U.S. patent application number 13/134210 was filed with the patent office on 2011-11-24 for high-carbon steel wire rod of high ductility.
This patent application is currently assigned to NIPPON STEEL CORPORATION. Invention is credited to Hitoshi Demachi, Nobuyuki Komiya, Makoto Kosaka, Nariyasu Muroga, Kenichi Nakamura, Seiki Nishida, Shouichi Ohashi, Susumu Sahara, Shingo Yamasaki.
Application Number | 20110284139 13/134210 |
Document ID | / |
Family ID | 38778746 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110284139 |
Kind Code |
A1 |
Nishida; Seiki ; et
al. |
November 24, 2011 |
High-carbon steel wire rod of high ductility
Abstract
A high-carbon steel wire rod of high ductility for steel cord
and the like is provided that experiences little breakage during
drawing. The high-carbon steel wire rod of high ductility is a
high-carbon steel wire rod fabricated by hot rolling that that has
a carbon content of 0.7 mass % or greater, wherein 95% or greater
of the wire rod metallographic structure is pearlite structure and
the maximum pearlite block size of pearlite at the core of the
hot-rolled wire rod is 65 .mu.m or less. The high-carbon steel wire
rod of high ductility has a tensile strength in a range of
{248+980.times.(C mass %)}.+-.40 MPa} and a reduction of area of
{72.8-40.times.(C mass %) %} or greater. The high-carbon steel wire
rod of high ductility is characterized in that the average pearlite
block size at the core of the hot-rolled wire rod constituted by
ferrite grain boundaries of an orientation difference of 9 degrees
or greater as measured with an EBSP analyzer is 10 .mu.m or greater
and 30 .mu.m or less.
Inventors: |
Nishida; Seiki; ( Tokyo,
JP) ; Yamasaki; Shingo; (Tokyo, JP) ; Demachi;
Hitoshi; (Tokyo, JP) ; Muroga; Nariyasu;
(Tokyo, JP) ; Ohashi; Shouichi; (Tokyo, JP)
; Nakamura; Kenichi; (Tokyo, JP) ; Kosaka;
Makoto; ( Tokyo, JP) ; Komiya; Nobuyuki; (
Tokyo, JP) ; Sahara; Susumu; (Tokyo, JP) |
Assignee: |
NIPPON STEEL CORPORATION
Tokyo
JP
|
Family ID: |
38778746 |
Appl. No.: |
13/134210 |
Filed: |
May 31, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11989676 |
Jan 28, 2008 |
|
|
|
PCT/JP2007/061497 |
May 31, 2007 |
|
|
|
13134210 |
|
|
|
|
Current U.S.
Class: |
148/598 |
Current CPC
Class: |
C21D 8/065 20130101;
C22C 38/002 20130101; C22C 38/18 20130101; D07B 1/066 20130101;
C22C 38/04 20130101; C22C 38/02 20130101; B21B 1/16 20130101 |
Class at
Publication: |
148/598 |
International
Class: |
C21D 9/52 20060101
C21D009/52; C21D 6/00 20060101 C21D006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2006 |
JP |
2006-153303 |
Claims
1-6. (canceled)
7. A method of production of a high-carbon steel wire rod of high
ductility, comprising the steps of: preparing steel comprised of,
by mass %, C: 0.7 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P:
0.02% or less, S: 0.02% or less, O: 18 to 30 ppm, and N: 0 to 40
ppm, with a balance of Fe and unavoidable impurities, conducting a
hot rolling the steel at a hot finish temperature of 800.degree. C.
or greater and 1050.degree. C. or less, carrying out coiling the
hot rolled steel at 800.degree. C. to 830.degree. C. within 10
seconds, conducting Stelmor cooling or direct patenting the coiled
steel by immersion in 500 to 570.degree. C. molten salt, wherein
95% or greater of the wire rod metallographic structure is pearlite
structure, maximum pearlite block size at a core of a cross-section
perpendicular to the wire rod axis is 65 .mu.m or less, a tensile
strength in the range of {248+980.times.(C mass %)}.+-.40 MPa} and
a reduction of area of the wire rod of {72.8-40.times.(C mass %) %}
or greater.
