JP3982069B2 - High Cr ferritic heat resistant steel - Google Patents
High Cr ferritic heat resistant steel Download PDFInfo
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- JP3982069B2 JP3982069B2 JP19308498A JP19308498A JP3982069B2 JP 3982069 B2 JP3982069 B2 JP 3982069B2 JP 19308498 A JP19308498 A JP 19308498A JP 19308498 A JP19308498 A JP 19308498A JP 3982069 B2 JP3982069 B2 JP 3982069B2
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- steel
- creep strength
- heat resistant
- toughness
- resistant steel
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
Description
【0001】
【発明の属する技術分野】
本発明は、高Crフェライト系耐熱鋼に係わり、さらに詳しくはボイラ、原子力発電設備および化学工業設備などの高温、高圧環境下で使用される熱交換用鋼管、圧力容器用鋼板、タービン用材料等に適した高温長時間クリープ強度と靭性に優れた高Crフェライト系耐熱鋼に関する。
【0002】
【従来の技術】
ボイラ、原子力発電設備および化学工業設備等の高温、高圧環境で使用される耐熱鋼には、一般に高温における強度、耐食性、耐酸化性および靭性等が要求される。
【0003】
これらの用途には、従来JISのSUS321H、SUS347H鋼などのオーステナイト系ステンレス鋼、2・1/4Cr−1Mo鋼などの低合金鋼、さらには9〜12Cr系の高Crフェライト鋼が用いられてきた。なかでも、高Crフェライト鋼は500℃〜650℃の温度において、強度および耐食性の点で低合金鋼よりも優れている。また、高Crフェライト鋼は、オーステナイト系ステンレス鋼に比べて安価であること、熱伝導率が高く、かつ熱膨張率が小さいことから耐熱疲労特性やスケール剥離が起こりにくいこと、さらには応力腐食割れを起こさないことなど数々の利点がある。
【0004】
近年、火力発電において熱効率の一層の向上を図るため、ボイラーの蒸気条件の高温高圧化が進められている。すなわち、超臨界圧条件である538℃、246気圧から、将来は625℃で300気圧というような超々臨界圧条件での操業が計画されている。このような蒸気条件の変化に伴い、ボイラ用鋼管等に対する要求性能は、ますます過酷化してきている。そのため、従来の高Crフェライト鋼では、上記のような高温における長時間クリープ強度に対して十分に応えることができない状況に至っている。
【0005】
オーステナイト系ステンレス鋼は上記のような過酷な条件に応えることのできる性能を備えているが高価である。そのため、オーステナイト系ステンレス鋼に比べて安価な高Crフェライト鋼を使用すべく、その特性改善の試みがなされている。
【0006】
特開平8−85850号、特開平9−71845号、特開平9−71846号各公報には、超超臨界圧条件用鋼として溶接継手部の高温長時間クリープ特性改善の点からNdを添加した耐熱鋼が開示されている。
【0007】
しかし、NdはNとの親和力が強い元素であり、Ndの一部は粗大なNdN介在物として残存するため、高N鋼においてはNdのクリープ強度改善効果が必ずしも充分発揮できていないという問題があった。
【0008】
火力発電ボイラ等の蒸気条件が前記した超々臨界圧条件での高Crフェライト鋼の使用に対しては、さらなるクリープ強度の向上が必要であり、そのためには焼戻し軟化抵抗を高めマルテンサイト組織の回復軟化現象をできるだけ高温長時間側まで遅らせることが重要である。
【0009】
【発明が解決しようとする課題】
本発明の課題は、625℃以上の高温蒸気下の使用に耐える高温長時間クリープ強度と靭性に優れた高Crフェライト系耐熱鋼を提供することにある。
【0010】
【課題を解決するための手段】
高Crフェライト系耐熱鋼に係わる本発明の要旨は、以下の通りである。
【0011】
(1)質量%で、
C:0.02〜0.15%、 Mn:0.05〜1.5%、
P:0.03%以下、 S:0.015%以下、
Cr:8〜13%、 W:1.5〜4%、
Co:2〜6%、 V:0.1〜0.5%、
Ta:0.01〜0.15%、 Nb:0.01〜0.15%、
Nd:0.001〜0.2%、 N:0.008%以下、
B:0.0005〜0.02%、 Al:0.001〜0.05%、
Mo:0〜1%、 Si:0.18〜1%、
Ca:0〜0.02%、 La:0〜0.2%、
Ce:0〜0.2%、 Y:0〜0.2%、
Hf:0〜0.2%
を含有し、残部がFe及び不可避的不純物からなる高温長時間クリープ強度と靭性に優れた高Crフェライト系耐熱鋼。
【0012】
(2)上記(1)記載の高Crフェライト系耐熱鋼において、下記式を満足する高Crフェライト系耐熱鋼。
【0013】
Nd(%)≦5×N(%)+0.1
本発明者らは、Ndを含有する高Crフェライト系耐熱鋼の高温長時間クリープ特性および靭性におよぼすNの影響について詳細に検討した。その結果、下記の知見を得て本発明を完成させた。
【0014】
