JPH04297537A - Ni-base alloy for high temperature water - Google Patents

Abstract

PURPOSE:To obtain an Ni-base alloy for high temp. water in which strength at the time of use in high temp. water is increased by improving an 'Inconel(R)' 718 alloy and improving corrosion resistance. CONSTITUTION:The alloy is an Ni-base alloy for high temp. water having a composition consisting of, by weight, 50.00-55.00% (Ni+Co), 0.65-1.16% Ti, <=0.001% B, <=0.08% C, <=0.35% Si, <=0.35% Mn, <=0.015% P, <=0.015% S, 2.80-3.30% Mo, <=0.10% Ta, <=0.05% Co, <=0.05% Cu, 0.20-0.80% Al, 4.75-5.50% (Nb+Ta), 17.00-21.00% Cr, and the balance Fe.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the improvement of Inconel 718 alloy, which is known as a high strength material with corrosion resistance and high temperature resistance.

0002

BACKGROUND OF THE INVENTION Inconel 718 alloy, which is a Ni-based alloy, is widely used as a high-temperature-resistant and high-strength material for main parts such as jet engines and nuclear reactor parts.

0003

[Problem to be solved by the invention] However, Inconel 7
Since Alloy 18 was originally developed for aircraft use,
The highest priority is placed on high-temperature strength, and the material is not made with a focus on corrosion resistance in high-temperature water or uniformity of structure. That is, Inconel 718 alloy usually contains 0.005 to 0.003 wt of boron.
% to provide strength at high temperatures. However, if some of the precipitated phases are stabilized by containing boron, a layered structure will remain on the high temperature side.

[0004] This lamellar structure is a structure in which precipitated phases are arranged in layers, and the structure is non-uniform in areas where this lamellar structure exists. Therefore, the presence of such a non-uniform structure reduces corrosion resistance and also reduces high temperature strength (decreases elongation), which poses a problem that adversely affects the mechanical properties and corrosion resistance of members using this alloy. .

[0005] Furthermore, it is said that the preferable solution treatment temperature for Inconel 718 alloy is 960 to 998°C. However, when actually used for high temperature water,
The solution treatment temperature is increased to the recrystallization region, that is, to about 1000°C. This solution treatment is a heat treatment performed to homogenize the crystal structure and remove residual stress in the member, but if this temperature is too high, the crystal grains will become coarser and the mechanical strength will decrease (yield strength will decrease). descend. On the other hand, if this temperature is too low, the layered structure and mixed grains described above will remain. This mixed grain is a crystalline state in which crystals with different grain sizes coexist, and the presence of this mixed grain also poses a problem that leads to a decrease in corrosion resistance and mechanical strength. Therefore, Inconel 718
When performing solution treatment of alloys, it is necessary to very precisely adjust the heat treatment temperature.

The present invention has been made to solve the above problems, and by changing the composition of Inconel 718 alloy, it improves corrosion resistance in high-temperature water, and also improves corrosion resistance at a temperature higher than that of conventional solution treatment. The objective is to be able to obtain a material with fine grains and a uniform crystal structure by processing at low temperatures.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the Ni-based alloy for high-temperature water according to the present invention has Ni+Co: 50.
00-55.00wt%, Ti: 0.65-1.15w
t%, B: 0.001wt% or less, C: 0.08wt%
Below, Si: 0.35wt% or less, Mn: 0.35wt
% or less, P: 0.015wt% or less, S: 0.015w
t% or less, Mo: 2.80 to 3.30wt%, Ta: 0
．． 10wt% or less, Co: 0.05wt% or less, Cu:
0.05wt% or less, Al: 0.20-0.80wt%
, Nb+Ta:4.75-5.50wt%, Cr:17
．． It is characterized by having a composition of 00 to 21.00 wt%, the balance being Fe.

[0008]

[Function] In the Ni-based alloy for high-temperature water according to the present invention, the boron content in the conventional Inconel 718 alloy is usually 0.
0.001wt when it is 005~0.003wt%
One of the features is that it is kept below %. That is,
By suppressing the boron content, the corrosion resistance is improved by making the crystal grains more uniform. Also, 920-990
A fine-grained material with less segregation (uniform structure) can be obtained even by treatment at a solution temperature that is relatively low in degrees Celsius.

The composition specifications of the prototype 718 alloy are shown below.

