TECHNICAL FIELD
[0001] The present invention relates to titanium copper, a method for producing titanium
copper, and an electronic component. For example, the present invention relates to
titanium copper, a method for producing the titanium copper and an electronic component
using the titanium copper, which are suitable for use in electronic components such
as connectors, battery terminals, jacks, relays, switches, autofocus camera modules,
and lead frames.
BACKGROUND ART
[0002] Recently, progressing miniaturization of electronic components such as lead frames
and connectors used in electric/electronic devices and on-board components is bringing
about remarkable tendencies to narrow a pitch and reduce a height of a copper alloy
member forming an electronic component. A smaller connector has a narrower pin width,
resulting in a smaller folded shape, so that the copper alloy member to be used is
required to have high strength in order to obtain required spring properties. In this
respect, a copper alloy containing titanium (hereinafter referred to as "titanium
copper") has a relatively high strength and the best stress relaxation resistance
among copper alloys. Therefore, the titanium copper has been traditionally used as
a signal system terminal member.
[0003] The titanium copper is an age-hardening copper alloy, which has a good balance between
strength and bending workability, and additionally exhibits particularly improved
characteristics among various copper alloys in terms of stress relaxation resistance.
Therefore, developments have been made to improve properties such as strength and
bending workability while maintaining the stress relaxation resistance of the titanium
copper.
[0004] Japanese Patent Application Publication No.
2014-185370 A (Patent Document 1) describes a Cu-Ti-based copper alloy sheet having improved bending
workability while maintaining high strength and having improved fatigue resistance
while maintaining good stress relaxation resistance, wherein the copper alloy has
a composition of 2.0 to 5.0% by mass of Ti, 0 to 1.5% by mass of Ni, 0 to 1.0% by
mass of Co, 0 to 0.5% by mass of Fe, 0 to 1.2% by mass of Sn, 0 to 2.0% by mass of
Zn, 0 to 1.0% by mass of Mg, 0 to 1.0% by mass of Zr, 0 to 1.0% by mass of Al, 0 to
1.0% by mass of Si, 0 to 0.1% by mass of P, 0 to 0.05% by mass of B, 0 to 1.0% by
mass of Cr, 0 to 1.0% by mass of Mn, and 0 to 1.0% by mass of V, the total content
of Sn, Zn, Mg, Zr, Al, Si, P, B, Cr, Mn and V among these elements being 3.0% or less,
the balance being Cu and inevitable impurities, wherein the copper alloy sheet has
a metal structure in which a maximum width of grain boundary reaction type precipitates
is 500 nm or less and a density of granular precipitates having a diameter of 100
nm or more is 10
5/mm
2 or less in a cross section perpendicular to a thickness direction.
[0005] Japanese Patent Application Publication No.
2010-126777 A (Patent Document 2) describes a copper alloy sheet having improved bending workability
while maintaining high strength, wherein the copper alloy sheet has a composition
of 1.2 to 5.0% by mass of Ti, the balance being Cu and inevitable impurities, wherein
an average crystal grain size is from 5 to 25 µm, and a ratio (maximum crystal grain
size - minimum crystal grain size) / average crystal grain size is 0.20 or less, in
which the maximum crystal grain size is a maximum value of average values of the crystal
grain sizes in the respective regions of a plurality of regions having the same shape
and sizes, which are randomly selected on the sheet surface, the minimum crystal grain
size is a minimum value among average values of crystal grain sizes in the respective
regions, and the average crystal grain size is an average value of the average values
of the crystal grains in the respective regions, and wherein the copper alloy sheet
has a crystal orientation satisfying I{420} / I
0{420} > 1.0, in which the I{420} is an X-ray diffraction intensity of a {420} crystal
plane on a sheet surface of the copper alloy sheet, and the I
0{420} is an X-ray diffraction intensity of a {420} crystal plane of pure copper standard
powder.
[0006] Japanese Patent Application Publication No.
2008-308734 A (Patent Document 3) describes a copper alloy sheet material having improved bending
workability and improved stress relaxation resistance, as well as improved spring
back, wherein the copper alloy sheet has a composition of 1.0 to 5.0% by mass of Ti,
the balance being Cu and inevitable impurities, and wherein the copper alloy sheet
has a crystal orientation satisfying I{420} / I
0{420} > 1.0, and has an average crystal grain size of 10 to 60 µm.
