A method for preparing duplex steel based on continuous casting powder

Abstract

The present invention relates to a method for preparing duplex steel based on continuous casting flux, which includes steps such as hot metal pretreatment, smelting, refining, and continuous casting. By defining the continuous casting flux and the addition method, and coordinating with the settings of parameters in each step before and during continuous casting, the smooth progress of continuous casting is ensured, and adverse phenomena such as thick slag rings during continuous casting are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of steel preparation, and in particular to a method for preparing dual-phase steel based on continuous casting mold slag. Background Art

[0002] One of the biggest problems with the use of high-aluminum steel continuous casting mold protection slag is the appearance of a coarse slag ring at the meniscus of the crystallizer, which seriously affects the filling of the protection slag on the meniscus and below, resulting in uneven thickness of the slag film. Sometimes, a complete slag film cannot even be formed in the gap between the billet shell and the crystallizer wall, which hinders the lubrication of the casting by the protection slag and weakens the uniform heat transfer. In the case of mild problems with the casting quality, there will be production accidents such as bonding and steel leakage. Therefore, when selecting high-aluminum steel continuous casting protection slag, try to choose a formula that is not easy to crystallize and has good vitrification properties, but it is difficult for existing continuous casting protection slags to solve this technical problem.

[0003] The Chinese invention patent publication CN114130972A discloses a non-reactive protective slag for continuous casting crystallizer of fluorine-free high-aluminum steel, which improves the lubricity of the ingot by improving the component content. However, since steel smelting is a complete process, the improvement of continuous casting protective slag is one aspect. After determining the continuous casting protective slag, the coordination of the front-end and rear-end process parameters with the continuous casting protective slag setting is very important. The patent does not mention the technical solution of how to coordinate the continuous casting protective slag with the front-end and rear-end processes to maximize its effectiveness, so it does not achieve its best effect. Summary of the invention

[0004] In order to solve the above-mentioned technical problems, the present invention provides a method for preparing dual-phase steel based on continuous casting mold slag.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] A method for preparing a dual-phase steel based on continuous casting protective slag, wherein the chemical composition of the dual-phase steel is: C: 0.150-0.180wt%, Mn: 1.90-2.10wt%, S≤0.007wt%, P≤0.020wt%, Si: 0.32-0.48wt%, Als: 0.650-0.780wt%, Alt: 0.650-0.800wt%, Cr: 0.12-0.28wt%, Ti: 0.006-0.018wt%, N≤0.007wt%, Nb+Ti≤0.15wt%, Cr+Mo≤1.40wt%, B≤0.005wt%, Cu≤0.20wt%, Ni≤0.30wt%, V≤0.20wt%, Ni+Cr+Mo≤1.5wt%, and the balance is Fe and unavoidable impurities.

[0007] The steps include:

[0008] (1) Hot metal pretreatment: First, add 2.6 - 2.8 kg / ton of hot metal limestone into the hot metal ladle, and then, at a heating rate of 10 - 13 °C / h, raise the temperature in the hot metal ladle to the preheating temperature of 730 - 820 °C. Then, add hot metal into the hot metal ladle. The temperature of the incoming hot metal is 1330 - 1500 °C. Then, add a desulfurizer into the hot metal ladle and stir for desulfurization. The stirring time is 9 - 15 min. After that, skim the slag. The skimmed surface area of the desulfurized slag is ≥85%. The temperature of the treated hot metal is 1280 - 1500 °C.

[0009] (2) Smelting: Use a converter for smelting. Add scrap steel and the hot metal desulfurized in step (1) into the converter. The temperature of the hot metal entering the furnace is 1220 - 1500 °C, and the scrap ratio entering the furnace is 2 - 15 wt%. The number of bottom blowing holes at the furnace bottom is greater than or equal to 4. After blowing to 55 - 69% of the oxygen supply, start bottom blowing nitrogen with a flow rate of 18 - 22 m 3 / min. After blowing to 83 - 86% of the oxygen supply, switch the bottom blowing nitrogen to bottom blowing argon with a flow rate of 20 - 40 m 3 / min. The free oxygen at the end point of converter smelting is 100 - 700 ppm, C at the end point of converter smelting: 0.13 - 0.16 wt%, S ≤ 0.01, Alt: 0.6 - 0.79 wt%. The tapping temperature of the converter is 1570 - 1620 °C. During tapping, add a modifying agent and alloy materials. The modifying agent is quicklime and / or fluorite, and the alloy materials are ferrosilicon, ferromanganese, ferrochrome, and an aluminum-containing deoxidizer.

