JPH0533090A - Nickel-base heat resistant alloy - Google Patents

Abstract

PURPOSE:To obtain an Ni-base heat resistant alloy having excellent high temp. strength and high corrosion resistance and usable as a high temp. strength member. CONSTITUTION:This is an Ni-base heat resistant alloy contg. <=0.10% C, >1.0 to 5.0% Si, <=0.2% Mn, <=5% Cr and 5.5 to 13% Al, furthermore contg. one or more kinds among 0.001 to 0.03% B, 0.01 to 0.3% Zr, 0.05 to 1.0% Hf, 0.05 to 1.0% Ti and 0.001 to 0.02% Mg and the balance Ni or Ni and <=5% Fe with inevitable impurities. In addition to the above components, furthermore, one or more kinds of elements selected from the group of 0.5 to 5% Mo and 1.0 to 10% W and the group of 0.3 to 3% V, 0.5 to 5% Nb and 1.0 to 10% Ta can be incorporated. In addition to the above components, moreover, one or more kinds among 0.01 to 0.25% Y, 0.01 to 0.25% La and 0.01 to 0.25% Ce can be incorporated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has high strength at high temperature and excellent corrosion resistance. In particular, it decomposes raw materials such as naphtha, propane, ethane, and gas oil with steam at a high temperature of 800 ° C. or higher to produce a petrochemical base such as ethylene. The present invention relates to a Ni-based heat-resistant alloy suitable as a raw material for a pipe used for producing a product, that is, a decomposition furnace pipe for an ethylene plant.

[0002]

2. Description of the Related Art The use conditions of cracking furnace tubes for ethylene plants have been increasing with increasing demands for synthetic resins in recent years, 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 operation, carbon is precipitated on the inner surface of the cracking furnace tube (this phenomenon is called coking), and as the amount of precipitation increases, there is a problem in operation such as an increase in ΔP and a decrease in heating efficiency. Therefore, in actual operation, so-called decoking work is regularly performed to remove carbon deposited by air or steam, but during that time, there are serious problems such as operation stoppage and man-hours of work. Such coking and problems associated therewith become more serious as the size of the cracking furnace tube becomes a small-diameter tube that 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 Therefore, it has been proposed to prevent Fe and Ni, which are catalytic elements that promote carbon precipitation, from floating to the surface and suppress 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, Japanese Patent Laid-Open No. 57-23050. .

However, the above conventional technique still has the following problems.

From the viewpoint of preventing coking, JP-A-2-83
When a high Cr alloy as disclosed in Japanese Patent No. 36 is applied as a high temperature strength member, it is necessary to increase the amount of Ni in the alloy to austenite the metal structure, but the high temperature strength is lower than that of the conventional alloy. Even if an expensive element such as Mo or W is added for strengthening, not only the intermetallic compound that does not contribute to the high temperature strength is precipitated to cause an embrittlement phenomenon but also the effect of improving creep rupture strength is small. . Therefore, it is difficult to use such a high Cr alloy alone as a high temperature strength member. Therefore, in the invention of Japanese Patent Application Laid-Open No. 2-8336, a double pipe is used in combination with another high-strength material. However, the double pipe has a high manufacturing cost and is problematic in terms of economy and reliability. There are many.

In order to have both excellent caulking resistance and excellent carburization resistance, the amount of Cr in the alloy should be increased.
Although it is necessary to increase the amount of Si as well, Si is a strong ferrite-forming element similar to Cr, and is also an element that promotes the precipitation of intermetallic compounds that reduce toughness. That is, even if an alloy having such a composition is obtained, it is still difficult to use it as a high-temperature strength member, and it must be applied as a double pipe in combination with other materials.

[0008]

DISCLOSURE OF THE INVENTION The present invention is excellent in high-temperature strength and corrosion resistance, and particularly excellent in carburization resistance and coking resistance even in a pyrolysis environment in which carburization and oxidation are repeated, such as in a cracking furnace tube for an ethylene plant. It is an object of the present invention to provide an austenitic heat resistant alloy which has the properties and creep rupture strength sufficient for use as a high temperature strength member.

[0009]

The gist of the present invention is as follows.
It is a Ni-based heat-resistant alloy. In addition,% related to alloy component content
All mean% by weight.

