JP3827988B2 - Austenitic stainless steel with excellent steam oxidation resistance, carburization resistance and σ embrittlement resistance - Google Patents

Description

【００３４】
各冷延焼鈍板から試験片を切り出し、スケール剥離試験，浸炭試験及びσ脆化試験に供した。
スケール剥離試験では、露点８０℃の水蒸気酸化雰囲気中で、JIS Z2282に準拠して加熱２５分→冷却５分の断続加熱を１０００℃で５００サイクル繰り返し、試験前後の重量変化から耐スケール剥離性を評価した。
浸炭試験では、固形浸炭剤に埋没させた試験片に８００℃×２０００時間又は１０００℃×２００時間の加熱浸炭処理を施し、加熱浸炭処理前後の重量変化から耐浸炭性を評価した。
σ脆化試験では、試験片を８００℃で１０００時間加熱した後、JIS Z2242に準拠した衝撃試験によって室温でのシャルピー衝撃値を測定し、シャルピー衝撃値から耐σ脆化性を評価した。
【００３５】
表２の調査結果にみられるように、No.１〜９の本発明鋼は、何れも水蒸気酸化雰囲気中での耐スケール剥離性及び耐浸炭性がNo.１０のSUS304，No.１１のSUS310S，No.１２のNCF800より優れており、耐σ脆化性もSUS310Sより優れていた。
他方、No.１０のSUS304相当鋼では、耐σ脆化性に優れているものの、Ｓｉ含有量が少ないため耐スケール剥離性及び耐浸炭性が大きく劣っていた。No.１１のSUS310S相当鋼は、Ｓｉ含有量が少ないため耐スケール剥離性及び耐浸炭性が劣っており、更に多量のＣｒを含むことから耐σ脆化性にも劣っていた。No.１２のNCF800相当鋼は、Ｓｉ含有量が少ないため耐スケール剥離性に劣っており、更にＮｉ含有量が多いことから８００℃の耐浸炭性に劣っていた。
【００３６】
Ｓｉ含有量が本発明で規定した下限１．５質量％に満たないNo.１３の比較鋼は、耐浸炭性に劣っていた。Ｓｉ含有量が少なくREMを添加していないNo.１４の比較鋼は、耐スケール剥離性及び耐浸炭性の双方が本発明鋼に比較して大幅に劣っていた。REM無添加のNo.１５の比較鋼は、本発明鋼と同程度の耐浸炭性及び耐σ脆化性を示すものの、耐スケール剥離性に劣っていた。過剰量のＳｉを含むNo.１６,１７の比較鋼や過剰量のＣｒを含むNo.１８の比較鋼は、良好な耐スケール剥離性及び耐浸炭性を示すものの、耐σ脆化性に劣っていた。
以上の対比から、適正量のＳｉを添加すると共にREMを複合添加することによって、耐スケール剥離性及び耐浸炭性が改善されることが確認される。
【００３７】

【００３８】
【発明の効果】
以上に説明したように、本発明のオーステナイト系ステンレス鋼は、特定量のＳｉを添加すると共に、Ｙ及びREMの１種又は２種以上を複合添加することによって、両立が困難と考えられてきた耐水蒸気酸化性，耐浸炭性及び耐σ脆化性を高レベルで確保している。このオーステナイト系ステンレス鋼は、優れた耐熱性を活用し、水蒸気及び浸炭性ガスの双方を含み、且つ加熱・冷却の繰返しが多い小型水素発生器の改質反応部材を初めとして、過酷な高温雰囲気に曝される構造部材として使用される。
【図面の簡単な説明】
【図１】 水蒸気酸化雰囲気における加熱・冷却の繰返しに起因したスケール剥離に及ぼすＳｉ及びREM含有量の影響を表したグラフ
【図２】 浸炭性雰囲気における耐浸炭性及び時効後の靭性に及ぼすＳｉ含有量の影響を表したグラフ[0001]
[Industrial application fields]
The present invention relates to an austenitic stainless steel excellent in steam oxidation resistance, carburization resistance and σ embrittlement resistance used as a component in an atmosphere containing a large amount of water vapor and carbon monoxide.
