Heat-resistant steel for use in high-temperature hydrogen atmosphere

Abstract

To produce a heat resistant steel used in a high temp. hydrogen atmosphere.SOLUTION: The heat-resistant steel for use in a high-temperature hydrogen atmosphere according to the present invention contains, by mass%, C: 0.1% to 0.6%, Si: 0.5% to 2.5%, Mn: 0.1% to 2.0%, P: 0.05% or less, S: 0.05% or less, Ni: 40.0% to 60.0%, Cr: 20.0% to 50.0%, and a balance of Fe and impurities, and may optionally further contain Mo: 0.01% to 7.0% and / or W: 0.01% to 7.0% or less, optionally Nb: 0.01% to 3.0%, and optionally Ti: 0.05% to 1.0%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a heat-resistant steel for use in a high-temperature hydrogen atmosphere, such as a hydrogen transport pipe or a heating pipe. [Background technology]

[0002] With the expansion of hydrogen use, attention has been drawn to the effect of reducing greenhouse gases such as CO2 through reduction reactions. For example, in the pig iron making process, coke is used as a reducing agent when reducing iron oxide to metallic iron, and CO generated by the combustion of the coke reduces the iron oxide to produce CO2. For this reason, Patent Document 1 proposes that a reducing gas containing hydrogen is injected into a blast furnace to reduce the iron oxide, thereby producing H2O as a product of the reduction, thereby reducing CO2 emissions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-144966 Summary of the Invention [Problem to be solved by the invention]

[0004] Hydrogen gas is supplied to the blast furnace through hydrogen transfer pipes, heating pipes, heat transfer pipes, etc. (hereinafter referred to as "hydrogen heating pipes"). For example, the concentration of hydrogen gas flowing inside the hydrogen heating pipe is 70% by volume or more, and the external environment is COG gas (coke oven gas, e.g., H2: 50% by volume, CH4: 30% by volume, CO: 10% by volume). To prevent a temperature drop inside the blast furnace due to the supply of hydrogen gas, the temperature of the hydrogen gas must be 600°C or higher. Specifically, hydrogen gas that is produced in another process and in a heated state is heated in the hydrogen heating pipe and then supplied to the blast furnace.

[0005] The temperature of the hydrogen gas supplied to the blast furnace is preferably above 1000°C. In this case, the temperature of the outer surface of the hydrogen heating tube and the temperature of the atmosphere on the outer surface of the tube will exceed 1000°C. However, there are currently no examples of hydrogen heating tubes being used in an environment where the temperature of the outer surface of the tube exceeds 1000°C.

[0006] In order to be used in a high-temperature, high-concentration hydrogen atmosphere, the hydrogen heating tube must be made of a steel material that has low hydrogen permeability, high creep properties, high-temperature strength, and low hydrogen corrosion resistance.

[0007] High hydrogen permeability reduces the amount of hydrogen during use, resulting in a lower yield. High creep properties are necessary to avoid fracture when used for long periods in high-temperature hydrogen atmospheres exceeding 600°C, and high-temperature strength is required for structural strength, as steel is used in high-temperature hydrogen atmospheres exceeding 600°C. Furthermore, in high-temperature hydrogen atmospheres exceeding 600°C, hydrogen reacts with carbon in the steel to produce methane (CH4), a phenomenon known as hydrogen erosion. The methane generated by this hydrogen erosion turns into gas, forming voids in the steel and causing deterioration of the steel.

[0008] An object of the present invention is to provide a heat-resistant steel for use in a high-temperature hydrogen atmosphere. [Means for solving the problem]

[0009] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is In mass%, C: 0.1% to 0.6%, Si: 0.5% to 2.5%, Mn: 0.1% to 2.0%, P: 0.05% or less, S: 0.05% or less, Ni: 40.0%~60.0%, Cr: 20.0% to 50.0%, and The balance is Fe and impurities, optionally, Mo: 0.01% to 7.0% and / or W: 0.01% to 7.0% or less; Optionally, Nb: 0.01% to 3.0% Optionally, Ti: 0.05% to 1.0% It may further include:

[0010] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is C: 0.2%~0.5%, Si: 1.8% to 2.5%, Mn: 0.1% to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 45.0%~50.0%, Cr: 40.0%~45.0%, W: 0.5% to 2.0% and moreover, Zr: Can contain 0.1% or less.

