EP1386012B1 - Method for enhancing the metallurgical quality of products treated in a furnace - Google Patents

Method for enhancing the metallurgical quality of products treated in a furnace Download PDF

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Publication number
EP1386012B1
EP1386012B1 EP02735468A EP02735468A EP1386012B1 EP 1386012 B1 EP1386012 B1 EP 1386012B1 EP 02735468 A EP02735468 A EP 02735468A EP 02735468 A EP02735468 A EP 02735468A EP 1386012 B1 EP1386012 B1 EP 1386012B1
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EP
European Patent Office
Prior art keywords
product
furnace
temperature
treated
atmosphere
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EP02735468A
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German (de)
French (fr)
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EP1386012A1 (en
Inventor
Savine Bockel-Macal
Olivier Delabroy
Olivier Louedin
Christel Champinot
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Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
Air Liquide SA
LAir Liquide SA a Directoire et Conseil de Surveillance pour lEtude et lExploitation des Procedes Georges Claude
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Priority claimed from FR0105634A external-priority patent/FR2824078B1/en
Priority claimed from FR0105633A external-priority patent/FR2824077B1/en
Application filed by Air Liquide SA, LAir Liquide SA a Directoire et Conseil de Surveillance pour lEtude et lExploitation des Procedes Georges Claude filed Critical Air Liquide SA
Publication of EP1386012A1 publication Critical patent/EP1386012A1/en
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    • 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
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/40—Arrangements of controlling or monitoring devices
    • 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
    • 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
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/36—Arrangements of heating devices
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • 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
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets

Definitions

  • the invention relates to a method for improving the quality metallurgy of products treated in an oven and in particular a furnace of reheating.
  • This invention applies to any type of product but more particularly to products treated in a reheating furnace such as, for example, for example, billets, blanks or slabs or any other material used by steelmakers in their production line (such as sheet metal, tubes, etc.).
  • the invention relates more particularly to a method of treatment of a metallurgical product in an oven, in which the product to be treat is introduced into the oven and then subjected to the desired treatment and then removed furnace, the furnace comprising heating means and in particular burners allowing to bring to different temperatures the different areas of the oven, the atmosphere in these different areas may have a identical or different composition according to the considered zones of said furnace.
  • the weathered area on the surface of these pieces is composed essentially two parts (see Fig 1), one located on the side of the atmosphere (upper scale), and the other in the vicinity of the metal (zone mixed).
  • the upper part generally comprises three compact layers of oxides: a layer of oxides Fe 2 O 3 (hematite), very thin (a few microns thick), a layer of magnetite (Fe 3 O 4 ) (4% of the total scale) and a layer of thick oxide FeO (wustite) (95% of the total scale total) more or less porous depending on the duration and the temperature of the reheating.
  • a layer of oxides Fe 2 O 3 hematite
  • very thin a few microns thick
  • Fe 3 O 4 4% of the total scale
  • FeO wustite
  • This calamine which adopts a parabolic appearance, is controlled by the diffusion of Fe 2+ ions in wustite and magnetite, and by the diffusion of oxygen O 2 - in hematite.
  • the lower part, mixed zone, is more or less large depending on the nature of the steel. It is located at the metal / scale interface, consisting of a FeO mixture and FeO reaction products with the oxides of certain alloying elements. This lower part also includes a zone of metal altered by various phenomena such as decarburization or internal oxidation. Decarburization is a phenomenon of solid state diffusion of carbon that reacts with FeO (and / or H 2 O) scale.
  • the iron and steel products can be oxidized (calamine) and decarburized (and all the more so for steels with high carbon).
  • the steelmaker will have to submit to his parts an additional operation to overcome these surface defects.
  • the oxide layer can be removed by different descaling techniques, the decarburization layer, which is an integral part of the part, can not be easily “gummed”: the surface of the product is deprived of a part of its carbon atoms, which causes a loss of the mechanical properties on the surface of the product (longevity, hardness ).
  • Oxidation or decarburization of steel in a heating furnace leads to a loss of raw material, which is known as a loss on ignition and degradation of the surface properties of products that are detrimental to the steelmaker.
  • Patent EP-A-0767353 also proposes to intervene on the oven atmosphere by zoning the oven, ie by isolating the furnace into several enclosures in which an atmosphere strongly oxidant is recommended in order to control training and quality of the calamine. In this case, the loss on ignition is not diminished but on the contrary increased, only a calamine quality control is assured.
  • the species H 2 O and CO 2 also have, according to the Applicant, an oxidizing role on the feedstock and are involved in the scale formation reactions and in the decarburization mechanisms. At present, it is not known to measure these species simply and quickly.
  • the operator follows an initial profile of temperature of the given product for a given furnace, depending on the type of load and production. This profile is known to the operator thanks to his know-how, either calculated from charts, or calculated using a adapted software.
  • thermocouples located in the vault of the oven. These thermocouples are arranged far from the load and are not representative of the heat flux received by the load, under the burners. An estimate of the relationship connecting the vault temperature (measured) and the temperature of the charge (information useful) is therefore necessary. This relationship is either empirical (knowledge-based operators) is calculated by the furnace control software.
  • this measure is a one-off measure usually located on the axis of the furnace and which does not take into account possible variations of the said parameter over the entire width of the oven.
  • the object of the present invention is to provide a method of driving of a furnace (temperature, composition of the atmosphere) and a method of associated control, making it possible to optimize both the metallurgical quality of a product, fire loss and thermal efficiency of an oven
  • the product to be treated has a temperature which increases between the moment when it is introduced and the moment when it is removed from the oven, the temperature rise curve having a slope which increases in a first interval of time.
  • time between the time t 0 for introducing the product into the oven and the instant t 1 at which the product reaches a surface temperature of 650 ° C. a substantially constant slope between the instant t 1 and the instant t 2 at which the product reaches a temperature of about 15% lower than the desired final surface temperature for the product to be treated when it leaves the oven, then a slope that decreases between time t 2 and time t 3 at which the product to be treated leaves the oven, in which process the heating power of the furnace is increased relative to its power when only aero-fuel burners are used so as to increase the slope of the temperature rise curve of the furnace.
  • the increase of the furnace heating power is obtained by means of oxy-fuel burners which constitute at least a part of the furnace heating means, in particular a portion of the furnace heating means corresponding to the zone. reached by the product between instants t 1 and t 2 . It is also possible to place this or these burner (s) oxy-fuel (s) in an area adjacent to the above-mentioned area, which indirectly allow to obtain the same power increase (in said area reached between times t 1 and t 2 , by the product).
  • the oxidizer supplied to the oxy-fuel burners constituting at least part of the oven heating means has at least 88% oxygen and preferably more than 90% oxygen, more preferably more than 95% oxygen.
  • the time of treatment of the product between temperatures of 700 ° C and 800 ° C achieved for the surface of the product is decreased by 15% to 50% of its reference value, preferably from 20 to 35% of its value, while the processing time between the temperatures of 700 ° C and the final temperature of the product surface is decreased between 3 and 25% of its reference value, preferably between 7% and 15% of its reference.
  • the atmosphere of the oven varies along the oven depending on the skin temperature of the product metallic.
  • the atmosphere of the oven in contact with the product to be treated comprises about 0.5% vol to 5% oxygen and preferably between 1.5 vol at 4 vol vol oxygen when the skin temperature T at the surface of the treated product is greater than or equal to equalization temperature T equ , which is equal to 85% of the temperature at the surface of the product (defatting temperature) at the oven outlet.
  • equalization temperature T equ is equal to 85% of the temperature at the surface of the product (defatting temperature) at the oven outlet.
  • the soaking temperature T equal is equal to 90% of the temperature of diversion.
  • the atmosphere in contact with the product to treat has an oxygen concentration of less than a few hundreds of ppm and a CO concentration between 0.1% and 15%, preferably 0.5% to 5% vol when skin temperature T on the surface the product is above 700 ° C and below the equalization temperature of the product, defined as being equal to 90% of the skin temperature of produced at the outlet of the oven.
  • the atmosphere in contact with the product to treat has an oxygen concentration between 0.5% and 4% flight and preferably between 2% and 3% vol when the skin temperature T to the surface of the product to be treated is less than 700 ° C.
  • the invention makes it possible to optimize the metallurgical quality of the products by optimizing the heating profile in the oven and improving the control of the composition of the oven atmosphere.
  • This control continuously monitors the O 2 and / or H 2 O and / or CO 2 contents of the atmosphere in the different zones of the furnace, and / or the temperature at the surface of the products to be treated, will preferably be carried out at using a laser diode.
  • This laser diode system called TDL (Tunable Diode Laser) makes it possible to measure the average concentration of gaseous species over the length of the optical path of the laser beam.
  • TDL Tunable Diode Laser
  • these laser diodes are sources of laser radiation some of which operate at room temperature while others must be cooled.
  • the emitted laser beam is generally adjustable in a wavelength range by varying the injection current in the laser source. It is then sufficient to choose adjustable laser beam sources in wavelength ranges that correspond to at least one of the characteristic lines of the absorption spectrum of the species to be detected.
  • the laser diode will preferably be placed close to the surface of the products, at a distance varying between 1 mm and 15 cm, preferably between 2 cm and 6 cm.
  • the curve (21) represents the heating curve of the product, for example the skin temperature of a billet or a slab in a reheating furnace.
  • this curve it is possible to define the times t 0 , t 1 , t 2 and t 3 respectively corresponding to the time t 0 for charging the product, at time t 1 for which the skin temperature reaches 650 ° C. at time t 2 for which the skin temperature is equal to 85% of the final temperature (or diversion) T out of the skin of the product, and finally at the time t 3 of the product is turned to its final temperature T out .
  • This defines a time interval ⁇ 1 corresponding to the time that the product surface passes between t 1 and t 2 . It is also possible to define a time ⁇ 2 corresponding to the time spent by the product between t 1 and t 3 .
  • the method according to the invention consists in reducing the time ⁇ 1 from 8% to approximately 40% of its reference value and preferably from 10% to approximately 30% of its reference value. This makes it possible to reduce the thickness of the decarburized layer by at least 20% according to the content of alloying elements and specifically the carbon content, compared with the method of the prior art using either the empirical conduct of the furnace by a skilled in the art is driving the furnace by temperature charts or software adapted. It is in particular the reduction of the time ⁇ 1 resulting in an increase of the slope of the curve 52 with respect to the slope of the curve 51 between the instants t 1 and t 2 corresponding to the temperatures of 650 ° C. and 85 ° C. % of the skin temperature at the furnace outlet which is fundamental according to the method of the invention, because it has been shown that it is in these temperature zones that the slope of the heating curve of the furnace had to be increased. produced if one wanted to obtain the expected gains.
  • the invention makes it possible to reduce the time ⁇ 2 between 5% and 30% of its reference value and preferably between 7 and 15% of its reference value. This reduces the mass of the scale between 5 and 30% depending on the nature of the steel.
  • This reduction of the times ⁇ 1 and ⁇ 2 is performed, according to the invention, by increasing the energy transferred to the product during the entire period of its stay in the oven.
  • This can be achieved by increasing the available energy (adding a source of energy, by open flame burners, radiant tubes or electrical resistors or induction heating) or by increasing the energy efficiency. available (enriching the combustion air with oxygen for example, up to 100% purity), preferably above 90% O 2 vol.
  • the maximum reduction of ⁇ 2 is determined by the respect of the thermal homogeneity constraint of the product at the furnace outlet, itself governed by the thermal conduction within the product.
  • the reduction of the times ⁇ 1 and ⁇ 2 corresponds either to a shortening of the furnace or to an acceleration of the speed of movement of the given products. products.
  • a second aspect of the invention is to control the profile of species compositions of the atmosphere in the oven and throughout the crossing of the oven by the product.
  • the composition of the atmosphere ie in particular the content of oxidizing elements in the atmosphere (O 2 , H 2 O, CO 2 ) is a parameter that is involved in the metallurgical quality of the product.
  • the quality of the product can be optimized by maintaining a higher or lower oxygen content depending on the zone of the furnace in which it will be located.
  • FIG. 3 which represents a reheating furnace, the meaning of circulation of the products (35) as well as that of the fumes is indicated.
  • the curve (30) represents the temperature rise curve of the product.
  • the load (35) undergoes a first rise in temperature in the zone (32). Then, the temperatures reach a decarb temperature T. This temperature is typically 700 ° C for steels and the decarburization will be more sensitive to this temperature as the carbon steel content is high. Beyond T decarb , and in the presence of oxidizing species, the decarburization and scale formation reactions accelerate: the temperature at which scale formation becomes effective is about 800 ° C for steels.
  • the product passes through the zone (33) and then enters the equalization zone (34) when it is at the equalization temperature (typically 1100 ° C.). This zone at very high temperature brings the product to its final temperature ( final T, typically 1200 ° C.) and is particularly critical for the formation of scale.
  • the access (36) is located in the equalization area (34), the access (37) is located in the heating zone (33), the access (38) is located in the zone (32) which contains the so-called recovery zone while the access (39) is located in the chimney (31).
  • the measurement of the concentration of the species oxidizing is effected by the accesses (36), (37), (38), (39), each access receiving a laser beam (via an optical fiber) or a beam transmitter laser, a receiver being provided on the opposite wall of the oven (or a mirror which returns the beam parallel to the incident beam, the receiver being placed next to the transmitter).
  • the fuel and combustive rates of the burners of the zone (32) will have to be adjusted, according to the invention, so as to generate an oxygen content in the atmosphere in this zone (32), measured by the corresponding laser diode, between 0.5% and 4% by volume and preferably between 2 and 3%.
  • this correction can be done by adding oxidizer lances, for example oxygen lances, the quantity injected being controlled by measuring the oxygen content of the laser diode.
  • the measurement is preferably carried out as close as possible to the product, in this zone (32) by the access (38), or by the access (39), ie in the flue pipe where the same oxygen content is going to be controlled. If the measurement shows an oxygen deficiency, the regulation of burners will have to correct this defect and increase the flow of oxidizer (oxygen) to the burners of the zone (32) or the previous zone.
  • a protective layer of Fe 2 O 3 and Fe 3 O 4 will be formed and reinforced by the presence of residual oxygen in the flue gases. These oxides will be formed at the expense of more plastic oxides such as FeO or FeSiO 4 , which in this case lead to a strong adhesion of the scale.
  • the protective regime (parabolic stage of oxidation) is established more rapidly for partial pressures of oxygen within the aforementioned range (0.5% to 4% vol.).
  • zone (33) temperature greater than T decarb and less than T equalization
  • the fuel and combustive rates of the burners of the zone (33) must be adjusted according to the invention so as to generate an oxygen content in the atmosphere. atmosphere close to zero.
  • the atmosphere will be deficient in oxygen, therefore in excess of fuel and in particular of CO.
  • the burners will be adjusted so that the concentration of O 2 close to zero and the concentration of CO between 0.1% and 15% of volume and preferably between 1 and 10%.
  • this zone at higher temperature it is sought to minimize the formation of calamine and decarburization by reducing the concentration of oxidizing species (O 2 , CO 2 , H 2 O).
  • the fuel and combustive flows of the burners of the zone (34) will have to be adjusted according to the invention so as to generate an oxygen content in the atmosphere of between 0.5 % and 5% vol. and preferably between 1.5 and 4% vol.
  • the measurement of this concentration is carried out closer to the product between 1 mm and 15 cm, by access (36).
  • this zone and in the presence of oxygen there is a consumption of the decarburized layer by oxidation which will be accompanied by an increase in porosity of the scale, which will facilitate its removal at the furnace outlet.
  • the access (39) makes it possible to check at any time the concentration of CO and O 2 in the fumes before their evacuation.
  • the reduction calamine mass obtained is between 5 and 25%, depending on the nature of the steel.
  • the thickness of the decarburized layer is generally a reduction of the thickness of the decarburized layer by at least 10%, depending on the alloying elements and specifically the carbon content.
  • the gains obtained with the control of the atmosphere can be cumulated with the gains obtained by reducing the times ⁇ 1 and ⁇ 2 described above.
  • Figure 4 illustrates the control of the temperature rise of the product according to the invention.
  • the invention consists in allowing the control of the rise in product temperature and burner setting by a local measurement, zone per area and a few cm above the load, the temperature of the oven atmosphere through a laser diode system.
  • thermocouple (48) shows the location of the product (42) and the thermocouple (48) according to the technique of the prior art.
  • the measurement of thermocouple (48) gives a temperature value in the furnace axis and far of the product (42).
  • the number of measurement points has here been limited to three. Preferably, between 1 and 10 measurement points will be used in an oven.
  • the oven (41) is equipped with accesses (43, 44, 45) located above the product (42).
  • the oven operator must respect at most a rising profile in product temperature (47). This profile is provided to the operator, either by experience either by an abacus or by a furnace control software.
  • the man of art had only the curve (46) describing the temperature of the vault in the axis of the furnace, of which, for example, the thermocouple (48) provides a measuring point, as shown on the curve.
  • the man of art now has access to measurements on the curve (47) that are directly related to the surface temperature of the product. The operator can so act on the power of the burners to find the desired level of temperature on the curve (47). If the measured temperature is too low, then the operator will increase the heating power in the near area the measuring point. Conversely, if the measured temperature is too high, then the operator will reduce the power in the area near the point of measured.
  • Some ovens use software called "Level 2" to reproduce whatever the heating conditions a rise in temperature of product, according to a given initial profile. The skilled person did not have until this day of any measurement to validate continuously the effect of the software. It's a Another aspect of the invention is to couple this software with the measurements of the product according to the invention, which makes it possible to have a verification systematically in real time the target temperature of the product.
  • FIG. 5 represents the heating curve (51) associated with a furnace for heating long billets.
  • the combustion is carried out with burners whose fuel is natural gas and the oxidizer of the preheated air, before implementation of the invention.
  • the parameters t 1 ,... And ⁇ 1 ,... are placed in parentheses when they relate to the curve 51, according to the prior art and are noted without parentheses when they refer to the curve 52).
  • the implementation of the invention is characterized by the replacement of existing burners whose oxidant is air, by burners whose oxidant has an oxygen concentration of greater than 21% by volume, and preferably greater than 88% . More preferably, the oxidant will be industrially pure oxygen.
  • the associated heating curve is the curve (52).
  • the times ⁇ 1 and ⁇ 2 are respectively reduced from 2100 to 1700 seconds and from 5300 to 4800 seconds.
  • the metallurgical quality of the process obtained according to the curve (52) will be significantly improved, thanks to the monitoring of the heating curve of FIG. 5, with the installation of laser diodes at the locations explained with reference to FIG. 3 and fig. 4, or any other measuring means allowing proper control of this heating profile.
  • FIG. 6 represents the quantity of calamine produced with the method described above.
  • the amount of scale (61) is associated with the reference situation
  • the calamine curve (62) is associated with the implementation of of the invention. Both curves have been normalized by the value maximum thickness of calamine obtained under the conditions (61).
  • the embodiment example below was implemented in a furnace of heating billets, 33 MW power and about 30m long.
  • the burners initially present on the furnace are so-called aero-fuel burners, the combustion air being preheated to 300 ° C.
  • the average concentration of O2 in the fumes can be measured by a standard oxygen sensor, but it may be better to a laser diode (of so-called "TDL" type) whose radius changes to a distance of less than 6 cm from the treated product to control finely and in real time a concentration shift from the above species to the surface of the product in order to better respect the imposed atmosphere profile in adequacy with the heating profile.
  • TDL laser diode
  • the implementation according to the invention allows reduce the calamine thickness by 11% (Fig. 7). According to the experiences, the thickness of the decarburized layer is reduced between 12 and 20%.

Abstract

The method and apparatus for enhancing the metallurgical quality of products treated in a furnace with several zones, wherein the temperature and the atmospheric conditions can be controlled. The applies to any type of product treated in a furnace, such as billets, blooms, slugs or slabs. Alternatively, this may be used by iron and steel manufacturers in the production line for sheets, plates, tubes, etc.

Description

L'invention concerne un procédé pour améliorer la qualité métallurgique de produits traités dans un four et notamment un four de réchauffage. Cette invention s'applique à tout type de produit mais plus particulièrement aux produits traités dans un four de réchauffage tel que, par exemple, des billettes, des ébauches ou des brames ou tout autre matériau utilisé par les sidérurgistes dans leur ligne de production (telles que les tôles, les tubes, etc .). L'invention se rapporte plus particulièrement à un procédé de traitement d'un produit métallurgique dans un four, dans lequel le produit à traiter est introduit dans le four, puis soumis au traitement souhaité, puis retiré du four, le four comportant des moyens de chauffage et notamment des brûleurs permettant de porter à une température variable les différentes zones du four, l'atmosphère dans ces différentes zones pouvant avoir une composition identique ou différente selon les zones considérées dudit four.The invention relates to a method for improving the quality metallurgy of products treated in an oven and in particular a furnace of reheating. This invention applies to any type of product but more particularly to products treated in a reheating furnace such as, for example, for example, billets, blanks or slabs or any other material used by steelmakers in their production line (such as sheet metal, tubes, etc.). The invention relates more particularly to a method of treatment of a metallurgical product in an oven, in which the product to be treat is introduced into the oven and then subjected to the desired treatment and then removed furnace, the furnace comprising heating means and in particular burners allowing to bring to different temperatures the different areas of the oven, the atmosphere in these different areas may have a identical or different composition according to the considered zones of said furnace.

