WO2024251972A1 - Patentage isotherme de fils d'acier - Google Patents

Patentage isotherme de fils d'acier Download PDF

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Publication number
WO2024251972A1
WO2024251972A1 PCT/EP2024/065781 EP2024065781W WO2024251972A1 WO 2024251972 A1 WO2024251972 A1 WO 2024251972A1 EP 2024065781 W EP2024065781 W EP 2024065781W WO 2024251972 A1 WO2024251972 A1 WO 2024251972A1
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WIPO (PCT)
Prior art keywords
liquid
cooling section
bath
steel wire
cooling
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Pending
Application number
PCT/EP2024/065781
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English (en)
Inventor
Gregory Lapeire
Christophe Mesplont
Wim VAN HAVER
Renaat Vandemeulebroecke
Wesley VER EECKE
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Bekaert NV SA
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Bekaert NV SA
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Publication of WO2024251972A1 publication Critical patent/WO2024251972A1/fr
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • 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
    • C21D9/562—Details
    • 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
    • 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
    • C21D9/5735—Details
    • 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
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Definitions

  • the present invention relates to a method and an equipment for controlled cooling steel wires to a predetermined temperature range, and for controlled heat removal during the transformation from austenite to pearlite.
  • a steel wire with excellent strain hardening is also provided.
  • EP0524689A1 discloses a process of patenting at least one steel wire with a diameter less than 2.8 mm.
  • the cooling is alternatingly done by film boiling in water during one or more water cooling periods and in air during one or more air cooling periods.
  • a water cooling period immediately follows an air cooling period and vice versa.
  • the speed of cooling in water is high, while the speed of cooling in air is much lower.
  • the high speed of cooling in water poses a serious risk of forming undesired, hard microstructures for wires with a diameter less than 2.8 mm.
  • Cooling in air in between cooling in water sections is performed in order to slow down the cooling of the steel wires.
  • the number of the water cooling periods, the number of the air cooling periods and the length of each water cooling period are so chosen so as to avoid the formation of martensite or bainite.
  • EP2951327A1 discloses a forced cooling process on straight steel wires having a diameter larger than 5 mm. An impinging liquid immersed inside a coolant bath is directed to the steel wire to accelerate the cooling speed of the heated steel wire. This “forced” cooling zone in the coolant bath is followed by a cooling zone in which an undisturbed (this means without impinging liquid on the boiling film around the wire) boiling film cools the wires further.
  • EP3568500A1 discloses an improved method of controlled cooling of one or multiple previously heated and substantially straight steel wire/wires of diameter larger than 2.8 mm to a predetermined temperature range.
  • the previously heated and substantially straight steel wire/wires along individual path/paths out of the first coolant bath/baths, i.e. at the exit of the “forced” cooling zone are further cooled down in air, and then guided along individual path/paths through one or multiple second coolant bath/baths.
  • the substantially straight steel wire/wires are subjected to a cooling transformation from austenite to pearlite.
  • the first aspect of the invention is a method of continuous controlled cooling and controlled heat transformation removal during the austenite-to pearlite transformation for of a plurality of heated steel wires having an austenite microstructure.
  • the plurality of steel wires comprises - and preferably consists out of - steel wires having a diameter larger than 3.0 mm and lower than 20.0 mm, e.g. steel wires having a diameter between 4.0 mm and 16.0 mm, e.g. between 5.0 mm and 14.0 mm.
  • Steel wires are preferably plain carbon steel wires, i.e. their chemical composition comprise between 0.02wt%C and 1.2wt%C.
  • steel wires have a near-eutectoid composition, i.e. the carbon content is comprised between 0.60wt%C and 0.95wt%C.
  • the method comprises the steps of: a) guiding the previously heated and substantially straight steel wire/wires along individual path/paths through a first cooling section.
  • the first cooling section comprises a bath liquid, wherein the bath liquid comprises water and a stabilizing additive.
  • the role of the stabilizing additive is to create a steam film around each steel wire itself along each individual path.
  • the first bath liquid in the first cooling section has a temperature of 80 °C or more.
