Method for heat treating steel products to forming heat

Abstract

The invention relates to a method for heat-treating steel products (1) to forming heat.

Description

[0001] The invention relates to a method for heat-treating steel products to forming heat.

[0002] Steel products that require heating to forming temperatures include slabs heated to rolling temperature, blocks, discs, or billets heated to rolling or forging temperature. These are heated in appropriate furnaces to a temperature of at least 950 °C to achieve a fully austenitic microstructure, depending on the composition, thereby reducing forming resistance. In practice, directly heated heat treatment furnaces are the standard. These furnaces, equipped with at least one, and preferably several, burners, have been fueled with fossil fuels, such as natural gas, for decades. Since combustion takes place within the heat treatment furnace, direct heating allows for the creation of a reducing or oxidizing furnace atmosphere, depending on the set air-fuel ratio (lambda value of the fuel gas).Furthermore, the fuel gas mixture and the oxidizing medium used, which can be either air or pure oxygen, have a significant influence on the resulting flue gas composition. The flue gas from the burner(s) in the heat treatment furnace thus contains a high proportion of water (H₂O) and, depending on the air-fuel ratio, fuel gas and oxidizing agent, either oxygen (O₂) and carbon dioxide (CO₂) or hydrogen (H₂) and carbon monoxide / carbon dioxide (CO / CO₂) as well as nitrogen (N₂). If a reducing furnace atmosphere is set with a lambda value < 1, the flue gas contains carbon monoxide (CO gas) to protect the steel product being heated from oxidation. However, a slightly oxidizing furnace atmosphere can also be set with a lambda value > 1.In this case, oxygen is also present in the flue gas, which causes targeted oxidation of the steel product being heated. However, atmospheric conditions can also lead to further interactions with the steel product. For example, the water content present in the atmosphere can dissociate first into molecular hydrogen (H₂) and then into atomic hydrogen (H) as a result of surface reactions and be absorbed into the steel via the surface.

[0003] As part of the globally required decarbonization, plants powered by fossil fuels are to be converted or retrofitted in the future to more environmentally friendly fuels or energy carriers, such as hydrogen, in order to reduce or ultimately completely avoid the use of fossil energy.

[0004] Decarbonization requires a reduction in the use of fossil fuels and energy sources, and consequently a reduction in CO2 emissions.

[0005] The steel processing industry is working at full speed to become climate-neutral as quickly as possible and thus meet the politically mandated climate targets. The applicant is also constructing new or retrofitting equipment to gradually replace fossil fuels with climate-neutral hydrogen; see the applicant's website: htt ps: / / www.thyssenkrupp / .com / de / newsroom / pressemeldungen / pressedetailseite / top-oberflächen-fur-die-automobilindustrie-thyssenkrupp-nimmt-neuen-hubbalkenofen-am-standortduisburg-in-betrieb-156354.

[0006] Furthermore, it is also known from the technical report "Strategies for the decarbonization of reheating and heat treatment processes in the steel industry" by Wuppermann et al., pp. 16 to 25, published on September 22, 2023 at https: / / www.tube.de / cgibin / md wiretube / lib / all / lob / return download.cgi, see scenario 4 on page 22, that a furnace chamber of a walking beam furnace for the reheating of slabs is heated openly using 160 side-wall and ceiling radiant burners, whereby the integration of suitable burners, which have been successfully tested on a trial scale using 100% H₂ and also mixtures of H₂ and natural gas, still needs to be implemented on an industrial scale after preparation.

[0007] Direct combustion of hydrogen as a fuel gas, or of hydrogen components within the fuel gas, results in higher furnace humidity and / or a higher partial pressure of water vapor in the furnace atmosphere compared to conventional natural gas combustion, due to the combustion reactions with air and / or oxygen. This higher partial pressure of water vapor means that an unintended additional hydrogen input into the steel product cannot be ruled out, leading to disadvantages in subsequent process stages, such as hydrogen embrittlement. These disadvantages can manifest themselves in immediately following processes, such as forming, as well as in further processing steps, such as surface finishing, and ultimately in product processing and component use.