L'environnement d'un acier (ou tout autre produit, notamment un produit métallique ou sidérurgique), lorsqu'il est porté à une température élevée lors d'un traitement thermique, est souvent une atmosphère oxydante vis-à-vis du métal. Cette situation peut conduire, d'une part, à l'oxydation du métal avec formation d'une couche superficielle de calamine et, d'autre part, à une décarburation de l'acier avec création d'un gradient de teneur en carbone au voisinage de la surface de la pièce.The environment of a steel (or any other product, especially a metal or steel product), when heated to a temperature high during heat treatment, is often an oxidizing atmosphere vis-à-vis the metal. This situation may lead, on the one hand, to the oxidation of the metal with the formation of a superficial layer of calamine and, on the other hand, a decarburization of steel with the creation of a carbon content gradient near the surface of the room.

La zone altérée à la surface de ces pièces se compose essentiellement de deux parties (voir Fig 1), l'une située du côté de l'atmosphère (calamine supérieure), et l'autre au voisinage du métal ( zone mixte).The weathered area on the surface of these pieces is composed essentially two parts (see Fig 1), one located on the side of the atmosphere (upper scale), and the other in the vicinity of the metal (zone mixed).

La partie supérieure comporte généralement trois couches compactes d'oxydes : une couche d'oxydes Fe2O3 (hématite), très mince (quelques microns d'épaisseur), une couche de magnétite (Fe3O4) (4% de la calamine totale environ) et une couche d'oxyde épaisse FeO (wustite) (95% de la calamine totale environ) plus ou moins poreuse selon la durée et la température du réchauffage.The upper part generally comprises three compact layers of oxides: a layer of oxides Fe 2 O 3 (hematite), very thin (a few microns thick), a layer of magnetite (Fe 3 O 4 ) (4% of the total scale) and a layer of thick oxide FeO (wustite) (95% of the total scale total) more or less porous depending on the duration and the temperature of the reheating.

La croissance de cette calamine, qui adopte une allure parabolique, est contrôlée par la diffusion des ions Fe2+ dans la wustite et la magnétite, et par la diffusion de l'oxygène O2 - dans l'hématite.
La partie inférieure, zone mixte, est plus ou moins grande selon la nature de l'acier. Elle est située à l'interface métal/calamine, constituée d'un mélange FeO et des produits de réaction de FeO avec les oxydes de certains éléments d'alliage. Cette partie inférieure comporte également une zone de métal altérée par divers phénomènes comme la décarburation ou l'oxydation interne. La décarburation est un phénomène de diffusion à l'état solide du carbone qui réagit avec la calamine FeO (et/ou H2O). La perméabilité de la calamine industrielle aux produits gazeux de l'oxydation du carbone (notamment le CO) rend cette oxydation pratiquement immédiate à la surface du métal. La décarburation est donc limitée par la diffusion du carbone à la température du traitement et est favorisée par l'aptitude des gaz formés (CO) à s'échapper de l'interface calamine-acier.The growth of this calamine, which adopts a parabolic appearance, is controlled by the diffusion of Fe 2+ ions in wustite and magnetite, and by the diffusion of oxygen O 2 - in hematite.
The lower part, mixed zone, is more or less large depending on the nature of the steel. It is located at the metal / scale interface, consisting of a FeO mixture and FeO reaction products with the oxides of certain alloying elements. This lower part also includes a zone of metal altered by various phenomena such as decarburization or internal oxidation. Decarburization is a phenomenon of solid state diffusion of carbon that reacts with FeO (and / or H 2 O) scale. The permeability of the industrial scale to the gaseous products of the oxidation of carbon (in particular CO) renders this oxidation practically immediate on the surface of the metal. Decarburization is therefore limited by the diffusion of carbon at the temperature of the treatment and is favored by the ability of the gases formed (CO) to escape from the calamine-steel interface.

Selon le profil thermique imposé et la composition de l'atmosphère (notamment la teneur en O2, H2O, CO2), les produits sidérurgiques peuvent être oxydés (calamine) et décarburés (et ce d'autant plus pour les aciers à haut carbone). Dans les deux cas, le sidérurgiste devra faire subir à ses pièces une opération supplémentaire visant à s'affranchir de ces défauts de surface. Alors que la couche d'oxyde peut être enlevée par différentes techniques de décalaminage, la couche de décarburation, qui fait partie intégrante de la pièce, ne peut pas être aisément « gommée » : la surface du produit est démunie d'une partie de ses atomes de carbone, ce qui engendre une perte des propriétés mécaniques en surface du produit (longévité, dureté ...).According to the imposed thermal profile and the composition of the atmosphere (in particular the content of O 2 , H 2 O, CO 2 ), the iron and steel products can be oxidized (calamine) and decarburized (and all the more so for steels with high carbon). In both cases, the steelmaker will have to submit to his parts an additional operation to overcome these surface defects. While the oxide layer can be removed by different descaling techniques, the decarburization layer, which is an integral part of the part, can not be easily "gummed": the surface of the product is deprived of a part of its carbon atoms, which causes a loss of the mechanical properties on the surface of the product (longevity, hardness ...).

L'oxydation ou la décarburation de l'acier en four de réchauffage entraíne ainsi une perte de matière première qu'on appelle perte au feu et une dégradation des propriétés de surface de produits qui sont préjudiciables au sidérurgiste.Oxidation or decarburization of steel in a heating furnace leads to a loss of raw material, which is known as a loss on ignition and degradation of the surface properties of products that are detrimental to the steelmaker.

Une contrainte importante qui va également influencer la qualité finale du produit à l'issue du procédé de réchauffage est la température finale du produit et de son homogénéité thermique, et ce quel que soit l'historique de la chauffe ayant eu lieu dans le four (temps passé à certains niveaux de température, ralentissement de la cadence suite à un incident laminoir etc...),. Tout défaut d'homogénéité thermique entraínera des défauts de structure et a posteriori des fragilités mécaniques des produits finis. Ces défauts peuvent également provoquer des arrêts voire des casses de certaines parties du laminoir (notamment des cages de laminoir).An important constraint that will also influence the final quality of the product at the end of the reheating process is the final temperature of the product and its thermal homogeneity, irrespective of the history of the heating having occurred in the oven (time spent at certain levels of temperature, slowing of the rate following a mill incident etc ...) ,. Any lack of thermal homogeneity will result in defects in structure and a posteriori of the mechanical fragilities of the finished products. These faults can also cause shutdowns or even breaks certain parts of the rolling mill (in particular mill stands).

Toute optimisation de la qualité métallurgique du produit devra respecter cette contrainte sur l'homogénéité thermique du produit. Lors de la conduite du four par l'opérateur, le contrôle et le respect de la montée en température du produit vont être déterminant pour assurer au final le respect de la contrainte sur l'homogénéité thermique.Any optimization of the metallurgical quality of the product should respect this constraint on the thermal homogeneity of the product. When operator's control of the oven, control and respect for the rise in temperature of the product will be decisive to ensure ultimately respect stress on thermal homogeneity.

Il est connu de l'homme de métier que pour éviter la décarburation et l'oxydation, il est recommandé de travailler sous atmosphère protectrice par combustion sous-stoechiométrique (mélange riche en combustible engendrant une atmosphère neutre, voire réductrice pour l'acier). Cette méthode est mise en oeuvre dans les procédés de galvanisation ( voir par exemple Galvanisation et aluminiage en continu, E. Buscarlet, Technique de l'ingénieur, 1996). It is known to those skilled in the art that to avoid decarburization and oxidation, it is recommended to work in a protective atmosphere by substoichiometric combustion (fuel-rich mixture generating a neutral atmosphere or reducing for steel). This method is used in galvanizing processes (see, for example , continuous galvanizing and aluminizing , E. Buscarlet, Technique de l'ingénieur , 1996).

Il est également connu de US-A-4,415,415 de traiter les produits dans une atmosphère contenant au moins 3% d'oxygène en volume, et ce sur toute la longueur du four, ce qui entraíne inexorablement la formation de calamine mais qui permet de contrôler la qualité de calamine qui devient dans ces conditions non adhérente et qui s' élimine facilement.It is also known from US-A-4,415,415 to process products in an atmosphere containing at least 3% oxygen by volume, and this on the entire length of the oven, which inevitably leads to the formation of calamine but that allows to control the quality of scale that becomes in these conditions not adherent and which eliminates easily.

L'utilisation de brûleurs oxy-combustibles pour réchauffer des billettes, par exemple, à une temperature supérieure à leur température de sortie du four, est connue de EP 0 630 978 A.The use of oxy-fuel burners to heat billets, for example, at a temperature above their outlet temperature of the oven, is known from EP 0 630 978 A.

Le brevet EP-A-0767353 propose également d'intervenir sur l'atmosphère du four en pratiquant un zonage du four, c'est à dire en isolant le four en plusieurs enceintes au sein desquelles une atmosphère fortement oxydante est préconisée afin de pouvoir contrôler formation et qualité de la calamine. Dans ce cas, la perte au feu n'est pas diminuée mais au contraire augmentée, seul un contrôle de la qualité de calamine est assuré.Patent EP-A-0767353 also proposes to intervene on the oven atmosphere by zoning the oven, ie by isolating the furnace into several enclosures in which an atmosphere strongly oxidant is recommended in order to control training and quality of the calamine. In this case, the loss on ignition is not diminished but on the contrary increased, only a calamine quality control is assured.

Les différentes méthodes connues de l'art antérieur suggèrent donc de traiter les produits soit dans une atmosphère oxydante, soit dans une atmosphère réductrice.The various methods known from the prior art therefore suggest treat the products either in an oxidizing atmosphere or in a reducing atmosphere.

