A smelting method of a titanium microalloyed Q355B steel

Abstract

This invention belongs to the field of metallurgical technology and relates to a smelting method for titanium microalloyed Q355B steel. It includes the following steps: 1) Converter smelting: bottom-blown nitrogen is used throughout the smelting process; the carbon content at the converter endpoint is controlled at 0.06–0.10%, the oxygen content at 300–450 ppm, and the final steel temperature is controlled at 1630–1640℃; 2) LF refining: the LF inlet temperature is controlled at 1550–1570℃; bottom-blown argon stirring is used throughout the LF refining process; after refining, deoxidation and slagging are performed; 3) Continuous casting. This method is used to reduce smelting costs, stabilize the effective titanium content in the steel, and improve product performance stability.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a smelting method for titanium microalloyed Q355B steel. Background Technology

[0002] As steel production technology develops towards high quality, high efficiency, and green practices, the application of microalloying elements in steel products is becoming increasingly widespread. Titanium is one of the important alloying elements in steel. With the advancement of smelting technology, the low cost and superior performance of Ti microalloying are becoming increasingly apparent, bringing broad application prospects for titanium microalloying. Titanium, as a microalloying element, mainly exists in steel as a solid solution in the iron matrix or as titanium-containing precipitates. Generally, the presence of titanium in steel can significantly refine grains, and its precipitation strengthening effect of carbonitrides or nitrides can significantly improve the strength of steel. Based on the influence of solid-solution titanium and titanium-containing precipitates on the recrystallization and phase transformation behavior of austenite, by adopting appropriate rolling processes, the austenite and ferrite structures can be refined to achieve a fine-grain strengthening effect. Simultaneously, the precipitation of TiC can also play a precipitation strengthening role. Therefore, using titanium microalloying to fully utilize its strengthening effect will greatly reduce the total alloy content added to molten steel, thereby reducing the alloying cost of a series of structural steels.

[0003] Currently, Q355B steel is widely used in engineering structures, mining machinery, and steel pipes, making it one of the steel grades commonly produced in large quantities by major domestic steel companies. Some steel companies use titanium microalloying to produce Q355B in order to reduce production costs. However, this method still suffers from poor performance stability, with product performance often inconsistent due to fluctuations in the effective titanium content. For example:

[0004] Patent CN 110229992 B discloses a smelting and production method for low-cost titanium microalloyed Q355B steel plates, including: 1) Raw material requirements: selecting low-sulfur and low-phosphorus molten iron. 2) Converter smelting: using a double-slag smelting process for deep dephosphorization. 3) Tapping: avoiding any spot blowing operations at the smelting endpoint; adding silicon-manganese alloy for deoxidation during tapping; ensuring the slag thickness in the ladle after tapping is ≤40mm. 4) Argon station treatment: maintaining argon bottom blowing after the molten steel arrives at the argon station; immediately feeding aluminum wire; after the aluminum wire is fed in, maintaining the Al content of the molten steel between 0.020% and 0.040%; maintaining soft argon blowing for 2-3 minutes, during which alloy fine-tuning is completed; then immediately feeding titanium-silicon-calcium composite cored wire. 5) Continuous casting with full-process protective pouring to ensure Al loss ≤0.003%. However, the performance stability is poor.

[0005] Therefore, how to formulate a reasonable smelting process and stabilize the effective titanium content is an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a low-cost smelting method for stabilizing the effective titanium content in titanium microalloyed Q355B steel, thereby reducing smelting costs, stabilizing the effective titanium content in the steel, and improving product performance stability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for smelting titanium microalloyed Q355B steel, comprising the following steps:

[0009] The Q355B steel, by weight percentage, comprises: C: 0.16-0.2%, Si: 0.05-0.3%, Mn: 0.35-0.55%, P≤0.035%, S≤0.035%, Ti: 0.035-0.055%, Al S 0.025-0.035%, CEV≤0.45, balance is iron and unavoidable impurities.

