Description:
TECHNICAL FIELD
The present invention relates to metallurgy. More particularly the invention relates to steel wire.

BACKGROUND
Bead wires are commonly used for reinforcement of rubber in tyres used in automobile industries. The most common bead wire size is 0.965mm which is drawn from 3.30mm patented wire. The pre-drawn wire of 3.30 mm diameter, drawn from 5.5mm wire rod is conventionally patented in molten lead bath and produces fumes during the process which is highly toxic in nature.
The first stage in manufacturing of bead wire is rod breakdown of 5.5mm HC68B high carbon wire rod to an intermediate wire diameter of 3.25 to 3.30mm. The current process flow consists of heating the pre-drawn wires in a fuel fired furnace continuously upto a temperature of 1000-1100°C. The wires are then immediately submerged into a molten Lead-bath maintained at 600-615°C and kept at sufficiently long period of time for the transformation to be completed isothermally. The scale produced in lead patenting is minimized as compared to the air patenting to a considerable extent because of less duration exposure to the atmosphere for oxidation. However, lead bath patenting process adds high cost and has environmental and health hazards.
In view of highly toxic nature of lead and increasing Government regulatory norms on use of lead, exploring alternate technologies are essential for wire industries.
Heat treatment of steel wires are elaborated in EP0524689B1, where phase transformation of austenite to pearlite is explained at different conditions. For patenting process, hot water with additives (e.g. soap, polyvinyl alcohol and polymer quenchants) were used as coolant. The water temperature was used preferably above 85°C. The patent was filed for patenting of steel wires of diameter below 1.8mm (1.5mm, 1.2mm and 0.8mm).
In WO2014118089A1, a method and an equipment is proposed by using forced water cooling of thick steel wires. This application pertains to thick steel wire and may not be suitable to wires with diameter 3.30 mm.
In WO2007023696A1, it was claimed that the direct heat treatment method of hot rolled wire rods where a loose coil-like hot rolled wire rods are cooled with coolant, but not cooled by immersing them into stored coolant but cooled by exposing them to the coolant flow. The said disclosure discloses complex process with degree of safety concern.
WO2012085651A1 claims a process for manufacturing of steel wires comprises as first step to heating up the wire until complete austenite phase forms followed by quick cooling to start the phase change in which the austenite structure is transformed into pearlite structure. There is chance of steel wire getting converted in martensite, which imparts brittleness and chance of breaking.
EP0216434A1 suggested a method and related apparatus for heat treatment of steels wires for patenting process. Steel wires are patented by heating in a furnace for austenitization and then cooled to a range of temperatures where phase transformation take place from austenite to fine pearlite. However, here hot water is used as a cooling medium. The said disclosure discloses energy intensive and complex process.

OBJECTS
An object of the invention is to provide an alternative of lead-patenting over steel wire with comparable properties.
Another object of the invention is to provide an alternative of Lead-patenting which is comparatively less environmentally hazardous.
Another object of the invention is to provide an alternative to the lead patenting which is comparatively safe.

DISCLOSURE OF THE INVENTION
The present invention provides an arrangement for controlled cooling of a steel wire, comprising:
a furnace (105), the furnace (105) being configured to homogenize the steel wire (104) of diameter 3.25-3.30 mm by austenitizing; and
a series with first water box (W1) or with first and second boxes (W1 and W2) or with first, second and third water boxes (W1, W2 and W3) in line with the furnace (105) to cool the steel wire (104) to achieve equalization temperature of the steel wire (104) 550-650°C.
The provision of series of water boxes to quench the surface of the wires to low temperatures, and during the air cooling period the core re-heats the surface by conduction of heat as the core remains hot. In case of similar treatment for more number of water boxes, till the surface and the core equalizes at the nose of the TTT at around 550 - 650°C, where fine pearlitic microstructure would be achieved.
The speed of the steel wire (104) for the series with first water box (W1), with first and second water boxes (W1 and W2), and with first, second and third water boxes (W1, W2 and W3) being 10 m/min, 21 m/min, 21-38 m/min respectively.
In a preferred embodiment, length of the first water box (W1), the second water box (W2) and the third water box (W3) is 100 mm, 50-100 mm and 100 mm respectively.
In a preferred embodiment, Length of separation (D1) between the furnace and the first water box (W1), (D2) between the first water box (W1) and the second water box (W2) and (D3) between the second water box (W2) and the third water box (W3) being 350 mm and 180 mm and 380 mm respectively.
In an embodiment, the steel wire temperature after the furnace exit is 970-1020 deg. C.
In an embodiment, the furnace is induction furnace.
In yet another embodiment, water flow rate in series with first water box (W1), with first and second water boxes (W1 and W2), and with first, second and third water boxes (W1, W2 and W3) is 2.3 liters per minute.
In yet another embodiment, the steel wire composition is C-0.671 wt%, Mn- 0.643 wt%, Cr-0.011 wt%, Si- 0.172 wt%, Ni- 0.019 wt%, balance being Iron and residual impurities (all in wt.%).
In still another embodiment, the homogenizing of the steel wire (104) by austenitizing is done at 950-1020°C.
In yet another embodiment, the water used in first, second and third water boxes (W1, W2 and W3) is normal water at room temperature.

BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1a, 1b & 1c depicts an arrangement for controlled cooling of a steel wire in accordance with an embodiment of invention.
FIG. 2 depicts schematic view of a water box of FIGS 1a-1c.
FIGS. 3a-3b depicts microstructure based on optical images of conventional lead patented steel wire and the steel wire cooled from the arrangement of FIGS 1a-1c.
Fig. 3c-3d depicts microstructure based on SEM images of conventional lead patented steel wire and the steel wire cooled from the arrangement of FIGS 1a-1c.
DESCRIPTION OF PREFERRED EMBODIMENTS
In accordance with an embodiment of the invention an arrangement (100) for controlled cooling of a steel wire (104) can be shown in FIGS. 1a, 1b and 1c. The arrangement (100) comprises of a furnace (105) configured to homogenize the steel wire (104) by austenitizing. The homogenizing of the steel wire by austenitizing is done at 950-1020°C. Austenitizing the steel wire is softened with austenitic microstructure. The steel wire (104) is of diameter of 3.25-3.30 mm.
The furnace (105) receives the steel wire from a casting unit (not shown) via a pay-off (106). The casting unit process the steel wire of 3.25-3.30 mm with composition C-0.671 wt%, Mn- 0.643 wt%, Cr-0.011 wt%, Si- 0.172 wt%, Ni- 0.019 wt%, balance being Iron and residual impurities (all in wt.%).
In an embodiment, the furnace is an induction furnace.
In another embodiment, the steel wire (104) is pre-drawn steel wire.
Post austenitizing, the steel wire (104) is conveyed to a series with first water box (W1) or with first and second water boxes (W1 and W2) or with first, second and third water boxes (W1, W2 and W3) for controlled cooling of the steel wire. Series of water box or boxes are in line with the furnace (105).
The heating rate at the furnace (105) can be kept appropriate so that the wire is austenized completely. Since the wire will have speed and the furnace have its own length therefore the wire needs to be present in furnace for sufficient time to get austenitized. In an embodiment, heating rate varies 370°C/s to 1480°C/s for line speed from 10 m/min to 40 m/min.
The water used for cooling the steel wire in water boxes (W1, W2 and W3) is normal water at room temperature.
The series with first water box (W1) is shown in FIG. 1a, series with two water boxes (W1 and W2) is shown in FIG. 1b and series with three water boxes (W1, W2 and W3) is shown in FIG. 1c.
The series with first water box (W1), or first and second water boxes (W1 and W2) or first, second and third water boxes (W1, W2 and W3) are configured to achieve equalization temperature of the steel wire (104) 550-650°C. The three arrangements individually are capable to achieve the equalization temperature of the steel wire (104) 550-650°C.
The water boxes quench the surface of the wires to low temperatures, further, during the air cooling period the core re-heats the surface by conduction of heat as the core remains hot. In case of more number of water boxes, similar treatment is carried out several times till the surface and the core equalizes at the nose of the TTT at around 550 - 650°C, where fine pearlitic microstructure would be achieved.
Post the series of water boxes, the steel wire is cooled in open atmosphere during coiling to normal temperature.
The series with water boxes (W1, W2 and W3) designed are of overflowing type and water flow can be adjusted for individual water box. In one of the embodiment the schematic view of water box (W1-W3) is shown in FIG. 2.
The length for (L) the water boxes (W1, W2, W3) are dissimilar and rest of the dimension is kept same for all the water boxes. The water boxes comprise three chambers, one inlet chamber (108) and two outlet chambers (112 and 116). Through the inlet chamber (108) fresh water is fed, and through the outlet chamber water flows out after cooling the steel wire (104) as a processed water. The inlet chamber is in the middle and outlet chambers are at its adjacent on both sides. Below the water boxes (W1-W3) comprises a storage (not shown) through which processed water goes out and fresh water box moves in the water box.
