JP2006052418A - METHOD FOR MANUFACTURING alpha+beta TYPE TITANIUM ALLOY - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an α+β type titanium alloy with a reduced number of forming steps. <P>SOLUTION: This manufacturing method comprises: a hydrogen absorption step of making the α+β type titanium alloy absorb hydrogen by holding the alloy in high-temperature hydrogen gas; a solution heat treatment step of subjecting the titanium alloy having absorbed hydrogen to solution heat treatment which heats the titanium alloy to the β-transformation temperature or higher, and then quenches it; a hot plastic working step of plastic-working the solution-treated titanium alloy with a hot working rate of 15% or higher per one time, for a plurality of times to refine crystals, so that the titanium alloy may not cause crack; and a dehydrogenation step of removing hydrogen from the titanium alloy after having been plastic-worked, by immediately holding it in a high temperature and vacuum atmosphere. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for refining an α + β type titanium alloy structure.

Among metal materials, titanium alloys have excellent mechanical properties and are lightweight, and thus are used for various applications. However, since the crystal grain size is increased and the mechanical strength is reduced in a normal processing method, a hydrogen treatment technique has been developed as a countermeasure (for example, see Patent Document 1).
JP 2002-88456 A (paragraph number [0010], claim 1)

Patent Document 1 is clear from the description of paragraph [0010], “In the method of the present invention, the β transformation point is lowered by the addition of hydrogen, and hot working in a lower temperature range is possible than before”. Thus, by carrying out hot plastic working in a lower temperature range, it is possible to suppress the coarsening of the crystal, and as a result, crystal refinement after plastic working can be achieved. If the crystal is fine, the mechanical properties are enhanced. It can be done.
The plastic working includes rolling forming and forging forming.

  Further, claim 1 of Patent Document 1 states that “a material obtained by adding 0.2 to 1.0% of hydrogen by weight% to an α + β type titanium alloy at a temperature of 650 to 850 ° C. with a processing rate exceeding 70%. After that, the hydrogen is removed at 550 to 680 ° C. in vacuum. In the examples, Ti-6Al-4V alloy (paragraph number [0016] second line) is clearly shown as the α + β type titanium alloy.

  The present inventors conducted an experiment to confirm the contents of the invention of Patent Document 1. The contents are shown in the following table.

  The material was a Ti-6Al-4V alloy, and 0.5 mass% of hydrogen was occluded in this alloy, and plastic working was performed at 750 ° C.

  In test number 1, the processing rate per time (stage) was set to 5%, and hot plastic working was performed so that the total processing rate reached 70%. The number of machining steps (stages) to achieve this total machining rate was 24. After plastic working, dehydrogenation treatment was performed, and when a cross section of the material was examined, no cracks were observed.

  In test number 2, the processing rate per time (stage) was set to 10%, and hot plastic working was performed so that the total processing rate reached 70%. The number of times of machining (number of stages) for achieving this total machining rate was 12 stages. After plastic working, dehydrogenation treatment was performed, and when a cross section of the material was examined, no cracks were observed.

  In test number 3, the processing rate per time (stage) was set to 15%, and the hot plastic working was performed so that the total processing rate reached 70%. The number of times of machining (number of stages) for achieving this total machining rate was 8 stages. The crack which can be visually confirmed in the middle of plastic working occurred, and it failed.

From the above experiment, the upper limit of the processing rate per process is 10%, and the required number of steps is 12 at 10%.
Currently, the upper limit of a multi-stage hot rolling mill that is commonly used is 10 stages. Since 12 steps are required at a processing rate of 10% and 24 steps are required at a processing rate of 5%, it is necessary to newly prepare dedicated equipment.

  If it is changed to a super multi-stage hot rolling mill exceeding 10 stages, the equipment cost is doubled. In addition, in order to heat the material once passed through the rolling mill and pass it through another rolling mill, a new dedicated facility is still necessary.

  This invention makes it a subject to provide the manufacturing method which can reduce the frequency | count of a process in an alpha + beta type titanium alloy.

In order to solve the above problems, the present inventors have made various studies and obtained the following knowledge in the process.
In the first place, the hydrogen treatment of titanium alloys is performed by hot plastic processing after the titanium alloy occludes hydrogen, and by introducing strain into the alloy, the hydride precipitates uniformly and finely, and the microstructure is formed by recrystallization. The purpose of this is to make the crystal grains finer.

  By the way, Al added for the purpose of improving the alloy quality makes it easy to produce titanium hydride if the added amount is excessive. This titanium hydride reduces ductility and induces cracking when the processing rate is increased. This is one of the reasons why the processing rate of one time has been limited to 10%.

From this knowledge, it was conceived that it is effective to reduce the addition amount of Al as a technique for suppressing the occurrence of cracking and increasing the processing rate.
Specifically, Ti-3Al-2., Which is obtained by halving Al, substantially halving V, and adding 2.5 to 3.5 mass% aluminum and 2.0 to 3.0 mass% vanadium. A 5V alloy is used as a starting material.

If the composition of the starting material changes, it is necessary to find processing conditions that are more suitable for this composition. Therefore, the processing conditions are examined.
The following table shows the contents and results of a test that investigated the relationship between hydrogen storage and structure.

  In any case, the material was a Ti-3Al-2.5V alloy, the plastic processing start temperature was (β transformation−100 = 580 ° C.), the processing rate per process was 15%, and the total processing rate was 80%.

