JP4061257B2 - Titanium alloy for heating wire and method for producing the same - Google Patents
Titanium alloy for heating wire and method for producing the same Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims description 39
- 229910001069 Ti alloy Inorganic materials 0.000 title claims description 24
- 238000004519 manufacturing process Methods 0.000 title claims description 7
- 230000009466 transformation Effects 0.000 claims description 19
- 239000010936 titanium Substances 0.000 claims description 12
- 229910045601 alloy Inorganic materials 0.000 claims description 10
- 239000000956 alloy Substances 0.000 claims description 10
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 claims 1
- 239000010959 steel Substances 0.000 claims 1
- 238000000137 annealing Methods 0.000 description 18
- 239000000463 material Substances 0.000 description 14
- 238000012360 testing method Methods 0.000 description 11
- 229910001120 nichrome Inorganic materials 0.000 description 10
- 238000005491 wire drawing Methods 0.000 description 5
- 229910018084 Al-Fe Inorganic materials 0.000 description 4
- 229910018192 Al—Fe Inorganic materials 0.000 description 4
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- 238000009864 tensile test Methods 0.000 description 4
- 229910000883 Ti6Al4V Inorganic materials 0.000 description 3
- 229910000765 intermetallic Inorganic materials 0.000 description 3
- 229910001040 Beta-titanium Inorganic materials 0.000 description 2
- 229910000599 Cr alloy Inorganic materials 0.000 description 2
- 229910002593 Fe-Ti Inorganic materials 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- 229910010169 TiCr Inorganic materials 0.000 description 1
- 229910010389 TiMn Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000010622 cold drawing Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 239000013065 commercial product Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000000113 differential scanning calorimetry Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
Description
本発明は、電気抵抗が高く、軽量で、通電時に発熱する電熱線用チタン合金に関する。 The present invention relates to a titanium alloy for a heating wire that has high electrical resistance, is lightweight, and generates heat when energized.
現在、一般家庭用電気製品から工業用加熱設備等の電熱線には、主にＮｉ−２０％Ｃｒ合金であるニクロム線が用いられている。これは、ニクロム線の室温から５００℃における電気抵抗が約１．０〜１．１μΩｍであり、室温強度及び高温強度が高いためである。
しかし、ニクロム線の電気抵抗は電熱線として用いるには十分とはいえず、密度も８．４×１０3 ｋｇ／ｍ3 と大きいため、発熱体の重量が重くなる。この電熱線のような用途には、ニクロム線よりも電気抵抗が高く、比強度が高いＴｉ−６Ａｌ−４Ｖ合金が適しているが、Ｔｉ−６Ａｌ−４Ｖ合金は、原料のＶが高価であり、また加工性が悪いため、直径１ｍｍ以下の線材に加工する際に、伸線と焼鈍とを何回も繰り返すことが必要であり、コストが高くなる。
At present, nichrome wire, which is a Ni-20% Cr alloy, is mainly used as a heating wire for general household electric appliances to industrial heating equipment. This is because the nichrome wire has an electric resistance of about 1.0 to 1.1 μΩm from room temperature to 500 ° C., and has high room temperature strength and high temperature strength.
However, the electric resistance of the nichrome wire is not sufficient for use as a heating wire, and the density is as large as 8.4 × 10 3 kg / m 3 , so that the heating element becomes heavy. For applications such as heating wires, Ti-6Al-4V alloys with higher electrical resistance and higher specific strength than nichrome wires are suitable, but Ti-6Al-4V alloys are expensive for the raw material V. Moreover, since workability is poor, it is necessary to repeat wire drawing and annealing many times when processing into a wire having a diameter of 1 mm or less, resulting in an increase in cost.
このような問題に対して、冷間加工性に優れた、Ｔｉ−Ａｌ−Ｍｏ−Ｃｒ系の高電気抵抗βチタン合金及びこれを用いた電磁調理器が提案されている（例えば特許文献１）。しかしこのβチタン合金は、ＡＳＴＭ Ｂ ７６−６５［１９７５］の、通電・休止の繰返し試験において抵抗変化が１０％に達するまでの時間が短いという問題があった。これは、準安定β型チタン合金は４００℃程度でα相が析出し、電熱線として５００℃程度で３００時間以上の長時間の使用により、体積分率で５０％にも及ぶα相が析出して電気抵抗が変化するためである。
本発明は、軽量で、長時間使用した際の電気抵抗の変化が小さい、安価なチタン電熱線及びその製造方法を提供するものである。 The present invention provides an inexpensive titanium heating wire that is lightweight and has a small change in electrical resistance when used for a long time, and a method for producing the same.
