KR20170125981A - α-β type titanium alloy - Google Patents

Abstract

? -Type titanium alloy alloy having high strength and excellent hot workability at the level of? -Type titanium alloy represented by Ti-6Al-4V and exhibiting machinability superior to that of Ti-6Al-4V. Wherein the α-β type titanium alloy comprises at least one element selected from the group consisting of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0%, Al: 2.0 to 8.5%, C: 0.08 to 0.25% 0 to 4.5% and Fe: 0 to 2.5%, and the balance of Ti and inevitable impurities.

Description

α-β type titanium alloy

The present invention relates to an? -? -Type titanium alloy. And particularly relates to an? -? -Type titanium alloy excellent in machinability.

The high strength α-β type titanium alloy typified by Ti-6Al-4V is lightweight, high strength, and highly corrosion resistant, and can be easily changed in strength level by heat treatment. come. In recent years, in order to further utilize these characteristics, there has been a tendency to develop various types of products such as automobile parts such as automobile parts for automobiles and motorcycles, sports goods including golf goods, civil engineering construction materials, various tools, And the application to the application is also expanding.

As the α-β-type titanium alloy, for example, Patent Document 1 shows an α-β-type titanium alloy extruded material excellent in fatigue strength and a method for producing the α-β-type titanium alloy extruded material. Specifically, the extruded material of the α-β type titanium alloy contains a specified amount of C and Al, 2.0 to 10.0% of the total of V, Cr, Fe, Mo, Ni, Nb and Ta, Of the primary α-phase is within a certain range and the direction of the long diameter of the primary α-lip more than 80% of the primary α-phase falls within the prescribed angle range and the average short diameter on the secondary α-phase is 0.1 μm or more.

Further, Patent Document 2 discloses an? -? -Type titanium alloy having a higher strength and higher castability than a Ti-6Al-4V alloy as a? -? -Type titanium alloy with an increased mono-composition. Specifically, it is preferable to use an α-β type titanium alloy containing a specified amount of Al, Fe + Cr + Ni, and C + N + O, further including a specified amount of V if necessary, and the balance of Ti and inevitable impurities Alloy.

However, in addition to the remarkably high production cost of the? -? -Type titanium alloy, particularly bad machinability is hindered from expanding the application of the? -? -Type titanium alloy, and the use range is limited . In view of this situation, in recent years, various types of titanium alloys having improved machinability have been proposed.

For example, Patent Document 3 discloses a method in which a rare earth element (REM, Rare Earth Metal) and Ca, S, Se, Te, Pb and Bi are appropriately contained to form a granular compound to suppress deterioration of toughness and ductility , And titanium alloys for connecting rods having improved machinability. Patent Document 4 also discloses a free-cutting titanium alloy in which hot workability is improved by including a rare earth element to improve machinability and incorporating B therein.

Patent Literature 5 discloses that the addition of REM to P and S, P and Ni, or P, S and Ni, and additionally these elements as free-cutting components reduces the ductility of the matrix and makes the inclusions finer, Discloses a free-cutting titanium alloy which is capable of securing hot workability while suppressing deterioration of fatigue strength while improving free cutting properties.

Patent Document 6 discloses an α-β type titanium alloy having excellent machinability and hot workability. The α-β type titanium alloy has a β-stabilization of V, Cr, Fe, Mo, Ni, Wherein the total area ratio of TiC precipitates in the structure is 1% or less and the average circle equivalent diameter of the TiC precipitates is in the range of 2.0 to 10% in total, and the balance Ti and impurities are contained, Is 5 mu m or less.

Japanese Patent Application Laid-Open No. 2012-52219 Japanese Patent Application Laid-Open No. 2010-7166 Japanese Patent Publication No. 6-99764 Japanese Patent Publication No. 6-53902 Japanese Patent No. 2626344 Japanese Patent Application Laid-Open No. 2007-84865

However, as in Patent Document 3 and Patent Document 4, metal inclusions are precipitated by REM, P is positively contained as in Patent Document 5 to form P inclusions, and TiC precipitates In the method of controlling the size, it is considered that the precipitation of these precipitates and inclusions is easily affected by the temperature and the cooling rate in the dissolving-forging process and it is difficult to control the size of the precipitates or the like. Further, depending on the shape and size of the material, the size of the precipitates and inclusions may easily vary. Therefore, there is a problem that precise management is required in the manufacturing process in order to precipitate a desired inclusion to obtain excellent machinability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-strength and high-strength α-β type titanium alloy level represented by Ti-6Al-4V, The present invention is to realize an? -? -Type titanium alloy having hot workability and exhibiting machinability superior to that of Ti-6Al-4V.

