JPS5813608B2 - Manufacturing method of high/low pressure type steam turbine rotor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides superior toughness and strength in parts exposed to low-temperature steam. The present invention also relates to a method of manufacturing a rotor for a high-low pressure integrated steam turbine in which the portion exposed to high-temperature steam exhibits excellent high-temperature cleave rupture strength.

Generally, in a commercial large-scale steam turbine rotor, the high-pressure section, intermediate-pressure section, and low-pressure section are each made of different materials depending on the required properties, depending on the steam temperature and pressure used.

However, rotors for steam turbines for private power generation of approximately 70 to 80 MW or less are made of the same material from the high pressure section to the low pressure section from the viewpoint of miniaturization and simplification of the mechanism.

In the past, steam turbines for private power generation used steam at a temperature of about 500°C at most, but in recent years, from the perspective of improving thermal efficiency, it has become desirable to use steam at temperatures above 500°C and increase capacity. It's coming.

In this type of rotor for high and low pressure integrated turbines used in private power generation steam turbines, a single rotor has high temperature strength in the high pressure section and intermediate pressure section, and toughness, tensile strength, and yield strength in the low pressure section. Although each of these requirements must be met, the following disadvantages have been observed in rotors made of materials with chemical compositions as shown in Table 1, which have been conventionally used as high/low pressure integrated rotors.

In other words, the attached figure shows an example of a cross-sectional view of a rotor for a high-low pressure integrated steam turbine, and the high-pressure part (part a) of the rotor made of the alloy composition shown in Table 1 has sufficient high-temperature strength. Moreover, it has drawbacks such as insufficient toughness of the low pressure part (part C).

Therefore, the present invention provides a method for manufacturing a rotor for a high-low pressure integrated steam turbine, which can exhibit excellent strength in the high-pressure section and low-pressure section, and excellent toughness in the low-pressure section, and can always perform the required functions. This is what we provide.

Hereinafter, the present invention will be explained in detail.The present invention has a carbon content of 0.20 to 0.35% by weight. Silicon 0.2% or less, manganese 1.0% or less, chromium 0.5-1.5%, nickel 1
．． 5% or less, molybdenum 0.5 to 1.5%, vanadium 0.15 to 0.3%, and the balance iron and incidental impurities. After melting and casting, the low alloy steel is forged and made into a rotor body for a steam turbine. 950° C. to 1.0° C. and the high-pressure portion and intermediate-pressure portion exposed to high-temperature steam when the steam turbine rotor body is assembled into a steam turbine.
00℃, and the low pressure part to 900℃~950℃
After heating to less than ℃ to austenitize, the average temperature change in the axial direction of the center of the element body is 50 to 500℃/h.
cooling and quenching at a cooling rate within the range of R and at a cooling rate that makes the average temperature change at the center of the high-intermediate pressure section and the low-pressure section the same; and tempering the quenched rotor body at 600 to 750 °C. A method for manufacturing a rotor for a high and low pressure integrated steam turbine, comprising the steps of:

The rotor manufactured by the method for manufacturing a high-low pressure integrated steam turbine rotor according to the present invention can be manufactured by a conventional rotor manufacturing method, for example, hardening the entire rotor body by forced air cooling.
Alternatively, compared to a rotor manufactured by quenching the entire rotor body by spray cooling, the entire rotor body exhibits a bainite phase, has excellent strength and toughness in the high-pressure part and low-pressure part, and has excellent strength and toughness in the high-pressure part. It also has excellent high-temperature strength in the high- and intermediate-pressure parts, making it suitable for practical use as a rotor for high- and low-pressure integrated steam turbines.

Here, we will explain the reasons for each limitation in the manufacturing method of the rotor for high and low pressure integrated steam turbines according to the present invention. First, in the composition ratio of low alloy steel, carbon improves hardenability and improves tensile strength and yield strength. However, if the amount is less than 0.2%, a ferrite phase will form and a bentnite structure will not be obtained, making it impossible to obtain the required tensile strength and proof stress. If it exceeds %, the toughness decreases, so it is set within this range.

Silicon and manganese are added as deoxidizing and desulfurizing agents, but if silicon is contained in large amounts, toughness will be impaired.
Also, since the degree of tempering embrittlement increases, it is set to 0.2% or less.

Further, manganese increases hardenability and improves tensile strength, but like silicon, a large amount of manganese impairs toughness, so the content is limited to 1% or less.

Chromium is an element necessary to improve strength and toughness at high temperatures, but if it is less than 0.5%, the effect will be small, and if it is contained in a large amount, high temperature strength and toughness will deteriorate, so it should be limited to 1.5% or less. .

