JP6477233B2 - Austenitic stainless steel - Google Patents

Description

  The present invention relates to an austenitic stainless steel.

  Austenitic stainless steel is used in various applications because of its excellent corrosion resistance. For example, the austenitic stainless steel pipe includes a heat transfer pipe such as a boiler and a heat exchanger, a pipe of a chemical plant, and the like. The austenitic stainless steel used for these applications is required to have particularly excellent corrosion resistance.

  For example, low carbon austenitic stainless steels such as SUS316L and SUS304L are excellent in corrosion resistance in the reactor water temperature range, and are therefore used as piping materials for reactors. The corrosion resistance of these austenitic stainless steels is due to a passive film mainly composed of Cr oxide on the steel surface.

  Piping materials for nuclear reactors are used in a high temperature water environment of about 300 ° C., which is the reactor water environment of a nuclear reactor, for a few years, and for a long time, more than 30 years. In such an environment, the corrosion rate of austenitic stainless steel is slow when viewed over a long period of time, but a sufficient passive film is not formed on the steel surface at the initial stage of use, and Ni, Co, A large amount of elution of Fe, Cr, etc. The eluted Ni and Co are transported to the core in the process of circulating the reactor water, and are activated to become radioactive isotopes with a long half-life and become the exposure source at the time of regular inspection. When the amount of eluted Ni and Co increases, the exposure dose of workers performing periodic inspections increases. In addition, the eluted Fe and Cr adhere to the surface of the core structure material and the fuel cladding tube. In addition, when forming a corrosion product, radioactive isotopes such as Ni and Co having a long half-life are incorporated. Therefore, elution of these metals is desired to be suppressed for a long time.

  In order to suppress metal elution in a nuclear environment, it is known that it is effective to form chromium oxide on the surface of a steel material. For example, Japanese Patent Application Laid-Open No. 2004-83965 (Patent Document 1) describes a hydrogen gas atmosphere in which an austenitic stainless steel pipe is controlled at a dew point of −25 ° C. to 0 ° C. or a mixed gas atmosphere of an inert gas and an inert gas. A method for producing an austenitic stainless steel pipe is disclosed in which an oxidation passivation film having a Cr / Fe atomic ratio ≧ 0.01 is formed at a thickness of 2 to 100 nm by performing a solution heat treatment.

  Japanese Patent Application Laid-Open No. 2-47249 (Patent Document 2) discloses heating made of stainless steel containing 12 to 20% Cr by mass, or stainless steel containing 12 to 20% Cr and 40% or less Ni. Disclosed is a heat treatment method for heat-treating a furnace tube in an inert gas atmosphere containing 0.01 to 0.5 vol% oxygen at a predetermined heating temperature and time to form an oxide film mainly composed of chromium oxide. Has been.

Japanese Patent Application Laid-Open No. 2002-121630 (Patent Document 3) and Japanese Patent Application Laid-Open No. 2003-239060 (Patent Document 4) describe an oxide film and an inner layer whose thickness is 180 to 1500 nm and whose outer layer is mainly MnCr ₂ O _4. Discloses an Ni-based alloy product having an oxide film mainly composed of Cr ₂ O ₃ and a method for producing the same.

JP 2004-83965 A JP-A-2-47249 JP 2002-121630 A JP 2003-239060 A

  Even if the austenitic stainless steel is heat-treated within the range of the heat treatment conditions disclosed in JP-A-2004-83965 (Patent Document 1) and JP-A-2-47249 (Patent Document 2), depending on the conditions The film composition and thickness were different, and the metal elution inhibitory effect was sometimes insufficient. In addition, JP 2002-121630 A (Patent Document 3) and JP 2003-239060 A (Patent Document 4) have been studied on Ni-based alloys, and therefore austenitic stainless steel is used as a base material. Differ in the diffusion rate of components and elements in the substrate. For this reason, the film composition obtained by heat treatment, the thickness, and the film form are all different, and the metal suppression effect is different.

  An object of this invention is to provide the austenitic stainless steel excellent in the metal elution-proof characteristic.

In order to suppress metal elution in austenitic stainless steel, it has been considered effective to form an oxide film mainly composed of Cr ₂ O ₃ on the surface of the steel material. However, as a result of investigations to further improve the metal elution suppression effect of the oxide film formed on the surface of the austenitic stainless steel material, the present inventors have obtained the following knowledge.

