JP2003201532A - Ni BASED ALLOY HAVING EXCELLENT CORROSION RESISTANCE TO INORGANIC ACID-CONTAINING SUPERCRITICAL WATER ENVIRONMENT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Ni based alloy which has excellent corrosion resistance to supercritical water containing inorganic acid such as hydrochloric acid caused by the decomposition and oxidation of organic harmful matters such as PCB (polychlorinated biphenyls) and dioxine, and to provide a member for a supercritical water process reaction vessel consisting of the Ni based alloy. <P>SOLUTION: The Ni based alloy having excellent corrosion resistance to inorganic acid-containing supercritical water environment has a composition containing 29 to <42% Cr, >1 to 3% Ta, 0.001 to 0.05% Mg, 0.001 to 0.04% N, and 0.05 to 0.5% Mn, and, if required, containing one or more kinds selected from 0.1 to 2% Mo, 0.05 to 1.0% Fe, and 0.01 to 0.1% Si, and the balance Ni with inevitable impurities, and in which the content of C included as the inevitable impurities is controlled to ≤0.05%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

This invention relates to supercritical water containing inorganic acids such as hydrochloric acid generated by decomposing / oxidizing organic harmful substances such as PCB and dioxin which are difficult to dispose as industrial waste. And excellent corrosion resistance N
The present invention relates to an i-based alloy and a member for a supercritical water process reaction vessel made of this Ni-based alloy.

[0002]

2. Description of the Related Art Water under a temperature / pressure exceeding a critical point (specifically, temperature exceeding 374 ° C./22.1 MPa /
Water under pressure) is called supercritical water, and supercritical water has the property of dissolving various substances. The water in this supercritical state becomes a non-condensable high-density gas state, which is extremely soluble at room temperature. It is said that even a non-polar or weakly polar substance having a small value (for example, a hydrocarbon compound or gas) can be completely dissolved, and the dissolved substance can be oxidized and decomposed by adding oxygen.

Organic toxic substances such as PCB and dioxin, which are difficult to dispose as industrial waste, are no exception. These organic toxic substances are completely dissolved in supercritical water, and oxygen is added to produce organic toxic substances. By reacting in supercritical water, it is oxidatively decomposed into harmless substances such as carbon dioxide and water as well as hydrochloric acid. Compared to conventional disposal methods by incineration, this process can be processed in a closed system, so there is no risk of environmental pollution due to effluent.

When such supercritical water is used as a reaction solvent to decompose and oxidize organic harmful substances such as PCB and dioxin to render them harmless, high temperature and high pressure (400 to 650 ° C., 2
In a device for detoxifying organic harmful substances, since an environment in which a high concentration of oxygen coexists with an inorganic acid such as hydrochloric acid generated after decomposition / oxidation in supercritical water of 2.1 to 80 MPa) The material of the process reaction vessel is required to have corrosion resistance against such supercritical water containing an inorganic acid.

Therefore, as a metal material used for a process reaction vessel using supercritical water, a Ni-based corrosion resistant alloy known for its high corrosion resistance is listed as a candidate for the process reaction vessel of the apparatus. For example, Inconel (trade name) 6
25 (specified by ASTM UNS N06625, and its component composition is, for example, Cr: 21.0% by mass).
%, Mo: 8.4%, Nb + Ta: 3.6%, Fe:
3.8%, Co: 0.6%, Ti: 0.2%, Mn:
0.2%, balance: Ni + unavoidable impurities) and Hastelloy (trade name) C-276 (ASTM U
It is specified by NS N10276, and its component composition is, for example, Cr: 15.5% by mass%, Mo: 16.
1%, W: 3.7%, Fe: 5.7%, Co: 0.5
%, Mn: 0.5%, and the balance: Ni + unavoidable impurities). Recently, there is also a report that a Ni-based alloy having a higher Cr content is more excellent in corrosion resistance against inorganic acid-containing supercritical water, and MC alloy (trade name) (composition composition is, for example, by mass% Cr : 44.1%, Mo: 1.0%, M
Ni-high Cr type alloys such as n: 0.2%, Fe: 0.1%, and the balance: Ni + unavoidable impurities) are attracting attention as reaction vessel materials.

[0006]

However, among the conventional Ni-based corrosion resistant alloys, Inconel 625 and Hastelloy C-276 have been proposed.
Since pitting corrosion occurs when it contacts supercritical water containing hydrochloric acid and its corrosion resistance is insufficient, it is difficult to operate for a long time even if it is used as a process reaction vessel material in a device that detoxifies organic harmful substances. there were. Further, even though MC alloy has sufficient corrosion resistance to supercritical water containing hydrochloric acid in the initial stage of operation, its phase stability is insufficient, so that phase transformation progresses at use temperature and corrosion resistance deteriorates. Therefore, long-term operation was difficult even when used in a reaction vessel.

