JP2022132929A - Manufacturing method for raw material for turbine blade - Google Patents
Manufacturing method for raw material for turbine blade Download PDFInfo
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- 239000002994 raw material Substances 0.000 title abstract 4
- 238000010438 heat treatment Methods 0.000 claims abstract description 84
- 239000000463 material Substances 0.000 claims abstract description 82
- 238000001816 cooling Methods 0.000 claims abstract description 57
- 238000005242 forging Methods 0.000 claims abstract description 46
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- 229910001105 martensitic stainless steel Inorganic materials 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
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- 238000004881 precipitation hardening Methods 0.000 description 2
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- 238000009864 tensile test Methods 0.000 description 2
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Abstract
Description
本発明は、タービンブレード用素材の製造方法に関するものである。 TECHNICAL FIELD The present invention relates to a method for manufacturing turbine blade blanks.
高温環境下で使用されるタービンブレードは、熱間鍛造により所定の形状に成形され、要求された特性を満足するように種々の熱処理が施される。タービンブレードに用いられる材質としては、Ｎｉ基合金、Ｔｉ基合金及びＦｅ基合金等があり、それぞれ、適切な熱処理条件は異なるものとなる。このうち、ステンレス鋼等のＦｅ基合金についても、種々の熱処理が必要となり、多くの提案がなされている。例えば、特開２０１６－１６６４０９号公報（特許文献１）には、鍛造プリフォーム（熱間鍛造材）に対して、約２０００～２１００°Ｆ（約１０９３～１１４９℃）の溶体化処理と約６００°Ｆ（約３１５℃）の焼戻しを行うことが開示されている。また、特開２０１５－７４８２２号公報（特許文献２）には、熱間鍛造後のステンレス部材（熱間鍛造材）を１０００℃以上に加熱して溶体化処理を行い、冷却中のステンレス部材の温度差を小さくする冷却を行う発明がある。 Turbine blades used in a high-temperature environment are formed into a predetermined shape by hot forging and subjected to various heat treatments so as to satisfy required characteristics. Materials used for turbine blades include Ni-based alloys, Ti-based alloys, Fe-based alloys, and the like, and appropriate heat treatment conditions are different for each. Of these, Fe-based alloys such as stainless steel also require various heat treatments, and many proposals have been made. For example, Japanese Patent Application Laid-Open No. 2016-166409 (Patent Document 1) discloses that a forging preform (hot forged material) is subjected to solution treatment at about 2000 to 2100 ° F (about 1093 to 1149 ° C) and about 600 It is disclosed to perform a 0°F (approximately 315°C) temper. In addition, in Japanese Patent Application Laid-Open No. 2015-74822 (Patent Document 2), a stainless steel member (hot forged material) after hot forging is heated to 1000 ° C. or higher to perform solution treatment, and the stainless steel member during cooling is treated. There is an invention that performs cooling to reduce the temperature difference.
熱間鍛造で所望の形状に成形したＦｅ基合金製の熱間鍛造材を、溶体化処理（溶体化処理は「焼入れ」と称される場合があり、以後、本発明では「焼入れ」と記す）、焼戻しを行ってタービンブレード用素材とした場合、要求特性は満足しているものの、例えば、結晶粒径がやや大きかったり、強度と靭性のバランスがやや悪くなる傾向にあったりする問題があった。
前述したＦｅ基合金製のタービンブレード用素材の発明は、焼入れや焼入れ以降の熱処理条件を制御して、タービンブレードに要求される特性や形状に調整することを目的とするものであり、従来から行われてきた提案は、その殆どがこの焼入れや焼入れ以降の熱処理に着目するものである。
しかしながら、上記の問題を解決するには、焼入れ以前の製造条件も含めて適正化することが重要であるが、焼入れ以前、すなわち、熱間鍛造以降の製造条件の適正化については、検討が不十分であるのが現状である。
本発明の目的は、Ｆｅ基合金製のタービンブレード用素材の製造方法において、熱間鍛造以降の製造条件を適正化することで、タービンブレード用素材の結晶粒をより一層、均一微細化することが可能で、機械的特性を改善可能なタービンブレード用素材の製造方法を提供することである。
A hot forged material made of an Fe-based alloy formed into a desired shape by hot forging is subjected to a solution treatment (solution treatment may be referred to as "quenching", and hereinafter referred to as "quenching" in the present invention. ), when tempered and used as a material for turbine blades, although the required characteristics are satisfied, there are problems such as the grain size being slightly large and the balance between strength and toughness tending to be slightly poor. rice field.
The aforementioned invention of a turbine blade material made of an Fe-based alloy aims at adjusting the properties and shape required for turbine blades by controlling the conditions of quenching and heat treatment after quenching. Most of the proposals that have been made focus on this quenching and heat treatment after quenching.
However, in order to solve the above problem, it is important to optimize the manufacturing conditions including those before quenching. At present, this is sufficient.
An object of the present invention is to make the crystal grains of the turbine blade material more uniform and fine by optimizing the manufacturing conditions after hot forging in a method for manufacturing a turbine blade material made of an Fe-based alloy. The object of the present invention is to provide a method for manufacturing a turbine blade material capable of improving mechanical properties.
