Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/54—Furnaces for treating strips or wire
  • C21D9/56—Continuous furnaces for strip or wire
  • C21D9/573—Continuous furnaces for strip or wire with cooling
  • C21D9/5732—Continuous furnaces for strip or wire with cooling of wires; of rods
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
  • B21C37/04—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of bars or wire
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/54—Furnaces for treating strips or wire
  • C21D9/64—Patenting furnaces

Definitions

• the present invention concerns a process and a plant for continuously manufacturing a steel wire, as well as such a steel wire and a cord formed with a plurality of such steel wires.
• the steel wires or cords can be used as structural reinforcement elements in the manufacture of elastomeric materials, like for example semifinished products intended for manufacturing tyres, tubes, conveyor belts, driving belts and cables.
• the steel wires can also be used for cutting materials.
• a cord is typically made by cording a plurality of suitable steel wires.
• the steel wires intended for manufacturing tyres comprise a steel core coated by at least one metal layer which provides for both protecting the underlying steel from corrosion and for providing a suitable adhesion of the metal wire or of the cord comprising said wire to the elastomeric material with which the wire or the cord are rubber coated, in addition to facilitating and improving the drawing process which the wire undergoes.
• the manufacture of steel wire typically provides a series of continuous machining and treatments, comprising at least: a first drawing, during which the steel wire is brought to a diameter that is suitable for the machining and for the subsequent treatments; austenitizing, during which the steel wire is heated to a temperature of 950-1100 °C and is kept at such a temperature for a period of time that is sufficient for the steel structure to entirely become austenite; a patenting, during which the steel wire is quickly cooled to about 550-600 °C and is kept at such a temperature for a period of time that is sufficient for the steel structure to become substantially pearlitic; a coating treatment, for example brassing, in which the steel wire is coated with metal or metal alloys for example with copper and zinc; a drawing, in which the diameter of the steel wire is reduced to the final desired value.
• austenite to refer to steel with a substantially entirely austenitic structure
• pearlite to refer to steel with a substantially entirely pearlitic structure.
• the desired phase transformation of the structure of the steel wire from austenite (solid solution of carbon in gamma iron) to pearlite (formed by lamellae of ferrite and of cementite) is indeed carried out as long as the initial cooling is quick enough, otherwise the austenite does not transform into pearlite but into bainite (acicular aggregate formed by ferrite and particles of cementite or complex carbides), which is a steel structure that is not desired, since it is not suitable for the subsequent drawing: by this it is meant that the mechanical characteristics of the steel wire after drawing are not optimal if the structure thereof comprises a considerable amount of bainite.
• the Applicant has found that it is possible to keep the austenitic structure of the steel wire even when subjecting it to slow cooling, after being austenitized at high temperature.
• the Applicant has thus found that it is possible to slowly lower the temperature of the steel wire, keeping its austenitic structure, and then quickly cool it in a simpler manner -thanks to the lower starting temperature- causing the desired transformation from austenite to pearlite, forming a wire which -once drawn- has excellent mechanical characteristics (for example high resistance, high elongation and high torsional and fatigue resistance).
• pearlite forming the wire mainly has a lamellar microstructure rather than a fragmented microstructure and again that such a lamellar structure is fine; by the term “fine” it is meant to indicate a lamellar microstructure in which the spacing is lower than about 100 nm.
• the Applicant has attributed to this fine lamellar pearlitic microstructure a greater capability of the wire of withstanding the subsequent drawing.
• the invention concerns a process for manufacturing a steel wire, comprising:
• said process comprises
• Patenting said steel wire comprises keeping said steel wire at said second predetermined temperature.
• the Applicant has been able to find that during the slow cooling, the steel wire substantially keeps its austenite structure unaltered; with the subsequent quick cooling, the steel wire is brought to the conditions wherein it can begin changing phase in which the austenitic structure is transformed into pearlitic structure.
• the beginning of the change of state can also occur at a relatively low temperature, at the second predetermined temperature of (550- 600 °C), i.e. at the ideal conditions for there to be the substantially total desired transformation into pearlite.
• the invention concerns a plant for the production of steel wire
• said plant comprises:
• Said plant further comprises
• the patenting section comprises:
• Further aspects of the invention concern a steel wire obtained according to the process of the first aspect of the invention, a process for manufacturing a steel cord which uses such a steel wire and a steel cord obtained with such a process.
• the steel wire for austenitizing has a diameter of 0.5-3.5 mm.
• the austenitizing of the steel wire is carried out at a temperature of 900-1000 °C.
• the slow cooling of the steel wire is carried out to a first predetermined temperature ranging from about 720 to about 800 °C.
• the slow cooling is carried out in a time period of 4- 0 s.
• drawing the steel wire is carried out until the wire has a diameter of 0.1-2 mm, even more preferably of 0.1-0.6 mm.
• the quick cooling of the steel wire is carried out to a second predetermined temperature ranging from about 550 °C to about 600 °C.
• the quick cooling is carried out in a time period of 0.5-2 s.
• keeping the steel wire substantially at said second predetermined temperature ranging from about 550 °C to about 600 °C is carried out for a time period of at least 3 s.
• the process comprises coating the steel wire with at least a metal or metal alloy layer.
• such a coating of the steel wire is carried out in order to brass said steel wire.
• the slow cooling is carried out in air.
• air in the present description, it is meant a gaseous atmosphere which mainly comprises air, but it is not excluded for there to be other secondary gaseous substances, for example due to the machining previously carried out or that occur immediately after, or that come from the steel itself in those temperature conditions.
• the slow cooling therefore, does not require a complex cooling system; it is sufficient to ensure an exchange of air that is suitable for taking away the heat necessary for the desired reduction of temperature.
• the quick cooling is carried out in molten lead bath.
• This system makes it possible to obtain, in a relatively simple manner, the desired quick lowering of the temperature thanks to the thermal conductivity of lead and thanks to the possibility of suitably adjusting the temperature of molten lead.
• the quick cooling is carried out by spraying cooling liquid. This system allows a better control of the temperature in the subsequent sections of the plant during the quick cooling.
• the keeping of the wire at a predetermined temperature is carried out in molten lead bath.
• This system makes it possible to take away, in a relatively simple manner, the great amount of heat necessary for the transformation of austenite into pearlite.
• the keeping of the wire at a predetermined temperature is carried out by spraying cooling liquid.
• This system allows the best control of the temperature during the keeping of the temperature during the phase change from austenite to pearlite, making it possible to keep track of the generated heat while the transformation is taking place.
• the steel wire reaches a maximum temperature of 950°C. Indeed, it has been found that the presence of the subsequent slow cooling makes it possible to carry out the austenitization at a temperature that is slightly lower than what is commonly used; it is thought -without by this wishing to give an interpretation of the physical phenomena which can occur during the process according to the invention- that the austenitization can be completed during the slow cooling. More preferably, during austenitization the steel wire reaches a maximum temperature of 930°C, even more preferably of 920°C. It has been found that with these temperatures the steel wire is substantially completely austenitic when the transformation of phase into pearlite starts. With this condition ensured, the advantage in terms of manufacturing costs which are obtained by reducing the temperature during austenitization, are evident.
• the steel wire reaches a minimum temperature of about 740-760°C.
• the steel wire reaches a minimum temperature of about 750°C.
• the steel wire in the quick cooling the steel wire reaches a minimum temperature of 550-650°C.
• the steel wire reaches a minimum temperature of 580-600°C.
• the coating of the steel wire comprises:
• the drawing is a drawing in wet conditions.
• the first subsection of the patenting section comprises a chamber in controlled atmosphere, passed through by the steel wire.
• the second subsection of the patenting section comprises a molten lead bath, passed through by the steel wire.
• the second subsection of the patenting section comprises a chamber with at least one sprayer, for spraying the steel wire with a cooling liquid spray.
• the second subsection of the patenting section comprises a molten lead bath, passed through by the steel wire, followed by a chamber with at least one sprayer, for spraying the steel wire with a cooling liquid spray.
• figure 1 is a diagram of the plant according to the invention
• figure 2 is a diagram of part of the plant of fig. 1 , according to an embodiment of the invention
• figure 3 is a diagram of part of the plant of fig. 1 , according to another embodiment of the invention.
• figure 4 is a diagram of part of the plant of fig. 1 , according to yet another embodiment of the invention.
• figure 5 is a diagram showing the course of the temperature of the steel wire during the process according to the invention;
