JP2002088441A - Heat resistant cast steel and its production method - Google Patents
Heat resistant cast steel and its production methodInfo
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- JP2002088441A JP2002088441A JP2000365258A JP2000365258A JP2002088441A JP 2002088441 A JP2002088441 A JP 2002088441A JP 2000365258 A JP2000365258 A JP 2000365258A JP 2000365258 A JP2000365258 A JP 2000365258A JP 2002088441 A JP2002088441 A JP 2002088441A
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、蒸気タービン車室
材料、蒸気タービン弁箱材料等として有用な耐熱鋳鋼お
よびその製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant cast steel useful as a steam turbine casing material, a steam turbine valve box material, and the like, and a method of manufacturing the same.
【０００２】[0002]
【従来の技術】火力発電プラントにおいて、蒸気タービ
ン車室や蒸気タービン弁箱などの高温部材に用いられる
耐熱鋳鋼材料として、従来から１．２５Ｃｒ−０．５Ｍ
ｏ鋳鋼や１Ｃｒ−１Ｍｏ−０．２５Ｖ鋳鋼などの低合金
耐熱鋳鋼が多用されている。2. Description of the Related Art In a thermal power plant, as a heat-resistant cast steel material used for high-temperature members such as a steam turbine casing and a steam turbine valve case, 1.25Cr-0.5M has been conventionally used.
Low alloy heat-resistant cast steels such as o-cast steel and 1Cr-1Mo-0.25V cast steel are frequently used.
【０００３】一方、近年の火力発電プラントでは、蒸気
の高温化が急速に進められている。これに伴い、高温部
材の材料を高Ｃｒ系耐熱鋳鋼に変更する動きが活発化し
ている。この種の高Ｃｒ系耐熱鋳鋼は、例えば特公平４
−５３９２８号公報や特公平３−８０８６５号公報に開
示されている。高Ｃｒ系耐熱鋳鋼は、高強度かつ耐高温
環境特性などに優れた特性を有しているので、蒸気の高
温化に伴う高温部材の肉厚増加を抑制できる。また、蒸
気タービンの起動停止に伴う熱応力を低減できるので、
蒸気タービンの運用性向上に寄与する。On the other hand, in recent thermal power plants, the temperature of steam is rapidly increasing. Along with this, the movement to change the material of the high temperature member to high Cr heat resistant cast steel has been activated. This kind of high Cr heat resistant cast steel is, for example,
No. 5,39,28 and Japanese Patent Publication No. 3-80865. Since the high Cr heat-resistant cast steel has characteristics such as high strength and high-temperature environment resistance, it is possible to suppress an increase in the thickness of a high-temperature member due to a high temperature of steam. In addition, since the thermal stress associated with starting and stopping the steam turbine can be reduced,
It contributes to improving the operability of the steam turbine.
【０００４】ところで、近年の火力発電プラントは、高
い熱効率とともに優れた経済性が要求される傾向にあ
る。このため、プラント構成材料は、従来のものと同等
か又はそれ以上の機械的性質や製造性を有するものと
し、かつ経済性にも優れたものとすることが不可欠とな
りつつある。このような要求を満たし得るものとして、
特開平２−２１７４３８号公報や特開平８−２６９６１
６号公報に開示された鋼を例示できる。[0004] Recent thermal power plants tend to require high thermal efficiency and excellent economic efficiency. For this reason, it is becoming indispensable for the plant constituent materials to have mechanical properties and manufacturability equal to or higher than those of conventional ones and to be excellent in economic efficiency. In order to meet such demands,
JP-A-2-217438 and JP-A-8-26961
No. 6 discloses steel.
【０００５】[0005]
【発明が解決しようとする課題】しかしながら、厚肉の
鋳造品として製造される高温部材の材料には、特開平２
−２１７４３８号公報や特開平８−２６９６１６号公報
に記載された鋼よりも優れた高温強度特性と優れた経済
性とを兼ね備えることが要求される。However, the material of the high-temperature member manufactured as a thick cast product is disclosed in
It is required that the steel has both high-temperature strength characteristics superior to steel described in JP-A-217438 and JP-A-8-269616 and excellent economic efficiency.
【０００６】本発明はこのような事情を考慮してなされ
たものであって、その目的とするところは、高温蒸気が
流通する環境下で優れた機械的性質を発揮するとともに
経済性に優れた耐熱鋳鋼およびその製造方法を提供する
ことにある。The present invention has been made in view of such circumstances, and it is an object of the present invention to exhibit excellent mechanical properties in an environment where high-temperature steam flows and to be economically efficient. An object of the present invention is to provide a heat-resistant cast steel and a method for producing the same.
【０００７】[0007]
【課題を解決するための手段】本発明者らは、高Ｃｒ系
鋳鋼に匹敵する高温強度特性を有する経済的な低合金耐
熱鋳鋼を開発すべく鋭意研究を積み重ねた結果、以下に
述べる本発明を完成させるに至った。Means for Solving the Problems The inventors of the present invention have conducted intensive studies to develop an economical low-alloy heat-resistant cast steel having high-temperature strength characteristics comparable to high Cr cast steels. Was completed.
【０００８】本発明に係る耐熱鋳鋼は、質量％で、Ｃ：
０．１５〜０．３％、Ｓｉ：０．１〜０．３０％、Ｍ
ｎ：０．０１〜０．１％、Ｃｒ：２．０〜２．５％、Ｍ
ｏ：０．３〜０．８％、Ｖ：０．２３〜０．３％、Ｗ：
１．６〜２．６％、Ｎ：０．００５〜０．０３％、Ｂ：
０．００１〜０．００４％を含有し、かつ不純物元素の
うちＮｉ：０．２％以下と、Ｐ：０．０３％以下と、
Ｓ：０．０１％以下とに制限し、かつ下式（１）により
求められるＢ当量が０．０２％以下と、下式（２）によ
り求められるＭｏ当量が１．４〜２．０％と、下式
（３）により求められるＣ当量が０．６５％以上とを満
たし、残部が鉄および不可避的不純物からなり、Ｍ２３
Ｃ６型炭化物と、Ｍ７Ｃ３型炭化物と、ＭＸ型炭窒化物
とからなる析出相が母相に微細析出した組織であり、か
つ母相に対する析出相の比が０．６〜１．０質量％であ
ることを特徴とする。[0008] The heat-resistant cast steel according to the present invention has a C:
0.15 to 0.3%, Si: 0.1 to 0.30%, M
n: 0.01 to 0.1%, Cr: 2.0 to 2.5%, M
o: 0.3-0.8%, V: 0.23-0.3%, W:
1.6 to 2.6%, N: 0.005 to 0.03%, B:
0.001 to 0.004%, and among the impurity elements, Ni: 0.2% or less, P: 0.03% or less,
S: It is limited to 0.01% or less, and the B equivalent obtained by the following formula (1) is 0.02% or less, and the Mo equivalent obtained by the following formula (2) is 1.4 to 2.0%. When filled and C equivalent amount calculated by the following equation (3) is 0.65% or more, and the balance of iron and unavoidable impurities, M 23
A C 6 type carbides, and M 7 C 3 type carbide precipitation phase consisting of MX-type carbonitrides are tissue was finely precipitated in the parent phase, and the ratio of precipitated phase to matrix phase 0.6 to 1. 0% by mass.
【０００９】 Ｂ当量＝Ｂ＋０．５Ｎ …（１） Ｍｏ当量＝Ｍｏ＋０．５Ｗ …（２） Ｃ当量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３） この場合に、前記Ｖの含有量を０．２３〜０．２７質量％とし、さらに、Ｎｂ を０．０１〜０．０６質量％含有し、下式（４）により
求められるＮｂ当量が０．１５％以下を満たすようにし
てもよい。B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3) In this case, V Is set to 0.23 to 0.27% by mass, Nb is further contained to 0.01 to 0.06% by mass, and the Nb equivalent determined by the following formula (4) satisfies 0.15% or less. It may be.
【００１０】Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４） また、前記Ｖの含有量を０．２３〜０．２７質量％と
し、さらに、Ｔｉ：０．００５〜０．０１質量％を含有
するようにしてもよい。Nb equivalent = Nb + 0.4C (4) Further, the content of V is set to 0.23 to 0.27% by mass, and the content of Ti is set to 0.005 to 0.01% by mass. You may.
【００１１】さらに、前記Ｖの含有量を０．２５〜０．
３％とするようにしてもよい。Further, the content of V is set to 0.25 to 0.5.
You may make it 3%.
【００１２】本発明に係る耐熱鋳鋼は、質量％で、Ｃ：
０．１５〜０．３％、Ｓｉ：０．１〜０．３０％、Ｍ
ｎ：０．４〜０．７％、Ｃｒ：２．０〜２．５％、Ｍ
ｏ：０．３〜０．８％、Ｖ：０．２３〜０．３％、Ｗ：
１．６〜２．６％、Ｎ：０．００５〜０．０３％、Ｂ：
０．００１〜０．００４％を含有し、かつ不純物元素の
うちＮｉ：０．５％以下と、Ｐ：０．０３％以下と、
Ｓ：０．０１％以下とに制限し、かつ下式（１）により
求められるＢ当量が０．０２％以下と、下式（２）によ
り求められるＭｏ当量が１．４〜２．０％と、下式
（３）により求められるＣ当量が０．６５％以上とを満
たし、残部が鉄および不可避的不純物からなり、Ｍ２３
Ｃ６型炭化物と、Ｍ７Ｃ３型炭化物と、ＭＸ型炭窒化物
とからなる析出相が母相に微細析出した組織であり、か
つ母相に対する析出相の比が０．６〜１．０質量％であ
ることを特徴とする。[0012] The heat-resistant cast steel according to the present invention contains, by mass%, C:
0.15 to 0.3%, Si: 0.1 to 0.30%, M
n: 0.4 to 0.7%, Cr: 2.0 to 2.5%, M
o: 0.3-0.8%, V: 0.23-0.3%, W:
1.6 to 2.6%, N: 0.005 to 0.03%, B:
0.001 to 0.004%, and among the impurity elements, Ni: 0.5% or less, P: 0.03% or less,
S: It is limited to 0.01% or less, and the B equivalent obtained by the following formula (1) is 0.02% or less, and the Mo equivalent obtained by the following formula (2) is 1.4 to 2.0%. When filled and C equivalent amount calculated by the following equation (3) is 0.65% or more, and the balance of iron and unavoidable impurities, M 23
A C 6 type carbides, and M 7 C 3 type carbide precipitation phase consisting of MX-type carbonitrides are tissue was finely precipitated in the parent phase, and the ratio of precipitated phase to matrix phase 0.6 to 1. 0% by mass.
【００１３】 Ｂ当量＝Ｂ＋０．５Ｎ …（１） Ｍｏ当量＝Ｍｏ＋０．５Ｗ …（２） Ｃ当量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３） この場合に、前記Ｖの含有量を０．２３〜０．２７質量
％とし、さらに、Ｔｉ：０．００５〜０．０１質量％、
Ｎｂを０．０１〜０．０６質量％含有し、下式（４）に
より求められるＮｂ当量が０．１５％以下を満たすよう
にしてもよい。B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3) In this case, V Is set to 0.23 to 0.27% by mass, and further, Ti: 0.005 to 0.01% by mass,
Nb may be contained in an amount of 0.01 to 0.06% by mass, and the Nb equivalent obtained by the following formula (4) may satisfy 0.15% or less.
【００１４】Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４） また、前記Ｖの含有量を０．２３〜０．２５質量％と
し、さらに、Ｔｉ：０．０１〜０．０２５質量％を含有
するようにしてもよい。Nb equivalent = Nb + 0.4C (4) Further, the content of V is set to 0.23 to 0.25% by mass, and the content of Ti is set to 0.01 to 0.025% by mass. You may.
【００１５】さらに、前記Ｖの含有量を０．２５〜０．
３％とするようにしてもよい。Further, the content of V is set to 0.25 to 0.5.
You may make it 3%.
【００１６】上記の各成分の働きおよび組成範囲の限定
理由を以下の（ａ）項〜（ｐ）項に説明する。なお、以
下の説明における％表示は、とくに断らない限り質量％
を意味する。The functions of the above components and the reasons for limiting the composition range will be described in the following items (a) to (p). In the following description, “%” indicates mass% unless otherwise specified.
