Partially reduced HBI and method for producing the same

Abstract

The present invention provides a semi-reduced iron biofill (HBI) with excellent meltability and apparent density suitable for sea transport, which can be produced from semi-reduced iron manufactured from low-grade iron ore or iron ore pellets. The semi-reduced HBI is hot-formed from semi-reduced iron, has a total iron content of 80-90% by mass, a metallization rate of 70-90%, and an apparent density of 5.0-5.5 g / cm³. 3 This is a semi-reduced HBI with a mass ratio of CaO to SiO2 (CaO / SiO2) of 0.10 to 0.70.

Description

[Technical Field]

[0001] This disclosure relates to a semi-reduced HBI and a method for producing the same. [Background technology]

[0002] Hot Briquette Iron (HBI) is a type of reduced iron that has been densified by hot compression molding at high temperatures.

[0003] Decarbonization of the steel industry is a global challenge, and one measure to reduce CO2 emissions from steelmaking processes is the need for increased production and use of HBI (Heat-Based Iron), which is made from reduced iron produced by natural gas or hydrogen. Conventional HBI is mainly used as a raw material for electric furnaces, and generally, HBI with a metallization rate of over 90% and a metallic iron content of 83% by mass or more (total iron content of 92% by mass or more) is used. To produce such high-grade HBI, conventionally, high-grade reduced iron obtained by reducing very high-grade iron ore or iron ore pellets with a total iron content of 67% by mass or more has been used. However, in recent years, with the depletion of high-quality iron ore, it has become difficult to obtain iron ore or iron ore pellets with a total iron content of 67% by mass or more. In particular, since auxiliary raw materials are added to iron ore pellets during their production, even higher-grade iron ore (for example, with a total iron content of approximately 67.5% by mass or more) is required to produce iron ore pellets with a total iron content of 67% by mass or more.

[0004] Therefore, it has become necessary to use reduced iron produced from low-grade iron ore or iron ore pellets (hereinafter also referred to as low-grade iron ore or iron ore pellets) with a total iron content of less than 67% by mass. However, low-grade iron ore or iron ore pellets contain a large amount of gangue, resulting in a relatively low iron content. Consequently, the metallic iron content of the reduced iron obtained by reducing them is low. In addition, when iron ore or iron ore pellets contain a large amount of gangue, their reducibility decreases, especially towards the end of the reduction process, making it difficult to obtain a high metallization rate. In other words, reduced iron produced from low-grade iron ore or iron ore pellets has a lower metallization rate and metallic iron content than reduced iron produced from high-grade iron ore or iron ore pellets. Therefore, HBI produced from such reduced iron (also referred to as low-grade HBI) has a lower metallization rate and metallic iron content compared to conventional HBI.

[0005] Patent Document 1 (Japanese Patent Publication No. 2009-79292) discloses a method for producing a reduced iron molded body, in which a reduced iron-containing material with a metallic iron content of 50% by mass or more and a carbon content of 5% by mass or less is produced in a rotary hearth reduction furnace (RHF), and this reduced iron-containing material is compressed and molded in a roller-type mold at a temperature of 500 to 800°C.

[0006] Patent Document 2 (Japanese Patent Publication No. 2008-127580) discloses an HBI composed of reduced iron with a carbon content of 0.1 to 2.5 mass% in the surface portion, which is the part up to a depth of 3 mm, and a higher carbon content in the center. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2009-79292 [Patent Document 2] Japanese Patent Publication No. 2008-127580 [Overview of the project] [Problems that the invention aims to solve]

[0008] When low-grade HBI is used in an electric arc furnace, the productivity of the electric arc furnace deteriorates significantly due to factors such as a decrease in iron yield caused by an increase in electric arc furnace slag and a worsening of power consumption per unit of electricity. Therefore, low-grade HBI is unsuitable as a raw material for electric arc furnaces. For this reason, it is desirable to perform final reduction of low-grade HBI in a blast furnace or other ironmaking furnace, and to further separate the molten iron from the slag. However, low-grade HBI has poor meltability, and when used in an ironmaking furnace, it has the problem of hindering the permeability of the furnace.