  • This step, called precooling step can be very short.
  • the pre-cooling zone may have a predetermined length L1 ; b) from a length L1 from the exit of the heating medium (e.g.
  • an impinging liquid introduced inside the first cooling section is directed towards the previously heated and substantially straight steel wire/wires over a certain length L2 along individual path/paths.
  • the impinging liquid is preferably introduced inside the first cooling section directly in the bath liquid, i.e. it is preferably immersed.
  • the impinging liquid decreases the thickness of the steam film or destabilizes the steam film, thereby increasing the speed of cooling over the length L2 along individual path/paths.
  • the intensity of the impinging liquids is individually set and/or controlled for each individual steel wire or for subsets of the plurality of steel wires. This step is the controlled cooling step.
  • the substantially straight steel wire/wires are still fully austenitic, i.e. no phase transformation has started; c)
  • the previously heated and substantially straight steel wire/wires are guided along individual path/paths out of the first cooling section to be further cooled down in one or more bath liquids and/or in air over a length L3.
  • the length L3 comprises the full length between the exit of the controlled cooling zone with length L2 and the entry into the controlled transformation zone with length L4.
  • the previously heated and substantially straight steel wire/wires leave the first cooling section and enter a second cooling section.
  • the length L3 mainly consists in a length in air.
  • the first and the second cooling section are the same.
  • the length L3 mainly consists in a length in coolant bath without impinging liquid, i.e. wherein a stable steam film is formed around the previously heated and substantially straight steel wire/wires.
  • the previously heated and substantially straight steel wire/wires can be guided along individual path/paths out of the bath liquid of the first cooling section to be further cooled down in air and re-enter in the same bath liquid.
  • This step is the homogenisation step. It allows better control of the temperature of previously heated and substantially straight steel wire/wires until the start of the austenite-to-pearlite transformation; d) The previously heated, substantially straight steel wire/wires are guided along individual path/paths through a second cooling section.
  • the second cooling section comprises a bath liquid, wherein the bath liquid comprises water and a stabilizing additive, wherein the bath liquid and the multiple previously heated and substantially straight steel wires create a steam film around each steel wire itself along each individual path and wherein an impinging liquid introduced inside the second cooling section is immediately directed towards the previously heated and substantially straight steel wire/wires over a certain length L4 along individual path/paths, wherein the impinging liquid decreases the thickness of the steam film or destabilizes the steam film, thereby removing the excess heat generated during the transformation from austenite to pearlite (i.e. the latent heat of transformation, or recalescence).
  • the impinging liquid is preferably introduced inside the second cooling section directly in the bath liquid, i.e. it is immersed.
  • the second bath liquid in the second cooling section has a temperature of 75 °C or more.
  • the bath liquid may comprise a stabilizing additive different from the stabilizing additive of the first cooling section.
  • the temperature of the bath liquid in the second cooling section may differ from the temperature of the bath liquid in the first cooling section.
  • the temperature difference between the bath liquid of the first and the second cooling sections is more than 5°C, i.e. the temperature of the bath liquid of the first first cooling section is at least 5°C higher or 5°C lower than the temperature of the bath liquid of the second cooling section.
  • the second cooling section may be the same as the first cooling section, i.e. the first cooling section and the second cooling section are connected, e.g. the recipient containing the bath liquid is the same. In that case the bath liquid has the same stabilizing additive and the same temperature in both the first and the second cooling sections.
  • This step is the controlled transformation step. e) The previously heated and substantially straight steel wire/wires are guided along individual path/paths out of the second cooling section to be further cooled down in air.
  • the method is also suitable for wires having a non-round section, e.g. flat wires, rectangular wires, or profiled wires, solving the inherent environmental issue caused by the large amount of lead drag-out generated during the classical lead-patenting process.
  • the steel wires can comprise a plurality of subsets, parallel to each other.
  • Each subset of wires can consist of wires of specific diameter and/or profile and specific alloy.
  • each steel wire - even steel wires of the same diameter or profile and same alloy - can be optimally patented taking differences in wire positions in the equipment and in previous process steps (e.g. in the heating furnace, in pickling... ) into account.
