US20200232063A1 - Method and furnace for thermally treating a high-resistance steel strip comprising a temperature homogenisation chamber - Google Patents

Method and furnace for thermally treating a high-resistance steel strip comprising a temperature homogenisation chamber Download PDF

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US20200232063A1
US20200232063A1 US16/722,637 US201916722637A US2020232063A1 US 20200232063 A1 US20200232063 A1 US 20200232063A1 US 201916722637 A US201916722637 A US 201916722637A US 2020232063 A1 US2020232063 A1 US 2020232063A1
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strip
temperature
chamber
homogenisation
oxidation
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Jean-Pierre Crutzen
Lutz Kümmel
Frank Maschler
Michel Renard
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Drever International SA
John Cockerill SA
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Drever International SA
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    • 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
    • C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
    • 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
    • C21D1/26—Methods of annealing
    • 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
    • C21D1/34—Methods of heating
    • 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
    • C21D1/34—Methods of heating
    • C21D1/52—Methods of heating with flames
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • 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
    • C21D9/562—Details
    • C21D9/563—Rolls; Drums; Roll arrangements
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising
    • C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
    • C23C8/18—Oxidising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/28—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity for treating continuous lengths of work

Definitions

  • the invention relates to a method for thermally treating a high-resistance steel strip.
  • the invention relates to a furnace for thermally treating a high-resistance steel strip.
  • Commonly used high-resistance steels comprise alloy elements, for example manganese, silicon, chromium and/or aluminium alloy.
  • alloy elements for example manganese, silicon, chromium and/or aluminium alloy.
  • the alloy elements present in the high-resistance steel can diffuse towards the surface of the steel and be rapidly oxidised due to the great affinity thereof for oxygen and this, even in radiant tube zones where the atmosphere is nevertheless reducing for iron oxides.
  • This selective oxidation creates surface defects which make it difficult to adhere the zinc coating (or other metal or alloy) applied during the galvanisation of the surface.
  • This wettability problem is a limiting aspect of the galvanisation which cannot be carried out correctly.
  • One particularly studied route consists of subjecting, in the annealing furnace, the surface of the strips to temperature and atmosphere conditions specific to rapidly and deeply oxidising the alloy elements and thus avoid the migration thereof into the surface. During this operation, an iron oxide layer is formed which will subsequently be removed in the following zones of the annealing furnace under a reducing atmosphere.
  • one of the aims of the present invention is to provide a method for thermally treating a high-resistance steel strip making it possible to obtain, on the surface thereof, an oxide formation with a more homogenous and more controlled thickness.
  • the inventors propose a method for thermally treating a scrolling high-resistance steel strip, said method comprising the following steps:
  • the method of the invention makes it possible, during the thermal treatment, thanks to the temperature homogenisation step, the oxidation of the strip having a surface which is more homogenous in temperature. This makes it possible for a growth of an oxide layer having a more homogenous thickness over the whole strip surface. A more homogenous oxide thickness on the surface of the strip makes it possible to have a subsequent, better controlled reduction of said oxide layer. Indeed, variations in the thickness of the oxide layer formed during the oxidation step require an adaptation of the reduction time during the reduction step, in order to reduce the oxide over the whole surface of the strip. Such an adaptation of the reduction time is based on larger oxide thicknesses for instance.
  • the method of the invention makes it possible for better control of the time of the reduction step, as it guarantees a more homogenous oxide thickness over the strip surface.
  • the method of the invention is particularly advantageous, as it makes it possible to compensate for the temperature inhomogeneity of the strip, in particular of the surface of the strip during step a) of heating the strip by direct flame.
  • the use of a zone for heating with a direct flame makes it possible for a rapid increase in temperature of the strip, at the expense of the temperature homogeneity of the metal product.
  • the oxidation chamber is positioned directly after the zone for heating with a direct flame, such that the oxidation is carried out on a strip, of which the temperature homogeneity is not well controlled.
