JP2008208413A - High-strength titanium alloy billet for cold forging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength titanium alloy billet for cold forging which is a billet for cold forging with a cylindrical shape and is characterized in having ≥700 MPa tensile strength by addition of low-cost reinforcing elements and also having superior cold forgeability (deformability and isotropy of metal flow) and where pressing is applied in a direction of height of the cylindrical shape. <P>SOLUTION: Respective contents of Fe, O, N and C as low-cost reinforcing elements and an oxygen equivalent value Q are regulated to values within prescribed ranges, respectively, to secure ≥700 MPa tensile strength. A β-phase composed of a body-centered cubic crystal having many slip systems is made present to some extent by making Fe content to 0.5 to 1.3 mass% and integrated crystal orientation of an α-phase as a main phase is regulated so that it satisfies prescribed relations in view of the slip systems and a cold forging direction to obtain cold forgeability more excellent than conventional ones. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a material for cold forging made of a titanium alloy having a cylindrical shape typified by a rod having a high tensile strength of 700 MPa or more. In addition, this cold forging material is subjected to compression processing in the height direction of the material cylinder in the cold forging process.

  Titanium alloys are suitable for fasteners such as bolts and nuts, and engine parts such as automobiles such as valve retainers because they are lightweight and require high strength. In order to obtain weight saving merit by using titanium, which differs depending on the use site, a tensile strength of at least 700 MPa, preferably 750 MPa or more is required. Typical α + β type titanium alloys include Ti-3Al-2.5V and Ti-6Al-4V, but they are not inexpensive because they contain a large amount of V, which is a relatively expensive element.

  In contrast, Patent Document 1, Patent Document 2, and Patent Document 3 propose titanium alloys containing neither Al nor V but containing Fe, O, N, etc. as relatively inexpensive reinforcing elements. . Hereinafter, [Fe] means Fe content (% by mass), [O] means O content (% by mass), and [N] means N content (% by mass).

In the invention described in Patent Document 1, the Fe content is 0.1 to 0.8% by mass, and the oxygen equivalent amount ([O] +2.77 “N” +0.1 [Fe]) is 0.35 to The tensile strength of 65 kgf / mm ² (637 MPa) or more is obtained by adjusting the content (mass%) of O and N so as to be 1.0, and further forming an α + β biphasic equiaxed structure or a lamellar phase microstructure. It is a thing. 1 and 2 of Patent Document 1, the oxygen equivalent value on the horizontal axis is about 0.42 or more, the tensile strength is 700 MPa or more, and the total elongation is about 22 to 25% or less.

  In the invention described in Patent Document 2, the Fe content is 0.9 to 2.3 mass%, the N content is 0.5 mass% or less, and the oxygen equivalent amount ([O] +2.77 “N”). By adjusting the O content so that +0.1 [Fe]) is 0.34 to 1.00, the tensile strength is 700 MPa or more and the elongation is 15% or more. Is. 1 and 2 of Patent Document 2, the oxygen equivalent value on the horizontal axis is 0.34 or more, the tensile strength is 700 MPa or more, and the total elongation is about 25 to 27% or less. Furthermore, when the tensile strength is 750 MPa or more, the total elongation is about 25% or less, and when the tensile strength is 850 MPa or more, the total elongation is 15% or less. In addition, some of the Fe content is substituted with Ni and Cr.

  In the invention described in Patent Document 3, O is 0.2 to 0.8 mass%, C is 0.01 to 0.15 mass%, N is 0.01 to 0.07 mass%, and Fe is 0.3 mass%. By containing ˜1.0% by mass, the tensile strength is 750 MPa or more. In addition, there are some in which Fe is replaced with Ni and Cr. From the Example of Table 1 of patent document 3, tensile strength is 753 Mpa or more and elongation (total elongation) is 23.5% or less with the round bar of diameter 20mm.

