JP4673631B2 - Titanium alloy wire excellent in cold workability and having a tensile strength of more than 620 MPa and less than 700 MPa - Google Patents

Description

  The present invention relates to a titanium alloy wire rod having a titanium alloy Ti-3Al-2.5V as a basic component and excellent in cold workability and having a tensile strength of more than 620 MPa and less than 700 MPa.

  Titanium alloy Ti-3Al-2.5V (hereinafter abbreviated as Ti325) is standardized as 61 types in JIS H 4650. This Ti325 has a lower strength than Ti64, although it has a strength lower than that of Ti64 by halving the addition amounts of Al and V, which are metal elements, to Ti-6Al-4V (hereinafter abbreviated as Ti64). It has a deformability and is known to have a high strength and a low cold deformability compared to industrial pure titanium JIS type 1, type 2 and type 3.

  As for the chemical composition of Ti325, in 61 types of JIS H 4650, Al is 2.5 to 3.5 mass%, V is 2 to 3 mass%, Fe is 0.25 mass% or less, and O is 0.15 mass%. Hereinafter, N (nitrogen) is 0.03 mass% or less, C (carbon) is 0.08 mass% or less, and H (hydrogen) is 0.015 mass% or less. The tensile properties of Ti325 are tensile strength 700 to 900 MPa and elongation 9% or more in 61 types of wire of JIS H 4650.

  Ti325 wire is often used for spectacle frames and the like, and is cold drawn to a thin diameter of about 2 mm. Furthermore, it is cold worked into a spectacle frame shape such as a flat cross section. Therefore, the improvement of cold workability is desired from the side using the wire made of Ti325.

  In Patent Document 1, as a titanium alloy having excellent cold workability, Al is 2.5 to 3.5% by mass, V is 2 to 3% by mass, O is 0.05 to 0.1% by mass, Nb Is disclosed in that a large amount of Nb has the effect of stabilizing the β phase and improving the cold workability.

  In Patent Document 2, as a titanium alloy excellent in cold workability and fatigue strength after brazing, a titanium alloy containing 0.5 to 2.3% by mass of Al and substantially free of a β-stabilizing element, Discloses a titanium alloy containing 4% by mass or less of Ga or 1% by mass or less of Si in the left alloy. In the region where Al is 2.3% by mass or less, even if cold rolling of 75% is performed, an ear crack is disclosed. It has been described that since it does not occur, it has sufficient cold workability and the fatigue characteristics of the spectacle frame and brazed portion where the crystal grains become coarse are also good.

JP 62-103330 A JP 2003-055725 A

  When the wire material of Ti325 is made of a material having a tensile strength satisfying JIS H 4650, it does not necessarily have sufficient cold workability when the wrought material is cold worked into a predetermined shape by drawing or the like. is there. Therefore, annealing (intermediate annealing) may be performed several times in the middle of cold working, which increases the manufacturing cost.

  On the other hand, by using industrial pure titanium JIS type 1, type 2 and type 3 with good cold workability, the number of intermediate annealings can be reduced, but fatigue is low because the strength is lower than Ti325. From the viewpoint of characteristics and the like, the cross-sectional area of the spectacle frame cannot be reduced, and the weight reduction rate becomes low.

  On the other hand, the melting point of Ti—Zr—Ni—Cu, which is a Ti-based brazing material used for spectacles, is 850 to 900 ° C., and the melting point of general Ag—Cu and Ag—Cu—Ni brazing materials 890-900 ° C. In the case of industrial pure titanium, since the β transformation point is 900 ° C. at the highest, the brazed portion and the heat affected zone are in the vicinity of the β transformation point or higher and grain growth occurs, so there is a problem in fatigue characteristics. On the other hand, since the β transformation point of Ti325 is about 935 ° C., which is higher than that of industrial pure titanium and the brazed part is less likely to grow, the alloy component of Ti325 is more brazed than that of industrial pure titanium. Suitable for fatigue characteristics.

