JPS6221854B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a corrosion-resistant Ni-based alloy that exhibits excellent stress corrosion cracking resistance as it is, without being subjected to solution treatment, even when 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. vessel,
Ni-based alloys containing 26 to 30% Mo are used in the manufacture of structural members such as chemical containers and chemical containers, which exhibit excellent corrosion resistance against these corrosive atmospheres and non-oxidizing acids. This conventional corrosion-resistant Ni-based alloy exhibits excellent corrosion resistance in the corrosive environment described above, and also exhibits excellent cold workability and weldability. On the other hand, as is clear from the Ni-Mo binary phase diagram, this conventional corrosion-resistant Ni-based alloy precipitates an intermetallic compound of Ni ₄ Mo at a temperature of 600 to 800°C, and this intermetallic compound improves toughness. Because this causes a decrease in ductility and stress corrosion cracking, it is usually put into practical use after being subjected to solution treatment. Therefore, even when this conventional corrosion-resistant Ni-based alloy is subjected to a thermal history such as welding, a solution treatment is performed to dissolve and eliminate intermetallic compounds precipitated by this welding. However, solution treatment applied to structural members after welding and assembly is not only limited by the structure and capacity, but also by the material of the mating member. Currently, the fields of application of Ni-based 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 found that the Mo :25 to 35%, Al: 0.3 to 2%, Fe: 0.5 to 6%, and if necessary, one or two of V, W, Cr, and Cu.
More than species: 0.1-4%, one or two of B and Ca: 0.001-4%
0.07%, Co: 0.5 to 5%, and the remainder is Ni and unavoidable impurities, and the content of C and Si as unavoidable impurities is low. , C: 0.1% or less, Si: 1% or less. Ni-based alloys exhibit excellent corrosion resistance in the above corrosive atmospheres and corrosive environments exposed to non-oxidizing acids, and have excellent cold workability and weldability. It has excellent properties, and does not precipitate intermetallic compounds even when subjected to heat history such as welding, so it can be put to practical use as it is without solution treatment. I gained knowledge. This invention was made based on the above knowledge, and the reason why the component composition range was limited as described above will be explained below. (a) Mo The Mo component has the effect of forming a solid solution in the base material and significantly improving corrosion resistance against corrosive atmospheres containing reducing gases and non-oxidizing acids.
If the content is less than 25%, the desired effect cannot be obtained, while if the content exceeds 35%, hot workability and room temperature toughness will deteriorate, so the content should be reduced to 25%. It was set at ~35%. (b) Al The Al component is a solid solution in the base material, and the oxygen content in the alloy is reduced to 0.006% (60 p.pm) or less, and the metal is added to the alloy heated to a temperature of 600 to 800°C. It has the effect of suppressing the precipitation of intermediate compounds and improving stress corrosion cracking resistance, but if the content is less than 0.3%, the desired effect cannot be obtained, while if it exceeds 2% Even if it is included, the effect of suppressing the precipitation of intermetallic compounds will not only be saturated, but also the corrosion resistance will tend to deteriorate in the above-mentioned corrosive environment, so the content was set at 0.3 to 2%. . (c) Fe The Fe component also has a solid solution in the base material like Al,
It has the effect of preventing the precipitation of intermetallic compounds even when subjected to thermal history such as welding, and improving stress corrosion cracking resistance, but if the content is less than 0.5%, the coexistence with Al will cause significant stress resistance. The effect of improving corrosion cracking resistance cannot be expected, and on the other hand, if the content exceeds 6%, the corrosion resistance under the above corrosive environment will deteriorate like Al, so the content should be reduced to 0.5 to 6%. It was determined that (d) V, W, Cr, and Cu 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. Since it has the effect of improving the strength of the alloy, it is included as necessary when these properties are required, but if the content is less than 0.1%, the desired effect of improving the above effect cannot be obtained,
On the other hand, even if the content exceeds 4%, further improvement effects cannot be obtained due to the above-mentioned action, so the content was determined to be 0.1 to 4% in consideration of economic efficiency. (e) B and Ca These components have a significantly high effect of suppressing the 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 ensured, while if the content exceeds 0.07%, the corrosion resistance in the above corrosive environment will decrease. The amount was determined to be 0.001-0.07%. (f) Co The Co 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. amount is 0.5%
If the content is less than 5%, the desired strength improvement effect cannot be obtained, while if the content exceeds 5%, the cold workability will decrease.
