JP6212976B2 - α + β type titanium alloy member and manufacturing method thereof - Google Patents

Description

  The present invention relates to an α + β type titanium alloy member having a high Young's modulus of 120 GPa or more and 140 GPa or less and a method for producing the same.

  The Young's modulus at room temperature of the titanium alloy is about 100 to 120 GPa for an α-type titanium alloy, α + β-type titanium alloy or the like mainly containing an α phase, and 70 to 90 GPa for a β-type titanium alloy mainly containing a β phase. However, even with a β-type titanium alloy, when the aging heat treatment is performed in the α + β two-phase region and the α-phase is precipitated, the Young's modulus can be increased to about 100 to 120 GPa, similar to the α-type titanium alloy and α + β-type titanium alloy. Is possible. As described above, a titanium alloy having a desired Young's modulus is used for the titanium alloy.

  As members for which a high Young's modulus is desired, there are two- or four-wheeled vehicle engine members as structural members, and golf clubs for general consumer products. However, titanium / titanium alloys, unlike steel materials, originally have low Young's modulus, and titanium alloys having a Young's modulus of 120 GPa or more are limited.

  In Patent Document 1, Mo is added to a Ti—Al—Fe system, and in mass%, 4.4% or more and less than 5.5% Al, 1.4% or more and less than 2.2% Fe, 2.5% A high-strength α + β-type titanium alloy containing Mo in an amount of not less than 5% and less than 5% and having impurities suppressed to less than 0.1% and C less than 0.01% is described. This alloy is subjected to various heat treatments to change the residual amount of β phase, thereby controlling the Young's modulus between 75 and 90 GPa. Among them, a method is described in which the Young's modulus is adjusted to 115 to 125 GPa by heating at 800 to 900 ° C. and then heating at 400 to 600 ° C. for 3 to 5 hours. However, this alloy uses an expensive element Mo, and in order to control it to a high Young's modulus, it is necessary to perform a long-time heat treatment for precipitating the α phase. There is a concern that will increase.

  Further, in Patent Document 2, as a titanium alloy for a golf club face, 4.7% to 5.5% Al, 0.5% to 1.4% Fe, 0.03% by mass%. A high-strength α + β-type titanium alloy having the following N and [O] eq calculated from [O] eq = [O] +2.77 [N] of 0.25% to 0.34% is described. Yes. By controlling the amount of Fe, Al, O, and N added to this alloy, it is possible to obtain characteristics that have a high Young's modulus and an excellent balance between strength and ductility when processing with a high degree of processing. Moreover, even if the degree of work is small, after one-way hot rolling in the β single-phase region or α + β two-phase region immediately below the β transformation point, or further, after one-way cold rolling in the same direction as the hot rolling direction By annealing under suitable conditions that are usually used and developing a transverse-texture, a high Young's modulus of around 140 GPa and excellent strength / ductility balance are obtained. However, in this method, processing with a high degree of processing or unidirectional rolling is a condition. For example, it is difficult to use this method for a product with few processing to the final shape.

JP 2010-1000094 A JP 2012-132057 A

  Therefore, an object of the present invention is to provide an α + β type titanium alloy that can obtain a high Young's modulus with an inexpensive alloy composition regardless of the production method.

  As a result of diligent studies to achieve the above-mentioned problems, the inventors have selected Al as the α-stabilizing element and inexpensive Fe as the β-stabilizing element, and appropriately controlled the addition amount to obtain a desired metal structure. It was found that a tensile strength of 800 MPa or more and a high Young's modulus of 120 GPa or more can be realized. At this time, after the β single-phase region heating, cooling may be performed at a cooling rate equivalent to or higher than air cooling, and the processing method before heat treatment is not limited.

