JP7129057B2 - Method for producing Ti-based alloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a Ti-based alloy suitable for watch exterior parts, having high hardness, excellent toughness such as impact resistance, and extremely low skin allergy occurrence.

In recent years, Ti-based alloys (titanium alloys) have been widely used as materials for watch exterior parts. Ti-based alloys are significantly lighter than conventionally used stainless steels, and have remarkably good corrosion resistance against seawater and the like. In addition, compared to stainless steel, which contains elements such as Ni and Cr that may cause skin allergies as main elements, Ti-based alloys can be configured without these elements. It can significantly reduce the chance of developing an allergy.

However, since conventional Ti-based alloys are soft, surface hardening treatment is essential in order to prevent scratches and improve aesthetics by mirror-polishing the surface. However, there is a problem that the surface roughness is deteriorated by this hardening treatment, the surface condition becomes a rough gray color, and the design is monotonous, which significantly impairs the sense of luxury. Therefore, there is a demand for a Ti-based alloy that does not require surface treatment, is a hard material, and can be mirror-polished. Specifically, a Ti-based alloy having a Vickers hardness of HV 580 or more is required, which is a unit of hardness.

In order to improve the hardness of Ti-based alloys, many proposals have been made so far to improve the composition of additive elements, but none of the proposals have provided sufficient hardness. Patent Document 1 discloses a titanium alloy for decoration containing 0.5% or more by weight of Fe relative to Ti. This is insufficient from the standpoint of preventing it and improving the mirror polishability.

Patent Document 2 proposes a Ti-based alloy containing 4.5% (wt%, hereinafter the same) Al, 3% V, 2% Fe, 2% Mo, and 0.1% O. The Vickers hardness of this Ti-based alloy is said to be HV440, which is still insufficient from the viewpoint of preventing scratches and improving mirror polishability.

In Patent Document 3, 4.0 to 5.0% aluminum by weight, 2.5 to 3.5% vanadium, 1.5 to 2.5% molybdenum, and 1.5 to 2.5% iron Titanium alloys are disclosed which contain titanium with the balance being titanium and unavoidable constituents. The Vickers hardness of this titanium alloy is not explicitly stated in the specification, but since its composition is not much different from that of Patent Document 2, the hardness is also considered to be lower than the target.

In Patent Document 4, it contains Nb at a ratio of more than 20% to 40% by mass, contains Ge at a ratio of 0.2% to 4.0%, and further contains Ta, W, V, Cr, Ni, Disclosed is a germanium-containing high-strength titanium alloy that contains one or more of Mn, Co, Fe, Cu, and Si in a total ratio of 15% or less, the balance being Ti and inevitable impurities, and having excellent cold workability. there is Although there is no explicit description of its Vickers hardness, it is unlikely that the hardness will significantly increase compared to the various titanium alloys mentioned above.

As described above, in order to improve the hardness of Ti-based alloys, various measures have been taken regarding additive elements. ing. As a result, there is a problem that the design becomes monolithic and the sense of quality is significantly impaired.

JP-A-7-62466 JP-A-7-150274 JP-A-9-145855 JP 2008-127667 A

As described above, it is strongly desired that the material itself of Ti-based alloys for watch exterior parts be much harder than conventional Ti-based alloys. However, in general, the harder the material, the more brittle it becomes, making it difficult to process into watch exterior parts and making it more likely to break when dropped. These problems need to be resolved. In other words, it is necessary to ensure a certain degree of toughness represented by the impact value. The standard for this is to secure an impact value equal to or higher than cemented carbide (a typical example is KV30), which has the lowest toughness among watch exterior materials currently in practical use. Specifically, it is to have an impact value exceeding 6.0 J/cm ² Charpy impact value with a room temperature unnotched test piece of KV30.

The present invention has been made in view of the above circumstances. It is an object of the present invention to provide a Ti-based alloy with a specific resistance of .0 J/cm ² or more.

