JPH10130813A - Heating furnace tube excellent in heat resistance, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating furnace tube capable of repeated use in an ultrahigh temp. region of >=1150 deg.C, and its production. SOLUTION: The heating furnace tube has a composition composed essentially of Mo and containing, by weight, <=15% Fe and alloying elements of the following groups A, B, and C: group A, 0-5%, in total of one or more elements among Cr, W, Ti, Nb, Ta, Co, Ni, Mn, and Cu; group B, 0-0.5%, in total, of either or both of C and N; group C, 0-0.1%, in total, of one or more elements among Ca, Mg, B, and REM. In this case, contents of Si and Al are higher in the surface layer part than in the inner part. The heating furnace tube is produced by subjecting a heating furnace tube of the above composition to pack cementation at >=1000 deg.C in a pack cementation agent having the following composition: 50-90% of penetrant (massive Si-base alloy containing <=10% Al); 0.5-5% of reaction accelerator; sintering inhibitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION
The present invention relates to a heating furnace tube having excellent heat resistance and usable in an ultra-high temperature range of up to 00 ° C. and a method for manufacturing the same.

[0002]

2. Description of the Related Art A bright annealing furnace is known as a furnace for heating a steel material without generating an oxide scale. In this furnace, the combustion gas flows into a heating furnace tube called a radiant tube, which indirectly heats the inside of the furnace while burning the inside of the tube, while the furnace atmosphere is made of a steel material as an artificially synthesized reducing gas. This type of furnace prevents oxidation. Since no oxide scale is generated on the steel material, it is possible to improve the yield of the scale loss, omit the pickling or descaling process, or prevent the surface quality of the product from deteriorating. For example, carbon steel, low alloy steel, etc. Widely used for heat treatment. In the following description, various furnaces prefixed with “bright” mean various furnaces “without generation of oxide scale”.

In this type of bright heat treatment furnace, the heat resistant temperature of the radiant tube material used is at most 115.
Since the temperature is up to about 0 ° C., the upper limit of the heating temperature of the steel material is about 1000 ° C. For this reason, the bright furnace can be applied to heat treatment of carbon steel or low alloy steel products, but cannot be applied in the following cases.

(A) Slabs, billets, etc. of carbon steel, low alloy steel, stainless steel, etc., are subjected to hot rolling at a temperature of 1200 to 130 before hot rolling.
When heating to 0 ° C.

(B) When the heating temperature exceeds 1000 ° C. as in the solution heat treatment of stainless steel, high Cr high Ni alloy, etc.

If a radiant tube material excellent in heat resistance which can be used in a temperature range of 1150 ° C. or more (hereinafter referred to as an ultra-high temperature range) is obtained, a bright furnace can be obtained in the above cases (a) and (b). Can be applied. As a result, various effects such as the above-described reduction in scale loss can be obtained as they are even in the case of heating at an ultra-high temperature, and also a great effect on quality improvement described below can be obtained.

(A) Since the decarburization of billets or slabs, which was impossible with the prior art, can be completely prevented, the surface quality of the final product can be significantly improved. A bright furnace capable of heating up to about 1300 ° C. can also be applied to stainless steel slab or billet heating, and can suppress abnormal oxidation of steel, which is a main cause of surface flaws during hot rolling, so it is revolutionary. Surface quality can be improved.

(B) When applied to a bright heat treatment furnace of stainless steel or high Cr high Ni alloy, etc., not only can the conventional pickling and descaling steps be omitted, but especially
In the prior art, since the formation of a Cr-free layer inevitably generated on the surface of the alloy can be prevented by the conventional technique using a high Cr austenitic alloy, there is an advantage that the corrosion resistance of the product is dramatically improved as compared with the conventional method.

For the purpose of obtaining such a great effect, there has been conventionally proposed a material for a radiant tube which can withstand use in an ultra-high temperature range.