本発明は上述した課題に鑑みてなされたものである。
すなわち本発明は、Ｆｅ基合金製の荒地を１ブローの熱間鍛造によりタービンブレード形状に成形して熱間鍛造材とする熱間鍛造工程と、前記熱間鍛造材に４５０～９００℃の温度範囲で加熱保持後、冷却する第１熱処理工程と、前記第１熱処理工程後の第１熱処理材に、９８０～１０８０℃の温度範囲で加熱保持後、冷却する第２熱処理工程の後、５００～６００℃の温度範囲で加熱保持後、冷却する第３熱処理工程とを含むタービンブレード用素材の製造方法である。
本発明においては、第３熱処理工程を２回以上繰返すことが好ましい。
The present invention has been made in view of the problems described above.
That is, the present invention includes a hot forging step in which a rough ground made of an Fe-based alloy is formed into a turbine blade shape by hot forging in one blow to obtain a hot forged material, and a temperature of 450 to 900 ° C. is applied to the hot forged material. A first heat treatment step of cooling after heating and holding in the range, and a second heat treatment step of cooling after heating and holding in the temperature range of 980 to 1080 ° C. for the first heat treated material after the first heat treatment step. and a third heat treatment step of cooling after heating and holding in a temperature range of 600°C.
In the present invention, it is preferable to repeat the third heat treatment step two or more times.
本発明によれば、熱間鍛造以降の製造条件を適正化することで、タービンブレード用素材の結晶粒をより一層、均一微細化することが可能で、機械的特性を改善することができる。 According to the present invention, by optimizing the manufacturing conditions after hot forging, it is possible to make the crystal grains of the turbine blade material even more uniform and fine, and to improve the mechanical properties.
先ず、本発明で規定する用語について説明しておく。
本発明が対象とする「Ｆｅ基合金」とは、含有する成分のなかで、Ｆｅを最も含むものを言い、典型的な材質しては析出硬化型ステンレス鋼やマルテンサイト系ステンレス鋼の組成を有する合金である。また、本発明で言う「熱間鍛造材」とは、熱間鍛造により所定の形状に成形したものであって、第１熱処理工程に供する素材となるものである。例えば、熱間鍛造後にばり取り等の形状調整を行ったものも熱間鍛造材である。また、「タービンブレード用素材」とは、本発明で規定する第３熱処理工程を終了したものを言う。
以下、本発明について、製造工程の順に説明する。
First, terms defined in the present invention will be explained.
The "Fe-based alloy" targeted by the present invention refers to those containing the most Fe among the contained components, and typical materials include precipitation hardening stainless steel and martensitic stainless steel. It is an alloy with Further, the "hot forged material" referred to in the present invention is formed into a predetermined shape by hot forging, and is used as a material to be subjected to the first heat treatment step. For example, a hot forged material is also one that has undergone shape adjustment such as deburring after hot forging. Further, the term "turbine blade material" refers to a material that has undergone the third heat treatment step specified in the present invention.
Hereinafter, the present invention will be described in the order of manufacturing steps.
＜熱間鍛造工程＞
先ず、所定の形状に成形されたＦｅ基合金製の荒地を準備する。準備した荒地表面はガラス潤滑剤で被覆しておくのが好ましい。ガラス潤滑剤で被覆することで熱間鍛造用素材の保温効果や鍛造用素材と金型との摩擦係数を下げることによる潤滑性向上、加熱によるスケール生成の抑制などの利点がある。被覆するガラス潤滑剤の厚さは３００～４５０μｍ程度でよく、荒地全体に被覆するのが好ましい。そして、所定の温度に加熱する。熱間鍛造温度の範囲は、Ｆｅ基合金の組成によって、やや異なる場合があるが、析出硬化型ステンレス鋼やマルテンサイト系ステンレス鋼の場合であれば、おおよそ９５０～１１００℃の範囲であれば良い。
加熱後の荒地（鍛造用素材）を熱間鍛造装置の下型上に載置して、上型と下型とによってタービンブレード形状に成形して熱間鍛造材とする。用いる熱間鍛造装置は特に限定しないが、全長が４０インチ以上のタービンブレード用素材とするには、油圧式熱間鍛造装置であれば良い。油圧式熱間鍛造装置であれば、１ブロー（１回の押圧）でタービンブレード形状に成形を行うことが可能である。１ブローの熱間鍛造で成形すると鍛造条件が安定することで、多ヒート成形品と比較し、より安定した引張強度及び延性が得られる。また、複数回の加熱を行う必要がないため、粗大粒成長を抑えられ、結晶粒がより一層、均一微細なマルテンサイト組織とすることができ、タービンブレードで厳しく要求されている結晶粒度規定や機械的特性の改善に効果がある。また、１ブロー成形は多ヒート成形に比べ、生産性の向上や環境負荷低減の効果が得られるため、１ブローの熱間鍛造を適用する。
<Hot forging process>
First, a rough ground made of an Fe-based alloy formed into a predetermined shape is prepared. The prepared rough surface is preferably coated with a glass lubricant. By coating with glass lubricant, there are advantages such as the heat retention effect of the hot forging material, the lubricity improvement by lowering the friction coefficient between the forging material and the die, and the suppression of scale formation due to heating. The thickness of the glass lubricant to be coated may be about 300 to 450 μm, and it is preferable to cover the entire rough ground. Then, it is heated to a predetermined temperature. The range of hot forging temperature may vary slightly depending on the composition of the Fe-based alloy, but in the case of precipitation hardening stainless steel and martensitic stainless steel, the range of about 950 to 1100 ° C. is sufficient. .
