JPH0219425A - Manufacture of turbine rotor - Google Patents

Abstract

PURPOSE:To manufacture a turbine rotor having no generation of alignment change by casting and forging an alloy steel having specific compsn. constituted of C, Mn, Si, Ni, Cr, Mo, V, W and Fe and thereafter subjecting it to specific heat treatment. CONSTITUTION:An alloy steel having the compsn. constituted of, by weight, 0.15 to 0.35% C, <=1.0% Mn, <=0.35% Si, 0.1 to 1.0% Ni, 0.5 to 3.0% Cr, 0.3 to 1.5% Mo, 0.1 to 0.4% V, 0.1 to 2.0% W and the balance Fe with inevitable impurities is melted to cast and is thereafter forged. The forgings of the alloy steel are annealed in the range of 1,000 to 1,100 deg.C, are gradually cooled and are converted into austenite. The annealings are furthermore subjected to heating treatment in the range of 950 to 980 deg.C and are hardened. After that, the alloy steel is tempered in the range of 600 to 750 deg.C to recover its toughness and ductility. In this way, the equalization of various characteristics is permitted, by which the turbine rotor having no generation of alignment change can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a turbine rotor that can exhibit excellent creep-rubber strength even when exposed to high-temperature steam.

(Prior art) In ultra-large prime movers, such as steam turbines, the temperature of the working fluid used differs depending on the location of one rotor (rotating shaft), so different compositions that can withstand each temperature are required. Sometimes used in combination. In particular, Cr Mo V steel is used for parts exposed to high-temperature and high-pressure steam, and a steel having an excellent composition in creep strength, creep roughness strength, fracture toughness, etc. is selected.

Even if a composition with excellent properties is selected and used in this way, when the rotor itself is inspected after being used for a long period of time, alignment changes (rotor bending) are found in the rotor itself. This may cause the center of gravity to change, causing vibrations during rotor rotation.

This phenomenon is most noticeable in areas directly exposed to high-temperature and high-pressure steam at the steam inlet, but a detailed analysis of these areas reveals that the creep strength, etc. around the circumference is not necessarily uniform. It comes from this. For this reason,
It is desired that creep strength etc. be made uniform.

(Problem M to be solved by the invention) As described above, in conventional turbine rotors, various properties such as creep strength are not uniform from part to part from the time of manufacture, and therefore alignment changes occur. In view of this, it is an object of the present invention to provide a method for manufacturing a turbine rotor in which various characteristics are already made uniform when the element body is manufactured.

[Structure of the invention]

(Means and actions for solving the problem) 0.5-3.0%, Mo 0.3-1.5%, V
After melting and casting an alloy steel with a composition consisting of o, 1 to 0.4%, Li 0.1 to 2.0%, the balance iron and incidental impurities, the forged alloy steel is 1000 to 1100%. ℃
It is annealed to austenite in the range of 950~
Heating in the range of 980℃, then 600-750℃
It consists of various steps of tempering within the range of .

The reason why the composition ratio of the alloy steel constituting the turbine rotor according to the present invention and the temperature of the heat treatment are limited will be explained below. Note that the composition numbers are weight ratios.

C: 0.15-0.35% Carbon improves hardenability, contributes to increasing tensile strength and yield strength, and is an element necessary to form carbides. If the amount is less than 0.15%, an undesirable ferrite phase will be formed, making it impossible to obtain the necessary tensile strength and yield strength, and if it exceeds 0.35%, the toughness will decrease. Preferably 0
．． It is 20-0.30%.

Si: 0.35% or less Silicon is added as a deoxidizing agent during melting, but if added in large quantities, a portion of it will remain in the steel as oxides, reducing toughness, so it should be kept at 0.35% or less. .

Manganese is added as a deoxidizing/desulfurizing agent during melting, and is an element that also improves hardness. However, if added in large amounts, the toughness decreases, so it is limited to 1.0% or less. Preferably 0.3~
It is 0.8%.