In test number 4, hydrogen was not occluded for comparison. When the structure after the treatment was examined, the particle diameter was 3 to 5 μm, and there was no effect of miniaturization. When the average particle size exceeds 1 μm, it is determined that the coarse particle size is less than 1 μm.
Test No. 5 occluded 0.2% by mass of hydrogen. When the structure after the treatment was examined, it was confirmed that the fine structure was good.

Test Nos. 6 to 8 occluded 0.4 mass%, 0.6 mass%, and 0.8 mass% of hydrogen. When the structure after the treatment was examined, it was confirmed that the fine structure was good.
Test No. 9 occluded 1.0 mass% of hydrogen. Examination of the treated structure revealed that it was refined but not uniform.

  Therefore, in order to obtain a fine microstructure with the Ti-3Al-2.5V alloy, the hydrogen storage amount needs to be set to 0.2 to 0.8 mass%.

  Next, since the plastic processing start temperature was examined, the contents and results are shown in the following table.

  In any case, the material was Ti-3Al-2.5V alloy, the hydrogen storage was 0.5% by mass, the processing rate at one time was 15%, and the total processing rate was 80%.

In test number 10, the plastic working was carried out at a plastic working start temperature of β-290 (390 ° C.). The ductility decreases because of the low temperature. Cracking occurred because of plastic working in this state.
In Test Nos. 11 to 13, the plastic working start temperature was increased, and plastic working was performed as β-225 (455 ° C.), β-100 (580 ° C.), and β-50 (630 ° C.), respectively. No cracking occurred. When other structures were applied and the structure was examined, it was confirmed that the structure was fine.
In test number 14, the plastic working was performed at a plastic working start temperature of β + 50 (730 ° C.). Since the plastic working was started above the β transformation point, the structure became abnormal.

  Therefore, in order to obtain a fine microstructure without cracking in the Ti-3Al-2.5V alloy, the plastic working start temperature is (β transformation point −225 ° C.) or more and (β transformation point −50 ° C.) or less. Must be set.

Next, since the processing rate of one time was examined, the contents and results are shown in the following table.
In addition, the processing rate of 1 time is defined by (the amount of plastic processing / the thickness immediately before). For example, if the thickness immediately before (before plastic processing) is 90 mm and the thickness after plastic processing is 81 mm, the amount of plastic processing is 9 mm (= 90-81), and the processing rate is 10% (= 9/90). Become. The immediately preceding thickness is not a constant value and decreases as the turn proceeds.

  In any case, the material was Ti-3Al-2.5V alloy, the hydrogen occlusion was 0.5% by mass, the plastic processing start temperature was (β transformation−100 = 580 ° C.), and the total processing rate was 70%.

In test number 15, plastic working was carried out with the rate of processing at one time set to 10%. Although cracking did not occur, the number of machining operations was 12 steps, and since it exceeded 10 steps, it was difficult to ensure industrial productivity.
In test number 16, plastic working was carried out with the processing rate per time set to 15%. No cracking occurred. The number of machining operations was 8 steps, which was less than 10 steps.
In Test No. 17, plastic working was performed with the processing rate per time set to 20%. No cracking occurred. The number of machining operations was 6 steps, which was less than 10 steps.
In test number 18, plastic working was carried out with the rate of one process set at 25%. No cracking occurred. The number of machining operations was 5 steps, which was less than 10 steps.
In Test No. 19, cracking occurred when plastic processing was performed with the processing rate per process set to 30%.

  Therefore, the Ti-3Al-2.5V alloy is free from cracks, and in order to reduce the number of times of processing, it is necessary to set the processing rate of one time to 15% to 25%.

  Next, since the total processing rate was examined, the contents and results are shown in the following table. The total processing rate is defined by (total plastic processing amount / initial thickness). For example, if the initial thickness is 100 mm and the thickness after a plurality of plastic workings is 26 mm, the plastic working amount is 74 mm (= 100−26) and the total working rate is 74% (= 74/100). ) Since the initial thickness is the thickness before plastic processing starts, it is constant.

  In any case, the material was Ti-3Al-2.5V alloy, the hydrogen storage was 0.5% by mass, the plastic processing start temperature was (β transformation−100 = 580 ° C.), and the processing rate at one time was 15%.

In test number 20, plastic working was performed with the total working rate set to 50%. A sufficient miniaturization could not be obtained due to insufficient plastic working.
In test number 21, plastic working was performed with the total working rate set to 60%. Good miniaturization was obtained.
In test numbers 22 and 23, plastic working was performed with the total working rate set to 70% and 80%. Good miniaturization was obtained.

  Therefore, in order to obtain a good microstructure with the Ti-3Al-2.5V alloy, the total processing rate needs to be 60% or more.

In summary, the invention according to claim 1 provides an α + β-type titanium alloy, a hydrogen storage treatment step of storing hydrogen by holding the titanium alloy in a high-temperature hydrogen gas, and titanium storing the hydrogen. A solution treatment process in which the alloy is heated to the β transformation point or higher and then rapidly cooled, and a hot plastic working process in which the crystal is refined by hot plastic processing of the titanium alloy after the treatment. And a dehydrogenation process for removing hydrogen by holding the titanium alloy after plastic working at a high temperature in a vacuum,
The α + β type titanium alloy to be prepared is a Ti-3Al-2.5V alloy obtained by adding 2.5 to 3.5 mass% aluminum and 2.0 to 3.0 mass% vanadium to titanium,
In the hydrogen storage treatment step, 0.2 to 0.8 mass% of hydrogen is stored in the titanium alloy,
In the hot plastic working step, the plastic working start temperature is set to (β transformation point−225 ° C.) or more and (β transformation point−50 ° C.) or less, and is defined as (plastic working amount / previous thickness). The processing rate is set to at least 15%, and the total processing rate defined by (total plastic processing amount / initial thickness) is set to at least 60%, and the plastic processing is performed a plurality of times.

