JP2009079240A - Austenitic stainless steel and producing method therefor, and structural material and piping in nuclear reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an austenitic stainless steel which is made hardly sensible and has excellent stress-corrosion cracking resistance, and even when the stress-corrosion crack is caused, hardly causes propagation of the stress-corrosion crack, since it has high stacking-fault energy value, and a producing method therefor, and the structural material thereof. <P>SOLUTION: The austenitic stainless steel is composed of, by wt.%, ≤0.030% C, ≤0.030% N, ≤0.1% Si, ≤1.0% Mn, 10-26% Ni, 15-30% Cr, ≤3.0% Mo and the balance substantially Fe with inevitable impurities, wherein solid-solution content of C is ≤0.010% and solid-solution content of N is ≤0.010%. Further, the constitution containing 0.01-2.0% Al and the constitution containing ≤1.0% one or more kinds selected from V, Ti and Nb can be adopted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to austenitic stainless steel, a method for producing the same, and a structure using the same.

Low-carbon austenitic stainless steel has been widely used as a constituent material for reactor piping and in-reactor structures because it is difficult to sensitize and has excellent stress corrosion cracking resistance under high-temperature and high-pressure water. In recent years, however, low carbon austenitic stainless steels have developed as intergranular stress corrosion cracks by causing stress corrosion cracking from areas hardened by grinder processing or welding thermal strain, even without sensitization or crevice corrosion. It became clear. Regarding the increase in stress corrosion cracking susceptibility due to cold working and welding thermal strain of this austenitic stainless steel, the cracking mechanism was unknown, and the elucidation of the cracking mechanism and the development of countermeasure materials based on it were considered urgent issues. .
WO05 / 068674 pamphlet

  The present invention has been made to solve the above problems, and provides an austenitic stainless steel excellent in durability by preventing an increase in stress corrosion cracking susceptibility due to cold working or welding thermal strain. It is aimed.

  The present inventors have responded to the above-mentioned problem "development of an austenitic stainless steel countermeasure material that is difficult to cause sensitization and crevice corrosion, is difficult to progress, and is difficult to progress due to the occurrence of intergranular stress corrosion cracking based on hardening by cold working or the like. '' I have been working on research for many years.

  Conventionally, some thought that the stacking fault energy value of austenitic stainless steel might contribute to the increase in stress corrosion cracking susceptibility due to cold working of austenitic stainless steel and welding thermal strain. However, the stacking fault energy value is determined by the chemical component, and it is said that it does not change by heat treatment or metal structure.

  However, the present inventors have a serious misunderstanding about the stacking fault energy value of austenitic stainless steel, and Ni, Cr, Mo, Si, Mn have the greatest influence on the stacking fault energy value of austenitic stainless steel. In addition to the amount of main alloy elements such as the amount, not the amount of C and N as chemical components, but the amount of solid solution C and the amount of solution N dissolved in the crystal matrix, that is, the matrix, was invented. In other words, in order to solve the above problems, it is important to increase the stacking fault energy value of austenitic stainless steel, but the conventional theory has been that "the stacking fault energy value is determined solely by chemical components. I thought that there was an error in the idea that “it does not change depending on the processing and heat treatment”. Not only the chemical components but also the amount of solid solution C and solid solution N are reduced by processing and heat treatment, thereby increasing the stacking fault energy value and opening the way for the development of countermeasures for austenitic stainless steel with excellent stress corrosion cracking resistance. I thought it was a thing, and have been experimenting.

The present inventors measured the stacking fault energy value for various low carbon austenitic stainless steels in which chemical components were systematically changed.
Conventionally, “the amount of C in the austenitic stainless steel does not affect the stacking fault energy value”, “the higher the C amount, the higher the stacking fault energy value”, or “the N amount in the austenitic stainless steel is As the content increases, the stacking fault energy value decreases, but there is no influence thereafter.
On the other hand, the present inventors have found from the above measurement results that “the stacking fault energy value of austenitic stainless steel is not determined by the amounts of C and N contained in austenitic stainless steel, but of austenitic stainless steel. It was determined by the amounts of C and N dissolved in the matrix, and it was found that the stacking fault energy value increases as the amount of C and N decreases. That is, it was found that the amount of C and N contained in the austenitic stainless steel matrix is important, not the amount of C and N contained in the component analysis by chemical analysis.