8. A method of production of a high-carbon steel wire rod of high
ductility according to claim 7, wherein the wire rod further
comprises, in mass %, one or more of Cr: 0.05 to 1.0% Mo: 0.05 to
1.0%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Ti: 0.005 to 0.1%, and B:
0.0005 to 0.006%.
9. A method of production of a high-carbon steel wire rod of high
ductility according to claim 7 or 8, wherein an average pearlite
block size at the core of the cross-section perpendicular to the
wire rod axis is 10 .mu.m or greater and 30 .mu.m or less.
10. A method of production of a high-carbon steel wire rod of high
ductility according to claim 7 or 8, wherein the wire rod
metallographic structure includes pro-euctoid ferrite at a volume
percentage of 2% or less.
Description
[0001] This application is a divisional application of U.S.
application Ser. No. 11/989,676, filed Jan. 28, 2008, a national
stage application of International Application No.
PCT/JP2007/061497, filed May 31, 2007, which claims priority to
Japanese Application No. 2006-153303, filed Jun. 1, 2006, each of
which is incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to high-carbon steel wire rod of high
post-hot-rolling ductility having a metallographic structure mainly
of pearlite. Specifically, this invention relates to piano wire or
high-carbon steel wire complying with JIS, more particularly to
hot-rolled wire of high-carbon steel that, as the final product
steel wire, is a fine wire of a diameter of around 0.1 to 2 mm
usable, for example, in steel cord, saw wire, hose wire, fine rope
and the like.
DESCRIPTION OF THE RELATED ART
[0003] Steel cords and other reinforcing wires used to reinforce
rubber products such as tires, conveyor belts and heavy-duty hoses
are manufactured from high-carbon steel wire rods. The high-carbon
steel wire rods are manufactured by hot rolling, followed by
descaling and then borax coating or Bonde coating to provide a
carrier coating, whereafter processing to a steel wire of 0.8 to
1.2 mm is optionally conducted by use of intermediate patenting. As
termed with respect to the present invention, the hot-rolled steels
are called "wire rods" and the steels of smaller diameter than the
hot-rolled steels fabricated by subsequent processing are called
"steel wires."
[0004] When the steel wires are to be used for steel cord, the
patenting is followed by brass plating and then further drawing to
steel wires of 0.15 to 0.35 mm diameter, whereafter the wires are
stranded into steel cord that is embedded in a rubber product for
use. Research is being continued on, for example, improvement of
workability in the secondary processing step and improvement of the
abrasion property of the drawing dice.
[0005] Publication of Japanese Examined Patent Application (Kokoku)
No. H3-60900, for example, teaches a wire rod whose C content is
0.59 to 0.86%, tensile strength is 87.5.times.C equivalent+27.+-.2
(kg/mm.sup.2) (C equivalent=C+Mn/5), and area accounted for by
coarse pearlite in the wire rod metallographic structure as
measured under a microscope at .times.500 is adjusted to
-60.times.C equivalent+69.5.+-.3(%). This wire rod is directed to
enabling the drawing dice to have excellent service life and
increases dice service life by specifying tensile strength and
controlling the volume fraction of coarse pearlite to within a
certain range. Although this patent publication focuses on coarse
pearlite structure with an eye to improving drawing dice service
life, it teaches nothing whatsoever regarding relationship with the
cause of breakage after direct drawing, which is the issue dealt
with by the present invention.
[0006] Japanese Patent Publication (A) No. 2000-63987 teaches a
high-carbon steel wire rod excellent in wire drawability wherein
90% or greater of the metallographic structure is pearlite
structure, and the pearlite has an average lamellar spacing of 0.1
to 0.4 .mu.m and an average colony diameter of 150 .mu.m or less.
