JP2017125223A - Golf club shaft and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf club shaft which has high strength and high toughness, little variation in the toughness and can be made lightweight.SOLUTION: The golf club shaft according to the present invention contains 0.4 mass% to 0.65 mass% of C, over 0 mass% and 0.80 mass% or less of Si, 0.1 mass% to 1.50 mass% of Mn, over 0 mass% and less than 0.30 mass% of Cr, at least one kind selected from a group consisting of 0.05 mass% to 0.40 mass% of V, 0.03 mass% to 0.15 mass% of Nb and 0.01 mass% to 0.10 mass% of Ti and the balance Fe with inevitable impurities. The golf club shaft also has metallographic structure in which an area ratio of undissolved cementite is 0.5% or less.SELECTED DRAWING: None

Description

  The present invention relates to a steel shaft used for a golf club (hereinafter referred to as “golf club shaft”) and a method for manufacturing the same.

A golf club shaft is required to have strength that does not break or break during use from the viewpoint of safety as well as improving the flight distance and processability of the ball. In recent years, there has also been an increasing demand for weight reduction of golf club shafts.
In order to reduce the weight of the golf club shaft, it is necessary to reduce the thickness or the diameter of the golf club shaft. However, when a steel pipe used as a material for a conventional golf club shaft is thinned or reduced in diameter, the break strength and fracture strength of the golf club shaft are reduced. Therefore, it is necessary to improve the strength and toughness of the golf club shaft in order to reduce the weight while ensuring the same safety as that of the conventional golf club shaft.
Conventionally, it has been disclosed that properties such as elasticity, strength and toughness of a golf club shaft can be improved by appropriately selecting a steel composition and heat treatment conditions (for example, Patent Documents 1 to 3).

Japanese Examined Patent Publication No. 3-44126 JP 2005-13535 A JP 2005-34517 A

However, since the conventional golf club shaft is not strong enough, it is not possible to reduce the weight while ensuring safety. In fact, to reduce the weight of the golf club shaft, the strength should be increased by at least 50 HV (preferably 100 HV) from the current level (usually 550 HV), and the toughness should be equal to or higher than the current level. Although it is necessary to ensure, a golf club shaft having such strength and toughness has not been obtained.
In order to increase the strength of the golf club shaft, it is conceivable to increase the amount of a component such as C or lower the tempering temperature. However, increasing the amount of a component such as C reduces toughness. Further, when the tempering temperature is lowered, the toughness is lowered or the toughness varies, so that the reliability is lowered.
The present invention has been made to solve the above-described problems, and provides a golf club shaft that has high strength and toughness, has little toughness variation, and can be reduced in weight, and a method for manufacturing the same. Objective.

  Therefore, as a result of continuing intensive research to solve the above problems, the present inventors have produced a suitable metal structure by appropriately selecting a steel composition and heat treatment conditions, thereby improving strength and toughness. It has been found that variation in toughness can be suppressed while increasing.

That is, the present invention includes 0.4 mass% to 0.65 mass% C, 0 mass% excess 0.80 mass% or less Si, 0.1 mass% to 1.50 mass% Mn, More than 0 mass% and less than 0.30 mass% Cr, 0.05 mass% to 0.40 mass% V, 0.03 mass% to 0.15 mass% Nb, and 0.01 mass% to 0.00. Including at least one selected from the group consisting of 10% by mass of Ti, with the balance being Fe and inevitable impurities, and having a metal structure in which the area ratio of undissolved cementite is 0.5% or less This is a golf club shaft.
The present invention also includes 0.4 mass% to 0.65 mass% C, 0 mass% excess 0.80 mass% Si, 0.1 mass% to 1.50 mass% Mn, More than 0 mass% and less than 0.30 mass% Cr, 0.05 mass% to 0.40 mass% V, 0.03 mass% to 0.15 mass% Nb, and 0.01 mass% to 0.00. After forming a shaft of a welded steel pipe containing at least one selected from the group consisting of 10% by mass of Ti and the balance being Fe and inevitable impurities, the area ratio of undissolved cementite is 0.5% A golf club shaft manufacturing method is characterized by quenching and tempering to the following.

  According to the present invention, it is possible to provide a golf club shaft that is high in strength and toughness, has little toughness variation, and can be reduced in weight, and a method for manufacturing the same.

Hereinafter, the golf club shaft of the present invention and the manufacturing method thereof will be described in detail.
The golf club shaft of the present invention includes C, Si, Mn, Cr, and at least one selected from the group consisting of V, Nb, and Ti, with the balance being Fe and inevitable impurities. In addition, the golf club shaft of the present invention further includes at least one selected from the group consisting of P and S, at least one selected from the group consisting of Ni and Mo, or B, as necessary. Can do.

