Technical field
[0001]
　The present invention relates to austenitic stainless steel.
Background technique
[0002]
　In Japan, since the 1990s, high temperature and high pressure of the boiler proceeds, ultra supercritical pressure steam temperature exceeds 600 ℃ (USC: Ultra Super Critical power) boiler has become mainstream.
　On the other hand, Europe, including China, even in the world of the boiler, CO of the global environment measures 2 from the point of view of reduction, high efficiency of USC boiler has been one after another construction.
　The steel material used in the piping of the heat exchanger tubes and a boiler for generating high-temperature, high-pressure steam in a boiler, high temperature strength is great hopes high steel, in recent years, various steel materials have been developed.
[0003]
　For example, Patent Document 1, excellent high-temperature strength and, 18Cr-based austenitic stainless steel excellent in steam oxidation resistance have been disclosed.
　Patent Document 2, austenitic stainless steel is disclosed having excellent high temperature corrosion thermal fatigue cracking.
　Patent Document 3 discloses excellent heat austenitic stainless steel high-temperature strength and耐繰flashing oxidation properties.
[0004]
　Patent Document 4, austenitic stainless steel is disclosed having excellent toughness even after prolonged exposure to high temperature environments.
　Patent Document 5 discloses 800 ° C. × at 600 hours creep rupture strength of more than 100MPa high strength austenitic stainless steel.
[0005]
　Patent Document 6, a method of securing to supplement the low strength of the low carbon stainless steel, high-temperature strength by utilizing the precipitation strengthening of the large amount of N (nitrogen) solution strengthening and nitride by adding (large amount N addition method) There has been disclosed.
[0006]
　Patent Document 1: Japanese Patent No. 3632672
　Patent Document 2: Patent No. 5029788 Patent Publication
　Patent Document 3: Japanese Patent No. 5143960
　Patent Document 4: Japanese Patent No. 5547789 discloses
　Patent Document 5: Japanese Patent No. 5670103
　Patent Document 6: JP No. 3388998 Publication
Summary of the Invention
Problems that the Invention is to Solve
[0007]
　Generally, in the heat exchanger tubes and the material steel design component composition which is used in the pipe of the boiler to be used in a high temperature range used in the high temperature range, high-temperature strength (e.g. creep strength), high-temperature corrosion resistance, steam oxidation resistance, thermal fatigue resistance while the like are important, the corrosion resistance in the temperature range of from room temperature to 350 ° C. vicinity (e.g., stress corrosion cracking resistance in water) is not important. The reason is that the corrosion resistance in the temperature range of from room temperature to 350 ° C. vicinity is because the addressed in construction technology or operational management techniques conventionally.
[0008]
　However, in recent years, welds, the heating installation parts, such as the bent portion, due to the precipitation of heterogeneous metal structure or nonuniform carbide, in water at ordinary temperature and low temperature (about 350 ° C. or less), the stress corrosion cracking It has become a major problem to occur.
　For example, when stopping the operation of the hydrostatic test or when the boiler of the boiler, in the heat exchanger tubes will be water stagnates for a long time, this time, there are cases where stress corrosion cracking is generated conspicuously.
[0009]
　Stress corrosion cracking of stainless steel, at the crystal grain boundary vicinity, by the formation of a low layer of deposited or Cr concentration in the Cr carbide (Cr depleted layer) is generated by the crystal grain boundary is easily selectively corroded.
[0010]
　As a method of preventing the stress corrosion cracking of 18Cr austenitic stainless steels, conventionally, to reduce the amount of C, a method of inhibiting the formation of grain boundary Cr carbide (low carbon method),
suppress the formation of grain boundary Cr carbide to form the MC carbides by adding high Nb and Ti carbides forming ability than Cr, the method of fixing the C (stabilization heat treatment process), with the addition of more than 22% Cr suppress the formation of Cr-depleted layer and a method for suppressing the intergranular selective corrosion (multimeric Cr addition method),
and the like are known.
[0011]
　However, there are problems in any of the methods.
　In low-carbon method, without generating a valid carbide high-temperature strength, high-temperature strength tends to decrease.
　In stabilizing heat treatment process, must be a stabilizing heat treatment at temperatures as low as 950 ° C., high temperature strength, in particular, tend to creep strength is impaired.
　In multimeric Cr addition method, since a brittle phase such as sigma phase is produced in large quantities, for the maintenance of stability and high-temperature strength of the metal structure, it is necessary to add the expensive Ni in large quantities, greatly it is material costs there is a tendency to rise.
[0012]
　The method described in Patent Document 6 (large amount N addition method) are devised methods as an alternative to conventional methods described above.
　The large amount N addition method, to compensate for the low strength of the low carbon stainless steel, utilizing precipitation strengthening of the solid solution strengthening and nitride by a large amount of N added is a way to ensure high temperature strength.
[0013]
　However, the method of Patent Document 6 (large amount N addition method), and generates a large amount of nitride, rather, a problem that stress corrosion cracking occurs, or, sufficient high-temperature strength in a high temperature range of not lower than 700 ° C. to give it has been found that there is a problem that is not.
[0014]
　The above-described circumstances, the 18Cr austenitic stainless steels, conventional, low-carbon method, stabilization heat treatment process, a large amount of Cr method, and regardless of the large amount N addition method, excellent high temperature strength and stress corrosion cracking resistance It is required to ensure.
　An object of the present invention, there is provided a 18Cr austenitic stainless steel, is to provide an excellent high temperature strength and stress austenitic stainless steel corrosion cracking resistance is ensured.
Means for Solving the Problems
[0015]
　The means for solving the above problems includes the following aspects.
[0016]
<1> component composition, by
mass%, C:
0.05
~ 0.13%, Si: 0.10 ~ 1.00%, Mn: 0.10
~ 3.00%, P: 0.040%
hereinafter, S: 0.020% or
less,
Cr: 17.00 ~
19.00%, Ni: 12.00 ~ 15.00%, Cu: 2.00
~ 4.00%, Mo: 0.01 ~ 2
% .00,
W: 2.00
~ 5.00%, 2Mo + W: 2.50 ~
5.00%, V: 0.01 ~ 0.40%, Ti: 0.05 ~
0.50%, Nb:
~
0.70% 0.15,
Al: 0.001 ~ 0.040%, B: 0.0010 ~ 0.0100%
N: 0.0010 ~ 0.0100%, Nd: 0.001 ~ 0.20
%, Zr: 0.002% or
less, Bi: 0.001% or
less, Sn: 0.010% or
less, Sb: 0.010% or
less, Pb: 0.001% or
less, As: 0.001% or
less, Zr + Bi + Sn + Sb + Pb + As: 0.020% or
less, O: 0.0090% or
less, Co: 0.80% or
less, Ca: 0.20% or
less, Mg: 0. 20% or less,
Lanthanide elements other than Nd, Y, Sc, Ta, Hf, and Re 1 or more kinds of 0.20% in total less, and,
the balance Fe and impurities,
　defined by the following formula (1) effective M amount Meff is, austenitic stainless steel is 0.0001 to 0.250%.
[0017]
　Effective M amount Meff = Nd + 13 · (B -11 · N / 14) -1.6 · Zr ... formula (1)
(In the formula (1), each element symbol represents the content of each element (mass%) .)
[0018]
<2> The component composition is, by mass%, Co: 0.01 ~ 0.80% , Ca: 0.0001 ~ 0.20%, and, Mg: 0.0005 ~ 0.20% of one or containing two or more austenitic stainless steel according to <1>.
