AFIELD OF THE INVENTION :
The present invention generally relates to high carbon steel wire for producing
automobile tires. More particularly, the invention relates to a process of
producing a drawn wire with bend value of at least 15 for bead application in
automobile tires.
BACKGROUND OF THE INVENTION ;
High carbon steel wires have great importance for technological applications due
to their very high strength and other mechanical properties. A good combination
of tensile strength - elongation, torsion and bend property makes this product
attractive. US patent 6264759 (Bae et.al) discloses a steel wire with superior
longitudinal cracking property by reducing the amount of pro-eutectoid ferrite
phase in the wire rod. US6322641 to Makil et al discloses a high strength wire
with superior longitudinal cracking properties by addition of boron in the steel.
US patent 6402858 describes importance of cleanliness of steel on the wire
quality specially used for rope, cord and bead application, and clean steel having
very low inclusion content, which exhibit excellent cold workability, as well as
excellent fatigue resistance. There is no prior art which discusses the bend
property of high carbon steel wire used for making tire bead and cord
applications. However, Zelin et.al (2007 WJI) reported that reduction/failure in
bending ductility due to surface defects (V type cracks), presence of martensite
on the surface of the wire.
High carbon' steel wire is used in the automobile industries (truck, bus, aircraft
tires) for making tire. Figure 1 shows a typical tire where the bead area along
with other components is indicated. Wire used for making bead helps to reinforce
the tire with rim so that the failure time can be extended and the safety of the
passenger can be increased. It is always desirable to reinforce rubber articles by
incorporating therein steel reinforcing elements. Pneumatic vehicle tires are often
reinforced with fine steel wires. Such tire bead wires are frequently composed of
high carbon steel or high carbon steel coated with a thin layer of brass coating.
This tire bead can be made using few wires which are embedded in rubber. In
most instances, depending upon the type of tire being reinforced, the property
requirement of the wire varies. Hence, it is important for the steel wire used as
reinforcing material must exhibit high tensile, torsion and bend properties.
Converting of the steel into a fine wire suitable for making tire bead component
involves several processing stages, including pre-drawing, patenting and
drawing, stress relieving and coating. The selected step in the processing to
achieve a steel wire with high value of bends can include many variations on
those processing stages.
During wire drawing the diameter of the wire reduces from its original diameter
to a smaller diameter by allowing the wire to pass through a number of dies.
Generally, the dies used for drawing are either tungsten carbide or diamond.
Drawing of the wire leads to decrease in the diameter of the wire as a result the
strength characteristics of the metal changes. Cold drawing can be done by using
either wet or dry lubricants. Formation of a wire with desired properties may
include multiple drawing steps both prior to and after patenting of the wire.
Patenting or low temperature heat-treatment from austenite phase field is
carried out to obtain a microstructure which combines high tensile strength with
high ductility, and thus impart to the wire the ability to withstand a large
reduction in area to produce the desired finished sizes possessing a combination
of high tensile strength and good toughness. Industrial patenting heat-treatment
is continuous process and consists of first heating the steel to at high
temperature to form homogeneous austenite, and then dipping the wire in a
liquid media at lower temperature which is predetermined. This treatment leads
to transformation of face centered cubic crystal to aggregate of body centered
crystals and orthorhombic crystals which is called pearlite. It is desired to form a
fully pearlitic structure during this heat-treatment but in most of the cases few
other phases (undissolved carbide, proeutectoid-ferrite, bainite, and martensite)
may be present.
To make a tire bead, one of the objectives is always to have a wire with superior
bend properties along with good combination of tensile properties. The final wire
which is used in the tire is in the stress relieved and coated condition. To
improve the bend value of the final wire it is very significant to improve the bend
value of the as drawn wire. i.e. the wire produced just after drawing. This is
because, in general, it has been a common phenomenon in this type of wires t
hat there are few points drop in the bend value in the final coated wire after
stress relieving as compared to the as drawn wire which is not undergone stess
relieving and coating treatment.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process of producing a
drawn wire with bend value of at least 15 for bead application in automobile
tires, which optimizes the heat-treatment and drawing parameters of high carbon
steel wire.
Another object of the invention is to propose a process of producing a drawn
wire with bend value of at least 15 for bead application in automobile tires,
which is enabled to control a patented wire through microstructure
differentiation.
SUMMARY OF THE INVENTION
The invention provides improved bend value of high carbon drawn steel wire
product by drawing a patented wire. The developed wire can be used for the
automobile industries (truck, bus, aircraft tires), for making tires and tire beads.
In a pneumatic tire there is always a bead area (shown by arrow in Figure 1)
which is made by using wires embedded with rubber. As the drawn wire with
superior bend property is achieved, the wire produced exhibits high durability
and safety.
According to the invention, a drawn wire product with superior bend properties is
produced by optimizing the heat treatment and drawing parameters. The
resulting microstructures of the heat treated materials have been characterized
to establish the optimum process parameters to produce a drawn wire with
improved bend value. The present invention discloses a higher bend value of 15
numbers can be achieved in the drawn wire by optimizing the heat treatment
and wire drawing condition.
Present invention is useful for the tire for automobile industries especially for
bus, or truck.
The present invention is simple to implement, and adaptable to the existing
production line without any modification. The invention enables to produce high
carbon steel wire with superior bends which increase the strength, duration and
safety of the tires and can be adapted the automotive tire industries.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a generic pictorial view of different components of a
tire.
Figure 2 - Shows a graphical representation of bend values of a as-
drawn wire at different heat-treatment conditions.