  • the stabilizing additive is provided to increase the stability of the vapor/steam film around the steel wires.
  • the stabilizing additive may comprise surface active agents such as soap, stabilizing polymers such as polyvinyl pyrrolidone, polyvinyl alcohol and/or polymer quenchants such as alkali polyacrylates or sodium polyacrylate or combinations thereof.
  • the additives are used to increase the thickness and stability of the vapor film around the steel wire.
  • the impinging liquid in the first cooling section has the same composition as the bath liquid of the first cooling section.
  • the impinging liquid in the second cooling section has the same composition as the bath liquid of the second cooling section.
  • the length and the position of the first cooling section and of the second cooling section are adjustable.
  • the intensity of the impinging liquid is steered independently in the first cooling section and in the second cooling section.
  • the intensity of the impinging liquid is individually set and/or controlled for each individual steel wire or for subsets of the plurality of steel wires by means of setting and/or controlling the flow rate of the liquid flows creating the impinging liquids.
  • This can e.g. be implemented by controlling the flow rate of the pump or pumps creating the liquid flows for the impinging liquids; or by controlling or setting one or a plurality of valves or orifices.
  • one or a plurality of sensors are provided.
  • Control of the intensity of the impinging liquids for each individual steel wire or for subsets of the plurality of steel wires is provided by means of a measurement by the one or the plurality of sensors for or at each individual steel wire; or for or at subsets of the plurality of steel wires.
  • Setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids is performed using the measured signals and a controller.
  • the sensor or sensors comprise or consist out of pressure sensors.
  • the pressure sensors are provided for measurement of the liquid pressure at the nozzles creating the impinging liquids; and the sensor measurements are used for setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids.
  • the sensor or sensors comprise or consist out of flow sensors.
  • the flow sensors are provided for measurement of the flow at the nozzles creating the impinging liquids; and the sensor measurements are used for setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids.
  • the intensity of the impinging liquid is steered by pressure sensors because keeping a constant pressure ensures a more stable cooling speed or a constant amount of heat removal, especially when some nozzles are worn, or clogged partly or fully by dirt.
  • one or a plurality of magnetic sensors are provided to measure the magnetic response of one or of subsets of the steel wires; and to provide feedback to adapt in a closed loop control the impinging liquids in the first cooling section and/or in the second cooling section.
  • the transformation from austenite to pearlite starts before the end of the homogenization step, e.g. 5cm before the end of length L3, and finishes before the end of the controlled transformation step with length L4.
  • the position of the second cooling section, the length L4 and intensity of the controlled transformation step provide a fine tuning of the microstructure during the phase transformation from austenite to pearlite.
  • the fineness of pearlite measured by the average interlamellar spacing as well as the volume fraction of coarse pearlite and bainite can be controlled so that an optimized microstructure - similar to or better than the microstructure obtained by patenting in molten lead - can be obtained.
  • the method of the invention provides a more isothermal patenting of steel wire without the use of harmful lead.
  • the wires obtained according to the method of the invention exhibit excellent strain hardening behavior.
  • the second aspect of the invention is an equipment for performing the method of the first aspect of the invention.
  • the equipment is particularly adapted for isothermal patenting of one or multiple previously heated and substantially straight steel wires, by controlled cooling to a predetermined temperature range, and controlled heat removal during the transformation from austenite to pearlite.
  • the equipment comprises: a) a first coolant bath for comprising a first coolant liquid; b) a second coolant bath for comprising a second coolant liquid; c) means for guiding the plurality of previously heated steel wires parallel to each other along individual paths through the coolant liquid contained in the first coolant bath; d) means for guiding the plurality of previously heated steel wires parallel to each other along individual paths through the coolant liquid contained in the second coolant bath; e) impinging liquid generator(s) immersed inside the first coolant bath(s), wherein the impinging liquid generator(s) are adapted to direct impinging liquid towards the steel wires over a certain length L2; f) impinging liquid generator(s) immersed inside the second coolant bath(s), wherein the impinging liquid generator(s) are adapted to direct impinging liquid towards the steel wires over a certain length L4; g) means for individually setting or controlling the intensity of the impinging liquids for each individual steel wire or for subsets of the
  • the equipment may consist of one single coolant bath comprising at least two different impinging liquid generators immersed inside the single coolant bath, wherein the impinging liquid generators are adapted to direct impinging liquid towards the steel wires over a certain length L2 and a certain length L4 separated by a certain length L3 wherein no impinging liquid is directed towards the steel wires.
