WO2016152663A1 - α-β型チタン合金 - Google Patents
α-β型チタン合金 Download PDFInfo
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- WO2016152663A1 WO2016152663A1 PCT/JP2016/058247 JP2016058247W WO2016152663A1 WO 2016152663 A1 WO2016152663 A1 WO 2016152663A1 JP 2016058247 W JP2016058247 W JP 2016058247W WO 2016152663 A1 WO2016152663 A1 WO 2016152663A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C14/00—Alloys based on titanium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
- C22F1/18—High-melting or refractory metals or alloys based thereon
Definitions
- the present invention relates to an ⁇ - ⁇ type titanium alloy.
- it relates to an ⁇ - ⁇ type titanium alloy having excellent machinability.
- High strength ⁇ - ⁇ type titanium alloys represented by Ti-6Al-4V are light weight, high strength, high corrosion resistance, and can easily change the strength level by heat treatment. It has been widely used mainly in the aircraft industry. In order to further utilize these characteristics, in recent years, automobile parts such as automobile and motorcycle engine parts, sports equipment such as golf equipment, civil engineering and building materials, various tools, eyeglass frames and other consumer goods fields, Application to deep seas and energy development applications is also expanding.
- Patent Document 1 discloses an ⁇ - ⁇ type titanium alloy extruded material excellent in fatigue strength and a method for producing the ⁇ - ⁇ type titanium alloy extruded material.
- the ⁇ - ⁇ type titanium alloy extruded material contains a specified amount of C and Al, and a total of any of V, Cr, Fe, Mo, Ni, Nb, and Ta is 2.0 to 10.0. %,
- the area ratio of the primary ⁇ phase is within a certain range, and the major axis direction of the primary ⁇ grains of 80% or more of the primary ⁇ phase falls within the specified angle range, and the secondary ⁇ phase It is shown that the average minor axis of the phase is 0.1 ⁇ m or more.
- Patent Document 2 discloses an ⁇ - ⁇ type titanium alloy for casting that has higher strength and superior castability than Ti-6Al-4V alloy. Yes. Specifically, there is shown an ⁇ - ⁇ type titanium alloy containing prescribed amounts of Al, Fe + Cr + Ni, and C + N + O, and further containing a prescribed amount of V as required, with the balance being Ti and inevitable impurities.
- Patent Document 3 a rare earth element (REM, Rare Earth Metal) and Ca, S, Se, Te, Pb, Bi are appropriately contained to form a granular compound, thereby suppressing a decrease in toughness and ductility.
- REM Rare Earth Metal
- Patent Document 4 also describes a free-cutting titanium alloy in which machinability is improved by containing a rare earth element and hot workability is improved by containing B.
- Patent Document 5 P and S, P and Ni, or P and S and Ni as free-cutting components, and addition of REM in addition to these elements, the reduction of the ductility of the matrix and the fineness of inclusions are disclosed.
- a free-cutting titanium alloy that improves hot-cutting properties while ensuring hot workability and suppressing a decrease in fatigue strength is described.
- Patent Document 6 discloses an ⁇ - ⁇ type titanium alloy excellent in machinability and hot workability, together with a prescribed amount of C and Al, and a prescribed amount of V, Cr, Fe, Mo, Ni, Nb, One type or two or more types from a ⁇ -stabilizing element group of Ta are included in a total of 2.0 to 10%, the balance is Ti and impurities, the average area ratio of TiC precipitates in the structure is 1% or less, and TiC A titanium alloy in which the average value of the average equivalent circle diameter of the precipitates is 5 ⁇ m or less is shown.
- the present invention has been made paying attention to the circumstances as described above, and the object thereof is ⁇ - ⁇ typified by Ti-6Al-4V without requiring strict control of the manufacturing process.
- An object is to realize an ⁇ - ⁇ type titanium alloy having high strength at the level of a type titanium alloy and excellent hot workability and exhibiting machinability superior to the above Ti-6Al-4V.
- the ⁇ - ⁇ type titanium alloy of the present invention that has solved the above problems is at least one of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0% by mass.
