JP6351149B2 - Titanium alloy and heat treatment method for the same - Google Patents

Description

  The present invention relates to a heat treatment method in a manufacturing process of a titanium alloy member by a powder method and a titanium alloy member subjected to the heat treatment, and more particularly to a heat treatment method for improving the workability of the titanium alloy member.

  Titanium alloys are composed of two phases, an α phase of hcp and a β phase of bcc, in an equilibrium state at room temperature. Depending on the ratio, an α alloy consisting of an α phase, an α and β phase (α + β) alloy, and a β phase It is broadly divided into β alloys and exhibits various mechanical properties.

  The proportion of α phase and β phase is determined by the composition of the titanium alloy and the thermomechanical treatment. The purpose of heat treatment of titanium alloy is to control the grain size and distribution of crystal grain size along with the release of strain introduced in the machining process, recrystallization, and recrystallization, and to realize a more stable crystal state. Is common.

  When a specific condition is satisfied, a so-called aging effect appears, and it is expected that the strength of the titanium alloy can be increased by the appearance of a precipitated phase accompanying heat treatment. Thus, it is considered that the properties of titanium alloys can be controlled over a wide range by changing the structure by thermomechanical treatment.

  Among titanium alloys, (α + β) type alloys represented by Ti-6Al-4V have poor cold workability, and are usually formed by processes such as rolling, extrusion, and forging at high temperatures.

On the other hand, the material molded by the powder method is reversely transformed into the β phase by leaving the α phase to some extent by solution treatment in which it is heated to (α + β) high temperature range below the β transformation point ( Tβ ) and then rapidly cooled. After that, an alloy excellent in ductility and toughness is obtained by increasing the strength by fine α phase precipitation from the untransformed β phase by aging treatment for about 5 hours in the (α + β) low temperature range around 500 ° C. There is a report that it is possible (see, for example, Non-Patent Document 1).

Such mechanical properties of the heat treated titanium alloy tensile strength (TS): about 1000 MPa, yield strength (YS): about 900 MPa (the ratio of resistance to hit tension strength (TS) (YS) is about 90%), Elongation: about 10% is common, and the main applications utilizing its high specific strength include various structural members, engine members, golf clubs and the like used in the space and aviation fields.

  By performing the processing described in the prior art, it is possible to remove the processing strain and control the crystal grain size and particle size accompanying recrystallization, which is effective in improving the ductility of the material. However, there was no technical idea of improving the workability of the titanium alloy by heat treatment of the titanium alloy.

Depending on the type of titanium alloy, the ductility may deteriorate due to heat treatment. However, in order to prevent the ductility from decreasing, the prior art also has a β transformation point ( Tβ ) or higher as a result of examination of the heating rate, temperature, time, and cooling rate. β transformation point ( Tβ ) ° C. + 100 ° C., heated at a heating rate of 2 ° C./second or more, held within 5 minutes, and then cooled at 2 ° C./second or more to achieve high strength, high toughness, high ductility (α + β ) Type titanium alloy is disclosed (for example, see Patent Document 1).

  Moreover, C contains more than 0.08% by mass%, 0.25% or less, Al contains 2.0 to 8.5%, and any one of V, Cr, Fe, Mo, Ni, Nb and Ta is contained. A technique of obtaining an (α + β) type titanium alloy having excellent fatigue strength by containing 2.0 to 10.0% in total is disclosed (for example, see Patent Document 2).

  In order to improve the workability, it is desirable that the high ductility and the degree of work hardening be low. However, a technique for realizing such a state by heat treatment is not well known.

  In general, titanium alloys have poor workability in cold or warm conditions, so the material processed by hot working is processed into the final shape by cutting, but the product rate of the material deteriorates, the life of the cutting tool deteriorates, etc. There is a problem and improvement is demanded.

JP-A-5-59509 JP 2012-52219 A

Masuo Sugawara, Yoshiya Kaieda, Yoshikuni Kaibe, Shin Miura: Iron and Steel (1990) Vol. 12, p2182;

  The present invention is intended to solve the above-described problems. By performing an appropriate heat treatment in the (α + β) region, the present invention has a higher elongation (EL) and tensile strength (TS) than before. It aims at providing the heat processing method of the titanium alloy which has workability higher than before by reducing a yield strength (YS), combining it.

  In view of this situation, the above-mentioned problems have been intensively studied. As a result, a titanium alloy mainly composed of a β phase subjected to a predetermined heat treatment, the abundance ratio of the β phase with respect to the parent phase in the titanium alloy is 50% to 80%. It has been found that a titanium alloy in the range of% shows not only high strength but also excellent elongation, and the present invention has been completed.