<3> The component composition, by mass%, lanthanide elements other than Nd, Y, Sc, Ta, Hf, and Re 1 kind or two or more, including 0.001 to 0.20 percent in total <1 > or austenitic stainless steel according to <2>.
<4> metal structure of ASTM grain size number of 7 or less <1> to <3> Austenitic stainless steel according to any one of.
<5> 700 ℃, 1 million hours creep rupture strength of at least 140MPa <1> ~ <4> Austenitic stainless steel according to any one of.
Effect of the Invention
[0019]
　According to the present invention, there is provided a 18Cr austenitic stainless steel, provides superior high temperature strength and stress austenitic stainless steel corrosion cracking resistance is ensured.
DESCRIPTION OF THE INVENTION
[0020]
　Hereinafter, embodiments of the present invention will be described.
　In this specification, numerical ranges expressed using "to" means a range including numerical values described before and after "to" as the lower and upper limits.
　Further, in this specification, showing the content of elements indicate a value of "%" and effective M amount Meff "%" are all means "% by mass".
　Further, in this specification, the content of C (carbon), may be referred to as "C content". It may be referred Similarly, the content of the other elements.
[0021]
　Austenitic stainless steel of the present embodiment (hereinafter, also referred to as "steel of the present embodiment") is a component composition, by mass%, C: 0.05 ~ 0.13%, Si: 0.10 ~ 1.00 %, Mn: 0.10 ~ 3.00%, P: 0.040% or less, S: 0.020% or less, Cr: 17.00 ~ 19.00%, Ni: 12.00 ~ 15.00% , Cu: 2.00 ~ 4.00%, Mo: 0.01 ~ 2.00%, W: 2.00 ~ 5.00%, 2Mo + W: 2.50 ~ 5.00%, V: 0.01 ~ 0.40%, Ti: 0.05 ~ 0.50%, Nb: 0.15 ~ 0.70%, Al: 0.001 ~ 0.040%, B: 0.0010 ~ 0.0100%, N: 0.0010 ~ 0.0100%, Nd: 0.001 ~ 0.20%, Zr: 0.002% or less, Bi: 0.001% or less, n: 0.010% or less, Sb: 0.010% or less, Pb: 0.001% or less, As: 0.001% or less, Zr + Bi + Sn + Sb + Pb + As: 0.020% or less, O: 0.0090% or less, Co: 0.80% or less, Ca: 0.20% or less, Mg: 0.20% or less, lanthanoid elements other than Nd, Y, Sc, Ta, Hf, and Re 1 or more kinds of: 0 in total. 20% or less, and the balance: Fe and impurities, is effective M amount Meff 0.0001 to 0.25% of a defined by the following formula (1).
[0022]
　Effective M amount Meff = Nd + 13 · (B -11 · N / 14) -1.6 · Zr ... formula (1)
(In the formula (1), each element symbol represents the content of each element (mass%) .)
[0023]
　The chemical composition of the steel of the present embodiment, Cr: 17.00 containing ~ 19.00%.
　That is, the steel of this embodiment, belong to the 18Cr based austenitic stainless steel.
　As described above, in the 18Cr austenitic stainless steels, conventional, low-carbon method, stabilization heat treatment process, a large amount of Cr method, and regardless of the large amount N addition method, excellent high-temperature strength and stress corrosion cracking resistance to ensure there is a demand.
[0024]
　According to the steel of the present embodiment, a conventional, low-carbon method, stabilization heat treatment process, a large amount of Cr method, and regardless of the large amount N addition method, is ensured excellent high temperature strength and stress corrosion cracking resistance that.
　The steel of the present embodiment, the reason for this effect is exhibited is estimated as follows. However, the present invention is not limited by the following speculation.
[0025]
　The steel of the present embodiment, the Nd and B, respectively added in combination with the content, further, by effective M amount Meff is adjusted to the above range, the grain boundary cleaning and strength improvement is achieved .
　Further, in the steel of the present embodiment, an impurity, Zr, Bi, Sn, Sb, Pb, and As (hereinafter, is also referred to as "impurity 6 element") by the content of limiting the above range, high purity can be achieved.
　Described above, the grain boundary cleaning, improve strength, and the high purity, low carbon method, stabilization heat treatment process, and regardless to any of a large amount of Cr method, excellent high temperature strength and stress corrosion cracking resistance There is believed to be secure.
[0026]
　Further, in the steel of the present embodiment, to reduce the N (nitrogen) and as possible (specifically 0.0100% or less), by the W added in an amount of above, stable precipitation of fine carbides and fine precipitation strengthening by precipitation of a Laves phase is considered to be made possible.
　As a result, regardless of the large amount N addition method (e.g., see Patent Document 6), in 18Cr austenitic stainless steels, considered excellent high-temperature strength is secured.
　This finding is a novel finding that contrary to the conventional common sense.
[0027]
　Usually, carbides and Laves phase, around the nitrides, and then preferentially deposited on the nitride crystal grain boundaries, impairing the high-temperature strength and corrosion resistance. That is, when the nitride is present, precipitation of fine carbides and precipitation of fine and stable Laves phase are both difficult and high-temperature strength is not improved. In particular, the presence of coarse Zr nitride, since precipitation of fine carbides and precipitation of fine and stable Laves phase becomes more difficult, as much as possible, it is necessary to reduce the N and Zr.
　However, N traces of form precipitation nuclei contributing fine carbides which improves the high temperature strength. Therefore, in the steel of the present embodiments, N, rather than the impurity elements, useful elements (specifically, from 0.0010 to 0.0100%) extremely low weight region managed by.
　The steel of the present embodiment, by setting the N content and from 0.0010 to 0.0100%, both precipitation strengthening and stable Laves phase precipitation strengthening and fine by fine carbide is effectively achieved, as a result, in a temperature range of not lower than 700 ° C., it is possible to secure the high temperature strength, stabilize the metal structure.
　That is, in the steel of the present embodiment, without depending on the precipitation strengthening of the nitride, can achieve high strength, and without the generation of embrittlement equality can be achieved to stabilize the metal structure. This approach is not in the prior art technique.
[0028]
　Hereinafter, first, it describes the chemical composition and its preferred embodiments of the steel of the present embodiment, subsequently, the effective M amount Meff (formula (1)) and the like will be described.
[0029]
　C: 0.05 ~ 0.13%
　C, the stabilization of the product and austenite structure of the carbide, furthermore, is an essential element for stabilization of the metal structure in improvement and high-temperature high-temperature strength.
　Steel of the present embodiment, without using the strengthening by the addition of N, also the stress corrosion cracking without reducing the C can be prevented.
　However, when the C content is less than 0.05%, since the stabilization of the metal structure in improving the high temperature creep strength at high temperature is difficult, the C content is 0.05% or more. C content is preferably 0.06% or more.
[0030]
　On the other hand, when the C amount exceeds 0.13%, coarse Cr carbide is precipitated at grain boundaries cause stress corrosion cracking or weld cracking, also toughness is reduced. Therefore, C content is 0.13% or less. C content is preferably 0.12% or less.
[0031]
　Si: 0.10 ~
　1.00% Si functions as a deoxidizer during steel making and is an element to prevent the steam oxidation at high temperatures. However, the Si content is less than 0.10%, since the effect of addition can not be obtained sufficiently, the amount of Si is 0.10% or more. Si content is preferably 0.20% or more.
[0032]
　On the other hand, Si content exceeds 1.00%, the workability is decreased, since a brittle phase such as sigma phase at elevated temperatures is deposited, Si content is set to 1.00% or less. Si content is preferably 0.80%.