(A) It is more effective to form an MnCr oxide layer (an oxide film mainly composed of MnCr ₂ O ₄ ) than an oxide film mainly composed of Cr ₂ O ₃ . In particular, the total thickness is more than 100 nm and not more than 200 nm, there is a region containing 40.0% or more Cr by mass% on the outer layer side, and 10.0% or more by mass% on the inner layer side. It was found that if a MnCr oxide layer having a Si-containing region is formed, the metal elution resistance characteristics much better than before can be obtained.

(B) Cr is an element that has the lowest oxygen potential and is easily oxidized among Fe, Cr, and Ni, which are main elements of austenitic stainless steel. On the other hand, general stainless steel contains about 0.5 to 2% of Mn and Si as deoxidizers. The oxygen potential is lower in the order of Si, Mn and Cr, and is preferentially oxidized from Si. Here, when a completely uniform Si oxide film is formed on the surface layer, the metal elution suppression effect cannot be obtained in high-temperature water. However, if the Si content is sufficiently small relative to the Cr content and the oxide film is formed under predetermined conditions, the Si oxide film does not sufficiently cover the steel surface. For this reason, oxides of Mn and Cr are scattered on the outer layer side through the defects. Thereafter, the MnCr ₂ O ₄ film grows in the outer layer, and the MnCr oxide grows so as to contain Si in the inner layer. In the austenitic stainless steel, the presence of a MnCr ₂ O ₄ film including them as an initial oxide is necessary. In particular, when the outer layer side contains a region containing 40.0% or more Cr by mass%, and the inner layer side contains a region containing 10.0% or more Si by mass% In addition, the metal elution resistance is dramatically improved.

(C) When the oxide film is analyzed in the thickness direction by a method such as AES (Auger electron spectroscopy), SIMS (Secondary Ion Mass Spectrometry), or GDS (Glow Discharge Spectroscopy), the metal elution is an oxidation containing Cr. It is suppressed with the formation of the film. The inventors preliminarily observed with a surface SEM after a dissolution test in 250 ° C. high-temperature high-pressure water simulating a nuclear reactor environment. As a result, some steel products had corrosion products including Cr, Ni, and Fe attached on the surface of some steel materials. The oxide film formed on the surface of these steel materials is a thin film mainly composed of Si or Mn, or even if MnCr ₂ O ₄ is formed, the film is uneven and has grown to a sufficient thickness. There was no film. In such a film, since a trace amount of metal elution occurs through defects, it is considered that the above corrosion product adhered to the steel material surface. Therefore, as a result of further examination of the Cr oxide film thickness, metal elution amount, and formation of corrosion products, it was found that when an MnCr oxide film having a thickness of more than 100 nm and 200 nm or less is formed, there is an effect of suppressing metal elution. .

(D) In order to form a desired MnCr oxide layer on the surface of austenitic stainless steel, it is necessary to adjust various conditions such as heating temperature, time, and dew point, and to control the amount of gas supplied to the steel surface. is there. The gas supply amount greatly affects the initial oxidation, and by supplying the gas at a rate of 5 to 15 L / min, the oxidation of Si proceeds rapidly, and uniform MnCr ₂ O ₄ can be formed in the outer layer.

  The present invention has been completed on the basis of the above findings (a) to (d), and is summarized as the following austenitic stainless steel.

(1) An austenitic stainless steel having a MnCr oxide layer on the surface layer,
Chemical composition is mass%,
C: 0.005-0.05%,
Si: 0.01 to 2.0%,
Mn: 0.5 to 2.0%
P: 0.04% or less,
S: 0.003% or less,
Ni: 8.0 to 22.0%,
Cr: 16.0 to 26.0%,
Mo: 0.05-3.0%
Cu: 0 to 1.0%
Ti: 0 to 0.1%,
V: 0 to 0.2%,
N: 0.15% or less,
Balance: Fe and impurities,
The MnCr oxide layer is
The total thickness is more than 100 nm and 200 nm or less,
In the thickness direction of the oxide layer, a Cr-concentrated layer containing 40.0% or more of Cr by mass% exists in a region having a distance of 0 to 100 nm from the surface layer, and the distance from the surface layer is 50 to 150 nm. In the region, the Si concentration layer containing 9.5 to 50.0% Si by mass% exists, and the position where the maximum value of Cr content in the Cr concentration layer exists is Exists on the surface layer side from the position where the maximum value of Si content in the Si concentrated layer exists,
Austenitic stainless steel.

(2) The austenitic stainless steel of (1) above,
Cu: containing 0.01 to 1.0%,
Austenitic stainless steel.