Means
【００１７】（ａ）Ｃ：０．１５〜０．３％ Ｃは、焼入れ性の確保、フェライトの生成抑制、析出強
化に寄与する炭化物もしくは炭窒化物として析出する働
きを有する。焼入れ性の確保およびフェライト生成の抑
制は、特に大型鋳塊を鋳造する場合に、厚肉部の機械的
性質を確保する上で重要である。Ｃ含有量を０．１５％
未満にすると、これらの働きが十分になされない可能性
がある。一方、０．３％を超えるＣ含有量にすると、析
出した炭化物の凝集を促進させるとともに溶接性を低下
させるおそれがある。(A) C: 0.15 to 0.3% C has a function of securing hardenability, suppressing formation of ferrite, and precipitating as carbide or carbonitride which contributes to precipitation strengthening. Ensuring hardenability and suppressing the formation of ferrite are important for ensuring the mechanical properties of the thick part, especially when casting large ingots. 0.15% C content
If it is less than these, these functions may not be sufficiently performed. On the other hand, if the C content exceeds 0.3%, the aggregation of precipitated carbides may be promoted and weldability may be reduced.
【００１８】（ｂ）Ｓｉ：０．１〜０．３％ Ｓｉは、脱酸剤としての働きを有するとともに良好な鋳
造性の確保や耐水蒸気酸化特性を高める働きを有する。
Ｓｉ含有量を０．１％未満にすると、これらの働きが十
分になされない可能性がある。一方、０．３％を超える
含有量にすると、靭性が低下して脆化を促進させるおそ
れがある。(B) Si: 0.1 to 0.3% Si has a function as a deoxidizing agent, and also has a function to secure good castability and enhance steam oxidation resistance.
If the Si content is less than 0.1%, these functions may not be sufficiently performed. On the other hand, if the content is more than 0.3%, the toughness may be reduced and embrittlement may be promoted.
【００１９】（ｃ）Ｍｎ：０．０１〜０．１％もしくは
０．４〜０．７％ Ｍｎは、脱硫剤としての働きを有する。Ｍｎ含有量を
０．０１％未満にすると、脱硫効果を奏することが困難
となる。０．１％を超えるＭｎ含有量にすると、クリー
プ強度を低下させるおそれがある。(C) Mn: 0.01 to 0.1% or 0.4 to 0.7% Mn has a function as a desulfurizing agent. When the Mn content is less than 0.01%, it is difficult to exhibit a desulfurization effect. If the Mn content exceeds 0.1%, the creep strength may be reduced.
【００２０】なお、本発明の耐熱鋳鋼を大型厚肉部品と
して使用する場合には、焼き入れ時の冷却速度の低下に
よって厚肉部におけるフェライトの生成傾向が高まるた
め、Ｍｎ添加量を増加させることが好ましい。厚肉部で
のフェライトの生成を完全に抑制するには０．４％以上
の添加が必要である。この場合に、Ｍｎ０．０１〜０．
１％添加の鋳鋼に比べるとＭｎ０．４％以上添加の鋳鋼
ではクリープ強度は若干低下するが、Ｍｎ添加量を０．
７％以下であればクリープ強度の著しい低下は回避でき
る。When the heat-resistant cast steel of the present invention is used as a large-sized thick-walled part, the cooling rate at the time of quenching lowers the ferrite generation tendency in the thick-walled part. Is preferred. To completely suppress the formation of ferrite in the thick portion, it is necessary to add 0.4% or more. In this case, Mn is 0.01 to 0.1.
The creep strength of the cast steel containing 0.4% or more of Mn is slightly lower than that of the cast steel containing 1% of Mn.
If it is 7% or less, a significant decrease in creep strength can be avoided.
【００２１】（ｄ）Ｃｒ：２．０〜２．５％ Ｃｒは、耐酸化性および耐食性を高める働きを有すると
ともに、析出強化に寄与する析出物として析出する働き
を有する。Ｃｒ含有量を２．０％未満にすると、これら
の働きが十分になされない可能性がある。２．５％を超
える含有量にすると、靭性および組織安定性を低下させ
るおそれがある。(D) Cr: 2.0 to 2.5% Cr has a function of improving oxidation resistance and corrosion resistance and a function of precipitating as a precipitate contributing to precipitation strengthening. If the Cr content is less than 2.0%, these functions may not be sufficiently performed. If the content exceeds 2.5%, toughness and structure stability may be reduced.
【００２２】（ｅ）Ｍｏ：０．３〜０．８％ Ｍｏは、固溶強化に寄与する働きおよび炭化物として析
出して析出強化に寄与する働きを有する。Ｍｏ含有量を
０．３％未満にすると、これらの働きが十分になされな
い可能性がある。０．８％を超えるＭｏ含有量にする
と、靭性を低下させるおそれやフェライトの生成を促進
させるおそれがある。(E) Mo: 0.3 to 0.8% Mo has a function of contributing to solid solution strengthening and a function of precipitating as carbide to contribute to precipitation strengthening. If the Mo content is less than 0.3%, these functions may not be sufficiently performed. If the Mo content is more than 0.8%, the toughness may be reduced or the formation of ferrite may be promoted.
【００２３】（ｆ）Ｗ：１．６〜２．６％ Ｗは、上記のＭｏと同様に、固溶強化に寄与する働きお
よび炭化物として析出して析出強化に寄与する働きを有
する。また、このＷは上記のＭｏとともに含有させるこ
とによって固溶強化作用をより顕著になすことができ
る。(F) W: 1.6 to 2.6% W has a function of contributing to solid solution strengthening and a function of precipitating as carbides and contributing to precipitation strengthening, similarly to Mo described above. Further, when W is contained together with the above-mentioned Mo, the solid solution strengthening action can be made more remarkable.
【００２４】固溶化Ｗ量を長期間にわたり高く維持する
ために、Ｗ含有量を１．６％以上とすることが必要であ
る。しかし、２．６％を超えるＷ含有量にすると、靭性
を低下させるおそれやフェライトの生成を促進させるお
それがある。In order to keep the amount of solution W high for a long period of time, it is necessary to make the W content 1.6% or more. However, when the W content is more than 2.6%, there is a possibility that toughness may be reduced and the formation of ferrite may be promoted.
【００２５】（ｇ）Ｂ：０．００１〜０．００４％ Ｂは、微量の添加で焼入れ性を高めるとともに、高温下
であっても、結晶粒界およびその近傍に析出する炭窒化
物を安定化させてそれらの粗大化を抑制する働きを有す
る。Ｂ含有量を０．００１％未満にすると、これらの働
きが不十分となる。０．００４％を超えるＢ含有量にす
ると、溶接性を損なうおそれがある。(G) B: 0.001 to 0.004% B enhances hardenability by adding a small amount, and stabilizes carbonitrides deposited at and around crystal grain boundaries even at high temperatures. And has the function of suppressing their coarsening. If the B content is less than 0.001%, these functions become insufficient. If the B content exceeds 0.004%, the weldability may be impaired.
【００２６】（ｈ）Ｎ：０．００５〜０．０３％ Ｎは、母相中に固溶して固溶強化に寄与する働きと窒化
物もしくは炭窒化物を生成して析出強化に寄与する働き
とを有する。Ｎ含有量を０．００５％未満にすると、こ
れらの働きが十分になされない可能性がある。０．０３
％を超えるＮ含有量にすると、窒化物もしくは炭窒化物
の粗大化が促進され、クリープ強度を低下させるととも
に粗大生成物の生成を促進させるおそれがある。このＮ
含有量は、０．０１〜０．０２５％の範囲内とすること
が好ましい。これにより、組織をより安定化させてクリ
ープ強度をより高めることができる。(H) N: 0.005 to 0.03% N contributes to solid solution strengthening by forming a solid solution in the matrix and contributes to precipitation strengthening by forming nitride or carbonitride. Have a function. If the N content is less than 0.005%, these functions may not be sufficiently performed. 0.03
If the N content exceeds%, the coarsening of the nitride or carbonitride is promoted, which may lower the creep strength and promote the generation of a coarse product. This N
The content is preferably in the range of 0.01 to 0.025%. Thereby, the structure can be further stabilized, and the creep strength can be further increased.
【００２７】 （ｉ）Ｖ：０．２３〜０．３％ （ｉ−１）Ｖ：０．２３〜０．２７％（Ｎｂ又はＴｉと
の複合添加の場合） （ｉ−２）Ｖ：０．２５〜０．３％（Ｖ単独添加の場
合） （ｉ−３）Ｖ：０．２３〜０．２５％（Ｔｉとの複合添
加の場合で、かつ、Ｔｉ添加量が０．０１〜０．０２５
％の場合） Ｖは、微細な炭窒化物として析出し、析出強化に寄与す
る働きを有する。Ｖと、後述のＮｂ又はＴｉとを複合添
加する場合、Ｖ炭窒化物以外にＮｂ又はＴｉの炭窒化物
が析出するため、Ｖ炭窒化物による析出強化の働きを補
完する。本発明では、ＶとＮｂ又はＴｉとの複合添加の
場合、Ｖ含有量を０．２３％以上とすることにより、Ｎ
ｂ又はＴｉ炭窒化物の析出とともに、Ｖ炭窒化物を高密
度にかつ適量析出させることができ、これにより回復が
起こるのを抑制できる。しかし、この場合に０．２７％
を超えるＶ含有量にすると、Ｖ炭窒化物の粗大化傾向が
大きくなるおそれがある。(I) V: 0.23 to 0.3% (i-1) V: 0.23 to 0.27% (in the case of complex addition with Nb or Ti) (i-2) V: 0 .25 to 0.3% (when V is added alone) (i-3) V: 0.23 to 0.25% (when combined with Ti and the amount of Ti added is 0.01 to 0) .025
%) V precipitates as fine carbonitrides and has a function of contributing to precipitation strengthening. When V and Nb or Ti, which will be described later, are added in a complex manner, Nb or Ti carbonitride precipitates in addition to V carbonitride, thereby complementing the function of precipitation strengthening by V carbonitride. In the present invention, in the case of a composite addition of V and Nb or Ti, the V content is set to 0.23% or more,
Along with the precipitation of b or Ti carbonitride, V carbonitride can be deposited at a high density and in an appropriate amount, whereby the occurrence of recovery can be suppressed. However, in this case 0.27%
If the V content exceeds the range, the tendency of V carbonitride to become coarse may increase.
【００２８】また、Ｔｉとの複合添加に限り、Ｖ含有量
を０．２５％以下に抑制し、Ｔｉ含有量を増加させるこ
とにより充分な析出量を確保できる。In addition, only in the case of the composite addition with Ti, a sufficient precipitation amount can be secured by suppressing the V content to 0.25% or less and increasing the Ti content.
【００２９】一方、ＮｂまたはＴｉを添加せずにＶのみ
を単独添加する場合には、Ｎｂ又はＴｉの炭窒化物の析
出量に相等する分量のＶ炭窒化物を析出させるためにＴ
ｉ又はＮｂとの複合添加の場合よりもＶ添加量を増加さ
せる必要がある。このため、Ｖ単独添加の場合には、Ｖ
含有量を０．２５〜０．３％に規定した。On the other hand, when only V is added without adding Nb or Ti, T is added in order to precipitate an amount of V carbonitride equivalent to the amount of Nb or Ti carbonitride.
It is necessary to increase the amount of V added as compared with the case of the composite addition with i or Nb. Therefore, when V alone is added, V
The content was defined as 0.25 to 0.3%.
【００３０】（ｊ）Ｎｂ：０．０１〜０．０６％ Ｎｂは、前述のＶおよび後述のＴｉと同様に微細な炭窒
化物として析出して析出強化に寄与する働きを有する。
Ｎｂ含有量を０．０１％未満にすると、上記の働きが十
分になされないおそれがある。０．０６％を超えるＮｂ
含有量にすると、粗大な炭窒化物が多量に析出し、析出
強化作用が認められなくなるおそれがある。(J) Nb: 0.01 to 0.06% Nb has a function of contributing to precipitation strengthening by precipitating as fine carbonitrides, like V described above and Ti described later.
If the Nb content is less than 0.01%, the above function may not be sufficiently performed. Nb exceeding 0.06%
When the content is set, a large amount of coarse carbonitrides may precipitate, and the precipitation strengthening effect may not be recognized.