  As described above, it has been thought that the stacking fault energy value is uniquely determined by the chemical composition of the material and does not change depending on the heat treatment conditions. Based on the knowledge that “the amount of stacking fault energy increases as the amount of solid solution C and N in the steel decreases,” “Austenitic stainless steel reduces the amount of solid solution C and N by heat treatment” It has been found that the stacking fault energy value of austenitic stainless steel increases as the amount of solid solution C and N decreases due to the cooling rate after solution treatment and the aging treatment and sensitization treatment after solution treatment. It was.

  In addition, the austenitic stainless steel with varying amounts of solute C and solute N, stacking fault energy values due to aging treatment and sensitization treatment after solution treatment and slight cold working and aging treatment and sensitization treatment As a result of the stress corrosion cracking test of the austenitic stainless steel with increased steel, the austenitic stainless steel with reduced solid solution C and N content and increased stacking fault energy value is superior in stress corrosion cracking resistance. I found it.

  Further, as the Mn content in the austenitic stainless steel increases, the amount of solute N also increases. Therefore, in order to increase the stacking fault energy value of the austenitic stainless steel, it has been found that the Mn content is preferably reduced as much as possible. It was.

  Furthermore, the inventors have taken the idea that increasing the stacking fault energy value of the material is synonymous with making the stacking fault less likely to occur, and therefore, body-centered cubic (BCC) and body-centered square It was thought that the intergranular stress corrosion cracking resistance would be improved by increasing the amount of δ ferrite and the amount of martensite generated in the austenitic stainless steel, since it is difficult for crystal grains (BCT) to cause stacking faults. The results confirming it by the stress corrosion cracking test of the specimen.

As a result, the susceptibility to intergranular stress corrosion cracking caused by hardening of austenitic stainless steel by cold working, etc. is not limited to chemical components, and processing before hardening treatment such as cold working and heat treatment after solution treatment. It has been found that it varies depending on the heat treatment conditions.
The present invention has been completed from such a viewpoint.

Further, the present invention is by weight%, C: 0.030% or less, N: 0.030% or less, Si: 0.1% or less, Mn: 1.0% or less, Ni: 10% or more and 26% or less, Cr: 15% or more and 30% or less, Mo: 3.0% or less, the balance being substantially composed of Fe and inevitable impurities, the amount of solid solution C is 0.010% or less, and the amount of solid solution N Is an austenitic stainless steel characterized by being 0.010% or less.
The amount of solid solution C and the amount of solid solution N are the amounts of C and N dissolved in the crystal matrix, that is, the matrix, and form C, N amounts and compounds precipitated as carbides and nitrides. C amount and N amount are not included. The rules regarding the solid solution C amount and the solid solution N amount are the same in the following configurations.

  Further, the present invention is by weight%, C: 0.030% or less, N: 0.030% or less, Si: 0.1% or less, Mn: 1.0% or less, Ni: 10% or more and 26% or less, Cr: 15% or more and 30% or less, Mo: 3.0% or less, Al: 0.01% or more and 2.0% or less, with the balance being substantially composed of Fe and inevitable impurities, and the amount of solid solution C Is an austenitic stainless steel characterized by having a solid solution N content of 0.010% or less.

  Further, the present invention is by weight%, C: 0.030% or less, N: 0.030% or less, Si: 0.1% or less, Mn: 1.0% or less, Ni: 10% or more and 26% or less, Cr: 15% or more and 30% or less, Mo: 3.0% or less, Al: 0.01% or more and 2.0% or less, any one or more selected from V, Ti and Nb: 1.0% or less each , The balance being substantially composed of Fe and inevitable impurities, the solid solution C amount being 0.010% or less, and the solid solution N amount being 0.010% or less. It provides steel.