[0009] Furthermore, according to the International Marine Solid Bulk Cargo Code (IMSBC Code), which specifies the regulations for the maritime transport of HBI, HBI is classified as DRI(A), molded at temperatures above 650°C, and has a capacity of 5000 kg / m³. 3 (5g / cm 3 It is defined as being formed into a briquette shape having a density of ) or higher.

[0010] However, Patent Documents 1 and 2 do not describe low-grade HBI that has excellent meltability and apparent density suitable for sea transport.

[0011] This disclosure aims to provide a semi-reduced HBI (Heat Bone Injection) that has excellent meltability and an apparent density suitable for sea transport, which can be used as a raw material from semi-reduced iron produced from low-grade iron ore or iron ore pellets. [Means for solving the problem]

[0012] The contents of this disclosure include the following aspects: <Aspect 1> This is a semi-reduced HBI obtained by hot-forming semi-reduced iron, The total iron content is 80-90% by mass. The metallization rate is 70-90%. Apparent density is 5.0-5.5 g / cm³ 3 And, The mass ratio of CaO to SiO2 (CaO / SiO2) is between 0.10 and 0.70. Half-reduced HBI. <Aspect 2> The Al2O3 content is 3.0% by mass or less. The semi-reduced HBI according to the above Aspect 1. <Aspect 3> The dropping start temperature is 1500 °C or lower, The semi-reduced HBI according to the above Aspect 1 or 2. <Aspect 4> The dropping start temperature is 1450 °C or lower, The semi-reduced HBI according to the above Aspect 1 or 2. <Aspect 5> The major axis is 10 to 100 mm, The semi-reduced HBI according to any one of the above Aspects 1 to 4. <Aspect 6> A method for producing the semi-reduced HBI according to any one of the above Aspects 1 to 5, Preparing a raw material mixture containing an iron oxide-containing raw material and an auxiliary raw material for basicity adjustment, and having a mass ratio (CaO / SiO2) of CaO to SiO2 of 0.10 to 0.70; Gas-reducing the raw material mixture at a temperature lower than 1200 °C to obtain semi-reduced iron having a total iron content of 80 to 90% by mass and a metallization rate of 70 to 90%; Forming the semi-reduced iron at a temperature of 700 °C or higher and a pressure of 200 MPa or higher to obtain semi-reduced HBI; A method for producing semi-reduced HBI, including the above steps.

Advantages of the Invention

[0013] According to the present disclosure, it is possible to provide semi-reduced HBI that uses semi-reduced iron produced from low-grade iron ore or iron ore pellets as a raw material, has excellent meltability, and has an apparent density that enables marine transportation.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram of the piston press molding machine used in the examples.

Modes for Carrying Out the Invention

[0015] The embodiments of the partially reduced HBI and its manufacturing method described herein will be explained in detail below. However, the partially reduced HBI and its manufacturing method described herein are not limited to the embodiments described below.

[0016] In this specification, the "~" symbol indicating a numerical range, unless otherwise specified, means that the numbers before and after it are included as the lower and upper limits. If multiple upper or lower limits are listed, a numerical range can be created from all combinations of upper and lower limits. Similarly, if multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining upper and lower limits from those ranges.

[0017] In this specification, HBI refers to "5 g / cm³ iron briquettes prepared at a temperature of 650°C or higher," as described in JIS M8700:2013 "Iron Ore and Reduced Iron - Terminology." 3 This means "reduced iron having the above apparent density." In this specification, "partially reduced" is used to exclude completely reduced iron, i.e., iron with a metallization rate of 100%.

[0018] Generally, low-grade HBI has poorer meltability compared to high-grade HBI. The inventors considered the cause of the poor meltability of low-grade HBI as follows: High-grade HBI is thought to melt in the blast furnace as follows: First, the HBI is heated in the blast furnace and the metallic iron portion softens. Next, carburization of the metallic iron progresses from the contact surface between the softened HBI and coke. Next, the HBI melts starting from the portion where the melting point has decreased due to carburization and drips down to the bottom of the furnace. On the other hand, in the case of low-grade HBI, gangue components such as SiO2 and Al2O3 in the HBI physically hinder contact between the metallic iron and coke. As a result, carburization is inhibited and meltability deteriorates. Therefore, the inventors considered that if the melting point of the gangue components could be lowered, carburization would proceed more easily and meltability would improve. Experimental studies have shown that the melting properties of HBI are improved by setting the mass ratio of CaO to SiO2 (CaO / SiO2) to a range of 0.10 to 0.70. While not bound by any particular theory, this is thought to be because, when the mass ratio of CaO to SiO2 (CaO / SiO2) is in the range of 0.10 to 0.70, the iron oxide and gangue components in HBI form a low-melting-point slag.