【００３１】（ｋ）Ｔｉ：０．００５〜０．０１％もし
くは０．０１〜０．０２５％ Ｔｉは、脱酸作用を有するとともに、微細な炭窒化物と
して析出し、析出強化に寄与する働きを有する。Ｔｉ含
有量を０．００５％以上とすることによりこれらの働き
を十分になすことができる。しかし、ＶとＴｉとの複合
添加において、０．０１％を超えるＴｉ含有量にする
と、粗大な炭窒化物を多量に析出し、析出強化作用が認
められなくなるおそれがある。ただし、複合添加される
Ｖ量を０．２５％以下に抑制した場合には、微細な炭窒
化物の析出強化作用をより効果的に発揮させるために
０．０１％を超えるＴｉ添加が有効となる。０．０２５
％を超えると粗大な炭窒化物の多量析出を誘発し、析出
強化作用が認められなくなる。(K) Ti: 0.005 to 0.01% or 0.01 to 0.025% Ti not only has a deoxidizing effect, but also precipitates as fine carbonitrides and contributes to precipitation strengthening. Having. By setting the Ti content to 0.005% or more, these functions can be sufficiently performed. However, if the content of Ti exceeds 0.01% in the composite addition of V and Ti, a large amount of coarse carbonitrides may precipitate, and the precipitation strengthening effect may not be recognized. However, when the amount of V added in combination is suppressed to 0.25% or less, it is effective to add more than 0.01% of Ti in order to more effectively exert the precipitation strengthening action of fine carbonitrides. Become. 0.025
%, Large amounts of coarse carbonitrides are induced, and no precipitation strengthening effect is observed.
【００３２】（ｌ）その他の元素 上記の各成分および主成分であるＦｅ以外に、不可避的
に含有される不純物は極力低減することが望ましい。特
に、Ｐ、Ｓ、Ｎｉなどの不純物元素は原料からの混入が
避けられない。原料の厳選や高度な溶解・製鋼技術によ
りこれらの元素の含有を低減できるが、経済的なもので
はない。このような観点から、Ｎｉ：０．２％以下、
Ｐ：０．０３％以下、Ｓ：０．０１％以下とした。(L) Other elements In addition to the above-mentioned components and Fe as the main component, it is desirable that impurities unavoidably contained be reduced as much as possible. In particular, impurity elements such as P, S, and Ni are inevitably mixed from the raw material. Although the content of these elements can be reduced by careful selection of raw materials and advanced melting and steelmaking techniques, it is not economical. From such a viewpoint, Ni: 0.2% or less,
P: 0.03% or less, S: 0.01% or less.
【００３３】なお、本耐熱鋳鋼を大型肉厚部品として使
用する場合には、焼入れ時の冷却速度の低下によって肉
厚部におけるフェライトの生成傾向が高まるため、Ｎｉ
添加量を増加させることが好ましく、また、より経済的
な優位性を指向した場合には、原料に混入するＮｉ量の
制限値は高い方が有効である。ただし、０．５％を超え
るとクリープ強度の低下を招くおそれがある。このよう
な観点から、Ｎｉ：０．２％以下もしくは０．５％以
下、Ｐ：０．０３％以下、Ｓ：０．０１％以下とした。When the heat-resistant cast steel is used as a large-sized thick part, the cooling rate at the time of quenching lowers the ferrite generation tendency in the thick part.
It is preferable to increase the amount of addition, and when more economical advantage is aimed at, the higher the limit value of the amount of Ni mixed into the raw material, the more effective. However, if it exceeds 0.5%, the creep strength may decrease. From such a viewpoint, Ni: 0.2% or less or 0.5% or less, P: 0.03% or less, and S: 0.01% or less.
【００３４】（ｍ）Ｂ＋０．５Ｎ≦０．２％ Ｂは、特にＮと化合しやすく、窒化ボロンとなりやす
い。この窒化ボロンは帯状又は粗大に鋳塊中に残存し、
機械的性質を低下させる。本発明では、Ｂ含有量とＮ含
有量の０．５倍量との和をＢ当量として定義し、このＢ
当量値の上限値を０．０２％とすることによりＢＮ化合
物の生成を抑制できる。(M) B + 0.5N ≦ 0.2% B is particularly apt to be combined with N and is likely to be boron nitride. This boron nitride remains in the ingot in the form of a band or coarsely,
Decreases mechanical properties. In the present invention, the sum of the B content and 0.5 times the N content is defined as B equivalent,
By setting the upper limit of the equivalent value to 0.02%, generation of a BN compound can be suppressed.
【００３５】（ｎ）１．４％≦Ｍｏ＋０．５Ｗ≦２．０
％ 前述したようにＭｏとＷとをともに含有させることによ
って固溶強化作用が顕著なものとなる。本発明では、Ｍ
ｏ含有量とＷ含有量の０．５倍量との和をＭｏ当量と定
義し、このＭｏ当量値を１．４〜２．０％の範囲内に規
定することにより、固溶強化作用がより顕著なものとな
り、かつフェライト生成を有効に抑制できる。(N) 1.4% ≦ Mo + 0.5W ≦ 2.0
% As described above, the inclusion of both Mo and W significantly enhances the solid solution strengthening action. In the present invention, M
The sum of the o content and 0.5 times the W content is defined as Mo equivalent, and by defining this Mo equivalent value in the range of 1.4 to 2.0%, the solid solution strengthening effect is improved. It becomes more remarkable, and generation of ferrite can be effectively suppressed.
【００３６】（ｏ）０．６５％≦Ｃ＋Ｍｎ／６＋Ｓｉ／
２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５＋Ｖ／１４ Ｃ元素で説明したように、焼入れ性確保およびフェライ
ト生成の抑制は、厚肉の鋳造物の機械的性質を向上させ
る上で重要である。本発明では、Ｃ含有量を（ａ）項に
示す成分範囲に限定するとともに、さらに、上記（３）
式「Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５
＋Ｍｏ／１５＋Ｖ／１４」から求められる値をＣ当量と
定義し、このＣ当量値の下限値を０．６５％と規定する
ことにより、溶接性を損なうことなく焼入れ性を確保で
き、かつフェライトの生成を抑制できる。(O) 0.65% ≦ C + Mn / 6 + Si /
As described for the 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14C element, ensuring hardenability and suppressing ferrite formation are important for improving the mechanical properties of a thick cast product. In the present invention, the C content is limited to the component range shown in the item (a), and the C content is further reduced in the above (3).
Formula "C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5
+ Mo / 15 + V / 14 "is defined as C equivalent, and by defining the lower limit of the C equivalent value as 0.65%, hardenability can be ensured without impairing weldability, and ferrite can be obtained. Generation can be suppressed.
【００３７】（ｐ）Ｎｂ＋０．４Ｃ≦０．１５％ Ｎｂを含有させた場合、大型鋳塊の凝固時に粗大なＮｂ
炭化物が析出し、このＮｂ炭化物が残存した場合に機械
的性質に悪影響を及ぼすことが知られている。本発明で
はＮｂ含有量とＣ含有量の０．４倍量との和をＮｂ当量
と定義し、Ｎｂを含有させる場合には、Ｎｂ当量値を
０．１５％以下と規定することにより粗大なＮｂ炭化物
の生成を抑制できる。(P) Nb + 0.4C ≦ 0.15% When Nb is contained, coarse Nb
It is known that when carbides precipitate and this Nb carbide remains, it adversely affects mechanical properties. In the present invention, the sum of the Nb content and the 0.4-fold amount of the C content is defined as Nb equivalent, and when Nb is contained, the Nb equivalent value is defined as 0.15% or less, whereby coarseness is obtained. Generation of Nb carbide can be suppressed.
【００３８】本発明の耐熱鋳鋼は、Ｍ２３Ｃ６型炭化
物、Ｍ７Ｃ３型炭化物およびＭＸ型炭窒化物が母相に微
細析出した組織である。この場合に、ＭはＣｒ、Ｍｏ、
Ｗ、Ｖ、Ｎｂ等の元素のうちから１種又は２種以上を組
み合わせたものからなり、ＸはＣ，Ｎ等の元素からなる
ものである。Ｍ２３Ｃ６型炭化物、Ｍ７Ｃ３型炭化物お
よびＭＸ型炭窒化物がからなる析出相の母相に対する質
量比を０．６〜１．０％と規定した理由を以下に説明す
る。The heat-resistant cast steel of the present invention has a structure in which M 23 C 6 type carbide, M 7 C 3 type carbide and MX type carbonitride are finely precipitated in the matrix. In this case, M is Cr, Mo,
It is composed of one or a combination of two or more of elements such as W, V and Nb, and X is composed of elements such as C and N. M 23 C 6 type carbide, explaining why the defined as 0.6 to 1.0 percent by mass ratio matrix of M 7 C 3 -type carbide and MX type carbonitrides consist precipitation phase below.
【００３９】上記の各析出物は後述する製造方法の焼も
どし工程で母相に析出させる。このとき、母相に対する
析出相の比を０．６質量％未満にすると、クリープ強度
とシャルピー衝撃特性とを良好なものとして両立できな
いおそれがある。一方、１．０質量％を超える質量比に
すると、高温使用下で母相から新たに析出してクリープ
強度の維持に寄与するＭＸ型炭窒化物の構成元素が母相
中から枯渇するため、高温下でのクリープ強度特性を安
定化させることが困難となる。Each of the above-mentioned precipitates is deposited on the mother phase in the tempering step of the production method described later. At this time, if the ratio of the precipitated phase to the mother phase is less than 0.6% by mass, there is a possibility that the creep strength and the Charpy impact characteristics may not be good and compatible. On the other hand, when the mass ratio exceeds 1.0% by mass, the constituent elements of the MX-type carbonitride which newly precipitate from the mother phase and contribute to maintaining the creep strength under high temperature use are depleted from the mother phase. It becomes difficult to stabilize the creep strength characteristics at high temperatures.
【００４０】以上説明した本発明の耐熱鋳鋼は、低合金
鋳鋼でありながら、定常運転時の最高使用温度が５３８
℃である蒸気タービン車室および蒸気タービン弁箱の材
料として優れた特性を示し、従来の１％ＣｒＭｏＶ低合
金耐熱鋳鋼を上回るクリープ破断強度を有する。したが
って、本発明の耐熱鋳鋼を定常運転時の最高使用温度が
５３８℃である蒸気タービン車室および蒸気タービン弁
箱の材料として用いることにより、車室や弁箱の肉厚を
薄肉化できる。具体的には、従来の１％ＣｒＭｏＶ低合
金耐熱鋳鋼を用いた場合に要する肉厚の約７５％に薄肉
化できる。The heat-resistant cast steel of the present invention described above is a low-alloy cast steel, but has a maximum operating temperature of 538 during steady operation.
It has excellent properties as a material for steam turbine casings and steam turbine valve cases at ℃, and has a creep rupture strength exceeding that of conventional 1% CrMoV low alloy heat-resistant cast steel. Therefore, by using the heat-resistant cast steel of the present invention as a material for a steam turbine casing and a steam turbine valve box having a maximum operating temperature of 538 ° C. during steady operation, the thickness of the casing and the valve box can be reduced. Specifically, the thickness can be reduced to about 75% of the wall thickness required when a conventional 1% CrMoV low alloy heat-resistant cast steel is used.
【００４１】また、定常運転時の最高使用温度が５６６
℃である蒸気タービン車室および蒸気タービン弁箱の材
料として本発明の耐熱鋳鋼を従来の高Ｃｒ系耐熱鋳鋼の
代わりに用いることができる。さらに、定常運転時の最
高使用温度が５９３℃である蒸気タービン車室の材料と
しても本発明の耐熱鋳鋼を用いることができる。これに
より、従来の高Ｃｒ系耐熱鋳鋼を用いた場合よりも肉厚
を約２５％増加させる必要が生じるものの、本発明の耐
熱鋳鋼は低合金であるため素材コストを大幅に低減でき
る。その結果、上記の車室および弁箱を従来よりも低コ
ストで製造できる。The maximum operating temperature during steady operation is 566.
