JP3230269B2 - Nickel-base heat-resistant alloy with excellent workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a petrochemical base such as ethylene, which decomposes raw materials such as naphtha, propane, ethane, and gas oil at a high temperature of 800 ° C. or more together with water vapor. The present invention relates to a nickel-base heat-resistant alloy suitable as a material for a tube used for producing a product, that is, a material for a decomposition furnace tube for an ethylene plant.

[0002]

2. Description of the Related Art With the recent increase in demand for synthetic resins, the use of cracking furnace tubes for ethylene plants tends to increase in temperature from the viewpoint of improving ethylene yield. Since the inner surface of such a cracking furnace tube is exposed to a carburizing atmosphere, a heat-resistant material excellent in high-temperature strength and carburizing resistance is required. On the other hand, during the operation, carbon is deposited on the inner surface of the cracking furnace tube (this phenomenon is called coking), and an increase in the amount of precipitation causes an adverse effect on the operation such as an increase in ΔP and a decrease in heating efficiency. Therefore, in the actual operation, a so-called decoking operation of periodically removing carbon deposited by air or water vapor is performed, but the operation stoppage and the number of man-hours during the operation become a serious problem. Such coking and the associated problems become more serious as the size of the cracking furnace tube becomes smaller, which is advantageous for improving the yield.

[0003] formed as a prior art for the purpose of preventing coking, for example in JP-A-2-8336, a strong, stable Cr ₂ 0 ₃ coating on the alloy surface by incorporating 28% or more Cr in the alloy It has been proposed to prevent Fe and Ni, which are catalytic elements that promote carbon deposition, from floating on the surface of the tube, thereby suppressing coking.

On the other hand, in order to improve the carburization resistance, it is known that it is effective to increase the Si content in the alloy as disclosed in, for example, JP-A-57-23050. .

[0005] However, the above-mentioned prior art still has the following problems.

When a high Cr alloy as disclosed in Japanese Patent Application Laid-Open No. 2-8336 is applied as a high-temperature strength member from the viewpoint of preventing coking, the amount of Ni in the alloy is increased to austenitize the metal structure. Although it is necessary, the high temperature strength is lower than that of the conventional alloy, and it is difficult to use this high Cr alloy alone as a high temperature strength member. Therefore, Japanese Patent Laid-Open No.
In the invention of Japanese Patent Application Laid-Open Publication No. H10-209, a double tube is used in combination with another high-strength material. However, the double tube has a high manufacturing cost and has many problems in terms of economy and reliability.

The present inventors have found that if the Al content in the alloy is increased and a strong and dense Al ₂ O ₃ coating is formed on the metal surface, the carburization resistance and the coking resistance will be higher than those of the conventional alloy. In addition to the above-mentioned patent application, it has been discovered that increasing the amount of Ni in such high-Al alloys results in the γ 'phase being finely precipitated in the matrix during use at high temperatures and improving the creep rupture strength. Filed as Hei 3-61821.

However, the alloy of the invention of Japanese Patent Application No. 3-61821 does not always have good workability because high-temperature strength is emphasized.

[0009]

The present invention is excellent in high-temperature strength and corrosion resistance, and is particularly excellent in a thermal decomposition and thermal cycle environment in which carburization, oxidation and temperature fluctuation are repeated, such as a cracking furnace tube for an ethylene plant. It is an object of the present invention to provide a heat-resistant alloy having carburization resistance and caulking resistance, having sufficient creep rupture strength for use as a high-temperature strength member, and having excellent workability.

[0010]

The gist of the present invention resides in the following nickel-base heat-resistant alloy. In addition, all the percentages related to the content of the alloy components mean weight%.

(1) By weight%, C: 0.10% or less, Si: 1.0%
Below, Mn: 0.2% or less, Cr: 5% or less, Al: 5.5 to 12%,
Fe: more than 5% up to 20%, and B: 0.001-0.
03%, Zr: 0.01-0.3%, Hf: 0.05-1.0%, Ti: 0.05
A nickel-base heat-resistant alloy containing at least one element of about 1.0% and Mg: 0.001% to 0.02%, the balance being Ni and unavoidable impurities.

(2) In addition to the above component (1), Mo: 0.5
A nickel-base heat-resistant alloy having excellent workability and high corrosion resistance, containing one or two kinds of -5% and W: 1.0-10%.

(3) In addition to the component (1) or (2), one or more of V: 0.3 to 3%, Nb: 0.5 to 5%, and Ta: 1.0 to 10% are further contained. Nickel-based heat-resistant alloy with excellent workability and high temperature strength and good corrosion resistance.