  • Oxidation achieved during the heating by direct flame makes an adjustment of the thickness of the FeO layer formed very difficult to control. Indeed, in EP 2 010 690 A1, it has been observed that for the same oxidising conditions at the level of the atmosphere during the heating by direct flame, an increased scrolling speed shows a thinner FeO layer with respect to lower scrolling speeds, demonstrating the great sensitivity of the method for forming iron oxide at different parameters brought into play.
  • An advantage of the method of the invention with respect to methods where the oxidation is achieved at the same time as the heating of the strip in a zone for heating with a direct flame is that the method of the invention makes it possible to separate the heating from the strip, the temperature homogenisation and the oxidation thereof with separate steps and furnace chambers. This makes it possible for better control of the parameters for forming iron oxide on the surface of the strip while enabling heating of the strip by direct flame.
  • the invention makes it possible to overcome the disadvantages of the heating by direct flame by introducing a temperature homogenisation chamber. Thanks to the invention, it is therefore possible to have a furnace having a very high quality of thermal treatment, as well as a better surface state of the strip before the galvanisation thereof and this for reasonable utilisation costs.
  • an oxygen volume concentration must be understood as an O 2 (volume) concentration.
  • the steps of the method of the invention are to be carried out according to the following order: step a), step b), step c), and step d).
  • the reduction zone has a reducing atmosphere having a hydrogen volume concentration greater than 3% and preferably greater than 5%, and even more preferably, greater than 8.
  • a hydrogen volume concentration greater than 3% and preferably greater than 5%, and even more preferably, greater than 8.
  • An advantage associated with such hydrogen volume concentrations in the reduction zone for these preferred embodiments, is to increase the guarantee that the reduction will take place.
  • the remainder of the composition of the atmosphere of the reduction zone comprises nitrogen.
  • a hydrogen (volume) concentration must be understood as an H 2 (volume) concentration.
  • the method of the invention is particularly effective for high-resistance steel strips, for example having a composition by weight in Cr less than 5%, preferably less than 3% and even more preferably, less than 1%.
  • a steel comprising alloy elements such as manganese, silicon, chromium and/or aluminium alloy is understood by the term “high-resistance steel”.
  • the strip has a thickness of between 0.3 mm and 3.2 mm.
  • the homogenisation chamber comprising at least one radiant heating tube is intended to make it possible for a standardisation/homogenisation of the temperature of the strip when the latter is present in the homogenisation chamber.
  • the temperature standardisation of the strip is produced progressively during the passage thereof in the homogenisation chamber in order to obtain a temperature as uniform as possible at the homogenisation chamber outlet.
  • the homogenisation chamber is not principally intended to make the average temperature of the strip vary but is rather intended to standardise the temperature of the strip.
  • radiant elements and/or heating elements can be present, which have a power which can be modified rapidly, which makes it possible to adjust the temperature rapidly so as to maintain an optimal temperature at the inlet of the oxidation chamber and to ensure a regular oxidation of the surface of the steel strip.
  • the temperature homogenisation chamber comprises two, three, or four radiant heating tubes.
  • the temperature of the strip is comprised in the present application as being a temperature measured on the surface of the strip and representing the temperature over the whole thickness of the strip. Indeed, for strips having a thickness of between 0.6 mm and 2.5 mm, the diffusion of the heat in the whole thickness is very rapid and it can therefore be estimated that a temperature of the strip at a point of the strip on the surface thereof is representative of the temperature in the whole of the thickness of the strip. This is particularly true when the strip is in a mainly homogenous temperature chamber. Thus, a temperature homogeneity or inhomogeneity can be characterised by surface temperature measurements of the strip in separate places.
  • a temperature inhomogeneity is observed over a strip section, when there is a temperature difference greater than 5%, preferably greater than 2% and even more preferably, greater than 1% between a point situated at the centre of the strip and a point situated on the edge of the strip.
  • the strip temperature is, for example, an average strip temperature taken over a strip section at several different points, for example the strip temperature is the average of the temperatures measured at the level of the two edges, as well as in the centre thereof.
