JP5371420B2 - Heat resistant cast steel and steam turbine main valves - Google Patents
Heat resistant cast steel and steam turbine main valves Download PDFInfo
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Abstract
Description
本発明は、耐熱鋳鋼および蒸気タービン主要弁に関する。 The present invention relates to a heat-resistant cast steel and a steam turbine main valve.
従来、蒸気温度が６００℃である蒸気タービンにおいては、主要弁（蒸気タービン主要弁）として高温強度に優れた鍛鋼が用いられている。ところが、主要弁の製造コストの低減という観点から、主要弁の材料として鍛鋼から鋳鋼への切り換えが望まれている。ここで、鋳鋼からなる主要弁に、鍛鋼からなる主要弁と同一の高温強度を持たせようとした場合、鋳鋼からなる主要弁を鍛鋼からなる主要弁と比べて厚肉で設計することが考えられるが、厚肉にした分、鋳造欠陥の発生確率が高くなり歩留まりを低下させる可能性がある。 Conventionally, in a steam turbine having a steam temperature of 600 ° C., forged steel having excellent high-temperature strength is used as a main valve (steam turbine main valve). However, switching from forged steel to cast steel is desired as the material of the main valve from the viewpoint of reducing the manufacturing cost of the main valve. Here, if the main valve made of cast steel is to have the same high-temperature strength as the main valve made of forged steel, the main valve made of cast steel may be designed to be thicker than the main valve made of forged steel. However, since the thickness is increased, the probability of occurrence of casting defects increases and the yield may be reduced.
そのため、上述した蒸気タービンの材料として、高温強度を有する種々の合金が開発されている。例えば、特許文献１には、６００℃においてクリープ破断強度が高い特性を有する１２Ｃｒ系耐熱鋼が開示されている。具体的には、特許文献１には、重量比でＣ：０．０５〜０．２％，Ｓｉ：０．０５〜１％，Ｍｎ：０．１〜１％，Ｎｉ：１．５％以下，Ｃｒ：９．０〜１３％，Ｍｏ：０．５〜２％，Ｎｂ：０．０５〜０．４％，Ｗ：０．０５〜０．８％を含み、残部鉄および不可避不純物からなり、−４０Ｃ−３０Ｎ−２Ｍｎ−４Ｎｉ＋Ｃｒ＋６Ｓｉ＋４Ｍｏ＋１．５Ｗ＋１１Ｖ＋５Ｎｂで表されるＣｒ当量が１０以下である１２Ｃｒ系耐熱鋼が開示されている。 Therefore, various alloys having high-temperature strength have been developed as the above-described steam turbine materials. For example, Patent Document 1 discloses a 12Cr heat-resistant steel having a high creep rupture strength at 600 ° C. Specifically, in Patent Document 1, the weight ratio is C: 0.05 to 0.2%, Si: 0.05 to 1%, Mn: 0.1 to 1%, Ni: 1.5% or less. , Cr: 9.0-13%, Mo: 0.5-2%, Nb: 0.05-0.4%, W: 0.05-0.8%, consisting of the balance iron and inevitable impurities A 12Cr heat resistant steel having a Cr equivalent of 10 or less represented by -40C-30N-2Mn-4Ni + Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb is disclosed.
しかしながら、上述した特許文献１記載の１２Ｃｒ系耐熱鋼を鋳造して作製された蒸気タービン主要弁に高温強度を持たせることができるものの、高温強度の更なる向上が望まれていた。 However, although the steam turbine main valve produced by casting the 12Cr heat resistant steel described in Patent Document 1 described above can have high temperature strength, further improvement in high temperature strength has been desired.
そこで、本発明は、前述した問題に鑑み提案されたもので、６００℃でのクリープ破断強度を向上させた耐熱鋳鋼および蒸気タービン主要弁を提供することを目的とする。 Therefore, the present invention has been proposed in view of the above-described problems, and an object thereof is to provide a heat-resistant cast steel and a steam turbine main valve having improved creep rupture strength at 600 ° C.
上述した課題を解決する第１の発明に係る耐熱鋳鋼は、
０．１０質量％≦Ｃ≦０．１４質量％、
０．２０質量％≦Ｓｉ≦０．４０質量％、
０．４質量％≦Ｍｎ≦１．０質量％、
Ｐ≦０．０２質量％、
Ｓ≦０．０１質量％、
０．５０質量％≦Ｎｉ≦０．８０質量％、
９．５質量％≦Ｃｒ≦１０．２質量％、
０．９２質量％≦Ｍｏ≦１．０７質量％、
０．９２質量％≦Ｗ≦１．０７質量％、
０．１８質量％≦Ｖ≦０．２５質量％、
０．０５質量％≦Ｎｂ≦０．１０質量％、
Ａｌ≦０．０２０質量％、
０．０３質量％≦Ｎ≦０．０６質量％、
残部がＦｅ及び不可避不純物からなり、
Ｃｒ＋６Ｓｉ＋４Ｍｏ＋１．５Ｗ＋１１Ｖ＋５Ｎｂ−４０Ｃ−３０Ｎ−３０Ｂ−２Ｍｎ−４Ｎｉ−２Ｃｏで表されるＣｒ当量が、８．５質量％以上１０．３質量％以下であり、
０．３０≦０．５Ｗ／（０．５Ｗ＋Ｍｏ）≦０．３７であり、
１０００℃以上１１００℃以下にて予備熱処理し、１０００〜１１００℃で溶体化・焼入れ熱処理し、６５０〜７３０℃で第１段焼戻し熱処理し、７００〜７５０℃で第２段焼戻し熱処理してなる
ことを特徴とする。
The heat-resistant cast steel according to the first invention for solving the above-described problem is
0.10 mass% ≦ C ≦ 0.14 mass%,
0.20 mass% ≦ Si ≦ 0.40 mass%,
0.4 mass% ≦ Mn ≦ 1.0 mass%,
P ≦ 0.02 mass%,
S ≦ 0.01 mass%,
0.50 mass% ≦ Ni ≦ 0.80 mass%,
9.5 mass% ≦ Cr ≦ 10.2 mass%,
0.92 mass% ≦ Mo ≦ 1.07 mass%,
0.92 mass% ≦ W ≦ 1.07 mass%,
0.18 mass% ≦ V ≦ 0.25 mass%,
0.05% by mass ≦ Nb ≦ 0.10% by mass,
Al ≦ 0.020 mass%,
0.03 mass% ≦ N ≦ 0.06 mass%,
Balance Ri Do Fe and unavoidable impurities,
Cr equivalent represented by Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C-30N-30B-2Mn-4Ni-2Co is 8.5 mass% or more and 10.3 mass% or less,
0.30 ≦ 0.5 W / (0.5 W + Mo) ≦ 0.37,
Preliminary heat treatment at 1000 ° C. to 1100 ° C., solution heat treatment and quenching heat treatment at 1000 to 1100 ° C., first stage tempering heat treatment at 650 to 730 ° C., and second stage tempering heat treatment at 700 to 750 ° C. It is characterized by the above.
