JPH059656A - Retaining ring for generator - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a retaining ring for a turbine generator, which is made of a non-magnetic iron-based alloy having both high strength and high toughness characteristics. [Composition] By weight, Mn: 17 to 25%, Cr: 1
7-25%, Ni: 3% or less, N: 0.5-1%, the balance consisting of Fe and inevitable impurities, and a power generation composed of a non-magnetic iron-based alloy with high strength and excellent toughness Retaining ring for machine [Effect] A retaining ring for turbine generator that is non-magnetic and has excellent resistance to stress corrosion cracking, and also prevents deterioration of notch toughness due to work hardening and has both high strength and high toughness. can get.

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 non-magnetic iron-based alloy having high strength and excellent notch 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
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. Since the toughness decreases with the increase, there is a problem that the desired toughness is not obtained even if the desired strength is obtained. Therefore, there is a demand for the development of a retaining ring that has characteristics such as non-magnetism, stress corrosion cracking resistance, and high strength that are peculiar to the retaining ring, and that is excellent in toughness. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a retaining ring for a turbine generator, which is made of a non-magnetic iron-based alloy having both high strength and high toughness characteristics. ..

[0004]

In order to solve the above-mentioned problems, the composition of the present invention has a weight% of Mn: 17 to 25.
%, Cr: 17 to 25%, Ni: 3% or less, N: 0.5
A retaining ring for a generator, containing 1% by weight, the balance being Fe and inevitable impurities, and made of a non-magnetic iron-based alloy having high strength and excellent toughness.

[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. The decrease in toughness depends on the distribution of dislocations introduced by cold working, and factors affecting the distribution of this dislocation are stacking fault energy (γ
_S ) and the plastic deformation conditions that directly affect the introduction of dislocation. Therefore, the inventor of the present application has found that 18% Mn-18% Cr-
In an iron-based alloy having a basic composition of N, the effect of components on the stacking fault energy (γ _S ) was investigated within a range that does not significantly affect the strength after cold working, and as a result, an appropriate amount of Ni By containing the above, it was found that the phenomenon of toughness reduction due to work hardening can be suppressed without impairing the strength, and based on this, the present invention was completed. 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 as shown in FIG. 2, when Ni is added to the iron-based alloy, the impact toughness of the cold-worked material is improved as the Ni content is increased. However, in the as-solution treated material, the impact of Ni addition on the impact toughness is not recognized. That is, by adding Ni, it is possible to prevent a decrease in toughness caused by work hardening as shown in FIG. However, 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 limited to 3%. The chemical compositions of the test materials shown in FIGS. 2 and 3 are as shown in Table 1.

[0010]

[Table 1]

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 2 was melted in a high frequency induction furnace to cast a 1 ton electrode for remelting electroslag. This electrode was remelted by electroslag to make a slab for the test material. Specimen N of Table 2 obtained by the above process
o. 1-No. No. 5 is an end ring material which constitutes the present invention. 6, No. 7 is a comparative material 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 processing performed almost the limit of cold working (about 40%) to increase 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. 6
Has a high strength but a slightly low notch toughness.
o. No. 7 has a low strength but a high notch toughness. On the other hand, No. 6 which is the retaining material according to the present invention. 1 to N
o. It was confirmed that the test material of No. 5 had high strength and high toughness.

[0014]

[Table 2]

[0015]

As described above, in% by weight, Mn:
17-25%, Cr: 17-25%, N: 0.5-1%
Is a non-magnetic iron-based alloy whose main composition is
%, It has become possible to provide a retaining ring for a turbine-generator that has a high strength and a high toughness while preventing a decrease in notch toughness due to work hardening.

[Brief description of drawings]

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

FIG. 2 is a graph showing the effect of Ni content on strength and toughness.

FIG. 3 is a graph showing the effect of Ni content on the reduction in toughness during work hardening.

[Procedure amendment]

[Submission date] August 12, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

[Table 1]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] Explanation of code

[Correction method] Added

[Correction content]

[Explanation of symbols] 1 rotor 2 shoulders 3 retaining ring

Claims (1)

Claims: 1. Mn: 17 to 25%, Cr:
17-25%, Ni: 3% or less, N: 0.5-1%, the balance being Fe and unavoidable impurities, and composed of a non-magnetic iron-based alloy with high strength and excellent toughness Retaining ring for generator characterized by