[0010] 1) Converter smelting:

[0011] Nitrogen was blown from the bottom throughout the smelting process.

[0012] The carbon content at the end of the converter is controlled at 0.06-0.10%, the oxygen content is 300-450 ppm, and the temperature of the molten steel at the end is controlled at 1630-1640℃.

[0013] 2) LF Refining:

[0014] The LF inlet temperature is controlled at 1550~1570℃;

[0015] LF refining employs bottom-blowing argon stirring throughout the process;

[0016] After refining, the material enters the station and undergoes deoxidation and slagging.

[0017] 3) Continuous casting.

[0018] As a further preferred embodiment of the present invention, in step 1), a top-and-bottom blown converter is used for smelting, and the nitrogen supply intensity is 0.05–0.10 Nm³. 3 / min / t.

[0019] As a further preferred embodiment of the present invention, in step 1), aluminum manganese ferromanganese, silicon manganese, and silicon ferromanganese are used for deoxidation and alloying during the steel tapping process. The amount of aluminum manganese ferromanganese added is 1.2 to 2.2 kg / t steel, the amount of silicon manganese added is 2.6 to 3.7 kg / t steel, and the amount of silicon ferromanganese added is 1.4 to 2.0 kg / t steel. The alloy is added uniformly when the molten steel has been tapped to one-fifth to one-quarter of its length, and is completed when the molten steel has been tapped to three-fifths to three-quarters of its length. The alloy is added in the direction of the impact zone of the steel flow.

[0020] As a further preferred embodiment of the present invention, in step 2), the LF refining adopts bottom blowing argon stirring throughout the process. In the early stage of strong stirring and shell breaking, the argon flow rate is 5-7 NL / min, and the argon blowing stirring time is 2-3 min. In the stage of adding slag with electricity to make white slag, the argon flow rate is 90-150 NL / min. In the stage of white slag refining and fine-tuning composition, the argon flow rate is 100-150 NL / min. Before leaving the station, a low-pressure soft blowing is adopted, with an argon flow rate of 50-70 NL / min and a soft blowing time of not less than 12 min.

[0021] Nitrogen addition during the LF refining process is controlled at 6–10 ppm.

[0022] As a further preferred embodiment of the present invention, in step 2), 70-80 m of high-calcium wire is fed per furnace before soft argon blowing.

[0023] As a further preferred embodiment of the present invention, in step 2), after refining, 30-40 kg / furnace of calcium carbide, 150-200 kg / furnace of lime, and 80-130 kg / furnace of aluminum slag are added for deoxidation and slag formation.

[0024] As a further preferred embodiment of the present invention, in step 2), the slag composition is controlled as follows: SiO2: 8-17%, CaO: 40-50%, Al2O3: 20-30%, MgO: 5-15%, TFe < 1.0%, basicity 3.0-5.0, and viscosity 0.25-0.45.

[0025] As a further preferred embodiment of the present invention, in step 2), the carbon, aluminum, silicon and manganese composition is adjusted, and the [Al] in the molten steel before adding titanium iron is controlled at 0.025% to 0.035%. When feeding titanium wire, the argon pressure is 0.3 to 0.4 MPa.

[0026] As a further preferred embodiment of the present invention, in step 3), continuous casting adopts full protective casting, and argon sealing process is adopted at the ladle long nozzle and submerged nozzle. The argon flow rate of the ladle long nozzle is 140-150 NL / min, and the argon flow rate of the submerged nozzle is 40-45 NL / min. The liquid surface of the tundish is covered with carbonized rice husks, and the amount added is 1-1.5 kg / t steel.

[0027] As a further preferred embodiment of the present invention, in step 3), the crystallizer adopts non-sinusoidal vibration, the superheat of the tundish is controlled at 10-20°C, the pulling speed is controlled at 1.1-1.3 m / min, the thickness of the protective slag is controlled at 45-60 mm, and the thickness of the liquid slag layer is controlled at 10-15 mm.

