JPS61291948A - Production of metallic material for nuclear reactor - Google Patents

Abstract

PURPOSE:To obtain a metallic material which can effectively prevent the generation of the creep embrittleness occurring in <10>B of a metallic material for a nuclear reactor which receives thermal neutron irradiation by preliminarily adding B-contg. raw material of which the quantity ratio <11>B(<10>B+<11>B) of the isotope <11>B of B is higher than the natural existence ratio to said material and subjecting the material to de-B refining. CONSTITUTION:The cause for the creep embrittleness by the thermal neutron irradiation lies in that He is generated by the reaction of <10>B in particular among the isotopes of B, i.e., <10>B(n,alpha)<7>Li reaction. In contrast therewith, <11>B is stable and does not induce the nuclear reaction to form He. The <11>B is there upon added positively to the metallic material such as carbon steel, low Cr-Mo steel or ferrite chromium steel in the process for producing such material in this invention. The quantity ratio of the <10>B in the total B(=<10>B+<11>B) contained in the molten metal, i.e., <10>B/(<10>B+<11>B) is thereby decreased and thereafter the molten metal is subjected to the de-B refining. As a result, the generation of the creep embrittleness occurring in the <10>B of the above-mentioned metallic material is effectively prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to nuclear reactor constituent materials subjected to neutron irradiation, for example, metal materials used as reactor vessel materials such as fast breeder reactors and light water reactors, especially trace amounts of boron (B). metal materials containing, such as carbon steel, low chromium molybdenum (Cr-Mo
) l! ! The present invention relates to a method for producing metal materials such as ferritic high chromium steel, stainless steel, and superalloys.

As is well known in the art, PA is a low carbon steel for reactor pressure vessels.
For example, A S T M 71 case A 533 B c
lass month 1. A308 class 3jg etc. are used. On the other hand, low Cr-MO steel, ferritic high chromium steel, and ferritic stainless steel are cheaper than austenitic stainless steel, and have superior properties than austenitic stainless steel. Application of steel for reactors, especially fast breeder reactors or nuclear fusion reactors, is being considered. Furthermore, since superalloys such as Inconel and Incoloy have excellent heat resistance and oxidation resistance, their application to nuclear reactor materials, particularly nuclear fusion reactors, is being considered.

On the other hand, austenitic stainless steel has been traditionally used as various constituent materials in nuclear reactors due to its excellent high-temperature strength and corrosion resistance, and is particularly used as reactor vessel material for fast breeder reactors and light water reactors that are subjected to thermal neutron irradiation. Its use is planned.

By the way, in the case of austenitic stainless steel, for example, the
As disclosed in Publication No. 9, etc., the addition of B makes carbides finer and more stable, suppresses grain boundary precipitation of carbides, strengthens grain boundaries, and improves strength, ductility, and workability. It is known to have an improving effect.

□ Problems to be solved by the invention As mentioned above, B for austenitic stainless steel
The addition of is effective from the viewpoint of grain boundary strengthening, but on the other hand, there are problems.

That is, in general, 8 is composed of two types of isotopes 1013.113, and the natural abundance ratio of To 3 is 19.6.
%, ++ (3 is about 80.4%, but among these isotopes, +oB has a particularly large absorption of thermal neutrons, so austenitic stainless steel containing 8 is used in reactor vessel materials etc. that are subjected to thermal neutron irradiation. When using 10
Even with relatively mild thermal neutron irradiation of n/C1r, 10B
(n, α)7Li nuclear reaction occurs and the OB collapses, and as a result, He generates gas, which promotes the generation and propagation of creep cracks and causes creep embrittlement.

Furthermore, even in austenitic stainless steels in which B is not added in a cumulative manner, austenitic stainless steels obtained through normal steelmaking processes contain at least several CDI of B; Even if it contains 103 (1, α
) Creep embrittlement may occur due to the 7Li reaction.

Furthermore, B should not be added to metal materials other than austenitic stainless steel, such as the aforementioned carbon steels, low Cr-Mol, ferritic high chromium steels, ferritic stainless steels, or superalloys. Even in cases where 8 is actively added, the metal material obtained after the smelting process usually contains at least several ppl of 8 as an impurity, and if 8 is actively added, even more B.
Contains. In these cases, as already explained for austenitic stainless steel, "B"
(n, α) 7Li nuclear reaction causes 10 [3 to decay, resulting in) 1e gas to be generated, and its 1-18
causes creep embrittlement.

This invention was made against the background of the above circumstances, and B.
Creep caused by +oB occurs when a gold-3 material containing 8 is used as a reactor constituent material that is subjected to thermal neutron irradiation, regardless of whether it is a metal material that actively adds B or simply contains B as an impurity. It is an object of the present invention to provide a method for manufacturing a metal material that can effectively prevent the occurrence of embrittlement.

