Titanium nails and titanium materials

Abstract

To provide a titanium nail which is made compatible in both the suppression of a bend and a collapse of a tip and followability.SOLUTION: In a titanium nail having a head part and a flank part connected to the head part and extending in a longitudinal direction, when making each Vickers hardness HV in a central position and each relative cross section area X are made to linearly approximate each other by a least square method so as to be indicated as [HV=aX+b] in each cross section vertical in a longitudinal direction in positions 1 / 10 L, 3 / 10 L, 1 / 2 L, 7 / 10 L and 9 / 10 L of the flank part from a starting point at the head part side when setting an entire length of the head part in the longitudinal direction as L, formulae of [-90≤a≤-50], [190≤b≤300] and [0.65≤R2] are satisfied.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to titanium nails and titanium materials. [Background technology]

[0002] Among nails, Japanese nails have been used in wooden buildings since ancient times. For example, in the renovation of traditional buildings such as important cultural properties, the Japanese nails used are reused.

[0003] Therefore, as described in Non-Patent Document 1, Japanese nails have been required to be resistant to bending even when repeatedly driven in and pulled out, and in particular, to have a small cross-sectional area at the tip that does not easily bend or crush. Furthermore, if the wood being driven into has hard knots, it has been required that the nail bend along the knot, so-called conformability. This is because if the conformability is poor and the wood splits up to the knot, the wood itself becomes unusable.

[0004] Therefore, in order to create Japanese nails that are resistant to bending and have sufficient strength to prevent the tip from easily bending, while also possessing flexibility, soft iron has traditionally been used for Japanese nails. On the other hand, soft iron Japanese nails are relatively heavy, and when many nails are used, the burden on the worker is significant. Furthermore, from a weight perspective, they also place a heavy load on buildings, so there was a desire for lighter nails. In addition, soft iron Japanese nails can rust depending on the environment, which can cause discoloration of valuable wood. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Yasuko Koshu, "Effects of Supersaturated Oxygen on Nonmetallic Inclusions and Oxide Film Formation in Japanese Nails for Construction," Doctoral Dissertation, Tokyo University of the Arts, 2015 (Heisei 27). [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the use of titanium Japanese nails is desired. By using titanium for Japanese nails, weight reduction can be achieved, and corrosion resistance can also be improved. However, titanium has low rigidity, and when used for nails, it can bend or the tip may be crushed. On the other hand, if titanium is made harder to suppress bending and tip crushing, the aforementioned flexibility deteriorates. For this reason, there has been a challenge in achieving both suppression of bending and tip crushing and flexibility in titanium Japanese nails.

[0007] The present invention aims to solve the above problems and provide a titanium nail that achieves both suppression of bending and tip crushing and conformability. [Means for solving the problem]

[0008] This invention was made to solve the above problems, and its essence is the titanium nail described below.

[0009] (1) Made of industrial-grade pure titanium or titanium alloy, A titanium nail having a head and a body connected to the head and extending in the longitudinal direction, When the total length of the body in the longitudinal direction is L, in the cross-sections perpendicular to the longitudinal direction at positions 1 / 10L, 3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the starting end on the head side of the body, A titanium nail that satisfies equations (ii) to (iv) below when the Vickers hardness HV at the center position and the relative cross-sectional area X are linearly approximated by the least squares method as shown in equation (i) below. HV = aX + b ... (i) -90 ≤ a ≤ -50 ···(ii) 190 ≤ b ≤ 300 ···(iii) 0.65 ≤ R 2 ...(iv) However, each symbol in the above formula is defined as follows: HV: Vickers hardness (HV1) at the center position of each cross-section when the test load is 1 kgf. X: The relative cross-sectional area, which is the ratio of the cross-sectional area of each cross-section to the cross-sectional area of the cross-section perpendicular to the longitudinal direction at the start end of the barrel portion R 2 : The contribution rate obtained when linearly approximated by the least squares method

[0010] (2) The difference between the average value HVs of the Vickers hardness at a position 100 μm in the central direction from the surface of each cross-section and the average value HVc of the Vickers hardness at the central position of each cross-section satisfies the following formula (v). The titanium nail according to (1) above. 30 ≦ HVs - HVc ≦ 200 ···(v) However, each symbol in the above formula (v) is defined as follows. HVs: The average value (HV0.1) of the Vickers hardness at a position 100 μm in the central direction from the surface of each cross-section when the test load is 100 gf HVc: The average value (HV1) of the Vickers hardness at the central position of each cross-section

[0011] (3) The chemical composition of the industrial pure titanium or titanium alloy is, by mass% Fe: 1.5% or less Cr: 1.5% or less Ni: 1.5% or less O: 0.25% or less N: 0.05% or less C: 0.10% or less [[ID=3C]] H: 0.015% or less The balance: Ti and impurities The titanium nail according to (1) or (2) above, which satisfies the following formula (vi). Fe + Cr + Ni ≦ 1.5 ···(vi) However, each element symbol in the above formula represents the content (mass%) of each element contained in the industrial pure titanium or titanium alloy, and is zero if not contained.

[0012] (4) The chemical composition of the industrial pure titanium or titanium alloy is, by mass%, in place of a part of the Ti Al: 2.0% or less Si: less than 0.5%, Sn: less than 2.0%, Zr: less than 3.0%, Cu: less than 1.8%, Nb: less than 1.0%, V: less than 2.0%, Mo: less than 2.0%, Mn: less than 1.0%, Co: less than 1.0%, Pd: less than 0.25%, and Ru: less than 0.25%, containing one or more selected from the group consisting of, the titanium nail according to (3) above.