[0007] Japanese Patent Application Publication No.
H07-258803 A (Patent Document 4) describes a method for producing a high-strength copper alloy
having improved strength and improved bending workability by adjusting production
steps from a solutionizing treatment to a cold rolling step, wherein the method comprises
subjecting to a copper alloy containing 0.01 to 4.0% of Ti, the balance being Cu and
inevitable impurities (1) a first solutionizing treatment carried out under heat treatment
conditions of a temperature of 800 °C or higher within 240 seconds and an average
crystal grain size of not more than 20 µm; (2) a first cold rolling carried out at
a working ratio of less than 80%; (3) a second solutionizing treatment carried out
under heat treatment conditions of a temperature of 800 °C or higher within 240 seconds
and an average grain size of from 1 to 20 µm or less; (4) a second cold rolling carried
out at a working ratio of 50% or less; and (5) an aging treatment at a temperature
of from 300 to 700 °C for 1 hour to less than 15 hours in this order.
CITATION LIST
Patent Literatures
[0008]
Patent Document 1: Japanese Patent Application Publication No. 2014-185370 A
Patent Document 2: Japanese Patent Application Publication No. 2010-126777 A
Patent Document 3: Japanese Patent Application Publication No. 2008-308734 A
Patent Document 4: Japanese Patent Application Publication No. H07-258803 A
SUMMARY OF INVENTION
Technical Problem
[0009] Recently, electronic devices are required to have higher reliability in addition
to higher functionality, and electronic components used for the electronic devices
are also required to have higher reliability. In particular, heat resistance is one
of important indices, which requires a higher level than the prior art. Titanium copper
is known to have relatively better stress relaxation resistance. However, the titanium
copper alloys disclosed in Patent Documents 1 to 4 still cannot provide sufficient
stress relaxation resistance, and so there is a need for further improvement of stress
relaxation resistance.
[0010] In view of the above problems, the present disclosure provides titanium copper having
improved stress relaxation resistance, a method for producing the titanium copper,
and an electronic component using the titanium copper.
Solution to Problem
[0011] As a result of intensive studies to solve the above problems, the present inventor
has found that a titanium copper having a certain relationship among pole densities
of <111>, <101> and <001> in an inverse pole figure in a rolling direction (RD) has
improved stress relaxation resistance.
[0012] In one aspect, a titanium copper according to an embodiment of the present invention
contains from 2.0 to 4.5% by mass of Ti, and a total amount of from 0 to 0.5% by mass
of at least one selected from the group consisting of Fe, Co, Ni, Cr, Zn, Zr, P, B,
Mo, V, Nb, Mn, Mg, and Si as a third element, the balance being copper and inevitable
impurities, wherein a pole density of <111> is from 2.5 to 4.5, and a pole density
of <001> is higher than that of <101>, in an inverse pole figure in a rolling direction.
[0013] In one aspect, a method for producing titanium copper according to an embodiment
of the present invention comprises casting a titanium copper ingot containing from
2.0 to 4.5% by mass of Ti, and a total amount of from 0 to 0.5% by mass of at least
one selected from the group consisting of Fe, Co, Ni, Cr, Zn, Zr, P, B, Mo, V, Nb,
Mn, Mg, and Si as a third element, the balance being copper and inevitable impurities,
and subjecting the cast ingot to hot rolling; and then carrying out a cold rolling
step and a subsequent final solutionizing treatment step, wherein the hot rolling
step comprises treating the ingot such that a compressive strain per pass is from
0.05 to 0.15 and a strain rate of a final pass is from 15.0 to 25.0, and wherein the
final solutionizing treatment step comprises carrying out a treatment at a heating
temperature (°C) of from 52 × X + 610 to 52 × X + 680 in which X is an addition amount
(% by mass) of Ti, for a residence time of from 50 to 200 seconds.
Advantageous Effects of Invention
[0014] According to the present invention, it is possible to provide titanium copper having
improved stress relaxation resistance, a method for producing the titanium copper,
and an electronic component using the titanium copper.
BRIEF DESCRIPTION OF DRAWINGS
[0015]
FIG. 1 is a view for explaining a measurement principle of a stress relaxation rate.