Further, nickel improves hardenability and improves strength and toughness at low temperatures, but since a large amount of nickel decreases high temperature strength, the content is limited to 1.5% or less.

Molybdenum is an element necessary to improve hardenability, improve high temperature strength, and prevent temper brittleness.
If it is less than 1.5%, the effect will not be sufficient, and if it is contained in a large amount, the toughness will decrease, so the content should be up to 1.5%.

Vanadium is an element necessary to improve high-temperature strength, but if it is less than 0.15%, the effect is not sufficient, and if it is contained in a large amount, the toughness deteriorates, so the content is limited to 0.3%.

Concerning temperature changes during austenitization during quenching, if the austenitization temperature in the low-pressure part is less than 900°C, a ferrite phase will be generated even after quenching, and no bainite structure will be obtained, resulting in material strength not being obtained. do not have.

Furthermore, since the toughness decreases at a temperature of 950° C. or higher, the temperature is set in this range.

On the other hand, the austenitizing temperature in the high pressure section and the intermediate pressure section is 95
If the temperature is below 0°C, the high-temperature strength of the rotor surface layer, which is the part where the turbine blades are embedded in the high-pressure and intermediate-pressure parts that are exposed to high-temperature steam during use of the steam turbine, cannot be obtained;
If the temperature exceeds 000°C, notch weakening is observed at high temperatures, so this range is set.

On the other hand, regarding the cooling rate during quenching, if the average cooling rate in the axial direction at the center of the element body is less than 50°C/hr, a ferrite phase will occur, resulting in poor strength;
Although a bainite phase can be obtained even when the temperature exceeds r, in practice it is difficult to obtain a cooling rate in the center of large materials such as rotor materials that exceeds 600°C/hr, so the above range is considered. shall be.

Further, the above-mentioned average cooling rate at the center of the high-intermediate pressure section and the low-pressure section is set to be the same.

Regarding the tempering temperature, if the temperature is less than 600°C, sufficient tempering effect cannot be obtained, and therefore good strength and toughness cannot be obtained, and if the temperature exceeds 750°C, the required strength cannot be obtained. It is.

Next, examples of the present invention will be described.

Four test pieces for rotor bodies were prepared by melting and forging low alloy steel having the chemical composition shown in Table 2.

Next, two of these test pieces were heated to 920°C and the remaining two to 970°C, and then baked at a cooling rate that simulated the cooling rate of the surface and center of the actual rotor body. After heating, it was tempered at 670°C.

Thereafter, a tensile test, a 50% FATT measurement using a 2 mm Notch Charpy impact test, and a high temperature creep rupture test were conducted.

In addition, in an actual rotor body, when the entire body is cooled by water spray, the cooling rate of the surface layer of the rotor body is about 60°C/hour for the high, medium, and low pressure parts, and the cooling rate of the center part is about 100°C/hour. It takes about an hour or more.

Table 3 shows the mechanical properties of the example alloys after each heat treatment.

Furthermore, Table 4 shows the mechanical characteristics of the rotor used as a conventional high/low pressure integrated rotor.

As is clear from Tables 3 and 4, compared to conventional high and low pressure integrated rotors, the manufacturing method of the high and low pressure integrated turbine rotor according to the present invention It is possible to manufacture a rotor that satisfies the required high-temperature strength, the required toughness for the low-pressure section, and the required mechanical properties, and is sufficiently usable for practical use.

[Brief explanation of the drawing]

The drawing shows an example of a cross section of a rotor for a high-low pressure integrated steam turbine. In the drawing, a and b are exposed to high-temperature steam,
C is a high-pressure section and an intermediate-pressure section that require high-temperature strength, and C is a low-pressure section that is exposed to low-temperature steam and requires toughness.

Claims (1)

[Claims] 1. Carbon 0.2-0.35%, silicon 0.2% or less, manganese 1.0% or less, chromium 0.5-1.5%,
Nickel 1.5% or less, molybdenum 0.5% to 1.5%
, a step of melting and casting low alloy steel consisting of 0.15 to 0.3% vanadium, balance iron and incidental impurities, and then forging to form a rotor body for a steam turbine, and a step of forming a rotor body for a steam turbine. 950 is the high-pressure part and intermediate-pressure part that are exposed to high-temperature steam when installed in a steam turbine.
℃ to 1,000℃, and the low pressure part to 90℃
After heating to less than 0°C to 950°C to austenitize, the average temperature change in the axial direction of the center of the element body is 50 to 6
a step of cooling and hardening in the range of 00°C/hour and at a cooling rate such that the above-mentioned average temperature change in the center of the high-intermediate pressure section and the low-pressure section is the same; 1. A method for manufacturing a rotor for a high-low pressure integrated steam turbine, comprising the step of tempering at ℃.