La mise en oeuvre de ces différentes méthodes présente en outre un inconvénient supplémentaire pour le traitement de produits sidérurgiques. En effet, il est important de pouvoir mesurer le caractère oxydant ou réducteur des atmosphères mises en jeu. La seule information disponible lors de la mise en oeuvre de ces procédés est fournie par des sondes de mesure situées, soit dans la voûte c'est à dire loin de la surface des produits, soit dans la cheminée du four. Ces mesures ne sont donc pas représentatives de la composition de l'atmosphère qui interagit directement avec le produit. En général, le seul paramètre mesurable de l'atmosphère est la teneur en oxygène. Cette information est généralement insuffisante : en effet, ce n'est pas parce que la quantité d'oxygène dans les fumées qui sortent du four est nulle que l'atmosphère du four au contact des pièces métalliques est nécessairement réductrice pour l'acier (voir par exemple, Combustion Engineering and Gas Utilisation, Ed. British Gas, 1992, page 23). Les espèces H2O et CO2 ont aussi selon la Demanderesse un rôle d'oxydant sur la charge et interviennent dans les réactions de formation de calamine et dans les mécanismes de décarburation. A l'heure actuelle, on ne sait pas mesurer ces espèces de façon simple et rapide.The implementation of these different methods also has an additional disadvantage for the treatment of steel products. Indeed, it is important to be able to measure the oxidizing or reducing character of the atmospheres involved. The only information available during the implementation of these methods is provided by measuring probes located either in the vault it is at say away from the surface of the products, either in the oven chimney. These measurements are therefore not representative of the composition of the atmosphere that interacts directly with the product. In general, the only measurable parameter of the atmosphere is the oxygen content. This information is generally insufficient: in fact, it is not because the quantity of oxygen in the smoke that comes out of the oven is zero that the atmosphere of the oven in contact with the metal parts is necessarily reducing for the steel (see for example, Combustion Engineering and Gas Use , Ed. British Gas , 1992 , page 23 ). The species H 2 O and CO 2 also have, according to the Applicant, an oxidizing role on the feedstock and are involved in the scale formation reactions and in the decarburization mechanisms. At present, it is not known to measure these species simply and quickly.

Pour effectuer la conduite du four et respecter la contrainte finale de l'homogénéité thermique du produit, l'opérateur suit un profil initial de température du produit donné pour un four donné, en fonction du type de charge et de production. Ce profil est soit connu de l'opérateur grâce à son savoir faire, soit calculé à partir d'abaques, soit encore calculé à l'aide d'un logiciel adapté. To carry out the operation of the oven and respect the final the product's thermal homogeneity, the operator follows an initial profile of temperature of the given product for a given furnace, depending on the type of load and production. This profile is known to the operator thanks to his know-how, either calculated from charts, or calculated using a adapted software.

Les seules informations disponibles pour l'opérateur et/ou les logiciels de conduite de four, sont les mesures délivrées par un ou plusieurs thermocouples situés dans la voûte du four. Ces thermocouples sont disposés loin de la charge et ne sont pas représentatifs du flux thermique reçu par la charge, sous les brûleurs. Une estimation de la relation reliant la température de voûte (mesurée) et la température de la charge (information utile) est donc nécessaire. Cette relation est soit empirique (basé sur le savoir faire des opérateurs) soit calculée par les logiciels de conduite de four.The only information available for the operator and / or software furnace control, are the measurements issued by one or more thermocouples located in the vault of the oven. These thermocouples are arranged far from the load and are not representative of the heat flux received by the load, under the burners. An estimate of the relationship connecting the vault temperature (measured) and the temperature of the charge (information useful) is therefore necessary. This relationship is either empirical (knowledge-based operators) is calculated by the furnace control software.

Non seulement, cette mesure n'est qu'une mesure indirecte de l'information nécessaire, mais la relation estimée peut se révéler de plus en plus inexacte lors du vieillissement du four, des caractéristiques thermiques des différentes charges et de la variation du type de combustible utilisé.Not only is this measure an indirect measure of the necessary information, but the estimated relationship may become increasingly more inaccurate when aging the oven, thermal characteristics different loads and the variation of the type of fuel used.

Enfin, cette mesure est une mesure ponctuelle habituellement située sur l'axe du four et qui ne rend pas compte des éventuelles variations dudit paramètre sur toute la largeur du four.Finally, this measure is a one-off measure usually located on the axis of the furnace and which does not take into account possible variations of the said parameter over the entire width of the oven.

Le fait de ne pas disposer de mesures au plus près du produit a pour conséquence une connaissance inexacte des temps caractéristiques du processus de chauffe de ces produits . Or on a constaté que ces caractéristiques avaient une forte influence sur les cinétiques d'oxydation et de décarburation de ceux-ci, une estimation incorrecte de ces temps pouvant avoir des conséquences graves sur la qualité finale métallurgique du produit.The fact of not having measures closer to the product has for consequence an inaccurate knowledge of the characteristic times of the process of heating these products. It has been found that these characteristics had a strong influence on oxidation kinetics and decarburization of these, an incorrect estimate of these times being have serious consequences on the final metallurgical quality of the product.

Le but de la présente invention est de fournir un procédé de conduite d'un four (température, composition de l'atmosphère) et un procédé de contrôle associé, permettant d'optimiser à la fois la qualité métallurgique d'un produit, la perte au feu et le rendement thermique d'un fourThe object of the present invention is to provide a method of driving of a furnace (temperature, composition of the atmosphere) and a method of associated control, making it possible to optimize both the metallurgical quality of a product, fire loss and thermal efficiency of an oven

Le procédé selon l'invention permet d'éviter les inconvénients précités et de remplir le but visé ci-dessus. The process according to the invention makes it possible to avoid the abovementioned disadvantages and fulfill the purpose referred to above.

Dans le procédé selon l'invention, le produit à traiter a une température qui augmente entre le moment où il est introduit et le moment où il est retiré du four, la courbe de montée en température ayant une pente qui augmente dans un premier intervalle de temps compris entre l'instant t0 d'introduction du produit dans le four et l'instant t1 auquel le produit atteint une température de surface de 650°C, une pente sensiblement constante entre l'instant t1 et l'instant t2 auquel le produit atteint une température d'environ 15 % inférieure à la température de surface finale souhaitée pour le produit à traiter lorsqu'il sort du four, puis une pente qui diminue entre l'instant t2 et l'instant t3 auquel le produit à traiter sort du four, procédé dans lequel on augmente la puissance de chauffe du four par rapport à sa puissance lorsque seuls des brûleurs aéro-combustibles sont utilisés de manière à augmenter la pente de la courbe de montée en température du produit à traiter, au moins pendant certaines périodes de traitement du produit dans le four entre les instants t1 et t2, ce qui engendre une diminution de la durée du traitement du produit à traiter et une diminution corrélative de l'épaisseur de la couche décarburée et/ou de la couche de calamine formée à la surface du produit.In the process according to the invention, the product to be treated has a temperature which increases between the moment when it is introduced and the moment when it is removed from the oven, the temperature rise curve having a slope which increases in a first interval of time. time between the time t 0 for introducing the product into the oven and the instant t 1 at which the product reaches a surface temperature of 650 ° C., a substantially constant slope between the instant t 1 and the instant t 2 at which the product reaches a temperature of about 15% lower than the desired final surface temperature for the product to be treated when it leaves the oven, then a slope that decreases between time t 2 and time t 3 at which the product to be treated leaves the oven, in which process the heating power of the furnace is increased relative to its power when only aero-fuel burners are used so as to increase the slope of the temperature rise curve of the furnace. at least during certain periods of treatment of the product in the oven between times t 1 and t 2 , which causes a decrease in the treatment time of the product to be treated and a corresponding decrease in the thickness of the layer decarburized and / or calamine layer formed on the surface of the product.

De préférence, l'augmentation de la puissance de chauffe du four est obtenue à l'aide de brûleurs oxy-combustibles qui constituent au moins une partie des moyens de chauffe du four, notamment une partie des moyens de chauffe du four correspondant à la zone atteinte par le produit entre les instants t1 et t2. Il est possible également de placer ce ou ces brûleur(s) oxy-combustible(s) dans une zone adjacente à la zone susnommée, qui permettrait indirectement d'obtenir la même augmentation de puissance (dans ladite zone atteinte entre les instants t1 et t2, par le produit).Preferably, the increase of the furnace heating power is obtained by means of oxy-fuel burners which constitute at least a part of the furnace heating means, in particular a portion of the furnace heating means corresponding to the zone. reached by the product between instants t 1 and t 2 . It is also possible to place this or these burner (s) oxy-fuel (s) in an area adjacent to the above-mentioned area, which indirectly allow to obtain the same power increase (in said area reached between times t 1 and t 2 , by the product).

D'une manière générale, le comburant fourni aux brûleurs oxy-combustibles constituant une partie au moins des moyens de chauffe du four, comporte au moins 88 % d'oxygène et de préférence plus de 90 % d'oxygène, encore plus préférentiellement plus de 95 % d'oxygène. In general, the oxidizer supplied to the oxy-fuel burners constituting at least part of the oven heating means, has at least 88% oxygen and preferably more than 90% oxygen, more preferably more than 95% oxygen.

On constate en général que le temps de traitement du produit entre les températures de 700°C et de 800°C atteintes pour la surface du produit, est diminué de 15% à 50% de sa valeur de référence, de préférence de 20 à 35% de sa valeur, tandis que le temps de traitement entre les températures de 700°C et la température finale de la surface du produit, est diminué entre 3 et 25% de sa valeur de référence, de préférence entre 7 et 15% de sa valeur de référence.In general, it is found that the time of treatment of the product between temperatures of 700 ° C and 800 ° C achieved for the surface of the product, is decreased by 15% to 50% of its reference value, preferably from 20 to 35% of its value, while the processing time between the temperatures of 700 ° C and the final temperature of the product surface is decreased between 3 and 25% of its reference value, preferably between 7% and 15% of its reference.

De manière préférentielle selon l'invention, utilisée seule ou en combinaison avec les autres variantes de l'invention, l'atmosphère du four varie le long du four en fonction de la température de peau du produit métallique.Preferably according to the invention, used alone or in combination with the other variants of the invention, the atmosphere of the oven varies along the oven depending on the skin temperature of the product metallic.

Selon une première variante de l'invention, utilisée seule ou en combinaison avec les autres variantes de l'invention, l'atmosphère du four au contact du produit à traiter comporte environ 0,5 % vol à 5 % d'oxygène et de préférence entre 1,5 vol à 4 % vol d'oxygène quand la température de peau T à la surface du produit traité est supérieure ou égale à la température d'égalisation Tegal, qui est égale à 85 % de la température à la surface du produit (température de défoumement) à la sortie du four. De préférence, la température d'égalisation Tegal est égale à 90 % de la température de détournement.According to a first variant of the invention, used alone or in combination with the other variants of the invention, the atmosphere of the oven in contact with the product to be treated comprises about 0.5% vol to 5% oxygen and preferably between 1.5 vol at 4 vol vol oxygen when the skin temperature T at the surface of the treated product is greater than or equal to equalization temperature T equ , which is equal to 85% of the temperature at the surface of the product (defatting temperature) at the oven outlet. Preferably, the soaking temperature T equal is equal to 90% of the temperature of diversion.