(1) C: 0.10% or less, Si: more than 1.0% 5.0
%, Mn: 0.2% or less, Cr: 5% or less, Al: 5.5-13%
In addition, B: 0.001 to 0.03%, Zr: 0.01 to 0.3
%, Hf: 0.05 to 1.0%, Ti: 0.05 to 1.0% and Mg: 0.0
Includes one or more of 01-0.02%, the balance Ni or Ni and 5%
A Ni-base heat-resistant alloy consisting of the following Fe and unavoidable impurities with excellent high-temperature strength and corrosion resistance.

(2) In addition to the above component (1), Mo: 0.
A Ni-based heat-resistant alloy containing 5 to 5% and W: 1.0 to 10% of one or two types, which has excellent high temperature strength and corrosion resistance.

(3) In addition to the above component (1), V: 0.3
~ 3%, Nb: 0.5 ~ 5% and Ta: 1.0 ~ 10% Ni-based heat resistant alloy with excellent high temperature strength and corrosion resistance.

(4) In addition to the above component (1), Mo: 0.
High temperature strength containing one or two of 5 to 5% and W: 1.0 to 10%, and one or more of V: 0.3 to 3%, Nb: 0.5 to 5% and Ta: 1.0 to 10% And a Ni-based heat-resistant alloy with excellent corrosion resistance.

(5) Further, Y: 0.01 to 0.25%, La: 0.01 to
Ni of any one of the above (1) to (4), which contains 0.25% and Ce: 0.01 to 0.25% and at least one of which is excellent in high temperature strength and corrosion resistance so that the total of these components does not exceed 0.25%. Base heat resistant alloy.

When particularly high strength is required, the C content of the alloys (1) to (5) above 0.02%,
It is recommended to select in the range of 0.10%.

[0016]

As described above, in order to improve the carburization resistance of the alloy,
It is known that it is effective to form a SiO ₂ film on the metal / scale interface by converting to Si. On the other hand, it is known that forming a Cr ₂ O ₃ film on the outermost oxide scale surface by increasing the Cr is effective for improving the coking resistance.

The inventors of the present invention also conducted research on the idea that formation of a strong and dense surface oxide film is effective for improving carburization resistance and coking resistance. As a result, by increasing the Al content in the alloy to form a strong and dense Al ₂ O ₃ film uniformly on the metal surface, the carburization resistance and coking resistance are significantly higher than those of conventional alloys. It has been found to improve. In addition, if the Al content is increased in this way and an appropriate amount of Si is contained, the metal and Al ₂ O ₃
It was found that a dense SiO ₂ film was formed at the interface with the film, and the carburization resistance and coking resistance were dramatically improved. Further, in such a high Al alloy, by increasing the amount of Ni, the γ'phase is finely precipitated in the matrix during use at high temperature,
Creep rupture strength is also greatly improved. Therefore, an alloy based on Ni and having a high Al content becomes a heat-resistant alloy having both corrosion resistance and high-temperature strength, and is suitable for the above-mentioned use as a high-temperature strength member.

The action and effect of the constituents of the alloy of the present invention and the proper content thereof will be described below.

C: An element effective for forming a carbide to improve the tensile strength and creep rupture strength required for heat-resistant steel, but if the content exceeds 0.10%, the ductility and toughness of the alloy decrease. growing. In particular, when importance is attached to ductility and toughness, it is desirable to control C to 0.02% or less. On the other hand, 0.02% when stressing creep rupture strength
And 0.10% or less of C is contained so that a relatively large amount of carbide is finely dispersed.

Si: an element required as a deoxidizing element, which contributes to the improvement of oxidation resistance and carburization resistance. In particular,
In a high Al alloy such as the alloy of the present invention, by containing an appropriate amount of Si
Al ₂ O ₃ a dense SiO ₂ film was formed with the film, has the effect of strengthening the Al ₂ O ₃ film supplementarily, carburization resistance is remarkably improved. The effect becomes remarkable when the content exceeds 1.0%. However, the excessive content of Si promotes the heterogeneous precipitation of intermetallic compounds and reduces the mechanical properties such as toughness, so the upper limit of Si is set to 5.0%.

Mn: Mn is an element effective as a deoxidizing element, but its content is 0.2% because it promotes the formation of spinel type oxide film, which is a cause of deterioration of coking resistance.
It is necessary to keep below.