  Moreover, in this invention, it is preferable that the amount of solid solution C and the amount of solid solution N are 0.007% or less by weight%.

  In the above-described low carbon austenitic stainless steel with increased stacking fault energy according to the present invention, not only increases the amount of Ni and decreases the amount of Si, Mn, etc., but also reduces the amount of solute C and amount of solute N. As a result, the stacking fault energy value is increased. Thereby, the hardening by the process distortion and welding heat influence distortion which become the cause of stress corrosion cracking can be suppressed.

In the present invention, the Mo content is 1.0% by weight, it is preferable Md ₃₀ points represented by the following formula is 10 ° C. or higher.

_{(Formula) Md 30 (℃) = 413-462x} (C + N) -9.2xSi-8.1xMn-13.7xNi-9.5xNi-18.5xMo
Md ₃₀ points means a processing temperature at which 50% processing-induced martensite is generated in 30% processing.

That is, in the austenitic stainless steel having the composition shown above, when the Mo content is 1.0% or less, if the chemical component is such that the Md ₃₀ point is 10 ° C. or higher, the cold-working causes a work-induced martensite. You can make your site easier to create. On the other hand, when the amount of Mo exceeds 1.0%, it is preferable to contain 10% or less of δ ferrite by weight.

Thus, by adjusting to a predetermined chemical component according to the Mo content, it is possible to optimize the amount of work-induced martensite generation. As a result, stacking faults can be made difficult to occur, and the stress corrosion cracking resistance can be improved.
For example, 304 stainless steel usually has a Ni content of 1 to 2% lower than 316 stainless steel, and the stacking fault energy value of 316 stainless steel is higher than 304 stainless steel. When steel has a Md of ₃₀ points higher than the processing temperature, cold-working causes work-induced martensite, which makes it difficult for stacking faults to occur. The stress corrosion cracking resistance becomes higher than that of 316 stainless steel.
On the other hand, when the Md ₃₀ point is lower than the processing temperature, processing-induced martensite is less likely to occur due to cold processing, and stacking faults are more likely to occur. The crackability is lower than 316 stainless steel.
Furthermore, the present inventors have found that when the amount of Mo exceeds 1.0%, it is preferable to contain 10% or less of δ ferrite by weight%.

In addition, the present invention is a steel piece (steel plate, forged steel product or steel pipe) made of any of the above austenitic stainless steel, subjected to a solution treatment at 1000 ° C. to 1150 ° C., and then subjected to cold working of 30% or less, Then, a carbon / nitride precipitation heat treatment is performed at 400 ° C. to 850 ° C. for 0.5 to 50 hours, and a method for producing an austenitic stainless steel is provided.
According to this manufacturing method, C and N can be precipitated at the grain boundaries from the stainless steel matrix by each treatment after the solution treatment, and the amount of solid solution C and N can be reduced. Thereby, austenitic stainless steel with improved stacking fault energy can be produced.

  Any of the above-mentioned austenitic stainless steels can be used particularly suitably as austenitic stainless steel for nuclear reactor members such as reactor piping or reactor internals. Moreover, the stainless steel obtained by the said manufacturing method can also be used suitably as a structural material of the piping for reactors, or a reactor internal structure as austenitic stainless steel for nuclear reactor members.

According to the present invention, the stacking fault energy of austenitic stainless steel can be increased, it is difficult to be sensitized, it has excellent resistance to stress corrosion cracking, and even if stress corrosion cracking occurs, it is difficult for stress corrosion cracking to propagate. Austenitic stainless steel can be obtained.
By applying the austenitic stainless steel of the present invention to a reactor pipe or a reactor internal structure which is a part of the reactor component, these reactor components can be used for a long period of time.

