Technical field
[0001]
The present invention relates to a heat resistant steel and heat transfer member, more particularly, it relates to a ferritic heat-resistant steels and ferritic heat transfer member used in the high temperature steam oxidation environment or the like.
BACKGROUND
[0002]
In thermal power plants, CO 2 from the viewpoint of emission reduction and economy of gas, improvement in the power generation efficiency is demanded. Therefore, high temperature and high pressure turbine steam pressure is underway. Heat transfer member used in the thermal power plants, long exposed to high temperature and high pressure steam. Heat transfer member, for example, a piping for boilers. Prolonged exposure to high temperature steam oxidation scales are produced on the surface of the heat transfer member. If steam oxidation resistance of the heat transfer member is not sufficient, a large amount of oxide scale is formed on the surface of the heat transfer member. By starting and stopping of the boiler, the heat transfer member thermally expand and contract. Therefore, if generation large amount of oxide scale, oxide scale causes clogging of the pipe by peeling. Further if the oxide scale was produced in large quantities, the heat conduction from the pipe outside to the inside pipe is inhibited by the oxidized scale. Therefore, in order to maintain a high temperature in the piping, it is necessary to provide more heat from the outside. Temperature rise of the pipe, causing a decrease in creep strength. Therefore, thermal power boiler, the heat transfer member for use in equipment such as turbines and steam pipes, high steam oxidation resistance is demanded.
[0003]
　As a material satisfying such characteristics for example, austenitic heat-resistant steel and heat resistant ferritic steels have been developed. Austenitic heat-resistant steel, for example, a Cr content of 18-25% by weight of austenitic heat-resistant steels. Ferritic heat-resistant steel, for example, Cr content of 8 to 13 wt% of the ferritic heat-resistant steel. Ferritic heat-resistant steel is less expensive than the heat-resistant, austenitic steels. Ferritic heat-resistant steel further lower thermal expansion coefficient than austenitic steels, and has high thermal conductivity. Therefore, the heat resistant ferritic steels are suitable as piping materials for thermal power plants. However, Cr content ferritic heat-resistant steel is lower than the Cr content of the austenitic heat-resistant steels. Therefore, steam oxidation resistance of ferritic heat-resistant steel is lower than the steam oxidation resistance of the austenitic heat-resistant steels. Therefore, heat resistant ferritic steel excellent in steam oxidation resistance is demanded.
[0004]
　Ferritic heat-resistant steel which suppresses detachment of the oxide scale, for example, disclosed in JP-A 11-92880 (Patent Document 1). Ferritic heat-resistant steel disclosed in Patent Document 1, the high-Cr-containing oxide film is formed on the surface during use a ferritic heat-resistant steel, the interface or the following diameter 1 micron in the vicinity of the oxide film ultrafine oxide is formed. This improves the adhesion between the oxide coating and the base metal, and are described in Patent Document 1.
[0005]
　How to improve the steam oxidation resistance by increasing the Cr concentration in the surface of the ferritic heat-resistant steel, for example, disclosed in Japanese 2007-39745 (Patent Document 2). In Patent Document 2, by supporting the powder particles containing Cr on the surface of the heat resistant ferritic steel containing Cr, to produce a high Cr oxide layer of Cr concentration in the ferritic steel surface at a high temperature. In this way, the resistance (water vapor) oxidizing ferritic steel containing Cr can be easily and economically improved, and is described in Patent Document 2.
[0006]
　By forming the Cr oxide film on the surface of the ferritic heat-resistant steel, a method of improving the oxidation resistance, for example, disclosed in Japanese 2013-127103 (Patent Document 3). Oxidation processing method of ferritic heat-resistant steel described in Patent Document 3, a mixed gas of carbon dioxide and an inert gas at a low oxygen partial pressure in the gas atmosphere, heat treatment of the heat resistant ferritic steel containing chromium Te, and forming an oxide film containing chromium on the surface of the heat resistant steel. In this way, the Cr concentration in the scale is increased, the oxidation resistance of ferritic heat-resistant steel can be easily and economically improved, and is described in Patent Document 3.
[0007]
　Ferritic heat-resistant steel having improved resistance to steam oxidation by the deposition of Cr to the surface of the ferritic heat-resistant steel, for example, disclosed in Japanese 2009-179884 (Patent Document 4). Ferritic heat resistant steel described in Patent Document 4 is a ferritic heat-resistant steel used in a high-temperature high-pressure steam environment, the powder Cr shots shot peening by the deposited Cr of, which are pre-oxidized It characterized by having a Cr oxide film on the substrate surface. The ferritic heat-resistant steel, prior to use in an oxidizing environment, the protective coating of the oxidation resistance of oxide is formed on the heat-resistant steel, steam oxidation resistance is improved, and in Patent Document 4 It has been described.
CITATION
Patent Document
[0008]
Patent Document 1: JP-A-11-92880
Patent Document 2: JP 2007-39745 JP
Patent Document 3: JP 2013-127103 Patent Publication
Patent Document 4: JP 2009-179884 JP
Summary of the Invention
Problems that the Invention is to Solve
[0009]
　However, even using the techniques described above, it is sometimes impossible to sufficiently increase the heat transfer characteristics and steam oxidation resistance of the heat transfer member. As described above, various studies have been made about a method of inhibiting the formation of oxide scale by forming a Cr oxide on the surface of the heat transfer member. However, the thermal conductivity of the Cr oxides is low. Therefore, if the formation of Cr oxides, although increasing steam oxidation resistance of the heat transfer member, decreases the heat transfer characteristics.
[0010]
　An object of the present invention, the heat transfer characteristics and resistance to steam oxidation in good ferritic heat transfer member, and to provide it a feasible ferritic heat resistant steel.
Means for Solving the Problems
[0011]
　Ferritic heat-resistant steel according to the present embodiment comprises a substrate and a oxide layer A on the surface of the substrate. The substrate, in mass%, C: 0.01 ~ 0.3%, Si: 0.01 ~ 2.0%, Mn: 0.01 ~ 2.0%, P: 0.10% or less, S 0.03% or less, 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%, and Re: 0 ~ the group consisting of 5.0% from 0.5 to 7.0% in total of one or two or more selected from, 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 to 0.1% B: 0 to 0.1% and rare earth element: 0 contained to 0.1% with a chemical composition the balance being Fe and impurities. Oxide layer A, in mass%, comprising a chemical composition containing 20-45% Cr and Mn in total. Oxide layer A comprises by mass%, Mo, Ta, a chemical composition containing 0.5-10% of one or two or more in total selected from the group consisting of W and Re.
[0012]
　Ferritic heat transfer member according to the present embodiment comprises a substrate and an oxide film on the surface of the substrate. The substrate having the above chemical composition. Oxide film includes an oxide layer B and the oxide layer C. Oxide layer B is Fe total 80% by volume% 3 O 4 and Fe 2 O 3 containing. Oxide layer C is disposed between the oxide layer B and the substrate. The chemical composition of the oxide layer C, and by mass%, Cr and Mn: 5% Ultra to 30% in total, and, Mo, Ta, 1 or two or more selected from the group consisting of W and Re: total containing from 1 to 15%.
Effect of the invention
[0013]
　Ferritic heat-resistant steel and ferritic heat transfer member according to the present embodiment is excellent in heat transfer characteristics and resistance to steam oxidation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
[1] Figure 1 is a cross-sectional view of the heat resistant ferritic steel according to the present embodiment.
FIG. 2 is a cross-sectional view of a ferritic heat transfer member according to the present embodiment.
DESCRIPTION OF THE INVENTION
[0015]
　Hereinafter, with reference to the accompanying drawings, the present embodiment will be described in detail. Its description will not be repeated the same reference numerals designate like or corresponding parts in FIG.
[0016]
　The present inventors have made various investigations on the heat resistant ferritic steel and ferritic heat transfer member. As a result, the following findings were obtained.
[0017]
　(1) heat resistant ferritic steel of the present embodiment can be utilized as a heat transfer member of the boiler piping. Heat transfer member of a boiler piping is in contact with high temperature steam. Prolonged exposure to high temperature steam, the surface of the heat transfer member is oxidized scale generates. Oxide scale consists of various oxides and impurities. Oxides, for example, Fe 3 O 4 , Fe 2 O 3 , and Cr 2 O 3 is like. Oxide scale to form an oxide film on the surface of the heat transfer member.
