WO2005078148A1

WO2005078148A1 - Metal tube for use in carburizing gas atmosphere

Info

Publication number: WO2005078148A1
Application number: PCT/JP2005/000892
Authority: WO
Inventors: Yoshitaka Nishiyama; Nobuo Otsuka; Takeo Kudo
Original assignee: Sumitomo Metal Industries, Ltd.
Priority date: 2004-02-12
Filing date: 2005-01-25
Publication date: 2005-08-25
Also published as: EP1717330A1; EP1717330B1; CA2556128A1; DK1717330T3; EP1717330A4; JPWO2005078148A1

Abstract

A metal tube for use in a carburizing gas atmosphere, which comprises a Cu-rich layer having a Cu concentration of 0.1 atomic % or more and a thickness of 0.3 nm or more in the surface portion thereof, and comprises a base material having an alloy composition, in mass %, wherein Cr: 15 to 35 %, Ni: 30 to 75 %, Al: 0.001 to 10 %, and Cu: 0.01 to 10 %. The metal tube may further comprise an oxide scale layer containing Cr as a main component and having a Cr content of 50 % or more or an oxide scale layer containing Cr and Al as main components and having a total content of (Cr + Al) of 50 % or more, on the outside of the above Cu-rich layer, and may still further comprise a second oxide scale layer containing Si as a main component and having a Si content of 50 % or more, between the above oxide scale layer and the above Cu-rich layer. The above metal tube has a function of shielding the base material from a carburizing gas, and is excellent in the resistance to metal dusting, to carburizing and to coking.

Description

Specification

Metal tube for use in carburizing gas atmosphere

Technical field

The present invention relates to a metal pipe which has high strength at high temperatures and excellent corrosion resistance and can be used in a carburizing gas atmosphere containing a hydrocarbon gas or a CO gas. INDUSTRIAL APPLICABILITY The metal tube of the present invention has excellent shielding performance for carburizing gas, and is suitable as a material for a cracking furnace tube, a reforming furnace tube, a heating furnace tube, a heat exchanger tube, or the like in a petroleum refining or petrochemical plant.

[0002] The present invention makes it possible to control the shielding properties of a metal tube used in a carburizing gas atmosphere against carburizing gas.

Background art

[0003] Demand for clean energy fuels such as hydrogen, methanol, liquid fuel (GTL) and dimethyl ether (DME) is expected to increase significantly in the future. Therefore, a reformer for producing synthesis gas becomes larger, and a device having higher thermal efficiency and suitable for mass production is required. Also

In order to improve energy efficiency, heat exchange for waste heat recovery is also required in conventional reformers at petroleum refining and petrochemical plants, ammonia and hydrogen production systems using petroleum, etc. Is increasingly used.

[0004] In order to effectively utilize the heat of such a high-temperature gas, it is important to perform heat exchange in a temperature range of 400 to 700 ° C, which is lower than conventionally targeted. For this reason, corrosion due to the carburizing phenomenon of high Cr high Ni metal materials used in metal tubes such as reaction tubes and heat exchangers in such a temperature range has become a problem.

[0005] The synthesis gas produced by the reformer, ie, H, CO, CO, H0, and meta

2 2 2

Gases containing hydrocarbons, such as hydrocarbons, come into contact with the metallic materials that make up the reaction tubes, which are the main part of the reformer, at a high temperature of around 1000 ° C or higher. In such a high temperature range, a dense oxide film composed of oxides of elements such as Cr and Si (that is, chromium oxide and silicon oxide), which has a large tendency to oxidize Fe or N, is formed on the surface of the metal material. Therefore, corrosion of the material is suppressed. However, in a relatively low temperature portion such as a heat exchange portion, the diffusion of elements from the inside of the material to the surface is insufficient, so that an acid having a corrosion inhibiting effect can be obtained. In addition to the delayed formation of the oxide film, the gas of the same composition also changes to become carburizable by the reforming reaction, resulting in carburization by intrusion of C from the metal surface.

[0006] In an ethylene cracking furnace tube or the like, when the carburizing of the metal material constituting the tube progresses and a carburized layer made of a carbide of a metal such as Cr or Fe is formed on the inner surface of the tube, the volume of that portion expands. . As a result, fine cracks are likely to occur, and in the worst case, the pipe is broken. In addition, carbon deposition (caulking) using a metal as a catalyst occurs on the metal surface exposed by the cracks, resulting in a reduction in the cross-sectional area of the pipe flow path and a reduction in heat transfer characteristics.

[0007] On the other hand, in an environment in which the carburizing property of gas is more severe, as seen in reforming furnace tubes and heat exchangers, phenomena such as carbides produced by carburizing become supersaturated and then graphite is directly deposited. As a result, the base metal is peeled off from the pipe surface and the pipe is reduced in thickness, and the corrosion and consumption of metal material called metal dusting progresses. Further, the peeled metal powder serves as a catalyst, and the above-described coking occurs.

[0008] If the cracks, corrosion, and clogging in the pipe due to carburization as described above increase, the operation may be interrupted due to equipment failure or the like. Therefore, sufficient consideration must be given to the selection of materials for metal pipes used in carburizing gas atmospheres.

[0009] Various countermeasures against corrosion due to carburization of metal materials and metal dusting have been conventionally studied.

For example, Japanese Unexamined Patent Publication No. 9-78204 describes an atmosphere of 400-700 ° C containing H, C〇, CO, and H〇.

2 2 2

Regarding the resistance to metal dusting in gas, it has been pointed out that an Fe-based alloy or an M-based alloy containing 11 to 60% (mass%, hereinafter the same) of Cr is superior. This patent publication discloses a material containing at least 24% Cr and at least 35% M for an Fe-based alloy, a material containing at least 20% Cr and at least 60% Ni for a Ni-based alloy, and further adding Nb to the material. Materials are disclosed. However, in general, increasing the amount of Cr or Ni cannot sufficiently suppress carburization, and it is desired to further suppress metal dusting.

[0010] In Japanese Patent Application Laid-Open No. 11-172473, in order to suppress corrosion due to metal dusting of a high-temperature alloy containing iron, nickel and chromium, groups VIII, IB, IV and IV of the periodic table of the elements are used. One or more metals selected from Group V and their mixtures are deposited on the surface of the metallic material by conventional physical or chemical means, annealed in an inert atmosphere, A thin layer of 0.01-10 μπι is formed on the surface of the material. In this case, Sn, Pb, Bi, etc. are particularly effective. This method appears to be ineffective initially, but with prolonged use, the thin layer will delaminate and become ineffective.

[0011] Japanese Patent Application Laid-Open No. 2003-73763 discloses an atmosphere gas containing 400, 700 ° C containing H, C〇, CO, and H 2 O.

2 2 2

Investigation of the interaction with C from the viewpoint of solute elements in iron with respect to the metal dusting resistance in steel shows that alloy elements with a positive interaction assistance coefficient Ω are effective in suppressing metal dusting. Is described. This patent publication discloses a metal material in which the contents of Cu and Co are controlled in addition to Si, Al and Ni. These alloy components dramatically increase the metal dusting property. Increasing the content of alloying elements such as Si, Al, and Cu lowers hot workability and weldability, so stable supply manufacturing and plant construction Considering this, there is still room for improvement.

[0012] In order to shield the metal from the carburizing gas, a method of subjecting the material to an oxidation treatment in advance and a technique of performing a surface treatment are also shown in the prior art.

For example, JP-A-53-66832 and JP-A-53-66835 disclose 25Cr to 20Ni (HK 40) low-Si heat-resistant steel and 25Cr to 35Ni low-Si heat-resistant steel in air at around 1000 ° C. A method for performing pre-oxidation for more than 100 hours is disclosed. Japanese Patent Application Laid-Open No. 57-43989 discloses a technique for pre-oxidizing an austenitic heat-resistant steel containing 20-35% Cr in the atmosphere. Japanese Patent Application Laid-Open No. H11-29776 proposes a method of improving the carburization resistance by heating a high M—Cr alloy in a vacuum to form a scale film. JP-T-2000-509105 proposes a method for improving carburization resistance by forming a concentrated layer of Si or Cr by surface treatment.