The rough ground (forging material) after heating is placed on the lower die of the hot forging device, and formed into a turbine blade shape by the upper and lower dies to obtain a hot forged material. The hot forging device to be used is not particularly limited, but a hydraulic hot forging device may be used to obtain a turbine blade material having a total length of 40 inches or more. If it is a hydraulic hot forging device, it is possible to form a turbine blade shape with one blow (one press). Forming by one-blow hot forging stabilizes the forging conditions, so that more stable tensile strength and ductility can be obtained than multi-heat forging products. In addition, since it is not necessary to heat multiple times, the growth of coarse grains can be suppressed, and the grains can be made into a more uniform and fine martensite structure. Effective in improving mechanical properties. In addition, one-blow hot forging is applied because one-blow forming is more effective in improving productivity and reducing environmental load than multi-heat forming.
＜第１熱処理工程＞
次に、本発明では、前記熱間鍛造材に対して、４５０～９００℃℃の温度範囲で加熱保持後、冷却する第１熱処理工程を行う。タービンブレード形状に成形された熱間鍛造材はマルテンサイト変態が生じ、高強度、低靭性な状態となり、熱間鍛造ままで放置すると焼割れを生じる可能性がある。そのため、熱間鍛造終了後、熱間鍛造材の表面温度が５０～１５０℃となった熱間鍛造材に対して、第１熱処理工程を適用する。この第１熱処理工程の温度が４５０℃未満であると、焼割れを防止することができない。また、９００℃を超える温度域では鍛造割れ防止の効果は飽和する。また、９００℃を超える温度域では、第１熱処理工程において粒成長が生じる可能性があり、その粗大粒は第２熱処理以降も残存し、狙いの機械的特性が得られない場合がある。そのため、第１熱処理工程の温度範囲は４５０～９００℃とする。
本発明において、第１熱処理工程の加熱保持時間は特に規定しないが、おおよそ３～６時間であれば良い。また、鍛造後熱処理工程の冷却は、空冷または空冷よりも遅い冷却速度で冷却するのが好ましい。これは空冷より速い速度で冷却すると冷却速度が不均一となり熱間鍛造材に変形が生じる可能性がある。好ましくは、空冷よりも遅い冷却度の炉冷を適用するのが良い。炉冷であれば、熱間鍛造材の割れをより確実に防止しつつ、熱間鍛造材の変形も抑制することができる。なお、この第１熱処理工程後の中間素材を「第１熱処理材」と記す。
<First heat treatment step>
Next, in the present invention, the hot forged material is subjected to a first heat treatment step of heating and holding in a temperature range of 450 to 900° C. and then cooling. A hot forged material formed into a turbine blade shape undergoes martensite transformation, resulting in a state of high strength and low toughness, and quench cracks may occur if left as is. Therefore, the first heat treatment step is applied to the hot forged material whose surface temperature has reached 50 to 150° C. after hot forging is completed. If the temperature of the first heat treatment step is less than 450°C, quench cracking cannot be prevented. Moreover, the effect of preventing forging cracks is saturated in a temperature range exceeding 900°C. In addition, in the temperature range exceeding 900° C., grain growth may occur in the first heat treatment step, and the coarse grains may remain even after the second heat treatment, and the desired mechanical properties may not be obtained. Therefore, the temperature range of the first heat treatment step is set to 450 to 900.degree.
In the present invention, the heating and holding time in the first heat treatment step is not particularly specified, but it may be about 3 to 6 hours. Further, the cooling in the post-forging heat treatment step is preferably air cooling or cooling at a slower cooling rate than air cooling. This is because if the cooling rate is faster than air cooling, the cooling rate becomes uneven and deformation may occur in the hot forged material. Furnace cooling with a slower cooling rate than air cooling is preferably applied. Furnace cooling can more reliably prevent cracking of the hot forged material and also suppress deformation of the hot forged material. The intermediate material after the first heat treatment step is referred to as "first heat treated material".
