Technical Field
[0001] The present invention relates to an α-β titanium alloy. More particularly, the present
invention relates to an α-β titanium alloy with excellent machinability.
Background Art
[0002] A high-strength α-β titanium alloy, typified by Ti-6Al-4V, can have its strength
level changed easily by a heat treatment, in addition to being lightweight and having
high strength and high corrosion resistance. For this reason, this type of α-β titanium
alloy has been hitherto used very often, especially in the aircraft industry. To further
make use of these characteristics, in recent years, applications of the α-β titanium
alloy have been increasingly expanded into the fields of consumer products, including
vehicle parts, such as engine members of automobiles or motorcycles, sporting goods
such as golf goods, materials for civil engineering and construction, various working
tools, and spectacle frames, the development fields of deep sea and energy, and the
like.
[0003] For example, as such an α-β titanium alloy, Patent Document 1 mentions an α-β titanium
alloy extruded material with excellent fatigue strength and a manufacturing method
for the α-β titanium alloy extruded material. Specifically, the α-β titanium alloy
extruded material includes specified contents of C and Al, and also includes 2.0 to
10.0% in total of one or more of V, Cr, Fe, Mo, Ni, Nb, and Ta, in which an area ratio
of a primary α-phase is within a certain range, a direction of a major axis of each
of 80% or more of primary α grains in the primary α-phase is positioned within a specified
angle range, and an average minor axis of α grains in a secondary α-phase is 0.1 pm
or more.
[0004] As the α-β titanium alloy with enhanced forgeability, Patent Document 2 mentions
an α-β titanium alloy for casting that has higher strength and more excellent castability
than a Ti-6Al-4V alloy. Specifically, this α-β titanium alloy mentioned includes specified
contents of Al, Fe + Cr + Ni, and C + N + O, and further a specified content of V
if needed, with the balance being Ti and inevitable impurities.
[0005] However, the α-β titanium alloy has extremely high manufacturing cost, and in addition,
especially bad machinability, which interferes with the expansion of the applications
of the α-β titanium alloy. The usage range is limited in practice. In view of such
circumstances, various titanium alloys with improved machinability have been recently
proposed.
[0006] For example, Patent Document 3 mentions a titanium alloy for a connecting rod that
has improved the machinability while suppressing the reduction in toughness and ductility
by containing rare earth elements (REM) and Ca, S, Se, Te, Pb, and Bi as appropriate
to form granular compounds. Patent Document 4 mentioned a free-cutting titanium alloy
that has improved the machinability by containing a rare earth element and improved
the hot workability by containing B.
[0007] Patent Document 5 mentions a free-cutting titanium alloy that achieves the reduction
in ductility of a matrix and the refinement of inclusions to improve the free cutting
properties, while suppressing the reduction in the fatigue strength and ensuring hot
workability, by adding P and S, P and Ni, or P, S and Ni, or further REM in addition
to these elements as free-cutting component.
[0008] Further, Patent Document 6 mentions an α-β titanium alloy with excellent machinability
and hot working. The α-β titanium alloy includes specified contents of C and Al and
2.0 to 10% in total of one or more elements selected from the group of β-stabilizing
elements consisting of respective specified contents of V, Cr, Fe, Mo, Ni, Nb, and
Ta, with the balance being Ti and impurities. In the titanium alloy, an average area
ratio of TiC precipitates in a microstructure is 1% or less, and an average value
of the average circle equivalent diameter of the TiC precipitates is 5 µm or less.
Prior Art Document
Patent Document
Disclosure of the Invention
Problems to be Solved by the Invention
[0010] In the methods like Patent Documents 3 and 4 mentioned above, metallic inclusions
are precipitated by using REM. In the method like Patent Document 5 mentioned above,
P is positively contained to form a P inclusion. In the method like Patent Document
6, the size of a TiC precipitate is controlled. However, in these methods, it is considered
that precipitation of these precipitates and inclusions are more likely to be affected
by the temperatures and cooling rates of melting to forging steps, thus making it
difficult to control the size of the precipitate or the like. Furthermore, the shape
or size of a raw material tends to cause variations in the size or the like of the
precipitate or inclusion. Thus, to achieve the excellent machinability by precipitating
inclusions of interest, there is a problem that strict control of a manufacturing
process is necessary.