  In addition, according to the production method of the present invention, the amount of solid solution C and N can be reduced by a simple heat treatment (charcoal / nitride precipitation heat treatment), is not easily sensitized, and has excellent stress corrosion cracking resistance. Stainless steel can be easily manufactured.

Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not limited to these embodiments.
In the austenitic stainless steel of the present invention, the contents of C, Si, Mn, P, S, Ni, Cr, Mo, and N are specified by weight%, and the balance is substantially made of Fe and inevitable impurities. Is. Hereinafter, the role of each element in the alloy will be described.

  C is an indispensable element for obtaining a predetermined strength in austenitic stainless steel and for stabilizing austenite. When heated at 400 ° C. to 850 ° C. or gradually cooled in this temperature range, Cr carbide It is well known that crystallization occurs at the grain boundaries and a Cr-deficient layer is formed around the precipitates, resulting in sensitization in which the grain boundaries are sensitive to corrosion. In order to suppress this sensitization, C Generally, the amount is made 0.03% or less.

However, if the C content is 0.03% or less, the strength is insufficient and the stability of austenite is insufficient. Therefore, conventionally, the strength of austenitic stainless steel is obtained in the same manner as C, and the austenite is stabilized. N, which is an important element, is added to ensure strength and stabilize austenite.
On the other hand, the inventors, when increasing the amount of solute C or solute N, easily harden when processing strain or thermal strain is applied, and precipitate Cr carbide or Cr nitride when affected by heat. However, the inventors have focused on the fact that the Cr content in the crystal matrix is lowered, and stress corrosion cracking tends to occur.
Then, the conventional common sense is broken, and in the present invention, it is considered that it is desirable to reduce the amount of solid solution C and the amount of solid solution N, and to reduce the amount of solid solution C and N to a level that can be stably lowered industrially. The solid solution C amount and N amount were 0.010% or less, preferably 0.007% or less. In addition, if possible, the amount of solid solution C and the amount of solid solution N may be further reduced, and the amount may not be detected in the measurement of the amount of solid solution.

In the production process of austenitic stainless steel, Si plays an important role as a deoxidizing material and is usually contained in an amount of about 0.5%. However, the inventors have noted that this austenitic stainless steel containing about 0.5% of Si is easily hardened when processing strain or thermal strain is applied. Therefore, it is desirable to reduce it as much as possible within a range where it can be stably reduced, and it is set to 0.1% or less, preferably 0.02% or less.
Therefore, the amount of deoxidizing element is insufficient, but the shortage has been solved by adding a small amount of Al, which also has the effect of fixing solute N, in a very small range. In the present invention, the Al addition amount is 0.01% or more and 2.0% or less.

Cr and Mo are known as extremely important elements for maintaining the corrosion resistance of austenitic stainless steel. However, Cr and Mo are ferrite-forming elements. If the amount of Cr and Mo is too high, the stability of austenite is improved. It is known to deteriorate, and to lower the ductility of austenitic stainless steel and deteriorate the workability. Therefore, conventionally, the amount of Cr and Mo has been kept from becoming extremely high.
In contrast, the present inventors have reduced the amounts of C, N and Si as much as possible in order to improve the stress corrosion cracking resistance, but at the same time, the ductility of the austenitic stainless steel can be increased. In order to prevent the austenite stability from decreasing by increasing the C and N amounts as much as possible, the Ni amount is increased to maintain the austenite stability.
As described above, when the amounts of C and N are reduced as much as possible, it is assumed that a predetermined strength level cannot be obtained because the strength decreases. In this case, the problem can be solved by increasing the thickness of the member, etc., so that the strength design can play the role of equipment and piping.

  Moreover, the austenitic stainless steel of this invention may contain 1 type, or 2 or more types among V, Ti, and Nb. These metals are more likely to form a compound with C than Cr, and the amount of dissolved C in the matrix decreases when added. These addition amounts in the present invention are all 1.0% or less.

