JP5201202B2 - Titanium alloy for golf club face - Google Patents

Description

  The present invention relates to a titanium alloy used for a face material of a golf club mainly including a driver.

  In recent years, the coefficient of restitution coefficient (SLE rule) has been introduced to golf clubs, and the types of titanium alloy materials used for golf club faces have changed greatly. Prior to enforcement of the coefficient of restitution, Ti-15% V-3% Cr-3% Sn-3% Al alloy with high Young's modulus and high resilience performance, high strength and excellent durability Β-type titanium alloys mainly composed of However, with the introduction of the restitution coefficient regulation, in order to satisfy the regulation by lowering the restitution coefficient with a β-type titanium alloy having a low Young's modulus, there is no other way than increasing the face plate thickness and increasing the rigidity of the face surface. Accordingly, when a β-type titanium alloy containing a large amount of expensive alloy elements such as V and Mo is applied to the face material, an increase in cost is inevitable. Furthermore, the specific gravity is larger than other titanium alloys, and the face becomes heavier as the plate thickness is increased. Thus, the volume of the golf club head using the β-type titanium alloy for the face is limited, and the sweet spot when hitting the ball becomes relatively small, which makes it difficult for the user to use. Thus, β-type titanium alloys are no longer the mainstream material for golf club faces.

  α + β-type titanium alloys, which have a higher Young's modulus than β-type titanium alloys, are now becoming mainstream as driver face materials. By using an α + β-type titanium alloy having a high Young's modulus, the coefficient of restitution is unlikely to be high even if the face is thinned, and the degree of freedom in thickness that satisfies the regulation of the coefficient of restitution is increased compared to a β-type titanium alloy. Further, the specific gravity is smaller than that of the β-type titanium alloy, and the capacity of the club head can be increased even with the same mass. Furthermore, since the content of the expensive alloy element is lower than that of the β-type alloy, there are many merits such as low material cost. As this α + β type titanium alloy, Ti-6% Al-4% V is typical, but other examples include Ti-5% Al-1% Fe, Ti-4.5% Al-3%. V-2% Fe-2% Mo, Ti-4.5% Al-2% Mo-1.6% V-0.5Fe-0.3% Si-0.03% C, Ti-6% Al- 6% V-2% Sn, Ti-6% Al-2% Sn-4% Zr-6% Mo, Ti-8% Al-1% Mo-1% V, Ti-6% Al-1% Fe, etc. Is used.

  If these alloys are used, even if the face thickness is made thinner than the face made of β-type titanium alloy, it is required by satisfying the coefficient of restitution coefficient and using a titanium alloy with an appropriate strength and ductility range. Durability can also be imparted. At this time, in high-grade golf clubs that require high durability even when the face thickness is thin, round bar products that can control the resilience performance by changing the face shape and structure, Young's modulus is 120 GPa or more, tensile strength It is desirable to have a thickness of 950 MPa or more and a breaking elongation of 15% or more. For a thin plate product having a low degree of processing during face molding, the Young's modulus is 135 GPa or more in one direction in the plate surface, the tensile strength is 1100 MPa or more, and the breaking elongation is 7%. It is desirable to have the above. At this time, it is desirable that the Young's modulus satisfies the above-mentioned value in order to satisfy the regulation of the coefficient of restitution, and the tensile strength and ductility to obtain good durability. However, α + β type alloys generally do not have good workability, and both high strength and high Young's modulus satisfying the requirements of high durability and coefficient of restitution are compatible with good hot workability even when the plate thickness is reduced. Alloys are limited.

  For example, Ti-6% Al-4% V alloy, which is the most versatile α + β type alloy, has sufficient strength and Young's modulus as a face material, and has already been widely used as a golf club face alloy. Yes. However, this alloy contains 6% Al, which exhibits solid solution strengthening ability at high temperatures and increases deformation resistance during hot working, has poor hot workability, and is an expensive β-stabilizing element There is a problem that 4% of V is contained and the material cost is relatively high.

