JPH02301537A - Precipitation hardening ni-base single crystal alloy having excellent stress corrosion cracking resistance - Google Patents

Abstract

PURPOSE:To improve the strength, stress corrosion cracking resistance and corrosion resistance of the alloy by adding Cu or furthermore Hf, Re, Mo, W and the like to an series precipitation hardening n-base single crystal alloy as alloy components. CONSTITUTION:An series precipitation hardening n-base single crystal alloy contg., by weight, 10 to 30% Cr, 0.1 to 5% Nb, 0.1 to 8% Ti, 0.1 to 8% Al and the balance Ni is incorporated with 0.05 to 0.5% Cu as a alloy additive to improve the stress corrosion cracking resistance. Or, 0.05 to 3% of one or both of Hf and Re are furthermore incorporated thereto to moreover improve the stress corrosion cracking resistance and 0.05 to 3% of one or both of Mo and W are added as well, by which the n-base single crystal alloy having improved corrosion resistance can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention basically consists of a γ' phase IN i in the matrix of the γ layer.
(AN, Ti)l or γ“ phase (N t 3N
A light water reactor for nuclear power generation, in which intermetallic compounds such as b) are precipitated, has a single crystal structure with the same crystal structure and orientation, has high strength and excellent corrosion resistance, and is located in a corrosive environment. The present invention relates to a precipitation-strengthened Ni-based alloy that exhibits excellent stress corrosion cracking resistance when used as bolt material, pin material, etc., which are structural members such as.

[Conventional technology]

Conventionally, since excellent corrosion resistance and high strength are required for manufacturing the above-mentioned bolt materials and pin materials, alloys with these characteristics, that is, in weight percent (hereinafter % indicates weight percent), Cr: 12-30%, Nb: 0.5-3%, Ti
A precipitation-strengthened Ni-based single crystal alloy is used, which has a composition of: 1 to 5% All, 0.2 to 3% All, and the remainder consisting of Ni and unavoidable impurities.

[Problem to be solved by the invention]

However, although the above-mentioned conventional precipitation-strengthened Ni-based single crystal alloy has high strength and excellent corrosion resistance, the corrosion resistance is insufficient when stress is applied in a corrosive environment like the bolt material mentioned above. It has the problem that it does not show any corrosion and is susceptible to stress corrosion cracking.

[Means to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors focused on the conventional precipitation-strengthened Ni-based single-crystal alloy and developed an alloy with excellent corrosion resistance without sacrificing its high strength and excellent corrosion resistance. As a result of research to impart stress corrosion cracking resistance to the conventional precipitation-strengthened Ni-based single crystal alloy,
Inclusion of Cu as an alloy component improves stress corrosion cracking resistance, and this improvement in stress corrosion cracking resistance is further improved by the inclusion of Hl' and Re.
They have found that the addition of Mo and W further improves corrosion resistance.

This invention was made based on the above findings, and includes: Cr: 10-30%, Nb: 0.1-5%, Ti:
0.1-8%, Ap: 0.1-8%, Cu: 0.
05 to 0.5%, and if necessary, one or two of H1' and Re 0.05 to 0.5%.
3%, and in addition to this, if necessary, one or two of Mc) and W: 0.05 to 3%, with the remainder consisting of Ni and unavoidable impurities. It is a precipitation-strengthened Ni-based single crystal alloy that has high strength, excellent corrosion resistance, and even better stress corrosion cracking resistance.

Next, the reason why the composition range of the Ni-based single crystal alloy of the present invention is limited as described above will be explained.

(a) CrC component has the effect of improving the corrosion resistance of the alloy, but if its content is less than 1096, the desired corrosion resistance cannot be secured, while if its content exceeds 30%,
As the solidification temperature range becomes wider, single crystallization becomes difficult, and as a result, the alloy becomes more likely to become polycrystalline.However, when comparing polycrystalline and single crystal structures, the stress corrosion cracking resistance of the former is significantly higher. The content was determined to be 10 to 30% since it would be inferior.

(b) Nb The Nb component combines with Ni to form a γ″ phase: (N + 3N
It forms an intermetallic compound consisting of b), which precipitates into the matrix of the γ phase and has the effect of improving the strength of the alloy.
If the content is less than 0.1%, the desired strength-improving effect cannot be obtained, while if the content exceeds 5%, the strength-improving effect is saturated and no further improvement effect can be obtained. Considering the properties, the content was determined to be 0.011 to 5%.

(c) Ti and A, Q These components have (N 1a(Ti,
l! ) form a γ′ phase consisting of an intermetallic compound of
It precipitates on the substrate together with the above γ ~ phase and has the effect of significantly improving the strength of the alloy, but the content is Ti:0.
．． If the content is less than 1% and A11): less than 0.1%, the desired strength improvement effect cannot be obtained;
If the i:8% and Al1:8% are exceeded, the solidification temperature range widens as in the case of Cr, making single crystallization difficult.
, A, Q: 0.1 to 8%.

(d) Cu The Cu component has the effect of improving the stress corrosion cracking resistance of the alloy, but if its content is less than 0.05%, the desired excellent stress corrosion cracking resistance cannot be ensured, On the other hand, if the content exceeds 0.5%, the strength of the alloy will decrease, so the content should be reduced to 0.05 to 0.5%.
It was determined that

(e) Hf and Re These components have the effect of further improving stress corrosion cracking resistance when coexisting with the Cu component, so they are included as necessary, but the content is 0.05 If the content is less than 3%, the desired improvement in the effect cannot be obtained, while if the content exceeds 3%, the alloy becomes brittle. Therefore, the content was set at 0.05 to 3%. .

