JP2014181383A - High corrosion resistance high strength stainless steel, structure in atomic furnace and manufacturing method of high corrosion resistance high strength stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high corrosion resistance high strength stainless steel suppressing stress corrosion crack, irradiation induced stress corrosion crack, crevice corrosion and the like in circumstance of being exposed to neutron irradiation environment.SOLUTION: The high corrosion resistance high strength stainless steel is an austenite stainless steel and has a chemical composition consisting of C of 0.04 mass% or less, Mn of 1.0 to 2.0 mass%, N of 9.0 to 13.0 mass%, Cr of 17.0 to 20.0 mass%, Ta of 13 times as C and 0.50 to 0.65 mass%, and the balance Fe and Nb with inevitable impurities. It has an austenite average crystal grain size number defined in JIS G 0551 of 10.0 to 13.0.

Description

  The present invention relates to a high-corrosion-resistant high-strength stainless steel with reduced susceptibility to radiation-induced stress corrosion cracking, a reactor internal structure using the same, and a method for producing a high-corrosion-resistant high-strength stainless steel.

As an example of an alloy composition of austenitic stainless steel for use in an environment that receives a high level of radiation irradiation such as the inside of a nuclear reactor, there is one described in Patent Document 1.
The technique described in Patent Document 1 is an improvement of type 304 austenitic stainless steel, which adds certain restrictions to the specific components of such standard austenitic stainless steel and provides additional alloy components in the correct proportions. The present invention relates to a specific alloy composition. Specifically, it consists of about 18-20% by weight Cr, about 9-11% by weight Ni, about 1.5-2% by weight Mn, and the balance Fe and incidental impurities. The carbon content of such alloy compositions, which is to comply with Type 304 austenitic stainless steel, is limited to about 0.02 to about 0.04 weight percent. Also, the total amount of Nb and Ta corresponds to a minimum of 14 times the carbon content and is limited to a maximum of about 0.65% by weight of the total alloy composition. Further, the Nb content is limited to about 0.25% by weight or less of the entire alloy composition, and the Ta content can take a value up to about 0.4% by weight of the entire alloy composition.

Japanese Patent Laid-Open No. 01-275740

In general, austenitic stainless steel is a material excellent in corrosion resistance. However, it has been pointed out that the susceptibility to irradiation-induced stress corrosion cracking increases when exposed to high-temperature high-pressure water and neutron irradiation environments in a nuclear reactor nuclear reactor, for example, a core of a light water reactor. In addition, with the aging of nuclear power plants, structural materials with higher strength are required.
In order to suppress sensitization by welding heat, SUS316L or SUS304L low carbon austenitic stainless steel with a reduced carbon content is used. However, in recent years, stress corrosion cracking, which is considered to be due to irradiation induction, has been confirmed in SUS316L sheaths and tie rods of control rods used in environments with high neutron irradiation. This is considered to be caused by hardening or irradiation-induced grain boundary segregation due to neutron irradiation of the material, and neutron irradiation damage must be suppressed.

In the technique described in Patent Document 1 described above, Nb and Ta stabilize carbon even after solution heat treatment by adding Nb and Ta, thereby suppressing stress corrosion cracking and irradiation-induced stress corrosion cracking, and the amount of Nb added By reducing the amount of Ta and increasing the amount of Ta added, it is said that it has the effect of facilitating handling as a short half-life Ta182 instead of the long half-life Nb94 generated by neutron absorption.
However, the stainless steel described in Patent Document 1 may not be able to satisfy the corrosion resistance and strength characteristics required for a reactor internal structure such as a control rod.

  The present invention relates to a high corrosion resistance high strength stainless steel in which the occurrence of stress corrosion cracking, irradiation induced stress corrosion cracking, crevice corrosion, etc. is suppressed in an environment exposed to a neutron irradiation environment, and a reactor internal structure using the same Provided is a method for producing a high-strength stainless steel with high corrosion resistance.