  • a target strip temperature is reached when the average strip temperature and the target strip temperature are equal, or in any case, have a difference less than 2%, preferably less than 1%.
  • the strip temperature remains mainly the same, but it is homogenised on the surface.
  • the oxidising atmosphere in the oxidation chamber has an oxygen volume concentration of between 1.5% and 5% and even more preferably of between 2% and 5%.
  • the oxidation chamber of the invention does not comprise any radiant heating tube inside it.
  • the oxidation chamber is confined, for example isolated, inside a radiant heating furnace section such that it is heated indirectly by the radiant heating tubes of the radiant heating furnace section.
  • the method according to the invention further comprises a step of homogenising the oxidising gas of the oxidation chamber comprising:
  • the heating by direct flame is used to clean the high-resistance steel strip (degreasing, for example).
  • the cleaning makes it possible, in particular, to remove the organic residue present on the surface of the steel strip.
  • the oxidation step is carried out at a strip temperature of between 650° C. and 750° C.
  • a strip temperature of between 650° C. and 750° C. makes it possible for good control of the oxidation kinetics of the surface of the strip during the passing thereof into the oxidation chamber, wherein the oxygen volume concentration is greater than 1%.
  • the oxygen volume concentration in the oxidation chamber is between 1.5% and 5% and even more preferably, between 2% and 5%. Controlling the homogeneity of the oxidation kinetics is ensured thanks to the passing of the strip into the homogenisation chamber.
  • the duration of exposure of said steel strip in the oxidation chamber is between 2 and 8 seconds, preferably going from 2 to 4 seconds.
  • the oxidation step is performed in a confined or relatively confined manner in the oxidation chamber.
  • RTF Radiant Tube Furnaces
  • the oxidation step is homogenous in that it makes it possible for the homogenous oxidation on the surface of said steel strip.
  • the oxidation step is carried out by propulsion of an oxidising gas by means of a carrier gas, preferably nitrogen.
  • a carrier gas preferably nitrogen.
  • the method according to the invention comprises the application of a pressure inside said oxidation chamber and in the remainder of the furnace, said pressures being substantially equal.
  • the method according to the invention makes it possible to maintain an easily controllable oxidation which avoids the disturbances caused by the atmosphere which surrounds the oxidation chamber.
  • heating step a), temperature homogenisation step b), as well as reduction step d) are carried out with a reducing atmosphere having a hydrogen volume concentration greater than 3%.
  • the reducing atmosphere in the reduction zone has an atmosphere having a hydrogen concentration of between 3% and 5%.
  • the reduction zone has a composition comprising a hydrogen concentration of between 3% and 5%, the remainder of the composition comprising nitrogen.
  • the temperature homogenisation step is carried out at a strip temperature of between 650° C. and 750° C.
  • such a temperature range makes it possible for good control of the kinetics for forming oxide in the oxidation chamber, i.e. in the presence of an oxygen volume concentration generally of between 1% and 5%.
  • a homogenisation at a target temperature means that there is a heat input to the strip strictly equal to the heat lost by the strip.
  • the homogenisation is achieved with a mainly zero heat input/loss balance so as to prevent the introduction of other temperature inhomogeneities to the strip.
  • the heating step a) is carried out, so as to obtain a strip temperature of between 650° C. and 750° C.
  • step a) is carried out under reducing conditions in the presence of carbon monoxide and hydrogen.
  • Such conditions are generated by using a non-stoichiometric fuel/oxidiser mixture and particularly low in oxygen.
  • the temperature homogenisation step is carried out with an atmosphere having an oxygen volume concentration less than 0.01% by volume, preferably with an atmosphere without oxygen.
  • the temperature homogenisation step is carried out in a chamber adjacent to the oxidation chamber, the atmosphere in the homogenisation chamber can be kept low, even very low, in oxygen. This can be made possible according to a preferred embodiment, by the presence of confinement means positioned between the oxidation chamber and the homogenisation chamber, for example by using an airlock.