Here the overflowing suggets to the water being fed in from inlet chamber and flows to the outlet chamber.
Length of the water boxes W1, W2 and W3 are 100 mm, 50-100 mm and 100 mm respectively.
Other dimensions of the W1-W3 can be width 115 mm and depth 50 mm.
Shown in FIG. 1a is the length of separation (D1) between the furnace (105) and the W1 being 350 mm.
Shown in FIG. 1b is length of separation (D1) between the furnace (105) and the W1, (D2) between W1 and W2 being 350 mm and 180 mm respectively.
Similarly, shown in FIG. 1c is the length of separation (D1) between the furnace (105) and W1, (D2) between W1 and W2, and (D3) between W2 and W3 being 350 mm, 180 mm and 380 mm respectively.
Water flow rate in series with first water box (W1), with first and second water boxes (W1 and W2), and with first, second and third water boxes (W1, W2 and W3) is 2.3 liters per minute.
The steel wire (104) temperature while moving in series of water box(es) (or furnace exit temperature) is 970-1020 deg. C and exit temperature after series with water box(es) is 550-650 deg. C. The exit temperature of 550-650 is so maintained that microstructure of wire transforms to pearlite with fine interlamellar spacing.
Appropriate speed of the steel wire maintained through the water boxes (W1-W3). The speed is decided based upon the number of water boxes in series. If the number of water boxes are more, then speed of the wire can be elevated. Whereas in case the number of water boxes are less the speed is kept low. This is so as to give sufficient time for cooling.
In an embodiment series with first water box (W1) has steel wire speed of 10 m/min.
In another embodiment series with first and second water boxes (W1 and W2) has speed of 21m/min.
In another embodiment series with first, second and third water boxes (W1, W2 and W3) has speed of 21 -38 m/min.
The obtained steel wire obtained through the arrangement has got the following
Microstructure: Pearlite (Fine)
Break Load: 890-940 Kgf
UTS: 103-109 Kg/mm2,
Torsion No: 35-44
% elongation: 6-7%
Reduction in area (R.A.): 32-49.9
Lamellar spacing in the microstructure: 110 to 128 nm.
The conventional property of the steel wire with Lead patenting is
Microstructure: Pearlite (Fine)
Break Load: 900-920 Kgf
UTS: 99-110 (Kg/mm2)
Torsion No: 35-40
%elongation: 7-8%
Reduction in area (R.A.): 45-47and
Lamellar spacing in the microstructure: 105-116 nm.
It could be observed that the similar property of Lead-patented wire can be achieved using water as a coolant.
EXPERIMENTAL ANALYSIS:
3 pilot lines were build. One pilot line was meant for series with first water box (W1). Other pilot line was meant for series with first and second water boxes (W1 & W2). Another pilot line was meant for series with first, second and third water boxes (W1, W2 and W3). The water boxes had controlled water flow rate to quench predrawned hot wire sequentially so that it equalizes at temperature of 550-650°C. Four such trials were conducted.
For each trial:
Diameter of the wire taken is 3.30 mm.
Composition was C-0.671 wt%, Mn- 0.643 wt%, Cr-0.011 wt%, Si- 0.172 wt%, Ni- 0.019 wt%, balance being Iron and residual impurities (all in wt.%)
Furnace: Induction furnace
Other parameters are given in Table 1 below:
Table 1
Trial No. Wire dia. Wire temp at furnace exit Wire linear speed Water box Length(mm) Distance between Water boxes (in mm) Inlet cooling water temp. Wire temperature after WB exit Average water flow rate
(mm) (oC) (m/min) WB1 WB2 WB3 *D1 *D2 *D3 (oC) (oC) (LPM)
1 3.30 980+10 21 (2nd WB series) 100 100 Not used 350 180 NA 30 570+ 10 2.3