[0010] (3) Ladle refining: After the converter taps, conduct LF furnace refining. The temperature of the molten steel entering the LF furnace is 1560 - 1610 °C. Bottom blow argon in the LF furnace with an argon flow rate of 50 - 100 L / min and an argon pressure of 0.3 - 0.4 MPa; supply power for heating with a current of 25000 - 35000 A. After 8 - 11 min of power supply heating, add limestone and fluorite into the LF furnace. The addition amount is such that the slag amount in the LF furnace is adjusted to 10 - 12 kg / ton of steel. Keep the white slag for more than 15 minutes, and then add calcium carbide in two batches for slag adjustment. The total amount of calcium carbide added is 1 - 1.5 kg / ton of steel. The first batch adds 40 - 60 wt% of the total amount. After the temperature reaches 1597 - 1622 °C, conduct soft blowing for 15 - 18 min, and then feed an iron-calcium wire with a feeding speed of 3 - 5 m / s. The temperature of the molten steel leaving the LF furnace is 1597 - 1622 °C, and the refining cycle of the LF furnace is 30 - 120 min.

[0011] (4) RH Furnace Refining: The molten steel obtained after the refining in step (3) is subjected to RH furnace refining. The temperature of the molten steel entering the RH furnace is 1592 - 1612 °C. Nitrogen and argon are used as the circulating gases to guide the circulation of the molten steel for RH refining. Nitrogen guides the circulation of the molten steel for degassing for 3 - 6 minutes at a flow rate of 110 - 165 m 3 / h, and then argon guides the circulation of the molten steel for degassing for 5 - 8 minutes at a flow rate of 180 - 195 m 3 / h. Then the argon flow rate is adjusted to 150 - 160 m 3 / h until the end of RH furnace refining. The vacuum time is 15 - 35 minutes, and the temperature of the molten steel leaving the RH furnace is 1552 - 1577 °C.

[0012] (5) Continuous Casting: The molten steel obtained after RH furnace refining is poured into the continuous casting tundish. A low-carbon covering agent is used to cover the molten steel in the tundish. The tundish is subjected to argon blowing treatment. The argon sealing flow rate of the long nozzle is 100 - 200 L / min, the argon blowing flow rates of the stopper rod and the upper nozzle are 3 - 5 L / min, and the argon flow rate for inter-slab blowing is 2 - 4 L / min. The molten steel in the tundish is continuously poured into the mold through the submerged nozzle, and then a non-reactive continuous casting flux is continuously added into the mold. The chemical composition of the non-reactive continuous casting flux is: CaO: 31 - 35.5 parts by weight, Al 2 O 3 : 31 - 35.5 parts by weight, SiO 2 : 2 - 6 parts by weight, B 2 O 3 : 4 - 6 parts by weight, Na 2 O: 8 - 11 parts by weight, CaF 2 : 5 - 8 parts by weight, MgO: 4 - 7 parts by weight, Li 2 O: 1 - 4 parts by weight, BaO: 6 - 9 parts by weight, graphite: 7 - 9 parts by weight, and carbon black: 0.5 - 1.5 parts by weight. The addition amount of the non-reactive continuous casting flux added into the mold is 0.35 - 0.6 kg / ton of steel, and the laying thickness of the non-reactive continuous casting flux is 10 - 18 mm. Then, a duplex steel slab is obtained through strand straightening and cooling.

