JPH0754087A - Heat resistant alloy excellent in carburization resistance - Google Patents

Abstract

PURPOSE:To improve the high temp. carburization resistance of a heat resistant alloy. CONSTITUTION:This heat resistant alloy has a chemical compsn. consisting of <=0.3% C, <=4% Si, <=3% Mn, <=10% Cr, <=10% Fe, 10-35% W, 2-8% Al and the balance Ni with inevitable impurities or further contg. 0.05-0.5% Ti and/or 0.05-0.5% Zr as elements for enhancing creep rupture strength and one or more kinds of elements selected among 0.001-0.5% Ca, <=0.5% Hf and <=0.5% Y as elements for increasing carburization resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to carburization resistance which is useful as a constituent material for high temperature heat resistance applications where carburization resistance is required, typically for pyrolysis / reformation reaction tubes of hydrocarbons in the petrochemical industry. The present invention relates to a high Al nickel-base heat resistant alloy having excellent properties.

[0002]

2. Description of the Related Art A tube for pyrolysis / reforming reaction of hydrocarbons, for example, a cracking tube for ethylene production, uses a naphtha passing through the tube at a high temperature / high pressure (temperature: about 750 to 1050 ° C,
It is a reactor that causes thermal decomposition under the conditions of pressure: about 10 kg / cm ² or more). In its actual use, solid carbon is deposited from the reaction system, adheres to the inner surface of the pipe wall, and causes a carburizing phenomenon in which it diffuses and enters the inside of the pipe wall. The occurrence of carburization causes deterioration of the pipe material, particularly embrittlement of the pipe body due to a decrease in ductility, and causes cracking of the pipe body under operating conditions of high temperature and high pressure. Therefore, the reaction tube is required to have carburization resistance as well as strength in a high temperature range, oxidation resistance, etc. in order to ensure good durability and operational safety. Conventionally, as the pipe material, HP standard high-Si material (0.4 C-1.75S)
i-25Cr-35Ni-Fe) and its HP improvement material (0.4C-1.75Si-25Cr-35Ni-Mo, Nb, W)
-Fe) is used, and in Japanese Patent Publication No. 63-4897, 0.4 C-35Cr-45Ni-W, Nb-Ti, Z.
r-Fe heat-resistant cast steel, JP-B-63-4898,
0.4 C-35Cr-35Ni-W, Nb-Ti, Zr-Fe
Heat resistant cast steels are each disclosed.

[0003]

Recently, in the thermal decomposition / reforming reaction operation, there is an increasing demand for high temperature operation exceeding about 1100 ° C. from the viewpoint of improving operation efficiency and productivity. However, the above-mentioned conventional pipe material can be used at a temperature of up to about 1050 ° C. or up to about 1100 ° C., and it is difficult to ensure stable operation in a high temperature environment exceeding it, and in particular, carburization resistance is high. Deterioration of the pipe material due to lack of water is unavoidable and the service life is unavoidably shortened. 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 1100 ° C. and is useful as a pipe material which enables stable operation.

[0004]

The heat resistant alloy of the present invention comprises:
C: 0.3% or less, Si: 4% or less, Mn: 3% or less,
Cr: 10% or less, Fe: 10% or less, W: 10-35
%, Al: 2 to 8%, the balance Ni and the unavoidable impurities. The heat-resistant alloy of the present invention is intended to further improve the material thereof, and if desired, in addition to the above-mentioned elements,
As an element for improving the high temperature creep rupture strength, Ti: 0.0
Ca: 0.001 to 0.5% as one or two elements selected from the group of 5 to 0.5% and Zr: 0.05 to 0.5%, and / or an element for improving carburization resistance. , Hf:
A chemical composition containing one or more elements selected from the group of 0.5% or less and Y: 0.5% or less is provided.