  • the first coolant bath and the second coolant bath are connected to form a single coolant bath, therefore comprising the same coolant liquid.
  • the third aspect of the invention is a patented steel wire having a fully pearlitic microstructure and excellent strain hardening.
  • the inventors have found that when patenting steel wire with lead-free methods from the prior art, although tensile properties close to tensile properties obtained with lead patenting could be reached, the strain hardening after drawing was lower compared to the strain hardening of lead-patented wire.
  • a pearlitic steel wire with excellent strain hardening preferably comprises between 0.60wt%C and 0.95wt%C, has an average interlamellar spacing, ILS, lower than 105nm, e.g. lower than 100nm, comprises less than 3vol% of coarse pearlite and less than 3vol% of bainite.
  • the pearlitic steel wire with excellent strain hardening of the invention has a surface that does not contain any trace or residues of Pb or any other metal used for isothermal transformation (Bi, Sn,).
  • This aspect provides the possibility to further process the patented wire, e.g. by providing a metallic coating such as but not limited to Zn, Zn alloys (e.g. Zn-AI, Zn-AI-Mg), Cu, Cu alloys... without contamination by other metals, ensuring better corrosion resistance, easier recycling and better sustainability.
  • a typical steel wire rod composition may comprise a carbon content between 0.60wt% and 0.95wt%, a manganese content between 0.20wt% and 0.90wt%, a silicon content between 0.10wt% and 1.40wt%, chromium from 0.05 to 0.40wt%, additional microalloying elements such as aluminum, vanadium and boron, the sum of which is between 0 and 0.20wt%, unavoidable impurities and the balance being iron.
  • Figure 1 shows an isothermal patenting concept according to the present invention.
  • Figure 2 shows a second embodiment of an isothermal patenting concept according to the present invention.
  • Figure 3 shows cooling curves of previously heated steel wires according to different routines.
  • Figure 4 shows strain hardening curves obtained during drawing steel wires that have been cooled according to the different routines of figure 3.
  • lengths L1 to L4 above-mentioned in the description and in the claims correspond to lengths L11 to L41 in figure 1 , and to lengths L12 to L42 in figure 2, respectively.
  • FIG. 1 schematically illustrates an isothermal patenting of one substantially straight steel wire according to the present invention.
  • a steel wire 10 is led out of a furnace 12 having a temperature T of about 1000 °C.
  • the wire running speed can be adjusted according to the diameter of the wire, e.g. between 5m/min and 80m/min, e.g. about 20 m/min.
  • a first cooling section comprises a first coolant bath
  • the first length L11 is the distance away from the exit of furnace 12 to the impinging liquid.
  • the second length L21 indicates the length used for forced coolant cooling process - forced coolant cooling length - in the first coolant bath.
  • the steel wire 10 is then led out of the first coolant bath and subjected to a slow cooling comprising non-forced cooling by immersion in one or more coolants and/or an air gap region.
  • the slow cooling region has a length L31 as indicated in figure 1.
  • the steel wire 10 is guided into a second cooling section comprising a second coolant bath 15 and immediately subjected to forced cooling.
  • the first length L11 defines the pre-cooling zone, it is the distance away from the exit of furnace 12 to the impinging liquid and is used to build a stable steam film around the steel wire 10.
  • the second length L21 defines the controlled cooling zone and indicates the length used for forced coolant cooling process.
  • the pressure and flow rate of the impinging liquid determine the intensity of the jets.
  • the aim of this section is to control the speed of cooling a previously heated wire 10 from austenite to a desired temperature before the start of the transformation to pearlite.
