JPH08291331A - Nonmagnetic holding ring for generator and its production - Google Patents

Abstract

PURPOSE: To produce a nonmagnetic holding ring for a generator in which grain boundary precipitation of carbide is prevented or controlled and, as a result, deterioration in ductility and toughness due to cold tube expanding for improving material strength is reduced and which is further excellent in ductility and toughness as well as in strength and particularly excellent in toughness in a radial direction (wall thickness direction). CONSTITUTION: A nonmagnetic iron-base alloy, containing 0.04-0.08wt.% C, is heated to 1100-1250 deg.C and formed into annular shape by hot forging at >=800 deg.C forging finishing temp., followed by rapid cooling by water cooling or oil cooling. After forged surface is removed by machining, the resultant ring is heated to 1000-1100 deg.C and water-cooled to undergo solution heat treatment. By this method, the nonmagnetic holding ring for generator can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-magnetic retaining ring for a generator and a method for manufacturing the same, and more particularly to a cylindrical shape made of non-magnetic steel used for supporting a field coil of a turbine generator. TECHNICAL FIELD The present invention relates to a structure (holding ring) and a method for manufacturing the same, and more particularly to a non-magnetic holding ring for a generator having improved radial (thickness direction) toughness and a method for manufacturing the same.

[0002]

2. Description of the Related Art A turbine generator used in a thermal power plant or the like has a cylindrical holding at both ends of the generator shaft in order to prevent the field coil wound around the generator shaft from being scattered by centrifugal force during its operation. A ring is provided. This retaining ring needs to be non-magnetic in order to improve power generation efficiency, and it is fixed to the generator shaft by shrink fit, rotates at a high speed of about 3000 to 3600 rpm during its use, and has a large diameter. Because of this, an extremely large centrifugal force acts, so the mechanical properties (strength, toughness, etc.), especially in the shrink-fitted part, are important in the radial direction, and in particular, the notch toughness in the radial direction is large. Required.

As such a retaining ring, an austite steel (structure: an austite structure at room temperature) has been conventionally used, and since the ausstate steel cannot increase the material strength by heat treatment such as quenching, it is cold. The material strength is increased by work hardening by hot working to secure the necessary strength as a retaining ring. This cold working is usually performed by cold pipe expansion because the retaining ring has a cylindrical shape.

Conventionally, various studies have been made on a non-magnetic retaining ring and a method of manufacturing the non-magnetic retaining ring.
56647, JP 5-9696, JP 62-297
No. 439 publication, technical paper `` G. Stein: Tech.Mitt.Krupp,
Werksberichte, Band 38 (1980) H.2 '', JP 60-14
Some are described in the 1823 publication.

[0005]

However, in the above-mentioned conventional non-magnetic retaining ring, if cold pipe expansion is performed to increase the material strength, the ductility and toughness decrease and the material becomes insufficient. There is a problem that the strength cannot be increased sufficiently. That is, by performing the cold pipe expansion, the metal flow in the steel structure is elongated in the circumferential direction, and the ductility in the radial direction of the retaining ring, which is the so-called grain direction, and the toughness such as the notch toughness decrease. This tendency becomes higher as the required material strength becomes higher, and as the pipe expansion amount increases, the ductility and toughness extremely decrease depending on the condition, and only extremely poor performance can be obtained. Such a problem exists in the non-magnetic retaining ring that has been conventionally used, and the above-mentioned ...
, The ones listed in, cannot solve the problem,
There is a similar problem.

The present invention has been made in view of such circumstances, and its purpose is to solve the problems of the above-mentioned conventional ones and to improve ductility and toughness by cold pipe expansion for increasing material strength. It is an object of the present invention to provide a non-magnetic retaining ring for a generator, which is excellent in ductility and toughness together with strength, and particularly excellent in toughness in the radial direction (thickness direction), and a manufacturing method thereof.

[0007]

In order to achieve the above object, as a result of intensive research, the non-magnetic retaining ring for a generator and the method for manufacturing the same according to the present invention have the following configurations. That is, the non-magnetic retaining ring according to claim 1 has C: 0.
Nonmagnetic iron-based alloy containing 04-0.08wt% 1100-1250 ℃
After heating, forging end temperature: after hot forging at 800 ℃ or more to form a ring shape, quenching with water cooling or oil cooling, then removing the forged skin by cutting, then 1000 ~ 1100 ℃ A non-magnetic retaining ring for a generator, characterized by being subjected to a solution treatment of heating and then water cooling.

The non-magnetic retaining ring according to claim 2 is further preheated to 150 to 250 ° C. after the solution treatment, and then subjected to pipe expanding processing at a pipe expansion end temperature of 100 ° C. or more.
The non-magnetic retaining ring for a generator as described. The nonmagnetic retaining ring according to claim 3, wherein the nonmagnetic iron-based alloy is
C: 0.04 to 0.08 wt%, Mn: 18 to 22 wt%, Cr: 18 to 20 wt%,
The non-magnetic retaining ring for a generator according to claim 1 or 2, wherein the non-magnetic iron-based alloy contains N: 0.5 wt% or more.