本発明者は、電気抵抗が大きく、比強度が高い各種チタン合金の室温〜５００℃における電気抵抗を測定し、長時間通電時の電気抵抗の変化に及ぼす成分及びミクロ組織の影響について検討を行い、Ｔｉ−Ａｌ−Ｆｅ合金の組織が安定であり、長時間使用時の電気抵抗の劣化が小さいことを見出した。 The present inventor measured the electrical resistance of various titanium alloys having high electrical resistance and high specific strength at room temperature to 500 ° C., and examined the influence of components and microstructure on the change in electrical resistance when energized for a long time. It has been found that the structure of the Ti—Al—Fe alloy is stable and the electrical resistance is less deteriorated when used for a long time.
本発明はこのような知見に基づくものであり、その要旨とするところは以下のとおりである。
（１） 質量％で、
Ａｌ：４．５〜５．５％、 Ｆｅ：０．４〜２．２％
を含有し、残部がＴｉ及び不可避的不純物からなることを特徴とする電熱線用チタン合金。
（２） 質量％でさらに、
Ｎｉ：０．０５〜０．１５％、 Ｃｒ：０．０５〜０．２５％、
Ｍｎ：０．０５〜０．２５％
の１種又は２種以上を含有し、Ｆｅ＋Ｎｉ＋Ｃｒ＋Ｍｎ：０．４〜２．２％を満足することを特徴とする請求項１記載の電熱線用チタン合金。
（３） ミクロ組織が等軸晶のα相とβ相からなり、β相の面積率が５〜３０％であり、残部がα相であることを特徴とする前記（１）又は（２）の電熱線用チタン合金。
（４） 室温〜５００℃での比抵抗が１．６０μΩｍ以上、５００℃での０．２％耐力が４００ＭＰａ以上であることを特徴とする前記（１）〜（３）の何れか１項に記載の電熱線用チタン合金。
（５） 前記（１）又は（２）記載の成分からなるチタン合金を溶解、鋳造し、加熱して、β変態点以下の温度で熱間加工し、β変態点以下の温度で熱間加工材焼鈍した後、冷間加工し、β変態点以下の温度で冷間加工材焼鈍することを特徴とする前記（１）〜（４）の何れか１項に記載の電熱線用チタン合金を製造する方法。
The present invention is based on such knowledge, and the gist thereof is as follows.
(1) In mass%,
Al: 4.5 to 5.5%, Fe: 0.4 to 2.2%
And a balance of Ti and inevitable impurities, and a titanium alloy for heating wire.
(2) Further in mass%,
Ni: 0.05 to 0.15%, Cr: 0.05 to 0.25%,
Mn: 0.05 to 0.25%
The titanium alloy for heating wires according to claim 1, wherein one or more of the following are contained and the content of Fe + Ni + Cr + Mn: 0.4 to 2.2% is satisfied.
(3) The microstructure (1) or (2), wherein the microstructure is composed of an equiaxed α phase and β phase, the β phase area ratio is 5 to 30%, and the remainder is the α phase. Titanium alloy for heating wire.
(4) The specific resistance from room temperature to 500 ° C. is 1.60 μΩm or more, and the 0.2% proof stress at 500 ° C. is 400 MPa or more. The titanium alloy for heating wires as described.
(5) The titanium alloy composed of the component described in (1) or (2) is melted, cast, heated, hot-worked at a temperature below the β transformation point, and hot-worked at a temperature below the β transformation point. The titanium alloy for heating wire according to any one of (1) to (4), wherein the titanium alloy for heating wire according to any one of the above (1) to (4) is subjected to cold working and annealing at a temperature not higher than the β transformation point. How to manufacture.
本発明によれば、軽量で電気抵抗が高く、長時間使用時の抵抗変化が小さいチタン合金電熱線を安価に提供することが可能になり、産業上の貢献が極めて顕著である。 According to the present invention, it is possible to provide a titanium alloy heating wire that is lightweight, has a high electrical resistance, and has a small resistance change when used for a long time at low cost, and the industrial contribution is extremely remarkable.