Conventionally, austenitic stainless steel is used in the form of a solution treatment in order to avoid sensitization, and a heat history at 400 ° C. to 850 ° C. is not added after the solution treatment. However, the present inventors have made the austenitic stainless steel less sensitized even when heat treatment is performed at 400 to 850 ° C. for 0.5 to 50 hours by setting the C and N amounts to 0.01% or less. It has been found that it is not a problem, and extremely fine Cr carbide and Cr nitride are precipitated, the amount of solid solution C and N in the matrix can be further reduced, and the stacking fault energy value can be increased. As a result, it has been found that the propagation rate of stress corrosion cracking in high-temperature and high-pressure water can be greatly reduced.
Therefore, in the production method of the present invention, in order to further reduce the amount of dissolved C and N in the matrix, after the solution treatment, cold work of 30% or less is performed, and then 0.5 to 50 at 400 to 850 ° C. It is preferable to perform a Cr carbide / Cr nitride precipitation treatment for a period of time.

  About the said austenitic stainless steel, it can use especially suitably, for example as piping for reactors or a structural material in a reactor. Moreover, the stainless steel obtained by the said manufacturing method can also be used suitably as a constituent material of piping for reactors, or a reactor internal structure. Specific embodiments will be described below with reference to the drawings.

  FIGS. 10 (a) and 10 (b) are explanatory views of the main parts of a boiling water reactor and a pressurized water reactor, respectively, and FIGS. 11 (a) and 11 (b) are respectively shown in FIG. It is a longitudinal cross-sectional view which shows the internal structure of a nuclear reactor.

  In FIG. 11, a fuel assembly (fuel rod) 41 for generating a nuclear reaction is installed inside a reactor core shroud 42 in a reactor pressure vessel 40, and a control rod guide tube is provided below or above the fuel assembly 41. Alternatively, a control rod drive mechanism 44 or the like is installed. These devices are fixed by a core support plate 45 and a fuel support fitting. Further, the uppermost portion of the fuel assembly 41 is fixed by an upper support plate 47.

  In the boiling water reactor shown in FIGS. 10 (a) and 11 (a), a steam separator is used to extract only steam from a gas-liquid two-phase flow generated by boiling in the fuel assembly 41 at the upper part of the core. 48, and further, a steam dryer 49 is installed in the upper part thereof, and an external recirculation circuit 52 in which the jet pump 50 and the recirculation pump 51 are combined is constituted separately from the main steam-water supply system. .

  Further, in the pressurized water reactor shown in FIGS. 10B and 11B, the hot water having a high temperature in the fuel assembly 41 is supplied to the steam generator 54 through the high temperature side pipe 53 to generate steam. The heat is exchanged in the vessel 54 and becomes a low temperature, and is returned to the reactor pressure vessel 40 through the primary coolant pump 55 through the low temperature side pipe 56. The low temperature side pipe 56 and the high temperature side pipe 53 are connected via a bypass pipe 59 having an on-off valve 58.

The present invention includes the above-described components such as various pipes and pumps constituting each system of the nuclear reactor and the circulation circuit, or the reactor internal structure such as the core shroud 42, the core support plate 45, the fuel support fitting, and the upper support plate 47. By using the austenitic stainless steel, stress corrosion cracking hardly occurs even in a high-temperature and high-pressure water environment, and it can be used for a long time. In addition, even if stress corrosion cracking occurs, it is difficult for stress corrosion cracking to propagate, so a remarkable effect can be obtained in improving the safety and reliability of the nuclear power plant.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not restrict | limited at all by these Examples.

Example 1
Table 1 shows conventional SUS316L (conventional material 1), 316NG (conventional material 2) and 310S (conventional material 3), which are widely used as nuclear materials, and the test materials that led to the present invention. The chemical composition (the content is all in wt%) is shown as prototype materials 1 to 47, and the composition is shown. Table 2 shows the processing and heat treatment conditions for each prototype shown in Table 1.