Ni: 0.1-1.0% Nickel is an element that suppresses the formation of δ ferrite and improves strength and toughness in low-temperature steam, but if it is less than 0.1%, the effect is weak, and if it is added in large amounts, Strength in high-temperature steam tends to decrease and embrittlement tends to be promoted. Therefore, it is selected in the range of 0.1 to 1.0%. Preferably it is in the range of 0.2 to 0.7%.

Cr: 0.5-3.0% Chromium is an element that improves hardenability and increases tensile strength, but if it is less than 0.5%, this effect cannot be obtained.

Moreover, if it exceeds 3.0%, the strength at high temperatures will decrease. For this reason, it is selected in the range of 0.5 to 3.0%. Preferably it is in the range of 0.8 to 2.0%.

Mo: 0.3-1.5% Molybdenum is an element necessary to improve hardenability, improve high-temperature strength, and prevent temper brittleness.

Therefore, if it is less than 0.3%, it is difficult to obtain the above characteristics.
Moreover, if it exceeds 1.5%, a ferrite phase will be generated, resulting in a decrease in toughness. 0.3-1.5% for the above reasons
The content is preferably selected within the range of 0.6 to 1.4%.
is within the range of

V: 0.1-0.4% Vanadium is an element necessary to improve high-temperature strength, but its effect is weak when it is less than 0.1%.

Moreover, if it exceeds 0.4%, a ferrite phase will be generated, causing a problem. Therefore, it was selected to be in the range of 0.1 to 0.4%.

Preferably it is in the range of 0.15 to 0.30%.

W: 0.1 to 2.0% Tungsten is an element that further improves creep roughness strength, and if it is less than 0.1%, it has no effect, and if it exceeds 2.0%, the toughness decreases. Therefore 0.1
The range was selected to be 2.0%. Preferably 0.15-0
．． The range is 50%.

Incidental impurities other than iron that are not included in the above composition include phosphorus and sulfur, but since these compositions are in trace amounts that cannot be removed by normal metallurgical means, their explanation will be omitted here. .

Next, the reason for selecting the temperature range for heat treatment will be explained.

Annealing temperature: too~1100° C. Annealing is performed in order to dissolve the coarse carbides in the CrMoV steel matrix and to remove the non-uniformity of the structure formed by forging. With this intention, 1
Heating is performed at a temperature of 000° C. or higher, and the temperature must be maintained for 5 hours or more. However, 1100
When the temperature exceeds ℃, the austenite crystal grains become coarser,
Even after quenching and tempering, sufficient toughness cannot be obtained.

For this reason, the temperature range is selected to be 1000 to 1100°C.

After annealing in the above temperature range, the material is slowly cooled to obtain austenitization of the structure.

Hardening temperature = 950-980°C During hardening, CrM. It is necessary to austenitize the vn4 base material and dissolve carbides etc. into the base material, but since it has already been annealed, it is appropriate to heat it at a slightly lower temperature than during annealing.

As a result of experiments, it was found that at temperatures below 950°C, solid solution of carbides was insufficient, and at temperatures above 980°C, coarsening of crystal grains was observed.

Therefore, a temperature range of 950-980°C was chosen. Note that the holding time after heating is preferably about 5 hours or more as in the case of annealing, and in general, CrMo
Since V-steel has excellent creep properties when it has an upper bainii 1 structure which is relatively easy to corrode, the quenching rate can be adjusted flexibly.

Tempering temperature = 600 to 750°C Tempering is a process performed to restore toughness and ductility to quench-hardened materials, but in the case of CrMo V steel, 600 to 750°C
If it is less than 00°C, sufficient toughness cannot be obtained, and if it exceeds 750°C, it will become soft and the tensile strength at room temperature will decrease. Therefore, it is preferable to carry out the temperature range of 600 to 750°C. Note that the heating holding time is determined based on the balance between strength, toughness, and ductility.

By heat treating alloy steel having the above composition,
Coupled with the austenitization of the element body, toughness and ductility are restored, resulting in uniform creep strength and high strength even when exposed to high temperature and high pressure steam.

(Example) A method for manufacturing a turbine rotor according to the present invention will be described in detail.

