WO2018003941A1 - フェライト系耐熱鋼及びフェライト系伝熱部材 - Google Patents
フェライト系耐熱鋼及びフェライト系伝熱部材 Download PDFInfo
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- WO2018003941A1 WO2018003941A1 PCT/JP2017/024012 JP2017024012W WO2018003941A1 WO 2018003941 A1 WO2018003941 A1 WO 2018003941A1 JP 2017024012 W JP2017024012 W JP 2017024012W WO 2018003941 A1 WO2018003941 A1 WO 2018003941A1
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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- 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
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/76—Adjusting the composition of the atmosphere
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
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- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- 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
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
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- 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
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
- C23C8/18—Oxidising of ferrous surfaces
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- 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
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
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- 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
Definitions
- the present invention relates to a heat resistant steel and a heat transfer member, and more particularly to a ferritic heat resistant steel and a ferritic heat transfer member used in a high temperature steam oxidation environment.
- Thermal power plants are required to improve power generation efficiency from the viewpoints of CO 2 gas emission suppression and economic efficiency. Therefore, the turbine steam pressure is being increased in temperature and pressure.
- Heat transfer members used in thermal power plants are exposed to high-temperature and high-pressure steam for a long time.
- the heat transfer member is, for example, boiler piping.
- oxide scale is generated on the surface of the heat transfer member.
- the steam oxidation resistance of the heat transfer member is not sufficient, a large amount of oxide scale is generated on the surface of the heat transfer member.
- the heat transfer member expands and contracts. Therefore, if a large amount of oxide scale is generated, the oxide scale peels off and causes clogging of piping.
- the oxide scale When a large amount of oxide scale is generated, the oxide scale further inhibits heat conduction from the outside of the pipe to the inside of the pipe. Therefore, in order to keep the temperature in the piping high, it is necessary to apply more heat from the outside. An increase in the temperature of the pipe causes a decrease in creep strength. Therefore, high steam oxidation resistance is required for heat transfer members used in equipment such as boilers for thermal power generation, turbines, and steam pipes.
- austenitic heat resistant steel and ferritic heat resistant steel have been developed as materials satisfying such characteristics.
- the austenitic heat resistant steel is, for example, an austenitic heat resistant steel having a Cr content of 18 to 25% by mass.
- the ferritic heat resistant steel is, for example, a ferritic heat resistant steel having a Cr content of 8 to 13% by mass.
- Ferritic heat resistant steel is less expensive than austenitic heat resistant steel.
- the ferritic heat resistant steel further has a lower thermal expansion coefficient and higher thermal conductivity than the austenitic heat resistant steel. Therefore, ferritic heat resistant steel is suitable as a piping material for thermal power plants.
- the Cr content of ferritic heat resistant steel is lower than the Cr content of austenitic heat resistant steel. Therefore, the steam oxidation resistance of ferritic heat resistant steel is lower than the steam oxidation resistance of austenitic heat resistant steel. For this reason, a ferritic heat resistant steel excellent in steam oxidation resistance is required.
- Patent Document 1 A ferritic heat-resistant steel in which the oxide scale is prevented from dropping is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-92880 (Patent Document 1).
- the ferritic heat resistant steel described in Patent Document 1 is a high Cr content ferritic heat resistant steel in which an oxide film is formed on the surface during use, and has a diameter of 1 micron or less at or near the interface with the oxide film. A very fine oxide is formed. For this reason, it is described in patent document 1 that the adhesiveness of an oxide film and a base material improves.
- Patent Document 2 A method for improving the steam oxidation resistance by increasing the Cr concentration on the surface of ferritic heat resistant steel is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-39745 (Patent Document 2).
- Patent Document 2 powder particles containing Cr are supported on the surface of a ferritic heat-resistant steel containing Cr, and a Cr oxide layer having a high Cr concentration is generated on the surface of the ferritic steel at a high temperature.
- Patent Document 2 describes that this method can easily and economically improve the (water vapor) oxidation resistance of ferritic steel containing Cr.
- Patent Document 3 discloses a method for improving oxidation resistance by forming a Cr oxide film on the surface of a ferritic heat resistant steel.
- the oxidation-resistant treatment method for ferritic heat-resistant steel described in Patent Document 3 includes heat-treating ferritic heat-resistant steel containing chromium in a low oxygen partial pressure gas atmosphere composed of a mixed gas of carbon dioxide and inert gas. Then, an oxide film containing chromium is formed on the surface of the heat-resistant steel.
- Patent Document 3 describes that this method can easily and economically improve the oxidation resistance of ferritic heat resistant steel by increasing the Cr concentration in the scale.
- a ferritic heat resistant steel having improved steam oxidation resistance by adhering Cr to the surface of the ferritic heat resistant steel is disclosed in, for example, Japanese Patent Application Laid-Open No. 2009-179884 (Patent Document 4).
- the ferritic heat-resistant steel described in Patent Document 4 is a ferritic heat-resistant steel used in a high-temperature and high-pressure steam environment, and is formed by pre-oxidizing Cr deposited by shot peening of a powder Cr shot material. It has a Cr oxide film on the substrate surface.
- Patent Document 4 states that this ferritic heat-resistant steel has improved steam oxidation resistance because a protective film of an oxidation-resistant oxide is formed on the heat-resistant steel before use in an oxidizing environment. Is described.
- the heat transfer characteristics and steam oxidation resistance of the heat transfer member may not be sufficiently improved.
- various studies have been made on methods for suppressing the generation of oxide scale by forming Cr oxide on the surface of the heat transfer member.
- the thermal conductivity of Cr oxide is low. For this reason, if Cr oxide is formed, the heat transfer property of the heat transfer member increases, but the heat transfer characteristics deteriorate.
- An object of the present invention is to provide a ferritic heat transfer member excellent in heat transfer characteristics and steam oxidation resistance, and a ferritic heat resistant steel capable of realizing it.
- the ferritic heat resistant steel according to the present embodiment includes a base material and an oxide layer A on the surface of the base material.
- the base material is, in mass%, C: 0.01 to 0.3%, Si: 0.01 to 2.0%, Mn: 0.01 to 2.0%, P: 0.10% or less, S : 0.03% or less, Cr: 7.0 to 14.0%, N: 0.005 to 0.15%, sol.
- the oxide layer A includes a chemical composition containing 20 to 45% in total of Cr and Mn by mass%.
- the oxide layer A includes a chemical composition containing 0.5 to 10% in total of one or more selected from the group consisting of Mo, Ta, W, and Re by mass%.
- the ferrite heat transfer member includes a base material and an oxide film on the surface of the base material.
- the substrate has the above chemical composition.
- the oxide film includes an oxide layer B and an oxide layer C.
- the oxide layer B contains 80% or more of Fe 3 O 4 and Fe 2 O 3 in total by volume.
- the oxide layer C is disposed between the oxide layer B and the base material.
- the chemical composition of the oxide layer C is, in mass%, Cr and Mn: more than 5% to 30% in total, and one or more selected from the group consisting of Mo, Ta, W and Re: in total Contains 1-15%.
- the ferritic heat resistant steel and ferritic heat transfer member according to the present embodiment are excellent in heat transfer characteristics and steam oxidation resistance.
- FIG. 1 is a cross-sectional view of the ferritic heat resistant steel according to the present embodiment.
- FIG. 2 is a cross-sectional view of the ferrite heat transfer member according to the present embodiment.
- the present inventors have conducted various studies on ferritic heat-resistant steel and ferritic heat transfer members. As a result, the following knowledge was obtained.
- the ferritic heat resistant steel of this embodiment can be used as a heat transfer member such as boiler piping.
- Heat transfer members such as boiler pipes are in contact with high-temperature steam.
- oxide scale is generated on the surface of the heat transfer member.
- the oxide scale consists of various oxides and impurities. Examples of the oxide include Fe 3 O 4 , Fe 2 O 3 , and Cr 2 O 3 .
- the oxide scale forms an oxide film on the surface of the heat transfer member.
- the thermal conductivity of the oxide film is low, the heat transfer characteristic from the outside of the heat transfer member to the inside of the heat transfer member is deteriorated. Therefore, in order to maintain the inside of the heat transfer member at a high temperature, it is necessary to apply a large amount of heat from the outside of the heat transfer member, and the heat transfer characteristics of the boiler are deteriorated. When a large amount of heat is applied from the outside of the heat transfer member, the creep strength of the heat transfer member may further decrease. Therefore, it is preferable that the thermal conductivity of the oxide film is high. However, when the thermal conductivity of the oxide film is too high, the heat of the high-temperature steam is transmitted to the inner surface of the heat transfer member.
- the transferred heat promotes the oxidation reaction on the inner surface of the heat transfer member, a large amount of oxide scale is generated on the inner surface of the heat transfer member. A large amount of oxide scale peels from the inner surface of the heat transfer member.
- the heat transfer member is a pipe, the peeled oxide scale causes clogging of the pipe. Therefore, the thermal conductivity of the oxide film needs to be controlled within a certain range.
- the thickness of the oxide film is preferably as thin as possible.
- Fe 3 O 4 and Fe 2 O 3 are formed thermodynamically and stably in a high-temperature steam oxidation environment (hereinafter also referred to as a high-temperature steam environment).