α相とβ相からなり、電気抵抗が高いチタン合金を電熱線として使用する場合、５００℃程度の高温で長時間、少なくとも３００時間程度、使用しても電気抵抗が変化しないことが重要である。本発明者は、成分、熱間加工時の加熱温度や焼鈍温度を変えてＴｉ−Ａｌ−Ｆｅ合金を製造し、５００℃で２００〜５００時間加熱した後の電気抵抗及びミクロ組織の変化を調査した。 When a titanium alloy consisting of an α phase and a β phase and having a high electric resistance is used as a heating wire, it is important that the electric resistance does not change even when used at a high temperature of about 500 ° C. for a long time, at least about 300 hours. . The present inventor manufactured Ti-Al-Fe alloys by changing the components, heating temperature and annealing temperature during hot working, and investigated changes in electrical resistance and microstructure after heating at 500 ° C for 200 to 500 hours. did.
その結果、Ｔｉ−４．５〜５．５％Ａｌ−０．４〜２．２％Ｆｅ合金は、５００℃での長時間の加熱後の電気抵抗の変化が小さく、特にミクロ組織が、面積率が３０％以内の等軸晶のβ相と残部が等軸晶のα相からなるチタン合金は、長時間使用される電熱線に好適であることが判明した。 As a result, the Ti-4.5 to 5.5% Al-0.4 to 2.2% Fe alloy has a small change in electric resistance after long-time heating at 500 ° C. It has been found that a titanium alloy consisting of an equiaxed β-phase with a rate of 30% or less and an equiaxed α-phase in the balance is suitable for heating wires used for a long time.
Ｔｉ−Ａｌ−Ｆｅ合金を５００℃程度で長時間加熱した際に電気抵抗を劣化させる原因として、Ｆｅ−Ｔｉの金属間化合物の析出、Ｔｉ3 Ａｌの短範囲秩序化が考えられる。しかし、Ｆｅ−Ｔｉの金属間化合物は非常に微細で、量も少なく、電気抵抗への影響は小さいため、電気抵抗を低下させる原因は、Ｔｉ3 Ａｌの短範囲秩序化である可能性が高い。そのため、Ａｌの含有量を適正な範囲とすることで、長時間加熱後の電気抵抗の劣化を抑制することができると考えられる。 Possible causes of electrical resistance degradation when a Ti—Al—Fe alloy is heated at about 500 ° C. for a long time include precipitation of Fe—Ti intermetallic compounds and short range ordering of Ti 3 Al. However, since the Fe-Ti intermetallic compound is very fine, the amount is small, and the influence on the electric resistance is small, the cause of lowering the electric resistance is likely to be the short range ordering of Ti 3 Al. . Therefore, it is thought that deterioration of electrical resistance after heating for a long time can be suppressed by setting the Al content within an appropriate range.
また、β相の面積率を３０％以内とすることが電気抵抗の劣化の抑制に有効である理由は、詳細は不明であるが、Ａｌの固溶量が少ないβ相の量を少なくすることにより、α相へのＡｌの濃化が抑制されて、Ｔｉ3 Ａｌの短範囲秩序化が抑制された可能性がある。 The reason why the area ratio of the β phase is within 30% is effective in suppressing the deterioration of electrical resistance is unknown in detail, but the amount of β phase with a small amount of Al solid solution should be reduced. As a result, the concentration of Al in the α phase may be suppressed, and the short range ordering of Ti 3 Al may be suppressed.
以下、本発明について詳細に説明する。
Ａｌは、チタンのα相を安定化する元素であり、電気抵抗を増大させる元素である。室温における電気抵抗をニクロム線の電気抵抗の約１．５倍、即ち１．６μΩｍ以上にするためには、Ａｌを４．５％以上添加することが必要である。一方、Ａｌを５．５％超添加すると、５００℃で３００時間以上加熱した後の電気抵抗が低下し、また、熱間加工時の変形抵抗が上昇して延性を損なうため、Ａｌの添加量の上限を５．５％以下とした。
Hereinafter, the present invention will be described in detail.