The heat-resistant cast steel of the present invention can be used in place of the conventional high Cr heat-resistant cast steel as a material for the steam turbine casing and the steam turbine valve case at a temperature of ° C. Further, the heat-resistant cast steel of the present invention can also be used as a material for a steam turbine casing having a maximum operating temperature of 593 ° C. during normal operation. Thus, although it is necessary to increase the wall thickness by about 25% as compared with the case of using the conventional high Cr heat-resistant cast steel, the heat-resistant cast steel of the present invention is a low alloy, so that the material cost can be significantly reduced. As a result, the vehicle compartment and the valve box described above can be manufactured at lower cost than before.
【００４２】さらに、定常運転時の最高使用温度が５９
３℃である蒸気タービン車室を製造するにあたり、本発
明の耐熱鋳鋼と従来の高Ｃｒ系耐熱鋳鋼とを組み合わせ
て用いることができる。すなわち、蒸気タービン車室の
高温蒸気流入部であって５７０℃以上の蒸気に晒される
部位に本発明の耐熱鋳鋼を用い、それ以外の部位は従来
の高Ｃｒ系耐熱鋳鋼または低合金耐熱鋳鋼を用い、本発
明の耐熱鋳鋼と従来の高Ｃｒ系耐熱鋳鋼または低合金耐
熱鋳鋼とを突き合わせ溶接して構成された蒸気タービン
車室を提供できる。この場合に用いられる高Ｃｒ系耐熱
鋳鋼の一例として、質量％で、Ｃ：０．１２〜０．１６
％、Ｓｉ：０．２〜０．３５％、Ｍｎ：０．５〜０．７
％、Ｎｉ：０．３〜０．６％、Ｃｒ：９．６〜１０．６
％、Ｍｏ：０．７〜１．０％、Ｖ：０．２〜０．３５
％、Ｎｂ：０．０７〜０．１３％、Ｎ：０．０３〜０．
０６％、Ｐ：０．０２％以下、Ｓ：０．０２％以下、Ａ
ｌ：０．０１％以下を含有し、残部が鉄および不可避的
不純物からなる耐熱鋳鋼を挙げることができる。また、
上記の低合金耐熱鋳鋼の一例としては、質量％で、Ｃ：
０．１２〜０．１８％、Ｓｉ：０．２〜０．６％、Ｍ
ｎ：０．５〜０．９％、Ｃｒ：１．０〜１．５％、Ｍ
ｏ：０．９〜１．２％、Ｖ：０．２〜０．３５％、Ｐ：
０．０２％以下、Ｓ：０．０１２％以下、Ｎｉ：０．５
％以下、Ａｌ：０．０１％以下を含有し、残部が鉄およ
び不可避的不純物からなる耐熱鋳鋼を挙げることができ
る。Further, the maximum operating temperature during steady operation is 59
In manufacturing the steam turbine casing at 3 ° C., the heat-resistant cast steel of the present invention and the conventional high Cr heat-resistant cast steel can be used in combination. That is, the heat-resistant cast steel of the present invention is used in a high-temperature steam inflow portion of a steam turbine casing and is exposed to steam at 570 ° C. or higher, and the other portions are made of conventional high Cr heat-resistant cast steel or low alloy heat-resistant cast steel. It is possible to provide a steam turbine casing configured by butt-welding the heat-resistant cast steel of the present invention and a conventional high-Cr heat-resistant cast steel or low-alloy heat-resistant cast steel. As an example of the high Cr heat resistant cast steel used in this case, C: 0.12 to 0.16 by mass%.
%, Si: 0.2 to 0.35%, Mn: 0.5 to 0.7
%, Ni: 0.3 to 0.6%, Cr: 9.6 to 10.6
%, Mo: 0.7 to 1.0%, V: 0.2 to 0.35
%, Nb: 0.07 to 0.13%, N: 0.03 to 0.1%.
06%, P: 0.02% or less, S: 0.02% or less, A
l: Heat-resistant cast steel containing 0.01% or less, with the balance being iron and unavoidable impurities. Also,
As an example of the above low alloy heat resistant cast steel, C:
0.12-0.18%, Si: 0.2-0.6%, M
n: 0.5 to 0.9%, Cr: 1.0 to 1.5%, M
o: 0.9-1.2%, V: 0.2-0.35%, P:
0.02% or less, S: 0.012% or less, Ni: 0.5
% Or less, Al: 0.01% or less, with the balance being iron and unavoidable impurities.
【００４３】次に、本発明に係る耐熱鋳鋼の製造方法に
ついて説明する。Next, a method for producing a heat-resistant cast steel according to the present invention will be described.
【００４４】本発明に係る耐熱鋳鋼の製造方法は、質量
％で、Ｃ：０．１５〜０．３０％、Ｓｉ：０．１〜０．
３％、Ｍｎ：０．０１〜０．１％、Ｃｒ：２．０〜２．
５％、Ｍｏ：０．３〜０．８％、Ｖ：０．２３〜０．３
％、Ｗ：１．６〜２．６％、Ｎ：０．００５〜０．０３
％、Ｂ：０．００１〜０．００４％を含有し、かつ下式
（１）により求められるＢ当量が０．０２％以下と、下
式（２）により求められるＭｏ当量が１．４〜２．０％
と、下式（３）により求められるＣ当量が０．６５％以
上とを満たし、かつ不純物元素のうちＮｉ：０．２％以
下と、Ｐ：０．０３％以下と、Ｓ：０．０１％以下とに
制限し、残部が鉄および不可避的不純物からなる鋳造物
を１０３０〜１０７０℃の温度域に加熱保持した後に焼
入れる工程と、この工程の後に６８０〜７４０℃の温度
域に焼もどす工程と、を備えたことを特徴としている。In the method for producing a heat-resistant cast steel according to the present invention, C: 0.15 to 0.30% and Si: 0.1 to 0.
3%, Mn: 0.01-0.1%, Cr: 2.0-2.
5%, Mo: 0.3-0.8%, V: 0.23-0.3
%, W: 1.6 to 2.6%, N: 0.005 to 0.03
%, B: 0.001 to 0.004%, and the B equivalent determined by the following formula (1) is 0.02% or less, and the Mo equivalent determined by the following formula (2) is 1.4 to 2.0%
And the C equivalent obtained by the following formula (3) satisfies 0.65% or more, and among the impurity elements, Ni: 0.2% or less, P: 0.03% or less, and S: 0.01 %, With the balance consisting of iron and unavoidable impurities being heated and maintained in a temperature range of 1030 to 1070 ° C., followed by quenching, and after this process, tempered to a temperature range of 680 to 740 ° C. And a process.
【００４５】 Ｂ当量＝Ｂ＋０．５Ｎ …（１） Ｍｏ当量＝Ｍｏ＋０．５Ｗ …（２） Ｃ当量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３） この場合に、前記Ｖの含有量を０．２３〜０．２７質量
％とし、さらに、Ｔｉ：０．００５〜０．０１質量％、
Ｎｂを０．０１〜０．０６質量％含有し、下式（４）に
より求められるＮｂ当量が０．１５％以下を満たすよう
にしてもよい。B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3) In this case, V Is set to 0.23 to 0.27% by mass, and further, Ti: 0.005 to 0.01% by mass,
Nb may be contained in an amount of 0.01 to 0.06% by mass, and the Nb equivalent obtained by the following formula (4) may satisfy 0.15% or less.
【００４６】Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４） また、前記Ｖの含有量を０．２３〜０．２７質量％と
し、さらに、Ｔｉ：０．００５〜０．０１質量％を含有
し、焼もどし工程では７２０〜７８０℃の温度域に加熱
することとしてもよい。Nb equivalent = Nb + 0.4C (4) Further, the content of V is set to 0.23 to 0.27% by mass, and Ti is further contained by 0.005 to 0.01% by mass. In the return step, heating may be performed to a temperature range of 720 to 780 ° C.
【００４７】さらに、前記Ｖの含有量を０．２５〜０．
３質量％とするようにしてもよい。Further, the content of V is set to 0.25 to 0.5.
You may make it 3 mass%.
【００４８】本発明の製造方法は、まず、前述の特定の
組成範囲を満たす各成分を含有した溶湯を砂型に鋳込ん
だ後、得られた鋳塊を焼鈍して鋳造物を得る。次いで、
この鋳造物を焼きならし処理（溶体化処理）する。In the production method of the present invention, first, a molten metal containing each component satisfying the above specific composition range is cast into a sand mold, and the obtained ingot is annealed to obtain a casting. Then
This casting is subjected to normalizing treatment (solution treatment).
【００４９】鋳造時の冷却過程においては、Ｖ、Ｔｉ、
Ｎｂが粗大な炭窒化物として残存する。本発明では焼き
ならし処理によりこれらの粗大な炭窒化物をオーステナ
イト基地中に溶解させる。このとき、焼きならし処理時
の加熱保持温度を１０３０℃未満にすると、上記の粗大
な炭窒化物をオーステナイト基地中に溶解させることが
困難となる。一方、焼きならし処理時に１０７０℃を超
える加熱保持温度にすると、基地がオーステナイト単相
領域を外れ、焼入れ後に得られる金属組織が不均一とな
る。これらのことから、焼きならし処理時の加熱保持温
度を１０３０〜１０７０℃の範囲に規定した。In the cooling process during casting, V, Ti,
Nb remains as coarse carbonitride. In the present invention, these coarse carbonitrides are dissolved in the austenitic matrix by normalizing. At this time, if the heating and holding temperature during the normalizing treatment is set to less than 1030 ° C., it becomes difficult to dissolve the coarse carbonitride in the austenite matrix. On the other hand, if the heating and holding temperature exceeds 1070 ° C. during the normalizing treatment, the matrix goes out of the austenitic single phase region, and the metal structure obtained after quenching becomes non-uniform. From these facts, the heating and holding temperature during the normalizing process was specified in the range of 1030 to 1070 ° C.
【００５０】次に、焼きならし処理を施した鋳造物に焼
もどし熱処理を施す。本発明では、Ｔｉ又はＮｂを添加
せずにＶを単独添加する場合には、焼もどし温度を６８
０〜７４０℃の温度域とする。焼もどし温度を６８０℃
以上とすることによって、Ｖ炭窒化物を微細に析出で
き、かつその析出量を十分に確保することができる。し
かし、７４０℃を超える焼もどし温度にすると、Ｖ炭窒
化物の析出密度が低下するおそれがある。Next, the cast material subjected to the normalizing process is subjected to a tempering heat treatment. In the present invention, when V is added alone without adding Ti or Nb, the tempering temperature is set to 68.
The temperature range is 0 to 740 ° C. 680 ℃ tempering temperature
With the above, V carbonitride can be finely precipitated and the amount of the precipitation can be sufficiently ensured. However, when the tempering temperature exceeds 740 ° C., the precipitation density of V carbonitride may decrease.
【００５１】一方、ＶとＴｉ又はＮｂとを複合添加する
場合には、焼もどし温度を７２０〜７８０℃の温度域と
する。これによりＮｂ又はＴｉの炭窒化物を微細に析出
でき、かつその析出量を十分に確保することができる。
しかし、７２０℃未満の温度域にすると、Ｎｂ又はＴｉ
の微細な炭窒化物の析出量を十分に確保できないおそれ
があり、７８０℃を超える温度域にすると、Ａ３変態点
に近づくか或いはこの変態点を超えるため、組織安定性
が低下するおそれがあるとともに、焼もどし処理が過剰
に施されて機械的性質を損なうおそれがある。これらの
ことからＶとＴｉ又はＮｂとを複合添加する場合には、
焼もどし温度を７２０〜７８０℃の温度域に規定した。On the other hand, when V and Ti or Nb are added in combination, the tempering temperature is set to a temperature range of 720 to 780 ° C. As a result, Nb or Ti carbonitrides can be finely precipitated, and the amount of precipitation can be sufficiently ensured.
However, when the temperature range is set lower than 720 ° C., Nb or Ti
Of there may not be sufficient precipitation amount of fine carbonitrides, when the temperature range exceeding 780 ° C., for more than or the transformation point closer to A 3 transformation point, possibly tissue stability decreases In addition, there is a possibility that the tempering treatment is excessively performed and mechanical properties are impaired. From these facts, when V and Ti or Nb are added in combination,
The tempering temperature was specified in a temperature range of 720 to 780 ° C.
【００５２】[0052]
【発明の実施の形態】以下、本発明の種々の好ましい実
施例について説明する。DESCRIPTION OF THE PREFERRED EMBODIMENTS Various preferred embodiments of the present invention will be described below.
