A short process smelting method for high phosphorus steel

Abstract

The present application relates to a kind of high phosphorus steel short process smelting method, mainly solve the problem of long production turnover time, poor castability of existing high phosphorus steel, the chemical composition of high phosphorus steel includes according to mass percentage content: [C]:0.07-0.1%, [Si]:0.3-0.4%, [Mn]:0.4-0.5%, [P]:0.07-0.11%, [S]:0-0.0125%, [Ti]:0.02-0.035%, [Cr]:0.3-0.4%, [Cu]:0.25-0.33%, the balance is iron and inevitable impurities.

Description

Technical Field

[0001] This invention relates to a smelting method, specifically a short-process smelting method for high-phosphorus steel, belonging to the field of iron and steel metallurgical technology. Background Technology

[0002] The traditional high-phosphorus steel smelting process follows the BOF-AR-LF-CC route. Converter smelting employs a conventional high-basicity, large-slag-volume, low-phosphorus steel smelting process. During tapping, ferrophosphorus is added to the molten steel for preliminary phosphorus alloying to meet the phosphorus content requirements of the steel grade. This method does not fully utilize the phosphorus in the molten iron, resulting in significant cost waste. The LF furnace serves as a buffer in the production process, incorporating heating, slag formation, desulfurization, and alloying processes. Phosphorus and titanium alloys are added to the LF furnace using an alloy feeding system. Conventional smelting methods aim to control the final phosphorus content in the converter to 0.01%. The process involves adding ferrophosphorus to the molten steel for alloying, using aluminum for deep deoxidation at tapping, and adding ferrotitanium alloys for further alloying. This process introduces a large amount of oxide inclusions, affecting continuous casting castability and causing cost waste.

[0003] A search of patent documents revealed a method for smelting high-phosphorus steel in a converter using low-temperature, low-silicon molten iron, Chinese patent application number CN201210296289.7. The method discloses adding scrap steel to the converter; adding quicklime initially and lowering the oxygen lance position by 10-20 cm below the normal position for oxygen blowing; adding dolomite all at once after 50-60 seconds of oxygen blowing; raising the oxygen lance position to the normal oxygen blowing position after 90-110 seconds of oxygen blowing and adding quicklime again; controlling the final steel temperature at 1670-1690℃, the final slag basicity at 2.5-3, and the total slag amount at the smelting endpoint at 40-50 kg / ton of steel. This method fully utilizes the low-temperature, low-silicon molten iron's ability to reduce phosphorus removal rates in the smelting of high-phosphorus steel. It can reduce the dephosphorization rate from over 85% in conventional smelting to 40-50%, effectively increasing the final phosphorus content during smelting. The amount of lime added is reduced from 40-60 kg / ton of steel to no more than 25 kg / ton, and the amount of phosphorus alloy used is also reduced; furthermore, it reduces waste slag emissions. However, the following problems exist:

[0004] 1. This method only reduces the dephosphorization rate by adjusting the lance position and the timing of adding slag material in the early stage of blowing, without dynamically adjusting the amount of slag material added according to the composition of molten iron, resulting in fluctuations in phosphorus content at the final stage.

[0005] 2. The final temperature of molten steel is between 1670 and 1690℃, which results in a significant waste of heat. At the same time, there are no clear requirements for the oxygen and slag (P2O5) at the final stage of the converter.

[0006] 3. This method lacks clear specifications for steel deoxidation and alloying, and cannot effectively solve the problem of large amounts of alumina inclusions and poor castability during the deoxidation and titanium alloying processes. Therefore, a new solution is urgently needed to address this technical problem. Summary of the Invention

[0007] This invention addresses the technical problems existing in the prior art by providing a short-process smelting method for high-phosphorus steel. It ensures a final phosphorus content of 0.05%-0.07% by regulating the amount of slag-forming material added during the smelting process according to the hot metal composition, dynamically adjusting the lance position during the blowing process, controlling the final temperature, oxygen content, and the content of (MgO) and (P2O5) in the slag. The method employs pre-deoxidation with silicon and low-alumina control during tapping to reduce the production of alumina inclusions. Titanium alloying is achieved through titanium wire feeding, reducing titanium alloy burn-off. This method avoids the long steel transfer time problem associated with traditional smelting processes using the LF path; eliminates the problem of fluctuating phosphorus content at the final stage due to fluctuations in hot metal composition and poor slag formation; and solves the problem of poor steel castability through low-alumina control and titanium wire feeding.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: a short-process smelting method for high-phosphorus steel, mainly solving the problems of long production turnaround time and poor castability of existing high-phosphorus steel. The chemical composition of the high-phosphorus steel, by mass percentage, includes: [C]: 0.07-0.1%, [Si]: 0.3-0.4%, [Mn]: 0.4-0.5%, [P]: 0.07-0.11%, [S]: 0-0.0125%, [Ti]: 0.02-0.035%, [Cr]: 0.3-0.4%, [Cu]: 0.25-0.33%, with the balance being iron and unavoidable impurities.

[0009] The method includes the following steps:

[0010] Step 1: Using molten iron and scrap steel as raw materials, smelt them in a converter at a ratio of 80-92% molten iron.