That is,
(1) by mass%, containing 4.7% to 5.5% Al, 0.8% to 2.1% Fe , 0.046% to 0.151% O , and The oxygen equivalent [O] eq represented by the formula (1) is 0.06% or more and 0.35% or less, and is an α + β type titanium alloy member made of the balance titanium and unavoidable impurities, wherein the metal structure has an area ratio. An α + β-type titanium alloy member having a tensile strength of 800 MPa or more, having a needle-like structure of 90% or more, a width in the minor axis direction of needle-like α grains of 10 μm or less, and a Young's modulus of 120 GPa or more and 140 GPa or less.
[O] eq = [O] +2.77 [N] ----- Formula (1)
Here, [O] and [N] are the contents of oxygen and nitrogen expressed in mass%, respectively.
(2) A titanium alloy processed by any one of rolling, forging, bar wire, or wire drawing is heated at a β transformation point or higher and 1158 ° C. or higher, and then cooled by a water cooling method. The method for producing an α + β-type titanium alloy member according to (1), characterized in that
(3) A titanium alloy processed by any one of rolling, forging, bar wire, or wire drawing is heated at a β transformation point or higher and 1158 ° C. or higher, and then cooled by a water cooling method. Characterized by the
It contains 4.7% or more and 5.5% or less of Al, 0.8% or more and 2.1% or less of Fe in mass%, and the oxygen equivalent [O] eq represented by the formula (1) is 0 0.06% or more and 0.35% or less, an α + β type titanium alloy member composed of the remaining titanium and inevitable impurities, wherein the metal structure is an acicular structure having an area ratio of 90% or more and the short axis of acicular α grains A method for producing an α + β-type titanium alloy member having a tensile strength of 800 MPa or more and having a direction width of 10 μm or less and a Young's modulus of 120 GPa or more and 140 GPa or less.
[O] eq = [O] +2.77 [N] ----- Formula (1)
Here, [O] and [N] are the contents of oxygen and nitrogen expressed in mass%, respectively.

  According to the present invention, a titanium alloy member capable of achieving a tensile strength of 800 MPa or more and a high Young's modulus of 120 GPa or more with only a simple heat treatment using an α + β type titanium alloy having a relatively inexpensive alloy composition, and a method for producing the same The industrial effects are immeasurable.

Diagram of acicular structure of α + β titanium alloy member according to the present invention

  The present invention will be described in detail below.

  First, the material index of the present invention will be described.

  The Young's modulus at room temperature of a titanium alloy is about 100 to 120 GPa for α-type titanium alloys, α + β-type titanium alloys, etc., which mainly have an α phase. However, a high Young's modulus is desired for a two-wheel or four-wheel vehicle engine member as a structural member, a golf club for general consumer goods, and the like. Therefore, a titanium alloy member capable of achieving a tensile strength of 800 MPa or more and a high Young's modulus of 120 GPa or more and a manufacturing method thereof have been devised.

  The reason for selecting the additive element shown in the present invention and the reason for limiting the content range are shown below. Henceforth, content of an addition element is shown by "mass%".

  Fe is a relatively inexpensive β-stabilizing element, and the β phase can be strengthened by adding Fe. In addition, since it is an element exhibiting high β-stabilizing ability, the amount added can be reduced. In order to obtain a tensile strength of 800 MPa or more, it is necessary to add 0.8% or more of Fe. On the other hand, in order to stabilize the β phase having a lower Young's modulus compared to the α phase, the Young's modulus becomes less than 120 GPa when added excessively. In addition, Fe is easily solidified and segregated in Ti, and for this reason, the amount of Fe added is set to 2.1% or less.

  Al is an α-stable element, and is an element that dissolves in the α phase and strengthens the solution. A feature is that it is an inexpensive element like Fe. In order to obtain a tensile strength of 800 MPa or more, it is necessary to add 4.7% or more of Al. On the other hand, when Al is added excessively, ductility and cold workability at high temperature and room temperature are lowered. Therefore, the amount of Al added is set to 5.5% or less.

  Both O and N are interstitial solid solution in the α phase, strengthening the α phase at room temperature. High strength and high Young's modulus can be achieved by the combined addition with Al. As described in Patent Document 2, from the similarity of the strengthening mechanism of O and N on Ti, the action of O and N on the strength at room temperature is represented by [O] eq shown in the above formula (1). Can be shown. Similar to Al, in order to obtain a tensile strength of 800 MPa or more, [O] eq needs to be 0.06% or more. On the other hand, if O or N is added excessively, ductility decreases with increasing strength, so [O] eq needs to be 0.35% or less.

  Other than the above, the titanium alloy is composed of the remaining titanium and inevitable impurities.

