JPH0335370B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a corrosion-resistant zirconium alloy. (Prior Art) Zirconium alloys have good corrosion resistance and are used for various purposes. For example, when used in water-cooled nuclear reactors, it is effective as the material for most of the reactor core structures. The conditions for this material to be met include a small thermal neutron absorption cross section, excellent environmental corrosion resistance, and sufficiently satisfactory mechanical properties. Materials that satisfy these requirements include Zircaloy-2, Zircaloy-4, and Ozenite.
0.5 and 1.0 are known. Zircaloy, auxenite, etc. are alloys made by mixing certain amounts of alloys such as iron, nickel, chromium, zirconium, niobium, tin, etc., but they have all the characteristics of the above alloys as core structural materials. For example, when used in a water-cooled nuclear reactor, under the harsh conditions of neutron irradiation, changes occur over time and the so-called nodular corrosion occurs in the form of white spots on the alloy surface. Corrosion products called . This phenomenon is a truly inconvenient phenomenon that grows under normal usage conditions. If this progresses, it is expected that a peeling phenomenon will occur and the main body will gradually become thinner and its mechanical strength will decrease. Moreover, this peeling phenomenon not only has other effects, but is also undesirable because the peeled corrosive substances may accumulate undesirably, impair heat conduction efficiency, and cause local overheating. In addition, this corrosive material contains a sufficient amount of radioactivity, and it is not preferable for this to accumulate in a portion. Various improvements have been made to solve the above problems. That is, US Pat. No. 3,005,706 discloses a zirconium alloy with a small amount of beryllium added, and US Pat. Nos. 3,261,682 and 3,150,972 disclose a zirconium alloy with at least one of potassium, yttrium, and calcium added. Proposed. Furthermore, according to Japanese Patent Application Laid-open No. 52-5629, the surface of parts made of zirconium alloy contains chemically inert gold, silver, platinum, nickel, etc.
There are also proposals for coating (metsuki, etc.) with chromium, iron, niobium, etc. However, adding beryllium, potassium, yttrium, calcium, etc. to zirconium alloys is not reliable and has not been put to practical use. Also, coating with gold, silver, platinum, etc. is not a good idea due to structural problems, and coating large components such as nuclear reactors is actually impossible. (Problems to be Solved by the Invention) Although such zirconium alloys are materials with excellent corrosion resistance, they still have problems such as the occurrence of nodular corrosion, and even better corrosion resistance is required. There is. Therefore, an object of the present invention is to provide a corrosion-resistant zirconium alloy that exhibits excellent corrosion resistance. [Structure of the Invention] (Means and Effects for Solving Problems) In order to elucidate the cause of corrosion of the above-mentioned zirconium alloy, the inventors conducted experiments and other studies from various angles and came to the following conclusion. In other words, most of the corrosion of zirconium alloys is caused by the alpha phase (hcp).
It has been confirmed that this occurs, so it is necessary to avoid this. In the high-temperature β region, a bcc crystal structure is assumed, and when this is rapidly cooled, an α phase is formed from the β region. This α phase has a different crystal structure from the above-mentioned α phase (sometimes called a martensitic structure), with grain boundaries or sub-grain boundaries distributed in a network pattern, and these crystal structures have excellent corrosion resistance. It exhibits favorable properties under high temperature and high radioactivity density conditions. That is, when rapidly cooled from the above region, the relationship of crystal orientation is (110)bcc/(0001)hcp, [111]bcc/[11
20] hcp. Furthermore, the α phase obtained by rapid cooling from the β region can be alloyed with other specific β phase stabilizing elements to the zirconium (Zr) base, thereby improving the hardenability by rapid cooling and making it extremely easy to process. It was found that α-phase crystal structure can be obtained by β-quenching. As mentioned above, it was confirmed that this material has extremely high corrosion resistance. If a large amount of β phase stabilizing element is added, the above β
The β phase is mixed into the α phase due to rapid cooling. This β phase has extremely high corrosion resistance. That is, the present invention contains at least one of molybdenum of 0.2% or more and niobium of 0.1% or more in a total amount of 2.0% or less by weight, Sn of 1.20 to 1.70% by weight, Fe of 0.07 to 0.20% by weight, 0.05-0.15 wt% Cr, 0.03-0.08 wt% Ni, Fe+Cr+Ni
Zr-based alloy (hereinafter referred to as Zircaloy-2) of 0.18 to 0.38% by weight and the remainder being substantially Zr, or 0.2% by weight
% or more of molybdenum and 0.1% or more of niobium in a total amount of 2.0% by weight or less,
1.20-1.70 wt% Sn, 0.18-0.24 wt% Fe,
0.07-0.3 wt% Cr, 0.28-0.37 wt% Fe+Cr
A corrosion-resistant zirconium alloy characterized by having a composition of a Zr-based alloy (hereinafter referred to as Zircaloy-4) in which the remainder is substantially Zr, and having an α-phase structure in which grain boundaries or sub-grain boundaries are distributed in a network shape. It is. The reason for limiting the amount of each addition in the above is that the upper limit is not preferable because alloying produces intermetallic compounds due to eutectoid or eutectic reactions, which deteriorates ductility and particularly deteriorates creep properties. The lower limit is β
This is because the α phase structure promoting effect due to rapid cooling no longer appears. In addition, when used in nuclear reactors, it is necessary to have a particularly small neutron absorption cross section, and the above Mo, Nb
It is preferable to suppress the amount of addition as much as possible. Therefore, the specific elements mentioned above may be combined in any way, but when they are contained in a small amount of 2% or less, it is effective with few precipitates, but when Mo is less than 0.2% and Nb is less than 0.1%, The effect could not be obtained sufficiently. Sn is Zr
It is the only additive that can be solid-dissolved in Zr, and it increases mechanical strength by solid-dissolving in Zr, but if it exceeds 1.7% by weight, processability deteriorates. Fe, Cr, and Ni are components that mainly improve corrosion resistance, but if Fe exceeds 0.24% by weight, Ni 0.08% by weight, Cr 0.15% by weight, or the sum of these exceeds 0.38% by weight, precipitates will form. It becomes coarse and causes local corrosion. A zirconium-based alloy containing a predetermined amount of at least one of Mo and Nb in Zircaloy-2 and 4 is rapidly cooled from the β region (high temperature range of approximately 900°C or higher) to form grain boundaries or sub-grain boundaries in the alloy. The alloy of the present invention is obtained by creating an α phase structure in which α is distributed in a network shape. Such quenching treatment may be performed only for alloy treatment. In other words, it is only necessary to change the structure to a β-quenched structure only in areas where corrosion resistance is required. After that, cold working and annealing are performed. Furthermore, a black oxide film may be provided by means such as autoclave treatment. (Example) Examples of the present invention will be described below. Example 1 As an example using the corrosion-resistant zirconium alloy according to the present invention, the weight ratio is 1.50%Sn-0.20%Fe-0.10%
Approximately 1% molybdenum was added to Zircaloy-4 having a Cr-remaining Zr composition, and the alloy containing the mixture was heated to approximately 890°C, and then rapidly cooled to room temperature at 200°C/sec to form an α-phase structure. Results of a forced autoclave corrosion test at 500°C and 107 kg/cm ² on a zirconium alloy channel plate annealed at 400°C and a channel plate made of Zircaloy-4, which has been commonly used. On the conventional Zircaloy-4 channel plate having the above composition, nodular corrosion began to occur after about 5 hours, and a peeling phenomenon occurred after about 15 hours. In contrast, the zirconium alloy channel plate of the present invention hardly changes over time. If the above test was continued further, peeling became severe after 100 hours, but this may mean that the mechanical strength deteriorates and the product becomes unusable. The product of the present invention shows almost no change even after 100 hours. That is, it was clear that there was no change in appearance or weight compared to the initial state, and that they remained almost constant. Figure 1 shows the above test results, where the vertical axis shows the increase in weight of the zirconium alloy (corrosion increase).
The horizontal axis shows usage time. and curve 1
Curve 2 shows the weight increase due to nodular corrosion that occurs with the use of the conventional zirconium alloy, and curve 2 shows the weight increase of the zirconium alloy of the present invention, and the difference is extremely remarkable. Example 2 Weight ratio: 1.50%Sn-0.17%Fe-0.10%Cr-0.06
0.5% by weight of Zircaloy-2 with Ni-Zr composition
Nb-added alloy is melted and forged to form a hollow billet, and then hot extruded to produce a fuel cladding tube. Next, it is heated to a temperature of 900°C and then rapidly cooled to form an α phase containing a β rapidly cooled phase (martensite phase). Next, a fuel cladding tube was created by repeating cold rolling and annealing. Example 3 Weight ratio: 1.50%Sn-0.17%Fe-0.10%Cr-0.06
%Ni-Zr composition Zircaloy-2 with a weight ratio of 0.4%
A fuel cladding tube was prepared in the same manner as in Example 2, except that an alloy containing 0.2% of Mo and 0.2% of Nb was used. Comparative Examples 1 to 3 Weight ratio: 2%Nb-0.5%Sn-0.3%Cr-Zr (Comparative Example 1), 2%Nb-0.5%Sn-0.3%Mo-Zr (Comparative Example 2), 5%Nb Each alloy having a composition of -1%Sn-0.2%Pd-Zr (Comparative Example 3) was prepared, and test pieces were created in the same manner as in Example 2 except for the following. The above Examples and Comparative Examples were subjected to a forced autoclave corrosion test at 500° C. and 107 Kg/cm ² , and the increase in corrosion weight after 24 hours was examined, and the results are shown in the table below.

