JPH01252751A - Co-based alloy having excellent corrosion resistance to molten carbonate - Google Patents

Abstract

PURPOSE:To provide the title alloy with excellent corrosion resistance and to regulate its toughness, strength, workability and electric conductivity in the use to sufficient level by specifying the content of C, Si, Cr, Al, Ni and Fe in a Co-based alloy. CONSTITUTION:The compsn. of a Co-based alloy is constituted of, by weight, <=0.30% C, <=0.20% Si, 15-30% Cr, 0.05-2% Al, <=25% Ni, <=15% Fe and the balance consisting of Co with inevitable impurities. If required, one or more kinds among <=0.5% Mn, <=3% Mo, <=3% W, <=1% Nb, <=0.1% N, <=1% Ti, <=0.3% Zr, <=0.03% B, <=0.5% Y and <=0.5% rare earths are furthermore added thereto. The Co-based alloy has excellent corrosion resistance to molten carbonate under the environment on both sides of the anode and cathode in a molten carbonate-type fuel cell.

Description

[Detailed Description of the Invention] C. Industrial Application Field] This invention is suitable as a material for parts that may come into contact with molten carbonate, such as current collector plates and separators of molten carbonate fuel cells. The present invention relates to a Co-based alloy that has excellent resistance to molten carbonate corrosion.

[Conventional technology]

Conventionally, Ni or NCF600 is used on the anode side as a material for separators and current collector plates in molten carbonate fuel cells.
However, 5US316 is used on the cathode side. The reason why the materials used for the anode and cathode are different in this way is that there is no alloy that can satisfy both corrosion resistance and conductivity on both the anode and cathode sides.

According to "Report of the 123rd Committee on Heat-Resistant Materials Vol. 27. Koji 3", a material in which M is added to 5tlS310S has been reported, but this material has the drawback of significantly decreasing toughness at the operating temperature. , cannot withstand long-term use.

[Problems to be Solved by the Invention] As mentioned above, in the past, different materials were used for the anode side and the cathode side for the separator and current collector plate of a molten carbonate fuel cell. There was a problem that the structure became complicated.

Clad plates of 5US316 and N1 or NCF600 have been used, but such clad plates are expensive and the corrosion resistance of 303316 is insufficient for long-term use. Therefore, there is a problem in that corrosion must be increased to a large extent.

Therefore, an object of the present invention is to provide a fuel cell that has excellent corrosion resistance in both the anode and cathode environments of a molten carbonate fuel cell, and has practically sufficient toughness, strength, workability, and electrical conductivity during use. The object of the present invention is to provide a Co-based alloy that has excellent molten carbonate corrosion resistance at a standard level.

[Means to solve the problem]

The Co5 alloy of the present invention having excellent molten carbonate corrosion resistance has the following properties: C: 0.30wt, % or less, Si: 0.20wt, % or less, Cr: 15-30wt, χ, JV
: 0.05~2wt, χ, Ni: 25wt,
% or less, Fe: 15wt, % or less, and, if necessary, a small amount selected from the group consisting of the following (both one element: An: 0.5wt, % or less, Mo: 3st, % or less, W: 3wt, %) Below, Nb: 1wt, % or less, N: 0.1wt, % or less, Ti: 1wt, % or less, Zr: 0.3wt, % or less, B: 0.03wt, % or less, Y: 0.5wt, % Below, rare earth elements: 0.5wt, % or less, and the remainder: Co
and unavoidable impurities.

Next, the reason why the chemical composition of the Co-based alloy of the present invention is limited within the above-mentioned range will be described below.

C: C has a deoxidizing effect and an effect of improving the high temperature strength of the alloy. However, its content is 0.30w
Even if t and χ are exceeded, no further improvement in high-temperature strength is observed, and when 0.30 wt and χ are exceeded, hot workability deteriorates on the contrary. Therefore, the content of C is 0.30wt
,% or less.

Although 31 Si is commonly added as a deoxidizer, we have found that SL is detrimental to the molten carbonate corrosion resistance of the alloy. Therefore, it is better to have a lower Si content, but melted raw materials generally contain a considerable amount of St. For example, the St content of ferrochrome is about 0.6 wt, χ. Therefore, considering the molten carbonate corrosion resistance and manufacturing cost, the upper limit was set to 0.20wt,
km limited location.

Cr; Cr has the effect of improving the molten carbonate corrosion resistance of the alloy in the cathode side environment.

However, if the content is less than 15i+t, 1,
On the other hand, if the content exceeds 30 wt, χ, the molten carbonate corrosion resistance in the anode side environment deteriorates, and hot workability also deteriorates.

Therefore, the content of Cr should be limited within the range of 15 to 30 wt, χ.

AZ: AZ has a deoxidizing effect, an effect of improving high temperature strength, and an effect of improving molten carbonate corrosion resistance. However, if the content is less than 0.05wt, χ, the desired effect cannot be obtained in the above action;
If it exceeds this, corrosion scale with poor electrical conductivity will occur and electrical resistance will increase. Therefore, the content of M is 0.05~
It should be limited within the range of 2-t, χ.

