JPH01184230A - Production of high-low pressure integral type rotor - Google Patents

Abstract

PURPOSE:To obtain a rotor which simultaneously has the mechanical characteristics required in both high and low pressure parts by forming the rotor in such a manner that the low pressure side part and high pressure side part have the same chemical components and changing heat treatment conditions at the time of producing the high-low pressure integral type rotor made of a low alloy steel. CONSTITUTION:The low alloy steel stock contg., by weight %, 0.15-0.30% C, <0.15% Si, <0.5% Mn, <0.015% P, 2,8-4.0% Cr, 0.4-2.0% Mo, 0.07-0.3% V, and <=0.015% in total Sb and Sn, or further 1 or >=2 kinds of 0.5-2.0% Ni and 0.01-0.1% Nb is forged to produce the rotor of the high-low pressure integral type having the high-pressure part for which high creep rupture strength is demanded and the low pressure part for which toughness is particularly demanded. The low pressure side is subjected to austenitization hardening at a relatively low temp. above the Ac3 point for the purpose of improving toughness and the high pressure side is hardened at the temp. above said temp. in order to assure the high-temp. creep rupture strength. The annealing is executed conversely at the temp. lower on the high pressure side than on the low pressure side.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a high and low pressure integrated turbine rotor shaft.

(Prior Art) Recently, there has been a trend for medium- and small-capacity turbines with outputs of up to about 200 MW to be made more compact by integrating the rotors of the high-pressure section and the low-pressure section.

This integrated rotor requires both creep rupture strength in the high-pressure part and toughness in the low-pressure part.
In addition to insufficient toughness, V-steel has a feeling that its fracture strength at high temperatures is somewhat insufficient considering the recent design stress requirements.
On the other hand, 3.5% Ni, which is used as a low-pressure loco
-Cr-M.

-V steel has extremely good toughness, but its creep rupture strength is insufficient, and it is not possible to satisfy both performances at the same time.

(Problems to be Solved by the Invention) The present invention provides a method for manufacturing an integrated low-couple that satisfies creep rupture strength and toughness at the same time.

(Means for Solving the Problems) The present inventors have constructed a system in which the high pressure section, which requires particularly high creep rupture strength, and the low pressure section, which requires particularly toughness, have the same chemical composition in the same rotor. It was concluded that by changing the heat treatment conditions, that is, by changing the quenching and tempering conditions for the high-pressure part and the low-pressure part, it is possible to provide each function.

That is, the turbine rotor according to the present invention having a chemical composition based on the C r -Mo -V system has C0
．． 15-0.30%, Si0.15% or less, Mn0.5
% or less, P0.015 or less, Cr more than 2.8% to 4.0%
, Mo0.4-2.0%, V0.07-0.3%, Sb
, the total amount of Sn is 0.05% or less, and if necessary 0.05% or less.
A material to which one or both of 5 to 2.0% Ni and 0.01 to 0.10% Nb is added, with the remainder consisting of Fe and unavoidable impurities, is heated to the austenitizing temperature of the low-pressure part and the high-pressure part. A high-low pressure integrated type with high creep rupture strength in the high-pressure part and high toughness in the low-pressure part by using a process that includes a quenching and tempering process with either or both of the temperature and tempering temperature different. It manufactures rotors.

In this case, the amounts of basic elements and other alloying elements to be contained in the material of the turbine rotor are determined in consideration of the usage conditions of the integral rotor. In other words, since the low pressure side is the steam outlet side and the steam temperature is low, it is natural that high toughness, especially the transition temperature, is required to prevent brittle fracture in the high stress field that occurs during high speed rotation. is required to be lower than the steam temperature.

On the other hand, since the high pressure side corresponds to the steam inlet side, the steam temperature is high, and therefore it is necessary that the creep rupture strength at the high steam temperature is high. Toughness and high-temperature creep rupture strength often have a contradictory relationship; increasing the creep rupture strength will result in lower toughness, and conversely, if measures are taken to improve the toughness, the creep rupture strength will deteriorate. , it is difficult with conventional technology to satisfy both characteristics at the same time.

Therefore, as countermeasures against these problems, conventional measures have been taken, such as performing quenching multiple times to make the structure finer, or adding Nb to utilize the effect of making the structure finer.

In addition, in the low-pressure high-pressure integrated rotor, 1% Cr, 1% Mo-
A method of adding Nb, Ni, etc. to 0.25V steel and further regulating the cooling rate during quenching to improve the high toughness of the low pressure part of the rotor and the creep rupture strength of the high pressure part (for example, Japanese Patent Publication No. 58-11504 Publications) etc. can be found here and there.

All of these methods are effective to a certain extent, and at least the various turbine rotors up to now have been able to satisfy the long-term durability requirements. It is difficult to satisfy these characteristics.

In addition, in high-low pressure integrated rotors, the low-pressure side part usually has a larger diameter than the high-pressure side part, and especially in the case of large-capacity power generation rotors, the diameter can reach more than 1500 m, for example, the center of the 1500φ The quenching cooling rate of the part is 50
'C/hr, which is extremely small. Regarding the integrated rotor according to the present invention, the toughness improves as the cooling rate increases, but although the cooling method is increased within the allowable range for manufacturing, there is a limit due to the large diameter; It is necessary to use appropriate ingredients to ensure sufficient adhesion.