[0013] These require special heat treatments and surface treatments, and are inferior in economy. Also, restoration of scale (scale regeneration) after exfoliation of the pre-oxidized scale or the surface treatment layer is not considered, so once the surface is damaged, the subsequent effects cannot be expected.

[0014] A method of adding H 2 S to the atmosphere gas is also considered. Force H S is used for reforming

twenty two

Its application is limited because it can significantly reduce the activity of the catalyst.

Therefore, there is still a need for a metal material that can sufficiently suppress metal dusting and satisfy the required characteristics such as manufacturability and weldability. Disclosure of the invention

[0015] The present invention provides a cracking furnace tube for ethylene plants, a reforming furnace tube, and the like, which has a function of shielding from carburizing gas and thereby exhibits excellent metal dusting resistance, carburizing resistance, and coking resistance. The purpose is to provide a metal tube suitable for use.

[0016] The inventors of the present invention analyzed the surface condition of various metal pipe materials in order to investigate the behavior of locally generating metal dusting, carburizing, and caulking (carbon deposition) even in a metal pipe having a high Cr content. Was done. As a result, if the oxide layer formed on the surface of the metal tube is dense, the above corrosion does not occur, but if a defect such as partial cracking or peeling occurs in the oxide layer, the oxide At the same time as C entered, it was found that the exposed metal acted as a catalyst to cause carbon deposition.

[0017] As a result of a detailed study of the phenomenon of C infiltration, hydrocarbons and CO gas are adsorbed on the metal surface, and then C is separated by dissociation. It was found that the invasion of C progressed through the dissociative adsorption process. As a result of further study on the dissociative adsorption, it was found that the presence of Cu, Ag or Pt was effective in suppressing the dissociative adsorption.

From the above mechanism, to suppress carburization and metal dusting, (1) a protective oxide scale or a thin layer formed by surface treatment is formed on the metal surface to block C, and (2) penetration C In addition to the means of reducing the flux (flux) of the gas, as a third means, it is effective to suppress the dissociative adsorption of gas. For this purpose, Cu, Ag, Pt It is important that these elements exist.

However, when these elements are added to the alloy, the possibility of inhibiting the manufacturability, weldability, resilience, and cracking properties is increased, and Ag and Pt increase costs. Therefore, it is desirable to minimize the content of these elements as much as possible without losing the above-mentioned resistance to carburization, resistance to metal dusting and resistance to coking.

The present inventors have focused on the fact that gas adsorption is a phenomenon that occurs on the surface of a metal material. If a Cu-enriched layer exists only on the metal surface, the dissociation of the adsorbed gas is essentially reduced. However, we thought that carburization and metal dusting could be suppressed. In other words, the Cu content in the metal material (alloy) is limited to a level that does not affect the manufacturability and weldability, but the Cu concentration on the surface is A confirmation test was conducted based on the idea that desired performance could be obtained by performing a process for increasing the performance.

[0021] FIGS. 1 (A) and 1 (B) show that the Cu content is different and therefore the surface Cu concentration is different by 25%.

Cr-35% Ni-bal.Fe alloy [Fig.1 (A)] or 25% Cr-55% Ni-2.5% A bal.Fe alloy [Fig.1 (B)] About 650 ° C, 60% CO-26% H -11.5% CO -2.5% H

This shows the relationship between the surface Cu concentration and the time during which pits are formed when a corrosion test is performed in O (vol%) gas. These figures show that when the Cu concentration on the metal surface exceeds 0.1 atomic%, the effect of suppressing pit generation, that is, metal dusting, appears. The Cu concentration is a value obtained by converting the measured value obtained by elemental analysis in the depth direction of the metal surface force by AES (Auger analysis) into atomic%. When there is an oxide scale layer mainly composed of Cr or Cr and A1 on the surface, or this oxide scale layer and further a second oxide scale layer mainly composed of Si, such an oxide scale layer is substantially removed. The measured value on the removed metal surface is defined as the Cu concentration.

[0022] Figs. 2 (A) and 2 (B) show the 25% Cr-35% Ni-0.5% Cu_bal.Fe alloy [Fig.2 (A)] or 25% Cr-55% Ni-2.5% A The relationship between the thickness of the Cu-enriched layer and the occurrence of pits when a Cu-enriched layer is formed on the surface of a 0.3% Cu-bal.Fe alloy [Fig. 2 (B)] under different conditions is shown. The corrosion test conditions are the same as above. The Cu concentration of the Cu-enriched layer of the test alloy is in the range of about 0.4-0.8 at.% 2 (A) and about 0.2-0.5 at.% [Fig.2 (B)]. These figures show that if the thickness of the Cu-enriched layer is 0.3 nm (nanometer) or more, the pit generation time is prolonged, that is, the metal dusting resistance is effective.

[0023] In order to confirm that when the oxide scale was formed on the metal surface, the Cu-enriched layer immediately below the oxide scale had an effect on the metal dusting resistance, FIG. 1 (A) and FIG. The same various plate-shaped test pieces as in the test shown in (B) were subjected to atmospheric oxidation treatment at 1100 ° C for 5 minutes to form an oxide scale, and then subjected to a corrosion test under the same conditions as above. Figure 3 (A) shows the results obtained with a 25% Cr_35% Ni-bal.Fe alloy, and Figure 3 (B) shows the results. /οΟ·_55%Μ-2.5. /. The results obtained with the bal.Fe alloy are shown below. The horizontal axis shows the Cu concentration immediately below the preliminary oxidation scale in atomic percent. From these figures, it can be seen that pits are suppressed by the presence of oxide scale on the metal surface in advance. The pits are further suppressed when the Cu concentration below the scale is 0.1 atomic% or more. Power to be done.

[0024] As can be seen, even if the oxide scale is previously formed on the surface, the formation of pits cannot be prevented because the metal surface is exposed when a defect occurs. On the other hand, if a Cu-enriched layer exists directly below the scale, defects occur in the pre-oxidized scale, and even if the metal surface is exposed, the exposed metal surface is a Cu-enriched layer. Adsorption is suppressed and pit formation is prevented.

[0025] In one aspect, the present invention based on such findings includes a base material containing 35% by mass of Cr: 15% by mass of Ni: 30% by mass, Al: 0.001 by 10%, and Cu: 0.01 to 10% by mass%. A metal tube provided with a Cu-enriched layer on its surface, wherein the Cu-enriched layer has a Cu concentration of 0.1 atomic% or more and a thickness of 0.3 band or more. This is a metal tube for use in a carburizing gas atmosphere.

[0026] The metal tube may further include an oxide scale layer having a Cr content of 50% by mass or more or a total content of Cr + Al of 50% by mass or more outside the Cu-enriched layer. In this case, a second oxide scale layer having a Si content of 50% by mass or more may be further provided between the oxide scale layer and the Cu-enriched layer.

[0027] The metal tube of the present invention may have an irregular inner surface and / or outer surface.

The base material is preferably, by mass%, C: 0.01-0.6%, Si: 0.01-5%, Mn: 0.01-10%, P: 0.08% or less, S: 0.05% or less, Cr: 15-35 %, Ni: 30% to 75%, Cu: 0.01% to 10%, N: 0.001% to 0.25%, Al: 0.001% to 10%, 0 (oxygen): 0.02% or less, with the balance being Fe and impurities. are doing. This chemical composition may further contain at least one element selected from the following (i) to (vi) in mass%.