[0019] [Half-reduced HBI] One embodiment of semi-reduced HBI is semi-reduced HBI obtained by hot-forming semi-reduced iron, having a total iron content of 80-90% by mass, a metallization rate of 70-90%, and an apparent density of 5.0-5.5 g / cm³. 3 This is a semi-reduced HBI with a mass ratio of CaO to SiO2 (CaO / SiO2) of 0.10 to 0.70. By keeping the mass ratio of CaO to SiO2 (CaO / SiO2) in the range of 0.10 to 0.70, the melting properties of semi-reduced HBI can be increased. If the amount of CaO is increased too much to raise the mass ratio of CaO to SiO2 (CaO / SiO2), the apparent density will decrease because the amount of CaO, which has a lower density than metallic iron, will increase.

[0020] The total iron content of semi-reduced HBI is preferably 82-90% by mass, more preferably 85-90% by mass. When the total iron content is 80% by mass or more, the gangue content is suppressed and moldability is ensured, making it easier to increase the apparent density of semi-reduced HBI. When the total iron content is 90% by mass or less, the range of usable raw materials can be increased.

[0021] The metallization rate of the partially reduced HBI is preferably 75% or higher, more preferably 80% or higher. A metallization rate of 70% or higher suppresses the content of iron oxide, which has a lower density than metallic iron, thus increasing the apparent density. The metallization rate can be increased by extending the reduction time in the process of obtaining the partially reduced iron raw material. From the viewpoint of production efficiency, the metallization rate may be 90% or less. The upper limit of the metallization rate may be 89% or less.

[0022] The Al2O3 content of the partially reduced HBI is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, and particularly preferably 1.0% by mass or less. When the Al2O3 content is 3.0% by mass or less, the viscosity of the formed slag is low, resulting in better melting properties of the partially reduced HBI. The lower limit of the Al2O3 content is not particularly limited, but may be, for example, 0.1% by mass or more, or 0.5% by mass or more.

[0023] The CaO content of the partially reduced HBI may be 0.2% by mass or more, 0.5% by mass or more, or 1.0% by mass or more, from the viewpoint of increasing solubility. The CaO content may be 3.0% by mass or less, 2.0% by mass or less, or 1.0% by mass or less, from the viewpoint of increasing apparent density.

[0024] The SiO2 content of the partially reduced HBI may be 1.0% by mass or more, 2.0% by mass or more, or 3.0% by mass or more, from the viewpoint of expanding the utilization of low-grade iron ore or iron ore pellets. The SiO2 content may be 6.0% by mass or less, 5.0% by mass or less, or 4.0% by mass or less, from the viewpoint of increasing the apparent density.

[0025] The total iron content of partially reduced HBI is measured according to JIS M 8212:2022 "Iron ore - Method for determining total iron - Titanium(III) chloride-reduced potassium dichromate titration method". The metallic iron content of partially reduced HBI is measured according to the metallic iron determination method described in the "Explanation" of JIS M 8213:1995 "Iron ore - Method for determining acid-soluble iron(II)". That is, it is measured by the bromine methanol solution / EDTA2Na solution titration method. The metallization rate is calculated by the following formula. Metallization rate (%) = [(Metallic iron content) / (Total iron content)] × 100

[0026] The CaO content of half-reduced HBI is a CaO equivalent value based on the Ca mass measured by ICP emission spectrometry. The SiO2 content of half-reduced HBI is an SiO2 equivalent value based on the Si mass measured by ICP emission spectrometry. The mass ratio of CaO to SiO2 (CaO / SiO2) is calculated from these CaO equivalent and SiO2 equivalent values.

[0027] The Al2O3 content of half-reduced HBI is an Al2O3 equivalent value based on the Al mass measured by ICP emission spectroscopy.

