U.S. patent application number 13/581494 was filed with the patent office on 2012-12-20 for strand for saw wire and manufacturing method thereof.
Invention is credited to Kenichi Nakamura, Masashi Sakamoto, Toshimi Tarui.
Application Number | 20120318410 13/581494 |
Document ID | / |
Family ID | 44763008 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120318410 |
Kind Code |
A1 |
Tarui; Toshimi ; et
al. |
December 20, 2012 |
STRAND FOR SAW WIRE AND MANUFACTURING METHOD THEREOF
Abstract
Regarding contents of C, Si, Mn and Cr, a value of parameter P
represented by the following (equation 1) is 1000 or more. A
metallic structure contains wire-drawn pearlite in an area ratio of
98% or more, a diameter is 0.05 mm to 0.18 mm, a tensile strength
is 4000 MPa or more, and a twist number in a twist test in which a
grip-to-grip distance is 100 mm, and a tension equal to a tensile
strength.times.a cross-sectional area of wire.times.0.5 is applied,
is 5 or more.
P=1098.times.[C]+98.times.[Si]-20.times.[Mn]+167.times.[Cr]
(equation 1) (in the (equation 1), [C], [Si], [Mn] and [Cr]
indicate contents (mass %) of C, Si, Mn and Cr, respectively.)
Inventors: |
Tarui; Toshimi; (Tokyo,
JP) ; Nakamura; Kenichi; (Tokyo, JP) ;
Sakamoto; Masashi; (Tokyo, JP) |
Family ID: |
44763008 |
Appl. No.: |
13/581494 |
Filed: |
April 7, 2011 |
PCT Filed: |
April 7, 2011 |
PCT NO: |
PCT/JP2011/058807 |
371 Date: |
August 28, 2012 |
Current U.S.
Class: |
148/506 ;
148/330; 148/332; 148/333; 148/334 |
Current CPC
Class: |
C21D 2211/009 20130101;
C21D 9/525 20130101; C21D 9/24 20130101; C21D 8/06 20130101; C22C
38/02 20130101; C22C 38/04 20130101; C22C 38/18 20130101; B23D
61/185 20130101; C22C 38/001 20130101 |
Class at
Publication: |
148/506 ;
148/333; 148/332; 148/330; 148/334 |
International
Class: |
C22C 38/34 20060101
C22C038/34; C21D 8/06 20060101 C21D008/06; C22C 38/24 20060101
C22C038/24; C22C 38/20 20060101 C22C038/20; C22C 38/22 20060101
C22C038/22; C21D 11/00 20060101 C21D011/00; C22C 38/40 20060101
C22C038/40 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 2010 |
JP |
2010-089590 |
Apr 8, 2010 |
JP |
2010-089591 |
Claims
1. A strand for saw wire, containing: in mass %, C: 0.87% to 1.2%;
Si: 0.02% to 2.0%; Mn: 0.1% to 1.0%; and Cr: 0.5% or less, wherein
regarding contents of C, Si, Mn and Cr, a value of parameter P
represented by a following (equation 1) is 1000 or more, a P
content is 0.015% or less, an S content is 0.015% or less, an N
content is 0.01% or less, a balance is composed of Fe and
inevitable impurities, a metallic structure contains wire-drawn
pearlite in an area ratio of 98% or more, a diameter is 0.05 mm to
0.18 mm, a tensile strength is 4000 MPa or more, and a twist number
in a twist test in which a grip-to-grip distance is 100 mm, and a
tension equal to a tensile strength.times.a cross-sectional area of
wire.times.0.5 is applied, is 5 or more.
P=1098.times.[C]+98.times.[Si]-20.times.[Mn]+167.times.[Cr]
(equation 1) (in the (equation 1), [C], [Si], [Mn] and [Cr]
indicate contents (mass %) of C, Si, Mn and Cr, respectively.)
2. The strand for saw wire according to claim 1, wherein a C
content is 0.92 mass % or more, the value of parameter P is 1050 or
more, and the metallic structure contains the wire-drawn pearlite
in an area ratio of 99% or more.
3. The strand for saw wire according to claim 1, wherein a tensile
strength under twisting is 85% or more of a tensile strength.
4. The strand for saw wire according to claim 1, wherein a tensile
elongation under twisting is 2% or more.
5. The strand for saw wire according to claim 1, wherein a
difference in Vickers hardness between a surface portion in which a
depth from a surface of the strand for saw wire is within a range
of the diameter.times.0.2 or less and a center portion in which a
distance from a center of the strand for saw wire is within a range
of the diameter.times.0.2 or less, is 100 or less.
6. The strand for saw wire according to claim 1, wherein a residual
stress of a surface portion of the strand for saw wire is -100 MPa
or less.
7. The strand for saw wire according to claim 1, further
containing, in mass %, at least one kind selected from a group
consisting of: Ni: 1.0% or less; Cu: 0.5% or less; Mo: 0.5% or
less; V: 0.5% or less; and B: 0.0050% or less.
8. A manufacturing method of a strand for saw wire, comprising:
performing hot rolling on a steel billet and cooling the resultant
at a rate of 10.degree. C./second or more so as to obtain a
hot-rolled wire rod whose diameter is 6 mm or less and having a
structure containing 97% or more of pearlite in which a thickness
of cementite is 0.03 .mu.m or less; performing primary wire drawing
on the hot-rolled wire rod so as to obtain a primary wire-drawn
material; performing final patenting treatment on the primary
wire-drawn material so as to obtain a patenting material having a
structure containing 98% or more of pearlite in which a thickness
of cementite is 0.02 .mu.m or less; and performing finish wire
drawing of the patenting material by setting a wire drawing strain
.epsilon. to less than 4.5, wherein the steel billet contains: in
mass %, C: 0.87% to 1.2%; Si: 0.02% to 2.0%; Mn: 0.1% to 1.0%; and
Cr: 0.5% or less, regarding contents of C, Si, Mn and Cr, a value
of parameter P represented by a following (equation 1) is 1000 or
more, a P content is 0.015% or less, an S content is 0.015% or
less, an N content is 0.01% or less, and a balance is composed of
Fe and inevitable impurities, and regarding the wire drawing strain
.epsilon., a value of parameter Q represented by a following
(equation 2) is 380 or more.
P=1098.times.[C]+98.times.[Si]-20.times.[Mn]+167.times.[Cr]
(equation 1)
Q=99.times.[C]+2.7.times.exp(.epsilon./2)/(0.075-0.0112.times.[C])
(equation 2) (in the (equation 1) and the (equation 2), [C], [Si],
[Mn] and [Cr] indicate contents (mass %) of C, Si, Mn and Cr,
respectively.)
9. The manufacturing method of a strand for saw wire according to
claim 8, wherein a C content of the steel billet is 0.92 mass % or
more, the value of parameter P is 1050 or more, the value of
parameter Q is more than 440, a structure of the hot-rolled wire
rod contains 98% or more of pearlite in which a thickness of
cementite is 0.03 .mu.m or less, and a structure of the patenting
material contains 99% or more of pearlite in which a thickness of
cementite is 0.02 .mu.m or less.
10. The manufacturing method of a strand for saw wire according to
claim 8, wherein the steel billet further contains, in mass %, at
least one kind selected from a group consisting of: Ni: 1.0% or
less; Cu: 0.5% or less; Mo: 0.5% or less; V: 0.5% or less; and B:
0.0050% or less.
11. The manufacturing method of a strand for saw wire according to
claim 8, wherein a finishing temperature of the hot rolling is
850.degree. C. or more.
12. The manufacturing method of a strand for saw wire according to
claim 8, wherein the performing final patenting treatment on the
primary wire-drawn material so as to obtain a patenting material
comprises: keeping a temperature of the primary wire-drawn material
within a range of 950.degree. C. to 1100.degree. C.; and
subsequently, keeping a temperature of the primary wire-drawn
material within a range of 520.degree. C. to 600.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention relates to a strand for saw wire used
for cutting a metallic material, a ceramic material, a
semiconductor material and the like, and a manufacturing method
thereof.
BACKGROUND ART
[0002] A saw wire is used for cutting Si single crystal, Si
polycrystal, sapphire, SiC single crystal and the like. Further, a
piano strand for saw wire, a steel strand for saw wire and the like
have been proposed (Patent Literatures 1 and 2). The saw wire is
required to have a small wire diameter and high strength.
[0003] Further, a strand for steel cord used for reinforcing a
tire, a belt and the like is also required to have a small wire
diameter and high strength, similar to the saw wire. Further,
various strands for steel cords have been proposed (Patent
Literatures 3 to 9).
[0004] As saw wires, there have been known a free-abrasive saw wire
and a fixed-abrasive saw wire. The fixed-abrasive saw wire is
formed such that an abrasive such as diamond is fixed on a strand
for saw wire by Ni-electrodeposition. The fixed-abrasive saw wire
is used for cutting sapphire used as a substrate for a
light-emitting diode (LED) and the like, SiC single crystal and the
like used for a semiconductor member and the like. Sapphire and SiC
single crystal are more expensive than Si single crystal. For this
reason, when cutting out a substrate from ingots of sapphire and
SiC single crystal, it is important to reduce a cutting cost.
Therefore, it has been required to further reduce a wire diameter
of a strand for fixed-abrasive saw wire. Under the present
situation, as a strand for fixed-abrasive saw wire, one having a
wire diameter of about 0.18 mm, which is smaller than the wire
diameter of the steel cord, has been mainly used.
[0005] However, when cutting of a material to be cut is performed
by using a saw wire with a small wire diameter, the saw wire is
likely to be broken during the cutting. When the saw wire is broken
during the cutting, the cutting has to be stopped at that point,
which results in reducing the yield. Therefore, the more expensive
the material to be cut, the higher the necessity for suppressing
the breakage of the saw wire.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Laid-open Patent Publication
No. 10-309627 [0007] Patent Literature 2: Japanese Laid-open Patent
Publication No. 2002-212676 [0008] Patent Literature 3: Japanese
Laid-open Patent Publication No. 2003-334606 [0009] Patent
Literature 4: Japanese Laid-open Patent Publication No. 08-291369
[0010] Patent Literature 5: Japanese Laid-open Patent Publication
No. 06-293938 [0011] Patent Literature 6: Japanese Laid-open Patent
Publication No. 11-199980 [0012] Patent Literature 7: Japanese
Laid-open Patent Publication No. 2009-280836 [0013] Patent
Literature 8: Japanese Laid-open Patent Publication No. 11-323496
[0014] Patent Literature 9: Japanese Laid-open Patent Publication
No. 11-269607
SUMMARY OF INVENTION
Technical Problem
[0015] The present invention has an object to provide a strand for
saw wire capable of suppressing a wire breakage at a time of
cutting a material to be cut, and a manufacturing method
thereof.
Solution to Problem
[0016] As a result of conducting earnest studies on the cause of
the occurrence of wire breakage, the present inventors found out
that a twisting of saw wire occurs at a time of cutting a material
to be cut, and the twisting is a main cause of the wire
breakage.
[0017] Further, the present inventors found out that a twist number
at which the breakage occurs in a twist test in which a
predetermined tension is applied is important, for suppressing such
a wire breakage. Conventionally, a reduction of area and a fracture
elongation in a tensile test, a twist number in a twist test, and
the like have been used as indexes for ductility of wire. However,
it is difficult to evaluate a breakage resistance based on these
indexes.
[0018] Further, the present inventors also found out that, in order
to improve the breakage resistance, suppression of generation of
structures other than wire-drawn pearlite (ferrite, bainite), and
suppression of wire drawing strain are important. Note that it is
assumed that the reason why the breakage resistance is improved by
suppressing the wire drawing strain is that a variation in a
cementite-cementite spacing (lamellar spacing) of pearlite is
suppressed. Here, the wire-drawn pearlite is a structure which is
formed by deforming a structure of pearlite through wire drawing.
Therefore, in the wire-drawn pearlite, ferrite and cementite are
elongated in a wire drawing direction due to an influence of the
wire drawing, and the ferrite and cementite are laminated in a
direction substantially perpendicular to the wire drawing
direction.
[0019] Further, the present inventors also found out that, in order
to manufacture a strand for saw wire with high strength while
suppressing the wire drawing strain, it is important that
respective contents of C, Si, Mn and Cr satisfy a certain
relation.
[0020] The present invention was made based on these findings. The
gist of the present invention is as follows.
