JPS59232231A - Manufacture of rotor for turbine - Google Patents

Abstract

PURPOSE:To improve the creep rupture strength of a rotor for a turbine at high temp. as well as the ductility and toughness by specifying the composition of a 12Cr type material for the rotor and limiting melting and heat treating methods. CONSTITUTION:The composition of a material for a rotor for a turbine formed by forging a steel ingot obtd. by electro-slag remelting is composed of, by weight, 0.1-0.25% C, <0.5% Si, 0.1-1% Mn, 0.1-1% Ni and/or Co, 9-13% Cr, 0.5-2% Mo, 0.1-0.3% V, 0.03-0.3% Nb and/or Ta, 0.5-2% W, 0.03-0.1% N, 0.005-0.05% B and the balance Fe with inevitable impurities. The material is heated at 1,020-1,150 deg.C, quenched, and tempered at 530-730 deg.C.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides 12
The present invention relates to a method of manufacturing a turbine rotor made of Cr-based heat-resistant steel.

[Technical Background of the Invention] In recent years, steam and gas temperatures used in steam turbines and gas turbines have been increasing in order to improve thermal efficiency.

By the way, one of the rotors with excellent creep rupture strength is 1.
．． There is a rotor made of 2Cr-Mo-V-Nb(Ta)-N steel, but in order to cope with future high temperatures, a 2C type rotor with even better creep rupture strength at higher temperatures is required. - One way to improve high-temperature creep rupture strength is to increase the quenching temperature, but melting in a high-frequency furnace or electric arc furnace, which is carried out with a conventional 12C rotor, is If the quenching temperature of a turbine rotor body manufactured by From the viewpoint of safety and reliability against brittle fracture, the quenching temperature of conventional 12C turbine rotors is usually 105% in consideration of creep rupture strength, ductility, and toughness.
Performed at 0°C.

[Object of the Invention] The present invention has been made in view of the above points, and the present invention has been made in view of the above-mentioned points. The object of the present invention is to provide a method for manufacturing a turbine rotor.

[Summary of the Invention] The present invention provides a chemical composition of a conventional 12Cr turbine rotor,
A wide range of real numbers and examples of melting methods, heat treatment methods, etc.
As a result of investigation, it was discovered that a 1,2 Cr-based turbine rotor can be obtained that has excellent creep rupture strength at high temperatures, as well as excellent ductility and brittleness.

That is, the 12C turbine rotor according to the present invention has a weight percentage of co, i~0.25%, SiO, 5% or less, Mn 0.1~1.0%, Cr 9.0~13.
0%, Ni, Co 0.1 to 1.0 inch, MO05 to 2.0 inch, ■ 0.1 to 0.3 inch, Nb, T
At least one kind of a 0.03-03%, W 0.5-2
．． 0%, NO, 03-0.1%, B O, 005-0
．． It has an alloy composition consisting of 0.5% balance Fe and incidental impurities, and is subjected to secondary melting by electroslag remelting, and the resulting steel ingot is forged to form a turbine rotor body, and then heated at 1020°C to 1150°C. This is a method for manufacturing a 12Cr-based turbine rotor having excellent high-temperature creep rupture strength, ductility, and toughness, which is characterized by heating to a temperature range of 530 to 730 °C, followed by quenching, and then tempering in a temperature range of 530 to 730 °C.

Here, the reason for the limitations on the composition, melting, and heat treatment of the 12Cr turbine rotor according to the method of the present invention will be explained.

C is an element necessary to ensure tensile strength and creep rupture strength. If it is less than 0.1%, a ferrite phase will form and the required properties cannot be obtained, and if it exceeds 0.25%, toughness will decrease. It is set in this range because it decreases.

Sl is an element added as a deoxidizing agent, but addition of a large amount deteriorates toughness, so the content is limited to 0.5% or less.