[0028] The apparent density of half-reduced HBI is 5.0 g / cm³, from the perspective of being suitable for maritime transport. 3 That concludes the explanation. The apparent density of half-reduced HBI can be improved by increasing the molding temperature and molding pressure. On the other hand, if the molding temperature and molding pressure are excessively high, wear and tear on the molding machine's mold is likely to occur. Therefore, the apparent density should be 5.5 g / cm³. 3 The following, or 5.4 g / cm³ 3 The following is acceptable:

[0029] The apparent density of half-reduced HBI is measured according to ISO 15968 "Direct reduced iron - Determination of apparent density and water absorption of hot briquetted iron (HBI)". Specifically, the apparent density is measured by the water immersion method.

[0030] The dropping start temperature for semi-reduced HBI is preferably 1500°C or lower, more preferably 1450°C or lower, even more preferably 1430°C or lower, and even more preferably 1400°C or lower. Since the molten iron temperature of a typical blast furnace is around 1500°C, it is considered that good permeability within the blast furnace can be ensured if the dropping start temperature is 1500°C or lower. Since the dropping start temperature for sintered ore, the main raw material for blast furnaces, is around 1450°C, a dropping start temperature of 1450°C or lower can contribute to further improvement of the permeability of the blast furnace. On the other hand, if the dropping start temperature is extremely low, there is a concern that it may worsen the permeability in the upper part of the blast furnace, so the dropping start temperature for semi-reduced HBI is preferably 1150°C or higher, more preferably 1200°C or higher, and even more preferably 1250°C or higher. The dropping start temperature for semi-reduced HBI is measured by the method described in the examples.

[0031] The shape of the semi-reduced HBI is not particularly limited. Specific examples include pillow-shaped, cylindrical, and prismatic shapes. When semi-reduced HBI is used in a blast furnace, the major axis of the semi-reduced HBI is preferably 140 mm or less, more preferably 100 mm or less, from the viewpoint of facilitating uniform charging of the semi-reduced HBI into the blast furnace and stabilizing the gas flow distribution inside the blast furnace. On the other hand, from the viewpoint of reducing the gas flow resistance inside the blast furnace, the major axis of the semi-reduced HBI is preferably 10 mm or more.

[0032] The major axis of the half-reduced HBI is determined according to its shape as follows: For a pillow block, it is the largest of the three axes: length, width, and thickness. For a cylinder, it is the larger of height and diameter. For a prism, it is the largest of the three axes: length, width, and height. Here, the width of the prism is the distance between the two parallel lines with the shortest distance between them that are tangent to the contour in a polygonal cross-section perpendicular to the height direction of the prism, and the length of the prism is the distance between two parallel lines that are perpendicular to the aforementioned two parallel lines and are tangent to the contour. Here, "tangent to the contour" means passing through at least one point of the contour and not passing through the interior of the polygonal cross-section. For other irregular shapes, when the HBI is placed on a horizontal plane, the vertical distance from the horizontal plane to the top of the HBI is defined as the thickness, the distance between the two parallel lines with the shortest distance between them that are tangent to the contour when viewed from directly above the HBI is defined as the width, and the distance between two parallel lines that are perpendicular to the aforementioned two parallel lines and are tangent to the contour is defined as the length. The longest of these three axes is defined as the largest. Here, "tangent to the contour" means passing through at least one point on the contour and not passing through the interior of the HBI when viewed from directly above the HBI. The longest axis of the half-reduced HBI is measured with calipers.

[0033] Partially reduced HBI can be used as a raw material for molten iron or molten steel. Partially reduced HBI can be used in furnaces having reduction and dissolution functions, such as blast furnaces, converters, or electric furnaces. Partially reduced HBI in one embodiment is for use in blast furnaces.

[0034] [Method for producing semi-reduced HBI] One embodiment of the method for producing semi-reduced HBI includes: preparing a raw material mixture containing an iron oxide-containing raw material and a secondary raw material for adjusting basicity, wherein the mass ratio of CaO to SiO2 (CaO / SiO2) is 0.10 to 0.70; gas-reducing the raw material mixture at a temperature of less than 1200°C to obtain semi-reduced iron having a total iron content of 80 to 90% by mass and a metallization rate of 70 to 90%; and molding the semi-reduced iron at a temperature of 700°C or higher and a pressure of 200 MPa or higher to obtain semi-reduced HBI. In order to achieve a mass ratio of CaO to SiO2 (CaO / SiO2) of 0.10 to 0.70 in the semi-reduced iron, a raw material mixture with a mass ratio of CaO to SiO2 (CaO / SiO2) of 0.10 to 0.70 is used.