[0013] Preferably, the chemical composition of the duplex steel product is as follows: C: 0.160 - 0.180 wt%, Mn: 1.95 - 2.10 wt%, S ≤ 0.005 wt%, P ≤ 0.018 wt%, Si: 0.35 - 0.45 wt%, Als: 0.650 - 0.780 wt%, Alt: 0.650 - 0.790 wt%, Cr: 0.15 - 0.25 wt%, Ti: 0.008 - 0.018 wt%, N ≤ 0.0050 wt%, Nb + Ti ≤ 0.15 wt%, Cr + Mo ≤ 1.40 wt%, B ≤ 0.005 wt%, Cu ≤ 0.20 wt%, Ni ≤ 0.30 wt%, V ≤ 0.20 wt%, Ni + Cr + Mo ≤ 1.5 wt%, and the balance is Fe and inevitable impurities.

[0014] Preferably, the desulfurizer in step (1) is limestone and / or quicklime, and the addition amount of the desulfurizer is calculated based on the effective calcium oxide in the desulfurizer, so that the addition amount of the effective calcium oxide is 1.8 - 2.3 kg / ton of hot metal.

[0015] Preferably, the addition amount of the modifying agent in step (2) is 3 - 6 kg / ton of steel.

[0016] Preferably, the feeding amount of the ferrocalcium wire in step (3) is 22 - 280 m.

[0017] Preferably, in the non-reactive continuous casting powder, W(CaO) / W(CaO + Al 2 O 3 ) is 0.4955 - 0.5105 (preferably 0.5011), W(CaO) / W(Al 2 O 3 ) is 0.990 - 0.999 (preferably 0.996), and the viscosity at 1300 °C is 0.19 - 0.23 Pa·S.

[0018] Preferably, in step (5), the water flow rate on the wide face of the mold is 4230 - 4270 L / min, the inlet pressure of the water on the wide face of the mold is 0.85 - 1.05 MPa, the water flow rate on the narrow face of the mold is 530 - 570 L / min, the inlet pressure of the water on the narrow face of the mold is 0.85 - 1.05 MPa, the vibration form of the mold adopts a sine form, and the liquid level fluctuation of the mold is -3 - 3 mm.

[0019] Preferably, in step (5), the continuous casting temperature during continuous casting is 1527 - 1542 °C.

[0020] Preferably, in step 3), the S content at the time of entering the LF furnace is ≤ 0.01 wt%, and the S content at the time of leaving the LF furnace is ≤ 0.005 wt%.

[0021] Preferably, in step 5), the back pressure of argon blowing through the stopper ≥ 0.05 bar, the back pressure of argon blowing through the upper nozzle ≥ 0.1 bar, and the back pressure of argon blowing between the slabs ≥ 0.1 bar.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) By specifically controlling various parameters in the molten iron pretreatment, smelting, two-stage refining, and continuous casting processes, and cooperating with the setting of specific continuous casting fluxes and the addition parameters of the continuous casting fluxes, especially the control of the content of stage elements, temperature, and slag in each step in combination with the specific continuous casting flux, and then cooperating with the addition parameters of the continuous casting flux, the slag-steel reaction of the continuous casting flux hardly occurs during the continuous casting process, and the crystallization mineral phase is mostly borate that is not easy to crystallize, effectively preventing the wanton development of the slag ring, ensuring lubricity, and ensuring the smooth progress of continuous casting.

[0024] (2) In the desulfurization pretreatment process of the present invention, limestone is first added and preheated by a specific heating rate before adding molten iron, and then a desulfurizing agent is added, and the slag removal parameters are defined, so that the desulfurization effect is strengthened. Thus, in combination with the control of the component content of the specific steel grade of the present invention, the treatment intensity of the S content is more friendly during the subsequent treatment processes of each step, and the coordination of desulfurization in the front and back steps is enhanced.

