Process for thoroughly warming steel products to shaping heat

Abstract

The invention relates to a process for thoroughly warming steel products (1) to shaping heat, and to a corresponding furnace (10).

Description

[0001] Process for heating steel products to forming heat

[0002] The invention relates to a method for heating steel products to forming heat and to a corresponding furnace.

[0003] Steel products that must be heated to forming temperature include slabs, which are brought to rolling temperature, ingots, discs, or billets, which are brought to rolling or forging temperature and heated in appropriate furnaces to a temperature of at least 950°C in order to achieve a fully austenitic microstructure, depending on the composition, which reduces forming resistance. In practice, directly heated heat treatment furnaces are used as standard. Equipped with at least one or preferably several burners, heat treatment furnaces have been fed with fossil fuels, such as natural gas, as standard for decades. Since combustion takes place in the heat treatment furnace, direct heating can be used to create a reducing or oxidizing furnace atmosphere, depending on the set air ratio (lambda value of the fuel gas).In addition, the fuel gas mixture and the oxidation medium used, which can include air or pure oxygen, have a significant influence on the resulting combustion gas composition. The heat treatment furnace therefore contains the combustion gas from the burner(s). This gas has a composition with a high proportion of water (H2O) and, depending on the air ratio, fuel gas and oxidant, 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, carbon monoxide (CO gas) is present in the combustion gas to protect the steel product to be 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 combustion gas, which causes a targeted oxidation of the steel product being heated. However, the atmosphere settings can also lead to further interactions with the steel product. For example, the water content in the atmosphere can dissociate, as a result of surface reactions, first into molecular hydrogen (H2) and then into atomic hydrogen (H), and then be absorbed into the steel through the surface. As part of the globally demanded decarbonization, plants powered by fossil fuels are to be converted or converted to more environmentally friendly fuels or energy sources, such as hydrogen, in the future in order to reduce or ultimately avoid the use of fossil energy.

[0004] Decarbonization requires a reduction in the use of fossil fuels and energy sources and, in turn, 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. For example, the applicant is also building or converting units to gradually replace fossil fuels with climate-neutrally produced hydrogen, see the applicant's website: https: / / www.thyssenkrupp.com / de / newsroom / pressemeldungen / pressetailseite / top- oberflachen-fur-die-automobilindustrie-thyssenkrupp-nimmt-neuen-hubbalkenofen-am-standort-duisburg-in-betrieb-156354

[0006] Furthermore, it is also known from the technical report on decarbonization "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 / cgi-bin / 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 openly heated by means of 160 sidewall and ceiling radiant burners. The integration of suitable burners, which have been successfully tested on a pilot scale using 100% H2 and also mixtures of H2 and natural gas, still needs to be implemented on an industrial scale after preparation.

[0007] When hydrogen is directly combusted as fuel gas or in the presence of hydrogen in the fuel gas, the combustion reactions with air and / or oxygen result 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 higher partial pressure of water vapor, unwanted additional hydrogen ingress into the steel product cannot be ruled out, leading to disadvantages in subsequent process steps, for example, hydrogen embrittlement. These disadvantages can become apparent both in the immediately subsequent processes, such as forming, and in further processing steps, such as surface finishing, or ultimately in further product processing and component use.

[0008] However, even during conventional natural gas combustion or metallurgical gas combustion, the metallurgical gas containing or consisting of one or more of the components coke gas, blast furnace gas, converter gas, etc., a water vapor partial pressure is also generated in the furnace atmosphere, so that even during conventional soaking, hydrogen ingress into the steel product cannot be completely ruled out.

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

[0010] This object is achieved by a method having the features of claim 1 and by a directly fired furnace or a directly fired portion of a furnace having the features of claim 10. Further embodiments are described in the subclaims.

[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 upon removal from the furnace is between 950 °C and 1400 °C, wherein the furnace comprises a plurality of burners which are operated with a fuel gas with a proportion of 0 vol.% to 100 vol.% hydrogen and an oxygen-containing gas, and from this a combustion gas is generated which fills the furnace chamber or the section of the furnace chamber and forms a furnace atmosphere with a combustion gas composition with a water vapor partial pressure depending on the composition of the fuel gas and the composition of the oxygen-containing gas.