[0011] Step 2, Process route BOF-AR-CC,

[0012] Step 3, Slag Control: A slag-free operation process is adopted. The total amount of lime is 10-20 kg / furnace. When the silicon content of the molten iron is >0.5%, an additional 4 kg / t of lime is added for every 0.1% increase in silicon content. This ensures that the slag basicity R is 2.5-3.5, the (MgO) content is 8.0% ± 1%, and the (P2O5) content is 3.5%-5.5%.

[0013] Step 4, Lance Position Control During Blowing: Ignite at 230cm during initial blowing; after slag formation, gradually reduce the lance position to 200cm; for 3000 Nm³ oxygen, lower the lance position to 180cm; adjust the lance position to 190cm at the end of the blowing process.

[0014] Step 5, Converter endpoint control: Target converter endpoint temperature 1635℃ + 15℃, endpoint carbon control 0.05% ± 0.01%, endpoint phosphorus control 0.03%–0.07%, endpoint oxygen content control 250–450 ppm.

[0015] Step 6, Deoxidation and Alloying during tapping: Deoxidation is performed using a composite aluminum deoxidizer during the tapping process. Low-titanium phosphorus ferrophosphate is added quantitatively at a rate of 300-500 kg / furnace for phosphorus alloying.

[0016] Step 7: During the tapping process, add 3 kg / t of desulfurized lime along with the steel stream. After tapping, add 1 kg / t of ladle slag composite deoxidizer to the slag surface.

[0017] Step 8: After tapping, add 100 kg of aluminum alloy to the surface of the molten steel. This can be added together with the ladle slag deoxidizer.

[0018] Step 9: After the molten steel is brought into the station and strongly stirred for ≥3 minutes, temperature is measured and samples are taken. Aluminum is added according to the target [Alt] 0.010%.

[0019] Step 10: After aluminum replenishment, stir with argon for ≥6 minutes, then add high-purity ferrotitanium. Do not perform vigorous stirring after titanium alloying.

[0020] Step 11: After titanium alloying for 3 minutes, feed in pure calcium wire, target [Ca]: 0.001%.

[0021] Step 12: After gently stirring for 5 minutes, pour the mixture onto the platform.

[0022] In step 3 of this invention, slag control involves adopting a slag-free operation process with a total lime content of 10-20 kg / furnace. When the silicon content in the molten iron is greater than 0.5%, an additional 4 kg / t of lime is added for every 0.1% increase in silicon content, ensuring that the slag basicity R is between 2.5 and 3.5, the (MgO) content is 8.0% ± 1%, and the (P2O5) content is between 3.5% and 5.5%. This is done both to fully utilize the phosphorus in the molten iron and to stably control the phosphorus content at the smelting endpoint.

[0023] In step 5 of this invention, the converter endpoint control is as follows: the target converter endpoint temperature is 1635℃, the endpoint carbon content is controlled at 0.05% ± 0.01%, the endpoint phosphorus content is controlled at 0.03% to 0.07%, and the endpoint oxygen content is controlled at 250 to 450 ppm. By controlling the oxygen content at the converter endpoint, the generation of deoxidation products is reduced.

[0024] Step 6 of this invention involves deoxidation and alloying during steel tapping: A composite deoxidation process is employed during tapping, with low-titanium ferrophosphorus added quantitatively at 300-500 kg / furnace. This composite deoxidation reduces the formation of alumina inclusions and improves spreadability.

[0025] In step 9 of this invention, after the molten steel is strongly stirred for ≥3 minutes upon entering the station, temperature is measured and samples are taken. Aluminum is added according to the target [Alt] 0.010%. This is to ensure low aluminum control of the molten steel and improve its castability.

[0026] In step 10 of this invention, after aluminum feeding, argon blowing and stirring are performed for ≥6 minutes. High-purity ferrotitanium is then added, and no strong stirring is performed after titanium alloying. Clearly defining the type of titanium alloy reduces inclusions introduced by the alloy and minimizes titanium loss during processing.

[0027] Through the above-described control steps, this invention can reduce the consumption of slag-forming materials during the smelting process, while improving the castability of molten steel and effectively increasing the number of consecutive castings.

[0028] Compared with the prior art, the present invention has the following positive effects: Compared with the conventional high-phosphorus steel smelting process, the short-process smelting method for high-phosphorus steel disclosed in the present invention reduces the slag-forming material from 30-40 kg / heat to 12-20 kg / heat, and increases the number of consecutive heats from 12 heats to 20 heats. Detailed Implementation

[0029] To enhance understanding of the present invention, detailed descriptions are provided below in conjunction with embodiments.

[0030] Example 1: A short-process smelting method for high-phosphorus steel disclosed in this invention includes the following steps:

[0031] 1) Using molten iron and scrap steel as raw materials, the molten iron is fed into the converter for smelting at a ratio of 80-92%.

[0032] 2) Process route BOF-AR-CC

[0033] 3) Slag control: A slag-free operation process is adopted, with a total lime content of 10-20 kg / furnace. When the silicon content of the molten iron is >0.5%, an additional 4 kg / t of lime is added for every 0.1% increase in silicon content, ensuring that the slag basicity R is 2.5-3.5 and the (MgO) content is 8.0% ± 1%.

