JPH07258780A - Heat resistant alloy excellent in carburization resistance - Google Patents

Abstract

PURPOSE:To improve the high-temp. carburization resistance of a heat resistant alloy used for a reaction tube for the petrochemical industry such as an ethylene cracking tube. CONSTITUTION:This heat resistant alloy consists of, by weight 0.1-0.5% C, <=4% Si, <=3% Mn, 40-50% Cr, 0.5-10% Mo, <=10% Fe, <=10% Fe, <=0.2% N, 0.02-0.5% Ti, 0.01-0.5% Zr and the balance essentially Ni, and optionally further contains 0.5-5% W, 0.5-5% W and 0.02-0.5% Al, 0.5-5% W and 0.3-2% Nb and/or 0.005-0.05% B, or 0.5-5% W, 0.02-0.5% Al and 0.3-2% Nb and/or 0.005-0.05% B.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a nickel-base heat-resistant alloy which is useful as a high-temperature heat-resistant application requiring carburization resistance, typically as a constituent material for pipes for pyrolysis reaction of hydrocarbons in the petrochemical industry. Regarding

[0002]

2. Description of the Related Art Pyrolysis furnace pipes for hydrocarbons, such as naphtha, are passed through the pipes at high temperature and high pressure (temperature: approx.
C. to 1100 ° C., a pressure of about 5Kg / cm ² or less) cracking tubes for producing ethylene performing thermal decomposition under the conditions of, its operating process, solid carbon is precipitated from the reaction system, the tube attached to the tube wall inner surface Carburizing phenomenon that diffuses and penetrates inside the wall occurs. The occurrence of carburization causes deterioration of the pipe material, particularly embrittlement of the pipe body due to a decrease in ductility, which causes cracking of the pipe body during high temperature / high pressure operation. Therefore, the reaction tube is required to have carburization resistance as well as strength in a high temperature range, oxidation resistance and the like in order to ensure durability and operational safety. Conventionally, as the tube material, HP material of ASTM standard (0.4
C-1.75Si-25Cr-35Ni-Fe), and its H
P improver (0.4 C-1.75 Si-25 Cr-35 Ni-Mo,
Nb, W-Fe) and the like are used, and also Japanese Patent Publication No. 63-48.
No. 97 discloses 0.4 C-35 Cr-45 Ni-W, Nb-
Ti, Zr-Fe heat-resistant cast steel, Japanese Patent Publication No. 63-4898 discloses 0.4 C-35Cr-35Ni-10Co-W, Nb-
Ti and Zr-Fe heat resistant cast steels are disclosed respectively.

[0003]

Recently, the above-mentioned thermal decomposition reaction operation is carried out at about 115 in terms of operation efficiency and productivity improvement.
The demand for high temperature operation around 0 ° C or higher is increasing. However, the above conventional tube material has a temperature of about 1100.
It can be used for temperatures up to about 1150 ° C, and it is difficult to ensure stable operation in high temperature environments exceeding that. In particular, the deterioration of the pipe material due to insufficient carburizing resistance is fast and the service life is long. Inevitable decline. Therefore, the present invention is intended to provide a heat-resistant alloy which exhibits excellent carburizing resistance even in a high-temperature operation exceeding a temperature of about 1150 ° C. and is useful as a pipe material which enables stable operation.

[0004]

The heat resistant alloy of the present invention comprises:
C: 0.1 to 0.5%, Si: 4% or less, Mn: 3% or less, Cr: 40% to 50%, Mo: 0.5 to 10%, F
e: 10% or less, N: 0.2% or less, Ti: 0.02 to
0.5%, Zr: 0.01 to 0.5%, balance substantially N
It has a chemical composition of i. If desired, the heat-resistant alloy of the present invention may contain W, Al, Nb,
The element selected from B is as follows (1) to (4)
A chemical composition containing one or a combination of two or more kinds is given. (1) W: 0.5 to 5%, (3) W:
0.5-5%, and Al: 0.02-0.5%,
(2) W: 0.5 to 5%, and one or two kinds selected from two elements of Nb: 0.3 to 2% and B: 0.005 to 0.05%, (4) W: 0. 0.5 to 5%, Al: 0.0
2 to 0.5%, and Nb: 0.3 to 2% and B: 0.0
One or two selected from two elements of 0.05 to 0.05%
seed.