  The main metal structure of the α + β type titanium alloy member of the present invention has a needle-like structure, and the width in the minor axis direction of each needle-like α grain is 10 μm or less. The α phase becomes needle-like crystal grains (hereinafter referred to as needle-like α grains, and the structure composed of such crystal grains is referred to as a needle-like structure), and is linear across the inside of one old β-phase crystal grain. In many cases, it grows up to the grain boundary of the old β phase (hereinafter referred to as the former β grain boundary). A needle-like crystal crosses the inside of the old β grains of equiaxed grains, and a needle-like structure is formed in which the needle-like axial direction differs depending on the old β grains. An example of a needle-like tissue according to the present invention is shown in FIG. As shown in the figure, the aspect ratio of one acicular α grain varies depending on the transformation start point, the growth direction, and the part of the old β grain. That is, since the aspect ratio of the acicular α grains in the present invention takes various values, the acicular α grains cannot be uniquely limited by the aspect ratio. The acicular structure (acicular α grains) in the titanium alloy member according to the present invention is preferably at least 90% or more in terms of area ratio. By controlling to this cross-sectional structure, it is possible to obtain an α + β type titanium alloy member having a Young's modulus of 120 GPa or more and a tensile strength of 800 MPa or more in combination with the above-mentioned components. Further, the narrower the width of the needle-like α grains, the higher the Young's modulus. In the examples of the present invention, even if a material having a narrow acicular α-grain width was used, the Young's modulus was approximately 140 GPa or less, so the upper limit of the Young's modulus was set to 140 GPa.

  Next, the manufacturing method of the (alpha) + (beta) type titanium alloy member of this invention is demonstrated.

  After the titanium alloy having the above component range is processed to a shape close to the final shape by various processing methods regardless of the processing method, it is heated to a β single-phase region above the β transformation point, and then cooled at a cooling rate equivalent to air cooling or higher. By doing so, the main metal structure is an acicular structure and the width of the acicular α grains in the minor axis direction can be 10 μm or less, and as a result, a high Young's modulus of 120 to 140 GPa can be obtained. That is, texture control or the like for achieving a high Young's modulus is unnecessary. The effect of the present invention is not affected by the production history and processing history of the target titanium alloy. Above the β transformation point, the chemical composition of most alloys is the β transformation point or higher because the structure during heat treatment (at the time of heating and holding) is a β single phase. However, even when the temperature is equal to or higher than the β transformation point, there is a possibility that the β single phase may not be formed by heating immediately above the β transformation point. In this case, it is desirable to perform heat treatment at a temperature higher than about the β transformation point + 20 ° C. On the other hand, the upper limit is set to the β transformation point + 200 ° C. because the heating temperature is not realistic from the viewpoint of cost, and the higher the temperature, the more the surface layer is oxidized and the yield is lowered. If the inside of the material is completely β single phase, the heating time may be short. After the heat treatment, a high Young's modulus can be achieved by cooling at a cooling rate equivalent to air cooling or higher. Here, the cooling rate equivalent to air cooling or higher is achieved by a cooling method using a gas such as air, water, water vapor mist, and He as a refrigerant, or a combination of one or more of the above cooling methods.

  Further, the titanium material according to the present invention may be subjected to a rolling process, a forging process, a bar wire process, or a wire drawing process before the heat treatment. It has been clarified that the Young's modulus in the direction perpendicular to the forging direction is higher when the process before the heat treatment is forged, and the Young's modulus in the longitudinal direction is higher when the round bar is rolled.