- Fe 3 O 4 and Fe 2 O 3 have a higher thermal conductivity. Therefore, if an oxide film containing a large amount of Fe 3 O 4 and Fe 2 O 3 is formed on the surface of the heat transfer member in contact with high-temperature steam, the thermal efficiency of the boiler is improved. However, the thermal conductivity of the oxide film containing a large amount of Fe 3 O 4 and Fe 2 O 3 is too high. Therefore, with this oxide film alone, as described above, a large amount of oxide scale is generated on the inner surface of the heat transfer member.
- a heat transfer member such as a boiler pipe
- the Cr concentration on the inner surface of the pipe is improved, and an oxide film containing a large amount of Cr 2 O 3 can be formed on the inner surface of the heat transfer member.
- an oxide film containing a large amount of Cr 2 O 3 has a low thermal conductivity. Therefore, the heat transfer characteristics of the heat transfer member are deteriorated. Therefore, the heat transfer characteristics of the boiler cannot be improved with this oxide film alone.
- an oxide film including two layers of an oxide layer having excellent heat transfer characteristics and an oxide layer having both steam oxidation resistance and heat transfer characteristics in a high-temperature steam environment is provided for the heat transfer member. Form on the inner surface. Thereby, it is possible to achieve both excellent heat transfer characteristics and excellent steam oxidation resistance.
- an oxide layer C is formed between the oxide layer B and the base material as an oxide layer that achieves both steam oxidation resistance and heat transfer characteristics.
- the oxide layer C contains 5% to 30% by mass in total of Cr and Mn, and 1 to 15% by mass in total of one or more selected from the group consisting of Mo, Ta, W and Re To do.
- the Cr oxide and Mn oxide increase the steam oxidation resistance of the substrate.
- the Cr content is too high, the heat transfer characteristics of the oxide film are degraded.
- the Mn content is too high, the creep strength of the substrate is lowered. Accordingly, the oxide layer C contains a total of more than 5% to 30% by mass of Cr and Mn.
- the thermal conductivity of the oxide layer C increases.
- the oxide layer C contains 1 to 15% by mass in total of one or more selected from the group consisting of Mo, Ta, W and Re.
- the oxide layer C has excellent heat transfer characteristics and excellent steam oxidation resistance.
- the chemical composition of the oxide layer A is 20% by mass and contains 20 to 45% of Cr and Mn in total.
- the chemical composition of the oxide layer A contains 0.5% to 10% in total of one or more selected from the group consisting of Mo, Ta, W and Re in mass%.
- the oxide layer A changes to an oxide film including the oxide layer B and the oxide layer C.
- the high temperature is, for example, 500 to 650 ° C.
- the ferritic heat resistant steel according to the present embodiment completed based on the above knowledge includes a base material and an oxide layer A on the surface of the base material.
- the base material is, in mass%, C: 0.01 to 0.3%, Si: 0.01 to 2.0%, Mn: 0.01 to 2.0%, P: 0.10% or less, S : 0.03% or less, Cr: 7.0 to 14.0%, N: 0.005 to 0.15%, sol.
- the oxide layer A includes a chemical composition containing 20 to 45% in total of Cr and Mn by mass%.
- the oxide layer A includes a chemical composition containing 0.5 to 10% in total of one or more selected from the group consisting of Mo, Ta, W, and Re by mass%.
- the ferritic heat resistant steel according to the present embodiment is excellent in heat transfer characteristics and steam oxidation resistance.
- the chemical composition of the base material of the ferritic heat resistant steel is a group consisting of Cu: 0.005 to 5.0%, Ni: 0.005 to 5.0%, and Co: 0.005 to 5.0%. You may contain 1 type, or 2 or more types selected from these.
- the chemical composition of the substrate is Ti: 0.01-1.0%, V: 0.01-1.0%, Nb: 0.01-1.0%, and Hf: 0.01-1 You may contain 1 type, or 2 or more types selected from the group which consists of 0.0%.
- the chemical composition of the base material is Ca: 0.0015 to 0.1%, Mg: 0.0015 to 0.1%, Zr: 0.0015 to 0.1%, B: 0.0015 to 0.1. %, And rare earth elements: one or more selected from the group consisting of 0.0015 to 0.1% may be contained.
- the ferrite heat transfer member includes a base material and an oxide film on the surface of the base material.
- the substrate has the above chemical composition.
- the oxide film includes an oxide layer B and an oxide layer C.
- the oxide layer B contains 80% or more of Fe 3 O 4 and Fe 2 O 3 in total by volume.
- the oxide layer C is disposed between the oxide layer B and the base material.
- the chemical composition of the oxide layer C is a total of more than 5% to 30% by mass of Cr and Mn, and a total of 1 to 15 selected from the group consisting of Mo, Ta, W and Re. Contains by mass%.
- the ferrite heat transfer member according to this embodiment is excellent in heat transfer characteristics and steam oxidation resistance.
- the oxide layer B contains 5% by mass or less of Cr and Mn in total.
- the oxide layer C contains 5% by volume or less of Cr 2 O 3 .
- the thermal conductivity of the oxide film is increased by suppressing the amount of Cr 2 O 3 having a low thermal conductivity. For this reason, the heat transfer characteristic of a boiler can be improved.
- ferritic heat resistant steel The shape of the ferritic heat resistant steel according to the present embodiment is not particularly limited.
- Ferritic heat resistant steels are, for example, steel pipes, steel bars, and steel plates.
- the ferritic heat resistant steel is a ferritic heat resistant steel pipe.
- An oxidation treatment is performed on the base material of the ferritic heat resistant steel according to the present embodiment.
- An oxidation layer A is formed on the surface of the base material of the ferritic heat resistant steel by the oxidation treatment.
- FIG. 1 is a cross-sectional view of a ferritic heat resistant steel according to the present embodiment.
- ferritic heat resistant steel 1 includes a base material 2 and an oxide layer A.
- the ferritic heat resistant steel 1 including the base material 2 and the oxide layer A is used as a heat transfer member in a high temperature steam environment.
- the oxide layer A changes to the oxide film 3 including the oxide layer B and the oxide layer C.
- the base material 2 has the following chemical composition.
- C 0.01 to 0.3% Carbon (C) stabilizes austenite. C further increases the creep strength of the substrate by solid solution strengthening. However, when the C content of the substrate 2 is too high, carbides are excessively precipitated, and the workability and weldability of the substrate 2 are deteriorated. Therefore, the C content is 0.01 to 0.3%.
- the preferable lower limit of the C content is 0.03%, and the preferable upper limit of the C content is 0.15%.
- Si 0.01 to 2.0% Silicon (Si) deoxidizes steel. Si further improves the steam oxidation resistance of the substrate 2. However, when the Si content is too high, the toughness of the substrate 2 is lowered. Therefore, the Si content is 0.01 to 2.0%.
- the minimum with preferable Si content is 0.05%, More preferably, it is 0.1%.
- the upper limit with preferable Si content is 1.0%, More preferably, it is 0.5%.
- Mn 0.01 to 2.0%
- Manganese (Mn) deoxidizes steel. Further, Mn combines with S in the substrate 2 to form MnS, and suppresses grain boundary segregation of S. Thereby, the hot workability of the base material 2 is improved.
- Mn content is 0.01 to 2.0%.
- the minimum with preferable Mn content is 0.05%, More preferably, it is 0.1%.
- the upper limit with preferable Mn content is 1.0%, More preferably, it is 0.8%.
- P 0.10% or less Phosphorus (P) is an impurity. P segregates at the crystal grain boundaries of the base material 2 and reduces the hot workability of the base material 2. Further, P is concentrated at the interface between the oxide film 3 and the base material 2 to reduce the adhesion of the oxide film 3 to the base material 2. Therefore, the P content is preferably as low as possible.
- the P content is 0.10% or less, preferably 0.03% or less.
- the lower limit of the P content is, for example, 0.005%.
- S 0.03% or less Sulfur (S) is an impurity. S segregates at the crystal grain boundaries of the base material 2, thereby reducing the hot workability of the base material 2. Further, S is concentrated at the interface between the oxide film 3 and the base material 2 to reduce the adhesion of the oxide film 3 to the base material 2. Accordingly, the S content is preferably as low as possible.
- the S content is 0.03% or less, preferably 0.015% or less.
- the lower limit of the S content is, for example, 0.0001%.
- Chromium (Cr) enhances the steam oxidation resistance of the substrate 2.
- Cr is further contained in the oxide film 3 as an oxide defined by Cr 2 O 3 and (Fe, Cr) 3 O 4 .
- Cr oxide increases the steam oxidation resistance of the substrate 2.
- the Cr oxide further enhances the adhesion of the oxide film 3 to the substrate 2.
- the Cr content is 7.0 to 14.0%.
- the minimum with preferable Cr content is 7.5%, More preferably, it is 8.0%.
- the upper limit with preferable Cr content is 12.0%, More preferably, it is 11.0%.
- N 0.005 to 0.15% Nitrogen (N) is dissolved in the base material 2 to increase the strength of the base material 2. N further forms an alloy component and nitride in the base material 2 and precipitates in the base material 2 to increase the strength of the base material 2. However, when the N content is too high, the nitride becomes coarse and the toughness of the base material 2 decreases. Therefore, the N content is 0.005 to 0.15%. The minimum with preferable N content is 0.01%. The upper limit with preferable N content is 0.10%.
