JPS6026638A - Corrosion-resistant ni alloy having superior resistance to stress corrosion cracking - Google Patents

Abstract

PURPOSE:To obtain a corrosion-resistant Ni alloy causing no stress corrosion cracking while holding its heat history given by welding or other processing by adding specified amounts of Mo and Fe to Ni. CONSTITUTION:This Ni alloy consists of, by weight, 25-35% Mo, 2-8% Fe and the balance Ni with inevitable impurities including <=0.01% C and <=0.1% Si. One or more groups selected among 0.1-4% one or more among V, W, Cr and Cu (a), 0.001-0.07% B and/or Ca (b), and 0.5-5% Co (c) may be substituted for part of the Ni in the alloy.

Description

[Detailed Description of the Invention] This invention relates to a corrosion-resistant Ni-based alloy that exhibits excellent stress corrosion cracking resistance in its original state without being subjected to solution treatment, even if subjected to thermal history such as welding. .

Conventionally, heat exchangers, for example, reaction vessels in chemical plants, which are generally exposed to corrosive atmospheres containing reducing gases such as hydrogen fluoride gas and hydrochloric acid gas, and non-oxidizing acids such as hydrochloric acid, sulfuric acid, and phosphoric acid. N containing Mo: 26-30, which exhibits excellent corrosion resistance against corrosive atmospheres and non-oxidizing acids, is suitable for manufacturing structural members such as containers and chemical containers.
Single-base alloys have been used.

This conventional corrosion-resistant N1-based alloy exhibits excellent corrosion resistance in the above-mentioned corrosive environment, and also exhibits excellent properties in cold workability and weldability.

On the other hand, this conventional corrosion-resistant N1-based alloy has a corrosion resistance of 600 to 8o, as is clear from the N1-M0 system binary phase diagram.

The intermetallic compound of Ni4Mo is completely precipitated at a temperature of has been done.

Therefore, even when this conventional corrosion-resistant Ni-based alloy is subjected to a thermal history such as welding, it is subjected to solution treatment to dissolve and eliminate intermetallic compounds precipitated by this welding.

However, solution treatment for structural parts after welding and assembly is not only limited by the structure and capacity, but also by the material of the mating member.For these reasons, conventional corrosion-resistant N1 At present, the fields of application of alloys are limited.

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to obtain a material that does not cause stress corrosion cracking even when subjected to thermal history such as welding, and as a result, Mo: Section 25-35.

Contains Fe: 2 to 8, and if necessary, one or more of V, W, Or, and O = 0.1 to 4, and B and Ca. Type 1 to Type 1: Type 2: 0.001 to 0
．． With Section 07.

Co: Contains one or more of the following three groups: 0.5 to 5, and the rest is N.
1- and unavoidable impurities, and the content of C and Sl as unavoidable impurities.

N1-based alloys with a: o, oi coefficient or less, Eli: 0.1 coefficient or less, exhibit excellent corrosion resistance in the above corrosive atmospheres and corrosive environments exposed to non-oxidizing acids, and are resistant to cold corrosion. It has excellent workability and weldability, and does not precipitate intermetallic compounds even when subjected to heat history such as welding. Therefore, it can be used for practical use without solution treatment and in the same state as it has undergone heat history. I learned that it is possible.

This invention was made based on the above knowledge, and the reason why the component composition range was limited to the above general range will be explained below.

(a) M.

The MO acid component dissolves in the base material and has the effect of significantly improving corrosion resistance against corrosive atmospheres containing all reducing gases and non-oxidizing acids, but if the content is less than 25%, the desired effect cannot be achieved. However, if the content exceeds 35%, the hot workability and room temperature toughness deteriorate, so the content was set at 25 to 35%.

(b) Fe The Fe component is a solid solution in the base material, and the alloy is heated at 600 to 800°C.
It also has the effect of preventing the precipitation of intermetallic compounds and thereby suppressing the occurrence of stress corrosion cracking when heated to a temperature of On the other hand, if the content exceeds 8 parts, the corrosion resistance under the above-mentioned corrosive environment will deteriorate, so the content was set at 2 to 8 parts.

(c) V, W, C! r, and Ou These components not only further improve corrosion resistance in the above-mentioned corrosive environment, but also suppress precipitation of intermetallic compounds to further improve stress corrosion cracking resistance, and further improve the strength of the alloy. Therefore, if these special orders are required, they are necessarily included, but if the content is less than 0.1, the desired effect of improving the above function cannot be obtained, and on the other hand, Even if the content exceeds 4%, no further improvement effect can be obtained due to the above action, so in consideration of economic efficiency, the content should be reduced to 0.1%.
It was decided that there would be 4 sections.