[0002]
[Prior art]
The oil refining process consumes a large amount of hydrogen in the hydrodesulfurization process, and thus requires a hydrogen production apparatus. In conventional hydrogen production equipment, hydrogen is generated by reforming LPG and gasoline together with steam in a high-temperature and medium-pressure catalyst atmosphere, so SCH22 (25Cr-20Ni-0.4C) specified in JIS G5122 , Forging materials such as centrifugal casting pipes such as SCH24 (25Cr-35Ni-0.4C) and NCF800 (20Cr-32Ni-Ti-Al) specified in JIS G5122 are used in the steam reforming reaction tubes (The Nikkan Kogyo Shimbun, published in 1995, “Stainless Steel Handbook 3rd Edition”, page 1196).
[0003]
On the other hand, along with the development of on-site and portable fuel cells, development and commercialization of hydrogen generators that are smaller than those for petroleum refining are being promoted in order to obtain hydrogen necessary for battery operation. Various fuels such as alcohol, city gas, LPG, kerosene, and gasoline have been studied as hydrogen sources. However, in order to cause a reforming reaction in a catalytic atmosphere containing steam, This is necessary even when using fuel.
[0004]
A small-sized hydrogen generator has a hydrogen supply amount that is not constant as compared with a large-sized device for oil refining, and the device is frequently started and stopped. From this form of use, it is required for the constituent members of the hydrogen generator that the oxide scale exfoliation resistance with repeated heating and cooling is excellent. Among them, the scale peeling resistance in an atmosphere such as a reforming reaction portion containing a large amount of water vapor and low oxygen is an important factor.
[0005]
Furthermore, in a small hydrogen generator using a hydrocarbon fuel, carbon monoxide, carbon dioxide and the like are included in the atmosphere after the reforming reaction in addition to water vapor and hydrogen. In particular, when a large amount of carbon monoxide is contained, a carburizing atmosphere is formed, and therefore carburizing becomes a problem in terms of material. In addition, if scale peeling in a steam oxidation atmosphere and carburization in a carburizing atmosphere overlap, severe material damage is expected as compared with conventional hydrogen generators for petroleum refining.
[0006]
Ferritic and austenitic heat resistant stainless steels are known as constituent materials that require high temperature characteristics. Ferritic stainless steel has a smaller coefficient of thermal expansion than austenitic stainless steel, and is excellent in adhesion of oxide scale. However, the C diffusion rate at a high temperature is faster than that of austenitic stainless steel and is inferior in carburization resistance. Ferritic stainless steel with a small coefficient of thermal expansion shows excellent thermal fatigue properties in environments exposed to repeated heating and cooling, but its high-temperature strength is lower than austenitic stainless steel, so deformation resistance during holding at high temperatures Inferior to (high temperature creep resistance). Among ferritic stainless steels, steel types containing a large amount of Al are excellent in both adhesion and carburization resistance of oxide scale, but are inferior in workability, weldability, and toughness, and are therefore welded like hydrogen generators. It is difficult to apply to structures.
[0007]
On the other hand, austenitic stainless steel is superior in workability and weldability to ferritic stainless steel and is relatively easy to apply to welded structures. However, due to the large coefficient of thermal expansion, the adhesion of oxide scale is essentially inferior compared to ferritic stainless steel. In order to improve the high temperature oxidation resistance and scale peel resistance of austenitic stainless steel, various improvements have been studied. For example, SUS XM15J1 (19Cr-13Ni-3.3Si), AISI314 (25Cr-20Ni-2Si), etc. to which Si is added, steel containing 4.5 to 6% by mass of Al (Japanese Patent Laid-Open No. 55-43498) Steel) with a composite addition of Al and Si (Japanese Patent Publication No. 54-12887), steel with a composite addition of REM (Rare Earth Metal) (Japanese Patent Publication No. 54-12890), etc. are austenitic stainless steels for heat-resistant members. Has been developed. With regard to carburization resistance, it is known that by making the total content of Cr and Si 30% by mass or more, it becomes a steel material having excellent carburization resistance (published in 1995 by Nikkan Kogyo Shimbun, Ltd., “Stainless Steel”. Handbook 3rd edition "page 407).