(4) In addition to the above components (1), (2) and (3), Y: 0.01 to 0.25%, La: 0.01 to 0.25% and
Ce: A nickel-based heat-resistant alloy containing at least one of 0.01 to 0.25% and having excellent workability and high temperature strength and good corrosion resistance.

When a particularly high strength is required, the C content of the alloys (1) to (4) exceeds 0.02%,
It is recommended to choose a range up to 0.10%.

[0016]

[Function] As described above, to improve the carburization resistance of the alloy, high Si
It is known that it is effective to form a SiO ₂ film on the metal / scale interface by the formation of a metal. On the other hand, to improve coking resistance, the surface of the outermost oxide scale is
It is also known that it is effective to form a Cr ₂ O ₃ film.

[0017] The present inventors have also conducted research on the belief that formation of a strong and dense surface oxide film is effective in improving carburization resistance and coking resistance. As a result, by increasing the Al content in the alloy and uniformly forming a strong and dense Al ₂ O ₃ film on the metal surface, the carburization resistance and coking resistance are remarkably higher compared to conventional alloys. Found to improve. Furthermore, in such high Al alloys, Ni
By increasing the amount, the γ 'phase is finely precipitated in the matrix during use at a high temperature, and the creep rupture strength is greatly improved. Therefore, an alloy based on Ni and having an increased Al content is a heat-resistant alloy having both corrosion resistance and high-temperature strength, and is suitable for the above-mentioned applications as a high-temperature strength member. The properties are not always good. The present inventors have further conducted research on the improvement of workability, and as a result, have found that the addition of an appropriate amount of Fe slightly lowers the high-temperature strength but significantly improves the workability.

Hereinafter, the function and effect of the components constituting the alloy of the present invention and the proper content thereof will be described.

C: An effective element for forming carbides to improve the tensile strength and creep rupture strength required as heat-resistant steel, but when the content exceeds 0.10%, the ductility and toughness of the alloy are reduced. growing. In particular, when emphasis is placed on ductility and toughness, it is desirable to suppress C to 0.02% or less. 0.02% when creep rupture strength is important
And up to 0.10% C to finely disperse relatively large amounts of carbides.

Si: An element necessary as a deoxidizing element, which also contributes to improvement in oxidation resistance and carburization resistance, its effect is relatively small in a high Al alloy such as the alloy of the present invention.
If Si is present in excess, carbides will precipitate unevenly and reduce mechanical properties such as toughness. Therefore, the content of Si is set to 1.0% or less.

Mn: Although Mn is an effective element as a deoxidizing element, it is an element that promotes the formation of a spinel-type oxide film which is a cause of deterioration of coking resistance.
%.

Cr: Cr is an element effective for improving oxidation resistance and coking resistance, but it is not necessary to contain a large amount in an alloy having a high Al content such as the alloy of the present invention. Further, when Cr is excessively contained, carbides are non-uniformly precipitated similarly to the case where Si is excessive, and mechanical properties such as toughness are reduced. Therefore, in the present invention, the Cr content is set to 5% or less.

Al: Al is an extremely effective element for improving carburization resistance and coking resistance, but in order to exert its effect, it is necessary to uniformly form a corundum-type Al ₂ O ₃ oxide film. is there. For that, at least 5.5%
Of Al is required. However, if Al exceeds 12.0%, ductility and toughness at room temperature and high temperature are significantly deteriorated and cannot be used as a high-temperature strength member. Therefore, the proper content of Al is 5.5 to 12.0%. By including Al in this range, the γ 'phase is finely precipitated during use, and the creep rupture strength is also improved.

B, Zr, Hf, Ti and Mg: These elements are mainly effective for strengthening the grain boundary of the alloy, and in order to exert their effects, B is 0.001% or more and Zr is 0.01% or more.
Hf is 0.05% or more, Ti is 0.05% or more, Mg is 0.001%
These are all necessary. However, if the content is excessive, the creep rupture strength is reduced again.
0.03%, Zr 0.3%, Hf 1.0%, Ti 1.0%, Mg 0.0
2%. These elements may be used alone or in combination of two or more.

Fe: Fe is a component that contributes to improving the hot workability of a nickel-base high Al alloy such as the alloy of the present invention. In order to exert the effect, an amount exceeding at least 5% is necessary, and the hot workability is improved as the content increases.
However, when the content exceeds 20%, the amount of the undissolved β phase increases, suppressing the growth of austenite crystal grains, and the creep rupture strength rapidly decreases. Therefore, the proper range of Fe exceeds 5%
Up to 20%.

