JPH09268337A - Forged high corrosion resistant superalloy alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forged high corrosion resistant superalloy produced by forging, used at high temp., and excellent in high temp. strength and corrosion resistance. SOLUTION: This alloy has a composition which consists of, by weight, <=0.015% C, <=1.0% Si, <=0.5% Mn, 15-25% Cr, <=20% Co, Mo and/or W in the range satisfying Mo+1/2W<=7%, 0.4-3% Al, 0.6-4% Ti, Nb and/or Ta in the range satisfying Nb+1/2Ta<=6%, 0.05-2% Re, <=20% Fe, and the balance Ni and in which Al+1/2Ti+1/4Nb+1/8Ta is regulated to 2-4.5%. It is preferable that either or both of <=0.01% B and <=0.1% Zr be incorporated to this alloy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super heat-resistant alloy which is manufactured by forging and is required to have high strength and corrosion resistance at high temperatures used in high temperatures such as disks and blades of gas turbines.

[0002]

2. Description of the Related Art As a super heat-resistant alloy used for gas turbine disks, blades, etc., conventionally, Waspaloy has been used.
Γ '(gamma prime) precipitation-strengthened Ni-based superheat-resistant alloys containing Al and Ti such as (trade name) are known. Since a gas turbine disk is required to have high tensile strength near 650 ° C., it is usually manufactured by forging. On the other hand, gas turbine blades are required to have high creep rupture strength,
It may be manufactured by precision casting, but part is manufactured by forging. In recent years, from the viewpoint of improving the life of gas turbine disks and blades, it has been desired to improve not only the strength but also the resistance to corrosion. Further, in order to reduce the cost of the fuel used, there are cases in which the S content in the fuel is increased and corrosion is promoted. Therefore, development of a material with improved resistance to corrosion is desired. By the way, for turbine blades produced by precision casting and casting such as unidirectional solidification, Al, Ti,
Although it contains a large amount of W, Mo, Ta, etc., it is known that the addition of Re improves the high temperature strength and the corrosion resistance for such a limited composition (JP-A-61-161). 28
No. 4545, disclosed in JP-A-7-70679).

[0003]

Since there is no restriction on hot workability, a large amount of Al, Re, etc. can be added to the above-mentioned cast alloy. However, if a large amount of elements such as Al and Re are added to a member manufactured by forging, forging is impossible. Therefore, it has been desired to improve the corrosion resistance while having an alloy composition that can be forged.

[0004]

As a result of various investigations, the present inventor has focused on Re, which has not been contained in conventional forged alloys, and made it contain a small amount of Re and further added elements such as Al, Ti and Mo. It has been found that by adjusting the amount, the corrosion resistance can be greatly improved without causing deterioration in forgeability. That is, the first invention of the present invention is, by weight%, C 0.015%
Below, Si 1.0% or less, Mn 1.0% or less, Cr15
-25%, Al 0.4-3%, Ti 0.6-4%, Re
0.05 to 2%, and Al + 1 / 2Ti is 2 to
It is a forged high-corrosion-resistant superheat-resistant alloy characterized by comprising the balance Ni and unavoidable impurities at 4.5%.

A second aspect of the present invention has the same basic composition as the first aspect of the invention, depending on the manufacturability of the forged member and the use conditions, a group of Mo and W, a group of Nb and Ta, or Co and Fe.
One or more of the above elements are added within a specific range, and in% by weight, C 0.015% or less, Si 1.0
% Or less, Mn 1.0% or less, Cr 15 to 25%, Co2
0% or less, 1 or 2 types of Mo and W are Mo + 1 / 2W
7% or less, Al 0.4% to 3%, Ti 0.6 to 4%,
6% of 1 or 2 of Nb and Ta with Nb + 1/2 Ta
Hereinafter, Re of 0.05 to 2% and Fe of 20% or less are contained, and Al + 1 / 2Ti + 1 / 4Nb + 1 / 8Ta is 2 to
It is a forged high-corrosion-resistant superheat-resistant alloy characterized by comprising the balance Ni and unavoidable impurities at 4.5%.

Furthermore, the third invention of the present invention is the desirable alloy composition of the first or second invention, in which C0.015 in% by weight is used.
% Or less, Si 0.2% or less, Mn 0.1% or less, Cr1
5 to 25%, Co 10 to 20%, 1 or 2 kinds of Mo and W in Mo + 1 / 2W, 2 to 6%, Al 0.8% to 3
%, Ti 1 to 4%, Re 0.05 to 2%, and A
1 + 1 / 2Ti is 2 to 4.5%, and the balance is Ni and inevitable impurities.