That is, the titanium alloy according to the present invention is a powder method titanium alloy produced by shaping by adding a powder of additive metal component to the titanium alloy powder, a main component β-phase, the mother of the titanium alloy The abundance ratio of the β phase to the phase is in the range of 50% to 80%.

In the titanium alloy according to the present invention are those wherein the 60% or less of yield strength tensile strength of the titanium alloy.

Furthermore, in the titanium alloy according to the present invention, a tensile strength of the titanium alloy is more than 1200 MPa, elongation is characterized in that 15% or more.

In the titanium alloy according to the present invention, the Vickers hardness of the titanium alloy is characterized in that it is less 390Hv.

Further, in the titanium alloy according to the present invention, the titanium alloy powder is a Ti-6Al-4V alloy, and the powder of the additive metal component is at least one selected from Cu, Fe, and Cr, and the Cu alloy It is a preferred embodiment to contain 0.5 to 4.0% of one or more elements of Fe, Cr.

In the heat treatment method for a titanium alloy according to the present invention, a titanium alloy having a workability of 3.5 or more and hot-worked in a temperature range of ( Tβ- 120) ° C. to Tβ ° C. is used in the atmosphere ( Tβ- 120 ) After cooling for 60 to 360 minutes in a temperature range of ° C to Tβ ° C, a preferred embodiment is to cool rapidly.

  In the present invention, when the titanium alloy having the above-described characteristics is subjected to the heat treatment, the elongation (EL) is 15% or more and the tensile strength (TS) is as high as 1200 to 1400 MPa, but the proof stress (YS) is 500. The effect is that a material as low as ˜700 MPa can be obtained.

The best embodiment of the present invention will be described in detail below.
Titanium alloy according to the present invention, first, the addition of additive element powder as required titanium alloy powder, hot extrusion, which has been formed by the densification treatment, such as a vacuum press or HIP process, subsequently, T [beta When the T is a β transformation point, a titanium alloy hot-worked in a temperature range of ( Tβ- 120) ° C. to Tβ ° C. with a workability of 3.5 or more is obtained in the atmosphere ( Tβ- 120) ° C. to Tβ ° C. A titanium alloy mainly composed of a β phase subjected to a heat treatment of rapid cooling after being held in a temperature range for 60 to 360 minutes, and the abundance ratio of the β phase to the parent phase in the titanium alloy is in the range of 50% to 80%. It is characterized by this. Here, the parent phase means the entire α phase and β phase. Here, the rapid cooling in the present invention means cooling using water or oil.

  Here, the β phase is mainly composed of a titanium alloy composed of a mixed phase of an α phase and a β phase in which the abundance ratio of the β phase with respect to the parent phase is within a range of 50% to 80% in the crystal structure. This is a preferred embodiment.

  If the β phase is less than 50%, the increase of YS due to the increase of the α phase causes a problem that YS / TS% increases and processing becomes difficult. On the other hand, if the β phase exceeds 80%, the β phase occupies most of the structure, so that YS decreases. However, TS further greatly decreases, and the problem that the strength significantly decreases occurs. Therefore, the titanium alloy according to the present invention is a titanium alloy mainly composed of a β phase, and the abundance ratio of the β phase to the parent phase in the titanium alloy is in the range of 50% to 80%. This is a preferred embodiment.

  By using an alloy having a crystal structure as described above, there is an effect that the yield strength is low and the workability is higher than the conventional one while having both high elongation and tensile strength compared to the conventional one. It is.

  Moreover, in the titanium alloy which concerns on this invention, there exists an effect that yield strength is 60% or less of tensile strength. The above properties have a yield strength of 60% or less with respect to the maximum tensile strength, which means that the ductility of the titanium alloy is excellent.

  Specifically, there is an effect that the titanium alloy has excellent properties having both elongation and strength such that the tensile strength of the titanium alloy is 1200 MPa or more and the elongation is 15% or more.

  In the titanium alloy according to the present invention, it is preferable that the Vickers hardness is 390 Hv or less, the hardness is lower than that of a generally-known titanium alloy, and in terms of machinability, It has excellent characteristics.

  By satisfying the mechanical characteristics, productivity of the cutting process is greatly improved, and as a secondary effect, there is an effect that the life of the chip when performing the cutting operation is greatly extended.

  The titanium alloy according to the present invention contains Al and V, and further preferably contains 0.5 to 4.0% of one or more elements of Cu, Fe, and Cr. .

  That is, the titanium alloy according to the present invention is a so-called 6Al4V alloy, and it is preferable that the alloy further contains at least one element of Cu, Fe, and Cr. .

  Specifically, by including 0.5 to 4.0 wt% of Cu, Fe, and Cr, the ratio of β phase can be controlled to 50 to 80%, and preferable characteristics according to the present invention can be obtained. This is an effect.