  • Such confinement means can be particularly desired as significant passages of gas or badly controlled passages of gas between the oxidation chamber and the reduction zone and/or the temperature homogenisation chamber, can lead to damaging gas exchanges between the different chambers of the furnace.
  • the oxygen escapes from the oxidation chamber to a chamber under reducing atmosphere, the water vapour content increases in this zone. Then, the increase in water vapour content impacts the dew point and can lead to undesired oxidation phenomena, like for example the oxidation of alloy compounds on the surface of the steel.
  • these alloy compounds have a great affinity for oxygen, and the selective oxidation thereof has a detrimental impact on the adhesion of the coating obtained after galvanisation.
  • the oxygen volume concentration in the oxidation chamber can represent a volume concentration, particularly sensitive to undesired gas exchanges with adjacent chambers.
  • the heating step a) is carried out with an atmosphere having an oxygen volume concentration less than 0.01% by volume, preferably with an atmosphere without oxygen.
  • the temperature homogenisation step is carried out by the scrolling of the strip in the proximity of said at least one radiant heating tube.
  • the advantage of scrolling of the strip in the proximity of a radiant heating tube is to make it possible to supply a quantity of heat to the strip, well controlled over the whole width of the strip.
  • the scrolling of the strip in the proximity of the radiant heating tube makes it possible for a heat exchange between the strip and the radiant heating tube.
  • This makes it possible to maintain the temperature of the strip, for example at the target temperature, while making it possible for a homogenisation of the temperature of the strip.
  • the invention makes it possible to benefit from the advantages of a heating by direct flame, while compensating for the disadvantages linked to the heating by direct flame (strip temperature inhomogeneity).
  • the strip scrolls at a distance from a radiant heating tube of between 0.1 m and 0.2 m.
  • said homogenisation section comprises at least two radiant heating tubes.
  • the metal product scrolls between said two radiant heating tubes.
  • the scrolling of the steel strip in front of the two radiant heating tubes makes it possible for an improvement of the temperature homogeneity of the steel strip by leaving more time for the steel strip to be balanced in temperature while receiving a quantity of heat from the radiant heating tubes making it possible to preserve a target strip temperature.
  • the target strip temperature is generally between 650° C. and 750° C. and corresponds to a temperature at which the oxidation of the oxidation chamber strip is well controlled. The same reasoning can be applied for three, four, six radiant heating tubes.
  • the heating of the strip in step a) is carried out until reaching a target strip temperature between 650° C. and 750° C.
  • the temperature homogenisation of the strip in step b) is carried out so as to homogenise the temperature of the strip according to said target temperature.
  • the homogenisation step of step b) makes it possible to keep the strip at the target temperature.
  • the heat communicated by the radiant heating tube(s) to the strip has the sole aim of maintaining the temperature of the strip according to the target temperature, as well as homogenising its temperature.
  • the radiant heating tubes during the temperature homogenisation step radiate towards the strip in a uniform manner, making it possible for good homogenisation of the temperature of the strip, on the surface, as well as according to the thickness of the strip.
  • one of the aims of the present invention is to provide a furnace for the thermal treatment of a high-resistance steel strip by scrolling, making it possible for an oxide formation on the surface of the strip with a more homogenous and more controlled thickness.
  • a furnace for the thermal treatment of a high-resistance metal strip by scrolling comprising:
  • the temperature homogenisation chamber is positioned between the zone for heating with a direct flame and the oxidation chamber.
  • a radiant heating furnace section is an RTF.
  • the homogenisation chamber is situated in the radiant heating furnace section, likewise the oxidation chamber.
  • said homogenisation chamber comprises at least two radiant heating tubes and even more preferably, at least three radiant heating tubes.
  • the number of radiant heating tubes in the homogenisation chamber makes it possible to define the length thereof, along which the strip can be balanced in temperature while remaining at the target strip temperature.
  • the number of radiant heating tubes and the length of the temperature homogenisation chamber depend on the zone for heating by a direct flame and on the temperature inhomogeneity of the strip which emerges, as well as the desired temperature homogeneity of the strip in the oxidation chamber.