  In the above, the example which used the Ti-3Al-2.5V alloy as the starting material was described. Next, an example in which the starting material is a Ti-3Al-2V-0.1S alloy will be described.

  That is, Al is halved, V is almost halved, 2.7 to 3.5 mass% aluminum and 1.6 to 3.4 mass% vanadium are added, and 0.05 to 0.20 mass% A Ti-3Al-2V-0.1S alloy to which sulfur is added is used as a starting material.

If the composition of the starting material changes, it is necessary to find processing conditions that are more suitable for this composition. Therefore, the processing conditions are examined.
The following table shows the contents and results of a test that investigated the relationship between hydrogen storage and structure.

  In all cases, the material was a Ti-3Al-2V-0.1S alloy, the plastic processing start temperature was (β transformation−100 = 600 ° C.), the processing rate per process was 15%, and the total processing rate was 80%.

In test number 24, hydrogen was not occluded for comparison. When the structure after the treatment was examined, the particle diameter was 3 to 5 μm, and there was no effect of miniaturization. When the average particle size exceeds 1 μm, it is determined that the coarse particle size is less than 1 μm.
Test numbers 25 to 27 occluded 0.2 mass%, 0.4 mass%, and 0.6 mass% of hydrogen. When the structure after the treatment was examined, it was confirmed that the fine structure was good.

Test No. 28 occluded 0.7% by mass of hydrogen. Cracks occurred at a total processing rate of 40%. Examination of the treated structure revealed that it was refined but not uniform.
Test No. 29 occluded 1.0 mass% of hydrogen. Cracks occurred at a total processing rate of 20%. Examination of the treated structure revealed that it was refined but not uniform.

  Therefore, in order to obtain a fine microstructure with the Ti-3Al-2V-0.1S alloy, the hydrogen storage amount needs to be set to 0.2 to 0.6 mass%.

  Next, since the plastic processing start temperature was examined, the contents and results are shown in the following table.

  In any case, the material was a Ti-3Al-2V-0.1S alloy, the hydrogen storage was 0.5% by mass, the processing rate at one time was 15%, and the total processing rate was 80%.

In test number 30, the plastic working was carried out at a plastic working start temperature of β-150 (550 ° C.). The ductility decreases because of the low temperature. Cracking occurred because of plastic working in this state.
In Test Nos. 31 to 33, the plastic working start temperature was raised, and plastic working was performed as β-125 (575 ° C.), β-100 (600 ° C.), and β-50 (650 ° C.), respectively. No cracking occurred. When other structures were applied and the structure was examined, it was confirmed that the structure was fine.
In test number 34, the plastic working was performed at a plastic working start temperature of β + 50 (750 ° C.). Since the plastic working was started above the β transformation point, the structure became abnormal.

  Therefore, in order to obtain a fine microstructure without cracks in the Ti-3Al-2V-0.1S alloy, the plastic working start temperature is (β transformation point −125 ° C.) or more (β transformation point −50 ° C.). Must be set to:

Next, since the processing rate of one time was examined, the contents and results are shown in the following table.
In addition, the processing rate of 1 time is defined by (the amount of plastic processing / the thickness immediately before). For example, if the thickness immediately before (before plastic processing) is 90 mm and the thickness after plastic processing is 81 mm, the amount of plastic processing is 9 mm (= 90-81), and the processing rate is 10% (= 9/90). Become. The immediately preceding thickness is not a constant value and decreases as the turn proceeds.

  In any case, the material was Ti-3Al-2V-0.1S alloy, the hydrogen storage was 0.5 mass%, the plastic processing start temperature was (β transformation−100 = 600 ° C.), and the total processing rate was 70%.

In test number 35, the plastic working was performed with the processing rate per time set to 10%. Although cracking did not occur, the number of machining operations was 12 steps, and since it exceeded 10 steps, it was difficult to ensure industrial productivity.
In the test number 36, the plastic working was performed by setting the processing rate at one time to 15%. No cracking occurred. The number of machining operations was 8 steps, which was less than 10 steps.
In test number 37, the plastic working was carried out with the rate of processing at one time set to 20%. No cracking occurred. The number of machining operations was 6 steps, which was less than 10 steps.
In Test No. 38, cracking occurred when plastic processing was performed with the processing rate of one time set at 25%.

  Therefore, the Ti-3Al-2V-0.1S alloy is free from cracks, and in order to reduce the number of times of processing, it is necessary to set the processing rate of one time to 15% to 20%.

  Next, since the total processing rate was examined, the contents and results are shown in the following table. The total processing rate is defined by (total plastic processing amount / initial thickness). For example, if the initial thickness is 100 mm and the thickness after a plurality of plastic workings is 26 mm, the plastic working amount is 74 mm (= 100−26) and the total working rate is 74% (= 74/100). ) Since the initial thickness is the thickness before plastic processing starts, it is constant.

  In any case, the material is Ti-3Al-2V-0.1S alloy, the hydrogen storage is 0.5 mass%, the plastic processing start temperature is (β transformation−100 = 600 ° C.), and the one-time processing rate is 15%. .

In test number 39, plastic working was performed with the total working rate set to 40%. A sufficient miniaturization could not be obtained due to insufficient plastic working.
In test number 40, the total working rate was set to 60% and plastic working was performed. A sufficient miniaturization could not be obtained due to insufficient plastic working.
In test numbers 41 and 42, the plastic working was performed with the total working rate set to 70% and 80%. Good miniaturization was obtained.