[0033]
　Mn: 0.10 ~
　3.00% Mn is to detoxify S by forming a S and MnS impurity element, it contributes to the improvement of hot workability, which contributes to the stabilization of the metal structure at a high temperature it is an element.
　However, the Mn content is less than 0.10%, since the addition effect is not sufficiently obtained, Mn content is set to 0.10% or more. Mn content is preferably 0.20% or more.
　On the other hand, when the Mn amount exceeds 3.00%, since the weldability and workability is lowered, the amount of Mn is not more than 3.00%. Mn content is preferably 2.60% or less.
[0034]
　P: 0.040% or less
　P is an impurity element, an element that inhibits workability and weldability.
　When the P content exceeds 0.040% workability and weldability is significantly reduced. Therefore, P content is set to 0.040% or less. P amount is preferably 0.030% or less, more preferably 0.020% or less.
[0035]
　P, because the less preferred, P amount may be 0%.
　However, P is might inevitably mixed from the steel material (ore, scrap, etc.) and reducing the P content to less than 0.001%, the production cost is greatly increased. Therefore, from the viewpoint of production cost, P amount may be 0.001% or more.
[0036]
　S: 0.020% or less
　S is an impurity element, workability, weldability, and is an element that inhibits stress corrosion cracking resistance.
　When S content exceeds 0.020% workability, weldability, and stress corrosion cracking resistance is remarkably lowered. Therefore, S amount is 0.020% or less.
　There is a case of adding S to improve fluidity during welding, but such a case, the addition of 0.020% or less. S content is preferably 0.010% or less.
[0037]
　S, since preferably as small, S amount may be 0%.
　However, S is might inevitably mixed from the steel material (ore, scrap, etc.) and to reduce the S content to less than 0.001%, the production cost is greatly increased. Therefore, from the viewpoint of production cost, S amount may be 0.001% or more.
[0038]
　Cr: 17.00 ~
　19.00% Cr, as the main element of 18Cr austenitic stainless steel, oxidation resistance, steam oxidation resistance, improved stress corrosion cracking resistance, and, the strength and the metal structure by Cr carbide an element which contributes to the stabilization.
　The Cr content is less than 17.00%, the addition effect is not sufficiently obtained. Therefore, Cr content is set to 17.00% or more. Cr content is preferably not less than 17.30%, more preferably at least 17.50%.
[0039]
　On the other hand, when the Cr content exceeds 19.00% in order to maintain the stability of the austenitic structure, other required a large amount of Ni, brittle phase is generated, the high-temperature strength and toughness is reduced. Therefore, Cr content is set to 19.00% or less. Cr content is preferably not more than 18.80%, more preferably at most 18.60%.
[0040]
　Ni: 12.00 ~
　15.00% Ni is an austenite forming element, as the main element of 18Cr austenitic stainless steel, the improvement of high temperature strength and workability, as well as contributing to the stabilization of the metal structure at a high temperature it is an element.
[0041]
　The Ni content is less than 12.00%, the addition effect is insufficient, also, Cr, W, and out of balance between the amount of ferrite forming elements such as Mo, high temperature brittle phase (sigma phase and the like) to promote the formation of. Therefore, Ni amount is set to 12.00% or more. Ni content is preferably 12.50% or more.
[0042]
　On the other hand, when the Ni content exceeds 15.00%, the high temperature strength and is uneconomical, or less. 15.00%. Ni amount is preferably 14.90%, more preferably not more than 14.80%, more preferably not more than 14.50%.
[0043]
　Cu: 2.00 ~
　4.00% Cu are fine, and precipitates as stable Cu phase at a high temperature, an element which contributes to the improvement of high-temperature strength.
　The Cu content is less than 2.00%, since the effect of addition can not be obtained sufficiently, the Cu content is 2.00% or more. Cu content is preferably 2.20% or more, and more preferably not less than 2.50%.
[0044]
　On the other hand, when the Cu content exceeds 4.00% workability, creep ductility, and strength is lowered. Therefore, Cu content is not more than 4.00%. Cu amount is preferably 3.90%, more preferably not more than 3.80%, more preferably not more than 3.50%.
[0045]
　Mo: 0.01 ~
　2.00% Mo is corrosion resistance, high temperature strength, and is an essential element in improving the stress corrosion cracking resistance. Further, Mo is a synergistic effect of the combined addition of is W, an element which contributes to the formation of long-term stability of Laves phase and a carbide at high temperatures.
[0046]
　The Mo content is less than 0.01%, the addition effect is not sufficiently obtained, Mo is 0.01% or more. Mo content is preferably 0.02% or more.
[0047]
　On the other hand, when the Mo content exceeds 2.00%, a brittle phase is produced in large quantities, workability, high temperature strength, and, since toughness is reduced, Mo is not more than 2.00%. Mo amount is preferably 1.80%, more preferably not more than 1.50%, more preferably not more than 1.30%.
[0048]
　W: 2.00 ~ 5.00%
　W, the corrosion resistance, high temperature strength, and is an essential element in improving the stress corrosion cracking resistance. Further, in a synergistic effect by combined addition with Mo, it is an element contributing to the precipitation of long stable Laves phase and a carbide at high temperatures. Further, W is, since the diffusion at high temperatures is lower than Mo, at elevated temperatures, an element which contributes to the stable long time maintenance of strength.
[0049]
　The W content is less than 2.00%, since the addition effect is not sufficiently obtained, W content is set to 2.00% or more. W amount is preferably 2.10% or more.
[0050]
　On the other hand, if the W amount exceeds 5.00%, a brittle phase is produced in large quantities, since workability and strength is lowered, the W content is not more than 5.00%. W content is preferably not more than 4.90%, more preferably not more than 4.80%, more preferably not more than 4.70%.
[0051]
　2Mo + W: 2.50 ~
　5.00% combined addition of Mo and W, the high-temperature strength, stress corrosion cracking resistance, and contributes to improvement of high-temperature corrosion resistance. 2Mo + W (wherein, Mo represents Mo content, W is. Hereinafter the same. Representing the W content) is less than 2.50%, it is not sufficiently obtained synergistic effect combined addition. Therefore, 2Mo + W is 2.50% or more. 2Mo + W is preferably not less than 2.60%, more preferably 2.80% or more, more preferably at least 3.00%.
[0052]
　On the other hand, if 2Mo + W exceeds 5.00%, it decreases the strength and toughness, also, the stability of the metal structure at a high temperature is reduced. For this reason, 2Mo + W is equal to or less than 5.00%. 2Mo + W is preferably 4.90% or less.
[0053]
　V: 0.01 ~ 0.40%
　V, together with Ti and Nb, forms fine carbide, an element which contributes to the improvement of high-temperature strength. The amount V is less than 0.01%, the addition effect is not sufficiently obtained, V amount is 0.01% or more. V content is preferably 0.02% or more.
[0054]
　On the other hand, when the amount of V exceeds 0.40%, the strength and the stress corrosion cracking resistance decreases, V content is set to 0.40% or less. V content is preferably less 0.38%.
[0055]
　Ti: 0.05 ~
　0.50% Ti, as well as V and Nb, forms fine carbides, thereby contributing to the improvement of high temperature strength, by fixing the C, suppress the precipitation of Cr carbides at grain boundaries and an element which contributes to the improvement of stress corrosion cracking resistance.
[0056]
　In conventional N addition of austenitic stainless steel, nitrides precipitated in bulk, not only the effect of N addition is not effectively expressed, stress corrosion cracking resistance by precipitation of coarse Cr carbides at grain boundaries is lowered .