[0005]

The nickel-base heat-resistant alloy of the present invention, having a high Al-containing composition, produces a dense oxide film on the surface,
The coating acts as an effective barrier to the diffuse penetration of C. The inner surface of the reaction tube is repeatedly subjected to a reducing atmosphere during high temperature operation and a weakly oxidizing atmosphere during decoking work for periodically removing the operation to remove carbon adhering to the inner surface of the tube wall. And undergoes a thermal cycle associated with the repetition. The reaction tube made of a heat-resistant alloy having a high Al-containing composition of the present invention causes deterioration (deterioration, cracking, peeling, etc.) of the oxide film on the surface of the tube wall even under such a change in the atmosphere in the tube and the action of heat cycle Without about 1100 ℃
It effectively functions as a barrier to prevent the diffusion and invasion of C in a high temperature environment exceeding 100 ° C, and protects the pipe body from deterioration due to carburization for a long period of time. Further, Cr is known as a main element for securing the oxidation resistance and high temperature strength of the heat resistant alloy, but the present invention limits this to a small amount and reacts with C that diffuses and penetrates into the alloy (Cr carbide). It is possible to stably maintain the high ductility by suppressing the generation of the above). For the lack of oxidation resistance and high temperature strength due to the limitation of the Cr content, the oxidation resistance is compensated by the effect of enriching the Al content, and the high temperature strength is improved by the addition of a large amount of elements such as W. By securing, about 1100
Combines the material properties required for use at temperatures above ℃.

The reasons for limiting the components of the heat resistant alloy of the present invention are as follows. C: 0.3% or less C enhances the castability of the alloy and facilitates the securing of casting quality in centrifugal casting of pipe materials. In terms of strength, it is an element that forms a solid solution in the alloy matrix and contributes to the improvement of high temperature strength, particularly creep rupture strength. However, in the present invention containing a large amount of W, when the amount of C exceeds 0.3%, the alloy hardens and causes embrittlement, so this is made 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 that serves 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: 10% or less Cr is a well-known element as a main component for enhancing the oxidation resistance and high temperature strength required for heat resistant alloys. But,
The solid solution Cr in the alloy base diffuses into the alloy C
Reacts preferentially with Cr to form a carbide and promotes embrittlement of the alloy. Therefore, in the present invention, in order to avoid the embrittlement of the alloy due to the formation of the carbide as much as possible, Cr is set to 10
%, So that high toughness can be maintained.

W: 10 to 35% W is a substitutional solid solution in the Ni base, and part of it is precipitated 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. In order to make this effect sufficient, the lower limit amount is 10%
I am trying. The effect is increased by increasing the addition amount, and the carburizing resistance of the alloy is also increased. However, if it exceeds 35%,
This is the upper limit because it impairs the ductility of the alloy.

Al: 2 to 8% Al forms a dense oxide film as a carburizing barrier on the surface of the alloy, and has the effect of significantly increasing the carburization resistance.
In addition, the formation of the oxide film ensures the oxidation resistance in the high temperature range. 2% to fully develop this effect
You need more than that. The effect is increased by increasing the amount, but if added too much, the ductility of the alloy is impaired, so the upper limit is 8%.

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

The heat-resistant alloy of the present invention is added with the following elements, if desired, in addition to the above-mentioned elements for the purpose of further improving the quality of the material. Ti: 0.05 to 0.5% Ti has an effect of improving creep rupture strength. Also,
Strengthens carburization resistance as a synergistic effect with Al. This effect is obtained by adding 0.05% or more, and the effect is increased 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.

Zr: 0.05 to 0.5% Zr solid-solution strengthens the austenite matrix of the alloy and increases the high temperature creep rupture strength. This effect appears by adding 0.05% or more, and the effect increases as the amount increases. However, adding more than 0.5% does not increase the effect,
On the contrary, the lowering of the cleanliness of the alloy causes the lowering of creep rupture strength, so this is the upper limit.

Ca: 0.001 to 0.5% Ca forms an oxide on the alloy surface in a high temperature range and is effective in improving carburization resistance. This carburizing resistance improving effect is
It is obtained by adding 0.001% or more. However, if added in a large amount, the weldability is impaired, so it should not exceed 0.5%.

Hf: 0.5% or less Hf has the effect of enhancing the carburization resistance of the alloy. The addition amount of up to 0.5% is sufficient to obtain this effect, and the addition amount exceeding this impairs the economical efficiency. Preferably 0.0
5 to 0.5%.