上述した課題を解決する第２の発明に係る耐熱鋳鋼は、
第１の発明に係る耐熱鋳鋼であって、
前記Ｃｒ当量が、９質量％以上１０．３質量％以下である
ことを特徴とする。
The heat-resistant cast steel according to the second invention for solving the above-described problem is
A heat-resistant cast steel according to the first invention,
The Cr equivalent is 9% by mass or more and 10.3% by mass or less.
上述した課題を解決する第３の発明に係る耐熱鋳鋼は、
第１の発明に係る耐熱鋳鋼であって、
０．３１≦０．５Ｗ／（０．５Ｗ＋Ｍｏ）≦０．３５である
ことを特徴とする。
The heat-resistant cast steel according to the third invention for solving the above-described problem is
A heat-resistant cast steel according to the first invention,
It is characterized by 0.31 ≦ 0.5 W / (0.5 W + Mo) ≦ 0.35.
上述した課題を解決する第４の発明に係る蒸気タービン主要弁は、
第１乃至第３の発明の何れか一つに係る耐熱鋳鋼で構成される
ことを特徴とする。
前記蒸気タービン主要弁としては、ボイラで得られた主蒸気を蒸気タービンに対して供給および停止を制御する主蒸気止め弁、蒸気量を加減して蒸気タービンの出力を調整する蒸気加減弁、再熱蒸気を蒸気タービンに対して供給および停止を制御するインターセプト弁などが挙げられる。
The steam turbine main valve according to the fourth invention for solving the above-described problem is
The heat-resistant cast steel according to any one of the first to third inventions is used.
The steam turbine main valve includes a main steam stop valve that controls supply and stop of main steam obtained from the boiler to the steam turbine, a steam control valve that adjusts the output of the steam turbine by adjusting the amount of steam, Examples include an intercept valve that controls supply and stop of hot steam to the steam turbine.
本発明に係る耐熱鋳鋼によれば、上記組成を有することから、６００℃でのクリープ破断強度を向上させることができる。 According to the heat-resistant cast steel according to the present invention, since it has the above composition, the creep rupture strength at 600 ° C. can be improved.
本発明に係る蒸気タービン主要弁によれば、上記組成を有する耐熱鋳鋼で構成されることで、６００℃でのクリープ破断強度が向上し、従来の鍛鋼で構成される蒸気タービン主要弁と比べて、製造コストを低減できる。 According to the steam turbine main valve according to the present invention, the creep rupture strength at 600 ° C. is improved by being composed of heat-resistant cast steel having the above composition, compared with the steam turbine main valve composed of conventional forged steel. Manufacturing cost can be reduced.
本発明に係る耐熱鋳鋼および蒸気タービン主要弁の実施形態について以下に説明する。 Embodiments of heat-resistant cast steel and steam turbine main valves according to the present invention will be described below.
［第一番目の実施形態］
本実施形態に係る耐熱鋳鋼は、０．１０質量％≦Ｃ≦０．１４質量％、０．２０質量％≦Ｓｉ≦０．４０質量％、０．４質量％≦Ｍｎ≦１．０質量％、Ｐ≦０．０２質量％、Ｓ≦０．０１質量％、０．５０質量％≦Ｎｉ≦０．８０質量％、９．５質量％≦Ｃｒ≦１０．２質量％、０．９２質量％≦Ｍｏ≦１．０７質量％、０．９２質量％≦Ｗ≦１．０７質量％、０．１８質量％≦Ｖ≦０．２５質量％、０．０５質量％≦Ｎｂ≦０．１０質量％、Ａｌ≦０．０２０質量％、０．０３質量％≦Ｎ≦０．０６質量％、残部が鉄および不可避不純物からなる組成を有するものである。
[First embodiment]
The heat-resistant cast steel according to the present embodiment has 0.10 mass% ≦ C ≦ 0.14 mass%, 0.20 mass% ≦ Si ≦ 0.40 mass%, 0.4 mass% ≦ Mn ≦ 1.0 mass%. P ≦ 0.02 mass%, S ≦ 0.01 mass%, 0.50 mass% ≦ Ni ≦ 0.80 mass%, 9.5 mass% ≦ Cr ≦ 10.2 mass%, 0.92 mass% ≦ Mo ≦ 1.07 mass%, 0.92 mass% ≦ W ≦ 1.07 mass%, 0.18 mass% ≦ V ≦ 0.25 mass%, 0.05 mass% ≦ Nb ≦ 0.10 mass% Al ≦ 0.020 mass%, 0.03 mass% ≦ N ≦ 0.06 mass%, and the balance is composed of iron and inevitable impurities.
Ｃ（炭素）は、熱処理時の焼入れ性を確保し、また焼戻し過程でＭ23Ｃ6型炭化物を析出させて高温強度を高め耐力や靭性を確保するために必要不可欠な元素である。Ｃは本発明に係る蒸気タービン主要弁（例えば、主蒸気止め弁や蒸気加減弁やインターセプト弁など）の材料に適した耐熱鋳鋼にとって必要な耐力や靭性を発現させている。しかしながら、Ｃの含有量が過剰量になると、靭性の低下を引き起こすと共に、Ｍ23Ｃ6型炭化物を過度に析出させ、マトリックスの強度を低下させて長時間側の高温強度を低下させる。したがって、Ｃの含有量を０．１０質量％以上０．１４質量％以下としている。 C (carbon) is an indispensable element for ensuring hardenability during heat treatment and for precipitating M 23 C 6 type carbides during the tempering process to increase high temperature strength and to ensure proof stress and toughness. C expresses the proof stress and toughness required for heat-resistant cast steel suitable for the material of the steam turbine main valve (for example, main steam stop valve, steam control valve, intercept valve, etc.) according to the present invention. However, when the content of C is excessive, toughness is lowered, and M 23 C 6 type carbide is excessively precipitated, the strength of the matrix is lowered, and the high temperature strength on the long time side is lowered. Therefore, the C content is set to 0.10% by mass to 0.14% by mass.
Ｓｉ（珪素）は、溶鋼の脱酸剤として効果があり、湯流れ性を確保するために必要な元素である。しかしながら、Ｓｉの含有量が過剰量になると、脱酸による生成物であるＳｉＯ2が鋼中に存在し、鋼の清浄度を害し靭性を低下させる。また、Ｓｉは金属間化合物であるラーベス相（Ｆｅ2Ｍ）の生成を促し、また粒界偏析などによりクリープ破断延性を低下させ、更に高温使用中において焼戻し脆性を助長する。したがって、Ｓｉの含有量を０．２０質量％以上０．４０質量％以下としている。 Si (silicon) is effective as a deoxidizer for molten steel, and is an element necessary for ensuring molten metal flowability. However, when the Si content is excessive, SiO 2 , which is a product of deoxidation, is present in the steel, which impairs the cleanliness of the steel and lowers the toughness. Si also promotes the formation of Laves phase (Fe 2 M), which is an intermetallic compound, reduces creep rupture ductility due to grain boundary segregation, and further promotes temper brittleness during high temperature use. Therefore, the Si content is set to 0.20 mass% or more and 0.40 mass% or less.