[0008]
[Problems to be solved by the invention]
However, conventional austenitic stainless steels do not necessarily have sufficient scale peel resistance under conditions exposed to heating and cooling in a combustion atmosphere containing some water vapor. In austenitic stainless steel containing a large amount of Cr and Si, a σ phase that is harmful to toughness after cooling is likely to occur during use at high temperatures, and there is a concern that the structure may be damaged when some kind of impact or vibration is applied.
[0009]
For this reason, the structural material of the small hydrogen generator is required to be excellent in the following characteristics.
(1) Scale peeling resistance to repeated heating and cooling in an environment containing a large amount of water vapor and a small amount of oxygen (some oxygen is not included depending on the reforming reaction) (2) Containing a large amount of water vapor and monoxide Carburization resistance to repeated heating and cooling in an environment containing carbon (3) σ embrittlement resistance after prolonged heating [0010]
In consideration of use as a welded structure, the following characteristics are also important.
(4) Excellent thermal fatigue characteristics and creep characteristics.
(5) Excellent workability, weldability and toughness.
Examples of general-purpose heat-resistant austenitic stainless steel include SUS304 (18Cr-8Ni), SUS309S (22Cr-12Ni), SUS310S (25Cr-20Ni) in addition to the above-mentioned SUS XM15J1 and NCF800. However, an appropriate component range satisfying the required characteristics (1) to (5) and advantageous in terms of cost has not been clarified, and it has been difficult to apply an appropriate material.
[0011]
[Means for Solving the Problems]
The present invention has been devised as a result of various studies of alloy compositions to satisfy the required characteristics as a component of a hydrogen generator. By strictly regulating the amount of alloy elements, the present invention has been proposed. An object of the present invention is to provide an austenitic stainless steel excellent in carburization resistance and σ embrittlement resistance.
[0012]
In order to achieve the object, the austenitic stainless steel of the present invention includes C: 0.02 to 0.10% by mass, Si: 1.5 to 2.5% by mass, Mn: 2.0% by mass or less, P : 0.04 mass% or less, S: 0.02 mass% or less, Ni: 7-12 mass%, Cr: 15-25 mass%, one or more of Y and REM (rare earth metal): in total 0.001-0.1 mass%, N: 0.02-0.20 mass% is included, It is characterized by the above-mentioned.
[0013]
This austenitic stainless steel has Nb: 0.05 to 0.5 mass%, Ti: 0.05 to 0.5 mass%, Mo: 0.1 to 4.0 mass%, Cu: 0.1 to 4 It is possible to include one or more of 0.0 mass%. Furthermore, you may add 1 type or 2 types of Al: 0.01-2.5 mass% and Ca: 0.001-0.1 mass% as needed.
[0014]
[Action]
As a result of investigating and examining the influence of alloy elements on steel material damage in a steam oxidation atmosphere and carburizing atmosphere in a temperature range of 600 to 1000 ° C., and the σ embrittlement sensitivity, the present inventors have obtained the following knowledge.
The scale peel resistance of the austenitic stainless steel in the steam oxidation atmosphere is inferior to the scale peel resistance in the atmospheric oxidation atmosphere, and the smaller the oxygen content, the larger the scale peel resistance. Specifically, when the reforming reaction portion of the hydrogen generator is divided into the heating side necessary for the reaction progress and the reforming reaction side by the catalyst, the scale peeling amount increases on the reforming reaction side with a small amount of oxygen. .