In order to solve the above problems, for example, the configuration described in the claims is adopted.
The present invention includes a plurality of means for solving the above-mentioned problems. For example, C: 0.04% by mass or less, Mn: 1.0 to 2.0% by mass, Ni: 9.0 -13.0% by mass, Cr: 17.0-20.0% by mass, Ta: C 13 times or more, 0.50 to 0.65% by mass, and the balance from inevitable impurities including Fe and Nb The austenite average grain size number specified by JISG0551 is 10.0 to 13.0.

According to the present invention, it is possible to provide a high-corrosion-resistant high-strength stainless steel in which occurrence of stress corrosion cracking, irradiation-induced stress corrosion cracking, crevice corrosion, and the like is suppressed in an environment exposed to a neutron irradiation environment. And, by taking advantage of the material characteristics of such high corrosion resistance high strength stainless steel of the present invention, the reduction in the susceptibility to irradiation-induced stress corrosion cracking, and the high strength due to the fine crystal structure, neutrons having energy of 0.1 MeV or more Is applied to nuclear reactor components or structures that are used in harsh environments that are irradiated by 0.5 × 10 ²¹ n / cm ² or more, improving the reliability of nuclear power plants and extending the service life Can be

It is a figure which shows the correlation with the cold rolling rate and the crystal grain diameter for the comparison of Example 1 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the correlation with the cold rolling rate and crystal grain diameter in Example 1 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the correlation with the cold rolling rate and crystal grain diameter in Example 1 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the correlation with the cold rolling rate and crystal grain diameter in Example 1 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the correlation with the average grain size number and aging heat processing time in Example 2 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the correlation with the average grain size number and aging heat processing temperature in Example 2 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the 0.2% yield strength in 100 degreeC of the material of this invention and the comparative material in Example 3 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a figure which shows the tensile strength in 100 degreeC of the material of this invention and the comparative material in Example 3 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. 4 is a side view and a top view of an outline of a test piece in a crevice corrosion test in Example 3. It is the figure which compared the maximum intergranular corrosion depth by the crevice corrosion of the material of this invention and the comparative material in Example 3 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is the figure which compared the number of the intergranular corrosion locations by the crevice corrosion of the material of this invention and the comparison material in Example 3 of the manufacturing method of the high corrosion resistance high strength stainless steel of this invention. It is a perspective view of the control rod to which the high corrosion resistance high strength stainless steel of the present invention is applied.

Embodiments of the high corrosion resistance high strength stainless steel and the reactor internal structure and the high corrosion resistance high strength stainless steel manufacturing method of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram showing the correlation between the cold rolling rate and the crystal grain size for comparison with Example 1 of the production method of the high corrosion resistance high strength stainless steel of the present invention, and FIG. 2 is the high corrosion resistance high strength stainless steel of the present invention. FIG. 3 is a diagram showing the correlation between the cold rolling rate and crystal grain size in Example 1 of the steel production method, and FIG. 3 is a diagram showing the cold rolling rate and crystal in Example 1 of the production method of the high corrosion resistance high strength stainless steel of the present invention. FIG. 4 is a diagram showing the correlation with the grain size, FIG. 4 is a diagram showing the correlation between the cold rolling rate and the crystal grain size in Example 1 of the production method of the high corrosion resistance high strength stainless steel of the present invention, and FIG. FIG. 6 is a diagram showing the correlation between the average grain size number and the aging heat treatment time in Example 2 of the method for producing high corrosion resistance high strength stainless steel, FIG. 6 shows the average in Example 2 of the method for producing high corrosion resistance high strength stainless steel of the present invention. Figure showing the correlation between grain size number and aging heat treatment temperature, 7 is a diagram showing the 0.2% proof stress at 100 ° C. of the material of the present invention and the comparative material in Example 3 of the production method of the high corrosion resistance high strength stainless steel of the present invention, and FIG. 8 is the high corrosion resistance high strength stainless steel of the present invention. The figure which shows the tensile strength at 100 degrees C of the material of this invention and the comparative material in Example 3 of the manufacturing method of steel, FIG. 9 is the side view and top view of the outline | summary of the test piece in the crevice corrosion test in Example 3, FIG. 10 is a diagram comparing the maximum intergranular corrosion depth due to crevice corrosion of the material of the present invention and the comparative material in Example 3 of the production method of the high corrosion resistance high strength stainless steel of the present invention, and FIG. 11 is a diagram showing the high corrosion resistance of the present invention. FIG. 12 is a diagram comparing the number of intergranular corrosion sites due to crevice corrosion between the material of the present invention and the comparative material in Example 3 of the method for producing high-strength stainless steel. FIG. It is a perspective view of a control rod.