[Table] [Effects of the invention] As explained above, according to the present invention, corrosion resistance,
A corrosion-resistant zirconium alloy particularly excellent in nodular corrosion resistance can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the characteristics of the corrosion-resistant zirconium alloy of the present invention in comparison with a conventional one.

Claims (1)

[Claims] 1. At least one of molybdenum and 0.1% or more of niobium in a total amount of 2.0% by weight or less, tin 1.20 to 1.70% by weight, iron 0.07 to 0.20% by weight, and chromium 0.05 to 0.1% by weight. 0.15% by weight, Nickel 0.03~
0.08% by weight, but the total amount of iron, chromium, and Ni
A corrosion-resistant zirconium alloy containing 0.18 to 0.38% by weight, the remainder consisting essentially of zirconium, and having an α-phase structure in which grain boundaries or sub-grain boundaries are distributed in a network shape. 2 At least one type of molybdenum of 0.2% or more by weight and niobium of 0.1% or more in a total amount of 2.0% by weight or less, tin 1.20-1.70% by weight, iron 0.18-0.24% by weight, chromium 0.07-0.13% by weight, but iron Corrosion resistance characterized by containing a total amount of chromium of 0.28 to 0.37% by weight, with the remainder consisting essentially of zirconium, and having an α-phase structure in which grain boundaries or sub-grain boundaries are distributed in a network pattern. Zirconium alloy.