  Therefore, in order to obtain a good microstructure with the Ti-3Al-2V-0.1S alloy, the total processing rate needs to be 70% or more.

In summary, the invention according to claim 2 provides an α + β-type titanium alloy, a hydrogen storage treatment step of storing hydrogen by holding the titanium alloy in a high-temperature hydrogen gas, and titanium storing the hydrogen. A solution treatment process in which the alloy is heated to the β transformation point or higher and then rapidly cooled, and a hot plastic working process in which the crystal is refined by hot plastic processing of the titanium alloy after the treatment. And a dehydrogenation process for removing hydrogen by holding the titanium alloy after plastic working at a high temperature in a vacuum,
The α + β type titanium alloy to be prepared is obtained by adding 2.7 to 3.5 mass% aluminum, 1.6 to 3.4 mass% vanadium, and 0.05 to 0.20 mass% sulfur to titanium. Ti-3Al-2V-0.1S alloy,
In the hydrogen storage process, 0.2 to 0.6 mass% of hydrogen is stored in the titanium alloy,
In the hot plastic working process, the plastic working start temperature is set to (β transformation point−125 ° C.) or more and (β transformation point−50 ° C.) or less, and is defined as (plastic working amount / previous thickness). The processing rate is set to at least 15%, and the total processing rate defined by (total plastic processing amount / initial thickness) is set to at least 70%.

  In the present invention, by reducing the amount of Al, which is an element that does not form a hydride, the precipitation of titanium hydride during hot plastic working is suppressed, embrittlement of the material is prevented, and the occurrence of cracks is consequently suppressed. . On the other hand, Ti-Fe-O alloys and Ti-Fe-O-N alloys have been studied as inexpensive alloys that can replace Ti-3Al-2.5V alloys and the like particularly in the temperature range near room temperature. These main strengthening elements are O or O and N, and since these elements have a large contribution rate of material strengthening, sufficient strength can be achieved even if the addition amount is small. Since N has the same effect as O, Ti—Fe—O and Ti—Fe—O—N alloys are equivalent.

The small amount added is expected to be an excellent material when considering plastic working in a hydrogenated state.
However, the hydrogen treatment is not effective for α-phase single-phase materials, and it is necessary to use an α + β two-phase alloy. Since Fe is a strong β-stabilizing element, a β phase can be formed at the grain boundary with a small amount of addition.
However, since Fe is an element that does not form a hydride like Al, excessive addition is not preferable because it promotes precipitation of titanium hydride. If an appropriate addition amount is selected, a Ti—Fe—O alloy as well as a Ti—Fe—O—N alloy may be a suitable material for hydrogen treatment.
Therefore, an example in which the starting material is a Ti-1Fe-0.3O alloy will be described next.

  That is, a Ti-1Fe-0.3O alloy obtained by adding 0.7 to 2.3 mass% of iron and 0.2 to 0.7 mass% of oxygen is used as a starting material.

If the composition of the starting material changes, it is necessary to find processing conditions that are more suitable for this composition. Therefore, the processing conditions are examined.
The following table shows the contents and results of a test that investigated the relationship between hydrogen storage and structure.

  In any case, the material was a Ti-1Fe-0.3O alloy, the plastic processing start temperature was (β transformation−100 = 590 ° C.), the processing rate at one time was 15%, and the total processing rate was 80%.

In test number 43, hydrogen was not occluded for comparison. When the structure after the treatment was examined, the particle diameter was 3 to 5 μm, and there was no effect of miniaturization. When the average particle size exceeds 1 μm, it is determined that the coarse particle size is less than 1 μm.
In Test No. 44, 0.3% by mass of hydrogen was occluded. When the treated tissue was examined, it was a heterogeneous tissue.

Test Nos. 45 to 47 occluded 0.4 mass%, 0.6 mass%, and 0.8 mass% of hydrogen. When the structure after the treatment was examined, it was confirmed that the fine structure was good.
Test No. 48 occluded 1.0 mass% of hydrogen. Examination of the treated structure revealed that it was refined but not uniform.

  Therefore, in order to obtain a good refined structure with the Ti-1Fe-0.3O alloy, the hydrogen storage amount needs to be set to 0.4 to 0.8 mass%.

  Next, since the plastic processing start temperature was examined, the contents and results are shown in the following table.

  The material was Ti-1Fe-0.3O alloy, the hydrogen occlusion was 0.5% by mass, the processing rate at one time was 15%, and the total processing rate was 40, 80%.

In test number 49, the plastic working was performed at a plastic working start temperature of β-300 (390 ° C.). Since the temperature was low, the ductility decreased, the total processing rate was 40%, and cracking occurred.
In test numbers 50 to 52, the plastic working start temperature was increased, and plastic working was performed as β-275 (415 ° C.), β-200 (490 ° C.), and β-75 (615 ° C.), respectively. No cracking occurred. When other structures were applied and the structure was examined, it was confirmed that the structure was fine.
In test number 53, the plastic working was performed at a plastic working start temperature of β-50 (640 ° C.). It became a heterogeneous structure.

  Therefore, in order to obtain a fine microstructure without cracks in the Ti-1Fe-0.3O alloy, the plastic working start temperature is (β transformation point −275 ° C.) or more and (β transformation point −75 ° C.) or less. Must be set.