(a) B and Oa These components have a significantly high effect of suppressing precipitation of intermetallic compounds, so they are included as necessary when even higher stress corrosion cracking resistance is required.

If the content is less than 0.001%, the desired excellent stress corrosion cracking resistance cannot be secured;
If the content exceeds 71i, the corrosion resistance in the above-mentioned corrosive environment will decrease, so the content 'f: 0.
It has been designated as Sections 001 to 007.

(θ)　C.

The COC component has the effect of improving alloy strength without impairing corrosion resistance and stress corrosion cracking resistance, so it is included as necessary when particularly strong strength is required. If the content is less than 5 parts, the desired strength-improving effect cannot be obtained, while if the content exceeds 5 parts, the cold workability will deteriorate. Therefore, the total content was set at 0.5 to 5 parts.

(f) Unavoidable impurities Among the unavoidable impurities, especially the content I-f of C and Sl
0.1 each C: 0.01 or less, Si: 0.1
You will not be able to pass unless you are below the relevant level. In other words, if the C component exceeds 0.01%, Mo will be absorbed as Mo carbide, and an MO-depleted layer will be formed at the grain boundaries, resulting in deterioration of intergranular corrosion resistance. On the other hand, Si has the effect of promoting the degassing of the molten metal and improving the flowability of the molten metal, so it is a useful component for producing a healthy ingot, but its content is If it exceeds a coefficient of 0.1, the formation of Mo carbides will be significantly promoted. Therefore, the upper limit of C and Sl: 0.014
and o, i% '1, respectively, must not be contained.

In addition, other unavoidable impurities include p and s.

It contains Mg, Mn7z, etc., but the content thereof is P: 0.05% or less and S: 0.05% or less.

Mg: 0.1% or less, and Mn: 2.5%
If it is below, the alloy properties will not be impaired in any way; rather, Mg and Mn have the effect of promoting degassing and suppressing the harmful effects of the P and S components, so the range is below the upper limit. It may be actively included in some cases.

Furthermore, as an alloy component, one or more of Ti, Zr, Nb, and Y are selected, and T is 0.
．． 05-0.5%, Zr: 0.05-0.5%,
Nt+: 0.05 to 0.5, and Y: 0.00
When contained in the range of 5 to 01#), these components combine with solid solution C to form carbides, and these carbides are dispersed and precipitated within the crystal grains, so that carbides are not precipitated at grain boundaries. As a result, intergranular corrosion resistance is improved.

Next, the N1-based alloy of the present invention will be specifically explained using examples.

Examples N1-based alloys 1 to 23 of the present invention and conventional Ni-based alloys having the compositions shown in Table 1 were melted and cast by a normal melting and casting method, and then hot-casted under the same normal conditions. Forged and hot-pressed 4'4 to make a hot-rolled plate with a thickness of 3m,
Subsequently, this hot-rolled sheet was subjected to a solution treatment in which it was maintained at a temperature of 1066° C. for 30 minutes and then cooled.

Then, from the hot rolled sheets of the N1-based alloys 1 to 23 of the present invention and the conventional N1-based alloy obtained as a result, the parallel length: 20
+mi
After a thermal history of heating and holding at 0°C for 20 minutes, the atmosphere i
N2 gas, 0.5 part N2 S04 and 0.5 part H
A 1:1 solution of acetone and alcohol containing Ctf was immersed in the solution in a stationary autoclave with a capacity of 4.5 t, the solution temperature: 150 ° C., and the strain rate was 28.
．． A stress corrosion cracking test was conducted at a low strain rate under the conditions of 3 x 10 seconds, the entire fracture surface was observed after the test, and the ratio (area ratio) of the stress corrosion crack surface (intergranular crack surface) to the entire fracture surface was calculated. . Therefore, the larger the area ratio of stress corrosion cracking fracture surfaces, the worse the stress corrosion cracking resistance.

Similarly, from the above-mentioned hot-rolled sheets of the present invention N1-based alloys 1 to 23 and the conventional N1-based alloy, width near 0 mm x length: 1
50 wn : Cut out a test piece with dimensions of 25 mm x length = 50 m, use this test piece, and heat at 20% H at a temperature of 150''C.
Using a grain boundary corrosion test under the condition of immersion in a C1 aqueous solution for 100 hours, the maximum erodibility A in the weld heat affected zone after the test was completely measured.