- the ⁇ - ⁇ type titanium alloy further includes, in mass%, V: more than 0% and 5.0% or less, Mo: more than 0% and 5.0% or less, Nb: more than 0% and 5.0% or less, and Ta : One or more elements selected from the group consisting of more than 0% and 5.0% or less may be contained in total exceeding 0% and 10% or less.
- the ⁇ - ⁇ type titanium alloy may further contain Si: more than 0% and 0.8% or less by mass%.
- the present invention has high workability such as high strength of ⁇ - ⁇ type titanium alloy represented by Ti-6Al-4V and excellent forgeability, and is superior to Ti-6Al-4V. It is possible to provide an ⁇ - ⁇ type titanium alloy that exhibits machinability and can ensure a good tool life.
- FIG. 1 is a photomicrograph of the titanium alloy of the present invention.
- the inventors of the present invention have made extensive studies to solve the above-mentioned problems. As a result, by including at least one of Cu and Ni in a specified amount, ductility at a high temperature is greatly improved. It has been found that the resistance is lowered, that is, the machinability is improved.
- the component composition of the ⁇ - ⁇ type titanium alloy of the present invention will be described in order from Cu and Ni which are features of the present invention.
- At least one element of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0% are dissolved in the ⁇ phase and ⁇ phase in the alloy at a high temperature. To increase the hot workability. Thereby, especially cutting resistance becomes low and machinability improves. These elements may be used alone or in combination of two kinds. If the content of each element is less than 0.1%, the effect of improving the ductility is small. Therefore, the content of each element is set to 0.1% or more. The content of each element is preferably 0.3% or more, more preferably 0.5% or more, respectively. On the other hand, when the content of each element exceeds 2.0%, a decrease in machinability due to an increase in hardness and a decrease in hot workability such as forgeability tend to occur. Therefore, the content of each element is set to 2.0% or less. The content of each element is preferably 1.5% or less, more preferably 1.0% or less.
- Al 2.0 to 8.5% Al is an ⁇ -stabilizing element and is contained to generate an ⁇ -phase. If the amount of Al is less than 2.0%, the ⁇ phase is generated too little to obtain sufficient strength. Therefore, the Al content is 2.0% or more.
- the amount of Al is preferably 2.2% or more, more preferably 3.0% or more.
- the Al amount is set to 8.5% or less.
- the amount of Al is preferably 8.0% or less, more preferably 7.0% or less, and still more preferably 6.0% or less.
- C 0.08 to 0.25%
- the amount of C is an element showing an effect of improving the strength, and in order to exert this effect, the amount of C needs to be 0.08% or more.
- the amount of C is preferably 0.10% or more.
- the C amount is 0.25% or less.
- the amount of C is preferably 0.20% or less.
- These elements are ⁇ -stabilizing elements. These elements may be used alone or in combination of two kinds. In order to exert the above effects, it is necessary to make these elements 1.0% or more in total.
- the content of these elements is preferably 2.0% or more in total, more preferably 3.0% or more in total.
- the lower limit of the content of these elements may be 1.0% or more as described above, and the lower limit of the content of each element is not particularly limited.
- the lower limit of the content of each element can be 0.5% or more, and further can be 1.0% or more.
- Fe is contained, the content can be 0.5% or more, and further 1.0% or more.
- the total amount of these elements is 7.0% or less. Preferably it is 5.0% or less in total, more preferably 4.0% or less in total. Even within the range of the total amount, when the amount of Fe is excessive, the ductility is significantly reduced. Therefore, the amount of Fe is suppressed to 2.5% or less.
- the amount of Fe is preferably 2.0% or less.
- the Cr content is 4.5% or less.
- the amount of Cr is preferably 4.0% or less, more preferably 3.0% or less.
- the ⁇ - ⁇ type titanium alloy of the present invention contains the above components, with the balance being Ti and inevitable impurities. Inevitable impurities include P, N, S, O and the like.
- the ⁇ - ⁇ type titanium alloy of the present invention has a P content of 0.005% or less, an N content of 0.05% or less, an S content of 0.05% or less, and an O content of 0.25% or less. ing.
- the ⁇ - ⁇ type titanium alloy of the present invention may further contain the following elements.
- V more than 0% and 5.0% or less
- Mo more than 0% and 5.0% or less
- Nb more than 0% and 5.0% or less
- Ta more than 0% and 5.0% or less
- elements in total more than 0% and 10% or less.
