Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/003—Apparatus
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/003—Apparatus
  • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
  • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
  • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
  • C23C2/0224—Two or more thermal pretreatments
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
  • C23C2/06—Zinc or cadmium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
  • C23C2/12—Aluminium or alloys based thereon

Definitions

• the invention relates to a method for hot-dip coating a flat steel product and to a hot-dip coating system.
• DFFs directly fired heat treatment furnaces
• Essential to the invention is that hydrogen in the fuel gas with a proportion of at least 10 to 100 vol.% is used for the DFF furnace, wherein if the fuel gas does not consist entirely of hydrogen, it may contain further proportions of methane and/or carbon monoxide in addition to hydrogen, and that the furnace atmosphere in the DFF furnace is brought into contact with at least one drying agent, which establishes a water vapor partial pressure in the furnace atmosphere of the DFF furnace that is lower compared to the water vapor partial pressure of the combustion gas.
• the second teaching relates to a melt exchange coating plant comprising a furnace and a pot for receiving a liquid metallic melt bath, wherein the furnace contains or consists of a preheating section, a heating and/or holding section, and a cooling section for a continuously passing steel flat product, wherein the preheating section is designed as a DFF furnace, wherein the DFF furnace has at least one burner which can be supplied with a fuel gas and an oxygen-containing gas, wherein the fuel gas and oxygen-containing gas are combustible in the burner to form a combustion gas with which a furnace atmosphere can be generated in the DFF furnace, wherein hydrogen can be provided at least partially as a fuel gas, and wherein at least one desiccant is provided for contact with the furnace atmosphere of the DFF furnace.
• Preheating a flat steel product in a steam atmosphere can alter the grain structure, potentially leading to undesirable, premature grain boundary oxidation, which in turn can cause coating and/or surface defects. Due to the accelerated oxidation and scale formation, grain boundary oxidation can also occur more rapidly and penetrate deeper into the substrate.
• Decarbonization in the application case of preheating a flat steel product in a DFF furnace in a hot-dip coating plant would therefore not only be a simple switch from fossil to non-fossil fuels, but would also involve a complex influence on the product parameters.
• This is necessary to establish an oven atmosphere in the DFF oven of a hot-dip coating system that has a lower water vapor partial pressure compared to the (pure) flue gas.
• an oven atmosphere can be established that largely corresponds to a conventional natural gas-fired oven atmosphere, so as not to have to change the existing process chain unnecessarily and to essentially maintain the standard process.
• the inventive measure allows for the adjustment of an oven atmosphere in the DFF oven of a hot-dip coating system to a level comparable to, or adaptable to, that of currently known natural gas-fired burners.
• the hydrogen used, at least partially, in the fuel gas can be produced and supplied, for example, by water electrolysis using renewable energies such as wind, water, and/or solar power. Any oxygen required can also be produced and supplied by electrolysis using renewable energies (solar, wind, water, etc.).
• the heating and/or holding of the preheated steel flat product takes place at a temperature between 400 °C, in particular between 500 °C, preferably between 600 °C, preferably between 700 °C and 950 °C, in particular a maximum of 900 °C, wherein a downstream part of the furnace following the DFF furnace (part) is provided with indirect firing for further heating and optional holding and thus annealing of the hot-rolled or cold-rolled steel flat product, for example a radiant tube furnace (RTF) with an adjustable furnace atmosphere, preferably with a reducing furnace atmosphere.
• RTF radiant tube furnace
• the cooling of the hot or annealed steel flat product is carried out to a temperature at least 50 K, in particular at least 40 K, preferably at least 30 K, preferably at least 20 K below to a maximum of 50 K, in particular a maximum of 40 K, preferably a maximum of 30 K, preferably a maximum of 20 K above a melting bath temperature, wherein the cooling furnace or part of the heat treatment furnace for cooling the hot-rolled or cold-rolled steel flat product is provided with indirect firing, essentially a radiant tube furnace (RTF), with an adjustable furnace atmosphere, preferably a reducing furnace atmosphere.
• RTF radiant tube furnace
• the temperature at the surface on one side of the steel flat product is measured, particularly with a pyrometer or other suitable measuring instruments.
• a pyrometer or other suitable measuring instruments can be determined.
• the temperature of the flat steel product in each area of the hot-dip coating plant is recorded using means known to those skilled in the art.
• the immersion of the cooled steel flat product into a metallic melt bath at a melt bath temperature, in order to coat the steel flat product with a metallic coating by means of hot-dip coating, is carried out essentially under a protective gas atmosphere in a known manner.
• the hot-dip coating system is preferably equipped with a horizontally designed oven, but can alternatively be designed in a vertical configuration.