Selon une autre variante de l'invention, utilisée seule ou en combinaison avec les précédentes, l'atmosphère au contact du produit à traiter comporte une concentration en oxygène inférieure à quelques centaines de ppm et une concentration en CO comprise entre 0,1 % et 15 %, de préférence 0,5 % à 5 % vol lorsque la température de peau T à la surface du produit est supérieure à 700°C et inférieure à la température d'égalisation du produit, définie comme étant égale à 90 % de la température de peau du produit à la sortie du four.According to another variant of the invention, used alone or in combination with the previous ones, the atmosphere in contact with the product to treat has an oxygen concentration of less than a few hundreds of ppm and a CO concentration between 0.1% and 15%, preferably 0.5% to 5% vol when skin temperature T on the surface the product is above 700 ° C and below the equalization temperature of the product, defined as being equal to 90% of the skin temperature of produced at the outlet of the oven.

Selon encore une autre variante de l'invention utilisée seule ou en combinaison avec les précédentes, l'atmosphère au contact du produit à traiter comporte une concentration en oxygène comprise entre 0,5 % et 4 % vol et de préférence entre 2 % et 3 % vol lorsque la température de peau T à la surface du produit à traiter est inférieure à 700 ° CAccording to yet another variant of the invention used alone or in combination with the previous ones, the atmosphere in contact with the product to treat has an oxygen concentration between 0.5% and 4% flight and preferably between 2% and 3% vol when the skin temperature T to the surface of the product to be treated is less than 700 ° C.

L'invention permet une optimisation de la qualité métallurgique des produits grâce à l'optimisation du profil de chauffe dans le four et un contrôle amélioré du profil de la composition de l'atmosphère du four. Ce contrôle suit de manière continue les teneurs en O2 et/ou H2O et/ou CO2 de l'atmosphère dans les différentes zones du four, et/ou la température à la surface des produits à traiter, sera réalisé préférentiellement à l'aide d'une diode laser. Ce système de diode laser appelé TDL pour « Tunable Diode Laser » en anglais) permet en effet de mesurer la moyenne des concentrations d'espèces gazeuses sur la longueur du chemin optique du faisceau laser. Pour plus de détails sur les diode laser et en particulier les diode laser de type TDL, on pourra se reporter à l'article de Mark G. Allen intitulé « Diode Laser Absorption Sensors for Gas Dynamic and Combustion Flows », Mes. Sci. Technology, 9, 1998, pages 545 à 562, et incorporé dans le présent texte à titre de référence. D'une manière générale, ces diodes laser sont des sources de rayonnement laser dont certaines opèrent à température ambiante alors que d'autres doivent être refroidies. Le faisceau laser émis est en générale ajustable dans un domaine de longueur d'ondes en faisant varier le courant d'injection dans la source laser. Il suffit alors de choisir des sources de faisceau laser ajustables dans des domaines de longueurs d'ondes qui correspondent à l'une au moins des raies caractéristiques du spectre d'absorption de l'espèce que l'on veut détecter. La diode laser sera de préférence placée à proximité de la surface des produits, à une distance variant entre 1 mm et 15cm, préférentiellement entre 2cm et 6cm. C'est aux environs de la surface du produit que les valeurs de pressions partielles en O2, H2O et CO2 ainsi de la température interviennent dans les mécanismes décrits plus haut : calamine et décarburation. Ce contrôle au plus près de la surface permet également le développement d'outils prédictifs et la bonne mise en oeuvre de la méthode proposée. The invention makes it possible to optimize the metallurgical quality of the products by optimizing the heating profile in the oven and improving the control of the composition of the oven atmosphere. This control continuously monitors the O 2 and / or H 2 O and / or CO 2 contents of the atmosphere in the different zones of the furnace, and / or the temperature at the surface of the products to be treated, will preferably be carried out at using a laser diode. This laser diode system called TDL (Tunable Diode Laser) makes it possible to measure the average concentration of gaseous species over the length of the optical path of the laser beam. For more details on the laser diode and in particular the TDL type laser diode, reference may be made to Mark G. Allen's article entitled "Laser Diode Absorption Sensors for Dynamic Gas and Combustion Flows", Mes. Sci. Technology, 9, 1998, pages 545-562, and incorporated herein by reference. In general, these laser diodes are sources of laser radiation some of which operate at room temperature while others must be cooled. The emitted laser beam is generally adjustable in a wavelength range by varying the injection current in the laser source. It is then sufficient to choose adjustable laser beam sources in wavelength ranges that correspond to at least one of the characteristic lines of the absorption spectrum of the species to be detected. The laser diode will preferably be placed close to the surface of the products, at a distance varying between 1 mm and 15 cm, preferably between 2 cm and 6 cm. It is around the surface of the product that the partial pressure values of O 2 , H 2 O and CO 2 and temperature are involved in the mechanisms described above: calamine and decarburization. This control closer to the surface also allows the development of predictive tools and the proper implementation of the proposed method.

L'invention sera mieux comprise à l'aide des exemples de réalisation suivants, donnés à titre non limitatifs, conjointement avec les figures, qui représentent :

  • La figure 2 décrit une courbe caractéristique d'évolution de la température du produit en fonction du temps, contrôlée selon le procédé de l'invention.
  • La figure 3, décrit l'application de l'invention au four de réchauffage.
  • La figure 4, décrit le contrôle de la montée en température du produit, selon l'invention.
  • La figure 5, décrit une courbe de température dans un four de réchauffage en fonction du temps.
  • La figure 6, une courbe de variation de la quantité de calamine en fonction du temps.
  • La figure 7, un autre exemple d'une courbe de variation de la quantité de la calamine en fonction du temps.
    • The invention will be better understood with the aid of the following non-limiting examples of embodiment, together with the figures, which represent:
  • FIG. 2 describes a characteristic curve of evolution of the product temperature as a function of time, controlled according to the method of the invention.
  • Figure 3 describes the application of the invention to the reheating furnace.
  • Figure 4 describes the control of the temperature rise of the product according to the invention.
  • Figure 5 depicts a temperature curve in a reheat furnace as a function of time.
  • Figure 6, a curve of variation of the amount of calamine as a function of time.
  • Figure 7, another example of a curve of variation of the amount of calamine as a function of time.

    • Sur la Fig. 2, la courbe (21) représente la courbe de chauffe du produit, par exemple la température de peau d'une billette ou d'une brame en four de réchauffage. Selon cette courbe, on peut définir les temps t0, t1, t2 et t3 correspondant respectivement au temps t0 d'enfournement du produit, au temps t1 pour lequel la température de peau atteint 650°C, au temps t2 pour lequel la température de peau est égale à 85 % de la température finale (ou de détournement) Tout de la peau du produit , et enfin au temps t3 de défournement du produit à sa température finale Tout. On définit ainsi un intervalle de temps Δ1 correspondant au temps que passe la surface du produit entre t1 et t2. On peut également définir un temps Δ2 correspondant au temps passé par le produit entre t1 et t3.In FIG. 2, the curve (21) represents the heating curve of the product, for example the skin temperature of a billet or a slab in a reheating furnace. According to this curve, it is possible to define the times t 0 , t 1 , t 2 and t 3 respectively corresponding to the time t 0 for charging the product, at time t 1 for which the skin temperature reaches 650 ° C. at time t 2 for which the skin temperature is equal to 85% of the final temperature (or diversion) T out of the skin of the product, and finally at the time t 3 of the product is turned to its final temperature T out . This defines a time interval Δ 1 corresponding to the time that the product surface passes between t 1 and t 2 . It is also possible to define a time Δ 2 corresponding to the time spent by the product between t 1 and t 3 .

    Le procédé selon l'invention consiste à réduire le temps Δ1 de 8 % à 40% environ de sa valeur de référence et de manière préférentielle de 10 % à 30% environ de sa valeur de référence. Ceci permet de diminuer l'épaisseur de la couche décarburée d'au moins 20% selon la teneur en éléments d'alliage et spécifiquement la teneur en carbone, par rapport au procédé de l'art antérieur utilisant soit la conduite empirique du four par un homme de métier expérimenté soit la conduite du four par des abaques de température ou un logiciel adapté. C'est en particulier la réduction du temps Δ1 se traduisant par une augmentation de la pente de la courbe 52 par rapport à la pente de la courbe 51 entre les instants t1 et t2 correspondant aux températures de 650° C et de 85 % de la température de peau à la sortie du four qui est fondamentale selon le procédé de l'invention, car on a mis en évidence que c'est dans ces zones de température qu'il fallait augmenter la pente de la courbe de chauffe du produit si l'on voulait obtenir les gains espérés.The method according to the invention consists in reducing the time Δ 1 from 8% to approximately 40% of its reference value and preferably from 10% to approximately 30% of its reference value. This makes it possible to reduce the thickness of the decarburized layer by at least 20% according to the content of alloying elements and specifically the carbon content, compared with the method of the prior art using either the empirical conduct of the furnace by a skilled in the art is driving the furnace by temperature charts or software adapted. It is in particular the reduction of the time Δ 1 resulting in an increase of the slope of the curve 52 with respect to the slope of the curve 51 between the instants t 1 and t 2 corresponding to the temperatures of 650 ° C. and 85 ° C. % of the skin temperature at the furnace outlet which is fundamental according to the method of the invention, because it has been shown that it is in these temperature zones that the slope of the heating curve of the furnace had to be increased. produced if one wanted to obtain the expected gains.

    De la même façon, l'invention permet la réduction du temps Δ2 entre 5 % et 30% de sa valeur de référence et de manière préférentielle entre 7 et 15% de sa valeur de référence. Ceci permet de diminuer la masse de la calamine entre 5 et 30% selon la nature de l'acier.In the same way, the invention makes it possible to reduce the time Δ 2 between 5% and 30% of its reference value and preferably between 7 and 15% of its reference value. This reduces the mass of the scale between 5 and 30% depending on the nature of the steel.

    Cette réduction des temps Δ1 et Δ2 est réalisée, selon l'invention, en augmentant l'énergie transférée au produit pendant toute la durée de son séjour dans le four. Cela peut être réalisé en augmentant l'énergie disponible (ajout d'une source d'énergie, par des brûleurs à flamme nue, des tubes radiants ou encore des résistances électriques ou du chauffage par induction) ou en augmentant le rendement de l'énergie disponible (enrichissement de l'air de combustion par de l'oxygène par exemple, jusqu'à 100% de pureté), de préférence au-delà de 90% O2 vol.This reduction of the times Δ 1 and Δ 2 is performed, according to the invention, by increasing the energy transferred to the product during the entire period of its stay in the oven. This can be achieved by increasing the available energy (adding a source of energy, by open flame burners, radiant tubes or electrical resistors or induction heating) or by increasing the energy efficiency. available (enriching the combustion air with oxygen for example, up to 100% purity), preferably above 90% O 2 vol.