One of the alloys of the present invention comprises the above components and the balance of Ni. Ni is an element that is indispensable for obtaining a stable austenite structure and ensuring carburization resistance. It is more desirable to increase the content of Ni in order to enhance the effect of precipitation strengthening by the γ 'phase. However, since the workability deteriorates, in the present invention, a nickel-based alloy containing an appropriate amount of Fe was selected.

The alloy of the present invention may further contain the following components in addition to the above-mentioned components.

Mo and W: Mo and W are mainly effective as solid solution strengthening elements, and increase the creep rupture strength by strengthening the austenite phase of the matrix. To achieve this effect, Mo should be 0.5% or more and W should be 1.0%
The above is necessary, but if it is contained excessively, not only intermetallic compounds which cause a decrease in toughness are precipitated, but also the carburization resistance and the coking resistance are deteriorated, so that Mo is up to 5% and W is 10%.
Should be suppressed by. When two of these are used in combination, the total content should be suppressed to 5% or less in Mo + (1/2) W.

V, Nb and Ta: These elements form a solid solution in the austenite phase and also form a solid solution in the γ 'phase and Cr carbide, thereby contributing to an improvement in creep rupture strength. To achieve this effect, V is 0.3% or more and Nb is 0.5%
As described above, Ta needs to be 1.0% or more, but if contained excessively, the toughness is reduced. Therefore, the upper limit is 3% for V, 5% for Nb,
And 10%.

When two or more kinds are added in combination, it is desirable that the total content is (5/3) V + Nb + (1/2) Ta 5% or less.

Y, La and Ce: These elements mainly improve the adhesion of the SiO ₂ or (Al, Cr) ₂ O ₃ film under thermal cycling conditions and are excellent even when used under temperature fluctuations. Carburization resistance and coking resistance are maintained. In order to exhibit the effect, each of Y, La and Ce requires 0.01% or more. However, if contained excessively, the workability is deteriorated, and the effect of improving the adhesion of the film is also saturated. Therefore, the upper limit is any of Y, La and Ce, respectively.
0.25%. One of these elements may be contained, or two or more of these elements may be added in combination.

Further, in the alloy of the present invention, one or more elements are selected from the three groups of the group consisting of Mo and W, the group consisting of V, Nb and Ta, and the group consisting of Y, La and Ce. You may make it contain.

The alloy of the present invention is used as a product such as a pipe after being smelted in a usual melting and refining process, and then casting, as it is, or after further processing processes such as forging, rolling, and extrusion. The product may be manufactured by powder metallurgy. The heat treatment promotes the homogenization of the structure and contributes to the improvement of the performance of the alloy of the present invention. In this case, the homogenization treatment is usually performed at 1200 to 1300 ° C., but it is also possible to use the casting or processing as it is.

[0034]

EXAMPLES Table 1-1 and Table 1-2 show the chemical compositions of the test materials. No. 1 to No. 32 are the alloys of the present invention, A to V are comparative alloys, and W, X and Y are conventional alloys. The ingot of the present invention and the comparative alloy were each subjected to solid solution heat treatment at 1225 ° C. after forging an ingot obtained by subjecting 17 kg of vacuum high frequency melting to forging into a 15 mm plate material. The conventional alloys W and X were subjected to high-frequency vacuum melting of 50 kg, forged and cold-rolled into a 10 mm-thick plate, and then subjected to solution heat treatment at 1250 ° C. Conventional alloy Y is an as-cast centrifugally cast tube having an outer diameter of 120 mm and a wall thickness of 10 mm.

Using these test materials, carburization resistance, coking resistance, high-temperature strength characteristics by a creep rupture test, and hot workability by a grease test were evaluated. The evaluation of carburization resistance was based on the solid carburization test method and the pelletized BaCO
₃ + 1150 ℃ × 100h using carburizing agent of charcoal (mixing ratio 3: 7)
, And evaluated by the average C increase before and after the test. The evaluation of coking resistance was 80 according to the gas carburizing test method.
A test was conducted at 1050 ° C. for 30 hours in an atmosphere of% CH ₄ + 20% H ₂ O, and the amount of carbon adhering to the surface of the test piece was evaluated. The evaluation of high-temperature strength properties was performed by a creep rupture test at 1100 ° C. and 1.0 kgf / mm ² . The hot workability was evaluated by a grease test under a condition that the strain rate was 1200 ° C. and the strain rate was 5 / sec. These test results are shown in Tables 2-1 to 2-2 and FIG.
4 to FIG.

FIG. 1 shows the effect of the Fe content in the alloy on the drawing value, that is, the hot workability, based on the results of Tables 2-1 and 2-2. It is a figure shown about comparative alloy code A to code F and code V corresponding to these. The symbols in the figure indicate the alloy numbers and symbols in Table 1-1 and Table 1-2. The curves showing the tendency are stratified and connected by the Al content in the alloy. It can be seen that the hot workability is remarkably improved from the Fe content of 5%, and improves with the increase of the Fe content to 20%.

