Method for heating metal materials, heating equipment, and operation method of heating furnaces.

Abstract

To provide a heating method of a metal material, a heating facility, and an operation method of a heating furnace for controlling a scale generation amount in an appropriate range when reducing an emission amount of carbon dioxide by using hydrogen or ammonia as a fuel gas of the heating furnace for heating the metal material.SOLUTION: A heating method of a metallic material includes: a first heating process for heating the metal material by burner heating using a hydrogen-based gas containing either or both of hydrogen and ammonia as a total amount as a fuel gas; and a second heating process for heating the metal material heated in the first heating process by electric heating in an inert gas atmosphere in a furnace. It is preferable that the first heating process is performed by burner heating using a fuel gas that is a mixed gas obtained by mixing a hydrogen-based gas with one or more gases selected from coal gas and a hydrocarbon-based gas. In the first heating process, the amount of water vapor in the furnace is preferably controlled within a predetermined range on the basis of the flow rate of the fuel gas used for burner heating.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for heating a metal material, a heating apparatus, and a method for operating a heating furnace using the same heating method. [Background technology]

[0002] In integrated steel mills, blast furnace gases emitted from the top of the blast furnace, which reduces iron ore to produce molten iron, as well as by-product gases generated in converters and coke ovens, have been effectively utilized as fuel gases. However, in recent years, with the demand for reducing carbon dioxide emissions, combustion technologies to reduce the amount of these by-product gases used have become necessary. For example, in the heating furnaces used to heat steel materials in the hot rolling lines of integrated steel mills, there is a need to reduce the amount of by-product gases used and thereby reduce carbon dioxide emissions. In this case, technologies that utilize hydrogen and ammonia as fuel gases in heating furnaces are attracting attention. That is, since hydrogen and ammonia do not contain carbon elements, when burned they mainly produce only water and nitrogen, so they have a significant effect in reducing carbon dioxide emissions, and their application to heating furnaces is desired.

[0003] Incidentally, in heating furnaces, scale (also called oxide scale) forms on the surface of the steel material during the heating process. The scale formed in heating furnaces is also called primary scale and is removed by descaling equipment placed on hot rolling lines, etc. Therefore, if the thickness of the scale formed in heating furnaces increases, the weight of the steel material that becomes steel sheet products decreases, which leads to a problem of reduced product yield.

[0004] On the other hand, foreign matter, such as impurities generated during casting or mold powder mixed in during casting, may be present near the surface of the steel material being charged into the heating furnace. If hot rolling is performed with impurities and foreign matter still present on the surface of the steel material extracted from the heating furnace, these will become trapped between the steel material and the rolling rolls, resulting in defects on the surface of the steel sheet. Therefore, the steel material is allowed to build up a certain thickness of scale in the heating furnace, and then the surface impurities and foreign matter are removed along with the scale using a descaling device before hot rolling is performed.

[0005] In other words, in steel heating furnaces, it is necessary to control scale formation to an appropriate level in order to suppress a decrease in product yield by suppressing excessive scale formation, and to suppress the occurrence of surface defects by actively generating a predetermined amount of scale.

[0006] Therefore, to solve these problems, control techniques for scale formation on steel surfaces have been proposed. Patent Document 1 discloses a method for non-oxidative heating of steel, which involves supplying a high-temperature, non-oxidizing gas preheated to a temperature above or approximately equal to the temperature of the steel being heated, around the steel in a heating furnace, as a technique to suppress excessive scale formation.

[0007] Patent Document 2 discloses a steel heating furnace comprising a plurality of regenerative heating devices that supply high-temperature inert gas into the furnace, and a plurality of gas burners that supply combustion gas into the furnace, wherein the supply of high-temperature inert gas and the supply of combustion gas are controlled to be independent of each other. This method allows for the heating of steel materials without oxidation by alternately supplying high-temperature inert gas from multiple regenerative heating devices.

[0008] On the other hand, as a technique for generating a predetermined amount of scale, Patent Document 3 discloses a method for heating steel materials to be subjected to hot rolling, in which moisture is supplied into the heating furnace to adjust the dew point inside the heating furnace. This is said to promote oxidation of the steel surface, and casting defects concentrated up to about 0.5 mm from the surface of the steel can be removed along with the scale, thereby improving the surface quality of steel plate products. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 9-20919 [Patent Document 2] Japanese Patent Publication No. 2000-248314 [Patent Document 3] Japanese Patent Application Publication No. 5-331532 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, when conventional technologies are applied to control the amount of scale formation on steel materials within an appropriate range in heating furnaces that use hydrogen or ammonia as fuel gas, the following problems arise.

[0011] The technology described in Patent Document 1 involves supplying a high-temperature, oxidation-free gas into a heating furnace in order to create a localized oxidation-free atmosphere around the steel material charged into the heating furnace. However, when hydrogen or ammonia is burned as a fuel gas in a heating furnace, the hydrogen in the fuel gas combines with the oxygen in the combustion air to produce water vapor. Therefore, even if an oxidation-free atmosphere is created in the heating furnace, there is a problem in that the generated water vapor promotes scale growth on the surface of the steel material.

[0012] The technique described in Patent Document 2 uses a regenerative heating device to recover the sensible heat of the exhaust gas generated by burning fuel gas with a heat storage body, and then supplies a high-temperature inert gas into the heating furnace by passing an inert gas through the heat storage body, aiming to suppress the scale growth of steel materials in the heating furnace. However, when hydrogen or ammonia is used as the fuel gas, since the heat storage body also recovers the water vapor in the exhaust gas, the inert gas passing through the heat storage body is humidified and supplied into the heating furnace. Therefore, even if a high-temperature inert gas is supplied into the heating furnace as described above, the generation of scale on the surface of the steel material is promoted by the water vapor, and thus there is a problem that the amount of scale generation cannot be controlled within an appropriate range.

[0013] Although Patent Document 3 can be expected to improve the surface quality of steel plate products by promoting the oxidation of the steel material surface by supplying moisture into the heating furnace, when hydrogen or ammonia is used as the fuel gas, the oxidation of the steel material is further promoted, resulting in excessive scale growth and the problem that the amount of scale generation cannot be controlled within an appropriate range.

[0014] The present invention has been made to solve the above problems, and its object is to provide a heating method, heating equipment, and operation method of a heating furnace for a metal material to control the amount of scale generation within an appropriate range when attempting to reduce the carbon dioxide emission amount by using hydrogen or ammonia as the fuel gas for a heating furnace that heats a metal material.

Means for Solving the Problems

[0015] The heating method of a metal material according to the present invention that advantageously solves the above problems is configured as follows.

[0016] [1] A first heating step of heating a metal material by burner heating using a hydrogen-based gas having either one or both of hydrogen and ammonia as the total amount as the fuel gas, and a second heating step of heating the metal material heated in the first heating step by electric heating with the furnace interior in an inert gas atmosphere. It is a heating method of a metal material including these steps. [2] In [1] above, in the first heating step of heating a metal material by burner heating using, as a fuel gas, a mixed gas in which one or more gases selected from coal gas and hydrocarbon gas are mixed with the hydrogen-based gas. [3] In [1] or [2] above, the first heating step is a method of heating a metal material, which controls the amount of water vapor in the furnace to be within a preset range based on the flow rate of the fuel gas used for the burner heating. [4] In [1] or [2] above, the first heating step is a method of heating a metal material, which controls the amount of water vapor in the furnace so that the thickness of the oxide layer formed on the surface of the metal material falls within a preset range based on at least one operating parameter selected from the heating time, heating temperature of the first heating step, and the flow rate of the fuel gas used for the burner heating. [5] In [1] or [2] above, the metal material is a steel material. The first heating step heats the metal material so that its surface temperature is 850 to 1050 °C, and the second heating step heats the metal material so that its surface temperature is 1050 to 1250 °C. It is a method of heating a metal material. [6] In [3] above, the metal material is a steel material. The first heating step heats the metal material so that its surface temperature is 850 to 1050 °C, and the second heating step heats the metal material so that its surface temperature is 1050 to 1250 °C. It is a method of heating a metal material. [7] In [4] above, the metal material is a steel material. The first heating step heats the metal material so that its surface temperature is 850 to 1050 °C, and the second heating step heats the metal material so that its surface temperature is 1050 to 1250 °C. It is a method of heating a metal material. [8] In [5] above, in the first heating step, the amount of water vapor in the furnace is controlled to 20 to 35% by volume. It is a method of heating a metal material. [9] In [6] above, in the first heating step, the amount of water vapor in the furnace is controlled to 20 to 35% by volume. It is a method of heating a metal material.

[10] In the above [7], the first heating step is a method for heating a metal material in which the amount of water vapor in the furnace is controlled to 20 to 35 volume percent.

[0017] The metal material heating equipment and heating furnace operation method according to the present invention, which advantageously solves the above problems, is configured as follows.

[11] A heating apparatus for metal materials comprising: a first heating furnace that heats a metal material by burner heating using a hydrogen-based gas consisting entirely of hydrogen and ammonia or both as fuel gas; and a second heating furnace into which the metal material discharged from the first heating furnace is charged and the metal material is heated by electric heating in an inert gas atmosphere inside the furnace.

[12] The metal material heating equipment is a first heating furnace that heats a metal material by burner heating using a mixed gas, which is obtained by mixing the hydrogen gas with one or more gases selected from coal gas and hydrocarbon gases, as the fuel gas in the above

[11] .

[13] In the above

[11] or

[12] , the first heating furnace is a heating equipment for metal materials having a flow rate setting unit for setting the flow rate of the fuel gas used for heating the burner and a steam amount control unit for controlling the amount of steam in the first heating furnace to a preset range.

[14] A method for operating a heating furnace that heats steel material using the metal material heating method described in [5] above.