FIG. 1 shows an example of a turbine rotor 1 to which the present invention is applied, and this turbine rotor 1 is used in a double-flow steam turbine.

A plurality of turbine blades 2 are arranged around the outer periphery of the turbine rotor 1.
has been planted. In addition, there is a nozzle box 3 in the center.
from which high-temperature, high-pressure steam, e.g. 566°C
, about 250 atg is divided to the left and right to the turbine blade 2.
is given to.

The turbine rotor 1 located near the spout of the nozzle box 3 receives steam heat to a temperature of 540°C.
Thereafter, the temperature was 520° C. on the outer periphery of the turbine blade 2a in the first stage, 500° C. on the outer periphery of the second stage turbine blade 2b, and 1o on the outer periphery of the journal portion 5 at the final end.

The temperature has fallen below ℃.

In producing a turbine rotor exposed to such severe steam conditions, the compositions shown in Table 1 were melted in an electric arc furnace, followed by vacuum agglomeration and vacuum degassing. Thereafter, it was forged into a cylinder with a diameter of 6001I11 and a length of 800mm, and a test piece was produced to imitate an actual turbine rotor material.

Table 1 This table compares conventional comparative example 1゜2 and examples 1, 2, and 3.4 according to the present invention for one composition. 0.20% tungsten is added to the composition of CrMo V steel.

Moreover, the tungsten of Examples 3 and 4 is increased by 0.45% by weight compared to the tungsten of Example 1.2. In addition, Comparative Example 1,
As can be seen from the table, No. 2 does not contain tungsten.

Next, with the composition shown in Table 1, the heat treatment temperature conditions were slightly changed, and the procedure was as follows! , ■ and heat treatment were performed. Figure 2 shows the heat treatment steps I and ■.

1st step temperature 1020℃ x temperature holding time 20Hr
teeth.

Temperature 97 in the second step for annealing the turbine rotor body
0 @
1r are the conditions respectively used for tempering.

Here, F and C indicate the furnace cooling section, and A and C indicate the air cooling section.

A test piece was cut out from the heat-treated turbine rotor body and tested for tensile strength, impact strength, and creep rupture strength.

Table 2 in the margin below shows the results of tensile tests at room temperature and 566°C, and the results of Charpy impact tests at room temperature. As can be seen from this table, although the comparative example and the example have similar results at room temperature, the result at high temperature 1 shows that the example has more tungsten added. Slightly expensive. In terms of toughness, the higher the quenching temperature, the lower the toughness than the lower quenching temperature, but there is almost no difference.

Table 3 Table 3 shows the test temperature: 600℃, load stress: 14kgf/m
”.

These are the results of two types of creep rupture tests of 17 kgf/+m''. From these test results, it is understood that Examples 1, 2, and 3.4 show higher values than Comparative Examples 1 and 2. Therefore, if the compositions of Examples 1, 2, and 3.4 are applied to an actual machine, it can be used with sufficient reliability even if the machine is exposed to high-temperature and high-pressure steam for a long time.

〔Effect of the invention〕

As explained above, the method for manufacturing a turbine rotor according to the present invention has a high creep strength even when exposed to high-temperature, high-pressure steam, and has uniform strength. Even when the rotor is applied to an actual machine, there is no change in alignment 1, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view of a turbine rotor applied to a steam turbine, and FIG. 2 is a schematic temperature distribution diagram showing heat treatment steps (1) and (2) in the method for manufacturing a turbine rotor according to the present invention.

Claims (1)

[Claims] Weight ratio: C0.15-0.35%, Mn1.0% or less, Si0.35% or less, Ni0.1-1.0%, Cr0
．． 5-3.0%, Mo0.3-1.5%, V0.1-0
．． After melting and casting an alloy steel with a composition consisting of 4% W, 0.1 to 2.0% W, and the balance iron and incidental impurities, it is forged, and the forged alloy steel is annealed in the range of 1000 to 1100°C. A method for manufacturing a turbine rotor, which comprises austenitizing, further heating in a range of 950 to 980°C, and then tempering in a range of 600 to 750°C.