FIG. 2 is a diagram showing the influence of the Fe content on the aperture values of the alloys Nos. 13 to 27 of the present invention in comparison with comparative alloy symbols G to U, respectively. It can be seen that even in these invention alloys, when the Fe content is within the range of the present invention, the hot workability is improved.

On the other hand, as is clear from Tables 2-1 and 2-2, the carburization resistance and the coking resistance are significantly improved as compared with the conventional alloy, and have the same performance as the comparative alloy. You can see that. This is due to the fact that by increasing the Al content in the alloy to 5.5% or more, a strong and dense single-layer corundum-type Al ₂ O ₃ oxide film was formed on the metal surface. In addition, the formation of such an Al ₂ O ₃ single-layer film in the range of 5.5% or more of Al can only be achieved by suppressing Mn in the alloy to 0.2% or less.

FIG. 3 shows alloys No. 1 to No. 12 of the present invention and
It is a figure which similarly shows the relationship between Fe content and creep rupture strength about No.28-No.30 and the comparative alloy code | cord | chord A-code | cord | chord F and code | cord | chord V corresponding to these, and is similarly layered by Al content. The creep rupture strength shows a tendency to slightly decrease with an increase in the Fe content, and some of the creep rupture strengths are lower than those of the comparative alloy, but are not so large. If the Fe content is up to 20%, it is significantly higher than the conventional alloys shown in Table 2-2. This is due to the fact that the γ 'phase precipitates finely in the matrix during use at high temperatures.

FIG. 4 shows the alloys Nos. 13 to 27 of the present invention and the corresponding comparative alloys G to U corresponding to these alloys.
It is a figure which shows the relationship between content and creep rupture strength. As is clear from FIG. 4 and Table 2-2, the creep rupture strength of these alloys of the present invention tends to be lower than that of the comparative alloy when Fe is contained.
It turns out that it is high.

[0041]

[Table 1-1]

[0042]

[Table 1-2]

[0043]

[Table 2-1]

[0044]

[Table 2-2]

[0045]

The alloy of the present invention is excellent not only in high-temperature strength, carburization resistance and coking resistance but also in workability. In particular, it is suitable as a cracking furnace tube for an ethylene plant, and can be used as a single tube without using a double tube.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the Fe content and hot workability for a part of a nickel-based alloy and a comparative alloy of the present invention.

FIG. 2 is a diagram showing the relationship between the Fe content and hot workability for another part of the nickel-based alloy and the comparative alloy of the present invention.

FIG. 3 is a graph showing the relationship between the Fe content and the creep rupture time at 1100 ° C. and 1.0 kgf / mm ² for a part of the nickel-base alloy and the comparative alloy of the present invention.

FIG. 4 is a graph showing the relationship between the Fe content and the creep rupture time at 1100 ° C. and 1.0 kgf / mm ² for another part of the nickel-based alloy and the comparative alloy of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-86840 (JP, A) JP-A-62-93334 (JP, A) JP-A-63-96235 (JP, A) JP-A-2- 259037 (JP, A) JP-A-2-8336 (JP, A) JP-A-57-23050 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 19/05

Claims (5)

(57) [Claims] (1) In weight%, C: 0.10% or less, Si: 1.0% or less, Mn: 0.2% or less, Cr: 5% or less, Al: 5.5 to 12%, Fe:
Contains more than 5% up to 20%, and B: 0.001-0.03
%, Zr: 0.01-0.3%, Hf: 0.05-1.0%, Ti: 0.05-
A nickel-base heat-resistant alloy containing 1.0% and one or more of Mg: 0.001 to 0.02%, with the balance consisting of Ni and unavoidable impurities having excellent workability and high temperature strength and good corrosion resistance. 2. In addition, Mo: 0.5-5% and W: 1.0-10%.
The nickel-base heat-resistant alloy according to claim 1, which comprises one or two of the following: 3. In addition, V: 0.3-3%, Nb: 0.5-5%
3. The nickel-base heat-resistant alloy according to claim 1 or 2, wherein said nickel-base heat-resistant alloy has excellent workability and high corrosion resistance. 4. In addition, Y: 0.01 to 0.25%, La: 0.01
The nickel-base heat-resistant alloy having excellent high-temperature strength and corrosion resistance excellent in workability according to any one of claims 1 to 3, containing at least one of 0.2 to 0.25% and Ce: 0.01 to 0.25%. 5. The nickel-base heat-resistant alloy according to claim 1, wherein the C content is more than 0.02% and not more than 0.10%.