<C: 0.4% by mass to 0.65% by mass>
C is a component that affects the strength, proof stress, and elasticity of the steel material after heat treatment, and the quenching hardness, strength, and the like vary depending on the C content. From the viewpoint of obtaining sufficient quenching hardness and strength, the C content needs to be 0.4% by mass or more. On the other hand, if the C content is too high, the ductility and toughness of the steel material after heat treatment are lowered, so the C content needs to be 0.65 mass% or less. The C content is preferably from 0.41% by mass to 0.64% by mass, more preferably from 0.415% by mass to 0.635% by mass, and even more preferably from the viewpoint of stably obtaining the above effects. It is 42 mass%-0.63 mass%.

<Si: 0 mass% excess 0.80 mass% or less>
Si is a component used as a deoxidizer for molten steel in the steelmaking stage. Moreover, Si has the effect | action which raises temper softening resistance. If the Si content is too high, the steel material (polished steel strip) becomes hard, so the productivity of the golf club shaft decreases. Moreover, grain boundary oxidation occurs in the manufacturing process (annealing process) of the steel material (polished steel strip), and the surface quality deteriorates. Therefore, the Si content needs to be 0% by mass and 0.80% by mass or less. The Si content is preferably 0.01% by mass to 0.78% by mass, more preferably 0.03% by mass to 0.75% by mass, and still more preferably 0.000% by mass from the viewpoint of stably obtaining the above effects. It is 04 mass%-0.73 mass%.

<Mn: 0.1% by mass to 1.50% by mass>
Mn is a component that improves hardenability. From the viewpoint of obtaining sufficient hardenability, the Mn content needs to be 0.1% by mass or more. On the other hand, if the Mn content is too high, the steel material (polished steel strip) becomes hard, so the productivity of the golf club shaft decreases. Moreover, the toughness of the steel material after heat treatment is also reduced. Therefore, the Mn content needs to be 1.50% by mass or less. The Mn content is preferably from 0.2% by mass to 1.48% by mass, more preferably from 0.3% by mass to 1.46% by mass, and even more preferably from the viewpoint of stably obtaining the above effects. It is 35 mass%-1.44 mass%.

<Cr: more than 0% by mass and less than 0.30% by mass>
Cr, like Mn, is a component that improves hardenability. If the Cr content is too high, the amount of cementite (undissolved cementite) produced during heat treatment increases. Cementite promotes the generation or propagation of cracks at the time of breakage, and causes a decrease in ductility and toughness. Therefore, Cr content needs to be 0 mass% excess and less than 0.30 mass%. The Cr content is preferably 0.01% by mass to 0.295% by mass, more preferably 0.015% by mass to 0.29% by mass, and still more preferably 0.8% from the viewpoint of stably obtaining the above effects. It is 02 mass%-0.285 mass%.

<V: 0.05 mass% to 0.40 mass%>
V is a component that contributes to refinement of crystal grains during the quenching process and improves toughness. From the viewpoint of sufficiently improving toughness, the V content needs to be 0.05% by mass or more. On the other hand, if the V content is too high, the above effect is saturated, so the V content needs to be 0.40% by mass or less. From the viewpoint of stably obtaining the above effects, the V content is preferably 0.06% by mass to 0.38% by mass, more preferably 0.065% by mass to 0.36% by mass, and still more preferably 0.8%. It is 07 mass%-0.35 mass%.

<Nb: 0.03 mass% to 0.15 mass%>
Nb, like V, is a component that contributes to crystal grain refinement during quenching and improves toughness. From the viewpoint of sufficiently improving toughness, the Nb content needs to be 0.03% by mass or more. On the other hand, if the Nb content is too high, the above effect is saturated, so the Nb content needs to be 0.15% by mass or less. The Nb content is preferably from 0.035% by mass to 0.14% by mass, more preferably from 0.04% by mass to 0.135% by mass, and still more preferably from the viewpoint of stably obtaining the above effects. It is 045 mass%-0.13 mass%.

<Ti: 0.01% by mass to 0.10% by mass>
Ti, like V and Nb, is a component that contributes to crystal grain refinement during quenching and improves toughness. Moreover, since Ti has a strong binding force with N, when it is blended together with B, the formation of BN can be suppressed and the effect of improving the hardenability by B can be ensured. From the viewpoint of sufficiently obtaining such effects, the Ti content needs to be 0.01% by mass or more. On the other hand, if the Ti content is too high, the above effects are saturated and the toughness may be lowered, so the Ti content needs to be 0.10% by mass or less. The Ti content is preferably from 0.012% by mass to 0.095% by mass, more preferably from 0.015% by mass to 0.09% by mass, and even more preferably from the viewpoint of stably obtaining the above effects. 018% by mass to 0.085% by mass.