Cr: Cr is an element effective for improving the oxidation resistance and the coking resistance, but it is not necessary to add a large amount in an alloy having a high Al content such as the alloy of the present invention. Further, if Cr is contained excessively, carbides are nonuniformly precipitated, and mechanical properties such as toughness are deteriorated. Therefore, in the present invention, the Cr content is 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%
Al is required. However, when Al exceeds 13.0%, ductility and toughness at room temperature and high temperature are significantly deteriorated, and it cannot be used as a high temperature strength member. Therefore, the proper content of Al is
It is 5.5-13.0%. By including Al in this range, the γ'phase is finely precipitated during use, and the creep rupture strength is also greatly 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%.
Above, Hf 0.05% or more, Ti 0.05% or more, Mg 0.001%
Above, each is necessary. However, if it is contained excessively, the creep rupture strength decreases again, so the upper limit is B.
0.03%, Zr 0.3%, Hf 1.0%, Ti 1.0%, Mg 0.
02% Only one of these elements may be contained, or two or more of them may be added in combination.

One of the alloys of the present invention is one in which, in addition to the above components, the balance is Ni. Ni is an element that is indispensable for obtaining a stable austenite structure and ensuring the carburization resistance. Particularly, it is more preferable for increasing the effect of precipitation strengthening by the γ ′ phase. Therefore, although the Ni-based alloy is selected in the present invention, the performance of the alloy of the present invention can be sufficiently maintained even if a part of Ni is replaced with Fe in the range of 5% or less in consideration of economical efficiency.

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

One or both of Mo and W: Mo and W are mainly effective as a solid solution strengthening element, and increase the creep rupture strength by strengthening the austenite phase of the matrix. In order to exert this effect, Mo is 0.5%.
As described above, W must be 1.0% or more. However, if it is contained in excess, not only the intermetallic compound that causes toughness decrease precipitates but also carburization resistance and coking resistance deteriorate, so Mo is limited to 5%. , W should be limited to 10%. Even when two kinds of these are used together, the total content is 5% at Mo + 1/2 W.
Should be kept below.

One or more of Nb, Ta and V: These elements form a solid solution in the austenite phase and γ '.
It also forms a solid solution in the phase and Cr carbide and contributes to the improvement of creep rupture strength. To exert its effect, Nb is 0.5%
As described above, Ta is required to be 1.0% or more and V is 0.3% or more. However, if excessively contained, toughness is deteriorated, so the upper limit is Nb.
5%, Ta 10%, and V 3%. When two or more kinds are added in combination, the total content is 5 / 3V + Nb + 1 / 2Ta and 5% or less.

Y, La and Ce: These elements mainly improve the adhesion of SiO ₂ and Al ₂ O ₃ coatings under thermal cycling conditions, and have excellent carburization resistance even when used under temperature fluctuation. Coking resistance is maintained. In order to exert the effect, each of Y, La and Ce needs to be 0.01% or more. However, if contained excessively, the workability deteriorates,
Further, the effect of improving the adhesion of the SiO ₂ or Al ₂ O ₃ coating is saturated, so the upper limits of Y, La, and Ce are each 0.25%. Only one of these elements may be contained, or two or more of them may be added in combination. However, in the case of performing this composite addition, the total of these elements should be 0.25 in order to maintain workability. The range should not exceed%.

One or more elements may be selected and contained from the above three groups of Mo and W, Nb, Ta and V, and Y, La and Ce.

The alloy of the present invention is manufactured as a product such as a pipe after being melted in a usual melting and refining process and then cast, as-cast, or further subjected to processing steps such as forging, rolling and extrusion. In addition, you may make it into a product by a powder metallurgy method. The heat treatment promotes the homogenization of the structure and contributes to the performance improvement of the alloy of the present invention. In this case, the homogenizing treatment is usually performed at 1200 to 1300 ° C., but it is also possible to use it as cast or as it is.

[0032]

Example 1 A low C (C ≦ 0.02%) alloy, which emphasizes toughness, was tested. Tables 1-1 and 1-2 show the chemical compositions of the test materials. No. 1 to No. 35 are alloys of the present invention, and A to
F is a comparative alloy. Inventive alloy and comparative alloy A,
For both B and F, an ingot 17 kg vacuum high frequency melting was subjected to solution heat treatment at 1250 ° C. Comparative alloys C and D are 50
After vacuum high-frequency melting in a vacuum, forging and cold rolling were performed to obtain a plate material having a thickness of 10 mm, and solution heat treatment was performed at 1250 ° C. Comparative alloy E is an as-cast centrifugal casting tube having an outer diameter of 120 mm and a wall thickness of 10 mm.