The high corrosion resistance high strength stainless steel according to the present invention is an austenitic stainless steel, C is 0.04% by mass or less, Mn is 1.0 to 2.0% by mass, and Ni is 9.0 to 13.0% by mass. %, Cr is 17.0 to 20.0 mass%, Ta is 13 times or more of C and 0.50 to 0.65 mass%, and the balance is Fe and an inevitable impurity containing Nb. It is what.
Moreover, the high corrosion resistance high-strength stainless steel according to the present invention is a stainless steel having an austenite average grain size number defined by JIS G 0551 in the range of 10.0 to 13.0.

  Hereinafter, each physical property value of the high corrosion resistance high strength stainless steel according to the present invention will be described.

1. About chemical components
In the high corrosion resistance high strength stainless steel according to the present invention, C is an element effective for obtaining strength. On the other hand, if the C content exceeds 0.04 mass%, carbides are likely to be generated at the grain boundaries of the weld heat affected zone, and the stress corrosion cracking resistance is reduced. Therefore, the upper limit of the C content is 0.04% by mass.

  In the high corrosion resistance high strength stainless steel according to the present invention, the Mn content is set to 1.0 to 2.0% by mass in order to give toughness of the material.

  In the high corrosion resistance high strength stainless steel according to the present invention, Ni is an element necessary for maintaining the corrosion resistance of the steel. Further, a content of 9.0% by mass or more is necessary as a stabilizing element for austenite. On the other hand, when the content exceeds 13.0% by mass, the hot workability is remarkably deteriorated. Therefore, the Ni content is 9.0 to 13.0 mass%.

  In the high corrosion resistance high strength stainless steel according to the present invention, Cr is an element necessary for maintaining the corrosion resistance of the steel. In order to ensure corrosion resistance, it is necessary to secure the content of 17.0% by mass or more. On the other hand, when the content exceeds 20.0 mass%, the material is easily embrittled and the material cost is significantly increased. Therefore, the Cr content is 17.0 to 20.0 mass%.

In the high corrosion resistance high strength stainless steel according to the present invention, Ta captures atomic vacancies generated by irradiation when dissolved in the material because Ta has a larger atomic radius than the average atomic radius of the constituent elements. In addition, irradiation damage can be suppressed by increasing the recombination probability with interstitial atoms.
Here, when atomic vacancies flow into the crystal grain boundary by diffusion, Cr atoms near the grain boundary diffuse in a direction away from the grain boundary, and the Cr concentration in the vicinity of the grain boundary is lower than the Cr concentration in the matrix. Causes Cr deficiency. However, when Ta captures atomic vacancies, diffusion of atomic vacancies into grain boundaries is suppressed, and grain boundary Cr deficiency is suppressed. On the other hand, when Ta is present as TaC, the interface between TaC and the matrix becomes an atomic vacancy annihilation site, so that grain boundary Cr deficiency can be suppressed as in the case where Ta is dissolved. Thus, the presence of Ta can suppress irradiation-induced grain boundary Cr deficiency, whether it is dissolved alone or as TaC, and is effective in suppressing irradiation-induced stress corrosion cracking. It is thought that there is. However, when C is present in the matrix more than necessary, in a place where welding heat is applied, so-called thermal sensitization occurs, which forms Cr carbide on the grain boundary and causes Cr deficiency, and stress corrosion cracking susceptibility increases. . Therefore, it is necessary to form TaC in order to reduce the concentration of dissolved C.
Based on the above principle, Ta needs to be 13 times the C content and 0.50% by mass or more. In view of deterioration in characteristics such as weldability, the upper limit is set to 0.65% by mass.
Further, when Ta stabilizes C, if 30% or more of the total amount of Ta is precipitated as TaC, an effect of stress corrosion cracking resistance is expected. In addition, since the precipitated and dispersed TaC acts as precipitation hardening in terms of strength and contributes to strength improvement, it is desirable that 30% or more of the total amount of Ta is precipitated as TaC. The amount of Ta deposited as TaC can be measured by quantitatively analyzing the electrolytic extraction residue collected by the constant current electrolysis method.