[0013] (5) A titanium nail according to any one of (1) to (4) above, which is a Japanese nail.

[0014] (6) A titanium material used as the material of the titanium nail according to any one of (1) to (5) above, composed of industrial pure titanium or a titanium alloy, having a 0.2% proof stress at room temperature of 215 MPa or more, [[ID=3..]] having a tensile strength of 340 to 510 MPa, and having an elongation of 23% or more, a titanium material. [Effect of the Invention]

[0015] [[ID=4..]]According to the present invention, a titanium nail that achieves both suppression of bending and tip crushing and followability can be obtained. [Brief Description of the Drawings]

[0016] [Figure 1] FIG. 1 is a diagram schematically showing an example of the shape of the titanium nail of the present embodiment. [Figure 2] FIG. 2 is a schematic diagram of the titanium nail viewed from a direction perpendicular to the longitudinal direction. [Figure 3] FIG. 3 is a schematic diagram when the Vickers hardness HV at the center position and the relative cross-sectional area X are plotted. [Figure 4]Figure 4 is a schematic diagram showing an example of a Japanese nail. [Figure 5] Figure 5 is a schematic diagram illustrating the method for evaluating nails. [Modes for carrying out the invention]

[0017] The inventors investigated the bending, tip deformation, and conformability of titanium nails and obtained the following findings (a) to (c).

[0018] (a) In order to suppress bending and tip crushing, it is effective to increase the Young's modulus of the material. On the other hand, due to its physical properties, it is difficult to increase the Young's modulus of titanium to the same level as steel. For this reason, it is conceivable to harden the entire nail. However, if the entire nail is hardened, the aforementioned flexibility is lost, and it becomes difficult to drive the nail in while bending it along the joint.

[0019] (b) Based on the above, the inventors considered providing a difference in hardness along the longitudinal direction of the nail. Generally, the cross-sectional area of ​​a nail is larger at the head and decreases towards the tip. For this reason, the tip side, which has a smaller cross-sectional area, is more prone to bending. Therefore, by providing a difference in hardness such that the tip side, which has a smaller cross-sectional area, is harder and the head side, which has a larger cross-sectional area, is softer, it is possible to improve conformability while suppressing bending, especially localized bending and tip crushing.

[0020] (c) To obtain nails that become harder towards the tip, it is effective to control the manufacturing conditions. First, the titanium material is heated to 750-875°C, and then hot forging is performed from the head side of the nail body towards the tip until the temperature drops below 500°C. Next, it is cooled to a temperature range of room temperature to 200°C. After that, the head of the nail is heated and hot forging is performed to shape the head. Normally, the hardness of a nail is roughly constant from the head to the tip, but these processes make it possible to obtain titanium nails that become harder towards the tip. It is desirable to control the gradient of the hardness difference within a predetermined range.

[0021] One embodiment of the present invention is based on the above findings. The requirements for the titanium nail of this embodiment will be described in detail below.

[0022] 1. Materials The nails in this embodiment are titanium nails. Here, titanium nails are nails made of titanium material. That is, nails made of industrial-grade pure titanium or titanium alloy.

[0023] 1-1. Industrial-grade pure titanium or titanium alloy Here, industrial-grade pure titanium refers to titanium material that does not contain any intentionally added elements, such as impurities and Ti, and typically has a Ti content of 98% by mass or more. Industrial-grade pure titanium has various standards, such as JIS Grade 1 to 4, or ASTM / ASME Grade 1 to 4. Common impurities in these types of industrial-grade pure titanium include C, H, O, N, and Fe.

[0024] Furthermore, titanium alloys are typically alloys containing 70% or more by mass of Ti. Examples of titanium alloys include α-type titanium alloys, α+β-type titanium alloys, or β-type titanium alloys. Examples of α-type titanium alloys include highly corrosion-resistant alloys (titanium alloys specified in JIS standards 11-13, 17, 19-22, and ASTM standards Grade 7, 11, 13, 14, 17, 30, 31, as well as titanium alloys containing small amounts of various other elements), Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.3Si-0.25Nb, etc.

[0025] Examples of α+β type titanium alloys include Ti-3Al-2.5V, Ti-5Al-1Fe, and Ti-6Al-4V. Examples of β type titanium alloys include Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-13V-11Cr-3Al, Ti-15V-3Al-3Cr-3Sn, Ti-20V-4Al-1Sn, and Ti-22V-4Al.

[0026] 1-2. Chemical composition of industrial-grade pure titanium or titanium alloys In the titanium nails of this embodiment, the type of industrial pure titanium or titanium alloy used as the material is not particularly limited, but it is preferable that the chemical composition, i.e., the range of content of each element, is within the following range. In the following description, "%" for content means "mass%".

[0027] Fe: 1.5% or less Fe is a β-phase stabilizing element and has the effect of improving tensile strength. It also has the effect of increasing the β-phase and improving hot workability. However, if the Fe content is excessive, segregation is likely to occur, resulting in a decrease in properties and increased susceptibility to cracking. For this reason, the Fe content is preferably 1.5% or less, and more preferably 1.3% or less. On the other hand, there is no particular lower limit, but based on the purity of industrial raw materials, the Fe content is preferably 0.02% or more, and more preferably 0.03% or more.

[0028] Cr:1.5% or less Like Fe, Cr has the effect of improving tensile strength and hot workability. However, if Cr is included in excess, segregation is likely to occur, which can result in a decrease in ductility and an increased susceptibility to cracking. For this reason, the Cr content is preferably 1.5% or less, and more preferably 1.3% or less. On the other hand, there is no particular lower limit, but based on the purity of industrial raw materials, the Cr content is preferably 0.003% or more, and more preferably 0.004% or more.