[0018]
　(2) A low thermal conductivity of the oxide film, the heat transfer characteristics of from the outside of the heat transfer member to the inside of the heat transfer member is lowered. Therefore, in order to maintain the interior of the heat transfer member to a high temperature, it is necessary to provide a large amount of heat from the outside of the heat transfer member, the heat transfer characteristics of the boiler is reduced. Furthermore, when the external heat transfer member gave a large amount of heat, there is a case where the creep strength of the heat transfer member is lowered. Thus, the thermal conductivity of the oxide film is preferably higher. However, when the thermal conductivity of the oxide film is too high, on the inner surface of the heat transfer member, transferred the heat of the high-temperature steam. Heat conducted, in order to promote the oxidation reaction of the inner surface of the heat transfer member, resulting a large amount of oxide scale on the inner surface of the heat transfer member. A large amount of oxide scale is peeled off from the inner surface of the heat transfer member. If the heat transfer member is a pipe, exfoliated oxide scale causes clogging of the piping. Thus, the thermal conductivity of the oxide film needs to be controlled to a certain range.
[0019]
　(3) when the thickness of the oxide scale is too thick, heat conduction is inhibited from outside of the heat transfer member to the inside of the heat transfer member. Therefore, heat transfer characteristics of the boiler is reduced. Therefore, the thickness of the oxide film, as thin as possible the better.
[0020]
　(4) Among the oxides mentioned above, Fe 3 O 4 and Fe 2 O 3 is a high-temperature steam oxidation environment (hereinafter, also referred to as high-temperature steam environment), the are thermodynamically stable form. Fe 3 O 4 and Fe 2 O 3 is further its high thermal conductivity. Therefore, Fe 3 O 4 and Fe 2 O 3 to a large amount of oxide film containing, by forming on the surface of the heat transfer member in contact with high temperature steam, thus improving the thermal efficiency of the boiler. However, Fe 3 O 4 and Fe 2 O 3 the thermal conductivity of the large amount of oxide film containing too high. Therefore, only the oxide film, as described above, a large amount of oxide scale occurs on the inner surface of the heat transfer member.
[0021]
　(5) In general, the heat transfer member of a boiler piping, improves the Cr concentration in the pipe inner surface, Cr 2 O 3 to form an oxide film containing a large amount of the inner surface of the heat transfer member many. Thus, generation of a large amount of oxide scale is suppressed, thereby improving the steam oxidation resistance of the heat transfer member. However, Cr 2 O 3 oxide film containing a large amount of the low thermal conductivity. Therefore, heat transfer characteristics of the heat transfer member is lowered. Therefore, only the oxide film can not be improved heat transfer characteristics of the boiler.
[0022]
　(6) Therefore, in a high-temperature steam environment, oxide layer having excellent heat transfer properties, and an oxide film comprising two layers of oxide layers achieve both the steam oxidation resistance and heat transfer characteristics of the heat transfer member formed on the inner surface. This allows both an excellent heat transfer characteristics and excellent resistance to steam oxidation.
[0023]
　(7) Fe total more than 80% by volume 3 O 4 and Fe 2 O 3 when they contain, the thermal conductivity of the oxide layer is high. Therefore, it is possible to improve the heat transfer characteristics of the boiler. Therefore, the surface of the heat transfer member in contact with high temperature steam, Fe total more than 80% by volume 3 O 4 and Fe 2 O 3 to form an oxide layer B containing.
[0024]
　(8) On the other hand, as the oxide layer which achieve both the steam oxidation resistance and heat transfer characteristics, the oxide layer C, is formed between the oxide layer B and the substrate. Oxide layer C 5% Cr and Mn in a total ultra to 30 mass%, and, Mo, Ta, 1 kind or amount of 1 to 15 wt% of two or more in total selected from the group consisting of W and Re to.
[0025]
　Cr oxides and Mn oxides enhance steam oxidation resistance of the substrate. However, if the Cr content is too high, the heat transfer characteristics of the oxide film is reduced. If Mn content is too high, the creep strength of the substrate is reduced. Accordingly, oxide layer C contains more than 5% to 30 mass% of Cr and Mn in total.
[0026]
　Mo, Ta, if the W and Re is contained in the oxide layer C, the thermal conductivity of the oxide layer C is increased. However, if the content of these elements is too high, steam oxidation resistance of the oxide layer C may be reduced. Accordingly, oxide layer C, Mo, Ta, containing 1 to 15 mass% in total of one or more members selected from the group consisting of W and Re.
[0027]
　Thus, oxide layer C has excellent heat transfer characteristics and excellent resistance to steam oxidation.
[0028]
　(9) in a high-temperature steam environment, in order to form an oxide layer B and the oxide layer C, and advance on the substrate, it is necessary to have to form an oxide layer A. The chemical composition of the oxide layer A, by mass%, containing 20-45% Cr and Mn in total. The chemical composition of the oxide layer A is a mass%, Mo, Ta, containing 0.5-10% in total of one or two or more selected from the group consisting of W and Re. When used in a high temperature steam environment, oxide layer A is changed to an oxide film comprising an oxide layer B and the oxide layer C. The high temperature for example, 500 ~ 650 ° C..
[0029]
　Ferritic heat-resistant steel according to the present embodiment has been completed based on the above findings includes a substrate, an oxide layer A on the surface of the substrate. The substrate, in mass%, C: 0.01 ~ 0.3%, Si: 0.01 ~ 2.0%, Mn: 0.01 ~ 2.0%, P: 0.10% or less, S 0.03% or less, 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% and Re: from 0 to the group consisting of 5.0% from 0.5 to 7.0% of one or more selected in total, 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 to 0.1% B: 0 to 0.1% and rare earth element: 0 contained to 0.1% with a chemical composition the balance being Fe and impurities. Oxide layer A, in mass%, comprising a chemical composition containing 20-45% Cr and Mn in total. Oxide layer A comprises by mass%, Mo, Ta, a chemical composition containing 0.5-10% of one or two or more in total selected from the group consisting of W and Re.
[0030]
　Ferritic heat-resistant steel according to the present embodiment is excellent in heat transfer characteristics and resistance to steam oxidation.
[0031]
　The chemical composition of the base material of the heat resistant ferritic steel, Cu: 0.005 ~ 5.0%, Ni: 0.005 ~ 5.0%, and, Co: the group consisting of from 0.005 to 5.0% it may contain one or more members selected from the.
[0032]
　Chemical composition of the base material, Ti: 0.01 ~ 1.0%, V: 0.01 ~ 1.0%, Nb: 0.01 ~ 1.0%, and, Hf: 0.01 ~ 1 it may contain one or more members selected from the group consisting of 2.0%.
[0033]
　The chemical composition of the substrate, Ca: 0.0015 ~ 0.1%, Mg: 0.0015 ~ 0.1%, Zr: 0.0015 ~ 0.1%, B: 0.0015 ~ 0.1 %, and rare earth elements: 0.0015 may contain one or more members selected from the group consisting of 0.1%.
[0034]
　Ferritic heat transfer member according to the present embodiment comprises a substrate and an oxide film on the surface of the substrate. The substrate having the above chemical composition. Oxide film includes an oxide layer B and the oxide layer C. Oxide layer B, Fe total 80% by volume% 3 O 4 and Fe 2 O 3 containing. Oxide layer C is disposed between the oxide layer B and the substrate. The chemical composition of the oxide layer C, 5% Cr and Mn in a total ultra to 30 mass%, and, Mo, Ta, 1 ~ in total one or two or more selected from the group consisting of W and Re 15 containing mass%.
[0035]
　Ferritic heat transfer member according to the present embodiment is excellent in heat transfer characteristics and resistance to steam oxidation.
[0036]
　Preferably, the oxide layer B contains 5 wt% or less of Cr and Mn in total.
[0037]
　Preferably, the oxidizing layer C, Cr 2 O 3 containing 5% by volume or less.
[0038]
　In this case, the thermal conductivity is low Cr 2 O 3 by suppressing the amount of precipitation of, the thermal conductivity of the oxide film increases. Therefore, it is possible to improve the heat transfer characteristics of the boiler.
[0039]
　It is described below in detail ferritic heat-resistant steel and ferritic heat transfer member according to the present embodiment. "%" Related elements, unless otherwise specified, it means mass%.
