Method for producing high-carbon steel by recarburizing high-phosphorus molten iron

Abstract

The invention discloses a method for producing high-carbon steel by recarburizing high-phosphorus molten iron, and belongs to the technical field of steel smelting. According to the method, on the premise that the flux cost and the slag amount are not increased, the phosphorus content of tapping can be stably controlled to be 0.010% or below by conducting deep dephosphorization operation on the converter end point, the molten iron adding amount is calculated according to the phosphorus content of a steel grade finished product and the phosphorus content of recarburized molten iron, the phosphorus increase of the molten iron added into the molten steel is controlled to be 0.007-0.012%, and the molten iron content is controlled to be less than 0.010%. The produced high-carbon steel meets the control requirements of finished products, solves the technical problem of large phosphorus increase caused by blending of high-phosphorus molten iron, reduces the consumption of a carburant, reduces the smelting cost, improves the quality of molten steel, and has a very good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel smelting, and particularly relates to a method for producing high-carbon steel by increasing carbon in high-phosphorus hot metal. Background Art

[0002] When producing high-carbon steel in a converter, the usual process is to lower the carbon content at the end point, with the final carbon content ≤ 0.06%. During the tapping process, a carburizer is added for carbon increase. The disadvantages are increased costs and more impurities brought in by the carburizer, which will cause the nitrogen and hydrogen contents in the molten steel to increase, having a greater impact on the quality of the molten steel. To improve the quality of the molten steel, many steel plants use the hot metal carbon-increasing process for producing high-carbon steel, that is, lowering the carbon content at the end point and adding corresponding amounts of hot metal into the ladle after tapping for carbon increase. While the added hot metal increases the carbon content of the molten steel, it also brings in the phosphorus and sulfur contents in the hot metal. The sulfur content can be removed by making a white slag in the LF furnace, but due to the fact that the molten steel has been calmed, it is difficult to remove the phosphorus content in the subsequent processes. Therefore, high-phosphorus hot metal limits the popularization of the hot metal carbon-increasing process for high-carbon steel.

[0003] Chinese invention patent CN111334632A discloses a method for directly producing low-phosphorus foundry hot metal and its production method. The hot metal includes: P ≤ 0.06%, Cr + V + Mo + Sn + Sb + Pb + Bi + Te + As + B + Al ≤ 0.11%. It can directly produce low-phosphorus foundry hot metal with high purity, stable composition, low phosphorus content, and good comprehensive performance, and can save the process cost of hot metal dephosphorization. Using ordinary ore powder can produce hot metal that fully meets the quality requirements of high-quality foundry pig iron at the present stage; and there is no need to use high-priced coke, eliminating high-energy-consuming and highly polluting pelletizing processes such as sintering and pelletizing, with low production operation costs. However, this patent mainly prepares low-phosphorus foundry hot metal, and there are significant differences in the composition between this low-phosphorus hot metal and high-carbon steel, which is not suitable for the hot metal carbon-increasing process of high-carbon steel. Therefore, researching and developing a process for producing high-carbon steel by increasing carbon in high-phosphorus hot metal through a converter is an important topic that needs to be studied urgently at present. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for producing high-carbon steel by increasing carbon in high-phosphorus hot metal. In the process of producing high-carbon steel, the present invention uses the existing high-phosphorus hot metal to add carbon to the molten steel, solves the technical problem of large phosphorus return in high-phosphorus hot metal, and reduces the production cost of high-carbon steel.

[0005] The purpose of the present invention is achieved in the following way:

[0006] The present invention provides a method for producing high-carbon steel by increasing carbon in high-phosphorus hot metal, including the following steps:

[0007] (1) Direct tapping of hot metal into the converter. The chemical composition and weight percentage of the hot metal are as follows: C: 3.0% - 5.0%, Si: 0.1% - 0.8%, Mn: 0.05% - 0.500%, P ≤ 0.20%, S ≤ 0.060%, and the balance is Fe and inevitable impurities. The temperature of the hot metal is controlled at 1300 - 1400 °C;

