JP7576585B2 - Low thermal expansion alloy - Google Patents
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Description
本発明は、熱間加工性に優れた低熱膨張合金に関する。 The present invention relates to a low thermal expansion alloy with excellent hot workability.
インバー系合金は、熱変形が小さく、寸法安定性に優れるため、インバー系合金の熱間加工材が、エレクトロニクスや半導体関連機器、レーザー加工機、超精密加工機器の部品材料として広く使用されている。 Invar alloys have little thermal deformation and excellent dimensional stability, so hot-worked Invar alloys are widely used as parts materials for electronics and semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment.
汎用のインバー系合金は、高Ｎｉ含有の低熱膨張Ｆｅ合金であり、オーステナイト単相組織で凝固するので、熱間加工の素材となるインゴット（鋳塊）には粗大な柱状晶が形成しやすくなる。それに伴い、低融点の硫化物系粗大介在物が結晶粒界に偏析して、熱間加工時に硫化物系介在物を起点とする割れが発生しやすくなる。 General-purpose Invar alloys are low-thermal expansion Fe alloys with high Ni content, and since they solidify in a single-phase austenite structure, coarse columnar crystals tend to form in the ingots that are used as raw materials for hot working. As a result, coarse sulfide inclusions with low melting points segregate at grain boundaries, making it easier for cracks to occur that originate from the sulfide inclusions during hot working.
特許文献１には、高強度で、かつ優れた熱間加工性を有し、製造コストが安価で、熱膨張係数の低いインバー系合金が提案されている。特許文献１の合金は、重量％にてＣ：０．０１５～０．１０％、Ｓｉ：０．３５％以下、Ｍｎ：１．０％以下、Ｐ：０．０１５％以下、Ｓ：０．００１０％以下、Ｃｒ：０．３％以下、Ｎｉ：３５～３７％、Ｍｏ：０～０．５％、Ｖ：０～０．０５％、Ａｌ：０．０１％以下、Ｎｂ：０．１５％以上１．０％未満、Ｔｉ：０．００３％以下、Ｎ：０．００５％以下、Ｂ：０．０００５～０．００５％を含有するとともに残部がＦｅおよび不可避的不純物よりなる。 Patent Document 1 proposes an Invar-based alloy that has high strength, excellent hot workability, low manufacturing costs, and a low thermal expansion coefficient. The alloy in Patent Document 1 contains, by weight, C: 0.015-0.10%, Si: 0.35% or less, Mn: 1.0% or less, P: 0.015% or less, S: 0.0010% or less, Cr: 0.3% or less, Ni: 35-37%, Mo: 0-0.5%, V: 0-0.05%, Al: 0.01% or less, Nb: 0.15% or more but less than 1.0%, Ti: 0.003% or less, N: 0.005% or less, B: 0.0005-0.005%, with the balance being Fe and unavoidable impurities.
特許文献２にも、熱間加工性に優れたインバー系の低熱膨張合金が提案されている。特許文献２の合金は、質量％で、Ｃ：０．０４％以下、Ｓｉ：０．１５超、０．５％以下、Ｍｎ：０．５％以下、Ｓ：０．０５０％以下、Ｎｉ：３１～３６％、Ｃｏ：２～６．５％、Ａｌ：０．０３超、０．２０％以下、Ｍｇ：０～０．０５％、Ｃａ：０～０．０２％、Ｃｅ：０～０．０５％、Ｌａ：０～０．０５％、Ｔｉ：０～０．０５％、Ｂ：０．００１～０．０２０％、及びＮ：０．００５０％以下を含有し、残部がＦｅおよび不可避的不純物であり、２５～１００℃における平均熱膨張係数が１×１０-6～８×１０-6／℃以下であり、９００℃における引張試験で測定した絞りが５０％以上である。 Patent Document 2 also proposes an Invar-based low thermal expansion alloy having excellent hot workability. The alloy of Patent Document 2 contains, by mass%, C: 0.04% or less, Si: more than 0.15 but 0.5% or less, Mn: 0.5% or less, S: 0.050% or less, Ni: 31-36%, Co: 2-6.5%, Al: more than 0.03 but 0.20% or less, Mg: 0-0.05%, Ca: 0-0.02%, Ce: 0-0.05%, La: 0-0.05%, Ti: 0-0.05%, B: 0.001-0.020%, and N: 0.0050% or less, with the balance being Fe and unavoidable impurities, has an average thermal expansion coefficient at 25-100°C of 1 x 10-6 to 8 x 10-6 /°C or less, and has a reduction in area measured in a tensile test at 900°C of 50% or more.