The α-β type titanium alloy according to the present invention, which can solve the above problems, contains at least one element selected from the group consisting of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0%, Al: 2.0 to 8.5% 0.08 to 0.25%, Cr: 0 to 4.5% and Fe: 0 to 2.5%, and the balance of Ti and inevitable impurities.

The above-mentioned? -? -Type titanium alloy further contains, by mass%, V: more than 0% and not more than 5.0%, Mo: not less than 5.0%, Nb: not more than 5.0% Or less, and more than 0% and not more than 10% of the total of at least one element selected from the group consisting of

The? -? -Type titanium alloy may further contain, in mass%, Si: more than 0% and not more than 0.8%.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a Ti-6Al-4V alloy which exhibits excellent machinability such as high strength of α-β type titanium alloy level represented by Ti-6Al-4V and superior hot workability, It is possible to provide an? -? -Type titanium alloy capable of securing a service life.

1 is a micrograph of a titanium alloy of the present invention.

The inventors of the present invention have conducted intensive studies in order to solve the above problems. As a result, particularly when at least one of Cu and Ni is contained in a specified amount, ductility at high temperature is significantly improved, and in particular, the cutting powder is formed thinly at the time of cutting due to the lowering of the deformation resistance The cutting resistance is lowered, that is, the machinability is improved. Hereinafter, the composition of the? -? -Type titanium alloy of the present invention will be described in order from Cu and Ni which are characteristics of the present invention.

At least one element selected from the group consisting of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0%

These elements are dissolved in the? -Phase and? -Phase in the alloy to increase the ductility at high temperature and improve the hot workability. As a result, the cutting resistance is lowered, and machinability is improved. These elements may be used alone or in combination. 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 was set to 0.1% or more. The content of each element is preferably 0.3% or more, and more preferably 0.5% or more. On the other hand, when the content of each element exceeds 2.0%, the hardness is increased and the hot workability such as a reduction in the workability is liable to be lowered. Therefore, the content of each element was 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 in order to generate an? -Phase. If the amount of Al is less than 2.0%, the generation of the alpha phase becomes too small and sufficient strength can not be obtained. Therefore, the amount of Al is 2.0% or more. The amount of Al is preferably 2.2% or more, and more preferably 3.0% or more. On the other hand, if the amount of Al exceeds 8.5% and the excess amount is present, the ductility deteriorates. Therefore, the Al content should be 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%

C is an element showing an effect of improving the strength. In order to exhibit this effect, the C content needs to be 0.08% or more. The amount of C is preferably 0.10% or more. On the other hand, if the C content exceeds 0.25%, coarse TiC that does not solidify in the? Phase remains and deteriorates the mechanical properties. Therefore, the C content should be 0.25% or less. The C content is preferably 0.20% or less.

At least one element selected from the group consisting of Cr: 0 to 4.5% and Fe: 0 to 2.5%

These elements are? Stabilizing elements. These elements may be used alone or in combination. In order to exhibit the above effect, it is necessary that the total of these elements is 1.0% or more. 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 is such that the total amount is 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 may be 0.5% or more, for example, when Cr is contained, and may be 1.0% or more. When Fe is contained, the Fe content can be 0.5% or more, and can be 1.0% or more.

On the other hand, when the total amount of these elements is excessive, ductility is deteriorated. Therefore, the total amount of these elements is 7.0% or less. Preferably not more than 5.0%, more preferably not more than 4.0% in total. Even if the total amount is within the range, in the case where the amount of Fe is excessive, deterioration of ductility becomes remarkable. Therefore, the amount of Fe is suppressed to 2.5% or less. The Fe content is preferably 2.0% or less. When the amount of Cr is excessive, the machinability is lowered. Therefore, the Cr content should be 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 comprises the above components, and the balance consists of Ti and inevitable impurities. As the inevitable impurities, P, N, S, O and the like can be mentioned. 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. The? -? -Type titanium alloy of the present invention may further contain the following elements.

At least one element selected from the group consisting of V: more than 0% to 5.0% or less, Mo: more than 0% to 5.0%, Nb: more than 0% to 5.0% % To less than 10%

These elements are? Stabilizing elements. These elements may be used alone or in combination of two or more. In order to produce the? phase, it is preferable that these elements are contained in a total amount of 2.0% or more, more preferably 3.0% or more in total. The total amount is more than 0%, and the lower limit of the content of each element is not particularly limited. The lower limit of the content of each element may be 0.5% or more, for example, 2.0% or more when V is contained. When Mo is contained, it can be 0.1% or more, and moreover 1.0% or more. When Nb is contained, it may be 0.1% or more, and more preferably 1.0% or more. When Ta is contained, it can be 0.1% or more, and more preferably 1.0% or more.