FIG. 2 is a view for explaining a measurement principle of a stress relaxation rate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(Ti Concentration)
[0016] Titanium copper according to an embodiment of the present invention has a Ti concentration
of from 2.0 to 4.5% by mass. The titanium copper has increased strength and increased
electrical conductivity by dissolution of Ti in a Cu matrix with a solutionizing treatment
and by dispersion of fine precipitates in the alloy with an aging treatment.
[0017] If the Ti concentration is less than 2.0% by mass, deposition of precipitates is
not sufficient and any desired strength cannot be obtained. If the Ti concentration
is more than 4.5% by mass, workability is deteriorated and the material is easily
cracked during rolling. In terms of a balance between strength and workability, a
preferable Ti concentration is from 2.5 to 3.5% by mass.
(Third Element)
[0018] The titanium copper according to an embodiment of the present invention contains
at least one of third elements selected from the group consisting of Fe, Co, Ni, Cr,
Zn, Zr, P, B, Mo, V, Nb, Mn, Mg, and Si, whereby the strength can be further improved.
However, if the total concentration of the third elements is more than 0.5% by mass,
the workability is deteriorated and the material is easily cracked during rolling.
Therefore, these third elements can be contained in a total amount of from 0 to 0.5%
by mass, and in view of the balance between strength and workability, the titanium
copper preferably contains one or more of the above elements in a total amount of
from 0.1 to 0.4% by mass. For each additive element, the titanium copper contains
from 0.01 to 0.15% by mass of each of Zr, P, B, V, Mg, and Si, and from 0.01 to 0.
3% by mass of each of Fe, Co, Ni, Cr, Mo, Nb and Mn, and from 0.1 to 0.5% by mass
of Zn.
(Inverse Pole Figure in RD Direction)
[0019] The titanium copper according to an embodiment of the present invention is characterized
that a pole density of <111> is controlled within a certain range in an inverse pole
figure in a RD direction, and a relationship between pole densities of <101> and <001>
is constant. More particularly, the pole density of <111> is from 2.5 to 4.5, and
the pole density of <001> is higher than the pole density of <101>. If both of these
conditions are satisfied, the stress relaxation resistance can be further improved.
[0020] Although the relationship between the inverse pole figure in the RD direction and
the stress relaxation resistance is not clearly understood, the pole density of <111>
lower than 2.5 or higher than 4.5 cannot improve the stress relaxation resistance.
Similarly, the pole density of <001> lower than that of <101> cannot improve the stress
relaxation resistance. Further, even if the pole density of <111> is from 2.5 to 4.5,
the pole density of <001> lower than that of <101> cannot improve the stress relaxation
resistance, or even if the pole density of <001> is higher than that of <101>, the
pole density of <111> lower than 2.5 or higher than 4.5 cannot improve the stress
relaxation resistance.
[0021] Although not limited to the following, the pole density of <111> is preferably from
2.7 to 4.3, and more preferably from 2.9 to 4.1. The pole density of <101> is typically
from 0 to 2.5, and the pole density of <001> is typically from 0.5 to 3.5.
[0022] As used herein, the "inverse pole figure in RD direction" refers to a measurement
result of the inverse pole figure in the RD direction in crystal orientation analysis
in EBSD (Electron Back Scatter Diffraction) measurement on a rolled surface using
an analysis software (for example, OIM Analysis available from TSL Solutions, Inc.)
attached to the EBSD. The Inverse pole figures can be obtained for the ND direction,
the RD direction, and the TD direction. However, in this embodiment, the inverse pole
figure in the RD direction is used in view of a stress axis applied when evaluating
the stress relaxation resistance. It should be noted that the pole density in a state
where the crystal orientation is random is 1.
[0023] In this embodiment, the following conditions are adopted for EBSD measurement:
- (a) SEM conditions
- Beam Conditions: an acceleration voltage of 15 kV and an irradiation current of 5
× 10-8 A;
- Work Distance: 25mm;
- Observation Field: 150 µm × 150 µm;
- Observation Surface: rolled surface;
- Pre-treatment of Observation Surface: The structure is allowed to appear by electropolishing
in a solution of 67% phosphoric acid + 10% sulfuric acid + water under conditions
of 15V for 60 seconds.
- (b) EBSD conditions
- Measurement Program: OIM Data Collection;
- Data analysis Program: OIM Analysis (Ver. 5.3); and
- Step Width: 0.25 µm.