To achieve this, it is necessary to add appropriate amounts of Cr and MO, which are effective elements for hardenability, and in some cases, add Ni according to the required degree of toughness.
It is necessary to add an appropriate amount of.

On the other hand, ensuring the high-temperature creep rupture strength necessary for the high-pressure side part is achieved by using Cr, M0. Utilizing the effect of improving creep rupture strength due to carbonitrides precipitated during tempering of V, Nb, etc. and during use at high temperatures, M0. ■Alternatively, by making full use of the solid solution strengthening effects of M and Nb as needed, we can create rotors with areas that have excellent toughness and high-temperature properties by using new manufacturing methods that can make the most of these effects, especially in the necessary areas of the rotor. In addition, the quenching and tempering conditions for maximizing the toughness after quenching and tempering with zero components are different from those for maximizing high temperature creep rupture strength with the same components. Although it depends on the diameter, it is better to set the quenching temperature of the part of the high-pressure side rotor higher than that of the part of the low-pressure side rotor to improve the high-temperature creep rupture strength.

On the other hand, since a higher tempering temperature is better for improving toughness, it is preferable to set the tempering temperature higher than the part of the high-pressure side rotor where high-temperature creep rupture strength is required.

In any case, the toughness, strength, high-temperature strength, and high-temperature creep rupture strength that should be ensured will differ depending on the rotor diameter, design temperature, and design stress, but the characteristics of each of the high-pressure side and low-pressure side are different from the components specified in the present invention. , can be ensured only by using different heat treatment conditions.

On the other hand, although the high and low pressure integrated low-pressure joints that are the object of the present invention are exposed to different temperatures on the high-pressure side and the low-pressure side, both have the possibility of causing deterioration in toughness during long-term use.

In particular, in the present invention, Mn is set to 0.5% or less in the quenched and tempered structure containing Cr and Ni, which are likely to cause deterioration of toughness, and further low P,
It has been found that by reducing Sb+Sn, this toughness deterioration can be made extremely small.

The present invention will be explained in detail below.

First, the reasons for limiting the chemical components constituting the rotor that is the object 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 0.15%, it may cause the formation of a ferrite phase after quenching or lack of hardness of the quenched structure, resulting in poor tensile strength after tempering. It is difficult to ensure strength and high temperature creep rupture strength. 0 again
．． If it exceeds 3%, toughness and ductility are significantly reduced. For this reason, C was limited to 0.15 to 0.30%.

St improves the strength, but if added in large amounts, it reduces toughness and causes embrittlement, especially when heated over a long period of time. Therefore, only the upper limit is set at 0.15%.

Mn solidly dissolves in the matrix and has the effect of increasing hardenability and improving strength and toughness. However, if the amount added is too large, it may cause embrittlement due to long-term heating.

In the present invention, measures against long-term heat embrittlement are more important than the above-mentioned strength and toughness, and the upper limit is set at 0.5%.

P is preferably as small as possible because it significantly promotes not only initial toughness but also long-term heating embrittlement, but in the present invention the upper limit is set to 0.015% for economic reasons.

Cr is a basic element of the rotor targeted by the present invention, and its purpose is to improve hardenability and after tempering, it enters into carbide M such as M 7 C3 and M 2 z Cb, stabilizes the carbide, and improves creep rupture strength. It is added to improve and maintain corrosion resistance at high temperatures.

That is, from a relatively low temperature of about 300°C to a high temperature of about 550°C.
It is necessary to add more than 2.8% Cr to the high-pressure low-pressure rotor side part, which is used in high-pressure environments up to 30 degrees, to improve high-temperature creep rupture strength, and to ensure hardenability to the low-pressure side rotor part. be. The reason why the upper limit is set at 4% is to prevent insufficient creep ductility at the operating temperature.

Mo has a solid solution strengthening effect, M 23 Cb has a stabilizing effect,
It has a precipitation strengthening effect as a Laves phase, and is added for the purpose of ensuring high temperature creep rupture strength. Lower limit 0.4%
The reason for setting the upper limit at 2.0% is that if it is less than 2.0%, the creep rupture strength against the environmental temperature on the high pressure side of the target rotor of the present invention, especially the long-term strength, cannot be maintained. If the amount exceeds 100%, there is little expectation of effectiveness with respect to the added amount, and it seems to be uneconomical.

■■4G+, v (CN) or M23 C6t
7) It enters M and produces a precipitation strengthening effect, which is extremely important in ensuring the high temperature creep rupture strength of the target rotor of the present invention. The lower limit was set at 0.07% because if the amount is less than this, these effects cannot be fully expected. On the other hand, if the amount added is too large, not only will these effects become saturated, but the toughness and creep ductility will decrease. . Therefore, the upper limit is 0.
It was set at 3%.