[0028] The nitrogen content in continuous casting should be controlled within 2 ppm, and the nitrogen content in the billet should be controlled within 30 ppm.

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] 1. The present invention adopts a full-process bottom-blowing nitrogen mode in the converter smelting process, which has low nitrogen cost. By comprehensively controlling the bottom-blowing nitrogen flow rate, the carbon content at the converter endpoint, the oxygen content at the converter endpoint, the temperature of the molten steel at the converter endpoint, and the timing and amount of deoxidizer added during the tapping process, the nitrogen absorption and denitrification of the molten steel in the converter can reach the optimal balance point. Under the condition of ensuring low cost, the nitrogen content of the tapped steel is controlled within 18ppm.

[0031] 2. The reasonable converter endpoint carbon-temperature conditions of this invention are beneficial to the control of nitrogen content in LF refining, and at the same time, they are beneficial to reduce the refining electrode power consumption by 25-30%.

[0032] 3. This invention achieves deep desulfurization by controlling the aluminum content in molten steel, using LF (sulfurization-reduction slag) to enhance desulfurization, controlling LF temperature, and controlling the bottom-blown argon flow rate. The sulfur content in the refined molten steel can be controlled below 40 ppm. Low nitrogen control is achieved through converter endpoint carbon-temperature control, converter bottom-blown nitrogen process control, LF foam slag covering the molten steel surface to reduce nitrogen absorption, and continuous casting protective pouring to further reduce nitrogen absorption, resulting in a billet nitrogen content below 30 ppm. Wherein, ω(Ti)e=ω(Ti)-3.42ω(N)-1.5ω(S), where: ω(Ti)e is the effective titanium mass fraction; ω(Ti) is the total titanium mass fraction; ω(N) is the nitrogen mass fraction; ω(S) is the sulfur mass fraction. By reducing the N and S content in the molten steel, the effective titanium content is stably controlled. Therefore, this invention employs deep desulfurization and low-nitrogen control to stably control the effective titanium content, resulting in stable product mechanical properties. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a smelting method for titanium microalloyed Q355B steel, the process route being: converter-LF refining-continuous casting.

[0035] 1) Converter smelting

[0036] The smelting process employs a top-and-bottom blown converter, with bottom-blown nitrogen supplied throughout the entire process at an intensity of 0.05–0.10 Nm³. 3 / min / t.

[0037] The carbon content at the converter endpoint is controlled within the range of 0.06 to 0.10% and kept stable, while the oxygen content is maintained at 300 to 450 ppm to prevent severe nitrogen absorption by the molten steel. The final molten steel temperature is controlled at 1630 to 1640℃.

[0038] During the tapping process, aluminum manganese ferromanganese, silicon manganese, and silicon ferromanganese are used for deoxidation and alloying, with addition amounts of 1.2–2.2 kg / t steel, 2.6–3.7 kg / t steel, and 1.4–2.0 kg / t steel, respectively. The alloy is added evenly starting when the molten steel reaches one-quarter of its total volume and finishing when the molten steel reaches three-quarters of its total volume. The alloy is added directly to the impact zone of the steel flow.

[0039] The slag-blocking system uses an automatic sliding plate to strictly control the amount of slag discharged.

[0040] Maintain the shape of the tapping spout during the tapping process to ensure the steel flow is round and does not disperse, thereby reducing nitrogen absorption.

[0041] Add 4-7 kg / t of synthetic slag after steel is released.

[0042] The nitrogen content in the steel tapped from the converter should be controlled below 18 ppm.

[0043] 2) LF Refining

[0044] The LF inlet temperature is controlled at 1550~1570℃.