The basic idea of solving the problem by the present invention is to obtain a β-type alloy with high toughness and then obtain a Ti-based alloy with improved hardness. Al, Zr, Si, and N are used as elements for improving hardness. However, since the addition of these elements tends to generate the α-phase that lowers the toughness, a β-stabilizing element is also added to prevent this. The β-stabilizing element also improves the hardness of the Ti-based alloy depending on the amount added.

In the manufacturing process of the Ti-based alloy, the alloy synthesized with a predetermined element ratio is subjected to high-temperature heat treatment, solution treatment is performed by rapidly cooling from a high temperature, and then aging treatment is performed at a low temperature to achieve age hardening. Realize

In general, there are many β-stabilizing elements in Ti-based or Ti—Al-based alloys, such as Cr, Mo, V, Mn, Fe, W, Nb, Ni, and Co. As industrial parts, Ti-based alloys having various characteristics have been developed by freely selecting them. However, it is not appropriate to use additive elements that may cause skin allergies in the watch exterior parts that are the object of the present invention. Therefore, from this point of view, in the present invention, Fe, Mo, and W are used as β-stabilizing elements. The β-stabilizing effect per unit addition amount of each element is different, and if the β-phase is extremely stabilized by adding a large amount, there is a problem such as a decrease in toughness. Therefore, it is necessary to find an appropriate addition amount of the β-stabilizing element.

Next, Al, Zr, Si, and N, which are additive elements, act in a complex manner to realize high hardness of the alloy obtained by the effects of solution treatment and subsequent aging treatment. If the amount added is small, there is no effect of improving the hardness, and if the amount added is too large, there is a problem that the toughness decreases. Therefore, it is necessary to find appropriate addition amounts of these elements as well. From these points of view, the inventors conducted many experiments to select the appropriate amount of each additive element. The present invention was made based on such experiments, and is characterized by the following configuration.

[1] A Ti-based alloy according to an aspect of the present invention contains at least one of Fe, Mo, and W, and contains 3.0 atomic percent or more and 8.0 atomic percent or less of Fe and 4.0 atomic percent of Mo. 1 atomic % or more and 9.0 atomic % or less, W of 0 atomic % or more and 3.0 atomic % or less, Al of 6.0 atomic % or more and 12.0 atomic % or less, and Zr of 0 atomic % or more and 2. 0 atomic % or less, 0 atomic % or more and 1.5 atomic % or less of Si, 0.4 atomic % or more and 1.5 atomic % or less of N, and Ti and unavoidable impurities as the balance, Al + 0.5 Si + 2 The alloy index represented by .5N+0.5Fe+0.3Mo+0.3W+0.3Zr is 10.5 or more and 17.0 or less.

[2] A method for producing a Ti-based alloy according to one aspect of the present invention is the method for producing a Ti-based alloy according to [1], in which a first heat treatment step is performed at a temperature of 900 degrees or more and 1200 degrees or less. , a solution treatment step by water cooling or oil cooling, and a second heat treatment step of performing heat treatment at a temperature of 400 degrees or more and 600 degrees or less.

[3] A watch component according to an aspect of the present invention is made of the Ti-based alloy according to [1].

The Ti-based alloy of the present invention is composed of elements that do not cause skin allergies, and the amounts of additive elements such as Fe, Mo, W, Al, Si, N, and Zr are optimized. Therefore, the Ti-based alloy of the present invention has excellent hardness (Vickers hardness of HV580 or more) and excellent impact properties (room temperature Charpy impact value with a non-notched test piece is 6.0 J / cm ² or more). In other words, by using the Ti-based alloy of the present invention, the problems of conventional Ti-based alloys, such as mirror polishability and scratch resistance, are remarkably improved. It is possible to provide a material for watch exterior parts that ensures

1 is an appearance photograph of an ingot made of a Ti-based alloy of Example 1 of the present invention. 2 is an appearance photograph of the ingot of FIG. 1 after a forging test;

Hereinafter, a Ti-based alloy, which is an embodiment to which the present invention is applied, will be described in detail with reference to the drawings. In addition, in the drawings used in the following explanation, in order to make the features easier to understand, the characteristic portions may be enlarged for convenience, and the dimensional ratios of each component may not necessarily be the same as the actual ones. do not have. Also, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be implemented with appropriate modifications within the scope of the invention.

