JPS6039152A - Manufacture of spring for nuclear reactor - Google Patents

Abstract

PURPOSE:To obtain a spring for a nuclear reactor with superior resistance to stress corrosion cracking by subjecting a precipitation strenghtening Ni alloy contg. specified amounts of Cr, Fe, Al, Ti and Nb to cold plastic working at a specified reduction of area between solid soln. treatment and aging stages. CONSTITUTION:The composition of a precipitation strengthening Ni alloy is composed of, by weight, 14-25% Cr, <30% Fe, 0.2-2% Al, 0.5-3% Ti, 0.7- 4.5% Nb and the balance Ni. The alloy is subjected to cold plastic working at >40-<60%, especially <=50% reduction of area between soln. heat treatment and aging (direct aging) stages. A spring for a nuclear reactor is manufactured using the resulting material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a member made of l'Ji-based alloy and a method for manufacturing the same, and particularly to one suitable for application to a spring for a nuclear reactor.

[Background of the invention]

Conventional springs for nuclear reactors have been produced mainly by subjecting them to solution treatment after melting, followed by cold rolling to give them 30 to 40% processing, and then subjecting them to aging treatment. These are manufacturing methods that use cold working and aging to ensure the high-temperature strength and spring characteristics required for spring materials for nuclear reactors. There has been a drawback in that studies regarding corrosion cracking resistance (hereinafter referred to as SCC resistance) have not necessarily been sufficiently conducted.

In particular, nuclear reactor springs (for example, BWR control rods, C springs in drive mechanisms) are often used in sensitive areas where gaps are formed under high stress, and SCC countermeasures are important.

Currently, Inconel (trade name) x750, which has high strength and high corrosion resistance, is used as springs for nuclear reactors, and most of them undergo 30 to 40% cold working after solution treatment, and then undergo aging. Manufactured using a processing (direct aging) process. The purpose of cold working after solution treatment is to obtain the final shape of the spring, while the aging treatment that follows cold working contributes to improving the spring properties and high-temperature strength of the spring material for nuclear reactors. It is something. However, even if 30 to 40% cold working is performed between solution treatment and aging treatment, it is unclear whether 30 to 40% cold working is effective in improving clearance SCC resistance, which is a practical problem. It has not been sufficiently considered.

Note that the interstitial SCC susceptibility of precipitation strengthened alloys is different from that of solid solution strengthened alloys, and no correlation between intergranular corrosion and SCC is observed.

[Purpose of the invention]

It is an object of the present invention to solve these conventional problems and provide a Ni-based alloy member with excellent SCC resistance and a method for manufacturing the same.

[Summary of the invention]

The present inventors changed the degree of cold working performed between solution treatment and aging treatment, and investigated the effect of the degree of cold working on clearance SCC resistance by a constant strain test with a gap in high-temperature, high-pressure pure water. did. As a result, we discovered the following new facts. (2) If 10 to 30% cold working is performed between the solution treatment and the direct aging treatment, the gap SCC susceptibility is greatly increased. However, if cold working is applied to more than 40% and less than 60%, the gap resistance S
Improvement in CC properties was observed.

[Embodiments of the invention]

An embodiment of the present invention will be described below. The material is Inconel X750 (trade name). Its main chemical components are 72
．． 92%Ni, 15.48%Cr, 6.91%Fe, 0
．． 57%At, 2.60%Ti, 0.95%Nb+Ta
, 0.04%C. Table 1 shows the results of a constant strain test with a gap in high-temperature, high-pressure pure water. The test conditions are as follows. Test temperature: 288tr.

Pressure: 86 Kg/tyn”, dissolved oxygen: 8P
F, IFi acid forming material graphite fiber wool, strain: approximately 1.0%, test time = 500 hours.

Table 1 In Table 1, the symbols indicate the following contents.

・: High cracking sensitivity (cracks of 1000I1m or more) 1; Medium cracking sensitivity (cracks of 200 μm to 1000 μm) 02 Low cracking sensitivity (cracks of 0 to 200 μm) Solid solution treatment (1066CX1 h → water cooling) and direct aging treatment (704
7: Cross section reduction rate 1 between X4 or 20h → air cooling)
When subjected to cold working from 0 to 50%, 10%, 20% and 3
The gap SCC susceptibility was clearly shown at 0% cold working, and 3
It is recognized from Table 1 that cold working of 0% or less is harmful to the gap SCC property. On the other hand, the degree of cold working is 45~
It is known that the gap SCC property becomes significantly smaller when it becomes 55%.

Note that the present invention can also be applied to ports for nuclear reactors.

〔Effect of the invention〕

For these reasons, when manufacturing reactor springs and bolts with excellent gap SCC resistance, it is necessary to use a material that is between the solution treatment and the aging treatment (direct aging treatment), exceeding 40% and less than 60%.
In particular, if cold plastic working is performed at 50% or less, a Ni-based alloy member with excellent SCC resistance can be obtained.

Agent: Patent Attorney Akio Takahashi

Claims (1)

[Claims] 1. In weight%, Cr14-25%, Fe50% or less, A
t0.2-2%, TiO, 5-3%, NbO, 7-4.
Using a precipitation-strengthened Ni alloy consisting of 5% Ni and the remainder substantially Ni, cold plastic working with a reduction in area of more than 40% and less than 60% is performed between the solution treatment and the aging treatment (direct aging treatment). A method of manufacturing a spring for a nuclear reactor, which is characterized by the following.