[0012] Essential to the invention is that a gas is additionally introduced into the furnace chamber or into the partial section of the furnace chamber of the furnace and mixed with the combustion gas in such a way that a water vapor partial pressure is established in the furnace atmosphere of the furnace chamber or of the partial section of the furnace chamber that is lower than the water vapor partial pressure of the combustion gas. The second teaching relates to a furnace with a directly fired furnace chamber or with a directly fired partial section of a furnace chamber, which comprises a plurality of burners which can be supplied with a fuel gas having a proportion of 0 vol.% to 100 vol.% hydrogen and an oxygen-containing gas, and which can be used to generate a furnace atmosphere in the furnace chamber or in the partial section of the furnace chamber by means of the resulting combustion gas. At least one means for introducing a gas into the furnace chamber or into the partial section of the furnace chamber of the furnace is additionally provided.

[0013] According to one embodiment, the means comprises at least one inlet nozzle, which is individually orientable and / or adjustable in spatial direction. This advantageously allows the inflow direction of the introduced gas into the furnace chamber or into the partial section of the furnace chamber to be influenced in order to force a forced flow within the furnace through the outflow and / or the impulse, thus forcing a (faster) mixing with the combustion gas.

[0014] Additionally or alternatively, the combustion gas can also flow in via one or more burners with a separate geometric arrangement, in particular to achieve (faster) mixing with the additional gas introduced.

[0015] The furnace can be designed in such a way and have corresponding means with which it is possible to pass the steel product to be soaked through the furnace either substantially continuously or quasi-continuously or preferably discontinuously, ie that a steel product is fed into the furnace, remains there until the forming heat is reached and then leaves the furnace in order to be fed to a forming process in the soaked state.

[0016] A preferential conversion from a fossil fuel (natural gas) to an alternative, hydrogen-containing fuel in a directly fired furnace for soaking a steel product to forming heat thus results in a modified furnace atmosphere with highly influential parameters regarding the material properties and surface of the steel product to be achieved. When hydrogen-containing fuels are burned, a larger amount of water vapor is generated than with natural gas, which ensures a higher water vapor partial pressure in the furnace atmosphere. This not only results in a greater tendency for oxidation (=scale formation) during soaking due to oxygen-affine elements in the steel product, but also increases or increases the hydrogen input into the steel product.

[0017] Decarbonization in a furnace with a directly fired furnace chamber or with a directly fired section of a furnace chamber for heating a steel product to forming heat would therefore not only be a simple switch from fossil to non-fossil fuels, but would also involve a complex manipulation of the product parameters.

[0018] An increase in hydrogen in the fuel gas and thus an increase in the water vapor partial pressure in the resulting combustion gas must be counteracted by "diluting" the combustion gas by targeted mixing with a gas in order to set a furnace atmosphere in the furnace which has a lower water vapor partial pressure compared to the (pure) combustion gas, in particular a furnace atmosphere can be set which approximately corresponds to a conventional natural gas-fired furnace atmosphere, in order to avoid having to change the existing process chain unnecessarily and to be able to essentially retain the standard process.

[0019] The determination or recording of a 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 using suitable measuring devices.

[0020] The preferred gas for introduction (and mixing) is a low-water vapor and / or low-hydrogen-free gas.

[0021] Low in water vapor means a water or water vapor content in the gas to be introduced of a maximum of 17.0 vol.-%, in particular a maximum of 12.0 vol.-%, preferably a maximum of 8.0 vol.-%, more preferably a maximum of 5.0 vol.-%, more preferably a maximum of 3.0 vol.-%, more preferably a maximum of 1.50 vol.-% and in particular > 0.10 vol.-%. Water vapor-free means that either no water or water vapor is contained or that the gas to be added may contain traces of up to a maximum of 0.10 vol.-%.

[0022] Low-hydrogen means a hydrogen content in the gas to be introduced of a maximum of 7.0 vol.%, in particular a maximum of 5.0 vol.%, preferably a maximum of 4.0 vol.%, more preferably a maximum of 2.50 vol.%, more preferably a maximum of 1.0 vol.%, more preferably a maximum of 0.50 vol.%, and in particular > 0.10 vol.%. Hydrogen-free means that either no hydrogen is present or that the gas to be added may contain traces of up to a maximum of 0.10 vol.%.

[0023] By means of the measure according to the invention, a furnace atmosphere of the furnace chamber or of the partial section of the furnace chamber for heating a steel product can be adjusted to forming heat, which can correspond to the currently known level of natural gas-fired burners or can be adapted thereto.