<P: 0 mass% excess 0.03 mass% or less>
P is a component that segregates at the austenite grain boundaries during the quenching process and reduces toughness by lowering the grain boundary strength. When it contains P, it is necessary to make P content into 0.03 mass% or less from a viewpoint of reducing the influence with respect to toughness. The Ti content is preferably 0.001% by mass to 0.028% by mass, more preferably 0.003% by mass to 0.026% by mass, and still more preferably 0, from the viewpoint of stably reducing the above influence. 0.005 mass% to 0.024 mass%.

<S: 0 mass% excess 0.02 mass% or less>
S is a component that forms MnS as a starting point of fatigue fracture in steel and causes to lower toughness. When it contains S, it is necessary to make S content into 0.02 mass% or less from a viewpoint of reducing the influence with respect to toughness. The S content is preferably from 0.001% by mass to 0.0198% by mass, more preferably from 0.0015% by mass to 0.0195% by mass, and even more preferably from the viewpoint of stably reducing the above influence. 0.002% by mass to 0.0192% by mass.

<Ni: 0.10% by mass to 2.00% by mass>
Ni, like Mn and Cr, is a component that improves hardenability. Unlike Mn and Cr, Ni has little effect on toughness even if contained in a relatively large amount. In order to sufficiently obtain the effect of improving hardenability, the Ni content needs to be 0.10% by mass or more. On the other hand, since Ni is expensive and excessive addition is economically disadvantageous, the Ni content needs to be 2.00% by mass or less. The Ni content is preferably from 0.20% by mass to 1.97% by mass, more preferably from 0.3% by mass to 1.93% by mass, and even more preferably from the viewpoint of stably obtaining the above effects. It is 4 mass%-1.90 mass.

<Mo: 0.10% by mass to 1.50% by mass>
Mo is an effective component for improving toughness. In order to sufficiently obtain the effect of improving toughness, the Mo content needs to be 0.10% by mass or more. On the other hand, if the Mo content is too high, the above effect is saturated, so the Mo content needs to be 1.50% by mass or less. From the viewpoint of stably obtaining the above effects, the Mo content is preferably 0.105% by mass to 1.48% by mass, more preferably 0.011% by mass to 1.46% by mass, and still more preferably 0.1% by mass. 0115% by mass to 1.45% by mass.

<B: 0.0005 mass% to 0.005 mass%>
B is a component which improves hardenability like Mn, Cr and Ni. In order to sufficiently obtain the effect of improving hardenability, the B content needs to be 0.0005% by mass or more. On the other hand, if the B content is too high, the above effect is saturated, so the B content needs to be 0.005 mass% or less. The B content is preferably 0.001% by mass to 0.0048% by mass, more preferably 0.0015% by mass to 0.0045% by mass, and still more preferably 0.000% by mass from the viewpoint of stably obtaining the above effects. 0018 mass% to 0.0042 mass%.

<Balance: Fe and inevitable impurities>
The balance other than the above components is Fe and inevitable impurities. Here, the inevitable impurities mean components that are difficult to remove, such as O and N. These components are inevitably mixed at the stage of melting the steel material.

<Cementite area ratio: 0.5% or less>
When the strength of the golf club shaft is increased, toughness variation may occur. In the present invention, it is found that this variation in toughness is caused by cementite remaining at the time of quenching (undissolved cementite), and by reducing the area ratio of cementite in the metal structure to 0.5% or less, the variation in toughness is reduced. It is preventing. Here, the area ratio of cementite means the area ratio of cementite in the entire arbitrary cross section of the steel material (golf club shaft) after quenching. The area ratio of cementite can be calculated by image analysis after observing it using a known means such as an optical microscope after performing color etching or the like on the cross section of the steel material. The area ratio of cementite is preferably 0.49% or less, more preferably 0.01% to 0.48%, and still more preferably 0.05% to 0.47, from the viewpoint of stably preventing variation in toughness. %.

<Manufacturing method>
The shaft for golf clubs of the present invention is manufactured by forming a welded steel pipe having the above steel composition into a shaft shape and then performing a quenching and tempering treatment at a predetermined temperature.
A welded steel pipe can be obtained by making a steel material adjusted to the above steel composition into a polished band steel according to a conventional method, and then pipe-forming it by a known welding method such as TIG welding or electric resistance welding. The conditions of this pipe making process are not particularly limited except that a steel material adjusted to the above steel composition is used.

