JP2003129192A - AUSTENITIC STAINLESS STEEL SUPERIOR IN STEAM OXIDATION RESISTANCE, CARBURIZATION RESISTANCE, AND sigma EMBRITTLEMENT RESISTANCE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an austenitic stainless steel which balances scale exfoliation resistance and carburization resistance with σ embrittlement resistance, at high levels. SOLUTION: The austenitic stainless steel includes 0.02-0.10% C, 1.5-2.5% Si, 2.0% or less Mn, 0.04% or less P, 0.02% or less S, 7-12% Ni, 15-25% Cr, 0.001-0.1% in total of one or more of Y and REM (rare-earth metals), and 0.02-0.20% N, and can further include, one or more of 0.05-0.5% Nb, 0.05-0.5% Ti, 0.1-4.0% Mo, and 0.1-4.0% Cu, and/or one or two of 0.01-2.5% Al and 0.001-0.1% Ca.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel excellent in steam oxidation resistance, carburization resistance and σ embrittlement resistance which is used as a constituent member in an atmosphere containing a large amount of steam and carbon monoxide. .

[0002]

2. Description of the Related Art A petroleum refining process consumes a large amount of hydrogen in a hydrodesulfurization process, and thus requires a hydrogen production device. In the conventional hydrogen production equipment, hydrogen is produced by reforming LPG and gasoline together with steam in a high temperature and medium pressure catalytic atmosphere. Therefore, SCH22 (25Cr-20Ni-0.4C) specified in JIS G5122 is used. , SCH24 (25Cr
-35Ni-0.4C) centrifugal force casting pipes and forged materials such as NCF800 (20Cr-32Ni-Ti-Al) specified in JIS G5122 are used for steam reforming reaction tubes (Nikkan Kogyo Shimbun). Co., Ltd., published in "Stainless Steel Handbook 3rd Edition", 1995, 11th
Page 96).

On the other hand, with the development of on-site type and portable fuel cells, the development and practical use of a hydrogen generator smaller than that for petroleum refining has been promoted in order to obtain hydrogen necessary for the operation of the cell. ing. Various fuels such as alcohol, city gas, LPG, kerosene, gasoline, etc. have been studied as hydrogen sources. However, in order to cause a reforming reaction in a catalyst atmosphere containing water vapor, high temperature heating at 600 to 1000 ° C. It is necessary even when using fuel.

A small-sized hydrogen generator does not have a constant supply of hydrogen as compared with a large-scale oil refining device, and the device is frequently started and stopped. From this usage pattern, it is required that the constituent members of the hydrogen generator have excellent resistance to peeling of the oxide scale due to repeated heating and cooling. Among them, scale peeling resistance in an atmosphere containing a large amount of water vapor and a small amount of oxygen such as a reforming reaction part is an important factor.

Further, in a small-sized hydrogen generator using a hydrocarbon fuel, carbon monoxide, carbon dioxide, etc. are contained in the atmosphere after the reforming reaction in addition to steam and hydrogen. In particular, when a large amount of carbon monoxide is contained, a carburizing atmosphere is created, so carburizing becomes a problem in terms of material. Moreover, when scale peeling in a steam oxidizing atmosphere and carburizing in a carburizing atmosphere are superimposed, severe material damage is expected as compared with the conventional hydrogen generating apparatus for petroleum refining.

As a constituent material required to have high temperature characteristics, heat resistant stainless steels such as ferritic and austenitic are known. The ferritic stainless steel has a smaller coefficient of thermal expansion than the austenitic stainless steel and has excellent adhesion to the oxide scale. However, the C diffusion rate at high temperature is higher than that of austenitic stainless steel, and the carburization resistance is poor. Ferrite stainless steel with a small coefficient of thermal expansion exhibits excellent thermal fatigue properties in an environment exposed to repeated heating and cooling, but its high-temperature strength is lower than that of austenitic stainless steel, so it is resistant to deformation during high-temperature holding. It is inferior in (high temperature creep resistance). Among ferritic stainless steels, steel grades containing a large amount of Al are excellent in both oxide scale adhesion and carburization resistance, but are inferior in workability, weldability and toughness. It is difficult to apply to structures.