On the other hand, if the total amount of these elements is excessive, the ductility deteriorates. Therefore, the total amount of these elements is preferably 10% or less, and more preferably 5.0% or less. Even if the total amount is within the range, if at least one of the elements is excessive, ductility is deteriorated. 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 not more than 0.8%

Si precipitates Ti ₅ Si ₃ in the titanium alloy. It is the concentration of stress when the cutting, the Ti ₅ Si _3, by the voids starting from the Ti ₅ Si _3, is apt to machining chips are divided. As a result, it is considered that the cutting resistance is lowered. In order to sufficiently exhibit this effect, it is preferable to contain Si at 0.1% or more, and more preferably at 0.3% or more.

On the other hand, if the amount of Si is excessive, the strength of the titanium alloy becomes excessively high, and the tool is remarkably worn or broken, and cutting becomes difficult. Therefore, the amount of Si is preferably 0.8% or less. , More preferably not more than 0.7%, further preferably not more than 0.6%.

As the titanium alloy of the present invention, the structure is composed of an alpha phase and a beta phase at room temperature, or a third phase composed of alpha phase, beta phase, and Ti ₂ Cu or Ti ₂ Ni, have. Further, in the case of containing Si, Ti ₅ Si ₃ precipitates in the titanium alloy as described above.

The method for producing the? -? -Type titanium alloy is not particularly limited, and for example, it can be produced by the following method. That is, a titanium alloy of the above-mentioned component is dissolved, hot working is performed on the ingot, that is, hot forging or hot rolling, and then annealing is performed if necessary. The hot working is carried out by heating the ingot to a temperature in the range of about the β transformation temperature T _β to (T _β +250) ° C., and adjusting the machining _ratio represented by "original cross-sectional area / Followed by roughing or rough rolling. Subsequently, finishing is performed at a processing _{ratio of} 1.7 or more at a temperature range of (T _? -50) to 800 占 폚. After the above-mentioned finishing, annealing may be performed at 700 to 800 占 폚, if necessary. Annealing may be carried out, for example, for 2 to 24 hours. Thereafter, if necessary, the aging treatment may be carried out.

On the other hand, T _{? Is obtained} from the following equation (1). The following formula (1) is based on Morinaga et al., &Quot; Design of Titanium Alloy Using d Electron Theory, " 42, No. 11 (1992), p. (1) to (3) in the following.

^{Boave = 0.326Mdave-1.95 × 10 -4} T β + 2.217 ··· (1)

In the formula (1)

Boave =? Xi? (Bo) i (2)

Mdave =? Xi? (Md) i (3)

T _? Is the? Transformation temperature (K)

.

In expression (2), when each element is represented by element i,

Boave represents the average value of the binding order Bo of the element i, Xi represents the atomic ratio of the element i, and (Bo) i represents the value of the binding order Bo of the element i.

In expression (3), when each element is represented by element i,

Mdave represents the average value of the d orbital energy parameter Md of the element i, Xi represents the atomic ratio of the element i, and (Md) i represents the value of the d orbital energy parameter Md of the element i.

The coupling order Bo of each element and the d orbital energy parameter Md are described in p. 616 < / RTI > Xi is obtained from the composition of the components. From these data, it is possible to obtain Boave and Mdave of each element including Ti, and substitute the equation (1) into T _? . On the other hand, there is no Bo or Md data of C in this document, but since C amount is small in the present invention, C is ignored and T _{? Is} calculated.

This application claims the benefit of priority based on Japanese Patent Application No. 2015-064275 filed on March 26, 2015, and Japanese Patent Application No. 2016-009417 filed on January 21, 2016. The entire contents of the specification of Japanese Patent Application No. 2015-064275 filed on March 26, 2015 and the entire contents of the specification of Japanese Patent Application No. 2016-009417 filed on January 21, 2016 are incorporated herein by reference do.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples, and it is of course possible to carry out the present invention by modifying it appropriately within a range suitable for the purposes All of which are included in the technical scope of the present invention.