Nj: Ni has the effect of improving the toughness of the alloy after aging. However, the Ni content is 25wt,
If χ is exceeded, the excellent high-temperature strength characteristic of Co-based alloys cannot be obtained. Therefore, the Ni content should be limited to 25 wt.% or less.

Fe: re is an effective element for reducing the cost of alloys. However, when the content exceeds 15 wt, χ, the molten carbonate corrosion resistance of the alloy on the anode side deteriorates. Therefore, the Fe content is 15ht,%
It should be:

Mn has desulfurization and deoxidizing properties, and Mo, W, Nb,
N.

Ti, Zr and B have the effect of improving the high temperature strength of the alloy, and Y and the rare earth element (Ce) have the effect of improving the high temperature strength of the alloy.

La, S, Nd, etc.) have the effect of improving the molten carbonate corrosion resistance of the alloy in the cathode environment. Therefore, in the Co-based alloy of the present invention, at least one of the above elements is added as necessary. The reason why the chemical composition was limited to the above-mentioned range will be described below.

Mn: If the Mn content exceeds 0.5 wt, χ, hot workability deteriorates and toughness decreases during use. Therefore, the Mn content should be limited to 0.5 wt.% or less.

Mo: When the Mo content exceeds 3 wt, χ, the weldability and hot workability of the alloy deteriorate. Therefore, hO
The content of should be limited to 3-11% or less.

W: When the W content exceeds 3 wt, χ, the weldability and hot workability of the alloy deteriorate. Therefore, the W content should be limited to 3 wt.% or less.

Nb: When the Nb content exceeds 1 st, χ, the weldability and hot workability of the alloy deteriorate. Therefore, Nb
The content should be limited to 1 wt.% or less.

N: When the N content exceeds Q, 1wt, χ, the hot workability of the alloy deteriorates. Therefore, the N content is 0.1
wt,% or less.

Ti: If the Ti content exceeds l wt, χ, the in-use toughness of the alloy deteriorates. Therefore, the content of Ti should be limited to 1-L8% or less.

Zr: When the amount of Zr exceeds 0.3wt, χ,
The hot workability of the alloy deteriorates. Therefore, the content of Zr should be limited to 0.3wt,X or less.

B: When the content of B exceeds 0.03wt, X, the weldability and hot workability of the alloy deteriorate. Therefore, the content of B should be limited to 0.03 wt.% or less.

Y: When the content of Y exceeds 0.5 wt, χ, the hot workability of the alloy deteriorates. Therefore, the content of Y is 0.5
wt,% or less.

Rare earth elements (Ce, La, Ss, Nd, etc.): When the content of rare earth elements exceeds 0.5 wt, χ, the hot workability of the alloy deteriorates. Therefore, the content of rare earth elements should be limited to 0.5 wt.% or less.

Next, the Co-based alloy of the present invention will be further explained using Examples while comparing it with Co-based alloys that are outside the scope of the present invention.

〔Example〕

As shown in Table 1, specimens 1 to 32 of the Co-based alloy of the present invention (hereinafter referred to as "specimens of the present invention") having chemical compositions within the range of the present invention, and Table 2 As shown in FIG.
was prepared by the method described below.

Present invention specimen Hill-32 and comparison specimen Nα1
Each of the alloys for preparing ~14 was melted in a 50 kg vacuum furnace and cast into slabs.The obtained slabs were then hot rolled to obtain hot rolled sheets with a thickness of 15+W. For each hot-rolled sheet thus obtained,
A thickness of 5 mm was obtained from each of the solution heat treated hot rolled sheets.

The test specimens of the present invention 1 to 32 have dimensions of 15 m in length and 25 m in width.
And comparative specimens 1 to 14 were cut out.

Next, the present invention specimens 1 to 32 and comparative specimen k
Charpy test absorbed energy (toughness), molten carbonate corrosion resistance and electrical resistance in the anode side environment and cathode side environment were measured for each of 1 to 14 by the methods described below, and the measurement results are shown in Table 3. and shown in Table 4.

(1) Charpy test absorbed energy: Each of the present invention specimens Floors 1 to 32 and comparative specimens Floors 1 to 14 was subjected to an aging treatment consisting of heating at a temperature of 650°C for 1000 hours. A 2 m V non-Charpy impact test piece was cut out from each of the aging-treated specimens, and a Charpy impact test was conducted using this test piece at a temperature of 0'C, and the absorbed energy was measured. .

(2) Molten carbonate corrosion resistance: Invention specimen Ntll~32 and comparative specimen Toru1~
On both surfaces of each of 14, zsOa and 6 at 38-0lχ
A suspension of a mixed salt with 2-〇1χLi1Cos suspended in an acetone solution was applied to a thickness of 10 μ/d.Next, each specimen coated with such a suspension was coated with 20
The sample was heated at a temperature of 650° C. for 20 hours in an anode-side environment of χHz-60χcot-2oχH,O, and the amount of decrease in weight after descaling compared to before heating was measured. In addition, each of the specimens was 15χ0!30X
Co! The cathode side was heated in an environment of 55χN□ at a temperature of 650''C for 20 hours, and the amount of decrease in weight after descaling compared to before heating was measured. Molten carbonate corrosion resistance was evaluated based on the amount of weight loss in the environment and cathode side environment.