• figure 6 is a table showing the results of tests carried out on steel wires.
• a plant 100 for manufacturing high resistance steel wire F comprises an inlet section 110 of the steel wire, an austenitizing section 120, a patenting section 130, a brassing section 140 and a drawing section 150.
• the patenting section 130 comprises a first subsection 131 and a second subsection 135, separate and different from the first subsection 131.
• the steel wire F is slow cooled to a first predetermined temperature ranged between 720 and 800 °C in a time period of 4-10 s.
• the steel wire is quick cooled to a second predetermined temperature ranged between 550 and 600 °C in a time period of 0.5-2 s and then is kept substantially at said second predetermined temperature ranged between 550 and 600 °C for a time period of at least 3 s.
• the expression “kept substantially at said second predetermined temperature” it is meant kept in a temperature range within about 30 °C or preferably 20°C, of the predetermined temperature. Such a temperature variation is connected to the exothermicity of the reaction of austenite-pearlite phase transformation which leads to the recalescence phenomenon, the increase tendency of the temperature of the wire during the phase transformation.
• the first subsection 131 of the patenting section 130 comprises a controlled atmosphere chamber 132, passed through by the steel wire F.
• the second subsection 135 of the patenting section 130 comprises a molten lead bath 136, passed through by the steel wire F.
• the second subsection 235 of the patenting section 230 comprises a chamber 237 with at least a sprayer 238, for spraying the steel wire F with a cooling liquid spray.
• the second subsection 335 of the patenting section 330 comprises a molten lead bath 336, passed through by the steel wire F, followed by a chamber 337 with at least one sprayer 338, for spraying the steel wire F with a cooling liquid spray.
• the steel used is a steel containing 0.2%- 1.0% of C (Carbon), preferably 0.6%-0.95% of C.
• a process according to the invention provides: providing a steel wire F, having a diameter of 0.5-3.5 mm; its austenitization, at a temperature of 900-1000 °C; its patenting; its brassing; its drawing, to a diameter of 0.1-2 mm, preferably 0.1-0.6 mm.
• patenting comprises slow cooling of the steel wire F at a temperature of 700-800 °C in a time period of 4-10 s; its quick cooling at a temperature of 550-600 °C in a time period of 0.5-2 s; keeping it at a temperature of 550-600 °C for a time period of at least 3 s.
• the arrangement of the steel wire F occurs in the inlet section 110, its austenitization in the austenitizing section 120, its patenting in the patenting section 130, the slow cooling in the subsection 131 , the quick cooling and keeping in the subsection 135.
• the slow cooling is carried out in air, in the chamber 132.
• the quick cooling is carried out in the molten lead bath 136.
• the quick cooling is carried out by spraying cooling liquid, in the chamber 237 by the sprayers 238.
• the keeping of the temperature is carried out in the molten lead bath 136, 336.
• keeping of the temperature is carried out by spraying cooling liquid, into the chamber 237, 337 by the sprayers 238, 338.
• the cooling liquid is water.
• the steel wire F reaches a maximum temperature of 950°C, more preferably of 930 °C and even more preferably of 920°C.
• the steel wire F reaches a first predetermined minimum temperature of 740-760X, more preferably of about 750°C.
• the steel wire F reaches a second predetermined minimum temperature of 550-650°C, more preferably of 580- 600°C.
• brassing comprises the application of a copper coating, the application of a zinc coating, and thermally diffusing the copper and the zinc applied.
• drawing is a drawing in wet conditions.
• Tests 1 * , 2 * , 3 * carried out on wires made with the processes according to the prior art compared with tests 4 ⁇ , 5 ⁇ carried out on wires made with the process according to the invention make it possible to highlight an increase in the mechanical qualities both before patenting and at the end in wires patented following the process according to the present invention. It should also be noted how the microstructures in the wires made with the process according to the present invention are decidedly better, in terms of fine pearlite and in terms of lamellar spacing.
• the Applicant has also been able to obtain a substantial improvement in the cording process thanks to the wires manufactured with the process according to the invention.
• the process for manufacturing a steel wire according to the invention makes it possible

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Metal Extraction Processes (AREA)

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• 2011
  • 2011-12-21 WO PCT/IB2011/003144 patent/WO2012085651A1/en active Application Filing
  • 2011-12-21 CN CN201180060015.1A patent/CN103314121B/zh not_active Expired - Fee Related
  • 2011-12-21 RU RU2013132962/02A patent/RU2604542C2/ru not_active IP Right Cessation
  • 2011-12-21 EP EP11815567.0A patent/EP2655677B1/en active Active
  • 2011-12-21 BR BR112013015116-1A patent/BR112013015116B1/pt active IP Right Grant
  • 2011-12-21 TR TR2018/10002T patent/TR201810002T4/tr unknown

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