Al is an element that stabilizes the α phase of titanium and is an element that increases electrical resistance. In order to make the electric resistance at room temperature about 1.5 times the electric resistance of nichrome wire, that is, 1.6 μΩm or more, it is necessary to add Al 4.5% or more. On the other hand, if Al is added in excess of 5.5%, the electrical resistance after heating at 500 ° C. for 300 hours or more is lowered, and the deformation resistance during hot working is increased to impair ductility. Was made 5.5% or less.
Ｆｅは、チタンのβ相を安定化する元素であり、Ａｌと複合添加することにより強度を向上する元素である。チタンを高強度化し、特に５００℃における０．２％耐力を４００ＭＰａ以上とするには、Ｆｅを０．４％以上添加することが必要である。一方、Ｆｅを２．２％超添加すると延性が低下し、冷間加工性が低下するため、Ｆｅの添加量の上限を２．２％以下とした。 Fe is an element that stabilizes the β phase of titanium, and is an element that improves the strength by being added in combination with Al. In order to increase the strength of titanium and in particular to make the 0.2% proof stress at 500 ° C. 400 MPa or more, it is necessary to add 0.4% or more of Fe. On the other hand, when Fe is added in excess of 2.2%, the ductility is lowered and the cold workability is lowered. Therefore, the upper limit of the amount of Fe is set to 2.2% or less.
更に、Ｎｉ，Ｃｒ，Ｍｎの１種又は２種以上を含有しても良い。
Ｎｉ，Ｃｒ，Ｍｎは、何れもＦｅと同様の効果を有する元素であり、この効果を得るには、Ｎｉ，Ｃｒ，Ｍｎの添加量の下限をそれぞれ０．０５％以上とすることが好ましい。一方、Ｎｉ，Ｃｒ，Ｍｎの添加量がそれぞれ０．１５％、０．２５％、０．２５％を超えると、金属間化合物相、例えばＴｉ2 Ｎｉ，ＴｉＣｒ2 ，ＴｉＭｎなどを生成し、冷間加工性が低下する。したがってＮｉ，Ｃｒ，Ｍｎの添加量を、それぞれ０．０５〜０．１５％、０．０５〜０．２５％、０．０５〜０．２５％とすることが好ましい。
また、Ｎｉ，Ｃｒ，Ｍｎの１種又は２種以上を添加する場合には、Ｆｅ，Ｎｉ，Ｃｒ，Ｍｎの総量は０．４〜２．２％とすることが好ましい。その理由はＦｅを単独で添加する場合と同様である。
Furthermore, you may contain 1 type, or 2 or more types of Ni, Cr, and Mn.
Ni, Cr and Mn are all elements having the same effect as Fe, and in order to obtain this effect, the lower limit of the amount of Ni, Cr and Mn added is preferably 0.05% or more. On the other hand, when the addition amounts of Ni, Cr, and Mn exceed 0.15%, 0.25%, and 0.25%, respectively, an intermetallic compound phase such as Ti 2 Ni, TiCr 2 , and TiMn is generated and cooled. Interworkability is reduced. Therefore, it is preferable that the addition amounts of Ni, Cr, and Mn be 0.05 to 0.15%, 0.05 to 0.25%, and 0.05 to 0.25%, respectively.
Moreover, when adding 1 type, or 2 or more types of Ni, Cr, Mn, it is preferable that the total amount of Fe, Ni, Cr, Mn shall be 0.4 to 2.2%. The reason is the same as in the case of adding Fe alone.
本発明の電熱線用チタン合金は、最密六方晶構造のα相と体心立方晶構造のβ相からなる。α相及びβ相は両者とも等軸晶であるが、エッチングを硝酸と沸酸の混合溶液を用いて行い、光学顕微鏡によりミクロ組織を観察すると、α相は白色、β相は灰色に見えるため、判別することができる。 The titanium alloy for heating wire of the present invention comprises a close-packed hexagonal structure α phase and a body-centered cubic structure β phase. The α and β phases are both equiaxed, but when the etching is performed using a mixed solution of nitric acid and hydrofluoric acid and the microstructure is observed with an optical microscope, the α phase appears white and the β phase appears gray. Can be discriminated.