a)Ndは、Nd酸化物として鋼中の酸素を固定し、クリープ強度に寄与する微細な炭化物を析出させる析出強化元素としてのNbやVの一部が酸化物になるのを抑制する効果がある。また、NdはNdC2等の炭化物を生成する作用があり、これらの炭化物は高温長時間側まで微細かつ安定に析出するため高温長時間クリープ強度の向上に寄与する。ところが、N(窒素)との親和力も大きく、Nを含有する鋼においては粗大なNdNが介在物となるため、NbやVの酸化物の生成を抑制する効果やNdC2 等の微細な炭化物を析出させることによる析出強化効果が不十分となり、クリープ強度改善効果が十分に発揮できない。
【0015】
b)Ndを含有する高Crフェライト系耐熱鋼においては、鋼中のN量を0.008%以下に抑制することにより、粗大なNdNの生成を防止することができ、その結果NbやVの微細な炭化物やNdC2等の微細な炭化物が高温長時間側まで安定して析出し、その結果、マルテンサイト組織の回復軟化現象が高温長時間側まで抑制され、クリープ強度が大幅に向上する。
【0016】
【発明の実施の形態】
以下、本発明の耐熱鋼の化学組成を限定した理由について説明する(以下、%は質量%を示す)。
【0017】
C:0.02〜0.15%
Cは炭化物MC(Mは合金元素)、M7C3およびM23C6 型炭化物を形成する[炭窒化物M(C、N)として形成される場合もある]。この炭化物は、クリープ強度の向上に寄与するとともに、C自身がオーステナイト安定化元素として組織を安定化する。0.02%未満では炭化物の析出が不十分であり、かつ、δフェライト量も多くなり充分なクリープ強度、靱性が得られない。しかし、0.15%を超えて多量に含有すると、使用時の初期から炭化物の凝集粗大化が起こるので、逆に長時間クリープ強度の低下を招き、加工性や溶接性も劣化させるので上限は0.15%とした。
【0018】
Mn:0.05〜1.5%
Mnは、脱酸およびSを固定する元素として有効で、オーステナイト安定化元素としても寄与する。それらの効果を得るためには0.05%以上必要であるが、1.5%を超えると靭性を劣化させるので0.05〜1.5%とした。
【0019】
P:0.03%以下、S:0.015%以下
不純物PおよびSは、熱間加工性、溶接性および靭性の観点からは低い方が望ましいが、それぞれ0.03%、0.015%までであれば本発明鋼の特性に直接影響しないため、上限をそれぞれ0.03%および0.015%とした。
【0020】
Cr:8〜13%
Crは、本発明鋼の高温における耐食性や耐酸化性、特に耐水蒸気酸化特性を確保するために不可欠な元素である。さらには炭化物を形成してクリープ強度を向上させる。その他、Cr主体の緻密な酸化皮膜を形成して耐食性および耐酸化性を向上させる作用があり、それらの効果を得るためには8%以上とする必要がある。しかし多量に含有させるとδ−フェライトの生成を促進して靭性の劣化をもたらすため、上限を13%とした。
【0021】
W:1.5〜4%
Wは、本発明鋼の主要な強化元素の一つである。Wは高温使用中にFe7W6型のμ相やFe2W型のラーベス相等の金属間化合物として微細に分散析出し、長時間クリープ強度の向上に寄与する。さらには、Cr炭化物中にも一部固溶して、炭化物の凝集、粗大化を抑制して強度の維持に寄与する。しかしながら、多量に含有させるとδ−フェライトの生成を促進するため、含有量を1.5〜4%とした。
【0022】
Co:2〜6%
Coは、オーステナイト安定化元素であり、Wを積極的に添加する本発明鋼においては必須の元素である。Coは同じオーステナイト安定化元素のNiと異なり、クリープ強度の低下をもたらすことなく、むしろクリープ強度を向上させる効果がある。これらの効果を発揮させるためには2%以上の添加が必要であるが、6%を超えて過剰添加すると鋼のAc1 変態点の低下が著しくなり、逆にクリープ強度が低下する。
【0023】
V:0.1〜0.5%
Vは、本発明鋼においては重要な元素で微細な炭窒化物を形成して、クリープ強度の向上に寄与する。その効果を発揮させるためには0.1%以上とする必要があり、0.5%を超えて含有させてもその効果は飽和するので、0.1〜0.5%とした。
【0024】
Ta、Nb:0.01〜0.15%
Ta、Nbは、Vと同様、微細な炭窒化物を形成して、クリープ強度の向上に寄与する元素である。その効果を発揮させるためには、それぞれ0.01%以上必要であるが、0.15%を超えて含有させてもその効果は飽和するので0.01〜0.15%とした。
【0025】
Nd:0.001〜0.2%
Ndは、NdC2等の炭化物が高温長時間側でも微細かつ安定に析出するためマルテンサイト組織の回復軟化の抑制に大きく寄与し、クリープ強度を大きく向上させる。その効果を発揮させるためには0.001%以上を含有させる必要があるが、0.2%を超えて過剰に含有させると靱性が劣化するので0.001〜0.2%とした。
【0026】
N:0.008%以下
Nは、Cと同様オーステナイト安定化元素として有効であるが、Ndを含有する鋼においては、N量が高くなると粗大なNdNが介在物として鋼中に残存するため、クリープ強度の向上効果が十分に発揮されず、かつ靱性も劣化する。したがって、Ndの効果を充分に発揮させるためには、鋼中のN量の上限は0.008%以下とする必要がある。そして、特に靱性を重視する場合には、NdとN量とのバランスを下式を満足する範囲で調整することが望ましい。
【0027】
Nd(%)≦5×N(%)+0.10(%)
B:0.0005〜0.02%
Bは、微量添加された場合にM23C6 型炭化物を微細に分散析出させる効果があり、高温長時間クリープ特性の向上に寄与する。また、厚肉材などで熱処理後の冷却が遅い場合には焼入れ性を高め、やはり高温強度の確保に重要な役割を果たす。その効果は、0.0005%以上で顕著となるが、0.02%を超えて含有させると粗大な析出物を形成し靭性を劣化させる。したがって、B含有量は0.0005〜0.02%とした。
【0028】
Al:0.001〜0.05%
Alは、溶鋼の脱酸剤として0.001%以上必要である。一方、0.05%を超えて多量に含有させるとクリープ強度の低下を招くので0.001〜0.05%とした。
【0029】
Si:0.18〜1%