[0015]
In order to reduce the amount of scale peeling, it is very effective to add a certain amount of Si and to slightly add one or more of Y and REM (hereinafter, Y is included in this specification). In this sense, “REM” is used as appropriate). Thereby, the increase in Cr content can be suppressed and the component design of the steel material excellent in σ embrittlement resistance becomes possible.
In order to improve both the carburization resistance and the σ embrittlement resistance while ensuring the scale peel resistance in a steam oxidation atmosphere, the Cr content is about 20% by mass and the Ni content is 10% by mass. It is effective to strictly regulate the Si content under conditions adjusted to the extent. Furthermore, the addition of Nb, Ti, Mo, and Cu improves the high-temperature strength, and the addition of Al and Ca improves the high-temperature oxidation resistance during continuous heating. Scale peelability, carburization resistance, and σ embrittlement resistance are not significantly impaired.
[0016]
Hereinafter, it will be described in more detail, including the process leading to the component design specified in the present invention.
FIG. 1 shows the results of investigating the effects of Si and REM on the scale peel resistance in a steam oxidation atmosphere by adding Si and REM in various amounts to steel containing 20Cr-11Ni as a basic component. In this test, REM was added as misch metal (mainly La, Ce, Nd) at the time of melting, and a total amount of REM was included. The scale peel resistance was evaluated based on the weight loss after 500 cycles of 1000 ° C. × 25 minutes heating → 5 minutes cooling in an atmosphere containing 80% water vapor.
[0017]
As is clear from FIG. 1, the amount of scale peeling significantly decreased with the increase of Si, and the resistance to scale peeling was remarkably improved by adding 1.5% by mass or more of Si. Further, REM was added in combination. This shows that the scale peel resistance is further improved. In FIG. 1, the damage levels of typical heat-resistant steels SUS310S and NCF800 are also shown. In order to develop characteristics equivalent to or better than these steel types, about 3% by mass is added when Si alone is added. The combined addition with REM requires about 1% by mass of Si.
[0018]
When the cross section of the test piece was observed after the scale peel test, the scale with good adhesion contained a Cr-rich oxide and Si was present in the internal oxide layer. Was not detected. From this result, although it is not necessarily clear why the scale peeling resistance in the steam oxidation atmosphere is improved, REM promotes the diffusion of Cr and Si, and generates a stable oxide having a strong environmental barrier, or It appears that REM itself has formed fine oxides to improve scale adhesion.
[0019]
Various amounts of Si were added to steel containing 20Cr-11Ni-0.04REM as a basic component, and the effects of Si content on carburization resistance and σ embrittlement resistance were investigated. In the carburizing test, a test piece embedded in a carburizing agent is heated for 200 hours at a temperature condition of 1000 ° C. where the most severe damage is expected among the maximum expected operating temperatures (600 to 1000 ° C.), and resistance to changes in weight before and after heating. Carburizability was evaluated. In the σ embrittlement resistance evaluation test, the test piece was heated to 800 ° C., which was exposed to the most severe σ embrittlement, for 1000 hours, and then the σ embrittlement resistance was evaluated by the Charpy impact value at room temperature.
[0020]
As shown in FIG. 2 showing the survey results, the carburization amount decreases with the increase of Si, and the carburization hardly occurs with the addition of 1.5 mass% or more of Si. This behavior corresponds well to the behavior of scale peeling resistance in a steam oxidation atmosphere (FIG. 1). In Fig. 2, the carburizing amount of steel type NCF800, which has excellent carburization resistance, is also shown, but adding 1.5% by mass or more of Si to this component system will exhibit carburizing resistance equivalent to or higher than that of NCF800. I understand. In addition to the test of FIG. 2, NCF800 was remarkably inferior to this component system in terms of carburization resistance when heated at 800 ° C. for 1000 hours or more. From these results, it can be said that the austenitic stainless steel according to the present invention is a steel type superior in carburization resistance compared to NCF800 in the temperature range of 800 to 1000 ° C.