  • the third cooling length L31 defines the homogenisation zone and comprises zones where the wire 10 is still immersed in the first coolant bath 14 of the first cooling section, but outside the controlled cooling length, optionally cooling zones in the air, and zones inside the second cooling bath 15 before reaching the controlled transformation zone.
  • the aim of this section is to precisely control the temperature at which the austenite-to-pearlite transformation starts.
  • the fourth cooling length L41 defines the controlled transformation zone and indicates the length used for forced coolant cooling control.
  • the pressure and flow rate of the impinging liquid determine the intensity of the jets.
  • the aim of this section is to remove the heat generated during the austenite-to-pearlite transformation and obtain a more isothermal transformation.
  • the length L41 should be long enough to cover the full phase transformation, i.e. when the wire 10 leaves the controlled transformation length the microstructure is fully pearlitic.
  • the pre-cooling zone may be short and may have a fixed predetermined length L11 , e.g. less than 1 m or less than 50cm.
  • the controlled cooling zone may have a variable predetermined length L21 depending on the wire diameter and compositions, or may be adjustable, e.g. by increasing the number of jets directing an impinging liquid under the wire 10.
  • the length L21 is fixed.
  • the homogenisation zone preferably has a variable length L31 , which is adjusted by moving the second cooling bath 15 in a direction parallel to the running direction of the wire 10.
  • FIG. 2 shows a second embodiment of the invention.
  • the pre-cooling zone has a length L12
  • the controlled cooling zone has a length L22.
  • the length L32 can be increased or decreased by means of e.g. guiding wheels lifting the wire 10 outside the first coolant bath 14 in the vertical direction.
  • This embodiment is illustrated in figure 2 where a single coolant bath 14 is used instead of two separate coolant baths 14 and 15. In that case it is also possible to skip the air gap and use the slow cooling in the coolant bath as a stable steam film is formed around the steel wire 10.
  • guiding wheels are represented, any other mean to create an homogenisation zone can be envisaged, such as e.g. by blowing high pressure air or by creating a depression in the coolant bath.
  • the controlled transformation zone may have a fixed predetermined length L41/L42, that is function of the wire diameter, speed and chemical composition, such that the length L41/L42 fully covers the transformation from austenite to pearlite.
  • the length L41/L42 is adjustable.
  • Pilot trials have been successfully done on steel wire with a diameter ranging from 3mm to 13mm and with carbon content between 0.60wt% and 0.95wt%.
  • examples below refer to the results of the trials done with a 6mm diameter wire having 0.80wt%C.
  • a wire rod with 8mm diameter has been previously drawn to 6mm.
  • the 6mm pre-drawn wire is heated in line in a resistive heating furnace under protective atmosphere comprising H2 and N2 to around 1000°C and submitted to different cooling paths according to the invention.
  • the linear speed of the 6mm wire is 20m/min.
  • Figure 3 illustrates the different cooling paths as simulated by a thermal model for the 0.80wt%C - 6mm wire pre-heated at 1000°C.
  • Sample A is cooled in molten lead at 550°C and is assumed to have the most isothermal transformation. However, it can be seen from the dotted curve in figure 3 that even in lead significant heat is generated during the austenite-to-pearlite transformation, causing the wire temperature to increase with approximately 50°C from about 555°C to 605°C.
  • Samples B, C and D are obtained according to the second embodiment by varying the respective lengths (referring to figure 2) L22, L32 and L42, and the jet intensities in the controlled cooling zone and in the controlled transformation zone (i.e. relative to the length L22 and L42).
  • Samples E and F are obtained according to the first embodiment by varying the respective lengths (referring to figure 1 ) L21 , L31 and L41 , and the jet intensities in the controlled cooling zone and in the controlled transformation zone (i.e. relative to the length L21 and L41 ).
  • Table 1 reports the cooling conditions, the microstructure and the tensile strength of samples A to F.
  • the microstructure is characterized by the amount of coarse pearlite (CP), and the volume fraction of bainite.
  • the structure components should be evaluated in general microscopic way, e.g. by light optical microscopy. Coarse pearlite is evaluated at magnification 500x. Higher bainite is evaluated at 500x or at 1000x if determination is not clear enough.
