Manufacturing method for low-phosphorus high-carbon steel

Abstract

To provide a modified brown coal briquette capable of saving energy by charging the same into a converter or an electric furnace in steelmaking, of reducing phosphorus while suppressing generation of carbon dioxide by reforming carbon dioxide into carbon monoxide, and of melting and producing high-grade high-carbon steel.SOLUTION: A modified brown coal briquette is obtained by molding and drying modified brown coal obtained by dehydrating and de-oiling brown coal to raise calorific value to enable long-distance transportation, and an ash composition is set to a predetermined ash composition.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a modified lignite briquette that can be used to produce high-quality high-carbon steel with dephosphorization while suppressing carbon dioxide generation. Low-grade lignite, which has a high moisture content, a high oxygen content, a low calorific value, is prone to pulverization by drying, and is not suitable for long-distance transportation or storage, is dehydrated and deoiled to increase its calorific value and enable long-distance transportation. Furthermore, by adding the modified lignite that meets a predetermined ash composition, molding and drying it into briquettes, and using it in a converter or an electric furnace in steelmaking, high-quality high-carbon steel can be produced.

Background Art

[0002] Conventionally, when steelmaking, briquettes of amorphous graphite are added to a converter or the like to supplement the carbon content, and the carbon in the pig iron in the converter and the carbon in the amorphous graphite briquettes are converted into carbon monoxide to suppress the generation of carbon dioxide.

[0003] For example, there is a prior art of a converter blowing operation method that can suppress the generation amounts of carbon dioxide and nitrogen by adding low-strength molding carbon (briquettes) for heat supply to the converter blowing operation (Reference 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The prior art described in Patent Document 1 is excellent in that it can produce steel with a relatively high carbon content by adding earthy graphite briquettes with a compressive strength of 90 kgf or less to a converter and smelting them, thereby suppressing the generation of carbon dioxide and nitrogen. However, it has the problem that it is not effective in reducing the phosphorus content of the steel, so it is not possible to obtain high-quality steel. Furthermore, conventionally, when a dephosphorization reaction is performed, a decarburization reaction also occurs simultaneously, so there is also the problem that low-phosphorus, high-carbon steel cannot be produced.

[0006] The present invention solves this problem and provides a modified lignite briquette that, when charged into a converter or electric furnace during steelmaking, can suppress the generation of carbon dioxide by modifying it into carbon monoxide, while simultaneously reducing phosphorus content and enabling the production of high-quality, high-carbon steel. [Means for solving the problem]

[0007] To achieve the above objective, the present invention relates to claim 1. Manufacturing method for low-phosphorus high-carbon steel This involves dehydrating and deoiling the lignite to increase its calorific value. geta Modified lignite briquettes are made by molding and drying modified lignite, The bulk density is 1.0 to 7.0 g / cc. ash composition However, CaO / SiO 2 By adding modified lignite briquettes with a carbon content of ≥0.3 to a converter or electric furnace, the foaming height of the slag is increased, reducing rephosphorustion, and high-carbon steel is produced by retaining carbon in the steel. It is characterized by the following:

[0008] This invention The revised version Limestone briquettes are manufactured by modifying lignite, which is unsuitable for long-distance transport and storage because it has a high moisture content, high oxygen content and low calorific value, and is prone to spontaneous combustion when dried and turns into powder. This modification increases the calorific value by dehydrating and deoiling the modified lignite, while retaining a certain amount of moisture prevents powdering and spontaneous combustion, thus enabling long-distance transport and storage. The modified lignite is then carbonized, the ash composition is adjusted to a predetermined level (especially the amounts of CaO / SiO2 and Fe), kneaded, molded, and then dried in a dryer.

[0009] invention The revised versionSince the modified lignite briquettes satisfy the required ash composition, they can be added to converters or electric furnaces during steelmaking. This suppresses carbon dioxide generation, and during smelting, the phosphorus in the pig iron is converted to an unstable P2O5 state. Then, by adjusting the ash composition, the CaO abundant in the modified lignite is converted to (CaO)4·P2O5 and fixed within the slag. Thus, dephosphorization can be reliably achieved. This allows for the production of high-quality low-phosphorus, high-carbon steel while suppressing carbon dioxide generation.

[0010] Furthermore, the present invention relates to claim 2. Manufacturing method for low-phosphorus high-carbon steel teeth, Modified lignite briquettes are made by dehydrating and deoiling lignite to increase its calorific value, then molding and drying the modified lignite. The bulk density is 1.0 to 7.0 g / cc. By adding modified lignite briquettes with an ash composition of t-Fe ≥ 5 (wt%) to a converter or electric furnace, the foaming height of the slag is increased, reducing rephosphorustion, and high-carbon steel is produced by retaining carbon in the steel. It is characterized by the following:

[0011] By adopting this configuration , revised Because the lignite briquettes can float in the steel bath within the converter instead of sinking, dephosphorization and carbon dioxide conversion to carbon monoxide can be reliably carried out in the slag at the top of the steel bath.