- These elements are ⁇ -stabilizing elements. These elements may be used alone or in combination of two or more. In order to generate the ⁇ phase, it is preferable to contain these elements in total of 2.0% or more, and more preferably 3.0% or more in total. The total amount may be more than 0%, and the lower limit of the content of each element is not particularly limited. For example, when V is contained, the lower limit of the content of each element can be 0.5% or more, and further 2.0% or more.
- the content can be 0.1% or more, and further 1.0% or more.
- the content may be 0.1% or more, and further 1.0% or more.
- the content can be 0.1% or more, and further 1.0% or more.
- the total amount of these elements is preferably 10% or less, more preferably 5.0% or less. Even if the total amount is within the range, the ductility deteriorates if at least one of the elements is excessive. Therefore, it is preferable that the upper limit of any element is 5.0% or less. Any element is more preferably 4.0% or less.
- Si more than 0% and 0.8% or less Si precipitates Ti 5 Si 3 in the titanium alloy. During cutting, stress is concentrated on the Ti 5 Si 3, by void the Ti 5 Si 3 starting from occurs, tends chips is divided. As a result, it is thought that cutting resistance falls. In order to fully exhibit this effect, it is preferable to contain 0.1% or more of Si, and more preferably 0.3% or more.
- the Si content is preferably 0.8% or less. More preferably, it is 0.7% or less, More preferably, it is 0.6% or less.
- titanium alloy of the present invention examples include those whose structure is composed of an ⁇ phase and a ⁇ phase at room temperature, or an ⁇ phase, a ⁇ phase, and a third phase such as Ti 2 Cu or Ti 2 Ni.
- Si is contained, Ti 5 Si 3 is precipitated in the titanium alloy as described above.
- the production method of this ⁇ - ⁇ type titanium alloy is not particularly limited, and for example, it can be produced by the following method. That is, it is manufactured by melting a titanium alloy having the above components and subjecting the ingot to hot working, that is, hot forging or hot rolling, followed by annealing if necessary.
- the hot working the ingot is heated to a temperature range of about ⁇ transformation temperature T ⁇ to (T ⁇ +250) ° C., and the working ratio is expressed by “original cross-sectional area / cross-sectional area after hot working”.
- Rough forging or rough rolling of about 1.2 to 4.0 is performed, and then finishing with a processing ratio of 1.7 or more is performed in a temperature range of about (T ⁇ ⁇ 50) to about 800 ° C.
- annealing may be performed at 700 to 800 ° C. as necessary. For example, annealing may be performed for 2 to 24 hours. Furthermore, you may give an aging treatment after that as needed.
- T ⁇ is obtained from the following formula (1).
- the following formula (1) is obtained by Morinaga et al., “Design of titanium alloy applying d-electron theory”, Light Metal, Vol. 42, no. 11 (1992), p. This corresponds to the equations (1) to (3) in 614-621.
- Boave 0.326Mdave-1.95 ⁇ 10 ⁇ 4 T ⁇ +2.217 (1)
- Boave ⁇ Xi ⁇ (Bo) i
- Mdave ⁇ Xi ⁇ (Md) i (3)
- T ⁇ is ⁇ transformation temperature (K) Means.
- the bond order Bo and the d-orbital energy parameter Md of each element are given in p. 616 in Table 1.
- Xi is determined from the component composition.
- These data determine the Boave and Mdave of the elements including Ti, by substituting the above equation (1) can calculate the T beta. In this document, there is no data on Bo or Md of C. However, since the amount of C is small in the present invention, C is ignored and T ⁇ is calculated.
- Example 1 The specimens were produced as follows. By button arc melting, ingots of titanium alloys having the composition shown in Table 1 and having a diameter of about 40 mm and a height of 20 mm were produced. In each example, the P amount was 0.005% or less, the N amount was 0.05% or less, the S amount was 0.05% or less, and the O amount was 0.25% or less. In Table 1, “-” means that the element is not added.