[0008] (2) Adopt a deep dephosphorization process at the end point of the converter. Argon is blown from the bottom of the converter, and the flow rate of bottom - blown argon is controlled at 10 - 20 Nm 3 / min. The oxygen lance selects the slag - splashing mode, and the lance position is 1 - 3 m above the molten steel surface in the converter. The nitrogen supply intensity is controlled at 2 - 4 Nm 3 / min.t, and the nitrogen supply time is controlled at 20 - 100 seconds. During this period, 0.5 - 5 kg / t of steel of ore is added. The composition of the ore is TFe: 60 - 70%, and the balance is impurities; The temperature before tapping is controlled at 1630 - 1680 °C, the oxygen value is 300 - 400 ppm, and the phosphorus content ≤ 0.010%;

[0009] (3) During tapping, silicon - manganese alloying is carried out without adding carburizer. Argon is blown from the bottom of the ladle during tapping, and the free space in the ladle is controlled at 500 - 800 mm during tapping; Tapping with slag - blocking;

[0010] (4) Pour high - phosphorus hot metal into the ladle, and the pouring amount is 5% - 10% of the weight of the molten steel. The finished product phosphorus content ≤ 0.025%;

[0011] (5) Start blowing argon from the bottom of the ladle, and the blowing argon flow rate is controlled at 60 - 100 m 3 / h. Blow argon for 1 - 10 minutes. After the argon - blowing ends, the molten steel is lifted to the LF refining position for treatment.

[0012] Based on the above technical solution, further, the chemical composition and weight percentage of the high - carbon steel are as follows: C: 0.40% - 0.50%, Si: 0.10% - 0.30%, Mn: 0.4% - 0.8%, P ≤ 0.030%, S ≤ 0.020%, and the balance is iron and inevitable impurities.

[0013] Based on the above technical solution, further, the chemical composition and weight percentage of the high - carbon steel are as follows: C: 0.44% - 0.48%, Si: 0.17% - 0.27%, Mn: 0.5% - 0.6%, P ≤ 0.025%, S ≤ 0.015%, and the balance is iron and inevitable impurities.

[0014] Based on the above technical solution, further, the chemical composition and weight percentage of the hot metal in step (1) are as follows: C: 4.0% - 4.8%, Si: 0.1% - 0.5%, Mn: 0.10% - 0.40%, P: 0.16% - 0.2%, S: 0.010% - 0.060%, and the balance is Fe and inevitable impurities.

[0015] Based on the above technical solution, further, in step (2), the converter end-point temperature is controlled at 1650 - 1680 °C, the end-point oxygen is 400 - 500 ppm, the end-point carbon content is ≤ 0.06%, the end-point silicon content is: 0.001% - 0.005%, the end-point manganese content is: 0.03% - 0.10%, the end-point phosphorus content is: 0.010% - 0.030%, and the end-point sulfur content is 0.010% - 0.030%.

[0016] Based on the above technical solution, further, in the process of silicon-manganese alloying in step (3), the silicon-manganese content is configured to the middle limit of the steel grade, and the argon flow rate for bottom blowing argon in the ladle is controlled at 50 - 150 m 3 / h, and the argon blowing is for 1 - 10 minutes.

[0017] Based on the above technical solution, further, the chemical composition and weight percentage of the high-phosphorus hot metal in step (4) are as follows: C: 3.0% - 5.0%, Si: 0.1% - 0.8%, Mn: 0.05% - 0.500%, P ≤ 0.20%, S ≤ 0.060%, and the balance is Fe and inevitable impurities, and the hot metal temperature is controlled at 1300 - 1400 °C.

[0018] The beneficial effects of the present invention compared with the prior art are as follows:

[0019] Without increasing the flux cost and slag volume, through deep dephosphorization operation of the converter end-point, the present invention can stably control the phosphorus content in the molten steel tapped to be below 0.010%. According to the phosphorus content of the finished steel grade and the phosphorus content of the carburized hot metal, the hot metal addition amount is calculated, and the phosphorus increase in the hot metal added to the molten steel is controlled within the range of 0.007 - 0.012%. The high-carbon steel produced meets the finished product control requirements, solves the technical problem of large phosphorus increase when high-phosphorus hot metal is added, reduces the consumption of carburizer at the same time, reduces the smelting cost, improves the quality of molten steel, and has very good application prospects. Specific Embodiments

[0020] The present invention will be described in detail below in conjunction with the embodiments. However, the implementation manners of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, without creative efforts, obtaining other similar embodiments all fall within the protection scope of the present invention.