The fact is, however, that the colony diameter obtained by ordinary
hot rolling is smaller than 150 .mu.m, and an improvement in
breakage property cannot necessarily be expected because the
ductility obtained when the colony diameter is controlled to 150
.mu.m or less is inconsistent.
[0007] Japanese Patent No. 3681712 teaches a high-carbon steel wire
rod excellent in drawability wherein 95% or greater of the wire rod
metallographic structure is pearlite structure, the pearlite has an
average nodule diameter (P) of 30 .mu.m or less and an average
lamellar spacing (S) of 100 nm or greater, and the value of F
obtained by the equation
F=350.3/ S+130.3/ P-51.7
is F>0, where P is represented in .mu.m and S in nm.
[0008] The invention taught by this patent publication controls the
lamellar spacing and nodule size by incorporating a cooling process
for isothermal holding during Stelmor cooling at the time of hot
rolling. However, in ordinary Stelmor cooling the cooling is
continuous, so that the range of lamellar spacing values is wide
and the range of nodule size values also becomes wide. In such a
case, good workability cannot be obtained no matter how small the
average values are made, and what is more, a problem of attendant
internal defects arises. Moreover, the patented invention is
directed to obtaining a wire rod excellent in high-speed
drawability by varying the cooling conditions after wire rod
rolling so as to adjust the structure into the range of F defined
by the foregoing equation. This is problematic, however, because
bringing the structure into the range of the equation requires use
of special heat treatment that is generally difficult to
implement.
SUMMARY OF THE INVENTION
[0009] Owing to the importance of good economy in secondary
processing, recent years have seen an increasing need for the
development of wire rod that resists occurrence of internal defects
during drawing and wire rod that even when processed with a
relatively large amount of working during primary drawing does not
experience an increase in breakage thereafter.
[0010] The present invention relates to high-carbon steel wire rod
utilized as piano wire rod, hard steel wire rod and the like for
use in finely drawn applications such as steel cord, belt cord,
rubber hose wire, rope wire and the like, and in light of the
foregoing circumstances, provides high-carbon steel wire rod of
high ductility that is excellent in post-hot-rolling drawability,
resists occurrence of internal defects at the time of drawing, and
enables omission of intermediate patenting.
[0011] The inventors achieved the present invention based on the
results of in-depth research regarding pearlite structure
hot-rolled wire rod whose secondary processability is unaffected by
omission of intermediate patenting. A summary of the invention
follows:
[0012] 1) A high-carbon steel wire rod of high ductility, which is
a high-carbon steel wire rod having a carbon content of 0.7 mass %
or greater, wherein 95% or greater of the wire rod metallographic
structure is pearlite structure and maximum pearlite block size at
a core of a cross-section perpendicular to the wire rod axis is 65
.mu.m or less.
[0013] 2) A high-carbon steel wire rod of high ductility according
to 1), having a tensile strength in a range of {248+980.times.(C
mass %)}.+-.40 MPa} and a reduction of area of {72.8-40.times.(C
mass %) %} or greater.
[0014] 3) A high-carbon steel wire rod of high ductility according
to 1) or 2), wherein an average pearlite block size at the core of
the cross-section perpendicular to the wire rod axis is 10 .mu.m or
greater and 30 .mu.m or less.
[0015] 4) A high-carbon steel wire rod of high ductility according
to any of 1) to 3), wherein the wire rod metallographic structure
includes pro-eutectoid ferrite at a volume percentage of 2% or
less.
[0016] 5) A high-carbon steel wire rod of high ductility according
to any of 1) to 4), wherein the wire rod comprises, in mass %, C:
0.7 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P: 0.02% or less, S:
0.02% or less, and a balance of Fe and unavoidable impurities.