1 to 9 are graphs showing the results of measuring the stacking fault energy for the prototype materials 1 to 47 shown in Table 1. FIG. The stacking fault energy can be measured using a known method. For example, measurement is performed by applying a specified strain to a test piece having a standard dimension and observing the structure.
In addition, all content of each element shown in FIGS. 1-9 is weight%.

FIG. 1 is a graph showing the relationship between the amount of dissolved C and stacking fault energy for prototype materials 1 to 8 shown in Table 1, and affects the stacking fault energy value that affects the stress corrosion cracking resistance of austenitic stainless steel. The influence of the amount of solid solution C is shown.
As the C content decreases, the stacking fault energy value of austenitic stainless steel increases, and the tendency appears when the solid solution C content is 0.03% or less, and becomes prominent at 0.01% or less, and 0.007% or less. In, it has increased remarkably.
Table 1 shows the total C amount of each prototype material, but the total C amount and the solute C amount are the same for the prototype materials 1 to 8 produced in this example (all It is confirmed that C is dissolved in the matrix).

FIG. 2 is a graph showing the relationship between the amount of solute N and stacking fault energy for the prototype materials 9 to 15 shown in Table 1, and affects the stacking fault energy value that affects the stress corrosion cracking resistance of austenitic stainless steel. The effect of the amount of dissolved N is shown. As the N content decreases, the stacking fault energy value of the austenitic stainless steel increases, and this tendency appears when the solid solution N content is 0.03% or less, and becomes noticeable at 0.01% or less, and 0.007% or less. It increased significantly.
In Table 1, the total N amount of each prototype material is displayed. However, for the prototype materials 9 to 15 produced in this example, the total N amount and the solute N amount coincide with each other (all It is confirmed that N is dissolved in the matrix.

  FIG. 3 is a graph showing the relationship between the Si amount and stacking fault energy for the prototype materials 16 to 20 in Table 1, and the Si amount affecting the stacking fault energy value that affects the stress corrosion cracking resistance of austenitic stainless steel. The impact of is shown. As the Si content decreased, the stacking fault energy value of the austenitic stainless steel increased, and this tendency appeared when the Si content was 0.1% or less, and became noticeable when it was 0.02% or less.

  FIG. 4 is a graph showing the relationship between the amount of Mn and the stacking fault energy for the prototype materials 21 to 23 (high C high N material) and the prototype materials 24 to 30 (low C low N material) in Table 1, and shows austenite. The effect of the amount of Mn on the stacking fault energy value that determines the stress corrosion cracking resistance of a stainless steel is shown. Regardless of the amount of C and the amount of N, as the amount of Mn decreases, the stacking fault energy value of the austenitic stainless steel increases. Furthermore, when the amount of Mn is 0.5% or less, the difference between the low C low N material and the high C high N material tends to increase, and the Mn amount is 0.21% or less and 0.02% or less. Became more noticeable as the number decreased. That is, it can be seen that in the austenitic stainless steel of the present invention, the effect of increasing the stacking fault energy value by adjusting the amount of Mn is improved as compared with the conventional product.

  FIG. 5 is a graph showing the relationship between the amount of Cr and stacking fault energy for prototype materials 32-35 (12-13Ni material) and prototype materials 36, 37, 39, 41 (15-25Ni material) in Table 1. The effect of Cr content on the stacking fault energy value that affects the stress corrosion cracking resistance of austenitic stainless steel is shown. The austenitic stainless steel increases as the Cr content increases in any of the prototype materials 32 to 35 in which the Ni amount is 12 to 13% by weight and the prototype materials 36, 37, 39, and 41 in which the Ni amount is 15 to 25% by weight. The stacking fault energy value of increases.