  In the titanium alloy of Patent Document 1, Nb is added in a large amount of 2.0 to 5.0% by mass, and Nb has a higher density than Ti and increases the density of the titanium alloy itself. Mass will increase. Moreover, since Nb is never cheap, it increases the cost of the titanium alloy.

  The titanium alloy of Patent Document 2 (Al is 0.5 to 2.3 mass%) has a total added amount of metal elements as compared with Ti325 (average is 3 mass% of Al and V is 2.5 mass%). As can be seen from the fact that it is low, the cold workability is considered to be better than that of Ti325. However, because the tensile strength is 446 MPa for Ti-1.5Al alloy, which is equivalent to industrial pure titanium JIS type 2 and does not reach Ti325, the frame is used to ensure fatigue life such as bending and twisting that occurs in spectacle frames. In view of weight reduction, Ti325 having higher strength is more desirable than Ti325.

  Therefore, the present invention maintains the β transformation point of Ti325, and has improved the cold workability while ensuring the tensile strength exceeding that of industrial pure titanium JIS3, Ti-3Al- having a tensile strength of more than 620 MPa and less than 700 MPa. The object is to provide a 2.5V titanium alloy wire. In addition, the maximum tensile strength of the industrial pure titanium JIS type 3 wire specified in JIS H 4650 is 620 MPa.

The present invention for solving the above problems is as follows.
(1) In mass%, Al is 2.5 to 3.5%, V is 2.0 to 3.0%, O is 0.09% or less , and the total concentration of N and C is 0.03% or less . A titanium alloy wire having a tensile strength of more than 620 MPa and less than 700 MPa excellent in cold workability, characterized by comprising the balance Ti and inevitable impurities.
(2) mass% Fe is equal to or less than 0.1%, titanium alloy wrought cold less than excellent tensile strength 620MPa ultra 700MPa that workability according to (1).

  Here, the wire has a circular cross section and a diameter of less than 8 mm.

The remaining impurities that do not define chemical components in the above (1) and (2) are small amounts that cannot be removed by steps such as scouring, dissolving, spreading, heat treatment, pickling, or mixed in these steps. This corresponds to, for example, H of 0.015 mass% or less.

  In addition, the tensile strength of less than 700 MPa deviates from the lower limit value of the tensile strength of the wire defined in JIS H 4650 61 type.

  According to the present invention, titanium having improved cold workability while maintaining the β transformation point of Ti325 corresponding to 61 types of JIS H 4650 and ensuring the tensile strength (over 620 MPa) exceeding JIS 3 types of industrial pure titanium. An alloy wire can be provided.

  As a result of intensive research to improve cold workability while securing a β-transformation point of Ti325 equivalent to 61 types of JIS H 4650 and tensile strength exceeding JIS 3 types of industrial pure titanium (620 MPa). The β transformation point and base strength of Ti325 are maintained by adjusting the concentrations of the additive elements Al and V to the standard ranges of 2.5 to 3.5% by mass and 2.0 to 3.0% by mass, respectively. However, cold workability is improved by reducing the concentration of O, N and C and lowering the tensile strength (lowering the tensile strength below the lower limit of 700 MPa of 61 types of wire of JIS H4650). I found what I could do. In addition, it has been found that cold workability can be further improved by lowering the Fe concentration.

First, in (1) and (2) of the present invention, the β transformation point is not lowered as compared with Ti325, which is the base composition. Therefore, in mass%, Al is 2.5 to 3.5%, and V is 2.0 to 2.0. The range was 3.0%. Further, defining Al and V as described above also has an effect of securing the base strength. Further, Fe, O, N, C, or H, which originally has a low content, has little effect on the β transformation point.

The lower limit value of the tensile strengths (1) and (2) of the present invention is set to exceed 620 MPa because it exceeds the upper limit value of 620 MPa, which is the upper limit value of industrial pure titanium JIS type 3.