[0029] Ni: 1.5% or less Ni, like Fe and Cr, has the effect of improving tensile strength and hot workability. However, if Ni is included in excess, segregation is likely to occur, resulting in a decrease in ductility and increased susceptibility to cracking. For this reason, the Ni content is preferably 1.5% or less, and more preferably 1.3% or less. On the other hand, there is no particular lower limit, but based on the purity of industrial raw materials, the Ni content is preferably 0.003% or more, and more preferably 0.004% or more.

[0030] Furthermore, when Fe, Cr, and Ni are included in combination as described above, it is preferable that their total content satisfies the following formula (vi). Fe + Cr + Ni ≤ 1.5 ···(vi) However, each element symbol in the above formula represents the mass percentage of each element contained in industrial pure titanium or titanium alloy, and zero is used if an element is not present.

[0031] If the total content of Fe, Cr, and Ni exceeds 1.5%, segregation is more likely to occur, and properties such as ductility tend to deteriorate. For this reason, the left-hand side value of equation (vi), which is the total content of Fe, Cr, and Ni, is preferably 1.5 or less. It is more preferable that the left-hand side value of equation (vi) be 1.3 or less, and even more preferable that it be 1.25 or less. The lower limit of the left-hand side value of equation (vi) is not particularly limited, but for example, it is preferably 0.03 or more.

[0032] O: 0.25% or less O has the effect of improving tensile strength. However, if the oxygen content is excessive, ductility decreases and cracking may occur easily. For this reason, the oxygen content is preferably 0.25% or less, and more preferably 0.2% or less. In this way, the oxygen content can be adjusted to obtain the desired strength. On the other hand, if the oxygen content is excessively reduced, the manufacturing cost of raw materials, etc., increases, so it is preferable that the oxygen content be 0.03% or more.

[0033] N: 0.05% or less N is an impurity element found in industrial-grade pure titanium or titanium alloys. Excessive N content reduces ductility and increases the likelihood of cracking. Therefore, the N content is preferably 0.05% or less, and more preferably 0.03% or less. While it is preferable to reduce N as much as possible, excessive reduction increases manufacturing costs. Therefore, the N content is preferably 0.001% or more.

[0034] C: 0.10% or less Carbon (C) is an impurity element found in industrial-grade pure titanium or titanium alloys. Excessive C content reduces ductility and toughness, making the material more prone to cracking. Therefore, the C content is preferably 0.10% or less, and more preferably 0.05% or less. While it is preferable to reduce C as much as possible, excessive reduction increases manufacturing costs. Therefore, the C content is preferably 0.001% or more.

[0035] H:0.015% or less H is an impurity element found in industrial-grade pure titanium or titanium alloys. Excessive H content reduces ductility and increases the likelihood of cracking. Therefore, the H content is preferably 0.015% or less, and more preferably 0.010% or less. While it is preferable to reduce H content as much as possible, excessive reduction increases manufacturing costs. Therefore, the H content is preferably 0.001% or more.

[0036] In addition to the elements listed above, one or more elements selected from Al, Si, Sn, Zr, Cu, Nb, V, Mo, Mn, Co, Pd, and Ru may be included within the ranges shown below. The reasons for limiting each element are explained below.

[0037] Al: 2.0% or less Al has the effect of improving tensile strength. For this reason, it may be included as needed. However, if Al is included in excess, ductility and toughness may decrease, and cracking may occur easily. For this reason, it is preferable that the Al content be 2.0% or less. It is more preferable that the Al content be 1.5% or less. On the other hand, in order to obtain the above effect, it is preferable that the Al content be 0.1% or more.

[0038] Si: 0.5% or less Si has the effect of improving oxidation resistance and strength. For this reason, it may be included as needed. However, if Si is included in excess, segregation is likely to occur, which can result in a decrease in ductility and toughness, and an increased susceptibility to cracking. For this reason, it is preferable that the Si content be 0.5% or less. It is more preferable that the Si content be 0.3% or less. On the other hand, in order to obtain the above effects, it is preferable that the Si content be 0.05% or more.

[0039] Sn: 2.0% or less Sn has the effect of improving strength. For this reason, it may be included as needed. However, if Sn is included in excess, cracking may occur easily. For this reason, it is preferable that the Sn content be 2.0% or less. It is more preferable that the Sn content be 1.5% or less. On the other hand, in order to obtain the above effect, it is preferable that the Sn content be 0.1% or more.

[0040] Zr: 3.0% or less Zr has the effect of improving oxidation resistance and strength. For this reason, it may be included as needed. However, if the amount of Zr is excessive, cracking may occur. For this reason, it is preferable that the Zr content be 3.0% or less. It is more preferable that the Zr content be 2.0% or less. On the other hand, in order to obtain the above effects, it is preferable that the Zr content be 0.1% or more.

[0041] Cu:1.8% or less Cu has the effect of improving strength. For this reason, it may be included as needed. However, if Cu is included in excess, segregation may occur, which can lead to increased cracking. For this reason, the Cu content is preferably 1.8% or less. A Cu content of 1.5% or less is more preferable. On the other hand, in order to obtain the above effect, a Cu content of 0.1% or more is preferable.

[0042] Nb: 1.0% or less Nb has the effect of improving oxidation resistance. For this reason, it may be included as needed. However, if Nb is included in excess, the manufacturing cost will increase. For this reason, it is preferable that the Nb content be 1.0% or less. It is more preferable that the Nb content be 0.5% or less. On the other hand, in order to obtain the above effect, it is preferable that the Nb content be 0.1% or more.