[0045] LF refining employs bottom-blowing argon stirring throughout the process. In the initial strong stirring and shell-breaking stage, the argon flow rate is 5–7 NL / min, and the stirring time is 2–3 min. During the slag addition and white slag formation stage, the argon flow rate is 90–150 NL / min. In the white slag refining and composition fine-tuning stage, the argon flow rate is 100–150 NL / min. Before leaving the station, low-pressure soft blowing is used, with an argon flow rate of 50–70 NL / min and a soft blowing time of no less than 12 min. This ensures that the slag layer is not blown open, preventing the molten steel surface from absorbing nitrogen, and also prevents excessive temperature drop in the molten steel.

[0046] After refining, 30-40 kg / furnace of calcium carbide, 150-200 kg / furnace of lime, and 80-130 kg / furnace of aluminum slag are added for deoxidation and slag formation. The slag composition is controlled as follows: SiO2: 8-17%, CaO: 40-50%, Al2O3: 20-30%, MgO: 5-15%, TFe < 1.0%, basicity 3.0-5.0, and viscosity 0.25-0.45. By producing slag with suitable basicity, good fluidity, and viscosity suitable for submerged arc operation, it is beneficial for slag foaming and submerged arc operation, increasing the area covering the molten steel and preventing the exposed surface of the molten steel from absorbing nitrogen.

[0047] The composition of carbon, aluminum, silicon, and manganese is adjusted, and the [Al] content in the molten steel is controlled at 0.025%–0.035% before the addition of titanium-iron to achieve rapid desulfurization and ensure stable titanium recovery. The argon pressure is controlled at 0.3–0.4 MPa when feeding the titanium wire.

[0048] Before soft argon blowing, feed 70-80m of high-calcium wire per furnace.

[0049] Nitrogen addition during the LF refining process is controlled at 6–10 ppm.

[0050] 3) Continuous casting

[0051] Continuous casting adopts full protective casting. The long nozzle and submerged entry nozzle of the ladle are sealed with argon gas. The argon gas flow rate is 140-150 NL / min and 40-45 NL / min, respectively. The liquid surface of the tundish is covered with carbonized rice husks, and the amount added is 1-1.5 kg / t steel.

[0052] The crystallizer uses non-sinusoidal vibration, the superheat of the tundish is controlled at 10-20℃, the pulling speed is controlled at 1.1-1.3m / min, the thickness of the protective slag is controlled at 45-60mm, and the thickness of the liquid slag layer is controlled at 10-15mm.

[0053] The nitrogen content in continuous casting should be controlled within 2 ppm, and the nitrogen content in the billet should be controlled within 30 ppm.

[0054] Example 1

[0055] 1) Converter smelting

[0056] The smelting process employs a top-and-bottom blown converter, with bottom-blown nitrogen supplied throughout the entire process at an intensity of 0.05–0.10 Nm³. 3 / min / t.

[0057] The final carbon content of the converter is controlled at 0.071%, the oxygen content at 404 ppm, and the final molten steel temperature at 1635℃.

[0058] During the tapping process, aluminum manganese ferromanganese, silicon manganese, and silicon ferromanganese are used for deoxidation and alloying, with addition amounts of 1.95 kg / t steel, 3.05 kg / t steel, and 1.45 kg / t steel, respectively. The alloy is added evenly starting when the molten steel reaches one-quarter of its total volume and finishing when the molten steel reaches three-quarters of its total volume. The alloy is added directly to the impact zone of the steel flow.

[0059] The slag-blocking system uses an automatic sliding plate to strictly control the amount of slag discharged.

[0060] Maintain the shape of the tapping spout during the tapping process to ensure the steel flow is round and does not disperse, thereby reducing nitrogen absorption.

[0061] After steel is released, 4.34 kg / t of synthetic slag is added.

[0062] The nitrogen content of the gas sample from the converter tapping process was 16 ppm, as determined by a nitrogen-oxygen analyzer.

[0063] 2) LF Refining

[0064] The LF inlet temperature is controlled at 1557℃.