[0021] Example 1

[0022] This embodiment provides a method for producing high-carbon steel by carburizing high-phosphorus hot metal. The chemical composition and weight percentage of the high-carbon steel are as follows: carbon content: 0.48%, silicon content: 0.17%, manganese content: 0.5%, phosphorus content ≤ 0.025%, sulfur content ≤ 0.015%, and the balance is iron and inevitable impurities. It is produced by a 260-ton converter, and the process route is converter - LF furnace - continuous casting.

[0023] Specifically, it includes the following steps:

[0024] 1) Direct tapping of hot metal into the converter, with a charging amount of 265 tons (the charging amount is 20 tons less than the same period last year): The chemical composition and weight percentage of the hot metal are: C: 4.5%, Si: 0.2%, Mn: 0.100%, P: 0.16%, S: 0.030%, and the balance is Fe and inevitable impurities. The hot metal temperature is 1350°C.

[0025] 2) The end-point temperature of the converter is 1660°C, the end-point oxygen is 450 ppm, the end-point carbon content is 0.04%, the end-point silicon content: 0.003%, the end-point manganese content: 0.05%, the end-point phosphorus content: 0.018%, and the end-point sulfur content is 0.025%. A deep dephosphorization process is adopted at the end-point. Argon is blown from the bottom of the converter, and the flow rate is selected as 15 Nm 3 / min; The oxygen lance is selected in the slag splashing mode, and the nitrogen supply intensity is controlled at 3.50 Nm 3 / min.t; The lance position is controlled at 2.6 m (the lance position is the relative height, relative to the molten steel level in the converter, and the height of the converter is 11.5 m). The nitrogen supply time is 30 seconds. During this period, 0.5 tons of ore is added. The ore composition is TFe: 65%, and the rest is oxygen and impurities such as P and S. The temperature is measured at 1650°C before tapping, the oxygen value is 380 ppm, and the phosphorus content is 0.008%.

[0026] 3) Silicon-manganese alloying during tapping. The silicon-manganese content is configured to the middle limit of the steel grade. During tapping, 1.8 tons of silicon-manganese and 0.25 tons of ferrosilicon are added, and no carburizer is added. Argon is blown from the bottom of the ladle during tapping, and the large argon flow rate is 90 m 3 / h, and it is blown for 2 minutes; When adding alloys, it is necessary to ensure melting to avoid alloy caking; During tapping, the clear height of the ladle is controlled at 700 mm; Tapping is carried out with slag blocking.

[0027] 4) Move the steel ladle car to the receiving position, and pour 20 tons of the previously prepared high-phosphorus hot metal (C: 4.5%, Si: 0.2%, Mn: 0.100%, P: 0.16%, S: 0.030%, and the balance is Fe and inevitable impurities, and the hot metal temperature is 1350°C) into the ladle. The actual phosphorus return is 0.012%, and the finished product phosphorus content is 0.022%, meeting the finished product control requirements.

[0028] 5) After pouring the molten iron, start the bottom blowing argon of the ladle, blow argon at medium flow rate (60 m 3 / h) for 1 minute. After the argon blowing is completed, take samples for temperature measurement, and lift the molten steel to the LF refining station for treatment.

[0029] Example 2

[0030] This example provides a method for producing high-carbon steel by increasing carbon in high-phosphorus molten iron. The chemical composition and weight percentage of the high-carbon steel are: carbon content: 0.44%, silicon content: 0.27%, manganese content: 0.6%, phosphorus content ≤ 0.025%, sulfur content ≤ 0.015%, and the balance is iron and inevitable impurities; it is produced by a 100-ton converter, and the process route is converter - LF furnace - continuous casting;

[0031] Specifically, it includes the following steps:

[0032] 1) Directly pour the molten iron into the converter. The charging amount is 101 tons (the charging amount is reduced by 7 tons year-on-year). The chemical composition and weight percentage of the molten iron are: C: 4.35%, Si: 0.3%, Mn: 0.18%, P: 0.18%, S: 0.020%, and the balance is Fe and inevitable impurities. The temperature of the molten iron is 1330 °C.