　The present inventors have found that in 18Cr austenitic stainless steel, by managing the amount of N in the extremely low level, the useful effect of the fine Ti carbides are exhibited, specifically, a fine Ti carbide fine Laves phase precipitates as nuclei, resulting was found that high-temperature strength of the steel is greatly improved.
[0057]
　The Ti content is less than 0.05%, the addition effect is not sufficiently obtained, the Ti content is 0.05% or more. Nb, combined addition of V is preferably, Ti content is preferably 0.10% or more.
[0058]
　On the other hand, if the Ti content exceeds 0.50%, precipitation of massive precipitated strength, toughness, and, since the stress corrosion cracking resistance decreases, Ti amount is 0.50% or less. Ti content is preferably 0.45% or less.
[0059]
　Nb: 0.15 ~
　0.70% Nb, together with V and Ti, to form a fine carbide, thereby contributing to the improvement of high temperature strength, by fixing the C, suppress the precipitation of Cr carbides at grain boundaries and an element which contributes to the improvement of stress corrosion cracking resistance.
　Moreover, Nb, like Ti, is an element contributing to the improvement of high-temperature strength due to precipitation of fine Laves phase.
[0060]
　The Nb content is less than 0.15%, since the addition effect is not sufficiently obtained, Nb content is set to 0.15% or more. Nb content is preferably 0.20% or more.
　On the other hand, when the Nb content exceeds 0.70% precipitates massive precipitate, strength, toughness, and, since the stress corrosion cracking resistance decreases, Nb content is set to 0.70%. Nb content is preferably 0.60%.
[0061]
　Al: 0.001 ~
　0.040% Al, at the time of steelmaking, acts as a deoxidizing element, is an element to clean the steel.
　The Al content is less than 0.001%, can not be achieved sufficiently cleaned steel, Al content is set to 0.001% or more. Al content is preferably 0.002% or more.
[0062]
　On the other hand, when the Al content exceeds 0.040% non-metallic inclusions are produced in large quantities, stress corrosion cracking resistance, high temperature strength, workability, toughness, and the stability of the metal structure at high temperatures decreases since, Al content is set to 0.040% or less. Al content is preferably less 0.034%.
[0063]
　B: 0.0010 ~ 0.0100%
　B is the combined addition of an important Nd in the steel of the present embodiment, an element for achieving the securing of excellent high temperature strength and stress corrosion cracking resistance, essential it is an element. B contributes segregated in the grain boundary, not only contributes to the improvement of high temperature strength, effective in improving the high temperature strength, the generation of carbides, miniaturization of Laves phase, and to stabilize the metal structure it is an element.
[0064]
　Further, B is harmless N a (present 0.0010 to 0.0100% in the steel of the present embodiment) as BN, an element which contributes to the improvement of high temperature strength and stress corrosion resistance.
[0065]
　The amount B is less than 0.0010%, B is present without being consumed as nitride, i.e., can not be ensured that contribute B which improves the high temperature strength and stress corrosion resistance. Therefore, when the B content is less than 0.0010%, the synergistic effect (This point will be described later) can not be obtained by the combined addition of Nd (and ensure an effective M amounts), high temperature strength and stress corrosion cracking resistance is not improved. Therefore, B content is set to 0.0010% or more.
　B amount is preferably 0.0015% or more.
[0066]
　On the other hand, when the B content exceeds 0.0100%, the generated boron compounds, workability, weldability, and, since the high temperature strength decreases, the amount of B is set to 0.0100% or less. B amount is preferably 0.0080%, more preferably 0.0060% or less.
[0067]
　N: 0.0010 ~
　0.0100% N (nitrogen), in the general 18Cr austenitic stainless steel, is a useful element for the improvement of high-temperature strength by precipitation strengthening of the solid solution strengthening and nitride. However, in the steel of the present embodiment, nitride since inhibit stress corrosion cracking resistance, N is the not added actively.
　However, N traces, so generates the precipitation nuclei of effective fine precipitates which improves the high temperature strength, in the steel of this embodiment, a trace amount to produce the precipitation nuclei of effective fine precipitates which improves the high temperature strength to allow the N in the range.
[0068]
　That is, the basic idea of ​​the steel of the present embodiment is not added to actively N, in that it allows the N in the range of trace differs from the prior art.
[0069]
　The N content is less than 0.0010%, the formation of precipitation nuclei of effective fine precipitates which improves the high temperature strength is difficult, the N content is 0.0010% or more. N content is preferably 0.0020% or more, more preferably 0.0030% or more.
[0070]
　On the other hand, when the N content exceeds 0.0100% nitrides are produced, since high temperature strength and stress corrosion cracking resistance decreases, the amount of N is set to 0.0100% or less. N content is preferably 0.0090% or less, and more preferably not more than 0.0080%, more preferably not more than 0.0070%.
[0071]
　Nd: 0.001 ~
　0.20% Nd is a synergistic effect (to be described later) by the combined addition of B, and an element which remarkably improves the high temperature strength and stress corrosion cracking resistance.
　As described above, in the steel of the present embodiment, finer effective carbide and Laves phase which improves the high temperature strength, and to ensure long-term stability, further, the combined addition of Nd and B, the crystal to strengthen the grain boundaries to improve the stress corrosion cracking resistance.
[0072]
　However, Nd is, N, O, and bonding force with S is extremely strong, be added as a metal Nd, it will be consumed by precipitation as hazardous precipitates hardly addition effect is sufficiently exhibited. Therefore, in order to obtain a sufficient effect of addition of Nd is minimized, N amount, O amount, and it is necessary to reduce the S content.
[0073]
　The Nd content is less than 0.001%, N content, O content, and even when the reduced S content, the addition effect of Nd is not sufficiently obtained. Therefore, Nd content is set to 0.001% or more. Nd content is preferably 0.002% or more, more preferably 0.005% or more.
[0074]
　On the other hand, if the Nd content exceeds 0.20%, the effect of addition is saturated, and generates the oxide inclusions, strength, processability, and economic efficiency is decreased. Therefore, Nd content is set to 0.20% or less. Nd content is preferably not more than 0.18%, more preferably not more than 0.15%, more preferably not more than 0.10%.
[0075]
　In terms easier to ensure an effective M amount Meff described above, Nd weight range is preferably from 0.002 to 0.15% and more preferably from 0.005 to 0.10%.
[0076]
　In the steel of the present embodiment, in order to secure the excellent characteristics of the steel of the present embodiment treats, Zr, Bi, Sn, Sb, Pb, As, and O as an impurity element, to limit the amount of these elements.
[0077]
　Usually, as a raw material of stainless steel, mainly uses a scrap such as alloy steel, this scrap, albeit in small amounts, Zr, Bi, include Sn, Sb, Pb, and As (impurity 6 elements) is ing. These impurity 6 elements, unavoidably mixed in a stainless steel (product).
[0078]
　Further, in the manufacturing process of stainless steel, the melting equipment and the like are contaminated in the production of other alloys, impurity 6 element from melting equipment or the like is mixed in a stainless steel (products), also O (oxygen), inevitably remain in the stainless steel.
[0079]
　In the steel of the present embodiment, in order to ensure excellent high-temperature strength and stress corrosion cracking resistance, Zr, Bi, Sn, Sb, Pb, As, and O was minimized, they are necessary to make the high purity steel .