[0035] Examples of iron oxide-containing raw materials include iron ore. The total iron content of the iron oxide-containing raw material can be appropriately selected considering the target total iron content of semi-reduced iron, etc. For example, the total iron content of the iron oxide-containing raw material is 57% by mass or more. More preferably, it is 58% by mass or more, even more preferably, 61% by mass or more, and even more preferably, 63% by mass or more. There is no upper limit to the total iron content of the iron oxide-containing raw material, but for example, it may be 70% by mass or less. From the viewpoint of using low-grade iron ore, the total iron content of the iron oxide-containing raw material may be less than 67% by mass.

[0036] The auxiliary raw materials used for basicity adjustment are not particularly limited as long as they yield CaO when oxidized (also called CaO sources). Examples of auxiliary raw materials for basicity adjustment include limestone, quicklime, slaked lime, dolomite, and calcined dolomite. The mass ratio of CaO to SiO2 (CaO / SiO2) in the raw material mixture can be adjusted, for example, by the amount of auxiliary raw materials added for basicity adjustment.

[0037] The total iron content of the raw material mixture can be appropriately selected considering the target total iron content of semi-reduced iron, etc. The total iron content of the raw material mixture is preferably 61% by mass or more, more preferably 63% by mass or more. The total iron content of the raw material mixture may be, for example, 70% by mass or less, 67% by mass or less, 66% by mass or less, or 65% by mass or less.

[0038] From the viewpoint of more efficiently lowering the melting point of gangue components, it is preferable that the gangue components and calcium are in contact in the raw material mixture. From this viewpoint, it is preferable to use iron ore pellets as the raw material mixture. When using iron ore pellets as the raw material mixture, it is preferable to add auxiliary materials for basicity adjustment during the production of the iron ore pellets. Specifically, iron ore pellets can be produced by mixing fine iron ore, auxiliary materials for basicity adjustment which are crushed as needed, and other components, granulating this mixture, and calcining it. Examples of other components include bentonite.

[0039] The reduction method used for reducing the raw material mixture is not particularly limited, and known reduction methods can be used. Examples of reduction methods include shaft furnace reduction processes, fluidized bed reduction processes, and rotary kiln reduction processes.

[0040] The reduction conditions should be adjusted so that the metallization rate of partially reduced iron is 70-90%. The metallization rate can be adjusted by, for example, the reducing gas flow rate, reducing gas concentration, reduction time, and reduction temperature.

[0041] When producing semi-reduced iron using a rotary hearth furnace (RHF) as described in Patent Document 1, it is essential to blend carbon as a reducing agent with the iron oxide-containing raw material. Consequently, a large amount of CO2 is emitted during production. In addition, the reduction temperature needs to be 1200°C or higher to improve the metallization rate and density of the semi-reduced iron. On the other hand, when producing semi-reduced iron by gas reduction at a temperature below 1200°C, such as in a shaft furnace reduction process, it is not necessary to blend carbon with the iron oxide-containing raw material. In addition, hydrogen and natural gas can be used as the reducing gas. Therefore, the method of producing semi-reduced iron by gas reduction at a temperature below 1200°C has the advantage of reducing CO2 emissions during production. Furthermore, since it is preferable to transport the semi-reduced iron produced in the reduction furnace to the next process at a high temperature without reheating and to compress and mold it, the gas reduction temperature is preferably 700°C or higher.

[0042] The molding machine used for compression molding of semi-reduced iron is not particularly limited. Specific examples thereof include a piston press molding machine and a roller press molding machine (also referred to as a briquetting machine).

[0043] <000,0194>When compression molding semi-reduced iron with a conventional metallization rate exceeding 90%, by setting the molding temperature to 650 °C or higher, metallic iron becomes more likely to plastically deform, and the apparent density can be made 5.0 g / cm 3 or higher. On the other hand, in order to make the apparent density of semi-reduced iron with a metallization rate of 90% or less 5.0 g / cm 3 or higher, it is necessary to plastically deform iron oxide as well. From the viewpoint of plastically deforming iron oxide, the molding conditions are that the molding temperature is 700 °C or higher and the molding pressure is 200 MPa or higher.