  • the number of radiant tubes and the length of the homogenisation chamber can also depend on the target temperature at the outlet of the homogenisation chamber.
  • the metal product is positioned scrolling between at least two radiant heating tubes.
  • Such an embodiment makes it possible for better homogenisation of the temperature of the strip as is described for the method according to the first aspect of the invention.
  • the furnace further comprises a first and a second roller for guiding the scrolling strip, the first roller being positioned downstream from the zone for heating with a direct flame and the second roller being positioned downstream from the oxidation chamber.
  • the strip is preferably maintained under traction in the homogenisation chamber, such that while scrolling, said strip describes a mainly rectilinear path during the passing thereof into the homogenisation chamber and into the reduction zone.
  • the first and second rollers are positioned such that said metal strip is stretched according to a mainly vertical orientation between said rollers.
  • a mainly vertical strip orientation corresponds to a strip orientation with respect to a flat floor describing an angle with the norm to the flat floor of between 0° and 15°.
  • the strip is under traction in the furnace, such that it is stretched during the passing thereof into the homogenisation chamber, then in the oxidation chamber.
  • the furnace is configured such that the metal strip is stretched according to a mainly horizontal orientation.
  • the oxidation chamber is further delimited by two airlocks which are each constituted by at least two airlock rollers.
  • two airlocks which are each constituted by at least two airlock rollers.
  • the oxidation chamber is confined from the homogenisation chamber and the reduction zone by two confinement means making it possible for the scrolling of the strip through said oxidation chamber, for example, the two confinement means are two airlocks.
  • the two confinement means are two airlocks.
  • the oxidation chamber is equipped with air vents in order to balance the inlet and outlet volumes to balance the pressure inside the chamber and also to reduce the possible gas transfers by leakages.
  • FIG. 1 shows an embodiment according to the invention
  • FIG. 2 shows an embodiment according to the invention
  • FIG. 3 shows a schematic view of the supply of a strip to a temperature homogenisation chamber, then to an oxidation chamber and the progression of the strip to a reduction zone.
  • FIG. 1 shows a schematic illustration of the furnace 1 according to the second aspect of the invention making it possible to implement the method according to the first aspect of the invention.
  • the furnace 1 comprises, in the scrolling direction of the strip 5 , a zone for heating with a direct flame 10 , a temperature homogenisation chamber 20 , an oxidation chamber 30 and a reduction zone 40 for reducing oxide and the thermal treatment of the strip.
  • the furnace 1 comprises a direct heating furnace section 2 comprising the zone for heating with a direct flame 10 and a radiant heating furnace section 3 comprising the temperature homogenisation chamber 20 , the oxidation chamber 30 and the reduction zone 40 .
  • the method according to the invention comprises the implementation of step a) for heating the strip 5 by direct flame in the zone for heating with a direct flame 10 .
  • the method then comprises the implementation of step b), i.e. the scrolling of the strip 5 in the proximity of at least one radiant heating tube 25 so as, for example, to leave time for the strip 5 preheated to a target temperature, to be homogenised in temperature, while preserving said target temperature.
  • the strip 5 can be heated in the homogenisation chamber 20 so as to have a (homogenised) outlet temperature greater than the inlet temperature.
  • the method then comprises the implementation of the oxidation step c), i.e.
  • the method for thermally treating a steel strip 5 comprises, after step c), step d) during which, the steel strip 5 oxidised in step c), undergoes a thermal treatment at a strip temperature up to 800° C. and preferably up to 850° C.
  • the strip 5 is subjected to a reducing atmosphere preferably comprising a hydrogen volume concentration greater than 3%, and more preferably, between 3% and 5%.
  • the remaining volume fraction being generally nitrogen.
  • the temperature of the thermal treatment in the reduction zone during step d) can be modified, relatively easily, without steps a), b) and c) being greatly modified.
  • FIG. 2 shows a view of the whole of a furnace 1 according to the second aspect of the invention, with a schematic representation of the progression of the strip 5 through the zone for heating with a direct flame 10 , the homogenisation chamber 20 , the oxidation chamber 30 and the reduction zone 40 comprised in the furnace 1 .