[0043] V:2.0% or less V has the effect of improving strength. For this reason, it may be included as needed. However, if V is included in excess, ductility and toughness may decrease, and the material may become more susceptible to oxidation when heated, making it prone to cracking. For this reason, the V content is preferably 2.0% or less. A V content of 1.0% or less is more preferable. On the other hand, in order to obtain the above effects, a V content of 0.1% or more is preferable.

[0044] Mo: 2.0% or less Mo has the effect of improving corrosion resistance. For this reason, it may be included as needed. However, if Mo is included in excess, segregation may occur, which can lead to increased cracking. For this reason, it is preferable that the Mo content be 2.0% or less. It is even more preferable that the Mo content be 1.0% or less. On the other hand, in order to obtain the above effect, it is preferable that the Mo content be 0.1% or more.

[0045] Mn: 1.0% or less Mn has the effect of improving tensile strength. However, if Mn is included in excess, segregation is likely to occur, which can result in a decrease in ductility and an increased susceptibility to cracking. For this reason, the Mn content is preferably 1.0% or less. More preferably 0.5% or less. On the other hand, in order to obtain the above effect, the Mn content is preferably 0.1% or more.

[0046] Co: 1.0% or less Co has the effect of improving tensile strength and corrosion resistance. However, if the co content is excessive, segregation is more likely to occur, which can result in a decrease in ductility and an increased tendency to crack. For this reason, it is preferable to keep the co content at 1.0% or less. It is even more preferable to keep the co content at 0.5% or less. On the other hand, in order to obtain the above effects, it is preferable to keep the co content at 0.1% or more.

[0047] Pd: 0.25% or less Pd has the effect of improving corrosion resistance. For this reason, it may be included as needed. However, if excessive Pd is included, the manufacturing cost will increase. For this reason, it is preferable that the Pd content be 0.25% or less. It is more preferable that the Pd content be 0.20% or less. On the other hand, in order to obtain the above effect, it is preferable that the Pd content be 0.04% or more.

[0048] Ru: 0.25% or less Ru, like palladium (Pd), has the effect of improving corrosion resistance. Therefore, it may be included as needed. However, excessive Ru content increases manufacturing costs. For this reason, it is preferable to keep the Ru content at 0.25% or less. It is even more preferable to keep the Ru content at 0.20% or less. On the other hand, in order to obtain the above effect, it is preferable to keep the Ru content at 0.04% or more.

[0049] In the chemical composition of this embodiment, the remainder consists of Ti and impurities. Here, "impurities" refers to components that are mixed in during the industrial production of industrial-grade pure titanium or titanium alloys due to various factors in the raw materials such as ore and scrap, and in the manufacturing process, and which are acceptable as long as they do not adversely affect this embodiment. Examples include, but are not limited to, Cl, Na, Mg, Ca, B, and Ta mixed in during the refining process, etc. Impurities are acceptable if the content of each element is 0.1% or less and the total amount is 0.5% or less.

[0050] The above chemical composition is the average chemical composition from 1 mm or more in depth from the surface. The content of each element can be measured by inert gas fusion infrared absorption spectroscopy, inert gas fusion thermal conductivity spectroscopy, high-frequency combustion infrared absorption spectroscopy, or inductively coupled plasma (ICP) emission spectroscopy.

[0051] 1-3. Strength of Titanium Material The strength of the titanium material used in the titanium nails of this embodiment is preferably within the following ranges. The 0.2% yield strength of the titanium material at room temperature is preferably 215 MPa or higher. The tensile strength of the titanium material is preferably in the range of 340 to 510 MPa, and the elongation of the titanium material is preferably 23% or higher. These characteristic values ​​can be determined by tensile testing in accordance with JIS Z 2241:2011.

[0052] 2. Distribution of hardness 2-1. Distribution of hardness in the longitudinal direction As shown in Figure 1, the titanium nail of this embodiment has a head 1 and a body 2 connected to the head 1 and extending in the longitudinal direction. The body 2 tapers towards the tip 4. In Figure 1, the cross-section of the body 2 is shown as approximately rectangular, but the cross-section of the body does not necessarily have to be approximately rectangular. For example, it may be approximately circular.

[0053] Here, assuming that the total length of the torso 2 in the longitudinal direction is L, the cross-sections perpendicular to the longitudinal direction of the torso at positions 1 / 10L, 3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the starting end 3 on the head side are defined as shown in Figure 2.

[0054] Furthermore, in the titanium nail of this embodiment, the Vickers hardness HV at the center position and the relative cross-sectional area X at each cross-section are approximated by a linear relationship using the least squares method as shown in equation (i) below. A detailed explanation follows.

[0055] HV = aX + b ... (i) However, each symbol in the above formula is defined as follows: HV: Vickers hardness (HV1) at the center of each cross-section when the test load is 1 kgf. X: Relative cross-sectional area, which is the ratio of the cross-sectional area of ​​each section to the cross-sectional area of ​​the section perpendicular to the longitudinal direction at the starting end of the torso on the head side.

[0056] Here, for example, the Vickers hardness HV at the center of a cross-section perpendicular to the longitudinal direction, at a position 1 / 10L from the starting end of the head side, is the Vickers hardness at the centroid of this cross-section. The centroid is, for example, the intersection of the diagonals if the cross-section is rectangular, and the center of the circle if the cross-section is circular. In the case of a roughly rectangular or circular cross-section, the centroid can be determined by approximating the cross-sectional shape to a rectangle or circle.

[0057] In this way, the Vickers hardness HV at the center position is measured in cross-sections perpendicular to the longitudinal direction at other positions (3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the starting end on the head side). In other words, there are five points where the Vickers hardness HV at the center position is measured.