[0025] (3) Since the steel smelting process is a basic process and is basically not changed, only the parameters therein are specifically defined to optimize the product and control the cost. The present invention specifically defines various parameters in the smelting, ladle refining, RH refining, and continuous casting processes, especially the setting of the blowing parameters at each stage, thereby optimizing the fluidity of the molten steel throughout the process and the rapid adjustment of the alloy composition, and strengthening the coordination with the continuous casting stage, so that the overall process technology is more optimized, the qualified stability of the product is ensured, and waste of raw materials is not caused (cost is reduced). Detailed Embodiments

[0026] The process technical solutions of the present invention are further described below by combining with embodiments. Unless otherwise stated, each feature is only an example of a series of equivalent or similar features. It is only for helping to understand the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0027] Example 1

[0028] A method for preparing dual-phase steel based on continuous casting powder, wherein the chemical composition of the dual-phase steel is: C: 0.170 wt%, Mn: 2.03 wt%, S: 0.001 wt%, P: 0.002 wt%, Si: 0.40 wt%, Als: 0.715 wt%, Cr: 0.2 wt%, Ti: 0.013 wt%, N: 0.001 wt%, Nb + Ti ≤ 0.15 wt%, Cr + Mo ≤ 1.40 wt%, B ≤ 0.005 wt%, Cu ≤ 0.20 wt%, Ni ≤ 0.30 wt%, V ≤ 0.20 wt%, Ni + Cr + Mo ≤ 1.5 wt%, and the balance is Fe and inevitable impurities.

[0029] It includes the following steps:

[0030] (1) Hot metal pretreatment: First, add 2.65 kg / ton of hot metal of limestone into the hot metal ladle, and then increase the temperature in the hot metal ladle to the preheating temperature of 780 °C at a heating rate of 10 - 13 °C / h. Then add hot metal into the hot metal ladle. The temperature of the incoming hot metal is 1390 °C. Then add desulfurizer into the hot metal ladle and stir for desulfurization. The stirring time is 12 min. After that, slag skimming is carried out, and the skimming bright surface area of desulfurization slag skimming ≥ 90%. The desulfurizer is limestone and / or quicklime, and the addition amount of the desulfurizer is calculated according to the effective calcium oxide in the desulfurizer, so that the addition amount of effective calcium oxide is 2.1 kg / ton of hot metal.

[0031] (2) Smelting: Adopt converter smelting. Add scrap steel and the hot metal after desulfurization in step (1) into the converter. The temperature of the incoming hot metal is 1350 °C, and the scrap ratio in the furnace is 6 wt%. The number of bottom blowing holes at the bottom of the furnace is greater than or equal to 4. After blowing to 58% of the oxygen supply amount, start bottom blowing nitrogen, and the nitrogen flow rate is 20 m 3 / min. After blowing to 5% of the oxygen supply amount, switch bottom blowing nitrogen to bottom blowing argon, and the nitrogen flow rate is 30 m 3 / min. The free oxygen at the end point of converter smelting is 100 - 700 ppm, the C at the end point of converter smelting is 0.145 wt%, S: 0.005, Alt: 0.6 - 0.7 wt%, the tapping temperature of the converter is 1590 °C. During tapping, add modifier and alloy materials. The modifier is quicklime and / or fluorite, and the alloy materials are ferrosilicon, ferromanganese, ferrochrome and aluminum-containing deoxidizer. The addition amount of the modifier is 3.9 kg / ton of steel.

[0032] (3) Ladle refining: After tapping from the converter, LF furnace refining is carried out. The temperature of the molten steel entering the LF furnace is 1590 °C. Argon is blown at the bottom of the LF furnace, with an argon flow rate of 80 L / min and an argon pressure of 0.35 MPa. Electric power is supplied for heating, with a current of 30000 A. After 10 minutes of electric heating, limestone and fluorite are added to the LF furnace, and the addition amount is such that the slag amount in the LF furnace is adjusted to 11 kg / ton of steel. The white slag is maintained for 18 minutes, and then calcium carbide is added in two batches for slag adjustment. The total amount of calcium carbide added is 1.2 kg / ton of steel, and 50 wt% of the total amount is added in the first batch. After the temperature reaches 1610 °C, soft blowing is carried out for 16 minutes, and then an Fe-Ca wire is fed at a feeding speed of 3.5 m / s. The temperature of the molten steel leaving the LF furnace is 1602 °C, and the refining cycle of the LF furnace is 55 minutes.

