JP2000192205A - Heat resistant alloy excellent in oxidation resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alloy exhibiting a reduced loss of oxidation and excellent oxidation resistance by allowing it to have a compsn. contg. specified ratios of C, Si, Mn, Ni, Cr, CuO, Ti, Al, and the balance Fe. SOLUTION: This heat resistant alloy is the one having a compsn. contg., by weight, 0.03 to 0.10% C, <=3.0% Si, <=1.5% Mn, 20 to 35% Ni, 12 to 25% Cr, 0.8 to 5.0% Cu, 0.1 to <0.5% Ti, 0.1 to <0.5% Al, and the balance Fe and excellent in oxidation resistance. Preferably, the alloy contains one or more kinds among the group of 0.1 to 0.5% Nb and Ta, <=1.5% Mo and <=3.0% W for increasing its high temp. strength, the group of 0.001 to 0.010% B and 0.001 to 0.1% Zr for increasing the grain boundaries and the group of 0.001 to 0.01% Ca and 0.001 to 0.01% Mg for reducing free S. Desirably, in the impurities, the content of P is controlled to <=0.025% and that of S to <=0.001%. It is suitable, e.g. for a member for a heating furnace in which heating at high temp. and cooling are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant alloy having excellent oxidation resistance suitable for various heat-resistant parts which repeatedly heat and cool to a high temperature, such as an automobile exhaust gas purifying apparatus.

[0002]

2. Description of the Related Art Conventionally, various heat-resistant parts which repeat heating and cooling, such as automobile exhaust gas purifying devices, heating furnace members, etc., include:
JIS NCF800 (C: 0.10% or less, Si:
1.00 or less, Mn: 2.50% or less, P: 0.030
Hereinafter, S: 0.015% or less, Ni: 30.00 to 3
5.00%, Cr: 19.0 to 23.00%, Cu:
0.75% or less, Al: 0.15 to 0.60%, Ti:
0.15 to 0.60%, with the balance substantially Fe) being widely used.

In the case where oxidation resistance at higher temperatures is required, JIS NCF601 (C: 0.10% or less, Si: 0.50% or less, Mn: 1.00% or less,
P: 0.030% or less, S: 0.015% or less, Ni:
58.0-63.00%, Cr: 21.00-25.
00%, Cu: 1.00% or less, Al: 1.00-1.
An iron-based superalloy such as 70% with the balance being substantially Fe) is used. However, the heat-resistant alloy of JIS NCF601 has a disadvantage that it contains a large amount of Ni and is expensive.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-resistant alloy which can be manufactured at a low cost and has a small oxidation loss even after repeated heating and cooling to a high temperature and has excellent oxidation resistance. And

[0005]

In order to solve the above-mentioned problems, the present inventors have made it possible to manufacture at low cost, and have excellent oxidation resistance with little oxidation loss even after repeated heating and cooling at high temperatures. After various studies on heat-resistant alloys,
When inexpensive Cu is contained in a heat-resistant alloy of JIS NCF800 and a heat-resistant alloy similar thereto in an amount of 0.8 to 5.0%, scale peeling can be suppressed. The present invention has been made based on the finding that it can be suppressed. That is, in the heat-resistant alloy having excellent oxidation resistance according to the present invention, C: 0.03 to 0.
10%, Si: 3.0% or less, Mn: 1.5% or less, N
i: 20 to 35%, Cr: 15 to 25%, Cu 0.8 to
5.0%, Ti: 0.1 to less than 0.5% and Al:
The alloy has an alloy composition containing 0.1 to less than 0.5% and the balance substantially consisting of Fe.

In order to solve the above-mentioned problems, in the heat-resistant alloy having excellent oxidation resistance according to the present invention, the alloy composition contains Nb: 0.1 to 0.5% and Ta: 0.1 to 0.5%.
5% of one or two groups, Mo: 1.5% or less and W: 3.0% or less, and B: 0.00
One or two groups of 1 to 0.010% and Zr: 0.001 to 0.1%, and one of Ca: 0.001 to 0.01% and Mg: 0.001 to 0.01% Alternatively, it is to have a component composition containing one or more of the two groups.