■ is an element added as a deoxidizing and desulfurizing agent, and if it is less than 0.1%, sufficient effects cannot be obtained, and if it exceeds 1.0%, the creep rupture strength will decrease, so Ni and CO should be in this range. This element is necessary to suppress the formation of ferrite phase and obtain a uniform martensitic structure, but 0.
If it is less than 1%, it is difficult to exhibit its effect, and in the case of Nt, if it exceeds 1.0, the creep rupture strength will decrease, and in the case of CO, it will be expensive, so this range is set.

Cr is an element necessary to obtain the mechanical properties of the rotor according to the present invention. If the amount is less than 9.0%, it is difficult to secure the required creep rupture strength, and if it exceeds 130%, the ferrite phase This range is set because creep rupture strength decreases.

MO is an element necessary to improve creep rupture strength and prevent temper brittleness. If it is less than 0.51, the effect will not be sufficient, and if it exceeds 2.0%, the creep rupture strength will decrease due to the formation of ferrite phase. This range is set because this may cause a decrease in hardness and toughness.

■ is an element necessary for improving creep rupture strength, but 0.
If it is less than 1%, the effect will not be sufficient, and if it exceeds 03%, a ferrite phase will be generated like MO, reducing the creep rupture strength, so this range is set.

Nb and Ta are 12C constituting the rotor according to the present invention.
"An element that is finely precipitated and dispersed as carbonitrides in the matrix of steel and improves creep rupture strength. Its amount is 0.03
If it is less than 0.3%, no sufficient effect will be obtained, and if it exceeds 0.3%, even if electroslag remelting is performed as described below, coarse carbonaceous substances will be formed in the center of the rotor, reducing ductility and toughness. This is the range for this reason. In addition, if very good creep rupture strength is required, it is desirable that at least one of Nb and Ta has a modulus of 0.13 or more. % is necessary, but since adding a large amount leads to the formation of a ferrite phase and lowers the creep rupture strength, the amount should be 2.0 or less.

N is an element necessary to suppress the formation of ferrite phase and to generate carbonitrides to improve creep rupture strength.
．． If it is less than 0.3%, the effect will not be sufficient, and it will be less than 0.1%.
This range was chosen because pinholes and blowholes will occur if it exceeds this range.

B is an element necessary to improve creep rupture strength, and 0
．． If it is less than 0.005%, sufficient effect cannot be obtained;
If it exceeds 5q6, forging cracks are likely to occur, so this range is set.

Next, electroslag remelting and heat treatment, which are important in the method of the present invention, will be described.

The reason for electroslag remelting is that it is an essential process along with the heat treatment described below in order to obtain a 12Cr turbine rotor with excellent high-temperature creep rupture strength, ductility, and toughness. 12C has low toughness and ductility when melted in a furnace or electric arc furnace, and is safe and reliable against brittle fracture.
In addition, when the quenching temperature is raised to improve the creep rupture strength, conventional high-frequency furnace melting and electric arc furnace melting have poor impact toughness and creep rupture ductility at room temperature. However, when the electroslag is remelted according to the method of the present invention, the impact toughness and creep rupture ductility are reduced to a small extent, and it is possible to obtain a 120r series turbine rotor with excellent safety and reliability against brittle fracture. I can do it.

In addition, in conventional 12Cr-based turbine rotors, molten metal melted in a high-frequency melting furnace or electric arc furnace is poured into a mold and solidified, so it takes time to solidify the molten metal, and coarse carbonitriding containing Nb and Ta occurs in the center of the turbine rotor. Until now, the content of Nb + Ta was usually only added to the range of 0.03 to 0.1 inch because it caused precipitation of substances and decreased toughness. No coarse segregation of carbonitrides in the center of the rotor, excellent high-temperature creep rupture strength, and excellent ductility and toughness.
A Cr-based turbine rotor can be obtained. 1020'
After heating to a temperature range of C to 1150'0, quenching is performed, and then 5
The reason why tempering is performed in the temperature range of 30'Q to 730'0 is that the quenching temperature is 1020' to dissolve carbonates and obtain a homogeneous martensitic structure and the required mechanical properties.
If the quench flow rate is less than 1150'O, it is not sufficient, and if the quenching flow rate exceeds 1150'O, the grain size increases and the toughness is impaired, so this range was selected. In order to improve the leap rupture strength, it is desirable to redecipitate a large amount of Nb-fTa carbonitride as a solid solution, and for this purpose, the quenching temperature should be set to 1080°C.
°C or higher, more preferably the quenching temperature is 1095 °C
It is better to make it more than that. Furthermore, if the tempering temperature is lower than 530°C, sufficient tempering will not be performed and the required toughness will not be obtained.
This range was set because if the temperature exceeds 30°C, the required tensile strength and yield strength cannot be obtained.