• the oxygen-containing gas for operating the burner can be air, for example ambient air, oxygen, or a combination of air and oxygen.
• the oxygen-containing gas and/or the fuel gas can be preheated before being fed to the combustion chamber to increase energy efficiency, for example to at least 200 °C, in particular to at least 300 °C, preferably to at least 400 °C.
• the preheating can, for example, be limited to a maximum of 500 °C.
• Preheating the fuel gas and/or the oxygen-containing gas can lead to an increase in the adiabatic flame temperature.
• Determining or measuring the partial pressure of water vapor in a furnace atmosphere is familiar to those skilled in the art. This can be done, for example, by measuring the dew point with suitable measuring devices.
• This configuration includes, for example, the use of 100% hydrogen; in other words, the fuel gas consists of hydrogen, whereby impurities in the fuel gas of up to 0.5% by volume, in particular up to 0.2% by volume, and preferably less than 0.1% by volume, are permitted, and where impurities cannot be avoided technically or only with considerable equipment effort.
• the fuel gas may contain additional proportions of methane ( CH4 ) and/or carbon monoxide (CO) to achieve a hydrogen content of 100% by volume, along with impurities, which are permitted up to 0.5% by volume, in particular up to 0.2% by volume, preferably less than 0.1% by volume. Traces of carbon dioxide ( CO2 ) up to 1.5% by volume may also be present.
• CH4 methane
• CO carbon monoxide
• blast furnace gas for example containing or consisting of one or more of the components coke oven gas, blast furnace gas, converter gas, smelter gas, etc., can be considered as a fuel alongside hydrogen.
• the temperature of the burner flame also influences the temperature of the furnace atmosphere.
• the combustion temperature with ambient air and natural gas is approximately 1970 °C, with ambient air and hydrogen approximately 2130 °C, with oxygen and natural gas approximately 2860 °C, and with oxygen and hydrogen approximately 3080 °C.
• the air ratio can be between 0.75 and 0.99, in particular to avoid the presence of oxygen (compounds) in the flue gas, or alternatively between 1 and 1.25, to control the amount of oxygen in the flue gas for targeted scaling, for example in certain products.
• the desiccant is preferably hygroscopic. It is particularly preferred that the desiccant be temperature-resistant up to 1500 °C, and more preferably has a melting point > 1600 °C.
• the desiccant has a water adsorption capacity of at least 20%, particularly at least 30%, preferably at least 35%, and, for example, up to a maximum of 80% by weight of the desiccant. This means that with the use of 100 kg of desiccant, a water adsorption capacity of at least 20% by weight, etc., can be ensured. If, for example, a water adsorption capacity of approximately 45% is possible, this would correspond to a water content of 45 kg and a total weight of 145 kg in the aforementioned example.
• the water adsorption capacity is determined, for example, under standard conditions, particularly at room temperature.
• the drying agent can contain or consist of silicon dioxide.
• the melting point of silicon dioxide is approximately 1710 °C.
• the drying agent can contain or consist of aluminum oxide.
• the melting point of aluminum oxide is approximately 2070 °C.
• It may also be a combination of silicon dioxide and aluminum oxide, for example with a mixing ratio between 5:95 and 95:5.
• a quantity or volume of a desiccant can be provided which is able to reduce the water vapor partial pressure in the furnace atmosphere by at least 30%, in particular at least 40%, preferably at least 50% and, for example, a maximum of 100% compared to the water vapor partial pressure of the flue gas.
• the desiccant can be arranged in a suitable receiving device, which allows for a spacing between the individual granule particles or grains of the desiccant in order to increase the surface area of the desiccant compared to to be able to provide, for example, a heaped material, which promotes water absorption.
• the individual granule particles or grains can be spherical with a diameter between 0.05 and 10 mm.
• the desiccant can be arranged in special receiving devices, which are designed to allow flow through them. Preferably, several receiving devices are provided, which are alternately fed into the oven via a suitable airlock device to reduce the water vapor partial pressure or used for drying during regeneration. Three or more receiving devices are particularly preferred.
• the desiccant Once the desiccant reaches saturation, i.e., its maximum water adsorption capacity, it can be regenerated relatively easily. This means that the absorbed water can simply evaporate when warm. Since the desiccant is already at a temperature corresponding to the temperatures prevailing in the furnace, for example, between 750 °C and 1400 °C, and is therefore hot, it must be exposed to an atmosphere with lower humidity (or water vapor partial pressure) to allow it to dry again. This atmosphere can be ambient air or another gas with low humidity, for example, ⁇ 30% relative humidity, or even no humidity at all, such as an inert gas. To accelerate the regeneration process, the desiccant can be exposed to a flowing gas or ambient air.