  Furthermore, Nb 94 having a long half-life produced by neutron absorption is produced and Nb94 is problematic in handling, so Nb is suppressed to the extent that it is included as an inevitable impurity.

2. About average grain size number
Furthermore, in the high corrosion resistance high strength stainless steel according to the present invention, it is desirable that the tensile strength at 100 ° C. is 470 MPa or more as a material constituting the reactor.
In order to achieve this strength requirement, it is necessary to form a fine crystal structure having an austenite average grain size number defined by JIS G 0551 of 10.0 or more. However, if the growth of crystal grains is suppressed too much, a non-uniform mixed grain structure tends to be formed. Therefore, an average crystal grain size number of 13.0 or less is realistic in terms of manufacturing method.

  Hereinafter, a method for producing a high-corrosion-resistant high-strength stainless steel for forming such a fine crystal structure having an average grain size number of 10.0 to 13.0 will be described.

  First, C is 0.04 mass% or less, Mn is 1.0 to 2.0 mass%, Ni is 9.0 to 13.0 mass%, Cr is 17.0 to 20.0 mass%, Ta is C An austenitic stainless steel having a chemical composition comprising 0.50 to 0.65% by mass at 13 times or more, the balance being Fe and inevitable impurities including Nb is prepared.

Next, the prepared austenitic stainless steel is subjected to solution heat treatment at 1050 ° C. to 1150 ° C. for 1 minute to 60 minutes, and then water-cooled.
In order to obtain a homogeneous solid solution structure in stainless steel, solution heat treatment is required at a temperature of 1050 ° C to 1150 ° C. Further, although it is necessary to adjust the conditions depending on the thickness of the material, it is appropriate to perform solution heat treatment for 1 minute to 60 minutes.

Cold rolling with a rolling rate of 30% to 80% is performed on the stainless steel after the solution heat treatment.
The average grain size number of austenitic stainless steel is generally less than 10.0. Therefore, in order to form fine crystals with an average grain size number of 10.0 or more, first, cold processing is performed to increase the number of recrystallization nucleation sites in the crystal grains of the original material after solution heat treatment. It is necessary to introduce dislocations to cause large plastic deformation. However, if the rolling rate is too large, the construction efficiency decreases. On the other hand, when the rolling rate is low, the subsequent aging heat treatment has insufficient sites for recrystallization, so that the recovery of dislocations can be suppressed, and the coarsening of the grains is caused by the introduced processing dislocations as the driving force. There is concern. Considering the above factors, the cold rolling rate is 30% to 80%.

Next, after this cold rolling, an aging heat treatment is performed at 850 ° C. to 1050 ° C. for 30 minutes to 120 minutes, and air cooling is performed.
In order to eliminate the dislocations generated by the previous cold rolling by recovery and promote recrystallization, it is necessary to perform an aging heat treatment at 850 ° C. to 1000 ° C. for 30 minutes to 120 minutes and air-cool.
The aging heat treatment also has a role of stabilizing the precipitation of TaC.