[0012] Furthermore, the present invention The revised version Low-quality lignite briquettes ,before The ash composition of the modified lignite is CaO / SiO2 ≥ 0.3. ru.

[0013] By adopting this configuration , revised Lignite briquettes can shorten the collapse time of bubbles in the slag. Bubbles are formed from minute particles that grow and collapse as they coalesce, so the shorter the collapse time, the faster the bubble diameter decreases. The smaller the bubble diameter, the higher the foaming height of the slag in the converter, reducing rephosphorization and ensuring a reliable dephosphorization reaction. This allows phosphorus to be fixed in the slag while retaining carbon in the steel, thus enabling the production of high-carbon steel. Therefore, high-carbon steel can be produced by performing the dephosphorization reaction while suppressing the generation of carbon dioxide.

[0014] Furthermore, the present invention The revised version Low-quality lignite briquettes ,beforeThe ash composition of the modified brown coal briquette is such that t-Fe ≥ 5 (wt%) ru.

[0015] By adopting this configuration , revised For the brown coal briquette, the smaller the diameter of the slag bubbles, the greater the buoyancy of the slag in the converter, the higher the froth height, the less rephosphorization, and the dephosphorization reaction can be reliably carried out. Phosphorus can be immobilized in the slag and carbon can be left in the steel, so high-carbon steel can be produced. Therefore, while suppressing the generation of carbon dioxide, the dephosphorization reaction can be carried out to produce high-carbon steel.

[0016] Also, in the present invention low The method for producing phosphorus high-carbon steel is ,before Using the above-mentioned modified brown coal briquette Ta.

[0017] By adopting this configuration , low If the method for producing phosphorus high-carbon steel is used, since a modified brown coal briquette satisfying a predetermined ash composition is used, low-phosphorus high-carbon steel can be produced.

Advantages of the Invention

[0018] By using the modified brown coal briquette of the present invention in a converter or an electric furnace, while suppressing the generation of carbon dioxide, dephosphorization can be carried out to suppress phosphorus to a predetermined value or less, and high-carbon steel with excellent carbon quality can be produced. Therefore, environmentally friendly and high-quality steel can be produced. In addition, since the sensible heat of the exhaust gas of the converter gas can be utilized, it can contribute to energy saving.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic plan view and a front view of the modified brown coal briquette according to this embodiment. [Figure 2] A table showing an example of the property comparison between earthy black coal and modified brown coal [Figure 3] It is a schematic diagram of the test converter used in this example. [Figure 4] A graph showing the blowing conditions in the test converter. [Figure 5] A graph showing the relationship between ηCO(CO2 / (CO+CO2)(%)) and converter gas temperature. [Figure 6] A graph showing the relationship between blowing time and ηCO(CO2 / (CO+CO2)(%)). [Figure 7] A graph showing the relationship between blowing time and slag height in a test converter. [Figure 8] A graph showing the relationship between smelting time and phosphorus content in molten iron in a test converter. [Figure 9] A graph showing the relationship between blowing time and carbon content in molten iron in a test converter. [Figure 10] This is a schematic cross-sectional view showing the conditions during the dephosphorization reaction of the test converter when earthy graphite briquettes are added and when reformed lignite briquettes are added. [Figure 11] A graph showing the relationship between the iron concentration in the slag and the diameter of bubbles generated at the slag-metal interface. [Figure 12] A graph showing the relationship between slag basicity (CaO / SiO2) and the bubble decay time constant τ in a converter. [Modes for carrying out the invention]

[0020] Preferred embodiments of the present invention are described below. However, the present invention is not limited to these embodiments, and any modifications, improvements, etc., that can achieve the objectives of the present invention are included within the scope of the present invention.

[0021] As shown in Figure 1, the modified lignite briquette 1 according to this embodiment is, for example, roughly square with rounded corners and sides of approximately 42 mm when viewed from above, and has a three-dimensional shape with a thickness of approximately 30 mm and a bulge in the center when viewed from the front, but is not particularly limited. The modified lignite briquette 1 is manufactured by dehydrating and deoiling lignite to produce modified lignite, which is then carbonized, kneaded, molded, and dried.