  Patent Document 1 proposes a low-cost alloy having a high specific strength similar to that of a Ti-6% Al-4% V alloy. This is to replace expensive and heavy specific elements such as V and Mo with low-cost and high β-stabilizing elements as β-stabilizing elements and to add a large amount of Al, which is an α-stabilizing element with low specific gravity. Therefore, it is an α + β type alloy aimed at high specific strength and low cost. However, this alloy contains 5.5 to 7% of Al and has a drawback that it is difficult to hot work. In particular, in order to reduce the processing cost of face material, it is desirable to supply a plate product that can be processed into a face shape only by a light press molding and polishing process. Shape building is difficult. In particular, during hot rolling, the appropriate hot rolling temperature range of this alloy is narrow, and if the temperature is lowered even a little more than that, there is a problem that ear cracks are likely to occur and the product yield is low.

  Patent Document 2 proposes a golf club head including a high-strength, low-resilience titanium alloy face. In the titanium alloy constituting the face, the contents of Al and Fe are regulated, and it is said that high Young's modulus and tensile strength can be obtained. Although a specific manufacturing method of this alloy is not described in Patent Document 2, an alloy composition containing inevitable impurities in Al and Fe shown in the claims, and a tensile strength of 1200 described in the claims. To obtain ˜1600 MPa, the manufacturing method is considerably limited. That is, such a strength cannot be obtained in the case of performing an annealing process after hot working such as hot rolling or forging, or after hot working or cold working. Furthermore, even when aging heat treatment is performed on a hot or cold processed product, a product in this strength range cannot be obtained. It can only be obtained if it is cold worked to a very high working rate. However, in that case, high strength can be obtained, but ductility is significantly reduced. In a golf club using a face in such a state, once a fatigue crack occurs on the face surface, the propagation cannot be suppressed. Thus, there has been a problem that the high durability required for recent golf club faces cannot be secured.

  Further, Patent Document 3 proposes a titanium alloy for a face in which a golf club head including a welded portion has high durability of the heat affected zone and the Young's modulus and strength can be adjusted by heat treatment. This is to adjust the strength by adding appropriate amounts of Al, Fe, O, and N, to improve the fatigue characteristics of the heat affected zone, and to control the Young's modulus by controlling the heat treatment conditions such as aging strengthening heat treatment. It is characterized by. However, after the application of Patent Document 3, the coefficient of restitution coefficient was enforced, and only an alloy having a high Young's modulus was required. With the alloy composition and heat treatment conditions described in Patent Document 3, the rebound There is a problem in that a high Young's modulus that satisfies the coefficient regulation may not be obtained.

JP 2004-10963 A JP 2006-212092 A Japanese Patent Laid-Open No. 2005-220388 Japanese Patent Laid-Open No. 2005-220388 JP 2008-106317 A JP 2008-133931 A

  An object of the present invention is to solve the above-mentioned problems and to provide an α + β type titanium alloy having a high Young's modulus and a high strength / ductility balance.

  The inventors added Al, O, and N for solid solution strengthening of the α phase, selected inexpensive Fe as a β stabilizing element, and appropriately limited the amount of addition of these elements, thereby reducing β at room temperature. It has been found that when the phase fraction is reduced, both high strength and high Young's modulus satisfying the coefficient of restitution coefficient can be achieved without depending on cold work strengthening or aging strengthening heat treatment. At the same time, it was found that the elongation at break was large and good, showed a high balance between strength and ductility, and high durability was obtained. Further, this alloy has a low specific gravity and is an optimal material for golf club face applications. Furthermore, compared with other α + β type alloys mainly composed of Ti-6% Al-4% V alloy, the content of Al which lowers hot workability is limited to be low, and the rolling load during hot rolling Therefore, scratches and ear cracks during hot rolling are less likely to occur, and therefore, there is an advantage that the manufacturability to products of all shapes including thin plates is good.

  This invention is made | formed based on the said knowledge, and makes the following means the main point.