[0040]
　[Ferritic heat-resistant steel]
　The shape of the heat resistant ferritic steel according to the present embodiment is not particularly limited. Ferritic heat-resistant steel, for example, steel pipes, steel bars, and steel. Preferably, the heat resistant ferritic steel is a ferritic heat-resistant steel. The oxidation treatment is performed to the substrate of the heat resistant ferritic steel according to the present embodiment. Oxide layer A is formed on the surface of a substrate of ferritic heat-resistant steel by oxidation treatment.
[0041]
　Figure 1 is a cross-sectional view of the heat resistant ferritic steel according to the present embodiment. Referring to FIG. 1, the heat resistant ferritic steel 1 includes a substrate 2, and an oxide layer A. The base member 2, the heat resistant ferritic steels 1 and a oxide layer A, as the heat transfer member is used in a high-temperature steam environment. Accordingly, oxide layer A is changed to the oxide film 3 including an oxide layer B and the oxide layer C.
[0042]
　[Chemical composition of the base material 2]
　substrate 2 has the following chemical composition.
[0043]
　C: 0.01 ~ 0.3%
　carbon (C) stabilizes the austenite. C further enhance the creep strength of the base material by solid solution strengthening. However, if the C content of the base material 2 is too high, carbides excessively precipitated, workability and weldability of the base material 2 is lowered. Therefore, C content is 0.01 to 0.3%. The preferable lower limit of C content is 0.03% and a preferable upper limit of C content is 0.15%.
[0044]
　Si: 0.01 ~ 2.0%
　silicon (Si) is deoxidized steel. Si further improve the steam oxidation resistance of the base material 2. However, if the Si content is too high, toughness of the base material 2 is lowered. Therefore, Si content is 0.01-2.0%. A preferable lower limit of Si content is 0.05%, more preferably 0.1%. The preferable upper limit of the Si content is 1.0%, more preferably 0.5%.
[0045]
　Mn: 0.01 ~ 2.0%
　of manganese (Mn) of deoxidizing steel. Mn further forms MnS by combining with S in the base material 2, to suppress the grain boundary segregation of S. Thereby, hot workability of the substrate 2 is improved. However, if the Mn content is too high, the base material 2 brittle becomes even, creep strength of the base material 2 is lowered. Therefore, Mn content is 0.01-2.0%. The preferable lower limit of the Mn content is 0.05%, more preferably 0.1%. The preferable upper limit of the Mn content is 1.0%, more preferably 0.8%.
[0046]
　P: 0.10% or less
　Phosphorus (P) is an impurity. P is segregated in the grain boundary of the substrate 2, it lowers the hot workability of the base material 2. P addition is enriched at the interface between the oxide film 3 and the substrate 2, thereby lowering the adhesion to the base material 2 of the oxide film 3. Accordingly, P content is preferably as small as possible. P content is 0.10% or less, preferably 0.03% or less. The lower limit of the P content is, for example, is 0.005%.
[0047]
　S: 0.03% or less
　of sulfur (S) is an impurity. S is segregated in the grain boundary of the substrate 2, it lowers the hot workability of the base material 2. S further be concentrated in the interface between the oxide film 3 and the substrate 2, thereby lowering the adhesion to the base material 2 of the oxide film 3. Thus, S content is preferably as small as possible. S content is 0.03% or less, preferably 0.015% or less. The lower limit of the S content is, for example, is 0.0001%.
[0048]
　Cr: 7.0 ~ 14.0%
　chromium (Cr) increases the steam oxidation resistance of the base material 2. Cr further, Cr 2 O 3 and (Fe, Cr) 3 O 4 contained in the oxide film 3 as an oxide as defined. Cr oxides enhance steam oxidation resistance of the substrate 2. Cr oxide further improve the adhesion to the base material 2 of the oxide film 3. However, if the Cr content is too high, Cr in the oxide film 3 2 O 3 increases the concentration of the heat transfer characteristics of the oxide film 3 is reduced. Therefore, Cr content is 7.0 to 14.0%. A preferable lower limit of Cr content is 7.5%, more preferably 8.0%. The preferable upper limit of the Cr content is 12.0 percent, still more preferably 11.0%.
[0049]
　N: 0.005 ~ 0.15%
　nitrogen (N) is a solid solution in the base material 2, increasing the strength of the substrate 2. N is further to form an alloy component in the base material 2 and the nitride deposited in the substrate 2, increasing the strength of the substrate 2. However, if the N content is too high, nitrides are coarsened, toughness of the base material 2 is lowered. Therefore, N content is 0.005 to 0.15%. The preferable lower limit of the N content is 0.01%. The preferable upper limit of the N content is 0.10%.
[0050]
　sol. Al: 0.001 ~ 0.3%
　aluminum (Al) is deoxidized steel. However, if the Al content is too high, the hot workability of the base material 2 is lowered. Therefore, Al content is 0.001 to 0.3%. A preferable lower limit of Al content is 0.005%, a preferred upper limit of Al content is 0.1%. In the present embodiment, the Al content is meant the acid-soluble Al (sol. Al).
[0051]
　Mo:
　0 ~ 5.0%, Ta: 0
　~ 5.0%, W: 0 ~ 5.0%, and
　Re: 0 ~ 1 or two or more selected from the group consisting of 5.0%: from 0.5 to 7.0% in total
　of molybdenum (Mo), tantalum (Ta), tungsten (W) and one or more members selected from the group consisting of rhenium (Re) is contained. Since these elements, also referred to as a specific oxide layer forming elements. Specific oxide layer formation elements, to form an oxide layer A on the surface of the substrate 2. Specific oxide layer forming element further under the high-temperature steam environment 500 ~ 650 ° C., to form an oxide film 3 including an oxide layer B and the oxide layer C. If also contain one kind of these elements, the effect is obtained. However, if the content of the specific oxide layer forming element too high, toughness of the base material 2, ductility and processability is lowered. Therefore, Mo content is 0-5.0%, Ta content is 0-5.0%, W content is 0-5.0%, Re content is 0-5.0 it is%. A preferable lower limit of Mo content is 0.01%, more preferably 0.1%. The preferable lower limit of the Ta content is 0.01%, more preferably 0.1%. The preferable lower limit of the W content is 0.01%, more preferably 0.1%. The preferable lower limit of the Re content is 0.01%, more preferably 0.1%. The preferable upper limit of the Mo content is 4.0%, more preferably from 3.0%. The preferable upper limit of the Ta content is 4.0%, more preferably from 3.0%. The preferable upper limit of the W content is 4.0%, more preferably from 3.0%. The preferable upper limit of the Re content is 4.0%, more preferably from 3.0%. The total content of the specific oxide layer forming element is 0.5 to 7.0%. The preferable lower limit of the total content of the specific oxide layer forming element is 0.6%, more preferably 1.0%. The preferable upper limit of the total content of the specific oxide layer forming element is 6.5%, more preferably from 6.0%.
[0052]
　Remainder of the substrate 2 of the heat resistant ferritic steel according to the present embodiment is Fe and impurities. In the present embodiment, the impurities, the ore or scrap is used as a raw material of steel, or refers to an element which is mixed from the environment or the like of the manufacturing process, contained in the range of the heat transfer member 4 according to the present embodiment does not adversely affect It is is say things. Impurity, for example, oxygen (O), in arsenic (As), antimony (Sb), thallium (Tl), a lead (Pb), bismuth (Bi) or the like.
[0053]
　Substrate 2 of the heat resistant ferritic steel according to the present embodiment further, in place of part of Fe, it may contain the following elements.
[0054]
　Cu:
　0 ~ 5.0%
　Ni: 0 ~ 5.0% Co: 0 ~ 5.0%
　copper (Cu), nickel (Ni) and cobalt (Co) is an arbitrary element may not contain . If contained, these elements stabilizes the austenite. Thus, the residual delta ferrite to lower the impact resistance of the substrate 2 is suppressed. If also contain one kind of these elements, the effect is obtained. However, if the content of these elements is too high, the long-term creep strength of the substrate 2 decreases. Therefore, Cu content is 0 to 5.0%, Ni content is 0 to 5.0%, Co content is 0 to 5.0%. The preferable upper limit of Cu content is 3.0%, more preferably 2.0%. The preferable upper limit of the Ni content is 3.0%, more preferably 2.0%. The preferable upper limit of the Co content is 3.0%, more preferably 2.0%. A preferable lower limit of the content of these elements is 0.005%, respectively.