[0033] 2) The end point temperature of the converter is 1655 °C, the end point oxygen is 420 ppm, the end point carbon content is 0.04%, the end point silicon content: 0.003%, the end point manganese content: 0.08%, the end point phosphorus content: 0.020%, and the end point sulfur content is 0.025%; a deep dephosphorization process is adopted at the end point, the converter bottom blows argon, and the flow rate is selected as 12 Nm 3 / min; the oxygen lance is selected in the slag splashing mode, and the nitrogen supply intensity is controlled at 3.0 Nm 3 / min.t; the lance position is controlled at 1.5 m (the lance position is the relative height, relative to the molten steel surface height of the converter), the nitrogen supply time is 30 seconds, and 0.2 tons of ore is added during this period. The ore composition is TFe: 65%, and the rest is oxygen content and impurities such as P and S; measure the temperature at 1640 °C before tapping, the oxygen value is 350 ppm, and the phosphorus content is 0.009%;

[0034] 3) Alloying with silicomanganese during tapping, the silicomanganese content is configured to the middle limit of the steel grade. During tapping, 0.7 tons of silicomanganese and 0.10 tons of ferrosilicon are added, and no carburizer is added. During tapping, start the bottom blowing argon of the ladle, and the large argon gas flow rate is 90 m 3 / h, blow for 2 minutes; ensure that the added alloy melts to avoid alloy caking; control the clear height of the ladle at 700 mm during tapping; tap with slag blocking;

[0035] 4) Place the steel ladle in the receiving position and pour the previously prepared high-phosphorus hot metal (C: 4.35%, Si: 0.3%, Mn: 0.18%, P: 0.18%, S: 0.020%, the balance is Fe and inevitable impurities, hot metal temperature 1330 °C) into the steel ladle. The pouring amount is 7 tons, the rephosphorization amount is 0.0126%, and the finished product phosphorus content is 0.0216%, meeting the finished product control requirements;

[0036] 5) After pouring the hot metal, start the bottom blowing argon of the steel ladle and blow argon at a medium flow rate (60 m 3 / h) for 1 minute. After the argon blowing is completed, the molten steel is lifted to the LF refining furnace.

[0037] Comparative Example 1

[0038] This comparative example provides a method for producing high-carbon steel by increasing carbon with high-phosphorus hot metal. The chemical composition and weight percentage of the high-carbon steel are: carbon content: 0.48%, silicon content: 0.17%, manganese content: 0.5%, phosphorus content ≤ 0.025%, sulfur content ≤ 0.015%, and the balance is iron and inevitable impurities; it is produced by a 260-ton converter, and the process route is converter - LF furnace - continuous casting;

[0039] Specifically, it includes the following steps:

[0040] 1) Directly pour the hot metal into the converter, with a charging amount of 265 tons (the charging amount is 20 tons less than the same period last year): The chemical composition and weight percentage of the hot metal are: C: 4.5%, Si: 0.2%, Mn: 0.100%, P: 0.16%, S: 0.030%, and the balance is Fe and inevitable impurities, and the hot metal temperature is 1350 °C.

[0041] 2) The converter end point temperature is 1660 °C, the end point oxygen is 450 ppm, the end point carbon content is 0.04%, the end point silicon content: 0.003%, the end point manganese content: 0.05%, the end point phosphorus content: 0.018%, and the end point sulfur content is 0.025%.

[0042] 3) Alloying with silicomanganese during tapping, configuring the silicomanganese content to the middle limit of the steel grade. Add 1.8 tons of silicomanganese and 0.25 tons of ferrosilicon during tapping, without adding carburizer. Start the bottom blowing argon of the steel ladle during tapping, with a large argon gas flow rate of 90 m 3 / h, blow for 2 minutes; ensure that the added alloy melts to avoid alloy caking; control the free space in the steel ladle at 700 mm during tapping; tap steel with slag blocking.