[0024] The hydrogen used at least in part in the fuel gas can, for example, be produced and provided in water electrolysis using renewable energies such as wind, water and / or sun.

[0025] The oxygen required for combustion can also be generated and provided by electrolysis using renewable energies (sun, wind, water, etc.).

[0026] The gas, particularly one that is low in water vapor, free of water vapor, and / or low in hydrogen, used for introduction and thus for mixing with the combustion gas, can contain or consist of nitrogen (N2), argon (Ar), carbon dioxide (CO2), carbon monoxide (CO), or a mixture thereof. For example, inert gases are used. Other gases or mixtures of gases that contain no or relatively low amounts of water and / or water vapor and / or hydrogen, or no or relatively low amounts of hydrogen compounds, and are suitable for a furnace for heating a steel product to forming heat, can also be used accordingly.

[0027] Alternatively, air (ambient air) can also be used.

[0028] The heating of a steel product to forming heat takes place in such a way that the temperature of the steel product when removed from the furnace is between 950 °C and 1400 °C, in particular at least 1050 °C, preferably at least 1100 °C, more preferably at least 1150 °C. The temperature of 1400 °C should not be exceeded in order 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 on the surface of the steel product, in particular with a pyrometer or other suitable measuring device. The temperature of the steel product can thus be recorded using means known to those skilled in the art. The temperature in the furnace chamber or the temperature of the atmosphere in the furnace chamber can certainly be higher.

[0029] The steel product can be in the form of a slab, an ingot, a disc or a billet.

[0030] Depending on the volume of the steel product to be soaked, and in particular also depending on the target forming temperature, a residence time in the furnace chamber or in the section of the furnace chamber can be between 10 minutes and 48 hours, in particular between 30 minutes and 24 hours, preferably between 1 hour and 12 hours.

[0031] The furnace with the directly fired furnace chamber or with the directly fired section of the furnace chamber for soaking a steel product to forming temperature can be a pusher beam furnace or a walking beam furnace designed to receive and soak slabs, ingots, slabs, or billets. Depending on the volume of the steel product to be soaked, a residence time of between 30 minutes and 6 hours can be considered.

[0032] Alternatively, the furnace for soaking a steel product to forming temperature can be a roller-hearth furnace designed to accommodate and soak forgings. Depending on the volume of the steel product to be soaked, a residence time of between 2 and 18 hours can be considered.

[0033] A steel product is cast from molten steel or a molten steel alloy into a slab, ingot, or billet. Using a conventional continuous casting plant as an example, molten steel or a molten steel alloy is traditionally poured into a mold and completely solidified into a strand, which is then drawn off and separated into several slabs of finite dimensions. The slabs are then allowed to cool to ambient temperature, particularly through natural cooling. For further processing, the slabs are (re)heated and thoroughly heated, for example, in a walking beam furnace or pusher furnace to forming temperature, thus preferably to rolling temperature.The shaping preferably comprises hot rolling in a hot rolling mill, which may comprise at least one hot rolling stand or preferably several, preferably up to seven hot rolling stands in a hot rolling mill, wherein optionally one or more, for example up to three roughing stands may be arranged in front of a hot rolling stand or a hot rolling mill in the process direction.

[0034] Alternatively, the forming process may also include forging, so that the steel product is heated in a furnace to forging temperature.

[0035] The processes for heating steel products in the form of slabs, blocks, discs or billets to forming heat and thus also the construction of corresponding furnaces are state of the art and therefore familiar to the expert.

[0036] 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 process 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.