Siは、溶鋼の脱酸剤として用いる。Siは、高温における耐水蒸気酸化特性の向上に対して有効であるが、1%を超えて多量に含有させると靭性の劣化を引き起こす。また、耐水蒸気酸化を重視するという観点からのSi量の下限は0.18%である。したがって、Si含有量は0.18〜1%とした。
【0030】
Mo:0〜1%
Moは、必要により含有させる元素で、固溶強化元素としてクリープ強度の向上に寄与するが、1%を超えて含有させると、ラーベス相等の金属間化合物が析出する。Mo含有鋼では、このような金属間化合物は極めて粗大に析出するためクリープ強度の向上には寄与せず、かつ、時効後の靱性も低下させる。したがって、Moの含有量は0〜1%とした。
【0031】
Ca、La、Ce、Y、Hf:Caは0〜0.02%、その他は0〜0.2%Ca、La、Ce、YおよびHfのうちの1種以上を必要により含有させる。これらの元素は、ごく微量の含有量でも結晶粒界を強化させてクリープ強度を向上させるとともに、熱間加工性の向上にも寄与する。しかし、過剰に添加すると熱間加工性が低下するため、これら元素の上限はCaは0.02%、La、Ce、YおよびHfは0.2%とした。
【0032】
真空誘導溶解炉にて、表1および表2に示す化学組成の直径144mmの50kgインゴットを溶製した。記号1、4、10、11、13、14、17、23および24が本発明鋼、記号A〜Lが比較鋼である。
【0033】
【表1】
【0034】
【表2】
【0035】
これらのインゴットを熱間鍛造後、熱間圧延によって20mm厚の鋼板とした。次いで、1050℃で1時間保持した後空冷(AC)し、さらに780℃で1時間保持して空冷(AC)する焼戻し処理をおこなった。これらの鋼板から、クリープ破断試験片およびシャルピー衝撃試験片を作製し、下記する条件でクリープ破断試験およびシャルピー衝撃試験を実施した。
【0036】
(1)クリープ破断試験
試験片 : 直径 6.0mm
標点間距離 30mm
保持温度: 650℃
負荷応力: 98MPa
(2)シャルピー衝撃試験
試験片 : 10mm×10mm×55mm
2mmVノッチ
試験温度: 0℃
これらの試験で測定したクリープ破断時間およびシャルピー衝撃値(J/cm 2)を表3および表4に示す。
【0037】
【表3】
【0038】
【表4】
【0039】
N量が0.008%以下の本発明鋼の記号1鋼および4鋼のクリープ破断時間は、それぞれの比較鋼であるN含有量が本発明で規定する範囲を超える記号A鋼および記号B鋼に比べて明らかに改善されていることがわかる。N低減によるクリープ破断寿命の改善効果は、本発明鋼の記号10、11、13、14鋼とそれぞれの比較鋼である記号F、G、I、J鋼との比較においても明瞭である。
【0040】
また、本発明鋼の記号24鋼は、NdとNの含有量が下式を満足しない場合である。この場合には下式を満足する本発明の記号17、23鋼に比べてクリープ破断寿命の差はほとんどないが、衝撃値が低めになることがわかる。したがって、靱性を重視する場合には下式を満足する範囲内でNd、N含有量を調整することが望ましい。
【0041】
Nd(%)≦5xN(%)+0.10(%)
【0042】
【発明の効果】
本発明の高Crフェライト耐熱鋼は、625℃以上の高温下で高温長時間クリープ強度と常温における靭性に優れており、原子力発電や化学工業等の分野で用いられる熱交換用鋼管、圧力容器用鋼板、タービン用材料として使用して優れた効果を発揮し、産業上極めて有益である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high Cr ferritic heat resistant steel, and more specifically, a heat exchange steel pipe, a pressure vessel steel plate, a turbine material, etc. used in high temperature and high pressure environments such as boilers, nuclear power generation facilities and chemical industrial facilities. The present invention relates to a high Cr ferritic heat-resistant steel excellent in high-temperature long-term creep strength and toughness that is suitable for high temperature.
[0002]
[Prior art]
In general, heat resistant steels used in high temperature and high pressure environments such as boilers, nuclear power generation facilities and chemical industrial facilities are required to have strength, corrosion resistance, oxidation resistance and toughness at high temperatures.
[0003]