[15] A method for operating a heating furnace that heats steel material using the metal material heating method described in [6] above.

[16] A method for operating a heating furnace that heats steel material using the metal material heating method described in [7] above. [Effects of the Invention]

[0018] According to the present invention, by using hydrogen or ammonia as fuel gas for the heating furnace, carbon dioxide emissions can be reduced, and the amount of scale formation can be controlled within an appropriate range, thereby reducing the occurrence of surface defects in metal materials and suppressing deterioration of product yield. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram showing a heating furnace according to one embodiment. [Figure 2] This is a diagram showing the arrangement of burner equipment in a heating furnace. [Figure 3] This is a diagram illustrating an example of a burner system configuration. [Figure 4] This diagram shows the configuration of the burners in the first heating furnace, illustrating the arrangement of burner equipment using coal gas and hydrogen-based burner equipment using hydrogen-based gas within the furnace. [Figure 5] This is a diagram illustrating an example of a hydrogen-based burner system configuration. [Figure 6] (a) is a front view of the second heating furnace using electric heating, and (b) is a side view of the second heating furnace. [Figure 7] This graph shows the temperature history of steel material heated by the metal material heating method of this embodiment. [Figure 8] This graph shows the effect of the surface temperature of steel on the thickness of scale formed on the surface of steel. [Figure 9] This graph shows the relationship between the scale thickness on the surface of the steel material and the heating time when the water vapor concentration inside the furnace is changed. [Figure 10] This graph shows the relationship between the surface temperature of a material heated in a combustion gas heating furnace and the scale thickness in a preliminary experiment. [Modes for carrying out the invention]

[0020] The heating equipment for metal materials according to this embodiment will be described below.

[0021] The metal material heating equipment according to this embodiment comprises a first heating furnace that heats the metal material by burner heating using a hydrogen-based gas consisting entirely of hydrogen and ammonia or both as fuel gas, and a second heating furnace into which the metal material discharged from the first heating furnace is charged and the metal material is heated by electric heating in an inert gas atmosphere inside the furnace.

[0022] First, let me explain the heating furnace equipped with a burner. <Heating equipment> Figure 1 schematically shows a cross-sectional view of a heating device for metal materials according to one embodiment of the present invention. The heating device is a device that places the material to be heated inside and raises its temperature to a predetermined temperature. The material to be heated is a metal material, but it may be an iron-based metal or a non-ferrous metal as long as it is a metal material that generates oxides (hereinafter referred to as scale) on its surface by oxidation. The heating temperature of the material to be heated is 500 to 1400°C. In the following, a heating device for heating steel will be described, with steel being the metal material.

[0023] The heating equipment 100 shown in Figure 1 is installed, for example, in a hot rolling line that manufactures steel plates or steel strips, and heats the cast steel material to a predetermined heating temperature (approximately 1100 to 1300°C). However, the steel material to be heated is not limited to slabs that become steel plate material, but also includes steel materials that become the raw material for structural steel, bars and wires, steel pipes, etc., such as billets and blooms. The heating equipment 100 includes a first heating furnace 1 that heats steel materials by burner heating using a hydrogen-based gas consisting entirely of hydrogen and ammonia or both as fuel gas, and a second heating furnace 2 into which steel materials discharged from the first heating furnace 1 are charged, and the inside of the furnace is heated by electric heating in an inert gas atmosphere to further heat the steel materials. Here, the process of heating the metal material to be heated in the first heating furnace is called the first heating process. The process of further heating the metal material to be heated in the second heating furnace is called the second heating process. Furthermore, it is preferable to install a control computer 101 in the heating equipment 100 to perform data analysis of various operating parameters in order to control the operation of the heating process.

[0024] <1st heating furnace> The first heating furnace 1 comprises a first charging section 8 for charging (hereinafter also referred to as loading) steel material S, and a first unloading section 9 for unloading (hereinafter also referred to as extracting) steel material S. For example, steel material (slabs) manufactured in a continuous casting line are transported to the charging side yard of the first heating furnace 1 and charged from the first charging section 8 into the first heating furnace 1 according to the production schedule of a hot rolling line or the like.

[0025] The interior of the first heating furnace 1 is divided into several zones, consisting of a preheating zone 3 divided into 1 to 3 zones, a heating zone 4 divided into 2 to 8 zones, and a soaking zone 5 divided into 1 to 3 zones, starting from the upstream side in the direction of steel material transport. A transport device 10 is arranged in the first heating furnace 1 to sequentially transport the steel material S from the first charging section 8 to the first discharge section 9. Each zone of the first heating furnace 1 is controlled to a different ambient temperature, and the first conveying device 10 conveys the steel material S in the order of preheating zone 3, heating zone 4, and uniform zone 5, so that the average temperature of the steel material S charged into the first heating furnace 1 gradually rises and is heated to a predetermined target heating temperature (first heating temperature) in the first heating furnace 1.

[0026] The first conveying device 10 is equipped with a support mechanism for steel materials S called a skid, which consists of a fixed skid 10a that supports the steel materials S and a movable skid 10b that lifts and moves the steel materials S. The movable skid 10b repeatedly moves up and down, forward, downward and backward within the first heating furnace 1 to convey the steel materials S toward the first discharge section 9.

[0027] The first heating furnace 1 is equipped with multiple burners 6 along the direction in which the steel material S is transported. The burners 6 are positioned to raise the temperature inside the first heating furnace 1 through combustion. When the temperature inside the first heating furnace 1 is raised by the burners 6, the temperature of the steel material S rises due to radiation from the furnace walls of the first heating furnace 1. Furthermore, flow of atmospheric gas may occur inside the first heating furnace 1, causing the steel material S to be heated by convection. In addition, the steel material S may be heated by the flame of the burner 6 directly contacting the steel material S. In any case, the burner 6 heats the steel material S inside the first heating furnace 1 by raising the temperature inside the first heating furnace 1.

[0028] The burners 6 are arranged in each of the multiple zones inside the first heating furnace 1. However, the number of zones and the number of burners do not necessarily have to be the same. In the first heating furnace 1 shown in Figure 1, an upper burner 6a is arranged on the upper side of the steel material S, and a lower burner 6b is arranged on the lower side of the steel material S, from the first charging section 8 to the first discharge section 9. In addition, although the first heating furnace 1 shown in Figure 1 schematically depicts a side burner that injects a flame from one side wall surface in the direction of the conveying direction of the steel material S toward the opposite side wall surface, an axial flow burner that injects a flame in the same direction as the conveying direction of the steel material S or a roof burner that injects a flame into the interior from the ceiling of the heating furnace may also be used.

[0029] Figure 2 shows the piping system of the burners 6 located in the first heating furnace 1, using a portion of the area constituting the first heating furnace 6 as an example. The burners 6 (upper burner 6a, lower burner 6b) located in the first heating furnace 1 are connected to a fuel gas supply system 31 that supplies fuel gas G and a combustion air supply system 32 that supplies combustion air A. The fuel gas supply system 31 and the combustion air supply system 32 are connected to blowers (not shown) and the like, and supply fuel gas G and combustion air A to the burners 6. As a result, fuel gas G and combustion air A are injected from the burner 6, and the fuel gas G diffuses and burns, blowing a flame into the inside of the heating furnace. Combustion air A may be air collected from the atmosphere. However, modified air, such as air from which nitrogen has been removed or air to which pure oxygen has been added, may be used as combustion air. Increasing the oxygen content of the combustion air promotes the oxidation reaction of fuel gas G and reduces the flow rate of combustion air supplied from the combustion air supply system 32, thereby reducing the power consumption of pumps and other equipment. In addition, combustion air A may be a mixed gas obtained by mixing oxygen with combustion exhaust gas. By lowering the oxygen content of the combustion air, the atmosphere inside the first heating furnace can be made a reducing atmosphere, and the reduction of nitrogen oxides produced by the combustion of ammonia and other substances is promoted.

[0030] Figure 3 shows a schematic diagram of the burner equipment 60 that performs burner heating. A burner refers to a device that injects a flame into a furnace, and specifically to the part that injects the flame into the furnace. Furthermore, burner equipment refers to the entire apparatus, including the ancillary equipment for injecting the flame.

[0031] The burner equipment 60 includes a burner nozzle 7 that forms a passage for fuel gas G and combustion air A for injecting a flame by the burner 6, a fuel gas supply system 31 that supplies fuel gas G to the burner nozzle 7, and a combustion air supply system 32 that supplies combustion air A to the burner nozzle 7. The burner nozzle 7 is, for example, a double-tube nozzle, in which fuel gas G is injected from the inside toward the furnace interior 38, and combustion air A is supplied from the outside. This forms a combustible mixture of fuel gas G and combustion air A, and a flame is injected from the burner 6 toward the interior of the first heating furnace 1.

[0032] The burner equipment 60 may be equipped with a fuel gas flow control valve 33 for adjusting the flow rate of fuel gas G supplied from the fuel gas supply system 31 to the burner nozzle 7, and a fuel gas flow meter 34 for measuring the flow rate of fuel gas G. This allows for adjustment of the combustion energy supplied to the first heating furnace 1. Furthermore, the burner equipment 60 may be equipped with a combustion air flow control valve 35 for adjusting the flow rate of combustion air A supplied from the combustion air supply system 32 to the burner nozzle 7, and a combustion air flow meter 36 for measuring the flow rate of combustion air A. This allows the burner 6 to adjust the air ratio of the fuel gas to the theoretical air amount.

[0033] Furthermore, the burner equipment 60 may use not only a nozzle with the double-pipe nozzle described above, but also a nozzle-mix type burner that mixes the fuel gas and combustion air midway through the burner nozzle. In this case, the combustion air may be preheated using exhaust gas or the like before it mixes with the fuel gas.