Ｍｎ（マンガン）は、溶鋼の脱酸、脱硫剤として有効な元素であると共に、焼入れ性を増大させて強度を高めるのに有効な元素である。また、Ｍｎは、δフェライトおよびＢＮの生成を抑制し、Ｍ23Ｃ6型炭化物の析出を促進するのに有効な元素である。しかしながら、Ｍｎの含有量の増加とともにクリープ破断強度を低下させる。したがって、Ｍｎの含有量を０．４質量％以上１．０質量％以下としている。 Mn (manganese) is an element effective as a deoxidizer and desulfurizer for molten steel, and is an element effective for increasing the hardenability and increasing the strength. Mn is an element effective in suppressing the formation of δ ferrite and BN and promoting precipitation of M 23 C 6 type carbide. However, the creep rupture strength decreases with increasing Mn content. Therefore, the Mn content is set to 0.4% by mass or more and 1.0% by mass or less.
Ｐ（リン）は、不純物元素として製鋼の原材料に混入され避けられないものであり、その含有量が少ないほど好ましいが、過度に低減させようとすると、経済性を損なうことから、その含有量を０．０２質量％以下としている。 P (phosphorus) is inevitably mixed into the raw material of steelmaking as an impurity element, and its content is preferably as small as possible. However, if it is attempted to reduce it excessively, the economy is impaired, so its content is reduced. It is 0.02 mass% or less.
Ｓ（硫黄）は、不純物元素として製鋼の原材料に混入され避けられないものであり、その含有量が少ないほど好ましいが、過度に低減させようとすると、経済性を損なうことから、その含有量を０．０１質量％以下としている。 S (sulfur) is an unavoidable element mixed in steelmaking raw materials as an impurity element, and its content is preferably as low as possible. However, if it is attempted to reduce it excessively, the economy is impaired, so its content is reduced. 0.01 mass% or less.
Ｎｉ（ニッケル）は、鋼の焼入れ性を増大させ、δフェライトの生成を抑制し、室温における強度および靭性を高める有効な元素である。また、これらの効果はＮｉおよびＣｒ両元素の含有量が多い場合には、その相乗効果により著しく増加する。しかしながら、Ｎｉの含有量が過剰量になると、高温強度（クリープ強度、クリープ破断強度）を低下させ、また、焼戻し脆性を助長する。したがって、Ｎｉの含有量を０．５０質量％以上０．８０質量％以下としている。 Ni (nickel) is an effective element that increases the hardenability of steel, suppresses the formation of δ ferrite, and increases the strength and toughness at room temperature. In addition, these effects are remarkably increased by the synergistic effect when the contents of both Ni and Cr are large. However, when the Ni content is excessive, the high temperature strength (creep strength, creep rupture strength) is lowered, and temper embrittlement is promoted. Therefore, the Ni content is set to 0.50 mass% or more and 0.80 mass% or less.
Ｃｒ（クロム）は、耐酸化性を付与し、Ｍ23Ｃ6型炭化物を析出させて高温強度を高めるために必要不可欠の元素である。しかしながら、Ｃｒの含有量が過剰量になると、δフェライトを生成し、高温強度および靭性を低下させる。したがって、Ｃｒの含有量を９．５質量％以上１０．２質量％以下としている。 Cr (chromium) is an indispensable element for imparting oxidation resistance and precipitating M 23 C 6 type carbide to increase the high temperature strength. However, when the Cr content is excessive, δ ferrite is generated, and the high temperature strength and toughness are reduced. Therefore, the Cr content is set to 9.5 mass% or more and 10.2 mass% or less.
Ｍｏ（モリブデン）は、焼入れ性を増大し、また、焼戻し時の焼戻し軟化抵抗を大きくして、常温の強度（引張り強さ、耐力）および高温強度の増大に有効な元素である。また、Ｍｏは固溶体強化元素として、また、Ｍ23Ｃ6型炭化物の微細析出を促進し、凝集を妨げる作用があると共に、その他の炭化物を生成して析出強化作用元素として、クリープ強度やクリープ破断強度などの高温強度の向上に非常に有効な元素である。 Mo (molybdenum) is an element that increases the hardenability and increases the temper softening resistance during tempering, and is effective in increasing the strength at normal temperature (tensile strength, proof stress) and high-temperature strength. In addition, Mo is a solid solution strengthening element, promotes fine precipitation of M 23 C 6 type carbides and hinders agglomeration, and generates other carbides as a precipitation strengthening action element, which provides creep strength and creep rupture. It is an extremely effective element for improving high temperature strength such as strength.
さらに、Ｍｏは０．５質量％以上添加すると、鋼の焼戻し脆性を阻止するのに有効な元素である。しかしながら、Ｍｏの含有量が過剰量になると、その効果が飽和し、かえって靭性を低下させる。したがって、Ｍｏの含有量を０．９２質量％以上１．０７質量％以下としている。 Furthermore, when Mo is added in an amount of 0.5% by mass or more, it is an effective element for preventing temper embrittlement of steel. However, when the Mo content is excessive, the effect is saturated, and the toughness is reduced. Therefore, the Mo content is set to 0.92 mass% or more and 1.07 mass% or less.
Ｗ（タングステン）は、固溶体強化元素として、クリープ強度やクリープ破断強度などの高温強度の向上に有効な元素であり、その効果がＭｏとの複合添加の場合に顕著である。しかしながら、Ｗの含有量が過剰量になると、δフェライトやラーベス相を生成するため、クリープ破断強度を劣化させると共に、靭性を低下させる。したがって、Ｗの含有量を０．９２質量％以上１．０７質量％以下としている。 W (tungsten) is an element effective for improving high-temperature strength such as creep strength and creep rupture strength as a solid solution strengthening element, and the effect is remarkable when combined with Mo. However, if the W content is excessive, δ ferrite and Laves phase are generated, so that the creep rupture strength is deteriorated and the toughness is lowered. Therefore, the W content is set to 0.92 mass% or more and 1.07 mass% or less.
Ｖ（バナジウム）は、常温における強度（引張り強さ、耐力）の向上に有効な元素である。さらに、Ｖは固溶体強化元素として、また、Ｖの微細な炭窒化物をマルテンサイトラス内に生成させる。これら微細な炭窒化物はクリープ中の転位の回復を制御してクリープ強度やクリープ破断強度など高温強度を増加させるため、Ｖは析出元素として重要な元素である。さらに、Ｖはある程度の含有範囲（０．０３〜０．３５質量％）の含有量であれば、結晶粒を微細化させて、靭性向上にも有効である。しかしながら、Ｖの含有量が過剰量になると、靭性を低下させると共に、炭素を過度に固定し、Ｍ23Ｃ6型炭化物の析出量を減じて高温強度を低下させる。したがって、Ｖの含有量を０．１８質量％以上０．２５質量％以下としている。 V (vanadium) is an element effective for improving the strength (tensile strength, yield strength) at room temperature. Further, V is a solid solution strengthening element, and V fine carbonitride is generated in the martensitic lath. Since these fine carbonitrides control the recovery of dislocations during creep and increase the high-temperature strength such as creep strength and creep rupture strength, V is an important element as a precipitation element. Furthermore, if V is a content within a certain range (0.03 to 0.35% by mass), it is effective for improving toughness by refining crystal grains. However, when the V content is excessive, the toughness is reduced, carbon is excessively fixed, the precipitation amount of M 23 C 6 type carbide is reduced, and the high temperature strength is reduced. Therefore, the content of V is set to 0.18% by mass or more and 0.25% by mass or less.