[0021] (1)
[0022] A strand for saw wire, containing: in mass %,
[0023] C: 0.87% to 1.2%;
[0024] Si: 0.02% to 2.0%;
[0025] Mn: 0.1% to 1.0%; and
[0026] Cr: 0.5% or less,
[0027] wherein
[0028] regarding contents of C, Si, Mn and Cr, a value of parameter
P represented by a following (equation 1) is 1000 or more,
[0029] a P content is 0.015% or less,
[0030] an S content is 0.015% or less,
[0031] an N content is 0.01% or less,
[0032] a balance is composed of Fe and inevitable impurities,
[0033] a metallic structure contains wire-drawn pearlite in an area
ratio of 98% or more,
[0034] a diameter is 0.05 mm to 0.18 mm,
[0035] a tensile strength is 4000 MPa or more, and
[0036] a twist number in a twist test in which a grip-to-grip
distance is 100 mm, and a tension equal to a tensile
strength.times.a cross-sectional area of wire.times.0.5 is applied,
is 5 or more.
P=1098.times.[C]+98.times.[Si]-20.times.[Mn]+167.times.[Cr]
(equation 1)
[0037] (in the (equation 1), [C], [Si], [Mn] and [Cr] indicate
contents (mass %) of C, Si, Mn and Cr, respectively.)
[0038] (2)
[0039] The strand for saw wire described in (1), wherein
[0040] a C content is 0.92 mass % or more,
[0041] the value of parameter P is 1050 or more, and
[0042] the metallic structure contains the wire-drawn pearlite in
an area ratio of 99% or more.
[0043] (3)
[0044] The strand for saw wire described in (1) or (2), wherein a
tensile strength under twisting is 85% or more of a tensile
strength.
[0045] (4)
[0046] The strand for saw wire described in any one of (1) to (3),
wherein a tensile elongation under twisting is 2% or more.
[0047] (5)
[0048] The strand for saw wire described in any one of (1) to (4),
wherein a difference in Vickers hardness between a surface portion
in which a depth from a surface of the strand for saw wire is
within a range of the diameter.times.0.2 or less and a center
portion in which a distance from a center of the strand for saw
wire is within a range of the diameter.times.0.2 or less, is 100 or
less.
[0049] (6)
[0050] The strand for saw wire described in any one of (1) to (5),
wherein a residual stress of a surface portion of the strand for
saw wire is -100 MPa or less.
[0051] (7)
[0052] The strand for saw wire described in any one of (1) to (6),
further containing, in mass %, at least one kind selected from a
group consisting of:
[0053] Ni: 1.0% or less;
[0054] Cu: 0.5% or less;
[0055] Mo: 0.5% or less;
[0056] V: 0.5% or less; and
[0057] B: 0.0050% or less.
[0058] (8)
A manufacturing method of a strand for saw wire, comprising:
[0059] performing hot rolling on a steel billet and cooling the
resultant at a rate of 10.degree. C./second or more so as to obtain
a hot-rolled wire rod whose diameter is 6 mm or less and having a
structure containing 97% or more of pearlite in which a thickness
of cementite is 0.03 .mu.m or less;
[0060] performing primary wire drawing on the hot-rolled wire rod
so as to obtain a primary wire-drawn material;
[0061] performing final patenting treatment on the primary
wire-drawn material so as to obtain a patenting material having a
structure containing 98% or more of pearlite in which a thickness
of cementite is 0.02 .mu.m or less; and
[0062] performing finish wire drawing of the patenting material by
setting a wire drawing strain .epsilon. to less than 4.5,
[0063] wherein
[0064] the steel billet contains:
[0065] in mass %,
[0066] C: 0.87% to 1.2%;
[0067] Si: 0.02% to 2.0%;
[0068] Mn: 0.1% to 1.0%; and
[0069] Cr: 0.5% or less,
[0070] regarding contents of C, Si, Mn and Cr, a value of parameter
P represented by a following (equation 1) is 1000 or more,
[0071] a P content is 0.015% or less,
[0072] an S content is 0.015% or less,
[0073] an N content is 0.01% or less, and
[0074] a balance is composed of Fe and inevitable impurities,
and
[0075] regarding the wire drawing strain .epsilon., a value of
parameter Q represented by a following (equation 2) is 380 or
more.
P=1098.times.[C]+98.times.[Si]-20.times.[Mn]+167.times.[Cr]
(equation 1)
Q=99.times.[C]+2.7.times.exp(.epsilon./2)/(0.075-0.0112.times.[C])
(equation 2)
[0076] (in the (equation 1) and the (equation 2), [C], [Si], [Mn]
and [Cr] indicate contents (mass %) of C, Si, Mn and Cr,
respectively.)
[0077] (9)
[0078] The manufacturing method of a strand for saw wire described
in (8), wherein
[0079] a C content of the steel billet is 0.92 mass % or more,
[0080] the value of parameter P is 1050 or more,
[0081] the value of parameter Q is more than 440,
[0082] a structure of the hot-rolled wire rod contains 98% or more
of pearlite in which a thickness of cementite is 0.03 .mu.m or
less, and
[0083] a structure of the patenting material contains 99% or more
of pearlite in which a thickness of cementite is 0.02 .mu.m or
less.
[0084] (10)
[0085] The manufacturing method of a strand for saw wire described
in (8) or (9), wherein the steel billet further contains, in mass
%, at least one kind selected from a group consisting of:
[0086] Ni: 1.0% or less;
[0087] Cu: 0.5% or less;
[0088] Mo: 0.5% or less;
[0089] V: 0.5% or less; and
[0090] B: 0.0050% or less.
[0091] (11)
[0092] The manufacturing method of a strand for saw wire described
in any one of (8) to (10), wherein a finishing temperature of the
hot rolling is 850.degree. C. or more.
[0093] (12)
[0094] The manufacturing method of a strand for saw wire described
in any one of (8) to (11), wherein the performing final patenting
treatment on the primary wire-drawn material so as to obtain a
patenting material comprises:
[0095] keeping a temperature of the primary wire-drawn material
within a range of 950.degree. C. to 1100.degree. C.; and
[0096] subsequently, keeping a temperature of the primary
wire-drawn material within a range of 520.degree. C. to 600.degree.
C.
Advantageous Effects of Invention
[0097] According to the present invention, it is possible to
realize both of high strength and high breakage resistance.
Therefore, when a saw wire is formed by using the strand for saw
wire, it is possible to suppress a breakage at a time of cutting a
material to be cut while reducing a cutting cost.
BRIEF DESCRIPTION OF DRAWINGS
[0098] FIG. 1 is a diagram illustrating a relation between a twist
number under tension and a number of breakage.
DESCRIPTION OF EMBODIMENTS
[0099] The present inventor conducted detailed analysis regarding a
relation between a breakage of saw wire that occurs during cutting
a material to be cut such as sapphire and SiC single crystal, and
ductility of strand for saw wire. As a result, it was clarified
that based on the conventional indexes such as the reduction of
area and the fracture elongation in the tensile test, the twist
number in the twist test, and the like, the breakage resistance of
the strand for saw wire cannot be sufficiently evaluated.
Conventionally, in the twist test, both ends of a test piece are
firmly gripped with a distance equal to 100 times a wire diameter
therebetween, and while making the wire to be tightened to a level
where it is not bent, one gripped portion is rotated in a certain
direction, and a twist number when the wire is broken is
measured.
[0100] Therefore, the present inventors studied about new indexes
for evaluating the breakage resistance of the strand for saw wire.
As a result, they found out that a twist number at which a breakage
occurs in a twist test in which a certain tension is applied (twist
number under tension) is important. For example, a twist number in
a twist test in which a grip-to-grip distance is set to 100 mm, and
a tension equal to "a tensile strength of wire".times."a
cross-sectional area of wire".times.0.5 is applied, is important.
In a conventional twist test, when a diameter of a wire is 0.3 mm,
a grip-to-grip distance is 30 mm, and a tension applied to the wire
is about a tension equal to "a tensile strength of wire".times."a
cross-sectional area of wire".times.0.1, at the maximum. Therefore,
in the twist test in which the grip-to-grip distance is set to 100
mm, and the tension equal to "a tensile strength of
wire".times."the cross-sectional area of wire".times.0.5 is
applied, the grip-to-grip distance is longer and the tension to be
applied is larger than the conventional twist test.
[0101] Since the twist number in the twist test in which the
certain tension is applied is important, good or poor of the
breakage resistance is conceivable to be largely influenced by a
curvature of a portion at which the breakage of the strand for saw
wire occurs, and the tension which is applied to the strand for saw
wire.
[0102] Further, it was clarified that tensile strength and
elongation when a strand for saw wire is gripped in a state where
twisting is applied several times without applying a tension
thereto and is subjected to a tensile test in that state, are also
effective indexes for evaluating the breakage resistance.
[0103] Further, it was clarified that as such indexes, a ratio of a
tensile strength in a state of applying 5 times of twisting
(tensile strength under twisting) with respect to a tensile
strength in a state of applying no twisting (tensile strength ratio
under twisting), and a fracture elongation in a state of applying 5
times of twisting (tensile elongation under twisting) are
particularly effective. It is conceivable that the reason why these
indexes are effective is that, during cutting a material to be cut,
a saw wire is twisted and then a tension is applied thereto. Here,
the tensile strength in a state of applying no twisting is a
tensile strength obtained through a normal tensile test.
[0104] Further, the present inventors conducted various analyses
regarding a relation between the twist number under tension, the
tensile strength ratio under twisting and the tensile elongation
under twisting, and a structural type, a residual stress and a
hardness distribution in a cross section perpendicular to a wire
drawing direction of the strand for saw wire. As a result, it was
clarified that fractions (ratios) of structures other than pearlite
(wire-drawn pearlite) (non-pearlite structures) such as grain
boundary ferrite and bainite, a difference in hardness between a
surface portion and a center portion, and a residual stress of the
surface portion exert influences on the twist number under tension,
the tensile strength ratio under twisting and the tensile
elongation under twisting. Further, it was also clarified that the
breakage resistance is influenced by a variation in a cementite
spacing (lamellar spacing) and a thickness of cementite in
pearlite.
[0105] Specifically, the present inventors found out that, for
suppressing the breakage of the strand for saw wire, the
suppression of generation of the non-pearlite structures, the
reduction in the difference in the hardness between the surface
portion and the center portion, and the application of compressive
residual stress to the surface potion, are also effective. Further,
the finding such that, qualitatively, the reduction in the
variation in the lamellar spacing and the reduction in the
thickness of cementite are effective for improving the breakage
resistance, was also obtained. Note that the grain boundary ferrite
is different from ferrite that forms layers with cementite
(lamellar ferrite), and is ferrite generated in a grain boundary of
prior austenite and then deformed through wire drawing.
[0106] The non-pearlite structures such as the grain boundary
ferrite and bainite cause intensive localized strain. Accordingly,
for improving the breakage resistance of the strand for saw wire,
it is particularly effective to reduce the fractions of the
non-pearlite structures. The grain boundary ferrite and bainite are
generated during cooling a hot-rolled wire rod. Therefore, for
example, by increasing a cooling rate after the hot rolling, it is
possible to suppress the generation of non-pearlite structures, and
to increase a fraction of pearlite structure of the hot-rolled wire
rod.
[0107] Further, in the pearlite structure, a portion with a large
lamellar spacing has a lower strength, and the strain is likely to
intensively occur on that portion. For this reason, when the
lamellar spacing is non-uniform, the breakage is likely to occur in
the portion with a large lamellar spacing. Therefore, it is further
preferable to reduce the variation in the lamellar spacing. Since
there is a tendency that the variation in the lamellar spacing is
larger as the wire drawing strain is increased, the breakage
resistance is conceivable to be improved by suppressing the wire
drawing strain.
[0108] Further, the present inventors studied about conditions for
manufacturing a strand for saw wire with a large twist number under
tension, high tensile strength ratio under twisting and tensile
elongation under twisting, and having a tensile strength of 4000
MPa or more. When manufacturing a strand for saw wire, for example,
a hot-rolled wire rod of high carbon steel is subjected to primary
wire drawing to have a predetermined wire diameter, and thereafter,
final patenting treatment, brass plating treatment, finish wire
drawing and the like are performed. Further, depending on a
diameter of a strand for saw wire to be manufactured, intermediate
heat treatment and intermediate wire drawing (secondary wire
drawing) are performed in accordance with need, after the primary
wire drawing and before the final patenting treatment process.
Specifically, processing similar to that for a strand for steel
cord is performed. Here, the patenting treatment is heat treatment
in which a structure of a primary wire-drawn material is turned
into austenite by keeping the primary wire-drawn material heated,
and thereafter, the material is quickly cooled to a pearlite
transformation temperature and is kept in this state so that the
structure is isothermally transformed to pearlite.