  In more detail, the formation process of such a needle-like structure will be described below. The titanium member before the heat treatment is a member processed by rolling or forging, and its metal structure is composed of α-phase crystal grains extending in the processed direction (hereinafter referred to as such crystal grains). The resulting structure is referred to as a stretched structure). When such a titanium member is heated to the β transformation point or more, the stretched structure or the α phase that has become equiaxed by recrystallization during heating is transformed into the β phase. The β grains at this time are equiaxed. Thereafter, it is cooled and transformed to the α phase again when the temperature becomes equal to or lower than the β transformation point. At this time, the origin of the α phase is often at the old β grain boundary. In the present invention, by cooling at a cooling rate equivalent to or higher than air cooling, the α phase becomes needle-like crystal grains, grows linearly across the inside of one old β grain, and extends to the old β grain boundary. There are many cases. That is, the acicular α grains grow so that the inside of the old β grains is linearly divided, and both end points of the acicular crystals are on the old β crystal grain boundaries. Eventually, acicular crystals traverse the inside of equiaxed old β grains, and an acicular structure is formed in which the axial direction of the needle varies depending on the old β grains. As shown in FIG. Further, a region that remains in the β phase without undergoing α transformation upon cooling, that is, a residual β phase exists between the acicular α grains. However, there is rarely a portion where the needle-like structure is not formed well, and such a portion is considered to be a case where the α phase remains without any β transformation during heating. The α grains other than such acicular alpha grains are crystal grains that are initially stretched crystal grains or equiaxed by recrystallization during heating even after cooling, and are in the background of the acicular structure. However, in some cases, the structure is such that stretched or equiaxed α grains are present. It is not preferable that such α grains exist. As described above, the acicular structure (acicular α grains) in the titanium alloy member according to the present invention is preferably at least 90% in terms of area ratio. As described above, the narrower the needle-like α grains, the higher the Young's modulus. That is, water cooling, which has a higher cooling rate than air cooling, reduces the width of the acicular α grains in the minor axis direction, and can achieve a high Young's modulus.

  The following examples illustrate the invention in more detail.

  <Example 1>

  A titanium alloy having the composition shown in Table 1 was melted by a vacuum arc melting method to cast a cylindrical ingot. This was hot forged into a billet with a diameter of 100 mm. After the billet was heated to 950 ° C., a round bar having a diameter of 18 mm was manufactured by hot rolling. After this bar was annealed at 800 ° C. for 2 hours, it was subjected to heat treatment for 20 minutes at the temperature shown in Table 1 (there was a comparative example in which some heat treatment was not performed) and cooled by the cooling method shown in Table 1 did. Thereafter, ASTM half-size tensile test pieces (parallel portion diameter 6.25 mm, length 32 mm) having an average diameter of 6 mm were collected and examined for tensile properties. A thermocouple was welded to the sample during the heat treatment and cooling, and the temperature during cooling was monitored at 0.5 second intervals. The cooling rate near the β transformation point is important for the formation of a metal structure that affects the tensile properties. However, when the sample is cooled below the β transformation point, the cooling rate rapidly decreases due to the latent heat of transformation until the β → α transformation starts and the transformation ends. Therefore, the cooling rate at the β transformation point of each sample was considered to be substantially equal to the cooling rate in the temperature range from the β transformation point + 50 ° C. to the β transformation point before the start of the β transformation point. This cooling rate was in the range of 2 ° C./s to 3 ° C./s in the case of air cooling, and in the range of 80 to 90 ° C./s in the case of water cooling (immersing the sample in a water bath). When the member was sufficiently small, it was confirmed that a cooling rate equivalent to air cooling or higher could be obtained even with gas cooling with He. At the time of collecting the tensile test piece, a test piece for optical microscope observation was taken from the vicinity of the tensile test piece, and an embedded polished sample having an L cross section (cross section parallel to the longitudinal direction) as an observation surface was prepared. Was observed after etching at room temperature using about 12% and hydrofluoric acid concentration of about 1.5%. At this time, while confirming the metal structure, the width in the short axis direction of the acicular α-grains (measured at 10 random points from each field of view and calculated the average value when measuring 20 fields in total) was measured. In addition, in the test piece that was water-cooled as a cooling method, since the width of the minor axis direction of the acicular α grains was narrow at the time of cross-sectional structure observation, and an accurate numerical value could not be measured with an optical microscope with low resolution, these acicular α The width in the minor axis direction of the grains is shown in Table 1 as 3 μm or less. Some of these test pieces have been confirmed to have a structure composed of fine acicular α grains by observation with a transmission electron microscope. Similarly, the area ratio of the needle-like tissue was calculated from the embedded sample for optical microscope observation. In addition, wrinkles and cracks during production were visually observed, and the presence or absence of wrinkles was also evaluated. These results are shown in Table 1.