[0005]

[Function] The nickel-base heat-resistant alloy of the present invention has high Cr and high S.
Due to the i-containing composition, a dense oxide film is formed on the surface, and the film functions as an effective barrier against C diffusion and penetration. The inner surface of the reaction tube is composed of a reducing atmosphere during high temperature operation and an oxidizing atmosphere during decoking operation to periodically remove the carbon adhering to the inner surface of the tube wall by interrupting the operation. Yes, and undergoes thermal cycles associated with the repetition. The reaction tube made of the heat-resistant alloy of the present invention having a high Cr / high Si content composition is capable of deteriorating (deteriorating, cracking / peeling) the oxide film on the surface of the tube wall even under such a change of the atmosphere in the tube or the action of heat cycle. Etc.) does not occur, and the oxide film functions as a stable barrier that prevents the diffusion and invasion of C in a high temperature environment exceeding about 1150 ° C., and protects the tubular body from deterioration due to carburization for a long period of time. The barrier function is further enhanced by adding Al or the like. The heat-resistant alloy of the present invention is made of Cr, Ni, Si,
Mo, Ti, Zr, etc., and W optionally added,
By containing Nb, B, etc., it also has oxidation resistance and high temperature strength capable of withstanding a high temperature environment exceeding about 1150 ° C.

The reasons for limiting the components of the heat resistant alloy of the present invention are as follows. C: 0.1 to 0.5% C enhances the castability of the alloy, facilitates securing the casting quality in the centrifugal force casting of the pipe material, and in terms of strength, it forms a solid solution in the austenite matrix of the alloy. It is an element that contributes to the improvement of high temperature strength, especially creep rupture strength. For this reason,
0.1% or more is required. The effect is increased by increasing the amount added, but if added in a large amount, the alloy hardens and causes embrittlement, so 0.5% is the upper limit.

Si: 4% or less Si is a deoxidizing element in the alloy melting step and has the effect of enhancing the fluidity of the molten alloy. Since the alloy of the present invention has a high Ni composition, the addition of Si is effective in reducing the viscosity of the molten alloy and improving the castability. Also, S
i forms an oxide film as a barrier against the diffusion and penetration of C on the alloy surface, and contributes to the improvement of carburization resistance. These effects increase as the amount of Si increases. Preferably,
It is 2% or more. However, if it exceeds 4%, the weldability required as a structural material cannot be secured, so it should not exceed 4%.

Mn: 3% or less Mn is a deoxidizing agent in the alloy melting process, and is effective in improving weldability by fixing and detoxifying S, which is an impurity in the alloy, as MnS. The addition amount up to 3% is sufficient for obtaining these effects, and there is no benefit of adding a large amount exceeding this, so the upper limit is 3%.

Cr: 40 to 50% Cr is a well-known element as a main component for increasing the oxidation resistance and high temperature strength required for heat resistant alloys, but in the present invention, the Cr formed on the alloy surface is Based on the finding that the oxide film has an excellent barrier function against the diffusion and penetration of C in the high temperature carburizing environment, it was decided to contain at least 40% of Cr in order to enhance its action.
However, if it exceeds 50%, the tendency of the ductility to decrease in the process of high temperature use becomes remarkable, so this is the upper limit.

Mo: 0.5-10% Mo is solid solution strengthening of austenite base and Cr-Mo.
The high temperature tensile strength is increased by the action of strengthening the grain boundary by forming a system carbide. This effect is obtained by adding 0.5% or more, and the effect increases as the amount increases. However, a large amount of C
Since excessive precipitation of r-Mo-based carbide causes a decrease in tensile ductility, the upper limit is 10%.

N: 0.2% or less N forms a solid solution in the alloy matrix and is effective in improving the high temperature tensile strength. However, if added in a large amount, the room temperature tensile ductility decreases, so the content is made 0.2% or less.

Ti: 0.02 to 0.5% Ti contributes to improvement of high temperature creep rupture strength by suppressing growth coarsening of secondary Cr carbide in the alloy in a high temperature environment. Further, in the composition of components containing Al, Al
Strengthens carburization resistance as a synergistic effect with. This effect is
It is obtained by adding 0.02% or more, and the effect is enhanced by increasing the amount. However, if it exceeds 0.5%, the effect is almost saturated, and the creep rupture strength is rather decreased as the amount increases, so this is made the upper limit. Preferably 0.04
~ 0.4%.

Zr: 0.01 to 0.5% Zr enhances the high temperature creep rupture strength by solid solution strengthening the alloy matrix. Further, it is effective in improving the thermal shock characteristics. To obtain this effect, at least 0.01% is required. The effect is increased by increasing the amount, but if it exceeds 0.5%, the cleanliness of the alloy will be impaired by increasing the amount of Zr oxide, and rather the creep rupture strength will decrease, so this is the upper limit. Preferably, it is 0.03 to 0.4%.