[0017] 6) A high-carbon steel wire rod of high ductility according
to 5), wherein the wire rod further comprises, in mass %, one or
more of Cr: 0.05 to 1.0%, Mo: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Ni:
0.05 to 1.0%, V: 0.001 to 0.1%, Nb: 0.001 to 0.1%, Ti: 0.005 to
0.1%, B: 0.0005 to 0.006%, O: 18 to 30 ppm, and N: 0 to 40 ppm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows correspondence between (a) cracks occurring
during drawing in the case of conducting ordinary Stelmor
processing and (b) pearlite block size.
[0019] FIG. 2 is shows change in pearlite block size between the
surface and core of a rolled wire rod.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The inventors discovered that when steel wire is drawn from
wire rod to the thickness at which final patenting is conducted
without conducting intermediate patenting, the steel wire may at
first sight appear not to decline in ductility with increasing
amount of working, but defects nevertheless occur internally and
are promoted during the ensuing patenting and the drawing
thereafter, sometimes leading to breakage.
[0021] Also in the case where severe working (i.e., working in
terms of true strain equal to or exceeding 2) is conducted during
primary drawing, it is necessary to ensure that the patenting and
other ensuing processes are not affected by controlling the wire
rod metallographic structure so as to prevent occurrence of
internal defects in primary drawing to the utmost, and also to
conduct primary drawing that minimizes occurrence of defects.
[0022] The inventors observed the internal defect sites after
primary drawing and studied the associated conditions, which are
complexly affected by numerous factors such as the mechanical
properties, processing conditions and wire rod structure. As a
result, they discovered that among these conditions, it is the
pearlite block size of the pearlite structure at the core of the
wire rod, as measured with an EBSP (Electron Back Scatter Pattern)
analyzer, that characterizes the structure readily experiencing
internal defects. A measurement method using an ordinary light
microscope cannot accurately ascertain the pearlite block size and
therefore does not enable determination of the structure that
impairs workability. An EBSP analyzer must therefore be used to
measure the pearlite block size.
[0023] Pearlite block size was measured with a system using a TSL
(TexSEM Laboratories) EBSP analysis unit in combination with a
Hitachi thermal FE-SEM (model S-4300SE). The pearlite block was
measured with the EBSP analyzer as the region with the same ferrite
crystal orientation, in accordance with the definition given by
Takahashi et al. in The Journal of the Japan Institute of Metals,
Vol. 42 (1978), p. 708. Since measurement using the structure
observed with a light microscope or the secondary electron image
obtained by SEM observation was found to be extremely difficult,
the pearlite block size was determined from the ferrite crystal
orientation map obtained by EBSP analysis. Differently from in the
ferrite single phase of low-carbon steel, countless small angle
boundaries are present in the ferrite crystal grains of pearlite
steel, even after patenting.
[0024] An investigation was therefore made regarding an appropriate
threshold angle above which the grain boundaries that have an
orientation difference of 15 degrees or greater and can be
recognized as ordinary crystal grain boundaries account for around
90% or greater of all grain boundaries. The best results were
obtained when the grain boundaries were defined as those obtained
using a boundary orientation difference of 9 degrees or greater.
Units constituted by boundaries having orientation differences of 9
degrees or greater were therefore defined as pearlite block
grains.
[0025] Through an extensive study of ways to control the pearlite
block size, the inventors discovered that occurrence of coarse
pearlite blocks can be prevented by control of oxygen amount along
with control of post-rolling finish-rolling temperature so as to
carry out Stelmor cooling with the .gamma. grain size in a
granulated state on the finish rolling exit side. When the .gamma.
grains are of mixed grain size, pearlite transformation occurs more
readily at small .gamma. grain regions, in which case the pearlite
transformation nuclei are present heterogeneously, so that pearlite
blocks grow easily to make the grain size large.
[0026] In order to make the .gamma. grain size after finish rolling
small, the steel is required to have an oxygen content of 18 ppm or
greater, preferably 20 ppm or greater. However, increasing oxygen
content increases the amount of inclusions and causes formation of
large inclusions. As this degrades ductility, the upper limit of
oxygen content is defined as 30 ppm.