(Structure of Ti-based alloy)
A configuration of a Ti-based alloy according to one embodiment of the present invention will be described. The Ti-based alloy contains at least one of iron (Fe), molybdenum (Mo), and tungsten (W) in the following proportions, and further aluminum (Al), zirconium (Zr), silicon (Si), and nitrogen. (N) in the following proportions:
Fe: 3.0 atomic % or more and 8.0 atomic % or less Mo: 4.0 atomic % or more and 9.0 atomic % or less W: 0 atomic % or more and 3.0 atomic % or less Al: 6.0 atomic % or more12. 0 atomic % or less Zr: 0 atomic % or more and 2.0 atomic % or less Si: 0 atomic % or more and 1.5 atomic % or less N: 0.4 atomic % or more and 1.5 atomic % or less Furthermore, the Ti-based The alloy contains titanium (Ti) and incidental impurities as the balance.

In addition, in the Ti-based alloy of the present embodiment, the alloy index represented by Al + 0.5Si + 2.5N + 0.5Fe + 0.3Mo + 0.3W + 0.3Zr is an amount obtained by multiplying the weight of each of the contained elements by a predetermined coefficient and summing them up. , from 10.5 to 17.0. If the alloy index is within this range, it is possible to obtain excellent hardness (Vickers hardness of HV580 or higher) and excellent impact properties (no notch at room temperature) by performing solution treatment, which is rapid cooling from a high temperature, and aging treatment. An alloy having a Charpy impact value of 6.0 J/cm ² or more on a test piece is obtained.

(Method for producing Ti-based alloy)
A main procedure for manufacturing the Ti-based alloy described above will be described. First, raw materials of Ti, Fe, Mo, W, Al, Si, N, and Zr are melted in a melting furnace, and the molten metal is put into a mold and solidified to obtain a Ti-based alloy (alloy forming step).

Next, this Ti-based alloy is placed in a heat treatment furnace and heated at a temperature of 1100° C. or more and 1250° C. or less for 30 minutes or more and 120 minutes or less. After that, the Ti-based alloy is taken out from the heat treatment furnace and hot forged at room temperature in the atmosphere (hot forging step). As a hot forging method, for example, upsetting (a method of compressing the material in the longitudinal direction) or stretch forging (a method of compressing the material in the radial direction) can be used. In addition to forging, other hot working methods such as rolling and extrusion may be used.

Next, the hot forged Ti-based alloy is placed in a heat treatment furnace and heated at a temperature of 900° C. or higher and 1200° C. or lower (preferably 1100° C.) for 30 minutes or more and 120 minutes or less (preferably 1 hour). state (first heat treatment step).

Subsequently, the heated Ti-based alloy is taken out from the heat treatment furnace, water-cooled or oil-cooled, and cooled to about room temperature (solution treatment). The cooling rate must be high, preferably faster than air cooling. The higher the cooling rate, the harder the Ti-based alloy obtained after the aging treatment described later.

Next, the cooled Ti-based alloy is placed in a heat treatment furnace and heated at a temperature of 400° C. to 600° C. (preferably 500° C.) for 10 hours to 200 hours (preferably 100 hours). By holding (second heat treatment step (aging treatment step)), the Ti-based alloy of the present embodiment is obtained.