[0033] (4) RH furnace refining: The molten steel obtained after refining in step (3) is subjected to RH furnace refining. The temperature of the molten steel entering the RH furnace is 1602 °C. Nitrogen and argon are used as circulating gases to guide the circulation of the molten steel for RH refining. Nitrogen guides the circulation of the molten steel for degassing for 5 minutes at a flow rate of 135 m 3 / h, and then argon guides the circulation of the molten steel for degassing for 6 minutes at a flow rate of 190 m 3 / h. Then the argon flow rate is adjusted to 155 m 3 / h until the end of RH furnace refining. The vacuum time is 25 minutes, and the temperature of the molten steel leaving the RH furnace is 1557 °C.

[0034] (5) Continuous casting: The molten steel obtained after RH furnace refining is poured into the continuous casting tundish. A low-carbon covering agent is used to cover the molten steel in the tundish. Argon blowing treatment is carried out in the continuous casting tundish. The argon sealing flow rate of the long nozzle is 150 L / min, the argon blowing flow rates of the stopper rod and the upper nozzle are 3.5 L / min, and the argon flow rate for argon blowing between the slabs is 3 L / min. The molten steel in the tundish is continuously poured into the mold through the submerged nozzle, and then a non-reactive continuous casting flux is continuously added to the mold. The chemical composition of the non-reactive continuous casting flux is as follows: CaO: 32.5 parts by weight, Al 2 O 3 : 33.5 parts by weight, SiO 2 : 3 parts by weight, B 2 O 3 : 5 parts by weight, Na 2 O: 9 parts by weight, CaF 2 : 6.2 parts by weight, MgO: 5.5 parts by weight, Li 2O: 3 parts by weight, BaO: 6.9 parts by weight, graphite: 8 parts by weight and carbon black: 1 part by weight; the addition amount of the non-reactive continuous casting flux added into the mold is 0.5 kg / ton of steel, and the laying thickness of the non-reactive continuous casting flux is 13 mm; then the dual-phase steel slab is obtained through straightening and cooling of the slab. The continuous casting temperature during continuous casting is 1527 - 1542 °C. In the said non-reactive continuous casting flux, W(CaO) / W(CaO + Al 2 O 3 ) is 0.5011, and W(CaO) / W(Al 2 O 3 ) is 0.996.

[0035] The water flow rate on the wide face of the mold is 4250 - 4260 L / min, the water inlet pressure on the wide face of the mold is 0.95 MPa, the water flow rate on the narrow face of the mold is 550 L / min, the water inlet pressure on the narrow face of the mold is 0.96 MPa, the vibration form of the mold adopts a sine form, and the liquid level fluctuation of the mold is -3 - 3 mm.

[0036] Comparative Example 1

[0037] Other settings of this comparative example are the same as those of Example 1, the difference is that the continuous casting flux used during the continuous casting process in step 5) is CaO: 39.32 parts by weight, MgO: 0.92 parts by weight, SiO 2 : 32.26 parts by weight, Al 2 O 3 : 1.4 parts by weight, Fe 2 O 3 : 0.55 parts by weight, C: 4.22 parts by weight, F: 9.2 parts by weight, Li 2 O: 3.7 parts by weight; the basicity R of the continuous casting flux is 1.24, the melting point is 1122 °C, the bulk density is 0.85 g / ml, and the viscosity is 0.08 Pa·S. By using the same step parameters as in Example 1 to prepare the same steel grade as in Example 1, it is found that during the continuous casting process, the reaction between the steel and the slag causes changes in the composition and properties of the flux, resulting in slag clumps in the mold, deteriorating the lubrication and heat transfer conditions of the billet shell in the slag channel, and seriously causing production accidents such as breakout. However, the above problems did not occur in Example 1, which also indicates that the flux of the present invention is closely coordinated with the specific steel grade and various parameters, and is the optimal configuration.