β相の面積率は、５％を下回ると５００℃における強度がやや低下し、３０％を超えると室温における強度がやや上昇し、室温での加工が困難になることがある。したがって、β相は５〜３０％であることが好ましい。β相の面積率の更に好ましい上限は２０％以下である。なおβ相の面積率は、光学顕微鏡を用いて撮影した組織写真を画像解析して求めることができる。 If the area ratio of the β phase is less than 5%, the strength at 500 ° C. is slightly decreased, and if it exceeds 30%, the strength at room temperature is slightly increased, and processing at room temperature may be difficult. Therefore, the β phase is preferably 5 to 30%. A more preferable upper limit of the area ratio of the β phase is 20% or less. The area ratio of the β phase can be obtained by image analysis of a tissue photograph taken with an optical microscope.
室温〜５００℃の比抵抗は、この温度範囲での任意の比抵抗を意味するものであり、１．６０μΩｍ以上にすれば、同等の電流値で、ニクロム線の２倍以上の発熱量が得られる。比抵抗の上限は規定しないが、通常は下限の約１．１５倍以内、即ち１．８４μΩｍ以下である。 The specific resistance at room temperature to 500 ° C means any specific resistance in this temperature range. If it is set to 1.60 μΩm or more, a calorific value more than twice that of nichrome wire can be obtained with an equivalent current value. It is done. Although the upper limit of the specific resistance is not specified, it is usually within about 1.15 times the lower limit, that is, 1.84 μΩm or less.
電熱線は、一般にコイル状に加工されて用いられるが、電流が流れるため導電性のある支持体を設けることが出来ない。したがって、実用上十分な長さの端子間距離が得られる電熱線コイルとするためには、ある程度の強度が要求される。本発明の電熱線用チタン合金では、室温における０．２％耐力と５００℃における０．２％耐力は比例しているため、５００℃における０．２％耐力を規定することが好ましい。
５００℃における０．２％耐力は、実用上十分な端子間距離の電熱線コイルを製造するためには、４００ＭＰａ以上であることが好ましい。また、５００℃における０．２％耐力の上限は、５００ＭＰａ以下とすることが好ましいが、これは室温での加工性を十分に加工するためである。
The heating wire is generally used after being processed into a coil shape. However, since a current flows, a conductive support cannot be provided. Therefore, a certain level of strength is required to obtain a heating wire coil that can provide a practically sufficient distance between terminals. In the titanium alloy for heating wire of the present invention, the 0.2% proof stress at room temperature is proportional to the 0.2% proof strength at 500 ° C., so it is preferable to define the 0.2% proof strength at 500 ° C.
The 0.2% proof stress at 500 ° C. is preferably 400 MPa or more in order to produce a heating wire coil having a practically sufficient distance between terminals. Further, the upper limit of 0.2% proof stress at 500 ° C. is preferably 500 MPa or less, which is to sufficiently process the workability at room temperature.
本発明の電熱線用チタン合金の製造方法は、溶解、鋳造、熱間加工、熱間加工材焼鈍、冷間加工、冷間加工材焼鈍からなる。冷間加工及び冷間加工材焼鈍は複数回繰り返しても良い。なお、線材を製造する場合には、熱間加工を熱間線材圧延とし、冷間加工を伸線加工とすれば良い。また板材を製造する場合には、熱間加工を熱間圧延とし、冷間加工を冷間圧延とすれば良い。 The manufacturing method of the titanium alloy for heating wires of this invention consists of melt | dissolution, casting, hot working, hot work material annealing, cold work, and cold work material annealing. Cold work and cold work material annealing may be repeated a plurality of times. In addition, when manufacturing a wire, what is necessary is just to make hot work into hot wire rolling and to make cold work into wire drawing. Moreover, when manufacturing a board | plate material, what is necessary is just to make hot processing into hot rolling and to make cold processing into cold rolling.
本発明は、熱間加工の加熱温度、熱延加工材焼鈍、冷間加工材焼鈍をβ変態点以下で行うものであるが、本発明において、β変態点とは、ミクロ組織がα相とβ相の２相組織からβ相単層に変態する温度であり、２相組織の上限温度と定義する。したがって、β変態点超ではβ相単相、β変態点以下ではα相とβ相の２相組織となる。β変態点は示差走査熱量分析装置により測定できる。 In the present invention, the heating temperature of hot working, hot-rolled material annealing, and cold-worked material annealing are performed at or below the β transformation point. In the present invention, the β transformation point means that the microstructure is the α phase. This is a temperature at which a β-phase two-phase structure is transformed into a β-phase monolayer, and is defined as an upper limit temperature of the two-phase structure. Accordingly, a β-phase single phase is formed above the β transformation point, and a two-phase structure of α phase and β phase is formed below the β transformation point. The β transformation point can be measured with a differential scanning calorimeter.