[0011] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is C: 0.4%~0.6%, Si: 0.5% to 1.5%, Mn: 0.1% to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 45.0%~50.0%, Cr: 25.0%~30.0%, W: 4.0% to 6.0% is.

[0012] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is C: 0.4%~0.6%, Si: 0.5% to 2.0%, Mn: 0.1% to 2.0%, P: 0.03% or less, S: 0.03% or less, Ni: 40.0%~46.0%, Cr: 30.0%~35.0%, Mo: 0.01% to 7.0% Ti: 0.05% to 0.5% moreover, Al: 0.5% or less, Pb: 0.01% or less, Sn: 0.01% or less, Zr: 0.01% or less may include:

[0013] The hydrogen heating tube of the present invention is It can be made from the heat-resistant steel used in a high-temperature hydrogen atmosphere described above.

[0014] The hydrogen heating tube is a centrifugally cast tube, The secondary dendrite arm spacing (DAS) on the outer circumferential surface may be 35.0 μm or less.

[0015] The secondary dendrite arm spacing (DAS) of the outer peripheral surface is preferably 90% or less of the secondary dendrite arm spacing (DAS) of the inner peripheral surface. [Effects of the Invention]

[0016] The heat-resistant steel for use in a high-temperature hydrogen atmosphere according to the present invention has low hydrogen permeability, high creep properties, high-temperature strength, and low hydrogen corrosion resistance, making it suitable for hydrogen heating pipes used for transporting, heating, heat exchange, etc. of high-temperature hydrogen gas. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram of a hydrogen permeation test device. [Figure 2] FIG. 2 is a microphotograph of the inner peripheral surface of the test piece 1. [Figure 3] FIG. 3 shows the measurement results of the secondary dendrite arm spacing (DAS) on the inner peripheral surface of the test piece 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail. Unless otherwise specified, "%" means % by mass.

[0019] The present invention relates to a heat-resistant steel for use in a high-temperature hydrogen atmosphere, which refers to an environment in which the steel comes into contact with hydrogen gas at a temperature of, for example, 600°C or higher, preferably 800°C or higher, and desirably 1000°C or higher but 1200°C or lower.

[0020] The heat-resistant steel for use in a high-temperature hydrogen atmosphere according to the present invention is suitable for use in hydrogen gas transfer pipes, heating pipes, heat transfer pipes, heat exchangers, etc. (hereinafter referred to as "hydrogen heating pipes") used to supply hydrogen gas as a reducing agent to a blast furnace. Of course, the use of the heat-resistant steel is not limited to this. For example, the pressure of the hydrogen gas flowing through the hydrogen heating pipe is 1.0 MPa or less.

[0021] The heat-resistant steel for use in a high-temperature hydrogen atmosphere of the present invention can be obtained, for example, by casting the following elements. The details will be described later, but the casting is, for example, centrifugal casting.

[0022] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is In mass%, C: 0.1% to 0.6%, Si: 0.5% to 2.5%, Mn: 0.1% to 2.0%, P: 0.05% or less, S: 0.05% or less, Ni: 40.0%~60.0%, Cr: 20.0% to 50.0%, and The balance consists of Fe and impurities.