    La réduction maximum de Δ2 est fixée par le respect de la contrainte d'homogénéité thermique du produit en sortie de four, elle-même gouvernée par la conduction thermique au sein du produit.The maximum reduction of Δ 2 is determined by the respect of the thermal homogeneity constraint of the product at the furnace outlet, itself governed by the thermal conduction within the product.

    Par rapport à une situation de référence donnée (four donné, production horaire donc vitesse de défilement des produits donnés), la réduction des temps Δ1 et Δ2 correspond soit à un raccourcissement du four, soit à une accélération de la vitesse de défilement des produits.With respect to a given reference situation (given furnace, hourly production and thus the speed of the given products), the reduction of the times Δ 1 and Δ 2 corresponds either to a shortening of the furnace or to an acceleration of the speed of movement of the given products. products.

    Un deuxième aspect de l'invention consiste à contrôler le profil de compositions des espèces de l'atmosphère dans le four et tout au long de la traversée du four par le produit.A second aspect of the invention is to control the profile of species compositions of the atmosphere in the oven and throughout the crossing of the oven by the product.

    En effet, la composition de l'atmosphère, c'est à dire notamment la teneur en éléments oxydants dans l'atmosphère (O2, H2O, CO2) est un paramètre qui intervient dans la qualité métallurgique du produit. Ainsi, pour un profil thermique donné, on peut optimiser la qualité du produit en maintenant une teneur en oxygène plus ou moins élevée selon la zone du four dans laquelle on se situera.Indeed, the composition of the atmosphere, ie in particular the content of oxidizing elements in the atmosphere (O 2 , H 2 O, CO 2 ) is a parameter that is involved in the metallurgical quality of the product. Thus, for a given thermal profile, the quality of the product can be optimized by maintaining a higher or lower oxygen content depending on the zone of the furnace in which it will be located.

    Sur la Fig. 3 qui représente un four de réchauffage, le sens de circulation des produits (35) ainsi que celui des fumées est indiqué. La courbe (30) représente la courbe de montée en température du produit.In FIG. 3 which represents a reheating furnace, the meaning of circulation of the products (35) as well as that of the fumes is indicated. The curve (30) represents the temperature rise curve of the product.

    Lors de sa circulation dans le four de réchauffage, la charge (35) subit une première montée en température dans la zone (32) Ensuite, les températures atteignent une température Tdécarb. Cette température est typiquement de 700°C pour les aciers et la décarburation sera d'autant plus sensible à cette température que la teneur de l'acier en carbone est élevée. Au-delà de Tdécarb, et en présence d'espèces oxydantes, les réactions de décarburation et de formation de calamine s'accélèrent : la température à laquelle la formation de calamine devient effective est d'environ 800°C pour les aciers. Le produit traverse la zone (33) puis entre dans la zone d'égalisation (34) quand il est à la température Tégalisation (typiquement 1100°C). Cette zone à très haute température amène le produit à sa température finale (Tfinal, typiquement 1200°C) et est particulièrement critique pour la formation de calamine.During its circulation in the heating furnace, the load (35) undergoes a first rise in temperature in the zone (32). Then, the temperatures reach a decarb temperature T. This temperature is typically 700 ° C for steels and the decarburization will be more sensitive to this temperature as the carbon steel content is high. Beyond T decarb , and in the presence of oxidizing species, the decarburization and scale formation reactions accelerate: the temperature at which scale formation becomes effective is about 800 ° C for steels. The product passes through the zone (33) and then enters the equalization zone (34) when it is at the equalization temperature (typically 1100 ° C.). This zone at very high temperature brings the product to its final temperature ( final T, typically 1200 ° C.) and is particularly critical for the formation of scale.

    Trois accès pour l'installation d'une diode laser sont prévus sur ce four. L'accès (36) est situé dans la zone d'égalisation (34), l'accès (37) est situé dans la zone de chauffe (33), l'accès (38) est situé dans la zone (32) qui contient la zone dite de récupération tandis que l'accès (39) est situé dans la cheminée (31).Three accesses for the installation of a laser diode are provided on this oven. The access (36) is located in the equalization area (34), the access (37) is located in the heating zone (33), the access (38) is located in the zone (32) which contains the so-called recovery zone while the access (39) is located in the chimney (31).

    Selon l'invention, la mesure de la concentration des espèces oxydantes est effectuée par les accès (36), (37), (38), (39), chaque accès recevant un faisceau laser (via une fibre optique) ou un émetteur de faisceau laser, un récepteur étant prévu sur la paroi opposé du four (ou bien un miroir qui renvoit le faisceau parallèlement au faisceau incident, le récepteur étant placé à côté de l'émetteur).According to the invention, the measurement of the concentration of the species oxidizing is effected by the accesses (36), (37), (38), (39), each access receiving a laser beam (via an optical fiber) or a beam transmitter laser, a receiver being provided on the opposite wall of the oven (or a mirror which returns the beam parallel to the incident beam, the receiver being placed next to the transmitter).

    Dans la zone (32) (température inférieure à Tdecarb), les débits de combustible et comburant des brûleurs de la zone (32) devront être réglés, selon l'invention, de manière à engendrer une teneur en oxygène dans l'atmosphère dans cette zone (32), mesurée par la diode laser correspondante, entre 0.5% et 4% en volume et de manière préférentielle entre 2 et 3%.In the zone (32) (temperature below T decarb ), the fuel and combustive rates of the burners of the zone (32) will have to be adjusted, according to the invention, so as to generate an oxygen content in the atmosphere in this zone (32), measured by the corresponding laser diode, between 0.5% and 4% by volume and preferably between 2 and 3%.

    Dans le cas où la zone (32) d'égalisation n'est pas équipée de brûleurs, cette correction peut se faire par l'ajout de comburant par des lances, par exemple des lances à oxygène, la quantité injectée étant contrôlée par la mesure de teneur en oxygène de la diode laser.In the case where the zone (32) of equalization is not equipped with burners, this correction can be done by adding oxidizer lances, for example oxygen lances, the quantity injected being controlled by measuring the oxygen content of the laser diode.

    La mesure est effectuée de préférence soit au plus près du produit, dans cette zone (32) par l'accès (38), soit par l'accès (39), c'est à dire dans le conduit d'évacuation des fumées où la même teneur en oxygène va être contrôlée. Si la mesure montre un défaut d'oxygène, la régulation des brûleurs devra corriger ce défaut et augmenter le débit de comburant (oxygène) aux brûleurs de la zone (32) ou de la zone précédente.The measurement is preferably carried out as close as possible to the product, in this zone (32) by the access (38), or by the access (39), ie in the flue pipe where the same oxygen content is going to be controlled. If the measurement shows an oxygen deficiency, the regulation of burners will have to correct this defect and increase the flow of oxidizer (oxygen) to the burners of the zone (32) or the previous zone.

    Dans la zone (32), une couche protectrice de Fe2O3 et Fe3O4 sera formée et renforcée par la présence d'oxygène résiduel dans les fumées. Ces oxydes seront formés au détriment des oxydes plus plastiques comme FeO ou FeSiO4, qui conduisent dans ce cas à une forte adhérence de la calamine. De plus, à faible température, le régime protecteur (stade parabolique de l'oxydation) s'établit plus rapidement pour les pressions partielles d'oxygène comprises dans l'intervalle pré-cité (0,5% à 4% vol.).In the zone (32), a protective layer of Fe 2 O 3 and Fe 3 O 4 will be formed and reinforced by the presence of residual oxygen in the flue gases. These oxides will be formed at the expense of more plastic oxides such as FeO or FeSiO 4 , which in this case lead to a strong adhesion of the scale. In addition, at low temperature, the protective regime (parabolic stage of oxidation) is established more rapidly for partial pressures of oxygen within the aforementioned range (0.5% to 4% vol.).

    Dans la zone (33) (température supérieure à Tdecarb et inférieure à Tégalisation), les débits de combustible et comburant des brûleurs de la zone (33) devront être réglés selon l'invention de manière à engendrer une teneur en oxygène dans l'atmosphère voisine de zéro. L'atmosphère sera en défaut d'oxygène, donc en excès de combustible et en particulier de CO. Grâce à la mesure effectuée par l'accès (37), les brûleurs seront réglés de sorte que la concentration en O2 voisine de zéro et la concentration en CO comprise entre 0,1% et 15% de volume et de manière préférentielle entre 1 et 10%. Dans cette zone à plus haute température, on cherche à limiter au maximum la formation de calaminé et la décarburation en réduisant la concentration des espèces oxydantes (O2, CO2, H2O).In zone (33) (temperature greater than T decarb and less than T equalization ), the fuel and combustive rates of the burners of the zone (33) must be adjusted according to the invention so as to generate an oxygen content in the atmosphere. atmosphere close to zero. The atmosphere will be deficient in oxygen, therefore in excess of fuel and in particular of CO. Thanks to the measurement made by the access (37), the burners will be adjusted so that the concentration of O 2 close to zero and the concentration of CO between 0.1% and 15% of volume and preferably between 1 and 10%. In this zone at higher temperature, it is sought to minimize the formation of calamine and decarburization by reducing the concentration of oxidizing species (O 2 , CO 2 , H 2 O).

    Dans la zone (34) (température supérieure à Tégalisation), les débits de combustible et comburant des brûleurs de la zone (34) devront être réglés selon l'invention de manière à engendrer une teneur en oxygène dans l'atmosphère comprise entre 0.5% et 5% vol. et de manière préférentielle entre 1.5 et 4% vol.. La mesure de cette concentration est effectuée au plus près du produit entre 1 mm et 15 cm, par l'accès (36). Dans cette zone et en présence d'oxygène, il y a une consommation de la couche décarburée par oxydation qui sera accompagnée d'une augmentation de porosité de la calamine, qui facilitera son élimination en sortie de four.In the zone (34) (temperature greater than T equalization ), the fuel and combustive flows of the burners of the zone (34) will have to be adjusted according to the invention so as to generate an oxygen content in the atmosphere of between 0.5 % and 5% vol. and preferably between 1.5 and 4% vol. The measurement of this concentration is carried out closer to the product between 1 mm and 15 cm, by access (36). In this zone and in the presence of oxygen, there is a consumption of the decarburized layer by oxidation which will be accompanied by an increase in porosity of the scale, which will facilitate its removal at the furnace outlet.

    L'accès (39) permet de vérifier à tout moment la concentration en CO et en O2 dans les fumées avant leur évacuation.The access (39) makes it possible to check at any time the concentration of CO and O 2 in the fumes before their evacuation.