More preferably, the alloy according to any one of the first to third inventions contains B0.01% or less and Zr0.1.
% Forged high corrosion resistant super heat resistant alloy containing 1 or 2% or less. Among the alloy compositions of the above first to third inventions, particularly preferably, by weight%, C 0.01% or less, S
i 0.2% or less, Mn 0.1% or less, Cr 18 to 21
%, Co12-15%, Mo3.5-5%, Al1.2
% To 3%, Ti 1.5 to 3%, Re 0.05 to 2%, B
0.003 to 0.01% and Zr 0.02 to 0.08% are included, and Al + 1 / 2Ti is 2.5 to 4% and the balance is Ni.
And inevitable impurities.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The action of each element in the alloy of the present invention will be described below. By forming a carbide, C contributes to prevention of crystal grain coarsening, increase in creep rupture strength and ductility. However, excessive addition lowers the strength by fixing Ti, Nb, and Ta, which contribute to the strength, as carbides, and further reduces the ductility in the direction perpendicular to the forging direction by forming striped carbides. Therefore, the range of C is limited to 0.015% or less. The desirable range of C is 0.01% or less. Si is added as a deoxidizing element and has the effect of improving the oxidation resistance, but excessive addition causes a drop in high temperature strength.
Is limited to 1.0% or less. Preferably it is 0.2% or less.

Mn is added as a desulfurizing element. However, excessive addition of Mn not only promotes the alloy deviation, but also deteriorates the high temperature mechanical properties, so that Mn is 1.0
% Or less. It is preferably 0.1% or less. C
r is an essential element for improving the oxidation resistance and corrosion resistance of the disks and blades of the gas turbine. In order to obtain the effect, at least 15% is necessary, but excessive addition destabilizes the structure and causes precipitation of σ phase and reduces ductility and toughness. Therefore, Cr is limited to 15 to 25%.
The preferable range of Cr is 18 to 21%.

Al is an essential element that forms a γ '(gamma prime) phase composed of Ni ₃ Al to increase the high temperature strength. To obtain that effect, at least 0.4% is necessary, but excessive addition lowers hot workability, so
It is limited to 0.4 to 3%. Desirable Al range is 0.8
˜3%, more preferably 1.2 to 3%. Similar to Al, Ti also forms a gamma prime phase and has a function of solid solution strengthening the gamma prime phase. In order to obtain the effect, at least 0.6% is required, but excessive addition causes the gamma prime phase to become unstable at high temperature, leading to coarsening at high temperature and forming a harmful η (eta) phase. On the contrary, Ti is limited to 0.6 to 4% because it lowers the high temperature strength.
The preferable range of Ti is 1 to 4%, more preferably 1.
5 to 3%.

Re is an important element for constituting the alloy composition of the present invention. It has been found that the addition of a small amount of Re significantly improves the corrosion resistance when using a forged member such as a disk or a plate of a gas turbine. To obtain the effect, 0.05% is necessary, but Re is a very expensive element, and excessive addition causes an increase in cost, so it is limited to 0.05 to 2%. Mo and W are homologous elements, and W has an atomic weight twice that of Mo. Therefore, the effect can be summarized as Mo + 1 / 2W. Mo and W are not necessarily added, but both elements have the effect of solid-solution strengthening the austenite base to increase high-temperature strength, and one or two kinds can be added if necessary. However, excessive addition deteriorates hot workability, and further
As in the case of (1) and (2), the precipitation of σ phase and the like reduces ductility and toughness.
It is preferable that it is 7% or less at o + 1 / 2W. Preferably,
Mo + 1 / 2W is 2 to 6%. Among Mo and W, it is more preferable to use Mo having a small atomic weight because the addition amount can be reduced and it is advantageous in terms of specific gravity and price. Therefore, Mo is more preferably 3.5 to 5%.

Nb and Ta are homologous elements, and Ta is Nb.
Since it has twice the atomic weight, the effect is approximately Nb + 1 /
Can be organized in 2Ta. Nb and Ta are not necessarily added, but both elements have the same effect of solid solution strengthening the gamma prime phase as Ti does. Therefore, if necessary, one or two kinds may be added to Ti to further add The high temperature strength can be increased. However, excessive addition causes the gamma-prime phase to become unstable at high temperature, leading to coarsening at high temperature, and not contributing to strengthening δ
This is not preferable because it forms a (delta) phase and rather lowers the high temperature strength and increases the cost. Therefore N
When one or two of b and Ta are added, Nb +
It is preferable that it is 6% or less at 1/2 Ta. Co does not necessarily have to be added, but since it has the effect of increasing the alloy matrix at high temperatures, it is preferable to add it as necessary. However, Co is an expensive element, so if Co is added,
The upper limit is preferably 20%. When adding Co, it is desirable to make it 10 to 20%.

It is desirable that Fe is not added when strength is important, but a small amount of Fe may be added because it has effects of cost reduction and improvement of hot workability. However, excessive addition lowers the high temperature strength, so even if it is added, it should be 20% or less. B and Zr do not necessarily have to be added, but since they have the effect of strengthening the grain boundaries of forged members such as disks and blades of gas turbines, and increasing the high temperature strength and ductility, they may be used alone or in combination as needed. Can be added. However, if excessively added, the melting point of the crystal grain boundary is lowered and the hot workability is deteriorated. Therefore, when it is added, B is 0.01% or less and Zr is 0.1% or less. Is good. Desirably B is from 0.003
0.01%, Zr is 0.02 to 0.08%, and more preferably, both elements are added in combination.