[0008] However, even in conventional natural gas combustion and / or blast furnace gas combustion, where the blast furnace gas contains or consists of one or more of the components coke oven gas, blast furnace gas, converter gas, melting furnace gas, etc., a partial pressure of water vapor is also generated in the furnace atmosphere, so that even in conventional heating, hydrogen ingress into the steel product cannot be completely ruled out.

[0009] The object of the present invention is to further develop the method for heat-treating steel products to forming heat in such a way that hydrogen input into the steel product can be substantially reduced or eliminated.

[0010] This problem is solved by a method having the features of claim 1 and by a directly fired furnace or a directly fired section of a furnace having the features of claim 8. Further embodiments are described in the dependent claims.

[0011] The first teaching relates to a method for heating a steel product to forming heat, wherein the heating of the steel product is carried out in a furnace with a directly fired furnace chamber or with a directly fired section of a furnace chamber, wherein the temperature of the steel product when removed from the furnace is between 950 °C and 1400 °C, wherein the furnace comprises several burners which are operated with a fuel gas containing 0 vol.% to 100 vol.% hydrogen and an oxygen-containing gas and from which a flue gas is generated which fills the furnace chamber or the section of the furnace chamber and forms a furnace atmosphere with a flue gas composition depending on the composition of the fuel gas and the composition of the oxygen-containing gas with a water vapor partial pressure.

[0012] Essential to the invention is that the furnace atmosphere in the furnace with the directly fired furnace chamber or with the directly fired section of the furnace chamber is brought into contact with at least one desiccant, which creates a water vapor partial pressure in the furnace atmosphere that is lower compared to the water vapor partial pressure of the flue gas.

[0013] The second teaching relates to a furnace with a directly fired furnace chamber or with a directly fired section of a furnace chamber, comprising several burners that can be supplied with a fuel gas containing 0 to 100% hydrogen by volume and an oxygen-containing gas, and by which a furnace atmosphere can be generated in the furnace chamber or in the section of the furnace chamber by the resulting flue gas. At least one desiccant is provided for contact with the furnace atmosphere in the furnace chamber or in the section of the furnace chamber.

[0014] The furnace can be designed and have appropriate means by which it is possible to guide the steel product to be heated through the furnace either substantially continuously or quasi-continuously, or preferably discontinuously, i.e., that a steel product is fed into the furnace, remains there until the forming heat is reached, and then leaves the furnace to be subjected to a forming process in the heated state.

[0015] Switching from a fossil fuel (natural gas) to an alternative, hydrogen-containing fuel in a directly fired furnace chamber or a directly fired section of a furnace chamber for heat-treating a steel product to forming heat results in a change in the furnace atmosphere, which has a significant impact on the material properties and surface of the steel product. When hydrogen-containing fuel gases are burned, a larger quantity of water vapor is generated compared to natural gas, resulting in a higher partial pressure of water vapor in the furnace atmosphere. This leads not only to a greater tendency for oxidation (scale formation) during heating by oxygen-affine elements in the steel product, but also to an increased hydrogen input into the steel product.

[0016] An increase in hydrogen in the fuel gas, and consequently an increase in the water vapor partial pressure in the resulting flue gas, must be counteracted by influencing the flue gas through a targeted shift in the thermodynamic processes within the furnace chamber. By using a desiccant, the water vapor in the furnace atmosphere can be absorbed, thereby reducing or even preventing hydrogen from entering the steel product, due to the resulting reduction in the water vapor partial pressure in the furnace atmosphere.

[0017] The furnace, with its directly fired furnace chamber or with its directly fired section of a furnace chamber, can be designed and have appropriate means by which it is possible to pass the steel product to be heat-treated either substantially continuously or almost continuously through the furnace, or preferably discontinuously, i.e., that a steel product is fed into the furnace, remains there until the forming heat is reached, and then leaves the furnace to be subjected to a forming process in the hot state.

[0018] The furnace can have one furnace chamber with direct firing, or several furnace chambers, at least one of which is directly fired, or several of which may be directly fired. Alternatively, the furnace can have one or more furnace chambers, where at least a section of at least one furnace chamber is directly fired.

[0019] Decarbonization in a furnace with a directly fired furnace chamber or with a directly fired section of a furnace chamber for heat-treating a steel product to forming heat would therefore not only be a simple switch from fossil to non-fossil fuels, but also involves a complex influence on the product parameters.