  • Higher bainite is a “feather-like” phase in a pearlite matrix, showing low contrast with the matrix phase.
  • magnification, number of fields, grid size is selected according ASTM E562.
  • the mean interlamellar spacing (ILS) of pearlite is determined according to Underwood’s method. It consists in superimposing an intersection grid of three circumferences in such a manner that the lines intersect the pearlite lamellae randomly in all directions.
  • the mean intercept I is obtained by dividing the total line length by the number of the lamellae intercepted of each grid line.
  • the mean true value of interlamellar spacing ILS is given by the equation below:
  • interlamellar spacing or “mean interlamellar spacing” or “average interlamellar spacing” or simply “interlamellar spacing” all refer to the mean true value of interlamellar spacing as defined above.
  • the space between the lamellae defines the interlamellar spacing and this distance can be measured by scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • ILS mean interlamellar spacing
  • TS tensile strength
  • Sample F has an optimized microstructure with ILS below 105nm, and less than 3vol% of coarse pearlite and less than 3vol% bainite.
  • Figure 4 shows that optimized sample F has not only a higher tensile strength after patenting compared to the lead patented sample A, but sample F has also similar strain hardening. The tensile strength of the drawn sample F is the highest of all samples.
  • the present invention allows a more isothermal patenting process without the use of molten metal detrimental for the environment.
  • the obtained wires can reach a tensile strength equivalent or higher than lead-patented wires, have same or better strain hardening that lead-patented wires and do not contain traces or residues of lead or other metal on their surface or at their interface with a metallic coating.

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  • Mechanical Engineering (AREA)
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Abstract

Un procédé et un équipement de patentage isotherme de fil d'acier sans plomb ou métal fondu, font appel au refroidissement contrôlé de fils d'acier à une plage de température prédéterminée, et à l'élimination de chaleur contrôlée pendant la transformation de l'austénite en perlite. Un fil d'acier ayant un excellent durcissement par écrouissage est obtenu.
PCT/EP2024/065781 2023-06-09 2024-06-07 Patentage isotherme de fils d'acier Pending WO2024251972A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP23178331 2023-06-09
EP23178331.7 2023-06-09

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0524689A1 (fr) 1991-07-22 1993-01-27 N.V. Bekaert S.A. Procédé de traitement thermique de fils d'acier
EP2951327A1 (fr) 2013-02-01 2015-12-09 NV Bekaert SA Refroidissement de fils d'acier épais par eau à circulation forcée
EP3150738A1 (fr) * 2014-06-02 2017-04-05 Nippon Steel & Sumitomo Metal Corporation Matériau de fil d'acier
EP3228721A1 (fr) * 2014-12-05 2017-10-11 Nippon Steel & Sumitomo Metal Corporation Fil machine en acier à haute teneur en carbone présentant d'excellentes propriétés de tréfilage
EP3568499A1 (fr) * 2017-01-12 2019-11-20 NV Bekaert SA Procédé et équipement de patentage contrôlé de fil d'acier

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0524689A1 (fr) 1991-07-22 1993-01-27 N.V. Bekaert S.A. Procédé de traitement thermique de fils d'acier
EP2951327A1 (fr) 2013-02-01 2015-12-09 NV Bekaert SA Refroidissement de fils d'acier épais par eau à circulation forcée
EP3150738A1 (fr) * 2014-06-02 2017-04-05 Nippon Steel & Sumitomo Metal Corporation Matériau de fil d'acier
EP3228721A1 (fr) * 2014-12-05 2017-10-11 Nippon Steel & Sumitomo Metal Corporation Fil machine en acier à haute teneur en carbone présentant d'excellentes propriétés de tréfilage
EP3568499A1 (fr) * 2017-01-12 2019-11-20 NV Bekaert SA Procédé et équipement de patentage contrôlé de fil d'acier
EP3568500A1 (fr) 2017-01-12 2019-11-20 NV Bekaert SA Procédé et équipement de patentage sans plomb

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