【００５３】（実施例１）電気炉にて組成を種々変化さ
せた溶湯を砂型に鋳込んで種々の鋳塊を得た後、得られ
た各鋳塊を焼鈍処理し、次いで焼きならし処理を施し、
つづいて焼もどし熱処理を施すことにより表１−１およ
び表１−２に示す鋼種Ｐ１〜Ｐ２５および鋼種Ｃ１〜Ｃ
９の各組成の供試鋳鋼を得た。焼きならし処理は、特定
温度域内の１０７０℃に加熱保持した後に油冷すること
により行なった。焼もどし熱処理時の加熱温度は鋼種に
応じて変更した。すなわち、Ｖを単独添加した鋼種（Ｐ
８〜Ｐ１３、Ｐ１９〜Ｐ２５、Ｃ１、Ｃ６、Ｃ７）の場
合には特定温度域内の７４０℃とし、ＶとＴｉ又はＮｂ
とを複合添加した鋼種（Ｐ１〜Ｐ７、Ｐ１４〜Ｐ１８、
Ｃ２〜Ｃ５、Ｃ８、Ｃ９）の場合には特定温度域内の７
６０℃とした。鋼種Ｐ１〜Ｐ２５は前述の特定範囲内の
組成であり、鋼種Ｃ１〜Ｃ２５は前述の特定範囲を逸脱
した組成である。(Example 1) A molten metal having a composition varied in an electric furnace was cast into a sand mold to obtain various ingots, and each of the obtained ingots was subjected to an annealing treatment and then a normalizing treatment. Subject to
Subsequently, by performing a tempering heat treatment, steel types P1 to P25 and steel types C1 to C shown in Table 1-1 and Table 1-2.
Test cast steels having the respective compositions of No. 9 were obtained. The normalizing process was performed by heating and holding at 1070 ° C. within a specific temperature range, followed by oil cooling. The heating temperature during the tempering heat treatment was changed according to the type of steel. That is, the steel type (P
8 to P13, P19 to P25, C1, C6, C7), the temperature is set to 740 ° C. within a specific temperature range, and V and Ti or Nb
(P1-P7, P14-P18,
In the case of C2 to C5, C8, C9), 7
60 ° C. Steel types P1 to P25 have compositions within the above-described specific range, and steel types C1 to C25 have compositions that deviate from the above-described specific range.
【００５４】[0054]
【表１−１】 [Table 1-1]
【００５５】[0055]
【表１−２】 [Table 1-2]
【００５６】得られた各供試鋳鋼から試験片を採取し、
それぞれ常温引張強さを測定した結果、７２０〜７７０
ＭＰａとなり、いずれの鋳鋼もほぼ同程度の常温引張強
さを有することが判明した。A test piece was collected from each of the obtained test cast steels,
As a result of measuring the room temperature tensile strength, 720 to 770 was obtained.
MPa, and all the cast steels were found to have almost the same room temperature tensile strength.
【００５７】次に、得られた鋳鋼から試験片を採取し、
６００℃の加熱温度下、引張荷重１４７ＭＰａでクリー
プ破断試験を行ない、破断に至るまでの時間（クリープ
破断時間）を調べた。また、得られた鋳鋼からＪＩＳ４
号２ｍｍＶノッチシャルピー衝撃試験片を採取して２０
℃の温度下でシャルピー衝撃試験を行ない、衝撃吸収エ
ネルギー（Ｊ）を調べた。以上の評価試験の結果を表２
に示す。なお、各鋳鋼の常温引張強さ（ＭＰａ）の実測
値を表２に併記した。Next, a test piece was collected from the obtained cast steel,
A creep rupture test was performed at a heating temperature of 600 ° C. under a tensile load of 147 MPa, and the time until rupture (creep rupture time) was examined. In addition, JIS4
No. 2 mm V notch Charpy impact test specimen was collected and 20
A Charpy impact test was conducted at a temperature of ° C. to determine the impact absorption energy (J). Table 2 shows the results of the above evaluation tests.
Shown in Table 2 also shows the measured values of the room temperature tensile strength (MPa) of each cast steel.
【００５８】[0058]
【表２】 [Table 2]
【００５９】表２の例１〜２５（鋼種Ｐ１〜Ｐ２５）の
各鋳鋼は、クリープ破断時間が３３６８〜６３２７時間
と長く、衝撃吸収エネルギーが５２〜９２Ｊと高い値を
示し、優れたクリープ強度特性を有するとともに優れた
耐衝撃性（靭性）を有することが判明した。これに対し
て、例２６（鋼種Ｃ１）、例２８（鋼種Ｃ３）および例
３４（鋼種Ｃ９）の各鋳鋼は、クリープ破断時間がそれ
ぞれ５１２時間、６８４時間、２８２０時間と短く、衝
撃吸収エネルギーがそれぞれ２９Ｊ、３５Ｊ、３５Ｊと
低い値を示し、クリープ強度特性および耐衝撃性（靭
性）が共に劣ることが判明した。また、例２７（鋼種Ｃ
２）および例３１（鋼種Ｃ６）の鋳鋼は、クリープ破断
時間がそれぞれ９３１２時間、３５２４時間となり長時
間ではあるものの、衝撃吸収エネルギーがそれぞれ４８
Ｊ、３４Ｊと低い値を示し、耐衝撃性（靭性）に劣るこ
とが判明した。さらに、例２９（鋼種Ｃ４）、例３０
（鋼種Ｃ５）、例３２（鋼種Ｃ７）および例３３（鋼種
Ｃ８）の各鋳鋼は、衝撃吸収エネルギーがそれぞれ８０
Ｊ、８２Ｊ、１２０Ｊ、８０Ｊと高い値を示すものの、
クリープ破断時間がそれぞれ１７５６時間、２９７８時
間、２４６０時間、２１２８時間と短くなり、クリープ
強度特性に劣ることが判明した。Each of the cast steels of Examples 1 to 25 (steel types P1 to P25) in Table 2 has a long creep rupture time of 3368 to 6327 hours, a high shock absorption energy of 52 to 92 J, and excellent creep strength characteristics. And excellent impact resistance (toughness). On the other hand, the cast steels of Example 26 (steel type C1), Example 28 (steel type C3) and Example 34 (steel type C9) have short creep rupture times of 512 hours, 684 hours and 2820 hours, respectively, and have a low shock absorption energy. The values were as low as 29 J, 35 J, and 35 J, respectively, and it was found that both the creep strength characteristics and the impact resistance (toughness) were inferior. Moreover, Example 27 (steel type C
The cast steels of 2) and 31 (steel type C6) had long creep rupture times of 9312 hours and 3524 hours, respectively, but had a shock absorbing energy of 48, respectively.
J and 34J, which were low values, were found to be inferior in impact resistance (toughness). Further, Example 29 (steel type C4), Example 30
(Steel type C5), the cast steels of Example 32 (Steel type C7) and Example 33 (Steel type C8) have a shock absorption energy of 80, respectively.
Although high values such as J, 82J, 120J and 80J are shown,
The creep rupture times were reduced to 1756 hours, 2978 hours, 2460 hours, and 2128 hours, respectively, indicating that the creep strength characteristics were poor.
【００６０】以上のことから、焼きならし処理時の加熱
保持温度を特定温度域とし、かつ焼もどし温度を特定温
度域として耐熱鋳鋼を製造するにあたり、前述の特定範
囲の組成に調整された鋼種Ｐ１〜Ｐ２５の場合（例１〜
２５）には、特定範囲を逸脱した組成に調整された鋼種
Ｃ１〜Ｃ９の場合（例２７〜３４）と同程度の常温引張
強さを有するのみならず、優れたクリープ強度特性と優
れた耐衝撃性（靭性）とを両立できることが判明した。From the above, when producing a heat-resistant cast steel with the heating and holding temperature during the normalizing process in the specific temperature range and the tempering temperature in the specific temperature range, the steel type adjusted to the above-described composition in the specific range is used. In the case of P1 to P25 (Example 1 to
25) has not only the same room temperature tensile strength as that of the steel types C1 to C9 adjusted to the composition deviating from the specific range (Examples 27 to 34), but also excellent creep strength characteristics and excellent resistance to heat. It has been found that both impact strength (toughness) can be achieved.
【００６１】（実施例２）実施例２では、表１−１およ
び表１−２に示す鋼種Ｐ３（ＶとＮｂとの複合添加
鋼）、鋼種Ｐ１１（Ｖ単独添加鋼）、鋼種Ｐ１５（Ｖと
Ｔｉとの複合添加鋼）および鋼種Ｐ２０（Ｖ単独添加
鋼）の各組成の鋳鋼を製造するにあたり、焼きならし処
理時の加熱保持温度および焼もどし処理時の加熱温度を
表３に示すように種々変更した。Example 2 In Example 2, steel types P3 (combined steel containing V and Nb), steel type P11 (steel with V alone), and steel type P15 (V) shown in Tables 1-1 and 1-2 were used. In the production of cast steels having the respective compositions of the steels with the composites of steel and Ti) and steel grade P20 (steel with V alone), the heating holding temperature during the normalizing process and the heating temperature during the tempering process are shown in Table 3. Was changed variously.
【００６２】得られた各鋳鋼について組織観察を行な
い、フェライト生成の有無、未固溶の粗大析出物の有無
を調べた。また、室温（２０℃）下で実施例１で説明し
たのと同様にシャルピー衝撃試験を行ない、衝撃吸収エ
ネルギー（Ｊ）を調べた。その評価結果を表３に示す。The structure of each of the cast steels thus obtained was observed, and the formation of ferrite and the presence of undissolved coarse precipitates were examined. Further, a Charpy impact test was performed at room temperature (20 ° C.) in the same manner as described in Example 1, and the impact absorption energy (J) was examined. Table 3 shows the evaluation results.
【００６３】[0063]
【表３】 [Table 3]
【００６４】加熱保持温度を特定温度域の下限値を下回
る１０２０℃として焼きならし処理を施した例３５〜３
８（鋼種Ｐ３、Ｐ１１、Ｐ１５、Ｐ２０）では、フェラ
イトの生成が観察されなかったものの、粗大析出物が未
固溶のまま存在することが判明した。一方、加熱保持温
度を特定温度域の上限値を超える１０８０℃として焼き
ならし処理を施した例５５〜５８（鋼種Ｐ３、Ｐ１１、
Ｐ１５、Ｐ２０）では、未固溶の粗大析出物が観察され
なかったものの、フェライトの生成が観察された。例３
５〜３８および例５５〜５８では衝撃吸収エネルギーが
高い値を示すものもあるが、それらは組織が不均一とな
り、耐衝撃性（靭性）以外の機械的性質に劣ることが判
明した。Examples 35 to 3 in which the heat-holding temperature was set to 1020 ° C. below the lower limit value of the specific temperature range and the normalizing treatment was performed.
In No. 8 (steel types P3, P11, P15, and P20), although formation of ferrite was not observed, it was found that coarse precipitates existed as undissolved. On the other hand, examples 55 to 58 (normal steel types P3, P11,
In P15 and P20), formation of ferrite was observed although no undissolved coarse precipitate was observed. Example 3
In some of Examples 5 to 38 and Examples 55 to 58, the impact absorption energy showed a high value, but it was found that these had an uneven structure and were inferior in mechanical properties other than impact resistance (toughness).
【００６５】加熱保持温度を特定温度域内の１０５０℃
として焼きならし処理を施したが、特定温度域の下限値
を下回る加熱温度で焼もどし熱処理を施した例３９（鋼
種Ｐ３）、例４３（鋼種Ｐ３）、例４７（鋼種Ｐ１
１）、例５１（鋼種Ｐ１５）では、フェライトの生成お
よび未固溶の粗大析出物が観察されなかったものの、衝
撃吸収エネルギーが４５Ｊ、２７Ｊ、２５Ｊ、４８Ｊと
低くなり、耐衝撃性（靭性）に劣ることが判明した。ま
た、加熱保持温度を特定温度域内の１０５０℃として焼
きならし処理を施したが、特定温度域の上限値を超える
加熱温度で焼もどし熱処理を施した例４２（鋼種Ｐ
３）、例４６（鋼種Ｐ１１）、例５０（鋼種Ｐ１５）お
よび例５４（鋼種Ｐ２０）では、フェライトの生成およ
び未固溶の粗大析出物が観察されなかったものの、衝撃
吸収エネルギーがそれぞれ１５Ｊ、１２Ｊ、１２Ｊ、１
５Ｊと著しく低下し、耐衝撃性（靭性）に極めて劣るこ
とが判明した。The heating and holding temperature is set to 1050 ° C. within a specific temperature range.
