JP2016183407A - α-β TYPE TITANIUM ALLOY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an α-β type titanium alloy having excellent hot workability and high strength at a level of an α-β type titanium alloy represented by Ti-6Al-4V, and exhibiting excellent machinability than that of the Ti-6Al-4V.SOLUTION: An α-β type titanium alloy includes, by mass%, at least one element selected from 0.1-2.0% Cu and 0.1-2.0% Ni, 2.0-8.5% Al, 0.08-0.25% C, and at least one element selected from 0-4.5% Cr and 0-2.5% Fe, in total 1.0-7.0%, and the balance Ti with inevitable impurities.SELECTED DRAWING: None

Description

  The present invention relates to an α-β type titanium alloy. In particular, it relates to an α-β type titanium alloy having excellent machinability.

  High strength α-β type titanium alloys represented by Ti-6Al-4V are light weight, high strength, and 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.

  As the α-β type titanium alloy, for example, Patent Document 1 discloses 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, as the α-β type titanium alloy extruded material, a specified amount of C and Al is contained, and any of V, Cr, Fe, Mo, Ni, Nb, and Ta is added in a total amount of 2.0 to 10.0. %, The area ratio of the primary α phase is within a certain range, and the major axis direction of the primary α grains of 80% or more of the primary α phase falls within the specified angle range, and the secondary α phase It is shown that the average minor axis of the phase is 0.1 μm or more.

  Further, as an α-β type titanium alloy with improved forgeability, Patent Document 2 discloses an α-β type titanium alloy for casting which has higher strength and superior castability than Ti-6Al-4V alloy. Yes. Specifically, there is shown an α-β type titanium alloy containing specified amounts of Al, Fe + Cr + Ni, and C + N + O, and further, if necessary, a specified amount of V, with the balance being Ti and inevitable impurities.

  However, in addition to the remarkably high production cost of α-β type titanium alloys, particularly poor machinability hinders the expansion of application of α-β type titanium alloys, and the range of use is limited. Is the current situation. In view of such circumstances, in recent years, various titanium alloys with improved machinability have been proposed.

  For example, in Patent Document 3, rare earth elements (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. However, a titanium alloy for connecting rods with improved machinability is described. 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.

  In 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.

  Further, in Patent Document 6, as an α-β type titanium alloy having excellent machinability and hot workability, each of prescribed amounts of V, Cr, Fe, Mo, Ni, Nb, together with prescribed amounts of C and Al, One type or two or more types from a β-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 μm or less is shown.

JP 2012-52219 A JP 2010-7166 A Japanese Patent Publication No. 6-99764 Japanese Patent Publication No. 6-53902 Japanese Patent No. 2626344 JP 2007-84865 A

  However, metal inclusions are deposited using REM as in Patent Document 3 and Patent Document 4, or P inclusions are formed by positively containing P as in Patent Document 5 or patents. In the method of controlling the size of TiC precipitates as described in Reference 6, the precipitation of these precipitates and inclusions is easily affected by the temperature and cooling rate in the melting-forging process, and the size of the precipitates can be controlled. It can be difficult. In addition, variations in the size of the precipitates and inclusions are likely to occur depending on the shape and size of the material. Therefore, there is a problem that strict management is necessary in the manufacturing process in order to obtain the desired machinability by depositing the target inclusions.

  The present invention has been made paying attention to the circumstances as described above, and the object thereof is α-β typified by Ti-6Al-4V without requiring strict management of the manufacturing process. It is to realize an α-β type titanium alloy having high strength at the level of a type titanium alloy and excellent hot workability and exhibiting machinability superior to the Ti-6Al-4V.

  The α-β type titanium alloy of the present invention that has solved the above-mentioned problems is at least one of Cu: 0.1 to 2.0% and Ni: 0.1 to 2.0% by mass. Elements: Al: 2.0-8.5%, C: 0.08-0.25%, and at least one of Cr: 0-4.5% and Fe: 0-2.5% It is characterized in that it contains 1.0 to 7.0% of the seed elements in total, and the balance is composed of Ti and inevitable impurities.

  The α-β 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.