[0109] In order to strengthen the strand for saw wire, it is
preferable to increase the wire drawing strain. On the other hand,
when the wire drawing strain (true strain) is increased, the
breakage resistance is reduced due to the variation in the lamellar
spacing, as described above. As a result, the twist number under
tension, the tensile strength ratio under twisting and the tensile
elongation under twisting tend to decrease. Namely, the realization
of high strength and the improvement in the breakage resistance are
in a tradeoff relation. Therefore, if the wire drawing strain is
reduced for the purpose of improving the breakage resistance, it is
difficult to secure the strength of 4000 MPa or more. In order to
secure the strength of 4300 MPa or more, in particular, it is
important to set the wire drawing strain to 4.5 or more, but it was
clarified that there is a tendency that, if the wire drawing strain
is set to 4.5 or more, the variation in the lamellar spacing
becomes large, resulting in that the breakage resistance is likely
to be decreased.
[0110] Therefore, in order to realize the suppression of the wire
drawing strain, the present inventors repeatedly conducted earnest
studies regarding a balance of contents of elements that contribute
to the improvement in the strength of the strand for saw wire. As a
result, they found out that, regarding the respective contents of
C, Si, Mn and Cr, when a value of parameter P represented by the
following (equation 1) is 1000 or more, the strength of 4000 MPa or
more can be obtained even if the wire drawing strain is suppressed,
and when the value is 1050 or more, the strength of more than 4300
MPa can be obtained.
P=1098.times.[C]+98.times.[Si]-20.times.[Mn]+167.times.[Cr]
(equation 1)
[0111] Here, [C], [Si], [Mn] and [Cr] indicate contents (mass %) of
C, Si, Mn and Cr, respectively.
[0112] Further, the present inventors found out that when
manufacturing a strand for saw wire, chemical components and a
cooling rate after hot rolling exert influences on a thickness of
cementite of a hot-rolled wire rod and a thickness of cementite
after patenting treatment. Specifically, if the cooling rate after
the hot rolling is set to 10.degree. C./second or more when the
value of the parameter P is 1000 or more, it is possible to obtain
a hot-rolled wire rod having a structure containing 97% or more of
pearlite in which a thickness of cementite is 0.03 .mu.m or less.
Further, they also found out that if the cooling rate after the hot
rolling is set to 10.degree. C./second or more when the value of
the parameter P is 1050 or more, it is possible to obtain a
hot-rolled wire rod having a structure containing 98% or more of
pearlite in which a thickness of cementite is 0.03 .mu.m or
less.
[0113] Further, it was also clarified that if the hot-rolled wire
rod is subjected to primary wire drawing, subjected to intermediate
heat treatment and intermediate wire drawing (secondary wire
drawing) according to need, and is subjected to final patenting
treatment, when the value of the parameter P is 1000 or more, it is
possible to obtain a patenting material having a structure
containing 98% or more of pearlite in which a thickness of
cementite is 0.02 .mu.m or less, and when the value of the
parameter P is 1050 or more, it is possible to obtain a patenting
material having a structure containing 99% or more of pearlite in
which a thickness of cementite is 0.02 .mu.m or less. Further, it
was clarified that the twist number under tension, the tensile
strength ratio under twisting and the tensile elongation under
twisting of a strand for saw wire obtained from such patenting
materials are remarkably improved.
[0114] Next, explanation will be made on a composition of the
strand for saw wire.
[0115] A wire for fixed-abrasive saw wire according to an
embodiment of the present invention contains, in mass %, C: 0.87%
to 1.2%, Si: 0.02 to 2.0%, Mn: 0.1 to 1.0%, and Cr: 0.5% or less.
Regarding contents of C, Si, Mn and Cr, a value of parameter P
represented by the above-described (equation 1) is 1000 or more.
Further, a P content is 0.015% or less, an S content is 0.015% or
less, and an N content is 0.01% or less. Further, a balance is
composed of Fe and inevitable impurities.
[0116] C: C increases a tensile strength after patenting treatment
and improves a hardening rate during wire drawing, resulting in
that the tensile strength can be increased with a small wire
drawing strain. When a content of C is less than 0.87%, it becomes
difficult to secure the strength of 4000 MPa or more with a small
wire drawing strain, and when the content of C is less than 0.92%,
it becomes difficult to secure the strength of more than 4300 MPa.
On the other hand, when the content of C exceeds 1.2%, a breakage
resistance is reduced, and further, proeutectoid cementite
precipitates to an austenite grain boundary to deteriorate wire
drawability. Therefore, the content of C is set to 0.87% to 1.2%.
Further, in order to secure the strength of more than 4300 MPa, the
content of C may be set to 0.92% to 1.2%.
[0117] Si: Si strengthens ferrite in pearlite to improve the
tensile strength, and also exhibits deoxidation function. When a
content of Si is less than 0.02%, the above effect is insufficient.
On the other hand, when the content of Si exceeds 2.0%, a hard
SiO.sub.2-based inclusion, which lowers wire drawability, is easily
generated, and further, ferrite and bainite being non-pearlite
structures increase in a hot-rolled wire rod. Therefore, the
content of Si is set to 0.02% to 2.0%.
[0118] Mn: Mn exhibits functions of deoxidation and
desulfurization, and increases hardenability to improve the tensile
strength after the patenting treatment. When a content of Mn is
less than 0.1%, the above effect is insufficient. On the other
hand, when the content of Mn exceeds 1.0%, bainite is easily
generated in the hot-rolled wire rod, and further, a treatment time
for completing the pearlite transformation during the patenting
treatment is lengthened, which results in reducing productivity.
Therefore, the content of Mn is set to 0.1% to 1.0%.
[0119] Cr: Cr is a useful element that contributes to refining of a
cementite spacing (lamellar spacing) in pearlite after performing
the hot rolling and after patenting treatment. In order to increase
the tensile strength after the patenting treatment and to improve a
hardening rate during wire drawing, 0.01% or more of Cr is
preferably contained. Further, in order to increase the strength
and to improve the breakage resistance, a content of Cr is more
preferably 0.03% or more, and is still more preferably 0.05% or
more. On the other hand, when the content of Cr exceeds 0.5%,
bainite is easily generated in the hot-rolled wire rod, and
further, a treatment time for completing the pearlite
transformation in the patenting treatment becomes long, which
results in reducing productivity. Therefore, the content of Cr is
set to 0.5% or less.
[0120] Further, in the present embodiment, it is important that the
value of the parameter P represented by the above-described
(equation 1) is 1000 or more, and the value is preferably 1050 or
more. When the value of the parameter P is less than 1000, it is
difficult to reduce fractions of the non-pearlite structures and to
reduce a thickness of cementite, resulting in that the improvement
in the breakage resistance is difficult to be achieved. Further,
since the strength of patenting material is insufficient, it is
difficult to secure the tensile strength of 4000 MPa or more if the
wire drawing strain is suppressed to be small for improving the
breakage resistance. As above, when the value of the parameter P is
less than 1000, it is difficult to reduce the variation in the
lamellar spacing to improve the breakage resistance while securing
the strength. Further, when the value of the parameter P is less
than 1050, if the wire drawing strain is suppressed to less than
4.5, it is difficult to secure the tensile strength of more than
4300 MPa. Note that since the ranges of the contents of C, Si, Mn
and Cr are set, the parameter P takes a value of 1595.1 or
less.
[0121] P: P reduces wire drawability and ductility. Therefore, a
content of P is set to 0.015% or less.
[0122] S: S reduces wire drawability and ductility. Therefore, a
content of S is set to 0.015% or less.
[0123] N: N reduces ductility. Therefore, a content of N is set to
0.01% or less.
[0124] Further, the strand for saw wire according to the present
embodiment may also contain at least one kind selected from the
group consisting of Ni: 1.0% or less, Cu: 0.5% or less, Mo: 0.5% or
less, V: 0.5% or less, and B: 0.0050% or less.
[0125] Ni: Ni acts to impart good wire drawability to pearlite
generated through the transformation during the patenting
treatment. However, even when a content of Ni exceeds 1.0%, the
effect comparable to the content is not obtained. Therefore, the
content of Ni is preferably set to 1.0% or less. Further, when the
content of Ni is less than 0.05%, the above effect is difficult to
be obtained. Therefore, the content of Ni is preferably set to
0.05% or more.
[0126] Cu: Cu is an element that contributes to high strengthening
owing to its precipitation hardening. However, even when a content
of Cu exceeds 0.5%, the effect comparable to the content is not
obtained. Therefore, the content of Cu is preferably set to 0.5% or
less. Further, when the content of Cu is less than 0.01%, the above
effect is difficult to be obtained. Therefore, the content of Cu is
preferably set to 0.01% or more.
[0127] Mo: Mo has effects of refining the lamellar spacing in
pearlite and increasing the tensile strength after the patenting
treatment. However, when a content of Mo exceeds 0.5%, the effect
comparable to the content is not obtained. Further, the pearlite
transformation is delayed, resulting in that a treatment time is
lengthened and productivity is lowered. Therefore, the content of
Mo is preferably set to 0.5% or less. Further, when the content of
Mo is less than 0.05%, the above effect is difficult to be
obtained. Therefore, the content of Mo is preferably set to 0.05%
or more.
[0128] V: V has effects of refining the lamellar spacing in
pearlite and increasing the tensile strength after the patenting
treatment. However, even when a content of V exceeds 0.5%, the
effect comparable to the content is not obtained. Therefore, the
content of V is preferably set to 0.5% or less. Further, when the
content of V is less than 0.05%, the above effect is difficult to
be obtained. Therefore, the content of V is preferably set to 0.05%
or more.
[0129] B: B has an effect of suppressing the generation of ferrite.
However, when a content of B exceeds 0.0050%, wire drawability is
low. Therefore, the content of B is preferably set to 0.0050% or
less. Further, when the content of B is less than 0.0001%, the
above effect is difficult to be obtained. Therefore, the content of
B is preferably set to 0.0001% or more.
[0130] Note that although Nb, Ti and Al may also be contained, it
is preferable that a Nb content is 0.01% or less, a Ti content is
0.01% or less, and an Al content is 0.005% or less. When the Nb
content exceeds 0.01%, a generation amount of carbonitride of Nb is
increased, and the carbonitride is likely to be coarse. For this
reason, a frequency of breakage of the saw wire is sometimes
increased. When the Ti content exceeds 0.01%, a frequency of
breakage of the saw wire is sometimes increased, due to the similar
reason to that of Nb. When the Al content exceeds 0.005%, an oxide
of Al increases, resulting in that the frequencies of the breakage
during the wire drawing and the breakage of the saw wire are likely
to increase. Based on these reasons, it is preferable that the Nb
content is 0.01% or less, the Ti content is 0.01% or less, and the
Al content is 0.005% or less.
[0131] Next, explanation will be made on a structure of the strand
for saw wire according to the embodiment of the present invention.
Note that micro-voids are not generated in the structure of the
strand for saw wire according to the present embodiment.
[0132] In the strand for saw wire according to the present
embodiment, a metallic structure contains a wire-drawn pearlite
structure in an area ratio of 98% or more. When the area ratio of
the wire-drawn pearlite structure is less than 98%, even if the
variation in the lamellar spacing falls within a predetermined
range, it is difficult to obtain a favorable twist number under
tension, resulting in that the realization of both of the high
strength and the breakage resistance is difficult. In order to
obtain the tensile strength of 4300 MPa or more, the area ratio of
the wire-drawn pearlite structure is preferably 99% or more.
[0133] Further, in order to improve the breakage resistance, it is
preferable that the variation in the lamellar spacing in the
wire-drawn pearlite structure is as small as possible. The level of
the variation is not particularly limited, but, for example, it is
preferable to reduce a ratio between a maximum value and a minimum
value of the lamellar spacing in a cross section perpendicular to a
wire drawing direction, and it is particularly preferable to set
the ratio to 10 or less. In order to suppress the variation in the
lamellar spacing, it is preferable to reduce the wire drawing
strain.
[0134] A diameter of the strand for saw wire according to the
present embodiment is 0.05 mm to 0.18 mm, and is preferably 0.08 mm
to 0.16 mm. Since the diameter is very small as described above, it
is possible to reduce a cutting cost of a material to be cut.
