JPH05105987A - Retaining ring for power generator - Google Patents

Abstract

PURPOSE:To provide a retaining ring for turbine generator combining the characteristics of high strength and high toughness and consisting of nonmagnetic iron-base alloy. CONSTITUTION:A retaining ring for turbine generator which is constituted of a nonmagnetic iron-base alloy having high strength and superior toughness and also having a composition consisting of, by weight, 17-25% Mn, 17-25% Cr, 0.5-1% N, 0.001-0.08% REM, and the balance Fe with inevitable impurities and containing, if necessary, <=3% Ni is produced. By this method, the retaining ring for turbine generator which is nonmagnetic and excellent in stress corrosion cracking resistance and in which toughness is improved by the improvement in structure and further deterioration in toughness due to work hardening is prevented and, as a result, high strength is combined with high toughness can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retaining ring for a turbine generator, which is made of a nonmagnetic iron-based alloy having high strength and excellent toughness.

[0002]

2. Description of the Related Art As shown in FIG. 1, a retaining ring 3 used by shrink-fitting a shoulder portion 2 of a rotor 1 of a turbine generator is non-magnetic for electromagnetic reasons, and has a high rotation speed. Since it is used in the state, it must have high strength and toughness. Conventionally, 18% Mn-5% Cr steel has been used as the material for this type of retaining ring, but this material easily causes stress corrosion cracking in the use environment, so from the viewpoint of stress corrosion cracking resistance. ,
In recent years, this material has been replaced with 18% Mn-18% Cr-N
Austenitic steel is used.

[0003]

However, in all of the conventional retaining ring materials, the desired strength is imparted by the work hardening by the pipe expanding work in the cold working. The toughness decreases with increasing temperature. As a result, although the yield strength or tensile strength satisfies the required value, there is a problem that desired toughness cannot be obtained.
In general, austenitic steel exhibits stable low temperature toughness even at low temperatures, so it may be used as a low temperature steel, but in high strength stainless steel with sufficient strength, cleavage fracture occurs due to transition behavior of impact absorption energy, It causes a decrease in toughness due to brittle fracture. In low alloy steels, it is recognized that controlling non-metallic inclusions to increase crack propagation resistance is effective in preventing brittle fracture, but austenitic steels have no such reports. ,
Furthermore, in austenitic steel strengthened by solid solution strengthening and work hardening, it is unknown how effective the control of the shape and distribution of nonmetallic inclusions is in improving toughness.
From the above viewpoint, the inventor of the present application has found that REM (1 of rare earth elements
The shape and distribution of the non-metallic inclusions are controlled by adding one or two or more of them, and the effect on the impact energy transition behavior was studied, and the present invention was accomplished. That is, the present invention has been made against the background of the above circumstances, by the following chemical composition, while ensuring properties such as non-magnetic, stress corrosion cracking resistance, high strength, which is a characteristic peculiar to the retaining ring, It is an object of the present invention to provide a retaining ring for a turbine generator having high toughness by adjusting non-metallic inclusions by adding an appropriate amount of REM.

[0004]

In order to solve the above-mentioned problems, the retaining ring for a generator according to the first invention of the present invention is, by weight%, Mn: 17 to 25%, Cr: 17%.
-25%, N: 0.5-1%, REM: 0.001-
It is characterized by containing 0.08%, the balance being Fe and inevitable impurities, and being composed of a non-magnetic iron-based alloy having high strength and excellent toughness. Further, the retaining ring for a generator of the second invention has a weight percentage of Mn: 17.
-25%, Cr: 17-25%, Ni: 3% or less, N:
0.5 to 1%, REM: 0.001 to 0.08%, the balance consisting of Fe and unavoidable impurities, and composed of a non-magnetic iron-based alloy with high strength and excellent toughness And

[0005]

The iron-based alloy forming the retaining ring for the generator of the present invention is strengthened by cold working, but at the same time, the toughness is inevitably lowered. This toughness is improved by the addition of REM. That is, REM has deoxidizing and desulfurizing effects, and oxides and sulfides are generated by adding REM to a molten metal, and removal of this improves cleanliness and internal non-metallic inclusions. The shape and distribution of can be controlled. As a result, the impact absorption energy is improved, the toughness is improved, and the decrease in toughness also depends on the distribution of dislocations introduced by cold working.
There are stacking fault energy (γ _S ) and plastic deformation conditions that directly affect the introduction of dislocations. The inventor of the present application investigated the influence of the components on the stacking fault energy (γ _S ) within a range that does not significantly affect the strength after cold working, and as a result, by containing an appropriate amount of Ni, The decrease in toughness due to work hardening could be suppressed without impairing the strength. Next, the reasons for limiting the component contents of the iron-based alloy constituting the retaining ring of the present invention will be described below. In addition, in the following description, the content of each component is shown by weight%.