[0027] When ordinary continuous cooling is used, the pearlite block
size varies from the surface layer toward the center of the wire
rod. And, as shown in FIG. 2, the pearlite block size varies at
locations outward from the center also in the case where the
ordinary Stelmor cooling process is conducted. In FIG. 2, each
pearlite block size shown is the average of values measured at
eight locations. Since the pearlite block size at the core differs
greatly even when the average value is the same, the inventors
studied what criteria should be used for the control in the case of
continuous cooling. They learned that the pearlite lamellae are
also coarse at the core region where the pearlite block size is
large and that the coarse pearlite portions become starting points
of breakage during drawing. Therefore, in order not to leave any
defects following primary drawing, it is necessary to control the
maximum value of the pearlite block size to 65 .mu.m or less. An
investigation of the relationship between the pearlite block size
and the breakage index of the final drawn wire showed that making
the pearlite block size at the core 65 .mu.m or less improves
drawability and enables reduction of wire breakage in the ensuing
drawing process.
[0028] The reasoning behind specification of the average value of
the pearlite block grains will now be explained. Owing to the use
of continuous cooling, the pearlite block grains are present in a
mixture of sizes. If the average pearlite block size is determined
by simple averaging based on the measurement of pearlite block size
made in this mixed condition, the numerous small pearlite blocks
present will make the average value so small that it does not
reflect the breakage property. The Johnson-Saltykov method of
calculating the average diameter of particle groups of mixed
particle size was therefore used to determine the average value of
the obtained pearlite block size as the average of values at 8
sites in each of the wire rod surface layer, 1/4 diameter region
and core region (1/2 diameter region), i.e., at a total of 24
sites. Details regarding the Johnson-Saltykov method can be found
in Quantitative Microscopy, R. T. DeHoff and F. N. Rhines, Ed.,
McGraw Hill Publishers, New York, N.Y., 1968, p169.
[0029] When the obtained average value is 10 .mu.m or less,
achievement of pearlite structure of 95% or greater is difficult
and the volume percentage of ferrite in the pearlite structure
becomes 2% or greater. The average pearlite block size therefore
needs to be made 10 .mu.m or greater. Moreover, if the average
value exceeds 30 the probability of coarse blocks being included is
very high in the case of continuous cooling, so that the average
must be controlled to 30 .mu.m or less.
[0030] At a tensile strength of less than {248+980.times.(C mass
%)-40 MPa}, the lamellar spacing of the pearlite structure becomes
so large as to make attainment of good workability impossible. The
tensile strength must therefore be controlled to not less than
{248+980.times.(C mass %)-40 MPa}. At a tensile strength of greater
than {248+980.times.(C mass %)+40 MPa}, large work hardening makes
post-drawing strength high so that ductility declines. The tensile
strength must therefore be controlled to not greater than
{248+980.times.(C mass %)+40 MPa}.
[0031] Reduction of area is preferably controlled to not less than
{72.8-40.times.(C mass %)}. At a reduction of area of less than
40%, internal defects occur readily during wire drawing. In order
to keep the reduction of area from falling below 40%, the volume
fraction of pro-eutectoid ferrite observed inside the wire rod
obtained by Stelmor cooling is controlled to 2% or less. When
present at a volume fraction exceeding 2%, the pro-eutectoid
ferrite tends to act as starting points of internal defects during
drawing and as starting points of internal defects during tensile
testing. Pro-eutectoid ferrite is therefore controlled to 2% or
less. Pro-eutectoid ferrite becomes a problem in the carbon content
region below 0.85 mass %. In the carbon content region of 0.85 mass
% and greater, pro-eutectoid ferrite is generally held to 2% or
less owing to the presence of abundant carbon content.
[0032] The reasons for limiting the components of the steel of the
high-carbon steel wire rod according to the present invention will
now be explained. All contents are expressed in mass %.