Next, since the processing rate of one time was examined, the contents and results are shown in the following table.
In addition, the processing rate of 1 time is defined by (the amount of plastic processing / the thickness immediately before). For example, if the thickness immediately before (before plastic processing) is 90 mm and the thickness after plastic processing is 81 mm, the amount of plastic processing is 9 mm (= 90-81), and the processing rate is 10% (= 9/90). Become. The immediately preceding thickness is not a constant value and decreases as the turn proceeds.

  In any case, the material was Ti-1Fe-0.3O alloy, the hydrogen storage was 0.5% by mass, the plastic processing start temperature was (β transformation−100 = 590 ° C.), and the total processing rate was 70%.

In the test number 54, the plastic working was performed with the processing rate per time set to 10%. Although cracking did not occur, the number of machining operations was 12 steps, and since it exceeded 10 steps, it was difficult to ensure industrial productivity.
In test number 55, the plastic working was performed with the processing rate per time set to 15%. No cracking occurred. The number of machining operations was 8 steps, which was less than 10 steps.
In test number 56, the plastic working was carried out with the rate of processing at one time set to 20%. No cracking occurred. The number of machining operations was 6 steps, which was less than 10 steps.
In the test number 57, the plastic working was performed with the processing rate of one time set to 25%. No cracking occurred. The number of machining operations was 5 steps, which was less than 10 steps.
In Test No. 58, when plastic working was performed with the processing rate per time set to 30%, cracks occurred.

  Therefore, the Ti-1Fe-0.3O alloy is free from cracks, and in order to reduce the number of times of processing, it is necessary to set the processing rate of one time to 15% to 25%.

  Next, since the total processing rate was examined, the contents and results are shown in the following table. The total processing rate is defined by (total plastic processing amount / initial thickness). For example, if the initial thickness is 100 mm and the thickness after a plurality of plastic workings is 26 mm, the plastic working amount is 74 mm (= 100−26) and the total working rate is 74% (= 74/100). ) Since the initial thickness is the thickness before plastic processing starts, it is constant.

  In any case, the material was Ti-1Fe-0.3O alloy, the hydrogen occlusion was 0.5% by mass, the plastic processing start temperature was (β transformation-100 = 590 ° C.), and the processing rate at one time was 15%.

In test number 59, plastic working was performed with the total working rate set to 40%. Due to inadequate plastic working, sufficient fineness could not be obtained, resulting in a non-uniform structure.
In test number 60, plastic working was performed with the total working rate set to 60%. Due to inadequate plastic working, sufficient fineness could not be obtained, resulting in a non-uniform structure.
In test numbers 61 and 62, plastic working was performed with the total working rate set to 70% and 80%. Good miniaturization was obtained.

  Therefore, in order to obtain a fine microstructure with the Ti-1Fe-0.3O alloy, the total processing rate needs to be 70% or more.

In summary, the invention according to claim 3 provides an α + β-type titanium alloy, a hydrogen occlusion treatment step in which hydrogen is occluded by holding the titanium alloy in high-temperature hydrogen gas, and titanium in which hydrogen is occluded. A solution treatment process in which the alloy is heated to the β transformation point or higher and then rapidly cooled, and a hot plastic working process in which the crystal is refined by hot plastic processing of the titanium alloy after the treatment. And a dehydrogenation process for removing hydrogen by holding the titanium alloy after plastic working at a high temperature in a vacuum,
The α + β type titanium alloy to be prepared is a Ti-1Fe-0.3O alloy obtained by adding 0.7 to 2.3 mass% of iron and 0.2 to 0.7 mass% of oxygen to titanium,
In the hydrogen storage treatment step, 0.4 to 0.8% by mass of hydrogen is stored in the titanium alloy,
In the hot plastic working process, the plastic working start temperature is set to (β transformation point −275 ° C.) or more and (β transformation point −75 ° C.) or less, and is defined as (plastic working amount / previous thickness). The processing rate is set to at least 15%, and the total processing rate defined by (total plastic processing amount / initial thickness) is set to at least 70%.

In the invention according to claim 1, since the addition amount of Al is almost halved compared to the conventional amount, it is possible to suppress the occluded hydrogen from being precipitated as a hydride, and to increase the processing rate per time to 15% or more, As a result, the number of machining operations can be reduced, the machining time can be shortened, and productivity can be improved.
If the hydrogen storage amount is less than 0.2% by mass, the effect of hydrogenation cannot be expected and the crystal grains cannot be refined. Moreover, when it exceeded 0.8 mass%, the uniform structure | tissue was not obtained. Therefore, a good microstructure is obtained by setting the hydrogen storage amount to 0.2 to 0.8 mass%.

By setting the plastic processing start temperature to (β transformation point −225 ° C.) or more and (β transformation point −50 ° C.) or less, there is no crack, and a good refined structure can be obtained.
By making the processing rate of 1 time 15% or more, the number of processings can be reduced and productivity can be increased.
By setting the total processing rate to 60% or more, a good microstructure can be obtained.

  Therefore, according to the first aspect of the present invention, there is provided a manufacturing method capable of reducing the number of processings in addition to being able to obtain a favorable refined structure without fear of cracking in an α + β type titanium alloy. Can do.

In the invention according to claim 2, since the addition amount of Al is almost half that of the conventional one, it is possible to suppress the occluded hydrogen from being precipitated as a hydride, and to increase the processing rate per time to 15% or more, As a result, the number of machining operations can be reduced, the machining time can be shortened, and productivity can be improved.
If the hydrogen storage amount is less than 0.2% by mass, the effect of hydrogenation cannot be expected and the crystal grains cannot be refined. Moreover, when it exceeded 0.6 mass%, the uniform structure | tissue was not obtained. Therefore, a good microstructure is obtained by setting the hydrogen storage amount to 0.2 to 0.6 mass%.

