JPS58174538A - Ni-based alloy member and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain the Ni-based alloy member excellent in proper stress corrosion cracking resistance and esp. useful as a spring or the like for a nuclear reactor, by letting the alloy comprise the specified amount of each of Cr, Fe, Al, Ti and Nb, and the balance Ni and have a precipitation-strengthened primary recrystallized structure. CONSTITUTION:The Ni-based alloy member comprising, by wt., 14-25% Cr, Fe<=30%, 0.2-2% Al, 0.5-3% Ti, 0.7-4.5% Nb and the balance Ni. By cold- working this Ni-based alloy member with the ratio of sectional reduction above 25%, for instance, between solution treatment and double-stage aging treatment, a spring or bolt for a nuclear reactor further improved in its crevice corrosion resistance and stress corrosion cracking resistance (resistance to SCC) can be manufactured.

Description

[Detailed description of the invention] Concerning Nokuku.

Conventional nuclear reactor springs have been produced mainly by subjecting the springs to solution treatment after melting, cold rolling to 30% to 40% processing, and then subjecting them to aging treatment. These are the ninth manufacturing methods that ensure the high-temperature strength and K spring characteristics required for nuclear reactor spring materials through cold working and aging, but they are difficult to manufacture in the gaps, which are particularly problematic when applied to actual equipment. A shortcoming is that stress corrosion cracking resistance (hereinafter referred to as SCC resistance) has not always been sufficiently studied.

In particular, springs for nuclear reactors (e.g. C of BWR control rod drive mechanism)
Spring) are often used in locations where gaps are formed under high stress, and SCC countermeasures are important. Currently, 9 Inconel (trade name) x 750, which has high strength and high corrosion resistance, is used as springs for nuclear reactors, and most of them are treated with 30-40% cold steel after solid solution treatment. It is manufactured using an aging process (direct aging). The purpose of cold working after solution treatment is to refine the crystal grains, but on the other hand, aging treatment that follows cold working with koji mold is used for spring materials for nuclear reactors. This contributes to improving strength.

However, between solid solution treatment and aging treatment, 30 to 40%
Even if cold working is applied, 30 to 40% of cold working is a practical problem.It has excellent clearance SCC property.8 Excellent CC property and 9N.
f! I-based alloy members and their manufacturing method. The purpose is to provide

The present inventors changed the degree of cold working carried out between the solution treatment and the aging treatment, and investigated the effect of the degree of cold working on the gap SCC resistance using constant strain tests with gaps in high-temperature, high-pressure pure water. This was investigated from both aspects of microscopic tissue observation. At the same time, a similar study was conducted regarding prescription cases (direct prescription and two-stage prescription). As a result, we discovered the following new facts. (2) If 10 to 30% cold carroe is applied between the solution treatment and the direct aging treatment, the gap SCCCC sensitivity is shown to be good. However, if 60% cold working is performed, the gap SCC resistance is improved, but in this case, it is difficult to determine the magnitude of the gap SCC susceptibility from the metal structure. ■If 10 to 20% cold working is performed between solution treatment and two-stage aging treatment, the gap SCC susceptibility is noticeable, but if the cold working exceeds the reference %, the gap SCCCC will increase. gender gradually decreases. In this case, the relationship between the cold work degree and the gap 8CC sensitivity can be easily determined from the metallographic structure. That is, in the case of cold working of 0% or more, where the gap SCC susceptibility is significantly small, -Kuki crystal grains are observed, whereas in the case of 10, where the gap SCC susceptibility is large.
This was not observed in ~20% cold working.From this, it was discovered that the SCC generation mechanism of the high-temperature underwater gap 8CC that occurs in the two-stage aged material is different from that in the directly aged material. .

The present invention has been made based on such knowledge, and the first invention is based on 14 to 25% of Cr and Fe of 14 to 25% by weight.
50% or less, At 0.2-2%.