この第１熱処理工程の温度範囲のうち、７００℃を超えて９００℃以下の温度範囲を選択すると、前述の熱間鍛造材の割れを防止する効果に加えて、熱間鍛造で生じた不均一な鍛造歪を低減させて、後述の第２熱処理工程以降に得られる結晶粒をより一層、均一微細化させることができ、より均一に機械的特性を改善することが可能となる。この７００～９００℃の温度範囲で行う第１熱処理工程を「高温側第１熱処理工程」と記す。この高温側第１熱処理工程の好ましい温度の下限は７５０℃であり、更に好ましくは７６５℃である。より好ましい温度の上限は８１０℃であり、更に好ましくは７９５℃である。この高温側第１熱処理工程を適用する場合の冷却速度は、空冷よりも遅い冷却度の炉冷を適用するのが良い。
なお、第１熱処理工程の温度範囲のうち、４５０～７００℃の範囲で行うものを「低温側第１熱処理工程」と記す。低温側第１熱処理工程は、前述の焼割れを防止することを主たる目的とするものである。焼割れを防止することを主たる目的とする場合、好ましい温度の下限は６２０℃であり、好ましい温度の上限は６８０℃である。この低温側第１熱処理工程を適用する場合の冷却速度は空冷または空冷よりも遅い炉冷でも差し支えない。
前述の高温側第１熱処理工程と低温側第１熱処理工程の選択は、目的に応じて適宜選択すれば良いが、例えば、第１熱処理工程の冷却を炉冷とした場合では、加熱炉を長時間占有することになる。特に、高温側第１熱処理工程を選択すると、加熱炉の占有時間が長くなるため、量産工程においては、加熱炉の占有時間も考慮して第１熱処理工程の処理温度を選択することが現実的である。なお、第１熱処理工程においては、例えば、低温側第１熱処理工程後に、高温側第１熱処理工程を組み合わせても差し支えない。
If a temperature range of more than 700 ° C. and 900 ° C. or less is selected from the temperature range of the first heat treatment step, in addition to the effect of preventing cracks in the hot forged material described above, unevenness caused by hot forging Forging distortion can be reduced, and the crystal grains obtained after the second heat treatment step, which will be described later, can be made more uniform and fine, and the mechanical properties can be improved more uniformly. The first heat treatment process performed in the temperature range of 700 to 900° C. is referred to as "high-temperature side first heat treatment process". A preferable lower limit of the temperature of the high temperature side first heat treatment step is 750°C, more preferably 765°C. A more preferable upper limit of the temperature is 810°C, more preferably 795°C. As for the cooling rate in the case of applying this high-temperature side first heat treatment step, it is preferable to apply furnace cooling with a cooling degree slower than that of air cooling.
Among the temperature range of the first heat treatment step, the one performed in the range of 450 to 700° C. is referred to as the “low temperature side first heat treatment step”. The primary purpose of the low temperature side first heat treatment step is to prevent the aforementioned quench cracks. When the main purpose is to prevent quench cracking, the preferred lower limit temperature is 620°C and the preferred upper limit temperature is 680°C. The cooling rate when applying the low-temperature side first heat treatment step may be air cooling or furnace cooling slower than air cooling.
The above-mentioned high-temperature side first heat treatment step and low-temperature side first heat treatment step may be selected as appropriate according to the purpose. will occupy your time. In particular, if the high temperature side first heat treatment step is selected, the occupancy time of the heating furnace becomes longer, so in the mass production process, it is realistic to select the treatment temperature of the first heat treatment step in consideration of the occupancy time of the heating furnace. is. In the first heat treatment step, for example, the first heat treatment step on the low temperature side may be combined with the first heat treatment step on the high temperature side.
＜第２熱処理工程（焼入れ）＞
本発明では、前記第１熱処理工程後の第１熱処理材に、９８０～１０８０℃の温度範囲で加熱保持後、冷却する第２熱処理工程を行う。この工程は前述した「焼入れ」と同じ処理であるため、以後、「焼入れ」と記す。
本発明において、焼入れ温度を９８０～１０８０℃としたのは、焼入れ温度が９８０℃未満になると炭化物が十分固溶しない温度領域であり、１０８０℃超えると高温保持により結晶粒粗大化や機械的特性の低下が生じるおそれがある。そのため、本発明では、焼入れを９８０～１０８０℃の温度範囲で加熱保持を行うものとする。好ましい焼入れ温度の下限は１０１０℃であり、好ましい焼入れ温度の上限は１０５０℃である。この焼入れにおいては、昇温時のヒートパターンを２段乃至４段の多段としても差し支えない。第１熱処理材がタービンブレード形状のものであるため、厚さの薄い翼部と厚さが厚い根部とが一体となっている。第１熱処理材を均一に近い状態で昇温させるには、多段で昇温するのが好ましく、例えば、４０インチ以上のタービンブレードとするものであれば、３段以上の多段とするのがよく、第１熱処理材の大きさによって、ヒートパターンを適宜変更すると良い。なお、焼入れの保持時間は特に規定しないが、おおよそ０．５～１．５時間であれば良い。なお、ここでいう加熱保持時間は最も高温（焼入れ温度）としたときの時間であり、焼入れ温度までの昇温途中で行う温度保持の時間は含めないこととする。
<Second heat treatment step (quenching)>
In the present invention, the first heat treated material after the first heat treatment step is subjected to a second heat treatment step of heating and holding at a temperature range of 980 to 1080° C. and then cooling. Since this process is the same as the above-described "quenching", it is hereinafter referred to as "quenching".