[0080]
　Zr: 0.002% or less
　Zr is normally not mixed, mixed from scrap, etc., and / or, dissolution facilities contaminated with the manufacture of other alloys, an oxide and nitride. Nitride functions as nuclei precipitates such as Laves phase is precipitated.
　However, the precipitates massive precipitates a nitride as a nucleus, high temperature strength and stress corrosion cracking resistance is inhibited.
[0081]
　Thus, Zr is an element harmful to the high temperature strength and stress corrosion cracking resistance. Therefore, in the excellent high-temperature strength and effective M amounts relations introduced in order to ensure the stress corrosion cracking resistance (Equation (1)), taking into account the negative effects Effect "- 1.6 - It provided the terms of Zr ".
[0082]
　Zr, because the less preferred, Zr amount is 0.002% near the analysis limit (0.001%) and upper limit. Zr content is preferably 0.001% or less.
　Zr amount may be 0%. However, Zr is inevitably about 0.0001% in some cases be mixed. Therefore, from the viewpoint of production cost, Zr amount may be 0.0001% or more.
[0083]
　Bi: 0.001% or less
　Bi is normally not mixed, mixed from scrap, etc., and / or, dissolution facilities contaminated with the manufacture of other alloys, inhibiting high-temperature strength and stress corrosion cracking resistance it is an element.
　Bi amount, it is necessary to be reduced as much as possible, the upper limit of Bi content, and 0.001% of analysis limit.
Bi amount may be 0%. However, Bi is inevitably about 0.0001% in some cases be mixed. Therefore, from the viewpoint of production cost, Bi amount may be 0.0001% or more.
[0084]
　Sn: 0.010% or less
　Sb: 0.010% or less
　Pb: 0.001% or less
　As: 0.001% or less
　Sn, Sb, Pb, and As, scraps, and / or the production of other alloys in easily mixed from contaminated dissolved facilities, is a difficult element to be removed by refining processes.
　However, the amount of these elements must be reduced as much as possible.
　Therefore, in consideration of the feed composition and refining limits, the upper limit of the Sn content and the amount of Sb, and 0.010%, respectively. Sn amount and the amount of Sb, respectively, is preferably 0.005% or less.
　Further, the upper limit of the amount of Pb and As weight, and 0.001%, respectively. Pb and As, respectively, and preferably not more than 0.0005%.
[0085]
　Sn amount, Sb amount, Pb amount, and As amount may be either 0%.
　However, these elements are inevitably about 0.0001% in some cases be mixed. Therefore, from the viewpoint of production cost, the amount of each element may also be 0.0001% or more.
[0086]
　Zr + Bi + Sn + Sb + Pb + As: 0.020% or less
　present invention steel, Zr, Bi, Sn, Sb, Pb, and As (impurity 6 elements), to inevitably contained, by the synergistic effect of the combined addition of Nd and B, excellent and in order to secure the high temperature strength and stress corrosion cracking resistance, not only to limit the content of impurities 6 elements separately, the sum of the content of impurities 6 elements (Zr + Bi + Sn + Sb + Pb + as; wherein each atomic symbol, the.) representing the content of each element is limited to 0.020% or less, it is necessary to achieve a more highly purified.
　The steel of the present embodiment, the sum of the content of impurity 6 elements is 0.020% or less.
　Total content of impurity 6 element is preferably 0.015% or less, more preferably 0.010% or less.
　On the other hand, from the viewpoint of ensuring the excellent high-temperature strength and stress corrosion cracking resistance, the sum of the content of impurity 6 element is preferably as little as possible. Therefore, the lower limit of the total content of impurity 6 elements is 0%.
[0087]
　O: 0.0090% or less
　after the molten steel refining, O unavoidably residual (oxygen) is an element that serves as an index of non-metallic inclusions amount.
　When O is more than 0.0090%, it will be consumed Nd generates the Nd oxide, generated by fine carbides or Laves phase can not be obtained the effect of improving high temperature strength and stress corrosion cracking resistance. Therefore, O amount is set to less 0.0090%. O amount is preferably 0.0080%, more preferably not more than 0.0070%, still more preferably 0.0050% or less.
[0088]
　O amount may be 0%. However, O after refining, inevitably about 0.0001% in some cases the residual. Therefore, from the viewpoint of production cost, O amount may be 0.0001% or more.
[0089]
　Component composition of the steel of the present embodiment, Co, Ca, and, one or more of Mg, and / or a lanthanoid element other than Nd, Y, Sc, Ta, Hf, and one of Re or it may contain more species.
　All of these elements is also an optional element. Therefore, the content of these elements, respectively, may be 0%.
[0090]
　Co: 0.80% or less
　Co can be a source of contamination in the manufacture of other steels. Therefore, Co content is 0.80% or less. Co content is preferably 0.60%.
　Steel of the present embodiment but need not contain Co (i.e., Co content may be 0%, but), to further stabilize the metal structure, from the viewpoint of further improving the high temperature strength, containing Co it may be.
　When the steel of the present embodiment contains Co, Co amount is preferably 0.01% or more, more preferably 0.03% or more.
[0091]
　Ca: 0.20% or less
　Ca is an arbitrary element, Ca amount may be 0%.
　Ca is an element that may be added as a finishing deoxidation. Since the steel of this embodiment contains Nd, in refining process, it is preferable to deoxidation by Ca. When the steel of the present embodiment contains Ca, from the viewpoint of obtaining a deoxidizing effect more effectively, Ca amount is preferably 0.0001% or more, more preferably 0.0010% or more.
[0092]
　On the other hand, when the Ca amount exceeds 0.20%, increasing the amount of nonmetallic inclusions, high temperature strength, resistance to stress corrosion cracking, and therefore toughness is reduced, the amount of Ca is set to 0.20% or less. Ca content is preferably 0.15% or less.
[0093]
　Mg: 0.20% or less
　Mg is an optional element, Mg amount may be 0%.
　Mg is the addition of small amount, which is an element contributing to the improvement high-temperature strength and corrosion resistance. When the steel of the present embodiment contains Mg, from the viewpoint of obtaining the effects more efficiently, Mg amount is preferably 0.0005% or more, more preferably 0.0010% or more.
[0094]
　On the other hand, when the Mg content exceeds 0.20%, the strength, toughness, so the corrosion resistance, and weldability is deteriorated, Mg content is set to 0.20% or less. Mg content is preferably 0.15% or less.
[0095]
　Lanthanide elements other than Nd, Y, Sc, Ta, Hf, and one or more of the total Re: 0.20% or less
　lanthanide elements other than Nd (i.e., La, Ce, Pr, Pm , Sm, Eu , Gd, Tb, Dy, Ho , Er, Tm, Yb, and Lu), Y, Sc, Ta , Hf, and Re are both optional elements, the total content of these elements is 0% it may be.
　Lanthanide elements other than Nd, Y, Sc, Ta, Hf, and Re is a costly, it is an element of an action to enhance the synergistic effect of the combined addition of Nd and B. When the steel of the present embodiment contains one or more of these elements, the total content of these elements is preferably 0.001% or more, more preferably 0.005% or more .
[0096]
　On the other hand, lanthanide elements other than Nd, Y, Sc, Ta, when Hf, and the total content of Re exceeds 0.20%, increasing the amount of nonmetallic inclusions, strength, toughness, corrosion resistance, and weldability since but decreases, the total content is at most 0.20%. The total content is preferably 0.15% or less.
[0097]
　Balance excluding the non above elements from chemical composition of the steel of the present embodiment is Fe and impurities.
　Impurities herein refers to a one or two or more elements other than the elements described above. The content of the above elements other than the element (impurity) are each preferably be limited to 0.010% or less, it is preferably limited to 0.001% or less.