[0044] If the molding temperature is excessively high, the mold of the molding machine is likely to be worn out. Therefore, the molding temperature is preferably 800 °C or lower. In order to keep the temperature of the semi-reduced iron high, a heating furnace may be provided between the reduction furnace and the molding machine as necessary. Alternatively, a molding machine having a heating function may be used.

[0045] If the molding pressure is excessively high, the mold of the molding machine is likely to be worn out. Therefore, the molding pressure is preferably 400 MPa or lower.

[0046] The molding pressure means the surface pressure applied to the molded product. In the case of a roller press molding machine, since the pockets on the roller surface, that is, the depressions for sandwiching and compression molding semi-reduced iron, are not flat, it is estimated that the surface pressure applied to the sample is non-uniform, but the value calculated from the following formula is determined as the molding pressure. Molding pressure (MPa) = Load (N) / Vertical length × Horizontal length of pocket (mm 2 )

[0047] The atmosphere used for compression molding is preferably an inert atmosphere, in order to prevent oxidation of the partially reduced iron during molding. Specifically, this includes a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, an argon atmosphere, a krypton atmosphere, and a mixture of these gases.

[0048] The semi-reduced HBI obtained by compression molding is cooled as needed. Cooling methods are not limited, but examples include immersion cooling, spray cooling, and airflow cooling. From the viewpoint of maintaining strength, slow cooling is desirable. In this respect, airflow cooling is preferred. [Examples]

[0049] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0050] Table 1 shows the composition of the iron ore used in the production of iron ore pellets. All iron ore was crushed to a size of 100 μm or less. Here, LOI (Loss on Ignition) is the weight loss rate compared to the weight before heating when the iron ore is heated to 1000°C. Specifically, the LOI was determined by the weight loss rate when 1 g of the sample was held at 1000°C for 60 minutes in an air atmosphere using a muffle furnace.

[0051] [Table 1]

[0052] Table 2 shows the raw material mixing conditions for iron ore pellet production. Bentonite was used as a binder and limestone as a secondary raw material for basicity adjustment in all mixing conditions. Both bentonite and limestone were crushed to a size of 100 μm or less.

[0053] [Table 2]

[0054] (Example 1) To the raw materials listed in Table 2, 8% by mass of water was added based on the total amount of raw materials and water, and the mixture was granulated using a pump pelletizer to produce 10-15 mm raw pellets. The raw pellets were calcined in an electric calcination furnace at 1300°C for 10 minutes. The composition of the obtained iron ore pellets is shown in Table 3.

[0055] To produce semi-reduced iron, 500 g of iron ore pellets with the composition shown in Table 3 were passed through a reducing gas mixture of 30% hydrogen and 70% nitrogen at a rate of 15 L / min at 900°C for 130 minutes. The chemical composition of the obtained semi-reduced iron was the same as that of semi-reduced HBI shown in Table 4. Semi-reduced HBI was produced by molding this semi-reduced iron as follows.

[0056] Figure 1 shows a schematic diagram of the piston press molding machine used for molding. A heater is installed around the mold with an inner diameter of 20 mm, allowing for compression molding while maintaining a high temperature. The piston press molding machine has a function that allows the inside of the furnace to be replaced with nitrogen gas.

[0057] First, 10g of partially reduced iron was placed inside the mold, and then the pressure rod was set. Next, the inside of the furnace was replaced with nitrogen gas. Then, the temperature was raised from room temperature to 700°C at a rate of 10°C / min. After holding at 700°C for 30 minutes, it was pressurized at 218 MPa for 30 seconds. After cooling to room temperature, the molded partially reduced HBI was recovered. The major axis of the partially reduced HBI was 20 mm. Table 4 shows the results of the component analysis and apparent density measurement of the partially reduced HBI.