(Stress Relaxation Resistance)
[0024] The titanium copper according to an embodiment of the present invention can have
improved stress relaxation resistance. In one Embodiment, it has a feature that a
stress relaxation rate is 10% or less after maintaining the titanium copper at 300
°C for 10 hours.
(Average Crystal Grain Size)
[0025] In one embodiment of the titanium copper according to the present invention, it is
preferable to control an average crystal grain size on the rolled surface to a range
of from 2 to 30 µm, more preferably to a range of from 2 to 15 µm, and even more preferably
a range of from 2 to 10 µm, from the viewpoint of improving the strength, bending
workability and fatigue characteristics with a good balance.
[0026] The average crystal grain size refers to an average crystal grain size in a case
where an orientation difference of 5° or more is regarded as a crystal grain boundary
by a crystal orientation analysis in EBSD (Electron Back Scattering Diffraction) measurement
on the rolled surface using an analysis software (e.g.,, OIM Analysis available from
TSL Solutions) attached to the EBSD, as with the average crystal grain size used for
calculating the coefficient of variation of the crystal grain size as described above.
(0.2% Yield Strength)
[0027] In one embodiment, the titanium copper according to the embodiment of the present
invention can achieve a 0.2% yield strength of 800 MPa or more in a direction parallel
to the rolling direction. The 0.2% yield strength of the titanium copper according
to the present invention is 850 MPa or more in a preferred embodiment, 900 MPa or
more in a more preferred embodiment, and 950 MPa or more in an even more preferred
embodiment.
[0028] The upper limit value of the 0.2% yield strength is not particularly limited from
the viewpoint of the intended strength of the present invention. However, in terms
of labors and costs, the upper limit is typically 1200 MPa or less, and more typically
1100 MPa or less.
[0029] In the present invention, the 0.2% yield strength of titanium copper in the direction
parallel to the rolling direction is measured in accordance with JIS-Z2241 (2011)
(Metal Material Tensile Test Method).
(Thickness of Titanium Copper)
[0030] In one embodiment, the titanium copper according to the present invention can have
a thickness of 1.0 mm or less, and in a typical embodiment, it can have a thickness
of from 0.02 to 0.8 mm, and in a more typical embodiment, it can have a thickness
of from 0.05 to 0.5 mm.
(Use)
[0031] The titanium copper according to the present invention can be processed into various
copper products, such as plates, strips, tubes, bars and wires. The titanium copper
according to the present invention can preferably be used as a conductive material
or a spring material in electronic parts including, but not limited to, switches,
connectors, autofocus camera modules, jacks, terminals (particularly battery terminals),
and relays. These electronic components can be used, for example, as on-board components
or components for electric/electronic devices.
(Production Method)
[0032] Hereinafter, the method for producing the titanium copper according to an embodiment
of the present invention includes casting an titanium copper ingot containing from
2.0 to 4.5% by mass of Ti, a total amount of from 0 to 0.5% by mass of at least one
selected from the group consisting of Fe, Co, Ni, Cr, Zn, Zr, P, B, Mo, V, Nb, Mn,
Mg, and Si as a third element, the balance being copper and inevitable impurities,
and subjecting the cast ingot to hot rolling, and then carrying out a cold rolling
step and a subsequent final solutionizing treatment step. Hereinafter, a suitable
production example of the titanium copper according to this embodiment is sequentially
described for each step.
<Production of Ingot>
[0033] Production of the ingot by melting and casting is basically carried out in a vacuum
or in an inert gas atmosphere. If the additive element remains un-melted during melting,
it does not effectively act on improvement of strength. Therefore, in order to eliminate
un-melted residue, a high melting point third element such as Fe and Cr should be
sufficiently agitated after being added, and then maintained for a certain period
of time. On the other hand, since Ti is relatively easily dissolved in Cu, it may
be added after the third element is melted. Therefore, to Cu is added at least one
selected from the group consisting of Fe, Co, Ni, Cr, Zn, Zr, P, B, Mo, V, Nb, Mn,
Mg, and Si so as to contain them in a total amount of from 0 to 0. 5% by mass and
then added Ti so as to contain it in an amount of from 2.0 to 4.5% by mass to produce
the ingot.