For these applications, austenitic stainless steels such as JIS SUS321H and SUS347H steel, low alloy steels such as 2 / 4Cr-1Mo steel, and 9-12Cr high Cr ferritic steels have been used. . Among these, high Cr ferritic steel is superior to low alloy steel in terms of strength and corrosion resistance at a temperature of 500 ° C. to 650 ° C. In addition, high Cr ferritic steel is less expensive than austenitic stainless steel, has high thermal conductivity, and has a low coefficient of thermal expansion. There are a number of advantages such as not causing any problems.
[0004]
In recent years, in order to further improve the thermal efficiency in thermal power generation, the steam conditions of boilers have been increased to high temperatures and pressures. That is, operation under super supercritical pressure conditions such as 538 ° C. and 246 atm., Which are supercritical pressure conditions, and 625 ° C. and 300 atm in the future is planned. With such changes in steam conditions, the required performance for steel pipes for boilers and the like has become increasingly severe. For this reason, conventional high Cr ferritic steels have not been able to sufficiently meet the long-term creep strength at high temperatures as described above.
[0005]
Austenitic stainless steel has the performance to meet the above severe conditions but is expensive. For this reason, attempts have been made to improve the characteristics of high Cr ferritic steel, which is less expensive than austenitic stainless steel.
[0006]
In JP-A-8-85850, JP-A-9-71845, and JP-A-9-71846, Nd was added as a super supercritical pressure condition steel from the viewpoint of improving high-temperature long-term creep characteristics of a welded joint. Heat resistant steel is disclosed.
[0007]
However, since Nd is an element having a strong affinity for N and a part of Nd remains as coarse NdN inclusions, the problem that Nd's creep strength improvement effect is not always sufficiently exhibited in high-N steels. there were.
[0008]
For the use of high Cr ferritic steel under the super-supercritical pressure conditions described above, such as a thermal power boiler, it is necessary to further improve the creep strength. For this purpose, the temper softening resistance is increased and the martensite structure is recovered. It is important to delay the softening phenomenon to the high temperature and long time as possible.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a high Cr ferritic heat resistant steel excellent in high temperature long time creep strength and toughness that can withstand use under high temperature steam at 625 ° C. or higher.
[0010]
[Means for Solving the Problems]
The gist of the present invention relating to the high Cr ferritic heat resistant steel is as follows.