[0058] Furthermore, the relative cross-sectional area X is the ratio of the cross-sectional area of ​​each section to the cross-sectional area of ​​the section perpendicular to the longitudinal direction at the starting end of the body on the head side. That is, in the body, the cross-sectional area of ​​the section perpendicular to the longitudinal direction at the starting end 3, which has the largest cross-sectional area, is set to 1, and the relative cross-sectional area X is the ratio of the cross-sectional areas of the sections perpendicular to the longitudinal direction at each position to this value. Since there is a relative cross-sectional area for each section, there are five in total.

[0059] Then, plot the Vickers hardness HV at the center of each cross-section and the corresponding relative cross-sectional area X, and organize them as shown in Figure 3. Using the obtained Figure 3, the relationship between the Vickers hardness HV at the center and the relative cross-sectional area X is approximated by a straight line using the least squares method, and the slope a, intercept b, and contribution coefficient R in equation (i) above are determined, and the titanium nail of this embodiment has a slope a, intercept b, and contribution coefficient R 2 The range satisfies equations (ii) to (iv) below.

[0060] -90 ≤ a ≤ -50 ···(ii) 190 ≤ b ≤ 300 ···(iii) 0.65 ≤ R 2 ...(iv) However, R in the above formula 2 It is defined as follows: R 2 : Contribution rate obtained when approximating by a straight line using the least squares method

[0061] Note that the probability rate R 2 This is an index that shows the degree of correlation between the Vickers hardness HV at the center and the relative cross-sectional area X, and is calculated using the following formula (a).

[0062]

number

[0063] Here, if the value of a, which is the slope, is less than -90, the head is too soft, and not only will local bending occur, but the desired strength may not be obtained, or the tip may become too hard and the followability may decrease. Therefore, the value of a shall be -90 or more. The value of a is preferably -85 or more. Note that local bending means that due to the presence of a soft or hard portion in the body of the nail, a part of the body is greatly bent or deformed. On the other hand, if the value of a exceeds -50, the slope becomes small, and it becomes difficult to provide a hardness difference from the tip to the head. As a result, local bending may occur or the followability may decrease. Therefore, the value of a shall be -50 or less. The value of a is preferably -55 or less.

[0064] Also, if the value of b, which is the intercept, is less than 190, the desired strength cannot be obtained. Also, the tip may be crushed. Therefore, the value of b shall be 190 or more. The value of b is preferably 200 or more. On the other hand, if the value of b exceeds 300, the hardness of the entire nail increases excessively and the followability decreases. Therefore, the value of b shall be 300 or less. The value of b is preferably 260 or less.

[0065] The contribution rate R 2 If it is less than 0.65, the correlation between the Vickers hardness HV at the center position and the relative cross-sectional area X is small, and it is considered that the nail contains a very soft portion and a very hard portion locally. As a result, local bending is likely to occur. Therefore, R 2 shall be 0.65 or more. R 2 is preferably 0.70 or more.

[0066] Note that in the titanium nail of this embodiment, the actual hardness is not particularly limited. From the viewpoint of suppressing local bending and tip crushing and ensuring followability, for example, the Vickers hardness at the center position of the cross-section is often in the range of 100 to 300 HV1. More preferably, it is 110 to 260 HV1. Since the head of the titanium nail of this embodiment is soft, the lower limit value is the hardness on the head side and the upper limit value is the hardness on the tip side.

[0067] In the titanium nail of this embodiment, the measurement position closest to the head is 1 / 10L from the starting end of the head side of the shank. Therefore, it is preferable that the Vickers hardness at the center of the cross-section perpendicular to the longitudinal direction at this position is 100 HV1 or higher. Similarly, the measurement position closest to the tip is 9 / 10L from the starting end of the head side of the shank. Therefore, it is preferable that the Vickers hardness at the center of the cross-section perpendicular to the longitudinal direction at this position is 300 HV1 or lower. It is also preferable that the hardness at other positions be within the range of 100 to 300 HV1.

[0068] To measure the Vickers hardness HV at the center, a hardness test is necessary. This hardness test should be performed with a test load of 1 kgf in accordance with JIS Z 2244:2009.

[0069] 2-2. Distribution of hardness towards the center As mentioned above, nails are often repeatedly pulled out and driven in. Therefore, excellent wear resistance is desirable. To improve the wear resistance of titanium nails, it is preferable to have a hardened layer on the surface that becomes softer towards the inside.

[0070] The hardened layer is typically 100 μm or thicker than the surface. Therefore, it is preferable that the difference between the average Vickers hardness HVs at a position 100 μm from the surface toward the center in each cross-section, and the average Vickers hardness HVc at the aforementioned center position in each cross-section, satisfies equation (v) below.

[0071] 30 ≤ HVs - HVc ≤ 200 ···(v) However, each symbol in equation (v) above is defined as follows: HVs: Average Vickers hardness (HV0.1) measured at a distance of 100 μm from the surface towards the center of each cross-section, when the test load is 100 gf. HVc: Average Vickers hardness value at the center of each cross-section (HV1)

[0072] To calculate the average Vickers hardness HVs at a distance of 100 μm from the surface toward the center, and the average Vickers hardness HVc at the center of each cross-section, a hardness test is necessary. When measuring the Vickers hardness at a distance of 100 μm from the surface toward the center, the test load should be 100 gf, and when measuring the Vickers hardness at the center of each cross-section, the test load should be 1 kgf. The hardness test should be performed with the specified test load and in accordance with JIS Z 2244:2009.