Fe: 10% or less Fe is not an essential constituent element of the heat-resistant alloy of the present invention, and if a large amount of Fe is contained, it causes a decrease in oxidation resistance. There is no real harm.
Mixing within this range is allowed. It is advantageous in terms of manufacturing cost of the alloy that the mixture of Fe is allowed.

Ni: Balance Component Ni is a main element that forms the austenite matrix of the alloy of the present invention, and is an element necessary for ensuring carburization resistance as well as oxidation resistance in a high temperature range.

The heat-resistant alloy of the present invention comprises W, Al, Nb, and B.
As described above, an element selected from the group (1) or a combination of two or more types is added. W: 0.5 to 5% W forms a substitutional solid solution in the austenite matrix, and partly precipitates at the grain boundaries. Due to the solid solution strengthening action and the precipitation strengthening action, the strength of the alloy in the high temperature region, particularly the creep rupture strength, is increased. To achieve this effect, 0.5% or more is required. The effect is increased by increasing the addition amount, and the carburization resistance of the alloy is also enhanced, but if it exceeds 5%, the ductility of the alloy is impaired, so this is made the upper limit. Preferably 1
~ 3%.

Al: 0.02 to 0.5% Al forms an oxide film on the surface of the alloy in a high temperature range and suppresses the diffusion and penetration of C. Further, the formation of the oxide film also enhances the oxidation resistance. This effect is obtained by adding 0.02% or more. However, if added in a large amount, the room-temperature elongation property of the alloy is deteriorated and the weldability is deteriorated.
Must not exceed%. Preferably 0.04 to 0.4
5%.

Nb: 0.3-2% Nb is NbC, (Nb, Ti) in the solidification process of the alloy casting.
It forms carbides such as C and double carbides and precipitates at the grain boundaries to strengthen the grain boundary fracture resistance in high temperature creep and improve the creep rupture life. This effect is obtained by adding 0.3% or more, and the effect increases with increasing amount, but if it exceeds 2%, the creep rupture strength rather decreases and the oxidation resistance also deteriorates. Preferably, it is 0.3 to 1.7%.

B: 0.005 to 0.05% B strengthens the grain boundaries of the alloy and enhances the high temperature creep rupture strength. To obtain this effect, at least 0.0
Need more than 05%. The effect increases with increasing dose,
On the other hand, the weldability is deteriorated, so 0.05% is made the upper limit. It is preferably 0.008 to 0.03.

P, S, and other impurities are allowed to be mixed within a range that is inevitably mixed by ordinary melting technology. For example, P of 0.04% or less and S of 0.04% or less are present. This does not impair the gist of the present invention.

A high temperature member made of the heat resistant alloy of the present invention, for example, a reaction tube such as a cracking tube is manufactured by centrifugal casting. When used as a reaction tube, the tube is
The entire wall thickness of the pipe wall does not necessarily have to be the heat-resistant alloy of the present invention, the pipe wall thickness is a two-layer laminated structure, and the heat-resistant alloy of the present invention is applied only to the inner layer requiring carburization resistance, The outer layer may be a double-layer tube to which another heat-resistant alloy (HP40 material or a known alloy used as an improved material thereof) is applied. The production of the double-layer pipe is by centrifugal casting,
It can be carried out by two-stage casting in which a melt of a heat resistant alloy to be an outer layer is cast to form an outer layer, and then a melt of the heat resistant alloy of the present invention is cast to form an inner layer.

[0022]

EXAMPLE A molten alloy produced in a high frequency induction melting furnace is subjected to centrifugal force casting to obtain a hollow cylindrical body. Tube size (as cast): outer diameter 138mm, wall thickness 20mm, length 570mm. A test piece is prepared from each test tube material, and the following high temperature test is performed.

[1] Carburizing test (1) Specimen size: width 25 mm, thickness 10 mm, length 70 m
m. (2) Test method: The test piece is a solid carburizing agent (Degussa KG30)
Embedded in the substrate, heated to 850 ° C., heated from that temperature to 1200 ° C. over 30 hours, held at the same temperature for 20 hours, and then cooled. Then, the test piece is heated and held at 1100 ° C. (atmosphere atmosphere) for 5 hours. This carburization treatment and oxidation treatment are repeatedly performed as one cycle (cyclic carburization test). Carburizing time (total): 200 Hr, oxidation processing time (total): 15 Hr. (3) Measurement of carburizing amount: After the cyclic carburizing test, chips at each position (0.5 mm interval) from the surface of the test piece to 3 mm in the depth direction were collected and the C content was measured by chemical analysis. C by carburizing by subtracting the amount of C before the test from the measured value
The increase amount (ΔC%) is calculated.