By setting the plastic working start temperature to (β transformation point −125 ° C.) or more and (β transformation point −50 ° C.) or less, there is no crack and a good refined structure can be obtained.
By making the processing rate of 1 time 15% or more, the number of processings can be reduced and productivity can be increased.
By setting the total processing rate to 70% or more, a good microstructure can be obtained.

  Therefore, according to claim 2, in the α + β type titanium alloy, there is no fear of occurrence of cracks, and a good refined structure can be obtained, and a manufacturing method capable of reducing the number of processings is provided. Can do.

In the invention according to claim 3, iron lowers the β transformation point, but oxygen raises the β transformation point, so that the addition amount of these elements is adjusted to an appropriate amount, and each processing condition is set, The processing rate of one time can be increased to 15% or more. As a result, the number of processings can be reduced, the processing time can be shortened, and productivity can be improved.
If the hydrogen storage amount is less than 0.4% by mass, the effect of hydrogenation cannot be expected and the crystal grains cannot be refined. Moreover, when it exceeded 0.8 mass%, the uniform structure | tissue was not obtained. Therefore, a good microstructure is obtained by setting the hydrogen storage amount to 0.4 to 0.8 mass%.

By setting the plastic working start temperature to (β transformation point −275 ° C.) or more and (β transformation point −75 ° C.) or less, there is no crack and a good microstructure can be obtained.
By making the processing rate of 1 time 15% or more, the number of processings can be reduced and productivity can be increased.
By setting the total processing rate to 70% or more, a good microstructure can be obtained.

  Therefore, according to claim 3, in the α + β type titanium alloy, there is no fear of occurrence of cracks, and a good refined structure can be obtained, and a manufacturing method capable of reducing the number of processings is provided. Can do.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a temperature curve diagram for the method for producing an α + β type titanium alloy of the present invention, where the horizontal axis represents time, the process is shown below the horizontal axis, and the vertical axis represents temperature.
In the hydrogen storage process, hydrogen is stored by holding the α + β type titanium alloy in high-temperature hydrogen gas.

In the solution treatment step, the titanium alloy in which hydrogen is occluded is heated to the β transformation point or higher, and then rapidly cooled to perform solution treatment.
In the hot plastic working process, the titanium alloy after the solution treatment is plastic processed hot to refine the crystal.
In the dehydrogenation process, the titanium alloy after plastic working is kept at high temperature and under vacuum to remove hydrogen.

  A normal manufacturing method not involving hydrogen treatment includes two steps, a solution treatment step and a hot plastic working step. In this case, since the crystal cannot be refined, hydrogen treatment is performed in the present invention. In this state, the residual hydrogen causes the alloy to become brittle, so that the hydrogen is quickly removed after the plastic working to eliminate the disadvantage. For this purpose, the method of the present invention comprises four steps.

  FIG. 2 is a correlation graph between the hydrogen storage amount and the β transformation point, the horizontal axis is the hydrogen storage amount stored in the α + β type titanium alloy, the vertical axis is the β transformation point temperature, and the curve is Ti-6Al-4V as a comparative example. Alloys, Ti-3Al-2.5V alloy, Ti-3Al-2V-0.1S alloy and Ti-1Fe-0.3O alloy as examples are shown.

  It has been known that when hydrogen is stored in an α + β type titanium alloy, the β transformation point is changed to a low temperature side by the action of hydrogen. In order to know how much the alloy composition varies depending on the alloy composition, the present inventors have investigated and graphed in detail.

  Then, although Ti-6Al-4V alloy changes gradually, Ti-3Al-2.5V alloy, Ti-3Al-2V-0.1S alloy, and Ti-1Fe-0.3O alloy as examples It was also found that the change rapidly in proportion to the hydrogen storage amount.

And the following can be said from this graph.
First, when a straight line is raised from 0.5 on the horizontal axis, the β transformation point of the Ti-6Al-4V alloy is 850 ° C., and the β transformation point of the Ti-3Al-2.5V alloy is 680 ° C.

  With the same hydrogen storage amount of 0.5% by mass, there is a difference of 170 ° C. between the β transformation points of both alloys, and the β transformation point of the latter Ti-3Al-2.5V alloy is as low as 680 ° C. Since the plastic working start temperature is determined corresponding to the β transformation point, if the β transformation point is low, the plastic working start temperature is set to the low temperature side. When the plastic processing start temperature is high, a lot of hard oxide film is generated on the surface of the alloy, and the plastic processing roll is damaged during the plastic processing, and the material is more likely to be damaged. In this respect, if the plastic working temperature can be lowered, the generation of an oxide film can be suppressed, and the generation of scratches on the raw material and the plastic processing roll can be suppressed.

  As a result, the Ti-3Al-2.5V alloy, Ti-3Al-2V-0.1S alloy, and Ti-1Fe-0.3O alloy of the present invention are more plastic working rolls than the conventional Ti-6Al-4V alloy. Therefore, it is possible to prolong the time until roll polishing and reduce the need for interrupting the plastic working operation, so that the productivity of hot plastic working can be greatly increased. Further, after processing, the oxide film and the oxygen diffusion layer on the surface are removed to make a product, but since this allowance can be eliminated, the yield of the material can be greatly improved.