The quenching process is performed by heating the formed welded steel pipe to a predetermined temperature and then quenching with oil. In this treatment, the metal structure is sufficiently austenitized by heating to a predetermined temperature, and the martensite structure is modified by oil quenching. Since the heating temperature during quenching is related to the amount of undissolved cementite that causes toughness variation, controlling the heating temperature can reduce undissolved cementite and suppress variation in toughness. it can.
In order to prevent toughness variation, it is necessary to quench at a heating temperature such that the area ratio of undissolved cementite is 0.5% or less. Although it is necessary to adjust heating temperature suitably according to steel composition, it is preferable to carry out at about 800 degreeC or more from a viewpoint of making a metal structure fully austenite and reducing undissolved cementite. Moreover, it is preferable that a heating temperature is 900 degrees C or less from a viewpoint of preventing that an austenite crystal grain coarsens. When determining the heating temperature for setting the area ratio of undissolved cementite to 0.5% or less, for example, the following operation may be performed. After performing quenching treatment at the above temperature, measure the area ratio of undissolved cementite, and if the value exceeds 0.5%, increase the heating temperature to perform the quenching treatment, and then determine the area ratio of undissolved cementite. Measure. By repeating this operation until the area ratio of undissolved cementite becomes 0.5% or less, the heating temperature can be determined.

  The tempering process is performed by heating the welded steel pipe subjected to the quenching process to a predetermined temperature. Although it is necessary to adjust the heating temperature at the time of a tempering process suitably according to steel composition, generally hardness can be controlled to 550HV-700HV by making heating temperature into 160 to 400 degreeC.

  As described above, by properly selecting the steel composition and the heat treatment conditions, both the strength and toughness of the golf club shaft can be improved, and thus the weight of the golf club shaft can be reduced.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not limited to the following Example.
After pickling the hot-rolled steel strip having the composition shown in Table 1 below, annealing and cold rolling were repeated to produce a cold-rolled steel strip (polished steel strip) having a thickness of 0.7 mm. Next, the cold-rolled steel strip was cut into a steel piece having a width of 60 mm, formed into an open pipe by a roll forming method, and then both ends in the width direction were electro-welded to produce a welded steel pipe having a diameter of 19 mm. The obtained welded steel pipe was drawn into a shaft shape, and then heated and held at a predetermined temperature for 10 minutes, and a quenching treatment was performed in which quenching was performed in 60 ° C. oil. Next, a tempering process was performed in which air was cooled by heating and holding at a predetermined temperature for 15 minutes to obtain a golf club shaft. Table 2 shows the heating temperature (quenching temperature) during the quenching process and the heating temperature (tempering temperature) during the tempering process.

A test piece was cut out from the golf club shaft obtained as described above, and the following evaluation was performed using the test piece.
<Hardness>
Hardness (HV) was measured using a Vickers hardness tester. The hardness is preferably 640 HV to 660 HV.
<Cementite area ratio>
The cross section of the test piece was colored with cementite, observed with an optical microscope, and calculated by image analysis. The observation area was an area of 61 μm × 61 μm.

<Toughness: Impact test>
In order to evaluate toughness, a test piece was prepared under the same conditions as described above using a steel strip with a thickness of 0.7 mm, and then a 2 mm U notch impact test was performed at room temperature using a Charpy impact tester. The impact value was measured. At this time, the measurement point per each test piece was set to 10, and those average values were represented as an impact value. Further, an A value (= 100 × standard deviation / average value), which is an index of variation in impact value, was calculated. In this evaluation, if the impact value is 46 J / cm ² or more and the A value is 10 or less, it can be said that the toughness of the golf club shaft is sufficient.
Each evaluation result is shown in Table 2.