In the present invention, the quenching temperature is set to 980 to 1080 ° C. This is a temperature range in which carbides do not sufficiently dissolve when the quenching temperature is less than 980 ° C., and when the quenching temperature exceeds 1080 ° C., the grain coarsening and mechanical properties are caused by holding at a high temperature. may cause a decrease in Therefore, in the present invention, quenching is performed by heating and holding in the temperature range of 980 to 1080°C. A preferable lower limit of the quenching temperature is 1010°C, and a preferable upper limit of the quenching temperature is 1050°C. In this quenching, the heat pattern at the time of temperature rise may be a multi-stage of 2 to 4 stages. Since the first heat-treated material is in the shape of a turbine blade, the thin blade portion and the thick root portion are integrated. In order to raise the temperature of the first heat-treated material in a nearly uniform state, it is preferable to raise the temperature in multiple stages. , the heat pattern may be appropriately changed according to the size of the first heat treatment material. The holding time for quenching is not particularly specified, but may be about 0.5 to 1.5 hours. The heating and holding time referred to here is the time when the highest temperature (quenching temperature) is reached, and does not include the temperature holding time during the temperature rise to the quenching temperature.
また、この焼入れ工程（第２熱処理工程）の冷却は、第１熱処理材がタービンブレード形状のものであるため、厚さの薄い翼部と厚さが厚い根部とが一体となっている。そのため、この第１熱処理材の焼入れ時の冷却を行う際には、翼部と根部の冷却速度が不均一となることを避け、冷却完了までの冷却速度の均一化をはかるため、厚さの薄い翼部に断熱性を有する断熱材を被覆して、根部の冷却速度に翼部の冷却速度を近づけて、根部と翼部との温度差を小さくする冷却を行うのが良い。ここで用いる断熱材は、柔軟性のある無機繊維であることが好ましい。なお、本発明で言う「無機繊維」とは、ガラス繊維、セラミック繊維などを含み、断熱性に優れるセラミック繊維を選択するのが好ましい。セラミック繊維の中でも、例えば、カオウール（登録商標）などであれば、入手のし易く、また安価であり、冷却する翼部の厚さに応じて被覆する厚さの調整も容易であることから特に好ましい。
また、焼入れ時の冷却については、前述のように、９８０～１０８０℃の高温領域から、冷却速度を均一に近づける冷却を行うことから、断熱材で被覆した第１熱処理材の根部を空冷または空冷よりも速い冷却速度で冷却することとし、翼部は前記根部の冷却速度に近づけるように冷却速度を調整するのが好ましい。これは機械的特性のバラつきを抑え、特に強度と延性のバランスを整えるためである。なお、以後、焼入れ工程後（第２熱処理工程後）の中間素材を「焼入れ材」または「第２熱処理材」と記す。
Further, in the cooling in this quenching step (second heat treatment step), since the first heat treated material is in the shape of a turbine blade, the blade portion with a small thickness and the root portion with a large thickness are integrated. Therefore, when cooling the first heat-treated material during quenching, it is necessary to reduce the thickness in order to avoid unevenness in the cooling rate between the wing portion and the root portion and to make the cooling rate uniform until the cooling is completed. It is preferable to cover the thin wings with a heat insulating material having heat insulating properties so that the cooling rate of the wings approaches the cooling rate of the roots, thereby reducing the temperature difference between the roots and the wings. The heat insulating material used here is preferably a flexible inorganic fiber. The "inorganic fibers" used in the present invention include glass fibers, ceramic fibers, etc., and it is preferable to select ceramic fibers that are excellent in heat insulation. Among ceramic fibers, for example, Kaowool (registered trademark) is easy to obtain and inexpensive, and it is easy to adjust the thickness of the coating according to the thickness of the blade to be cooled. preferable.
In addition, as for cooling during quenching, as described above, cooling is performed from a high temperature range of 980 to 1080 ° C. so that the cooling rate approaches uniformity. It is preferable to adjust the cooling rate of the wing portion so as to approach the cooling rate of the root portion. This is to suppress variations in mechanical properties, especially to balance strength and ductility. Hereinafter, the intermediate material after the quenching process (after the second heat treatment process) will be referred to as "quenched material" or "second heat treated material".
＜第３熱処理工程（焼戻し）＞
本発明では、焼入れした焼入れ材に第３熱処理工程施す。これは「焼戻し」と言わることがあり、以後、「焼戻し」と記す。
本発明で焼戻し温度を５００～６００℃としたのは、この温度範囲に加熱保持することで、焼入れ後に残存した未変態オーステナイトのマルテンサイト化を促進すること、また、過飽和に固溶した炭素を炭化物として析出させ、強度と延性のバランスのよい鍛造材を得ることが目的である。焼戻し温度が５００℃未満であると、未変態オーステナイトのマルテンサイト化が促進されないという問題がある。一方、焼戻し温度が６００℃を超えると強度と延性のバランスが崩れるという問題がある。そのため、本発明では、焼戻しを５００～６００℃の温度範囲で加熱保持を行うものとする。好ましい焼戻し温度の下限は５４０℃であり、好ましい焼戻し温度の上限は５７０℃である。この焼戻しの昇温についても、前述した焼入れ同様に多段のヒートパターンとするのが好ましい。なお、焼戻しの保持時間は特に規定しないが、おおよそ２～５時間であれば良い。なお、ここでいう加熱保持時間は最も高温（焼戻し温度）としたときの時間であり、焼戻し温度までの昇温途中で行う温度保持の時間は含めないこととする。
また、この焼戻し工程の冷却は、空冷または空冷よりも遅い冷却速度で冷却するのが好ましい。これは強度と延性のバランスを整えるためである。好ましくは、空冷を行うのが良い。なお、焼戻し温度は、前述する焼入れ温度よりも低いことから、焼戻しの冷却時においては、前述した焼入れ時の冷却のように、厚さの薄い翼部について断熱性を有する断熱材で被覆することは必ずしも必要ではない。
<Third heat treatment step (tempering)>
In the present invention, the quenched quenched material is subjected to the third heat treatment process. This is sometimes referred to as "tempering" and will hereinafter be referred to as "tempering".