[0033] C is an element that effectively enhances strength. For
obtaining a high-strength steel wire, C content must be made 0.7%
or greater. However, when C content is excessive, ductility tends
to be lowered by ready precipitation of pro-eutectoid cementite.
The upper limit of C content is therefore specified as 1.1%.
[0034] Si is an element required for deoxidation of the steel.
Since the deoxidation effect is insufficient at too low a content,
Si is added to a content of 0.1% or greater. Moreover, Si increases
post-patenting strength by dissolving into the ferrite phase in the
pearlite formed after heat treatment. But it also impairs heat
treatability. It is therefore kept to a content of 1.0% or
less.
[0035] P easily segregates and P concentrating at the segregation
sites dissolves into the ferrite to lower workability. P content is
therefore controlled to 0.02% or less.
[0036] S, if contained in a large amount, lowers the ductility of
the steel by forming much MnS. It is therefore controlled to a
content of 0.02% or less.
[0037] Mn is added to a content of 0.1% or greater in order to
impart hardenability to the steel. However, heavy addition of Mn
excessively prolongs transformation time during patenting. Addition
is therefore limited to 1.0% or less.
[0038] Cr is added to enhance steel strength. When included, it is
added to a content at which this effect is exhibited, namely to a
content of 0.05% or greater, and to a content of 1.0% or less,
namely to a content that does not give rise to a decrease in steel
wire ductility.
[0039] Mo is added to enhance steel strength. When included, it is
added to a content at which this effect is exhibited, namely to a
content of 0.05% or greater, and to a content of 1.0% or less,
namely to a content that does not give rise to a decrease in steel
wire ductility.
[0040] Cu is added to enhance corrosion resistance and corrosion
fatigue property. When included, it is added to a content at which
these effects are manifested, namely to a content of 0.05% or
greater. However, heavy addition tends to cause brittleness during
hot rolling, so the upper limit is defined as 1.0%.
[0041] Ni has an effect of increasing steel strength. When
included, it is added to a content at which the effect of addition
is manifested, namely to a content of 0.05% or greater. However,
since excessive addition lowers ductility, Ni content is held to
1.0% or less.
[0042] V has an effect of increasing steel strength. When included,
it is added to a content at which the effect of addition is
manifested, namely to a content of 0.001% or greater. However,
excessive addition lowers ductility, so the upper limit is defined
as 0.1%.
[0043] Nb has an effect of increasing steel strength. When
included, it is added to a content at which the effect of addition
is manifested, namely to a content of 0.001% or greater. However,
excessive addition lowers ductility, so the upper limit is defined
as 0.1%.
[0044] B has an effect of refining .gamma. grain size during
austenitization, and by this, of improving reduction and other
ductility properties. Therefore, when included, B is added to a
content at which its effect is manifested, namely to a content of
0.0005% or greater. However, addition to a content exceeding 0.006%
makes the transformation time at the time that transformation is
effected by heat treatment too long. The upper limit of B content
is therefore defined as 0.006%.
[0045] As the production method for obtaining the high-carbon steel
wire rod of high ductility according to the present invention, it
is preferable in hot rolling a billet having the aforesaid chemical
composition to conduct the hot rolling at a hot finish temperature
of 800.degree. C. or greater and 1050.degree. C. or less, then
carry out coiling at 800 to 830.degree. C. within 10 seconds, and
thereafter conduct Stelmor cooling or direct patenting by immersion
in 500 to 570.degree. C. molten salt.
EXAMPLES
[0046] The chemical compositions of specimen steels used in
prototyping are shown Table 1. Steels No. 1 to No. 18 are of
compositions controlled in accordance with the invention. Steels
No. 19 and No. 20 are Comparative Steels. Comparative Steel 19 is
lower in oxygen content than the Invention Steels and Comparative
Steel 20 is higher in oxygen content than the Invention Steels.