(i) Co: 0.01-5%,

(ii) one or two of Mo: 0.01-10% and W: 0.01 10%,

(iii) One or two types of Ti: 0.01 2% and Nb: 0.01-2%,

(iv) One or more of B: 0.001 0.1%, Zr: 0.001 0.1% and Hf: 0.001—0.5%,

(V) One or two of Mg: 0.0005 0.1% and Ca: 0.0005 0.1%, (vi) Υ: 0 · 0005—0.15%, La: 0.0005—0.15%, Ce: 0.0005—0.15%, and Nd: 0.0005—0.15% or more.

[0028] From another aspect, the present invention provides a base material containing ⁰ : ₀ mass, Cr: 15-35%, Ni: 30-75%, A1: 0.001-10%, Cu: 0.01-10%. In a metal tube used in a carburizing gas atmosphere, a Cu-enriched layer is formed on the surface of the metal tube, and the Cu-enriched layer has a Cu concentration of 0.1 atomic% or more, and A method for improving the metal dusting resistance, carburization resistance and coking resistance of the metal pipe, characterized in that the thickness of the thickened layer is 0.3 nm or more.

[0029] In this method as well, an oxide scale layer having a Cr content of 50% or more or a total content of Cr + Al of 50% by mass or more may be provided outside the Cu-enriched layer. A second oxide scale layer mainly composed of Si having a Si content of 50% or more may be provided between the kale and the Cu-concentrated layer.

[0030] The metal pipe of the present invention has a function of shielding from carburizing gas, and is excellent in metal dusting resistance, carburization resistance, and coking resistance. It can be used for cracking furnace tubes, reforming furnace tubes, heating furnace tubes, pipes, heat exchanger tubes, etc., and can greatly improve the durability and operation efficiency of the equipment. Brief Description of Drawings

[FIG. 1] FIGS. 1 (A) and 1 (B) show 25% Cr-35 having different Cu contents. ₃ is a graph showing the relationship between the surface Cu concentration and pit generation in the Ni-bal.Fe alloy and the 25% Cr_55% Ni_2.5% A bal.Fe alloy.

[FIG. 2] FIGS. 2 (A) and 2 (B) each show 25% Cr-35. /. 3 is a graph showing the relationship between the thickness of a Cu-enriched layer and the occurrence of pits in a Ni-0.5% Cu-baLFe alloy and a 25% Cr-55% Ni_2.5% A 0.3% Cu-bal.Fe alloy.

[FIG. 3] In FIGS. 3 (A) and 3 (B), the Cu content is different at 25 Q /. Cr_35Q /. 5 is a graph showing the relationship between the pit formation and the Cu concentration just below the oxide scale in the Ni_bal.Fe alloy and the 25% Cr-55% Ni_2.5% A bal.Fe alloy.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, the present invention will be described in more detail. In the following description, “% "" Means "% by mass".

The metal tube according to the present invention is composed of a base material containing 15 to 35% of Cr, 30 to 75% of Ni, 0.001 to 10% of Al, and 0.01 to 10% of Cu. With layers.

[0033] The Cu-enriched layer can be provided on one or both of the inner surface and the outer surface of the metal tube. The object of the present invention can be achieved by forming a Cu-enriched layer only on the surface of the metal tube exposed to the carburizing gas atmosphere. For example, in a reaction tube or a cracking furnace tube, a Cu-enriched layer can be formed on the inner surface, and in a heat exchange type reaction tube, a Cu-enriched layer can be formed on the outer surface. However, even in these cases, a Cu-enriched layer may be formed on both surfaces of the metal tube.

[0034] (i) Cu-enriched layer

“Cu-enriched layer” refers to a region having a concentration (% by mass) higher than the average Cu concentration (% by mass) of the base material, and the thickness of the Cu-enriched layer is determined on the metal surface (one or two layers on the metal surface). If there is more than one oxide scale layer, the position where the Cu concentration is equivalent to the average Cu concentration of the base metal from the interface with the innermost oxide scale layer (that is, the Cu-enriched layer and the base metal Distance in the depth direction (that is, in the radial direction of the metal tube) to the interface of the metal pipe.

The oxide scale layer that can be formed on the surface of the metal tube according to the present invention includes, for example, an oxide scale layer mainly composed of Cr (having a Cr content of 50% or more), an oxide scale layer mainly composed of Cr, and Si There can be a second oxide scale layer that is mainly (Si content is 50% or more) or an oxide scale layer that is mainly Cr + Al (the total content of Cr + Al is 50% or more).

[0036] The Cu concentration of the Cu-enriched layer refers to the average value of the Cu concentration in the layer. When the Cu concentration is measured by AES as in the embodiment, the average value of the measured values (atomic% conversion value) in the layer is defined as the Cu concentration of the Cu-enriched layer.

[0037] The Cu concentration and the thickness of the Cu-enriched layer can be measured using AES. AES can measure the concentration of metal elements on the surface by irradiating the surface with an electron bell and detecting the emitted electrons. By cutting a small piece from a part of the metal tube and performing AES while sputtering from the surface, it is also possible to analyze in the depth direction from the surface. In this way, by measuring the Cu concentration in the surface layer of the material in the depth direction until the Cu concentration becomes constant, the thickness of the Cu-enriched layer can be determined. The Cu concentration in the concentrated layer can be determined. [0038] The Cu-enriched layer is provided on the surface of the metal tube. The surface layer of a metal tube means the portion near the tube surface, and its location depends on the method of forming the Cu-enriched layer. That is, the Cu-enriched layer may be the outermost layer of the metal tube, but if one or more oxide scale layers exist outside the Cu-enriched layer, the Cu-enriched layer is oxidized. It exists between the scale layer and the base material.

[0039] The Cu concentration of the Cu-enriched layer is 0.1 atomic% or more. If the Cu concentration of the Cu-enriched layer is less than 0.1 atomic%, it will not be possible to perform the shielding function by suppressing the adsorption of hydrocarbons and C-dissociative gas such as C〇 during the operation of the plant. In addition, even when the oxide scale layer described above exists on the metal surface, if the Cu concentration of the Cu concentrated layer immediately below the metal oxide layer is less than 0.1 atomic%, the oxide scale layer may be damaged, such as cracking or peeling. The gas adsorption on the exposed metal surface cannot be suppressed when exposed. The Cu concentration of the Cu-enriched layer is preferably at least 0.3 at%, more preferably at least 1.0 at%.

[0040] The thickness of the Cu-enriched layer is 0.3 nm or more. If the thickness of the Cu-enriched layer is less than 0.3 nm, the shielding function cannot be achieved by suppressing adsorption of hydrocarbons and C-class gases such as CO from the carburizing gas during plant operation. The thickness of the Cu-enriched layer is preferably 0.5 nm or more.

The thickness of the Cu-enriched layer can be easily adjusted by, for example, changing the conditions of the alternating electrolytic treatment and the atmosphere control heat treatment. The upper limit of the thickness of the Cu-enriched layer is not particularly specified, but usually does not exceed 100 nm.

The means for generating the Cu-enriched layer is not limited to these, but includes “alternate electrolytic treatment”, “atmosphere control heat treatment”, “pickling treatment” and the like. These two or more techniques may be used in combination.

The most preferable of these methods is an alternating electrolytic treatment. Alternating electrolytic treatment is a method in which the potential applied to the metal is swept to a noble potential region where the alloying element dissolves in the electrolyte, and then swept to a lower potential region, thereby depositing Cu on the surface. It is. Cu is more electrically noble than Ni, Cr, and Fe, and thus precipitates preferentially in a low potential region. This treatment can form a Cu-enriched layer on the surface of the metal tube on the side where the electrolyte contacts. This process can reliably form a Cu-enriched layer. The thickness and Cu content of the Cu-enriched layer can be changed by applying potential and application time in the noble and noble potential regions.