[0073] Specifically, the Vickers hardness is determined at a point 100 μm from the surface toward the center (center of gravity) in each cross section perpendicular to the longitudinal direction at positions 1 / 10L, 3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the head end of the body, and the average of these five points is HVs. Similarly, the Vickers hardness is determined at the center (center of gravity) in each cross section perpendicular to the longitudinal direction at positions 1 / 10L, 3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the head end of the body, and the average of these five points is HVc.

[0074] Furthermore, if the middle value of equation (v), which is the difference between HVs and HVc, is less than 30, a hardened layer of sufficient hardness has not been formed, making it difficult to improve wear resistance. For this reason, it is preferable that the middle value of equation (v) be 30 or more, and more preferably 50 or more. On the other hand, if the middle value of equation (v) is greater than 200, an excessive hardened layer has been formed, and toughness and ductility tend to decrease. For this reason, it is preferable that the middle value of equation (v) be 200 or less, and more preferably 150 or less. The measurement of HVs and HVc can be carried out in the same manner as the hardness measurement method described above.

[0075] Furthermore, if equation (v) is satisfied, a hardened layer has been formed, and it is considered that the concentration of O at a position 100 μm from the surface toward the center is 1.5 times or more than the concentration of O at the center.

[0076] 3.Japanese nail The titanium nails of this embodiment can also be used as Japanese nails. Japanese nails are nails that have been used in traditional architecture, wooden Japanese boats, brewing barrels and tubs, and for fixing fired roof tiles. Japanese nails are nails whose dimensions are specified in the "sun" unit of the traditional Japanese measurement system and its auxiliary unit, "bu". When making Japanese nails, the processing of the body 2 may include, for example, chamfering the corner portion of the body 2 to give it a rounded shape. The corner portion of the body 2 may also be chamfered or protruding. Furthermore, as shown in Figure 4, Japanese nails with a rolled head 7 or a folded head 8 are also acceptable.

[0077] As shown in Figure 1, when the length of the long side or diameter (major axis) of the cross-section perpendicular to the longitudinal direction at a position 1 / 10L from the starting end of the head of the body is defined as the cross-sectional length of the body, it is preferable that the ratio of the cross-sectional length of the body (mm) to the total length of the Japanese nail (mm) (hereinafter also referred to as the "cross-sectional shape ratio") satisfies the following relationship. That is, when the total length of the Japanese nail is less than 1 sun 2 bu (approximately 36 mm), it is preferable that the cross-sectional shape ratio be in the range of 0.100 to 0.050. When the total length of the Japanese nail is 1 sun 2 bu (approximately 36 mm) or more, it is preferable that the cross-sectional shape ratio be in the range of 0.035 to 0.065.

[0078] Furthermore, it is preferable for Japanese nails to have a hammered pattern on their surface. A hammered pattern is a wave-like pattern that continues at regular intervals, with each wave being of a different size. This creates a pattern of irregularities with a depth of approximately 0.05 to 0.30 mm. The small irregularities of the hammered pattern increase the coefficient of friction at the contact surface, which can reduce the possibility of the nail loosening or coming out, and also help prevent corrosion.

[0079] 4. Manufacturing method The titanium nails of this embodiment can be reliably manufactured, for example, by the following manufacturing method.

[0080] 4-1.Primary hot forging Prepare a titanium material (industrial-grade pure titanium or titanium alloy) to be used as the nail material. The chemical composition of the titanium material is preferably within the range described above. Furthermore, the titanium material should be in wire form, with a 0.2% yield strength of 215 MPa or higher at room temperature, a tensile strength of 340-510 MPa, and an elongation of 23% or higher. The cross-section of the titanium material is not particularly limited; it may be rectangular or circular.

[0081] This titanium material is heated to 750-875°C, and then hot-forged until the temperature drops to below 500°C to primarily form the body. In the primary hot forging, the body is hot-forged from the head end to the tip. This is because hot-forging from the head end to the tip allows the range of values ​​a and / or b to be within the range of this embodiment. This hot forging is called primary hot forging.

[0082] If the heating temperature during primary hot forging is less than 750°C, the low heating temperature may prevent sufficient strain from being introduced, resulting in the values ​​of a and / or b falling outside the range of this embodiment. Therefore, the heating temperature during primary hot forging should be 750°C or higher.

[0083] On the other hand, if the heating temperature during primary hot forging exceeds 875°C, the material may become soft due to overheating, and the range of value a may fall outside the range of this embodiment. Furthermore, manufacturability will decrease. Therefore, the heating temperature during primary hot forging should be 875°C or lower. The heating time is not particularly limited, but may exceed 30 seconds. It should be selected as appropriate and necessary.

[0084] After heating the titanium material to the above range, hot forging is performed until the temperature of the titanium material drops below 500°C. If the primary hot forging is completed when the temperature of the titanium material exceeds 500°C, the range of values ​​a and / or b may fall outside the range of this embodiment. By performing the primary hot forging under the above conditions, strain accumulates more significantly in areas with smaller cross-sectional areas, resulting in more pronounced work hardening. Furthermore, as strain accumulates, the crystal grains become finer, leading to improved strength.

[0085] The atmosphere during the primary hot forging is not particularly limited. For example, a combustion atmosphere such as air, charcoal, gas, or oil may be used. Reheating may also be performed during the primary hot forging. The number of reheating cycles is not particularly limited. The heating time during reheating is preferably 30 seconds or less, and preferably 5 seconds or less. If the heating time during reheating exceeds 30 seconds, the material may soften too much, causing the values ​​of a and / or b to fall outside the range of this embodiment. Other conditions for hot forging are also not particularly limited. They should be adjusted to obtain the desired properties.