The manufacturing method according to claim 4 is C: 0.04 to 0.
A non-magnetic iron-based alloy containing 08wt% is heated to 1100 to 1250 ° C, hot forged at a forging end temperature of 800 ° C or higher to form a ring, and then rapidly cooled by water cooling or oil cooling. A method for producing a non-magnetic retaining ring for a power generator, which comprises removing a forged skin by cutting and then subjecting the solution to heat treatment at 1000 to 1100 ° C. and then water cooling.

According to the fifth aspect of the present invention, after the solution treatment, preheating is further performed at 150 to 250 ° C., and then the tube expansion process is performed at a tube expansion end temperature of 100 ° C. or more. It is a manufacturing method of a magnetic holding ring. The manufacturing method according to claim 6, wherein the non-magnetic iron-based alloy is C: 0.04 to 0.
08wt%, Mn: 18-22wt%, Cr: 18-20wt%, N: 0.5wt%
A non-magnetic iron-based alloy containing the above is used.
It is a method for manufacturing a non-magnetic retaining ring for a generator as described.

[0011]

[Function] When the reduction of ductility and toughness due to cold pipe expansion for increasing the material strength is examined from a more metallographic viewpoint, grain boundary protrusion of carbide exerts a particularly large effect.
The ductility and toughness are reduced in combination with the circumferential extension of the metal flow. That is, if there are grain boundary protrusions of carbide, or if the number thereof is large, the tensile ductility and notch toughness decrease, and particularly when subjecting to pipe expansion processing, the crystal grains are elongated in the circumferential direction and the directionality is changed. If there are carbides (grain boundary protrusions) at the crystal grain boundaries, or if there are many carbides, the ductility and notch toughness in the radial direction (transverse direction), which is the direction perpendicular to the circumferential direction, decreases. To do. In this way, the grain boundary protruding state of the carbide has a great influence.

Therefore, if the grain boundary protrusion of such carbides is prevented, or suppressed or reduced, even if the metal flow is extended in the circumferential direction by cold pipe expansion, the ductility and toughness are less deteriorated. It is possible to suppress or reduce the deterioration of ductility and toughness due to cold pipe expansion, and it is therefore excellent in ductility and toughness together with strength, and particularly excellent in radial (thickness direction) toughness.

Therefore, in order to achieve the object of the present invention, intensive studies have been conducted on the composition and manufacturing conditions of the non-magnetic retaining ring, and as a result, the composition and manufacturing conditions capable of preventing, suppressing or reducing grain boundary protrusion of carbides have been determined. Headline, and thus
It has been found that the deterioration of ductility and toughness due to cold pipe expansion can be suppressed or reduced, excellent ductility and toughness can be obtained together with high strength, and particularly the toughness in the radial direction (thickness direction) can be significantly improved. The present invention has been completed based on such knowledge, and has the above-described configuration.

That is, in the method for producing a non-magnetic retaining ring for a generator according to the present invention, a non-magnetic iron-based alloy containing C: 0.04 to 0.08 wt% is heated to 1100 to 1250 ° C., and a forging end temperature: 80.
After hot forging at 0 ℃ or more to form a ring, quenching with water cooling or oil cooling, then removing the forged skin by cutting, heating to 1000 ~ 1100 ℃, then water cooling solution treatment (The manufacturing method according to claim 4).

In this way, the following is obtained. When the C content is 0.08 wt% or less, the driving force for carbide grain boundary cracking becomes low.

In the hot forging, the forging end temperature is set to 800 ° C. or higher, and after the hot forging, it is rapidly cooled by water cooling or oil cooling so that the grain boundary cracking of carbides is rapidly cooled in the temperature range of 800 to 500 ° C. Therefore, the grain boundary protrusion of carbide is prevented or suppressed. That is, since grain boundary precipitation of carbide occurs between 800 and 500 ° C, grain boundary precipitation of carbide can be prevented or suppressed by quenching this temperature range, and grain boundary precipitation of carbide can be minimized. .

Next, the forged skin is removed by cutting to improve the heat transfer from the surface to the inside. After the cutting process, a solution treatment of heating to 1000 to 1100 ° C. and then water cooling is performed, so that a small amount of carbide precipitated in the previous step is solidified (melts into the matrix) and disappears or disappears. At this time, the improvement of the heat transfer property by the cutting work serves to enhance the rapid cooling effect during water cooling and prevent precipitation of the carbide after solid solution.