Ｎｂ（ニオブ）は、引張り強さや耐力などの常温強度、並びにクリープ強度やクリープ破断強度などの高温強度の増大に有効な元素であると共に、微細なＮｂＣを生成し結晶粒を微細化させ、靭性向上に非常に有効な元素である。また、一部が焼入れの際に、固溶して焼戻し過程で上記のＶ炭窒化物と複合したＭＸ型炭窒化物を析出し、高温強度を高める作用がある。しかしながら、Ｎｂの含有量が過剰量になると、炭素を過度に固定してＭ23Ｃ6型炭化物の析出量を減少し、高温強度を低下させる。したがって、Ｎｂの含有量を０．０５質量％以上０．１０質量％以下としている。 Nb (niobium) is an element effective for increasing normal temperature strength such as tensile strength and yield strength, and high-temperature strength such as creep strength and creep rupture strength, and also produces fine NbC to refine crystal grains and toughness. It is an extremely effective element for improvement. In addition, when part of the steel is hardened, MX-type carbonitride compounded with the above-mentioned V carbonitride is precipitated in a solid solution and tempering process, thereby increasing the high temperature strength. However, when the Nb content is excessive, the carbon is excessively fixed, the amount of precipitation of M 23 C 6 type carbide is reduced, and the high temperature strength is lowered. Therefore, the Nb content is set to 0.05% by mass or more and 0.10% by mass or less.
Ａｌ（アルミニウム）は、Ｎとの親和力が強い強窒化物形成元素であり、ラーベス相の析出を促進して、クリープ破断強度を低下させる。したがって、Ａｌの含有量を０．０２０質量％以下としている。 Al (aluminum) is a strong nitride-forming element having a strong affinity for N, and promotes the precipitation of the Laves phase and reduces the creep rupture strength. Therefore, the Al content is set to 0.020 mass% or less.
Ｎ（窒素）は、Ｖの窒化物を析出したり、また固溶した状態でＭｏやＷと共同でＩＳ効果（侵入型固溶元素と置換型固溶元素の相互作用）により高温強度を高めたりする作用がある。しかしながら、Ｎの含有量が過剰量になると、延性を低下させる。したがって、Ｎの含有量を０．０３質量％以上０．０６質量％以下としている。 N (nitrogen) increases the high-temperature strength due to the IS effect (interaction between interstitial solid solution elements and substitutional solid solution elements) in combination with Mo and W in the form of precipitates of V nitrides and solid solutions. There is an effect that. However, when the N content is excessive, ductility is reduced. Therefore, the N content is set to 0.03% by mass or more and 0.06% by mass or less.
上述した組成の耐熱鋳鋼に対して、予備熱処理、溶体化・焼入れ熱処理、第１段焼戻し熱処理、第２段焼戻し熱処理を順次行うことにより、６００℃の蒸気中で使用可能な蒸気タービン主要弁などを製造できる。 Steam turbine main valves that can be used in steam at 600 ° C by performing preliminary heat treatment, solution heat treatment / quenching heat treatment, first-stage tempering heat treatment, and second-stage tempering heat treatment on heat-resistant cast steel having the composition described above. Can be manufactured.
予備熱処理により、本実施形態に係る耐熱鋳鋼にて、鋳造中に発生する偏析を除去する。また、パーライト変態を促進させることで、微細粒化を図ることができる。溶体化処理により、添加元素であるＮｂをオーステナイト中に固溶し、焼戻し熱処理中にＭＸ炭窒化物を析出させ、高温強度を向上させている。第１段焼戻し熱処理により、焼入れ後の残留オーステナイトを完全に除去し、また、炭化物および金属間か動物を析出させ、高温強度特性を向上させている。第２段焼戻し熱処理により、応力除去焼鈍も兼ねており、また、炭化物、炭窒化物ならびに金属間化合物を析出させ、高温強度特性を向上させている。 By the pre-heat treatment, segregation that occurs during casting is removed in the heat-resistant cast steel according to the present embodiment. Further, by promoting the pearlite transformation, it is possible to achieve fine granulation. By solution treatment, Nb, which is an additive element, is dissolved in austenite, and MX carbonitride is precipitated during tempering heat treatment to improve high-temperature strength. The first stage tempering heat treatment completely removes the retained austenite after quenching, precipitates carbides and intermetallics, and improves high temperature strength characteristics. The second-stage tempering heat treatment also serves as stress relief annealing, and precipitates carbides, carbonitrides and intermetallic compounds to improve the high-temperature strength characteristics.
予備熱処理温度について説明する。
本実施形態に係る耐熱鋳鋼にて、Ｎｂを固溶させるため、予備熱処理温度を１０００℃以上にしている。また、粒の粗大化を抑制するため、予備熱処理温度を１１００℃以下にしている。
The preliminary heat treatment temperature will be described.
In the heat-resistant cast steel according to the present embodiment, the pre-heat treatment temperature is set to 1000 ° C. or higher in order to dissolve Nb. Moreover, in order to suppress the coarsening of a grain, the preliminary heat treatment temperature is set to 1100 ° C. or lower.
次に、溶体化・焼入れ熱処理温度について説明する。
本実施形態に係る耐熱鋳鋼はＭＸ型炭窒化物を析出させ高温強度を高める効果からＮｂを０．０５質量％以上０．１０質量％以下添加している。この効果を発現させるためには溶体化熱処理時にＮｂを完全にオーステナイトに固溶させることが不可欠である。しかしながら、Ｎｂは焼入れ熱処理温度を１０００℃未満にした場合、凝固時に析出した粗大な炭窒化物が熱処理後も残存し、クリープ破断強度の増加に対し完全に有効には働き得ない。この粗大な炭窒化物を一旦固溶させ炭窒化物として高密度に析出させるためにはオーステナイト化がより進行する１０００℃以上のオーステナイト化温度からの焼入れが必要になる。一方、１１００℃を超えると本実施形態に係る耐熱鋳鋼の場合、δフェライトが析出する温度域に靭性を低下させる。よって、焼入れ熱処理温度範囲を１０００〜１１００℃としている。
Next, the solution treatment / quenching heat treatment temperature will be described.
In the heat-resistant cast steel according to the present embodiment, 0.05 mass% or more and 0.10 mass% or less of Nb is added from the effect of precipitating MX type carbonitride and increasing the high temperature strength. In order to exhibit this effect, it is indispensable to completely dissolve Nb in austenite during solution heat treatment. However, when the quenching heat treatment temperature is less than 1000 ° C., Nb remains coarse carbonitride deposited during solidification even after the heat treatment, and cannot work completely effectively against an increase in creep rupture strength. In order to once dissolve this coarse carbonitride and precipitate it as a carbonitride at a high density, quenching from an austenitizing temperature of 1000 ° C. or higher at which austenitizing further proceeds is necessary. On the other hand, when the temperature exceeds 1100 ° C., in the case of the heat-resistant cast steel according to the present embodiment, the toughness is lowered in the temperature range where δ ferrite precipitates. Therefore, the quenching heat treatment temperature range is set to 1000 to 1100 ° C.