[0055]

　Ti:
　0 ~ 1.0% V: 0 ~ 1.0%
　Nb: 0 ~ 1.0% Hf: 0 ~ 1.0%
　of titanium (Ti), vanadium (V), niobium (Nb), and hafnium (Hf ) is arbitrary element, it may not be contained. If contained, these elements form carbides, nitrides or carbonitrides in combination with carbon and nitrogen. These carbides, nitrides and carbonitrides will precipitate strengthening substrate 2. If also contain one kind of these elements, the effect is obtained. However, if the content of these elements is too high, the processability of the base material 2 is lowered. Therefore, Ti content is 0-1.0%, V content is 0-1.0%, Nb content is 0-1.0%, Hf content is 0-1.0 it is%. The preferable upper limit of the Ti content is 0.8%, more preferably 0.4%. The preferable upper limit of the V content is 0.8%, more preferably 0.4%. The preferable upper limit of Nb content is 0.8%, more preferably 0.4%. The preferable upper limit of the Hf content is 0.8%, more preferably 0.4%. A preferable lower limit of the content of these elements is 0.01%, respectively.
[0056]
　Ca:

　0 to 0.1% Mg: 0 to 0.1% Zr:
　0 to 0.1% B: 0 to 0.1%
　rare earth element: 0 to 0.1%
　of calcium (Ca), magnesium (Mg) , zirconium (Zr), boron (B) and rare earth elements (REM) are optional elements it may not be contained. If contained, these elements strength of the substrate 2, enhances the workability and oxidation resistance. If also contain one kind of these elements, the effect is obtained. However, if the content of these elements is too high, toughness and weldability of the base material 2 is lowered. Therefore, Ca content is 0-0.1%, Mg content is 0-0.1%, Zr content is 0-0.1%, B content is 0-0.1 a%, REM content is 0 to 0.1%. The preferable upper limit of the Ca content is 0.05%. The preferable upper limit of the Mg content is 0.05%. The preferable upper limit of the Zr content is 0.05%. The preferable upper limit of the B content is 0.05%. The preferable upper limit of the REM content is 0.05%. A preferable lower limit of the content of these elements are each 0.0015%. Here, the REM, atomic number 39 No. yttrium (Y), lanthanum atomic number 57th a lanthanoid (La) ~ atomic numbers 71 No. lutetium (Lu) and atomic number 89 No. actinium is actinides is one or more elements selected from the group consisting of (Ac) ~ 103 No. lawrencium (Lr).
[0057]
　[Oxide layer A]
　with respect to the substrate 2 having the chemical composition described above, an oxidation process. By oxidation treatment, the oxide layer A is formed on the surface of the substrate 2. Ferritic heat resistant steels 1 and a oxide layer A of the substrate 2 and the substrate 2 of the surface is used in a high-temperature steam environment. In a high-temperature steam environment, oxide layer A, while maintaining the steam oxidation resistance, changes in the oxide film 3 having excellent heat transfer characteristics. That is, oxide layer A, as a material for forming an oxide film 3 including an oxide layer B and the oxide layer C. Although oxide layer A mechanism is not clear that changes in the oxide film 3, the oxide layer A is presumed to contribute to the formation of the primary oxidation layer C.
[0058]
　The thickness of the oxide layer A is not particularly limited. Be made of any slightly oxidized layer A, the oxide film 3 is formed. Preferably the thickness of the oxide layer A, is 0.2μm or more. In this case, in a high-temperature steam environment, it can be uniformly formed stably the surface of the substrate 2 an oxide film 3. Therefore, it becomes easy to completely cover the substrate 2 with the oxide film 3. As a result, the thermal conductivity increases at the surface of the ferritic heat transfer member 4. More preferably, the thickness of the oxide layer A is 1.0μm or more. The thickness of the upper limit of the oxide layer A is not particularly limited but, in consideration of mass productivity, and preferably 20μm or less.
[0059]
　The thickness of the oxide layer A is obtained by the following method. Cutting perpendicularly the ferritic heat-resistant steel 1 subjected to oxidation treatment described later to the surface. If ferritic heat-resistant steel 1 is a steel pipe, perpendicular to the axial direction of the steel pipe cutting the ferritic heat-resistant steels 1. Relative cross section including the surface of the heat resistant ferritic steel 1, and observed with a JEOL (JEOL Ltd.) manufactured by a scanning electron microscope (SEM). If ferritic heat-resistant steel 1 is a steel pipe, performing SEM observation with respect to a cross section including an inner surface of the steel pipe. Observation magnification is 2000 times. In observation field, ferritic heat-resistant steels 1 surface (ferritic heat-resistant steel 1 in the case of the steel pipe inner surface) to measure the thickness of the oxide layer on. Measurements are made for four cross-sections different ferritic heat-resistant steel 1. Ferritic heat-resistant steel 1 in the case of steel pipes, in 45 ° pitch, measured in 4 places. The average value of the measurement results and the thickness of the oxide layer A.
[0060]
　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 is less than 20% of the oxide layer A, in a high-temperature steam environment, the total content of Cr and Mn in the oxide layer C is below 5%. In this case, the thermal conductivity of the oxide layer C is too high. In this case, steam oxidation resistance of ferritic heat transfer member 4 is lowered. On the other hand, if it exceeds 45% the total content of Cr and Mn in the oxide layer A, in a high-temperature steam environment, the total content of Cr and Mn in the oxide layer C exceeds 30%. In this case, the thermal conductivity of the oxide layer C is too low. As a result, heat transfer characteristics of the ferritic heat transfer member 4 is lowered. Therefore, the chemical composition of the oxide layer A contains 20 to 45% of Cr and Mn in total. The preferable lower limit of the total content of Cr and Mn in the oxide layer A is 22%. The preferable upper limit of the total content of Cr and Mn in the oxide layer A is 40%.
[0061]
　Further the chemical composition of the oxide layer A, Mo, Ta, containing 0.5-10% of one or more members selected from the group consisting of W and Re and (specific oxide layer forming element) in total. If the total content is less than 0.5% of the particular oxide layers forming element of the oxidized layer A, in a high-temperature steam environment, the total content of the specific oxide layer forming element of the oxidized layer C is less than 1%. In this case, the thermal conductivity of the oxide layer C is too low. As a result, heat transfer characteristics of the ferritic heat transfer member 4 is lowered. On the other hand, the total content of the specific oxide layer forming elements oxide layer A if it exceeds 10%, in a high-temperature steam environment, the total content of the specific oxide layer forming element of the oxidized layer C is more than 15%. In this case, the thermal conductivity of the oxide layer C is too high. As a result, steam oxidation resistance of ferritic heat transfer member 4 is lowered. Therefore, the chemical composition of the oxide layer A contains 0.5 to 10% specific oxide layer formed elements in total. The preferable lower limit of the total content of the specific oxide layer forming element is 1%. The preferable upper limit of the total content of the specific oxide layer forming element is 8%.
[0062]
　Cr and Mn in the oxide layer A, and the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) is calculated in the following manner. Cutting perpendicularly the ferritic heat-resistant steel 1 subjected to oxidation treatment described later to the surface. If ferritic heat-resistant steel 1 is a steel pipe, perpendicular to the axial direction of the steel pipe cutting the ferritic heat-resistant steels 1. Relative cross section including the surface of the heat resistant ferritic steel 1, using a JEOL (JEOL Ltd.) manufactured by a scanning electron microscope (SEM), to observe. (If ferritic heat-resistant steel 1 is a steel pipe inner surface) surface of the ferritic heat resistant steels 1 identifies the oxide layer A which appears at a relatively white contrast. In the thickness center of the oxide layer A, performing elemental analysis using a JEOL (JEOL Ltd.) manufactured by a field emission electron probe microanalyzer device (FE-EPMA). Conditions of elemental analysis, detector: 30 mm 2 SD, accelerating voltage: 15kV, measurement time: 60 seconds. Elemental analysis is performed for four cross-sections different ferritic heat-resistant steel 1. If ferritic heat-resistant steel 1 is a steel pipe, with 45 ° pitch, to elemental analysis by four. Among the compositions of each element obtained, the composition excluding the amount of oxygen (O) and carbon (C) and 100%. Calculating the ratio of the total amount of Cr and Mn (mass%). Calculating a ratio of the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) (wt%). The total content of Cr and Mn of the average of four elemental analysis oxide layer A (wt%), and, the total content of the specific oxide layer forming element oxide layer A (Mo, Ta, W and Re) the amount (wt%).