[0007]

Next, the reason why the alloy composition of the heat-resistant alloy having excellent oxidation resistance of the present invention is limited as described above will be described. C: 0.03 to 0.10% C is an element that forms a carbide with Cr, Ti, Nb, Ta, Mo, and W and is contained in order to increase the high-temperature strength of the alloy. If it is less than 0.10%, the expected high-temperature strength cannot be obtained. If it exceeds 0.10%, a large amount of coarse carbides is formed, which not only decreases the strength and toughness but also reduces the Cr content in the matrix.
And the oxidation resistance is also deteriorated.
03 to 0.10%. Si: 3.0% or less Si is an element to be contained as a deoxidizing agent at the time of melting and refining and to be included in order to improve the oxidation resistance. Therefore, the content is set to 3.0% or less.

Mn: 1.5% or less Mn is an element to be contained as a deoxidizing agent at the time of melting and refining like Si, but when contained in a large amount, oxidation resistance, hot workability and high-temperature strength are reduced. Therefore, the content is 1.
5% or less. Ni: 20 to 35% Ni is an element contained to stabilize the austenite phase and increase the high-temperature creep strength, but if it is less than 20%, the austenite phase becomes unstable, and if it exceeds 35%, the cost increases. Therefore, the content is set to 20 to 35%.

Cr: 12 to 25% Cr is an element contained to improve the oxidation resistance and to form a Cr carbide to increase the high-temperature strength. However, if it is less than 12%, the expected effect cannot be obtained. , More than 25%, promotes the precipitation of the sigma phase and lowers the high-temperature strength, toughness and hot workability.
%. Cu: 0.8 to 5.0% Cu is an element contained to suppress the separation of oxide scale generated on the alloy surface at a high temperature and to improve the oxidation resistance particularly in an environment where heating and cooling are repeated. , But 0.
If the content is less than 8%, the effect is small, and if it exceeds 5.0%, the hot workability is reduced, so that the content is 0.8 to 5.0.
%.

Ti: 0.1 to less than 0.5% Ti forms carbides to increase the high-temperature strength, and when held for a long time at 550 to 700 ° C., precipitates a γ ′ phase together with Al and causes a high temperature. Since the strength is further increased, it is an element to be contained. However, if it is less than 0.1%, the expected high-temperature strength cannot be obtained, and if it is 0.5% or more, the hot workability deteriorates. 0.1 content
To less than 0.5%. Al: 0.1 to less than 0.5% Al is contained as a deoxidizing agent at the time of melting and refining, improves oxidation resistance, and when held at 550 to 700 ° C. for a long time, γ of the intermetallic compound '(Ni ₃ Al) phase is precipitated to further increase the high-temperature strength. Therefore, it is an element to be contained. However, if it is less than 0.1%, the expected oxidation resistance and high-temperature strength cannot be obtained. When the content exceeds 0.5%, the hot workability deteriorates.
To less than 0.5%.

Nb and Ta: 0.1 to 0.5% Nb and Ta form carbides like Ti to increase the high-temperature strength, and when kept at 550 to 700 ° C. for a long time, metal together with Al Since the intermetallic compound forms γ 'and further increases the high-temperature strength, it is an element to be contained. However, if it is less than 0.1%, the expected oxidation resistance and high-temperature strength cannot be obtained. If the content exceeds the above, the hot workability and the oxidation resistance decrease, so that the content is set to 0.1.
1% to 0.5%. Mo: 1.5% or less, W: 3.0% or less Mo and W are formed in order to increase the high-temperature strength by partially forming carbides and to increase the high-temperature strength mainly by solid solution hardening of the matrix. Although it is an element to be contained, if it is contained in a large amount, not only does the cost rise, but also the oxidation resistance and hot workability decrease, so the content of Mo is 1.5%.
Hereinafter, W is set to 3.0% or less.

B: 0.001 to 0.010%, Zr:
0.001 to 0.1% B and Zr are elements contained to segregate at the grain boundaries and strengthen the grain boundaries. However, if the content is less than 0.001%, the effect is not obtained, and B is 0%. If the content exceeds 0.010% and Zr exceeds 0.1%, the hot workability deteriorates.
Is 0.001 to 0.010%, and Zr is 0.001 to 0.
1%. Ca: 0.001 to 0.01%, Mg: 0.001 to
0.01% Ca and Mg are elements contained to form stable sulfides to reduce free S and improve oxidation resistance.
If the amount is less than 0.001%, the effect cannot be obtained. If the amount is more than 0.01%, not only does the oxidation resistance decrease, but also the hot workability and high-temperature strength decrease. 0.001 to 0.01% of Ca, 0.001 of Mg
To 0.01%.