[2] Creep rupture test Creep rupture time (Hr) in accordance with JIS G2272
Ask for. Test piece: parallel part diameter 5 mm, test condition: temperature 1150 ° C., tensile stress 10.8 MPa.

[3] Oxidation test (1) Specimen: width 15 mm, thickness 5 mm, length 25 mm (the surface is ground with sandpaper of grinding number # 400). (2) Test method: Test piece heating furnace (atmosphere: atmosphere, temperature:
After 1 hour at 1150 ° C., after holding for 50 hours, the heat pattern of furnace cooling is repeated 4 times as one cycle. Oxidation time (total): 50 Hr x 4 = 200 Hr. After the test, the surface scale is removed, and the weight loss is determined by weight measurement (g / cm ² , average value of 3 test pieces).

Table 1 shows the chemical composition (wt%) of the test pipe material, and Table 2 shows the test results. FIG. 1 illustrates the details of the C increase distribution in the depth direction of the test piece for the carburizing test results shown in Table 2. Specimen Nos. 1 to 7 are invention examples, No. 11
And 12 are comparative examples (corresponding to HP materials). As is clear from the above test, the heat-resistant alloys of the invention examples are conventional materials.
It has outstanding carburization resistance far superior to No. 11 and No. 1 (HP material), and is excellent in high temperature creep strength and oxidation resistance, and the difference in high temperature characteristics between them is obvious.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

EFFECTS OF THE INVENTION The heat-resistant alloy of the present invention has high-temperature carburization resistance far superior to that of conventional heat-resistant alloys, and responds to the recent demand for high-temperature operation as a reaction tube material for the petrochemical industry such as ethylene cracking tubes. In addition, the improved material properties enable improved durability and safe and smooth operation. Further, the heat-resistant alloy of the present invention is not limited to the above-mentioned applications, and is also useful as a material for a hearth roll in a steel heat treatment furnace, a radiant tube, or the like.

[Brief description of drawings]

FIG. 1 is a graph showing the distribution in the depth direction of the amount of carbon increase due to carburization of a test piece in a carburization test.

Claims (5)

[Claims] 1. C: 0.1 to 0.5%, Si: 4% or less, Mn: 3% or less, Cr: 40% to 50%, Mo:
0.5-10%, Fe: 10% or less, N: 0.2% or less, Ti: 0.02-0.5%, Zr: 0.01-0.
A heat-resistant alloy with excellent carburization resistance consisting of 5% and Ni as the balance. 2. C: 0.1 to 0.5%, Si: 4% or less, Mn: 3% or less, Cr: 40% to 50%, Mo:
0.5-10%, Fe: 10% or less, N: 0.2% or less, Ti: 0.02-0.5%, Zr: 0.01-0.
5%, W: 0.5-5%, the balance being a heat-resistant alloy consisting essentially of Ni with excellent carburization resistance. 3. C: 0.1 to 0.5%, Si: 4% or less, Mn: 3% or less, Cr: 40% to 50%, Mo:
0.5-10%, Fe: 10% or less, N: 0.2% or less, Ti: 0.02-0.5%, Zr: 0.01-0.
5%, W: 0.5-5%, Al: 0.02-0.5%,
The balance is a heat-resistant alloy that consists essentially of Ni and has excellent carburization resistance. 4. C: 0.1 to 0.5%, Si: 4% or less, Mn: 3% or less, Cr: 40% to 50%, Mo:
0.5-10%, Fe: 10% or less, N: 0.2% or less, Ti: 0.02-0.5%, Zr: 0.01-0.
5%, W: 0.5 to 5%, and Nb: 0.3 to 2%,
B: A heat-resistant alloy excellent in carburization resistance consisting of one or two kinds selected from 0.005 to 0.05% and the balance substantially consisting of Ni. 5. C: 0.1 to 0.5%, Si: 4% or less, Mn: 3% or less, Cr: 40% to 50%, Mo:
0.5-10%, Fe: 10% or less, N: 0.2% or less, Ti: 0.02-0.5%, Zr: 0.01-0.
5%, W: 0.5-5%, Al: 0.02-0.5%,
And Nb: 0.3 to 2%, B: 0.005 to 0.05
%, A heat-resistant alloy with excellent carburization resistance consisting of one or two selected from the group consisting of Ni and the balance substantially consisting of Ni.