Since Sb and Sn significantly promote grain boundary embrittlement during long-term heating, it is preferable to reduce them as much as possible, but like other unavoidable elements, there are economical problems in reducing them, and especially when embrittlement is The sum of Sn and Sb is set to 0.
0.015% or less.

Furthermore, in addition to these basic elements, Ni and Nb may be added as necessary.
Even if it is added, it is possible to ensure the desired characteristic values on the high-pressure side and low-pressure side of the integrated rotor, which is the object of the present invention.

That is, Ni basically has the effect of improving the toughness of the base iron, increasing the hardenability by lowering the transformation point, and improving the strength after quenching and tempering. The lower limit amount for fully utilizing these effects is 0.5%.

This is why the lower limit of the Ni content is set at 0.5%. Moreover, if the amount added is too large, there is a risk that the precipitated carbides will aggregate and the creep rupture strength will decrease.

The maximum required amount is 2.0% from the viewpoint of the effect on creep rupture strength seen from the usage environment on the high pressure side and the improvement of toughness on the low pressure side, which is the object of the present invention, and the upper limit was determined for this reason.

Nb exists finely as carbonitrides at austenite grain boundaries and within grains during heating, and suppresses grain growth due to the pinning effect. Also, it alone lowers the transformation point of steel and improves hardenability. Carbonitrides that precipitate during tempering or long-term heating have the effect of significantly increasing creep rupture strength.

The lower limit amount for making these effects effective is 0.01%. On the other hand, if the amount added is too large, significant agglomeration and coarsening of Nb carbonitrides may occur, which may reduce creep rupture strength. Furthermore, there is a risk that coarse eutectoid crystals of Nb carbides are formed when the copper ingot is solidified, resulting in a significant decrease in toughness. This is why the upper limit amount is set to 0.1%.

Steel containing these various elements is forged and used as a rotor material, but in the next process it is heat-treated including quenching and tempering in order to give it the characteristics required for the high-pressure side and low-pressure side parts of the rotor. However, the austenitizing temperature during quenching is preferably relatively low on the low pressure side for the purpose of improving toughness and at least 1 Ac point to reduce the grain size, while on the high pressure side it is desirable to have a relatively low austenitizing temperature for the purpose of improving toughness. This is preferable in terms of ensuring high-temperature creep rupture strength.

A higher tempering temperature is better for ensuring toughness, and a lower tempering temperature is preferable for ensuring strength. Therefore, so-called gradient heat treatment in which the heat treatment temperatures are different on the low-pressure side and the high-pressure side is an important technical element of the present invention. The different temperatures specified in the present invention refer to the adoption of heat treatment conditions that intentionally vary the set temperatures as described above, and the difference is an industrially possible control limit of at least 2°C or more. say.

(Example) Steel having the chemical components shown in Table 1 was melted, steel slabs were prepared by the method shown outside the table, and simulated heat treatment was performed at the shaft center position under the manufacturing conditions shown in Table 2.

As shown in the margin of Table 2, the quenching temperature and tempering temperature were set to be different between the high-pressure side and the low-pressure side. After tempering, a tensile test at room temperature and an impact test at various temperatures were conducted.
ATT (fracture transition temperature) was determined.

In addition, for those subjected to heat treatment conditions corresponding to a part of the high-pressure side rotor, a creep test was conducted at 550°C, and the 105 hr creep rupture strength was determined by extrapolation.

In addition, a Charpy impact test was conducted after heating at 550° C. for 1000 hours and compared with that before the heat treatment.

The results of these tests are shown in Table 2.

According to these, the steels A-1 to A-6 according to the present invention all have the high toughness and high creep rupture strength, which are the objectives of the present invention, in the low-pressure part and the high-pressure part, respectively, and can be used to manufacture the specified integrated rotor. I found out that it is possible.

On the other hand, B1 and B2 have chemical components that do not fall within the specifications of the present invention, and both exhibit inferior toughness and creep rupture strength, clearly showing the difference due to the effects of the present invention.

(The following is a blank space, continued on the next page) IS- (Effect of the invention) As is clear from the above examples, according to the present invention, the creep rupture strength is higher than that obtained by the conventional method. It becomes possible to manufacture an integrated high and low pressure rotor having a good high pressure part and a low pressure part with excellent toughness, and the industrial effect is significant.

Agent: Patent Attorney Tatsuo Cha Noki Procedural amendment (voluntary) February 19, 1985

Claims (1)

[Claims] 1% by weight: C0.15-0.3%, Si0.15% or less, Mn0.5% or less, P0.015 or less, Cr more than 2.8%-4.0%, Mo0.4 ~2.0%, V0.07~0.3%, the total of Sb and Sn is 0.015% or less, the balance is composed of Fe and inevitable impurities,
A method for manufacturing a high-low pressure integral rotor, comprising a quenching and tempering step in which either or both of the quenching austenitizing temperature and tempering temperature of the low pressure side portion and the high pressure side portion are made different. 2 Ni0.5-2.0%, Nb0.01-0.10%
Claim 1 consisting of an ingredient added with either one or both of the following:
A method for manufacturing a high and low pressure integrated rotor described in .