[0020] Determining or measuring the humidity or water vapor partial pressure 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.

[0021] The desiccant is preferably hygroscopic. It is particularly preferred that the desiccant be temperature-resistant up to 1500 °C, and further 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.

[0022] According to one embodiment, the drying agent can contain or consist of silicon dioxide. The melting point of silicon dioxide is approximately 1710 °C.

[0023] According to one embodiment, the drying agent can contain or consist of aluminum oxide. The melting point of aluminum oxide is approximately 2070 °C.

[0024] It may also be a combination of silicon dioxide and aluminum oxide, for example with a mixing ratio between 5:95 and 95:5.

[0025] The desiccant can be used in granular form. By selecting different particle sizes when using granules, an optimized packing density of the granule particles and an optimized surface area for reaction with the humid oven atmosphere can be achieved.

[0026] The hydrogen used, at least partially, in the fuel gas can be produced and supplied, for example, in water electrolysis using renewable energies such as wind, water and / or sun.

[0027] The heat treatment of a steel product to forming temperature is carried out in such a way that the temperature of the steel product upon removal from the furnace is between 950 °C and 1400 °C, in particular at least 1050 °C, preferably at least 1100 °C, and more preferably at least 1150 °C. The temperature of 1400 °C should not be exceeded to avoid partial melting and / or excessive scaling of the steel product. For ecological and economic reasons, the temperature is limited, in particular, to a maximum of 1320 °C, preferably to a maximum of 1280 °C. The temperature is measured, for example, on one side of the surface of the steel product, in particular with a pyrometer or other suitable measuring instruments. Thus, the temperature of the steel product can be determined using methods known to those skilled in the art. The temperature in the furnace chamber, or the temperature of the atmosphere in the furnace chamber, may well be higher.

[0028] The steel product can be in the form of a slab, a block, or a billet.

[0029] Depending on the volume of the steel product to be heated, and in particular also depending on the target forming temperature, the residence time in the furnace chamber or in the section of the furnace chamber can be between 10 minutes and 24 hours, in particular between 30 minutes and 20 hours, preferably between 1 hour and 12 hours.

[0030] The furnace with the directly fired furnace chamber or the directly fired section of the furnace chamber for heat-treating a steel product to forming heat can be a pusher beam furnace or a walking beam furnace, designed to receive and heat slabs, blocks, or billets. Depending on the volume of the steel product to be heat-treated, a residence time of between 30 minutes and 6 hours can be considered.

[0031] Alternatively, the furnace used to heat-treat a steel product to forming temperature can be a roller hearth furnace, which is designed to hold and heat forgings. Depending on the volume of the steel product to be heat-treated, a residence time of between 2 and 18 hours can be considered.

[0032] A steel product is cast from molten steel or a molten steel alloy into a slab, block, or billet. Using a known continuous casting plant as an example, molten steel or a molten steel alloy is classically poured into a mold and solidifies completely into a strand. This strand is then drawn off and cut into several slabs of finite dimensions, after which the slabs are allowed to cool to ambient temperature, primarily through natural cooling. For further processing, the slabs are reheated and heated through to forming temperature, preferably rolling temperature, in a walking beam furnace or a pusher furnace.The forming process preferably comprises hot rolling in a hot rolling mill, which may include at least one hot rolling stand or preferably several, preferably up to seven, hot rolling stands in a hot rolling stage, wherein optionally one or more, for example up to three, roughing stands may be arranged in the process direction in front of a hot rolling stand or a hot rolling stage.

[0033] Alternatively, the shaping process can also include forging, so that the heat treatment of the steel product in a furnace is carried out at forging heat.

[0034] The processes for heat-treating steel products in the form of slabs, blocks or billets to forming heat, and thus also the construction of corresponding furnaces, are state of the art and therefore familiar to the expert.

[0035] Air, for example ambient air, oxygen, or a combination of air and oxygen can be used as the oxygen-containing gas for operating the burners. 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. Preheating can, for example, be limited to a maximum of 1000 °C. Preheating the fuel gas and / or the oxygen-containing gas can lead to an increase in the adiabatic flame temperature.