(3) Electrical Resistance Each of the specimens tested for molten carbonate corrosion resistance in the cathode environment according to (2) above was
The specimens were sandwiched between two porous NiO plates impregnated with a mixed solution of iSOs and 62*olχLigCo3, and each of the specimens sandwiched between the porous NiO plates was then sandwiched between thin gold plates. After pressing and heating this at a temperature of 650'C, a terminal is attached to the thin gold plate,
The electrical resistance was measured by the four-terminal method.

Table 3 Table 3 Table 4 As is clear from Tables 3 and 4, Si and M
Comparative specimen Tetsu 1, which is made of a Fe-based alloy with a high n content outside the range of the present invention and does not contain Go or M, has low Charpy absorbed energy and low absorption energy in the anode and cathode environments. Both corrosion weight loss is large, S
The content of i is beyond the scope of the present invention, and Co,
Comparative specimen Koji 2, which is made of an Nl-based alloy that does not contain Cr or M, has extremely large corrosion loss in the cathode side environment and has a low Cr content that is outside the range of the present invention. 3, there is a lot of corrosion loss in the cathode side environment.
Comparative specimens 4 and 5, in which the content of IV is higher than the range of the present invention, have high electrical resistance, and comparative specimen 5 has low Charpy absorbed energy, Si
Comparative specimen Nn whose content exceeds the range of the present invention
Samples No. 6 and 7.8 have a large amount of corrosion loss in the cathode side environment, comparative specimens N117 and 8 have low Charpy absorbed energy, and No. 8 has a large corrosion loss in the anode side environment.

Comparative specimen 11, in which the content of Mo and W is outside the range of the present invention and is high, and the content of klO1Fe is high and out of the range of the present invention. Comparative specimen k12 whose Nb content is outside the range of the present invention, comparative specimen k13 whose Nb content is high outside the range of the present invention, and comparative specimen A14 whose W content is high beyond the range of the present invention. Both have low Charpy absorbed energy,
→-N tote≠The mark X in Table 4 indicates that the various properties described above are poor.

On the other hand, specimens N111 to 32 of the present invention all had high Charpy absorbed energy (excellent toughness, small corrosion loss in the anode and cathode environments, and low electrical resistance).

As mentioned above, the content of Si and Cr has a great influence on corrosion loss, and the content of M has a great influence on electrical resistance.
The figure shows Si content and corrosion i% in the cathode side environment! It is a graph showing the relationship with I. In Fig. 1, the ○ mark indicates the specimen of the present invention, the Δ mark indicates the comparative specimen, and the squares attached to each town indicate the hidden specimen.As is clear from Fig. 1, the Si content is exceeds 0.20wt, χ, the corrosion loss in the cathode side environment becomes significantly large.

FIG. 2 is a graph showing the relationship between Cr content and corrosion loss in the cathode side environment. The O mark, the Δ mark, and the marks attached to each town in Fig. 2 are the same as above. As is clear from FIG. 2, when the Cr content is less than 15 wt.1, the corrosion loss in the cathode side environment becomes significantly large.

FIG. 3 is a graph showing the relationship between M content and electrical resistance. The O mark, Δ mark, and the marks attached to each town in Figure 3 are the same as above. As is clear from Figure 3, M
When the content exceeds 2-t, χ, the electrical resistance increases significantly.

〔Effect of the invention〕

As described above, the Co-based alloy of the present invention has excellent molten carbonate corrosion resistance in both the anode and cathode environments of molten carbonate fuel cells, and has a toughness of 2.
Strength, workability, and electrical conductivity during use are at a practically sufficient level. As described above, the present invention brings about many excellent industrial effects, such as being able to extend the life of current collector plates and separators of molten carbonate fuel cells.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between Si content and corrosion loss in the cathode environment, Figure 2 is a graph showing the relationship between Cr content and corrosion loss in the cathode environment, and Figure 3 is a graph showing the relationship between M content and corrosion loss in the cathode environment. It is a graph showing the relationship with electrical resistance.

Claims (1)

[Claims] 1. C: 0.30wt. % or less, Si: 0.20wt. % or less, Cr: 15-30wt. %, Al: 0.05-2wt. %, Ni: 25wt. % or less, Fe: 15wt. % or less, and the remainder: A Co-based alloy with excellent molten carbonate corrosion resistance, characterized by consisting of Co and inevitable impurities. 2, C: 0.30wt. % or less, Si: 0.20wt. % or less, Cr: 15-30wt. %, Al: 0.05-2wt. %, Ni: 25wt. % or less, Fe: 15wt. % or less, at least one element Mn selected from the group consisting of: 0.5wt. % or less, Mo: 3wt. % or less, W: 3wt. % or less, Nb: 1wt. % or less, N: 0.1wt. % or less, Ti: 1wt. % or less, Zr: 0.3wt. % or less, B: 0.03wt. % or less, Y: 0.5wt. % or less, rare earth elements: 0.5wt. % or less, and the remainder: A Co-based alloy with excellent molten carbonate corrosion resistance, characterized by consisting of Co and inevitable impurities.