Specifically, it is possible to enhance utilization efficiency of
the material to be cut. Thus, the strand for saw wire may be
favorably used for thinly cutting an expensive material such as
sapphire and SiC single crystal, and the like. When the wire
diameter is less than 0.05 mm, the tensile strength and the
breakage resistance sometimes are insufficient. Further, when the
wire diameter exceeds 0.18 mm, the cutting cost at the time of
cutting increases, which results in reducing the utilization
efficiency of the material to be cut.
[0135] As described above, the strand for saw wire according to the
present embodiment is extremely thin, so that a high tensile
strength is required. This is because, in order to cut the material
to be cut with high accuracy, there is a need to apply a high
tension. A tensile strength of the strand for saw wire according to
the present embodiment is 4000 MPa or more, and is preferably more
than 4300 MPa, so that a high tension may be applied to the strand
for saw wire when cutting the material to be cut such as sapphire
and SiC single crystal. Note that an upper limit of the tensile
strength is not particularly limited, but, it is preferably 5200
MPa or less. When the tensile strength exceeds 5200 MPa, there is a
possibility that the breakage resistance is reduced.
[0136] Further, in the present embodiment, a difference in Vickers
hardness (HV hardness difference) between a surface portion in
which a depth from a surface of the wire is within a range of "a
wire diameter".times.0.2 or less and a center portion in which a
distance from a center of the wire is within a range of "the wire
diameter".times.0.2 or less, is preferably 100 or less. When the HV
hardness difference is 100 or less, it is possible to obtain
further excellent ductility and twist characteristics. Further, the
HV hardness difference is more preferably 50 or less. In order to
reduce the HV hardness difference, it is effective to increase the
strength through the adjustment of components contained in the
strand for saw wire, and it is particularly important that the
value of the parameter P is 1000 or more.
[0137] Further, in order to reduce the HV hardness difference, it
is important to suppress heat generation during processing in
finish wire drawing. Further, in order to suppress the heat
generation during processing, for example, technologies of reducing
a wire drawing speed, using a diamond die, adjusting a shape of die
such as a die angle, controlling a reduction of area in a final die
to 10% or less, using a lubricant with a friction coefficient of
0.1 or less, controlling a temperature of the lubricant to
70.degree. C. or less and the like, are effective. Further, it is
possible to reduce the HV hardness difference also by performing
straightening process after the finish wire drawing. By
appropriately combining these technologies, it becomes possible to
reduce the HV hardness difference more securely and easily.
[0138] When cutting an ingot with using a saw wire including the
strand for saw wire according to the present embodiment, which is,
for example, a fixed-abrasive saw wire or a free-abrasive saw wire,
a tension is applied to the strand for saw wire. Accordingly, for
suppressing the wire breakage, it is preferable that a compressive
residual stress is applied to the surface portion of the strand for
saw wire. For instance, the residual stress in the surface portion
is preferably -100 MPa or less. A sign of residual stress is given
based on a tensile direction which is set as positive, so that when
the residual stress is -100 MPa or less, it means that the
compressive residual stress is 100 MPa or more. When the residual
stress of the surface portion of the wire is -100 MPa or less, it
is possible to obtain further excellent breakage resistance. Here,
the surface portion corresponds to a portion in which, for example,
a depth from a surface of the strand for saw wire falls within a
range of "a wire diameter".times.0.2 or less.
[0139] In order to make the residual stress of the surface portion
to be the compressive residual stress, the adjustment of components
contained in the strand for saw wire is effective, and it is
particularly important that the value of the parameter P is 1000 or
more. Further, it is possible to apply the residual stress of -100
MPa or less to the surface portion, also by controlling the
reduction of area in the final die to 10% or less or by performing
the straightening process or shot peening treatment after the
finish wire drawing.
[0140] As described above, the twist number in the twist test in
which the grip-to-grip distance is set to 100 mm, and the tension
equal to "the tensile strength of wire".times."the cross-sectional
area of wire".times.0.5 is applied (twist number under tension), is
quite effective as an index for the breakage resistance of the
strand for saw wire. FIG. 1 illustrates an example of a relation
between the twist number under tension and the number of wire
breakage of a fixed-abrasive saw wire during cutting sapphire. The
number of wire breakage on a vertical axis indicates the number of
wire breakage per 1000 km of the fixed-abrasive saw wire length. As
is apparent from FIG. 1, when the twist number under tension is
less than 5, the number of wire breakage is significantly large,
and when the twist number under tension is 5 or more, the number of
wire breakage is extremely small. Therefore, the twist number under
tension is set to 5 or more. Further, as illustrated in FIG. 1,
when the twist number under tension is 8 or more, the number of
wire breakage is further reduced, so that the twist number under
tension is preferably 8 or more. When the twist number under
tension is 8 or more, further excellent breakage resistance can be
obtained.
[0141] Further, in the strand for saw wire according to the present
embodiment, the ratio of the tensile strength under twisting with
respect to the tensile strength in a state of applying no twisting
(tensile strength ratio under twisting), is preferably 85% or more.
Further, the tensile elongation under twisting is preferably 2% or
more. As described above, the tensile strength under twisting and
the tensile elongation under twisting are the tensile strength and
the fracture elongation when the tensile test is performed in a
state of applying 5 times of twisting to the wire. The tensile
strength ratio under twisting and the tensile elongation under
twisting are suitable as indexes for the breakage resistance of a
saw wire including the strand for saw wire. In order to further
reduce the frequency of wire breakage, the tensile strength ratio
under twisting is more preferably 90% or more.
[0142] Note that when measuring the tensile strength under twisting
and the tensile elongation under twisting, both ends of a test
piece may be gripped in a state where a grip-to-grip distance is
set to 100 mm and twisting may be applied 5 times without applying
a tension, and the test piece may be subjected to a tensile test in
that state, for example.
[0143] The variation in the lamellar spacing and the non-pearlite
structures are conceivable as a cause of deterioration of the
tensile strength and elongation during conducting the tensile test
in a state of applying 5 times of twisting. Therefore, in order to
enhance the tensile strength ratio under twisting and the tensile
elongation under twisting, it is preferable to realize the
reduction in the variation in the lamellar spacing and the
reduction in the non-pearlite structures.
[0144] Next, explanation will be made on a manufacturing method of
the strand for saw wire according to the present embodiment.
[0145] When manufacturing the strand for saw wire according to the
present embodiment, first, a steel billet having the aforementioned
chemical components is subjected to hot rolling and is then cooled
to obtain a hot-rolled wire rod. Subsequently, primary wire drawing
of the hot-rolled wire rod is performed to obtain a primary
wire-drawn material. After that, final patenting treatment is
performed on the primary wire-drawn material to obtain a patenting
material. Subsequently, finish wire drawing of the patenting
material is performed.
[0146] Note that depending on a diameter of a strand for saw wire
to be manufactured, it is sometimes difficult to obtain a
predetermined diameter only by the primary wire drawing. In such a
case, it is also possible to perform intermediate heat treatment
and intermediate wire drawing (secondary wire drawing) between the
primary wire drawing and the final patenting treatment.
[0147] Further, it is also possible to perform plating treatment on
the patenting material between the final patenting treatment and
the finish wire drawing. In this case, the finish wire drawing may
be performed on the patenting material which has been subjected to
the plating treatment.
[0148] In the present embodiment, a diameter of the hot-rolled wire
rod is set to 6 mm or less. When the diameter of the hot-rolled
wire rod exceeds 6 mm, it is difficult to obtain a predetermined
diameter only by the primary wire drawing, and there arises a
necessity for increasing the number of the aforementioned
intermediate wire drawing and intermediate heat treatment to obtain
the predetermined diameter, which results in reducing productivity.
Further, when the number of the intermediate wire drawing and the
intermediate heat treatment is increased, a surface appearance of
the patenting material becomes rough, resulting in that,
conclusively, the twist number under tension, the tensile strength
ratio under twisting, and the tensile elongation under twisting of
the strand for saw wire are reduced. Note that in order to further
reduce the number of the intermediate wire drawing and the
intermediate heat treatment, the diameter of the hot-rolled wire
rod is preferably set to 5 mm or less. Further, the diameter of the
hot-rolled wire rod is preferably set to 3 mm or more. This is
because, when the diameter of the hot-rolled wire rod is set to
less than 3 mm, productivity of the wire rod at the time of the hot
rolling is reduced.
[0149] A temperature condition in the hot rolling is not
particularly limited, but, a temperature at which finish rolling is
performed (finishing temperature) is preferably set to 850.degree.
C. or more. When the finishing temperature is less than 850.degree.
C., there is a possibility that a large amount of grain boundary
ferrite is generated during cooling after the hot rolling, and the
hot-rolled wire rod having a structure containing a predetermined
amount of pearlite is difficult to be obtained.
[0150] In the present embodiment, a cooling rate after the hot
rolling is set to 10.degree. C./second or more. As described above,
if the cooling rate after the hot rolling is set to 10.degree.
C./second or more when the value of the parameter P is 1000 or
more, it is possible to obtain a hot-rolled wire rod having a
structure containing 97% or more of pearlite in which a thickness
of cementite is 0.03 .mu.m or less. Further, if the cooling rate
after the hot rolling is set to 10.degree. C./second or more when
the value of the parameter P is 1050 or more, it is possible to
obtain a hot-rolled wire rod having a structure containing 98% or
more of pearlite in which a thickness of cementite is 0.03 .mu.m or
less. The cooling rate may be controlled through air blasting, for
example. Further, it is also possible to control the cooling rate
based on a wire diameter after the hot rolling. In order to
suppress the generation of non-pearlite structure, which is bainite
in particular, it is particularly preferable to control the cooling
rate within a temperature range from the finishing temperature to
520.degree. C. to 650.degree. C., at which the pearlite
transformation is started. Further, it is also possible to perform
the patenting treatment by quickly immersing the wire rod after the
hot rolling in a molten salt bath of 520.degree. C. to 580.degree.
C. In this case, the cooling rate in the molten salt is 150.degree.
C./second or more.
[0151] When the fraction of pearlite is less than 97%, micro-voids
are generated in a non-pearlite portion, which results in reducing
the twist number under tension, the tensile strength ratio under
twisting, and the tensile elongation under twisting of the strand
for saw wire. Further, when a thickness of cementite contained in
pearlite exceeds 0.03 .mu.m, minute micro-voids are generated in
the vicinity of cementite during the primary wire drawing, which
reduces ductility of the strand for saw wire. Therefore, the
structure of the hot-rolled wire rod is made to contain 97% or
more, preferably 98% or more of pearlite in which a thickness of
cementite is 0.03 .mu.m or less.
[0152] As described above, the patenting treatment is the heat
treatment in which a structure of a primary wire-drawn material is
turned into austenite by keeping the primary wire-drawn material
heated, and thereafter, the material is quickly cooled to a
pearlite transformation temperature and is kept in this state so
that the structure is isothermally transformed to pearlite. If such
patenting treatment is performed after the primary wire drawing,
when the value of the parameter P is 1000 or more, it is possible
to obtain a patenting material having a structure containing 98% or
more of pearlite in which a thickness of cementite is 0.02 .mu.m or
less, and when the value of the parameter P is 1050 or more, it is
possible to obtain a patenting material having a structure
containing 99% or more of pearlite in which a thickness of
cementite is 0.02 .mu.m or less, as described above.
[0153] In the patenting treatment, the temperature for keeping the
primary wire-drawn material heated to turn the structure into
austenite is preferably set to 950.degree. C. to 1100.degree. C.,
and the temperature for keeping the primary wire-drawn material
cooled to make the structure to be isothermally transformed to
pearlite (to cause pearlite transformation) is preferably set to
520.degree. C. to 600.degree. C. Further, the temperature for
making the structure to be isothermally transformed to pearlite is
more preferably 550.degree. C. or more and/or 580.degree. C. or
less. A bath used for causing the pearlite transformation is not
particularly limited, but, a Pb bath and a fluidized bed furnace
are preferable.
[0154] The fraction of pearlite in the structure of the patenting
material after the final patenting treatment is set to 98% or more,
and is preferably set to 99% or more, in order to obtain sufficient
twist number under tension, tensile strength ratio under twisting
and tensile elongation under twisting of the strand for saw wire.
When the fraction of pearlite is less than 98%, there is a case
where, during the finish wire drawing, micro-voids are generated
from ferrite and bainite being the non-pearlite structures as
starting points, which causes wire breakage. Further, when the
non-pearlite structures increase, the twist number under tension,
the tensile strength ratio under twisting and the tensile
elongation under twisting of the strand for saw wire sometimes are
insufficient.