- sol. Al 0.001 to 0.3%
- Aluminum (Al) deoxidizes steel. However, when the Al content is too high, the hot workability of the substrate 2 is lowered. Therefore, the Al content is 0.001 to 0.3%.
- the preferable lower limit of the Al content is 0.005%, and the preferable upper limit of the Al content is 0.1%.
- the Al content means acid-soluble Al (sol. Al).
- Mo 0 to 5.0%
- Ta 0 to 5.0%
- W 0 to 5.0%
- Re 0 to 5.0%
- Mo molybdenum
- Ta tantalum
- W tungsten
- Re rhenium
- these elements are also referred to as specific oxide layer forming elements.
- the specific oxide layer forming element forms the oxide layer A on the surface of the substrate 2.
- the specific oxide layer forming element further forms the oxide film 3 including the oxide layer B and the oxide layer C in a high temperature steam environment of 500 to 650 ° C. If one of these elements is contained, this effect can be obtained.
- the Mo content is 0 to 5.0%
- the Ta content is 0 to 5.0%
- the W content is 0 to 5.0%
- the Re content is 0 to 5.0%. %.
- the minimum with preferable Mo content is 0.01%, More preferably, it is 0.1%.
- the minimum with preferable Ta content is 0.01%, More preferably, it is 0.1%.
- the minimum with preferable W content is 0.01%, More preferably, it is 0.1%.
- the minimum with preferable Re content is 0.01%, More preferably, it is 0.1%.
- the upper limit with preferable Mo content is 4.0%, More preferably, it is 3.0%.
- the upper limit with preferable Ta content is 4.0%, More preferably, it is 3.0%.
- the upper limit with preferable W content is 4.0%, More preferably, it is 3.0%.
- the upper limit with preferable Re content is 4.0%, More preferably, it is 3.0%.
- the total content of the specific oxide layer forming elements is 0.5 to 7.0%.
- the minimum with preferable total content of a specific oxide layer forming element is 0.6%, More preferably, it is 1.0%.
- the upper limit with preferable total content of a specific oxide layer forming element is 6.5%, More preferably, it is 6.0%.
- the balance of the base material 2 of the ferritic heat resistant steel according to the present embodiment is Fe and impurities.
- impurities refer to ores and scraps used as a raw material for steel, or elements mixed in from the environment of the manufacturing process, etc., and are contained within a range that does not adversely affect the heat transfer member 4 according to the present embodiment. Says what is done. Impurities are, for example, oxygen (O), arsenic (As), antimony (Sb), thallium (Tl), lead (Pb), bismuth (Bi), and the like.
- the base material 2 of the ferritic heat resistant steel according to the present embodiment may further contain the following elements instead of a part of Fe.
- Cu 0 to 5.0% Ni: 0 to 5.0% Co: 0 to 5.0% Copper (Cu), nickel (Ni) and cobalt (Co) are optional elements and may not be contained. When included, these elements stabilize austenite. Thereby, the residual of the delta ferrite which reduces the impact resistance of the base material 2 is suppressed. If one of these elements is contained, this effect can be obtained. However, when the content of these elements is too high, the long-term creep strength of the substrate 2 is lowered. Therefore, the Cu content is 0 to 5.0%, the Ni content is 0 to 5.0%, and the Co content is 0 to 5.0%.
- the upper limit with preferable Cu content is 3.0%, More preferably, it is 2.0%.
- the upper limit with preferable Ni content is 3.0%, More preferably, it is 2.0%.
- the upper limit with preferable Co content is 3.0%, More preferably, it is 2.0%.
- the minimum with preferable content of these elements is 0.005%, respectively.
- Ti 0 to 1.0% V: 0 to 1.0% Nb: 0 to 1.0% Hf: 0 to 1.0% Titanium (Ti), vanadium (V), niobium (Nb) and hafnium (Hf) are optional elements and may not be contained. When included, these elements combine with carbon and nitrogen to form carbides, nitrides or carbonitrides. These carbides, nitrides, and carbonitrides precipitate and strengthen the base material 2. If one of these elements is contained, this effect can be obtained. However, when the content of these elements is too high, the workability of the substrate 2 is lowered.
- the Ti content is 0 to 1.0%, the V content is 0 to 1.0%, the Nb content is 0 to 1.0%, and the Hf content is 0 to 1.0%. %.
- the upper limit with preferable Ti content is 0.8%, More preferably, it is 0.4%.
- the upper limit with preferable V content is 0.8%, More preferably, it is 0.4%.
- the upper limit with preferable Nb content is 0.8%, More preferably, it is 0.4%.
- the upper limit with preferable Hf content is 0.8%, More preferably, it is 0.4%.
- the minimum with preferable content of these elements is 0.01%, respectively.
- Ca 0 to 0.1% Mg: 0 to 0.1% Zr: 0 to 0.1% B: 0 to 0.1%
- Rare earth elements 0 to 0.1% Calcium (Ca), magnesium (Mg), zirconium (Zr), boron (B), and rare earth element (REM) are optional elements and may not be contained. When contained, these elements enhance the strength, workability and oxidation resistance of the substrate 2. If one of these elements is contained, this effect can be obtained. However, when the content of these elements is too high, the toughness and weldability of the base material 2 are lowered. Therefore, the Ca content is 0 to 0.1%, the Mg content is 0 to 0.1%, the Zr content is 0 to 0.1%, and the B content is 0 to 0.1%.
- the REM content is 0 to 0.1%.
- the upper limit with preferable Ca content is 0.05%.
- the upper limit with preferable Mg content is 0.05%.
- the upper limit with preferable Zr content is 0.05%.
- the upper limit with preferable B content is 0.05%.
- the upper limit with preferable REM content is 0.05%.
- the minimum with preferable content of these elements is 0.0015%, respectively.
- REM means yttrium (Y) with atomic number 39, lanthanum (La) with atomic number 57 as lanthanoid to lutetium (Lu) with atomic number 71, and actinium with atomic number 89 as an actinoid. (Ac) to one or more elements selected from the group consisting of No. 103 Lorencium (Lr).
- Oxide layer A An oxidation treatment is performed on the substrate 2 having the above-described chemical composition. An oxidation layer A is formed on the surface of the substrate 2 by the oxidation treatment.
- the ferritic heat resistant steel 1 including the base material 2 and the oxide layer A on the surface of the base material 2 is used in a high temperature steam environment. Under a high-temperature steam environment, the oxide layer A changes to the oxide film 3 having excellent heat transfer characteristics while maintaining the steam oxidation resistance. That is, the oxide layer A is a material for forming the oxide film 3 including the oxide layer B and the oxide layer C. Although the mechanism by which the oxide layer A changes to the oxide film 3 is not certain, it is presumed that the oxide layer A mainly contributes to the formation of the oxide layer C.
- the thickness of the oxide layer A is not particularly limited. If even a small amount of oxide layer A is formed, oxide film 3 is formed.
- the thickness of the oxide layer A is preferably 0.2 ⁇ m or more. In this case, the oxide film 3 can be stably and uniformly formed on the surface of the substrate 2 in a high-temperature steam environment. Therefore, it becomes easy to completely cover the base material 2 with the oxide film 3. As a result, the thermal conductivity at the surface of the ferrite heat transfer member 4 is increased. More preferably, the thickness of the oxide layer A is 1.0 ⁇ m or more.
- the upper limit of the thickness of the oxide layer A is not particularly limited, but is preferably 20 ⁇ m or less in consideration of mass productivity.
- the thickness of the oxide layer A is obtained by the following method.
- a ferritic heat-resistant steel 1 subjected to an oxidation treatment described later is cut perpendicularly to the surface.
- the ferritic heat resistant steel 1 is a steel pipe
- the ferritic heat resistant steel 1 is cut perpendicular to the axial direction of the steel pipe.
- the cross section including the surface of the ferritic heat resistant steel 1 is observed using a scanning electron microscope (SEM) manufactured by JEOL (JEOL Ltd.).
- SEM scanning electron microscope
- JEOL JEOL Ltd.
- the thickness of the oxide layer on the surface of the ferritic heat resistant steel 1 (the inner surface when the ferritic heat resistant steel 1 is a steel pipe) is measured.
- the measurement is performed on four different cross sections of the ferritic heat resistant steel 1.
- the ferritic heat resistant steel 1 is a steel pipe, it is measured at four positions at a 45 ° pitch.
- the average value of the measurement results is defined as the thickness of the oxide layer A.
- the chemical composition of the oxide layer A contains 20 to 45% of Cr and Mn in total. If the total content of Cr and Mn in the oxide layer A is less than 20%, the total content of Cr and Mn in the oxide layer C is 5% or less in a high-temperature steam environment. In this case, the thermal conductivity of the oxide layer C becomes too high. In this case, the steam oxidation resistance of the ferrite heat transfer member 4 is lowered. On the other hand, if the total content of Cr and Mn in the oxide layer A exceeds 45%, the total content of Cr and Mn in the oxide layer C exceeds 30% in a high-temperature steam environment. In this case, the thermal conductivity of the oxide layer C becomes too low.