[0011]
(1) In mass%,
C: 0.02-0.15%, Mn: 0.05-1.5%,
P: 0.03% or less, S: 0.015% or less,
Cr: 8 to 13%, W: 1.5 to 4%,
Co: 2 to 6%, V: 0.1 to 0.5%,
Ta: 0.01 to 0.15%, Nb: 0.01 to 0.15%,
Nd: 0.001 to 0.2%, N: 0.008% or less ,
B: 0.0005 to 0.02%, Al: 0.001 to 0.05%,
Mo: 0 to 1%, Si: 0.18 to 1%,
Ca: 0 to 0.02%, La: 0 to 0.2%,
Ce: 0 to 0.2%, Y: 0 to 0.2%,
Hf: 0 to 0.2%
A high Cr ferritic heat-resistant steel excellent in high-temperature long-term creep strength and toughness, which contains Fe and the balance of Fe and inevitable impurities.
[0012]
(2) The high Cr ferritic heat resistant steel according to the above (1), which satisfies the following formula.
[0013]
Nd (%) ≦ 5 × N (%) + 0.1
The present inventors examined in detail the influence of N on the high-temperature long-term creep characteristics and toughness of high Cr ferritic heat-resisting steel containing Nd. As a result, the following knowledge was obtained and the present invention was completed.
[0014]
a) Nd fixes oxygen in steel as an Nd oxide, and has an effect of suppressing a part of Nb and V as a precipitation strengthening element for precipitating fine carbides contributing to creep strength to be oxides. is there. Also, Nd is an effect of generating carbides such as NDC 2, these carbides contributes to an improvement in high-temperature long-time creep strength and precipitate finely and stably to high temperature for a long time side. However, the affinity with N (nitrogen) is also large, and in steel containing N, coarse NdN becomes an inclusion, so the effect of suppressing the formation of oxides of Nb and V and fine carbides such as NdC 2 are reduced. The precipitation strengthening effect due to precipitation becomes insufficient, and the effect of improving the creep strength cannot be sufficiently exhibited.
[0015]
b) In the high Cr ferritic heat-resistant steel containing Nd, by suppressing the N content in the steel to 0.008% or less , it is possible to prevent the formation of coarse NdN. Fine carbides and fine carbides such as NdC 2 are stably precipitated to the high temperature long time side. As a result, the recovery softening phenomenon of the martensite structure is suppressed to the high temperature long time side, and the creep strength is greatly improved.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reason why the chemical composition of the heat resistant steel of the present invention is limited will be described (hereinafter, “%” represents “% by mass”).
[0017]
C: 0.02-0.15%
C forms carbides MC (M is an alloying element), M 7 C 3 and M 23 C 6 type carbides [may be formed as carbonitride M (C, N)]. This carbide contributes to the improvement of creep strength and C itself stabilizes the structure as an austenite stabilizing element. If it is less than 0.02%, the precipitation of carbide is insufficient, and the amount of δ ferrite increases, so that sufficient creep strength and toughness cannot be obtained. However, if the content exceeds 0.15%, agglomeration and coarsening of carbide occurs from the initial stage of use, and conversely, the creep strength decreases for a long time, and the workability and weldability deteriorate, so the upper limit is 0.15%.
[0018]
Mn: 0.05 to 1.5%
Mn is effective as an element for fixing deoxidation and S, and also contributes as an austenite stabilizing element. In order to obtain these effects must be at least 0.05%, but the 0.0 5 to 1.5% since deteriorates the toughness exceeds 1.5%.
[0019]
P: 0.03 % or less, S: 0.015% or less Impurities P and S are preferably lower from the viewpoint of hot workability, weldability, and toughness, but 0.03% and 0.015%, respectively. The upper limit is set to 0.03% and 0.015%, respectively, because it does not directly affect the properties of the steel of the present invention.
[0020]
Cr: 8-13%
Cr is an indispensable element for ensuring the corrosion resistance and oxidation resistance at high temperatures of the steel of the present invention, particularly the steam oxidation resistance. Furthermore, a carbide is formed to improve the creep strength. In addition, it has a function of improving the corrosion resistance and oxidation resistance by forming a dense oxide film mainly composed of Cr, and in order to obtain these effects, it is necessary to be 8% or more. However, if contained in a large amount, the formation of δ-ferrite is promoted and the toughness is deteriorated, so the upper limit was made 13%.
[0021]
W: 1.5-4 %
W is one of the main strengthening elements of the steel of the present invention. W is finely dispersed and precipitated as an intermetallic compound such as Fe 7 W 6 type μ phase and Fe 2 W type Laves phase during high temperature use, and contributes to improvement of creep strength for a long time. Further, it partially dissolves in the Cr carbide, thereby suppressing the agglomeration and coarsening of the carbide and contributing to the maintenance of strength. However, if it is contained in a large amount, the production of δ-ferrite is promoted. 5 to 4%.