  The cold workability of the wire was evaluated based on the limit drawing rate during cold drawing and the limit reduction rate during flat rolling. Here, the limit drawing rate is the maximum reduction in the cross-sectional area where surface cracks do not occur due to cold drawing, and the limit reduction rate is the maximum reduction where surface cracks do not occur when rolling the wire with upper and lower flat rolls. It is a rate (a reduction rate obtained from the height after reduction with respect to the initial wire diameter). Flat rolling was adopted as a cold working method simulating the processing from a wire rod to a cross-sectional shape of a spectacle frame (a flat or flat shape instead of a circle). As a result of examining the relationship between these cold workability indexes and various material factors, it was found that the tensile strength and the concentrations of O, N, and C are related. Since N and C were added in a very small amount, they could be sorted by the total concentration of both.

  Figure 1 shows the relationship between tensile strength, critical drawing rate, and critical reduction rate for Ti-325 wire samples with various concentrations of O, N, and C shown in Table 1 (O concentration, total concentration of N and C). 1 and FIG. It means that cold workability is so good that a limit drawing rate and a limit reduction rate are large. Sample A and Sample A in Table 1 are conventional examples of Ti325 with an O concentration exceeding 0.09 mass% or a combined concentration of N and C exceeding 0.03% by mass. Sample C in Table 1 has an O concentration of 0.05 to 0.09 mass% and a total concentration of N and C of 0.02 to 0.03 mass%. Sample D has an O concentration of 0.05 to 0.09 mass%. Sample in which the total concentration of N and C is less than 0.02% by mass, and the sample O is an O concentration of less than 0.05% by mass and the total concentration of N and C is 0.02 to 0.03% by mass. The mosquito has an O concentration of less than 0.05% by mass and a total concentration of N and C of less than 0.02% by mass, and the sample key has an O concentration of 0.05 to 0.09% by mass and the total concentration of N and C is Each example is 0.02 to 0.03% by mass and the Fe concentration is not 0.1% by mass.

  Here, in the cold wire drawing test, a hole die was passed using a wire having an initial diameter of 6.5 to 7 mm. For lubrication, the surface of the wire was subjected to bonderite treatment. The surface of the wire processed at various wire drawing rates was visually observed to evaluate the presence or absence of cracks, and the maximum wire drawing rate at which no surface cracks occurred was defined as the critical wire drawing rate. In the cold flat rolling test, a wire rod having an initial diameter of about 2 mm was reduced with upper and lower flat rolls. The surface of the wire processed at various rolling reductions (the rolling reduction obtained from the height after flat rolling with respect to the initial diameter) is visually observed to evaluate the presence or absence of cracks, and the maximum rolling reduction at which surface cracks do not occur is limited. It was defined as the rolling reduction. The tensile strength in FIGS. 1 and 2 is a value obtained by pulling the wire in the longitudinal direction. The tensile strength of the wire was adjusted by annealing conditions after cold drawing or light drawing after annealing. In addition, the tensile test was implemented by the method based on JISZ2241 in the test piece shape prescribed | regulated to JISZ2201.

  These cold workability indexes had no correlation with the ductility of the tensile test, and a good correlation was obtained with the tensile strength. This is presumably because Ti325 is mainly composed of a dense hexagonal α phase, so that the anisotropy of the deformability is large and the ductility (elongation, drawing value) of the tensile test does not change as much as the strength difference. For example, when comparing the ductility of tensile strengths of about 650 MPa and about 720 MPa, in the lines, the elongation is about 12% and the drawing value is about 65%. There is no difference.

  From FIG. 1 and FIG. 2, when the tensile strength is reduced, both the critical drawing rate and the critical reduction rate are improved. In addition, when the tensile strength is small as the total concentration of O concentration and N and C is small, the critical drawing rate and the critical compression rate are shifted to an improved side, and the tensile strength is equivalent. However, when the O concentration and the total concentration of N and C are smaller, these cold workability indexes tend to be higher. It can be seen that the concentration of O, N and C in addition to the tensile strength which is a material factor influences cold workability. Note that the tensile strength of Sample A having a high O concentration and Sample A having a high total concentration of N and C did not decrease to less than 700 MPa even after annealing at 750 ° C. for 1 hour and further at 850 ° C. for 1 hour.