[0065] LF refining employs bottom-blowing argon stirring throughout the process. In the initial strong stirring and shell-breaking stage, the argon flow rate is 5 NL / min, and the stirring time is 2 min. During the slag addition and white slag formation stage, the argon flow rate is 99 NL / min. In the white slag refining and composition fine-tuning stage, the argon flow rate is 110 NL / min. Before leaving the station, a low-pressure soft-blowing process is used, with an argon flow rate of 50 NL / min and a soft-blowing time of 12 min. This ensures that the slag layer is not blown open, preventing the molten steel surface from absorbing nitrogen, and also prevents excessive temperature drop in the molten steel.

[0066] After refining, 30 kg / furnace of calcium carbide, 160 kg / furnace of lime, and 80 kg / furnace of aluminum slag are added for deoxidation and slag formation. The slag composition is controlled as follows: SiO2: 14.51%, CaO: 45.15%, Al2O3: 23.85%, MgO: 13.21%, TFe: 0.34%, basicity 3.11, and viscosity 0.3. By producing slag with suitable basicity, good fluidity, and viscosity suitable for submerged arc operation, it is beneficial for slag foaming and submerged arc operation, increasing the area covering the molten steel and preventing the exposed surface of the molten steel from absorbing nitrogen.

[0067] The composition of carbon, aluminum, silicon, and manganese was adjusted, and the [Al] content in the molten steel was controlled at 0.025% before the addition of titanium-iron alloy to achieve rapid desulfurization and ensure stable titanium recovery. The argon pressure was controlled at 0.35 MPa during titanium wire feeding.

[0068] Before soft blowing argon, feed 80m of high-calcium wire per furnace.

[0069] The nitrogen and oxygen meter was used to test the LF barrel samples, and the nitrogen increase during the LF refining process was controlled at 8 ppm.

[0070] 3) Continuous casting

[0071] The continuous casting adopts full protective casting. The long nozzle and submerged entry nozzle of the ladle are sealed with argon gas. The argon gas flow rates are 148NL / min and 44.9NL / min, respectively. The liquid surface of the tundish is covered with carbonized rice husks, and the amount added is 1.2kg / t steel.

[0072] The crystallizer uses non-sinusoidal vibration, the superheat of the tundish is controlled at 15℃, the pulling speed is controlled at 1.2m / min, the thickness of the protective slag is controlled at 56mm, and the thickness of the liquid slag layer is controlled at 11mm.

[0073] The nitrogen content of the cast billet was measured using a nitrogen-oxygen analyzer and found to be 26 ppm.

[0074] ω(Ti)e=ω(Ti)-3.42ω(N)-1.5ω(S), where: ω(Ti)e is the effective titanium mass fraction; ω(Ti) is the total titanium mass fraction; ω(N) is the nitrogen mass fraction; and ω(S) is the sulfur mass fraction.

[0075] According to the analysis of the refined composition, ω(Ti) is 0.042%, ω(N) in the billet is 0.0026%, ω(S) in the billet is 0.004%, effective titanium ω(Ti)e is 0.0271%, upper yield strength is 438 MPa, tensile strength is 559 MPa, elongation after fracture is 29%, and longitudinal impact energy at 20℃ is 59 J.

[0076] Example 2

[0077] 1) Converter smelting

[0078] The smelting process employs a top-and-bottom blown converter, with bottom-blown nitrogen supplied throughout the entire process at an intensity of 0.05–0.10 Nm³. 3 / min / t.

[0079] The final carbon content of the converter is controlled at 0.066%, the oxygen content at 351 ppm, and the final molten steel temperature at 1631℃.

[0080] During the tapping process, aluminum manganese ferromanganese, silicon manganese, and silicon ferromanganese are used for deoxidation and alloying, with addition amounts of 2.14 kg / t steel, 2.8 kg / t steel, and 1.65 kg / t steel, respectively. The alloys are added evenly starting when the molten steel reaches one-quarter of its total volume and finishing when the molten steel reaches three-quarters of its total volume. The alloys are added directly to the impact zone of the steel flow.