[0043] 4) Place the steel ladle in the receiving position and pour the pre-prepared high-phosphorus hot metal (C: 4.5%, Si: 0.2%, Mn: 0.100%, P: 0.16%, S: 0.030%, the balance being Fe and inevitable impurities, hot metal temperature 1350°C) into the steel ladle. The pouring amount is 20 tons. The actual phosphorus return is 0.012%, and the finished product phosphorus content is 0.030%, exceeding the finished product control requirement (the upper limit of the finished product phosphorus content is 0.025%). This ladle of steel is cold recycled.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing high-carbon steel by carburizing high-phosphorus hot metal, characterized in that, It includes the following steps: (1) Direct tapping of converter hot metal. The chemical composition and weight percentage of the hot metal are as follows: C: 3.0% - 5.0%, Si: 0.1% - 0.8%, Mn: 0.05% - 0.500%, P ≤ 0.20%, S ≤ 0.060%, and the balance is Fe and inevitable impurities. The temperature of the hot metal is controlled at 1300 - 1400°C; (2) At the end of the converter blowing process, a deep dephosphorization process is adopted. Argon is blown from the bottom of the converter, and the flow rate of bottom blowing argon is controlled at 10 - 20 Nm 3 / min. The oxygen lance is selected in the slag splashing mode, and the lance position is 1 - 3 m above the molten steel surface in the converter. The nitrogen supply intensity is controlled at 2 - 4 Nm 3 / min.t, and the nitrogen supply time is controlled at 20 - 100 seconds. During this period, 0.5 - 5 kg of ore per ton of molten steel is added. The composition of the ore is: TFe: 60 - 70%, and the balance is impurities. The temperature before tapping is controlled at 1630 - 1680 °C, the oxygen content is 300 - 400 ppm, and the phosphorus content is ≤0.010%; (3) During tapping, silicon-manganese alloying is carried out without adding carburizer. Bottom argon blowing of the ladle is started during tapping, and the free space in the ladle is controlled at 500 - 800 mm during tapping; slagging-off tapping; (4) Pour high-phosphorus hot metal into the ladle, and the pouring amount is 5% - 10% of the weight of the molten steel, and the finished product phosphorus content ≤ 0.025%; (5) Turn on the bottom argon blowing of the ladle, and control the argon blowing flow rate at 60 - 100 m 3 / h. Argon is blown for 1 - 10 minutes. After the argon blowing is completed, the molten steel is lifted to the LF refining position for treatment.

2. The method according to claim 1, characterized in that, The chemical composition and weight percentage of the high-carbon steel are as follows: C: 0.40% - 0.50%, Si: 0.10% - 0.30%, Mn: 0.4% - 0.8%, P ≤ 0.030%, S ≤ 0.020%, and the balance is iron and inevitable impurities.

3. The method according to claim 1, characterized in that The chemical composition and weight percentage of the hot metal described in step (1) are as follows: C: 4.0% - 4.8%, Si: 0.1% - 0.5%, Mn: 0.10% - 0.40%, P: 0.16% - 0.2%, S: 0.010% - 0.060%, and the balance is Fe and inevitable impurities.

4. The method according to claim 1, wherein In step (2), the converter end-point temperature is controlled at 1650 - 1680°C, the end-point oxygen is 400 - 500 ppm, the end-point carbon content ≤ 0.06%, the end-point silicon content: 0.001% - 0.005%, the end-point manganese content: 0.03% - 0.10%, the end-point phosphorus content: 0.010% - 0.030%, and the end-point sulfur content is 0.010% - 0.030%.

5. The method according to claim 1, characterized in that, In step (3), bottom argon blowing of the ladle lasts for 1 - 10 minutes.

6. The method according to claim 1, characterized in that The chemical composition and weight percentage of the high-phosphorus hot metal described in step (4) are as follows: C: 3.0% - 5.0%, Si: 0.1% - 0.8%, Mn: 0.05% - 0.500%, P ≤ 0.20%, S ≤ 0.060%, and the balance is Fe and inevitable impurities. The temperature of the hot metal is controlled at 1300 - 1400°C.