- the chemical composition of the oxide layer A contains 20 to 45% of Cr and Mn in total.
- a preferable lower limit of the total content of Cr and Mn in the oxide layer A is 22%.
- a preferable upper limit of the total content of Cr and Mn in the oxide layer A is 40%.
- the chemical composition of the oxide layer A further contains 0.5 to 10% in total of one or more selected from the group consisting of Mo, Ta, W and Re (specific oxide layer forming elements). If the total content of the specific oxide layer forming elements in the oxide layer A is less than 0.5%, the total content of the specific oxide layer forming elements in the oxide layer C is less than 1% in a high-temperature steam environment. In this case, the thermal conductivity of the oxide layer C becomes too low. As a result, the heat transfer characteristics of the ferrite heat transfer member 4 are deteriorated.
- the chemical composition of the oxide layer A contains a total of 0.5 to 10% of the specific oxide layer forming elements.
- a preferable lower limit of the total content of the specific oxide layer forming elements is 1%.
- a preferable upper limit of the total content of the specific oxide layer forming elements is 8%.
- the total content of Cr and Mn in the oxide layer A and the specific oxide layer forming elements is calculated by the following method.
- a ferritic heat-resistant steel 1 subjected to an oxidation treatment described later is cut perpendicularly to the surface.
- the ferritic heat resistant steel 1 is a steel pipe
- the ferritic heat resistant steel 1 is cut perpendicular to the axial direction of the steel pipe.
- the cross section including the surface of the ferritic heat resistant steel 1 is observed using a scanning electron microscope (SEM) manufactured by JEOL (JEOL Ltd.).
- SEM scanning electron microscope
- elemental analysis is performed using a field emission electron probe microanalyzer (FE-EPMA) manufactured by JEOL (JEOL Ltd.).
- the conditions for elemental analysis are detector: 30 mm 2 SD, acceleration voltage: 15 kV, and measurement time: 60 seconds.
- the elemental analysis is performed on four different cross sections of the ferritic heat resistant steel 1.
- the ferritic heat resistant steel 1 is a steel pipe, elemental analysis is performed at four positions at a 45 ° pitch.
- the composition excluding the amounts of oxygen (O) and carbon (C) is defined as 100%.
- the ratio (mass%) of the total amount of Cr and Mn is calculated.
- the ratio (mass%) of the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) is calculated.
- the average value of elemental analysis values at four locations is the total content (% by mass) of Cr and Mn in the oxide layer A, and the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) in the oxide layer A Amount (mass%).
- the manufacturing method of the ferritic heat resistant steel 1 includes a preparation process and an oxidation treatment process.
- the base material 2 having the above-described chemical composition is prepared.
- the base material 2 is manufactured from the raw material which has the above-mentioned chemical composition.
- the material may be slabs, blooms and billets manufactured by a continuous casting method.
- the material may be a billet manufactured by an ingot-making method.
- the heating temperature in manufacturing the material is, for example, 850 to 1200 ° C.
- the prepared material is charged into a heating furnace or a soaking furnace and heated.
- the base material 2 is manufactured by hot-working the heated material.
- Hot working is, for example, the Mannesmann method.
- a material is pierced and rolled into a raw tube using a piercing machine.
- the material is stretch-rolled and shaped-rolled using a mandrel mill and a sizing mill.
- the temperature of hot working is, for example, 850 to 1200 ° C.
- the base material 2 is manufactured as a seamless steel pipe.
- the manufacturing method of the base material 2 is not limited to the Mannesmann method, and the material may be manufactured by hot extrusion or hot forging.
- the substrate 2 may be a steel plate.
- the raw material is hot-worked and the base material 2 is manufactured as a steel plate.
- the base material 2 may be manufactured as a welded steel pipe by processing a steel plate into a steel pipe by welding.
- An oxidation treatment is performed on the substrate 2 described above.
- the oxidation treatment is performed by heating the substrate 2 in a gas atmosphere containing CO, CO 2 and N 2 .
- the CO / CO 2 ratio of the gas used for the oxidation treatment is 0.6 or more in volume ratio.
- preferential oxidation of Fe can be suppressed.
- a total of 20% by mass or more of Cr and Mn is contained on the surface of the base material 2, and further, an oxide layer A containing a total of 0.5% by mass or more of the specific oxide layer forming element is formed. .
- the oxide layer A changes to the oxide film 3 after the steam oxidation treatment described later.
- the upper limit of the CO / CO 2 ratio is not particularly set, but 2.0 is preferable in consideration of operational practicality.
- the (CO + CO 2 ) / N 2 ratio of the gas used for the oxidation treatment is 1.0 or less in volume ratio.
- the substrate 2 is carburized.
- Cr and Mn in the oxide layer A form carbides.
- the total content of Cr and Mn in the oxide layer A is less than 20%.
- the (CO + CO 2 ) / N 2 ratio has no particular lower limit, but is preferably 0.1 in view of operational practicality.
- the temperature of the oxidation treatment is 900 to 1130 ° C. If the oxidation treatment temperature is less than 900 ° C., the outward diffusion of the specific element of the base material 2 is slow, so that the total content of the specific oxide layer forming elements of the oxide layer A becomes too low. In this case, the total content of the specific oxide layer forming elements in the oxide layer C becomes too low in a high temperature steam environment. As a result, the thermal conductivity of the oxide layer C becomes too low. As a result, the thermal conductivity on the surface of the ferrite heat transfer member 4 is lowered. For this reason, the heat-transfer characteristic of the ferrite-type heat transfer member 4 falls.
- the oxidation treatment temperature is 900 to 1130 ° C.
- the minimum with preferable oxidation treatment temperature is 920 degreeC, More preferably, it is 950 degreeC.
- a preferable upper limit of the oxidation treatment temperature is 1120 ° C.
- Oxidation time is 1 minute to 1 hour. If the oxidation treatment time is too short, the concentration of the specific oxide layer forming elements occurs, so that the total content of the specific oxide layer forming elements in the oxide layer A exceeds 10%. Therefore, the total content of the specific oxide layer forming elements of the oxide layer C exceeds 15% in a high temperature steam environment. As a result, the thermal conductivity on the surface of the ferrite heat transfer member 4 becomes too high. On the other hand, if the oxidation treatment time is too long, productivity decreases. In view of productivity, it is preferable that the oxidation treatment time is short. If the oxidation treatment time is too long, Fe is preferentially oxidized, so that the total content of Cr and Mn in the oxide layer A is less than 20%. Therefore, the oxidation treatment time is 1 minute to 1 hour. Preferably, the upper limit of the oxidation treatment time is 30 minutes, more preferably 20 minutes. Preferably, the lower limit of the oxidation treatment time is 3 minutes.
- Tempering low temperature annealing
- the oxidation treatment may be performed on the entire base material 2, it may be performed only on the surface (for example, the inner surface of the steel pipe) where the base material 2 is in contact with high-temperature steam.
- the oxidation treatment may be performed once or a plurality of times.
- degreasing, washing, and the like may be performed. Even if degreasing and washing are performed, the oxide layer A is not affected. Even if degreasing or washing is performed, it does not affect the subsequent formation of the oxide film 3.
- the ferritic heat resistant steel 1 of the present embodiment can be manufactured by the above manufacturing method.
- the ferrite heat transfer member 4 includes a base material 2 and an oxide film 3.
- the base material 2 of the ferritic heat transfer member 4 is the same as the base material of the ferritic heat resistant steel 1 described above. Therefore, the chemical composition of the base material 2 of the ferritic heat transfer member 4 is the same as the chemical composition of the base material 2 of the ferritic heat resistant steel 1 described above.
- the shape of the ferrite heat transfer member 4 according to the present embodiment is not particularly limited.
- the ferrite heat transfer member 4 is, for example, a tube, a rod, or a plate material. When it has a tubular shape, the ferrite heat transfer member 4 is used as, for example, a boiler pipe. Therefore, preferably, the ferrite heat transfer member 4 is a ferrite heat transfer tube.
- FIG. 2 is a cross-sectional view of the ferrite heat transfer member 4 according to the present embodiment.
- ferrite-based heat transfer member 4 includes base material 2 and oxide film 3.
- the oxide film 3 includes an oxide layer B and an oxide layer C.
- oxide film 3 An oxide film 3 is formed on the surface of the base material 2 by subjecting the ferritic heat resistant steel 1 including the base material 2 and the oxide layer A to a steam oxidation treatment.
- oxide film 3 is an oxide film including two layers of oxide layer B and oxide layer C.
- the oxide film 3 includes an oxide layer B. Therefore, the oxide film 3 is excellent in heat transfer characteristics.
- the oxide film 3 includes an oxide layer C. Therefore, the oxide film 3 is excellent in both steam oxidation resistance and heat transfer characteristics. That is, the oxide film 3 is excellent not only in steam oxidation resistance but also in heat transfer characteristics.
- the oxide layer B is formed on the uppermost layer of the ferrite heat transfer member 4.
- the oxide layer C is disposed between the oxide layer B and the substrate 2.
- the oxide layer B corresponds to the inner surface side of the boiler pipe, and the base material 2 corresponds to the outer surface side of the boiler pipe.
