JPH06228709A - Austenitic iron-base alloy with irradiation resistance - Google Patents

Abstract

PURPOSE:To provide an austenitic iron-base alloy suitable for nuclear reactor equipment material and improved in intergranular corrosion cracking resistance. CONSTITUTION:In an austenitic stainless steel, as austenitic stainless steel of ordinary purity, having a composition consisting of, by weight, 10.0-18.0% nickel, 16.0-18.0% chromium, 2.0-3.0% molybdenum, <=0.03% carbon, <=2.0% manganese, <=0.01% phosphorus, <=0.005% sulfur, <=0.5% silicon, and the balance essentially iron, respective amounts of nickel, chromium, molybdenum, manganese, and iron are regulated so that the electron hole concentration, represented by (electron hole concentration)=[0.66Xnickel(atomic %)+2.66Xiron(atomic %)+3.66 Xmanganese(atomic %)+4.66X(chromium(atomic %)+molybdenum (Atomic %)]divided by 100, becomes <=2.75. By this method, austenite phase can be stabilized and intergranular corrosion resistance to irradiation can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic iron-base alloy, and more particularly to an austenitic iron-base alloy suitable for reactor internal equipment and having excellent corrosion resistance.

[0002]

2. Description of the Related Art Reactor internal equipment such as austenitic stainless steel control rods and instrumentation tubes are placed in an environment of high temperature pure water and are relatively expensive as compared with other constituent materials of the reactor. It is receiving neutron irradiation. On the other hand, austenitic stainless steel in high temperature pure water may cause intergranular stress corrosion cracking (IGSCC). The main factor on the material side of IGSCC is the formation of grain boundary carbides due to thermal cycles such as welding and the accompanying formation of a chromium depletion layer near the grain boundaries, that is, welding sensitization. However,
It has also been reported that solution-exposed austenitic stainless steel, which has not been sensitized at all, exhibits higher intergranular corrosion cracking susceptibility when irradiated, as compared with the non-irradiated material.

The influence of irradiation on materials is that irradiation-induced segregation causes concentration of Si (silicon) and P (phosphorus) and Cr (chromium).
It is conceivable that the corrosion resistance of the grain boundary is reduced due to the lack of slag at the grain boundary. The formation of a chromium-deficient layer by irradiation does not involve the formation of grain boundary carbides, unlike welding sensitization.

High-purity austenitic stainless steel is
Focusing on the concentration of impurity elements among the above factors, it was developed for the purpose of having excellent performance of intergranular corrosion cracking resistance even when high irradiation is performed by limiting the amount of impurity elements. In addition, as a document related to this type of technology, for example, “Grain boundary corrosion of austenitic steel” (JS
Armijo: Intergranular Corrosion of Nonsensitized
Austenitic Steels, Corrosion vol.24 p.24 (1968))
, Or “Deformation characteristics of austenitic stainless steels and Ni-based alloys in BWR and PWR cores”
(F. Garazarolli et al .: Deformability of Austeniti
c Stainless Steel and Ni-base Alloy in the core of
a Boilling and a Pressurized Water Reactor, Proc.
Int. Symp. Environmental Degradation of Materials
in Nuclear System-Water Reactors, Montery, Cal. U.
SA, Sep. p. 442 (1983)).

In order to prevent the formation of a chromium deficient layer by irradiation, an element having a larger atomic radius than that of chromium in stainless steel is added to trap excess atomic vacancies generated by irradiation and to cause grain boundaries. Has been reported to suppress chromium deficiency in Japan (Japanese Patent Application Laid-Open No. HEI-2)
-4945).

[0006]

However, it has been clarified that the intergranular corrosion cracking resistance of all of the above austenitic stainless steels may not always be improved as intended. It is considered that this is because the austenite phase becomes unstable due to excessive lattice defects generated by irradiation, and the corrosion resistance decreases. Also,
When stress is applied like stress corrosion cracking, the tendency is expected to become remarkable.

The present invention has been made in view of the above circumstances, and in an ordinary-purity austenitic stainless steel, an austenite iron base alloy capable of improving intergranular corrosion cracking resistance by preventing destabilization of the austenite phase by irradiation. The purpose is to provide.

[0008]

The above-mentioned object is to achieve nickel 1
0.0-18.0 wt%, chromium 16.0-18.0 wt%, molybdenum 2.0-3.0 wt%, carbon 0.03
Weight% or less, manganese 2.0 weight% or less, phosphorus 0.01
Wt% or less, sulfur 0.005 wt% or less, silicon 0.5
By adjusting the amounts of nickel, chromium, molybdenum, manganese, and iron so that the electron vacancy concentration represented by the following formula is 2.75 or less in an austenitic stainless steel whose weight ratio is less than or equal to and the balance is mainly iron To be achieved. Electron vacancy concentration = {0.66 x nickel atom% + 2.66 x iron atom% + 3.66 x manganese atom% + 4.66 x (chromium atom% + molybdenum atom%)} ÷ 100

[0009]

Function: Ni 10.0-18.0 wt%, Cr 1
6.0-18.0 wt%, Mo 2.0-3.0 wt%,
C 0.03 wt% or less, Mn 2.0 wt% or less, P
0.01 wt% or less, S 0.005 wt% or less, Si
In an austenitic stainless steel of 0.5% by weight or less and the balance mainly consisting of Fe, nickel, chromium, molybdenum, manganese and iron are added so that the electron vacancy concentration shown by the above formula becomes 2.75 or less. By adjusting, the austenite phase of the mother phase can be stabilized.