The reason why the tempering temperature is set to 500 to 600 ° C. in the present invention is that by heating and holding in this temperature range, the untransformed austenite remaining after quenching is promoted to martensite, and the supersaturated solid solution carbon is removed. The purpose is to obtain a forged material with a good balance of strength and ductility by precipitating it as carbide. If the tempering temperature is less than 500°C, there is a problem that conversion of untransformed austenite to martensite is not promoted. On the other hand, if the tempering temperature exceeds 600°C, there is a problem that the balance between strength and ductility is lost. Therefore, in the present invention, tempering is performed by heating and holding in the temperature range of 500 to 600°C. The preferred lower limit of tempering temperature is 540°C, and the preferred upper limit of tempering temperature is 570°C. As for the temperature rise for this tempering, it is preferable to use a multistage heat pattern as in the case of the quenching described above. The holding time for tempering is not particularly specified, but may be about 2 to 5 hours. The heating and holding time referred to here is the time when the temperature is set to the highest temperature (tempering temperature), and does not include the temperature holding time during the temperature rise to the tempering temperature.
Moreover, the cooling in this tempering step is preferably air cooling or cooling at a cooling rate slower than air cooling. This is to balance strength and ductility. Air cooling is preferred. In addition, since the tempering temperature is lower than the quenching temperature described above, when cooling for tempering, the thin wings should be covered with a heat insulating material having heat insulating properties, as in the cooling during quenching described above. is not necessary.
また、本発明においては、この焼戻しを２回以上繰返すことができる。２回以上繰り返すことで焼入れ後に残存した未変態オーステナイトのマルテンサイト化を確実に促進させ、未変態オーステナイトを限りなくゼロとするためである。そのため、焼戻しにおいては、２回以上繰り返すことが好ましい。なお、焼戻しを行う回数の上限は最大で３回であれば良い。３回を超えて焼戻しをおこなっても、前記の繰り返し焼戻しの効果がより一層高まることは期待できない。好ましくは２回で良い。
本発明によれば、熱間鍛造以降の製造条件を適正化することで、タービンブレード用素材の結晶粒をより一層、均一微細化し可能で、機械的特性を改善することができる。なお、本発明のタービンブレード用素材の製造方法は、マルテンサイト系ステンレス鋼の組成を有するものに有効である。前述の「マルテンサイト系ステンレス鋼」とは、前述した熱処理によってマルテンサイト組織とすることが可能で、マルテンサイト組織とすることで硬化させることが可能なＣｒを１０．５％以上含む鋼である。
Moreover, in the present invention, this tempering can be repeated twice or more. This is because by repeating the heat treatment two or more times, the untransformed austenite remaining after quenching is surely promoted to become martensite, and the amount of untransformed austenite is reduced to zero. Therefore, it is preferable to repeat tempering twice or more. In addition, the upper limit of the number of times of tempering should be 3 times at maximum. Even if tempering is performed more than 3 times, it cannot be expected that the effect of repeated tempering will be further enhanced. Twice is preferable.
According to the present invention, by optimizing the manufacturing conditions after hot forging, the crystal grains of the turbine blade material can be made more uniform and fine, and the mechanical properties can be improved. The method for producing a turbine blade material according to the present invention is effective for those having a composition of martensitic stainless steel. The above-mentioned "martensite stainless steel" is a steel containing 10.5% or more of Cr that can be formed into a martensite structure by the above-mentioned heat treatment and can be hardened by forming a martensite structure. .
以下に、本発明を実施例で詳しく説明する。
Ｆｅ基合金製の荒地として、マルテンサイト系ステンレス鋼（ＪＩＳ規格ＳＵＳ４０３の改良鋼）のＦｅ基合金製の荒地を準備した。荒地は、熱間鍛造にて所定の形状に成形した。前記の荒地を８０～９０℃に加熱し、荒地の表面全体にガラス潤滑剤を３００～４５０μｍ程度の厚さで被覆した。この荒地を９５０～１１００℃に加熱保持して鍛造用素材とした。
前記の鍛造用素材を油圧式熱間鍛造装置の下型上に載置して、上型と下型とによって１ブローの熱間鍛造で４０インチのタービンブレード形状に成形して本発明の熱間鍛造材（Ｎｏ．１）とした。
また、従来例として、前記と同じ組成のＦｅ基合金製の荒地を用いて、熱間型打鍛造と再加熱を複数回繰返して４０インチのタービンブレード形状に成形して従来例の熱間鍛造材（Ｎｏ．１１）とした。
EXAMPLES The present invention will be described in detail below with examples.