JP-A-1-252747 Japanese Patent No. 3426605 JP 2004-269982 A

  Many of the above-described parts are required to have both high strength and cold forgeability because they are formed by cold forging. One of the cold forgeability is to have a deformability for obtaining a predetermined shape. This deformability corresponds to the ductility of the material, and in addition to the dense hexagonal crystal (hereinafter referred to as a slip deformation direction). The titanium α phase having hcp) is affected by the hcp accumulation orientation. In addition, in the titanium α phase to which the strengthening element is added, twin deformation like soft industrial pure titanium JIS type 1 and JIS type 2 hardly occurs and is limited to slip deformation only.

  Moreover, in actual component manufacturing, in order to maintain a high material yield, the isotropy of the metal flow by cold forging becomes an important factor of cold forgeability more than deformability. For example, when cold forging a cylindrical material in the height direction, paying attention to the metal flow in the radial direction of the cylindrical bottom surface (circular), if the metal flow is isotropic, the material will have a similar circular cross section Deforms while maintaining However, when there is a difference in the metal flow depending on the radial direction rather than isotropic, it becomes an ellipse or a square instead of a similar circular section as shown in FIG. For this reason, the metal flow is insufficient with respect to a predetermined shape to be obtained by cold forging, or on the contrary, it partially overflows, and the material yield is reduced.

  Patent Document 1, Patent Document 2, and Patent Document 3 contain an inexpensive reinforcing element and have a tensile strength of 700 MPa or more and a certain degree of ductility (total tensile elongation), but are applied to obtain an actual molded part. In cold forging, when cold forging a cylindrical material in its height direction, depending on the shape, cold forgeability (deformability, isotropic metal flow) may be insufficient. It is a problem.

  Therefore, the present invention is a cold forging material having a cylindrical shape, has a tensile strength of 700 MPa or more by the addition of an inexpensive reinforcing element, and has better cold forgeability (deformability, metal flow). It is an object of the present invention to provide a material for cold forging made of high-strength titanium alloy in which compression is applied in the height direction of a cylindrical shape characterized by having isotropic properties.

In order to solve the above problems, the gist of the present invention is as follows.
(1) In mass%, Fe is 0.5 to 1.3%, N is 0.001 to 0.05%, C is 0.001 to 0.15%, and O is an oxygen equivalent amount of the formula [1]. X-ray diffraction intensity from each crystal plane of the titanium α-phase, which is a cold forging material containing Q in a range of 0.34 to 0.55, and the balance being Ti and inevitable impurities I is in the relationship of the formulas [2], [3], [4], and [5], and the tensile strength is 700 MPa or more. Material for cold forging made of high-strength titanium alloy to which processing is applied.
Oxygen equivalent amount Q = [O] +2.77 [N] +0.086 [Fe] (1) formula [0] where [O] is the O content (mass%), and [N] is the N content ( Mass%) and [Fe] are Fe contents (mass%).
The magnitude relationship of the X-ray diffraction intensity I measured in the cylindrical L cross section is
I (0 0 0 2)> I (1 0 −1 0) (2) Formula I (0 0 0 2)> I (1 0 −1 1) (3) Formula Cylindrical T The magnitude relationship of the X-ray diffraction intensity I measured in the cross section is
I (1 0 −1 0)> I (0 0 0 2) (4) Formula I (1 0 −1 0)> I (1 0 −1 1) (5) Formula where I (0 0 0 2), I (1 0 −1 0), and I (1 0 −1 1) are respectively a (0 0 0 2) plane of a titanium α phase that is a dense hexagonal crystal, (1 0 − 1 0) plane,
It is the diffraction intensity from the (1 0 -1 1) plane. The L cross section is a cross section that forms a rectangle parallel to the height direction of the cylindrical material, and the T cross section is a cross section that forms a circle perpendicular to the height direction of the cylindrical material.
(2) A titanium alloy bar wire for cold header processing having a diameter of 16 mm or less in the high-strength titanium alloy cold forging material according to claim 1.

  Here, the L cross section and the T cross section of the cold forging material having the above-described columnar shape are specifically the cross sections shown in FIG. 2A and 2B correspond to the L cross section and the T cross section, respectively.