[0021]
As for the resistance to σ embrittlement when heated at 800 ° C., the Charpy impact value decreases as Si increases, and the toughness is remarkably inferior when Si exceeds 2.5 mass%. For this reason, in order to improve the carburization resistance while ensuring toughness after heating, it is important to strictly regulate the Si content in the range of 1.5 to 2.5 mass%.
From the above results, it can be said that in order to obtain a small hydrogen generator having sufficient durability, Si and REM are added in combination and the Si content must be strictly adjusted.
[0022]
Next, alloy components and contents contained in the austenitic stainless steel of the present invention will be described.
C: 0.02-0.10 mass%
It is an alloy component effective for improving the high-temperature strength, and the strength improving effect becomes remarkable at 0.02% by mass or more. However, when an excessive amount of C exceeding 0.10% by mass is included, embrittlement due to precipitation of carbides, bead cracking during welding, and the like are likely to occur. The range of preferable C content is 0.04-0.08 mass%.
[0023]
Si: 1.5 to 2.5% by mass
It is an alloy component necessary for obtaining the required characteristics of the hydrogen generator, and the addition of 1.5 mass% or more of Si greatly improves the scale peeling resistance in a steam oxidation atmosphere and the carburization resistance in a carburizing atmosphere. Moreover, the composite addition with N exhibits the effect of increasing the high temperature strength. However, when an excessive amount of Si exceeding 2.5% by mass is added, σ embrittlement is promoted, and the weldability and hot workability are adversely affected. The range of preferable Si content is 1.5-2.0 mass%.
[0024]
Mn: 2.0% by mass or less This is an alloy component that makes it possible to save expensive Ni from a component balance that takes into account the amount of δ ferrite and the amount of work-induced martensite. However, when an excessive amount of Mn exceeding 2.0% by mass is added, high temperature oxidation resistance tends to decrease. A preferable range of the Mn content is 0.5 to 1.5% by mass.
P: 0.04 mass% or less While increasing the high-temperature strength, it is a component that decreases the corrosion resistance and high-temperature oxidation resistance. Moreover, in the case of an austenite single phase structure, it segregates at a grain boundary and reduces hot workability. For this reason, the lower the P content, the better. The upper limit of the P content is set to 0.04% by mass.
[0025]
S: 0.02 mass% or less Like P, it is a component that adversely affects hot workability. When S is excessively contained, corrosion resistance and high-temperature oxidation resistance also deteriorate. Therefore, the upper limit of the S content is set to 0.02% by mass.
Ni: 7 to 12% by mass
It is a basic component contained in austenitic stainless steel, and if it is less than 7% by mass, a large amount of δ ferrite phase is likely to be produced, and the high-temperature oxidation resistance and hot workability are reduced. Conversely, when the Ni content exceeds 12% by mass, an austenite single phase tends to be formed, and in this component system containing Si, hot workability and weldability are lowered. On the other hand, as for carburization resistance, generally, the higher the Ni content, the better. However, in the temperature range of 700 to 900 ° C., the carburization resistance tends to decrease. Further, excessive addition of Ni is not preferable from the viewpoint of steel material cost. The range of preferable Ni content is 10-12 mass%.
[0026]
Cr: 15-25% by mass
It is an indispensable alloy component for stainless steel, and 15% by mass or more of Cr is required to ensure sufficient high-temperature oxidation resistance and corrosion resistance. However, an excessive amount of Cr exceeding 25% by mass improves the carburization resistance but tends to cause σ embrittlement and reduces hot workability. The range of preferable Cr content is 18-22 mass%.
[0027]
One or more of Y and REM (rare earth metal): 0.001 to 0.1% by mass in total
It is an alloy component that improves the scale peel resistance in a steam oxidation atmosphere, and contributes to the improvement of hot workability by fixing S in steel. Even if a trace amount is added, the scale peel resistance is improved. However, the effect of improving the scale peel resistance becomes remarkable by adding 0.001% by mass of one or more of Y and REM. The effect of improving the scale peel resistance is saturated by the addition of a total of 0.1% by mass, and excessive addition exceeding 0.1% by mass adversely affects the hot workability. Industrially, REM is often added as a Y alloy, La alloy, Ce alloy, or misch metal (including La, Ce, Nd, etc.), but any element belonging to group IIIA in the periodic table may be used. . The preferable content of Y and REM is in the range of 0.02 to 0.1% by mass.