Example 39 (steel type P3), Example 43 (steel type P3), and Example 47 (steel type P1) in which the normalizing treatment was performed as the heat treatment, but the tempering heat treatment was performed at a heating temperature lower than the lower limit of the specific temperature range.
1) In Example 51 (steel type P15), although the formation of ferrite and undissolved coarse precipitates were not observed, the shock absorption energy was low at 45 J, 27 J, 25 J, and 48 J, and the impact resistance (toughness) was low. Turned out to be inferior. Further, the normalizing treatment was performed with the heating holding temperature set to 1050 ° C. within the specific temperature range, but the tempering heat treatment was performed at a heating temperature exceeding the upper limit value of the specific temperature range.
3) In Example 46 (steel type P11), Example 50 (steel type P15) and Example 54 (steel type P20), although ferrite formation and undissolved coarse precipitates were not observed, the shock absorption energy was 15 J, respectively. 12J, 12J, 1
It was found to be remarkably reduced to 5 J and extremely poor in impact resistance (toughness).
【００６６】これに対して、焼きならし処理時の加熱保
持温度を特定温度域内の１０２０℃とし、かつ焼もどし
熱処理時の加熱温度を特定温度域内とした例４０，４１
（鋼種Ｐ３）、例４４，４５（鋼種Ｐ１１）、例４８，
４９（鋼種Ｐ１５）、例５２，５３（鋼種Ｐ２０）で
は、フェライトの生成および未固溶の粗大析出物が観察
されず、均一なベイナイト組織であり、衝撃吸収エネル
ギーがそれぞれ７０Ｊ、８５Ｊ、６８Ｊ、７５Ｊ、５８
Ｊ、７５Ｊ、７６Ｊ、８９Ｊと高くなり、優れた耐衝撃
性（靭性）を有することが判明した。このように、特定
範囲の組成であって、特定温度域に加熱保持する焼きな
らし処理を施し、かつ特定温度域に加熱する焼もどし熱
処理を施した鋳鋼は、未溶解の粗大生成物が残存せず、
フェライトの生成が防止された均一な組織を呈し、良好
な機械的性質を有している。On the other hand, Examples 40 and 41 in which the heating and holding temperature during the normalizing treatment was set to 1020 ° C. within the specific temperature range, and the heating temperature during the tempering heat treatment was set within the specific temperature range.
(Steel type P3), Examples 44 and 45 (Steel type P11), Example 48,
In No. 49 (steel type P15) and Examples 52 and 53 (steel type P20), no formation of ferrite and undissolved coarse precipitates were observed, the bainite structure was uniform, and the impact absorption energy was 70 J, 85 J, 68 J, respectively. 75J, 58
J, 75J, 76J, and 89J, which proved to have excellent impact resistance (toughness). As described above, cast steel having a composition in a specific range, subjected to normalizing treatment for heating and holding in a specific temperature range, and subjected to tempering heat treatment for heating to a specific temperature range, has undissolved coarse products remaining. Without
It has a uniform structure in which the formation of ferrite is prevented, and has good mechanical properties.
【００６７】（実施例３）実施例３では、表１−１およ
び表１−２に示す鋼種Ｐ３、Ｐ１１、Ｐ１５およびＰ２
０の各組成の鋳鋼を製造するにあたり、焼きならし処理
時の加熱保持温度を１０５０℃に固定し、焼もどし熱処
理時の加熱温度を種々変更した。Example 3 In Example 3, steel types P3, P11, P15 and P2 shown in Tables 1-1 and 1-2 were used.
In producing cast steels having the respective compositions of No. 0, the heating and holding temperature during normalizing treatment was fixed at 1050 ° C., and the heating temperature during tempering heat treatment was variously changed.
【００６８】得られた各供試鋳鋼から採取した試験片の
質量をあらかじめ測定した後、試験片を１０体積％アセ
チルアセトン−１体積％塩化テトラメチルアンモニウム
が混合されたメタノール溶液中に浸漬し、つづいて電気
分解により母相をメタノール溶液中に溶解させ、残さを
回収してその質量を測定した。そして、メタノール溶液
に浸漬する前の試験片の質量から残さの質量を差し引い
て母相の質量を求め、残さの質量を母相の質量で除して
母相に対する析出相の質量比を算出した。After measuring the mass of the test piece collected from each of the test cast steels obtained in advance, the test piece was immersed in a methanol solution containing 10% by volume of acetylacetone and 1% by volume of tetramethylammonium chloride. The mother phase was dissolved in a methanol solution by electrolysis, the residue was recovered, and its mass was measured. Then, the mass of the mother phase was obtained by subtracting the mass of the residue from the mass of the test piece before being immersed in the methanol solution, and the mass ratio of the precipitated phase to the mother phase was calculated by dividing the mass of the residue by the mass of the mother phase. .
【００６９】また、得られた各供試鋳鋼につき、引張荷
重を１９６ＭＰａとした以外は実施例１で説明したのと
同様なクリープ破断試験およびシャルピー衝撃試験を行
なってクリープ破断時間および衝撃吸収エネルギーを調
べた。その評価結果を表４に示す。The obtained test cast steels were subjected to the same creep rupture test and Charpy impact test as described in Example 1 except that the tensile load was changed to 196 MPa, and the creep rupture time and the shock absorption energy were measured. Examined. Table 4 shows the evaluation results.
【００７０】[0070]
【表４】 [Table 4]
【００７１】特定温度域の下限値を下回る焼もどし温度
とした例５９（鋼種Ｐ３；焼もどし温度６９０℃）、例
６４（鋼種Ｐ１１；焼もどし温度６６０℃）、例６８
（鋼種Ｐ１５；焼もどし温度６７０℃）および例７３
（鋼種Ｐ２０；焼もどし温度６７０℃）の鋳鋼は、母相
に対する析出相の質量比がそれぞれ０．５５質量％、
０．４９質量％、０．５８質量％、０．５１質量％とな
り、いずれも前述の特定範囲の下限値を下回ることが判
明した。これらの例５９、例６４、例６８および例７３
の鋳鋼は、クリープ破断時間がそれぞれ１８３０時間、
１４５１時間、１３８９時間、１５６２時間と長くな
り、優れたクリープ強度特性を有するものの、衝撃吸収
エネルギーがそれぞれ２５Ｊ、２７Ｊ、２５Ｊ、２８Ｊ
と著しく低くなり、耐衝撃性（靭性）に極めて劣ること
が判明した。Example 59 (steel type P3; tempering temperature 690 ° C.), Example 64 (steel type P11; tempering temperature 660 ° C.), Example 68 in which the tempering temperature was lower than the lower limit of the specific temperature range.
(Steel type P15; tempering temperature 670 ° C) and Example 73
(Steel type P20; tempering temperature 670 ° C.) has a cast phase having a mass ratio of the precipitated phase to the matrix of 0.55 mass%,
It was 0.49% by mass, 0.58% by mass, and 0.51% by mass, all of which were found to be lower than the lower limit of the above specific range. These examples 59, 64, 68 and 73
The cast steel has a creep rupture time of 1830 hours each,
It becomes long as 1451 hours, 1389 hours, and 1562 hours, and has excellent creep strength characteristics, but the impact absorption energy is 25 J, 27 J, 25 J, and 28 J, respectively.
, And proved to be extremely poor in impact resistance (toughness).
【００７２】また、特定温度域の上限値を超える焼もど
し温度とした例６３（鋼種Ｐ３；焼もどし温度７９０
℃）、例６７（鋼種Ｐ１１；焼もどし温度７８０℃）、
例７２（鋼種Ｐ１５；焼もどし温度７９０℃）および例
７６（鋼種Ｐ２０；焼もどし温度７８０℃）の鋳鋼は、
母相に対する析出相の質量比がそれぞれ１．０５質量
％、１．０３質量％、１．１０質量％、１．０８質量％
となり、いずれも前述の特定範囲の上限値を超えること
が判明した。これらの例６３、例６７、例７２および例
７６の鋳鋼は、衝撃吸収エネルギーがそれぞれ１１５
Ｊ、１５０Ｊ、１３５Ｊ、１２０Ｊとなり、優れた耐衝
撃性（靭性）を有するものの、クリープ破断時間がそれ
ぞれ５９７時間、４２４時間、２８９時間、４８０時間
と著しく短くなり、クリープ強度特性に極めて劣ること
が判明した。Further, Example 63 in which the tempering temperature exceeded the upper limit of the specific temperature range (steel type P3; tempering temperature 790)
° C), Example 67 (steel type P11; tempering temperature 780 ° C),
The cast steels of Example 72 (steel type P15; tempering temperature 790 ° C.) and Example 76 (steel type P20; tempering temperature 780 ° C.)
The mass ratio of the precipitated phase to the mother phase is 1.05% by mass, 1.03% by mass, 1.10% by mass, and 1.08% by mass, respectively.
It was found that both exceeded the upper limit of the above-mentioned specific range. The cast steels of Examples 63, 67, 72 and 76 have impact absorption energies of 115
J, 150J, 135J, and 120J, and although having excellent impact resistance (toughness), the creep rupture times are remarkably shortened to 597 hours, 424 hours, 289 hours, and 480 hours, respectively, and the creep strength characteristics are extremely poor. found.
【００７３】これに対して、焼もどし温度を特定温度域
内とした例６０〜６２（鋼種Ｐ３；焼もどし温度：７２
０，７３０，７７０℃）、例６５，６６（鋼種Ｐ１１；
焼もどし温度：７３０，７４０℃）、例６９〜７１（鋼
種Ｐ１５；焼もどし温度：７３０，７７０，７７５℃）
および例７４，７５（鋼種Ｐ２０；焼もどし温度：７３
０，７４０℃）の各鋳鋼は、母相に対する析出相の質量
比がそれぞれ０．６３質量％、０．７５質量％、０．９
２質量％、０．６４質量％、０．８８質量％、０．６９
質量％、０．８１質量％、０．９５質量％、０．７１質
量％、０．９５質量％と特定の範囲内となることが判明
した。これらの例６０〜６２、例６５，６６、例６９〜
７１および例７４，７５の各鋳鋼は、クリープ破断時間
がそれぞれ１７２１時間、１６５６時間、１０２３時
間、１２９２時間、１２０１時間、１３３８時間、１２
４３時間、１０３３時間、１４８６時間、１１７８時間
と長くなり、かつ衝撃吸収エネルギーがそれぞれ６５
Ｊ、７０Ｊ、８５Ｊ、６８Ｊ、９６Ｊ、５８Ｊ、７５
Ｊ、８０Ｊ、７６Ｊ、９２Ｊと高い値を示すことから、
優れたクリープ強度特性を有するとともに優れた耐衝撃
性（靭性）を有することが判明した。On the other hand, Examples 60 to 62 in which the tempering temperature was within a specific temperature range (steel type P3; tempering temperature: 72)
0,730,770 ° C), Examples 65,66 (steel type P11;
Tempering temperature: 730, 740 ° C), Examples 69 to 71 (steel type P15; tempering temperature: 730, 770, 775 ° C)
And Examples 74 and 75 (steel type P20; tempering temperature: 73)
0,740 ° C.), the mass ratio of the precipitated phase to the parent phase was 0.63% by mass, 0.75% by mass, 0.9% by mass, respectively.
2 mass%, 0.64 mass%, 0.88 mass%, 0.69
It turned out that it was in a specific range of mass%, 0.81 mass%, 0.95 mass%, 0.71 mass%, 0.95 mass%. These Examples 60 to 62, Examples 65 and 66, and Examples 69 to
The cast steels of Example 71 and Examples 74 and 75 had creep rupture times of 1721 hours, 1656 hours, 1023 hours, 1292 hours, 1201 hours, 1338 hours, and 12 hours, respectively.
43 hours, 1033 hours, 1486 hours, 1178 hours, and the shock absorption energy was 65
J, 70J, 85J, 68J, 96J, 58J, 75
Since J, 80J, 76J, and 92J show high values,
It has been found that it has excellent creep strength characteristics and excellent impact resistance (toughness).