T・10.5~3%, NbO, 7~4.5%, balance N1
The main objective is to provide a 7'Ni alloy member with excellent stress corrosion cracking resistance. Togaku's I; C Rin I's +4f
) The second invention of Tokiyoshi Hikima9 is the electric switch%, Cr14~
25%, pe30% or less, At0.2-2%, 'i'i
0.5-3%, Nb45-8%, MO8% or more F, balance -
The object of the present invention is to provide a member made of an N1-based alloy, which is made of Ni, is precipitation-strengthened, has a 1,^ crystal structure, and has excellent stress corrosion cracking resistance.

Furthermore, the third invention has an important % of Cr of 14 to 25%, p
The gist of the present invention is a method for manufacturing a member made of a Ni-based alloy with e30% or less, At 0.2 to 2%, and Ti.

The reasons for limiting the ingredients in the present invention will be described below.

Cr: Cr needs to be at least 14% in terms of SCC resistance, but on the other hand, if it exceeds 25%, hot workability will be impaired, resulting in the formation of chromatic flakes known as the TCP phase.
The cold workability 9 mechanical properties and corrosion resistance are reduced due to the formation of harmful phases, so the content was set at 14 to 25%.

pe: pe stabilizes the base structure and improves corrosion resistance. However, if the content of F is too high, Laves
30% ≧Fe is recommended because it causes harmful phases such as phase.

At, T1, and Nb all form intermetallic compounds with Ni and contribute to precipitation strengthening. In order to provide age hardening ability, the trap contains at least -0.2% At and 0.5% T! A combination of sb, At and TM(2)il is required.
By increasing Nb and adding Nb, a high-strength alloy suitable for the purpose can be obtained. - If the amount of blade metal is too large, the characteristics will deteriorate, so At is 0.2 to 2%, and T straight is 0.
5 to 3%, and in the first invention 1NbFi
o, 7 to 4.5%.

In the second invention, KMoi is further included. M.O.
Coexists with Cr to ensure sufficient 8CC resistance. However, if the amount of MO is too large, the workability will deteriorate, and a harmful phase will be produced that will deteriorate the corrosion resistance and mechanical properties, making it difficult to roll the material.

Also in the second invention, Nb has a greater effect on precipitation strengthening than At or TI, and it is necessary to add Nb for rounding to obtain the high hardening ability required for springs, but if too much Nb is added, coarse carbides are formed. Deterioration of mechanical properties and deterioration of workability may occur due to the formation of intermetallic compounds and intermetallic compounds. Therefore, in the second invention, Nb was set at 45 to 8%.

In the third invention, the temperature of the solidification treatment is preferably 950 to 1150C. In addition, as a two-stage aging treatment, after holding at 800 to 900 CVC for 1 to 30 hours, cooling, and then heating at 600 to 750 C for 1 to 30 hours.
Explain how to make time work.

FIGS. 1(a) and 1(c) show an expansion spring 12 used for attaching the graphite seal 11 to the inner wall of the index tube 10. This expansion spring 12 has notch 1
3, the width is 10 am, and the diameter Fi is 60-. This was manufactured by F.

@1 Figure (C), 1) shows the rounded garter spring 22 to which the graphite seal 21 of the piston tube 201C is attached. This garter spring 22 has a coil shape, with a coil length of 166 cm and a core wire diameter of 0.36 cm. This is Soru 4 Ko Reisaku, Ko 4 Sonku.

After manufacturing, it is manufactured by solid solution treatment, 9F=N#4# (processing of 1% or more is added during heating), and two-stage aging treatment.

FIG. 1(e) shows nine springs 32 provided between the tie plate 30 and channel box 31, and FIG. 1(e) shows nine springs 41 provided in the cap screw 40. 32 and 41 are round and manufactured in the same manner as the expansion springs 12 shown in FIGS. 1(a) and 1(b).
In Figure (f), 42 is Garnconel X750 (product name) and Inconel 718 (-product name). Its main chemical components are Inconel x 750, 7m92% Ni,
15.48%Cr.

6.91%F・, 0957%At, 2,60%T1゜0
．． 95%Nb+Ta, 0.04%c, (7nea $
A/7182>! 5L47%Ni, 18.37%cr,
0.40% At, 0.85% Ti, 5. Q6%N b+
It is Ta.