熱間加工の加熱温度は、熱間加工をβ変態点以下で行うために、材料全体が均一に加工される温度として８５０〜９５０℃が好ましい。これは、伸び・絞りを向上させるためである。熱間加工をβ変態点以下の２相領域で行うと、ミクロ組織は等軸のα相とβ相の混合組織となる。このようなミクロ組織からなるチタン合金は、延性・加工性に優れ、伸線加工の際に割れ・断線を生じ難い。一方、熱間加工をβ変態点以上で行うと、ミクロ組織は針状のα相と等軸のβ相の混合組織となり、延性が低下する。なお、熱間加工も８５０〜９５０℃の範囲で行うことが好ましい。 The heating temperature for hot working is preferably 850 to 950 ° C. as the temperature at which the entire material is uniformly processed in order to perform hot working at the β transformation point or lower. This is to improve the elongation / drawing. When hot working is performed in a two-phase region below the β transformation point, the microstructure becomes a mixed structure of equiaxed α and β phases. A titanium alloy having such a microstructure is excellent in ductility and workability, and is not easily cracked or disconnected during wire drawing. On the other hand, when hot working is performed at the β transformation point or higher, the microstructure becomes a mixed structure of acicular α phase and equiaxed β phase, and ductility decreases. In addition, it is preferable to perform hot processing in the range of 850-950 degreeC.
熱間加工後、β変態点以下の温度で熱間加工材焼鈍により熱間加工組織を再結晶させる。これは、β変態点超の温度で焼鈍するとα相がβ相に変態して、結晶粒が粗大化し易くなり、電気抵抗、強度が低下するためである。熱間加工材焼鈍の焼鈍温度は、β変態点以下であれば等軸α相とβ相の混合組織が得られるが、粗粒化させず、加工組織を完全に再結晶させる温度として、７００〜８００℃が好ましい。熱間加工材焼鈍の保持時間は、０．５時間未満では再結晶が不十分になることがあり、２時間を超えると粗粒化することがあるため、０．５〜２時間が好ましい。 After hot working, the hot work structure is recrystallized by annealing the hot work material at a temperature equal to or lower than the β transformation point. This is because if the annealing is performed at a temperature higher than the β transformation point, the α phase is transformed into the β phase, the crystal grains are easily coarsened, and the electrical resistance and strength are lowered. As long as the annealing temperature of the hot work material annealing is equal to or lower than the β transformation point, a mixed structure of equiaxed α phase and β phase can be obtained. ˜800 ° C. is preferred. The holding time of the hot work material annealing is preferably 0.5 to 2 hours because recrystallization may be insufficient if it is less than 0.5 hours and coarsening may occur if it exceeds 2 hours.
また、冷間加工材焼鈍をβ変態点以下で行う理由、焼鈍温度の好ましい範囲、保持時間の好ましい範囲は、熱間圧延材焼鈍と同様である。冷間での伸線加工と焼鈍は、必要に応じて１回以上繰り返すことが好ましく、工程省略によるコスト低減の観点から２回以内が好ましい。 The reason why the cold work material annealing is performed below the β transformation point, the preferable range of the annealing temperature, and the preferable range of the holding time are the same as those of the hot rolled material annealing. The cold wire drawing and annealing are preferably repeated once or more as necessary, and preferably within 2 times from the viewpoint of cost reduction by omitting the steps.
表１に示した成分の、ニクロム線であるＮｏ．２を除くチタン合金を溶解し、鋳造して約７ｋｇの鋳塊とした。これらを８５０〜９００℃に加熱し、８５０〜９００℃で熱間線材圧延して、直径約６．５ｍｍの線材とした。得られた線材を７５０℃で１時間焼鈍した後、冷間での伸線加工と７５０℃で３０分保持する焼鈍を２回繰り返し、更に直径０．５ｍｍまで伸線加工し、７５０℃で１時間焼鈍した。 Of the components shown in Table 1, Ni. The titanium alloy except 2 was melted and cast into an ingot of about 7 kg. These were heated to 850 to 900 ° C. and hot wire rolled at 850 to 900 ° C. to obtain a wire having a diameter of about 6.5 mm. After the obtained wire was annealed at 750 ° C. for 1 hour, cold drawing and annealing at 750 ° C. for 30 minutes were repeated twice, and further drawn to a diameter of 0.5 mm. Time annealed.