(1) By mass%, 4.7 to 5.5% Al, 0.5 to 1.4% Fe, 0.03% or less N, and calculated from the formula (1) [O] An α + β type titanium alloy hot-rolled sheet for golf club face comprising O and N satisfying eq of 0.256 to 0.34%, the balance being Ti and inevitable impurities, and having a Young's modulus in the sheet width direction of 135 GPa or more An α + β-type titanium alloy hot-rolled sheet for a golf club face, characterized by having a tensile strength in the sheet width direction of 1100 MPa or more and a breaking elongation in the sheet width direction of 7% or more.
Here, the plate width direction is a direction perpendicular to the hot rolling direction within the plate surface.
[O] eq = [O] +2.77 [N] (1)
Here, [O] is the oxygen concentration (mass%), and [N] is the nitrogen concentration (mass%).
(2) The α + β-type titanium alloy hot-rolled sheet for golf club faces according to (1) above, having a transverse-texture.
(3) A method for producing an α + β type titanium alloy hot-rolled sheet for a golf club face as described in (1) or (2) above, wherein the titanium alloy slab is brought into the β single phase region or the α + β2 phase region immediately below the β transformation point. A method for producing an α + β-type titanium alloy hot-rolled sheet for a golf club face, which is heated and hot-rolled in one direction to obtain a titanium alloy hot-rolled sheet.
(4) By mass%, 4.7 to 5.5% Al, 0.5 to 1.4% Fe, 0.03% or less N, and calculated from the formula (1) [O] α + β-type titanium alloy round bar for golf club face comprising O and N satisfying eq of 0.256 to 0.34%, the balance being Ti and unavoidable impurities, and having an axial Young's modulus of 120 GPa or more and a shaft An α + β-type titanium alloy round bar for a golf club face, characterized by having a tensile strength in the direction of 950 MPa or more and an elongation in the axial direction of 15% or more.
[O] eq = [O] +2.77 [N] (1)
Here, [O] is the oxygen concentration (mass%), and [N] is the nitrogen concentration (mass%).

  The present invention can provide an α + β type titanium alloy characterized by having a high strength / ductility balance and Young's modulus.

  In order to solve the above-mentioned problems, the present inventors have investigated in detail the influence of the component elements and the production method on the material properties of the titanium alloy. As a result, by controlling the amount of Fe, Al, O, N added, the thickness was reduced. To produce α + β type titanium alloys with high strength and ductility balance and high Young's modulus required for high-grade gork club face materials that require high durability and good hot workability Found that is possible. In particular, it is required as a high-end golf club face without sacrificing ductility by regulating the addition amount of O and N, which have the function of strengthening by dissolving in the α phase, within the proper range using the [O] eq formula. It was found that high strength and Young's modulus can be secured. Furthermore, in the present invention alloy, in which α is mainly strengthened by adding mainly O and N in Al, when producing plate products, the texture that causes material anisotropy is remarkably developed by unidirectional hot rolling or cold rolling. However, material anisotropy occurs in which the Young's modulus and strength in the sheet width direction, which is a direction perpendicular to the rolling direction, are increased as compared to the rolling direction.

  In the golf club face surface, it is sufficient that the Young's modulus and the tensile strength achieve the target values in the longitudinal direction of the golf club face surface. Therefore, the Young's modulus and the tensile strength may be realized in at least one direction of the plate. And in a thin plate product, it is possible to implement | achieve the target about the Young's modulus and tensile strength about a rolling width direction by performing unidirectional rolling. That is, if the longitudinal direction of the golf club face is taken as the plate width direction, a high Young's modulus and tensile strength in one direction required for the golf club face (longitudinal direction of the golf club face) can be obtained. .

  The present invention has been made based on the above findings. The reasons for selecting the various additive elements shown in the present invention and the reasons for limiting the addition amount range are shown below.

  Fe is an inexpensive additive element among the β-phase stabilizing elements and has a function of strengthening the β-phase. In addition, since the β-stabilizing ability is high, the β-phase can be stabilized even with a relatively low addition amount. In order to obtain the strength required for a golf club face, it is necessary to add 0.5% or more of Fe. On the other hand, Fe is easily solidified and segregated in Ti, and if added in a large amount, the volume fraction of the β phase, which has a lower Young's modulus compared to the α phase, increases, and the bulk Young's modulus decreases. Young products have a Young's modulus of 120 GPa and thin products have a Young's modulus of less than 135 GPa in one direction within the plate surface, making it difficult to satisfy the rebound coefficient regulation as a golf club face. Considering these effects, the upper limit of the amount of Fe added is set to 1.4%. In addition, in order to emphasize strength characteristics and to reliably satisfy the coefficient of restitution due to a decrease in Young's modulus, it is desirable that the lower limit of Fe addition is 0.7% and the upper limit is 1.2%.