  No. The comparative example described in 1 is a case where heat treatment after processing was not performed. The metal structure was an elongated structure extending in the longitudinal direction, which is the processing direction, and was not an acicular structure. In this case, the Young's modulus was less than 120 GPa, and a high Young's modulus was not obtained.

  No. 2 to No. The comparative example 6 is a case where it is cooled with water after being kept at 1100 ° C. for 20 minutes. In all cases, a high Young's modulus of 120 GPa or more was obtained. No. In the comparative example described in 2, a tensile strength of 800 MPa or more was obtained, but hot rolling and cracking considered to be caused by a large amount of Al addition occurred. No. In the comparative example described in 3, the addition amount of Al was small, and a strength of 800 MPa or more was not obtained. No. In the comparative example described in No. 4, the Fe addition amount was small, and a strength of 800 MPa or more was not obtained. No. In the comparative example described in No. 5, although a tensile strength of 800 MPa or more was obtained, hot rolling and cracking considered to be caused by the amount of Fe added occurred. No. In the comparative example described in No. 6, [O] eq was increased by increasing the amount of O, and although a tensile strength of 800 MPa or higher and a Young's modulus of 120 GPa or higher were obtained, the ductility decreased. Then, the crack at the time of manufacture considered to be confirmed was confirmed.

  No. 7 to No. Twelfth invention example is a result of evaluating a manufactured round bar using an ingot produced by changing the addition amount of Al and Fe so that [O] eq is about 0.15%.

  No. The example of invention described in 7 is the case where it cools by air after hold | maintaining for 20 minutes at 1050 degreeC. The metal structure was mainly an acicular structure, and the width of each acicular α-grain was 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more were obtained. No. The invention example of 8 is a case where it cools with water after hold | maintaining for 20 minutes at 1050 degreeC. Also here, the metal structure is mainly an acicular structure, and the width of each acicular α particle is 3 μm or less, and the width of the acicular α particle is narrower than that of the air-cooled material. Moreover, both tensile strength and Young's modulus were higher than those of air-cooled materials.

  No. The invention example described in No. 9 7 and no. This is a case where air cooling is performed after holding for 20 minutes at 1100 ° C., which is 50 ° C. higher than the invention example described in 8. As in the case of heating at 1050 ° C., the metal structure is mainly an acicular structure, the width of each acicular α-grain is 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more are obtained. No. The invention example described in 10 is a case where it is cooled with water after being kept at 1100 ° C. for 20 minutes. Also here, the metal structure is mainly a needle-like structure, and the width of each needle-like α grain is 3 μm or less. The width of the needle-like α grains was narrower than that of the ninth invention example. Moreover, both tensile strength and Young's modulus were higher than those of air-cooled materials.

  No. The invention example described in 11 is a case of air cooling after holding at a higher temperature of 1150 ° C. for 20 minutes. The metal structure was mainly an acicular structure, and the width of each acicular α-grain was 10 μm or less, the tensile strength was 800 MPa or more, and the Young's modulus was 120 GPa or more. No. The example of invention described in 12 is a case where it is cooled with water after being kept at 1200 ° C. for 20 minutes. The metal structure was mainly a needle-like structure, and the width of each needle-like α grain was 3 μm or less. No. Compared with 11 invention examples, the tensile strength and Young's modulus were further improved, the tensile strength was 800 MPa or more, and the Young's modulus was 120 GPa or more.

  No. 13 and no. The invention example of 14 is the result of evaluating a manufactured round bar using an ingot produced so that [O] eq is about 0.06%. No. The example of invention described in 13 is the case of air cooling after holding at 1100 ° C. for 20 min. Even when [O] eq was decreased, the metal structure remained mainly acicular, and the width of each acicular α grain was 10 μm or less. These had a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more. No. The example of invention described in 14 is a case where it is water-cooled after holding at 1100 ° C. for 20 minutes. No. Compared with the thirteen invention examples, the individual acicular α grains of the acicular structure were further finer, the tensile strength and Young's modulus were further improved, and good results were shown.