[0011] The present invention has been made in view of the foregoing circumstance, and it
is an object of the present invention to achieve an α-β titanium alloy that has high
strength and excellent hot workability of the level of the α-β titanium alloy, typified
by the Ti-6Al-4V, while exhibiting more excellent machinability than the Ti-6Al-4V,
without the necessity for the strict control or the like of the manufacturing process.
Means for Solving the Problems
[0012] An α-β titanium alloy according to the present invention, which can solve the above-mentioned
problem, is defined in claim 1.
Effects of the Invention
[0013] Accordingly, the present invention can provide the α-β titanium alloy that has high
strength and excellent hot workability, such as forgeability, of the level of an α-β
titanium alloy, typified by the Ti-6Al-4V, and also exhibits more excellent machinability
than the Ti-6Al-4V, making it possible to ensure satisfactory lifetime of working
tools.
Brief Description of the Drawings
[0014] Fig. 1 is a photomicrograph of a titanium alloy according to the present invention.
Mode for Carrying Out the Invention
[0015] The inventors have intensively studied to solve the foregoing problems. As a result,
it has been found that especially, a specified content of at least one of Cu and Ni
is contained in a titanium alloy, thereby significantly improving the ductility of
the titanium alloy at high temperatures. In particular, thin chips are formed on the
titanium alloy during a cutting process due to the reduction in deformation resistance,
leading to a reduced cutting resistance, i.e., improving the machinability thereof.
The composition of the α-β titanium alloy according to the present invention will
be described in sequence below, starting from Cu and Ni, which are the features of
the present invention.
Cu: 0.1-2.0%.
[0016] Cu is solid-soluted into the α-phase and the β-phase in the alloy, thereby increasing
its ductility at a high temperature and improving the hot workability. Thus, especially,
the cutting resistance of the titanium alloy becomes lower, and the machinability
thereof is improved. If the content of Cu is less than 0.1%, the effect of improving
the ductility is lessened. Thus, the content of Cu is set at 0.1% or more. The content
of Cu is preferably 0.3% or more, and more preferably 0.5% or more. In contrast, if
the content of Cu exceeds 2.0% by mass, the hardness of the titanium alloy is increased,
thereby making it more likely to reduce the machinability and the hot workability,
such as forgeability. Thus, the content of Cu is set at 2.0% or less. The content
of Cu is preferably 1.5% or less, and more preferably 1.0% or less.
Al: 2.0 to 8.5%
[0017] Al is an α-stabilizing element and thus is contained in the titanium alloy to form
the α-phase. If the Al content is less than 2.0%, the formation of the α-phase is
lessened, failing to obtain sufficient strength. Thus, the Al content is set at 2.0%
or more. The Al content is preferably 2.2% or more, and more preferably 3.0% or more.
Meanwhile, if the Al content exceeds 8.5% to become excessive, the ductility of the
titanium alloy is degraded. Thus, the Al content is set at 8.5% or less. The Al content
is preferably 8.0% or less, more preferably 7.0% or less, and still more preferably
6.0% or less.
C: 0.08 to 0.25%
[0018] C is an element that exhibits the effect of improving the strength of the titanium
alloy. To exhibit such an effect, the C content needs to be 0.08% or more. The C content
is preferably 0.10% or more. Meanwhile, if the C content exceeds 0.25%, coarse TiC
particles not solid-soluted in the α-phase will remain, thus degrading the mechanical
properties of the titanium alloy. Therefore, the C content is set at 0.25% or less.
The C content is preferably 0.20% or less.
1.0 to 7.0% in total of at least one element of Cr: 0 to 4.5% and Fe: 0 to 2.5%
[0019] These elements are β-stabilizing elements. These elements may be used alone or in
combination. To exhibit the above-mentioned effects, the total content of these elements
needs to be 2.0% or more. The total content of these elements is preferably 3.0% or
more. The lower limit of the total content of these elements only needs to be 2.0%
or more as mentioned above, and the lower limit of the content of each of these elements
is not limited specifically. Regarding the lower limit of the content of the individual
element, for example, when Cr is contained in the titanium alloy, the lower limit
of Cr content can be set at 0.5% or more, and further 1.0% or more. When Fe is contained
in the titanium alloy, the lower limit of Fe content can be set at 0.5% or more, and
further 1.0% or more.