[0155] Further, when a thickness of cementite contained in pearlite
of the patenting material exceeds 0.02 .mu.m, minute micro-voids
are generated in the vicinity of cementite during the finish wire
drawing, which reduces the twist number under tension, the tensile
strength ratio under twisting and the tensile elongation under
twisting of the strand for saw wire. Therefore, the structure of
the hot-rolled wire rod is made to contain 98% or more, preferably
99% or more of pearlite in which a thickness of cementite is 0.02
.mu.m or less.
[0156] In order to make a thickness of cementite after the final
patenting treatment to be 0.02 .mu.m or less, it is important to
set, regarding the composition of the steel billet, the value of
the parameter P to 1000 or more, preferably 1050 or more, and then
to set the temperature for making the structure to be isothermally
transformed to pearlite to 520.degree. C. to 600.degree. C.
[0157] In the present embodiment, a diameter after the finish wire
drawing is set to 0.05 mm to 0.18 mm. This is for the reduction in
the cutting cost of a saw wire using the strand for saw wire, and
the like.
[0158] The present inventors conducted studies regarding a relation
between the tensile strength and the breakage resistance of the
strand for saw wire, and the C content and the wire drawing strain
in the finish wire drawing (true strain in wire drawing). As a
result, they found out that, regarding a wire drawing strain
.epsilon. in the finish wire drawing, when a value of parameter Q
represented by the following (equation 2) is 380 or more, excellent
tensile strength and breakage resistance can be obtained.
Q=99.times.[C]+2.7.times.exp(.epsilon./2)/(0.075-0.0112.times.[C])
(equation 2)
[0159] Here, [C] indicates the C content (mass %).
[0160] When the value of the parameter Q is less than 380, it is
difficult to secure the tensile strength of 4000 MPa or more. In
order to secure the tensile strength of more than 4300 MPa, it is
preferable that the value of the parameter Q exceeds 440. Further,
as described above, when the wire drawing strain .epsilon. is 4.5
or more, the variation in the lamellar spacing is large, resulting
in that the twist number under tension, the tensile strength ratio
under twisting and the tensile elongation under twisting are
reduced, and the breakage resistance is likely to be reduced.
Therefore, the wire drawing strain .epsilon. is set to less than
4.5. Note that since the ranges of the content of C and the wire
drawing strain are set, the value of the parameter Q becomes 535 or
less. Further, when the value of the parameter Q exceeds 535, the
breakage resistance of the strand for saw wire is likely to be
reduced.
[0161] Although a method for the finish wire drawing is not
particularly limited, it is preferable to perform the finish wire
drawing with using a diamond die at a predetermined wire drawing
speed. Processing conditions such as a shape of die such as a die
angle, as well as a reduction of area in a final die, a type of
lubricant and the like are not particularly limited, but, they are
preferably selected so that a difference in Vickers hardness (HV
hardness difference) between a surface portion in which a depth
from a surface of the strand for saw wire is within a range of "a
wire diameter".times.0.2 or less and a center portion in which a
distance from a center of the wire is within a range of "the wire
diameter".times.0.2 or less, is 100 or less, as described above.
This is for obtaining excellent ductility and twist
characteristics.
[0162] It is also possible to perform, before and/or after the
finish wire drawing, Cu--Zn plating, Cu plating and/or Ni plating
in accordance with need, thereby forming a plating film on a
surface of the wire rod. Further, it is also possible to perform
bluing treatment for removing stress after the finish wire drawing.
The bluing treatment is preferably performed within a temperature
range of 150.degree. C. to 400.degree. C.
[0163] It is also possible to perform straightening process after
the finish wire drawing. In this case, it is possible to further
reduce the HV hardness difference between the surface portion and
the center portion of the strand for saw wire, and to easily apply
a residual stress of -100 MPa or less to the surface portion of the
strand for saw wire. It is possible to easily make the residual
stress of the surface portion of the strand for saw wire to be -100
MPa or less, also by performing shot peening treatment after the
finish wire drawing.
[0164] The strand for saw wire according to the present embodiment
can be manufactured as above.
[0165] The strand for saw wire according to the present embodiment
has properties such that the wire diameter is small, the tensile
strength is high, and the breakage resistance is excellent.
Accordingly, when, in particular, the strand for saw wire is used
for a saw wire, it is possible to reduce a cutting cost at a time
of cutting an expensive ingot such as sapphire and SiC single
crystal, and the like. Further, it is possible to prevent the wire
breakage during a cutting operation. Therefore, industrial
contribution is quite remarkable. Note that the strand for saw wire
according to the present embodiment is quite suitable for a
fixed-abrasive saw wire, but, it is also possible to be used for a
free-abrasive saw wire.
EXAMPLE
[0166] Next, experiments conducted by the present inventors will be
described. Conditions and so on in these experiments are only
examples adopted for confirming feasibility and effects of the
present invention, and the present invention is not limited to
these examples.
[0167] (First Experiment)
[0168] In a first experiment, first, steel billets having chemical
components presented in Table 1 (steels No. 1A to 1W) were
subjected to hot rolling, and then cooled at cooling rates
presented in Table 2, thereby obtaining hot-rolled wire rods with
diameters presented in Table 2 (tests No. 1-1 to No. 1-44). Finish
rolling in the hot rolling was conducted within a temperature range
of 920.degree. C. to 950.degree. C. The cooling rates were
controlled through air blasting. Further, by methods described
below, a fraction of pearlite structure and a thickness of
cementite of each of the hot-rolled wire rods were measured.
Results thereof are presented in Table 2.
[0169] In the measurement of the fraction of pearlite structure of
each of the hot-rolled wire rods, pictures of 15 visual fields or
more were photographed at a magnification of .times.2000 with a
scanning electron microscope (SEM). Further, an area fraction of
pearlite structure in each visual field was measured through image
processing, and an average value of the area fractions was set as a
fraction of pearlite structure of the hot-rolled wire rod. Note
that a location at which observation (photographing) was performed
was set to a position apart from a surface of the hot-rolled wire
rod by about d/4 (d: diameter of hot-rolled wire rod).
[0170] In the measurement of the thickness of cementite of each of
the hot-rolled wire rods, a sample for observation under
transmission electron microscope (TEM) was taken from an
overlapping portion of wire rod of the hot-rolled wire rod, which
had been rolled in a coil shape after the hot rolling. Further,
visual fields perpendicular to cementite plate were selected, and
pictures of 10 visual fields or more were photographed at a
magnification of .times.10000 to .times.20000, with the TEM.
Further, a thickness of cementite in each visual field was
measured, and an average value of the thicknesses was set as a
thickness of cementite of the hot-rolled wire rod. Note that a
location at which observation (photographing) was performed was set
to a position apart from a surface of the hot-rolled wire rod by
about d/4.
TABLE-US-00001 TABLE 1 STEEL CHEMICAL COMPONENT (MASS %) No. C Si
Mn Cr P S N Ni Cu Mo V B PARAMETER P NOTE 1A 0.89 0.14 0.32 0.18
0.007 0.011 0.0037 -- -- -- -- -- 1015 EXAMPLE 1B 1.12 0.26 0.36
0.22 0.009 0.004 0.0032 -- -- -- -- 0.0016 1285 1C 0.90 0.22 0.12
0.46 0.005 0.005 0.0029 -- -- -- -- -- 1084 1D 1.05 0.35 0.40 0.10
0.005 0.006 0.0047 0.27 -- -- -- -- 1196 1E 0.94 0.29 0.36 0.21
0.009 0.005 0.0041 -- -- -- -- -- 1088 1F 0.97 0.18 0.36 0.30 0.007
0.006 0.0025 -- 0.14 -- -- -- 1126 1G 0.97 1.45 0.32 0.36 0.007
0.007 0.0031 -- -- -- -- -- 1261 1H 1.02 0.20 0.29 0.24 0.009 0.009
0.0041 -- -- -- -- -- 1174 1I 0.99 0.18 0.44 0.18 0.004 0.007
0.0024 -- -- 0.04 -- 0.0010 1126 1J 1.00 0.22 0.64 0.36 0.008 0.009
0.0042 0.15 0.10 -- -- -- 1167 1K 1.18 0.18 0.30 0.19 0.007 0.008
0.0040 -- -- -- -- -- 1339 1L 0.95 0.09 0.57 0.32 0.007 0.008
0.0020 -- -- -- 0.19 -- 1094 1M 0.98 0.55 0.19 0.14 0.008 0.009
0.0036 -- -- 0.03 0.04 0.0014 1150 1N 0.99 0.32 0.35 0.27 0.007
0.006 0.0024 0.08 -- -- -- 0.0016 1156 1O 1.15 0.71 0.96 0.08 0.007
0.008 0.0031 -- -- -- -- -- 1326 1P 1.09 0.17 0.41 0.04 0.006 0.009
0.0027 -- -- -- -- 0.0022 1212 1Q 0.82 0.21 0.48 0.00 0.012 0.006
0.0038 -- -- -- -- -- 911 COMPARATIVE 1R 0.80 0.19 0.46 0.15 0.008
0.010 0.0046 -- -- -- -- -- 913 EXAMPLES 1S 1.02 2.14 0.79 0.23
0.006 0.005 0.0022 -- -- -- -- -- 1352 1T 0.93 0.22 0.53 0.00 0.007
0.007 0.0026 -- -- -- -- -- 1032 1U 1.27 0.16 0.80 0.40 0.006 0.009
0.0042 -- -- -- -- -- 1461 1V 0.98 0.56 1.95 0.18 0.006 0.006
0.0023 -- -- -- -- -- 1122 1W 0.92 0.20 0.46 0.82 0.006 0.009
0.0036 -- -- -- -- -- 1158 n.b.) Underline means that the value is
out of the range of the present invention or out of the desirable
range. n.b.) "--" of the selective element means that the element
is not added o purpose.
TABLE-US-00002 TABLE 2 HOT-ROLLED WIRE ROD COOLING FRACTION
THICKNESS TEST STEEL DIAMETER RATE OF PERLITE OF CEMENTITE No. No.
(mm) (.degree. C./SEC) (%) (.mu.m) NOTE 1-1 1A 5.0 16 98.4 0.015
EXAMPLE 1-2 1A 4.6 18 98.6 0.015 1-3 1A 4.2 18 98.5 0.015 1-4 1B
4.1 19 99.2 0.020 1-5 1B 3.0 24 99.4 0.017 1-6 1C 4.5 19 98.3 0.014
1-7 1C 4.8 20 98.3 0.014 1-8 1C 5.0 22 98.2 0.015 1-9 1D 3.9 23
99.1 0.016 1-10 1D 4.1 21 99.2 0.017 1-11 1E 4.8 23 98.8 0.014 1-12
1E 3.9 21 98.7 0.016 1-13 1F 5.0 17 98.9 0.016 1-14 1F 4.1 19 98.9
0.015 1-15 1G 4.3 21 98.9 0.015 1-16 1G 3.6 23 98.8 0.014 1-17 1H
3.9 22 98.9 0.015 1-18 1H 4.5 18 98.9 0.016 1-19 1I 4.7 19 98.7
0.017 1-20 1I 3.3 22 98.6 0.014 1-21 1J 3.0 25 99.0 0.014 1-22 1J
3.7 22 98.9 0.015 1-23 1K 3.2 24 99.4 0.017 1-24 1K 3.8 21 99.3
0.019 1-25 1L 3.7 22 98.8 0.014 1-26 1L 4.4 19 98.7 0.015 1-27 1M
3.2 23 98.8 0.016 1-28 1M 3.9 20 98.9 0.015 1-29 1N 4.4 19 98.9
0.017 1-30 1N 3.6 23 99.1 0.016 1-31 1O 4.1 20 99.3 0.018 1-32 1O
3.3 21 99.3 0.018 1-33 1P 4.2 19 99.2 0.018 1-34 1P 3.4 20 99.1
0.017 1-35 1Q 5.6 14 96.4 0.013 COMPARATIVE 1-36 1R 5.1 16 96.7
0.012 EXAMPLE 1-37 1S 4.0 20 96.5 0.017 1-38 1T 4.7 17 98.6 0.015
1-39 1U 3.3 23 98.4 0.022 1-40 1V 4.2 18 96.0 0.016 1-41 1W 5.2 15
96.5 0.014 1-42 1K 4.5 7 99.2 0.032 1-43 1C 7.0 16 98.0 0.015 1-44
1O 4.1 20 99.3 0.018 n.b.) Underline means that the value is out of
the range of the present invention.
[0171] Thereafter, primary wire drawing was performed to obtain
primary wire-drawn materials with a predetermined wire diameter.