  No. 15 and no. Inventive example 16 is the result of evaluating a manufactured round bar using an ingot produced so that [O] eq is about 0.35%. No. The example of invention described in 15 is the case of air cooling after holding at 1100 ° C. for 20 min. Even when [O] eq increases, the metal structure after heat treatment mainly shows a needle-like structure, the width of each acicular α-grain is 10 μm or less, a tensile strength of 800 MPa or more, and a Young of 120 GPa or more. Showed the rate. No. The example of invention described in 16 is the case where it is water-cooled after holding at 1100 ° C. for 20 minutes. Even in this case, the metal structure mainly showed a needle-like structure, and the width of each needle-like α grain was 3 μm or less. No. Compared with the invention example of 14, the width | variety of each acicular (alpha) grain was also narrow, and the tensile strength and the Young's modulus improved further.

  No. 17 to No. The invention example described in No. 23 is No. 23. 14 is a result of performing a similar tensile test on the obtained test piece using an ingot having the same composition as the material shown in the invention example described in 14, changing the heating temperature during heat treatment based on the β transformation point. .

  No. 17 and no. The example of invention described in 18 is a case where the heating temperature at the time of heat treatment is β transformation point + 20 ° C. No. The example of invention described in 17 is the case where it cools by air after hold | maintaining for 20 minutes at 978 degreeC. The metal structure was mainly an acicular structure, and the width of each acicular α-grain was 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more were obtained. No. The example of invention described in 18 is a case where it is cooled with water after being kept at 978 ° C. for 20 minutes. Also in this case, the metal structure was mainly a needle-like structure, and each needle-like α grain became finer than the air-cooled material, and the tensile strength and Young's modulus were further improved.

  No. 19 and no. The example of invention described in 20 is a case where the heating temperature at the time of the heat treatment is β transformation point + 100 ° C. No. The example of invention described in 19 is the case of air cooling after holding at 1058 ° C. for 20 min. Even when the heating temperature was increased, the metal structure was mainly a needle-like structure, the width of each acicular α-grain was 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more were obtained. No. The example of invention described in 20 is a case where it is cooled with water after being kept at 1058 ° C. for 20 minutes. Also in this case, the metal structure was mainly a needle-like structure, and the width of each needle-like α grain was narrower than that of the air-cooled material, and the tensile strength and Young's modulus were further improved.

  No. 21 and no. The invention example described in No. 22 is a case where the heating temperature at the time of the heat treatment is β transformation point + 200 ° C. No. The invention example described in No. 21 is a case where air cooling is performed after holding at 1158 ° C. for 20 minutes. No. Even when the heating temperature was higher than that of the invention example described in Item 19, the metal structure was mainly a needle-like structure. Moreover, the width | variety of each acicular (alpha) grain of this structure | tissue is 10 micrometers or less, The tensile strength of 800 MPa or more and the Young's modulus of 120 GPa or more were shown. No. The invention example described in No. 22 is a case where it is cooled with water after being held at 1158 ° C. for 20 minutes. Even when water-cooled, the metal structure was mainly a needle-like structure, and the width of each needle-like α grain was narrower than that of the air-cooled material. Also, the tensile strength and Young's modulus were good.

  No. The invention example described in No. 23 is a case where the heating temperature at the time of the heat treatment is kept at 1208 ° C. which is the β transformation point + 250 ° C. for 20 minutes and then air-cooled. Again, no. A metal structure and tensile properties (tensile strength and Young's modulus) almost equivalent to those of 21 invention examples were obtained. However, since the heat treatment temperature was heated at a high temperature of 1200 ° C. or higher, the material surface was violently oxidized and the yield was greatly reduced.

  No. 24 to No. The invention example described in No. 31 is No. 31. 15 is a result of performing a similar tensile test on the obtained test piece using an ingot having the same composition as that of the material shown in Example 15 of the invention, changing the heating temperature during heat treatment based on the β transformation point. .

  No. The invention example described in No. 24 is a case where the heating temperature at the time of the heat treatment is kept at 1058 ° C. which is the β transformation point + 10 ° C. for 20 minutes and then air-cooled. No. Compared with the raw material without heat treatment of the comparative example described in 1, the Young's modulus was high and reached 120 GPa. However, from the cross-sectional structure observation, equiaxed α-grains that seem to have been recrystallized during heating until reaching the β region partially remain, and the region that was not completely β-transformed is about 10%. It was big. This is considered to be because the heating was just above the β transformation point and the heating time was as short as 20 min. The region transformed to β phase by heat treatment (the remaining about 90% region) was again α transformed into a needle-like structure in the subsequent cooling process, and the width of the needle-like α grains was 10 μm. In addition, in the test piece which extended the holding time during heat processing, hold | maintained at 1058 degreeC for 60 minutes, and was air-cooled, Example No. As described in Example 25, it was confirmed that about 98% of the cross-sectional structure is a needle-like structure, and when heat treatment is performed immediately above the β transformation point, a sufficiently long holding time is set. Is preferred.