[0020] In contrast, when the total content of these elements is excessive, the ductility
of the titanium alloy is degraded. Thus, the total content of these elements is set
at 7.0% or less. The total content of these elements is preferably 5.0% or less, and
more preferably 4.0% or less. Even when the total content of these elements is within
the above-mentioned total content range, if the Fe content is excessive, the degradation
in the ductility becomes significant. Thus, the Fe content should be restrained to
2.5% or less. The Fe content is preferably 2.0% or less. Meanwhile, if the Cr content
is excessive, the machinability of the titanium alloy is degraded. Thus, the Cr content
is set at 4.5% or less. The Cr content is preferably 4.0% or less, and more preferably
3.0% or less.
[0021] The α-β titanium alloy according to the present invention contains the above-mentioned
components, with the balance being Ti and inevitable impurities. The inevitable impurities
may include P, N, S, O, and the like. In the α-β titanium alloy according to the present
invention, the P content is restrained to 0.005% or less; the N content is restrained
to 0.05% or less; the S content is restrained to 0.05% or less; and the 0 content
is restrained to 0.25% or less. The α-β titanium alloy according to the present invention
may further contain the following elements.
[0022] More than 0% and 10% or less in total of one or more elements selected from the group
consisting of V: more than 0% and 5.0% or less, Mo: more than 0% and 5.0% or less,
Nb: more than 0% and 5.0% or less, and Ta: more than 0% and 5.0% or less
[0023] These elements are β-stabilizing elements. These elements may be used alone or in
combination. To form a β-phase, the total content of these elements is preferably
2.0% or more and more preferably 3.0% or more. As long as the total content of these
elements is more than 0%, the lower limit of the content of the individual element
is not limited specifically. Regarding the lower limit of the content of the individual
element, for example, when V is contained in the titanium alloy, the lower limit of
V content can be set at 0.5% or more, and further 2.0% or more. When Mo is contained
in the titanium alloy, the lower limit of Mo content can be set at 0.1% or more, and
further 1.0% or more. When Nb is contained in the titanium alloy, the lower limit
of Nb content can be set at 0.1% or more, and further 1.0% or more. When Ta is contained
in the titanium alloy, the lower limit of Ta content can be set at 0.1% or more, and
further 1.0% or more.
[0024] In contrast, if the total content of these elements is excessive, the ductility of
the titanium alloy is degraded. Thus, the total content of these elements is 10% or
less and preferably 5.0% or less. Even when the total content of these elements is
within the above-mentioned range, if the content of at least one element of them is
excessive, the ductility of the titanium alloy is degraded. Thus, the upper limit
of the content of any of these elements is preferably 5.0% or less. The content of
any of these elements is more preferably 4.0% or less.
Si: more than 0% and 0.8% or less
[0025] Si acts to precipitate Ti
5Si
3 in the titanium alloy. During cutting, stress is concentrated on the Ti
5Si
3, causing voids from Ti
5Si
3 as a starting point, which makes it easy to separate chips. Consequently, the cutting
resistance is supposed to be reduced. To efficiently exhibit this effect, the Si content
is preferably 0.1% or more, and more preferably 0.3% or more.
[0026] Meanwhile, if the Si content is excessive, the strength of the titanium alloy becomes
extremely high, whereby a working tool might be worn significantly or broken, which
makes it difficult to cut the titanium alloy. Accordingly, the Si content is set at
0.8% or less. The Si content is more preferably 0.7% or less, and still more preferably
0.6% or less.
[0027] The titanium alloy according to the present invention has the microstructure at room
temperature that is composed of the α-phase and the β-phase, or the α-phase, the β-phase,
and a third-phase, such as Ti
2Cu or Ti
2Ni. When Si is contained in the titanium alloy, Ti
5Si
3 is precipitated in the titanium alloy as mentioned above.