[0023] The reasons for limiting the ingredients are as follows:

[0024] C: 0.1% to 0.6% C has the effect of increasing high-temperature creep rupture strength. It also combines with Ti, Nb, Cr, etc. to form carbides, which have the effect of increasing high-temperature strength. Furthermore, carbides are said to reduce the amount of hydrogen that permeates through grain boundaries. To achieve these effects, at least 0.1% C is included. However, if the content is too high, primary carbides of Cr7C3 tend to form widely, and secondary carbides precipitate excessively during heat treatment, resulting in a decrease in ductility and toughness. For this reason, the upper limit is set at 0.6%.

[0025] Si: 0.5% to 2.5% Silicon acts as a deoxidizer, improving the cleanliness and fluidity of the molten metal, and forms oxides to improve corrosion resistance, such as oxidation resistance. A content of 0.5% or more is required. However, excessive silicon content can lead to the precipitation of low-melting-point compounds, resulting in reduced high-temperature creep rupture strength, ductility, toughness, and weldability. Therefore, the upper limit of the silicon content is set at 2.5%.

[0026] Mn: 0.1% to 2.0% Mn acts as a deoxidizer to increase the cleanliness of the molten metal, fix S in the molten metal, and improve weldability and ductility. A content of 0.1% or more is required. However, excessive addition of Mn reduces high-temperature creep rupture strength and oxidation resistance. Therefore, the upper limit of Mn content is set at 2.0%.

[0027] P: 0.05% or less, S: 0.05% or less P and S are impurities that are inevitably mixed in during melting, and a content of 0.05% or less is acceptable. The amount of these impurities mixed in is preferably small, and even zero is acceptable.

[0028] Ni: 40.0% to 60.0% Ni is an element necessary for stabilizing the austenite metal structure of heat-resistant steel. Ni also improves heat resistance, such as high-temperature creep rupture strength and high-temperature strength, and adding it as a base metal component in place of Fe can improve heat resistance. Furthermore, when added in combination with Cr, or selectively with W, Ti, or Zr, Ni contributes to improving high-temperature strength and oxidation resistance. It is also known as an element that contributes to improving nitriding resistance. For this reason, Ni should be contained in an amount of at least 40.0%. However, adding excessive Ni saturates its effects and is also economically disadvantageous, so the upper limit is set at 60.0%.

[0029] Cr: 20.0% to 50.0% Cr improves high-temperature strength, oxidation resistance, and heat resistance. Cr also combines with C to form carbides, which have the effect of increasing high-temperature creep rupture strength, and also forms oxides, which have the effect of increasing corrosion resistance. Therefore, the Cr content is set at 20.0% or more. However, excessive addition of Cr leads to a decrease in ductility, so the upper limit is set at 50.0%.

[0030] Remainder: Fe and impurities The balance is Fe and impurities. Impurities include those that are inevitably mixed in during melting. Fe is an element that promotes the penetration and diffusion of nitrogen into the material, and the less Fe there is, the better for nitriding resistance. Although it is the balance, it is desirable that Fe be 40.0% or less.

[0031] The heat-resistant alloy having the above-described structure may selectively contain the following elements.

[0032] W: 0.01% to 7.0% and / or Mo: 0.01% to 7.0% W and Mo are elements that dissolve in the base metal, strengthen the austenite phase of the base metal, and have similar properties that improve creep rupture strength. Either one or both can be selectively added. The lower limit of each content is 0.01%. However, excessive W and Mo content reduces ductility and carburization resistance. Furthermore, excessive W and Mo content reduces the oxidation resistance of the base metal, so the upper limit is set at 7.0% for each.

[0033] Nb: 0.01% to 3.0% Nb is an element that easily forms carbides and contributes to improving high-temperature creep rupture strength and high-temperature tensile strength. Therefore, it is preferable to selectively add Nb. The lower limit of Nb is preferably 0.01%. On the other hand, excessive addition of Nb leads to a decrease in creep rupture strength and an increase in creep elongation, so the upper limit is set to 3.0%, preferably 1.5%.