(3) The austenitic stainless steel according to (1) or (2) above,
Ti: 0.005 to 0.1% and / or V: 0.01 to 0.2%,
Austenitic stainless steel.

(4) The austenitic stainless steel according to any one of (1) to (3) above,
Of the corrosion products containing Cr, Ni and Fe on the steel surface after being kept in pure water at 250 ° C. for 100 hours, the adhesion frequency of the corrosion products having an equivalent circle diameter of 200 nm or more is 1 / μm ^2. Austenitic stainless steel that is:

  (5) A nuclear power plant structure comprising the austenitic stainless steel according to any one of (1) to (4) above.

According to the present invention, the metal elution resistance is excellent, and the elution of metal components is extremely small even in a high temperature water environment. Therefore, the austenitic stainless steel according to the present invention is suitable for a nuclear plant member such as a reactor pipe.

Depth direction composition distribution diagram of oxide layer of example (a) No. 4 (b) No. 2 tissue distribution chart

1. Chemical composition The reasons for limitation of each element in the chemical composition of the austenitic stainless steel according to the present invention are as follows. In the following description, “%” of the content of each element means “mass%”.

C: 0.005-0.05%
C is contained in an amount of 0.005% or more for the purpose of deoxidation. However, in order to prevent precipitation of grain boundary carbides, the content is made 0.05% or less. A preferable upper limit is 0.04%, and a more preferable upper limit is 0.020%. A preferred lower limit is 0.007%.

Si: 0.01 to 2.0%
Si is contained in an amount of 0.01% or more for the purpose of deoxidation. However, excessive content promotes the formation of inclusions, so the content is made 2.0% or less. A preferable upper limit is 1.5%, and a more preferable upper limit is 1.0%. Moreover, a preferable minimum is 0.1% and a more preferable minimum is 0.05%.

Mn: 0.5 to 2.0%
Mn has an effect of forming an oxide film having excellent metal elution resistance together with Cr. Mn also has a deoxidizing effect. Therefore, 0.5% or more of Mn is contained. However, Mn combines with S to form a sulfide. This sulfide preferentially concentrates on the surface of the weld during welding. Therefore, if the sulfide concentrated on the surface of the weld becomes excessive, the corrosion resistance of the steel material is lowered, so the Mn content is set to 2.0% or less. A preferable upper limit is 1.8%, and a more preferable upper limit is 1.5%. A preferred lower limit is 0.8%.

P: 0.04% or less P is an element present in steel as an impurity. When the content is excessive, the weldability is lowered, so the content is made 0.04% or less. A preferable upper limit is 0.03%, and a more preferable upper limit is 0.025%.

S: 0.003% or less S is an element present in steel as an impurity. If the content becomes excessive, sulfides concentrated on the surface of the welded portion increase and the corrosion resistance of the steel material is lowered, so the content is made 0.003% or less. A preferable upper limit is 0.002%, and a more preferable upper limit is 0.0015%.

Ni: 8.0 to 22.0%
Ni is an important element for stabilizing the austenite phase and maintaining the corrosion resistance. For this reason, it is made to contain 8.0% or more. However, the effect will saturate even if the content is increased, and it will only increase the price. Therefore, the Ni content is 22.0% or less. A preferable upper limit is 20.0%, and a preferable lower limit is 9.5%.

Cr: 16.0 to 26.0%
Cr is an indispensable element for maintaining corrosion resistance. Cr forms an oxide film on the surface of the steel material, and the Cr content may decrease in the base material immediately below the oxide film. Therefore, Cr is contained 16.0% or more. On the other hand, when the Cr content is increased, Ni must be increased in order to stabilize the austenite phase, leading to an increase in the price of the steel material. Therefore, it is necessary to avoid excessive inclusion of Cr, and the upper limit is made 26.0%. A preferable upper limit is 24.5% and a preferable lower limit is 17.5%.

Mo: 0.05-3.0%
Mo has an effect of suppressing sensitization and is an effective element for improving the corrosion resistance of the base material, so 0.05% or more is contained. However, excessive content precipitates at the grain boundary as a Laves phase and promotes sensitization, so the upper limit is made 3.0%. A preferred upper limit is 2.5%. A preferred lower limit is 0.1%, and a more preferred lower limit is 0.2%.

