Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
  • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and W
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/325—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with layers graded in composition or in physical properties
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
  • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F15/00—Other methods of preventing corrosion or incrustation

Definitions

• Metal tube for use in carburizing gas atmosphere Metal tube for use in carburizing gas atmosphere
• 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.
• 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.
• the present invention makes it possible to control the shielding properties of a metal tube used in a carburizing gas atmosphere against carburizing gas.
• a dense oxide film composed of oxides of elements such as Cr and Si that is, chromium oxide and silicon oxide
• Cr and Si that is, chromium oxide and silicon oxide
• 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.
• 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.
• Japanese Unexamined Patent Publication No. 9-78204 describes an atmosphere of 400-700 ° C containing H, C ⁇ , CO, and H ⁇ .
• 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.
• Japanese Patent Application Laid-Open No. 2003-73763 discloses an atmosphere gas containing 400, 700 ° C containing H, C ⁇ , CO, and H 2 O.
• 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.
• 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.
• 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.
• 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.
• 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
• flux flux
• penetration C it is effective to suppress the dissociative adsorption of gas.
• Cu, Ag, Pt It is important that these elements exist.
• 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.
• FIGS. 1 (A) and 1 (B) show that the Cu content is different and therefore the surface Cu concentration is different by 25%.
• 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%.
• AES Alger analysis
• 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)].
• 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
• Figure 3 (B) shows the results. / ⁇ _55% ⁇ -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.
• 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.
• 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.
• 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.
• 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%.
• 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%.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• a Cu-enriched layer can be formed on the inner surface
• a Cu-enriched layer can be formed on the outer surface.
• a Cu-enriched layer may be formed on both surfaces of the metal tube.
• 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).
• the Cu concentration of the Cu-enriched layer refers to the average value of the Cu concentration in the layer.
• the average value of the measured values (atomic% conversion value) in the layer is defined as the Cu concentration of the Cu-enriched layer.
• 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.
• 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.
• 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 ⁇ 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%.
• 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.
• 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.
• 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.
• the Cu concentration in the surface layer can be increased to form a Cu-enriched layer.
• 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 (B) Oxide scale layer
• 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.
• 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.
• 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.
• the oxide scale layer (B) is an oxide scale force mainly composed of Si.
• 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.
• 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.
• 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.
• 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%.
• 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.
• 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.
• 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).
• the alloy 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).
• the alloy 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).
• the alloy 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).
• the more preferred range is 0.01% —0.3%.
• 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%.
• 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%.
• 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%.
• 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.
• 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%.
• 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%.
• 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.
• the base metal alloy needs to contain 0.01% or more Cu.
• a preferred range for the Cu content is 0.03-5%, and a more preferred range is 0.1-3%.
• 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%.
• 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.
• 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%.
• the A1 content is preferably less than 1.5%.
• 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%.
• 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%.
• 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%.
• 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.
• the preferred range is 0.01-1.5%, and the more preferred range is 0.02-1.2%.
• B 0.001—0.1%
• Zr 0.001—0.1%
• 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 ⁇ ?) Deteriorates weldability.
• Mg 0.0005—0.1%
• 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.
• excessive addition of these elements deteriorates the weldability, so the upper limits are each set to 0.1%.
• 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%.
• 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
• 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.
• 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.
• 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.
• 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.
• 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.
• ACE1 alternating electrolytic treatment
• ACHT atmosphere control heat treatment
• some metal pipes were shot peened (abbreviated as SP) on the outer surface of the pipe to introduce distortion into the metal surface.
• the Cr-based oxide scale layer (A) and the Si-based oxide scale layer (B) were formed during the 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.
• 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.
• 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.
• 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. .
• 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.
• 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
• a pit occurrence time of 1000 hours means that a pit occurred after 1000 hours.
• 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.
• 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.
• SB Shotblast last
• ACEI Alternating treatment
• He Pickling
• HD Pickling descaling
• Mac Luo grinding
• ACHT Atmosphere control
• SP Shot peening
• Grd Grinder grinding
• the underline also deviates from the specified range force of the present invention.
• Ffifg charcoal resistance 15% CH 4 - 3 0 /. C0 2 -82% H 2 gas, 1050 ° CX 300B.
• 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.
• this metal pipe is inferior in carburization resistance with a large amount of penetration C of 2%.
• the conditions in which the Cu concentration and the thickened layer thickness of the Cu-enriched layer are specified in the present invention 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.
• 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.
• 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.
• ACHT atmosphere control heat treatment
• 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.
• 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.
• 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.
• 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.
• the oxide scale layer (A) generated by the atmosphere control heat treatment was mainly composed of Cr and A1, so that the Cr + The total content of Al was measured by EDX.
• 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.
• the underline of 0.02 Zr is out of the range of the present invention.
• SB Shot blast
• ACB Alternating 3 ⁇ 4
• Pic Release
• RD Pickling descaling
• Mac Thigh grinding
• ACHT Atmosphere control treatment
• SP Three-pinning
• Grd Grinder grinding
• ACHT Atmosphere control heat treatment
• SP Shot pinning
• Grd Grinder grinding
• 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.
• this metal pipe has a low penetration carburization capacity of ⁇ .0% and is inferior in carburization resistance.
• 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.
• 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.
• the amount of intrusion C is large and the carburization resistance is poor.

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