- This ingot is heated to 1200 ° C., rough forged at a processing ratio of 2.4 expressed by “original cross-sectional area / cross-sectional area after hot working”, and then at 870 ° C., the processing ratio is 4.4. And finished by forging. Thereafter, annealing was performed at 750 ° C. for 12 hours to obtain a test material. In addition, as shown in the comparative example 7 of following Table 1, the thing which the crack produced by rough forging did not perform finish forging.
- hot workability was evaluated by hot forgeability in this example.
- the machinability was evaluated as follows for the samples having good forgeability. That is, a test piece having the following size was collected from the test material and subjected to a cutting test under the following cutting conditions. The machinability is measured by measuring the cutting resistance in the cutting direction from the start of cutting to the end of cutting using a cutting dynamometer, model: 9257B manufactured by Kistler, and calculating the average value of the cutting resistance from the start of cutting to the end of cutting. The average cutting resistance was obtained. When a general ⁇ - ⁇ type titanium alloy Ti-6Al-4V was subjected to a cutting test under the same conditions, the average cutting resistance was 180 N. Therefore, in this Example 1, the average cutting resistance was more than 180 N. The case where it was low was evaluated as excellent in machinability, and the case where the average cutting resistance was 180 N or more was evaluated as inferior in machinability.
- Cutting condition test piece height 10 mm x width 10 mm x length 150 mm
- Tool Sandvik carbide tip S30T (Nose 0.4mm) Sandvik end mill R390 (diameter 20mm, single blade)
- Cutting speed Vc 100 m / min
- Axial cut depth 1.2mm
- Radial cut depth 1mm
- Feed rate 0.08mm / blade cutting length: 150mm
- Cutting oil None
- the tensile strength of the ⁇ - ⁇ type titanium alloy of the present invention was also measured. Specifically, using the titanium alloys of Example 1, Example 3, and Comparative Example 1, a tensile test was performed under the conditions of the following test piece shape and the following test speed. As a result, it was 948 MPa in Example 1, 1125 MPa in Example 3, and 948 MPa in Comparative Example 1. Both strengths were high and Ti-6Al-4V, a general ⁇ - ⁇ type titanium alloy, was annealed. Strength of material: higher than 896 MPa. Specimen shape: ASTM E8 / E8M FIG. 8 Specimen3 Test speed: 4.5mm / min
- Table 1 shows the forgeability evaluation results and average cutting resistance values.
- Table 1 shows the following. It can be seen that Examples 1 to 8 all satisfy the prescribed component composition in the present invention, and all can be forged well and have excellent forgeability. Furthermore, in these examples, it can be seen that the average cutting resistance is smaller than that of Ti-6Al-4V, which is a general ⁇ - ⁇ type titanium alloy, and also has good machinability.
- Comparative Examples 1 to 7 did not satisfy the component composition defined in the present invention, the results were inferior in forgeability or in machinability.
- the comparative example 1 did not contain both Cu and Ni, the average cutting resistance increased.
- Comparative Example 1 has the same component composition as that of Patent Document 6.
- the average cutting resistance was sufficiently reduced and good machining was achieved. It can be seen that it is necessary to contain a specified amount of at least one of Cu and Ni as in the present invention in order to reliably obtain the properties.
- Comparative Example 2 is an example containing Ni, but the amount of Ni is excessive
- Comparative Example 5 is an example containing Cu, but the amount of Cu is excessive, so both have an average cutting resistance higher than 180N.
- the machinability deteriorated.
- Comparative Example 3 and Comparative Example 6 since the respective amounts of Cu and Ni were excessive, both had an average cutting resistance higher than 180 N, resulting in poor machinability.
- Comparative Example 4 because of the excessive amount of Cu, forgeability decreased.
- Comparative Example 7 the amounts of Cu and Ni were extremely excessive, so that cracking occurred at the stage of rough forging, resulting in poor forgeability.
- Example 2 In this example, the effect of Si in particular on machinability was examined. As shown in Table 2, ingots with various amounts of Si were produced, and specimens were obtained in the same manner as in Example 1. In each example, the P amount was 0.005% or less, the N amount was 0.05% or less, the S amount was 0.05% or less, and the O amount was 0.25% or less. In Table 2, “-” means that the element is not added.