  Ti325, which has a tensile strength of 700 MPa or more, has a limit drawing ratio of 70% and a limit reduction ratio of 35%. Therefore, the higher limit values are 75% and the limit reduction ratio is 40%. Was the threshold value of the present invention, and the range of the O concentration, the total concentration of N and C, and the tensile strength in which the cold workability index was equal to or greater than the threshold value was defined as the range of the present invention.

In the present invention (1), limit drawing ratio as represented by the sample c ~ Ca 75% or more, since the limit rolling reduction is more than 40%, the O concentration 0.09 wt% or less, and N The total concentration of C was 0.03% by mass or less , and the tensile strength was less than 700 MPa.

Also, the tensile strength is stable since the increasing cold workability indicators Oite the present invention (1), less than 620MPa ultra 690MPa is preferable.

The Fe concentration is 0.25% by mass or less in 61 types of JIS H 4650, but it is possible to reduce the Fe concentration to less than 0.1% by mass as in the case of O, N and C. because of the action to improve the sexual index, the present invention (2) is a Oite Fe concentration was less than 0.1 mass% in the present invention (1). The sample key in Table 1 is an example in which the Fe concentration is less than 0.1% by mass, and chemical components other than the Fe concentration are almost the same as those of the sample C. The Fe concentration is 0.089% and 0.198% by mass for Sample K and Sample U, respectively. When both are compared, as shown in FIG. 1 and FIG. The sample key having the lower tensile strength and the Fe concentration of less than 0.1% by mass is higher. Since Fe is an element that stabilizes the β phase, it promotes the concentration of the α phase stabilizing elements O, N, and C into the α phase, so that the deformability of the α phase is suppressed. In addition, the decrease in Fe concentration is considered to have contributed to the improvement of cold workability.

  In the present invention, from the viewpoint of cold workability, although there is no reason to particularly limit the lower limit concentration of O, N, C, Fe, as industrial production capacity, each lower limit concentration is mass%, O is 0.02%, N is 0.002%, C is 0.002%, and Fe is about 0.005%.

  The present invention (1) will be described in further detail using the following Example 1.

  First, the chemical components of the materials A to R used in Table 2 are shown, and the rightmost column of Table 2 shows the claims of the present invention to which each material component corresponds, and the material symbols D to R correspond. . Tables 3-1, 3-2, and 3-3 show the history and limit drawing ratio of the wire after cold drawing, and Table 4 shows the history, tensile strength, and flatness of the wire after cold drawing. Indicates the critical rolling reduction during rolling. In addition, the corresponding claim is shown in the rightmost column of Table 3-1, Table 3-2, Table 3-3, and Table 4.

  The wire used for the cold wire drawing for evaluating the critical wire drawing ratios of Table 3-1, Table 3-2, and Table 3-3 has a diameter of 6.5 to 7 mm, and Tables 3-1 and 3- 2. Vacuum annealing was performed under various conditions shown in the column “History after cold drawing” in Table 3-3, and a part of the wire was lightly drawn after that. For cold drawing, a hole die was used, and the surface of the wire was subjected to bonderite treatment for lubrication. The wire rod used for flat rolling for evaluating the critical rolling reduction in Table 4 was about 2 mm in diameter, and was subjected to vacuum annealing under various conditions shown in the column of “History after cold drawing” in Table 4. The department then performed light wire drawing. In addition, by visually observing the surface of the wire processed by cold drawing or flat rolling, the presence or absence of cracks is evaluated, and the maximum drawing rate or rolling reduction at which surface cracks do not occur is the critical drawing rate, It was defined as the critical reduction rate. Further, the tensile strength is a value obtained by pulling the wire in the longitudinal direction, and a tensile test was performed by a method conforming to JIS Z 2241 with the shape of a test piece defined in JIS Z 2201.

  From Table 3-1, conventional example No. of wire rods using material symbols A, B, and C which are conventional components. 1-1, 1-2, 1-3, and 1-4 have a limit drawing ratio of 70%, which is less than 75%. Of the wires using the material symbols D, E, and L corresponding to the present invention (1), the tensile strength is more than 620 MPa and less than 700 MPa. 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-13 have a limit drawing ratio of 75% or more, which is higher than the conventional example. These tensile strengths exceed 620 MPa and are higher than the standard upper limit value of JIS H4650 industrial pure titanium JIS type 3 wire. On the other hand, the comparative example No. in which the tensile strength of those using the same material symbols E and L as above is 700 MPa or more. 1-11, 1-12, and 1-14 have a limit drawing ratio of 70% as in the conventional example, which is less than 75%.