  According to the present invention, a cold forging material having a cylindrical shape has a tensile strength of 700 MPa or more, further 750 MPa or more by addition of an inexpensive strengthening element, and more excellent cold forgeability (deformability, metal) It is possible to provide a material for cold forging made of high-strength titanium alloy to which compression processing is applied in the height direction of a cylindrical shape characterized by having a flow isotropic property. This makes it possible to manufacture a lightweight and high-strength titanium alloy cold forged part while maintaining a higher material yield and at a lower cost than in the past.

  The inventors have added a tensile strength of 700 MPa or more and better cold forgeability (deformability) by adding inexpensive reinforcing elements Fe, O, N, C and controlling the crystal orientation of the titanium α phase (hcp). In addition, we conducted extensive research on a cold-forging material made of high-strength titanium alloy that has a cylindrical shape that combines the isotropic nature of metal flow. As a result, the tensile strength of 700 MPa or more is secured by the content of Fe, O, N, C and the oxygen equivalent amount Q of the above-mentioned formula [1], and the Fe content is 0.5 to 1.3% by mass. As a result, a β phase composed of body-centered cubic crystals (hereinafter referred to as bcc) having many slip systems is present to some extent, and the accumulated crystal orientation of the main phase α phase (hcp) is determined by the slip system and the cold forging direction. In consideration of the above, by controlling as in the above formulas [2], [3], [4], [5], cold forgeability (deformability, isotropic metal flow) superior to conventional ones It was found that can be obtained.

  The basis for setting each element of the present invention will be described below.

  First, it will be described that in a high-strength titanium alloy containing Fe, N, O, and C, the cold forgeability can be improved by controlling the α-phase (hcp) integrated crystal orientation.

  In the case of the pattern of FIG. 3 in which the magnitude relationship between the X-ray diffraction intensity from the L cross section and the T cross section of the cylindrical sample that is a cold forging material, the metal flow isotropic when compressed in the height direction. It is very good, and a decrease in deformability accompanying an increase in material strength is suppressed. When a cylindrical sample having a diameter of 10.5 mm and a height of 7 mm is used and compressed in the height direction, the difference between the major axis and the minor axis after compression is 0.5 mm or less when 3.5 mm is compressed, and is 0. As small as 65 mm or less, this corresponds to ± 1.6% or less of the average diameter after compression. Here, as shown in FIG. 1, after compressing in the height direction, the diameter of the cross-sectional area of the hatched line in FIG. 1 (b) was measured with calipers, and the maximum value was the major axis and the minimum value was the minor axis. As will be described later, the limit upsetting rate corresponding to the deformability can be maintained at 70% or more in the predetermined component range even if the material strength is increased.

  In the pattern of FIG. 3, even if there is a slight difference in the relative intensity ratio, the above-described [2], [3], [4], and [5] satisfy the magnitude relationship of the above expressions. It was possible to achieve excellent cold forgeability.

  The reason why the cold forgeability is excellent is as follows. The pattern in FIG. 3 can be interpreted as having many ccp axes in the circumferential direction of the cold forging material having a cylindrical shape. It is known that the sliding direction of hcp is perpendicular to the C axis of hcp. This is because, when the cylindrical substrate is compressed in the height direction, the α-phase (hcp) slip direction is more aligned in the radial direction in the pattern of FIG. 3, and slip deformation tends to occur in the cylindrical radial direction.

  On the other hand, in the case of the pattern of FIG. 4, when the cylindrical sample is similarly compressed in the height direction, the difference between the major axis and the minor axis is 0.6 mm or more at 3.5 mm compression and 1 mm or more at 4.5 mm compression. It is large, which corresponds to ± 2 to 2.7% or more with respect to the average diameter after compression. Assuming that the cold forging is used, a difference of up to 1 mm is insufficient for product accuracy. Further, the limit upsetting rate corresponding to the deformability tends to decrease in response to the increase in material strength. Thus, in the case of the pattern of FIG. 4, it becomes impossible to ensure sufficiently high cold forgeability. The pattern of FIG. 4 shows that the hcp C-axis is aligned in the radial direction of the cylinder, and in this case, there are very few slip systems in which the material can flow in the radial direction when compressed in the height direction. Because.