When the oxide scale layer is present on the metal surface, the atmosphere control heat treatment Alternatively, by forming a Cr + Al-based oxide scale or a second Si-based oxide scale, the Cr, Al, and Si concentrations immediately below the oxide scale decrease, so that the Cu concentration becomes relatively higher than the inside of the base material, A Cu-enriched layer can be formed.

[0043] Further, by preferentially dissolving elements other than Cu by using the pickling treatment, the Cu concentration in the surface layer can be increased to form a Cu-enriched layer.

Even if an oxide scale layer is formed on the surface of the metal tube by oxidation heat treatment after alternating electrolysis or pickling, a Cu-enriched layer is formed between the oxide scale layer and the base metal alloy. Power S can.

(Ii) Oxide scale layer

As the oxide scale layer, a first oxide scale layer mainly composed of Cr or Cr + Al [hereinafter referred to as an oxide scale layer (A)] is preferably present on the surface of the metal tube. Oxide scale layer [hereinafter referred to as oxide scale layer (B)].

[0045] The oxide scale layer (A) has an oxide scale force mainly composed of Cr or Cr + Al. Whether this oxide scale is mainly composed of Cr or mainly composed of Cr + Al depends on the A1 content in the alloy. Generally, when the A1 content is 1.5% or more, the oxide scale is mainly composed of Cr + Al, and when the A1 content is less than 1.5%, the oxide scale is mainly composed of Cr.

In order to form the oxide scale layer (A), the metal tube may be heated in an oxidizing atmosphere to a temperature at which surface oxidation occurs. The thickness of the formed oxide scale layer can be changed depending on conditions such as heating temperature, time, and partial pressure of oxygen in the atmosphere. The oxygen partial pressure should be higher than the dissociation pressure of Cr-based oxide. The composition of the oxide scale layer is determined solely by the alloy composition of the base material.

[0047] A skeneole oxide layer mainly composed of Cr or Cr + Al is very important from the viewpoint of metal dusting resistance, carburization resistance and coking resistance. An oxide scale layer mainly composed of Cr with a Cr content of 50% or more has excellent shielding properties against penetration of highly dense carbon into steel. And the total content of A1 is 50. The oxide scale layer mainly composed of Cr + Al having a ratio of / o or more has a higher density and exhibits excellent protection. All of these oxide scale layers are thermodynamically stable up to high temperatures even in a high-temperature carburizing environment such as an ethylene cracking furnace, and have long-term protection. In addition, all of these oxide scale layers are resistant to coking. Since the catalytic action is small, coking on the metal surface is suppressed. As a result, the thermal conductivity to the fluid in the pipe is maintained well for a long time, and the yield of reaction products such as olefins is stabilized.

[0048] When the Cr content or the total content of Cr + Al (when the oxide scale also contains A1) is 80% or more, the scale layer becomes denser, and carbon invades steel. On the other hand, it is effective as a strong shielding layer. As a result, the carburization resistance is dramatically improved. Further desirable Cr content or Cr + Al content is 85% or more.

[0049] The oxide scale layer (B) is an oxide scale force mainly composed of Si. In order to generate this oxide scale layer, the oxide scale layer may be heated to a temperature at which surface oxidation occurs in an oxidizing atmosphere. The thickness of the oxide scale layer to be formed can be changed depending on conditions such as heating temperature, time, and partial pressure of oxygen in the atmosphere. The composition of the oxide scale layer is determined solely by the base steel composition.

When an oxide scale layer (B) of S cast having a Si content of 50% or more is to be generated, it is preferably present between the Cu-concentrated layer and the oxide scale layer (A). The oxide scale layer (B) promotes the uniform formation of the above-described oxide scanole layer (A), and the damaged portion is regenerated when the oxide scale layer (A) is damaged, such as cracking or peeling. It has the function of assisting in this.

[0051] In order to form the oxide scale layer (B) mainly composed of Si between the Cu-concentrated layer and the oxide scale layer (A), a gas having an oxygen partial pressure equal to or higher than the dissociation pressure of the oxide mainly composed of Cr is used. If the metal chamber is heated in the middle, the dissociation pressure of the oxide mainly composed of Si is smaller than the dissociation pressure of the oxide mainly composed of Cr, so that the inner oxide scale layer (B) and the outer oxide scale layer (A ) Can be formed at the same time. The thickness of each oxide scale layer can be changed depending on the heating temperature and time.

[0052] The oxide scale layer (B) can be easily formed by increasing the Si content in the base alloy (for example, to 0.4% or more).

The thickness of the oxide scale layer can be measured, for example, by observing a cross-sectional micro sample with an optical microscope. The element content of the oxide scale layer (A) and the oxide scale layer (B) can be measured by EDX (energy monodisperse X-ray spectrometer). The measurement is generally performed by performing C element deposition on the surface using a cross-sectional micro sample and then performing elemental quantitative analysis by EDX. The element content in the scale is the elemental content measured for each of the target scale layers. From the analysis results, it can be determined as the value of the Cr, Al, and Si contents when the total amount of metal elements alone is 100%.

[0053] The inner surface and / or outer surface of the metal tube according to the present invention may be a surface having an irregular shape such as having a projection or having an irregular cross section. Generally, a surface having such an irregular cross section is susceptible to attack by a carburizing gas, so that the oxide scale is easily peeled off. However, according to the present invention, since the inner surface and / or the outer surface of the metal tube have high carburization resistance and a high ability to repair the coating, the inner surface and the Z or outer surface having such an irregular cross section are provided. The effect of the present invention is particularly remarkable in the case of a bent metal tube.

The metal material (base material) constituting the metal tube according to the present invention has the following composition (% by mass except for the Cu concentration (expressed in atomic%) of the Cu-concentrated layer, and the balance Fe and impurities). Preferably, the alloy has

[0055] C: 0.01—0.6%

In order to secure high-temperature strength, it is effective to contain 0.01% or more of C. If the C content exceeds 0.6%, the toughness of the alloy becomes extremely poor. Preferred range of C content is 0.01%-0.45%

The more preferred range is 0.01% —0.3%.

[0056] Si: 0.01-5%

Since Si has a strong affinity for oxygen, it promotes the uniform formation of a Cr-based oxide scale layer (A). This effect is exhibited by containing 0.01% or more of Si. However, if the Si content exceeds 5%, the weldability deteriorates and the structure becomes unstable. The preferred range of the Si content is 0.1-3%, and the more preferred range is 0.3-2.5%.

[0057] However, when the A1 content is 1.5% or more, the coexistence of Si and A1 extremely deteriorates the weldability and also makes the structure unstable, so the upper limit of the Si content is set to 1%. Is preferred. In this case, the more preferable range of the Si content is 0.05 to 0.6%.

[0058] Mn: 0.01 10%

Mn is added in an amount of 0.01 Q / o or more to improve deoxidation and processability. Since Mn is an austenite forming element, it is possible to partially replace Ni with Mn. However, the addition of excess Mn inhibits the formation of an oxide scale layer mainly composed of Cr, The upper limit of the amount is 10%. A preferred range of the Mn content is 0.1-5%, and a more preferred range is 0.1-2%.

[0059] P: 0.08% or less, S: 0.05% or less

P and S segregate at the grain boundaries and degrade hot workability. Therefore, it is preferable to reduce as much as possible, but excessive reduction leads to high cost, so P: 0.08. / o or less, S: 0.05% or less. Preferably, P: 0.05% or less, S: 0.03% or less, more preferably, P: 0.04% or less, S: 0.015% or less.

[0060] Cr: 15 35%

Cr is an important element in the present invention. In order to stably form a Cr-based oxide scale, it is necessary to contain 15% or more of Cr. If the alloy contains more than 1.5% of A1, a denser and more protective oxide scale will be formed, consisting mainly of Cr and A1. However, since excessive Cr addition deteriorates the structure stability as well as the processability, the upper limit is set to 35%. A preferred range of the Cr content is 20-33%, and a more preferred range is 22-32%.