Means to Solve the Problem As already mentioned, the cause of creep embrittlement due to thermal neutron irradiation is the reaction of B to B, that is, the 1- 1e, whereas ++3 is stable and does not cause He generation nuclear reaction. Therefore, in this invention, carbon steel, low Cr
- In the manufacturing process of metal materials such as MOm, ferritic high chromium steel, ferritic stainless steel, austinitic stainless steel, or superalloy, stable II 39 can be actively added to the molten metal in advance. 103 out of all B (-”B+”B) included
By lowering the 10B ratio, that is, B/ (B + +IB), and then performing B-refining, the absolute - target total daily amount (=+oB++IB) will not change, but problems will arise due to thermal neutron irradiation. This made it possible to obtain a metal material with a low ratio of .

That is, in the method for producing a metal material for a nuclear reactor of the present invention, when producing a boron-containing gold material for a nuclear reactor used in an environment subjected to thermal neutron irradiation, the isotope I of B is prepared in advance.
+ 13 in the amount ratio 11B/('O8+ ``B'') higher than the natural abundance ratio - element-containing raw material is added, and then 1!
03 content is reduced.

Detailed Description for Practical Flow of the Invention In the method of the present invention, the quantity ratio of II B, that is, ++ 3 / (+0
ra where the value of 3 + ++ 3) is higher than the natural abundance ratio
81 raw materials containing elemental gold are added in advance. That is, the natural abundance ratio of the isotope 10[3,,118 of 8 is, as already mentioned, 108:19.6%, II B: 80.
4%, a boron-containing raw material containing B containing more than 80.4% of B, such as Fe-8 alloy, boron oxide (8203), and WAR (83803), is added. However, in the actual process, Fe
The quantitative ratio of the isotope nB of 8 in the boron-containing raw material such as -B alloy is desirably 90% or more from the viewpoint of manufacturing cost and the effect of preventing creep axis formation after thermal neutron irradiation. In other words, 90% or more of n B and 10% of +o
It is desirable to add a boron-containing raw material composed of B.

Such boron-containing raw materials are used in the process of smelting the target metal material. It may be added before RB is performed. That is, generally carbon steel, low Cr-MOWA
For smelting of ferritic high chromium products, stainless steels, or superalloys, smelting is performed by preliminary molten metal treatment, and then rough decarburization is performed in a converter or electric furnace.
It is usually produced by vacuum decarburization in an OD furnace, RH degassing tank, or AOD furnace, and in some cases, only the steps after the electric furnace of the above steps are used. In those cases, B removal proceeds along with decarburization, so
The boron-containing raw material may be added during pretreatment of hot metal, during rough decarburization in a converter or electric furnace, or added together with smelting raw materials or alloy raw materials before the start of rough decarburization,
Further, depending on the case, it may be added to the molten metal before vacuum decarburization.

In this way, the 1 ratio of I + 3 “B/ (”B + ”B
) is higher than the natural abundance ratio, by actively adding B-containing raw materials containing 111 elements, the ratio of ``B/ (``B + ``B)'' to the total amount of elements contained in the molten metal. The amount of the W4 element-containing raw material to be added should be determined when the effect of adding B is not expected in the final product (that is, when B remains only as an impurity). , should be determined according to the 1laB rate in de-smelting, and if the final product is expected to have the effect of adding 8 such as grain boundary strengthening as described above, the target remaining JIB amount and !!2B It may be determined according to removal 81 in smelting.

In de-B smelting, as is clear from the examples described later, although the total amount of 81 remaining in the molten metal decreases,
The proportion of isotope I+ 3°10 B in the residual B remains unchanged. Therefore, after B-free production, a metal material is obtained in which all 81 has been reduced to the required concentration and the amount ratio of B in the residual B is higher than the natural abundance ratio "B/'("B + "B)". In other words, this metal material can be
Behind isotopes 113 and 103 in residual B, thermal neutrons @
The amount ratio of the isotope +03, which reacts with radiation and causes creep embrittlement, is lower than the natural abundance ratio, so compared to conventional metal materials with the same total residual B content, the content of This means that l will be less.
As a result, the risk of creep embrittlement due to thermal neutron irradiation can be reduced compared to conventional metal materials.

In addition, when smelting steel such as stainless steel or low carbon steel, II! Fe5i (ferrosilicon), FeMn (ferromanganese), SiMn for the purpose of
(silicon manganese), etc., but in that case, it is normal that these additive raw materials also inevitably contain B, so considering the reach B gate of IB2B smelting invasion, It is desirable to use additive raw materials containing as little 8 and 1 as possible.