[0037] In order to be able to reduce the water vapor partial pressure in the furnace atmosphere, a flow rate of the gas to be introduced should be set as a function of the volume of the furnace chamber into which the gas is introduced, such that at least the volume of the furnace chamber can be filled in one hour, in particular at least 1.5 times the volume of the furnace chamber per hour, preferably at least 2 times the volume of the furnace chamber per hour, preferably at least 2.5 times the volume of the furnace chamber per hour.The flow rate is set and limited such that it can fill a maximum of 50 times the volume of the furnace chamber per hour, in particular a maximum of 25 times the volume of the furnace chamber per hour, preferably a maximum of 15 times the volume of the furnace chamber per hour, more preferably a maximum of 10 times the volume of the furnace chamber per hour, in order, for example, not to adversely affect the thermal energy through the resulting combustion gas. Knowing the volume, it is then possible to convert to common values ​​in liters per second or per minute or cubic meters per minute or per hour. In particular, hydrogen can be contained in the fuel gas in a proportion of at least 10 vol.%. Preferably, hydrogen can be contained in the fuel gas in a proportion of at least 30 vol.%. Preferably, hydrogen can be contained in the fuel gas in a proportion of at least 60 vol.%.Particularly preferably, hydrogen can be present in the fuel gas in a proportion of at least 80 vol. Further preferably, hydrogen can be present in the fuel gas in a proportion of at least 98 vol. One embodiment, for example, comprises 100% use of hydrogen; in other words, the fuel gas consists of 100 vol.% hydrogen or almost 100 vol.%, with impurities in the fuel gas being permitted at up to 0.5 vol.%, in particular up to 0.2 vol.%, preferably less than 0.1 vol.%. Impurities cannot be avoided technically or can only be avoided with considerable equipment expenditure.

[0038] If the fuel gas does not consist entirely of hydrogen, it may contain, in addition to hydrogen, further proportions of methane (CH4) and / or carbon monoxide (CO) to make up to 100 vol.%, together with impurities which are permitted up to 0.5 vol.%, in particular up to 0.2 vol.%, preferably less than 0.1 vol.%.

[0039] For example, when using natural gas, the proportions of the main component methane can vary and thus also include other components such as ethane, propane, ethylene and butane individually or in combination.

[0040] In order to avoid negatively impacting the energy of the combustion gas and / or even to increase energy efficiency, it may be advantageous if, according to one embodiment, the gas, in particular one that is low in water vapor, free of water vapor, and / or low in hydrogen, is heated before being introduced into the furnace chamber or into the partial section of the furnace chamber. To substantially maintain the energy level of the combustion gas, the gas, in particular one that is low in water vapor, free of water vapor, and / or low in hydrogen, is heated to a temperature that preferably corresponds to the temperature of the combustion gas between + / - 300°C. The temperature can thus correspond to a temperature window between minus and plus 300°C relative to the temperature of the combustion gas. The temperature of the combustion gas can be measured using means known to those skilled in the art.

[0041] In order to economically utilize the exhaust gas discharged from the furnace chamber or a subsection of the furnace chamber, a mixed gas consisting of combustion gas and introduced gas, particularly low-water vapor and / or low-hydrogen-free gas, it may be advantageous to use part or all of the exhaust gas to heat the gas, particularly low-hydrogen and / or low-water vapor-free gas, before introducing it. In this case, too, the means for exhaust gas utilization or heat transfer are known to those skilled in the art. Alternatively or additionally, the oxygen-containing gas and / or the fuel gas can also be heated / preheated accordingly.

[0042] Alternatively or in addition to the use of exhaust gases, the (additional) heating or preheating can also be carried out by other means, for example electrically, if a higher temperature level is required compared to the exhaust gas temperature.

[0043] 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, and with ambient air and hydrogen, approximately 2130 °C. Combustion with oxygen and natural gas is approximately 2860 °C, and with oxygen and hydrogen, approximately 3080 °C.

[0044] The burners can be operated with an air ratio between 0.75 and 1.25. The air ratio can be in particular between 0.75 and 0.99, in particular between 0.80 and 0.98, preferably between 0.85 and 0.97, preferably between 0.90 and 0.96, to avoid the presence of oxygen (oxygen compounds) in the combustion gas, or alternatively between 1 and 1.25, in particular between 1.02 and 1.20, preferably between 1.05 and 1.18, preferably between 1.08 and 1.12, to control the amount of oxygen in the combustion gas for targeted scaling, for example, with certain products.

[0045] The invention is explained in more detail using the following embodiments in conjunction with the drawing.

[0046] The drawing shows the invention using a schematic illustration as an example. 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 (11.3) with a proportion of 0 vol.%, in particular at least 10 vol.% to 100 vol.%, of hydrogen and an oxygen-containing gas (11.4), and which, through the resulting combustion gas (11.9), creates a furnace atmosphere.

[0047] (10.1) can be produced in the furnace chamber or in the partial section of the furnace chamber, see Figure 2, which is a schematic sectional view in direction II, see Figure 1.