特許文献１に開示されているインバー系合金は、Ｓを０．００１０％以下（好ましくは０．０００５％以下）と極めて低Ｓ化することで熱間加工性の向上を図っている。これを実現するには、高価な低Ｓ原料を適用する必要があり、また、高度な設備を利用した溶鋼脱硫が不可欠となるため、制約が大きく、かつ製造コストが増加するという課題がある。 The Invar alloy disclosed in Patent Document 1 aims to improve hot workability by reducing the S content to an extremely low level of 0.0010% or less (preferably 0.0005% or less). To achieve this, it is necessary to use expensive low-S raw materials, and molten steel desulfurization using advanced equipment is essential, which creates significant restrictions and increases manufacturing costs.
また、特許文献２に開示されているインバー系合金は、Ｂが熱間加工性の向上を図る上で重要な役割を果たしている。しかし、Ｂは鋼中への溶解度が極めて低く、また酸素、窒素との親和力が大きいことから、ｐｐｍオーダーの狭い管理幅で添加することが難しく、熱間鍛造時のインゴット割れを確実に防止するのが困難であるという課題がある。また、熱間加工性評価の指標とした絞り値を測定したときの引張試験の歪速度が０．０７～０．０８s-1であり、実際の熱間加工条件に比べて極めて小さい歪速度であることから、合金材料の熱間加工性評価試験方法としての妥当性に疑問がある。 In addition, in the Invar alloy disclosed in Patent Document 2, B plays an important role in improving hot workability. However, since B has an extremely low solubility in steel and has a high affinity with oxygen and nitrogen, it is difficult to add B in a narrow control range on the order of ppm, and it is difficult to reliably prevent ingot cracking during hot forging. In addition, the strain rate of the tensile test when measuring the reduction of area, which is an index of hot workability evaluation, is 0.07 to 0.08 s -1 , which is an extremely small strain rate compared to the actual hot working conditions, and therefore there is a question about the validity of this method as a test method for evaluating the hot workability of alloy materials.
本発明は、低熱膨張セラミックスや石英ガラスと同等の低い熱膨張係数を有し、低コストでかつ安定的に提供可能な熱間加工性に優れる低熱膨張合金を提供することを課題とする。 The objective of the present invention is to provide a low-thermal expansion alloy that has a low thermal expansion coefficient equivalent to that of low-thermal expansion ceramics and quartz glass, has excellent hot workability, and can be provided stably at low cost.
本発明者らは、低熱膨張セラミックスや石英ガラスと同等の低い熱膨張係数を有し、低コストでかつ安定的に提供可能な熱間加工性に優れる低熱膨張合金を得るべく鋭意検討した。その結果、ＣとＮｂ、およびＳとＣａの各元素の組合せに対する関係式に基づいた範囲で各元素を添加することより、熱間加工性に優れた低熱膨張合金が低コスト、かつ安定的に得られることを見出した。 The inventors have conducted extensive research to obtain a low-thermal expansion alloy with excellent hot workability that has a low thermal expansion coefficient equivalent to that of low-thermal expansion ceramics and quartz glass and can be provided stably at low cost. As a result, they have discovered that by adding each element within the range based on the relational formula for the combination of each element, C and Nb, and S and Ca, a low-thermal expansion alloy with excellent hot workability can be obtained stably at low cost.