  Here, FIG. 3 and FIG. 4 illustrate the X-ray diffraction intensity from each surface of the titanium α phase (hcp) as relative intensity in the L cross section and the T cross section of the cylindrical sample. Used a Cu tube. Further, the difference in cold forgeability due to the above hcp accumulation orientation was the same at both annealing temperatures of 750 ° C. and 800 ° C., and the influence of the annealing temperature was extremely small.

  In addition, the cylindrical sample used for the above-mentioned compression test annealed the bar wire which carried out hot rolling on various conditions (temperature, a processing rate, a rolling schedule, etc.), or the bar wire which added cold drawing further. Made from material by machining.

  From the above, because of the excellent cold forgeability in the pattern size relationship of FIG. 3, in claim 1 of the present invention, the sizes of the equations [2], [3], [4], and [5] Satisfy the relationship.

  In addition, materials satisfying the pattern of FIG. 3 (relationships of equations [2], [3], [4], and [5]) have a difference in Vickers hardness between the L cross section and the T cross section. It is characterized by being about 10 to 30 points larger than the T section. This is the result of the hcp orientation accumulation as shown in FIG. 3 because the α-phase hcp bottom surface is harder.

  The bar wire having the characteristics shown in FIG. 3 corresponds to finish rolling, in which, when the bar wire is hot-rolled, the post-rolling stage is processed with a cross-section reduction rate of 50% or more in a temperature range of 740 to 840 ° C. It is important to carry out bar rolling with a relatively large processing amount in a relatively narrow temperature range in the latter stage of rolling. On the other hand, the bar wire having a pattern different from that of FIG. 3 represented by FIG. 4 has either a temperature range outside the above range or a small cross-sectional reduction rate.

  Next, the component range of the present invention will be described in the case of satisfying the pattern of FIG. 3 (relationship of [2], [3], [4], [5] equations).

  Fe is a substitutional element that stabilizes the titanium β phase which is bcc. Since bcc has many slip systems compared with hcp, it contributes to the improvement of cold workability. In order to improve the cold forgeability, the Fe content needs to be 0.5% by mass or more. In addition, in order to improve cold forgeability more stably, the Fe content is preferably more than 0.8% by mass.

  On the other hand, since Fe is easily segregated during solidification, if it is contained in a large amount, the isotropy of metal flow during cold forging may be impaired due to component segregation. From the viewpoint of securing an isotropic metal flow during cold forging, it is necessary to pay attention to Fe segregation as much as or more than before, and in the present invention, the Fe content is set to 1.3% by mass or less.

  When the content of N, O, and C is increased to increase the strength, the accumulation direction of the α phase (hcp) is changed to the pattern of [2], [3], [4], and [5] in FIG. Even if satisfying the relationship), if it exceeds a certain content, the cold forgeability decreases in response to the increase in strength. In the present invention, the α phase orientation accumulation having the magnitude relationship shown in FIG. 3 is adopted, so that the α phase slip deformation becomes easier with respect to the compression in the height direction, and the deformability accompanying the increase in strength is improved. Make up for the decline. However, when the content range of the present invention is exceeded, the lowering of the deformability becomes dominant, and the effect of the α-phase crystal orientation accumulation becomes insufficient. From the above, as a component range in which the tensile strength is 700 MPa or more and the above-described excellent cold forgeability is obtained, in claim 1 of the present invention, Fe is 0.5 to 1.3 by mass%. %, N is 0.001 to 0.05%, C is 0.001 to 0.15%, and O is contained in a range where the oxygen equivalent amount Q of the formula [1] is 0.34 to 0.55. It was. Preferably, since excellent cold forgeability is maintained even at higher strength, the Fe content is more than 0.8% and not more than 1.3% by mass%, and N is 0.001. -0.04%, C is 0.001-0.05%, and O is the range where the oxygen equivalent amount Q of the formula [1] is 0.37-0.5.