[0081] The slag-blocking system uses an automatic sliding plate to strictly control the amount of slag discharged.

[0082] Maintain the shape of the tapping spout during the tapping process to ensure the steel flow is round and does not disperse, thereby reducing nitrogen absorption.

[0083] After steel is released, 6.62 kg / t of synthetic slag is added.

[0084] The nitrogen content of the gas sample from the converter tapping process was 18 ppm, as determined by a nitrogen-oxygen analyzer.

[0085] 2) LF Refining

[0086] The LF inlet temperature is controlled at 1560℃.

[0087] LF refining employs bottom-blowing argon stirring throughout the process. In the initial strong stirring and shell-breaking stage, the argon flow rate is 6 NL / min, and the stirring time is 2.5 min. During the slag addition and white slag formation stage, the argon flow rate is 130 NL / min. The argon flow rate is also 130 NL / min during the white slag refining and composition fine-tuning stages. Before leaving the station, a low-pressure soft-blowing process is used, with an argon flow rate of 51 NL / min and a soft-blowing time of 12 min. This ensures that the slag layer is not blown open, preventing the molten steel surface from absorbing nitrogen, and also prevents excessive temperature drop in the molten steel.

[0088] After refining, 30 kg / furnace of calcium carbide, 180 kg / furnace of lime, and 130 kg / furnace of aluminum slag are added for deoxidation and slag formation. The slag composition is controlled as follows: SiO2: 14.03%, CaO: 48.99%, Al2O3: 26.19%, MgO: 6.24%, TFe: 0.71%, basicity 3.49, and viscosity 0.35. By producing slag with suitable basicity, good fluidity, and viscosity suitable for submerged arc operation, it is beneficial for slag foaming and submerged arc operation, increasing the area covering the molten steel and preventing the exposed surface of the molten steel from absorbing nitrogen.

[0089] The composition of carbon, aluminum, silicon, and manganese was adjusted, and the [Al] content in the molten steel was controlled at 0.03% before the addition of titanium-iron to achieve rapid desulfurization and ensure stable titanium recovery. The argon pressure was controlled at 0.35 MPa when feeding the titanium wire.

[0090] Before soft blowing argon, feed 80m of high-calcium wire per furnace.

[0091] The nitrogen and oxygen analyzer was used to test the LF barrel samples, and the nitrogen increase during the LF refining process was controlled at 7 ppm.

[0092] 3) Continuous casting

[0093] The continuous casting adopts full protective casting. The long nozzle and submerged entry nozzle of the ladle are sealed with argon gas. The argon gas flow rates are 149NL / min and 44.5NL / min, respectively. The liquid surface of the tundish is covered with carbonized rice husks, and the amount added is 1.3kg / t steel.

[0094] The crystallizer uses non-sinusoidal vibration, the superheat of the tundish is controlled at 14℃, the pulling speed is controlled at 1.2m / min, the thickness of the protective slag is controlled at 53mm, and the thickness of the liquid slag layer is controlled at 12mm.

[0095] The nitrogen content of the cast billet was measured using a nitrogen-oxygen analyzer and found to be 27 ppm.

[0096] ω(Ti)e=ω(Ti)-3.42ω(N)-1.5ω(S), where: ω(Ti)e is the effective titanium mass fraction; ω(Ti) is the total titanium mass fraction; ω(N) is the nitrogen mass fraction; and ω(S) is the sulfur mass fraction.

[0097] According to the analysis of the refined composition, ω(Ti) is 0.041%, ω(N) in the billet is 0.0027%, ω(S) in the billet is 0.0038%, effective titanium ω(Ti)e is 0.0261%, upper yield strength is 436 MPa, tensile strength is 549 MPa, elongation after fracture is 27%, and longitudinal impact energy at 20℃ is 58 J.