[0048] Hydrogen can be provided partially in the fuel gas (11.3) or completely as fuel gas (11.3). In addition, at least one agent (11.1), preferably several agents

[0049] (11.1) for introducing a gas (11.5), in particular one low in water vapor and / or low in hydrogen, into the furnace chamber or the partial section of the furnace chamber of the furnace (10). Thus, in particular, a gas (11.5) low in water vapor and / or low in hydrogen is additionally introduced and mixed with the combustion gas (11.9) such that a water vapor partial pressure is established in a furnace atmosphere (10.1) of the furnace chamber or the partial section of the furnace chamber that is lower than the water vapor partial pressure of the combustion gas (11.9).

[0050] The means comprises at least one inlet nozzle (11.1), which can be individually aligned and / or adjusted, for example, in spatial direction. This allows, for example, the inlet direction (11.10) of the introduced gas to be specifically influenced such that the impulse forces a forced flow within the furnace (10) and thus a mixture with the combustion gas (11.9).

[0051] In order to orientate oneself to a known furnace atmosphere (10.1) in the furnace chamber or in the partial section of the furnace chamber of the furnace (10), which is conventionally established, for example, by natural gas firing, and to approximate this despite the use of hydrogen in the fuel gas, the volume of the fuel gas and the gas to be introduced can be determined in a standard manner, particularly as a function of the volume of the furnace chamber or the partial section of the furnace chamber of the furnace (10). The volume of the fuel gas depends on the heat output required to heat the steel product (1) through and through and is based on a control of the material temperatures required for the soaking process.The volume of gas to be introduced is determined from the volume of the fuel gas and thus from the chemical elements resulting from combustion and the volume in the furnace chamber or in the partial section of the furnace chamber of the furnace (10), preferably corrected by appropriate standard analytical measurements of the furnace atmosphere (10.1). Before being introduced (11.10) into the furnace (10), the gas (11.5), which is particularly low in water vapor and / or low in hydrogen, can be heated. The oxygen-containing gas (11.4), not shown, can also be preheated before combustion. An exhaust gas (11.7) can be removed from the furnace chamber or the partial section of the furnace chamber, which can be used partially or completely to heat the gas (11.5), which is particularly low in water vapor and / or low in hydrogen, by means of a suitable heat exchanger (11.6).Alternatively or additionally, the gas (11.5), which is particularly low in water vaporZ-free and / or low in hydrogenZ-free, can be heated, in particular additionally, for example by an electrical heating device (11.8), shown in dashed lines, with which a temperature increase of the gas (11.5), which is particularly low in water vaporZ-free and / or low in hydrogenZ-free, above the temperature of the exhaust gas (11.7) would also be possible.

[0052] With the furnace atmosphere (10.1) adjusted according to the invention, a thorough heating of the steel product (1) is not possible, despite the use of non-fossil fuels, if hydrogen is used in proportions between 10 and 100 vol.-% / o in the fuel gas (11.3).

[0053] In laboratory-scale studies, a gas-fired furnace with a furnace volume of 0.04 m 3different fuel gas compositions, such as natural gas (a) and mixtures of natural gas and hydrogen with 25 vol.-° / o (b), 50 vol.-° / o (c) and 75 vol.-° / o (d) as well as 100% hydrogen (e), burned with oxygen and an air ratio of approx. 1.05, resulting in different furnace atmospheres with different furnace humidities or increasing water vapor partial pressures.

[0054] 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 and burned with one of the above-mentioned fuel gas compositions (a) to (e). The residence time for all samples was approximately 60 minutes; the samples were heated thoroughly in the furnace and removed at a temperature of approximately 1000 °C. After removal, the samples were quenched and deep-frozen. The hydrogen ingress in the samples was analyzed using thermal desorption mass spectrometry (TDMS), which is standard for hydrogen detection (see Table 1).

[0055] Table 1

[0056] As a result of the reaction processes taking place, with increasing hydrogen content in the fuel gas, significantly more water is produced 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 H, as well as the adsorption and absorption of H.

[0057] Additional samples of the same dimensions were combusted with 100% hydrogen in the fuel gas and oxygen at an air / fuel ratio of approximately 1.05, with different gases being introduced to reduce the water vapor partial pressure in the furnace atmosphere. The flow rates of the fuel gas and that of the oxygen were constantly regulated to maintain a temperature of 1000 °C. In a first series of tests, nitrogen was additionally introduced as a water vapor-free and hydrogen-free (inert) gas, and in a second series of tests, air (ambient air) was additionally introduced as a water vapor-free and hydrogen-free gas, each at different flow rates of 5 l / min (a), 10 l / min (b), and 15 l / min (c). The residence time for all samples was approximately 60 minutes; the samples were thoroughly heated in the furnace and each removed at a temperature of approximately 1000 °C. After removal, the samples were quenched and deep-frozen.The hydrogen input into the samples was analyzed using TDMS, see Table 2.