  Al is a stabilizing element of the titanium α phase, has high solid solution strengthening ability, and is an inexpensive additive element. By the combined addition with O and N described later, it is a necessary strength level that can ensure durability as a high-grade golf club face, with a round bar product having a tensile strength of 950 MPa or more, and a thin plate product in one direction within the plate surface. In order to obtain a tensile strength of 1100 MPa or more, the lower limit of the addition amount was set to 4.7%. On the other hand, if Al is added over 5.5%, the deformation resistance becomes too high, the ductility is lowered, and the ductility required for durability as a golf club face cannot be achieved, and the hot deformation resistance increases. This results in a decrease in hot workability. Therefore, the amount of Al needs to be 5.5% or less.

  Both O and N have an interstitial solid solution in the α phase and have the effect of strengthening the α phase by solid solution strengthening at a temperature near room temperature. By combined addition with Al, it becomes possible to achieve high strength and also high Young's modulus. On the other hand, unlike Al, since hot deformation resistance is not increased, the amount of Al added can be suppressed by adding O and N. As described in Patent Documents 4 to 6, from the similarity of the strengthening mechanism of O and N on Ti, the action of O and N on the strength at room temperature is represented by the formula [1] It can be uniquely expressed by eq. When O and N are added so that [O] eq is less than 0.25%, a round bar product exhibits a sufficient durability as a high-grade golf club face, a tensile strength of 950 MPa or more for a round bar product, and an in-plane product for a thin plate product It is impossible to stably obtain a tensile strength of 1100 MPa or more in one direction. In addition, when O and N in the range where [O] eq exceeds 0.34% are added, the strength becomes too high and the ductility decreases, and a breaking elongation of 7% can be secured in one direction within the plate surface of the thin plate product. Disappear. Therefore, the lower limit of [O] eq represented by formula (1) is set to 0.25% and the upper limit is set to 0.34%.

In the case of a sheet product, the Young's modulus E in the sheet width direction of a unidirectional hot-rolled or cold-rolled titanium alloy within the chemical component range defined in the present invention is expressed by the formula (2) within the range of [O] eq. ) And increased in proportion to [O] eq. This is because the β phase that lowers the Young's modulus decreases due to an increase in the α phase stabilizing element. By adding O and N within the range of [O] eq of the present invention, the Young's modulus in the plate width direction can be about 140 GPa.
E = 41.2 [O] eq + 130.2 Formula (2)

  With regard to the amount of N added, when N exceeding 0.030% is added by a normal method using sponge titanium containing a high concentration of N, undissolved inclusions called LDI (Low density Inclusion) are likely to be generated. Since the product yield is low, 0.030% was made the upper limit.

  At this time, if the rebound coefficient can be kept low by controlling the face shape with a relatively large degree of processing when forming into a face shape such as a round bar or a thick plate, the above component range is included. As a result, a golf club face having excellent characteristics can be obtained. The alloy of the present invention having the above component range is suitable as a face material because it has relatively good workability.

  On the other hand, when manufacturing thin sheet products with little room to keep the coefficient of restitution low due to the shape of the face, only a slight processing is performed to form the face shape, and when a texture called Transverse-texture is developed, Tensile strength and Young's modulus are increased, which is preferable as a golf club face material. Limit the content of Al, Fe, and O to the above-mentioned component ranges, and heat them in the β single phase region or α + β2 phase region temperature just below the β transformation point and hot-roll in one direction, or, in the same direction as the hot-rolling direction. Transverse-texture is easy to develop when annealed under suitable conditions that are normally used after cold rolling in one direction, and the strength and Young's modulus in the plate width direction increase, making it possible to produce the optimal material for the face. is there.

  The reason for rolling in one direction consistently from the start to the end of hot or cold rolling when manufacturing this thin plate material is the purpose of the present invention. This is in order to efficiently obtain a transverse-texture that can obtain a rate. Thus, by arranging the titanium alloy thin plate having a high Young's modulus and strength / ductility balance in the longitudinal direction of the golf club face or in the direction close to it, the rebound coefficient can be regulated and high durability can be achieved. It is possible to manufacture the face provided.

