Heat-resistant steel used in high-temperature hydrogen atmosphere

Abstract

The present invention provides heat-resistant steel for use in a high-temperature hydrogen atmosphere. This heat-resistant steel for use in a high-temperature hydrogen atmosphere comprises, in mass%, 0.1-0.6% C, 0.5-2.5% Si, 0.1-2.0% Mn, not more than 0.05% P, not more than 0.05% S, 40.0-60.0% Ni, and 20.0-50.0% Cr, with the balance being Fe and impurities. The heat-resistant steel can selectively comprise 0.01-7.0% Mo and / or not more than 0.01-7.0% W, can selectively comprise 0.01-3.0% Nb, and can selectively comprise 0.05-1.0% Ti.

Description

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

[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.

[0002] With the expansion of hydrogen use, CO ２ For example, in the iron-making process, coke is used as a reducing agent when iron oxide is reduced to metallic iron, and the CO generated by the combustion of coke reduces the iron oxide to CO ２ Therefore, in Patent Document 1, a reducing gas containing hydrogen is blown into a blast furnace to reduce iron oxide, and the product of the reduction is converted into H ２ As O, CO ２ We are working to reduce emissions.

[0003] Japanese Patent Application Laid-Open No. 2022-144966

[0004] Hydrogen gas is supplied to the blast furnace through a hydrogen transfer pipe, a heating pipe, a heat transfer pipe, etc. (hereinafter referred to as "hydrogen heating pipe"). 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, for example, H ２ : 50% by volume, CH ４ % and CO: 10% by volume. In order to prevent a temperature drop inside the blast furnace due to the supply of hydrogen gas, the temperature of the hydrogen gas is required to be 600°C or higher. Specifically, hydrogen gas that has been produced in another process and is in a heated state is heated in a hydrogen heating tube 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 use 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] This is because high hydrogen permeability reduces the amount of hydrogen during use, resulting in a decrease in yield. High creep properties are necessary to avoid fracture when used for long periods in a high-temperature hydrogen atmosphere exceeding 600°C, and high-temperature strength is required as a structural member since the steel is used in a high-temperature hydrogen atmosphere exceeding 600°C. Furthermore, in a high-temperature hydrogen atmosphere exceeding 600°C, hydrogen reacts with carbon in the steel to form methane (CH ４ This phenomenon is called hydrogen erosion. Methane generated by this hydrogen erosion turns into gas, forming voids in the steel, which leads to 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.

[0009] The heat-resistant steel for use in a high-temperature hydrogen atmosphere of the present invention consists, in mass%, of 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 being Fe and impurities, and may further contain, optionally, 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%.

[0010] The heat-resistant steel used in a high-temperature hydrogen atmosphere of the present invention contains 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 can further contain Zr: 0.1% or less.

[0011] The heat-resistant steel used in a high-temperature hydrogen atmosphere of the present invention has the following composition: 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%.

[0012] The heat-resistant steel used in a high-temperature hydrogen atmosphere of the present invention contains 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%, and can further contain Al: 0.5% or less, Pb: 0.01% or less, Sn: 0.01% or less, and Zr: 0.01% or less.

[0013] The hydrogen heating tube of the present invention 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, and the secondary dendrite arm spacing (DAS) of the outer circumferential surface can 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.

[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.

[0017] Fig. 1 is an explanatory diagram of a hydrogen permeation test apparatus. Fig. 2 is a microphotograph of the inner peripheral surface of a test piece 1. Fig. 3 shows the measurement results of the secondary dendrite arm spacing (DAS) of the inner peripheral surface of the test piece 1.

[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 for use in a high-temperature hydrogen atmosphere of the present invention contains, 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 being 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, C is contained in an amount of at least 0.1%. However, if the content is too high, Cr ７ C ３ Primary carbides are likely to be widely formed, and secondary carbides are excessively precipitated during heat treatment, resulting in a decrease in ductility and toughness. For these reasons, the upper limit is set to 0.6%.