- Example 2 Using the above test material, the presence or absence of a precipitated phase was confirmed as described below, and in Example 2, Vickers hardness was measured as an index of strength. Furthermore, while evaluating forgeability similarly to Example 1, machinability was evaluated as follows. For reference, No. 2 in Table 2 is used. As for Example 3, when the tensile strength was measured in the same manner as in Example 1, it was 968 MPa, and the strength of a general ⁇ - ⁇ type titanium alloy Ti-6Al-4V annealed material: higher than 896 MPa. .
- FIG. 3 An example observed with the above microscope is shown in FIG. FIG. 3, and the arrow is one of the precipitated phases.
- Vickers hardness HV Vickers hardness HV was measured at five points under the condition of a load of 10 kgf, and the average value was obtained.
- the machinability was evaluated as follows for all the examples of Table 2 that had good forgeability evaluated in the same manner as in Example 1. That is, a test piece having the following size was collected from the test material and subjected to a cutting test under the following cutting conditions. The machinability is measured by measuring the cutting resistance in the cutting direction from the start of cutting to the end of cutting using a cutting dynamometer, model: 9257B manufactured by Kistler, and calculating the average value of the cutting resistance from the start of cutting to the end of cutting. The average cutting resistance was obtained. When a general ⁇ - ⁇ type titanium alloy Ti-6Al-4V is subjected to a cutting test under the same conditions, the average cutting resistance is 122 N. Therefore, in this Example 2, the average cutting resistance is more than 122 N. The case where it was low was evaluated as excellent in machinability, and the case where the average cutting resistance was 122 N or more was evaluated as inferior in machinability.
- Cutting condition test piece height 10 mm x width 10 mm x length 60 mm
- Tool Sandvik carbide tip S30T (Nose 0.4mm) Sandvik end mill R390 (diameter 20mm, single blade)
- Cutting speed Vc 100 m / min
- Cutting oil None