[0007]

Therefore, the present inventors show sufficient corrosion resistance in such an inorganic acid-containing supercritical water environment and 400 to 650 ° C. in order to enable further long-term operation.
In order to obtain a Ni-based alloy having excellent phase stability in, As a result, Cr in mass% (hereinafter,% represents mass%):
Ni-based alloy containing 29 to less than 42% Ta: more than 1 to 3
%, Mg: 0.001 to 0.05%, N: 0.00
1 to 0.04% and Mn: 0.05 to 0.5%, and if necessary, Mo: 0.1 to 2%, F
e: 0.05 to 1.0% and Si: 0.01 to 0.1
% As a unavoidable impurity, and 0.0% as a unavoidable impurity.
A Ni-based alloy having a composition adjusted to 5% or less has excellent corrosion resistance in an inorganic acid-containing supercritical water environment and excellent phase stability. We have obtained the finding that it can be used for a longer period of time when it is used as a process reaction vessel material in an apparatus for detoxifying substances.

The present invention has been made on the basis of such findings, and (1) Cr: 29 to less than 42%, T
a: more than 1 to 3%, Mg: 0.001 to 0.05%, N:
A composition containing 0.001 to 0.04%, Mn: 0.05 to 0.5%, the balance of Ni and unavoidable impurities, and adjusting the amount of C contained as unavoidable impurities to 0.05% or less. An Ni-based alloy having excellent corrosion resistance to an inorganic acid-containing supercritical water environment, (2) Cr: 29 to less than 42%,
Ta: over 1 to 3%, Mg: 0.001 to 0.05%,
N: 0.001-0.04%, Mn: 0.05-0.5
%, C: 0.05% or less, and Mo: 0.1
Ni-based alloy containing ~ 2%, the balance consisting of Ni and unavoidable impurities, and having a composition in which the amount of C contained as unavoidable impurities is adjusted to 0.05% or less and having excellent corrosion resistance to supercritical water environment containing inorganic acid , (3) Cr: 29 to 42
%, Ta: more than 1 to 3%, Mg: 0.001 to 0.0
5%, N: 0.001 to 0.04%, Mn: 0.05 to
0.5%, and further contains 1 or 2 of Fe: 0.05 to 1.0% and Si: 0.01 to 0.1%, the balance being Ni and inevitable impurities. , A Ni-based alloy having excellent corrosion resistance to an inorganic acid-containing supercritical water environment having a composition in which the amount of C contained as unavoidable impurities is adjusted to 0.05% or less, (4) Cr: 29 to less than 42%,
Ta: over 1 to 3%, Mg: 0.001 to 0.05%,
N: 0.001-0.04%, Mn: 0.05-0.5
%, Further containing Mo: 0.1 to 2%, further comprising Fe: 0.05 to 1.0% and Si: 0.01 to.
Inorganic acid-containing supercritical water containing one or two of 0.1%, the balance being Ni and inevitable impurities, and having a composition in which the amount of C contained as inevitable impurities is adjusted to 0.05% or less. Ni-based alloy with excellent corrosion resistance to the environment,
(5) A member for a supercritical water process reaction vessel made of a Ni-based alloy having the composition described in (1), (2), (3) or (4) above.

Next, the reasons for limiting each element in the alloy composition of the Ni-based alloy of the present invention will be described in detail.

Cr, Ta: In a supercritical water environment in which hydrochloric acid is mixed, the corrosion resistance is remarkably improved by containing Cr and Ta at the same time, but in this case, it is necessary to contain 29% or more. However, if it is contained in an amount of 42% or more, the phase stability deteriorates in combination with Ta and the corrosion resistance decreases, so the Cr content was set to 29 to less than 42%. More preferably, it is 30 to less than 38%. Similarly, Ta must be contained in an amount of more than 1%, but if it is contained in an amount of more than 3%, phase stability deteriorates in combination with Cr, and corrosion resistance decreases, which is not preferable.
Therefore, the content of Ta is set to more than 1 to 3% (more preferably 1.1 to 2.5%).

N and Mn: Coexistence of N and Mn can improve the phase stability. That is, N and Mn have an effect of stabilizing the Ni-fcc phase, which is the mother phase, and making it difficult for the second layer to precipitate. However, if the content of N is less than 0.001%, there is no phase stabilizing effect, while if it exceeds 0.04%, a nitride is formed and corrosion resistance deteriorates in an inorganic acid-containing supercritical water environment. The N content is 0.001 to 0.04% (more preferably 0.005 to 0.03%. Similarly, if the Mn content is less than 0.05%, there is no phase stabilizing effect. On the other hand, if the content of Mn exceeds 0.5%, the corrosion resistance in an inorganic acid-containing supercritical water environment deteriorates.
Content of 0.05 to 0.5% (more preferably 0.
06% to 0.1%).

