Semi-reduced HBI and production method therefor

Abstract

Provided is semi-reduced HBI for which semi-reduced iron produced from low-grade iron ore or iron ore pellets can be used as a raw material and which has excellent meltability and has an apparent density that makes marine transportation possible. The semi-reduced HBI is obtained by hot forming semi-reduced iron. The semi-reduced HBI has a total iron content of 80-90 mass%, a metallization rate of 70-90%, an apparent density of 5.0-5.5 g / cm3, and a mass ratio of CaO to SiO2 (CaO / SiO2) of 0.10-0.70.

Description

Partially reduced HBI and method for producing the same

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

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

[0003] Decarbonizing the steel industry has become a global challenge, particularly regarding CO2 emissions from steelmaking processes. ２ As one measure to reduce emissions, there is a need to expand the production and use of HBI (Heat-Based Iron) made from reduced iron obtained by reducing 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. In order 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 during the production of iron ore pellets, 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.

[0007] Japanese Patent Publication No. 2009-79292 Japanese Patent Publication No. 2008-127580

[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 production. 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 hinders the permeability of the furnace.

[0009] Also, according to the International Maritime Solid Bulk Cargo Code (IMSBCC Code), which is a regulation regarding the marine transportation of HBI, HBI is classified as DRI (A), formed at a temperature of 650°C or higher, and formed into a briquette shape having a density of 5000 kg / m ３ (5 g / cm ３ ) or more.

[0010] However, Patent Documents 1 and 2 do not describe low-grade HBI having excellent meltability and an apparent density that can be transported by sea.

[0011] An object of the present disclosure is to provide a 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 can be transported by sea.

[0012] The content of the present disclosure includes the following aspects. <Aspect 1> A semi-reduced HBI obtained by hot-forming semi-reduced iron, having a total iron content of 80 to 90% by mass, a metallization rate of 70 to 90%, an apparent density of 5.0 to 5.5 g / cm ３ and a mass ratio (CaO / SiO ２ ) of CaO to SiO ２ of 0.10 to 0.70. <Aspect 2> The semi-reduced HBI according to Aspect 1, having an Al ２ O ３ content of 3.0% by mass or less. <Aspect 3> The semi-reduced HBI according to Aspect 1 or 2, having a dropping start temperature of 1500°C or lower. <Aspect 4> The semi-reduced HBI according to Aspect 1 or 2, having a dropping start temperature of 1450°C or lower. <Aspect 5> The semi-reduced HBI according to any one of Aspects 1 to 4, having a major diameter of 10 to 100 mm. <Aspect 6> A method for producing the semi-reduced HBI according to any one of Aspects 1 to 5, including an iron oxide-containing raw material and a raw material for adjusting basicity, and having a mass ratio (CaO / SiO ２ ) of CaO to SiO ２Prepare a raw material mixture in which () is 0.10 to 0.70, gas-reducing the raw material mixture at a temperature below 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 shaping 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 this.

[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 can be transported by sea.

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

[0015] Hereinafter, embodiments of the semi-reduced HBI and its manufacturing method of the present disclosure will be described in detail. However, the semi-reduced HBI and its manufacturing method of the present disclosure are not limited to the following embodiments.

[0016] In this specification, "~" indicating a numerical range is used to mean including the numerical values described before and after as the lower limit value and the upper limit value, unless otherwise specified. When multiple upper limit values or lower limit values are described, a numerical range can be created from all combinations of the upper limit value and the lower limit value. Similarly, when multiple numerical ranges are described, separate numerical ranges can be created by individually selecting and combining the upper limit value and the lower limit value from those numerical ranges.

[0017] In this specification, HBI means "reduced iron having an apparent density of 5 g / cm or more briquetted at a temperature of 650 °C or higher" as described in JIS M8700:2013 "Iron Ore and Reduced Iron - Terms". In this specification, "semi-reduced" is used to mean excluding those that are completely reduced, that is, those with a metallization rate of 100%. ３ The above-mentioned apparent density.