  No. 26 and no. The example of invention described in 27 is a case where the heating temperature during the heat treatment is set to the β transformation point + 20 ° C. No. The invention example described in No. 26 is a case of air cooling after holding at 1068 ° C. for 20 min. The metal structure was mainly an acicular structure, and the width of each acicular α-grain was 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more were obtained. No. The example of invention described in 27 is the case where it is water-cooled after holding at 1068 ° C. for 20 min. Also in this case, the metal structure was mainly a needle-like structure, and each needle-like α grain became finer than the air-cooled material, and the tensile strength and Young's modulus were further improved.

  No. 28 and no. The example of invention described in 29 is a case where the heating temperature at the time of the heat treatment is β transformation point + 100 ° C. No. The example of invention described in 28 is a case where it is air-cooled after holding at 1148 ° C. for 20 minutes. Even when the heating temperature was increased, the metal structure was mainly a needle-like structure, the width of each acicular α-grain was 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more were obtained. No. The example of invention described in 29 is the case where it cools with water after hold | maintaining for 20 minutes at 1148 degreeC. Also in this case, the metal structure was mainly a needle-like structure, and the width of each needle-like α grain was narrower than that of the air-cooled material, and the tensile strength and Young's modulus were further improved.

  No. 30 and no. The example of invention described in 31 is a case where the heating temperature at the time of heat treatment is β transformation point + 200 ° C. No. The invention example described in 30 is a case where air cooling is performed after holding at 1248 ° C. for 20 minutes. No. Even when the heating temperature was higher than that of the invention example described in 28, the metal structure was mainly a needle-like structure. Moreover, the width | variety of each acicular (alpha) grain of this structure | tissue is 10 micrometers or less, The tensile strength of 800 MPa or more and the Young's modulus of 120 GPa or more were shown. No. The example of invention described in 31 is a case where it is water-cooled after holding at 1248 ° C. for 20 minutes. Even when water-cooled, the metal structure was mainly a needle-like structure, and the width of each needle-like α grain was narrower than that of the air-cooled material. Also, the tensile strength and Young's modulus were good.

  <Example 2>

  The above-mentioned Example 1 was an example using a round bar. Next, an example using a forging material will be shown. At this time, No. 1 in Example 1 was used. An ingot having the same composition as the material shown in FIG. A titanium alloy having the composition shown in Table 2 was melted by a vacuum arc melting method to cast a cylindrical ingot. This was hot forged into a billet with a diameter of 100 mm. After heating the billet to 950 ° C., a round bar having a diameter of 17 mm was manufactured by hot rolling. The round bar was heated at 950 ° C. for 30 min, and then hot forged to produce a flat forged material of 70 mmL × 40 mmW × 4.5 mmt. Using this forged material, heat treatment was carried out at 1050 to 1200 ° C. shown in Table 2 for 20 minutes (there was a comparative example in which some heat treatment was not performed), and cooling was performed by the cooling method shown in Table 2. Thereafter, a JIS13B half-size plate-like tensile test piece (4 mmt) was sampled and examined for tensile properties. In the same manner as in Example 1, when collecting a tensile test piece, a test piece for observation with an optical microscope was collected from the vicinity, and an L-section embedded polishing sample was prepared and observed after etching at room temperature using a nitric hydrofluoric acid aqueous solution. At this time, the metal structure was confirmed, and the width of the acicular α grains in the minor axis direction and the area ratio of the acicular structure (measurement conditions were the same as in Example 1) were measured. These results are shown in Table 2.

  No. The comparative example described in 32 is a case where heat treatment after processing was not performed. The metal structure was an elongated crystal grain structure extending in the processing direction and was not an acicular structure. In this case, the Young's modulus was less than 120 GPa, and a high Young's modulus was not obtained.