[0028]
N: 0.02 to 0.20 mass%
It is an important alloy component for increasing the high temperature strength of austenitic stainless steel, and the effect of increasing the high temperature strength becomes significant when the N content is 0.02% by mass or more. However, when an excessive amount of N exceeding 0.20% by mass is included, an adverse effect on workability appears. The range of preferable N content is 0.05-0.15 mass%.
Nb: 0.05 to 0.5% by mass
It is an alloy component added as necessary, and exhibits the effect of fixing C and improving the intergranular corrosion resistance of steel. In addition, this component system containing Si also works to increase the high-temperature strength by the combined addition with N. Such an effect appears remarkably when 0.05% by mass of Nb is added. However, when an excessive amount of Nb exceeding 0.5% by mass is added, it combines with the high-temperature strengthening element N, and becomes a precipitate harmful to the high-temperature strength. The excessive addition of Nb also causes the generation of the σ phase.
[0029]
Ti: 0.05 to 0.5% by mass
It is an alloy component that is added as necessary, fixing C and improving intergranular corrosion resistance, and also effectively working to improve high-temperature strength. However, excessive addition of Ti causes the hot workability and the surface properties of the steel sheet to deteriorate. Then, when adding Ti, Ti content is defined in the range of 0.05-0.50 mass%.
Mo: 0.1-4.0 mass%, Cu: 0.1-4.0 mass%
It is an alloy component added as necessary, and both exhibit the effect of improving high temperature strength and corrosion resistance. However, excessive addition of Mo and Cu not only increases the steel material cost, but also causes a decrease in hot workability and toughness of the steel. Therefore, when adding Mo and Cu, the contents of Mo and Cu are determined in the range of 0.1 to 4.0% by mass, respectively.
[0030]
Al: 0.01 to 2.5% by mass
Although it is an alloy component added as necessary and is an effective component for improving high-temperature oxidation resistance, excessive addition adversely affects the hot workability and σ embrittlement resistance of steel. Then, when adding Al, Al content is defined in the range of 0.01-2.5 mass%.
Ca: 0.001 to 0.1% by mass
It is an alloy component added as necessary, and exhibits the effect of improving high-temperature oxidation resistance in the same manner as REM. However, excessive addition adversely affects hot workability, so when adding Ca, the Ca content is set in the range of 0.001 to 0.1 mass%.
[0031]
Other components contained in the austenitic stainless steel are not particularly defined in the present invention, but it is preferable to reduce O, Sn, Pb, etc., which are general impurity elements, as much as possible. More preferably, the upper limit of O is set to 0.02% by mass, and the upper limit of Sn and Pb is set to 0.1% by mass. By further strictly controlling the upper limit of these components, hot workability and weldability are improved. It is maintained at a higher level. Further, components such as Mg, B, and Co that are known as elements effective for improving hot workability and toughness are not particularly defined in the present invention, and may be appropriately added as necessary. Is possible.
[0032]
【Example】
Various molten steels having the compositions shown in Table 1 were prepared by vacuum melting, and cold-rolled annealed plates having a thickness of 2.0 mm were manufactured through hot rolling, annealing, cold rolling, and annealing processes. In the table, Nos. 1 to 9 are steels according to the present invention, and Nos. 10 to 18 are comparative steels. Of the comparative steels, No. 10 is SUS304 equivalent steel, No. 11 is SUS310S equivalent steel, and No. 12 is NCF800 equivalent steel.
[0033]

[0034]
A test piece was cut out from each cold-rolled annealed plate and subjected to a scale peeling test, carburization test, and σ embrittlement test.