Mn: 17-25% Mn is one of the basic constituent components of the iron-based alloy of the present invention. To stabilize the austenite phase and improve strength, toughness, and cold workability, Mn is 17 % Or more, it is necessary to contain it, but if it is contained in excess of 25%, the work hardening coefficient decreases, so the above range was made.

Cr: 17 to 25% Cr, like Mn, is also one of the basic constituent components of the iron-based alloy. Mn content 17-25%, N content 0.5-1%
In order to form a stable austenite phase and to impart stress corrosion cracking resistance, the C content of 17% or more is preferable.
r must be included. However, C exceeds 25%
When r is contained, ferrite is precipitated and the nonmagnetic property cannot be maintained, so the content is limited to the above range.

N: 0.5 to 1% N is also one of the basic constituent components of the iron-based alloy. N is an austenite stabilizing element, and if it is contained in an amount of 0.5% or more to form a solid solution in the austenite structure, the strength and toughness are improved, but if it exceeds 1%, the strength is improved, but the toughness is improved. Since it decreases, it is limited to the above range.

Ni: 3% or less Ni is an austenite stabilizing element, and when Ni is added to the iron-based alloy of the present invention, the impact toughness of the cold-worked material is improved as the Ni content increases, but As it is, no effect of Ni addition on impact toughness was observed.
That is, by adding Ni, it is possible to prevent a decrease in toughness caused by work hardening. But,
If the content exceeds 3%, the work hardening coefficient decreases and the strength of the cold-worked material decreases, so the upper limit of the Ni content is set to 3
Limited to%.

REM: 0.001 to 0.08% REM controls the shape and distribution of nonmetallic inclusions to improve toughness. However, if the content is less than 0.001%, the above-mentioned effects cannot be observed. Further, if the content exceeds 0.08%, an oxide is excessively generated, rather the cleanliness is lowered, and as a result, the impact toughness is lowered.
Therefore, the content of REM is limited to the above range.

Inevitable Impurities : Inevitable impurities in the iron-based alloy include C and S.
Examples of the impurities include i, P, S, Cu, and Al. These impurities are mixed in from the raw material for melting or in the refining process, and it is desirable to reduce them as much as possible. Note that C
It is desirable to reduce as much as possible from the viewpoints of improving toughness and corrosion resistance, but at the current refining technology level, maximum 0.08
Up to about%, it is contained as an unavoidable impurity. Also, Si
Is added as a deoxidizer, and therefore remains as an unavoidable impurity at 0.6% or less.

[0012]

Example An alloy having the composition shown in Table 1 was melted in a high frequency induction furnace to cast a 1 ton electroslag remelting electrode. This electrode was remelted by electroslag to make a slab for the test material. Specimen N of Table 1 obtained by the above process
o. 1-No. No. 8 is an end ring material which constitutes the present invention. 9-11 are comparative materials outside the scope of the present invention. These ingots were heated to 1200 ° C., forged into a retaining ring, rough-cut, and then heated to 1100 ° C. for solution treatment. Subsequent hole expansion was performed to achieve almost the limit of cold working (38%), increasing the strength of the material.

Table 2 shows the mechanical properties of the central portion of the wall thickness after cold working. As is clear from the table, the comparative material No. 9,
No. 10 has high strength but low toughness, and Comparative material 11 has high toughness but low strength. On the other hand, No. 6 which is the retaining material according to the present invention. 1-No. It was confirmed that the test material of No. 8 had high strength and high toughness.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

As described above, in% by weight, Mn:
17-25%, Cr: 17-25%, N: 0.5-1%
A non-magnetic iron-based alloy whose main composition is
By adding 0.01 to 0.08% and, if desired, Ni up to 3%, the structure is improved and the toughness is improved, and the toughness is prevented from lowering due to work hardening.
It has become possible to provide a retaining ring for a turbine generator that has both high strength and high toughness.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a usage state of a retaining ring.

[Explanation of symbols]

 1 Rotor 2 Shoulder 3 Retaining Ring

[Procedure amendment]

[Submission date] December 11, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

[0014]

[Table 1]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

[0015]

[Table 2]

Claims (2)

[Claims] 1. Mn: 17 to 25% by weight, Cr:
17-25%, N: 0.5-1%, REM: 0.001
Retaining ring for generator, characterized by containing 0.08% to 0.08% and the balance Fe and unavoidable impurities, and composed of a non-magnetic iron-based alloy with high strength and excellent toughness. 2. By weight%, Mn: 17-25%, Cr:
17-25%, Ni: 3% or less, N: 0.5-1%, R
EM: Retaining for a generator characterized by containing 0.001 to 0.08%, the balance being Fe and inevitable impurities, and composed of a non-magnetic iron-based alloy having high strength and excellent toughness ring