On the other hand, austenitic stainless steel is
It has better workability and weldability than ferritic stainless steel, and is relatively easy to apply to welded structures. However, due to its large coefficient of thermal expansion, the adhesion of oxide scale is essentially inferior to that of ferritic stainless steel. In order to improve the high-temperature oxidation resistance and scale peeling resistance of austenitic stainless steel, various improvements have been studied so far. For example, SUS XM15 with Si added
J1 (19Cr-13Ni-3.3Si), AISI314 (25Cr-20
Ni-2Si) or the like, steel containing 4.5 to 6% by mass of Al (JP-A-55-43498), steel containing Al and Si in combination (JP-B-54-12887), A steel containing composite addition of REM (rare earth metal) (Japanese Patent Publication No. 54-12890) has been developed as an austenitic stainless steel for heat resistant members. Regarding carburization resistance, it is known that a steel material having excellent carburization resistance can be obtained by setting the total content of Cr and Si to 30% by mass or more (Nikkan Kogyo Shimbun).
Issued in 1995, "Stainless Steel Handbook, 3rd Edition", p. 407).

[0008]

However, conventional austenitic stainless steels do not always have sufficient scale peeling resistance under the conditions of being exposed to heating and cooling in a combustion atmosphere containing a small amount of water vapor. Austenitic stainless steels containing a large amount of Cr and Si are likely to generate a σ phase, which is harmful to the toughness after cooling, during use at high temperatures, and there is a concern that the structure will be damaged when some shock or vibration is applied.

Therefore, the structural material of the compact hydrogen generator is required to have the following excellent characteristics. Scale peeling resistance against repeated heating / cooling in an environment containing a large amount of water vapor and a small amount of oxygen (oxygen does not exist at all depending on the reforming reaction) In an environment containing a large amount of water vapor and containing carbon monoxide Carburization resistance to repeated heating / cooling σ embrittlement resistance after long-term heating

Further considering the use as a welded structure, the following characteristics are also important. Excellent thermal fatigue and creep properties. Excellent workability, weldability and toughness. As general-purpose heat-resistant austenitic stainless steel, in addition to the above-mentioned SUS XM15J1 and NCF800, SUS304 (18Cr-8
Ni), SUS309S (22Cr-12Ni), SUS310S (25Cr
-20Ni) and the like. However, the appropriate component range satisfying the required properties (1) to (4) and being advantageous in terms of cost has not always been clarified, and it has been difficult to apply appropriate materials.

[0011]

The present invention was devised as a result of various studies on alloy compositions to satisfy the required characteristics as a constituent member of a hydrogen generator, and strictly regulates the amount of alloying elements. By doing so, it is an object of the present invention to provide an austenitic stainless steel excellent in scale peeling resistance, carburization resistance and σ embrittlement resistance.

In order to achieve the object, the austenitic stainless steel of the present invention has 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% by mass or less, S: 0.02% by mass or less, Ni: 7 to 12% by mass, Cr: 15 to 25 mass%, one or more of Y and REM (rare earth metal): 0.001 to 0.1 mass% in total, N: 0.02 to 0.2
It is characterized by containing 0 mass%.

This austenitic stainless steel is N
b: 0.05 to 0.5 mass%, Ti: 0.05 to 0.5
% By mass, Mo: 0.1-4.0% by mass, Cu: 0.1-
It may contain 4.0% by mass of one kind or two or more kinds.
Further, if necessary, Al: 0.01 to 2.5 mass%, C
a: 0.001 to 0.1 mass% of 1 type or 2 types may be added.

[0014]

The present inventors have obtained the following findings as a result of investigating and examining the influence of alloying elements on the damage of steel materials in the steam oxidizing atmosphere and the carburizing atmosphere in the temperature range of 600 to 1000 ° C. and further on the susceptibility to σ embrittlement. It was The scale delamination resistance of the austenitic stainless steel in the steam oxidizing atmosphere is inferior to that in the atmospheric oxidizing atmosphere, and the smaller the oxygen content, the larger the scale delamination amount. Specifically, if the reforming reaction portion of the hydrogen generator is divided into the heating side required for the progress of the reaction and the reforming reaction side by the catalyst, the scale peeling amount increases on the reforming reaction side where the oxygen amount is small. .