  As a result, there is an effect that a titanium alloy having excellent properties such as ductility and strength as described above can be selected.

In the titanium alloy heat treatment method according to the present invention, a titanium alloy having a workability of 3.5 and hot-worked in a temperature range of ( Tβ- 120) ° C. to Tβ ° C. in the atmosphere ( Tβ- 120) ° C. It is preferable to rapidly cool after holding for 60 to 360 minutes in a temperature range of ~ Tβ ° C. The degree of processing here is defined as (cross-sectional area of the sample before processing) / (cross-sectional area of the sample after processing).

If the hot working temperature is less than ( Tβ- 120) ° C., the deformation resistance may exceed the equipment capacity and the machining may become impossible. Further, since an excessive load is applied to the material, it may cause cracks during processing. On the other hand, if it exceeds Tβ ° C., the ductility decreases due to the generation of coarse β particles. Therefore, the hot working temperature according to the present invention is preferably in the range of ( Tβ- 120) ° C. to Tβ ° C.

If the holding temperature in the air after the hot working is less than ( Tβ- 120) ° C., the abundance ratio of the β phase with respect to the parent phase becomes less than 50%, and the ductility decreases. On the other hand, if it exceeds Tβ ° C., the ductility decreases due to the generation of coarse β particles. Therefore, the holding temperature in the atmosphere according to the present invention is preferably in the range of ( Tβ- 120) ° C. to Tβ ° C. In this example , Tβ of 920 ° C. was used .

  In the present invention, the holding time of the titanium alloy in the holding in the atmosphere is preferably 60 to 360 minutes.

  When the holding time is less than 60 minutes, the soaking of the titanium alloy cannot be achieved, the abundance ratio of the α phase and the β phase in the titanium alloy is generated, and the fracture starts from the portion where the abundance ratio of the α phase is high. It becomes easy. On the other hand, when the holding time exceeds 360 minutes, the particles become coarse due to heating for a long time and the ductility decreases. Therefore, the heat treatment time of the titanium alloy according to the present invention is preferably 60 to 360 minutes.

  In the present invention, it is preferable to rapidly cool after the heat treatment. By bringing the β-rich state in the hot state to room temperature by rapid cooling, it is possible to obtain an excellent elongation.

  Here, the cooling rate on the material surface by rapid cooling is preferably 10 to 300 ° C./second, and more preferably 20 to 200 ° C./second. The internal temperature of the material follows the slow heat from the cooling medium on the surface of the material and the heat conduction inside the material.

  By heat-treating the titanium alloy having the workability as described above in the temperature range described above, and then performing water cooling treatment, it is possible to produce a titanium alloy that not only exhibits high strength but also has excellent ductility. There is an effect.

  Here, the titanium alloy according to the present invention is a titanium alloy powder, after blending various metal powders so as to have a target alloy composition, after densifying to obtain a sintered body, A preferred embodiment is to heat-treat the sintered body after plastic working.

  The plastic strain of the plastic working as described above is preferably in the range of 3.5-25. By applying plastic strain to the above-described range, it is possible to efficiently refine the crystal grains by a subsequent heat treatment.

  As described above, the titanium alloy according to the present invention has an effect of exhibiting not only tensile strength but also excellent ductility.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
The equipment and conditions used in the examples are listed below.
1. Titanium alloy powder 1) Raw material: Cutting chips of titanium 64 alloy 2) Titanium alloy powder: produced by HDH method 3) Particle size: 10 μm to 250 μm
2. Additive element powder 1) Additive element: Copper 2) Average particle size: about 6 μm
3) Addition amount: 0.5 to 4.0 wt%
3. Densification treatment 1) Means: hot extrusion, vacuum press or HIP treatment 2) Densification temperature: 900 ° C. to 930 ° C.
4). Plastic working 1) Means Hot rolling Rolling ratio: 3.5-25
Hot forging Forging ratio: 3.5-28
2) Processing temperature: 850C-890C °
5. Heat treatment An annealing treatment was performed on the titanium material subjected to the plastic working treatment.
1) Temperature: 850C-900C
2) Atmosphere: Air atmosphere 3) Rate of temperature increase: 15 ° C./min 4) Holding time: 60 to 360 minutes 5) Cooling method: water cooling or oil cooling

[Example 1]
The above titanium alloy powder was used as a raw material, which was put into a capsule and densified by hot extrusion. The densified titanium sintered body was hot-rolled to obtain a bar having a diameter of 9.5 mm. When the crystal structure of the bar material obtained by holding the obtained bar material at 870 ° C. for 60 minutes and then subjecting it to water cooling was investigated, the ratio of the β phase crystal structure to the parent phase was 60%. The mechanical properties of the titanium alloy were EL: 21.4%, TS: 1286 MPa, YS: 526 MPa, and YS was 41% of TS. The Vickers hardness was 375 Hv.