[0063]
　[Ferritic manufacturing method of heat resistant steels 1]
　Production method of ferritic heat-resistant steel 1 according to this embodiment includes a preparation step and oxidation step. The preparation process prepares the base material 2 having the chemical composition described above. Substrate 2 is prepared from a material having a chemical composition described above. Material, slabs produced by continuous casting, may be a bloom and billet. Material may be a billet produced by an ingot-making method. The heating temperature at the time of manufacturing the material for example, is 850 ~ 1200 ° C..
[0064]
　For example, when manufacturing the steel tube, and heating was charged a prepared material into a heating furnace or soaking furnace. The heated material to hot working to produce a base material 2. Hot working example, a Mannesmann process. Mannesmann method, the material, piercing rolling to mother pipe using a piercing mill. Subsequently, a method of drawing and rolling and shaped rolling material using a mandrel mill and a sizing mill. Temperature of hot working example, 850 ~ 1200 ° C.. Thereby producing a substrate 2 as a seamless steel pipe. Preparation of the substrate 2 is not limited to the Mannesmann process, it may be produced by hot extrusion or hot forging the material. Further, with respect to the substrate 2 produced by hot working, may be carried out heat treatment may be carried out cold working. Substrate 2 may be steel. If the base member 2 and the steel sheet, to produce a substrate 2 material as processed steel sheet hot. By welding and processing the steel sheet to the steel pipe may be produced a substrate 2 as a welded steel pipe.
[0065]
　[Oxidation treatment step]
　The oxidation treatment is performed with respect to the above-described substrate 2. Oxidation treatment, CO, CO 2 and N 2 by heating the base material 2 in a gas atmosphere containing. CO / CO gas used for the oxidation treatment 2 ratio is 0.6 or more by volume. CO / CO 2 to ratio by 0.6 or more, it is possible to suppress the preferential oxidation of Fe. As a result, on the surface of the substrate 2, containing 20 wt% or more of Cr and Mn in total, further oxide layer A containing the specific oxide layer forming elements than 0.5 mass% in total is formed . Oxide layer A after the steam oxidation process to be described later, changes in the oxide film 3. CO / CO 2 ratio is not particularly an upper limit, in consideration of the practicality of the operation, 2.0 is preferred.
[0066]
　On the other hand, in the present embodiment, (CO + CO gas used in the oxidation treatment 2 ) / N 2 the ratio is 1.0 or less by volume. (CO + CO 2 ) / N 2 ratio is more than 1.0, the substrate 2 is carburization. Therefore, Cr and Mn in the oxide layer A to form a carbide. As a result, the total content of Cr and Mn in the oxide layer A is less than 20%. (CO + CO 2 ) / N 2 ratio is not particularly provided the lower limit, in consideration of the practicality of the operation, preferably 0.1.
[0067]
　Temperature of the oxidation treatment is 900 ~ 1130 ° C.. If it is less than the oxidation treatment temperature is 900 ° C., since out-diffusion of a specific element of the base material 2 is slow, the total content of the specific oxide layer forming element of the oxidized layer A is too low. In this case, in a high-temperature steam environment, the total content of the specific oxide layer forming element in oxide layer C is too low. As a result, the thermal conductivity of the oxide layer C is too low. As a result, thermal conductivity at the surface of the ferrite based heat transfer member 4 is lowered. Therefore, heat transfer characteristics of the ferritic heat transfer member 4 is lowered. If it exceeds the oxidation treatment temperature is a 1130 ° C., the diffusion of Cr and Mn is high, the total content of Cr and Mn in the oxide layer A exceeds 45%. As a result, in a high-temperature steam environment, the total content of Cr and Mn in the oxide layer C exceeds 30%. In this case, the thermal conductivity of the oxide layer C is too low. As a result, heat transfer characteristics of the ferritic heat transfer member 4 is lowered. Accordingly, the oxidation treatment temperature is 900 ~ 1130 ° C.. A preferred lower limit of the oxidation treatment temperature is 920 ° C., more preferably from 950 ° C.. The preferable upper limit of the oxidation treatment temperature is 1120 ° C..
[0068]
　Oxidation processing time is 1 minute to 1 hour. If the oxidation treatment time is too short, since the occurring enrichment of a particular oxide layer forming elements, the total content of the specific oxide layer forming element of the oxidized layer A exceeds 10%. Therefore, in a high-temperature steam environment, the total content of the specific oxide layer forming element of the oxidized layer C is more than 15%. As a result, the thermal conductivity is too high at the surface of the ferritic heat transfer member 4. On the other hand, if the oxidation treatment time is too long, productivity is lowered. In view of productivity, the oxidation treatment time is preferably short. Oxidation time further if too long, since Fe is oxidized preferentially, the total content of Cr and Mn in the oxide layer A is less than 20%. Therefore, oxidation treatment time is 1 minute to 1 hour. Preferably, the upper limit of the oxidation treatment time is 30 minutes, more preferably from 20 minutes. Preferably, the lower limit of the oxidation treatment time is 3 minutes.
[0069]
　Tempering after the oxidation treatment (low temperature annealing) may be performed. Furthermore, the oxidation treatment may be performed on the entire substrate 2, but the surface of the substrate 2 is in contact with high temperature steam (e.g., the inner surface of the steel pipe) may be carried out only.
[0070]
　Oxidation treatment may be performed once, or may be performed multiple times. After the oxidation treatment, to remove dirt and oil adhering to the surface of the substrate 2, it may be carried out degreasing or cleaning or the like. Be carried out degreasing and cleaning, etc., it does not affect the oxide layer A. Be carried out degreasing and cleaning, etc., it does not affect the subsequent formation of the oxide film 3.
[0071]
　Ferritic heat resistant steels of the present embodiment can be manufactured by the above manufacturing method.
[0072]
　[Ferritic heat transfer member 4]
　ferritic heat transfer member 4 according to this embodiment and a substrate 2 and the oxide film 3. Substrate 2 ferritic heat transfer member 4 is the same as ferritic heat-resistant steels 1 of the substrate 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 substrate 2 of the ferritic heat-resistant steels 1 above. The shape of the ferrite based heat transfer member 4 according to the present embodiment is not particularly limited. Ferritic heat transfer member 4, for example, a tube, a rod or plate material. If having a tubular shape, ferritic heat transfer member 4, for example, is used as a boiler pipe, or the like. Thus preferably, ferritic heat transfer member 4 is a ferritic heat transfer tubes.
[0073]
　Figure 2 is a cross-sectional view of a ferritic heat transfer member 4 according to this embodiment. Referring to FIG. 2, the ferrite based heat transfer member 4 comprises a base material 2, the oxide film 3. Oxide film 3 includes an oxidized layer B and the oxide layer C.
[0074]
　[Oxide film 3
　with respect to the ferritic heat-resistant steel 1 comprising a substrate 2 and the oxide layer A, by performing the steam oxidation process, the oxide film 3 is formed on the surface of the substrate 2. Referring to FIG. 2, the oxide film 3 is an oxide film comprising two layers of oxide layer B and the oxide layer C. Oxide film 3 includes an oxide layer B. Therefore, oxide film 3 has excellent heat transfer characteristics. Oxide film 3 including the oxide layer C. Therefore, oxide film 3 is excellent in both the steam oxidation resistance and heat transfer characteristics. That is, the oxide film 3 is not steam oxidation resistance but also excellent heat transfer characteristics. Oxide layer B is formed on the uppermost layer of ferritic heat transfer member 4. Oxide layer C is disposed between the oxide layer B and the substrate 2. If ferritic heat transfer member 4 of the pipe boiler, oxide layer B is equivalent to the inner surface side of the boiler tubing, the substrate 2 corresponds to the outer surface side of the boiler pipes. In this case, oxide layer B is in contact with high temperature steam.