Note that forging becomes extremely difficult when the amount of gamma prime increases. The gamma prime amount is the Al equivalent (Al + 1 / 2Ti + 1 / 4Nb + 1 /
8%), but if this amount is 2% or less, high temperature strength is not sufficient, and if it exceeds 4.5%, forging becomes difficult, so Al + 1 / 2Ti + 1 / 4Nb + 1/8
Ta is limited to 2 to 4.5%. When Nb and Ta are not added, Al + 1 / 2Ti is more preferably 2.5.
~ 4%. The following elements may be included in the alloy of the present invention within the ranges shown. P ≦ 0.04% S ≦ 0.03% Cu ≦ 0.30% V ≦ 0.5% Mg ≦ 0.02% Ca ≦ 0.02%

[0015]

Example An alloy having the composition shown in Table 1 was melted by vacuum induction melting to prepare a 10 kg ingot and then forged into a 30 mm square bar. Among them, the alloys 1 to 18 of the present invention and the comparative alloy 20 could be forged, but the comparative alloy 21 could not be forged because cracks occurred during the forging. This is due to the large amount of Al and Ti, and it is necessary to set Al, Ti, Nb and Ta within the composition range of the alloy of the present invention in order to enable forging. Oil-cooling after holding 4 hours at 1010 ° C, oil-cooling after holding 4 hours at 840 ° C, 16H at 760 ° C.
After holding r, a heat treatment of air cooling was performed. After that, it was processed into a predetermined test piece shape and various evaluations were performed. The tensile test was performed at room temperature and 540 ° C. The creep rupture test was conducted under the conditions of a temperature of 815 ° C. and a stress of 180 MPa. For further evaluation of corrosion resistance, Na ₂ SO ₄ 90% + NaCl 10
% Of the corrosive agent was applied to the sample so as to be 20 mg / Cm ² , the sample was held at 800 ° C. for 20 hours, and then the scale was removed to obtain the corrosion weight loss.

[0016]

[Table 1]

Table 2 shows the tensile strength at room temperature, the tensile strength at 540 ° C., the creep rupture time at 815 ° C. and 180 MPa, and the corrosion weight loss.

[0018]

[Table 2]

From the results shown in Table 2, it is understood that all the alloys of the present invention have good mechanical properties, the corrosion weight loss is obviously smaller than that of the comparative alloy 20, and the corrosion resistance is improved.

[0020]

EFFECT OF THE INVENTION By using the alloy of the present invention, it is possible to improve the corrosion resistance of gas turbine disks, blades, etc., and it is possible to improve the efficiency of gas turbines, extend their service lives, and lower the quality of fuel. .

Claims (5)

[Claims] 1. C 0.015% or less by weight%, Si
1.0% or less, Mn 1.0% or less, Cr 15 to 25%,
Al 0.4-3%, Ti 0.6-4%, Re 0.05-
A forged high-corrosion-resistant superheat-resistant alloy containing 2% and Al + 1 / 2Ti of 2 to 4.5% and the balance Ni and inevitable impurities. 2. C 0.015% or less by weight%, Si
1.0% or less, Mn 1.0% or less, Cr 15 to 25%,
Co 20% or less, 1 or 2 types of Mo and W Mo + 1
7% or less at / 2W, Al 0.4% to 3%, Ti 0.6 to
4%, 1 or 2 of Nb and Ta is Nb + 1 / 2Ta
6% or less, Re 0.05 to 2%, Fe 20% or less, and Al + 1 / 2Ti + 1 / 4Nb + 1 / 8Ta 2 to 4.5% with the balance Ni and inevitable impurities. Corrosion resistant super heat resistant alloy. 3. C 0.015% or less by weight%, Si
0.2% or less, Mn 0.1% or less, Cr 15 to 25%,
Co10 to 20%, Mo + and 1 or 2 kinds of Mo +
2 to 6% at 1/2 W, Al 0.8% to 3%, Ti 1 to 4
%, Re 0.05 to 2%, and Al + 1 / 2Ti
Is 2 to 4.5% and the balance consists of Ni and unavoidable impurities. A forged high corrosion resistant super heat resistant alloy. 4. The forged high-corrosion-resistant superheat-resistant alloy according to claim 1, which contains one or two of B 0.01% or less and Zr 0.1% or less. 5. C. 0.01% or less, Si0.
2% or less, Mn 0.1% or less, Cr 18-21%, Co
12-15%, Mo 3.5-5%, Al 1.2% -3
%, Ti 1.5 to 3%, Re 0.05 to 2%, B0.0
03-0.01%, including Zr 0.02-0.08%,
Further, a forged high corrosion resistance super heat resistant alloy, characterized in that Al + 1 / 2Ti is 2.5 to 4% and the balance is Ni and inevitable impurities.