  Hereinafter, with reference to Examples 1-4, it demonstrates that a stainless steel of this invention is a material which has a favorable characteristic, showing a specific example.

(Example 1 and Comparative Example 1)
First, specimens having the chemical composition (mass%) shown in Table 1 were prepared by vacuum melting.
No. All the materials 1 to 4 were subjected to solution heat treatment at 1050 ° C. for 30 minutes and water cooling after hot rolling.
Further, in order to examine the influence of the Ta content, a No. 1 content of Ta of 0.65% by mass or more was used. 5, no. No. 6 two types of prototype materials (comparative materials) were prepared. 1-No. Solution heat treatment was performed under the same conditions as in the material No. 4.
No. 10 is a commercially available SUS316L prepared as a comparative material. 11 is SUS304L as a comparative material.

In order to examine the appropriate range of the cold rolling rate, No. Several plate material test pieces were prepared from one material, and each was subjected to solution heat treatment.
Then, after performing cold rolling with a rolling rate of 25%, 35%, 50%, and 75%, aging heat treatment was performed at a temperature of 950 ° C. for 120 minutes. After the aging heat treatment, the crystal grain size distribution was measured by an electron backscatter diffraction method (hereinafter referred to as EBSD). FIG. 1 shows the measurement result at a rolling rate of 25%, FIG. 2 shows the measurement result at a rolling rate of 35%, FIG. 3 shows the measurement result at a rolling rate of 50%, and FIG. 4 shows the measurement result at a rolling rate of 75%.
The EBSD measurement was performed using an orientation microscope (OIM) manufactured by TSL, which was attached to an FE-SEM (S-4300SE) manufactured by Hitachi High-Technology. The measurement area was 1 × 1 mm and measurement step = 2 μm. 1 to 4, the horizontal axis is the crystal grain size, and the vertical axis is the ratio of the total number of crystals, that is, the frequency of the grain size. The distribution range of the crystal grain size number corresponding to the crystal grain size of each test piece and the average crystal grain size number were calculated.
The average grain size number G is represented by the following formula (1) according to the definition of JIS G 0551. In the formula (1), m is the number of crystals per 1 mm ² cross-sectional area.

  Therefore, when the crystal grain size is d, m can be expressed by the following formula (2). The unit of d is μm. That is, the smaller the crystal grain size d, the larger the average crystal grain size number G.

  Based on the above formulas (1) and (2), the average grain size number was calculated according to the method of JIS G 0551. Table 2 summarizes the crystal grain size and the average grain size number under each rolling rate.

As shown in FIG. 1 and Table 2, the crystal grain size of the test piece having a rolling rate of 25% was distributed in a wide range of 2.5 μm to 80 μm, and it was found that the uniformity of the structure was low. This is presumably because rolling was insufficient and non-uniform recrystallization occurred due to dislocation sites.
On the other hand, the crystal grain sizes of the test pieces at the rolling rates of 35%, 50%, and 75% shown in FIGS. 2 to 4 and Table 2 are distributed over a small range of 0.5 μm to 30 μm as a whole. It was found that tissue uniformity appeared.
From the result of the above average grain size number, in order to obtain stainless steel having an average grain size number of 10.0 to 13.0, it is considered that a rolling rate of 30% or more is necessary. Considering the actual production efficiency and the distribution of crystal grain size shown in FIGS. 2 to 4, it is expected that the operability is better when the rolling rate is 80% or less, and the efficiency with which fine crystals are obtained. Can be maintained high.

  Based on the above results, it was found that the optimum construction range for cold rolling was a rolling rate of 30% to 80%.