[0075]
　[Oxide layer B]
　oxide layer B, Fe total 80% by volume% 3 O 4 and Fe 2 O 3 containing. Fe 3 O 4 and Fe 2 O 3 thermal conductivity is high. Thus, the thermal conductivity of the oxide layer B is high, conveys into the interior of the ferritic heat transfer member 4 without decreasing significantly the heat given from the outside of a ferrite based heat transfer member 4. Therefore, it is possible to improve the heat transfer characteristics of the boiler. Preferably, the oxidizing layer B, Fe total 90% by volume% 3 O 4 and Fe 2 O 3 containing. Preferably, Fe oxide layer B 2 O 3 content is less than 20% by volume. More preferably, the oxide layer B is Fe 3 O 4 made of.
[0076]
　The oxide layer B, there are cases where some of the Cr and Mn contained in the base material 2 is contained in a oxide. Cr 2 O 3 is particularly low thermal conductivity. Therefore, Cr oxide layer B 2 O 3 content is preferably as low as. Therefore, preferably, the chemical composition of the oxide layer B, by mass%, containing less than 5% of Cr and Mn in total. More preferably, the chemical composition of the oxide layer B, and mass%, containing 3% or less of Cr and Mn in total.
[0077]
　The preferred thickness of the oxide layer B is 10 ~ 400 [mu] m.
[0078]
　[Oxide layer C]
　oxide layer C is disposed between the oxide layer B and the substrate 2, in contact with the substrate 2.
[0079]
　The chemical composition of the oxide layer C contains more than 5% to 30% of Cr and Mn in total. In the oxidation layer C, Cr and Mn, (Fe, M) 3 O 4 is present as the oxide represented in a chemical formula. Wherein the M, Cr and Mn is substituted. (Fe, M) 3 O 4 and the oxide represented by the chemical formula, Fe 3 O 4 has the same so-called spinel crystal structure, an oxide partially substituted in Cr and Mn of Fe. If the total amount of Cr and Mn contained in the oxide layer C is 5% or less, Fe in the oxidation layer C 3 O 4 and Fe 2 O 3 can not be suppressed ratio. In this case, the thermal conductivity of the oxide layer C is too high. Therefore, a large amount of oxide scale occurs on the inner surface of the ferrite based heat transfer member 4. On the other hand, if 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 is too low. In this case, the heat transfer characteristics of the boiler is reduced. Therefore, the content of Cr and Mn in the oxide layer C is more than 5% to 30% in total. Thus, while maintaining the steam oxidation resistance, it can be controlled thermal conductivity of oxide layer C in an appropriate range. In the oxidation layer C, preferred lower limit of the total content of Cr and Mn is 10%, more preferably 13%. In the oxidation layer C, a preferred upper limit of the total content of Cr and Mn is 28%, more preferably 25%.
[0080]
　Oxide layer C, Mo, Ta, containing 1-15% in total of one or more members selected from the group consisting of W and Re. Specific oxide layer forming element oxide layer C (Mo, Ta, W and Re) total content of is less than 1%, the thermal conductivity of the oxide layer C is too low. On the other hand, if the total content of the specific oxide layer forming element of the oxidized layer C is more than 15%, the thermal conductivity of the oxide layer C is too high. In this case, steam oxidation resistance of ferritic heat transfer member 4 is lowered. Accordingly, the total content of the specific oxide layer forming element of the oxidized layer C is 1 to 15%. The preferable upper limit of the total content of the specific oxide layer forming element in oxide layer C (Mo, Ta, W and Re) is 10%, more preferably 9%. The preferable lower limit of the total content of the specific oxide layer forming element in oxide layer C (Mo, Ta, W and Re) is 1.5%.
[0081]
　Oxide layer C is further an oxide majority has a spinel type crystal structure described above, Cr 2 O 3 is preferably at most 5% by volume. Low Cr thermal conductivity 2 O 3 generation of suppressing the 5 vol% or less, and generating the oxide having a spinel-type crystal structure, can control the heat conductivity of the oxide layer C in an appropriate range. Cr in the oxidation layer C 2 O 3 content of preferably not more than 5 vol%, further preferably 3% by volume or less.
[0082]
　The thermal conductivity of the oxide layer C, 1.2 ~ 3.0 W · m -1 · K -1 preferably controlled in the range of. The thermal conductivity of the oxide layer C · m 1.2 W -1 · K -1 if more, heat conduction from the outside of the ferrite based heat transfer member 4 to the inside of the ferritic heat transfer member 4 is not inhibited, heat transfer characteristics of the boiler is increased and stabilized. On the other hand, the thermal conductivity of the oxide layer C · m 3.0 W -1 · K -1 if less, the heat of high-temperature steam transmitted to the substrate 2 of the surface can be controlled stably. Accordingly, excessive heating of the substrate 2 of the surface is suppressed, the oxidation reaction of the substrate 2 of the surface is suppressed. Therefore, generation of a large amount of oxide scale in the substrate 2 surface is stable suppression. As a result, steam oxidation resistance of ferritic heat transfer member 4 is increased and stabilized. Thus, the thermal conductivity of the oxide layer C, 1.2 ~ 3.0 W · m -1 · K -1 preferably controlled in the range of. In this case, it is easy to improve the steam oxidation resistance of ferritic heat transfer member 4 without impairing the heat transfer characteristics. In the oxidation layer C, the lower limit of the more preferred thermal conductivity · m 1.3 W -1 · K -1 is, more preferably · m 1.4 W -1 · K -1 is. In the oxidation layer C, the upper limit of the more preferred thermal conductivity · m 2.8W -1 · K -1 is, more preferably · m 2.5 W -1 · K -1 is.
[0083]
Fe 　oxide layer B 3 O 4 and Fe 2 O 3 volume ratio is measured by the following method. Cutting perpendicularly the ferritic heat transfer member 4 after subjected to steam oxidation process described below to the surface. If ferritic heat transfer member 4 of the tube, perpendicular to the axial direction of the tube to cut the ferritic heat transfer member 4. To the cross-section (observation surface) including the oxide layer B, performing composition analysis of the oxide layer B using a JEOL (JEOL Ltd.) manufactured by a field emission electron probe microanalyzer device (FE-EPMA). Conditions of composition analysis, the detector: 30 mm 2 SD, accelerating voltage: 15kV, measurement time: 60 seconds. Detects the Fe and O (oxygen) by composition analysis and to identify the region that does not detect Cr. Subsequently, all the specified region Fe 3 O 4 or Fe 2 O 3 to make sure that it has at composition analysis. Then, the intensity of Fe binarization processing in the oxidation layer B of the observation plane. In this case, the extraction target of the gray scale is 1/10 or more of the maximum intensity. Binarization on the black region after reduction, (Fe specified region 3 O 4 and Fe 2 O 3 to make sure that it contains all check regions that have a) the other regions. Second after digitizing process, by measuring the area ratio of the black areas in the oxidation layer B of the observation plane is subtracted from 100%. The resulting area ratio Fe in the oxidation layer B 3 O 4 and Fe 2 O 3 and the volume ratio of.
[0084]
Cr 　oxide layer C 2 O 3 volume ratio is measured by the following method. Cutting perpendicularly the ferritic heat transfer member 4 after subjected to steam oxidation process described below to the surface. If ferritic heat transfer member 4 of the tube, perpendicular to the axial direction of the tube to cut the ferritic heat transfer member 4. To the cross-section (observation surface) including the oxide layer B and the oxide layer C, subjected to SEM observation, it identifies the oxide layer C. In SEM observation, the oxide layer B and the oxide layer C distinguished by the contrast difference obtained by backscattered electron image of SEM (BSE). Oxide layer B contrast is lighter than oxide layer C. Against oxidation layer C, Fe oxide layer B 3 O 4 and Fe 2 O 3 in a similar manner to obtain the volume ratio of, Cr 2 O 3 obtains the volume ratio. That is, for cross-section (observation surface) including the oxide layer C, performing a composition analysis using JEOL (JEOL Ltd.) manufactured by a field emission electron probe microanalyzer device (FE-EPMA). Conditions of composition analysis, the detector: 30 mm 2 SD, accelerating voltage: 15kV, measurement time: 60 seconds. It detects the Cr and O (oxygen) by composition analysis and to identify the area is not detected Fe. Subsequently, all the specified region Cr 2 O 3 be confirmed by composition analysis to have a. Then, the strength of Cr binarization processing in the oxidation layer C of the observation plane. In this case, the extraction target of the gray scale is 1/10 or more of the maximum intensity. Binarization on the black region after reduction, (Cr specified region 2 O 3 to make sure that it contains all check regions that have a) the other regions. Seeking area ratio of black areas after the binarization processing of the observation plane is subtracted from 100%. The resulting area ratio Cr in the oxidation layer C 2 O 3 and the volume ratio of.