2 3.30 980+10 10 (1st WB series) 100 Not used Not used 350 NA NA 30 560+ 10 2.3

3 3.30 1000+10 38 (3rd WB series) 100 50 100 350 180 380 30 640+ 10 2.3

4 3.30 980+10 21 (3rd WB series) 100 50 100 350 180 380 30 590+ 10 2.3

*D1 is distance between the furnace and W1
*D2 is distance between W1 and W2
*D3 is distance between W2 and W3
The steel wire is never quenched below the Bs (Bainite Start) or Ms (Martensite Start) temperatures.
The samples of the steel wire were cut from each trial and comprehensively characterized. The mechanical properties are tabulated in Table 2 and compared with conventional Lead patented wires (Table 3).
Table 2. Properties of water patented wires
Trial No. Wire dia. Break Load UTS Torsion Fracture %Elongation Reduction in area
(mm) (Kgf) (Kg/mm2) (Nos) (Flat/helical) (GL=200mm) %
1 3.30 910 105 36 Flat 9% 45
2 3.30 940 109 35 Flat 6% 32
3 3.30 890 103 44 Flat 6% 49.9
4 3.30 890 104 42 Flat 7% 49.2
Table 3. Properties of Lead patented wires
Lead patented steel wire with diameter 3.27 mm
Wire dia. Break Load UTS Torsion Fracture %Elongation Torsion Reduction in area
(mm) (Kgf) (Kg/mm2) (Flat/helical) (GL=200mm) Nos %
3.27 900-920 99-110 Flat 7-8% 35-40 45-47
The achieved mechanical properties of the water patented steel wire are very much comparable to the Lead patented wires.
The microstructure of conventional Lead patented steel wire with Fine pearlitic structure and no resolved pearlite shown in FIG. 3a. The steel wire as obtained through the arrangement (100) has got comparable microstructure to lead patented wire with slightly coarser structure as shown in FIG. 3b (as per the Trial 4 in Table 1 and 2).
Similarly, Interlamellar spacing of the conventional lead patented steel wire is 105-116 nm with volume fraction of pearlite: 99% as shown in FIG. 3c. The Interlamellar spacing of the steel wire obtained through the arrangement (100) is 110-128 nm with volume fraction of pearlite: 99% as shown in FIG. 3d (as per the Trial 4 in Table 1 and 2).

ADVANTAGES:
The disclosure discloses an alternative method of lead-patenting over steel wire.
The disclosure provides an alternative method of Lead-patenting which is not environmentally hazardous.
The arrangement as described has low investment cost, low running cost and low maintenance cost.
The arrangement is comparatively safe.

Claims:WE CLAIM:
1. An arrangement (100) for controlled cooling of a steel wire (104), the arrangement (100) comprising:
a furnace (105), the furnace (105) being configured to homogenize the steel wire (104) of diameter 3.25-3.30 mm by austenitizing; and
a series with first water box (W1) or with first and second boxes (W1 and W2) or with first, second and third water boxes (W1, W2 and W3) in line with the furnace (105) to cool the steel wire (104) to achieve equalization temperature of the steel wire (104) 550-650°C.

2. The arrangement (100) as claimed in claim 1, wherein the speed of the steel wire (104) for the series with first water box (W1), with first and second water boxes (W1 and W2), and with first, second and third water boxes (W1, W2 and W3) being 10 m/min, 21 m/min, 21-38 m/min respectively.

3. The arrangement as claimed in claim 1, wherein length of the first water box (W1), the second water box (W2) and the third water box (W3) is 100 mm, 50-100 mm and 100 mm respectively.

4. The arrangement (100) as claimed in claim 1, wherein length of separation
(D1) between the furnace and the first water box (W1),
(D2) between the first water box (W1) and the second water box (W2) and
(D3) between the second water box (W2) and the third water box (W3) being 350 mm and 180 mm and 380 mm respectively.

5. The arrangement (100) as claimed in claim 1, wherein the steel wire temperature after the furnace exit is 970-1020 deg. C.

6. The arrangement (100) as claimed in claim 1, wherein the furnace is induction furnace.

7. The arrangement (100) as claimed in claim 1, wherein water flow rate in series with first water box (W1), with first and second water boxes (W1 and W2), and with first, second and third water boxes (W1, W2 and W3) is 2.3 liters per minute.
8. The arrangement as claimed in claim 1, wherein the steel wire (104) composition is C-0.671 wt%, Mn- 0.643 wt%, Cr-0.011 wt%, Si- 0.172 wt%, Ni- 0.019 wt%, balance being Iron and residual impurities (all in wt.%).

9. The arrangement as claimed in claim 1, wherein the homogenizing of the steel wire (104) by austenitizing is done at 950-1020°C.

10. The arrangement as claimed in claim 1, wherein the water used in first, second and third water boxes (W1, W2 and W3) is normal water at room temperature.

Dated 01st day of January 2021