Table 1 shows the results of a constant strain test with a gap in high-pressure pure water. The test conditions are as follows. Test temperature [:288C
, Pressure "86 h/cm", Dissolved oxygen: 8 pyn,
@Interforming material 2 graphite fiber wool, strain: approximately 1.0%, test time: 500 hours.

Chapter 1 Table In the ts1 table, the symbols indicate the following contents.

・: High crack sensitivity (cracks of 1000 μm or more) 0: Medium crack sensitivity (cracks of 200'Lm-1000 srn) 02 Low crack sensitivity (cracks of 0 to 200 μm) For Inconel X750, cold lI5 processing with 60% solution treatment When subjected to cold processing of 10%, 20%, and 30%, the gap SCC sensitivity was clearly shown, and it can be concluded from Table 1 that cold working of 30% or less is harmful in terms of gap SCC property. . Even in the case of direct aging treatment, the degree of cold working is 60%.
In this case, the gap SCC property becomes smaller, but the machining becomes stronger. Note that it is difficult to determine IiI& of the gap SCC susceptibility of an aged material directly from the metallographic structure.

When solid solution treatment (106[1"X1h → water cooling) and two-stage processing are applied, the gap 8CC sensitivity is large at 10% and 20% cold working, and the resistance is low at cold working of 30% or more. Clearance and SCC properties are significantly improved.

Figures 2 and 2, p'□i- are micrographs showing the relationship between the gap and SCC sensitivity of Inconel X750 and the metallographic structure.
It was corroded by immersion in tHs80a)K.

The 1s2 figure is a book that was directly aged, and the 1X3 figure is a book that was subjected to two-stage aging treatment. In each figure, (a) is cold worked *io%, 0)) is 20%, and (C) is Same as 30%.

(d) is 60%. In the case of direct aging treatment, grains become finer as the degree of cold working increases, but the gap SCC
No correlation was found between sensitivity and metallurgy. On the other hand, in the case of two-stage aging treatment, only intergranular corrosion was observed in the metal structure that showed a large gap 8CC sensitivity;
This shows that there is a significant correlation between the gap SCC sensitivity and the resistance of this alloy. This 9-crystal is determined by the degree of cold working and intermediate heat treatment conditions, progresses as the degree of cold working increases, and significantly improves the gap resistance.

For these reasons, it is known that it is practical and beneficial to use a nine-atom, one-wood bolt with excellent gap SCC resistance.
A friend discovered that it could be easily determined from (A recrystallization behavior).

In the case of Inconel 718, as in the case of Inconel x 750, it was found that if the metal structure after the secondary and final aging treatment was changed to a recrystallized structure, the gap resistance to 8CC would be extremely good.

As described above, according to this embodiment, the N1-based alloy has a shear l reduction rate of 3-a% or more between the solution treatment and the two-stage aging treatment, and has excellent SCC resistance. A manufactured member is provided.

[Brief explanation of drawings]

Figures 1 (a) to (0 are schematic diagrams showing the shape of reactor springs, Figures 2 (a) to (d) and Figures 3 (a) to (d) t
It is a micrograph of the metal structure of fNi & alloy. 10... Index tip, 12... Expansion spring, 2o... Piston tube 2
2... Gertus Gering, 3o Riiprate, :1 ゛Z mouth (be) 2 Kaya, Kushiku 3, (qλ (no)

Claims (1)

[Claims] 1. In weight%, Cr14-25%, l'e 30% or less,
The N14 alloy material according to item 1, which has a dense crystal structure of AtO, 2 to 2%, Tlα 5 to 3%, and Nb0.7, and has excellent stress corrosion cracking resistance. 3. Weight %: Cr 14-25%, Fe 50% or less, k
The Ni-based alloy member according to item 3 for stress corrosion resistance, which is precipitation-strengthened by 2 to 2% tO, 0.5 to 3% T, 4.5 Nb, and has a recrystallized structure. 5. In weight%, Cr14-25%, Fe50% or more F, A
tO, 2~2%, 't"io, s~3% 1Nb0.7~
The alloy consisting of 4.5% and the balance N1 was aged at 800 to 9 JIOC for 1 to 30 hours,
7. The method according to claim 5 or 6, wherein the member is a nuclear reactor spring Ac.