Mg: Mg is also a component for improving phase stability, but if its content is less than 0.001%, there is no phase stabilizing effect, while if it exceeds 0.05%, it contains an inorganic acid. Since the corrosion resistance in supercritical water environment deteriorates, M
The content of g was set to 0.001 to 0.05% (more preferably 0.002% to 0.04%).

Mo: Mo has an effect of further improving the corrosion resistance particularly in a supercritical water environment containing hydrochloric acid, so it is added as necessary. In that case, 0.1% or more of Mo exhibits the effect. However, if the content exceeds 2%, the phase stability deteriorates. Therefore, Mo contained in the Ni-based alloy of the present invention
Was set to 0.1 to 2%. More preferably more than 0.1 %%
It is less than 0.5%.

Fe and Si: Since Fe and Si have the effect of improving the strength, they are added as necessary.
Although e shows an effect by containing 0.05% or more,
If the content exceeds 1%, the corrosion resistance in an inorganic acid-containing supercritical water environment deteriorates, which is not preferable. Therefore, F
The content of e is 0.05% to 1% (more preferably, 0.
1 to 0.5%). Similarly, if Si is contained by 0.01% or more, it is effective, but if it exceeds 0.1%, the corrosion resistance in an inorganic acid-containing supercritical water environment deteriorates, which is not preferable. Therefore, if the Si content is 0.
01% to 0.1% (more preferably 0.02 to 0.1
%).

C: C is contained as an unavoidable impurity,
When a large amount of C is contained, it forms a carbide with Cr in the vicinity of the crystal grain boundary and deteriorates the corrosion resistance. Therefore, the smaller the content of C, the more preferable, and the upper limit of the content of C contained in the unavoidable impurities is set to 0.05%.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In each case, raw materials having a low C content were prepared, and these were melted and cast in a usual high frequency melting furnace to produce an ingot having a thickness of 12 mm. This ingot was homogenized at 1230 ° C. for 10 hours,
While maintaining the temperature within the range of 1000 to 1230 ° C, the thickness of 1 mm is reduced by one hot rolling, and finally 5 m.
The Ni-based alloy sheet of the present invention having the composition shown in Tables 1 to 3 by having a thickness of m, further holding at 1200 ° C. for 30 minutes, water-quenched for solution treatment, and then buffing the surface. 1-21, comparative Ni-based alloy plates 1-
11 was produced. Further, commercially available Ni-based alloy plates 1 to 3 having the composition shown in Table 3 and having a thickness of 5 mm were prepared. These Ni-based alloy plates 1 to 21 of the present invention, comparative Ni-based alloy plates 1 to 11 and conventional Ni-based alloy plates 1 to 3 are each longitudinal:
A solution test piece was prepared by cutting into a size of 10 mm and width: 50 mm. Furthermore, in order to evaluate the influence of phase stability on the corrosion resistance to an inorganic acid-containing supercritical water environment, the Ni-based alloy plates 1 to 21 of the present invention, comparative Ni-based alloy plates 1 to 11 and conventional Ni-based alloy plate 1 are used. 100 to 550 ° C for a test piece consisting of
An aging treatment for holding for 0 hours was performed to prepare an aging material test piece.

Next, a flow-type corrosion tester using Hastelloy C-276 tube as an autoclave was prepared. The Hastelloy C-276 tube in this flow-through type corrosion tester is designed so that the test solution is pressed in from one end by a high-pressure pump and the test solution comes out from the other end.
The test solution inside the 276 tube can ensure a predetermined flow rate. Further, the test solution is heated by a heater provided in the Hastelloy C-276 tube portion, and the test solution can be kept at a predetermined temperature. Further, the test solution discharged from the other end of the Hastelloy C-276 tube in the flow-type corrosion test apparatus is collected in the reservoir tank via the pressure reducing valve.

A corrosion test was performed on the following inorganic acid-containing supercritical water simulation test solution using the flow type corrosion test apparatus. As test solution, fluid temperature: 550 ° C, pressure: 40MP
a, Dissolved oxygen amount: 8 ppm in supercritical water with hydrochloric acid: 0.05
A supercritical aqueous solution (hereinafter referred to as a PCB or dioxin-decomposing supercritical water simulation test solution) expected to be produced when decomposed / oxidized PCB / dioxin mixed with mol / kg was prepared. The above-mentioned PCB or dioxin-decomposing supercritical water simulated test solution is press-fitted into a Hastelloy C-276 tube in a flow-type corrosion tester, and the flow rate of PCB or dioxin-decomposing supercritical water simulated test solution inside the Hastelloy C-276 tube is 6 g / min
To form a supercritical water environment containing an inorganic acid, and under the environment, the Ni-based alloy sheets 1-2 of the present invention are controlled.
1. The presence or absence of pitting corrosion on the surface of the test piece was confirmed by holding the solution-solubilized material test piece consisting of the comparative Ni-based alloy sheets 1 to 11 and the conventional Ni-based alloy sheets 1 to 100 for 100 hours, and the results are shown in the table. It showed in 1-3.