(r) Mo and W These components have the effect of further improving the corrosion resistance of the alloy when coexisting with Cr, so they may be included as necessary, but if their content is less than 0.05%, the corrosion resistance will decrease. However, if the content exceeds 3%, the alloy becomes brittle, so the content was set at 0.05 to 3%.

Note that when the Ni-based single crystal alloy of the present invention contains one of B and Zr or 2N, these components segregate at the interface of dendrites unique to cast alloys, and as a result, the alloy becomes difficult to machine. It is recommended to include it when free machinability is required, as it further improves the cutting properties, but the content is preferably 0.005 to 0.5%, which is (
If it is less than 1,005%, the desired improvement effect cannot be obtained;
．． This is because if it exceeds 5%, the alloy strength will decrease.

〔Example〕

Next, the Ni-based single crystal alloy of the present invention will be specifically explained using examples.

Using an ordinary high-frequency induction furnace, prepare molten metals having the compositions shown in Table 1, and cast them to a diameter of 8h+.
The ingot was made into an ingot with a length of 100 + + m and then melted in a crucible in a vacuum furnace, then cast into a ceramic mold also placed in the vacuum furnace, and heated by a high-frequency heating coil placed around the ceramic mold. The ceramic mold is pulled out from the tropics at a predetermined pulling speed within the range of 100 to 300 dragons/hr, and the outer diameter is 1.
A round bar-shaped slab with dimensions of 0 m + g 100 to 20 at a given temperature within the range
Inventive Ni-based alloy slabs 1 to 25 and comparative Ni-based alloy slabs 1 to 9 were manufactured by performing aging treatment for 0 hours.

In addition, all of the comparative Ni-based alloy slabs 1 to 9 have one of the constituent components ff1 (marked with * in Table 1) outside the scope of the present invention.

Next, the crystal structure of the various Ni-based alloy slabs obtained as a result was observed using a metallurgical microscope, and the tensile strength at room temperature was measured for the purpose of evaluating the strength. Part diameter: 5III11 x Gauge distance: 20■
A tensile test piece of m was cut out, and using this tensile test piece, HBO; As B) about 500 ppm,
L i OH: (as Ll) approximately 2 ppm, N2:
Approximately 30cc-8TP1kg・N20, DO:5ppb
Below, C1-: 0. pH containing Ippa+ or less:
With the test piece immersed in an aqueous solution of about 7.
320℃, pressure +157kg/cl! .

A low strain rate tensile test (S S RT method) is performed under the condition of strain rate: 0.5 μs/sin, the fracture surface after fracture is observed, the stress corrosion cracking fracture surface rate is measured, and the corrosion resistance is further evaluated. For the purpose, after immersion in the above aqueous solution at room temperature for 500 hours,
Reduced corrosion! A DI fixed corrosion resistance test was conducted. These results are shown in Table 1.

〔Effect of the invention〕

From the results shown in Table 1, the Ni-based alloy slabs 1 to 1 of the present invention
No. 25 has a single crystal structure in which intermetallic compounds consisting of γ′ phase and γ′ phase are dispersed and precipitated in a γ phase matrix,
It has high strength and excellent stress corrosion cracking resistance and corrosion resistance, and in particular, it has even better stress corrosion cracking resistance than comparative Ni-based alloy slab 8, which corresponds to conventional Ni-based single crystal alloys. On the other hand, comparative Ni-based alloy slabs 1 to 9
As can be seen, it is clear that even if the content of any one of the constituent components falls outside the scope of the present invention, at least one of the above-mentioned properties will be inferior.

As mentioned above, the Ni-based single-crystal alloy of the present invention has - high strength and excellent corrosion resistance comparable to conventional Ni-based single-crystal alloys of the same type, and even better stress corrosion cracking resistance. Furthermore, the stress corrosion cracking resistance is further improved by the inclusion of Hr and Re, and the corrosion resistance is further improved by the inclusion of Mo and W. Therefore, these properties are required, for example, for nuclear power generation in a corrosive environment. When used as a structural member for light water reactors and the like, it has industrially useful properties such as allowing stable use over an extremely long period of time and providing high reliability.

Claims (1)

[Claims] (1) Cr: 10-30%, Nb: 0.1-5%, Ti
:0.1~8%, Al:0.1~8%, Cu:0.05
A precipitation-strengthened Ni-based single crystal alloy with excellent stress corrosion cracking resistance, characterized by having a composition (weight %) of ~0.5% and the remainder consisting of Ni and unavoidable impurities. (2) Cr: 10-30%, Nb: 0.1-5%, Ti
:0.1~8%, Al:0.1~8%, Cu:0.05
~0.5%, and further contains one or two of Hf and Re: 0.05~3%, and the remainder is Ni and unavoidable impurities (wt%). A precipitation-strengthened Ni-based single crystal alloy having excellent stress corrosion cracking resistance. (3) Cr: 10-30%, Nb: 0.1-5%, Ti
:0.1~8%, Al:0.1~8%, Cu:0.05
~0.5%, one or two of Hr and Re: 0.05 to 3%, and one or two of Mo and W: 0.05 ~3%
A precipitation-strengthened Ni-based single crystal alloy having excellent stress corrosion cracking resistance, characterized in that it has a composition (weight %) of the following, with the remainder consisting of Ni and unavoidable impurities.