Cu: 0 to 1.0%
Since Cu is an element effective for stabilizing the passive film and improving the corrosion resistance of the base material, it may be contained as necessary. However, if excessively contained, Cu segregates at the grain boundaries and promotes surface cracks and weld cracks during hot working, so the upper limit is made 1.0%. A more preferred upper limit is 0.5%. In order to acquire said effect, it is preferable to make it contain 0.01% or more. A more preferred lower limit is 0.05%.

Ti: 0 to 0.1%
V: 0 to 0.2%
Ti and V have an effect of suppressing sensitization, and have an effect of further improving the intergranular corrosion resistance of the base material. Therefore, one or both of them may be contained as necessary. However, when these elements are contained excessively, the hot workability deteriorates. Therefore, when these elements are contained, the Ti content is 0.1% or less and the V content is 0.2% or less. And In order to obtain the above effects, Ti is preferably contained in an amount of 0.005% or more and V is contained in an amount of 0.01% or more. A more preferred lower limit is 0.02% for Ti and 0.05% for V. A more preferable upper limit is 0.05% for Ti and 0.15% for V.

N: 0.15% or less N has an effect of improving strength. However, N combines with Cr in the steel to form Cr nitride, and when the amount is excessive, the grain boundary corrosion resistance is lowered. Therefore, the N content is 0.15% or less. A preferable upper limit is 0.12%, and a more preferable upper limit is 0.10%. Although the above effect can be obtained even in a trace amount, the effect is significant when N is contained in an amount of 0.05% or more.

  The chemical composition of the austenitic stainless steel according to the present invention contains each of the above elements, with the balance being Fe and impurities. The term “impurities” as used herein refers to components that are mixed due to raw materials such as ore and scrap and other factors when industrially producing steel materials.

2. Oxide Film The austenitic stainless steel according to the present invention has a MnCr oxide layer on its surface. This MnCr oxide layer has a total thickness of more than 100 nm and not more than 200 nm, and in the thickness direction of the oxide layer, in a region where the distance from the surface layer is 0 to 100 nm, by mass%, 40.0% or more of Cr A Cr-concentrated layer containing Si, a Si-concentrated layer containing 9.5 to 50.0% Si in mass% in a region having a distance of 50 to 150 nm from the surface layer, and The position where the maximum value of Cr content in the Cr concentrated layer is present on the surface layer side than the position where the maximum value of Si content in the Si concentrated layer is present.

Si-enriched layer Si and Mn have a lower oxygen potential than Cr and are easily oxidized. For this reason, first, an oxide containing Si is formed on the surface layer of the austenitic stainless steel according to the present invention. However, since the Si content contained in the austenitic stainless steel according to the present invention is small compared to the Cr content, it does not sufficiently cover the steel surface, and oxides of Mn and Cr are formed through the defects. It will be scattered on the outer layer side. At this time, since the Si oxide is scattered on the inner layer side, rapid oxidation of the outer layer is suppressed, and as a result, a dense MnCr oxide layer is formed on the outer layer. Thereafter, a MnCr oxide layer (MnCr ₂ O ₄ film) grows in the outer layer, and a MnCr oxide grows so as to contain Si in the inner layer.

  Here, when a completely uniform Si oxide film is formed on the surface layer, the metal elution suppression effect in high-temperature water is not sufficient, and a dense MnCr oxide layer cannot be formed on the outer layer. For this reason, in the thickness direction of the oxide layer, a Si-concentrated layer containing 9.5 to 50.0% Si by mass% is present in a region having a distance of 50 to 150 nm from the surface layer. . If the Si content in the MnCr oxide layer is too high, a dense MnCr oxide layer cannot be formed in the outer layer. Therefore, the content is preferably 30.0% or less, and preferably 20.0% or less. More preferably.

About Cr Concentrated Layer The outer layer of the MnCr oxide layer is generated by diffusion of Mn and Cr contained in the base material and the inner layer to the outer layer. In the present invention, in the thickness direction of the oxide layer, a Cr concentrated layer containing 40.0% or more of Cr by mass is present in a region having a distance of 0 to 100 nm from the surface layer. For this reason, compared with the oxide of Mn alone, MnCr ₂ O ₄ is easily generated during the use of steel, and as a result, the metal elution resistance is dramatically improved. If the Cr content in the MnCr oxide layer is too high, pore-like defects may be formed. This is because the oxide layer having too high Cr content means that the oxide layer is thick. Therefore, the Cr content in the Cr concentrated layer is preferably 70.0% or less.