Figure 3 - a bar chart showing comparative bend values of prior art
drawn wire and the inventive drawn wire.
Figure 4 - Shows a microstructure of a high carbon steel wire used for
producing a drawn wire product of higher bend value according to the invention.
Figure 5 - Shows a schematic flow process of producing a drawn wire
product according to the invention.
DETAILS DESCRIPTION OF THE INVENTION
The chemical composition of the steel is : 0.5-1.1 %C, 0.35-0.9%Mn, 0.15-0.5
Si, 0.006-0.01%N, 0.009-0.025 % S and 0.01-0.035 % P (all values in wt %).
The steel was cast and rolled into 5.5 mm wire rod followed by pickling. The wire
rod was cold drawn to certain diameter called pre-drawn wire followed by
austenitizing (high temperature heat-treatment) and patenting (low temperature
heat-treatment in liquid a media set at predetermined temperature). The wire

coming out from low temperature heat-treatment bath was given subjected to
treatment followed by cold drawing to achieve fine wire with diameter less than
1.0 mm. Bend testing of the as-drawn wire samples were carried out using large
number of sample. Microstructural characterization of the wires heat-treated
using different condition was carried out in detail.
Figure 2 shows the bend value of the newly developed drawn steel wire as a
function of heat-treatment temperature used for the wire to be used for wire
drawing. The X-axis of the figure indicates range of temperature used for heat-
treatment and Y axis indicates the no of bends achieved in the as drawn wires
after heat treatment of the pre-drawn wire using different condition in the
present study. This is clear from figure 2 that there is strong role of low
temperature heat-treatment used for the pre-drawn wire on the bend property of
the drawn wire. It has been found that for a particular heat-treatment condition
the bend value achieved in the drawn wire is superior. A chart depicted in figure
3 shows comparative bend values of the existing drawn wire and also for the
newly developed drawn wire. This figure tells that the average bend value of the
developed wire could be achieved as high 15 numbers due to modification of
heat-treatment condition and drawing condition as compared to the existing
drawn wire for which the average bend value found 12 numbers. It is also
evident from this figure that the present invention leads to at least 3 point
increase in the bend value in the developed wire as compared to its counterpart.
Figure 4 shows typical pearlitic microstructure of the low temperature heat-
treated wire used for further drawing to achieve superior bends. This figure
represents pearlitic microstructure which is composed of alternate layer of ferrite
and cementite lamellae. The microstructure was taken at very high magnification
which indicates the fineness of the microstructure. Such a fine microstructure
has been found to be beneficial for wire drawing with specified drawing condition
to develop fine wire with higher bend values according to the present invention.
In the microstructure apart from elongated ferrite and cementite, some other
phase like proeutectoid ferrite could also be found very less in amount. Figure 4
Outline of the process of producing a drawn wire product for tire bead
application.
The present invention discloses that low temperature heat-treatment or
patenting heat-treatment condition can be optimized to produce a drawn wire
product with superior bend properties. The average bend value in the wire is
achieved as high as 15 numbers. The bend value obtained in the drawn wire is
found to be considerably higher than the bend value obtained in the drawn wire
of prior art.
WE CLAIM :
1. A process of producing a drawn wire product with bend values of at
least 15 obtained within a composition range 0.6-1.1%C, 0.5-0.9%Mn,
0.10-0.5 Si, 0.006-0.01%N, 0.009-0.025 % S and 0.01-0.035% P,
Balance Fe (all values in wt%) for bead application in automobile tires,
wherein a hot rolled wire rod under reheating temperature in the
range 1100-1200°C and lying head temperature in the range 815 to
910°C, is adapted, wherein
wherein the hot rolled wire rod is pre-drawned to achieve a diameter
in the range 2.8 to 3.4 mm from 5.5 mm.
wherein the pre-drawn wire is austenitized by heating the wire at high
temperature and passing the wire through a furnace maintained in the
temperature range 950 to 1151°C,
wherein the wire in the pre-drawn wire from the austenitized condition
is dipped into a liquid media to reduce the temperature of the pre
drawn wire from high austenitization state to a low furnace
temperature varying in the range 500 to 675°C.
2. The process as claimed in claim 1, wherein prior to wire drawing an
additional surface treatment is given to the wire.
3. The process as claimed in claim 1 or 2, where the wire drawing speed
is maintained in the range 5 to 25 meter per second.
4. A process of producing a drawn wire product with bend values of at
least 15 for bead application in automobile tires as substantially
described and illustrated herein with reference to the accompanying
drawings.

The invention relates to a process of producing a drawn wire product with bend
values of at least 15 obtained within a composition range 0.6-1.1%C, 0.5-
0.9%Mn, 0.10-0.5 Si, 0.006-0.01%N, 0.009-0.025 % S and 0.01-0.035% P,
Balance Fe (all values in wt%) for bead application in automobile tires, wherein a
hot rolled wire rod under reheating temperature in the range 1100-1200°C and
lying head temperature in the range 815 to 910°C, is adapted, wherein wherein
the hot rolled wire rod is pre-drawned to achieve a diameter in the range 2.8 to
3.4 mm from 5.5 mm. wherein the pre-drawn wire is austenitized by heating the
wire at high temperature and passing the wire through a furnace maintained in
the temperature range 950 to 1151°C, wherein the wire in the as-drawn
condition is dipped into liquid media to reduce the temperature of the wire from
high austenitization state to a low furnace temperature varying in the range 500
to 675°C.