[0034] The burner equipment shown in Figure 2 has a combustion air supply system 32 that supplies combustion air to the burners 6, and is equipped with a combustion air flow control valve 35 that adjusts the flow rate of combustion air supplied to each individual burner 6, and a combustion air flow meter 36 that measures the flow rate of combustion air. However, it is not necessary to provide a combustion air flow control valve 35 or a combustion air flow meter 36 for each burner 6; multiple burners can be grouped together, and the flow rate of combustion air can be adjusted on a group basis.

[0035] [Burner heating using coal gas] Conventional steel heating furnaces have used by-product gases generated at steel mills and other facilities as fuel gas supplied to the burner equipment. By-product gases are mainly gases obtained from coal, and coal Coal gas is also called coal gas because it is produced as a result of incomplete combustion. Coal gas includes coke oven gas, blast furnace gas, converter gas, and electric furnace gas. Blast furnace gas is a by-product gas produced when iron ore is reduced in a blast furnace to produce pig iron. Coke oven gas is a by-product gas produced when coal is carbonized at high temperatures to produce coke. Converter gas is a by-product gas produced in the steelmaking process in a converter. Electric furnace gas is a by-product gas produced by the incomplete combustion of auxiliary fuel (carburizer) used in an electric furnace. By-product gases have various component compositions depending on the process by which they are produced.

[0036] For example, blast furnace gas typically has a composition of 21-30% by volume of carbon monoxide (a combustible component), 50-60% by volume of nitrogen (a non-combustible component), and 10-22% by volume of carbon dioxide. The lower heating value of blast furnace gas is 3.45 MJ / Nm³. 3 It is approximately as follows: Coke oven gas typically has a composition of 46-60% hydrogen by volume, 20-35% methane by volume, 5-10% carbon monoxide by volume, and 2-4% hydrocarbons such as ethylene by volume. The lower heating value of coke oven gas is 18.0 MJ / Nm³ 3 The converter gas contains approximately 75% carbon monoxide by volume, approximately 13% carbon dioxide by volume, and also contains trace amounts of oxygen, nitrogen, and hydrogen. The lower heating value of the converter gas is 8.2 MJ / Nm³. 3The typical composition of electric furnace gas is approximately 10% carbon monoxide, 22% carbon dioxide, 5% oxygen, and 56% nitrogen. The lower heating value of electric furnace gas is 2.8 MJ / Nm³. 3 It is to that extent. Furthermore, coal gas includes a mixture of blast furnace gas, coke oven gas, and converter gas (sometimes called M gas). This mixture of coal gases with different calorific values ​​supplies the necessary heat to heat the material being heated, ensuring stable operation of the heating furnace.

[0037] <Hydrogen-based burner equipment> In this embodiment, the heating equipment 100, at least one of the burner equipment arranged in the first heating furnace, uses hydrogen and ammonia as fuel gases. Hereinafter, among the burner equipment arranged in the heating furnace, burner equipment that uses a fuel gas containing hydrogen-based gas, consisting entirely of either hydrogen or ammonia, or both, will be referred to as hydrogen-based burner equipment. Furthermore, the hydrogen and ammonia used as fuel gas will be referred to as hydrogen-based gases.

[0038] First, we will describe an embodiment in which a hydrogen-based gas containing either hydrogen or ammonia, or both, as the entirety is used as fuel.

[0039] Hydrogen is a colorless gas at room temperature, with an ignition point of 560°C and a lower heating value of 10.5 MJ / Nm³. 3 This is the extent of the problem. When hydrogen is burned, the flame temperature is high and the combustion speed is fast, so the tip of the burner nozzle tends to become hot. Therefore, it is preferable to use a burner nozzle that mixes the hydrogen with combustion air after it is injected. This allows for slow combustion and reduces the heat load on the burner nozzle. In a hydrogen-based burner system using hydrogen as the fuel gas G, for example, the flow rate of hydrogen injected from the burner is 185 Nm³. 3 / hr, combustion air flow rate 370~601Nm 3 Combustion is performed under operating conditions of / hr.

[0040] Ammonia is a colorless gas at room temperature, with an ignition point of 651°C and a lower heating value of 14.1 MJ / Nm³.3 is at this level. When ammonia is burned, since the flame temperature is relatively low and the combustion speed is slow, the combustion reaction of ammonia can be stabilized by using a burner nozzle in a form that actively mixes ammonia and combustion air. In a hydrogen-based burner facility that uses ammonia as fuel gas G, as an example, the flow rate of ammonia injected from the burner is 185 Nm 3 / hr, and combustion is carried out under operating conditions where the flow rate of combustion air is 370 - 601 Nm 3 / hr.

[0041] The hydrogen-based burner facility 70 applied to this embodiment can use the same one as the burner facility 60 shown in FIG. 3. That is, the hydrogen-based burner facility 70 is the same burner facility as the one that uses coal gas as fuel gas, and is a burner facility that uses a hydrogen-based gas HG as fuel gas G. By using a hydrogen-based gas as fuel gas, the generation of carbon dioxide is suppressed, so the amount of carbon dioxide discharged from the heating furnace can be reduced.

[0042] The configuration of the hydrogen-based burner facility 70 applied to this embodiment will be described using FIG. 3. The hydrogen-based burner facility 70 performs burner heating that injects a flame into the furnace using a combustion air A with a hydrogen-based gas HG as fuel gas G. The hydrogen-based burner facility 70 includes a burner nozzle 7 for injecting a flame into the furnace, a fuel gas supply system 31 that supplies fuel gas G to the burner nozzle 7, and a combustion air supply system 32 that supplies combustion air A to the burner nozzle 7. The burner nozzle 7 is, for example, a double-pipe nozzle. The fuel gas G is injected from the inside toward the furnace 38, and the combustion air A is supplied to the outside. Thereby, a combustible mixture in which the combustion air A is mixed with the hydrogen-based gas HG as the fuel gas G is formed, and a flame is injected from the burner 6 toward the inside of the first heating furnace 1.

[0043] The hydrogen-based burner equipment 70 preferably includes a fuel gas flow rate adjustment valve 33 for adjusting the flow rate of fuel gas G supplied from the fuel gas supply system 31 to the burner nozzle 7, and a fuel gas flow meter 34 for measuring the flow rate of fuel gas G. Furthermore, the hydrogen-based burner equipment 70 preferably includes a flow rate setting unit 47 for setting the flow rate of the hydrogen-based gas. The flow rate setting unit 47 is, for example, a control controller, which issues a control command to adjust the valve opening of the fuel gas flow rate adjustment valve 33 so that the actual flow rate measured by the fuel gas flow meter 34 matches the preset flow rate setting value of the hydrogen-based gas HG. This allows control of the combustion energy of the flame injected from the hydrogen-based burner equipment 70 into the first heating furnace 1 and the amount of carbon dioxide emitted from the first heating furnace 1.

[0044] In addition to the flow rate setting unit 47, the hydrogen burner equipment 70 preferably includes a steam amount control unit 48 that controls the amount of steam in the first heating furnace 1 to a preset range. The steam amount control unit 48 is configured, for example, by a computer. The steam volume control unit 48 calculates the amount of steam inside the first heating furnace 1 and sends a command to the flow rate setting unit 47 for the flow rate setting value of the hydrogen gas HG supplied to the hydrogen burner equipment 70 so that the calculated amount of steam inside the furnace falls within a preset target range for the amount of steam (steam target range). Since the amount of steam in the first heating furnace 1 affects the scale formation behavior on the surface of the steel material S, the steam amount control unit 48 can control the scale formation behavior on the surface of the steel material S by sending a command to the flow rate setting unit 47 for the flow rate setting value of the hydrogen gas HG. In this case, it is preferable to install a dew point meter 49 inside the first heating furnace 1 and estimate the amount of water vapor inside the first heating furnace 1 based on the dew point information acquired by the dew point meter 49. The method for estimating the amount of water vapor inside the first heating furnace 1 will be described later.

[0045] Figure 4 shows an example in which a burner 60 using coal gas CG as fuel gas G and a hydrogen-based burner 70 using hydrogen-based gas HG as fuel gas G are arranged inside the first heating furnace 1. In this case, the fuel gas supply system that supplies fuel gas G to the burner nozzle 7 of the burner 60 is connected to the coal gas CG supply source, and the burner 60 injects a flame from the combustion of coal gas into the inside of the first heating furnace 1. On the other hand, the fuel gas supply system that supplies fuel gas G to the burner nozzle 7 of the hydrogen-based burner equipment 70 is connected to the hydrogen-based gas HG supply source, and the hydrogen-based burner equipment 70 injects a flame from the combustion of hydrogen-based gas into the first heating furnace 1. In this case, the combustion air supply system that supplies combustion air A to the burner equipment 60 and the hydrogen-based burner equipment 70 may be shared by the burner equipment 60 and the hydrogen-based burner equipment 70.

[0046] The first heating furnace shown in Figure 4 includes a hydrogen-based burner system that uses hydrogen-based gas HG as fuel gas G, compared to a conventional heating furnace that uses coal gas CG as fuel gas G. As a result, carbon dioxide emissions from the heating furnace are reduced.

[0047] <Other embodiments of hydrogen-based burner equipment> Another embodiment of the hydrogen-based burner equipment is described, in which a mixed gas is used as the fuel gas, which is obtained by mixing hydrogen-based gas with one or more gases selected from coal gas and hydrocarbon gases. Here, a mixed gas refers to a case where a hydrogen-based gas containing either hydrogen or ammonia, or both, is mixed with coal gas (containing hydrogen) or hydrocarbon gases (such as methane, ethane, or propane).

[0048] Hydrogen-based burner equipment may use a mixed gas containing hydrogen-based gas HG as fuel gas G, mixed with other fuels. For example, a mixed gas of hydrogen-based gas and coal gas can be used as fuel gas G.