[0098]
　Component composition of the steel of the present embodiment, the effective M amount Meff which is defined by the following equation (1) is 0.0001 to 0.250%.
　The following describes effective M amount Meff.
[0099]
　Effective M amount Meff = Nd + 13 · (B -11 · N / 14) -1.6 · Zr ... formula (1)
(In the formula (1), each element symbol represents the content of each element (mass%) .)
[0100]
　Effective M amount Meff is essential need to improve the high temperature strength and stress corrosion cracking resistance, which is an index that defines the quantitative relation between Nd and B.
[0101]
　Formula defining the effective M amount Meff (1), in order to ensure excellent high-temperature strength and stress corrosion cracking resistance, which is a relational expression of the present invention have found.
　Equation (1) is basically the amount of Nd effectively function to ensure the excellent high temperature strength and stress corrosion cracking resistance, by adding the amount of B which functions also effectively, and excellent high temperature it is a relational expression of subtracting the amount of harmful Zr to ensure strength and stress corrosion cracking resistance.
[0102]
　The steel of the present embodiment, in order to ensure excellent high-temperature strength and stress corrosion cracking resistance, to reduce as much as possible N, inhibiting the production of nitrides.
　However, when manufacturing industrial steel, a certain amount of N, inevitably mixed into the steel. N mixed in steel, to form a BN, it is impossible to obtain the advantageous effects of B. Therefore, it is necessary to ensure the B that does not bind to N.
[0103]
　In the above formula (1) which defines the effective M amount Meff, part of "(B-11 · N / 14)" are not bound to the N of the amount of B to function effectively (i.e., the addition B B is the quantity).
　In the above formula (1), by a "(B-11 · N / 14 ) " and (N and unbound B amount) was 13 times "13 · (B-11 · N / 14) " , to weight the amount of B to function effectively. Here, 13-fold, the ratio of the atomic weight of B atomic weight of Nd relative to (≒ 11) (≒ 144) .
　In the above formula (1), and adds obtained above to "13 · (B-11 · N / 14) " of the amount of Nd ( "Nd + 13 · (B-11 · N / 14) "). Nd, like B, and an element that effectively functions to ensure excellent high temperature strength and stress corrosion cracking resistance.
[0104]
　In the above formula (1), in addition to "Nd + 13 · (B-11 · N / 14)", a term which subtracts the amount of harmful Zr to ensure excellent high temperature strength and stress corrosion cracking resistance "-1.6 · Zr "exists.
[0105]
　Zr impurity elements, an action which forms nitrides and oxides, counteracting the synergistic effect of the combined addition of Nd and B.
　In equation (1), by by multiplying the atomic weight of Zr atomic weight of Nd relative to (≒ 91) to (≒ 144) is the ratio of 1.6 (≒ 144/91) in the amount of Zr and "1.6Zr" , and weighted on the attenuation effect of Zr.
　In equation (1), the "1.6Zr" is subtracted from the "Nd + 13 · (B-11 · N / 14) ".
[0106]
　As described above, the effective M amount Meff defined by formula (1), the amount of Nd and B necessary to obtain the excellent high-temperature strength and stress corrosion cracking resistance, and excellent high-temperature strength and resistance to it is possible to quantify the limit amount of harmful Zr to ensure stress corrosion cracking resistance (specific example is detailed in example).
[0107]
　When effective M amount Meff is less than 0.0001%, it is difficult to obtain excellent high-temperature strength and stress corrosion cracking resistance. Therefore, effective M amount Meff is 0.0001% or more. Effective M amount Meff is preferably 0.001% or more, more preferably 0.002% or more, further preferably 0.010% or more.
　Incidentally, effective M amount Meff, if N amount or Zr amount is large, it may be negative.
[0108]
　On the other hand, when the effective M amount Meff exceeds 0.250% addition the effect of improving high temperature strength and stress corrosion cracking resistance by effective M amount Meff is lowered economical saturated, strength, toughness, processability, and , weldability decreases. Therefore, effective M amount Meff is 0.250% or less. Effective M amount Meff is preferably 0.200% or less, more preferably 0.150%.
[0109]
　The steel of the metal structure of the present embodiment is not particularly limited.
　Steel metal structure of the present embodiment, from the viewpoint of further improving the high temperature strength (e.g. high temperature creep strength of 700 ℃ ~ 750 ℃), is preferably a coarse metal structure.
　Specifically, the steel of the present embodiment is preferably a metal structure ASTM grain size number of 7 or less.
　Steel metal structure of the present embodiment, if it is 7 or less coarse grain structure in ASTM grain size number, the grain boundary sliding creep, change in metal structure due to diffusion of elements through the crystal grain boundaries, and, sigma phase the effect of suppressing the generation of precipitation sites is considered to be achieved.
　Therefore, the steel of the metal structure of the present embodiment, it is 7 or less coarse grain structure in ASTM grain size number is preferably from the viewpoint of further improving the high temperature strength.
[0110]
　In a general steel, the steel of the metal structure is a coarse metal structure, due to the segregation of impurity elements at grain boundaries, tend to stress corrosion cracking is likely to occur.
　However, in the steel of the present embodiment, the high purity, the segregation of impurity elements at grain boundaries is reduced. Therefore, in the steel of the present embodiment, if a coarse metal structure (for example, if the metal structure ASTM grain size number of 7 or less) even in stress corrosion cracking is suppressed (i.e., excellent stress corrosion cracking resistance is maintained).
[0111]
　From the above viewpoint, ASTM grain size number of the metal structure of the steel of the present embodiment is preferably 7 or less, more preferably 6 or less.
　There is no particular limitation on the lower limit of the ASTM grain size number of the metal structure, from the viewpoint of suppressing degradation and weld cracks creep ductility, the lower limit of the ASTM grain size number of the metal structure is preferably 3.
[0112]
　Steel of the present embodiment, as described above, high-temperature strength (particularly, the creep rupture strength) excellent.
　There is no particular limitation on the specific range of high-temperature strength of the steel of the present embodiment, the steel of this embodiment, 700 ° C., it is preferable creep rupture strength of 10,000 hours is not less than 140 MPa.
[0113]
　Here, 700 ° C., a temperature higher than the actual operating temperature.
　Therefore, 700 ° C., it creep rupture strength of 10,000 hours is not less than 140 MPa, indicating that superior conspicuously high temperature properties.
　Specifically, 700 ° C., high temperature strength creep rupture strength of 10,000 hours is not less than 140MPa, as a conventional 18Cr austenitic stainless steel, 347H steel is widely used in the world (18Cr-12Ni-Nb-based) than is also remarkably excellent high-temperature strength (for example, in Table 3 below, reference inventive steels 1 to 20 and Comparative steel 21).
[0114]
　Creep rupture strength less than 140MPa is readily accomplished by extension of the prior art, the creep rupture strength is at least 140MPa, the achieving an extension of the prior art is difficult.
　In this regard, according to the steel of the present embodiment, suitability of the component composition, suitability of the effective M amount Meff by Nd content and the B content, high purity due to a limitation in the amount of impurity elements, the like, carbides and creep the fine precipitation of Laves phase which precipitates during the actual use temperature higher than 700 ° C., 1 million hours creep rupture strength 140MPa or more (excellent high-temperature strength) can be achieved.
[0115]
　To a method of manufacturing the steel of this embodiment is not particularly limited, it can be appropriately adopted method known austenitic stainless steels.