[0018] Generally, low-grade HBI has poorer meltability compared to high-grade HBI. The inventors considered the reason for 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, carburizing 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 carburizing and drips down to the bottom of the furnace. On the other hand, in the case of low-grade HBI, SiO in the HBI ２ Al ２ O ３ These gangue components physically hinder contact between metallic iron and coke. As a result, carburizing is inhibited and meltability deteriorates. Therefore, the inventors hypothesized that if the melting point of the gangue components could be lowered, carburizing would proceed more easily and meltability would improve. Experimental investigations revealed that CaO and SiO ２ The mass ratio of (CaO / SiO ２ It was found that the melting properties of HBI improved by setting the ratio to a range of 0.10 to 0.70. Although not bound by any particular theory, this is because CaO and SiO ２ The mass ratio of (CaO / SiO ２ This is thought to be because setting the value in the range of 0.10 to 0.70 causes the iron oxide and gangue components in HBI to form a low-melting-point slag.

[0019] [Semi-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 CaO and SiO ２ The mass ratio of (CaO / SiO ２ ) is a semi-reduced HBI with a value of 0.10 to 0.70. CaO and SiO ２ The mass ratio of (CaO / SiO ２ By setting the ratio to a range of 0.10 to 0.70, the solubility of half-reduced HBI can be increased. By increasing the amount of CaO, the solubility of CaO and SiO ２ The mass ratio of (CaO / SiO ２If the ) value is increased too much, the amount of CaO, which has a lower density than metallic iron, increases, and the apparent density decreases.

[0020] The total iron content of semi-reduced HBI is preferably 82 to 90% by mass, more preferably 85 to 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, thereby 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] Al of half-reduced HBI ２ O ３ The content 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. ２ O ３ When the content is 3.0% by mass or less, the viscosity of the formed slag is low, resulting in better melting of the semi-reduced HBI. ２ O ３ There is no particular lower limit to the content, but it 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 melting properties. 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] SiO of half-reduced HBI ２The content 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. ２ The 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 semi-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 semi-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)". Specifically, it is measured by the bromine methanol solution / EDTA2Na solution titration method. The metallization rate is calculated using 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. SiO of half-reduced HBI ２ The content is based on the Si mass measured by ICP emission spectrometry. ２ These are converted values. CaO and SiO ２ The mass ratio of (CaO / SiO ２ ) These CaO equivalent values ​​and SiO ２ It is calculated from the converted value.

[0027] Al of half-reduced HBI ２ O ３ The content is based on the Al mass measured by ICP emission spectrometry. ２ O ３ This is a converted value.

[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 / cm³３ 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 a half-reduced HBI is determined according to its shape as follows: For a pillow-shaped structure, 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 the HBI is viewed from directly above 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 the largest. Here, "tangent to the contour" means passing through at least one point on the contour and not passing through the inside of the HBI when the HBI is viewed from directly above. 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 partially reduced HBI for blast furnaces.

[0034] [Method for producing half-reduced HBI] One embodiment of the method for producing half-reduced HBI includes an iron oxide-containing raw material and a secondary raw material for adjusting basicity, and comprises CaO and SiO ２ The mass ratio of (CaO / SiO ２ The process includes: preparing a raw material mixture having a ratio of 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. CaO and SiO in semi-reduced iron ２ The mass ratio of (CaO / SiO ２The raw material mixture consists of CaO and SiO such that the ratio is between 0.10 and 0.70. ２ The mass ratio of (CaO / SiO ２ Use those with a value between 0.10 and 0.70.

[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 for adjusting basicity are not particularly limited as long as they yield CaO when oxidized (also called CaO sources). Examples of auxiliary raw materials for adjusting basicity include limestone, quicklime, slaked lime, dolomite, and calcined dolomite. CaO and SiO in the raw material mixture ２ The mass ratio of (CaO / SiO ２ This 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, for example, by the reducing gas flow rate, reducing gas concentration, reduction time, reduction temperature, etc.

[0041] When producing partially reduced iron using a rotary heat furnace (RHF) as described in Patent Document 1, it is essential to blend carbon material as a reducing agent with the iron oxide-containing raw material. Therefore, CO2 is released during production. ２ A large amount of CO2 is emitted. In addition, the reduction temperature needs to be 1200°C or higher in order to improve the metallization rate and density of the semi-reduced iron. On the other hand, when semi-reduced iron is produced by gas reduction at temperatures below 1200°C, such as in the shaft furnace reduction process, the addition of carbon material to the iron oxide-containing raw material is unnecessary. 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 temperatures below 1200°C is advantageous in terms of CO2 emissions during production. ２ It has the advantage of reducing emissions. 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 include piston press molding machines and roller press molding machines (also called briquetting machines).