• the desiccant can, for example, be equipped with a color indicator that changes color depending on the moisture content.
• This indicator can be used, for instance, through monitoring to determine when the desiccant needs to be replaced. The replacement is preferably carried out during operation.
• the desiccant in the form of granular particles or grains, can be blown into the DFF furnace via at least one inlet nozzle, which can be individually aligned and/or adjusted in the spatial direction, along with a carrier gas, preferably a dry protective gas, such as nitrogen.
• a carrier gas preferably a dry protective gas, such as nitrogen.
• the carrier gas can also be introduced via one or more burners with a separate geometric arrangement, in order to achieve, in particular, (faster) contact with the blown-in desiccant.
• the desiccant can also be introduced into the atmosphere of the DFF furnace via a suitable airlock, for example a rotary valve.
• the desiccant leaves the DFF furnace with the exhaust gas.
• a special filter device would need to be used in the exhaust system of the DFF furnace to filter the blown-in desiccant and separate it from the exhaust gas. This would allow the desiccant to be reused and reintroduced into the cycle.
• the flat steel product can be coated with a zinc-based coating.
• the metallic melt bath can contain or consist of additional elements such as aluminum with a content of up to 15 wt.%, in particular up to 10 wt.%, preferably up to 8 wt.%, more preferably up to 5 wt.%, and/or magnesium with a content of up to 15 wt.%, in particular up to 10 wt.%, more preferably up to 8 wt.%, more preferably up to 5 wt.%.
• the metallic melt bath can contain or consist of magnesium with a content of at least 0.3 wt.%, in particular at least 0.6 wt.%, more preferably at least 0.9 wt.%. Additionally or alternatively, aluminum can be present alongside magnesium in a concentration of at least 0.1 wt.%, and in particular at least 0.3 wt.%, to improve, for example, the bonding of the metallic coating to the steel flat product and, in particular, to essentially prevent the diffusion of iron from the substrate into the coating during heat treatment of the coated steel flat product, thus ensuring, for example, good adhesion.
• the thickness of the metallic coating on each side can be adjusted between 1.5 and 60 ⁇ m, in particular between 2 and 50 ⁇ m, and preferably between 3 and 30 ⁇ m, using known stripping nozzles arranged above the melt pool.
• the metallic molten bath contains or consists of magnesium within the aforementioned limits, aluminum within the aforementioned limits, and the remainder zinc along with unavoidable impurities.
• the resulting metallic coating on the flat steel product is known in the professional world as zinc-magnesium (ZM) or Zn-Al-Mg.
• the aluminium content in the metallic melt bath is 1.1 to 8 wt.%, in particular 1.2 to 5 wt.%.
• the magnesium content in the metallic melt bath is 1.1 to 8 wt.%, in particular 1.2 to 5 wt.%.
• the coating may also contain only zinc with small amounts of aluminum alongside unavoidable impurities, also known in specialist circles as "Z".
• Unavoidable impurities such as elements from the group consisting of silicon, antimony, lead, titanium, calcium, manganese, tin, lanthanum, cerium and chromium, may be present individually or in combination in the metallic melt bath up to a total of 0.5 wt.%, in particular up to 0.3 wt.%.
• the steel flat product can be coated with an aluminum-based coating.
• the metallic melt bath can contain or consist of, in addition to aluminum and unavoidable impurities, optionally up to 15 wt.% Si, optionally up to 4 wt.% Fe, and optionally up to 1.0 wt.% alkali or alkaline earth metals.
• the silicon content in the metallic melt bath is either 0.2 to 4.5 wt.% or 7 to 13 wt.%, in particular 8 to 11 wt.%.
• the optional iron content comprises 0.2 to 4.5 wt.%, in particular 1 to 4 wt.%, preferably 1.5 to 3.5 wt.%.
• the optional content of alkali or alkaline earth metals comprises 0.01 to 1.0 wt.% magnesium, in particular 0.1 to 0.7 wt.% magnesium, preferably 0.1 to 0.5 wt.% magnesium. Furthermore, the optional content of alkali or alkaline earth metals may in particular comprise at least 0.0015 wt.% calcium.
• the steel flat product can be coated with an aluminum-based coating.
• the metallic melt bath can contain or consist of, in addition to aluminum and unavoidable impurities, 2 to 24 wt.% zinc, 1 to 7 wt.% silicon, optionally 1 to 8 wt.% magnesium if the silicon content is between 1 and 4 wt.%, and optionally up to 0.3 wt.% total lead, nickel, zirconium, or hafnium.
• the thickness of the metallic coating on each side can be set between 1 and 60 ⁇ m, in particular between 2 and 50 ⁇ m, preferably between 3 and 30 ⁇ m.
