement. At the same time, it is an object of the present invention to provide a turbine rotor that suppresses carbon (C) segregation at the center of the rotor and is inexpensive.

[0008]

The composition of the turbine rotor of the present invention is C: 0.10 to 0.35% by weight,
Si: 0.3% or less, Mn: 1.0% or less, Ni: 1.
0-2.0%, Cr: 1.5-3.0%, Mo: 0.9
~ 1.3%, V: 0.10 to 0.35%, Nb: 0.0
1 to 0.15%, W: 0.1 to 1.5%, and the balance Fe and incidental impurities.

[0009]

In the turbine rotor having the above structure, it has high tensile strength under relatively low temperature steam conditions, high creep rupture strength even under high temperature conditions, little embrittlement, and carbon ( C) Segregation is suppressed and the life is extended.

The purpose of adding each component and the reason for limiting the composition of the turbine rotor of the present invention are as follows.

1. C (Carbon) Carbon stabilizes the austenite phase during quenching,
Further, carbide is generated to increase the tensile strength, but for that purpose, 0.10% or more is necessary. However, if it exceeds 0.35%, the carbide becomes excessive, which not only lowers the strength but also lowers the notch toughness. Therefore, the amount of carbon is in the range of 0.10 to 0.35%, preferably 0.
18 to 0.30%.

2. Si (silicon) Silicon is added as a deoxidizing agent at the time of melting, but if a large amount of this is added, a part of it remains in the steel as an oxide, which adversely affects the notch toughness. Therefore, the amount of silicon added is 0.3% or less, preferably 0.1% or less.

3. Mn (manganese) Manganese is added as a deoxidizing / desulfurizing agent at the time of melting. However, if a large amount of manganese is added, the notch toughness decreases, so the addition amount is 1.0% or less, preferably 0.7%. % Or less.

4. Ni (Nickel) Nickel is an austenite-forming element and is effective in stabilizing the austenite phase during quenching and heating and preventing the formation of ferrite phase during quenching and cooling. Further, it is effective in increasing tensile strength and toughness. In order to obtain the tensile strength and toughness required for the turbine rotor of the present invention, it is necessary to add more than 1.0%. However, 2.0%
If it is added over the range, on the contrary, the creep rupture strength decreases,
Since the embrittlement tends to be promoted, the addition amount is 1.0 to
The range is 2.0%, and preferably 1.3 to 1.8%.

5. Cr (Chromium) Chromium is an element necessary for preventing oxidation and improving strength and toughness. 1.5 for this purpose
%, It is necessary to add more than 3.0%, but if it exceeds 3.0%, conversely, notch toughness and strength decrease and journal characteristics also decrease. Therefore, the amount of chromium added is 1.5-3.0%.
Range, preferably 1.8 to 2.5%.

6. Mo (Molybdenum) Molybdenum is an element effective for improving the hardenability of steel and increasing the tensile strength and creep rupture strength. In order to obtain the tensile strength and creep rupture strength required for the turbine rotor of the present invention, it is necessary to add more than 0.9%. However, when it exceeds 1.3%, not only the creep rupture strength is lowered, but also the toughness is remarkably lowered. Further, the segregation of the components in the central portion of the turbine rotor, especially the segregation of C (carbon), becomes noticeable. Therefore, the amount of molybdenum added is in the range of 0.9 to 1.3%, preferably 1.0 to 1.2%.

7. V (Vanadium) Vanadium is an element effective in improving the hardenability of steel and increasing the creep rupture strength. In addition, it is also effective in achieving a finer crystal grain. In order to exert its effect, it is necessary to add 0.10% or more, but 0.35%
If it exceeds 1.0, notch toughness and strength will decrease, so 0.10
The range is 0.35%, preferably 0.15 to 0.30%.

8. Nb (niobium) Niobium is an element effective in refining crystal grains. In order to exert its effect, 0.01% or more must be added. However, if over 0.15% is added, on the contrary, coarse carbonitrides are formed and the notch toughness is reduced.
Range of 0.01 to 0.15%, preferably 0.02
It is set to 0.10%.

9. W (Tungsten) Tungsten is an element effective in improving high temperature strength by solid solution strengthening. 0.1% to exert its effect
The above additions are necessary. However, if added over 1.5%, the notch toughness will decrease, so 0.1-1.5%
Range, preferably 0.2 to 0.8%.

Incidentally, it is desirable that the impurities contained incidentally when the above-mentioned components and Fe as the main component are dissolved are small.

[0021]

EXAMPLES Examples and comparative examples and their test results will be described below with reference to the drawings and tables.