Therefore, it is possible to prevent or suppress or reduce the grain boundary protrusion of the carbide, and therefore, it is possible to suppress or reduce the deterioration of the ductility and the toughness due to the cold pipe expansion, and, by extension, the ductility and the toughness are excellent together with the strength. A non-magnetic retaining ring for a generator having excellent toughness in the direction (thickness direction) can be obtained.

Here, the amount of C in the non-magnetic iron-based alloy is 0.04 to
0.08 wt% means that if it is less than 0.04 wt%, austenite becomes unstable and non-magnetic becomes unstable.
This is because if it exceeds wt%, the driving force for the grain boundary protrusion of carbides becomes high and the suppression of grain boundary protrusions of carbide becomes insufficient, and eventually the toughness becomes insufficient.

In hot forging, the heating temperature before hot forging is
The temperature of 1100 to 1250 ℃ means that if the temperature is less than 1100 ℃, the deformation resistance is high and sufficient plastic flow cannot be obtained, so it is difficult to make the crystal grains uniform, and if it exceeds 1250 ℃, the so-called burning (combustion) phenomenon occurs. Induced, processing cracks are more likely to occur,
This is because it is not suitable for forging. The forging end temperature is set to 800 ° C or higher because when it is lower than 800 ° C, grain boundary precipitation of carbides cannot be rapidly quenched in the temperature range of 800 to 500 ° C, which suppresses grain boundary precipitation of carbides. This is because the toughness cannot be obtained and the toughness is insufficient.

The solution treatment temperature is set to 1000 to 1100 ° C. The reason why the solution treatment temperature is 1000 to 1100 ° C. is that if the temperature is less than 1000 ° C., the solid solution of the carbide becomes insufficient and the toughness becomes insufficient, and if it exceeds 1100 ° C., the crystal grains grow and become coarse. This is because sufficient strength cannot be obtained, or the ultrasonic wave transmission becomes poor, making it difficult to check the internal quality.

The non-magnetic retaining ring for a generator according to the present invention comprises a non-magnetic iron-based alloy containing C: 0.04 to 0.08 wt%.
After heating to 00 ~ 1250 ℃, forging finish temperature: 800 ℃ or more hot forging to form a ring shape, then quenching with water or oil cooling, then removing the forged skin by cutting, 1000
The non-magnetic retaining ring according to claim 1, which has been subjected to solution treatment by heating to ˜1100 ° C. and then cooling with water. Since this is obtained by the above-mentioned manufacturing method (the manufacturing method according to claim 4), grain boundary protrusion of carbides is prevented or suppressed. Therefore, ductility and toughness due to cold pipe expansion are reduced. The deterioration can be suppressed or reduced, and after cold-expanding, the ductility and toughness as well as the strength are excellent, and particularly the toughness in the radial direction is excellent.

After the solution heat treatment, in the tube expansion processing, it is desirable to preheat the tube to 150 to 250 ° C. and then to perform the tube expansion processing so that the tube expansion end temperature is 100 ° C. or more. A non-magnetic retaining ring, the manufacturing method according to claim 5. This is because the deformability of the material (the slipperiness of the crystal) is improved, and as a result, it is possible to prevent the generation of microvoids due to the carbon compound or inclusions.

As the non-magnetic iron-based alloy, C: 0.04 to
A material containing Mn, Cr, N in addition to 0.08 wt% can be used. In this case, the Mn amount is 18 to 22 wt% and the Cr amount is 18 to 22 wt%.
It is preferable that the content of 20 wt% and the amount of N be 0.5 wt% or more (the non-magnetic retaining ring according to claim 3 and the manufacturing method according to claim 6). The reason is described below.

Mn is an austenite former, and 18 wt% or more is required to improve the solubility of N, which is another austenite former, but if it exceeds 22 wt%, it is too much and the work hardening rate becomes small. , Hot workability deteriorates. Therefore, Mn: 18 to 22 wt% is set.

Cr has the same effect as manganese, and the lower limit is set to 18 wt% for the same reason. However, if it exceeds 20 wt%, the amount is too large to form δ ferrite and the toughness decreases.
In particular, when the amount of Cr exceeds the amount of Mn, austenite becomes unstable. From this point of view, Cr: 18 to 20 wt% is set.

N is an austenite former and C
Similarly, the austenite is stabilized to stabilize the non-magnetic property, but if it is less than 0.5 wt%, its effect cannot be exhibited, and therefore, it is set to 0.5 wt% or more. At this time, N does not form grain boundary precipitates and deteriorates the properties unlike C, so the higher the content, the better. In addition, the solubility of N is about 0.8 to 0.9 wt% within the above range of Mn and Cr contents, and it is impossible to add more than this by the ordinary steelmaking method. Therefore, it is not necessary to set the upper limit.