<Homogenized Annealing and Hot Rolling>
[0034] Since solidifying segregation and crystallized matters produced during the production
of the ingot are coarse, it is desirable to dissolving them in the parent phase as
much as possible to decrease them, and eliminate them as much as possible, by homogenized
annealing. This is because it is effective in preventing cracks due to bending. More
particularly, after the ingot production step, homogenized annealing is preferably
carried out by heating at 900 to 970 °C for 3 to 24 hours, and the hot rolling is
then preferably carried out. In order to prevent liquid metal embrittlement, it is
preferable that a temperature before and during the hot rolling is preferably 960
°C or less, and that a temperature is preferably 700 °C or more for a pass from an
original thickness to an entire working ratio of 80%.
[0035] In the present embodiment, a compressive strain per pass is from 0.05 to 0.15, and
a strain rate of a final pass is from 15.0 to 25.0/s, and in a preferred embodiment,
from 18.0 to 22.0/s. This can allow the pole density of <111> and the relationship
between the pole densities of <101> and <001> in the inverse pole figure in the RD
direction to be controlled to the above ranges. The compressive strain per pass can
be calculated by dividing a compressive strain η = In {(cross-sectional area before
hot rolling) / (cross-sectional area after hot rolling)} by the total number of passes
in hot rolling. Further, the strain rate ε (/s) is calculated from the following equation
(1):
[Equation 1]
in which H
0 is a sheet thickness (mm) on an inlet side, n is a rotation speed (rpm) of a rolling
roll, R is a radius (mm) of the rolling roll, and r' is a working ratio ((sheet thickness
on inlet side) - (sheet thickness on outlet side / sheet thickness on inlet side).
<Cold Rolling and Annealing>
[0036] After the hot rolling, cold rolling is carried out. The working ratio of the cold
rolling is typically 60% or more. The working ratio per pass can be obtained according
to the following Equation (2), where T
0 is a thickness of the ingot before rolling by the pass and T is a thickness of the
ingot at the end of rolling by the pass:
Annealing can be then carried out. The annealing is typically carried out at 900
°C for 1 to 5 minutes. The cold rolling and annealing can be repeated as needed.
<First Solutionizing Treatment
[0037] A first solutionizing treatment is preferably carried out after repeating the cold
rolling and annealing as needed. Here, the reason why the solutionizing treatment
is carried out in advance is to reduce burdens in a final solutionizing treatment.
That is, in the final solutionizing treatment, it is not a heat treatment for dissolving
second phase grains and solutionizing is already achieved, so it is sufficient to
cause recrystallization while maintaining that state and thus to be a light heat treatment.
More particularly, the first solutionizing treatment may be carried out at a heating
temperature of from 850 to 900 °C for 2 to 10 minutes. In this case, it is preferable
to increase the heating rate and the cooling rate as much as possible so that the
second phase grains do not precipitate. It should be noted that the first solutionizing
treatment may not be carried out.
<Intermediate Rolling>
[0038] Intermediate rolling is then carried out. The working ratio of the intermediate rolling
is typically 60% or more.
<Final Solutionizing Treatment
[0039] In the final solution treatment, it is desirable to dissolve precipitates completely.
However, if heating is carried out at an elevated temperature until the precipitates
are completely eliminated, the crystal grains tends to coarsen. Therefore, the heating
temperature is near a solid solution limit of the second phase grain composition.
More particularly, the heating temperature (°C) is in a range of from 52 × X + 610
to 52 × X + 680 where X is an addition amount (% by mass) of Ti.
[0040] In a case where the heating temperature is lower than 52 × X + 610 °C, it causes
non-recrystallization, and in a case where the heating temperature is higher than
52 × X + 680, the crystal grain size becomes coarse. In both cases, the strength of
titanium copper finally obtained is decreased.
[0041] The pole density of <111> and the relationship between the pole densities of <101>
and <001> in the inverse pole figure in the RD direction can be controlled by adjusting
a heating time in the final solutionizing treatment. The heating time can be, for
example, from 50 to 200 seconds, and typically from 90 to 180 seconds.
<Final Cold Rolling>
[0042] Final cold rolling is carried out following the final solutionizing treatment. The
final cold rolling can increase the strength. In order to obtain good stress relaxation
resistance, the working ratio is preferably from 5 to 50%, and more preferably from
20 to 40%.