  The titanium alloy of the present invention inevitably contains H, Ni, Cr, Mo, Mn, Si, S, etc., as in the case of ordinary pure titanium or titanium alloy. It is less than 0.05% by mass. However, as long as the effects of the present invention are not impaired, the content is not limited to less than 0.05% by mass.

  Further, when the α phase is set to the accumulating orientation of the present invention, when a tensile test is performed in the height direction of the cylindrical material, the total elongation is 25 to 30% or more in the past (Patent Documents 1, 2, and 3). It is located higher than. In the component range of the present invention, the tensile strength in the annealed state is 700 MPa or more, further increased to over 750 MPa and to about 850 MPa, but the total elongation can still be maintained at 25 to 30%. Decrease in elongation can be suppressed.

  The allowable load applied to the mold during cold forging is limited by the material of the mold. By limiting the diameter of the cold forging material in the form of a cylinder to 16 mm or less, the load applied to the mold can be reduced, and the freedom of both the mold material and the forging shape is increased, and the effects of the present invention are achieved. Can make the most of it. Further, in cold forging, the cold header processing is a continuous processing from a bar wire material, so the productivity is very high. On the other hand, higher levels are required for the material, such as uniformity of deformation, stability of deformation, and the size of burrs generated. In view of the above, in claim 2 of the present invention, the high strength titanium alloy cold forging material of claim 1 is a titanium alloy rod for cold header processing having a diameter of 16 mm or less.

  The invention is explained in detail using the following examples.

  Table 1 shows the magnitude relationship between the component (Fe, O, N, C), the oxygen equivalent amount Q (formula [1]), and the X-ray diffraction intensity from each hcp crystal plane of the α-phase. ([2] to [5] formulas) and cross-section Vickers hardness (L cross-section and T cross-section and their differences). Table 2 shows the tensile strength, total elongation, the limit upsetting rate of the cylindrical material, and the difference between the major axis and the minor axis.

  The Example shown in Table 1 annealed at 750 degreeC the rod wire which hot-forged and hot-rolled the ingot and was processed into diameter 13mm. X-ray diffraction intensity was measured using a Cu tube. The cross-section Vickers hardness was determined by measuring the entire diameter range at 1 mm intervals from the surface within the cross-section with a load of 9.8 N, and calculating the average value. Tensile strength and total elongation were measured by performing a tensile test at a distance between gauge points of 25 mm using a test piece having a parallel part with a diameter of 6.25 mm and a length of 32 mm.

  The limit upsetting rate is a cylindrical material with a processed diameter of 10.5 mm and a height of 7 mm. After compressing the compression amount in the height direction at intervals of 0.5 mm, the surface is observed with the naked eye. The presence or absence of cracks was evaluated. The difference between the major axis and the minor axis after compressing the cylindrical shape in the height direction is that the processed cylindrical material with a diameter of 10.5 mm and a height of 7 mm is compressed in the height direction with a compression amount of 3.5 mm and 4.5 mm. After that, it was measured using calipers. In the case of a compression amount of 4.5 mm, since some cracks were observed after compression exceeding the limit upsetting rate, measurement of the major axis and the minor axis was not performed.

  Sample No. which is an example of the invention. 3-1, 4, 5, 6, 7-1, 8, 9, 10-1, 11, 12, 13-1, 14, 15-1 have a tensile strength of 700 MPa or more and a limit upsetting ratio of 70. The difference between the major axis and the minor axis is as small as 0.5 mm or less when compressed to 3.5 mm and 0.65 mm or less when compressed to 4.5 mm, and the isotropy of the metal flow is also good. In addition, a component is the preferable range mentioned above (Fe exceeds 0.8% and 1.3% or less by mass%, N is 0.001-0.04%, C is 0.001-0.05%, O Sample No. 1 in which the oxygen equivalent amount Q of the formula [1] is 0.37 to 0.5) and the X-ray diffraction intensity magnitude relationship satisfies the relationships of the formulas [2] to [5] 6,7-1,8,9,10-1,11,12 has a higher tensile strength of 750 MPa or more and a very good cold forgeability.