なお、表１のニクロム線を除くチタン合金のβ相変態点は、示差走査熱量分析装置で測定した結果、全て９００℃以上であった。ニクロム線は市販品を入手し、試験に供した。
これらの供試材から各種試験片を切出し、電気抵抗を測定し、室温引張試験、５００℃における高温引張試験を行って、０．２％耐力・引張強度・伸びを測定し、寿命試験を行った。
In addition, as a result of measuring with the differential scanning calorimetry apparatus, all the (beta) phase transformation points of the titanium alloy except the nichrome wire of Table 1 were 900 degreeC or more. A Nichrome wire was obtained as a commercial product and used for testing.
Various test pieces are cut out from these test materials, the electrical resistance is measured, the room temperature tensile test and the high temperature tensile test at 500 ° C. are performed, the 0.2% proof stress / tensile strength / elongation are measured, and the life test is performed. It was.
電気抵抗は、室温と５００℃で４端子法によって行い、５００℃における電気抵抗は加熱炉中に試料を置いて測定した。室温引張試験は、試料の長さを約２００ｍｍとし、クロスヘッドスピードを、０．２％耐力までは２ｍｍ／分、それ以降は２０ｍｍ／分として行った。高温引張試験は、試料の長さを約３００ｍｍとし、加熱炉中で５００℃に１５分間保時した後、クロスヘッドスピードを、０．２％耐力までは０．１ｍｍ／分、それ以降は３ｍｍ／分として行った。 The electric resistance was measured by a four-terminal method at room temperature and 500 ° C., and the electric resistance at 500 ° C. was measured by placing a sample in a heating furnace. In the room temperature tensile test, the length of the sample was about 200 mm, and the crosshead speed was 2 mm / min up to 0.2% proof stress, and 20 mm / min thereafter. In the high-temperature tensile test, the length of the sample is about 300 mm, and after holding at 500 ° C. for 15 minutes in a heating furnace, the crosshead speed is 0.1 mm / min until 0.2% proof stress, and thereafter 3 mm. Per minute.
寿命試験は長さ約２２０ｍｍの試料を切出し、試料の温度が５００℃になるように、３０分間通電、１５分間休止させる操作を１回とし、５００℃における電気抵抗の変化が初期値の１０％以上となる回数（１０％抵抗変化回数という）及び断線するまでの回数（破断回数という）を測定した。各種試験は同一条件の試料３個で実施し、その平均値を表２に示した。 In the life test, a sample having a length of about 220 mm is cut out, and the operation of energizing for 30 minutes and resting for 15 minutes is performed once so that the temperature of the sample becomes 500 ° C., and the change in electric resistance at 500 ° C. is 10% of the initial value. The number of times (referred to as 10% resistance change) and the number of times until disconnection (referred to as the number of breaks) were measured. Various tests were performed on three samples under the same conditions, and the average values are shown in Table 2.
ミクロ組織は、試料断面を鏡面研磨した後、硝酸と沸酸の混合溶液でエッチングし、光学顕微鏡を用いて観察した。α相は白色、β相は灰色に見えるため、光学顕微鏡組織写真を画像解析ソフトにより二値化し、β相の面積率を求めた。
結果を表２に示す。表２において、試験Ｎｏ．３〜５及びＮｏ．７〜９，１１，１３〜１７，１９は本発明の実施例であり、室温及び５００℃での電気抵抗がＮｏ．２のニクロム線よりも５０％以上高く、かつ寿命試験において、１０％抵抗変化回数及び破断回数が５００回以上であった。
The microstructure was mirror-polished on the sample cross section, etched with a mixed solution of nitric acid and hydrofluoric acid, and observed using an optical microscope. Since the α phase appears white and the β phase appears gray, the optical microscope texture photograph was binarized using image analysis software, and the area ratio of the β phase was determined.