[0049] Figure 5 shows another example of a hydrogen-based burner system, a hydrogen-based burner system 71 that uses a mixed gas of hydrogen-based gas HG and coal gas CG as fuel gas G. The hydrogen-based burner system 71 shown in Figure 5 is similar to the hydrogen-based burner system 70 shown in Figure 3 in that it includes a burner nozzle 7 that releases a flame into the heating furnace, a fuel gas supply system 31 that supplies fuel gas G to the burner nozzle 7, and a combustion air supply system 32 that supplies combustion air A to the burner nozzle 7. Also similar in that combustion air A is supplied from the combustion air supply system 32 to the burner nozzle 7, forming a combustible mixture of fuel gas G and combustion air A, and a flame is released from the burner 6 toward the inside of the first heating furnace.

[0050] On the other hand, the fuel gas supply system 31 of the hydrogen-based burner equipment 71 shown in Figure 5 includes a mixing unit 40 that mixes hydrogen-based gas HG supplied through the hydrogen-based gas supply system 45 with coal gas CG supplied through the coal gas supply system 46. The mixing unit 40 generates fuel gas G by mixing the hydrogen-based gas HG and coal gas CG. The fuel gas G generated in the mixing unit 40 is further mixed with combustion air A to form a combustible mixture, which is then injected as a flame from the burner 6 into the heating furnace 1.

[0051] The mixing section 40 refers to the point where the hydrogen gas supply system 45, which supplies hydrogen gas HG, and the coal gas supply system 46, which supplies coal gas CG, merge. The hydrogen gas HG and coal gas CG are supplied from their respective supply pipes and, upon merging, mixing occurs without the need for a special stirring mechanism. Therefore, the mixing section 40 only needs to be configured as a certain space in the area where these supply pipes intersect.

[0052] However, the mixing unit 40 may be equipped with static mixing equipment such as a static mixer, or a dynamic mixer with an agitation function. This is preferable because it results in a more uniformly mixed gas of hydrogen-based gas HG and coal gas CG.

[0053] The hydrogen-based burner equipment 71 may be equipped with a hydrogen-based gas flow control valve 41 for adjusting the flow rate of hydrogen-based gas HG supplied to the mixing section 40 through the hydrogen-based gas supply system 45, and a hydrogen-based gas flow meter 42 for measuring the flow rate of hydrogen-based gas HG. The hydrogen-based burner equipment 71 may also be equipped with a coal-based gas flow control valve 43 for adjusting the flow rate of coal-based gas CG supplied to the mixing section 40 from the coal-based gas supply system 46, and a coal-based gas flow meter 44 for measuring the flow rate of coal-based gas CG.

[0054] These methods allow for adjustment of the mixing ratio of hydrogen-based gas HG and coal gas CG contained in fuel gas G. When the mixing ratio of hydrogen-based gas HG in fuel gas G increases, the effect of reducing carbon dioxide emissions from the first heating furnace 1 becomes greater compared to conventional burner heating using only coal gas CG as fuel gas.

[0055] On the other hand, when using ammonia as a hydrogen-based gas, ammonia is a non-flammable fuel and is more difficult to ignite and burns more slowly than general fuel gases. Therefore, if the mixing ratio of ammonia in fuel gas G becomes large, combustion in burner 6 may become unstable. By adjusting the mixing ratio of ammonia in fuel gas G to coal gas, it is possible to reduce carbon dioxide emissions while ensuring the stability of burner heating.

[0056] Preferably, the hydrogen-based burner equipment 71 is further equipped with a flow rate setting unit 47 for setting the flow rate of hydrogen-based gas HG supplied to the mixing unit 40. The flow rate setting unit 47 is, for example, a control controller, and it issues a control command to adjust the valve opening of the hydrogen-based gas flow control valve 41 so that the actual flow rate measured by the hydrogen-based gas flow meter 42 matches the preset flow rate setting value of the hydrogen-based gas HG. This makes it possible to control the combustion energy of the flame injected from the hydrogen-based burner equipment 71 into the first heating furnace 1 and the amount of carbon dioxide emitted from the first heating furnace 1.

[0057] Furthermore, in addition to the function of setting the flow rate of hydrogen-based gas HG supplied to the mixing unit 40, the flow rate setting unit 47 may be configured to give a control command to adjust the valve opening of the coal gas flow control valve 43 so that the actual flow rate measured by the coal gas flow meter 44 matches the set flow rate of coal gas CG, which is set in advance. This makes it possible to individually set the flow rates of hydrogen-based gas HG and coal gas CG supplied to the mixing unit 40, and to adjust the combustion energy supplied to the first heating furnace 1 and the amount of carbon dioxide emitted from the first heating furnace 1.

[0058] The hydrogen burner equipment 71 may be equipped with a steam volume control unit 48 in addition to the flow rate setting unit 47, which controls the amount of steam in the first heating furnace 1 to a preset range. The function of the steam volume control unit 48 is the same as that of the steam volume control unit 48 described in Figure 3 above.

[0059] When burning a mixture of coal gas (M gas) and hydrogen (hydrogen-based gas), the hydrogen mixing ratio (the ratio of the hydrogen flow rate supplied through the hydrogen-based gas supply system 45 to the flow rate of M gas and hydrogen supplied through the hydrogen-based gas supply system 45) can be arbitrarily selected. For example, if the hydrogen mixing ratio is 60%, the hydrogen flow rate injected from the burner will be 111 Nm³. 3 / hr, M gas flow rate 74Nm 3 / hr, combustion air flow rate 370~601Nm 3 Combustion is carried out under operating conditions of / hr. The M gas composition is 20% carbon monoxide, 13% carbon dioxide, 24% hydrogen, 13% methane, 1.2% hydrocarbons such as ethylene, and 28.8% nitrogen. When burning a mixture of M gas and ammonia, combustion becomes unstable if the ammonia mixing ratio (the ratio of the ammonia flow rate supplied through the hydrogen gas supply system 45 to the flow rate of ammonia supplied through the hydrogen gas supply system 45 to the flow rate of M gas and ammonia supplied through the hydrogen gas supply system 45) is too high. Therefore, the ammonia mixing ratio is kept at around 50%. As an example, if the ammonia mixing ratio is 30%, the ammonia flow rate injected from the burner will be 50 Nm³. 3 / hr, M gas flow rate 117Nm 3 The combustion air flow rate is 480-624 Nm³ / hr. 3 Combustion is carried out under operating conditions of / hr.

[0060] <Second heating furnace> The second heating furnace 2 performs a second heating process in which the metal material heated in the first heating furnace 1 is further heated by electric heating while controlling the atmosphere inside the furnace to an inert gas atmosphere.

[0061] The second heating furnace 2 shown in Figure 1 includes a second charging section 26 for charging steel materials S heated in the first heating furnace 1, and a second unloading section 27 for unloading (extracting) the steel materials S. When the steel materials S heated in the first heating furnace 1 are unloaded from the first unloading section 9 of the first heating furnace, they are transferred to the second charging section 26 of the second heating furnace 2 by a transfer device 14 located between the first heating furnace 1 and the second heating furnace 2. Next, the steel material S is loaded into the second heating furnace 2 from the second charging section 26, and the second heating process is performed. The steel material S after the second heating process is discharged from the second discharge section 27. For example, if the heating equipment 100 is located in a hot rolling line where steel materials are hot-rolled, the steel material S discharged from the second heating furnace 2 has its primary scale removed by a descaling device in the hot rolling line, and then hot rolling is performed.

[0062] The interior of the second heating furnace 2 is divided into one or more zones, and the average temperature of the steel material S charged into the second heating furnace 2 is controlled to reach a predetermined target heating temperature (second heating temperature). The second heating furnace 2 shown in Figure 1 is equipped with a non-oxidizing heating zone 21 as one of its zones.

[0063] The target heating temperature (second heating temperature) in the second heating furnace 2 is set higher than the target heating temperature (first heating temperature) in the first heating furnace 1, thereby further heating the steel material S. The second heating furnace 2 is equipped with a second conveying device 28 that sequentially transports the steel material S from the second loading section 26 to the second discharge section 27. The second conveying device 28 is equipped with a support mechanism for the steel material S called a skid, and consists of a fixed skid 28a that supports the steel material S and a movable skid 28b that lifts and moves the steel material S. The movable skid 28b moves the steel material S toward the second discharge section 27 by repeatedly moving up and down, forward, down and backward within the second heating furnace 2.

[0064] The second heating furnace 2 is equipped with an inert gas supply unit 23 for controlling the atmosphere inside the furnace to that of an inert gas. The inert gas supply unit 23 is, for example, a gas injection nozzle that injects gas into the second heating furnace 2. The inert gas supply unit 23 is connected to an inert gas supply source, and inert gas NAG is supplied into the second heating furnace 2 through the inert gas supply system 30. The inert gas NAG can be nitrogen gas, argon, helium, etc., which suppress the progression of oxidation of the steel material S. The inert gas supply system 30 may include an inert gas flow rate control valve 25 for adjusting the flow rate of inert gas NAG supplied into the second heating furnace 2, and an inert gas flow meter 24 for measuring the flow rate of inert gas NAG. This allows the atmosphere inside the second heating furnace 2 to be adjusted to be non-oxidizing.

[0065] There are two methods for supplying inert gas into the second heating furnace 2: a furnace pressure control method and a flow rate control method. The furnace pressure control method involves supplying inert gas from the inert gas supply unit 23 so that the atmospheric pressure inside the second heating furnace 2 is within a predetermined range. In the case of the furnace pressure control method, for example, the supply flow rate of the inert gas NAG is controlled so that the pressure inside the second heating furnace 2 is between 3 and 7 kPa. The flow rate control method involves supplying inert gas from the inert gas supply unit 23 so that the flow rate of inert gas supplied to the second heating furnace 2 is within a predetermined range. In the flow rate control method, the amount of inert gas supplied differs depending on the internal volume of the second heating furnace 2, but for furnace capacity 1 m³ 3 2-4m per unit 3 A supply of inert gas is provided at a rate of approximately / hr. Note that if the temperature of the inert gas NAG supplied from the inert gas supply unit 23 into the second heating furnace 2 is low, the ambient temperature inside the second heating furnace 2 may decrease. Therefore, it is advisable to preheat the inert gas NAG to a temperature of 200°C or higher before supplying it.