[0028] A manufacturing method for the α-β titanium alloy is not limited specifically. However,
the α-β titanium alloy can be manufactured, for example, by the following method.
That is, the α-β titanium alloy is manufactured by smelting titanium alloy material
with the above-mentioned components, casting to produce an ingot, and then performing
hot working, i.e., hot forging or hot-rolling on the ingot, followed by annealing
as needed. The above-mentioned hot working involves: heating the ingot in a temperature
range of a β-transformation temperature T
β to approximately (T
β + 250)°C, followed by rough forging or rough rolling at a processing ratio of approximately
1.2 to 4.0, which is represented by "original cross-sectional area/cross-sectional
area after the hot working"; and then performing finish processing at a processing
ratio of 1.7 or more in a temperature range of approximately (T
β - 50) to 800°C. After the above-mentioned finish processing, annealing may be performed
at a temperature of 700 to 800°C as needed. The annealing is performed, for example,
for two to 24 hours. Then, an aging treatment may be performed as needed.
[0030] When each element is represented as an element i in the formula (2), Boave is an
average value of a bond order Bo of the element i, Xi is an atomic ratio of the element
i, and (Bo)i is a value of the bond order Bo of the element i.
[0031] When each element is represented as an element i in the formula (3), Mdave is an
average value of a d-orbital energy parameter Md of the element i, Xi is an atomic
ratio of the element i, and (Md) i is a value of the d-orbital energy parameter Md
of the element i.
[0032] The bond order Bo and the d-orbital energy parameter Md of each element are mentioned
in Table 1 at p.616 of the above-mentioned reference. Xi is determined from the composition.
From these data, Boave and Mdave of each element including Ti are determined and substituted
into the above-mentioned formula (1), thereby making it possible to calculate a T
β. Note that this reference does not have data on Bo and Md of C. However, since the
C content in the present invention is small, C is neglected to calculate the T
β.
Examples
[0033] The present invention will be more specifically described below by way of Examples,
but is not limited to the following Examples. It is obvious that various modifications
can be made to these examples as long as they are adaptable to the above-mentioned
and below-mentioned concepts and are included within the scope of the present invention
as defined by claim 1.
[First Example]
[0034] Test materials were fabricated in the following way. The titanium alloy with each
composition shown in Table 1 below was processed by button arc melting to manufacture
an ingot with a size of about 40 mm in diameter × 20 mm in height. In any example,
the P content was restrained to 0.005% or less; the N content was restrained to 0.05%
or less; the S content was restrained to 0.05% or less; and the O content was restrained
to 0.25% or less. In Table 1, the mark "-" means that the corresponding element was
not contained. The ingot was heated to 1,200°C and subjected to the rough forging
at a processing ratio of 2.4, represented by the "original cross-sectional area/cross-sectional
area after the hot working", followed by forging at a processing ratio of 4.4 at 870
°C to perform finish processing. Thereafter, annealing was performed on the forged
material by holding it at 750°C for 12 hours, thereby producing a test material. Note
that as shown in Comparative Example 7 of Table 1 below, a test material in which
a crack occurred by the rough forging was not subjected to the finish forging.
Evaluation on Forgeability
[0035] In this example, the hot workability was evaluated by the hot forgeability. In detail,
the presence or absence of a crack in each of forging steps, namely, the rough forging
and the finish forging mentioned above, was evaluated. That is, the surface of the
above-mentioned test material after each forging step was visually observed. The test
materials having any crack were rated as NG, while the test materials having no cracks
were rated as OK. Then, the test materials rated as OK in terms of both the rough
forging and the finish forging were evaluated to have excellent forgeability.
Evaluation on Machinability
[0036] The test materials having good forgeability were evaluated for the machinability
as follows. That is, a test specimen with the size below was taken out of the above-mentioned
test material, and a cutting test was performed on the test specimen on the cutting
conditions below. The machinability was evaluated as an average cutting resistance
by measuring a cutting resistance in the cutting direction with a Kessler's cutting
dynamometer, Model: 9257 B, from the start to the end of cutting and then determining
an average value of the cutting resistance from the start to the end of the cutting.