In the scale peeling test, in a steam oxidation atmosphere with a dew point of 80 ° C, intermittent heating for 25 minutes → cooling for 5 minutes is repeated 500 cycles at 1000 ° C in accordance with JIS Z2282. evaluated.
In the carburization test, a test carburized in a solid carburizing agent was subjected to a heat carburization treatment at 800 ° C. for 2000 hours or 1000 ° C. for 200 hours, and carburization resistance was evaluated from a change in weight before and after the heat carburization treatment.
In the σ embrittlement test, the test piece was heated at 800 ° C. for 1000 hours, and then the Charpy impact value at room temperature was measured by an impact test according to JIS Z2242, and the σ embrittlement resistance was evaluated from the Charpy impact value.
[0035]
As can be seen from the results of the investigation in Table 2, the No. 1-9 steels of the present invention are No. 10 SUS304 and No. 11 SUS310S. , No. 12 NCF800, and σ embrittlement resistance was also superior to SUS310S.
On the other hand, No. 10 steel equivalent to SUS304 was excellent in σ embrittlement resistance, but was poor in scale peel resistance and carburization resistance because of its low Si content. The No. 11 SUS310S equivalent steel was inferior in scale peel resistance and carburization resistance due to its low Si content, and further inferior in σ embrittlement resistance because it contained a large amount of Cr. No. 12 NCF800 equivalent steel was inferior in scale peel resistance due to its low Si content, and further inferior in carburization resistance at 800 ° C. due to its high Ni content.
[0036]
The No. 13 comparative steel whose Si content was less than the lower limit of 1.5% by mass defined in the present invention was inferior in carburization resistance. The No. 14 comparative steel with a low Si content and no REM added was significantly inferior in both scale peel resistance and carburization resistance to the steel of the present invention. The comparative steel of No. 15 with no REM addition showed carburization resistance and σ embrittlement resistance comparable to the steel of the present invention, but was inferior in scale peel resistance. The No. 16 and 17 comparative steels containing an excessive amount of Si and the No. 18 comparative steel containing an excessive amount of Cr show good scale peel resistance and carburization resistance, but are inferior in σ embrittlement resistance. It was.
From the above comparison, it is confirmed that by adding an appropriate amount of Si and adding REM in combination, the scale peeling resistance and the carburization resistance are improved.
[0037]

[0038]
【The invention's effect】
As described above, the austenitic stainless steel of the present invention has been considered to be difficult to achieve both by adding a specific amount of Si and adding one or more of Y and REM in combination. High levels of steam oxidation resistance, carburization resistance and σ embrittlement resistance are ensured. This austenitic stainless steel utilizes harsh high-temperature atmospheres, including reforming reaction members for small hydrogen generators that use both excellent heat resistance, contain both water vapor and carburizing gas, and are frequently heated and cooled. Used as a structural member exposed to
[Brief description of the drawings]
FIG. 1 is a graph showing the effects of Si and REM content on scale peeling due to repeated heating and cooling in a steam oxidizing atmosphere. FIG. 2 is a graph showing the effects of carburization resistance and toughness after aging in a carburizing atmosphere. Graph showing the effect of content

Claims (2)

C: 0.02-0.10 mass%, Si: 1.5-2.5 mass%, Mn: 2.0 mass% or less, P: 0.04 mass% or less, S: 0.02 mass% or less , Ni: 7-12 mass%, Cr: 15-25 mass%, one or more of Y and REM (rare earth metal): 0.001-0.1 mass% in total, N: 0.02- An austenitic stainless steel containing 0.20% by mass, having the balance of Fe and inevitable impurities, and excellent in steam oxidation resistance, carburization resistance and σ embrittlement resistance.   Furthermore, Nb: 0.05 to 0.5 mass%, Ti: 0.05 to 0.5 mass%, Mo: 0.1 to 4.0 mass%, Cu: 0.1 to 4.0 mass%, Al The austenitic stainless steel according to claim 1, comprising one or more of: 0.01 to 2.5 mass%, Ca: 0.001 to 0.1 mass%.

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