  Next, examples of the wire rod of the present invention (1) shown in Table 4 will be described. From Table 4, the conventional example No. of the wire using the material symbols A and B which are the conventional components. The critical rolling reduction of 4-1, 4-2, and 4-3 is 35%, which is not as high as 40%. Of the wires using the material symbol E corresponding to the present invention (1), the tensile strength is more than 620 MPa and less than 700 MPa. As for 4-4, 4-5, and 4-6, the critical rolling reduction is 40% or more, which is higher than the conventional example. These tensile strengths are over 620 MPa, which is higher than the standard upper limit value of JIS H4650 industrial pure titanium JIS type 3 wire. On the other hand, Comparative Example No. 1 using the same material symbol E as described above and having a tensile strength of 700 MPa or more. 4-7 and 4-8 have a critical rolling reduction of 35% as in the conventional example, which is less than 40%.

The present invention ( 1) will be described in further detail using the following Example 2.

  The cold workability of the wire will be described from Table 3-2.

In the present invention (1), Example yo Ri N and materials symbol F of total concentration is not low chemical components of C, and of which the tensile strength of the wire with G less than 700MPa at 620MPa than No. 2-1, 2-2, 2-3, 2-4 have a limit drawing ratio of 75% or more, which is higher than the conventional example, and the limit drawing ratio is higher on the side where the tensile strength is lower. It has become. For example, Example No. of material symbol G. 2-2 and 2-3, was used as an example of equivalent tensile strength material symbol E No. It can be seen that the limit drawing ratio is higher than those of 1-7 and 1-9.

In the present invention (1), yo Ri O concentration low not material symbol H chemical components, are among the tensile strength of the wire using the I is less than 700MPa at 620MPa than Example No. 2-7,2-8,2-9,2-12 is in higher values than conventional limit drawing ratio of 75% or more examples, the limit drawing ratio in the tensile strength of the lower side is higher It has become. For example, in Example No. 2-7,2-8 used was an example of equivalent tensile strength material symbol E No. It can be seen that the limit drawing ratio is higher than those of 1-7, 1-8, and 1-9.

  On the other hand, even if the same material symbols G and H are used, Comparative Example No. 1 having a tensile strength of 700 MPa or more. In 2-5, 2-6, 2-10, and 2-11, the critical wire drawing ratio is 70%, which is less than 75%.

Next, examples of the wire of the present invention ( 1 ) shown in Table 4 will be described. From Table 4, in the wire using the material symbol G corresponding to the present invention ( 1 ) in the chemical component, the tensile strength is more than 620 MPa and less than 700 MPa. Nos. 4-9, 4-10, 4-11, and 4-12 are Nos. Using the material symbol E which is an example in which the critical rolling reduction is 40% or more and the total concentration of N and C is higher . Compared to 4-4 and 4-5, it can be seen that the critical rolling reduction is higher on the side where the tensile strength is lower.

Among the wires using the material symbol H corresponding to the present invention ( 1 ), the chemical strength of Example No. 1 having a tensile strength of more than 620 MPa and less than 700 MPa. Nos. 4-14, 4-15, and 4-16 are Nos. Using the material symbol E which is an example in which the critical rolling reduction is 40% or more and the O concentration is higher . Compared to 4-4 and 4-5, it can be seen that the critical rolling reduction is higher on the side where the tensile strength is lower.

  On the other hand, even if the same material symbols G and H are used, Comparative Example No. 1 having a tensile strength of 700 MPa or more. 4-13 and 4-17 have a critical rolling reduction of 35% and 40%.