  As described above, the present invention has a Si concentrated layer on the inner layer side of the oxide layer, prevents abrupt oxidation of the outer layer, and causes a Cr concentrated layer having excellent metal elution resistance to exist on the outer layer side, that is, It is important that the position where the maximum value of the Cr content in the Cr concentrated layer exists is closer to the surface layer than the position where the maximum value of the Si content in the Si concentrated layer exists.

Total thickness of MnCr oxide layer: more than 100 nm and not more than 200 nm When the total thickness of the MnCr oxide layer is thin, defects exist and metal elution from the base material cannot be sufficiently suppressed. In addition, since Cr diffuses slower than Mn, in order to obtain excellent metal elution resistance by providing a region containing 40.0% or more of Cr in mass% on the outer layer side, 100 nm It is important to have a film thickness that exceeds. On the other hand, if the total thickness is too thick, pore-like defects are formed in the film, and the amount of metal elution increases. Therefore, the total thickness is 200 nm or less. A preferable lower limit of the total thickness is 120 nm. A preferable upper limit of the total thickness is 160 nm.

3. Method for Forming MnCr Oxide Layer In the present invention, there is no particular limitation on the formation method as long as a predetermined MnCr oxide layer can be formed on the surface layer of austenitic stainless steel. For example, it can be formed under the following conditions.

  In order to form a MnCr oxide layer that satisfies the above conditions on the surface of the austenitic stainless steel, the atmosphere during the heat treatment is important. The atmosphere is hydrogen gas and the dew point is in a specific range. In particular, in order to produce a dense outer layer, it is important that the amount of water contained in the atmosphere is in the range of 100 to 2250 ppm. In particular, 2000 ppm or less is preferable.

  The amount of gas supply greatly affects the initial oxidation. In order to obtain a desired inner layer, it is important to supply a gas satisfying the above conditions at 5 to 15 L / min. As a result, the oxidation of Si proceeds rapidly, and a uniform and dense MnCr oxide can be formed in the outer layer.

  The MnCr oxide layer is preferably formed during the solution heat treatment of austenitic stainless steel. The temperature range is 1000-1100 degreeC. The heat treatment time is set to a time exceeding 3 minutes in consideration of the effect of solid solution. Desirably, the time exceeds 5 minutes. However, if the heat treatment time is too long, the manufacturing cost is increased, and the formed oxide layer becomes thick, which may deteriorate the metal elution resistance. Therefore, the heat treatment time is preferably 15 minutes or less, and more preferably 10 minutes or less.

  Austenitic stainless steel having the chemical composition shown in Table 1 was melted in vacuum, and hot forging and hot rolling were performed to produce a hot rolled plate having a thickness of 6 mm. The obtained hot-rolled sheet was cold-rolled to produce a cold-rolled sheet having a thickness of 4 mm. A strip-shaped test piece having a thickness of 2 mm, a width of 10 mm, and a length of 50 mm was collected from the obtained cold-rolled plate, and the surface was polished with wet emery paper No. 600 and then degreased with acetone. This strip-shaped test piece was inserted into a quartz tube and subjected to a heat treatment at 1060 ° C. for 5 to 10 minutes while aeration of hydrogen gas controlled at a moisture content of 100 to 2250 ppm at 5 L / min.

<Composition distribution in the depth direction of the oxide layer (oxide film)>
The composition distribution in the depth direction of the oxide layer was measured with a glow discharge optical emission spectrometer (hereinafter referred to as GDS). The total thickness of the MnCr oxide layer was calculated from the intersection of the extension line of the Cr enriched part in the depth direction distribution and the extension line of the part where the concentration is constant in the base material.

<Metal dissolution test>
A strip test piece on which pure water and an oxide layer were formed was put in a pure Ti tube having an inner diameter of 20 mm, and both ends were sealed with pure Ti swage locks and kept at 250 ° C. for 100 hours. In order to evaluate the elution amounts of Cr, Ni and Fe, tubes and swage locks made of Ti were used. After maintaining at 250 ° C. for 100 hours, the solution in the tube was sampled and analyzed with an inductively coupled plasma light emitting device (hereinafter referred to as ICP-MS). The metal elution amount was evaluated assuming that the elution amount of each metal in the example in which the oxide layer was not formed was 100%, and 10% or less was judged to be effective.