[0036] In order to reduce the water vapor partial pressure in the furnace atmosphere, 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.

[0037] The desiccant can be arranged in a suitable receiving device, which allows for spacing between the individual granules or grains of the desiccant. This increases the surface area of ​​the desiccant compared to, for example, a bulk material, thus promoting water absorption. The individual granules or grains can be spherical with a diameter between 0.05 and 10 mm. The desiccant can be arranged in special receiving devices that 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.

[0038] According to an alternative embodiment, the desiccant, in the form of granular particles or grains, can be blown into the furnace via a carrier gas, preferably a dry protective gas such as nitrogen, through at least one inlet nozzle, which can be individually aligned and / or adjusted in the spatial direction. This advantageously allows the inflow direction of the carrier gas to be added for the desiccant to be influenced in the furnace, so that the outflow and / or the impulse forces a forced flow within the furnace and thus contact with the flue gas.

[0039] Additionally or alternatively, the carrier gas can also be introduced via one or more burners with a separate geometric arrangement, in order to achieve (faster) contact with the blown-in desiccant in particular.

[0040] Alternatively, the desiccant can also be introduced into the atmosphere of the slab furnace via a suitable airlock, for example a rotary valve.

[0041] The desiccant, blown in or introduced as an example, leaves the slab furnace with the exhaust gas. For this purpose, a special filter device would be required in the slab furnace's exhaust system 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.

[0042] Once the desiccant reaches saturation, i.e., its maximum water adsorption capacity, it can be regenerated relatively easily; that is, the absorbed water can simply evaporate while still warm. Since the desiccant is already at a temperature corresponding to the temperatures prevailing in the furnace, for example, between 950 °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.

[0043] 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.

[0044] In particular, hydrogen can be present in the fuel gas at a proportion of at least 10 vol%. Preferably, hydrogen can be present in the fuel gas at a proportion of at least 30 vol%. Preferably, hydrogen can be present in the fuel gas at a proportion of at least 60 vol%. Particularly preferably, hydrogen can be present in the fuel gas at a proportion of at least 80 vol%. Further preferably, hydrogen can be present in the fuel gas at a proportion of at least 98 vol%. One embodiment, for example, includes the use of 100% hydrogen; in other words, the fuel gas consists of 100 vol% hydrogen or nearly 100 vol%, wherein impurities in the fuel gas of up to 0.5 vol%, in particular up to 0.2 vol%, preferably less than 0.1 vol%, are permitted, and where impurities cannot be avoided technically or only with considerable equipment effort.

[0045] If the fuel gas does not consist entirely of hydrogen, it 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.

[0046] For example, when using natural gas, the proportions of the main component methane can vary and may also include other components, such as ethane, propane, ethene and butane, individually or in combination.

[0047] Additionally or alternatively, 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.

[0048] Furthermore, 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.

[0049] The burners can be operated with an air-fuel ratio between 0.75 and 1.25. The air-fuel ratio can be, in particular, between 0.75 and 0.99, more specifically between 0.80 and 0.98, preferably between 0.85 and 0.97, more preferably between 0.90 and 0.96, to avoid the presence of oxygen (compounds) in the flue gas, or alternatively between 1 and 1.25, more specifically between 1.01 and 1.20, more preferably between 1.02 and 1.15, more preferably between 1.03 and 1.10, to control the amount of oxygen in the flue gas for targeted scaling, for example in certain products.

[0050] Air, for example ambient air, oxygen, or a combination of air and oxygen can be used as the oxygen-containing gas for operating the burners. 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. Preheating can, for example, be limited to a maximum of 1000 °C. Preheating the fuel gas and / or the oxygen-containing gas can lead to an increase in the adiabatic flame temperature.

[0051] The oxygen that may be needed for combustion can also be generated and provided by means of electrolysis using renewable energies (sun, wind, water, etc.).

[0052] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the drawing.