[0022] An example of a method for producing modified lignite briquettes of this embodiment is shown. The lignite used as the raw material for modified lignite briquettes 1 has a high moisture and oxygen content, resulting in a low calorific value. Furthermore, it easily pulverizes upon drying and spontaneously ignites, making it unsuitable for long-distance transport and storage. This lignite is, for example, treated with water to make a lignite water slurry, then subjected to hydrothermal treatment at 350°C and 240 atmospheres with the addition of a catalyst. After that, the gas is removed by depressurization, and the water and oil are separated by distillation to produce modified lignite. Since the modified lignite is dehydrated, it has a high calorific value. Also, because it retains some moisture, it is less likely to pulverize and does not spontaneously ignite, so it can be safely transported over long distances from overseas by ship. An example of the properties of modified lignite (after carbonization) is shown in Figure 2. As shown in Figure 2, compared to conventionally used clay graphite in steelmaking, it has a higher total calorific value of 7,480 cal / kg, a high iron concentration (t-Fe) of 18.9 in the ash composition (wt%), and a high basicity of 0.51 in CaO / SiO2.

[0023] The modified lignite is carbonized, then adjusted to a predetermined ash composition, kneaded, molded, and dried to produce the modified lignite briquette 1 of this embodiment. Note that modified lignite that already satisfies the predetermined ash composition before adjustment, such as the lignite with the ash composition shown in Figure 2, does not require further adjustment of the ash composition.

[0024] In this embodiment, the modified lignite briquette 1 is solidified, molded, and dried, and preferably has a bulk density of 1.0 to 7.0 g / cc. This bulk density allows it to float rather than sink in the steel in the converter, so that dephosphorization, carbon dioxide conversion to carbon monoxide, and other dephosphorization reactions can be reliably carried out in the slag at the top of the steel bath.

[0025] The modified lignite briquette 1 according to this embodiment is used by being fed into a converter or electric furnace along with the main raw material pig iron and other auxiliary raw materials during steelmaking. [Examples]

[0026] Next, an example of how to use the modified lignite briquette 1 according to this embodiment is shown. An experiment using the modified lignite briquette 1 according to this embodiment was conducted using the test converter 100 shown in Figure 3. The test conditions were as follows: the size of the test converter 100 was 0.5 tons, oxygen blown from above, inert gas blown from below, and the internal volume of the iron shell of the test converter was 0.9 m³. 3 Brick interior volume 0.4m 3 , top-blown oxygen flow rate ratio ~4.0Nm 3 For bottom blowing, the gas used is nitrogen or argon, with a gas flow rate of approximately 0.16 Nm³ / min / ton. 3 The procedure was performed with a rate of 1 / min / ton, 4 tuyeres, and a single-hole tuyere configuration. The molten iron (metal) 2 was 400mm deep, with a slag-metal interface 4 above it, and slag 3 floating above the molten steel 2. Then, H slag The height from the bottom of the test converter to the top of the slag is measured, and the P and C concentrations of the manufactured steel are determined.

[0027] Then, under the blowing conditions shown in Figure 4, oxygen was blown upwards (2.0 Nm). 3 ( / min / ton) Blowing time 30 minutes and Ar bottom blowing (0.12Nm) 3 The process was carried out for 30 minutes at a rate of 0.5 kg / min. Additionally, 20 charges of modified lignite briquettes (total 20 kg / ton) were applied for 13 minutes.

[0028] The results are shown in Figure 5. In this embodiment, the modified lignite briquette 1 was added, and the soil-like graphite was blown for 30 minutes, while the sample without the addition was blown for 25 minutes. As can be seen from this figure, when the modified lignite briquette 1 was added according to this embodiment, ηCO(CO2 / (CO+CO2)) was lower than in the sample without the addition and in the sample with soil-like graphite. C(sol) + CO2(g) = 2CO(g) This accelerated the process, and the reforming reaction of CO2 to CO was confirmed. Furthermore, since the amount of heat absorbed was compensated for by the sensible heat of the exhaust gas of the test converter, an energy-saving effect was also confirmed.

[0029] Figure 6 shows the relationship between blowing time and ηCO(CO2 / (CO+CO2)). From this figure, it can be seen that when the modified lignite briquette 1 according to this embodiment is used, the generation of CO2 can be kept low from the time the briquette 1 is added. Therefore, when the modified lignite briquette 1 according to this embodiment is used, CO2 generation is suppressed and environmentally friendly operations can be performed.