次に、焼戻し熱処理温度について説明する。
上述した焼入れ後の耐熱鋳鋼に対して、６５０〜７３０℃の温度範囲において第１段焼戻し熱処理が行われる。第１段焼戻し熱処理温度が６５０℃未満であると、未変態オーステナイトを完全にマルテンサイトラスにすることができない。他方、第１段焼戻し熱処理温度が７３０℃を越えると、第２段焼戻し熱処理の効果が十分に得られない。よって、第１段焼戻し熱処理温度範囲を６５０〜７３０℃としている。
Next, the tempering heat treatment temperature will be described.
The first-stage tempering heat treatment is performed on the heat-resistant cast steel after quenching in the temperature range of 650 to 730 ° C. If the first-stage tempering heat treatment temperature is less than 650 ° C., the untransformed austenite cannot be made completely martensitic. On the other hand, if the first-stage tempering heat treatment temperature exceeds 730 ° C., the effect of the second-stage tempering heat treatment cannot be sufficiently obtained. Therefore, the first-stage tempering heat treatment temperature range is set to 650 to 730 ° C.
続いて、第１段焼戻しを行った耐熱鋳鋼に対して、７００〜７５０℃の温度範囲において第２段焼戻し熱処理が行われる。第２段焼戻し熱処理温度が７００℃未満であると、Ｍ23Ｃ6型炭化物およびＭＸ型炭窒化物の析出が十分に平衡値まで到達することができず、析出物の体積率が相対的に低下する。しかも、このような不安定な状態にあるこれらの析出物は、その後の６００℃を越える高温で長時間のクリープを受けると、さらに析出が進行するとともに凝集粗大化が著しくなる。他方、第２段焼戻し熱処理温度が７５０℃を越えると、マルテンサイトラス内のＭＸ型炭窒化物の析出密度が低下すると共に、焼戻しが過剰になり、かつオーステナイトへの変態点Ａc1点（約７８０℃）に接近する。よって、第２段焼戻し熱処理温度範囲を７００〜７５０℃としている。 Subsequently, a second-stage tempering heat treatment is performed on the heat-resistant cast steel subjected to the first-stage tempering in a temperature range of 700 to 750 ° C. When the second-stage tempering heat treatment temperature is lower than 700 ° C., the precipitation of M 23 C 6 type carbide and MX type carbonitride cannot sufficiently reach the equilibrium value, and the volume fraction of the precipitate is relatively descend. In addition, when these precipitates in such an unstable state are subjected to creep at a high temperature exceeding 600 ° C. for a long time, precipitation further proceeds and aggregation coarsening becomes remarkable. On the other hand, when the second-stage tempering heat treatment temperature exceeds 750 ° C., the precipitation density of the MX type carbonitride in the martensite lath decreases, the tempering becomes excessive, and the transformation point A c1 to the austenite (about 780). ℃). Therefore, the second-stage tempering heat treatment temperature range is set to 700 to 750 ° C.
したがって、本実施形態に係る耐熱鋳鋼によれば、上記組成を有することで、６００℃でのクリープ破断強度を向上させることができる（具体例は後述する）。 Therefore, according to the heat resistant cast steel according to this embodiment, the creep rupture strength at 600 ° C. can be improved by having the above composition (a specific example will be described later).
また、６００℃でのクリープ破断強度が向上した耐熱鋳鋼を得ることができるので、ボイラで得られた６００℃の主蒸気を蒸気タービンに対して供給および停止を制御する主蒸気止め弁、蒸気量を加減して蒸気タービンの出力を調整する蒸気加減弁、再熱蒸気を蒸気タービンに対して供給および停止を制御するインターセプト弁などの蒸気タービン主要弁に用いることができる。 Further, since a heat-resistant cast steel having improved creep rupture strength at 600 ° C. can be obtained, a main steam stop valve for controlling supply and stop of main steam at 600 ° C. obtained in the boiler to the steam turbine, and the amount of steam It can be used for a steam turbine main valve such as a steam control valve that adjusts the output of the steam turbine by adjusting the output and an intercept valve that controls supply and stop of reheated steam to the steam turbine.
［第二番目の実施形態］
本実施形態に係る耐熱鋳鋼は、前述した第一番目の実施形態に係る耐熱鋳鋼において、下記の（１）式に示すＣｒ当量が８．５質量％以上１０．３質量％以下からなる組成を有するものであり、好適にはＣｒ当量が９質量％以上１０．３質量％以下からなる組成を有するものである。
[Second Embodiment]
The heat resistant cast steel according to the present embodiment has a composition in which the Cr equivalent represented by the following formula (1) is 8.5% by mass or more and 10.3% by mass or less in the heat resistant cast steel according to the first embodiment described above. Preferably, the Cr equivalent has a composition of 9 mass% or more and 10.3 mass% or less.
Ｃｒ当量が以下の（１）式を満たすものである。 The Cr equivalent satisfies the following formula (1).
Ｃｒ当量（質量％）＝Ｃｒ＋６Ｓｉ＋４Ｍｏ＋１．５Ｗ＋１１Ｖ＋５Ｎｂ−４０Ｃ−３０Ｎ−３０Ｂ−２Ｍｎ−４Ｎｉ−２Ｃｏ ・・・（１） Cr equivalent (mass%) = Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C-30N-30B-2Mn-4Ni-2Co (1)
本実施形態に係る耐熱鋳鋼および蒸気タービン主要弁は、δフェライトが混在すると、高温クリープ破断強度および低温靭性が低くなるので、その組成が均一な焼戻しマルテンサイト組織であることが好ましい。焼戻しマルテンサイト組織を得るために、上述した式（１）で示されるＣｒ当量を１０．３質量％以下としている。一方、Ｃｒ当量を低くくし過ぎると、高温クリープ強度が低下するため、Ｃｒ当量を８．５質量％以上とし、好ましくは９質量％以上としている。 The heat-resistant cast steel and the steam turbine main valve according to the present embodiment preferably have a tempered martensite structure with a uniform composition because the high temperature creep rupture strength and the low temperature toughness are reduced when δ ferrite is mixed. In order to obtain a tempered martensite structure, the Cr equivalent represented by the above-described formula (1) is 10.3 mass% or less. On the other hand, if the Cr equivalent is too low, the high temperature creep strength decreases, so the Cr equivalent is set to 8.5% by mass or more, preferably 9% by mass or more.
したがって、本実施形態に係る耐熱鋳鋼によれば、上記組成を有し、且つ、上記（１）式で示されるＣｒ当量が８．５質量％以上１０．３質量％以下であり、好ましくは９質量％以上１０．３質量％以下であることで、６００℃でのクリープ破断強度を向上させることができる（具体例は後述する）。 Therefore, according to the heat-resistant cast steel according to the present embodiment, the Cr equivalent represented by the above formula (1) is 8.5 mass% or more and 10.3 mass% or less, preferably 9 The creep rupture strength at 600 ° C. can be improved when the content is from mass% to 10.3 mass% (specific examples will be described later).