- the oxide layer B is in contact with high-temperature water vapor.
- the oxide layer B contains 80% or more of Fe 3 O 4 and Fe 2 O 3 in total by volume.
- the thermal conductivity of Fe 3 O 4 and Fe 2 O 3 is high. Therefore, the thermal conductivity of the oxide layer B is high, and the heat applied from the outside of the ferrite heat transfer member 4 is transferred to the inside of the ferrite heat transfer member 4 without greatly decreasing. For this reason, the heat transfer characteristic of a boiler can be improved.
- the oxide layer B contains 90% or more of Fe 3 O 4 and Fe 2 O 3 in total by volume.
- the Fe 2 O 3 content of the oxide layer B is less than 20% by volume. More preferably, the oxide layer B is made of Fe 3 O 4 .
- the oxide layer B may contain a part of Cr and Mn contained in the base material 2 as oxides. Cr 2 O 3 has particularly low thermal conductivity. For this reason, the Cr 2 O 3 content of the oxide layer B is preferably low. Therefore, preferably, the chemical composition of the oxide layer B is 5% by mass and contains 5% or less of Cr and Mn in total. More preferably, the chemical composition of the oxide layer B is mass% and contains 3% or less of Cr and Mn in total.
- the preferred thickness of the oxide layer B is 10 to 400 ⁇ m.
- the oxide layer C is disposed between the oxide layer B and the substrate 2 and is in contact with the substrate 2.
- the chemical composition of the oxide layer C contains Cr and Mn in total exceeding 5% to 30%.
- Cr and Mn exist as oxides represented by the chemical formula of (Fe, M) 3 O 4 .
- Cr and Mn are substituted for M.
- the oxide represented by the chemical formula of (Fe, M) 3 O 4 is an oxide having the same so-called spinel crystal structure as that of Fe 3 O 4 and in which part of Fe is substituted with Cr and Mn.
- the total amount of Cr and Mn contained in the oxide layer C is more than 30%, the thermal conductivity of the oxide layer C becomes too low. In this case, the heat transfer characteristics of the boiler are deteriorated. Therefore, the total content of Cr and Mn in the oxide layer C is more than 5% to 30%. Thereby, the heat conductivity of the oxide layer C can be controlled within an appropriate range while maintaining the steam oxidation resistance.
- the minimum with the preferable total content of Cr and Mn in the oxide layer C is 10%, More preferably, it is 13%.
- the upper limit with preferable total content of Cr and Mn in the oxide layer C is 28%, More preferably, it is 25%.
- the oxide layer C contains 1 to 15% in total of one or more selected from the group consisting of Mo, Ta, W and Re. If the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) in the oxide layer C is less than 1%, the thermal conductivity of the oxide layer C becomes too low. On the other hand, when the total content of the specific oxide layer forming elements in the oxide layer C exceeds 15%, the thermal conductivity of the oxide layer C becomes too high. In this case, the steam oxidation resistance of the ferrite heat transfer member 4 is lowered. Therefore, the total content of the specific oxide layer forming elements in the oxide layer C is 1 to 15%.
- the upper limit with preferable total content of the specific oxide layer formation element (Mo, Ta, W, and Re) in the oxide layer C is 10%, More preferably, it is 9%.
- a preferable lower limit of the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) in the oxide layer C is 1.5%.
- the oxide layer C is an oxide having the above-mentioned spinel crystal structure, and Cr 2 O 3 is preferably 5% by volume or less.
- Cr 2 O 3 is preferably 5% by volume or less.
- the thermal conductivity of the oxide layer C is preferably controlled in the range of 1.2 to 3.0 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 . If the thermal conductivity of the oxide layer C is 1.2 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 or more, the heat conduction from the outside of the ferrite heat transfer member 4 to the inside of the ferrite heat transfer member 4 is not hindered, The heat transfer characteristics of the boiler are stably increased. On the other hand, if the thermal conductivity of the oxide layer C is 3.0 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 or less, the heat of the high-temperature steam transmitted to the surface of the substrate 2 can be stably controlled.
- the thermal conductivity of the oxide layer C is preferably controlled in the range of 1.2 to 3.0 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 . In this case, it is easy to improve the steam oxidation resistance of the ferrite heat transfer member 4 without impairing the heat transfer characteristics.
- a more preferable lower limit of the thermal conductivity in the oxide layer C is 1.3 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , and more preferably 1.4 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 .
- the upper limit of the more preferred thermal conductivity is 2.8W ⁇ m -1 ⁇ K -1, more preferably from 2.5W ⁇ m -1 ⁇ K -1.
- the volume ratio of Fe 3 O 4 and Fe 2 O 3 in the oxide layer B is measured by the following method.
- the ferrite heat transfer member 4 after the steam oxidation treatment described later is cut perpendicularly to the surface.
- the ferrite heat transfer member 4 is a tube
- the ferrite heat transfer member 4 is cut perpendicular to the axial direction of the tube.
- the composition analysis of the oxide layer B is performed on the cross section (observation surface) including the oxide layer B using a field emission electron probe microanalyzer device (FE-EPMA) manufactured by JEOL (JEOL Ltd.).
- the conditions of composition analysis are: detector: 30 mm 2 SD, acceleration voltage: 15 kV, measurement time: 60 seconds.
- a region where Fe and O (oxygen) are detected by composition analysis and Cr is not detected is specified. Subsequently, it is confirmed by composition analysis that all the specified regions have Fe 3 O 4 or Fe 2 O 3 .
- the intensity of Fe is binarized in the oxide layer B on the observation surface. At this time, the gray scale extraction target is 1/10 or more of the maximum intensity. It is confirmed that the black region after binarization includes all regions other than the specified region (the region that has been confirmed to have Fe 3 O 4 and Fe 2 O 3 ).
- the area ratio of the black region in the oxide layer B on the observation surface is obtained and reduced from 100%. The obtained area ratio is defined as the volume ratio of Fe 3 O 4 and Fe 2 O 3 in the oxide layer B.
- the volume ratio of Cr 2 O 3 in the oxide layer C is measured by the following method.
- the ferrite heat transfer member 4 after the steam oxidation treatment described later is cut perpendicularly to the surface.
- the ferrite heat transfer member 4 is a tube
- the ferrite heat transfer member 4 is cut perpendicular to the axial direction of the tube.
- SEM observation is performed on the cross section (observation surface) including the oxide layer B and the oxide layer C, and the oxide layer C is specified.
- the oxide layer B and the oxide layer C are distinguished by the contrast difference obtained by the backscattered electron image (BSE) of the SEM.
- the oxide layer B has a brighter contrast than the oxide layer C.
- the volume ratio of Cr 2 O 3 is determined in the same manner as the method for determining the volume ratio of Fe 3 O 4 and Fe 2 O 3 of the oxide layer B. That is, composition analysis is performed on the cross section (observation surface) including the oxide layer C using a field emission electron probe microanalyzer device (FE-EPMA) manufactured by JEOL (JEOL Ltd.). The conditions of composition analysis are: detector: 30 mm 2 SD, acceleration voltage: 15 kV, measurement time: 60 seconds. A region where Cr and O (oxygen) are detected by composition analysis and where Fe is not detected is specified. Subsequently, it is confirmed by composition analysis that all the specified regions have Cr 2 O 3 .
- FE-EPMA field emission electron probe microanalyzer device
- the intensity of Cr is binarized in the oxide layer C on the observation surface.
- the gray scale extraction target is 1/10 or more of the maximum intensity. It is confirmed that the black area after binarization includes all areas other than the specified area (the area that has been confirmed to have Cr 2 O 3 ).
- the area ratio of the black area after the binarization processing of the observation surface is obtained and subtracted from 100%. Let the obtained area ratio be the volume ratio of Cr 2 O 3 in the oxide layer C.
- the total content of Cr and Mn in the oxide layer B and the oxide layer C and the total content of the specific oxide layer forming elements are obtained by the same method as that for the oxide layer A.
- the oxide layer B and the oxide layer C are distinguished by the contrast difference obtained by the backscattered electron image (BSE) of the SEM.
- the oxide layer B has a brighter contrast than the oxide layer C. Elemental analysis is performed at the center of the thickness of the oxide layer B and at the center of the thickness of the oxide layer C under the same conditions as in the case of the oxide layer A.
- the total content (% by mass) of Cr and Mn and the total content of specific oxide layer forming elements are the same as in the case of the oxide layer A.
- the amount (mass%) is obtained.
- the thermal conductivity of the oxide layer C is obtained by the following method. After mechanically removing the oxide layer B of the ferrite heat transfer member 4, the bulk density, specific heat and thermal diffusivity of the oxide layer C including the substrate 2 are measured. Next, after the oxide layer C is mechanically removed, the bulk density, specific heat, and thermal diffusivity of the substrate 2 are measured in the same manner.
- the bulk density is in [rho, the C p specific heat, thermal diffusivity is substituted into D.
- the preferable lower limit of the thickness of the oxide layer C is 10 ⁇ m.
- the thickness of the oxide film 3 is not particularly limited, but is preferably thinner.