<Aging Treatment>
[0043] An aging treatment is carried out following the final cold rolling. Preferably, it
is carried out by heating at a material temperature of from 300 to 500 °C for 1 to
50 hours, and more preferably heating at a material temperature of from 350 to 450
°C for 10 to 30 hours. The aging treatment is preferably carried out in an inert atmosphere
such as Ar, N
2 and H
2 in order to suppress generation of an oxide film.
[0044] In summary, the method for producing the titanium copper according to the embodiment
of the present invention includes:
a step of casting a titanium copper ingot containing from 2.0 to 4.5% by mass of Ti,
and a total amount of from 0 to 0.5% by mass of at least one selected from the group
consisting of Fe, Co, Ni, Cr, Zn, Zr, P, B, Mo, V, Nb, Mn, Mg, and Si as a third element,
the balance being copper and inevitable impurities;
a hot rolling step of treating the cast ingot such that a compressive strain per pass
is from 0.05 to 0.15 and a strain rate of a final pass is from 15.0 to 25.0/s; and
a final solutionizing treatment of treating the ingot at a heating temperature (°C)
in a range of from 52 × X + 610 to 52 × X + 680 for a retention time of from 20 to
200 seconds, in which X is an addition amount (% by mass) of Ti.
[0045] It will be appreciated by a person skilled in the art that steps such as grinding,
polishing, and shot blast pickling for removing oxide scales on the surface may be
carried out between the above steps.
EXAMPLES
[0046] Hereinafter, while Examples of the present invention are shown below together with
Comparative Examples, these are provided for better understanding of the present invention
and its advantages, and are not intended to limit the invention.
[0047] Each alloy containing the alloy components as shown in Table 1, the balance being
copper and inevitable impurities, was used as an experimental material to investigate
effects of production conditions of the alloy components, hot rolling and final solutionizing
treatment on the pole density of <111> and the relationship between the pole densities
of <101> and <001> in the inverse pole figure in the RD direction, and on the stress
relaxation resistance.
[0048] First, 2.5 kg of electrolytic copper was melted in a vacuum melting furnace, and
each third element was added at each mixing ratio as shown in Table 1, and Ti was
then added at each mixing ratio as shown in Table 1. After sufficient consideration
was given to the retention time after the addition such that there was no un-melted
residue of the added elements, these were injected into a mold in an Ar atmosphere
to produce about 2 kg of each ingot.
[0049] The ingot was subjected to homogenized annealing at 950 °C for 5 hours, followed
by hot rolling at 900 to 950 °C to obtain a hot rolled sheet having a thickness of
10 mm. After descaling by chamfering, cold rolling and annealing were repeated to
obtain a raw strip thickness (1.5 mm), and a first solutionizing treatment was carried
out for the raw strip. The first solutionizing treatment was carried out by heating
at 850 °C for 8 minutes, and then cooling in water. The intermediate cold rolling
was then carried out, followed by the final solution treatment, and followed by cooling
in water. Then, after descaling by pickling, the final cold rolling was carried out
at a working ratio of 25% to obtain a sheet thickness of 0.1 mm, and finally the aging
treatment was carried out under conditions of 400 °C for 20 hours to prepare each
sample for Examples and Comparative Examples.
[0050] The following evaluations were conducted for the produced samples:
(0.2% Yield Strength)
[0051] Each JIS 13B sample was prepared, and the 0.2% yield strength in the direction parallel
to the rolling direction was measured using a tensile tester according to the measurement
method as described above.
(Average Crystal Grain Size)
[0052] After a sheet surface (rolled surface) of each sample was polished and etched, each
sample was measured for an average crystal grain size in the case where an orientation
difference of 5° or more was regarded as a crystal grain boundary, by crystal orientation
analysis in EBSD (Electron Back Scatter Diffraction) measurement (e.g., OSL Analysis
available from TSL Solutions) using an analysis software attached to the EBSD.
(Inverse Pole Figure)
[0053] An inverse pole figure in the RD direction was measured by crystal orientation analysis
in an EBSD (Electron Back Scatter Diffraction) measurement on a rolled surface using
an analysis software attached to the EBSD (for example, OIM Analysis available from
TSL Solutions), and pole densities of <111 >, <101 >, <001> were evaluated. A case
where the pole density of <001> was higher than the pole density of <101> was determined
to be "○", and a case where the pole density of <101> was less than or equal to the
pole density of <001> was determined to be "x".
