JPS60138054A - Rotor for steam turbine - Google Patents

Abstract

PURPOSE:To provide superior creep rupture strength at high temp. to a rotor for a steam turbine by using an Fe alloy obtd. by combinedly adding most properly adjusted amounts of Nb and Ta to a Cr steel having a specified composition. CONSTITUTION:A rotor for a steam turbine is made of an Fe alloy consisting of, by weight, 0.05-0.3% C, <=0.3% Si, 0.1-1.0% Mn, 0.5-2.0% Ni, 9.0-13.0% Cr, 0.5-2.0% Mo, 0.1-0.3% V, 0.01-0.10% Nb, 0.01-0.10% Ta (Nb+Ta=0.03- 0.20%), 0.03-0.1% N and the balance Fe with accompanying impurities. The rotor has a long rupture life, superior elongation, high reduction of area and a high impact value at high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a turbine rotor, and more particularly, to a turbine rotor having excellent creep rupture strength and ductility under high temperature conditions.
The present invention relates to a steam turbine rotor having toughness.

[Technical background of the invention and its problems]

Conventionally, ICrM has been used as a rotor material for steam turbines.
o Low Cr alloy steels such as V copper or 12Cr base steels are mainly used. These rotor materials have a temperature of 566℃
, 246 atg as a material for turbine rotors operated under main steam conditions.

However, in recent years, from the standpoint of improving thermal efficiency, the capacity of steam turbines has been increased and the steam used has become higher in temperature and pressure, and the conditions of use have become increasingly severe. In high-temperature steam turbines where the main steam temperature is 600°C or higher, the conventional I Cr Mo V steel or 12Cr base steel is
Creep rupture strength and thermal fatigue strength are insufficient, and the strength is unsatisfactory.

[Purpose of the invention]

The present invention has been made in view of the above points, and has excellent creep rupture strength under high temperature conditions, ductility,
An object of the present invention is to provide a steam turbine rotor that is also excellent in toughness.

[Summary of the invention]

It is already known that creep rupture strength is improved by adding Nb or Ta to Cr-based steel, such as 12 Cr Mo V steel. However, in large components such as turbine rotors, depending on the amount of Nb and Ta added, they may segregate and promote the formation of ferrite or coarse carbide, resulting in a significant decrease in tensile and Lubuture ductility. There is.

As a result of repeated research focusing on the above-mentioned points, the inventor has found that
By adding teeth and Ta in combination and adjusting the amount of addition optimally, problems such as segregation mentioned above can be reduced, and it has excellent creep rupture strength at high temperatures, as well as low ductility and toughness. It has been discovered that a turbine rotor with further improvements can be obtained.

The present invention was completed based on Tsuchiba's knowledge. That is, the steam turbine rotor of the present invention has a weight ratio of C
0105~0.3chi, 810.3 or less, Mn O, 1
~1.0%, NiO85~2.5%, Cr9.0~1
3.0%, Mo 0.5-2.0%, ■0.1-0.
3 yen, Nb O, 01~0.10%, Ta O, Of~
Contains 0.10%, NO, 0.03 to 0.1%, and N
The total amount of b and Ta is 0.03 to 0.20%,
It is characterized in that the remainder is formed of an Fe-based alloy consisting of Fe and incidental impurities.

[Detailed description of the invention]

The present invention will be explained in more detail below. In the following description, "%" representing the composition is based on weight unless otherwise specified.

The steam turbine rotor of the present invention is made of an Fe-based alloy with a specific composition. The purpose of adding each component in the alloy and the reason for limiting the composition are as follows.

First, C is an essential element for increasing mechanical strength at high temperatures, and 0.05 qb or more is required to obtain creep rupture strength and tensile strength.

However, if it is added in excess of 0.3%, excessive carbides will be produced, causing aggregation and coarsening during high-temperature use, which will not only reduce creep rupture strength but also lead to a decrease in fracture ductility and toughness.

Si is added as a deoxidizing agent, but if added in a large amount, the toughness decreases, so it is set to 0.3 or less.

Mn is added as a desulfurization/deoxidizing agent, and has a content of 0.
Add 1% to 1.0%. If it is less than 0.1%, the effect is not sufficient, while if it is added in excess of 1%, the creep rupture strength is reduced.

N1 is an effective element for suppressing the formation of ferrite phase in the center of the rotor where the quenching cooling rate is low, obtaining a uniform martensitic structure, and imparting toughness at room temperature. 5-2.5% is added. 0.5
If the amount is less than 2.5 qb, the effect of addition is poor, and if it is added in excess of 2.5 qb, the high temperature strength decreases.

Cr is an element necessary to improve various mechanical properties required for rotor materials, such as creep rupture strength and toughness, and has a rating of 9.0 to 13. Add O1.

If it is added in an amount exceeding 13%, a ferrite phase will be formed, which will conversely reduce the creep rupture strength.

Mo is an element necessary for improving creep rupture strength and preventing temper brittleness, and is added in an amount of 0.5 to 2.0. If it is less than 0.5 inches, the effect is not sufficient, and 2.
Addition of more than 0% leads to a decrease in creep rupture strength and toughness due to the formation of a ferrite phase.