[0061] M: 30-75%

M is an element capable of obtaining a stable austenite structure in accordance with the Cr content, and is therefore contained in an amount of 30 to 75%. Also, when C enters steel, it has a function to reduce the penetration speed. However, an unnecessarily high content of M causes high costs and difficulty in manufacturing. The preferred range of the Ni content is 35-70%, and the more preferred range is 40-65%.

[0062] Cu: 0.01-10%

Cu is one of the most important elements in the present invention. Cu has a very large effect of suppressing the adsorption of carburizing gas to the metal surface. In order to form a 01 enriched layer with a Cu concentration of 0.1 atomic% or more on the surface layer, the base metal alloy needs to contain 0.01% or more Cu. On the other hand, if Cu is added in excess of 10%, the hot workability is significantly reduced. A preferred range for the Cu content is 0.03-5%, and a more preferred range is 0.1-3%.

[0063] N: 0.001—0.25%

N is an element effective for improving high-temperature strength. To achieve this effect, N should be contained at 0.001% or more. An excessive amount of soybean paste greatly impairs processability, so the upper limit is 0.25%. The preferred N content range is 0.001% 0.2%. [0064] However, when the Al content is 1.5% or more, the N content is preferably 0.1% or less because A1 and N form a compound and lower the creep strength. The more preferable range of the N content in this case is 0.001% -0.05%.

[0065] A1: 0.001-10%

Al is an element effective for improving hot workability even in a trace amount. Therefore, A1

Add at least 0.001%. For this purpose, it is preferable to contain A1 in an amount of 0.01% or more.

[0066] A1 also contributes to the formation of a dense and highly protective oxide scale mainly composed of Cr and A1 when the oxide scale is previously formed on the surface and when exposed to a carburizing gas environment. . Further, even when an oxide scale is not formed in advance, an oxide scale mainly composed of A1 and A1 is generated in a use environment, so that metal dusting resistance and carburization resistance of the metal pipe can be significantly improved. For this purpose, it is effective to contain 1.5% or more of A1. On the other hand, when A1 is contained in an amount exceeding 10%, a hardenable precipitate is precipitated in the alloy, so that the toughness and creep ductility of the alloy are significantly reduced. When forming an oxide scale layer mainly composed of Cr and A1, the preferred range of the A1 content is 2 to 8%, the more preferred range is 2 to 4%, and the most preferred range is 2.2 to 3.5%.

[0067] However, in order to generate an oxide scale layer (B) mainly composed of Si, the A1 content is preferably less than 1.5%. In this case, the more preferable range of the A1 content is 0.01 to 1.2%, and the most preferable range is 0.01 to 0.5%.

[0068] Oxygen (〇): 0.02% or less

Oxygen exists as an impurity. If the oxygen content exceeds 0.02%, a large amount of oxide-based inclusions are present in the alloy, reducing workability and causing metal tube surface flaws.Therefore, the upper limit of the oxygen content is set to 0.02%. I do.

[0069] In addition to the above alloying elements, at least one of the following elements can be added as desired.

Co: 0.01-5%

Since Co has the effect of stabilizing the austenite phase, part of Ni is 0.01. It can be replaced with Co over / o. On the other hand, if Co is added in excess of 5%, the hot workability of the alloy becomes significant. Decline. The preferred range of the Co content is 0.01-3%.

[0070] 1 or 2 types of Mo: 0.01-10% and W: 0.01-10%

Mo and W are both solid solution strengthening elements and are effective in improving the high temperature strength of the alloy. In order to exert its effect, each can be added in an amount of 0.01% or more. However, excessive addition of each of these elements impairs processability and inhibits tissue stability. Therefore, the content of both Mo and W should be 10% or less. For both Mo and W, the preferred range is 0.01-8%, and the more preferred range is 0.1-5%.

[0071] One or two kinds of Ti: 0.01 2% and Nb: 0 · 01 2%

Ti and Nb have a great effect on improving high-temperature strength, ductility and toughness even with a very small amount of added syrup. However, if each is less than 0.01%, the effect cannot be obtained, and if it exceeds 2%, workability and weldability are reduced. For both Ti and Nb, the preferred range is 0.01-1.5%, and the more preferred range is 0.02-1.2%.

[0072] One or more of B: 0.001—0.1%, Zr: 0.001—0.1% and Hf: 0.001—0.5%

B, Zr and Hf are all effective elements for strengthening grain boundaries and improving hot workability and high-temperature strength properties.However, if less than 0.001%, the effect cannot be obtained and excessive addition (More than 0.1% for B and Zr, more than 0.5% for ΗΠ?) Deteriorates weldability.

[0073] One or two types of Mg: 0.0005—0.1% and Ca: 0.0005—0.1%:

Mg and Ca are both effective elements for improving hot workability, and the effect is remarkable at 0.0005% or more. However, excessive addition of these elements deteriorates the weldability, so the upper limits are each set to 0.1%.

[0074] Y, La, Ce, Nd: one or more of 0.0005-0.15% each:

Y, La, Ce, and Nd are effective elements for improving oxidation resistance, but their effects are not obtained at less than 0.0005%, and excessive addition lowers the workability, so the upper limit is set. To 0.15%. The preferable lower limit of the amount of added kamitsu of each of these elements is 0.005%.

[0075] The metal pipe having a function of shielding from carburizing gas according to the present invention can be obtained by combining means selected from melting, forging, hot working, cold working, welding, and the like. What is necessary is just to shape | mold into a required metal tube shape, such as a tube. Alternatively, it may be formed into a required metal tube shape by a method such as powder metallurgy or centrifugal structure. [0076] The surface of the metal tube after the final heat treatment may be subjected to surface processing such as pickling, shot blasting, mechanical cutting, grinder polishing, and electrolytic polishing. It is also possible to combine a plurality of these. After that, a Cu-enriched layer is generated by the means described above. The formation of the oxide scale (A) and the oxide scale (B) may be achieved at the time of the final heat treatment, or may be formed by performing a heat treatment after the surface processing treatment or the treatment for forming the Cu-enriched layer.

[0077] It should be noted that even if the metal pipe according to the present invention has one or more protruding shapes on the inner surface and / or outer surface of the tube, it does not impair the function of shielding from carburizing gas at all. ,. Examples of such a protrusion shape include a fin tube used for an ethylene cracking furnace tube, and can be formed, for example, during hot working or by welding.

The following examples illustrate the present invention, and the present invention is not limited to these examples. In Examples,% is mass% unless otherwise specified.

Example 1

[0079] This example illustrates the case where the A1 content of the base material is less than 1.5% and an oxide scale is formed, where a Cr-based oxide scale layer is formed.

Each metal material having the chemical composition shown in Table 1 was melted in a high-frequency heating vacuum furnace to form a billet, and the billet was subjected to hot forging and cold rolling to obtain a gold material having an outer diameter of 56 mm and a wall thickness of 6 mm. A genus tube was made. The metal tube was uniformly subjected to solution heat treatment at 1200 ° C for 10 minutes in air. Next, the metal pipe was cut into round slices having a length of about 30 mm, and a portion of the cut metal pipe was shot blasted (only on the outer surface) (abbreviated as SB), pickled (abbreviated as Pic), pickled descaling ( PiD), machine cutting IJ (outer surface only) (abbreviated as Mac), grinder grinding (abbreviated as Grd), or a combination of these surface treatments. Thereafter, each metal tube was subjected to alternating electrolytic treatment (abbreviated as ACE1) or atmosphere control heat treatment (abbreviated as ACHT) to form a Cu-enriched layer on the inner and outer surfaces of the tube. In addition, some metal pipes were shot peened (abbreviated as SP) on the outer surface of the pipe to introduce distortion into the metal surface. In this example, the Cr-based oxide scale layer (A) and the Si-based oxide scale layer (B) were formed during the atmosphere control heat treatment. By this atmosphere control heat treatment, a Cu-enriched layer was formed inside the oxide scale layer at the same time as the oxide scale layer was formed. In this example, it was demonstrated that a Cu-enriched layer Therefore, the surface treatment and the alternating electrolytic treatment were not performed on the metal tube that had been subjected to this heat treatment.