As described above, the Ti-based alloy according to the present embodiment is composed of elements that do not cause skin allergies, and the amounts of additive elements such as Fe, Mo, W, Al, Zr, Si, and N are optimized. It is Therefore, the Ti-based alloy according to the present embodiment has excellent hardness (Vickers hardness of HV580 or more) and excellent impact properties by performing high-temperature heat treatment, solution treatment for rapid cooling from high temperature, and aging treatment. (The Charpy impact value of a test piece without a notch at room temperature is 6.0 J/cm ² or more). In other words, by using the Ti-based alloy according to the present embodiment, the mirror polishability and scratch resistance, which were problems of conventional Ti-based alloys, are remarkably improved, and furthermore, the impact properties required during production and use, etc. It is possible to provide a material for watch exterior parts in which toughness is ensured.

Hereinafter, the effects of the present invention will be made clearer by way of examples. It should be noted that the present invention is not limited to the following examples, and can be modified as appropriate without changing the gist of the invention.

(Example 1)
FIG. 1 is an example of an appearance photograph of an ingot 100 used in the experiment. Each ingot was made by high frequency melting using a yttria crucible. The procedure for the fabrication will be described.

Raw materials used for melting were sponge Ti, Al pellets, granular raw materials of Fe, Zr and Si, and powder raw materials of Mo, W and TiN. The total amount of ingredients was approximately 800 g. The melting operation was carried out by introducing argon gas after evacuating the inside of the melting furnace chamber. After all raw materials were melted, it was held for about 3 minutes, and the melted raw materials were poured into a cast iron mold. As the casting mold, a cylindrical casting part having a diameter of 40 mm and a height of 100 mm was used. When pouring the molten metal, an alumina funnel was placed on it, and the funnel was filled halfway with the molten metal. The melt in the funnel served as a riser to reduce casting defects of the ingot in the mold. In FIG. 1, the upper conical portion 100A is the feeder portion solidified in the funnel, cut at position C shown in FIG. (referred to as ) was used in subsequent tests.

The ingot 100B was heated to 1200° C. and hot forged. The forging direction was upset forging in the longitudinal direction L of the ingot 100B, and the ingot 100B with a length of 100 mm was forged to 25 mm by only one compression. An example of a photograph of the appearance of the material 110 after forging is shown in FIG.

Next, the entire forged material 110 was heated at 1100° C. for 1 hour (first heat treatment) and then oil-cooled (solution treatment). Furthermore, after that, an aging treatment (second heat treatment) was performed at 500° C. for 100 hours.

The following (a) to (c) evaluations were performed on the forged material after the aging treatment.

(a) Evaluation by Vickers hardness measurement with a load of 50 kgf on a test piece cut out from a cross section of a forging material and polished.
Specifically, when a diamond indenter is pressed against the test piece with a load of 50 kgf, the length of the diagonal line of the recessed portion is measured, and the area of the recessed portion is calculated from this length. Calculate the Vickers hardness using the value.

(b) For the purpose of simple evaluation of toughness, evaluation by observation with an optical microscope or the like for the presence or absence of cracking at the end of the recessed portion (indentation end) during Vickers hardness measurement with a load of 50 kgf.

(c) Evaluation by room temperature Charpy impact test of unnotched specimens processed from forged materials after aging treatment.
Specifically, the test piece is broken by hitting it with a hammer, and the energy required for breaking (Charpy impact value) is measured, which is used as an index for evaluating the toughness of the test piece.

In the same procedure as in Example 1, Ti-based alloys (ingots) having different compositions from the Ti-based alloy of Example 1 were produced as samples of Comparative Examples 1-12 and Examples 2-24. The above evaluations (a) to (c) were performed on them. Tables 1 and 2 summarize the compositions and various evaluation results of the forging materials produced as Comparative Examples 1 to 12 and Examples 1 to 24, respectively.

In the above evaluation (a), an alloy with a Vickers hardness of HV580 or more was judged to be an appropriate alloy, and an alloy with a Vickers hardness of less than HV580 was judged to be an unsuitable alloy.