<Observation test after dissolution test>
Since the elution metal supersaturated at 250 ° C. adheres to the surface of the test piece as a corrosion product at normal temperature, the surface of the test piece after being held in pure water at 250 ° C. for 100 hours is confirmed by a scanning electron microscope. (Hereinafter referred to as SEM). Among the corrosion products including Cr, Ni and Fe, when the adhesion frequency of the corrosion product having an equivalent circle diameter of 200 nm or more is 1 piece / μm ² or less, the corrosion product is assumed not to occur, When the adhesion frequency exceeded 1 piece / μm ² , the corrosion product was considered to be generated.

  These results are also shown in Table 2. In addition, in the thickness direction of the MnCr oxide layer, for an example in which a Cr concentrated layer containing 40.0% or more of Cr by mass% exists in a region whose distance from the surface layer is 0 to 100 nm, Table 2 shows the maximum value of Cr content in the layer and the position (peak depth) at which the maximum value exists. In addition, in the thickness direction of the MnCr oxide layer, an example in which a Si concentrated layer containing 9.5 to 50.0% Si by mass% exists in a region having a distance of 50 to 150 nm from the surface layer. The maximum value of the Si content in the Si concentrated layer and the position (peak depth) where the maximum value exists are shown in Table 2. No. About 2 and 4, the depth direction composition distribution map of an oxide layer is shown in FIG.

As shown in Table 2, no. No. 2 is an example in which there is no MnCr oxide (MnCr ₂ O ₄ ) as an oxide film and only an Si oxide, but the total amount of metal elution is about half that of the example without an oxide film (No. 1). However, the amount is large.

No. Nos. 3 to 5 are examples in which a desired MnCr oxide (MnCr ₂ O ₄ ) was formed, and in all cases, the metal elution amount was sufficiently reduced. In particular, the total metal elution amount tends to decrease as the total thickness of the MnCr oxide increases. However, in the case where the total thickness of the MnCr oxide exceeded 100 nm (No. 6), the elution amount showed a tendency to increase again.

No. No. 7 has a total thickness of MnCr oxide (MnCr ₂ O ₄ ) of less than 100 nm, and a Cr concentration containing 40.0% or more of Cr in mass% in a region whose distance from the surface layer is 0 to 100 nm. This is an example in which the formation layer is not formed. In this example, suppression of the metal elution amount was insufficient.

No. Nos. 8 and 9 Although the chemical composition of the base material is different from 3 to 5, it is an example in which a desired MnCr oxide (MnCr ₂ O ₄ ) was formed, and the metal elution amount could be suppressed.

  According to the present invention, the metal elution resistance is excellent, and the elution of metal components is extremely small even in a high temperature water environment. Therefore, the austenitic stainless steel according to the present invention is suitable for a nuclear plant member such as a reactor pipe.

Claims (5)

An austenitic stainless steel having a MnCr oxide layer on the surface layer,
Chemical composition is mass%,
C: 0.005-0.05%,
Si: 0.01 to 2.0%,
Mn: 0.5 to 2.0%
P: 0.04% or less,
S: 0.003% or less,
Ni: 8.0 to 22.0%,
Cr: 16.0 to 26.0%,
Mo: 0.05-3.0%
Cu: 0 to 1.0%
Ti: 0 to 0.1%,
V: 0 to 0.2%,
N: 0.15% or less,
Balance: Fe and impurities,
The MnCr oxide layer is
The total thickness is more than 100 nm and 200 nm or less,
In the thickness direction of the oxide layer, a Cr-concentrated layer containing 40.0% or more of Cr by mass% exists in a region having a distance of 0 to 100 nm from the surface layer, and the distance from the surface layer is 50 to 150 nm. In the region, the Si concentration layer containing 9.5 to 50.0% Si by mass% exists, and the position where the maximum value of Cr content in the Cr concentration layer exists is Exists on the surface layer side from the position where the maximum value of Si content in the Si concentrated layer exists,
Austenitic stainless steel. The austenitic stainless steel according to claim 1,
Cu: containing 0.01 to 1.0%,
Austenitic stainless steel. The austenitic stainless steel according to claim 1 or 2,
Ti: 0.005 to 0.1% and / or V: 0.01 to 0.2%,
Austenitic stainless steel. The austenitic stainless steel according to any one of claims 1 to 3,
Of the corrosion products containing Cr, Ni and Fe on the steel surface after being kept in pure water at 250 ° C. for 100 hours, the adhesion frequency of the corrosion products having an equivalent circle diameter of 200 nm or more is 1 / μm ^2. Austenitic stainless steel that is:   The structure for nuclear power plants comprised with the austenitic stainless steel in any one of Claim 1-4.