[0053] The drawing shows the invention using a schematic illustration as an example. Figure 1 Figure 1 shows a furnace (10) for heating a steel product (1) to forming heat. The furnace (10) can be designed as a walking beam furnace, pusher furnace, or roller hearth furnace for receiving and heating slabs, blocks, discs, billets, or forgings. The furnace (10) has a directly fired furnace chamber or a directly fired section of a furnace chamber. The directly fired furnace chamber or the directly fired section of the furnace chamber of the furnace (10) comprises several burners (11) which can be supplied with a fuel gas (11.1) containing 0 vol.%, in particular at least 10 vol.% to 100 vol.% hydrogen, and an oxygen-containing gas (11.2), and by means of the resulting flue gas (11.3) a furnace atmosphere (10.1) can be generated in the furnace chamber or in the section of the furnace chamber, cf. Figure 2 ,which is a schematic sectional view in direction II, see. Figure 1 .

[0054] Figure 1 further shows that the thoroughly heated steel product (1), for example in the form of a slab, can be removed from the furnace (10) and fed to a further processing, for example a hot rolling mill (100) for hot rolling, in order to produce a hot strip (1').

[0055] Hydrogen can be provided proportionally in the fuel gas (11.1) or entirely as fuel gas (11.1). The furnace atmosphere (10.1) in the furnace (10) with the directly fired furnace chamber or with the directly fired section of the furnace chamber is brought into contact with at least one desiccant (20), which establishes a water vapor partial pressure in the furnace atmosphere (10.1) that is lower than the water vapor partial pressure of the flue gas (11.3).

[0056] 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 furnace (10) in a receiving device via suitable means (22) to reduce the water vapor partial pressure in the furnace atmosphere (10.1) in a working position. When the desiccant (20) in contact with the furnace atmosphere (10.1) reaches saturation, it is discharged from the furnace (10) via the means (22) to dry in a regeneration position. During this regeneration, the hot desiccant (20) can be exposed to the environment or, for example, actively aerated with ambient air to accelerate the regeneration process.Simultaneously or before the discharge of the contacting desiccant (20), a further desiccant (20) is introduced into the oven (10) 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.

[0057] Alternatively or additionally, the desiccant (20) can be arranged outside the oven (10), for example in one or preferably several receiving devices, wherein the desiccant (20) is brought into contact with the gas of the oven atmosphere (10.1) via lines and preferably via a suction inlet (21) and, after contact, is returned to the oven (10) at a reduced water vapor partial pressure. When the desiccant (20) in contact with the oven atmosphere (10.1) reaches saturation, another desiccant (20), not shown here, is supplied with the gas of the oven atmosphere (10.1) according to the aforementioned procedure. The saturated desiccant (20) is regenerated by supplying the hot desiccant (20) with ambient air or a substantially dry gas to dry it.

[0058] The desiccant (20), shown in dashed lines, can also be blown into the oven as granular particles or granules with a carrier gas (12) via at least one inlet nozzle, which can be individually aligned and / or adjusted in the spatial direction.

[0059] With the furnace atmosphere (10.1) set according to the invention, heating the steel product (1) does not result in an increased or additional hydrogen input into the steel product (1) despite the use of non-fossil fuels, if hydrogen is used in proportions between 0, in particular between 10 and 100 vol.% in the fuel gas (11.1).

[0060] In laboratory-scale investigations, different fuel gas compositions, such as natural gas (a) and mixtures of natural gas and hydrogen with 25 vol% (b), 50 vol% (c) and 75 vol% (d) as well as 100% hydrogen (e), were burned with oxygen and an air ratio of approximately 0.95 in a gas-operated furnace with a furnace volume of 0.04 m³. This resulted in different furnace atmospheres with different furnace humidities and increasing water vapor partial pressures.

[0061] For each furnace process parameter, three thick steel samples, each measuring 10 x 5 x 0.4 cm, were cut from hot-rolled strip material. These samples were provided and each was burned with one of the aforementioned fuel gas compositions (a) to (e). The residence time for all samples was approximately 15 minutes, during which time the samples were thoroughly heated in the furnace and removed at a temperature of approximately 1250 °C. After removal, the samples were quenched and deep-frozen. The hydrogen content of the samples was analyzed using thermal desorption mass spectrometry (TDMS), a standard method for hydrogen measurement (see Table 1), with mean values ​​given below. Table 1 Fuel gas a b c d e Hydrogen in [ppm] < 0,4 0,68 0,85 1,12 1,57

[0062] As a result of the reaction processes, significantly more water is produced with increasing hydrogen content in the fuel gas than in conventional combustion processes with natural gas. The increasing water vapor partial pressure (furnace humidity) leads to an increase in surface reactions, which include the dissociation of H₂ to H₂ as well as the adsorption and absorption of H₂.