(Stress Relaxation Resistance)
[0054] The stress relaxation rate after maintaining each sample at 300 °C for 10 hours was
measured. Each strip-shaped sample having a width of 10 mm and a length of 100 mm
was collected such that a longitudinal direction of the sample was parallel to the
rolling direction. As shown in FIG. 1, a deflection of y
0 was applied to the sample at a position of I = 50 mm as a working point to apply
a stress (s) corresponding to 80% of the 0.2% yield strength in the rolling direction.
The y
0 was determined by the following equation:
in which:
E is a Young's modulus in the rolling direction, and t is a thickness of the sample.
The load was removed after heating at 300 °C for 10 hours, and an amount of permanent
deformation (height) y was measured as shown in FIG. 2 to calculate the stress relaxation
rate {[y (mm) / y
0 (mm)] × 100 (%)}.
[0055] When the stress relaxation rate was 10% or less, the stress relaxation resistance
was considered to be good (○).
[Table 1]
Examples |
Production Conditions |
Final Characteristics |
Component (% by mass) |
Hot Rolling |
Final Solutionizing Treatment |
YS (MPa) |
Average Grain Size (µm) |
Inverse Pole Figure in RD Direction |
Stress Relaxation Property after 300 °C × 10h |
Ti |
Additive Element |
Compressive Strain per Pass (-) |
Strain Rate of Final Pass (/s) |
Temperature (°C) |
Retention Time (s) |
Pole Density of <111> |
Higher Pole Density of <001> than <101> |
Example 1 |
3.3 |
0.15Fe |
0.12 |
19.5 |
810 |
150 |
924 |
4 |
3.3 |
○ |
○ |
Example 2 |
3.3 |
0.15Fe |
0.06 |
19.5 |
810 |
150 |
911 |
5 |
2.8 |
○ |
○ |
Example 3 |
3.3 |
0.15Fe |
0.14 |
19.5 |
810 |
150 |
932 |
4 |
3.5 |
○ |
○ |
Example 4 |
3.3 |
0.15Fe |
0.12 |
16.0 |
810 |
150 |
914 |
4 |
3.4 |
○ |
○ |
Example 5 |
3.3 |
0.15Fe |
0.12 |
23.5 |
810 |
150 |
939 |
5 |
3.5 |
○ |
○ |
Example 6 |
3.3 |
0.15Fe |
0.12 |
19.5 |
785 |
150 |
888 |
3 |
2.9 |
○ |
○ |
Example 7 |
3.3 |
0.15Fe |
0.12 |
19.5 |
840 |
150 |
926 |
13 |
3.4 |
○ |
○ |
Example 8 |
3.3 |
0.15Fe |
0.12 |
19.5 |
810 |
55 |
924 |
4 |
3.3 |
○ |
○ |
Example 9 |
3.3 |
0.15Fe |
0.12 |
19.5 |
810 |
195 |
905 |
10 |
3.1 |
○ |
○ |
Example 10 |
3.3 |
- |
0.12 |
19.5 |
810 |
150 |
897 |
24 |
3.2 |
○ |
○ |
Example 11 |
2.2 |
- |
0.12 |
19.5 |
750 |
150 |
814 |
26 |
2.6 |
○ |
○ |
Example 12 |
4.3 |
- |
0.12 |
19.5 |
865 |
150 |
1030 |
15 |
4.3 |
○ |
○ |
Example 13 |
3.3 |
0.15Mn-0.05Mo |
0.08 |
18.6 |
810 |
150 |
967 |
5 |
3.2 |
○ |
○ |
Example 14 |
3.3 |
0.15Co-0.05Zr-0.05V |
0.09 |
22.3 |
800 |
150 |
911 |
7 |
2.9 |
○ |
○ |
Example 15 |
3.3 |
0.1Zn-0.1Nb-0.1Si |
0.11 |
22.1 |
800 |
150 |
884 |
9 |
3.3 |
○ |
○ |
Example 16 |
3.3 |
0.35Ni-0.1Mg |
0.11 |
19.3 |
790 |
150 |
890 |
9 |
3.3 |
○ |
○ |
Example 17 |
3.3 |
0.25Cr-0.05P |
0.13 |
20.7 |
825 |
150 |
901 |
7 |
3.5 |
○ |
○ |
Example 18 |
3.3 |
0.15B |
0.08 |
17.7 |
825 |
150 |
917 |
14 |
3.1 |
○ |
○ |
Comparative Example 1 |
3.3 |
0.15Fe |
0.04 |
19.5 |
810 |
150 |
921 |
5 |
2.2 |
○ |
× |
Comparative Example 2 |
3.3 |
0.15Fe |
0.17 |
19.5 |
810 |
150 |
914 |
4 |
4.8 |
○ |
× |
Comparative Example 3 |
3.3 |
0.15Fe |
0.12 |
13.0 |
810 |
150 |
913 |
5 |
2.7 |
× |
× |
Comparative Example 4 |
3.3 |
0.15Fe |
0.12 |
26.5 |
Not Produced |
- |
- |
|
- |
- |
Comparative Example 5 |
3.3 |
0.15Fe |
0.12 |
19.5 |
770 |
150 |
835 |
Non-recrystallized |
5.4 |
○ |
× |