Using these test materials, carburization resistance, caulking resistance, and high temperature strength characteristics were evaluated by a creep rupture test. Carburization resistance was evaluated by solid carburizing test method using heat treatment of 1150 ℃ × 100h with carburizing agent of BaCO ₃ + charcoal (mixing ratio 3: 7) in the form of pellets, and evaluated by the average C increase before and after the test. did. For some test materials,
In order to evaluate the carburization resistance under heat cycle environment,
A heat treatment was also performed 5 times at 1150 ° C. for 20 hours, and a comparison with a material for continuous heat treatment for 100 hours was performed.

The coking resistance was evaluated by a gas carburizing test method at 1050 ° C. for 30 hours in an atmosphere of 80% CH ₄ + 20% H ₂ O, and the amount of C adhering to the surface of the test piece was evaluated. Further, some of the test materials were subjected to repeated tests at 1050 ° C. × 6 h × 5 times in the same manner as in the evaluation of carburization resistance, and compared with the 30 h continuous test. High temperature strength characteristic evaluation is 1100
The creep rupture test was conducted at 1.0 ° C and 1.0 kgf / mm ² .
Some of the test materials were subjected to a high temperature tensile test at 1100 ° C and a toughness test after aging treatment at 1050 ° C for 3000 hours. The results of these tests are summarized in Tables 2 and 3.

1 and 2 are graphs showing the effect of the Al content of the alloy on the carburization resistance and coking resistance, from the results of Table 2. Also, FIG. 3 and FIG.
Is a graph showing the effects of the Y, La and Ce contents of the alloy on the carburizing resistance under the conditions of continuous heating and thermal cycle heating, from the results of Tables 2 and 3. The symbols in these figures indicate alloy Nos. In Tables 2 and 3. From these figures and Table 2, in the alloy of the present invention having Al of 5.5 to 13%,
It can be seen that carburization resistance and coking resistance are significantly improved over Comparative Alloy A having less than 5.5% and Alloys C, D and E having high Cr. This is because Al in the alloy is increased to 5.5% or more and Si is also increased, so that a strong and dense single-layer corundum type Al ₂ O ₃ oxide film is formed on the metal surface, and dense SiO _{2 This} is due to the formation of the film. The formation of such a dense and strong coating with Al content of 5.5% or more can be achieved only by suppressing Mn in the alloy to 0.2% or less.

Regarding the effects of Y, La and Ce,
As is clear from the alloys Nos. 32 and 33 of the present invention shown in FIGS. 3 and 4 and Table 3, the carburization resistance and the resistance to carburization, especially under the heat cycle heating condition, can be improved by adding one or more kinds within the scope of the present invention. It can be seen that the coking property is greatly improved. This is because S, which segregates Y, La and Ce at the metal / film interface, is fixed in the metal as a sulfide, and Al ₂ O ₃ and
This is because the adhesion of the SiO ₂ film is improved and the peeling resistance is improved.

On the other hand, the alloy of the present invention No. 4 and the comparative alloy F
As is clear from the comparison with, the creep rupture life is significantly improved by increasing Al to 5.5% or more and increasing Ni. This is due to the fine precipitation of the γ'phase in the matrix during use at high temperatures.

FIGS. 5 and 6 are graphs of the Al content, the tensile strength at 1100 ° C. and the creep rupture time (1.0 kgf / mm ² ) similarly from the results of Table 2. As shown in these figures, in the range defined by the present invention, the high temperature tensile strength and the creep rupture life are further improved with the increase of Al. However, when the Al content exceeds 13% and becomes excessive, the high temperature strength improving effect is saturated as in Comparative Alloy B, and as shown in Table 2, the toughness after aging is significantly reduced. Such alloys are problematic for use as high temperature strength members.

By the way, in order to improve the high temperature strength of a high Al-Ni based alloy such as the alloy of the present invention, Table 1-1 and Table 2
As shown in No. 1 to No. 16 of No. 17, it is essential to contain an appropriate amount of at least one of B, Zr, Hf, Ti and Mg.
~ 24, more than one Mo, W or Nb, T
By containing at least one of a and V and adding them in combination, the high temperature strength is further improved. Incidentally, the tendency of deterioration of carburization resistance and coking resistance due to the inclusion of these reinforcing elements is not particularly recognized within the scope of the present invention.