- the heat transfer characteristics of the ferrite heat transfer member 4 are enhanced. For this reason, the heat transfer characteristic of a boiler can be improved. If the ferrite heat transfer member 4 is used for a long time, the oxide film 3 becomes thick. Even when the temperature of the steam oxidation treatment of the ferrite heat transfer member 4 is high, the oxide film 3 becomes thick. If an oxidation process and a steam oxidation process described later are performed, the oxide layer B and the oxide layer C are formed with almost the same thickness. Therefore, when the oxide layer C is thin, the oxide film 3 is also thin.
- the thicknesses of the oxide layer B and the oxide layer C are obtained by a method similar to the method for obtaining the thickness of the oxide layer A.
- a ferritic heat transfer member 4 after a steam oxidation treatment described later is prepared. SEM observation is performed on the prepared ferrite heat transfer member 4 by the same method as the method for obtaining the thickness of the oxide layer A.
- the oxide layer B and the oxide layer C are distinguished by the contrast difference obtained from the SEM reflected electron image.
- the oxide layer B has a darker contrast than the oxide layer C.
- the thicknesses of the oxide layer B and the oxide layer C are obtained by the same method as the method of obtaining the thickness of the oxide layer A.
- the manufacturing method of the ferritic heat transfer member 4 according to the present embodiment includes a steam oxidation treatment step.
- Steam oxidation treatment is performed on the ferritic heat-resistant steel subjected to the oxidation treatment described above.
- the steam oxidation treatment is performed by exposing the ferritic heat resistant steel to steam at 500 to 650 ° C. If the steam oxidation treatment is 100 hours or longer, the upper limit of the treatment time is not particularly limited.
- the oxide layer A changes to the oxide film 3 including the oxide layer B and the oxide layer C. Thereby, the oxide film 3 including the oxide layer B and the oxide layer C is formed on the substrate 2.
- the ferrite heat transfer member 4 according to the present embodiment can be manufactured through the above steps.
- the ferritic heat resistant steel 1 of the present embodiment By exposing the ferritic heat resistant steel 1 of the present embodiment to a high temperature steam environment, the same effect as that obtained when the steam oxidation treatment is performed can be obtained. That is, if the ferritic heat resistant steel 1 of the present embodiment is exposed to a high temperature steam environment for 100 hours or more, the ferritic heat transfer member 4 can be manufactured without performing the steam oxidation treatment.
- Each steel slab having the chemical composition shown in Table 1 was manufactured, and oxidation treatment and steam oxidation treatment were performed under the conditions shown in Table 2. Specifically, an ingot having a chemical composition shown in Table 1 was melted. Each ingot obtained was subjected to hot rolling and cold rolling to produce a steel plate, which was used as a base material. Test pieces were prepared from the obtained base materials, and each test piece was subjected to oxidation treatment under the conditions shown in Table 2.
- test piece was subjected to steam oxidation treatment under the conditions shown in Table 2. The following measurement tests were performed on the obtained test pieces.
- the oxide layer A of these test numbers has a total of 20 to 45% of Cr and Mn, and one or more selected from the group consisting of Mo, Ta, W, and Re in a total of 0.5. Contained 10%.
- the oxide layer B formed on the base material after the steam oxidation treatment contained Fe 3 O 4 and Fe 2 O 3 in a total of 80% or more by volume.
- the total content of Cr + Mn in the oxide layer C was more than 5% to 30%, and the total content of the specific oxide layer forming elements was 1 to 15%.
- the thermal conductivity of the oxide layer C was in the range of 1.2 to 3.0 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , indicating excellent thermal conductivity. Further, the oxide layer C had a thickness of 60 ⁇ m or less, and exhibited excellent steam oxidation resistance.
- the thermal conductivity of the oxide layer C was less than 1.2 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 . Since the total amount of the specific oxide layer forming elements of the oxide layer C was less than 1%, it is considered that the thermal conductivity was lowered.
- the chemical composition was appropriate, but the CO / CO 2 ratio in the oxidation treatment was less than 0.6. Therefore, the total content of Cr and Mn in the oxide layer A was less than 20%. Therefore, the total content of Cr and Mn in the oxide layer C became 5% or less, and the thermal conductivity of the oxide layer C exceeded 3.0 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 . Further, since the Fe 3 O 4 volume fraction in the oxide layer B was less than 80%, the inward flux of oxygen increased, the growth of the oxide layer C was promoted, and the thickness of the oxide layer C exceeded 60 ⁇ m.
- test number 16 Although the chemical composition was appropriate, the oxidation treatment time was too short. Therefore, the total content of the specific oxide layer forming elements in the oxide layer A was 12.9%, which was too high. Therefore, the total content of the specific oxide layer forming elements in the oxide layer C was 17.2%, which was too high. As a result, the thermal conductivity of the oxide layer C was 3.5 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , which was too high. In Test No. 16, the thickness of the oxide layer C exceeded 60 ⁇ m. This is probably because the thermal conductivity of the oxide layer C was too high.
- Test No. 18 did not contain any specific oxide layer forming element. Therefore, although the manufacturing method was appropriate, the total content of the specific oxide layer forming elements in the oxide layer A was less than 0.1%, which was too low. Therefore, the total content of the specific oxide layer forming elements in the oxide layer C is less than 0.1% and is too low. As a result, the thermal conductivity of the oxide layer C was 1.1 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , which was too low.
- the thermal conductivity of the oxide layer C was 0.8 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , which was too low.
- the Cr content was too low. Therefore, although the manufacturing method was appropriate, the total content of Cr and Mn in the oxide layer A was 16.3%, which was too low. Therefore, the total content of Cr and Mn in the oxide layer C was 1.3%, which was too low. As a result, the thermal conductivity of the oxide layer C was 3.3 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , which was too high. In Test No. 20, the thickness of the oxide layer C exceeded 60 ⁇ m. This is probably because the thermal conductivity of the oxide layer C was too high.
- the content of the specific oxide layer forming element was too high. Therefore, the total content of the specific oxide layer forming elements in the oxide layer A was 13.9%, which was too high. Therefore, the total content of the specific oxide layer forming elements in the oxide layer C was 18.6%, which was too high. As a result, the thermal conductivity of the oxide layer C was 3.8 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , which was too high. In Test No. 21, the thickness of the oxide layer C exceeded 60 ⁇ m. This is probably because the thermal conductivity of the oxide layer C was too high.
- the chemical composition was appropriate, but the (CO + CO 2 ) / N 2 ratio exceeded 1.0. Therefore, the total content of Cr and Mn in the oxide layer A was 10.6%, which was too low. Therefore, the total content of Cr and Mn in the oxide layer C was 4.6%, which was too low. As a result, the thermal conductivity of the oxide layer C was 3.4 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 , which was too high. In Test No. 22, the thickness of the oxide layer C exceeded 60 ⁇ m. This is probably because the thermal conductivity of the oxide layer C was too high.