また、６００℃でのクリープ破断強度が向上した耐熱鋳鋼を得ることができるので、蒸気温度が６００℃である蒸気タービンの主蒸気止め弁および蒸気加減弁ならびにインターセプト弁などに用いることができる。 Further, since a heat-resistant cast steel having improved creep rupture strength at 600 ° C. can be obtained, it can be used for a main steam stop valve, a steam control valve, an intercept valve, and the like of a steam turbine having a steam temperature of 600 ° C.
［第三番目の実施形態］
本実施形態に係る耐熱鋳鋼は、前述した第一番目または第二番目の実施形態に係る耐熱鋳鋼において、０．３０≦０．５Ｗ／（０．５Ｗ＋Ｍｏ）≦０．３７である組成を有するものであり、好適には０．３１≦０．５Ｗ／（０．５Ｗ＋Ｍｏ）≦０．３５である組成を有するものである。
[Third embodiment]
The heat-resistant cast steel according to the present embodiment has a composition of 0.30 ≦ 0.5 W / (0.5 W + Mo) ≦ 0.37 in the heat-resistant cast steel according to the first or second embodiment described above. And preferably has a composition of 0.31 ≦ 0.5 W / (0.5 W + Mo) ≦ 0.35.
ＷとＭｏの質量比を調整することで、クリープ破断強度の低下を抑制できる。 By adjusting the mass ratio of W and Mo, a decrease in creep rupture strength can be suppressed.
したがって、本実施形態に係る耐熱鋳鋼によれば、上記組成を有し、且つ、０．５Ｗ／（０．５Ｗ＋Ｍｏ）が０．３０以上０．３７以下であり、好ましくは０．３１以上０．３５以下であることで、６００℃でのクリープ破断強度を向上させることができる（具体例は後述する）。 Therefore, according to the heat-resistant cast steel according to the present embodiment, it has the above composition, and 0.5 W / (0.5 W + Mo) is 0.30 or more and 0.37 or less, preferably 0.31 or more and 0.00. By being 35 or less, the creep rupture strength at 600 ° C. can be improved (specific examples will be described later).
また、６００℃でのクリープ破断強度が向上した耐熱鋳鋼を得ることができるので、蒸気温度が６００℃である蒸気タービンの主蒸気止め弁および蒸気加減弁ならびにインターセプト弁などに用いることができる。 Further, since a heat-resistant cast steel having improved creep rupture strength at 600 ° C. can be obtained, it can be used for a main steam stop valve, a steam control valve, an intercept valve, and the like of a steam turbine having a steam temperature of 600 ° C.
本発明に係る耐熱鋳鋼の効果を確認するために行った確認試験を以下に説明するが、本発明は以下に説明する確認試験のみに限定されるものではない。 Although the confirmation test performed in order to confirm the effect of the heat-resistant cast steel which concerns on this invention is demonstrated below, this invention is not limited only to the confirmation test demonstrated below.
［確認試験］
下記の表１は、本発明に係る耐熱鋳鋼の化学組成（各値共に質量％）を示すものである。試料は、蒸気主要弁の弁室の厚肉部を想定して、高周波誘導溶解炉にて１５０ｋｇ溶解し、砂型に鋳込み、鋳塊（試験体１〜７および比較体１〜６）を作製した。試験体１〜７が本発明に係る耐熱鋳鋼であり、比較体１〜６が従来材の鋳鋼（比較材）である。試験体１〜７および比較体１〜６のいずれの試料も、１０７０℃×８ｈ炉冷の焼鈍処理後、蒸気主要弁の弁室の肉厚部を想定し、１０７０℃×８ｈ加熱保持後空冷の焼準、７３０℃×８ｈ加熱保持後空冷の一次焼戻し（第１段焼戻し熱処理）及び７５０℃×８ｈ加熱保持後空冷の二次焼戻し（第２段焼戻し熱処理）を行った。
[Confirmation test]
Table 1 below shows the chemical composition of the heat-resistant cast steel according to the present invention (both values are mass%). Assuming the thick part of the valve chamber of the steam main valve, 150 kg of the sample was melted in a high-frequency induction melting furnace and cast into a sand mold to prepare ingots (test bodies 1 to 7 and comparative bodies 1 to 6). . Test bodies 1 to 7 are heat-resistant cast steels according to the present invention, and comparative bodies 1 to 6 are conventional cast steels (comparative materials). Any sample of the test bodies 1 to 7 and the comparative bodies 1 to 6 is assumed to be a thick portion of the valve chamber of the steam main valve after annealing at 1070 ° C. × 8 h, and then air-cooled after heating at 1070 ° C. × 8 h. Tempering, air-cooled primary tempering (first stage tempering heat treatment) after heating at 730 ° C. × 8 h, and air-cooling secondary tempering (second stage tempering heat treatment) after holding at 750 ° C. × 8 h.
下記の表２は、試験体１〜７および比較体１〜６のＣｒ当量（質量％）および０．５Ｗ／（０．５Ｗ＋Ｍｏ）を示すものである。 Table 2 below shows the Cr equivalent (mass%) and 0.5 W / (0.5 W + Mo) of the test bodies 1 to 7 and the comparative bodies 1 to 6.
表３は室温の引張特性、６００℃、１５０ＭＰａ、クリープ破断時間の試験結果を示すものである。試験片は上記鋳塊（試験体１〜７および比較体１〜６）の肉厚１５０ｍｍ部の中心部より採取した。なお、Ｃｒ当量（質量％）は上記の（１）式より求めた。δフェライト量を点算法により求めた。観察視野を４０とした。 Table 3 shows the test results of tensile properties at room temperature, 600 ° C., 150 MPa, and creep rupture time. The test piece was sampled from the center of the ingot (test bodies 1 to 7 and comparative bodies 1 to 6) having a thickness of 150 mm. In addition, Cr equivalent (mass%) was calculated | required from said (1) Formula. The amount of δ ferrite was determined by a point calculation method. The observation visual field was set to 40.