  FIG. 6 is a graph showing the relationship between the amount of Ni and stacking fault energy for the prototype materials 32 and 38 (15-18Cr material) and the prototype materials 34 to 37 and 39 to 41 (20-25Cr material) in Table 1. The influence of the amount of Ni on the stacking fault energy value that affects the stress corrosion cracking resistance of austenitic stainless steel is shown. As the Cr content increases in any of the prototype materials 32 and 38 having a Cr content of 15 to 18% and the prototype materials 34 to 37 and 39 to 41 having a Cr content of 20 to 25%, the austenitic stainless steel The stacking fault energy value increases.

  FIG. 7 is a graph showing the relationship between the amount of Mo and stacking fault energy for the prototype materials 42 to 47 in Table 1, and the amount of Mo affecting the stacking fault energy value that affects the stress corrosion cracking resistance of austenitic stainless steel. The impact of is shown. As the amount of Mo increases, the stacking fault energy value of austenitic stainless steel increases.

(Example 2)
Next, the stress corrosion crack growth rate was measured using 304 stainless steel with Md of ₃₀ points changed. Table 3 shows the chemical components (% by weight) of the test materials used.

The stress corrosion crack growth test was conducted with the following equipment and procedure.
The prototype material shown in Table 3 was processed into a stress corrosion crack growth test piece having the shape shown in FIG. These test pieces were subjected to a 1500 hour stress corrosion crack growth test in the autoclave shown in FIG. 9 under the test conditions shown below.

[Test equipment]
In the cyclic autoclave for stress corrosion cracking test shown in FIG. 9, the water quality is adjusted with the make-up water tank 11, degassed with N ₂ gas, and then fed into the autoclave as the test container 19 through the preheater 15 with the high-pressure metering pump 12. Send high temperature and high pressure water and circulate a part. In the previous stage of the preheater 15, a regenerative heat exchanger 14 for connecting a cooler 16 is provided. The test vessel 19 is covered with an electric furnace 18.

[Test conditions]
Corrosion potential: 200 mV
Conductivity: 0.3 μS / cm
pH (25 ° C.): 6.5
Temperature: 288 ° C
Cl concentration: 20 ppb

Table 4 shows an austenitic stainless steel (prototype material 48, 50-54) having a high Md ₃₀ point and high work-induced martensite made in the present invention, conventional material 3, and a low Md ₃₀ point No. 49 shows a comparison of the stress corrosion crack growth rate with 49.
Conventional material 3 and Md ₃₀ point low No. Austenitic stainless steels (prototype materials 48, 50 to 54) in which work-induced martensite is produced in the present invention show a stress corrosion crack growth as compared with 49 showing a large crack growth rate. Thus, it can be seen that it has excellent SCC resistance.

(Example 3)
Next, an austenitic stainless steel (prototype material 43) having a high stacking fault energy value according to the present invention and the conventional material 3 were subjected to a stress corrosion crack growth test equivalent to that in Example 2. Table 5 shows a comparison of stress corrosion crack growth rates between the prototype material 43 and the conventional material 3.

  As shown in Table 5, the austenitic stainless steel (prototype material 43) having a high stacking fault energy value according to the present invention is stressed compared to the conventional material 3 exhibiting a large crack growth rate. It can be seen that no corrosion crack crack growth was observed and that the film had excellent SCC resistance.

Moreover, the aging treatment was performed on the conventional material 3 under various conditions to produce prototype materials, and a stress corrosion cracking growth test equivalent to that in Example 2 was performed on these materials. Table 6 shows the results.
As shown in Table 6, the crack growth rate can be reduced by applying an aging treatment to the stainless steel after the solution treatment. From this, it can be seen that the stress corrosion cracking property is improved by reducing the amount of dissolved C and the amount of dissolved N by aging treatment.

  The austenitic stainless steel of the present invention is difficult to sensitize, has excellent resistance to stress corrosion cracking, and even if stress corrosion cracking occurs, it is difficult for stress corrosion cracking to propagate. From the viewpoint of improving the safety and reliability of the nuclear power plant, the industrial significance is extremely large.