  Sample No. Q is 0.3, which is below the lower limit of the present invention. No. 1 has a tensile strength of less than 700 MPa. Sample No. 2 has a Q of 0.43 and a tensile strength of 776 MPa, but Fe is 0.34% by mass, which is outside the lower limit of the present invention, and the limit upsetting rate is 64.3%, which is the same tensile strength. It is low compared with the invention example (sample No.7-1, 8, 9) which has strength. On the other hand, sample No. N, C, Q exceeded the upper limit of the present invention. 16-1, 16-2, and 17 have a limit upsetting ratio as low as 50% even when the magnitude relationship of the X-ray diffraction intensity satisfies the conditions of the present invention, and the cold forgeability is not good.

  Even if the component is within the range of the present invention, the sample No. 2 in which the magnitude relationship of the X-ray diffraction intensity does not satisfy the equations [2] to [5]. 3-2, 7-2, 10-2, 13-2, 15-2 are examples of the present invention having the same components (No. 3-1, 7-1, 10-1, 13-1, 15-1). In comparison, the marginal upsetting ratio is low, and the difference between the major axis and the minor axis exceeds 0.6 mm when compressed by 3.5 mm and exceeds 1 mm when compressed by 4.5 mm.

  Here, Sample No. whose X-ray diffraction intensity magnitude relationship satisfies the conditions of the present invention. 3-1,4,5,6,7-1,8,9,10-1,11,12,13-1,14,15-1 are the post-rolling stages during hot rolling of bar wires. In the temperature range of 740 to 840 ° C., the cross-sectional reduction rate is 50% or more, while the X-ray diffraction intensity magnitude relationship does not satisfy the conditions of the present invention. 3-2, 7-2, 10-2, 13-2, and 15-2 were either in the temperature range outside the above range or the cross-section reduction rate was small.

  The present invention will be described in further detail using the following examples.

  Tables 3 and 4 show the sample Nos. 6 and sample no. 9 shows the processing / annealing process and characteristics of various bar wires having the same component composition as No. 9. Sample No. A-1 to A-4 are sample Nos. 6 and sample no. B-1 to B-8 are sample Nos. 9 is the same component. Table 3 shows the respective processing / annealing steps, the magnitude relationship of the X-ray diffraction intensity, and the cross-section Vickers hardness. Table 4 shows the tensile strength, total elongation, and cold forgeability.

  Here, the wire having a drawing rate of 62% has a diameter of 8 mm. Therefore, a tensile test piece having a parallel part diameter of 4 mm was used for the tensile test. In addition, for the evaluation of cold forgeability (limit upsetting rate, metal flow isotropic), a cylindrical specimen having a diameter of 7.5 mm and a height of 5 mm is used, and this shape is another thick bar wire. It is similar to the sample (diameter 10.5 mm, height 7 mm) evaluated.

  The difference between the major axis and the minor axis is the same as in [Example 1], after compressing the height by 50% (the test piece having a diameter of 10.5 and a height of 7 mm is compressed by 3.5 mm and the diameter is 7.5 mm. For a 5 mm high test piece, 2.5 mm compression) and after about 64% height compression (10.5 diameter and 7 mm high test piece, 4.5 mm compression, 7.5 mm diameter and 5 mm high test) It measured to 3.2 mm compression in the piece.