本発明は上記知見に基づいて完成されたものであり、以下の手段を提供する。 The present invention was completed based on the above findings and provides the following:
（１）質量％で、Ｃ：０．０５～０．１２％、Ｓｉ：０．２％以下、Ｍｎ：０．２～０．５、Ｓ：０．０１％以下、Ｎｉ：３１．０～３３．０％、Ｃｏ：４．０～６．０、Ｎｂ：０．３５～０．８８％、Ｃａ：０．０３５％以下を含有し、Ｎｉ＋０．８Ｃｏで表されるＮｉ当量：３５．５～３６．５％、Ｃ含有量を［Ｃ］、Ｎｂ含有量を［Ｎｂ］としたとき、［Ｃ］≧［Ｎｂ］×７．７４の場合、［Ｎｂ］×１．１３で表され、［Ｃ］＜［Ｎｂ］×７．７４の場合、［Ｃ］×８．７４で表される、化学量論的なＮｂＣ：０．４０～１．０％、かつ２．０≦Ｃａ／Ｓ≦４．０であり、残部がＦｅおよび不可避的不純物からなり、１０～４０℃における平均熱膨張係数が０．５×１０-6／℃以下であることを特徴とする低熱膨張合金。 (1) In mass%, C: 0.05 to 0.12%, Si: 0.2% or less, Mn: 0.2 to 0.5, S: 0.01% or less, Ni: 31.0 to 33.0%, Co: 4.0 to 6.0, Nb: 0.35 to 0.88%, Ca: 0.035% or less, Ni equivalent expressed as Ni + 0.8Co : 35.5 to 36.5%, A low thermal expansion alloy characterized in that, when the C content is [C] and the Nb content is [Nb], if [C]≧[Nb]×7.74, it is expressed as [Nb]×1.13, and if [C]<[Nb]×7.74, it is expressed as [C]×8.74, and the alloy contains 0.40-1.0% stoichiometric NbC, 2.0≦Ca/S≦4.0, the balance being Fe and unavoidable impurities, and the average thermal expansion coefficient at 10-40°C is 0.5× 10-6 /°C or less.
（２）歪速度が１ｓ-1以上の引張試験における９００℃の絞り値が６０％以上であることを特徴とする（１）に記載の低熱膨張合金。 (2) A low thermal expansion alloy according to (1), characterized in that the reduction in area at 900°C in a tensile test at a strain rate of 1 s or more is 60% or more.
本発明によれば、低熱膨張セラミックスや石英ガラスと同等の低い熱膨張係数を有し、低コストでかつ安定的に提供可能な熱間加工性に優れる低熱膨張合金が得られる。このため、本発明の低熱膨張合金は、高い熱的寸法安定性と良好な内部品質が望まれる素材等に好適である。 According to the present invention, a low thermal expansion alloy is obtained that has a low thermal expansion coefficient equivalent to that of low thermal expansion ceramics and quartz glass, has excellent hot workability, and can be provided stably at low cost. Therefore, the low thermal expansion alloy of the present invention is suitable for materials that require high thermal dimensional stability and good internal quality.
以下、本発明の実施形態について詳細に説明する。
なお、以下の説明において、成分組成に関する「％」は特に断りのない限り「質量％」を表すものとする。また、以下の説明において、熱膨張係数は、αと記載する場合がある。
Hereinafter, an embodiment of the present invention will be described in detail.
In the following description, "%" regarding the composition of a component represents "mass %" unless otherwise specified. In the following description, the thermal expansion coefficient may be referred to as α.
まず、成分組成について説明する。 First, let me explain the composition of the ingredients.