[0022]
Co: 2-6%
Co is an austenite stabilizing element and is an essential element in the steel of the present invention to which W is positively added. Unlike Ni, which is the same austenite stabilizing element, Co has the effect of improving creep strength without causing a decrease in creep strength. In order to exert these effects, addition of 2% or more is necessary. However, if over 6% is added, the Ac 1 transformation point of the steel is remarkably lowered, and the creep strength is lowered.
[0023]
V: 0.1-0.5%
V is an important element in the steel of the present invention and forms fine carbonitrides and contributes to the improvement of creep strength. In order to exhibit the effect, it is necessary to be 0.1% or more, and even if contained over 0.5%, the effect is saturated. 1 to 0.5%.
[0024]
Ta, Nb: 0.01 to 0.15%
Ta and Nb are elements that, like V, form fine carbonitrides and contribute to the improvement of creep strength. In order to exert the effect, 0.01% or more is necessary for each. However, even if the content exceeds 0.15%, the effect is saturated, so the content was made 0.01 to 0.15%.
[0025]
Nd: 0.001 to 0.2%
Nd contributes greatly to the suppression of the recovery and softening of the martensite structure because carbides such as NdC 2 are finely and stably precipitated even at a high temperature for a long time, and the creep strength is greatly improved. In order to exert the effect, it is necessary to contain 0.001% or more, but if it exceeds 0.2% and excessively contains, the toughness deteriorates, so the content was made 0.001 to 0.2%.
[0026]
N: 0.008% or less N is effective as an austenite stabilizing element as in C. However, in steel containing Nd, when N content increases, coarse NdN remains in the steel as inclusions. The effect of improving the creep strength is not sufficiently exhibited, and the toughness is also deteriorated. Therefore, in order to fully exhibit the effect of Nd, the upper limit of the N content in the steel needs to be 0.008% or less . And especially when toughness is emphasized, it is desirable to adjust the balance between Nd and N amount within a range satisfying the following expression.
[0027]
Nd (%) ≦ 5 × N (%) + 0.10 (%)
B: 0.0005 to 0.02%
B, when added in a small amount, has the effect of finely dispersing and precipitating M 23 C 6 type carbides, and contributes to the improvement of the high temperature and long term creep characteristics. In addition, when the cooling after heat treatment is slow due to a thick material or the like, the hardenability is enhanced and it also plays an important role in securing high temperature strength. The effect becomes remarkable at 0.0005% or more. However, if the content exceeds 0.02%, coarse precipitates are formed and the toughness is deteriorated. Therefore, the B content is set to 0.0005 to 0.02%.
[0028]
Al: 0.001 to 0.05%
Al is required to be 0.001% or more as a deoxidizer for molten steel. On the other hand, if it is contained in a large amount exceeding 0.05%, the creep strength is reduced, so the content was made 0.001 to 0.05%.
[0029]
Si: 0.18 to 1%
Si is used as a deoxidizer soluble steel. Si is effective against improving the steam oxidation resistance at high temperatures, to spawning a large amount of the inclusion of the toughness deteriorates more than 1%. The lower limit of the Si amount in terms of emphasizing resistant steam oxidation is 0.18%. Therefore, the Si content is set to 0.18 to 1%.
[0030]
Mo: 0 to 1%
Mo is an element that is included as necessary, and contributes to the improvement of creep strength as a solid solution strengthening element. However, if it is included in an amount exceeding 1%, an intermetallic compound such as a Laves phase is precipitated. In the Mo-containing steel, such an intermetallic compound precipitates very coarsely, so it does not contribute to the improvement of the creep strength, and the toughness after aging is also lowered. Therefore, the Mo content is set to 0 to 1%.
[0031]
Ca, La, Ce, Y, Hf: Ca is 0 to 0.02%, and others are 0 to 0.2%. One or more of Ca, La, Ce, Y, and Hf are contained as necessary. These elements strengthen the grain boundaries and improve the creep strength even with a very small content, and contribute to the improvement of hot workability. However, since hot workability deteriorates when added in excess, the upper limit of these elements was set to 0.02% for Ca and 0.2% for La, Ce, Y and Hf.
[0032]
In a vacuum induction melting furnace, a 50 kg ingot having a chemical composition shown in Tables 1 and 2 and having a diameter of 144 mm was melted. Symbols 1 , 4, 10 , 11, 13, 14, 17, 23 and 24 are steels of the present invention, and symbols A to L are comparative steels.