As shown in Table 2, the steel type is No. Sample Nos. A to I and an area ratio of undissolved cementite of 0.5% or less In 1-3, 5-6, and 8-11 and 12 (Example), strength and toughness were high, and there was little variation in toughness.
On the other hand, the steel type is No. Even if it is C, E, or I, sample No. in which the area ratio of undissolved cementite exceeds 0.5%. In 4, 7, and 12 (comparative examples), although the strength was high, there was a large toughness variation (A value) and insufficient toughness (impact value).
The steel grade is No. Sample No. J. In 14 (Comparative Example), the C content of the steel was too high, so the cementite area ratio increased, the toughness (impact value) was low, and the toughness variation (A value) also increased. The steel type is No. Sample No. J. In No. 15 (Comparative Example), although the quenching temperature was increased in order to reduce the cementite area ratio, the toughness (impact value) was still low and the toughness variation (A) was not sufficient.
The steel grade is No. Sample No. K. In 16 (Comparative Example), the C content of the steel was too low, so that sufficient hardness could not be obtained. Therefore, no evaluation other than hardness was performed.
The steel grade is No. Sample No. L being L In No. 17 (Comparative Example), the Mn content of the steel was too high, so the cementite area ratio increased, the toughness (impact value) was low, and the toughness variation (A value) also increased. The steel type is No. Sample No. L being L In No. 18 (Comparative Example), although the quenching temperature was increased to reduce the cementite area ratio, the toughness (impact value) was still low.

The steel grade is No. Sample no. In 19 (comparative example), the Cr content of the steel was too high, so the variation in cementite area ratio and toughness (A value) also increased. The steel type is No. Sample No. M. In 20 (Comparative Example), the quenching temperature was increased in order to reduce the cementite area ratio, but the toughness (impact value) was low and the toughness variation (A value) was also large.
The steel grade is No. Sample No. N In No. 21 (Comparative Example), since the S content of the steel was too high, the toughness (impact value) was low and the toughness variation (A value) was also large. The steel type is No. Sample No. N In No. 22 (Comparative Example), when the quenching temperature was increased, the variation in toughness (A value) was reduced, but the toughness (impact value) was not sufficiently improved.
The steel grade is No. Sample no. In No. 23 (Comparative Example), V, Nb or Ti was not contained, so the toughness (impact value) was low and the toughness variation (A value) was also large. The steel type is No. Sample no. In 24 (Comparative Example), when the quenching temperature was increased, the variation in toughness (A value) was reduced, but the toughness (impact value) was not sufficiently improved.

  As can be seen from the above results, according to the present invention, it is possible to provide a golf club shaft that is high in strength and toughness, has little toughness variation, and can be reduced in weight, and a method for manufacturing the same.

Claims (10)

  0.4 mass% to 0.65 mass% C, 0 mass% excess 0.80 mass% or less Si, 0.1 mass% to 1.50 mass% Mn, 0 mass% excess 0. From less than 30 wt% Cr, 0.05 wt% to 0.40 wt% V, 0.03 wt% to 0.15 wt% Nb and 0.01 wt% to 0.10 wt% Ti. A golf club shaft comprising: a metal structure including at least one selected from the group consisting of Fe and inevitable impurities, and an undissolved cementite area ratio of 0.5% or less.   2. The golf according to claim 1, further comprising at least one selected from the group consisting of P in excess of 0 mass% and 0.03 mass% or less in P and S in excess of 0 mass% and 0.02 mass% or less. Club shaft.   3. At least one selected from the group consisting of 0.10 mass% to 2.00 mass% Ni and 0.10 mass% to 1.50 mass% Mo is further included. A shaft for a golf club as described in 1.   4. The golf club shaft according to claim 1, further comprising 0.0005 mass% to 0.005 mass% of B. 5.   5. The golf club shaft according to claim 1, wherein the golf club shaft has a hardness of 640 HV to 660 HV.   0.4 mass% to 0.65 mass% C, 0 mass% excess 0.80 mass% or less Si, 0.1 mass% to 1.50 mass% Mn, 0 mass% excess 0. From less than 30 wt% Cr, 0.05 wt% to 0.40 wt% V, 0.03 wt% to 0.15 wt% Nb and 0.01 wt% to 0.10 wt% Ti. A welded steel pipe containing at least one selected from the group consisting of Fe and inevitable impurities, and after being formed into a shaft shape, it is quenched so that the area ratio of undissolved cementite is 0.5% or less And tempering the golf club shaft.   The welded steel pipe further includes at least one selected from the group consisting of P exceeding 0 mass% and 0.03 mass% or less and P exceeding 0 mass% and 0.02 mass% or less. 6. A method for producing a golf club shaft according to 6.   The welded steel pipe further includes at least one selected from the group consisting of 0.10 mass% to 2.00 mass% Ni and 0.10 mass% to 1.50 mass% Mo. A method for manufacturing a shaft for a golf club according to claim 6 or 7.   The method for manufacturing a shaft for a golf club according to any one of claims 6 to 8, wherein the welded steel pipe further contains 0.0005 mass% to 0.005 mass% B.   The method for producing a golf club shaft according to any one of claims 6 to 9, wherein a tempering temperature is 160 ° C to 400 ° C.