[0058] (Examples 2-7, Comparative Examples 1-4) Iron ore pellets were manufactured in the same manner as in Example 1, except that the blending conditions shown in Table 2 were used. The composition of the obtained iron ore pellets is shown in Table 3. Semi-reduced iron was manufactured in the same manner as in Example 1, except that the iron ore pellets having the chemical composition shown in Table 3 were used and the molding pressure was as described in Table 3. Semi-reduced HBI was obtained by molding the obtained semi-reduced iron. The chemical composition of semi-reduced iron and semi-reduced HBI was the same. Table 4 shows the component analysis and apparent density measurement results of semi-reduced HBI.

[0059] [Table 3]

[0060] (Evaluation of melting properties) Meltability was evaluated using the load softening test apparatus described in Reference 1 (Hosoya et al., Iron and Steel, Vol. 83 (1997), pp. 97-102). This test apparatus consists of two Tamman electric furnaces arranged in upper and lower stages and connected by flanges. The lower furnace is used for gas preheating, allowing the preheated gas to be introduced into the upper reduction furnace. 100 g of semi-reduced HBI was charged into the upper reduction furnace (inner diameter 85 mm), and then coke was charged to the top and bottom of this semi-reduced HBI with a layer thickness of 20 mm, and the load softening test was performed. The reducing gas composition, heating rate, and load were the same experimental conditions as in Reference 1. Specifically, up to 800°C, N2 gas (100 vol%) was used, and thereafter, reducing gas (CO: 29.4 vol%, H2: 3.6 vol%, and N2: 67.0 vol%) was circulated at a constant flow rate of 34 NL / min. The heating rate was set at 10°C / min up to 1000°C and 5°C / min thereafter. The load was kept constant at 90kPa from 800°C onward. The temperature at which the first drop was detected by the drop detector installed at the bottom of the furnace was defined as the drop start temperature. The test was terminated when the temperature reached 1550°C. In this test, a drop start temperature of 1500°C or lower was judged to indicate good meltability. This is because the molten iron temperature of a typical blast furnace is around 1500°C. The results are shown in Table 4.

[0061] [Table 4]

[0062] Examples 1-7 had a dropping initiation temperature of 1500°C or lower and exhibited good meltability. In particular, Examples 1-6 had a dropping initiation temperature of 1450°C or lower and exhibited even better meltability. Comparative Example 1, which had a low mass ratio of CaO to SiO2 (CaO / SiO2), did not drop when it reached 1550°C and exhibited poor meltability. Comparative Examples 2-3, which had a high mass ratio of CaO to SiO2 (CaO / SiO2), had a dropping initiation temperature higher than 1500°C and exhibited poor meltability. Comparative Example 4 had a low molding pressure and an apparent density of 5.0 g / cm³. 3 It did not reach its destination. [Explanation of symbols]

[0063] 12 Pressure Rod 14 molds 16. Nitrogen gas introduction piping 18 Furnace body 20 Heater 22 base 24 Semi-reduced iron 26 Exhaust piping 100 Piston Press Molding Machine

Claims

1. This is a semi-reduced HBI obtained by hot-forming semi-reduced iron, The total iron content is 80-90% by mass. The metallization rate is 70-90%. The apparent density is 5.0–5.5 g / cm³. ３ And, CaO and SiO ２ The mass ratio of (CaO / SiO ２ ) is between 0.10 and 0.70, The Al₂O₃ content is 1.0% by mass or less. Half-reduced HBI.

2. The dripping start temperature is 1500°C or lower. The half-reduced HBI according to claim 1.

3. The dripping start temperature is 1450°C or lower. The half-reduced HBI according to claim 1.

4. The major axis is 10 to 100 mm. The half-reduced HBI according to claim 1.

5. A method for producing half-reduced HBI according to any one of claims 1 to 4, It contains iron oxide-containing raw materials and auxiliary raw materials for adjusting basicity, and contains CaO and SiO ２ The mass ratio of (CaO / SiO ２ Prepare a raw material mixture in which the ratio is 0.10 to 0.70, The aforementioned raw material mixture is gas-reduced at a temperature below 1200°C to obtain semi-reduced iron having a total iron content of 80-90% by mass and a metallization rate of 70-90%. The aforementioned semi-reduced iron is molded at a temperature of 700°C or higher and a pressure of 200 MPa or higher to obtain semi-reduced HBI. A method for producing half-reduced HBI, including the method described above.

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