When performing the cutting test on Ti-6Al-4V as a general α-β titanium alloy on the
same conditions, an average cutting resistance was 180 N. Because of this, in the
first example, the test materials having an average cutting resistance of lower than
180 N were evaluated to be superior in the machinability, while the test materials
having an average cutting resistance of 180 N or higher were evaluated to be inferior
in the machinability.
Cutting Conditions
[0037] Test Specimen: 10 mm in height × 10 mm in width × 150 mm in length
Tool: Carbide tip S30T (nose 0.4 mm) manufactured by Sandvik Corporation
[0038] End mill R390 manufactured by Sandvik Corporation (20 mm in diameter, one blade)
Cutting speed Vc: 100 m/min
Cutting amount in the axial direction: 1.2 mm
Cutting amount in the radial direction: 1 mm
Feeding speed: 0.08 mm/blade
Cutting length: 150 mm
Cutting oil: None
Measurement of Tensile Strength
[0039] The tensile strength of the α-β titanium alloy according to the present invention
was also measured for reference. In detail, the titanium alloys of Examples 1 and
3, and Comparative Example 1 were used and subjected to the tensile test on the following
conditions of the shape and testing speed of the test specimen. As a result, the test
materials had a strength of 948 MPa in Example 1, 1, 125 MPa in Example 3, and 948
MPa in Comparative Example 1, all of these strengths being relatively high. Specifically,
the strengths of these test materials exhibited higher strength than the strength
of 896 MPa of an annealed material of Ti-6Al-4V as a general α-β titanium alloy.
Shape of Test Specimen: ASTM E8/E8M Fig. 8 Specimen 3
Test Speed: 4.5 mm/min
[0040] The evaluation result of the above-mentioned forgeability and an average cutting
resistance are also shown in Table 1.
[Table 1]
|
Composition (% by mass) Balance being Ti and inevitable impurities |
Tβ |
Forgeability |
Average cutting resistance |
Cu |
Ni |
Si |
Al |
C |
Cr |
Fe |
(°C) |
Rough forging |
Finish forging |
(N) |
Example 1 |
0.5 |
0.5 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
976 |
OK |
OK |
148 |
Example 2 |
1.0 |
1.0 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
974 |
OK |
OK |
170 |
Example 3 |
2.0 |
2.0 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
969 |
OK |
OK |
167 |
Example 4 |
- |
0.5 |
- |
4.5 |
0.10 |
- |
1.2 |
1,010 |
OK |
OK |
129 |
Example 5 |
0.5 |
0.5 |
- |
4.5 |
0.10 |
- |
1.2 |
1,011 |
OK |
OK |
148 |
Example 6 |
- |
1.0 |
- |
4.5 |
0.10 |
- |
1.2 |
1,006 |
OK |
OK |
140 |
Example 7 |
1.0 |
1.0 |
- |
4.5 |
0.10 |
- |
1.2 |
1,009 |
OK |
OK |
146 |
Example 8 |
2.0 |
2.0 |
- |
4.5 |
0.10 |
- |
1.2 |
1,004 |
OK |
OK |
155 |
Comparative Example 1 |
- |
- |
- |
4.5 |
0.10 |
2.5 |
1.2 |
979 |
OK |
OK |
199 |
Comparative Example 2 |
- |
3.0 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
957 |
OK |
OK |
229 |
Comparative Example 3 |
3.0 |
3.0 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
965 |
OK |
OK |
241 |
Comparative Example 4 |
4.0 |
- |
- |
4.5 |
0.10 |
2.5 |
1.2 |
989 |
OK |
NG |
- |
Comparative Example 5 |
6.0 |
- |
- |
4.5 |
0.10 |
2.5 |
1.2 |
994 |
OK |
OK |
234 |
Comparative Example 6 |
4.0 |
4.0 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
960 |
OK |
OK |
261 |
Comparative Example 7 |
6.0 |
6.0 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
950 |
NG |
- |
- |
[0041] Table 1 shows the following. Examples 1-8, none of which fall within the scope of
protection as defined in claim 1, were found to enable good forging and to have excellent
forgeability. Furthermore, these examples were found to have a lower average cutting
resistance than that of Ti-6Al-4V as a general α-β titanium alloy and also to have
good machinability.