Therefore, in the austenite iron-based alloy of the present invention, the destabilization of the austenite phase due to irradiation is prevented and the corrosion resistance can be improved. Since the instability of the phase is remarkable when stress is applied, the stabilization of the austenite phase largely contributes to the improvement of stress corrosion cracking resistance. In addition, the stabilization of the phase promotes the recombination of excess lattice defects generated by irradiation, and can also suppress the irradiation-induced grain boundary segregation, which is also effective in improving the intergranular corrosion crack resistance. is there.

The smaller the electron vacancy concentration, which is the austenite phase stability parameter, the more stable the austenite phase. As can be seen from the formula of electron vacancy concentration,
Since the electron vacancy concentration decreases as the amount of nickel increases, the austenite phase becomes stable, and it is considered that deterioration of corrosion resistance due to irradiation can be prevented. However, in the case of a high nickel alloy, nickel precipitates are generated by irradiation, and therefore corrosion resistance is not necessarily improved. Therefore, the determination of phase stability using the electron vacancy concentration is effective only for the iron-based alloy in the nickel concentration range of the present invention.

[0012]

Embodiments of the present invention will be described with reference to the drawings.
% By weight, Ni 10.0-18.0%, Cr 16.
0 to 18.0%, Mo 2.0 to 3.0%, C 0.03
% Or less, Mn 2.0% or less, P 0.01% or less, S
In an austenitic stainless steel containing 0.005% or less, Si 0.5% or less, and the balance mainly Fe, various kinds of austenite iron-based alloys were manufactured by variously changing the electron vacancy concentration shown in the above formula. , And the stress corrosion cracking test was carried out by neutron irradiation, and the effect of electron vacancy concentration on the stress corrosion cracking susceptibility by irradiation was investigated.

The results are shown in FIG. In FIG. 1, the vertical axis represents the grain boundary fracture surface ratio, and the larger the value, the greater the stress corrosion cracking susceptibility. The horizontal axis represents the electron vacancy concentration. As shown in this figure, it is understood that the smaller the electron vacancy concentration, the smaller the intergranular fracture surface ratio and the better the stress corrosion cracking resistance.

Among the alloys shown in FIG. 1, the following 4
The composition of the seed alloys is as follows: Alloy with electron vacancy concentration 2.878 (point on the right side of No. 1 in the figure): Nickel 1
0.9 wt% (10.4 atom%), chromium 18.1 wt% (19.4 atom%), molybdenum 2.2 wt% (1.
3 atom%), carbon 0.02 wt% (0.09 atom%),
Manganese 1.5% by weight (1.5 atom%), phosphorus 0.00
4 wt% (0.007 atom%), sulfur 0.002 wt%
(0.003 atomic%), silicon 0.03% by weight (0.0
6 atom%), balance iron

Alloy with electron vacancy concentration of 2.795 (fourth point from the left in the figure): 12.4 wt% (11.7 at%) nickel, 17.2 wt% (18.4 at%) chromium. , Molybdenum 2.1% by weight (1.2 atom%), carbon 0.01
Wt% (0.05 atom%), manganese 1.4 wt%
(1.4 atom%), phosphorus 0.008 wt% (0.01 atom%), sulfur 0.003 wt% (0.005 atom%),
0.42% by weight of silicon (0.8 atom%), balance iron

Alloy with electron vacancy concentration of 2.775 (second point from the left in the figure): 14.0 wt% (13.3 atom%) of nickel, 16.5 wt% (17.7 atom%) of chromium , Molybdenum 2.3% by weight (1.3 atomic%), carbon 0.01
Wt% (0.05 atom%), manganese 1.4 wt%
(1.4 atom%), phosphorus 0.005 weight% (0.009
Atomic%), sulfur 0.002% by weight (0.003 atomic%), silicon 0.25% by weight (0.50 atomic%), balance iron.

Alloy with electron vacancy concentration of 2.725 (point on the left side in the figure): 15.8 wt% (15.0 atom%) of nickel, 16.1 wt% (17.3 atom%) of chromium, Molybdenum 2.4% by weight (1.4 atomic%), carbon 0.02% by weight (0.09 atomic%), manganese 1.5% by weight (1.
5 atom%), phosphorus 0.004 wt% (0.007 atom%), sulfur 0.002 wt% (0.003 atom%), silicon 0.03 wt% (0.80 atom%), balance iron.

[0018]

As described above, in the austenitic iron-based alloy of the present invention, nickel, chromium, molybdenum, manganese and iron are adjusted within a predetermined concentration range so that the electron vacancy concentration becomes 2.75 or less. As a result, it is possible to provide a material for nuclear reactor reactor equipment that is resistant to stress corrosion cracking even when exposed to neutron irradiation and has excellent intergranular corrosion cracking resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a grain boundary fracture surface ratio and an electron vacancy concentration.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G21C 17/10

Claims (1)

[Claims] 1. Nickel 10.0-18.0% by weight, chromium 16.0-18.0% by weight, molybdenum 2.0-
3.0 wt%, carbon 0.03 wt% or less, manganese 2.
0 wt% or less, phosphorus 0.01 wt% or less, sulfur 0.00
In an austenitic stainless steel containing 5% by weight or less, silicon 0.5% by weight or less, and the balance mainly consisting of iron,
An irradiation-resistant austenitic iron-based alloy having an electron hole concentration represented by the following formula of 2.75 or less. Electron vacancy concentration = {0.66 x nickel atom% + 2.66 x iron atom% + 3.66 x manganese atom% + 4.66 x (chromium atom% + molybdenum atom%)} ÷ 100