　Steel of the present embodiment may be a heat-treated steel plate or steel pipe.
　The heating temperature in the heat treatment is easily obtained coarse tissue, a point which makes it easy to improve high-temperature strength (e.g. creep rupture strength), preferably 1050 ~ 1250 ° C., and more preferably from 1150 ℃ ~ 1250 ℃.
　There is no particular limitation on the mode of cooling after heating in the heat treatment may be a quenching (e.g. water cooling), may be air-cooled, quenched are preferred, water cooling is more preferable.
[0116]
　The heat treatment is performed steel or steel, for example, preparing a steel plate or steel pipe having a chemical composition of the steel of the present embodiment described above, the prepared steel or steel, for example, 1050 ~ 1250 ° C. (preferably 1150 ° C. ~ It was heated to 1250 ° C.), and then obtained by cooling.
　Steel or steel having the above component composition (steel plate or steel pipe before heat treatment) both be prepared according to conventional methods.
　Steel pipe having the above chemical composition, for example, by casting a molten steel having the component composition described above as a steel ingot or steel slab, the obtained steel ingot or steel slab, hot extrusion, hot rolling, hot forging , cold drawing, cold rolling, can be prepared by subjecting the cold forging, and at least one processing selected from the group consisting of cutting.
[0117]
　It has been described above steel according to the present embodiment.
　Steel applications of the present embodiment is not particularly limited, steel of the present embodiment can be applied to any application ensuring high temperature strength and stress corrosion cracking resistance are required.
　Steel of the present embodiment, for example, a boiler, a chemical pressure-resistant heat exchanger tubes or pipes, such as a plant, the preferred material steel and the like; heat forging; heat bars; heat the steel sheet.
　Steel of the present embodiment, in particular, the internal pressure-resistant heat exchanger tubes provided in the boiler (e.g., outer diameter 30 ~ 70 mm, thickness 2 ~ 15 mm heat- and pressure-resistant heat exchanger tubes), or pipe of the boiler ( for example, a particularly preferred outer diameter 125 ~ 850 mm, a steel material of the pipe) thick 20 ~ 100 mm.
Example
[0118]
　Next, a description will be given of an embodiment of the present invention, conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is, in this single condition example the present invention is not limited. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0119]
　In this embodiment, the smelted 30 kinds of steels showing the component composition shown in Table 1 and Table 2 (Table 1 continued).
　In Table 1 and Table 2, steels 1 to 20, invention steels (hereinafter, respectively, also referred to as inventive steels 1 to 20) are examples of the present invention is a steel 21-30 are comparative steels are comparative examples (hereinafter, respectively referred to as comparative steels 21-30).
[0120]
　Comparative Steel 21 is a general-purpose 347H (18Cr-12Ni-Nb) steel, which is a standard material for comparing the prior art invention steels 1 to 20.
[0121]
　When melting the invention steels 1 to 20, as a Fe source, using a high purity Fe obtained through the secondary refining by a blast furnace converter smelting and vacuum oxygen degassing process, as an alloying element, pre using high purity alloy elements were analyzed. Furthermore, prior to melting the invention steels 1 to 20, a furnace for melting the invention steels 1 to 20 was sufficiently cleaned, specially considered so impurity contamination does not occur.
　In the preparation of the inventive steels 1 to 20 are the special administrative above (specifically, Zr, Bi, Sn, Sb, Pb, and As) impurity 6 elements, O amount, and N amount is limited, the Nd content and the B content was controlled within a proper range.
[0122]
　When melting the comparative steels 23-30 were also used Fe source of the high-purity, but melting the comparative steels 23-30, further to adjust the component composition in the following manner.
　When melting the comparative steels 21,23,24,27, and 29, intentionally, by adding at least one kind of impurity 6 element and O (oxygen).
　When melting the comparative steels 21, 24, and 26, intentionally, it was added N (nitrogen).
　When melting the comparative steels 21 to 23, 25, 27, and 28, at least one of B and Nd was not added.
　When melting the comparative steel 21, the shortage amount of Cu, and Mo, W, V, and the no-addition of Ti.
　When melting the comparative steel 30 was insufficient addition amount of W.
[0123]
[Table 1]

[0124]
[Table 2]

[0125]
- Description of Table 1 and Table 2 -
, numbers indicate the content of each element (mass%).
And numerical Underlined is a value outside the range of the chemical composition in the present embodiment.
In each steel, the balance excluding the elements shown in Table 1 and Table 2 is Fe and impurities.
· Meff was calculated based on the equation (1) above. Here, the amount of Zr is about the steel is less than 0.001 percent (in Table 2 referred to as "<0.001"), the Zr content 0%, was calculated Meff.
Subtotal (X) (specifically, Zr, Bi, Sn, Sb, Pb, and As) impurity 6 element shown the total amount of (mass%). The content is for elements of less than 0.001 percent (in Table 2 referred to as "<0.001"), was calculated subtotal (X) is 0% content.
[0126]

　Table 1 and the steel component composition shown in Table 2 were melted by vacuum melting, by casting to obtain a steel ingot of 50 kg.
　The resulting steel ingot by hot forging to obtain a steel plate having a thickness of 15 mm.
　By cutting the surface of the steel sheet obtained thickness 15 mm, to obtain a steel plate having a thickness of about 12 mm.
　To steel obtained a thickness of about 12 mm, by applying cold rolling at a reduction of area of about 30%, to obtain a plate-shaped test material having a thickness of about 8 mm.
　The test material was heated to for 15 minutes in 1200 ° C., after holding, by water cooling, to the test material was heat-treated at 1200 ° C..
[0127]

　the ASTM grain size of the test material after the heat treatment was measured in accordance with ASTM E112. Measurement position of the ASTM grain size was a thick central portion and around the longitudinal section of the test material.
　The results are shown in Table 3.
[0128]

　from the test material after the heat treatment, the longitudinal direction of the test material and the longitudinal direction, 6mm, were cut creep rupture test piece parallel portion 30 mm. Using this creep rupture test specimen, 700 ° C., to implement long-term creep rupture test of more than 10,000 hours, as a high-temperature strength, 700 ° C., it was measured creep rupture strength of 10,000 hours (MPa).
　The results are shown in Table 3.
[0129]

　from the heat treatment after the test materials were cut corrosion test strip of width 10 mm × thickness 4 mm × length 40 mm. The cut corrosion test piece, hereinafter referred to as "base material".
　To the base material, 10 hours at 650 ° C., and was heated aging treatment.
　To the base material after the heat aging, Strauss test (ASTM A262, Practice E: sensitization Evaluation) was performed to determine the presence or absence of depth 100μm or more cracks.
　The above results are shown in Table 3.
[0130]

　from the heat treatment after the test materials were cut corrosion test strip of width 10 mm × thickness 4 mm × length 40 mm.
　The cut test piece, Gleeble testing machine (vacuum, conduction heating) used, 950 ° C., heated 25 seconds. After heating, by cooling by blowing He, to obtain weld HAZ equivalent material (HAZ equivalent material).
　The obtained weld HAZ equivalent material, as in the stress corrosion cracking test of the base metal, conducted heat aging treatment and Strauss test to determine the presence or absence of depth 100μm or more cracks.
　The results are shown in Table 3.
[0131]
[table 3]

[0132]
　As shown in Table 3, the metal structure of the inventive steels 1 to 20 and comparative steels 21-30 were both ASTM grain size number of 7 or less coarse grain structure.