[0066] The inert gas atmosphere inside the second heating furnace 2 can be determined by sampling the atmospheric gas inside the furnace and using an oxygen concentration meter. Alternatively, the oxygen concentration of the inert gas atmosphere inside the second heating furnace 2 can be measured by inserting the probe of the oxygen concentration meter into the second heating furnace 2. It is preferable to control the oxygen concentration inside the furnace to a low level, preferably 10 ppm or less. Therefore, it is preferable to maintain the pressure inside the second heating furnace 2 higher than atmospheric pressure to prevent outside air from entering the furnace. Furthermore, if the oxygen concentration inside the second heating furnace 2 exceeds a preset value, the flow rate of inert gas NAG supplied from the inert gas supply unit 23 into the second heating furnace 2 may be increased.

[0067] Electric heating is applied to the second heating furnace 2 as a heating means for carrying out the second heating process. Electric heating is a heating method that uses electricity to heat a metal material.

[0068] For the electric heating used to perform the second heating step, resistance heating or induction heating can be applied. Resistive heating is a method of heating metal materials by passing an electric current through a resistive heating element and utilizing the resulting Joule heating. There are two methods of resistive heating: indirect resistive heating and direct resistive heating. Indirect resistance heating is a heating method that transfers heat generated by a resistance heating element to a metal material through radiation, convection, and conduction. Direct resistance heating is a method that generates Joule heat in a metal material, thereby directly heating the metal material. Induction heating is a non-contact heating method that uses electromagnetic induction to pass an electric current through a metal material, causing it to self-heat. Electric heating can heat metal materials without using oxygen, making it easier to maintain an inert gas atmosphere in the second heating furnace 2. Furthermore, by using electricity generated from renewable energy sources such as solar power and wind power as the power source for electric heating, carbon dioxide emissions can be reduced compared to conventional gas heating using hydrocarbon-based fuel gases.

[0069] For the electric heating that performs the second heating step, indirect resistance heating is preferred. This is because indirect resistance heating is less affected by the shape of the metal material, the atmospheric gas and temperature inside the furnace, and allows for easy control of the heating temperature of the metal material. When indirect resistance heating is applied to the second heating furnace 2, it is preferable to use Kanthal wire or Pyromax wire made of Fe-Cr-Al alloy as the resistance heating element. Alternatively, platinum wire, molybdenum, tungsten, etc. may also be used as the resistance heating element.

[0070] Figure 6 shows an example of a second heating furnace 2 that performs electric heating by indirect resistance heating. The electric heating section 22 that performs indirect resistance heating consists of a resistance heating element 51 and a heat-resistant tube 52. Power is supplied to the resistance heating element 51 via a power supply cable 53 from a power source (not shown) installed on the outside of the furnace wall 54 of the second heating furnace 2. As a result, the resistance heating element 51 generates heat by Joule heating. The heat-resistant tube 52 is a tubular member into which the resistance heating element 51 is inserted. The heat-resistant tube 52 radiates the heat emitted by the resistance heating element 51 into the second heating furnace 2. As a result, the steel material S inside the second heating furnace 2 is heated. The heat-resistant tube 52 can be made of Fe-Cr-Al alloy, ceramics, NiCr alloy, etc. The heat-resistant tube 52 is not limited to a straight shape as long as it is cylindrical, and may be bent to increase the radiant area. The heat-resistant tube 52 is preferably installed along the furnace wall 54 inside the second heating furnace 2. The distance between the heat-resistant tube 52 and the steel material S should be 0.5 to 2.0 m. The resistance heating element inserted inside one heat-resistant tube is preferably set to have a heating capacity of about 20 to 100 kW. Multiple resistance heating elements are preferably arranged inside the second heating furnace 2, and their total heating capacity should be about 10 to 15 MW.

[0071] [Transfer device] The first heating furnace 1 and the second heating furnace 2 are separated so that the internal atmospheric gases do not flow between them. In the heating equipment 100 shown in Figure 1, the first discharge section 9, which is the outlet for discharging steel material S from the first heating furnace 1, and the second charging section 26, which is the charging inlet for charging steel material S into the second heating furnace 2, separate the internal atmospheric gases of the first heating furnace 1 and the second heating furnace 2 from each other. Then, in accordance with the opening and closing operation of the first discharge section 9, the transfer device 14 transfers the steel material S to the second heating furnace 2 and charges it into the second heating furnace 2 from the second charging section 26. As a result, the steel material S heated in the first heating furnace 1 is further heated in the second heating furnace 2.

[0072] The transfer device 14 is a device that has the function of transferring the steel material S from the first discharge section 9 to the second loading section 26. For example, a conveying machine for transferring high-temperature steel material S may be used, such as a table roll, trolley, crane, forklift, or chain. Preferably, the transfer device 14 has the capacity to transfer the steel material S discharged from the first discharge section 9 to the second loading section 26 in about 10 to 60 minutes. This is because if the waiting time between the first heating furnace 1 and the second heating furnace 2 is long after the first heating process, the temperature of the steel material S will decrease, and scale will easily grow on the surface of the steel material S due to oxygen in the outside air, and this is to prevent that.

[0073] In the heating equipment shown in Figure 1, the first discharge section 9 of the first heating furnace 1 and the second charging section 26 of the second heating furnace 2 are separated. This is to allow the steel material S discharged from the first discharge section 9 to be temporarily held before being charged into the second charging section 26.

[0074] The specific transfer method involves first temporarily opening the door of the first unloading section 9 when unloading steel material S from the first heating furnace 1, and having the steel material S wait in a waiting position. Next, the door of the first unloading section 9 is closed to prevent the furnace gas from the first heating furnace 1 from leaking out of the first unloading section 9. After that, the door of the second loading section 26 is temporarily opened, the steel material S is loaded into the second heating furnace 2, and then the door of the second loading section 26 is closed. This prevents combustion gases from the first heating furnace 1 from flowing into the second heating furnace 2, thereby ensuring that an inert atmosphere is maintained inside the second heating furnace 2. The first discharge section 9 of the first heating furnace 1 and the second charging section 26 of the second heating furnace 2 should be separated by a distance sufficient to allow the steel material S to be temporarily held there.

[0075] <Methods for heating metal materials> Next, a method for heating a metal material will be described. The method for heating a metal material according to this embodiment includes a first heating step of heating the metal material by burner heating using a fuel gas containing a hydrogen-based gas consisting entirely of hydrogen and ammonia or both, and a second heating step of heating the metal material heated in the first heating step by electric heating in an inert gas atmosphere inside the furnace.

[0076] The first heating step and the second heating step can be performed using the heating equipment 100 described above. Figure 7 shows an example of the temperature history of steel material heated by the metal material heating method of this embodiment. The steel material S is heated to the target heating temperature of the first heating step (first heating temperature) in the first heating step. Then, after a transfer time for transferring from the first heating furnace 1 to the second heating furnace 2, the second heating step is performed in the second heating furnace 2, and after being heated to the target heating temperature of the second heating step (second heating temperature), it is extracted from the heating equipment 100.

[0077] The first heating step involves heating the metal material to a first heating temperature using a heating means that includes burner heating in a first heating furnace 1, where hydrogen-based gas HG is used as fuel gas G. In the first heating process, burner heating is performed using hydrogen-based gas HG, so water vapor is generated by the combustion of hydrogen and ammonia contained in the fuel gas G. In this situation, water penetrates from the surface of the metal material in the first heating furnace 1, and the oxygen that makes up the water molecules oxidizes the metal material in the first heating furnace 1 and releases hydrogen. The hydrogen diffuses inside the oxide layer formed on the surface of the metal material, and at the interface between the oxide layer and the base material, it combines with the oxygen in the oxide layer to generate water vapor. Subsequently, the generated water vapor further oxidizes the metal material, thereby promoting the formation of the oxide layer.

[0078] Therefore, in heating furnaces that use hydrogen or ammonia as fuel gas, water vapor contained in the combustion gas penetrates the interface with the oxide layer of the metal material, promoting oxidation of the metal material. As a result, even when the atmosphere inside the heating furnace is controlled to be non-oxidizing, it is difficult to suppress scale formation on the metal material. On the other hand, if foreign matter such as impurities generated during casting or mold powder mixed in during casting is present on the surface of the metal material before it is charged into the heating equipment 100, the combustion of hydrogen-based gas can promote scale formation on the metal material. Thus, by removing the oxide layer using a descaling device or the like after the material is removed from the heating equipment 100, the occurrence of surface defects in the metal material can be suppressed.

[0079] In this embodiment, it is preferable to provide a flow rate setting unit 47 in the hydrogen-based burner equipment of the first heating furnace and control the flow rate of the hydrogen-based gas HG supplied to the burner nozzle 7. By changing the flow rate of the hydrogen-based gas HG, the amount of water vapor generated in the first heating furnace 1 changes, thereby allowing control of the thickness of the oxide layer formed on the surface of the metal material. In other words, as an operating parameter for the first heating process, the amount of steam in the furnace can be controlled based on the fuel gas flow rate so that the thickness of the oxide layer formed on the surface of the metal material falls within a predetermined range. Furthermore, the operating parameters for controlling the amount of steam in the furnace can be set based on the heating time or heating temperature of the first heating process, in addition to the fuel gas flow rate.