<Example 1>
A titanium material having the composition shown in Table 1 was melted by a vacuum arc melting method, and this was hot-forged into a billet having a diameter of 100 mm. This billet was heated to 950 ° C., and then a φ18 mm round bar was manufactured by hot rolling. The round bar was annealed at 800 ° C. for 2 hours, and then a JIS No. 14 tensile test piece having an average diameter of 6 mm was collected and examined for tensile properties. Further, the depth of the hot-rolled scratch was measured as a depth from the surface of the hot-rolled scratch opening with a laser three-dimensional roughness meter (○: maximum scratch depth ≦ 0.5 mm, x: maximum scratch depth) ≧ 0.5 mm). In order to obtain good durability as a high-grade golf club face round bar material, it is necessary to have a tensile strength of about 950 MPa or more and a breaking elongation of 15% or more. Further, a Young's modulus of 120 GPa or more is necessary. The results are also shown in Table 1.

  In Table 1, test numbers 1 and 2 are the results for Ti-6% Al-4% V alloy and Ti-7% Al-1% Fe, respectively. In both test numbers 1 and 2, the tensile strength (TS) exceeds the target value of 950 MPa, but hot-rolled scratches with a depth of 0.5 mm or more have occurred, and hot workability is poor.

  On the other hand, test numbers 4, 5, 8, 9, 12, 13, 15, 16, 18, 19, and 20, which are examples of the present invention, have a high tensile strength (TS) of 950 MPa or more and 15%. A high elongation at break (EL) is exhibited, and a face having excellent durability can be produced.

  On the other hand, in the test numbers 3, 7, and 11, the tensile strength is 950 MPa or less, which is not sufficient as a face material. This is because the amounts of Al, Fe, and [O] eq were below the lower limit of the present invention in the order of test numbers 3, 7, and 11, respectively, so that the solid solution strengthening ability was not sufficient and the tensile strength was low. .

  In Test Nos. 6 and 14, the elongation at break is less than 15%, sufficient ductility is not retained, and high durability cannot be imparted. Test No. 6 was because the addition amount of Al exceeded the upper limit of the present invention, and because [O] eq exceeded the upper limit in Test No. 14, each increased strength and decreased ductility. In test number 17, N was added in excess of the upper limit of the present invention, and the occurrence of LDI was confirmed, so the test was stopped.

  Among the above, in test numbers 6 and 17, surface defects having a depth exceeding 0.5 mm occurred frequently after hot rolling. In Test No. 6, Al that decreases hot workability was added in excess of the upper limit of the present invention, and hot-rolled scratches were generated. In Test No. 17, LDI was generated due to excessive N content, and the vicinity of the surface was recognized as a defect.

  In test number 10, the amount of Fe was too high and the Young's modulus was below 120 GPa.

  From the above results, the titanium alloy having the element content defined in the present invention has high tensile strength and elongation at break, excellent material characteristics as a golf club face material, and good hot workability. . On the other hand, if the amount of the alloying element defined in the present invention is deviated, the hot workability is lowered and the necessary material properties such as tensile strength and ductility cannot be satisfied.

<Example 2>
By the vacuum arc melting method, titanium materials having chemical compositions shown in Test Nos. 5, 9, and 12 in Table 1 were melted and hot forged to obtain a slab having a thickness of 180 mm. This slab was hot-rolled in one direction under the conditions shown in Table 2 to produce a hot-rolled sheet having a thickness of 4 mm. When this was shot blasted and pickled to remove the oxide scale, the surface scratch depth was measured with a depth gauge to evaluate hot workability (○: maximum scratch depth ≦ 0.3 mm, ×: maximum Scratch depth ≧ 0.3 mm). The results at this time and the results of examining the tensile properties are also shown in Table 2.