Regarding impurities, P is preferable because it makes the matrix brittle and lowers the ductility. Therefore, it is preferable that the content of P is less than 0.030% because the influence on the alloy is small and the cost is not increased. , 0.030% or less, preferably 0.025% or less. S itself oxidizes at a high temperature, and furthermore, this oxide remarkably accelerates the oxidation rate of the alloy and promotes peeling of the oxide scale. Therefore, it is preferable to reduce S as much as possible. If the content is less than 0.01%, preferably less than 0.0%
It is preferably set to 01 or less.

The heat-resistant alloy having excellent oxidation resistance according to the present invention comprises N
A known alloy having a similar content of i and Cr, for example, JIS
It can be manufactured by the same manufacturing method as the alloy of NCF800. The heat-resistant alloy having excellent oxidation resistance according to the present invention is used for heating at a high temperature such as a vehicle exhaust gas purification device, a heating furnace member, a boiler member, an incinerator member, and a combustion member of a heating device. And cooling are repeated.

[0015]

Next, embodiments of the present invention will be described.

EXAMPLES Each alloy having the composition shown in Table 1 was melted in a high-frequency induction furnace and cast to obtain a 50 kg ingot. After hot forging and hot rolling of this ingot, cut out a test piece,
A heat treatment of heating at 1050 ° C. for 1 hour followed by oil cooling was performed to obtain a test piece for an oxidation test. 1000 ° C using this test piece
Was carried out in accordance with JIS Z 2282, and the oxidation increase was measured. The results are shown in Table 2 below.

[0016]

[Table 1]

[0017]

[Table 2]

From these results, the oxidation weight gain of the examples of the present invention is 40.8 to 69.6 mg / cm ² , while that of the comparative example is 46.4 to 79.2 mg / cm ^2.
In the examples of the present invention containing Cu, the average was reduced by about 12% compared to the comparative example not containing Cu. Further, when examined in detail, No. 1 and No. 2 of the example were No. 11 and N of the comparative example containing no Cu.
Oxidation weight gain was reduced by about 14% as compared with o.12. In addition, in No. 3 of the high Si example, the oxidation increase was reduced by about 12% as compared with No. 13 of the comparative example which did not contain Cu, and Cu was contained even in the high Si alloy. The effect was recognized.

In order to improve the high temperature strength, Nb,
Examples No. 4 to No. 6 containing Ta, Mo, and W
In the case of No. 14 which contained Nb and Mo and did not contain Cu, the oxidation weight gain was reduced by about 12 to 18%. In addition, No. 7 and No. 8 of the examples containing B and Zr in order to strengthen the grain boundaries have an increased oxidation weight increase compared to No. 5 and No. 6 of the examples not containing B and Zr. I didn't. In addition, in order to form a stable sulfide and reduce free S while reducing S significantly, No. 9 and No. 10 of the examples containing Ca and Mg significantly reduce S. Without the Ca, Mg, Cu
No. 14 was reduced by about 26% as compared with No. 14, and N of the example containing neither Ca nor Mg was not significantly reduced.
Compared with o.8, it is about 11% and about 15% lower.

[0020]

According to the present invention, the above structure, that is, inexpensive C
By containing 0.8 to 5.0% of u, there is an excellent effect that the oxidation resistance at high temperatures is improved as compared with those not containing Cu.

Claims (5)

[Claims] C .: 0.03 to 1% by weight (the same applies hereinafter)
0.10%, Si: 3.0% or less, Mn: 1.5% or less, Ni: 20 to 35%, Cr: 12 to 25%, Cu
0.8 to 5.0%, Ti: 0.1 to less than 0.5% and Al: 0.1 to less than 0.5%, the balance being substantially F
A heat-resistant alloy having excellent oxidation resistance, characterized by having an alloy composition of e. 2. The method according to claim 1, wherein Nb: 0.1 to 0.1.
A heat-resistant alloy excellent in oxidation resistance, characterized by containing one or two kinds of 5% and Ta: 0.1 to 0.5%. 3. The method according to claim 1, wherein Mo:
A heat-resistant alloy excellent in oxidation resistance, comprising one or two kinds of 1.5% or less and W: 3.0% or less. 4. The method according to claim 1, wherein B: 0.001 to 0.010% and Zr: 0.0
A heat-resistant alloy excellent in oxidation resistance, characterized in that it contains one or two kinds of 01 to 0.1%. 5. The method according to claim 1, wherein the content of Ca is 0.001 to 0.01% and the content of M is
g: A heat-resistant alloy excellent in oxidation resistance, characterized by containing one or two kinds of 0.001 to 0.01%.