To reduce the amount of scale peeling, a certain amount of Si
It is very effective to add 1 type or 2 types or more of Y and REM in combination with each other (hereinafter, in the present specification, “REM” is appropriately used to include Y). As a result, the increase of Cr content can be suppressed and the σ
It is possible to design the composition of steel materials with excellent brittleness. In order to improve both carburization resistance and σ embrittlement resistance while ensuring scale peeling resistance in a steam oxidation atmosphere, Cr is used.
It is effective to strictly control the Si content under the condition that the Ni content is adjusted to about 20 mass% and the Ni content is adjusted to about 10 mass%. Furthermore, addition of Nb, Ti, Mo and Cu improves high temperature strength, and addition of Al and Ca improves high temperature oxidation resistance during continuous heating. However, if the addition amount of these optional components is properly controlled, Scale peelability, carburization resistance, and σ embrittlement resistance are not significantly impaired.

Hereinafter, the process of reaching the component design specified in the present invention will be described more specifically. 20Cr-11Ni
Fig. 1 shows the results of investigating the effects of Si and REM on the scale delamination resistance in a steam oxidizing atmosphere by adding Si and REM in various amounts to a steel containing as a basic component. In this test, misch metal (mainly La, C
e, Nd), REM is added, and the total amount is about 0.
Includes 04 mass% REM. The scale peeling resistance was evaluated by the amount of weight loss after repeating 500 cycles in one cycle of heating at 1000 ° C. for 25 minutes and cooling for 5 minutes in an atmosphere containing 80% steam.

As is clear from FIG. 1, the scale peeling amount is remarkably reduced with an increase in Si, and the scale peeling resistance is remarkably improved by adding Si in an amount of 1.5% by mass or more. It can be seen that the scale peeling resistance is further improved by the combined addition. Figure 1 also shows the damage levels of SUS310S and NCF800, which are typical heat-resistant steels. In order to develop characteristics equal to or higher than those of these steel types, when Si alone is added, about 3% by mass, RE
The combined addition of M requires about 1% by mass of Si.

When the cross section of the test piece was observed after the scale peeling test, the scale having good adhesion contained a Cr-rich oxide and Si was present in the internal oxide layer.
No oxide or elemental enrichment containing was detected. From this result, although the reason why the scale peeling resistance in the steam oxidizing atmosphere is improved is not always clear, REM shows that
It can be seen that the diffusion of r and Si was promoted, a stable oxide having a strong environmental barrier ability was generated, or REM itself formed a minute oxide to improve the scale adhesion.

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, the assumed maximum operating temperature (600 to 1000 ° C)
Of these, the temperature condition that causes the most severe damage is 1000 ° C.
The test piece immersed in the carburizing agent was heated for 200 hours, and the carburization resistance was evaluated from the weight change before and after heating. In the σ embrittlement resistance evaluation test, the σ embrittlement resistance was evaluated by the Charpy impact value at room temperature after heating the test piece to 800 ° C, which is exposed to the most severe σ embrittlement, for 1000 hours.

As shown in FIG. 2 showing the result of the investigation, S
The amount of carburization decreases as i increases, and almost no carburization occurs when Si is added in an amount of 1.5% by mass or more. This behavior corresponds well to the behavior of scale peeling resistance in a steam oxidizing atmosphere (FIG. 1). Figure 2 also shows the carburizing amount of steel type NCF800, which has excellent carburizing resistance. By adding 1.5% by mass or more of Si to this component system, NCF800
It can be seen that carburization resistance equivalent to or higher than that is exhibited. Regarding the carburization resistance when heated at 800 ° C. for 1000 hours or more separately from the test of FIG.
Was significantly inferior. From these results, the austenitic stainless steel according to the present invention is 800-1000.
It can be said that it is a steel type with superior carburization resistance compared to NCF800 in the temperature range of ℃.