[0033]
[Table 1]
[0034]
[Table 2]
[0035]
These ingots were hot forged and then hot rolled to form 20 mm thick steel plates. Next, after holding at 1050 ° C. for 1 hour, it was air-cooled (AC), and further held at 780 ° C. for 1 hour to air-cool (AC). A creep rupture test piece and a Charpy impact test piece were prepared from these steel plates, and a creep rupture test and a Charpy impact test were performed under the following conditions.
[0036]
(1) Creep rupture test
Test piece: Diameter 6.0 mm
Distance between gauge points 30mm
Holding temperature: 650 ° C
Load stress: 98 MPa
(2) Charpy impact test
Test piece: 10 mm x 10 mm x 55 mm
2mmV notch
Test temperature: 0 ° C
Tables 3 and 4 show the creep rupture time and Charpy impact value (J / cm 2 ) measured in these tests.
[0037]
[Table 3]
[0038]
[Table 4]
[0039]
Symbol N content is 0.008% or less of the present invention steels 1 Steel and 4 creep rupture time of the steel, symbol A steel and symbols B steel is N content are the respective comparative steels outside the range defined in the present invention It can be seen that there is a clear improvement compared to. The effect of improving the creep rupture life due to the reduction of N is also clear in comparison between the steels of the present invention, the steels 10, 11, 13, 14 and the steels F, G, I, J, which are comparative steels.
[0040]
Further, Symbol 24 steel of the present invention steel is a case where the content of Nd and N does not satisfy the following formula. In this case, there is almost no difference in the creep rupture life compared to the steels of symbols 17 and 23 of the present invention satisfying the following formula, but it can be seen that the impact value is lower. Therefore, when importance is attached to toughness, it is desirable to adjust the Nd and N contents within a range satisfying the following formula.
[0041]
Nd (%) ≤ 5 x N (%) + 0.10 (%)
[0042]
【The invention's effect】
The high Cr ferritic heat resistant steel of the present invention is excellent in high temperature long-term creep strength and toughness at room temperature at a high temperature of 625 ° C. or higher, and is used for heat exchange steel pipes and pressure vessels used in fields such as nuclear power generation and chemical industry. It is used as a steel plate and turbine material and exhibits an excellent effect and is extremely useful in industry.
Claims (2)
C:0.02〜0.15%、 Mn:0.05〜1.5%、
P:0.03%以下、 S:0.015%以下、
Cr:8〜13%、 W:1.5〜4%、
Co:2〜6%、 V:0.1〜0.5%、
Ta:0.01〜0.15%、 Nb:0.01〜0.15%、
Nd:0.001〜0.2%、 N:0.008%以下、
B:0.0005〜0.02%、 Al:0.001〜0.05%、
Mo:0〜1%、 Si:0.18〜1%、
Ca:0〜0.02%、 La:0〜0.2%、
Ce:0〜0.2%、 Y:0〜0.2%、
Hf:0〜0.2%
を含有し、残部がFe及び不可避的不純物からなることを特徴とする高温長時間クリープ強度と靭性に優れた高Crフェライト系耐熱鋼。% By mass
C: 0.02-0.15%, Mn: 0.05-1.5%,
P: 0.03% or less, S: 0.015% or less,
Cr: 8 to 13%, W: 1.5 to 4%,
Co: 2 to 6%, V: 0.1 to 0.5%,
Ta: 0.01 to 0.15%, Nb: 0.01 to 0.15%,
Nd: 0.001 to 0.2%, N: 0.008% or less ,
B: 0.0005 to 0.02%, Al: 0.001 to 0.05%,
Mo: 0 to 1%, Si: 0.18 to 1%,
Ca: 0 to 0.02%, La: 0 to 0.2%,
Ce: 0 to 0.2%, Y: 0 to 0.2%,
Hf: 0 to 0.2%
A high Cr ferritic heat resistant steel excellent in high-temperature long-term creep strength and toughness, characterized in that it contains Fe and the balance is Fe and inevitable impurities.
Nd(%)≦5×N(%)+0.1The high Cr ferritic heat resistant steel according to claim 1, wherein the high Cr ferritic heat resistant steel excellent in high temperature long time creep strength and toughness satisfying the following formula.