[0086] Here, in order to obtain a titanium nail that satisfies equation (v) and has improved wear resistance, it is preferable to perform rough forging in an atmospheric environment before the hot forging process described above, if necessary. In rough forging, it is preferable to heat the entire titanium material to 850°C or higher and perform hot forging. Furthermore, it is preferable that the heating time at this time be 10 minutes or more. This is because by heating at a high temperature and performing hot forging, the titanium material incorporates oxygen from the atmospheric environment, causing solid solution strengthening and forming a hardened layer. In addition, in order to suppress significant oxidation due to heating, it is preferable that the heating temperature during rough forging be 920°C or lower.

[0087] Rough forging is a process of crushing and removing the brittle scale layer and significantly oxygen-enriched layer that form on the outermost surface during heating. Therefore, there is no particular limit to the temperature at which rough forging is completed, but it is preferable to perform rough forging at 500°C or below. If a hardened layer can be formed by work hardening, this may be done. Furthermore, there is no particular order in which rough forging is performed.

[0088] 4-2. Cooling Next, the titanium material that has undergone the hot forging process described above is cooled to a temperature range of room temperature to 200°C. This cooling process is performed to prevent the temperature at the tip from exceeding 650°C, which is the point at which processing strain is released, during the subsequent secondary hot forging. If the material is not cooled to the above temperature range, areas that are locally soft or hard may occur, resulting in R 2 The value may become smaller.

[0089] 4-3.Secondary hot forging Next, the portion of the titanium material that will become the head, which has been cooled to the above temperature range, is heated again in the temperature range of 750-875°C and hot forged. If the entire piece is heated and hot forged, the tip may soften, and a and / or b may no longer satisfy the scope of this embodiment. Also, localized softening may occur, R 2 The value of this can also become large. This type of hot forging is called secondary hot forging. In secondary hot forging, the head is shaped into the desired form. The shape of the head is not particularly limited, but examples include folded, rolled, and rolled head.

[0090] If the heating temperature during secondary hot forging is below 750°C, the low temperature makes it difficult to achieve the desired head shape. Therefore, the heating temperature during secondary hot forging should be 750°C or higher. On the other hand, if the heating temperature during secondary hot forging exceeds 875°C, the head becomes soft due to overheating, making it difficult to obtain the desired properties afterward. Manufacturability also decreases. Therefore, the heating temperature during secondary hot forging should be 875°C or lower. The heating time is not particularly limited. From the viewpoint of manufacturability, the above heating time may be greater than 30 seconds. It should be selected as appropriate and necessary.

[0091] The atmosphere during secondary hot forging is not particularly limited. For example, a combustion atmosphere such as air, charcoal, gas, or oil may be used. Reheating may also be performed during secondary hot forging. The number of reheating cycles is not particularly limited. Furthermore, the heating time during reheating is preferably 30 seconds or less, and preferably 5 seconds or less. In addition, other conditions for secondary hot forging are not particularly limited. They should be adjusted to obtain the desired characteristics.

[0092] Through this process of primary hot forging, cooling, and secondary hot forging, the tip end, which has a smaller cross-sectional area, requires fewer reheating cycles and its temperature rises less rapidly throughout the series of processes up to the secondary hot forging. As a result, the processing strain from hot forging is maintained more towards the tip end, and the tip end, with its smaller cross-sectional area, hardens more due to the processing. This results in a titanium nail of this embodiment that has a difference in hardness between the tip and the head end. Note that during the secondary hot forging, some minor processing such as shape correction may be performed as needed, and this will not impair the characteristics of the titanium nail of this embodiment.

[0093] The titanium nails according to the present invention will be described in more detail below with reference to examples, but the titanium nails of this embodiment are not limited to these examples. [Examples]

[0094] Titanium materials (wires) having the chemical composition shown in Table 1 were prepared, and titanium nails were manufactured. Tensile tests were conducted to investigate the tensile properties of the titanium materials. The tests were conducted in accordance with JIS Z 2241:2011. The manufacturing conditions for each nail were as shown in Table 2. When reheating was performed during the primary hot forging, the reheating temperature was the same as the initial heating temperature. In some cases where rough forging was performed, the material was cooled to below 500°C after rough forging.

[0095] [Table 1]

[0096] [Table 2]

[0097] (Hardness test and calculation of relative cross-sectional area X) For the obtained nails, cross-sections perpendicular to the longitudinal direction were cut from the shank at positions 1 / 10L, 3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the starting end of the head side. The hardness of the center and the relative cross-sectional area X of each cross-section were calculated. In addition, the hardness at a position 100 μm from the surface toward the center was also measured for each of the above cross-sections. The test load was set to correspond to each position, and the hardness test was performed in accordance with JIS Z 2244:2009. In the example of the present invention described later, all hardness measurement points were between 100 and 300 HV1.

[0098] (Abrasion resistance test) A marking pen with a 1mm diameter tip made of cemented carbide (G2) was used to scratch the surface of a nail multiple times, and the resulting marks were visually observed. Specifically, the marking pen was held in the hand, and the nail was scratched 5 to 10 times in lengths of approximately 2 to 5 mm, as if writing. The marks were evaluated as × if they were clearly visible to the naked eye, and ○ if they were not clearly visible. Examples of ○ were evaluated as having good wear resistance.

[0099] (Nail evaluation test) We evaluated the deformation, bending, and conformability of nail tips when driving nails into knots in wood, as well as their ability to conform to hard materials. For this evaluation, we used spheres made of high-carbon chromium steel (SUJ2 of JIS G 4805), which is harder than titanium and iron and has an HV equivalent to 800, to simulate wood knots.