Looking at the σ embrittlement resistance at 800 ° C. heating, the Charpy impact value decreases with increasing Si,
The toughness is remarkably inferior when Si is added in excess of 2.5 mass%. From this, in order to improve the carburization resistance while ensuring the toughness after heating, the Si content is 1.5 to 2.5% by mass.
It is important to strictly regulate the range. From the above results, it can be said that in order to obtain a small-sized hydrogen generator having sufficient durability, Si and REM are added together and the Si content is strictly adjusted.

Next, the alloy components and contents contained in the austenitic stainless steel of the present invention will be described. C: 0.02 to 0.10% by mass It is an alloy component effective in improving high temperature strength, and the effect of improving strength becomes remarkable at 0.02% by mass or more. But 0.10
When an excessive amount of C exceeding mass% is included, embrittlement due to the precipitation of carbides and bead cracking during welding are likely to occur. The preferred C content range is 0.04 to 0.0.
It is 8% by mass.

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% by mass or more of Si results in scale peeling resistance in a steam oxidizing atmosphere and The carburizing resistance in the carburizing atmosphere is significantly improved. Further, it has the effect of increasing the high temperature strength by the combined addition with N. However, 2.5 mass%
If an excessive amount of Si exceeding the above is added, σ embrittlement is promoted, and the weldability and hot workability are adversely affected. A preferable Si content range is 1.5 to 2.0 mass%.

Mn: 2.0% by mass or less It is an alloy component that enables the saving of expensive Ni from the component balance considering the amount of δ ferrite and the amount of work-induced martensite. However, an excess amount of M exceeding 2.0% by mass
When n is added, the high temperature oxidation resistance tends to decrease. The preferable range of Mn content is 0.5 to 1.5 mass%. P: 0.04% by mass or less While increasing the high temperature strength, it is a component that reduces corrosion resistance and high temperature oxidation resistance. Further, in the case of an austenite single phase structure, it segregates at the grain boundaries to reduce hot workability. Therefore, the lower the P content, the more preferable, and the upper limit of the P content was set to 0.04 mass%.

S: 0.02 mass% or less Like P, it is a component that adversely affects the hot workability, and if S is contained in excess, corrosion resistance and high temperature oxidation resistance also decrease. Therefore, the upper limit of the S content is set to 0.02% by mass. Ni: 7 to 12 mass% It is a basic component contained in austenitic stainless steel. If it is less than 7 mass%, a large amount of δ ferrite phase is likely to be generated, and high temperature oxidation resistance and hot workability are deteriorated. On the contrary, when the Ni content exceeds 12 mass%, an austenite single phase is likely to be formed, and the hot workability and the weldability are deteriorated in this component system containing Si. On the other hand, the carburization resistance is generally improved as the Ni content increases, but 700 to 900
On the contrary, in the temperature range of ℃, the carburizing resistance tends to decrease. Further, excessive addition of Ni is not preferable from the viewpoint of steel material cost. The preferable Ni content range is 10 to 12% by mass.
Is.

Cr: 15 to 25% by mass , which is an essential alloying component for stainless steel, contains 15% by mass or more of C in order to secure sufficient high temperature oxidation resistance and corrosion resistance.
r is required. However, if an excessive amount of Cr is contained in excess of 25 mass%, although carburization resistance is improved, σ embrittlement is likely to occur and hot workability is deteriorated. The preferable Cr content range is 18 to 22 mass%.

One or two of Y and REM (rare earth metal)
Above: 0.001 to 0.1% by mass in total is an alloying component that improves scale peeling resistance in a steam oxidizing atmosphere, and contributes effectively to the improvement of hot workability by fixing S in steel. To do. Even if added in a small amount, the scale peeling resistance is improved, but the effect of improving the scale peeling resistance becomes remarkable by adding 0.001% by mass of one or more of Y and REM. The effect of improving scale peeling resistance is saturated by the addition of 0.1 mass% in total, and 0.1 mass%
On the contrary, excessive addition exceeding 5 adversely affects the hot workability. REM is industrially used for Y alloy, La alloy, Ce alloy,
It is often added as a misch metal (including La, Ce, Nd, etc.), but any element belonging to Group IIIA in the periodic table may be used. The preferred content of Y and REM is 0.
It is in the range of 02 to 0.1% by mass.