[0098] The upper and lower limits of the process parameters (such as temperature, time, etc.) and the range values ​​of the present invention can all achieve the method, and examples are not listed here.

[0099] All aspects not described in detail in this invention can be covered using conventional technical knowledge in the field.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for smelting titanium microalloyed Q355B steel, comprising the following steps: 1) Converter smelting: Bottom-blown nitrogen is used throughout the smelting process; the nitrogen supply intensity is 0.05–0.10 Nm³. 3 / min / t; The carbon content at the final stage of the converter is controlled at 0.06-0.10%, the oxygen content is 300-450 ppm, and the final steel temperature is controlled at 1630-1640℃. 2) LF Refining: The LF inlet temperature is controlled at 1550–1570℃; LF refining adopts bottom blowing argon stirring throughout the process; after refining, deoxidation and slag formation are carried out; in the early stage of strong stirring and shell breaking, the argon flow rate is 5–7 NL / min, and the argon blowing stirring time is 2–3 min; in the stage of adding slag with electricity to form white slag, the argon flow rate is 90–150 NL / min; in the stage of white slag refining and fine-tuning composition, the argon flow rate is 100–150 NL / min; before leaving the station, low-pressure soft blowing is adopted, with an argon flow rate of 50–70 NL / min and a soft blowing time of not less than 12 min; the nitrogen increase during the LF refining process is controlled at 6–10 ppm; 3) Continuous casting: Continuous casting employs full protective casting. Argon sealing is used at the long nozzle and submerged entry nozzle of the ladle. The argon flow rate at the long nozzle of the ladle is 140–150 NL / min, and the argon flow rate at the submerged entry nozzle is 40–45 NL / min. The liquid surface of the tundish is covered with carbonized rice husks, with an addition rate of 1–1.5 kg / t of steel. The crystallizer uses non-sinusoidal vibration. The superheat of the tundish is controlled at 10–20°C, the casting speed is controlled at 1.1–1.3 m / min, the thickness of the protective slag is controlled at 45–60 mm, and the thickness of the liquid slag layer is controlled at 10–15 mm. The nitrogen addition during continuous casting is controlled to be less than 2 ppm, and the nitrogen content of the billet is controlled to be less than 30 ppm.

2. The smelting method according to claim 1, characterized in that, In step 1), aluminum manganese ferromanganese, silicon manganese, and silicon ferrosilicon are used for deoxidation and alloying during the tapping process. The amount of aluminum manganese ferromanganese added is 1.2 to 2.2 kg / t steel, the amount of silicon manganese added is 2.6 to 3.7 kg / t steel, and the amount of silicon ferrosilicon added is 1.4 to 2.0 kg / t steel. The alloy is added evenly when the molten steel has been tapped to one-fifth to one-quarter of its length, and is completed when the molten steel has been tapped to three-fifths to three-quarters of its length. The alloy is added to the impact zone of the steel flow.

3. The smelting method according to claim 1, characterized in that, In step 2), before soft argon blowing, feed 70-80m of high-calcium wire per furnace.

4. The smelting method according to claim 1, characterized in that, In step 2), after refining, 30-40 kg / furnace of calcium carbide, 150-200 kg / furnace of lime, and 80-130 kg / furnace of aluminum slag are added for deoxidation and slag formation.

5. The smelting method according to claim 1, characterized in that, In step 2), the slag composition is controlled as follows: SiO2: 8-17%, CaO: 40-50%, Al2O3: 20-30%, MgO: 5-15%, TFe < 1.0%, basicity 3.0-5.0, and viscosity 0.25-0.

45.

6. The smelting method according to claim 1, characterized in that, In step 2), the carbon, aluminum, silicon and manganese composition is adjusted, and the [Al] in the molten steel before adding titanium iron is controlled at 0.025% to 0.035%. When feeding titanium wire, the argon pressure is 0.3 to 0.4 MPa.