[0080] In the alternating electrolytic treatment, in a sulfuric acid bath at pH = 3, application is repeated alternately at a noble potential of +1.1 V and a low potential of −0.6 V (both vs. SCE) for 0.15 seconds each. The application was performed for a total of 120 seconds. However, in Comparative Examples 4-B and 17-A of Table 2, the noble potential was changed to one 0.25 V. The atmosphere heat treatment, the oxygen partial pressure 10- ¹ 10- ⁸ MPa: was performed by heat treatment of hypoxia Kiri囲vapor 1120- 1220 ° CX 3 minutes (the remaining hydrogen gas and water vapor).

[0081] A 20 mm square test piece was cut out from each of the above metal tubes, and the Cu concentration on the surface of the test piece was measured in the depth direction by AES, and the Cu-enriched layer was determined based on the Cu content of the base material. Was determined, and its thickness and Cu concentration were determined.

[0082] For the metal tube subjected to the atmosphere control heat treatment, the oxide scale layer formed on the surface was measured in addition to the AES measurement for the Cu-enriched layer described above. That is, first, a cross-sectional micro-mouth test piece was prepared, and the thickness of the oxide scale layer was measured by microscopic observation. Using the same test piece, the Cr content and the Si content of the Cr-based oxide scale layer (A) and the Si-based oxide scale layer (B) on the surface were measured by EDX, respectively. These contents were measured at any three locations for each of the target scale layers, and the Cr, Al, and Si contents were calculated when the total amount of metal elements was 100%, and calculated from their average values. .

[Evaluation of metal dusting resistance]

A test piece having a width of 20 mm and a length of 25 mm was cut out from the above metal tube. This test piece was heated at 650 ° C in a carburizing gas atmosphere of 60% CO-26% H-11.5% CO-2.5% HO by volume ratio.

2 2 2

The test piece was taken out at regular intervals during this period, and the test piece was taken out at regular intervals and the surface was visually observed to determine the presence or absence of pits, and the time until the occurrence of pits was recorded. Table of results

See Figure 2. In Table 2, for example, a pit occurrence time of 1000 hours means that a pit occurred after 1000 hours.

[0084] [Carburization resistance evaluation]

A test piece having a width of 20 mm and a length of 30 mm was cut out from the metal tube. The specimen was kept at 1050 ° C for 300 hours in a carburizing gas atmosphere with a volume ratio of 15% CH -3% CO -82% H.

4 2 2

The amount of C (% by mass) invading the base material was measured as follows. [0085] After removing the oxide scale formed on the surface of the test piece after holding in the gas atmosphere, metal chips were sampled at a 0.5 mm pitch in the depth direction from the surface, and 0.5 to 1.0 mm deep. The amount of C at the depth of 1.0-1.5 mm was quantified by chemical analysis, and after reducing the amount of the base metal C before the test, the average value of both C amounts was defined as the amount of invading C at a depth of 1 mm. Table 2 also shows the results.

[0086] [Table 1] Alloy base metal chemical composition (% by mass) balance Fe + impurities

Underlines also deviate from the range of the present invention. [0087] [Table 2-1]

') SB: Shotblast last, ACEI: Alternating treatment, He: Pickling, HD: Pickling descaling, Mac: Luo grinding, ACHT: Atmosphere control, SP: Shot peening, Grd: Grinder grinding;

2 ¹ cut! ^ Kale layer: (A) = Cr-based acid layer, (B) = S-cast acid layer; 3 ⁾ Metal dusting resistance: 60% CO- 26% _{_{H 2 - 11.5% C0 2 -}} 2.5 0 / oH 2 0, gas (650¾); *赚炭_{resistance: 15% CH 4 -3% C0} 2 - 82% Η 2 gas, 1050 ° CX 300 hours.

The underline also deviates from the specified range force of the present invention.

[0088] [Table 2-2] Metal-resistant.

Solution solubilization Cu concentration Kale layer ³ charcoal) Testability ³⁾

Of metal tube after gold

Material Cu concentration Thickness (A) Cr amount (B) Si amount Pit generation Intrusion. amount

No. Processing step ')

No. Genko ⁰ /. ) (Nm) («*%) 0 ■ (h) (K»%)

26 26- A SB → ACE1 1.02 0.5--> 1000 0.5

27 27-A HD → ACE1 1.32 0.4--1000 0.6

28 28-A SB → ACE1 0.40> 1--〉 1000 0.3

29 29-A HD → ACE1 0.39 0.4--> recitation 0.2

30 30- A SB— ACE1 1.11 0.5-― 1000 0.4

31 31-A RD → ACE1 0.53 0.6 one-> 1000 0.4

32 32- A ACHT 0.43 0.5 71-Layer 0 0.3

33 33-A SB—ACE1 Not detected 0--100 100 1.9

RD → ACE1 →

34 34- A 15.5 0.2--> 1000

SP

35 35-A SB → ACE1 32.1 0.3--Layer 0 g 0.1

"SB: Shot blast, ACE1: Alternating treatment, Rc: Pickling, PiD: Pickling descaling, Mac: Leak grinding, ACHT: Atmosphere control heat treatment, SP: Shot peening, Grd: Grinder shelf IJ;

2) Acid it ^ Kale layer: (A) = Cr-based layer! ^ Kale layer, (B) = S cast layer.

9 resistant metal Dasute Ing resistance: 60% CO-26% H 2 - 11.5% C0 2 - 2.5% H 2 〇, gas ftSOt);

) Ffifg charcoal _{^{resistance: 15% CH 4 - 3 0}} /. C0 ₂ -82% H ₂ gas, 1050 ° CX 300B.

Underlines depart from the scope of the present invention.

[0089] As can be seen from Table 2, the metal pipe of alloy No. 33 whose chemical composition deviates from the condition specified in the present invention has a short pit generation time of less than 100 hours, and has poor metal dusting resistance. In addition, this metal pipe is inferior in carburization resistance with a large amount of penetration C of 2%.

[0090] On the other hand, among the metal tubes of alloy numbers 1-32 and 34-35 whose chemical compositions satisfy the conditions specified in the present invention, the conditions in which the Cu concentration and the thickened layer thickness of the Cu-enriched layer are specified in the present invention. The test metal tube that satisfies the above requirements has excellent metal dusting resistance, which has a long time until the occurrence of pits, has less than 1% penetration C, and has excellent carburization resistance. However, a test metal tube in which at least one of the Cu concentration and the thickness of the Cu-enriched layer does not satisfy the conditions specified in the present invention has a short time until the occurrence of pits, is inferior in metal dusting resistance, and has a low penetration rate. It has a high C content and is inferior in carburization resistance.

[0091] Also, from Table 2, it can be seen that a Cu-enriched layer can be formed just below the oxide scale layer generated by this heat treatment simply by performing the atmosphere control heat treatment (ACHT) on the metal tube. In the oxide scale layer, when the Si content is as low as about 0.01%, the force S generated only by the Cr-based oxide scale layer (A), and under the heat treatment conditions used in this example, the Si content is about Above 0.4%, it appears that a silicon-based oxide scale layer (B) is continuously and significantly formed between the oxide scale layer (A) and the Cu-enriched layer. Example 2

[0092] This example illustrates a case where the A1 content of the base material is 1.5% or more and an oxide scale is formed, and an oxide scale layer mainly composed of Cr and A1 is formed. Since the A1 content is as high as 1.5% or more, the Si content is set to 1% or less for the above-described reason.