%. (g) Unavoidable impurities Among the unavoidable impurities, the content of C and Si in particular must be 0.1% or less for C and 1% or less for Si, respectively. In other words, if a large amount of C component exceeding 0.1% is present, Mo will be absorbed as Mo carbide, and a 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 degassing of the molten metal and improving the flowability of the molten metal, so it is a useful component for producing a sound ingot, but if its content is 1. %, the formation of Mo carbides is significantly promoted. Therefore, the upper limit values of C and Si should not be exceeded: 0.1% and 1%, respectively. In addition, when used in harsh environments such as high-temperature corrosive environments or high concentrations of cyclic gases or non-oxidizing acids, the upper limits of C and Si should be set to C:
0.02%, Si: 0.1%. In addition, other unavoidable impurities include P,
Contains S, Mg, Mn, etc., but the content is P: 0.05% or less and S: 0.05%, respectively.
Hereinafter, if Mg: 0.1% or less and Mn: 2.5% or less, the alloy properties will not be impaired in any way, but rather Mg and Mn will promote degassing and suppress the harmful effects of P and S components. Therefore, it may be actively included within the range below the above upper limit. Furthermore, as alloy components, one or more of Ti, Zr, Nb, and Y are added, respectively: Ti: 0.05 to 0.5%, Zr: 0.05 to 0.5%, Nb:
When contained in the ranges of 0.05 to 0.5% and Y: 0.005 to 0.1%, these components combine with solid solution C to form carbides, and these carbides are dispersed and precipitated within the crystal grains, so that they are not present at the grain boundaries. Carbides are prevented from precipitating, and as a result, intergranular corrosion resistance is improved. Next, the Ni-based alloy of the present invention will be specifically explained with reference to Examples. Examples Ni-based alloys 1 to 36 of the present invention having the respective compositions shown in Table 1 were produced by a normal melting and casting method.
After melting and casting a conventional Ni-based alloy, hot forging and hot rolling were performed under the same normal conditions to obtain a hot rolled sheet with a thickness of 3 mm. : After heating and holding at 1066°C for 30 minutes, solution treatment was performed by cooling with water. Next, the resulting Ni-based alloy 1 of the present invention
~

【table】

[Table] A test piece with dimensions of parallel part length: 20 mm x parallel part width: 4 mm x thickness: 2 mm was prepared by machining from hot rolled sheets of 36 and conventional Ni-based alloy, and this test piece was After a thermal history of heating and holding at 750°C for 15 minutes and heating and holding at the _same temperature for 60 minutes, the atmosphere was _N2 gas and a mixture of acetone and alcohol containing 0.5% _H2SO4 and 0.5% HCl was applied. :1 Immerse in the solution in a static autoclave with a capacity of 4.5, solution temperature: 150°C, strain rate: 8.3×
A stress corrosion cracking test was performed at a low strain rate under the condition of 10 ^-7 sec ^-1 , the fracture surface was observed after the test, and the ratio (area rate) was calculated. Therefore, the larger the area ratio of stress corrosion cracking fracture surfaces, the poorer the stress corrosion cracking resistance. Similarly, the above-mentioned Ni-based alloys 1 to 36 of the present invention
And from conventional hot-rolled Ni-based alloy sheet, width: 25mm x
A test piece with dimensions of length: 50 mm x thickness: 2 mm was created by machining, and using an autoclave,
A corrosion test was conducted under the condition of immersion in a boiling 20% HCl aqueous solution for 96 hours, and the weight loss after the test was measured and converted into an annual value. The results of these tests are shown in Table 1. From the results shown in Table 1, the Ni-based alloys 1 to 36 of the present invention exhibit excellent stress corrosion cracking resistance and excellent corrosion resistance despite having a thermal history of heating at 750°C. In contrast, it is clear that conventional Ni-based alloys have significantly inferior stress corrosion cracking resistance. As mentioned above, the Ni-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. It exhibits stress corrosion cracking resistance, so there is no need for solution treatment after welding, and furthermore, intermetallic compounds do not precipitate during strain relief annealing after cold working, so this can be avoided. It has industrially useful properties such as no annealing cracking and therefore can be applied to a wide range of fields where these properties are required.