N: 0.02 to 0.20% by mass It is an important alloy component for increasing the high temperature strength of austenitic stainless steel, and the N content of 0.02% by mass or more has a remarkable effect of increasing the high temperature strength. become. But 0.2
If an excessive amount of N exceeding 0 mass% is contained, workability is adversely affected. The preferable range of N content is 0.05 to
It is 0.15 mass%. Nb: 0.05 to 0.5 mass% is an alloy component added as necessary, and has the function of fixing C and improving the intergranular corrosion resistance of steel. Also, S
In the present component system containing i, it also works to increase the high temperature strength by composite addition with N. Such an effect is 0.
It appears remarkably with addition of 05 mass% Nb. But 0.5
When an excessive amount of Nb exceeding mass% is added, it is combined with N which is a high temperature strengthening element and becomes a precipitate harmful to high temperature strength. Nb
Excessive addition of γ also promotes generation of σ phase.

Ti: 0.05 to 0.5 mass% An alloy component added as necessary, which fixes C to improve intergranular corrosion resistance and also effectively acts at improving high temperature strength. To do. However, excessive addition of Ti causes deterioration in hot workability and surface properties of the steel sheet. Therefore, when adding Ti, the Ti content is set in the range of 0.05 to 0.50 mass%. Mo: 0.1-4.0 mass%, Cu: 0.1-4.0 quality
%% This is an alloy component added as necessary, and both have the effect of improving high temperature strength and corrosion resistance. However, excessive addition of Mo and Cu not only raises the cost of steel materials, but also causes the deterioration of hot workability and toughness of steel.
Therefore, when Mo and Cu are added, each is 0.1
The content of Mo and Cu is set in the range of up to 4.0 mass%.

[0030]Al: 0.01 to 2.5 mass% It is an alloy component that is added as needed and has high temperature oxidation resistance.
On the other hand, it is an effective component for improving the
Workability and σ embrittlement resistance are adversely affected. So Al
When added, the Al content is in the range of 0.01 to 2.5 mass%.
Determine the amount. Ca: 0.001-0.1 mass% It is an alloy component that is added as needed, similar to REM.
It has the effect of improving high temperature oxidation resistance. However, excessive addition
Addition of Ca has an adverse effect on hot workability, so Ca is added.
In case of Ca content in the range of 0.001 to 0.1% by mass
Determine.

Other components contained in the austenitic stainless steel are not particularly specified in the present invention, but general impurity elements such as O, Sn and Pb are preferably reduced 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, but by further strictly controlling the upper limits of these components, hot workability and weldability are improved. Maintained at an even higher level. Further, the components such as Mg, B, and Co, which are known as effective elements for improving hot workability and toughness, are not particularly specified in the present invention, and may be appropriately added if necessary. It is possible.

[0032]

[Example] Various molten steels having the compositions shown in Table 1 were prepared by a vacuum melting method, and subjected to hot rolling, annealing, cold rolling, and annealing steps to obtain a sheet thickness of 2.0 m.
m cold rolled annealed sheet was manufactured. In the table, Nos. 1 to 9 are steels according to the present invention, and Nos. 10 to 18 are comparative steels. Among the comparative steels, No. 10 is SUS304 equivalent steel, No. 11 is SUS310S equivalent steel, and No. 12 is NCF800 equivalent steel.

[0033]

A test piece was cut out from each cold rolled annealed plate and subjected to a scale peeling test, a carburizing test and a 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 was repeated at 1000 ° C. for 500 cycles in accordance with JIS Z2282, and scale peeling resistance was determined from the weight change before and after the test. evaluated. In the carburizing test, the test piece immersed in the solid carburizing agent was 800 ℃ × 20
A heating carburization treatment was performed for 00 hours or 1000 ° C. × 200 hours, and the carburization resistance was evaluated from the weight change before and after the heating carburization treatment. In the σ embrittlement test, after heating the test piece at 800 ° C. for 1000 hours, the Charpy impact value at room temperature was measured by the impact test according to JIS Z2242, and the carburization resistance was evaluated from the Charpy impact value.