[Example 1]

The following materials were prepared for the test materials. By-arc melting, an ingot having a diameter of about 40 mm and a height of 20 mm was produced as a titanium alloy having the respective composition shown in Table 1 below. On the other hand, in either example, the P content was 0.005% or less, the N content was 0.05% or less, the S content was 0.05% or less, and the O content was 0.25% or less. In Table 1, " - " means that the element is not added. The ingot was heated to 1200 DEG C and rough-forged at a machining ratio of 2.4, which was expressed by "the original cross-sectional area / cross-section after hot working". Subsequently, the ingot was subjected to forging at 870 DEG C with a machining ratio of 4.4. Thereafter, annealing was performed at 750 占 폚 for 12 hours to obtain a publicly known material. On the other hand, as shown in Comparative Example 7 in Table 1 below, finishing forging was not performed in the case where cracks were formed by roughing.

Evaluation of mono-composition

The evaluation of the hot workability was evaluated by mono-composition in the hot state in this embodiment. Specifically, evaluation was made as to whether or not cracks were formed in the respective forging of the rough forging and finishing forging. That is, the surface of the specimen was observed with naked eyes after each forging, and it was judged as NG when the crack occurred and OK when the crack did not occur. It was evaluated that the case of OK in both roughing and finishing forging was excellent in mono-composition.

Evaluation of machinability

The evaluation of the machinability was carried out as follows. That is, a specimen of the following size was taken from the specimen, and a cutting test was conducted under the following cutting conditions. The cutting resistance was measured in the cutting direction from the beginning of cutting to the end of cutting by using a cutting dynamometer, model: 9257B manufactured by Kisler, and the average value of the cutting resistance from the beginning of cutting to the end of cutting was measured as the average cutting resistance Respectively. When the cutting test was conducted under the same conditions as that of the ordinary? -? -Type titanium alloy Ti-6Al-4V, the average cutting resistance was 180 N. Therefore, in this first embodiment, the case where the average cutting resistance is lower than 180 N, And when the average cutting resistance was 180 N or more, it was evaluated that the machinability was poor.

Cutting condition

Test piece: Height 10mm × width 10mm × length 150mm

Tool: Carbide tip made by Sandvik S30T (nose 0.4mm)

      End mill R390 (diameter 20 mm, one blade) manufactured by Sandvik Co.,

Cutting speed Vc: 100 m / min

Axial infeed: 1.2mm

Diameter infeed: 1mm

Feeding speed: 0.08mm / day

Cutting length: 150mm

Coolant: None

Measurement of tensile strength

The tensile strength of the? -? -Type titanium alloy of the present invention was also measured. Specifically, the titanium alloys of Examples 1 and 3 and Comparative Example 1 were subjected to a tensile test under the conditions of the following test pieces and the following test speed. As a result, the strength was 948 MPa in Example 1, 1125 MPa in Example 3, and 948 MPa in Comparative Example 1. The strength of the annealed material of Ti-6Al-4V, which is a general α-β type titanium alloy, was 896 MPa High strength.

Specimen configuration: ASTM E8 / E8M Fig. 8 Specimen 3

Test speed: 4.5 mm / min

The evaluation results of the monoclinic composition and the values of the average cutting resistance are shown in Table 1.

Table 1 shows the following. All of Examples 1 to 8 satisfied the component compositions defined in the present invention, all of which can be favorably forged, and have excellent mono-composition. Further, in these examples, it is understood that the average cutting resistance is smaller than that of Ti-6Al-4V, which is an ordinary? -? -Type titanium alloy, and satisfactory machinability is also obtained.

On the other hand, all of Comparative Examples 1 to 7 did not satisfy the component composition defined in the present invention, resulting in poor mono-composition or poor machinability. Specifically, in Comparative Example 1, since neither Cu nor Ni was contained, the average cutting resistance was increased. This Comparative Example 1 has the same composition as in Patent Document 6. In contrast to Examples 1 to 3 and Comparative Example 1 in which the elements other than Cu and Ni and the amounts thereof are the same as those in Examples 1 to 3, in order to sufficiently reduce the average cutting resistance and securely obtain good machinability, It is necessary to contain at least one of Cu and Ni in a specified amount as in the invention.

Comparative Example 2 is an example including Ni, but since the amount of Ni is excessive, and Comparative Example 5 is an example including Cu, since the amount of Cu is excessive, the average cutting resistance becomes higher than 180N in all cases and the machinability is deteriorated. In Comparative Example 3 and Comparative Example 6, since the amounts of Cu and Ni were excessive, the average cutting resistance was higher than 180 N, resulting in poor machinability.