[0038] Comparative Example 2

[0039] The other settings of this comparative example are the same as those of Example 1, except that the steel grade smelted is different from that of Example 1. Specifically, for the dual-phase steel, C: 0.08 wt%, Si: 0.05 wt%, Mn: 1.98 wt%, P: 0.001 wt%, S: 0.001 wt%, Als: 0.62 wt%, N: 0.001 wt%, Cr: 0.25 wt%, Nb: 0.019 wt%, Ti: 0.018 wt%, Mo: 0.21 wt%, B: 0.0018 wt%, and the balance is Fe and inevitable impurities. By using the same step parameters as in Example 1 and the same continuous casting mold powder, it is found that during the continuous casting process, the lubrication and heat transfer conditions of the billet shell in the mold are not good, and quality defects such as surface cracks appear in the produced billets, while the above problems do not occur in Example 1, which also shows that the setting of the steel grade and the mold powder in the present invention is the optimal matching method.

[0040] The well-known technologies in the art involved in the present invention are not elaborated in detail. The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing dual-phase steel based on continuous casting mold powder, characterized in that, the chemical composition of the dual-phase steel by wt% is: C: 0.160 - 0.180%, Mn: 1.95 - 2.10%, S ≤ 0.005%, P ≤ 0.018%, Si: 0.35 - 0.45%, Als: 0.650 - 0.780%, Alt: 0.650 - 0.790%, Cr: 0.15 - 0.25%, Ti: 0.008 - 0.018%, N ≤ 0.0050%, Nb + Ti ≤ 0.15%, Cr + Mo ≤ 1.40%, B ≤ 0.005%, Cu ≤ 0.20%, Ni ≤ 0.30%, V ≤ 0.20%, Ni + Cr + Mo ≤ 1.5%, with the balance being Fe and unavoidable impurities; including the steps: (1) Hot metal pretreatment: First, add 2.6 - 2.8 kg / ton of hot metal of limestone into the hot metal ladle, then raise the temperature to 730 - 820 °C at a rate of 10 - 13 °C / h, then add hot metal into the hot metal ladle, the temperature of the incoming hot metal is 1330 - 1500 °C, then add a desulfurizing agent and stir for desulfurization, the stirring time is 9 - 15 min, then skim the slag, the skimming bright surface area of desulfurization and slag skimming is ≥ 85%, and the temperature of the treated hot metal is 1280 - 1500 °C; (2)Smelting: Conduct smelting in a converter. Add scrap steel and the hot metal obtained in step (1) into the converter. The temperature of the hot metal entering the furnace is 1220 - 1500 °C, the scrap ratio entering the furnace is 2 - 15 wt%, the number of bottom blowing holes at the furnace bottom is more than 4. After blowing to 55 - 69% of the oxygen supply amount, start bottom blowing nitrogen with a flow rate of 18 - 22 m 3 / min. After blowing to 83 - 86% of the oxygen supply amount, switch to bottom blowing argon with a flow rate of 20 - 40 m 3 / min. The free oxygen at the end point of converter smelting is 100 - 700 ppm, C at the end point of converter smelting: 0.13 - 0.16 wt%, S ≤ 0.01 wt%, Alt: 0.6 - 0.79 wt%. The tapping temperature is 1570 - 1620 °C. During tapping, add a modifying agent and alloy materials. The modifying agent is quicklime, and the alloy materials are ferrosilicon, ferromanganese, ferrochrome, and an aluminum-containing deoxidizer; (3) LF refining: The temperature of the molten steel entering LF is 1560 - 1610 °C, bottom-blow argon, the argon flow rate is 50 - 100 L / min, and the argon pressure is 0.3 - 0.4 MPa; power on for heating, the current is 25000 - 35000 A, after 8 - 11 min, add limestone and fluorite into LF, the addition amount is such that the LF slag amount is adjusted to 10 - 12 kg / ton of steel, keep the white slag for more than 15 minutes and then add calcium carbide in two batches to adjust the slag, the total addition amount is 1 - 1.5 kg / ton of steel, the first batch is added 40 - 60 wt%, after the temperature reaches 1597 - 1622 °C, perform soft blowing, the soft blowing time is 15 - 18 min, then feed an Fe-Ca wire, the wire feeding speed is 3 - 5 m / s, the temperature of the molten steel leaving the station is 1597 - 1622 °C, and the LF refining cycle is 30 - 120 min; (4)RH refining: The molten steel temperature at the RH station is 1592 - 1612 °C. Nitrogen and argon are used as the circulating gases to guide the circulation of the molten steel for RH refining. Nitrogen guides the circulation of the molten steel for degassing at a flow rate of 110 - 165 m 3 / h for 3 - 6 minutes, and then argon guides the circulation of the molten steel for degassing at a flow rate of 180 - 195 m 3 / h for 5 - 8 minutes. Then the argon flow rate is adjusted to 150 - 160 m 3 / h until the end of RH refining. The vacuum time is 15 - 35 minutes, and the molten steel temperature at the outgoing station is 1552 - 1577 °C; (5) Continuous casting: Pour the molten steel after RH refining into the tundish of continuous casting, cover the molten steel with a low-carbon covering agent, blow argon into the tundish of continuous casting, the argon sealing flow rate of the long nozzle is 100-200 L / min, the argon blowing flow rate of the stopper rod and the upper nozzle is 3-5 L / min, and the argon blowing flow rate between slabs is 2-4 L / min; Continuously pour the molten steel in the tundish into the mold through the submerged nozzle, and then continuously add a non-reactive continuous casting flux into the mold. Its chemical composition by weight is: CaO: 31-35.5 parts, Al 2 O 3 : 33.5-35.5 parts, SiO 2 : 2-3 parts, B 2 O 3 : 4-6 parts, Na 2 O: 8-11 parts, CaF 2 : 5-8 parts, MgO: 5.5-7 parts, Li 2 O: 1-4 parts, BaO: 6.9-9 parts, graphite: 8-9 parts, carbon black: 1-1.5 parts; The addition amount in the mold is 0.35-0.6 kg / ton of steel, and the laying thickness is 10-18 mm; Then obtain the duplex steel slab through strand straightening and cooling.