The graph which shows the relationship between the amount of solute C and stacking fault energy. The graph which shows the relationship between solid solution N amount and stacking fault energy. The graph which shows the relationship between Si amount and stacking fault energy. The graph which shows the relationship between Mn amount and stacking fault energy. The graph which shows the relationship between Cr amount and stacking fault energy. The graph which shows the relationship between Ni amount and stacking fault energy. The graph which shows the relationship between Mo amount and stacking fault energy. The figure which shows CT test piece shape for a stress corrosion crack crack propagation test. The system block diagram of the circulation type autoclave for a stress corrosion cracking test. (A) Boiling water reactor, (b) The principal part explanatory drawing of a pressurized water reactor. FIG. 11 is a cross-sectional view showing an internal configuration of each nuclear reactor in FIG. 10.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Gas cylinder, 11, 30 ... Make-up water tank, 12 ... High pressure metering pump, 13 ... Accumulator, 14, 32 ... Regenerative heat exchanger, 15, 34 ... Preheater, 16, 33 ... Cooler, 17 ... High pressure disk filter , 18 ... Electric furnace, 19, 35 ... Test container, 20 ... Pressure regulating valve, 21 ... Safety valve

Claims (9)

% By weight
C: 0.030% or less,
N: 0.030% or less,
Si: 0.1% or less,
Mn: 1.0% or less,
Ni: 10% or more and 26% or less,
Cr: 15% to 30%,
Mo: 3.0% or less,
And the balance substantially consists of Fe and inevitable impurities,
An austenitic stainless steel having a solid solution C content of 0.010% or less and a solid solution N content of 0.010% or less. % By weight
C: 0.030% or less,
N: 0.030% or less,
Si: 0.1% or less,
Mn: 1.0% or less,
Ni: 10% or more and 26% or less,
Cr: 15% to 30%,
Mo: 3.0% or less,
Al: 0.01% or more and 2.0% or less,
And the balance substantially consists of Fe and inevitable impurities,
An austenitic stainless steel having a solid solution C content of 0.010% or less and a solid solution N content of 0.010% or less. % By weight
C: 0.030% or less,
N: 0.030% or less,
Si: 0.1% or less,
Mn: 1.0% or less,
Ni: 10% or more and 26% or less,
Cr: 15% to 30%,
Mo: 3.0% or less,
Al: 0.01% or more and 2.0% or less,
Any one or more selected from V, Ti, and Nb: 1.0% or less,
And the balance substantially consists of Fe and inevitable impurities,
An austenitic stainless steel having a solid solution C content of 0.010% or less and a solid solution N content of 0.010% or less.   The austenitic stainless steel according to any one of claims 1 to 3, wherein the amount of solid solution C and the amount of solid solution N are 0.007% or less by weight%. Mo content is 1.0% or less by weight%,
The austenitic stainless steel according to any one of claims 1 to 4, wherein the Md ₃₀ point represented by the following formula is 10 ° C or higher.
(formula)
Md ₃₀ (° C.) = 413-462 × (C + N) −9.2 × Si−8.1 × Mn−13.7 × Ni−9.5 × Ni−18.5 × Mo   The austenitic stainless steel according to any one of claims 1 to 4, wherein the Mo content exceeds 1.0% by weight and includes δ ferrite of 10% or less by weight. .   A steel slab made of steel having the component composition according to any one of claims 1 to 4 is subjected to a solution treatment at 1000 ° C to 1150 ° C, and then cold-worked at 30% or less, and thereafter A method for producing an austenitic stainless steel, characterized by performing a carbon / nitride precipitation heat treatment at 400 ° C to 850 ° C for 0.5 to 50 hours.   A reactor internal structure comprising the austenitic stainless steel according to any one of claims 1 to 6.   An in-reactor pipe comprising the austenitic stainless steel according to any one of claims 1 to 6.

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