Furthermore, it goes without saying that the m81 building is not limited to smelting only once, but may be smelted twice or more, thereby reducing the 10B by -1.

Examples [Example 1] First, an example of the present invention applied to the production of austenitic stainless steel will be described together with a comparative example.

wt% co, os%, 3i 0.50%, Mnl
, 00%, p 0.020%, 3 o, ooe%, Ni
5tJS 30 consisting of 9.0%, Cr18.3%, Bo, ooos%, and the balance consisting of Fe and inevitable impurities.
When manufacturing 4 steel by vacuum decarburization that also serves as rough decarburization in a converter and decarburization in a VOD furnace, the on-site manufacturing conditions are 4! Simulated small experiment fJ! [The following (A>, (
B-removal smelting was performed under the three conditions shown in B) and (C).

In addition, 8 content as an impurity in molten iron before smelting (to)
In either case, 101)D! It is.

(A) B5pp without adding any boron-containing raw materials! B-free smelting was carried out up to (11f!1ll).

(B) 80%Fe-20%B alloy in which the amount of B (“B+”B) is the natural abundance ratio (approximately 80%),
Add 101)p in ENI and 1i12 until B5pp injection
B smelting was performed (Comparative Example 2).

(C) The natural abundance ratio (
80% Fe-2 which is 98% higher than 80%
A 0% B alloy was added at a daily rate of 40 op-p, and B-removal smelting was carried out to B5 pp (Example 1a of the present invention).

(D) Same 80% Fe as used in (C) above
-20B alloy is added in B amount of 501)11m, B
De-8 smelting was carried out to 45 ppl (Example 1 of the present invention).
b).

In either case, samples were taken at any time from the start to the end of the B removal smelting, and the total daily amount and 10B amount (10 days + 11B) were measured. The results are shown in FIGS. 1 and 2.

FIG. 2 particularly shows the cases of Comparative Example 1 in which no boron-containing raw material was added and Comparative Example 2 in which a boron-containing raw material was added with a natural abundance ratio of to B.
In the case of
It only decreased from pm to 5 ppm, and the amount of B (
``B + +'B ) f) value during smelting 1111 was constant at approximately 0.2, which is the natural abundance ratio.In addition, in the case of Comparative Example 2, 81 was smelted by adding B before B removal smelting. 2 at the start of training
0111)■, and finally decreased to 51)Ill, but the added B is ++3/(+03+I+ 3
) is the natural abundance ratio, so 10B/
The value of (10B + IIB) was approximately constant at 0.2.

On the other hand, in Fig. 1, the quantity ratio of II B is 11B, / (+03
+1113) value is much higher than the natural abundance ratio9
This figure shows the cases of Examples 1a and 1b of the present invention in which a boron-containing raw material containing 8% B was added, and in this case, the addition of the boron-containing raw material increased the l ratio of 103+'B/ at the start of B removal. (IOB + IIB) becomes 0.05, and the amount ratio of 10B is kept almost constant throughout the subsequent complete B-removal WJ, and finally the IOB sinking is 0.05, which is the same as in Comparative Examples 1 and 2. We were able to obtain significantly less austenitic stainless steel than would otherwise be possible.

In Example 1 above, de-B smelting was shown as a laboratory example, but this does not particularly limit the gil method. ,Electric furnace,
De-B in VOD furnace, AOD furnace, RH degassing tank, etc.
Of course, everything is applicable, including smelting.

Furthermore, in the above Example 1, 80%Fe-20%B was used as a boron-containing raw material to reduce the IOB quantity ratio.
Although an alloy is used, it goes without saying that the same effect can be obtained by using other boron-containing raw materials such as ferroboron.

[Example IM 2] Next, an example in which the method of the present invention is applied to the production of low carbon steel will be described together with a comparative example.

When smelting low carbon steel with the target component compositions shown in A and B in Table 1 in accordance with the conventional method, a boron raw material enriched in oB compared to the natural abundance ratio is added at the final stage of smelting, and then the boron is removed. Performed smelting. Table 2 shows the t in molten iron before tI manufactured by plAB.
o B @, increase Bf during dissolution due to added boron raw material
l and its II3 amount ratio in the added boron raw material, i.e., the amount of B ('B+ +'B), the IOB ratio immediately after addition of the boron raw material Fl, the total 81 of the removal of 81, and the +oBl ratio, that is, +O8/
(108+ IIB), "B" is also shown. In Table 2, i (α5 and Ni7 are comparative examples in which one raw material was not added according to the conventional method, and Nα6 is II 13 This is a comparative example in which one raw material with a natural abundance ratio was added.