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Abstract
Description
本実施形態によるフェライト系耐熱鋼の形状は、特に限定されない。フェライト系耐熱鋼はたとえば、鋼管、棒鋼、及び鋼板である。好ましくは、フェライト系耐熱鋼は、フェライト系耐熱鋼管である。本実施形態によるフェライト系耐熱鋼の基材に対して酸化処理を行う。酸化処理によりフェライト系耐熱鋼の基材の表面に酸化層Aが形成される。
基材2は、以下の化学組成を有する。
炭素(C)は、オーステナイトを安定化させる。Cはさらに、固溶強化により基材のクリープ強度を高める。しかしながら、基材2のC含有量が高すぎる場合、炭化物が過剰に析出し、基材2の加工性及び溶接性が低下する。したがって、C含有量は0.01~0.3%である。C含有量の好ましい下限は0.03%であり、C含有量の好ましい上限は0.15%である。
シリコン(Si)は鋼を脱酸する。Siはさらに、基材2の耐水蒸気酸化性を向上する。しかしながら、Si含有量が高すぎる場合、基材2の靱性が低下する。したがって、Si含有量は0.01~2.0%である。Si含有量の好ましい下限は0.05%であり、さらに好ましくは0.1%である。Si含有量の好ましい上限は1.0%であり、さらに好ましくは0.5%である。
マンガン(Mn)は鋼を脱酸する。Mnはさらに、基材2中のSと結合してMnSを形成し、Sの粒界偏析を抑制する。これにより、基材2の熱間加工性が向上する。しかしながら、Mn含有量が高すぎる場合、基材2が脆くなりさらに、基材2のクリープ強度が低下する。したがって、Mn含有量は0.01~2.0%である。Mn含有量の好ましい下限は0.05%であり、さらに好ましくは0.1%である。Mn含有量の好ましい上限は1.0%であり、さらに好ましくは0.8%である。
燐(P)は不純物である。Pは、基材2の結晶粒界に偏析して、基材2の熱間加工性を低下させる。Pはさらに、酸化皮膜3と基材2との界面に濃化して、酸化皮膜3の基材2に対する密着性を低下させる。したがって、P含有量はなるべく低い方が好ましい。P含有量は0.10%以下であり、好ましくは0.03%以下である。P含有量の下限はたとえば、0.005%である。
硫黄(S)は不純物である。Sは、基材2の結晶粒界に偏析して、基材2の熱間加工性を低下させる。Sはさらに、酸化皮膜3と基材2との界面に濃化して、酸化皮膜3の基材2に対する密着性を低下させる。したがって、S含有量はなるべく低い方が好ましい。S含有量は0.03%以下であり、好ましくは0.015%以下である。S含有量の下限はたとえば、0.0001%である。
クロム(Cr)は、基材2の耐水蒸気酸化性を高める。Crはさらに、Cr2O3及び(Fe、Cr)3O4で定義される酸化物として酸化皮膜3中に含有される。Cr酸化物は基材2の耐水蒸気酸化性を高める。Cr酸化物はさらに、酸化皮膜3の基材2に対する密着性を高める。しかしながら、Cr含有量が高すぎる場合、酸化皮膜3中のCr2O3の濃度が高くなり、酸化皮膜3の伝熱特性が低下する。したがって、Cr含有量は7.0~14.0%である。Cr含有量の好ましい下限は7.5%であり、さらに好ましくは8.0%である。Cr含有量の好ましい上限は12.0%であり、さらに好ましくは11.0%である。
窒素(N)は、基材2中に固溶し、基材2の強度を高める。Nはさらに、基材2中の合金成分と窒化物を形成して基材2中に析出し、基材2の強度を高める。しかしながら、N含有量が高すぎる場合、窒化物が粗大化し、基材2の靱性が低下する。したがって、N含有量は0.005~0.15%である。N含有量の好ましい下限は0.01%である。N含有量の好ましい上限は0.10%である。
アルミニウム(Al)は鋼を脱酸する。しかしながら、Al含有量が高すぎる場合、基材2の熱間加工性が低下する。したがって、Al含有量は0.001~0.3%である。Al含有量の好ましい下限は0.005%であり、Al含有量の好ましい上限は0.1%である。本実施形態において、Al含有量とは、酸可溶性Al(sol.Al)を意味する。
Ta:0~5.0%、
W:0~5.0%、及び
Re:0~5.0%からなる群から選択される1種又は2種以上:合計で0.5~7.0%
モリブデン(Mo)、タンタル(Ta)、タングステン(W)及びレニウム(Re)からなる群から選択される1種又は2種以上が含有される。これらの元素を以降、特定酸化層形成元素ともいう。特定酸化層形成元素は、基材2の表面に酸化層Aを形成する。特定酸化層形成元素はさらに、500~650℃の高温蒸気環境下で、酸化層B及び酸化層Cを含む酸化皮膜3を形成する。これらの元素のうち1種類でも含有されれば、この効果が得られる。しかしながら、特定酸化層形成元素の含有量が高すぎる場合、基材2の靱性、延性及び加工性が低下する。したがって、Mo含有量は0~5.0%であり、Ta含有量は0~5.0%であり、W含有量は0~5.0%であり、Re含有量は0~5.0%である。Mo含有量の好ましい下限は0.01%であり、さらに好ましくは0.1%である。Ta含有量の好ましい下限は0.01%であり、さらに好ましくは0.1%である。W含有量の好ましい下限は0.01%であり、さらに好ましくは0.1%である。Re含有量の好ましい下限は0.01%であり、さらに好ましくは0.1%である。Mo含有量の好ましい上限は4.0%であり、さらに好ましくは3.0%である。Ta含有量の好ましい上限は4.0%であり、さらに好ましくは3.0%である。W含有量の好ましい上限は4.0%であり、さらに好ましくは3.0%である。Re含有量の好ましい上限は4.0%であり、さらに好ましくは3.0%である。特定酸化層形成元素の合計含有量は、0.5~7.0%である。特定酸化層形成元素の合計含有量の好ましい下限は0.6%であり、さらに好ましくは1.0%である。特定酸化層形成元素の合計含有量の好ましい上限は6.5%であり、さらに好ましくは6.0%である。
Ni:0~5.0%
Co:0~5.0%
銅(Cu)、ニッケル(Ni)及びコバルト(Co)は任意元素であり、含有されなくてもよい。含有される場合、これらの元素はオーステナイトを安定化させる。これにより、基材2の耐衝撃性を低下させるデルタフェライトの残留が抑制される。これらの元素のうち1種類でも含有されれば、この効果が得られる。しかしながら、これらの元素の含有量が高すぎる場合、基材2の長時間クリープ強度が低下する。したがって、Cu含有量は0~5.0%であり、Ni含有量は0~5.0%であり、Co含有量は0~5.0%である。Cu含有量の好ましい上限は3.0%であり、さらに好ましくは2.0%である。Ni含有量の好ましい上限は3.0%であり、さらに好ましくは2.0%である。Co含有量の好ましい上限は3.0%であり、さらに好ましくは2.0%である。これらの元素の含有量の好ましい下限は、それぞれ0.005%である。
V:0~1.0%
Nb:0~1.0%
Hf:0~1.0%
チタン(Ti)、バナジウム(V)、ニオブ(Nb)及びハフニウム(Hf)は任意元素であり、含有されなくてもよい。含有される場合、これらの元素は、炭素及び窒素と結合して炭化物、窒化物又は炭窒化物を形成する。これらの炭化物、窒化物及び炭窒化物は、基材2を析出強化する。これらの元素のうち1種類でも含有されれば、この効果が得られる。しかしながら、これらの元素の含有量が高すぎる場合、基材2の加工性が低下する。したがって、Ti含有量は0~1.0%であり、V含有量は0~1.0%であり、Nb含有量は0~1.0%であり、Hf含有量は0~1.0%である。Ti含有量の好ましい上限は0.8%であり、さらに好ましくは0.4%である。V含有量の好ましい上限は0.8%であり、さらに好ましくは0.4%である。Nb含有量の好ましい上限は0.8%であり、さらに好ましくは0.4%である。Hf含有量の好ましい上限は0.8%であり、さらに好ましくは0.4%である。これらの元素の含有量の好ましい下限は、それぞれ0.01%である。
Mg:0~0.1%
Zr:0~0.1%
B:0~0.1%
希土類元素:0~0.1%
カルシウム(Ca)、マグネシウム(Mg)、ジルコニウム(Zr)、ボロン(B)及び希土類元素(REM)は任意元素であり、含有されなくてもよい。含有される場合、これらの元素は基材2の強度、加工性及び耐酸化性を高める。これらの元素のうち1種類でも含有されれば、この効果が得られる。しかしながら、これらの元素の含有量が高すぎる場合、基材2の靱性及び溶接性が低下する。したがって、Ca含有量は0~0.1%であり、Mg含有量は0~0.1%であり、Zr含有量は0~0.1%であり、B含有量は0~0.1%であり、REM含有量は0~0.1%である。Ca含有量の好ましい上限は0.05%である。Mg含有量の好ましい上限は0.05%である。Zr含有量の好ましい上限は0.05%である。B含有量の好ましい上限は0.05%である。REM含有量の好ましい上限は0.05%である。これらの元素の含有量の好ましい下限は、それぞれ0.0015%である。ここで、REMとは、原子番号39番のイットリウム(Y)、ランタノイドである原子番号57番のランタン(La)~原子番号71番のルテチウム(Lu)及び、アクチノイドである原子番号89番のアクチニウム(Ac)~103番のローレンシウム(Lr)からなる群から選択される1種又は2種以上の元素である。
上述の化学組成を有する基材2に対して、酸化処理を行う。酸化処理により、基材2の表面に酸化層Aが形成される。基材2と基材2の表面の酸化層Aとを備えるフェライト系耐熱鋼1は、高温蒸気環境下に用いられる。高温蒸気環境下において、酸化層Aは、耐水蒸気酸化特性を保持したまま、伝熱特性に優れる酸化皮膜3に変化する。すなわち、酸化層Aは、酸化層B及び酸化層Cを含む酸化皮膜3を形成するための素材となる。酸化層Aが酸化皮膜3に変化する仕組みは定かではないが、酸化層Aは、主に酸化層Cの形成に寄与すると推察される。