In addition, in the method for manufacturing a turbine rotor according to the method of the present invention, both the electroslag remelting and heat treatment described above are indispensable, and if even one of them is lacking, it will not be possible to obtain excellent creep rupture strength at high temperatures and ductility. It is not possible to obtain a 120mm turbine rotor with high and toughness.

[Embodiments of the invention] A turbine rotor model (
After fabricating a specimen with a diameter of 600 mm and a length of 800 mm, various tests were conducted.

The turbine rotor models of Examples 1, 2, and 3.4 according to the present invention were created by mixing the raw materials to have the alloy composition shown in Table 1, melting them in an electric arc furnace, and then using them as consumable electrodes for electroslag remelting. Get the ingot cast into the mold.

Subsequently, electroslag was remelted using this ingot as a consumable electrode, and then casting was performed to obtain a turbine rotor model body. Furthermore, this turbine rotor model body was subjected to the heat treatment listed in Table 1, and then machined to create a turbine rotor model ('Jta).

Furthermore, in Comparative Examples 1 and 2, the molten metal melted in an electric arc furnace was poured into a mold in the same manner as the conventional melting method for 12Cr-based turbine rotors. After obtaining an ingot, this was forged to form a turbine rotor model body. Heat treatment listed in Table 1, Comparative Example 1 is conventional heat treatment, Comparative Example 2
After applying heat treatment to a high quenching temperature, it was machined to create a turbine rotor model.

For testing, test pieces were cut out for each of the turbine rotor models obtained as described above, and a tensile test, an impact test, and a creep rupture test were conducted.

Table 2 shows the results of the tensile test and impact test, and Table 3 shows the results of the creep rupture test.

As is clear from Table 2 X, bottom f, and Tables 2 and 3 below, the 12Cr-based turbine rotor model according to the method of the present invention has superior tensile strength, elongation, and large aperture compared to the comparative example. , and has significantly high impact toughness. Furthermore, compared to Comparative Example 1, which is a conventional 12Cr rotor material, the creep rupture strength is the same or higher, and the creep rupture strength is also superior.

For these reasons, the 12Cr-based turbine rotor material according to the method of the present invention has excellent room temperature and high temperature strength, as well as ductility and
It also has excellent toughness and is industrially useful.

Agent: Patent Attorney Noriyuki Chika (1 other person)

Claims (1)

[Claims] (1) C011 to 0.25% by weight, Si□
, 5% or less, Mn 0.1-1.0%s Ni, Co
(7) At least one 0.1-1.0% Cr9.
0-13.0%, Mo 0.5-2.0%, Vo, 1-
o, 3%, at least one of Nb and Ta, 0.03 to 0.
3%, W 0.5-2.0%, NO, 03-0.1%,
B O,005~0.05t16The balance is Fe and incidental impurities, and the steel ingot obtained from electroslag remelting is forged to form a turbine rotor body, and then heated at 1020~1150°. O+7) A method for manufacturing a turbine rotor, which comprises heating to a temperature range of 1 degree, quenching, and then tempering at a temperature range of 530 to 730 degrees Celsius. (2. A method for manufacturing a turbine rotor, characterized in that in claim 1, at least one of Nb and Ta is 0.13 to 0.3% by weight. (3) % Claims A method for manufacturing a turbine rotor, characterized in that in item 1 or 2, the quenching temperature is set in a range of 1080°C to 1150°C.