[0085]
　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 (Mo, Ta, W and Re) is determined in a manner similar to oxidation layer A. In SEM observation, the oxide layer B and the oxide layer C distinguished by the contrast difference obtained by backscattered electron image of SEM (BSE). Oxide layer B contrast is lighter than oxide layer C. Under the same conditions as in the case of the oxidation layer A, thickness center of oxide layer B, and the elemental analysis in the thickness center of the oxide layer C performed. The composition of each of the obtained element, as in the case of oxide layer A, the total content of Cr and Mn (wt%), and, the total content of the specific oxide layer forming elements (Mo, Ta, W and Re) determine the amount (mass%).
[0086]
　The thermal conductivity of the oxide layer C is determined by the following method. After mechanical removal of the oxide layer B of the ferrite based heat transfer member 4, to measure the bulk density of the oxide layer C comprising a substrate 2, the specific heat and thermal diffusivity. Then, after mechanically removing the oxide layer C, similarly to the base material 2, to measure the bulk density, specific heat and thermal diffusivity. The difference between the respective measured values in terms of the measured value of the oxide layer C, by substituting the following equation can be obtained a thermal conductivity kappa.
　= [rho × kappa C p × D
　, where the bulk density is in the [rho, C p is the specific heat, thermal diffusivity is substituted into D.
[0087]
　A preferred lower limit of the thickness of the oxide layer C is 10 [mu] m.
[0088]
　Thickness of the oxide film 3]
　The thickness of the oxide film 3 is not particularly limited, is preferably thin. When the thin oxide film 3, increased heat transfer characteristics of the ferritic heat transfer member 4. Therefore, it is possible to improve the heat transfer characteristics of the boiler. If ferritic heat transfer member 4 for a long time used, the oxide film 3 becomes thicker. Even when the temperature of the steam oxidation process of the ferrite based heat transfer member 4 is high, the oxide film 3 becomes thicker. By performing the oxidation treatment and steam oxidation process described below, the oxide layer B and the oxide layer C is formed in almost the same thickness. Therefore, if the oxide layer C is thin, the oxide film 3 becomes thinner.
[0089]
　The thickness of the oxide layer B and the oxide layer C is determined in a manner similar to obtain the thickness of the oxide layer A. Preparing a ferritic heat transfer member 4 after subjected to steam oxidation process to be described later. Against the prepared ferrite based heat transfer member 4 performs SEM observation in the same manner as for determining the thickness of the oxide layer A. The oxide layer B and the oxide layer C, distinguished by the contrast difference obtained by reflection electron image of SEM. Oxide layer B contrast is darker than oxide layer C. In a manner similar to the method for determining the thickness of the oxide layer A, obtains the thickness of the oxide layer B and the oxide layer C.
[0090]
　[Ferritic heat transfer member 4 of Production Method]
　method of manufacturing a ferritic heat transfer member 4 according to this embodiment includes a steam oxidation process.
[0091]
　[Steam oxidation treatment step]
　performs steam oxidation process to the ferritic heat-resistant steel having been subjected to oxidation treatment described above. Steam oxidation treatment, a heat resistant ferritic steels, performed by exposure to 500 ~ 650 ° C. in steam. If steam oxidation treatment over 100 hours, the upper limit of the treatment time is not particularly limited. By steam oxidation, oxide layer A is changed to the oxide film 3 including an oxide layer B and the oxide layer C. Thus, the oxide film 3 including the oxide layer B and the oxide layer C, is formed on the substrate 2.
[0092]
　Through the above steps, it can produce a ferritic heat transfer member 4 according to this embodiment. The ferritic heat-resistant steels of the present embodiment by exposing to a high temperature steam environment, the same effect as when subjected to steam oxidation process is obtained. That is, the heat resistant ferritic steel 1 according to the present embodiment if Sarase over 100 hours in a high-temperature steam environment, even without applying the steam oxidation process, ferritic heat transfer member 4 can be produced.
Example
[0093]
　To produce a respective slab having the chemical compositions shown in Table 1, was subjected to oxidation treatment and steam oxidation treatment under the conditions shown in Table 2. Specifically, it was smelted ingots having chemical compositions shown in Table 1. The resulting hot-rolled and cold-rolled to produce a steel sheet was performed for each ingot, as a base material. Obtained a test piece was prepared from each substrate for each test piece, the oxidation treatment was carried out under the conditions shown in Table 2.
[0094]
[Table 1]

[0095]
[Table 2]

[0096]
　Thickness measurement test of the oxide layer A]
　The thickness of the oxide layer A of each specimen was determined in the manner described above. The results are shown in Table 2.
[0097]
　[Content measurement test of metallic elements of the oxide layer A]
　with respect to the cross section of each specimen was determined and the content of each metal element in the manner described above. Oxidation layer A, the total content of Cr and Mn (wt%), and were determined Mo, Ta, a total amount of W and Re (mass%). The results are shown in Table 2.
[0098]
　For each test piece was subjected to steam oxidation treatment under the conditions shown in Table 2. The obtained test pieces were subjected to the following measurement test.
[0099]
[Fe 　oxide layer B 3 O 4 and Fe 2 O 3 volume ratio, and, Cr oxide layer C 2 O 3 volume ratio measurement test]
　with respect to the cross section of each test piece (i.e., the oxide layer B cross section) , Fe in the manner described above 3 O 4 and Fe 2 O 3 calculated on the total volume ratio of the. Furthermore, Cr respect to the cross-section of the oxide layer C 2 O 3 was determined volume ratio of. The results are shown in Table 2.
[0100]
　[Content measurement test of metal elements]
　relative to the cross-section of each specimen was determined and the content of each metal element in the manner described above. Oxidation layer B, determined the total content of Cr and Mn (mass%). The results are shown in Table 2. Oxidation layer C, the total content of Cr and Mn (wt%), and were determined Mo, Ta, a total amount of W and Re (mass%). The results are shown in Table 2.
[0101]
　[Measurement of Thermal Conductivity Test oxide layer C]
　The thermal conductivity of the oxide layer C of each specimen was determined in the manner described above. The results are shown in Table 2.
[0102]
　Thickness measurement test of the oxide layer C]
　The thickness of the oxide layer C of each specimen was determined in the manner described above. The results are shown in Table 2.
[0103]
　[Evaluation Results]
　Table 1 and Table 2, the chemical composition and manufacturing conditions of the steel with test Nos. 1, 3, 6, 9 to 15, and 17 were suitable. Therefore, oxide layer A 20 to 45% total Cr and Mn of these test numbers, and Mo, Ta, W, and one selected from the group consisting of Re or two or more in total 0.5 It was contained to 10 percent. Accordingly, oxide layer B formed on the substrate after the steam oxidation treatment Fe total 80% by volume% 3 O 4 and Fe 2 O 3 contained. Furthermore, Cr + Mn total content of the oxidized layer C is more than 5% and 30%, the total content of the specific oxide layer formed element was 1-15%. As a result, the thermal conductivity of the oxide layer 1.2 ~ 3.0 W C · m -1 · K -1 exhibited becomes excellent thermal conductivity in the range of. Oxide layer C is further thickness becomes 60μm or less, exhibited excellent resistance to steam oxidation.
[0104]
　On the other hand, Test No. 2, although the chemical composition was appropriate, because the oxidation treatment temperature is too high, the total amount of Cr and Mn in the oxide layer A exceeds 45%. Therefore, more than 30% of Cr + Mn amount of oxide layer C, thermal conductivity · m 1.2 W -1 · K -1 becomes less than.
[0105]
　Test No. 4, although the chemical composition was suitable and did not form an oxide layer A without oxidation treatment. Therefore, the thermal conductivity of the oxide layer C · m 1.2 W -1 · K -1 becomes less than. Because the total amount of the specific oxide layer forming element of the oxidized layer C was less than 1%, it is considered to have reduced the thermal conductivity.