The results are shown in Table 2. In Table 2, test no. 3-5 and no. 7-9, 11, 13-17, and 19 are examples of the present invention, and the electrical resistance at room temperature and 500 ° C. is No. 7. It was 50% or more higher than the Nichrome wire No. 2 and in the life test, the 10% resistance change frequency and the fracture frequency were 500 times or more.
一方、比較例であるＮｏ．１は、Ｔｉ−Ａｌ−Ｍｏ−Ｃｒ合金の一例であり、寿命試験で１０％抵抗変化回数が５００回を超えなかった。Ｎｏ．２は、Ｎｉ−２０％Ｃｒ系のニクロム線であり、組織観察を行っていないためβ相の面積率の測定は未実施であり、「−」で示しており、室温及び５００℃における電気抵抗値が小さい。Ｎｏ．６、Ｎｏ．１８は、それぞれＡｌ，Ｆｅの添加量が本発明の範囲よりも少ないため、５００℃における０．２％耐力が４００ＭＰａよりも低い。 On the other hand, No. which is a comparative example. 1 is an example of a Ti—Al—Mo—Cr alloy, and the 10% resistance change number did not exceed 500 times in the life test. No. No. 2 is a Ni-20% Cr-based nichrome wire, and since the structure observation was not performed, the measurement of the area ratio of the β phase was not performed, and is indicated by “−”, and the electric resistance at room temperature and 500 ° C. The value is small. No. 6, no. No. 18 has a lower 0.2% proof stress at 400 ° C. than 400 MPa because the added amount of Al and Fe is less than the range of the present invention.
Ｎｏ．１０は、Ａｌの添加量が本発明の範囲よりも多いため熱間延性が悪く、熱間加工時に表面に割れが入り、以降の伸線加工ができなかった。Ｎｏ．１２，２０は、それぞれＦｅ及びＦｅ，Ｎｉ，Ｃｒ，Ｍｎの合計添加量が本発明の範囲よりも多く、Ｎｏ．２１はＴｉ−６Ａｌ−４Ｖであり、冷間加工性が悪く、直径６．５ｍｍから０．５ｍｍまでの伸線する際に破断したため、試験片を採取することができなかった。 No. In No. 10, since the amount of Al added was larger than the range of the present invention, the hot ductility was poor, the surface was cracked during hot working, and subsequent wire drawing could not be performed. No. Nos. 12 and 20 have a total addition amount of Fe and Fe, Ni, Cr and Mn exceeding the range of the present invention. No. 21 was Ti-6Al-4V, which had poor cold workability and was broken when drawn from a diameter of 6.5 mm to 0.5 mm, so that a test piece could not be collected.
本発明のＴｉ−Ａｌ−Ｆｅ合金は、電気抵抗が十分高く、長時間又は繰返し用いても電気抵抗の変化が小さいことから、誘導加熱して利用する用途の一例である電磁調理器用の板材としても利用することが可能である。 The Ti-Al-Fe alloy of the present invention has a sufficiently high electric resistance, and since the change in electric resistance is small even when used for a long time or repeatedly, as a plate material for an electromagnetic cooker that is an example of an application that is used by induction heating. Can also be used.
Claims (5)
Ａｌ：４．５〜５．５％、
Ｆｅ：０．４〜２．２％
を含有し、残部がＴｉ及び不可避的不純物からなることを特徴とする電熱線用チタン合金。 % By mass
Al: 4.5 to 5.5%,
Fe: 0.4-2.2%
And a balance of Ti and inevitable impurities, and a titanium alloy for heating wire.
Ｎｉ：０．０５〜０．１５％、
Ｃｒ：０．０５〜０．２５％、
Ｍｎ：０．０５〜０．２５％
の１種又は２種以上を含有し、
Ｆｅ＋Ｎｉ＋Ｃｒ＋Ｍｎ：０．４〜２．２％
を満足することを特徴とする請求項１記載の電熱線用チタン合金。 In mass%,
Ni: 0.05 to 0.15%,
Cr: 0.05 to 0.25%,
Mn: 0.05 to 0.25%
1 type or 2 types or more of
Fe + Ni + Cr + Mn: 0.4-2.2%
The titanium alloy for heating wire according to claim 1, wherein:
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