  Further, when a horizontal line is drawn from 800 ° C. on the vertical axis, the hydrogen storage amount of the Ti-3Al-2.5V alloy is 0.25 mass%, and the hydrogen storage amount of the conventional Ti-6Al-4V alloy is 1.0 mass. %become. That is, the effect of occluding as much as 1.0% by mass of hydrogen in the Ti-6Al-4V alloy can be obtained by 0.25% by mass of hydrogen in the Ti-3Al-2.5V alloy.

By storing hydrogen in the alloy and plastic processing by hot plastic processing, the alloy is distorted to precipitate hydride uniformly and finely, and it becomes the nucleus of microstructure formation by recrystallization. is there. However, increasing the hydrogen storage amount makes the alloy brittle and reduces ductility.
Therefore, it is desirable that the hydrogen occlusion amount is small if a refinement effect can be ensured.
In this respect, the Ti-3Al-2.5V alloy can be said to be a preferable alloy because it can reduce the amount of occluded hydrogen. The same applies to Ti-3Al-2V-0.1S alloy and Ti-1Fe-0.3O alloy.

  In addition, in the hydrogen storage process of FIG. 1, if the hydrogen storage amount is small, the processing time can be shortened and the productivity can be increased. In addition, since the consumption of hydrogen gas as a raw material can be suppressed, the manufacturing cost can be reduced.

(Experimental example)
Experimental examples according to the present invention will be described below. Note that the present invention is not limited to experimental examples.
The experimental conditions are as follows.

・ Starting materials:
Starting material components:
Ti-3Al-2.5V alloy obtained by adding 3.1 mass% aluminum and 2.4 mass% vanadium to titanium,
Ti-3Al-2V-0.1S alloy obtained by adding 3.1% aluminum, 1.9% vanadium and 0.12% sulfur by mass to titanium,
Ti-1Fe-0.3O alloy obtained by adding 1.1 mass% iron and 0.31 mass% oxygen to titanium,
Starting material size: Test piece machined to 25mm thickness x 25mm width x 100mm length

・ Hydrogen storage process:
The test piece is housed in a vacuum heat treatment furnace, evacuated, heated, and occluded hydrogen in an 800 ° C. hydrogen gas atmosphere. The amount of hydrogen occluded is controlled by time. When the time has elapsed, heating is stopped, the vacuum is exhausted, and the hydrogen is removed from the furnace.

・ Solution treatment process:
The test piece in which hydrogen is occluded is placed in a furnace, heated to a β transformation point + 100 ° C. in an air atmosphere, held for 3600 seconds (1 hour), then transferred to a water bath and rapidly cooled to perform solution treatment.

Intermediate material: A secondary test piece having a thickness of 7 mm, a width of 7 mm, and a length of 50 mm is cut out from the solution-treated test piece.

・ Hot plastic working process:
The second test piece is placed in a furnace and heated to the plastic processing start temperature. Then, the plastic processing is performed a plurality of times with a processing rate of one time being 15%. The oxide film on the surface is removed from the third test piece after plastic working.

・ Dehydrogenation process:
The third test piece is placed in a vacuum heat treatment furnace and kept in vacuum at 873 ° C. for 3600 seconds (1 hour) to remove hydrogen. When the holding time has passed, cool it down in the furnace.

・ Microscopic observation:
The test piece having been subjected to the above processing is cut, and the cut surface is observed with a metal microscope to observe the presence or absence of cracks, whether the crystal grains are miniaturized, and whether the crystal grains are uniformly aligned.

  The results are described in tabular form in [Means for Solving the Problems], and will be omitted.

Although not described in detail, a Ti-3Al-2.5V alloy obtained by adding 2.5 mass% aluminum and 2.0 mass% vanadium, 3.5 mass% aluminum, and 3.0 mass% The same result was obtained for the Ti-3Al-2.5V alloy obtained by adding the above vanadium.
Therefore, the present invention can be applied to a Ti-3Al-2.5V alloy obtained by adding 2.5 to 3.5 mass% aluminum and 2.0 to 3.0 mass% vanadium to titanium.

Moreover, Ti-3Al-2V-0.1S alloy which added 2.7 mass% aluminum, 1.6 mass% vanadium, and 0.05 mass% sulfur, 3.5 mass% aluminum, and 3 An equivalent result was obtained for a Ti-3Al-2V-0.1S alloy obtained by adding 0.4% by mass of vanadium and 0.20% by mass of sulfur.
Therefore, the present invention provides Ti--, which is obtained by adding 2.7 to 3.5% by mass of aluminum, 1.6 to 3.4% by mass of vanadium and 0.05 to 0.20% by mass of sulfur to titanium. Applicable to 3Al-2V-0.1S alloy.

Further, a Ti-1Fe-0.3O alloy obtained by adding 0.7 mass% iron and 0.2 mass% oxygen, adding 2.3 mass% iron and 0.7 mass% oxygen. Similar results were obtained for the Ti-1Fe-0.3O alloy.
Therefore, the present invention can be applied to a Ti-1Fe-0.3O alloy obtained by adding 0.7 to 2.3 mass% of iron and 0.2 to 0.7 mass% of oxygen to titanium.

Next, experimental results on mechanical properties are described below.
About the raw material which performed the hydrogen treatment about the Ti-3Al-2.5V alloy, the Ti-3Al-2V-0.1S alloy, and the Ti-1Fe-3O alloy, and the raw material which performed other treatment processes without performing only the hydrogen treatment A tensile test was performed at room temperature.
The hydrogen treatment conditions are the same for each alloy: hydrogen addition amount: 0.5%, solution temperature: β transformation point + 100 ° C., plastic working temperature: β transformation point−100 ° C., single plastic working rate: 15%, total Plastic working rate: 80%, dehydrogenation temperature: 600 ° C. Moreover, the crystal grain diameters of the test materials are all 0.5 to 1 μm for the hydrogen-treated material and 3 to 5 μm for the material not subjected to the hydrogen treatment.