In the evaluation of (b) above, the alloy in which cracks did not occur was judged to be an appropriate alloy, and the alloy in which cracks occurred was judged to be an inappropriate alloy.

In the evaluation of (c) above, the reference value is 6.0 J/cm ² , which is the KV30 impact value of cemented carbide with the lowest toughness as a watch exterior material currently in practical use. The alloys that showed less than this reference value were judged to be unsuitable alloys.

The sample of Comparative Example 1 (Alloy No. 1) has an alloy index of 10.3, which is below the lower limit of 10.5 for the alloy index specified in the above embodiment. Therefore, the Vickers hardness is less than HV580, and the hardness is insufficient, so the sample of Comparative Example 1 is judged to be an unsuitable sample.

The sample of Comparative Example 2 (Alloy No. 2) has an alloy index of 17.2, which exceeds the upper limit of 17.0 for the alloy index specified in the above embodiment. Therefore, cracks occurred at the ends of the indentations during the Vickers measurement, and from this, the sample of Comparative Example 2 is judged to be an unsuitable sample.

The sample of Comparative Example 3 (Alloy No. 3) has an Fe composition ratio of 2.5 atomic percent, which is below the lower limit of 3.0 atomic percent of the Fe composition ratio defined in the above embodiment. Therefore, the Vickers hardness is less than HV580, and the hardness is insufficient, so the sample of Comparative Example 3 is judged to be an unsuitable sample.

The sample of Comparative Example 4 (Alloy No. 4) has an Fe composition ratio of 8.5 atomic percent, which exceeds the upper limit of 8.0 atomic percent of the Fe composition ratio defined in the above embodiment. Therefore, cracks occurred at the ends of the indentations during the Vickers measurement, and from this, the sample of Comparative Example 4 is judged to be an inappropriate sample.

The sample of Comparative Example 5 (Alloy No. 5) has a Mo composition ratio of 3.5 atomic percent, which is below the lower limit of 4.0 atomic percent of the Mo composition ratio specified in the above embodiment. . Therefore, the Vickers hardness is less than HV580, and the hardness is insufficient, so the sample of Comparative Example 5 is judged to be an unsuitable sample.

The sample of Comparative Example 6 (Alloy No. 6) has a Mo composition ratio of 9.5 atomic percent, which exceeds the upper limit of 9.0 atomic percent of the Mo composition ratio defined in the above embodiment. Therefore, cracks occurred at the edge of the indentation during Vickers measurement, and the Charpy impact value was less than 6 J/cm ² and the toughness was insufficient. Therefore, the sample of Comparative Example 6 was judged to be an inappropriate sample. be done.

The sample of Comparative Example 7 (Alloy No. 7) has a W composition ratio of 3.5 atomic percent, which exceeds the upper limit of 3.0 atomic percent of the W composition ratio specified in the above embodiment. Therefore, cracks occurred at the ends of the indentations during the Vickers measurement, and from this, the sample of Comparative Example 7 is judged to be an inappropriate sample.

The sample of Comparative Example 8 (Alloy No. 8) has an Al composition ratio of 5.5 atomic percent, which is below the lower limit of 6.0 atomic percent of the Al composition ratio specified in the above embodiment. . Therefore, the Vickers hardness is less than HV580, and the hardness is insufficient, so the sample of Comparative Example 8 is judged to be an unsuitable sample.

The sample of Comparative Example 9 (Alloy No. 9) has an Al composition ratio of 12.5 atomic percent, which exceeds the upper limit of 12.0 atomic percent of the Al composition ratio defined in the above embodiment. Therefore, cracks occurred at the edge of the indentation during Vickers measurement, and the Charpy impact value was less than 6 J/cm ² and the toughness was insufficient. Therefore, the sample of Comparative Example 9 was judged to be an inappropriate sample. be done.