Ｃは、合金中にＮｂを含有する場合、Ｎｂと結合してＮｂＣを形成し、結晶粒の粗大化を抑制し、それに伴い、低融点の硫化物系の粗大化を抑制し、熱間割れを防止する効果がある。有効な熱間割れ防止効果は、ＮｂＣが一定範囲の量になるようにＣおよびＮｂ含有量をコントロールすることで得られる。しかし、Ｃ含有量が０．０５％未満では熱間割れ防止効果が少なく、また、０．１２％超ではＮｂＣが過大となり、かえって熱間加工性の低下を招くほか、工具寿命の低下が無視できなくなる。加えて、ＮｂＣ形成に必要な量を超えたＣは基地に固溶して基地中Ｃ濃度を高め、経年変化（長期的な寸法変化）を助長する。したがって、Ｃ含有量を０．０５～０．１２％の範囲とする。 When Nb is contained in the alloy, C combines with Nb to form NbC, which inhibits the coarsening of crystal grains and, in turn, inhibits the coarsening of low-melting-point sulfides, and has the effect of preventing hot cracking. An effective hot crack prevention effect can be obtained by controlling the C and Nb contents so that the amount of NbC is within a certain range. However, if the C content is less than 0.05%, the hot crack prevention effect is small, and if it exceeds 0.12%, the NbC becomes excessive, which leads to a decrease in hot workability and a decrease in tool life that cannot be ignored. In addition, C in excess of the amount necessary for NbC formation dissolves in the matrix, increasing the C concentration in the matrix and promoting aging (long-term dimensional change). Therefore, the C content is set to the range of 0.05 to 0.12%.
Ｓｉは、脱酸材として添加してもよいが、Ｓｉ含有量が０．２％を超えるとαが増加する。このため、Ｓｉ含有量を０．２％以下とする。 Si may be added as a deoxidizer, but if the Si content exceeds 0.2%, α will increase. For this reason, the Si content should be 0.2% or less.
Ｍｎは、脱酸材およびＳと結合してＭｎＳを形成して熱間加工性を向上させるので添加する。しかし、その含有量が０．２％未満ではその効果が十分得られず、また、０．５％超では、αの増大により所望のαが得られなくなる。したがって、Ｍｎ含有量を０．２～０．５％の範囲とする。 Mn is added because it combines with deoxidizers and S to form MnS, improving hot workability. However, if the content is less than 0.2%, this effect is not fully achieved, and if it exceeds 0.5%, the desired α cannot be obtained due to the increase in α. Therefore, the Mn content is set in the range of 0.2 to 0.5%.
Ｓは不可避的不純物として含有される元素で、大部分が硫化物系介在物として存在する。硫化物系介在物が結晶粒界に偏析すると、熱間加工性が大きく劣化するが、後述のＣａ添加により、無害化することができる。しかし、その含有量が０．０１％超では、無害化のために添加するＣａが増大して溶湯の清浄度が低下してかえって熱間加工性が低下する。したがって、Ｓ含有量を０．０１％以下とする。 S is an element contained as an unavoidable impurity, and exists mostly as sulfide inclusions. When sulfide inclusions segregate at grain boundaries, hot workability is significantly degraded, but this can be rendered harmless by adding Ca, as described below. However, if the S content exceeds 0.01%, the amount of Ca added to render the inclusions harmless increases, reducing the cleanliness of the molten metal and actually degrading hot workability. Therefore, the S content is set to 0.01% or less.
Ｎｉは後述のＣｏとともにαを低下させる必須の元素である。本発明の低熱膨張合金は、後述するように、低熱膨張のセラミックスや光学ガラス等と一体で使用することを意図しており、以下に示すＣｏとの相乗効果によってαを所望の０．５ｐｐｍ／℃以下に調整する。しかし、その含有量が３１．０％未満では、低温における組織の安定性が低下し、３３．０％超では、後述のＮｉ当量範囲に従ったＣｏが少なくなって所望のαが得られなくなる。したがって、Ｎｉ含有量を３１．０～３３．０％の範囲とする。 Ni is an essential element that, together with Co, described below, lowers α. As described below, the low thermal expansion alloy of the present invention is intended to be used together with low thermal expansion ceramics, optical glass, etc., and α is adjusted to the desired 0.5 ppm/°C or less through the synergistic effect with Co, described below. However, if the Ni content is less than 31.0%, the stability of the structure at low temperatures decreases, and if it exceeds 33.0%, the amount of Co according to the Ni equivalent range described below decreases, making it impossible to obtain the desired α. Therefore, the Ni content is set to the range of 31.0 to 33.0%.