【００７４】（実施例４）電気炉にて組成を種々変化さ
せた溶湯を砂型に鋳込んで表５−１および表５−２に示
す鋼種Ｐ２６〜Ｐ３３および鋼種Ｃ１０〜Ｃ１２の各組
成の供試鋳鋼を得た。焼ならし処理は特定温度域内の１
０４０℃に過熱保持した後に空冷することにより行っ
た。焼戻し熱処理時の加熱温度は鋼種に応じて変更し
た。すなわち、Ｖを単独添加した鋼種（Ｐ２６〜Ｐ２
９、Ｃ１０〜Ｃ１２）の場合には特定温度域内の７３０
℃とし、ＶとＴｉを複合添加した鋼種（Ｐ３０〜Ｐ３
３）の場合には特定温度域内の７４０℃とした。鋼種Ｐ
２６〜Ｐ３３は前述の特定範囲内の組成であり、鋼種Ｃ
１０〜Ｃ１２は前述の特定範囲を逸脱した組成である。(Example 4) A molten metal having various compositions changed in an electric furnace was cast into a sand mold to provide steel compositions P26 to P33 and steel compositions C10 to C12 shown in Tables 5-1 and 5-2. A test cast steel was obtained. Normalization is performed within a specific temperature range.
It carried out by air-cooling after holding overheating at 040 degreeC. The heating temperature during the tempering heat treatment was changed according to the type of steel. That is, the steel type to which V was independently added (P26 to P2
9, C10 to C12), 730 within the specific temperature range
° C and a steel type (P30-P3
In the case of 3), the temperature was set to 740 ° C. within a specific temperature range. Steel type P
26 to P33 are compositions within the specific range described above,
10 to C12 are compositions that deviate from the specific range described above.
【００７５】得られた各供試鋳鋼から試験片を採取し、
それぞれ常温引張強さを測定した結果、７２０〜７７０
ＭＰａとなり、いずれの鋳鋼もほぼ同程度の常温引張強
さを有することが判明した。また、得られた鋳鋼からＪ
ＩＳ４号２ｍｍＶノッチシャルピー衝撃試験片を採取し
て２０℃の温度下でシャルピー衝撃試験を行い、衝撃吸
収エネルギー（Ｊ）を調べた。A test piece was collected from each of the test cast steels obtained,
As a result of measuring the room temperature tensile strength, 720 to 770 was obtained.
MPa, and all the cast steels were found to have almost the same room temperature tensile strength. In addition, J
An IS4 2 mm V notch Charpy impact test piece was sampled and subjected to a Charpy impact test at a temperature of 20 ° C. to examine the impact absorption energy (J).
【００７６】次に、得られた鋳鋼から試験片を採取し、
６００℃の加熱温度下、引張荷重１４７ＭＰａでクリー
プ破断試験を行い、クリープ破断時間を調べた。なお、
いずれの供試鋳鋼も肉厚５００ｍｍの中心部相当でのフ
ェライト生成は認められなかった。以上の評価試験の結
果を表６に示す。Next, a test piece was obtained from the obtained cast steel,
A creep rupture test was performed at a heating temperature of 600 ° C. under a tensile load of 147 MPa, and the creep rupture time was examined. In addition,
In any of the test cast steels, formation of ferrite was not observed in the center portion having a thickness of 500 mm. Table 6 shows the results of the above evaluation tests.
【００７７】表６の例７７〜例８４（鋼種Ｐ２６〜Ｐ３
３）の各鋳鋼は、クリープ破断時間が３１８９〜４３０
１時間と長く、衝撃吸収エネルギーが７２〜９６Ｊと高
い値を示し、優れたクリープ強度特性を有するととも
に、優れた耐衝撃性（靭性）を有することが判明した。
これに対して、例８５（鋼種Ｃ１０）、例８６（鋼種Ｃ
１１）および例８７（鋼種Ｃ１２）の各鋳鋼は、衝撃吸
収エネルギーがそれぞれ１２０Ｊ、９８Ｊ、１０５Ｊと
高いものの、クリープ破断時間がそれぞれ２１４５時
間、２１９６時間、２０９８時間と短くなり、クリープ
強度特性に劣ることが判明した。Examples 77 to 84 of Table 6 (steel types P26 to P3
3) Each of the cast steels has a creep rupture time of 3189 to 430.
As long as one hour, the impact absorption energy showed a high value of 72 to 96 J, and it was found to have excellent creep strength characteristics and excellent impact resistance (toughness).
On the other hand, Example 85 (steel type C10) and Example 86 (steel type C10)
11) and the cast steels of Example 87 (steel type C12) have high impact absorption energies of 120 J, 98 J and 105 J, respectively, but have short creep rupture times of 2145 hours, 2196 hours and 2098 hours, respectively, and are inferior in creep strength characteristics. It has been found.
【００７８】次に、Ｐ３０の組成を有する鋳鋼につい
て、実施例３と同様の焼ならしを施した後、焼戻し熱処
理時の加熱温度を種々変更して、それらから抽出残渣を
回収し、焼戻し後の母相に対する析出相の質量比を算出
した。その結果を表７に示す。Next, the cast steel having the composition of P30 was subjected to normalization in the same manner as in Example 3, and then the heating temperature during the tempering heat treatment was changed in various ways to collect the extracted residue therefrom. The mass ratio of the precipitated phase to the parent phase was calculated. Table 7 shows the results.
【００７９】特定温度域の下限値を下回る焼戻し温度６
９０℃とした例８８の鋳鋼は、母相に対する析出相の質
量比が０．５２％となり、いずれも前述の特定範囲の下
限値を下回ることが判明した。この鋳鋼のクリープ破断
時間は１７２２時間と長いものの、衝撃吸収エネルギー
が２９Ｊと著しく低く、耐衝撃性に劣ることが判明し
た。Tempering temperature below the lower limit of the specific temperature range 6
In the cast steel of Example 88 at 90 ° C., the mass ratio of the precipitated phase to the parent phase was 0.52%, and it was found that all were below the lower limit of the specific range described above. Although the creep rupture time of this cast steel was as long as 1722 hours, the impact absorption energy was extremely low at 29 J, and it was found that the impact resistance was poor.
【００８０】また、特定温度域の上限値を越える焼戻し
温度７９０℃とした例９１の鋳鋼は、母相に対する析出
相の質量比が１．１０％となり、前述の特定範囲の上限
値を超えることが判明した。この鋳鋼は衝撃吸収エネル
ギーが１５０Ｊと優れた耐衝撃静質を有するものの、ク
リープ破断時間が５０８時間と著しく短くなり、クリー
プ強度に極めて劣ることが判明した。Further, in the cast steel of Example 91 in which the tempering temperature was 790 ° C. exceeding the upper limit value of the specific temperature range, the mass ratio of the precipitated phase to the mother phase was 1.10%, which exceeded the upper limit value of the specific range described above. There was found. Although this cast steel had an excellent impact absorption static energy of 150 J, the creep rupture time was significantly shortened to 508 hours, and it was found that the creep strength was extremely poor.
【００８１】これに対して、焼戻し温度を特定温度域内
とした例８９（焼戻し温度７２０℃）および例９０（焼
戻し温度７４０℃）の鋳鋼では、母相に対する析出相の
質量比がそれぞれ０．６５％および０．８９％となり、
優れたクリープ強度特性（１６９０時間、１３２９時
間）とともに、優れた耐衝撃性（７２Ｊ、９５Ｊ）を有
することが判明した。On the other hand, in the cast steels of Example 89 (tempering temperature 720 ° C.) and Example 90 (tempering temperature 740 ° C.) in which the tempering temperature was within a specific temperature range, the mass ratio of the precipitated phase to the parent phase was 0.65, respectively. % And 0.89%,
It was found to have excellent creep strength characteristics (1690 hours, 1329 hours) as well as excellent impact resistance (72J, 95J).
【００８２】以上のことから、焼ならし処理時の加熱保
持温度を特定温度域とし、かつ焼戻し温度を特定温度域
として耐熱鋳鋼を製造するにあたり、前述の特定範囲の
組成に調整された鋼種Ｐ２６〜Ｐ３３は、厚肉部であっ
てもフェライトの生成が生じず、特定範囲を逸脱した組
成に調整された鋼種Ｃ１０〜Ｃ１２と同程度の常温引張
強さを有するのみならず、優れたクリープ強度特性と優
れた靭性を両立できることが判明した。From the above, when manufacturing a heat-resistant cast steel with the heating and holding temperature during the normalizing process in the specific temperature range and the tempering temperature in the specific temperature range, the steel type P26 adjusted to the composition in the above-described specific range was used. -P33 has no room temperature tensile strength of steel types C10-C12 adjusted to a composition that deviates from a specific range without producing ferrite even in a thick portion, and also has excellent creep strength It has been found that both characteristics and excellent toughness can be achieved.
【００８３】[0083]
【表５−１】 [Table 5-1]
【００８４】[0084]
【表５−２】 [Table 5-2]
【００８５】[0085]
【表６】 [Table 6]
【００８６】[0086]
【表７】 [Table 7]
【００８７】[0087]
【発明の効果】以上詳述したとおり、本発明によれば、
高温蒸気が流通する環境下で優れた機械的性質を発揮す
るとともに経済性に優れた耐熱鋳鋼およびその製造方法
を提供することができる。このため、本発明の耐熱鋳鋼
を用いた蒸気タービン車室や蒸気タービン弁箱は、過酷
な高温蒸気条件下においても高い信頼性を発揮し、蒸気
タービンの性能、運用性、経済性の向上に貢献できる
等、有益な効果がもたらされる。As described in detail above, according to the present invention,
It is possible to provide a heat-resistant cast steel which exhibits excellent mechanical properties in an environment where high-temperature steam flows and is economical, and a method for producing the same. For this reason, steam turbine casings and steam turbine valve casings using the heat-resistant cast steel of the present invention exhibit high reliability even under severe high-temperature steam conditions, and improve steam turbine performance, operability, and economic efficiency. Beneficial effects such as contribution can be obtained.
Claims (16)
ｉ：０．１〜０．３０％、Ｍｎ：０．０１〜０．１％、
Ｃｒ：２．０〜２．５％、Ｍｏ：０．３〜０．８％、
Ｖ：０．２３〜０．３％、Ｗ：１．６〜２．６％、Ｎ：
０．００５〜０．０３％、Ｂ：０．００１〜０．００４
％を含有し、かつ不純物元素のうちＮｉ：０．２％以下
と、Ｐ：０．０３％以下と、Ｓ：０．０１％以下とに制
限し、かつ下式（１）により求められるＢ当量が０．０
２％以下と、下式（２）により求められるＭｏ当量が
１．４〜２．０％と、下式（３）により求められるＣ当
量が０．６５％以上とを満たし、残部が鉄および不可避
的不純物からなり、Ｍ２３Ｃ６型炭化物と、Ｍ７Ｃ３型
炭化物と、ＭＸ型炭窒化物とからなる析出相が母相に微
細析出した組織であり、かつ母相に対する析出相の比が
０．６〜１．０質量％であることを特徴とする。 Ｂ当量＝Ｂ＋０．５Ｎ …（１） Ｍｏ当量＝Ｍｏ＋０．５Ｗ …（２） Ｃ当量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３）C. 0.15 to 0.3% by mass, S
i: 0.1 to 0.30%, Mn: 0.01 to 0.1%,
Cr: 2.0 to 2.5%, Mo: 0.3 to 0.8%,
V: 0.23-0.3%, W: 1.6-2.6%, N:
0.005 to 0.03%, B: 0.001 to 0.004
%, And among the impurity elements, Ni: 0.2% or less, P: 0.03% or less, S: 0.01% or less, and B obtained by the following equation (1). Equivalent 0.0
2% or less, the Mo equivalent determined by the following equation (2) satisfies 1.4 to 2.0%, and the C equivalent determined by the following equation (3) satisfies 0.65% or more, with the balance being iron and It becomes unavoidable impurities, and the M 23 C 6 type carbide, and M 7 C 3 type carbide precipitation phase consisting of MX-type carbonitrides are tissue was finely precipitated in the parent phase, and the precipitated phase to the matrix phase The ratio is 0.6 to 1.0% by mass. B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3)
量％とし、さらに、Ｎｂ：０．０１〜０．０６質量％を
含有し、下式（４）により求められるＮｂ当量が０．１
５％以下を満たすことを特徴とする請求項１に記載の耐
熱鋳鋼。 Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４）2. The method according to claim 1, wherein the content of V is 0.23 to 0.27% by mass, Nb: 0.01 to 0.06% by mass, and the Nb equivalent obtained by the following formula (4) is: 0.1
The heat-resistant cast steel according to claim 1, wherein 5% or less is satisfied. Nb equivalent = Nb + 0.4C (4)
量％とし、さらに、Ｔｉ：０．００５〜０．０１質量％
を含有することを特徴とする請求項１に記載の耐熱鋳
鋼。3. The content of V is set to 0.23 to 0.27% by mass, and further, Ti: 0.005 to 0.01% by mass.