[0030] Furthermore, Figure 7 shows the relationship between blowing time and slag height H, Figure 8 shows the relationship between blowing time and phosphorus P concentration in metal 2, and Figure 9 shows the relationship between blowing time and carbon C concentration in metal 2. From Figures 8 and 9, it can be seen that when the modified lignite briquette 1 of this embodiment is used, the P concentration becomes approximately 0% after 30 minutes, but the C concentration is approximately 1.5%. Therefore, it was found that high-carbon steel can be produced while sufficiently dephosphorizing. Accordingly, when the modified lignite briquette 1 of this embodiment is used, dephosphorization can be reliably performed and high-carbon steel with a carbon content of 0.5% or more can be produced, that is, CO2 generation can be suppressed and dephosphorization can be reliably performed, and high-quality high-carbon steel can be produced.

[0031] Furthermore, Figure 7 shows that when performing a dephosphorization reaction while maintaining the carbon concentration, using the modified lignite briquette 1 according to this embodiment results in a higher slag height H compared to cases without additives or when using soil-like graphite.

[0032] Therefore, after thorough investigation, as shown in Figure 10, the dephosphorization reaction in conventional earthy graphite briquettes involves the reaction of P in metal 2 with O2 from top-blown smelting at the slag-metal interface 4. 4P + 5O2 = 2(P2O5) However, this state is unstable, and P returns to the metal 2 (re-phosphorusting), so dephosphorization is not reliably performed. However, since the modified lignite briquette 1 according to this embodiment has a high basicity CaO / SiO2, at the slag-metal interface 4 4P + 5O2 + 8CaO = 2(P2O5) + 8CaO As a result, within slag 3, the slag height H increases. 2(P2O5) + 8CaO = 2(CaO)4·P2O5 As a result, P is fixed within the slag 3, ensuring dephosphorization. Furthermore, by increasing the slag height H, it was found that rephosphorization is reduced, ensuring dephosphorization and enabling the production of high-carbon steel.

[0033] Furthermore, it was found that increasing the slag height H requires reducing the diameter of the bubbles and shortening the bubble collapse time constant τ. Therefore, to reduce the diameter of the bubbles, as shown in Figure 11, by referring to Graph 101 in "Ogawa, Yuji; Tokumitsu, Naoki; Iron and Steel, 87 (2001) 1, 14-20," it was found that if the amount of t-Fe 11 in the ash composition of the modified lignite briquette 1 is 5 (wt%) or more, preferably 10 or more, the bubbles will become smaller. Also, to shorten the bubble collapse time constant τ, as shown in Figure 12, by referring to Graph 111 in "Tachikawa, Masayoshi; Shimada, Michihiko; Ishibashi, Masayoshi; Shiraishi, Koremitsu: Iron and Steel 55 (1969) S92," it was found that if the CaO / SiO2 ratio in the modified lignite briquette 1 is 1.3 or more, the bubble collapse time constant τ will be shortened. Here, since CaO is added as a secondary raw material during steelmaking, by correcting for its ratio of 1.0, the CaO / SiO2 value of the modified lignite briquette (12) should be 0.3 or higher, preferably 0.5 or higher, according to the correction graph 112. [Industrial applicability]

[0034] It can be widely used in the field of steelmaking. [Explanation of Symbols]

[0035] 1: Modified lignite briquettes 2: Molten steel (metal) 3: Slag 3-1: Slag (stable state) 4: Slag-metal interface 5: Top surface of the slag H slag Height from the bottom of the test converter to the top of the slag 11: Line where t-Fe≧5(wt%) 12: The line where CaO / SiO2 ≥ 0.3 100: Test converter 101: A line showing the relationship between the iron concentration in the slag and the diameter of the slag bubbles generated at the slag-metal boundary. 111: Line showing the relationship between iron concentration in slag and bubble diameter generated at the slag-metal interface. For the 112:111 line, a correction line has been created by reducing it by 1.0 to account for auxiliary materials.

Claims

1. A method for producing low-phosphorus high-carbon steel, characterized by adding modified lignite briquettes, which are obtained by dehydrating and deoiling lignite to increase its calorific value, molding and drying the modified lignite briquettes having a bulk density of 1.0 to 7.0 g / cc and an ash composition of CaO / SiO₂ ≥ 0.3, to a converter or electric furnace, thereby increasing the foaming height of the slag, reducing rephosphorusting, and producing high-carbon steel by leaving carbon in the steel.

2. A method for producing low-phosphorus high-carbon steel, characterized by adding a modified lignite briquette, which is obtained by molding and drying modified lignite obtained by dehydrating and deoiling lignite to increase its calorific value, having a bulk density of 1.0 to 7.0 g / cc and an ash composition of t-Fe ≥ 5 (wt%), to a converter or electric furnace, thereby increasing the foaming height of the slag, reducing rephosphorusting, and producing high-carbon steel by leaving carbon in the steel.

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