  No. The example of invention described in 33 is a case where it is air-cooled after being kept at 1050 ° C. for 20 minutes. The metal structure was mainly an acicular structure, and the width of each acicular α-grain was 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more were obtained. No. The example of invention described in 34 is a case where it is cooled with water after being kept at 1050 ° C. for 20 minutes. Also here, the metal structure is mainly an acicular structure, and the width of each acicular α particle is 3 μm or less, and the width of the acicular α particle is narrower than that of the air-cooled material. Moreover, both tensile strength and Young's modulus were higher than those of air-cooled materials.

  No. The invention example described in 35 is a case where air cooling is performed after holding at 1100 ° C. for 20 minutes. As in the case of heating at 1050 ° C., the metal structure is mainly an acicular structure, the width of each acicular α-grain is 10 μm or less, and a tensile strength of 800 MPa or more and a Young's modulus of 120 GPa or more are obtained. No. The invention example described in 36 is a case where it is cooled at 1100 ° C. for 20 minutes and then cooled with water. Also here, the metal structure is mainly a needle-like structure, and the width of each needle-like α grain is 3 μm or less. The width of the acicular α grains was narrower than the 35 invention examples. In addition, the tensile strength and Young's modulus were slightly higher than those of the air-cooled material.

  No. The example of invention of 37 is a case where it cools by air after hold | maintaining for 20 minutes at 1200 degreeC of higher temperature. The metal structure was mainly an acicular structure, and the width of each acicular α grain was 10 μm or less. The tensile strength was 800 MPa or more and the Young's modulus was 120 GPa or more. No. The example of invention described in 38 is a case where it cools with water after hold | maintaining for 20 minutes at 1200 degreeC. The metal structure is mainly a needle-like structure. Compared to 37 invention examples, the width of each acicular α grain was also narrow. Moreover, the tensile strength was 800 MPa or more and the Young's modulus was 120 GPa or more.

  As described above, even when a round bar or a forged material is used, when the metal structure is an acicular structure and the width of the acicular α grains is 10 μm or less, the tensile strength is 800 MPa or more and the Young is 120 GPa or more. The rate was obtained. Also, good characteristics were obtained even when actual products were produced from these.

Claims (3)

4.7% or more and 5.5% or less of Al, 0.8% or more and 2.1% or less of Fe 2 , 0.046% or more and 0.151% or less of O , and the formula (1 ) Is an α + β type titanium alloy member consisting of the remaining titanium and inevitable impurities, the metal structure having an area ratio of 90% or more. An α + β-type titanium alloy member having a tensile strength of 800 MPa or more, wherein the acicular structure of the needle-like α grains has a width in the minor axis direction of 10 μm or less and a Young's modulus of 120 GPa or more and 140 GPa or less.
[O] eq = [O] +2.77 [N] ----- Formula (1)
Here, [O] and [N] are the contents of oxygen and nitrogen expressed in mass%, respectively. A titanium alloy processed by any one of rolling, forging, bar wire, or wire drawing is heated at a β transformation point or higher and 1158 ° C. or higher, and then cooled by a water cooling method. The manufacturing method of the alpha + beta type titanium alloy member of Claim 1. A titanium alloy processed by any one of rolling, forging, bar wire, or wire drawing is heated at a β transformation point or higher and 1158 ° C. or higher, and then cooled by a water cooling method. To
  It contains 4.7% or more and 5.5% or less of Al, 0.8% or more and 2.1% or less of Fe in mass%, and the oxygen equivalent [O] eq represented by the formula (1) is 0 0.06% or more and 0.35% or less, an α + β type titanium alloy member composed of the remaining titanium and inevitable impurities, wherein the metal structure is an acicular structure having an area ratio of 90% or more and the short axis of acicular α grains A method for producing an α + β-type titanium alloy member having a tensile strength of 800 MPa or more and having a direction width of 10 μm or less and a Young's modulus of 120 GPa or more and 140 GPa or less.
[O] eq = [O] +2.77 [N] ----- Formula (1)
  Here, [O] and [N] are the contents of oxygen and nitrogen expressed in mass%, respectively.