  Table 2 shows the results of the plate products having chemical compositions shown in Test Nos. 5, 9, and 12 in Table 1, respectively. Of these, all the plates manufactured under the conditions shown in Table 2 sufficiently satisfy the tensile strength (1100 MPa or more) and Young's modulus (135 GPa or more) in the plate width direction, which are required for thin plate products used for golf club faces. At the same time, the breaking elongation in the plate width direction is 7% or more, and the golf club face manufactured using these plate materials has both characteristics suitable for the coefficient of restitution coefficient and good durability. Moreover, the surface defect of the depth exceeding 0.3 mm does not generate | occur | produce in a hot-rolled pickling board, but shows favorable hot ductility. Accordingly, these thin plate materials are suitable as golf club face materials.

  In particular, test numbers 21, 23, 24, 26, 28, 29, 31, 33, and 34 have a high Young's modulus of 142 GPa or more in the plate width direction, and when compared with an alloy having the same chemical composition, test number 22 , 25, 27, 30, 32, and 35, the tensile strength is high, and it has excellent performance with respect to the coefficient of restitution and good durability. This is because in test numbers 22, 25, 27, 30, 32, and 35, the heating temperature before hot rolling was a relatively low temperature in the α + β2 phase region, so α + β2 just below the β single phase region or β transformation point. Compared to the case of heating up to the phase temperature, the transverse-texture development was less and the material anisotropy did not increase, whereas test numbers 23, 24, 28, 29, 33, and 34 were heated to the β single phase region. This is because, by hot rolling, the transverse-texture has developed and the material anisotropy in the plate surface has increased, and both high Young's modulus and high tensile strength have been obtained in the plate width direction.

  From the above results, titanium having an additive element in the component range shown in the present invention has high Young's modulus, tensile strength and ductility in the plate width direction in order to have excellent characteristics as a plate material for golf club face. The alloy can be produced by unidirectional hot rolling.

  The titanium alloy of the present invention has a Young's modulus of 120 GPa, a tensile strength of 950 MPa, and a breaking elongation of 15% or more for round bar products, and a thin plate product has a Young's modulus of 135 GPa, a tensile strength of 1100 MPa, and a breaking elongation of 7 in one direction in the plate surface. As a result, when processed into a golf club face, the material satisfies the restitution coefficient regulation and has excellent durability and can provide a material suitable for high grade golf club face applications. It has become.

Claims (4)

In mass%, 4.7 to 5.5% Al, 0.5 to 1.4% Fe, 0.03% or less N, and [O] eq calculated from Equation (1) is 0. .Alpha. + Beta type titanium alloy hot-rolled sheet for golf club face comprising O and N satisfying 256 to 0.34%, the balance being Ti and unavoidable impurities, the Young's modulus in the sheet width direction being 135 GPa or more, the sheet width An α + β-type titanium alloy hot-rolled sheet for a golf club face, characterized by having a tensile strength in the direction of 1100 MPa or more and a breaking elongation in the sheet width direction of 7% or more.
Here, the plate width direction is a direction perpendicular to the hot rolling direction within the plate surface.
[O] eq = [O] +2.77 [N] (1)
Here, [O] is the oxygen concentration (mass%), and [N] is the nitrogen concentration (mass%).   The α + β type titanium alloy hot-rolled sheet for golf club faces according to claim 1, which has a transverse-texture.   A method of manufacturing an α + β type titanium alloy hot-rolled sheet for a golf club face according to claim 1 or 2, wherein the titanium alloy slab is heated to a β single phase region or an α + β2 phase region immediately below the β transformation point. A method for producing an α + β-type titanium alloy hot-rolled sheet for a golf club face, comprising hot rolling in a direction to obtain a titanium alloy hot-rolled sheet. In mass%, 4.7 to 5.5% Al, 0.5 to 1.4% Fe, 0.03% or less N, and [O] eq calculated from Equation (1) is 0. .Α + β type titanium alloy round bar for golf club face comprising O and N satisfying 256 to 0.34%, remaining Ti and inevitable impurities, axial Young's modulus being 120 GPa or more, axial tension An α + β-type titanium alloy round bar for a golf club face, having a strength of 950 MPa or more and an axial breaking elongation of 15% or more.
[O] eq = [O] +2.77 [N] (1)
Here, [O] is the oxygen concentration (mass%), and [N] is the nitrogen concentration (mass%).