[0080] Furthermore, a steam amount control unit 48 is provided to control the amount of steam in the first heating furnace 1 to a preset range, and the flow rate setting value of the hydrogen gas HG supplied to the burner nozzle 7 is set to the flow rate setting unit 47 based on the amount of steam in the furnace of the first heating furnace 1 calculated by the steam amount control unit 48.

[0081] In this case, the water vapor amount control unit 48 estimates the amount of water vapor in the first heating furnace 1 based on the dew point information acquired by the dew point meter 49 installed in the first heating furnace 1, and sends a command to the flow rate setting unit 47 for the flow rate setting value of the hydrogen gas HG supplied to the burner nozzle 7 so that the estimated amount of water vapor falls within a preset target range of water vapor amount (water vapor target range). This makes it possible to control the amount of scale formation on the surface of the metal material during the first heating process.

[0082] The method for estimating the amount of steam inside the first heating furnace 1, performed by the steam amount control unit 48, will be explained below. First, the water vapor quantity control unit 48 acquires the dew point measurement of the atmospheric gas obtained by the dew point meter 49. From the acquired dew point measurement, the water vapor pressure of the atmospheric gas is calculated using the known relationship between saturated water vapor quantity and temperature. Then, the volume fraction of water vapor contained in the atmospheric gas is determined from the calculated water vapor pressure and the pressure (total pressure) of the atmospheric gas, and the amount of water vapor inside the first heating furnace 1 can be calculated from the furnace volume of the first heating furnace 1. As a known relationship between saturated water vapor amount and temperature, for example, Tenens' equation or Murray's equation may be applied. In this way, the water vapor amount control unit 48 can estimate the amount of water vapor inside the first heating furnace 1.

[0083] An example of heating a steel material will be described as a method for heating a metallic material. In this embodiment, it is preferable that the steel material S be heated to a surface temperature of 850 to 1050°C as the first heating step. In the first heating step, burner heating using hydrogen-based gas HG is performed in the furnace, so the water vapor contained in the combustion gas of the hydrogen-based gas HG promotes the oxidation of the steel material S, and a predetermined scale thickness can be generated by the time the first heating step is completed.

[0084] As a result, even if the steel material before the first heating process contains foreign matter such as impurities generated during casting or mold powder mixed in during casting, the occurrence of surface defects can be suppressed by removing the scale using a descaling device or the like after the first and second heating processes are completed.

[0085] However, if the first heating temperature is less than 850°C, a scale of the appropriate thickness may not be generated, so the first heating temperature should be 850°C or higher. More preferably, the first heating temperature should be 900°C or higher, and even more preferably 950°C or higher. On the other hand, if the first heating temperature exceeds 1050°C, the thickness of the scale generated in the first heating step becomes too thick, reducing the product yield, so the first heating temperature should be 1050°C or lower.

[0086] Here, it is known that scale growth of the steel material in the first heating furnace 1 is diffusion-limited and increases exponentially with respect to the surface temperature, as shown in equation (1).

number

[0087] Figure 8 shows an example of measuring the thickness of scale formed on the surface of a steel material after heating it for 30 minutes while maintaining a predetermined temperature in a steam atmosphere. From Figure 8, it can be seen that the higher the surface temperature of the steel material, the thicker the scale becomes, and that scale growth accelerates rapidly when the surface temperature exceeds 1050°C. Furthermore, in steel materials containing alloying elements such as Cu and Si, a composite oxide with concentrated Cu and Si is formed at the interface between the base material and the scale. This is because when the surface temperature of the steel exceeds 1050°C, the composite oxides of Cu and Si may melt, which can further accelerate the oxidation of the base material near the interface between the base material and the scale. For these reasons, the first heating temperature in the first heating step is preferably 1050°C or lower.

[0088] Furthermore, it can be difficult to directly measure the temperature of the steel material S being transported inside the first heating furnace 1. Therefore, it is advisable to use a temperature model to calculate the temperature of the steel material S, estimate the surface temperature of the steel material S inside the first heating furnace 1, and control the operating conditions of the first heating process so that the estimated temperature becomes the first heating temperature.

[0089] In this case, the temperature model of the steel material inside the heating furnace takes into account the effect of radiant heat from the furnace walls to the steel material, and the surface temperature of the steel material is calculated based on the measured ambient temperature inside the heating furnace and the position information (tracking information) of the steel material inside the heating furnace. The temperature model of the steel material is preferably configured to be installed on the control computer (process computer) 101 to perform the temperature calculation. One method for calculating temperature is to replace the steel material with a mesh divided into finite sections in the thickness and width directions, and then solve the heat conduction equation using the finite difference method or finite element method based on the temperatures at positions in the thickness and width directions. In this case, the surface temperature of the steel material is the temperature calculated for the mesh located at the outermost layer in the thickness direction.

[0090] In the first heating step, it is preferable to control the amount of water vapor in the first heating furnace 1 to 20-35 volume percent by setting the flow rate of the hydrogen-based gas HG used for burner heating. If the amount of water vapor in the first heating furnace 1 during the first heating step is less than 20 volume percent, the thickness of the scale formed on the surface of the steel material may be insufficient. On the other hand, if the amount of water vapor in the first heating furnace 1 exceeds 35 volume%, scale is likely to grow on the surface of the steel material, and excessive scale may be generated. From this viewpoint, the amount of water vapor in the first heating furnace 1 is more preferably 24 volume% or more and 30 volume% or less.

[0091] Figure 9 shows an example of investigating the thickness of scale generated on the surface of steel material S when the first heating temperature of the steel material S to be heated in the first heating step is set to 1000°C and the amount of water vapor in the furnace is controlled to 10% by volume and 25% by volume. In this case, it is known in advance that a scale generation amount of 500 μm in thickness is necessary to remove the casting defects present on the surface of the steel material before the first heating step is performed.

[0092] Figure 9 shows that when the amount of water vapor in the furnace is low at 10% by volume, the thickness of the scale formed on the surface of the steel material is less than 500 μm. Therefore, in order to generate a scale of sufficient thickness on the surface of the steel material S in the first heating process, the heating time of the first heating process needs to be extended, which leads to the problem of reduced production efficiency of the heating equipment 100. On the other hand, when the amount of water vapor in the furnace is 25% by volume, the thickness of the scale formed on the surface of the steel material becomes 500 μm or more, confirming that sufficient scale is formed to remove casting defects present on the surface of the steel material.

[0093] The metal material heating method of this embodiment further involves a second heating step in which the metal material heated in the first heating step is further heated by electric heating while controlling the furnace to an inert gas atmosphere. In this case, the target heating temperature in the second heating step (second heating temperature) is set to a higher temperature than the target heating temperature in the first heating step (first heating temperature) to further heat the steel material S.

[0094] In the second heating process, the furnace is controlled to maintain an inert gas atmosphere, and electric heating without oxygen is performed, thereby suppressing the growth of the oxide layer on the surface of the metal material formed in the first heating process. As a result, after the first and second heating processes are completed, the oxide layer formed on the surface of the metal material is removed by a descaling device, etc., which suppresses the occurrence of surface defects in subsequent manufacturing processes. In addition, since an excessive oxide layer is not formed on the surface of the metal material, a decrease in product yield is also suppressed.

[0095] The second heating step will be explained using a method for heating steel as an example. In the method for heating steel, it is preferable to heat the steel so that its surface temperature reaches 1050 to 1250°C during the second heating step. In the second heating step, the atmosphere inside the second heating furnace 2 is controlled to be an inert gas atmosphere, so oxidation of the steel S is suppressed. Furthermore, in the second heating furnace 2, the steel material S is heated by electric heating, eliminating the need to inject oxygen into the furnace for combustion and preventing oxidation of the surface of the steel material S by excess oxygen. In other words, as shown in Figure 8, while the thickness of the scale formed on the surface of the steel material increases rapidly when the surface temperature exceeds 1050°C in an atmosphere containing water vapor, the growth of scale is suppressed in the second heating process, which uses electric heating in an inert gas atmosphere.

[0096] However, if the second heating temperature is less than 1050°C, the second heating temperature may be lower than the first heating temperature, resulting in wasted energy required to heat the steel. Therefore, it is preferable to set the second heating temperature higher than the first heating temperature, so that the second heating temperature is 1050°C or higher. On the other hand, there is no specific upper limit set for the second heating temperature, but for steel materials used in hot rolling lines, etc., it is practical to set the upper limit at 1250°C. If the second heating temperature exceeds 1250°C, the energy required to heat the steel material becomes excessive.

[0097] Furthermore, regarding the temperature of the steel material S in the second heating process, similar to the first heating process, it is preferable to estimate the surface temperature of the steel material using a temperature model that calculates the temperature of the steel material S inside the heating furnace, and then control the operating conditions of the second heating process so that the estimated temperature becomes the second heating temperature.

[0098] From the above, the heating method for metal materials according to this embodiment promotes the growth of the oxide layer formed on the surface of the metal material in the first heating step. Subsequently, in the second heating step, in which the metal material is heated to a higher temperature, the growth of the oxide layer is suppressed, thereby suppressing the occurrence of surface defects in the metal material and preventing a decrease in product yield. In the first heating step, the metal material is heated by burner heating of a fuel gas consisting entirely of hydrogen and ammonia, or both. This reduces the amount of carbon dioxide emitted from the heating equipment 100 compared to conventional burner heating using only carbon-based gas.

[0099] <Other embodiments of the method for heating metallic materials> Another embodiment of the metal material heating method according to this embodiment is a method for heating a metal material in which the first heating step controls the amount of water vapor in the furnace so that the thickness of the oxide layer formed on the surface of the metal material is within a preset range, based on at least one operating parameter selected from the heating time of the first heating step, the heating temperature, and the flow rate of the fuel gas used for burner heating. This makes it possible to further suppress the decrease in product yield while suppressing the occurrence of surface defects in the metal material.