2. The method for preparing dual-phase steel based on continuous casting mold powder according to claim 1, characterized in that, the desulfurizing agent in step (1) is limestone and / or quicklime, and the addition amount of the desulfurizing agent is calculated based on the effective calcium oxide in the desulfurizing agent, so that the addition amount of the effective calcium oxide is 1.8 - 2.3 kg / ton of hot metal.

3. The method for preparing dual-phase steel based on continuous casting mold powder according to claim 1, characterized in that, the addition amount of the modifying agent in step (2) is 3 - 6 kg / ton of steel.

4. The method for preparing dual-phase steel based on continuous casting mold powder according to claim 1, characterized in that, the feeding amount of the Fe-Ca wire in step (3) is 22 - 280 m.

5. The method for preparing dual-phase steel based on continuous casting mold powder according to claim 1, characterized in that, The W(CaO) / W(CaO + Al 2 O 3 ) in the non-reactive continuous casting powder is 0.4955 - 0.5105, the W(CaO) / W(Al 2 O 3 ) is 0.990 - 0.999, and the viscosity at 1300 °C is 0.19 - 0.23 Pa•S.

6. The method for preparing dual-phase steel based on continuous casting mold powder according to claim 1, characterized in that, In step (5), the water flow rate on the wide face of the mold is 4230 - 4270 L / min, the inlet pressure of the water on the wide face of the mold is 0.85 - 1.05 MPa, the water flow rate on the narrow face of the mold is 530 - 570 L / min, the inlet pressure of the water on the narrow face of the mold is 0.85 - 1.05 MPa, the vibration form of the mold adopts a sine form, and the liquid level fluctuation of the mold is -3 - 3 mm.

7. The method for preparing dual-phase steel based on continuous casting flux according to claim 1, characterized in that, in step (5), the continuous casting temperature during continuous casting is 1527 - 1542 °C.

8. The method for preparing dual-phase steel based on continuous casting flux according to claim 1, characterized in that, in step 3), the S content at the time of LF furnace charging is ≤ 0.01 wt%, and the S content at the time of LF furnace tapping is ≤ 0.005 wt%.

9. The method for preparing dual-phase steel based on continuous casting flux according to claim 1, characterized in that, in step 5), the back pressure of argon blowing through the stopper rod ≥ 0.05 bar, the back pressure of argon blowing through the upper nozzle ≥ 0.1 bar, and the back pressure of argon blowing between plates ≥ 0.1 bar.