ここで、上述した試験体１〜７および比較体１〜６におけるＣｒ当量に対する引張試験による室温伸びとδフェライト量の関係について図１に示す。この図１にて、菱形印が試験体１〜７および比較体１〜６の室温伸び（％）を示し、四角印が試験体１〜７および比較体１〜６のδフェライト（％）を示す。この図１に示すように、Ｃｒ当量が大きくなるにつれてδフェライト量が多くなり、１０．３質量％を越えると急激に多くなることを確認した。他方、室温伸びが、Ｃｒ当量が大きくなるにつれて低下していることを確認した。そのため、Ｃｒ当量を１０．３質量％以下にすることが必要であるが明らかとなった。なお、Ｃｒ当量が８．５質量％程度では特に室温伸びへの影響は無いことを確認した。すなわち、Ｃｒ当量を、８．５質量％以上１０．３質量％以下を示す領域Ａの範囲内とし、好適には９．０質量％以上１０．３質量％以下を示す領域Ｂの範囲内とすることが望ましいことを確認した。 Here, FIG. 1 shows the relationship between the room temperature elongation and the amount of δ ferrite by the tensile test with respect to the Cr equivalent in the above-described test bodies 1 to 7 and comparative bodies 1 to 6. In FIG. 1, rhombus marks indicate room temperature elongation (%) of test bodies 1 to 7 and comparative bodies 1 to 6, and square marks indicate δ ferrite (%) of test bodies 1 to 7 and comparative bodies 1 to 6. Show. As shown in FIG. 1, it was confirmed that the amount of δ ferrite increased as the Cr equivalent increased, and increased rapidly when it exceeded 10.3% by mass. On the other hand, it was confirmed that the room temperature elongation decreased as the Cr equivalent increased. Therefore, it has become clear that the Cr equivalent needs to be 10.3% by mass or less. In addition, when Cr equivalent was about 8.5 mass%, it confirmed that there was no influence on room temperature elongation especially. That is, the Cr equivalent is in the range of region A showing 8.5% by mass or more and 10.3% by mass or less, preferably in the range of region B showing 9.0% by mass or more and 10.3% by mass or less. Confirmed that it is desirable to do.
上述した０．５Ｗ／（０．５Ｗ＋Ｍｏ）とクリープ破断時間の関係を図２に示す。この図２にて、菱形印が試験体１〜７のクリープ破断強度を示し、四角印が比較体１〜５のクリープ破断強度を示す。この図２に示すように、０．５Ｗ／（０．５Ｗ＋Ｍｏ）が曲線Ｌ１近傍にあり、０．５Ｗ／（０．５Ｗ＋Ｍｏ）の増加に伴って、クリープ破断時間が長くなり、０．５Ｗ／（０．５Ｗ＋Ｍｏ）が０．３４程度でクリープ破断時間が最大値となることを確認した。また、０．５Ｗ／（０．５Ｗ＋Ｍｏ）が０．３４よりも増加していくと、それに応じてクリープ破断時間が短くなっていくことを確認した。よって、クリープ破断の観点から、ＷとＭｏの添加量が、０．５Ｗ／（０．５Ｗ＋Ｍｏ）を０．３０以上０．３７以下の範囲内（領域Ｃ内）、好適には０．３１以上０．３５以下範囲内（領域Ｄ内）に調整する必要があることが明らかとなった。 FIG. 2 shows the relationship between 0.5 W / (0.5 W + Mo) and creep rupture time. In FIG. 2, rhombus marks indicate the creep rupture strength of the test bodies 1 to 7, and square marks indicate the creep rupture strength of the comparative bodies 1 to 5. As shown in FIG. 2, 0.5 W / (0.5 W + Mo) is in the vicinity of the curve L 1, and with an increase of 0.5 W / (0.5 W + Mo), the creep rupture time becomes longer, and 0.5 W / It was confirmed that the creep rupture time was the maximum when (0.5W + Mo) was about 0.34. Further, it was confirmed that when 0.5 W / (0.5 W + Mo) increased from 0.34, the creep rupture time was shortened accordingly. Therefore, from the viewpoint of creep rupture, the addition amount of W and Mo is within a range of 0.5W / (0.5W + Mo) from 0.30 to 0.37 (in the region C), preferably 0.31 or more. It became clear that it was necessary to adjust within the range of 0.35 or less (in the region D).
クリープ強度低下現象は、種々の析出物および転移組織の変化が重畳するなかで特に長時間側ではラーベス相の析出・粗大化にともなうＭｏおよびＷの固溶量低下による転位の易動度の増加に起因すると考えられる。すなわち、ＭｏおよびＷの組成比の違いにより長時間後のラーベス相の析出挙動が異なり、クリープ破断強度に影響する。上記の０．５Ｗ／（０．５Ｗ＋Ｍｏ）を０．３０以上０．３７以下の範囲に調整することで、クリープ破断強度が最大値を示すことが明らかとなった。 Decrease in creep strength is caused by the increase in dislocation mobility due to the decrease in the solid solution amount of Mo and W accompanying the precipitation and coarsening of Laves phase, especially in the long time period, while various precipitates and changes in the transition structure overlap. It is thought to be caused by. That is, the Laves phase precipitation behavior after a long time varies depending on the composition ratio of Mo and W, which affects the creep rupture strength. It was revealed that the creep rupture strength showed the maximum value by adjusting the above 0.5 W / (0.5 W + Mo) to the range of 0.30 or more and 0.37 or less.
ここで、Ｍｏの含有量とクリープ破断時間の関係を図３に示す。この図３にて、菱形印が試験体１〜７のクリープ破断強度を示し、四角印が比較体１〜６のクリープ破断強度を示す。この図３に示すように、Ｍｏ含有量が曲線Ｌ２近傍にあり、Ｍｏ含有量の増加に伴ってクリープ破断時間が長くなり、Ｍｏ含有量が０．９８質量％程度でクリープ破断強度が最大値となることを確認した。また、Ｍｏ含有量が０．９８質量％よりも増加していくと、それに応じてクリープ破断時間が短くなっていくことを確認した。よって、クリープ破断の観点から、Ｍｏ含有量を０．９２質量％以上１．０７質量％以下の範囲内（領域Ｅ内）に調整することで、クリープ破断強度が最大値を示すことが明らかとなった。 Here, the relationship between the Mo content and the creep rupture time is shown in FIG. In FIG. 3, rhombus marks indicate the creep rupture strength of the test bodies 1 to 7, and square marks indicate the creep rupture strength of the comparative bodies 1 to 6. As shown in FIG. 3, the Mo content is in the vicinity of the curve L2, the creep rupture time becomes longer as the Mo content increases, and the creep rupture strength is maximum when the Mo content is about 0.98% by mass. It was confirmed that Further, it was confirmed that when the Mo content increased from 0.98% by mass, the creep rupture time was shortened accordingly. Therefore, from the viewpoint of creep rupture, it is clear that the creep rupture strength shows the maximum value by adjusting the Mo content within the range of 0.92 mass% or more and 1.07 mass% or less (in the region E). became.
Ｗの含有量とクリープ破断時間の関係を図４に示す。この図４にて、菱形印が試験体１〜７のクリープ破断強度を示し、四角印が比較体１〜５のクリープ破断強度を示す。この図４に示すように、Ｗ含有量が曲線Ｌ３近傍にあり、Ｗ含有量の増加に伴ってクリープ破断時間が長くなり、Ｗ含有量が１．０２質量％程度でクリープ破断強度が最大値となることを確認した。また、Ｗ含有量が１．０２質量％よりも増加していくと、それに応じてクリープ破断時間が短くなっていくことを確認した。よって、クリープ破断の観点から、Ｗ含有量を０．９２質量％以上１．０７質量％以下の範囲内（領域Ｆ内）に調整することで、クリープ破断強度は最大値を示すことが明らかとなった。 The relationship between the W content and the creep rupture time is shown in FIG. In FIG. 4, the diamond marks indicate the creep rupture strength of the test bodies 1 to 7, and the square marks indicate the creep rupture strength of the comparative bodies 1 to 5. As shown in FIG. 4, the W content is in the vicinity of the curve L3, the creep rupture time becomes longer as the W content increases, and the creep rupture strength is maximum when the W content is about 1.02% by mass. It was confirmed that Further, it was confirmed that when the W content was increased from 1.02% by mass, the creep rupture time was shortened accordingly. Therefore, from the viewpoint of creep rupture, it is clear that the creep rupture strength shows the maximum value by adjusting the W content within the range of 0.92 mass% or more and 1.07 mass% or less (region F). became.