(2) is an element necessary for increasing high-temperature notch toughness and improving creep rupture strength, and is added in the range of 0.1 to 0.3. If it is less than 0.1%, the effect is not sufficient; on the other hand,
If added in excess of 0.3%, the above M.

As in the case of , a ferrite phase is produced, reducing creep rupture strength and toughness.

Nb and Ta are finely dispersed and precipitated as carbonitrides in the matrix of 12Cr base steel, which improves creep rupture strength and is effective in improving toughness by refining the crystal grains. Nb O,01~0
．． 10%, Ta 0001-0.10%.

Furthermore, the total addition amount of Nb and 1 is 0.03 to 0.20
%, more preferably 0.03~
It is 0.1%. The total amount of Nb and Ta added is 0.03
If the amount is less than 0.20%, no sufficient effect will be obtained; on the other hand, if the amount is more than 0.20%, coarse eutectic carbonitrides will segregate in the center of the steel ingot. Furthermore, the present invention is characterized in that excellent high-temperature strength properties are achieved by adding Nb and Ta in combination rather than singly. In this case, Nb/T'&
The ratio is preferably 0.5 to 7, more preferably 1
A range of 6 to 6 is desirable in order to further improve the breaking strength.

N is an element necessary for suppressing the formation of 7E2ite and forming carbonitrides to improve creep rupture strength, and is added in an amount of 0.03 to 0.1%.

If it is less than 0.03%, the effect is not sufficient;
If it is added in excess of 1%, pinholes and blowholes will occur, which is undesirable.

It is desirable that impurities incidentally included when adding the above components and Fe as the main component be as small as possible.

In order to obtain the turbine rotor of the present invention, first, various raw material metals are mixed and melted in a vacuum or in the atmosphere, and after deoxidation, a Fe-based alloy molten metal having substantially the above composition is obtained. Next, this is cast, and further casting is performed as necessary to form a material in the shape of a turbine rotor. Next, the turbine quadrant of the present invention is obtained by subjecting this material to necessary post-treatments such as heat treatment and surface polishing. Note that the above-mentioned heat treatment of the turbine rotor material can be carried out according to a conventional method, but it is not necessary to stick to the conventional quenching temperature of 1020 to 1070 °C, and if the creep rupture strength is important, the above-mentioned temperature or higher can be applied.
Furthermore, when improving toughness is important, heat treatment can be performed at a temperature lower than this. Further, when manufacturing the rotor, it is also possible to apply vCG and ESB.

[Examples and comparative examples of the invention]

After melting 50 alloy samples having the composition shown in Table 1 below (numbers in the table mean weight percent), vacuum carbon deoxidation was performed and casting to obtain material samples.

The ingots of each of these samples were forged at 1200℃,
Thereafter, after austenitizing at 1050°C x 8 Hr, quenching was performed at a cooling rate of 100°C/Hr, and 570°C x 10
Two-stage tempering was performed at 640° C. for 30 hours.

Note that the quenching cooling rate was simulated for the center hole of the actual rotor. The samples thus obtained were subjected to a tensile test, a Charpy impact test, and a creep rupture test. The test results are shown in Table 2 below.

In the above table, Example 6 has a maximum diameter of 1.2 m and a weight of 2000
After austenitizing the 0 kill forged product at IQ 50℃ x 24 hours, oil quenching, 570℃ x 36 hours,
Two-stage tempering was performed at 640°C for 56 hours.

In Table 2 [! rLCJ indicates a sample taken from the center forging direction on the ToP side of the forged product, [BCL J indicates Bot
A sample taken from the center forging direction on the tom side is shown, l-
MCLJ indicates a sample taken from the center forging direction in the central part, and "McTJ means a sample taken from the same part as the MCL above and from a direction perpendicular to the forging direction and the radial direction. As is clear from the results in the table, no significant difference was observed in the tensile test results or impact values for the samples collected from any site, and furthermore, in the Loveture test, no significant difference was observed between MCT and MSR. All of them showed better values than the comparative examples.

〔Effect of the invention〕

As is clear from the results of the above Examples and Comparative Examples, the steam turbine rotor of the present invention has superior lubricant life, elongation, and aperture than conventional materials under high-temperature conditions of up to 600°C. , tensile test results and impact values are overall superior to conventional materials.

Therefore, the steam turbine rotor of the present invention is suitable as a no-rotor for a steam turbine operated under higher temperature conditions than conventional ones.

Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] 1. By weight: C0005~0.3%, SlO, 3%
Below, MnO, 1-1.0%, NiO05-2.5
%, Cr 9.0-13.0%, MoO, 5-2
．． 0%, Vo, 1-0.3%, Nb O, 01-0.
10%, TaO, 01~0.10%, N0603~
Contains 0.1%, and the total amount of Nb and Ta is 0.0
3 to 0.20%, with the remainder being Fe and incidental impurities. 2. The steam turbine rotor according to claim 1, wherein the total amount of Nb and Ta is 0.03 to 0.10%. 3. The steam turbine rotor according to claim 1, wherein the weight ratio of Nb/f'a is 0.5 to 7.