[0047] The steels were prepared in a full-scale furnace to have the
compositions shown in Table 2 and continuously cast into bloom of
500.times.300 mm cross-sectional dimensions. The bloom was
thereafter reheated and rolled with a billeting mill to obtain a
122 mm-square billet. The steel was then reheated to the .gamma.
region, hot rolled to 5.5 mm-diameter wire rod, finish rolled,
controlled to a coiling temperature of 850 to 900.degree. C. in 10
seconds, and continuously subjected to Stelmor cooling divided into
four zones. The wire rod manufacturing conditions are shown in
Table 2. Table 2 also shows the mechanical properties and the
maximum and average values of the measured pearlite block sizes of
the wire rods obtained under the manufacturing conditions shown in
the same Table.
[0048] Wire rods No. 1, No. 2 and, No. 6 to No. 21 in Table 2 were
manufactured in accordance with the invention. Wire rods No. 3 to
No. 5, No. 22 and No. 23 were manufactured for comparison.
[0049] In Table 2, the symbol .largecircle. indicates that when,
for the purpose of investigating primary drawability, the wire rod
was drawn from the diameter of 5.5 mm to a diameter of 1.0 mm with
the die approach angle at 20 degrees, neither breakage nor
abnormality in the tensile tests conducted at the individual passes
occurred. In addition, for the purpose of investigating secondary
drawability, the wire rod was drawn from the diameter of 5.5 mm to
a diameter of 1.56 mm, brass plated and further drawn from the
diameter of 1.56 mm to a diameter of 0.2 mm, whereafter the 0.2
mm-diameter wire was subjected to drawing under a weight of 100 kg
or greater to determine the wire breakage index. When the wire
breakage index was good, it was designated by the symbol
.largecircle.. In Table 2, the symbol X indicates that the result
for the item concerned was unsatisfactory.
[0050] The invention wire rods No. 1, No. 2, and No. 6 to No. 21
exhibited good results for both primary drawability and secondary
drawability.
[0051] Comparative wire rod No. 3, made with a comparative steel,
had a maximum pearlite block size value exceeding 65 .mu.m owing to
the high finishing temperature and therefore exhibited poor results
for both primary drawability and secondary drawability.
[0052] Comparative wire rod No. 4 had a maximum pearlite block size
value exceeding 65 .mu.m owing to the high coiling temperature and
therefore exhibited poor results for both primary drawability and
secondary drawability.
[0053] Comparative wire rod No. 5 had a tensile strength (TS) below
the invention range because the air flow in Stelmor cooling was at
a moderate level. In this case, too, poor results were exhibited
for both primary drawability and secondary drawability.
[0054] Comparative wire rod No. 22 was made of a steel of a
chemical composition whose oxygen content was below the invention
range. The maximum value of the pearlite block size at the core
region of the wire rod was greater than that defined by the
invention.
[0055] Comparative wire rod No. 23 was made of a steel of a
chemical composition whose oxygen content was below the invention
range. Although the maximum value of the pearlite block size at the
core region of the wire rod met the requirement of the invention,
the total amount of inclusions was large owing to the high oxygen
content and the secondary drawability was therefore low.