Ｃｏは、０．５ｐｐｍ／℃以下の極めて小さいαを得るために、前述のＮｉと共に添加する。そのために、Ｃｏ量は４．０％以上必要である。しかし、後述のＮｉ当量範囲に従うと、Ｃｏ量が６．０％超では、Ｎｉ量が少なくなって低温における組織の安定性が低下する。したがって、Ｃｏ含有量を４．０～６．０％の範囲とする。 Co is added together with the aforementioned Ni to obtain an extremely small α of 0.5 ppm/°C or less. To achieve this, the Co content must be 4.0% or more. However, according to the Ni equivalent range described below, if the Co content exceeds 6.0%, the Ni content becomes too small and the structure stability at low temperatures decreases. Therefore, the Co content is set in the range of 4.0 to 6.0%.
Ｎｉ当量は、Ｎｉ+０．８×Ｃｏで表され、所望のαを得るための指標である。本発明の低熱膨張合金は低熱膨張のセラミックスや光学ガラス等と一体で使用することを目的としたものであり、αを所望の０．５ｐｐｍ／℃以下に調整するために、Ｎｉ当量は３５．５～３６．５％の範囲とする。 The Ni equivalent is expressed as Ni + 0.8 x Co, and is an index for obtaining the desired α. The low thermal expansion alloy of the present invention is intended to be used together with low thermal expansion ceramics, optical glass, etc., and in order to adjust α to the desired 0.5 ppm/°C or less, the Ni equivalent is set to the range of 35.5 to 36.5%.
Ｃａは、熱間加工性の改善に対して重要な元素である。Ｃａは、前記のようにＳと結びついてＣａＳを形成して、硫化物を高融点のＣａＳにすることにより、硫化物を粒内に生成させ、結晶粒界への偏析を防止する。さらに、介在物の形態を球状に変えて熱間加工時の応力の集中を防ぐ。Ｃａ量が０．０３５％超では、本発明合金のＳの上限濃度である、０．０１％に対して、過剰となり、溶湯の清浄度が低下して熱間加工性向上効果が低下する。したがって、Ｃａ含有量は０．０３５％以下とする。 Ca is an important element for improving hot workability. As mentioned above, Ca combines with S to form CaS, which converts sulfides into CaS with a high melting point, generating sulfides within the grains and preventing segregation to grain boundaries. Furthermore, it changes the shape of inclusions to spherical shapes, preventing stress concentration during hot working. If the Ca content exceeds 0.035%, it will be in excess of the upper limit of S concentration in the alloy of the present invention, which is 0.01%, and the cleanliness of the molten metal will decrease, reducing the effect of improving hot workability. Therefore, the Ca content is set to 0.035% or less.
Ｃａ／Ｓは、硫化物をＣａＳに形態制御するために重要な指標である。Ｃａ／Ｓが２．０未満であれば、ＭｎＳの形態を十分に制御できず硫化物が球状化しにくい。一方、Ｃａ／Ｓが４．０を超えれば、粗大なＣａ系酸化物が生成して、熱間割れ防止効果が低下する。したがって、Ｃａ／Ｓを２．０～４．０の範囲とする。 Ca/S is an important index for controlling the morphology of sulfides to CaS. If Ca/S is less than 2.0, the morphology of MnS cannot be sufficiently controlled, and the sulfides are difficult to spheroidize. On the other hand, if Ca/S exceeds 4.0, coarse Ca-based oxides are generated, reducing the effect of preventing hot cracking. Therefore, Ca/S is set to the range of 2.0 to 4.0.
Ｎｂは、Ｃと結合してＮｂＣを形成し上述のように、結晶粒の粗大化を抑制することによって、低融点硫化物の粗大化を抑制し、熱間割れを防止する。顕著な熱間割れ防止効果は、上述したように、ＮｂＣが一定範囲の量になるようにＣおよびＮｂをコントロールすることで得られる。しかし、Ｎｂ含有量が０．３５％未満および０．８８％超えでは所望のＮｂＣ量が得られない。したがって、Ｎｂ含有量を０．３５～０．８８％とする。 Nb combines with C to form NbC, which, as mentioned above, inhibits the coarsening of crystal grains, thereby inhibiting the coarsening of low-melting-point sulfides and preventing hot cracking. As mentioned above, a significant effect in preventing hot cracking can be obtained by controlling C and Nb so that the amount of NbC is within a certain range. However, if the Nb content is less than 0.35% or more than 0.88%, the desired amount of NbC cannot be obtained. Therefore, the Nb content is set to 0.35-0.88%.