[0063] Further samples of the same dimensions were combusted with 100% hydrogen in the fuel gas and oxygen with an air-fuel ratio of approximately 0.95. Different amounts of silicon dioxide were introduced into the furnace atmosphere as a desiccant to reduce the water vapor partial pressure. The amounts used were 300 g and 650 g. The residence time for all samples was approximately 15 minutes, during which time the samples were thoroughly heated in the furnace and removed at a temperature of approximately 1250 °C. After removal, the samples were quenched and deep-frozen. The hydrogen input into the samples was analyzed using TDMS. The average hydrogen input for the samples containing 300 g of desiccant in the furnace atmosphere was 1.4 ppm, and for the samples containing 650 g of desiccant, it was 0.86 ppm. The average hydrogen input without desiccant was 1.57 ppm.

[0064] 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. By including at least one drying agent and bringing it into contact with the furnace atmosphere, thereby reducing the water vapor partial pressure and / or the dew point in the furnace atmosphere, the hydrogen ingress is significantly reduced. This, in turn, reduces the hydrogen ingress and the associated potential embrittlement and further processing problems.

Claims

1. A method for heat-treating a steel product (1) to forming heat, wherein the heat-treatment of the steel product (1) is carried out in a furnace (10) with a directly fired furnace chamber or with a directly fired section of a furnace chamber, wherein the temperature of the steel product (1) upon removal from the furnace is between 950 °C and 1400 °C, wherein the furnace comprises several burners (11) which are operated with a fuel gas (11.1) having a hydrogen content of 0 vol.% to 100 vol.% and an oxygen-containing gas (11.2) and from which a flue gas (11.3) is generated which fills the furnace chamber or the section of the furnace chamber and forms a furnace atmosphere (10.1) with a flue gas composition (11.3) with a water vapor partial pressure that depends on the composition of the fuel gas (11.1) and the composition of the oxygen-containing gas (11.2). characterized by the fact thatthe furnace atmosphere (10.1) in the furnace (10) is brought into contact with the directly fired furnace chamber or with the directly fired section of the furnace chamber with at least one desiccant (20), which results in a water vapor partial pressure in the furnace atmosphere (10.1) which is lower compared to the water vapor partial pressure of the flue gas (11.3).

2. The method of claim 1, wherein the drying agent (20) contains or consists of silicon dioxide.

3. Method according to any of the preceding claims, wherein the drying agent (20) contains or consists of aluminium oxide.

4. Method according to one of the preceding claims, wherein the desiccant (20) is provided in an amount capable of reducing the water vapor partial pressure in the furnace atmosphere by at least 30% compared to the water vapor partial pressure of the flue gas (11.3).

5. Method according to any of the preceding claims, wherein the drying agent (20) has a water adsorption capacity of at least 20%.

6. Method according to one of the preceding claims, wherein the steel product (1) heat-treated to forming heat is subjected to hot rolling.

7. Method according to any one of claims 1 to 5, wherein the steel product (1) heat-treated to forming heat is subjected to forging.

8. Furnace (10) with a directly fired furnace chamber or with a directly fired section of a furnace chamber, comprising several burners (11) which can be supplied with a fuel gas (11.1) containing 0 vol.% to 100 vol.% hydrogen and an oxygen-containing gas (11.2) and by the resulting flue gas (11.3) can generate a furnace atmosphere (10.1) in the furnace chamber or in the section of the furnace chamber, characterized by the fact thatat least one desiccant (20) is provided for contact with the furnace atmosphere (10.1) in the furnace chamber or in the section of the furnace chamber.

9. Oven according to claim 8, wherein the desiccant (20) is arranged in a unit.

10. Oven according to claim 8 or 10, wherein the desiccant (20) can be brought into a working position and into a regeneration position via means (22).

11. Oven according to claim 8 or 10, wherein the desiccant (20) can be blown into the DFF oven as granular particles or granules with a carrier gas (12) via at least one inlet nozzle.

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