[0025] Si: 0.5% to 2.5% Si acts as a deoxidizer to improve the cleanliness and fluidity of the molten metal, and forms oxides to improve corrosion resistance such as oxidation resistance. The content of 0.5% or more is required. However, excessive addition of Si leads to the precipitation of low-melting-point compounds, resulting in a decrease in high-temperature creep rupture strength, ductility, toughness, and weldability. For this reason, the upper limit of the Si content is set to 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. 0.1% or more of Mn is included. However, excessive addition of Mn leads to a decrease in high-temperature creep rupture strength and a decrease in oxidation resistance. Therefore, the upper limit of Mn is set to 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 mixing amount of 0.05% or less is acceptable. The amount of these impurities mixed in is preferably small, and may be zero.

[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 Ni as a base metal component in place of Fe can improve heat resistance. Ni also contributes to improving high-temperature strength and oxidation resistance when added in combination with Cr or selectively added W, Ti, or Zr. Ni 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 has the effect of increasing corrosion resistance by forming oxides. Therefore, Cr should be contained in an amount of 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] The balance is Fe and impurities. The impurities include impurities that are inevitably mixed in during melting. Fe is an element that promotes the penetration and diffusion of nitrogen in the material, and the less Fe, the better for nitriding resistance. Although it is the balance, Fe is preferably 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 material, strengthen the austenite phase of the base material, and have equivalent properties of improving creep rupture strength. Either one or both can be selectively included. The lower limit of each content is 0.01%. However, excessive inclusion of W or Mo leads to a decrease in ductility and carburization resistance. Furthermore, excessive inclusion of W or Mo leads to a decrease in the oxidation resistance of the base material, so the upper limit is set to 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 include 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 increase high-temperature creep strength and high-temperature strength. Similarly to Cr, Ti is expected to pin nitrogen atoms by forming nitrides and inhibit 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 a decrease in the alloy's fluidity, resulting in poor castability, and can also make machining difficult. Therefore, when added, the upper limit is set to 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 to 0.1%.

[0036] In addition, the following elements can be selectively added to increase the cleanliness of the steel material and to improve creep rupture strength, tensile strength, and ductility, particularly 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 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 of the present invention for use in a high-temperature hydrogen atmosphere comprises: 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%, the balance being Fe and impurities, and further containing Zr: 0.1% or less.

[0038] Furthermore, the heat-resistant steel used in a high-temperature hydrogen atmosphere of the present invention consists of: 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%, the balance being Fe and impurities.

[0039] Furthermore, the heat-resistant steel for use in a high-temperature hydrogen atmosphere of the present invention comprises 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%, the balance being Fe and impurities, and further contains Al: 0.5% or less, Pb: 0.01% or less, Sn: 0.01% or less, and Zr: 0.01% or less.

[0040] The heat-resistant steel of the present invention used in a high-temperature hydrogen atmosphere 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. As a result, hydrogen permeation is suppressed and hydrogen permeability can be reduced 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 a high-temperature environment 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 casting 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 a high-temperature environment 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 fact that the base material can be controlled to an austenitic structure, that C forms more stable carbides with Cr, Ti, Nb, W, etc., and that the primary carbides formed during casting have a composition that promotes the precipitation of secondary carbides in the high-temperature operating environment. This formation of stable carbides in the steel inhibits reactions with the absorbed hydrogen and prevents void nucleation. Furthermore, the dispersed stable aged carbides have a pinning effect on dislocations due to the absorbed hydrogen, inhibiting the formation of voids due to dislocation movement and inhibiting the progression of creep deformation and creep rupture. This results in reduced 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 pipe (centrifugally cast pipe) 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, the difference in secondary dendrite arm spacing (DAS) between the outer peripheral surface and the inner peripheral surface can be increased by increasing the wall thickness of the hydrogen heating pipe.

[0047] As described above, controlling the secondary dendrite arm spacing (DAS) can suppress hydrogen permeation in a high-temperature atmosphere. 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 peripheral 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.