As a material having excellent heat resistance at an extremely high temperature of 1150 ° C. or more, a refractory metal such as Mo (refrac.
For example, silicide MoSi ₂ of tory metal) is known. As one example, there has been proposed a heating furnace tube of MoSi ₂ in which a porosity is set to 2% by volume or less by centrifugally casting a molten metal including Mo and Si constituting MoSi ₂ at a specific mold rotation speed ( JP-A-07-331377).

Further, Si: 35-45%, Co: 25%
Hereinafter, a Mo-Si based alloy containing Ni: 25% or less and Fe: 10% or less and having excellent heat resistance is also disclosed (Japanese Patent Application No. 07-78747).

The techniques disclosed in Japanese Patent Application Laid-Open No. 07-331377 and Japanese Patent Application No. 07-78747 are disclosed in
It is intended to apply a kind of ceramic mainly composed of Mo silicide as a heating furnace tube.

However, these centrifugally cast tubes are damaged when subjected to bending in a hot or cold state, so that it is difficult to form them into panels or the like. In addition, since it is a ceramic, it has a problem that it cannot be welded by an existing welding method such as a TIG welding method.

Further, there has been disclosed a molybdenum alloy comprising Si: 0.3% or more and less than 20%, with the balance being Mo and having a high creep resistance in a temperature range of 1300 to 2000 ° C. (International Publication No. WO85). / 03953).

[0015] However, although this alloy has excellent creep resistance, it is easily burned off in a high-temperature oxidizing environment such as combustion gas, which is severely oxidative, and cannot be applied to the environment aimed at by the present invention. There is a problem.

Further, MoSi is added to Nb using a slurry.
₂ has been disclosed (TAKircher et. Al: Materials Science and Engi).
neering, A155 (1992) p.67).

However, in the case of an Nb tube coated with MoSi ₂ using a slurry, the treated coating is easily cracked and peeled off in the heating and cooling process, as shown in the document,
It has the disadvantage of burning out in a very short time.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-resistant material which can be bent by hot or cold and which can be welded by a conventional welding method and which can be repeatedly used in an ultra-high temperature range of 1150 ° C. or more. It is an object of the present invention to provide a heating furnace tube having excellent heat resistance and a manufacturing method thereof.

[0019]

Means for Solving the Problems The present inventors have studied the strength in ultra-high temperature range, bending at room temperature or hot, and weldability of various materials, and confirmed the following items. Was completed.

(A) Among heat-resistant metals, Mo-based alloys can be processed and welding can be performed by ordinary TIG welding. Therefore, the base alloy of the heating furnace tube is an alloy containing Mo as a main component.
That is, the Mo-based alloy is the most promising.

(B) However, since the Mo-based alloy is easily oxidized and burned out in a combustion gas environment, it is necessary to apply an oxidation-resistant coating on the surface of the heating furnace tube.

(C) In the heating furnace or the heat treatment furnace which is the object of the present invention, periodic inspection is performed every January to three months.
Heating and cooling are repeated in the heating furnace tube. Therefore M
The coating applied to the o-based alloy needs to have not only high-temperature oxidation resistance but also strong properties such that peeling and cracking do not occur due to repeated heating and cooling. As a method for achieving such an object, it is effective to form a coating film in which a content of Si or Al is increased in a certain range of a surface layer portion by diffusion infiltration treatment.

The present invention has been completed by combining the above items, actually repeating the heating and cooling to an extremely high temperature, confirming the effects thereof, and repeatedly improving.

The gist of the present invention is the following heating furnace tube and a method of manufacturing the same.

(1) An alloy tube containing Mo as a main component and containing Fe: 15% or less and the following alloy elements A, B, and C in terms of% by weight. A heating furnace tube having a higher heat resistance than the inside in the surface layer portion (referred to as [Invention 1]).