Comparative Example 6 |
3.3 |
0.15Fe |
0.12 |
19.5 |
850 |
150 |
834 |
38 |
2.1 |
○ |
× |
Comparative Example 7 |
3.3 |
0.15Fe |
0.12 |
19.5 |
810 |
40 |
929 |
Mixed Grain |
4.4 |
× |
× |
Comparative Example 8 |
3.3 |
0.15Fe |
0.12 |
19.5 |
810 |
220 |
846 |
32 |
2.7 |
× |
× |
Comparative Example 9 |
3.3 |
0.2Co-0.2Mn-0.2Zn |
Not Produced |
|
- |
|
- |
- |
Comparative Example 10 |
1.7 |
0.15Fe |
0.12 |
19.5 |
725 |
150 |
789 |
18 |
2.2 |
× |
× |
Comparative Example 11 |
4.7 |
0.15Fe |
Not Produced |
|
- |
|
- |
- |
[0056] In each of Examples 1 to 18, the stress relaxation rate after maintaining at 300
°C for 10 hours was 10% or less, indicating improved stress relaxation resistance.
[0057] On the other hand, in Comparative Example 1, the compressive strain per pass was
too low and thus the pole density of <111> was lower than 2.5, so that an improved
stress relaxation resistance as compared with Examples 1 to 18 could not be obtained.
In Comparative Example 2, the compressive strain per pass was too high, and thus the
pole density of <111> was too much higher than 4.5, so that an improved stress relaxation
resistance as compared with Invention Examples 1 to 18 could not be obtained.
[0058] In Comparative Example 3, the strain rate of the final pass was too low, so that
the pole density of <001> has lower than that of <101 >, whereby an improved stress
relaxation resistance as compared with Examples 1 to 18 could not be obtained. In
Comparative Example 4, the strain rate of the final pass was too high, so that the
shape during rolling was poor, whereby the production was impossible.
[0059] In Comparative Example 5, the temperature of the final solutionizing treatment was
too low, and thus the pole density of <111> was higher than 4.5, so that an improved
stress relaxation resistance as compared with Examples 1 to 18 could not be obtained.
In Comparative Example 6, the temperature of the final solutionizing treatment was
too high, and thus the pole density of <111> was lower than 2.5, so that an improved
stress relaxation resistance as compared with Examples 1 to 18 could not be obtained.
[0060] In Comparative Example 7, the retention time of the final solutionizing treatment
was too short, so that the crystal grain size was of mixed grain type, and the pole
density of <001> was lower than that of <101 >, whereby an improved stress relaxation
resistance as compared with Examples 1 to 18 could not be obtained. In Comparative
Example 8, the retention time of the final solutionizing treatment was too long, the
crystal grain size was coarsened, and the pole density of <001> was lower than that
of <101 >, whereby an improved stress relaxation resistance as compared with Examples
1 to 18 could not be obtained.
[0061] Comparative Examples 9 to 11 show cases where the addition amount of titanium or
the third element was not appropriate. In Comparative Examples 9 and 11, the amounts
of the additive element and titanium were too high, respectively, so that cracking
occurred during hot rolling, and production was thus impossible. In Comparative Example
10, the addition amount of Ti was too low, so that the pole density of <111> was lower
than 2.5 and the pole density of <001> was lower than that of <101>, whereby an improved
stress relaxation resistance as compared with Examples 1 to 18 could not be obtained.