Subsequently, final patenting treatment was performed to obtain
patenting materials with wire diameters presented in Table 3. In
the final patenting treatment, temperatures of the materials were
maintained at an austenitizing temperature of 980.degree. C. for 45
seconds, and were kept at a pearlite transformation temperature of
575.degree. C. for 30 seconds. As a bath for causing pearlite
transformation, a Pb bath was used. Note that in the test No. 1-44,
the pearlite transformation temperature in the final patenting
treatment was set to 620.degree. C.
[0172] Subsequently, by methods described below, a fraction of
pearlite structure and a thickness of cementite of each of the
patenting materials were measured. Further, a tensile strength of
each of the patenting materials was measured based on JIS Z 2241.
Results thereof are presented in Table 3.
[0173] The measurement of fraction of pearlite structure of each of
the patenting materials was conducted through a method similar to
that of the measurement of fraction of pearlite structure of each
of the hot-rolled wire rods. Incidentally, a location at which
observation (photographing) was performed was set to a position
apart from a surface of the patenting material by about d.sub.p/4
(d.sub.p: diameter of patenting material).
[0174] The measurement of thickness of cementite of each of the
patenting materials was conducted through a method similar to that
of the measurement of thickness of cementite of each of the
hot-rolled wire rods. However, a location at which observation
(photographing) was performed was set to a position apart from a
surface layer of the patenting material by about d.sub.p/4
(d.sub.p: wire diameter of patenting material).
TABLE-US-00003 TABLE 3 PATENTING MATERIAL TENSILE FRACTION
THICKNESS TEST STEEL DIAMETER STRENGTH OF PERLITE OF CEMENTITE No.
No. (mm) (MPa) (%) (.mu.m) NOTE 1-1 1A 1.51 1406 98.6 0.009 EXAMPLE
1-2 1A 1.15 1392 98.7 0.009 1-3 1A 0.73 1415 98.7 0.009 1-4 1B 1.08
1656 99.7 0.011 1-5 1B 0.57 1632 99.7 0.012 1-6 1C 0.67 1466 98.8
0.009 1-7 1C 1.29 1475 98.9 0.009 1-8 1C 1.10 1477 98.8 0.009 1-9
1D 0.91 1568 99.7 0.011 1-10 1D 0.78 1579 99.6 0.010 1-11 1E 1.09
1460 99.4 0.010 1-12 1E 1.32 1478 99.4 0.009 1-13 1F 0.47 1507 99.6
0.010 1-14 1F 0.88 1512 99.5 0.010 1-15 1G 1.09 1632 99.2 0.009
1-16 1G 0.49 1620 99.2 0.010 1-17 1H 0.94 1565 99.8 0.011 1-18 1H
1.08 1577 99.7 0.010 1-19 1I 0.62 1508 99.6 0.010 1-20 1I 1.43 1521
99.5 0.009 1-21 1J 0.51 1549 99.7 0.010 1-22 1J 1.06 1560 99.6
0.009 1-23 1K 1.17 1701 99.8 0.012 1-24 1K 1.10 1687 99.9 0.013
1-25 1L 0.51 1615 99.4 0.010 1-26 1L 0.97 1624 99.4 0.009 1-27 1M
1.03 1551 99.6 0.010 1-28 1M 0.79 1573 99.5 0.009 1-29 1N 0.85 1538
99.7 0.010 1-30 1N 1.10 1530 99.7 0.010 1-31 1O 1.04 1679 99.8
0.012 1-32 1O 0.43 1688 99.9 0.011 1-33 1P 0.88 1594 99.8 0.011
1-34 1P 0.92 1585 99.7 0.012 1-35 1Q 1.04 1273 97.6 0.009
COMPARATIVE 1-36 1R 1.58 1282 97.7 0.008 EXAMPLE 1-37 1S 0.58 1674
97.8 0.011 1-38 1T 1.38 1404 99.1 0.010 1-39 1U 0.88 1707 99.9
0.014 1-40 1V 1.04 1414 96.8 0.011 1-41 1W 0.48 1449 97.4 0.009
1-42 1K 1.10 1683 99.9 0.013 1-43 1C 0.67 1458 98.7 0.009 1-44 1O
0.74 1460 99.4 0.021 n.b.) Underline means that the value is out of
the range of the present invention or out of the desirable
range.
[0175] Subsequently, brass plating was applied to each of the
patenting materials. Thereafter, finish wire drawing was performed
to obtain strands for saw wires with diameters presented in Table
4. The finish wire drawing was conducted under conditions in which
wire drawing strains presented in Table 4 were provided, a diamond
die with a die angle of 10.degree. was used, and a wire drawing
speed was set to 900 m/minute. Further, a reduction of area in a
final die was set to 4% to 7%. Further, a lubricant with a friction
coefficient of 0.1 or less was used, and a temperature of the
lubricant was controlled to 70.degree. C. or less. After the finish
wire drawing, a roller-type straightening machine was used to
perform straightening process.
TABLE-US-00004 TABLE 4 STRAND FOR SAW WIRE WIRE DRAWING PARA- TEST
STEEL DIAMETER STRAIN METER No. No. (mm) .epsilon. Q NOTE 1-1 1A
0.18 4.25 436 EXAMPLE 1-2 1A 0.14 4.21 429 1-3 1A 0.08 4.43 468 1-4
1B 0.16 3.81 401 1-5 1B 0.08 3.94 421 1-6 1C 0.09 4.00 396 1-7 1C
0.17 4.05 404 1-8 1C 0.14 4.12 415 1-9 1D 0.12 4.05 427 1-10 1D
0.10 4.10 436 1-11 1E 0.14 4.11 420 1-12 1E 0.16 4.22 438 1-13 1F
0.06 4.12 426 1-14 1F 0.11 4.17 435 1-15 1G 0.16 3.83 382 1-16 1G
0.07 3.89 390 1-17 1H 0.12 4.11 433 1-18 1H 0.14 4.08 428 1-19 1I
0.08 4.11 428 1-20 1I 0.18 4.15 434 1-21 1J 0.07 3.98 409 1-22 1J
0.14 4.05 420 1-23 1K 0.18 3.74 400 1-24 1K 0.16 3.86 418 1-25 1L
0.07 3.96 398 1-26 1L 0.14 3.88 386 1-27 1M 0.14 4.00 409 1-28 1M
0.10 4.13 430 1-29 1N 0.11 4.10 426 1-30 1N 0.15 3.98 407 1-31 1O
0.14 4.02 438 1-32 1O 0.06 3.95 427 1-33 1P 0.12 3.98 422 1-34 1P
0.12 4.07 437 1-35 1Q 0.10 4.69 509 COMPARATIVE 1-36 1R 0.16 4.58
483 EXAMPLE 1-37 1S 0.08 3.95 407 1-38 1T 0.14 4.57 503 1-39 1U --
-- -- 1-40 1V 0.13 4.15 433 1-41 1W 0.06 4.14 422 1-42 1K 0.16 3.86
418 1-43 1C 0.09 4.00 396 1-44 1O 0.10 3.99 433 n.b.) Underline
means that the value is out of the range of the present invention
or out of the desirable range.
[0176] Regarding each of the strands for saw wires manufactured as
above, a fraction of wire-drawn pearlite structure, a ratio between
a maximum value and a minimum value of lamellar spacing, a tensile
strength, a twist number under tension, a tensile strength ratio
under twisting, a tensile elongation under twisting, a difference
in Vickers hardness (HV hardness difference), and a residual stress
of a surface portion were measured, through methods described
below. Results thereof are presented in Table 5.
[0177] In the measurement of fraction of wire-drawn pearlite
structure of each of the strands for saw wires, pictures of 15
visual fields or more were photographed at a magnification of
.times.10000 to .times.20000 with the SEM. Further, an area
fraction of wire-drawn pearlite structure in each visual field was
measured through image processing, and an average value of the area
fractions was set as a fraction of wire-drawn pearlite structure of
the strand for saw wire. Note that a location at which observation
(photographing) was performed was set to a position apart from a
surface of the strand for saw wire by about d.sub.w/4 (d.sub.w:
diameter of strand for saw wire).
[0178] In the measurement of the ratio between the maximum value
and the minimum value of the lamellar spacing, observation of
structure was conducted with the TEM at a magnification of
.times.100000, in which the maximum value and the minimum value of
the lamellar spacing were measured, and a ratio between these
values was calculated.
[0179] The tensile strength of each of the strands for saw wires
was measured based on JIS Z 2241. At this time, a grip-to-grip
distance was set to 100 mm.
[0180] In the measurement of the twist number under tension, a
twist test was conducted in which a grip-to-grip distance was set
to 100 mm, and a twisting speed was set to 60 rpm while applying a
tension equal to "a tensile strength".times."a cross-sectional area
of wire".times.0.5, and the twist number until the occurrence of
breakage was measured. The test was performed 5 times on each of
the strands for saw wires, and an average value of the twist
numbers was set as the twist number under tension.
[0181] In the measurement of the tensile strength ratio under
twisting and the measurement of the tensile elongation under
twisting, the strand for saw wire was twisted 5 times by setting a
grip-to-grip distance to 100 times a wire diameter, and then
subjected to a tensile test, in which tensile strength and
elongation were measured. Further, a quotient obtained by dividing
the tensile strength achieved in the tensile test by a tensile
strength in a state of applying no twisting (tensile strength ratio
under twisting) was calculated. The test was performed 5 times on
each of the strands for saw wires, and average values of the
aforementioned quotients (tensile strength ratios under twisting)
and elongations were set as the tensile strength ratio under
twisting and the tensile elongation under twisting,
respectively.
[0182] In the measurement of the difference in Vickers hardness (HV
hardness difference), a Vickers hardness of a surface portion in
which a depth from a surface of the strand for saw wire is within a
range of "a wire diameter".times.0.2 or less and a Vickers hardness
of a center portion in which a distance from a center of the strand
for saw wire is within a range of "the wire diameter".times.0.2 or
less, were measured based on JIS Z 2244. Subsequently, a difference
thereof was calculated.
[0183] In the measurement of the residual stresses of the surface
portions of the strands for saw wires, the strands for saw wires
with a length of 100 mm were arranged with no space therebetween,
and by using X-ray, the residual stresses in a wire drawing
direction in center portions of the arranged strands for saw wires
were measured.
[0184] [Table 5]
[0185] As presented in Table 5, in the tests No. 1-1 to No. 1-34
being examples of the present invention, excellent properties were
achieved such that the tensile strength was 4000 MPa or more, the
twist number under tension was 5 or more, the tensile strength
ratio under twisting was 80% or more, and the tensile elongation
under twisting was 2% or more. Namely, the strands for saw wires
with high strength and high ductility were realized.
[0186] On the contrary, the tests No. 1-35 to No. 1-41 are
comparative examples in which the chemical components of the steel
billets and/or the conditions in the finish wire drawing were out
of the range of the present invention.
[0187] Specifically, in the test No. 1-35, the C content was less
than the lower limit of the present invention, Cr was not
contained, and the value of the parameter P represented by the
(equation 1) was less than 1000. In the test No. 1-36, the C
content was less than the lower limit of the present invention, and
the value of the parameter P was less than 1000. Accordingly, in
the tests No. 1-35 and No. 1-36, the fractions of pearlite
structures in the hot-rolled wire rods, the patenting materials and
the strands for saw wires were less than the lower limits of the
present invention. Further, work hardening rates were low.
Accordingly, there was conducted the finish wire drawing in which
the wire drawing strain was 4.5 or more, in order to achieve the
tensile strength of 4000 MPa or more. As a result, it was not
possible to achieve sufficient twist number under tension, tensile
strength ratio under twisting, and tensile elongation under
twisting. Further, as a result of conducting observation of
structures with the TEM at a magnification of .times.100000 in
cross sections perpendicular to the wire drawing direction of the
strands for saw wires in the tests No. 1-35 and No. 1-36, it was
confirmed that, qualitatively, there were provided large variations
in the lamellar spacing.
[0188] In the test No. 1-37, the Si content exceeded the range of
the present invention, resulting in that the non-pearlite structure
was excessively generated. For this reason, in the test No. 1-37,
the fractions of pearlite structures in the hot-rolled wire rod,
the patenting material and the strand for saw wire were less than
the lower limits of the present invention. Therefore, it was not
possible to achieve sufficient twist number under tension, tensile
strength ratio under twisting, and tensile elongation under
twisting.