(Example 2 and Comparative Example 2)
Furthermore, in Table 1 of Example 1, the No. of the material of the present invention. Several plate specimens were produced from the three materials, and 50% cold-rolled after solution heat treatment. Then, it fixed at the temperature of 900 degreeC and 1000 degreeC, and implemented the aging heat processing which changed time from 10 minutes to 150 minutes. Cooling after aging heat treatment was air cooling. Thereafter, the average grain size number of each test piece was measured. FIG. 5 shows the change in the average grain size number in the aging heat treatment at 900 ° C. for 10 minutes to 150 minutes after 50% cold rolling. For comparison, No. 1 was subjected only to solution heat treatment and not subjected to aging heat treatment. An average grain size number of 1 was measured. The result is represented by a plot of the heat treatment time of 0 minutes in FIG.

As shown in FIG. 5, when the aging heat treatment time was between 10 minutes and 30 minutes, the average crystal grain size number tended to increase as the heat treatment time increased. This is because recrystallization has not been completely completed in a short-time heat treatment of 30 minutes or less, and a fine crystal and a coarse crystal of the original material are mixed to form a non-uniform microstructure. Conceivable.
On the other hand, it was found that when the aging heat treatment time was between 30 minutes and 120 minutes, the average grain size number was constant at approximately 12.5 and a stable microstructure was obtained.
However, when the aging heat treatment time was between 120 minutes and 150 minutes, the growth of crystal grains was accelerated by the aging heat treatment, and the average grain size number became smaller than 10.0, and a tendency to decrease was exhibited.

  Further, as shown in FIG. 5, in the heat treatment at 1000 ° C., the average grain size number tended to be lower than 900 ° C., but if the heat treatment time was between 30 minutes and 120 minutes, the average of 10.0 or more It was found that the grain size number could be maintained.

  From the above results, the average grain size number is 10.0 to 13.0 and uniform by performing air-cooling after performing aging heat treatment at a temperature near 900 ° C. for 30 minutes to 120 minutes after cold rolling. It was found that an austenitic high corrosion resistance high strength stainless steel having a fine crystal structure can be produced.

(Example 3 and Comparative Example 3)
No. 1 of the present invention material in Table 1 of Example 1. The material 1 was subjected to 50% cold rolling after the solution heat treatment, and further subjected to air-cooling aging heat treatment at a temperature of 850 ° C. to 1050 ° C. for 120 minutes. FIG. 6 shows the average grain size number at each temperature.

As shown in FIG. 6, it was found that in the temperature range of 850 ° C. to 1000 ° C., no significant decrease in the average grain size number appeared, and the crystal grain size was good.
However, it has been found that when the temperature is higher than 1000 ° C., grain growth after recrystallization is promoted, and the average grain size number decreases.
From the above results, a fine crystal structure having an average grain size number of 10.0 to 13.0 is formed in stainless steel having the chemical composition of the present invention by aging heat treatment at a temperature of 850 ° C. to 1000 ° C. for 120 minutes and air cooling. I knew it was possible.

(Example 4 and Comparative Example 4)
The material of the present invention is mainly applied to structures used in a nuclear reactor. In addition, some materials used for structures used in nuclear reactors may require high strength. For this reason, the mechanical properties of 0.2% proof stress at least at 100 ° C. are 175 MPa or more and tensile strength is 475 MPa or more.
Therefore, No. of the material of the present invention in Table 1 of Example 1 subjected to aging heat treatment at 900 ° C. for 120 minutes and air cooling after 50% cold rolling. Ten to four materials were subjected to a tensile test at 100 ° C. to obtain mechanical properties. For comparison, no cold rolling and no aging heat treatment were performed, and no solution No. was subjected to only solution heat treatment. 1 and comparative material No. Ten SUS316L was also subjected to a tensile test under the same conditions. The number of repetitions of all tensile tests was 2. FIG. 7 shows an average value of 0.2% proof stress of each material at 100 ° C., and FIG. 8 shows an average value of tensile strength of each material at 100 ° C.