[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]

[0051] <Hydrogen Permeation Test> The hydrogen permeation test was carried out using a hydrogen permeation test apparatus 10 shown in FIG. 1. In the hydrogen permeation test apparatus 10, a double pipe 12 (a 32A Sch20 pipe (450 mm) made of SUS304 with a flange welded) was placed in a tubular furnace 11 (ARF-50K, manufactured by Asahi Rika Seisakusho Co., Ltd.), and a tubular furnace heater 13 (width 260 mm) was placed on the outer periphery of the double pipe 12. A flow rate controller 15 (mass flow controller, manufactured by Kofloc Corporation: 8500MC) was supplied from an argon gas cylinder 14 to the double pipe 12. 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 the test tube 16 described below, a thermocouple 17 (Sheath K, manufactured by Okazaki Seisakusho Co., Ltd.) for temperature measurement was also placed in the double pipe 12.

[0052] Test tubes 16 (20 mm diameter, 250 mm length, 5 mm thickness) of 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 into the 100 mm 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 pipe 12, and while hydrogen gas was introduced into the test tube 16 so that the pressure gauge 19 reached 0.1 MPa, the tubular furnace heater 13 was operated. The test was carried out in two patterns, with the temperature detected by the thermocouple 17 being 800°C and 1000°C. The hydrogen gas leaking into the double pipe 12 was measured using a gas chromatograph 20 (GC-2014AT manufactured by Shimadzu Corporation) and recorded on a recorder (LR8410 manufactured by Hioki E.E. Corporation, not shown), and the hydrogen permeability (Ncc mm / cm ２ The results are shown in Table 2.

[0054]

[0055] Referring to Table 2, hydrogen gas permeation was confirmed in both Inventive Example 1 and Comparative Example 1, and the higher the temperature, the higher the hydrogen permeability. Comparing Inventive Example 1 and Comparative Example 1, it can be seen that Inventive 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 are observed.

[0057] The obtained test specimens were scanned using 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 arm spacing measurement was to be performed, and the intersection of the measurement line and the secondary dendrite arm was specified. The distance between the intersections (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 location, and the following "number + μm" is the distance between the intersections, 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 peripheral surface, middle, and inner peripheral surface of each test piece, and the average of these measurements and the overall average were calculated. The results are shown in Table 3.

[0059]

[0060] Referring to Table 3, the secondary dendrite arm spacing (DAS) on the outer peripheral surface was smaller than those 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 the test specimens was small, which resulted in many grain boundaries, i.e., a small structure, making it possible to further reduce hydrogen permeation. Also, the secondary dendrite arm spacing (DAS) on the outer periphery side was small, and there were many obstacles, including carbides, at the grain boundaries, which reduced 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.

[0063] 10 Hydrogen permeation test device 11 Tubular furnace 12 Double tube 13 Tubular furnace heater 16 Test tube L Secondary dendrite arm spacing (DAS)

Claims

1. A heat-resistant steel for use in a high-temperature hydrogen atmosphere, consisting, by mass%, of: 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 being Fe and impurities, and optionally further containing 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%.

2. A heat-resistant steel for use in a high-temperature hydrogen atmosphere according to claim 1, which contains: 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 further contains Zr: 0.1% or less.

3. A heat-resistant steel for use in a high-temperature hydrogen atmosphere according to claim 1, comprising: 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%, and W: 4.0% to 6.0%.

4. A heat-resistant steel for use in a high-temperature hydrogen atmosphere according to claim 1, which contains 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%, and further contains Al: 0.5% or less, Pb: 0.01% or less, Sn: 0.01% or less, and Zr: 0.01% or less.

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

6. A hydrogen heating tube according to claim 5, which is a centrifugally cast tube and has a secondary dendrite arm spacing (DAS) on the outer circumferential surface of 35.0 μm or less.

7. A hydrogen heating tube according to claim 6, wherein the secondary dendrite arm spacing (DAS) on the outer circumferential surface is 90% or less of the secondary dendrite arm spacing (DAS) on the inner circumferential surface.

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