[0093] Using each of the metal materials having the chemical compositions shown in Table 3, a test metal tube was produced in the same manner as described in Example 1. However, in Comparative Examples 2-B and 6-C of Table 4, the noble potential was changed to 0.25 V in the alternating electrolytic treatment.

[0094] For the prepared metal tube, the composition of the oxide scale layer, the thickness and the Cu concentration (atomic%) of the Cu-enriched layer, and the evaluation test of the metal dusting resistance and the carburization resistance were also performed in Examples. The procedure was the same as in 1. However, since the metal pipe of this example has a high A1 content of 1.5% or more, it has better metal dusting resistance and carburization resistance than the metal pipe manufactured in Example 1. Therefore, in the metal dusting resistance evaluation test, the test time was extended from 1000 hours in Example 1 to 3000 hours, and in the carburization resistance evaluation test, the test temperature was increased from 1050 ° C to 1100 ° C. Conditions were more stringent.

[0095] In this example, since the A1 content was as high as 1.5%, the oxide scale layer (A) generated by the atmosphere control heat treatment (ACHT) was mainly composed of Cr and A1, so that the Cr + The total content of Al was measured by EDX. In addition, all of the test metal tubes subjected to the atmosphere control heat treatment had a Si content of less than 0.3%, and the oxide scale layer (B) mainly composed of Si was not formed in the form of a continuous layer. The measurement of the scale layer (B) was not performed.

[0096] Table 4 summarizes the above measurement results.

[0097] [Table 3]

Alloy Base metal Chemical composition (mass%) balance Fe + impurities

Να C Si Mn P S Cr Ni Al Cu N 瞧 Other

0.004 B, 0.003 Ca,

1 0.06 0.08 0.22 0.007 0.00 0.001 20.5 67.2 3.1 1.5 0.011 0.006

2.0 Mo

2 0.01 0.11 0.19 0.005 less 0.001 19.9 68.1 2.9 0.1 0.012 0.003 0.003 Ca, 0.04 La

3 0.02 0.33 0.15 0.021 Ku 0.001 '25.5 65.5 2.9 0.1 0.007 0.004 0.004 Hf, 0.11 Ti

4 0.03 0.21 0.11 0.011 0.001 21.1 68.1 2.6 1.5 0.005 0.003 0.04 Ce, 1.1 W

5 0.06 0.01 0.02 0.014 0.011 26.6 63.5 2.5 1.5 0.001 0.008 0.08 Nb

6 0.06 0.03 0.11 0.011 0.005 30.1 60.2 2.9 0.2 0.011 0.005 0.002 Mg

7 0.01 0.09 0.19 0.002 0.001 16.4 62.5 1.6 1.1 0.008 0.003 0.05 Y

8 0.09 0.33 0.45 0.017 0.003 22.1 64.2 3.2 0.7 0.005 0.004 0.03 Zr

9 0.02 0.87 0.25 0.018 0.007 24.3 56.3 1.8 0.2 0.006 0.006 7.1 Mo

10 0.02 0.33 0.22 0.022 0.003 22.1 57.3 3.1 0.2 0.006 0.006-

11 0.03 0.54 0.29 0.025 0.002 19.8 37.1 2.9 0.3 0.001 0.015 1.2 Co, 0.01 La

12 0.03 0.14 0.19 0.016 0.009 21.1 63.2 2.6 0.5 0.005 0.009 1.15 Ή, 0.002 Mg

13 0.03 0.22 0.18 0.012 0.022 20.4 67.4 2.9 0.1 0.004 0.006 2.1 Mo, 0.11 Nb

14 0.02 0.18 2.50 0.011 0.021 25.4 66.4 3.1 0.8 0.187 0.006-

0.5 W, 0.05 Nb,

15 0.06 0.08 0.02 0.054 0.011 26.5 63.2 3.6 1.2 0.014 0.004

0.003 B

16 0.03 0.11 0.44 0.028 0.007 25.3 60.1 3.1 0.2 0.028 0.004 0.02 Ce, 0.004 Ca

0.11 Ti, 0.005 Ca,

17 0.08 0.06 1.06 0.002 0.001 20.3 73.4 2.8 0.2 0.015 0.006

0.04 Nd

18 0.05 0.15 0.26 0.004 0.032 18.7 66.3 8.5 3.9 0.001 0.005 0.23 Co, 0.003 Mg

19 0.01 0.21 0.29 0.007 0.002 20.4 45.0 2.8 1.4 0.004 0.004 0.81 Co

20 0.33 0.28 3.34 0.008 d 0.001 22.1 58.4 2.6 1.1 0.011 0.004 0.05 Co, 1.9 Mo

21 0.07 0.16 0.15 0.002 <0.001 24.7 65.0 2.9 0.2 0.023 0.004 0.11 Hf, 0.03 Co

22 0.06 0.06 0.08 0.013 0.002 26.0 63.3 3.2 2.8 0.009 0.005 1.8 Mo, 0.03 Zr

23 0.09 0.19 0.15 0.019 0.004 19.1 53.5 4.3 1.4 0.019 0.003 0.86 W, 0.004 Ca

24 0.03 0.29 0.18 0.023 0.005 24.3 60.2 2.6 1.3 0.008 0.005 0.32 Nb, 0.04 Nd

25 0.01 0.20 0.04 0.029 0.003 22.0 58.3 2.6 1.5 0.007 0.005 0.007 B, 0.002 Mg

26 0.07 0.25 0.15 0.012 less 0.001 24.4 63.0 2.9 0.4 0.021 0.005 0.26 W

27 0.07 0.12 0.20 0.015 0.005 23.2 66.2 3.1 2.4 0.010 0.005 0.43 Ti

28 0.04 0.11 0.15 0.014 0 plate 19.9 57.6 3.6 2.4 0.021 0.004 0.031 B

29 0.03 0.04 0.13 0.021 0.005 22.1 59.2 3.1 1.2 0.011 0.003 0.03 Hf

30 0.03 0.22 0.11 0.026 0.003 23.0 58.3 2.9 1.8 0.007 0.004 0.015 Ca

31 0.04 0.25 0.13 0.008 d 0.001 21.9 63.2 3.4 1.2 0.008 0.004 0.05 La

32 0.06 0.12 0.09 0.012 less 0.001 25.9 62.9 3.1 0.8 0.019 0.003 0.03 Ce

33 0.09 0.07 0.13 0.019 0.002 20.0 56.3 4.1 1.4 0.019 0.004 0.05 Nd

34 0.04 0.15 0.08 0.020 0.003 23.1 58.4 3.6 1.2 0.013 0.004-

35 0.05 0.24 0.14 0.024 0.003 22.1 58.2 3.1 1.8 0.016 0.004-

36 0.07 0.35 0.21 0.011 0.002 24.9 59.1 2.6 0 0.030 0.009-

0.05 La, 6.5 o,

37 0.09 0.11 0.15 0.017 0.001 203.4 57.9 2.8 7.9 0.007. 0.004

The underline of 0.02 Zr is out of the range of the present invention.