In Comparative Example 4, since the amount of Cu was excessive, the mono-composition was lowered. In Comparative Example 7, since the amounts of Cu and Ni were remarkably excessive, cracks were generated in the step of joining and the result was that the mono-composition was inferior.

[Example 2]

In this embodiment, the influence on the machinability, especially when containing Si, was studied. As shown in Table 2, an ingot having various Si contents was produced, and a specimen was obtained in the same manner as in Example 1. [ On the other hand, in either example, the P content was 0.005% or less, the N content was 0.05% or less, the S content was 0.05% or less, and the O content was 0.25% or less. In Table 2, " - " means that the element is not added.

The presence of the precipitated phase was confirmed by using the above-mentioned material as described below, and in Example 2, Vickers hardness was measured as an index of strength. In addition, evaluation was made on the mono-composition in the same manner as in Example 1, and the machinability was evaluated as follows. On the other hand, for reference, 3, the tensile strength was measured in the same manner as in Example 1. As a result, the strength was higher than 968 MPa and the strength of the annealed material of Ti-6Al-4V, which is a general α-β type titanium alloy, was 896 MPa.

Evaluation of presence or absence of precipitation

The cross section was mirror-polished and subjected to an acid treatment to the extent that the grain boundary was observed by using hypochloric acid. The resultant was subjected to FE-SEM (Field Emission-Scanning Electron Microscope) at a magnification of 4000, 40 탆 in total were observed for 10 days. A case in which five or more precipitated phases having a circle-equivalent diameter of 2 탆 or more were identified as a total of 10 above were evaluated as "precipitated phases", and a case where the total number of the above 10 fields was 4 or less was evaluated as " Respectively. On the other hand, the precipitation phase is Ti ₅ Si ₃ , which is confirmed by X-ray diffraction (X-ray diffraction).

An example observed with the above microscope is shown in Fig. Fig. 3, and the arrow is one of the precipitated phases.

Measurement of Vickers hardness HV

Five points of Vickers hardness HV were measured under the condition of a load of 10 kgf, and an average value thereof was determined.

Evaluation of machinability

Evaluation of machinability was performed as in Example 1, that is, all the examples in Table 2 were evaluated as follows. That is, a specimen of the following size was taken from the specimen, and a cutting test was conducted under the following cutting conditions. The cutting resistance was measured in the cutting direction from the beginning of cutting to the end of cutting by using a cutting dynamometer, model: 9257B manufactured by Kisler, and the average value of the cutting resistance from the beginning of cutting to the end of cutting was measured as the average cutting resistance Respectively. When the cutting test was conducted under the same conditions as the ordinary? -Type titanium alloy Ti-6Al-4V, since the average cutting resistance was 122N, in Example 2, the case where the average cutting resistance was lower than 122N was evaluated as machinability And when the average cutting resistance was 122 N or more, it was evaluated that the machinability was poor.

Cutting condition

Test piece: Height 10mm × width 10mm × length 60mm

Tool: Carbide tip made by Sandvik S30T (nose 0.4mm)

      End mill R390 (diameter 20 mm, one blade) manufactured by Sandvik Co.,

Cutting speed Vc: 100 m / min

Axial infeed: 1.2mm

Diameter infeed: 1mm

Feeding speed: 0.08mm / day

Cutting length: 15mm

Coolant: None

These results are shown in Table 2.

Table 2 shows the following. Namely, the same composition as in Example 1 of Table 1 was obtained. 1 and No. 2. 2 to 6, particularly the contents other than Si were the same as those in Example 1 of Table 1 above. As can be seen from the contrast of 2 to 4, it can be seen that by containing Si, the average cutting resistance can be further reduced as compared with the case of not including Si, and sufficiently high machinability can be secured. On the other hand, 7 or No. In the case where the Si content is excessive as shown in Fig. 8, the hardness becomes excessively high, and the average cutting resistance becomes rather high, or the tool is damaged.

Claims (3)

In terms of% by mass,
At least one element selected from the group consisting of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0%
Al: 2.0 to 8.5%
C: 0.08 to 0.25%, and
At least one element selected from the group consisting of Cr: 0 to 4.5% and Fe: 0 to 2.5%
, And the balance of Ti and inevitable impurities. The method according to claim 1,
Further, in terms of% by mass,
At least one element selected from the group consisting of V: more than 0% to 5.0% or less, Mo: more than 0% to 5.0%, Nb: more than 0% to 5.0% ≪ RTI ID = 0.0 >%< / RTI > 3. The method according to claim 1 or 2,
Further, in terms of% by mass,? -Type titanium alloy containing Si: not less than 0% and not more than 0.8%.

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