ＮｂＣは、上記のように結晶粒の粗大化を抑制する効果があり、その化学量論的な含有量は、Ｃ含有量を[Ｃ]、Ｎｂ含有量を[Ｎｂ]としたとき、[Ｃ]≧[Ｎｂ]×７．７４の場合、[Ｎｂ]×１．１３で表され、[Ｃ]＜[Ｎｂ]×７．７４の場合、[Ｃ]×８．７４で表される。この化学量論的なＮｂＣの含有量が０．４０％未満では割れ防止効果が少なく、また、１．０％超では、ＮｂＣが過剰となって却って熱間加工性が低下する。したがって、化学量論的なＮｂＣの含有量の範囲は０．４０～１．０％の範囲とする。 As mentioned above, NbC has the effect of suppressing the coarsening of crystal grains, and its stoichiometric content is expressed as [Nb] x 1.13 when [C] ≥ [Nb] x 7.74, where [C] is the C content and [Nb] is the Nb content, and is expressed as [C] x 8.74 when [C] < [Nb] x 7.74. If the stoichiometric NbC content is less than 0.40%, the crack prevention effect is small, and if it exceeds 1.0%, the NbC becomes excessive and the hot workability is deteriorated. Therefore, the stoichiometric NbC content range is set to 0.40-1.0%.
成分組成の残部は、Ｆｅおよび不可避的不純物である。不可避的不純物とは、本発明で規定する成分組成を有する鋼を工業的に製造する際に、原料や製造環境等から不可避的に混入するものをいう。 The balance of the composition is Fe and inevitable impurities. Inevitable impurities refer to substances that are inevitably mixed in from raw materials, the manufacturing environment, etc., when steel having the composition specified in this invention is industrially manufactured.
以上の化学成分を有する合金により、熱間加工性に優れた低熱膨張部材を得ることができる。 By using an alloy with the above chemical composition, it is possible to obtain a low thermal expansion part with excellent hot workability.
本発明の成分組成を有する低熱膨張合金は、低熱膨張のセラミックスや光学ガラス等と一体で使用することを意図しており、１０～４０℃における平均熱膨張係数が０．５×１０-6／℃以下である。 The low thermal expansion alloy having the composition of the present invention is intended to be used together with low thermal expansion ceramics, optical glass, etc., and has an average thermal expansion coefficient of 0.5×10 -6 /° C. or less at 10 to 40° C.
本発明の低熱膨張合金の製造に用いる装置および方法は特に限定されるものではなく、従来使用される装置および方法を用いることができる。鋳造されたインゴットを熱間加工後、所定の機械加工等により、低熱膨張部材を得ることができる。 The apparatus and method used to manufacture the low thermal expansion alloy of the present invention are not particularly limited, and conventional apparatus and methods can be used. After hot working the cast ingot, a low thermal expansion component can be obtained by a specified machining process, etc.
本発明の低熱膨張合金の熱間加工性は、サーメックマスター試験に代表される熱間加工再現試験における絞り値を測定することで評価できる、具体的には、本発明の低熱膨張合金は、９００℃における１ｓ-1以上の歪速度の引張試験で測定された絞り値が６０％以上であることが好ましい。 The hot workability of the low thermal expansion alloy of the present invention can be evaluated by measuring the reduction of area in a hot working reproduction test such as a THERMEC MASTER test. Specifically, the low thermal expansion alloy of the present invention preferably has a reduction of area of 60% or more as measured in a tensile test at 900°C and a strain rate of 1 s or more.