Claims (1)

[Claims] 1 Contains Mo: 25 to 35%, Al: 0.3 to 2%, Fe: 0.5 to 6%, and the remainder is Ni and unavoidable impurities (weight %), A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized in that the contents of C and Si as unavoidable impurities are: C: 0.1% or less, Si: 1% or less. 2 Contains Mo: 25 to 35%, Al: 0.3 to 2%, Fe: 0.5 to 6%, and further contains one or two of V, W, Cr, and Cu.
Species or higher: Contains 0.1 to 4%, with the remainder consisting of Ni and unavoidable impurities (wt%), and the content of C and Si as unavoidable impurities, respectively, C: 0.1% or less , Si: 1% or less, a corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance. 3 Contains Mo: 25-35%, Al: 0.3-2%, Fe: 0.5-6%, and further contains one or two of B and Ca: 0.001-
0.07%, with the remainder consisting of Ni and unavoidable impurities (wt%), and the contents of C and Si as unavoidable impurities are respectively: C: 0.1% or less, Si: 1% A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized by the following. 4 Contains Mo: 25-35%, Al: 0.3-2%, Fe: 0.5-6%, and further contains Co: 0.5-5%, with the remainder consisting of Ni and unavoidable impurities (the above % by weight), and the contents of C and Si as inevitable impurities are respectively C: 0.1% or less and Si: 1% or less, and has excellent stress corrosion cracking resistance. Ni-based alloy. 5 Contains Mo: 25 to 35%, Al: 0.3 to 2%, Fe: 0.5 to 6%, and further contains one or two of V, W, Cr, and Cu.
More than species: 0.1-4%, one or two of B and Ca: 0.001-4%
0.07%, with the remainder consisting of Ni and unavoidable impurities (wt%), and the contents of C and Si as unavoidable impurities are respectively: C: 0.1% or less, Si: 1% A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized by the following: 6 Contains Mo: 25 to 35%, Al: 0.3 to 2%, Fe: 0.5 to 6%, and further contains one or two of V, W, Cr, and Cu.
Species: 0.1 to 4%, Co: 0.5 to 5%, and the remainder is Ni and unavoidable impurities (weight%), and the content of C and Si as unavoidable impurities is , C: 0.1% or less, Si: 1% or less, respectively.A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance. 7 Contains Mo: 25-35%, Al: 0.3-2%, Fe: 0.5-6%, and further contains one or two of B and Ca: 0.001-2%.
0.07%, Co: 0.5 to 5%, and the remainder is Ni and unavoidable impurities (weight%), and the contents of C and Si as unavoidable impurities are as follows: C: A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized by: 0.1% or less, Si: 1% or less. 8 Contains Mo: 25 to 35%, Al: 0.3 to 2%, Fe: 0.5 to 6%, and further contains one or two of V, W, Cr, and Cu.
More than species: 0.1-4%, one or two of B and Ca: 0.001-4%
0.07%, Co: 0.5 to 5%, and the remainder is Ni and unavoidable impurities (weight%), and the contents of C and Si as unavoidable impurities are as follows: C: A corrosion-resistant Ni-based alloy with excellent stress corrosion cracking resistance, characterized by: 0.1% or less, Si: 1% or less.