[0189] In the test No. 1-38, Cr was not added. For this reason, the
work hardening rate was low. Accordingly, there was conducted the
finish wire drawing in which the wire drawing strain was 4.5 or
more in order to achieve the tensile strength of 4000 MPa or more.
As a result, it was not possible to achieve sufficient twist number
under tension, tensile strength ratio under twisting, and tensile
elongation under twisting of the strand for saw wire. Further, the
TEM observation similar to that for the strands for saw wires in
the tests No. 1-35 and No. 1-36 was conducted, and it was confirmed
that, qualitatively, there was provided a large variation in the
lamellar spacing.
[0190] In the test No. 1-39, the C content exceeded the range of
the present invention, and proeutectoid cementite was generated.
For this reason, in the test No. 1-39, the wire breakage frequently
occurred during the finish wire drawing, and it was not possible to
manufacture the strand for saw wire.
[0191] In the test No. 1-40, the Mn content exceeded the range of
the present invention. In the test No. 1-41, the Cr content
exceeded the range of the present invention. Accordingly, in the
tests No. 1-40 and No. 1-41, bainite was excessively contained in
the hot-rolled wire rods and the patenting materials, resulting in
that the fractions of pearlite structures in the hot-rolled wire
rods, the patenting materials and the strands for saw wires were
less than the lower limits of the present invention. Therefore, it
was not possible to achieve sufficient twist number under tension,
tensile strength ratio under twisting, and tensile elongation under
twisting.
[0192] The tests No. 1-42 and No. 1-43 are comparative examples in
which the conditions of the hot rolling were out of the range of
the present invention.
[0193] Specifically, in the test No. 1-42, the cooling rate after
the hot rolling was less than the lower limit of the present
invention, resulting in that cementite was thick. For this reason,
micro-voids were generated in the strand for saw wire, and it was
not possible to achieve sufficient twist number under tension and
tensile strength ratio under twisting.
[0194] In the test No. 1-43, the diameter of the hot-rolled wire
rod exceeded the range of the present invention, so that the
intermediate wire drawing and the intermediate heat treatment were
repeatedly conducted. As a result, it was not possible to achieve
sufficient twist number under tension and tensile strength ratio
under twisting of the strand for saw wire.
[0195] In the test No. 1-44, the thickness of cementite of the
patenting material exceeded the range of the present invention,
resulting in that micro-voids were generated in the strand for saw
wire. For this reason, it was not possible to achieve sufficient
twist number under tension, tensile strength ratio under twisting,
and tensile elongation under twisting. Note that in the test No.
1-44, the temperature of the patenting treatment (620.degree. C.)
was higher than the desirable temperature range (520.degree. C. to
600.degree. C.)
[0196] (Second Experiment)
[0197] In a second experiment, first, steel billets having chemical
components presented in Table 6 (steels No. 2A to 2W) were
subjected to hot rolling, and then cooled at cooling rates
presented in Table 7, thereby obtaining hot-rolled wire rods with
diameters presented in Table 7 (tests No. 2-1 to No. 2-45). Finish
rolling in the hot rolling was conducted within a temperature range
of 920.degree. C. to 950.degree. C. The cooling rates were
controlled through air blasting. Further, by methods similar to
those of the first experiment, a fraction of pearlite structure and
a thickness of cementite of each of the hot-rolled wire rods were
measured. Results thereof are presented in Table 7.
TABLE-US-00005 TABLE 6 STEEL CHEMICAL COMPONENT (MASS %) No. C Si
Mn Cr P S N Ni Cu Mo V B PARAMETER P NOTE 2A 0.94 0.18 0.30 0.27
0.007 0.005 0.0029 -- -- -- -- -- 1089 EXAMPLE 2B 1.12 0.26 0.36
0.22 0.009 0.004 0.0032 -- -- -- -- 0.0016 1285 2C 1.10 0.18 0.30
0.17 0.008 0.007 0.0031 -- -- 0.03 -- 0.0018 1248 2D 1.05 0.35 0.40
0.10 0.005 0.006 0.0047 0.27 -- -- -- -- 1196 2E 0.96 0.22 0.33
0.47 0.008 0.005 0.0034 -- -- -- -- -- 1148 2F 0.97 0.18 0.36 0.30
0.007 0.006 0.0025 -- 0.14 -- -- -- 1126 2G 1.17 1.32 0.29 0.13
0.008 0.005 0.0024 -- -- -- -- -- 1430 2H 1.02 0.20 0.29 0.24 0.009
0.009 0.0041 -- -- -- -- -- 1174 2I 0.99 0.18 0.44 0.18 0.004 0.007
0.0024 -- -- 0.04 -- 0.0010 1126 2J 1.00 0.22 0.64 0.36 0.008 0.009
0.0042 0.15 0.10 -- -- -- 1167 2K 1.18 0.18 0.30 0.19 0.007 0.008
0.0040 -- -- -- -- -- 1339 2L 1.14 0.07 0.61 0.16 0.005 0.006
0.0028 -- -- -- 0.13 -- 1273 2M 0.98 0.55 0.19 0.14 0.008 0.009
0.0036 -- -- 0.03 0.04 0.0014 1150 2N 0.99 0.32 0.35 0.27 0.007
0.006 0.0024 0.08 -- -- -- 0.0016 1156 2O 1.15 0.71 0.96 0.08 0.007
0.008 0.0031 -- -- -- -- -- 1326 2P 1.09 0.17 0.41 0.04 0.006 0.009
0.0027 -- -- -- -- 0.0022 1212 2Q 0.82 0.21 0.48 0.00 0.012 0.006
0.0038 -- -- -- -- -- 911 COMPARATIVE 2R 0.80 0.19 0.46 0.15 0.008
0.010 0.0046 -- -- -- -- -- 913 EXAMPLE 2S 1.02 2.14 0.79 0.23
0.006 0.005 0.0022 -- -- -- -- -- 1352 2T 0.93 0.22 0.53 0.00 0.007
0.007 0.0026 -- -- -- -- -- 1032 2U 1.27 0.16 0.80 0.40 0.006 0.009
0.0042 -- -- -- -- -- 1461 2V 0.98 0.56 1.95 0.18 0.006 0.006
0.0023 -- -- -- -- -- 1122 2W 0.92 0.20 0.46 0.82 0.006 0.009
0.0036 -- -- -- -- -- 1158 n.b.) Underline means that the value is
out of the range of the present invention or out of the desirable
range. n.b.) "--" of the selective element means that the element
is not added o purpose.
TABLE-US-00006 TABLE 7 HOT-ROLLED WIRE ROD COOLING FRACTION
THICKNESS TEST STEEL DIAMETER RATE OF PERLITE OF CEMENTITE No. No.
(mm) (.degree. C./SEC) (%) (.mu.m) NOTE 2-1 2A 3.2 20 98.7 0.015
EXAMPLE 2-2 2A 5.5 18 98.6 0.016 2-3 2A 4.3 18 98.7 0.015 2-4 2B
4.1 19 99.2 0.020 2-5 2B 3.0 24 99.4 0.017 2-6 2C 4.8 21 98.9 0.018
2-7 2C 3.7 23 99.0 0.016 2-8 2D 3.9 23 99.1 0.016 2-9 2D 4.1 21
99.2 0.017 2-10 2E 5.0 18 98.8 0.016 2-11 2E 3.4 23 99.1 0.014 2-12
2F 5.0 17 98.9 0.016 2-13 2F 4.1 19 98.9 0.015 2-14 2G 3.8 24 99.5
0.018 2-15 2G 3.0 19 99.4 0.017 2-16 2H 3.9 22 98.9 0.015 2-17 2H
4.5 18 98.9 0.016 2-18 2I 4.7 19 98.7 0.017 2-19 2I 3.3 22 98.6
0.014 2-20 2J 3.0 25 99.0 0.014 2-21 2J 3.7 22 98.9 0.015 2-22 2K
3.2 24 99.4 0.017 2-23 2K 3.8 21 99.3 0.019 2-24 2K 3.0 25 99.4
0.018 2-25 2L 3.0 20 99.2 0.016 2-26 2L 4.2 22 99.3 0.018 2-27 2M
3.2 23 98.8 0.016 2-28 2M 3.9 20 98.9 0.015 2-29 2M 4.8 20 98.9
0.015 2-30 2N 4.4 19 98.9 0.017 2-31 2N 3.6 23 99.1 0.016 2-32 2O
4.1 20 99.3 0.018 2-33 2O 3.3 21 99.3 0.018 2-34 2P 4.2 19 99.2
0.018 2-35 2P 3.4 20 99.1 0.017 2-36 2Q 5.6 14 96.4 0.013
COMPARATIVE 2-37 2R 5.1 16 96.7 0.012 EXAMPLE 2-38 2S 4.0 20 96.5
0.017 2-39 2T 4.7 17 98.6 0.015 2-40 2U 3.3 23 98.4 0.022 2-41 2V
4.2 18 96.0 0.016 2-42 2W 5.2 15 96.5 0.014 2-43 2K 4.5 7 99.2
0.032 2-44 2B 7.5 15 99.1 0.022 2-45 2O 4.1 20 99.3 0.018 n.b.)
Underline means that the value is out of the range of the present
invention.
[0198] Thereafter, primary wire drawing was performed to obtain
primary wire-drawn materials with a predetermined wire diameter.
Subsequently, final patenting treatment was performed to obtain
patenting materials with wire diameters presented in Table 8. In
the final patenting treatment, temperatures of the materials were
maintained at an austenitizing temperature of 980.degree. C. for 45
seconds, and were kept at a pearlite transformation temperature of
575.degree. C. for 30 seconds. As a bath for causing pearlite
transformation, a Pb bath was used. Note that in the test No. 2-45,
the pearlite transformation temperature in the final patenting
treatment was set to 620.degree. C.
[0199] Subsequently, by methods similar to those of the first
experiment, a tensile strength, a fraction of pearlite structure
and a thickness of cementite of each of the patenting materials
were measured. Results thereof are presented in Table 8.
TABLE-US-00007 TABLE 8 PATENTING MATERIAL TENSILE FRACTION
THICKNESS TEST STEEL DIAMETER STRENGTH OF PERLITE OF CEMENTITE No.
No. (mm) (MPa) (%) (.mu.m) NOTE 2-1 2A 1.02 1480 99.4 0.009 EXAMPLE
2-2 2A 0.63 1493 99.5 0.010 2-3 2A 1.50 1475 99.5 0.010 2-4 2B 1.00
1646 99.6 0.012 2-5 2B 0.56 1635 99.6 0.012 2-6 2C 1.31 1639 99.6
0.012 2-7 2C 0.89 1627 99.7 0.012 2-8 2D 1.24 1572 99.7 0.011 2-9
2D 0.78 1574 99.7 0.010 2-10 2E 1.08 1540 99.5 0.011 2-11 2E 0.59
1535 99.6 0.010 2-12 2F 0.58 1505 99.6 0.010 2-13 2F 1.09 1506 99.4
0.010 2-14 2G 0.98 1720 99.8 0.013 2-15 2G 0.72 1714 99.7 0.012
2-16 2H 0.88 1568 99.7 0.011 2-17 2H 1.12 1566 99.7 0.010 2-18 2I
0.73 1510 99.6 0.010 2-19 2I 1.20 1519 99.7 0.011 2-20 2J 0.54 1555
99.6 0.010 2-21 2J 1.27 1551 99.6 0.009 2-22 2K 0.83 1690 99.8
0.014 2-23 2K 1.12 1686 99.9 0.013 2-24 2K 0.72 1694 99.9 0.013
2-25 2L 0.56 1673 99.8 0.012 2-26 2L 0.91 1689 99.9 0.012 2-27 2M
0.59 1584 99.5 0.010 2-28 2M 1.12 1581 99.6 0.009 2-29 2M 0.93 1589
99.6 0.009 2-30 2N 0.89 1541 99.8 0.010 2-31 2N 1.37 1549 99.7
0.011 2-32 2O 1.14 1675 99.8 0.012 2-33 2O 0.49 1683 99.8 0.011
2-34 2P 0.80 1591 99.8 0.012 2-35 2P 1.18 1583 99.8 0.012 2-36 2Q
1.04 1273 97.6 0.009 COMPARATIVE 2-37 2R 1.58 1282 97.7 0.008
EXAMPLE 2-38 2S 0.65 1651 97.3 0.011 2-39 2T 1.02 1410 99.1 0.010
2-40 2U 0.88 1707 99.9 0.014 2-41 2V 1.11 1420 96.9 0.011 2-42 2W
0.53 1463 97.5 0.009 2-43 2K 1.27 1675 99.9 0.013 2-44 2B 0.85 1635
99.7 0.012 2-45 2O 0.85 1469 99.4 0.022 n.b.) Underline means that
the value is out of the range of the present invention.