  As shown in Table 4, sample Nos. Within the scope of the present invention. A-1, A-2 and No. B-1, B-2, B-3, and B-4 have a high tensile strength of 750 MPa or more, a limit upsetting ratio of 78% or more, and a difference between the major axis and the minor axis is 0% after compression by 50% in height. 0.5 mm or less, height is about 64%, and after compression is 0.65 mm or less. On the other hand, even for the same component, the sample No. whose X-ray diffraction intensity magnitude relationship does not satisfy the conditions of the present invention. A-3, A-4, and NoB-5, B-6, B-7, and B-8 have a low limit upsetting rate of about 64% and a large difference between the major axis and the minor axis. In addition, sample no. B-4 and B-8 are values in which the difference between the major axis and the minor axis is small compared to others. This is because the size of the test piece subjected to the compression test is small. The difference between the major axis and the minor axis (absolute value) itself is the sample number of the invention. B-4 is smaller, but when compared by the ratio to the average diameter after compression, Sample No. B-4 is ± 1.5%, sample No. as a comparative example. B-8 is ± 2.4%, which is the same level as those of other inventive examples and other comparative examples. Here, Sample No. whose X-ray diffraction intensity magnitude relationship satisfies the conditions of the present invention. A-1, A-2 and No. B-1, B-2, B-3, and B-4 were subjected to processing with a cross-section reduction rate of 50% or more in the temperature range of 740 to 840 ° C. in the post-rolling stage when the bar wire was hot rolled. On the other hand, Sample No. whose X-ray diffraction intensity magnitude relationship does not satisfy the conditions of the present invention. A-3, A-4, and NoB-5, B-6, B-7, and B-8 had either a temperature range outside the above range or a small cross-sectional reduction rate.

  As described above, as long as it is within the scope of the present invention, it exhibits high tensile strength and excellent cold forgeability regardless of differences in the processing of bar wire and annealing, and the effects of the present invention are obtained. Yes.

It is a figure explaining the major axis and minor axis at the time of compressing a column-shaped raw material to a height direction. It is a figure which shows the L cross section and T cross section of a cylindrical raw material. It is a figure which shows the magnitude relationship of the X-ray diffraction intensity from each crystal plane of the titanium alpha phase in the L cross section and T cross section of a cylindrical raw material. It is a figure which shows the magnitude relationship of the X-ray diffraction intensity from each crystal plane of the titanium alpha phase in the L cross section and T cross section of a cylindrical raw material.

Claims (2)

In mass%, Fe is 0.5 to 1.3%, N is 0.001 to 0.05%, C is 0.001 to 0.15%, and O is the oxygen equivalent amount Q of the formula [1] is 0. .34 to 0.55, the balance is a cold forging material comprising a columnar shape composed of Ti and inevitable impurities, and the X-ray diffraction intensity I from each crystal plane of the titanium α phase is [2], [3], [4], [5] are related, and the tensile strength is 700 MPa or more. In the cold forging process, compression is applied in the height direction of the cylindrical shape. High strength titanium alloy cold forging material.
Oxygen equivalent amount Q = [O] +2.77 [N] +0.086 [Fe] (1) formula [0] where [O] is the O content (mass%), and [N] is the N content ( Mass%) and [Fe] are Fe contents (mass%).
The magnitude relationship of the X-ray diffraction intensity I measured in the cylindrical L cross section is
I (0 0 0 2)> I (1 0 −1 0) (2) Formula I (0 0 0 2)> I (1 0 −1 1) (3) Formula Cylindrical T The magnitude relationship of the X-ray diffraction intensity I measured in the cross section is
I (1 0 −1 0)> I (0 0 0 2) (4) Formula I (1 0 −1 0)> I (1 0 −1 1) (5) Formula where I (0 0 0 2), I (1 0 −1 0), and I (1 0 −1 1) are respectively a (0 0 0 2) plane of a titanium α phase that is a dense hexagonal crystal, (1 0 − It is the diffraction intensity from the (1 0) plane and the (1 0 -1 1) plane. The L cross section is a cross section that forms a rectangle parallel to the height direction of the cylindrical material, and the T cross section is a cross section that forms a circle perpendicular to the height direction of the cylindrical material.   The high strength titanium alloy cold forging material according to claim 1, wherein the diameter of the titanium alloy bar wire is 16mm or less for cold header processing.

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