The sample of Comparative Example 10 (Alloy No. 10) has a Si composition ratio of 2.0 atomic percent, which exceeds the upper limit of 1.5 atomic percent of the Si composition ratio defined in the above embodiment. Therefore, cracks occurred at the ends of the indentations during the Vickers measurement, and from this, the sample of Comparative Example 10 is judged to be an unsuitable sample.

The sample of Comparative Example 11 (Alloy No. 11) has a N composition ratio of 0.35 atomic percent, which is below the lower limit of 0.4 atomic percent of the N composition ratio specified in the above embodiment. . Therefore, the Vickers hardness is less than HV580, and the hardness is insufficient, so the sample of Comparative Example 11 is judged to be an unsuitable sample.

The sample of Comparative Example 12 (Alloy No. 12) has an N composition ratio of 1.75 atomic percent, which exceeds the upper limit of 1.5 atomic percent of the N composition ratio defined in the above embodiment. Therefore, cracks occurred at the edge of the indentation during Vickers measurement, and the Charpy impact value was less than 6 J/cm ² and the toughness was insufficient. Therefore, the sample of Comparative Example 12 was judged to be an inappropriate sample. be done.

In the samples of Examples 1 to 24 (alloy numbers 13 to 36), the composition ratios (at%) of all the contained elements are all within the range specified in the above embodiment, and the alloy index is also It is within the range specified in the above embodiment. Therefore, the Vickers hardness is HV580 or more, which is sufficient, no cracking occurs at the end of the indentation during Vickers measurement, and the Charpy impact value is 6 J/cm ² or more. Sufficient toughness. Therefore, the samples of Examples 1 to 24 are all judged to be proper samples.

The Ti-based alloy of the present invention requires hardness and toughness, and can be widely used as a material for composing exterior parts of timepieces that are used in contact with the human body.

100... Ingot 100A... Conical portion of ingot 100B... Rod-like portion of ingot 110... Forging material

Claims (2)

At least one of Fe and Mo is included, Fe is 3.0 atomic % or more and 8.0 atomic % or less, and Mo is 4.0 atomic % or more and 9.0 atomic % or less,
Furthermore, Al is 6.0 atomic % or more and 12.0 atomic % or less, Zr is 0 atomic % or more and 2.0 atomic % or less, Si is 0 atomic % or more and 1.5 atomic % or less, and N is 0.4 atomic % or more. Containing at a rate of 1.5 atomic % or less, and containing Ti and unavoidable impurities as the balance,
In atomic %, the alloy index represented by Al + 0.5Si + 2.5N + 0.5Fe + 0.3Mo + 0.3W + 0.3Zr is 10.5 or more and 17.0 or less,
A method for producing a Ti-based alloy having a Vickers hardness of HV580 or more and a Charpy impact value of 6.0 J/cm2 ^or more ,
A first heat treatment step of performing heat treatment at a temperature of 900° C. or higher and 1200° C. or lower;
a water-cooled or oil-cooled solution treatment process;
and a second heat treatment step of performing heat treatment at a temperature of 400° C. or higher and 600° C. or lower. Contains 3.0 atomic % of W,
Furthermore, Al is 6.0 atomic % or more and 12.0 atomic % or less, Zr is 0 atomic % or more and 2.0 atomic % or less, Si is 0 atomic % or more and 1.5 atomic % or less, and N is 0.4 atomic % or more. Containing at a rate of 1.5 atomic % or less, and containing Ti and unavoidable impurities as the balance,
In atomic %, the alloy index represented by Al + 0.5Si + 2.5N + 0.5Fe + 0.3Mo + 0.3W + 0.3Zr is 10.5 or more and 17.0 or less,
A method for producing a Ti-based alloy having a Vickers hardness of HV580 or more and a Charpy impact value of 6.0 J/cm2 ^or more ,
A first heat treatment step of performing heat treatment at a temperature of 900° C. or higher and 1200° C. or lower;
a water-cooled or oil-cooled solution treatment process;
and a second heat treatment step of performing heat treatment at a temperature of 400° C. or higher and 600° C. or lower.

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