As is clear from the above composition table, the Ni-based alloy for high-temperature water according to the present invention has a reduced boron content, so the high-temperature strength is somewhat lower than that of the conventional alloy, but the corrosion resistance is significantly improved. do. For this reason, when corrosion resistance is more important, such as when applying to parts used in high-temperature water such as for nuclear power, strength is reinforced by improving corrosion resistance. A decrease in is hardly a problem.

Furthermore, by suppressing the boron content, the solid solution of the precipitated phase can be achieved at a lower temperature than before (approximately 10 to 20°C).
Therefore, in the solution treatment, the precipitated phase can be sufficiently dissolved in solid solution and a fine grain structure can be obtained without raising the temperature to the recrystallization region as in the conventional solution treatment. As a result, in addition to the advantage that solution treatment can be easily performed, there are advantages in that this easy solution treatment significantly increases corrosion resistance and increases elongation at high temperatures. Note that the proof stress and tensile strength at high temperatures tend to decrease slightly when the amount of boron added is reduced, but as the above-mentioned strength increases by making the crystal grains more uniform and finer, there is almost no problem as a whole. Not. Hereinafter, the present invention will be explained in more detail through Examples.

0012

[Example] New composition of N for high temperature water according to an example of the present invention
The composition of the i-based alloy is shown below.

Next, the heat treatment conditions in the above example will be described. First, the above-mentioned solution treatment is performed at a temperature range of 920 to 990° C. for one hour or more, and after this treatment, it is rapidly cooled. Then, after aging treatment is performed at a temperature range of 710 to 730° C. for 8 hours or more, slow cooling is performed to cool down the entire furnace after the treatment. Furthermore, another aging treatment is performed at a temperature range of 610 to 630° C. for 8 hours, and then rapidly cooled. Here, the aging treatment is performed as a precipitation hardening treatment to increase high temperature strength.

[0014] A table comparing the structures of this example prepared in this way and a conventional steel (Inconel 718) is shown below. For comparison with the conventional example, a sample that was solution-treated at 1000° C. or higher was also prepared.

[0015] This treatment temperature refers to the temperature of solution treatment.

As mentioned above, in conventional steel, the stripes (layered structure) do not disappear unless the steel is solution-treated at 1010°C or higher;
Coarse grains occur when treated at 980°C, but in the new composition steel of this example, no stripes were observed even when the treatment temperature was 980°C, and uniform fine grains were obtained throughout. Ta.

Next, the results of the corrosion rupture test are shown in FIG. Here, a high temperature (360°C) circulating aqueous solution (500pp
A U-shaped bending test was performed in
Only the results of checking each condition every 1,000 hours are shown, but in this example, all the samples showed better corrosion resistance than conventional steel.

[0018]

[Effects of the Invention] As explained above, in the Ni-based alloy for high-temperature water according to the present invention, by suppressing the boron content, it is easy to dissolve some precipitates that are difficult to dissolve in solid solution during solution treatment. As a result, the structure becomes fine particles with a uniform structure, thereby improving corrosion resistance.

Furthermore, since the solid solution of the precipitated phase can be achieved at a lower temperature than the conventional solution treatment temperature, temperature control during the solution treatment becomes easier.

In addition, even with such a simple solution treatment at a temperature lower than conventional methods, the precipitated phase can be sufficiently dissolved in solid solution.
It also has the advantage of providing a fine-grained structure.

As a result, the Ni-based alloy for high-temperature water according to the present invention has the advantage that corrosion resistance and mechanical strength (mainly high-temperature elongation) are significantly improved compared to conventional alloys.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of a corrosion rupture test of a new composition steel according to an example of the present invention and a conventional steel.

Claims (1)

[Claims] [Claim 1] Ni+Co: 50.00 to 55.00
wt%, Ti: 0.65 to 1.15 wt%, B: 0.0
01wt% or less, C: 0.08wt% or less, Si: 0.
35wt% or less, Mn: 0.35wt% or less, P: 0.
0.015wt% or less, S: 0.015wt% or less, Mo:
2.80 to 3.30 wt%, Ta: 0.10 wt% or less, Co: 0.05 wt% or less, Cu: 0.05 wt% or less, Al: 0.20 to 0.80 wt%, Nb + Ta: 4
．． 75-5.50wt%, Cr:17.00-21.0
A Ni-based alloy for high temperature water with a composition of 0 wt% and Fe: balance.