As shown in FIGS. 7 and 8, both the 0.2% proof stress and the tensile strength of the material of the present invention are higher than those of SUS316L, which is a comparative material. In particular, no. For No. 1, 0.2% proof stress and tensile strength satisfy the required values even with only solution heat treatment. However, there is almost no margin.
On the other hand, No. 1 was subjected to cold rolling and aging heat treatment after solution heat treatment. The materials 1 to 4 have a tolerance of 100 MPa or more from each required value in 0.2% proof stress and tensile strength, can be satisfied with a high safety factor design considering probability theory, and have practicality Expected enough. From the above results, in order to satisfy the tolerance required for the design considering the probability theory, the solution heat treatment and cooling under the above-mentioned conditions are applied to the stainless steel having the chemical composition of the present invention shown in Table 1. It was found that the average grain size number needs to be 10.0 or more by performing hot rolling and aging heat treatment.

Next, crevice corrosion characteristics in high-temperature and high-pressure water were evaluated.
No. 1 of the present invention material in Table 1 of Example 1. 1 to 4 and the prototype No. 5, no. Two strip test pieces each having a length of 10 mm, a width of 50 mm and a plate thickness of 1.5 mm were collected from No. 6 (12 sheets in total), and the surface was finished to 600 with water-resistant abrasive paper. The test pieces 1 made of the same material were faced to each other as shown in FIG. For comparison, the same manufacturing method as that for the material of the present invention was used. 10 SUS316L and no. Four strip test pieces (total 8 pieces) were prepared from 11 SUS304L, and two test pieces 1 of the same material were joined by spot welding 2. Thereby, a gap was formed between the two test pieces.
These test pieces were left in an environment of 288 ° C., dissolved oxygen concentration of 8 ppm, conductivity of 1.0 to 1.2 μS / cm ² and γ-ray dose rate of 20 kGy / h, and a 1000 hour immersion test was performed. After the immersion test, the specimen was cut at the center of the specimen parallel to the longitudinal direction of the specimen, and the corrosion state of the cross section was observed. The maximum depth of intergranular corrosion of each test piece is shown in FIG. 10, and the number of corrosion locations is shown in FIG.

As shown in FIG. 10 and FIG. 11, intergranular corrosion was observed in all materials.
In FIG. 10, SUS316L as a comparative material has a maximum corrosion depth of more than 130 μm for all four test pieces, and SUS304L has an average maximum corrosion depth of about 100 μm. Observed.
On the other hand, the present invention material No. In Nos. 1 to 4, the intergranular corrosion depth in each test piece was less than 60 μm at the maximum and 35 μm on average, which was about 1/3 or less of SUS316L and about 1/2 or less of SUS304L, respectively.

Furthermore, in FIG. 11, the number of locations of intergranular corrosion of SUS316L was 75 on average for each test piece, and SUS304L was 52 on average for each test piece.
On the other hand, this invention material No. 1 to 4 averaged 17 locations for each test piece, which were about ¼ or less of SUS316L and ½ or less of SUS304L, respectively, and were found to have good corrosion resistance.
On the other hand, prototype material No. with increased Ta content was obtained. 5 and no. In the test piece of No. 6, the intergranular corrosion depth shown in FIG. However, the number of corrosion locations shown in FIG. It became about 1.5 times that of the present invention material of 1-4, and it was found that if the Ta content is too high, the corrosion density tends to increase.
From the above results, it was found that the material of the present invention has better crevice corrosion resistance than ordinary austenitic stainless steel. It was also found that the Ta content should be 0.65% by mass or less in order to reduce the intergranular corrosion density.

(Example 5)
The high-corrosion-resistant high-strength stainless steel described above can be used for a reactor internal structure irradiated with 0.5 × 10 ²¹ n / cm ² or more of neutrons having an energy of 0.1 MeV or more.

  The case where the high corrosion resistance high-strength stainless steel of Example 1 is used for a control rod having the fastest neutron irradiation damage rate among reactor internal structures and equipment will be described below.