[0100] In this embodiment, a target range (scale target range) for the thickness of the oxide layer formed on the surface of the metal material in the first heating step is set in advance. The scale target range should be set to a range equivalent to the thickness from the surface where foreign matter, such as impurities generated during casting or mold powder mixed in during casting, is distributed near the surface of the metal material before the first heating step is performed. For example, the scale target range for the metal material to be heated should be set to about 50 to 1000 μm. If the metal material is steel, it should be set to 300 to 600 μm. This is because foreign matter, such as impurities generated during casting or mold powder mixed in during casting, is often found in large quantities in the range of approximately 300 to 600 μm from the surface of the steel material.

[0101] On the other hand, the scale thickness formed on the surface of the metal material in the first heating step is due to the growth of oxides. It is best to estimate using a mathematical model that models the behavior (scale thickness prediction model). The scale growth of steel can be estimated using the following equation (2).

number

[0102] The scale thickness prediction model, determined in advance as described above, is installed in the control computer 101, which sets the operating conditions of the heating equipment 100. Based on the information acquired by the control computer 101 from the first heating furnace 1, the predicted value of the scale thickness generated on the surface of the metal material is calculated.

[0103] Specifically, the system obtains operating parameters for the first heating furnace 1 from the control computer 101 (acquisition step). Next, based on the obtained operating parameters for the first heating furnace 1, it predicts the scale thickness at the end of the first heating process (prediction step). Then, it determines whether the predicted scale thickness (predicted scale thickness) is within a preset scale target range (determination step). In the determination step, if the predicted scale thickness is within the scale target range, a command is issued to the control computer 101 to maintain the current operating conditions of the first heating furnace 1. On the other hand, if the predicted scale thickness is not within the scale target range in the determination step, a setting command is issued to the control computer 101 to change the operating parameters of the first heating furnace 1 (setting step).

[0104] The setting step issues setting commands to the control computer 101 for the operation parameters of the first heating furnace 1, which are at least one of the following: the heating time of the first heating process, the heating temperature, and the flow rate of the fuel gas used for burner heating, which contains hydrogen-based gas consisting entirely of either hydrogen or ammonia, or both. Since the ratio of hydrogen-based gas contained in the fuel gas is predetermined, the flow rate of the hydrogen-based gas HG may be used as the flow rate of the fuel gas.

[0105] By changing the heating time of the first heating step, the scale thickness of the metal material generated in the first heating step changes. Furthermore, by changing the heating temperature of the first heating step (the ambient temperature in each zone inside the first heating furnace), the scale thickness of the metal material generated in the first heating step also changes. In this case, the heating temperature of the first heating step should be changed by altering the ambient temperature of the uniform zone. On the other hand, changing the flow rate of the hydrogen-based gas HG used in the first heating process changes the amount of water vapor generated by the burner heating, which in turn changes the scale thickness of the metal material. Among these, the parameter to be changed as an operating parameter for the first heating process is the flow rate of the hydrogen-based gas HG used for burner heating. Changing the heating time of the first heating process may reduce the efficiency of the heating equipment 100. Also, when changing the heating temperature of the first heating process, it may take time for the ambient temperature inside the furnace to change because the furnace volume of the first heating furnace is large. [Examples]

[0106] The effects of this embodiment will be described in detail below based on the examples, but the present invention is not limited to these examples.

[0107] <Example 1> As an embodiment of the present invention, an example of heating steel material using a test apparatus that simulates the first and second heating steps described above will be explained. The test apparatus used in this embodiment consists of a combustion gas heating furnace that performs burner heating and an electric heating furnace that can control the atmosphere inside the furnace to an inert gas atmosphere.

[0108] The combustion gas heating furnace used for the first heating process has internal dimensions of 800 mm in height, 500 mm in width, and 1000 mm in length. Burners are positioned on the top and bottom surfaces of the test specimen to be placed inside the furnace, and the furnace is configured to receive a mixed gas of hydrogen-based gas and coal gas from the fuel gas supply system. The hydrogen-based gas used in the mixed gas was ammonia, and the coal gas used was M gas, which was a mixture of by-product gas generated at the steel mill.

[0109] The combustion conditions used in the example were ammonia flow rate supplied to the burner of 67 Nm³. 3 / hr, M gas flow rate 100Nm 3 The volume ratio of ammonia in the mixed gas was set to 40% and the volume ratio of M gas to 60% (as per hour). The M gas used had a composition that, under conditions of complete combustion, emitted 13% by volume of carbon dioxide in the exhaust gas. In contrast, in the example, the burner heating conditions were set so that the carbon dioxide concentration in the exhaust gas during the first heating process was 8% by volume by adjusting the mixing ratio of ammonia.

[0110] The electric heating furnace used for the second heating process also had dimensions of 800mm in height, 500mm in width, and 1000mm in length. Argon was supplied as an inert gas to the electric heating furnace, and the pressure inside the furnace was controlled to 5kPa by adjusting the opening of the inert gas flow control valve. A resistance heating element made of Kanthal wire was placed inside the electric heating furnace to perform indirect resistance heating of the material to be heated.

[0111] In this example, carbon steel with a thickness of 220 mm, a width of 300 mm, and a length of 500 mm was used as the metal material to be heated. The material to be heated was taken from the slab after casting by machining, and a Φ0.5 mm K-type sheathed thermocouple was attached to the center of the width and length of the plate at a depth of 2 mm from the surface. The heating behavior of the material to be heated during the first and second heating processes was measured, and the surface temperature of the material to be heated was estimated based on the measurement results.

[0112] Here, the relationship between the first heating temperature and the scale thickness formed on the surface of the heated material was investigated in advance by changing the heating conditions in the combustion gas heating furnace. Figure 10 shows the relationship between the surface temperature of a material heated in a combustion gas heating furnace and the scale thickness. The scale thickness was determined by removing the material from the combustion gas heating furnace and immediately water-cooling it once the set surface temperature was reached, thereby preventing further scale growth. Evaluation samples were then taken from the heated material by machining, and the scale thickness was determined by observing the cross-section of the material with an optical microscope.

[0113] Figure 10 shows that in a combustion gas heating furnace, the higher the surface temperature of the heated material, the thicker the scale becomes, and the scale thickness increases rapidly when the surface temperature exceeds 1050°C.

[0114] In contrast, in the inventive example, the first heating temperature was set to 1050°C, and the second heating temperatures were set to 1100, 1150, and 1200°C. A first heating step was performed using a combustion gas heating furnace, and a second heating step was performed using an electric heating furnace. First, the material to be heated was placed in the combustion gas heating furnace, and the first heating step was performed so that the first heating temperature reached 1050°C. Then, while maintaining the heated state of the material to be heated, it was placed in the electric heating furnace and heated to the second heating temperature. Furthermore, although the material to be heated was temporarily exposed to the atmosphere from the time it was removed from the combustion gas heating furnace until it was charged into the electric heating furnace, the duration of this exposure was only 20 seconds. Therefore, it was considered that scale growth on the material to be heated between the completion of the first heating process and the start of the second heating process was substantially negligible. Once the surface temperature of the material to be heated reached the second heating temperature during the second heating process, the material to be heated was removed from the electric heating furnace and immediately cooled with water to prevent further scale growth. The scale thickness formed on the surface of the material to be heated was then measured using the same method as described above.

[0115] Figure 10 shows the scale thickness generated on the heated material according to the example. As can be seen from the figure, when the material to be heated was raised to 1100-1200°C according to the example, the scale thickness formed on the material was approximately 400-410 μm, which is only a slight increase from the temperature of 1050°C at the end of the first heating step. In other words, compared to the results of a preliminary experiment using only the first heating step, it was confirmed that the scale thickness generated on the heated material was suppressed at the same second heating temperature. In other words, according to this embodiment, it was confirmed that by using ammonia, a hydrogen-based gas, in the first heating step, the carbon dioxide concentration in the exhaust gas can be reduced compared to when coal gas is used as fuel, and the excessive increase of the oxide layer on the heated material due to the water vapor generated by the combustion of ammonia can be suppressed.

[0116] <Example 2> As a second embodiment of the present invention, another example of heating steel material using the test apparatus used in the above embodiment will be described. However, in this embodiment, the fuel gas supply system of the combustion gas heating furnace that performs the first heating step can be configured by changing the connection of the supply piping to set conditions in which hydrogen, ammonia, and coal gas are used individually as fuel gas G, and conditions in which a mixed gas is used which is a mixture of two or more fuel gases selected from hydrogen, ammonia, and coal gas.

[0117] Furthermore, in this embodiment, the fuel gas supply system and combustion air supply system of the combustion gas heating furnace are equipped with a fuel gas flow meter and a combustion air flow meter, respectively, to measure the flow rates of fuel gas G and combustion air A supplied to the burner equipment. In addition, the fuel gas supply system and combustion air supply system are equipped with a fuel gas flow control valve and a combustion air flow control valve, respectively, to adjust the amount of fuel gas G and combustion air A supplied to the burner nozzle.

[0118] Furthermore, atmospheric gases inside the combustion gas heating furnace were sampled for each test condition, and the atmosphere inside the furnace was measured using a dew point meter and a gas analyzer. The coal gas used was M gas, as in the above example. In the first heating step using the above test apparatus, the flow rate of hydrogen-based gas HG was adjusted so that the carbon dioxide concentration in the exhaust gas discharged from the combustion gas heating furnace was 9 volume% or less under all conditions. The electric heating furnace used for the second heating step was the same as in the above embodiment. Argon was supplied as the inert gas, and the pressure inside the furnace was controlled to 5 kPa by adjusting the opening of the inert gas flow control valve.