  • the strip 5 describes a succession of vertical passes during which it scrolls through the direct heating furnace section 2 , then the radiant heating furnace section 3 . After having scrolled through the zone for heating with a direct flame 10 , the strip 5 enters into the radiant heating furnace section 3 through the homogenisation chamber 20 .
  • the zone for heating with a direct flame 10 comprises two pass lines. Then, the strip 5 is directed towards the temperature homogenisation chamber 20 .
  • the pass line comprising the temperature homogenisation chamber 20 and the oxidation chamber 30 is situated in the RTF section (radiant heating furnace section) of the furnace 1 .
  • the oxidation chamber 30 is at a similar temperature of the RTF section which surrounds it while being preferably isolated at the level of the oxygen and hydrogen content.
  • the reduction zone 40 comprises a series of vertical passes surrounded by radiant heating tubes 25 making it possible for an adjustment of the temperature of the strip 5 in order to carry out a desired thermal treatment of the high-resistance steel strip 5 .
  • FIG. 3 shows a schematic view of the supply of the strip 5 to the temperature homogenisation chamber 20 , then to the oxidation chamber 30 and the progression of the strip 5 to the reduction zone 40 .
  • FIG. 3 shows a particular embodiment of the temperature homogenisation chamber 20 which illustrates, by way of example, three radiant heating tubes 25 arranged such that the strip 5 passes, in the proximity during the scrolling thereof, into the temperature homogenisation chamber 20 .
  • the temperature homogenisation chamber 20 illustrated makes it possible for good homogenisation of the temperature of the strip 5 at a target temperature, the target temperature being defined according to the composition of the steel. Thus, an oxide thickness specifically defined and homogenous over the whole of the surface of the strip 5 can be obtained.
  • a steel strip 5 is supplied in a zone for heating with a direct flame 10 and is heated under reducing conditions, in the presence of carbon monoxide and hydrogen, preferably so as to reach a strip temperature of between 650° C. and 750° C.
  • the steel strip is then brought towards the oxidation chamber 30 which is confined in the section of the radiant heating furnace (RTF), where the oxidation occurs with an oxygen content greater than 1%.
  • RTF radiant heating furnace
  • This oxidation step makes it possible for the formation on the surface of an iron oxide layer, for example.
  • the oxide layer is removed during the step of thermally treating in a reducing atmosphere, in order to proceed with the galvanisation step according to a method well-known to a person skilled in the art.
  • Method for thermally treating a scrolling high-resistance steel strip 5 comprising the following steps:
  • a homogenisation chamber 20 comprising at least one radiant heating tube 25 , so as to homogenise a temperature of the strip 5 after the passing thereof into the zone for heating with a direct flame 10 ;

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US16/722,637 2019-01-23 2019-12-20 Method and furnace for thermally treating a high-resistance steel strip comprising a temperature homogenisation chamber Abandoned US20200232063A1 (en)

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US11414738B2 (en) * 2016-10-14 2022-08-16 Liberty Performance Steels Limited Manufacture of a stress relieved length of steel having an oxidised surface layer
EP4303516A1 (en) * 2022-07-05 2024-01-10 John Cockerill S.A. Device for improving preoxidation in an annealing furnace

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RU2766264C2 (ru) 2022-02-10
BE1026986A1 (fr) 2020-08-17
EP3686534A1 (fr) 2020-07-29
BR102020001356A2 (pt) 2020-08-04
RU2019142708A (ru) 2021-06-21
RU2019142708A3 (zh) 2021-12-09
ES2874752T3 (es) 2021-11-05
CN111471847B (zh) 2023-10-31
MX2019015493A (es) 2020-07-28
CN111471847A (zh) 2020-07-31
EP3686534B1 (fr) 2021-03-10
BE1026986B1 (fr) 2020-08-25
SI3686534T1 (sl) 2021-07-30
KR20200092253A (ko) 2020-08-03

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