[0034] Ti: 0.05% to 1.0% Ti is added to form carbides and improve high-temperature creep strength and high-temperature strength. Similarly to Cr, Ti is expected to pin nitrogen atoms by forming nitrides, suppressing the growth of nitride layers due to nitrogen diffusion. To achieve these effects, Ti can be selectively added. A suitable lower limit for Ti is 0.05%. However, Ti is also an element that readily bonds with N, which can lead to poor castability due to a decrease in the alloy's fluidity and potentially make machining difficult. Therefore, if Ti is added, its upper limit should be 1.0%, preferably 0.5%.

[0035] Zr: 0.1% or less Like Ti, Zr is selectively added to improve oxidation resistance and high-temperature compressive creep strength. Zr also has a denitrification effect. However, Zr reduces hot plastic workability (e.g., bending), so if added, the upper limit is set at 0.1%.

[0036] In addition, the following elements can be selectively added to increase the cleanliness of the steel material and, in particular, to increase creep rupture strength, tensile strength, and ductility at high temperatures. These elements are trace elements that are inevitably mixed in during melting, and excessive addition may degrade the properties of the heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention. Therefore, the upper limits of the trace elements are set as follows: Cu:0.05% or less Co:0.05% or less V:0.05% or less Al: 0.05% or less N: 0.05% or less O: 0.05% or less Pb: 0.01% or less Sn: 0.01% or less Zn: 0.01% or less La: 0.01% or less Ce: 0.01% or less As: 0.01% or less Bi:0.01% or less Se: 0.01% or less Sb: 0.01% or less B: 0.01% or less

[0037] As a specific embodiment, the heat-resistant steel used in a high-temperature hydrogen atmosphere of the present invention is C: 0.2%~0.5%, Si: 1.8% to 2.5%, Mn: 0.1% to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 45.0%~50.0%, Cr: 40.0%~45.0%, W: 0.5% to 2.0%, The balance is Fe and impurities, moreover, Zr: Contains 0.1% or less.

[0038] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is C: 0.4%~0.6%, Si: 0.5% to 1.5%, Mn: 0.1% to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 45.0%~50.0%, Cr: 25.0%~30.0%, W: 4.0% to 6.0% The balance consists of Fe and impurities.

[0039] The heat-resistant steel used in the high-temperature hydrogen atmosphere of the present invention is C: 0.4%~0.6%, Si: 0.5% to 2.0%, Mn: 0.1% to 2.0%, P: 0.03% or less, S: 0.03% or less, Ni: 40.0%~46.0%, Cr: 30.0%~35.0%, Mo: 0.01% to 7.0% Ti: 0.05% to 0.5%, The balance is Fe and impurities, moreover, Al: 0.5% or less, Pb: 0.01% or less, Sn: 0.01% or less, Zr: 0.01% or less Includes:

[0040] The heat-resistant steel of the present invention used in high-temperature hydrogen atmospheres has low hydrogen permeability. This is because the Si, Cr, Fe, and Al contained in the steel form oxides, and because Cr, Ti, Nb, W, and other elements form carbides, and the base material can be controlled to have an austenitic structure. This makes it possible to suppress hydrogen permeation and reduce hydrogen permeability compared to conventional materials such as SUS310S.

[0041] Furthermore, the heat-resistant steel of the present invention for use in a high-temperature hydrogen atmosphere has excellent creep properties. This is due to the fact that the heat-resistant steel of the present invention is a casting with a high Ni and Cr content, that Ti, Nb, W, etc. form carbides, and that the upper limits of unavoidable trace elements are limited. This allows the steel to have high high-temperature creep rupture strength in high-temperature environments of 600°C, preferably 800°C or higher, and desirably 1000°C or higher.

[0042] The heat-resistant steel of the present invention for use in a high-temperature hydrogen atmosphere has high high-temperature strength. This is due to the fact that the heat-resistant steel of the present invention is a cast product with a high Ni and Cr content, that Ti, Nb, W, etc. form carbides, and that the upper limits of unavoidable trace additive elements are limited. This allows the steel to have high high-temperature strength in high-temperature environments of 600°C, preferably 800°C or higher, and desirably 1000°C or higher.