It was confirmed that the Ti-3Al-2.5V alloy was improved by about 19% from 626 MPa to 746 MPa in 0.2% proof stress by hydrogen treatment. The elongation of both materials was about 20%, and no decrease in elongation was observed due to the increase in strength.
It was confirmed that the Ti-3Al-2V-0.1S alloy was improved by 0.2% in the 0.2% proof stress from 706 MPa to 863 MPa by hydrogen treatment. The elongation of both materials was about 18%, and no decrease in elongation was observed due to the increase in strength.

The Ti-1Fe-3O alloy was confirmed to have an approximately 9% improvement in 0.2% proof stress from 575 MPa to 627 MPa by hydrogen treatment. The elongation of both materials was about 23%, and no decrease in elongation was observed due to the increase in strength.
According to the present invention, a refined structure was obtained with high productivity, and as a result, a great increase in strength of 9 to 22% was achieved without a decrease in elongation.

  The α + β type titanium alloy manufactured by the manufacturing method of the present invention is suitable for application mainly to high strength, high toughness, high corrosion resistance and the like.

  The method for producing an α + β type titanium alloy of the present invention is suitable for producing a titanium alloy used as a material for structural parts such as automobile parts.

It is a temperature curve figure for the manufacturing method of the alpha + beta type titanium alloy of this invention. 5 is a correlation graph between hydrogen storage amount and β transformation point.

Claims (3)

An α + β-type titanium alloy is prepared, and the titanium alloy is stored in a high-temperature hydrogen gas to store hydrogen, and the hydrogen-occluded titanium alloy is heated to the β transformation point or higher, and then A solution treatment process for solution treatment by rapid cooling, a hot plastic working process for finely processing crystals by hot plastic processing of the titanium alloy after this treatment, and a titanium alloy after plastic working at high temperature and vacuum In a method for producing an α + β type titanium alloy comprising a dehydrogenation treatment step of removing hydrogen by holding it underneath,
The α + β type titanium alloy to be prepared is a Ti-3Al-2.5V alloy obtained by adding 2.5 to 3.5 mass% aluminum and 2.0 to 3.0 mass% vanadium to titanium,
In the hydrogen storage treatment step, 0.2 to 0.8 mass% of hydrogen is stored in the titanium alloy,
In the hot plastic working step, the plastic working start temperature is set to (β transformation point −225 ° C.) or more (β transformation point −50 ° C.) and defined as (plastic working amount / thickness immediately before). The processing rate is set to at least 15%, and the total processing rate defined by (total plastic processing amount / initial thickness) is set to at least 60% to perform plastic processing a plurality of times. Type titanium alloy manufacturing method. An α + β-type titanium alloy is prepared, and the titanium alloy is stored in a high-temperature hydrogen gas to store hydrogen, and the hydrogen-occluded titanium alloy is heated to the β transformation point or higher, and then A solution treatment process for solution treatment by rapid cooling, a hot plastic working process for finely processing crystals by hot plastic processing of the titanium alloy after this treatment, and a titanium alloy after plastic working at high temperature and vacuum In a method for producing an α + β type titanium alloy comprising a dehydrogenation treatment step of removing hydrogen by holding it underneath,
The α + β type titanium alloy to be prepared is prepared by adding 2.7 to 3.5 mass% aluminum, 1.6 to 3.4 mass% vanadium and 0.05 to 0.20 mass% sulfur to titanium. Ti-3Al-2V-0.1S alloy
In the hydrogen storage treatment step, 0.2 to 0.6 mass% of hydrogen is stored in the titanium alloy,
In the hot plastic working step, the plastic working start temperature is set to (β transformation point−125 ° C.) or more (β transformation point−50 ° C.) and defined as (plastic working amount / immediate thickness). The processing rate is set to at least 15%, and the total processing rate defined by (total plastic processing amount / initial thickness) is set to at least 70% to perform plastic processing a plurality of times. Type titanium alloy manufacturing method. An α + β-type titanium alloy is prepared, and the titanium alloy is stored in a high-temperature hydrogen gas to store hydrogen, and the hydrogen-occluded titanium alloy is heated to the β transformation point or higher, and then A solution treatment process for solution treatment by rapid cooling, a hot plastic working process for finely processing crystals by hot plastic processing of the titanium alloy after this treatment, and a titanium alloy after plastic working at high temperature and vacuum In a method for producing an α + β type titanium alloy comprising a dehydrogenation treatment step of removing hydrogen by holding it underneath,
The α + β-type titanium alloy to be prepared is a Ti-1Fe-0.3O alloy obtained by adding 0.7 to 2.3 mass% iron and 0.2 to 0.7 mass% oxygen to titanium,
In the hydrogen storage treatment step, 0.4 to 0.8 mass% of hydrogen is stored in the titanium alloy,
In the hot plastic working step, the plastic working start temperature is set to (β transformation point −275 ° C.) or more and (β transformation point −75 ° C.) or less, and is defined as (plastic working amount / thickness immediately before). The processing rate is set to at least 15%, and the total processing rate defined by (total plastic processing amount / initial thickness) is set to at least 70% to perform plastic processing a plurality of times. Type titanium alloy manufacturing method.

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