  Further, the α-β type titanium alloy may further contain Si: more than 0% and 0.8% or less by mass%.

  According to the present invention, it has high workability such as high strength of α-β type titanium alloy represented by Ti-6Al-4V and excellent forgeability, and is superior to Ti-6Al-4V. It is possible to provide an α-β type titanium alloy which 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 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. Hereinafter, the component composition of the α-β 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% These elements are dissolved in the α phase and β phase in the alloy at 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 α-stabilizing element and is contained to generate an α-phase. If the amount of Al is less than 2.0%, the α 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. On the other hand, when the Al content exceeds 8.5% and becomes excessive, ductility deteriorates. Therefore, 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%
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. On the other hand, if the amount of C exceeds 0.25%, coarse TiC that does not dissolve in the α phase remains, and the mechanical properties deteriorate. Therefore, the C amount is 0.25% or less. The amount of C is preferably 0.20% or less.

1.0 to 7.0% in total of at least one element selected from Cr: 0 to 4.5% and Fe: 0 to 2.5%
These elements are β-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. For example, when Cr is contained, the lower limit of the content of each element can be 0.5% or more, and further can be 1.0% or more. When Fe is contained, the content can be 0.5% or more, and further 1.0% or more.

  On the other hand, ductility also deteriorates when the total amount of these elements is excessive. Therefore, the total 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. In addition, when the amount of Cr is excessive, machinability is lowered. Therefore, 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 α-β 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. In the α-β type titanium alloy of the present invention, the P amount is 0.005% or less, the N amount is 0.05% or less, the S amount is 0.05% or less, and the O amount is 0.25% or less. ing. The α-β 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, and Ta: more than 0% and 5.0% or less One or more elements in total, more than 0% and 10% or less. These elements are β-stabilizing elements. These elements may be used alone or in combination of two or more. In order to generate the β 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. When Mo is contained, the content can be 0.1% or more, and further 1.0% or more. When Nb is contained, the content may be 0.1% or more, and further 1.0% or more. When Ta is contained, the content can be 0.1% or more, and further 1.0% or more.

  On the other hand, if the total amount of these elements is excessive, ductility deteriorates. Therefore, 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.

  On the other hand, if the amount of Si is excessive, the strength of the titanium alloy becomes too high, and the tool is significantly worn or chipped, making cutting difficult. Therefore, 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.

Examples of the titanium alloy of the present invention include those whose structure is composed of an α phase and a β phase at room temperature, or an α phase, a β phase, and a third phase such as Ti ₂ Cu or Ti ₂ Ni. When Si is contained, Ti ₅ Si ₃ is precipitated in the titanium alloy as described above.

The manufacturing method of this (alpha) -beta type titanium alloy is not specifically limited, For example, it can manufacture with 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. In the hot working, the ingot is heated to a temperature range of about β transformation temperature T _β to (T _β +250) ° C., and the working ratio is expressed as “original cross-sectional area / cross-sectional area after hot working”. performs coarse forging or rough rolling of approximately 1.2 to 4.0, followed by _(T β -50) ~800 in a temperature range of about ° C., performs finishing of the above processing 1.7. You may anneal at 700-800 degreeC after the said finishing as needed. Annealing is performed for 2 to 24 hours, for example. Furthermore, you may give an aging treatment after that as needed.

The above _Tβ 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 _β +2.217 (1)
In equation (1),
Boave = ΣXi · (Bo) i (2)
Mdave = ΣXi · (Md) i (3)
T _β is β transformation temperature (K)
Means.
In formula (2), when each element is expressed as element i,
Boave is the average value of the bond order Bo of the element i, Xi is the atomic ratio of the element i, and (Bo) i is the value of the bond order Bo of the element i.
In formula (3), when each element is expressed as element i,
Mdave is the average value of the d orbital energy parameter Md of the element i, Xi is the atomic ratio of the element i, and (Md) i is the value of the d orbital energy parameter Md of the element i.

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 _Tβ is calculated.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[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.