[0100] Specifically, as shown in Figure 5, hemispherical holes with a diameter of 20 mm were pre-drilled in both cypress boards, and a 20 mm diameter sphere of high-carbon chromium steel was sandwiched in the hemispherical hole. Multiple nails were then driven into the four sides of the sphere to secure the upper and lower cypress boards. In this way, a 20 mm diameter sphere of high-carbon chromium steel was sandwiched between the two cypress boards, upper and lower.

[0101] Then, a mark is drawn on the upper side of the cypress board to indicate the center of the carbon-chromium steel sphere. The nail, which will be the test specimen, is driven into the marked position with a hammer. If the nail is driven all the way in, it is marked as a pass (○), and if the nail cannot be driven in further, it is marked as a fail (×). The dimensions shown in Figure 5 are the dimensions used to evaluate a nail that is 2 sun 5 bu (75 mm) long. The results are summarized below and shown in Table 3.

[0102] [Table 3]

[0103] Tests No. 1 to 40 satisfied the requirements of this embodiment. As a result, localized bending and tip crushing were suppressed, and the followability was also good. On the other hand, tests No. 41 to 51, which did not satisfy the requirements of this embodiment, exhibited localized bending or tip crushing, or reduced followability.

[0104] Furthermore, for Test No. 24 and Test No. 3, the oxygen concentration in the surface layer, the oxygen concentration in the center, and the oxygen concentration at the midpoint between the surface and the center were measured, and the results are shown in Table 4. From this, it can be seen that if equation (v) is satisfied, an oxygen-enriched hardened layer has been formed.

[0105] [Table 4] [Explanation of symbols]

[0106] 1.Head 2. Torso 3. The starting end of the torso on the head side. 4. The tip of the body 7. Opening pages 8. Folding floor

Claims

1. Made from industrial-grade pure titanium or titanium alloy, A titanium nail having a head and a body connected to the head and extending in the longitudinal direction, When the total length of the torso in the longitudinal direction is L, in the torso at positions 1 / 10L, 3 / 10L, 1 / 2L, 7 / 10L, and 9 / 10L from the starting end on the head side, in each cross section perpendicular to the longitudinal direction, A titanium nail that satisfies equations (ii) to (iv) below when the Vickers hardness HV at the center position and the relative cross-sectional area X are linearly approximated by the least squares method as shown in equation (i) below. HV=aX+b...(i) -90≦a≦-50...(ii) 190≦b≦300...(iii) 0.65≦R ２ ・・・(iv) However, each symbol in the above formula is defined as follows: HV: Vickers hardness (HV1) at the center position of each cross-section when the test load is 1 kgf. X: Relative cross-sectional area, which is the ratio of the cross-sectional area of ​​each cross-section to the cross-sectional area of ​​the cross-section perpendicular to the longitudinal direction at the starting end of the body. R ２ : Contribution rate obtained when approximating by a straight line using the least squares method

2. The titanium nail according to claim 1, wherein the difference between the average Vickers hardness HVs at a position 100 μm from the surface toward the center in each cross section and the average Vickers hardness HVc at the center position in each cross section satisfies the following equation (v). 30≦HVs-HVc≦200...(v) However, each symbol in equation (v) above is defined as follows: HVs: The average value of the Vickers hardness (HV0.1) at a position 100 μm from the surface toward the center of each cross-section, when the test load is 100 gf. HVc: The average value of the Vickers hardness at the center of each cross-section (HV1)

3. The chemical composition of the aforementioned industrial pure titanium or titanium alloy is, in mass%, Fe: 1.5% or less, Cr: 1.5% or less, Ni: 1.5% or less, O: 0.25% or less, N: 0.05% or less, C: 0.10% or less, H: 0.015% or less, The remainder consists of Ti and impurities. A titanium nail according to claim 1, satisfying the following formula (vi). Fe+Cr+Ni≦1.5...(vi) However, each element symbol in the above formula represents the content (mass %) of each element contained in industrial pure titanium or titanium alloy, and zero is used if the element is not present.

4. The chemical composition of the aforementioned industrial pure titanium or titanium alloy is, in mass%, Fe: 1.5% or less, Cr: 1.5% or less, Ni: 1.5% or less, O: 0.25% or less, N: 0.05% or less, C: 0.10% or less, H: 0.015% or less, The remainder consists of Ti and impurities. A titanium nail according to claim 2, satisfying the following formula (vi). Fe+Cr+Ni≦1.5...(vi) However, each element symbol in the above formula represents the content (mass %) of each element contained in industrial pure titanium or titanium alloy, and zero is used if the element is not present.

5. The chemical composition of the aforementioned industrial pure titanium or titanium alloy is such that a portion of the Ti is replaced by, in mass%, Al: 2.0% or less, Si: 0.5% or less, Sn: 2.0% or less, Zr: 3.0% or less, Cu: 1.8% or less, Nb: 1.0% or less, V: 2.0% or less, Mo: 2.0% or less, Mn: 1.0% or less, Co: 1.0% or less, Pd: 0.25% or less, Ru: 0.25% or less, The titanium nail according to claim 3, comprising one or more selected from the group consisting of the following.

6. The chemical composition of the aforementioned industrial pure titanium or titanium alloy is such that a portion of the Ti is replaced by, in mass%, Al: 2.0% or less, Si: 0.5% or less, Sn: 2.0% or less, Zr: 3.0% or less, Cu: 1.8% or less, Nb: 1.0% or less, V: 2.0% or less, Mo: 2.0% or less, Mn: 1.0% or less, Co: 1.0% or less, Pd: 0.25% or less, Ru: 0.25% or less, The titanium nail according to claim 4, comprising one or more selected from the group consisting of the following.

7. A Japanese-style nail, made of titanium, as described in any one of claims 1 to 6.

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