As the Fe-based alloy rough ground, a Fe-based alloy rough ground of martensitic stainless steel (improved steel of JIS standard SUS403) was prepared. The rough ground was formed into a predetermined shape by hot forging. The rough ground was heated to 80 to 90° C., and the entire surface of the rough ground was coated with a glass lubricant to a thickness of about 300 to 450 μm. This rough ground was heated and held at 950 to 1100° C. to obtain a forging material.
The forging material is placed on the lower die of a hydraulic hot forging device, and formed into a 40-inch turbine blade shape by one-blow hot forging with the upper die and the lower die. A forged material (No. 1) was used.
In addition, as a conventional example, hot die forging and reheating were repeated multiple times using a Fe-based alloy rough ground having the same composition as the above, and the conventional hot forging was performed to form a 40-inch turbine blade shape. material (No. 11).
前記の熱間鍛造材について、下記の表１に示す条件で熱処理を行いタービンブレード用素材とした。なお、本発明の第１熱処理工程は低温側第１熱処理工程とし、熱間鍛造終了後、熱間鍛造材の表面温度が５０～１５０℃の範囲であることを確認し、第１熱処理工程用の加熱炉に投入した。焼入れの昇温時のヒートパターンは３段の多段処理とし、１段目は７００～８００℃で０．５～２時間の保持、２段目は１０００℃で１５～３０分の保持後に、３段目（焼入れ温度）の１０３０℃に昇温した。１段目から３段目までの昇温速度は１００～１５０℃／時間とした。また、焼入れの冷却時は、翼部に断熱性を有する断熱材（カオウール）で被覆しつつ、その厚さを調整し、根部との冷却速度を均一化した。表１に示したのは焼入れ温度である。
また、焼戻しの昇温時のヒートパターンも３段の多段処理とし、１段目は３５０～４５０℃で０．５～２時間の保持、２段目は５１０～５４０℃で０．５～２時間の保持後に、３段目（焼戻し温度）の５４５℃（２回目は５６０℃）に昇温した。１段目から３段目までの昇温速度は５０～１００℃／時間とした。また、焼入れの冷却時は、そのまま空冷した。表１に示したのは焼戻し温度である。なお、表１中の「ＡＣ」は空冷、「ＦＣ」は炉冷である。
The above hot forged material was heat treated under the conditions shown in Table 1 below to obtain a turbine blade material. The first heat treatment step of the present invention is the low-temperature side first heat treatment step, and after hot forging is completed, it is confirmed that the surface temperature of the hot forged material is in the range of 50 to 150 ° C., and the first heat treatment step is performed. was put into the heating furnace. The heat pattern at the time of temperature rise in quenching is a multi-stage treatment of three stages, the first stage is held at 700 to 800 ° C. for 0.5 to 2 hours, and the second stage is held at 1000 ° C. for 15 to 30 minutes, followed by 3 steps. The temperature was raised to 1030° C. for the step (quenching temperature). The heating rate from the first stage to the third stage was 100 to 150° C./hour. During cooling during quenching, the wings were covered with a heat insulating material (kaowool) having heat insulating properties, and the thickness of the heat insulating material was adjusted to equalize the cooling rate with the root. Table 1 shows the quenching temperatures.
In addition, the heat pattern at the time of temperature rise in tempering is also a multistage treatment of three stages, the first stage is 350 to 450 ° C. and 0.5 to 2 hours, and the second stage is 510 to 540 ° C. and 0.5 to 2 hours. After the holding time, the temperature was raised to 545° C. (560° C. for the second time) in the third step (tempering temperature). The heating rate from the first stage to the third stage was 50 to 100° C./hour. Moreover, at the time of cooling for quenching, it was air-cooled as it was. Table 1 shows tempering temperatures. In addition, "AC" in Table 1 is air cooling, and "FC" is furnace cooling.
上述のタービンブレード用素材から引張試験片及びシャルピー衝撃試験片を採取し、ＡＳＴＭ－Ａ３７０に則って機械試験を行った。試験片の採取位置は、引張試験片は根部及び翼部の製品厚みの中心とし、シャルピー衝撃試験片は根部の製品厚みの中心とし、その位置から試験片を採取した。機械試験結果を表２に示す。
表２に示すように本発明のタービンブレード用素材の０．２％耐力、引張強さ、伸び及び絞りは、従来例とほぼ同じ結果となった。タービンブレード用素材の根部の衝撃値については、４０Ｊ以上に大幅に改善された。
A tensile test piece and a Charpy impact test piece were taken from the turbine blade material described above, and a mechanical test was performed according to ASTM-A370. The test pieces were taken from the center of the product thickness of the root and wing portions for the tensile test pieces, and the center of the product thickness of the root portion for the Charpy impact test pieces. Table 2 shows the mechanical test results.
As shown in Table 2, the 0.2% proof stress, tensile strength, elongation and area of reduction of the turbine blade material of the present invention were almost the same as those of the conventional example. The root impact value of the turbine blade material was greatly improved to 40 J or more.