本実施形態によるフェライト系耐熱鋼1の製造方法は、準備工程及び酸化処理工程を含む。準備工程では、上述の化学組成を有する基材2を準備する。基材2は上述の化学組成を有する素材から製造する。素材は、連続鋳造法により製造されたスラブ、ブルーム及びビレットであってもよい。素材は、造塊法により製造されたビレットであってもよい。素材を製造する際における加熱温度はたとえば、850~1200℃である。
上述の基材2に対して酸化処理を行う。酸化処理は、CO、CO2及びN2を含むガス雰囲気中で基材2を加熱することにより行う。酸化処理に用いるガスのCO/CO2比は、体積比で0.6以上とする。CO/CO2比を0.6以上とすることで、Feの優先的な酸化を抑制できる。その結果、基材2の表面に、合計で20質量%以上のCr及びMnを含有し、さらに、合計で0.5質量%以上の特定酸化層形成元素を含有する酸化層Aが形成される。酸化層Aは、後述の水蒸気酸化処理後に、酸化皮膜3に変化する。CO/CO2比は特に上限を設けないが、操業上の実用性を考慮して、2.0が好ましい。
本実施形態によるフェライト系伝熱部材4は基材2と酸化皮膜3とを備える。フェライト系伝熱部材4の基材2は上述のフェライト系耐熱鋼1の基材と同じである。したがって、フェライト系伝熱部材4の基材2の化学組成は上述のフェライト系耐熱鋼1の基材2の化学組成と同じである。本実施形態によるフェライト系伝熱部材4の形状は、特に限定されない。フェライト系伝熱部材4はたとえば、管、棒又は板材である。管状の形状を有する場合、フェライト系伝熱部材4はたとえば、ボイラ用配管等として使用される。したがって好ましくは、フェライト系伝熱部材4は、フェライト系伝熱管である。
基材2と酸化層Aとを備えるフェライト系耐熱鋼1に対して、水蒸気酸化処理を行うことによって、基材2の表面に酸化皮膜3が形成される。図2を参照して、酸化皮膜3は、酸化層B及び酸化層Cの2層を含む酸化皮膜である。酸化皮膜3は、酸化層Bを含む。そのため、酸化皮膜3は伝熱特性に優れる。酸化皮膜3は酸化層Cを含む。そのため、酸化皮膜3は耐水蒸気酸化性及び伝熱特性の両方に優れる。つまり、酸化皮膜3は、耐水蒸気酸化性のみならず、伝熱特性にも優れる。酸化層Bは、フェライト系伝熱部材4の最上層に形成される。酸化層Cは、酸化層Bと基材2との間に配置される。フェライト系伝熱部材4がボイラ用配管の場合、酸化層Bが、ボイラ用配管の内表面側に相当し、基材2が、ボイラ用配管の外表面側に相当する。この場合、酸化層Bは、高温の水蒸気と接する。
酸化層Bは、体積%で合計80%以上のFe3O4及びFe2O3を含有する。Fe3O4及びFe2O3の熱伝導率は高い。したがって、酸化層Bの熱伝導率は高く、フェライト系伝熱部材4の外部から与えられた熱を大きく減少させることなくフェライト系伝熱部材4の内部へと伝える。このため、ボイラの伝熱特性を向上できる。好ましくは、酸化層Bは、体積%で合計90%以上のFe3O4及びFe2O3を含有する。好ましくは、酸化層BのFe2O3含有量は20体積%未満である。さらに好ましくは、酸化層BはFe3O4からなる。
酸化層Cは、酸化層Bと基材2との間に配置され、基材2と接する。
κ=ρ×Cp×D
ここで、ρにはかさ密度、Cpには比熱、Dには熱拡散率が代入される。
酸化皮膜3の厚さは、特に限定されないが、薄い方が好ましい。酸化皮膜3が薄いと、フェライト系伝熱部材4の伝熱特性が高まる。このため、ボイラの伝熱特性を向上できる。フェライト系伝熱部材4が長時間使用されれば、酸化皮膜3は厚くなる。フェライト系伝熱部材4の水蒸気酸化処理の温度が高い場合も、酸化皮膜3は厚くなる。後述の酸化処理及び水蒸気酸化処理を行えば、酸化層B及び酸化層Cは、ほとんど同じ厚さで形成される。したがって、酸化層Cが薄い場合、酸化皮膜3も薄くなる。
本実施形態によるフェライト系伝熱部材4の製造方法は、水蒸気酸化処理工程を含む。
上述の酸化処理を施したフェライト系耐熱鋼に対して水蒸気酸化処理を行う。水蒸気酸化処理は、フェライト系耐熱鋼を、500~650℃の水蒸気に晒すことによって行う。水蒸気酸化処理は100時間以上であれば、処理時間の上限は特に限定されない。水蒸気酸化処理により、酸化層Aが酸化層B及び酸化層Cを含む酸化皮膜3に変化する。これにより、酸化層B及び酸化層Cを含む酸化皮膜3が、基材2上に形成される。
各試験片の酸化層Aの厚さを、上述の方法で求めた。結果を表2に示す。
各試験片の断面に対して、上述の方法で各金属元素の含有量を求めた。酸化層Aについて、Cr及びMnの合計含有量(質量%)、及び、Mo、Ta、W及びReの合計含有量(質量%)を求めた。結果を表2に示す。
各試験片の断面(つまり、酸化層Bの断面)に対して、上述の方法でFe3O4及びFe2O3の合計体積率を求めた。さらに、酸化層Cの断面に対してCr2O3の体積率を求めた。結果を表2に示す。
各試験片の断面に対して、上述の方法で各金属元素の含有量を求めた。酸化層Bについて、Cr及びMnの合計含有量(質量%)を求めた。結果を表2に示す。酸化層Cについて、Cr及びMnの合計含有量(質量%)、及び、Mo、Ta、W及びReの合計含有量(質量%)を求めた。結果を表2に示す。
各試験片の酸化層Cの熱伝導率を、上述の方法で求めた。結果を表2に示す。
各試験片の酸化層Cの厚さを、上述の方法で求めた。結果を表2に示す。
表1及び表2を参照して、試験番号1、3、6、9~15、及び17の鋼の化学組成及び製造条件は適切であった。そのため、これらの試験番号の酸化層AはCr及びMnを合計で20~45%、及びMo、Ta、W、及びReからなる群から選択される1種又は2種以上を合計で0.5~10%含有した。これにより、水蒸気酸化処理後に基材に形成された酸化層Bは体積%で合計80%以上のFe3O4及びFe2O3を含有した。さらに、酸化層CのCr+Mn合計含有量が5%超~30%であり、特定酸化層形成元素の合計含有量が1~15%であった。その結果、酸化層Cの熱伝導率は1.2~3.0W・m-1・K-1の範囲内となり優れた熱伝導率を示した。酸化層Cはさらに、厚さが60μm以下となり、優れた耐水蒸気酸化性を示した。
2 基材
3 酸化皮膜
4 フェライト系伝熱部材
A 酸化層A
B 酸化層B
C 酸化層C
Claims (7)
- 基材と、
前記基材の表面に酸化層Aとを備え、
前記基材は、
質量%で、
C:0.01~0.3%、
Si:0.01~2.0%、
Mn:0.01~2.0%、
P:0.10%以下、
S:0.03%以下、
Cr:7.0~14.0%、
N:0.005~0.15%、
sol.Al:0.001~0.3%、
Mo:0~5.0%、Ta:0~5.0%、W:0~5.0%及びRe:0~5.0%からなる群から選択される1種又は2種以上:合計で0.5~7.0%、
Cu:0~5.0%、
Ni:0~5.0%、
Co:0~5.0%、
Ti:0~1.0%、
V:0~1.0%、
Nb:0~1.0%、
Hf:0~1.0%、
Ca:0~0.1%、
Mg:0~0.1%、
Zr:0~0.1%、
B:0~0.1%、及び、
希土類元素:0~0.1%を含有し、残部がFe及び不純物からなる化学組成を有し、
前記酸化層Aは、
質量%で、
Cr及びMn:合計で20~45%、及び、
Mo、Ta、W及びReからなる群から選択される1種又は2種以上:合計で0.5~10%、
を含有する化学組成を含む、フェライト系耐熱鋼。 - 請求項1に記載のフェライト系耐熱鋼であって、
前記基材の化学組成は、
Cu:0.005~5.0%、
Ni:0.005~5.0%、及び、
Co:0.005~5.0%からなる群から選択される1種又は2種以上を含有する、フェライト系耐熱鋼。 - 請求項1又は請求項2に記載のフェライト系耐熱鋼であって、
前記基材の化学組成は、
Ti:0.01~1.0%、
V:0.01~1.0%、
Nb:0.01~1.0%、及び、
Hf:0.01~1.0%からなる群から選択される1種又は2種以上を含有する、フェライト系耐熱鋼。 - 請求項1~請求項3のいずれか1項に記載のフェライト系耐熱鋼であって、
前記基材の化学組成は、
Ca:0.0015~0.1%、
Mg:0.0015~0.1%、
Zr:0.0015~0.1%、
B:0.0015~0.1%、及び、
希土類元素:0.0015~0.1%からなる群から選択される1種又は2種以上を含有する、フェライト系耐熱鋼。 - 請求項1~請求項4のいずれか1項に記載の化学組成を有する基材と、
前記基材の表面に酸化皮膜とを備え、
前記酸化皮膜は、
体積%で合計80%以上のFe3O4及びFe2O3を含有する酸化層Bと、
前記酸化層Bと前記基材との間に配置される酸化層Cとを含み、
前記酸化層Cの化学組成は、
質量%で、
Cr及びMn:合計で5%超~30%、及び、
Mo、Ta、W及びReからなる群から選択される1種又は2種以上:合計で1~15%を含有する、フェライト系伝熱部材。 - 請求項5に記載のフェライト系伝熱部材であって、
前記酸化層Bの化学組成は、
質量%で、
Cr及びMn:合計で5%以下を含有する、フェライト系伝熱部材。 - 請求項5又は請求項6に記載のフェライト系伝熱部材であって、
前記酸化層Cは、
体積%で5%以下のCr2O3を含有する、フェライト系伝熱部材。
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JP2022501515A (ja) * | 2018-09-28 | 2022-01-06 | コーニング インコーポレイテッド | オーステナイト変態温度を上昇させた合金金属、及びこれを含む物品 |
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CN112501510A (zh) * | 2020-11-27 | 2021-03-16 | 天津职业技术师范大学(中国职业培训指导教师进修中心) | 一种高铝铁素体耐热钢及其制备方法 |
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