[0119] In this embodiment as well, carbon steel with a plate thickness of 220 mm, a plate width of 300 mm, and a plate length of 500 mm was used as the metal material to be heated. The material to be heated was taken from the slab after casting by machining, and a Φ0.5 mm K-type sheathed thermocouple was attached to the center of the plate width and length at a depth of 2 mm from the surface. The heating behavior of the material to be heated during the first and second heating processes was measured, and the surface temperature of the material to be heated was estimated based on the measurement results.

[0120] In this embodiment, the material to be heated was placed in a combustion gas heating furnace, and a first heating step was performed so that the first heating temperature reached 900 to 1200°C. Subsequently, while maintaining the heated state of the material, it was placed in an electric heating furnace, and a second heating step was performed so that the second heating temperature reached 1200°C.

[0121] Furthermore, the material to be heated was temporarily exposed to the atmosphere between its removal from the combustion gas heating furnace and its entry into the electric heating furnace. However, this period was only 20 seconds, and it was considered that scale growth on the material to be heated between the completion of the first heating process and the start of the second heating process was practically negligible. Once the surface temperature of the material to be heated reached the second heating temperature during the second heating process, the material was removed from the electric heating furnace and immediately water-cooled to prevent further scale growth. Then, evaluation samples were taken from the heated material by machining, and the cross-section of the heated material was observed with an optical microscope to determine the scale thickness.

[0122] Here, the thickness at which foreign matter, such as impurities generated during casting and mold powder mixed in during casting, is distributed was identified from the component composition of the carbon steel used as the material to be heated, and the target scale range was set to 350 to 550 μm. In other words, if the scale thickness generated on the evaluation sample taken from the heated material is less than 350 μm, the scale thickness may be insufficient, potentially leading to surface defects when the material is subjected to hot rolling or other processes. On the other hand, if the scale thickness from the heated material exceeds 550 μm, excessive scale formation may lead to a decrease in product yield. Based on the above, a heated material was judged to pass (○) if its scale thickness was within the target scale range of 350 to 550 μm. On the other hand, a heated material was judged to fail (×) if its scale thickness was outside the target scale range of 350 to 550 μm.

[0123] The heating conditions and test results are shown in Table 1. Conditions 1 to 9 are examples in which a first heating step is performed in which the material to be heated is heated by burner heating using a fuel gas containing either hydrogen or ammonia as a hydrogen-based gas, and a second heating step is performed in which the material heated in the first heating step is further heated by electric heating while controlling the furnace to an inert gas atmosphere. In conditions 1 to 9, the first heating temperature in the first heating step was set to 900 to 1060°C, and the second heating temperature in the second heating step was set to 1200°C. In conditions 3, 4, and 9, a hydrogen-based gas was used alone as the fuel gas, while in the other examples of inventions, a mixed gas of hydrogen-based gas and M gas was used as the fuel gas. Table 1 shows the mixing ratio (volume ratio of hydrogen gas HG) of hydrogen-based gas HG supplied from the hydrogen-based gas supply system 45 included in fuel gas G. In this case, when using a fuel gas consisting entirely of hydrogen and ammonia, or both, the mixing ratio of hydrogen-based gas HG is 100%. Furthermore, the "water vapor amount" in Table 1 shows the result of calculating the amount of water vapor in the combustion gas heating furnace using the known relationship between saturated water vapor amount and temperature, based on the measurement results of the dew point, pressure, and temperature of the atmospheric gas in the combustion gas heating furnace.

[0124] As can be seen from Table 1, in the inventive examples of conditions 1 to 9, the scale thickness generated on the evaluation sample taken from the heated material was within the scale target range of 350 to 550 μm, and therefore it was judged as passing (○). In particular, under conditions 1 to 7, excessive scale formation was suppressed because the first heating temperature in the first heating step was in the range of 900 to 1050°C. Furthermore, because the amount of water vapor inside the furnace was in the range of 20-32 volume%, an appropriate scale thickness was generated. As a result, under conditions 1-7, the scale thickness generated on the evaluation sample was 40 A scale thickness with little variation was obtained, ranging from 0 to 500 μm. In contrast, in comparative examples 10 and 11, the first heating temperature in the first heating step was set to 1200°C and heating was performed using a combustion gas heating furnace without applying the second heating step, resulting in excessive scale thickness. Furthermore, under condition 12, the first heating step was omitted, and the second heating temperature in the second heating step was set to 1200°C, with heating performed only in an electric heating furnace. In this case, because the scale thickness of the material being heated was too thin, when the heated steel was rolled using a laboratory rolling mill, surface defects were generated on the surface of the steel.

[0125] From the above, it was found that this embodiment reduces carbon dioxide emissions by using hydrogen or ammonia as fuel gas for the heating furnace, and also suppresses deterioration of product yield while controlling the amount of scale formation within an appropriate range, thereby reducing the occurrence of surface defects in metal materials.

[0126] [Table 1] [Explanation of symbols]

[0127] 100 Heating equipment 101 Control Computer S steel material D. Direction of steel material transport A Combustion air G Fuel gas CG Coal Gas HG Hydrogen Gas NAG inert gas 1 1st heating furnace 2 Second heating furnace 3. Pre-tropical 4. Heating Zone 5 Kin Tropical 6 burners 6a Upper burner 6b Lower burner 7 Burner Nozzles 8. First Loading Section 9. First Loading Section 10. First conveying device 10a Fixed skid 10b Mobile skid 13, 29 Exhaust duct 14 Transfer device 21 Non-oxidizing heating zone 22 Electric heating section 23 Inert gas supply unit 24 Inert Gas Flow Meter 25. Inert gas flow control valve 26 Second Loading Section 27 Second Loading Section 28. Second conveying device 28a Fixed skid 28b Mobile skid 30 Inert gas supply system 31 Fuel gas supply system 32 Combustion air supply system 33 Fuel gas flow control valve 34 Fuel gas flow meter 35 Combustion air flow control valve 36 Combustion air flow meter 37, 54 Furnace wall 40 Mixing section 41 Hydrogen-based gas flow control valve 42 Hydrogen-based gas flow meter 43 Coal gas flow control valve 44 Coal gas flow meter 45 Hydrogen-based gas supply system 46 Coal gas supply system 47 Flow rate setting section 48. Water vapor quantity control unit 49 Dew point meter 51 Resistive heating element 52 Heat resistant tube 53 Power supply cable 55 Insulator 56 Support stand 60 Burner Equipment 70, 71 Hydrogen-based burner equipment

Claims

1. A first heating step involves heating a metal material charged into a furnace by burner heating using a hydrogen-based gas, which consists entirely of hydrogen and ammonia, or both, as the fuel gas. The process includes a second heating step in which the metal material heated in the first heating step is heated by electric heating in an inert gas atmosphere inside the furnace. A method for heating metallic materials.

2. The method for heating a metal material according to claim 1, wherein the first heating step is to heat the metal material by burner heating using a mixed gas obtained by mixing the hydrogen-based gas with one or more gases selected from coal gas and hydrocarbon-based gases as the fuel gas.

3. The first heating step controls the amount of water vapor in the furnace to a preset range based on the flow rate of the fuel gas used for heating the burner. A method for heating a metallic material according to claim 1 or 2.

4. The first heating step is performed based on at least one operating parameter selected from the heating time of the first heating step, the heating temperature, and the flow rate of the fuel gas used for heating the burner. The thickness of the oxide layer formed on the surface of the metal material is within a predetermined range. Control the amount of steam inside the reactor, A method for heating a metallic material according to claim 1 or 2.

5. The aforementioned metal material is steel, The first heating step involves heating the metal material so that its surface temperature reaches 850 to 1050°C. The second heating step involves heating the metal material so that its surface temperature reaches 1050 to 1250°C. A method for heating a metallic material according to claim 1 or 2.

6. The aforementioned metal material is steel, The first heating step involves heating the metal material so that its surface temperature reaches 850 to 1050°C. The second heating step involves heating the metal material so that its surface temperature reaches 1050 to 1250°C. A method for heating a metal material according to claim 3.

7. The aforementioned metal material is steel, The first heating step involves heating the metal material so that its surface temperature reaches 850 to 1050°C. The second heating step involves heating the metal material so that its surface temperature reaches 1050 to 1250°C. The method for heating a metallic material according to claim 4.

8. In the first heating step, the amount of steam in the furnace is controlled to 20 to 35 volume percent. A method for heating a metallic material according to claim 5.

9. In the first heating step, the amount of steam in the furnace is controlled to 20 to 35 volume percent. A method for heating a metallic material according to claim 6.

10. In the first heating step, the amount of steam in the furnace is controlled to 20 to 35 volume percent. A method for heating a metallic material according to claim 7.

11. A first heating furnace that heats a metal material by burner heating using a hydrogen-based gas, which consists entirely of hydrogen and ammonia or both, as the fuel gas, A second heating furnace is used to heat the metal material discharged from the first heating furnace, and the inside of the furnace is heated by electric heating in an inert gas atmosphere. Equipped with, The first heating furnace is equipped with a plurality of burners along the direction of transport of the metal material, and at least one burner is configured to perform burner heating. Heating equipment for metal materials.

12. The first heating furnace uses a mixed gas, obtained by mixing the aforementioned hydrogen-based gas with one or more gases selected from coal gas and hydrocarbon-based gases, as the fuel gas, and heats a metal material by burner heating. A heating apparatus for metal materials according to claim 11.

13. The first heating furnace is, A flow rate setting unit for setting the flow rate of the fuel gas used for heating the burner, A steam amount control unit that controls the amount of steam in the first heating furnace to a preset range, Having, A heating apparatus for metal materials according to claim 11 or 12.

14. A method for operating a heating furnace that heats a steel material using the method for heating a metallic material described in claim 5.

15. A method for operating a heating furnace that heats a steel material using the method for heating a metallic material described in claim 6.

16. A method for operating a heating furnace that heats a steel material using the method for heating a metallic material described in claim 7.

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