As clearly shown in Table 2, according to the method of this invention,
The total B content in the steel after de-8 refining is almost the same as that of the comparative example in which no ferrous raw material was added and the comparative example in which the natural abundance ratio of boron was added, but the +oB content ratio was 103 in low carbon steel.

[Example 3] Next, an example in which the method of the present invention was applied to the production of low Cr-MO steel and ferritic high chromium steel will be described together with a comparative example.

When smelting according to the conventional method to achieve the target component compositions shown in C, D, and E in Table 3, a boron raw material enriched with II8 than the natural abundance ratio is added at the final stage of smelting, and then WA8
I had fun. Table 4 shows the amount of to in molten iron before B-free smelting.
B @, added! ! The increase in 8M in molten steel due to the raw material and the II Bm ratio in the added boron raw material, that is, 118/
(IOB+”B), boron raw material addition directly! (7) 108
After 11QBtjM (7) Total Bl 1081 ratio i.e. 1
037 (+03 10t+3) and 103 mother are also shown. In Table 4, Na7, No. 9, and Sho 10 were prepared according to the conventional method, and N11L8 was a comparative example in which no raw material was added. This is a comparative example.

As is clear from Table 4, according to the method of this invention,
The total Bfl in the steel after de-Japanese smelting is almost the same as that of the comparative example in which no boron raw material was added and the comparative example in which a boron raw material with a natural abundance ratio of +113 was added, but the +03ffl ratio was significantly reduced. , +03 Absolute Detective has also decreased significantly,
Therefore, it can be seen that the method of the present invention is effective for reducing +oB of low Cr-Mo'IA and ferritic high chromium steel.

[Example 4] Further, an example in which the method of the present invention is applied to the production of a superalloy will be described together with a comparative example.

When smelting Incoloy 800H alloy and Inconel 625 alloy with the target component compositions shown in Table 5, an N raw material enriched with nB than the natural abundance ratio is added to the T'# end shoulder, and then B is removed. Performed smelting.

Table 6 shows the increased Bfi in the molten steel due to TOB@ in the alloy molten metal before removal of 8'lll, the added:IN raw material, and the II 3 in the added steel raw material, i ratio, ``B/('OB+
11B), 10B after IIIJtl addition VX, Theory 8
Total Bj after refining, + OB bottle ratio, IQ 13 /
(Io 3 + IT 3), "aB" is also shown. tB is 6 in Table 6 and magic 5 is added [) α7 is according to the conventional method and does not add 1 Sakuharai to C-mochi. Comparative example, N
α6 is 113 ii ratio is natural abundance ratio r, Ri elemental 1;
This is a comparative example of six bottles.

As is clear from Table 6, according to the method of this invention,
Made by IAMB? The total daily amount in the alloy after II is the comparative example in which no allotropic raw material is added and II.3.31 ratio is f of the natural abundance ratio.
α is almost the same as that of the comparative example in which one elemental material was added, but 10
3 The quantity ratio has decreased significantly! The absolute value of 1 in OB is also significantly reduced.2 Therefore, the method of the present invention
It can be seen that this method is also effective in reducing 0B.

In each of Examples 1 to 4 above, austenitic stainless steel, low CI'-Mail, ferritic chrome steel, and superalloy were shown, but metal materials such as ferritic stainless steel and martensitic stainless steel It goes without saying that this invention is also effective when applied to stainless steel edges.

Effects of the Invention As is clear from the examples described above, according to the method of the present invention, the abundance of +03, which causes a nuclear reaction that causes creep embrittlement when exposed to thermal neutron irradiation, is lower than that of conventional metals. It is possible to obtain a metal material n lower than that of the material. In other words, according to the method of the present invention, B-containing metal materials with little risk of creep embrittlement even when subjected to thermal neutron irradiation can be produced. This makes it possible to apply metal materials with grain boundary reinforcement, etc., and at the same time, it also becomes possible to prevent the risk of creep embrittlement due to thermal neutron irradiation even for metal materials that contain B only as an impurity.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the changes in the amount of B in molten iron and OB/ (+OB+ ll8) in B-removal smelting in Example 1 of the present invention, and Fig. 2 is a graph showing the changes in B content in molten iron and OB/(+OB+ ll8) in Comparative Example 1 and Comparative Example 2 using the conventional method. BIi and “B/” in molten iron in de-B smelting
It is a graph showing the transition of (IOB+I'B).

Claims (1)

[Claims] When smelting metal materials for nuclear reactors used in a neutron irradiation environment, the amount ratio of B isotope ^1^1B is determined in advance.
A method for producing a metal material for a nuclear reactor, which comprises adding a boron-containing raw material having a boron content of 1^1B/(^1^0B+^1^1B) higher than the natural abundance ratio, and then smelting the boron-free material.