[0042] In contrast, all Comparative Examples 1 to 7 did not satisfy the composition specified
by the present invention and thereby were consequently inferior in forgeability or
machinability. In detail, in Comparative Example 1, neither Cu nor Ni was contained,
resulting in a high average cutting resistance. Comparative Example 1 had the same
composition as that mentioned in Patent Document 6. The comparison of the above-mentioned
Examples 1 to 3 with Comparative Example 1 in which the constituent elements, other
than Cu and Ni, and their contents are the same as those in Examples 1 to 3 shows
that in order to surely obtain good machinability by sufficiently decreasing the average
cutting resistance, it is necessary to contain a specified content of at least one
of Cu and Ni, as mentioned in the present invention.
[0043] In Comparative Example 2, which contained Ni, the Ni content was excessive. In Comparative
Example 5, which contained Cu, the Cu content was excessive. In both examples, the
average cutting resistance was higher than 180 N, resulting in bad machinability.
In Comparative Examples 3 and 6, the respective contents of Cu and Ni were excessive.
In both comparative examples, the average cutting resistance was higher than 180 N,
resulting in bad machinability.
[0044] In Comparative Example 4, since the Cu content was excessive, the forgeabililty was
degraded. In Comparative Example 7, since the respective contents of Cu and Ni were
drastically excessive, cracking occurred at the stage of the rough forging, resulting
in degradation in the forgeability.
[Second Example]
[0045] In the second example, the influence of the Si content, especially, on the machinability
were studied. As shown in Table 2, various ingots with different Si contents were
manufactured to produce test materials in the same way as that in the first example.
In any example, the P content was restrained to 0.005% or less; the N content was
restrained to 0.05% or less; the S content was restrained to 0.05% or less; and the
O content was restrained to 0.25% or less. In Table 2, the mark "-" means that the
corresponding element was not contained.
[0046] Each of the above-mentioned test materials was used to confirm the presence or absence
of a precipitation phase, as mentioned below, and the Vickers hardness of the test
material was measured as an index of strength in the second example. Furthermore,
the forgeability of the test material was evaluated in the same way as that in the
first example, and the machinability thereof was evaluated as mentioned below. For
reference, the tensile strength of test material No. 3 in Table 2 was measured in
the same way as that in the first example. This test material No. 3 had a tensile
strength of 968 MPa, which was higher than a strength, i.e., 896 MPa of an annealed
material of Ti-6Al-4V as the general α-β titanium alloy.
Evaluation on Presence or Absence of Precipitation Phase
[0047] The cross section of the test material was polished to a mirror-smooth state, followed
by acid treatment using hydrofluoric acid to an extent that crystal grain boundaries
could be seen, and then visually observed at ten field of views, each field of view
having a size of 40 pm × 40 µm, with a field emission-scanning electron microscope
(FE-SEM) at a magnification of 4,000 times. The test materials in which the precipitation
phase with a circle equivalent diameter of 2 µm or more was recognized at five or
more of the above-mentioned ten field of views in total were evaluated to be in the
"presence" of the precipitation phase. The test materials in which the precipitation
phase was recognized at four or less of the above-mentioned ten field of views in
total were evaluated to be in the "absence" of the precipitation phase. Note that
the above-mentioned precipitation phase was separately recognized as Ti
5Si
3 by an X-ray diffraction (XRD).
[0048] Fig. 1 shows one example of a photomicrograph observed with the above-mentioned microscope.
Fig. 1 is one obtained by measurement of the test material No. 3 shown in Table 2,
with an arrow indicating one precipitation phase.
Measurement of Vickers Hardness HV
[0049] A Vickers hardness HV was measured at five sites of each test material on the condition
of a load 10 kgf, and the measured values were averaged. In this way, an average value
of the Vickers hardness was determined.