[0043] The heat-resistant steel of the present invention for use in high-temperature hydrogen environments exhibits low hydrogen corrosion. This is due to the ability to control the base material to an austenitic structure, the fact that C forms more stable carbides with Cr, Ti, Nb, W, etc., and the fact that the primary carbides formed during casting have a composition that promotes the precipitation of secondary carbides in high-temperature environments. This formation of stable carbides in the steel inhibits reactions with the absorbed hydrogen and prevents void nucleation. Furthermore, the dispersed stable aged carbides provide a pinning effect for dislocations based on the absorbed hydrogen, inhibiting void formation due to dislocation movement and inhibiting the progression of creep deformation and creep rupture. This reduces hydrogen corrosion.

[0044] The heat-resistant steel of the present invention to be used in a high-temperature hydrogen atmosphere is preferably produced into a tubular shape by casting. Among the casting methods, centrifugal casting is preferable to static casting, as described below. The casting conditions are adjusted to control the size of the microstructure, thereby reducing hydrogen permeation.

[0045] In the present invention, attention is focused on dendrites as the microstructure, and the distance between the centers of the branching secondary dendrite arms that grow from the sides of the primary dendrite arms is controlled.

[0046] Specifically, the secondary dendrite arm spacing (DAS) on the outer peripheral surface of the hydrogen heating tube (centrifugally cast tube) obtained by centrifugal casting is controlled to be 35.0 μm or less. More preferably, the secondary dendrite arm spacing (DAS) on the outer peripheral surface is 90% or less of the secondary dendrite arm spacing (DAS) on the inner peripheral surface. For example, by increasing the wall thickness of the hydrogen heating tube, the difference in secondary dendrite arm spacing (DAS) between the outer peripheral surface and the inner peripheral surface can be increased.

[0047] As described above, controlling the secondary dendrite arm spacing (DAS) can suppress hydrogen permeation in high-temperature environments. This is because hydrogen has a small atomic radius and a large diffusion coefficient. Therefore, hydrogen permeates metals and leaks out of the tube, especially at high temperatures. During this process, hydrogen passes through grain boundaries in the steel. The inventors discovered that the fewer grain boundaries there are in the steel, i.e., the larger the structure, the greater the hydrogen permeation rate. The inventors also discovered that the more obstacles, such as carbides, present at the grain boundaries, the less hydrogen can permeate. Therefore, in the present invention, hydrogen permeation is reduced by suppressing dendrite growth on the outer surface of a hydrogen heating tube, reducing the structure, and increasing the number of grain boundaries.

[0048] For the above-mentioned purposes, it is preferable to perform casting by centrifugal casting, which has a higher cooling capacity for the molten metal than static casting. Furthermore, in centrifugal casting, it is preferable to use a metal frame as the centrifugal casting mold, which has a higher cooling capacity than a sand mold. In centrifugal casting, by specifying the thickness of the centrifugal casting mold, the type of coat, and the coat thickness according to the casting weight and the product wall thickness, it is possible to suppress the microstructure of the outer peripheral surface of the hydrogen heating tube, i.e., the growth of dendrites, thereby making the structure smaller and increasing the number of grain boundaries. [Example]

[0049] Hydrogen heating tubes (test tubes) were manufactured with the alloy compositions (units: mass %, balance: Fe and impurities) shown in Table 1. All of the inventive examples were centrifugal cast, while the comparative examples were forged. Hydrogen permeation tests were conducted on Inventive Example 1 and Comparative Example 1, and secondary dendrite arm spacing (DAS) measurements were conducted on Inventive Examples 1 to 3. In Table 1, "zero" means no content or a content that was too small to be measured.