[0133]
　As shown in Table 3, high-temperature strength of the invention steel 1-20, an excellent strength of at least 147 MPa, was about 1.5 times or more the high temperature strength of the comparative steel 21 (generic 347H steel).
　On the other hand, high-temperature strength of the comparative steels 21-30 are following a low strength 137 MPa, it was inferior in comparison with the high-temperature strength of the invention steel 1-20.
[0134]
　As shown in Table 3, the inventive steels 1 to 20, the invention steels, both base metal and weld HAZ equivalent material, or more cracking depth 100μm was not confirmed. From these results, invention steels 1 to 20 was demonstrated to have an excellent stress cracking resistance.
　Meanwhile, the comparative steels 21-28, more crack depth 100μm was confirmed.
[0135]
　More specifically, the comparative steels 21 B also Nd is also additive-free, and, B is being added comparative steels 22, 23, 25 Nd is not added, and the results of 27, the addition of Nd it has been demonstrated to be effective in improving the high temperature strength and stress corrosion cracking resistance.
[0136]
　Although Nd and B are added in combination, is an excessive amount of N, from the results of Comparative Steel 26 Meff is less than 0.0001 wt%, N content is not more 0.0100% or less, is Meff to be 0.0001 to 0.250%, it has been demonstrated to be effective in improving the high temperature strength and stress corrosion cracking resistance.
[0137]
　Further, Meff are in the range of 0.0001 to 0.25 percent, is O amount is 0.0090% greater, from the results of Comparative Steel 24 N amount is 0.0100%, the O amount is or less 0.0090% N amount not more 0.0100% or less, it has been demonstrated to be effective in improving the high temperature strength and stress corrosion cracking resistance.
　Why the high temperature strength of the comparative steel 24 is low, Nd and B, respectively, will be consumed as an oxide or nitride, fine precipitation strengthening due to not expressed, and is presumed.
[0138]
　Further, from the results of comparative steels 28, B the amount of not less than 0.0010%, it has been demonstrated to be effective in improving the high temperature strength and stress corrosion cracking resistance.
　Further, from the results of comparative steels 29, that the amount of Zr is less than 0.002% has proved to be effective in improving the high temperature strength.
　Further, from the results of comparative steels 30, that the W content is 2.00% or more, it has been demonstrated to be effective in improving the high temperature strength.
[0139]

　invention steel 1, 10, and 17, as well as, for comparative steels 21 and 23, in order to examine the relationship between the grain size and the stress corrosion cracking of the steel, the following test was performed .
[0140]
　First, the heat treatment of 1200 ° C. as described above has been subjected test material, by the method described above, the measurement of ASTM grain size, stress corrosion cracking test of the base metal, and was carried out stress corrosion cracking test of the weld HAZ equivalent material. However, here, the stress corrosion cracking test of the base metal and weld HAZ equivalent material, as well as measuring the depth of the crack was observed the state of cracks in detail.
　The results are shown in Table 4.
[0141]
　Then, the test material before the heat treatment of 1200 ° C. as described above is performed by heating to 1125 ° C., and held at this temperature for 15 minutes, after holding, by water cooling, to the test material, the heat treatment of 1125 ° C. It was applied.
　The heat treatment of 1125 ° C. is applied test material, similar to the heat treatment 1200 ° C. is applied test material, the measurement of ASTM grain size, stress corrosion cracking test of the base metal, and stress corrosion cracking in the weld HAZ equivalent material the test was carried out.
　The results are shown in Table 4.
[0142]
[Table 4]

[0143]
　Table 4 and as shown in Table 3 above, inventive steels 1, 10, and 17, and, in the comparative steels 21 and 23, the metal structure of the test materials subjected to the heat treatment at 1200 ° C. is, ASTM grain size number of 7 or less It was a coarse grain structure.
　On the other hand, as shown in Table 4, invention steels 1, 10 and 17, and, in comparative steels 21 and 23, the metal structure of the test materials subjected to the heat treatment at 1125 ° C. is, ASTM grain size number of 8 or more fine grained structure It became.
[0144]
　Further, as shown in Table 4, the inventive steels 1, 10, and 17, even when there either fine tissues (ASTM grain size number 8 or higher) and coarse tissue (ASTM grain size number of 7 or less), compared to comparative steels 21 and 23, stress corrosion cracking has been sufficiently reduced.
　For these invention steels, comparative steels 21 and 23, even when there either fine tissues (ASTM grain size number 8 or higher) and coarse tissue (ASTM grain size number of 7 or less), cracking due to stress corrosion cracking tests depth is at 2mm or more, remarkable stress corrosion cracking occurs. In particular, the weld HAZ equivalent material, generated many more cracks 3 mm.
[0145]
　As described above, the invention steels 1,10, and 17, as compared with the comparative steels 21 and 23, the stress corrosion cracking has been significantly reduced.
[0146]
　The disclosure of Japanese Patent Application 2015-114665 its entirety is incorporated herein by reference.
　All documents described herein, patent applications, and technical standards, each individual publication, patent application, and that the technical specification is incorporated by reference to the same extent as if marked specifically and individually, It incorporated by reference herein.

The scope of the claims
[Claim 1]
Component composition, by
mass%, C:
0.05
~ 0.13%, Si: 0.10 ~ 1.00%, Mn: 0.10
~ 3.00%, P: 0.040% or
less, S 0.020% or
less,
Cr:
17.00 ～ 19.00 Pasento, Ni: 12.00 ～ 15.00 Pasento,
Cu: 2.00 ～ 4.00 Pasento, Mo: 0.01 ～ 2.00 Pasento ,
W:
2.00
~ 5.00%, 2Mo + W: 2.50
~ 5.00%, V: 0.01 ~ 0.40%, Ti: 0.05
~ 0.50%, Nb: 0.15 0.70%
~
Al:
0.001 ~ 0.040%, B: 0.0010 ~
0.0100%, N: 0.0010 ~ 0.0100%, Nd: 0.001 ~
0.20%, Zr 0.002% or
less, Bi: 0.001% or
less, Sn: 0.010% or
less, Sb: 0.010% or
less, Pb: 0.0 Less than
1%, As: 0.001% or
less, Zr + Bi + Sn + Sb + Pb + As: 0.020% or
less, O: 0.0090% or
less, Co: 0.80% or
less, Ca: 0.20% or
less, Mg: 0.20% Less than,
Lanthanide elements other than Nd, Y, Sc, Ta, Hf, and Re 1 or more kinds of 0.20% in total less, and,
the balance Fe and impurities,
　defined by the following formula (1) austenitic stainless steels effective M amount Meff is 0.0001 to 0.250 percent.
　Effective M amount Meff = Nd + 13 · (B -11 · N / 14) -1.6 · Zr ... formula (1)
(In the formula (1), each element symbol represents the content of each element (mass%) .)
[Claim 2]
　The component composition, by mass%, Co: 0.01 ~ 0.80%, Ca: 0.0001 ~ 0.20%, and, Mg: 0.0005 ~ 0.20% 1 or more types of austenitic stainless steel according to claim 1 comprising a.
[Claim 3]
　The component composition, by mass%, lanthanide elements other than Nd, Y, Sc, Ta, Hf, and Re 1 kind or two or more, including from 0.001 to 0.20 percent in total claim 1 or claim austenitic stainless steel according to claim 2.
[Claim 4]
　Austenitic stainless steel according to any one of claims 1 to 3 metallographic ASTM grain size number of 7 or less.
[Claim 5]
　700 ° C., 1 million hours creep rupture strength of not less than 140MPa claims 1 to austenitic stainless steel according to any one of claims 4.