As can be seen from the survey results in Table 2, No. 1
All of the steels of the present invention Nos. 9 to 9 have No. 10 scale peeling resistance and carburization resistance in steam oxidizing atmosphere, SUS304, No. 11
SUS310S, No.12 NCF800, and σ embrittlement resistance were also superior to SUS310S. On the other hand, the No. 10 SUS304 equivalent steel was excellent in σ embrittlement resistance, but was significantly inferior in scale peeling resistance and carburization resistance due to the low Si content. No. 11 SUS310S equivalent steel is inferior in scale peeling resistance and carburization resistance due to its low Si content.
Further, since it contained a large amount of Cr, it was also inferior in σ embrittlement resistance. The No. 12 steel equivalent to NCF800 was inferior in scale delamination resistance due to its low Si content, and was inferior in carburization resistance at 800 ° C due to its high Ni content.

The lower limit of the Si content specified by the present invention is 1.5.
The comparative steel of No. 13, which was less than mass%, was inferior in carburization resistance. No.1 with low Si content and no added REM
The comparative steel of No. 4 was significantly inferior in both scale peeling resistance and carburization resistance to the steel of the present invention. No. without REM additive
Comparative steel No. 15 has carburization resistance and σ resistance similar to those of the steels of the present invention.
Although it showed brittleness, it was inferior in scale peeling resistance.
No. 16 and 17 comparative steels containing excess Si and excess C
The comparative steel No. 18 containing r showed good scale peeling resistance and carburization resistance, but was inferior in σ embrittlement resistance.
From the above comparison, it is confirmed that the scale peeling resistance and the carburization resistance are improved by adding an appropriate amount of Si and adding REM together.

[0037]

[0038]

As described above, the austenitic stainless steel of the present invention is not compatible with each other by adding a specific amount of Si and adding one or more of Y and REM together. The steam oxidation resistance, carburization resistance, and σ embrittlement resistance, which have been considered to be the above, are secured at a high level. This austenitic stainless steel utilizes excellent heat resistance, contains both steam and carburizing gas, and has a severe high temperature atmosphere including reforming reaction members of small hydrogen generators that often undergo repeated heating and cooling. Used as a structural member exposed to.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of Si and REM contents on scale delamination caused by repeated heating and cooling in a steam oxidizing atmosphere.

FIG. 2 is a graph showing the effect of Si content on carburizing resistance in a carburizing atmosphere and toughness after aging.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiyuki Fujimura             4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nissin             Steel Business Division, Stainless Steel Company (72) Inventor Yoshiaki Hori             4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nissin             Steel Business Division, Stainless Steel Company (72) Inventor Toshiro Nagoshi             4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nissin             Steel Business Division, Stainless Steel Company (72) Inventor, Masanori Kadowaki             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. (72) Inventor Yukinori Akiyama             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd.

Claims (2)

[Claims] 1. C: 0.02 to 0.10 mass%, Si:
1.5 to 2.5 mass%, Mn: 2.0 mass% or less, P:
0.04 mass% or less, S: 0.02 mass% or less, Ni:
7-12% by mass, Cr: 15-25% by mass, Y and REM
One or more (rare earth metal): 0.001 in total
To 0.1% by mass, N: 0.02 to 0.20% by mass, the balance being substantially Fe composition, and austenite excellent in steam oxidation resistance, carburization resistance and σ embrittlement resistance. Series stainless steel. 2. Nb: 0.05 to 0.5% by mass, T
i: 0.05 to 0.5 mass%, Mo: 0.1 to 4.0 mass%, Cu: 0.1 to 4.0 mass%, Al: 0.01 to
The austenitic stainless steel according to claim 1, containing one or more of 2.5 mass% and Ca: 0.001 to 0.1 mass%.