[0050] [Table 1]

[0051] <Hydrogen permeation test> The hydrogen permeation test was performed using a hydrogen permeation test apparatus 10 shown in Figure 1. The hydrogen permeation test apparatus 10 consisted of a tubular furnace 11 (ARF-50K, manufactured by Asahi Rika Seisakusho Co., Ltd.) with a double-walled tube 12 (a 32A Sch20 tube (450 mm) made of SUS304 with a flange welded) placed inside, and a tubular furnace heater 13 (260 mm wide) placed around the outer periphery of the double-walled tube 12. Argon gas was supplied to the double-walled tube 12 from an argon gas cylinder 14 via a flow controller 15 (mass flow controller, 8500MC, manufactured by Kofloc Corporation). The argon gas used was argon gas with a purity of 99.999% or higher, manufactured by Taiyo Nippon Sanso JFP Corporation. In addition to a test tube 16 (described below), a thermocouple 17 (Sheath K, manufactured by Okazaki Seisakusho Co., Ltd.) for temperature measurement was also placed inside the double-walled tube 12.

[0052] Test tubes 16 (diameter 20 mm, length 250 mm, thickness 5 mm) of Invention Example 1 and Comparative Example 1 were inserted into the double pipe 12. The test tubes 16 were configured so that one end was closed by welding a flange, and the closed end was inserted 100 mm into the double pipe 12. Hydrogen gas was supplied from a hydrogen gas cylinder 18 into the open end of the test tube 16 while the pressure was measured with a pressure gauge 19 (IPT general pressure gauge manufactured by Daiichi Keiki Seisakusho Co., Ltd.). The hydrogen gas used was manufactured by Taiyo Nippon Sanso JFP Corporation and had a purity of 99.999% or higher.

[0053] Argon gas was sealed inside the double tube 12, and hydrogen gas was introduced into the test tube 16 so that the pressure gauge 19 reached 0.1 MPa, while the tubular furnace heater 13 was operated. The test was carried out with two patterns, with the thermocouple 17 detecting temperatures of 800°C and 1000°C. The hydrogen gas leaking into the double tube 12 was measured using a gas chromatograph 20 (Shimadzu Corporation: GC-2014AT) and recorded on a recorder (not shown, Hioki E.E. Corporation: LR8410), and the hydrogen permeability (Ncc·mm / cm 2 The results are shown in Table 2.

[0054] [Table 2]

[0055] Referring to Table 2, hydrogen gas permeation was confirmed in both Invention Example 1 and Comparative Example 1, and the higher the temperature, the higher the hydrogen permeability. Comparing Invention Example 1 and Comparative Example 1, it can be seen that Invention Example 1 was able to reduce hydrogen gas permeation by approximately 30% compared to Comparative Example 1.

[0056] <Secondary dendrite arm spacing (DAS) measurement> Next, the secondary dendrite arm spacing (DAS) was measured for Inventive Examples 1 to 3. For Inventive Examples 1 to 3, hydrogen gas supply pipes with an outer diameter of 65 mm and a thickness of 15 mm were centrifugal cast, and the resulting hydrogen gas supply pipes were cut in the thickness direction, embedded in resin, polished, mirror-finished, etched, washed with water, and dried to obtain Test Specimens 1 to 3. Figure 2 is a microphotograph of the inner peripheral surface of Test Specimen 1. Referring to the figure, dendrites and carbides around the dendrites can be observed.

[0057] The obtained test specimens were loaded into the image analysis software WinROOF Material Option according to the secondary branch method described at https: / / www.shodensha-inc.co.jp / solution / das / . Next, a measurement line was drawn with the mouse at the location of the arm group where the arm spacing measurement was to be performed, and the intersection point of the measurement line and the secondary dendrite arm was specified. The distance between the intersection points (symbol L) was then measured as the secondary dendrite arm spacing (DAS), as shown in Figure 3. In the square frame in Figure 3, "L + number" indicates the measurement point, and the following "number + μm" is the distance between the intersection points, which indicates the secondary dendrite arm spacing (DAS).