Alloying elements Group A: 0 to 5% in total of one or more of (Cr, W, Ti, Nb, Ta, Co, Ni, Mn, Cu) Group B: One or more of (C, N) Group C: 0% to 0.1% of the total of one or more of (Ca, Mg, B, REM) (2)% by weight, Fe: 15% or less and the following alloys An alloy tube containing Mo as a main component, which includes the elements A, B, and C, is mixed with a diffusion / penetration treatment agent having the following component composition.
A method for manufacturing a heating furnace tube having excellent heat resistance for performing diffusion and infiltration treatment in a temperature range of 000 ° C. or higher (referred to as [Invention 2]).

Alloying elements Group A: 0 to 5% in total of one or more of (Cr, W, Ti, Nb, Ta, Co, Ni, Mn, Cu) Group B: One or more of (C, N) 0 to 0.5% in total of group C: 0 to 0.1% in total of one or more of (Ca, Mg, B, REM) Diffusion infiltration treatment agent A massive Si-based alloy containing 10% or less of Al Some penetrants:
A diffusion infiltration treatment agent containing 50 to 90%, a reaction accelerator: 0.5 to 5%, and a sintering inhibitor.

In the above, the alloy mainly containing Mo containing 15% or less of Fe is a Mo-based alloy containing at least one of Group A, Group B, and Group C. Therefore, the case where none of the alloy elements of the group A, the group B, and the group C is included, that is, the substantial Mo—Fe alloy and the substantial Mo is also applicable.

In [Invention 1], the “surface layer” means S
Assuming that the contents of i and Al are distributed from the surface to the inside, the term "from the surface to at least the position of the surface layer at a depth of 0.1 mm" is usually used. To the position where it entered.

"The content of both Si and Al is higher in the surface layer than in the interior" means that the depth from the surface is 0.1 mm.
Means that the content of Si and Al at the position is higher than the inside by 0.1% or more, respectively. The measurement of the content of Si or Al at each position of the surface layer is performed by EPMA (Electron P).
robe Micro-Analyser) or the like.

In the following description, a portion having a high Si or Al content formed on the surface layer of the heating furnace tube by the diffusion and infiltration treatment may be simply referred to as a “coating”. Therefore, the "depth of the surface portion subjected to the diffusion and infiltration treatment" and the "film thickness" indicate the same.

In the above [Invention 2], the term "bulk Si-based alloy" refers to a relatively small-sized "lumpy" alloy, and includes a part in the category of "powder". "Lump" means not a needle, a planar shape, a flat body, etc., and is, for example, a cube, a rectangular parallelepiped having a length ratio of a long side to a short side of about 2 or less, or a ratio of a long diameter to a short diameter. Corresponds to a spheroid of about 2 or less. "Lump particle size" refers to the major diameter of the lump.

As used herein, the term "heat resistance" means a property having all of "high temperature strength and creep performance", "high temperature oxidation resistance" and "peeling resistance".

[0034]

Next, the reason why the present invention is limited as described above will be described. In the following description, “%” indicates “% by weight” unless otherwise specified.

1. Material of Heating Furnace Tube The material of the heating furnace tube is an alloy containing Mo as a main component and containing the following alloys.

Fe: 15% or less The heating furnace tube of the present invention contains 15% or less of Fe. Fe is desirably 10% or more to reduce the cost of the alloy tube. However, if it exceeds 15%, the melting point of the alloy decreases, and the alloy melts at an extremely high temperature, which is the operating temperature range.

In addition to the above-mentioned Fe, alloy components of the above-mentioned alloying elements A group, B group,
Group C is included.

Next, the reason why the range of each group is limited will be described.

Group A: The elements of Group A may not be contained. All of the elements in Group A have an effect of improving high-temperature strength in an ultra-high temperature range. That is, these alloy elements form a solid solution in the matrix and contribute to improvement of the high-temperature strength of the heating furnace tube. If the use temperature is high and the effect is desired to be obtained positively, the effect is included. However, if the effect is less than 0.1%, the effect is not clearly exhibited. On the other hand, if the total of them exceeds 5%, a brittle second phase (for example, Cr ₂ Mo) precipitates in the metal structure and causes a decrease in the toughness of the heating furnace tube.
And

