JPH064900B2 - Corrosion resistance High strength Ni-based alloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-strength Ni-based alloy having good corrosion resistance to non-oxidizing acids such as sulfuric acid, hydrochloric acid, and hydrofluoric acid.

[Conventional technology and its problems]

Solid solution strengthened Ni-based alloys such as Alloy 625 and Hastelloy C are known as alloys having good corrosion resistance to non-oxidizing acids such as sulfuric acid, hydrochloric acid and hydrofluoric acid. However, none of these alloys has sufficient strength, and the tensile strength thereof is 100 Kgf / mm ² or less under ordinary heat treatment conditions.

On the other hand, among precipitation-strengthened Ni-based alloys such as Alloy 718, there are many high-strength alloys with a tensile strength exceeding 110 Kgf / mm ² , but none of these were developed for corrosion resistance to acids. Therefore, the corrosion resistance to non-oxidizing acids such as sulfuric acid, hydrochloric acid and hydrofluoric acid is not sufficient. Precipitation hardening type stainless steels such as 17-4PH are also used as high strength corrosion resistant materials, but although these have sufficient corrosion resistance to oxidizing acids such as nitric acid, they do not contain sulfuric acid, hydrochloric acid, hydrofluoric acid, etc. It has almost no corrosion resistance to oxidizing acids. Therefore, the conventional alloy has a shortcoming that its life is short for applications such as molding equipment parts such as resin and rubber, electroplating parts, and semiconductor manufacturing equipment parts.

An object of the present invention is to provide a high strength Ni-based alloy having good corrosion resistance to non-oxidizing acids such as sulfuric acid, hydrochloric acid and hydrofluoric acid.

[Means for solving problems]

The Ni-based alloy of the present invention contains 4 to 16% by weight of Cr and 9 to 20% by weight.
Mo, 0.2-1.0% Al, Ti more than 1.0% and less than 4%, 10%
Fe below and C below 0.1%, Nb below 6% and 12%
1 or 2 of the following Ta is included, and Ti + 1 / 2Nb + 1 / 4Ta is 2
.About.5%, and the balance is substantially Ni except impurities.

Cr is an element necessary to enhance corrosion resistance. If it is at least 4%, an effective corrosion resistance cannot be obtained, but if it exceeds 16%, harmful intermetallic compounds are formed and the ductility of the alloy is lowered. Therefore, Cr is 4 to 16%. The preferred Cr range is 7 to 14%
Is.

Mo is an indispensable element for enhancing the corrosion resistance to non-oxidizing acid, and at least 9% is necessary, but if it exceeds 20%, harmful intermetallic compounds are produced, which lowers the corrosion resistance and at the same time the ductility of the alloy. Lowers the hot workability. Therefore, Mo is 9 to 20%. The preferred range is 10 to
17%.

Al is an essential element for stably precipitating the γ'phase or the γ "phase, and at least 0.2% is necessary, but if it exceeds 1.0%, the hot workability deteriorates. 1.0
%. The preferred range is 0.3-1.0%, especially 0.4-0.6%
Is.

Ti is an element indispensable for strengthening the precipitation by forming the γ'phase represented by Ni ₃ (Al, Ti). It is necessary to exceed 1.0%, but if it exceeds 4%, hot workability Is deteriorated, so it is limited to more than 1.0% and 4% or less. A preferred range is more than 1.0% and 3% or less, and particularly more than 1.0% and 2% or less.

Fe has a function of enhancing hot workability, so a small amount is useful, but if it is excessively large, corrosion resistance and strength are deteriorated, so the content is limited to 10% or less. It is preferably 8% or less.

C combines with Ti, Mo, Ta, etc. to form stable MC-type carbides and plays a role of preventing excessive coarsening of austenite crystal grains during solution treatment, so a small amount of C is necessary. If it exceeds 0.1%, carbides are excessively formed and the hot workability is impaired, so C is limited to 0.1% or less. It is preferably 0.01 to 0.05%.