[0058] Table 2

[0059] It is clearly visible that at a low flow rate the effect of the inert gas is higher compared to air, but this can be brought to a comparable level by increasing the flow rate threefold.

[0060] As expected, the heating of steel products to forming heat with increased water vapor partial pressure in the furnace atmosphere due to at least partial combustion of hydrogen in the fuel gas leads to a significant hydrogen ingression into the steel product. By introducing additional low-water vapor and / or low-hydrogen-free gas streams or by purging the furnace atmosphere and the associated reduction of the water vapor partial pressure or the dew point in the furnace atmosphere, the hydrogen ingress is significantly reduced. This reduces the hydrogen ingress and the associated potential embrittlement and further processing problems.

Claims

Claims 1. A method for heating a steel product (1) to forming heat, wherein the heating 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) when removed from the furnace (10) is between 950 °C and 1400 °C, wherein the furnace (10) comprises a plurality of burners (11) which are operated with a fuel gas (11.3) with a proportion of 0 vol.% to 100 vol.% hydrogen and an oxygen-containing gas (11.4), and from this a combustion gas (11.9) is generated, which fills the furnace chamber or the section of the furnace chamber and creates a furnace atmosphere (10.1) with a gas temperature which depends on the composition of the fuel gas (11.3) and the composition of the oxygen-containing gas (11.4) forms a combustion gas composition with a water vapor partial pressure, characterized in that a gas (11.5) is additionally introduced into the furnace chamber or in the partial section of the furnace chamber of the furnace (10) and mixed with the combustion gas (11.9) in such a way that a water vapor partial pressure is established in the furnace atmosphere (10.1) of the furnace chamber or the partial section of the furnace chamber which is lower than the water vapor partial pressure of the combustion gas (11.9).

2. Method according to claim 1, wherein a low-water vapor, Z-free and / or low-hydrogen Z-free gas is used as the gas (11.5) for introduction.

3. Method according to one of the preceding claims, wherein a flow rate of the gas (11.5) is adjusted as a function of the volume of the furnace chamber into which the gas (11.5) is introduced, such that at least the volume of the furnace chamber can be filled in one hour and at most 50 times the volume of the furnace chamber per hour.

4. Method according to one of the preceding claims, wherein the gas (11.5) is heated before being introduced into the furnace chamber or into the partial section of the furnace chamber of the furnace (10).

5. The method according to claim 4, wherein the heating is carried out to a temperature which corresponds to the temperature of the combustion gas (11.9) between + / - 300 °C.

6. Method according to one of claims 4 or 5, wherein an exhaust gas (11.7) is discharged from the furnace chamber or the partial section of the furnace chamber, which exhaust gas is used partly or completely for heating the gas (11.5).

7. Method according to one of the preceding claims, wherein the burners (11) are operated with an air ratio between 0.75 and 1.

25.

8. Method according to one of the preceding claims, wherein the steel product (1) heated to forming heat is fed to a hot rolling process.

9. Method according to one of claims 1 to 7, wherein the steel product (1) heated to forming heat is fed to a forging.

10. Furnace (10) with a directly fired furnace chamber or with a directly fired section of a furnace chamber, which comprises a plurality of burners (11) which can be supplied with a fuel gas (11.3) with a proportion of 0 vol.% to 100 vol.% hydrogen and an oxygen-containing gas (11.4) and by means of the resulting combustion gas (11.9) a furnace atmosphere (10.1) can be generated in the furnace chamber or in the section of the furnace chamber, characterized in that in addition at least one means (11.1) for introducing a gas (11.5) into the furnace chamber or in the section of the furnace chamber of the furnace (10) is provided.

11. Oven according to claim 10, wherein the means comprises at least one inlet nozzle (11.1) which is individually alignable and / or adjustable in the spatial direction.

12. Furnace according to claim 10 or 11, wherein the furnace (10) is a pusher beam furnace or a walking beam furnace designed to receive and heat through slabs, blocks, discs or billets.

13. Furnace according to claim 10 or 11, wherein the furnace (10) is a roller hearth furnace designed to receive and heat through forgings.

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