[0200] Subsequently, brass plating was applied to each of the
patenting materials. Thereafter, finish wire drawing was performed
to obtain strands for saw wires with diameters presented in Table
9. The finish wire drawing was conducted under conditions in which
wire drawing strains presented in Table 9 were provided, a diamond
die with a die angle of 10.degree. was used, and a wire drawing
speed was set to 900 m/minute. Further, a reduction of area in a
final die was set to 4% to 7%. Further, a lubricant with a friction
coefficient of 0.1 or less was used, and a temperature of the
lubricant was controlled to 70.degree. C. or less. After the finish
wire drawing, a roller-type straightening machine was used to
perform straightening process.
TABLE-US-00008 TABLE 9 STRAND FOR SAW WIRE WIRE DRAWING PARA- TEST
STEEL DIAMETER STRAIN METER No. No. (mm) .epsilon. Q NOTE 2-1 2A
0.12 4.28 449 EXAMPLE 2-2 2A 0.07 4.41 473 2-3 2A 0.16 4.48 486 2-4
2B 0.13 4.09 445 2-5 2B 0.07 4.15 455 2-6 2C 0.16 4.20 461 2-7 2C
0.10 4.38 494 2-8 2D 0.15 4.22 456 2-9 2D 0.09 4.32 474 2-10 2E
0.13 4.24 445 2-11 2E 0.07 4.26 449 2-12 2F 0.07 4.22 443 2-13 2F
0.12 4.41 478 2-14 2G 0.13 4.03 443 2-15 2G 0.09 4.17 467 2-16 2H
0.10 4.36 477 2-17 2H 0.14 4.16 441 2-18 2I 0.08 4.41 481 2-19 2I
0.14 4.30 461 2-20 2J 0.06 4.39 479 2-21 2J 0.15 4.28 459 2-22 2K
0.10 4.23 479 2-23 2K 0.14 4.15 465 2-24 2K 0.08 4.40 511 2-25 2L
0.07 4.17 462 2-26 2L 0.12 4.05 442 2-27 2M 0.07 4.28 455 2-28 2M
0.13 4.30 459 2-29 2M 0.10 4.45 487 2-30 2N 0.11 4.19 441 2-31 2N
0.16 4.30 461 2-32 2O 0.15 4.06 445 2-33 2O 0.06 4.19 467 2-34 2P
0.09 4.36 488 2-35 2P 0.14 4.27 472 2-36 2Q 0.10 4.69 509
COMPARATIVE 2-37 2R 0.16 4.58 483 EXAMPLE 2-38 2S 0.08 4.19 446
2-39 2T 0.10 4.65 520 2-40 2U -- -- -- 2-41 2V 0.13 4.29 457 2-42
2W 0.06 4.36 460 2-43 2K 0.16 4.15 465 2-44 2B 0.11 4.10 447 2-45
2O 0.10 4.29 485 n.b.) Underline means that the value is out of the
range of the present invention.
[0201] Regarding each of the strands for saw wires manufactured as
above, a fraction of wire-drawn pearlite structure, a ratio between
a maximum value and a minimum value of lamellar spacing, a tensile
strength, a twist number under tension, a tensile strength ratio
under twisting, a tensile elongation under twisting, a difference
in Vickers hardness (HV hardness difference), and a residual stress
of a surface portion were measured, through methods similar to
those of the first experiment. Results thereof are presented in
Table 10.
TABLE-US-00009 TABLE 10 STRAND FOR SAW WIRE FRACTION RATIO TENSILE
OF BETWEEN TWIST STRENGTH TENSILE WIRE- MAX. AND NUMBER RATIO
ELONGATION HV DRAWN MIN. OF TENSILE UNDER UNDER UNDER HARDNESS
RESIDUAL TEST STEEL PERLITE LAMELLAR STRENGTH TENSION TWISTINIG
TWISTING DIFFER- STRESS No. No. (%) SPACING (MPa) (TIME) (%) (%)
ENCE (MPa) NOTE 2-1 2A 99.5 8.3 4367 10.8 94 2.9 43 -540 EXAMPLE
2-2 2A 99.6 8.9 4583 10.1 92 3.0 36 -562 2-3 2A 99.6 9.0 4690 7.0
92 2.8 48 -424 2-4 2B 99.8 7.6 4484 11.4 96 2.6 30 -667 2-5 2B 99.8
7.9 4580 11.2 96 2.4 32 -670 2-6 2C 99.6 8.0 4541 11.8 96 2.9 27
-590 2-7 2C 99.8 8.8 4795 11.2 94 3.0 36 -607 2-8 2D 99.6 8.1 4379
13.9 97 3.2 29 -619 2-9 2D 99.7 8.6 4538 13.5 97 2.9 37 -594 2-10
2E 99.7 8.2 4604 12.8 95 2.8 47 -709 2-11 2E 99.6 8.3 4639 13.9 97
3.3 40 -682 2-12 2F 99.6 7.7 4369 11.6 97 3.0 29 -710 2-13 2F 99.5
9.0 4687 11.2 96 3.1 34 -712 2-14 2G 99.9 7.4 4693 12.3 94 3.1 42
-590 2-15 2G 99.7 7.9 4812 11.7 93 2.8 49 -584 2-16 2H 99.8 8.8
4685 10.7 92 3.1 18 -579 2-17 2H 99.7 7.8 4356 11.1 96 3.2 12 -595
2-18 2I 99.6 9.0 4574 10.6 96 3.0 29 -458 2-19 2I 99.7 8.4 4393
11.9 97 3.1 23 -436 2-20 2J 99.7 8.9 4751 9.8 94 2.9 33 -481 2-21
2J 99.7 8.4 4562 10.7 97 3.2 21 -516 2-22 2K 99.9 8.1 4797 11.7 92
3.0 49 -631 2-23 2K 99.8 7.9 4703 10.6 94 3.1 40 -673 2-24 2K 99.9
9.0 5163 10.1 92 3.0 24 -707 2-25 2L 99.9 7.9 4708 11.2 92 2.9 37
-744 2-26 2L 99.9 7.4 4517 13.6 98 3.0 22 -757 2-27 2M 99.6 8.4
4500 9.3 93 3.2 23 -838 2-28 2M 99.5 8.5 4532 9.8 93 3.1 34 -871
2-29 2M 99.6 9.0 4727 5.5 91 2.8 45 -346 2-30 2N 99.8 8.0 4375 13.1
97 2.9 28 -615 2-31 2N 99.8 8.4 4553 12.6 97 3.0 39 -686 2-32 2O
99.8 7.6 4327 11.9 94 3.1 29 -580 2-33 2O 99.9 8.0 4523 9.6 93 3.0
29 -557 2-34 2P 99.8 8.7 4593 10.8 97 3.2 29 -549 2-35 2P 99.8 8.4
4448 10.1 96 3.3 39 -564 2-36 2Q 97.6 11.5 4125 2.1 54 1.8 88 -428
COMPAR- 2-37 2R 97.8 10.9 4141 2.4 62 1.6 75 -401 ATIVE 2-38 2S
97.5 8.1 4434 1.3 58 1.4 42 -289 EXAMPLE 2-39 2T 99.1 11.2 4243 1.7
70 1.8 68 -389 2-40 2U -- -- -- -- -- -- -- 2-41 2V 96.8 8.6 4130
2.6 71 1.6 42 -304 2-42 2W 97.4 8.5 4437 3.0 68 1.1 64 -458 2-43 2K
99.9 8.0 4660 4.1 74 1.5 55 -631 2-44 2B 99.8 7.8 4577 4.6 77 1.8
37 -623 2-45 2O 99.4 8.6 4301 3.5 54 1.6 80 -259 n.b.) Underline
means that the value is out of the range of the present
invention.
[0202] As presented in Table 10, in the tests No. 2-1 to No. 2-35
being examples of the present invention, excellent properties were
achieved such that the tensile strength was 4300 MPa or more, which
is a favorable value, the twist number under tension was 5 or more,
the tensile strength ratio under twisting was 80% or more, and the
tensile elongation under twisting was 2% or more. Namely, the
strands for saw wires with high strength and high ductility were
realized.
[0203] On the contrary, the tests No. 2-36 to No. 2-42 are
comparative examples in which the chemical components of the steel
billets and/or the conditions in the finish wire drawing were out
of the range of the present invention.
[0204] Specifically, in the test No. 2-36, the C content was less
than the lower limit of the present invention, Cr was not
contained, and the value of the parameter P was less than 1000. In
the test No. 2-37, the C content was less than the lower limit of
the present invention, and the value of the parameter P was less
than 1000. Accordingly, in the tests No. 2-36 and No. 2-37, the
fractions of pearlite structures in the hot-rolled wire rods, the
patenting materials and the strands for saw wires were less than
the lower limits of the present invention. Further, work hardening
rates were low. Accordingly, there was conducted the finish wire
drawing in which the wire drawing strain was 4.5 or more, in order
to achieve the tensile strength of 4000 MPa or more. As a result,
it was not possible to achieve sufficient twist number under
tension, tensile strength ratio under twisting, and tensile
elongation under twisting. Further, as a result of the TEM
observation, it was confirmed that, qualitatively, there were
provided large variations in the lamellar spacing.
[0205] In the test No. 2-38, the Si content exceeded the range of
the present invention, resulting in that the non-pearlite structure
was excessively generated. For this reason, in the test No. 2-38,
the fractions of pearlite structures in the hot-rolled wire rod,
the patenting material and the strand for saw wire were less than
the lower limits of the present invention. Therefore, it was not
possible to achieve sufficient twist number under tension, tensile
strength ratio under twisting, and tensile elongation under
twisting.
[0206] In the test No. 2-39, Cr was not added. For this reason, the
work hardening rate was low. Accordingly, there was conducted the
finish wire drawing in which the wire drawing strain was 4.5 or
more in order to achieve the tensile strength of 4000 MPa or more.
As a result, it was not possible to achieve sufficient twist number
under tension, tensile strength ratio under twisting, and tensile
elongation under twisting of the strand for saw wire. Further, as a
result of the TEM observation, it was confirmed that,
qualitatively, there was provided a large variation in the lamellar
spacing.
[0207] In the test No. 2-40, the C content exceeded the range of
the present invention, and proeutectoid cementite was generated.
For this reason, in the test No. 2-40, the wire breakage frequently
occurred during the finish wire drawing, and it was not possible to
manufacture the strand for saw wire.
[0208] In the test No. 2-41, the Mn content exceeded the range of
the present invention. In the test No. 2-42, the Cr content
exceeded the range of the present invention. Accordingly, in the
tests No. 2-41 and No. 2-42, bainite was excessively contained in
the hot-rolled wire rods and the patenting materials, resulting in
that the fractions of pearlite structures in the hot-rolled wire
rods, the patenting materials and the strands for saw wires were
less than the lower limits of the present invention. Therefore, it
was not possible to achieve sufficient twist number under tension,
tensile strength ratio under twisting, and tensile elongation under
twisting.
[0209] The tests No. 2-43 and No. 2-44 are comparative examples in
which the conditions of the hot rolling were out of the range of
the present invention.
[0210] Specifically, in the test No. 2-43, the cooling rate after
the hot rolling was less than the lower limits of the present
invention, resulting in that cementite was thick. For this reason,
micro-voids were generated in the strand for saw wire, and it was
not possible to achieve sufficient twist number under tension and
tensile strength ratio under twisting.
[0211] In the test No. 2-44, the diameter of the hot-rolled wire
rod exceeded the range of the present invention, so that the
intermediate wire drawing and the intermediate heat treatment were
repeatedly conducted. As a result, it was not possible to achieve
sufficient twist number under tension and tensile strength ratio
under twisting of the strand for saw wire.
[0212] In the test No. 2-45, the thickness of cementite of the
patenting material exceeded the range of the present invention,
resulting in that micro-voids were generated in the strand for saw
wire. For this reason, it was not possible to achieve sufficient
twist number under tension, tensile strength ratio under twisting,
and tensile elongation under twisting. Note that in the test No.
2-45, the temperature of the patenting treatment (620.degree. C.)
was higher than the desirable temperature range (520.degree. C. to
600.degree. C.)
INDUSTRIAL APPLICABILITY
[0213] The present invention may be utilized in industries related
to saw wires used for cutting various materials, for example.
* * * * *