These results are shown in Table 1.

From the results shown in Table 1, the N1-based alloys of the present invention, 1 to 2
3 shows excellent stress corrosion cracking resistance and excellent corrosion resistance even though they have a thermal history of heating at 750°C, whereas conventional Ni-based alloys have poor stress corrosion cracking resistance. It was of significantly inferior quality.

As mentioned above, the N1-based alloy of the present invention has excellent corrosion resistance, cold workability, and weldability, and does not precipitate intermetallic compounds even when subjected to thermal history. Since it exhibits stress corrosion cracking resistance, it is not necessary to perform solution treatment after welding, and furthermore, it does not cause precipitation of intermetallic compounds even during strain relief annealing after cold working. There is no occurrence of annealing cracks due to this, and therefore it has industrially useful properties, such as being able to be applied to a wide range of fields where these properties are required.

Applicant: Mitsubishi Metals Corporation Agent Tomi 1) Kazuo and 1 other person

Claims (8)

[Claims] (1) Mo: 25-35% Fe: 2-84, all contained, with the remainder consisting of N1 and unavoidable impurities (weight ratio), and the content of C and Sl as unavoidable impurities , respectively, a: 0.01 or less. Si: Q, Level 1 and below. A corrosion-resistant N1-based alloy with excellent stress corrosion cracking resistance. (2) MO: 25-35%, Fe: 2-8%, all contained, and further. One or more of V, W, Or, and Ou = 0.1 to 4 ratio. and the remainder is Ni and unavoidable impurities (weight ratio), and the contents of C and Sl as unavoidable impurities are a: o and oi ratio or less, respectively, Si: 0.1 A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized by the following: (3) Contains Mo: 25 to 35, Fe: 2 to 8, and further [. One or two of B and Ca = 0.001 to 0
．． 07%, with the balance consisting of N1 and unavoidable impurities (weight ratio), and the content of C and Sl as unavoidable impurities is below c:o, oi ratio, respectively, Si :0. A corrosion-resistant Ni-based alloy having a stress corrosion cracking resistance of less than or equal to 1. (4) A composition containing MO: 25 to 35s, Fe: 2 to 8 parts, and further Oo: 0.5 to 5 parts, with the remainder consisting of Ni and unavoidable impurities (wt%) and the contents of C and Sl as unavoidable impurities are, respectively, c:o, 01% or less, and Si:Q, 1% or less. A corrosion-resistant N1-based alloy with excellent stress corrosion cracking resistance. (5) Contains Mo: 25-35%, Fe: 2-8 L, and further contains one or more of V, W, Or, and Cu, and B and One or two of Ca: 0.001-0
．． Section 07. , with the remainder consisting of N1 and unavoidable impurities (the above weight %), and the contents of C and Sl as unavoidable impurities, respectively. C! A corrosion-resistant Ni-based alloy having excellent stress corrosion cracking resistance. (6) Contains Mo: 25 to 35 parts, Fe: 2 to 8 parts, and further contains one or more of VI WI Crl and O: 0.1 to 4 parts, and Oo: 0.5 to 5, and has a composition (weight ratio) with the remainder consisting of Ni and unavoidable impurities, and the C and Si contents of -C as unavoidable impurities are respectively C: 0 A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized by having a coefficient of .01 or less.Si: a coefficient of 0.1 or less. (7) MO: 25-35%, Fe: 2-8%, and further contains one or two of B and Cta 20,001-
With the 0.07 section. Co: Q, 5 to 5%, all contained, the balance 9 being N] and unavoidable impurities (hereinafter referred to as "double weight"), and the contents of C and Si as unavoidable impurities, respectively. A corrosion-resistant N1-based alloy having excellent stress corrosion cracking resistance, characterized in that: 0:0.01 or less, Si: 0.1 or less. (8) Contains MO: 25-35%, Fe: 2-8%, and further contains. v+ W r-Cr and one or more of Ou: 0.1 to 4. One or two of B and Oa 20,001-0
．． Section 07 and Co: Section 0.5 to 5. , with the remainder consisting of Ni and unavoidable impurities (the above weight %), and the contents of C and Si as unavoidable impurities, respectively. A corrosion-resistant N1-based alloy with excellent stress corrosion cracking resistance, characterized in that: 0:0.01 or less; Si: 0.1qb or less.