本発明のタービンブレード用素材（Ｎｏ．１）と従来例のタービンブレード用素材（Ｎｏ．１１）の断面金属組織を図１と図２にそれぞれ示す。本発明及び従来例共に金属組織はマルテンサイト組織を呈しているため、結晶粒度番号は旧オーステナイト粒界で読み取った。結晶粒度番号は、その数値が大きいほど結晶粒が小さく、ＡＳＴＭ－Ｅ１１２の規定にしたがって測定した。図１に示すように、本発明のタービンブレード用素材の平均結晶粒度番号は６．０～７．０であるのに対し、図２で示した従来例のタービンブレード用素材の平均結晶粒度番号は４．５～５．０であった。また、最大結晶粒度番号は、本発明のタービンブレード用素材が４．０～５．０であるのに対して、従来例のタービンブレード用素材は３．０であった。この結果から、本発明のタービンブレード用素材の方が、平均結晶粒度番号及び最大結晶粒度番号ともに、微細となっていることを確認した。なお、金属組織観察用試験片の採取位置はタービンブレード用素材の根部、翼部の製品厚みの中心である。
本発明は１ブローの熱間鍛造によりタービンブレード形状に成形したため、型打鍛造と再加熱を複数回繰返してタービンブレード形状に成形した従来例と比較して熱間鍛造過程における結晶粒成長を抑えることができる。そして、適切な第１熱処理工程、第２熱処理工程および第３熱処理工程を行うことで、タービンブレード用素材の平均結晶粒度番号は５．０より細粒となり、最大結晶粒度においても３．５を下回る範囲まで粗大化することを抑制でき、より微細な結晶粒径とすることができる。これらのことによって、結晶粒が粗大化することなく均一微細であったため、タービンブレード用素材の衝撃値が大幅に改善されたと考えられる。
1 and 2 show cross-sectional metallographic structures of a turbine blade material (No. 1) of the present invention and a conventional turbine blade material (No. 11), respectively. Since the metallographic structure of both the present invention and the conventional example exhibits a martensite structure, the grain size number was read at the prior austenite grain boundary. The larger the grain size number, the smaller the grain, and was measured according to ASTM-E112. As shown in FIG. 1, the average grain size number of the turbine blade material of the present invention is 6.0 to 7.0, whereas the average grain size number of the conventional turbine blade material shown in FIG. was 4.5-5.0. Further, the maximum grain size number of the turbine blade material of the present invention was 4.0 to 5.0, whereas the conventional turbine blade material was 3.0. From these results, it was confirmed that the turbine blade material of the present invention has finer grains in both the average grain size number and the maximum grain size number. The position of the specimen for metallographic observation was taken at the center of the product thickness of the root portion and blade portion of the turbine blade material.
In the present invention, since the turbine blade shape is formed by one-blow hot forging, the grain growth in the hot forging process is suppressed compared to the conventional example in which die forging and reheating are repeated multiple times to form the turbine blade shape. be able to. By appropriately performing the first heat treatment step, the second heat treatment step and the third heat treatment step, the average grain size number of the turbine blade material becomes finer than 5.0, and the maximum grain size is 3.5. It is possible to suppress coarsening to a lower range, and to obtain a finer crystal grain size. As a result of these factors, the crystal grains were uniform and fine without coarsening, and it is believed that the impact value of the turbine blade material was greatly improved.
以上、説明するように、本発明によれば、Ｆｅ基合金製のタービンブレード用素材の製造方法において、熱間鍛造以降の製造条件を適正化することで、タービンブレード用素材の結晶粒をより一層、均一微細化し可能で、機械的特性を改善可能であることが分かる。
As described above, according to the present invention, in the method for producing a turbine blade material made of an Fe-based alloy, by optimizing the production conditions after hot forging, the crystal grains of the turbine blade material are further reduced. It can be seen that the particles can be made even more uniform and the mechanical properties can be improved.
Claims (2)
前記熱間鍛造材に４５０～９００℃の温度範囲で加熱保持後、冷却する第１熱処理工程と、
前記第１熱処理工程後の第１熱処理材に、９８０～１０８０℃の温度範囲で加熱保持後、冷却する第２熱処理工程の後、５００～６００℃の温度範囲で加熱保持後、冷却する第３熱処理工程と、
を含むタービンブレード用素材の製造方法。 A hot forging step of forming a rough ground made of an Fe-based alloy into a turbine blade shape by hot forging in one blow to obtain a hot forged material;
A first heat treatment step of cooling the hot forged material after heating and holding at a temperature range of 450 to 900 ° C.;
After the first heat-treated material after the first heat treatment step, after the second heat treatment step of heating and holding in a temperature range of 980 to 1080 ° C., cooling, after heating and holding in a temperature range of 500 to 600 ° C. a heat treatment step;
A method of manufacturing a turbine blade blank comprising:
The method for manufacturing a turbine blade material according to claim 1, wherein the third heat treatment step is repeated two or more times.
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| JP2021031679A JP2022132929A (en) | 2021-03-01 | 2021-03-01 | Manufacturing method for raw material for turbine blade |
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