FIG. 12 shows a control rod using boron carbide as a neutron absorber.
The control rod mainly includes a roller 3, a cooling hole 4, a neutron absorption rod 5, a sheath 6, a connector 7, a connector socket 8, a handle 9, and a tie rod 10. For these, the high corrosion resistance and high strength stainless steel described in Example 1 is used.

  Since the control rod has a gap, there is a possibility of crevice corrosion, and there is also a possibility of generating irradiation-induced stress corrosion cracking. Therefore, by using the high corrosion resistance high strength stainless steel of the present invention, which is excellent in crevice corrosion resistance and stress corrosion cracking resistance and also effective in suppressing irradiation damage, control rod crevice corrosion and radiation induced stress corrosion cracking. This makes it possible to provide a long-life and highly reliable control rod.

  In addition, since the high corrosion resistance high strength stainless steel of the present invention can be manufactured as members of various shapes such as rods, thin plates, tubes, etc., not only control rods using boron carbide but also hafnium is used for neutron absorbers It can also be applied to control rods.

In addition, austenitic stainless steels conventionally used in nuclear reactors cause irradiation-induced stress corrosion cracking when neutrons having an energy of 0.1 MeV or more are irradiated by 0.5 × 10 ²¹ n / cm ² or more. May occur.
Therefore, not only control rods, but also reactor internal structures and equipment, such as boiling water reactor core shrouds, upper lattice plates, core support plates, pressurized water reactor baffle plates, former plates, baffles, By using the austenitic stainless steel of the present invention for former bolts, a nuclear reactor and a nuclear power plant having excellent long-term reliability can be obtained.

  In addition, this invention is not restricted to said embodiment, A various deformation | transformation and application are possible.

1 ... crevice corrosion test piece,
2 ... Spot weld,
3 Roller
4 ... cooling holes,
5 ... Neutron absorber rod,
6 ... sheath,
7 ... Connector,
8 ... Connector socket,
9 ... handle,
10 ... Tie rod.

Claims (5)

C: 0.04 mass% or less, Mn: 1.0 to 2.0 mass%, Ni: 9.0 to 13.0 mass%, Cr: 17.0 to 20.0 mass%, Ta: 13 of C It contains 0.50 to 0.65% by mass at least twice, and the chemical composition composed of inevitable impurities including Fe and Nb in the balance,
An austenite average grain size number specified in JIS G0551 is 10.0 to 13.0. A high corrosion resistance and high strength stainless steel. In the high corrosion resistance high strength stainless steel according to claim 1,
The high corrosion resistance high strength stainless steel has a 0.2% proof stress at 100 ° C. of 175 MPa or more and a tensile strength of 475 MPa or more. A reactor internal structure disposed inside the nuclear reactor,
The high-corrosion-resistant high-strength stainless steel according to claim 1 or 2 is used for the reactor internal structure irradiated with 0.5 × 10 ²¹ n / cm ² or more of neutrons having energy of 0.1 MeV or more. Characteristic reactor internal structure. In the nuclear reactor structure according to claim 3,
The reactor internal structure is a control rod. C: 0.04 mass% or less, Mn: 1.0 to 2.0 mass%, Ni: 9.0 to 13.0 mass%, Cr: 17.0 to 20.0 mass%, Ta: 13 of C 1 to 60 minutes at 1050 ° C. to 1150 ° C. with respect to the austenitic stainless steel having a chemical composition comprising 0.50 to 0.65% by mass and the balance being inevitable impurities including Fe and Nb Performing a water-cooled solution heat treatment;
A step of performing cold rolling at a rolling rate of 30% to 80% after the solution heat treatment;
A step of performing an aging heat treatment at 850 ° C. to 1050 ° C. for 30 minutes to 120 minutes after the cold rolling;
And a step of air-cooling after the heat treatment. A method for producing a high corrosion-resistant high-strength stainless steel.

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