Group B: The elements of Group B may not be contained. Each of the elements in group B, like the elements in group A, has an effect of improving high-temperature strength in an ultra-high temperature range. That is, these alloy elements form a solid solution in the matrix and contribute to improvement of the high-temperature strength of the heating furnace tube. When used for heating of a low-alloy steel slab before rolling or the like, and when it is desired to further increase the high-temperature strength, it is included as necessary. However, if the content is less than 0.01%, the improvement in high-temperature strength is insufficient, so that if the content is to be included, the content of 0.1% is not preferable.
Desirably, it is not less than 01%. On the other hand, if the sum of them exceeds 0.5%, Mo carbides and nitrides are excessively precipitated in the metal structure to cause a decrease in toughness, so the upper limit is made 0.5%.

Group C: The elements of Group C need not be contained. All elements of group C improve the workability of the alloy. That is, these elements react with O (oxygen) in the alloy, reduce the amount of dissolved oxygen having an effect of impairing the workability of the alloy, and contribute to improving the workability of the heating furnace tube. For this reason, it is included when it is used for a member requiring a large processing. However, if the content is less than 0.001%, the workability is not sufficiently improved. On the other hand, if their total content exceeds 0.1%, the workability is rather reduced.
1%.

The above Mo-based alloy contains unavoidable impurities such as P, S and O which cannot be removed by a normal manufacturing method.

2. Assuming that the distribution of the content of Si and Al decreases from the surface to the interior, the content of Si and Al must be higher than that of the interior at least at a position of 0.1 mm from the surface. No. Heat resistance cannot be ensured unless the contents of Si and Al are higher than the inside at least at a depth of 0.1 mm. As described above, a depth of 0.1 mm and a height higher than the inside means 0.1 mm.
% Or higher.

Further, in order to ensure oxidation resistance in an ultra-high temperature range, it is desirable that the total content of Si and Al is 35% or more at a position of a surface layer portion having a depth of 0.1 mm.
If the sum of Si and Al at this position is less than 35%, the following problem occurs, and the object of the present invention may not be achieved.

(A) Al having excellent oxidation resistance in an ultra-high temperature range
Films such as ₂ O ₃ and SiO ₂ are not uniformly formed on the alloy surface.

(B) If the total thickness of Si and Al is 35% or more and the coating thickness is less than 0.1 mm, the S in the surface layer portion may be used for a long time (for example, about 10,000 hours) in an ultra-high temperature range.
i and Al diffuse into the Mo-based alloy as a substrate, and the content of Si and Al in the coating decreases, and the oxidation resistance of the coating deteriorates.

Therefore, it is desirable that the total content of Si and Al should be 35% or more at the position of the surface layer portion having a depth of 0.1 mm. At this time, as described above, it is assumed that the concentration distribution of Si and Al is a distribution that decreases from the surface to the inside, and this assumption is always satisfied.

On the other hand, at the point of the surface layer portion having a depth of 0.1 mm, S
If the sum of i and Al exceeds 45%, the peeling resistance may deteriorate. The thickness of the coating is preferably as thick as possible from the viewpoint of oxidation resistance. However, if the coating having a total of 35% of Si and Al exceeds 0.3 mm, the thermal shock resistance may be deteriorated. Because of the increased cost, the thickness of the coating film should be less than 0.1.
It is preferably about 3 mm or less.

3. Diffusion and infiltration treatment Next, the reasons for limiting the diffusion and infiltration treatment conditions will be described.

3-1. Diffusion-penetration treatment agent The diffusion-penetration treatment is performed in the above-mentioned diffusion-penetration treatment agent. Note that the “diffusion infiltration agent” may be simply referred to as “treatment agent”.

The reason why the treatment material is limited to the above-mentioned component composition is as follows.

Penetrant: The reason why a Si-based alloy containing 10% or less of Al is used as the penetrant is to improve the adhesion of the film produced by the diffusion-penetration treatment, that is, the peeling resistance. If Al exceeds 10%, no SiO ₂ film is formed on the surface of the material, and the oxidation resistance is deteriorated. On the other hand, when the Al content is less than 0.1%, a film having excellent peeling resistance may not be obtained, so that the content is preferably 0.1% or more.