[0106]
　Test No. 5, although the chemical composition was appropriate, because the oxidation treatment temperature is too low, the total amount of the specific oxide layer forming element of the oxidized layer A is 0.4%, was too low. Therefore, the total amount of the specific oxide layer forming element of the oxidized layer C is less than 1.0%. As a result, the thermal conductivity of the oxide layer C · m 1.0 W -1 · K -1 a, was too low.
[0107]
　Test No. 7, although the chemical composition was appropriate, CO / CO in the oxidation process 2 ratio was below 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 is 5% or less, the thermal conductivity of the oxide layer C · m 3.0 W -1 · K -1 exceeded. Further, Fe in the oxide layer B 3 O 4 inward flux of oxygen the volume ratio falls below 80% increases, the growth of the oxide layer C is promoted, the thickness of the oxide layer C exceeds 60 [mu] m.
[0108]
　Test No. 8, although the chemical composition was appropriate, oxidation treatment time was too long. Therefore, the total content of Cr and Mn in the oxide layer A is 6.5%, was too low. Therefore, the total content of Cr and Mn in the oxide layer C is 3.2%, was too low. As a result, thermal conductivity 3.2 W · m oxide layer C -1 · K -1 , and the too high. Test No. 8 further, the thickness of the oxide layer C exceeds 60 [mu] m. Presumably because the thermal conductivity of the oxide layer C is too high.
[0109]
　Test No. 16, although the chemical composition was appropriate, oxidation treatment time was too short. Therefore, the total content of the specific oxide layer forming element of the oxidized layer A is 12.9%, was too high. Therefore, the total content of the specific oxide layer forming element of the oxidized layer C is 17.2%, was too high. As a result, the thermal conductivity of the oxide layer C · m 3.5 W -1 · K -1 a, was too high. Test No. 16 In addition, the thickness of the oxide layer C exceeds 60 [mu] m. Presumably because the thermal conductivity of the oxide layer C is too high.
[0110]
　Test No. 18 did not contain any specific oxide layer forming elements. Therefore, the manufacturing method despite which was appropriate, the total content of the specific oxide layer forming element of the oxidized layer A is less than 0.1%, was too low. Therefore, the total content of the specific oxide layer forming element of the oxidized layer C is less than 0.1%, was too low. As a result, the thermal conductivity of the oxide layer C · m 1.1 W -1 · K -1 a, was too low.
[0111]
　Test No. 19, Cr content was too high. Therefore, the manufacturing method despite were appropriate, the total content of Cr and Mn in the oxide layer A is 47.6% was too high. Therefore, the total content of Cr and Mn in the oxide layer C is 56.7% was too high. As a result, thermal conductivity 0.8 W · m oxide layer C -1 · K -1 , and the too low.
[0112]
　Test No. 20, Cr content is too low. Therefore, the manufacturing method despite were appropriate, the total content of Cr and Mn in the oxide layer A is 16.3%, was too low. Therefore, the total content of Cr and Mn in the oxide layer C is 1.3%, was too low. As a result, the thermal conductivity of the oxide layer C · m 3.3 W -1 · K -1 a, was too high. Test No. 20 The thickness of the oxide layer C exceeds 60 [mu] m. Presumably because the thermal conductivity of the oxide layer C is too high.
[0113]
　Test No. 21, the content of the specific oxide layer formed element was too high. Therefore, the total content of the specific oxide layer forming element of the oxidized layer A is 13.9%, was too high. Therefore, the total content of the specific oxide layer forming element of the oxidized layer C is 18.6%, was too high. As a result, the thermal conductivity of the oxide layer C · m 3.8W -1 · K -1 a, was too high. Test No. 21 In addition, the thickness of the oxide layer C exceeds 60 [mu] m. Presumably because the thermal conductivity of the oxide layer C is too high.
[0114]
　Test No. 22, although the chemical composition was appropriate, (CO + CO 2 ) / N 2 exceeds the ratio of 1.0. Therefore, the total content of Cr and Mn in the oxide layer A is 10.6%, was too low. Therefore, the total content of Cr and Mn in the oxide layer C is 4.6%, was too low. As a result, the thermal conductivity of the oxide layer C · m 3.4 W -1 · K -1 a, was too high. Test No. 22 In addition, the thickness of the oxide layer C exceeds 60 [mu] m. Presumably because the thermal conductivity of the oxide layer C is too high.
[0115]
　It has been described an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Accordingly, the present invention is not limited to the embodiments described above, it can be implemented by changing the above-described embodiments without departing from the scope and spirit thereof as appropriate.
DESCRIPTION OF SYMBOLS
[0116]
　1 ferritic heat-resistant steels
　second substrate
　3 oxide film
　4 ferritic heat transfer member
　A oxide layer
　A B oxide layer
　B C oxidized layer C

The scope of the claims
[Requested item 1]
　A substrate,
　and an oxide layer A on the surface of the substrate,
　wherein the substrate is
　a
　mass%,
　C: 0.01 ~ 0.3%, Si: 0.01 ~
　2.0%, Mn:
　~ 2.0% 0.01, P: 0.10% or
　less, S: 0.03% or
　less,
　Cr: 7.0 ~ 14.0%, N: 0.005 ~
　0.15%, sol. Al:
　0.001 - 0.3 Pasento, Mo: 0 to 5.0%, Ta: 0 to 5.0%, W: 0 to 5.0% and Re: from 0 to the group consisting of 5.0% one or more selected:
　from
　0.5 to 7.0% in total, Cu: 0 ~ 5.0%,
　Ni: 0 ~ 5.0%, Co: 0 ~
　5.0%, Ti:
　~
　1.0%
0,
　1.0%, Hf: 0 ~ 1.0%, Ca:
　0 ~ 0.1%, Mg: 0 ~ 0.1
　% Zr: 0
　to 0.1% B: 0 to 0.1 percent, and,
　rare earth elements: 0 contained to 0.1% has a chemical composition the balance being Fe and impurities,
　the oxidation layer A,
　in
　mass%, Cr and Mn: 20 ~ 45% in total,
　and, Mo, Ta, 1 or two or more selected from the group consisting of W and Re: 0.5 ~ 10% in total ,
　including a chemical composition containing, Blow Door heat-resistant steel.
[Requested item 2]
　A ferritic heat-resistant steel according to claim 1,
　the chemical composition of the base
　material,
　Cu: 0.005 ~ 5.0%, Ni: 0.005 ~ 5.0%,
　and, Co: 0. one or containing two or more, heat resistant ferritic steels are selected from the group consisting of from 005 to 5.0%.
[Requested item 3]
　A ferritic heat-resistant steel according to claim 1 or claim 2,
　the chemical composition of the
　substrate,
　Ti: 0.01 ~ 1.0%, V: 0.01 ~
　1.0%, Nb: 0.01 to 1.0%,
　and, Hf: containing one or two or more selected from the group consisting of 0.01 to 1.0%, ferritic heat resistant steel.
[Requested item 4]
　A ferritic heat-resistant steel according to any one of claims 1 to 3,
　the chemical composition of the
　substrate, Ca:
　0.0015 ~ 0.1%, Mg: 0.0015 ~ 0.
　% 1,
　Zr: 0.0015 ~ 0.1%, B: 0.0015 ~ 0.1%, and,
　rare earth elements: 0.0015 to 1 kind or two kinds selected from the group consisting of 0.1% containing more, ferritic heat resistant steels.
[Requested item 5]
　A substrate having a chemical composition according to any one of claims 1 to 4,
　and an oxide film on the surface of said substrate,
　said oxide film,
　Fe total 80% by volume% 3 O 4 and Fe 2 O 3 and the oxide layer B containing,
　and a oxide layer C which is located between the oxide layer B and the base material,
　the chemical composition of the oxide layer C,
　by mass%,
　Cr and Mn: 5% ultra to 30% in total,
　and, Mo, Ta, 1 or two or more selected from the group consisting of W and Re: containing 1 to 15% in total, ferritic heat transfer Element.
[Requested item 6]
　A ferritic heat transfer member according to claim 5,
　wherein the chemical composition of the oxide layer B,
　by mass%,
　Cr and Mn: containing less than 5% in total, ferritic heat transfer member.
[Requested item 7]
　A ferritic heat transfer member according to claim 5 or claim 6,
　wherein the oxide layer C is
　5% or less Cr by volume% 2 O 3 containing, ferritic heat transfer member.