The retaining ring for a generator according to the present invention has, for example, as shown in the partial sectional view of FIG. 1, a fitting portion 3 formed on an end 2 of a rotating shaft 1 of the generator and a lug at a corner. Part 4
Are fitted and fitted by shrinkage fitting, and the coil end turn 5 and the support ring 6 are fixedly used on the inner circumference thereof. Incidentally, R in FIG. 1 indicates a retaining ring.

[0029]

EXAMPLES Using alloys having the compositions (chemical components) shown in Table 1,
A non-magnetic retaining ring was manufactured under the manufacturing conditions shown in the table. Then, a test piece was sampled from the ring and a mechanical property evaluation test (tensile test, impact test, etc.) was performed. The results are shown in Table 2.

As can be seen from this table, No. 1 and No. 2 according to the examples of the present invention are the same as N according to the comparative example (conventional method).
Excellent mechanical properties, especially notch toughness value in the radial direction (absorbed energy value by Charpy impact test: vE _RT ) compared to those of o.3 to 6 It is confirmed that the non-magnetic retaining ring according to the present invention exhibits a particularly excellent radial toughness value, which is about 2 times of the conventional method Nos. 5 and 6 and about 3 to 4 times.

The difference between the embodiment of the present invention and the comparative example is as follows.
Corroborated by metallurgical investigations. That is, observation of microstructure and C, Cr, and X-ray microanalyzer
When elements such as N were analyzed, in the case of the comparative example, cracks were observed at the grain boundaries, and C and C in the cracks were observed.
The Cr concentration was higher than those in the matrix, and it was verified that the protrusions were chromium carbides (Fig. 2,
3). On the other hand, in the example of the present invention, such a protrusion was not observed (Figs. 4 and 5).

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

EFFECTS OF THE INVENTION The present invention has the above-described constitution and functions, and prevents grain boundary protrusion of carbides from being suppressed or suppressed.
Therefore, there is little decrease in ductility and toughness due to cold pipe expansion to increase the material strength, and by extension, excellent ductility and toughness along with strength, especially a non-magnetic retaining ring for generators that is excellent in radial (thickness direction) toughness. There is an effect that can be obtained.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view in the vicinity of a non-magnetic retaining ring in a generator.

FIG. 2 is a diagram showing a result of a distribution investigation of N and Cr by an X-ray microanalyzer for a retaining ring according to a comparative example.

FIG. 3 is a diagram showing a result of a C distribution investigation by an X-ray microanalyzer for a retaining ring according to a comparative example.

FIG. 4 is a diagram showing a result of Cr distribution investigation by an X-ray microanalyzer for a retaining ring according to an example of the present invention.

FIG. 5 is a diagram showing N and C distribution survey results by an X-ray microanalyzer for a retaining ring according to an example of the present invention.

[Explanation of symbols]

1--Rotary shaft, 2--End, 3--Mating part, 4--Lag, 5--
Coil end turn, 6--support ring, R--retaining ring.

Claims (6)

[Claims] 1. A non-magnetic iron-based alloy containing C: 0.04 to 0.08 wt% is heated to 1100 to 1250 ° C., and forging end temperature is 800 ° C.
After forming into a ring shape by hot forging as described above, it is rapidly cooled by water cooling or oil cooling, and then the forged skin is removed by cutting, then heated to 1000 to 1100 ° C. and then solution cooled by water cooling. A non-magnetic retaining ring for a generator characterized by the following. 2. After the solution treatment, the temperature is further 150 to 250 ° C.
The non-magnetic retaining ring for a generator according to claim 1, wherein the non-magnetic retaining ring is pre-heated and then subjected to a tube expansion process at a tube expansion end temperature of 100 ° C. or more. 3. The non-magnetic iron-based alloy as C: 0.04 to
0.08wt%, Mn: 18-22wt%, Cr: 18-20wt%, N: 0.5w
A non-magnetic iron-based alloy containing t% or more is used.
Alternatively, the non-magnetic retaining ring according to 2 above. 4. A non-magnetic iron-based alloy containing C: 0.04 to 0.08 wt% is heated to 1100 to 1250 ° C., and forging end temperature: 800 ° C.
After forming into a ring shape by hot forging as described above, it is rapidly cooled by water cooling or oil cooling, and then the forged skin is removed by cutting, then heated to 1000 to 1100 ° C. and then water cooled to perform solution treatment. A method of manufacturing a non-magnetic retaining ring for a generator, comprising: 5. After the solution treatment, the temperature is further 150 to 250 ° C.
5. The method for producing a non-magnetic retaining ring for a generator according to claim 4, wherein the tube is preheated to a tube, and then the tube is expanded at a tube expansion end temperature of 100 ° C. or more. 6. The non-magnetic iron-based alloy as C: 0.04 to
0.08wt%, Mn: 18-22wt%, Cr: 18-20wt%, N: 0.5w
The method for manufacturing a non-magnetic retaining ring for a generator according to claim 4, wherein a non-magnetic iron-based alloy containing t% or more is used.