[0034] (P2O5) is between 3.5% and 5.5%.

[0035] 4) Gun position control during blowing process: Ignite at 230cm during the initial blowing, and gradually reduce to 200cm after slag formation. When the oxygen content is 3000Nm3, reduce the gun position to 180cm. Adjust the gun position to 190cm at the end of the blowing process.

[0036] 5) Converter endpoint control: Target converter endpoint temperature 1635℃ + 15℃, endpoint carbon control 0.05% ± 0.01%, endpoint phosphorus control 0.03% to 0.07%, endpoint oxygen content control 250 to 450 ppm.

[0037] 6) Deoxidation and alloying during tapping: Deoxidation is carried out by composite aluminum deoxidizer during the tapping process, and low titanium ferrophosphorus is added quantitatively at 250-500 kg / furnace for phosphorus alloying.

[0038] 7) During the tapping process, add 3 kg / t of desulfurized lime along with the steel stream. After tapping, add a ladle slag composite deoxidizer to the slag surface.

[0039] 1 kg / t.

[0040] 8) After tapping, add 100 kg of aluminum alloy to the surface of the molten steel. It can be added together with the deoxidizer of the ladle slag.

[0041] 9) After the molten steel is stirred vigorously for ≥3 minutes, the temperature is measured and a sample is taken. Aluminum is added according to the target [Alt] 0.010%.

[0042] 10) After aluminum replenishment, blow argon and stir for ≥6 minutes, then add high-purity ferrotitanium. After titanium alloying, perform strong stirring.

[0043] 11) After titanium alloying for 3 minutes, pure calcium wire is fed in, with a target [Ca] of 0.001%.

[0044] 12) After stirring gently for 5 minutes, pour the mixture onto the platform.

[0045] The converter in this embodiment of the invention is a 250t converter, and the process parameters of the embodiment are shown in Table 1.

[0046] Table 1 Specific process parameters of the method embodiment of the present invention

[0047]

[0048] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A short-process smelting method for high-phosphorus steel, characterized in that, The chemical composition of high-phosphorus steel, by mass percentage, includes: [C]: 0.07-0.1%, [Si]: 0.3-0.4%, [Mn]: 0.4-0.5%, [P]: 0.07-0.11%, [S]: 0-0.0125%, [Ti]: 0.02-0.035%, [Cr]: 0.3-0.4%, [Cu]: 0.25-0.33%, with the balance being iron and unavoidable impurities.

2. The short-process smelting method for high-phosphorus steel according to claim 1, characterized in that, The method includes the following steps: Step 1: Using molten iron and scrap steel as raw materials, smelt them in a converter at a ratio of 80-92% molten iron. Step 2, Process route BOF-AR-CC, Step 3, Slag Formation Control: Step 4: Gun position control during the blowing process. Step 5: Converter endpoint control. Step 6, Deoxidation and Alloying during tapping: Deoxidation is performed using a composite aluminum deoxidizer during the tapping process. Low-titanium phosphorus ferrophosphate is added quantitatively at a rate of 300-500 kg / furnace for phosphorus alloying. Step 7: During the tapping process, add 3 kg / t of desulfurized lime along with the steel stream. After tapping, add 1 kg / t of ladle slag composite deoxidizer to the slag surface. Step 8: After tapping, add 100 kg of aluminum alloy to the surface of the molten steel. This can be added together with the ladle slag deoxidizer. Step 9: After the molten steel is brought into the station and strongly stirred for ≥3 minutes, temperature is measured and samples are taken. Aluminum is added according to the target [Alt] 0.010%. Step 10: After aluminum replenishment, stir with argon for ≥6 minutes, then add high-purity ferrotitanium. Do not perform vigorous stirring after titanium alloying. Step 11: After titanium alloying for 3 minutes, feed in pure calcium wire, target [Ca]: 0.001%. Step 12: After gently stirring for 5 minutes, pour the mixture onto the platform.

3. The short-process smelting method for high-phosphorus steel according to claim 2, characterized in that, Slag control in step 3: A slag-free operation process is adopted, with a total lime content of 10-20 kg / furnace. When the silicon content of the molten iron is greater than 0.5%, an additional 4 kg / t of lime is added for every 0.1% increase in silicon content, ensuring that the slag basicity R is 2.5-3.5, the (MgO) content is 8.0% ± 1%, and the (P2O5) content is 3.5%-5.5%.

4. The short-process smelting method for high-phosphorus steel according to claim 2, characterized in that, Step 4, lance position control during blowing process: Ignite at 230cm during initial blowing, gradually reduce to 200cm after slag formation, and reduce to 180cm for 3000Nm3 oxygen content; adjust the lance position to 190cm at the end of blowing.

5. The short-process smelting method for high-phosphorus steel according to claim 2, characterized in that, Step 5, Converter endpoint control: Target converter endpoint temperature 1635℃ + 15℃, endpoint carbon control 0.05% ± 0.01%, endpoint phosphorus control 0.03% to 0.07%, endpoint oxygen content control 250 to 450 ppm.

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