[Example 2]
Various changes were made in the processing temperature, processing degree, and annealing temperature of the titanium alloy material used in Example 1, and various changes were made to β relative to the parent phase. YS / TS and Vickers of the titanium alloy material obtained in each case The effect on hardness was investigated, and the results are shown in Table 1. From the results in Table 1, it was confirmed that the ratio of the crystal structure of the β phase to the parent phase according to the method for producing a titanium alloy according to the present invention is in a preferable range of 50 to 80%.

[Example 3]
Various changes were made in the amount of copper powder added to the titanium alloy material used in Example 1, and the ratio of the crystal structure of the β phase to the parent phase obtained in each case was investigated. Indicated. From the results of Table 2, it was confirmed that the addition amount of the copper powder to be added according to the method for producing a titanium alloy according to the present invention is in a preferable range of 0.5 to 4.0 wt%.

[Example 4]
The amount of iron powder added to the titanium alloy material used in Example 1 was variously changed, and the ratio of the crystal structure of the β phase to the parent phase obtained in each case was investigated. The results are shown in Table 3. Indicated. From the results of Table 3, it was confirmed that the amount of iron powder added according to the method for producing a titanium alloy according to the present invention is in a preferred range of 0.5 to 4.0 wt%.

[Example 5]
Various changes were made in the amount of chromium powder added to the titanium alloy material used in Example 1, and the ratio of the crystal structure of the β phase to the parent phase obtained in each case was investigated. The results are shown in Table 4. Indicated. From the results of Table 4, it was confirmed that the amount of copper powder added according to the method for producing a titanium alloy according to the present invention is in a preferred range of 0.5 to 4.0 wt%.

[Example 6]
Various changes were made in the processing temperature, degree of processing and annealing temperature of the titanium alloy material used in Example 1, the heat treatment temperature was changed in various ways, and the YS / TS and Vickers hardness of the titanium alloy material obtained in each case were changed. The results are shown in Table 5. From the results of Table 5, it was confirmed that the heat treatment temperature according to the method for producing a titanium alloy according to the present invention is in a preferable range of ( Tβ- 120) to Tβ ° C.

[Example 7]
The effect of the titanium alloy material on YS / TS and Vickers hardness was investigated under the same conditions except that the cooling method was changed from water cooling to oil cooling in Example 1, and the results are shown in Table 6. From the result of Table 6, it was confirmed that the ratio of the crystal structure of the β phase to the parent phase according to the method for producing a titanium alloy according to the present invention is in a preferable range of 50 to 80%.

[Comparative Example 1]
In Example 1, except that the cooling method was air cooling, a titanium alloy in which the ratio of the β phase crystal structure to the parent phase was 60% was manufactured, and the tensile strength and elongation with respect to this were examined. The mechanical properties of the titanium alloy were TS: 1334 MPa, YS: 1202 MPa, EL: 9.4%, and YS was 90% of TS. The Vickers hardness was 452 Hv. Compared with Example 1, YS / TS was as high as 90%, and the elongation was inferior.

The α + β-type titanium alloy according to the present invention has a low YS and is not suitable for applications requiring mechanical strength, but sports equipment represented by implant materials such as artificial bones and artificial roots, golf heads, and baseball bats. Furthermore, application to suspensions represented by springs for transportation equipment is expected.

Claims (3)

A titanium alloy manufactured by a powder method in which a powder of an additive metal component is added to a titanium alloy powder and molded,
The titanium alloy mainly comprises a β phase ,
The tensile strength is 1200 MPa or more, the elongation is 15% or more, the yield strength is 60% or less of the tensile strength, the Vickers hardness is 390 Hv or less,
A titanium alloy characterized in that the abundance ratio of the β phase to the parent phase in the titanium alloy is in the range of 50% to 80%.   The titanium alloy powder is a Ti-6Al-4V alloy, the powder of the additive metal component is at least one selected from Cu, Fe, and Cr, and one or more elements of Cu, Fe, and Cr The titanium alloy according to claim 1, characterized by containing 0.5 to 4.0%.   3. The heat treatment method for a titanium alloy according to claim 1, wherein when Tβ is a β transformation point, the heat treatment is performed at a workability of 3.5 or more and a temperature range of (Tβ−120) ° C. to Tβ ° C. 3. A method for heat-treating a titanium alloy, characterized by holding the processed titanium alloy in the atmosphere (Tβ-120) ° C. to Tβ ° C. for 60 to 360 minutes and then rapidly cooling the titanium alloy.