    Lorsque l'on contrôle ainsi l'atmosphère, selon l'invention, la réduction de la masse de calamine obtenue est entre 5 et 25%, selon la nature de l'acier.When thus controlling the atmosphere, according to the invention, the reduction calamine mass obtained is between 5 and 25%, depending on the nature of the steel.

    De la même façon, on note en règle générale, une réduction de l'épaisseur de la couche décarburée d'au moins 10%, selon la teneur en éléments d'alliage et spécifiquement la teneur en carbone. Similarly, there is generally a reduction of the thickness of the decarburized layer by at least 10%, depending on the alloying elements and specifically the carbon content.

    Les gains obtenus avec le contrôle de l'atmosphère sont cumulables avec les gains obtenus par réduction des temps Δ1 et Δ2 décrits ci-dessus.The gains obtained with the control of the atmosphere can be cumulated with the gains obtained by reducing the times Δ 1 and Δ 2 described above.

    La figure 4 illustre le contrôle de la montée en température du produit selon l'invention. L'invention consiste à permettre le contrôle de la montée en température du produit et le réglage des brûleurs par une mesure locale, zone par zone et à quelques cm au-dessus de la charge, de la température de l'atmosphère du four grâce à un système de diode laser.Figure 4 illustrates the control of the temperature rise of the product according to the invention. The invention consists in allowing the control of the rise in product temperature and burner setting by a local measurement, zone per area and a few cm above the load, the temperature of the oven atmosphere through a laser diode system.

    Sur la figure 4, le four (41) montre l'emplacement du produit (42) et du thermocouple (48) selon la technique de l'art antérieur. La mesure du thermocouple (48) donne une valeur de température dans l'axe du four et loin du produit (42).In FIG. 4, the oven (41) shows the location of the product (42) and the thermocouple (48) according to the technique of the prior art. The measurement of thermocouple (48) gives a temperature value in the furnace axis and far of the product (42).

    Selon l'invention on met en place une ou plusieurs diode laser pour mesurer une valeur de température moyenne le long du chemin optique dans la largeur du four.
    Une telle disposition permet :

    • Une mesure moyenne le long du four, plus représentative du produit qu'une mesure ponctuelle en voûte.
    • Une mesure proche du produit donc directement liée à la température de surface du produit qui est à l'équilibre avec la température du gaz en contact avec la dite surface.
    • Une quantification de la relation entre température de voûte et température du produit qui était effectuée empiriquement dans l'état de l'art (en conservant le thermocouple de voûte).
    According to the invention, one or more laser diodes are set up to measure an average temperature value along the optical path in the width of the oven.
    Such an arrangement allows:
    • An average measurement along the furnace, more representative of the product than a point measurement in vault.
    • A measurement close to the product therefore directly related to the surface temperature of the product which is in equilibrium with the temperature of the gas in contact with said surface.
    • A quantification of the relationship between vault temperature and product temperature that was performed empirically in the state of the art (keeping the vault thermocouple).

    Sur la figure 4, le nombre de points de mesures a ici été limité à trois. De préférence, on utilisera entre 1 et 10 points de mesure dans un four.In FIG. 4, the number of measurement points has here been limited to three. Preferably, between 1 and 10 measurement points will be used in an oven.

    Le four (41) est équipé des accès (43, 44, 45) situés au dessus du produit (42). The oven (41) is equipped with accesses (43, 44, 45) located above the product (42).

    L'opérateur du four doit respecter au maximum un profil de montée en température du produit (47). Ce profil est fourni à l'opérateur, soit par son expérience soit par une abaque, soit par un logiciel de conduite de four.The oven operator must respect at most a rising profile in product temperature (47). This profile is provided to the operator, either by experience either by an abacus or by a furnace control software.

    Pour contrôler la montée en température du produit (47), l'homme de l'art ne disposait jusque là que de la courbe (46) décrivant la température de la voûte dans l'axe du four, dont, par exemple, le thermocouple (48) fournit un point de mesure, comme illustré sur la courbe. Selon l'invention, l'homme de l'art a maintenant accès aux mesures situées sur la courbe (47) qui sont directement liées à la température de surface du produit. L'opérateur peut donc agir sur la puissance des brûleurs pour retrouver le niveau souhaité de température sur la courbe (47). Si la température mesurée est trop basse, alors l'opérateur augmentera la puissance de chauffage dans la zone proche du point de mesure. A l'inverse, si la température mesurée est trop haute, alors l'opérateur réduira la puissance dans la zone proche du point de mesure.To control the temperature rise of the product (47), the man of Until now, art had only the curve (46) describing the temperature of the vault in the axis of the furnace, of which, for example, the thermocouple (48) provides a measuring point, as shown on the curve. According to the invention, the man of art now has access to measurements on the curve (47) that are directly related to the surface temperature of the product. The operator can so act on the power of the burners to find the desired level of temperature on the curve (47). If the measured temperature is too low, then the operator will increase the heating power in the near area the measuring point. Conversely, if the measured temperature is too high, then the operator will reduce the power in the area near the point of measured.

    L'invention présente également l'avantage suivant :The invention also has the following advantage:

    Certains fours utilisent un logiciel dit de « Niveau 2 » pour reproduire quelles que soient les conditions de chauffe une montée en température du produit, selon un profil initial donné. L'homme de métier ne disposait jusqu'à ce jour d'aucune mesure pour valider en continu l'effet du logiciel. C'est un autre aspect de l'invention que de coupler ce logiciel avec les mesures directes du produit selon l'invention, ce qui permet d'avoir une vérification systématique en temps réel de la température visée du produit.Some ovens use software called "Level 2" to reproduce whatever the heating conditions a rise in temperature of product, according to a given initial profile. The skilled person did not have until this day of any measurement to validate continuously the effect of the software. It's a Another aspect of the invention is to couple this software with the measurements of the product according to the invention, which makes it possible to have a verification systematically in real time the target temperature of the product.

    Exemple 1 :Example 1

    Un premier exemple de mise en oeuvre est décrit à l'aide de la figure 5 qui représente la courbe de chauffe (51) associée à un four de réchauffage de billettes de grande longueur. La combustion est réalisée avec des brûleurs dont le combustible est du gaz naturel et le comburant de l'air préchauffé, avant mise en place de l'invention. (Sur cette figure 5, les paramètres t1, ... et Δ1, ... sont mis entre parenthèses lorsqu'ils concernent la courbe 51, selon l'art antérieur et sont notés sans parenthèses lorsqu'ils se réfèrent à la courbe 52).A first example of implementation is described with reference to FIG. 5 which represents the heating curve (51) associated with a furnace for heating long billets. The combustion is carried out with burners whose fuel is natural gas and the oxidizer of the preheated air, before implementation of the invention. (In this FIG. 5, the parameters t 1 ,... And Δ 1 ,... Are placed in parentheses when they relate to the curve 51, according to the prior art and are noted without parentheses when they refer to the curve 52).

    La mise en oeuvre de l'invention se caractérise par le remplacement des brûleurs existants dont le comburant est de l'air, par des brûleurs dont le comburant a une concentration en oxygène supérieure à 21% en volume, et de préférence supérieure à 88%. Plus préférentiellement, le comburant sera de l'oxygène industriellement pur. La courbe de chauffe associée est la courbe (52). On remarque que les temps Δ1 et Δ2 sont réduits respectivement de 2100 à 1700 secondes et de 5300 à 4800 secondes. La qualité métallurgique du procédé obtenu selon la courbe (52) sera nettement améliorée, grâce au suivi de la courbe de chauffe de la fig. 5, avec l'installation de diodes laser aux emplacements explicités en regard de la fig. 3 et fig. 4, ou tout autre moyen de mesure permettant un contrôle convenable de ce profil de chauffe.The implementation of the invention is characterized by the replacement of existing burners whose oxidant is air, by burners whose oxidant has an oxygen concentration of greater than 21% by volume, and preferably greater than 88% . More preferably, the oxidant will be industrially pure oxygen. The associated heating curve is the curve (52). We note that the times Δ 1 and Δ 2 are respectively reduced from 2100 to 1700 seconds and from 5300 to 4800 seconds. The metallurgical quality of the process obtained according to the curve (52) will be significantly improved, thanks to the monitoring of the heating curve of FIG. 5, with the installation of laser diodes at the locations explained with reference to FIG. 3 and fig. 4, or any other measuring means allowing proper control of this heating profile.

    La figure 6 représente la quantité de calamine produite avec la méthode décrite ci-avant. La quantité de calamine (61) est associée à la situation de référence, la courbe de calamine (62) est associée à la mise en oeuvre de l'invention. Les deux courbes ont été normalisées par la valeur maximum de l'épaisseur de calamine obtenue dans les conditions (61).FIG. 6 represents the quantity of calamine produced with the method described above. The amount of scale (61) is associated with the reference situation, the calamine curve (62) is associated with the implementation of of the invention. Both curves have been normalized by the value maximum thickness of calamine obtained under the conditions (61).

    La mise en oeuvre du procédé selon l'invention, réduisant Δ1 de 19 % et Δ2 de 9.5 % permet de réduire la quantité de la calamine en moyenne de 8% (Fig. 6). Selon les expériences, l'épaisseur de la couche décarburée est réduite entre 9 et 17%.The implementation of the process according to the invention, reducing Δ 1 by 19% and Δ 2 by 9.5% reduces the amount of calamine by an average of 8% (FIG 6). According to the experiments, the thickness of the decarburized layer is reduced between 9 and 17%.

    Exemple 2 :Example 2

    L'exemple de réalisation ci-après a été mis en oeuvre dans un four de réchauffage de billettes, de 33 MW de puissance et de 30m de long environ. Les brûleurs présents initialement sur le four sont des brûleurs dit aéro-combustibles, l'air de combustion étant préchauffé à 300°C.The embodiment example below was implemented in a furnace of heating billets, 33 MW power and about 30m long. The burners initially present on the furnace are so-called aero-fuel burners, the combustion air being preheated to 300 ° C.