It is desirable that the bulk of the Si-based alloy containing Al has a particle size of about 0.1 to 3 mm. 0.1 ~
When a lump of Si-based alloy having a particle size of 3 mm is used as a penetrant,
i, SiCl ₄ , AlCl ₄ as carrier gas of Al
Contact the entire surface of the material to be treated without bias, and Al and Si can be uniformly diffused from the entire surface. As a result, a uniform coating is obtained on the material to be processed.

If the Si-based alloy exceeds 90% in the penetrant, the penetrant sinters into the heating furnace tube after the diffusion and infiltration treatment, and the heating furnace tube and the penetrant cannot be separated. 90% or less. On the other hand, when the content of the Si-based alloy is 5
When the content is less than 0%, a coating excellent in oxidation resistance and peeling resistance is not formed on the surface layer of the heating furnace tube, so that the content is set to 50% or more.

Reaction accelerator: NH ₄ C is used as the reaction accelerator.
1 and chlorides and bromides such as NaCl and NH ₄ Br can be used. If the total of these reaction accelerators is less than 0.5%, a coating rich in oxidation resistance and peeling resistance is not uniformly formed on the surface layer of the heating furnace tube.
5% or more is required. However, if the content exceeds 5%, hydrochloric acid or bromic acid gas is generated during the diffusion and infiltration treatment, which is not preferable in terms of work, so the upper limit is set to 5%.

Sintering inhibitor: Al ₂ O ₃ is used as a sintering inhibitor.
Chemically stable and inexpensive compounds such as mullite and mullite can be used. The sintering inhibitor is 5 to 5 in the diffusion infiltration agent.
It is desirable to be in the range of 0%. If it is less than 5% in the diffusion infiltration treatment agent, sintering prevention is not sufficient, while if it exceeds 50%, no film is formed.

3-2. Diffusion-penetration treatment Diffusion-penetration treatment temperature: When the temperature of the diffusion-penetration treatment is less than 1000 ° C., the diffusion reaction is slowed, the treatment time is required for a long time, and the treatment cost is increased. On the other hand, in practical use, 1
It is desirable that the temperature be about 200 ° C. or less.

Diffusion infiltration time: Diffusion infiltration time is 1
It is desirable that the time be longer than the time. Diffusion infiltration time 1
When the time is less than the time, a film having sufficient oxidation resistance and peel resistance may not be obtained. On the other hand, if the time is too long, an unnecessarily thick film having a high content of Al and Si may be formed and the peeling resistance may be degraded. In addition, the cost required for the diffusion and infiltration treatment is increased, so that it is less than about 50 hours. desirable.

Atmosphere: It is desirable to perform the diffusion and infiltration treatment in a non-oxidizing atmosphere. Usually, the reaction is performed in a hydrogen atmosphere, but it is not always necessary to use hydrogen as long as oxidation can be prevented.

[0060]

EXAMPLES Next, the effects of the present invention will be described with reference to examples.

Table 1 shows the chemical composition of a Mo-based alloy melted in an electric arc furnace to produce a heating furnace tube.

[0062]

[Table 1]

From the Mo-based alloy ingot shown in Table 1, a ring having an outer diameter of 50 mm, a thickness of 5 mm, and a length of 100 mm was hollowed out to obtain a model of a heating furnace tube. The alloys shown in Table 1 have been confirmed in advance that the alloy can be bent or welded by the TIG method.

Table 2 shows the composition of the diffusion / penetration treatment agent used in the experiment. The Si-based alloy used was a lump (powder) having a particle diameter of 0.3 mm. Table 3 shows the conditions of the diffusion and infiltration treatment.