Table 1 shows the raw material blending components of Comparative Examples 1-8 and Examples 1-5.

[0023]

[Table 1] In Comparative Examples 1 to 8 and Examples 1 to 5, raw materials were mixed so as to have a predetermined alloy composition, melted by a high frequency vacuum melting method, and then cast into a mold to obtain ingots. After machining the surface of this ingot by machining,
It was charged into a heavy oil furnace, heated to 1200 ° C., press-forged, and forged into a round bar having a diameter of 30 mm.

The composition of Comparative Example 1 is 1% CrM which has been conventionally used in a high temperature turbine rotor for thermal power generation.
Corresponds to oV steel. Further, the composition of Comparative Example 2 has been conventionally used in a low temperature turbine rotor for thermal power generation.
Corresponds to 5% NiCrMoV steel. Although Comparative Examples 3 to 8 are not used as the current turbine rotor material, they were especially manufactured to study the effect of Mo in the present invention. Comparative Examples 1-8 and Examples 1-5
Table 2 shows the heat treatment conditions.

[0025]

[Table 2] Next, each test material was machined to prepare a test piece, and a tensile test, a Charpy impact test and a creep rupture test were performed. The results of the tensile test and the Charpy impact test are shown in Table 3, and the result of the creep rupture test is shown in Table 4.

[0026]

[Table 3]

[Table 4] The tensile test was conducted at room temperature. In addition, Table 3 also shows the elongation after breakage and the drawing.

The Charpy impact test was carried out at a plurality of temperatures ranging from room temperature to 200 ° C. to determine the fracture surface transition temperature. Creep rupture tests were conducted over a period of 14 kgf / mm ² and 17 kgf / mm ² stress at 600 ° C..

Further, for Comparative Examples 1 to 3, 5, 6 and 8 and Examples 1 to 3, in order to compare and evaluate the degree of segregation of C (carbon) component in the central portion of the rotor when the turbine rotor was manufactured, An ingot of 500 kg was manufactured for each, and the C (carbon) content in the central part was evaluated. The ratio of C (carbon)% in the upper part of the ingot to C (carbon)% in the lower part of the ingot is defined as "segregation ratio", and the results of the "segregation ratio" of each material are shown in Table 5.

[0029]

[Table 5] Based on the above results, the fracture surface transition temperature, the creep rupture time and the "segregation ratio" are arranged by Mo content.
Shown in.

Considering these experimental results, first, from the test results shown in Table 3, Example 1 according to the present invention is shown.
It is understood that all of Nos. 5 to 5 show good tensile strength, proof stress, elongation, and drawing which are equal to or higher than those of Comparative Examples 1 to 8 and have sufficient mechanical properties at a relatively low temperature. To be done. In particular, in each of the examples, the strength was remarkably improved and the fracture surface transition temperature was low (in other words, the toughness was improved) as compared with Comparative Example 1.

Next, from the test results shown in Table 4, all of Examples 1 to 5 according to the present invention have significantly better creep rupture time than Comparative Examples 2 to 8 It can be seen that the characteristics are comparable to those of Comparative Example 1, which is a rotor material for a high-pressure turbine. Furthermore, from the test results of Table 5, Examples 1 to 3 according to the present invention are Comparative Examples 6 and 8.
Shows a much smaller "segregation ratio" than that of the conventional high-pressure turbine rotor material and low-pressure turbine rotor material shown in Comparative Examples 1 and 2 and a small "segregation ratio". It is understood that the turbine rotor according to the invention does not cause problems with manufacturing component segregation.

FIG. 1 which summarizes these results by Mo content.
According to the above, it can be clearly understood that all of the properties of toughness, creep rupture time and "segregation ratio" are extremely excellent in the Mo content range of 0.9 to 1.3%.

[0033]

As described above, since the turbine rotor according to the present invention is excellent in tensile strength and toughness, it is possible to use long blades on the low pressure stage side and has high creep rupture strength. Therefore, it can be used for a long period of time even in a high temperature steam environment.

[Brief description of drawings]

FIG. 1 is a graph showing the results of arranging fracture surface transition temperature, creep rupture time, and “segregation ratio” by Mo content.

Claims (1)

[Claims] 1. The composition of the turbine rotor is, by weight ratio,
C: 0.10 to 0.35%, Si: 0.3% or less, M
n: 1.0% or less, Ni: 1.0 to 2.0%, Cr:
1.5-3.0%, Mo: 0.9-1.3%, V: 0.
10 to 0.35%, Nb: 0.01 to 0.15%, W:
A turbine rotor comprising 0.1 to 1.5% and the balance Fe and incidental impurities.