Evaluation of forgeability Evaluation of hot workability was evaluated by hot forgeability in this example. In detail, it evaluated by the presence or absence of the crack in each forging of the said rough forging and finish forging. That is, the surface of the test material was visually observed after each forging, and it was determined that the case where cracks occurred was NG, and the case where cracks did not occur was OK. And in both rough forging and finish forging, the case of OK was evaluated as being excellent in forgeability.

Evaluation of machinability 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. And when Ti-6Al-4V which is a general α-β type titanium alloy is subjected to a cutting test under the same conditions, the average cutting resistance is 180 N. Therefore, in Example 1, the average cutting resistance is more than 180 N. The case where it was low was evaluated as being excellent in machinability, and the case where the average cutting resistance was 180 N or more was evaluated as being 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

Measurement of tensile strength For reference, the tensile strength of the α-β 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 of which were high in strength and annealed with Ti-6Al-4V, which is a general α-β type titanium alloy. Strength of material: higher than 896 MPa.
Specimen shape: ASTM E8 / E8M FIG. 8 Specimen3
Test speed: 4.5mm / min

  The evaluation results of forgeability and the value of average cutting resistance are shown in Table 1.

  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 α-β type titanium alloy, and also has good machinability.

  On the other hand, since Comparative Examples 1-7 do not satisfy the prescribed component composition in the present invention, the forgeability is poor or the machinability is poor. In detail, since 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. When the Examples 1 to 3 are compared with the Comparative Example 1 containing elements other than Cu and Ni and the amounts thereof are the same as those of Examples 1 to 3, the average cutting resistance is sufficiently reduced and good machining is 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, and 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. In 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.

  In Comparative Example 4, the forgeability decreased because the amount of Cu was excessive. In 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.

  While using the said test material and confirming the presence or absence of a precipitation phase as follows, in Example 2, Vickers hardness was measured as an intensity | strength parameter | index. Furthermore, while evaluating forgeability similarly to Example 1, machinability was evaluated as follows. For reference, No. 2 in Table 2 is used. 3, the tensile strength was measured in the same manner as in Example 1. The tensile strength was 968 MPa, and the strength of the annealed material of Ti-6Al-4V, which is a general α-β type titanium alloy, was higher than 896 MPa. .

Evaluation of Presence of Precipitated Phase After cross-section polishing and acid treatment to the extent that grain boundaries can be seen using nitric hydrofluoric acid, FE-SEM (Field Emission-Scanning Electron Microscope, Field Emission Scanning Electron Microscope) Then, a total of 10 fields of view size of 40 μm × 40 μm were observed at a magnification of 4000 times. Then, the case where five or more precipitated phases having an equivalent circle diameter of 2 μm or more were confirmed in total for the above 10 visual fields was evaluated as “precipitated phase”, and the case where the total number of the 10 visual fields was 4 or less was evaluated as “precipitated phase“ None. The above precipitated phase is confirmed separately by XRD (X-Ray Diffraction, X-ray diffraction) to be a Ti ₅ Si _3.

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

Measurement of 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.

Evaluation of machinability 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. And when Ti-6Al-4V, which is a general α-β type titanium alloy, 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 being excellent in machinability, and the case where the average cutting resistance was 122 N or more was evaluated as being 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
Axial cut depth: 1.2mm
Radial cut depth: 1mm
Feed rate: 0.08mm / blade cutting length: 15mm
Cutting oil: None

  These results are also shown in Table 2.

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, especially 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 by including Si, the average cutting resistance can be further reduced as compared with the case where Si is not included, and sufficiently high machinability can be secured. 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.

Claims (3)

% By mass
At least one element of Cu: 0.1-2.0% and Ni: 0.1-2.0%,
Al: 2.0 to 8.5%,
C: 0.08 to 0.25%, and
1.0 to 7.0% in total of at least one element selected from Cr: 0 to 4.5% and Fe: 0 to 2.5%
An α-β type titanium alloy characterized in that the balance is made of Ti and inevitable impurities. Furthermore, 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: more than 0% and 5.0% or less The α-β-type titanium alloy according to claim 1, comprising one or more elements in total exceeding 0% to 10%. Furthermore, (alpha) -beta type titanium alloy of Claim 1 or 2 containing Si: more than 0% and 0.8% or less by mass%.