[0065]

[Table 2]

[0066]

[Table 3]

The above ring was subjected to a diffusion permeation treatment using a treating agent shown in Table 2 under the conditions shown in Table 3 in a H ₂ gas flow by a powder packing method, and then the thickness and film thickness of the obtained surface layer portion were obtained. The contents of Si and Al therein were analyzed. In Table 3, the coating thickness represents the distance from the surface to a position where the sum of Al and Si is higher than the inside. In addition, Si or Al
Indicates the content of Si or Al at a position of 0.1 mm from the outermost surface.

Table 3 shows the thickness of the coating and the contents of Si and Al in the coating.

The ring subjected to the diffusion and infiltration treatment was subjected to a heat cycle test of heating and cooling to room temperature after heating at 1450 ° C. for 100 hours in air, and 10 heat cycles of heating and cooling. The sex was evaluated. The oxidation resistance was evaluated by increasing the oxidation, and the peel resistance was evaluated by the presence or absence of peeling of the coating.

Table 4 shows the results of these tests.

[0071]

[Table 4]

Test No. 33, which is a comparative example, shows that Al
Was not higher than the inside by 0.1% or more, and the coating was peeled off, and the high-temperature oxidation resistance was extremely low. Test No. 34, which is also a comparative example, shows that a coating having a high content of Al and Si was not formed on the surface layer portion due to the use of the treatment agent H outside the range of the present invention as the diffusion and infiltration treatment agent, resulting in burnout after the heat cycle test. Was. In the test No. 36 of the comparative example, since the mother alloy contained 20.6% of Fe, the melting point of the alloy was lowered, and the alloy was partially melted at the oxidation resistance test temperature of 1450 ° C. to evaluate the oxidation resistance. Could not do.

On the other hand, it was confirmed that the ring according to the present invention withstands severe heat cycles of heating and cooling, and shows good oxidation resistance even at an extremely high temperature of 1450 ° C.

[0074]

According to the present invention, there is provided a heating furnace tube having extremely excellent high-temperature oxidation resistance in an ultra-high temperature oxidizing gas atmosphere exceeding 1150 ° C. and a method for producing the same. The Mo-based alloy according to the present invention is not only easily bent and welded as a heating furnace tube with conventional equipment, but also has a coating by diffusion infiltration processing, so that it can withstand high temperature strength and thermal shock in an ultra-high temperature range. It has sufficient peeling resistance.

By using the present invention for a radiant tube, it is possible to manufacture a bright furnace in which the material to be heated has a heating temperature of about 1300 ° C., and various scales including scale loss generated in the steel manufacturing process. Problems can be solved at once, and epoch-making surface quality improvement can be obtained.

Claims (2)

[Claims] 1. An alloy tube containing Mo as a main component and containing at least 15% by weight of Fe and the following alloy elements A, B and C, wherein the content of both Si and Al is in the surface layer. Heating furnace tube excellent in heat resistance characterized in that it is higher than the inside in the part. Alloying element Group A: Total of one or more of (Cr, W, Ti, Nb, Ta, Co, Ni, Mn, Cu) is 0 to 5% Group B: Total of one or more of (C, N) 0-0.5% Group C: Total of one or more of (Ca, Mg, B, REM) is 0-0.1% 2. A diffusion / penetration treatment agent having the following composition with respect to an alloy pipe containing 15% or less of Fe by weight and containing Mo as a main component and containing the following alloy elements A, B and C: A method of manufacturing a heating furnace tube having excellent heat resistance, wherein diffusion heat treatment is performed in a temperature range of 1000 ° C. or more. Alloying elements Group A: 0 to 5% in total of one or more of (Cr, W, Ti, Nb, Ta, Co, Ni, Mn, Cu) Group B: Total of one or more of (C, N) 0 to 0.5% Group C: 0 to 0.1% in total of one or more of (Ca, Mg, B, REM) Diffusion infiltration agent Penetrant which is a massive Si-based alloy containing 10% or less of Al :
A diffusion infiltration treatment agent containing 50 to 90%, a reaction accelerator: 0.5 to 5%, and a sintering inhibitor.