- Table 2 shows the following. That is, No. of the same component composition as Example 1 of Table 1. 1 and no. No. 2 to 6, particularly No. in which the content other than Si is the same as Example 1 in Table 1 above. As is clear from the comparison with 2 to 4, it can be seen that the inclusion of Si can further reduce the average cutting resistance and ensure sufficiently high machinability as compared with the case where Si is not included. On the other hand, no. 7 or No. As shown in FIG. 8, when the Si content was excessive, the hardness became too high, and on the contrary, the average cutting resistance was increased and the tool was damaged.
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Abstract
Description
これらの元素は、合金中のα相およびβ相に固溶し、高温での延性を増大させ、熱間加工性を向上させる。それにより特に切削抵抗が低くなり、被削性が向上する。これらの元素は、単独で用いてもよいし2種を併用してもよい。各元素の含有量が0.1%未満だと上記延性向上の効果が小さい。よって各元素の含有量を0.1%以上とした。各元素の含有量は、好ましくはそれぞれ0.3%以上、より好ましくはそれぞれ0.5%以上である。一方、各元素の含有量が2.0%を超えると、硬度が上昇することによる被削性の低下や鍛造性等の熱間加工性の低下が生じやすくなる。よって各元素の含有量を2.0%以下とした。各元素の含有量は、好ましくはそれぞれ1.5%以下であり、より好ましくはそれぞれ1.0%以下である。
Alはα安定化元素であり、α相を生成させるために含有させる。Al量が2.0%未満だとα相の生成が過少になり、十分な強度が得られない。よってAl量は2.0%以上とする。Al量は、好ましくは2.2%以上、より好ましくは3.0%以上である。一方、Al量が8.5%を超えて過剰になると、延性が劣化する。よってAl量は8.5%以下とする。Al量は、好ましくは8.0%以下、より好ましくは7.0%以下、更に好ましくは6.0%以下である。
Cは、強度向上効果を示す元素であり、この効果を発揮させるには、C量を0.08%以上とする必要がある。C量は好ましくは0.10%以上である。一方、C量が0.25%を超えると、α相中に固溶されない粗大なTiCが残留し、機械的特性が劣化する。よってC量は0.25%以下とする。C量は好ましくは0.20%以下である。
これらの元素はβ安定化元素である。これらの元素は、単独で用いてもよいし2種を併用してもよい。上記効果を発揮させるには、これらの元素を合計で1.0%以上とする必要がある。これらの元素の含有量は、好ましくは合計で2.0%以上、より好ましくは合計で3.0%以上である。これらの元素の含有量の下限は、上記の通り合計量が1.0%以上であればよく、個々の元素の含有量の下限は特に限定されない。個々の元素の含有量の下限は例えば、Crを含有させる場合、0.5%以上とすることができ、更には1.0%以上とすることができる。Feを含有させる場合は、0.5%以上とすることができ、更には1.0%以上とすることができる。
これらの元素はβ安定化元素である。これらの元素は、単独で用いてもよいし2種以上を併用してもよい。β相を生成させるためには、これらの元素を合計で2.0%以上含有させることが好ましく、より好ましくは合計で3.0%以上である。合計量が0%超であればよく、個々の元素の含有量の下限は特に限定されない。個々の元素の含有量の下限は例えば、Vを含有させる場合、0.5%以上、更には2.0%以上とすることができる。Moを含有させる場合、0.1%以上、更には1.0%以上とすることができる。Nbを含有させる場合、0.1%以上、更には1.0%以上とすることができる。Taを含有させる場合、0.1%以上、更には1.0%以上とすることができる。
Siは、チタン合金中にTi5Si3を析出させる。切削時、このTi5Si3に応力が集中し、このTi5Si3を起点にボイドが発生することで、切粉が分断されやすくなる。その結果、切削抵抗が低下すると考えられる。この効果を十分に発揮させるには、Siを0.1%以上含有させることが好ましく、より好ましくは0.3%以上である。
Boave=0.326Mdave-1.95×10-4Tβ+2.217・・・(1)
式(1)において、
Boave=ΣXi・(Bo)i・・・(2)
Mdave=ΣXi・(Md)i・・・(3)
Tβはβ変態温度(K)
を意味する。
式(2)において、各元素を元素iと表現したとき、
Boaveは元素iの結合次数Boの平均値、Xiは元素iの原子比率、(Bo)iは元素iの結合次数Boの値を示す。
式(3)において、各元素を元素iと表現したとき、
Mdaveは元素iのd軌道エネルギーパラメータMdの平均値、Xiは元素iの原子比率、(Md)iは元素iのd軌道エネルギーパラメータMdの値を示す。
供試材を以下の要領で製作した。ボタンアーク溶解により、下記表1に示す各成分組成のチタン合金であってサイズが直径約40mm×高さ20mmの鋳塊を製造した。尚、いずれの例も、P量は0.005%以下、N量は0.05%以下、S量は0.05%以下、かつO量は0.25%以下にそれぞれ抑えられていた。また、表1において「-」はその元素を添加していないことを意味する。この鋳塊を、1200℃に加熱し、「元の断面積/熱間加工後の断面積」で表される加工比2.4で粗鍛造し、次いで870℃で、加工比を4.4として鍛造で仕上加工した。その後、750℃で12時間保持する焼鈍を施して供試材を得た。尚、下記表1の比較例7に示す通り、粗鍛造で割れが生じたものは仕上鍛造を行わなかった。