• Unavoidable impurities such as elements from the group consisting of antimony, lead, titanium, manganese, tin, lanthanum, cerium and chromium, may be present individually or in combination in the metallic melt bath up to a total of 0.5 wt.%, in particular up to 0.3 wt.%.
• Figure 1 shows a hot-dip coating system (100) comprising a furnace (10) and a pot (20) for receiving a liquid metallic melt bath (S).
• the furnace (10) includes a preheating section (11), a holding section (12), and a cooling section (13) for a continuously passing steel flat product (1).
• the steel flat product (1) is preheated and held at a temperature between 400 and 950 °C.
• the heated steel flat product (1) is held at a temperature preferably between 600 and 950 °C.
• the warm steel flat product (1) is cooled to a temperature at least 50 K below and at most 50 K above the melt bath temperature.
• the preheating section (11) is designed as a DFF oven and is described in detail in Figure 2 outlined.
• the DFF furnace (11) has at least one burner (11.2) which can be supplied with a fuel gas (11.3) and an oxygen-containing gas (11.4), wherein the fuel gas (11.3) and oxygen-containing gas (11.4) can be combusted in the burner (11.2) to form a flue gas (11.9) with which a furnace atmosphere (11.11) can be generated in the DFF furnace (11), cf.
• Figure 2 which is a schematic sectional view in direction II, see. Figure 1 .
• Hydrogen can be provided partially or completely as fuel gas (11.3).
• the hydrogen used, at least partially, in the fuel gas can be produced and provided, for example, in water electrolysis using renewable energies such as wind, water, and/or solar power (not shown here).
• At least one desiccant (20) is provided for contact with the furnace atmosphere (11.11) of the DFF furnace (11).
• hydrogen in the fuel gas (11.3) is used for the DFF furnace (11) with a proportion of at least 10 to 100 vol%, whereby if the fuel gas (11.3) does not consist entirely of hydrogen, it may contain additional proportions of methane and/or carbon monoxide, and that the furnace atmosphere (11.11) in the DFF furnace (11) is brought into contact with at least one desiccant (20), which results in a water vapor partial pressure in the furnace atmosphere (11.11) of the DFF furnace (11) that is lower compared to the water vapor partial pressure of the flue gas (11.9).
• the desiccant (20) can be arranged in a receiving device (not shown) and contains or consists of silicon dioxide or aluminum oxide.
• the desiccant (20) can be introduced into the DFF oven (11) via suitable means (22) in a receiving device to reduce the water vapor partial pressure in the oven atmosphere (11.11) in a working position.
• the desiccant (20) in contact with the oven atmosphere (11.11) reaches saturation, it is discharged from the DFF oven (11) via the means (22) to dry in a regeneration position.
• the hot desiccant (20) can be exposed to the environment or, for example, actively aerated with ambient air to accelerate the regeneration process.
• another desiccant (20) is introduced into the DFF oven (11) to ensure a continuous reduction of the water vapor partial pressure.
• the desiccant (20) is shown by way of example in three receiving devices. A locking device (not shown) is provided for each device.
• the desiccant (20) can be arranged outside the DFF oven (11), for example in one or preferably several receiving devices, wherein the desiccant (20) is brought into contact with the gas of the oven atmosphere (11.11) via lines and preferably via a suction inlet (21) and, after contact, is returned to the DFF oven (11) at a reduced water vapor partial pressure.
• the desiccant (20) in contact with the oven atmosphere (11.11) reaches saturation
• another desiccant (20) is supplied with the gas of the oven atmosphere (11.11) according to the aforementioned procedure.
• the saturated desiccant (20) is regenerated by exposing the hot desiccant (20) to ambient air or a substantially dry gas to dry it.
• the desiccant (20) can also be granular particles or granules with a carrier gas (12) blown into the DFF oven via at least one inlet nozzle, which can be individually aligned and/or adjusted in the spatial direction.
• preheating of the hot-rolled or cold-rolled flat steel product (1) is possible without the disadvantages of altered or different oxidation/scale formation on the surface of the flat steel product (1) despite the use of non-fossil fuels, if hydrogen with proportions between 10 and 100 vol.% in the fuel gas (11.3) is used.
• Heating steel products to forming temperatures with an increased water vapor partial pressure in the furnace atmosphere due to at least partial combustion of hydrogen in the fuel gas, leads, as expected, to a significant hydrogen ingress into the steel product.
• the hydrogen ingress is significantly reduced. This, in turn, reduces the hydrogen ingress and the associated potential embrittlement and further processing problems.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
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• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Coating With Molten Metal (AREA)

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Citations (6)

• 2024
  • 2024-06-17 EP EP24182577.7A patent/EP4667613A1/fr active Pending

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