Here, the test results for the ingot material as an example of the alloy of the present invention are shown. However, the carburizing resistance and the coking resistance do not change even if processing such as forging, hot rolling, and cold rolling is performed, and rather the mechanical properties such as toughness are improved by homogenizing the structure. Further, the alloy of the present invention is an excellent high-temperature strength member even if it is manufactured as a powder and processed into a pipe material or the like by the powder metallurgy method.

[0041]

[Table 1-1]

[0042]

[Table 1-2]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Example 2] With particular emphasis on high temperature strength, an alloy having a relatively high C content was tested. Table 4 shows the chemical composition of the test materials. No. 1 to No. 11 are alloys of the present invention,
A and B are comparative alloys. The manufacturing method of the alloy of the present invention and the comparative alloy was also the same as in Example 1. However, the solution heat treatment temperature of the alloy of the present invention was set to 1270 ° C.

The carburization resistance and coking resistance test conditions are the same as in Example 1. The high temperature tensile test and creep test are the same as in Example 1, 1100 ° C, and 50 ° C higher than that.
It was carried out at 1150 ° C. The results of these tests are shown in Table 5.

As is clear from Table 5, the influence of Al on the carburizing resistance and coking resistance is low C of Example 1.
It is no different from the case of alloy. On the other hand, comparing the mechanical properties, the impact value after aging at 1150 ° C is rather low, but the high temperature strength shows a sufficiently high value even at 1150 ° C, so it can be used at higher temperatures. It will be possible.

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

The alloy of the present invention is excellent not only in carburization resistance and coking resistance but also in extremely high temperature strength. This alloy is particularly suitable as a cracking furnace tube for an ethylene plant, and can be used as a single tube without forming a double tube. Excellent in reliability.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between Al content and carburization resistance of Ni-based alloys of the present invention and comparative alloys.

FIG. 2 is a diagram showing the relationship between the Al content and the coking resistance of the Ni-based alloy of the present invention and the comparative alloy.

FIG. 3 shows Y, La, and Ce of Ni-based alloys of the present invention and comparative alloys.
It is a figure which shows the relationship between content and carburization resistance under a continuous heating and a heat cycle heating condition.

FIG. 4 Y, La and Ce of the Ni-based alloy of the present invention and the comparative alloy
It is a figure which shows the relationship between content and caulking resistance under conditions of continuous heating and thermal cycle heating.

FIG. 5 shows the Al content of the Ni-based alloy of the present invention and the comparative alloy.
It is a figure which shows the relationship with the tensile strength in 1100 degreeC.

FIG. 6 shows the Al contents of the Ni-based alloy of the present invention and the comparative alloy.
It is a figure which shows the relationship with the creep rupture time of 1100 degreeC and 1.0 kgf / mm < ² >.

Claims (6)

[Claims] 1. By weight%, C: 0.10% or less, Si: more than 1.0% and up to 5.0%, Mn: 0.2% or less, Cr: 5% or less, Al: 5.5.
~ 13%, B: 0.001-0.03%, Zr: 0.01
~ 0.3%, Hf: 0.05 ~ 1.0%, Ti: 0.05 ~ 1.0% and
Mg: contains 0.001 to 0.02% of 1 or more, and the balance is Ni or Ni
Ni-based heat-resistant alloy with excellent high-temperature strength and corrosion resistance consisting of 5% or less of Fe and inevitable impurities. 2. In addition to the components of claim 1, Mo: 0.5-
A Ni-base heat-resistant alloy containing 5% and W: 1.0 to 10% of one or two types, which has excellent high temperature strength and corrosion resistance. 3. In addition to the components of claim 1, V: 0.3-3
%, Nb: 0.5 to 5% and Ta: 1.0 to 10%, a Ni-base heat resistant alloy excellent in high temperature strength and corrosion resistance. 4. In addition to the components of claim 1, Mo: 0.5-
5% and W: 1.0 to 10% of one or two kinds, and V:
A Ni-base heat-resistant alloy containing at least one of 0.3 to 3%, Nb: 0.5 to 5%, and Ta: 1.0 to 10% and having excellent high-temperature strength and corrosion resistance. 5. Y: 0.01 to 0.25%, La: 0.01 to 0.25
% And Ce: 0.01 to 0.25%, at least one of which is contained, and the sum of these components does not exceed 0.25%. Ni-based heat-resistant alloy excellent in high temperature strength and corrosion resistance according to any one of claims 1 to 4. . 6. A Ni-base heat-resistant alloy excellent in high temperature strength and corrosion resistance according to any one of claims 1 to 5, which has a C content of more than 0.02% and 0.10% or less.