熱間加工性の評価を、本実施例では熱間での鍛造性で評価した。詳細には、上記粗鍛造と仕上鍛造の各鍛造時での割れの有無で評価した。即ち、各鍛造後に前記供試材の表面を目視で観察し、割れが生じている場合をNG、割れが生じていない場合をOKと判断した。そして、粗鍛造と仕上鍛造のいずれにおいてもOKの場合を鍛造性に優れると評価した。
前記鍛造性が良好であったものを対象に、被削性の評価を下記の通り行った。即ち、前記供試材から、下記サイズの試験片を採取し、下記の切削条件で切削試験を行った。そして被削性は、キスラー社製の切削動力計、型式:9257Bを用いて切削開始から切削終了までの切り込み方向の切削抵抗を測定し、この切削開始から切削終了までの切削抵抗の平均値を平均切削抵抗として求めた。そして、一般的なα-β型チタン合金であるTi-6Al-4Vを同条件で切削試験した場合、平均切削抵抗は180Nであることから、この実施例1では、平均切削抵抗が180Nよりも低い場合を被削性に優れていると評価し、平均切削抵抗が180N以上の場合を被削性に劣ると評価した。
試験片:高さ10mm×幅10mm×長さ150mm
工具:サンドビック社製超硬チップ S30T(ノーズ0.4mm)
サンドビック社製エンドミルR390(直径20mm、1枚刃)
切削速度Vc:100m/min
軸方向切り込み量:1.2mm
径方向切り込み量:1mm
送り速度:0.08mm/刃
切削長さ:150mm
切削油:無し
参考までに本発明のα-β型チタン合金の引張強度も測定した。詳細には、実施例1、実施例3、および比較例1のチタン合金を用い、下記試験片形状および下記試験速度の条件で引張試験を行った。その結果、実施例1では948MPa、実施例3では1125MPa、比較例1では948MPaであり、強度についてはいずれも高めであり、一般的なα-β型チタン合金であるTi-6Al-4Vの焼鈍材の強度:896MPaよりも高い強度を示した。
試験片形状:ASTM E8/E8M Fig.8 Specimen3
試験速度:4.5mm/min
本実施例では、Siを含む場合の、特に被削性に及ぼす影響について検討した。表2に示す通り、Si量が種々の鋳塊を製造し、実施例1と同様にして供試材を得た。尚、いずれの例も、P量は0.005%以下、N量は0.05%以下、S量は0.05%以下、かつO量は0.25%以下にそれぞれ抑えられていた。また、表2において「-」はその元素を添加していないことを意味する。
断面を鏡面研磨し、硝フッ酸を用いて粒界が見られる程度の酸処理を行った後、FE-SEM(Field Emission-Scanning Electron Microscope、電界放射型走査電子顕微鏡)にて、倍率4000倍で、視野サイズ40μm×40μmを合計10視野観察した。そして、円相当直径2μm以上の析出相が、上記10視野の合計で5つ以上確認できた場合を析出相「あり」と評価し、上記10視野の合計で4つ以下の場合を析出相「なし」と評価した。尚、上記析出相は、Ti5Si3であることをXRD(X‐Ray Diffraction、X線回折)で別途確認している。
荷重10kgfの条件でビッカース硬さHVを5点測定し、その平均値を求めた。
実施例1と同様に評価した鍛造性が良好であったもの、即ち表2の全ての例を対象に、被削性の評価を下記の通り行った。即ち、前記供試材から、下記サイズの試験片を採取し、下記の切削条件で切削試験を行った。そして被削性は、キスラー社製の切削動力計、型式:9257Bを用いて切削開始から切削終了までの切り込み方向の切削抵抗を測定し、この切削開始から切削終了までの切削抵抗の平均値を平均切削抵抗として求めた。そして、一般的なα-β型チタン合金であるTi-6Al-4Vを同条件で切削試験した場合、平均切削抵抗は122Nであることから、この実施例2では、平均切削抵抗が122Nよりも低い場合を被削性に優れていると評価し、平均切削抵抗が122N以上の場合を被削性に劣ると評価した。
試験片:高さ10mm×幅10mm×長さ60mm
工具:サンドビック社製超硬チップ S30T(ノーズ0.4mm)
サンドビック社製エンドミルR390(直径20mm、1枚刃)
切削速度Vc:100m/min
軸方向切り込み量:1.2mm
径方向切り込み量:1mm
送り速度:0.08mm/刃
切削長さ:15mm
切削油:無し
Claims (3)
- 質量%で、
Cu:0.1~2.0%、およびNi:0.1~2.0%のうちの少なくとも1種の元素、
Al:2.0~8.5%、
C:0.08~0.25%、ならびに、
Cr:0~4.5%、およびFe:0~2.5%のうちの少なくとも1種の元素を合計で1.0~7.0%
を含み、残部がTiおよび不可避不純物からなることを特徴とするα-β型チタン合金。 - 更に、質量%で、
V:0%超5.0%以下、Mo:0%超5.0%以下、Nb:0%超5.0%以下、およびTa:0%超5.0%以下よりなる群から選択される1種以上の元素を、合計で0%超10%以下含む請求項1に記載のα-β型チタン合金。 - 更に、質量%で、Si:0%超0.8%以下を含む請求項1または2に記載のα-β型チタン合金。
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