[0043] When compressing semi-reduced iron, which has a metallization rate of over 90%, raising the molding temperature to 650°C or higher makes the metallic iron more susceptible to plastic deformation, resulting in an apparent density of 5.0 g / cm³. ３ This makes it possible to achieve the above. On the other hand, the apparent density of semi-reduced iron with a metallization rate of 90% or less is 5.0 g / cm³. ３ To achieve the above, the iron oxide also needs to be plastically deformed. From the perspective of plastically deforming the iron oxide, the molding conditions are a molding temperature of 700°C or higher and a molding pressure of 200 MPa or higher.

[0044] If the molding temperature is set too high, wear and tear on the molding machine's mold is likely to occur. Therefore, the molding temperature is preferably 800°C or lower. To maintain a high temperature of semi-reduced iron, a heating furnace may be provided between the reduction furnace and the molding machine as needed. Alternatively, a molding machine with a heating function may be used.

[0045] If the molding pressure is excessively high, wear and tear on the molding machine's mold is likely to occur. Therefore, the molding pressure is preferably 400 MPa or less.

[0046] Molding pressure refers to the surface pressure applied to the molded product. In the case of a roller press molding machine, the surface pressure applied to the sample is presumed to be uneven because the pockets on the roller surface, i.e., the depressions for compressing and molding the semi-reduced iron, are not flat. However, the value calculated from the following formula is determined as the molding pressure: Molding pressure (MPa) = Load (N) / Length of pocket × Width (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. While not limited to a specific method, cooling methods 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.

[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 particle 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]

[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]

[0054] (Example 1) To the blended raw materials listed in Table 2, water was added at a rate of 8% by mass based on the total amount of the blended raw materials and water, and the mixture was granulated in 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, 10 g of partially reduced iron was placed inside the mold, and then the pressurizing 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 produced 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 produced 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 results of the component analysis and apparent density measurement of semi-reduced HBI.

[0059]

[0060] (Evaluation of Meltability) 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 gas preheated to a high temperature 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 the 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. That is, the gas was N up to 800°C. ２ Gas (100% by volume), reducing gas (CO: 29.4% by volume, H) above 800°C ２: 3.6% by volume, and N ２ A 67.0% resistance rating was passed through the furnace at a constant flow rate of 34 NL / min. The heating rate was 10°C / min up to 1000°C and 5°C / min thereafter. The load was kept constant at 90 kPa from 800°C onwards. 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 onset temperature. The test was terminated when the temperature reached 1550°C. In this test, a drop onset 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]

[0062] Examples 1 to 7 had a dropping start temperature of 1500°C or lower and exhibited good meltability. In particular, Examples 1 to 6 had a dropping start temperature of 1450°C or lower and exhibited even better meltability. CaO and SiO ２ The mass ratio of (CaO / SiO ２ Comparative Example 1, which had a low ) value, did not drop when it reached 1550°C, indicating poor meltability. CaO and SiO ２ The mass ratio of (CaO / SiO ２ Comparative Examples 2 and 3, which had high values, had a dropping start temperature higher than 1500°C and 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.

[0063] 12 Pressurized rod 14 Mold 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. 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 CaO and SiO ２ The mass ratio of (CaO / SiO ２ A semi-reduced HBI with a value between 0.10 and 0.

70.

2. Al ２ O ３ The semi-reduced HBI according to claim 1, wherein the content is 3.0% by mass or less.

3. The semi-reduced HBI according to claim 1 or 2, wherein the dropping start temperature is 1500°C or lower.

4. The semi-reduced HBI according to claim 1 or 2, wherein the dropping start temperature is 1450°C or lower.

5. The semi-reduced HBI according to claim 1 or 2, wherein the major axis is 10 to 100 mm.

6. A method for producing half-reduced HBI according to claim 1 or 2, comprising an iron oxide-containing raw material and a secondary raw material for adjusting basicity, comprising CaO and SiO ２ The mass ratio of (CaO / SiO ２ A method for producing half-reduced HBI, comprising: preparing a raw material mixture having a ratio of 0.10 to 0.70; gas-reducing the raw material mixture at a temperature of less than 1200°C to obtain half-reduced iron having a total iron content of 80 to 90% by mass and a metallization rate of 70 to 90%; and molding the half-reduced iron at a temperature of 700°C or higher and a pressure of 200 MPa or higher to obtain half-reduced HBI.

Images