4-1] Supply metal

□ Solution soaking Cu concentration ΰ1 acidity! ^ Kale layer 赚 Coal test Dusting ³ )

Material Concentration Thickness (A) Cr + Al signal + »Pit generation Penetration

Να treatment process 〖)

Να (atom ^_0/0) (nm) (% by weight) Time (h) ( «*%)

1 1-A SB → Hc → ACEl 0.9 0.6 ―〉 3000 0.4

2 2- A SB → ACE1 0.3 0.3-2500 0.6

2-B SB → Rc → ACEl <0.1 0.3-200 1.6

2-C RD → ACE1 0.35 0.5-3000 0.6

2- D PD → Hc → ACEl 0.35 0.5 ― 3000 0.6

2-E Mac → ACEl 0.3 0.3-3000 0.6

2-F Mac → Pic → ACH 0.25 0.3-2500 0.7

2-G ACHT 0.2 0.8 90 2500 0.7

3 3- A ac → ACEl 0.1 0.3-2000 0.6

4 4- A SB → Hc → ACEl 1.1 0.4 ― 3000 0.4

5 5-A ACHT 1.3 0.3 80> 3000 0.4

6 6-A HD- → ACE1 0.3 0.4-3000 0.4

6-B SB → ACH 0.3 0.4-3000 0.4

6-C SB → ACS 0.3 01-200 1.5

7 7- A SB → Rc → ACEl 0.7 0.5-2500 0.7

8 8-A SB → Rc → ACEl 0.55 0.6-> 3000 0.3

9 9-A PD → ACE1 0.3 0.3-2500 0.6

10 10-A RD → ACE1 0.45 0.4-3000 0.5

11 11-A Mac → ACEl 0.4 0.3-2500 0.7

12 12- A ac → ACEl 0.6 0.4 ―> 3000 0.4

13 13-A ac- → ACE1 0.4 0.7-3000 0.6

14 14- A PiD → ACH 0.8 0.5-> 3000 0.4

15 15- A SB—ACE1 1.2> 1-> 3000 0.3

16 16- A ac → Rc- → ACEl 0.35 0.9-3000 0.5

17 17- A PD → ACE1 0.3 0.6-2500 0.7

18 18-A ACHT 4.2 1> 95> 3000 0.2

19 19-A SB → Rc → ACEl 1.1 0.6-> 3000 0.4

20 20-A ACHT 1.3 0.6 70> 3000 0.4

21 21-A Mac → ACEl 0.2> 1-2500 0.5

22 22-A SB → ACE1 3.0 0.6-> 3000 0.3

23 23-A HD → ACE1 1.3 0.3-> 3000 0.2

24 24- A HD → ACE1 1.2 0.3-> 3000 0.3

25 25-A Grri → ACH 1.0> 1-> 3000 0.3

. SB: Shot blast, ACB: Alternating ¾ || treatment, Pic: Release, RD: Pickling descaling, Mac: Thigh grinding, ACHT: Atmosphere control treatment, SP: Three-pinning, Grd: Grinder grinding;

² ) Acid layer: (A) = acid layer mainly composed of Cr and A1;

³⁾ resistant metal Dasute Ing resistance: 60% CO-26% H 2 - 11.5% C0 2 - 2.5% H 2 0, gas (650);

⁴⁾ Manchar: 15% CH ₄ — 3% C〇 ₂ -82% H ₂ gas, 1100 ° C × 300 hours.

Underlines depart from the scope of the present invention. 2] Supply metal

Solution heat treatment Cu concentrated bl acid

Test Dusting ³⁾ Charcoal ft ⁴ ) Gold

Material Concentration Thickness (A) Cr + Al total amount Pit generation Penetration C amount

Να treatment process')

No. Genko ⁰ /. ), Nm) (mass ⁰ /.) Class (h) (mass ⁰ /.)

26 26-A ac → ACEl 0.4 0.6-〉 3000 0.5

27 27- A ACE1 2.1 0.7 ―> 3000 0.3

28 28- A ACE1 1.3 0.9-> 3000 0.2

29 29-A RD → ACE1 1.4 0.6〉 3000 0.3

30 30-A Grd → ACEl 0.9 0.4-> 3000 0.5

31 31-A ACH 0.5> 1-> 3000 0.3

32 32- A PD → ACE1 2.1 0.7-> 3000 0.4

33 33- A SB → ACE1 1.2 0.4-〉 3000 0.3

34 34- A ACE1 1.7 0.3-2500 0.2

35 35-A ACHT 1.0 0.9 75> 3000 0.3

36 36-A SB → ACE1 Cannot be detected 0-200 2.0

37 37-A ACE1 12.4 0.8-> 3000 0.1

⁰ SB: Shot blast, ACE1: Alternating treatment, Pic: Pickling, PiD: Acid descaling, Mac

ACHT: Atmosphere control heat treatment, SP: Shot pinning, Grd: Grinder grinding;

2) Acid layer: (A) = acid layer mainly composed of Cr and A1;

3 ¹ resistant metal Dasute Ing _{resistance: 60% CO- 26% H 2} - 11.5% C0 2 - 2.5% H 2 0, gas (650 "Ό;

⁴⁾ Charcoal _{resistance: 15% CH 4 - 3%} C0 2 - 82% gas, 1100 X 300 hours.

Underlines deviate from the specified range of the present invention.

[0100] As can be seen from Table 4, the metal pipe of alloy No. 36, whose chemical composition deviates from the condition specified in the present invention, is inferior in metal dusting resistance with a short pit generation time of 200 hours. In addition, this metal pipe has a low penetration carburization capacity of ^ .0% and is inferior in carburization resistance.

[0101] On the other hand, of the metal tubes of alloy numbers 1-135 and 37 whose chemical composition satisfies the conditions specified in the present invention, the conditions specified in the present invention for the Cu concentration and the thickened layer thickness of the Cu-enriched layer are as follows. The test metal tube that satisfies is excellent in metal dusting resistance, which has a long time until the occurrence of pits, has less than 1% penetration C, and has excellent carburization resistance. However, a test metal tube in which at least one of the Cu concentration and the thickness of the Cu-enriched layer does not satisfy the conditions specified in the present invention has a short time to pit generation and is inferior in metal dusting resistance. However, the amount of intrusion C is large and the carburization resistance is poor.

[0102] Compared to Example 1, it can be seen that, by increasing the A1 content of the base material, both the metal dusting resistance and the carburization resistance become higher.

Claims

The scope of the claims

Mass ^{_{0/0, Cr: 15 35}} %, Ni: 30- 75%, Al: 0.001- 10%, Cu: 0.01- 10% A matrix power composed metal tube containing, the metal tube For use in carburizing gas atmosphere, characterized by having a Cu-enriched layer on the surface layer, characterized in that the Cu-enriched layer has a Cu concentration of 0.1 atomic% or more and a thickness of 0.3 band or more. Metal tube.

The metal tube according to claim 1, further comprising an oxide scale layer having a Cr content of 50% by mass or more or a total content of Cr + Al of 50% by mass or more outside the Cu-enriched layer.

3. The metal tube according to claim 2, further comprising a second oxide scale layer having a Si content of 50% by mass or more between the oxide scale layer and the Cu-enriched layer.

4. The metal tube according to claim 1, wherein the inner surface and / or the outer surface of the tube have an irregular shape.

The base material is, in mass%, C: 0.01-0.6%, Si: 0.01-5%, Mn: 0.01-10%, P: 0.08% or less, S: 0.05% or less, Cr: 15-35%, Ni : 30-75%, Cu: 0.01-10%, N: 0.001-0.25%, Al: 0.001-10%, 0 (oxygen): 0.02% or less, with the balance being Fe and impurities, 5. The metal tube according to claim 1, wherein the metal tube is shifted.

The metal tube according to claim 5, wherein the chemical composition further contains, in mass%, at least one element selected from the following (i) to (vi).

(i) Co: 0.01-5%,

(ii) one or two kinds of Mo: 0.01-10% and W: 0.01-10%,

(iii) 1 or 2 types of Ti: 0 · 01—2% and Nb: 0.01—2%,

(iv) One or more of B: 0.001 0.1%, Zr: 0.001 0.1% and Hf: 0.001 0.5%

(V) One or two of Mg: 0.0005 0.1% and Ca: 0.0005 0.1%,

(vi) One or more of Y: 0.0005-0.15%, La: 0.0005—0.15%, Ce: 0.0005—0.15%, and Nd: 0.0005-0.15%.