Further, in order to evaluate the influence of phase stability on the corrosion resistance to the supercritical water environment containing an inorganic acid, the Ni-based alloy plates 1 to 21 of the present invention and the comparative Ni-based alloy plates 1 to 1 are used.
1 and the conventional Ni-based alloy plates 1 to 3 were held in the above-mentioned inorganic acid-containing supercritical water environment for 100 hours to confirm the presence or absence of pitting corrosion on the surface of the aging material test piece. Are shown in Tables 1 to 3.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

From the results shown in Tables 1 to 3, Ni of the present invention was obtained.
It can be seen that the base alloy plates 1 to 21 do not cause pitting corrosion and have excellent corrosion resistance as compared with the conventional Ni base alloy plates 1 and 2 in both the solution-solubilized material test piece and the aging material test piece. However, it is found that at least one of the corrosion resistance of the solution-solubilized material test pieces and the corrosion resistance of the aged material test pieces of the comparative Ni-based alloy sheets 1 to 5, which are out of the scope of the present invention, is inferior, which is not preferable.

[0024]

As described above, the Ni-based alloy of the present invention has excellent corrosion resistance in a supercritical water environment containing hydrochloric acid, can be used for a longer period of time, and can be used for environmentally friendly disposal such as detoxification of PCBs or dioxins. It brings excellent effects. The Ni-based alloy of the present invention is most effective when used in a supercritical water environment containing hydrochloric acid as described above.
Not limited to this, sulfuric acid, phosphoric acid, hydrofluoric acid,
It can also be used in supercritical water environments containing nitric acid, supercritical water environments containing chloride salts such as sodium chloride, magnesium chloride, calcium chloride, and supercritical water environments containing ammonia. Therefore, space-related waste, nuclear-related waste It can also be applied to supercritical water equipment materials for the disposal of materials, electronic power related waste, and general industrial waste. Further, when the Ni-based alloy of the present invention is used as a reaction process container of the apparatus main body, the outside is made of a strength material such as stainless steel, and the inner surface is made of the Ni-based alloy of the present invention.
The base alloy may be clad or lined.

Claims (5)

[Claims] 1. In mass%, Cr: 29 to less than 42%, T
a: more than 1 to 3%, Mg: 0.001 to 0.05%, N:
A composition containing 0.001 to 0.04%, Mn: 0.05 to 0.5%, the balance of Ni and unavoidable impurities, and adjusting the amount of C contained as unavoidable impurities to 0.05% or less. An Ni-based alloy having excellent corrosion resistance to an inorganic acid-containing supercritical water environment characterized by having. 2. In mass%, Cr: 29 to less than 42%, T
a: more than 1 to 3%, Mg: 0.001 to 0.05%, N:
0.001-0.04%, Mn: 0.05-0.5%,
C: Contains less than 0.05%, and Mo: 0.1-2
%, The balance consists of Ni and unavoidable impurities,
An Ni-based alloy having excellent corrosion resistance to a supercritical water environment containing an inorganic acid, which has a composition in which the amount of C contained as unavoidable impurities is adjusted to 0.05% or less. 3. In mass%, Cr: 29 to less than 42%, T
a: more than 1 to 3%, Mg: 0.001 to 0.05%, N:
It contains 0.001 to 0.04%, Mn: 0.05 to 0.5%, and further Fe: 0.05 to 1.0% and Si:
It has a composition containing one or two of 0.01 to 0.1%, the balance consisting of Ni and unavoidable impurities, and having the amount of C contained as unavoidable impurities adjusted to 0.05% or less. A Ni-based alloy having excellent corrosion resistance to a supercritical water environment containing a characteristic inorganic acid. 4. In mass%, Cr: 29 to less than 42%, T
a: more than 1 to 3%, Mg: 0.001 to 0.05%, N:
0.001 to 0.04%, Mn: 0.05 to 0.5%, Mo: 0.1 to 2%, and F
e: 0.05 to 1.0% and Si: 0.01 to 0.1
%, Containing 1 or 2 of the above, the balance being Ni and unavoidable impurities, and having a composition in which the amount of C contained as unavoidable impurities is adjusted to 0.05% or less. N with excellent corrosion resistance to critical water environment
i-based alloy. 5. A member for a supercritical water process reaction vessel, comprising a Ni-based alloy having the composition according to claim 1, 2, 3 or 4.