TABLE-US-00001 TABLE 1 Steel No. C Si Mn P S Cr N O Other Remark 1
0.72 0.19 0.49 0.010 0.009 -- 21 23 Invention 2 0.82 0.18 0.51
0.010 0.007 -- 21 24 -- Invention 3 0.92 0.19 0.51 0.008 0.008 --
19 23 -- Invention 4 0.92 0.19 0.31 0.009 0.009 0.21 19 24 --
Invention 5 0.96 0.19 0.31 0.008 0.009 0.22 20 22 -- Invention 6
1.02 0.19 0.31 0.009 0.009 0.19 19 23 -- Invention 7 0.92 0.90 0.32
0.009 0.008 0.19 29 21 B: 0.002 Invention 8 1.02 0.90 0.60 0.009
0.009 0.1 29 23 -- Invention 9 1.02 0.90 0.32 0.009 0.009 0.1 34 23
Mg: 0.05, B: 0.0025 Invention 10 0.82 0.19 0.21 0.010 0.008 -- 26
28 Mo: 0.1 Invention 11 0.82 0.20 0.49 0.011 0.008 -- 24 18 Cu: 0.1
Invention 12 0.82 0.20 0.48 0.009 0.007 -- 23 22 Ni: 0.1 Invention
13 0.82 0.21 0.49 0.009 0.006 -- 26 24 V: 0.07 Invention 14 0.82
0.19 0.49 0.009 0.005 -- 28 26 Nb: 0.05 Invention 15 0.82 0.19 0.49
0.015 0.004 -- 21 25 -- Invention 16 0.82 0.20 0.30 0.010 0.008
0.15 34 25 V: 0.07, B: 0.002 Invention 17 0.82 0.19 0.50 0.010
0.009 -- 22 23 Ti: 0.002, B: 0.002 Invention 18 0.82 0.20 0.55
0.012 0.008 -- 21 22 Invention 19 0.82 0.21 0.30 0.009 0.008 -- 38
17 -- Comparative 20 0.82 0.20 0.32 0.010 0.008 -- 23 45 --
Comparative
TABLE-US-00002 TABLE 2 Average Wire Finishing Coiling Max pearlite
pearlite Rod Steel No. temp temp Air flow TS RA block size block
size Primary Secondary No. (see Table 1) (.degree. C.) (.degree.
C.) (Stelmor vane opening) (MPa) (%) (.mu.m) (.mu.m) drawing
drawing Remark 1 1 1048 890 All-100 1020 46 54 28 .largecircle.
.largecircle. Invention 2 2 1045 880 All-100 1032 44 58 29
.largecircle. .largecircle. Invention 3 2 1120 890 All-100 1032 42
67 26 X X Comparative 4 2 1052 900 All-100 1101 41 67 27 X X
Comparative 5 2 1049 890 50-50-100-100 1018 38 78 36 X X
Comparative 6 3 1038 880 All-100 1124 39 43 23 .largecircle.
.largecircle. Invention 7 4 1040 880 All-100 1132 38 54 25
.largecircle. .largecircle. Invention 8 5 1065 880 All-100 1190 36
57 28 .largecircle. .largecircle. Invention 9 6 1043 880 All-100
1220 34 58 26 .largecircle. .largecircle. Invention 10 7 1066 880
All-100 1116 38 62 25 .largecircle. .largecircle. Invention 11 8
1059 880 All-100 1215 37 61 25 .largecircle. .largecircle.
Invention 12 9 1072 880 All-100 1253 36 64 26 .largecircle.
.largecircle. Invention 13 10 1041 880 All-100 1063 43 56 27
.largecircle. .largecircle. Invention 14 11 1062 880 All-100 1074
44 59 28 .largecircle. .largecircle. Invention 15 12 1053 880
All-100 1076 42 58 24 .largecircle. .largecircle. Invention 16 13
1052 880 All-100 1058 41 57 25 .largecircle. .largecircle.
Invention 17 14 1063 880 All-100 1062 41 62 24 .largecircle.
.largecircle. Invention 18 15 1037 880 All-100 1088 45 63 27
.largecircle. .largecircle. Invention 19 16 1039 880 All-100 1087
43 61 26 .largecircle. .largecircle. Invention 20 17 1047 880
All-100 1071 44 57 26 .largecircle. .largecircle. Invention 21 18
1061 880 All-100 1066 43 54 28 .largecircle. .largecircle.
Invention 22 19 1054 880 All-100 1054 41 72 31 X X Comparative 23
20 1067 880 All-100 1076 39 66 28 .largecircle. X Comparative
[0056] The high-carbon steel wire rod of high ductility according
to the present invention enables manufacture of excellent extra
fine wire of high fatigue strength that is capable of reducing the
weight and prolonging the service life of rubber products.
* * * * *