Nb or Ta forms a γ ″ phase represented by Ni ₃ (Al, Nb, Ta). Since the γ ″ phase has a precipitation strengthening action similar to the γ ′ phase, a part of the γ ′ phase is converted to the γ ″ phase. Since γ ″ has a larger precipitation strengthening effect per the same precipitation amount than γ ′, it is desirable that a small amount of γ ″ be present, but γ ″ has a ductility lowering effect than γ ′. Since it is large, it is not preferable to replace all γ ′ with γ ″, because ductility is extremely reduced, and if Nb or Ta necessary to form γ ″ is excessively added, the hot work Nb and Ta are limited to 6% and 12% or less, respectively, because they significantly deteriorate the workability. Preferably, Nb is 5% or less and Ta is 8% or less.

Ti, Nb, and Ta are elements that generate Ni ₃ (Al, Ti, Nb, Ta) type precipitation strengthening phases, and they are compatible with each other, but if the amount of precipitation strengthening phase is too small, it is sufficient. If the strength is not obtained and the amount is too large, the ductility is lowered and the hot workability is deteriorated. Therefore, the total amount of these elements must be within a certain range when converted with the same element equivalent. Since the atomic weights of Nb and Ta are approximately twice and four times that of Ti, respectively, if the Ti equivalent is expressed as Ti + 1 / 2Nb + 1 / 4Ta, then in the case of the alloy of the present invention, this amount is in the range of 2-5%. It is necessary to be. The preferred range is 2.5-4%.

Ni is a basic element that constitutes the alloy of the present invention, and has the functions of forming γ ′ and γ ″ phases and stabilizing the austenite matrix.

The impurity elements usually contained in the alloy of the present invention include Si and M.
n, P, S, Mg, Ca, O, N, etc. Each of these does not substantially impair the properties of the alloy within the following ranges.

Si 0.5% or less Mn 1.0% or less P 0.05% or less S 0.05% or less Mg 0.05% or less Ca 0.03% or less O 0.01% or less N 0.02% or less The alloy of the present invention is solution treated at 950 to 1150 ° C and 600 to 800 ° C. The high strength property is imparted by performing the aging treatment.

〔Example〕

Inventive alloys and conventional alloys having the compositions shown in Table 1 were produced,
The heat treatment was performed under the conditions shown in Table 2. No. 1 in Table 1
0 and NO.11 are alloy 62, which is a solid solution strengthened Ni-based alloy, respectively.
5 and Hastelloy C, NO.12 is precipitation strengthened Ni-based alloy Alloy 718, and NO.13 is precipitation hardened stainless steel.
It is 17-4PH.

For each alloy, boiling water solution of 10% sulfuric acid, 5%
Corrosion rates were measured in boiling hydrochloric acid and 25% hydrofluoric acid at room temperature. Furthermore, 0.2% proof stress, tensile strength, elongation, drawing and hardness were measured as mechanical properties at room temperature. The results are shown in Table 3.

From Table 3, the corrosion resistance of the alloy of the present invention to non-oxidizing acids such as H ₂ SO ₄ , HCl and HF is almost the same level as Alloy 625 and Hastelloy C, and it is the same as that of the conventional precipitation strengthened Ni-based alloy Alloy 718. By comparison, it can be seen that it is significantly superior. It is also understood that precipitation hardening type stainless steel such as 17-4PH has almost no corrosion resistance to non-oxidizing acid.

On the other hand, Table 3 also shows that the strength of the alloy of the present invention is significantly higher than that of Alloy 625 and Hastelloy C.

〔The invention's effect〕

As described above, the alloy of the present invention has both good corrosion resistance and high strength against non-oxidizing acids such as sulfuric acid, hydrochloric acid and hydrofluoric acid. Therefore, it is advantageously used for parts that require both corrosion resistance and high strength (high hardness) against non-oxidizing acid, such as conductor rolls for various electroplating, metal molds for injection molding of plastics containing chlorine and fluorine, screws, etc. can do.

Claims (1)

[Claims] 1. By weight, 4-16% Cr, 9-20% Mo, 0.2-
1.0% Al, more than 1.0% and less than 4% Ti, less than 10% Fe and 0.1
% Or less C, 6% or less Nb and 12% or less Ta, 1 or 2
Including a seed, Ti + 1 / 2Nb + 1 / 4Ta is 2 to 5%, and the balance is substantially Ni except impurities, and is a high-strength Ni group having good corrosion resistance to a non-oxidizing acid. alloy.