    La figure 7 compare, pour un profil de chauffe identique, la quantité de calamine produite par (courbe 71) en suivant une atmosphère de chauffe dont la concentration d'oxygène dans les fumées humides est constante et égale à 3.5 % volumique, et la quantité de calamine produite (courbe 72) en suivant une atmosphère de chauffe dont la concentration d'oxygène dans les fumées humides varie de la manière suivante :

    • environ 1.5% O2 (à 20 % près) quand la température de peau T est supérieure à la température d'égalisation Tégalisation (définie comme étant comprise entre 85% et 90% de la température de défournement),
    • environ 0% d'O2 (jusqu'à quelques centaines de ppm) et une concentration de CO entre environ 0.5% et 3% (à 20 % près) pour Tdécarb < T < T égalisation, Tdécarb étant la température de début de la d écarburation (700°C)
    • environ 2% d'O2 (à 20 % près) quand la température de peau T est inférieure à Tdécarb
    FIG. 7 compares, for an identical heating profile, the amount of scale produced by (curve 71) following a heating atmosphere whose oxygen concentration in the humid fumes is constant and equal to 3.5% by volume, and the quantity of calamine produced (curve 72) by following a heating atmosphere whose oxygen concentration in the humid fumes varies as follows:
    • about 1.5% O 2 (to within 20%) when the skin temperature T is greater than the equalization temperature T equalization (defined as being between 85% and 90% of the dewatering temperature),
    • about 0% O2 (up to a few hundred ppm) and a CO concentration between about 0.5% and 3% (to within 20%) for T decarb <T <T equalization , T decarb being the start temperature of debarking (700 ° C)
    • about 2% O 2 (to within 20%) when the skin temperature T is less than T decarb

    La concentration moyenne en O2 dans les fumées peut être mesurée par une sonde à oxygène usuelle, mais il peut être préférable de mettre en oeuvre une diode laser (de type dit « TDL ») dont le rayon passe à une distance de moins de 6 cm environ du produit traité pour contrôler finement et en temps réel une variation de concentration des espèces ci-dessus à la surface du produit afin de mieux respecter le profil d'atmosphère imposé en adéquation avec le profil de chauffe.The average concentration of O2 in the fumes can be measured by a standard oxygen sensor, but it may be better to a laser diode (of so-called "TDL" type) whose radius changes to a distance of less than 6 cm from the treated product to control finely and in real time a concentration shift from the above species to the surface of the product in order to better respect the imposed atmosphere profile in adequacy with the heating profile.

    La mise en oeuvre selon l'invention, selon cet exemple 2, permet de réduire l'épaisseur de la calamine de 11% (Fig. 7). Selon les expériences, l'épaisseur de la couche décarburée est réduite entre 12 et 20%.The implementation according to the invention, according to this example 2, allows reduce the calamine thickness by 11% (Fig. 7). According to the experiences, the thickness of the decarburized layer is reduced between 12 and 20%.

    Claims (11)

    1. Method of treating a metallurgical product in a furnace, in which the product to be treated is introduced into the furnace and then subjected to the desired treatment before being removed from the furnace, the furnace comprising heating means and especially burners for raising the various zones of the furnace to a variable temperature, it being possible for the atmosphere in these various zones to have an identical or different composition depending on the zones in question of said furnace, in which method the product to be treated has a temperature that increases between the moment when it is introduced into the furnace and the moment when it is removed therefrom, the temperature rise curve having a slope that increases over a first time interval between the time to of introduction of the product into the furnace and the time t1 at which the product achieves a surface temperature of 650°C, an approximately constant slope between the time t1 and the time t2 at which the product reaches a temperature about 15% below the desired final surface temperature of the product to be treated when it leaves the furnace, then a slope that decreases between the time t2 and the time t3 at which the product to be treated leaves the furnace, in which method the heating power of the furnace is increased relative to its power when only air/fuel burners are used, so as to increase the slope of the curve giving the rise in temperature of the product to be treated, at least during certain periods of treatment of the product in the furnace between the times t1 and t2, thereby reducing the duration of the treatment of the product to be treated and correspondingly reducing the thickness of the decarburized layer and/or the layer of scale formed on the surface of the product.
    2. Method according to Claim 1, characterized in that the increase in the heating power of the furnace is obtained by means of oxyfuel burners that constitute at least part of the heating means of the furnace, especially part of the heating means of the furnace corresponding to the zone reached by the product between the times t1 and t2.
    3. Method according to Claim 2, characterized in that the oxidizer delivered to the oxyfuel burners, constituting at least part of the heating means of the furnace, contains at least 88% oxygen, preferably greater than 90% oxygen and even more preferably greater than 95% oxygen.
    4. Method according to one of Claims 1 to 3, characterized in that the time for treating the product between the temperatures of 700°C and 800°C reached by the surface of the product is reduced by 15% to 50% of its reference value, preferably by 20 to 35% of its value.
    5. Method according to one of Claims 1 to 4, characterized in that the treatment time between the temperatures of 700°C and the final temperature of the surface of the product is reduced by between 3 and 25% of its reference value, preferably between 7 and 15% of its reference value.
    6. Method according to one of Claims 1 to 5, characterized in that the atmosphere of the furnace varies along the furnace according to the skin temperature of the metallurgical product.
    7. Method according to one of Claims 1 to 6, characterized in that the atmosphere of the furnace on contact with the product to be treated contains about 0.5 to 5 vol% oxygen and preferably between 1.5 to 4 vol% oxygen when the skin temperature T at the surface of the treated product is greater than or equal to the equalization temperature Tequal, which is equal to 85% of the temperature at the surface of the product (discharge temperature) as it leaves the furnace.
    8. Method according to Claim 7, characterized in that the equalization temperature Tequal is equal to 90% of the discharge temperature.
    9. Method according to one of Claims 1 to 8, characterized in that the atmosphere on contact with the product to be treated has an oxygen concentration of less than a few hundred ppm and a CO concentration of between 0.1 and 15 vol%, preferably 0.5 to 5 vol%, when the skin temperature T at the surface of the product is above 700°C and below the equalization temperature of the product, defined as being equal to 90% of the skin temperature of the product as it leaves the furnace.
    10. Method according to one of Claims 1 to 9, characterized in that the atmosphere in contact with the product to be treated has an oxygen concentration of between 0.5 and 4 vol% and preferably between 2 and 3 vol% when the skin temperature T at the surface of the product to be treated is below 700°C.
    11. Method according to one of Claims 1 to 10, characterized in that at least one of the parameters of the atmosphere in at least one zone of the furnace is analysed by means of a diode laser, the beam of which is located at a minimum distance from the surface of the product of between 1 cm and 6 cm at least at a point on the surface of said product.
    EP02735468A 2001-04-26 2002-04-19 Method for enhancing the metallurgical quality of products treated in a furnace Expired - Lifetime EP1386012B1 (en)

    Applications Claiming Priority (5)

    Application Number Priority Date Filing Date Title
    FR0105634 2001-04-26
    FR0105634A FR2824078B1 (en) 2001-04-26 2001-04-26 PROCESS FOR CONTROLLING THE PROFILE OF AN OVEN AND IMPROVING THE PROCESSED PRODUCTS
    FR0105633 2001-04-26
    FR0105633A FR2824077B1 (en) 2001-04-26 2001-04-26 PROCESS FOR IMPROVING THE METALLURGICAL QUALITY OF PRODUCTS PROCESSED IN AN OVEN
    PCT/FR2002/001361 WO2002088402A1 (en) 2001-04-26 2002-04-19 Method for enhancing the metallurgical quality of products treated in a furnace

    Publications (2)

    Publication Number Publication Date
    EP1386012A1 EP1386012A1 (en) 2004-02-04
    EP1386012B1 true EP1386012B1 (en) 2005-03-16

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    EP02735468A Expired - Lifetime EP1386012B1 (en) 2001-04-26 2002-04-19 Method for enhancing the metallurgical quality of products treated in a furnace

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    EP (1) EP1386012B1 (en)
    CN (1) CN1505687A (en)
    AT (1) ATE291101T1 (en)
    CA (1) CA2444399C (en)
    DE (1) DE60203280T2 (en)
    ES (1) ES2240752T3 (en)
    WO (1) WO2002088402A1 (en)

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    RU2324745C2 (en) * 2006-02-26 2008-05-20 Игорь Михайлович Дистергефт Method of thermal processing of metal in combustion furnace of either direct or indirect reheating (variants), method of burning of mixture of liquid or gazeous fuel and heated air in combustion furnace of either direct or indirect reheating, heating mechanism (variants) and regenerative capping (variants) to implement these procedures
    JP5059379B2 (en) * 2006-11-16 2012-10-24 株式会社神戸製鋼所 Hot briquette iron for blast furnace charging raw material and method for producing the same
    SE531990C2 (en) * 2007-01-29 2009-09-22 Aga Ab Process for heat treatment of long steel products
    FR2920438B1 (en) * 2007-08-31 2010-11-05 Siemens Vai Metals Tech Sas METHOD FOR IMPLEMENTING A LINE OF CONTINUOUS DINING OR GALVANIZATION OF A METAL STRIP
    CN104865196A (en) * 2014-09-09 2015-08-26 浙江迪特高强度螺栓有限公司 Measuring method of carbon content inside mesh belt heat treatment furnace
    US20170094730A1 (en) * 2015-09-25 2017-03-30 John Justin MORTIMER Large billet electric induction pre-heating for a hot working process
    CN117212812B (en) * 2023-11-09 2024-02-23 陕西宝昱科技工业股份有限公司 Combustion machine switching mechanism and combustion furnace system

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    FR2174657A1 (en) * 1972-03-06 1973-10-19 Ferodo Sa Chlutchplate heat treatment - accelerated by heating to alpha iron to austenite change point
    US4357135A (en) * 1981-06-05 1982-11-02 North American Mfg. Company Method and system for controlling multi-zone reheating furnaces
    US4415415A (en) * 1982-11-24 1983-11-15 Allegheny Ludlum Steel Corporation Method of controlling oxide scale formation and descaling thereof from metal articles
    US4606529A (en) * 1983-09-20 1986-08-19 Davy Mckee Equipment Corporation Furnace controls
    TW265286B (en) * 1993-06-23 1995-12-11 Gas Res Inst
    IT1281420B1 (en) * 1995-09-13 1998-02-18 Danieli Off Mecc EQUALIZATION PROCEDURE IN A HEATING FURNACE WITH A CONTROLLED OXIDATION ENVIRONMENT AND HEATING FURNACE
    FR2794132B1 (en) * 1999-05-27 2001-08-10 Stein Heurtey IMPROVEMENTS RELATING TO HEATING OVENS OF STEEL PRODUCTS

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    EP1386012A1 (en) 2004-02-04
    ES2240752T3 (en) 2005-10-16
    US6955730B2 (en) 2005-10-18
    CA2444399A1 (en) 2002-11-07
    CA2444399C (en) 2010-08-24
    US20040140024A1 (en) 2004-07-22
    DE60203280T2 (en) 2006-03-30
    ATE291101T1 (en) 2005-04-15
    CN1505687A (en) 2004-06-16
    DE60203280D1 (en) 2005-04-21
    WO2002088402A1 (en) 2002-11-07

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