Nd (%) ≦ 5 × N (%) + 0.1
Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
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JP19308498A JP3982069B2 (en) | 1998-07-08 | 1998-07-08 | High Cr ferritic heat resistant steel |
EP99925355A EP1103626B1 (en) | 1998-07-08 | 1999-06-16 | HIGH Cr FERRITIC HEAT RESISTANCE STEEL |
PCT/JP1999/003231 WO2000003050A1 (en) | 1998-07-08 | 1999-06-16 | HIGH Cr FERRITIC HEAT RESISTANCE STEEL |
DE69904336T DE69904336T2 (en) | 1998-07-08 | 1999-06-16 | HIGH CHROME, HEAT RESISTANT, FERITIC STEEL |
US09/754,050 US20020020473A1 (en) | 1998-07-08 | 2001-01-05 | Heat resistant high chromium ferritic steel |
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JP19308498A JP3982069B2 (en) | 1998-07-08 | 1998-07-08 | High Cr ferritic heat resistant steel |
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JP3982069B2 true JP3982069B2 (en) | 2007-09-26 |
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EP (1) | EP1103626B1 (en) |
JP (1) | JP3982069B2 (en) |
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WO (1) | WO2000003050A1 (en) |
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US6696016B1 (en) * | 1999-09-24 | 2004-02-24 | Japan As Represented By Director General Of National Research Institute For Metals | High-chromium containing ferrite based heat resistant steel |
KR100708616B1 (en) * | 2000-08-19 | 2007-04-18 | 두산중공업 주식회사 | Low Activation High Chromium Ferritic Heat Resistant Steels for Fission Reactor, Fast Breed Reactor and Fusion Reactor |
JP2002146484A (en) * | 2000-11-10 | 2002-05-22 | Sanyo Special Steel Co Ltd | High strength ferritic heat resistant steel |
JP4614547B2 (en) * | 2001-01-31 | 2011-01-19 | 独立行政法人物質・材料研究機構 | Martensitic heat resistant alloy with excellent high temperature creep rupture strength and ductility and method for producing the same |
WO2006109664A1 (en) * | 2005-04-07 | 2006-10-19 | Sumitomo Metal Industries, Ltd. | Ferritic heat-resistant steel |
US20070087250A1 (en) * | 2005-10-13 | 2007-04-19 | Lewis Daniel J | Alloy for fuel cell interconnect |
DE102005061790A1 (en) * | 2005-12-23 | 2007-07-05 | Mtu Aero Engines Gmbh | Material for component of gas turbine comprises matrix based on iron alloy with intermetallic material of Laves phase |
JP5256279B2 (en) * | 2007-03-29 | 2013-08-07 | アルストム テクノロジー リミテッド | Creep resistant steel |
JP5206676B2 (en) * | 2007-06-04 | 2013-06-12 | 新日鐵住金株式会社 | Ferritic heat resistant steel |
EA017766B1 (en) * | 2008-03-11 | 2013-03-29 | Государственное Научное Учреждение "Физико-Технический Институт Национальной Академии Наук Беларуси" | Heat-resistant casting steel |
CN104907470B (en) * | 2015-04-27 | 2017-01-11 | 上海宏钢电站设备铸锻有限公司 | 13Cr9Mo2Co1NiVNbNB steel forged piece manufacturing method |
JP6575392B2 (en) * | 2015-05-19 | 2019-09-18 | 日本製鉄株式会社 | High Cr ferritic heat resistant steel |
CN108754335B (en) * | 2018-08-22 | 2019-09-10 | 武汉钢铁有限公司 | A kind of the welding structure fire-resistant and weather-resistant steel and production method of yield strength >=550MPa |
JP2020131289A (en) * | 2019-02-21 | 2020-08-31 | 株式会社神戸製鋼所 | WELD MATERIAL FOR HIGH-Cr FERRITIC HEAT-RESISTANT STEEL |
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JP3364322B2 (en) * | 1994-06-03 | 2003-01-08 | 川崎製鉄株式会社 | Stainless steel for automotive exhaust manifolds with excellent manufacturability, workability and high-temperature strength after long-term aging at high temperatures |
JP3480061B2 (en) * | 1994-09-20 | 2003-12-15 | 住友金属工業株式会社 | High Cr ferritic heat resistant steel |
JP3531228B2 (en) * | 1994-09-20 | 2004-05-24 | 住友金属工業株式会社 | High Cr ferritic heat resistant steel |
JP3310825B2 (en) * | 1995-07-17 | 2002-08-05 | 三菱重工業株式会社 | High temperature steam turbine rotor material |
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JP3322097B2 (en) * | 1995-10-26 | 2002-09-09 | 住友金属工業株式会社 | High strength, high corrosion resistant ferritic steel welding material with excellent weldability |
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DE69904336T2 (en) | 2003-08-21 |
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