The present invention in a total concentration of O concentration and N and C is lower than both (1) will be described. From Table 3-2, exemplary Material symbol K, is among the tensile strength of the wire with M less than 700MPa at 620MPa than Example No. 2-15, 2-16, 2-17, 2-18, and 2-21 have a limit drawing ratio of 75% or more, which is higher than that of the conventional example, and the O concentration or The limit drawing rate is higher than the embodiment using the material symbols F, G, H, and I in which either the total concentration of N or C is higher. From Table 4, exemplary Material symbol K, is among the tensile strength of the wire with M less than 700MPa at 620MPa than Example No. In 4-18, 4-19, 4-20, 4-21 and 4-23 , the critical rolling reduction is 45% or more, and either the O concentration or the total concentration of N and C is on the low tensile strength side. It is higher than the embodiment using higher material symbols E, G, H.

  On the other hand, even in the same material symbols K and M, Comparative Example No. 1 having a tensile strength of 700 MPa or more. 2-19, 2-20 and No. 2-4. 4-22 does not reach the limit drawing rate of 75% or the limit reduction rate of 40%.

The present invention further illustrate the present invention (2) using the Example 3 below.

  The cold workability of the wire will be described from Table 3-3 and Table 4.

From Table 3-3, the tensile strength is 620 MPa among the wires using the material symbols N, O, P, Q, and R corresponding to the chemical component of the present invention ( 2 ) whose Fe concentration is less than 0.1 mass%. Example No. above 700 MPa in excess. 3-1, 3-2, 3-3 , 3-4 , 3-7 , 3-8 , 3-9 , 3-10 are the material symbols D to N in Tables 3-1 to 3-3, O concentrations, the total concentration of N and C, and the tensile strength is compared with and what equivalent embodiments, the limit drawing ratio is in the upper. For example, No. using the material symbol E which is an embodiment of the present invention (1). No. 1-7, 1-8, 1-9, 1-10 and No. using material symbol N which is an embodiment of the present invention ( 2 ). When 3-1, 3-2, 3-3 and 3-4 are compared, it can be seen that the latter has a higher limit drawing rate.

Next, examples of the wire rod according to the present invention ( 2 ) shown in Table 4 will be described. Examples in which the tensile strength is more than 620 MPa and less than 700 MPa among the wires using the material symbols N, O, P and Q corresponding to the chemical component of the present invention ( 2 ) whose Fe concentration is less than 0.1 mass% No. 4-24, 4-25, 4-26, 4-28, 4-29, 4-30 are O concentration, the total concentration of N and C, and E, G having higher tensile strength and equivalent Fe content. Compared to the examples using H, K, and M , the critical rolling reduction is higher. For example, using the Material symbol E No. 4-4, 4-5, 4-6 and No. using the material symbol N which is an embodiment of the present invention ( 2 ). Comparing 4-24, 4-25, and 4-26, it can be seen that the latter has a higher critical rolling reduction.

  On the other hand, even though the same material symbol N is used, the comparative example No. of the wire having a tensile strength of 700 MPa or more. 3-5, 3-6 and no. 4-27 does not reach the limit drawing rate of 75% or the limit reduction rate of 40%.

  In addition, as a result of measuring a beta transformation point by the differential thermal analysis method (DTA) using the wire which made each chemical component of Table 2 a raw material, it was in the range of 920-940 degreeC, and was the temperature exceeding 900 degreeC. .

It is a figure which shows the relationship between O density | concentration in Ti-3Al-2.5V wire manufacture, the total density | concentration of N and C, tensile strength, and a limit wire drawing rate. It is a figure which shows the relationship between O density | concentration in Ti-3Al-2.5V wire manufacture, the total density | concentration of N and C, tensile strength, and a critical rolling reduction.

Claims (2)

In mass%, Al is 2.5 to 3.5%, V is 2.0 to 3.0%, O is 0.09% or less , the total concentration of N and C is 0.03% or less , and the balance A titanium alloy wire having a tensile strength of more than 620 MPa and less than 700 MPa excellent in cold workability, characterized by comprising Ti and inevitable impurities. By mass%, wherein the Fe is less than 0.1%, cold workability excellent tensile strength 620MPa ultra 700MPa than titanium alloy wire according to claim 1.

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