さらに、熱膨張係数をより低くするための熱処理を施してもよい。この熱処理を施す場合は、機械加工前、すなわち、熱間加工後に施す。具体的な熱処理条件は、熱間加工後の合金素材を、好ましくは７５０～１０５０℃、より好ましくは８５０～９５０℃に加熱して、素材の肉厚２５ｍｍ当り０．５～２ｈｒ保持した後、急冷する。冷却速度は１００℃／ｍｉｎ以上とする。 Furthermore, a heat treatment may be performed to further reduce the thermal expansion coefficient. If this heat treatment is performed, it is performed before machining, i.e., after hot working. The specific heat treatment conditions are to heat the alloy material after hot working to preferably 750 to 1050°C, more preferably 850 to 950°C, and hold for 0.5 to 2 hours per 25 mm of material thickness, and then rapidly cool. The cooling rate is 100°C/min or more.
低熱膨張化熱処理の後に、３００～３５０℃で、素材の肉厚２５ｍｍ当り１～４ｈｒ保持し、その後炉冷等の徐冷する応力除去焼きなましを施してもよい。 After the low thermal expansion heat treatment, the material may be held at 300-350°C for 1-4 hours per 25 mm of thickness, and then subjected to stress relief annealing, which involves slow cooling by furnace cooling or other methods.
大気溶解による表１に示す成分組成の溶湯を、φ１２０×２７０の鋳型に鋳造し、得られたインゴットを後述の評価試験用供試材とした。 The molten metal with the composition shown in Table 1 was melted in air and cast into a φ120×270 mold, and the resulting ingot was used as the test material for the evaluation tests described below.
合金の熱間加工性の評価は、インゴットを８５０℃で２ｈｒ保持後水冷し、さらに３２５℃で４ｈｒ保持後炉冷した後、φ１０ｍｍ×１００ｍｍの試験片を採取して、表２に示す条件で引張試験を行い、絞りを値測定して行った。測定結果を表１に示す。 The hot workability of the alloy was evaluated by holding the ingot at 850°C for 2 hours, water cooling, and then holding it at 325°C for another 4 hours and furnace cooling. Test pieces measuring φ10 mm x 100 mm were then taken and subjected to tensile testing under the conditions shown in Table 2, and the reduction in area was measured. The measurement results are shown in Table 1.
また、合金の熱間加工性の確認は、インゴットを□７５ｍｍ×５４０ｍｍに熱間鍛造した後、鍛造物を六面加工して表面スケール等を除去し、□７０ｍｍ×４００ｍｍの加工品とした後、表面の浸透探傷試験によって行った。熱間加工性の評価は、キズ等による指示模様が認められなかったものを「○」、指示模様が認められたものを「×」とした。さらに鍛造物を８５０℃で２ｈｒ保持後水冷し、さらに３２５℃で４ｈｒ保持後炉冷した後、φ６ｍｍ×５０ｍｍの熱膨張係数測定用の試験片を採取し、１０～４０℃間の平均熱膨張係数を測定した。これらの測定結果も表１に示す。 The hot workability of the alloy was confirmed by hot forging the ingot to a size of 75 mm x 540 mm, machining the forged product on all six sides to remove surface scale, and then forming a product of 70 mm x 400 mm. The surface was then subjected to a penetrant inspection. Hot workability was evaluated as follows: "Good" indicates that no indications due to scratches were observed, and "Poor" indicates that indications were observed. The forged product was then held at 850°C for 2 hours, water-cooled, and then held at 325°C for 4 hours, furnace-cooled. Test pieces of 6 mm x 50 mm in diameter were then taken for measuring the thermal expansion coefficient, and the average thermal expansion coefficient between 10 and 40°C was measured. The results of these measurements are also shown in Table 1.
表１に示すように、本発明の低熱膨張合金は、１０～４０℃間の平均熱膨張係数が０．５ｐｐｍ／℃以下であり、さらに９００℃での引張試験において、３．１ｓ-1という大きな歪速度で６０％以上の絞り値を示した。 As shown in Table 1, the low thermal expansion alloy of the present invention has an average thermal expansion coefficient of 0.5 ppm/°C or less between 10 and 40°C, and furthermore, in a tensile test at 900°C, it showed a reduction in area of 60% or more at a high strain rate of 3.1 s -1 .
これに対して比較例では、熱間加工性、熱膨張係数の少なくとも一方で目標の特性が得られなかった。 In contrast, the comparative examples did not achieve the target properties in terms of at least one of hot workability and thermal expansion coefficient.
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