Y: 0.5% or less Y is an element effective in improving the carburization resistance, like the above Hf. This effect is sufficiently obtained at the addition of 0.5% or less, and there is no advantage to add beyond that. Preferably, it is 0.05 to 0.5%.

The amounts of P, S, and other impurities are in the range in which they are inevitably mixed by the usual melting technique, for example, 0.04%.
The presence of the following P and 0.04% or less S does not impair the gist of the present invention.

The 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 cast steel of the present invention is applied only to the inner layer requiring carburization resistance, The outer layer may be a two-layer pipe to which another heat-resistant cast steel (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.

[0020]

Example A hollow cylindrical body is obtained by subjecting a heat-resistant cast steel melt produced in a high-frequency induction melting furnace to centrifugal force casting. Tube size (after machining): outer diameter 138mm, wall thickness 20mm, length 570mm.
Table 1 shows the chemical composition (wt%) of the test tube materials. No. 1
No. 5 is an invention example, Nos. 11 and 12 are comparative examples (HP high Si
Material equivalent).

[Carburization test] (1) Test method A test piece (15 ^t × 25 ^W × 70 ^L ) was cut out from each test tube body and embedded in a solid carburizing agent (Degussa KG30) in a cylindrical container, and firstly at 850 ° C. Heated to 115 ° C from that temperature
Cyclic carburizing test in which the temperature is raised to 0 ° C over 30 hours, the temperature is kept for 18 hours, and then the temperature is lowered to room temperature 17 times repeatedly. [Test time: (30+
18) Hr × 17 = 816 Hr] is performed. After the test, in the thickness direction from the surface of the test piece, up to a depth of 5 mm, chips are collected from each position at a pitch of 0.5 mm, the C content is measured by chemical analysis, and the C content before the test is determined from the measured value. Is subtracted to obtain the amount of carbon increase due to carburization.

(2) Test Results FIG. 1 shows the distribution of the carbon increase amount at each position (0.5 mm interval) in the depth direction from the surface of the test piece for each test material. From the figure, the heat-resistant alloys (Nos. 1 to 5) of the invention examples are No. 11 and No. 12 (HP high Si) which are typical conventional materials.
Carburizing resistance is significantly higher than that of the conventional material, and the difference from the conventional material is obvious.

[0023]

[Table 1]

[0024]

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 a distribution in the thickness direction of an increase amount of carbon due to carburization of a test piece in a carburization test.

Claims (4)

[Claims] 1. C: 0.3% or less, Si: 4% or less, M
n: 3% or less, Cr: 10% or less, Fe: 10% or less,
A heat-resistant alloy with excellent carburization resistance consisting of W: 10-35%, Al: 2-8%, and the balance Ni. 2. C: 0.3% or less, Si: 4% or less, M
n: 3% or less, Cr: 10% or less, Fe: 10% or less,
W: 10-35%, Al: 2-8%, and Ti: 0.
A heat-resistant alloy having excellent carburization resistance, which is composed of one or two elements selected from the group of 05 to 0.5% and Zr: 0.05 to 0.5%, the balance Ni and inevitable impurities. 3. C: 0.3% or less, Si: 4% or less, M
n: 3% or less, Cr: 10% or less, Fe: 10% or less,
W: 10-35%, Al: 2-8%, and Ca: 0.
001 to 0.5%, Hf: 0.5% or less, Y: 0.5%
A heat-resistant alloy having excellent carburization resistance, which comprises one or more elements selected from the following groups, the balance Ni and inevitable impurities. 4. C: 0.3% or less, Si: 4% or less, M
n: 3% or less, Cr: 10% or less, Fe: 10% or less,
W: 10-35%, Al: 2-8%, and Ti: 0.
05: 0.5%, Zr: 0.05-0.5%, 1 or 2 elements selected from the group, Ca: 0.001-
A heat-resistant alloy excellent in carburization resistance, which is composed of one or more elements selected from the group consisting of 0.5%, Hf: 0.5% or less, and Y: 0.5% or less, the balance Ni, and inevitable impurities.