[0058] The secondary dendrite arm spacing (DAS) (unit: μm) was measured at 30 locations on the outer surface, middle, and inner surface of each test piece, and the average and overall average were calculated. The results are shown in Table 3.

[0059] [Table 3]

[0060] Referring to Table 3, the secondary dendrite arm spacing (DAS) on the outer peripheral surface was smaller than that on the middle and inner peripheral surfaces. Specifically, the secondary dendrite arm spacing (DAS) on the outer peripheral surface was 35.0 μm or less and 90% or less of the secondary dendrite arm spacing (DAS) on the inner peripheral surface.

[0061] In particular, the secondary dendrite arm spacing (DAS) on the outer periphery of all test specimens is small, meaning there are many grain boundaries, i.e., the structure is small, which can reduce hydrogen permeation. Also, the secondary dendrite arm spacing (DAS) on the outer periphery is small, and there are many obstacles, including carbides, at the grain boundaries, which can reduce the amount of hydrogen permeation.

[0062] The above description is for the purpose of explaining the present invention, and should not be construed as limiting the invention described in the claims or narrowing its scope. Furthermore, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications are possible within the technical scope described in the claims. [Explanation of symbols]

[0063] 10 Hydrogen permeation test equipment 11 Tube furnace 12 double tube 13 Tubular furnace heater 16 test tubes L Secondary Dendrite Arm Spacing (DAS)

Claims

1. In mass%, C: 0.1% to 0.6%, Si: 0.5% to 2.5%, Mn: 0.1% to 2.0%, P: 0.05% or less, S: 0.05% or less, Ni: 40.0% to 60.0%, Cr: 20.0% to 50.0%, and The balance is Fe and impurities, optionally, Mo: 0.01% to 7.0% and / or W: 0.01% to 7.0% or less; optionally, Nb: 0.01% to 3.0%; optionally, Ti: 0.05% to 1.0%; further comprising: Heat-resistant steel used in high-temperature hydrogen atmospheres.

2. C: 0.2% to 0.5%, Si: 1.8% to 2.5%, Mn: 0.1% to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 45.0% to 50.0%, Cr: 40.0% to 45.0%, W: 0.5% to 2.0% and moreover, Zr: 0.1% or less; The heat-resistant steel for use in a high-temperature hydrogen atmosphere according to claim 1.

3. C: 0.4% to 0.6%, Si: 0.5% to 1.5%, Mn: 0.1% to 1.5%, P: 0.03% or less, S: 0.03% or less, Ni: 45.0% to 50.0%, Cr: 25.0% to 30.0%, W: 4.0% to 6.0% That is, The heat-resistant steel for use in a high-temperature hydrogen atmosphere according to claim 1.

4. C: 0.4% to 0.6%, Si: 0.5% to 2.0%, Mn: 0.1% to 2.0%, P: 0.03% or less, S: 0.03% or less, Ni: 40.0% to 46.0%, Cr: 30.0% to 35.0%, Mo: 0.01% to 7.0%, Ti: 0.05% to 0.5%; moreover, Al: 0.5% or less, Pb: 0.01% or less, Sn: 0.01% or less, Zr: 0.01% or less Including, The heat-resistant steel for use in a high-temperature hydrogen atmosphere according to claim 1.

5. A heat-resistant steel for use in a high-temperature hydrogen atmosphere according to any one of claims 1 to 4, Hydrogen heating tube.

6. It is a centrifugally cast pipe, The secondary dendrite arm spacing (DAS) of the outer peripheral surface is 35.0 μm or less. The hydrogen heating tube according to claim 5.

7. The secondary dendrite arm spacing (DAS) of the outer peripheral surface is 90% or less of the secondary dendrite arm spacing (DAS) of the inner peripheral surface. The hydrogen heating tube according to claim 6.

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