図５に試験体Ｎｏ．４と比較体Ｎｏ．６について、種々条件においてクリープ破断試験を行い、ＬＭＰ（Ｌａｒｓｏｎ−Ｍｉｌｌｅｒ Ｐａｒａｍｅｔｅｒ）法にて整理した結果を示す。この図５にて、丸印が試験体４の場合を示し、菱形印が比較体６の場合を示す。この図５に示すように、試験体Ｎｏ．４が、比較体Ｎｏ．６と比べてクリープ破断強度が向上していることを確認した。 In FIG. 4 and Comparative No. 6 shows a result of conducting a creep rupture test under various conditions and arranging by a LMP (Larson-Miller Parameter) method. In FIG. 5, the circle marks indicate the case of the test body 4, and the diamond marks indicate the case of the comparison body 6. As shown in FIG. 4 is Comparative No. Compared to 6, it was confirmed that the creep rupture strength was improved.
ＬＭＰが以下（２）式を満たすものである。 LMP satisfies the following expression (2).
ＬＭＰ＝（絶対温度）×（ｌｏｇ（ｔｒ）＋２５）／１０００ ・・・（２） LMP = (absolute temperature) × (log (tr) +25) / 1000 (2)
したがって、本実施例に係る耐熱鋳鋼によれば、上記組成を有することで、６００℃でのクリープ破断強度を向上させることができる。 Therefore, according to the heat-resistant cast steel according to this example, the creep rupture strength at 600 ° C. can be improved by having the above composition.
本発明に係る耐熱鋳鋼および蒸気タービン主要弁が上記組成を有することから、６００℃でのクリープ破断強度を向上させることができるので、産業上、極めて有益に利用することができる。 Since the heat-resistant cast steel and the steam turbine main valve according to the present invention have the above-described composition, the creep rupture strength at 600 ° C. can be improved, so that it can be used extremely beneficially in the industry.
Claims (4)
０．２０質量％≦Ｓｉ≦０．４０質量％、
０．４質量％≦Ｍｎ≦１．０質量％、
Ｐ≦０．０２質量％、
Ｓ≦０．０１質量％、
０．５０質量％≦Ｎｉ≦０．８０質量％、
９．５質量％≦Ｃｒ≦１０．２質量％、
０．９２質量％≦Ｍｏ≦１．０７質量％、
０．９２質量％≦Ｗ≦１．０７質量％、
０．１８質量％≦Ｖ≦０．２５質量％、
０．０５質量％≦Ｎｂ≦０．１０質量％、
Ａｌ≦０．０２０質量％、
０．０３質量％≦Ｎ≦０．０６質量％、
残部がＦｅ及び不可避不純物からなり、
Ｃｒ＋６Ｓｉ＋４Ｍｏ＋１．５Ｗ＋１１Ｖ＋５Ｎｂ−４０Ｃ−３０Ｎ−３０Ｂ−２Ｍｎ−４Ｎｉ−２Ｃｏで表されるＣｒ当量が、８．５質量％以上１０．３質量％以下であり、
０．３０≦０．５Ｗ／（０．５Ｗ＋Ｍｏ）≦０．３７であり、
１０００℃以上１１００℃以下にて予備熱処理し、１０００〜１１００℃で溶体化・焼入れ熱処理し、６５０〜７３０℃で第１段焼戻し熱処理し、７００〜７５０℃で第２段焼戻し熱処理してなる
ことを特徴とする耐熱鋳鋼。 0.10 mass% ≦ C ≦ 0.14 mass%,
0.20 mass% ≦ Si ≦ 0.40 mass%,
0.4 mass% ≦ Mn ≦ 1.0 mass%,
P ≦ 0.02 mass%,
S ≦ 0.01 mass%,
0.50 mass% ≦ Ni ≦ 0.80 mass%,
9.5 mass% ≦ Cr ≦ 10.2 mass%,
0.92 mass% ≦ Mo ≦ 1.07 mass%,
0.92 mass% ≦ W ≦ 1.07 mass%,
0.18 mass% ≦ V ≦ 0.25 mass%,
0.05% by mass ≦ Nb ≦ 0.10% by mass,
Al ≦ 0.020 mass%,
0.03 mass% ≦ N ≦ 0.06 mass%,
Balance Ri Do Fe and unavoidable impurities,
Cr equivalent represented by Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb-40C-30N-30B-2Mn-4Ni-2Co is 8.5 mass% or more and 10.3 mass% or less,
0.30 ≦ 0.5 W / (0.5 W + Mo) ≦ 0.37,
Preliminary heat treatment at 1000 ° C. to 1100 ° C., solution heat treatment and quenching heat treatment at 1000 to 1100 ° C., first stage tempering heat treatment at 650 to 730 ° C., and second stage tempering heat treatment at 700 to 750 ° C. A heat-resistant cast steel characterized by the above.
前記Ｃｒ当量が、９質量％以上１０．３質量％以下である
ことを特徴とする耐熱鋳鋼。 The heat-resistant cast steel according to claim 1 ,
The heat resistant cast steel, wherein the Cr equivalent is 9% by mass or more and 10.3% by mass or less.
０．３１≦０．５Ｗ／（０．５Ｗ＋Ｍｏ）≦０．３５である
ことを特徴とする耐熱鋳鋼。 The heat-resistant cast steel according to claim 1 ,
0.31 <= 0.5W / (0.5W + Mo) <= 0.35, The heat resistant cast steel characterized by the above-mentioned.
ことを特徴とする蒸気タービン主要弁。 A steam turbine main valve comprising the heat-resistant cast steel according to any one of claims 1 to 3 .
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| JP2008334153A JP5371420B2 (en) | 2008-12-26 | 2008-12-26 | Heat resistant cast steel and steam turbine main valves |
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| JP2010156011A JP2010156011A (en) | 2010-07-15 |
| JP5371420B2 true JP5371420B2 (en) | 2013-12-18 |
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| WO2016136888A1 (en) * | 2015-02-27 | 2016-09-01 | 国立研究開発法人物質・材料研究機構 | Ferrite-based heat-resistant steel and method for producing same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS6376854A (en) * | 1986-09-18 | 1988-04-07 | Kawasaki Steel Corp | Heat resistant ferritic steel having superior strength at high temperature |
| JPH0770713A (en) * | 1993-07-07 | 1995-03-14 | Japan Steel Works Ltd:The | Heat resistant cast steel |
| JP4509664B2 (en) * | 2003-07-30 | 2010-07-21 | 株式会社東芝 | Steam turbine power generation equipment |
| JP4602163B2 (en) * | 2005-05-31 | 2010-12-22 | 株式会社東芝 | Heat-resistant steel member and manufacturing method thereof |
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