The heat-resistant cast steel according to claim 1, further comprising:
％とすることを特徴とする請求項１に記載の耐熱鋳鋼。4. The heat-resistant cast steel according to claim 1, wherein the V content is 0.25 to 0.3% by mass.
０．３％、Ｓｉ：０．１〜０．３０％、Ｍｎ：０．４〜
０．７％、Ｃｒ：２．０〜２．５％、Ｍｏ：０．３〜
０．８％、Ｖ：０．２３〜０．３％、Ｗ：１．６〜２．
６％、Ｎ：０．００５〜０．０３％、Ｂ：０．００１〜
０．００４％を含有し、かつ不純物元素のうちＮｉ：
０．５％以下と、Ｐ：０．０３％以下と、Ｓ：０．０１
％以下とに制限し、かつ下式（１）により求められるＢ
当量が０．０２％以下と、下式（２）により求められる
Ｍｏ当量が１．４〜２．０％と、下式（３）により求め
られるＣ当量が０．６５％以上とを満たし、残部が鉄お
よび不可避的不純物からなり、Ｍ２３Ｃ６型炭化物と、
Ｍ７Ｃ３型炭化物と、ＭＸ型炭窒化物とからなる析出相
が母相に微細析出した組織であり、かつ母相に対する析
出相の比が０．６〜１．０質量％であることを特徴とす
る。 Ｂ当量＝Ｂ＋０．５Ｎ …（１） Ｍｏ当量＝Ｍｏ＋０．５Ｗ …（２） Ｃ当量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３）5. The heat-resistant cast steel has a C content of 0.15% by mass.
0.3%, Si: 0.1 to 0.30%, Mn: 0.4 to
0.7%, Cr: 2.0 to 2.5%, Mo: 0.3 to
0.8%, V: 0.23-0.3%, W: 1.6-2.
6%, N: 0.005 to 0.03%, B: 0.001 to
0.004%, and among the impurity elements, Ni:
0.5% or less, P: 0.03% or less, S: 0.01
% Or less and B determined by the following equation (1)
The equivalent is 0.02% or less, the Mo equivalent determined by the following formula (2) satisfies 1.4 to 2.0%, and the C equivalent determined by the following formula (3) satisfies 0.65% or more; The balance consisting of iron and unavoidable impurities, M 23 C 6 type carbides,
A structure in which a precipitated phase composed of M 7 C 3 type carbide and MX type carbonitride is finely precipitated in the matrix, and the ratio of the precipitated phase to the matrix is 0.6 to 1.0% by mass. It is characterized by. B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3)
量％とし、さらに、Ｔｉ：０．００５〜０．０１質量
％、Ｎｂ：０．０１〜０．０６質量％を含有し、下式
（４）により求められるＮｂ当量が０．１５％以下を満
たすことを特徴とする請求項５に記載の耐熱鋳鋼。 Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４）6. The content of V is set to 0.23 to 0.27% by mass, and further, Ti: 0.005 to 0.01% by mass and Nb: 0.01 to 0.06% by mass. The heat-resistant cast steel according to claim 5, wherein the Nb equivalent obtained by the following equation (4) satisfies 0.15% or less. Nb equivalent = Nb + 0.4C (4)
量％とし、さらにＴｉを０．０１〜０．０２５質量％含
有することを特徴とする請求項５に記載の耐熱鋳鋼。7. The heat-resistant cast steel according to claim 5, wherein the content of V is 0.23 to 0.25% by mass, and 0.01 to 0.025% by mass of Ti is further contained.
％とすることを特徴とする請求項５に記載の耐熱鋳鋼。8. The heat-resistant cast steel according to claim 5, wherein the V content is 0.25 to 0.3% by mass.
ｉ：０．１〜０．３０％、Ｍｎ：０．０１〜０．１％、
Ｃｒ：２．０〜２．５％、Ｍｏ：０．３〜０．８％、
Ｖ：０．２３〜０．３％、Ｗ：１．６〜２．６％、Ｎ：
０．００５〜０．０３％、Ｂ：０．００１〜０．００４
％を含有し、かつ不純物元素のうちＮｉ：０．２％以下
と、Ｐ：０．０３％以下と、Ｓ：０．０１％以下とに制
限し、かつ下式（１）により求められるＢ当量が０．０
２％以下と、下式（２）により求められるＭｏ当量が
１．４〜２．０％と、下式（３）により求められるＣ当
量が０．６５％以上とを満たし、残部が鉄および不可避
的不純物からなる鋳造物を１０３０〜１０７０℃の温度
域に加熱保持した後に焼入れる工程と、この工程の後に
６８０〜７８０℃の温度域に焼きもどす工程と、を備え
たことを特徴とする耐熱鋳鋼の製造方法。 Ｂ等量＝Ｂ＋０．５Ｎ …（１） Ｍｏ等量＝Ｍｏ＋０．５Ｗ …（２） Ｃ等量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３）9. In mass%, C: 0.15 to 0.3%, S
i: 0.1 to 0.30%, Mn: 0.01 to 0.1%,
Cr: 2.0 to 2.5%, Mo: 0.3 to 0.8%,
V: 0.23-0.3%, W: 1.6-2.6%, N:
0.005 to 0.03%, B: 0.001 to 0.004
%, And among the impurity elements, Ni: 0.2% or less, P: 0.03% or less, S: 0.01% or less, and B obtained by the following equation (1). Equivalent 0.0
2% or less, the Mo equivalent determined by the following equation (2) satisfies 1.4 to 2.0%, and the C equivalent determined by the following equation (3) satisfies 0.65% or more, with the balance being iron and A step of heating and holding the casting made of unavoidable impurities in a temperature range of 1030 to 1070 ° C. and then quenching, and after this step, a step of tempering to a temperature range of 680 to 780 ° C. Manufacturing method of heat-resistant cast steel. B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3)
質量％とし、さらに、Ｎｂを０．０１〜０．０６質量％
含有し、下式（４）により求められるＮｂ当量が０．１
５％以下を満たし、前記焼もどし工程では、７２０〜７
８０℃の温度域に加熱することを特徴とする請求項９に
記載の耐熱鋳鋼の製造方法。 Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４）10. The content of V is from 0.23 to 0.27.
% By mass, and Nb is 0.01 to 0.06% by mass.
And the Nb equivalent determined by the following formula (4) is 0.1
5% or less, and 720 to 7 in the tempering step.
The method for producing a heat-resistant cast steel according to claim 9, wherein the steel is heated to a temperature range of 80 ° C. Nb equivalent = Nb + 0.4C (4)
質量％とし、さらに、Ｔｉ：０．００５〜０．０１質量
％を含有し、前記焼もどし工程では、７２０〜７８０℃
の温度域に加熱することを特徴とする請求項９に記載の
耐熱鋳鋼の製造方法。11. The content of V is from 0.23 to 0.27.
%, And further contains 0.005 to 0.01% by mass of Ti, and in the tempering step, 720 to 780 ° C.
The method for producing a heat-resistant cast steel according to claim 9, wherein the steel is heated to a temperature range of:
量％とし、前記焼きもどし工程では、６８０〜７４０℃
の温度域に加熱することを特徴とする請求項９に記載の
耐熱鋳鋼の製造方法。12. The content of V is set to 0.25 to 0.3% by mass, and in the tempering step, 680 to 740 ° C.
The method for producing a heat-resistant cast steel according to claim 9, wherein the steel is heated to a temperature range of:
Ｃ：０．１５〜０．３％、Ｓｉ：０．１〜０．３０％、
Ｍｎ：０．４〜０．７％、Ｃｒ：２．０〜２．５％、Ｍ
ｏ：０．３〜０．８％、Ｖ：０．２３〜０．３％、Ｗ：
１．６〜２．６％、Ｎ：０．００５〜０．０３％、Ｂ：
０．００１〜０．００４％を含有し、かつ不純物元素の
うちＮｉ：０．５％以下と、Ｐ：０．０３％以下と、
Ｓ：０．０１％以下とに制限し、かつ下式（１）により
求められるＢ当量が０．０２％以下と、下式（２）によ
り求められるＭｏ当量が１．４〜２．０％と、下式
（３）により求められるＣ当量が０．６５％以上とを満
たし、残部が鉄および不可避的不純物からなる鋳造物を
１０３０〜１０７０℃の温度域に加熱保持した後に焼入
れる工程と、この工程の後に６８０〜７８０℃の温度域
に焼きもどす工程と、を備えたことを特徴とする耐熱鋳
鋼の製造方法。 Ｂ当量＝Ｂ＋０．５Ｎ …（１） Ｍｏ当量＝Ｍｏ＋０．５Ｗ …（２） Ｃ当量＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／１５ ＋Ｖ／１４ …（３）13. A method for producing a heat-resistant cast steel, comprising:
C: 0.15 to 0.3%, Si: 0.1 to 0.30%,
Mn: 0.4-0.7%, Cr: 2.0-2.5%, M
o: 0.3-0.8%, V: 0.23-0.3%, W:
1.6 to 2.6%, N: 0.005 to 0.03%, B:
0.001 to 0.004%, and among the impurity elements, Ni: 0.5% or less, P: 0.03% or less,
S: It is limited to 0.01% or less, and the B equivalent obtained by the following formula (1) is 0.02% or less, and the Mo equivalent obtained by the following formula (2) is 1.4 to 2.0%. And a step of quenching after heating and holding a cast comprising the iron equivalent and the unavoidable impurities in a temperature range of 1030 to 1070 ° C. in which the C equivalent obtained by the following formula (3) satisfies 0.65% or more. And a step of tempering to a temperature range of 680 to 780 ° C. after this step. B equivalent = B + 0.5N (1) Mo equivalent = Mo + 0.5W (2) C equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 15 + V / 14 (3)
質量％とし、さらに、Ｔｉ：０．００５〜０．０１質量
％、Ｎｂを０．０１〜０．０６質量％含有し、下式
（４）により求められるＮｂ当量が０．１５％以下を満
たし、前記焼もどし工程では、７２０〜７８０℃の温度
域に加熱することを特徴とする請求項１３に記載の耐熱
鋳鋼の製造方法。 Ｎｂ当量＝Ｎｂ＋０．４Ｃ …（４）14. The content of V is from 0.23 to 0.27.
%, And further contains 0.005 to 0.01% by mass of Ti and 0.01 to 0.06% by mass of Nb, and the Nb equivalent obtained by the following formula (4) satisfies 0.15% or less. 14. The method for producing a heat-resistant cast steel according to claim 13, wherein in the tempering step, heating is performed to a temperature range of 720 to 780C. Nb equivalent = Nb + 0.4C (4)
質量％とし、さらにＴｉ：０．０１〜０．００２５質量
％を含有し、前記焼もどし工程では、７２０〜７８０℃
の温度域に加熱することを特徴とする請求項１３に記載
の耐熱鋳鋼の製造方法。15. The content of V is from 0.23 to 0.25.
%, And further contains 0.01 to 0.0025% by mass of Ti, and in the tempering step, 720 to 780 ° C.
The method for producing a heat-resistant cast steel according to claim 13, wherein the steel is heated to a temperature range of:
量％とし、前記焼きもどし工程では、６８０〜７４０℃
の温度域に加熱することを特徴とする請求項１３に記載
の耐熱鋳鋼の製造方法。16. The content of V is set to 0.25 to 0.3% by mass, and in the tempering step, 680 to 740 ° C.
The method for producing a heat-resistant cast steel according to claim 13, wherein the steel is heated to a temperature range of:
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012167307A (en) * | 2011-02-10 | 2012-09-06 | Mitsubishi Heavy Industries Compressor Corp | Method for producing cast steel product |
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| JP3998413B2 (en) | 2007-10-24 |
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