Evaluation on Machinability
[0050] The test materials evaluated to have good forgeability in the same way as that in
the first example, that is, all examples shown in Table 2 were evaluated for the machinability
as follows. That is, a test specimen with the size mentioned below was taken out of
the above-mentioned test material, and a cutting test was performed on the test specimen
on the cutting conditions below. The machinability was evaluated as an average cutting
resistance by measuring a cutting resistance in the cutting direction by the Kessler's
cutting dynamometer, Model: 9257 B, from the start to the end of cutting and then
determining an average value of the cutting resistance from the start to the end of
the cutting. When performing the cutting test on Ti-6Al-4V as the general α-β titanium
alloy on the same conditions, an average cutting resistance was 122 N. Because of
this, in the second example, the test materials having an average cutting resistance
of lower than 122 N were evaluated to be superior in the machinability, while the
test materials having an average cutting resistance of 122 N or higher were evaluated
to be inferior in the machinability.
Cutting Conditions
[0051] Test Specimen: 10 mm in height × 10 mm in width × 60 mm in length
Tool: Carbide tip S30T (nose 0.4 mm) manufactured by Sandvik Corporation
[0052] End mill R390 manufactured by Sandvik Corporation (20 mm in diameter, one blade)
Cutting speed Vc: 100 m/min
Cutting amount in the axial direction: 1.2 mm
Cutting amount in the radial direction: 1 mm
Feeding speed: 0.08 mm/blade
Cutting length: 15 mm
Cutting oil: None
[0053] These results are also shown in Table 2.
[Table 2]
No. |
Composition (% by mass) Balance being Ti and inevitable impurities |
Tβ |
Precipitation phase |
HV |
Forgeability |
Average cutting resistance |
|
Cu |
Ni |
Si |
Al |
C |
Cr |
Fe |
(°C) |
|
|
Rough forging |
Finish forging |
(N) |
1 |
0.5 |
0.5 |
- |
4.5 |
0.10 |
2.5 |
1.2 |
976 |
Absent |
298 |
OK |
OK |
111 |
2 |
0.5 |
0.5 |
0.1 |
4.5 |
0.10 |
2.5 |
1.2 |
993 |
Present |
316 |
OK |
OK |
99 |
3 |
0.5 |
0.5 |
0.3 |
4.5 |
0.10 |
2.5 |
1.2 |
1,027 |
Present |
320 |
OK |
OK |
105 |
4 |
0.5 |
0.5 |
0.8 |
4.5 |
0.10 |
2.5 |
1.2 |
1,110 |
Present |
335 |
OK |
OK |
112 |
5 |
0.3 |
0.3 |
0.3 |
4.5 |
0.10 |
2.5 |
1.2 |
1,028 |
Present |
316 |
OK |
OK |
106 |
6 |
2.0 |
2.0 |
0.5 |
4.5 |
0.10 |
2.5 |
1.2 |
1,054 |
Present |
365 |
OK |
OK |
120 |
7 |
2.0 |
2.0 |
1.0 |
4.5 |
0.10 |
2.5 |
1.2 |
1,137 |
Present |
380 |
OK |
OK |
134 |
8 |
2.0 |
2.0 |
2.0 |
4.5 |
0.10 |
2.5 |
1.2 |
1,303 |
Present |
397 |
OK |
OK |
Measurement was impossible due to damage to a working tool |
[0054] None of the example alloys 1-7 in table 2 fall within the scope of protection as
defined by claim 1. Table 2 shows the following. That is, as clearly shown, the test
material No. 1 having the same composition as that in Example 1 of Table 1 were compared
with test materials No. 2 to 6, particularly, test materials No. 2 to 4 in which the
contents of elements other than Si were the same as those in Example 1 of Table 1.
Based on the comparison, the arrangement that contains Si in the titanium alloy made
it possible to further reduce the average cutting resistance and to ensure the sufficiently
high machinability, compared to a case in which Si was not contained. In contrast,
when the Si content was excessive, like the test materials No. 7 and No. 8, the hardness
of the titanium alloy becomes extremely high, increasing the average cutting resistance
and also causing inconveniences, such as a damage of a working tool.